. ESL tat/11W» Geology and Base-Metal @575 Pt heposits of West Shasta ”g? Copper-Zinc District \W Shasta County, California GEOLOGICAL SURVEY PROFESSIONAL PAPER 285 Prepared 1'72 cooperation wit/z t/ze State of Calzforaia, Department of Natural Resources, Dz'm'yioa of M z'nes Geology and Base-Metal Deposits of West Shasta Copper-Zinc District Shasta County, California By A. R. KINKEL, JR., W. E. HALL, and J. P. ALBERS GEOLOGICAL SURVEY PROFESSIONAL PAPER 285 Prepared in cooperation wita tae State ofCa/zforaia, Department of Natural Resources, Division of M iaes UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1956 Pmomomfl UNITED STATES DEPARTMENT OF THE INTERIOR Fred A. Seaton, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, U. S. Government Printing Oflice Washington 25, D. C. 5? E75 €47, V, 28354771 gé EARTH SCIENCES CONTENTS 4 “m" Page Page Abstract ____________________________________________ 1 Base-metal deposits—Continued Introduction ________________________________________ 3 Character and distribution _______________________ 79 Climate and vegetation __________________________ 4 Structural features ______________________________ 80 Physical features _______________________________ 6 Form of the ore bodies _______________________ 80 Previous work and acknowledgments ______________ 7 Type of contacts between ore and wall rocks _____ 81 Geologic formations _________________________________ 8 Relationship of ore bodies to structures in the Copley greenstone ______________________________ 9 host rock _________________________________ 81 Balaklala rhyolite _______________________________ ll. , ,_ Relationship to stratigraphy ______________ 81 General description _________________________ 17—- V ~ . v .7- Relationship to folds and foliation _________ 81 Distribution and relationship to other rocks-“ _ 18 Relationship to faults _____________________ 83 Stratigraphic relationship ____________________ 19 Mineralogic description __________________________ 84 Petrographic description _____________________ 22 General features ____________________________ 84 Nonporphyritic rhyolite _________________ 23 Hypogene minerals __________________________ 85 Medium-phenocryst rhyolite _____________ 24 Ore minerals ____________________________ 85 Coarse-phenocryst rhyolite _______________ 26 Gangue minerals _________________________ 88 Pyroclastic beds _________________________ 28 Supergene minerals _________________________ 89 Tufl' beds ______________________________ 29 Oxide zone _____________________________ 89 Origin of the Balaklala rhyolite _______________ 31 Sulfide zone ______________________________ 89 Kennett formation ______________________________ 32 Paragenesis ________________________________ 90 Bragdon formation ______________________________ 38 Relationship of hydrothermal alteration to massive Chico formation _________________________________ 41 sulfide ore ____________________________________ 91 Red Bluff formation _____________________________ 42 Genesis of the hypogene ores _____________________ 93 Recent deposits ___________________________________ 42 Oxidation and enrichment _______________________ 96 Intrusive rocks ______________________________________ 43 Age of mineralization ____________________________ 99 Mule Mountain stock ____________________________ 43 Summary of base-metal ore controls ________________ 100 Shasta Bally batholith ___________________________ 48 Exploration possibilities of the West Shasta district- - 101 Minor intrusive rocks ____________________________ 50 Description of deposits ______________________________ 102 Rocks intruded before Nevadan orogeny ________ 50 Akers prospect _________________________________ 102 Rocks intruded after Nevadan orogeny _______ ,. _ 51 Balaklala mine _________________________________ 102 Structure ___________________________________________ 53 Geology of the mine area ____________________ 103 General features ________________________________ 53 Ore deposits ________________________________ 105 Structure of individual areas ______________________ 55 Balaklala Angle Station gossan ___________________ 107 The mineral belt ____________________________ 55 Crystal Copper prospect _________________________ 109 Kennett and Bragdon formations ______________ 56 Early Bird mine ________________________________ 109' Copley greenstone in the Igo and Whiskytown Golinsky mine __________________________________ 114 quadrangles ______________________________ 57 Great Verde prospect ____________________________ 116 Shasta Bally batholith _______________________ 58 Iron Mountain mine ____________________________ 117 Mule Mountain stock ________________________ 59 History and production ______________________ 117 Location of volcanic centers ______________________ 59 Formations in the mine area _________________ 118 Physiographic features _______________________________ 6O Ore deposits _________________________ ‘.7 ______ 118 Geologic history _____________________________________ 63 Character ______________________________ 118 Rock alteration _____________________________________ 65 Distribution of minerals _________________ 119 Dynamic metamorphism _________________________ 66 Disseminated copper ore _________________ 120 Igneous metamorphism __________________________ 67 Structural features of the ore bodies _______ 120 Metamorphism related to plugs of Balaklala Relationship of ore bodies to structures in rhyolite __________________________________ 67 the host rock __________________________ 123 Metamorphism related to the Mule Mountain Faults _________________________________ 123 stock ____________________________________ 67 Hydrothermal alteration of the wall rocks- __ 124 Metamorphism related to the Shasta Bally Summary of features controlling ore deposi- batholith _________________________________ 67 tion _________________________________ 124 Weathering _____________________________________ 74 Oxidation and enrichment ___________________ 125 Origin of the albite ___________________________________ 74 Exploratory drilling _________________________ 126 Base-metal deposits _________________________________ 76 Drilling data ___________________________ 126 General features ________________________________ 76 Description of the core __________________ 127 History of the mining district _____________________ 76 Geologic results of drilling _______________ 129 Production _____________________________________ 78 Keystone mine _________________________________ 129 III 685 IV CONTENTS Page Description of deposits—Continued Description of deposits—~Continued King Copper prospect ___________________________ 131 Shasta King mine _______________________________ Lone Star prospect ______________________________ 132 Balaklala rhyolite ___________________________ Mammoth mine ________________________________ 133 Ore body, _ - _______________________________ History, production, and grade _______________ 133 Faults _________________________________ Geology of the mine area ___________________ 133 Ore controls ____________________________ Formations ____________________________ 133 Oxidation and enrichment _______________ Folds __________________________________ 134 Exploration possibilities __________________ Faults- A , ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 134 Spread Eagle prospect _______________ , ____________ Ore bodies _________________________________ 135 Stowell mine ___________________________________ Character and distribution, _______________ 135 Sugarloaf prospect _ _'_ ___________________________ Oxidation and enrichment _______________ 137 Sutro mine _____________________________________ Hydrothermal alteration _________________ 137 Selected bibliography ________________________________ Ore controls- _ _ - _________________________ 137 Index _____________________________________________ PLATE FIGURE 13. 14. 15. ILLUSTRATIONS [Plates 1-21 in pocket] Geologic map of the West Shasta copper-zinc district, Shasta County, Calif. Geologic sections of the West Shasta copper-zinc district. . Map showing trend of planar structures in the West Shasta copper-zinc district. Map showing location of mines, principal prospects, and areas favorable for prospecting. Composite map of underground workings of the Balaklala and Keystone mines. Geologic sections through the Keystone and Balaklala mines. Map and sections of the Golinsky mine. . Map of underground workings of the Iron Mountain mine. . Geologic map and sections of the Iron Mountain area. . Geologic sections through the ore bodies of the Iron Mountain mine. Map and section showing ore bodies of the Iron Mountain mine. . Geologic maps and sections of underground workings of the Keystone mine. . Geologic maps and sections of the Lone Star prospect. . Composite map of underground workings, Mammoth mine. . Geologic map and sections of the Mammoth mine. Structure contour map of the Mammoth mine. . Geologic maps of the 200, 300, 470, 500, 540, and 670 levels of the Mammoth mine. Geologic map of the Shasta King mine. . Geologic map and sections of underground workings of the Shasta King mine. . Map of underground workings of the Stowell mine showing Outline of gossan. . Map of underground workings and geologic sections of the Sutro mine. . Index map showing the location of the West Shasta copper-zinc district ___________________________________ . Map showing location of principal mines and generalized geologic setting of the West Shasta copper-zinc district__ Geologic column in the West Shasta copper-zinc district _________________________________________________ . Volcanic breccia near the top of Copley greenstone in Grizzly Gulch in the VVhiskytown quadrangle ___________ Partial section of the Copley greenstone along the Sacramento River about 1% miles N. 70° W. of Redding, Calif 1 Photomicrograph of amygdaloidal keratophyre _________________________________________________________ . Photomicrograph of Copley greenstone showing variolitic texture _________________________________________ . Photomicrograph of the Copley greenstone showing pilotaxitic texture _____________________________________ . Photomicrograph of altered porphyritic albite diabase ___________________________________________________ . Photomicrograph of metagabbro containing plagioclase laths showing saussuritic alteration ___________________ . Partial section in the Copley greenstone that contains interbedded rhyolitic flows and pyroclastic rocks ________ . Vertical section across the contact between the Balaklala rhyolite and shale of the Kennett formation east of the Golinsky mine ____________________________________________________________________________________ Coarse-phenocryst Balaklala rhyolite containing quartz phenocrysts _______________________________________ Platy medium- phenocryst rhyolite near Mount Shasta mine east of Clear Creek ___________________________ Myrmekitic intergrowth of quartz and albite in medium-phenocryst Balaklala rhyolite ______________________ Page 138 140 140 142 142 143 144 144 146 149 149 151 155 Page 12 12 13 14 15 16 17 18 20 25 26 FIGURE 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. 55. 56. 57. 58. 59. 60. 61. 62. 63. 64. CONTENTS Photomicrograph of dark quartz phenocryst in coarse-phenocryst rhyolite __________________________________ Pyroclastic layer in middle unit of the Balaklala rhyolite northwest of the Mammoth mine in the canyon of Little Backbone Creek _______________________________________________________________________________ Photomicrograph of bedded rhyolitic tuf‘f- _____________________________________________________________ Accretionary lapilli rhyolitic tuff ______________________________________________________ . ________________ Kennett formation northeast of Backbone Creek arm of Shasta Lake ______________________________________ Partial section beneath the limestone of the Kennett formation on the east side of Backbone Ridge, Behemotosh quadrangle _______________________________________________________________________________________ Chert conglomerate of the Bragdon formation __________________________________________________________ Intrusive breccia near Spring Creek. Reworked Copley greenstone fragments in albite granite matrix __________ Photomicrograph of albite granite showing early stage in the formation of a pseudophenocryst of quartz (Q) that is interpreted as having replaced plagioclase (P) __________________________________________________ Photomicrograph of hornblende-quartz diorite, a varietal type of the Mule Mountain stock __________________ Sketch of intrusive breccia along diabase dike in shale of the Kennett formation _____________________________ Map of West- Shasta copper—zinc district showing relationship of main folds to the mineral belt and main in- trusive rocks ______________________________________________________________________________________ Cross section of shale and sandstone of the Bragdon formation in road cut __________________________________ Small thrust in shale of the Bragdon formation in Backbone Creek _________________________________________ View looking westward from Shasta Dam showing general accordance of summit elevations and entrenched val- leys on left ___________________________________________________________________________________________ Formation of topographic flats ________________________________________________________________________ Drainage pattern, West Shasta copper-zinc district ______________________________________________________ Photomicrograph of extremely sheared coarse-phenocryst rhyolite from the margin of the coarse—phenocryst rhyolite plug near the Uncle Sam mine _______________________________________________________________ Formation of porphyroblasts of hornblende in hybrid Copley greenstone near contact with the Clear Creek plug- _ Fragment of banded hornblende gabbro cut by hornblende dikelet ________________________________________ Fragment of hornblende gabbro showing “angular unconformities” cut by a dikelet 0f hornblendite __________ Intrusive breccia containing fragments of gabbro, hornblendite, and Copley greenstone in a matrix of hornblende diorite ___________________________________________________________________________________________ Diagrammatic drawing showing the relationship between bedding-plane foliation, fracture cleavage, and pyri- tized zones at the Mammoth mine ____________________________________________________________________ Photomicrograph of ore from the Mammoth mine _________________________________________________________ Photomicrograph of ore from the Golinsky mine _________________________________________________________ Photomicrograph of ore from the Early Bird mine ______________________________________________________ High-grade zinc-copper ore from the Shasta King mine; white, chalcopyrite; gray, sphalerite __________________ Photomicrograph of polished section of zinc ore from Mammoth mine. Corroded quartz gangue (dark) in sphalerite (light) forming an island-and—sea texture ___________________________________________________ Photomicrograph of thin section of massive sulfide ore from the Balaklala mine showing the feathery character of quartz (light) surrounding pyrite grains (dark) _____________________________________________________ Gossan derived from massive sulfide ore _______________________________________________________________ Relict nodule of massive sulfide in gossan ________________________________________________________________ View of opencut at Balaklala mine showing part of the middle unit of the Balaklala rhyolite _________________ Map of workings of Balaklala Angle Station gossan _____________________________________________________ Geologic map of the Early Bird mine area _______________________________________________________________ Early Bird mine, map and sections ____________________________________________________________________ Map of adits of the Early Bird mine ________________________________________ - __________________________ Diagrammatic section showing the relationship between the Shasta King and the Great Verde ore zones _______ Photomicrograph of polished section of gossan that contains maghemite ___________________________________ Map of No. 8 mine and ore bodies, Iron Mountain mine _________________________________________________ Sections of No. 8 mine ore bodies, Iron Mountain mine __________________________________________________ Map of Iron Mountain area showing location of diamond-drill holes and geologic cross section through drill holes- Graphic 10g of diamond—drill hole of the Iron Mountain mine _____________________________________________ Location of the King Copper and Sugarloaf prospects in relation to nearby mines and prospects ______________ Shasta King mine. A, View from the south. B, Diagram in lower half of figure is sketch drawn from photo— graph ___________________________________________________________________________________________ Columnar sections of tuff and volcanic breccia above the gossan, Shasta King mine __________________________ Details of sulfide contacts, Shasta King mine. A, Upper ore contact in the stope on the 870-foot level near cross section F—F’. B, Section looking northeastward along fault 12 _________________________________________ Map of underground workings, Spread Eagle prospect ___________________________________________________ Levels and sample cuts of Spread Eagle prospect _______________________________________________________ Generalized projection looking northwestward through the Stowell mine showing the relationship of the ore bodies to the base of the upper unit of the Balaklala rhyolite ___________________________________________ V Page 27 29 30 30 35 37 40 44 _ 46 47 51 53 57 57 61 62 63 68 72 73 73 73 88 89 98 98 104 108 110 111 113 117 119 121 122 127 128 130 139 140 141 145 147 148 VI TABLE CONTENTS TABLES Page 1. Temperature and precipitation, Redding, Calif., and nearby localities _______________________________________ 6 2. Chemical analyses of spilite ___________________________________________________________________________ 14 3. Chemical analyses of extrusive and intrusive phases of Balaklala rhyolite ___________________________________ 23 4. Analyses of albite granite and quartz diorite from the Mule Mountain stock- 1-; ,,,,,,,,, , __________________ 44 5. Production and grade of ore from the West Shasta copper-zinc district- _ __ _ _ _ _ __ _ _' _________________________ 78 6. Production and grade of copper and zinc ore from five mines in the West Shasta copper—zinc district ___________ 79 7. Production and grade of ore from the Balaklala mine ____________________________________________________ 103 8. Arithmetic average of three separate sets of samples from Balaklala Angle Station gossan- ___________________ 109 9. Production and grade of ore from the Early Bird mine ___________________________________________________ 112 10 Ore mined by American Smelting and Refining Co. and Backbone Gold Mining Co _______ ; __________________ 114 11. Production and grade of ore from the Iron Mountain mine _______________________________________________ 118 12. Copper content of the upper part of the Old Mine ore body _______________________________________________ 126 13. Annual production and grade of ore from the Mammoth mine, 1905-25 ____________________________________ 133 14. Production and grade of stopes and other ore blocks of the Mammoth mine _________________________________ 136 15. Production and grade of hand—sorted zinc ore from the Mammoth mine ____________________________________ 136 16. Production and grade of ore from the Shasta King mine __________________________________________________ 140 GEOLOGY AND BASE-METAL DEPOSITS OF THE WEST SHASTA COPPER-ZINC DISTRICT, SHASTA COUNTY, CALIFORNIA By A. R. KINKEL, Jr., W. E. HALL, and J. P. ALBERS AB STRACT The Shasta copper-zinc district of northern California is in the foothills of the Klamath Mountains at the north end of the Sacramento Valley. The district contains two main areas of base-metal ore deposits that are called the West Shasta copper-zinc district and the East Shasta copper—zinc district. The West Shasta district, the subject of this report, is a well- defined, northeastward-trending district about 8 miles long and 2 miles wide, west of the Sacramento River. The south end of the district is 9 miles northwest of Redding, the county seat of Shasta County. The West Shasta copper-zinc district includes nine base- metal mines that have been productive, and many prospects. The ore consists of large bodies of massive pyrite that con- tain copper and zinc sulfides and minor amounts of gold and silver. The ore bodies have been mined primarily for copper and zinc, although massive pyrite has been mined at the Iron Mountain mine for sulfur. Only the Iron Mountain mine has been operated continuously in recent years. The Paleozoic rocks of the West Shasta district range in age from Middle Devonian to Mississippian. Mesozoic rocks, if they were present, have been eroded except for remnants of the Chico formation of Late Cretaceous age. The Chico is overlain by the Red Bluff formation of Pleistocene age and by Recent stream gravels. The Paleozoic rocks are intruded by a pluton of albite granite, the Mule Mountain stock, and by a pluton of biotite-quartz diorite, the Shasta Bally batho- lith. These intrusives are probably of Late Jurassic or Early Cretaceous age. The oldest formation that is exposed in the West Shasta district is the Copley greenstone of probable Middle Devonian age. It is composed of volcanic flows, volcanic breccia, and tuffs of intermediate and basic composition, and of a few beds of shale and rhyolitic tuft. The lower part of the formation con- tains massive flows; the upper part contains much pillow lava and pyroclastic material. The formation is at least 3,700 feet thick, but the base is not exposed in the mapped area. The Balaklala rhyolite of Middle Devonian age conform- ably overlies the Copley greenstone, although in the eastern part of the mapped area the Balaklala rhyolite wedges out and locally interfingers with the Copley greenstonc. In this area the upper part of the Copley greenstone appears to be equivalent in age to the Balaklala rhyolite. A transition zone, which contains material that is characteristic of both units, locally lies between the two formations. The Balaklala rhyolite is composed of soda-rich rhyolitic flows and pyroclastic mate- rial. The stratigraphy in the Balaklala rhyolite has been mapped on the basis of bedded pyroclastic rocks, and on the size of quartz phenocrysts and other lithologic differences in the rhyolite flows. Nonporphyritic rhyolite and porphyritic rhyolite containing phenocrysts of quartz and plagioclase are lithologic subdivisions; the porphyritic rhyolite is further sub- divided into medium-phenocryst rhyolite containing quartz phe- nocrysts 1 to 4 millimeters in diameter and coarse-phenocryst rhyolite with quartz phenocrysts more than 4 millimeters in diameter. The Balaklala is here subdivided into lower, middle, and upper stratigraphic units. Nonporphyritic rhyolite pre- dominates in the lower unit of the Balaklala; medium-pheno- cryst rhyolite predominates in the middle unit; and coarse- phenocryst rhyolite is characteristic of the upper unit. The Balaklala rhyolite is probably 3,500 feet thick in the central part of the district, but forms a volcanic pile that thins on the edges. The Kennett formation of Middle Devonian age overlies the Balaklala rhyolite. The Kennett is composed of black siliceous shale, gray shale, rhyolitic tuff, and limestone. The rhyolitic tuff of the Kennett formation is interbedded with shale and grades downward through a transition zone to rhyolitic tuft beds that are part of the upper unit of the Balaklala rhyolite. The maximum thickness of the Kennett formation is probably not more than 400 feet, but folding and repetition by faulting make it impossible to obtain an exact thickness. The Kennett formation is missing in the westernmost part of the area, where the Bragdon formation lies conformably on the Balaklala rhyolite. The Bragdon formation of Mississippian age conformably overlies the Kennett formation in much of the mapped area, although outside this area part of the Kennett was apparently uplifted by warping and an erosional unconformity separates the two formations. The Bragdon formation is composed largely of gray— and tan-weathering shale, but it also contains beds of conglomerate, grit, and sandstone. The Bragdon forma- tion is 3,500 feet thick in the mapped area, but only the lower part of the formation is present. Diller estimated that the Bragdon is 6,000 feet thick. The Mule Mountain stock of albite granite intrudes the Cop- ley greenstone and the Balaklala rhyolite. It is a sodaa‘ich siliceous intrusive rock that is composed principally of albite and quartz with minor amounts of epidote. Locally, it contains hornblende. It is probably syntectonic (Nevadan) in age. The Shasta Bally batholith is composed predominantly of biotite—quartz diorite. It intrudes the Copley greenstone, the Bragdon formation, and the albite granite in the mapped area; west of the mapped area it is nonconformably overlain by rocks of Early Cretaceous age. It is a post—tectonic intrusive of Late Jurassic or Early Cretaceous age. The Chico formation of Late Cretaceous age is present as erosion remnants in a few places in the mapped area. It is composed of shale, sandstone, and conglomerate. A major un— conformity separates the Chico from the pre-Cretaceous rocks. The Chico formation is gently tilted, but is not folded or meta- morphosed as are the underlying rocks. 2 GEOLOGY AND BASE-METAL DEPOSITS, WEST SHASTA COPPER-ZINC DISTRICT The Red Bluff formation of Pleistocene age overlies the Chico unconformably. It is composed of poorly cemented sand, gravel, and conglomerate that form a veneer on cut surfaces and form part of the fill of the old Sacramento Valley. The Red Bluff formation is deeply entrenched by the present streams. The Paleozoic rocks in the West Shasta district are folded into a broad anticlinorium that contains many small folds; the axis of the anticlinorium trends N. 15" E. in the central part of the mineral belt through Iron Mountain and Behemotosh Mountain. It has a culmination over the central part of the mineral belt and plunges north at a low angle at the north edge of the mapped area and south at a low angle at the south end of the mineral district. It is interrupted by the Mule Mountain stock south of Iron Mountain. The anticlinorium is flanked by broad synclines on the east and west. Although folding is on such a broad scale that the average dip of the flanks of the anticlinorium is not more than 20°, dips of indi- vidual beds range from horizontal to 90°. The rocks are strongly folded in some areas, but adjacent areas are only mod- erately folded. Folding is particularly erratic in distribution where there is a great difference in the competence of adjacent rocks, as between beds of tuff and thick massive flows, and between shale and conglOmerate. Foliation is common in many parts of the district, although the rocks in many places contain no planar structures. The rocks range from those that are strongly deformed with schistose or gneissic structure through moderately folded rocks having fracture cleavage to rocks that are almost undeformed. In parts of the district foliation is parallel to bedding; in other parts it cuts across the bedding. Where foliation is most intense it is rarely possible to determine the relationship be- tween foliation and bedding. The Mule Mountain stock was in- truded into rocks that were already foliated, as it cut across and crumpled the foliation around its borders. The Shasta Bally batholith formed a zone of amphibolite, gneiss, and mig- matite from the Copley greenstone along its border. Faults are abundant in the district. The main faults have two dominant directions, N. 20°~45° W. and N. 60°—80° E.; in both groups the north side is generally downthrown relative to the south. The Shasta copper-zinc district has produced 54 percent of the copper in California through 1946; the major part of the production has come from the West Shasta copper—zinc dis- trict. The zinc production has been small because the ore was direct—smelted and zinc was not recovered; bodies of high-grade zinc ore were mined and treated separately. Gold and silver have been recovered from gossan that overlies massive sulfide ore at Iron Mountain and from sulfide ore that was smelted for copper. Through 1951, 3,600,000 tons of pyrite from the Iron Mountain mine had been treated for its sulfur content, but sulfur was not recovered at any of the other mines. Several thousand pounds of cadmium were recovered from zinc-rich ore at the Mammoth mine. The copper—Zinc ore deposits of the West Shasta district are bodies of massive pyrite that contain chalcopyrite and sphalerite and minor quantities of gold and silver. The most striking features of the ore are its uniformity, its lack of megascopic gan- gue minerals, and its sharp boundary with barren or weakly pyritized wall rocks. The ore has a brassy, metallic appear- ance, and some large ore bodies contain as little as 3.5 per- cent acid insoluble material. In most ore bodies the massive sulfide is separated from barren wall rock by a thin selvage of gouge; gradational contacts between ore and wall rock are very rare. Most of the ore bodies of the district have a lentic- ular form and are flat lying; their greatest dimension is in a horizontal plane. Several ore bodies are saucer shaped, one is domal, and one is synclinal. Steeply dipping ore bodies are not characteristic of the district, but they do occur in the Hornet mine at Iron Mountain, in the Golinsky mine, and in the Sutro mine. The bodies of massive sulfide ore, before postmineral faulting, ranged in size from that of the largest body, at the Iron Moun- tain mine, which has a length of 4,500 feet, a width of several hundred feet, and thickness of slightly more than 100 feet, to small bodies only a few tens of feet in maximum dimensions. Some individual ore bodies are discrete lenses in a broad mineral- ized zone, but at a few mines an originally continuous ore body has been offset by faults into separate blocks of ore. All the massive sulfide bodies contain some copper and zinc minerals, but some massive pyrite bodies, as the Hornet ore body at Iron Mountain, contain too little copper or zinc to repay mining as a copper-zinc ore. The only value of the low-grade pyritic bodies at present is in their sulfur content, as the iron— rich residue from roasting has not been utilized. Massive pyrite that is low in copper and zinc occurs both as separate bodies and as low—grade parts of ore bodies that contain minable amounts of copper and zinc. In some mines the upper or lower part of a flat—lying massive sulfide ore body contains so little copper and zinc that it has been left in place. Ore bodies that contain minable amounts of copper and zinc are identical with low—grade pyritic bodies in other respects. Massive sulfide ore that contains a high percentage of zinc occurs mainly at the Mammoth mine, although zinc was recovered from parts of the Richmond ore body at Iron Mountain. Some disseminated copper ore occurs in the No. 8 mine ore body of the Iron Mountain mine and in the Balaklala mine beneath the massive sulfide ore bodies. This copper ore con- sists of chalcopyrite and pyrite in about equal amounts as veinlets and disseminations in siliceous schistose rock; there is no gradation between the massive sulfide ore and the siliceous disseminated copper ore. Three main basemetal ore controls can be recognized in the copper—zinc district. These are: stratigraphic control within the Balaklala rhyolite; structural control by folds and foliation; and feeder fissures along which the solutions ascended. A conjunction of the three types of ore controls was probably a prerequisite for the formation of a major ore body. The minable massive sulfide ore bodies that have thus far been found in the West Shasta district are at the same strati- graphic horizon throughout the district, in the upper part of the middle unit of the Balaklala rhyolite. Ore occurs through a stratigraphic thickness of 600 feet in the Balaklala rhyolite at Iron Mountain, and it is possible that locally the favorable zone may have a greater thickness. The top of this zone is the base of the upper unit of the Balaklala rhyolite, which is composed of coarsephenocryst rhyolite or tuft, but the lower limit is not marked by distinctive flows. The upper part of the middle unit is a group of discontinuous flows and lenticular beds of coarse and fine pyroclastic rocks. The heterogeneous nature of this material is such that the detailed stratigraphy at each mine is unique, yet the fact that this heterogeneous group is capped by a recognizable unit over most of the district makes it possible to locate the ore zone at one general horizon with a fair degree of certainty. Pyritization in this zone is much more widespread and continuous than the scattered distribution of known ore bodies would indicate. Many exploratory drill holes have dis- closed heavily pyritized rock in the favorable zone at c0nsider- ABSTRACT 3 able distances from known ore, and hidden ore bodies have been located by systematically drilling areas in the favorable zone. At some places the character of the rock that was replaced to form ore bodies can be determined; the favored host rock for ore bodies appears to be porphyritic rhyolite that has 2- to 3—millimeter quartz phenocrysts, particularly where this rock is overlain by thinly bedded tuft‘ or fine pyroclastic rocks. Individual ore bodies or groups of ore bodies tend to be con- centrated on or near the axes of broad folds. The ore bodies were formed both in anticlines and in synclines, although those in synclines predominate if basin-shaped structures are in- cluded with the synclines. Examples of ore bodies formed in synclines or basin—shaped warps are: the Richmond ore body of the Iron Mountain mine, ore bodies of the Balaklala and Shasta King mines, and probably the ore body of the Early Bird mine. The broad ore zone at the Mammoth mine is on an arch or dome—shaped structure, and at many places mineral- ization favored the crests of small folds. The ore bodies at the Sutro and Keystone mines and the Old Mine ore body at Iron Mountain are probably on the flanks of folds. Bedding-plane foliation and fracture cleavage had a consider— able effect in localizing ore bodies. The intersection of steep fracture cleavage with gently dipping bedding-plane folia- tion has provided a shattered area with an impervious cap that has localized some ore bodies. Some faults formed before mineralization and acted as channelways for ore-bearing solutions. They generally cut the folds and the foliation at a considerable angle and influenced localization of ore bodies in certain parts of the folds. ' Many favorable areas where the ore zone has not been eroded remain to be explored, but other large areas can be eliminated for geologic reasons. Areas that are worthy of exploration are those within the main northeastward-trending mineral belt that contain the middle unit of the Balaklala rhyolite; those that can be eliminated are areas in which the middle unit is missing because of erosion or because of original lenticularity and non- deposition, and areas covered by a considerable thickness of younger sediments. The stratigraphic sequence is the principal feature used in delimiting areas in which new ore bodies may be found. In areas where the rocks of the middle unit have been eroded or were not deposited it appears most unlikely that prospecting would lead to the discovery of bodies of massive sulfide ore. The lateral controls that can be used for prospecting are much less definite, and although crests and troughs of folds are prob- ably more favorable than the flanks of folds, the empirical method of testing the ore-bearing zone between known ore bodies, and testing for extensions of ore in known mines appears to be the most promising. Detailed mapping of folds, foliation, zones of hydrothermal alteration, and possible feeder fissures would probably lead to more detailed controls for guiding exploration. INTRODUCTION The Shasta copper-zinc district of northern Califor- nia has yielded 54 percent of the copper produced in the State through 1946 (Eric, 1948, p. 202). The western part of the district, which has produced most of the ore, is called the West Shasta copper-zinc district and is the subject of this report. This base-metal mining district lies west of the Sacramento River, in the foot- hills ot the Klamath Mountains that border the north- west end of the Sacramento Valley (fig. 1). 379725—56—2 The district is the western part of the ore~bearing area formerly known as the Shasta copper belt, or in the older writings as a “copper are.” It was thought to be crescent-shaped and to extend entirely around the head of the Sacramento Valley with the convex side of the arc to the north. Recent studies have shown that the so-called copper are consists of two districts at either end of the are that have distinctly different geologic structures and ore occurrences, and that there is only sporadic and unconnected copper mineraliza- tion between the two districts. In recent publications (Kinkel and Albers, 1951; Kinkel and Hall, 1951) the two principal base-metal districts have been named the )Vest Shasta copper-zinc district and the East Shasta copper—zinc district. The West Shasta base-metal dis- trict extends from the Iron Mountain mine at the south to the Sutro mine at the north. The East Shasta base-metal district includes the area from the. After- thought and Donkey mines near the settlement of Ingot on U. S. Highway 299 east to the Bully Hill, Rising Star, and Copper City mines on the north side of the Pit River, 9 miles to the northwest, The location of the West Shasta copper-azinc district and the principal base-metal mines are shown in figure 2. The area mapped includes the Igo, )Vhiskytown, and Shasta Dam 71/2-minute quadrangles, and approximate- ly the southern two-thirds of the Behemotosh Moun- tain quadrangle. The northern part of the Behemo— tosh Mountain quadrangle was not mapped because it is remote from the mineral district and is underlain entirely by umnineralized rocks of the Bragdon forma- tion. The mines are in a northeastward-trending area about 8 miles long and 2 miles wide in the Whiskytown, Shasta Dam, and Behemotosh Mountain quadrangles. The West Shasta copper-zinc district overlaps and in- cludes several gold-producing districts, but this report does not include a separate description of them. These districts are described in reports by Ferguson (1914, p. 22—79) and Averill (1933, p. 5—73), and in many reports of the California Division of Mines. Parts of the mapped area are crossed by State and Federal highways, and the main line of the Southern Pacific Railroad is only a few miles east of the mining district (fig. 1). Bedding, Calif, 2% miles south of the Shasta Dam quadrangle (fig. 2), is the county seat of Shasta County, and is the principal city at the head of the Sacramento Valley. In 1950 the popu— lation was 10,734. Redding is at the junction of the main north-south U. S. Highway 99, and the east- west U. S. Highway 299. Other small towns and settle- ments in the mapped area are Igo, Whiskytown (Schill- ing), Summit City, Buckeye, and the U. S. Bureau of Reclamation headquarters at Toyon. The old smel- GEOLOGY AND BASE-METAL DEPOSITS, WEST SHASTA COPPER-ZINC DISTRICT 124° 123° 122° 121° 120° __ _ O O N _ __ __ _.- __ _J 420 I I I I . @ 41° //V I2: 41° MMe ' V fv m E , < 3% //l‘ MOUNT LASSEN I> { 0 40° \i> 40° NdSHinOS E 39° 39° ‘ . V2 ’0 38° 1 "WW ' 38° H FRANCISCO / a \I\ 124° 123° 122° 121° 120° FIGURE 1,—Index map showing the location of the West Shasta copper—zinc district. INTRODUCTION 5 EXPLANATION 122“22’30” f" : ... ' 40°52’30” Biotin-quartz diorite KT \/ \T V/(x C I ‘ .\ . \ Albite yanite \ _ \ Paleozoic sedimentary rocks X/ T... - q . 33’3"” m e ‘ ' i . a -\ s . . ““ ‘ ' 000‘s ’\ * 5 Balaklala rhyolite v” e .x\ ‘ fifi \ .ozgzgzo s .z3; . ‘ ‘ O '9 j k : é ‘ \ 5:30.. €.o:o'o‘o’o’ v 1 # \— . O. Copley greenstone 9‘ ‘ \ . O. C 9% . :o’o'd ' Massive sulfide mine 0“? on '0“ . -. I "* w: » ’0‘ 1 O 4 Mlles Ni l_|_L,., . ,l—l “L. l .50 <94? 122°37’30” . >1: /UNCLE V7 ‘////%/A V e 4 A \V/smsraez . o Wax/{1M ‘ t WELLA O o s 9‘9“ 9‘9‘ 0 9.0 _ 9 91 l , «2‘4 , / Q, . on , ‘ 5".” ’1 Q‘? s ” 5'” x o I V . \o .. < 4 ' ’9‘ Io". i4... " > A. > 3'34".”«4‘f3'3'3o *\ L ”in r» v v V oooou ’09 0 990.00, 00 p 4 a .x n o woo >. ’0‘!!! {I a v :.:.:.,.~ v . v . 000 4 4 s ‘ . => .55 $3,: r~ < i \l r i LL75 7440°37'30” 122°22’30" BEDDING 122‘15' , 4100 _ WI INDEX MAP ,. . KEY TO ,, . I m 2 OUADRANGLES \ w ‘ f l 1. SchellMln(1950) ’ V l 2. Lamoine (1946) , v; ‘ 3. French Gulch(1948) . V» / l 3 4. Reddlng(1946) ‘ l' \l N g *% 40°30 V Z 39.90.30. 122°37'30” 122°30’ These Quadrangles are from enlarged Geology by A. R. Kinkel. Jv., W. E. Hall. parts ol three Quadrangles shown and J. P Albers on index map and are not publish- ed separately as topographic maps FIGURE 2.—Map showing location of principal mines and the generalized geologic setting of the West Shasta copperzinc district. ter town of Coram, on the Sacramento River, below Shasta Dam is now abandoned and the former town of Kennett above Shasta Dam is under water. In 1951 only the southernmost mines in the district—w the Iron Mountain mine and the Lone Star prospect—— were accessible by road. A branch line of the Southern Pacific Railroad was rerouted in 1950 to the west of the Sacramento River as far as Shasta Dam to provide rail service to the dam and loading facilities for the ore from the Iron Mountain mine. The Iron Mountain mine, which was the only mine operating in the W’est Shasta district in 1952, can be reached by a surfaced road that branches north from U. S. Highway 299W about 3 miles west of Bedding. The Lone Star prospect is accessible along a State For- est—Service road either by way of the South Fork Mountain fire—lookout station, or along a dirt road that extends past the Iron Mountain mine. The old road from the former smelter town of Coram, just below Shasta Dam, to the Balaklala mine was repaired in 1951 so that it was possible to drive from Coram to the Balaklala mine; this is a steep one—way dirt road that washes out during the rainy season. The road from the Squaw Creek arm of Shasta Lake to the Uncle Sam and Clipper gold mines was passable in 1950 but is narrow and tortuous and parts of it are covered by wash and debris each spring. Other mines in the district are accessible only on foot or with horses after ferrying across Shasta Lake. Private boat service is available on Shasta Lake, and the U. S. Bureau of Reclamation has at times supplied barge service to some of the mine owners. However, a road along the west side of Shasta Lake to make accessible the central and northern part of the mineral belt for renewed operations in the district was under construction in 1952. CLIMATE AND VEGETATION Climate and vegetation vary greatly within short distances in the West Shasta district because of the difference in topography. The southeast edge of the mapped area is at the end of the Sacramento Valley and has an altitude of 700—800 feet, whereas the western and northwestern parts of the area are in the rugged Klamath Mountains that reach an altitude of 5,189 feet at South Fork Mountain. Temperatures at lower alti- tudes are high in the summer but moderate in the win- ter. Daytime temperatures of 110°F are not unusual from June through September; higher temperatures have been recorded. A period of 10 days to 2 weeks of high temperature in the summer is generally followed by a comparable period in which the daytime tempera— ture does not exceed 95°. Table 1 gives data on the temperature at Bedding and at two localities in the mountainous area nearby; Mount Shasta City is 50 miles airline north of Bedding at an altitude of 3,555 feet and Weaverville is 29 airline miles west of Bedding at an altitude of 2,047 feet. The humidity at the head of the Sacramento Valley is very low in the summer. Winter temperatures in the Sacramento Valley drop several degrees below freezing a few nights of the year but hard freezes that cause trouble with exposed water- lines occur only at the higher altitudes. Winter tem- peratures well above freezing are the rule. 6 GEOLOGY AND BASE-METAL DEPOSITS, WEST SHASTA COPPER-ZINC DISTRICT TABLE 1.——Tempemture and precipitation, Redding, Calif, and nearby localities [Data furnished through courtesy of E. L. Felton, U. S. Weather Bureau, 1952] 1 Y . . Locality January February March A pril ‘ May June July August Seggem- October 1\ (geim Depgrm Annual Average temperature CT) I Bedding ,,,,,,,,,,,,,,,,,,,,,,,,,, 45. 3 49. 3 I 53. 9 59. 8 i 66. 8 75. 0 82. 0 80. 6 74.0 64. 6 54. 3 46. 7 62. 7 Mount Shasta City,_ . i 33. 4 36. 8 l 40‘ 8 46. 4 i 53. 4 60. 6 67. 9 66.4 58. 8 51. 2 41. 4 34. 8 49. 3 WeaverVille, ,,,,,,,,,,,,,,,,,,,,, 37. 4 42. 0 ‘ 46. 4 51. 3 1 57. 8 64. 7 71. 4 70.0 63. 1 54. 5 44. 4 38. 3 53. 4 1 Average maximum temperature (° F) Bedding __________________________ 53.8 58. 3 63. 9 71. 2 i 79. 1 88. 0 96. 6 95. 4 87. 9 76. 8 64. 2 55. 2 74. 2 , . 41. 6 46. 6 52. 9 59. 2 68. 2 75. 2 84. 8 84. 5 75. 9 66. 1 52. 7 43. 9 62. 6 Weaverville ...................... 47. 2 54.5 61. 3 68. 0 i 76. 4 85. 1 94. 6 94.0 85.8 73. 9 57. 7 47. 2 70. 5 Average minimum temperature (°F) Bedding ____________________ _ 37. 0 40, 3 E 43. 7 48. 3 54. 2 i 61. 3 67. 3 65. 5 60. 1 52.5 44. 2 38. 4 51. 1 lVIOUnt Shasta City 24. 5 26. 7 29. 4 33. 6 38. 7 t 44. 3 49. 0 46. 9 41. 9 36. 4 30. 0 25. 7 35. 6 VV'eaVBrVille .......... 27. 6 29. 6 31. 4 34. 9 39. 2 l 44. 2 48. 1 45. 7 ‘ 40. 3 34. 8 31. 1 29. 3 36. 4 t i 1 Average precipitation (inches) 1 Bedding __________________________ 7. 19 5. 99 4. 96 2. 93 1. 83 0. 86 0. 11 0. 06 0.67 2. 26 4. 06 6. 48 37. 40 Mount Shasta City ,,,,,,,,, _, 6. 07 5. 29 4. 65 2. 65 1. 81 . 94 . 17 . 22 . 85 2. 46 3. 95 5. 52 34. 58 Weaverville ________________ _. 6. 59 5. 61 3. 99 2. 79 1. 50 . 82 . 13 . 12 . 59 2. 26 4. 89 6. 49 35. 78 Volmers __________________________ 10. 74 11. 85 9. 21 4. 97 ‘| 3. 01 1. 88 . 23 14 . 65 6. 32 6. 35 11. 63 66. 98 The amount and type of precipitation also varies with the altitude and the season. Snow is common above an altitude of 1,500 feet, and the higher moun- tains in the district are snow covered most of the win- ter. During some winters snow falls at the valley level but seldom lasts more than a few days. Precip- itation is rare even at higher altitudes from the middle of May until the middle of October. The average pre- cipitation at Bedding and at nearby points is given in table 1. The weather station at Volmers (Delta) 24 airline miles north of Redding is an area of unusually high precipitation; several of these areas of high pre- cipitation occur north and west of Redding. The lower parts of the area are covered by a growth of Chaparral, including much manzanita (Arctosta- pity/Zoe Sp.) that locally is so dense as to be almost im- penetrable. Digger pine (Pinus sabiniana), ponderosa pine (Pinus ponderosa), sugar pine (Pinus Zamberti- one) and Douglas—fir (Pseudotsuga tawifolia), Califor- nia black oak (Quercus kelloggz'i), canyon live oak (Querous chrysolepis) and interior live oak (Quercus wislizenii) grow in the district, but smelter smoke, disas- trons fires, and logging near the head of the valley have destroyed the natural balance of vegetation. Most of the lower slopes are subject to rapid erosion because of the loss of ground cover. The land at higher altitudes was originally heavily timbered with coniferous trees, but much of the best timber was cut for mining operations. Patches of good timber still remain and second-growth timber is com- ing back in some areas that were denuded by fire or by logging, but in other areas a brush cover has in- hibited second-growth timber. PHYSICAL FEATURES Most of the “fest Shasta district is in the Klamath Mountains that border the Sacramento Valley. Part of the district is underlain by a cut surface and a construc— tional surface consisting of gravel of the Red Bluff formation and is generally considered a part of the val- ley. The two principal drainage systems are those of the Sacramento River and of Clear Creek. Throughout most of the district these streams have cut deep canyons, although traces of older broad valleys remain at some places. Tributaries to the main streams make a pattern of rugged youthful canyons separated by long spur ridges. The hillsides are steep; many slopes are near the angle of repose whereas others have not reached this stage and have little or no soil or rock debris. The mountainous areas fall into three groups. A low foothill range east of Clear Creek, dominated by Mule Mountain at an altitude of 2,330 feet, lies on the west side of the Sacramento Valley in the Igo quad- rangle. A second group, the high mountainous area west of Clear Creek, part of which is included in the Igo quadrangle, reaches an altitude of 6,962 feet at Bully Choop Mountain west of the mapped area. The mountains in the northern and western part of the dis- trict comprise the third group. They are separated from the Mule Mountain range by the low divide be- tween thiskytown and Old Shasta and by several higher divides west of thiskytown. Rounded, sub- INTRODUCTION 7 dued landforms predominate in the Mule Mountain range although the canyons are steep and V-shaped. The Shasta Bally range also contains many rounded landforms; rugged topography is rare except in the V—shaped canyons. The topography in the mountain- ous area in the north and northwestern part of the dis- trict, on the other hand, is generally rugged except along the crest of ridges. The rounded crest of these ridges, as seen from the valley, is deceptive and conceals the fact that many of the slopes below the ridge are steeper than the angle of repose. PREVIOUS WORK AND ACKNOWLEDGMENTS Many geologists have worked on the geology of Shasta County and the surrounding area, and without this background the work on this report would have been much more diflicult. Some features of the geol- ogy of the Shasta County base—metal district were de— scribed in connection with the gold—mining activity, which started a few months after the discovery of gold at Sutters Mill in El Dorado County, but no major study of the geology of the district, except for strati- graphic studies by Smith (1894, p. 588—612) and Hershey (1901, p. 225—245), was made until Diller in 1901—4 mapped the Redding quadrangle for the U. S. Geological Survey. The results of his work were pub- lished in 1906 (Diller, 1906), and have been invaluable for all later work. The writers were continually impressed during the course of their field studies by Diller’s accurate observa- tions and his sound conclusions, which were based on a broad knowledge of the geology of northern California. Diller’s emphasis was on the structure and strati- graphic sequence in the district; he gave only a cursory study to the base-metal mines that were at that time just beginning their main period of operation. The rapidly increasing importance of copper mining in the district in the early part of the century made it advisa- ble for the U. S. Geological Survey to continue its work here and to put more emphasis on mineral possibilities. In 1906—7 Graton (1909, p. 71—111) mapped areas around the principal mines in the West Shasta district in more detail and on larger scale topographic maps than were available to Diller. Ferguson (1914, p. 22—79) and Averill (1933, p. 3- 73) described the gold deposits of the district, and added information on the general geology. Hinds (1933, p. 77—122) reported on the geology of the dis— trict and extended his geologic study to the west and northwest of the area covered by Diller. During 1932— 34 G. F. Seager collected much information on the base— metal mines of the district and mapped areas in the central part of the “Vest Shasta District. This infor- mation is given in an unpublished report of the Cali- fornia Division of Mines, 1934. This report is the result of a cooperative project with the State of California, Department of Natural Resources, Division of Mines. Field work by the senior writer was begun in November 1945. J. P. Albers was with the project from 1946 to 1949 when he left to begin geologic work in the East Shasta copper-Zinc dis- trict. W. E. Hall was assigned to the project in 1949 and remained until the work was completed. The writers were assisted. in the work by R. F. Johnson dur— ing 1948—49 and by Juan Rossi and Victor Hollister in the summer of 1948. Field work was completed in 1951. A. R. Kinkel, Jr. and W. E. Hall prepared the report in 1951—52. The writers acknowledge their debt to the. staffs of all the mining companies in the district. Access to all the information compiled by the mining companies as well as access to the mines was given to the writers, in addition to many suggestions and discussions on the geology of the mines. Without this cooperation, the present study would have been impossible. R. T. )Valker and “Y. J. “Talker provided data on the Shasta King mine as well as production data on some of the other mines in the district and they engaged in many stimulating discussions of the geology in the field with the writers. Data were obtained from geologists of the Coronado Copper and Zinc Co., particularly on sam- pling and mine mapping that was done in 1948 by the \Vest Shasta Exploration Co., a subsidiary of the Coro- nado Copper and Zinc Co. Maps of all the mines owned by the United States Smelting Refining and Min- ing Co., as well as production and assay data, and much geologic information, were furnished by that company. R. N. Hunt of the United States Smelting Refining and Mining Co. contributed information on the geology of the Mammoth mine. \V. A. Kerr, owner of the mines that were formerly owned by the Balaklala Consolidated Copper Co., made data available on the Balaklala and Early Bird mines, and the Balaklala Angle Station gossan. Much use has been made of unpublished ma- terial collected by G. F. Seager in 1934 on the mines of the district. Some data available to him at that time were not available at a later date, and his compilation of information on the Balaklala mine was particularly useful. The writers wish to thank the staff of the Iron Moun- tain mine of the Mountain Copper Co., Ltd. for many courtesies and for aid in compiling the records of the operation of that mine for the past 50 years. Much detailed information on the mine was furnished by C. W. McClung, T. P. Bagley, and R. K. McCallum. 8 GEOLOGY AND BASE—METAL DEPOSITS, WEST SHASTA COPPER-ZINC DISTRICT Particular credit is due 0. H. Hershey 1 for informa— tion on the geology of the underground workings at the Iron Mountain mine. Hershey collected information as a consulting geologist for many years at Iron Moun- tain during the earlier years of the mine’s operation, and his unpublished reports and drill logs were used in the writers’ study of the Iron Mountain mine. Most of the ore bodies of the district were inaccessi- ble at the time of the study, and had been so for many years. The cooperation and interest of the mining companies in compiling all records that were still avail- able so that a complete picture of the metallization of the district could be had has aided the writers greatly. GEOLOGIC FORMATIONS The formations in the West Shasta copper—zinc dis— trict range in age from Devonian( ?) to Recent (pl. 1). The oldest formation exposed is the Copley greenstone of probable Middle Devonian age. It is composed of intercalated volcanic flows, pillow lavas, volcanic breccias and tufts, most of which are intermediate or basic in composition, and minor, thin, lenticular beds of tuff and shale. The formation is at least 3,700 feet thick, but the base is not exposed in the mapped area. Lack of a distinctive horizon marker in the greenstone and the destruction of primary features by metamor- phism makes it impossible to estimate thickness in most parts of the district. The Balaklala rhyolite is a group of light-colored soda-rich rhyolitic flows and pyroclastic rocks that overlie the Copley greenstone conformably. Pyroclas- tic rocks make up about one-fourth of the formation. The Balaklala rhyolite formed as a broad elongate volcanic dome, extruded from many vents; the forma- tion is much less extensive laterally than the Copley greenstone. Nonporphyritic rhyolite and porphyritic rhyolite containing phenocrysts of quartz and plagio- clase are lithologic subdivisions; the porphyritic rhyo- lite is further subdivided into flows that contain small phenocrysts and those that contain large phenocrysts. It is possible to map a stratigraphic sequence in the Balaklala rhyolite by using these lithologic subdivisions along with bedded pyroclastic rocks. All the known base-metal ore bodies of the West Shasta district are in the Balaklala rhyolite. Two features on the geologic maps require explana- tion. One is the inclusion of all rhyolitic rocks with the Balaklala rhyolite, whether they are intrusive or extrusive masses; the other is the subdivision of the Balaklala rhyolite on a lithologic rather than on a stratigraphic basis. 1 Hershey, O. H., Private reports prepared for the Mountain Copper (30., Ltd. On the areal geologic map and on most of the geologic maps of mine areas, intrusive rhyolite is not distin- guished from extrusive rhyolite. Subdivisions of the Balaklala rhyolite that can be mapped are based on lithologic differences rather than on a stratigraphic succession. Nevertheless in spite of local recurrence of lithologic types, these subdivisions fall into a se- quence sufliciently common and distinctive to be referred to as the lower, middle, and upper units of the Balaklala rhyolite. All rhyolitic rocks, whether they are the rhyolitic flows of the Balaklala or rhyolitic rocks of the Balaklala type in the underlying Copley greenstone, are shown as Balaklala rhyolite. Although the rhyo- litic rocks are easily distinguished at most places from the mafic rocks of the Copley greenstone, the mode of emplacement of the rhyolitic rocks is not everywhere evident. Unless pyroclastic material is present, or un« less the rocks are exceptionally well exposed, it is com- monly impossible in the field to determine whether a particular sheet of rhyolite was intruded into the Cop- ley greenstone as a dike or a sill, whether the sheet of rhyolite represents an early flow of rhyolitic material in the Copley, or whether the rhyolite is a flow that overlies the Copley and is part of the Balaklala rhyolite. For this reason, all the rhyolitic material is given the symbol for Balaklala rhyolite. The Balaklala rhyolite is subdivided into lithologic types even though three stratigraphic units are recog— nized in the Balaklala, because the determination of stratigraphic units is impossible outside the central part of the district where all the units are present. The Balaklala rhyolite is a volcanic pile that commonly con- tains many lithologic types at one general horizon; the repetition of lithologic types from the same vent and repetition caused by overlapping flows and pyroclastic material from different vents, and the lenticular nature of the volcanic units make it impossible to deter- mine the stratigraphic position of an individual flow or pyroclastic bed without taking the sequence into consideration. The Kennett formation, which is composed of black cherty shale, tuff, and limestone, conformably overlies the Balaklala rhyolite where the latter rock was depos— ited. The Kennett overlies Copley greenstone locally where no Balaklala is present. It was dated by Schuch— ert as Middle Devonian in age (Diller, 1906, p. 2) on the basis of abundant fossils collected from the lime- stone. The greatest thickness of Kennett formation is in Backbone Creek in the northern part of the West Shasta district where Diller measured a section that was 865 feet thick. However, the actual thickness is less, as the beds are repeated by faulting in the area where the section was measured. GEOLOGIC FORMATIONS 9 The Bragdon formation, which is dated as Mississip— pian in age by Diller (1906, p. 3), rests upon the Kennett formation and shows no evidence of a major unconformity in the West Shasta district. However, outside this district warping uplifted the Kennett, and in these areas of uplift an erosional unconformity is present between the Kennett and the Bragdon forma- tions. The Bragdon is predominantly shale but con- tains conglomerate and sandstone. North of Backbone Creek shale and conglomerate of the Bragdon forma- tion is 3,500 feet thick where mapped by the writers, but this represents only the lower part of the forma- tion, which continues north of the mapped area for about 11 miles. The Bragdon formation may be 6,000 feet thick in the Bedding 30—minute quadrangle, ac- cording to Diller (1906, p. 3). Two large plutons intrude the layered rocks of the district. The older pluton is the Mule Mountain stock consisting largely of albite granite, which intrudes the Copley greenstone and the Balaklala rhyolite. This stock was intruded as an elongate body the shape of which was determined by structures formed in the enclosing rocks by the Nevadan orogeny. It is syntec- tonic but later movements have locally sheared the al- bite granite near its margins. The younger pluton is the Shasta Bally batholith composed of a biotite-quartz diorite. This younger pluton intrudes the Copley greenstone, the Bragdon formation, and the albite granite in the \Vest Shasta district. The biotite-quartz diorite is dated by Hinds (1934, p. 182—192) as Late Jurassic in age. It is overlain outside the mapped area nonconformably by strata that belong to the Paskenta and Horsetown formations of Early Cretaceous age. The albite-granite pluton was named the Mule Moun- tain stock by Hinds (1933, p. 105) and the biotite— quartz diorite pluton Was named the Shasta Bally batholith by the same author. Hypabyssal intrusive rocks include dikes and sills of diabase, andesite porphyry, lamprophyre, hornblend- ite, diorite porphyry, dacite porphyry, quartz latite porphyry, and porphyritic rhyolite. The porphyritic rhyolite dikes are pre-Mississippian in age as they do not intrude the Bragdon formation ; some were probably feeders for the Balaklala rhyolite flows. Dikes other than the rhyolite cut the Bragdon formation and are post-Mississippian in age. Cemented gravels of the Chico formation of Late Cretaceous age and of the Red Bluff formation of Pleistocene age unconformably overlie the Copley greenstone in the southeast corner of the Shasta Dam and Igo quadrangles. The geologic column in the West Shasta copper—zinc district is shown in figure 3. . Litholo 'c Thickness Age Formation descriptidn (in feet) Alluvium, surface mantle, Recent landslide deposits, 0—150 gravel - Red Blufi Partly to well- 7 Pleistocene formation J gravel 0 100 Cretaceous Chico formation Sandstone, shale, 07200 conglomerate Hamblendii‘m. lamprophyre iorite. cite. porphyry. Hypabyeeal quartz latite xiprph , Late Jurassic "““mve andesfle pom m: 0, C diabase Shasta Bally Biotitequam batholith diorite Jurassid?) Mule Mountain stock Albite granite Mississippian Bragdon formation Shale, ‘sandstone, 3500+ . Limestone. black Kennett formation cherty shale, tufl' 0-400 Middle Devonian Porphyritic and non- . porphyritic rhyolite Balaklala rhyolite rhyolitic pyroclastic’ 045500”) rocks ‘ Greensmne, keratophyre. Middle Devoniant?) Copley greenstone meta-andesite, pyroclam :3700 +— tic rocks, metagabbro FIGURE 3.—Geologic column in the West Shasta copper-zinc district, Shasta County, Calif. The Paleozoic rocks in the West Shasta copper-zinc district are folded into a broad arch that contains many small folds and forms a broad, low anticlinorium. The axis of the anticlinorium trends N. 15° E. in the central part of the mineral belt and passes through Iron Moun- tain and Behemotosh Mountain (pl. 1). Beds on the flanks of this fold generally dip at angles of 20°—30°, but locally they may be vertical; beds in the central part of the district generally dip at low angles. The broad arch has a gentle culmination in the central part of the mining district at the Uncle Sam mine; in the northern part of the. district, north of the Mammoth mine, this structure plunges gently to the north. The arch is broken by many faults and at the south end by intru- sive masses. Two sets of faults are prominent; one set strikes N. 20°—45° “7., and the other strikes N. 60°— 80° E. Both vertical and horizontal movements are recognized; in nearly all the faults the north block is downthrown. COPLEY GREENS’I‘ONE DISTRIBUTION The Copley greenstone is the basement rock in the West Shasta copper—zinc district and is the most exten- sively exposed formation. It was originally called Copley meta-andesite by Diller but the name was changed to Copley greenstone by Kinkel and Albers (1951) because the latter name is more expressive of the lithology. The principal areas underlain by this for— mation are in the Shasta Dam quadrangle, of which 70 percent is underlain by Copley, and in the Igo and thiskytown quadrangles, where the Copley greenstone is exposed in a belt 9 miles long striking N. 10° W. between the albite granite and the biotite-quartz diorite plutons. Windows of Copley greenstone are also ex- posed through the overlying Balaklala rhyolite in deep 10 GEOLOGY AND BASE-METAL DEPOSITS, WEST SHASTA COPPER-ZINC DISTRICT canyons that cut through the mining district. It im- mediately underlies the Bragdon formation in part of the thiskytown quadrangle, and is brought to the sur- face by a large fault in the northwest quarter of that quadrangle. Although the structure of the copper-zinc district is that of a broad low arch with its axis through the heart of the mining district, the younger Balaklala rhyolite crops out mainly along the crest of the arch and the older Copley greenstone crops out as parallel bands on the flanks of the arch. This apparent anomaly is caused by the rugged topography, the pinching out of the rhyolite toward the flanks of the arch, and by fault- ing. The Balaklala rhyolite, which is thick at the crest of the arch and is thin on the flanks, forms the crests of the rugged hills in the mining district whereas the greenstone forms the lowlands of broad rolling hills. THICKNESS AND RELATIONSHIP TO OTHER ROCKS Partial sections of the Copley greenstone have been measured by Louderback (1928, p. 56—59) and by Hinds (1933, p. 87). Louderback measured a partial section, now flooded, near Kennett that showed a thickness of 2,000 feet; Hinds measured two sections: one on Stacy Creek measured 1,200 feet, and the other on Shirttail Peak measured 1,500 feet. The writers measured a partial section of Copley, 3,700 feet thick, in Modesty Gulch in the \Vhiskytown quadrangle. The Copley greenstone may be 6,000 feet thick in the belt that is exposed between the albite granite and the biotite—quartz diorite plutons in the Igo quadrangle. The biotite-quartz diorite intrudes the Copley in the southwestern part of the Igo quadrangle, and here it has metamorphosed part of the Copley to hornblende schist, amphibolite, and migmatite. The foliation has a uniform N. 300 W'. strike and dips 60° NE. in this belt and except for local transgressions is parallel to the biotite-quartz diorite contact. This foliation may also be parallel to bedding, although in most places in this belt bedding in the Copley is obscure. The only defi- nite bedding is near Brandy and Boulder Creeks where a few shaly tuff beds were seen to be conformable to foliation. If the foliation is parallel to bedding in most of the belt, a section of Copley 6,000 feet thick is exposed. However, much of the banding is caused by metamorphic differentiation by solutions traveling along planes of foliation and it may or may not be parallel to bedding. The Copley greenstone is overlain by Balaklala rhyo— lite and has a gradational contact with the Balaklala. ,A pyroclastic layer ranging from a thin bed to as much as 150 feet in thickness is present at many places at or near the top of the Copley. The pyroclastic layer con- tains rounded fragments of Balaklala—type nonpor- phyritic and porphyritic rhyolite in a tuffaceous, andesitic matrix. It is conformable with the overlying Balaklala rhyolite. A few thin bands of Copley—type greenstone flows and pyroclastic rocks are interbedded in the lower 200 to 300 feet of the Balaklala rhyolite. They indicate that eruption of rocks of intermediate composition con— tinued sporadically after eruption of Balaklala rhyo— lite started and they are regarded as part of the Balaklala rhyolite. The Copley greenstone is cut by many intrusive bodies. The Mule Mountain stock intrudes the Copley in the eastern part of the Igo quadrangle and in the southern parts of the thiskytown and Shasta Dam quadrangles, and the Shasta Bally batholith intrudes the Copley in the western third of the Igo quadrangle. The Copley is also cut by many dikes and sills of non- porphyritic and porphyritic rhyolite. Some of these dikes and sills were feeders for the Balaklala rhyolite flows and pyroclastic material. Others, consisting of sugary, aplitic rhyolite may be related to the stock of albite granite. The best exposures of these dikes are in the western part of the Shasta Dam quadrangle, on Copley Mountain, and in Spring Creek. Dikes of horn— blendite, diabase, diorite porphyry, dacite porphyry, quartz latite porphyry, and lamprophyre also cut the Copley greenstone. GENERAL DESCRIPTION The Copley greenstone consists of interlayered vdl- canic flows, tufi's, agglomerate, and a few thin layers of tufl’aceous shale and black shale of small areal extent. No distinctive horizon marker was recognized in the Copley, and the stratigraphic units are extremely len- ticular. The lower and middle parts of the exposed section of Copley consist predominantly of fine—grained chloritic lava flows and tufl' beds of keratophyric com- position, and some shale. The upper part is composed largely of amygdaloidal pillow lava, fine to coarse pyro- clastic material, and diabase. The top of the Copley consists of extensive but not continuous volcanic breccia as much as 150 feet thick, which generally is too thin to be shown on the quadrangle niaps. The Copley is strongly metamorphosed by the Shasta Bally batholith in the western part of the Igo quad- rangle and is progressively less metamorphosed east- ward away from the batholith. In the western part of the quadrangle, near the contact with the Shasta Bally batholith, the Copley is altered by contact metamor— phism to amphibolite, epidote amphibolite, and horn- blende gneiss and migmatite for as much as 4,000 feet from the contact. In some areas the Copley is strongly foliated, but in others it is massive; it is altered to COPLEY GREENSTONE 11 chlorite-quartz-albite-epidote rock (green schist facies of Eskola) and few original minerals are preserved in the recrystallized rocks. However, megascopic tex- tures are preserved except in the metamorphic zone along the Shasta Bally batholith, or where the Copley is foliated. East of the Sacramento River in the east— ern part of the mapped area the rocks are much less foliated and altered. ‘ The Copley is composed of keratophyre, spilite, and albite diabase, and some meta~andesite and meta—gab— bro. In the field it was not possible to differentiate be- tween these petrographically different types of rocks, and they were mapped on megascopically recognizable types such as greenstone flows, pillow lava, amygdaloi- dal greenstone, greenstone tuff, or coarser pyroclastic material. Nearly all these rocks are of keratophyric composition, however, except for a small amount of spilite and albite diabase. Meta—andesite, which cannot be differentiated in the field from keratophyre or spilite, crops out only in the eastern part of the area in the Shasta Dam quadrangle. The lithologic types are de— scribed, but the petrographic description is given sepa- rately because of the difficulty of correlating the two in the field. LITHOLOGIC DESCRIPTION F inc—grained chloritic lava and tuf—The lower and middle parts of the Copley are mainly light to dark- green, fine—grained lava and tufi of keratophyric com- position. Some flows are finely porphyritic and include phenocrysts of plagioclase, orchlorite pseudomorphic after hornblende, in an aphanitic, greenish groundmass. In the western part of the district much of the fine— grained Copley is massive and hard due to metamor- phism by the Shasta Bally batholith and to a lesser degree by the Mule Mountain stock. The Copley is softer and more chloritic and is foliated in the central part of the district and in the western part of the Shasta Dam quadrangle. Locally the fine-grained Copley, es- pecially fine tuffaceous material, is schistose; foliation is emphasized by weathering, and road cuts commonly ex- pose hard, massive lava under a few feet of soft chlo- ritic, schistose greenstone. Amygdaloidal greenstones are abundant locally. The amygdules have smooth, rounded outlines, and rarely show evidence of stretching. Most of the amygdules are 4—5 millimeters in diameter, although some are as much as 2% centimeters in diameter. Quartz, calcite, chlorite, epidote, clinozoisite, albite, and zeolites are common vesicle fillings. Calcite is commonly removed from calcite-filled amygdules by weathering leaving a vesicular rock. Pillow Zamora—Pillow lavas are abundant in the upper 1,000 feet of the Copley, and in most places they are associated with volcanic breccia. Three varieties of pillow lavas occur in the district. One variety in Modesty Gulch in the \Vhiskytown quadrangle has pil- lows that average 2 feet in diameter. A cross section of an individual pillow shows a dense light-green core about 20 inches in diameter surrounded by a rim of darker green amygdaloidal lava a few inches thick. The amygdules are about a quarter inch in diameter and are filled with quartz or chlorite. Pillows of this variety are in a layer about 20 feet thick, which is under- lain by about 200 feet of dark-green lava that weathers into rounded forms 1—2 feet in diameter that have no apparent internal structure. In the second variety of pillow lava, also in Modesty Gulch, the cores of the pillows are light colored and siliceous and almost without exception contain much white vein quartz. The average major axis of the ellip- tical pillow cores is about 18 inches; the minor axis is about 8 inches. The cores are surrounded by a rim of variolite 2—3 inches thick. The variolite has rounded white spots, 2e3 millimeters in diameter, which make up 75 percent of the material of the rim, in a dark-green chloritic matrix. This pillow layer is about 100 feet thick in Modesty Gulch, where it was traced for more than a mile. A third variety of pillow lava is exposed in Boulder Creek north of the Hornet mine at Iron Mountain. The pillows average 8 feet in diameter and have sharp- edged rims about 1 foot thick. The rims are a lighter shade of green than the centers and are slightly amygda- loidal. Coarse volcanic breccia—The areas of pyroclastic material shown on the geologic map do not have sharp boundaries at many places and contain smaller irregu— lar areas of nonpyroclastic material. The map shows the principal areas that contain much pyroclastic mate- terial, but many small areas throughout the Copley in. addition to those shown contain pyroclastic rocks. However, large bodies of greenstone. do not contain pyroclastic material and for this reason an attempt has been made to differentiate these bodies from areas that are composed predominantly of pyroclastic material. Most of the coarse pyroclastic material lies in the upper part of the Copley greenstone. The volcanic breccia consists largely of a mixture of bombs, lapilli, irregu- lar-shaped fragments, and ropy material in a greenish, aphanitic matrix having the same general appearance as the rock that forms the fragments. The bombs and fragments rarely are more than 6 inches in diameter and average about 4 inches. All gradations are pres- ent between ropy lava, lava with a few bombs and frag- ments, and pyroclastic layers composed almost entirely of bombs and fragments. ' 12 The bombs in the pyroclastic layers are commonly well rounded and are of slightly different color than the matrix (fig. 4). Some angular fragments as well as FIGURE AiriVolcanic breccia near the top of Copley greenstone in Grizzly Gulch in the Whiskytown quadrangle. bombs in volcanic breccia have light-colored rims suggesting that the rims may have resulted from reac- tions between the fragment and the matrix or from fumarolic action. A distinctive volcanic breccia is exposed at many places at the top of the Copley, and forms a transition between Copley greenstone and Balaklala rhyolite. This breccia contains rounded, light-colored fragments, generally 3—4: inches in diameter but locally as much as 1 foot in diameter, in a green chloritic matrix. Some fragments are porphyritic and nonporphyritic rhyo- lite; others which may be silicified greenstone, are light colored and have abundant quartz amygdules and chlorite flecks. This breccia is as much as 150 feet thick, and is well exposed in the head of Modesty Gulch south of Mad Mule Mountain but it is present at many other localities in the transition zone along the Copley- Balaklala contact. Shale and shaly tuf—Beds of shale are interbedded in the Copley greenstone east of the Old Diggings dis— trict in the Shasta Dam quadrangle; they are exposed in road cuts along the road to the Walker gold mine and north and south of the road. Some are black or gray siliceous shale that closely resembles the siliceous shale of the Kennett formation. These shale beds are interlayered with thin beds of tan sandy shale, shaly EAST WEST x t: g ‘ x cu 3: a) x ,2 3 > x ‘ "a 3‘5 8 ‘ a: :w " “ :3 21: ‘ x '_L ml: , ,g :4: x x u— m 3 x x g 25m W: x 1h 8 . / on: m x , 21:0 Ind-Om x . ‘ W—_ 493.0 . fl 2 ,// 1 ~/ //,I < L ’V/n A / _ / 0 N _ 7 ‘ E8 g < , "' ._Q} // a)”, 0 5 v 4 $8 3% v4 4 an; 13m 4 ER 2'0 7 < //1{// 5%: / r T /v/ . /\ A E"; 8 . . “ Sag ~~ were.“ u o ODE-En O ”a: m 2 N F 4.2 13 IL < _: 'Ua: 0: :2: on“ ‘U A , > L =mm‘o3 V —Emm r k mwnnv . 22255 <‘ r omofiu — CU! <. (5594—: .4» “3,323 >.L--"“_ 8 'r>'xEng°0 «of < ‘r.‘ P ‘ T \7 A . > v ‘la 0 I: 39,35 4 12 0’ c a q, 0 E do 1 . 3:9 ES ,, a .- L» «r, 23:5 as “ _.I: w 8“\/3= gtvgm _, 1: 30 c- \I/ \/ n: ._uo O .\-2\ 3: ST“ N\’ In / 3 Ian-o ‘\,.:‘ r— --— 0\ mx‘.» 32 m :\ . ,_N H I LL'O 0 ° 5 H _. C) gee: o “09“.,0 ac .-_¢ >. 0-! —;E.:: up. tron” $0.- E~:e 25:1: mgmo .— dw—SE a) cm. £ ‘17. ! l GEOLOGY AND BASE-METAL DEPOSITS, WEST SHASTA COPPER-ZINC DISTRICT Partial section of the Copley greenstone along the Sacramento River about 11/2 miles N. 70" W. of Bedding, Calif. FIGURE 5. COPLEY GREENSTONE 13 tufi', and Copley-type flows. A similar series of inter- bedded siliceous, cherty shale and greenstone crops out in the canyon of the Sacramento River outside the map area about 11/2 miles west of Redding (fig. 5). These shale beds may be a continuation of the shale near the Walker mine. In some areas rhyolitic'tuff and shale occur together in the Copley as in Brandy Creek and east of Coram. A few thin beds of shaly tufi and black shale are exposed in road cuts on the logging roads near the head of Brandy Creek and in the canyon of Boulder Creek in the Igo quadrangle. Also, some of the strongly sheared rocks in the Copley probably are shaly tufl' as they are associated with volcanic breccia. However, they are so altered that it is difficult to be certain of their original character. PETROGRAPHIC DESCRIPTION Ifemtopbywa—Most of the Copley greenstone is keratophyre. The keratophyres are greenish, apha— nitic rocks that commonly are foliated and chloritized and locally are schistose. Some are silicified and are difficult to distinguish megascopically from Balaklala rhyolite. Although many of the primary structures and textures are destroyed, pyroclastic, amygdaloidal, and pillow structures, and pilotaxitic, porphyritic, and variolitic textures have been recognized Where the rocks are not foliated. Most of the keratophyres have a pilotaxitic texture and are composed of albite or sodic oligoclase, chlorite, secondary quartz, zoisite, clinozoisite, epidote, montmo— rillonite, green biotite, leucoxene, and small amounts of calcite, relict hornblende, apatite, and opaque minerals. Plagioclase, chlorite, and secondary silica commonly constitute more than 90 percent of the rock. The plagioclase is mostly cloudy owing to inclusions of chlorite and in places epidote or zoisite, and it may be either massive or lath shaped. It ranges in composi- tion from AbmAn3 to Ab78An22. Mafic minerals include chlorite, epidote, clinozoisite, zoisite, and relict hornblende. Horn‘blende is largely altered to chlorite and epidote, and only rarely is relict primary hornblende present. Chlorite is the predomi- nant mafic mineral; it occurs as pseudomorphs after hornblende, as tiny flakes disseminated through plagio- clase, as irregular patches and veinlets through the matrix, and as filling of amygdules. The chlorite has negative elongation and the indices of refraction are: n¢=1.617 and n,=1.622; it probably is prochlorite. Epidote, clinozoisite, and zoisite are present as tiny in- clusions in plagioclase and as fillings in some amyg- dules. They occur in quantities sufficient to account for an original plagioclase only slightly more calcic than the albite now present. Veinlets of quartz are common. ,. Aniygdaloidal structures are coiinnon in the kerato- phyres (fig. 6). The amygdules are quartz, chlorite, epidote, calcite, zoisite, albite, and zeolites listed in ap- Gro und- FIGURE 6.~Photomicrograph of amygdaloidal keratophyre. mass composed of laths of albite (AbgoAnm) with interstitial chlorite and minor eipdote. Amygdule filling (a) is calcite and minor epidote and quartz. Crossed nicols, X 20. proximately decreasing order of abundance. Most of the amygdules are 2 to 3 millimeters in diameter and are spherical or ellipsoidal. Some quartz amygdules are as much as 2.5 centimeters in diameter. Although distorted amygdules have been recognized in the west- ern part of the district, most amygdules show no evi- dence of distortion. Some of the keratophyres have a variolitic texture (fig. 7) instead of the more common pilotaxitic texture. The variolites are conspicuous megascopically on a weathered surface and stand out as round white spots 1 to 2 millimeters in diameter in a dark—green chloritic matrix. Some pillow structures have rims of variolite. The variolites are made up of radial growth of un- twinned plagioclase that ranges in composition from AbmAn8 t0 Abg5An15 and contain 5—10 percent tiny disseminated grains of quartz and a little chlorite and zoisite. Variolitic growths constitute as much as 75 percent of the rock, and the rest is mainly interstitial chlorite. 14 GEOLOGY AND BASE-METAL DEPOSITS, ,. LAI'hotomicrograph of Copley greenstone showing variolitic FIGURE texture. Yariolites are Crossed nicols, X 14. sodic oligoclase surrounded by chlorite. ifi'pilite—Spilite comprises only a small percentage of the Copley. Spilite that crops out on Vista Point in sec. 22, T. 33 N., R. 5 N., 1 mile south of Shasta Dam is a hard light—green aphanitic rock containing quartz- tilled amygdules. The rock is finely porphyritic and has a few unaltered phenocrysts of augite and plagio- clase in an aphanitic groundmass. The phenocrysts range from 1~2 millimeters in diameter. Under the microscope the spilite is seen to be com- posed of phenocrysts of albite, aug‘ite, olivine, and epidote in a tine—grained holocrystalline groundmass made up of albite, augite, epidote, hornblende, and chlorite. Albite phenocrysts are clear unzoned crystals as much as 0.75 millimeter long and are twinned ac- cording to Carlsbad and albite twin laws. They have a composition of Ab93A117. Euhedral angite pheno— crysts as much as 2 millimeters in diameter comprise about 5 percent of the rock. Some augite crystals are unaltered, whereas others are partly altered to epidote and chlorite. A few unaltered olivine phenocrysts are present, but most of the olivine is partly altered to chlorite. The groundmass has a pilotaxitic texture, and is com- posed predominantly of albite, augite, and epidote. The albite laths in the groundmass are clear and unaltered and have sharp albite twinning. Some unaltered augite WEST SHASTA COPPER—ZINC DISTRICT occurs in the groundmass, but most of it is altered to epidote and chlorite. Composition of the spilite is given in table 2. Analy- ses 0f spilite from Oregon and California and a com- puted analysis of average spilite as given by N. Sun- dius are listed for comparison. The spilite from Shasta County contains more alu- mina. and magnesia and less ferrous iron than the aver- age spilite as listed by Sundius. TABLE 2,—0hcmical analyscs of spilite Samples: 1. From sec. 22, ’l‘. 33 N., R. 5 W., 1 mile south of Shasta Dam, Calif. Analyst, R. N Eecher. 2. From NEM sec. 35, T. 7 S., R. 42 E., Baker quadrangle, Oregon.1 Analyst. J. F. Fairchild. 3. Average spilite according to N. Sundins.2 l Spilite Average spilite Constituent 1 2 d 53. 15 51. 22 14.39 13.66 1. 28 2. 84 9. 33 9. 20 4.7 4. 55 7. 04 6. 89 4. 58 4. 93 l, 01 . 75 . 19 l. 88 2. 02 ____________ l. 50 3. 32 . 10 . 94 19 .29 14 .25 [J ............ Tr, ,,,,,,,,,,,, 100. 09 99. 66 100. 72 1 Analysis 8 (Gilluly, 1935, p. 234). 2 Sundius, N. (1930). The spilite differs from the keratophyres in showing more of a basaltic character. The spilite has relict olivine and augite and contains abundant epidote, whereas hornblende is the only relict mineral in the keratophyres, which are composed predominantly of albite and chlorite and contain very little epidote. ZlIeta-a/ndesite.——Tlie meta-andesites are hard, dark green to greenish-gray aphanitic rocks that commonly are finely porphyritic. The phenocrysts are mostly plagioclase but some are relict hornblende and augite. Amygdaloidal structures are common. Locally shear- ing is intense and the rock is altered to chlorite schist. The ineta-andesite is composed of plagioclase, chlo- rite, epidote, clinozoisite, augite, hornblende, montmo- rillonite and some quartz and accessory opaque min- erals. .It has a pilotaxitic texture (fig. 8). Plagio- clase, epidote, clinozoisite, and chlorite commonly make up 90 percent or more of the rock. However, as much as 30 percent augite and hornblende are present in the least metamorphosed andesite. Augite commonly oc- curs as corroded relicts in epidote and clinozoisite, but may also be found as tiny euhedral phenocrysts. Green hornblende laths are also present in the least altered andesites, but they are replaced by chlorite and epidote in the meta-andesites. COPLEY GREENSTONE 15 FIGURE 8.—Photomicrograph of meta-andesite of the Copley greenstone with pilotaxitic texture. Rock (Ab71An29) with interstitial chlorite, epidote, and magnetite. nicols, X 14. is composed of plagioclase laths CrOssed Plagioclase typically makes a felted texture of lath- shaped crystals. In a single thin section plagioclase ranges in composition from albite to andesine. Clear plagioclase laths with sharp albite twin lines are ande— sine; in laths of oligoclase composition slight saussu« ritic alteration has occurred, and tiny epidote and zoisite inclusions are present. Albite that locally replaces the original andesine is very cloudy and is massive and untwinned and has negative relief. In the field it is impossible to separate the kerato- phyres from meta—andesite. Textu ‘ally the two rocks are similar, but differences can be recognized under the microscope. “'hereas chlorite is the predominant mafic mineral in the keratophyres, the predominant mafic minerals in the meta-andesite are epidote and clino- zoisite, which replace augite and hornblende and are present as inclusions in plagioclase that has saussuritic alteration. The spilite is distinguished from the meta- andesite by its many unaltered phenocrysts of augite, albite, and olivine in a groundmass of albite, augite, and epidote. Much of the albite is in clear euhedral laths. The composition of the plagioclase in the meta- andesite ranges from albite to andesine; the albite was formed by saussuritic alteration. The meta—andesites have about the same mineralogic character as the spilite, although spilite contains relict olivine phenocrysts, and meta-andesite in contrast, has relict hornblende phenocrysts. Diabase émd albite diabase—Locally diabase and albite diabase are present in the Copley greenstone, probably as sills and dikes. They are hard dark—green, fine-grained rocks composed of plagioclase, hornblende, augite, chlorite, epidote, calcite, and some quartz, apa- tite, and magnetite. Some of the diabase is porphy- ritic (fig. 9), and the texture is ophitic where the rock is unaltered. All the diabase is altered to some extent, and part of it is completely altered to secondary minerals. Augite is mostly replaced pseudomorphously by green horn— blende, but a few relict cores of augite are present. Epidote and chlorite are the predominant mafic min- erals, and in some specimens they have completely re- placed hornblende. there the alteration is most in- tense, the original ophitic texture is nearly destroyed. Plagioclase ranges in composition from albite to andesine and everywhere contains inclusions of epidote and zoisite. The plagioclase in the diabase in the east- ern part of the Shasta Dam quadrangle is saussuriti- cally altered and has many relict cores of andesine. There is no doubt in the eastern part of the Shasta Dam quadrangle that the origin of the albite is by saussuritic alteration of an originally more calcic plagioclase. Some of the diabase in the thiskytown quadrangle that is no more altered than that in the Shasta Dam quadrangle has albite as the only plagioclase, and is an albite diabase. The plagioclase contains some inclu— sions of epidote and zoisite but not enough to account for an originally andesine or labradorite composition by saussuritic alteration. The albite diabase has an ophitic texture similar to the diabase. Metagabbro.—One specimen from north of the Gran- nim mine in the \Vhiskytown quadrangle is a metagab- bro. It is probably part of a small body intrusive into the Copley but the outcrop is too poor to be certain of the shape. The rock has a granitoid texture and has an average grain size of about half of a millimeter. It is very altered and is composed of plagioclase, horn- blende, epidote, chlorite, a little relict olivine, calcite, and magnetite (fig. 10). The plagioclase is albite or sodic oligoclase formed by saussuritic alteration. Hornblende is pseudomorphous after augite. Similar small bodies of metagabbro intrude the Balaklala rhyo- lite southwest of the Stowell mine, west of the Sutro mine, and in the Shasta Dam quadrangle. Keratophyre tuff.—Pyroclastic rocks make up 25 per- cent or more of the Copley greenstone. They range in texture from tuif that is too fine grained to recognize the individual grains to coarse breccia containing frag- ments more than a foot in diameter. Most of the tufl' 16 GEOLOGY AND BASE-METAL DEPOSITS, WEST SHASTA COPPER—ZINC DISTRICT FIGURE {Lil’holomicrograph of altered porphyritic albite diabase. beds are extremely sheared and are altered to fine- grained chlorite, epidote, quartz, albite, montinorillo— nite, and possibly other minerals too fine to recognize. lWany beds that are extremely sheared and altered are probably tutl' because they grade laterally or upward into coarse pyroclastic material. AGE The Copley greenstone is believed to be Middle De- vonian in age, but no fossils have been found to ac- curately date it. It conformably underlies the Balak- lala rhyolite, and the upper part of the Balaklala has been dated as of Middle Devonian age. Therefore the main part of the Copley is probably Middle De- vonian or possibly slightly older. Some of the rocks mapped as Copley along the east edge of the Shasta. Dam quadrangle are younger than some of the Balaklala rhyolite, although all are green- stone with no distinct lithologic break between them and the main part of the Copley. Diller’s Bass Moun— tain diabase (Diller, 1906, p. 7 ), which he considered to be Mississippian in age, lies mostly east of the mapped area, but extends into the southwestern part of the Crossed nicols. X 15. Shasta Dam quadrangle. Diller’s description of the Bass Mountain diabase is as follows: The Bass Mountain diabase of the southern slope of Bass Mountain is generally a dark, somewhat greenish, compact lava which is not porphyritic, but is occasionally vesicular and more frequently fragmental. Where fresh this lava has darker spots of augite embedded in the lighter colored groundmass. Diller correlated this band of greenish lava and pyro- clastic material, which crops out south and east of Bass Mountain and extends to the southeastern part of the Shasta Dam quadrangle, with what he considered to be flows interbedded with the Bragdon formation in the vicinit y of Middle Salt Creek in the Lainoine 15-minute quadrangle 8 miles north of Backbone Creek. The band he mapped as Bass Mountain diabase southeast of Bass Mountain underlies the Bragdon formation (Dil- ler, 1906, p. 7) . Therefore the correlation of this band with beds interbedded in the upper part of the Brag- don seems doubtful. Hinds (1933, p. 91) called the Bass Mountain diabase of Diller’s Bass Mountain basalt because of the surficial origin of the rocks. Hinds states that the Bass Moun— tain basalt rests unconformably on the Copley meta— «COPLEY GREENSTONE 17 FIGURE 10.——Pliotomicrograp11 of metagabbro showing plagioclase laths showing saussuritic alteration. Crossed nicols, X 15. andesite and the Kennett formation and is inter-bedded with and overlain by Bragdon strata in the area from Bass Mountain southward to Newton. The basis for this statement is not known, as he does not show any Bragdon in this area on the map, and it is not further explained in the text. The writers were not able to map a lithologic or a time break in the greenstone in the mapped area, and they consider all the greenstone to be Copley, with the Copley becoming less altered and less metamorphosed to the east, although recognizing that it became younger also. J. P. Albers and J. F. Robertson, who in 1951 mapped the southeastern part of the Lamoine 15- minute quadrangle adjoining the West Shasta district, mapped the continuation of the same rock units (the Balaklala rhyolite and‘slightly metamorphosed green- stone pyroclastic rocks) that crop out along the north- eastern border of the Shasta Dam quadrangle in the West Shasta district. They found tutf beds in the Balaklala that strike northeast and dip 40°—60° SE. under slightly metamorphosed greenstone that corre- lates with the pyroclastic greenstone along the eastern border of the Shasta Dam quadrangle shown on plate 1. These greenstone pyroclastic rocks, in turn, dip under shale of the Kennett and Bragdon formations. Thus it seems probable that flows and pyroclastic rocks of intermediate to basic composition were being erupted in the Shasta Dam quadrangle while Balaklala rhyolite type flows and pyroclastic rocks as well as flows and pyroclastic materials of intermediate composition were erupted to the northeast in the Lamoine quadrangle. The pyroclastic greenstone in the eastern part of the Shasta Dam quadrangle (Diller’s Bass Mountain (lia— base) apparently is younger than part of the Balaklala rhyolite and older than the Kennett formation. BALAKLALA RHYOLITE GENERAL DESCRIPTION The Balaklala rhyolite is made up of many rhyolitic flows and beds of coarse and fine pyroclastic material that together form a broad elongate volcanic pile. Al- though the rocks of the Balaklala include many litho— logic types that can be mapped separately, they are almost identical chemically and mineralogically. The mode of formation of the rocks and their reaction to the secondary processes to which they have been subjected account for many of the differences in appearance. there the rhyolitic rocks are not weathered and are not 18 GEOLOGY AND BASE-METAL DEPOSITS, WEST SHASTA COPPER—ZINC DISTRICT deformed, they typically are hard light-gray or light- green felsitic rocks, many of which contain megascopi— cally Visible quartz and feldspar phenocrysts. The number and size of the phenocrysts vary in different flows, and this feature has been used to distinguish between flows that are otherwise identical. Amygda- loidal, flow-banded, flow-brecciated, and platy rhyolitic rocks are varietal types of flows. Pyroclastic rocks range in texture from coarse volcanic breccia or con- glomerates through lapilli tufl’ to shaly tufl". Foliation has been formed in the rhyolite by dynamic metamorphism. Sericite schist has been formed from rhyolite in some areas; sheeted rhyolite has formed in other areas. The rhyolite is altered in some places to dark-green or dark—gray rocks and in other places to shades of pink, lavender, green, or white by regional metamorphism or by hydrothermal alteration. The common hydrothermal alterations are pyritization, silicification, and sericitization. Much of the rhyolite is iron stained. DISTRIBUTION AND RELATIONSHIP TO OTHER ROCKS The Balaklala rhyolite crops out in a belt 16 miles long and 5 miles wide that strikes N. 15° E. from the south half of the “lliiskytown quadrangle to the southwest quarter of the Behemotosh quadrangle. It forms the rugged hills west of the Sacramento River from South Fork Mountain and Iron Mountain in the. VVhiskytown quadrangle northeast to Mammoth Butte and Behemotosh Mountain in the Behemotosh Moun- tain quadrangle. The total thickness of the siliceous flows and pyroclastic rocks may be as much as 3,500 feet; it is thickest in the central part of the district and thins toward the periphery but varies greatly in thickness from place to place because of the difference in the amount of material that was extruded from many separate vents. Small dikes, sills, and plugs of Balaklala rhyolite cut the underlying Copley greenstone throughout the mapped area. Also some thin, Balaklala rhyolite-type pyroclastic and flow rocks are in areas that are predom- inantly Copley greenstone (fig. 11). In the eastern part of the area, the eruption of lava of Copley green- stone continued while lava of Balaklala rhyolite was erupting farther west, and at some places the two lava types interfinge' and are contempO‘aneous. Some of the bands of rhyolite in the Copley greenstone are erosion remnants in the troughs of synclines along the thin outermost edges of the volcanic pile, but others are rhyolitic material that was erupted locally before the WEST EAST ; fl.— 92 gs .2. En 2 30 +43 '— E°m A. _ \— gm ‘:E u, m n) >\ N 0 H ._ ' x_ __u> «ms? 4: q L1:). 23:0- :m 2‘0 :Vl 0.: .- m- —m Ln: 2‘ o _ “‘0 3E... 3 1: a) DJ .0 'U .__3 u ”an o. >‘—‘ ‘43 o m ‘-— - . 9:33 3:33,. .29; .o— a, ..: L m an = ._ ~ 2.9 30v “’3 tea gEU figs E 0% 355 Baa—gab: sag mg a 50 :>. “:0 "" “ND ‘- c C‘- ocEfi using, ctgw €23 g a); : >~Q~EOIU=z0 wcv : “mo . 9f: '7) EBDU‘OZN“ S 9:20 of“ ME no; a) acre ”'3 -:N.,; 4.: MC“? G :0: >U m 1” :‘Vu >.t« m ' >~: :13” or— j >~m m ”EEww zwmcfiEQ o c» —o 2) n ‘Oflezem n:t~m.-gog >55, am mg 5 gain.” 56022‘95» .c‘“ 8 8 '5 mmN w a. (scam! ‘5 c: ‘ l #__ m . v p .- r7 ~ 1‘ My < i . , \ it , A ) (7 A1 A. _‘ V 7‘ 7 V A. 4 s A < . a . .) E, \. < ,\ V 1 => >L m A > 4», E) 7‘7 ext 2 < L 4 a x > A v 4 S J L V r7 t A , a x . V” ,, AV .Nv ,1 v- _ 7% Thickness, Infeet 150 200 FIGURE 11.——Partial section in the Copley greenstone that contains interbedded rhyolitic flows and pyroclastic rocks, showing distribution of map units in the Balaklala rhyolite on the east flank of Behemotosh Mountain. Locality is 4,000 feet N. 15" \V., from the Walker mine. eruption of the flows of Copley greenstone had ceased and are interlayered with the Copley. Examples of rhyolitic flows that are infolded in the Copley are some of the rhyolite in the southwest quarter of the Whisky- town quadrangle, and some rhyolite along the Sacra- mento River in the southern part of the Shasta Dam quadrangle. Rhyolitic flows and pyroclastic rocks that are interlayered with the flows of Copley greenstone are generally in the upper part of the Copley and near the Copley-Balaklala contact; they can “arely be distin— guished from rhyolitic sills in the Copley unless they are accompanied by rhyolitic pyroclastic material. At many places along the Copley-Balaklala contact there is a transition zone. At these places, the upper part of the Copley contains bombs and fragments of rhyolite similar to Balaklala rhyolite, mixed with Cop— ley greenstone pyroclastic material. At some localities the transition zone grades downward into mafic pillow lava and upward into rhyolitic pyroclastic rocks. Minor flows of Copley greenstone~type lava and pyroclastic rocks are interlayered with the Balaklala rhyolite at some localities. These have been distin- guished on the geologic map from the Copley green- stone because they are flows younger than part of the Balaklala; the same differentiation could not be made for early flows of rhyolite in the Copley because sills of Balaklala rhyolite in the Copley are common. It was diflicult to determine whether some areas of greenstone in the Balaklala near the Stowell mine are windows of the underlying Copley, or whether they are younger greenstone flows in the Balaklala, but they are shown on the geologic map as greenstone flows in the Copley. BALAKLALA RHYOLITE 19 The Balaklala is conformably overlain by the Ken— nett formation. At many places—as along the east side of Backbone Creek between Upper Limestone Val- ley and Lower Limestone Valley; along the road to the Mammoth mine; east of the Golinsky mine; and in the vicinity of Butcher Creek—rhyolitic tuff and pyro- clastic material grades upward into shale and sand- stone of the Kennett without a stratigraphic break. The lower limit of the Kennett is placed where shale predominates over rhyolitic tutf. STRATIGRAPHIC RELATIONSHIP The Balaklala rhyolite is a complexly interlayered broad volcanic pile. Although the volcanic rocks were extruded from many vents, and sills and dikes of the same age and lithology intrude the flows, a recognizable stratigraphy is present in the pile, so that the group of . volcanic rocks that were extruded early in the sequence can be mapped separately from those extruded later. Geologic mapping has shown that there was a pro- gressively coarser crystallization of phenocrysts of quartz and feldspar in the magma chamber from which the flows were derived, and although there. are many exceptions and reversals, the earliest and most wide- spread flows were nonporphyritic, later flows contained phenocrysts 1—4 millimeters in diameter, and the latest flow contained coarse phenocrysts more than 4 milli- meters across. These types have been used as lithologic units on the maps, but it was found that the strati- graphic significance of the lithologic types must be interpreted with caution; later rhyolitic rocks intrude earlier flows as dikes and sills that are not always dis- tinguishable; in areas where vents were quiescent for long periods some types of flows are absent; and lava from several vents interfinger. About one—fourth of the Balaklala rhyolite is made up of fine- to coarse-rhyolitic pyroclastic material. Al- though pyroclastic beds are widely distributed through- out the Balaklala, they are more common in some parts of the stratigraphic section than in others. Concen- trations of pyroclastic material are most common in the upper part of the lower unit of the Balaklala in the central part of the district, and in the upper part of the middle unit. Pyroclastic beds are also present locally at the base and at the top of the upper unit of coarse-phenocryst rhyolite and form transition zones to the rocks above and below. The pyroclastic rocks range in size from small bodies a few tens of feet in length to continuous layers that have been traced for several thousand feet. They are composed of shaly . tufi', crystal tuff, lapilli tufl", fine and coarse volcanic breccia, flow breccia, and volcanic conglomerate. . It is not always possible to determine whether a volcanic breccia. was of pyroclastic origin or whether it is a flow breccia which was formed by the breakage and inclusion of fragments of crust into the liquid interior of a flow. Generally, if the fragments and matrix were of the same material, the breccia was regarded as a flow breccia. Much of the pyroclastic material is water deposited, but some areas of pyroclastic material are roughly equi- dimensional in plan and may have been formed as ex- plosion pipes of volcanic breccia. Few widespread tuff layers that would serve as horizon markers have been found in the. Balaklala. Individual flows and pyroclastic beds are lenticular, and only a few can be traced for as much as 3,000 feet. The most notable ex- ception is the cumulo dome of coarse-phenocryst rhyo- lite that forms the upper unit of the Balaklala rhyolite from the Stowell mine to the Golinsky mine—a dis- tance of about 6 miles. All the flows in the Balaklala rhyolite except the in- terlayered mafic flows are of uniform chemical and mineralogic composition, and where pyroclastic mate- rial was absent it was impossible to map individual flows except by texture. The phenocryst size is the main criterion used in mapping individual flows. In flows of porphyritic rhyolite in the “lest Shasta dis- trict, the quartz and feldspar phenocrysts maintain a nearly uniform maximum size, and a seriate texture is - seldom present. Megascopically, the quartz pheno— crysts are conspicuous, whereas the feldspar pheno— crysts blend with the groundmass and are inconspicu- ous. The same criterion of phenocryst size was used by Gavelin (1939, p. 146) in mapping similar soda-rich rocks in the Malanas district, Sweden. Flow-banding is common in some of the nonporphyritic rhyolite at the base of the Balaklala, and was an aid locally in mapping structure. It is uncommon in the porphyritic rhyolite. Three texturally distinctive varieties of rhyolite make up the flow and pyroclastic rocks of the Balak- 1ala: (1) nonporphyritic rhyolite, in which quartz grains are microscopic, except a few as much as 1 milli- meter in diameter; (2) medium~phenocryst rhyolite, in which quartz phenocrysts range from 1 to 4 milli— meters; and (3) coarse-phenocryst rhyolite, in which quartz phenocrysts are more than 4 millimeters. The nonporphyritic rhyolite is characteristic of the lower part of the volcanic sequence, the medium-phenocryst rhyolite of the middle part, and the coarse-phenocryst rhyolite is characteristic of the upper part. Each of the three distinctive varieties of rhyolite is somewhat irregularly distributed laterally, so that at many places, especially around the periphery of the volcanic pile, only one or two varieties are present. The variety 20 GEOLOGY AND BASE—METAL DEPOSITS, WEST SHASTA COPPER—ZINC DISTRICT most characteristic of a particular part of the sequence at places contains minor flows, pyroclastic layers, and dikes of the other kinds. Provided these deviations are kept in mind, it is convenient and useful to refer to lower, middle, and upper units of the Balaklala rhyo- lite, to emphasize the stratigraphic significance of the three distinctive varieties of rhyolite. Recognition of this general sequence has led to a practical interpreta- tion of structure and favorable zones for ore in many of the mine areas; more widely it clarifies the regional structure and provides a basis for mineral exploration. The lithologic description of the lower, middle, and upper units of the Balaklala rhyolite is given below. Generalized stratigraphy of the Balaklala rhyolite Um't Transition zone to Kennett for- mation. Description Feet Tuff containing some quartz pheno- 0*300 crysts more than 4 millimeters in diameter and rhyolitic tuif interbedded with thin shale beds. Coarse-phenocryst rhyolite contain- ing quartz phenocrysts more than 4 millimeters in diameter. Transition zone at the base locally is composed of coarse- phenocryst rhyolite tuff and breccia. Predominantly flows of medium- phenocryst rhyolite and pyro- clastic material with quartz phenocrysts 1 to 4 millimeters in diameter but contains many small flows of nonporphyritic rhyolite. Widespread pyroclas- tic beds in the upper part of the middle unit. Contains a few small mafic flows of Copley greenstone—type lava. Predominantly nonporphyritic rhyolite and rhyolitic pyrov elastic material but includes a few flows of medium-phenocryst rhyolite and a few mafic flows. Mixed mafic and silicic pyro- clastic rocks. Upper __________ 0—1, 400 Middle _________ 0—1, 500 Lower __________ 0—2, 000 Transition zone to C o p 1 e y greenstone. 0—150 The early rhyolitic flows that form the lower unit of the Balaklala are more widespread and continuous than later flows. The lower unit consists mostly of non- porphyritic rhyolite, some of which is flow banded, but it also contains rhyolitic tuff and volcanic breccia. Flow-banded rhyolite (part of which may be tuff) and flow breccia are more common in the lower unit than in the middle, and shaly tuff is less common. Sev- eral varieties of pyroclastic breccias are in the lower unit; they are predominantly flow breccias, but some contain principally fragments of flow—banded rhyo- lite in an unbanded, tuffaceous matrix; others contain fragments of nonporphyritic rhyolite in a matrix of crystal tuff with quartz and albite crystals, and still others have fragments of porphyritic and nonporphy- ritic rhyolite together with fragments of greenstone in a matrix that may be either felsic or mafic. A few flows of medium-phenocryst rhyolite. and pyroclastic mate- rial, and a few Copley greenstone—type mafic flows, are inter-layered with the predominantly nonporphyritic rhyolite of the lower unit of the Balaklala. This unit is as much as 2,000 feet thick at some places, although at other places rocks of the middle unit rest on Copley greenstone where the flows of the lower unit were not deposited. The middle unit of the Balaklala, the medium—pheno- cryst rhyolite, consists characteristically of porphyritic rhyolitic flows and pyroclastic material containing quartz and feldspar phenocrysts 1—4 millimeters in diameter. It contains many flows of nonporphyritic rhyolite in some localities, and at such places it is difli- cult to distinguish the lower unit of the Balaklala from the middle unit. The upper part of the middle unit contains abundant pyroclastic layers in the medium— phenocryst rhyolite, but flow breccias are rare. The pyroclastic layers in the lower and middle units are well exposed north of the Mammoth mine in the canyon of Little Backbone Creek, and in the North Fork of Squaw Creek arm of Shasta Lake. North of the Mam- moth mine single beds of coarse pyroclastic rocks have been traced continuously for more than 3,000 feet, and in this locality the pyroclastic beds attain a thickness of 300 feet. The upper part of the middle unit of the Balaklala is the ore zone, and the deposits occur as replacement bodies in medium—phenocryst rhyolitic flows that lie beneath pyroclastic beds. The flows of the middle unit of the Balaklala did not extend as far laterally in some areas as those of the lower unit, but they are more extensive than those of the upper unit. The middle unit is generally 500 to 1,500 feet thick, but at a few places the upper unit rests directly on the lower unit. The upper unit of the Balaklala is characteristically a single, continuous body of massive, uniform, coarse— phenocryst rhyolite, which contains many quartz and feldspar phenocrysts that are more than 4 millimeters in diameter. Most of the upper unit is structureless, without bedding or layering, and locally the rocks are poorly foliated. This unit is about 1,400 feet thick at Mammoth Butte, but thins abruptly toward the periphery. Although rare Within the main body of the upper unit, a few beds of pyroclastic rocks do occur. These rocks, composed in part of coarse-phenocryst rhyolite, are common at the top and bottom of the BALAKLALA RHYOLITE 21 upper unit and as extensions, in the same stratigraphic horizon, beyond the periphery of the massive, non- pyroclastic part of the upper unit. The coarse—pheno— cryst rhyolite forms a cumulo dome, and the massive structureless character of a large part of the rock tends to obscure the less prominent areas of associated coarse— phenocryst pyroclastic rocks that give evidence of its surface origin. The pyroclastic rocks are described in more detail than their relative abundance would jus- tify because they are horizon markers and because they are critical features used in determining the origin of the main body of coarse-phenocryst rhyolite. Only one area of pyroclastic rocks is recognized within the main body of the upper unit of the Balaklala rhyolite; this area is exposed on the southeast side of Mammoth Butte above Shoemaker Springs and above the Mammoth mine, where a layer of coarse pyroclastic material 70 feet thick contains fragments of coarse— phenocryst rhyolite mixed with fragments of nonpor- phyritic rhyolite in a tuifaceous matrix. A thin bed of tufi' or fine volcanic breccia that con- tains quartz phenocrysts more than 4 millimeters in diameter occurs at many places at the base of the coarse— phenocryst rhyolite of the upper unit. Tuff beds are also present above this rhyolite and are interbedded with thin beds of shale of the overlying Kennett for- mation. The pyroclastic zones in the uppermost and lowermost parts of the upper unit are widely distrib- uted but are characteristically lenticular and discon- tinuous, although locally they may be traced, except for erosion gaps in the present topography, over an area of several square miles. The coarse-phenocryst rhyolite is overlain by a fine volcanic breccia and sandy tuff that contains fragments of this rhyolite. The volcanic breccia is overlain in turn by interbedded crystal tuff, fine-grained tuff beds, tuffaceous shale, and thin beds of gray shale. The beds of tuff and fine pyroclastic material at the top of the coarse—phenocryst rhyolite are best exposed on the ridge east of the Mammoth mine, about 70.0 feet west of the prominent outcrop of limestone of the Kennett formation. This tufiaceous zone is also well exposed east of the Golinsky mine (fig. 12). The tuft beds grade upward into shale of the Kennett, and the contact between Balaklala and Kennett is placed where shale predominates over tuff. One of the most continuous zones of pyroclastic mate— rial is the transition zone at the base of the upper unit of the Balaklala rhyolite, directly under the coarse- phenocryst rhyolite. This zone is commonly made up of one or more beds of tuff and is 10 to 50 feet thick, Approximate thickness, in feet Siliceous black shale of the Kennett formation, overlain by limestone - Rusty pyritized zone along contact Rhyolitic tuff 540 50 Fine-grained sandstone .‘ Poorl bedded rhyolitic tu with minor beds 75 of crystal tuff - . Very well bedded rhyolitic tuff, - ., in part banded. Beds of shaly tuff and crystal tuff. Crystal tuffs contain black quartz pheno- crysts and crystal chips as much as 5 mm across. Some pheno- crysts are imbedded in well bedded shaly tuff Volcanic breccia, 4~inch fragments of bluish-white porphyritic rhyolite with 4-to 5rmm quartz phenocrysts. Part of this looks like tuff 1 w Rhyolitic tuff breccia 35 20 20 Nonporphyritic rhyolite underlain i by porphyritic rhyolite FIGURE 12.—~Vertica1 section across the contact between the Balaklala rhyolite and shale of the Kennett formation east of the Golinsky mine. but, where it is composed mostly of coarse pyroclastic material, it is as much as 150 feet thick. Even this pyro- clastic zone, it must be emphasized, is made up of several discontinuous pyroclastic beds, and in many places the transition zone is absent. Beds of‘tuff also overlie the dome of coarse—phenocryst rhyolite and one coarse pyro- clastic bed is interbedded with the coarse—phenocryst rhyolite west of the Mammoth mine. The pyroclastic zone that underlies the coarse-phenocryst rhyolite con- sists mostly of light—colored, rhyolitic tuff or fine pyro- clastic material, although a coarse pyroclastic layer occurs 500 feet south of the Copper Crest ore body of the Mammoth mine. The pyroclastic zone under the coarse-phenocryst rhyolite is exposed at many places in the Mammoth mine area; it is also exposed under the coarse-phenocryst rhyolite north and northeast of the Uncle Sam mine, at an altitude of about 2,750 feet, and at the surface over much of the topographic flat be- tween the Keystone and Stowell mines. The coarse-phenocryst rhyolite dome is not as ex- tensive laterally as the tuff beds above and below it, and where the coarse-phenocryst rhyolite wedges out, the overlying and underlying tuif beds merge and con- tinue beyond the limits of the dome. The composition and texture of the pyroclastic beds in the transition zone at the base of the upper unit of the Balaklala rhyolite are not uniform. The transition zone consists predominantly of thin—bedded rhyolitic 22 GEOLOGY AND BASE—METAL DEPOSITS, WEST SHASTA COPPER—ZINC DISTRICT FIGURE 13.~Coarse-phenocryst Balaklala rhyolite containing dark quartz phenocrysts, many Of the dark phenocrysts are angular clasts Of quartz, and the rock may be a crystal turf. tuff interbedded with tuff containing quartz crystals and chips that are more than 4 millimeters in diameter. A coarse-phenocryst rhyolite containing dark—gray tO smoky quartz phenocrysts in a greenish-gray matrix is associated at many places with the tuff layer at the base of the coarse—phenocryst rhyolitic dome (fig. 13). In most places the rhyolite containing smoky quartz phe- nocrysts is a tuff, but in other places the matrix is too altered to be certain. Lithic tufi‘ containing fragments of coarse-phenocryst rhyolite is fairly common, and at some places the tuff grades into volcanic breccia and fragments of nonporphyritic and porphyritic rhyolite one—half to 2 inches in diameter in a matrix Of fine tuft or crystal tufl'. Some of the fragments Of rhyolite in this volcanic breccia are well rounded and appear to be waterworn, and part of the bed is a volcanic conglom— erate. The transition zone at many places grades downward into the tutf and flows of the middle unit of the Balaklala. The center Of the cumulo dome of the coarse-pheno- cryst rhyolite is probably about 1 mile southwest Of the Mammoth mine. that appear to have been the main feeders for this rhyolite are exposed near the Uncle Sam gold mine. There the tuff of the upper unit of the Balaklala at the base Of the dome Of coarse-phenocryst rhyolite, and the underlying flows and pyroclastic rocks Of the middle unit have gentle dips. They are cut by plugs of coarse—phenocryst rhyolite that have steep contacts. These plugs, which were the feeders for the dome, cut the coarse-phenocryst rhyolitic tuff at the base of the dome although at this locality they cannot be traced intO the main dome of coarse-phenocryst rhyolite because of an erosion gap in the present topography. PETROGRAPHIC DESCRIPTION The silicic flows and pyroclastic beds of the Balaklala rhyolite are leucocratic rocks that have a very high soda content. The composition Of the Balaklala is shown in table 3. The rhyolite contains mainly albite and quartz and some epidote, orthoclase, chlorite, sericite, clay minerals, and magnetite. Some glass was present, but it is now devitrified. BALAKLALA TABLE 3.——0hemical analyses of ewtrusive and intrusive phases of Balaklala rhyolite . Flow of medium-phenocryst rhyolite from Igo quadrangle. Analyst, M. K. Carron. . Flow of coarse-phenocryst rhyolite near Balaklala mine. Analyst, W. J. Blake, r. . Wgathered coarse-phenocryst rhyolite from Balaklala mine. Analyst, W. J. lake Jr. . Dike of ’coarsc-phenocryst rhyolite near north portal of Spread Eagle mine.1 . Plug of coarse-phenocryst rhyolite near Clipper mine.2 . Rhyolite from Iron Mountain mine.3 monum— Chemical analyses Constituent 2 1Analysis from Butler, B. S., 1909, Pyrogenetic epidote: Am. Jour. 801., 4th ser., v. 8 2'Analysis from notes of Graton, L. C.. and Butler, G. S., 1906, U. S. Geo]. Survey. 3Analysis from notes of Diller, J. 8., 1901—04, U. S. Geo]. Survey. NONPORPHYRITIC RHYOLITE The nonporphyritic rhyolite is a dense felsitic rock without megascopic- phenocrysts or with only sparsely disseminated quartz and feldspar phenocrysts as much as 1 millimeter in diameter in an aphanitic groundmass. The color ranges from white to light bluish green and buff, and more rarely to red, greenish black, and black. At the surface the nonporphyritic rhyolite is generally hard and siliceous looking, but locally is soft and al- tered. Some of the nonporphyritic rhyolite is banded, as shown by the delicate flow lines that are brought out by weathering, by color differences, or by stretched vesicles that are filled with quartz and epidote. Con- torted flow banding is common, but in some localities the flow structures are regular, and in the field it is difficult to distinguish whether the banding was due to flow, to schistosity, or to bedding in a fine-grained tuff. Much of the banded rhyolite proved to be tuff when examined under the microscope. A dark-green- ish-black aphanitic rock that was mapped as black fel- site is exposed in the lower part of the middle unit of the Balaklala in the northern part of the district. The dark felsite is in part dacite and in part dacitic tuff. It has sharp contacts with the lighter colored soda rhyo- litic flows and pyroclastic rocks. The rhyolite is called nonporphyritic if it contains no phenocrysts or only sparsely disseminated quartz and albite phenocrysts less than 1 millimeter 'm diameter. RHYOLITE 23 The quartz phenocrysts are subhedral and are shattered by closely spaced fractures. The albite phenocrysts in the nonporphyritic rhyolite are lath shaped, while those in the medium— and coarse-phenocryst rhyolite are more nearly equant in outline. Carlsbad twinning is pre- dominant; albite twinning is much rarer than in the albite phenocrysts in the porphyritic rhyolite. The groundmass is a fine-grained aggregate of albite and quartz that contains some chlorite, epidote, clay minerals, sericite, and hydromica, and small quantities of apatite, magnetite, biotite, and sphene. The ground- mass texture may be pilotaxitic, trachytic, or micro- granitoid, and fluidal, microspherulitic, and amygda— loidal structures are common. Where unaltered, the groundmass consists mainly of a felted mass of albite laths averaging about 0.1 milli- meter in length, and interstitial quart-z. Albite ranges in composition from Ab95An5 to AbggAng. In some specimens the albite laths are alined and flow around phenocrysts, forming a trachytic texture. A few thin veinlets containing albite and quartz cut the rhyolite. Mafic minerals are secondary green biotite, chlorite, and epidote, which occur in fractures in the rock and as vesicle fillings. All gradations exist from unaltered nonporphyritic rhyolite consisting mainly of quartz and albite to sheared and altered rhyolite composed of quartz, chlorite, sericite, hydromica, clay minerals, epidote, and green biotite. Much of the nonporphyritic rhyolite consists of a granular aggregate of quartz, sericite, chlorite, epidote, clay minerals, and magnetite, and has a uniform grain size of 0.01 to 0.02 millimeter. Some of the nonpor- phyritic rhyolite shows excellent fluidal structures in ordinary light. Glob‘ulites of magnetite are drawn out to form sinuous bands. These structures are not evi— dent under crossed nicols, which brings out a micro- granular texture. This texture probably indicates a devitrified glass, as the microgranular texture does not reflect the fluidal structures. Microspherulitic structures are common in the non- porphyritic rhyolite but are rare in the porphyritic rhyolite, which has a slightly coarser grained ground- mass. These microspherulites are most common in the rhyolite that has a pilotaxitic or trachytic texture. The spherulites are 0.1 to 0.3 millimeter in diameter and have a fibrous, radial growth. In some, the fibers have a positive relief and consist entirely of quartz; others have a strong negative relief and consist of albite and possibly cristobalite. Most of the spheru- lites have a random pattern, although some are ar- ranged in chains. Some of the nonporphyritic rhyo- lite has many rounded forms of quartz about 0.1 to 0.3 24 GEOLOGY AND BASE—METAL DEPQSITS, WEST SHASTA COPPER-ZINC DISTRICT millimeter in diameter. They have the same shape as the microspherulites, but most of them have no internal structure. They probably are spherulites that have been replaced by quartz. Amygdaloidal structures are present in the nonpor- phyritic rhyolite, but are absent in the porphyritic rhyolite. The vesicles are lenticular and are as much as 1 centimeter long and 3 millimeters wide. They are filled with quartz, epidote, and chlorite. A dark—greenish-black felsitic rock that occurs locally in the middle and lower units of the Balaklala rhyolite is in part dacite and in part dacitic tuft. Some layers of this rock are uniformly dark throughout, as observed in the beds near the Shasta King mine, whereas others are mottled or have irregular dark seams through a lighter green matrix. The dacite forms separate flows or pyroclastic layers interbedded with the lighter colored rhyolite and has sharp contacts with the rhyo- lite. It forms a very small part of the lower unit of the Balaklala near the Shasta King mine. The dacitic flows have a trachytic texture and contain plagioclase, epidote, quartz, and chlorite. The dacite contains at least 20 percent epidote, which gives the rock its dark color. Epidote is in part disseminated through the rock, and in part fills vesicles and fractures The pla- gioclase is unzoned oligoclase (AbsoAn20) and is much more calcic than in other flows in the Balaklala. Al- though no primary mafic minerals remain, the large percentage of epidote suggests that mafic minerals were present and that they were altered to epidote dur- ing regional metamorphism. The epidote is later than the quartz veinlets that cut the rock, as shown by re— placement of originally continuous quartz veinlets by ' epidote. Much of the dark felsite has a elastic texture and is a fine—grained dacitic tufl’. No gradation be— tween dacite and rhyolite is evident—either in the field or from the petrographic study. Diamond drilling at Iron Mountain revealed a mottled siliceous, chloritized nonporphyritic rhyolite. The rock is composed mainly of quartz and chlorite and contains some hydromica, sericite, calcite, epidote, pyrite, and chalcopyrite. The chlorite is prochlorite and has the following optical properties : optic sign posi— tive, na=1.608, and 717:1.615. The rhyolite has been sheared and brecciated, and the original texture has been destroyed except for some round, radial quartz growths that are probably silicified spherulites. Locally the mottled, dark—green, chloritic rock looks like Copley greenstone. Some of the chloritic rock has a few quartz phenocrysts and is a chloritized rhyolite, but one 10-foot layer, which contains finely disseminated leu- coxene and no quartz may be a thin flow of andesite in— terlayered with the Balaklala rhyolite. MEDIUM-PHENOCRYST RHYOLITE Medium-phenocryst rhyolite is a porphyritic rock that has quartz and feldspar phenocrysts 1 to 4 milli— meters in diameter in an aphanitic groundmass. The color may be white, buff, light cream, gray, light green- ish gray, or pink. This rhyolite ranges in structure from hard unsheared rhyolite to a strongly foliated rock that contains quartz phenocrysts in a groundmass of secondary minerals. The porphyritic rhyolite gen— erally consists of about 10—20 percent quartz and feld— spar phenocrysts in a felsitic groundmass. Quartz phenocrysts are conspicuous and constitute from 5 to 20 percent of the rock. The quartz commonly occurs in the form of glassy, euhedral stubby dipyramids. Usually one rhombohedron predominates and the prism faces are absent; this combination gives a pseudocubical form to many of the phenocrysts. Some of the quartz phe- nocrysts are rounded or anhedral. Glomerocrysts, that is, clusters of 2-millimeter quartz phenocrysts aggre- gating 6 to 12 millimeters in diameter, are common, and they caused some trouble in mapping on the basis of phenocryst size. However, the size of indi- vidual phenocrysts in the glomerocryst can usually be recognized. Feldspar phenocrysts are as abundant as quartz phe- nocrysts in the unaltered rock, but in much of the per- phyritic rhyolite the feldspar crystals are completely altered to sericite and clay minerals. They are euhe- dral and average about the same size as the quartz phenocrysts. No mafic minerals are recognizable megascopically in most of the rhyolite, but locally small amounts of epidote were observed. , Platy, medium-phenocryst rhyolite makes up much of the Balaklala rhyolite roof pendant that projects into the Mule Mountain stock along Clear Creek, east and south of VVhiskytown, and occurs also on Iron Mountain peak. The rock is a light—greenish-gray me- dium—phenocryst rhyolite that has well-formed parting planes one—fourth to 1 inch apart. Although the part- ing planes appear to be parallel when Viewed from a dis- tance, in detail the plates are lenticular and few of them can be traced as much as 10 feet (fig. 14). The porphyritic rhyolite between plates is massive and unsheared. The platy structure probably is a primary flow structure that differs in origin from the sheeted rhyolite and from rhyolite having closely spaced frac- ture cleavages. Under the microscope the medium-phenocryst rhyo- lite is seen to be a porphyritic rock consisting of 1— to 4- millimeter quartz and feldspar phenocrysts in an extremely fine grained holocrystalline groundmass of pilotaxitic or microgranitoid texture. Spherulitic BALAKLALA Note the lenticular character of the plates. east of Clear Creek. structures and granophyric textures are rarely found. No seriate texture was observed; the change from pheno- crysts to fine-grained groundmass is extremely abrupt. The rock consists mainly of albite and quartz, and small amounts of sericite, hydromica, epidote, chlorite, clay minerals, probable orthoclase, zoisite, biotite, carbonate, magnetite and sphene listed in decreasing order of abun- dance. The unaltered rock contains more than 90 per- cent albite and quartz. Generally the albite in the groundmass is partly altered to sericite and hydromica, and to smaller amounts of kaolinite, chlorite, epidote, and zoisite. Where shearing is pronounced, only quartz phenocrysts remain in a completely secondary ground- mass. PHENOCRYSTS Quarter—Quartz phenocrysts constitute from 5 to 20 percent of the rock; quartz also constitutes about one-third of the groundmass, and is present in veinlets with or without albite. The quartz phenocrysts range in outline from rounded to stubby dipyramids. They are colorless or are red due to thin coatings of hematite around and in cracks through them. Liquid inclusions are abundant, but are lacking in the quartz of the groundmass and veinlets. Most of the quartz pheno- crysts have straight, sharp faces against the ground- mass, but a few are extremely corroded. The quartz phenocrysts in both sheared and un- sheared porphyritic rhyolite are typically shattered by closely spaced, uniformly distributed fractures. The shattering probably was caused by shrinking in conver- sion from beta to alpha quartz during cooling (Wright and Larsen, 1909, p. 438). RHYOLITE 25 Albite.—Albite occurs as euhedral phenocrysts in about the same number as quartz phenocrysts, but is also found as a felted mass of tiny laths in the ground- mass, as intergrowths with quartz, and in quartz-albite veinlets cutting the rock. Many of the albite pheno- crysts have indices of refraction less than 1.54 and have the maximum extinction angle perpendicular to (010), X’ to (010) of 15° to 16°, showing that the albite is more sodic than Ab95An5; the phenocrysts range in composition from AbQGAm to AbggAns. They are not zoned, and have both albite and Carlsbad twinning. Zoisite and epidote are found in a few phenocrysts, but many are unaltered and contain no inclusions. Epidote.—Epidote, in amounts usually less than 5 percent, is disseminated as tiny grains throughout the groundmass, and occurs locally in small amounts in altered albite, and as phenocrysts that look pseudo- morphic after pyroxene. Orthoclase. A feldspar, which is probably ortho— clase, is irregularly distributed in the groundmass in a few thin sections; it has a negative optic sign, negative relief, and an optic angle of about 800. GROUN DMASS The holocrystalline groundmass of the unaltered porphyritic rhyolite consists predominantly of al- bite and quartz, but contains small quantities of ortho- clase(?), epidote, and magnetite. The albite in the groundmass has the same composition as that in the phenocrysts. Groundmass textures are pilotaxitic, mi- crogranitoid, myrmekitic, and granophyric. The most characteristic groundmass has a. pilotaxitic texture and consists of a felted mass of unoriented plagioclase laths and interstitial quartz, small amounts of orthoclase ( ’2), epidote, and magnetite. Pilotaxitic texture is.domi- nant in the nonporphyritic rhyolite, which has the finest grained groundmass; microgranitoid texture is more common in the medium-phenocryst rhyolite, which has a more coarsely grained groundmass. Myrmekitic and granophyric textures are less common and probably in- dicate reworking of the original rock by deuteric solutions. Some of the porphyritic rhyolite with the finest grained groundmass contains spherulitic structures. These are colorless microscopic spheres that show a dark cross under crossed nicols. The spherulites consist of a radial fibrous growth that has positive relief and is probably quartz. Veinlets of quartz and albite cut the rock; the com- position of the albite in these veinlets is AbggAné. The veinlets have sharp walls and usually cause no change in the texture or composition of the adjacent groundmass, but in a few sections a recrystallization of 26 GEOLOGY AND BASE—NIETAL DEPOSITS, WEST SHASTA COPPER—ZINC DISTRICT the groundmass to a micrographic intergrowth was observed. Micrographic and myrmekitic textures are common. Abundant myrmekitic intergrowths of albite and quartz surround quartz phenocrysts or replace the rhyolite groundmass. Most of the quartz phenocrysts have megascopically straight crystal faces, but thin sections show that they are extremely irregular. The quartz in the myrmekitic intergrowth surrounding the quartz phenocrysts is in optical continuity with the phenocryst, and grows out from it. Some quartz phenocrysts have cores of myrmekitic intergrowths of quartz and albite (fig. 15) . ' Micrographic intergrowths are present mainly in albite phenocrysts and less commonly surround them. These inter-growths are much coarser than the myr- mekite and seem to be a replacement by quartz along cleavage planes in albite. COARSE-PHENOCRYST RHYOLITE The coarse—phenocrysts rhyolite is similar in appear- ance to the medium-phenocryst rhyolite except that the quartz and albite phenocrysts are more than 4 milli— meters in diameter. W'here unweathered most of the rhyolite is a hard massive leucocratic rock that contains 20 to 30 percent quartz and albite phenocrysts in an aphanitic matrix; mafic minerals constitute less than 5 percent. This leucocratic rock is white, cream, light greenish gray, or buff. Over much of the district it has a soft “punky” appearance near the surface due to alteration of the feldspar to clay minerals. Both extrusive and intrusive coarse-phenocryst rhyo- lite is present. The main extrusive mass is at Mammoth Butte, where it forms a cumulo dome that has an ex— posed thickness of about 1,400 feet. At least 90 per- cent of this dome consists of homogeneous, leucocratic, porphyritic rhyolite containing subhedral to euhedral quartz phenocrysts as much as 1 centimeter in diameter, and euhedral albite phenocrysts as much as 6 milli- meters, in a white, cream, or light greenish-gray apha- nitic groundmass. Intrusive coarse-phenocryst rhyolite forms plugs, sills, and dikes. At the Uncle Sam mine in the central part of the mining district, plugs consisting of this rhyolite constitute the main conduit for the extrusive coarse—phenocryst rhyolite dome. Other plugs, sills, FIGURE 15.—)Iyrmekitic intergrowth of quartz and albite in medium—phenocryst Balaklala rhyolite. Crossed nicols, X 50. BALAKLALA and dikes of this rhyolite occur in the lower and middle units of the Balaklala rhyolite and in the Copley greenstone. EXTRUSIVE COARSE-PHENOCRYST RIIYOLITE The extrusive coarse-phenocryst rhyolite is a porphy- ritic rock that contains mainly quartz and albite, but also contains biotite, epidote, zoisite, chlorite, sericite, hydromica, clay minerals, and magnetite. Quartz and albite phenocrysts constitute 20 to 30 percent of the rock in about equal amounts. The groundmass has a microgranitoid texture. No flow-banding or spherulitic structures are present such as are common in the non- porphyritic rhyolite. Quartz phenocy'*ysts.—Quartz phenocrysts generally are as stubby dipyramids that range from 2 to 10 milli- meters in diameter, but. some are irregular or rounded. Most of them have a milky color; however, some are dark gray or smoky (fig. 13). The dark color is due to dark, minute dustlike inclusions near or along arcuate frac- tures in the quartz (fig. 16). FIGURE 16,—Photomicrograph of dark quartz phenocryst in coarse- Dark color is due to minute dark Inclusions Crossed nicols. X 4‘2. phenocryst rhyolite. along‘ arcuate fractures. Most of the quartz phenocrysts in the coarse-pheno- cryst rhyolite are shattered by minute, closely spaced fractures similar to those in the medium-phenocryst rhyolite. This shattering is probably due to inversion from beta to alpha quartz. Megascopically the quartz phenocrysts seem to have sharp, straight faces. I’nder the microscope some crystals are seen to be very ir- regular in outline and have thin growth rims. The growth rims and the original quartz phenocryst both contain liquid inclusions, but the growth rims are not crackled. Quartz grains in the groundmass next to a 379725—56—3 27 RHYOLITE quartz phenocryst are commonly in optical continuity with the phenocryst. Many quartz phenocrysts show strain shadows. The shattering that caused the strain shadows formed more widely spaced and irregularly distributed fractures than the crackling believed to have formed during inversion of the quartz. The irregular fractures in the quartz causing the strain shadows were probably formed during orogeny. Albite phenocrysts.—Albite phenocrysts, ranging from 3 to 6 millimeters in diameter, constitute 15 to 25 percent of the rock. They are most commonly euhedral but some are irregular in outline. The composition of the albite ranges from Ab97A113 to AbggAng. The phenocrysts are unzoned and have albite and Carlsbad twinning. All the albite phenocrysts are altered to some extent and are replaced by sericite, hydromica, chlorite, clay minerals, and epidote. Chlorite and hy'dl'oniica are the most abundant alte‘ation products; epidote is rarely present in the albite. E pidote.——Epid0te constitutes as much as 5 percent of the coarse-phenocryst rhyolite. It is in grains less than 0.2 millimeter across that are disseminated throughout the groundmass, or is in clusters of tiny granules that may aggregate 4 millimeters across. Some of the epidote is pseudomorphic after hornblende. Groundmass.—The groundmass has an equigranular texture and is composed mainly of quartz and albite, but also contains chlorite, biotite, epidote, sericite, hy- dromica, clay minerals, and magnetite. The grain size averages about 0.2 millimeter. No flow or spherulitic structures are present. The groundmass of the ex- trusive coarse-phenocryst rhyolite is coarser grained than the groundmass of the smaller phenocryst rhyolite and is equigranular instead of pilotaxitic. Quartz and albite are the principal constituents, but chlorite, in irregular patches as much as 11/2 millimeters in diam- eter, is sparsely disseminated through the matrix and along fractures. Some of the chlorite has an anomalous blue interference color. Green biotite is present but includes chlorite as a secondary mineral along fractures and in irregular clusters. Both minerals generally con- stitute less than 5 percent of the rock. Myrmekitic and micrographic intergrowtli‘sof quartz and albite are present similar to those in the medium- phenocryst rhyolite. Micrographic intergrowths are more abundant and are formed in isolated albite pheno- crysts as centripetal replacement by quartz along cleav- age planes in albite. In some instances the whole phenocryst may be a micrographic intergrowth, but generally an unreplaced core of albite remains. Myr- mekitic intergrowths are in the center of a few quartz phenocrysts and in the groundmass surrounding quartz 28 GEOLOGY AND BASE—METAL DEPOSITS, WEST SHASTA COPPER-ZINC DISTRICT phenocrysts, and have a finer texture than the micro- graphic- intergrowths. There is no pronounced foliation in the coarse-pheno- cryst rhyolite. The secondary minerals are unoriented in contrast to the medium—phenocryst rhyolite, which may have oriented sericite and hydromica. However, near the Mammoth mine the rocks are poorly foliated near the thin edge of the coarse-phenocryst rhvolite dome. INTRUSIVE COARSE-PHENOCRYST RHYOLITE The intrusive coarse—phenocryst rhyolite is commonly a. white to greenish—white porphyritic rock containing quartz and albite phenocrysts as much as 7 millimeters in diameter in a siliceous aphanitic groundmass. Plugs of coarse-phenocryst rhyolite cut the lower unit of the Balaklala rhyolite at the Uncle Sam gold mine in the central part of the mining district, and these plugs constitute the main conduit for the extrusive coarse- phenocryst rhyolite dome. Most of the plugs consist of white hard porphyritic rhyolite that is extremely silicified; parts of the rock contain more than 50 per— cent quartz. No matic minerals are visible megascopi- cally. The intrusion of the plugs must have been accom- panied by explosive activity, as the plugs and the sur- rounding nonporphyritic rhyolite, for several hundred feet, are shattered. This shattering permitted the rock to be more thoroughly altered by hydrothermal solu- tions than the unshattered rhyolite. Little spots and irregular masses of talc as much as 4 inches long are disseminated through much of the altered rock; in some places the rhyolite was altered to a quartz-talc rock. Silicification of the coarse-phenocryst rhyolite plugs and the nonporphyritic rhyolite near the plugs is much more widespread than the talc alteration. The quartz causes a wholesale replacement of the originally porphyritic rhyolite; this replacement decreases the size of the individual phenocrysts and increases the grain size of the groundmass, giving the rhyo- lite a granitoid appearance. Albite phenocrysts are extremely corroded, and albite occurs as irregular relict grains in secondary quartz. The quartz and quartz-talc alteration is not limited to the plugs, but extends out into the shattered wall rock of nonporphyritic rhyolite. “There the alteration is intense, it is impossible to distinguish whether the rock was part of the coarse-phenocryst rhyolite plug or part of the surrounding nonporphyritic rhyolite. A plug of coarse-phenocryst chloritic rhyolite ex— posed in the adit of the Uncle Sam gold mine, 1,800 feet from the portal, has a different appearance and composition from the other plugs in the Uncle Sam mine area. It is composed of a hard greenish-gray rhyolite that has no distinct porphyritic texture, but by close examination some glassy, anhedral quartz phenocrysts can be outlined in a green secondary groundmass. The nonporphyritic rhyolite wall rock of this plug is altered to a predominantly quartz-chlorite rock. Under the microscope the greenish-gray por— phyritic rhyolite is seen to be composed of quartz and albite phenocrysts in a groundmass of quartz, albite, epidote, hornblende, chlorite, sericite, talc, clay min- erals, sphene, and magnetite. Much of the rock is re- placed by quartz and a few sulfide minerals. Quartz and albite occur as anhedral to subhedral phenocrysts as much as 5 millimeters in diameter in a groundmass averaging 0.5 millimeter in grain size. Albite is clouded by inclusions of epidote and by veinlets of chlorite and sericite that have cut through and replaced it. Euhedral green hornblende grains 0.2-milli1neter across, which appear to be primary, make up as much as 2 percent of the rock; the hornblende is in part re— placed pseudomorphously by epidote. The darker color of the rock is due to the presence of 15 to 20 percent chlorite that has replaced albite. The plagioclase phe— nocrysts are unzoned crystals that have albite twin— ning. They have an extinction angle of 15° in sections perpendicular to (010), ,X’ to (010), which corresponds to albite of composition Ab95Ang... The difference in mineralogy 0f the darker colored plug in the adit of the Uncle Sam gold mine is not understood. The talc alteration of nearby plugs in this area indicates the addition of magnesia-rich solutions. Possibly primary hornblende in the darker colored plu’g favored the for- mation of chlorite and epidote by the magnesia—rich hydrothermal solutions rather than talc, as in the other plugs in the vicinity of the Uncle Sam gold mine. PYROCLASTIC BEDS The rhyolitic pyroclastic beds consist of shaly tutt’, crystal tufl', lapilli tutl', fine and coarse volcanic breccia, flow breccia, and volcanic conglomerate. In most of the pyroclastic beds the fragments are angular to sub- rounded and consist of coarse material, but in a few beds the fragments are well rounded and resemble: volcanic conglomerate. The character of the material in a single pyroclastic bed is rarely uniform; coarse unstratified rock is commonly interlayered with finer pyroclastic rocks and with well-bedded tuff. Figure 17 shows the nature of a pyroclastic bed located 2,800 feet northwest of the Mammoth mine in the middle unit of the Balaklala rhyolite. The base is a jumble of coarse unstratified material that has fragments of porphyritic and nonporphyritic rhyolite. Some of these fragments are flow banded. This unstratified material is overlain by a poorly bedded fine pyroclastic BALAKLALA FIGURE 17.71’3'1'oclastic layer in middle unit of the Balaklala rhyolite northwest of the Mammoth mine in the canyon of Little Backbone Creek. Coarse-porphyritic and nonporphyritic rhyolite fragments as much as a foot in diameter below, grading to rhyolitic tuff and shaly tuft‘ above. breccia, which is in turn overlain by a well-bedded rhyolitic tuif and shaly tuif. Unsorted, angular frag- ments are. characteristic of many of the volcanic, breccias. The beds range from fine, well-bedded, apparently water—deposited, shaly layers of tuif, through tuif con- taining quartz and albite crystals or crystal fragments, to lithic tuff containing fragments of porphyritic and nonporphyritic rhyolite as much as a quarter of an inch in diameter. Most of the fine tuff layers are well bedded; some are apparently reworked and contain waterworn fragments. In most of the crystal and lithic tntl' layers the bedding is not apparent or is poorly developed. Most of the beds are only a few inches to a few feet thick and have a lateral extent of a few hundreds of feet. They may either lens out or grade into volcanic breccia. A group of tufl' beds, such as a deposit in a basin, is much more extensive and in some places can be traced for several thousand feet. The larger units of tuii‘ are composed of several individual beds; they commonly grade downv'ard into coarser pyroclastic layers, although there may be no uniform sequence of rhyolite flows, tufi', and breccia. Mino ' amounts of fine-grained dacitic tuft beds are present in both the lower and middle units of the Balaklala. They are exposed along the trail to the Shasta King mine on the South Fork of Squaw Creek. The dacitic tuft” beds are dark-greenish-black, aphanitic rocks that have a cherty appearance. In the field they were mapped as black felsite, but under the microscope a clastic. texture was recognized in some of the dacitic rockl. 29 RHYOLITE Tuff beds containing quartz and feldspar crystals and chips more than 4 millimeters in diameter are charac- teristic. of the pyroclastic zone at the base of the coarse- phenocryst. rhyolite. The tuffaceous origin of some of the crystal tufl's is difficult to recognize. Quartz crys- tals, more than 4 millimeters across are identical to the quartz phenocrysts in the coarse-phenocryst rhyolite in an apparently aphanitic matrix. These crystal tuff beds, though, have a heterogeneous character in con— trast to the uniform character of the coarse-phenocryst rhyolite. Quartz crystals in the tufl' have a very uneven distribution, and the crystal tuif beds grade laterally and vertically into rhyolitic tuff beds that have no quartz crystals. Also, the quartz crystals in the tuff are more rounded than those in the coarse-phenocryst rhyolite, and chips of phenocrysts are common. An- other characteristic of the crystal tufl' is a much higher ratio of quartz t0 feldspar phenocrysts than is present- in the porp'hyritic rhyolite; the ratio of quartz to feld— spar phenocrysts in the porphyritic rhyolite is about 1 z 1. TUFF BEDS l'nder the microscope the rhyolite tuff is seen to have the same mine ‘alogy as the flow rocks of the Balaklala rhyolite, although the proportions of minerals are usu- ally different. They contain grains of quartz and albite and lithic fragments of porphyritic and nonporphyritic rhyolite in a tine—grained clastic matrix of quartz, seri— cite, hydromica, chlorite, albite, kaolinite, montmoril— lonite and less commonly rutile, magnetite, biotite, and zeolites. Albite is usually much more altered than in the rhyolite flows, and is often completely altered to sericite, hydromica, chlorite, and clay minerals. Albite when unaltered has the composition AbgfiAin to Abngns, similar to that in flows in the Balaklala rhyolite. Many of the tufl‘ layers in the Balaklala are easily recognizable as they are well bedded or contain lithic fragments. However many of the tine—grained tuif and crystal-tuff layers have no apparent bedding, and megascopically they have an aphanitic matrix; these are difficult to recognize in the field as tuff because their elastic nature is not apparent. The rhyolite tuff beds have the following characteristics by which they may be recognized where bedding and elastic textures are not obvious in an outcrop: 1. In thin sections, minerals in the matrix of the tuff beds have a rounded, elastic texture. This is much more conspicuous under the microscope in plane light than under crossed nicols. 2. Angular chips of phenocrysts are common. 3. Quartz and feldspar fragments and crystals have a hetero— geneous distribution, whereas the distribution of quartz alld feldspar phenocrysts in the porphyritic rhyolites is much more uniform. 30 GEOLOGY AND BASE-METAL DEPOSITS, 4. The matrix of the tuff is heterogeneous. I’arts may be very fine grained and others rather sandy. 5. Quartz fragments and crystals greatly predominate over feld- spar fragments and crystals. (5. Quartz and feldspar phenocrysts tend to be more anhedral than those in the rhyolite flows, and they commonly are rounded. l. Porphyritic or nonporphyritic rhyolite fragments may be present‘ but they are rarely abundant or conspicuous in the tine—grained tuif or crystal tuff beds. These criteria were developed by the microscopic study of fine-grained rocks that were obviously bedded and of elastic origin. Points 2, 3, 5, and 6 are criteria in recognizing crystal tufl' in the field. Megascopic grains of quartz and feldspar commonly have rounded outlines, although euhedral crystals and crystal chips are present. The distribution of the megascopically visible quartz and feldspar grains is not uniform, and in places they may be completely lacking. Quartz is often the only mineral that can be recognized in crystal tutf; where feldspar is discernible, a ratio of quartz to feldspar phenocrysts of 3:1 or 1:1 is common, Whereas the ratio of quartz to feldspar phenocrysts in porphyritic rhyolite flows is about 1: 1. Points 1 and 4 are the most reliable criteria for rec- ognizing fine-grained tutf or crystal tuff microscop: ically. Particularly the round clastic appearance of FIGURE 18.fil’hotomicrograph of bedded rhyolitic tuff. Fragments are all angular quartz clasts in a fine clastic matrix of quartz, sericite, and minor albite. Crossed nicols, X 14. WEST SHASTA COPPER-ZINC DISTRICT the matrix is characteristic of most of the fine-grained rhyolitic tutf and crystal tuif in this district. A photomicrograph of rhyolitic tufl' is shown in fig- ure 18. An unusual rhyolitic tufl' containing pellets is found in the Iron Mountain area. It is a fine-grained, buff- colored, partly iron—stained tuff that contains spherical and ellipsoidal pellets of the same composition as the matrix (fig. 19). Most of the pellets range in size from spheres 2 millimeters in diameter to prolate ellipsoids 18 millimeters long with a minor axis of 10 millimeters. Small pellets are sparsely disseminated, whereas the larger ones may constitute as much as 30 percent of the rock. The pellets are harder and more resistant to erosion than the matrix and stand out on weathered surfaces (fig. 19). These rocks are very fine grained elastic rhyolitic tuif beds composed of quartz, sericite, and hydromica. The pellets have a megascopic concentric structure, but commonly contain fragments that have microspherulitic structure. Following the classification of “Ventworth and VVil- liams (1932, p. 37), this rock is an accretionary lapilli tutf. Similar tufl' pellets have been called volcanic pisolites, mud balls, and mud pellets (Williams, 1926, p.232). They have been described by Richards and Bryan (1927, p. 51—60) from the Brisbane tuff of Aus- tralia and by Pratt (1916, p. 450—455) from the 1911 eruption of Taal volcano in southwestern Luzon, Philip- pine Islands. The pellets were found on the slopes and the margin of Taal volcano 6—8 kilometers from the crater (Pratt, 1916, p. 451). FIGURE 1!).iAccretionary lapilli rhyolitic tuff. prolate ellipsoids having an average major axis of 6 millimeters. composition of the pellets and the matrix is the same. Most of the pellets are The BALAKLALA RHYOLITE 31 The tutf pellets are formed 111 the ail by the aggreg. - tion of very fine tuff particles by condensing steam. “lentworth and Williams (1932, p. 37) note that sim- ilar pellets may be formed less commonly by rolling of lapilli nuclei over fresh ash surfaces. The pellets ill the “rest Shasta district lack the lapilli nuclei and un- doubtedly fell to the earth as spherical mud balls that were later distorted during orogeny. They indicate that part of the Balaklala rhyolite was above water when the pellet tutf was formed. The lower and middle units of the Balaklala rhyolite contain some very fine grained dactic tuif beds. They are dark greenish-black rocks that commonly have a mottled appearance due to light-green spots or irregular light-colored veinlets. Megascopic grains of quartz may be present in an aphanitic matrix. The fine—grained dacitic tuif beds are composed of quartz, epidote, calcite, albite, zeolites, chlorite, and some clay minerals. The feldspars are saussuritically altered to epidote, 'alcite, and zeolites. The dark color is due to tinely disseminated epidote; the mottled appearance of lighter green is caused by silicification. ORIGIN OF THE BALAKLALA RHYOLITE The Balaklala rhyolite was named and fir st described in detail by Diller (1906, p. 6), who described the Bala- klala rhyolite as a series of siliceous lava and tuff beds. Graton (1909, p. 81) later studied part of the Shasta copper-zinc district and concluded that the Balaklala rhyolite of Diller was intrusive into the surrounding rocks, and he called it an alaskite porphyry. All intrusive origin for the rhyolitic rocks was ac— cepted by all the geologists who published information 011 this area. after Graton’s work (Averill, 193. , p. 122; Ferguson, 1914, p. 30; Hinds, 1933, p. 107; Seager, 1939, p. 1958—1959), although geologists for some mining c0111- panies continued to regard the rocks as flows and py- roclastic rocks.2 Mapping by the writers has shown that Diller was correct in his belief that the rhyolitic rocks are of volcanic origin, and they have revived Diller’s name of Balaklala rhyolite for the formation. The disagreement among geologists 011 the mode of origin of the Balaklala rhyolite stems largely from the difliculties inherent in the interpretation of complex volcanic structures. Owing to inadequate exposures and insufficient information 011 the area as a whole, the origin and relationship of individual rock types and structures is diflicult to determine. The essential prob- lem ill determining the origin of the Balaklala rhyolite is whether the rhyolite is entirely intrusive, whether it is in part older and in part younger than the Kennett formation, or whether it is a volcanic pile composed 2 Based on private reports of the 11 ining companies. mainly of extrusive rock but containing some intrusive rock. An important part of this problem is the origin of the upper unit of the coarse-phenocryst rhyolite. The lower and middle units of the rhyolite are con- sidered by the writers to be unquestionably extrusive because of the large amount of pyroclastic material interlayered in the rhyolite. The upper unit, however, is a broad, flat-lying body of massive rock as lunch as 1,400 feet thick that contains very little pyroclastic material; its mode of origin is not obvious. The mas- sive character of this rock suggests that it might be either an intrusive. sill or a laccolith between the Ken- nett formation alld the middle unit of the Balaklala rhyolite, but the writers believe that the field evidence favors its formation as a volcanic dome extruded on the middle unit of the Balaklala rhyolite before Ken- nett time. The discussion of the origin of the coarse- phenocryst rhyolite is given ill full, both because the upper coarse-phenocryst rhyolite contains the least internal evidence of its surficial origin, and because the ore-bearing zone lies at or a short distance below the base of the upper unit of the Balaklala, and this contact is used as a horizon marker throughout the district in the search for ore bodies. The evidence that has been adduced by others in pos- tulating the intrusive character of all or part of the Balaklala rhyolite can be summarized as follows: 1. Dikes or sills of rhyolite are reported to cut all' the en- closing rocks, including the Kennett formation. .2. The absence of a basal conglomerate and of debris from Balaklala rocks in the overlying Kennett formation shows that the Kennett was not deposited on the surface of the Balaklala. 3. Breccias, which are interpreted as autobreccias in an in- trusive, rather than as volcanic breccias. 4. The absence of glass in the rhyolite. Evidence that is thought by some geologists of the milling companies to demonstlate the intrusive natule of the uppel (-oalse- -phenoc1ysts 1hyolite is: “Xenoliths” of shale l'hvolite. 6. The coal se phenoclyst lllyolite appeals to have metamor- phosed the (Well) mg Shale. . The intrusion of the lhyolite crumpled the overlying shale along the contract of the intrusive rock. 8. The lower and middle units of the Balaklala rhyolite are foliated but the upper unit is not, indicating intrusion after the foliation was formed. occur in the coarse-phenocryst A discussion of the specific points is given because it is recognized that some of the field evidence is con- troversial and open to several interpretations. 1. The tqu beds, coarse and fine pyroclastic material, and some shaly material that are interlayered with the rhyolite are adequately described under “Pyroclastic rocks.” The large amount of pyroclastic material and the fish plate found in one tuf'f bed appear to the writers to give conclusive evidence that the rocks of the lower 32 GEOLOGY AND BASE—METAL DEPOSITS, WEST SHASTA COPPER—ZINC DISTRICT and middle units of the Balaklala rhyolite originated at the surface. However, many bodies of rhyolite have been intruded into their present position as sills, dikes, necks, and probably in a few places as breccia pipes; at many places, unless pyroclastic beds occur there are no petrographic features of the rhyolite bodies to indi- cate that one was intrusive and another was extrusive. Feeders for a rhyolite flow may cut all the underlying rocks, but the writers have found no locality where rhyolite intrudes the Kennett formation. Rhyolitic tuif beds, particularly crystal tuff, occur in the transi- tion zone between the upper unit of the Balaklala rhyo- lite and the Kennett formation and in the lower part of the Kennett formation at some places. It is prob- ably these occurrences, interpreted as rhyolitic sills, that led earlier writers to believe that rhyolite intrudes the Kennett formation. 2. Basal conglomerate and waterworn rhyolitic debris would not be expected at the base of the Kennett formation, as the fish plate that was found in tufi' in the upper part of the Balaklala rhyolite, and other evidence given under “Geologic history,” indicate that the Balaklala was deposited largely at or below sea level. Debris derived from a few volcanic islands that projected above water level would be similar in appear- ance to the waterworked tuff beds that are found in the transition zone between Balaklala and Kennett. 3. Bodies of breccia where the groundmass and frag- ments are alike are flow breccias formed by the incor— poration of crustal material in a flow, rather than being examples of autobrecciation in an intrusive. They are layered rocks, commonly bounded by other types of pyroclastic layers. 4. Some textures that appear to be caused by devitri- fication of glass and some fluidal textures have been seen in thin sections, but they are rare. Apparently very little glass was formed in the rhyolites. 5. No xenoliths of shale of the Kennett formation in rhyolite were found by the writers. The xenoliths of shale between “sills” of rhyolite, reported at some of the mines, are interlayered rhyolitic crystal tutf and shale in the transition zone between Balaklala and Kennett formations. 6. The hard, bedded material under the coarse- phenocryst rhyolite that has been called metamor— phosed shale or hornfels at the Mammoth mine was found to be a normal soft, shaly tuff where it was traced away from the mine. Thin sections showed that the hard, flinty character of the tuff bed at the mine was due to hydrothermal silicification. 7. The crumpling at the shale-rhyolite contact and the difference in the amount of foliation between the rocks of the middle and upper units of the Balaklala are due to their difference in competence as described under “Relationship to folds and foliation.” Some minor crumpling is due to syngenetic sliding. Evidence for an extrusive origin for the upper coarse-phenocryst rhyolite unit of the Balaklala in particular is: 1. The presence of a tuff bed which contains frag— ments of coarse-phenocryst rhyolite and coarse quartz crystals along the base of the dome of coarse pheno— cryst rhyolite. These beds indicate an explosive phase of the rhyolite before the extrusion of the thick dome. The base of the main body of the rhyolite is everywhere conformable to this tuff except at the vent. 2. The gradational contact at the top of the upper unit of the Balaklala rhyolite. from coarse-phenocryst rhyolitic tuff t0 shaly tuff and shale at some localities indicates an explosive phase after the extrusion of the main body of coarse phenocryst rhyolite, and indicates continuous deposition. 3. The tufl' and pyroclastic rocks above and below the main body of massive coarse-phenocryst rhyolite come together at the edge of the dome, and continue as one zone of tuff beyond the limits of the dome. 4. The presence of at least one coarse pyroclastic layer in the rhyolite dome, which contains rounded fragments of coarse-phenocryst rhyolite mixed with other varieties of rhyolite, shows that the formation of the dome was interrupted locally by a period of ex- plosive activity during which a coarse pyroclastic layer was deposited. 5. Lack of any apophyses of rhyolite extending up into the shale of the Kennett formation is negative evidence that the coarse—phenocryst rhyolite is not in- trusive, although a few dikes accompanying the rhyolitic tuff beds in the lower part of the Kennett might be expected. KENNETT FORMATION The Kennett formation is composed almost entirely of shale and limestone, but minor beds of shaly tuff and crystal tufl' are interbedded with shale near the base of the formation. The shale forms the lower part of the formation; it is commonly a black siliceous thinly bedded rock which is locally crumpled and cut by a network of tiny quartz veins. The limestone forms the upper part of the formation and is largely a coral reef. Fairbanks (1903, p. 48) first described the shale and limestone between Squaw Creek and Backbone Creek and north of Backbone Creek, and Smith (1894, p. 591) credits him with naming these strata the Sacramento formation in a manuscript. However, Smith (1894, p. 591) called these rocks the Kennett limestone and shale and implied in a table that the Sacramento for- mation and Kennett limestone and shale are equivalent. KENNETT FORMATION 33 Subsequently the term Sacramento formation was dropped and the term Kennett formation was used by later writers (Diller, 1906, p. 2; Graton, 1909, p. 79). DISTRIBUTION The Kennett formation is exposed throughout the northern part of the ‘Vest Shasta district as discontinu- ous erosion remnants on present topography of a former much more continuous formation. Most of the Ken- nett caps hills or ridges, and is seldom found in the valleys. The Kennett formation is most extensively exposed in the southern part of the Behemotosh Mountain quad— rangle. It is exposed northeast of Backbone Creek on the southwestern slope of Backbone Ridge between the Bragdon formation to the northeast and the Balaklala rhyolite to the southwest, and as erosion remnants on the crests of hills and ridges southwest of Backbone Creek to Mammoth Butte. Good exposures are found above the road leading from Shasta Lake to the Golin- sky mine and along the upper part of the road from Shasta Lake to the Mammoth mine. The Kennett is also exposed as a thin, discontinuous band as much as 800 feet wide between the Balaklala and the Bragdon formations in the northeastern part of the W'hiskytown quadrangle and the southwestern part of the Behemo- tosh Mountain quadrangle from Mad Mule Mountain to Behemotosh Mountain, and as isolated remnants rest- ing on Copley greenstone on the east side of Shasta Lake in the northeastern part of the Shasta Dam quad- rangle. THICKNESS AND RELATIONSHIP TO UNDERLYING ROCKS The maximum thickness of the Kennett formation in the lVest Shasta district is probably not more than 400 feet, although Diller (1906, p. 2) describes a partial section 865 feet thick, and Staiifler (1930, p. 95—96) describes a section 815 feet thick. This discrepancy is in part due to repetition of beds by faulting and in part to a lesser thickness of material which is here included in the Kennett. Geologic scotion northeast of Backbone Creek (Stmtffer) Mississippian : Bragdon formation: Feet 9. Conglomerate with quartz pebbles and fos- siliferous fragments, these latter often dissolved leaving holes ___________________ 30 Devonian: Kennett formation : 8. Shale, mostly dark, with thin sandy beds____ 150 7. Limestone, massive, light-gray containing a small amount of chert. Part is filled with corals ___________________________________ 100 6. Sandstone, thin—bedded; and dark-gray shale- 140 5. Limestone, dark-gray to bluish ______________ 10 Devonian—Continued Kennett formation—Continued Feet 4. Shale, cherty, gray _________________________ 150 3. Limestone, thin-bedded to massive, often cherty and parts of it full of various types of corals. A black chert band at the base_-_ 200 2. Shale, siliceous, often sandy and usually very thin bedded. Shale mostly black to gray and often partly metamorphosed ___________ 65 Balaklala rhyolite: 1. Rhyolite. The thickness of Kennett formation is here consid— ered to be less than the 800+ feet shown by Diller and Stauffer because there appears to be repetition by fault- ing of the limestone and adjacent shale beds. There is no evidence that there is more than one limestone layer; although the outcrop is poor where the upper limestone beds are shown in Diller’s and Staufi'er’s sections, these are probably fault slivers rather than separate beds of limestone. The Backbone Creek fault projects through where the dike of Birdseye porphyry cuts the Kennett at this locality and repeats part of the section. The following geologic section was measured by the writers on a ridge in sec. 22, T. 34 N., R. 5 “7., that projects westerly into the Backbone Creek arm of Shasta Lake immediately south of Lower Limestone Valley. Geologic section northeast of Backbone Creek [The base of the section is at lake level, altitude, 1,000 feet] Bragdon formation: Feet Shale, light-brown and gray; and sandy shale _____ 500+ N0 outcrop _______________________________________ 250 Rhyolitic tuff, brown, sandy, not well bedded; some well-bedded sandy mudstone. Some of the tuffa- ceous rock contains 1/8 t0 14 inch lithic fragments (poor exposure) ________________________________ 50: Kennett formation: Mudstone, dark-gray, siliceous, possibly cherty, simi- lar to the siliceous dark-gray shale that weathers light gray below the limestone (poor exposure)__ Mudstone, limy, siliceous, 2- to 6-inch beds. Abundant martinioid brachiopods in lower 6 inches _________ 6 Limestone, light-gray to bluish-gray, bedded. Con- tains abundant corals. The upper 25 feet contains brachiopods and cup corals (lower contact not exposed) ___________________ .4 __________________ 200i Shale, black, siliceous, in part cherty, 1- to 6-inch beds. Locally crumpled ________________________ Balaklala rhyolite: l’orphyritic rhyolitic tuff containing 3- to 4-millimeter quartz crystals. The tuff is well bedded but does not part on bedding planes. Bedding is marked by color bands and by compositional and grain-size variations. The top 6 inches to 3 feet is slightly crumpled and iron stained and contains small, local areas of gossan and minor siliceous black shale lenses mixed with the tufl _______________________ Porphyritic rhyolite containing 1- to 2-millimeter quartz phenocrysts. Light-gray to light-green felsitic matrix __________________________________ 200+ ~i -1 H- 40i— 34 GEOLOGY AND BASE—NIETAL DEPOSITS, This is the most complete section now available above the level of Shasta Lake, but it is incompletely exposed. Measurements start from the lakeshore at an altitude of 1,000 feet, and the stratigraphic thicknesses were meas- ured by altimeter readings or were estimated because the beds are locally crumpled and exact contacts are not exposed. Staufl’er’s section includes the shale above the lime- stone as far as the first conglomerate of the Bragdon formation as part of the Kennett formation and gives the thickness of shale above the limestone as 150 feet. Diller does not mention the first overlying conglomerate specifically, but he also includes 140 feet of shale above the limestone as a part of the Kennett formation, and presumably placed the top of the Kennett at the first conglomerate bed above the limestone. The writers see no advantage and much difficulty in including shale above the limestone as part of the Kennett formation. There is no change in the lithology of the shale above and below the first conglomerate bed above the lime- stone, the contacts are conformable, and deposition ap~ parently has been continuous. Also, the conglomerate beds are not everywhere present, and even where pres- ent they are lenticular, and the “first” conglomerate in one area is not at the same stratigraphic horizon as the “first” conglomerate in a nearby area. Therefore the writers have considered the shale below the first con- glomerate in this locality to be part of the Bragdon formation, and they have placed the contact of Kennett and Bragdon at a lithologic break at the top of the limestone where it is present or at the top of black, siliceous shale where limestone is absent. The maximum thickness of the Kennett formation appears to be about 400 feet in the ll'est Shasta district. The greatest thickness of the Kennett is exposed south— west of Backbone Creek on Quarry Ridge east of the Golinsky mine. In this area the uppermost part of the limestone has been eroded in the present erosion cycle and the rocks are locally crumpled, but a thickness of 350 to 400 feet of the Kennett is exposed. On the ridge between Little Backbone (‘reek and Squaw Creek the Kennett is so crumpled that no accurate measurement of thickness is possible, but an estimate of thickness based on lithology is 300 to 400 feet. The shale, sandstone, and tufl' beds of the Kennett formation grade downward conformably into breccia, tuff, and flow—banded facies of the Balaklala rhyolite. This gradation is clearly shown in many outcrops scat— tered throughout the area. The best exposures show- ing this sedimentary relationship are on the northeast side of Backbone Creek between the Upper Limestone and Lower Limestone Valleys and just east of the Mam- moth mine on the road leading from Shasta Lake to the WEST SHASTA COPPER-ZINC DISTRICT mine. The contact of Balaklala and Kennett forma— tions also is exposed in some of the tributaries both north and south of Little. Backbone Creek and in Butcher Creek and the small gullies east of Butcher Creek. The lower contact of the Kennett is placed between the dark—gray to black cherty or sandy shale and the light—tan to light-green rhyolite or rhyolitic tuff. In some places the contact is sharp; in others it is grada— tional; for example, east of the Mammoth mine, the contact is placed where shale predominates over rhyo- litic tuft. On Behemotosh Mountain limestone rests directly on rhyolitic tuft of the middle unit of the Balaklala rhyolite. N o shale is present under the lime- stone, and no bedding can be seen in the tuft ; it seems probable that this locality is one in which the tuft was deposited above sea level and remained above‘it during early Kennett time. The tuff sank below lor was eroded to sea level in late Kennett time, and coral limestone was deposited on the tuft. RELATIONSHIP BETWEEN THE KENNETT AND THE BRAGDON FORMATIONS Diller (1906, p. 2—3) and Staufl'er (1930, p. 95—96) believed that the Kennett formation was overlain un- conformably by the Bragdon formation and that much of the Kennett was eroded before the Bragdon was de- posited. Their evidence for this is that the Kennett differs in thickness in several parts of the area, that it is missing in some areas, and that fragments of Kennett limestone are present in the Bragdon conglomerate. The writers believe that the Kennett is essentially con- formable under the Bragdon in the \Vest Shasta dis- trict. Although they recognize that. minor erosional unconformities and depositional overlaps occur locally, fairly well exposed sections across the Kennett-Bragdon contact on the northeast side of Backbone Creek and along the continuous band of Kennett that crops out in the northeast quarter of the VVhiskytown quadrangle show no evidence of an angular unconformity, channel- ing, or a major erosion period before the deposition of. the Bragdon in these areas. Sedimentation seems to have been continuous in these areas; it is improbable that an interval of erosion sufficient to remove the lime- stone and some of the Kennett would have left a layer of shale of the Kennett of uniform thickness for an outcrop length of 5 miles, such as occurs in the VVhisky- town quadrangle. The limestone that forms a thick bed in the Behemo- tosh Mountain quadrangle occurs in the \Vhiskytown quadrangle as only a few scattered lenses; but such iso- lated lenses also occur in the Kennett east of the Be- hemotosh Mountain quadrangle. There is no evidence KENNETT FORMATION 35 that the limestone was once a continuous bed over the entire area which was removed by erosion before the deposition of the Bragdon, but there is evidence of patchy deposition of limestone, and there are consider- able areas where it was not deposited. It is a coral reef- type limestone; its greatest thickness probably is at Backbone Creek, and it thins to isolated patches away from this center. In places where the limestone is missing, the shales of the Bragdon and Kennett are con- formable and the contact is drawn at the upper limit of the dark siliceous shale that characterizes the Kennett. It seems probable that the volcanic pile of Copley and Balaklala rocks was built up. to or near sea level and coral reefs formed on the seamount and rimmed pro- jecting volcanic islands; cessation of volcanic activity, erosion of volcanic islands, and continued subsidence lowered the surface below the coral zone and allowed the deposition of Bragdon sediments. The variation in the thickness of the shale in the Kennett formation, and absence of the shale in some areas, is not regarded as evidence for a major erosional unconformity, although local erosion undoubtedly oc- curred. The variations in thickness that are found can be explained by unequal deposition on a surface of relief, erosion by currents of high points on the sea floor, differential compaction over topographic highs, and syngenetic sliding. The Kennett was not deposited in areas that were above sea level; erosion of these areas contributed part of the tufl' that is in the lower part of the shale of the Kennett in some areas. In the vicinity of the Mammoth mine, evidence for the deposition of the Kennett on a surface of. relief is the different thick- ness and type of material in the Kennett. The thick- ness of the Kennett rocks below the limestone ranges from a few feet to slightly more than 100 feet, and the composition ranges from siliceous black shale to mixed shale and tuif and in one locality to a crystal tufl'. The nature of the limestone, a coral—reef type, is further evidence of a nearshore environment. As great masses of the volcanic rocks which formed the Balaklala rhyolite were poured out on the sea floor, it is probable that the base of the volcanic pile subsided as the top rose, and that the submarine vol- canic pile was a broad low dome. Large basins, such as the one north of the Mammoth mine were present, in which conside ‘able thicknesses of bedded, water- deposited tufl' and volcanic conglomerate collected; they indicate a local surface of low relief. Some of the mate- rial appears to be waterworn and may have been derived from projecting volcanic islands. On the other hand, it is possible that some of the Kennett was deposited on fairly steep initial slopes; syngenetic sliding at the 379725—56 4 base of the Kennett indicates that the Kennett was deposited on a sloping surface. The Kennett formation did not completely cover the volcanic seamount, parts of which were at times above sea level. In some places local topographic highs in the dome of Balaklala rhyolite were present, as north of Spring frulch in the IVhiskytown quad “angle just west of peak 3,893. The Kennett never covered these local peaks so that the Bragdon formation \ 'as deposited as an overlap on the Balaklala with no erosional 11n- conformity . Also, the Kennett sedimentary rocks were not deposited on the Balaklala over the center of the volcanic highland, as in the NIV14 Sec. 14, T. 33 N., R. 6 “7., shales of the Bragdon rest directly on soft por— phyritic rhyolitic tuff. As described under “Geologic history,” fragments of fossiliferous limestone that have been identified as limestone of the Kennett in conglomerate beds in the Bragdon prove that some limestone of the Kennett was eroded and incorporated in the younger strata of the Bragdon. The lack of evidence of erosion except locally, and the evidence of continuous deposition in much of this area, however, implies that warping occurred; the “Test Shasta district remained largely a depressed area of essentially continuous sedimentation while areas out- side this district were uplifted and eroded, and con- tributed debris to the Bragdon sediments. LITHOLOGIC DESCR IPTION The Kennett formation is composed predominantly of dark—gray to black siliceous shale, and massive fos- siliferous limestone; rhyolitic tufl' and tutfaceous shale are prominent in the lower part of the formation. Some conglomerate, limy shale, sandstone, and porphyritic rhyolite occur locally in the black shale. The fossilifer- ous limestone and black siliceous shale are the distinc- tive lithologic units by which the Kennett is recognized (fig. 20). View looking northeastward. Bold limestone outcrop of the Kennett formation on ridge ((1) : black siliceous shale of the Kennett formation (1)); tuff in the Balaklala rhyolite (c). Shasta Lake. 36 GEOLOGY AND BASE-METAL DEPOSITS, WEST SHASTA COPPER—ZINC DISTRICT Black siliceous shale layers, which locally are cherty, compose the lower part of the Kennett at most locali- ties, although interbedded tuff and shale form the base of the formation at some places. Except for two small localities of limestone, the basal black cherty shale is the only Kennett stratum that is present southwest from Behemotosh Mountain to Mad Mule Mountain in the Behemotosh Mountain and IVhiskytown quadrangles. No fossils were found in this black siliceous shale layer, but it was correlated with the Kennett because of its stratigralfliic position and because of the similarity in the lithologic character of the black siliceous shale to that present in the Kennett elsewhere. Two small lenses of limestone in the black siliceous shale further suggest that this layer is Kennett. Black siliceous shale is also present under the limestone in most exposures in the Behemotosh Mountain quadrangle; it ranges in thick- ness from a few inches to 150 feet. The black shale layers are in part thinly bedded; bedding planes marked by color bands range in width from less than a milli- meter to several inches; parting planes are 1 to 6 inches apart. The black shale layers are commonly contorted and are cut by many thin quartz veinlets. All the black shale beds are siliceous and carbonaceous and contain quartz, carbonaceous material, sericite, clay minerals, limonite after pyrite, sphene, and rutile. They contain angular quartz grains averaging about 0.1 millimeter indiameter in a fine—grained matrix of carbonaceous material, sericite, quartz, clay minerals, sphene, and rutile in which the grains average about 0.01 millimeter across. Locally the black shale is cherty and contains poorly preserved structures that are prob— ably radiolaria. The cherty units are brittle and were crackled during orogen y. The fractures are filled with quartz, but there was little or no introduction of quartz through the matrix. Locally two sets of quartz vein- lets, which intersect the bedding at 45°, are prominent. The black siliceous, clastic shale beds rarely contain the abundant quartz veinlets that occur in the cherty units. Other rocks in the Kennett formation below the lime- stone are coarse- to fine-grained tufl“, conglomerate, sandstone, siltstone, and porphyritic rhyolite. All these rock strata are lenticular, and collectively they form units of heterogeneous clastic and pyroclastic material. The largest areas of these lenticular masses of tuffaceous sediments are in the Butcher Creek basin southeast of Mammoth Butte and in the Sl/Z sec. 26 and the NVV14 sec. 35, T. 34 N, R. 5 “L, northeast of the Backbone Creek arm of Shasta Lake. Locally a particular bed within this zone is distinctive enough to be traced in mapping, for example, the coarse-grained tufl' bed that lies under black cherty shale on the north side of the Squaw Creek arm of Shasta Lake. This coarse-grained tuff layer extends from Butcher Creek eastward to the point where the divide separating Squaw Creek from Little Backbone Creek intersects the lake level—a dis- tance of about 2 miles. This bed averages about 100 feet in thickness, and it is composed of pea-sized frag— ments of rhyolite and greenstone. It. is considered part of the Kennett rather than Balaklala rhyolite because at the eastern end it overlies black cherty shale. Con- glomerate occurs in small, irregular pods in this hetero- geneous zone, but makes up less than 1 percent of the Kennett at this locality and is not present elsewhere. The conglomerate is composed of angular to subrounded fragments of shale and chert averaging half an inch in diameter embedded in a silty matrix. Individual lenses of conglomerate commonly are 1 to 3 feet thick and 5 to 10 feet long. A layer of flow-banded porphyritic rhyolite that has small dark—gray and colorless quartz phenocrysts is exposed in the vicinity of Butcher Creek. This porphy- ritic rhyolite appears to lie conformably between sedi- mentary layers of the Kennett formation; it has an average thickness of about 30 feet and can be traced with a fair degree of certainty for about 1 mile. A similar body of rhyolite that appears to be interbedded with shale is located about 1,000 feet north of the one at Butcher Creek, but» poor exposure and many faults make its inclusion in the Kennett formation question- able; it may be an inlier of Balaklala rather than inter- bedded in the Kennett roCks. Rhyolitic tutf beds and possibly thin rhyolitic flows are interbedded with sandy or tutl‘aceous shale at some places and these tutf beds are gradational to porphyritic rhyolitic tuff at the top of the Balaklala rhyolite. A good exposure of the gradational contact between the Balaklala and Kennett formations is on the ridge east of the Mammoth mine. At this locality there is a grad- ual change, through a stratigraphic thickness of about 100 feet, from porphyritic and nonporphyritic tufi and tuff breccia containing some sandy tuff and gray shale beds upward to predominantly gray to tan shale and a few rhyolitic tutf beds. Most of the rhyolite in this transition zone is definitely tuffaceous, but some consists of massive light-green felsitic rocks that may be either sills or flows. No crosscutting relationship was ob- served. The contact between the Balaklala rhyolite and the Kennett formation is also well exposed east of the Golinsky mine (fig. 12). The considerable thicknessesof pyroclastic rocks of Balaklala rhyolite type that occur in the lower part of the Kennett formation indicate that eruptions of Balaklala rhyolite type rocks continued into Kennett time. Some feeders for the overlying pyroclastic rocks KENNETT FORMATION 37 may cut the lower strata of the Kennett, but no such crosscutting relationship has been observed by the writ- ers. However, much of the rhyolitic pyroclastic rocks inter-bedded with the Kennett are water deposited; they are not necessarily derived from explosive activity during Kennett time, but may in part be due to the reworking of rhyolitic tuff on volcanic islands and the deposition of these tuff beds along shorelines where they were interlayered with shale of the Kennett. The limestone in the Kennett formation is a thinly to thickly bedded but. in part massive rock that is light to bluish gray. The lower part of the limestone is mostly massive or thickly bedded and contains only sparse corals. The upper ‘50 feet is highly fossiliferous and contains abundant coral debris and some chert nod— ules and bands. Most of the corals are concent ‘ated in definite bands in the limestone. A few brachiopods oc- cur in the upper 25 feet but were not found in the lower part of the limestone. Much of the upper part of the limestone is of clastic origin. Limestone talus commonly covers the contact between the limestone and the underlying shale. The writers found this contact exposed at only one point on the east side of Backbone Creek in Dark Canyon at an alti- Approximate thickness, m feet Limestone of the Kennett formation 5 Dark-green chloritic shale, well-bedded. 1-inch beds lnterbedded gray shale and 7 siliceous black shale; some sandy layers, 17 to 67inch beds 1 Shaly tuff well-bedded rhyolitic crystal 5 tuff with black quartz phenocrysts Gradational contact Rhyolitic tuff, in part crystal 10 tuff. Contains 1-to4« inch beds of black siliceous shale Gradational contact Black siliceous shale of the Kennett formation FIGURE 21.—Partial section beneath the limestone of the Kennett formation on the east side of Backbone Ridge, Behemotosli Mountain quadrangle. tude of 1,550 feet. Figure 21 gives a section across the contact at this point. V Balaklala rhyolite-type rhyolitic tuif thus is present at both the upper and lower contact of the Kennett limestone. The limestone is all very fine grained, but is not re- crystallized to marble. Thin veinlets filled with white calcite are common in the limestone; in places these tend to dissolve out at the surface. Void spaces left by solu- tion of these veinlets and vertical fiuting (lapiés) formed by rainwater, make the surface of the limestone quite cavernous. Logan (1947, p. 324) has the following statement on the composition of the limestone of the Kennett: The few analyses available show 95 to 97 percent calcium car— bonate, 1 to 4.4 percent silica, 0.7) to 2.25 percent magnesium carbonate, and very little iron oxide and alumina. However, it must have been on the average of good quality as lime made from it was used over a large part of northern California, the old kiln at Briggsville having supplied lime to many pioneer towns of early mining days, and the deposits near Kennett having been in operation from at least 1884 until 1925. This limestone was mined from a quarry on the ridge in the “71/; sec. 34, T. 34 N., R. 5 W. An analysis of the limestone of the Kennett from a sample collected by the writers in sec. 4, T. 33 N., R. 5 “7., along the road from Shasta Lake to the Mammoth mine was made by the Calaveras Cement Co. Analysis of limestone of the Kennett formation Percent Si02 ______________________________________ 0. 22 Feg( )3 ________________ n __________________ . 12 A1203 ___________________________________ . 26 CaCOa __________________ F _______________ 99. 84: Mg() ___________________________________ 0 100. 44 AGE The age of the Kennett formation has been estab- lished as Middle Devonian from fossil collections made by Fairbanks, and referred to by Smith (1894, p. 591), and from collections by Diller (Diller, 1906, p. 2; Diller and Schuchert, 1894., p. 416—422), Stauifer (1930, p. 95—96), and the writers. Diller collected fossils from shale and limestone in the Kennett formation. He collected the fossils from the shale near the Sacramento River a short distance north of Morley, which was 2.6 miles N. 25° E. of the former town of Kennett, and from the Kennett formation near Backbone Creek. This fossil locality is now flooded by Shasta Lake. (‘harles Schuchert studied Diller’s col- lection and concluded that it is of Middle Devonian age (Diller, 1906, p. 2). A fossil collection was made of the upper 25 feet of the limestone of the Kennett formation and the over— 38 GEOLOGY AND BASE—METAL DEPOSITS, WEST SHASTA COPPER-ZINC DISTRICT lying 6-foot calcareous shale bed from a ridge northeast of the Backbone Creek arm of Shasta Lake in sec. 22, T. 34 N., R. 5 W . and referred to G. Arthur Cooper of the U. S. National Museum, who reports: The specimens from the Kennett limestone definitely belongs to the Middle Devonian. Those specimens from the limy shale horizon may be Middle Devonian but might be from the lower part of the Upper Devonian. The martinioid is difficult to identify but suggests, Devonian relationships rather than Mississippian. ’ Dr. Cooper identified the following fauna: Calcareous shale bed: Martinioid brachiopod Leivorhy’nclws ( ‘2) sp. Limestone of the Kennett formation: Heliolites sp. Amphipora sp. Atrypa sp. A. sp. aff. A. spinosa Schizophoria sp. (large) Cup corals (poor) BRAGDON FORMATION DISTRIBUTION The Bragdon formation, which was named from the community of Bragdon on the Trinity River 8 miles south of Trinity Center by Hershey (1904, p. 347—360), occurs as an arcuate band 17 miles long and as much as 4 miles wide at the north end of the West Shasta dis— trict. It is part of a much larger area continuing north- ward that covers most of the Schell Mountain and Lamoine quadrangles between the Trinity and the McCloud Rivers. Erosion remnants of the Bragdon also cap the peak 3,500 feet northeast of Behemotosh Moun- tain in the Behemotosh Mountain quadrangle and in the N‘Vl/L sec. 14, T. 33 N., R. 6 “7., in the \Vhiskytown quadrangle. Shale and grit that are probably part of the Bragdon formation are exposed also on Jerusalem Creek 10 miles west of Igo, on the southwest flank of the Shasta Bally batholith. The Bragdon originally covered the West Shasta district, but was entirely eroded from some areas before deposition of the Cre- taceous sediments. THICKNESS AND STRATIGRAPHIC RELATIONSHIP The Bragdon formation overlies the Kennett forma- tion, but in some places the Kennett was not deposited or was locally eroded, and in these places the Bragdon rests upon either the Balaklala rhyolite or (‘opley green- stone. On the west side of the W'hiskytown quadrangle the Bragdon rests directly on Copley, and the Kennett probably was not deposited here, as the band of black siliceous shale of the Kennett that extends almost con- tinuously for a distance of about 15 miles to the north- east does not underlie the Bragdon continuously west of Iron Mountain. Much of the contact between the Bragdon formation and Balaklala rhyolite in the Behemotosh Mountain quadrangle is a fault contact. The fault, along Back- bone Creek drops the Bragdon into contact with the Balaklala for a distance of 2.75 miles. A fault contact also separates the Balaklala and Bragdon northwest of Behemotosh Mountain in the Behemotosh Mountain quadrangle and in sec. 22 (projected), T. 33 N., R. 6 “7., in the thiskytown quadrangle. The contact between the Copley and Bragdon in the northwestern part of the thiskytown quadrangle north of Shirttail Peak. is a fault contact striking northeast that brings the Copley up on the northwest side against the Bragdon. At most places in the mapped area the contact be- tween the Kennett and Bragdon formations is sharp and conformable, and was placed at the top of the black siliceous or cherty shale of the Kennett or at the top of the limestone where it overlies the cherty shale beds. ()n the northeast side of the Backbone Creek arm of Shasta Lake, it was difficult to place the contact. A lenticular mass of interlayered sandy, rhyolitic tufl', *alcareous shale, and dark nonsiliceous shale separate limestone of the Kennett and dark siliceous and cherty shale from the typical light—brown and gray shale of the Bragdon. The record of sedimentation here appears to be complete; there are no signs of channeling or erosion of the top of the limestone. The only feature that suggests an erosional unconformity is some red- banded sandstone above the limestone that resembles sandstone oxidized at the surface. The sedimentary rocks in the Backbone Creek locality grade upward from calcareous shale through sandy and tuffaceous beds to tan shale layers that are uniform as far as the first conglomerate of the Bragdon. In the eastern part of the VVhiskytown quadrangle a sharp lithologic break between cherty and *silicitied shale and noncherty shale marks the contact between Kennett and Bragdon rocks, but the two types of shale are conformable. The top of the Bragdon is not exposed in the West Shasta district. Diller (1906, p. 3) reports, however, that the Bragdon is overlain conformably by the Baird formation northeast of the “'est Shasta district in the Lamoine quadrangle. He places the top of the Bragdon at the top of the highest conglomerate bed. In the Behemotosh Mountain quadrangle a partial section of the Bragdon has a thickness of 3,500 feet from Backbone Creek to the north edge of the mapped area on Backbone Ridge, but this is only the lower part of the formation, and the thickness may be con- siderably greater, as the Bragdon extends northward from the mapped area for a distance of about 11 miles.» BRAGDON‘ FORMATION 39 The thickness of the Bragdon may be considerably more than 3,500 feet in the \Vhiskytown quadrangle, but the whole area is so broken up by faults that no section can be measured or even closely estimated. An ill-defined zone of conglomerates occurs in the lower part of the ‘ Bragdon, but a few conglomerate beds occur above and below this zone. The base of the main zone of con— glomerate in the Bragdon in the “’hiskytown quad- rangle is about 500 feet above the base of the Bragdon and the top of the zone is about 1,500 feet above the base of the Bragdon. The least faulted partial section of the Bragdon in the ‘Vliiskytown quadrangle extends f1'()n'i’"the Balak- lala-Bragdon contact near the Bright Star mine in the \Vhiskytown quadrangle N. 26° \V. to the center-“Of the syncline 3,000 feet north of hill 3564, which is south of Cline Gulch; the thickness of the Bragdon in this area is 1,450 feet. From theicenter of this syncline eastward the Bragdon has a fairly uniform strike of N. 10° to 30° \V. and dips 15° to 70° XV. These dips give an apparent thickness to the Bragdon of 15,000 feet. However, most of this area contains the main conglomerate zone of the Bragdon, and apparently is mostly within the lower 2,000 to 3,000 feet of the Brag- don which is here cut by a Series of northwest-striking faults that drop the west side and continually repeat the section. These faults are generally poorly exposed and occupy debris filled canyons, but they are marked by the abrupt termination of a series of conglomerate beds. Some of the faults have prominent topographic expression as seen on aerial photographs. Diller (1906, p. 3) stated that the maximum thickness of the Bragdon in the Bedding (30-minute) quadrangle may be as much as 6,000 feet, but that the broad area of the Bragdon is so affected by small folds that its thick- ness is difficult to determine. He states that south of Castella on Hazel Creek, where the Bragdon forms a band between the Kennett and Baird formations, the thickness is estimated at 2,900 feet. LITHOI.OGIC DESCRIPTION The Bragdon formation in the lVest Shasta district is compOsed of interstratified shale, siltstone, sandstone, grit, conglomerate, and a small amount of rhyolitic tuif, and at one locality contains a small flow of matic lava. Beds of shale make up more than 75 percent of the formation. They are dark greenish gray to black on unweathered surfaces, but are butt' to brown on weath— ered surfaces. The shale is thinly bedded, and the stratification is easily recognized by parting and by color differences, or by variations in grain size in adja- cent laminae. Thin beds of sandy shale and grit inter- bedded with the shale also show the structure in the shale. Bedding in the shale is very regular. In places graded bedding is common, but little crossbedding or channeling was observed. Thin siltstone and fine—grained sandstone layers are inter-bedded with shale throughout the Bragdon. The sandstone beds are generally a few inches to a few feet thick, but beds of gritty sandstone as much as 50 feet thick occur north of Backbone Creek and near the head of Spring Creek. These beds are commonly light gray or buff colored, although some are dark gray. The dark sandstone beds contain abundant rock fragments of shale and chert and are graywacke. The characteristic beds of conglomerate in the Brag- don are the most distinctive feature of this formation; they do not occur in older or younger formations. The only known occurrence of coarse detrital material at the base of the Bragdon in this district is just above the junction of Jackass and Backbone Creeks along the north edge of the mapped area. At this locality a bed of grit 10 to 20 feet thick lies along the contact between shale of the Bragdon and the underlying Balaklala rhyolite; None of the Kennett formation is exposed at this locality, although Kennett strata crop out a short distance to the southeast. The grit at the base of the Bragdon is composed of angular chips of chert and quartz, one-eighth to one—quarter inch in diameter, in a dark-gray sandy matrix. Other than this, basal con— glomerate and grit are lacking along the base of the Bragdon. Conglomerate beds are concentrated between 503 and 1,500 feet above the base of the Bragdon in one general zone. However, some thin beds occur higher in the sec- tion north of Backbone Creek, and lower in the section northwest of Iron Mountain, but they are more len- ticular and less abundant in these areas. “Vithin the general zone there are usually at to 6 persistent con- glomerate beds that can be traced from‘a few thousands of feet to several miles whereas many lenticular beds can be traced only for a few hundred feet. The general zone contains more individual conglomerate beds in the ‘Vhiskytown quadrangle than in the Behemotosh Moun- tain quadrangle. These individual sandstone and con- glomerate beds reach their maximum thicknesses near the headof Spring Creek. . The conglomerate beds are most commonly 10 to 20 feet thick, but they range from several feet to as much as 100 feet in thickness. There is no apparent relation- ship between the thickness of the bed and the size of the constituent pebbles. The thicker beds are generally composed of several conglomerate layers separated by siliceous gritty sandstone and minor shale which to- gether make a persistent, mappable unit. The con- glomerate beds within the general zone are also 40 GEOLOGY AND BASE-METAL DEPOSITS, WEST SHASTA COPPER—ZINC DISTRICT separated by shale, which locally is extremely contorted. As the conglomerate beds are much more resistant to erosion than the shale, they form conspicuous, bold outcrops. The large areas of conglomerate in the W’hiskytown quadrangle, such as that at the head of Spring Creek, are in part dip slopes. The contacts between conglomerate and shale beds are sharp and smooth, although channeling is present at the top of a few conglomerate beds . In no place was a transition zone observed between conglomerate and shale, although there are transition zones between con- glomerate and grit and sandstone. The matrix of the conglomerate beds is hard and siliceous, and the rock commonly breaks smoothly across the pebbles. Some of the finer beds, composed mainly of closely packed chert pebbles, have a siliceous cement with scarcely any sandy matrix. These finer beds are commonly cut by thin quartz veinlets that pass through the pebbles. The coarser conglomerate beds, which are poorly sorted, commonly have 25 to 50 percent dark- sandy or gritty matrix material. The conglomerate is composed mainly of black and light-gray or white chert pebbles, but it also contains pebbles of dark-gray, tan, and red chert, banded chert, vein quartz, shale, sandstone, and limestone in a dark- or light-colored siliceous, sandy, or gritty matrix. The pebbles range in outline from angular to subrounded, and within most beds they are fairly uniform in size; they constitute from 50 to more than 90 percent of the rock. Most of the pebbles are 14 to 11/2 inches across, although fragments as much as 1 foot in diameter are present in a few beds. Sphericity of the pebbles is poor, although most have well-rounded corners; large fragments are more rounded than the smaller ones. The length of the shale fragments commonly is four or five times greater than the thickness. The chert pebbles have an oblate shape in most beds and are well oriented (fig. 22). In other beds the pebbles are equidimensional, more angular, and consist of several lithologic types. Pebbles of limestone and sandstone are most abundant in the coarser con— glomerate beds. The limestone pebbles are weathered out at the surface, giving a vuggy appearance to the rock. Many of the limestone fragments contain corals. The conglomerate of the Bragdon formation as a whole probably should be classed mainly as a polymic« tic conglomerate, even though most of the beds are com- posed largely of chert pebbles, because they contain metastable fragments such as limestone and shale, and the interstitial material of most beds is a graywacke. Many oligomictic conglomerate rocks are present, how- ever; they consist almost entirely of chert pebbles in a light—colored matrix, and generally Show much better FIGURE 22.—Chert conglomerate of the Bragdon formation. are sn'brounded and well oriented and almost all are white, gray, or Fragments tan chert. Smaller fragments are more angular than the larger ones sorting and rounding than the polymictic conglomerate. The large pebbles or boulders are all contained in the polymictic conglomerate beds. Few fragments of definitely igneous rock are present in the conglomerate beds. Several pebbles of rhyolite containing feldspar phenocrysts were found in the con- glomerate on the west side of the Sacramento arm of Shasta Lake. The writers identified rhyolite, green- stone, and fragments of quartz and feldspar pheno- crysts in thin sections of rocks collected by C. M. Gil- bert, from the divide north of Blue Mountain on the road from Trinity Center to Volmer, north of the West Shasta district. Diller (1906, p. 3) states that most of the Bragdon was derived from the Kennett, and the following is quoted from him: Fossils collected from pebbles in the conglomerate at a large number of localities throughout the Bragdon area were referred to Professor Schuchert and Dr. Girty, and all of them so far as determinable, with one possible but doubtful exception found on Bailey Creek, were reported as Devonian, like those already known in the Kennett region, and show clearly that the COD- glomerate is later than the middle Devonian. The limestone and dark-chert pebbles are similar to the chert and limestone of the Kennett, but the light— gray and red chert and the sandstone pebbles in the BRAGDON FORMATION conglomerate of the Bragdon are unlike anything the ' writers observed 111 the Kennett 111 this area, and they ‘ wele p1 obably derived from a banded chert. They may have been derived from the Chanchelulla formation of Hinds (1932) southwest of the “lest Shasta district; the rocks of Hinds‘ Chanchelulla, which apparently lie 1 under rocks correlated with the Copley greenstone, are . described as containing thinly bedded and banded gray { and less commonly red and green cherts (Hinds, 1933, , p. 85). North of Backbone Creek two black siliceous shale , bands each about 100 feet thick are interbedded with conglomerate and shale of the Bragdon, but this is the I only locality at which siliceous shale was found in the Bragdon. Lithologically these beds are Similar to the black siliceous shale of the Kennett. A small band of amygdaloidal g1 eenstone is inter— bedded in the shale of the Bragdon along the northwest edge of the mapped area, about 2,500 feet west of the junction of Beartrap and Backbone Creeks. Exposures are poor in this area, but the greenstone is apparently a flow about 150 feet thick that is interbedded in the shale of the Bragdon. The flow is a dense dark amygdaloidal greenstone that resembles the Copley greenstone. The relatively thin, even bedding of the shale and silt- stone, the repeated alternate bedding of clay— and silt- sized material, the sparsity of fossils, and the absence of ripple marks all suggest that the Bragdon formation originated as an offshore deposit 011 a slope below wave base (clino environment of Rich) (Rich, 1950, p. 717— 741; 1951, p. 1«20). However, the widespread but lenticular conglomerate and sandstone in the Bragdon indicates either that deposition was partly under shelf conditions, or that conglomerate beds were spread from the shelf area onto the upper part of the slope during periods of storm. The latter assumption seems most probable as the conglomerate and sandstone beds are lenticular and erratic in vertical distribution. The slope was probably gentle, so no syngenetic sliding occured in the shale. , Interbed movement and low—angle thrust faults of Small displacement are common at the base of the Bragdon. These are particularly prominent along Backbone Creek due to movement in the incompetent shale in the Bragdon above the competent Balaklala rhyolite; some of the thrust faults in this area may be related to movement along the steep fault in Backbone Creek. AGE The Bragdon formation is noteworthy because of the paucity of fossils. No fossils were found in 22 square miles of Bragdon that was mapped in the “lest Shasta 41 district; however, outside this area some fossil localities are known. Hershey (190-1, p. 317—360) regarded the Bragdon as being of Jurassic age. Diller (1906, p. 3; 1905, p. 379—387) proved the Bragdon to be of Paleozom age, and he has the following report on the age of the Bragdon from fossil localities in the northern part of the Bedding 30-minute quadrangle about 12 miles north of the West Shasta area. In the sandstones and shales fossils were found at half a dozen localities. A11 important occurrence is upon the divide south west of Nawtawakit ”or High Mountain, where the sandstones, conformably interbedded with characteristic Bragdon con- glomerate, contain shells which Dr. Girty reports as “Paleozoic and without much doubt early Carboniferous, related to the Baird.” The fossils, among which is a large “Spirifer of the SZWXHHS type,” occur in several beds well exposed and are un— doubtedly 0f the Bragdon horizon. Perhaps the most important locality is beside the railroad 11/2 miles northeast of Lamoine, where fossils were found in the sandstone adjoining the Bragdon conglomerate. From this locality Dr. Girty reports Schizodus sp.7 Loxmmcma sp., Plcuro- tomuriu? sp., and Straparollux aft. S. Litmus. There is no room for doubt that these fossils belong to the Bragdon and are not derived from an older formation, and Dr. Girty remarks that if this be admitted “no other conclusion is possible than that the Bragdon is a Paleozoic formation. Indeed, it is clearly safe to say that the horizon is not later than Baird. for the local faunas have many points of resemblance with that of the Baird and none at all with those of the overlying Carboniferous forma— tions.” CHICO FORMATION Shale, sandstone, and conglomerate of the Chico formation crop out in the southeastern part of the Shasta Dam quadrangle. The continuation of this ex- posure of the Chico south and east of the Shasta Dam quadrangle was mapped by Diller (1906, p. 6). A small area of conglomerate of the Chico occurs in the south- east corner of the Igo quadrangle. The. (‘hico formation in the Shasta Dam quadrangle is composed of tan to brown well-bedded shale, sandy shale, sandstone, and some conglomerate. The rock is well cemented, and the shale breaks along bedding planes. The sandstone is locally feldspathic, and at these places contains angular to subangular fragments of feldspar. The conglomerate is made up of sub- angular to subrounded pebbles of shale, rhyolite, and greenstone as much as 6 inches across in a sandy matrix. Lenses of forebedded sandstone are found in the con- glomeratic facies. The shale ranges in composition from coarse-bedded brown sandy shale to thin-bedded tan mudstone. The contact between the Chico formation and the underlying Copley greenstone is exposed at several places in the Shasta Dam quadrangle. The Chico rests unconformably 011 all the older rocks, but no basal con- glomerate is present. Most of the exposures of the base 42 GEOLOGY AND BASE-METAL DEPOSITS, of the Chico in the Shasta Dam quadrangle show that shale of the Chico formation rests on soft, deeply weathered Copley greenstone. The maximum dip of the Chico rocks in the Shasta Dam quadrangle is 15°. Dips range from 8° to 15°, averaging about 100 SE. This dip appears to be uni- form throughout the small area where the Chico is exposed; no evidence was seen of local deformation. No fossils were found in the Chico of the Shasta Dam quadrangle, but in this area the formation was mapped as Chico by Diller and it apparently correlates with part of the Upper Cretaceous Chico formation mapped by Diller (1906, p. 6) and Hinds (1933, p. 112—114) in nearby areas. RED BLUFF FORMATION Erosion remnants of the Red Bluff formation are along Clear Creek in the southeastern part of the Igo quadrangle and in the southeastern part of the Shasta Dam quadrangle. The formation is widely distributed in the north end of the Sacramento Valley east and south of the copper—zinc district. Anderson (1933, p. 238—239) reports that the coarser gravels are found near Bedding at the head of. the valley and that the deposit. contains more sand near Red Bluff, 30 miles to the south. The Shasta copper—zinc district lies in the foot- hills from which part of the gravel and sand of the Red Bluff were derived, however, and the gravel and sand of the Red Bluff formation extended in embay- ments up canyons in these foothills and formed a veneer on stream-cut surfaces that slope gently up toward the foothills. Recent erosion has removed the Red Bluff from most of the canyons and has exhumed topography of an older cycle in most of the valley of the foothills. The Red Bluff formation is composed principally of well-rounded boulders, many of which are elongate, flattened, oblate, or discoidal, set in an iron-stained matrix of sand and some clay. Fragments range in size from fine gravel to boulders several feet long; the average boulder is 6 to 12 inches across. The formation as a whole is poorly sorted, but lenses of well-bedded sand and sandy clay are common at some places. These lenses range from a few inches to 50 feet or more in length. F oreset beds are present in some of the sandy lenses. The formation is well cemented in most parts of the district; river cliffs 100 feet high rise vertically, and except in the weathered zone much of the formation is hard and impervious. In other parts of the district, as at the Piety Hill (or Hardscrapple) mine (Logan, 1926, p. 186) about 1 mile northeast of Igo, the gravel is poorly cemented; and hydraulic methods were used to recover the gold at the base of the Red Bluff formation. WEST SHASTA COPPER-ZINC DISTRICT The formation is distinguished from the Recent gravel by its degree of cementation and iron staining and by its position which commonly is well above the present streams. In some canyons in the foothills, 110w- ever, it is difficult to distinguish between the gravel beds of the Red Bluff formation and those that were formed 011 small terraces that were cut during the in— cising of the present streams. In such areas, the gravel beds are shown 011 the map with the symbol for the Red Bluff formation followed by a question mark. Anderson (1933, p. 238—239) reports that: The age of the Red Bluff formation is usually assigned to the Pleistocene although no paleontological evidence is at hand to substantiate this. The basis of the age determination appears to be the distinctive red color of the matrix as contrasted to the dominant grays of the Recent alluvial deposits and the fact that the Red Bluff formation is unconformable above the Tehama and Tuscan formations. Since the present streams have frequently cut their canyons as deep as 300 feet (Iron Canyon) below the lied Bluff, it does not seem desirable to place the Red Bluff in the Recent. RECENT DEPOSITS The main areas of Recent deposits are shown on the geologic map of the district (pl. 1). No attempt was made to delineate small areas of alluvium or shallow but extensive mantle soil and rock where sufficient outcrops were exposed to permit the mapping of the underlying rocks. The areas of soil and rock mantle and alluvium shown on the map are those that are extensive enough to mask bedrock geology and that make it impossible to extend geologic contacts across covered areas with any degree of certainty. Three types of Recent deposits are distinguished on the geologic maps. The pattern for alluvium, Qal, in- cludes residual soil and residual-debris mantle of sev- eral types that is essentially in place or has been moved only a few feet or tens of feet by such processes as soli- fluction. Material that has moved appreciably from its place of origin under the influence of gravity is distin— guished from the mantle by the symbol le. This com- prises landslides, slump, rockslides, debris flows, and mudflows. Deposits of sand and gravel in the present streams have the symbol Qg. Little residual soil remains on the higher slopes, but in places these slopes are covered with rock debris or with a thin layer of soil and rock debris. Alluvium and surface mantle, for the most part, are limited to valleys and to the low foothills, particularly where the under- lying rock is greenstone. In these areas, the mantle ranges from well-developed soil that is suitable for agriculture in the valleys to mixed soil and rock debris on hillsides that is suitable at some places for vineyards or orchards. Soil, except in alluvial valleys, is reddish and iron stained. Areas in the higher foothills and RECENT DEPOSITS 43 mountains that are marked Qal are covered with a mix- ture of coarse and fine rock debris that contains enough soil in the interstices of the rocks at many places to sup- port a dense growth of Chaparral. These areas are par- ticularly common on north- or east—facing slopes. Little or no soil has formed where the bedrock is rhyo— lite, but north-facing slopes even on rhyolite will sup— port a brush cover. An exception to the lack of soil on rhyolite and the lack of soil at higher altitudes occurs on the coarse-phenocryst Balaklala rhyolite. Here considerable areas of mixed soil and rock debris are formed, partly because the coarse-phenocryst rhyolite weathers more easily than other varieties of rhyolite and partly because some of this rock is at or near the alti- tude of the old Klamath surface, described under “Physiographic features,” and was deeply weathered during an earlier cycle. Landslides, and earth and rock masses that have moved by flowage, cover considerable areas; the larger slides measure several thousand feet across. These larger slides are true landslides in the upper part, but the middle and lower parts have moved largely as mud- fiows or earthfiows. Therefore the. upper part may be composed of large slide blocks that are only slightly displaced from each other, while the lower part is a jumble of soil and rock debris. The Balaklala Angle Station gossan landslide apparently is an example where both types of movement have occurred (p. 107). Some of the old landslides have not been reactivated recently, but others, for example, the landslide at the head of Motion Creek, which was active in 1950—51, dam the streams and form mudfiows that destroy roads and bridges. Even old landslides that appear to be stabilized move to some extent during the rainy season. The old landslide on which the mine plant of the Moun- tain Copper Co. was built many years ago has moved enough to crack some of the concrete building foundations. Recent sand and gravels, Qg, were of commercial importance to the district as a source of placer gold. Nearly all the deposits of sand and gravel in large and small streams have been placered at least once in the search for gold, and along streams such as “’hisky Creek, much of the gravel was neatly stacked by the miners by hand in order to reach bedrock. The chan— nels of the Sacramento River and Clear Creek have been dredged along parts of their courses. The alluvium in the present streams ranges from deposits that contain boulders 10 feet across, as along Brandy Creek or Eagle Creek, to broad sand bars that occur along parts of Clear Creek and. the Sacramento River. Most of the deposits of sand and gravel in the West Shasta district are too small or too difficult to reach to be of interest as commercial sources of sand and gravel. INTRUSIVE ROCKS MULE MOUNTAIN STOCK The Mule Mountain stock (Hinds, 1933, p. 105), which consists of trondhjemite and albite granite, and some quartz diorite, underlies most of the southwestern quarter of the Shasta Dam quadrangle and the south- eastern quarter of the “'hiskytown quadrangle. This stock includes the hornblende-quartz diorite of Diller (1906, p. 8) and part of the alaskite porphyry of Graton (1909, p. 81). The stock has an oval-shaped outcrop pattern that is 10 miles long from north to south and is 5 miles wide (pl. 1). The outcrop pattern centers about the town of Shasta, and the stock includes Mule and Democrat Mountains. Good exposures of the stock may be seen in the road cuts along U. S. Highway 299‘" near the town of Shasta, along the Iron Mountain road near Spring Creek, and in Clear Creek canyon west of Mule Mountain. Bikes of albite granite are common in the Copley greenstone near the contact with the stock. The Mule Mountain stock is deeply weathered, and road cuts more than 50 feet high near Shasta are en- tirely in white crumbly. disintegrated albite granite. l‘nweathered albite granite is exposed in some of the deep canyons, for example, Clear Creek and Spring Creek canyons. The stock is heterogeneous; it consists of a generally leucocratic, holocrystalline granitoid rock that ranges in composition from albite granite to hornblende-quartz diorite, but is here generally referred to as albite gran- ite. Essential minerals are quartz, plagioclase, and epidote. Most of the stock is a granitoid rock of the composi- tion of trondhjemite, and is a leucocratic soda-rich quartz diorite that contains sodic oligoclase and quartz, and 10 to 15 percent interstitial epidote and chlorite, and that has an average grain size of about :2 milli- meters. This phase is considered to be the composition of the original, unaltered intrusive. In places the rock has been extremely reworked by late magmatic solutions and is an albite granite. The altered rock has a pseudoporphyritic texture containing quartz “phenocrysts” 4—6 millimeters in diameter in a white groundmass of albite and quartz that averages 2 millimeters in grain size and that contains 5 to 10 per- cent epidote in clusters from 2 to 6 millimeters in diameter. Large parts of the Mule Mountain stock were altered by late magmatic solutions that added silica and soda. The altered parts of the stock have gradational contacts to the unaltered or slightly altered 4:4 GEOLOGY AND BASE-METAL DEPOSITS, WEST SHASTA COPPER—ZINC DISTRICT trondhjemite. The principal bodies of altered rock are outlined on the geologic map (pl. 1). Quartz “pheno- crysts” are limited mainly to the altered areas, although some of the trondhjemite also contains added quartz as pseudophenocrysts. Chemically and mineralogically the equig 'anular trondhjemite and the white pseudoporphyritic albite granite are similar. They are composed mainly of quartz, albitic plagioclase, epidote, and chlorite. The commonly equigranular trondhjemite contains slightly more CaO, FeO, and Fe203 and slightly less NazO and SiOz than the porphyritic albite granite (table 4). In the field the difference is more apparent, as the pseudoporphyritic albite granite is whiter and looks more siliceous than the equigranular trondhjemite. The epidote is finely disseminated throughout the equigranu— lar trondhjemite, but is regrouped in clusters ranging from 2 to 6 millimeters in diameter in the albite granite. TABLE 4.——Analyscs of albite granite and quart: diorite from the Mule Mountain. stock [Samples 1, 4, 5, by U. S Geol. Survey rapid-analysis method. Analysts, 8. M. Berthold and E. A. \ygaard. Samples2, 3, 6, analyst M. K. Carron] 1 2 3 4 5 6 75.8 76.48 13.9 13.09 .92 .64 144 .79 1.9 . 1.2 .43 4 101 100. 24 [Computed by the CIPW system] Quartz ,,,,,,,,,,,,,,,,,,,,,,,,, 30.18 39. 66 43.08 46 68 42. 48 43 40 Orthoclase. 5.00 4. 45 2. 78 7. 23 2. 78 2. 78 Albite,.__ 27 25 34 48 31. 96 29. 87 37. 20 37. 72 Anorthltc" 23 35 10 56 10.79 5. 84 9.45 8.34 Cornndum. ,,,,,,, 2. 75 2. 24 4.69 2 75 2.14 Diopside _____ 1. 44 ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Hypersthene, 8.63 3 58 2.11 2. 64 3 96 3 01 Magnetite" 2 .12 1 96 2. 78 116 9‘5 9‘3 Ilmenitc" .(11 . 46 . 47 . 46 .30 . 46 Hematite ............................................... 1. 28 . 32 ,,,,,,,, 98 78 97 90 96. 21 99. 85 100.17 98. 78 1 Includes gain due to oxidation of FeO. 1. Hornblende-quartz diorite, sec. 36, T. 33 N ., R. 6 W. 2-3. Trondhjemite from Whiskytown quadrangle, California. 4. “P0rphyritic” albite granite with epidote from sec. 6, ’1‘. 32 N., R. 5. Siliceous, “porphyritic” albite granite from Highway 299W, 0. 25 5mile east of branch road to South Fork Lookout station. 6. Siliceous, “porphyritic” albite granite from Whiskytown quadrangle, California. Intrusive breccias are abundant in the northeastern part of the stock (fig. 23). They formed where the albite granite of the Mule Mountain stock shattered and partly absorbed Copley greenstone. The fragments of greenstone range in size from tiny relicts to as much as 7 feet in diameter. Many are blocky and irregular in outline and look like they were formed by breaking up \ Reworked Copley FIGURE 23.7Int1'usive breccia near greenstone fragments in albite granite matrix. Spring Creek. of an originally massive rock, but possibly 25 percent of the fragments are elongate and oriented, and were derived from foliated greenstone. Some are corroded until only wisps of the original fragment can be seen. There is some correlation between the size of a frag— ment and the amount of recrystallization and granitic material that has been added. Many large fragments are little-altered Copley greenstone that show amygda- loidal and pillow structures. Smaller fragments are reworked to a granular rock containing feldspar, horn— blende, and quartz porphyroblasts as much as 1 centi- meter in diameter in a fine-grained groundmass. In Spring Creek the fragments of reworked greenstone average about 3 by 4 inches across, and hornblende porphyroblasts 1 to 2 millimeters in diameter have been formed in a fine—grained groundmass that has a grano— blastic texture. The matrix between the fragments in the intrusive breccia is coarsegrained pseudoporphyritic albite gran- ite. Where the fragments are small and have been ex— tensively reworked, the matrix of albite granite has assimilated the greenstone and is more basic and con— tains unaltered hornblende crystals. The rock in the resistant knob of hornblende-quartz diorite that lies 011 the west edge of the intrusive breccia area on the Iron Mountain road, where the road crosses Spring Creek, is an example of contamination by absorbed material from the greenstone. The knob is a hard massive dark-gray granitoid hornblende—quartz diorite. It contains about 2 percent dark fine-grained xenoliths. These xenoliths have euhedral porphyroblasts of hornblende 1 to 2 millimeters long that are identical With the horn- blende in the enclosing massive hornblende-quart di- orite. Throughout the hornblende-quartz diorite are INTRUsIVE ROCKS 45 many tiny areas of mafic minerals that have a texture similar to that of the xenoliths, and are the remnants of former fragments. The hornblende in the intrusive matrix was derived from assimilation of basic xenoliths, and the resultant rock is more basic than the original magma. This knob of hornblende-quartz diorite, which has the appearance of being the least altered variety of the Mfile Mountain stock, is actually more basic than the original magma because of contamination by re- wor King and incorporation of much greenstone. The Mule Mountain stock is cut by many veins of quartz and some dikes of aplite. The quartz veins range in thickness from 2 inches to several feet. They contain small amounts of pyrite, chalcopyrite, and cal- cite, and some are auriferous and have been mined for their gold content. Aplite dikes are common in the trondhjemite and albite granite on Mule Mountain and in the greenstone near the contact with albite granite. They are commonly less than 1 foot thick and have sharp walls. Some of the aplite in dikes has quartz phenocrysts and resembles Balaklala rhyolite; the ap— lite dikes can be distinguished by their sugary ground- mass. Inclusz‘ons.——Porphyritic Balaklala rhyolite and greenstone inclusions locally are abundant in the Mule Mountain stock. Inclusions of Balaklala rhyolite are inconspicuous as they are the same color and have the same mineralogy as the trondhjemite and albite granite. However, along the western and northwestern contact between the Mule Mountain stock and Balaklala rhyo- lite many inclusions of porphyritic rhyolite in albite granite can be recognized by their aphanitic ground- nxass, whereas the albite granite has a granitoid ground- mass. Greenstone inclusions are more abundant than those of rhyolite. In addition to the intrusive breccia described above, many large inclusions of schistose (‘opley greenstone are exposed in road cuts on U. S. Highway 299“r near Shasta and along the road to the Forest Service lookout station on South Fork Mountain. Some of these inclusions are several hundred feet long and only 6 to 8 feet thick; at first glance they resemble matic dikes, but amygdules and pillow structures are preserved in the larger inclusions, some of which are probably roof pendants. The Mule Mountain stock generally has a sharp con— tact with the Copley greenstone and the Balaklala rhyo— lite. Balaklala rhyolite is unaltered where it is in con- tact with trondhjemite or albite granite because of the similarity in mineralogic character and chemical com— position; the contact metamorphic halo in the green- stone surrounding the intrusive is more pronounced. Near Matheson, and on the west side of Slick Rock jreek south of Iron Mountain, the greenstone has been metamorphosed for several hundred feet from the con- tact of albite granite. ll’ithin 50 feet of the intrusive the chloritic Copley greenstone is recrystallized to a fine-grained rock containing mainly plagioclase and hornblende. This grades outward into greenstone with lumps and knots of epidote and finally into a foliated chloritic greenstone. “chin the metamorphic halo the foliated character of the greenstone is destroyed. The contact of the Mule Mountain stock is generally parallel to the foliation in the intruded rock, but locally cuts across foliation. Apparently the Copley green- stone was already foliated when the albite granite was intruded. However, some diastrophism occurred after the intrusion of albite granite, as its borders are locally sheared parallel to the regional foliation. Therefore the intrusion is believed to be syntectonic with the Ne- vadan orogeny. The albite granite is older than the Shasta Bally batholith, as it is intruded northeast of Igo by the batholith (pl. 1). PETROGRAPHIC DESCRIPTION Tmndhjemite.—About 65 percent of the Mule Moun- tain stock consists of a hypidiomorphic granitoid rock composed of quartz and plagioclase, and 10 to 15 per— cent mafic minerals that consist only of green biotite, epidote, and chlorite. Accessory minerals are apatite, sphene, and magnetite. Hornblende was not observed in this rock. Much of the rock is equigranular and averages 2 millimeters in grain size, but in places rounded quartz masses as much as 8 or 9 millimeters in diameter that resemble phenocrysts are abundant. The distribution of the mafic minerals is a characteristic feature of the rock. These minerals are very fine grained and are interstitial to plagioclase, being present in thin stringers and lenses that wrap around the plagioclase. The rock is composed of 60 to 65 percent plagioclase, which is subhedral and shows both Carlsbad and albite twinning. The plagioclase is strongly altered to seri- cite, and a few cores are saussuritized. Most of the plagioclase is sodic oligoclase ranging in composition from Ab90A1110 to Ab‘8.;A1114. Zoning is inconspicuous except in a few grains that have a slightly more calcic core. The mafic minerals include epidote, chlorite, and green biotite listed in decreasing order of abundance. Epidote is present in saussuritic cores of plagioclase and as an interstitial mineral associated with clilorite and green biotite. Chlorite occurs in thin interstitial veinlets; it has a distinct anomalous blue interference color. Green biotite is present in very small quantities; it is a mineral of late magmatic origin and is associated with sericite in fractures in quartz. 4:6 GECLOGY AND BASE~METAL DEPOSITS, WEST SHASTA COPPER-ZINC DISTRICT Quartz, a late mineral, occurs as anhedral grains that average about 2 millimeters in diameter, and constitutes about 20 to 30 percent of the rock. It replaces plagio— clase and fills the spaces between these grains, but also locally forms 1)selulophenocrysts. These quartz pseudo— phenocrysts are aggregates of quartz grains that replace the plagioclase (fig. 2‘4). FIGURE 2{fil’hotomicrograph of albite granite showing early stage in the formation of a pseud‘ophenocryst of quartz (q) that is interpreted as having replaced plagioclase (p). “Porplzyritic” albite granite—This granite is a white, hypidiomorphic granular rock containing rounded quartz pseudo'pl1enocrysts 6 to 10 millimeters in diam- eter in a granitoid groundmass that averages 11/2 milli— meters in grain size. It is similar to the albite granite described by Gilluly at Sparta, Oreg. (Gilluly, 1933) and to the albite granites associated with spilitic suites described by Dewey and Flett (1911, p. 202—209, 2-11— 218), and by Harwood and “Wide (1909, p. 549—554;). The rock contains mainly quartz and albite and less than 10 percent epidote and chlorite. Epidote occurs in clusters commonly 2-6 millimeters in diameter in con— trast to the thin veinlets of epidote in the largely equi- granular trondhjemite. The “porphyritic” albite granite constitutes about one-third of the Mule Mountain stock. It appears as large irregular bodies throughout the trondhjen'lite mass where late magmatic solutions rich in soda and silica replaced the original trondhjemite. Contacts be— tween the two types of rocks are gradational. Under the microscope the rock is seen to contain mainly quartz, albite, and epidote, and small amounts of chlorite, zoisite, biotite, sericite, apatite, and opaque minerals. Quartz and albite make up more than 90 percent of the rock. Albite is in subhedral grains and is extremely corroded by quartz. Albite ranges in com- position from Ahmakn4 to AbggAnu. The plagioclase rarely contains any epidote or clinozoisite, but some of the albite is strongly altered to sericite. Quartz is one of the last minerals to crystallize. It is interstitial to albite, and where the large pseudopheno- crysts formed, it corroded the albite as shown by many relicts of albite through the quartz. Both quartz and albite show strong cataclastic structures. Mortar struc- ture is common, and all the quartz has nndulatory ex- tinction. The quartz is full of tiny rounded fluid inclusions. Large areas of myrmekite replace grains of quartz and albite in albite granite. Several distinct inter— growth textures are present (Sederholm, 1916; Gilluly, 1933, p. 71—72; and Alling, 1936, p. 163—172). The most common pattern has tiny, corroded, hook-shaped masses of albite in a sea of clear quartz. The quartz and albite are in optical continuity over areas of several square millimeters. The intergrowth seems to replace earlier quartz and albite and is interpreted as a simultaneous recrystallization caused by late magmatic solutions. Another less common intergrowth texture has slender irregular rods of albite in quartz, and both minerals are in optical continuity. The rods of albite grade into unreplaced albite crystals, and are oriented parallel to cleavage planes of the unreplaced albite. This texture is due to replacement of albite by quartz along cleavage planes. The third type of intergrowth is myrmekite. The edges of the myrmekitic intergrowths are coarser than the centers and grade into a normal granitoid texture. Albite in the myrmekite has the composition AbgfiAnl, whereas the subhedral albite crystals have a composition about AbgoAnm. Apparently the last hydrothermal solutions were the most sodic and formed the intergrowth textures. The mafic minerals include green biotite, epidote, and chlorite. Biotite is interstitial to quartz and albite, and is in clusters of small plumose growths intergrown with sericite. The biotite is either a late primary mineral or an early hydrothermal mineral. Epidote is the princi- pal matic mineral. It is found in clusters as much as 6 millimeters in diameter that are made up of individual crystals as much as 2 millimeters in length. The epidote is much coarser than in the equigranular trondhjemite and only in a few slides were tiny epidote grains seen in the plagioclase crystals. Evidently the epidote was recrystallized by deuteric solutions into these coarsely crystalline knots. The epidote content was decreased from about 20 percent in the equigranular trondhjemite to less than 10 percent in the silicified “porphyritic” albite granite. INTRUSIVE ROCKS 47 Light green chlorite commonly surrounds epidote and thins out from epidote clusters into reinlets along grain boundaries of quartz and albite. Inclusions of opaque minerals that are altered to leucoxene are abundant in the chlorite. Euhedral apatite and sphene crystals occur in minor quantities as accessory minerals. Hornblende—quartz diorite—This rock is localized in a small body several hundred feet in diameter in the north end of the Mule Mountain stock in Spring Creek at the crossing of the Iron Mountain road. The horn- blende—quartz diorite grades to the north and east into an intrusive breccia in Copley greenstone and to the south and west into trondhjemite. It is a dark gray hard equigranular granitoid rock, formed by assimila- tion of greenstone by trondhjemite. The average grain size is 2 millimeters. The rock consists mainly of quartz, plagioclase, hornblende, chlorite, and epidote and some sphene, apatite, and magnetite. Fine-grained dark-gray xenoliths of altered greenstone make up about 2 percent of the body. They range in size from tiny wisps to ellipsoidal or irregular fragments as much as 6 inches in diameter. The xenoliths have hazy bor- ders with the hornblende-quartz diorite. Subhedral grains of plagioclase that are extremely altered to epidote, clinozoisite, and sericite constitute about 60 percent of the rock. Albite twinning is com- mon but is inconspicuous owing to saussuritic alteration. Thin rims of clear albite-oligoclase on the altered plagioclase are common. The original plagioclase was probably much more calcic, but no relicts of it were observed in the saussurite. The hornblende-quartz diorite contains about 25 per- cent quartz. Quartz is present as anhedral aclastic gains that are interstitial to plagioclase. (Quartz has corroded plagioclase as shown by many irregular relicts of plagioclase (fig. 25). Hornblende and chlorite make up about 10 percent of the rock. Hornblende is in subhedral grains that are pleochroic from light to dark green. (‘hlorite and epi- dote are pseudomorphic after hornblende. A plife.——Aplite dikes that have sharp walls and are usually less than a foot thick cut the albite granite on Mule Mountain, and similar dikes cut the Copley green— stone near the albite granite contact. Some of the ap- ‘lite contains euhedral quartz phenocrysts, commonly 2 millimeters in diameter, in a tine-grained sugary groundmass of quartz, albite, minor chlorite, sphene, epidote, and leucoxene. The groundmass of the aplite has a microgranitoid texture. Myrmekitic and micro- graphic intergrowths of albite and quartz are abundant in the aplite. I‘VIGI'RE 25.7~Photomicrograph of hornblende—quartz diorite. a varietal type of the Mule Mountain stock. Plagioclase has cores with strong saussuritic alteration and some clear rims of albite (all). Some quartz (4]) has replaced the plagioclase. Crossed nicols, X14. AGE The Mule Mountain stock is dated as Late Jurassic in age, although the youngest rocks that are intruded by the Mule Mountain stock are the Balaklala rhyolite of Middle Devonian age. Diller correlates the Mule Mountain stock with a small plug of. albite granite (hornblende-quartz diorite of Diller) that intrudes Bully Hill rhyolite of Triassic age in the Bedding quadrangle 11/2 miles southeast of Oak Run and 6 miles southeast of the Afterthought mine (Diller, 1906, p. 8). The Mule Mountain stock, in turn, is intruded by satel- litic bodies of the Shasta Bally batholith in the south- eastern part of the Igo quadrangle (pl. 1). The Mule Mountain stock was syntectonic with the Nevadan orogeny of Late Jurassic or Early Cretaceous age. This stock was intruded after the orogeny foliated and regionally metamorphosed the Copley greenstone, but early enough for the later phases to affect the albite granite of the stock itself. The albite granite is elon— gated with the regional foliation and its elongate shape was apparently determined by regional structures formed during orogeny, but massive albite granite in some places cuts directly across foliated Copley green- stone. The albite granite locally metamorphosed the Copley greenstone to amphibolite and epidote amphibo- lite, and if the latter rocks had been present during the main part of the orogeny, they should have been reduced by retrograde metamorphism to chlorite-albite schists 48 GEOLOGY AND BASE-METAL DEPOSITS, WEST SHASTA COPPER-ZINC DISTRICT similar to the mineralogy of the Copley elsewhere in the district. The albite granite is itself locally sheared or sheeted parallel to its contact; the writers believe this is due to movements in the closing phases of the Nevadan orogeny, as the areas of foliation near the borders of the stock are too widespread to be accounted for by post-orogenic local movements. SHASTA BALLY BATHOLITI-I DISTRIBUTION AND GENERAL FEATURES The Shasta Bally batholith is the largest pluton in the Bedding area, and it underlies most of the western half of the Igo quadrangle. Several small satellitic bodies crop out to the east between the Shasta Bally batholith and the Mule Mountain stock (pl. 1). Re— gionally the batholith crops out for a distance of 30 miles in a N. 20° \V. direction, mostly beyond the mapped area, and has a maximum width of 10 miles. Most of the batholith is a biotite-hornblende-quartz diorite, but it ranges in composition near the edge and in. satellite bodies from gabbro to granodiorite. The color ranges from dark gray in the gabbro to nearly white or light gray in the granodiorite, The batholith is a single intrusive; there is no evidence of multiple intrusion of the rock types that differ slightly from each other. The rock is here called a biotite-quartz diorite even though hornblende is a common constituent, as hornblende is rarely visible megascopically in the main body of the intrusive. The principal minerals are quartz, feldspar, biotite, and hornblende. The rock has a granitoid texture and the average grain size is about 2 millimeters. Porphyritic textures are rare, in contrast to the prominent pseudoporphyritic textures of the Mule Mountain stock. The main part of the batholith intrudes Copley green— stone in the mapped area, but the satellitic plug along Clear Creek in the southern part» of the Igo quadrangle intrudes the Mule Mountain stock of albite granite also. In the southern part of this quadrangle the border of the batholith is darker than the interior, and much of the border phase is hornblende diorite. It has a sharp contact with Copley greenstone, which is recrystallized to a fine-grained amphibolite, but the hornblende diorite grades into biotite-quartz diorite toward the interior. In the northern part of the Igo quadrangle near Brandy Creek the contact between granitic rock and greenstone is less distinct; massive quartz diorite, which is the pre— dominant rock along this part of the contact, grades outward to a migmatite that has interlayered dark and light bands. The migmatite zone is described under “Igneous metamorphism.” The border of the batholith commonly has a planar structure due to primary foliation parallel to the con- tact and at a few localities alined hornblende gives the rock a linear'element, but the interior is mostly massive. The foliated quartz diorite is slightly coarser grained than the interior of the batholith and contains more mafic minerals, averaging about 40 percent hornblende and biotite. The batholith was intruded in the form of a large schlieren arch, and its top was probably only a short distance above the peaks from Shasta Bally to Grouse Mountain. Primary foliation, shown by alinement of minerals and inclusions and by segregation of minerals in bands of different composition, is limited to the bor— ders of the batholith and to the peaks and high ridges in the central part. In the east part of the batholith the primary foliation strikes N. 20° “Y. parallel to the contact and dips 60° to 70° E. “Yestward toward the center the foliation becomes flatter until it is nearly horizontal on the peaks between Shasta Bally and Grouse NIountain, which are probably near the top of the intrusive. On the west side of the intrusive, out- side of the mapped area, the foliation dips steeply west. I nclusz'ons.—Near the border of the intrusive, sporadic small dark spindle- to pancake—shaped amphibolitic in- clusions 1 to 3 inches in diameter and one-half inch thick are found. The inclusions are alined parallel to the primary foliation of the quartz diorite. They are much liner grained than the quartz diorite in which they are enclosed and have a crystalloblastic texture. These in— clusions are probably reworked fragments from the Copley greenstone. PETROGRAPHIC DESCRIPTION Although the Shasta Bally batholith and the small satellite bodies of granitic rock are all part of one intru- sive, which is uniform in composition throughout most of the body, several varietal types have been recognized in the field and in thin sections. The varietal types, par- ticularly those in the Clear Creek plug, are described in detail as some of them show the effect on the quartz diorite magma of assimilation of greenstone. The varie- tal types are granodiorite, hornblende diorite, and gabbro; these are limited to the border of the batholith or to satellite plugs. Biotitaquartz diorite.—Biotite‘quartz diorite consti- tutes about 90 percent of the batholith. It is an equi— granular rock averaging about 2 millimeters in grain size. Essential minerals are quartz, plagioclase, biotite, and hornblende, and less common constituents and ac- cessory minerals include orthoclase, epidote, chlorite, kaolinite, apatite, magnetite, zircon, and allanite. Plagioclase constitutes 45 to 50 percent of the rock. It occurs as subhedral chunky grains that have promi- nent albite twinning and commonly show Carlsbad and INTRUSIVE ROCKS 49 pericline twinning. Zoning is prominent, and cores are commonly Ab68A1132 to Ab60A1140 and rims Ab75An25 to .AbTOJ/Xngo. Most of the quartz diorite contains 20 to 25 percent quartz as anhedral grains that are commonly interstitial to plagioclase. Hornblende and biotite constitute 15 to 25 percent of the rock; normally biotite is slightly more abundant than hornblende. Hornblende forms euhedral crystals that are pleochroic from light to dark green. Anhedral grains of biotite have the following pleo- chroism: X=colorless; Y=Z=dark—brown to reddish— brown; it is in part altered to chlorite. A maximum of 5 percent orthoclase may occur as tiny, anhedral interstitial grains. It is more abundant in the quartz diorite in which biotite is the predominant mafic mineral. Common accessory minerals are sphene, apatite, zircon, and magnetite. They are most common as euhedral inclusions in biotite. Allanite is found rarely as an accessory mine ‘al. (imaodz’orite.—Small areas of granodiorite that crop out in the southern part of the I go quadrangle are prob- ably small intrusive bodies that are differentiates of the quartz diorite, but the contact relationship is not ex- posed. The granodiorite is a light-gray fine-grained rock that contains mainly quartz, orthoclase, and plagio- clase and less than 10 percent biotite and 1 percent hornblende. Apatite, sphene, zircon, and magnetite are common accessory minerals. The granodiorite contains 45—60 percent plagioclase and 10~15 percent orthoclase. Twinning and zoning of the plagioclase are similar to those of the quartz diorite. Plagioclase has cores that range in composition from AbnAn28 to AbgsAn37 and rims of Ab75Ang5. ()rthoclase is usually interstitial to plagioclase. Both microper- thite and antiperthite are present. In the microper- thite thin stringers of oligoclase are included in ortho- clase and probably formed by exsolution. In the anti- perthite, cores of plagioclase are nearly half replaced by thin veinlets, and a ramifying network, of orthoclase stringers whereas the rims contain no orthoclase. Myrmekite containing tiny stringers and hook-shaped forms of quartz in orthoclase, although not observed in the quartz diorite, is common in the granodiorite. Hornblende diorite.—This rock is concentrated near the borders of the intrusive and in the small satellitic bodies. It differs from the quartz diorite mainly in that it contains a more calcic plagioclase, contains less than 5 percent quartz, and contains more hornblende than biotite. The hornblende diorite is an equigranular, medium coarse-grained, dark-gray rock that contains mainly plagioclase and hornblende and small amounts of augite, orthoclase, quartz, epidote, sphene, magnetite, apatite, and zircon. Plagioclase constitutes 50 to 60 percent of the rock and is andesine—labradorite that is zoned from cores of AbmAn52 to rims of AbsgAmg. Albite twinning is prominent while pericline and Carlsbad twinning are less common. Hornblende, as euhedral crystals 3 to 4 millimeters in diameter that poikilitically enclose pla- gioclase, magnetite, and apatite constitutes as much as 40 percent of the rock. The hornblende is strongly pleochroic from light to dark green. Augite forms the cores of a few hornblende crystals. In places quartz and orthoclase are present in small amounts as inter- stitial small grains. Sphene, apatite, zircon, and mag- netite are common accessory minerals. The hornblende diorite and the quartz diorite prob- ably are part of a single intrusive. This intrusive as- similated part of the Copley greenstone as it. was in— truded, reworking the chloritic Copley greenstone to hornblende and plagioclase. GabZ)rro.—Coarse-grained hornblende gabbro occurs as small dikes and irregular bodies near the margin and in the roof rock of the. Clear Creek plug in the Igo quadrangle, which is a satellitic. body of the Shasta Bally batholith. The biotite-quartz diorite in the in— terior of the Clear Creek plug, as locally in the Shasta Bally batholith, grades outward through hornblende- quartz diorite to hornblende diorite near the border. The contact of the hornblende diorite with the albite granite is sharp, whereas the contact with Copley green- stone is gradational and the gradation extends into gabbro that was formed in situ by metasomatism of the Copley greenstone. This metasomatism is described under “Metamorphism related to the Shasta Bally batholith.” AGE The Shasta Bally batholith is Late Jurassic or Early Cretaceous in age. It was not afiected by the Nevadan orogeny and cuts directly across foliation formed during the Nevadan orogeny of Late Jurassic or Early Cre— taceous age. Also the Shasta Bally batholith has metamorphosed the Copley greenstone to amphibolite, gneiss, and migmatite, but no retrograde metamorphism has been superposed on the altered zones by later orogeny. The Shasta Bally batholith is overlain nonconform— ably by beds of the middle part of the Paskenta forma— tion of Anderson (1902) and Horsetown formation of Lower Cretaceous age west of the “’est Shasta district (Hinds, 1934, p. 182—192). Hinds states that Lower Cretaceous fossils present at many horizons show that the strata in contact with the [Shasta Bally] batholith range from Middle Paskenta (Valanginian) on the western side to Lower Horsetown (Hauterivian) on the eastern according to information furnished me by Dr. F. M. Anderson [(1933)] 50 GEOLOGY AND BASE—METAL DEPOSITS, WEST SHASTA COPPER-ZINC DISTRICT On the basis of geologic and paleontologic evidence the intrusion of the Shasta Bally batholith thus oc- curred after the Nevadan orogeny of Jurassic age but before the deposition of the Lower Cretaceous strata which nonconformably overlie the batholith. A 50-p0und sample of the Shasta Bally batholith was collected for age determination by the Larsen method. David Gottfried of the U. S. Geological Survey labora- tory (1954, oral communication) reports the age of the intrusion as 97 million years. MINOR INTRUSIVE BODIES Small intrusive bodies are abundant in the (‘opley greenstone and the Balaklala rhyolite, and to a lesser extent in the Kennett and Bragdon formations and in the Shasta Bally and Mule Mountain plutons. These minor intrusions were emplaced before and after the Nevadan orogeny. The intrusions of pre-orogenic age include amphibolite, diabase, and nonporphyritic and porphyritic rhyolite; the younger intrusions include lamprophyre, andesite, diorite porphyry, dacite por— phyry, quartz latite porphyry, and aplite. ROCKS INTRUDET) BEFORE THE NEVADAN OROGENY Rhyolz'te.——Minor intrusives are preponderant in Small stocks, plugs, dikes, and sills of Balaklala—type rhyolite in Copley greenstone and Balaklala rhyolite. Many small irregular stocks, plugs, and dikes of por- phyritic and nonporphyritic rhyolite that were feeders for the flows of Balaklala age cut the underlying Copley and the older parts of the Balaklala. ()ther small rhyo- litic dikes and sills cut the Copley throughout the mapped area. However, rhyolitic flows also occur in the Copley near the top of the formation, and Balaklala rhyolite is infolded in the Copley. In the absence of bedding, it is difficult to differentiate the form in which the rhyolite occurs, and all bodies of rhyolite that are lithologically identical with Balaklala rhyolite are given that symbol. Bodies of intrusive rhyolite, being largely feeders for the overlying flows, are described with the Balaklala, rhyolite. H omblendite.-—A few hornblendite and serpentinized hornblendic dikes or sills are in the Copley in the Igo quadrangle and in the southern part of the Shasta Dam quadrangle. They range in thickness from a fraction of an inch to several hundred feet. Some hornblendite dikes are in the southern part of the Shasta Dam and “lhiskytown quadrangles. They are dark-green porphyritic mafic dikes 50—60 feet thick that have phenocrysts of hornblende and augite as much as 1 centimeter in diameter in an aphanitic chloritic matrix. Under the microscope they are seen to contain mainly hornblende and small amounts of augite, olivine, and opaque minerals. The mafic minerals are in part altered to epidote, antigorite, and talc. The dikes 0r sills have chilled borders against Copley greenstone, and some are cut by lamprophyre dikes. Diabase.—Dikes and sills of diabase cut all rocks in the district older than the Shasta Bally batholith. The intrusive bodies range from a few feet to about 200 feet in thickness and are as much as 5,600 in length. They are fine-grained massive dark—gray to greenish—gray rocks that are locally finely porphyritic. Phenocrysts where unaltered are plagioclase and hornblende, but commonly these are altered to epidote and chlorite. The diabases are all altered to some extent, although megascopically they look like unaltered rocks. They are composed of plagioclase, hornblende, epidote, chlo— rite, calcite, quartz, biotite, and magnetite and have a relict ophitic texture. Plagioclase ranges in composi- tion from albite (AbgfiAm) to labradorite (Akbar—X1159). “'here unaltered, it is labradorite and occurs as clear lath-shaped crystals that have prominent albite twili- ning in a groundmass of chlorite and epidote. Most of the plagioclase has saussuritic alteration and is cloudy, massive albite containing inclusions of epidote. Mafic minerals in the diabase are mainly chlorite and epidote and have some relict cores of hornblende and minor secondary biotite. Augite, which was probably orig- inally present, is completely altered. Quartz is present in minor quantities as tiny interstitial grains. Most of the quartz appears to be primary, although some may be released silicz. Calcite is in irregular patches and veinlets in plagioclase and filling fractures in the rock. A few diabase intrusive bodies associated with kera- tophyre in the central part of the district are albite diabase. . ‘ The diabase may be of several ages. It has all under- gone some alteration, probably during regional meta- morphism. The albite diabase, which is intrusive into keratophyres of the Copley greenstone, is probably of Devonian age, although the evidence is not conclusive. It may be related to an albitic suite of spilite, kera-' tophyre, and soda rhyolite that is of Devonian age. Some diabase dikes and sills cut the Kennett and Bragdon formations and are post—Mississippian in age. They appear to be similar to the diabase dikes cutting the Copley in many places in the eastern part of the Shasta Dam quadrangle. The dikes occur as sharp-walled straight bodies that maintain fairly uniform widths in competent rocks, but they are less regular in shale. Figure 26 shows the mashing that accompanies intrusion at some places in the shale. INTRUSIVE ROCKS 51 and angular diabase fragmentsjffi, In mashed,rcrruglpl£sh3|g 3 Diabase dike\ 7 50 0 l I l l l l l 100 Feet FIGURE 26.—Sketch of intrusive breccia along diabase (like in shale of the Kennett formation. ROCKS INTRUDED AFTER THE NEVADAN OROGENY Most, of the minor post-Nevadan intrusive bodies are felsic dikes and sills related to the Shasta Bally batho- lith and lamprophyre dikes that cut the Mule Mountain stock of Jurassic( ?) age. The felsic dikes include dio- rite porphyry, dacite porphyry, quartz latite porphyry, and aplite. Two groups of diorite porphyry and dacite porphyry dikes and sills are recognized in the field. The first group has large, conspicuous, white, zoned plagio— clase phenocrysts and locally is called Birdseye por- phyry; the second group has a much less pronounced porphyritic texture and is part of a group of intrusive dikes and sills that range in composition and texture from diorite porphyry t0 aplite. This group has a much more restricted areal distribution than the Birdseye porphyry and is localized within a few miles of the con- tact of the Shasta Bally batholith. The rocks of second group are here referred to under felsic dikes. Birdseye porphyry—This light-gray to buff-colored conspicuously porphyritic rock contains phenocrysts of plagioclase, hornblende, and biotite in a fine—grained to aphanitic groundmass.. The composition ranges from diorite porphyry to dacite porphyry, and large and small dikes and sills cut all the rocks in the district ex- cept the biotite—quartz diorite of the Shasta Bally batho- lith. The name Birdseye porphyry was applied by the local miners to these porphyritic dikes, presumably be- cause the centers of the zoned feldspar phenocrysts weather out and somewhat resemble the pupil of an eye. Diller (1906, p. 7) called the dikes dacite porphyry; Ferguson (1915, p. 245) called a similar dike at the Mad Mule mine in the Iron Mountain quadrangle a dio- rite porphyry. The term “Birdseye porphyry” as ap- plied locally will be used throughout this report. The most prominent areas of Birdseye porphyry are on Mad Mule Mountain, at the Uncle Sam mine, and in the Behemotosh Mountain quadrangle northeast of Backbone Creek. At the Mad Mule mine a dike of Birdseye porphyry, striking east-west and dipping 40° to 60° N., is exposed for more than 1,000 feet along the strike. It is reported by Ferguson (1915, p. 245) to have a maximum thickness of about 150 feet. The dike is at the contact between shale of the Bragdon formation to the north and Balaklala rhyolite to the south, but its south contact may be a fault. It contains large euhedral plagioclase phenocrysts as much as 1 centimeter long in a gray aphanitic groundmass. About 2,500 feet to the northwest, at the Bright Star mine northwest of Mad Mule Mountain, and extending to the southwest, are two irregular areas of Birdseye porphyry that may be large sills, although the outcrops are not suflicient to be certain of contact relationships. Both outcrops are 400 to 600 feet wide; one is 1,700 feet long and the other 2,000 feet long in a northeasterly di— rection. The rock is a dacite porphyry containing eu- hedral platy phenocrysts of plagioclase as much as 1 centimeter long in a gray fine-grained groundmass of plagioclase and hornblende. Another large area of Birdseye porphyry is northeast of Backbone Creek where a vertical dike 100 feet thick striking N. 60° ll'. is exposed for a length of 6,200 feet. The dike is intruded along a strong fault zone several hundred feet wide in shales of the Bragdon formation and has enclosed two large fault slivers. One is a sliver of probable Kennett limestone; the other is crumpled shale of the Bragdon. The porphyry has euhedral plagioclase phenocrysts 1 centimeter long in a gray aphanitic groundmass. Many smaller Birdseye porphyry dikes are exposed throughout the district; most are about 10 feet thick and are too small to show on the geologic map of the district. In all the dikes plagioclase forms conspicuous large euhedral phenocrysts; one dike located 2,000 feet northwest of the Friday-Lowden adit contains unori- ented plagioclase phenocrysts 2.5 by 2.5 by 0.5 centi- meters. The Birdseye porphyry generally contains about 20 to 30 percent plagioclase phenocrysts that range from 5 to 8 millimeters in length, and contains less than 5 percent small, inconspicuous hornblende phenocrysts in a dark-gray microgranitoid groundmass 0f plagioclase, quartz, hornblende, epidote, chlorite, apatite, magne- tite, and carbonate. There is a distinct hiatus between size of phenocryst and groundmass, with no seriate tex— ture between them. Some of the Birdseye porphyry contains quartz phenocrysts and as much as 20 percent quartz in the groundmass. The rock is called a dacite porphyry if it contains more than 5 percent quartz in the groundmass. Diorite porphyry contains less than 5 percent quartz and has a granular groundmass. 52 GEOLOGY AND BASE-METAL DEPOSITS, WEST SHASTA COPPER-ZINC DISTRICT Under the microscope the Birdseye porphyry is seen to have markedly zoned plagioclase phenocrysts; oscil- latory zoning is common. The plagioclase in the diorite porphyry is zoned from cores of Absgi‘ung to rims of Ab58An42; in the dacite porphyry the plagioclase is zoned from cores of AbBOAn40 to rims of AbMAn36 and is slightly altered to sericite, epidote, carbonate, and kaolinite. Alteration in places is more intense along certain zones in the plagioclase, and the central part of the crystals weathers more rapidly than the rims. Hornblende is the most common mafic phenocryst, al- though a little green biotite is present in some. Horn- blende occurs as green euhedral crystals that are strongly pleochroic. They are commonly 2—3 millimeters long and are much less conspicuous than the large white plagioclase phenocrysts. Hornblende is less commonly altered to green biotite or epidote. The groundmass consists predominantly of plagio- clase, quartz, hornblende, and green biotite and some orthoclase, carbonate, epidote, sphene, apatite, and mag- netite, and has a microgranitoid texture. Plagioclase in the groundmass usually is much more altered to sericite or kaolinite than the plagioclase phenocrysts. The Birdseye porphyry commonly is an unaltered, unsheared rock. Some parts of it, however, have been sheared by faulting and are hydrothermally altered. Plagioclase is partly altered to sericite, and small pyrite cubes may be disseminated through the altered rock as reported by Ferguson (1915, p. 245) at the Mad Mule mine. The Birdseye porphyry is probably Late Jurassic or Early Cretaceous in age. As far as is known the dikes are localized within about 20 miles of the contact of the Late Jurassic or Early Cretaceous granitoid rocks of the Klamath Mountains. They intrude the Mule Moun- tain stock of albite granite, which is Jurassic( ?) in age. They are in turn cut by lamprophyre dikes associated with the Shasta Bally batholith. FeZs-z'c (Z7766 make—Many small dikes and sills local- , ized in the Copley greenstone are within 3 miles of the eastern contact of the Shasta Bally batholith. They are mostly quartz latite porphyries, but range in com- position and texture from diorite porphyry to aplite. A cluster of these dikes or sills is localized in the south- ern part of the Igo quadrangle between Igo and Mule Mountain. They strike north to northwest and dip 45° to 75° NE. conformable with foliation in the Copley. The bodies are 10 to 50 feet thick and are as much as 3,000 feet long. These dikes apparently are not related to the many porphyritic rhyolite dikes in the same area, which are composed mainly of quartz and albite and are similar to the Balaklala rhyolite. The dikes are not differentiated on the surface map and are all shown as felsic dikes. The dikes are of probable Late Jurassic or Early Cretaceous age; they have the same minerals al- though in different proportions as the Shasta Bally batholith and are probably related to it. Andesite porphyry—Some dikes of andesite por- phyry, less than 50 feet thick and several hundred feet long, are present at Merry Mountain and Grizzly Gulch in the “Illiskytown quadrangle, at the Reid mine in the Old Diggings district in the Shasta Dam quadrangle, and near Brandy Creek in the Igo quadrangle. The dikes are all too small to be shown on the geologic map of the district. They are dark-greenish-gray porphy- ritic rocks containing phenocrysts of hornblende as much as 6 millimeters long and phenocrysts of plagio- clase as much as 2 millimeters long in a very fine grained groundmass. The dikes cut the Copley greenstone at Merry Mountain, in Grizzly Gulch, and at the Reid mine, and cut albite granite at Brandy Creek. The andesite porphyry contains 20 to 30 percent phenocrysts of hornblende and about 10 percent plagio- clase in a groundmass of plagioclase, hornblende, biotite, chlorite, epidote, magnetite, and apatite. Hornblende occurs as subhedral green crystals that have poor aline- ment. They have the following pleochroism: X=light yellowish green, Y=green, Z= dark green. Plagioclase consists of subhedral grains as much as 2 millimeters across. They are andesine and are commonly zoned from cores of Ab52An4g to rims of Ab57Aii43, and are twinning mainly by the Carlsbad law and somewhat by broad albite twinning. Most of the plagioclase is clear and unaltered although some cores are slightly cloudy due to alteration to zoisite, calcite, and kaolinite. Green biotite, a secondary mineral, ()Ccurs in veinlets that cut hornblende and plagioclase. Magnetite and to a lesser extent apatite are common accessory minerals. The andesite porphyry has been sheared in places, but not metamorphosed; the hornblende is only slightly al- tered to chlorite, and the plagioclase is somewhat altered to kaolinite and zoisite. The age of the dikes is not known with certainty. They cut the albite granite, which is J urassic( ?) in age. They are unmetamorphosed so are probably younger than the Late Jurassic or Early (‘retaceous orogeny. Lamprop[tyres—The dikes classified as lamprophyres are all extremely fine grained hard dark-gray to black rocks with a slight greenish cast and resemble basalt. They occur as dikes as much as 50 feet thick that intrude Copley greenstone, Balaklala rhyolite, and albite gran- ite. Some contain small megascopic phenocrysts of hornblende and less commonly plagioclase. Most of the lamprophyres occur in albite granite on the west side of the Mule Mountain stock in the vicinity of Mule Moun« tain, or they intrude the Copley near the albite granite INTRUSIVE contact. They cut dikes of Birdseye porphyry in the Copley. Although they appear to be unaltered rocks in the hand specimen, in thin section the . are seen to be altered. The lamprophyres contain plagioclase, biotite, epi- dote, chlorite, and carbonate, and some quartz or amphi— bole may be present. Plagioclase ranges in composition from andesine (Ab59A1141) in the least altered dikes to albite (AbglAng) in the most altered. The more calcic plagioclase occurs in laths from 0.2 to 1 millimeter long and has a pilotaxitic texture. Albite and Carlsbad twinning is common in the andesine, and broadly spaced albite twinning is present in albite. The plagioclase is more massive and has many inclusions of carbonate, epidote, and zoisite in the more altered lamprophyres. Biotite is the most common mafic mineral in the least altered lamprophyres and may constitute as much as 20 percent of the rock. It is rarely found as phenocrysts, but occurs as tiny flakes 0.1 to 0.2 millimeters long, and is pleochroic from X=very light green to Y=Z=dark- olive green. Biotite is in part altered to chlorite even in the least altered rocks, and is completely altered to chlorite in some. Actinolite is present in some of the lamprophyres. It has an acicular habit; needles as much as 0.5 millimeter long are in subparallel arrange- ment. The actinolite is pleochroic from light to dark green, and probably is of secondary origin. The least altered lamprophyres contain biotite and 5 to 10 percent epidote as phenocrysts as much as 1 milli- meter long. The amount of epidote and zoisite increases as the degree of alteration increases and the lime con- tent of the plagioclase decreases. The epidote appears to be pseudomorphous after amphibole. The most altered lamprophyres are composed only of albite, chlorite, carbonate, epidote, and secondary quartz. The original calcic plagioclase has altered to albite and contains inclusions of epidote, zoisite, and carbonate. The mafic minerals are altered to chlorite and epidote. Some pyrite occurs in a few dikes. The lamprophyres are probably Late Jurassic or Early Cretaceous in age and may be younger than the Shasta Bally batholith. They cut Birdseye porphyry, which is younger than the Nevadan orogeny and which is probably related to the Shasta Bally batholith. The lamprophyres cut albite granite, which is Jurassic( ?) in age. STRUCTURE GENERAL FEATURES The principal structural feature of the rocks of the lVest Shasta copper-zinc district is a broad central anticline and flanking synclines that trend a little east of north through the district (fig. 27). The anticline is gently arched along its axis and has a culmination ROCKS 53 EXPLANATION 7* 7:2?f24203gg’30” fi—z . t i', Shasta Salty batholith Bialilt quartz Violin :\/\r L./—. Mule Mountain stock mm gmm Syncline, snowing position 01 trough and direction 0! plunge Anuclme, shown: cresthne and direction at plunge Horizontal fold axis —?—? Probable extensmn o! lold ‘A‘ 40°37’30" 122°22’30“ Conant me unpublished min by V. F. Hollister 4955' 7* THU E NORTH .9 S O z 9 «‘7 5 a 5 Miles Geology by A. R. Kinkel, Jr. 492329373 w. E. Hall and J. P. Alha- FIGURE 27.—Map of West Shasta copper-zinc district showing relation- ship of main folds to the mineral belt and main intrusive rocks. over the northern part of the mining district. It plunges north at. a low angle near the north edge of the mapped area, and plunges slightly to the south in the central part of the district; the southern part of the folded structure is interrupted by the Mule Moun- tain stock of albite granite. The synclines lie east and west of the central part of the mining district. The trough of the eastern syncline is horizontal; the western syncline plunges north at the north edge of the mapped area, but its southward extension (and a parallel syn- cline) is cut out and distorted by the Mule Mountain stock and Shasta Bally batholith. The trough of the eastern syncline is marked by the erosion remnants of shale of the Kennett formation at an altitude of about 1,500 feet along the east side of the Shasta Dam quadrangle north of Central Valley. The crest of the central anticline west of this syncline trends 54 GEOLOGY AND BASE—METAL DEPOSITS, WEST SHASTA COPPER-ZINC DISTRICT N. 20° E. across Mammoth Butte and Iron Mountain, and the horizon of the base of the Kennett in the eastern syncline is estimated to have been at an altitude of ab011tv5,000 feet at the crest of the central anticline. Westward from the crest to the trough of the western syncline along the head of “'hisky (‘reek the base of the Kennett drops to an altitude of 1,550 feet. Thus the crest of the central anticline at its highest point rises 3,500 feet above the troughs of the flanking syn— clines, although part of this difference in altitude is due to the thick section of Balaklala rhyolite in the central part of the area. Although the folding is on such a broad scale that the average dip of the flanks of the central anticlinorium is not more than 20°, dips on bedding in individual folds of the anticlinoriuni range from horizontal to 90°. The rocks are strongly folded in some areas ad- j acent to areas of moderately folded rocks; local crump- ling is particularly intense where there is a great difference in the competence of adjacent. rocks, as be- tween conglomerate and shale, 01' where thin—bedded tuff of the Copley greenstone is interlayered with mas- sive flows, if these beds are in zones of deformation. The irregularity in the amount and degree of folding is apparently due largely to the lenticularity of flows and small intrusive rocks and the consequent abrupt differences in competence. Although the small folds generally pa ‘allel the trend of the anticlinorium, local folds may be at variance with the regional pattern where regional stresses were transformed by a body of heterogeneous rock into many local stresses of varying intensity and direction. Strong foliation is present in many parts of the dis- trict, and is largely coincident with areas of folded rocks. IVhere the rocks are not folded, foliation is con- fined to local zones of shearing. Foliation ranges from schist and gneiss, through moderately folded rocks that contain fracture cleavage, to flat-lying volcanic and sedimentary rocks that show only minor interbed move- ment or bedding-plane cleavage. Bands of strongly foliated rocks a few tens of feet to several hundreds of feet in width Occur adjacent to rocks that have only weak fracture cleavage, and the alternation of strongly and weakly foliated rocks is one of the characteristic features of the district. The explanation for this lies in many local geologic features, including differences in competence and composition of adjacent beds, but- tressing effects, and the location of intrusive masses. In parts of the district, foliation is parallel to bed‘ (ling where this can be determined by interlayered shale or tuff; in other parts of the district it crosscuts the bedding. However, where foliation is most intense, even compositional differences are obscured, or meta- morphic differentiation has formed banded rocks that simulate bedded structures. In such strongly foliated rocks it is rarely possible to determine the relationship between foliation and bedding. The distribution of strongly foliated rocks is related in part to the location of large intrusive masses, but some of it shows no apparent relationship to these rocks. A steep foliation, that has some regularity, is poorly defined throughout much of the district. F oliation is warped, folded, and crumpled in many limited areas (pls. 1 and 3). It is impossible to explain the dif— ferences in the amount of folding, crumpling, and foliation entirely by regional compressive stresses that acted on heterogeneous rocks, even if buttressing is con- sidered to be effective locally. The changes in strike and dip of bedding and foliation, and local crumpled areas, suggest that the intrusions crumpled the rocks locally during their emplacement. The albite granite of the Mule Mountain stock was intruded into rocks that were already foliated, as it cuts across the foliation at some places and crumples the preexisting foliation at others. The younger biotite-quartz diorite of the Shasta Bally batholith crumpled the rocks locally, but formed a zone of amphibolite, gneiss, and migmatite from the greenstone along its border; secondly planar structures in the recrystallized greenstone are mostly parallel to the contact, and possible preexisting struc- tures are destroyed in such areas. Faults are very common in the district, and where the rocks are well exposed on the surface or in underground workings a great many can be located. In most of the district, however, they are difficult to locate because of poor exposures along fault zones, and unless distinctive rocks are offset, faults undoubtedly would be missed. Many of the faults at the Iron Mountain mine, for in— stance, could not have been mapped at the surface if they had not first been located in underground workings and projected to the surface. There are two preferred directions of N. 20°—55° W. and N. GOO—80° E. for some of the main faults. Faults in the Bragdon formation in the “'hiskyt-own quad- rangle trend N. 20°—f5° “I. They are steep faults that have the southeast side offset downward relative to the southwest. Their extension from the sedimentary rocks into the greenstone can rarely be traced because the greenstone along the projection of these faults is sheared and contains few distinctive units. The large fault that extends N. 55° \V. across the Igo quadrangle is poorly exposed along most of its length and in the western part of the quadrangle is about parallel to foliation. Some of the faults that trend N. 200—450 \V. are occupied by quartz veins. These veins are often continuous for sev— eral hundreds of feet to a thousand feet or more in con- STRUCTURE 55 trast to unoriented veins, which tend to be less extensive or regular. (Quartz veins that strike N. 200—450 \V. are most prevalent in the Shasta Dam and Behemotosh Mountain quadrangles. Steeply dipping faults that trend N. (SW—80O E. are exposed in many mines of the district, and as described under “Ore deposits,” are economically important as they apparently control ore deposition. These faults are mineralized at many places and may have acted as channels for ore-bearing solutions. Faults that strike N. GOO—80° E. occur in the Iron Mountain, Stowell, Balaklala, Mammoth, and Golinsky mines. On all of these faults, the north side is downthrown relative to the south, and the offset ranges from 200 to 700 feet where the amount is known. STRUCTURE OF INDIVIDUAL AREAS THE MINERAL BELT The mineral belt in the \Vest Shasta copper—zinc dis- trict includes the areas of base-metal sulfide mineral deposits, which extend from about 2 miles north of the Mammoth mine to about 1 mile south of the Iron Moun- tain mine (fig. 27). It has no reference to the distribu- tion of gold deposits, which extend over an area much larger than the base—metal deposits. The mineral belt is bounded 011 the east by the main body of Copley green- stone, where the Balaklala rhyolite has been removed by erosion, and onthe west by the overlying shale of the Bragdon formation. It may extend farther west than shown on figure 27, but no information is available on such an extension because of the thick cover of younger shale beds. Most bedding and volcanic-flow contacts in the rocks of the mineral belt have gentle dips, generally less than 30°, and although the rocks are warped into many broad folds and domical structures, they are not strongly folded except in local areas. The sedimentary rocks of the Bragdon formation, which are continuous around the nose of the central anticline north of the Mammoth mine, indicate a plunge of probably less than 10° where the Balaklala rhyolite dips under the Brag- don. The plunge of the Balaklala rhyolite north of the Mammoth mine may be even less than that in the Bragdon north of the northwestward—trending fault in Backbone Creek; the fault cuts across the nose of the anticline, and the rocks south of the fault appear to be plunging less steeply than those north of the fault. The Balaklala and Copley formations are not exposed again along the strike of the anticline for about 8 miles to the north, where a window of these rocks is exp0sed on Dog Creek. Irregular gentle warping, shown by bedding in tuff in the Balaklala rhyolite, or by the contact between the upper and middle units of the Balaklala, is the char- acteristic structure along the crest of the central anti~ cline from the Sutro, Golinsky, and Mammoth mines in the north to the Stowell mine in the south. Basin- shaped warps are present at the Balaklala and the Shasta King mines, but the Mammoth and probably the Keystone mines are on arched or domical structures. Other basin-shaped structures, in addition to warps due to folding, occur where thick lenticular deposits, either pyroclastic layers or flows, were deposited in a primary sedimentary basin. Between the Mammoth and the Sutro mines this type of basin is filled with coarse pyro- clastic rocks and tuff. South of the Stowell mine the broad central anticline is more closely compressed and passes into a series of folds which extend through the Iron Mountain mine area. Here the flanks of the folds dip as steeply as GOO—70°. These folds, in turn, are cut off by the Mule Mountain stock of albite granite. ‘ On the east flank of the central anticline the beds dip gently east from-the Golinsky mine, and the Balaklala rhyolite is overlain by the Kennett formation. How- ever, south of this area and east of the Spread Eagle and Sugarloaf prospects‘and the Iron Mountain mine, the rocks are strongly folded into many smaller, less regular anticlines and synclines. On the west flank of the central anticline, the dips are regular and gentle, and the Balaklala rocks are overlain by the Kennett and the Bragdon formations. Here again, as the south- ern part of the anticline is approached, the broad struc- ture disappears into smaller, less regular folds. Many of the rocks in the mineral belt are weakly foliated or sheeted, but some are strongly foliated in local bands. Difference in competence and the lenticu- larity of most of the flows and pyroclastic rocks have greatly affected the localization and distribution of the weaker types of foliation and sheeting; bands of strong foliation cut through all rock types. Two types of folia- tion are present: one is a steeply dipping planar struc- ture that ranges from rather widely spaced jointing or closely spaced sheeting to fracture cleavage that has films of alined secondary minerals along closely spaced planes. The rock between cleavage planes in this type of planar structure is unaffected; flow cleavage is com— mon locally along zones of intense movement, but these zones are rare in the mineral belt. The second type of foliation common in the mineral belt is bedding-plane foliation formed by flexural—slip during folding. Even though most of the folding is gentle, bedding-plane foliation is locally well developed, probably because of the great difference in competence in the layered rocks. This type of foliation forms in zones that contain tuft beds and volcanic breccia that were 56 less competent than the flows, and adjustment between flows was taken up along the flow contacts rather than within the flows. Planar structures are not evenly distributed in the rocks. A thick flow, such as the coarse-phenocryst rhyolite, acts as a competent body and is foliated much less than the underlying series of lenticular flows and pyroclastic rocks. Steep foliation is more common in some areas on the axes than on the flanks of folds. Thus, under some conditions, a body of foliated rock has a linear element, that is, certain flows are foliated, more strongly along fold axes, and form an elongate body that is limited above and below by less foliated flows and which plunges with the fold axes. KENNETT AND BRAGDON FORMATIONS The Kennett and Bragdon sedimentary rocks are characterized by alternate competent and incompetent layers, which almost entirely controlled their reaction to stresses. The formations are composed principally of thin bedded shale and siltstone, which acted as in- competent units, but they also contain beds of chert and siliceous shale, limestone, and many beds of sandstone and conglomerate, which formed competent layers. The common form of disturbance is a broad folding of all the sedimentary rocks, accompanied at many localities by mashing and crumpling and much interbed slippage in incompetent layers, particularly where they are in- terbedded with competent layers. The broad folds can be traced by following the beds of conglomerate and sandstone, which do not reflect the crumpling and mash— ing of the shale; attitudes of shale beds between con- glome ‘ate or sandstone are unreliable indicators of structure at most localities because of local crumpling. Fold axes in shale between competent layers commonly are unoriented because the competent unit is broken into blocks that have been mashed into the adjoining incom— petent layers. Boudinage structure occurs along some conglomerate and sandstone beds, particularly where these are overlain and underlain by a considerable thick- ness of shale. Isoclinal folds are rare, but close folds are common, having amplitudes of a few feet to several hundred feet and dips on the flanks that. range from 30° to 60°. In common with the other parts of the district, the distribution of folds and crumples in the sedimentary rock is erratic. Rocks that are strongly folded and cut by many small faults are overlain and underlain by rocks that have regular bedding for a considerable distance, and the areas of strong disturbance have little continuity, that is, they can seldom be followed in one direction for any great distance. this is due to the difference in reaction to stress be- To some extent GEOLOGY AND BASE-METAL DEPOSITS, WEST SHASTA COPPER-ZINC DISTRICT tween a thick sequence of shale that contains no conglomerate, as in the shale above and below the main conglomerate zone, and a sequence in which shale and conglomerate alternate. However, part of the main conglomerate zone is only weakly folded, and the in- terbedded shale beds in these places show only minor interbed slippage; localized stresses apparently account for the strong disturbance of the sedimentary rocks in some areas. The Kennett formation, throughout much of the dis- trict, contains a thin-bedded black siliceous shale inter- layered with chert at the base of the formation. This lower part of the Kennett is intensely crumpled in many exposures. It rests on rhyolite or greenstone, both of which were apparently more competent rocks than the siliceous shale, and interbed movement that occurred between the Kennett and the underlying formations was taken up largely in the siliceous shale. Considerable movement must have taken place to account for the crumpling in the basal Kennett, but the contact between the thick beds of underlying lava and overlying shale would be a plane of strong disturbance during folding. Although cleavage is parallel to bedding in most of the shale of the Bragdon formation, locally a steep slaty cleavage is formed where the shale has been closely folded. This steep slaty cleavage may strike parallel to bedding but have a steeper dip, or it may be trans- verse cleavage at any angle to the bedding. Pencil structure, formed by the intersection of slaty cleavage and bedding, is common in the crests of these minor folds; the slaty cleavage and pencil structures locally obscure the bedding. The steep slaty cleavage and the pencil structure rarely can be followed along strike in the field because they are commonly prominent only in one series of beds and extend along the axes of plunging folds. The structures may be entirely absent in overlying or underlying beds of different. competence, or only fracture cleavage or bedding-plane foliation may be present in these beds. Flexural-slip folding, in which interbed movement forms bedding-plane cleavage (that is sometimes cut by poorly defined frac- ture cleavage) in the incompetent beds and strong steep joints in the competent beds, can be seen at many places. Figure 28 is a sketch of a road cut in shale and sand- stone of the Bragdon that illust 'ates this type of folding. The pebbles in many of the conglomerate beds are elongate and are alined parallel to the bedding. This is apparently a primary feature, as elongate pebbles occur in areas where there is no other evidence of dis- turbance of the sediments. However, at a few localities where folding has been intense, the pebbles are stretched, and their long dimension is not parallel to STRUCTURE 57 x ",4 l l H, W 7 Horizontal and vertical scale \ FIGURE 28.~Cross section of shale and sandstone of the Bragdon forma- tion in road. cut. Joints formed in competent standstone beds at right angles to bedding. Bedding-plane foliation and weak fracture cleavage formed in shale beds. the bedding. Rock flowage has occurred at these locali— ties, but without the formation of foliation in the conglomerate; no foliated conglomerates occur in the district. The Kennett and Bragdon formations are cut by steep normal and flat thrust faults. The normal faults trend N. 20°—40° IV. and N. 60°—80° E., which is the same direction as those in the Copley and Balaklala rocks. The northeast and northwest sides are down— thrown, as shown by the repetition of the main con— glomerate beds. Fault zones are rarely exposed because the mashed shale beds do not crop out, but can be traced by a combination of exposures in canyons, slickensided float, abrupt termination of conglomerate beds, and the pattern on aerial photographs. At some places the faults cause a mashing of the shale for several hundred feet ; at others the disturbance of the shale is very slight. Where the faults are exposed, as in deep canyons, the brecciated zone ranges from a few feet to 50 feet in width and consists of jet black shiny slickensided len- ticles of foliated shale. Very little clay gouge is pres- ent. The faults having the widest zones of mashing are those that form the contact between the sediments and the rhyolite in Backbone Creek and between the green- stone and the sedimentary rocks just east of Shirttail Peak. Low-angle thrust faults are common in some localities in the sediments. They are prominent along Backbone Creek and in the area east and south of Shirttail Peak. The clip of these faults ranges from nearly horizontal to 40°; they tend to cross bedding at a low angle for a few hundred feet, then turn parallel to the bedding and disappear in bedding-plane movement. Figure 29 shows a thrust fault near the junction of Backbone and Fall Creeks. The faults that cut the sediments are not mineralized as a rule, although a few are accompanied by quartz veins that contain sulfides, as at the Gladstone and « fiLevej of Backbone greg}; 25 O iii.1 l Horizontal and vertical sca|e 50 Feet l FIGURE 29.—Sma11 thrust fault in shale of the Bragdon formation in Backbone Creek. American gold mines, or are occupied by dikes of Birds- eye porphyry (dacite porphyry) that is hydrothermally altered. COPLEY GREENSTONE IN THE IGO AND WHJISKYTOWN QUADRANGLES The structural features in the Copley greenstone in the western part of the district were formed in part by regional stresses and in part by the intrusion of the two large plutons in the Igo quadrangle. Deformation in the greenstone consists largely of broad open folds away from the intrusions, but adjacent to them the greenstone beds are altered to amphibolite schist, gneiss, and mig- matite. Local zones of shearing, ranging from tight fault zones to wide bands of chlorite schist, are common throughout the greenstone. ‘ Most of the Copley greenstone in the VVhiskytown quadrangle north of Clear Creek and west of IVhisky Gulch contains gentle open folds, and weak foliation. Individual flows, such as the layer of pillow lava and pyroclastic rocks east of Grizzly Gulch, can be traced continuously for several thousand feet, and the flows have gentle dips. The rocks are not sheared except where fault zones cut through the gently dipping lavas; the flow contacts, and the pyroclastic and tuff beds, pre- serve their original characteristics. South and south- east of this area the greenstone becomes more deformed as the intrusive masses are approached, until near the intrusion the greenstone has been altered and strongly deformed. In the eastern part of the \Vhiskytown quadrangle a foliated structure was present in the Copley greenstone before the intrusion of the Mule Mountain stock. In this area unfoliated albite granite cuts across foliated greenstOne and in places crumples the foliation. The small plug of albite granite in the northeastern part 58 GEOLOGY AND BASE-METAL DEPOSITS, WEST SHASTA COPPER—ZINC DISTRICT of the Igo quadrangle also appears to have crumpled the foliation, as if by a shoulderng action, along the north edge of the intrusion (pl. 3). The Shasta Bally batholith of biotite-quartz diorite formed migmatite, gneiss, and amphibolite schist from the greenstone for a considerable distance from its con— tact. F oliation in the Copley greenstone generally parallels the contact of the batholith, but it is not at all certain how much of this foliation was formed by the intrusion of the batholith. At some places gneissic structure probably follows a previous foliation in the greenstone (which may or may not be parallel to the bedding), and at other places it follows primary bed- ding structures. Primary structures in the Copley greenstone are largely destroyed by recrystallization in the gneissic zone, but a few beds of black shale occur in the recrystal- lized greenstone in Brandy and Boulder Creeks in the Igo quadrangle and the gneissic structure is parallel to the bedding at these points. Gneissic structure, marked by differing degrees of recrystallization, is also parallel to the bedding where the batholith intrudes shale of the Bragdon formation east of Buckhorn Suin— mit on U. S. Highway 299‘". However, along the edge of the batholith north of Andrews Creek, and at the Greenhorn mine west of the Igo quadrangle, the intrusive contact cuts across the gneissic banding that follows earlier foliation in the greenstone. Recrystal- lization tended to work out along primary structures in the wall rOcks and along the outer edge of the gneissic zone, where it has extended in long tongues into the greenstone along lines of earlier foliation. It is not pos— sible to determine at most places whether the earlier foliation is parallel to bedding or not. Recrystallization tended to follow and emphasize any structure that was in the wall rocks at the time of the intrusion of the batholith, but it is also possible that locally the paral- lelism between the planar structures in the intrusive mass and in the wall rocks was formed by frictional drag along the walls of the intrusion. The small plug of biotite-quartz diorite in Clear Creek in the southeastern part of the Igo quadrangle crumpled the foliation of the Copley greenstone along its north— ern border, but in places also cuts across the foliation. The screen. of greenstone between the Mule Mountain stock and the Shasta Bally batholith, being affected by both intrusions, contains no relict primary structures. This greenstone is a strongly foliated chlorite or amphibolite schist near the Mule Mountain stock and an amphibolite gneiss near the Shasta Bally batholith. At most places the foliation in the screen is parallel to the contacts of the intrusions, but in a few places is dis— cordant to them at the immediate contact. SHASTA BALLY Only a small part of the Shasta Bally batholith is included in the Igo quadrangle, but reconnaissance across most of the batholith has shown that the struc- tures in the mapped area are typical. Reconnaissance trips were made across the batholith at Bully Choop Mountain west of the thiskytown quadrangle, and across parts of the Trinity Alps to the northwest. The batholith is at least 20 miles long in a northwesterly direction, and as much as 9 miles wide. In contrast to the Mule Mountain stock, the Shasta Bally batholith contains primary planar and linear structures. Pri- mary foliation is common along much of its contact, but linear structures are limited to alined hornblende prisms on the southern part of the contact in the Igo quad- rangle, where more hornblende is present than elsewhere in the intrusion. Foliation in the intrusive mass is invariably parallel to the contact. It is a primary flow structure that shows a bandng of oriented light and dark minerals. Along the contact of the intrusion, there is no difficulty in the field in distinguishing between rock that was molten and is flow banded, and altered greenstone in which much granitic material was added to the greenstone BATHOLITH .(migmatite zones), although mineralogically the two may be similar. Primary structures are more common near the edge of the intrusion than in the interior, but they are formed in the interior in the parts that are topographically high, and thus near the roof of the intrusion. Flow banding is regular and uniform at most localities (pl. 2), and dips steeply to the east on the eastern side of the intrusion, parallel to the contact. In the central part of the batholith, in the headwaters of Eagle Creek and north of Bully Choop Mountain to the west, the dip of the flow banding ranges from 10° to horizontal. “'est of Bully Choop Mountain along the west edge of the intrusion, only a small amount of flow banding was observed, but all of it dips steeply to the west. It thus appears that the Shasta Bally batho- lith forms a schlieren arch, and that the top lies only a short distance above the present erosion surface. The exposures of many large and small bodies of the same rock for many miles to the northwest along the strike of the Shasta Bally batholith, and the wide metamor- phic halo that parallels this zone suggest that the in— trusions are only the top of a much larger underlying mass. Alined hornblende laths give a linear character to the rock at a few places. The distribution of the laths is so limited and erratic, however, that no general aline— ment can be traced except in the area north of the town of Igo. In this area the alinement of hornblende laths is roughly S. 30° 14).; the plunge is 45° SE. ‘ places, but these are fault zones. . brecciation occur locally in which angular to rounded . blocks of albite granite are embedded in a matrix of ‘ the same material. ‘ cias. ‘ mashed to some extent, and cataclastic structures are STRUCTURE ‘ J ointing is common in some parts of the intrusion, {but absent in others. Too little of the batholith is exposed in the mapped area to justify a detailed study ‘of the jointing, but no marked pattern was recognized. ‘A few aplite dikes cut the biotite-quartz diorite, but they do not appear to follow a regional joint pattern. Faults are not common in the Shasta Bally batholith ; in the area included in the Igo quadrangle. A few .faults can be traced for several hundreds of feet in the .Silver Falls mine northwest of Igo and at other pros- ipects in that area, but faults generally are rare in all ‘parts of the batholith, either in the mapped area or to ‘the west and north. MULE MOUNTAIN STOCK The massive granitoid Mule Mountain stock contains :no planar structures that are related to its intrusion. .The stock is slightly foliated, but it transgresses the . foliation of the enclosing greenstone at many places. . At a few localities foliation extends from the wall rocks . into the intrusion and decreases in intensity. It seems ‘ probable that late orogenic stresses followed lines of ‘ earler foliation, and extended it from the wall rocks 3 into the intrusive mass. Local schistose bands range in ‘ width from a few feet to several tens of feet at a few Some areas of auto- They are probably intrusive brec- Much of the rock in the outcrop is shattered and ‘ commonly seen in thin sections. Xenoliths of the intruded rocks are common in the- Mule Mountain stock, particularly along its northeast- . ern border. These are of two types: elongate schlieren of greenstone that range from large bodies to mere wisps of mafic minerals, and angular to rounded fragments of ‘ greenstone formed by brecciation and penetration of ‘ the wall rocks by the intrusion. These contact breccias are described under albite granite. Their occurrence well into the intrusion near its northeast border (pl. 1), and large masses of greenstone in the intrusive body 1 south of the South Fork Mountain in the Whiskytown quadrangle, suggest that some of this material occurs as roof pendants, and that in these areas the top of the stock was not far above the present erosion surface. The small plug of albite granite in the northeastern corner of the Igo quadrangle contains a planar struc- ture that is most strongly developed in the southwestern half of the plug, where the albite granite is a leucocratic gneiss. The gneissic structure is parallel to and con- tinuous with the gneissic structure in the surrounding greenstone. It was formed by recrystallization under 379725—56—5 59 stress due to the intrusion of the Shasta Bally batholith, and contains material added from the batholith. LOCATION OF VOLCANIC CENTERS Two centers of eruption of the rhyolitic rocks are known, and several other localities are regarded as probable centers. None have been located that might have been the source of the mafic rocks of the Copley greenstone. The best exposure of an eruptive center, which was the source of the cumulo dome of coarse-phenocryst rhyolite and its associated pyroclastic rocks, is in the vicinity of the Uncle Sam gold mine. Erosion of part of this center below the level of its surface flows has ex- posed a broad volcanic neck that is complex in structure. The wall rocks of this volcanic neck are principally non- porphyritic rhyolite, whereas the central part exposed in the long adit of the Uncle Sam mine is composed mainly of coarse-phenocryst rhyolite, but bodies of non- porphyritic rhyolite were also found. Most of the coarse—phenocryst rhyolite in the main vent is identical in appearance with the same rock that occurs as a cumulo dome, except that it contains chlorite and has been silicified. In the immediate vicinity of the main vent, coarse-phenocryst rhyolite occurs as vertical dikes, lens-shaped masses, and stockworks in the shat- tered walls. Many xenoliths of nonporphyritic rhyo— lite are present, but some of the bodies of nonpor- phyritic rhyolite probably represent wall rock that is in place, the coarse-phenocryst rhyolite having been intruded on both sides of such bodies. The vent must be several thousand feet across, although some of this area is occupied by shattered wall rock and screens of wall rock and flows cover the northern half of the vent. Excellent exposures of the south side indicate that the coarse-phenocryst rhyolite forced its way into the rocks in several large and small coalescing strands, rather than as a single body. Much of the wall rock was shattered, probably by explosive activity at the time of the earliest extrusion of the coarse-phenocryst pyro- clastic material that underlies the main dome of coarse- phenocryst rhyolite. A second vent, the outline of which is below the level of Shasta Lake except on the south side, is exposed in the northeast corner of the Shasta Dam quadrangle. A jumble of several types of rhyolitic material was thrown for several thousand feet from the second vent. To the south the fragments decrease in size and quantity, until about 1 mile distant only a few rhyolitic fragments can be found in a matrix of greenstone tuff. Distribution of rhyolitic flows and pyroclastic beds indicate the presence of other vents in the district. Rhyolitic flows probably did not extend far from their 60 GEOLOGY AND BASE-METAL DEPOSITS, source, nor did relatively thin beds and stubby lenses of coarse pyroclastic material originate far from their present position. A vent probably existed near the southeast corner of the Igo quadrangle because Of the concentration of thin rhyolitic sills, flows, and minor pyroclastic beds in that area. A group of radially ar- ranged rhyolitic dikes on Copley Mountain suggests that this may be a deeply eroded vent. The group of rhyolitic flows and pyroclastic beds east of the Sacra- mento River in the south central part of the Shasta Dam quadrangle suggest a vent in that vicinity, because many of the pyroclastic beds contain coarse fragments and many of the flows are thin. It seems probable, for the same reasons, that vents were present near Merry Moun- tain, near the small plug of albite granite in the north- west corner of the Igo quadrangle, and near W’hisky— town. In addition to a main vent at the Uncle Sam mine, there were probably several along what is now the min— eral, belt. The interlayering of many lenticular flows and pyroclastic beds, and the impossibility of deter- mining more than a generalized stratigraphic sequence for the different types of flows makes it probable that the volcanic material came from many vents. In addi- tion, some of the bodies of pyroclastic material have rounded outlines and may represent breccia pipes or breccia-clogged volcanic necks. PHYSIOGRAPHIC FEATURES The lVest Shasta district is in the southeastern part of the Klamath Mountains in the Pacific Border physio- graphic province as described by Fenneman (1931). Two landscape forms stand out prominently in the dis— trict. One is the deeply dissected mountains and foot- hills that cover most of the district; the other is the broad, flat terrace that lies about 200 feet above the Sacramento River. Traces of early topographic cycles are found in the higher mountainous area, but few traces of them remain in the foothills. A surface with low or moderate relief existed in Plio- cene or Miocene time in most of the area now occupied by the Klamath Mountains (Diller, 1894, p. 404, 1902, p. 9; Fenneman, 1931, p. 4654471 ; Hershey, 1904, p. 423— 4.74; Lawson, 1894, p. 241—271) it is here referred to as the old Klamath surface. ITplift of the area into a high plateau in Pliocene or early Quaternary time renewed the cutting power of the streams, which deeply dissected the old surface. Viewed from the present 'al- leys, no indication of the old surface can be seen in the lVest Shasta district, but from points of vantage, such as Shirttail Peak or Mad Mule Mountain in the VVhisky— town quadrangle, an old surface can be inferred from WEST SHASTA COPPER-ZINC DISTRICT the general accordance in altitude of ridges and peaks. As Cotton (1949, p. 138) points out: Accordance of summit levels does not indicate with certainty the destruction of an uplift plane, but the former existence of such a surface may usually be inferred with a fair degree of confidence where accordance is well marked with a restored surface either plane or domed. Figure 30, a view from Shasta Dam of the mountains in the lVest Shasta district, shows the general accord— ance in the altitude of the peaks. The old Klamath surface was probably a surface of moderate relief, as the accordance of the altitudes of lidges and peaks, though reasonably close, is not close enough, to imply a level plateau before it was dissected. This surface sloped easterly. The highest part of the peneplain over the Salmon, Yollo Bally, and Trinity Mountains west of the Sacramento River is at an alti— tude ranging from 6,000 to 7,000 feet. In the Shasta mineral belt to the east of this mountainous areas, there is a good accordance of many ridges and peaks at an altitude of about 4,000 feet, although a few peaks are above this general level. The relatively level ridge that extends north from Iron Mountain, and many other ridges north and northwest of Iron Mountain have an altitude of about 4,000 feet, but a few peaks lie above this level, for example those east of Shirttail Peak, which have altitudes between 4,000 and 4,600 feet. These probably are monadnocks on the old surface, rather than a higher surface, as there is little summit accordance above 4,000 feet. It is possible that part of the old Klamath surface may be an exhumed surface of low relief that was pres- ent at the base of the Cretaceous rocks. These are con- siderably softer than the pre-Cretaceous rocks, and scattered outcrops north and west of the West Shasta district suggest that Cretaceous rocks may have oc— curred at about the level of the old Klamath surface in part of this area. Isolated rounded stream cobbles, commonly of rock types foreign to the lVest Shasta dis— trict, are found on many of the highest ridges and peaks; they may be residual from gravel of Cretaceous age. The levels of a few terraces below 4,000 feet are discernible. They are remnants of erosion surfaces of low relief located on the sides of canyons and may represent a system of dissected terraces. At a few localities these terraces contain a thin veneer of gravel, but generally the surface is covered, and its shape is modified by slope wash. One of these terrace remnants occurs between the altitudes of 3,450 and 3,650 feet in the West Shasta district. The difference in altitude between the terrace above the Keystone mine at 3,450 feet, that northwest of Sugarloaf Mountain, indicated PHYSIOG RAPHIC FEATURE S 6]. Hills are underlain mostly by Balaklala rliyolite. FIGURE 30.—View looking westward from Shasta Dani showing general accordance of summit elevations and entrenched valleys on left. by the ridge at 3,550 feet, and the ridge northwest of South Fork Mountain at about 3,100 feet may be due to valley floors on separate drainage systems, or to dif- ferent distances from the heady 'aters in the same d ~ain- age basin. An old valley floor remains at a few places that probably represents a terrace at an altitude of about 2,250—2,300 feet. The old valley floor of the Sacramento River, in which the present river is entrenched, is a broad level valley several hundred feet above the present river bed in the Vicinity of Bedding, but it grades into the foot- hills a short distance to the north. The broad floor of the old 'alley, at an altitude of about 725 feet, slopes gently to the southeast and is a striking feature of the landscape. The area near the foothills is a terrace cut into the bedrock by the Sacramento River and is bor- dered by pediments and by fans formed by tributaries. A few miles downstream from the foothills the bedrock is veneered with gravels 0f the Red Bluff formation, which thickens toward the main part of the valley. The Recent streams are so deeply entrenched into the old valley floor where it was composed of gravel of the Red Bluff formation that in some places only remnants of the floor remain. Traces of older landscapes generally are preserved only on the higher slopes in the mountainous area, but locally the interfluves between the deeply incised present tributaries are smooth. Headward erosion of tribu- taries and the destruction of interfluves by slumping is rejuvenating the topography of much of the district. Also, some of the ridges and peaks of moderate altitude below the old Klainath surface have subdued and rounded forms and a gentle summit convexity, indi- cating a mature topography. Traces of this mature topography are found mainly above 2,500 feet, and it appears probable that in addition to the Klamath sur- face, a later mature surface formed in parts of the dis- trict when the main streams were below an altitude of 2,000 to 2,500 feet (allowing for uplift since that time). In some parts of the district, lower slopes, generally less than 2,000—2,500 feet in altitude, have accumulated rock debris and soil as much as 100 feet thick. The un— stratified deposit is composed of rock fragments as much as 1 foot in diameter in a matrix of red soil. This unusually thick mantle was formed by solifluction and rainwash from the higher slopes, many of which now are bare. The eroded material aggraded lower slopes, and the increased runoff on the denuded upper slopes accelerated the process. Steep—walled gullies, as much as 75 feet deep along the road to the Mammoth mine, are now working headward in the mantle of wash and are restoring graded slopes in continuity with the upper slopes. 62 Landslides are a common feature of the district be- cause the walls of gullies and the canyon slopes along most of the streams are oversteepened. They range from small mudflows and slump along gullies to large slides and earth flows that are several thousand feet across. Slumping occurs along oversteepened drainage areas where the soil and subsoil cover is deep or where the rocks are soft and deeply weathered. Slump and solifluction supply much debris to the streams during the rainy season; larger slumped areas cause temporary dams across the streams, and the breakdown of the loose damming material causes disastrous floods in some canyons. The geologic map (pl. 1) shows the larger landslides. They are generally shallow, and sliding apparently has taken place on several spoon-shaped surfaces in the upper part of the slide and as a mudflow in the lower part. There are gradations between extensive solifluc— tion, debris slides, and true slides that are bounded by sharply defined planes of slippage. The tops of the slides do not have a backward slope, as erosion along scarps and aggrading of the flattened top forms a flat area that slopes with the topography but is flatter than the hill slope. Gullies cut in the older slides show that the jumbled material is unstratified, or poorly stratified. The thickness of some of the larger slides is known either from drill holes, as at Iron Mountain, or from deep gullies that have exposed the bottom of the slide. They are unusually shallow; it is doubtful if the thickness of the larger slides exceeds 200 to 300 feet. The recognition of landslides is of importance in the district because much ill—advised prospecting has been done in material that is not in place, and because the topographic flats at the top of landslides that may still be active provide what appear to be attractive plant sites in the generally steep topography. Not all flat or gently sloping areas are due to landslides; the recognié tion of landslides may be difficult unless recent gullies expose the jumbled material that composes the slide. Flat or gently sloping areas that suggest landslide tops occur at many places, but some topographic flats are remnants of older landscapes, or are due to differential erosion (fig. 31). The canyon side of an old terrace level, where it has been oversteepened by Recent stream erosion, is a favorite place for a landslide. The present dendritic drainage pattern appears to be superposed from the old Klamath surface onto the older rocks, and except in local areas and where streams fol- low well developed faulting or sheeting in the older rocks, the streams are not controlled by structures in the underlying rocks (fig. 32). However, some of the streams have become adjusted to the underlying rock structure as the more resistant rhyolite and the plutons GEOLOGY AND BASE-METAL DEPOSITS, WEST SHASTA COPPER-ZINC DISTRICT Oversteepened by the formation of a cut terrace I l Aggraded material _ _ _ a Terrace level Oversteepened by a landslide scarp Aggraded material ._ _ _Terrace level B Oversteepened by the formation of a cut terrace Aggraded material _ vTerrace level ‘ K. \" v Slumping along the front of a 4% cut terrace. Local flats may be developed at several elevations Resistant rock V . D STRUCTURAL TERRACE FORMED BY DIFFERENTIAL EROSION FIGURE 31.—F0rmation of topographic flats. Four proc— esses, all of which are represented in the West Shasta copper-zinc district. underlie much of the higher topography and the less resistant greenstone occurs mainly in the lower areas. Most of the streams are cutting narrow V-shaped can- yons at the present time, but where bodies of harder rocks have impeded downcutting, a few streams have reaches with a low gradient and locally some gravel fill. In a region where there are a few large permanent PHYSIOGRAPHIC FEATURES 122°22'30” 40°52’3V’ 122°30’ TRUE NORTH s 7 i i @077 ~ ~>~—440337so" l 1: 122°22'30" 3 , a l l / Hue, ‘ (is l % , ‘ Raiding l l \ M i 1 0 {Miles 1 \y ,,4\ ~ A , ir~74f40“30' 122°30’ FIGURE 32.—~Drainage pattern, West Shasta copper-zinc district. streams but many small streams that run only in the rainy season, the difference in topographic expression between the two types is noticeable. The large streams at some places cut more rapidly than the tributaries, and the tributaries have discordant junctions along many of the permanent streams. Hanging junctions of this type are common along Clear Creek below thisky- town and along some sections of Backbone and \Vhisky Creeks. Main streams such as Clear Creek in the Igo quadrangle occupy narrow, youthful valleys that are entrenched in broad older valleys. Small patches of gravel of the Red Bluff formation occur on the mature slopes of the broad old valley of Clear Creek. The scattered remnants of this soft and easily eroded formation suggest that the broad valley may be an exhumed surface formed during a much earlier cycle. The grade of Clear Creek and slope of 63 the canyon walls are complex where the stream crosses rocks that differ in their resistance to erosion; sections of the stream have a low gradient, and at a few places the stream is braided and is aggrading, but at other places rapid downcutting is taking place. The intermittent streams form narrow canyons that have a steep gradient and oversteepened walls. Minor deposits of gravel, which were important sources of placer gold, have collected where the gradient has not been sufficient to transport large boulders. In these areas a small reach of the stream has been aggraded, but most of the intermittent streams during the rainy sea- son consist of rapids and waterfalls in narrow, V-shaped, brush-clogged valleys. Gully erosion is widespread; a large part of the gullying was initiated or greatly ac- celerated by the removal of the timber for mining pur- poses and the destruction of timber, brush, and grass cover by fumes from heap roasting and smelters during the early mining operations. The Sacramento River near Redding is entrenched as much as 200 feet below the level of the broad valley, at an altitude of about 725 feet, that was formed at an earlier stage. North of Bedding the broad valley disap- pears where the Sacramento River enters the mountain- ous area, and in most of the West Shasta district, and to the north, the river occupies a deep narrow canyon. The canyon at Shasta Dam afforded a good location for a dam because above this point the present river valley widened at many places and contained bottom land along reaches with a low gradient that allowed a large area for water storage. GEOLOGIC HISTORY The geologic record in the ”West Shasta district from Middle Devonian time through part of the Mississip- pian appears to be one of continuous sedimentation and volcanic activity. The deposition of a great thickness of marine sediments (Hinds, 1933, p. 81—86), exposed in Trinity County and probably present under the rocks exposed in the West Shasta district, was interrupted in the Middle Devonian by the outpouring of mafic and siliceous lava on the ocean floor. Sedimentation was resumed in the Middle or Late Devonian, and the sedi- mentary sequence continued into the Mississippian. In the “rest Shasta district, the upper part of the Missis- sippian is eroded, and only the younger rocks of Cre- taceous and Recent age crop out. In nearby areas, however, the record of post-Mississippian sedimenta- tion and volcanic activity is more complete. Rocks of Pennsylvanian and early Permian age are absent, but late Permian, Triassic, and Lower Jurassic sedimen— tary and volcanic rocks occur immediately to the east of the lVest Shasta district (Diller, 1906, p. 10). 64 GEOLOGY AND BASE-METAL DEPOSITS, WEST SHASTA COPPER-ZINC DISTRICT Orogeny occurred in the Late Jurassic or Early Cre- taceous, accompanied by the intrusions of batholiths; a major unconformity separates the rocks of Paleozoic : age from those of Late Cretaceous age and a major non- conformity separates the Shasta Bally batholith of Late Jurassic 0r Early Cretaceous age from the over— lying Lower Cretaceous Paskenta and Horsetown formations of Hinds (1933, p. 113) that crop out south- west of the \Vest Shasta district. Another erosional gap in the sedimentary record occurs between the Upper Cretaceous and the Eocene rocks. Sedimentation in the Eocene and Pliocene was probably partly in oceanic bays and partly in fresh water in the southern part of the area, but volcanic highlands were formed in the northern part. Pliocene rocks in the Redding area con- sist largely of subaerial lava flows and mudflows (Hinds, 1933, p. 116). The oldest formation in the )Vest Shasta district is the Copley greenstone of probable Middle Devonian age. The Copley is probably underlain by rocks that crop out west of the Shasta Bally batholith; these are the Chanchelulla formation of Hinds (1932), the Salmon hornblende schist, and the Abrams mica—schist that are described by Hinds (1933, p. 78) as underlying the Copley, and thus are of pre—Middle Devonian age. The latter formations contain a large amount of sedi- mentary material that was probably deposited in oceanic basins, but they contain some mafic lavas that are inter— bedded with the sedimentary material. The mafic flows have a sporadic distribution in the formations that underlie the Copley indicating that volcanic activity began slowly at isolated points during the sedimentary cycle preceding the Copley and gained in intensity and areal extent until mafic flows and pyro— clastic material constituted almost the entire deposit over a large area. The Copley has a large areal extent as compared with its thickness. It is composed of many mafic flows and bodies of pyroclastic material, none of which themselves are widespread. The formation covers an area of at least 1,000 square miles. Its limited thickness, the pres— ence of pillow lavas, water-deposited tuff and shaly tuff, the minor local folding in shaly layers that was caused by syngenetic sliding, and the lack of widespread beds of tuff, all suggest that the formation was built up under water on the underlying sedimentary formations. The Copley flows and pyroclastic rocks must have been de- rived from many widely scattered vents, as the indi- vidual flows can rarely be traced for more than a few thousand feet, and the bodies of pyroclastic rock tend to be stubby lenses that cover irregular areas of very limited horizontal extent. 0 Rhyolitlc lava and pyroclastic material began to erupt " at a few centers in the widespread area of mafic flows 'in the latter part of the main period of deposition of the Copley, and in the upper part of the Copley rhyo- litic material is fairly common in widely scattered lo- calities. In the )Vest Shasta district centers of eruption of the rhyolitic rocks (the Balaklala rhyolite) formed at about the end of deposition of the Copley, and al- though there was an overlap in some areas, the begin- ning of the main period of rhyolitic eruptions marks the end of the major eruptions of mafic flows. A well- defined transition zone between mafic and rhyolitic flows is present at many places; it is marked by coarse, un— sorted, rhyolitic and mafic bombs and fragments in a matrix of Copley greenstone type fragmental lava. The Balaklala rhyolite was also deposited at or near sea level. It is composed of a series of flows, coarse and fine pyroclastic material, and tuff layers, some of which are water deposited; individual flows are less wide- spread than those of the Copley, probably because the rhyolitic flows were more viscous. Underwater deposi- tion of most of the Balaklala rhyolites is indicated by: water-deposited tuff, the absence of widespread tuff beds, rhyolitic flows immediately overlying pillow lavas, local folding that resulted from syngenetic sliding in the water-deposited tuff beds, a fish plate found in the tuff of the upper part of the Balaklala, and the thick, stubby, irregularly outlined bodies of coarse pyroclastic material. However, waterworn fragments in volcanic breccia and accretionary lapilli tut? indicate that part of the volcanic pile extend above sea level, probably as a group of volcanic islands. The break between mafic and silicic flows was not abrupt, as a few mafic, Copley—type flows persist into the lower part of the rhyolitic sequence. Several vol- canic centers that were the source of the rhyolitic flows, and pyroclastic beds of the Balaklala rhyolite have been located, and many others were probably present. The Balaklala rhyolite formed a broad, elongate, volcanic dome about 3,500 feet thick, 16 miles long, and 3 miles wide. The wide areal extent of these siliceous, rhyolitic flows as con'lpared with their thickness is probably due to their eruption from many vents in the early part of the eruptive cycle. The rhyolite in the upper part came largely from a main, centrally located vent. It seems reasonable to assume that the volcanic com— plex of Copley and Balaklala rocks did not build a vol- canic pile on the ancient sea floor that was equal in height to the total thickness of the two formations (esti- mated at 7,000—10,000 feet). Compaction nf the under- lying sediments under load, subsidence due to the out- pouring of lava, and isostatic adjustment probably reduced the absolute elevation of the lava. A broad GEOLOGIC 1 ' ‘underwater dome or sea ridge of moderate relief along which volcanic islands were Scattered must have re- mained, however, because of the distribution and char-' ‘acter of the overlying Kennett formation. The Balaklala rhyolite is overlain conformably by ‘the Kennett formation of Middle Devonian age. The ‘gradation between the two formations is so complete ‘that the boundary between the formations at some places ‘has been drawn arbitrarily where shale predominates ‘ over tufi'. there the Kennett formation was deposited :on rhyolitic flows, the contact is sharp, although the ivolcanic activity did not end abruptly; a few rhyolitic . flows and many beds of tuif occur in the lower part of i the Kennett, interbedded with shale. The lower part 1 of the Kennett in most areas is composed of black sili- ceous and cherty shale that contain some radiolaria, ‘ and it seems probable that some of the silica was derived ‘ from volcanic activity. The middle part of the Kennett ‘ is composed of black shale, and the upper part is a bed i of coral limestone 250 feet thick. Corals and broken ‘ coral debris indicate deposition in relatively shallow ‘ water. This is substantiated by the distribution of the ‘ Kennett, which was deposited near the outer edge of the ‘ volcanic highland, but which is not believed to have ‘ covered some of the central parts of the volcanic pile. Diller (1906, p. 3) believed that an unconformity was present between the Kennett formation and the over- lying Bragdon formation because of the boulders of fossiliferous limestone of the Kennett in the conglomer— ate of the Bragdon, the absence of the Kennett in some areas where the Bragdon rests directly on the underly— ing Balaklala or Copley rocks, and the difference in the thickness of the Kennett in several parts of the district. Boulders derived from the Kennett indicate erosion of that formation. However, the lack of any evidence of a stratigraphic break between the Kennett and the Bragdon in the lVest Shasta area leads the writers to conclude that the Kennett was warped fol- lowing deposition, and that in some area outside of this district the Kennett was raised above sea level and subjected to erosion. The “Test Shasta area remained under water throughout Kennett and Bragdon time and received continuous sedimentation except where volcanic islands projected above water level during Kennett time. The range in the thickness of the Kennett is not as great as Diller and others supposed, as described under “Kennett formation,” and the difference in thickness is best explained by the deposition of the Kennett against a volcanic pile that had moderate relief, and that in places extended above sea level. It seems more probable that the Kennett did not completely cover local sea- mounts on the volcanic pile than that it was eroded 65 HI STORY from these points by subaerial erosion, although erosion by currents, syngenetic sliding, differential compaction, and limited deposition on areas of higher relief prob- ably played a part in forming a deposit of unequal thickness. The Bragdon formation of Mississippian age, which overlies the Kennett, is a thick deposit of well-bedded shale and conglomerate that was deposited in water of moderate depth. No basal conglomerate is in the Brag- don, which again suggests that there was continuity of sedimentation between the Kennett and the Bragdon in this district. Following the deposition of the Bragdon a great thickness of sedimentary rocks was deposited, but they have been eroded from the lVest Shasta district. They have been mapped by Albers and Robertson3 in the East Shasta area, and by Diller (1906, p. 4—6). These deposits include beds of shale, sandstone, limestone, and volcanic material that range in age from Mississippian to Recent; major gaps in the sedimentary cycle occur between the Brock shale of Triassic age and the Modin formation of Jurassic age, between the Potem forma- tion of Jurassic age and the Chico formation of Late Cretaceous age, and between the Chico formation and the formations of Tertiary age (Diller, 1906, p. 4—6). Orogeny in this district has been dated as Late Jurassic or Early Cretaceous from several lines of evi- dence that are given under “Metamorphism,” “Mule Mountain stock,” and “Shasta Bally batholith.” Two plutons, the older of albite granite and the younger of biotite-quartz diorite, were intruded into the rocks of the district; they are both dated as of Late Jurassic or Early Cretaceous age (Hinds, 1934, p. 182—192), but the orog- eny and igneous intrusion deformed the rocks into a series of broad folds that contain local areas of close folding. Rocks at many places were foliated, and local shear zones and faults were formed. All the rocks older than the Shasta series were deformed by the orogeny, but the Shasta series was deposited nonconformably on the Shasta Bally batholith. ROCK ALTERATION All the rocks older than Late Jurassic have been altered from their original character to some extent by dynamic and igneous metamorphism, hydrothermal alteration, and by weathering. Some of the alteration was described under “Geologic formations” in describ- ing the appearance of the rocks. This is especially true of the description of the Copley greenstone and in de- scribing the contact relationship between the Copley aAlbers, J. 1)., and Robertson, J. R, Geology and ore deposits of the East Shasta copper-zinc district, Shasta County, Calif. U. S. Geol. Survey. I'rof. Paper. [In preparation] 66 GEOLOGY AND BASE-METAL DEPOSITS, WEST SHASTA COPPER—ZINC DISTRICT greenstone and the Shasta Bally batholith and the Mule Mountain stock. Also some alteration is described under “Ore deposits” in the description of the hydro- thermal alteration related to the ore deposits. The purpose of this section is to summarize the processes that have affected the rocks since their crystallization or cementation, and to give a detailed description of the igneous metamorphism along the edge of the Shasta Bally batholith. Although the types of metamorphism can at some places be related to particular processes, it is not possible to separate the different types in all instances. Thus hydrothermal metamorphism is superposed on dynamic and igneous metamorphism, and the effect is dependent on stability relationship between the solutions and the different end products of dynamic or igneous meta— morphism. Along the borders of the Shasta Bally batholith, igneous metamorphism is superposed on the products of dynamic metamorphism. Likewise, no line can be drawn between late magmatic and hydrothermal alteration in the albite granite. The changes in the composition and the mineral assemblage that occur in the greenstone at its contact with the Shasta Bally batholith are due largely to igneous metamorphism. Much material has been added from the intrusion, and the mineral assemblage at some places is determined almost entirely by the amount of material that has been introduced from the intrusive mass. The mode of introduction, however, includes much more than metaso— matism, for it ranges from direct additions of molten material in the migmatites to minor solutions carrying only the constituents of feldspar and quartz or solutions that probably had only a catalytic effect in hastening mineral changes. Thermal and dynamic metamorphism also effected changes in the mineral assemblage. Deformation accompanying intrusion and the con— comitant cataclastic structures that were produced aided the penetration of solutions from the igneous mass over a much larger area than could be effected by purely thermal metamorphism. The heating of the pore solu- tions and the cataclastic effects due to orogeny and syn- tectonic intrusions allowed the activated pore solutions to migrate and effect recrystallization. In many parts of the district, the increase of permeability due to dy- namic metamorphism has locally influenced other types of metamorphism. It cannot be assumed that different rocks underwent the same degree of metamorphism because they are associated in the field. Whether igne- ous metamorphism was carried to completion or not, in many localities, depended on a difference in the ease of access of solutions, which is in turn dependent on both primary and secondary structures. Some areas are more foliated than others and during igneous meta- morphism solutions worked out along the more foli- ated bands and emphasized this foliation by mimetic crystallization. The principal mineralogic changes that are attribut- able to metamorphism are the formation of minerals of the green schist facies caused by both dynamic and igneous metamorphism, and the formation of amphibo- lite, gneiss, and migmatite by igneous metamorphism. DYNAMIC METAMORPHISM Dynamic metamorphism is defined by Turner (1948, p. 5) as the structural and mineralogic reconstitution of the rocks during deformation caused by orogenic crustal movements. This type of metamorphism has affected all the rocks older than the biotite-quartz diorite of the Shasta Bally batholith. The effectiveness of dynamic metamorphism varies widely throughout the district. Bands in which the rocks are well foliated are separated by areas in which the rocks are massive, and bands of foliated rock lens out along strike. The preservation of original textures, the lack of cataclastic structures, and the absence of sutured mineral contacts in most of the rocks show the lack of over-all shearing and crushing. The foliation at most localities has a regional trend, although it diverges from this trend in local areas. The alternation of foliated and massive rocks at some places suggests that zones of foliation reflect deep crustal breaks that are represented in the rocks now exposed at the surface by narrow zones of strongly foliated rocks or faults, or by wider zones of less strongly foliated rocks. Recrystalli- zation of primary rock minerals is strongest where movement was limited to narrow zones; where move- ment was absorbed over a wide zone, oriented minerals are commonly limited to closely spaced planes, and the rock between the planes does not contain oriented minerals. The grade of dynamic metamorphism decreases from the western part of the Whiskytown quadrangle east- ward to the eastern part of the Shasta Dam quadrangle. In the central and western parts of the area the Copley was altered to minerals of the green schist facies, which involves the alteration of the mafia minerals to epidote and chlorite and the alteration of plagioclase to albite and small amounts of epidote, zoisite, and carbonates. The green schist facies is widespread, although both foliated rocks and minerals of the facies are more com- mon in the western than in the eastern part of the district. Although the Balaklala rhyolite and the sedimentary rocks were folded and locally sheared, they were much less affected mineralogically by orogenic stresses than the Copley. The principal alterations in the Balaklala ROCK ALTERATION rhyolite are the occurrence of sericite, hydromica and chlorite in some of the rhyolite. ‘ Sericitization is common through much of the lower and middle units but not in the upper unit of the Balak- lala. Some of this alteration may be an early phase of the period of ore deposition, although much of it is widespread and has no apparent spatial relationship to massive sulfide deposits. “Iliere the rhyolite has been foliated and has closely spaced sheeting or schistosity, sericite is formed along the planes of movement. Move- ment continued after the formation of the sericite, however, as bands of sericite schist are locally crenu- ilated; deformation outlasted recrystallization. Dynamic stresses possibly caused some of the minor ichloritic alteration which gives the rhyolite a light— ‘green color. F eldspar was replaced by chlorite along scleavage planes, and veinlets and irregular patches of chlorite were formed through the groundmass. The chloritic alteration is most intense in the few dacitic flows of the Balaklala, although it is present to some ex- ‘ tent in all the Balaklala. “rhere the chloritic alteration ‘ is prevalent, as on South Fork Mountain in the ‘Vliisky- town quadrangle, the resulting product is difficult to distinguish in the field from Copley greenstone. Most of the Balaklala rhyolite is poorly foliated. ‘ Fracture cleavage predominates, and ranges from a ‘ poorly defined sheeting having little or no alinement of minerals to a quartz-sericite schist in strong shear zones. Bedding—plane foliation is present to a lesser extent and is localized in thin tuffaceous beds and along . flow contacts. Orogenic stresses have had little effect upon the sedi- mentary rocks except for the formation of local bed- ding-plane cleavage, fracture cleavage in folds in shale beds, and crumpling in the shale near competent conglomerate beds. IGNEOUS METAMORPHISM Igneous metamorphism includes all the mineralogic and textural changes induced in a solid rock by the in- trusion of a plutonic body. This includes the meta— morphic changes brought about by the heat of the intrusion and those that are caused by fluids—either gaseous or hydrothermal—given off by the. intrusive mass during its emplacement and cooling. Both altera- tion within the igneous rock and of the surrounding invaded rock are included. Metamorphisni of the invaded rocks has been caused by three different intrusive masses—the plugs of coarse- phenocryst rhyolite near the Uncle Sam mine, the Mule Mountain stock of albite granite, and the Shasta Bally batholith of biotite—quartz diorite. ‘ 379725—56——6 67 METAMORPHISM RELATED TO PLUGS 0F BALAKLALA RHYOLITE The only alteration definitely related to the Balaklala rhyolite is the intense silicification and quartz-talc a1- teration around the plugs of coarse-phenocryst rhyolite in the vicinity of the Uncle Sam and Clipper gold mines. The alteration of the plugs and the surrounding non- porphyritic and medium-phenocryst Balaklala rhyolite is most intense in brecciated areas. Apparently pre- intrusive explosions, possibly of phreatic origin, shat- tered the rhyolitic rocks, and the coarse—phenocryst rhyolite magma quietly welled up in some of the shat- tered zones. In these zones, and in associated shattered zones that do not contain magma, late magmatic solu- tions entered and almost completely replaced the rhyo- lite, forming irregular areas of highly silicified rock that are conspicuous owing to their resistant character and to their white color. Although the parent rock contains very little mag- nesia the solutions must have been rich in it, as local areas of quartz-talc alteration are present along the margins of the plug as well as in the silicified zones. Small lenses and pockets of talc as much as 6 inches long occur near the margins of the silicified coarse-phe- nocryst rhyolite plug in a road cut 300 feet south of the Uncle Sam gold mine adit, and on the road between the Uncle Sam and Clipper mines. Also, quartz—talc schist occurs near the margin of the plug along the road from the Uncle Sam gold mine to the North Fork of Squaw Creek. Strong cataclastic structures are pres— ent in the rhyolite near the margins of the plug, where the rock is replaced by quartz and talc (fig. 33). The magnesia may have been derived from the underlying Copley greenstone. METANIORPHISM RELATED TO THE MULE MOUNTAIN STOCK The wall rock of the Mule Mountain stock has been altered in only a few areas, and to a limited extent, but this stock has been widely altered by deuteric or hydro- thermal (late magmatic) solutions, and by assimilation of the wall rocks. In places the Copley greenstone is recrystallized to amphibolite and epidote amphibolite as much as 200 feet from the albite granite contacts. This alteration destroys the texture of the original rock; the altered rock consists of hornblende, epidote, and andesine, but there has been little or no change in chemical composi- tion. The amphibolite is formed by recrystallization of the Copley caused by heat and solutions from the intrusion and has little or no gain or loss of material. On weathered surfaces the recrystallized greenstone is difficult to recognize from the green schist facies of the 68 GEOLOGY AND BASE—METAL DEPOSITS, FIGURE 33.—Photomicrograph of extremely sheared coarse-phenocryst rhyolite from the margin of the rhyolite plug near the Uncle Sam mine. The rhyolite is almost completely replaced by quartz (q) and talc (t), forming a quartz-talc schist. Crossed nicols, X 14. normal greenstone, but the more granular texture of the amphibolite is readily recognizable on unweathered surfaces. Near the intrusion of the albite granite the Copley greenstone in some places is silicified and is cut by abun- dant veinlets of quartz, forming a stockwork of green- stone fragments separated by quartz veinlets. Much of the alteration related to the Mule Mountain stock is endomorphic. This includes propylitization, albitization, silicification, and changes in the composi- tion of the intrusion where wall rocks were assimilated. Propylitization, which involves the alteration of the mafic minerals to epidote and chlorite and the altera— tion of the more calcic plagioclase to albite, epidote, zoisite, and carbonates, is confined to the mafic horn- blende—quartz diorite part of the Mule Mountain stock. The alteration is only partly completed; most of the plagioclase is altered, but some relict hornblende remains. Silicification and albitization occur together in irreg- ular areas throughout the leucocratic phases of the stock and are prevalent in brecciated areas within the stock. The alteration is believed to be largely by deuteric solu- tions. The altered rock chemically is only slightly more sodic and silicic than the unaltered trondhjemitic in» trusive mass, but its megascopic appearance and texture are much different. The alteration has caused a bleach— ing of the rock, a coarsening of grain size, and the WEST SHASTA COPPER-ZINC DISTRICT formation of a pseudoporphyritic texture containing quartz grains in clusters a quarter of an inch in diameter in a finer grained granitoid matrix. Quartz was the last mineral to crystallize in the unaltered albite granite, so it is difficult to distinguish magmatic quartz from hydrothermal quartz. Thin veinlets of quartz cut the rock and replace plagioclase along grain boundaries. The plagioclase in the bleached, “porphyritic” albite granite is clear and is more sodic than the plagioclase in the unaltered trondhjemite. METAMORPHISM RELATED TO THE SHASTA BALLY BATHOLITH The Shasta Bally batholith has had a considerable effect upon the Copley greenstone, which is metamor- phosed to amphibolite, hornblende gneiss, and epidote amphibolite as much as 4 miles from the eastern con- tact of the batholith, and which is altered to gabbro in the borders of the Clear Creek plug of biotite-quartz diorite. The g'ade of metamorphism decreases east- ward away from the contact, but the Copley is altered to amphibolite and hornblende gneiss as far as 4,000 feet from the batholith. The gneiss and the amphibo- lite grade eastward t0 epidote amphibolite, farther out to greenstone consisting of albite, chlorite, epidote, and quartz (green schist facies). Amphibolite facées.—Two distinct rock types are present in the amphibolite facies, which extends as far as 4,000 feet east of the contact of the Shasta Bally batholith. One type is an amphibolite that has been essentially unmodified chemically by the biotite-quartz diorite, and the other is a banded dark quartz-horn- blende gneiss or migmatite that, in part, has much added material. The amphibolite is a megascopically finely crystalline dark-greenish-gray rock that has a uniform foliation striking about N. 20° 'W. and dipping mostly 60°~70° E. It makes up 75 percent or more of the amphibolite facies and is cut by many thin veinlets of epidote, or quartz and epidote. Locally quartz augen 2 to 3 inches long are abundant. The contact between the biotite-quartz diorite and the amphibolite is sharp, and locally the biotite-quartz diorite transgresses the foliation of the amphibolite. Under the microscope the amphibolite is seen to be composed of hornblende, biotite, plagioclase, calcite, chlorite, orthoclase, epidote, quartz, and magnetite, and has a crystalloblastic texture. Hornblende and plagioclase make up more than 90 percent of the rock. Hornblende occurs as green, anhedral, acicular crystals averaging 1 millimeter in length and 0.3 millimeter in ROCK ALTE RATION width in a matrix of clear plagioclase. The acicular crystals are unoriented in the plane of foliation. The hornblende has the following optical properties: optic Sign negative; 2Vg70°; indices na=1.650i0.003, a5=1.664i0.003; 71,=1.675i0.003. These optical properties correspond to green hornblende. The pla- gioclase is clear and has very little albite twinning. Its composition ranges from oligoclase to calcic andesine ‘(AbGBAnsg—AbmAnw). Biotite, orthoclase, and quartz are present in minor quantities as small interstitial grains. Locally porphyroblasts of plagioclase or hornblende ‘as much as a quarter of an inch in diameter have :formed. They are particularly abundant in the am- ‘phibolitic zone at the north end of the small plug on Clear Creek in the Igo quadrangle, but, they are rare in the amphibolitic zone along the margin of the Shasta ‘Bally batholith. The porphyroblasts are found in the jCopley mainly where it forms a thin cover or roof over .the intrusive mass. The migmatite, which is the second type of rock in j the amphibolite facies, is best exposed in the Igo quad- irangle in the Brandy Creek area and near the small “ plug on Clear Creek. In the Brandy Creek area, where .gneissic structure of the migmatite parallels the in- ‘trusive contact, three lithologic zones are recognized jin the transition from Copley greenstone to biotite- . quartz diorite. The outermost zone is a dark horn- ‘ blende gneiss that is extremely well banded and has : alternating dark and light bands one-eighth inch to 1 . inch thick. The bands at first glance give the appear- ‘ ance of being regular and straight, but in detail they ; are lenticular, and none can be traced for more than 10 . feet. The dark hornblende gneiss, which has had little : added material, grades toward the biotite-quartz diorite . contact to leucocratic gneiss that has only 5 to 10 percent ‘ mafic minerals, and has had much added material. The ‘ leucocratic gneiss grades to foliated biotite-quartz diorite within the border of the batholith. The first two units constitute a migmatite zone between Copley greenstone and the Shasta Bally batholith. The outermost zone, of dark hornblende gneiss, con— sists of hornblende, plagioclase, quartz, chlorite, biotite, epidote, orthoclase, magnetite, apatite, and sphene, listed in order of decreasing abundance. It has well— formed cataclastic structures now partly obscured by recrystallization. The dark bands contain more than 50 percent hornblende and a lesser amount of biotite and chlorite. The light bands contain mostly quartz and plagioclase (Ab5oAn50) and some orthoclase. Mor- 69 tar structures and augen are common in localized areas, and there is a marked lineation shown by acicular horn- blende crystals and by plagioclase and quartz augen. The grain size averages about 0.2 millimeter. The augen in the dark bands in the hornblende gneiss, as in the amphibolite, are probably formed by meta- morphic difl’erentiation. The augen contain the same minerals as the amphibolite, but they have a greater concentration of the light minerals. Although the acicular amphibole crystals bend around some of the quartz augen, in most of them the amphibole needles project into the augen with no deflection but in much less concentration. Some of the amphibole crystals within the augen have a tendency to be oriented toward the center. The mineralogic character of the light bands in the hornblende gneiss are identical to the dark bands, but they have a concentration of light—colored minerals. There is no change in grain size between the dark and light bands, and they have interlocking grains at the contact. The plagioclase has the same composition (Ab50Aii50) in both bands. Apparently the light and dark bands and the augen both formed by metamor- phic differentiation (Eskola, 1932‘, p. 68—77; McCallien, 1934, p. 11—27; Read, 1933, p. 317—328; Stillwell, 1918, p. 354—396; Turner, 1941, p. 1—16, 1948, p. 137—147) in the hornblende gneiss, with possibly small addition of material, in contrast to the leucocratic gneiss in which much granitic material has been added. In a few places there has been lit-par—lit injection of fine—grained hornblende diorite, quartz latite porphyry, and aplite dikes parallel to the banding of the gneiss. These injected bands have sharp contacts with the dark and light bands of the hornblende gneiss and have many crosscutting relationships with the hornblende gneiss. Toward the contact of the Shasta Bally batholith the dark hornblende gneiss in the migmatite zone grades into the second Zone, in which the color is lighter and the banding is much less pronounced. This leucocratic gneiss contains 80 to 90 percent quartz and plagioclase, and small amounts of orthoclase, hornblende, biotite, epidote, muscovite, magnetite, apatite, and sphene. Alinement of hornblende, biotite, and chlorite, and quartz-plagioclase augen impart a pronounced linea- tion to the rock, although the mafic minerals are uni- formly distributed through the rock in contrast to the concentration of mafic minerals in bands in the horn- blende gneiss. The grain size is generally coarser in the leucocratic gneiss and ranges from 1 to 2 milli- meters across where the rock is not sheared. Adjoin- 70 GEOLOGY AND BASE—METAL DEPOSITS, ing bands of quartz grains may have very different grain sizes, but all the grains in a single lens or band are nearly the same size, as described by Sander (1938, p. 29). Cataclastic structures are much more strongly developed in the leucocratic gneiss than in the dark hornblende gneiss. Mortar structure, porpliyroclasts, and local formation of mylonite are common. Cata- clastic structures are mostly healed by quartz. Ortho— clase and muscovite are late minerals, and in part fill fractures that cut across both foliated and cataclastic structures, which are parallel. Plagioclase in the leucocratic gneiss has a composition of AbfigAn”, which is about the same as that of the cores of the plagioclase in the biotite-quartz diorite (p. 49), in contrast to the more calcic plagioclase (AbsOAnSO) in the hornblende gneiss. The plagioclase thus becomes less calcic with the decrease in proportion of mafic minerals. Also, in the gradation from dark hornblende gneiss to leucocratic gneiss, hornblende de- creases and quartz increases. Cataclastic structures increase, and much of the leucocratic gneiss is a my- lonite. Chlorite, epidote, and some of the amphibole in the mylonitic bands are late minerals and wrap around quartz and plagioclase porphyroclasts. The leucocratic gneiss zone is exposed for a width of 100 feet in Brandy Creek, and grades to hornblende gneiss away from the batholith. Toward the batho— lith there is a covered zone for 125 feet; then an out- crop of coarse—grained biotite-quartz diorite showing primary foliation. The foliated biotite-quartz diorite contains about 40 percent biotite and hornblende, where- as the leucocratic gneiss contains less than 10 percent mafic minerals, most of which are biotite, Chlorite, and epidote. About 1,000 feet north of Brandy Creek the contact between leucocratic gneiss and foliated biotite- quartz diorite is sharp and conformable. E pidote amphibolite facies.—The amphibolitic rocks grade to the east, away from the biotite-quartz diorite, to greenstone containing epidote and fibrous amphibole, and finally to chloritic lavas. The greenstone contain- ing fibrous hornblende are light to dark green hard, locally massive rocks and are epidote amphibolites. They are usually lighter in color and are harder and more massive than the chloritic lava. Locally they are cut by abundant veinlets of quartz and epidote or have a lumpy appearance due to formation of knots of epi- dote the size of a fist. Quartz augen 2 to 3 inches long are common. Under the microscope the epidote amphibolite is seen to contain plagioclase, fibrous amphibole, Chlorite, epi- dote, zoisite, calcite, quartz, pyrite, and magnetite. Pla- WEST SHASTA COPPER-ZINC DISTRICT gioclase is slightly more calcic than that in the chloritic lava, but it is more sodic than that in the amphibolitic facies. It ranges in composition in the epidote amphi- bolite from AbgoAn10 to AbmAngs. Plagioclase in the chloritic lava ranges from AbwAn3 to Ab78An22; that in the amphibolite facies from AbggAn32 to AbsoAnm. The amphibole is fibrous to acicular and grains are commonly less than 1 millimeter long. Locally the amphibole is oriented, but more commonly it is un- oriented in plagioclase that may either be massive or have a felted texture. The amphibole is colorless to light green and has the following optical properties: Optic sign negative 2Vg80°; Z/\c=14°; and indices of refraction na=1,603i0.003; n5: 1615:0003; ny=1.625:0.003. These optical properties fit tremolite most closely. Epidote is present in clusters commonly 1 t0 2 millimeters but as much as 3 inches in diameter, in veinlets with quartz cutting the rock, and as amygdule fillings. Quartz occurs as amygdule fillings and as veinlets cutting the rock. The amount of amphibole decreases to the east away from the biotite-quartz diorite contact, and the amount of chlorite increases toward the east. The texture changes from crystalloblastic in the amphibolite and epidote amphibolite to pilotaxitic in the green schist facies. The Copley greenstone has been altered by hydro- thermal emanations from the biotite—quartz diorite and to a lesser extent by lit-par-lit injection. The amphi- bolite was formed by recrystallization of chloritic lava—— aided by heat and fluids from the biotite—quartz diorite intrusive mass—with essentially no change in chemical composition. The amphibolite consists mainly of andesine plagioclase and hornblende, although it con- tains a little interstitial orthoclase and quartz, which suggests that there has been a little potash and silica metasomatism. In some places, particularly along the contact of the Clear Creek plug, intrusive breccia formed at the con— tact between biotite—quartz diorite and amphibolite or migmatite. The fragments in the intrusive breccia in- clude all the rock types in the amphibolite 0r migmatite zone. The leucocratic gneiss could not have been formed by lit—par—lit injection and assimilation of Copley green- stone as it is more felsic than either the biotite-quartz diorite or the Copley greenstone. Some lit-par-lit in- jection is recognized, but it is on a small scale. The dikes injected into the gneiss are generally parallel to the gneissic structure, but they have sharp contacts with the gneiss and some have crosscutting relationship. as those in the biotite-quartz diorite. . was crushed by the intrusion of the batholith, and the ROCK ALTERATION The migmatite \\ as p1 obably formed by fluids giv en off ahead of the intrusion that reworked and replaced the Copley greenstone. This conclusion is the same as that of Sederholm (1926, p. 131) and Stark (1935, p. 1) ‘in their descriptions of migmatites from Finland and ‘Colorado. The replacement of Copley is nearly com- :plete in the leucocratic gneiss zone, and there are all gradations in the replacement from dark hornblende gneiss to leucocratic gneiss. The metasomatism was done by solutions rich 1n silica, soda, and potash to form a gneiss that 18 more felsic than either the host lock 01 1 the parent magma. The crushing of the migmatite was protoclastic, simi- lar to that described by \Vaters and Krauskopf at the border of the Coville batholith (Waters and Kraus- j kopf, 1941, p. 1412). Although the migmatite probably . formed slightly before the intrusion of the Shasta Bally ‘ batholith, the minerals in the migmatite are the same The migmatite ‘ cataclastic structures were healed by silica-rich solutions ‘ from the batholith. Quartz and plagioclase are in part 1 crushed and drawn out, but these cataclastic structures are tra-nsgressed and healed by quartz and plagioclase which are similar in appearance to the crushed minerals, and are about the same age. The contact of migmatite and amphibolite with the Shasta Bally batholith is generally sharp, although in a few places intrusive breccias were formed with a ma- trix of biotite-quartz diorite. The intrusive breccias are described under “Shasta Bally batholith.” Ptygmatic folding occurs in the migmatite at a few places, but generally the wall rocks of the intrusion were not plastic. The sharp, in part transgressive, contact between bio- tite-quartz diorite and migmatite and amphibolite, and the incorporation of fragments of migmatite and am- phibolite in the intrusive breccias at the border of the intrusion, indicate that these rocks were formed prior to the intrusion. The intimate relationship between crush- ing of the migmatite, healing and transgression of cata- clastic structure by minerals‘identical to those within the intrusion, and the local lit-par-lit injection indicate the approximate consanguinity of the migmatite and biotite-quartz diorite intrusion. An explanation for the local transgressive relationship and for the great range in the width of the amphibolite, gneiss, and migmatite zones might be, as Durrell (1940, p. 108) suggested for the granitic rocks of the Visalia quadrangle, that the magma continued to advance while cooling so that the contact aureole formed at the period of highest tempera- 71 ture would be locally destroyed by the advancing magma. there the Clear Creek plug is in contact with the Copley, the greenstone has been reconstituted to form the rock units listed below. These changes in the green- stone are well exposed along the eastern contact and in the roof of the plug in Clear Creek canyon. The rock units that are exposed in Clear Creek, listed roughly in paragenetic sequence, are: 1. Greenstone recrystallized to fine-grained amphibolite with little added material. 2. Hybrid rock containing fine-grained, recrystallized greenstone with porphyroblasts of hornblende and stringers and lenses of hornblendite. 3. Fine-grained hornblende gabbro containing porphyroblasts of hornblende a quarter of an inch in diameter. 4. Dikes and veinlets of coarse-grained hornblendite. 5. Coarse-grained, nodular hornblende gabbro containing 40 to 50 percent rounded hornblende crystals three-eighths of an inch in diameter. 6. Banded gabbro and gabbro showing “unconformities.” 7. Intrusive breccia containing fragments of units 1—6 in a matrix of hornblende-quartz diorite and hornblende diorite. The first alteration of the greenstone was recrystal- lization to a fine—grained amphibolite and epidote am- phibolite, and the formation of knots of epidote. This alteration was a simple recrystallization of the green- stone to amphibolite containing hornblende and an- desine or labradorite, and little or no material was added. The alteration is similar to that along the south— ern margin of the Shasta Bally batholith. The am- phibolite ranges from several hundred to a thousand feet in width along the northeast contact of the plug. Near the intrusion, porphyroblasts of hornblende that average about 5 millimeters in diameter'were formed along fractures in the amphibolite (fig. 34). Further recrystallization resulted in formation of lenses and veinlets of hornblende gabbro, which locally were mo- bilized and have intruded amphibolite. In places the amphibolite has recrystallized to form a fine—grained nodular gabbro containing 20~25 percent of spherical aggregates of hornblende crystals in a matrix of horn— blende and labradorite that average about 0.3 milli— meter. This fine-grained nodular hornblende gabbro is i11- truded by coarse-grained nodular hornblende gabbro composed of 50 percent spherical aggregates of horn- blende crystals 5—10 millimeters across and interstitial labradorite averaging 1 millimeter in length. The nodular gabbro has the same mineralogy as the nodular hornblende gabbro, and apparently resulted from the further recrystallization and some remelting, which 72 GEOLOGY AND BASE—METAL DEPOSITS, WEST SHASTA COPPER—ZINC DISTRICT FIGURE 34.—F0rmation of porphyroblasts of hornblende in hybrid Copley greenstone near contact with the Clear Creek plug. The coarser stringers have the composition of hornblende gabbro. caused mobilization of the matrix and intrusion of the nodular gabbro as a thick melt or mush. The spherical aggregates of hornblende crystals in the nodular horn— blende gabbro are recrystallized to large single horn- blende crystals or are party recrystallized to an aggre- gate of several large ones. This melt or mush of nodular gabbro filled fractures in the nodular horn- blende gabbro and amphibolite, and also formed small plugs of nodular gabbro in the amphibolite. Some small local pegmatitic lenses in the nodular gabbro have euhedral hornblende crystals 1 to 2 inches long in coarse plagioclase. These mafic pegmatitic lenses are erratically distributed through the nodular gabbro. Some of the hornblende gabbro has a well—formed banding (fig. 35). Dark bands 1—2 inches thick, that are predominantly of hornblende, are separated by light bands a quarter of an inch thick that are predominantly of plagioclase. The grain size averages about 21/2 milli- meters in diameter. The banding is not uniform, but bends in all directions. The banding in the gabbro may be due either to sep- aration of felsic and mafic minerals during the emplace- ment and crystallization of the gabbro, or to the forma- tion of the banded gabbro in place by recrystallization of a banded migmatite similar to the one at Brandy Creek described under “Igneous metamorphism.” The latter seems more likely to the writers, as the banded gabbro has some relicts locally of fine-grained horn- blende gabbro similar to the matrix of much of the recrystallized greenstone. ROCK ALTERATION FIGI‘RE 35.~Ii‘1‘:1g111ent of banded hornblende gahbro cut by hornblendite (likelot. The handed gabbro is a large fragment in an intrusive breecia with a matrix of hornblende diorite. In a few places the bands in the hornblende gabbro show several “1inconformities” (fig. 36). The “uncon— ‘ for-mities” were probably formed while the gabbro was still in a plastic state. Eroding of the banded gabbro by the magma and the concomitant fragmentation and rotation of the banded gabbro by stresses from the in- trusion probably caused these “angular unconforn’iities” and formed the intrusive breccias. The banded gabbro showing “angular uncon- Scale shown by 50-0th FIGURE 36.——Fragment of hornblende gabhro formities" cut by a dikelet of hornhlendite. piece. 73 is intruded by the fine-grained hornblende-quartz dio- rite of the Clear Creek plum There has been some lit- par—lit injection of hornblende—quartz diorite bands 1 to 2 inches thick parallel to the layering in the gabbro, and some of the hornblende-quartz diorite bands cut across the layering in the banded gabbro. Dikelets of hornblendite cut the hybrid rocks and the gabbro. They range from small lenses several inches long to dikelets as much as 2 inches thick and several tens of feet long. The hornblendite dikelets occur only in the hybrid zones about the Clear Creek plug and in Brandy Creek near the margin of the Shasta Bally batholith. These dikelets could be one of the mobilized products formed by the recrystallization of the green- stone to hornblende gabbro and separation of the horn— blende and plagioclase either by gravity or by squeezino'. Intrusive breccias that contain fragments of amphib— olite, bande( gabbro, hybrid greenstone, hornblendite, and hornblende gabbro in a matrix of hornblende—quartz diorite (fig. 37) occur at the margin of the (‘lear (‘reek FIGURE 37.—Intrusive breccia containing fragments of gabbro, horn— blendite, and Copley greenstone in a matrix of hornblende diorite; greenstone (a), gabbro (b), hornblendite (c), silicified greenstone (d), hornblende diorite matrix (6). plug. The fragments of the hybrid rock and gabbro in the intrusive breccias date the formation of the gabbro as slightly earlier than the intrusion of the plug. Also some bands of hornblende-quartz diorite similar to the rock in the margin of the plug cut the banded gabbro. The spatial relationship of the gabbro and hybrid rocks to the margin of the plug dates their formation just before or during the emplacement of the plug. The ground was under strong stress at the time of the formation of the hybrid rocks and of the nodular gabbro, probably due to the force of the intrusion, and the amphibolite and hybrid rocks were shattered and contorted in many places. This shattering was prob- ably augmented by the buttreSSing effect of the Mule 74 GEOLOGY AND BASE—METAL DEPOSITS, WEST SHASTA COPPER-ZINC DISTRICT Mountain stock, as the shattered amphibolite and hybrid rock lie between the plug of biotite-quartz diorite and the earlier stock of albite granite; this shattering per- mitted thorough soaking of the greenstone by solutions emanating from the intrusion. WEATHERING lVeathering has not been an important factor in the alteration of the rocks except in the Mule Mountain stock of albite granite and to a lesser extent in the Copley greenstone. The feldspar in the greenstone is altered to clay minerals at the surface, and weathering emphasizes the schistosity. lVeathering has had little effect upon the nonporphyritic and medium-phenocryst Balaklala rhyolite, but the coarse-phenocryst Balaklala rhyolite at the surface has a “punky” look due to altera- tion of the feldspar to clay minerals. Both kaolinite and nontronite are present. Kaolinite is prevalent as an alteration of the albite phenocrysts and is abundant in the groundmass of the weathered rhyolites. N on- tronite commonly forms cross-fiber veinlets in fractures in quartz phenocrysts. Feldspar phenocrysts in the porphyritic rhyolite are altered to clay minerals and blend with the groundmass and thus are less prominent than quartz phenocrysts. The albite granite is deeply weathered. Road cuts that are 50 feet deep near the town of Shasta on U. S. Highway 299W are entirely in white crumbly, disin— tegrated albite granite. Mechanical disintegration has been more active than chemical decomposition in the weathering of the rock, and much of the feldspar in the disintegrated rock appears to be little altered. Be- cause of the deep disintegration, unweathered exposures of albite granite are present only in the deep canyons as in Clear or Spring Creeks. The other intrusive and sedimentary rocks were very little affected by weathering. The massive sulfide deposits have been oxidized to a gossan capping that ranges in thickness from a few feet at the Balaklala and Mammoth mines to a maximum of 400 feet along the footwall of the Camden fault at the Iron Mountain mine. The mineralogy of the oxidized sulfides is discussed under “Ore deposits.” ORIGIN OF THE ALBITE The rocks in the West Shasta district are a. typical spilitic suite as described by many writers including, among others, Benson (1915, p. 121—173), Dewey and Flett (1911, p. 202—209, 241—248), Gilluly (1935, p. 225— 252, 336—352), Peach and others (1911), and Sundius (1930, p. 1—17). The rocks of the spilitic suite that occur in this area are spilite, keratophyre, soda-rich rhyolite, albite diabase, and albite granite. Field and microscopic evidence indicates that the albite in the soda-rich rocks of the lVest Shasta district was formed at different times and by several processes; both primary and secondary albite are present. All of the evidence that was seen indicates that the albite in the sodic Balaklala rhyolite is primary. In the green- stone some of the albite is known to be secondary, and the evidence for a primary origin of the remainder is less conclusive than in the rhyolite. Albite in the albite granite is secondary, and the rock formed by the albitiza- tion of trondhjemite. Field evidence is conclusive that albitization of the trondhjemite is later and is unrelated in time to the formation of albite in the Balaklala rhyo— lite and Copley Lgreenstone. The Copley greenstone was composed predominantly of albite and chlorite at the time of intrusion of the Mule Mountain stock, and it was altered by contact metamorphism to an amphi— bolite containing andesine and hornblende as much as 200 feet from the contact. The plagioclase in the phenocrysts and in the ground- mass of the Balaklala rhyolite is uniformly albite, as is the plagioclase in rhyolitic tuff, and no relicts of a more calcic plagioclase core are present. The composition of the albite in the phenocrysts and in the groundmass is about the same and ranges from AbDGAm to AbmAng. The albite in the groundmass has a felted texture in most of the rhyolite, although trachytic textures and spheru- litic structures are present. Trachytic texture and fluidal structures are reflected by unaltered albite laths in the groundmass of the nonporphyritic rhyolite. The albite in the unaltered, unsheared rhyolite is in clear laths that have sharp albite and Carlsbad twin lines and commonly have no inclusions. Broken fragments of plagioclase in crystal tuff are uniformly albite. Thin lenticular dacitic flows and dacitic tuff layers are interbedded in the rhyolite in some areas. The plagioclase in the dacite is unzoned oligoclase and has composition AbgoAnZO, but the plagioclase in the ad— j acent rhyolite is albite. It would be difficult to account for the difference in composition of the plagioclase in adjoining rocks by albitization that was so thorough and widespread that it removed all traces of an origi- nally more calcic plagioclase in cubic miles of rhyolite. At a few localities the rhyolite is cut by sharp-walled quartz—albite veinlets. The material in the veinlets is coarser grained than in the groundmass, but the texture and composition of the groundmass is unchanged. The albite in the veinlet is introduced, but there is no evi- dence that it is other than primary in the groundmass. The albite in the veinlets is AbgfiAm, which is the com- position of the most sodic albite in the groundmass. Myrmekitic and micrographic textures are not un- common in the porphyritic rhyolites. The time of ORIGIN OF origin of these intergrowths is not known with cer- tainty, as micrographic intergrowths of quartz and albite are found mainly in isolated albite phenocrysts surrounded by a quartz-albite groundmass having a pilotaxitic texture, but they also occur localized near the grain boundaries of quartz phenocrysts and in iso- lated patches in the groundmass. A few micrographic intergrowths, which were observed near quartz-albite ‘veinlets, were probably formed at the same time as the :veinlets, but some euhedral albite crystals having a micrographic texture were deposited in crystal tuft ; the ‘micrographic intergrowth apparently formed before ‘the crystal was incorporated in the tufi as nearby crys- ‘tals of albite contain no myrmekite. No myrmekite is ‘present in the matrix of tuft. Similar isolated euhedral ‘albite phenocrysts that have micrographic intergrowths :in porphyritic rhyolite apparently formed during crystallization of the rhyolite. The evidence is not conclusive whether the albite in ‘the keratophyre and spilite flows and tuff beds is of :primary or secondary origin. The composition of the ‘plagioclase ranges from AbmAn3 to Ab78A1122. ‘ of the albite is cloudy due to inclusions of chlorite and, j in places, epidote or zoisite, and the plagioclase is either ‘ equant or lath shaped. Secondary albite occurs where . some veinlets of quartz and albite cut the keratophyres, ‘ amygdules are present partly filled with albite, and I some of the feldspar has saussuri‘tic alteration. . ever, it is doubtful that the original plagioclase was Most How- ‘ more calcic than oligoclase, as the percentage of epidote ‘ and zoisite inclusions is too small to account for albite or sodic oligoclase by saussuritic alteration of original : andesine or labradorite, which composition would be expected if the rock were originally an andesite or ba- salt. Also, a few specimens of variolite are only slightly ‘ altered and have spherulitic growths of oligoclase of ‘ composition AbsfiAn15 and minor interstitial small an— ‘ hedral grains of quartz. Some keratophyres with pilotaxitic texture have clear . laths of plagioclase that range in composition from AbgoAn10 to AbgsAnls. These plagioclase laths have both albite and Carlsbad twinning. A finely porphy- ritic spilite from near Shasta Dam has clear, unzoned plagioclase phenocrysts with Carlsbad and albite twin- ning in a groundmass of clear plagioclase laths. Both the phenocrysts and the groundmass have a composi- tion of Ab93A117. The plagioclase in these rocks is prob— ably original. The albite granite of the Mule Mountain stock formed by albitization of trondhjemite by late magmatic solu- tions that penetrated large areas of the stock in the most sheared parts and added soda and silica. The albite in these areas is clear or is altered to sericite. In THE ALBITE 75 the parts of the stock least altered by late magmatic solutions, the albite is clouded by abundant inclusions of epidote, zoisite, and sericite; this cloudy albite is embayed and replaced by quartz and clear albite in the areas altered by late magmatic solutions. Micro- graphic and myrmekitic textures locally are common in these altered parts in the stock, but are rare in the unaltered parts of the stock. Primary and secondary albite are both evident in the rocks of the West Shasta district. Secondary albite is indicated in crosscutting quartz albite veinlets, in amyb- dules filled with albite, and in micrographic and myrme- kitic intergrowth controlled by grain boundaries. Evi- dence for the primary origin of most of the albite is less direct; it is indicated by the uniform composition and texture of the albite throughout wide areas of Ba— laklala rhyolite, the occurrence of oligoclase instead of albite in dacitic rock interlayered with rhyolite, the lack of replacement textures or crosscutting veinlets in most of the rhyolite, the secondary relationship of replace- ment albite where it is present, broken crystals of albite and of fragments of micrographic intergrowths in tuff where the albite apparently has been formed before its incorporation into the tuft, and preservation of primary textures and structures in rhyolite and greenstone. It is improbable that albitizing solutions derived from one rather limited source, such as the albite granite, could account for the complete alteration of all feldspar in a wide variety of rocks over a large area. The evidence. favors the derivation of the albite from several, possibly related, sources. The primary albite is related to a soda-rich magma chamber that probably is related to a geosynclinal environment. Dikes and sills of rhyolite both earlier and later than the flows of Balaklala rhyo- lite contain albite of the same composition and texture as the rhyolite of the flows, which suggests that all came from the same magmatic source. The secondary albite is derived in part from soda-rich volcanic emanations and from late magmatic solutions. The albitic spilites, keratophyres, and soda rhyolites are volcanic flows that were predominantly of submarine origin, and it is prob- able that part of the soda content of some of these rocks was derived from sea water. Whether the magma chamber was contaminated by absorption of salt water, whether the intrusive rocks were contaminated by en— trapped salt water in the wall rocks during the process of emplacement, or whether the intrusive rocks absorbed soda from sea water after extrusion on the sea floor is speculative. A group of soda-rich, silicic rocks that may be re— lated to a single intermittent or long-enduring magma chamber is an interesting feature in the West and East Shasta districts. The latter district includes the After- 76 thought, Bully Hill, and Rising Star mines about 14 miles east of the mines in the West Shasta district. The rocks are the Balaklala rhyolite, the albite granite, the Bully Hill rhyolite, and the associated sodic mafic rocks that occur in both districts. Igneous and sedimentary layered rocks formed in a geosynclinal environment that lasted from pre-Middle Devonian to Middle J uras- sic time. The Balaklala rhyolite is of Middle Devonian age and the Bully Hill rhyolite is of probable Triassic age yet the two rocks are essentially identical in appear- ance and mineralogy. The albite granite was intruded in Late Jurassic or Early Cretaceous time. Probably a relationship is indi ~ated here between a geosynclinal environment, sodic igneous rocks, and sodic emanations. Evidence may indicate a magma chamber of exceed- ingly long duration that contained rocks of an unusual and distinctive type. The albite granite may be an intrusion of the residual magma that remained after the extrusion of the Balaklala rhyolite and Bully Hill rhyolite. GEOLOGY AND BASE-METAL DEPOSITS, BASE-METAL DEPOSITS GENERAL FEATURES The copper-zinc ore deposits of the lVeSt Shasta dis— trict occur as massive pyrite bodies that contain chal- copyrite and sphalerite, and some gold and silver. The most striking features of the ore bodies, which have a brassy metallic appearance, are the absence of mega- scopic gangue minerals and the sharp boundaries against barren or weakly pyritized wall rock. The in- soluble material consists of quartz, sericite, clay min- erals, and unreplaced rock, and ranges in content from as little as 3.5 to as much as 35.5 percent, probably averaging about 15 percent. The massive sulfide ore is commonly separated from barren wall rock by a thin selvage of gouge; gradational contacts between ore and wall rock are rare. In a few areas, usually near or adjacent to bodies of massive pyritic ore, chalcopyrite occurs as veinlets and disseminated grains in the rock in sufficient quantity to be minable. Pyrite is subordinate to chalcopyrite in these areas, and the ore consists predominantly of quartz and chalcopyrite. Most of the ore bodies of the district are lenticular and flat lying and their greatest. dimensions are in a horizontal plane; several are saucer shaped; one is domical; and one is synclinal. Although steeply dip- ping bodies are not characteristic. of the district, they do occur at the Hornet mine at Iron Mountain, and at the Golinsky and Sutro mines. At the Iron Mountain mine the massive sulfide ore bodies, before postmineral faulting, ranged in size from a maximum of about 4,500 feet in length, several hun- WEST SHASTA COPPER—ZINC DISTRICT dred feet in width, and more than 100 feet in thickness to small bodies having maximum dimensions of only a few feet. Most of the individual ore bodies that have been mined were several hundred feet wide and 20 to 50 feet thick. Many ore bodies are discrete lenses in a broad mineralized zone, but at some mines an originally continuous ore body has been offset by postmineral faulting into separate blocks of ore; these are mined separately and are named as individual ore bodies. HISTORY OF THE MINING DISTRICT Interest in the mineral possibilities of the Shasta area was first aroused by the discovery of gold placers in Clear Creek at a point about 8 miles southwest of the present city of Bedding. Major P. B. Reading diScov- ered gold in Shasta County in March 1848 following his visit to the newly discovered gold locality at Sutter’s ‘ Mill in El Dorado County. Gold was mined in Shasta lounty as early as 1849 by emigrants traveling along the Lassen trail. Reading Springs, named Shasta in 1850, was the terminal point of one of the western routes to California that skirted Mount Lassen on the north and crossed the Sacramento River at a ford near Red— ding. The discovery of rich placer gold led to an influx of prospectors and miners soon after the discovery. The earliest settlement at that time was the town of Shasta, which is 3 miles west of Bedding. As the interest was primarily in the rich deposits of placer gold, little attention was paid by miners to de- posits of base metals that were found while prospecting for gold. Transportation difficulties and the lack of treatment plants in the early days of the district ruled out the mining of any minerals other than precious metals. Copper ore in Shasta County was known at an early date, however, as Aubury (1902, p. 24) reports that Langley’s State Register for 1859 says, in part, regarding the copper resources of the state: The ore from the vicinity of the Pitt and McCloud Rivers, Shasta County, is said to excell in richness the celebrated Ari- zona mines, and to contain in addition a considerable quantity of gold. Copper mining along the foothill copper belt of Cali- fornia was begun in 1860 and Aubury (1902, p. 25) reports: The copper excitement thus started quickly spread, and in a few months it filled the State. The period of 1862—63 was marked by a speculative mania, the organization of hundreds of copper mining companies, and the wildcat exploitation of slight surface prospects. In spite of the information on the presence of copper in Shasta County in Langley’s early report, the copper mining boom of the 1860’s did not result in the exploita‘ tion of any copper mines in the “Test Shasta district, ‘ stampede to the region ensued. ‘ in a news letter to the Mining and Scientific Press from a Whis- ‘ keytown correspondent in June 1880. He writes in part: “At BASE-METAL DEPOSITS although some copper ore was mined in the East Shasta district as early as 1865. Miners searching for gold inade sporadic attempts to mine some of the outcrops of the base-metal ore bodies that were enriched in gold, but without much success, and Aubury (1902, p. 31) ‘reports: In 1893, but two years before the beginning of the career of the iMountain Copper Company, copper was not even mentioned in a ireview 0f the mineral resources of Shasta County in a local ‘paper. However, the enormous gossan at the Iron Mountain linine attracted attention and in the early part of the sixties the mine was acquired by “'illiam Magee and j held for its possible future value as an iron ore. The discovery of silver ore in the gossan at Iron Mountain in 1879 created a great deal of local excite— ment. Aubury reports (1902, p. 36) : This dlSCOVGI' ' \YaS S0011 IlOiNEG abl‘Oad and a characteristic 3 The popular effect TS \\'911 shown ‘ this particular time, in this part of Shasta County, the silver ‘ boom is up high, and such expressions as ‘the most extensive ‘ quent. and the richest silver ledge the world has ever seen” are fre- Some five or six miles from the ancient town of Shasta 'as known to exist what was called Iron Mountain. Nothing was expected of it and no one prospected there. A curious ex— pert came from the city and has been secretly looking at its formations, assays have been made of his finds, and now the whole country is wild and claims are staked off for miles. A new silver belt has been discovered, the assays of which go away up into the hundreds.” A plant. for extracting silver from the gossan at Iron Mountain was built in 1879 by James Sallee, lVilliam Magee, and Charles Camden, and some intermittent mining was done in the silver-rich parts of the gossan from 1879 to 1895. The size and importance of the base— metal ore deposits were first realized in 1895, when pros- pecting was begun on the base-metal ores that had been found during the mining for silver. The Mountain Copper Co., Ltd. began mining copper ore in 1897; this operation revived prospecting for copper, and within the next decade most of the major mines in the lVest Shasta district had been discovered. Transportation of ore and supplies has been a con- siderable expense to the mines in the “rest Shasta dis— trict. because of the steep topography. The ores at Iron Mountain were first hauled to the main line of the Southern Pacific Railway by a branch—line railway that was completed in 1896. The branch line was abandoned in 1922 and since that time the ore has been taken from the mine to the railway by an aerial t “am. Tucker reports (1926, p. 153) : The ore from the Keystone and Stowell mines was trans- ported by aerial tram t0 bunkers at the Balaklala mine, then 77 by aerial tram to Coram, from which point it was hauled by train over the Southern Pacific tracks to the smelter at Ken- nett. Ore from the Sutro mine was trammed by mules to bunkers at the Mammoth mine. The ore from the Mammoth mine was drawn from mine chutes on the 500—foot level, into narrow-gauge railroad cars, and taken over a 2-mile electric railroad equipped with two 25-ton electric locomotives, six 25- ton steel gondola cars, and nine 10-t,on flat cars to ore bins with a capacity of 1000 tons. From these bins the ore was taken over an incline gravity railroad in skips to another set of bins. The gravity railroad has a length of 4,000 feet and a drop in this distance of 1,700 feet. The skips have a capacity of 20 tons of ore and travel at a speed of 2,000 feet a minute. From these lower bins the ore was taken to the smelter over a steam rail- road operated with three 40—ton locomotives and 22 standard steel railroad cars. The capacity of the transportation system is about 1,500 tons of ore per day. The first smelter in Shasta County was erected in 1875 in the East Shasta district. In the West Shasta district, the smelter built by the Mountain Copper Co., Ltd. began operations at the town of Keswick on the Sacramento River in 1896, and at the peak of its opera— tions in 1901 was treating 1,000 tons of ore per day. The sulfur content of the Iron Mountain ore was first reduced by heap roasting in piles of ore that were scat- tered along the railway and fired by cordwood. As much as 350,000 tons of ore was burning at one time in heaps, before charging into the blast furnace. Sulfur was not recovered from the ores of the Iron Mountain mine until about 1906. Inasmuch as the market for sulfuric acid was in the San Francisco Bay area, the Keswick smelter was dismantled in 1906 and moved to Martinez on the bay. A smelter for treating ores from the Balaklala mine was built in 1906 at Coram, which is about 1 mile below Shasta Dam, but the smelter was closed in 1911 and has been dismantled. A smelter for the ores mined by the United States Smelting Refining and Mining Co. was built 11/2 miles from Keswick in 1907. After 1919 it was operated for only a short period during 1924, and was dismantled in 1925. Copper production was at its height in the district from 1898 to 1919, and except for a spurt in production during 1924, the production has declined since 1919. Operations of some of the mines in the “Test Shasta district ceased when there was still ore in working faces, and known ore reserves. The reason for this was that the smelters along the Sacramento River that treated their ores were closed by smoke-damage litigation, and in most cases, ore reserves were not suflicient to justify the erection of a smelter at a new location. Zinc was recovered in the West Shasta district only at the Mammoth and the Iron Mountain mines. At the Mammoth mine, small bodies of high-grade zinc ore were mined separately from the copper ore and sent 78 GEOLOGY AND BASE-METAL DEPOSITS, to a zinc refinery for treatment. The zinc in the massive sulfide ore that was mined for copper was not recovered. At Iron Mountain, although all the zinc contained in ores that were direct—smelted was lost, ore from the Mattie and the Richmond Extension ore bodies was treated in a flotation plant that was erected in 1942, and zinc and copper concentrates were recovered. PRODUCTION The Shasta copper—zinc district is preeminent in copper production in California, although the produc- tion in this district since the end of World War I has been small. The copper from the East and lVest Shasta districts accounts for 54 percent of the copper produced from California to 1946, and the lVest Shasta district accounts for the major part. Zinc production has been small, although if zinc had been recovered from all the ore that was direct-smelted for copper, this district would rank among the major zinc-producing districts of the State. The value of the ore as it was mined and treated in the early days of the district gives an errone— ous impression of the present or future value of ore of this type in the Shasta district, as neither the zinc nor the sulfur was recovered from most of the ore. Also, no attempt has been made to utilize iron in the residues that result from the removal of base metals and sulfur from the ore. Residues from similar ores in other coun— tries are used as an iron ore. Table 5 gives the production of the “lest Shasta dis- trict except for the gold and silver that was produced from 1879 to 1897 from the gossan at Iron Mountain; 110 record of this gold and silver was found by the writers. The data in table 5 are from many sources, not all of which are in complete agreement, although checking WEST SHASTA COPPER-ZINC DISTRICT the figures from one source against those from another has shown that there is essential agreement in the figures for most of the mines. Most of the production data were obtained from private reports of R. T. Walker, the United States Smelting Refining and Mining Co., the Coronado Copper & Zinc Co., the Mountain Copper Co., Ltd., and from TV. A. Kerr. More detailed information on the source of the data is included in the description of each mine under “Description of deposits.” No production is known from the Spread Eagle, Sugarloaf, Balaklala Angle Station, Great Verde, Crys- tal, and King Copper prospects. The exploitation of lode-gold mines and of the lime— stone resources of the district was stimulated by the operation of the smelters. The need for siliceous flux in the smelters aided lode-gold mining, as quartz veins with a small amount of gold could be mined at that time for the silica content as well as the gold. Quarries were opened in the limestone of the Kennett to provide flux for the smelters. The Holt and Gregg quarry, 4 miles from Kennett on the road to the Golinsky mine, supplied the Kennett and Keswick smelters, and lime was also burned for other commercial uses. The Ken- nett limestone quarry was located half a mile northwest of the town of Kennett. An analysis of the lime in this quarry showed carbonate of lime 95.2, silica, 4.4, mag— nesia 0.5 percent, and a trace of carbon (Irelan, 1888, p. 572). Logan (1947, p. 234) reports: Statistics beginning with 1896, credit [Shasta] County with an output of 247,778 barrels of lime and 711,064 tons of lime- stone. The larger part of both came from the Kennett lime- stone tributary to Kennett, although quarries in the Hosselkus limestone were operated near Furnaceville and on the west side of Brock Mountain. TABLE 5.—‘Pr0duction and grade of ore of the West Shasta copper-zinc district [Published with permission of the owners. For source of production data refer to “Description of deposits”] Ore Grade Mines G 1d ' S l ' ,. Production 0 i ‘ yer Copper Zinc Iron Sulfur Insoluble I‘md (short tons) $313335) i‘ 5231,1533) (percent) 1 (percent) (percent) (percent) (percent) l Iron Mountain: i i ‘ Richmond ore body (treated by flotation), Copper-zinc _______ l 380, 000 0.02 1. 00 2. 00 3. 50 Old Mine 01e body ________________________ Copper ____________ ‘ 1 608, 000 .04 1. 00 7. 50 I 2. 0—5. 0(?) N0. 8 (disseminated ore) _______________________ do _____________ 1 820, 000 .001 .04 3. 50 _ Hornetand Richmond-Complex ore bodies, Pyrite for sulfur...‘ 3, 600, 000 .02 . 80 .40 . D _ G ,_ .. ,638.000 .07 8.21 ____________ . 3, 311,145 .038 2. 24 3 99 Do,“ ' W _ 84,000 .078 5.79 2.40 Balaklala. . ______ _ _ _ 1, 200, 000 . 028 1. 00 2. 80 Shasta King.. ...... _ .l 2 83, 889 . 034 1. 01 2. 92 Keystone. _ _ _ ______ _ . 121, 802 .06 2. 70 6.00 Stowell ____________ . l 39. 53s .03 1. 09 3. 05 Sutl'o ....... 35, 307 . 08 6. 40 7. 44 Early Bird. ‘ 40,116 .032 1. so 4. 28 _ Golinsky ______________________________________ l 4 6, 267 .134 4. 61 3. 57 ‘ l 1 Not recovered. j 2 .Essays are for 68,889 tons mined by United States Smelting, Refining, and M in- ng o. ‘ a Assay from 11 stope samples. 4 Assays are for 3,078 tons mined by United States Smelting, Refining, and Min- ing Co. 5 Assay from 10 stope samples. ° SiOz. BASE-METAL DEPOSITS CHARACTER AND DISTRIBUTION Most of the ore in the W'est Shasta district is the massive sulfide type. Minor varietal difierences occur and some disseminated copper ore has been found, but the relatively small amounts of ore of other types only emphasize the predominance of the massive sulfide ore. The varietal types of ore, found either adjoining the characteristic massive sulfide ore, or as separate bodies, are: banded massive sulfide, ores that contain a high percentage of zinc, chalcopyrite ore that normally con- tains chalcopyrite and pyrite in equal amounts in a siliceous matrix, and bodies of magnetite. To these .might be added some areas of heavily pyritized rock that could, under some conditions, be mined for their :sulfur content. 1 With few exceptions, during mining the distinction ‘between ore and waste in massive sulfide bodies was : determined by the copper content. The ore was for the imost part treated by direct smelting, and zinc, iron, “ and sulfur were lost. Massive pyrite that contained . only small amounts of copper was considered waste at ‘ all the mines except Iron Mountain. Small bodies of , high-grade zinc ore were mined separately at the Mam- . moth mine, and zinc was recovered by flotation from the Richmond Extension ore body at Iron Mountain, but 3 most of the zinc mined in this district was lost, although i the content of zinc generally exceeds copper. An exact ratio between copper and zinc in the ores of the district cannot be obtained because of the lack of assays on zinc at many of the mines. All the reliable data on zinc content of mined ore are listed in table 6. I TABLE 6.——Prodaction and grade of copper and zinc ore from five mines in West Shasta copper-zinc district [Sulfur was recovered only by the Mountain Copper Co., Ltd.] G rade . Production M me (short tons) Copper Z inc (percent) (percent) Balaklala _____________________________________ 1, 200, 000 2. 8 1. 3 Golinsky ,,,,,,,,,,,,,,,,,,,,,,,,,,,,, _ . . 3. 078 3. 57 8. 9 Iron Mountain (Richmond ore body) ._ 380, 000 2. 0 3. 5 Keystone. ,_ 121, 802 6.0 8.0 Mammoth... 3, 395, 145 . 3. 95 4. 62 i The massive sulfide ore is well named; in many ore bodies sulfide minerals, principally pyrite, make up 90 to 95 percent of the mass, and the ore has a brassy metallic appearance. In a few specimens grains of sul- fide are too small to be distinguished megascopically; in other specimens clusters of coarse pyrite cubes as much as 5 millimeters across are set in a matrix of fine- grained pyrite that has an average grain size of 0.5 millimeter or less. Differences are so slight that speci- mens from one mine cannot be distinguished from those 79 from another mine; ores in the same mine vary as much in appearance as ores from different mines in the district. The massive sulfide ore is generally structureless. Minor color differences due to a greater or smaller con- tent of chalcopyrite or sphalerite are seen locally. Parts of ore bodies that contain more than the normal amount of interstitial gangue minerals form irregular areas that have indefinite boundaries. Some ore tends to be well jointed and breaks into blocks; nearby parts of the same ore body are very strong, and the ore breaks with an almost conchoidal fracture. In large bodies of massive pyrite, such as those at Iron Mountain, the walls and back in open stopes stand well if a screen of ore a few feet thick is left between the stope and the wall rock. Walls of waste rock will slough into the open stope if the ore is mined to the wall. At a few locations the massive pyrite is veined by either chalcopyrite, sphalerite, quartz, or calcite. The veins are small, rarely more than 1 inch thick, and are not common. Massive sulfide that contains small quantities of cop- per and zinc occurs at many of the mines; it is valuable at present only for sulfur, which has been recovered from ore from the Iron Mountain mine. The massive sulfide that contains low—grade copper and zinc occurs as separate ore bodies and also in parts of ore bodies that contain higher grade copper and zinc. Large bodies of massive sulfide in the Iron Mountain, Mam- moth, and Keystone mines contain low-grade copper and zinc. In some mines the upper or the lower part of a flat—lying ore body contained too little copper or zinc to mine for these metals and was left in place. In other mines, or at a different locality in the same mine, irregular areas within one ore body may be lower in copper and zinc than other areas. The range in grade is not great, and the appearance and character of the ore is the same. The contact is gradational be- tween massive sulfide that was considered “ore” and massive sulfide that was considered “waste,” and in these places the exploitation of a stope depended on the copper and zinc assays. All massive sulfide contains some copper and zinc—the lowest-grade mass, the Hor- net ore body at Iron Mountain, contains 0.5 to 1.0 per- cent of copper. Content of copper and zinc as shown in assays is the only distinguishing feature between high-grade and low-grade copper and zinc ore bodies. Indistinctly banded to well-banded massive sulfide ore occurs at a few places in some mines. The banding is caused by dark-gray parallel streaks of sphalerite, or more rarely by streaks of chalcopyrite. The streaks range from a few millimeters to l centimeter in width and have hazy, indefinite boundaries; they generally 80 GEOLOGY AND BASE—METAL DEPOSITS, WEST SHASTA COPPER-ZINC DISTRICT parallel the foliation in the wall rocks, according to observers whohave seen this type of ore in underground exposures in the district (Walker, R. T., Bagley, T. P., and Hunt, R. N., oral communication; Hershey, O. H., private report for the Mountain Copper Co., Ltd.) . EX— amples of banding due to alternate layers of coarse and fine pyrite, similar to that described by Brownell and Kinkel (1935, p. 27 7), were seen at Iron Mountain, but they are not common. Ptygmatic folding in banded ore, such as that described by Gavelin in the ores of the Maliinas district (Gavelin, 1939, p. 141) has not been observed here. Small areas of high—grade zinc ore occur at the Iron Mountain mine; the Richmond Extension ore body con- tained sufficient zinc in veinlets and in grains interstitial to pyrite to justify making a zinc concentrate by flota- tion. Massive sulfide that contains a high percentage of grained than most massive sulfide, and is found as small isolated ore bodies for the most part, rather than as zinc-rich parts of the main ore bodies as at the Iron Mountain mine. High-grade zinc ore bodies were mined at the Mammoth mine. Although they have the mega— scopic appearance of a massive sulfide ore, the percent of insoluble material was 35.5 before and 16.8 after sorting.4 Ore that consists of chalcopyrite and pyrite as vein- lets and disseminations in schistose rock occurs in quan- tity at the Iron Mountain mine, and is described in de- tail in the description of that mine. The ore consists of chalcopyrite stringers and veinlets, largely parallel to the foliation, and of disseminated grains of chalcopy- rite in siliceous foliated rhyolite. The pyrite content generally equals chalcopyrite and occurs as discrete grains. The body of disseminated ore is separated from the nearby massive sulfide ore bodies by barren rock; there is no gradation between the two types at the Iron Mountain mine. The only other known occurrence of disseminated copper ore in the district is at the Balaklala mine. At .‘this mine, the disseminated copper ore lies below the ‘u‘ massive sulfide body and is in contact with it. Veins and stringers of chalcopyrite in siliceous rhyolite par- allel the contact of the massive sulfide body. The ton— nage of disseminated or vein chalcopyrite ore at the Balaklala mine is small. Deposits of disseminated pyrite, although not now commercial, under some conditions could be a source of sulfur. These deposits differ from the massive sulfide ore in that they contain much gangue and unreplaced ‘Data furnished by Mining Co. the United States Smelting Refining and X that they contain no gold or silver. rock, do not have sharp boundaries, and the pyrite is coarser grained. The pyrite thus far exposed in the Sugarloaf prospect east of Iron Mountain is of this type. Similar deposits occur in the district; some are separate bodies, but others form bands adjacent to or near bodies of massive sulfide. Deposits of disseminated pyrite con- tain 50 to 70 percent of pyrite, commonly as separate euhedral crystals (cubes) in a matrix that is composed almost entirely of secondary quartz. Such bodies rarely have sharp walls, and they fade out into weakly pyri- tized rocks and may contain much unreplaced rock ma- terial. Little copper and no zinc accompanies this type of ore, and the few assays that are available indicate No gradation be- tween the normal massive sulfide ore and the pyrite- quartz rock has been seen in any of the mines, except at \ the ends of some ore bodies. zinc occurs mainly in the Mammoth mine; it is coarser , STRUCTURAL FEATURES FORM OF THE ORE BODIES In the major mines in the district the ore zone dips gently or is flat lying; within the zone, most of the individual ore bodies are flat lying. The length and width are commonly 2—10 or more times greater than the thickness. Most of the ore bodies occur as pods, lenses, pancake—, kidney- or cigar-shaped forms, al— though a few small ones have irregular shapes. Many are bent or warped. The Iron Mountain ore body, which has a lenticular vertical cross section in the cen- tral part, is also synclinal; the Balaklala and Shasta King ore bodies are lenticular in vertical cross section but are sancer- or basin-shaped forms. The ore zone at the Mammoth mine occurs along the crest of a broad elongate arch, and is thickest along the crest. The small Mattie ore body at Iron Mountain has a flat-lying cigar- shaped form. The Early Bird ore body also is horizon- tal, but has a lenticular and in part synclinal vertical cross section. The only lenticular ore body that has a steep plunge is in the Golinsky mine. W’here primary rock structures can be determined, the flat-lying or gently dipping ore zones generally fol- low primary structures in the enclosing rocks, such as contacts between flows, but the location of some of the smaller, steeply dipping ore bodies is probably con- trolled by a steep foliation. Metallization, which consists chiefly of pyritization, is widespread in the district. Bodies of partly pyritized rock cover an area of several square miles; most of the rock contains some pyrite. Massive sulfide ore bodies occur as sharply bounded discrete bodies in the broad zone of pyritization or ore zone. There is no correlation in many instances between the amount of scattered pyrite in the broad zone of pyritization and the location BASE-METAL DEPOSITS 81 of bodies of massive sulfide ore, and there is normally no gradation between pyritized rock and massive sulfide. ‘The distribution of the ore bodies, pyritized rock and hydrothermal alteration is shown on plate 4. No pat— tern in the lateral distribution of mines is shown on the niap, but this lack of pattern is somewhat deceptive, as described under “Summary of base-metal ore controls.” The vertical location of the ore zone is controlled by the stratigraphy in the Balaklala rhyolite. Ore bodies have been discovered, with a few exceptions, only Where the favorable zone has been exposed along the walls of can- yons and has not been removed by erosion. TYPES OF CONTACTS BETWEEN ORE AND WALL ROCKS j The contact is sharp at most places between massive sulfide bodies that normally contain less than 10 percent of gangue minerals and wall rock that normally con- tains less than 10 percent of pyrite, or no pyrite at all. There are no frozen contacts between massive sulfide and wall rock. The contact between massive sulfide and {wall rock is generally marked by a gouge of white clay that ranges from a thin film to a zone several feet in thickness. The rock near most contacts is hydrother— imally altered and foliated; there is normally a gradation Ibetween gouge and foliated wall rock, and at some places the foliated wall rock grades within a few feet ‘to nonfoliated wall rock. In this type, the massive sul- fide ends abruptly against gouge; the sulfide has a smooth wall, but shows slickensides or other evidence of movement at only a few places. No change in the i appearance of the massive sulfide near contacts is ap- jparent. Relict quartz phenocrysts from the rhyolite j can be found in the foliated rock and at a few places j they have been found in the White clay gouge. ‘ Although many ore bodies have blunt, rounded ends . and a sharp contact with barren wall rock a few have : gradational contacts between the massive sulfide and wall rock. At the Shasta King mine, for example, mas- : sive sulfide grades to pyritized rock along the ends of ‘ the ore body. The sulfides at these places replaced foli- ‘ ated rocks preferentially along the foliation. At Iron ‘ Mountain a few contacts were seen in which the foliated wall rock contained streaks of disseminated pyrite cubes parallel to the foliation and to the massive sulfide. In this example, and as mentioned above, there is evidence that the foliation was presulfide in age. At a few localities foliated rock adjoining the mas- sive sulfide may contain irregular bodies of pyrite a few inches to a few feet long, which have hazy, grada- tional boundaries. A main gouge is always present at the outer edge of this pyritized zone; such contacts indicate incomplete replacement along a gouge. RELATIONSHIP OF ORE BODIES TO STRUCTURES IN THE HOST ROCK RELATIONSHIP TO STRATIGRAPHY The minable ore bodies that have thus far-been found are at the same general stratigraphic zone in the Balak- lala rhyolite throughout the district, and even where no ore bodies occur, the rocks at this zone are more or less pyritized. The favorable stratigraphic zone is the group of flows and pyroclastic rocks that underlie the base of the coarse—phenocryst rhyolite in the central part of the district, or below the tuft beds that are the stratigraphic equivalent of the coarse—phenocryst rhyo- lite in the outer parts of the district. Ore occurs through a stratigraphic thickness of 600 feet at Iron Mountain, and the ore zone may locally have a greater thickness. In terms of the three units of the Balaklala. rhyolite, as described in detail under “Balaklala rhyo— lite,” the ore zone is along the upper part of the middle unit. Details of the types of rock associated with the ore bodies are included in the descriptions of the individual mines. The upper part of the middle unit of the Balaklala rhyolite is called the favorable zone, or the ore zone, as it contains all the known ore bodies in the mineral belt. It is composed of a group of discontinuous flows, and of lenticular beds of coarse and fine pyroclastic ma- terial; more of the bedded, water—deposited tuff and volcanic conglomerate is present in this zone than in any other zone in the Balaklala. The heterogeneous nature of this material makes the detailed stratigraphy at each mine unique, yet it is possible to locate the ore zone with a fair degree of certainty because this heter- ogeneous group is capped by a recognizable unit throughout the district. Thus at the Iron Moun’ain mine, although the coarse—phenocryst rhyolite flow was either eroded or did not extend as far south as Iron Mountain, the lithology of the tufi' beds above the ore zone is characteristic of the tufi' beds that are the strati- graphic equivalent of the transition zone at the base of the upper unit of the Balaklala, and the rocks in which the ore occurs are lithologically characteristic of the middle unit of the Balaklala. Similarly, the tufi' beds that overlie the Stowell and Keystone mines and the Spread Eagle prospect are characteristic of the material that occurs either as the stratigraphic extension of the coarse-phenocryst rhyolite or of the material that forms a transition zone immediately below this rhyolite of the upper unit. In the Balaklala, Mammoth, and Sutro mines, the ore bodies lie in the middle unit of the Balaklala rhyo- lite immediately below the coarse—phenocryst rhyolite, but the Shasta King ore body is lower in the middle unit, probably several hundred feet below the base of 82 GEOLOGY AND BASE-METAL DEPOSITS, the upper unit, which is eroded from above the Shasta King. The ore body at the Golinsky mine is also prob- ably several hundred feet below the base of the upper unit, although the relationship at this mine is not as clear as at the other mines. The thickness and types of flows, and the amount and type of pyroclastic material varies widely in the middle unit, and this unit cannot be used alone as a horizon marker. It is necessary to use a combination of the lithologic types characteristic of the upper unit, and the widespread nonporphyritic flows of the lower unit, as well as medium-phenocryst flows and tuff beds of the middle unit, to determine the stratigraphic posi- tion of the ore zone at any one locality. Pyritization in the ore zone is more widespread than the position and the extent of the known ore bodies on plate 4 would indicate. Many drill holes in the cen- tral part of the district have cut through the coarse- phenocryst rhyolite and into the upper part of the mid- dle unit. Most of the holes drilled between known ore bodies encountered pyritized rock at the stratigraphic position of the ore zone; they show that the pyritized zone is continuous although massive sulfide ore is in discrete bodies. At some places the character of the rock that was replaced by ore can be determined; the favored host rock for ore bodies appears to be a porphyritic rhyolitic flow that contains 2- to 3-millimeter quartz phenocrysts. In most ore bodies this rock was unsheared at the time of replacement, and commonly the ore-bearing flow is overlain by thinly bedded tufi' or fine pyroclastic ma- terial. This is particularly well shown at the Shasta King mine, in the glory hole at the Balaklala mine, and at the Mammoth mine. RELATIONSHIP TO FOLDS AND FOLIATION Individual ore bodies, as well as broad pyritized zones that contain several ore bodies, tend to be concentrated on or near the axes of folds. Although synclinal and basin-shaped ore bodies predominate, ore bodies were formed both in anticlines and in synclines, but some occur on the flanks of folds. At a few mines the pri- mary layering of the host rock is not sufficiently ap- parent to allow the mapping of detailed structures, and the relationship between primary structures and the location of ore is not known. Bedding is well developed in some types of volcanic material in the West Shasta district, but is lacking in others. Where bedded pyroclastic rocks are present, the large and small folds and warps in the rocks can be recognized, but in parts of the area only the broad structures such as can be interpreted on the basis of large units are decipherable. At the mines where bedded material is present or flow contacts can be WEST SHASTA COPPER—ZINC DISTRICT mapped, it was possible to relate the location of ore to the location of folds. Examples of ore bodies in synclines or basin—shaped warps are the Richmond ore body of the Iron Mountain mine and the Balaklala, Shasta King, and probably the Early Bird mines; in these mines the plunge of the folds is gentle. The general ore zone at the Mammoth mine is on a broad arch or dome—shaped structure, and some individual ore bodies within this zone are on minor arch structures. At many places in the district pyritization favors the crests of small folds, or is concentrated under flat rolls in the dip. The Sutro, Keystone, and Stowell mines and the Old Mine ore body of the Iron Mountain mine are probably on the flanks of broad folds, although the folds at these mines could not be mapped in detail except at Iron Mountain. The rhyolitic rocks in the mineral belt are only locally ‘ strongly foliated probably because the folds are broad, but the two types of foliation that develop in flexural- slip folding, both bedding—plane foliation and fracture cleavage, have had a considerable eflect on ground prep- aration before ore deposition. _ Flexural-slip folding, in which movement along bed- ding planes is concentrated in the incompetent layers, is found locally in the West Shasta district. The platy minerals that are formed in these layers are oriented parallel to bedding (Knopf and Ingerson, 1938, p. 159— 161; Swanson, 1941, p. 1256). This bedding—plane folia- tion is concentrated along layers of bedded pyroclastic material, and appears to be as strongly developed on the axes as on the flanks of folds, suggesting some slippage parallel to fold axes. This type of foliation is most common where bedded material between flows is a few inches to a few feet thick; where the bedded material is thicker, foliation is commonly limited to a zone at the top or bottom of the bed. Poorly developed to well-developed fracture cleavage in competent layers occurs in conjunction with bedding- plane foliation. Fracture cleavage as here used follows the usage of ‘Leith (1923, p. 148—150) and Balk (1936, p. 706); the cleavage ranges from slightly more than subparallel jointing to foliated rocks with reorientation of minerals along cleavage planes. The common type of fracture cleavage in the district has the appearance of closely spaced sheeting in which the rock is divided into lenticles of unaltered rock separated by seams of oriented sericite. The cleavage planes are spaced a few milli— meters to 4 centimeters apart. In a few areas the planes of sheeting on which sericite has formed are so closely spaced that the rock has the appearance of a sericite schist, although in thin section the distinction between sericite seams and rock that has not been recrystallized is sharp. BASE-METAL DEPOSITS Fracture cleavage is found at many places in the district, but is not widespread in the sense that it is cohtinuous. The characteristic feature of this type of foliation is the range in intensity of sheeting in short distances and the lack of continuity either along or across the strike. The lack of continuity may be more apparent than real, as the bodies of sheeted rock have a jplunging linear element. Sheeting may occur in one flow along a fold axis but not in the overlying or under— lying flows because of a difference in competence. In plunging folds the body of sheeted rock would appear as an irregular area in a horizontal plane. The fracture cleavage is steep, and although it tends to have a re- gional orientation and is related to folding, it is not axial plane cleavage. 3 During the folding steep fracture cleavage formed in parts of the lower and middle units of the Balaklala rhyolite, particularly along axes of folds, but cleavage is rare in the upper unit except in the thin, outer edges of the coarse-phenocryst rhyolite dome. Locally it is well developed in the flows underlying the upper unit, particularly in flows capped by fairly continuous beds of pyroclastic material. The coarse—phenocryst rhyo— lite is the most competent rock in the Balaklala, but the nonporphyritic rhyolite of the lower unit and the Jmedium-phenocryst rhyolite of the middle unit are also lcompetent except where they contain layers of bedded 83 pyroclastic material. Bedding-plane movement accom- panied by foliation was concentrated in the layers of bedded pyroclastic material in the upper part of the middle unit where these beds are most common (fig. 38). The intersection of steep fracture cleavage and flat foliation controlled by bedding is one of the principal factors that localized the ore on folds, because a zone of rock With steep fractures was formed along the crest of a fold or dome under a relatively impervious cover formed by beds with flat foliation. RELATIONSHIP TO FAULTS Premineral and postmineral faults are present in the district. Most of the ore bodies are localized near major faults or shear zones that trend about N. 70° E., but are not necessarily adjacent to them. In a few places it is evident that these premineral faults were feeder chan- nels for mineral-bearing solutions. At Iron Mountain, the Camden-Sugarloaf fault is . premineral, and may have been a channel for the min— . eral-bearing solutions that formed the main ore bodies as well as the areas of pyritized and altered rock that are present along the fault southwest and northeast of the main ore bodies. Similarly, the ore bodies at the Balaklala mine are localized near the Balaklala fault, and at the Mammoth mine they are localized near the California fault. SE ". Erosion surface ’..%.;'.V. NW. I 999» . . "9....,..\ ...9.. .. o... .. .. 7 Va o9320:9303o3030zoz‘3o303a.avz.’a3£o3§®303£€3zavaas ma .‘3’9‘9’.’.’.’9‘.’.§’.’...’.’.’.’99)’.’.’93”.’.’.’.’.’.$’.’.’.’. .’.’.‘9~.~.'.'." M... 9’.’.’.’.‘9’.’.’.’.’.’.’.’.’.’.’.’.‘.’.’.’.9~.3.’.’.’.’.’. .’ ’.’.’.’.’.’.’9’.’.’9’.’9’ " V°'°‘"‘° ' 9............ .099; ftaaee.......‘9.9........... ’.’.‘.’.’.’.’.’.’9’ V “*€%3‘9’.’.’9’.”:’.’.’.’9’.’.’. i .......... l .,f\.....’......,.,. . y . .3.:.:.:.:.:.:.:.:.’ 1 * Q.:.:.:.:.:.:.:.:9z.,.,.’ “zaxaarcsaaaz'asr .... .. ‘9 _ f‘ x. Q‘...’...... l, tuff an volcanic brecua ZMZW I” k‘fi‘23393‘303’3’3”: ‘ Wm” ' ‘3’“ ‘9‘ A ., GWW-IJ 7' u. MW‘fi‘W \Nfi% fiW§®fig§9 { Ore zone tag i “We. l 0" M “W l Fracture cleavage 4—D Foliation parallel to bedding Approximate scale FIGURE 38.—Diagrammatic drawing showing the relationship between bedding-plane foliation, fracture cleavage, and pyritized zones at the Mammoth mine. 84 GEOLOGY AND BASE-METAL DEPOSITS, Premineral and postmineral faults can be distin- guished, even though in most examples postmineral movement has occurred along a fault that was originally premineral in age. Evidence that a fault is premineral in age is shown by pyritized and hydrothermally altered rock along the walls, or centers of metallization at several points along the fault. Ore bodies that form along a fault and terminate abruptly against it with no evidence of being cut off, also indicate that the fault guided solution travel. Contacts of ore bodies that show banding parallel to shear zones, consisting of al- ternating bands of pyritized and barren rock, are inter— preted as incomplete replacements of sheared rock along the fault. Postmineral faults, many of which contain several feet of gouge, offset ore bodies from a few inches to as much as 300 feet. Few ore bodies in the district still retain their original form; most are divided by post- mineral faults into separate blocks of ore that were mined individually. Thus at Iron Mountain, the Old Mine, Brick Flat, Richmond, and the Hornet ore bodies, each of which is offset several hundred feet from the other by faults, were originally parts of one continuous body of ore. The Balaklala, Shasta King, and Early Bird ore bodies are cut by faults that offset the original ore bodies into separate blocks. Many postmineral faults in massive sulfide, with a displacement from a few inches to a few tens of feet, are seen in underground workings. Along these faults the face of the sulfide body has a striated brassy mirrorlike slickensided sur‘ face; on other postmineral faults a gouge is present. This gouge consists of crushed sulfide minerals and small rounded slickensided fragments of ore in a clay- ]ike matrix that is colored dark gray by the crushed sulfides. I MINERALOGIC DESCRIPTION GENERAL FEATURES The mineralogy of the hypogene sulfide ore bodies in the “Vest Shasta district is not complex. The ore bodies are massive sulfide that contains mainly pyrite, chal- copyrite, and sphalerite, and minor amounts of magne- tite, galena, tetrahedrite, and pyrrhotite. Gangue minerals are quartz, sericite, chlorite, calcite, barite, and zoisite. The sulfide ores contain small amounts of gold and silver, but no silver minerals or gold were recog- nized. Sulfide minerals constitute from a minimum of about 65 to a maximum of about 98 percent of the massive sulfide ore. Assays of samples from 1,400 feet of drill core of massive sulfide ore from the Hornet ore body at the Iron Mountain mine averaged 2.68 percent silica, and the average of 3,600,000 tons mined from this ore body was only 3.5 percent insoluble material. The zinc ore mined at the Mammoth mine averaged 35.5 WEST SHASTA COPPER-ZINC DISTRICT percent insoluble material, the highest of any of the massive sulfide ores, but this included barren rock as the ore after sorting contained only 16.8 percent insoluble. Two small bodies of iron oxides that contain magne- tite, hematite, and limonite are in the Iron Mountain area. These are replacement bodies of iron oxides that are separated from the massive pyritic ore by porphyrit- ic rhyolite, and their genetic relationship to the massive sulfide deposits is not known. Specimens of magnetite found on the dump at the Spread Eagle mine, indicate that bodies of magnetite are present in the mine. Mag- netite also occurs as tiny grains in a few specimens of massive sulfide ore, but it is not common. Scheelite is not known in the massive sulfide deposits. However some of the biotite-quartz diorite in Clear Creek in the Igo quad “angle has thin coatings of schee- lite along fractures. The mineralogic study of the \Vest Shasta copper- zinc district is incomplete. The Iron Mountain mine was the only operating mine in the district during the period of investigation from November 1945 to June 1952, although many of the workings in ore at the Shasta King and Early Bird mines were accessible. Specimens of sphalerite from the Yolo zinc ore body of the Mammoth mine were studied from the Lindgren col- lection, which was kindly loaned to the writers by Prof. Robert R. Shrock of Massachusetts Institute of Tech- nology. Other specimens of zinc-rich ore from the Mammoth mine were studied from the Grotefend col- lection, which is on display at the California Division of Mines office in Redding, Calif. Some specimens of zinc- rich ore collected along the tramline near the Stowell mine were studied, together with specimens of pyritic ore from mine dumps. The supergene—enriched ore was not observed underground, and only a few specimens were available for examination from the Old Mine ore body at the Iron Mountain mine. The list of minerals in the West Shasta copper—zinc district is tabulated below. Jlincrals in West Shasta coppereiac district Hypngene minerals : ()re minerals : Uhalcopyrite _________ CuFeS: Galena ______________ l’bS lold ________________ Au Greenockite( ‘:) ______ (ids Hematite ____________ F9203 Ilmenite _____________ FeTiOa Magnetite ____________ FexOl Pyrite _______________ Fesg Pyrrhotite ___________ FeHS Sclieelite ____________ CaW04 Silver _______________ Ag Sphalerite ___________ ZnS BASE-METAL DEPOSITS 85 Minerals in West Shasta copper-zinc district—€011. Hypogene minerals—Continued ‘ Ore minerals—~Continued Talc ________________ HgMg. ( SiOa) .-, - H20( 1') Tennantite __________ SCUzS‘2(Cu1“€)S‘2AS2S3 Tetrahedrite _________ soms- (CuFe) S 22811283 Gangue minerals: Barite _______________ BaSOi Calcite ______________ 03.003 Chlorite _____________ (Mg,1<‘e)5(A1,Fe+++)2Si30m(0H)s Quartz ______________ SiOZ Sericite and hydro— mica ______________ KAhSHOm ( 0H) 2 Zoisite ______________ Ca2A13( S104) 3 (OH) Stipergene minerals : Oxide zone: Antlerite ____________ C113(OH)4SOA Azurite ______________ Cl13( (7.092 (0H) 2 Chalcanthite _________ CUSW'SI’LO Copper ______________ Cu Cuprite ______________ Cuo Copiapite( ?) ________ Basic ferric sulfate. Goslarite ____________ ZnSO. - THZO Limonite ____________ Hydrous iron oxides. Maghemite __________ F9203 , Malachite ___________ OH (OH) 2 ' CuCOg . Melanterite __________ F9504 - 7H20 j Silver ________________ Ag . Smithsonite( ?) ______ ZHC03 ‘ Sulfur ______________ S .i Wad ________________ Hydrous manganese oxide. Sulfide zone: Chalcocite ___________ Cqu Covellite ____________ CuS HYPOGENE MINERALS ORE MINERALS Chaimpyritc, CuFeSZ.——Chalcopyrite is present in all the massive sulfide deposits in the district, in the dis- ;seminated copper depOsits of the No. 8 mine and the . adjoining Confidence-Complex ore bodies at Iron Moun- 3 tain, and in the disseminated ore at the Balaklala mine. It also occurs in minor quantities in the gold-quartz 'j veins in the district. In many of the low-grade pyritic . deposits, such as the Hornet ore body which averaged only 0.40 percent copper, chalcopyrite cannot be detected f except under a microscope. It commonly occurs, along 3 with a little sphalerite and gangue minerals, as a thin . network 0.2 to 0.3 millimeter thick surrounding grains 3 of pyrite and through fractures in pyrite. In massive ‘ sulfide ore, the chalcopyrite has little corrosive effect upon pyrite, and mainly replaced a thin selvage of gangue minerals between pyrite grains, or forms poorly defined streaks, irregular patches, or veinlets a few inches thick in massive pyrite. All the zinc ore contains some chalcopyrite, either as minute globules of chalcopyrite, which are unevenly dis- : tributed through the sphalerite and which may have formed by unmixing during cooling (Buerger, 1934, p. 525~530), or as streaks or irregular masses in massive sphalerite. In places the chalcopyrite occurs as irregu— lar, worm—shaped inclusions that form a pseudoeutectic texture. Some chalcopyrite was observed in the gold-quartz veins in the Igo area, in the Igo quadrangle; in the Old Diggings district, in the Shasta Dam quadrangle; and at the Uncle Sam mine, in the central part of the district. Quartz-chalcopyrite veins occur in the No. 8 mine and the Confidence-Complex workings at the Iron Mountain mine. Galena, PbS.-—Galena was observed only in specimens from the zinc-rich Yolo ore body at the Mammoth mine, and in the zinc—rich parts of pyritic ore bodies, at the Iron Mountain, Stowell, Sutro, Golinsky, and Shasta King mines; it is always associated with sphalerite. Gralena occurs as irregular grains 0.1 to 0.2 millimeter in diameter in gangue minerals in sphalerite, along con- tacts between gangue and sphalerite, and as inclusions in sphalerite. Figure 39 is a polished section of zinc- rich ore from the Mammoth mine, which contains galena ( 9) that appears to be corroding sphalerite (8). Gold, Au.——Gold occurs in small amounts in massive sulfide deposits in the “rest Shasta copper-zinc district; it also occurs in gold-quartz veins in the Uncle Sam and Clipper mines in the central part, of the base-metal dis— trict and in many quartz veins of the district, although Galena A few grains of pyrite (p), quartz (dark gray), and chalcopyrite (c). X 50. FIGURE 39r~Pliotomicrograph of ore from the Mammoth mine. ((1) appears to corrode sphalerite (a). 86 GEOLOGY AND BASE-METAL DEPOSITS, WEST SHASTA COPPER-ZINC DISTRICT it is rare in veins in the biotite-quartz diorite. Placer gold has been mined from most of the stream gravels and from a few areas in the gravel of the Red Bluff formation. Gold in recoverable amounts occurs in most of the massive sulfide deposits and in gossan derived from these deposits, but no gold was found in the polished sections studied. Greenoclcite(?), 0dS.—No cadmium minerals were definitely recognized in the massive sulfide ore, although in one specimen of zinc—rich ore from the Mammoth mine, thin films of a yellow, transparent mineral be- tween a limonite coating and massive sulfide may be greenockite. Cadmium was recovered during 1917—18 from the ores of the Mammoth mine. Spectrographic analyses of massive sulfide ore from the Mammoth, Early Bird, Balaklala, and Iron Mountain mines were made by the Geological Survey. A specimen of zinc- rich ore from the Mammoth mine contained 0.1 to 1 percent cadmium, and a specimen of massive pyritic ore from the Balaklala mine contained 0.01 to 0.1 percent cadmium. The other samples all had less than the threshold value of 0.01 percent of cadmium. Hamilton (1922, p. 241), reporting on the Mammoth mine, says: Cadmium there occurs [at the Mammoth mine] associated With zinc sulfide, sphalerite, probably as the sulfide greenockite. Eakle (1928, p. 47) states: Cadmium as greenockite occurs in the copper—zinc ores of [Shasta] County and the Mammoth Copper Company recovers it in their electrolytic zinc plant. Murdock and “Ebb (1948, p. 164) report: Several thousand pounds of cadmium were produced [1917—18] at the Mammoth Copper Company plant, presumably from cadmium in the sphalerite. This may in part be as greenockite associated with the sphalerite * * * Hematite, F 6203.—Specular hematite, which is strongly anisotropic from colorless to brownish-purple, makes up about 10 percent of the two small magnetite bodies at Iron Mountain. This mineral has a radial, platy structure, the plates of which are 0.5 to 1 milli- meter long. No hematite was observed in primary mas- sive sulfide ore. I lmem'te, F e] ’2'03.—Ilmenite was not observed in any of the massive sulfide deposits, but it occurs in small quantities in the two magnetite bodies at Iron Mountain as tiny irregular plates intergrown with magnetite. A sample of the magnetite contained 0.25 percent titanium oxide. Magnetite, F6304.—Magnetite occurs at Iron Moun- tain as two lenses several hundred feet long that lie along the side of, but not in contact with, the massive sulfide ore. Other occurrences are at the Spread Eagle mine, where magnetite was found on a dump, and as minute black grains, that megascopically, are visible disseminated through some of the high-grade chalcopy- rite-pyrite ore from the Clark ore body of the Mammoth mine. Under the microscope magnetite is seen to be dis- seminated through gangue that is interstitial to pyrite. Pyrite, F eSZ.—Pyrite is the predominant mineral in the massive sulfide deposits. The pyrite ranges in con— tent from about 96 percent in the Hornet ore body of the Iron Mountain mine to less than 10 percent in the zinc ore bodies of the Mammoth mine. It is dissemi— nated through much of the Balaklala rhyolite in amounts about as much as 15 percent by weight, par- ticularly where the rhyolite is hydrothermally altered. Pyrite is also widely disseminated in all the pre-Creta- ceous rocks, although it is rarely present in the Shasta Bally batholith. Megascopically, massive pyritic ore looks very fine grained, but it contains a few disseminated 1— to 2- millimeter euhedral pyrite cubes or, less commonly, pyritohedrons, and some irregular clumps of more coarsely crystalline pyrite averaging as much as 2 milli- meters in grain size. Under the microscope the pyrite is seen to be in euhedral, subhedral, and fractured grains about 0.1 to 0.4 millimeter in diameter separated by a thin net- work, from 0.05 to 0.5 millimeter thick, of chalcopyrite, some sphalerite, and quartz and rock gangue (figs. 40 FiGI‘RE 40.—Pliotomicrograph of ore from the Golinsky mine. (11) with minor chalcopyrite (v) and quartz and rock gangue (dark gray), X 50. Pyrite BASE—METAL DEPOSITS 87 and 41). In places pyrite forms a granular aggregate without the thin network of gangue and chalcopyrite. The pyrite that is disseminated throughout much of the Balaklala rhyolite is much coarser grained than that in the massive sulfide ore. Individual grains are gen- erally 1 to 2 millimeters in diameter but a few cubes are as much as 1 centimeter. This more coarsely crystalline pyrite commonly occurs as euhedral cubes or less com- monly as pyritohedrons. Pyrrhotz’te, F61_XAS'.——Py'1'1‘liotite was observed in only one polished section of a high—grade chalcopyrite ore from the Iron Mountain mine. This polished section contains massive pyrrhotite surrounding pyrite. Scheelite, CalV04.—Thin films of scheelite are pres— ent in biotite—quartz diorite along Clear Creek in the Igo quadrangle. No scheelite was observed in any of the massive sulfide deposits. Silver, Ag.—No silver minerals have been seen in any massive sulfide deposits, although silver has been re— covered from the ore. The Old Mine ore body at Iron Mountain averaged 1.0 ounce of silver per ton. Copper ore produced from the Mammoth mine averaged 2.24; ounces of silver, and the zinc ore averaged 5.79 ounces of silver per ton. T etrahedrite is present in the zinc- rich ore and may account for a higher silver content. High-grade silver veins were mined during the late 19th century in the South Fork mining district 21/2 miles northwest of Igo in the Igo quadrangle (Tucker, 1926, p. 201—210). Tucker reports that these veins FIGURE 41.—Photomicrograph of ore from the Early Bird mine. Pyrite (p), quartz and rock gangue (dark gray), and minor chalcopyrite (c), X 50. contained native silver, tetrahedrite, argentiferous galena, sphalerite, pyrite, and small amounts of gold in quartz veins in granodiorite. The principal mine was the Silver Falls mine. Sphalerz'te, Z71S.—Most of the sphalerite in the mas- sive sulfide deposits is a fine-grained, reddish-black va- riety that probably contains considerable iron. Few cleavage faces as much as 1 millimeter in diameter are visible. Sphalerite occurs with chalcopyrite in lenses, veinlets, and irregular gray masses in pyritic ore bodies, in minor quantities with chalcopyrite and gangue in the network around grains of pyrite, and in isolated zinc- rich ore bodies as in the Yolo and 313 ore bodies at the Mammoth mine. Sphalerite in the Yolo zinc ore body is lighter colored and much coarser grained than that found in other zinc ore bodies in the district. The sphalerite in this ore body has a resinous color in speci- mens from the Lindgren collection and has cleavage faces that range from 2 to 10 millimeters in diameter. Sphalerite actively corroded pyrite when it was in- troduced; and where much sphalerite is present, the pyrite content is very low. In high—grade sphalerite ore chalcopyrite alvays occurs as streaks, lenses, or irregu- lar areas, as in figure 42, and as minute blebs or tiny, irregular-shaped inclusions erratically distributed through sphalerite. The Zinc-rich ore contains more insoluble material than the massive pyrite. Polished sections of zinc- rich ore contain 25 to 35 percent corroded relicts of quartz and rock gangue. These relicts are 0.5 to 1 milli- FIGURE 42.—High-grade zinc»copper ore from the Shasta King mine. White, chalcopyrite ; gray, sphalerite, X 50. 88 GEOLOGY AND BASE-METAL DEPOSITS, FIGIYRE 43.vr‘Photomicograph of polished section of zinc ore from Mam~ moth mine. Corroded quartz gangue (dark) in sphalerite (light) forming an island-and-sea texture. Ordinary light, X 25. meter in diameter and are distributed through the sphalerite forming an island-and-sea texture (fig. 43). Talc, [hilly/AS603) 5 1120 ( .5’) .-Talc is not associated with base-metal ore, but it occurs in a pyritized shear zone in Copley greenstone at the Ganim mine, which is situated 21/2 miles northwest of \Vhiskytown in the W'hiskytown quadrangle. It also occurs in hornblende bodies near the margin of the biotite—quartz diorite in the Igo quadrangle, and in the plug of coarse—pheno— cryst rhyolite near the Uncle Sam mine. Two grades of talc are found in the Ganim mine; one is nearly pure talc or steatite, whereas the other is a mixture of talc and carbonate, not usable as steatite (Page and lVright).5 The tale occurs in a zone of ill- tensely sheared pyritized and altered greenstone 100 feet wide and 1,200 feet long. The talc near the Uncle Sam mine is in intensely sheared and silicified rhyolite. It occurs as small pockets and lenses less than 6 inches long in quartz-talc schist in the margin of the plug of coarse-phenocryst rhyolite, and in nonporphyritic rhyolite near this plug. Tennanrtite, 50u2S-2(0uF e)S “31482193 and Tetrahed- rite, 501tv28'2(01(F6)8'215'!)2S3.~—-Tetl‘alledl'lie or ten- nantite (or both) is present in small quantities in the zinc—rich ore inthe district. They are in anhedral grains up to 0.7 millimeter in diameter in sphalerite, chalcopyrite, and galena and have mutual borders with sphalerite and chalcopyrite. 5Page, B. M., and Wright, L. A., 1943, Unpublished geologic maps and sections of the Ganim talc mine, Shasta County, Calif.: In open file of U. S. Geol. Survey. WEST SHASTA COPPER-ZINC DISTRICT The mineral was determined by etch tests as being in the isomorphous series tetrahedrite-tennantite. Seager in an unpublished report, 1934, identified tetrahedrite from the Mammoth mine and tennantite from the Golin- sky mine. GANGUE MINERALS Bam’te, BaSO,.~—Barite is rarely present in the W’est Shasta district (Graton, 1910, p. 102) , although it is one of the common gangue minerals in the East Shasta copper-zinc district. Tiny plates of barite were recog— nized in a thin section and a polished section of zinc ore from the Mammoth mine. Spectrographic analyses of ore from the Mammoth, Early Bird, and Balaklala mines showed 0.01 percent barium. Seager noted small amounts of barite in the sulfide ore from the Golinsky mine and in the gossan from the Mammoth mine. Graton (1910, p. 102) reports a small amount of barite in the Mammoth sulfide ore, the Mam- moth gossan, and in the sulfide ore from the Golinsky mine. Calcite, 0a6’03.—Calcite is a minor gangue mineral in the massive sulfide ore. It is present in veinlets, ir- regular patches, and in vugs in the massive sulfide. Chlorite (319,196) (Alfie) 2822.010 ( 0H) 8.—Ch]orite is present at some places in a thin network between sul- fide grains. Flakes of this mineral are interlayered with sericite and are commonly oriented perpendicular to the grain boundaries of the sulfide minerals. Chlorite is a much less characteristic gangue mineral than sericite. ' Quartz, S502.—Quartz is the predominant gangue mineral in the massive sulfide ore bodies of the West Shasta district. It occurs as a network surrounding grains of sulfides; in thin veinlets, which may contain small amounts of calcite, cutting the sulfides; and as isolated grains, some of which resemble unreplaced quartz phenocrysts of the Balaklala rhyolite. The quartz in the network surrounding sulfide grains in massive sulfide ore commonly has a characteristic feathery habit (fig. 44). The orientation of the quartz is commonly perpendicular to sulfide grain boundaries, but may have any orientation. Quartz surrounding euhedral pyrite cubes disseminated through hydro— thermally altered rhyolite is commonly oriented per— pendicular to the pyrite faces. Some quartz grains in the massive sulfide ore appear to be relict quartz phenocrysts. They are isolated, poorly preserved dipyramids of quartz about 2 milli— meters in diameter irregularly and sparsely distributed through the ore. Graton (1910, p. 100) also noted these relict quartz phenocrysts in the ore. Sericite-hydromica, K A 138223010 ( 0H ) 2.—Sericite and hydromica occur with quartz, chlorite, and chalcopyrite BASE—METAL DEPOSITS 89 f FIGURE 44:~Photomic1‘ogra1111 of thin section of massive sulfide. ore from the Balaklala mine showing”r the feathery character of quartz (light) surrounding pyrite grains (dark). in a network surrounding sulfide grains. They may be in part- recrystallized rock gangue minerals. Some of the sericite and hydromica is oriented perpendicular to pyrite faces and is inter-layered with feathery quartz and chlorite in flakes generally 0.2 to 0.3 millimeter long. The mica flakes are commonly gently curved, apparently by stress caused by the crystallization of pyrite. Zoz'site, (Ya2irll;,(i\'7i0,)3(OH).—Zoisite is a very minor gangue mineral observed in thin sections of ore from the Mammoth mine. It is in anhedral grains associated with sericite and chlorite gangue. The zoisite is probably a relict rock gangue mineral. SUPER GENE )IINERALS OXIDE ZONE Supergene enrichment of the massive sulfide ore has been of little economic ii1’1portance in the \Vest Shasta district except at the Old Mine ore body at Iron Moun- tain and possibly at the Mammoth and Golinsky mines. As the Old Mine ore body vas mined out during the early part of this century, little is known of the second— ary minerals that were present in the enriched zone. Only a few specimens of supergene ore were available for study by the writers. (h-aton (1910, p. 100—107), who worked in the district during its early history, noted azurite, chalcanthite, native copper, cuprite, gos- larite, limonite, 111agnetite, malachite, 111ela11terite, and Crossed nicols, X 50. sm itl1sonite( ?). Diller (1906, p. 12) noted native silver associated with native copper in fractures in the gossan. The writers also noted antlerite coating fractures in supergene enriched ore from the Old Mine ore body. Basic iron sulfate is present in the gossan quarry at the Iron Mountain mine. It forms a yellow, ocherous, earthy, loose powder coating much of the oossan. This mine1al may be copiapite. Seagei in his unpublished repo1t states that small ciystals of native sulfu1 in the 11011 \[ountain gessan were observed by L. Raymond, formerly of the Moun- tain Copper Co., Ltd. Black earthy manganese oxide (wad) is admixed with iron oxides in the gossan It forms stains along: frac- tures in the gossan and coats some of the siliceous cells of the gossan hIaghemite, desc1ibed on page 119, occurs in the gossan at the I1 on Mountain mine. Gossans of individual ore deposits are discussed under “Description of deposits.” The most prominent gossans are at the Iron Mountain, Shasta King, Balfaklala, Balaklala Angle Station, and the Stowell mines. SULFIDE ZONE UllfchOCizfe, Uzz,S.—Small amounts of sooty chal— ('ocite were noted coating fractures in many specimens of massive sulfide ore found 011 the mine dumpsy‘ Chal- l 90 GEOLOGY AND BASE—METAL DEPOSITS, WEST SHASTA COPPER-ZINC DISTRICT cocite was abundant in the Old Mine ore body at Iron Mountain, and a small amount is present in the pyritic ore below the gossan in adit 8 of the Shasta King mine. Seager reports sooty chalcocite in specimens of ore from the Mammoth, Sutro, and Golinsky mines. He states that some of the Golinsky ore consisted almost entirely of black crumbly chalcocite enclosing a few residual grains of pyrite, sphalerite, and tennantite. Supergene enrichment took place by the selective re- placement of chalcopyrite and sphalerite by chalcocite. This mineral occurs as minute veinlets in fractures in chalcopyrite and sphalerite, but is absent where the fractures cut pyrite. Covellite, 0uS.—Covellite is intergrown with chal- cocite in veinlets through chalcopyrite and sphalerite, and along grain boundaries. Covellite commonly forms a thin film on the outside of thin supergene veinlets, whereas chalcocite is in the center of the veinlets. Secondary silver minerals—The sandy disintegrated sulfides immediately below the gossan in the Old Mine ore body at Iron Mountain contain abundant secondary silver minerals. This zone was mined as a silver ore in the early days of the district; it is described under the “Iron Mountain mine.” PARAGENESIS Six stages of mineralization are recognized in the formation of the massive sulfide deposits. The first five stages are hypogene; the sixth stage is supergene. The first stage is earlier than the massive sulfide ore bodies and consisted of silicification, deposition of some dissem- inated pyrite, and the formation of sericite, hydromica, and chlorite in the wall rocks. 'lhe next five stages produced the massive sulfide ore. The stages are as follows: (1) Early barren stage. (2) Pyrite stage, containing small amounts of pyrrhotite and magnetite. (3) Chalcopyrite-quartz stage, containing small amounts of sphalerite. (4) Sphalerite-chalcopyrite stage, containing small amounts of tetrahedrite, tennantite, and galena. (5) Quartz-calcite stage. (6) Oxidation and enrichment stage. Early barren stage—The early barren stage can be divided into three substages—(l) a widespread intro- duction of quartz-pyrite, (2) an apparently later min- eralization of sericite-hydromica that is more closely associated spatially with ore, and (3) a chloritic alteration. The quartz-pyrite substage affected a large part of the lower and middle units of the Balaklala rhyolite, and, in places, the lower tufl'aceous zone at the base of the upper unit. Euhedral pyrite cubes and pyrito- hedrons, commonly ranging from 1 to 2 millimeters in diameter, are disseminated through the Balaklala in amounts generally less than 10 percent by weight. In addition milky quartz that contains pyrite formed stringers 3—4 inches thick. The weathering of the dis- seminated pyrite and stringers of quartz—pyrite forms the widespread iron-staining in the rhyolite. This Sub- stage is so widespread that it cannot be used as a guide to ore, except as it marks a broad zone in which hydro- thermal solutions were present. Intense sericite—hydromica alteration of the Balak— lala rhyolite is localized near ore bodies, as observed at the Iron Mountain, Balaklala, and Mammoth mines, but it is not necessarily adjacent to ore nor does it assure the presence of ore. It does not form alteration halos around ore bodies in the manner of those described by Sales and Meyer (1948) at Butte. The solutions that deposited the massive sulfide ores apparently fol— lowed more restricted channels than the solutions that formed sericite-hydromica in the rocks, and the earlier and later solutions did not always follow the same chan- nels. Where sericite and hydromica are formed, the rhyolite is altered to a soft white crumbly mass that contains small amounts of disseminated pyrite. This alteration zone has no systematic relationship to massive sulfide ore; it may be adjacent to the ore or may be several hundred feet away in any direction. Hard un— altered rhyolite separates the sericite-hydromica zone at some places from massive sulfide ore. At the surface the zone of sericite~hydromica alteration locally has a lavender color owing to the weathering of pyrite to hematite, and the selective adhesion of the hematite to the sericite. The sericite-hydromica zone is probably later than the disseminated pyrite minerals as the seri— cite-hydromica has a more local distribution and closer association to massive sulfide ore bodies. Also sericite- hydromica is localized in some places along the bound- aries of pyrite cubes. Chloritic alteration that probably preceded sulfide mineralization occurs with the disseminated chalcopy- rite ore at the N0. 8 mine at Iron Mountain, in the U. S. Geological Survey diamond drill hole at Iron Mountain, and at the west end of adit 6 at the Shasta King mine. This chloritic alteration of the rhyolite is not widespread, but at some places seems to be asso- ciated with disseminated chalcopyrite. Possibly it formed a rock particularly favorable for the later deposition of chalcopyrite. Pyrite stage—Pyrite, was the first mineral deposited in the formation of the massive sulfide deposits, and the bulk of the pyrite was deposited before the mineral- ization of the chalcopyrite-quartz stage. Large bodies of extremely fine grained pyrite, which contain a few euhedral 1- to 5-millimeter pyrite cubes and pyrito- BASE—METAL DEPOSITS 91 hedrons, were formed by the replacement of Balaklala rhyolite. A thin network of quartz and sericite-hy- clromica, which probably are minerals formed from relict rock gangue, remains between individual pyrite grains. This network of quartz and hydromica averages about 25 percent of the mass by volume but the net- work was largely replaced by minerals of the chalco- pyrite-quartz stage. ‘ Small amounts of magnetite and pyrrhotite were probably deposited during the pyrite stage, although their relationship is not definitely known. Magnetite Occurs as minute anhedral grains disseminated through the quartz-sericite—hydromica network. Pyrrhotite was Observed only in one specimen from Iron Mountain; it occurred With pyrite and was veined by sphalerite. The large pyritic bodies probably formed after the minerals of the barren stage, as veinlets of massive . sulfide ore cut and corrode relicts of spongy—textured ‘ pyrite—quartz rock that formed during stage (1) in the ‘ gossan quarry at Iron Mountain. The euhedral pyrite : cubes and pyritohedrons that are disseminated through 5 the massive sulfide ore are similar in size and appear- “ ance to the disseminated pyrite grains and may be unreplaced coarse—grained pyrite of the barren stage. Much silica but, no copper and zinc ore minerals ac- companied the early barren stage; little silica, much py- rite, and possibly minor amounts of ore minerals accompanied the pyrite stage, which is much more localized than the early barren stage of mineralization. OhaZcopyrite-quartz stage—The pyritic bodies and enclosing rocks were fractured before the minerals of the chalcopyrite-quartz stage began to deposit. Quartz crystallized before the other minerals in this stage, and filled fractures in pyrite and in the gangue network be- tween pyrite grains. Chalcopyrite and minor amounts of sphalerite were deposited after quartz, as these min— erals contain corroded relicts of quartz, but spatially they are closely associated with it. Chalcopyrite greatly predominates over sphalerite in this stage and minor amounts of pyrite accompanied the quartz and chalcopy- rite. The minerals of this stage mainly replace the selvage network of rock gangue around pyrite. There was little corrosion of the pyrite, so a network pattern surrounding pyrite grains was largely retained, but with quartz, chalcopyrite, and sphalerite replacing the network of gangue minerals. The disseminated chal- copyrite and chalcopyrite-quartz veins at the No. 8 mine that underlie the massive sulfide ore bodies at Iron Mountain were probably formed in this stage. Sphalerz'te-chalcopym‘te stage—The minerals depos- ited during this stage listed in decreasing order of abun- dance are 'sphalerite, chalcopyrite, galena, tetrahedrite, and tennantite, but there is no clear break at some places 379725—56—7 between the chalcopyrite—quartz stage (3) and the sphalerite-chalcopyrite stage (4). Sphalerite was de- posited in small amounts in the chalcopyrite-quartz stage, but it is more abundant than chalcopyrite in the sphalerite-chalcopyrite stage. The two stages are evi- dent at some localities where one or the other greatly predominated. Sphalerite forms streaks, lenses, and veinlets cutting the massive pyrite ore, and forms isolated pods of high— grade zinc ore, as in the Yolo zinc lens at the Mammoth mine, that replace rhyolite. Sphalerite had an extreme- ly corrosive effect upon pyrite in this stage, and the streaks and lenses of sphalerite in massive pyritie ore contain only a few percent of corroded relict pyrite. Sphalerite and chalcopyrite were deposited contempo- raneously, as they have mutual contacts, and each min- eral contains corroded relicts of the other. The tiny blebs of chalcopyrite in sphalerite may have formed by unmixing. Either tetrahedrite or tennantite is found as small inclusions in sphalerite. It has mutual contacts with sphalerite and is veined by galena. Probably the tetra- hedrite or tennantite were deposited near the end of the sphalerite-chalcopyrite stage but before deposition of galena. Galena was the last mineral to deposit in this stage. It veins sphalerite and is present mostly along bound- aries between sphalerite and gangue. Quartz-calcite stage—A small amount of quartz and calcite was deposited after the sulfide mineralization. Both occur as small, sharp-walled veinlets cutting mas- sive sulfide ore and as small irregular masses in sulfide ore. Oxidation and enrichment stage—~Siipergene enrich— ment was of little importance in the West Shasta dis- trict except in the Old Mine ore body at Iron Mountain and the gossan ore body at the Mammoth mine. The enrichment at these mines is described under “Iron Mountain mine” and “Mammoth mine.” The enriched ore was mined out many years ago, So a mineralogic study could not be made. RELATIONSHIP OF HYDROTHERMAL ALTERATION T0 MASSIVE SULFIDE ORE Hydrothermal alteration processes that are believed to be genetically related to ore deposits are silicification, sericitization, and chloritization. However, at many places no close spatial relationship was recognized be- tween hydrothermally altered rock and massive sulfide deposits. Evidence indicates that the most probable sites for the deposition of sulfide minerals are in areas of hydrothermal alteration where the rocks of the dis— trict were open to solution travel, but the evidence does 92 GEOLOGY AND BASE—METAL DEPOSITS, WEST SHASTA COPPER-ZINC DISTRICT not indicate that sulfide minerals necessarily are present. The larger areas of hydrothermal alteration are shown on plate 4. Intense silicification generally is spatially related to sulfide mineralization, but is too widespread to be a direct guide to massive sulfide ore. Although largely limited to the main mineral belt, silicification is not necessarily more intense in areas where massive sulfide ore was deposited. At Iron Mountain, relict nodules of rhyolite in gossan are silicified, and bodies of second- ary quartz that contain as much as 50 percent euhedral pyrite cubes and pyritohedrons are present as relicts in gossan derived from massive sulfide ore. These pyrite- quartz relicts are believed to represent more siliceous areas, probably formed during the early barren stage of mineralization, that were replaced by early pyrite. Wall rock that contains pyrite and silica of the early stages occurs along the side of the ore bodies at Iron Mountain; at some places it is in contact with massive sulfide ore, but at others the silicified rock is separated from ore bodies by rhyolite that contains no secondary silica or pyrite. The porphyritic rhyolite immediately adjacent to most of the ore bodies of the district is only slightly silicified, and relict nodules of nonporphyritic and por- phyritic rhyolite in massive sulfide ore, such as those in the Shasta King and Balaklala mines, are not silici— fied. However, quartz—pyrite bands are common near or between many of the ore bodies of the district, and the transition zone of tqu at the base of the coarse phenocryst rhyolite at the Mammoth mine is strongly silicified in the mine area, but is not silicified away from it. Bands of quartz and silicified rhyolite that contain from a few percent to 50 percent pyrite are abundant in the lower and middle units of the Balaklal a rhyolite. These bands are more abundant near or between ore bodies, and they may be useful in delimiting general areas favorable for ore deposits. Localities where the rocks have been altered to seri- cite-hydromica commonly occur along the main ore zone, but sericitic rocks are formed by regional metamor- phism as well as hydrothermal metamorphism, and it is not always possible to distinguish between the two proc- esses. In the mineral belt sericitic rocks are commonly associated spatially with silicified rocks, although the rocks are either sericitized or silicified but not both. These zones of soft, crumbly, intensely sericitized rhyo— lite are mainly concentrated in the general area of known ore deposits. All gradations exist between slightly altered rhyolite and a rock containing relict quartz phenocrysts in a secondary matrix of quartz, sericite, hydromica, hematite, and pyrite, or limonite pseudomorphous after pyrite. All the sericitic rock contains minor amounts of disseminated pyrite in the form of euhedral 1- to 2—millimeter cubes, and seams and flakes of hydromica intimately mixed with sericite. The color of the soft, altered rock is predominantly white but ranges from white to light pink and shades of laven- der, red, and purple. Sericitic alteration is particularly common around the Iron Mountain and Balaklala mines, but some areas of strongly sericitized rhyolite occur away from known ore bodies. Much of the por— phyritic rhyolite about 1 mile south of Iron Mountain on the north and east sides of South Fork Mountain is altered to a crumbly pink to lavender rock, by hydro- thermal solutions. Although the area is one of strong hydrothermal alteration, no massive sulfide deposits have been found. Owing to hydrothermal alteration and weathering the color of the altered rhyolite ranges from pink to lavender. This color is found only in porphyritic rhyo— lite that has been hydrothermally altered to a rock con- taining sericite, hydromica, and pyrite. The pink is due to selective adhesion of minute hematite specks, derived from oxidation of pyrite, on sericite and hydromica. Lavender—pink altered rocks occur on South Fork Mountain, Iron Mountain, and at the Balaklala and Mammoth mines. In some places the whole rock is uni- formly lavender-pink. Under the microscope the color is seen to be due to minute flecks of hematite dissemi- nated through the groundmass, and to thin coatings of hematite along cracks that cut across schistosity and cut through sericite veinlets. At other localities only quartz and feldspar phenocrysts are colored. In these, the lavender-pink color is due to thin coatings of hematite surrounding phenocrysts, and in cracks through pheno— crysts. Pyrite casts and dark—red hematite are dissemi— nated through the groundmass. The color of the quartz and feldspar phenocrysts is caused by migration of ferric iron due to weathering of pyrite. The lavender—pink alteration is commonly found along the main ore zone because it forms only where the rocks contain sericite, hydromica, and pyrite, and these altered areas are commonly associated with ore. The mineralogy of the soft pink, lavender, and purple rhyolite is the same as that of the soft white altered rhyolite except for the amount of hematite present. Quartz is the only relict primary mineral. Albite is altered to sericite and hydromica. The sericite has the following optical properties: 71a=1.565i0.003 n,=1.598:0.003 birefringence=0.033 BASE-METAL DEPOSITS 93 Hydromica is present in nearly equal amounts with sericite and is intergrown with the sericite. It has the following optical properties: Ma=1.560i0.003 725:1.569i0003 717:].580i0.003 birefringence=0.020 elongationzpositive At some places it is difficult to determine how much of the sericitelike alteration of the surface rock is due to hydrothermal solutions and how much is due to acid solutions formed from weathering of the sulfide minerals. Rock that lies downhill from oxidizing ore bodies is partly altered to claylike products and may have been altered mainly by acid surface waters. there such rock is most intensely altered, it can be crumbled apart in the hand; the disintegration of the rock is largely due to alteration of feldspar to clay minerals by reaction with acid solutions derived from weathering of sulfide minerals, and in the field such argillic alteration could not be distinguished from sericitic alteration at some places. Chloritic alteration is due largely to regional meta- morphism, but some chlorite appears to be of hydro- thermal origin. All the Balaklala rhyolite was replaced by chlorite to some extent during regional metamor- phism, but at Iron Mountain a more intense chloritic alteration seems to be genetically related to the deposits of disseminated chalcopyrite. Seager in his unpub- lished report noted chloritic alteration that is related to chalcopyrite mineralization at Iron Mountain in the disseminated chalcopyrite deposits of the No. 8 mine ore body. Rhyolite in core from the Geological Survey diamond—drill hole at Iron Mountain is in- tensely altered at places to a secondary chlorite-quartz rock and chalcopyrite is more common in the chloritized rhyolite than in the siliceous rhyolite. Although the chlorite may have been introduced by the solutions that deposited the chalcopyrite, it seems more probable that the chlorite was earlier and formed a favorable host rock for chalcopyrite deposition. GENESIS OF THE HYPOGENE ORES The base-metal ore bodies and the widespread dis- seminated pyrite ~in the West Shasta district were formed by the replacement of parts of certain favorable zones in the Balaklala rhyolite. The evidence for a re- placement origin is indicated by relict rock structures in the mineralized areas, and by the detailed control of mineral localization along preexisting rock structures such as foliation. Evidence for this mode of origin for the disseminated'pyrite is convincing, and a replace- ment origin was recognized by all the geologists who have worked in the district. There are many features of the massive sulfide bodies for which the writers can offer no adequate explanation. The most puzzling fea— ture of the ore deposits is the presence of sharply bounded bodies of massive sulfide that contain gold, sil- ver, copper, and zinc in a general zone of disseminated pyrite that contains little or none of the ore minerals. The absence of relict rock or other evidence of replace- ment in the massive sulfide ore except for a few poorly— preserved quartz crystals that appear to be relict quartz phenocrysts cannot be adequately explained. The lack of evidence for a mode of origin other than replacement for these massive-sulfide bodies does not warrant the assumption that their formation was by replacement. Evidence. favoring a replacement origin for pyritized rock, as distinguished from the massive—sulfide deposits, is abundant; the effectiveness of pyritization ranges from the formation of a few scattered pyrite cubes in otherwise unaltered rock to bands of quartz-pyrite rock. The disseminated pyrite is euhedral, and the cubes and pyritohedrons are rarely in contact with each other; even in the quartz-pyrite rock the pyrite does not tend to grow in clumps around a center of crystallization or to form bodies of massive pyrite. The quartz and heavily disseminated pyrite that form the quartz-pyrite rock commonly occur in poorly de— fined bands and lenticular bodies. These are oriented parallel to preexisting rock structures such as foliation, bedding, or flow contacts, but the outlines of the pyrit- ized areas are not sharp ; they fade out into barren rock. Pyritized rock is concentrated in the flat—lying ore zone, and is almost without exception sharply bounded at the top by the base of the coarse-phenocryst rhyolite, which forms the “cap rock.” The lower boundary and the edges of the pyritized zone are hazy. Bodies of massive sulfide, on the other hand, are sharply bounded by a thin band of gouge at almost all localities; the sharply bounded lenses of sulfide are generally in contact with rocks that contain little or no pyrite as described under “Types of contacts between ore and wall rock.” Rock containing sparse, scattered pyrite grades to heavily pyritized rock, but gradations from heavily pyritized rock to a massive sulfide ore, except at the ends of a few ore bodies, were seen at only one locality, in the Shasta King mine. Interpretation is equivocal that most structures in the massive sulfide ore are actually formed by replace- ment, such as banding in the ore, which is interpreted as replacement along planes of foliation. The massive sulfide ore contains a few poorly preserved quartz dipyramids that are probably relict quartz phenocrysts 94 GEOLOGY AND BASE-METAL DEPOSITS, from the rhyolite and some anhedral quartz grains that may be corroded phenocrysts. Gavelin also notes relict quartz phenocrysts in the massive sulfide ore at Bjur- liden (Gavelin, 1939, p. 99—102). Thin sections of massive sulfide ore show that at some places the pyrite grains are surrounded by thin films of quartz, sericite, and chlorite, which represent recrystallized host rock material. At the few localities where there is a grada- tional contact from massive sulfide to a foliated sericitic wall rock at the ends of some ore bodies, a complete gradation from pyritized rock to massive sulfide can be traced, and the observer has no doubt that the sulfides have replaced the rock at these points. A further difference between massive sulfide ore and zones of disseminated pyrite is that most of the bodies of massive sulfide contain copper and zinc minerals and appreciable amounts of gold and silver, but the areas of pyritized rock contain only small amounts of copper minerals, no visible zinc minerals, and no gold and silver, as far as is known. In the description of the ores of the Malanas district (ores that are remarkably similar to ores of the Shasta district) Gavelin (1939, p. 146) emphasizes the distinction in mode of origin between massive sulfide and disseminated pyrite. The evidence for this distinction is not only the sharp con— tact at most places between the two types, but also the difference in the distribution of the metallic elements in the two types (Gavelin, 1939, p. 181). The same distinction was made by Brownell and Kinkel (1935, p. 274) between the massive sulfide and the: dissemi— nated ores at Flin F1011, Manitoba. The sharp contacts between massive sulfide ore and schist and pyritized schist were pointed out by Emmons (1910, p. 55) at the Milan mine in New Hampshire. The reason for the sharp distinction between massive sulfide ore bodies and zones of pyritized rock in this dis- trict. is not known. No direct evidence has been found here that would suggest that the massive sulfide ore was emplaced as a concentrated plastic mass as was postu- lated by Odman for the ores at Boliden (Odman, 1941, p. 159), by Spurr (1933, p. 110—122) for the ore of the Mandy mine, and in a somewhat modified form, as ad- vocated by Gavelin for some of the ores of the Malanas district (Gavelin, 1939, p. 127—130). No apophyses of ore that resemble intrusive apophyses such as occur at Boliden and at the Mandy mine are found in the ores of the Shasta district, nor was ptygmatic folding seen here in the banded ores, such as was found in the ores of the Malanas district and the Mandy mine. Ptygmatic fold- ing in banded sulfide ore has been interpreted by Gave- lin and by Spurr at Boliden and at the Mandy mine as indicating plastic flow during the intrusion of a sulfide magma, although Bastin (1950, p. 74) and Emmons WEST SHASTA COPPER-ZINC DISTRICT (1910, p. 58) interpret similar structures as evidence that the banded ore has been crumpled after its forma- tion by movement during regional metamorphism. The massive sulfide ore in the “lest Shasta district is locally crushed and fractured to a moderate extent, but the fractures are healed by minerals of a later stage; there is no evidence that the ores were affected by dy- namometamorphism. Odman and Gavelin recognize replacement phenom- ena at the ends of some massive sulfide ore bodies and these phenomena are seen in the “Vest Shasta district also at only such places. The perplexing question of whether the evidence of replacement observed along the edges of an ore body (or body of rock) illustrates the mode of formation of the entire body, or whether in a body formed by other means, they are phenomena that are restricted to the edges, cannot be settled for the ores of the West Shasta district. The writers favor a re— placement origin for the massive sulfide ore as well as for the widespread pyrite for the following reasons: (1) Replacement phenomena are evident in the zones of dis— seminated pyrite ; (‘2) replacement is evident at the ends of some massive sulfide bodies; (3) paragenesis suggests that the minerals were deposited in sequence. Minerals of succeeding stages followed channels different from those followed by earlier minerals, and deposited in dif- ferent areas at some places, thus ruling out a paragenetic magmatic sequence of crystallization in the strict sense; and (4) internal structures are not present that would indicate an intrusive origin. The most probable explanation'for the presence of sharply bounded bodies of massive sulfide in a zone of disseminated pyrite appears to be that some massive sulfide bodies were formed at a slightly different time and under the influence of different controls than the pyritized zones, and that some massive sulfide bodies formed in places where, for a time, the solutions were confined to restricted channels and effected com- plete replacement. In this district both of these con- trols were probably effective in some ore bodies, whereas in other ore bodies one control predominated. Pyritized rock is so widespread in the district that it cannot be related to localized individual feeder channels. The solutions that deposited widespread disseminated pyrite along the mineral belt also carried quartz ; hydro- thermal quartz is less widespread than pyrite. Quartz deposited with pyrite principally where pyritization was more intense; weakly pyritized rock generally is not silicified. It seems probable that solutions that rose along a few main channels in the deeper levels spread into the rocks along zones of fracture cleavage in the rhyolite. The rhyolite rocks were probably the first that the solutions contacted that were sufficiently brittle BASE-METAL DEPOSITS 95 to allow fracture cleavage to form and be preserved, and solutions are thought to have traveled along these fractured zones away from main feeders for consider- able distances and deposited widespread pyrite. Solu- tions in the zones of fracture cleavage were widespread, and were not confined to small areas except locally. The solutions were channeled by the gouge of premineral faults, and the increased flow along these paths, to- gether with the erratic distribution of zones of fracture cleavage, account for the differences in the intensity of pyritization. Some areas of heavily pyritized rock probably were formed where solutions, rising along zones of steep fracture cleavage, came in contact with flat bedding— plane foliation, or impervious beds. These structures deflected the flow of solutions into more confined chan— nels resulting in more complete replacement of the rocks. Minor increases in solution pressure at points where the flow was disrupted or confined to a smaller channel may also have aided in effecting a more thorough pene— tration of parts of the rocks by the ore—bearing solu-- tions. The pyritized rock in the ore zone along the base of the upper unit of the Balaklala rhyolite was probably formed in this manner, but the formation of bodies of massive sulfide ore probably required that the channels be further confined by bands of fault gouge, or that the solutions reached limited areas in which ground preparation was particularly favorable. Such favorable areas are along the axes of some folds, where these were cut by gouge-bearing faults. These faults were thus not necessarily feeder channels, even though. sulfide bodies occur in proximity to them. Strong and widespread pyritization is not only con- fined to the rhyolite, but it also is confined at many places to flows of one type and at one horizon. This suggests that although structural control and ground preparation is of great importance, minor chemical dif- ferences may possibly have helped to determine which of several flows in the same area were replaced. Studies of polished sections of the cres show that although there are overlaps in the sequence of mineral deposition, there were definite periods in which the deposition of one mineral predominated. Pyrite that formed during the period of widespread pyritization is associated with only small amounts of chalcopyrite and no sphalerite, gold, or silver as far as is known. In polished sections of ore the chalcopyrite and sphalerite not only formed after the main part of the pyrite, but a period of minor movement occurred before the intro- duction of these minerals, as they are present in frac— tures in the pyrite and in shattered pyrite. Copper- and zinc-bearing solutions, which probably also carried the gold and silver and other minor metals and some pyrite, had a much more limited distribution than the earlier solutions that deposited principally pyrite and quartz. The later solutions followed more restricted channels, although these were confined to the central part of the ore zone and coincide largely with areas of most intense pyritization. However, some of the channels that were filled during the early quartz and pyrite stage were not reopened, others were opened only to a limited extent, and some new channels were formed. Thus while the copper and zinc minerals fol— low the pyrite zone fairly closely, they are not coexten- sive with it. There was also a break at some places between the deposition of chalcopyrite and sphalerite. Chalcopy- rite is earlier than sphalerite in most of the ore, and there was a change in the character of the solutions between the main periods of deposition of chalcopyrite and of sphalerite. The copper-bearing solutions like those that formed the disseminated ore in the No. 8 mine at Iron Mountain, deposited pyrite as well as chal- copyrite. The copper ore in the No. 8 mine contained no sphalerite, and very little gold and silver. It should be pointed out here that although the chalcopyrite— quartz stage as seen in polished sections is not accom- panied by the deposition of any pyrite, the ore. in the No. 8 mine contains about equal amounts of chalcopy- rite and pyrite. This is either an instance where the chalcopyrite-bearing solutions followed the same chan— nel as the earlier pyrite-depositing solutions and one was superimposed on the other, or it is a locality where chalcopyrite and pyrite were deposited from the same solution. The latter hypothesis is the most probable explanation, as the chalcopyrite and pyrite are coex- tensive throughout the No. 8 mine. The zinc-bearing solutions deposited no pyrite and had a very corrosive effect on preexisting pyrite. Also some high-grade zinc ore bodies at the Mammoth mine were formed along a different channel than that along which the major pyritic bodies formed, indicating a time interval be- tween the two types of deposits. The source of the solutions that deposited the base metals and performed the hydrothermal alteration is not known, but some discussion of their possible sources may be justified. It is possible that the solutions were derived from either the albite granite or from the biotite-quartz diorite, but it is also possible that they were solutions that were mobilized as a result of orogeny and were not necessarily of direct igneous origin. The albite granite is locally pyritized and altered, and solution action is commonly localized along zones of foliation or along fractures. Although this pluton is not extensively mineralized, nevertheless it is mineral- ized at many places throughout the exposed area, most 96 GEOLOGY AND BASE-DIETAL DEPOSITS, WEST SHASTA COPPER~ZINC DISTRICT commonly along structures that apparently formed during regional metamorphism. There is no indication that mineralization or alteration is more common in the borders or in the wall rocks. The only suggestion that mineralization is related to this pluton is in the geographic location of the mineral belt at the north end of the elongate pluton and the presence of minor pyritization that is concentrated in the wall rocks at the south end. Pyrite is the most abundant sulfide mineral in the pluton, but gold-quartz veins are common within the intrusive mass, and some quartz veins con— tain pyrite, chalcopyrite, gold, and small amounts of galena. This mineralization apparently is not related genetically or spatially to the massive sulfide-type min- eralization, and as described under “Age of mineraliza— tion,” there are reasons for believing that the main period of mineralization is younger than the albite granite. Mineralized or hydrothermally altered rocks in the biotite—quartz diorite pluton are extremely rare except in a limited area. near the border of the intrusion, at the Silver Falls mine about 21/2 miles northwest of the town of I go in the Igo quadrangle. In this area silver- rich quartz-pyrite—chalcopyrite-galena veins formed along northerly trending faults in the biotite—quartz diorite. The wall rock of these veins is biotite-quartz diorite that is altered to soft silvery quartz—mica schist. Pyrite occurs only in a few thin seams in the main mass of the pluton. Mineralization is equally rare in the zone of contact metamorphosed rocks along the walls of the intrusion, or in the surrounding greenstone. The only apparent relationship between the biotite— quartz diorite pluton and mineralization is one of broad geographic correlation. This pluton is mineralogically similar to some of the granitic intrusive rock of the Sierra Nevada, it has the same northwesterly trend, and is apparently of the same age as the granitic rocks of the Sierra Nevada. On a statewide scale there is a correlation between base—metal deposits, many of which have a high content of pyrite or pyrrhotite, along the west side of the granitic rocks of the Sierra Nevada and those of Shasta, Trinity, and Siskiyou Counties in northern California. Such a correlation does not neces— sarily imply a genetic relationship between granitic rocks and base—metal mineralization; it might imply only a correlation between structural conditions that favored the introduction of granitic rocks and mineral- bearing solutions. The correlation between plutonic rocks and mineral— ization could also result from the catalytic effect of orogeny. Although no direct evidence of such an or— igin is likely to be found, the type of base—metal deposits and the accompanying hydrothermal alterations that occur in the Shasta district may be explained in this way without the introduction of material from an ig- neous source. If pore solutions in deeply buried rocks, or water expelled from hydrous minerals during meta— morphism, were heated and mobilized by igneous intru- sion and orogeny, it is probable that they could collect and transport elements for deposition at higher hori— zons. Thus the leaching of rocks which have a high— silica content such as the Abrams mica-schist that occurs west of this district and is thought to underlie the Copley (Hinds, 1933, p. 81), the alteration of the andesites of the Copley to greenstone, the albitization of some of the Copley rocks, and the formation of granitic gneiss and amphibolite from the Copley rocks could account for the migratory solutions of all the elements (with the possible exception of potassium) necessary to form the zones of epidotized, chloritized, silicified, and sericitized rocks in the overlying formations. Similarly, much of the iron and relatively small amounts of copper and zinc minerals and minor metals that form the ore deposits could have been derived by leaching of the rocks that underlie these deposits, possibly with additions from magmatic emanations. Leaching of the wall rocks of the solution channels is indicated by the difference between the ores in the East and ”West Shasta districts. The ores of the two districts are similar except that in the East Shasta dis— trict the ores contain large amounts of gypsum and anhydrite, whereas those of the lVest Shasta district contain neither of these minerals. The ores of the East Shasta district are probably underlain at depth by the McCloud limestone, but no limestone is known to occur under the ores of the “Test Shasta district. It seems probable that the presence of gypsum and anhydrite in one district and not in the other is best accounted for by the presence or absence of limestone along the solution channels. OXIDATION AND ENRICHMENT Oxidation and enrichment. are relatively unimportant in the \Vest Shasta district. The flat—lying ore bodies crop out in areas of steep topography in most of the district, and except at Iron Mountain oxidized rock extends only a short distance below the surface. At Iron Mountain the Old Mine ore body crops out and dips about parallel to the hill slope; under these condi- tions much of the ore in the Old Mine ore body was converted to gossan, and an enriched zone was present under the gossan. 0mMarion—Prominent gossans have formed where bodies of massive sulfide ore crop out, and broad areas of iron—stained rock occur where there is widespread pyritized rock. In these areas, the pyrite has been de- BASE-METAL DEPOSITS 97 composed at the surface, and the rock is stained by transported limonite. Cavities after pyrite are gen— erally free of limonite at the surface, but limonite-filled cavities and relict pyrite are present a few inches below the surface. Hard brown limonite pse‘udomorphs after pyrite cubes are common at some localities and may be picked up on the surface where soft rocks are deeply weathered. The decomposition of pyrite rarely extends more than a few feet below the surface in zones of dis- seminated pyrite, although limonite staining may go deeper. WVhere sulfide bodies form dip slopes, as in parts of the Iron Mountain ore body, most of the sul- fide has been altered to gossan; but where the flat-lying massive sulfide bodies crop out in areas of steep topog- raphy, as at the Shasta King, Stowell, and Balaklala mines, the gossan capping rarely extends into the hill for more than 50 feet. The gossan at the Iron Mountain mine is the most extensive in the district, and is well exposed in the quarry. This gossan is described under “Iron Moun- tain mine,” but some general features that are pertinent to the oxidation of the ores of the district are described here. The ore bodies at each end of the ore zone at Iron Mountain have been altered to gossan, where the zone is exposed at the surface; the central part lies under a ridge and is not oxidized. The horizontal Hornet ore body is oxidized at the exposed end, and at the top of the ore body where the rock cover is less than 150 feet thick. No oxidation occurred along the top of the Richmond ore body, which lies 350—450 feet below the surface, or along the top of the Brick Flat ore body, which is in some places as little as 100 feet below the surface. The Old Mine massive sulfide ore, on the other hand. was almost completely oxidized; it cropped out at the surface, and inasmuch as the dip of the ore body is parallel to the hill slope, the entire length of the ore body \‘as exposed to oxidation. Oxidation extends to a considerable depth where a steeply dipping ore body crops out at the surface; along parts of the Camden ore body at Iron Mountain oxidized minerals extend locally to a depth of 500 feet. W'here ore bodies do not crop out, as little as 50—100 feet of rock is sufficient cover to prevent oxidation of the sulfides, even though the ore body is cut by steep faults that reach the surface. Gossan derived from massive sulfide ore is resistant to weathering and commonly forms bold outcrops. Even where the outcrop of a. massive sulfide body is covered by wash, float boulders of gossan can usually be found in the debris below the covered outcrop. The appearance of the gossan derived from massive sulfide ore is distinctive, and differs from gossan derived ‘ from quartz-pyrite rock or from heavily pyritized rock. This distinction is of economic importance because, with only minor exceptions, deposits of massive sulfide con- tain gold, silver, and copper and zinc minerals, whereas heavily pyritized rock contains none of these minerals. It can be assumed that gossan derived from massive sulfide ore, and which contains gold as a relict mineral, indicates the presence of copper and zinc minerals in the sulfide zone beneath the gossan. As far as the writers could determine, there are no exceptions to this generalization in the “rest Shasta district. Gossan derived from massive sulfide is composed largely of hard dark-reddish—brown limonite that has an irregular, cellular texture, and contains “ather widely spaced, irregularly distributed ribs of silica (fig. 45). This silica is secondary, as most of the massive sulfide ore contains too little quartz or relict-rock material between the grains of pyrite to form a quartz skeleton upon removal of the pyrite by oxidation, and the silica septa that are in the gossan have no counterpart in the primary ore. The cellular gossan containing silica septa makes up the bulk of the gossan, but dense limonite occurs both as irregular areas in the gossan and as rims surrounding nodules of relict sulfide. Relict nodules of massive sulfide ore in gossan have Sharp boundaries (fig. 46), and are commonly rimmed by a band of dense limonite 1 to 4 inches thick between the cellular limonite and the sulfides (fig. 46). It is evident that silica as well as iron was redistributed around some sulfide nodules in the oxidized zone. Bodies of relict sulfide ranging in size from small nodules to masses 10 to 20 feet long locally show a char— acteristic zoning and alteration of the sulfides. This alteration consists of a zone of silica at the contact be- tween limonite and sulfides and the formation of a zone of dense limonite between the sulfide nodule and the cel- lular limonite. The zone of silica consists of a friable White silica sponge a few millimeters to 3 or 4 centime- ters thick and contains very thin, closely spaced septa; the contact is gradational against the sulfides, but sharp against the dense limonite. Neither the sulfides nor the silica sponge are iron stained. The dense limonite forms a hard reddish—brown band around the sulfide mass, and has a sharp contact on its inner edge against the silica sponge, but a gradational contact to porous limonite at its outer edge. The band of dense limonite maintains a width of 1 to as much as 4 inches as it encroaches on the sulfides, regardless of the size of the relict sulfide mass. Some relict—sulfide nodules contain more silica than is commonly present in massive sulfide ore. Possibly these are relicts of the early silica stage, although sim— ilar areas of high-silica content were not seen in the ore in underground workings. It seems equally possible 98 GEOLOGY AND BASE—METAL DEPOSITS, WEST FIGURE 45.»—Gossan derived from massive sulfide ore. SHASTA COPPER—ZINC DISTRICT Limonite with irregularly distributed ribs of secondary silica. The size or shape of the cells is not inherited from the primary ore. that the silica that was mobilized during oxidation re- placed some of the sulfides in local areas. Also, small nodules of soft, friable silica sponge surrounded by a rim of dense limonite are found in the gossan; these are pyrite free and resemble the friable silica sponge that formed bet ween the sulfide and the dense limonite, which suggest that the nodules represent the last stages of py- rite removal when all the iron from the nodule had moved outward into the rim of dense limonite. FIGURE «la—Relict nodule of massive sulfide in g‘ossan. Dense limonite separates sulfides from cellular limonite. The common succession of silica sponge, dense limon- ite, and cellular limonite that contains ribs of secondary silica, from the center of a relict—sultide nodule outward, indicates the sequence of oxidation. Silica was trans— ported from the center outward, the strongest precipi- tation being at the edge of the sulfides, although it may have first replaced part of the sulfides. Iron i'as trans— ported outward past the band of iron-free sili "a sponge and deposited as dense limonite. As the dense limonite- sili ‘a sponge zone encroached on the sulfides, the cellular limonite encroached on the band of dense limonite, so that the latter maintains about a uniform thickness. No correlation \ 'as possible between types of massive sulfide gossan and the copper-zinc content of the pri- mary ore as no detailed information is available on the grade of the massive sulfide below most gossans. Collapse breccia was observed in the gossan at Iron Mountain, and may have been present at other mines. The decrease in volume \ 'as large where gossan formed from massive sulfide ore. as much iron was removed and large caves lined with botryoidal and stalactitic limo- nite have been found. Angular rock fragments 50 feet or more from the valls of the gossan in this breccia at Iron Mountain indicate a considerable collapse of the walls and roof. It is probable that some of the gossans observed at the surface in the district represent, only a small part of the width of the massive sulfide ore BASE-METAL DEPOSITS 99 that was present before oxidation and consequent col- lapse of the walls. The schistose character of much of the wall rock would allow a considerable dilation toward the gossan without an obvious appearance of collapse in the outcrop. Enrichment—Gold occurs in gossan as a residual en- richment, and silver and copper have been enriched in the upper part of the sulfide ore below the gossan. Zinc that was present in the primary ore has been re- moved. The weight of the gossan at the Iron Mountain mine is reported by the mine staff as 165 pounds per cubic foot. Jackson and Knaebel (1932, p. 125) report 100 to 125 pounds per cubic foot. The massive sulfide ore weighs 265 pounds per cubic foot. Gold in Iron Mountain gossan averaged 0.073 ounce per ton but gold in the massive sulfide ore averaged 0.01 ounce per ton, which appears to be a normal residual enrichment of about 2: 1, due to loss of weight in the formation of gossan. Silver is enriched along the contact between massive sulfide and gossan. No records remain of the silver- mining operations that were carried on in the late 1800’s at the Iron Mountain mine, which is the only massive sulfide deposit at which silver ore was mined, but some assays are reported by the Mountain Copper Co., Ltd. (C. \V. McClung, 19-17, oral communication) to have been as high as several hundred ounces of silver per ton. The zone of silver enrichment above the Old Mine ore body at Iron Mountain \‘as fairly extensive owing to its favorable topographic setting, but at other mines this zone is only a few inches thick. Few ex- posures of the enriched zone remain at any of the mines, but where it has been seen, it is a zone of sandy, dis- integrated sulfides, locally stained gray by chalcocite. The sandy sulfides contain some clay and silica sand or silica sponge. The enriched zone is similar in many respects to the enriched zone over the massive sulfide ore at Flin Flon, Manitoba (Brownell and Kinkel, 1935, p. 269—270) except that it is less extensive at all the mines except the Iron Mountain mine. Data on the enrichment in copper are available only for the Iron Mountain, Golinsky, and Mammoth mines, and supergene enrichment was of economic importance only at these mines; assay data are given in the descrip— tions of these mines. The topography over parts of these ore bodies favored the oxidation of the ore, result- ing in appreciable enrichment in copper in the sulfide body under the gossan. The secondary copper mineral was probably largely sooty chalcocite; no copper oxides, carbonates, or silicates are present. At most of the mines the occurrence of fiat—lying ore bodies in areas of steep topography did not favor oxidation, and little or no enrichment is present. Also, as noted above, ore 379725;;36i—8 bodies under 50—100 feet of rock cover were not affected by oxidation. AGE OF MINERALIZATION The base-metal mineralization, as distinct from the gold mineralization, in the Shasta district is probably Late Jurassic or Early Cretaceous in age, but no direct evidence was found in the “Test Shasta district to accu- rately date the mineralization. All the massive sulfide deposits in the )Vest Shasta district occur in the Bala- klala rhyolite of Middle Devonian age, but the Bragdon formation of Mississippian age and the Mule Mountain stock of albite granite of Late Jurassic or Early Cre- taceous age are also slightly mineralized. The Upper Cretaceous rocks in the )Vest Shasta district and the Lower Cretaceous (Paskenta and Horsetown of Ander— son (1902)) rocks west of the district are not mineralized. Base-metal ores, similar to those in the lVest Shasta district, occur in Balaklala rhyolite at the Greenhorn mine, 9 miles west of Iron Mountain, and in Bully Hill rhyolite and the Pit formation of Triassic age in the East Shasta district. The mineralization in the East and West Shasta districts is so similar in its distinctive mineralogy, hydrothermal alteration, and geologic setting that it would be a remarkable coincidence if it were not all the same age. The age of base-metal mineralization can be dated fairly closely by relating it to the period of orogeny. The youngest formation near the head of the Sacra- mento Valley that was affected by the orogeny is the Potem formation of Jurassic. age (Diller, 1906, p. 5). The oldest formation that is of postorogenic age is the upper part of the Horsetown formation, which noncon« formably overlies the Shasta Bally batholith 18 miles southwest of Bedding, and which is Early Cretaceous in age (Anderson, 1933, p. 1259; Hinds, 1933, p. 113). The location of many base-metal ore deposits of the W'est Shasta. district was controlled by structures that were formed during the main period of orogeny. The ores at the Mammoth mine are in a structural arch, and those at Iron Mountain, Balaklala, and Shasta King mines are in structural troughs. The ore deposits at the Iron Mountain, Balaklala, and Mammoth mines are also spatially related to major east—west faults. The folding, and probably also the faulting, occurred during the Late Jurassic or Early Cretaceous orogeny, al- though the only definite dating of the. faults is post- Bragdon (Mississippian) in age in the “Test Shasta district and post—Triassic in age in the East Shasta dis— trict. Flat bedding—plane foliation and steep fracture cleavage, formed during orogeny, are major ore controls. It therefore seems certain that the period of base-metal 100 lnineralization was later than the main period of orogeny during which these controlling structures were formed. No intrusive bodies are present to which the ore de- posit-s can be related with certainty, either spatially or genetically. Syntectonic stocks of albite granite of Late Jurassic or Early Cretaceous age that have the closest spatial relationship to the base-metal deposits are the Mule Mountain stock of albite granite, at the south end of the W est Shasta mineral belt, and a stock of albite granite near the bridge over the Pit River 011 U. S. Highway 99N, but this stock is 5 miles west of the Bully Hill mine and 13 miles west of the After- thought mine in the eastern part of the East Shasta district. Another small stock of albite granite is shown by Diller (1906) to be 6 miles southeast of the After— ‘ thought mine. The Mule Mountain stock is cut by gash veins that have a filling of gold—quartz and small amounts of pyrite, chalcopyrite, and galena; foliated zones in the albite granite contain a little pyrite but the stock does not contain any base-metal ore. The Shasta Bally batholith of biotite—quartz diorite, which is also of Late Jurassic or Early Cretaceous age, is in the southwestern part of the Igo quadrangle, but no similar intrusive is present in the East Shasta district; ore de- posits in the East Shasta district are almost 30 miles from the Shasta Bally batholith. The dikes of dacite porphyry and quartz latite porphyry that are related to the Shasta Bally batholith are not mineralized and do not show any evidence of hydrothermal alteration ex- cept where dikes of Birdseye porphyry are adjacent to later gold-quartz veins: Some of the faults that cut the massive sulfide depos— its show premineral and postmineral movement. The writers interpret the premineral movement on these faults as having taken place during the later part of the period of orogenic stress, and the postmineral move- ment as the minor readjustments during the relaxation of the stress. The mineral deposits are controlled by structural features formed during the orogeny, but the Cretaceous rocks, and the dikes related to the Shasta Bally batholith of postorogenic age are unaffected by this 1’1'1ineralization. Thus all the evidence indicates a Late Jurassic or Early Cretaceous age for the base- metal deposits of the Shasta. copper-zinc district. SUMMARY OF BASE—METAL ORE CONTROLS Three main controls of the massive sulfide ores can be recognized in the copper—zinc district; these are the stratigraphic control in the Balaklala rhyolite, the structural control by folds and foliation, and the feeder— fissures along which the solutions ascended. All the base-metal ore bodies in the “Vest Shasta dis- trict are in the Balaklala rhyolite, and are limited to GEOLOGY AND BASE-METAL DEPOSITS, WEST SHASTA COPPER-ZINC DISTRICT one stratigraphic zone in the rhyolite. This zone com— prises the flows and pyroclastic material of the upper part of the middle unit in the Balaklala. Scattered pyritized rock and local areas of fairly strongly pyrit— ized rock are found in the lower unit of the Balaklala, but no ore bodies are known in this unit. Likewise, the upper unit, of coarse-phenocryst rhyolite, is not known to contain ore bodies with the possible exception of one small ore body near the base of the unit at the Mam— moth mine. All the known ore is in the middle unit of the Balaklala, and Where the stratigraphy can be mapped in detail, the ore is in the upper part of the middle unit. Ore bodies are localized along broad folds and warps, although they show little preference between anticlines and synclines. The mineral belt as a whole follows the trend of a series of broad folds that constitute a gently arched anticlinorium that has a low culmination in the central part of the mineral belt. There is good correla— tion between the axis of the anticlinorium and the min- eral belt, and between the culmination and the central part of the mineral district. The southwest end of the anticlinorium is cut by‘intr usions but at the noitheast end there is little mineralization where the folds plunge beneath the ove1 lying sediments. Individual ore bodies are localized along minor folds, basins, and small arch or dome structures. The intersection of steep f1 actuie cleavage and gently dipping bedding plane foliation has provided a shat- tered area capped by impervious material that has local- ized some ore bodies. The amount of foliation is de— pendent on the competence of the rocks and on their stratigraphic position in folds. “Iliere much bedded pyroclastic material is present at the base of the upper unit, bedding-plane foliation has formed, but steeply foliated rocks in the lower and middle units of the Balaklala rhyolite are generally capped by unfoliated rock of the upper unit. Some faults of premineral age have acted as channel- ways for ore-bearing solutions. They generally cut across the strike of folds and foliation at a considerable angle, and are influential in localizing ore bodies in cer- tain parts of a fold. A conjunction of the three types of ore controls was probably a necessary prerequisite to the formation of a major ore body. Two other types of ore controls for base—metal de- posits can be mentioned, although their importance can- not be evaluated. One of these is the presence of a very thick cover of shale that overlay the Balaklala rhyolite at the time of ore deposition. This cover of shale was relatively impervious to solutions, as fractures in the brittle rocks below tend to die out on entering the shale. An impervious “cap rock” many thousands of feet thick BASE-METAL over the anticlinorium would hardly fail to have a ponding or channeling effect on rising solutions. Another possible control of ore localization is the ten— dency for solutions that rose along steep feeder channels to leave these channels and follow fractured zones in gent-1y plunging folds. The importance of this type of control for ores in this district has been advocated by Walker (written communication), and the continuity of the pyritized rock (but not massive sulfide ore) at the orezone, as indicated by surface exposures and by drill holes, lends weight to this concept. Known feeder fis- sures are widely spaced, although undoubtedly some have not been recognized, but pyritized rock along the ore zone occurs at considerable distances from possible feeder channels. In addition, some ore bodies have formed where no feeder fissure is recognizable. It thus seems probable that the ore-bearing solutions did travel laterally for considerable distances from the steep feeder channels in some instances, probably guided by relatively more pervious channels formed along the in— tersection of fracture cleavage and bedding-plane folia- tion in the crests and troughs of folds. Such solutions probably account for the widespread pyrite formed dur- ing the early pyrite-quartz stage. EXPLORATION POSSIBILITIES OF THE WEST SHASTA DISTRICT Many favorable areas where the ore zone has not been eroded remain to be explored in the W'est Shasta dis— trict. The areas that are worthy of exploration contain the middle unit of the Balaklala rhyolite within the limits of the main mineral belt; those that can be elimi— nated are areas in which the middle unit has been eroded ,_ or was not deposited, or where it is covered by a con— siderable thickness of younger sedimentary rocks. These covered areas are eliminated because they are off the trend of the main mineral belt and because favorable structures and mineralized zones cannot be delimited. Base-metal ore bodies may be present under the sedimentary rocks, although the main covered areas lie either 011 the flanks of the anticlinorium or farther down the plunge from the culmination of the folding; both of these locations are less favorable for prospect- ing than the higher parts of the folded structure along the trend of the mineral belt. The areas within which it is probable that new bodies of massive sulfide ore can be found are outlined on plate 4. This map shows faults, areas of hydro— thermally altered rocks, pyritized rocks, and the known ore bodies and major prospects. Plate 4 also shows the location of the exploratory drill holes that already have ' been drilled, with the exception of some holes drilled near known ore. 101 DEPOSITS The principal feature used in determining areas in which new ore bodies may be found within the mineral belt is the stratigraphic sequence, as all known ore in the district thus far has been found in the middle unit of the Balaklala rhyolite. In addition, the largest ore bodies occur in the upper part of the middle unit, par« ticularly where it contains much bedded pyroclastic material. No minable ore bodies have been found in the upper or lower units, although the lower unit is heavily pyritized at some places. No massive sulfide deposits have been found in the underlying Copley greenstone. The Copley is exposed in very few places along the mineral belt, and the possibility of copper deposits in the chloritic rocks of the Copley along feeder channels should not be ignored. However, the Copley is deeply buried along most of the mineral belt and evidence of feeder channels in certain areas is indicated, but not proved. In addition, the broad expanse of Copley that is exposed in the mapped area, which includes areas within the mineral belt, contains scarcely any copper minerals. No massive pyritic bodies are known in the iopley except the small bodies explored at the Akers prospect on Squaw Creek, and a few very small bodies in the southeast corner of the Igo quadrangle.G No ore bodies or mineralized rocks have been found in the upper unit of the Balaklala, but areas in which this unit is present are considered favorable for exploration, be- cause the middle unit can be assumed to underlie the upper. N0 lateral controls for ore can be used with certainty to eliminate areas, where the middle unit of the Balak- lala is known to be present. Although most ore occurs along the crests or troughs of gentle folds or warps, some ore occurs on the flanks of folds, and these struc- tures, while probably less favorable, cannot be elimi- nated from exploration. The most favorable areas in which to search for new ore bodies are between known ore bodies along the trend of the mineral belt, which is also the trend of foliation and folded structures. Equally favorable areas, in some instances, are the extensions of folded structures beyond known ore bodies. Other particularly favorable, but less obvious, areas lie along the trend of fissures that appear to be main feeder channels, where these fissures cross folds in the productive zone. Less favorable areas are where the middle unit of the Balaklala rhyolite is thin, or where the upper part of the middle unit has been eroded. Areas Where the rocks are closely folded are less favorable than those in which the dips are gentle. 6Reconnaissance in the unmapped area southeast of Mule Mountain suggests that prospecting for base-metal ore bodies in the hydrothermally altered rhyolite in this area is warranted. 102 Some bodies of rocks that are lithologically similar to those of the middle unit are shown on the geologic maps, but they are not included in the favorable zones because they are intrusive rhyolite or because they are off the trend of the main mineral belt and are not mineralized or hydrothermally altered. Some exploration holes have been drilled along the trend of the ore zone, particularly between the Keystone and the Stowell mines and at several other localities. Many of these holes penetrated the ore zone and cut pyritized rock, but none penetrated massive sulfide ore, as far as is known. The position of the drill holes is shown on plate 4. Some of the holes were drilled in areas which the writers consider the most favorable geologically, and they reduce the possibility of locating new ore in these areas; they do not eliminate the areas because most of the holes are widely spaced, and because ore bodies may occur on either side of a line of holes that follows the main ore trend. Plate 4 shows the particularly favorable places within the more promising areas in which to start exploration for new ore bodies. These areas are not listed in order of favorability. ( 1) The area between the Balaklala and the Keystone mines. Drilling already done indicates that there is a good possibility of bodies of massive sulfide ore between these two mines. (2) East and southeast of the Balaklala mine. Considerable drilling has been done in this area but the possibilities are not exhausted. (3) The area between the Keystone and Stowell mines. A line of drill holes cut the ore zone at a moderate depth, and additional drilling should be done northwest and southeast of this line of holes. (4) Southwest of the Early Bird mine. (5) The area immediately north of the Shasta King mine should be prospected for a continuation of the Shasta King ore zone. This could be done by underground exploration from the workings of the Shasta King mine. (6) The hydrothermally altered rocks north of the anticline which has a core of Copley greenstone (2,000 feet northwest of the Brick Flat and Richmond ore bodies at the Iron Mountain mine) should be explored. (7) The area under Sugar-loaf Mountain between the Busy Bee workings at the northeast end of the Iron Mountain ore bodies and the Sugar-loaf mine probably contains massive sul- fide bodies. However, the character of the ore in the Busy Bee workings and the Sugar-loaf mine suggests that these sulfide bodies contain very little copper or zinc, and the topography makes exploration by drilling diflicult. (8) Southwest of the Mammoth mine. The contact between the upper and middle units of the Balaklala rhyolite may be expected to flatten southwest of the Friday Lowden workings of the Mammoth mine, and the ore bodies in the Mammoth mine are larger where the contact has a gentle dip than where it has a steep dip, as in the Friday Lowden workings. (9) The area immediately northeast of the Golinsky mine. (10) Northwest of the Sutro mine. (11) Southwest of the Balaklala Angle Station gossan. GEOLOGY AND BASE-METAL DEPOSITS, WEST SHASTA COPPER-ZINC DISTRICT DESCRIPTION OF DEPOSITS AKERS PROSPECT The Akers prospect (pl. 4) is in the canyon of Squaw Creek in secs. 6 and 7, T. 33 N., R. 5 W., at an altitude of 1,100 feet; the portals of the several adits are about 300 feet west of the southeast corner of sec. 6. A pyritized shear zone oriented N. 10° “7., 48° E. cuts the Copley greenstone and intrusive rhyolitic dikes at the adits. Some massive pyrite and pyritized rock is on the dumps. Another adit is 700 feet north of Squaw Creek at an altitude of about 1,400 feet. The only in- formation on the ore or on the underground workings is that given by Tucker (1926, p. 144). He reports, in part: The ore occurs in small irregular lenticular ore bodies, along irregular fissures, one of which trends north and south, with a dip of 60° east, and the other having a N. 40° W. trend. The ore is chiefly pyrite with more or less chalcopyrite and occa- sional traces of bornite, and carries $2 per ton in gold and silver. The present work is confined to No. 3 tunnel, where a series of parallel north and south and a N. 40° W. fracture are being drifted on ; and some small lenses of ore have been exposed along these fractures, varying in width from 2 inches to 2 feet, and from 10 to 15 feet in length. . . . 0n the claims located on the south side of Squaw Creek are two tunnels which have lengths of 100 feet. In the lower tunnel, which is driven on a N. 40° W. fracture, a small lens of ore 40 feet in length and about 2 feet in width has been developed. Samples taken from this orebody are reported to carry from 2 percent to 6 percent copper. The prospect has been inactive since shortly after 1926. BALAKLALA MINE The Balaklala mine is located in secs. 11, 12, 13, and 14, T. 33 N., R. 6 VV., on the southern slope of the rugged canyon of Squaw Creek at an altitude of 2,250 feet in the central part of the West Shasta copper-zinc district. The mine is owned by W. A. Kerr. It was accessible by car in 1950 along a steep one-way dirt road that started from the site of the old smelter town of Coram on the Sacramento River. lVashouts from the winter rains make this road impassable each year, although a few days work with a bulldozer is usually sufficient to make the road passable again. The mine has not operated since 1928; a fire in 1924 destroyed the mine plant, and another fire in 1931 destroyed the tram terminal and ore bunkers. The 16,500—foot aerial tramway on which ore was once hauled from the mine to a smelter on the Sac- ramento River is down, and the towers have burned. The Balaklala smelter at Coram on the Sacramento River was closed in 1911 because of smoke-damage suits and was dismantled in 1926. Recent salvage operations for scrap metal have removed the vestiges of the mine plant. IV. A. Kerr owns a group of claims that contain sev- eral individual ore bodies. These are in the Balaklala BALAKLALA MINE mine: the Balaklala Angle Station gossan; the Early Bird mine; and the Vulcan (Great Verde) prospect (pl. 4). The Balaklala mine contains two large ore bodies, the Windy Camp, and its faulted extension, the VVeil, and several smaller ore bodies and prospects. Although the Balaklala ore bodies were among the early discoveries in the district, the date is not known. Information on the history of the mine is mainly from reports of the California Division of Mines, but also from an unpublished report by G. F. Seager and from private mine reports. The mine was first named the Balaklava mine, and is listed as a “quartz” mine in the report of the Cali- fornia State Mineralogist for 1894 (Anon, 1894, p. 245), but by 1896 the name had been changed to Balaklala, and it has been subsequently known by that name. Adits were driven into the gossan at the outcrop of the \Vindy Camp, \Veil, and Balaklala Angle Station gos- sans from 1890 to 1900. The Windy Camp ore body cropped out as a large gossan, but its faulted extension, the )Veil, cropped out only as fringes of gossan along the northeasterly edge of the ore body. The VVeil ore body was located mainly by drilling. Many smaller ones did not crop out and were located by drilling. The Balaklala mine was operated by the Balaklala Mining Co. of San Francisco, but was leased by them to the Western Exploration Co. in 1902. The latter company explored the mine, and by early 1902, exten- sive drilling and 3,500 feet of drifting and crosscutting had been done. The property was taken over in 1905 by the First National Copper Co. and operated under the name of the Balaklala Consolidated Copper Co. This company operated the mine from 1906 to 1911, and 103 from 1914( ?) to May 1919, when work was suspended. The mine was leased by the Mammoth Copper Co. (United States Smelting Refining and Mining Co.) and was reopened in November 1923. No mining was done until 1924, but during 1924—25 some ore was re- moved from the Windy Camp and High Grade ore bodies. In March 1926 the Balaklala mine was leased to the Mason Valley Mining Co. This company mined 5,000 tons of ore from pillars in the Windy Camp and North W’eil 170 ore bodies from March 1926 to May 1928, when the mine was again closed. It has not oper- ated since 1928. The mine has been inaccessible for many years, but the portal of tunnel 8 from the open— cut was reopened by a private company in 1948. Bad air and caved stopes allowed only a limited examination of the underground workings at this level. Production and grade of ore. About 1,200,000 tons of ore has been produced from the Balaklala mine, but the exact total is not known. Estimates range from 900,000 to 1,200,000 tons. Table 7 gives the data on production and grade of ore compiled by the writers from many sources. The greatest average daily ton- nage produced from the mine was 300 tons per day in 1918. GEOLOGY OF THE MINE AREA Stratigraphy.——The rocks in the mine area include the lower part of the upper unit of the Balaklala rhyo- lite and the upper part of the middle unit of the Bala- klala. The upper unit (“cap rock”) includes massive coarse-phenocryst rhyolite and the pyroclastic rocks of the transition zone between the upper and middle units of the Balaklala. This massive coarse-phenocryst rhy— olite, which overlies the ore zone, is well exposed in the TABLE 7.—P1'oduction and grade of ore from the Balaklala mine 1 [Published with permission of the owners] Grade . .. - . . Production 1 ‘ i Ore body or periods of mine operation (short tons) Gold Silver i Copper Zinc Iron Sulfur i Silica l £23123?) 18:11:]:ng ‘ (percent) (percent) (percent) (percent) (percent) 1 __ -i ; J Weill ____________________________________________________ 720,000 ................ i 0.025 0. 8 l 2. 75 l l Windy Camp.“ _ 295,000 _ i .02 . 8 2. 50 North \Veil 170 .. . 03 1. 0 3. 4 High Grade... .10 5.0 12.0 9, 83, 84, 153.... .......... .... .. . 025 1.0 \ 2. 85 Bull ................................ 2,000 (approx) ........ I .048 4. 0 10.0 North Wei! 3 .................................................................... . 025 . 8 i 2. 75 Wéndy Calm}; and High Grade (mined by Mammoth ________________________ l .026 .96 i 2. 5G opper 0. .2 é Balaklala mine operation, 1915—19 3 _______________________ 351,171 4 _______________ i .031 1, 0 i 3. 08 ____________ l ______________________________ Wei] (assays by Calif. Div. Mines)5 _____________________________________________ 1‘ .0228 .82 i 2. 734 ____________ 29.1 i ____________ 29.8 Windy Camp (assays by Calif. Div. Mines) 5 ____________________________________ i .025 .85 l 2. 46 ____________ 29.8 ____________ 23. 5 4 l . .3 Balaklala ore bodies (assays by Calif. Div. Mines) 6 _____________________________ i .03 .9 1 2. 7 2 2 31. 5 35. 2 21. 4 {$20 i Ales Pyritic ore remaining in mine (estimated grade) 2 _______ i ________________________ .02 .86 i 2. 40 ____________ i 34. 8 39. 4 18. 3 Total .............................................. i 1,200,000 (estimate)____ .028 1.0 2. 80 1.30) ............ . ....................... .. l i i 1 Source of data, Seagcr, G. F. (unpublished report 1934, quoting S. A. Holman, manager and general superintendent of mine), unless otherwise noted. 1 Data from United States Smelting Refining and Mining Co. 3 W. A. Kerr, Balaklala Consolidated Copper Co. 4 This figure includes ore from some of the ore bodies above. 5 Calif. State Min. Bur., 1908, Bull. 50, p. 90. 6 Calif. State Min. Bur. 1926, v. 22, p. 145. FIGURE 47.—View of opencut at Balaklala mine showing part of the middle unit of the Balaklala rhyolite. rhyolite fragments as much as 12 inches in diameter; white porphyritic rhyolite (b) with 2~millimeter quartz phenocrysts; nonporphyritic rhyolite pyroclastic bed (0) ; mineralized rhyolite ((1) that contains a few small quartz phenocrysts and is strongly altered: massive sulfide ore (0). Note the irregular Contact to ore. opencut Where the overlying rocks have been dropped to the level of the ore zone by the Balaklala fault, and is also exposed on the road from the opencut to the portal of the VVeil tunnel, and on the ridges above the opencut. The coarse-phenocryst rhyolite is a hard light—gray to white rock in unweathered exposures, but weathers to soft, punky light-tan rock. The rock is massive and essentially structureless, except for a local formation of what appears to be flow banding. The phenocrysts ob- served in hand specimens are predominantly quartz, although locally, as in the area north and west of the portal of the keystone mine, feldspar phenocrysts are prominent. In thin sections, feldspar and quartz pheno— crysts are seen to be equal in amount, but weathering makes the feldspar difficult to recognize. The pheno- crysts are abundant and range from 8 to 5 millimeters across. GEOLOGY AND BASE—METAL DEPOSITS, WEST SHASTA COPPER-ZINC DISTRICT Coarse pyroclastic layer (a) with The massive coarse-phenocryst rhyolite in this area is underlain by shaly tuff and coarse and fine pyroclas~ tic material, which is exposed above the ore in the glory hole (fig. 47) and on the ridges south and southwest of it. The different types of pyroclastic material have little horizontal continuity, but the zone as a unit is continuous. The pyroclastic material ranges from a thin black shale containing minor tuft layers, to tan, shaly tufl' and thin beds of lapilli tuif that have a maxi- mum thickness of 40 feet, 2,500 feet east of the mine, to coarse lapilli tuff mixed with coarse volcanic breccia that contains rounded fragments 6 inches in diameter. A few of the larger fragments have lighter or darker colored rims and appear to be volcanic bombs. Some fragments of coarse-phenocryst rhyolite occur in the volcanic breccia, and chips of quartz phenocrysts as much as 4 millimeters across are common in layers of BALAKLALA MINE crystal tuif. Some of the bedded material appears to be arkosic. The contact between the massive coarse-phenocryst rhyolite and the underlying rocks of the transition zone east of the opencut is sharp, but to the south, the massive rhyolite thins abruptly and interfingers with tutf. The facies change occurs between the opencut and the sum- mit of the ridge south of the Keystone mine. Shaly and rhyolitic tutf layers are interbedded with coarse-pheno- cryst porphyry flows on the ridge east of the Balaklala mine. The contact between the upper and the middle units of the Balaklala rhyolite is at the base of the trans- ition zone. The upper part of the middle unit of the Balaklala in the mine area is composed of porphyritic rhyolite con— taining 1- to 3-millimeter quartz phenocrysts, volcanic and flow breccia that contains fragments of porphyritic and nonporphyritic rhyolite, and flows of nonpor- phyritic rhyolite. Geologic structure 0 f the mine area—The rocks in the mine area have been gently folded and warped and are cut by many faults. A poorly developed steeply dip- ping foliation has been superposed on the rocks of the middle unit. Dips as high as 75° have been measured in bedded tuff near the mine, but dips of 10°~30° are more common. The folds could not be mapped in detail because of the limited exposures of bedded material and the lack of sufficient underground data from mine work- ings and drill holes. However, several small synclines and anticlines were recognized on the basis of bedding in tuff and from the outcrop pattern, but little parallelism between the axes of these small folds or warps is ap- parent. Dips on bedded rocks at the surface near the Windy Camp—Weil ore body indicate that the flows that contain this ore body have a basin shape in the mine area. Two similar folds occur east of the ore body, but these folds appear to be offset by the faults in the two gulches immediately east of the Balaklala mine and could not be traced. Many faults are present in the underground work- ings; the larger ones are shown on the map of under- ground workings (pl. 5). Most of these faults have a small offset and cannot be recognized at the surface. The Balaklala fault, however, has a vertical displace- ment of about 220 feet, and can be traced west of the mine with fair accuracy for 1% miles. It is a steeply dipping normal fault that is downthrown on the north. ORE DEPOSITS General descriptions—The mine was inaccessible in 1934 when G. F. Seager was doing geologic work in the West Shasta copper-zinc district, but he was able to obtain a great deal of detailed information from S. A. 105 Holman, who was manager and general superintendent during much of the time when the mine was operating. The ore of the Balaklala mine occurs as large, flat— lying, tabular bodies of massive pyrite that contain copper and zinc minerals and small amounts of gold and silver. Two large ore bodies and many small ones are present in the mine (pls. 5 and 6). The two large ore bodies, the ‘Vindy Camp and the \Veil, before being separated by the Balaklala fault, were formerly one elongate basin—shaped lens of pyritic ore. The smaller ore bodies are all massive sulfide ore, although the cop- per and zinc content varies considerably. The “Vindy Camp-“Veil ore body before faulting was 1,400 feet long and slightly less than 500 feet wide. If the gossan in the vicinity of adits 1, 2, 3, and 4 is an extension of this ore zone, as is indicated by cross section H—I—J—K, plate 6, the ore lens was 1,800 feet long. In addition, fairly continuous mineralization at the ore zone has been demonstrated by drilling between the Balaklala and the Keystone mines, which lies 1,400 feet southwest of adit 1, and between the northwest end of the stopes on the )Veil ore body and the sulfide bodies in the Horse tunnel. The operators of the Balaklala mine recognized the basinlike shape of the prefaulted ore body, and the presence of an ore zone, as their extensive exploration by drilling appears to have taken this structure into account. The lowest point in the ore body is in the cen- tral part of stope 5 (pl. 5) From this point the base of the ore zone rises (correcting for offset on the Bala- klala fault) 135 feet to the High Grade stope to the north, 154 feet to stope 16 to the northeast, 100 feet to the 158 ore body to the southeast, and 340 feet to the gossan in adit 1 to the southwest. The rise to the north- west is not as steep as in other directions. Drill holes show that the basin structure flattens to the southwest (pl. 6, D—E—F—G). Character of the ore bodies.———The ore in the Balaklala mine is a hard fine-grained pyritic ore that contains chalcopyrite and sphalerite and small amounts of gold and silver. The ore as mined contained 23 percent SiO2 (in some of the early reports, no distinction is made between silica and insoluble material), but this was in part due to remnants of unreplaced rock in the ore and to small included bands of waste; the ore had an average weight of 7.25 cubic feet to the ton. The aggregate thickness of the sequence of rhyolitic rocks in the ore zone as here used is at least 300 feet. The top of this sequence is the base of the upper unit of the Balaklala rhyolite, and occurs throughout the district, but the base of the ore zone is not marked by any stratigraphic break and includes the lowest known ore. In areas between individual ore bodies, the 106 pyritized zone is commonly limited to a thin layer a few feet to a few tens of feet thick immediately below the base of the upper unit. Thus in the general ore- bearing area the mineralized zone is continuous, al- though individual drill holes may cut through areas that contain no massive. sulfide, and locally little or no pyrite. Massive sulfide ore bodies occur as sharply bounded masses in a general ore zone of weakly pyritized to well-pyritized rock. The outlines of the stopes on the composite map of the Balaklala mine (pl. 5) commonly mark the limits of the massive sulfide ore, and beyond those limits the wall rock is either barren or weakly pyritized. There is a sharp contact along most stope walls between the massive sulfide body and the wall rock. However, a considerable amount of massive sulfide ore that was below a minable grade or was inaccessible from work- ings remains in place in some areas, as along the south— east edge of the “findy Camp ore body (pl. 6, H—I—J) , and massive sulfide, observed in some drill holes, has not been mined. Also, at a few places, the end of a stope marks the point at which lenses of ore wedge down to ore that was too thin to be minable. However, according to Holman’s description, the edges of most of the sulfide bodies were smooth and sharp, although curved. One main layer in the ore zone includes the lVindy Camp-“Veil ore bodies and is fringed with smaller ore bodies, but. a few lie above or below the principal ore layer. The North )Veil 170, the High Grade stope, the Bull, and stopes 3, 8, S), 84, 92, and 153 were isolated ore bodies, not connected to the main sulfide mass in the \Vindy Camp—“’eil except by the weakly pyritized and locally barren ore zone. The Bull is an isolated bean— shaped ore body well below the main ore layer. The North )Veil 170 lies above the )Veil, and stope 92 lies below the main zone of the \Vindy Camp. The North lVeil 3, although it is connected with the “’eil, lies in part about 20 feet below the main \Veil. The oc— currence of ore bodies at several levels in the ore zone is shown on the cross section, but it is probable that some of these are fault segments. The ore bodies east of the “’indy Camp are isolated sulfide bodies, however, as the rock between stope 84 and the ‘Vindy Camp is either slightly pyritized or barren rhyolite where it is cut by drill holes. Ore was found in two drill holes southeast of stope 5 (pl. 5), which extends the ore in this stope toward stope 9, but an area of barren ground is probably present between stopes 9 and 5. The thickness of the massive sulfide ore in individual ore bodies ranges from a few feet to 75 feet. The lV'ndy Camp—“Veil ore body reaches a maximum thick- GEOLOGY AND BASE-METAL DEPOSITS, WEST SHASTA COPPER—ZINC DISTRICT ness of 75 feet in the central part of the lens from which the ore decreases in thickness in all directions. The North “'eil 170 is a lens-shaped ore body that lies about 65 feet above the top of the \Veil; it pinches out to the north, south, and east, but is reported to be termi- nated on the west by a fault that dips 45° E. The average thickness is 25 feet, and the maximum is 40 feet. Ore body 153 averages 20 feet in thickness; no. 81, 20 feet; no. 83, 25 feet; and no. 9, 30 feet. Stope 92, lying west of the lVindy Camp, averages 25 feet in thickness. The grade of the Balaklala ore is in general uniform, but some separate ore bodies and a few masses within the larger bodies differ considerably from the general average. Table 7 gives the assay data that are known on different ore bodies. The )Veil was of uniform grade throughout, including the North lVeil 3, but in the main \Vindy Camp ore body, richer grade ore occurred in the lower 10 feet in the opencut. This higher grade ore extended 200 feet east of the opencut, and averaged 5 percent copper, 0.036 ounce of gold, and 1.0 ounce of silver. The ore lying southwest and west of the open- cut averaged 1.75 percent copper. Seager reports that near the base of the ore body in the opencut, and east under the portal of tunnel 8, flat-lying bands of chal- copyrite from 2 to 12 inches thick cut the massive pyrite and replace porphyritic rhyolite. No reason is known for the localization of high copper content in ore bodies such as the High Grade (12.0 percent copper) and the Bull (10 percent copper). In each of these ore bodies the gold content increases with the copper, but the grade of the zinc remains constant, suggesting that copper and gold are closely associated at the Balaklala mine. Ore contro?s.——The broad ore control for the main ore zone at the Balaklala mine is the contact between the overlying upper unit of the Balaklala rhyolite and the middle unit of the Balaklala. All ore occurs at or a short distance below this contact. More detailed ore controls appear to be the basin-shaped fold in the rocks and the thin layers of bedding—plane foliation in the flat-lying bed of pyroclastic rock and shaly tuff that immediately overlies the main ore zone. Rounded nodules of unreplaced rock 2 to 12 inches in diameter occur in the ore in the opencut. Most of the rock remnants are composed of porphyritic rhyolite containing 2—millimeter phenoerysts, but some are frag- ments of nonporphyritic rhyolite. The massive sulfide ore appears to have replaced both varieties of rhyolite, but apparently did not replace the overlying pyroclastic material. Many faults are present in the mine area, but no evi- dence of feeder channels was seen, except that some ore BALAKLALA MINE ' bodies stop abruptly against faults, and no faulted ex- tensions of such ore bodies have been found. Exploration possibilities.—Even though a large amount of exploratory drilling has been done in and around the Balaklala mine, some favorable areas re- main to be explored. The most favorable zones are between the \Vindy Camp ore body and the Keystone mine ore bodies, which lie 1,800 feet to the southwest. Some drilling has been done in this area, and pyritized rocks were found in the ore zone. Additional prospect,— ing should be done to the south and east of the present holes. A large area of the ore zone lies south and east of the small lens of ore at the Horse tunnel. In this area the ore Zone immediately under the base of the upper unit is covered by rhyolite of the upper unit. Drilling, based on detailed mapping of the folds and faults, might lead to the discovery of new ore bodies in this area. The possibility of finding small isolated bodies of ore below the main W’indy Camp-VVeil ore body is indicated by the present drill holes. Some additional exploration below the main ore zone seems warranted if the lower mine levels are reopened. BALAKLALA ANGLE STATION GOSSAN The Balaklala Angle Station gossan crops out in sec. 7, T. 33 N., R. 5 “7., about 1 mile east of the Balaklala mine, along the road leading from Coram to the mine. The prospect is at an altitude of 2,500 feet and is north and immediately below the Balaklala Angle Station on the old Balaklala tram line (pl. 4). This gossan has been explored by many shafts, short adits, and drill holes, but no unoxidized sulfide has been found (fig. 48). None of the gossan has been mined. The prospect is owned by the Balaklala Con- solidated Copper Co. Geology—T he gossan lies immediately below the base of the upper unit of the Balaklala rhyolite, which in this area is composed largely of pyroclastic material. These pyroclastic rocks comprise poorly bedded tuif, much of which contains quartz crystals more than 5 millimeters across, and fine volcanic breccia that con— tains many lithic fragments of nonporphyritic rhyolite. The gossan is in a hydrothermally altered porphyritic rhyolite that is light greenish gray to pink or lavender, and contains 2- to 3—millimeter quartz phenocrysts. Part of the rock that contains the gossan appears to be pyroclastic material. Rocks of the upper and middle units of the Balaklala in this area are strongly pyritized and hydrothermally altered and are punky white, or light—greenish rocks, or have shades of blue—green, red, or lavender. 107 A notable feature. of the Balaklala Angle Station gos- san is that the gossan and enclosing rocks are not in place, but are parts of a shallow landslide. This slide, in turn, is only one of a series that are present as far as the canyon of Squaw Creek 2,500 feet to the north. The jumbled, broken character of the gossan and enclosing rocks in the slides is shown in the deep washes on the hill slopes below the gossan and in the many shallow shafts and adits in the gossan. At some places in the slide the rocks are broken and disoriented; at others the gossan and enclosing rocks are broken into rather large blocks that have moved only small amounts. One shaft 49 feet deep exposes large blocks of unbroken rock that has tufl’aceous layers conformable to the general southwesterly dip, but the gossan and rock surrounding these large blocks is crushed and broken by the move- ment of the slide. The large scarp behind the landslide is little eroded, although soil creep and wash have completely covered the sole of the slide. The maximum amount of move- ment that could have occurred is somewhat less than 200 feet vertically, and the appearance of the topography indicates that the movement was probably not much more than 100 feet. Ore deposit—Gossan from massive sulfide is exposed at the surface and in shallow workings, but much of the material that is intermingled with the true gossan is derived from silicified rhyolite that contained from a small percentage to 50 percent pyrite. The gossan and oxidized, pyritized rhyolite occur as boulders as much as 10 feet in diameter scattered over the surface, and none of it is considered to be in place. It is impossible to outline areas of gossan and heavily pyritized rock in more than a. general way. The gossan appears to dip about 20° ST“, comparable to the apparent southwesterly dip of the enclosing pyro— clastic beds, although no reliable attitudes could be ob- tained on the latter. The gossan is at least 15 feet thick in one adit and locally may be thicker, but it seems doubtful that a large area of continuous gossan is pres- ent. Rather, the gossan is probably in small bodies surrounded by strongly pyritized rock, although the jumbled character of the rocks in the slide may contrib- ute to this assumption. This deposit is of interest because of the relatively high gold content of some of the gossan, and because of the possibility of finding an unoxidized extension of the deposit to the southwest or west. The gossan has been extensively sampled, but most of the. samples were taken from dumps or from gossan exposed in pits and adits. An arithmetic average of three separate sets of samples is shown in table 8. 108 GEOLOGY AND BASE-METAL DEPOSITS, WEST SI-IASTA COPPER-ZINC DISTRICT TRUE NORTH mm % Ail/W Wm § Minor gossan float /2375 / (r \\\\\\\\\\li\\li\\\lllllf///// \ / / / < WWW/7% / \l“ 3 o, / / / x l j i :I ,, ,u // ,‘/ i Exploration Co. Published with permission of Balaklala Consolidated Copper 00., owner [1:4 ! M H IJ H U __Ji H <1 r—‘2‘5D~ \ \1,\ \,\¥ \\\ g Compiledzgm‘meivs furniisned by West 51;; 7 7 7 float EXPLANATION 3:: Caved adit Vertical shaft <<<_( Caved inclined shaft, chevr‘ons‘ point down Trench \ Mir/W \\§\\\ 6 _‘-—F\‘\ (:3) /§ 9: / / Opencut_ v v / . ,/—'\ Willi /,.,2/ \ // , / ll/ / //// 50 0 150 Feet 1 l l l l i I 1 | Contour interval 25 feet Dalum is approximate sea level FIGURE 48.—Map of the Workings of the Baluklala Angle Station gossan. BALAKLALA ANGLE STATION GOSSAN TABLE 8,—Arith1rietic average of three separate sets of samples from the Balaklala Angle Station gossan [Data furnished by Coronado Copper and Zinc Co. and the United States Smelting, Refining and Mining 00.] Gold (ounces Silver (ounces Sample per ton) per ton) Group: 1 .............................. 0. 118 1. 4 2 _______________________________ 124 3. 24 3 _______________________________ 178 2. 04 Churn-drill samples indicate that an appreciable part of the gossan will average 0.25 ounce of gold per ton (R. T. Walker and W. J. Walker, written communica- tion). All the samples show that the Balaklala Angle Station gossan carries appreciably more gold than gos- san in other parts of the district. As discussed on page 97, the writers believe that the evidence indicates that this gossan was derived from a deposit of massive sulfide that contains not only pyrite but also sulfides of copper and zinc. The area between the Balaklala Angle Station gossan and the Spread Eagle, Keystone, and Balaklala mines is almost entirely covered by the upper unit of the Ba— laklala rhyolite. Many warps in the base of the upper ’ unit are shown by dips in tufi beds, but reliable attitudes on bedding are too scattered to outline the folds or warps in detail. The gentle southwest dip of the tuff beds at the Balaklala Angle Station gossan must flatten and reverse to a northeast dip to the southwest and west of the gossan, as the base of the upper unit of the Balaklala in these directions is at a higher altitude than it is at the Balaklala Angle Station gossan, although the difference in altitude may be due in part to faulting. Much of the upper unit west and southwest of the Balaklala Angle Station gossan is pyritized and hydro- thermally altered to a white to lavender argillic rock. Thus almost the entire area between the Balaklala Angle Station gossan and the Balaklala, Keystone, and Spread Eagle mines is worthy of exploration because the ore zone is concealed in this area, and much of the overlying upper unit of the Balaklala rhyolite contains products of hydrothermal alteration. CRYSTAL COPPER PROSPECT The Crystal Copper prospect is on a small, north- ward-flowing tributary stream in the canyon of the South Fork of Squaw Creek about 2,000 feet north of the Early Bird mine. It is in sec. 11, T. 33 N., R. 6 W., at an altitude of 2,300 feet (pl. 4). Exploration work consists of many short adits driven into mineral- ized zones in rhyolite. The property is owned by the United States Smelting Refining and Mining Co. 109 Geology—The prospect occurs in a flow of porphy- ritic rhyolite containing 2-millimeter phenocrysts, which is interlayered with minor pyroclastic rocks and flow breccia. The flow of porphyritic rhyolite is sur- rounded by nonporphyritic rhyolite a few hundred feet from the workings; its stratigraphic position is not known. Foliation is limited to narrow zones, and most of the rocks are massive. Ore deposita—Bands of pyritized rhyolite and small lenses of gossan are prominent in the mine area. The general trend of mineralization appears to be N. 20° E. The rock on the dumps is silicified rhyolite that con- tains as much as 50 percent disseminated pyrite. No massive sulfide ore was seen on the dumps, but one gossan 2 feet thick was apparently derived from massive sulfide. Some of the rock in the pyritized areas has been hydrothermally altered to soft white claylike products. No ore has been mined from this prospect. EARLY BIRD MINE The Early Bird mine is owned by the Balaklala Con- solidated Copper Co. It is located in sec. 11, T. 33 N., R. 6 TV. at an altitude of 2,700 feet on the south side of the canyon of the south fork of Squaw Creek. The mine is on an isolated body of massive sulfide ore about 1 mile west of the Balaklala mine (pl. 4). A level road once extended from the Balaklala mine to the Early Bird mine. Although this road was not passable in 1951, it could be made passable with a small amount of repair. The mine was explored by a main adit 350 feet long, and by 460 feet of drifts under the ore body. The portal of the main adit was caved in 1951, but was opened for a short time in 1948. The underground workings, which were examined by the senior author and were mapped by O. W. J arrell,7 were open and accessible except for the first 50 feet near the portal, when the mine was reopened in 1948. Some work was done on small outcrops of gossan near the upper adit (fig. 49) probably as early as 1908, but the ore body was discovered by drilling in 1918. Min- ’ing began in 1922, when the mine was leased to the United States Smelting Refining and Mining Co. This company mined a small tonnage of selected high-grade copper ore during 1922—25. The mine was leased to the Mason Valley Mines Co., 1926—28, during which time the major part of the stoping was done. The produc- tion from the Early Bird mine is given in table 9. 7Map furnished by the West Shasta Exploration Co. 110 GEOLOGY AND BASE-METAL DEPOSITS, WEST SHASTA COPPER—ZINC DISTRICT EXPLANATION E < z c: . U ‘ ’— Slope wash 5 o r 1_‘ ver 1\ l / \ 1 / g 7/ \ / P 3 Porphyri‘tic‘rhyolife‘: 2 mm E Z _ - quartz phenocrysis z 2 o 2 .“ - a 5 ‘e o 11 ‘3 0 m i / 71; /‘ m i//\\///)\ N Nonporphynlic rhyolite , Indefinite contact 1 i i Projecnon of underground workings ‘ 1 .2 Diamond-drill hole ' ._ ~19v/K. outcro 2 ' . \ p1 / /1\ 1/4 1 , 1 a: E1 1/0; 0 .12 21 1/0 :1 E 51 /§ 1 A“ 1/ \ ASSAYS, m PERCENT) r” ,,,,,, . 77777 ~ ”7 7 . ~ ,7 ~ ~- ...7.,,,,, ~y~~~ia EBODV 1. 11 1 DRILL mchK-1 ‘ ‘ P ‘ 1 HOLE NESS 1 1 SlLVER 1 COP ER1 SILICA 1 SULFUR IRON 1 .-.-.,1 (1620-5. .,,1 .., J o ‘ ‘ 1 1 1 1 V ' 7’7" ’ifi‘F"’"’ "1’” ‘ 1 1 20 1 0.02 i 1.96 1 3.80 1 ‘ 1 1 2 1 20 1 1 1.30 ‘ 2,70 1 23.20 1 34,10 1 1 3 1 32 l ‘ 1.38 1 2.78 1 6.94 1 44.90 1 39.90 4 1 24 1 1 1.56 ‘ 2.90 1 11.40 1 43.10 ‘ xiLfi\M,,_,\¥,,i M , ., u; ,fie,_1¥_ 1 Furnished by W. A, Kerr, Balaklala Consolidated Copper Co. 1 Some gossan '/ 3700 100 0 300 Feet L .1. :v, 47*, ., .‘LH,‘.‘.‘ HL.._ Contour interval 20 feet Datum :5 mean sea level > Geology by A. R. Kinkel, Jr. Base furnished by West Shasta Exploration Co. Published with permission of the Balaklala Consolidated Copper 00., owner FIGURE 49.—Geologic map of the Early Bird mine area. EARLY BIRD MINE 111 " Strike and dip cl sulfide fw, lootwall; hw, hanging wall 70 i _1_ £0— _. ; A’ Fault, showing dip; dashed where approxrmately ,— 2740‘ located; U, upthrown side; D, downthrown side __.# EXPLANATION l A’ ’1‘» 191/,2‘ , 7‘4 , A l / Massive sulfide are l / E 1 /’E (w so hw l5 0 _1.—L—— _ ._ .— g /a Sullide contact. showing dip; dashed m [3’ where approximately locatedl l 2 S’ iw, lootwall; hw, hanging wall 1‘ >— 33 M so [5 1 3 4. # ’ l l Outline of stone Fault at 2720’ 15 Main fault at 2700’ d Ponal oi a it Main fault at 2763’ ' Underground worldn—gE—da—shed where projected below stopes " ’3‘ 45“ raise to surface ’7: ‘ (caved) , ,—- '— . lncllned workings, chevrons paint down a Foot of raise 2 o \ 414/4] Location of sample \ Outline of stope r If 27 60' Aim ,¢ ‘ / r g 2740' Al 44L! “r N \l N ‘2 i F2720 i L 2700’ ## ##### ####J_# ##16 Q r \\ ,A N s .. Q l L _ ## ## 1 l i A , . - '_ ,_ ' _ r -‘ ' , 2740' __..# , A ” ' g _ ', , _ Outline of stope i H J'h- ’ ' -fl'**~~ ~~~~~~ i L ,, , , y a y: 1 ~ _ _ 2720' I - _ 2700' 4 From maps furnished by the West Shasta Exploration Co. Published 7 Geology by Oscar W. JarrelL Formerly with permission of the Balaklala Consolidated Copper Co., owner Geologist, West Shasta Exploration Co. FIGURE 50.#Early Bird mine. Composite map of mine level and projection of stopes and ore outline at stope level. 112 TABLE 9,—P1'oductt'on and grade of ore from the Early Bird mine [Data furnished by R. ’1‘. Walker and W. A. Kerr. Zinc content not given in assays] Grade P d t' Operator (sfigrtiufoliisl Gold Silver Copper (ounces (ounces (per- per ton) per ton) cent) United States Smelting Refin- ing and Mining Co., 1922—25, 5, 116 0. 015 0. 4] 10. 27 Mason Valley Mines Co- - _ V, 35, 000 . 034 2. 00 3. 40 Geology—The Early Bird ore body is in light-gray siliceous, porphyritic rhyolite that contains 2-millimeter phenocrysts, typical of the middle unit of the Balaklala rhyolite, but it is overlain by a flow of nonporphyritic rhyolite. The ore body is near the top of the Balaklala rhyolite, however, as shale of the Kennett. formation crops out on the ridge about 300 feet higher than the mine. The upper unit of the Balaklala appears to wedge out a short distance cast of the Early Bird mine, and the base of the Kennett formation takes the place of the base of the upper unit as a stratigraphic marker. The ore body probably occurs between 200 and 300 feet stratigraphically below shale of the Kennett formation, although the attitude of the beds is not known in detail because of the poor outcrop in the mine area. Ore body—The Early Bird ore body is a flat—lying elongate body of massive sulfide that is cut by a cross fault. (fig. 50). The fault divides the ore body into two separate blocks; the south block is about 30 feet higher than the north. The stoped part of the ore body is 428 feet long, but the exposed strike-length of ore is 460 feet, and the faces of both the north and south stopes are in ore. The ore averages about 55 feet in width and has a maximum width of 85 feet; it averages about 15—20 feet in thickness, although the thickness is not uniform. The maximum stope height is 20 feet and the maximum thickness of ore is probably not more than 30 feet. - The north end of the ore body has a synclinal shape as shown in section 0—6”, figure 50; the footwall con— tacts are exposed in the north stope, and in the north drift below the stope (fig. 51). In the south stope the ore has a uniform west dip at the south end but. is cut by a fault on the west side (fig. 50, A—A’ and B—B’). Dips on the footwall of the ore in the central part of the south ore body indicate that it also has a synclinal shape. The ore is dense, metallic looking, and structureless and has no visible gangue minerals. It is cut by a few veinlets of chalcopyrite, sphalerite, and quartz. The appearance and grade of the ore is uniform. The contacts are sharp between maissive sulfide and rhyolite containing 2—millimeter quartz phenocrysts that forms the wall rock of the deposit. Foliation is GEOLOGY AND BASE—METAL DEPOSITS, WEST SHASTA COPPER-ZINC DISTRICT not as well developed at the contact of the rhyolite and the ore as it is near the wall rock of most of the massiVe sulfide bodies of the area. A thin yellowish sericite or clay gouge ranging from a quarter of an inch to rarely 2 inches in thickness is present along much of the ore contact, but this might be due to minor postmineral movements. No frozen contacts were seen, and the wall rocks contain pyrite at only a few places. Most ore con- tacts in the Early Bird mine are regular, smooth planes that are sharply curved in places. The continuity of many contacts is broken by cross faults that have a dis- placement of a few feet, but no persistent direction or offset is apparent in these small faults. Crushed sul— fides along minor faults and slickensided surfaces are locally present in the ore, but not along the contact be- tween massive sulfide and wall rock. In polished section the ore is composed largely of fractured anhedral pyrite grains as much as 1 milli— meter in diameter. Chalcopyrite occurs interstitial to and in fractures in pyrite. Sphalerite is interstitial to pyrite and at some places to chalcopyrite. The gangue minerals are quartz and minor amounts of calcite. The ore is not oxidized at its upper contact in the backs of the stopes, 150 feet below the surface. Drill holes show no enrichment in copper or silver at the top of the ore. The low silver content and absence of silver enrichment in the high-grade copper ore mined by the United States Smelting Refining and Mining Co. (table 9) also show that the high copper content of this ore was not due to enrichment. Other than this small tonnage of high—grade copper ore, the ore samples are very uniform in grade. Ore from four drill holes aver— aged 0.03 ounce of gold, 1.53 ounces of silver, and 3.01 percent of copper, which checks fairly closely with the record of production if the small tonnage of high—grade copper ore is omitted. No zinc assays are available. The drill holes shown on figure 49 did not reveal the limits of the ore along its strike. If the ore continues unfaulted horizontally northward, it should crop out about 1,000 to 1,500 feet from the end of the north stope. In this stope the north face has a larger area than most cross sections of the ore body, and ore can be expected to continue for some distance north of this stope face. The fact that its outcrop has not been located at the surface may be due to the absence of good outcrops in the mine area. and on the slopes to the north, or its northerly extension may be dropped by faulting. No exploration has been done to the south of the ore body, and although the face of the south stope contains less than the average cross section of ore, a large area of favorable ground remains to be explored south of the Early Bird ore body. EARLY BIRD MINE E X P LA N ATION ovvJ Balaklala rhyolite Massive sulfide.ore A7D v _‘ P7— Contact, showing dip; dashed where approximately located; queried where inferred 40 Waste In floor, ore in back Fauit, showing dip; dashed where approximately locate ?__—.__? Probable fault Foot of raise or winze MA IN A BIT 2697' TRUE NORTH UPPER ADI1 El 2812’ 2 ft. lens: sandy pyrite de$ 10" E. 40 0 i 120 Feet L J Geology by Oscar W. Jarreil. Formerly From maps furnished by the West Shasta Geologist, West Shasta Exploration Coo Exploration Co. Published with per- mission of the Balaklala Consolidated Copper 00., owner FIGURE 51.—~Map of adits of the Early Bird mine. 113 114 GEOLOGY AND BASE—METAL DEPOSITS, GOLINSKY MINE The Golinsky mine is 1 mile northeast of the Mam- moth mine on the northeast side of Little Backbone Creek, in sec. 28, T. 33 N., R. 5 V“, at an altitude of 1,840 feet. Access to the Golinsky mine was cut off when Shasta reservoir was flooded. In 1950 the mine was owned by the U. S. Government. The mine is accessible only by boat to a road that leads from Shasta Lake to the mine. The road, about 2 miles long from the lake to the mine, was not passable in 1950, but it could be repaired by putting culverts in the washed-out parts. The mine workings are inaccessible, and the mine plant has been dismantled. The outcrop of gossan was discovered before 1902, as Aubury (1902, p. 90) reports 750 feet of exploratory work had been done by that date. The mine was owned in 1902 by B. Golinsky of Kennett. During 1906—7 the mine was under lease to the American Smelting and Refining Co. This company mined 3,078 tons of sulfide ore and shipped it to the Tacoma smelter for treatment. The mine was idle from 1907 until 1931, when it was leased to Vickery Brothers, who attempted to recover the gold and silver from the gossan, but the process used was not successful. In 1935 the mine was leased to the Backbone Gold Mining Co.; this company built a road from the old town of Kennett to the mine and installed a small smelter at the mine. During their operations, 3,189 tons of ore was mined and treated in the smelter, but the mine was closed again in 1937 and has not been operated since. Table 10 gives data on production. TABLE 10.—Ore mined by American Smelting and Refining Co. and Backbone Gold Mining 00.1 Grade of ore mined by American Smelting and Refining 00. [Tons mined—3,078] Gold ________________________________ ounces per ton-- 0. 134 Silver ________________________________________ (lo---- 4. 61 Copper _____________________________________ percent__ 3. 57 Zinc __________________________________________ (lo--_.. 8. 0 Sulfur- -_do--__ 30. 7 Iron __________________ _-do--__ 23.6 Silica _____________________________ (lo____ 27. 1 Production of ore mined by Backbone Gold Mining Co. [Tons sucked—3,189] Matte produced ______________________________ tons_--_ 398. 5 Gold _________________________________________ ounces-- 551. 54 Silver _________________________________________ (lo--__ 11,123 Copper ______________________________________ p011nds-- 91, 689 1 Data from U. S. Bureau of Reclamation, unpublished report by E. C. Galbraith and W. I. Gardner. The gossan at the Golinsky mine was mined in a broad, shallow opencut in an attempt to recover the gold that the gossan contained. The subsequent slumping and the soil that was washed into the cut have concealed the geology near the outcrop of the ore body. Three WEST SHASTA COPPER-ZINC DISTRICT samples taken at the surface in gossan by the U. S. Bureau of Reclamation contained 0.01 ounce of gold and 2.28 ounces of silver. Samples taken by the United States Smelting Refining and Mining Co. on the gossan exposed in the underground workings assayed much higher than the U. S. Bureau of Reclamation assays at the surface. The weighted average of 13 samples taken on gossan underground showed that the gossan con- tained 0.36 ounce of gold, 8.10 ounces of silver, 1.20 per- cent copper, trace of zinc, 24.0 percent iron, 6.4 percent sulfur, and 47.4 percent silica.8 Geology—The massive sulfide ore body at the Golin- sky mine lies just above a gently dipping contact be— tween siliceous white foliated, nonporphyritic rhyolite below, and massive tan soft, porphyritic rhyolite above. The nonporphyritic rhyolite below the ore body is a » heterogeneous mixture of flow-banded rhyolite and rhyolitic pyroclastic material. Several types of pyro- clastic rocks are present, but none of it shows bedding. Coarse and fine volcanic breccias composed of rounded knobs of rhyolite in a matrix of rhyolite, probably a flow breccia, are mixed with stubby layers of nonbrec- ciated rhyolite. One bed of volcanic breccia in Little Backbone Creek below the mine is composed of a felsitic, green chloritic matrix that contains 3-inch oval bombs of white rhyolite containing closely packed chlorite and quartz amygdules. Much of the rhyolite below the mine has a steeply dipping foliation, and sericite or clay minerals are formed along closely spaced planes. Locally the rock is pyritized. The nonporphyritic rhyolite and volcanic breccia grades upward into a tuffaceous bed that is commonly present along the lower contact of the overlying por- phyritic rhyolite in this area. The tuffaceous bed is not found at the mine and may be thin or absent, but is well exposed several thousand feet north and south of the mine. This bed is a well-bedded, water-deposited crystal tufi', that contains material ranging from grit to fine volcanic conglomerate. It dips gently to the west, somewhat flatter than the hill slope. The tufl? bed is overlain by medium—phenocryst por- phyritic rhyolite about 100-200 feet thick, but part of the hillside appears to be almost a dip slope, and the thickness is difficult to estimate due to the absence of bedding. Most of the porphyritic rhyolite contains 2- to 3-millimeter quartz phenocrysts, and is interlayered with pyroclastic rocks and thin layers of rhyolite or rhyolitic tufi’, which is the typical lithology of the mid- dle unit of the Balaklala rhyolite. However, some bodies of coarse-phenocryst rhyolite characteristic of the rock in the upper unit of the Balaklala are present BData furnished by United States Smelting Refining and Mining Co. GOLINSKY and these probably are intrusive masses, but some may be local bodies of extrusive coarse-phenocryst rhyolite that here antedate the main period of extrusion of this rock and occur as small flows in the middle unit. The base of the upper unit of the Balaklala rhyolite is marked by a layer of locally well-bedded crystal tuff that lies beneath shale of the Kennett formation on the ridge above the mine, but it is not certain whether the coarse-phenocryst rhyolite that lies a short distance above the Golinsky ore body is an extrusive mass and therefore part of the upper unit of the Balaklala rhyo- lite or whether it is an intrusion into the middle unit. Ore body—The Golinsky ore body is a relatively small steeply dipping lens of massive sulfide. It is ex- plored by two adits and by several intermediate levels (pl. 7). The massive sulfide has sharp boundaries along the sides of the lens, and in the northeast end of the ore body on the 55—foot level the ore is basin shaped or keel shaped.9 At the west end of the ore on the 55—foot level, the lens of massive sulfide pinches out along a clay seam in a shear zone, as it does at the east end of the level of tunnel 1. At the east end of the 70-foot level and along the southeast edge of the ore on the 55—foot level, the contact is gradational to pyritized rock, or to rock con- taining scattered bodies of massive sulfide. Likewise, the ore pinches out in the winze below the 55—foot level at the west end of the ore body (pl. 7, 0—0’). The ore is shown on the underground map as localized in a shear zone that strikes N. 60° E. and dips 55°—60O SE.; the shear zone was not seen on the surface. The following information on the appearance of the ore is taken from a report furnished by the United States Smelting Refining and Mining Co.: At about the centre of the workings, the fractured zone widens and makes a shoot of ore that has maximum dimensions of about 30 feet Wide, 65 feet long, and 60 feet high as stoped. This zone narrows to the east and west of the main lens. The hanging wall is generally pretty well defined, with porphyry and some bunches of sulphides south of it. The ore is not quite so sharply limited on the north, and sometimes ore makes out irregularly into the footwall. A coarse, firmly cemented breccia-zone often occurs on the footwall. Crossrutting has exposed no ore to the north or south of the main fracture-zone. Above the sulphide orebody, is oxidized material and gossan, extending to the surface. Generally speaking, the main orebody shows in plan as a lens-shaped mass, thick in the middle, thin on the edges, oc- cupying a widened bend in the fractures. In vertical cross- section, the main orebody would also show as a lens, grading into gossan above and thus losing its upper outline, and grading into waste and tailing out to a thin edge shortly below the 55-ft. level. uThe information on the underground geology of the mine is derived largely from a private report furnished by the United States Smelting Refining and Mining Co., but it is in part from a report furnished by the U. S. Bureau of Reclamation, from an unpublished report by G. F. Seager, and from other sources. MINE 115 The sulphide ore is a mixture of compact sulphides, with bands of light and dark clay, soft sulphides, and quartz, mixed with some bands of porphyry. The banding is parallel to the walls, and some bands of clean sulphide are as much as 6 ft. wide. An old crosssection through the main orebody, made in 1903, shows a large horse of waste occurring as an inverted wedge in the centre of the main sulphide body. Seager in his unpublished report noted that much sooty chalcocite \ 'as present locally and that all the ore appears to be somewhat. enriched in copper. The stope outlines are not sufliciently known to be shown on plate 7. The main stope probably extended from the 70—foot level to the level of tunnel 1, and a small stope extends 45 feet up along the raise at the east end of this level. However, old maps from different. sources are not in agreement on the extent of stoping. X0 exploratory work was done along the strike of the ore lens except on the 84—foot level. The ore lens at each end pinches down to a narrow band of sulfide or pinches out completely, and there was little evidence to encour- age exploration. The steep topography above the mine and the lack of pyritization or hydrothermal alteration discouraged surface exploration. In spite of these fea- tures, the present study of the geologic setting of the deposit suggests that exploration to the northeast along the trend of the shear zone is warranted because miner- alized rocks are exposed northwest of the mine, and because the main ore zone is concealed along the ex- tension of the shear zone. The steep ore lens as far as known appears to be localized along a steeply dipping shear zone. However, as the rocks above the mine contain local pyroclastic beds that dip gently southwest parallel to the over— lying shale contact, flat structures similar to those known to have localized ore at other mines are present. The southwesterly dip of these structures make surface drilling to the ore zone feasible, despite the steep topog- raphy above the mine. Any flat-lying ore zone would lie within reach of drilling even near the crest of the ridge. A broad warp or arch structure that might localize mineralization occurs northeast of the mine. The ridge east of the mine that is capped by limestone of the Kennett formation marks the crest of a broad warp trending north or northwest. The. southwest flank of the \‘arp is eroded, but it apparently had a more gentle dip than the northeast flank; this warped structure is of the type that is favorable for ore deposi- tion elsewhere in the district. Pyritized rock is present northwest and northeast of the Golinsky mine. Gossan occurs at the base of the upper unit of the Balaklala rhyolite northwest of the Golinsky mine across the North Fork of Little Back- bone Creek, at what is considered to be the ore zone throughout the district. Also, a minor amount of 116 gossan occurs in the lower unit of the Balaklala north- east of the Golinsky mine near Backbone Creek, but the favorable middle unit is eroded in this area. The Golinsky ore body is probably in the lower part of the middle unit of the Balaklala, and the rock stratigraph- ically above the mine and below the horizon of the upper unit, marked by the crystal tuff beds along the base of the shale of the Kennett formation, is favorable for prospecting. The Mammoth and the Golinsky mines are both as- sociated with steeply dipping faults or shear zones. Al- though these zones are not definitely known to be feeder channels, the California fracture at the Mammoth mine is about in line with the shear zone at the Golinsky mine, and there are pyritized rocks in the lower unit of the Balaklala along the trend of the shear zone between the two mines, and extending northeastward from the Golinsky mine. It can be assumed that there is a trend of mineralization from the Mammoth mine through the' Golinsky mine and on to the northeast. The favor— able zone is eroded in Little Backbone and Backbone Creeks, but it is present under the crest of the warps, which trend northwestward, northward, and northeast- ward from the Golinsky mine. GREAT VERDE PROSPECT The Great Verde prospect, formerly known as the Vulcan group of claims, is in sec. 11, T. 33 N., R. 6 VV., on the north side of Squaw Creek immediately west of the Shasta King mine. The former Vulcan camp which was on the ridge about 1,500 feet east of the upper work- ings, is completely dilapidated, and all trails to the prospect have been washed out and overgrown. Con- siderable exploratory work was done, beginning about 1900, but no ore was mined from the property. Short adits were driven in a prominent gossan outcrop near the top of the ridge at an altitude of about 2,600 feet, and a 1,500—foot exploration adit was driven north from Squaw Creek at an altitude of about 2,000 feet to pro- spect under the gossan. A small amount of drilling was done near the upper workings, but the writers could find no record of these holes. The claims are owned by W. A. Kerr. Geology—The gossan at the upper workings, at an altitude of 2,600 feet, lies immediately below the base of the upper unit of the Balaklala rhyolite. The upper unit (“cap rock”) is here composed of crytal tuif that contains quartz phenocrysts more than 5 millimeters across; it is underlain by buff-colored shaly tufi'. Only the lowest part of the upper unit is exposed where it caps the ridge; the remainder has been removed by erosion. The gossan occurs in porphyritic rhyolite of the middle unit of the Balaklala, which is thin at the GEOLOGY AND BASE—METAL DEPOSITS, WEST SHASTA COPPER-ZINC DISTRICT Great Verde, as it is at the Early Bird mine to the south, and is composed largely of pyroclastic material. Poor outcrop, strong hydrothermal alteration, and mixtures of porphyritic and nonporphyritic rhyolite to the north of the Great Verde make it impossible to outline the lower boundaries of the middle unit accurately in this area. Also, a varietal type of rhyolite below the Great Verde, shown on the quadrangle map (pl. 1) as belong- ing in the lower unit of the Balaklala rhyolite, locally contains 1—millimeter quartz phenocrysts, as at the Shasta King mine. No sharp division can be made between the middle and lower units in the vicinity of the Shasta King, Great Verde, and Early Bird mines, but at all these localities, the middle unit appears to be relatively thin. Ore deposit—A small amount of gossan derived from massive sulfide crops out at the upper workings and is exposed in several short adits. Some relict massive pyrite in gossan was seen on the dumps, but no infor- mation was available on the grade of the gossan or sul- fides. Much of the material in the outcrop is gossan derived from heavily pyritized rock rather than gossan from a massive sulfide body. A poorly exposed zone of strongly pyritized rhyolite, some of which contains 1—millimeter quartz phenocrysts, occurs west and southwest of the upper workings of the Great Verde and about 200 feet vertically below the upper adit. Float boulders of gossan from massive sul- fide were found on this hill slope, but they may have come either from the ore zone at the upper workings or from the lower mineralized zone. There is no indica- tion that sulfide was found in the 1,500-foot adit that was driven north from the level of Squaw Creek; the adit probably is too low in the stratigraphic sequence and is below the ore zone. Some of the operators in the district believed that the Great Verde was a faulted segment of the Shasta King ore body as noted by Seager in his unpublished report. A strong fault occurs at the west edge of the Shasta King ore body, and the rocks west of this fault have moved up relative to the east side. However, the two deposits are believed to be discrete ore bodies because they are not in the same stratigraphic position in the middle unit of the Balaklala rhyolite, and because the major trend of the Shasta King is northeast-southwest rather than east—west (Kinkel and Hall, 1951, p. 7). The possibility of locating ore bodies at the Great Verde depends upon the stratigraphic correlation be- tween the rocks of the Shasta King mine and those at the Great Verde. The ore body at the Shasta King mine cannot be much less than 350 feet below the contact be- tween the upper and middle units of the Balaklala, that is, it is on an horizon that is stratigraphically low in the GREAT VE RDE PROSPECT NW. hyoh‘te (“c GREAT VERDE LOWER AD/T 0 l l l l | l Z ’7/////////// Midd ' //// 6 unit of t Great Verde W he BalakIa/a rh . . . . er horizm‘ ~ ~ \ yOIIte Stratigraphic separation \ \ \ about 150 feet \ \‘ \ \ D *1 Approximate vertical and horizontal scale 117 _§0 rock") SUrfaCe --.-'.‘ \Ef’hf???,K}T‘.3.HPP§Chorizon e'0ded Stratigraphic separation about 350 feet 500 Feet FIGURE 52.—Diagrannnatic section showing the relationship between the Shasta King and the Great Verde ore zones. middle unit. The upper ore zone at the base of the up- per unit is eroded at the Shasta King mine, but hydro- thermal alteration and mineralization occur at this stratigraphic horizon north of the Shasta King. Thus the lower, or Shasta King ore zone, could be correlated with the lower ore zone west and southwest of the Great Verde if, as seems probable, the middle unit of the Bala— klala thins to the west (fig. 52). The Great Verde gOSSan at the upper workings could not be a faulted extension of the Shasta King ore body because it lies at a different stratigraphic horizon in the Balaklala. The upper gossan at the Great Verde probably can be correlated with the n’iineralization under the base of the upper unit north of the Shasta King mine. On the above hypothesis, a part of the area north of the Great Verde might warrant prospecting for the Shasta King ore zone, although it is probable that lower zones do not have as much continuity as the main ore zone. IRON MOUNTAIN MINE The Iron Mountain mine, which is owned and oper- ated by the Mountain Copper Co., Ltd., is the southern- most mine in the \Vest Shasta copper—zinc district. The mine is 17 miles by road northwest of Bedding and lies at an altitude of 2,600 feet; a hard-surfaced county road connects the Iron Mountain mine with U. S. Highway 299117. The Southern Pacific Railroad passes through Bedding, and the ore from the mine is carried to a spur of the railroad by an aerial tramway. The information on the Iron Mountain mine is sum- marized from a more detailed report by Kinkel and Albers (1951). HISTORY AND PRODUCTION The first claims on the large gossan outcrops on Iron Mountain were staked in the early 1860’s and held for the future value of the gossan as iron ore. Silver ore was discovered in the gossan in 1879 and some explora- tory work and mining were done in the silver—rich parts. At that time little interest was shown in the dissemi- nated chalcopyrite and the massive sulfide ores that were found in the search for precious metals. It V: s not until 1895, when a thorough prospecting of Iron Mountain disclosed large bodies of copper-bearing sul- fides, that the mineral possibilities of the region‘now known as the lVest Shasta copper-zinc district were recognized. Silver ores were mined intermittently in the gossan at Iron Mountain from 1879 to 1897, when the present owners, the Mountain Copper Co., Ltd. (formerly Mountain Mines, Ltd.) began mining the massive sul- fide ores for their copper content. This company has operated the mine continuously since 1897. The ex- ploration of separate bodies of sulfide ore led to the naming of individual ore bodies as different mines, al- though they were mined as part of one operation by the Mountain Copper Co., Ltd. Thus the Old Mine ore body, the No. 8 mine, and the Hornet mine are separate and were worked at different times, but all are part of the Iron Mountain mine (pl. 8). Copper has been produced by the Mountain Copper Co., Ltd., from direct-smelting ore, from sulfide ore treated in a flotation plant, and from the leaching of pyritic ore that was mined for its sulfur content. The Iron Mountain mine produced 197 ,951,7 38 pounds of copper by the end of 1919 from direct-smelting ore, but 118 GEOLOGY AND BASE-METAL DEPOSITS, WEST SHASTA COPPER-ZINC DISTRICT TABLE 11.~Production and grade of ore from the Iron Mountain mine [Data furnished by the Mountain Copper Co., Ltd] l 3 Grade ‘ Production . Ore and source . I ‘ (Shomtor‘s) Gold (ounces) Silver (ounces; Copper Zinc Iron Sulfur Insoluble ‘ per ton) per ton) i (percent) (percent) (percent) (percent) (percent) Copper-zinc (flotation plant) ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 380,000 0.02 1. 00 2. 00 . 3. 50 40. 5 47. 0 6. 5 Copper (Old Mine ore body) 1, 608, 000 .04 1.00 l 7. 50 Copper (disseminated) 820,000 .001 .04 l 3.50 Pyrite for sulfur ..... . 3,600,000 .02 .80 l .40 ___ Gossan ................. ‘ 2, 638, 000 .073 8.21 I ____________ __ 1 Estimated. figures are not available for the total copper produc- tion since that date as copper production was reported only by counties. After 1919, the principal periods of copper production from ore of the Iron Mountain mine were in 1925, 1928—30, and 1943—47. Minor copper pro- duction was maintained between these periods by leach- ing of ore that was mined for sulfur. Gold and silver have been extracted from the gossan overlying the massive sulfide ore of the Old Mine ore body. From 1889 to 1898, 38,000 tons of gossan that contained 8 ounces of silver to the ton was mined. The gold content of this ore is not known. From 1929 to 1942, 2,600,000 tons of gossan that contained 8.3 ounces of silver and 0.073 ounce of gold per ton was mined. The tonnage and grade of ore are summarized in table 11. The copper-zinc ore that was treated in the flota- tion plant was mined from the Richmond and Mattie ore bodies. The disseminated copper ore came from the No. 8 mine and the Confidence-Complex vein system. Most of the pyrite mined for sulfur came from the Hornet ore body, although some came from the Rich- mond-Complex ore body. FORMATIONS IN THE MINE AREA The Copley greenstone, the Balaklala rhyolite, and the albite granite are the only rock units that occur in the immediate Vicinity of the Iron Mountain mine. These are shown on the surface map and on the cross sections (pl. 19). The Copley greenstone in the mine area is composed of chloritized mafic flows and minor pyroclastic mate- rial; the greenstone ranges from well-sheared to mas- sive rocks and is pyritized only in small, local areas. It underlies the Balaklala rhyolite. The Balaklala rhyolite in the mine area probably includes the upper, middle, and lower units, although shearing, folding, original lenticularity of flows and pyroclastic rocks, and an abnormal amount of intrusive rhyolite make the stratigraphy within the Balaklala un- usually difficult to decipher at Iron Mountain. It is particularly difficult at this mine to distinguish between the middle and the lower units, and the two units may not be separable as distinct stratigraphic units at. this locality. Also, most of the typical coarse-phenocryst rhyolite of the upper unit has been eroded in the mine area; only the transition zone of tufl and coarse-pheno‘ cryst pyroclastic material that is characteristic of the material along the contact between the upper and the middle units remains. The Iron Mountain mine was mapped early in the present study, and subsequent work in other parts of the district proved to the writers that the rock mapped as coarse-phenocryst rhyolite at the Iron Mountain mine (Dbx3 on pl. 9) is not typical of the rhyolite of the upper unit elsewhere in the district, but is a coarser phenocryst facies of the middle unit, and is limited to the vicinity of the Iron Mountain mine. The fourfold lithologic division of the rhyolite based on phenocryst sizes, which was used in the mapping of the Iron Mountain mine in the earlier stages of the work and which could be maintained in the mine area, was later revised to a threefold division for the district as a whole. The small and medium-phenocryst rhyolites of the earlier work at the Iron Mountain mine were grouped together under medium—phenocryst rhyolite in the later work in the ‘Vest Shasta district because these subdivisions could not be maintained elsewhere. ORE DEPOSITS CHARACTER The two types of ore in the Iron Mountain mine are massive pyrite bodies, that contain chalcopyrite and sphalerite, and zones of disseminated chalcopyrite and quartz-chalcopyrite veins in schistose rock. The massive sulfide is much more abundant than the dissemi- nated ore. Disseminated ore occurs only in the No. 8 mine and the adjoining Confidence-Complex ore bodies. All other ore bodies in the Iron lVIOuntain mine are massive pyritic bodies. The principal minerals are pyrite, chalcopyrite, and sphalerite. Galena, pyr- rhotite, tetrahedrite, and magnetite have been seen in a few specimens, and the ore contains recoverable amounts of gold and silver. The only gangue minerals seen are very small amounts of quartz and calcite, both of which occur as interstitial grains to the sulfide min- erals and as veinlets cutting the ore. IRON lVIOUNTAIN LIINE In addition to the sulfide ores at the Iron Mountain mine, three small, lenticular bodies of magnetite oc- cur about 700 feet south of the Iron Mountain quarry (pl. 9). These are isolated from the main body of py— ritized rock and massive sulfide by several hundred feet of unmineralized rock, and contain little or no pyrite and no copper or zinc minerals. Drilling has shown that the base of the lenses is at shallow depths. Part of the lenses are solid magnetite, some of which is polar but they contain some hematite, which is in part a sur— face alteration product. At the edges of the lenses, the magnetite is disseminated in rhyolite. Maghemite, ferromagnetic ferric oxide, is reported in gossan at Iron Mountain by Sosman and Posnjak (1925, p. 332—333). On the supposition that the maghemite might have been collected from the surface of the magnetite bodies, a sample of the magnetite that contained some brown, rusty material was sent to Charles Milton of the U. S. Geological Survey for study and analysis. The analysis of the sample of magnetite is given below: Analysis of magnetite from Iron Mountain mine [A11alysts, Michael Grasso and Leonard Shapiro] Percent Total Fe as Fe203 _____________________________________ 92. 27 FeO _________________________________________________ 20. 63 Actual Fegog‘ __________________________________________ 69. 34 TiO-i _________________________________________________ .24 1 By calculation. Milton (written communication) found no maghemite to be present and reported on the sample as follows: Calculations of an analysis [by Grasso and Shapiro] together with optical data indicate that the composition of the ore is about: 70 percent magnetite, 10 percent hematite, 20 percent limonite and gangue. There is no reason, from any data at hand, to belieVe that maghemite is present in this sample. However, in other samples, collected from gossan from massive sulfide on Brick Flat (east of the reservoir shown on pl. 9), Milton found maghemite, and reported : One thin and three polished sections were studied, as follows: 692. Very slightly magnetic. Microscopically shows structure as shown in [fig 53]; the bright areas are composites mainly hematite, with probably maghemite. The outer zone of the net- work appears to be hematite (anisotropic bright steel gray) and the interior part maghemite (isotropic, darker gray). A thin section shows angular (fractured) quartz and opaque iron oxide. 693. Similar to following, more or less. 694. This appears to be somewhat more dense than the other two specimens, and is also darker, as well as much Inore mag- netic. In polished section it shows the same micro-botryoidal texture, apparently consisting essentially of hematite, maghem- ite, and limonite. A few specks of pyrite are present. and also some pinkish mineral with the reflectivity of magnetite, which it strongly resembles except for being translucent (giving strong internal reflections). It is, therefore, probably rutile. 119 An X—ray study of the magnetic powder by Fred A. Hildebrand (IW'X—314) gave the following: Hematite and moderate amounts of niaghemite and quartz. The maghemite has a unit cell slightly larger than the cells of other magheinite patterns in the X-ray file. The micro-structure of the iron oxide minerals strongly sug- gests crystallization from a gel. No separate bodies of magnetite are known in the area where the samples that contain maghemite were col- lected, nor is any visible in the ore in the under- ground workings. Magnetometer readings in the area of Brick Flat showed a considerable range, but whether this is due to maghemite or magnetite in the ore is not known. The maghemite was probably derived from lepidocrocite, as suggested by Sosman and Posnjak (1925, p. 329—342), and not by oxidation of magnetite. FIGURE 53.—Photomicrograph of polished section of gossan that con- tains maghemite. Iron Mountain mine, X 160. DISTRIBUTION OF MINERALS The mineral content of the massive sulfide and of the disseminated ores is essentially the same but the pro- portions of minerals differ considerably between the two types. The disseminated ore contains predomi- nantly pyrite and chalcopyrite in sericitic and siliceous rocks, and contains many chalcopyrite—bearing quartz veins. Pyrite and chalcopyrite generally are present in about equal amounts. Only minor amounts of sphal- erite, gold or silver occur in the disseminated ore. The massive sulfide ore, on the other hand, is composed al- most entirely of pyrite, but contains chalcopyrite and sphalerite in small amounts distributed throughout the massive sulfide bodies, and local concentrations of these 120 GEOLOGY AND BASE—METAL DEPOSITS, minerals occur. Gold and silver are present in recover~ able amounts only in the massive sulfide ore-bodies. The detailed distribution of chalcopyrite and sphal- erite in the massive sulfide ore is not well known. How— ever, as all the larger concentrations of these minerals were mined as base—metal ore, the location of stopes that were mined for the copper and zinc content shows the location of these concentrations. The record is incom- plete, as small bodies of base-metal ore have been found at some localities in the mine where such ore could not be mined separately from the massive pyrite. The copper—zinc ore is found principally along the edges and bottoms of thick massive sulfide bodies that as a whole contain little chalcopyrite or sphalerite, but it is not everywhere present along such boundaries. In other parts of the mine, chalcopyrite and sphalerite occur in minable quantities throughout massive sulfide ore bodies, but these localities are generally in the thin— ner parts of the sulfide mass. DISSEMINATED COPPER ORE A body of disseminated chalcopyrite and pyrite un- derlies the Old Mine ore body. Where the disseminated ore lies beneath the Old Mine ore body, it was mined through the workings of the No. 8 mine, but its exten— sion to the northeast of the Old Mine ore body is known as the Confidence-Complex vein system. The location of this disseminated and vein-type copper ore is shown in plates 8 andlll. Two principal types of ore, which occur together or separately, are present in the No. 8 mine. One type consists of chalcopyrite grains, veinlets, and fairly solid masses of coalesced chalcopyrite veinlets that replaced schistose porphyritic rhyolite. Pyrite is subordinate in amount to chalcopyrite and occurs as scattered an— hedral grains. Many small and discontinuous faults and gouge zones are present, and the largest ore bodies occur at intersections of these gouge or fracture zones. The second ore type, quartz—chalcopyrite veins, is less abundant but occurs locally in or near the borders of the disseminated ore. The quartz—chalcopyrite veins of the Confidence—Complex workings occur as fracture fillings. In the southwest end of the Confidence-Com- plex workings the ore zone contains disseminated chalcopyrite and quartz—chalcopyrite veins. The north- east end of the Confidence-Complex workings contains principally quartz-chalcopyrite veins along a fault that has formed several inches to several feet of gouge. The shapes of the No. 8 mine ore bodies are shown in figures 54 and 55. The ore in the N0. 8 mine occurred along shear zones, particularly along intersecting shear zones or intersecting minor faults. The ore bodies are reported by the mine staff to parallel the schistosity of the replaced rock. Plate 11, which was compiled from WEST SHASTA COPPER-ZINC DISTRICT stope maps, shows the shapes of the mined ore bodies. The material between ore bodies was, in places, miner- alized rock that contained too little copper to be mined. Consequently, the map shows the major ore shoots but not the extent of mineralization. There are two main ore bodies in the No. 8 mine, and each is arcuate in horizontal section. This curvature of the ore bodies is best shown on the 2,350-foot level in the east ore shoot and on the 2,500— and 2,610-foot levels in the west ore shoot (fig. 54). Sections A—A' and B—B’ (fig. 55) illustrate the echelon pattern of individual ore shoots and indicate that the thickest parts of most of the ore bodies correspond to marked changes in dip. STRUCTURAL FEATURES OF THE ORE BODIES The massive sulfide deposits, which make up the bulk of the ore of the Iron Mountain mine, are enormous L masses composed almost entirely of pyrite. Except in the vicinity of the Old Mine ore body, the wall rocks are virtually unmineralized. The massive sulfide ore bodies differ in shape and attitude (pl. 10). The Hornet is nearly vertical. The Mattie is cigar shaped and hor— izontal; its faulted extension has not been located and may have been removed by erosion. The rounded base of the erosion remnant of the Old Mine ore body sug— gests that before erosion it was a large, gently dipping, lens—shaped or synclinal mass. The Richmond and Com- plex, taken together, have a synclinal shape, and the Brick Flat also may be in part synclinal, although its shape is determined only by rather widely spaced drill holes. The No. 8 mine and the Confidence-Complex ore bodies (pl. 8) are in zones of chalcopyrite—bearing, seri- citic, porphyritic rhyolite, and along quartz-chalcopy- rite Veins or minor faults. The Hornet, Richmond, Complex, and Brick Flat massive sulfide ore bodies were one continuous body be- fore they were displaced by the Scott and Camden faults. It also seems possible that the New Camden ore body is a faulted segment of the Complex, but the rela- tionship between these two is not well known. The lon- gitudinal section (pl. 11) suggests that the ore in the gossan area, which occurs updip from the Old Mine ore body and the No. 8 mine, is a faulted part of the Brick Flat. It is probable that all the major ore bodies at the Iron Mountain mine were one continuous deposit before postmineral faulting, but small, isolated ore lenses also occur, such as the Mattie and Okosh, which lie along the side of the main ore body. The massive sulfide ore that is exposed in the upper Busy Bee adit (pls. 8, 9, and 11) has been explored only to a limited extent. The lower Busy Bee adit is barren but a crosscut 130 feet in from the portal of the upper adit exposed massive sulfide that is 45 feet in width, 121 IRON MOUNTAIN MINE u 82 300 Feet sin No. 8 mine a v m e n _p_ _O_ " Em _ _..m._ _ _w._ _ _m_ dm _t_n. _s_u" .1 M. _m_e_ .l n .m m L nuv EXPLANATION Slopes in No. 8 mine at levels indicated Outline of underlying ore shoot Oulline of Old Mine massive sulfide body at 2730 feet elevation Outline of 6TH'iliii'né'fié's'é'iCe'HIVide body at 2640 feet elevation Nole: Secfions shown on figure 55 Datum is mean sea level moon: 1500N Lawn (Compiled from maps furnished by the Mountain Copper Co., Ltd.) Map of No. 8 mine ore bodies, Iron Mountain mine. FIGURE 54. 122 AND GEOLOGY Compiled from maps furnished by The Mountain Copper Co., Ltd. FIGURE 55.—Sections of No. 8 mine ore bodies, Iron Mountain mine. Old Mine ore body ATTATTTAY 4 § T4” L4 _ A 7 fl” fATT"’ATT’474T”T”T" F“ ”i ‘é’ Q g BASE-METAL DEPOSITS, WEST SHASTA COPPER-ZINC DISTRICT EXPLANATION Gossan from masswe sulfide are Massive sulfide are r M—‘j Disseminated ore, in part projecied to sections Inferred coniact ~See fiw": 54 for location of sections Duum is mun sea Iowa] 0 1 Geoloy by A. R. Kinkel, Jr. and J. P. Albers Location of sections is shown on figure 54. IRON and the face of the adit is in massive sulfide. This massive sulfide resembles the sulfide of the Hornet ore body, and contains little copper or zinc. It is bounded on both sides by steeply dipping faults that have about 1 foot of gouge; these faults are probably the continua- tion of those that are along the walls of the Hornet ore body. RELATIONSHIP OF ORE BODIES T0 STRUCTURES IN THE HOST ROCK The relationship between ores and rock structures at Iron Mountain is similar to those described at the Mam- moth mine, where the relationship is more clearly ex- posed in steep-walled canyons. Rock structures that were formed by flexural—slip folding are prominent at the Iron Mountain mine, as at the Mammoth mine. Foliation near the massive sulfide contact is always parallel to the contact, and at no place does the ore cont-act cut across foliation. The massive sulfide shows no tendency to finger into foliated rocks except in a few minor occurrences at the ends of small ore bodies. On the other hand, zones of disseminated pyrite that parallel the ore bodies and chalcopyrite zones in the N0. 8 mine are replacements of foliated rocks along the planes. of foliation. The sulfides show no evidence of crushing or rounding and were obviously deposited in a foliated rock, and the foliation controlled the direc- tion of travel of the sulfide-bearing solutions. The contact between massive sulfide ore and the en- closing porphyritic or nonporphyritic rhyolite is usually abrupt, although several contacts showing what appears to be gradational replacement have been found. At most localities no Visible change can be seen in the massive sulfide ore as the contact is approached and the contact has massive sulfide on one side, and unmin- eralized soft white claylike gouge on the other. This gouge is commonly more than a foot thick, but it grades from structureless white gouge against the ore to strongly sheared, sericitized, porphyritic rhyolite as the more solid wall rock is approached. It consists of highly sheared, altered, porphyritic rhyolite, as relict quartz phenocrysts occur in the claylike part of the gouge. Gouge occurs along all observed contacts, even though it may be less than an inch thick. The gouge along the contact locally contains some pyrite in the foot-wall of the Richmond ore body. In these places, the gouge contains less clay and is a sericite schist, but a narrow clay seam separates the massive pyrite from the sheared, pyritized wall rock. The pyrite is in small euhedral grains that show no evidence of crushing, and poorly defined layers of disseminated pyrite in the sericite schist parallel the ore contact and extend several feet into the footwall, diminishing in 379725—56—V79 lVI(')L‘.\‘TAII{’ 123 )IINE pyrite content as the distance from the ore increases. The mineralized layers have indistinct boundaries and are a replacement of foliated material parallel to the contact. A few quartz veinlets or irregular bodies of more siliceous material may also parallel the ore con- tact,>but no chalcopyrite has been found in these zones. It should be emphasized, however, that along most ore contacts the wall rock contains little or no pyrite. Specimens of ore from the Iron Mountain mine that contain streaks of chalcopyrite and sphalerite were seen on dumps, but none was found in place. Members of the mine staff report that the southeast wall of the Hornet and the northwest wall of the Mattie contained a little banded ore, but most of the ore at Iron Moun— tain is massive and structureless. FAULTS Movement has occurred at or near the contact of all the massive sulfide ore bodies. It. is not possible to determine how much of the gouge along the ore con- tact is premineral in origin, having acted as a guide for sulfide replacement, and how much is due to post- mineral movement. At many places massive sulfide ore is slickensided—on slips within ore bodies, on walls against contact gouge zones, and on fragments of sul— fide within the gouge zones. Gouges that contain crushed sulfide grains and broken or slickensided frag- ments of massive sulfide ore are postmineral faults, and all faults on which ore bodies are offset contain crushed and slickensided sulfides. The major postmineral faults in the mine are the Scott, the Camden, and the J faults, but only the Cam- den is both postmineral and premineral. The Scott fault is curved in strike and dip. It is unquestionably a. postmineral fault as it contains much crushed sulfide ore and fragments of slickensided sulfides. The fault zone, where it is exposed in underground workings, is 3 to 5 feet wide and contains many anastomosing slick— ensides and much dark—gray to white gouge. However, it is reported to be less than a foot thick at a few locali- ties at the end of the Hornet ore body. The Scott is a normal fault that dips about 50° NE, but it flattens along the lower part of the Hornet ore body. The movement on the Scott fault was essentially dip slip, and the Hornet ore body has been dropped 250 feet below the corresponding section of the Richmond— Complex. Flat-dipping faults have also been reported along the top of the Hornet and across the northeast part of the Complex ore body near the Scott fault, but little information is available on these faults. The Camden fault can be seen in many places in the underground workings; in most of these exposures it consists of 1—5 feet of gouge and sheared rock that con- 124 tains crushed sulfides, but the width of the fault zone is at least 50 feet where it is exposed at the west end of the 2,600—foot level. The fault forms the southeast _ wall of the Complex ore body and turns to form the south end of the Richmond ore body, which is the offset part of the Brick Flat ore body. The Camden splits .into several strands near its west end. The first dis- placement on the Camden resulted in a dip-slip move- ment of about 350 feet and occurred along the main Camden and the fault that is now called the Camden North fault, which at the time of the. first displacement vas a continuation of the main Camden. Movement then occurred on the J fault, displacing the western part of the Camden. Renewed movement along the main (lamden displaced the J fault, forming a new break called the Camden South fault, which is a continuation of the main Camden west of the J fault. The Camden North fault displaced the Richmond from the Brick Flat ore body, and the Camden South fault displaced the Brick Flat from the now oxidized, updip extension of the Old Mine ore body. The dis- placement along the Camden fault is also shown by the offset of the Copley greenstone and Balaklala rhyo- lite. contact shown on sections 38 and 44, plate 9. A strong fault zone occurs along the northwest side of the Hornet ore body, and faults along its southeast side are reported to have been seen underground. The alinement of these faults with the Camden suggests that movement along them may also have. occurred be- fore and after mineralization, as on the Camden. A continuation of these faults to the northeast into Sugar- loaf mountain is known as the Sugarloaf fault. Many small postmineral faults are found within the ore bodies. These can best be seen along the massive sulfide contact, where they offset the contact as much as 50 feet. They are marked by slickensided surfaces in massive sulfide ore, or by gouge. However, some gouge within the main sulfide mass is so continuous, and so far from the boundaries of the ore, that it can only represent sheared remnants of unreplaced rock or pre- mineral fault gouge. HYDROTHERMAL ALTERATION OF THE WALL ROCKS The rocks in the vicinity of the Iron Mountain mine have been altered by sericitization, siliciti ‘ation, chlori- tization, and pyritization. Sericite and hydromica are widespread and although at some places they probably were formed by hydro~ thermal solutions related to the ore-bearing solutions, at other places they have no close spatial relationship to metallization. In places intensely altered zones of sericite and hydromica are closely associated with ore bodies, but they do not necessarily form halos around GEOLOGY AND BASE-METAL DEPOSITS, WEST SHASTA COPPER-ZINC DISTRICT them. The altered rock is either white or lavender. The alteration of feldspar in rhyolite to sericite and hydromica occurs along the walls of ore bodies and along faults, and as irregular zones in rhyolite near but not necessarily adjacent to ore bodies. Sericitic wall rock is found at the ore boundaries as a gradation between gouge and the less sheared rock, but this sericite may have been deposited before mineralization and may not have been formed by the ore-depositing solutions, as large bodies of sericite schist are found far from known ore zones. Silicified rocks are common at Iron Mountain; leached bodies of pyritized and silicified rock show all grada— tions from rock with a few pyrite casts in a silica matrix to a porous silica sponge in which the silica occurs as septa between pyrite grains. \Vhere pyrite did not re- place all the rock, relict quartz phenocrysts of the por- phyritic rhyolite are found in a rock that is composed almost entirely of secondary silica. Silicification in the mineralized zone is not always coextensive with pyritiza— tion, but zones of strong silicification in the porphyritic rhyolite appear to indicate the main solution channel- ways in the mineral belt. Pyritization at the Iron Mountain mine is more lim- ited in distribution than any of the alterations pre- viously described. It occurs in broad mineralized zones, but massive sulfide bodies are limited to a small part of the pyritized zones. Massive sulfide deposits in the Iron Mountain area are associated with pyritized rock, but the bodies of pyritized rock are commonly not in immediate contact with massive sulfide ore bodies. On the other hand, large pyritized areas that contain neither massive sulfide ore bodies nor copper or zinc minerals are found in the district. The im- mediate walls of the massive sulfide ore bodies at the Iron Mountain mine contain little or no pyrite except in the vicinity of the Old Mine ore body. Bodies of disseminated pyrite parallel the sulfide deposits in the same mineralized zone, but disseminated pyrite does not occur as a halo around most of the massive sulfide ore bodies in the Iron Mountain mine. SUMMARY 0].“ FEATURES CONTROLLING ORE DEPOSITION The broad controls believed to be responsible for the localization of ore at the Iron Mountain mine are the folds that. acted as a guide for solution travel, the thick cover of shale that was present several hundred feet above the ore zone at the time of ore deposition, and the main feeder channels. More detailed controls that served to localize individual ore bodies are preferred layers in the flows and pyroclastic rocks of the Balak- lala rhyolite, fractures that served as feeder channels, IRON LIOUNTAIN MINE and premineral fault gouge that confined the solutions to limited areas. The massive sulfide ore. contains few recognizable remnants of unreplaced rock. Exposures showing in- completely replaced rock can be seen in some of the quarry benches, and these exposures suggest that re— placement favors massive porphyritic rhyolite that contains 2- to 4-millimeter quartz phenocrysts. Massive nonporphyritic rhyolite, flow-banded rhyolite, and rhyolitic volcanic breccia seem to be unfavorable host rocks in the Iron Mountain area. There is no indica- tion that massive sulfide ore preferentially replaced more foliated parts of the rock at this mine, although the widespread disseminated pyrite tends to concentrate along broad zones of foliation. Feeder channels and bands of fault gouge guided the mineral-bearing solutions in detailed control. “Vhere these channels were not confined by gouge, zones of disseminated pyrite that lack sharp walls and only partly replace the host rock were formed; but where bands of gouge were present the mineral—bearing solu- tions were confined and locally replaced all the rock. Evidence of premineral bands of gouge is indicated where some bands extend into the ore in the form of long narrow sheets that show too little movement of the ore bodies on either side of the gouge to account for its formation as dragged wall rock. This gouge was present at the time of mineralization but was not re- placed. Although clay gouge occurs at the contact of all the ore bodies, some of this type of gouge may have been formed by minor movement of the sulfide bodies against hydrothermally altered rocks, and does not represent a large amount of movement or necessarily a premineral gouge. The Camden and Sugarloaf faults, which may be the same fault or may be en echelon in the vicinity of the Hornet ore body, are premineral in age. This is shown by the presence of gossan and of pyritized and hydrothermally altered rocks along both faults. The Camden fault and its probable continuation to the east, the Sugarloaf, appear to have been the channel for the solutions that formed the Busy Bee, Hornet, Richmond-Complex, and Brick Flat ore bodies, as well as the small areas of gossan shown along the eastern and western extensions of these faults. The Camden probably was not the feeder channel for the formation of the Old Mine ore body and N0. 8 mine ore body be- cause these dip away from the fault and because of the upward-branching ore pattern in the N0. 8 mine. Un- recognized or concealed solution channels probably are south of these ore bodies. Concentrations of chalcopyrite and sphalerite in the massive sulfide deposits, With the exception of those in 379725—56———10 125 the Old Mine ore body, all lie near the Camden fault, marking this as a feeder. These concentrations are found in the Mattie, the southeast side of the Complex, in the Richmond, and in the Brick Flat ore bodies along the north branch of the Camden fault. The concentra- tion of chalcopyrite at the base of some of the ore bodies adjoining the Camden fault also indicates that upward- moving, copper-bearing solutions were traveling along it. OXIDATION AND ENRICHME‘NT Two types of gossan have been distinguished at the Iron Mountain mine (pl. 9). One of these was derived from disseminated pyrite and ranges from rock con- taining scattered pyrite casts to rock and silica sponge in which the rock structure is preserved, but which may have contained 50 percent or more pyrite. Rock that is estimated to have contained less than 10 percent pyrite is not shown as gossan on the map. The second type of gos— san is that derived from massive sulfide ore. This gossan contains no discernible traces of the original rock structure. It consists of limonite in the form of earthy, spongy, and cellular masses with quartz septa (fig. 45), or of limonite crusts and dense limonite, or a breccia of angular fragments of rock and vein quartz embedded in limonite. Small relict nodules of massive pyrite have been found in gossan within 10 feet of the surface in the upper part of the gossan quarry at Iron Mountain (fig. 46). However, the high relief and broken, porous char- acter of the ground allows more or less complete leach- ing and oxidation to a depth of several hundred feet throughout most of the mineral zone. The deepest oxidation extended down along the footwall of the Cam- den fault, where oxidized material is found locally at a depth of 400 feet. The copper-bearing disseminated ore does not crop out. N o correlation was possible between the types of limonite found in the gossan and the copper content of the massive sulfide bodies. In gossan derived from pyritized rock, bands of the rock parallel to the schistosity are locally completely replaced by silica and pyrite in ribbonlike structures. The ribbons commonly contain more than 50 percent silica and tend to stand out as resistant ribs of silica. sponge 0n weathered surfaces. Material between the mineralized bands contains less silica and pyrite, or it may be entirely unmineralized. Supergene enrichment—The Old Mine ore body is the only body of sulfide ore in the Iron Mountain mine that contained supergene copper minerals. The other ore bodies in the mine area were either completely con- verted to gossan and the copper has been removed or they were protected from oxidation by gouge along 126 the top of the ore bodies. No secondary copper min- erals are visible in the gossan. The gossan above the Old Mine ore body contained 0.4 percent copper and no zinc, but a thin enriched zone in decomposed sulfides along the irregular base of the gossan had a high con- tent of copper and an exceptionally high content of silver. This ore zone is reported to have been several feet thick and to have consisted of clay, and black de- composed sandy sulfides that graded downward into massive sulfide ore. N0 assay records are available but considerable silver ore was mined from the enriched layer. A few specimens of ore from the Old Mine ore body have been collected from dumps on the property. They are fine-grained massive sulfide ore that has a bluish color. Thin seams of chalcocite can be seen in the hand specimens, and other secondary sulfide minerals may be present. The following assays compiled by Seager in an unpublished report indicate the amount of copper enrichment in the upper part of the Old Mine ore body. (See table 12.) The average gold content of the gossan above the Old Mine ore body is 0.073 ounce per ton and that of the massive sulfide ore below the gossan is 0.04 ounce per ton. This is a residual enrichment caused by leaching and oxidation of the sulfide minerals. The average weight of the gossan is 165 pounds per cubic foot and that of the sulfide ore is 275 pounds per cubic foot. TABLE 12.—Ooppcr content of the upper part of the Old Mine ore body, Iron Mountain minc A] t d Average ti u e copper Ore (feet) content (percent) 1 Gossan ................................................ Above 2,741 0. 25 Massive sulfide" m", , ,,,,,, , , 2, 741 10. 0 D0 _____ 2. 732 10. 0 D0. 2. 720 8. 0 Do. 2, 710 8. 0 D0, 2, 682 6. 0 D0,, ...... 2. 614 6. 0 2, 601 3. 5 “later—soluble gold and mercury have been reported by the mine staff and in publications as occurring in the gossan at Iron Mountain. In describing the cyanid- ing of the gossan Averill (1938, p. 329) reports: One interesting problem solved is the detection of water- soluble gold. Difficulty was at one time experienced in making assay-values check with mill—recovery. Experiments showed that in some samples as much as 44% of the gold would dis— solve in distilled water. This gold was at first supposed to be in a colloidal state, but tests proved that it is not. Finally micro—chemical tests with pyridine showed the presence of gold chloride (AuClg). Of the gold in the Ore, it is not unusual for 10% to 13% to be in this water-soluble form. All of the ore does not contain it. GEOLOGY AND BASE-METAL DEPOSITS, WEST SHASTA COPPER-ZINC DISTRICT Jackson and Knaebel (1932, p. 125) report that the gossan contained 0.4 percent copper, 50—55 percent iron, 5—10 percent silica, and a little arsenic and mercury, and that from a production of 543 tons per day, 40 pounds of mercury was recovered by a condenser at each monthly cleanup. It seems improbable that water-soluble gold or mer- cury occurred naturally in the gossan. It seems more likely that these metals were added to the gossan by losses during early milling operations for gold and silver, in the amalgamating and chloriding plants. In the silver plant, which was destroyed by fire in 1897, silver—bearing gossan was mixed with salt and roasted, and about 200 pounds of quicksilver was added for each 4 tons of pulp before pan amalgamation (Kett, 1947, p. 108). No gold could be panned from gossan at the Iron Mountain mine, probably because it occurs in extremely fine particles. Silver and zinc have been removed from the gossan over the Old Mine ore body, and although the silver appears to have been precipitated at the contact be- tween the gossan and the sulfides, no bodies of secondary zinc minerals have been found. EXPLORATORY DRILLING AT IRON MOUNTAIN In 1950—51 a diamond—drill hole 1,798 feet deep was drilled at Iron Mountain to obtain additional informa- tion about the rock structure and to explore. a syncline similar to the structure that localizes the ore bodies in the Iron Mountain mine. This syncline lies parallel to and 1,500 feet southeast of the Iron Mountain ore bodies. Feeder channels were thought to be present south of the Richmond—Complex ore bodies, and the hole was drilled to explore the area where these feeder channels would intersect the large syncline. The outline of the area and the location of the drill hole is shown on figure 56. No deep exploratory work had been done in the syn- cline south of the ore bodies before this drilling, and no mineralization was known in the area. Geologic mapping suggested that the favorable zone of porphy- ritic rhyolite should be at a vertical depth of about 800 feet. In addition, mineralization is known to trend toward this syncline in the disseminated chalcopyrite ore of the Confidence-Complex vein system. DRILLING DATA The drill hole was started on an inclination of 701,63“ and on a bearing of N. 421/2° IV. It was anticipated that the hole would cut through the Balaklala rhyolite into Copley greenstone at a depth of about 1,200 feet. However, the syncline proved to be much deeper than (7 IRON Outlines of ore bodies are at elevations shown 2400 TRUE NORTH lVIOUNTAIN MINE 4000f: EXPLANATION Fifi Bafildala rhyolite, undifferentiated on map x 2 ‘ Porphyritic rhyolite with quartz phenocrysts 2 to 4 mm i i 3 Tom ‘ i iDbxl' phenocrysts O to 2mm / 2 t / i Horizontal projection of drill hole DEVONIAN Balaklala rhyolite 4 “Aggggiu 4 4 A 4 4 Dbr , l l l l l L'_ l Porphyritic rhyolite with quartz i l l l i_.# Nonporphyritic rhyolite iDbbi g4 Tuif and volcanic breccia ‘ Dbm i L ,4 Mafic flow 4 r W27 / i mg i i 4 A t Copley greenstone J DEVONIAM?) Massive sulfide are Contact, dashedvThEr—e—approirimately located or projected; dotted where interred u! %‘_?_ Fault. showing dip; dashed where approxi- mately located; queried where probable Mountain Copper Co., Ltd A 3 5007 l v 4 End of drill hole is 550 feet northeast of section L i , Datum is mean sea level FIGURE 56.—Map of Iron Mountain area showing location of section tlu‘oug was expected, and the hole was still in Balaklala rhyo— lite at a depth of 1,798 feet, where it was abandoned be- cause of deflection. From a bearing of N. 421/2° W. at the collar the hole deflected to S. 571/2O E. at 1,760 feet, and from a dip of 701/2° it flattened to 38°. DESCRIPTION OF THE CORE The diamond—drill core consisted of porphyritic and nonporphyritic rhyolite, rhyolitic pyroclastic material, and a small amount of chloritic rock. A geologic col- ‘Vertical projection of drill hole Geology by A. R. Kinkel, th, J, P, Albers, and W. E, Hall U. upthrown side; D, downthrown side so Vertical fault i SOUTH FAULT Syncline ‘3 Outline of favorable area \ V §\ > < 1000’ r < 1500 j Dar-rm Diamond-drill hole, showing projection to surface and length from collar _i,,, .‘r ,7‘.‘_—4~1500’ 1000 Feet ,_l U. S. Geologic Survey diamond-drill hole and geologic cross 11 drill hole. umnar section of the hole is given in figure 57. Above a depth of 520 feet the core was predominantly porphyri- tic rhyolite and contained 2- to 3-millimeter quartz and feldspar phenocrysts in an aphanitic groundmass. The porphyritic rhyolite was weathered and contained clay minerals and limonite to a depth of 266 feet. Below 520 feet the core was mainly siliceous nonporphyritic rhyolite and had a mottled appearance due to irregular patches and streaks of chlorite. In three places chlorite was very abundant, and the rock was composed only of 128 GEOLOGY AND BASE—METAL DEPOSITS, WEST SHASTA COPPER-ZINC DISTRICT Surface I Continued from lower left Dbb Db m EXPLANATION ’ — 1 Vertical 100, __ Dbr scale Dbr — . . —— —700' .~-.:. 0.8,1.26,0.0 _ ‘ ’ Porphyritic rhyolite, phenocrysts 174 mm 0 HO 9 Dbrn o o o 0 °. Dbrn 50 05 001 . 1 '. f3 Nonporphyritic rhyolite 5: r " D Z I .,00. 05,0. 01:): 3.5.0.50, trace _ “1100’ E s —600 2.8,0.23,0.005 —_ ;< Dbb ,5 1.0,0.02,0.005 4‘ ~ _ : 2 E __ > 1'0'0'05’0'0 ’j E Volcanic breccia and tuff ‘3 £3 1.0,0.08,0.0 —-"- . Dbc 1.5,0.05,0.0 —-..' ' ' — Dbr" — 300’ _- . ‘ _» ; —1200’ Chloritized rhyolite ~500' 2.0,0.03,o.005 ——.=--: _-.. 2' 7 .‘ _— _‘ 1' Dbrn 2.5.0.03, trace —- " _— J a Greenstone 0.3,0.02, trace Dbr K 3,1,0.03,0.01 . Dbm - :.~:. —1300' .. —400’ _ - . - . . Pyrite and chalcopyrite, . . ' - - 2 - . ' ' streaks and disseminations .3Dprn‘ ““’ . I ‘ o o °o°° a 00000 ° 0 %_ , Argillic alteration , Dbr 500 -300 22,005, trace _ . . Dbb ——-Dbr ~~~~ Shear zone Dbrn Dbc L gm fASSPg DATA G Id ._ .3__ , _ , en 0 opper 0 600 Dbr 1500 sample (feet) (percent) 02.62er ton l—200’ 2.2 1.05 .01 1.5,1.07, trace a; 4.0002, trace —« — 700‘ — 1600’ ~100' ‘ . 0. 1.0.0 ' Dbrn 7 0, 5 05 _800' H , _ Dbrn 1700 0 O.5,0.43,0.0— \ 2.0020 trace-—1~:-'::'-z:.‘-__ I I 900 Bottom 1798 Continued at upper right FIGURE 57.~Graphic 10g of the U. S. Geological Survey diamond-drill hole at the Iron Mountain mine. IRON MOUNTAIN MINE quartz and chlorite. Most of the core contains a little disseminated pyrite in the form of tiny cubes. Pyrite was more abundant where the rock was sheared, and some of the core contains abundant disseminations and seams of pyrite as much as 6 inches thick for distances of as much as 6 feet. However, bodies of massive pyrite similar to those at the Iron Mountain mine were not found. Twenty-two samples of core were assayed for copper and gold; the assays are shown on the columnar section (fig. 57). Parts of the core that contain no visible chal- copyrite were not assayed even though they are pyri- tized. The rhyolite that contains chalcopyrite gener- ally contains more chlorite than the average rhyolite of the district, and in places the rhyolite that contains chalcopyrite has been largely replaced by quartz and chlorite. GEOLOGIC RESULTS OF DRILLING The drill hole at Iron Mountain indicates abundant pyrite and some chalcopyrite at a considerable distance from known ore bodies, but evidence of bodies of com- mercial ore was not found. The cores show chalcopy- rite at depth in the syncline southeast of the known ore bodies, and indicate either that additional feeder chan- nels occur in this area, or that copper-bearing solutions entered the wall rock from known feeder channels, such. as the Camden fault, at a considerable depth below the known ore bodies. In addition the drilling demon- strates that detailed geologic mapping of the lenticular, obscurely bedded volcanic rocks will yield sufficient information to predict the occurrence and shape of folded structures, such as the syncline that was drilled. KEYSTONE MINE Locationv.—The Keystone mine is in sec. 14, T. 33 N., R. 6 “7., about half a mile southwest of the Balaklala mine. The portal of the Keystone adit is at an alti- tude of 3,000 feet on the south slope of the canyon of Squaw Creek. The mine was made accessible in 1950 by the repair of a steep dirt road that extends beyond the Balaklala mine. History and production—Little is known of the early history of the Keystone mine. Assessment work had been done on the mine by 1902 (Aubury, 1902, p. 90), but no additional work had been done up to 1908 (Aubury, 1908, p. 100). Exploratory work was carried on in 1918, and the Keystone is listed as a pro- ducing mine in 1923 in the California State Mining Bureau report for that year. The mine was active until the fall of 1925. It was operated by the United States Smelting Refining and Mining Co. and is still owned by that company. The Keystone mine has not operated 129 since 1925, and the portals of the main adits are caved. The accompanying maps (pls. 5, 6) of the mine are based upon existing mine maps and records and are in part interpretations of such data by the writers. The recorded tonnage and grade of mined ore is 122,000 tons that averaged 0.06 ounce of gold, 2.7 ounces of silver, 6.0 percent copper, 8.0 percent zinc, 30 percent iron, 35 percent sulfur, and 15 percent insoluble material. Geology of the mine mean—The geologic setting of the Keystone mine is similar to that of the Balaklala mine to the north (pls. 5 and 6, H—I—J). The ore bodies are overlain by a gently dipping contact between the upper and middle units of the Balaklala rhyolite. Nothing is known of the rock type in the middle unit of the Balaklala adjacent to the ore, as the underground workings are inaccessible. Where this zone is exposed at the surface near the portal of the Keystone adit, the upper part of the middle unit is porphyritic rhyolite that contains 1- to 2-millimeter quartz phenocrysts, and nonporphyritic rhyolite. A very small amount of yellow rhyolitic tuff and local areas of rhyolitic breccia occur along the contact. The bed of coarse volcanic breccia above the ore at the glory hole of the Balaklala mine 2,000 feet to the northeast lenses out along the contact before it reaches the Keystone portal. The ore bodies of the Keystone mine occur in the updip exten- sion of the productive zone that contains the Balaklala ore bodies. The upper unit of the Balaklala rhyolite near the portal of the Keystone adit is a coarse-pheno- cryst tufi' that contains a few bodies of massive coarse- phenocryst rhyolite. Character of the ore bodies.——At the time of mine operation, the massive sulfide ore in the Keystone mine was subdivided on the basis of copper content into minable and below minable grade. Both types of ore are massive sulfide bodies, but minable ore occurs in some parts of the mine as separate bodies and in other parts as copper—rich parts of large masses of pyrite that otherwise are very low in copper. Some large bodies of massive pyrite occur that contain a little cop— per or zinc (pl. 12). The ore bodies in the Keystone mine are in a produc- tive zone, at least 300 feet thick, in the middle unit immediately below the base of the upper unit of the Balaklala rhyolite. Some of the ore lies just below the contact, but the major part of it was mined 50—80 feet below this contact. The higher grade copper ore is ~ bounded at most contacts by strong shear zones, and may have replaced sheared rock. Stopes outline tabular, gently dipping copper-rich ore bodies that parallel the contact between the upper and middle units of the Bala- I klala rhyolite, but most of these ore bodies dip 5°—10° ‘ more steeply than this contact. The average thickness ‘ 130 GEOLOGY AND BASE—METAL DEPOSITS, WEST SHASTA COPPER—ZINC DISTRICT F900 0 EV KEYSTONE MINE 3500 TRUE NORTH KING COPPER PROSPECT 3000 Sugarloaf Mtn >< El 3909’ * LONE STAR ( PROSPECT SUGARLOAF > PROSPECT @650 ore body El 3835’ ADIT / ‘Hornet ore body .. Iron Mountain»mine IPON MOUNTAIN ‘Q MINE ‘90 o \ 1000 O 5000 Feet l 1 1 w | I I I I l J a Contour interval 500 feet k9000 \Cl‘eef Datum is approximate sea level \) L ° ' SPREAD EjGLE PROSPECT _/ STOWELL MINE O / 2o FIGURE 58.——Locati0n of the King Copper and Sugarloat prospects In relation to nearby mines and prospects. KEYSTONE of ore in the stopes ranged from 10 to 20 feet and the maximum thickness was 50 feet. The Keystone mine contains large bodies of massive sulfide ore of low copper content. As the ore was direct- smelted at the time of mine operation, these bodies did not constitute ore. Consequently their limits were not completely outlined by drilling. Some bodies of low- grade massive sulfide are cut by mine workings, but, what appear to be some of the largest bodies are indi- cated only by a few drill holes. These low-grade bodies are also bounded by faults or shear zones where they were exposed in the mine workings. Higher grade cop— per ore bodies occur as parts of lower grade sulfide masses on levels 300 and 318 (pl. 12) , but at most places the two types form separate bodies. The massive sul— tide bodies that have low copper content are not sufii- ciently explored to allow an estimate of tonnage, but it probably is large. The grade of the low-copper pyritic ore, from records of the United States Smelting Re- fining and Mining Co., is 0.01 ounce of gold, 03 ounce of silver, 0.54 percent copper, and 43 percent sulfur. The copper content as indicated by available data ranges from 0.1 to 2.5 percent. These massive sulfide bodies are similar to the Hornet ore body at the Iron Mountain mine. Ore controls and exploration. possibilities—The main ore control at the Keystone mine is the contact between the upper and middle units of the Balaklala rhyolite. The writers have no information on rock types in the mine other than the location of the contact between these two units, and no folds in this contact are known un- less the curved contact between the two units that is shown on the 275—foot level indicates a minor fold. A vertical control by the contact seems obvious, but no horizontal controls are known. There is a suggestion, however, that some of the ore bodies may have formed against or along faults. At several places the bodies of massive sulfide ore are terminated by steep faults. Faulted extensions of these ore bodies have not been found in existing mine workings and drill holes. Such steep faults may have been feeder channels for ore solu- tions, which deposited ore bodies along fiat subsidiary shear zones. The productive zone, that is, the one immediately be- low the upper unit of the Balaklala rhyolite, is covered in the area between the Keystone and the Stowell mines, a distance of 3,000 feet. The productive zone should extend throughout most of this area at a moderate depth, as the upper unit of the Balaklala is known to be about 500 to 6.00 feet thick where it has been drilled between the two mines. A limited amount of explora- tory drilling has been done between the Keystone and 131 NIINE the Stowell mines, but a large area east, south, and west of the Keystone remains to be explored. KING COPPER PROSPECT The King Copper prospect is located in sees. 23 and 24, T. 33 N., R. 6 “7., on the northeast side of Spring Creek (pl. 4). Many prospect adits were driven on pyritized zones in the Balaklala rhyolite, but no min- able ore was developed. Aubury (1902, p. 81) reports that the King Copper prospect was explored by about 1,000 feet of adits by 1902, and apparently little work has been done since that time. The property is now owned by R. T. Walker and WV. J. \Valker. Geology—The rocks in the vicinity of the King Cop- per prospect are interlayered flows of porphyritic and nonporphyritic rhyolite that contain much flow breccia and some pyroclastic material. They probably belong to the middle unit of the Balaklala, although as at the Sugarloaf prospect to the southwest (fig. 58) their stratigraphic position is obscure because of the difficulty in distinguishing the middle and the lower units of the Balaklala in this area. The Copley greenstone crops out about 3,000 feet southeast of the prospect, and marks the lower limit of the Balaklala rhyolite. The rocks near the prospect have a steep foliation, but no bedding was found. Ore deposita—Many pyritized zones are in the vicinity of the King Copper prospect, and areas of strongly foliated rhyolite have been hydrothermally altered to soft crumbly white and lavender rock. Zones of hydrothermal alteration and pyritization range from scattered thin seams to fairly well defined bands several tens of feet in width. Most of the pyritized bands are also silicified. The bands are classed as pyritized, hydrothermally altered rhyolite rather than gossan, as the material consists of scattered euhedral pyrite in silicified, argillized rhyol ite, or in secondary silica. The most heavily pyritized material on the dumps of the King Copper adits contains only about 50 percent pyrite. A few small lenticular bodies of gossan, less Balaklala in this area. The Copley greenstone crops out near some of the adits, but the only body of gossan that appears promising at the surface is one that crops out immediately above the second adit from the north as shown on figure 58. This gossan occurs in silicified porphyritic rhyolite; it is 2 feet thick and possibly 50 feet in strike length. It dips flatly to the north and appears to be localized where the normally steep folia- tion bends and lies flat. Diller (1906, p. 13) reports that The general trend of the small ore body of the King Copper, on the slope of Spring Creek is N. 70°—76° W. It dips 84° SW. and apparently agrees quite closely with the position of the 132 Spread Eagle ore body, transverse to the general direction of the Iron Mountain lode. The location of the ore body referred to by Diller is not known. The area between the Sugarloaf and the King Copper prospects, and northeast of the King Copper, is one in which pyritization is Widespread, and these prospects appear to be alined along the trend of a mineralized belt, but no bodies of massive sulfide have been located in the zones of pyritization. LONE STAR PROSPECT The Lone Star prospect, which is owned by the Moun- tain Copper Co., Ltd., is at the southwest end of the West Shasta copper-zinc district in sec. 27, T. 33 N ., R. 6 IV. It is accessible either by a road from the Iron Mountain mine or by a road that extends north along the ridge from the South Fork Mountain lookout sta- tion. The prospect is on a massive sulfide body that is explored by two short adits, but no ore has been mined. An inconspicuous gossan is exposed where the ore body crops out on a steep hillside. The rocks near the ore body are largely covered by slope wash. Geology 0 f the mine area—The massive sulfide body at the Lone Star mine is in porphyritic Balaklala rhyo— lite, but nonporphyritic rhyolite, tuffaceous shale, and amygdaloidal andesite occur near the ore body (pl. 13). Both the porphyritic and the nonporphyritic rhyolite are light-green siliceous weakly foliated rocks. The porphyritic rhyolite contains quartz phenocrysts that average about 2 millimeters in diameter. The thin flow of amygdaloidal greenstone which crops out south of the ore body, is a dark—green chloritic rock. At the surface the fillings of the closely spaced, round vesicles in the greenstone have been dissolved, leaving iron- stained cavities. The bed of tuffaceous shale north of the ore body is a poorly exposed, buff—colored rock without distinct bed- ding. The shale apparently ]ies at about the same hor- izon as the bedded crystal tutf and tuffaceous shale that occurs at Iron Mountain just northwest of the Brick Flat ore body (Kinkel and Albers, 1951, pl. 1). These shale beds are correlated with the crystal tuft, 800 feet northeast of the Lone Star prospect, in which a fossil was found that was determined by D. H. Dunkle of the National Museum as a fish plate from an euarthrodiran fish close to 7 ’itaniehthys of Middle Devonian age. The tuffaceous shale and crystal tuff in this area are at the horizon of the transition zone between the upper and middle units of the Balaklala rhyolite, but it is doubt- ful that the upper unit extended this far southwest. GEOLOGY AND BASE—LIETAL DEPOSITS, WEST SHASTA COPPER-ZINC DISTRICT Ore deposit—The gossan at the Lone Star prospect is a typical massive sulfide gossan composed of dense and cellular limonite, but is in part a collapse breccia, which contains fragments of wall rock cemented by li- monite, The gossan forms an arch. At this prospect material formed by the cementation of soil and dump material by iron-bearing waters that issue from the mine portal superficially resembles gossan. It is apparent from surface exposures and from drill- ing that the ore body was essentially a flat-lying lens of massive sulfide with sharp contacts. The wall rock, including the fragments in the collapse breccia, is only slightly pyritized. The adits were not accessible, but a lack of gossan in dumps, and underground maps made by L. C. Raymond for the Mountain Copper Co., Ltd., indicate that the gossan extended only a few tens of feet in from the surface. Most of the mineralization in the underground workings was massive sulfide. The size of the ore body is not adequately determined. Maps and assays furnished by the. Mountain Copper Co., Ltd., show that drill hole 5 cut 45 feet of massive sulfide along the length of the ore body, but as indicated in plate 13, the total length of the lens may be about 85 feet. The width in the upper adit is about 20 feet, and the maximum thickness is about 10 feet. The ore body is cut by many small faults, but it is not known whether the small slivers of ore. are faulted segments of a for— merly continuous massive sulfide body, or isolated lenses of massive sulfide. Assays of diamond-drill core and of ore from the dump show that this small ore body contains more cop- per than most of the ore at the Iron Mountain mine, and that it resembles some of the smaller higher grade satellite ore bodies at other mines in the district. The ore contains visible chalcopyrite and sphalerite in mas- sive pyrite and few gangue minerals. Individual assays of the massive sulfide from drill core range in copper content from 0.62 to 6.89 percent, but the average of the ore cut by drill holes is 3.74 percent copper. No assays were made for gold, silver, or zinc. Ore specimens on the dump appear to contain more sphalerite than chal- copyrite. A prominent, steeply dipping, east-west fault is ex- posed in surface cuts north of the ore body. The north side is thought to be the downthrown block as the shale that crops out north of the prospect is not found to the south. The amount of vertical (and possibly horizon- tal) movement is not known, but three holes drilled in the doWnthrown block failed to locate a faulted exten- sion of the ore body. It seems probable that a faulted extension of the known ore body is north of the fault, either below or to one side of the present drill holes. MAIVIMOTH MINE MAMMOTH MINE The Mammoth mine is in the northern part of the West Shasta copper-zinc district in sec. 32, T. 34 N ., R. 5 W., on the south side of Little Backbone Creek at an altitude of about 3,000 feet. The mine is owned by the United States Smelting Refining and Mining Co. Dur— ing mining operations from 1905 to 1925 the mine was accessible by standard gage railroad up Little Back- bone Creek and by funicular from the railroad siding to the mine’s main adit, the 470—foot level. The flooding of Shasta Lake in 1944 submerged Little Backbone Gulch and the lower part of an unimproved road to the mine. The road is 3 miles long, and climbs 2,000 feet in that distance. In 1950 this road was not passable for a car. The mine was closed in 1925 and the mine plant removed. The report and the accompanying maps (pls. 14, 15) on the mine were prepared by combining the surface geologic mapping, done by the U. S. Geological Survey, and the underground geologic information obtained from mine records. As many of the workings in the vicinity of the ore bodies, including all the stopes, were inaccessible at the time of study, no underground map- ping was done. Information in this report is summar- ized from a more detailed report on the mine by Kinkel and Hall (1952). HISTORY, The date of discovery of the Mammoth mine is not known but it is assumed to have been after 1880 and PRODUCTION, AND GRADE 133 probably before 1890. George Graves is reported to have discovered the ore body, and before 1900 a Mr. Nelson worked the property on a small scale to recover the gold from the gossan. The Mammoth Copper Mining Co., a subsidiary of the United States Smelting Refining and Mining Co. acquired the property in 1904 and began large-scale mining operations in 1905. The mine was operated continuously from 1905 to 1919 but was closed from 1919 to 1923. Operations were resumed late in 1923 but were again suspended in 1925. N0 ore has been mined since 1925, although some exploratory work has been done. Plate 14 shows the extent of the mine workings. Table 13 gives the production data of copper and zinc ore from the Mammoth mine, 1905—25. The gross value of the recovered gold, silver, and copper was $51,970,290 and the value of the recovered zinc was $4,525,870. - GEOLOGY OF THE MINE AREA FORMATIONS Only the Balaklala rhyolite and the Kennett. forma- tion crop out in the vicinity of the Mammoth mine (pl. 15). A small remnant of the lower part of the Kennett formation consisting of interbedded gray shale and water-laid rhyolitic tuff, and arkose is exposed in the southeast corner of the mapped area. The Kennett formation lies conformably on the Balaklala rhyolite and dips gently east. TABLE 13.-—Amzual production and grade of ore from the Mammoth mine, 1905—25 [Data furnished by the United States Smelting Refining and Mining 00.] Grade ' Year Production Gold Silver C The Ins lubl I on Sulfur (short (ounces (ounces opper ‘1 0 e r tons) per ton) per ton) (percent) (percent) (percent) (percent) (percent) Copper ore 13, 868 0. 029 1. 94 4. 30 ________________________________________________ 181, 733 . 048 2. l2 3. 95 3. 30 9. 5 39.0 42. 2 201, 124 . 039 1. 94 4. 15 4. 70 7. 7 38. 4 44. 5 311, 997 . 033 1. 90 4. 03 4. 70 12. 6 35. 6 41. 9 370, 985 . 036 2. 13 4. 15 4. 70 13. 2 34. 9 42. 0 315, 189 . 038 2. 38 3. 83 4. 40 15. 1 34. 2 40. 7 269, 438 . 032 2. 26 4. 06 4. 20 12. 4 35. 4 44. 7 273, 555 . 034 2. 24 3. 47 4. 20 12. 6 34. 0 40. 9 269, 233 . 036 2. 19 3. 58 3.80 14. 9 32. 7 39.8 227, 459 . 043 2. 28 3. 96 4. 10 12.5 33. 9 40. 3 242, 573 . 038 2. 21 3. 75 3. 80 12.8 33. 3 40. 0 223, 458 . 042 2. 74 4. 77 4. 20 13. 8 32. 6 37. 6 147, 340 . 040 2.46 4. 22 3. 80 20. 4 31. 4 35. 6 76, 079 . 040 2. 29 3. 91 4. 30 14. 2 32.4 37. 6 37, 733 . 040 2. 50 4. 10 3. 70 14. 4 32. 9 37. 8 9, 221 . 050 2. 85 4. 42 5. 00 16. 6 33. 2 36. 9 115, 814 045 2. 39 4. 27 3. 70 13. 5 35. 2 40. 2 34. 346 . 037 2. l7 4. 34 4. 30 11.0 36. 6 41. 4 Total and weighted averages. ___________________________________ 3,311, 145 .038 2. 24 3. 99 4. 20 13.3 34. 3 l 40. 4 Zinc ore 1914-15 _________________________________________________________________ 84, 000 i 0.078 1 5. 79 ‘ 2. 40 ‘ 21.10 i ____________ i ____________ i ____________ Total and weighted averages _____________________________________ l 3. 395, 145 i .039 ‘ 2. 32 ‘ 3. 95 ‘ 4. 62 i ____________ k ____________ ‘ ____________ 379725—56—11 134 The Balaklala rhyolite in the mine area consists of porphyritic and nonporphyritic rhyolitic flows and in- tercalated coarse and fine rhyolitic pyroclastic material. Parts of the upper, middle, and lower units of the Bala- klala are exposed; the ore zone is in the uppermost part of the middle unit, immediately under the base of the upper unit. The lower unit of the Balaklala in the mine area con- sists mainly of light—gray to light-green nonporphyritic rhyolite, and rhyolitic tufi' and Volcanic breccia, but locally it contains a few porphyritic flows. Most of the lower unit is exposed in the deep canyon of Little Back- bone Creek north of the mine where it is highly pyri— tized at many localities. The middle unit of the Balaklala in the mine area ranges in thickness from 150 to about 300 feet. It con- sists mainly of light—green to light-gray porphyritic rhyolitic flows and pyroclastic rocks containing 1- to 4— millimeter phenocrysts of quartz and feldspar. The upper part of the middle unit contains abundant, al— though discontinuous, coarse and fine pyroclastic ma— terial and some water-deposited tntf beds. The upper unit of the Balaklala in the mine area con- sists of coarsely porphyritic rhyolite containing quartz and feldspar phenocrysts, some of which are more than 4 millimeters in diameter. T t is about 1,400 feet thick at Mammoth Butte, 1 mile west of the Mammoth mine, but thins rapidly toward the east over the mine area. Part of the upper unit has been removed by erosion except in the southeast corner of the mapped area (pl. 15). A thin bed of tufl' or volcanic breccia is present at many localities at the base of the upper unit. This pyroclastic bed is generally 10 to 50 feet thick, but where it is composed mainly of volcanic breccia, it is as much as 150 feet thick. The upper unit of coarse-phenocryst rhyolite and the tufi'aceous bed at the base of this unit form the “cap rock” for the ore deposits, which were deposited just below the base of. the “cap rock.” FOLDS The bedding in the mine area is delineated by the contact between the overlying coarse—phenocryst rhyo- lite and the underlying medium-phenocryst rhyolite and nonporphyritic rhyolite, or by bedded tuff at the base of the coarse—phenocryst rhyolite. The structure contour map (pl. 16) shows that a slightly elongate arch trends N. 45° E. and has a cul- mination in the central part of the group of ore bodies. There are also many smaller arches or elongated topo- graphic “highs,” the alinement of which appears to have no relation to the alinement of the main arch. The sedimentary material at the base of the coarse- phenocryst rhyolite delineates the folded structures. GEOLOGY AND BASE—METAL DEPOSITS. WEST SHASTA COPPER-ZINC DISTRICT Bedded material is shown at the base of the coarse- phenocryst rhyolite on the underground maps furnished by the United States Smelting Refining and Mining Co. Evidence from correlation with the surface mapping done by the writers and from thin sections, indicates this material is a tuff bed. Dips and strikes in the bedded material on underground maps show that in most places the bedding is parallel to the contact of the coarse-phenocryst rhyolite (pl. 15). Some random orientation of bedding has been observed, but such variations may be caused by close folding, faulting, or minor intrusions of coarse-phenocryst rhyolite. At the Mammoth mine the degree and type of foliation that is formed is dependent on the competence of the rock units. The nonporphyritic rhyolite, the medium- phenocryst rhyolite, and the thick, massive coarse- phenocryst rhyolite are competent rocks. Pyroclastic beds at the base of the coarse—phenocryst rhyolite form an incompetent layer that covers a considerable area. During the folding in the mine area steep fracture cleav- age—with some recrystallization and alinement of min- eral grains parallel to cleavage planes—formed in the nonporphyritic and medium—phenocryst rhyolite, par- ticularly near the axes of folds. Movement along the bedding planes, resulting in a secondary foliation parallel to the bedding planes, was concentrated in the pyroclastic layers at the base of the coarse-phenocryst rhyolite. In the overlying massive coarse—phenocryst rhyolite steep fracture cleavage is locally present, but it is rare because of the great thickness and competence of this rock. mums Several large fault zones and many small faults are shown on the maps of the mine levels. They are of several ages, as shown by one fault cutting another; most are probably pOStmineral in age, but some may be premineral. The principal faults are the California, the 313 (and its possible extension, the Yolo), the 12-drift, the Schoolhouse, the Gossan, the Friday, and the Clark. On all these faults, the north or east side has moved down relative to the south or west. The hori— zontal component is not known except on the California fault, where it is about 250 feet. Few of the faults can be located or traced for any dis- tance on the surface. Their location as shown on plate 15 is based largely on a projection of the faults from their known position underground. Except for short sections of the California, Schoolhouse, and Gossan faults, where these are exposed at the surface, informa- tion on the faults is taken from the underground maps of R. N. Hunt, from R. T. Walker (oral communica- tion), and from the writers’ brief underground exami- nation of the California fault. NIAMMOTH MINE The California fault zone is a group of subparallel and branching fault planes rather than a single plane, and, as seen underground, the zone does not have sharp boundaries at all localities. At some exposures the rock between the individual fault planes is massive and little altered; at others the fault consists of a zone of gouge and crushed quartz—sericite rock containing many anas- tomosing shear planes. Hydrothermally altered rock is not prominent in the exposures seen underground although some sericite is present, but hydrothermally altered rock is recognized along the surface exposure of this fault, as weathering has emphasized the difference between altered and unaltered rock. The porphyritic rhyolite along the California fault at the surface is altered to white and pink clay minerals and sericite, but this alteration extends only 5 to 10 feet on either side of the fault. The California is probably a premineral fault, but postmineral movement has also occurred as shown by offset ore bodies. The north block moved east and down, but the exact amount of movement is not known. The ore bodies plunge at a low angle to the southwest along the fault, so that the present position of offset segments of ore bodies could be due either to mainly dip—slip or strike-slip movement. The 12—drift fault and the 313 fault, and its possible extension, the Yolo, are shown on the maps of the mine levels (pl. 17) and on the cross sections (pl. 15). The vertical offset on each of these faults is about 40 feet, and the rocks on the north side moved down relative to the south, but nothing is known about a possible hori- zontal offset. They are probably older than the Cali— fornia fault as the underground maps suggest that they are offset by it. The Schoolhouse fault is exposed only on the 670- foot level (pl. 17) and for a short distance on the sur- face. The approximate vertical offset of the base of the coarse-phenocryst rhyolite at the surface appears to be about 100 feet, where the rocks on the north side moved down relative to the south, although exposures are poor where the fault cuts this contact. The offset on the Schoolhouse fault appears to be less in the east end of the mapped area than in the west. The rhyolite along the Schoolhouse fault at the surface is pyritized and altered to clay minerals. The Gossan fault is exposed on the 670—foot level for a short distance on the surface. The rocks on the east side of the fault are dropped relative to those on the west; on the basis of a doubtful correlation of rock types the vertical offset is about 50 feet. The rhyolite is pyritized and altered to clay minerals along the outcrop of this fault. 135 Several north—dipping faults that strike N. 60°—80° W. are in the vicinity of the Friday Lowden and Hanley ore bodies at the southwest end of the mine. The Fri- day fault is one of this group of faults that cut the Friday Lowden ore body and may offset it. The total offset on this group of faults may be considerable, but no data are available. The Clark fault, which is a minor fault, has an offset of 10—20 feet. The rocks on the north side have moved down relative to the south (pl. 15). ORE BODIES CHARACTER AND DISTRIBUTION The ore bodies of the Mammoth mine are large, flat- lying, tabular bodies of copper- and zinc—bearing mas- sive pyritic ore which extend along a horizontal distance of 4,200 feet. The northeast end of the ore zone has been eroded, and exploration has not delimited the southwesterly extension; the central part has a width of 1,000 feet. Although minable ore bodies occur throughout the ore zone, it is not all ore (pl. 14). Indi- vidual stopes reach a maximum horizontal dimension of 900 by 500 feet and the maximum thickness of ore is 110 feet; ore bodies range from these maxima down to small stopes from which only a few hundreds of tons were mined. The ore zone lies along the crest of a broad arch in the rocks, and all known ore occurs at or a short distance below the contact between the coarse- phenocryst rhyolite and the underlying rhyolitic tuff and flows (pl. 15). The ore formed by replacement of rocks in the uppermost part of the middle unit of the Balaklala rhyolite. Table 14 gives data on the production and grade of stopes and other ore blocks; it also shows the uniformity of the gold, silver, and copper content of all the copper ore bodies, and the sharp distinction between high-grade copper and high—grade zinc ore. The pyritic ore that un- derlies the copper ore bodies contains a smaller quantity of copper than the massive sulfide that was mined for copper, but the ore is the same type. Table 15 gives information on the proportion of metals in the zinc-rich parts of the ore bodies. The grade of the material sorted from the ore of high zinc content was calculated from the known assays. It is apparent, for instance, that the discarded material sorted from the zinc ore was rock that contained some copper, gold, silver, zinc, and iron but contained more rock material by volume than is contained in massive sulfide (45.3 percent by weight insoluble). The figures suggest that the discarded material consisted of rock containing stringers of the massive sulfide type of ore in essentially unmineralized rock, rather than that the discarded material contained disseminated minerals. 136 GEOLOGY AND BASE-METAL DEPOSITS, WEST SHASTA COPPER—ZINC DISTRICT TABLE 14.—Production and grade of stapes and other ore blocks of the Mammoth mine [Data furnished by the United States Smelting Refining and Mining 00.] Grade Production __ Ore body ( . short tons) Gold Silver C . oppcr , Zinc Lead Iron Sulfur Insoluble (0mg?) per (0111:3315) per (percent) (percent) (percent) (percent) (percent) (percent) Copper ore Gossan (oxidized) _______________________________________ 10, 000 0. 10 15.0 0.5 ________________________ Gossan (sulfide)_,. ______________ 65, 000 .04 7.0 10.0 Copper Crest. .. ____________ 5, 000 .04 2.0 4.0 . M ' 1, 970,145 . 03 1.8 3.8 , 000 . 04 2. 2 3. 8 . 2, 000 . 03 2. 0 3. 0 . 100, 000 . 04 2. 2 3. 8 , , 000 . 03 2. 0 3. 0 . ........ 385, 000 . 04 3. 0 4. 5 . ________________ 200, 000 04 3. 0 4. 5 . ................ 100, 000 04 3. 0 4. 5 _ ________________ 2, 000 03 2. 0 3. 5 _ Friday Lowden_ ______________ 100, 000 . 04 3. 0 5. 0 _ Hanley __________________________________________________ 60,000 .04 3. 0 6. 0 ________________________ Zinc ore Grade of sorted ore l Yolo ____________________________________________________ 58, 000 0. 12 5. 44 2. 20 36. 20 3. 00 10. l 25. 2 20. 7 Copper Crest. ____________________________________________________________ 473 ,,,,,,,,, 33. 30 ____________ 9. 2 24. 7 19. 8 313 _____ 27. 70 1. 00 9. 5 23. 5 31.8 Graton. 36. 35 1. 40 .................................... Metcalf _____________________________________________________________________________________________________________ Grade of unsorted ore 1 Total 1 _____________________________________________ 84,000 . 078 5. 79 2. 4O 21. 10 ____________ 12. 6 ____________ 35. 5 Pyritic ore underlying copper are bodies Main (separate blocks)_. 0.04 1.0 2.0 45.0 Do . 03 . 4 . 5 40. 0 . 03 . 2 . 5 45. 0 . 01 . 6 . 5 35. 0 . 03 1. 0 1. 2 40. 0 _ . . 04 1. 1 2. 2 45. 0 0 ......................................... . . 01 . 3 . 5 40. 0 313, at 390-foot level .................................................... .05 1. 1 2.0 40.0 Total ____________________________________________________________ . 028 . 56 9 ____________________________________ 41. 4 ____________ 1 See table 15. Little information is available to the writers on the appearance of the copper—zinc ore underground, or on the nature of the contact between ore and wall rock. Specimens that the writers collected from dumps and along the tramline, and analyses of ore showing the higher content of insoluble material, indicate that al— though most of the ore was a massive pyrite; some contained more quartz and altered, unreplaced rock ma- terial than the massive pyritic ore of the Iron Mountain and Shasta King mines. However, observers who have seen the ore underground have noted that quartz is ‘arely Visible megascopically in the Mammoth mine ore except where a few late veinlets out both the ore and the wall rocks. Frozen contacts between ore and wall rocks are re- ported to be rare; at most contacts, as in the other mines in the district, ore is separated from rhyolite by a clay gouge selvage. R. N. Hunt (oral communication) TABLE 15.—Production and grade of hand-sorted zinc are from the Mammoth mine 1 [Data furnished by the United States Smelting Refining, and Mining Co.) Grade Produc- Ore (:liiii-t Gold Silver Cop— Zinc Iron Insol- tons) (ounces (ounces per ( r- ( er- uble L per per (per- egreit) cgnt) (per- ton) ton) cent) ‘ cent) Crude ore produced ______ 84,000 0.078 5. 79 2. 40 21. 10 12. 6 35. 5 Sorted ore Shipped _______ 28, 800 . 111 9. 51 2. 4 39. 6 8. 9 16. 8 Percent increase or de- crease .................. —~65. 7 +42. 3 +63. 6 0 +87. 5 —29. 4 —52. 6 Discard calculated ....... 55, 200 .061 3. 82 2. 4 11. 42 14. 6 45.3 1 See table 14. states that many ore bodies had sharp, smooth outlines. In these the contacts between the massive sulfide and wall rock were sharp; the ore was separated from the wall rock by a thin selvage of gouge at the ends as well as along the top and bottom of the ore bodies, and the wall rock contains little or no pyrite. Contacts of this NIAlVIMOTI-I lVIINE type are similar to those at Iron Mountain and at the Shasta King mine. R. T. “Valker (oral communica- tion) , however, reports that the material between some of the stopes (and sometimes beneath them) was massive sulfide containing less copper than the ore that was mined. The ore zone was continuous between these stopes, and some stope outlines mark only the economic limit of mining. Thus, although many stopes were mined to a sharp waste wall at the ends of the ore bodies and on all sides, at some places an individual stope does not represent the extent or continuity of a body of mas- sive sulfide, which may be of considerably greater extent than is indicated by the outline of the stope. The ore zone at the Mammoth mine extends S. 70° WV. for 3,000 feet from the outcrop of the Main ore body to the deepest exploratory workings southwest of the Friday Lowden. The general trend of individual ore bodies—and of the zone as a whole, if the Gossan ore body is included—is more nearly S. 60° WV. Part of the zone is eroded between the Gossan and Main ore bodies (pl. 15). Although the Gossan ore body lies at a lower stratigraphic horizon than the main part of the mineralized zone, it seems reasonable to assume that ore bodies were present along the eroded upper part of the zone and its eroded extension northwest of the Gos- san ore body. The zone must have been at least 4,200 feet long, and may have been considerably longer. The plunge of the ore zone ranges from almost hori- zontal to vertical, but averages only 14° from the out- crop of the Main ore body to the deepest known ore. A few large and many small faults cut the ore bodies. Small faults are marked by slickensided surfaces. The larger faults appear to have offset ore bodies several hundred feet, and the present distribution of these ore bodies is due in part to postmineral faulting. OXIDATION AND ENRICHMENT The gossans at the outcrops of the ore bodies at the Mammoth mine are not large or conspicuous, consider— ing the size and extent of the. ore bodies. Gossans about 10 feet thick occur where the tips of the Main and VVin- slow ore bodies crop out, but most of the gossan is thin— ner. Rock that contains disseminated pyrite is much more extensive at the Surface than massive sulfide ore, and upon oxidation of the pyrite forms considerable areas of rusty rhyolite (pl. 15). Only a few small nodules of massive sulfide ore were found in the outcrop of the Main ore body, and R. N. Hunt and R. T. Walker (oral communication) state that oxidation extended as much as 150 feet in from the present erosion surface. 137 Super-gene enrichment has not taken place on a large scale at the Mammoth mine, although some secondary enrichment has occurred as a result of oxidation of the ore near the outcrop. The Gossan, and possibly the Main and \Vinslow ore bodies were partly oxidized and enriched, but figures on the metal content of the 0xi~ dized and enriched ore are available only for the Gossan ore body. Specimens of enriched ore were not available to the writers, and the mineralogy of the enriched ore is not known. Seager in his unpublished report noted that chalcocite and covellite are present in specimens of enriched ore from the Mammoth mine. Production data on the Gossan ore body are given in table 14. The enrichment indicated for it is about the same as that in the Old Mine ore body at the Iron Moun- tain mine (Kinkel and Albers, 1951, p. 18). The gold content of the enriched oxidized ore is about twice that of the primary ore, owing to 105s of weight in the forma— tion of gossan from massive sulfide. HYDROTHERMAL ALTERATION Alteration ranges in the mine area from unaltered porphyritic rhyolite to altered rock having relict quartz phenocrysts in a matrix of secondary minerals. The rocks have been altered by regional metamorphism, hy- drothermal alteration, weathering, or by a combination of these processes. The altered porphyritic rhyolite is white, lavender, buff, or light green. Hydrothermal origin is evidenced by the conspicuous white alteration of the rhyolite around ore bodies and along fractures in the ore zone; the intensely altered rock is composed of quartz and sericite, and crumbles apart in the hand. ORE CONTROLS The four controls that are thought to be of major im— portance in localizing the ore at the Mammoth mine are: (1) stratigraphic control, (2) structural control by foliation, (3) structural control by the main arch and minor flexures, and (4) location of feeder fissures. The ore zone is restricted to the rocks that immedi- ately underlie the coarse-phenocryst rhyolite, as shown in the cross sections (pl. 15). This zone contains much bedded pyroclastic material, principally discontinuous tufl' beds and lenses of volcanic breccia, but it also con- tains flows of medium-phenocryst rhyolite. Mapping done by the writers at the Iron Mountain and Shasta King mines shows that the massive sulfide ore prefer- entially replaced porphyritic rhyolite with 2- to 3-milli- meter quartz phenocrysts. Although no direct evidence is available on the nature of the rock that was replaced by the ore bodies of the Mammoth mine, the medium- phenocryst rhyolite in the ore zone at the Mammoth mine suggests that this may be the host rock here also. 138 The rocks are not strongly foliated in the Mammoth area, probably because the folds are broad, but two types of foliation that have had a considerable effect on ground preparation before ore deposition are evident. at the Mammoth mine. The first type is a foliation par- allel to bedding planes that is localized along flow con- tacts, particularly where there is much pyroclastic ma- terial between adjacent flows. The second type is a steep fracture cleavage at a high angle to the bedding that forms most strongly near the axes of folds. The foliation ranges from poorly defined sheeting without noticeable reorientation of minerals, through well— formed sheeting with sericite oriented along discrete planes, to a sericite schist in which only lenticles of unsheared rock remain. The intersection of steep fracture cleavage with folia- tion parallel to the bedding plane is an important ore control at the Mammoth mine because it formed a zone of fractured rock along the crest of an arch under a relatively impervious cover of unfractured rock. Most of the ore bodies in the Mammoth mine lie along the culmination of an arch in the rhyolite. This is shown 011 the structure contour map (pl. 16) and on the level maps. In addition to the main arch extending from the outcrop to the Friday Lowden and Hanley ore bodies at the southwest end of the mine, several smaller arches that appear to localize individual ore bodies are present. Broad minor arches extend over the Clark body, the northwestern extension of the Main, the 473, and the 313 ore bodies. The Copper Crest appears to lie on the northward-plunging nose of a major arch. The ore zone at the culmination of this arch has been eroded. Faults or shear zones that acted as feeder channels are difficult to recognize with certainty, but faults that appear to have a control on mineral deposition or rock alteration may tentatively be regarded as feeder chan- nels for solutions. The faults along which claylike hydrothermal alteration Occurs are the California, the Schoolhouse, the Gossan (these last two are exposed on the surface for a short distance only), and the unnamed fault that lies about 200 feet south of the Copper Crest ore body. All these except the Gossan fault dip steeply and trend northeast. The California fault cuts the trend of the ore zone at a low angle, and lies 400 feet northwest of the ore bodies at the southwest end of the known ore zone. The local— ization of ore near the California fault suggests it was a feeder for the whole ore zone, and that the ore solu- tions left it at a point below the Friday Lowden ore body and traveled upward along the main arch struc— ture rather than along the fault. However, the presence of several small ore bodies on the 200-foot level (pl. 17) GEOLOGY AND BASE—METAL DEPOSITS, WEST SHASTA COPPER-ZINC DISTRICT that are apparently alined along the California fault indicates either that some solutions continued up along the fault, or that solutions traveled along the arch and deposited ore against the fault where it cuts the arch. The alinement of the zinc-rich ore bodies (473, 313, Graton, Yolo, and possibly the Copper Crest) along the 313 fault and its probable extension, the Yolo, is conspicuous and suggests that the introduction of zinc into the ore was primarly along the 313 fault. This fault may have reopened slightly after the main period of copper deposition. The conjunction of the major ore controls is not mere coincidence. Lenses of pyroclastic material initiated local folding because, in contrast to massive flows, they form a less competent layer and because a change in dip, along the boundaries of a lens in this instance, is a fav- ored locus for the start of a fold. Movements along the bedding plane were most pronounced in folded areas, and fracture cleavage formed mainly in the axial re- gions of folds. The relationship, if any, between the location of feeder fissures and the other ore controls is not known. SHASTA KING MINE The Shasta King mine is in the central part of the West Shasta copper-zinc district near the bottom of a narrow canyon of Squaw Creek in sec. 12, T. 33 N., R. 6 W., about 19 miles by road from Redding. Access to the mine by automobile was not possible, however, dur- ing 1949 because of washouts near the mine. By re- building about 11/2 miles of road it would be possible to drive from Shasta Dam to the mine. A hard—sur- faced road extends from Redding to Shasta Dam. The topography in the vicinity of the mine is rugged. In the canyon of Squaw Creek few slopes are less than 35° and Slopes of 50° are common. The flat—lying ore body of the Shasta King mine crops out about 150 feet above Squaw Creek and has been explored by adits in the canyon wall (fig. 59). The Shasta King mine was operated from 1902 to 1909 by the Trinity Copper Corp., and the ore was shipped to the Balaklala smelter at Coram, Calif. The property was idle from 1909 to 1917, when it was leased to the United States Smelting Refining and Mining Co., who operated the mine from 1918 to 1919. Opera- tions were stopped at the mine in March 1919, and a fire destroyed the mine camp, Boralma, in 1924, but most of the mine workings were open and accessible in 1949. The mine was purchased by the present (1952) owners, R. T. Walker and W. J. \Valker, in 1944. Data on the amount of copper produced from the Shasta King mine are incomplete. The production figures tabulated in table 16 were furnished by R. T. Walker and W. J. Walker. 139 SHASTA KING MINE 50 100 Feet 0 LA+L-L Approximate scale Gossan AD/T 2 D Gossan oADIT 8 FAULT FIGURE 59.—-Shasta King mine. A, View from the south. B, Diagram is sketch drawn from photograph. 140 GEOLOGY AND BASE—METAL DEPOSITS, The ore contains substantial amounts of zinc, but as it was not recovered in the smelters, no estimate of the content of the mined ore can be made. A probable copper-zinc ratio of 1 : 3 is indicated by assays furnished by Walker and Walker of stope and pillar samples taken in 1948. These assays averaged 2.5 percent copper and 7.61 percent zinc. TABLE 16.—Production and grade of ore from the Shasta King mine Grade Prtoduc- Operator (sheift Gold Silver Copper tons) (ounces (ounces (per- per ton) per ton) l cent) Trinity Copper Corp., 1908— 09 _____________________ 15, 000 (1) (I) (1) United States Smelting and Refining and Mining 00., 1918—19 ________________ 68, 889 0.034 1.01 2. 92 1 Unknown. BALAKLALA RHYO LITE The ore body of the Shasta King mine has replaced the Balaklala rhyolite; no other formations are exposed in the vicinity of the mine (pl. 18). The rocks adjoin- ing the ore are porphyritic and nonporphyritic varieties of the Balaklala rhyolite and well~bedded rhyolitic wt? and volcanic breccia. The nonporphyritic rhyolite is locally flow banded. Although the nonporphyritic rhyolite contains a few quartz and feldspar phenocrysts less than 1 millimeter in diameter, it is mainly nonpor- phyritic, which distinguishes it from other flows. The porphyritic units of the Balaklala rhyolite of the Shasta King mine are subdivided into two principal rock types: (1) medium-phenocryst rhyolite containing quartz phenocrysts 1 to 4 millimeters in diameter; (2) [om—rm I . . a . . ’ 1“: 4L2 i ‘ . ' . ’ . ’ . ‘i Porp’hyritic rhyolite T a ,7 Thin-bedded shaly » " ” rhyolitic tuff ’ Thick~bedded rhyolitic tuff ". and fine volcanic breccia 8'— l Porphyritic rhyolite, _ Flhyolitic tuff WEST SHASTA COPPER-ZINC DISTRICT coarse-phenocryst rhyolite containing phenocrysts more than 4 millimeters in diameter. The first type comprises several individual flows, including flow-banded porphy- ritic rhyolite, rhyolite with abundant small feldspar phenocrysts, and a dark-purple porphyritic rhyolite; it was not possible to map these varieties separately be- cause the underground exposures were inadequate. The second type, the po‘rphyritic rhyolite containing large quartz phenocrysts, appears to have intruded the rhyo- litic flows in the mine area. A bed of tuff and volcanic breccia that lies immedi- ately above the gossan at the surface is also found in the back of the stopes in the southwestern part of the mine. The bed is composed of shaly rhyolitic tufl' that is inter- layered with fine and coarse volcanic breccia. The tufi' is variable in texture along the strike of the bed where it is exposed at the surface. The southwestern part is composed principally of layered tufi ; the central part contains mixed shaly tuff and volcanic breccia ; and the northeastern part consists almost entirely of coarse vol- canic breccia that is underlain by a thin layer of tufl. Columnar sections of the bed at the surface are shown in figure 60. ORE BODY The Shasta King ore body is a lenticular body of mas- sive sulfide that contains, in addition to pyrite, copper and zinc minerals and small amounts of gold and silver. The ore body crops out along the steep north slope of the canyon of Squaw Creek and has been partly removed by erosion. The remnant of the ore body has the shape of an elongated shallow basin that trends northeast- ward. The outcrop of the ore body has a length of 590 feet and a maximum thickness of 42 feet. Underground work has shown its width to be at least 500 feet. Gossan Note: See plate 18 for location locall tuffaceous . y of sections 6~12 in. porphyritic rhyolite fragments lrl coarse volcanic breccva With minor tuff \ ’\ 3S: l * e ' . ‘ \ Thin-bedded shaly rhyolitic tuff AT SECTION A-A’ FIGURE 60.~Columnar sections of tufi and volcanic breccia above the gossan, Shasta King mine. lnterlayeted thin-bedded tuff and volcanic breccia AT SECTION B—B’ Fairly well bedded volcanic breccia Thin-bedded shaly rhyolitic tuff Gossan AT SECTION C-C’ See plate 18 for location of sections. SHASTA KING MINE crops out on the opposite side of the canyon southwest of the mapped area, which suggests that the ore body was much larger before erosion. The ore is thickest where it is exposed at the present erosion surface. In places it thins to a few feet toward the northwest, but exploration has not delimited the northern boundary. The ore body is explored by adits, and most of the mine workings were open and accessible in 1949. The location and geology of the underground workings are shown on plate 19. The Shasta King ore body is continuous through the mine (pl. 19). The ore is uniform and structureless in appearance, and is composed principally of massive pyrite and lesser amounts of chalcopyrite and sphaler- ite. The pyrite is anhedral and commonly fine grained, the gains average 1 millimeter in diameter. Mega- scopic chalcopyrite and sphalerite in small irregular masses can be seen in the massive sulfide ore, but no megascopic veinlets of chalcopyrite or sphalerite were found. The ore contains very little gangue except near the margins of the ore body. A few nodules of porphy— ritic rhyolite containing 2—millimeter quartz pheno- crysts, which are unreplaced remnants of the host rock, occur in the central part of the massive sulfide ore. Such nodules are common at the upper contact of the ore body at several places in the mine. The nodules 141 range in diameter from less than an inch to several feet. Some are rounded and have sharp contacts with sulfide ore; others are irregular and the boundaries are grada- tional from barren rock, through pyritized rock, to massive sulfide. The contact between massive sulfide ore and the wall rock is sharp at some places and gradational at others. Where the contacts are sharp, the massive sulfide ore ends abruptly against an unmineralized white clay and sericite schist that constitutes a strong gouge. This type of contact is exposed in the backs of some of the stopes on the 830-foot level, where the ore ends against fault 1, and on the 910-foot level along faults 10 and 11. The gouge and sericite schist are a foot thick in only a few places; they contain no crushed sulfides, and the porphyritic rhyolite outside the gouge zone is unsheared at most localities. Other contacts between ore and wall rock show a gradation from massive sulfide to unmin- eralized rock, and bodies of partly replaced porphyritic rhyolite remain in the ore. Soft, sandy— or sugary—look- ing sulfides occur near some edges of the ore body. At these places the ore ranges from 30 to 90 percent pyrite in schistose sericitic rock, and minable ore is determined by assays. Relict quartz phenocrysts that average about 2 millimeters in diameter remain in the partly replaced rock. Back of stope : Sheared porphyritic rhyolite Replacement of volcanic breCCIa by sulfide ore Massive sulfide ore Base of ore not exposed Sill of stope UPPER ORE CONTACT IN THE STOPE ON THE 870 LEVEL A 10 . 0 30 Feet L.— Unsheared porphyritic rhyolite Gossa n Rhyollte. Adit, 20 ft long -‘ 900 LEVEL SECTION LOOKING NORTHEAST ALONG FAULT 12 FIGURE (il.—-Details of sulfide contacts, Shasta King mine. A, Upper ore contact in the stope on the 870-foot level near cross section F—F’ ; B. section looking northeast along fault 12. 142 GEOLOGY AND BASE—METAL DEPOSITS, The rock near the ore contact is in many places hydro- thermally altered and schistose. Consequently it is diffi— cult to differentiate the porphyritic and nonporphyritic types Of rhyolite, but the porphyritic types can in places be distinguished by the relict quartz phenocrysts. They are present in the less altered facies of the rock above the ore, in nodules of waste, and at a few localities below the ore. Information on the types of rock surrounding the ore body is obtainable only from a few drifts and a few exposures in stopes at the edges Of the ore body, or from pieces Of rock that have fallen from the backs Of stopes. The base of the ore is not exposed in most of the stopes. Although the ore is generally underlain by nonporphyritic rhyolite, it is underlain in a few places by porphyritic rhyolite that was not completely replaced by the ore tO the nonporphyritic rhyolite con— tact. The ore at the west end of adit 6 is underlain by chloritic rock. This rock is a chloritized facies of the nonporphyritic rhyolite. It is not a mafic flow inter— ]ayered with the Balaklala rhyolite because it contains a few l—millimeter quartz phenocrysts and resembles chloritized rhyolite found at a few other places in the district. The principal ore minerals are pyrite, chalcopyrite, sphalerite, and small amounts of galena, and tetrahed- rite. Small amounts of gold and silver were recovered from the ore, although nO free gold was seen. Silver is present in ore without tetrahedrite. Sulfide minerals constitute 85—90 percent of the ore body. The gangue consists Of unreplaced nodules Of porphyritic rhyolite, unreplaced quartz phenocrysts, sericite, and introduced quartz. Quartz and sericite are present throughout the ore body, whereas the nodules of porphyritic rhyolite are concentrated near the borders. FAULTS Faults, which are both premineral and postmineral in age, are conspicuous in surface and underground ex- posures. Only the most important faults have been given numbers on the geologic maps and sections, but many other faults undoubtedly exist outside the ex— plored area. The premineral faults are nos. 3, 5, and 12 (pl. 19). The evidence for a premineral age is the presence Of pyrite, and pyrite casts filled with iron oxide, along the faults away from the ore bodies, and hydrothermal clay minerals along the faults. Pyrite occurs as much as 75 feet vertically above the gossan 0n the fault 3. In addition, a small fault in adit 6 (870-f00t level) 2,340 feet east on the coordinate system, contains small lenses of massive sulfide ore that apparently formed in place along the fault. Hydrothermal alteration was Observed along fault 6; this fault may be premineral in age but WEST SHASTA COPPER-ZINC DISTRICT may have moved again after mineralization. Faults 3 and 5 also moved both before and after the sulfides were deposited. All the faults except 12 have some postmineral move- ment. The direction of displacement on fault I was determined from the position of mafic flows that crop out to the west (pl. 18). Geologic evidence outside Of the mine area indicates that these mafic flows are lower in the stratigraphic sequence than the rocks exposed to the east. The vertical Offset on the fault is several hun- dred feet or more. The direction Of offset on fault 8 is not known with certainty, but the northeast side is probably upthrown relative to the southwest. The di- rection and amount Of postmineral dip-slip movement on faults 2, 5, 6, and 7 are shown by the offset of the gossan at the surface. Faults 2, 5, and 7 must have moved horizontally as well as vertically, as the Offset of the gossan at the surface, where the dip is steeper, is greater than the Offset of the ore underground, where the dips are at low angles. In addition, the thickness of the gossan is not the same on opposite sides Of these faults at the surface. The ore body thins toward the northwest, and horizontal movement along northwest- ward—trending faults would result in differences in thickness of the ore on opposite sides of the faults. ORE CONTROLS The Shasta King ore body formed by the partial to complete replacement, of a thin flow of porphyritic rhy- olite that lies between a bed of pyroclastic rock above and a flow of nonporphyritic rhyolite below. The ore body is conformable with the contacts Of the flow, but it does not everywhere completely replace the flow of porphyritic rhyolite. The porphyritic rhyolite that is the host rock of the ore body contains 2- to 3—millimeter quartz phenocrysts that are distributed through a very fine grained siliceous groundmass. Smaller feldspar phenocrysts are present but are not prominent. The unreplaced remnants of the porphyritic rhyolite in the ore are generally massive and unsheared. Many frag— ments of the porphyritic rhyolite remain as unreplaced or partly replaced remnants in the massive sulfide ore, and all gradations are present between unreplaced por- phyritic rhyolite and massive sulfide ore. Although assays are not available, visual inspection shows that the only sulfide in the transition zones between ore and waste is pyrite, and that copper and zinc minerals are limited to massive sulfide ore. The ore contacts are sharp against clay and sericite gouge at some places, but are not as sharply defined between massive sulfide ore and hydrothermally altered wall rock. I’Vhere a transition zone is present between ore and wall rock, pyrite replaces preferentially the SHASTA KING MINE schistose part of the rock. “Tithin the transition zones, anastomosing bands of foliated sericite cut the massive porphyritic rhyolite, but lenticular bodies of unsheared rock a few inches to a few feet in length remain. Dur— ing the period of ore formation pyrite appears to have completely replaced the foliated (sheared) parts of the porphyritic rhyolite before it replaced the massive nodules. The porphyritic rhyolite above the ore in the central part of the ore body is unsheared. The evidence at the Shasta King mine indicates that the scattered residual nodules of waste in the ore, and the unreplaced part of the flow of porphyritic rhyolite that contains the ore, were not replaced because they were not sheared. The isolated unreplaced remnants of rock in the main body of the massive sulfide ore differ in origin and ap— pearance from the partly replaced volcanic breccia in the back of the stopes at the northeast end of the mine in the stope on the 870-foot level (fig. 61A). Many contacts between the ore and the porphyritic rhyolite are sharp. These contacts are marked by bands of white clay gouge that range in thickness from a frac- tion of an inch to a foot. The wall rock is locally schistose behind the gouge, but there are no sulfide min— erals in the gouge or in the foliated wall rock at these localities. The fact that the sericite bands at ore con- tacts are foliated parallel to it indicates that this zone is not due to hydrothermal alteration alone. Ore solutions were apparently stopped by premineral foli- ated bands of gouge and sericite at these points. There is no evidence of postmineral movement, such as crushed or slickensided sulfides, that would be sufficient to orient the sericite parallel to the sulfide contact. A few bands of gouge, ranging from a. thin film to a foot in thickness, are found in the massive sulfide ore. The gouge is com- posed of soft, sticky clay and has a sharp contact with the massive sulfide ore. These bands in the ore appear to be unreplaced bands of premineral gouge. The ore along fault 6 on the 870-foot level (pl. 19) is in sharp contact with unn'iineralized fault gouge as much as a foot thick, except in the vicinity of adit 6. At this locality the contact is sharp but irregular and does not lie against the fault, and the massive sulfide ore has smooth, curved contacts with porphyritic rhyo- lite. There is no gouge at the contact and no evidence of movement, although a claylike alteration of the porphyry a few millimeters thick occurs at a few contacts. A bed of tuff and volcanic breccia overlies the gossan at the outcrop of the ore body, but is found in the stopes only in the southwestern and (less definitely) in the northeastern parts of the mine. lVell-bedded shaly tuff occurs in the back of the stope on the 830-foot level, and material closely resembling the volcanic breccia occurs 143 in the back of the stope on the 870—foot level. In this stope the fragments of porphyritic rhyolite in the ore at its upper contact closely resemble the volcanic breccia exposed at the surface (fig. 60). In addition, the mas- sive sulfide ore, now represented by gossan, replaced tufl' and volcanic breccia in the vicinity of cross sec— tion (#0 at the surface. The fragments of porphyritic rhyolite in the ore (fig. 61A) have been interpreted by Some observers as a. breccia formed by replacement along fractures, but the fragments are not of uniform rock type, nor do they have the same type of alteration. Some fragments are silicified, contain no sulfide min— erals, and have sharp, smooth boundaries. ()ther frag- ments are soft and are replaced by pyrite, sericite, and clay minerals. The soft fragments commonly have gradational boundaries against InaSSive sulfide ore. The fragments of porphyritic rhyolite in the ore in the lower part of the breccia are alined parallel to the ore contact. It seems probable that the breccia fragments in the ore represent unreplaced fragments in the volcanic breccia—tutt' bed and that this bed caps the ore in both the northeastern and southwestern stopes. The tuff bed can thus be expected to lie a short distance above the ore in the central part of the mine unless it pinches out between the outcrop and the stopes. The openings that served as channels for the ore- forming solutions have not been located. Faults 3, 5, and 12 are mineralized, but only near the gossan. Fault 12' contained as much as 4 feet of massive sulfide ore, which is now oxidized to gossan along the fault below the base of the main ore body (fig. 6113) , but the massive sulfide changes to slightly mineralized rock less than 50 feet below the ore body. One or all of these faults may have been feeders to the ore body, but it is equally probable, as suggested by R. T. lValker and WV. J. Walker (oral communication), that ore solutions travel- ing horizontally would tend to work out along premin- eral faults of this type, which would then simulate feeder channels in appearance. OXIDATION AND ENRICHMENT The gossan that formed from oxidation of the massive sulfide ore extends from the outcrop of the ore body into the wall of the canyon, for 30—50 feet. Steep topog- raphy and a shaly tuff cover have prevented extensive oxidation of the ore, and relict nodules of massive sul» fide ore occur in the gossan less than 10 feet from the surface. The gossan is solid and resistant to erosion. It is composed of dense to cellular limonite that contains minor septa of secondary silica forming a coarse silica sponge in the limonite. No collapsed breccia was seen in the gossan, and there is little transported limonite. 144 The rhyolite below the gossan is iron stained only along fractures. No assays are available on the gold content of the gossan. On the basis of data from other mines in the district, it can be assumed that the gossan contains about twice as much gold as the primary ore because of re— sidual enrichment of gold. The weight of the gossan is roughly half that of the massive sulfide ore, and little or no leaching of gold occurs in gossans of this type else- where in the district. Secondary copper minerals are rare, but a little chal- cocite occurs in the sulfide ore just below the gossan in adit 8. EXPLORATION POSSIBILITIES The stratigraphic zone in which the Shasta King ore body occurs has not been explored north of the mine. The ore body thins to the north, but some massive sulfide ore is found in the most northerly mine workings (pl. 19, E~E’). It seems probable that additional exploration to the north along the ore zone would disclose other ore bodies, because the district habit of the ore bodies is to occur as discontinuous bodies of minable ore in a general ore zone. The Shasta King ore zone is present in places for a mile or more north of the mine and the more favorable zone just below the base of the upper unit may also be present north of the mine (pl. 4). The Shasta King ore zone could be explored by following the ore north from the underground workings or by surface drilling. SPREAD EAGLE PROSPECT The Spread Eagle prospect is 4,500 feet southeast of the Balaklala mine in sec. 13, T. 33 N., R. 6 “7., and lies in a steepvsided amphitheater at the head of Motion Creek at an altitude of about 3,000 feet. It was not accessible by road in 1951, but during the active explo- ration of the prospect a road extended from the Balaklala Angle Station to the prospect. This road is washed out at many places, but it could be made passable with a small amount of repair. This prospect was discovered some time before 1902, as Aubury (1902, p. 82) reports: About 1,500 feet of tunnels, mainly driven by the Scottish American Syndicate, of Denver, Colorado, under bond, show considerable bodies of ore, including some of excellent grade. W. C. Onn and sons owned the prospect in 1902. By 1908, 3,000 feet of exploratory work had been done. The property was acquired in 1913 by the United States Smelting Refining and Mining Co., the present owners. Geology of the mine arena—The Spread Eagle pros- pect occurs near the gently dipping contact between the upper and middle units of the Balaklala rhyolite. The GEOLOGY AND BASE-METAL DEPOSITS, WEST SHASTA COPPER—ZINC DISTRICT upper unit in this area consists predominantly of tuif that is poorly bedded, but that locally contains coarser pyroclastic material. Quartz phenocrysts 3 to 5 milli- meters in diameter are prominent in most of this unit, and it is considered to be the “cap rock,” although very little of the unit originated as a flow. This tuff corre- lates with the tuff at the base of the coarse-phenocryst rhyolite at the Balaklala and other mines. The contact between the upper and middle units is gradational, and near the portal of the 475-foot tunnel (fig. 62) this zone consists of a volcanic breccia in which rounded knobs of rhyolite are embedded in a tuif that contains 3- to 5-millimeter quartz phenocrysts. The uppermost part of the middle unit of the Balaklala rhyolite in this area is composed of a fairly persistent bed of coarse volcanic breccia. Below this, beds of pyroclastic rocks alternate with medium-phenocryst (1 to 4 mm) rhyolite. A layer of rock of doubtful origin occurs in the mine area just below the main gossan. East of the 475-foot tunnel, where this layer is about 100 feet thick, it dips loo—20° NW'. into the ridge. It can be traced for sev- eral thousand feet northeast of the prospect, and ranges from a few feet to 100 feet in thickness. The upper part is a green, amygdaloidal, chloritic rock that resembles andesite, but the lower part is light colored and appears to be rhyolite. East and northeast of the gossan the rock is light greenish white with l—millimeter dark spots, probably chlorite, and is not amygdaloidal. Parts of the layer show sharply defined columnar jointing, and it appears to be a sill of rhyolite that is locally amygdaloidal and is in part chloritized. Although the upper and middle units of the Balaklala rhyolite are foliated, the upper unit is less foliated than the middle. The foliation strikes northeast and dips steeply. Most of the rocks in the vicinity of the Spread Eagle prospect are heavily pyritized. From the sum— mit of the ridge above the mine at 3,7 00 feet to the low- est mine workings at 2,537 feet, discontinuous, often lenticular, bands of rock a few feet thick containing as much as 30—50 percent pyrite alternate with thicker bands containing smaller amounts of pyrite. All the rock contains a few percent pyrite, and the entire area above the mine workings is heavily iron stained. Pyri- tization appears to be controlled by the steep foliation of the rocks; the most foliated rocks are the most heavily pyritized. Ore deposit—A gossan from massive sulfide 20—30 feet thick is exposed at the surface, and has been ex- plored by adits. Other than the description of the adits in this ore body, little information is available on the type or amount of mineralization that was found in this exploratory work. It is apparent from old maps and 145 .330 .3550 33am £25on Ewdfi cdoaw awn—3.83 casouwuowaa we EWEIINM. "EDGE SPREAD EAGLE PROSPECT 3mm % do mEEs. ucm BEE»: \\ . wczEEw wmuflm Etc: 9: E «5:253— Rmmm E _ _ _ _ _ . . _ 6 sun. o8 a 8m x I. Nmmw W ‘ 38cm NchamoN m _ // 7 HLHON 3081 o~ .muom / z; .mwmwfi ,fl, \ 5 5 5 = = : :1 z / /.l : . __ mo 2%: 5 “5.3.95 $2 = t \\ \\\\ xxx \\ \\ \\ \\\ 35:53 “52:93:: \\\\ { \\\ \\\ \\\ :33 Eon 29556323; BEBE \\ NH \\ 3w : W 3E3 .o 33. .0 c8: : X N. 5/,“ / 2W 4 SE; a 3?. .o .8“. 4er E //a,,‘ SE almm is. 2,8“ c on :5 v.3 xx?» :3 E38 xxx“ \AVO/ HT ZO_hi;\‘%\ \ \ 35 \s [ab 1 - T. EXPLANATION N. K K 35 N. Contact -\ l ,, , ,. _ \ "‘/ fl " \' ’. - ' '1 / I -\::"::/ . ‘ " 5“. , ‘ - ' l N , \‘ V \ , , , ,7 § Dashed where approximately located , " ’ ’:/~ ‘ \, __ . ~ ’ . . y . . a. 50/ \ . . § OOH 50/ 93‘ Unconsolidated deposits >. _________ OOH Qal, soil, talus, and slope wash; l 3:: Indefinite contact le’ landslide, Qg, sand and grave E Includes gradational contacts, inferred xi Lu contacts, and indefinite boundaries ~ I— . f 3: ‘ 30 § 0 _._LD’__L_ _ § Fault, showing dip Kw jg Dashed where approximately located; 3 Sand and gravel U, upthrown side; D, downthrown side ‘1‘ Qrb?, probably Red Blufi” but may l be in part recent depostts J .74, it? 90 . .__+._ s "’ - § oo:§go°°°o°o::g::°: 8 Vertical fault G o°g°o§g§b°3 00 80 “J E; °o€g°oo°3°o§8°°° 52 ‘ L: . Chico formation 5 ...... -------- ... 3 Sandstone, shale, minor conglomerate 5 Concealed fault a b __2_ _..7_ ' x y, « l Probable fault ( ‘. r y - «a. Ip (My, hb .— 1 Lam 1-0 h re Hornblendite Metagabbro - p p y Thrust fault T, upper plate 'I I A” . ap Strike and dip of beds Birdseye porphyry Andesite porphyry Felsic dike rocks Includes diorite porphyry ' Related to biotite-quartz diorite. and dacite porphyry includes daclite porphyry and 0,) i0 . iorite or r i P P y y 8 Strike of vertical beds Lu 0 z < E e [I . .. 0 Horizontal beds Shasta Bally batho-‘ith g Biotite-quarludiqmite B 435 :3 Strike and dip of foliation \ . . . , ; s - T :J .. - -, ., > 34 ’5 430 . T. N. Strike of vertical foliation 34 Mule l/Iountam stock N. ag, trondhjimite; _ag1, siliceous, 65 pseudoparphyritic albite gran- 72.1 ite; agz WWW/we breccia Strike and dip of foliation and plunge of lineation db 47/ , J Strike and dip of primary flow Diabase banding in granitic rocks Alined crystals or inclusions 1 37 E A. ‘ & Strike and dip of flow banding » a in rhyolite and greenstone . (n Bragdon formatlon a Mbds shale and siltstone; Mbdc, con- 9 90 glonerate, sandstone, and grit; M bd , E D} black szlweous shale e Strike of vertical flow banding in rhyolite and greenstone W .35 Strike and dip of sheeting Kennett formation so Dk , chert and black and gray shale, Al. ”’03“?! siliceous; Dkl, limestone ; Strike and dip of compositional 13kt, tufiaceous sedimentary rock 2 layering in gneiss and other ‘2': metamorphosed rocks f0 > E as Strike and dip of joints Balaklala rhyolite Dbc, porphyritic rhyolite containing quartz phenocrysts larger than 1; mm (coarse phenocryst rhyolite), characteristic of the upper unitof the Balaklala; Dbm, porphyritic rhyolite containing quartz phe- 430 nocrysts 1% mm in diameter (nedium phenocryst rhyolite), characteristic of the middle unit of the _ . _ . Balaklala; Db, nonporphyritic rhyolite, characteristic of the lower unit of the Balahlala; Dbp, vol— Strlke of vertlcal Jomts _ canic breccia—includes coarse volcanic breccia, tufi breccia, volcanic conglomerate, and flow breccia; Dbt, tufi‘ and tufi‘aceous sedimentary rock; Dbg, greenstone; Dbgp, greenstone pyroclastic rock _ 6% N Mine X ‘1‘. 2 Prospect E Z \\\ I l // Copley greenstone i; :\\\"“o; Dc, keratophyre, spilite, and meta—andesite; Dcp, Lu Dump pyroclastic rock; Dcs1 , shale, shaly tufi‘, and D sandstone; Dcs2 , greensone tufi; rhyolite tufi; k and greens-tone brecciafi‘ézg, gneiss, migmatite ‘x r m and amphibolite J Spring 122°37/3OI' 35,00” 32/30” R. 6 W. 40°45'00“ . 45/ L OOH T. 33 N. 42I 42’ 30/ 30,, . l 40/ 38// OO// .1.>.x . o -u ... u o _ u . a .0. '..I 0".. n. n. u . u -' T. 32 N. 37/ " I 40°37’30" 30" 27/30“ 25/00” 0 , R. 5 W 122 22 30// ’3‘ .1 s X t s \. 122°30’ ‘ 122°15’ 41°00’ 41°00’ : ' . _ LAMOINE ptpvp,‘ , QUADRANGLE ....... _ I . 1:.» 400142521049 . 400 _ »- ........ - . . - 7/ 35/ . . .. . -- 00” *4" - __ __ . ' '- . - . . ' ' FRENCH GULCg , _ _ -- . »- ' . . ., ' _ . QUADRANGLE/ REDDING "2:35“ ._ ‘i' . :f . ' ' I / QUADRANGLE _, 1:.- ' . ”fl 1:: ' - .. I ' 40°30/ % 40°30, 122°45’ 122015/ INDEX MAP SHOWING AREA MAPPED GEOLOGIC MAP 32/ 30“ . OF WEST SHASTA COPPER-ZINC DISTRICT, 32’ - 30/! .. SHASTA COUNTY, CALIFORNIA Geology by A, R. Kinkel, Jr., W. E. Hall, and J. P. Albers Scale 1:24,000 1 « 0 3 Miles ' Contour interval 50 feet Datum is mean sea level .-. .; - , .. ..... .0 a _ - .". '.'.‘ 35/00” 32/30” lNTERlOR—GEOLOGICAL SURVEY, WASHINGTON. D. 4003000” . M ““23“ 122°30’00“ 40030’00” 12203780” UNITED STATES DEPARTMENT OF THE INTERIOR Sea level ' Sea level Sea level A GEOLOGICAL SURVEY PREPARED IN COOPERATION WITH THE STATE OF CALIFORNIA DEPARTMENT OF NATURAL RESOURCES DIVISION OF MINES AI Sea level Sutro ore body Golinsky ore body Bend In section SHASTA LAKE SHASTA LAKE *- 1000’ Sea level IRON MOUNTAIN STOWELL MINE Bend In sectlon KEYSTONE MINE BALAKLALA MINE Bend in section (3 Bend In section SHASTA KING MINE UNCLE SAM GOLD MINE ADIT Gossa n ore body projected EXPLANATION 3/ J Massive sulfide Contact, dashed where approximately located Inferred contact Approximate fault __ _._7___ __ Probable fault Fault, showing direction of movement Qal, le, unconsolidated deposits; bp, Birdseye porphyry; qu, Shasta Bally batholith; ag, Mule Mountain stock, undifferentiated; Mbds, Mbdc, Bragdon formation; Dk, Dkt, Dkl, Kennett formation; Dbc, Dbm, Db, Dbp, Dbt, Dbg, Balaklala rhyolite; Dc, ch , Dcp, Dcsz, Copley greenstone. For full description see explanation on plate 1 SHASTA LAKE PROFESSIONAL PAPER 285 PLATE 2 I SHASTA LAKE l Geology by A. R. Kinkel, Jr., W. E. Hall, CI V4000 4000/ Sea level lNTERIOR'GEOLOGICAL SURVEY. WASHINGTONJ’J C. GEOLOGIC SECTIONS OF THE WEST SHASTA COPPER-ZINC DISTRICT, SHASTA COUNTY, CALIFORNIA Scale 1224,000 2 Miles Datum is mean sea level and J. P. Albers, 195] UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY “L I \ 3438 2/\<\ 2/ I 45 a D x \N; ' MA MULE M'l \\ 55 25 \,.. .3057 G 25 0 (Oak olwm 70 ll , :A (55 5 50 ‘ r 4; BouI‘w 32I9 3730” $4365 .5645 A 4622 3602 \ PREPARED IN COOPERATION WITH THE STATE OF CALIFORNIA DEPARTMENT OF NATURAL RESOURCES DIVISION OF MINES If " mo 117’ TI? ’ / M 32 / BEHEMOTOSH MTN 49m Shuemnkur of a”, AM MOTH BUTTE Spring \_:\70* \ - SHASI'A NA'i‘IIETM‘L FOREST I <9 .1526 PROFESSIONAL PAPER 285 II 7W o Cree/r D Efii‘E/‘g‘ru -—< 34 warez“ Gumh PLATE 3 Soh 2818 60 55 II 14m ,4» r 7 NaaHinos A ‘,9.w~4~ 5 /65/ \\60 so 1245 / /\\LI: f j/(L/w ’xi“ ’3 43/ \r is Mi 1 g? J39- X.\ " '1?“ 1 I .\ bi/x‘zfi/ \r‘ ~]~_ 1,151] " ”UL \ / lVil/ I \(/\;“(\i ,Ll\/’l‘\/\‘/\ V}; 1&1le {Nay/‘agx, . 1w l-Vb/i‘rz + + + + _ \fi + I + + + + + + + + $0 + 4! + ‘+ + + + + 39+ + (j + + I + + + + “ + + ‘7‘ + + + do + + + +w+ + + + + + + + + + + + + + + + + + + + + + + +66%” + +‘ + // + + +3 + + + . ATlo ‘ QUART: "HILL x.\ \ EXPLANATION ' \\ \l‘ /.\'/\ R m /\ Mule Mountain stock Albite granite + + + + + + + + + Shasta Bally batholith Biatite-quartz diorite Kennett and Bragdon formations Undifferentiated MISSISSIPPIAN AND DEVONIAN ‘3 T E 2 L20 ‘5 _ I Dig Copley greenstone and Balaklala rhyolite J E > Undifferentiated Q g :60 90 Trend of planar structures, showing dip Includes primary and secondary foliatian, sheeting, flow banding, and metamor- phic differentiation banding Contact T Boundary of Mule Mountain stock southeast of the mapped quadrangles is from an unpublished map by V. F. Hollister. Dotted Contact has not been mapped SHASTA COUNTY, CALIFORNIA Scale 1148000 I 1 l MAP SHOWING TREND OF PLANAR STRUCTURES IN THE WEST SHASTA COPPER-ZINC DISTRICT, 3 Miles J PREPARED IN COOPERATION WITH THE STATE OF CALIFORNIA UNITED STATES DEPARTMENT OF THE INTERIOR DEPARTMENT OF NATURAL RESOURCES PROFESSIONAL PAPER 285 PLATE 4 GEOLOGICAL SURVEY DIVISION OF’MINES I 5 II I 0,?“ , M IkiNQ «:___ ~ .i'iigz"§&\" 9“ II ‘ I V\ /L H .215 \\ XV ’3 Tm“ , I, I W“ IfRV/R\‘w%s\\ ‘ § 1 ' «\ #1 °3~ l I‘ “ . - k2“ , x \‘i v V 1‘ c “Kg \ ‘ 5 " \ r 1 > I. o . v ,. I .I ~ . ~ I “v e I§\ ’4 I 29/2,. \ - ‘gq ratifi§ I \ .l/ 6 . , Its/NNXR “t ‘ was «I II “'7', Vw l, ‘ I v~ t. \ t v I \\ ,- 1m ~t\‘\~:e' sex .-« W“ ’K \‘o v Q _ h t, - ,. W. ées‘t‘g‘W} “ - 3R~e¥§kx\i“ 1769 9' ., c < ’~ ‘3‘ ‘ \-, x. \ , . wees») wt an . r>/I«\I I , ‘5 m ii ‘3?" mam“ 7! -’ ‘\\» ‘ ' ‘ " <\- /J ’ n, i‘figvfin‘.‘gfil\\fle ‘” . W @K ‘I < » I\ “ baggK‘ ‘\§‘Wt\7’ )\ \\’§ “N 1/ H3 \ I ~-—«: aw a ‘ I'» r \ 3:“: ‘ I 5.35% Q‘J‘i: figs: r£$2§§§fvéi§>gfik , f _ lug.“ .- a. '2-\ “M. x I . ,b , \ , ~ . as, . , It. _‘\\H§;I$J§~‘Ié\§%§ml. A (q 4’, an:- 4 as f \r t f" Af¢%}%! Mia/{122 If]: {'17 WW§¢ #0 v 0' ‘ 2-2" w I?“ :9? I I V \‘I'ii‘k’égga. ‘9 ‘l 'J satin “it — Ivan ‘l 9; *— r . Q’o ’» 34» Rat??? . I M” x A} WW”! ‘Q‘fi’li — V 5’ Mai”): 0‘ ‘ \ , . «f v ./\,_v ( "r”;\ we h ‘mi “3 \\ _ x V ' .2 o J ~‘ s,“ k: . t. I "W V... I l \‘ s2“ W \"\“ gs“:- 3 $\, ., \stt \ sewn“; , 3. 32‘s “ANN 94% \ I x A \ x i ”3%“ \ x 45' OO” a. 50"? ‘\:,?“\\ ’NQ'O- ‘ \ h. \\S®§\'\§\\§‘§n‘ ' p 222 a s i ' 0? MMIZQQ'IIIfis we». I . ”NW! \\ ' * Wits v @N‘Nli we. NM” I 22"37’30" 40"45’00” I ~‘\ \ Q <fl\\\\,\,a¢ w,» \ 2% , wees sew \M ‘s: mime»; J - WM: ”NI“ » Nose . am _ ‘0‘ ,. "9476" sass “\‘% 2% :67 ” It .4 T. “(LN-:43. a «2:92.. A , ‘ {K “SEN km.» “s ’ :. a, ‘2' ”I :II XI)" ITZ'EP’BU' EXPLANATION Areas that are most favorable for prospecting for bodies of massive sulfide, as they contain all or most of the upper part of the middle unit of the Balaklala rhyolite and are mineralized and hydrothermally altered Permissive areas along the ore zone in which bodies of massive sulfide may exist. These are areas in which most of the middle unit of the Balaklala rhyolite is present u A‘A A“ A Gossan and heavily pyritized rock Pyritized rock Rock with only minor scattered pyrite is not included Hydrothermally altered rocki Argillic alteration, silicification, and pink hematitic alteration o '5 Outline of known ore bodies, projected to surface Contact Fault, dashed where approximately located; dotted where concealed —__7—____?_ Probable fault 2a Mine X Prospect 0 Diamonddrill hole Some holes close to ore bodies not shown ‘ ,\ / / ' ‘JI ' L( 4/35/26?» \‘ \, ./ f/ ’ 1% ‘J NEWS/’9'» 5) ("L )1 //,-I NV: 4,; J / (1 IN I /w 9qu ¢ / K H I / // \\‘\_,”T' \ , 'Ioaa MAP SHOWING LOCATION OF MINES, PRINCIPAL PROSPECTS, AND AREAS FAVORABLE FOR PROSPECTING IN THE WEST SHASTA COPPER-ZINC DISTRICT, SHASTA COUNTY, CALIFORNIA Scale 1:48.000 1 O 3 Miles I I l I l I _ 1 I Contour interval 50 feet Datum is mean sea [eve] II K I IIN ‘4“\ WW“ mrzmonrczoLochL sunvzv wasnmavou D c M F7230: r , . , w ‘ _ \ mg 006 ° 00‘ (wood "1) 9s— 0 SZLéLi ' VINHOdl—IVD ‘AiNnOD VLSVHS ‘SHIGOE 380 GNV Si'and ‘IVdDNIHd SNIMOHS ‘SENIW HNOLSAHM CINV V'IV'IMVWVE HHL :JO SDNIMHOM GNHOHSHEGND d0 uolssluuad ,saaww um pausuqnd 'uolunado .sauuu an; o pouad an; sump papdmoo mp punmmapun uusgxa p mum: aux Kq unnumdlwu! UP 5: am .auum and“ HI pwmdxa ‘XDINJ H 0H 310 WWW]; \ / '1 , \ ‘ ,/ \ \ 3mm V‘IV’IXV‘IVE ' \ ,,// \ \ J, m .\ <_" m 4222; 0°“6 % % /@”9 9 and no «menus in sumpas LamN \ 4, ‘ J} x r, \ ’ \ / soda}; ,0 suouzmo mo“ JD sup! ‘0 \ \/,/ sue-male ”Is an uMDus summon \ sup: u: apmns // \ d \\ amos puE urssog) p tum ‘ ‘ x / \ sum/m4 ssuww pauuau‘ \ . H -7“ . , V _ , , °° ' - \ / \ ~-—- »7 \ , - . _» . . ~ ' ‘ 0961 ‘1‘ K _ , \ uv a|qgssaoauul sum up. \ fi uamg amw mam ‘sSuwaM ‘ w Oulm ”y 'sfiuwoM [Mao \ Molaq :uauM panop 'sluwoM , / ,,fi__w._/_,A~A \ /' sluwom mm Mops} 61mm pauup 'saams S ENE 53: uadva wuoussamud sauvw gn uolswq sanmosaa mmEN p wamuedaq Ewmmra p0 ams am mm ummadao: u! panama ,zasz / // \ / / \ / fl ‘ \ / // \\ alum 1a am My an /,/ \\ \ , \ Z / \ 1 [/6/7 \ // \ W m m. .0 .00, / " / \\ 0822 {dz/16????) . ' / x\ s: I, ’ \ /V/(7% ‘ // ‘\\ lnzuado ,/ \\ //,% _\ N ”Mm“, / /«’ \ J. x //fl6€V ) El Z; / />< M 5" // / \ ‘Q 5\ f\7//39 52/ ,2 V ' r // \ “PL // \ ‘9 oévz/f’ // El O; A003 380 :91 / \ \ 7* (/4 :; /Vlksé{s/;//////// / oln // \ ‘ “"2‘ 21mm ,/"/ I ’ NEW! ’/ / //",/ 11 N / \ \\ 1 *— ,/' J/ / / ///////"2“ \ > \ // \ uMmuldn ‘n 1mm. Ameuuxomdv \ \\ //¢////// /: E V V , / / \ hiuM pausepidlonfluwaus‘uned / ’ / ‘> * I ‘ — 4 /\////////%I \ g f ' i/ 9392 _ \ ’05 n \ ‘ //é//L//€E?//////% \ I? .' /9;®@ U k \\ NO(J.VNV"IdX3 m /3dOLS II M \ A5996” , v \ _ 92; , Jl ‘ , \ (530“ V» I A y); salaoél 3&0 - ~ ‘ A wmzmm dwvo AGNIM padms qumd m «, v'\ » ,V ’ ,8 .0252 . ~ A008 380 ‘I‘Iflfl 103;; )2 {my 'I A. \ I .g \\ // / a I’ "a Np \ / , ,, \ / \ / / 7 /¢\ loavzé. ‘ \ . \\ ///7 Miggefs fife 7] K .BWIHS on W: / /// I3 HLEON s /% f \ ezaztgjms? / / . fl / my} s’uav \ / / \// //éf ~wa k (/ ,oezz , 1/ y .n / / //j~ a may / 9L“ /( 13,61 00 __,_#_W //, . . , v ’ 7W x, , , 1/ , / // / 4/, ' /' 1 L; '9 , / /' / men was; < l ( , \\ r, H K 95/ \ K \x; 5 [rare 4/ 7 2 . v I . ’ a I,/// \ ‘ ~ . ’ ' / \ , . 1/ \ / ‘ / : ' W s ,/ , ‘ , > _ / / ’ ' ‘ . ' > - / \ L w ‘ - » / m 0 00 ; , , ‘ _ ’ / , (50' \ “00° 0;; V ' 9/ / J AZAMnS ~IVCJIENJ'IOEE) HOIHHlNI 3H1 JO 1N3W18V430 531113 03mm UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY Prepared in cooperatior with the State ofCaIiforna Department of Natural resources Division of Mines PROFESSIONAL PAPER 285 PLATE 6 3500’- 3400’- 3300’— 3200’— 3100’— 3000'— 2900’- KEYSTONE MINE 2800" \ /\ / ’f I I 2700’“ , w \/ {A /\l 7 \— ”2700 f / \ /\ , / \ ‘\/\\/l \/\ 1 \T/ \ / 2600’~ : / \/7/\’ L\;>‘—26001 2500., :f - jggzsoo’ 24oo'~ I, " Wm‘m” ~24oo' 2300’“ ~2300’ ,_ ~2200' 2200 BALAKLALA MINE 2100’— *2100' 2000’ 2000’ EXPLANATION I \ /»" I/ \ ,7 '/' \ / \ g 53, : ’ / 1 \ I /' \ . £ E Upper unit consisting of coarse , 2900’s I .E‘ phenocryst rhyolite (“cap rock") ' I“ E 2800’— % E Middle unit consisting of undiffer- 2700’ \’\/ ~~~~~ m I entiated medium-phenocryst _ ' """" rhyolite, nonporphyritic rhyolite, WNW/,9 M2,. . l and rhyolitic pyroclastic rock » ~ 777' ”- 2600’— V,»»;l)221't(/77Z‘///@ A?!” \? \ / Tanya/WWKMIM/a WWI/”W ' 2500,_ ’0” Massive sulfide that contained a enough copper to constitute \\\\\ ore at the time of operation 24oo'— . ' ‘ *2////// " - “(Mar/.1. 7.2"5? 230m BALAKLALA MINE “”2”?" 2300 Massive sulfide below mina'ble \ I::Zcr::::::::::::::::::::::::::::::::::::::’ grade at the time Of operation 2200’“ 2200’ ___A___‘_‘_##~m Indefinite contact ZIOO’A 2100' __7~____ _?_ _ __ _7_ Probable contact 2000’ 2000’ _ — —. Note: See plate 5 for location of sections 300 0 - L l 1 I | l Datum is mean sea [eve] 900 Feet l Indefinite fault or shear zone ?— _7— Probable, fault or shear zone (3:2:QZZZZD‘: Stopes and development workings, dashed where projected Outline of massive sulfides; in part projected; in part from drill holes Probable outline of massive sulfide These sections are interpretations by the authors of existing underground data compiled during the period of the mines' operations GEOLOGIC SECTIONS THROUGH THE KEYSTONE AND BALAKLALA MINES, SHASTA COUNTY, CALIFORNIA 379725 0 ~56 (In pocket) UNITED STATES DEPARTMENT OF THE lNTERlOR GEOLOGICAL SURVEY Prepared in cooperation with the State of California Department of Natural Resources Division of Mines PROFESSIONAL PAPER 285 PLATE 7 ‘ EXPLANATION W Massive sulfide \ Gossan I, a 4 V N , V ' 4 , a 4 D ti o .1 “ LLLAL Breccia 52 flLLL L ,, A _ ALL Contact, showrng dip, dashed where approximately located: queried where probable 55 Probable fault, showing dip / J / / / Foot of raise or winze / Head of raise or winze Inclined workings,_ ‘ chevrons pomt dowri i i J Tunnel 1 - l _ ‘ saga. » - :'.':I:,:Ii:} 55 level l! Raise at l surface I / T 'QI'IJe'I“ I / / ‘ Pit ' E if / / ‘\ Ud d k' {he h ‘ I \ n ergroun wor ings, as e y; ere { 5 23‘ / I \ \\_./2070 ‘X protected (sections and level maps) , E e l l . 4 . _. I g I; I“ } \ \\, //////ll\\\\\ & \\> '— 53 I . \\?050\L“\7 u_»_ ///////m\\\\ 3 ll \ Dump \ \ \\“ \rzaaow '*~~\\ ' ’ \ . i \\ vi ‘\ \ o, \ \\ ‘\ 0‘ ' ’ , \ ,flfiw \«e 7% \ ‘‘‘‘‘ 50 0 150 F r o I ,7 * IL I l i i ee ,l \ i ,,,,, L//' \ I Contour interval 20 feet ,’ \i—r’ \ ‘\ ‘ ,'_ Datum 15 mean Sea level y/ ‘ M~—\{ § A: g m g — E) z / 8 V I) C Q) A m % 8' E I q) CI 2000, . g 2000' 4‘ a: E g L , , 1950’ 1950/ t TUNNEL 11:] g 4, l ‘ m (7/2 LEVEL J AZE] 7o LEVEL 1 I , ‘ Breccia contains VI ’_ ’ ,_ . 1900’ 1900 T 4‘ some sulfides/\j[%23D-—Ifi LESVSEL ! 4 ‘r ’ l L D31 LEVEL l i l‘ “ I l l ' : ‘ 1850’ 18505 b ' L [I TUNNEL 2 ‘ TUNNEL 2 III L} J— l~ 55 LEVEL 70 LEVEL TUNNEL 1 LEVEL A A A B \ B Gossanh C\ \ \ C Raise to surface \ / \ \ \ \ \ Gossan \ \ // \ ,/ \ Ore has sharp, 70level basin~shaped bottom\ - / / Massive sulfide \ grades into waste \ \ . BI Winzeto \ ' tunnel2 C’ Cr Compiled by A. R. Kinkel, Jr. from mapsfurnlshed by US. Bureau MAPS AND SECTIONS OF THE GOLINSKY MINE. SHASTA COUNTY, CALIFORNIA “‘Rec‘am‘w" 379725 0 -56 (In pocket) UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY Prepared In cooperation with the State of California Department of Natural Resources Division of Mines PROFESSIONAL PAPER 285 PLATE 8 Ff , 6000 90°“ 4 v // / \ // / \\ / / / \ / ,r \ / / \\ / .’// \ / ’ \\ \L ,r \ / \\ ,/ [,x \ \ / 570% / L_ 4’ \ L / \ '. \\ \ L \ / / , . , \\ / \ \\ . . ‘ // / / \_ » / / \\ // ‘ / _ / . q . / \ * / 4 “ \ / \\ _\ /' Outline of Brick Flat 2% .4 ./ '« J/P “ - ’ \L \ ,/ ore body. Not stoned. / ‘ M v *\ \‘\ Outlinedlby drilling / / ‘ Ny/ .»- ' ' . . ' . \ _ ‘ 2844 -- V 'v V. ' , .fl . Richmond-Complex ore body, / \L R 2770, n . o . - ‘ ', . outline of workings / \\ / Lifeggnce line . 3 \ L. . L\ > r + fa r+ + amid ' , 3H, / ' + e + <0 < x274” . l 3 l g m Albite granite a o: _, L) F « EXTRUSIVE INTRUSIVE / / Porphyritic rhyolite with quartz / phenocrysts more than 4 mm / i :“\"\\‘§“‘~‘X“‘§\‘»‘. :‘\‘\"‘§\‘& VINE \ ~ \\ / ‘ : ~\\ }\\ ‘ x, p \ ‘ ‘ flibxnt“ g ,7 || %I1:\\:; / Nekm§k° t\\‘\‘€\{§§x§»}: “‘ 'I/ s” s go ::T,\F7,"\\ , Porphyritic rhyolite with quartz \\’ \ {Elf ' phenocrysts 2 to 4 mm ’ <9 9 000 33 2:3 Ignaz <, Von/«rm .« ~ ~ , , , —, , \ a ”117VDDX1157i iris/om 11X: 3 i fihfllfli’x’i/{F "Eff/‘21:“ E < . 7: Porphyritic rhyolite With quartz g E phenocrysts 0 to 2 mm 3 g . C! CD /\/\\/=//\\4‘” / = 3:” ’Dbx \j I :1 ’:// ” ~/ I _, - / 7Q: // i ” 5111:» Z Z”: /7\\///I//=\\\: Nonporphyritic rhyolite » . ‘_ .. 1‘3: V\\§\~ \\\\\ . : . » .‘ 3. . «\t .- ~ -,V . ~ ‘ i’fl‘...,‘p \\ \ x , ' .\ A . ‘ - . w , . _ _ = . ' . 3$.\\\“(§\\“~\\ . V , , - \ ‘ \‘\\‘ ' ‘ - ‘ - . \ A , . v "' s \\ . ‘ Volcanic brecc1a and tufi" sec» ‘ s , i - _ ._ . ., . , )\\‘_ < 7 A < V om; ‘ , 4 Dbm 4 2 L < 4 V < (“‘4‘ .‘~\‘\\\\ ‘ Mafic flows J ’ gig/,4“ a: \ \ . k A “‘ ii’ \\ H / ‘ E z Rf :L,,’IV"<‘__ g e erence "”6 Copley greenstone J g 0 \ Magnetite-hematite rock \ *w‘x‘tV \\ ‘3: N‘s \\ {c&§§\\. \ , \ ‘ ., . I . ’ t l 1 ‘ \s «s \\ . ' \¢ \ " ‘ ‘ ~ . ‘3 A .. . “ ,\ k~ - \\// »’ , - \\‘§ ' , ' A ‘ ' " ‘ , ‘ \\\ \\ , ,‘-\\“~~ ‘ Mm. ‘ \\»\ _\\ \ . V q gas. \7 , _ ,_ > § .\‘ Gossan from masswe sulfide ore \. \\ \¢ \\ . \ \\\\\\ ~ \ ~ 1’ / . § \ \ / /,\ \\\-\‘~\ \ . \ ‘ \‘> .\ ~ “$8 \‘ \ ‘ l _/, , ~ \\ \=II///_ s. \\&\ p/ ‘ ’ . , ‘ , ‘ 2&s\« ‘ ~' *\ \ \\ >\‘ ‘ H ‘ ‘7 “V0 17 //// / ~ \~ ~ I \ ‘ r i ‘ s \ . ‘ . , - '. 'i I \ \\§§; \ 1 (I , ‘ p, .‘ . ‘ \§ 8 \- _ \l ,4/ , x > ,\, I... i . A V 4/ , . ‘ \os \éll/Ilixflfliu/ \ \ “ ‘ v ‘ x ‘ , ‘y ", , ‘ » \a‘/\‘ IS: "m ‘ "I \ I ‘ ' II”! \'/ '7“ ' ' [I] ' ,, \ A ‘ ~ ‘ 4“, VHS/IX \ N l . /‘e A/ . v a , ~ ~ _ /« 7 . . ':\\,‘ ”I” , 1' / V § u \\/§ , » ‘ ‘ Gossan from dlssemmated sulfides \§\§ I, I 7“)\/l\\”“‘ ’ \ \ ‘ V a ‘ \:‘\\:\ - Rock that contains 10 to 75 percent sulfides \\ “e t ”I \ Massive sulfide ore Sections only E Disseminated chalcopyrite ore 2,: Sections only “I,“ ‘ - ' /I\ \ _. . .,\\ s . l , , . . . \\\\\\iiliilll"'f/// ‘ ' - , - - »- ~ . q - , , \\\\\\\\li\lilliiiIHI// A . . y - 4 s . ,3 - 3 . , . - a . - t v v 4 . - / \ s\\\\\\\mmuu - . . . -. . , _ , , . » 4- . _ -v 3 - - . , 3_4_#_46 §§ \\\\\\\\\mw// . I . - . '. _ - l V ’ ' - ' ‘ ‘ ' a -' l ’ / Contact, showing dip ear: Q§W -. . . - . -- . . l ~ ‘ . / \ Contact \ Approximately located on map \ and section. Also where pro- \ jected to plane of section \\ Contact, indefinite or inferred 85 ._ ._ .l_ .9. .._7_ U . Fault, showing dip Approximately located; queried where probable; U, upthrown “\ (“v side; D, downthrown side _\\. o. « \\‘§:‘~§§\\: \\\ \Q‘VV“ so a ——+——— Vertical fault ._ _ _ ... _ _ Fault, showing relative movement Dashed where approximately located 7 Arrows on sections only 000 4/ A Anticline, approximately located i— Dbx2 \ Syncline, approximately located : KN». "‘\ I/ 39? 42 \\ R\$\ \ ’~>\” ‘4' \x\ \‘»‘:\'. . _ fue‘ag ,; 3 Deg K’fgj \Q\§\\\ Db Strike and dip of beds - l u~‘~‘\~ \ x 3000/— :3 A” ':\2\:’(\‘\\\ [A ’ H —3000/ =\ _ ‘ v. H \: ~- ». " ‘1\»‘ I 1 _ ”’3‘ xx» \‘\<‘ c \ \ ~ m _ A ~ - s \ * \\ \«s‘x‘xx‘x .» ‘= - _ ' . 0‘ \\\\\\\\‘ \\ \k\ , ~:- ,.\“~\ 3 A — so ‘\\\§\§§V§\\\N\{§\‘\:t§\\\ 53$ ’ \ ' , ' . . ’ $§§§29\§§\%§\ \\ =¢\\ \\§\\’> \l/ ' ‘V \ A ~ '- ’ \\\§f\\§‘§\\\\f\3\{$\\\\\‘\\ DbrwL W I ‘ ' ' ‘ 4 15 \\‘§<§\§\\\;\\\\Q<\\1 wigs/€432)? Strike and dip of foliation .- “\ ‘ ‘\\\ “3 ‘v\\§‘ e“ b . _ . - Dbx3 \E §~‘1‘\‘\\\‘\\ \\ “o \ \ ,’I \\\w _ u ‘ ' r , _ _ l , I. 4 , “ ‘__ é \\ \\\ \\\\\ § \4 ’\§=\ 4/"? / \ ‘ . - . , e\\ v w x“: T§‘r‘\\\\\\\ \\\‘\;\§\\\\\Q§\X§\\\{\\V‘\ é «‘,,\:/,,su/.. 2500 — 2500 V4“ \ ks\\\\\§\\: \ 3 » \\\\§\\\\Q;\'\\§\\\T*-\\’Il s1, = ’\\=“ \\ \ws ~2soo/ X '1‘ 4i \ \v\~\~\\\::\\\‘\{$44i \\\\\§\‘ ‘ “ \\ ‘Qh‘t‘tssQOVE \\’u \ , ’uwfa/ -' ‘ , _ _ _ . \\ Db” L A‘\\\\\\“\‘§\\§- - '-\ ‘~\ \ ‘\§\\’\\‘ \§- § ,r \”:” (J \\ = 2/- 7 Strike of vertical foliation ” \\ ' e “W“ L, “w ‘\\.\\~\\\\~ 00% ‘:\\\.‘\\\i\ \\\\»“’_\ l/\ ’/ Q \\// "25 W 1‘ _ / ‘\‘\\\\§\\\ \\ A \‘t \ ‘ es s" ,‘4 - Dbx \\ ”4, s‘f/k an \~\\\ - .\.\~ Wee/4-2,wu, ,.l _ / c \\ \ t . \\ t \\ = u ‘ = _ / = \\\> \\ ~ ‘ , \ ” 8 /-’2 — § /_/‘.< : _ Dip of foliation {3 9 § ‘ Sections only _ D: i’ _ a; ‘5; D: m 2000/ 2000/ 2000/ 2000/ . Scarp of cavmg ground .flq—n-r-rrr‘rr-n—H, . i Opencut so: ' \ s‘o » \\‘\ . ‘\\\‘ .« \\ Adlt \ \ \ A\\\ :~\ 3 \ \.‘ x 3 , \ \\ . ' \§§\§\¥\\§\ \=u\\/\\ .- :‘\\‘<‘\\ \‘§\\\ \\\\\ ‘ )+- x“. / ’/ ,, r , \-‘ x , Cave ' \‘ 3V //\\/’ \// \\ \X/{/ 7 \\‘\‘§\\\\\\\;\‘Q\>\\\\\ 4 \\ I d adlt \ 2km]? 9% ">»\\\\§k&\t.\ ‘ —3000/ “\\\\"\“s\’i“ ‘ 3 \ \ «\‘Dbx \\/. ‘25,,“ ~ ~\\ gs; \\3,\\‘\'§\ \ ‘. Dbxl "‘h a ' \V w fill/M M ‘2’ ‘\\‘ \Q‘;\\t‘\\¥§\§£§$ \ WW - .' '~ ~ . ‘ ~‘\\\ \ t ”2/5 \I 12/» _ x.\ \‘\\‘= M . ‘W ‘k ; §\\~ m¢ \' \ =///.’l« A \‘\.c‘ ._ \ \\\ Narrow-gage railroad “\\ _.\.\ \\\t\ .s\ t ’ e\\\\‘§\\\\;\\\:\\\\\\\\?$vx§\\e \\.\.\\~ \Q Q \ \ ”I/‘L’L ch §\‘\N\\ {3E\\‘.\ In part, cable car . m \sts\\\\ \\\\\\\§\\Q\\\\\\§\\\ was \‘s w - ' — “ 0“: \\\§‘\‘~\\\\\\\\\\\\\\\\\§\\\§\\\\\\\ mam <33, x W\‘\<§\~§\ ‘ 0 “3.x: - x .“ -\\~ A \\\,\\\\\ ¢\\\§{\ i_ g” \ \ t \ \ .. p. \ \ \\\\\ x“ \\ \\‘ / __ ‘\‘\\\\\\ ‘\\\\\\\\- . - ‘\\ \\ \\ \\\\ \\ \ \“U N\\:‘ ~‘\\.\-\\:t\ \\\\\ \\ \ x \ \\\ x‘ \ // §\\\\\\ it is \\ ss- _ 3 , t\\\ \§§\/\“\§§\ \V \ \ \ A‘:\\\\\\ ,_ Dump \ \bo €\\\‘\\\\~\\R‘\ \~\ \ \\~§ 22 , \\\\§§\\\~\\~ \\ 2500/ . 3w 3 x - ~\\ ‘ »t\\“ ‘ \ —2500/ 2500/ _ s \\\\ \st 8- .3 2500’ \ \ \\ \ .‘ ‘ \\ \\\\~\ ~ ' _ m _ t; 2: \\\\\\\~3 g 33 ea ions only / \\ \\\\ \‘\\§ -.-. _ ~— / D \W 8 g _ R \\“\\> 0:) —-—- — — —- ~— — -— — §Q§s % - Approximate property line 3% a: ‘K‘ _ . A l — § ch<, ._ —6-T——_______ 2000/ \ ‘ 2000i 2000/ at me of underground 2000, ore bodies 38’ Dbx — Sections A-A’ and B-B’ and shown on figure 55. . , \\\\ \ \ / \ Sections 26726’, 28728’, 30—30’, 32—32’, 34—34’, - ~ ;\:\ \ 4 3333' 33332323334033 . ~. \\\ u\ ‘x A \\ = , I, ‘ , “ ,, \\ V \ .\ V\Q‘\\\\ \‘§\\\\\\\ 9\\\\\ \\\\ i \\ bx ¢\ h 1 10 an £F56 \\\\\\\Q 0 __\ . \qm\o\\\\\\§ \ \ CE], \= \I/ I" \N\ ”3“ § // = \\ 0‘ S own on p ate § \ \\' u $\\ “‘3‘ , T \§\\/\ =\\Dbx7\\* . ex \ c s / . l \\ ‘ l‘ \\~“\\\\\\ \ \\\\ ‘ . \\\\‘ \. \\ . x . ‘ ‘ _ \\ \\ ‘\ / ‘ \\"<\\\‘ \" $3 \‘$\\ ‘ \s\\x \\ ‘ ‘ ' ' - \/\” ‘V/ ” o / . ‘ - * . . t \ ' . . ‘ _ \\\//\/.V. \‘\°\\§k\x§ \‘\\\, . > . \\\‘\\. \\§\ . , . . ‘ . /“\ _ ‘-\ N1,‘DC \Q‘ ‘ A \\ ts ,. . .,-_ .2 \‘ v: \ \ ‘ is \\ 2 5 \\ :\~\\~\\~\ t - l \ w‘n \- sch \\ // , 2 , \\\§\ 4 \ N” \\ \ § l/3/,§\\\,,= “va g \\‘\ ‘ ‘4. —2500/ in u - _ E w _ £3 .E {D ' ‘ z _ o 5 .— _ 3.2 h m m 2000’ 7000 2000, —2500’ . , l/ * Dbx // /I “1/ \ , I“ D . ll \\¢\1¢\\"//II\\”II‘II \yflibfi ‘ l . . _ tins” l¢\\// “3““g. ““4““? “s §,\\~‘,.\‘\\;//n \ \F/z * \f'I¢\\J§////”\x ‘ ~ ; >\\\ ll * \\ \\ e - N33,, i\ ~ >11? 1| 2000’ ‘ ‘ 2000/ Topographic base furnished by the Mountain Copper 00.. Ltd., with m-remon—asommcu sunv:v,wA5HxNGToN, 0.5, M «723°: Geology by A. R. Kinkel, Jr. and J. P, Aibers addmons by A. R3 Kinkei.Jr., and J. P. Aim. coordinates“ GEOLOGIC MAP AND SECTIONS OF THE IRON MOUNTAIN AREA. SHASTA COUNTY, CALIFORNIA those used by the the Mountain Copper 00., Ltd. 500 0 1000 Feet b—H |——l l——l Contour interval 50 feet Datum is mean sea level UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY PREPARED IN COOPERATION WITH THE STATE OF CALIFORNIA DEPARTMENT OF NATURAL RESOURCES PROFESSIONAL PAPER 285 PLATE 10 CAMDEN SOUTH a; .E m o c E‘.’ :1) a) n: \ Brick Flat ore body CAMDEN NORTH FAULT Reference line SECTION 26 s 26' Brick F§at ore body \\ w’ ‘ SECTION 28‘ 28’ Richmond ore body Reference line SECTION 30~30' —3000’ CAMDEN SOUTH FAULT Reference Iine Complex ore body I CAMDEN NORTH FAULT Balaklala rhyolite Reference line Reference IIne SECTION 32,732! SECTION 34*34’ SECTION 35*35' Reference line Reference line m SECTION 37~37' Richmond ore body Reference line PARTIAL SECTION 387*38' ./ g . - .r3ooor Dbx2\ Complex / _ ore body Reference IIne . ‘ EXPLANATION (EXTRUSIVE INTRI‘ISIVEN I\:\’~\7 I/ I: /:\/\ (ADM \L \/,\ Dim/7, /\\/I\/\/'\ /\/\\/ Dip of bedding <—-—> Dip of foliation Note: See plate 9 for location of sections DEVONIAN DEVONIANI?) Prepared in cooperation wrth the State of Callfornia Department of Natural Resources ATE DEPARTMENT OF THE INTERIOR , . , UNITED ST GSEOLOGICAL SURVEY , DIvrslon of Mmes . ,. . _ 7 PROFESSIONAL BAPER 285 PLATE 11 \\0 {04? (0" , 'o‘o‘o‘o‘. . O O o "3‘. . v v v v o'c’o‘e‘o’o .. v'ozo::’¢‘o:o:o:o:o‘ ’ ‘ ’ “sewev’4“3¢a¢s * 0.0.0.0x’ Q o o o .3 o 00.0 C4 9.30%? 4/ 90¢ 0671/ 4 of. o : 0&3 o 0 $5232.: ‘o‘o’o‘o'c iUVVK fifififi 0,. o o e o 0.9 o o o o 9' c .1 oooo. o. ,0... O O 4 ‘0‘. ‘9 § 0 z o <9 ,0; e Jvfi 0.0 o ‘3 ~°¢°o O O ,z}%% 009550 90%... 0 ‘fi . o o o o 9 o i? o: 94% 09 o o o O. gtg‘o; o o 9900 0.0 fifodb 09.909 dQ5 ‘p o. o §¥5 same 3223322233. CAMDE FAULT 3 ” Brick Flat ore body Rlchmond~Complex ore body __ \ , EXPLANATION ,0 o o 0.. b a Busy Bee ore body Q I p O O 13:33. ' O O 50.. l l 3300' l New Camden ore bodyk % ; Masswe sulfide ore Dissemrnated ore and veins o ‘3‘ a 9‘ .6 o ":as: "10"”. ' 3 to a§¥%%5 ,0 o 79 . v0 0 ‘fi’ 30 .000. fing gfiylb o o . :0 0.. 0‘ v r ‘\ 'o c c ‘1 o . '0 o‘ c o’ .c o 0.09 o o o ‘3 a 9 Q; 0...: Gossan 0 o 90 0.09009 0.3.. 9,: 0.0, o o o o o f o 0.0:. '9’. ,0 o 4” o u . Q .. 00 i5? Confidence-Complex ore body , , ._ mflea‘vfhefi e S 2680’ ,r -_ approximately located 0 av :2... 3 t ’020 0 $0 .0 o o o 0:. ’0 O a fi Fault. showmg relative move- ment; dashed where approx- imately located Note: Sections 15, 22, 29, 38, 44, and 58 are also shown on plate 9 / W Okosh ore body Outlines of ore bodies are at elevations shown 'v ffidbo ‘ o‘.:%:::g::z:§z‘:$:o:o o'o‘g" $.03 0.: 5%; o..:, '4?” "a; ': 2 00. o b _ , . O 0... O k h' b d ‘ T ‘ ”' ’ V n 5 ' ' V «o. o .055 96:3. 0 as are 0 y _ a a... 'g, . 1 . a, ‘. 900 ,9, . Rlchmond-Complex ore body § 0::5 : O O .‘OO O. sszaassss Q n %o‘:::% 9' “’0’ ' > " ’ V ' '-_v 0 0.0080... «mgfl , _ ' -' - ~ , , - ' , ‘ e - 3:83.»: 2 ’ ' 0 § E Disseminated org, projected to section, \ , . V I » in ' WW}; 0" ‘L V 1 _ . . 4 »_ ., , , , . . . , , , , , . _ ‘Lzooo' Comprled In part from maps furnished by , . " ' ' , , Geology by A. R. Kmkel, Jr. and J. P. Albers The Mountain >Copper Co., Ltd. C A L] FO R N lA 1000 Feel . r J 379725 0 —56 (In pocket) Datum rs mean sea level Prepared in cooperation with the State of California UNITED STATES DEPARTMENT OF THE INTERIOR Department of Natural Resources GEOLOGICAL SURVEY Division of Mines PROFESSIONAL PAPER 235 PLATE 12 15,6008 1 1 1 MAP OF 275 LEVEL. EAST ADIT, 310 LEVEL AND 315 LEVEL SILL, 31 12’ oo LEVEL , , Floor, 3088'\ \ 15,8008 \' 27s LEVEL 20 25 /. EXPLANATION A ’/ SILL. 3110’,‘ /" . / ‘ / ‘ I 1/ R’ C’ J/ :i /\ \ / /i \ 300LEVEL/Q \ ~I DQi/C” ’\ \/I l /" \" 7 \/ i \\ \’://\/\///\/\/I/\IL Floor,3088’ m \\/\,(i/\\ i/ii~/\i/\i/\I \\/\\/i\/\/\i//\/ i 7\>\’/\/ B‘ /Li:/ui,\:i:<\;294 :’ 1000N ,, AL , > / -, '--/ lOOON 18 cnosscur \% ORE BODY '. E B, GRATON P D» ORE BODY _; / ‘I , g\ . O SIER ' \ORE BODIA’ 0 >' - / 50 ' r I I. ,IT‘ISL’O .. ‘1 ./ «. . \‘\ Wig. ORE/ . W I 1/ 1-“ ' veonv/fjge fl ‘ ‘u 2,. 7. // / f . _ _ ‘ x / ‘ , 00 00 A FRIDAY LOWDE ORE BODY 47%8‘55VEL / ,B / 10008 10005 11 415 LEVEL 2922' \ 2871’ Cr 2833’ 470 LEVEL 2822’ EXPLANATION § Portal 20008 Caved portal 20008 8 Foot of raise or winze 2 Head of raise or winze 3:643: Underground workings, showing elevation, dashed where level IS proiected :¥:Tz _ / .. Inclined workings, chevrons point down W717 /\ Maxrmum outline of stones / %} X784, Note: Sections also shown on plate 15 2821’ / \4 \\ \ 870 LEVEL \ 2426’ 30008 _ 30008 N X 2450’ w;¢[ r 400 ’W 2421 1* l ‘ . i) I 1200 Feet Datum is mean sea level 3 3 “J 0 § § 8 § § Furnished by the United States Smelting N Refining and Mining Co. COMPOSITE MAP OF UNDERGROUND WORKINGS, MAMMOTH MINE, SHASTA COUNTY. CALIFORNIA 379725 0 (In pocket) PREPARED IN COOPERATION WITH THE STATE OF CALIFORNIA DEPARTMENT OF NATURAL RESOURCES PROFESSIONAL PAPER 285 PLATE 15 UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY DIVISION OF MINES 3 g 8 o 8 8 8 8 ‘ III 2 A 19§\\ , / ,to Q‘,"7\|%\m— fl ”he?“ 3: ,\»\ \/ — /\\i\/\/ ’,\ \ \/\>/’\-/\/\I\/\ \/ /,/T/\/\1 \/\; 5' g A,\ ,Ox’I7’1?,/:,<\),I\\/\>\<'>, 01‘, r, Ij’N \L‘I_)‘/_\‘I_\/\\\,’\-,‘>3\,Y§)\7\/’:’:\IL\ / \I‘V OMS/1:39»; \ / I \ _ — _ - H3500 z u \ \~< /\—/\/\_ I‘ \ \ \\/\7 \’\/‘~\\’-’/(\KI,‘I’:I‘,‘\I; F HA= ~“ \ ~ \\\/\/‘\/\\/\/\I\ -I’ L "/\’\/I w /_\\\///\ \x/\ /\/I / \ ./__._I I \l\ \\\\ I 3 ‘ >/:\/7.FI7) Sty/IV):I\'€I7Q EXPLANATION \‘/\//{‘/\/\:I:,\\ :I//\/‘\I \/\ (901/50 \,\\)(I,\—,:/, \;\7\—.\‘/\L\/L, :/ Sis/w I~‘I<\/I-:c,\’Q\L,~’\7JII’I> I1/I\’<7\’/<‘,:I l /I\E>R ,, ,I > \, E I /, ,\,\\/ on /\ /\ \\ "i\\ ,\\\I /\ _/I / _/ \I\I /‘ \/ o , \ / \ \I_\/ - I ~ , 9‘ L‘lr IL‘/—\/\\/ TIQI:\I\/\I_\”:/~ //\ I/ ' ’ \ / \/\\ U \ \\ I’I‘ / ‘ \—~X > ’1 \ ‘I ’\/{i/\/ (PVC/J > . .......... , Colluvium ( \\>/\/\\/<7/ \l/’\/\/\7\_/~\]/\/\\// \‘ VA" \‘/\{”\7‘/\/\:/ A E ’\/\\ / /\/\/ \\ \\/\ Lu §/\‘I"\0//7’I>‘\“ /\\’\\/\\’/ILI\ \\/‘\D/I/ ~\I/\ ,_ \Ll /\,/\L\/;I: \‘/\, \I ,\’.“/\l \ 0 o>/_\\/\;,,\I\\I/I\)\\// \\,\/_\ \‘ \l/\\\/~/\I\/\/\/\, / \/ -.:-, —3oooI , \V‘x/EQD \/ \,/~_,\,/ I , I \ l/I\/ I/ I/‘ \ I/I ~ /\/\- Landslide /\/\\/\\’/IT\7\\/I/ / ' ~‘\ \ \ \\\/\/I/\I/I "’ OOON w, ‘/\ /\‘l\l‘\ — , I \ — 3 3, 5/l\/‘\I\\ \\ \/I\L\/\/\\ ; .-/>\’ / \\/\_"I 9”.) o \ \/\ /\/\/\/\/ 4\ f \\ [00:8 r' ‘70 LEVEL\ I (0.: I\ //\l\’l"T _ a: I— IEI,\// — /\_\/\l __________ . MafchIke P, E TKH540 LEVEL \/\// r \ I 7:. u_ 0 BY /I/ \ \\ (1/ . v H \ _\ , /, 7\ y A ~ \ I I I ‘ \ \ ‘ / /\ I\ / \ | \ \ \ \p \///,, --\I \/\/-/,/ / -I\/‘/JVI}"\ {W \V L \I \ _ Q,.\~/, :/\/\——/ _. / \ A 1'1 \QI‘TI; It, \II/Is' _\ _I/ \ /\ ._ .. \ '7 /.\ Kennett formation I» /<—/=M" \\ ‘ ,\/\/\/|/\,\/'\_\/ \» - , \n’ ( / \ /\/ \ / A // .\ I be 2500'— /\ / _2500: EE’K/I/I‘il‘? I\~- \ ’II—W“ I - \ \IJ/x' \_ _ //\~\ /\\\ /\_7I\/l<&"\< Purphyritic rhyolite with \_/_> /\/\\'\/\\/i\/ quartz phenocrysts z e \ —, ij‘ [\9\\:>\ KW ’ ‘ ’ ’/\"\”\I‘I/\l\ 5 5‘ lax/KW/ H; I \ [\7I:1/\\/>I\\ m , / ,_ = \ /) \ / E .. , . \\¢ \ r 396?: ‘ II I, 0‘ ‘2 1 \IIT\/‘/I\“1/ / I" ‘ I V ’V/ \ /l\/ m lessthan 4 mm _. _ / ,. — .— V a _ 741~4@7;(;\ minems AI! TI - ' VII I\ » - .- L‘ TIM/(\“V/I Vi‘ Iv}? I ‘2 . \ 1, ~ VOICaI’IIC brecha, Includes , \/ )5»? 1‘ 11:33 \ \ I \ , / Ii fill/"N I: f coarse VOICaI'IlC breCCIa, s _ \ 'T‘W‘fiy>4’<¥(:j‘:\\7fl_}g;%fi _ :‘ 2000 “M“ “‘"T "T“ - 2000 j s as’; m” breccm,_and “9‘” d \ \\ fl‘R/ ‘xjsx‘, Egéw: WEI, \/ 2 \nLg breCCIaIUndIffererItIate -— / \I/ rife —- I. . I 1000:. - I «##thme :‘IHH I "2?I¢°'ph.¥::;:.':z‘:::I-I3:' °" ‘ “ \ ~ W Pun ' \I/‘_ x r)! erenI 4 \,\ ~ \V H7414 .\-'f~ \\- ~ ‘2 " x \’I\ , I/Ifi v H _ \ug El???" ’9’! 337915“ R? "V ‘ 1/1“ 0:163qu IT“? fie. / ,_ , ,- - A, I 4, «44/ Io II x x. waw V ,W I ON MAP ON SECTIONS ////// W/y/ 47/ / W ///,/I//, , . /’ Caving ,‘—. _ Gossan derlved grom Ore Ibody massive sul i 9 mg R \ ,7 I * ~ ,\\\ \\\\ m/b 17/» Cam I IIIININWW - , ground , $§\\\‘\\\\V\\\\\\‘\\\'\\\t§®\\\\\\}IQI ’/ B Bl ‘ N \\\\\\\\\\\\>\\\,\\ (“III/I277 3500’— ”3500' Gossan derived from disseminated / \///\/ WIIII‘ \/,/\< pyrite (rook thatcontained 1&75 \,/\ /\\_ # \/ II , \/ \/\T7m {11' /’ , percent pyrite) /,I “kW/J I \‘/(,(\l,\’//\/(/‘\(l’/\,\7\/’\/,\/\l/\l\‘\\\7\_ \/\""L\I\/\I ‘1 Illll'" ICC :IQIVA‘ It, /\ g, p I: \1 \/\TI/\//\ (\ /‘\I,\ ,3) /\ ’;:’I\, (2 gym: t W «>00 v) 79/1 ’ ”I I: 60020 "'>’\\‘/\’7(‘X‘ ,\ I, I ‘ /\I —— ‘ ’ ‘ / - / ' (> \/ ’Sl/ / (I‘, \ )3; j\\ /‘\/,\/\>/\\\//:\/<|>)/\/I\\’/I\‘ \ L 0 Ore body promoted to sectIon /‘\\/<\ l>> [\7\/ Clix \ \/,\ / \ / \ / s — I / ~\ \ ~/ ’ : /I\l’/\>I,‘I§’\/\'/ <,\ [\‘/'/\‘l’\/\l/—\/\\(DIP/\i’QU/r, ’;\/\ I/ l‘ : \I‘AI/ ~L1\/\/\ ’\/\/\‘ \I/11“/\\_/\/ I\I\\//\\ >1; > C5 II-III‘III/J/I'I/IQ -/I////// ’ \L" \‘I‘J/KO: \A’ \" 7 V010 ’I\/’/I\‘7\\/ ‘0’ ‘l‘ I \D \ II: I, I ,.~«- \‘\/\,\, \ /\/\‘/\‘I\/\.\/‘ /\ —\'/_\ ‘ I. I/ I ”III/WWI,” //////7///, 1/4 /’|\/\|\,_\/f\\\\/> / I, ’/ \/J_/\l/ ,\I/I\//\ ,\ <‘/‘\/\I |\\ /’\/ _ /K\/ \) Hycllrothermally alftered rockI‘j Arglzlllc , \VIIIIIMHI‘: I ,I I /////I/ //// V1,] 00 ‘\,/\/\,\/\ \/_\ I/\ I\/\ \‘\/,\ I I,\/ \/ L / /\ / y/ \ I / / \ ateratlon, SIIICI ICatIon, an pIn O, I H WWW W / ’ 3000I__><’,7\’l< 'lC/\_//'§‘I\‘/_\‘I7_\I:\_/I:’V CA7 \' I7 \— ‘ //////1/‘V//’7//// /l\7\/\ ‘,‘\/\7 _\/\\,\ \7\’/\\ QT\/_\ I\\')\:\‘LT/> I \ < 7///////-//?.,, \/\V\/I/\\/\\/\TI\/\/\'\//\‘C\"I:I\<‘/—\‘/"<\I' /~_ "/ .é/ /\I/,‘/\\\I\\ /\-/\_,\—I\,\\\// /\/,\:\l /\\/ 1/} //, \7’\\/\/’\l\’/\\<>l\/l\\/ \‘I‘l‘ I A ’ ’\/\/ \ Quartzvem I\“/|\I>\/l\\‘ \/ I IH'p/ ,l I/I/\/\L WoxcwH w \ / , /\ \ - Sin/I(?'\')~\T:f_\/I/O |I 4—— \ - / \ / - - )(J x‘ < ’ \ l ‘- Contact, showmg mo (/10 ': Dasha-i where .ppmn'mavegy/ocaw \ I ~ ‘/ \‘I_\ \ __________ Indefinite contact '2500' . 65 Yw. . . _ u 1 $473 A“ Q- / D ~— § \\ I /l \ I \ / \ / / \ Fault, showing dip / \ / / \\ / \ Dashed where appr'OXImate/y Anew; ‘ / _/ \ u, upf/Il‘own sun; D, dawnr/Imwn safe 2(2 I \ : .............. Concealed fault 7___.7 x . I \— Probable fault x 10008 2000: 2000' ___._90____ Vertical fault Fault, showing relatIve movement 20 O. Strike and dip of beds 3500'. C3500 45m Strike of vertical beds ea? “:11, 4' , / 4 . . . . I I, 7LQ>H Strike and mo of folIatIon; querIed (>,’\/)\,~ where dip is doubtful -,\/ \1 _ so :/\ + / \ Strike of vertical foliation /\ \ A I ,, ;) L ,x K :5/ , I s \ Z /_ \/\/\ \/\/\/ - - V; r 7\ /\ 3000’ I/ \\'/ \I/ \ /_\ \ , \\I \ \ Stope outIIne, projected ‘//\\,’ - I< \ T \/ I/ \‘/\///\\\’»H\/ ~3000’ 20003 was}. 1 , - A I‘." 2900 I If» F/ ‘0 \j /I. l\/I E \ \\ ‘, - (1- ' _ \ _ _ __ V .> H: Irv: 3/6002, «7'69 209/; I : I ,x I > I / \ I 1 II / Add /7 /, .\/"/\\//‘\/_\ i—,<,\ I\v\/\7 \/ \_ \\ \ /| \’/\ \‘~ ’u/sl \/’/\/\/ —‘/ \X— — \ I \ / \ / , / / \ / \I|\/ -1) /,\/ ”Nd“ \ \/,\\// \\\I/\I >+— _/ ’ / C :\ /\ a _ , 0"“ \l/[\/'/’\ /\ /:I/\/‘\/ ~ CE 0 2 Lu :3 a: I— 473 RAISE I3 FAULT AT 2600' I T 2700' lOOON > , ' AT 2800) 1000p; AT 2900' AT 3000 (J $3003 AT 3l00' 18 CROSSCUT 2900 I ORE BODY “/2? 313 ORE BODY / 8:900 ‘ ‘50 CALIFORNIA FA LT AT 2700’ Z/ , //// I o V “290 /CALIFORN|A FAULT AT 2300' 00' 0 V \ I / o uLT 1 30 ‘, AT 3l0 I; \ I I FA ULT ’ ‘ ’ ‘ @ VORNIA SHAS A FA \ / R20 2143—7335: ; cALI ., \\ ’I I It . \ 1 AT 26“) ’2’ "’W ,. 39°, . 4’ , ’ \\ I I CALIFORNIA HAUL Ill/W _- ., IA rcr/ W \ \ I ’ oRN CALIFORNIA FAULT AT 2900( Q, ‘g 7‘ ‘ / \ \ I / Il/// . — ‘ /” Lt FR“ / / WINSLOW \ \ I , . j/ff/ I . - «’CAUF R“ ,J , A ORE BODY \\ I I / ’ 1 ’ 07, I’ ‘ j. ‘ , . ‘ /// \ ‘ I , » ,1 /, [1/ l ’ I , a/ , & SIERRA ‘33 , , I I I /, ./ ORE BODY / %00 I 1‘ I II ' ~’ 1' ~ — i 3 I 1 £350 [7/ . . 3 12 DRIFT FAULT AT 3000’ I\ \ I I ' ‘ I /YO o / 12 DRIFT FAULTl AT 3100' l \\ I I. /YOLO (3l3) FAULT A1 3000' o/fi” (5% \\ I \ I I / YOLO (3l3) FAULTIAT 310a; I7 } / l \ I I 00 “79% , I 7 7/ I I I I STARROW 00 I l l ORE BODY \ “7, I [I I Q I a? "x ORE BODY // CPPER CREST ORE BODV 10008 10008 20005 20005 I 1200 Feet I __LL“ AL _ 5‘ 7‘ g I 0 Lu 8 8 N 30005 g 2 Igooos 30008 Theology byA R Kinkel, Jr. andW. E Hall STRUCTURE CONTOUR MAP OF THE MAMMOTH MINE. SHASTA COUNTY, CALIFORNIA 379725 0 -56 (In pocket.) UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY PREPARED IN COOPERATION WITH THE STATE OF CALIFORNIA DEPARTMENT OF NATURAL RESOURCES DIVISION OF MINES PROFESSIONAL PAPER 285 PLATE l7 /B 3 3 o I m g E 0 CI IV EOOON 3100‘ \\\\\\N\C‘\\ \ \\\s “x \ B/ ZOOOW IOOOW 00 IOOOE 3000N N‘QV \ 3055' ZOO LEVEL Surface at 2840 feet 470 LEVEL 3 O o O N 30005 20005 3000N 3000N 3 O O O (\l Porphyritic rhyolite in this area may be an 500 |_ EV E L intrusive mass that lies below the main body 666' E 3 8 8 ZOOON 10003 8 S 8 10003 1000N IOOON EV 00 / /B 6 70 L EV E L é Ci 2 \ 10008 10008 E X P L A N A T I O N >- E 65 I: 1 u m . _r '0— _ '- \/ t I '5‘ Fault, showrng dip;tdlaslhed - w ere approxrma e y o» I» Maflc dike 8 cated. U, upthrown side; D downthrown side - 90 Vertical fault 2 Porphyritic rhyoiite with :5 uartz phenocrysts more Tuft z ,5 E t an 4 mm S ‘f; g Strike and dip of beds Geology not known % E 50 E Volcanic breccia . . , . B" , m Nonporphyri rc rhyolite .3" d Strike and dip of foliatlon porphyntic rhyolite With J uartz phenocrysts less / t an 4 mm Adit Caved adlt Pyritized rock at altitude El Of level Foot of raise or winze 20008 20008 00 Z “’I Head of raise or winze I — ________ 0'3“” °f ore and 0'5 Workings, dashed wnere seams at altitude of projected to altitude level of level Note: Sections also shown on plate 15 *19 :7“ ’ A r z ‘7: Geology not known 4% IE CAT 300 I— EV E I_ / Projectioneolglore above g 5 “J l: D B / to _ — 7 E é“ // Contact, showing , ashed § where approximately K located 1/\ 540 L EV E L / g 100 I 0 I J I 500 Feet 8 E E E g o O 8 8 O o 8 ° “‘ s o 8 10008 N 2 0 10005 H 30003 30005 H lNTERIORrGEOLOGiCAL sum/EV wasHiNGroN,n c M n-zsos Geology by A R Kinkel J, and W E Hall Maps are interpretations by the authors of existing under- ground data compiled during the period of the mine’s operation GEOLOGIC MAPS OF THE 200, 300, 470, 500, 540, AND 670 LEVELS OF THE NAMMOTH MINE, SHASTA COUNTY, CALIFORNIA ' ; _ Prepared in cooperation with the ' " State of California UNITED STATES DEPARTMENT OF THE INTERIOR Department of Natural Resources GEOLOGICAL SURVEY :18 Division of Mines PROFESSIONAL PAPER 285 PLATE 18 % 8 i ‘ g vH§<”W2“4q 8 g EXPLANATKDN O o o /,\\7/ \‘////u=’= O 0 L0 00 o 4\“//==\\////\// o 00 .—l r—l -. N J—\~4_“_‘1//\\// :: : “é, (\l (\l >- ~19y° , ‘i \ / \‘:4/:L/4s’¢s\ g" a: 2 \\ .0 \ {Sc/ICJ‘FJQII Z ll , E L , ‘ \x;§l>>.’:'/\‘ (9 k \17‘ /’\:/ g 6’ . ,\ \I\ l i Porphyritic rhyolite with quartz phenocrysts more than 4 mm 26OON ‘ , aéOON I i \ \ \ L \ / \ l \ / / K \ Porphyritic rhyolite with quartz 3 phenocrysts less than 4 mm 3 z i? 5 SI 3 g I> x Lu «1 Q E m H“?- N": . MEAT-7259.5 Mafic flow __L~___ Contact, showing dip; dashed where \ \ / \ - . 3 \\\\\\§\§\\‘< ififil‘éxé'é‘fiéiiaylé‘3fated' med \\\\\\\\\\ \\\:\\ . - $ \\ \ \\\\\ \ 65 Ifi§§§$§h§§§Nfix> _____%_i.___ ...... -* \ > “. F n, h ‘ d‘ ;d h d h \ II\\\§X\%§\\\\: C A’)‘ aaupprzx?n‘éilart‘gly Iligacataesd;ed(;’t’teedre where concealed. U, upthrown- side; D, downthrown side 90 _—_+_—_ Vertical fault __7_ _ _ _?_ Probable fault I8 Strike and dip of beds \\\\\\ \\\\\\\\\\\\\\:// mu \ JII\\\\\\\\\\\\\\\\ WWNW i" 'J"'\' “m“ ‘L a, Strike and dip of foliation /// \\\\\ \ l\\\\\\\\ , / \ C27 / I \, \ Adit \7. Caved adit 1800N 830—845 levels —"'865Iévéi_— 870 level _§o—o_lévE—" 16OON ///Il\\ ’7/x/n\\\\ Dump >(BM 1636 US. Geological Survey bench mark 24OOE 26OOE 800E Topography by W‘ E. Hall Sections appear on plate 19 INTERIORVGEOLOGICAL sum/Ev. WASHINGTON, D, c M R-2305 N Geology by A. R. Kinkel, Jr. and W. E. Hall, 1950 GEOLOGIC MAP OF THE SHASTA KING MINE, SHASTA COUNTY, CALIFORNIA 100 0 L I I 390 Feet Contour interval 25 feet — Datum is mean sea level I I I l UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY PREPARED IN COOPERATION WITH THE STATE OF CALIFORNIA DEPARTMENT OF NATURAL RESOURCES DIVISION OF MINES PROFESSIONAL PAPER 285 PLATE 19 ifiow G x mugomu 5 IV on,” \ Macflsne\ ‘24'rvr. DpV‘ l316.6' 2200N 2200N I Sandy sulfides incom~ = i plete replacement )5 i "I I’ I “2; I * I _ fragments I fi ‘i’y / n are In back C , a If Sandy sulfides lncom-’ i plate replacement .1, \ £2, El In , g' I I I I’ / 6; ZOOON 200047? MAP OF UPPER LEVELS .y u \ u m ‘6 5 \ E E 0 L L El 8 8 5. .— _ N 1: E o z u «a G?” g | ’2, \ 9400'“ 2400N Irregular grad tional Contact Irregular gr 6’ ational con I Isl Soft,s sugary sulfides v incomplete replacement 0/2, 3 \v 2200N A \ L1 3 E 200 N 9 1787.2’ MAP OF LOWER LEVELS w 3’ § \ ISOOL 1 700" y 330 LE VEL %'> m “’o B 2 100% 19009 1800’— to 2000L 19OOL 1800 ’4 1700’ 2100’ i 1900’ a 1500’ * FI -? 100’ ~1800’ 2000i 1800 {IOU/4;: l 1900 / t .5 ‘ 7" \I 1 4v // :4 \x ’/ {I .» I V’I 1/ L:I’/ i Ms II [IT I Q, ‘ “MIMI/w 00416:! . II [I , 72 000’ ‘1900’ *1800’ ~1700’ l 600’ D 2100’ 2000’ 1 900’< 18002: 1700’— ’ H 2100’ 20004 1900’ 47005 E2100 HZOOU’ «In; I t , ~ :mrlkzIrI; ‘1800’ -I700’ SCALE FOR UPPER AND LOWER LEVELS 290 Feet See plate 18 for seruans on surface Baiaklala rhyolite [Mien/ed Level plans furnlshed by R T, Walker and W J Walker, owners GEOLOGIC MAPS AND SECTIONS OF UNDERGROUND WORKINGS OF THE SHASTA KING MINE. SHASTA COUNTY, CALIFORNIA _J Geology byA R Klnkel‘ Jr andW E Hall,1950 EXPLANATION Colluvlum 8mm“ only Porphyritic rhyolite with quartz phenocrysts more than 4 mm Porphyritic rhyolite with quartz phenocrysts less than 4 mm Nonporphyrmc rhyolite Pro/eater! Massive sulfide ore Contact, showing dip Lang Ilruhal when; appmximmm located: Mort dillhua where III/men 99 _,7 Venical Contact _J: _.._ Fault. showing dip Dashed when approximate/v ed 90 Vertical fault _7_.__?_ Probable lault | cllned workings n Chm/Iona paint damn Caved or inaccessible workings IE Foot uf raise or wlnze Z Head of raise or winze L L _ I , . Underground workings, dashed where projectemdctted where caved‘ Section: only Dump Sections nIIIy OUATERNARY DEVONIAN Prepared In coopevallon with the State at Cafirovma UMTED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY TRUE Ngfi’II-I . . 7?,“ Elevamn or; these aans nol known MBXIDTEIYS,(E(I)CI;1"QSS/ g? I? fl , Some slopes In 0st area Furmshed by me Unwed States Smeltmg Reimmg and Mlmng C0. (approx) Depamnent 0f Namval Resources DrvIsmn 07 Mmes PROFESSIONAL PAPER 285 PLATE 2O EIevaIIon . not known \ \\ / ',- \ \ J Buoy ov masswe suIiIdz pam;\ _\s\ ouumed thIsavaa ”a? \, ElevatIon no! known >6 Stoped above .\ 340 Ievel / , \ 4, Li;/ “I” ‘ \ Ivl ‘EIevanon not known EXPLANATION El Shaft x./ / AdiK Intevmmtg @ and 390 leveIs EIevalIon not known Opencu! 5 Four o1 ralse 0v winze ~ , e 7 7 '523 TeveI < IZI . . Head>of leis: or winze LEE erfsngEel SAMPLES IN GOSSAN Assays are ounces of guld per ton Sample cm; 307d. 0 0.045 ounces .—A‘M¢~——— Sample cut, goId, 0.045 0.095 ounces —-—— Sample cut; gold, 0 095 0.20 uunces 300 Fee! I MAP OF UNDERGROUND WORKINGS OF THE STOWELL MINE. SHOWING OUTLINE OF GOSSAN. SI‘IASTA COUNTY, CALIFORNIA 379725 0 -56 (In pocket) UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY Prep-red in cooperation with the Sun of California ‘ Department of Natural Resources Division 0' Mines PROFESSIONAL PAPER 25 PLATE 21 TRUE NORTH EXPLANATION 60l_____ Fault, showing dip; dashed where approxrmately located ROUN CE “STOPE Surface opening SUTRO AD/T ‘ STOPE \ Outline of stope Foot of raise or winze 4 t 3633’ \\ \\ Head of raise or winze SUTRO 29 TUNNEL EXPLANATION Mafic dike Povphyritic rhyohte with quartz phenocrysts more than 4 mm ‘/I/L/\~/ Bedded tuff 903/ [r c 1‘ » Balaklala rhyolite Undifferentiated middle unit of m Ore body on section I I I I I the Balaklala rhyolite Contact, dashed where approximately located Inferred contact Fault, dashed where approximately located :33: _ - Workings, dashed where prolected to section SUTRO 29 TUNNEL Bend in section c, (”Map ‘n‘iH ,\‘,\’/\/ CIT/(P I \ \ “IN/JAN) \/_\/ (UTA/Cm /\7‘\/\ ’\/\I / _. I? HAZARD, $70 *STOPE\ \ \\\ / ‘I l / / / Veg—Me; 4 A” ‘ JET/CG ~/\ ,7 I I 7N \\ / \ SUTRO ADIT STOPE e /\ \ x . ’ / «\ //\ /I/ / J ‘ ,yv/“(i‘i/K, \, s , I -_ ‘01: \’\\l1\77\'/ / \ v \ \l 7 ,\\, \‘/\ ’\ — , — >1 ’ .\<<‘ \/ / «J/‘A \ \r,\/\\ \/_ \ 3, ,\/~\\\'\/1\/"/ A|/\\\\»\ \/\/\/ ‘ \ / \ /\':‘4\\f,\:\;:\3\\\ \/:/;:/I\/\// \“ /, \/‘/\r u I r/ c ;I\: (I LIN—C T__\SUTRO 29 TUNNEL _ ’\ \/ \/\\/\L/\/ >:\\_\‘:/\\\ .4 7‘ \/\/\/\/\’\, /\ \ fl/II//I\/\‘\/\ '/\/I/ ,\ E SUTRO ADIT STOPE _ / \ \ / \ \ / “l\4 \" EVEL VOA, \,< ,. /<,,_7 \ pg, LI/ \ I) \\/’\\/\I’r/\/_/\\ /[\"/ I/ \ ‘ ’fl -: ‘ /‘ \ \ I :pi‘M/V \1\/\/\I? 3’s; \ ' -; x / ;:> / :I/\>/,,>\/\1I\/)//\, \ ‘\ , , ‘ f /, \ , \ W \ /l\ /I \ / / ‘ \ via! ,, _\ v \ M / \ /\/,\/» ‘ y /_\\r\‘/ / ‘ X / \ \ c \ ‘\7\ \e\ /\/\/\\# / __ 4.. _. *_ 443‘", — — —— —— ——* <' _ MAS '\I\ I\\/‘\ \/ 4w \— /\/I_,/ ’{/\I\I I\‘I '2\71\/\\ \/ ‘/\r\\)\ ¥ _\ 2 I/ \g/ ‘ \VI//\/,I,I‘I / :\L‘/\‘r\L\//\ \ \//\,’l\/, /_I/\/.f / \r‘ (\/ I/O' LA / m Wm / I(VI , _\,\/\\,:\ \/ "l , «(pf/MINI \w/ILI \ m/ ’\,\I p C WC \ My , ,//\, \/ ‘Ju /I/ \\_u _I/\//\C\/17I\ 10' \/\ eq- '\/\\ fi/u I;{\ij>\i\> ’ l\[\/‘f\ . p75 \x/I/\/:"I,\ . VI“ - ,\\// >I’ . \C /\/\',\,,2 I", I (<3SUTR'0 29 TUNNEL — 3800’ ;7\\/\\ \/I7\7\7 /\/ \ i \ \ \/\/ \ ,C, C \ \/ \e37oor \’\\,/\\/ E '/I\ ,/,\,‘\\7\‘/\ ’0/11; (I /\~ rs /\//\ I7 y\(_\/ ,V\ \\\ ”I /.I IVS}; x-Jm Maps and sections are interpretations by the_authors of existing underground data complied during the perlod of the mine's operation MAP OF UNDERGROUND WORKINGS AND GEOLOGIC SECTIONS OF THE SUTRO MINE‘ SHASTA COUNTY, CALIFORNIA 500 Feet r 4 Datum [5 mean sea lave] Complled by A. R. Kinkle, Jr., W, E. Hai and J. P. Albers 379725 0 --56 (In pocket) \LEU C) L (/(I Ma Pa» 1:743é fie and Correlation of the Chattanooga Shale and , the Maury Formation ‘ E GEOLOGICAL SURVEY] PROFESSI'ONAL PAPER/ 286 ('“\ ‘ ‘3 S JAN 14 1957 ”Mag! 98““ ' WP“- 'rn-I At'v-‘O—fl- mN—wwm J14; 1:»1337 g 3 E i z" s i Age and Correlation ofthe Chattanooga Shale and the Maury Formation By WILBERT H. HASS L I. r' "I ._ '7' I », . GEOLOGICAL SURWEY PROFESSIONAL PAPER 286 ro— 14 contrz'ém‘z'm to t/ze Devonian and M z'ssz'mzppz'afl Mace-Male free/em, eased 072 coma’om‘ studies UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1956 UNITED STATES DEPARTMENT OF THE INTERIOR Fred A. Seaton, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, U. S. Government Printing Office Washington 25, D. C. nude EARTH um SCIENCES ' LIBRARY CONTENTS Page Page Abstract ___________________________________________ 1 Maury formation ___________________________________ 23 Introduction _______________________________________ 2 Standard section of the Maury formation __________ 23 Previous work ______________________________________ 3 Age and characteristics __________________________ 23 Chattanooga shale __________________________________ 13 Measured sections __________________________________ 26 Standard section of the Chattanooga shale _________ 13 Conodont collections ________________________________ L8 Hardin sandstone member _______________________ 15 Literature cited _____________________________________ 44 Dowelltown member ____________________________ 16 Index _____________________________________________ 47 Gassaway member ______________________________ 20 ILLUSTRATIONS [PL 1, in pocket; pls. 2—5 follow index] PLATE 1. Collecting localities, Chattanooga shale and Maury formation. 2. Conodonts from the Maury formation. 3. Conodonts from the Gassaway member of the Chattanooga shale. 4. Conodonts from the Dowelltown member of the Chattanooga shale. 5. Type section of the Chattanooga shale, Cameron Hill, Chattanooga, Tenn. . Page FIGURE 1. Range of significant conodont genera and species in the Chattanooga shale of the Eastern Highland Rim, in Tennessee ........................................................................................ 17 TABLES Page TABLE 1. Standard section of the Chattanaoga shale _______________________________________________________________ 12 2. Comparison of stratigraphic limits of Campbell’s type sections of his Dowelltown and Gassaway formations and the amended section adopted for this report ____________________________________________________________ 16 3. Distribution of easily recognized conodont species of the basal sandstone of the Dowelltown member where the Chattanooga. shale section is essentially complete, and of the Trousdale shale of Pohl _______________________ 18 4. Distribution of significant conodont species present in the lower fauna of the Gassaway member ________________ 21 5. Distribution of significant conodont species present in the major part of the Maury formation __________________ 25 6. Conodont collections from the Chattanooga shale, Maury formation, and New Providence shale _______________ 38 7. Distribution of conodont species ____________________________________________________________________ In pocket 8. Distribution of conodont species ____________________________________________________________________ In pocket III AGE AND CORRELATION OF THE CHATTANOOGA SHALE AND THE MAURY FORMATION By WILBERT H. HAss ABSTRACT The Chattanooga shale and the overlying Maury formation of central Tennessee and adjacent States belong to the Devonian and Mississippian black—shale sequence. This sequence occurs throughout much of the interior of the United States and a part of Canada. The Chattanooga shale is herein considered to be of Late Devonian age though the oldest beds of the formation could be of late Middle Devonian age. The Maury formation is herein considered to be of Mississippian (Kinderhook and possibly Osage) age with one exception—in a part of north-central Tennessee the basal bed of the Maury is classified as very late Devonian. The age designations, faunal zonations, and cor- relations of the paper are based, for the most part, on a study of the conodonts in 325 collections from 65 measured sections; conodonts in 186 collections from 27 of the measured sections are mentioned by number. The Chattanooga shale has three members: the Hardin sand- stone, the Dowell'town, and the Gassaway (youngest). The Hardin sandstone member grades into the overlying Dowelltown member. It is a local thickening of the basal sandstone bed of the Chattanooga shale, and is restricted to the vicinity of Wayne, Perry, Lawrence, and Hardin Counties, Tenn., and to the adjoin- ing part of Alabama. The Hardin consists chiefly of siliceous fine-grained sand and silt, and is as much as 16 feet thick. It is herein classified as early Late Devonian though some part of the member could be late Middle Devonian. The basal sandstone bed of the Chattanooga shale commonly ranges in thickness from a featheredge to about 0.5 foot, though, as stated above, to the southwest of the Nashville Basin, it is thicker and is there called the Hardin sandstone member. This basal sandstone is a transgressive deposit, for in some areas it is apart of the Dowelltown member and elsewhere, where the Dowelltown is absent, it is a part of the Gassaway member. Along the Eastern Highland Rim where it is a part of the Dowell- town member, the basal sandstone contains early Late Devonian conodonts like these in the lowermost part of the New Albany shale of Indiana and the “conodont bed” of the Genundewa limestone lentil of the Geneseo shale of New York; but where the older beds of the Chattanooga shale are missing, as, for example, near the crest of the Cincinnati anticline, and in south-central Tennessee and north-central Alabama, the basal sandstone con- tains younger Late Devonian conodonts. Good sections of the Chattanooga shale are exposed along the Eastern Highland Rim of central Tennessee from southern J ack- son County south into Coffee and Bedford Counties. Through- out much of that area the formation is between 25 and 35 feet thick and its subdivisions—the Gassaway and the Dowelltown members—are well developed. In the above-mentioned area of the Eastern Highland Rim, the Dowelltown is between 10 and 17.5 feet thick and consists of two persistent litho- logic units: a lower one which is predominantly black shale, and an upper one which is primarily a grayish mudstone, near the top of which occurs a bentonite bed, about 0.1 foot thick. This bentonite bed is probably present throughout at least 4,000 square miles of east—central Tennessee. Along the outcrop, northward from southern Jackson County—except in the Flynn Creek structure—the Dowelltown is probably less than 10 feet thick. Also, it wedges out southward in the Sequatchie Valley of eastern Tennessee and has not been recognized in south-central Tennessee or in north-central Alabama. On the west flank of the Cincinnati anticline the Dowelltown is commonly a sandy black shale, and is as much as 17 feet thick. At Olive Hill, Hardin County, where its relationships to the Hardin sandstone member are evident, the Dowelltown is 31.8 feet thick. The Dowelltown is assigned by the writer to the Upper Devonian Finger Lakes, Chemung, and basal Cassadaga stages of Cooper (Cooper and others, 1942) ; however, its basal beds may belong to the uppermost part of the Middle Devonian. The Gassaway member is chiefly a thin—bedded, grayish-black shale, though along a part of the Eastern Highland Rim, it can be subdivided into two black-shale units and an intervening thin zone consisting of gray mudstone and black shale. The member is between 12 and 21 feet thick along the Eastern High- land Rim but is thinner in south-central Tennessee and north- central Alabama. It is absent throughout most of Lawrence County, Tenn. and parts of the adjacent counties; on the other hand, it is at least 46.4 feet thick in south-central Kentucky. Phosphatic nodules occur in the youngest beds of the Gassaway member. These nodule-bearing beds range in thickness from a featheredge in DeKalb County, Tenn., to more than 8 feet in the vicinity of Somerset, Pulaski County, Ky. The Gassaway member contains two distinct conodont faunas. The older fauna ranges throughout most of the Gassaway in- terval and its widespread occurrence indicates that during some part of Gassaway time, deposition of sediments took place throughout most of the central Tennessee area. Beds having this older fauna are correlated with the lower part of the Ohio shale of Ohio and Kentucky; the Antrim shale as exposed in the Paxton shale pit West of Alpena, Mich.; the major part of the middle division of the New Albany shale of Indiana; a faunal zone of the middle division of the Arkansas novaculite of Arkan— sas and Oklahoma; a faunal zone of the Woodford chert of Oklahoma; and a faunal zone that ranges throughout most of the Chattanooga shale of northeastern Oklahoma. All these formations or parts of formations are classified as Late Devonian. The Chattanooga shale and the Maury formation probably are separated by an unconformity throughout much of south- central Tennessee and north—central Alabama for, there, the youngest beds of the Gassaway member have not been recog- nized. These youngest beds have phosphatic nodules and conodonts like those in the upper part of the Upper Devonian 1 2 CHATTANOOGA SHALE AND MAURY FORMATION Ohio shale of Ohio and Kentucky, and in that part of the Sander- son formation of Campbell (1946) which, at the type locality of the Sanderson, near New Albany, Ind. contains phosphatic nodules and directly underlies Campbell’s Falling Run member of his Sanderson formation. The present writer classifies the Falling Run member as early Mississippian (Kinderhook) and the underlying beds of the type Sanderson as Late Devonian. The Maury formation is a well-defined lithologic unit where- ever it underlies the Fort Payne chert but its top is indefinite wherever it underlies beds identified in the literature as the Ridgetop shale and the New Providence shale. The formation is generally,1.5 to 3.0 feet thick and consists for the most part of grayish-yellow, green, and greenish-gray, glauconitic mud- stones. Phosphatic nodules are commonly scattered throughout the Maury and at many localities also occur as a course or bed at or near the base of the formation. In a part of north-central Tennessee this nodule bed contains Late Devonian conodonts like those in the youngest beds of the Gassaway member of the Chattanooga shale, but elsewhere in central Tennessee, it con- tains early Mississippian (Kinderhook) conodonts. The phos- phatic-nodule bed at the base of the New Providence shale of south-central Kentucky has a similar Mississippian conodont fauna and, therefore, the writer considers the Maury formation to be the biostratigraphic equivalent of the lower part of the New Providence shale. There are several distinct conodont faunas in the Maury for— mation. In a part of north-central Tennessee, a thin grayish- black shale occurs just above the aforementioned basal phos— phatic-nodule bed that contains Late Devonian conodonts. This black shale has an early Mississippian conodont fauna; but the conodonts that seem to range throughout most of the Maury formation are like those in the Sunbury shale of Ohio and Kentucky; the uppermost part of the New Albany shale of Indiana; the Bushberg sandstone member of the Sulphur Springs formation and the Hannibal shale, both of Missouri; beds near the top of the middle division of the Arkansas novaculite of Arkansas and Oklahoma; a faunal zone of the Woodford chert of Oklahoma; and a faunal zone of the Chattanooga shale of northeastern Oklahoma. All these formations or parts of forma- tions are classified as Mississippian (Kinderhook). At some localities the Maury formation contains conodonts of late Kinder- hook age and probably others of early Osage age. INTRODUCTION Because the Chattanooga shale of central Tennessee is a potential source of oil, uranium, and other materials, members of the United‘Stat-es Geological Survey have been investigating that formation. This report on the age and correlation of the Chattanooga shale and the Maury formation is a part of that study. The Chattanooga shale, which, when first delimited by Hayes (1891, 1892, 1894a, 1894b, 1894c, 1894d, 1895), included the beds herein called the Maury for— mation, is a part of the Devonian and Mississippian black-shale sequence. This sequence is present through— out much of the interior of the United States and a part of Canada. It varies in age from place to place and is known by many different names; usually, the oldest beds are considered to be of late Middle Devonian age and the youngest, of early Mississippian age. Numerous papers have been written on the age and correlation of these beds but much of the record is incorrect because it is based on inadequate data, for the black shales do not contain—except at a few widely spaced localities— the fossils commonly used in stratigraphic paleontology. Instead, the recognizable fauna and flora consist chiefly of inarticulate brachiopods, a few arthropods, fish remains, conodonts, and plant fragments and spores. Of these, conodonts are the best fossils on which to base an age determination or correlation. In central Tennessee the black shales unconformably over- lie beds of Ordovician, Silurian, and Devonian ages and underlie beds of Mississippian age. This report is based on a study of conodonts in 325 collections from 65 measured sections. However, in order to avoid a great duplication of data, only 186 of these collections from 27 0f the measured sections are mentioned by number in the report. The stratigraphic position of each collection has been referred either to the Chattanooga shale—Maury formation contact or to the Chattanooga shale—New Providence shale contact. Conodonts in most of the 186 collections are listed either in table 7 or in table 8; and the localities from which the collections came are indicated in plate 1. Locality data are given on pages 26 to 38, and infor— mation pertaining to individual collections is listed on pages 38 to 43. Some of the conodonts considered significant in determining the age and correlation of the Chattanooga shale and the Maury formation are illustrated in plates 2—4, and their stratigraphic range in the Chattanooga shale of the Eastern Highland Rim of central Tennessee is recorded in figure 1. All speci- mens illustrated in this paper have been deposited in the United States National Museum. Locality num- bers are the same as those used by L. C. Conant and V. E. Swanson in a paper they are now preparing on the Chattanooga shale. Many conodonts that belong chiefly to the bladelike and barlike genera have been disregarded because the species of these genera are not easily differentiated. Molds of conodonts are common in the black shales, and rubber replicas were made of many such specimens as an aid to their identification. The stratigraphic classification used in this paper was agreed upon during a field conference held May 4 to 7, 1952, in central Tennessee between P. E. Cloud, Jr., J. S. Williams, L. C. Conant, V. E. Swanson, and the writer. The classification follows: Mississippian: Maury formation: throughout much of the area the basal bed of the Maury contains many phosphatic nodules. This nodule bed is classified as early Mississippian except in a part of north-central Tennessee Where it is probably of very late Devonian age. INTRODUCTION 3 Upper Devonian: Chattanooga shale: Gassaway member Dowelltown member Hardin sandstone member Field work was begun in June 1944 when A. L. Slaughter, S. E. Clabaugh, and the writer did reconnais— sance work on the Devonian and Mississippian black shales of the eastern United States. Outcrops in central Tennessee—at Horseshoe Bend on the Caney Fork in White County (locality 88) and in the Flynn Creek area of Jackson County (locality 54)—were measured and sampled, and it was partly through these investigations that the potentialities of the black shales in a part of the Eastern Highland Rim of Tennessee as a source of uranium became evident. During June 1947 the writer collected conodonts from some of the sections in central Tennessee and south—central Ken— tucky that Campbell (1946) listed in his paper on the New Albany shale; also, in June 1947, the writer (Hass, 1948) discovered a thin bed of bentonite in the upper part of the Dowelltown member of the Chattanooga shale. The type area of the Chattanooga shale was first studied by the writer (Hass, 1947b) during the summer of 1947. In November 1947 the United States Geological Survey placed a party in central Tennessee for the purpose of investigating the Chattanooga shale for the Raw Materials Division of the Atomic Energy Commission. L. C. Conant was in charge of the investigation, and the writer, who was with the party intermittently, was responsible for the paleontologic and some of stratigraphic phases of the work. V. E. Swanson joined the party in June 1949 and worked mostly in the area between the Western Highland Rim of central Tennessee and the Tennessee River. He worked also in northwest Georgia, north Alabama, and northeast Mississippi. The following field men assisted in the measurement and interpretation of sections: R. C. Robeck, 1947—49; R. E. Smith, 1947—48; Andrew Brown, 1947—49; and W. A. Heck, 1948. Most of the collections were prepared in 1948 and 1949 by L. A. Shirley, W. M. Hisey, and Alford Rarick, all of whom were geology students at the University of Alabama. - PREVIOUS WORK The literature on the age and correlation of the black-shale sequence of central Tennessee and nearby States contains many Conflicting opinions. Witness, for example, some of the ideas that have been held: Safford (1851) regarded the “Black or bituminous slate” of central Tennessee as one of his five major stratigraphic units. He assigned it to the Devonian but several years later he (1856, p. 148, 149) placed the “Black slate” in the Carboniferous as the lowest division of that system. Even so, Safford (1856, p. 158) mentioned in a footnote that the age of the “Black slate” is in doubt. In his “Geology of Tennessee” Safl'ord (1869, p. 150, 151) regarded the black shale as of Devonian age. He (1869, p. 330, 331) stated that to the west of the Cumberland tableland the “Black shale group” or “Black shale formation” consists of three parts, which from top to bottom are: 1. A thin bed of argillaceous, fetid, concretionary bodies commonly called “kidneys”. 2. Black shale. 3. A dark-gray sandstone which is bituminous, fetid, and commonly fined grained. This sandstone was reported to range in thickness from a few inches to 15 feet and to form conspicuous ledges in Wayne, Hardin, and southwest Lewis Counties, Tenn. The divisions of Safl’ord’s “Black shale group” have been recognized by subsequent workers, but, as indi- cated on the following pages, these divisions have been treated in various ways. Killebrew and Safford (1874, p. 28, 39) briefly men- tioned the “Black shale” of Tennessee. They assigned it to the Devonian “Hamilton period.” And Smith (1878, p. 10, 11; 1890, p. 154, 155) who worked in Alabama considered the “Black shale” of that State to be of Devonian age. The name “Chattanooga black shale” was proposed by Hayes (1891, p. 142, 143) as a substitute for Smith’s (1878, p. 10, 11; 1890, p. 154, 155) and Safford’s (1869, p. 330) nongeographic term “Black shale.” It in- cluded the beds between the Rockwood formation of Silurian age and the Fort Payne chert of Carboniferous age. Hayes’ (1892, 1894a, 1894b, 1894c, 1894d, 1895) “Chattanooga black shale” consists of two units: a lower black shale and an upper gray one which com- monly contains a layer of round concretions. He placed the formation in the Devonian and designated the outcrop at the north end of Cameron Hill in Chattanooga, Tenn, as the type locality. Safford and Killebrew (1900, p. 104) proposed a classification of the black-shale sequence that differed from previous ones. They used several new strati- graphic names: ‘ Carboniferous: Mississippian or Subcarboniferous: Maury green shale (ball or kidney phosphate) Devonian: Black shale (Chattanooga shale) Swan Creek phosphate Hardin sandstone The Maury green shale of Safford and Killebrew (1900, p. 104, 141—143) is the top division of Safl'ord’s (1869) “Black shale group”, and the gray—shale unit of Hayes’ (1892, 1894a, 1894b, 1894c, 1894d, 1895) “Chattanooga black shale.” The Maury was described as ranging from a few inches to 5 feet in thickness, as containing concretions of calcium phosphate, and as including the beds between the Tullahoma formation and the underlying “Black shale (Chattanooga shale).” It was named for Maury County. Safford and Kille- brew (1900, p. 104, 138, 139) proposed the name “Swan Creek phosphate” for a phosphatic bed which they stated ranges from 10 to 50 inches in thickness in Lewis and Hickman Counties, Tenn, and from 1 to 10 inches, in the adjacent area. In the present paper the name “Swan Creek phosphate” is not used. The bed so identi— fied by Safiord and Killebrew is the basal sandstone of the Gassaway member. The Hardin sandstone of Safford and Killebrew (1900, p. 104, 137) is the lower division of Safl'ord’s (1869) “Black shale group.” Hayes and Ulrich’s (1903) Chattanooga shale— which they also refer to as the “Chattanooga forma- tion”—is the “Chattanooga black shale” of Hayes (1891). As so defined, their Chattanooga shale includes Safl’ord and Killebrew’s (1900) Maury green shale, Black shale (Chattanooga shale), Swan Creek phosphate, and Hardin sandstone. Hayes and Ulrich (1903, ex- planation of correlation table) classified the Chatta— nooga shale as Devonian, stating that it “seems to represent the whole of, and perhaps more than, the upper Devonian deposits of Pennsylvania and New York.” Ulrich (1905, p. 24, 25) suggested that the Devonian black shale should be called the Ohio shale because that name had priority over other geographic names in- cluding Chattanooga shale and New Albany shale. Also, he divided the Mississippian into two divisions of undesignated rank: the Tennessean, which included Chester and Meramec rocks, and the Waverlyan, which included Osage and Kinderhook rocks. Grabau (1906, p. 612, 613) regarded the “Black shale” of the southern United States as a basal deposit—a residual soil of an ancient peneplain, very fine and very carbonaceous, and the result in many places of the solution of calcareous strata. [He believed that] this soil was worked over by the transgressing Mississippian sea, which re- arranged it, washed it from the higher points, and collected it in greater thickness in the depressions of the old peneplain. As the water deepened, deposition of calcareous shales or of lime— stones followed, the transition being a perfect one—sometimes gradual, sometimes abrupt. Grabau held that the name Ohio shale—of Late Devon- ian age—could not be used for the transgressive “Black shale” of the southern United States. He suggested that the name “Chattanooga shale” might be used if it CHATTANOOGA SHALE AND MAURY FORMATION were “dissociated from the idea of any definite age relations.” In 1911 Ulrich proposed a new classification of the Paleozoic. In this classification Mississippian rocks were assigned either to the Tennessean system, which included those of Meramec and Chester ages, or to the Waverlyan system, which included those of Kinder- hook and Osage ages. Ulrich refused to accept such stratigraphic concepts as facies faunas and lithofacies; moreover he was of the opinion that the geologic sys- tems should be delimited by widespread pronounced unconformities. Because of these views, Ulrich pro- posed that a new series—the Chattanoogan—be in- serted into the Waverlyan system below the Kinder— hookian. The general time scale of the Waverlyan according to Ulrich (1911, pl. 29) and the formations in middle Tennessee assigned to that system follow: General time scale Middle Tennessee formations Waverlyan: Osagian: Keokuk Late Burlington Early Burlington Fern Glen Kinderhookian: Chouteau Hannibal Glen Park Louisiana Chattanoogan: Sunbury Berea Bedford Cleveland By 1911 Ulrich’s (1911, p. 426) studies had led him to believe that much of the black-shale sequence of the interior of the United States is post-Devonian, for, with the exception of “the lower part of the ‘New Albany shale,’ which is probably of Devonian age,” he knew of no deposits of unquestionable Late Devonian age in Kentucky, Tennessee, Arkansas, or Oklahoma. In 1911 Bassler (1911, p. 214) also considered the Chattanooga shale and its thin basal sandstonefi identified as the Hardin sandstone member—as the first post-Devonian deposit of central Tennessee. The basal sandstone was reported to contain reworked silicified fossils of Ordovician, Silurian, and Devonian ages in addition to many specimens of fish teeth and conodonts that Bassler thought are like those that Newberry (1875) had found in the Cleveland shale of Ohio. A similar conodont fauna was believed (Bassler, 1911, p. 214) to be present in the black-shale portion of the Chattanooga shale. ,Bassler believed that two Tennessee formations of Waverlyan age had been deposited in a number of closely spaced embayments. He (Bassler, 1911, 1). Fort Payne chert New Providence shale Tullahoma of Hayes and Ulrich Ridgetop shale Maury shale Black shale Chatta- nooga Hardin sandstone PREVIOUS WORK 5 216) proposed the name “Ridgetop shale” for the older formation and designated the outcrops along the Louisville and Nashville Railroad between Bakers in Davidson County and Ridgetop in Robertson County as the type locality. The Ridgetop shale according to Bassler (1911, p. 223) is early Kinderhookian. The New Providence shale is the other Waverlyan formation that Bassler believed was deposited in a number of embayments. He (1911, p. 218—220, 223) was of the opinion that the formation is early Osagian and regarded the exposures at Whites Creek Springs (Crocker Springs), Davidson County, Tenn., as the most “important Waverlyan section of Tennessee.” Kindle (1912b) believed that it is possible to have different contemporaneous faunas and distinct lithofacies represented in the rocks of the same basin of deposition; and instead of accepting the idea that the Chattanooga shale is Mississippian because it is separated from the underlying rocks by a widespread unconformity, Kindle placed most of the black-shale sequence of the eastern United States in the Devonian. According to Kindle (1912a, p. 136) the hiatus at the base of the Chattanooga shale represents the early Genesee, the late Hamilton, or both. Kindle (1912a, p. 130—135) believed that so far as the Chattanooga shale is concerned, Bassler’s (1911) paper on “The Waverlyan period of Tennessee” can be reduced to the following three propositions: 1. The Chattanooga shale of central Tennessee is distinct from the black shales designated as the Chatta— nooga shale in the U. S. Geological Survey folios of eastern Tennessee. Kindle rejected this proposition; he regarded the black shales of central and eastern Tennessee as correlatives and as Devonian in age. General time scale Ohio section Waverlyan: Osagian Kinderhookian Chattanoogan: Sunbury Sunbury shale Berea Berea sandstone Bedford Bedford shale Cleveland Cleveland shale Olmsted Olmsted shale Huron Huron shale Devonian: Neodevonian: Chemung Chagrin formation Portage (? break) Genesee ? Genesee shale Ulrich (1912, p. 158) did not believe that the Cleve- land-Olmsted-Huron sequence could be a black litho- facies which grades eastward into the gray, Upper Devonian, Chagrin shale—a view held at least in part by many geologists, including Prosser (1912, p. 515—518), Kindle (1912b), Kindle (in Prosser, 1912, p. 518), and 366719—56—2 His opinion was based on his finding identical conodont faunas in the shales of the two areas. 2. The Chattanooga shale is a correlative of the Cleveland shale of Ohio. Kindle did not take issue with this proposition, but stated that, in his opinion, the Chattanooga shale is probably a correlative not only of the Cleveland shale othio but also “of much of the remainder of the Ohio shale as well.” 3. The Cleveland shale of Ohio is of Waverlyan age. Kindle disagreed with this proposition. According to Kindle, the evidence, submitted by Newberry and re- stated by Bassler, in support of a Waverlyan age for the Cleveland shale is incorrect. That age designation was based in part on the reported presence of Carboni- ferous fishes in the Cleveland shale; but, according to Kindle, such fishes have not been found by subsequent workers. Instead, Kindle claimed some of the Cleve— land fishes are similar to those present in rocks of accepted Devonian age. As for the conodont fauna of the Cleveland shale, which Bassler claimed is also in the Chattanooga shale of central Tennessee, Kindle stated that the recorded evidence indicated a Devonian age. Ulrich (1912, p. 157, 162, 164) regarded diastrophism as the ultimate basis for the division of the geologic column into systems. He clarified his stand on the time- stratigraphic limits of the Chattanoogan series, stating that the Cleveland shale, as previously delimited by him, consists of the Cleveland shale, Olmsted shale, and Huron shale of other authors—that is, the Chattanoogan series embraces the formations from the base of the Huron shale to the top of the Sunbury shale. These forma- tions and their correlatives in Tennessee, according to Ulrich, are given below. Tennessee seclion g3” Sunbury shale equivalent 0 O a: a“: 73 ‘3 33 i a: F: . O 7 Cleveland shale equivalent G. A. Cooper (Cooper and others, 1942, p. 1764). Instead, Ulrich (1912, p. 159, 166) held that the Cleveland—Olmsted-Huron sequence wedges out east- ward on top of the Chagrin shale which in turn wedges out westward. The wedging out in different directions of these two rock sequences was due, in Ulrich’s 6 CHATTANOOGA SHALE AND MAURY FORMATION opinion (1912, p. 159), to a tilting of the North American Continent; this tilting permitted the sea to invade the Continent from the north-middle—Atlantic area in the Late Devonian and from the Gulf of Mexico in Chatta— noogan time. Ulrich (1912, p. 158) believed that there is a close and undeniable similarity in the conodont- and fish faunas 0f the Cleveland shale and the Huron shale—faunas which, he claimed, are quite unlike those “in the supposed intervening Chagrin shale.” However, his opinion regarding the close similarity of the cono— dont faunas of the Cleveland shale and the Huron shale is open to question. The writer (Hass, 1947a) has studied the conodont faunas of these two shales and has found them to be dissimilar. According to Ulrich (1912, p. 170, 171) In Tennessee, more particularly in the west middle part of the state, a . . . [time] break is indicated by the Maury shale, a thin glauconite bed often filled with phosphatized concretions, that probably represents surficial decomposition and subsequent recementation. This layer was referred to the top of the Chat- tanooga by Hayes and Ulrich [1903], which is correct if we con- sider chiefly the origin of its material. But if the date of its recementation and the fact that its top includes both reworked and transported material is brought into the foreground, the layer becomes debatable ground. On the latter grounds, I [Ulrich] take it, Safford [and Killebrew, [1900], and more recently Bassler [1911], have classified the Mau‘ry shale as post-Chatta- noogan. Ulrich did not favor this classification. On practical grounds he preferred to place the Maury green shale of Safi'ord and Killebrew (1900) in the Chattanooga shale, instead of regarding it as the recemented basal deposit of the immediately overlying formation. Otherwise, he claimed, the age of the Maury, even in the same general area, would differ from outcrop to outcrop. For example, where directly overlain by the Ridgetop shale, the recemented Maury would be of early Kinder- hook age; where directly overlain by the New Provi- dence shale, it would be of early Osage age; and where directly overlain by the Fort Payne chert, it would be of late Osage age. To Ulrich (1912, p. 162) the term “Chattanooga shale” as used by many of his contemporaries refers to the entire black-shale sequence present “between the middle Devonian and the first limy or sandy beds of the Mississippian.” In Ulrich’s opinion, the following two distinct groups of black shales are present within this interval: 1. A younger group of Waverlyan age, which includes the Chattanooga shale of the middle Tennessee area. 2. An older group of Devonian age, of which the Genesee segment is the most important. Although Ulrich (1912, p. 164, 166, 167) believed that representatives of both groups are probably in Ken- tucky, he was of the opinion that only the upper part of the younger group (Cleveland shale and Sunbury shale equivalents) is in central Tennessee. The Hardin sandstone was considered to be the transgressive basal bed of the Chattanooga shale. Drake (1914), in his paper on the economic geology of the Waynesboro quadrangle in Tennessee considered the Chattanooga shale and the Hardin sandstone mem— ber to be of Late Devonian age. He referred to the Maury green shale of Safford and Killebrew (1900) as the Maury glauconitic member of the Ridgetop shale and believed it rested unconformably upon either the Chattanooga shale or the Hardin sandstone member. In 1915, Ulrich (1915, p. 96—99) stated that his ”Chattanoogan is approximately contemporaneous with the Kinderhookian series.” The presence of a widespread unconformity beneath the Chattanooga shale was cited as evidence for placing that formation in the Mississippian. Also, he regarded the Ridgetop shale of Tennessee as of late Kinderhook age—rather than early, as previously held—and stated that inas— much as the Ridgetop grades into the underlying Chattanooga shale, the latter formation is inferred to be “at least in part, of early Mississippian age.” Shaw and Mather (1919, p. 48—51) reported on the Chattanooga shale in Allen County, Ky. In their paper, the shale was classified as Devonian. They pub- lished a paleontological report by Ulrich, who stated that the fossils from an upper horizon of the Chat- tanooga shale indicate an early Mississippian (Berea “grit” and Sunbury shale) age, and those from a lower horizon indicate a possible “late Devonian but more probably [a] very early Mississippian (Cleveland shale) age.” Ulrich identified Lingula cf. L. subspatulata [probably = Barroisella campbelli Cooper], ?Pseud0— bornia, “Sporangites huronensis” [Tasmanites humm— ensis (Dawson)], and conodonts in a collection from the lower part of the Chattanooga shale; and Lingula, melie, Orbiculoidea newberryi, and conodonts in collections from the upper part of the shale. He also reported on some fossils that were collected by Wallace Lee and Mather from a thin conglomeratic sandstone at an exposure on “Bledsoe Creek, 2 or 3 miles north of Bransford,” Sumner County, Tenn. (See Mather, 1920, p. 19, 20.) This sandstone is Campbell’s (1946) Bransford sand— stone member of his Gassaway formation. Ulrich recognized some fish bones and teeth, including a Cladodus tooth, and two species of Lingula in the collec— tion from the sandstone in addition to conodonts which he stated are like those “commonly found in the Cleve- land shale in Ohio, in the lower and middle parts of the Chattanooga shale in the Appalachian region, and in the phosphatic basal deposit of the same formation in central Tennessee.” He suggested that the sandstone might represent a part of the Berea sandstone of Ohio. PREVIOUS WORK 7 Shaw and Mather’s report on Allen County, Ky., was followed by Mather’s (1920) paper on an adjoining area in Sumner County, Tenn. In Mather’s paper the Chattanooga shale was officially classified by the United States Geological Survey and the State Geo- logical Survey of Tennessee as Devonian or Carbon— iferous; but Mather (1920, p. 19) personally considered the Chattanooga shale of northern Tennessee and southern Kentucky to be of early Mississippian age. He stated that the black-shale sequence consists of two divisions or formations: “the lower of these formations may be of Devonian age, but the upper, in the writer’s [Mather’s] opinion, must be considered Mississippian . ’ ’ Miser (1921, p. 16, 23, 24) classified the Chattanooga shale as Devonian or Carboniferous. He considered the Hardin sandstone to be a member of the Chat- tanooga shale and placed the Maury glauconitic mem- ber of the Ridgetop shale in the Carboniferous. Swartz (1924, p. 24) proposed the name “Glendale shale” for “a thin, hard, gray shale crowded with Lingula melie” that overlies the Chattanooga shale and underlies the Fort Payne chert in the vicinity of Chattanooga, Tenn. The Glendale shale of Swartz is considered herein to be the upper division of Hayes’ (1891, 1892, 1894a, 1894b, 1984c, 1894d, 1895) “Chattanooga black shale,” and the Maury green shale of Stafford and Killebrew (1900). Swartz, however, was of the opinion that his Glendale shale consists of beds which, prior to his work, had been included in the Fort Payne chert. He correlated his Glendale with the lower part of the Cuyahoga shale of Ohio; this correlation was based on the presence in both formations of numerous phos- phatic brachiopods, identified as Lingula melie. He (1924, p.24—26) regarded an exposure near Apison, Tenn, as important for determining the age and cor- relatives of the Chattanooga shale. His section is given below: ' Ft. Payne chert. peg; Hard gray shale, full of concretions, becoming much darker towards the base. From 4 to 6 inches above the base are found Lingula melie abundant ,,,,,,,,,,,,,,,,,,,,, 1,. .............. 2 11 Black shale ,,,,,,,,,,,,,,,, . ____________________ 2 10% Light to somewhat dark gray clay shale, contain- ing, about 6 inches above the base, Lingula 17rm'nensis, Orbiculoidea ovate var. transverse 11. var., Schuchertella sp., Rhipidomella sp., Chonetes acutz‘liratus Girty, and a poorly preserved rhyn- Inches chonelliform brachiopod ,,,,,,,,,,,,,,,,,,,,,, 1 10 Black shale ___________________________________ 10 8 Very argillaceous sandstone ____________________ 4 Rockwood formation: gray, greenish, and buff arenaceous shale and argillaceous sandstone. Swartz’s (1924, p. 25, 26) remarks on the Apison section follow: The fossiliferous gray shale 0f the above section furnishes the“ key to the situation. Chonetes acutiliratus Girty (in manu— script) was originally described from the Bedford shale of Ohio. The Rhipidomella sp. is very similar to if not identical with a form from the Bedford shale of Ohio also being described by Girty. Lingula irvinensis was originally described from the Bedford—Berea shale of Indian Fields, Kentucky. Both the fossils and lithology serve to identify it with the Bedford-Berea Wedge traced to east central Kentucky by Morse and Foerste in 1909. This correlation is further strengthened by its position between two black shales. , Swartz also wrote that the black shale immediately overlying the above-mentioned gray fossiliferous shale contains [the] abundant and characteristic Lingula melie. This fact, together with its position above a gray shale containing a Bedford—Berea fauna, and below a second gray shale which appears to represent the lower part of the Cuyahoga shale of Ohio, makes highly probable its correlation with the Sunbury shale of Ohio. The stratigraphic succession would also appear to demand the correlation of the lower black shale with the Cleveland shale of the Ohio section. Swartz (1924, p. 26) also investigated the type locality of the Chattanooga shale at the north end of Cameron Hill in Chattanooga, Tenn. His section is given below: Ft. Payne chert. Feet Glendale shale: hard gray shale with some concre— tions toward the base ______ . __________________ 2 4 Black shale ____________________________________ % Mottled brown and gray shale __________________ Black shale __________________________________ 8 0 Concealed. He (Swartz, 1924, p. 26) commented that Although no fossils were found in it, it is thought that the mottled shale probably represents the Bedford-Berea interval. In that event the overlying % inch black shale is all that is left of the Sunbury shale of the Apison section. The main mass of the shale at the type locality is thus of Cleveland age. Inches As for the Maury shale of central and western Tennessee, Swartz (1924, p. 28, 29) stated that it is separated from the Chattanooga shale by “a marked unconformity” and that it is older in central Tennessee where, at Eulie, Sumner County [sic] it contains fossils of Hamburg oolite age, than in western Tennessee where, at Linden, Perry County, it contains “in addi— tion to Ridgetop forms, a number of species hitherto known only from the basal Ft. Payne chert.” Ulrich and Bassler (1926) published a descriptive paper on the conodont, faunas of two formations: the Rhinestreet shale (=Aittica shale of Chadwick, 1923) at Shaletown, Erie County, N. Y., and the basal sand- stone of the Chattanooga shale at Mount Pleasant, Maury County, Tenn. (vicinity of locality 154 of pres- ent paper), which they considered to be the Hardin sandstone. The paleontologic data published by Ulrich and Bassler are intended to support their opinion that two groups of beds are involved in the black-shale 8 CHATTANOOGA SHALE AND MAURY FORMATION problem: an older group of Devonian age and a younger one, which includes the Chattanooga shale, of early hlississippian age. Among the conodonts Ulrich and Bassler (1926) described from the basal sandstone at Mount Pleasant, Tenn, the following are regarded by the present writer to be characteristic of the Upper Devonian Gassaway member of the Chattanooga shale (fig. 1): Names used in present paper Ancyrognathus bifurcata (1,71— rich and Bassler) Palmatolepis glabra Ulrich and Bassler Names used by Ulrich and Bassler, 1996‘ Palmatolepis bifurcata Ulrich and Bassler Palmatolepis glaber Ulrich and Bassler Palmatolepis perlobata Ulrich and Bassler Palmatolepis extralobata Ulrich and Bassler Palmatolepis peculiaris Ulrich and Bassler Polygnathas confluens Ulrich and Bassler Palmatolepis perlobata Ulrich and Bassler Polylophodonta confluens (1,71- rich and Bassler) Ulrich and Bassler’s Rhinestreet shale (=Attica shale of Chadwick, 1923) conodont fauna includes Prioniodus alatas Hinde. This species is in the lower— most beds of the Upper Devonian Dowelltown member of the Chattanooga shale. In Butts’ (1926) paper, the Chattanooga shale of Alabama was officially classified by the United States Geological Survey and the Geological Survey of Ala— bama as Devonian or Carboniferous. Butts (1926, p. 161), however, classified the Chattanooga shale of southwestern Tennessee and Alabama as Mississippian and correlated it with the Sunbury shale of Ohio; how- ever, the explanation of plate 48 of his paper states that the black-shale fossils illustrated on that plate occur in the Cleveland shale as well as in the Sunbury shale. Butts’ conodonts were collected at Quicks Mill, about 4 miles west of New Market, Madison County, Ala. (locality 127 of present paper). Among those he illustrated are Ancyrognathas bifurcata (Ulrich and Bassler), Palmatodella delicatala Bassler, and Poly— lophodonta confluens (Ulrich and Bassler). These conodonts have not been found by the present writer in either the Cleveland member of the Ohio shale (for- merly Cleveland shale) or the Sunbury shale, but they have been found by him in the Huron member of the Ohio shale. The conodonts illustrated by Butts (1926) were later described and figured by Holmes (1928). Swartz (1927) reported on the black-shale sequence of eastern Tennessee and the adjacent part of Virginia. He considered his Chattanooga shale of that area“ which corresponds to the upper black-shale unit of Campbell’s (1894) “Chattanooga black shale” and to the Big Stone Gap shale of Stose (1923)—t0 be partly of Devonian and partly of Mississippian age and divided it into an upper and a lower black shale and a middle gray shale. Swartz proposed the following names for his divisions: Big Stone Gap member (youngest) Olinger member Cumberland Gap member (oldest) Swartz also held (1927, p. 494, 499) that the name Big Stone Gap shale of Stose (1923) must be abandoned, because it refers to beds considered by Swartz to be the exact equivalent of the Chattanooga shale 0f the type area. However, believing that Stose’s name should be preserved, Swartz (1927, p. 494) proposed that it be redefined so as to apply only to the upper member of Swartz’s Chattanooga shale. According to Swartz (1927, p. 498) a well-marked unconformity / separates his Big Stone Gap member from his Olinger member throughout southeastern Tennessee; he (1927, p. 497) also stated that his “Olinger member was deposited concomitantly with the upper part of the Cumberland Gap member.” In discussing the sections he published in 1924, Swartz (1927) stated that all three members of his Chattanooga shale are at the type locality of the forma- tion on Cameron Hill as well as at the locality near Apison. His assignment of the beds at. these two localities follows: Type locality of Chattanooga shale, north end of Cameron Hill, Chattanooga, Hamilton County, Tenn. [Swartz, 1927, p. 486, modified by present writer] Chattanooga shale: Big Stone Gap member: Feet Inches Black shale ,,,,,,,,,,,,,,,,,,,,,,,,,,, 0 9/; Unconformity. Olinger member: Gray clay shale _______________________ 0—9 Cumberland Gap member: Black shale __________________________ 8 0 Sertion near Apison, approximately 16 miles east of Chattanooga, Hamilton Counti, Tenn. [Swartz, 1927, p. 485, modified by present writer] Chattanooga shale: Big Stone Gap member: Feet Black shale with Lingula melie _________ 2 Unconformity. Olinger member: Gray clay shale with Lingula irvinensis, Rhipidomella sp., and abundant Cho- netes acutiliratus? ___________________ 1 10 Cumberland Gap member: Black shale ___________________________ 10 8 Inches 10% Holmes (1928) described a conodont fauna from the Chattanooga shale at Quicks Mill, Madison County, Ala. (locality 127 of present paper). She regarded the Chattanooga shale as of Mississippian age. Among PREVIOUS WORK 9 the conodonts she described, the writer of this paper regards the following species as characteristic of the Upper Devonian Gassaway member of the Chatta- nooga shale (fig. 1): ' Names used in present paper Palmatolepis glabra Ulrich and Bassler Palmatolepis perlobata Ulrich and Bassler Names used by Holmes, 1928 Palmatolepis elongata Holmes Palmatolepis perlobata Ulrich and Bassler Polygnathus gyratilineata Holmes Polggnathus pergyrata Holmes Polygnathus trilobata Holmes Polygnathus concentrica Ulrich and Bassler Polygnathas rhomboidea Ulrich and Bassler Palmatolepis inequalis Holmes Polylophodonta confluens Ul— rich and Bassler Ancyrognathus bifurcata (Ul— rich and Bassler) Palmatodella delicatula Bass- Palmatodella delicatula Ulrich ler and Bassler Morse (1928) named the black-shale sequence of northeast Mississippi the Whetstone Branch shale. This formation was described as consisting chiefly of black shale together with some sandy shales and a few sandstones. Morse (1928, p. 36) found Lingula sp., Tentaculites sp., and other fossils in the shale and con- cluded that because of the fossils, and especially because of its unconformable relation to other beds of more definite age, the Whetstone Branch formation is referred to the Devonian. It belongs, therefore, to the lower and greater part of the Chattanooga shale of the type locality. Swartz later (1929) reported more fully on the Chattanooga shale of northeastern Tennessee and the adjacent part of Virginia, and (1929, p. 447, 448) con- cluded ‘ that the Chattanooga shale in Tennessee and Virginia, with the possible exception of the lower part of the Cumberland Gap member, is M ississippian throughout. This is especially true in the type area about Chattanooga where the Cumberland Gap member, which there comprises almost the entire Chattanooga shale, is represented by its upper part only, the part which intertongues with the Mississippian Olinger member. Savage (1930) identified the black-shale sequence of Kentucky with the New Albany shale. He (1930, p. 16-21) listed some of the fossils in the black shales and stated that these fossils indicate a Late Devonian (Tully and Genesee) age. Pohl (1930a, p. 62) considered some of the black shales of northern Tennessee to be of Genesee age, but stated that “because of the unestablished relations of the Genesee equivalent in Tennessee the name Trous- dale shale is here tentatively proposed for” these 1 The italics are Swartz’s. shales. Later, he (1930b, p. 152) suggested a correla- tion of the Trousdale with the “Genesee-Portage black shales of the northeastern Devonian.” Pohl (1930b, p. 151) also stated that the term “Chattanooga shale” cannot be used to refer to the entire black-shale - sequence because the type Chattanooga shale, according to Swartz, is Mississippian. He, therefore, proposed to restrict the name “Chattanooga shale” to deposits of "post-Devonian—pre—Osage" age. Pohl’s (1930b) classification of the black-shale sequence of central Tennessee follows: Mississippian: Kinderhookian: Chattanooga shale (widespread occurrence): Upper black shale; a correlative of the Sunbury shale of Ohio and Kentucky. Widespread unconformity representing the Berea sandstone and Bedford shale interval of Ohio and Kentucky. Lower black shale; a correlative of the Cleveland shale of Ohio and Kentucky. Upper Devonian: Trousdale shale (local occurrence): a correlative 0f Genesee and Portage rocks of the northeastern States. Morse (1930) published a second paper on the black shale of northeast Mississippi. Previously he (1928) had named this shale, the Whetstone Branch shale, had correlated it with a part of the Chattanooga shale, and had classified it as Devonian. Morse’s conclusions were based partly on fossils—which include Tentacnlites— and partly on the supposed presence of an important widespread unconformity at the top of the Whetstone Branch shale. Morse (1928) named the overlying formation the Carmack limestone and considered it to be of Mississippian age. He (1930, p. 72) stated that the basal foot of his Carmack limestone consists “of long flat shalelike pebbles in a dark matrix of oolitic and green sand texture. Some of the larger rounded masses may be concretions instead of pebbles, and some of them give the test for phosphate.” This. description suggests that the basal bed of the Carmack limestone of Morse is the upper division of Safl’ord’s (1869) black—shale sequence, the upper unit of Hayes’ (1891, 1892, 1894a, 1894b, 1894c, 1894d, 1895) “Chat— tanooga black shale,” and the Maury green shale of Safford and Killebrew (1900). Jewell (1931, p. 22, 37), because of his work in Hardin County, Tenn, considered the “Chattanooga forma- tion” to be of Mississippian age and to consist of the Maury glauconitic member at the top, a Black shale member, and the Hardin sandstone member at the base. He (1931, p. 38) held that the Chattanooga. is set off by unconformities from the adjacent formations and regarded the break at the base of the Chattanooga 10 CHATTANOOGA SHALE AND MAURY FORMATION as more important than the one at the top. Jewell (1931, p. 41) placed the Maury glauconitic member in the “Chattanooga formation” instead of in the over- lying Ridgetop shale because to him the Maury seems to be absent throughout most of Hardin County. Jewell argued that if the Maury were the basal bed of the Ridgetop shale, its geographic distribution should conform closely with that of the Ridgetop shale. As a result of their work in south—central Kentucky, Savage and Sutton (1931) considered the black-shale sequence of that State tobe chiefly of Late Devonian age, though partly of early Mississippian (Kinderhook) age. In their opinion the Upper Devonian portion is widespread in its occurrence; it contains beds of Tully and Genesee ages and, in addition, may include younger Devonian beds. .They stated that in south—central Kentucky the Mississippian portion of the black—shale sequence—which contains megafossils—is restricted in its occurrence and lies unconformably uponvthe Devo— nian black shales. In 1932, in keeping with the philosophical concepts expressed in his 1911 paper, Bassler stated (1932, p. 7) “that many of the important formations [in central Tennessee] are restricted to small areas and . thin out along the old shore lines instead of passing laterally into diflerent rock types holding distinct fossils.” In the same paper (1932, p. 136 passim) he also classified the Chattanooga shale and the Hardin sandstone member in the areas he mapped as lowermost Mississippian and placed both stratigraphic units in the “Chattanooga group.” He (1932, p. 143) believed that the “Maury green shale” represents the introductory stage of whatever formation directly overlies it—that is, at some localities, as at Bakers Station, Davidson County (Bassler, 1932, p. 140), the Maury is in the basal Ridgetop shale and is of Kinderhook age; at other localities, as at Whites Creek Springs (Crocker Springs), Davidson County (1932, p. 147), it isin the basal New Providence shale and is of early Osage age; and at still other localities (1932, p. 179), it is in the basal Fort Payne chert and is of late Osage age. Bass— ler further mentioned (1932, p. 133) that “in northern Tennessee the lower part of the Black shale is separated from the upper by a well-marked unconformity and, moreover, contains Devonian fossils. This Devonian part of the shale does not apparently extend southward over the Nashville Dome to any great distance.” On figure 4 of Bassler’s (1932) paper, this Devonian black shale is called the “Chattanooga shale (lower)” in order to distinguish it from his Mississippian or “Chat- tanooga shale (upper)” black shale. Also on figure 4, Bassler shows the Hardin sandstone as a transgressive sandstone that is partly of Devonian age and partly of early M ississippian age. According to Wilson and Spain (1936) the Ridgetop shale is not a valid stratigraphic unit; in their opinion, it is merely a phase of the New Providence shale and is of early Osage (Fern Glen) age. Their opinion was based on field and faunal studies. Wilson and Spain classified the “Maury shale” as a member of the Chat- tanooga shale. Klepser (1937, p. 187) thought that “the Chattanooga and Maury formations are merely facies develop— ments or shore phases of the New Providence, Fort Payne, and possibly Warsaw formations. They be— come increasingly younger toward the south.” Stock— dale’s (1939, p. 54,55) opinions are similar to those of Klepser (1937). “Because of the established facies relationships of the Devonian of New York and Pennsylvania,” Cooper (Cooper and others, 1942, p. 1736) regarded “much of the black shale of Ohio, Indiana, Kentucky, Illinois, and Michigan” as Devonian; but he was unde- cided as to how some of the black shale of the southern States should be classified and, therefore, on the correla- tion chart that accompanies the paper, he placed most of the Chattanooga shale and the Hardin sandstone of west Tennessee in the Devonian or Mississippian. He regarded the Trousdale shale of Pohl as late Middle Devonian and correlated it with the Geneseo shale of New York. Guy Campbell (1946) has published a comprehen- sive paper on the stratigraphy of the Devonian and Mississippian black shales'of the eastern interior of the United States. His (1946, p. 881 passim) classification for central Tennessee follows: Maury shale: Mississippian (Osage): Considered to be the basal bed of the Fort Payne chert and the New Providence shale. Chattanooga shale: Mississippian (Kinderhook): Westmoreland shale Eulie shale Gassaway formation: Bransford sandstone member Upper Devonian: DOWelltown formation: Hardin sandstone member Middle Devonian: Trousdale formation Campbell named all the above-listed divisions of the Chattanooga shale with the exception of the Trousdale and the Hardin sandstone. Campbell’s Trousdale formation is the Trousdale shale of Pohl. Pohl (1930b) considered his formation to be of Late Devonian (Genesee—Portage) age, but Campbell, as did Cooper (Cooper and others, 1942, chart 4), preferred to assign the formation to the late Middle Devonian. In the present report the name “Trousdale formation” » PREVIOUS WORK 1 1 or “Trousdale shale” is not used; beds so identified by Campbell, Pohl, and Cooper are placed in the Upper Devonian Dowelltown member of the Chattanooga shale. The type localities of Campbell’s (1946, p. 886) Dowelltown and Gassaway formations are located along the Eastern Highland Rim of central Tennessee: the Dowelltown is in DeKalb County, the Gassaway in Cannon County. Campbell placed his Dowelltown formation in the Upper Devonian and his Gassaway formation in the lower Mississippian. In the present report the Dowelltown and the Gassaway are both classified as Upper Devonian and are considered to be members of the Chattanooga shale rather than distinct formations. Campbell stated (1946, p. 883) that to the east of the Central Basin, in DeKalb County and adjacent territory, the Dowelltown shows deposition under normal con- ditions for the formation and consists of a lower and an upper member, each with a lower bed of fissile black shale and an upper bed with interbedded layers of gray and black shale. The two members are delimited by Barroisella n. sp. and Spathiocaris, which occur in the lower member but not in the upper. This is in harmony with the characters of the Blackiston [formation] in Indiana. ‘The Hardin sandstone according to Campbell (1946, p. 881, 892) is the basal sandstone member of his Dowell- town formation. Campbell (1946, p. 881, 884) correlated his Gassaway formation with his Sanderson formation, stating that its “only change in character from the Sanderson of Kentucky and Indiana is in the addition of a layer of sandstone at the base.” The Bransford sandstone member of Campbell is at the base of his Gassaway formation throughout the northwestern part of the Nashville Basin. At its type locality on Bledsoe Creek, 3.6 miles north of Bransford, Sumner County, Tenn., the Bransford sandstone is as much as 0.25 foot thick and consists of very—light-gray to dark-gray iron-oxide- stained unsorted rounded grains of quartz sand together with bone fragments, teeth, conodonts, and iron sulfide grains and nodules. The Bransford sandstone, accord- ing to Campbell (1946, p. 884), occurs “at the level of the marked faunal break between the Blackiston and Sand— erson [formations] in Indiana and at the level of the lithic break between the Olmsted and Cleveland [shales] in Ohio.” In Shaw and Mather (1919) and Mather (1920), Ulrich said that this sandstone might correlate with the Berea sandstone of Ohio; and Pohl (1930b) believed that it occurs at the level of an unconformity which corresponds to the Berea sandstone and Bedford shale interval of Ohio. The name “Bransford sandstone” is not used in the present paper; the bed so designated by Campbell is not named. Campbell’s Eulie shale and Westmoreland shale are thin beds that crop out in the vicinity of eastern Sumner County, Tenn. The Eulie shale is a gray to greenish—gray mudstone that contains phosphatic nod- ules. Campbell held that this shale is of early Mississip— pian age, but the present writer classifies it as very late Devonian. The Westmoreland shale is a grayish- black shale which locally contains phosphatic nodules. Campbell, as does the writer, classified this bed as early Mississipian. The names “Eulie shale” and “West- moreland shale” are not used herein; the beds so named by Campbell are placed in the Maury formation and are not named. The writer, in an abstract entitled The Chattanooga shale type area (1947b, p. 1189), stated that the Chatta— nooga shale in the vicinity of Chattanooga, Tenn., consists of an upper and a lower black shale and a middle gray shale. He wrote: At the Apison locality [locality 228, see p. 36], the upper black shale member contains lower Mississippian conodonts and is correlated with the Sunbury shale of Ohio. The lower black shale member . , . contains conodonts that correlate it with the Huron shale of Ohio, a formation that the U. S. Geological Survey classifies as Upper Devonian. The middle gray shale member contains Huron conodonts, but its age is equivocal as J. H. Swartz has reported macrofossils from it which he con- sidered to be of early Mississippian age. . . . The presence'of Huron conodonts in the lower black shale member of the Chatta- nooga disproves the thesis, held by some workers, that, as a unit, the Chattanooga shale is younger than the black shale sequence of the N orth-Central States. Herein, the above—mentioned upper black shale is placed in the Maury formation and the middle gray shale and the lower black shale in the Upper Devonian Gassaway member of the Chattanooga shale. Stockdale (1948, p. 265, 266) regarded the Chatta- nooga shale as a time-transgressing unit that resulted from the deposition of near-shore sediments in a south- ward advancing sea. He published the above quota- tion from Hass (1947b) and argued against the strati— graphic usefulness of conodonts, suggesting in the form of a question that they are facies fossils that “might have remained unchanged throughout a considerable span of time and might now be found as a fossil assem- blage coextensive with the given lithologic, time- transgressing unit.” According to Weller and others (1948, chart 5, column 86) the Chattanooga shale of central Tennessee consists of two parts. Rocks of the lower part are of Late Devonian age and rocks of the upper part are partly of Mississippian or Devonian (Fabius group of their Kinderhookian series) age and partly of Missis— sippian (Easley group of their Kinderhookian series) age. The authors (1948, p. 105) commented on the CHATTANOOGA SHALE AND MAURY FORMATION TABLE 1.~Standard section of the Chattanooga shale System Series Formation Informal field names Thickness (feet) Description Fort Payne chert MISSISSIPPIAN Maury formation Limestone, light-gray,- numerous cherty beds 2.3 Mudstone, light- to medium-bluish-gray. Phosphatic nodules throughout interval; nodules in basal 0.4 ft embedded in olive-gray sandy matrix and classified as Upper Devonian DEVONIAN Upper Devonian Gassaway member Top black shale 6.9 Shale, grayish-black, carbonaceous, tough; iron sulfides common as grains, nodules, and lenses. Phos- phatic nodules present in topmost 0.45 ft. They are embedded in black shale and separated from underlying beds of unit by a 0.04 ft thick olive- gray sandstone Upper black shale Upper gray beds 2.3 Shale, grayish-black, carbonaceous, tough; interbedded with thin gray mudstone beds. A finely laminated bed, 0.13 ft thick, at base Middle black shale 7.5 Shale, grayish-black, carbonaceous, tough Chattanooga shale Dowelltown member Middle gray beds 9.2 Mudstone; consists of alternating, thin, greenish-gray, grayish—olive, and grayish—brown beds together with a few thin grayish-black shale beds. A bentonite bed, 0.09 ft thick, is present 0.82 - 0.91 ft bel‘ow top Lower black shale 6.2 Shale, grayish-black, carbonaceous, tough. A basal sandstone, as much as 0.2 ft thick, may be present; it is grayish black, poorly sorted, and consists chiefly of rounded grains of quartz sand ORDO- VICIAN Limestone, gray CHATTANOOGA SHALE 13 widespread occurrence of an unconformity at the base of the black-shale sequence; stating that if diastrophism is accepted as the ultimate basis for the sub- division of geologic time, and if plants and animals are believed to have altered in response to the resulting physical changes, a good case can be made for accepting this unconformity as the [Devonian and Mississippian] systemic boundary. It is evident from the above resumé that the age and correlation of the Chattanooga shale have been con- troversial subjects for many years. Ellison (1946, p. 102) summarized the status of the problem as follows: there exist three present-day interpretations of the age of the Chattanooga and its equivalents. The paleobotanists, some conodont workers, and the United States Geological Survey geologists have much evidence that these formations are in the greater part Devonian in age. A number of Workers, including some petroleum geologists and a few State Geological Survey men, prefer to remain neutral and classify the Chattanooga problem as Mississippian-Devonian. Many petroleum geolo- gists, some conodont workers, and a number of State Geological Survey men believe that these beds are definitely Mississippian in age. CHATTANOOGA SHALE Hayes (1891, p. 142, 143) proposed the name “Chatta- nooga black shale” as a substitute for Smith’s (1878, 1890) and SafI’ord’s (1869) nongeographic term “Black shale.” The first reference to the Chattanooga shale is brief. It appears as part of the descriptive matter of a geologic column and indicates that the “Chatta— nooga black shale” is of Devonian age, that it is overlain by the Fort Payne chert of Carboniferous age and underlain by the Rockwood formation of Silurian age, and that it is as much as 35 feet thick. Hayes’ (1892, 1894a, 1894b, 1894c, 1894d, 1895) “Chattanooga black shale” consists of two lithologic units: an upper gray shale, 3 to 4 feet thick, which commonly contains a layer of concretions; and a lower black shale. Out— crops at the north end of Cameron Hill in Chattanooga, Tenn., were designated the'type locality. The best exposure at the type locality is pictured in plate 5. Swartz (1924, p. 24) named the upper gray —shale unit of Hayes’ “Chattanooga black shale” the Glendale shale. Swartz, however, was of the opinion that the beds he identified as Glendale were, prior to his work, a part? of the Fort Payne chert. The name “Glendale shale” is not used herein; beds so named by Swartz are called the Maury formation. STANDARD SECTION OF THE CHATTANOOGA SHALE The best exposures of the Chattanooga shale in central Tennessee are situated along the Eastern High- land Rim from Jackson County southward to Coffee and Bedford Counties. Throughout much of that area the Chattanooga shale is between 25 and 35 feet thick and at most localities consists of the lithologic divi- sions given in table 1. Because the type section of Campbell’s Dowelltown formation and the type sec- tion of his Gassaway formation—both herein reduced to the rank of members of the Chattanooga shale—are not exceptional exposures, and because the type locality of the Chattanooga shale on Cameron Hill in Chatta- nooga, Tenn., is a poor exposure (see pl. 5), a standard section for the Chattanooga shale has been proposed by L. C. Conant, V. E. Swanson, and the writer. This section is a cut on Tennessee Highway 26, at the east approach to the bridge over Caney Fork, 7.1 miles east of the courthouse at Smithville, DeKalb County, Tenn. The standard section is locality 76. (See table 1 for description.) The type locality of Campbell’s Dowelltown forma- tion (1946, p. 886) is given as “one and one half miles east of Dowelltown, DeKalb County, Tennessee.” No section was found at that distance east of the com- munity of Dowelltown, but there is an exposure, 3.1 miles east of Dowelltown, on the portion of Tennessee Highway 26 that was abandoned as the main highway in 1953. This exposure is taken to be Campbell’s type locality. The section given below was measured after the Chattanooga shale and the Maury formation inter- val had been completely exposed. The section is locality 95. Section 3.1 miles east of Dowelltown, Tenn. [See locality 95, pl. 1] Mississippian: Fort Payne chert. Maury formation (in part): Mudstone, yellowish-brown to bluish-gray, iron-oxide-stained, laminated; a few phosphatic nod- ules present __________________ Mudstone, olive-gray, laminated__ . 6 Shale, grayish-black, tough; with course of phosphatic nodules at Fee/5 top _________________________ . 2 Mudstone, iron-oxide-stained _____ . 1 Course of phosphatic nodules _____ . l Mudstone, greenish-gray, lam- inated, iron-oxide-stained ______ . 2 Devonian: Maury formation (in part): Course of large phosphatic nodules embedded in iron-oxide-stained mudstone ___________________ . 3 14 CHATTANOOGA SHALE AND MAURY FORMATION Section 3.1 miles east of Dowelltown, Tenn.——Continued Devonian—Continued Chattanooga shale: Gassaway member: Upper black shale: Top black shale: Fee; Shale, grayish-black, carbonaceous, tough; bedding undulating _____ Course of phosphatic nodules em- bedded in grayish-black shale-_ . 2 Shale, grayish—black, carbonaceous, tough; iron sulfides present as 0.3 grains and nodules ____________ . 2 Course of phosphatic nodules em- bedded in grayish-black shale" . 1 Shale, grayish-black, carbonaceous, laminated, tough; iron sulfides present as nodules, grains, and paper-thin layers ______________ Upper gray beds: Shale, grayish-black, carbonaceous, tough, with iron sulfides present as nodules, grains, and paper- thin layers; alternating with thin beds of grayish-olive to greenish- gray mudstone. The laminated bed, commonly present at the base of this unit, was not recognized ____________________ Middle black shale: Shale, grayish-black, carbonaceous, tough, with iron sulfides present as nodules, grains, and paper— thin layers ___________________ Dowelltown member: Middle gray beds: Mudstone, alternating thin green- ish-gray, grayish-olive, olive- gray, and grayish-brown beds together with a few thin grayish- black shale beds. A very light- gray iron-oxide-stained bentonite bed, 0.07 ft thick, present 0.53 to 0.60 ft below top ___________ Lower black shale: Shale, grayish-black, carbonaceous, tough; iron sulfides present as nodules, grains, and paper-thin layers; a few thin grayish-olive to greenish-gray siltstone beds- _ 5.8 2.2 4.2 7.9 Total ___________________ 30. 5 Ordovician. The thicknesses recorded above differ from Camp— bell’s (1946, p. 886) measurements. However, his description of the section is sufliciently detailed for one to determine that the limits of his type Dowell- town formation are as indicated in table 2. Thus, with reference to the lithologic divisions of the Chatta- nooga shale used in the present paper, Campbell’s type Dowelltownrincludes the beds from the base of the lower black shale to the top of the upper gray beds. Also, the beds Campbell assigned to his Gassaway formation belong to the top black shale, and those he identified as the Maury shale and “N eW Providence(?) soft blue shale” belong to the Maury formation. The type locality of Campbell’s (1946, p. 886) Gassa- way formation is “on [Tennessee] Highway 53, 5 miles south of Gassaway, Cannon County, Tennessee.” There are two exposures on Highway 53 within 0.4 mile of each other, one on the north side of a hill and the other on the south side of the same hill. Although it is not certain which outcrop is the type section of the Gassaway, the northern one is so taken because the upper black shale is better exposed there. The section given below is a composite one; the lower black shale and the middle gray beds were trenched and measured at the southern exposure, the upper black shale and the Maury formation at the northern outcrop. This is locality 100. Section 5 miles south of Gassawai , Tenn. [See locality 100, pl. 1] Mississippian: Fort Payne chert. Maury formation: Feet Mudstone, bluish-green, laminated; phosphatic nodules present, but not common. Topmost 0.6 ft contains glauconite ____________ Mudstone, greenish-gray; iron sul— fide nodule course present 0.15— 0.19 ft below top _____________ . 3 Mudstone, bluish—green; phos- phatic nodules present, espe- - cially at top __________________ . 8 Mudstone, greenish-gray, lami— nated _______________________ . 4 Shale, grayish—black, carbonaceous" . 35 Sandstone, iron—oxide-stained__ __ . 15 2.2 Devonian: Chattanooga shale: Gassaway member: Upper black shale: Top black shale: Shale, grayish-black, carbonaceous, very well laminated, tough; iron sulfides present as grains and nodules. Weathered outcrop is distinctly banded. N0 phos— phatic nodules in upper part of this unit _____________________ 5. 6 CHATTANOOGA SHALE 15 Section 5 miles south of Gassaway, Tenn.—~Continued Devonian—Continued Chattanooga shale—Continued Gassaway member—Continued Upper black shale—Continued Upper gray beds: Fm Shale, grayish-black, carbonaceous, tough, alternating with thin beds of grayish-olive to greenish-gray mudstone; iron sulfides present. as grains and nodules. A lain- inated bed, 0.25 ft thick, con— sisting of alternating paper- thin layers of grayish-black shale and iron-oxide-stained fine to very fine sand at base ________ Middle black shale: Shale, grayish-black, carbonaceous, tough, with iron sulfides present as nodules, grains, and paper- thin layers ___________________ 6. 2 Dowelltown member: Middle gray beds: Mudstone, alternating thin green- ish-gray, grayish—olive, olive— gray, and grayish-brown beds together with a few thin grayish- black shale beds. The thin bontonite bed commonly present near the top of this interval was not recognized __________________ 8. 5 Lower black shale: Shale, grayish-black, carbonaceous, tough; iron sulfides present as nodules, grains, and paper-thin layers. Few thin grayish—olive to greenish—gray mudstone beds, 6. 35 Sandstone, consisting chiefly of rounded quartz grains and cono— donts; iron oxide stained ______ .05 Total ___________ . _______ 33. 20 Ordovician . Campbell’s (1946, p. 886) measurements differ from the thicknesses recorded above, but his description of the section indicates that he regarded the limits of his Dowelltown formation, at the type locality of his Gassaway formation, to be as shown in table 2. Thus, with reference to the lithologic divisions of the Chatta- nooga shale used in the present paper, the Dowelltown of Campbell is the lower black shale and the middle gray beds; and the type Gassaway formation is the upper black shale. The Maury formation includes beds that Campbell identified as Maury shale and Fort Payne chert. The above discussion is summarized in table 2, which shows that the basal beds of Campbell’s type Gassaway formation are the exact correlatives of the topmost beds of his type Dowelltown formation. Therefore, Camp— bell’s DOWelltown formation has been amended so as to consist only of the lower black shale and middle gray beds. The stratigraphic limits of Campbell’s Gassaway formation are not changed; they correspond to those of the upper black shale. Table 2 also indicates that Campbell’s formations are herein treated as members of the Chattanooga shale. HARDIN SANDSTONE MEMBER The Hardin sandstone member underlies the Dowell- town member. It is a part of the widespread basal sandstone of the Chattanooga shale and is restricted to the vicinity of Wayne, Perry, Lawrence, and Hardin Counties, Tenn. and the adjoining part of Alabama. It is as much as 16 feet thick and consists chiefly of siliceous fine-grained sand and silt. The Hardin sand- stone member is well exposed along a secondary road by a stone church, 0.15 mile south of United States Highway 64 at Olive Hill, Hardin County, Tenn. where it grades into the overlying beds of the Dowelltown member. The section at Olive Hill is locality 239. Although conodonts have not been found in the Hardin sandstone member, the writer did collect a few speci- mens of Palmatolepz's um'cowvis Miller and Youngquist (pl. 4, figs. 7, 8) from the overlying Dowelltown member at Olive Hill, Hardin County (locality 239). These specimens came from 8.5 to 17.5 feet below the top of the Chattanooga shale and, as indicated in figure 1, they belong to a species which does not range above the Dowelltown member along the Eastern Highland Rim of central Tennessee. Because Palmatolepis unicornis is present in the over- lying beds and because the Hardin sandstone member grades into the Dowelltown member, the writer suggests that the Hardin is of early Late Devonian age, though it is possible that some part of the member could be slightly older. The Hardin is probably about the same age as the basal sandstone of the Dowelltown member of the Eastern Highland Rim area and the basal part of the Dowelltown member of north-central Tennessee. Ulrich and Bassler (1926) considered the Hardin sandstone member to be a widespread basal deposit of Mississippian age. They described some conodonts collected from a thin sandstone at an exposure west of Mount Pleasant, Tenn, and identified the bed from which their fossils came as the Hardin sandstone. As 16 CHATTANOOGA SHALE AND MAURY FORMATION TABLE 2.——Comparison of stratigraphic limits of Campbell’s type‘sections of his Dowelltown and Gassaway formations and the amended section adopted for this report This report Guy Campbell, 1946 Formation Informal Type locality of Type locality of names Dowelltown formation Gassaway formation Fort Payne Fort Payne Fort Payne chert chert chert Maury New Providence( ?)shale formation Maury shale Maury shale Top Q: Gassaway v—1 0 jg black "‘ '0 formation Gassaway Gassaway . at .81 .3: 8 shale ,0 member '3 Upper gray formation 56 beds Upper (u & Middle 2: Dowelltown to D black .9 member +3 0 shale g 0 Middle 3-. ‘3 :9. Upper a, e Dowelltown gray :: ‘8 Dowelltown E, Lower g 5 member 9 beds 3 3-7 33 at °’ Dowelltown E g .s: member g 3 :4 .Lower black ’ Q . o 3 Lower 0 member Q Dowelltown shale member stated above on page 8, Ulrich and Bassler’s (1926) fauna includes Ancyrogathus bifurcata, Palmatolepis glabra, Palmatolepis perlobata, and Polylophodonta con- fluens. Along the Eastern Highland Rim of central Tennessee, these species, as a group, are a part of the lower fauna of the Upper Devonian Gassaway member. (See fig. 1.) It is the writer’s opinion, therefore, that the thin sandstone bed from which Ulrich and Bassler’s (1926) conodont fauna came is neither the same age as the Hardin sandstone member of the present report nor of early Mississippian age. DOWELLTOWN MEMBER The Dowelltown member is well developed along the Eastern Highland Rim of central Tennessee—from southern Jackson County to the vicinity of Manchester in Coffee County. In that area, it is between 10 and 17.5 feet thick and consists of a lower grayish—black shale unit and an upper predominantly gray mudstone unit. The lower black shale unit is as much as 10.6 feet thick—except in the Flynn Creek structure where, within a mile of locality 54, it is probably on the order of 150 feet thick. The upper division of the Dowell- town member is called the middle gray beds. This unit is as much as 9.7 feet thick and consists chiefly of gray mudstone together with a few thin layers of grayish-black shale. Individual beds commonly range between 0.01 and 0.3 foot in thickness. Where weath- ered, many of these beds are yellowish or brownish, but some are greenish. In central Tennessee, during Dowelltown time, the basins of deposition appear to have been partly dc- limited by the Cincinnati anticline and a slightly ele— vated area in south-central Tennessee and the adjacent 17 CHATTANOOGA SHALE 532558 5 h83H fianEwfia 533$ 25 we 35% amoosafimno on: 5 $62; can 53% unofivoaou BEoEdwE .«o eucam1A mmbcrm Eu: 9:. 532m 313k: i=3 9.. ‘05: Gaga—0:1 2.: a... . . 533 9... 6:5 ‘ . . :~ 2»: E. . . . .. 35: 18:5: 33E < .3 3ss§§ quI flgbxhtm 353.33% 35: SEE!“ SEEKSXE < .3. 53:38: < dm 5.33555 m .am swungw :5me 3332 5395: < in §Su§e§v~ 3:595; v...- EES figs: issugfiw Sta-«m gas?» 35E=§< 3:31am SSELS: 338. ESPN «mica—50> .2; 5:5 38.53- ggufifik ll?lllll?l 202 v.5 , Eus— vcn :chflm S3335 §Su§m§wfl tufimom can :25: Seuss? A w 5.38 . .. 1 = w _ a. Sign 05 5:5 33% . . . R 20: «En 525m 3825 . . . c. ( dm ESSEESN .20: “En 5355 533% §Se§um Eu: ucn .8955 w :31. . . . h E»! 23 a 3.53.. . _ . c .07an EB 5:5 3335 . ~ ‘ . n. €0.38 .23 5. V 4 . . : E»: van .5955 5335» 3&32E5ul :5: EH :omcflmv §u§w msgfiaafiuaw I :fi: 25 . 3:53. a“ an 2505 u...» c. . Fort Paynev chert Maury formation < m: yxgmii I 4¢¢¢fi¢+§ gnaw sum—s ask henna mvvn >mhu if: in; 23:: Bazm xum; .oaa: muwn >~Lm 33:2 32: xon; .osog .mnEmE xn‘smmmmc .mnEcE 5‘61;on w_m;m mmoozn2nzo :n_:o>wo .qu: z<_mm.mw_mw_s_ Z<_zo>mo 25050on EXPLANATION nodules Cheny ' M udstone Bentonite bed Black shale 18 CHATTANOOGA SHALE AND MAURY FORMATION part of Alabama. Also, the axis of the Cincinnati anticline seems to have trended southwestward from eastern Macon County, Tenn, into central Maury County, where it merged with the aforementioned ele— vated area of south-central Tennessee. The writer believes this to have been the case because the Dowell— town member wedges out toward these structurally higher areas. These areas seem also to have effectively prevented the eastward transport of coarse arenaceous material, for to the west of them the Dowelltown is commonly sandy from bottom to top, whereas to the east the member is sandy only at the base. A basal sandstone is present at many localities. This sand- stone commonly ranges from a featheredge to several tenths of a foot in thickness, though to the southwest of the Nashville Basin, it is thicker and there is called the Hardin sandstone member; it contains fish remains, conodonts, and reworked fossils. The color of the basal sandstone is light to dark gray where freshly exposed, and light to dark brown where weathered. A bentonite bed (Hass, 1948), which averages 0.1 foot in thickness, is present within a foot or two of the top of the Dowelltown member throughout at least 4,000 square miles of east-central Tennessee. This bed has been recognized along the Eastern Highland Rim from the vicinity of the Flynn Creek structure in J ack- son County (locality 54) to the vicinity of Shelbyville in Bedford County. It has also been seen on the west side of the Nashville Basin in southeast Williamson County (locality 185), in the Sequatchie Valley of eastern Tennessee (localities 215 and 220), near Dayton in Rhea County, and in cuttings from wells drilled in the area east of the Nashville Basin. This bentonite bed is an excellent datum. Its wide- spread occurrence supports the writer’s opinions on the age and correlation of the Chattanooga shale as based on conodonts and disproves the thesis suggested by Grabau (1906) and later adopted by Klepser (1937) and by Stockdale (1939, 1948) that the black-shale sequence of the southern United States is a time- transgressing unit that resulted from the deposition of near-shore sediments in a southward advancing sea. Along the Eastern Highland Rim of central Tennessee where the Chattanooga shale is best developed, the stratigraphic ranges of distinctive conodont genera and species have been found to be constant with reference to the bentonite bed (see figure 1); were it otherwise, there would be reason for believing that conodonts are of no use to the stratigraphic paleontologist. Conodonts are abundant in the basal sandstone of the Dowelltown member. Where the Chattanooga shale is well developed—as in the vicinity of the standard section (locality 76)—the basal sandstone contains conodonts like those in Pohl’s (1930a, 1930b) Trousdale TABLE 3.-Distribution of easily recognized conodont species of the basal sandstone of the Dowelltown member where the Chattw nooga shale section is essentially complete, and of the Trousdale shale of Pohl N o. of figure 1 2 3 on pl. 4 ‘ Ancyrodella rotundiloba (Bryant). . . . ....... . .......... 21 ______ x x Bryantodus Sp. A .......................... 23 x ____________ Hibbardella sp. A ............................... 22 ............ x Palmatolepis unicornis Miller and Youngquist.. 7, 8 x ............ Polygnathus linguiformis Hinde ................ 16, 17 x x x pennata Hinde _____________________________ 2, 3 x x x Prioniadus alatus Hinde”; ______________________________ 24 x x x 1. Trousdale shale of Pohl (1930a, 1930b). Included in Dowelltown member of Chattanooga shale in present report. Writer’s collections. 2. Blocher formation of Campbell (1946); species illustrated by Huddle (1934) as part of lower conodont fauna of New Albany shale of Indiana. 3. “Conodont bed” of Genundewa limestone lentil of the Geneseo shale of New York. Writer’s collections; some species illustrated by Hinde (1879), Bryant (1921), and Branson and Mob] (1933). shale of north-central Tennessee, Campbell’s (1946) Blocher formation of Indiana, and the “conodont bed” of the Genundewa limestone lentil of the Geneseo shale of New York. The distribution of the easily recognized conodont species of the basal sandstone along the Eastern Highland Rim and of the Trousdale shale of Pohl is given in table 3. The species listed in table 3, however, represent only a small part of the conodont fauna, as most of the specimens in this sandstone are indeterminable fragments. In addition to the stratigraphic distribution given in table 3, specimens identified as Bryantodus sp. A in this report are similar to some of the bryantodids in the “conodont bed” of the Genundewa limestone lentil of the Geneseo shale of New York; to some of the bryantodids described from the Rhinestreet shale (=Attica shale of Chadwick, 1923) of New York by Ulrich and Bassler (1926); as well as to other bryan- todids described from the lower part of the Attica shale of Chadwick (1923) by Youngquist, Hibbard, and Reimann (1948). Also, some of the specimens listed herein as Palmatolepis unicornis Miller and Youngquist resemble Palmatolepis pnnctata (Hinde) from the “Genesee shale” of New York and the Rhinestreet shale (=Attica shale of Chadwick, 1923). Prioniodus alatus Hinde is in the Rhinestreet shale (=Attica shale of Chadwick, 1923), and Polygnathas linguiformis Hinde occurs in some Middle Devonian limestones of Ohio. Hibbardella sp. A (pl. 4, fig. 22) is known only through fragmentary material. It has a short tongues like posterior bar which supports one or two minute denticles. Polygnathus sp. A (pl. 4, fig. 19) which has rostral ridges adjacent to the blade, and Ancyrodella sp. B (pl. 4, fig. 20) which has a posteriorly trending sec- _ondary carina on the outer platform are both shown in figure 1 as doubtfully in the basal sandstone of the Dowelltown member along the Eastern Highland Rim CHATTANOOGA SHALE 19 of central Tennessee. Both species have been found in the beds that Pohl named the Trousdale shale. Herein these beds are placed in the Dowelltown mem- ber and they are probably the same age as the basal sandstone of the Dowelltown member of the Eastern Highland Rim area. Ancyrodella. sp. B is also in the basal sandstone 0f the Dowelltown at locality 220 in southeastern Tennessee and locality 204 near Nashville. The writer has not differentiated the species of I criodus (pl. 4, figs. 4—6) that occur in the Chattanooga shale. However, the stratigraphic range of Icm'odus is recorded on figure 1 because the writer considers this genus to be an index of the Middle and Upper Devonian. Although no recognizable unreworked megafossils have been found in the basal sandstone of the Chattanooga shale along the Eastern Highland Rim, such fossils are known to occur in association with some of the cono- donts listed in table 3 in Pohl’s Trousdale shale of north-central Tennessee and in Campbell’s Blocher formation of Indiana. The writer, as well as Campbell (1946, p. 883), has collected Schizobolus sp. from Pohl’s Trousdale shale. This brachiopod, which, according to Cooper (Cooper and others, 1942, p. 1761 and chart 4), ranges from near the top of the Middle Devonian into the lower part of the Upper Devonian, is an im- portant element of the Geneseo fauna. The Blocher formation of Campbell is the same part of the New Albany shale from which Huddle’s (1934) lower cono— dont fauna came. According to Campbell (1946, p. 841) “Chonetes lepidus Hall, Leiorhynchus quadricosta— tum Hall, and Styliolt'nafissurella intermittens Hall are common to abundant at many localities” in the lower bed of the Blocher and Leiorhynchus, Stylioli'na, and T entaculites gracilistm'atus Hall are abundant in the next higher bed of the formation. Also Schizobolus concentricus Vanuxem is in the basal foot of Campbell’s Blocher at a few localities. Campbell (1946) classified his Blocher formation and Pohl’s Trousdale shale as Middle Devonian, but some of the earlier workers classified these same strati- graphic units as Upper Devonian. Kindle (1899, p. 111), for example, stated that the fauna of the New Albany shale seems to be an equivalent of the fauna of the Genesee shale of New York; later, he (1900, p. 569) concluded that the formation seems to be a cor- relative of both the Genesee and the Portage of New York. Huddle (1934, p. 17) placed the lower part of the New Albany shale (Campbell’s Blocher formation) in the Genesee. As for the Trousdale shale, Pohl (1930b) considered his formation to be of Genesee- Portage age. Cooper (Cooper and others, 1942, chart 4), however, classified the lower part of the New Albany shale (Blocher formation of Campbell), the Trousdale shale of Pohl, the Geneseo shale in New York, and other black shales throughout the interior of the United. States as late Middle Devonian. At the present time, the United States Geological Survey classifies the Genundewa limestone as a lentil of the Geneseo shale which, in turn, is the basal forma— tion of the Genesee group. Because the Federal Survey classifies the Genesee group as early Late Devonian, and because Pohl’s Trousdale shale and the basal sandstone of the Chattanooga shale—where that formation is best developed~c0ntain conodonts like those in the Genun- dewa limestone lentil and the younger beds of the New York section, the writer of this report classifies the basal beds of the Dowelltown member as early Late Devonian. An early Late Devonian age designation applies to the basal sandstone only where the Chattanooga shale section is as complete as it is along the Eastern Highland Rim. Elsewhere in central Tennessee the age of this Sandstone is younger; for example, at locality 154, near Mount Pleasant in Maury County, the basal sandstone contains Ancyrognathus bifurcata, Palmatolepis glabm, Palmatolepis perlobata, and Polylophodonta confluens; and at locality 126a, near Fayetteville in Lincoln County, the basal sandstone contains, among others, Ancyrognathus bifurcata, Palmatolegn's distorta, Pal- matolepis glabra, Palmatolepis perlobata, Palmatolepis quadrantinodosa, Palmatolepis subperlobata, Palmatolepis sp. A, and Polylophodonta confiuens. The stratigraphic ranges of these species in the Chattanooga shale of the Eastern Highland Rim area indicate that the basal sandstone at localities 154 and 126a is a part of the Gassaway member. (See fig. 1.) Along the Eastern Highland Rim in the vicinity of the standard section, beds of the Dowelltown member above the basal sandstone contain several distinctive conodont species. With the exception of Polygnathus pennata (pl. 4, figs. 2, 3)~—which ranges upward for several feet above the basal sandstone—and Palmato- lepis unicornis (pl. 4, figs. 7, 8)—which ranges through—- out most of the Dowelltown interval—the species in the basal sandstone of the Eastern Highland Rim area have not been recognized in collections from the overlying beds of the Chattanooga shale. Palmatolepis subrecta Miller and Youngquist (pl. 4, figs. 9—15) is another easily recognized conodont species of the Dowelltown; it ranges from the lower beds of the lower black shale into the basal beds of the overlying Gassaway member. P. subrecta, according to the writer (Hass, 1951, p. 2536), was described by Miller and Youngquist (1947) from material collected at the type locality of the Sweetland Creek shale near Muscatine, Iowa, and it, or a very closely related species, is also present in the basal beds of the Dunkirk shale of New York; P. subrecta may also be conspecific with Palmatolepis flabelliformis described by Stauffer from the Olentangy shale. The oflicial classification of the United States Geological Survey places the Olentangy shale and the Dunkirk shale in the Upper Devonian 20 but it places the Sweetland Creek shale in the Devonian or Mississippian. It is quite possible, however, that the Sweetland Creek shale contains beds of several different ages and it is the writer’s opinion that those beds at the type locality of the Sweet- land Creek shale, from which Miller and Youngquist (1947, pp. 501—17) obtained their conodonts, are Upper Devonian. Miller and Youngquist (1947, p. 502) have suggested that the Grassy Creek shale of Missouri may be approximately contem— poraneous with the Sweetland Creek shale of Iowa. Be this as it may, the present writer regards the beds from which Miller and Youngquist’s conodont fauna came as being older than the beds from which Branson and Mehl (1934a) obtained their Grassy Creek conodont fauna. The writer (Hass, 1951, p. 2534-2536) has collected Palmatolepis subrecta from the Arkansas novaculite at Caddo Gap, Montgomery County, Ark, where the species is in a faunal zone approximately 184 feet below the top of the middle division. This portion of the middle division of the Arkansas novaculite is classified as Upper Devonian. ‘ Ancyrognathus sp. A (pl. 4, fig. 1), distinguished by narrow upturned platforms, and Ancyrodella Sp. A (pl. 4, fig. 18), a rather generalized form, are represented in the collections by only a few specimens. The occur- rence of these two species is recorded in order to help establish the stratigraphic range of Ancyrognathus and Ancyrodella. The writer is of the opinion that Amy- rognuthus is an index of the Upper Devonian and that Ancyrodella ranges from the Middle Devonian into the Upper Devonian; however, some stratigraphers believe that these two genera—as well as Icm'odus, Palmatolepis, and Polylophodonta—range naturally into the lower beds of the Mississippian. As indicated on figure 1, along the Eastern Highland Rim of central Tennessee, the stratigraphic range of all 5 above—mentioned genera is restricted to the Devonian. Palmatolepis marginata Stauffer (pl. 4, figs. 25, 26) ranges from near the base of the Dowelltown member into the basal beds of the Gassaway. This species was first described from the Olentangy shale of Ohio and has since been recognized in a faunal zone of the middle division of the Arkansas novaculite, where it is asso— ciated with Palmatolepis subrecta. Ancyrognathus eu- glypheus (pl. 4, fig. 27), which is characterized by the abrupt heightening of the distal end of the blade, ap— pears to be restricted to the Dowelltown member. This species is in the Olentangy shale of Ohio and a faunal zone of the Woodford chert of Oklahoma. Recently the writer made serial collections of cono- dont material from the Upper Devonian succession of western New York and found. that the highest strati- graphic appearance of any of the above—mentioned cono- donts of the Dowelltown member is in the Dunkirk shale member of the Perrysburg formation. The Dun— kirk is classified by Cooper (Cooper and others, 1942) as basal Cassadaga stage. The writer is of the opinion, CHATTANOOGA SHALE AND MAURY FORMATION therefore, that the Dowelltown member of the Chatta- nooga shale correlates in a general way with Copper’s Finger Lakes, Chemung, and basal Cassadaga stages of the Upper Devonian. The basal beds of the Dowelltown member, however, could be upper Middle Devonian. As indicated in table 2, the Dowelltown member of the Chattanooga shale is the lower member of Camp- bell’s type Dowelltown formation. Campbell (1946, p. 881, 883) correlated the lower member of his Dowelltown formation with the lower member of his Blackiston formation of Indiana. This correlation appears to have been based chiefly on the belief that Barroisella and Spathiocaris are restricted to the lower member of each formation. Because of the stratigraphic position of the beds involved, the writer considers this correlation to be essentially correct. However, the reported occurrence. (Campbell, 1946, p. 844, 845) in the lower member of Campbell’s Blackiston formation of Ancyrognathus bifurcata, Palmatodella delicatula, Palme— tolepis glabra, Palmatolepis parlobata, and Palmatolepis subperlobata indicates that, based on conodonts, a part of this lower member is a correlative of the upper mem- ber of Campbell’s Dowelltown formation (Gassaway member of Chattanooga shale ,of present report) instead of the lower member of his Dowelltown forma— tion (Dowelltown member of present report). GASSAWAY MEMBER Along much of the Eastern Highland Rim, as well as in north—central Tennessee, in the vicinity of Nashville, and in south—eastern Tennessee, the Gassaway member is between 12 and 21 feet thick. It is commonly less than 6 feet thick along the west and south margins of the Nashville Basin, and is even absent throughout most of Lawrence County, Tenn. and parts of adjacent counties. On the other hand, the Gassaway is as much as 46.4 feet thick in the vicinity of Somerset, Pulaski County, Ky. Throughout a large part of the Eastern Highland Rim the Gassaway member consists of two black—shale units and an intervening zone of alternating thin beds of gray mudstone and black shale. These three units are called informally the middle black shale (lowermost unit), the upper gray beds, and the top black shale (topmost unit); combined, they are the upper black shale. Phosphatic nodules occur in the very youngest beds of the Gassaway member; these nodules are commonly scattered throughout the shale, though at some places they also form one or more courses. At most localities the phosphatic nodules in the Gassaway member are smaller than those in the basal bed of the overlying Maury formation. The Gassaway member contains two conodont faunas whose stratigraphic ranges overlap slightly. As indi- cated in figure 1, the species of the older fauna range, CHATTANOOGA SHALE 21 TABLE 4.—Distribution of significant conodont species present in the lower fauna of the Gassaway member No. on— Pl. Fig. Ancyrognalhus bifurcata (Ulrich and Bassler) ............................... 3 25, 26 x x x x x x Palmatodella delicatula Bassler _________________________ x x x x x x Palmatalepis distorta Branson and Mehl, 2 1 x __._ x ____________ glabm Ulrich and Bassler ............ 3 15-17 x x x x x x perlobata Ulrich and Bassler __________ 3 19—21 x x x x x x rugosa Branson and Mehl _________________________ x ____________________ subperlobata Branson and Mehl ..... 3 4—9 x ________________ x Polylophodoma confluent (Ulrich and Bassler) _______________________________ 3 10 x ___. x ________ x 1. Lower part of the Ohio shale of Ohio and Kentucky. Writer's collections; Hass (1947a). 2. Antrim shale; exposure in Paxton shale pit near Alpena, Alpena County, Mich. Writer‘s collections. 3. Blackiston formation of Campbell (1946); species illustrated by Huddle (1934) as part of middle conodont fauna of New Albany shale of Indiana. 4. Faunal zone, 46.5 to 140 feet below top of middle division of Arkansas novaculite, Caddo Gap, Montgomery County, Ark. Writer’s collections; Hass (1951). 5. Fauna] zone of Woodford chert of Oklahoma. Writer’s collections. 6. Fauna] zone of Chattanooga shale of northeast Oklahoma. Writer’s collections. as a unit, throughout most of the Gassaway member, whereas those of the younger fauna range throughout only the very. topmost beds of the member. In north- central Tennessee the younger fauna is also found in the phosphatic—nodule bed at the base of the Maury forma- tion. The older or lower conodont fauna of the Gassa— way member includes the species given in table 4. The species listed in table 4 make possible a correla— tion of all but the youngest beds of the Gassaway mem- ber with the lower part of the Ohio shale of Ohio and Kentucky; the Antrim shale as exposed in the Paxton shale pit west of Alpena, Mich; the major portion of the middle division of the New Albany shale (most of Campbell’s Blackiston formation) of Indiana; a faunal zone of the middle division of the Arkansas novaculite of Arkansas and Oklahoma which, at Caddo Gap, Montgomery County, Ark., is 46.5 to 140 feet below the top of the middle division; a faunal zone of the Woodford chert of Oklahoma; and a faunal zone that ranges throughout most of the Chattanooga shale of northeastern Oklahoma. The formations or parts of formations mentioned above are placed in the Upper Devonian series. Recently, the writer found conodonts similar to those listed in table 4 in the Gowanda shale member of the Perrysburg formation of western New York. The Gowanda shale member is placed in Cooper’s (Cooper and others, 1942) Cassadaga stage of the Upper Devonian. Other species in this fauna—which, in the writer’s opinion, indicate a Late Devonian age—are Ancyrogna— thus quadrant Branson and Mehl, Palmatolept's gracilis Branson and Mehl, Palmatolept's quadrantinodosa Bran— son and Mehl (pl. 3, fig. 11), Palmatolepis sp. A (pl. 3, figs. 1-3, 13)——a species with distinctly noded platforms anterior to the azygous node—and Prioniodus mutabilts Branson and Mehl. The thalli of Foerstia—a small sargassoid alga of probable fucoidal affinity (J. M. Schopf, February 1953, oral communication)~——have been found associated only with conodonts like those in the lower fauna of the Gassaway member. Good specimens of this plant have been collected by the writer from the Gassaway member of the Chattanooga shale in Kentucky and Tennessee (localities 14, 225, 228); from the Chattanooga shale of southwestern Virginia (Little Stone Gap), and northeastern Okla- homa (Spavinaw Dam section); and from the lower part of the Ohio shale of Ohio (The Narrows, near Columbus; and from a core 'at the limestone mine at Barberton, between 1,429 and 1,527 feet below the surface). The information now on hand indicates that Foerstt'a is restricted stratigraphically to rocks of Late Devonian age that contain conodonts like those in the lower faunal zone of the Gassaway member. The widespread occurrence of the older fauna of the Gassaway member indicates that during some part of Gassaway time, the sea in which the Chattanooga shale was deposited covered most, if not all, of central Tennes- see and the adjoining parts of Kentucky, Alabama, Georgia and Mississippi. Swartz (1924, 1927, 1929; see also p. 7-9 and 25, 26 of the present paper) subdivided the Chattanooga shale into the Big Stone Gap member (youngest), the Olinger member, and the Cumberland Gap member. He believed that the Olinger member interfingers with the Cumberland Gap member and that, with the possible exception of the lowest beds of the Cumberland Gap member, the Chattanooga shale of Tennessee and south— western Virginia is definitely of Mississippian age. However, some of Swartz’s conclusions are herein con- sidered to be invalid, as they are based in part on Swartz’s interpretation of a megafauna collected near Apison, Tenn. (locality 228). Swartz believed that this fauna consists of Mississippian fossils and corre— lated the 2-foot-thick bed in which the fauna occurs with the Bedford shale and Berea sandstone wedge of Ohio and Kentucky and with the Olinger member of his Chattanooga shale of eastern Tennessee and south- western Virginia. Swartz’s fossils were not available for study and comparison with the writer’s poorly preserved specimens from the same bed. G. A. Cooper, of the United States National Museum, who examined the writer’s collection stated (July 1947, oral communi- cation) that, with the exception of an Orbiculoidea sp., the preservation of the fossils is such that even generic determinations are not justified. In 1947 the writer (Hass, 1947b) stated that the. age of the above-men- tioned fossiliferous bed is equivocal, but he now believes that this bed, as well as the underlying black shale, belongs in the Upper Devonian, Gassaway member. The writer’s opinion is based on the fact that all of the 22 CHATTANOOGA SHALE AND MAURY FORMATION species given below occur in the aforementioned black shale, and that the first three listed also occur in the 2- foot—thiek bed from which Swartz’s fossils came. Foerstia sp. (a sargassoid alga of probable fucoidal affinity). Palmatolepis distorta Branson and Mehl (pl. 2, fig. 1). Palmatolepis glabra Ulrich and Bassler (pl. 3, figs. 15—17). Ancyrognathus bifurcata (Ulrich and Bassler) (pl. 3, figs. 25, 26). Palmatodella delicatula Bassler. Palmatolepis pcrlobata Ulrich and Bassler (pl. 3, figs. 19—21). Palmatolepis rugosa Branson and Mehl. Polylophodonta confluens (Ulrich and Bassler) (pl. 3, fig. 10). As delimited by the writer, the Chattanooga shale at its type locality (locality 226) is the Cumberland Gap member of Swartz’s section (see p. 8). The immediately overlying beds, which Swartz assigned to his Olinger member and his Big Stone Gap member, are herein placed in the Maury formation. Identifiable conodonts were found in the type Chattanooga at only one place, about 350 feet south of the north end of Cameron Hill; there, molds of Palmatolepis perlobata (pl. 3, figs. 19—21), Palmatolepis sp. B (pl. 3, fig. 18)-—— which is based on a single specimen whose outer plat— form resembles that of Palmatolepis rugosa Branson and Mehl#Hindeodella sp., and other barlike conodonts, were collected from the upper foot of the shale. The occurrence of Palmatolepis perlobata in the topmost foot of the Chattanooga shale indicates that at its type locality the shale is Devonian and assignable, at least in part, to the Gassaway member. Sedimentation appears to have been continuous in the vicinity of the standard section (locality 76) during late Dowelltown and early Gassaway time. Were it otherwise, the bentonite bed which is within a foot or two of the top of the Dowelltown member would probably not be present today throughout more than 4,000 square miles of east—central Tennessee. Under such conditions, mixing of conodont faunas does not seem probable and therefore on figure 1 Ancyrognathus bifurcata, Palmatolepis gracilis, Palmatolepis subper— lobata, and Palmatolepis sp. A are indicated as ranging down into the topmost beds of the Dowelltown member and Palmatolepis marginata and Palmatolepis subrecta as ranging up into the basal beds of the Gassaway member. However, sedimentation was not continuous during late Dowelltown and early Gassaway time throughout all of central Tennessee. For example, the topmost beds of the Dowelltown member are missing from the section in the vicinity of the type locality of Camp— bell’s Gassaway formation (locality 100). Also, a thin sandstone bed is at the base of the Gassaway member along the northwest rim of the Nashville Basin (for example, at localities 204, 205 and 206). This sand- stone is Campbell’s Bransford sandstone member of his Gassaway formation. The conodont fauna of this sandstone contains reworked specimens, for in addi- tion to those that are characteristic of the lower fauna of the Gassaway member along the Eastern High- land Rim, it also contains numerous representatives of species which, along the Eastern Highland Rim, are restricted to the Dowelltown member. (See figure 1. Also see table 8, locality 204, collections 328, 335; and locality 206, collection 451.) At Bransford (local— ity 206) this sandstone unconformably overlies the Dowelltown member of the Chattanooga shale. The main area of deposition during latest Gassaway time was in north—central Tennessee and the adjacent part of Kentucky. The strata resulting from this deposition commonly contain phosphatic nodules which, in addition to being scattered throughout the interval, are locally concentrated into‘ one or more courses. These beds have not been recognized along the Eastern Highland Rim very much farther south than the standard section (locality 76) in DeKalb County; nor have they been recognized in south-central Tennessee and the adjacent part of Alabama. Northward from the vicinity of the standard section to Somerset, Pulaski County, Ky. (locality 6), however, this'interval gradu- ally increases in thickness from a featheredge to 8 feet. A thin bed containing phosphatic nodules has been ob- served at the top of the Gassaway member at a few exposures in the Sequatchie Valley, including locality 220 near Dunlap, where it is one foot thick, and locality 215 in Bledsoe County, where it is 2.2 feet thick; also, the nodule bed is in the top of the Gassaway member along United States Highway 64, 1.8 miles west of Olive Hill, Hardin County, where it is 0.1 foot thick; and at Bakers Station, Davidson County, (locality 204), where it is 0.7 feet thick. The nodule bed is more than 2 feet thick in Macon County, Tenn. and about 6 feet thick in Clay County, Tenn. The topmost beds of the Gassaway member have a small, distinctive set of conodonts. As indicated in figure 1, these conodonts, though characteristic of that portion of the Gassaway which contains phosphatic nodules, range into slightly older beds where they are associated with conodonts that range throughout the older portions of the Gassaway member. In a part of north-central Tennessee the conodonts that characterize the topmost beds of the Gassaway are also in the very oldest beds of the Maury formation. The species in question are: Hindeodella sp. A (pl. 3, figs. 27, 28); this species has a long downward-trending anterior bar. Spathognathodus aculeatus (Branson and Mehl). Spathognathodus inomatus (Branson and Mehl) (pl. 3, figs. 22— 24 . Spatiognathodus disparilis (Branson and Mehl). MAURY FORMATION 23 The Chattanooga shale and the Maury formation are evidently separated by an unconformity throughout much of south-central Tennessee and north—central Alabama for in that area the youngest beds of the Gassaway member—those characterized by phosphatic nodules and the conodonts listed above—have not been recognized. Instead, the beds directly beneath the Maury formation contain the conodonts of the lower fauna of the’Gassaway member. Some of the conodonts of the lower fauna have also been found as reworked material in the basal 0.05 foot of the Maury formation. The conodont fauna of the youngest beds of the Gassaway is like that in the upper part of the Ohio shale of Ohio and Kentucky, as well as in that part of Campbell’s (1946) Sanderson formation which, at the type locality of the Sanderson, near New Albany, Ind., directly underlies Campbell’s Falling Run member of the Sanderson and contains phos'phatic nodules. The Falling Run member is considered by the writer to be of early Mississippian age but he regards the immediately underlying beds of the Sanderson at the type locality of that formation to be of Late Devonian age and to be a correlative of the upper part of the Ohio shale of Ohio and Kentucky. The oldest beds of the type Sanderson, however, contain the same conodont fauna as the underlying Blackiston formation of Campbell (1946); the writer correlates these beds with the lower part of the Ohio shale. MAURY FORMATION Safford and Killebrew (1900, p. 104, 141—143) proposed the name “Maury green shale” for the beds between the “Black shale (Chattanooga shale)” and their Tul— lahoma formation. They considered the Maury to be of early Carboniferous age and described it as consisting of green or greenish shale with embedded concretions of calcium phosphate. Some stratigraphers have classi- fied the Maury as the topmost member of the Chatta— nooga shale; others have considered it to be a distinct formation; and still others have regarded it as the basal bed of the immediately overlying formation. STANDARD SECTION OF THE MAURY FORMATION The Maury formation of the present paper is the ”Maury green shale” of Safford and Killebrew, who designated Maury County, Tenn., as the type locality. L. C. Conant, V. E. Swanson, and the writer failed to find an adequate exposure of the formation in Maury County and therefore selected an exposure near Cross Key in Williamson County as the standard section (locality 185). This is given below. Section along south side of road near top of west slope of Pull Tight Hill, 13.5 miles southeast of Franklin and 1.2 miles east of Cross Key, Williamson County, Tenn. [Measurements of Chattanooga shale by V. E. Swanson) Mississippian: Fm Fort Payne chert: Limestone, gray, cherty. Maury formation: Mudstone, grayish—yellow, green, greenish-gray; lowermost 0.3 ft dark gray to greenish black. Phosphatic nodules throughout interval as well as in a course, 0.3—0.6 ft thick, 0.3—0.9 ft above base __________________________ 1. 5 Devonian: Chattanooga shale: Gassaway member: Shale, grayish-black, carbonaceous, tough; phosphatic nodules throughout interval- 1. 6 Shale, grayish-black, carbonaceous, tough_ 2. 1 Siltstone, dark—gray ______________________ 1 Shale, grayish—black, carbonaceous, tough- 1. 6 Dow elltown member: Mudstone _____________________ _ _________ . 45 Bentonite ______________________________ . 05 Mudstone _________ . _____________________ . 2 Sandstone _____________________________ ' . 2 Mudstone and interbedded thin grayish- black carbonaceous shale ______________ 4. 3 Shale, grayish—black, carbonaceous, tough- 7.0 Covered _______________________________ 1. 0 Total ____________________________ 20. 10 Ordovician. The lithologic characteristics, the stratigraphic posi— tion, and the fauna of the Glendale shale of Swartz (1924) are similar to those of the Maury formation of central Tennessee, and it is the writer’s opinion that these names refer to the same lithologic unit. The name “Maury formation” is used in the present report in preference to Glendale shale because Maury is an older and better known name. AGE AND CHARACTERISTICS The Maury formation is an easily recognized unit wherever it is overlain by the Fort Payne chert, but its top'is indefinite wherever it is overlain by either the Ridgetop shale or the New Providence shale. The Maury consists chiefly of grayish-yellow, green, and greenish—gray mudstone. Grayish-black shale is pres— ent at some localities. Phosphatic nodules are generally scattered throughout the formation and at many out- crops are also concentrated into a course at or very near the base. Generally, the formation is between 1.5 and 3.0 feet thick, though at one locality (228) it is more than 7 feet thick. The Maury is chiefly of Kinderhook age; however, the youngest beds of the formation are probably of Osage age and the oldest 24: CHATTANOOGA SHALE AND MAURY FORMATION beds in a part of north-central Tennessee are probably of very late Devonian age. The formation contains several distinct conodont faunas. At many places along the north and west margins of the Nashville Basin of Tennessee, the Maury formation appears to grade into the overlying formation. At some localities (for example, Bakers Station, locality 204) the overlying formation has been identified in the literature as the Ridgetop shale—a formation classified as Kinderhook by the United States Geological Sur- vey~but at other nearby outcrops (for example, Whites Creek Springs or Crocker Springs, locality 203) the overlying strata have been identified as the New Providence shale*a formation classified as Osage by the United States Geological Survey. Wilson and Spain (1936) have a different opinion, they regard the Ridgetop shale as a phase of the New Providence shale and as Osage in age. Be this as it may, the writer of the present report restricted his investigations to 1 or 2 feet of beds, directly on top of the Chattanooga shale, that contain for the most part phosphatic nodules, glauconite, and conodonts of Kinderhook age. The writer has not concerned himself with the problems of the age, nomenclature, or stratigraphy of the beds commonly called Ridgetop shale and New Providence shale, except to note that the basal beds of the New Providence in south—central Kentucky are of Kinder- hook age and are the biostratigraphic equivalent of the Maury formation of Tennessee. The course of phosphatic nodules at the base of the hiaury formation may be a transgressive deposit, because in a part of north-central Tennessee the nodule bed contains conodonts like those in the youngest beds of the underlying Gassaway member of the Chatta— nooga shale, whereas in west-central Tennessee, and south—central Kentucky—where the nodules occur at the base of the New Providence shale—the bed contains conodonts of early Mississippian (Kinderhook) age. On the other hand, there could be two distinct phos— phatic-nodule beds, as no correlative 0f the Bedford shale and Berea sandstone of Ohio has been definitely recognized in central Tennessee. Some stratigraphers might prefer to place the thin phosphatic—nodule bed of north-central Tennesseehthat contains conodonts like those in the youngest beds of the Gassaway mem— ber~in the Chattanooga shale, and to regard the Maury formation as entirely of Mississippian age. (See descriptions of sections at localities 39, 60, 74, 75, 76, 78, 91, 92, 95, 206, and 207.) However, from the viewpoint of the field man who is concerned with delimiting easily recognized mappable units, the afore- mentioned phosphatic—nodule bed is a good base for the Maury formation of central Tennessee, and for that reason, L. C. Conant’s party placed the nodule bed in the Maury formation. It is the writer’s opinion that if a correlative of the Bedferd shale and Berea sandstone interval of Ohio is present in central Tennessee, it is probably the grayish—black shale that Campbell called ‘ the Westmoreland shale. . The conodonts in the phosphatic-nodule bed that indicate a very Late Devonian age are Hindeodella sp. A (pl. 3, figs. 27, 28), Spathognathodus aculeatus (Bran- son and Mehl), Spathognathodus disparilis (Branson and Mehl), and Spcthognavthodus inomatus (Branson and Mehl) (pl. 3, figs. 22—24). The last—named species, however, ranges into younger beds, as it has been recognized in collections from the Bedford shale of Ohio and the Louisiana limestone of Missouri; both forma— tions are Mississippian. In these two formations, however, Spathognathodus inornatus is associated with conodonts unlike those in the nodule bed of north- central Tennessee. Conodonts in the phosphatic—nodule bed of the Maury formation that indicate a Mississippian (Kinder- hook) age are listed in table 5. These conodonts have been recognized in many collections in west-central Tennessee including those from localities 203 and 204 in Davidson County; 163, 165, 168, and 250 in Hickman County; 249 in Perry County; and 134 in Marshall County. The same conodonts are also in the phos— phatic—nodule bed at the base of the New Providence shale in south-central Kentucky, for example, at locality 6, in Pulaski County; 11 in Russell County; and 14 in Cumberland County. At several localities in north-central Tennessee, a grayish-black shale overlies the aforementioned phos— phatic—nodule bed that contains Upper Devonian conodonts. This shale is 0.2 foot thick at locality 92 in DeKalb County; 0.5 foot thick at locality 207 in Sumner County, where it has been designated the type of the Westmoreland shale by Campbell (1946, p. 885); and 1.0 foot thick at locality 206, also in Sumner County. The shale is 0.35 foot thick at locality 100 in Cannon County. The following species have been recognized in one or more collections from this shale: Gnathodus sp. B. Polygnathus communis Branson and Mehl (pl. 2, figs. 2—5). Spathognathodus aciedentatus (E. R. Branson) (pl. 2, fig. 26). Spathognathodus sp. A (pl. 2, fig. 19). Hindeodella Sp. A (pl. 3, figs. 27, 28). The first three species listed above are characteristic of the Mississippian and range into the overlying beds of the NIaury formation. The remaining two have not been recognized in younger beds. One of these, Hindeodella sp. A, ranges down into the topmost beds. of the Gassaway member of the Chattanooga shale. The other, Spathognathodus sp. A, is represented in the writer’s collections by only one specimen; this species MAURY FORMATION TABLE 5.—~Distribution of significant conodont species present in the major part of the Maury formation No. of flgure12345678910 on 131.2 Dinoduafreaosus(E.R.Branson) ______________ ..__.. x x x ............ Elictognathus bialeta (Branson and Mehl) _______________________________________ ___ x x ___ x x _.. lacerete (Branson and Mehl) _____ 21,22 x x x x x x x x x Piuecognethus profuude (Branson and Me hl _______________________________ 17 ... x _____._._ x Polyguethus allocate (Cooper) __________ 18 .._ __. _._ .._ ... x longiposticeBransonandMehl _____ 28 .._ x x .J.__. x Pseudolpolwuethus prime Branson and Me ................................ 24 x x x x x x x Siphouodelle duplicate (Branson and ............................... 0—11 x x x x x x duplicate (Branson and Mehl) var. ............................... 13,23 ___ _.__._ x .__ x _ x x lobete(BransonandMeh1) _________ 25 ___ x x _ quadruplicate(BransonandMehl). 29 x x x x 1: x x sexplicate (Bransonand Mehl) ..... 30 x x x . Spathoguethodus eciedeutetus (E. R Branson) ............................ 26 x x x ... x x _ x Polyguethus comment‘s Branson and Mehl ................................ 2—5xxxxxx xx inometeE. R Branson ____________ 14,15 ___ x x x ... x x x x 1. Sunbury shale of Ohio (Hass,1947a). 2. Bushberg sandstone member of the Sulphur Springs formation of Missouri (Branson and Mehl,1934b). 3. Hannibal shale of Missouri (E. R. Branson, 1934). 4. Chouteau limestone of Missouri (Branson and Mch1,1 1938 38). 5. Upper fauna] zone of N ew Albany shale of Indiana (Huddle, 1934). 6. Pre—Welden shale interv al of Oklahoma (Cooper, 1939). Middle division of Arkansas novaculite, Caddo Gap, Ark., 18 8—19.51‘t below top of middle division (Bass, 1951). Middle division of Arkansas novaculite, Caddo Gap, Ark” 20 0-20. 2 it below top of middle division (Hess, 1951). 9. Middle division of Arkansas novaculite, Caddo Gap, Ark., 28. 0—28. 5 it below top of middle division (Hass, 1.951 10. Faunal zone in Chattanooga shale of northeastern Oklahoma. Writer‘ 5 collec- tions. has a spinelike denticle on the inner lip of the pulp cavity, and in that feature, resembles a distinctive spathognathodid of the Bedford shale of Ohio. Un- fortunately, a good rubber replica of the spinelike den- ticle—which is approximately as high as the blade— could not be made. (See pl. 2, fig. 19.) A single speci- men of Polygnethus commuuis Branson and Mehl has been found in the prepared material of collection 172 from the topmost 0.3 foot of the Gassaway member at locality 207. Because this is the only known occurrence of the species in rocks of Late Devonian age, the writer prefers to regard the presence of P. communis in collec- tion 172 as having resulted either through a strati- graphic leak or through a mixing of collections. The latter is a likely possibility, as lithologically, at locality 207, chips from the topmost beds of the Gassaway member and those from the grayish-black shale of the Maury formation are indistinguishable. The conodont species that appear to range throughout a large part of the Maury formation are listed in table 5. The name Siphonodelle duplicete (Branson and Mehl) refers to specimens which, like the types of the species, have transverse ridges on the oral surface of both plat— forms, and the name Siphonodelle duplicete (Branson and Mehl) var. A is used for specimens that differ from the types by having nodes rather than transverse ridges on the oral surface of the inner platform. Most of the species listed in table 5 belong to one of the fol- 25 lowing genera: Dinodus, Elictognethus, Pinecoguethus, Pseudopolygnethus, and Siphouodelle. It is the writer’s opinion that these genera as well as G'nethodus are index fossils of the post-Devonian. The conodonts listed in table 5 make it possible to correlate part of the Maury with the Sunbury shale of Ohio; the uppermost part of the New Albany shale of Indiana; the Bushberg sand- stone member of the Sulphur Springs formation and the Hannibal shale, both of Missouri; beds near the top of the middle division of the Arkansas novacvlite of Arkansas and Oklahoma; a faunal zone of the Chatta— nooga shale of northeastern Oklahoma; and a faunal zone in the lower part of C. L. Cooper’s (1939) pre- Welden shale of Oklahoma. All these formations or parts of formations are classified as Mississippian. The writer believes that the Maury formation is a biostratigraphic equivalent of the basal portion of the New Providence shale of south-central Kentucky; that is, the New Providence shale contains beds of Kinder- hook age. This opinion is held because identical species of Kinderhook conodonts are present in the basal beds of the New Providence shale in south-central Ken- tucky—including the exposures at localities 6, 11, and 14—and in the Maury formationmincluding exposures at locality 204, the type locality of the Ridgetop shale, and at locality 203, the local standard section of the New Providence shale. A few specimens of Siphonodelle sp. A (pl. 2, fig. 12) have been collected from the Maury formation at locality 205 in Sumner County, Tenn, and from the phosphatic- nodule bed at the base of the New Providence shale at locality 6 in Pulaski County, Ky. This species has an outer platform whose oral surface is nearly smooth; it has not been recognized in any of the formations listed in table 5, but it has been observed by the writer in collections from the Mississippian Chappel limestone of Texas. A single specimen of Spethognethodus sp. B (pl. 2, fig. 27) has been found in the Maury formation at locality 205 in Sumner County, Tenn. This specimen resembles Spethognethodus aciedentetus, but differs in that the lateral expansions of its pulp cavity are more asymmetric. A few of the conodont species listed in table 5 have been found in the Maury formation at locality 226, the type locality of the Chattanooga shale, and at locality 228, an exposure near Apison, Tenn. Cono- donts collected at the type locality of the Chattanooga shale include Polyguethus communis Branson and Mehl (pl. 2, figs. 2—5) and Siphonodelle duplicate (Branson and Mehl) (pl. 2, figs. 6—11). These fossils came from an interval of small phosphatic nodules and olive-gray to dark-gray shale that is 0.4 to 0.45 foot above the Chattanooga shale and Maury formation 26 contact. Swartz placed this bed in the Chattanooga shale and identified it as his Big Stone Gap member. (See p. 7-9 for a review of Swartz’s papers.) However, for the reasons given on page below, the present writer prefers to place the above-mentioned bed in the Maury formation. The thin gray mudstone bed at the type locality of the Chattanooga shale, which Swartz identi- fied as his Olinger member of the Chattanooga shale, is also placed in the Maury formation because its lithologic character more closely resembles that of the Maury formation than that of the underlying grayish— black Chattanooga shale, which at locality 226 is deformed and slickensided. The Maury formation at locality 228 consists of two lithologic units: a greenish-gray mudstone, 3 feet thick, and an underlying grayish-black shale, which, because the shale is slightly deformed, varies in thickness from 3.8 to 4.7 feet along the face of the outcrop. Both units contain numerous phosphatic nodules. N o cono- donts were collected from the greenish-gray mudstone, but the following species have been found in the under— lying grayish-black shale: Elictognathus lacerata (Branson and Mehl) (pl. 2, figs. 21, 22). Pseudopolygnathus prima Branson and Mehl (pl. 2, fig. 24). Siphonodella duplicate (Branson and Mehl) (pl. 2, figs. 6—11). Siphonodella duplicata (Branson and Mehl) var. A (pl. 2, figs. 13, 23). Palmatolepis distorta Branson and Mehl (pl. 2, fig. 1). These conodonts, with the exception of Palmatolepis distorta, are characteristic of the lower Mississippian (Kinderhook) and are like those in the Maury formation of the central Tennessee area. Palmatolepis distorta must have been reworked into the Maury formation for elsewhere in Tennessee it is a typical fossil of the lower fauna] zone of the Gassaway member of the Chattanooga shale. (See figure 1.) Locality 228 is the only one at which a thick black shale of Mississippian age was recognized. Swartz, like the writer, correlated this shale with the Sunbury shale of Ohio and Kentucky. However, Swartz—who worked in eastern Tennessee and southwestern Vir— ginia, where the black—shale sequence contains beds of both Devonian and Mississippian ages—preferred to place the above—mentioned black shale of Mississippian age in the Chattanooga shale and identified it as the Big Stone Gap member; whereas, the present writer—— who worked in central Tennessee, where the Chatta- nooga shale is definitely of Devonian age—prefers to place this shale, as well as the beds mentioned above, in the Maury formation. This stratigraphic assign- ment is made because the beds in question either con— tain conodonts like those in the Maury formation of central Tennessee or have a lithology similar to that formation. Moreover, the Maury, as delimited in the CHATTANOOGA SHALE AND MAURY FORMATION present paper, lies uncon’formably on the Chattanooga. shale throughout much of southeastern Tennessee with the youngest beds of the Gassaway member miss- ing from the section. These beds are discussed on pages 21—23. In addition to conodonts that indicate an early Kinderhook age, the Maury formation at some localities contains still younger conodonts. These fossils include Gnathodus punctatus (Cooper) (pl. 2, fig. 20) and Bactrognathus sp. Gnathodus punctatus is represented in the writer’s collections by a single specimen which came from locality 134 near Cornersville, Marshall, County, Tenn., where it is associated with Gnathodus— sp. A (pl. 2, fig. 16), a gnathodid that resembles Gnatho—v dus delicatus Branson and Mehl from the Chouteau limestone of Missouri. Gnathodus punctatus is also in a faunal zone of the Chappel limestone of Texas; in both C. L. Cooper’s Welden limestone and the topmost bed of Cooper’s (1939) pre-Welden shale of Oklahoma; and in beds between 11.5 and 19.5 feet below the top of the middle division of the Arkansas novaculite at Caddo Gap, Montgomery County, Ark. (See Hass, 1951). The Chappel limestone, the Welden limestone, and the above mentioned beds of the middle division of the Arkansas novaculite are all classified as of late Kinderhook (Chouteau) age. Bactrognathus sp. has been found in collections from the Maury formation at the following localities: 89 and 95 in DeKalb County, 249 in Perry County, and 250 in Hickman County. The genus Bactrognathus ranges from the upper Kinder— hook into the lower Osage. Collection 15003 from the top 3.6 feet of the Maury formation at locality 95 in DeKalb County, Tenn, and collection 350 from 0.5 to 0.8 foot above the base of the New Providence shale at locality 6 in Pulaski County, Ky., each contain a few specimens of an elongate pseudopolygnathid which in this paper is listed as Pseudopolygnathus sp. These specimens resemble Pseudopolygnathus striata. Mehl and Thomas from the Fern Glen limestone of Missouri. A few specimens of Taphrognathus have been found in the Maury formation at localities 165 and 250 in Hickman County, Tenn. This genus has not been recorded in the literature as ranging into rocks older than those of Keokuk age. It cannot be determined from the material at \hand whether these specimens oc- cur naturally in the Maury formation or whether they are there as the result of a stratigraphic leak. MEASURED SECTIONS The locality numbers used in this paper are the same as those that will be used in a report on the Chattanooga shale and related rocks of central Ten— nessee and nearby areas which L. C. Conant and V. E. Swanson are preparing. (See pl. 1.) MEASURED LOCALITY 6.-—In cut and on hillside below Oil Center Road, just east of the crossing over Big Clifty Creek, 5.4 miles west of Somerset, Pulaski County, Ky. Mississippian: New Providence shale: The basal part of this formation is con- sidered to be the biostratigraphic equiva- lent of the Maury formation of Tennessee. It is a dark-gray glauconitic mudstone. A course of phosphatic nodules is situated 0.3—0.45 ft above base. Feet Devonian: Chattanooga shale: Gassaway member: Shale, grayish-black, carbonaceous, tough; phosphatic nodules scattered throughout- Shale, grayish-black, carbonaceous, tough; iron sulfides present as grains, nodules, and thin seams. N0 fossils obtained from basal 4.5 ft; this part may belong to Dowelltown member __________________ Dowelltown member: Sandstone, consisting chiefly of rounded grains of quartz sand, calcareous bond_ __ . 4 Shale, grayish-black, carbonaceous, tough__ 2 Sandstone, consisting chiefly of rounded grains of quartz sand, calcareous bond-_ . 4 8.0 38. 4 Total ____________________________ Boyle limestone. 47. 4 LOCALITY 11.——Cut on State Highway 35, 1.5 miles south-southeast of Rowena and just north of the county line, Russell County, Ky. Mississippian: New Providence shale: The basal part of this formation is con- sidered to be the biostratigraphic equiva- lent of the Maury formation of Tennessee. It is a light-gray siltstone with a concen- tration of large phosphatic nodules in the basal 0.4 ft. Feet Devonian: Chattanooga shale: Gassaway member: Shale, grayish-black, carbonaceous, tough. Phosphatic nodules scattered throughout, some as much as 0.6 ft long. Iron sulfides present as grains and nodules--- Shale, grayish-black, carbonaceous, tough. Iron sulfides present as grains, nodules, and thin seams _______________________ Mudstone, various shades of gray and green- ish-gray, laminated, weathers hackly; interbedded with thin grayish-black carbonaceous shale. Iron sulfides present as grains and nodules. Basal 0.02 ft sandy _______________________________ 4.6 25. 8 4.9 Total ____________________________ 35. 3 Ordovician. SECTIONS 27 LOCALITY 14.—Cut on State Highway 90, 1.25 miles west of Burkesville, Cumberland County, Ky. Mississippian 2 New Providence shale: The basal part of this formation is con- sidered to be the biostratigraphic equiva- lent of the Maury formation of Tennessee. It is a greenish-gray mudstone with a concentration of large phosphatic nodules in the basal 0.6 ft. Feet Devonian: Chattanooga shale: Gassaway member: Shale, grayish-black, carbonaceous, tough; phosphatic nodules throughout _________ 4. 1 Shale, grayish—black, carbonaceous, tough- 13. 5 Mudstone, dark-gray, alternating with thin beds of grayish-black carbonaceous shale- l. 3 Mudstone, dark-gray ____________________ l. 9 Sandstone, consisting chiefly of rounded grains of quartz sand __________________ . 1 Total ____________________________ 20. 9 Ordovician. LOCALITY 39.—Cut on State Highway 56‘, 1.7 miles south of Gainesboro, Jackson County, Tenn. Mississippian: Fort Payne chert: Basal beds include a coarse textured, lenticu- lar, biohermal mass. Pelmatozoan col— umnals abundant, megafossils present. Basal beds somewhat cherty. Maury formation (in part): Mudstone, dusky-green to dusky-yellow__ "Mudstone, yellowish-gray to olive-gray; phosphatic nodules scattered throughout- Feet Devonian: Maury formation (in part): Persistent course of phosphatic nodules, 0.5 ft thick, embedded in grayish-blue— green to dusky—blue-green glauconitic mudstone which is underlain by dark- gray to olive-gray crossbedded siltstone. Chattanooga shale: Gassaway member: Shale, grayish-black, carbonaceous, tough. Phosphatic nodules throughout interval and concentrated in two courses; the main course located approximately 1ft below top; the other, approximately 3.2 ft below top. Iron sulfides present as grains and nodules ____________________ 4. Shale, grayish—black, carbonaceous, tough; iron sulfides present as grains, nodules, and 1.0 ‘1 paper-thin layers _____________________ 6. 5 Shale, grayish-black, carbonaceous, tough; alternating with thin beds of greenish- gray mudstone. Iron sulfides present as grains _______________________________ 3. 8 28 CHATTANOOGA SHALE AND MAURY FORMATION LOCALITY 39—Continued Devonian—Continued Chattanooga shale—Continued Dowelltown member: Fm Mudstone, greenish-gray, banded; alter- nating with thin beds of grayish-black carbonaceous shale and sandy beds. Iron sulfides present as grains, nodules, and thin seams _______________________ 5. 9 Total ____________________________ 23. 40 Ordovician. LOCALITY 54.~—Cut on road leading northwest from State Highway 56 into the Flynn Creek structure, 1.2 miles from Highway 56' and 6.5 miles (airline) south—southeast of the courthouse at Gainesboro, J aekson County, Tenn. [Chattanooga shale measurements made by W. A. Heck, March 1, 1948] Mississippian: Fort Payne chert: Limestone, cherty. New Providence shale: Feet Mudstones, bluish-green and greenish—gray. Thin siliceous layers, iron sulfide grains, and pelmatozoan columnals present. A course of siliceous geodes up to 0.1 ft in diameter at base ____________________ 7. 2 Maury formation: Mudstone, greenish and brownish, glau- conitic _______________________________ . 4 Mudstone, yellowish-gray to Olive-gray, laminated. Iron sulfides present as grains. Phosphatic nodules scattered through- out _________________________________ 1. 8 Devonian: Chattanooga shale: Gassaway member: Shale, grayish-black, carbonaceous, tough. Phosphatic nodules scattered throughout interval. Iron sulfides present as grains and nodules __________________________ 2. 5 Shale, grayish-black, carbonaceous, tough. Iron sulfides present as grains __________ 9. 3 Shale, grayish-black, carbonaceous, tough, with iron sulfides present as grains; alter- nating with thin beds of grayish-olive to greenish-gray mudstones. A laminated bed, 0.1 ft thick, present at base ________ 1. 4 Shale, grayish-black, carbonaceous, tough. Iron sulfides present as grains __________ 2. 3 Dowelltown member: Mudstone; alternating thin greenish-gray, grayish-olive, olive-gray, and grayish- brown beds together with a few thin grayish-black-shale beds. A light-gray iron-oxide-stained bentonite bed, 0.1 ft thick, present 0.4-0.5 ft below top ______ 3. 4 Shale, grayish-black, carbonaceous, tough; iron sulfides present as grains ___________ 6. 2 LOCALITY 54—Continued Devonian—Continued Chattanooga shale—Continued Dowelltown member—Continued Fm Sandstone, iron-oxide-stained, consisting chiefly of rounded quartz grains. Lower surface uneven. Thickness ranges from 0.25—0.5 ft; average ___________________ 0. 4 Total ____________________________ 34. 9 Ordovician. . LOCALITY 60.—Cut on United States Highway 70N, 0.8 mile west of Chestnut Mound, Smith County, Tenn. Mississippian : Fort Payne chert: Fm Limestone, blocky, interbedded with chert. Maury formation (in part): Mudstone, grayish—green, laminated _______ 3. 1 Devonian: Maury formation (in part): Course of large phosphatic nodules em- bedded in dark-gray shale and mudstone- 1. 2 Chattanooga shale: Gassaway member: Shale, grayish-black, carbonaceous, tough. Phosphatic nodules scattered through- out. Iron sulfides present as grains and nodules ______________________________ Shale, grayish-black, carbonaceous, tough, laminated; iron sulfides present as grains, nodules, and thin layers _______________ 7. 3 Shale, grayish-black, carbonaceous, tough; interbedded with thin beds of gray mud- stone. A laminated bed, which ranges from 0.3—0.13 ft in thickness, present at the base ___________________________ Shale, grayish-black, carbonaceous, tough__ Dowelltown member: Mudstone, alternating thin greenish-gray, grayish-Olive, olive-gray, and grayish- brown beds, together with a few thin grayish-black shale beds. A medium- dark-gray bentonite bed (very light gray and iron oxide stained where weathered), 0.1 ft thick, present 1.3—1.4 ft below top _________________________________ 5. 3 Shale, grayish-black, carbonaceous, tough; interbedded with thin gray mu‘dstone 3.4 N.“ l-‘O beds ________________________________ 2. 3 Mudstone, gray; interbedded with a few thin grayish-black carbonaceous shale beds-________7 ______________________ 3.8 Sandstone, iron-oxide-stained, consisting chiefly of rounded grains of quartz sand__ . 1 Total ____________________________ 31. 6 Ordovician. MEASURED SECTIONS LOCALITY 74.—Face of Taylor Creek Falls (Fanchers Mill), about 10 miles (airline) northwest of Sparta, White County, Tenn. [Modified from notes of Ralph Smith, dated May 19, 1948] Mississippian: Fort Payne chert. Maury formation (in part): Mudstone, grayish-green _________________ Feet 1. 6 Devonian: Maury formation (in part): Course of large phosphatic nodules em— bedded in grayish~black, carbonaceous shale. Iron sulfides present as grains and nodules ______________________________ . . 9 Chattanooga shale: Gassaway member: Shale, grayish-black, carbonaceous, tough; scattered phosphatic nodules ___________ Shale, grayish-black, carbonaceous, tough__ Shale, grayish-black, carbonaceous; inter- bedded thin beds of gray mudstone _____ Shale, grayish—black, carbonaceous. A laminated bed, 0.15 ft thick, present 1.25—1.40 ft below top _________________ Dowelltown member: Mudstone; alternating thin greenish-gray, grayish-olive, olive-gray, and grayish- brown beds, together with few thin gray— ish-black shale beds. A bentonite bed, 0.12 ft thick, present 0.93—1.05 ft below top _________________________________ Shale, grayish-black, carbonaceous, tough__ 5‘!“ an 8.4 9.4 6.7 Total ____________________________ 39. 2 Ordovician. LOCALITY 75.—Cut on abandoned farm road, 0.5 mile northwest of point on State Highway 26 where descent starts to the east end of the Sligo Bridge over the Caney Fork, and 5.8 miles (airline) east of the courthouse at Smithoille, DeKalb County, Tenn. Mississippian: Fort Payne chert. Maury formation (in part): Mudstone, grayish-green _________________ Feet 2. 1 Devonian: Maury formation (in part): Course of large phosphatic nodules ________ . 3 Chattanooga shale: Gassaway member: Shale, grayish-black, carbonaceous, tough“ Shale, grayish—black, carbonaceOus, with some interbedded gray mudstones. A laminated bed, 0.2 ft thick, consisting of alternating paper-thin layers of black shale and gray fine to very fine sandstone at base ______________________________ Shale, grayish—black, carbonaceous, tough__ Dowelltown member: Mudstone; alternating thin greenish-gray, grayish-olive, olive-gray, and grayish- brown beds, together with a few thin grayish-black shale beds. A bentonite bed, 0.11 ft thick, present 0.67—0.78 ft below top ____________________________ 7.7 5'!" «cs 9.3 366719—56—3 29 LOCALITY 7 5—Continued Devonian—Continued Chattanooga shale—Continued Dowelltown member—Continued F“; Shale, grayish-black, carbonaceous, tough__ 6. 9 Sandstone, brownish to grayish-black, poorly sorted, consisting chiefly of rounded grains of quartz sand __________________ . 2 ‘ TotaL; __________________________ 36. 1 Ordovician. LOCALITY 76.-—Cut on State Highway 26’, at east approach to the Sligo Bridge over the Caney Fork, 5.9 miles (airline) or 7 .1 miles by road east of the courthouse at Smithville, DeKalb County, Tenn. Standard section of the Chattanooga shale, described on page 12. LOCALITY 78,—Cut on that portion of State Highway 26' abandoned in 1948, approximately 0.6 mile southeast of the eastern approach to Sligo Bridge over the Caney Fork on the present State Highway 26, and 5.9 miles (airline) east of the courthouse at Smithville, DeKalb County, Tenn. Mississippian: Fort Payne chert. Maury formation (in part): Mudstone, olive-gray, laminated, slightly glauconitic ___________________________ Feet 2. 1. Devonian: Maury formation (in part): Course of large phosphatic nodules ________ . 3 Chattanooga shale: Gassaway member: Shale, grayish-black, carbonaceous, tough__ Shale, grayish-black, carbonaceous, tough, interbedded with thin beds of gray mud- stone. A laminated bed, 0.25 ft thick, consisting of alternating, paper—thin layers of black shale and gray very fine grained sand at base _______________ Shale, grayish-black, carbonaceous, tough- _ Dowelltown member: Mudstone, alternating thin greenish-gray, grayish-olive, olive-gray, and grayish— brown beds, together with a few thin grayish-black shale beds. A bentonite bed, 0.11 ft thick, present 0.69—0.80 ft below top _____________________________ 9. 7 Shale, grayish-black, carbonaceous, tough- _ 4. _5 Sandstone, grayish-black, consisting chiefly of rounded grains of quartz sand ________ . 2 7.0 9°99 paw Total ____________________________ 35. 5 Ordovician. LOCALITY 88.—Horseshoe Bend; along the right bank of the Caney Fork, 4.8 miles (airline) west-northwest of United States Highway 70S at the community of Walling, White County, Tenn. [This locality is now below the normal pool level of a reservoir] Mississippian: Fort Payne chert: Limestone, gray, bedded, cherty, with siliceous geodes. Uneven contact with underlying beds. 30 CHATTANOOGA SHALE AND MAURY FORMATION LOCALITY 88——Continued Devonian: Chattanooga shale: Gassaway member: Upper black shale: Feet Mudstone, greenish-gray to olive-gray- 0. 7 Mudstone, greenish-gray to olive-gray, indurated, blocky; iron sulfides pres- ent as grains and nodules __________ Shale, grayish—black, carbonaceous, tough; iron sulfides present as grains and nodules ______________ Dowelltown member: Middle gray beds: Mudstone; alternating thin greenish- gray, grayish-olive, olive-gray, and grayish-brown beds, together with a few thin grayish-black shale beds. A medium—dark-gray bentonite bed, 0.1 ft thick, present 1.22—1.32 ft below top _______________________ Lower black shale: Shale, grayish-black, carbonaceous, tough; iron sulfides present as grains ___________________________ 1.0 13. 7 5.5 10. 6 Total ________________________ 31. 5 Ordovician. Locality 88 is now below the normal pool level of a reservoir. The Maury formation was not recognized at this locality. The mudstone beds just beneath the Fort Payne chert contain numerous conodonts like those that characterize the lower faunal zone of the Gassaway member of the Chattanooga shale and in- clude Ancyrognathus bifurcata, Palmatolepis glabra, Palmatolepis perlobata, Palmatolepis subperlobata, and Polylophodonta confiuens. The Maury formation could have been cut out of the section through faulting as elsewhere, within a mile or two of locality 88, the Chattanooga shale and Maury formation interval has been greatly contorted and ranges from 3 to 6 feet in thickness. LOCALITY 89.—Face of waterfall on Pine Creek, 4.4 miles (airline) west of confluence with Carley Fork and 3.3 miles (airline) south- east of the courthouse at Smithville, DeKalb County, Tenn. Mississippian: Fort Payne chert: Limestone, blocky, interbedded with chert. Maury formation: Fm Mudstone, grayish-green, laminated _______ 1. 6 Mudstone, medium-gray to olive-gray, laminated ____________________________ . 3 LOCALITY 89—Continued Devonian: Chattanooga shale: Gassaway member: Fm Shale, grayish—black, carbonaceous, tough_- 5. 0 Shale, grayish-black, carbonaceous, tough; interbedded with thin beds of gray mud- stone. A laminated bed, 0.19 ft thick, consisting of paper-thin layers of black shale and gray very fine grained sand at base ______________________________ Shale, grayish-black, carbonaceous, tough- Dowelltown member: Mudstone: alternating thin grayish-green, grayish—olive, olive—gray, and grayish- brown beds, together with a few thin grayish—black shale beds. A bentonite bed, 0.08 ft thick, 0.60—0.68 ft below top _________________________________ Shale, grayish-black, carbonaceous, tough. Basal contact under water. Measured-- 5'.“ “to 9.3 6.7 Total exposed ____________________ 32. 9 Ordovician. LOCALITY 91.-—Cut on farm road, one mile north of State Highway 26‘ and 3.4 miles northeast of the courthouse at Smithrille, DeKalb County, Tenn. - Mississippian : Fort Payne chert. Maury formation (in part): Fm Mudstone, grayish~green, laminated _______ 2. 1 Devonian: Maury formation (in part): Course of phosphatic nodules embedded in gray mudstone _______________________ . 1 Chattanooga shale: Gassaway member: Shale, grayish-black, carbonaceous, tough- Shale, grayish-black, carbonaceous; inter- bedded with thin gray mudstones. A laminated bed, consisting of alternat- ing paper-thin layers of black shale and gray very fine grained sand at base _________________________________ Shale, grayish-black, carbonaceous, tough- Dowelltown member: Mudstone; alternating thin greenish-gray, grayish-olive, olive-gray, and grayish- brown beds, together with few thin grayish-black shale beds. A bentonite 7.0 5'.” Oath bed, 0.1 ft thick, 0.6—0.7 ft below top-__ 9. 3 Shale, grayish-black, carbonaceous, tough- 5. 9 Sandstone, iron~oxide-stained, consisting chiefly of rounded grains of quartz sand_ . 1 Total ____________________________ 34. 5 Ordovician. MEASURED SECTIONS 31 LOCALITr 92.—Cut on the Holmes Creek road, 1.6 miles north of the courthouse at Smithville, DeKalb County, Tenn. Mississippian : Fort Payne chert: Covered, float only. Maury formation (in part): Covered interval. Fm Mudstone, grayish-green, laminated _______ 1. 0 Shale, grayish-black, carbonaceous, tough_- . 2 Mudstone, gray ________________________ . 4 Devonian: Maury formation (in part): Course of phophatic nodules embedded in gray mudstone _______________________ . 5 Chattanooga shale: Gassaway member: Shale, grayish—black, carbonaceous, tough; scattered phosphatic nodules ___________ . 2 ' Shale, grayish-black, carbonaceous, tough__ Shale, grayish-black, carbonaceous, tough; interbedded with thin beds of gray mudstone. A laminated bed, 0.2 ft thick, consisting of alternating paper- thin layers of black shale and gray very fine grained sand at base ______________ Shale, grayish—black, carbonaceous, tough“ Dowelltown member: Mudstone, alternating thin grayish-green, grayishwlive, olive-gray, and grayish- brown beds, together with a few thin grayish-black shale beds. A bentonite bed, 0.12 ft thick, present 0.50—0.62 ft below the top ______________________ Shale, grayish-black, carbonaceous, tough__ saw [00 as: r—IO Total _____________________________ 32. 3 Ordovician. LOCALITY 95.—-—Cut on that portion of State Highway 26 abandoned as the main highway in 1.953, 3.1 miles east of Dowelllown, DeKalb County, Tenn. Regarded as the type locality of Campbell’s Dowelltown formation. This section is described on pages 13, 14. LOCALITY 100.—Cut on State Highway 53, about 5 miles by road south of Gassaway, Cannon County, Tenn. Type locality of Campbell’s Gassaway formation. This section is described on pages 14, 15. LOCALITY 107.—Deep out on United States Highway 41, 1 mile northwest of Noah and 10.1 miles northwest of Manchester, Coffee County, Tenn. Mississippian: Fort Payne chert. Maury formation: Feet Mudstone, light-greenish—gray to grayish- yellow - green, laminated, iron - oxide - stained ______________________________ 0. 9 LOCALITY 107—Continued Devonian: Chattanooga shale: Gassaway member: Feet Shale, grayish-black, carbonaceous, tough__ 0. 2 Mudstone, gray, iron-oxide—stained ________ 2 Shale, grayish-black, carbonaceous, tough; iron sulfides present as grains and nodules. Interval contains a few mudstone beds 0.01-0.08 ft thick _____________________ 5. ] Shale, grayish-black, carbonaceous, tough, alternating with thin beds Of grayish—olive to greenish-gray siltstone; iron sulfides present as grains and nodules. A lami- nated bed, 0.4 ft thick, consisting of alternating, paper-thin layers of grayish- black shale and iron-oxide-stained very fine grained sand at base ______________ Shale, grayish-black, carbonaceous, tough" P‘!‘ ooze Dowelltown member: Mudstone; alternating thin greenish-gray, grayish-olive, olive—gray, and grayish- brown beds, together with a few thin grayish-black shale beds. A bentonite bed, 0.05 ft thick, present 1.16-1. 21 ft below top ____________________________ Shale, grayish— black, carbonaceous, tough; a few thin gray mudstone beds. Iron sul- fides present as grains and nodules ______ Sandstone, medium-light—gray to grayish- black, calcareous. Consists chiefly of rounded quartz grains and iron sulfide grains and stringers. Top 0.45 ft Of interval contains thin layers of grayish- black, carbonaceous shale ______________ . 6 9.4 7.5 Total ____________________________ 30. 8 Ordovician. LOCALITY 126a.—In gully about 100 feet south of United States Highway 241, 4 miles south of the courthouse at Fayetteville, Lincoln County, Tenn. Mississippian: Fort Payne chert. , Maury formation: Feel Mudstone, light - greenish — gray to pale ~ greenish-yellow where freshly exposed, and yellowish-orange where weathered. Basal 0.5 ft greenish gray, indurated_-__ Devonian: ’ Chattanooga shale: Gassaway member: , Shale, grayish-black, carbonaceous, tough; iron sulfides preseint as grains, nodules, and paper-thin layers. The shale beds, which may be as much as 0.1 ft thick, are separated by reddish-brown silty beds as much as 0.02 ft thick __________________ 32 CHATTANOOGA SHALE AND MAURY FORMATION LOCALITY 126a—Continued Devonian—Continued Chattanooga shale—Continued Gassaway member—Continued Sandstone; light olive gray where freshly ex- posed, but yellowish brown and moderate brown where weathered; somewhat fri- able, consists chiefly of rounded grains of quartz sand. Iron sulfides common in top Feet 0.1 ft ________________________________ 0. 7 Total ____________________________ 7. 4 Ordovician. LOCALITY l27.—0uicks Mill on Flint River, about 4 miles west of New Market, Madison County, Ala. Section measured along mill race, approximately 0.2 mile upstream from Quicks Mill. [Holmes (1928) conodont fauna came from vicinity of this locality] M ississippian: Fort Payne chert: Limestone, yellowish—gray. Maury formation: Feet Course Of large phosphatic nodules em- bedded in gray siltstone ________________ 0. 3 Devonian: Chattanooga shale: Gassaway member: Shale, dark-gray to grayish—black, carbona— ceous, tough; iron sulfides present as grains _______________________________ 5. 0 Total _____________________________ 5. 3 Water level of mill race. LOCALITY 134.—Cut on south side of State Highway 129, 0.9 mile west of junction with United States Highway 31A in Cornersville, Marshall County, Tenn. Mississippian : Fort Payne chert. Maury formation: Feet Mudstone, light-greenish—gray, iron-oxide- stained, with few phosphatic nodules in basal 0.2 ft ___________________________ l. 3 Devonian: Chattanooga shale: Gassaway member: Mudstone, pale-olive ____________________ Shale, dark-gray, carbonaceous, silty ______ Claystone, light-green and orange-brown, laminated ____________________________ . 4 Shale, grayish-black, carbonaceous, tough; with persistent sandy bed, 0.6 ft thick, at base _________________________________ 3. 4 Shale, grayish—black, with paper-thin silty seams; iron sulfides are present as grains and nodules __________________________ ' 1. 0 Total- __________________________ 8. 7 Ordovician. LOCALITY 154.— Cut on road to Hampshire, 3.8 miles west of United States Highway 43 at Mount Pleasant, Maury County, Tenn. [Ulrich and Bassler’s (1926) “Hardin sandstone" conodont fauna came from this vicinity. See Bassler (1932, p. 141) for his description of section] Mississippian: Ridgetop shale: Mudstone, laminated, light-bluish-gray to greenish-gray. Approximately _________ Maury formation: Mudstone, greenish-gray and yellowish- brown, glauconitic, phosphatic grains common; course of phosphatic nodules in basal 0.2 ft ___________________________ . 8 Feet 13. 0 Devonian: Chattanooga shale: Sandstone, several shades of brown, in- durate, poorly sorted. Consists chiefly of quartz sand together with phosphatic grains, glauconite, bones and conodonts__ . 6 Total___________-________’ ________ 14.4 Ordovician. LOCALITY 163,— Cut on State Highway 50, 3 miles southwest of the main intersection at Cable, Hickman County, Tenn. Mississippian : Maury formation: Mudstone, light-olive-gray, glauconitic; few Feet phosphatic nodules ____________________ 0. 2 Course of large phosphatic nodules em- bedded in light-olive-gray mudstone; glauconitic ___________________________ . 3 Devonian: Chattanooga shale: Gassaway member: Shale, grayish-black, carbonaceous, tough-- 1. 0 Total ____________________________ 1. 5 Covered. LOCALITY 165.—Cut on State Highways 48 and 100; 2 miles northeast of Centerville, Hickman County, Tenn. Mississippian: Fort Payne chert: Limestone, cherty; basal foot weathered reddish-brown and dusky red. Maury formation: Feet Course of large phosphatic nodules em- bedded in a glauconitic grayish-olive mudstone ,,,,, . ,,,,,,,,,,,,,,,,,,,,,,, 0. 6 Devonian: Chattanooga shale: Gassaway member: Shale, grayish-black, carbonaceous, tough__ Sandstone, consisting chiefly of rounded grains of quartz sand. Upper 0.25 ft bluish-gray to olive gray; lower 0.35 ft iron oxide stained _____________________ . 6 3.6 Total ____________________________ 4. 8 Silurian. MEASURED SECTIONS LOCALITY 168.—C’ut on State Highway 50, about 3.5 miles southeast of Centerville, Hickman County, Tenn. Mississippian: Fort Payne chert. Maury formation: Feet Course of large phosphatic nodules em— bedded in dusky-yellow-green to grayish- olive, glauconitic mudstone ____________ 0. 7 Devonian: Chattanooga shale: Gassaway member: Shale, grayish-black carbonaceous, tough- _ 4. 2 Sandstone, bluish—gray to olive-gray, un- sorted; consisting of quartz grains, phos- phatic pellets, bone fragments, cono— donts, and iron sulfide grains, nodules, and lenses ___________________________ . 7 Total ____________________________ 5. 6 . Silurian. LOCALITY 185.—Standard section of the Maury formation. South side of a road 13.5 miles (airline) southeast of Franklin and 1.2 miles east of the road junction at Cross Key, Williamson County, Tenn. This section is described on page 23. LOCALITY 203.—-L0cal standard section of the New Providence shale. Cited in literature as Whites Creek Springs, but locally known as Crocker Springs, about 10.5 miles (airline) north of State Capitol in Nashville and 1.3 miles north of community of Alount Hermer, Davidson County, Tenn. [The following description is from L. C. Conant's notes of April 29, 1952] Mississippian: New Providence shale. Maury formation: Feet Top indefinite. Greenish—gray, glauconitic mudstone. Phosphatic nodules numer— ous and as much as 0.75 ft long. Interval poorly exposed; approximate thickness- _ l. 0 Devonian: Chattanooga shale: Gassaway member: Shale, grayish—black, massive. Probable duplication of beds through faulting _____ 24. O Dowelltown member(?): ' Shale, grayish-black, hackly in top 2 ft. Remainder of interval mostly concealed- _ 5. 0 Covered. Estimated thickness _________ 1. 0—2. 0 Shale, grayish-black, massive; exposed in creek bed. Base not exposed. Approxi- mate thickness of exposed beds __________ 3. 0 Total-”v. _ .. _-_. 34. 0—35. 0 33 LOCALITY 204.—Type locality of the Ridgetop shale, in cuts along the tracks of the Louisville and Nashville Railroad at Bakers Station, Davidson County, Tenn. From community of Ridgetop go south 3 miles on United States Highway 41 to road junction, turn west onto secondary road, go 0.7 mile to cuts along railroad tracks. The Gassaway member was measured in a cut at Bakers Station crossing, the Dowelltown member in a cut 1,560 ft south of the Bakers Station crossing. Mississippian: Ridgetop shale (only basal beds described): Feet Limestone, cherty, fossiliferous ___________ 1. 3 Mudstone, gray, laminated _______________ 1. 5 Maury formation: ‘ Mudstone, glauconitic ___________________ . 3 Mudstone, gray ________________________ . 7 Course of large phosphatic nodules embed- ded in gray mudstone _________________ . 6 Mudstone, gray and dark—brown, lami- nated ________________ * _________________ . 3 Devonian: Chattanooga shale: Gassaway member: Shale, grayish-black, carbonaceous, tough; phosphatic nbdules throughout --------- .7 Shale, grayish-black, carbonaceous, tough; iron sulfides present as grains and nodules. A persistent re—entrant zone, 0.3 ft thick, present 2.0—2.3 ft above base _________________________________ 10. 5 Shale, grayish-black, carbonaceous, tough; numerous iron sulfide grains and nodules- 1. 0 Sandstone (Bransford sandstone of Camp- bell, 1946),1 yellowish-gray, iron—oxide- stained; unsorted, consisting chiefly of rounded quartz grains, bone fragments, teeth, and conodonts __________________ .4 Dowelltown member: Shale, dark-gray to grayish-black, carbona- ceous, tough _________________________ . 5 Mudstone, dark-gray, hackly, iron sulfides present as grains and thin seams ________ 3. 1 ' Sandstone, medium-light-gray, iron-oxide— stained, friable; ranges in thickness from 0.02—0.13 ft; average ------------------ . 1 Shale, grayish-black to dark-gray, carbona- ceous, laminated ______________________ . 35 Mudstone, sandy, laminated. Upper half consists of alternating paper-thin layers of dark-gray shale and light-gray mud- stone; lower half consists chiefly of quartz sand _________________________________ . 15 Shale, grayish-black, carbonaceous, tough; interbedded thin gray beds and lenses of mudstone and sandstone. Iron sulfides present as grains and nodules ___________ Sandstone, dark-gray to medium-dark-gray, 11.7 unsorted; consists chiefly of rounded grains of quartz sand __________________ 1. 0 Total ---------------------------- 34. 20 Silurian. 1 Section carried 1,560 it south of Bakers Station crossing on this sandstone. 34 LOCALITY 205.—-Cut on State Highway 109, 5.5 miles north of Gallatin, Sumner County, Tenn. Mississippian: New Providence shale (basal portion): Chert, porous, weathered, iron-oxide-stained- Siltstone, indurated, laminated, greenish- gray to pale-olive; basal 0.15 ft contains glauconite and phosphatic nodules ______ Maury formation: Mudstone, plastic, dusky-yellow to greenish- gray, glauconitic. Contact with overlying New Providence shale indefinite ________ . 9 Mudstone, grayish-green, glauconitic ______ . 3 Course of large phosphatic nodules em- bedded in dark-gray siltstone. Largest nodule observed measured 2.5 y 0.1 by . 0.3 ft _______________________ 1 ________ . 2 Devonian: l Chattanooga shale: ‘ Gassaway member: “ Shale, grayish-black carbonaceous, tough; no phosphatic nodules recognized in top- most portion of interval. Lowehr portion disturbed ____________________________ Sandstone (Bransford sandstone of Camp- bell, 1946), very light gray to dark-gray, iron-oxide-stained, poorly sorted, in- durated; consists chiefly of rounded grains of quartz sand. Lenticular, ranges from featheredge to 0.2 ft in thickness, average- . 1 Dowelltown member: Shale, grayish-black, with sandy lenses; beds of interval disturbed. Base not ex- posed; estimated thickness _____________ Feet 2. 0 16. 0 15.0 Total ____________________________ 44. 0 Covered. LOCALITY 206. —Type locality of Campbell’s Bransford sandstone member of his G’assaway formation. In west bank of Bledsoe Creek which parallels United States Highway 81E, 3.6 miles north of intersection with State Highway 10A at Bransford, Sum- ner County, Tenn. Mississippian: New Providence shale: Fm Limestone interbedded with mudstone. Unit greenish gray and light bluish gray, crinoidal. Grades into overlying cherty limestones. Maury formation (in part): , Covered, probably Maury formation, esti- mated thickness ______________________ 1. 0 Shale (Westmoreland shale of Campbell, 1946), grayish-black to black, carbona- ceous, tough; iron sulfides present as grains and nodules ____________________ l. 0 9.5. CHATTANOOGA SHALE AND MAURY FORMATION LOCALITY 206—Continued Devonian: Maury formation (in part): Feet Mudstone (upper part of Eulie shale of Campbell, 1946), yellowish-gray to pale- olive-gray, indurated ________________ 0. 2 Course of large phosphatic nodules (lower part of Eulie shale of Campbell)___.'_ - _ _ . 3 Chattanooga shale: Gassaway member: Shale, grayish—black, carbonaceous, tough; iron sulfides present as grains and nodules. Phosphatic nodules common, may be as much as 1 ft in length _________________ . 5 Shale, grayish—black, carbonaceous, tough; iron sulfides present as grains, nodules, and seams. A few very thin beds of gray mudstone ____________________________ Sandstone (Type Bransford sandstone of Campbell, 1946), very light gray to dark- gray, iron-oxide-stained; poorly sorted, indurated; consists chiefly of rounded grains of quartz sand, bone fragments, fish teeth, conodonts, and iron sulfide grains and nodules. Base uneven. As much as 0.25 ft thick; average _________ . 2 Dowelltown member: Shale, grayish-black, carbonaceous, tough; ‘ a few thin beds of gray mudstone present. Rocks of interval weather to small chips and dip about 8° NW _________________ Shale (Trousdale shale of Pohl, 1930a), grayish-black, carbonaceous; interbedded ' with medium—gray to dark-gray calcareous sandstones that consist chiefly of rounded grains of quartz sand. Iron sulfides present as grains and nodules_____ _ _ _ - _ - 15. 5 15.0 2.0 Total ............................. 35. 7 Silurian. LOCALITY 207.—Type locality of Campbell’s Westmoreland shale; 200 yards north of Garretts Creek Church and 5.6 miles by road north of Westmoreland, Sumner County, Tenn. Mississippian: New Providence shale: Limestone, crinoidal, light—gray; interbed- ded with thin greenish-gray calcareous silty beds. Maury formation (in part): Covered _______________________________ Mudstone, light-gray ____________________ . 2 Shale (type Westmoreland shale of Camp- bell, 1946), grayish-black, carbonaceous; a few phosphatic nodules, as much as 0.3 ft long, throughout interval. Iron sul- fides present as grains _________________ . 5 Feet MEASURED SECTIONS ' 35 LOCALITY 207—Continued Devonian: Maury formation (in part): Fm Mudstone (upper part of Eulie shale of Campbell, 1946), Olive-gray, medium- gray, and greenish-gray ________________ 0. 4 Course of large phosphatic nodules (lower part of Eulie shale of Campbell, 1946)“ . 2 Chattanooga shale: Gassaway member: Shale, grayish-black, carbonaceous, tough; iron sulfides present as grains. Few phos- phatic nodules embedded in top 0.1 ft. Basal contact covered. Measured ______ 6. 0 Total ____________________________ Covered, creek level. 7.5 LOCALITY 215.—Road cut and hillside, 2 miles east of road junc tion near Cedar Ridge, northeast corner of Melvine quadrangle, Bledsoe County, Tenn. Mississippian: Fort Payne chert: Limestone, cherty. Maury formation: Feet Mudstone; predominantly yellow green, friable. Indurated and dark gray at base. Phosphatic nodules throughout interval- 1. 5 Devonian: Chattanooga shale: Gassaway member: Shale, grayish-black, carbonaceous; phos- phatic nodules present _________________ . 4 Mudstone, light-gray ____________________ . 2 Shale, grayish—black, carbonaceous; phos- phatic nodules present _________________ 1. 6 Shale, grayish-black, carbonaceous, some- what disturbed. Iron sulfides present as grains _______________________________ 10. 7 Dowelltown member: Mudstone: alternating thin greenish-gray, grayish-olive, olive—gray, and grayish- brown beds, together with a few thin grayish-black shale beds. A light—gray bentonite bed, 0.14 ft thick, present 0.43—- 0.57 ft below top. This interval is poorly exposed and somewhat disturbed _______ 7. 4 Shale, grayish-black, disturbed ___________ 2. 5 Sandstone, consists chiefly of rounded grains of quartz sand ________________________ . 2 Total ____________________________ 24. 5 Silurian. LOCALITY 220.—West slope of Walden Ridge. C’ut along State Highway 8, 1 mile southeast of junction with State Highway 98, near Dunlap, Sequatchie County, Tenn. Mississippian : Fort Payne chert: Limestone, cherty, blocky; basal 0.25 ft weathered. LOCALITY 220—Continued Mississippian—Continued Maury formation: Feet Mudstone, plastic, grayish-green to dusky- green; phosphatic nodules abundant- _ _ - Mudstone, indurated, dusky-yellow-green; phosphatic nodules abundant; calcareous- siliceous geodes in top 0.4 ft ____________ 1. 1 Mudstone, indurated, greenish-gray to dark- greenish—gray; phosphatic nodules in top 0.5 ft ________________________________ 1. 7 Devonian: Chattanooga shale: Gassaway member: Shale, grayish-black, tough. Numerous phosphatic nodules throughout interval, also concentrated in a persistent course 0.9—1.0 ft below top. Iron sulfides present as grains and nodules ___________ 1. 0 Shale, grayish-black, tough, very thinly bedded. Iron sulfides common as grains, nodules, and paper-thin layers _________ 4. 2 Shale, grayish-black, somewhat disturbed. Iron sulfides present as grains and nodules ______________________________ 7. 4 Dowelltown member: Bentonite bed, 0.04—0.15 ft thick _________ . 15 Shale, grayish-black, alternating with thin beds of light— to medium-gray mudstone- . 95 Sandstone, indurated; light gray where freshly exposed and dark rusty brown where weathered. Thickness varies from 0.3—0.6 ft; average __________________ .—- . 5 Total ____________________________ 17. 10 Silurian. LOCALITY 225.——Type locality of the Glendale shale of Swartz (1924). Hillside exposure along railroad tracks, just southwest of junction of State Highway 27 (not United States Highway 27) . and State Highway 8, North Chattanooga, Hamilton County, Tenn. Mississippian: Fort Payne chert: Limestone, cherty, blocky; basal 0.25 ft weathered. Fm Maury formation (Glendale shale of Swartz): Mudstone, plastic, grayish-green to dusky- green; phosphatic nodules and calcareous- siliceous geodes common _______________ Mudstone. Top 0.25 ft somewhat plastic, predominantly grayish yellow green to dusky yellow green; phosphatic nodules and calcareous-siliceous geodes abundant. Bottom 0.85 ft indurated, dusky yellow green; phosphatic nodules present but not abundant ________________________ 1. 1 Mudstone, indurated, laminated, greenish- gray to dark-greenish—gray; phosphatic nodules scarce ________________________ . 7 Mudstone, indurated, olive-gray __________ Course of phosphatic nodules in olive-gray silty matrix __________________________ . 2 0.2 o p—n l 36 CHATTANOOGA SHALE A‘ND MAURY FORMATION LOCALITY 225——Continued M ississippian—Continued Maury formation—Continued Fee; Mudstone, less indurated than middle por- tion of formation, olive-gray, with few phosphatic nodules in basal 0.1 ft and a concentration of conodonts in paper-thin layer at very base _____________________ 0. 5 Devonian: Chattanooga shale: Gassaway member: Shale, carbonaceous, grayish-black, tough. Exposed _____________________________ 2. 3 Total ____________________________ 5. 1 Covered. LOCALITY 226.—Type locality of the Chattanooga shale. Hillside exposure at the north end of Cameron Hill, Chattanooga, Hamilton County, Tenn. [See pl. 5] Mississippian : Fort Payne chert: Fee, Limestone, cherty, blocky; basal beds locally weathered to a porous, somewhat friable, reddish-brown rock. Maury formation: Mudstone, plastic, grayish-green to dusky»~ green; phosphatic nodules and calcareous- siliceous geodes common _______________ Mudstone, Top 0.25 ft somewhat plastic, predominately greenish gray to light olive brown; bottom 0.35 ft indurated, dusky yellowish green. Phosphatic nodules throughout ___________________________ . 6 Mudstone, indurated, pale-olive and gray- ish-olive. Phosphatic nodules scarce__ 1. Course of small phosphatic nodules em- bedded in olive-gray to dark-gray shale-_ Mudstone, indurated, olive-gray __________ [O A O 01 Devonian: Chattanooga shale: Gassaway member: Shale, carbonaceous, grayish-black, in- competent, fractured; slickensided sur- faces common; iron sulfides present as stringers, paper-thin layers, nodules, and clusters of pyrite crystals ______________ 7. 0 Total ____________________________ 9. 45 Silurian. LOCALITY 228,—Cut along tracks of Southern Railroad, immediately south of the Ooltewah—Apison road crossing. About 1 mile east of Collegedale and 2 miles west of Apison, Hamilton County, Tenn. Mississippian : Fort Payne chert: Limestone, cherty, blocky; basal beds locally weathered to a porous, somewhat friable, reddish-brown rock. LOCALITY 228—Continued Mississippian—Continued Maury formation: Feet Mudstone, plastic, dusky-green to dusky- yellow-green ; phosphatic nodules common and as much as 0.5 ft long ____________ 0.25 Mudstone, indurated, dark-greenish-gray; phosphatic nodules common, irregularly shaped, as much as 0.2 ft long __________ 2.25 Mudstone, indurated, olive-black to olive— gray; phosphatic nodules present, as much as 0.2 ft long ________________________ .5 Shale, carbonaceous, dark-gray to grayish- black, incompetent; phosphatic nodules abundant, as much as 0.1 ft long; iron sulfides present as grains and nodules. Thickness varies from 3.8—4.7 ft; average- 4. 2 Sandstone, indurated, brownish-black; com- posed chiefly of rounded grains of quartz sand cemented with iron sulfides _______ . 2 Devonian: Chattanooga shale: Gassaway member: Mudstone, indurated, olive-gray to olive- black ________________________________ . 2 Claystone; pale olive to grayish olive where freshly expOSed and dark yellowish orange where weathered ______________________ 1. 3 Mudstone, grayish-olive. Poorly preserved megafossils ___________________________ . 3 Mudstone, indurated, olive-gray, sandy__-- . 2 Shale, carbonaceous, grayish-black; rounded grains of quartz sand common; iron sul- fides present as grains and paper-thin layers- ----——-~---——-----—-----——---.- 1.5 Mudstone, olive-gray; thickness varies from 0.02—0.17 ft; average __________________ . 1 Shale, carbonaceous, grayish—black: rounded grains of quartz sand____'____-_; _______ 1.0 Mudstone, olive-gray. Thickness varies from 0.02—0.33 ft; average _____________ . 2 Shale, carbonaceous, grayish-black; rounded grains of quartz sand __________________ 5. 6 Mudstone, indurated, olive-gray, inter- bedded with grayish-black shale; numer— ous rounded grains of quartz sand; also irregularly shaped, very light gray to greenish-gray granules and pebbles of siltstone. Thickness varies from 2.5—3.0 ft; average ___________________________ 2. 7 Sandstone, indurated, blocky; dark gray where freshly exposed and moderate brown where weathered ________________ . 2 Total ____________________________ 20. 70 Silurian. Through faulting, some of the beds in the lower part of the Chattanooga shale at locality 228 appear to have been duplicated. The stratigraphic thickness of the shale is probably about 10 feet. MEASURED SECTIONS LOCALITY 235.—Type locality of Whetstone Branch shale of Morse (1928), Whetstone Branch, Tishomingo County, Miss. From junction of State Highways 25 and 72 in I uka go north on Highway 25 for 3.5 miles; turn north onto well-traveled secondary road; go 3.6 miles to road fork, continue north; go 3.1 miles to road fork, continue north; go 0.8 mile and immediately after crossing tributary of Whetstone Branch, turn onto dirt road that parallels Whetstone Branch; go 0.5 mile. The best outcrop is along the north bank of Whetstone Branch, about 300 feet from its confluence with the Tennessee River. Mississippian : Carmack limestone of Morse: Limestone, bluish-gray. Maury formation: Fm Course of large phosphatic nodules em- bedded in glauconitic mudstone. (Basal bed of Morse’s Carmack limestone) _____ 0. 5 Devonian: Chattanooga shale (Whetstone Branch shale of Morse): Gassaway member: Mudstone, gray, indurated, siliceous; nu- merous grains and stringers of iron sulfide _______________________________ . 1 Mudstone, gray, indurated; numerous con- odonts in basal 0.1 ft __________________ . 5 Shale, grayish-black, carbonaceous, tough; iron sulfides present as grains, nodules, and lenses ___________________________ . 8 Sandstone, grayish-black, lenticular, cal- careous, crossbedded; iron sulfides present as grains and nodules. The sandstone beds are 0.3~0.4 ft thick and are separated by thinner undulating beds of grayish- black carbonaceous shale ______________ 1. 2 Dowelltown member: Sandstone and shale similar to that above. The topmost 1 or 2 ft of interval may belong to the Gassaway member. Ex- posed _______________________________ 9. 5 Total exposed ____________________ 12. 6 Bed of Whetstone Branch. LOCALITY 239.—In gutter and bed of secondary road by stone church, 0.15 mile south of United States Highway 64 at Olive Hill, Hardin County, Tenn. [The description and thickness of the lithologic units given below are after V. E. Swanson’s notes of July 1, 1949. The present writer is responsible for assigning beds to the Gassaway and Dowelltown members of the Chattanooga shale] Mississippian: Ridgetop shale. Maury formation: Total thickness not determinable, top not exposed. Sandstone unit at base, 0.5 ft thick, contains abundant glauconite, abundant phosphatic nodules, some mar- casite nodules, and siliceous geodes. Conformable with Chattanooga shale. Approximately _______________________ 866719-58——4 Feet 1.0 37 LOCALITY 239—Continued Devonian : Chattanooga shale: Gassaway member: Feet Shale; weathered to chocolate-brown clay- like material _________________________ O. 9 Covered _______________________________ 3. 3 Shale, grayish-black, finely laminated _____ .4 Dowelltown member: Covered _______________________________ 1. 5 Siltstone, light-gray to light-buff; some- what ferruginous ______________________ 3. 4 Sandstone, buff, medium-grained; very friable on weathered surfaces ___________ . 6 Shale, dark-gray to grayish-black; thin marcasite lenses ______________________ 2. T Sandstone, light-gray to yellowish-gray, fine grained, individual beds as much as 0.3 ft thick ________________________________ 1. 7 Shale, gray to chocolate-brown (probably weathered grayish-black shale) _________ 1. 2 Sandstone, probably gray where unweathered. Surface iron oxide stained. Small mar- casite nodules present _________________ . 3 Shale and some siltstone. Dominantly grayish-black shale which weathers light gray to tan. Shale grades into thin silt- stone beds which commonly are dark gray and have black lamellae _______________ 7. 5 Shale and sandstone beds, alternating; each bed approximately 0.4 ft thick. The shale beds are grayish black and the sandstone beds have grayish-black lamel- lae. Marcasite present ________________ 4. Sandstone, buff to gray, fine-grained ______ . 3 Sandstone and siltstone; gray sandstone interbedded with grayish-black siltstones. Thin zones appear to be crossbedded, slightly calcareous; marcasite nodules H present. Surface with iron oxide stain__ 5. 8 Covered_____________'_ _________________ 1.0 Sandstone, gray to buff, very fine grained“ . 2 Siltstone, gray to dark-gray ______________ . 6 Hardin sandstone member: Sandstone, bufl‘ to gray, fine-grained, mas— sive to poorly bedded. Top 2.7 ft well exposed; additional 10 ft poorly exposed. Base covered _________________________ 12. 7 Total ____________________________ 49. 2 Covered. LOCALITY 249.—Vicinity of city pumphouse. along small stream valley, west of State Highway 100, 0.2 mile northeast of court- house at Linden, Perry County, Tenn. Additional exposures along Highway 100, 0.25 mile from courthouse. Mississippian: Maury formation: ' Feet Course of large phosphatic nodules em- bedded in fine-grained, glauconitic, light- olive-gray, iron-oxide-stained sandstone. Thickness varies from 0.15 — 0.9 ft _____ O. 9 38 LOCALITY 249—Continued Devonian: Chattanooga shale: Gassaway member: Feet Shale, dark-gray to grayish-black, carbo- naceous, tough _______________________ 5. 2 Sandstone, brownish-gray, interbedded with dark-gray shale _______________________ . 5 Dowelltown member: Shale, dark-gray to grayish-black, carbo- naceous, tough _______________________ 1.0 Hardin sandstone member: Sandstone, fine-grained __________________ 2. 5 Total ____________________________ 10. 1 Quall limestone. LOCALITY 250.—E’xposure to east of the entrance to the Hayes and Elkins limestone mine; 100 ft north of State Highway 100, 0.5 mile west of the intersection at Pleasantville, Hickman County, Tenn. Mississippian: Fort Payne chert(?): Limestone, bluish; grading into basal silty limestone. Maury formation: Feet Mudstone, olive-gray, laminated __________ 2. 0 Mudstone, glauconitic ___________________ , 5 Course of large phosphatic nodules em- bedded in glauconitic mudstone _________ . 2 TABLE 6.— Conodont collections from the Chattanooga CHATTANOOGA SHALE AND MAURY FORMATTON LOCALITY 250—Continued Mississippian—Continued Maury formation—Continued Mudstone, glauconitic ___________________ Feet 0. 2 Devonian: Chattanooga shale: Gassaway member: Shale, grayish-black, carbonaceous, tough; Palmatolepis glabra Ulrich and Bassler present at very base of interval _________ Sandstone, grayish-black; consisting chiefly of rounded quartz grains _______________ . 3 Total ___________________________ 4. 7 Silurian. CONODONT COLLECTIONS Listed below are data pertaining to the conodont collections mentioned by number in the text. Almost all the collections were prepared in 1948 and 1949, at which time each was given the number listed in the first, or left-hand, column of table 6. Subsequently, each collection was given the permanent number listed in column 2 of the table. In this column the letter “C” affixed to a collection number indicates that the number is from the “Carboniferous” catalog, and the letters “SD,” that the number is from the “Silurian and Devonian” catalog. * shale, Maury formation, and New Providence shale [Stratigraphic position given with reference to top of Chattanooga shale, base of Maury formation, or base of New Providence shale. All collections made by W. H. Hass] Collection Locality No. U S‘ S" S Date Stratigraphic position his ‘in Description 3 15500—0 Nov. 14, 1947 Maury formation: 0.3—0.5 ft above base __________ 78 Cut on that portion of State Highway 26 abandoned in 1948; approximately 0.6 mile southeast of eastern approach to Sligo Bridge over the Caney Fork on present State Highway 26 and 5.9 miles (airline) east of the courthouse at Smithville, DeKalb County, Tenn. 5 3650—SD Nov. 14,1947 Chattanooga shale, Gassaway member: 1.3—1.7 78 Same as collection 3. ft below top. 7 3651-SD Nov. 19, 1947 Chattanooga shale, Dowelltown member: 2710— 92 Cut on the Holmes Creek road, 1.6 miles north of the courthouse at Smith- 29.0 it below top. ville, DeKalb County, Tenn. 9 3652—SD Nov. 19,1947 Chattanooga shale, Dowelltown member: 92 Same as collection 7. basal 1.5 ft or 28.7—30.2 it below top. 11 3653-SD Nov. 19,1947 Chattanooga shale, Dowelltown member: 92 Same as collection 7. 20.0—20.3 it below top. 15 15501—0 Dec. 18,1947 Maury formation: basal 0.05 ft .................. 89 Face of waterfall on Pine Creek, 4.4 miles (airline) west of confluence with Caney Fork and 3.3 miles (airline) southeast of the courthouse at Smith- ville, DeKalb County, Tenn. 17 15502~C Nov. 29,1947 Maury formation: 0.9—1.1 ft above base .......... 92 Same as collection 7. 18 3654—SD Nov. 14,1947 Chattanooga shale, Gassaway member: 3.5—4.0 78 Same as collection 3. it below top. _ 19 3655—SD Nov. 19,1947 Chattanooga shale, Gassaway member: 9.4— 92 Same as collection 7. 10.5 it below top. 21 3656-SD Nov. 13,1947 Chattanooga shale, Gassaway member: 12.07 78 Same as collection 3. 12.6 it below top. . 22 15503—0 J an, 22,1948 Maufy formation: 0.15—0.5 it above base ........ 100 Type locality of Campbell’s Gassaway formation. Cut on State Highway 53, about 5 miles by road south of Gassaway. Cannon County, Tenn. There are two exposures within 0.4 mile of each other: one on the north slope of a hill, the other on the south slope. All collections mentioned in this report from this locality are from the outcrop on the north slope. 23 3657—SD Nov. 20,1947 Chattanooga shale, Gassaway member: 1.1—1.6 92 Same as collection 7. it below top. 24 3799—SD Nov. 12,1947 Chattanooga shale, Dowelltown member: 20.0— 78 Same as collection 3. 20.7 It below top. CONODONT COLLECTIONS 39 TABLE 6.— Conodont collections from the Chattanooga shale, Maury formation, and New Providence shale— Continued {Stratigraphic position given with reference to top of Chattanooga shale, base of Maury formation, or base of New Providence shale. 'All collections made by W. H. Hassl Collection Locality No. U‘ if 5 Date Stratigraphic position Np'}: fin Description 26 3658—SD Jan. 8,1948 Chattanooga shale, Gassaway member: 1187— 95 Regarded as the type locality of Campbell’s Dowelltown formation. Cut 11.9 it below top. on that portion of State Highway 26 abandoned as the main‘highway in 1953, 3.1 miles east of Dowelltown, DeKalb County, Tenn. 27 3659—SD Jan. 15,1948 Chattanooga shale, Gassaway member: 4.5—4.9 95 Same as collection 26. ft below top. 3660~SD Jan. 22,1948 Chattanooga shale, Gassaway member: 8.5—9.3 100 Same as collection 22. ft below top. 3661-~SD Jan. 19,1948 Chattanooga shale, Dowelltown member: 145- 95 Same as collection 26. 14.8 ft below top. ‘30 3662—SD Jan. 19,1948 Chattanooga shale, Dowelltown member: 21.5— 95 Same as collection 26. 22.5 it below top. 31 3663—SD Jan. 22, 1948 Chattanooga shale, Gassaway member: top 0.4 ft. 100 Same as collection 22. 32 3664-SD Jan. 15,1948 Chattanooga shale, Gassaway member: 9.5-9.7 95 Same as collection 26. it below top. 33 3665—SD Jan. 15, 1948 Chattanooga shale, Gassaway member: 2.3—3.6 ft 95 Same as collection 26. below top. 34 3666—SD J an. 15, 1948 Chattanooga shale, Gassaway member: 6.2—6.5 ft 95 Same as collection 26. below top. 85 3667—SD Jan. 22, 1948 Chattanooga shale, Gassaway member: 2.3-2.7 ft 100 Same as ccllection 22. below top. 40 3668—SD J an. 15, 1948 Chattanooga shale. Gassaway member: top 0.8 it. 95 Same as collection 26. 42 3669—SD Jan. 24,1948 Chattanooga shale, Dowelltown member: 24.5— 95 Same as collection 26. 25.4 it below top. - 43 3670—SD J an. 22, 1948 Chattanooga shale, Gassaway member: 12.8— 100 Same as collection 22. 13.5 it below top. 44 3671-SD Jan. 22,1948 Chattanooga shale, Gassaway member: 2.0—2.3 100 Same as collection 22. it below top. 46 3672—SD Nov. 20,1947 Chattanooga shale, Dowelltown member: basal 91 Cut on farm road, 1 mile north of State Highway 26 and 3.4 miles north- 0.1ft or 32.2—32.3 ft below top. east of the courthouse at Smithville, DeKalb County, Tenn. 47 3673-SD Nov. 12, 1947 Chattanooga shale, Dowelltown member: basal 78 Same as collection 3. 0.2 ft or 32.9—33.1 it below top. '48 3674—SD Nov. 29, 1947 Chattanooga shale, DOWelltown member: basal 75 Cut on abandoned farm road, 0.5 mile northwest of point on State Highway 0.2 ft or 33.5—33.7 ft below top. 26 where deScent starts to the east end of the Sligo Bridge over the Caney Fork, and 5.8 miles (airline) east of the courthouse at Smithville, DeKalb County, Tenn. 49 15504—0 Jan. 2, 1948 Maury formation: 0.5-0.9 ft above base .......... 89 Same as collection 15. 50 15505-0 Jan. 2,1948 Maury formation: top 0.1 ft or 1.8—1.9 ft above 89 Same as collection 15. base. 51 15596—0 Jan. 22, 1948 Maury formation: 0.5-1.7 it above base .......... 100 Same as collection 22. 55 15507—0 June 26, 1947 Maury formation: 3.8—4.1 ft above base __________ 228 Out along tracks of the Southern Railroad, immediately south of the Oolte- wah-Apison road crossing. About 1 mile east of Collegedale and 2 miles west of Apison, Hamilton County, Tenn. 64 3675—SD June 28,1947 Chattanooga shale, Gassaway member: 7.0—8.0 228 Same as collection 55. it below top. 65 3676—SD June 27,1947 Chattanooga shale, Gassaway member: 3.6—4.6 228 Same as collection 55. ft below top. 66 3677-SD June 26,1947 Chattanooga shale, Gassaway member: top 0.2 228 Same as collection 55. ft. , 67 3678-SD June 28,1947 Chattanooga shale, Gassaway member: 0.2-1.4 228 Same as collection 55. ft above base or 11.9—13.1 it below top. 68 3679-SD June 27, 1947 Chattanooga shale, Gassaway member: 2.0— 228 Same as collection 55. 2.7 it below top. 69 3680—SD July 1,1947 Chattanooga shale, Gassaway member: top 1.0 226 Type locality of the Chattanooga shale. Hillside exposure, about 350 ft ft. ‘ south of the north end of Cameron Hill, Chattanooga, Hamilton County, Tenn. 71 3681—SD June 24, 1947 Chattanooga shale, Gassaway member: top 2.3 225 Type locality oi Swartz’s Glendale shale. Hillside exposure along railroad it. tracks, just southwest oi junction of State Highway 27 (not United States Highway 27) and State Highway 8, North Chattanooga, Hamilton County, Tenn. 72 3682-SD June 24, 1947 Chattanooga shale, Gassaway member: top 0.9 ft. 225 Same as collection 71. 73 15508—0 June 26, 1947 Maury formation: 4.2-4.4 ft above base ______ 228 Same as collection 55. 74 15509-0 June 23, 1947 Maury formation: 0.4—0.45 ft above base .......... 226 Type locality of the Chattanooga shale. Hillside exposure at the north end of Cameron Hill, Chattanooga, Hamilton County, Tenn. 76 3683—SD June 28,1947 Chattanooga shale, Gassaway member: 8.7-9.5 228 Same as collection 55. it below top. 77 3684—SD June 24, 1947 Chattanooga shale, Gassaway member: top 0.9 it , 225 Same as collection 71. 82 3685—SD June 26,1948 Chattanooga shale, Gassaway member: 4.7—5.2 126a In gully about 100 it south of United States Highway 241, 4 miles south it below top. of the courthouse at Fayetteville, Lincoln County, Tenn. 83 3686—SD May 20, 1948 Chattanooga shale, Gassaway member: 4.1—4.5 207 Type locality of Campbell's Westmoreland shale, 200 yards north of ft below top. Garretts Creek Church and 5.6 miles by road north of Westmoreland, Sumner County, Tenn. 40 CHATTANOOGA SI-IALE AND MAURY FORMATION TABLE 6.——Conodont collections from the Chattanooga shale, Maury formation, and New Providence shale—Continued [Stratigraphic position given with reference to top of Chattanooga shale, base of Maury formation, or base of New Providence shale. All collections made by W. H. Hass} Collection Locality No. U” $33 S Date Stratigraphic position N19]. '1“ Description 84 3687-SD May 19,1948 Maury formation: basal 0.5ft .................... 74 Face of Taylor Creek Falls (Fanchers Mill), about 10 miles (airline) north west of Sparta, White County, Tenn. 85 3688—SD J line 22, 1948 Chattanooga shale, Dowelltown member: 12.9— 107 Deep cut on United States Highway 41, 1 mile northwest of Noah and 10.1 13.2 ft below top. miles northwest of Manchester, Coffee County, Tenn. 86 3689—SD May 31, 1948 Chattanooga shale, Gassaway member: 10.7-11.2 6 In cut and on hillside below the Oil Center Road, just east of the crossing it below top. over Big Clifty Creek, 5.4 miles west of Somerset, Pulaski County, Ky. 95 3690—SD May 20,1948 Chattanooga shale, Gassaway member: 0.3—0.7 60 Cut on United States Highway 70N, 0.8 mile west of Chestnut Mound, it below top. Smith County, Tenn. 100 3691—SD May 20, 1948 Chattanooga shale, Gassaway member: top 0.2 ft. 207 Same as collection 83. 102 3692-SD May 22, 1948 Chattanooga shale, Dowelltown member: 18.5- 107 Same as collection 85. 19.0 it below top. 103 3693-SD June 22, 1948 Chattanooga shale, Dowelltown member: 22.2— 107 Same as collection 85. 22.7 it below top. 104 3694—SD June 23, 1948 Chattanooga shale, Gassaway member: top 0.6 ft. 107 Same as collection 85. 106 3695—SD May 20, 1948 Chattanooga shale, Gassaway member: 13.6-13.9 60 Same as collection 95. ft below top. 107 3696—SD May 26,1948 Chattanooga shale, Dowelltown member: 01- 39 Cut on State Highway 56. 1.7 miles south of Gainesboro, Jackson County, 0.3 ft above base or 21.7—21.9ft below top. Tenn. 110 3697-SD June 2,1948 Chattanooga shale. Gassaway member: 19.6—21.0 11 Cut on State Highway 35, 1.5 miles south-southeast of Rowena and just ft below top. north of the county line, Russell County, Ky. 111 3698-SD June 2,1948 Chattanooga shale, Gassaway member: 10.6—11.6 11 Same as collection 110. it below top. 112 3699—SD June 2, 1948 Chattanooga shale, Gassaway member: 30.0—30.4 11 Same as collection 110. it below top. 113 15510—0 May 20,1948 Maury formation: 0.6—1.1 ft above base. This 207 Same as collection 83. is from Campbell‘s type Westmoreland shale. 115 3700—SD June 2,1948 Chattanooga shale, Gassaway member: 19.6-21.0 11 Same as collection 110. ft below top. 116 3701—SD June 2,1948 Chattanooga shale, Gassaway member: basal 0.1 11 Same as collection 110. ft or 35.2-35.3 ft below top. 119 3702—SD May 26,1948 Chattanooga shale, Gassaway member: 4.9-5.2 39 Same as collection 107. it below top. 120 3703—SD May 17, 1948 Chattanooga shale, Dowelltown member: basal 76 Standard section of the Chattanooga shale. Cut on State Highway 26, at 0.6 ft or 31.5—32.1 ft below top. the east approach to the Sligo Bridge over the Caney Fork, 5.9 miles (airline) or 7.1 miles by road east of the courthouse at Smithville, DeKalb County, Tenn. 123 3704-SI) May 31,1948 Chattanooga shale, Gassaway member: 12.4—13.1 6 Same as collection 86. it below top. 126 3705—SD May 20, 1948 Chattanooga shale, Gassaway member: top 39 Same as collection 107. 0.8 ft. 129 3706—SD June 28,1948 Chattanooga shale, Gassaway member: 8.9—9.9 220 West slope of Walden Ridge. Cut on State Highway 8, 1 mile southeast It below top. of junction with State Highway 28, Sequatchie County, Tenn. 130 3707~SD May 31.1948 Chattanooga shale, Gassaway member: 14.3—14.7 6 Same as collection 86. ft below top. 131 3708—SD June 27, 1948 Chattanooga shale, Gassaway member: top 0.5 ft. 126a Same as collection 82. 133 3709—SD May 20,1948 Chattanooga shale. Gassaway member: 6.7—7.0 60 Same as collection 95. ft below top. 137 15511—0 June 14,1948 Maury formation: 0.6—0.66 ft above base. This 207 Same as collection 8'3. is from basal 0.06 ft of Campbell’s type West- moreland shale. 138 3710—SD J unc 16,1947 Chattanooga shale, Gassaway member: 0.6—1.0 206 Type locality of Campbell’s Bransford sandstone member of his Gassaway it below top. formation. in west bank of Bledsoe Creek which parallels United States Highway 31E, 3.6 miles north of intersection with State Highway 10A at Bransford, Sumner County, Tenn. 143 3711—SD June 23, 1948 Chattanooga shale, Gassaway member: 11.5—12.5 107 Same as collection 85. ft below top. 144 3712—SD June 16,1947 Chattanooga shale, Gassaway member: 1.5—2.0 206 Same as collection 138. it below top. 145 3713—SD June 29, 1948 Chattanooga shale, Gassaway member: 1.5—2.1 ft 220 Same as collection 129. below top. 146 37l4—SD June 16, 1947 Chattanooga shale, Gassaway member: 12.5—12.9 206 Same as collection 138. _ It below top. 149 3715—SD May 26,1948 Chattanooga shale, Gassaway member: 4.4—4.6 39 Same as collection 107. ft below top. 150 3716—81) June 28,1948 Chattanooga shale, Gassaway member: 4.4—5.2 220 Same as collection 129. it below top. 151 3717—SD June 22,1948 Chattanooga shale, Dowelltown member: 27.7— 107 Same as collection 85. 28.4 it below top. 153 3718—SD June 17,1947 Chattanooga shale, Gassaway member: 6.0—6.5 206 Same as collection 138. ft below top. CONODONT COLLECTIONS 41 TABLE 6.—Conodont collections from the Chattanooga shale, Maury formation, and New Providence shale— Continued [Stratigraphic position given with reference to top of Chattanooga shale, base of Maury formation, or base of New Providence shale. All collections made by W. H. Hass] Collection Locality No. U- SN (3' 5 Date Stratigraphic position 12°]; ‘1“ Description 154 3719—SD June 16, 1947 Chattanooga shale, Gassaway member: 10.5— 206 Same as collection 138. 10.8 it below top. 155 3720—SD June 17,1947 Chattanooga shale, Dowelltown member: 206- 206 Same as collection 138. 22.1 it below top. 157 3721~SD June 19, 1947 Chattanooga shale, Gassaway member: 13.7- 100 Same as collection 22. 14.1 {t below top. 158 15512—0 June 16,1947 Maury formation: 0.5-1.5it above base. This is 206 Same as collection 138. from Campbell's Westmoreland shale. 159 3722—SD J true 18, 1947 Chattanooga shale, Gassaway member: 8.6—8.8 it 95 Same as collection'26. below top. 160 3723—SD June 18,1947 Chattanooga shale, Dowelltown member: 14.1— 95 Same as collection 26. 14.5 it below top. 161 3724-SD May 17, 1948 Chattanooga shale, Dowelltown member: 76 Same as collection 120. 20.1—20.2 it below top. 162 3725—SD June 23, 1948 Chattanooga shale, Gassaway member: 0.4—1.4 107 Same as collection 85. it below top. 165 15513—0 June 14, 1947 Maury formation: 0.6—1.1 ft above base. This is 207 Same as collection 83. from Campbell’s type Westmoreland shale. 167 3726—SD June 18,1947 Chattanooga shale, Gassaway member: 0.8—1.1 95 Same ascollection 26. it below top. 169 3727-SD June 17,1947 Chattanooga shale, Dowelltown member: 206 Same as collection 138. 31.2—33.2 it below top. This is from Pohl’s Trousdale shale. 172 3728s-SD June 14, 1947 Chattanooga shale, Gassaway member: top 0.3 207 Same as collection 83. ft. 173 3729—SD June 18, 1947 Chattanooga shale, Gassaway member: 11.4—12.2 95 Same as collection 26. it below top. 175 3730—SD Mar. 9,1948 Chattanooga shale, Gassaway member: top 0.9 220 Same as collection 129. it. 176 3731—SD Mar. 2,1948 Chattanooga shale, Gassaway member: 14.3—14.4 206 Same as collection 138. it below top. 179, 3732-SD May 26, 1948 Chattanooga shale, Gassaway member: top 0.8 39 Same as collection 107. it. 189 3733—SD May 26,1948 Chattanooga shale, Gassaway member: 2.3—3.1 39 Same as collection 107. it below top. 181 3734-SD June 19,1947 Chattanooga shale, Gassaway member: 8.0—8.5 100 Same as collection 22. ft below top. 182 3735—SD June 18,1947 Chattanooga shale, Dowelltown member: 95 Same as collection 26. 20.9—21.9 it below top. 184 3736—SD May 31,1948 Chattanooga shale, Gassaway member: 9.6—9.9 6 Same as collection 86. it below top. 185 3737—SD June 18, 1947 Chattanooga shale, Gassaway member: 10.4—11.4 95 Same as collection 26. it below top. 186 3738-SD June 18,1947 Chattanooga shale, Dowelltown member: 95 Same as collection 26. 14.5—14.8 it below top. 189 3739—SD Jan. 19, 1948 Chattanooga shale, Dowelltown member: 95 Same as collection 26. 18.0—18.3 it below top. 191 3740—SD May 19,1948 Chattanooga shale, Gassaway member: 4.0—4.3 74 Same as collection 84. it below top. 192 3741—SD June 10,1948 Chattanooga shale, Gassaway member: 907—91 296 Same as collection 138. ft below top. 193 3742-SD June 10,1948 Chattanooga shale, Gassaway member: 7.4—7.6 206 Same as collection 138. ‘ it below top. 195 3743-SD May 26,1948 Chattanooga shale, Gassaway member: 5.4—5.8 39 Same as collection 107. it below top. 199 3744-SD June 2, 1948 Chattanooga shale, Gassaway member: 31.3-31.9 11 Same as collection 110. it below top. 290 3745—SD May 31,1948 Chattanooga shale, Gassaway member: 8.6-9.0 6 Same as collection 86. it below top. 201 3746—SD _'May 31,1948 Chattanooga shale, Gassaway member: 4.3—4.6 6 Same as collection 86. it below top. 202 3747-SD {May 26,1948 Chattanooga shale, Dowelltown member: 164 39 Same as collection 107. 17.0 it below top. 207 3748-SD June 2, 1948 Chattanooga shale, Gassaway member: 19.6-21.0 11 same as collection 110. it below top. 208 3749—SD May 26,1948 Chattanooga shale, Gassaway member: 10.7~11.0 39 Same as collection 107. it below top. 211 3750-SD June 3,1948 Chattanooga shale, Gassaway member: 4.2—4.6 11 Same as collection 110. it below top. 42 [Stratigraphic position given with reference to top of Chattanooga shale, base of Maury formation, or base of New Providence shale. CHATTANOOGA SHALE AND MAURY FORMATION TABLE 6.— Conodont collections from the Chattanooga shale, Maury formation, and New Providence shale—Continued All collections made by W. H. Hassl Collection U. .G.S. No. on No. SNo. Date Stratigraphic position pl. 1 Description 213 3751—SD June 14, 1948 Chattanooga shale, Gassaway member: top 0.7 It_ 204 Type locality of the Ridgetop shale, cuts along the tracks of the Louisville and Nashville Railroad at Bakers Station, Davidson County, Tenn. From community of Ridgetop go south for 3 miles on United States Highway 41 to road junction; turn west onto secondary road, go 0.7 mile to cuts along railroad tracks. The Gassaway member was measured in a cut at Bakers Station crossing, the Dowelltown member in a cut 1,560 ft south of Bakers Station crossing. 214 3752—SD June 10, 1948 Chattanooga shale, Dowelltown member: 18.7— 206 Same as collection 138. 19.2 it below top. 216 3753-SD June 10,1948 Chattanooga shale, Dowelltown member: 27.5- 206 Same as collection 138. 27.8 it below top. 218 3754—SD June 10,1948 Chattanooga shale, Dowelltown member: 18.7— 206 Same as collection 138. 19.2 it below top. 220 3755—SD June 14,1948 Chattanooga shale, Gassaway member: 12.1—12.2 204 Same as collection 213. it below top. 224 3756—SD June 14,1948 Chattanooga shale, Gassaway member: 4.4—4.7 204 Same as collection 213. it below top. 225 3757—SD June 1,1948 Chattanooga shale, Gassaway member: 34.4— 6 Same as collection 86. 34.9 ft below top. 227 3758—SD June 3,1948 Chattanooga shale, Gassaway member: 7.2—8.1 11 Same as collection 110. it below top. 228 3759—SD June 1, 1948 Chattanooga shale, Gassaway member: 39.4— 6 Same as collection 86. 39.7 it below top. 229 3760—SD June 1, 1948 Chattanooga shale, Gassaway member: 34.4— 6 Same as collection 86. 34.9 it below top. 230 3761—SD June 3, 1948 Chattanooga shale, Gassaway member: top 11 Same as collection 110. 0.4 ft. 231 3762—SD June 1, 1948 Chattanooga shale, Gassaway member: 41.3— 6 Same as collection 86. 41.6 it below top. 232 3763-SD May 29,1948 Chattanooga shale, Gassaway member: 1.4—1.7 6 Same as collection 86. it below top. 236 3764—SD Jan. 15,1948 Chattanooga shale, Gassaway member: 6.2—6.5 95 Same as collection 26. it below top. 237 3765—SD Jan. 22, 1948 Chattanooga shale, Gassaway member: top 0.4 it. 100 Same as collection 22. 238 3766—SD Jan. 22, 1948 Chattanooga shale, Gassaway member: 128— 100 Same as collection 22. 13.5 it below top. 239 3767-SD Jan. 15,1948 Chattanooga shale, Gassaway member: 4.5—4.9 95 Same as collection 26. it below top. 240 3768—SD Jan. 19, 1948 Chattanooga shale, Dowelltown member: 21.5— 95 Same as collection 26. 22.5 it below top. 241 3769—SD Jan. 15,1948 Chattanooga shale, Gassaway member: 9.5—9.7 95 Same as collection 26. it below top. 242 3770—SD Jan. 22,1948 Chattanooga shale, Gassaway member: 2.3—2.7 100 Same as collection 22. it below top. 243 3771—SD Jan. 22,1948 Chattanooga shale, Gassaway member: 8.5—9.3 100 Same as collection 22. it below top. 244 15514—0 Jan. 22, 1948 Maury formation: 0.15—0.5 ft above base _________ 100 Same as collection 22. 245 3772—SD Jan. 22, 1948 Chattanooga shale, Gassaway member: top 0.4 it. 100 Same as collection 22. 328 3773~SD June 14, 1948 Chattanooga shale, Gassaway member: 12.2— 204 Same as collection 213. 12.6 it below top. 329 3774—SD June 14,1948 Chattanooga shale, Dowelltown member: 190— 204 Same as collection 213. 19.5 ft below top. 331 3775—SD May 26, 1948 Maury formation: basal 1.0 ft ___________________ 39 Same as collection 107. 332 3776—SD May 26,1948 Chattanooga shale, Dowelltown member: 203— 39 Same as collection 107. 20.5 it below top. . 334 15515—0 June 12, 1948 Maury formation: 0.3—0.9 it above base .......... 204 Same as collection 213. 335 3777—SD June 24, 1948 Chattanooga shale, Gassaway member: 12.2—12.6 204 Same as collection 213. ft below top. 336 3778—SD June 24,1948 Chattanooga shale, Dowelltown member: 19.0— 204 Same as collection 213. 19.5 it below top. , 337 15516—0 June 11,1948 Maury formation: 1.2—1.4 it above base .......... 205 Out on State Highway 109, 5.5 miles north of Gallatin, Sumner County, Tenn. 344 3779—SD May 26, 1948 Chattanooga shale, Dowelltown member: 19.6— 39 Same as collection 107. 19.7 it below top. TABLE 6.—Co'nodont collections from the Chattanooga shale, Maury formation, and New Providence shale—— Continued CONODONT COLLECTIONS 43 [Stratigraphic position given with reference to top of Chattanooga shale, base of Maury formation, or base of New Providence shale. All collections made by W. H. Hass] Collection Locality N0. U- if" S: Date Stratigraphic position Np", 3” Description 345 15517—0 May 26, 1948 Maury formation: 1.0—2.5 it above base..." .. __ _ 39 Same as collection 107. 348 15518—0 May 29, 1948 New Providence shale: basal 0.5 ft .............. 6 Same as collection 86. 349 15519—0 May 29, 1948 New Providence shale: basal 0.5 ft ............... 6 Same as collection 86. 350 15520—0 May 29, 1948 New Providence shale: 0.5—0.8 ft above base ..... 6 Same as collection 86. 352 3780—SD June 1,1948 Chattanooga shale, Dowelltown member: 47.0— 6 Same as collection 86. 47.4 it below top. 353 15521—0 June 3, 1948 New Providence shale: basal 0.3 it .............. 11 Same as collection 110. 354 15522—0 June 11, 1948 Maury formation: 0.5—1.2 ft above base .......... 205 Same as collection 337. 355 15523-0 June 11, 1948 Maury formation: 0.2—0.5 ft above base...__.__.. 205 Same as collection 337. 357 ‘ 3781—SD June 14, 1948 Chattanooga shale, Dowelltown member: basal 204 Same as collection 213. 1.0 ft or 28.5-29.5 ft below top. 391 3782—SD Nov. 14, 1947 Maury formation: basal 0.5 ft ................... 92 Same as collection 7. 392 3783-SD N 0v. 14, 1947 Maury formation: basal 0.3 ft ................... 78 Same as collection 3. 400 15524—0 Mar. 11, 1948 Maury formation: 0.2-0.3 ft above base .......... 228 Same as collection 55. 421 3784—SD June 14, 1947 Maury formation: basal 0.6 ft. This is from 207 Same as collection 83. Campbell’s Eulie shale. 423 3785—SD June 16, 1947 Maury formation: basal 0.1 it. This is from 206 Same as collection 138. Campbell’s Eulie shale. 426 3786—SD June 18, 1947 Maury formation: basal 0.3 ft ................... 95 Same as collection 26. 428 15525—0 June 19, 1947 Maury formation: 1.7-2.0 ft above base .......... 100 Same as collection 22. 433 3787—SD Nov. 11, 1947 Chattanooga shale, Dowelltown member: basal 107 Same as collection 85. 0.2 It or 29.8—30.0 it below top. 451 3788-SD Mar. 2, 1948 Chattanooga shale, Gassaway member: 16.0—16.2 206 Same as collection 138. it below top. This is from Campbell’s type Bransford sandstone member of his Gassaway formation. 460 3789—SD Mar. 11,1948 Chattanooga shale, Gassaway member: 1.5—1.8 228 Same as collection 55. it below top. 461 15526—0 Mar. 11,1948 Maury formation: basal 0.05 it __________________ 225 Same as collection 71. 452 15527—0 Mar. 11, 1948 Maury formation: 1.1—2.0 ft above base __________ 225 Same as collection 71. 472 15528—0 June 27, 1948 Maury formation: entire formation, 1.5 ft thick.. 1263 Same as collection 82. 473 3790—SD June 27,1948 Chattanooga shale, Gassaway member: basal 126a Same as collection 82. 0.7 ft or 5.2—5.9 it below top. . 474 3791-SD June 28, 1948 Chattanooga shale, Dowelltown member: basal 220 Same as collection 129. 0.5 ft or 13.7—14.2 it below top. 591 3792—SD July 5, 1949 Chattanooga shale, Gassaway member: basal 168 Out on State Highway 50, about 3.5 miles southeast of Centerville, 1 0.3 ft or 4.6—4.9 it below top. Hickman County, Tenn. 647 155290 Sept. 1,1949 Maury formation: entire formation, 1.3 ft thick.. 134 Out on south side of State Highway 129, 0.9 mile west of junction with United States Highway 31A in Cornersville, Marshall County, Tenn. 652 3793—SD Sept. 2,1949 Chattanooga shale, Gassaway member: top 1.0 185 Standard section of the Maury formation. South side of a road 13.5 miles ft. (airline) southeast of Franklin and 1.2 miles east of the road junction at Cross Key, Williamson County, Tenn. 653 3794—SD Sept. 2,1949 Chattanooga shale, Gassaway member: 1.0—1.6 185 Sameas collection 652. ft below top. 654 3795—SD Sept. 2,1949 Chattanooga shale, Gassaway member: 3.7—3.8 185 Same as collection 652. ft below top. ' 655 3796—SD Sept. 2,1949 Chattanooga shale, Gassaway member: 2.4—2.5 185 Same as collection 652. ft below top. 656 3797—SD Sept, 2,1949 Chattanooga shale, Dowelltown member: 7.0— 185 Same as collection 652. 7.5 it below top. 657 3798—SD Sept. 2,1949 Chattanooga shale, Dowelltown member: 7.8- 185 Same as collection 652. 8.8 it below top. ' 11113 11113—0 Mar. 2,1948 Chattanooga shale, Dowelltown member: basal 206 Same as collection 138. 2 ft or 31.2—33.2 it below top. This is from Pohl‘s Trousdale shale. 15000 15000—0 June 25, 1950 Maury formation: basal 0.3 it. This is from 206 Same as collection 138. Campbell’s Eulie shale. 15001 15001—C June 12, 1950 Maury formation: basal 0.7 ft ................... 168 Same as collection 591. 15002 15002—0 June 12, 1950 Maury formation: 1.0—1.5 ft above base .......... 39 Same as collection 107. 15003 15003—0 June 17, 1950 Maury formation: 0.9—4.5 ft above base____.. _. ._ 95 Same as collection 26. 15004 15004—C June 14, 1948 Maury formation: basal 0.3 ft ................... 75 Same as collection 48. 44 LITERATURE CITED Bassler, R. S., 1911, The Waverlyan period of Tennessee: U. S. Nat. Mus. Proc., v. 41, no. 1851, p. 209—224. 1932, The stratigraphy of the central basin of Tennessee: Tenn. Div. Geology Bull. 38, 268 p., 49 pls., 4 figs., 4 maps. Branson, E. B., and Mehl, M. G., 1933, A study of Hinde’s types of conodonts preserved in the British Museum, in Conodont studies no. 2: Mo. Univ. Studies, v. 8, no. 2, p. 133—156, 165—167, pls. 11, 12. 1934a, Conodonts from the Grassy Creek shale of Mis- souri, in Conodont studies no. 3: Mo. Univ. Studies, v. 8, no. 3, p. 171—259, pls. 13—21. (Date of imprint, 1933.) ~———- 1934b, Conodonts from the Bushberg sandstone and equivalent formations of Missouri, in Conodont studies no. 4: Mo. Univ. Studies, v. 8, no. 4, p. 265—299, 335—338, pls. 22—24. (Date of imprint, 1933.) ~———— 1938, Conodonts from the Lower Mississippian of Mis- souri, in Branson, E. B., and others, Stratigraphy and Pal- eontology of the Lower Mississippian of Missouri, pt. 2: M0. Univ. Studies, v. 13, no. 4, p. 128—148, 203—206, pls. 33, 34. Branson, E. R., 1934, Conodonts from the Hannibal formation of Missouri, in Conodont studies no. 4: Mo. Univ. Studies, v. 8, no. 4, p. 301—334, 338—343, pls. 25—28. (Date of imprint, 1933.) Bryant, W. L., 1921, The Genesee conodonts: Buffalo Soc. Nat. Sci. Bull., v. 13, no. 2, 59 p., 16 pls., 7 figs. Butts, Charles, 1926, The Paleozoic rocks, in Adams, G. I., and others, Geology of Alabama: Ala. Geol. Survey Special Rept. no. 14, p. 41—230, pls. 3—76, figs. 2—4. Campbell, Guy, 1946, New Albany shale: Geol. Soc. America Bull., v. 57, p. 829—908, 3 pls., 7 figs. Campbell, M. R., 1894, Description of the Estillville quadrangle, Ky.—Va.—Tenn.: U. S. Geol. Survey Geol. Atlas, folio 12. Chadwick, G. H., 1923, Chemung stratigraphy in western New York [abs]: Geol. Soc. America Bull., v. 34, p. 68, 69. Cooper, C. L., 1939, Conodonts from a Bushberg-Hannibal horizon in Oklahoma: Jour. Paleontology, v. 13, p. 379—422, pls. 39—47, 2 figs. Cooper, G. A., and others, 1942, Correlation of the Devonian sedimentary formations of North America: Geol. Soc. America Bull., v. 53, p. 1729—1794, 1 pl., 1 fig. Drake, N. F., 1914, Economic geology of the Waynesboro quad- rangle, in The resources of Tennessee: Tenn. Div. Geology, v. 4, p. 99—120, 2 figs. Ellison, S. P., Jr., 1946, Conodonts as Paleozoic guide fossils: Am. Assoc. Petroleum Geologists Bull., v. 30, p. 93—110, 3 figs. Grabau, A. W., 1906, Types of sedimentary overlap: Geol. Soc. America Bull., v. 17, p. 567—636, 17 figs. Hass, W. H., 1947a, Conodont zones in Upper Devonian and lower Mississippian formations of Ohio: Jour. Paleontology, v. 21, p. 131—141, 1 fig. —— 1947b, The Chattanooga shale type area [abs]: Geol. Soc. America Bull., v. 58, p. 1189. 1948, Upper Devonian bentonite in Tennessee: Am. Assoc. Petroleum Geologists Bull., v. 32, p. 816—819. »————« 1951, Age of Arkansas novaculite: Am. Assoc. Petroleum Geologists Bull., v. 35, p. 2526—2541, 1 p1. Hayes, C. W., 1891, The overthrust faults of the southern Appa— lachians: Geol. Soc. America Bull., V. 2, p. 141—154, pls. 2, 3. ' ————— 1892, Geology of north-eastern Alabama, and adjacent portions of Georgia and Tennessee: Ala. Geol. Survey Bull., no. 4, 85 p., 1 pl., 15 figs, geologic map. CHATTANOOGA SHALE AND MAURY FORMATION Hayes, C. W., 1894a, Description of the Ringgold quadrangle, Ga.-Tenn.: U. S. Geol. Survey Geol. Atlas, folio 2. 1894b, Description of the Kingston quadrangle, Tenn.: U. S. Geol. Survey Geol. Atlas, folio 4. 18940, Description of the Chattanooga quadrangle, Tenn.: U. S. Geol. Survey Geol. Atlas, folio 6. -——~— 1894d, Description of the Sewanee quadrangle, Tenn.: U. S. Geol. Survey, Geol. Atlas, folio 8. 1895, Description of the McMinnville quadrangle, Tenn.: U. S. Geol. Survey Geol. Atlas, folio 22. Hayes, C. W., and Ulrich, E. 0., 1903, Description of the Colum bia quadrangle, Tenn.: U. S. Geol. Survey Geol. Atlas, folio 95. Hinde, G. J., 1879, On conodonts from the Chazy and Cincinnati group of the Cambro-Silurian, and from the Hamilton and Genesee-shale divisions of the Devonian, in Canada and the United States: Geol. Soc. London Quart. Jour., v. 35, p. 351—369, pls. 15—17. Holmes, G. B., 1928, A bibliography of the conodonts with descriptions of early Mississippian species: U. S. Nat. Mus. Proc., v. 72, art. 5, 38 p., 11 pls. Huddle, J. W., 1934, Conodonts from the New Albany shale of Indiana: Bull. Am. Paleontology, v. 21, no. 72, 136 p., 12 pls., 3 figs. Jewell, W. B., 1931, Geology and mineral resources of Hardin County, Tennessee: Tenn. Div. Geology Bull. 37, 117 p., 9 pls., 3 figs. Killebrew, J. B., and Safford, J. M., 1874, Introduction to the resources of Tennessee: Tenn. Bureau of Agriculture, 1st. and 2d. Repts., 1,193 p., geologic map. Kindle, E. M., 1899, The Devonian and lower Carboniferous faunas of southern Indiana and central Kentucky: Bull. Am. Paleontology, v. 3, no. 12, 111 p., 2 figs. 1900, The Devonian fossils and stratigraphy of Indiana: Ind. Dept. Geol. and Nat. Res, 25th Ann. Rept., p. 529— 758, 773—775, 31 pls. 1912a, The unconformity at the base of the Chattanooga shale in Kentucky: Am. Jour. Sci., 4th ser., v. 33, p. 120— 136, 3 figs. 1912b, The stratigraphic relations of the Devonian shales of northern Ohio: Am. Jour. Sci., 4th ser., v. 34, p. 187— 213, 3 figs. Klepser, H. J., 1937, The Lower Mississippian rocks of the Eastern Highland Rim: Abstracts of Doctor’s Dissertations, no. 24, Ohio State Univ. Press, p. 181—187. Mather, K. F., 1920, Oil and gas resources of the northeastern part of Sumner County, Tenn.: Tenn. Div. Geology Bull. 24--2B, 39 p. Miller, A. K., and Youngquist, Walter, 1947, Conodonts from the type section of the Sweetland Creek shale in Iowa: Jour. Paleontology, v. 21, p. 501—517, pls. 72—75. Miser, H. D., 1921, Mineral resources of the Waynesboro quad- rangle Tennessee: Tenn. Div. Geology Bull. 26, 171 p., 16 pls., 7 figs. Morse, W. C., 1928, Paleozoic rocks of Mississippi: Jour. Geology, v. 36, p. 31—43, 1 fig. 1930, Paleozoic rocks: Miss. Geol. Survey Bull. 23, 212 p., 23 pls., 15 figs. Morse, W. C., and Foerste, A. F., 1909, The Waverly formations of east-central Kentucky: Jour. Geology, v. 17, p. 164—177. Newberry, J. S., 1875, Descriptions of fossil fishes, in Newberry, J. S., and others, Geology and Paleontology, pt. 2, Paleon- tology: Ohio Geol. Survey, Rept., v. 2, p. 1—64, pls. 54—59. Pohl, E. R., 1930a, Devonian formations of the Mississippi basin: Tenn. Acad. Sci. Jour., v. 5, p. 54—63. LITERATURE CITED 45 Pohl, E. R., 1930b, The black shale series of central Tennessee [abs]: Am. Jour. Sci., 5th ser., v. 20, p. 151—152. Prosser, C. S., 1912, The Devonian and Mississippian formations of northeastern Ohio: Ohio Geol. Survey, 4th ser., Bull. 15, 574 p., 33 pls., 1 fig. Safl’ord, J. M., 1851, The Silurian Basin of Middle Tennessee, with notices of the strata surrounding it: Am. Jour. Sci., 2d ser., v. 12, p. 352—361, geologic map. 1856, A geological reconnoissance of the State of Ten- nessee: lst biennial report presented to the 31st general assembly of Tennessee, 164 p. 1869, Geology of Tennessee, 550 p., 7 pls., geologic map. Safford, J. M., and Killebrew, J. B., 1900, The elements of the geology of Tennessee, 264 p. Savage, T. E., 1930, The Devonian rocks of Kentucky: Ky. Geol. Survey, ser. 6, v. 33, p. 1—161, 4 pls., 52 figs. Savage, T. E., and Sutton, A. H., 1931, Age of the black shale in south-central Kentucky: Am. Jour. Sci., 5th ser., v. 22, p. 441—448, 1 fig. Shaw, E. W., and ,Mather, K. F., 1919, The oil fields of Allen County Kentucky: U. S. Geol. Survey Bull. 688, .126 p., 10 pls., 10 figs. Smith, E. A., 1878, Outline of the geology of Alabama, 68 p., geologic map. 1890, Geology of the valley regions adjacent to the Cahaba field, in Squire, Joseph, Report on the Cahaba coal field: Ala. Geol. Survey, Special Rept. no. 2, p. 133—180, pls. 6, 7, geologic map. Stockdale, P. B., 1939, Lower Mississippian rocks of the east- central interior: Geol. Soc. America Special Papers, no. 22, 248 p., 26 pls., 2 figs. ‘ 1948, Some problems in Mississippian stratigraphy of the southern Appalachians: Jour. Geology, v. 56, p. 264—268. Stose, G. W., 1923, Pre-Pennsylvanian rocks, in Eby, J. B., and others, The geology and mineral resources of Wise County and the coal—bearing portion of Scott County, Var. Va. Geol. Survey Bull., no. 24, p. 22—62, pls. 7—10, figs. 2, 3. Swartz, J. H., 1924, The age of the Chattanooga shale of Ten- nessee: Am. Jour. Sci., 5th ser., v. 7, p. 24—30. 1927, The Chattanoogan age of the Big Stone Gap shale: Am. Jour. Sci., 5th ser., v. 14, p. 485—499, 2 figs. 1929, The age and stratigraphy of the Chattanooga shale in northeastern Tennessee and Virginia: Am. Jour. Sci., 5th ser., v. 17, p. 431—448. 3 figs. Ulrich, E. 0., 1905, Geology and general relations, pt. 1, in Ulrich, E. 0., and Smith, W. S. T., The lead, zinc, and fluorspar deposits of western Kentucky: U. S. Geol. Survey Prof. Paper 36, p. 1—105, pls. 1—7. 1911, Revision of the Paleozoic systems: Geol. Soc. America Bull., v. 22, p. 281—680, pls. 25—29. 1912, The Chattanoogan series with special reference to the Ohio shale problem: Am. Jour. Sci., 4th ser., v. 34, p. 157—183, 3 figs. 1915, Kinderhookian age of the Chattanoogan series [abs]: Geol. Soc. America Bull., v. 26, p. 96—99. Ulrich, E. 0., and Bassler, R. S., 1926, A classification of the toothlike fossils, conodonts, with descriptions of American Devonian and Mississippian species: U. S. Nat. Mus. Proc., v. 68, art. 12, 63 p., 11 pls., 5 figs. Weller, J. M., and others, 1948, Correlation of the Mississippian formations of North America: Geol. Soc. America Bull., v. 59, p. 91—196, 2 pls., 7 figs. Wilson, C. W., Jr., and Spain, E. L., Jr., 1936, Age of Mississip- pian “Ridgetop shale” of central Tennessee: Am. Assoc. Petroleum Geologists Bull. v. 20, p. 805—809, 1 fig. Youngquist, Walter, Hibbard, R. R., and Reimann, I. G., .1948, Additions to the Devonian conodont faunas of western New York: Jour. Paleontology, v. 22, p. 48—59, pls. 14, 15. Page Abstract ________________________________________ 1-2 eciedentetus, Spathognethodus. 24, 25; pl. 2 eculeetus, Spathognathodus.. 17, 22, 24 ecutiliretus, Chonetes _____________ 7 elatus, Prioniodus ______________________ 8, 17, 18; pl. 4 allocate, Polygeethus ____________ 25; pl. 2: tables 7, 8 Ancyrodelle rotuudilobe __________________ 17, 18; pl. 4 sp. B _________________________________ 17, 18; pl. 4 Aucyrogriethus bifurcate _______________ 8, 9, 21, 22; pl. 3 euglypheua ________________________ 17, 20; pl. 4 quadrete ________________ _._. 17, 21 Apison, Tenn __________________________________ 7 Bactrogriethus sp ___________________________ 26; table 7 Berroisella cempbelli .................. . 6 Bentonite bed in Dowelltown member . 18 bielete, Elictognethus ........................... 25 bifurcate, Ancyroguethus ______________ 8, 9, 21, 22; pl. 3 Big Stone Gap member of Chattanooga shale___ 8 Big Stone Gap shale ____________________________ 8 Bryeutodue sp. A .......................... 17, 18; pl. 4 Campbell, Guy, quoted ______________________ 11 Carmack limestone ___________________________ 9 Chattanooga, Tenn _____________________________ 8 Chattanooga shale, collecting localities. _ 38—43; pl. 1 standard section _.._ 12,13 type section ............ 8, 13—15; pl. 5 See also names of individual members. Chonetes ecutiliretus ________ 7 Cladadus _________________ 6 Cleveland member of Ohio shale _______________ 8 cammum’a, Polygeethus., _______ 24,25; p]. 2; tables 7,8 coufluem, Polvlophodorita _____________ 8, 9, 21, 22; pl. 3 Conodont species, distribution .................. 18, 21, 25, 38—43; tables 7, 8 Cumberland Gap member of Chattanooga shale. 8 delicetula, Pelmatodelle ____________________ 8, 9, 21, 22 Dinodus fragesua _______________________________ 25 disperilis, Spathogriathodus _________________ 17, 22, 24 distorta, Pelmetolepis _______________ 17. 21, 22, 26; pl. 2 Dowelltown formation of Guy Campbell, section at type locality .................. 13—14, 16 Dowelltown member of Chattanooga shale ..... 16—20 duplicate, Siphoriadelle ____________________ 25, 26; pl. 2 Elictognathus bielete ____________________________ 25 lecerata ______________________________ 25, 26; pl. 2 euglypheue, Ancyrognethus._ 17, 20; pl. 4 Eulie,Tenn. _. _ .... 7 Eulie shale ________________ 11 Foérstie sp ______________________________________ 21, 22 fregosus, Dinodus 25 Gassaway formation of Guy Campbell, section at type locality ____________________ 14—15, 16 Gassaway member of Chattanooga shale _______ 20—23 glebra, Pelmatolepis ........ ._. 8, 9, 17, 21, 22; pl. 3 Glendale shale ______________ 7, 13 Guathedus punctetus __________________________ 26; pl. 2 sp. A ________ . 26; pl. 2; tables 7, 8 sp. B ____________ 24; tables 7, 8 Grabau, A. W., quoted. ...... 4 orecilis, Palmetolepis ________________________ 17, 21, 22 Hardin sandstone member of Chattanooga shale. 15-16, 37 Bass, W. H., quoted ________________________ 11, 19-20 INDEX Page Hibbardella sp. A ..................... 17, 18; pl. 4 Hindeodclle sp. A.. . 17, 22, 24; pl. 3 sp ____________________ , 22 Huron member of Ohio shale. . 8 huronemis, Sporengires _________________________ 6 Icriodus sp ________________________________ 17, 20; pl. 4 inometa, Polygnethus ________________________ 25; pl. 2 inornatus, Spathognethodus ____________ 17, 22, 24; pl. 3 irvirtensis, Lingule ______________________________ I 7 linguiformix, Polugnathus _________________ 17, 18; p]. 4 longipostice, Polygnethus _____________________ 25; pl. 2 lecerete, Elictoguathus.._, . ____________ 25, 26; pl. 2 Linden, Tenn ____________ 7 Lingule irvineusis ..................... 7 melie _________________ 7 subspetulete __________ 6 sp ............ 9 lobeta, Siphouodelle. _ _ _ . 2 merginete, Pelmetalepsis ________________________ 17,22 Maury formation, collecting localities ..... 38—43; pl. 1 Maury formation, standard section ____________ 23 melie, Lingula _________________________________ 7 Morse, W. C., quoted _________________________ 9 Mount Pleasant, Tenn ........................ 7,8 mutebilia, Prioniodus ___________________________ 17,21 New Market, Ala ______________________________ 8. 32 New Providence shale col[ecting localities. . . 43; pl. 1 uewherryi, Orbiculoidee ___________________________ 6 Ohio shale ______________________________________ 8 Olinger member of Chattanooga shale. 8 Orbiculoidce newberryi .............. 6 ovate transverse ___________________________ 7 Sp _________________________________________ 21 ovate transverse, Orbiculaidee ................... 7 Palmetodelle dclicatula ...y .................. 8, 9,21, 22 Pelmetolepis distorte...- ________ 17, 21, 22, 26; pl. 2 elongate .......................... 9 8, 9, 17, 21,22; pl. 3 _______ 17, 21,22 inequalis._ margiuete. perlabata ................... 8, 9, 17, 21, 22; pl. 3 punctute ............ quedrentinodosa ..... rugose ................................... 17, 21, 22 subperlobeta. ,_ 17, 21, 22; pl. 3 subrecte... . 17,19 20; pls. 3,4 unicorm’s .. 15, 17, 18; pl. 4 sp. A..._ .................. 17, 21,22; pl.3 permete, Polypnethus .................... 17, 18; pl. 4 perlobete, Palmetolepis.... ______ 8, 9, 17, 21, 22; pl. 3 Pinacognathus profunda ______________________ 25; pl. 2 Polyguethus ellocota ............... 25; pl. 2; tables 7, 8 communis _________________ 24, 25; pl. 2; tables 7, 8 couceutrice. _ . . 9 coufluem....... 8 oyratilimeta. __ 9 iuomete ............................. 25; pl. 2 linguiformis _________________________ 17, 18; pl. 4 longipostice ______________________________ 25; pl. 2 pemtata .............................. 17,18; pl.4 pergyrete __________________________________ 9 rhomboidee .................................. 9 C Polygrtethus altocote—Continued sp. A .............. .. 17, 18; pl. Polylophodonte confluent. 8, 9, 21,22; pl. 3. prime, Pseudopolwnethus _________________ 25,26; pl. 2 Priom'odus eletus ........................ 8, 17, 18; pl. 4 mutabilis ......... 17,21 profuude, Pineccanafhus ..................... 25; pl. 2 Pseudohornie ................................... 6 Pseudepolugriethus prime __________________ 25,26; pl. 2 striate ............................. 26‘ sp ....................... . 26; tables 7, 8 punctetus, Gnathodus ________________________ 26: pl. 2 quadrantirtodosa, I’elmetolepiL. .. 17,21; pl. 3. quedrete, Ancyrognethus ........... 17,21 quadruplicate, Siphonodella ___________________ 25; pl. 2' Quicks Mill, Ala _______________________________ 8. 32 Rhinestreet shale ............................... 7. 8 Rhipidomelle sp... 7 Ridgetop shale _____________________________ 4, 5, 33 rotundiloba, Aucyrodelle ___________________ 17, 18' pl. 4 rugose, Palmatolepis _________________________ 17,21, 22' Schuchertelle sp ................................. 7 sarplicete, Siphonodelle _______________________ 25; pl. 2 Shaletown, N. Y ............................... 7 Siphonodella duplicate _____________ 25, 26; pl. 2 lobete _______________________ _ 25; pl. 2 quadruplicate. _ 25; pl. 2 serplicata. _ _ . 2 sp.A..____._. .2 Spathognathodus eciedmtetus ............. 24,25; pl. 2 eculeetue ______________________________ 17 , 22, 24 disperilis ______________________________ 17, 22, 24 inometus ...... 17, 22, 24; pl. 3. sp A _____________________ 24; pl. 2 sp. B ____________________________________ 25; pl. 2 Sporertgites huronensis ............. 6 Standard section, Chattanooga shale ______ 12. 13 Maury formation ___________________________ 23. Stratigraphic classification proposed, by Safiord and Killebrew ......... 3. by Ulrich ______________________ 4, 5» for this report ______________________________ 2—3’ Stratigraphic sections, measured for this report. 12—15, 23, 26—38 quoted, from J. H. Swartz ................. 7, 8 from E. R. Polil _______ 9 striata, Pseudopolygnethus. . ...... 26 sub perlobete Palmetolepis .............. 17, 21, 22; pl. 3' subrecte, Pelmetolepis _______________ 17, 19, 20; pls. 3. 4 subspetulete, Lingule ........................... 6 Sunbury shale ................................. 8: Swartz, J. H., quoted ......................... 7, 9‘ Tephrognethus _________________________________ 26- Tesmenites huronensis ......................... 6 Tenteculites sp _________________________________ 9 transversa, Orbiculez'dee ovate... T Trousdale shale _______________________________ 9, 10, 11 Ulrich, E. 0., quoted ........................... 6» enicorm‘s, Pelmetolepis _________________ 15,17,18; pl. 4 Weller, J. M., quoted ..................... 13 Westmoreland shale. __ ............ 11 Whetstone Branch shale ........................ 6 47 PLATES 2—5 FIGURE 1. 6—11. 12. 13, 23. 14, 15. 16. 17. 18. 19. 20. 21, 22. 24. 25. 26. 27. 2s. 29. 30. PLATE 2 [Figures are 30 times natural size] Palmatolepis distorta Branson and Mehl. Oral view. Rubber replica, collection 400, USNM 123466. , Polygnathus communis Branson and Mehl. Oral views. 2, Collection 74, USNM 123467; 3, rubber replica, collection 113, USNM 123468; 4, collection 355, USNM 123469; 5, collection 355, USNM 123470. Siphonodella duplicata (Branson and Mehl). Oral views. 6, Rubber replica, collection 400, USNM 123471; 7, rubber replica, collection 55. USNM 123472; 8, collection 74, USNM 123473; 9, collection 355, USNM 123474; 10, collection 355, USNM 123475; 11, collection 355, USNM 123476. Siphonodella sp. A. Oral View. Collection 355, USNM 123477. Siphonodella duplicata (Branson and Mehl) var. A. Oral v1ews 13, Rubber replica, collection 55, USNM 123478; 23, rubber replica, collection 73, USNM 123479 Polygnathus inomata E R. Branson. Oral views. 14, Collection 354, USNM 123480; 15, collection 355, USNM 123481. Gnathodus sp. A. Oral view. Collection 647, USNM 123482. Pinacognathus profunda (Branson and Mehl). Lateral view. Inner side, collection 355, USNM 123483. Polygnathus allocota (Cooper). Lateral view. Collection 355, USNM 123484. Spathognathodus sp. A. Lateral View. Rubber replica, collection 113, USNM 123485. Gnathodus punctatus (Cooper). Oral view. Collection 647, USNM 123486. Elictognathus lacerata (Branson and Mehl). Lateral views. 21, Inner side, collection 355, USNM 123487; 22, outer side, collection 355, USNM 123488. Pseudopolygnathus prima Branson and Mehl. Oral View. Collection 355, USNM 123489. Siphonodella lobata (Branson and Mehl). Oral view. Collection 355, USNM 123490. Spathognathodus aciedentatus (E. R. Branson). Lateral view. Collection 355, USNM 123491. Spathognathodus sp. B. Oral view. Collection 355, USNM 123492. Polygnathus longipostica Branson and Mehl. Oral view. Collection 355, USNM 123493. Siphonodella quadruplicata (Branson and Mehl). Oral View. Collection 355, USNM 123494. Siphonadella seapticata (Branson and Mehl). Oral View. Collection 355, USNM 123495. PLATE 2 PROFESSIONAL PAPER 286 GEOLOGICAL SURVEY CONODONTS FROM MAURY FORMATION GEOLOGICAL SURVEY PROFESSIONAL PAPER 286 PLATE 3 g '9 3 fl Figures 1—3, 13. 4—9. 10. 11. 12, 14. 15—17. 18. 19-21. 22—24. 25, 26. 27, 2s. PLATE 3 [Figures are 30 times natural size] Palmatolepis sp. A. Oral views. 1, Rubber replica, collection 28, USNM 123496; 2, rubber replica, collection 28, USN M 123497; 3, collection 157, USNM 123498; 13, rubber replica, collection 243, USNM 123499. Palmatolepis subperlobata Branson and Mehl. Oral views. 4, Rubber replica, collection 157, USNM 123500; 5, rubber replica, collection 157, USN M 123501; 6, rubber replica, collection 157, USNM 123502; 7, rubber replica, collection 243, USNM 123503; 8, rubber replica, collection 43, USN M 123504; 9, rubber replica, collection 43, USNM 123505. Polylophodonta confluens (Ulrich and Bassler). Oral view. Rubber replica, collection 243, USNM 123506. Palmatolepis quadrantinodosa Branson and Mehl. Oral View. Rubber replica, collection 18.1, USNM 123507. Palmatolepis subrecta Miller and Youngquist. Oral views. 12, collection 157, USNM 123508; 14, rubber replica, collection 157, USNM 123509. Palmatolepis glabra Ulrich and Bassler. Oral views. 15, Rubber replica, collection 28, USNM 123510; 16, rubber replica, collection 28, USNM 123511; 17, rubber replica, collection 243, USNM 123512. Palmatolepz's sp. B. Oral view. Rubber replica, collection 69, USNM 123513. Palmatolepis perlobata Ulrich and Bassler. Oral views. 19, Rubber replica, collection 181, USNM 123514; 20, rubber replica, collection 69, USNM 123515; 21, rubber replica, collection 31, USNM 123516. Spathognathodus inomatus (Branson and Mehl). , Lateral views. 22, Inner side, collection 167, USNM 123517; 23, inner side, collection 201, USNM 123518; 24, outer side, collection 180, USNM 123519. Ancyrognathus bifurcata (Ulrich and Bassler). Oral views. 25, Rubber replica, collection 28, USNM 123520; 26, collection 242, USNM 123521. Hindeodella sp. A. Lateral views. 27, Inner side, collection 167, USNM 123522; 28, inner side, collection 167, USNM 123523. PLATE 4 ‘ [Figures are 30 times natural size ‘ Figure 1. Ancyrognathus sp. A. ‘ Oral view. Rubber replica, collection 182, USNM 123524 ‘, 2, 3. Polygnathus pennata Hinde. 2, Aboral view, collection 169, USN M 123525; 3, oral view, collection 11113, USN M 123526. 4. Icriodus sp. 1 Oral view. Rubberreplica, collection 240, USNM 123527. “ 5. I criodus sp. Lateral view. Rubber replica, collection 42, USNM 123528. 1 6. I criodus sp. 1 Oral View. Collection 11113, USNM 123529. ‘ 7, 8. Palmatolepis unicorm's Miller and Youngquist. ‘ Oral views. 7, Collection 7, USNM 123530; 8, rubber replica, collection 7, USN M 123531. 9—15.Palmatolep2's subrecta Miller and Youngquist Oral views. 9, rubber replica, collection 186, USNM 123532, 10,1rubber replica, collection 186, USNM 123533; 11, rubber replica, collection 186, USNM 123534, 12, rubber replica, collection 186, USNM 123535; 13, rubber replica, collection 186, USNM 123536, 14, rubber replica, collection 186, USN M 123537; 15, rubber replica, collection 182, USN M 1235381 16,17. Polygnathuslinguifarmis Hinde. Oral views. 16, collection 357, USN M 123539; 17, collection 169,‘ USNM 123540. 18. Ancyrodella sp. A. Oral view. Rubber replica, collection 240, USN M 123541. ‘, 19. Polygnathus sp. A. Oral View. Collection 169, USNM 1235421 20. Ancyrodella sp. B. Oral view. Collection 474, USN M 123543. 21. Ancyrodella rotundiloba (Bryant). Oral view. Collection 46, USN M 123544. 22. Hibbardella Sp. A. Oral view. Collection 48, USNM 123545. 23. Bryantodus sp. A. ‘ Lateral view. Collection 11113, USN M 123546. 24. Priom'odus alatus Hinde. Lateral view. Inner side, collection 46, USN M 123547. ‘ 25, 26. Palmatolepis margmata Staufl‘er. ‘ Oral v1ews 25, Rubber replica, collection 240, USNM 123548; 26, rubber replica, collection 240, USN M 123549. 27. Ancyrognathus euglypheus Staufler. Oral view. Rubber replica, collection 42, USNM 123550. PLATE 4 PROFESSIONAL PAPER 286 GEOLOGICAL SURVEY CONODONTS FROM DOWELLTOWN MEMBER OF CHATTANOOGA SHALE WMmmm—ZZm—H .Hfibm Q A\ ILLINOIS/ ’ A] WEST \ \ — ( \\ / 670 \ r \ r, ,_, \vIRGINIA \ l // \/\/ 6. D: \ — “ J K E N T u c KY v SOMERSET \ I MISSOURI ,VIRGINIA \/\~7\Il \ \ P U L A S K I \ A LI /—m , . \ I \ / \I ARKANSAS (r T E/N/N/E/S/s E/E CAROLINA_ B A R R E N ___—__ /\/ /[___ W1: :, SOUTH v/\‘# ’ I CAROLINA u I I I I \ / lva | \ I / /MlS$lSSIPP| lI ALABAMA \ GEORGIA ‘ K ROWENA ’ 'NDEXMAP \ / \__/CUMBERLANDI I__ __ I l 7/ SCOTTSVILLE \ BUR 5”“ \ W A Y N E / _ _ I I I I D R/ / I . A L L E N M o N R o E 'c L I N T o N \ / .. KF;_NTU_____CKY _ / l __—— —— _ — K — _— ' T "f TENNESSEE 207:] ’—— —— —- lpI C K E TT —— f —— ___ I I WESTMORELAND Y ' ,V-\ \ \ ___ ___ 0c 1IR 0 B E RTSON/ 206. M A C O N h\ ”i __ 30— —.__ U C] k \ \ , ~I ; I I BRANSFORD EULIE 205. \ l \ m \ 63 \ J ‘ {\J I 2 6‘ Q ’ S U M g E R TROUSDALE \i \ I / - /‘ ’9 ”IT" ’flIMKERs STATION GALLATIN I / 9 I 2\_’ _ ‘ I (v Io:\2°4‘ IOVERTONK r m T \4 v< .203 .J‘ACKSON P/ \ ' I 4’ WHITES CREEK 054 \ ) V\ U3 J\ I ’ I , SPRINGS \ x / m \\ ? I. 60. CHESTNUT MOUND ’ \1 6 \ I‘_\ / I.” \ < D w I L s o N s __l -4 I I “J a.) NASHVILLE -— I h" I .l 5A V I D S O N \NASHVILLE ‘QE 0 \I N__ 1‘ ~ I \ 36°>— ' \ Q \ 95 __\ l I 1‘ FRANKLIN:I \ 3 N I/ RUTHERFORD~Z~GA55AWAY\ 1.4-8 H I c K M A N i (9 100. D E K A L B __ O N \ _M _ A I\w I. I A M s Q~ WOODBURb" \ I' *——1 \\r-’ & I D‘ / —’I - I CENTERVILLE .165 \L B A S l N I D Q- \ lC A N N o N/ I .163 .168 I lu V CROSS KE;, ‘3?- I \ 182K I‘ _ VAN B UREN I PERRY \.250 x7 v ‘\ [\Q‘ WA R RE N»\ ‘ // I 243’ \ M (”A U R Y I V /Y(9 LINDEN W / N COLUMBIA " Q, I NOAH \ h\\ I J 3 D f l .107 \ / / f 1540 /\ B E D F o R D I \ fi/ 30; I L E w I s DMOUNT PLEASANT/ c o F F E E , B '— E \——l DSHELBYVILLE ' I: (\f— i , \ _ MAR SHA L L\ MANCHESTER I I L__1 I ~ / ___—I r/ \Vq 31134 \ /’ L G R U N D Y I’DUNLAP \ / CORNERSVILLE —\ f r \ SEQUATCH I E I _ I V\ (W \ ( ’5: Palmtolepis perlobam Ulrich and Bassler 3 lHl ' X X X X ® X X X X X X X ' X X X X X L X X I X X x x * mgasa Branson and Mehl X I quadrantimdosa Branson and Mehl 3 11 ® X 4* l— subperlobata Branson and Mehl 3 4 9 X X ®® X ® X X X X X X X X x SD. A 3 173,13 ®® X X ® X x X . gracilis Branson and Mehl I X X glamelrichandBassler 3 15'” I XX XXX®® XXXXXXXXXXX XX X XX XX XX X ><><>< ><><>< ' lgulmtodelladelicatulaBassler ><><><><><><><><>< ><><><><><>< ILL x x x 1: myroymzthus befincata (Ulrich and Bassler) 3 25, 26 X ® ® X X X X X X J X X X J qmdram Branson and Mehl X X J Pfikmiodus mutabilis Branson and Mehl 3 12 14 X X X X X i x . . Palmtozem‘s submm Miller and Youngquist 4 9'15 X X X® X X X @X 09 X . X X W X X x x X x x (5 marginata Stauffer 4 25, 26 X x x x ® >< __ >< X X ‘1 ' Ancyrogmlthus euglypheus Stauffer 4 27 X ® __ X x x x X Palmatolepis unicorm's Miller and Youngquist 4 7: 3 X ® X X X X X X t ’7 Ancy’rognathus sp.A 4 1 ® >< Ancyrodella sp. A 4 18 ® g . rotundi'loba (Bryant) 4 21 _ X X X . w B 4 20 # Bryantodus sp. A 4 23 A —I L X ® Hlbbameua 5p. A 4 22 M ()3) X x Polygmthus penml‘a Hinde 4 23 X X x x x x linguiformis Hinde 4 16' 17 I X X X x x . WM” alums Hinde 4 24 —“ a Figured specimen from collection not listed on r X X ’ 1071341148 599‘ 4 4’6 —~ this table or table 8 ® ® I X X X Amyrodella fragments fit I Only one specimen collected X X X X X X X X X X X I I_X X X X X X X AWWOQMMMS fragments ~——— ()9 Figured specimen from this collection X X X X X I IX X X X X Icr'wdus fragments X X X X X X I I I X I I IX L X X X x Palmtolem's fragments X I I I X J I ' IXI I I I I I I X X X X X Polyloplwdonm fragments X I I I L I I I I I I I I DISTRIBUTION OF CONODONT SPECIES 366719 0 -56 (In pocket) PROFESSIONAL PAPER 286 TABLE 8 GEOLOGICAL SURVEV I Locality 11 Locality 6 Locality 39 Locality 206 Locality 207 Locality 204 Locality 168 Locality 125 a Locality 228 Locality 226 Locality 225 _ Chattanooga Chattanooga Chattanooga Chattano a Chattanoo a Proazznce Chattanooga shale nominee Chattanooga shale f Matty Chattanooga shale N f Mautry Chattanooga shale fumigizn 6:522:28 f:;::on Chattanooga 5::Leelltown fongzm G shZIe f Maury shale f Maury Chattanooga shale Maury shaleog Maury shale 8 shale Gassaway member shale Gassaway member DEFI‘I‘SFI’IEZIH orma '0" Gassaway member Bazaar” orma '0" Gassaway member Dowelltown member membery Gassaway member member Sing: ormation (iii-:33 ormatron Gassaway member formation (33:23:: formation Gnaigveary I I ~ . StratirahicdistanceofcollectionfromtheNew - ~m-szosobbaznzn binary Ambmzuasagagrxb ‘s. io-‘rzi‘: 3259;.‘954596. 5.75705”. 3132‘": bohoaaqoah 5534;1anng >35??? Bibi“. 272 372%:sz inn-r: R by a? r9553? afaaz Nhkmbb; g b big 3‘2”?“ Profiidznceshale—Chattanoogashalecontactor 1; 3"”2333‘88‘53 c??? fQTT;?$§33§ L? (7'7” C"?‘?Tm“f; 3-??33‘ ”'13? TNfNZ$§E$ E‘EQ‘RRQ‘ 7H3)? O‘o‘f c" ‘?"$$§ $$$ ? ‘7‘ T oven? ‘77? Dir-(7.7.7004? o“ T To‘ crib“, ‘ 2 ‘28?»- :- 33: Siamese; “3-333- 2:; 2 2 2 2 g g :2 2:2 Collectionnumber ________________________ g §E§E§HES§§ fifig §§§§$22§§m§ g Egg fjgjaa§ §§INB Egg §§28§:::H 32mm§§ £22§ ESQ § E§§§§ 3&5 § g S ESE I33§ 8§$$$$m ,3 g (fig QR: .4 M A to Plate Figure I I I I I I I o Gnathodus sp.A 2 15 X Pseudopolyg‘nathus Sp, 13 X X Pol thus allocota (Cooper) 2 cflunm Branson and Mehl 2 2‘5 X X X X X X 69 X I X ® X Elictognathus lacerata (Branson and Mehl) 2 21v 22 X X X Gnatiwdus so. B X X X X X __ Palygnathus inomam E R. Branson 2 14' 15 X X X X longipostica Branson and Mehl 2 28 X Pseudopolygnathus prime. Branson and Mehl 2 24 X , X X X X X Siphzmodella duplwata (Branson and Mehl) 2 5'11 I X _ _ ®® ® >< dupliwta (Branson and Mehl) var. A 2 13'23 I X X . X X X X ®® >< qwzdmplioatamranson and Mehl) 2 29 X X X X X SD. A 2 12 x Spathoggrathodus aciedentatus (E, R. Branson) 2 26 X X X X Gmthodus fragments X X Psmdopolygnathus fragments _fi X I I X X Siphmwdella fragments X X A X ‘ X .X X Spathogmthodus sp. A 2 19 F i ® Hindeodella SD, A 3 27,28 X X X X X X X X X X X X X X X X X X Spathogmthodus inormtus(Branson and Mehl) 3 22 2L X X X ®X X X X I X X X ® X X X X X X X X X X X X disparitis (Branson and Mehl) X X X X X I _ aculeatus (Branson and Mehl) X X X X X X X X X X X X I X >< X X X X Polylophodtmta confluent; (Ulrich and Bassler) 3 10 ‘ X X X X X X X Palmatolqrisperbobata Ulrich and Bassler 3 1921 ' X X X X XX X X X X X X X X X X X X X X X X X X X x x X X 69 x >< x x mgosa Branson and Mehl X X X X X X X X X quadrantinodosa Branson and Mehl 3 ,L X X X X X X x subperlobata Branson and Mehl 3 4’9 j X X: X X x X x >< Sp, A 3 1 3,13 l i ( x glabraUlrichandBassler 31517! , XXXXXXX XXXXX XX XX XXXX X XXX X XXX X XXXXX X XXX Palmatodella delicatula Bassler X X X X X X X X X X X X x x x Ancyrognatus Mfurcatu (Ulrich and Bassler) 3 25' 26 L I X X X X X X quadrata Branson and Mehl ’ >< Palmatolepis Sp. 8 18 ® Prikmibdus mutabilis Branson and Mehl X ' X x x x x X x mfluens Branson and Mehl X Palmatolepis gracilis Branson and Mehl X X X X X X x Pelekysgnathus inclinata Thomas 3 1 14 X I I Palmwbepis subrecta Miller and Youngquist 4 £15 X X X X I I X X X x marginuta Stauffer 4 25, 25 X Ancyrogmthus euglypheue Stauffer 4 27 h - g ? X X X X Palmatolepis unicomis Miller and Youngquist 4 7'8 X X X I X X X Ancyrogmthus sp. A 4 1 I l I I I x Ancy'rodella so. A 4 18 I I X 0 rotu‘mfiloba (Bryant) 4 21 ? X x x x sp. B 4 20 X x X Bryantodus so A 4 23 X ® X X X Hibbu'rdella so. A i 22 X x X Polyg'nathus pennata Hinde 4 2'3 X X X X X X X ®® X X X X X X X lingm'formis Hinde 4 16, 17 X X X ® X X ® X 0 Prionoodus alatus Hinde 4 24 X X X X X X X Imodus spp. 4 476 X ® X x x X Polygnathus SD, A 4 19 —' O Figured specimen from collection not listed on F'“ X ® Ancgrodella fragments X __ this table or table7 __ X X X X X X X X x x X X x X Ami/709mm“? fragments _, I Only one specimen collected —~— X X X X 10M“ fragments ' X —— ® Figured specimen from this collection ——— X X X X X X X X Palmwlm fragments —» @ Figured specimen was only one collected ——« I X X X X X X Polyhmhodo’nta fragments . l . I I . | l . . i i i . . i i X X L i i X LII IIIIIIIIIIIIIIIII IIIIIII DISTRIBUTION OF CONODONT SPECIES 366719 0 -56 (In pocket)