UC BERKELEY MASTER NEGATIVE STORAGE NUMBER 03-67.79 (National version of master negative storage number: CU SN03067.79) MICROFILMED 2003 UNIVERSITY OF CALIFORNIA AT BERKELEY LIBRARY PHOTOGRAPHIC SERVICE REPRODUCTION AVAILABLE THROUGH INTERLIBRARY LOAN OFFICE MAIN LIBRARY UNIVERSITY OF CALIFORNIA _ BERKELEY, CA 94720-6009 __ COPYRIGHT The copyright law of the United States (Title 17, United States Code) governs the making of photocopies or other reproductions of copyrighted materials including foreign works under certain conditions. In addition, the United States extends protection to foreign works by means of various international conventions, bilateral agreements, and proclamations. Under certain conditions specified in the law, libraries and archives are authorized to furnish a photocopy or other reproduction. One of these specified conditions is that the photocopy or reproduction is not to be "used for any purpose other than private study, scholarship, or research.” If a user makes a request for, or later uses, a photocopy or reproduction for purposes in excess of "fair use," that user may be liable for copyright infringement. University of California at Berkeley reserves the right to refuse to accept a copying order if, in its judgment, fulfillment of the order would involve violation of copyright law. Inman, W. E. Origin and occurence of the magmatic nickeliferous pyrrhotite at Julian, California 1919 BIBLIOGRAPHIC RECORD TARGET University of California at Berkeley Library Master negative storage number: 03-67.79 (national version of the master negative storage number: CU SN03067.79) GLADIS NUMBER: 184787253A FORMAT : BK AD:991009/FZB LEVEL: BLT:am DCF:a (CSC:d MOD: BL:7 UD:030604 /MAP CP: cau L:eng INT: GPC: BIO: FIC: CON: ARCV: PC: PD:1919/ REP: CPI1: FSI: 11LC: II: 040 CUScCU 090 SbDISS.INMAN.GEOL 1919 100 1 Inman, W. E. 245 10 Origin and occurence of the magatic nickeliferous pyrrhotite at Julian, California. 260 $c1919. 300 80 p. :%5bcol ill., maps :5Cc29 cm. 502 Thesis (B.S. in GeoLOGY)-- University of California, Berkeley, June, 1919. 610 20 University of California, Berkeley.SbDept. of Geology and GeophysicsS$SxDissertations. 690 0 Dissertations, Academic$xUCBSxGeology$y1911-1920. Microfilmed by University of California Library Photographic Service, Berkeley, CA FILMED AND PROCESSED BY LIBRARY PHOTOGRAPHIC SERVICE, UNIVERSITY OF CALIFORNIA, BERKELEY, 94720 DATE: 08/03 REDUCTION: 10 X FILMED AND PROCESSED BY LIBRARY PHOTOGRAPHIC SERVICE, UNIVERSITY OF CALIFORNIA, BERKELEY, 94720 DATE: 08/03 REDUCTION: 10 X of the MAGMATIC NICKELIFEROUS PYRRHOTITE at Julian, California LIBRARY COPY We E. Inman OUTLINE WG SW GA WN RE GES Se GS aww eee a Field Work Location Topography PART I -- AREAL GEOLOGY General Features SCHIST-GNEISS SERIES - General Features 1. 2 Se Sehist Megascopic Description Gneiss General Features . Megascopic Description Granite Pegmatites General Features Origin and Correlation BASIC INTRUSION Form and Extent Weathering and Outcrops General Character 1. 2. Gabbro and Norite General Features. Gabbro and Olivine Gabbro Megascopic Description Microscopic Features Alteration Norite General Features Microscopic Description Pyroxenite General Features. Augite Porphyry General Features Associate Dikes Hornblende Gabbro Pegmatite Dikes Conclusion PART II -- ECONOMIC GEOLOGY Location of Main deposit Development and Exploration Outecrops I. ASSOCIATE ROCKS a. Classification b. General Relations ¢c. Detailed Descriptions a. OSCHIST-GNEISS General Occurrence Megascoplc Features i Microscopic Features 3 Origin and Correlation b. BASIC INTRUSION l. Norite General Occurrence 3 Megascopic Features ! Microscopic Features 4 2. Olivine Norite General Occurrence Microscopic Features 3. Peridotite : General Occurrence Megascoplc Features Microscopic Features. Bel a fs ge Be i 3 ome fa Ss li. Troctolite General Occurrence Microscopic Features SLi Si aban 5. Associate Dikes i (a) Hornblende Gabbro A General Features Megascoplc Features Microscopic Features Origin and Correlation (b) Pegmatites General Occurrence Megascopic Features Microscopic Features Origin and Correlation 11. 111. 8. b. Ce. d. €. fe IV, RELATIONS OF DISSEMINATED METALLIC MINERALS TO General Considerations ‘Microscopic Features THE MASSIVE SULPHIDE DEPOSIT SUMMARY CONCLUSICNS THE ROCCE~-FORMING SILICATES Conclusions General Occurrence Outerop Form Megascopic Features Microscopic Features Metallic Minerals Original Silicate Minerals Oxidized Zone. Introduction Field Work. The data for this article were collected by Messrs. F. S., Hudson and W. E. Inman during the early part of the Summer of 1917. Two weeks were spent in the field, examining the Friday Mine, studying the surface exposures and collecting specimens. Mr. F.S.Hudson revisited the region during the summer of 1918 and in his report, now in pPdparation, will give a complete account of the areal zoology, No suitable topographic map was available for mapping this area. In consequence the surface relations were outlined, as on the areal geology sheet, by magnetic bearings and paced distances. Location. The locality in which this deposit occurs is situated about four miles south of Julian, in the Ramona Quadrangle. This region is near the crest of the Peninsula Range which extends southward and forms the peninsula of Lower California. Topography. The main feature of the area is a long ridge ( extending approximately northwest and southeast, with an average elevation of 5000 feet. A press Drainage to the east of this ridge reaches the Salton Sea while to the west the waters flow into the Pacific. On the northeast side the ridge (not named on topographic sheet) drops sharply, forming one wall of Banner and Chariot canyons. This slope is suggestive of a fault scarp, the face of the ridge lying in a straight line for several miles. The appearance of this slope 1s illustrated in Fig. 1, Pl. I. The surface here is being rapidly eroded by intermittent stream action, producing narrow, steep gullies with intervening sharp ridges. On the southwest slope of the ridge, on which the mine lies, the topographic features are in strong contrast to those briefly described above. (Pl. 1, Fig. 2) The general slope of the ridge is much less here. Minor features are of more rounded form, distinctly older than features developed on the opposite side. A few miles to the south and east the country : has a much less rugged aspect than in the vicinity of : the intrusion, the area described above. This region is typified by broader and longer valleys, separated by low lying, well rounded hills (Pl. II, Figs. 3 and lL). The different character of this area is due to fact that practically the whole surface is of a schistose rock which is very susceptible to weathering and erosion. Fig. 1. Northeast slope of main ridge, looking north. Banner Canyon in distance. Fig. 2. View of opposite side of ridge shown above. The small white area on the left is the dump the Friday Mine. Stone. 2 . ode Is! ANVIL ONIAAD AAJ AO AMV.LTA Fig. 3. Cuyamaca Lake. The open rolling topography developed in schist 1s seen here. Fig. LL. Cuyameca Lake, looking south from North Peak. REAL GEOLOGY -- A PART 1 RE Ri : a R—— PART I -- AREAL GEOLOGY General Features. The formations present consist broadly of a schist-gneiss series invaded by a basic intrusive mass. These two may be grouped as follows: A. Basic Intrusive l. Main Intrusion a. Gabbro b. Norite ¢. Pyroxenite d. Augite Porphyry 2. Hornblende Gabbro Dikes 3. Pegmatite Dikes B. Schist-Gneiss Series | 1. Schist 2. Gneiss 3. Granite Pegmatites A detailed description of the individual members of these series follows, taking up the oldest formation first. SCHIST-GNEISS SERIES - General Features This series is the oldest member of the region and is intruded by all other formations. The schist 1s the only representative of sedimentary origin, the gneiss and later intrusives being igneous. Northwesterly from the vicinity of the mine the schist-gneiss:# extends beyond the limits of the map and has been observed as far northward as Julian. In the opposite direction, to the southeast the series was seen to be continuous for over six miles. These formations, especially to the southeast, develop a low-lying, rolling topography. The valleys have gently sloping floors, well covered with soil and separated by low, rounded hills. Outcrops are uncommon, and where seen are the result of local induration or of an area originally more compact and dense than the average. Schist. Megascople Description. The schist is an : even-grained, moderately compacted rock. When fresh the ] color 1s light grey, streaked with darker bands. It is usually weathered and of a yellowish or reddish yellow grey, due to limonite. It 1s composed of grains of quartz and feldspar, with flakes of biotite lying in - 3 Ss parallel, oriented positions. The feldspar and quartz comprise 85 to 95 per cent of the whole. The schist is uniform throughout. No limestone occurs and but a very small amount of intercalated argillite. Layers of this argillite are not over ome-quarter inch $n thickness and are only developed locally. The degree of schistosity varies. In some areas it 1s well developed while elsewhere this feature does not appear in the hand specimen. In all cases, however, a larger view of an outcrop will show banding of the rock. » Along the contact with the basic intrusion a schist is found of hard, recrystallized rock, with a vitreous luster. This is due to thermal effects and does not extend far into the schist. Gneiss. . General Features. A part of the area mapped as schist consists of a granite gneiss, younger than the schist which it invades. The outlines of these areas were not mapped for the present investigation.® The gneiss was found in contact with the basic intrusion at several points. It occurs both on the east and west margins and is of similar nature in all areas observed. Megascopic Description. The granite gneiss is of light grey color, carrying dark bands enriched in biotite. It is composed of 30% to LO0% quartz, 50% to 60% feldspar and 10% biotite. The gneissic structure is due to the orientation of biotite flakes and their segregation in bands or layers. This structure is not always seen and in such cases the normal granitic texture appears in a very loosely compacted mass. In certain areas the gneiss is present as repeated, thin injections, layers of schist and gneiss alternating. This injection gneiss is crumpled and contorted to a high degree, developing a complex structure. - 12 - The weathered gneiss is a granular incoherent mass of reddish or brownish grey. This mass breaks up into a coarse sandy soil, similar to that of the schist but composed of larger grains. % Granite Pegmatites. A General Features. Occurring in the schist- 3 gneiss series are a nunber of pegmatite dikes. These vary in widths from a few inches to fifteen feet and show corresponding lengths, the largest dike being several hundred feet long. The dikes are found cutting the schistosity planes at every angle, usually at a high dip. Certain of these dikes, cutting across the schistosity, have short apophyses lying parallel to the strike of the schist. Such apophyses show rolled and : contorted forms, the walls of the dike swelling, pinching ARLE SDR Ei EE and developing knotty forms. In other cases the dikes pg wm Log ri a or are fractured and broken, apophyses being devoid of the effects produced in the contorted forms. ; i The pegmatite is coarsely crystalline, con- dsting of quartz and feldspar, with biotite in minor amounts. No tourmaline or muscovite is present. Origin and Correlation. These pegmatites are believed to be the final magmatic product derived from the now gneissic granite intrusion. Evidence dupporting this hypothesis is chiefly of a negative character. - 10 -13 = There are no other intrusives to which these emanations may be referred. They have formed during a period earlier than the invasion of the basic intrusive and are different mineralogically from the pegmatites of this magma » The pegmatites of this character were formed during and after that period in which schistosity developed. This is evidenced by the occurrence of the rolled, twisted and contorted dikes, and by stages of deformation passing from this form to those dikes showing fracturing only. BASIC INTRUSION: Form and Extent. The basic intrusion lies within the schist- gneiss series which it has invaded. It is very irregular in shape and belongs to the aggressive type of intrusions. Several embayments of this magma, and apophyses, are lying outside the general margin of the main mass. The general form is roughly elliptical with the greatest direction lying north and south, eight miles in length. The shorter east-west axis is three miles in length along the line of maximum width of the intrusion. T™e part of this intrusion mapped on the areal geology sheet, and the area studied for this paper, consists of one of these tongues or apophyses extending from the main intrusive mass into the schist-gnelss area. - 13 =- - 1 - This apophysis lies at the extreme north end of the large mass to which it is connected. The length of this area is about one and one-half miles north and south, and three quarters of a mile equals the greatest width. The contact between this intruded body and the older series is a curving, sinuous line, marked by many reéntrant angles extending into the schist and gneiss. No apparent relation exists between the plane of this contact and the mass form of the intrusion. In places the contact parallels the strike of the schis- ( tosity and at nearby points cuts directly across these planes. The dip relations show an equal variety of attitudes. At some points the schist dips under the intrusion and at a distance of two or three hundred feet it will be found dipping away. These dips vary in mag- nitude from 90° to 20°, both away from and towards the invading body. Weathering and Outcrops. The norite-gabbro or basic intrusion is suscep- tible to weathering agencies. It breaks down readily, forming a heavy, red, clay soil. Due to this heavy soil, and a dense growth of vegetation over a large part of its ( surface, good exposures are not common. -illy = General Character. A study of these exposed portions of the norite-gabbro mass show 1t to be of a varied nature. Variations occur in granularity, or size of crystal grains, in texture and in mineral and chemical composition. The size of mineral grains varies widely, showing fine, medium, and coarse-granular development. All rocks are holocrystalline, none occurring with glassy matrix. Texture is found in granitic, poikilitic and ophitic patterns, and of these the latter two are the common, typical occurrence. The coarsest granitic texture is found chiefly in the segregations rich in pyroxene but not olivine. The poikilitic and ophitic textures are found in the normal types of gabbro and norite, and in those areas especially rich in olivine. As is seen from the group of rocks listed under the head of Basic Intrusives, a number of different mineralogical and chemical types are presente. The areas in which these various types of rocks are found cannot be separated one from another by any sharp line. There appears to be a gradation from one to the other. This gradation does not take place within any set limit of space. -15 = - 16 - A detailed account of the rocks of the basic intrusion is given in the following paragraphs. The types present at the surface which are also present in the mine are omitted from this discussion, other than to outline their broader features. This is done in order to avoid repetition. These rocks will be discussed in the following order, according to their grouping: Basic Intrusive Gabbro Olivine gabbro Norite Olivine norite Pyroxenite - Augite porphyry Associate Dike Rocks Hornblende gabbro Pegmatite The norites and the associate dike rocks will be mentioned, but briefly, in this section of the paper. They are dealt with more fully in the part devoted to economic geology. Gabbro and Norite. General Features. These types occur over the greater part of the basic intrusion and together consti- tute the major portion of it. They are the types normal to the general magma, other types having: formed as segre- gated products. They are quite similar in general appear- ance and only in specimens high in the content of rhombic pyroxene can the norite be distinguished. Gabbro (Sp. 105-106-107-110) | Megascopic Description. Specimens of | gabbro are of uniform character. They are of a dark gray color with a slight greenish cast. This color is characteristic of fresh specimens, which are not always obtainable. Most of these rocks at the surface are of a brownish red color, due to the weathering action on the sulphides and ferro-magnesian minerals present. The texture is holocrystalline, medium granular, granitic or poik=- 1litic. The specimens are composed of approximately equal proportions of plagioclase and ferro-magnesian mineral . The plagioclase shows the albite twinning often combined with the Carlsbad. The dark minerals are amphibole and pyroxene, the former predominant. In some of the areas the gabbro is characterized by small rounded grains of olivine, occurring in poikilitic fashion and more segregated in small patches than other minerals. Pyrrhotite can be seen with the naked eye in practically all of these rocks and in the few cases where it was not seen, its former presence is inferred from patches of limonite present. The pyrrhotite occurs disseminated in individual isolated blebs. Chalcopyrite occurs in mach less abundance. Brown blotite occurs as an occa- sional accessory. Microscopic Features. The average gabbro specimen has the following mineralogical composition. - 18 =- The minerals are arranged in the order in which the ma jor portion of them crystallized, bytownite being the only one not occurring strictly in the given order. 1. Apatite = = «= = = = = = -=-xx % 2. Ferromagnesian minerals Augite or diopside - - - 14% Brown hornblende - - - - 20% 3. Labradorite - - - = = = - = 659 Li. Opaque minerals - - = - - = 1% The texture in most cases is ophitic, some slides showing this more prominently than others. Small euhedral crystals of bytownite occur imbedded in large crystals, or irregular patches of the pyroxenes or hornblende. The feldspar continued to form after the ferromagnesian minerals had crystallized. The feldspar is seen in subhedral to anhedral form, and occupying interstitial spaces. The two types of minerals, except- ing the euhedral bytownite, develop allotriomorphiec relations, indicating contemporaneous crystallization of the greater part of the rock. The hornblende, occurring in this manner is the common brown hornblende and is of primary magmatic origin, The pyroxene occurs both as augite and diopside but both do not appear in the same spe cluen, Apatite occurs inall specimens of the gabbro, in fact it is present in all rock types. -'18 = It forms small euhedral crystals that have crystallized out. of the magma before all other minerals. Euhedral magnetite occurs in several of the specimens contempora- neous with the apatite. As the opaque minerals appear in all specimens and all rock types, save the pegmatites, they will be dealt with in a subsequent section, covering all cases. See section on Economic Geology "Relatims of the Metallic Minerals to the Rock Forming Silicates." The boundaries of all minerals, excepting those included euhedral forms, show as curving lines. The feldspars and ferromagnesian minerals are mutually embayed. All relations are typical of nearly contempo- raneous crystallization of the major portion of the con- stituents. A small part of the feldspar formed first, and the remaining portion continued to form until solidification was accomplished. Olivine Gabbro. (Sp. 132.) Specimens of olivine gabbro vary considerably in their mineral content. A specimen from the southern end of the mapped apophysis has the following characteris- ties, the minerals being present in their given amounts: Apatite - - - - - - =~ Olivine - - -» ~- = -' = Bytownite - - = - - = Brown hornblende- - Opaque minerals - - - The rock is of ophitic texture. Small euhedral crystals of bytownite occur included in olivine, brown hornblende and in larger anhedral bytownite. Olivine occurs included in the hornblende and also occurs in the general field. In this latter position it is idiomorphic to the bytownite, forming rounded grains. Apatite occurs in small euhedral forms as an accessory mineral. Alteration. The gabbros show practically no alteration. In some cases the hornblende has altered to chlorite to a slight extent. Olivine has developed a narrow rim of serpentine but the attack has not yet reached into the cracks of this mineral. The typical mesh work produced in the serpentinization of olivine is entirely lacking. Some limonitic stains occur but represent a transferred product rather than ah alteration in place and has probably originated at the exposed surface of the outcrop. It may be noted here that the hornblende does not appear as an alteration product. In some cases it is seen rimming or moulded on pyroxene crystals. The crystallographic and optical orientation of the two minerals do not coincide as they would did the hornblende form from the augite. The hornblende is concluded to have formed in the magma as a primary mineral. “' 80 - Norite. (Sp. 104-106-109-115-127) General Features. Norite occurs at numerous places over the intrusion and cannot be said to be centralized in any particular portion. The rock 1s dari grey in color, composed of approximately equal amounts of the dark and light minerals. The light mineral is plagioclase showing the characterizing twinning in combination with the Carlsbad. The dark constituents are chiefly badack amphibole and a bronzy lustered rhombic pyroxene. Small flakes of brown biotite were observed as an occasional accessory. This type of rock is ophitic in texture, small grains of plagioclase occurring imbedded in patches of the ferromagnesian minerals. These patches are lO to 50 millimeters in length in some instances, grading down to medium sizes. The effect of these areas 1s to I SE on mms give the rock a very splotched appearance. / Another type occurs which appears to be granitic at first sight. A closer examination reveals the ophitiec texture developed here as well as in the rocks of the above characteristics. Microscopic Description. Although the complete description of the norites is given in the section devoted to economic geology, a few statements will be given here. - 2] iw These statments pertain to certain occurrences or charac- teristics not seen in specimens from the mine. The rhombic pyroxene, though generally hypers- thene, is found to be present as enstatite in some in- stances. In Some cases these pyroxenes show a faint pleochroism from a faint pink to a greenish tint. The usual occurrence is colorless. Brown hornblende occurs for the most part contemporaneous or slightly earlier than the bytownite. It also occurs partly reimming or moulded on the ends of the rhombic pyroxene, tending to lengthen the crystal. A third form of brown hornblende was noted in one instance. Here it is seen filling a minute fracture cutting across all other silicates present. At certain points this veinlet widens into areas twice its width. This veinlet has no connection with any of the sulphides in the rock. At one point the veinlet, did it pursue its general rectilinear course, would cut directly across a sulphide bleb. The fracture is, however, offset at the bleb and passed around it. The veinlet of this secondary hornblende is then of an age or formation period later than the solidification of this bleb. This is evidence in favor of the primary origin of the sulphide and that it has not been introduced to its present position by mineralizing action. Olivine is present as a characterizing mineral in certain of the norites. (Sp. 130) - DD See A OA RIE asin Pyroxenite. (Sp. 100 - 133.) General Features. Pyroxenite is found in two areas exposed at the surface, One of these areas lies to the northwest of the mine, a short distance, and the other lies to the east. The two are separated by a gabbro-norite area and are entirely disconnected. This rock is greenish gray in color with a peculiar bronzy luster. It is composed chiefly of a rhombic pyroxene with minor amounts of olivine and plagioclase. These minerals are set in the pyroxene in poikilitiec fashion. The rock 1s extremely coarse textured, individual grains of an inch to an inch and a half being developed. Such occurrences sare exceptional, the general size being between one-quarter to one-half inches. Porphyritic Gabbro. (Sp. 12.) General Features. Rocks of this nature occur in the creek bed to the southwest of Tallys (see map of Areal Geology) and are well exposed. They are of limited extent and grade into normal gabbro. a Their color 1s light grey, spotted with black subhedral augite. A small amount of hornblende is present also. The lighter areas are chiefly feldspar with 10% or 15% pale greenish olivine. The augite constitues about one-third of the rock. Strictly speaking this rock would not be classed as a porphyry, though such is its general appearance. - 23 The augite forms long prismatic crystals, averaging over eight millimeters. They include small rounded grains of olivine. The feldspar occurs in holo- crystalline, medium granular grains. Inclusions or segregations of a dark, medium-grained gabbroid rock occur in the matrix of this "augite porphyry." Sueh inclusions are in drawn-out sinuous forms typical of movement in the magma after segregation had taken place. The outcrop of this rock type is illustrated in Plate III, Fig. 5. Associate Dikes. Hornblende Gabbro. (Sp. 113-119) Several dikes of this type were seen, some lying in fractures in gabbro and others lying between the intrusive and schist-gneiss series. The dikes in the basic intrusion are of variable widths, many of them being but a few incheswide, while others may reach a thickness measurable in feet. One dike, lying between gabbro and norite is over 0 feet wide. These hornblende gabbro dikes are composed of a uniform, fine-grained rock, fresh and unaltered. It is of black color, composed mainly of black amphiboles in long narrow prismatic forms, without definite orienta- tion in the rock. Plagioclase occurs in minor amounts. - 2l - Plate TII. | hn Hi. Fig. 5. outcrop of augite porphyry and gabbro in creek.bed Ba nd west of Tallys. Note light colored segregations in center Hh of photograph. Both pyrrhotite and chalcopyrite are present in small amounts. The latter is less commonly seen and 1s wanting in some specimens. They occur together or singly in isolated blebs. These dike rocks are identical with those occurring in the mine. pegmatite Dikes. (Sp. 116) The distribution of these dikes, like that of the gabbro dikes, is general. Varying widths are observed but they do not usually outerop for any dis tance in their strike direction. Quartz and orthoclase are the maln constituents. In a large dike of this nature, near the southern end of the mapped area, an outcrop of LO feet width is exposed. This dike is composed of quartz, orthoclase, tourmaline, and muscovite. The orthoclase and quartz are intergrown in perfect coarse grephic structure. These minerals form the greater part of the dike. One local area is composed of a conspicuous amount of muscovite, probably forming 40% of this particular area, fifteen feet or so in width. Tourmaline occurs irregularly in black subhedral crystals. Conclusion. These dikes are evidently of the same origin as those occurring in the mine, namely, from the differentiation of the basic intrusion. -“ 26 = i { ! § } i Lite PART II =-- ECONOMIC GEOLOGY ECONOMIC GECLOGY Location of Main Deposit. The segregated sulphide deposit and its associated rocks described in this paper are situated in T 13 S, R 4 E, in the Ramona Quadrangle, San Diego county, California. The deposit is opened up by the Friday line, owned by the Friday Copper Mining Company, of San Diego. The mine is 33 miles south of Julian, the nearest town. This town may be reached from San Diego by auto stage. The route is over the main road from San Diego to Imperial, via Ramona, and is about 60 miles from San Biego. The direction traveled is northeast from this latter city. Development and Exploration. Development work has not been carried forward to any extent at the mine and that which has been done is of explorative nature. A forty- or fifty-foot shaft was first sunk on an iron gossan cropping out west of the present shaft. As no ores were found beneath the gossan, this first shaft was abandoned when a depth of 50 feet had been reached. After a considerable lapse of time the present shaft was sunk about 60' to the east of the first shaft. The new shaft is7two-compartment., combination shaft. The vertical section of the shaft reaches a depth of 133 feet from the collar. - D8 Below this an inclined single compartment extends downward at an angle of 60° for a distance of LO feet. Two levels extend northeasterly from the shaft, one from the 150-foot level and the other from the bottom of the inelined section. Bach of these levels is about 175 feet long with drifts end cross- cuts leading to the ore. A shallow winze has been sunk in the massive ore on the upper level. The mine is not being worked at present, either for development or commercial purposes. There is not sufficient ore in sight to warrant the expense of a reduction plant and the nearest plant for such ores 1s too distant to ship at a profit. Excepting the Friday Mine, practically no exploratory work has been done. A few trenches, and a short tunnel a quarter of a mile north of the mine, comprise the total of such work. Outerops Outeropping of oxidized ore 1s seen in two places only, one at the mine and one on the hillslope to the north, a distance of approximately one-fourth of a mile. These outcrops are similar in composition, texture and appearance. They consist of an iron gossan, composed mainly of dark, reddish brown limonite. It 1s of a spongy or porous nature in general, though some of it is rather dense. Some of this dense material is 1imonite in a black cherty form. - 29 = Ther is very little of this gossan at the mine and it is in no wise referable to the ore found. It is seen about 60 feet west of the present shaft and the old shaft, now filled, was located at this point. No ore was found beneath this gossan. This fact, in conjanction with the fact that this outcropping occurs at least 150 feet from the vertical projection of the main sulphide body, leads to the conclusion that this oxidation product is not an expression of the main ore body. It is believed this represents an individual body that has been completely oxidized, and all values leached. The gossan north of the mine 1s similarly untelated to ore. A tunnel has been dirven under this out cropping, at a level about 30 feet vertically lower. No ore, or evidence of it, occurs in this tunnel. The gossan, and oxidized ore similar to that above the ore in the mine, indicates that this was a small isolated mass of ore, probably a local segregation. ASSOCIATE ROCKS: Classifiaction. A nutter of rock varieties are exposed in the mine workings. These may be classed as follows: - 30 = le. Schist-Gneiss 2. Basic Intrusives ) Norite ) Peridotite 8 ) . Troctolite ) Ore b. Complementary Dikes l. Hornblende Gabbro 2. Pegmatite. General Relations. Of these the schist-gneiss is§ the oldest, coming from the underlying formations into which the basic intrusive has forced its way. The schist-gneiss is in blocks of tabular form, three in number, which owe their present position to faulting. This faulting occurred shortly after the intrusion of the hornblende gabbro and before the formation of the greater part of the pegmatites. The rocks of section "a," norite, peridotite, troctolite, and the ore as well, were formed contempora- neously and under similar conditions. These various types grade one into the other, excepting the ore. No definite line can be said to mark their limitations, nor are they confined to single areas. - 3] = They have all been crushed, faulted and mechanically deformed to an equal extent. The sulphide deposit is believed to have assumed its present form during this period. Suc ceeding the above stage of rock formation was a period of movement. The first effect of this was to fracture the solidified shell of the basic intrusion. The fractures so produced were intruded by the comple- mentary hornblende-gabbro dikes. These do not occur in widths exceeding ten inches, but are very persistent in their longitudinal direction. After the intrusion of these complementary dikes, accumulated stresses resulted in faulting. This faulting brought into the intrusives of the mine the schigt-gnelss slabs and also dislocated a portion of the sulphide segregation. The pegmatite dikes were formed following this period of faulting. That some of them had formed previous to this period is seen by the faulted dike occurring at the second level (250 level). Most of the pegmatite, however, formed subsecuent to faulting and it is clearly the youngest formation present. DETAILED DESCRIPTION OF FORMATIONS. SCHIST-GNEISS: General. The schist-gneiss slabs lie between two well - 32 defined fault surfaces in every case. These surfaces are slightly curved and are seen to diverge and converge somewhat from place to place. Their distance apart, or the thickness of the slabs varies, from two to twelve feet. Three such slabs are observed on the | : second level, but one of them being exposed in the upper workings. The slab of greatest extent lies between surfaces whose general strike is N 76°E, dipping 65°s. The tendency for the development of curved surfaces is more marked on this alab than on the other two. The strike and dip of the fault sur- faces and of the schistosity planes is practically | identical. Faulting, slightly later than that which has introduced this slab, has affected it. A second slab of schist is seen in the drift leading to the ore on the lower level. This slab 1s not as well defined as the one described above. it is seen to lie between two faults whose surfaces converge downward and to the east. The average strike is N 66°W and dips are southward. The fault marking on the north or foot wall side of this slab dips 80° to the southwest while the hanging wall fault dips but [0° southwest. This eecond slab of schist 1s terminated at its north- west extremity by a third slab, striking N 20%w and 0 dipping 65 northeast. The average thickness of this slab is 3 feet, though it widens somewhat at the southern portion exposed, where it also warps to the southwest. iB - TET me SERRE TE A clay gouge has developed along all these fault surfaces, from six to twelve inches in thickness. In places it 1s macaceous, and has developed at the expense of the schist rather than of the intrusive. This is to be expected as the schist is much less resistant and comract than the igneous rock. \ Megascople Features. The slabs are composed almost wholly of schist, the granite gneiss not appearing. A part of these schist slabs is injection gneiss, by virtue of the pegmatitic material carried. The schist is grey in color, and in most cases loosely cemented, breaking and crumbling wi th the fingers being possible. A few areas are dense and hard, and can only be broken with the hammer. The § greater portion of the schist is composed of fine grains. A These grains may vary in both directions, some being 3 coarser and others of shale being finer. The schistosity 1s well developed, marked by the orientation of biotite 1 flakes. Some of the schist appears to owe its 3 character to original bedding. Thin bands of argillite 4 alternate with bands or layers of a coarser nature. ; The coarser material is composed of quartz, feldspar 1 and biotite. - 34 - A Pegmatitic material has been injected into the schist along its planes, producing an injection gnelss. The pegmatitic material is largely quartz, with a less amount of feldspar and accessory biotite. The usual texture is granitic, though some layers of this material appear to have a vein texture or structure. It 1s badly crushed and was injected into the schist before faulting brought the schist to its present position. Microscopic Reatures. Several specimens of schist were studied with the microscope by using grains of this material immersed in oils. The greater portion of the schist, from 85% to 95% is quartz. The remaining portion is biotite, and an occasional grain of feldspar. The quartz carries rod-like inclusions of apatite and some opaque mineral. The opaque mineral is also in rod-like form, and hemi- morphic. It is definitely different from an y opaque mineral of the intrusive rocks. The biotite occurs as a green pleochroic variety and also in the common brown form. In some cases the biotite is almost wholly of this green variety, while in others this is of le 8s importance and at times entirely lacking. - 35 = AN Origin and Correlation. From a study of the schist, found both in the mine and over large surface areas, it is goncluded to have formed from a medium to fine-grain sandstone in which a few very thin layers of clay were deposited. The material was somewhat feldspathic. Conditions under which this formation was deposited did not vary greatly, no beds of limestone or shale of any extent being found. This sandstone was me tamorphosed by moderate pressure and heat, the quartz, probably some of the biotite, and the feldspars being primary in their form. No material has been added to this schist during its metamorphism. The schist of the mine is clearly of the same series as that exposed at the surface. As no fossils were found and mapping was not extensive, it is not possible to state to what geologic period these formations belong. BASIC INTRUSION: General Features. The basic intrusion forms the country rock of the mine and is the rock with which the ore is associated. It is composed of a variety of types which, as has been stated, merge, one into another, and cannot be separated by any definite line. - 36 = It has been faulted, as is seen by the occurrence of the schist-gneiss series. It has also suffered fracturing, the lines of which have been injected by hornblende gabbro, and later offered means of access for the pegmatites. Deformation has also sheared and me shed certain areas, developing shear planes and crushed rock, some of which is scarcely recognizable. In these crushed areas both the felds- pars and the ferromagnesian minerals have suffered decomposition. The shear planes usually develop: curved surfaces, lying around an uncrushed, more or less spherical mass of material. NORITE: General. (Sp. 19-6- 10-65) (Note ~- all numbers ofer 1 and less than 28 are on lst level; others, 2nd) The norite is the most abundant type of rock found in the mine. The greater part of the rock ex- posed in the Wpper workings is of this nature. It also occurs on the secondlevel, between the foot of the incline and the faulted pegmatite dike (Map 250 level). Megascopic Features. The norite is composed of olivine, plagioclase, amphibole and bronzite, carrying blebs of pyrrhotite and chalcopyrite. The ferromagnesian minerals consistute 60% to TO% of the rock; plagioclase 10% to 15%; olivine 10% to 15%; and the sulphides less than 5%. - 37 = The olivine 1s not present in all specimens. It is dark gray in color, slightly greenish, and when the content of rhombic pyroxene is high has a slight bronzy luster. Microscopic Features. ] The norite, not carrying olivine has the 3 following mineralogical composition, the minerals being 3 stated in the order of crystallization. 1 l. Apatite xx % 1 2. Hypersthene 25% 3 3. Brown hornblende 10% A — li. Bytownite 60% 1 5. Opaque minerals (less than) 5% Both ophitic and granitic textures are observed in these norites. In the type h: ving granitic texture the normal order of crystallization was followed, the more basic minerals being the first ot separate out. The final result is an allotriomorphic aggregate of anhedral grains. In the ophitic texture a small amount of ] bytownite has separated in euhedral orvstals before the formation of the hornblende, in which they are imbedded. The hypersthene rarely includes bytownite and is for the most part idomorphic relative to it. It is apparent the normal order has not been departed from to any great extent. - 58. The hypersthene develops short subhedral prisms and is nearly colorless. Its relations to other minerals shows it to have formed first in the crystal lization. Bytownlte is for the greater part in anhedral forms, twinned on the albite, pericline or Carlsbad laws, or by a combination of these. Certain of the Car lsbad twins have developed a slight zonary growth. Brown noviiviende occurs in small amounts, enclosing euhedral bytownite. It is accompanied in some specimens by even smaller amounts of augite. Apatite occurs as an accessory mineral in its typical euhedral vod form, As the occurrence and composition of the opaque minerals is the same in all of the igneous rocks, they will be dealt, with in a section devoted to them. The norite has suffered practically no altera- tion. In two spec inent, Zo okeh from the foot wall of the fault in the winze, and one from an uncrushed rounded fragment occurring in a sheared zone, this same fact was noted. The latter also occurred very near the ore body. There has been some alteration of hypersthene to chlorite, this product being less than 1% of the hypersthene present. This is the extent of the alteration. - 39 = OLIVINE NORITE: (Sp. 12-18-43) General features. Specimens of this type are found in several areas on both levels. One small area is located in contact with the ore. Another area lies near the north end of the upper level. In the lower level, rock of this nature occurs on the northwall, between the foot of the incline and the schist-intrusive contact, to the east. This olivine norite grades into normal norite by the subtraction of olivine and into peridotite by the addition of this mineral. Near the ore this rock occurs ag rounded lumps in the basic intrusive, of near spherical form. They are extremely dense, heavy, tough aggregates, carrying a high amount of bronzite. Several such masses occur, varying in diameter from eight inches to two feet. A specimen taken from such a mass was found to have the following mineralogical composition: 1. Apatite = = =» = = =» xx% 2. Olivine - = - = - - 10% Zz, Hornblende (brown)- - 5% 4, Hypersthene - - = =~ = 75% 5. Bytownite =. = w= w= = = 8% 6. Opaque minerals - - - - 2% The above is the general order of formation. A poikilitic texture of medium granularity is developed. - JO = i oH i si] Hornblende and olivine are included in larger areas or patches of hypersthene, giving the rock its texture. The hornblende is cmsidered primary and the whole rock is fresh and free from any notable amount of alteration products. There has been a small amount of chlorite produced at the expense of the hypersthene. It is believed these spherical masses represent local segregations in the magma, in areas that have become highly concentrated in the hypersthene molecules. The rounded form is partly due to shearing forces which have smoothed off irregularities of the n mass but were unable to affect the main body. | As the more normal olivine norite does not carry such a high hypersthene content and is only an intermediate type between norite and peridotite, no detailed description is given. PERIDOTITES: (Sp. L6-60-76-91) General Features. Perlidotite was found on the lower level only. It occurs here along the drift leafiing to the ore, and in both of the short crosscuts, one on each side of tle ore. Locally this becomes a normal light gray granitic gabbro, or norite rock, as it does near the junction of the two schist slabs (map 250 level). - 41 - Megascopic Features. The peridotite is a very dark, greenish | grey rock. In some specimens it appears to be almost | wholly composed of small rounded olivine grains, while in other cases this mineral does not constitute over 50% of the matrix. The olivine is set in pyroxene and amphibole in poikilitic fashion. Pyroxene appears developed in patches, some of which approximate an ineh in length with a width half as great. Pyrrhotite | appears plentifully in these rocks, but disseminated irregularly throughout. It appears more concentrated in certain small patches, one-half to one inch in size. Microscopic Features. The peridotite has the following mineralogical composition, the constituents being listed in their general order of formation. | | 1. Magnetite, spatite - = - - - - xx% | 2. Olivine - - - - - - - - 50 to 80% : | 3, Hypersthene - - - - - - 15 " 0% J | he. Augite - -- - - - - -20 " lof 3 5. Brown hornblende - - - 5 a 3 4. Brvtomite - - == - - = 5 " 0F i 7. Opaque mineral (euhedral) 4 less than - - - - - 5% - 12 - The composition of the peridotite varies between the limits above set. Were more slides © examined it is believed the variations would show a gradual decrease of the olivine and a relative increase of the other mineral constituents. Such a gradation would end in normal norite. The texture developed is poikilitic. The amphibole and pyroxenes have caught up and included the olivine crystals. The amount of these minerals may be wery small, but they are optically oriented as a unit crystal over a relatively large area. The hypersthene is seen in the subhedral scattered forms. It is decidedly pleochroic, the color changing from a colorless or very faint green to a pinkish tint. The augite occurs similarly to the hypersthene, and on an average in equal amounts. It carries a narber of minute needle-like inclusions, arranged in schiller structure. These may be so numerous towards the center of the crystal as to make it appear almost opaque. They are usually wanting around the margins. Brown hornblende is present also, but in small amounts. ¥t+ is concluded to be primary as augite, from which it might form, carries these inclusions, which are wanting in the hornblende. Furthermore there is nothing to indicate that the conversion of any of the augite has taken place. As this process involves a hydrochemical action we would expect a notable amount of olivine to - L3 - be affected, and the hypersthene as well. This we do not find. A small amount of bytownite appears in one specimen, as an anhedral, interstitial mineral. Specimens carrying this feldspar would be classed as picrite. Alteration of this type is somewhat greater than the average, owing to the higher percentage of easily altered minerals present. Rims of chlorite or serpentine have developed about the olivine in some instances. The hornblende has also produced chlorite and probably one-third of the hornblende originally present 1s so changed. The alteration of hornblende to chlorite is further evidence of its primary nature. Both the olivine and hornblende must have been present when the chloritization occurred. Agencies forming hornblende and altering olivine, would not be expected to also alter the hornblende being formed. TROCTOLITE: (Sp. 70) General Features. One specimen, teken from the crosscut directly north of the ore, lower level, proved to be troctolite. It is dark gray, medium crystalline rock, of poikilitic texture. The olivine present is in part imbedded in the plagioclase. The rock appears to he composed of approximately equal amounts of plagioclase and dark minerals, olivine and amphibole. - hla Microscopic Reatures. The troctolite has the following percentage composition, the minerals being listed in the general sequence of formation. Magnetite, spinel, apatite. Olivine 50% Hornblende 17% Bytownite 30% Opaque minerals 39 The olivine, set in the hornblende, cives the rock a poikilitic texture. The olivine is for the most part in granitic relations to the other minerals. The hornblende, which indludes the olivine, is of the brown variety. In some instances it merely rims a single olivine crystal, though usually several are included within its borders. Spinel occurs in this specimen only. It appears in subhedral to anhedral form, is of green color and isotropic. Though it is listed with the accessories as one of the first minerals formed, it has for the most part crystallized after the olivine. This troctolite has been altered to an extent comparable to that in the peridotite. Olivine has been altered to a fibrous aggregate of serpentine about its borders and less commonly along cracks within the crystal. - L5 - - 546 - The bytownite is slightly sericitized, the process being in the initial stage. Complementary Dikes. HORNBLENDE GABBRO: (Sp. 17-28-58) General Features. Occurring throughout the mine are hornblende gabbro dikes, filling fractures in the main intrusive body. They have formed later than the ore as a dike of this material is seen to penetrate it along a fracture plane. (Pl. IV, Fig. 6) They were intruded previous to the faulting which brought in the schist slabs as these faults cut the gabbro dikes. (Map 250 level) That they are also younger than the pegmatites is seen by these pegmatites truncating the dikes in several points (Pl. IV, Fig. 7 and map of 250 level). J Megascoplec Features. The hornblendic dike rock is a fine-grained gabbro, uniformly fresh and unaltered. It is of black | color, largely composed of amphibole in long, narrow prismatic form. These black amphibole crystals vary J in length from one to fou millimeters, and lie in various, unoriented attitudes. Plagioclase occurs in minor amounts, relative to the hornblende. Both pyrrhotite and chalcopyrite are seen in the hand specimen. = hE The chalcopyrite is in minor amounts and is not commonly seen. Tt occurs in small isolated blebs. The notable feature of these rocks is their fresh, unaltered condition and their uniformity as to compo- sition, texture, color, and general appearance. Microscopic Features. The percentage composition and order of crystallization is as follows: 1. Apatite xx% 2. Brown hornblende 60% 3, Pyroxene ; 10% li. Labradorite 29% 5. Opaque minerals 1% The texture of these rocks is wholly allotrio- morphic. The hornblende is idiomorphic towards the labradorite and tends to develop much larger opystals, but without form. The texture is peculiar to these dikes. The pyroxenes and feldspar 1s later in crystallizing than is the hornblende, considered in general. The hornblende is often grouped in several closely spaced crystals, with but little or no feldspars intervening (Pl. V, Fig. 8). The form of these feldspars resemble the hook shapes often used as criteria for replacement. - L7 - - 18 - This fact is seen to some extent in Pl. V, Fig. 8, though it appears more evident in other cases. It is also seen in this figure that the feldspars enter embayments in the hornblende exactly as the sulphides do in certain instances (Pl. V, Fig.9a). Some green hornblende occurs but the brown variety is more common. Augite or diopside is present in one or two cases. It is not an essential mineral and 1s of interstitial nature. The feldspar present, labradorite, is more towards the acid end of the series than is the feldspar J of the norite-gabbro series. It is twinned on the albite, pericline and Carlsbad laws, and shows a zonary develovment in some instances. Origin and Correlation. These dikes are similar in composition to the general intrusive body with which they are associated. The notable difference 1s that the characterizing mineral is hornblende, with augite and diopside are relatively not prominent, and no Fhomble pyroxene occurs. The feldspar, labradorite, is more acid than the feldspar of the main intrusives group. The opaque minerals, as seen from a polished surface, are identical with those of the norite, gabbro, peridotite, etc. In view of these facts it is concluded these dikes heve originated in the still fluid portion of the basic magma, after solidification of the outer shell. = hB = They represent a late concentration product. The dominance of the hornblende is due to a concentration of water in this still molten magma greater than that which was present when the magma initiated its crystal- lization. The lower temperature and the increased dresuiive were also conducive to its formation. This dike material was squeezed into the solidified outer shell of the basic intrusion following an early period of fracturing. This period followed the formation of the ore and was previous to the main period of famlting as has already been shown. Not only are these dikes cut by the faults but they fail to enter the schist slabs or to lie along the fault surface. In short, these dikes ave resulted from mag- matic differentiation. Following a period fracturing in the late magmatic period, they were intruded into the fissures developed in the outer shell of the main igneous mass. PEGMATITES: (Sp. 53-39) General Features. Pegmatites occur at several points along the second or lower level. In the winze on the upper level a series of elliptical nubbins occur in alignment in a crushed portion of oxidized ore. These are apparently fragments of a pegmatite dike that has pene- trated the ore. - L9 - CA Yr Tsp - 50 - This point is not conclusively proven. This occurrence is figured in Plate IV, Fig. 6. The average width of these dikes is not over six or eight inches. At one point, near the junction of the level leading from the incline and the drift to the ore (Map 250 level), is a body of coarse pegmatitic material of considerable volume. The relations of this mass are illustrated in Plate IV, Fig. 7, drawn to scale. At this point the pegmatite cuts a hornblende dike and intrudes or penetrates the schist slab, placing it later than both these members. Megascopic Features. The pegmatite is seen to have both microcrystalline and coarse crystalline pegmatitic structure. The two may occur in the same deposit, the gradation from one type to the other taking place in a short distance. The fine-grained material is mainly quartz with some feldspar and accessory biotite. The quartz usually lies to the outside of the pegmatite dike while the bilotite is more plentiful towards the center. Tourmaline occurs also in pegmatites of medium coarseness. It could not be detected megascopically in the finer grained texture. The very coarse crystalline type of pegmatite is composed of quartz, orthoclase, plagioclase, black tourmaline, and brown biotite. - 50 = Plate IV. SATS VEN Ore Floor... Fig. 6. N-S section through massive sulphide. Note hornbldnde gabbro dike, shown in red, penetrating ore. Nubbins of supposed pegmatite in purple. (Scale 1 in.= 5') 7 NINH TN Nay Fig. 7. E-W sectlon through mass of pegmatite, penetrating schist and truncating the hornblende gabbro diké shown in red. - 52 - The orthoclase is the main constituent and develops massive crystals twelve to sixteen inches long. Quartz occurs interstitially and also intergrown with the feldspar. Tourmaline is seen in two forms. The first of these is of black color, and in long tapering euhedral crystals. They attain a length of eight or ten inches in some cases, and are from an inch to two inches in diameter, Small crystals occur as well, and more commonly. There 1s a second form of tourmaline inter- grown with quartz and feldspar, evidently formed contem- poraneously. The tourmaline crystals have been fractured, broken into curves, and offset. These fractures are filled and cemented with quartz and feldspar. Biotite is less common in these coarse pegmatites than in the finer grained type. it forms in flat plates, one-half to one inch across. Microscopie Description. A specimen of micropegmatite has the following composition, the minerals having formed in the order given: l. Tourmaline xx% 2. Andesine 25 2. Orthoclase 50 Lh. Quartz 25 - 52 - The texture of this rock is granitic. Tourmaline occurs sparingly as an euhedral mineral, one of tre first minerals to crystallize. The felds- par is andesine, with a minor amount of labradorite present. Specimens of the coarser pegmatite show orthoclase present in phenocrysts and forming a much srggton portion of the rock. The other constiduents were noted in fine-grained allotriomorphic relations. Origin and Correlation. Due to thelr mineralogical composition and | (1) their manner of occurrence these dikes are believed to represent the "acid extracts" of the magma in which they occur. They cannot be ascribed to the pegmatite occurring in the schist series as they belong to a mach younger sequence of events. No magma later than the basic intrusion is known to exist from which they might be derived. These pegmatites represent the last stages of mineralization by the cooling magma. They comprise the youngest rock formation seen in the mine or at the surface. RELATIONS OF DISSEMINATED METALLIC MINERALS TO THE ROCK FORMING SILICATES: General Considerations. In order to study the relations of the opaque minerals to the silicates, thin sections were made with - h3 » a polish on the upper side. The polish permits the cover glass to be left off without interfering with ordinary petrographic work and permitting microchemical tests. Specimens of hornblende gabbro, norite and peridotite from the mine samples, and norite and olivine norite from the surface were so prepared. The opaque minerals observed were the same species in all cases, and were similar in distribution and sequence of formation. The opaque minerals were identified under the reflecting microscope and checks made on concentrates from which the section was prepared. Microscopic Features. The metallic minerals observed in the slides were magnetite and pyrrhotite. The relative proportions of these two minerals, in respect to one another, vary, the magnetite being present in lesser quantities. The portion of the rocks constituted by these two minerals is also variable, but is rarely over 24. Chalcopyrite was not seen in any of the sections made Ae unaided eye has been distinguished in each of the igneous rock types present. Its occurrence is similar to the pyrrho- tite and anhedral magnetite but is present in less quantity. The ratio of these minerals to one another and to the rock as a whole varies, not only in different types but also in rocks of the same type. - 5l - hele Sh Tenn Een A GR This may be noted even in an area as small as that of a single slide. Texturely, excepting the magnetite whieh occurs in euhedral forms, the metallic lustered minerals bear the same relations to the silicates that are seen in the silicates themselves. The evidence shows these metallic minerals are contemporaneous. Their most common occurrence is in interstitial form. In some instances they appear enclosed within the silicate minerals in isolated blebs, due to entrapped molten material, The interstitial masses are of ten moulded on a straight boundary of a sllicate, either feldspar or ferromagnesian. In some instances the boundary is marked by a smooth curving line, showing embayments in the silicates and similar embayments inthe sulphide. (Plate VI, Fig. 10) Hook shapes are occasionally developed, and it can be seen they owe this form to their interstitial nature in practigéally all cases. These hook shapes are not confined to the opaque minerals hut are seen inthe feldspars as well. Likewise the feldspars lie in embayments within ferromagnesian minerals in relations identical to those between opaque minerals and silicates. The sulphides may penetrate the silicates along cleavages, cracks or other lines of weakness. In most cases the distance these minerals are penetrated is very short. - BG = Ckeavage planes of the ferromagnesian minerals and twinning planes of the feldspars offer such means of aceess, to the sulphides. In rare cases the sulphide may cut entirely across a silicate crystal. This 1s seen in Plate V, Figl 9a, where the two segments of a hornblende crystal marked Hoy, Hoy, have been so separated. The two segments now lie at an angle of four or five degrees to one another. It is evident they were broken by lateral pressure, allowing the still molten sulphide to pinetrate along this opening so formed. Some corro- sion has also occurred. This corrosion also appears to have taken place in a few other cases. In Fig. 9a, Plate V, a tongue of sulphide is seen lying embayed in the prismatic face of a hornblende crystal. Although such instances suggest corrosion, a more substantial explanation is offered. The hornblende in crystal lizing has been forced to grow around the sulphide. This theory is evidenced by finding masses of sulphides wholly enclosed and by the radial cracks developed about this sulphide tongue. Similar cracks are seen about the enclosed masses in Fig. 8, Plate i The metallic minerals show no preference for any particular silicate, being associated with feldspar as well as the ferromagnesian minerals. In no case were the sulphides or magnetite connected in any way with - 56 =- Fiz. 8S. Showing relations of hornblende (Ho) and plagloclase (fel) in hornblende gabbro. cracks about the sulphide (black). (In this and the following camera lucida drawings, Mag = 80 dia.) Fig. 9a. C sulphide Sb. sulphide Hornblende (Ho) crystal penetrated by (black). Note Hornblende cr bleb (black) ° radial cracks. ystal (Ho, Hop) cut by Plate V,. Note radial Plate VI 10. Relations of disseminated sulphide (S) augite (aug.) and plagioclase (fel), Fig. 11. Pseudomorphs of calcite after hornblende and auglte, occurring in massive pyrrhotite (po.). Chlorite (Cl) replacing calcite. : i i L - 50 = veinlets, extended fractures, channels for entrance of mineralizers, or with secondary Products. The mineral relations and textures here described are identical with those described in the pyrrhotite magmatic segregation at Elkhorn, Montana. See: Adolph Knopf, "Magmatic Sulphide Ore Body at Elkhorn, Montana" - Ec. Geol., Vol. 8, p. 323. The description of the rock surrounding the ore body in this deposit might well be applied to the granitic textured rocks of the Friday Mine region. The occurrence of the pyrrhotite at Elkhorn is comparable in every way to the occurrence in these rocks of the basic intrusion described in. this article. The pyrrhotite of this Golden Curry Hine is undeniably formed by magmatic segregation. Conclusions. The magnetite appears in two distinct forms, crystallizing from the magma during different periods. - The euhedral form is always included in a silicate and was one of the earliest minerals to separate out, being contemporaneous with apatite. The second tvpe is anhedral and is contemporaneous with the sulphides, pyrrhotite and chalcopyrite. These two magnetite and pyrrhotite are seen in aottact along straight, sharp lines without one replacing the other. - 59 = a O Tr The sulphides have formed later than the ferromagnesian minerals and for the most part later than the plagioclase. The embayments of sulphide in ferromagnesian minerals, and curved rounded forms of these silicates are largely due to magmatic corrosion, without entire resorption. Such embayments are occupied by feldspar as well as by sulphide. They are similar to embayments seen in i quartz phenocrysts in rhyolite. Corrosion by the sulphides and magnetite has taken place to minor extent. 3 The opaque minerals are primary constituents of the magma i intruding the schist-gneiss series. No evidence 1s seen upholding the theory that these minerals owe their presence to the miners lizers as advanced by Tolian and Rogers in their paper on "Magmatic Sulfid Ores." All evidence points to these minerals having formed from constituents present in the magma at the time of its solidification and before. They have not vean introduced to their present position, but have solidified in place. THE SULPHIDE SEGREGATION: General Occurrence. The nickel=-cobalt-bearing sulphide is found well within the limits of the basic intrusion, over a quarter of a mile from its nearest border (see map Areal Geology)e “i Bl) It also appears to have formed within the interior of r the mass when considered in a vertical section. To the E north the intrusion reaches an elevation 500 feet greater than that of the sulphide level. To the east and west the intrusive rocks are found at much lower levels, while d to the south, across a valley, we find gabbro at the summit of North Peak some 1500 feet above the mine horizon. In the mine itself, the sulphide 1s overlain by over il DNS a gg Lb SS Ry 100 feet of the intrusive which also forms the basal member or support of the segregation. .- The mass appears ‘then, to be unrelated to any of the marginal facies of the silicate mass in which it occurs, either in respect to plan or elevation. Qutcrops » There 1s no surface expression of the main segregation. As previously stated, the iron gossan found west of the shaft is so situated that it cannot be reffered to as an oxidized portion of the main sul- phide mass. Form. The shape of the segregation is not definitely known as its boundaries are not completely exposed. Enough data were collected, however, to project these boundaries with a fair degree of certainty (see mine maps end Plate IV, Fig. 6). “- BY - The sulphide segregation is of an irregular elongated form. The northern end of the mass is cut by a fault striking N 75°E and dipping 80° to the south. The direction of movement on this surface was practically parallel to the dip, the hanging wall moving up in respect to the foot. The net slip was not over forty feet apparently. The faulted portion of this body in the foot wall section is found on the lower level and is a small mass. The southern end of the main body is also terminated by a fault but one of less displacement as it does not appear on the lower level. A small sliver of badly altered sulphides is also present within schist, on the upper level. This body is bounded by faults to which it owes its present position. The actual line of contact of the segregation and the country rock is slightly sheared and crushed in most places. Neither along such contacts, nor along the few normal contacts was there any evidence of gradation to be seen. There appears to be a fairly sharp division between the massive sulphide and silicate rock. No alteration of country rock has taken place by those agencies segregating the sulphides, nor by any other agencies to any noteworthy extent. Some of the freshest specimens were taken within a few inches of the sulphide . The segregation shows no evidence that its present position 1s due to any faulting or fissuring. The form and occurrence do not suggest the mass has been intruded to its present position, no apophyses or tongues extend- °® ing from the mass, There is no apparent pre-mineral fault or line of weakness to provide access for this body. The segregation itself shows no vein structure nor solution channels, being massive throughout. it is, from all evidence, an isolated mass. Megascopic Features. The ore minerals that can be distinguished megascopically are pyrrmotite, chalcopyrite and an occa- sional amall amount of a white, metallic lustered mineral, identified as smaltite. The gersdorffite cannot usually be detected and its presence was proven by the study of polished surfaces. Texturally the ore may be described by the term granitic. Allotriomorphic grains of pyrrhotite constitute by far the greatest amount of the substances present. The usuallcolor is steel grey, but where the pyrrhotite is fresh the typical bronze color is seen. The pyrrhotite ocours in grains varying from medium to coarse. It is of steel gray or bronze color, accordingly as it is fresh or slightly oxidized. A platy structure is seen, due to the well developed basal cleavage. - 63% - The chalcopyrite occurs in scattered irregular blebs and patches of small size, exhibiting no structure. It is apparently interstitial. This minerals is noted occurring not only in all sulphide specimens but 1s seen in isolated thin flakes along shear plenes in the norite- gabbro. It does not occur at distances greater than three to four feet from the contact and the amount within this limit is small. one or two flakes of bornite were assoclated with it. Altrough the smaltite can rarely be seen in a hand specimen, its larger textural relations were determined from a sawed surface. It occurs in small veinlets, traversing the other minerals and showing a center line of calcite. In some parts of the specimen these veinlets form a residual network, the greater part of the pyrrhotite having been leached out, leaving the smaltite behind. This smaltite constitutes but a small portion of the mass, usually less than 5%. The nickel mineral, which has been identified as gersdorffite, is rarely seen with the unaided eye. It appears in scattered irregular masses of small size. The gangue is chlorite, in platy aggregates, and some unaltered ferromagnesian minerals. This gangue comprises various amounts of the ore, averaging 20% in some cases, while in other instances it is not over 104 of the sulphide body. - Gh = Microscopic Features. The following minerals have been determined with the aid of the reflecting microscope, using methods | described in Murdock's book on this subject. The ore minerals, in order of their sequence are: l. Pyrrhotite 65 to 75% J 2. Chalcopyrite 2." WZ | 3. Gersdorffite 15 " 67% | Lh. Smaltite 8 "% eo | Associated with the ore is 10% to 20% of gangue minerals, composed of chlorite, calcite, augite and hornblende. PYRRHOTITE: The texture of the ore is determined by pyrrhotite, the first ore mineral of importance to form. The exception to this 1s magnetite which occurs in euhedral octahedrons imbedded in the pyrrhotite. The pyrrhotite forms grains ranging from a few millimeters to a centimeter and a half in size. These grains have formed simultaneously, developing the texture known as allotriomorphic in granitic rocks. Basal cleavage is prominent and affords a record of stresses applied to the ore. The cleavage planes are buckled and bent slightly, in some cases fractured and offset a fraction of a millimeter. This compressive force seems to have re been applied before the solidification of other minerals as they dre not similarly effected by these forces. - 65 = CHALCOPYRITE: The chalcopyrite occurs interstitially between the pyrrhotite grains. An occasional bleb is seen enclosed in the pyrrhotite in an 1solated position. Where in contact with pyrrhotite the boundary is marked by smooth, clean-cut, definite lines. No intermediate zone, or product, is formed and replacement does not appear to have taken place. The chalcopyrite shows no tendency to enter cleavages of the pyrrhotite. It is believed to have formed entirely as an interstitial mineral, with a minor amount forming within pyrrhotite from an entrapped liquid melt. GERSDORFFITE: The gersdorffite occurs in irregular interstitial masses, often associated with chalcopyrite which it replaces to some extent. It shows definite crystallinity. Hexagonal cleavage is well developed. The various areas of this mineral are not connected, the form being that which would result from the formation of pyrrhotite crystallizing and leaving a small amount of sulphide still molten, This molten sulphide fills interstitial spaces with wedge-shaped apophyses, These bleb forms occur in broken continuity, precisely as though a small drop of solution had been surrounded by the precipitating () pyrrhotite and forced into residual spaces with the pyrrhotite, - 66 - Both pyrrhotite and chalcopyrite have been replaced or corroded by this mineral to some extaat. Rarely, an apophysis of gersdorffite will extend into a pyrrhotite crystal. Such offshoots quickly wedge out (see Pl. VII, Fig. 124 and Fie. 13). The pyrrhotite cleavage has little effect on the boundaries of these wedges and no influence on their direction. Such apophyses are usually of a single, nearly straight mass and in but one or two instances are branches formed (Pl. VII, Fig. 12a). These replacements are clearly by a different process than that effected by solutions. This is shown by a comparison of the above figures with Figures 1 and 15 of Pl. VIII, where calcite and smaltite replace the pyrrhotite. Gersdorffite 1s later than chalcopyrite in cpystallization. This is evidenced by the f omer entering along pyrrhotite and chalcopyrite contacts in a manner illustrated in Plate IX, Fig. 16. The chal- copyrite is also replaced by gersdorffite in a manner similar to that by which this latter mineral replaces pyrrhotite (Pl. VII, Fig. 12b). Fragments of chal- copyrite also occur included well within gersdorffite. The chalcopyrite shows every stage of replacement. Where this process has just begun the gersdorffite occurs as a partial rim about an interstitial mass of the chalcopyrite. - 67 = Z Plate VII Fig. 12a. Gersdorffite (ger.) penetrating pyrrhotite & in 12b, similarly penetrating chalcopyrite (cps). Note blunt terminations of apophyses and regular outlines. Fig. 13. Gersdorffite (ger.) replacing pyrrhotite (po.), later calcite (ca.) replacing both. Plate VIII. BR : ni A on aT eat dl Ow Loss Af £9 a REE aE Fig. 1. Calcite (ca.) replacing pyrrhotite. Note : irregular nature of boundaries and shapes of residual | pyrrhotite fragments. 1 ( Co Fig. 15. Concentric banding of smaltite (sm.) and ( calcite (blue shaded bands) replacing pyrrhotite (DOe)e Banded forms are cut by later calcite (ca.) 7 Plate IX. be ho Fig. 16. Two stages in the replacement of chalco- pyrite (cp.) by gersdorffite (ger.). The figure on right shows most advanced stage. - 71 - This rim next completely surrounds the chalcopyrite. Beyond this stage small fragments of chalcopyrite remain imbedded in fragmental or lenticular form, show- ing this mineral has once been present in greater amounts, That some of the chalcopyrite is contemporaneous with the gersdorffite is seen by a jagged, serrated boundary between the two, induced by the stronger crystal- lizing tendency of the gersdorffite. In a few cases, tongues of chalcopyrite extend into the gersdorffite for a short distance. In one case the chalcopyrite has entered the cleavage of the nickel mineral, breaking out a small block from the main mass of gersdorffite. SMALTITE: Following the formation of the above minerals was a period of fracturing, producing fissures throughout the mass of ore. These fissures are microscopic, the forces producing them being evidently of no great mag- nitude. This fracturing permitted the entrance of solutions by which niekel-beariis smaltite and calcite were deposited. This smaltite shows no cleavage or other crystallographic features in either of its two modes of occurrence. It is present in two forms, both being replacements of gersdorffite and pyrrhotite. - 71 = a _. The attack ofi pyrrhotite is the most advanced and of greatest extent, the pyrrhotite being the more unstable of the two minerals under the then existing conditions. The smaltite occurs in two forms, as veinlets and in concentric arrangement with calcite. The veinlets are very irregular and ramifying, branching and rebranching. The result 1s best described by the term dendritic, though this term 1s not commonly used in such a sense. In some instances the pyrrhotite is almost wholly displaced, thou-h smaltite is usually not abundant. These veinlets show a seriter line of calcite marking the solution channels, and a change in character of solution as well. The concentric banding of calcite and smaltite is more abundant than the occurrence in veinlets. Alternate bands of calcite and smaltite occur in regular fashion, as illustrated by Fig. 15, Plate VIII. The shaded blue portions represent the calcite and the dark brown the smaltite. In nearly every instance the smaltite is preceded by a calcite layer in contact with the pyrrhotite. These concentric arrangements are believed to be a natural expression of Liesegang bands, produced by effects of diffusion. Following this stage a slight fissuring occurred and in the opening produced calcite was deposited, without replacement of fissure walls. - 72 = RE rl A S. - rt eT cm Chlorite entered also, continuing after calcite had ceased to form. Chlorite is seen replacing all minerals in veinlets and plates. These plates may develop considerable size and are euhedral in many cases. A slight readjustment of gersdorffite and chalcopyrite has taken place also. Secondary forms of these minerals have been transported microscopitally short distances, the space which they formerly occupied being distinguishable. Original Silicate Minerals. The minerals included under this heading are those that crystallized before the solidifcation of the ore. Such minerals prove to be brown or green horn- blende and augite. These minerals are present in idio- morphic, and hypidiomorphic form. Pseudomorphs of cal- clte after these minerals occur, showing near perfect crystal outline (Pl. VI, Fig. 11). In most cases hypi- diomorphiec forms occur usually partly calcitized with one or two crystal boundaries developed, others being definite, smooth, curved lines. Such forms have probably suffered partial magmatic corrosion by the ore melt. There is no tendency for the silicates to be penetrated along lines of weakness, the boundaries being smooth uninterrupted curves. There are no well developed embayments in silicates, nor reentrants. The effect, on the whole, 1s one of allotriomorphic crystallization, due . to neutral interference of simultaneously growing crystals, with some corrosion attending. - 73 = Oxidized Zone. 4 zone of considerable oxidized material occurs above the sulphides in the ypper level. The contact between the completely oxidized portion and the unoxidized is a definite surface. The two do not merge or show any gradation. This surface is not con- fined to a single horizon but is very irregular. Partially oxidized material occurs below this contact in several small, scattered area. These areas are not over a foot in diameter in any case, and are usually much less. They do not represent an important feature in view of quantity. The wholly oxidized minerals comprise a light porous mass of reddish yellow limonite. Pale green aggregates of euhedral chlorite flakes are disseminated throughout the mass. This material is identical with that which comes from the deposit at the tunnel on the slope north of the mine. The partly oxidized mass is composed largely of pink erythrite and a grey white powdery substance, probably a nickel sulphate or arsenate. These two substances occur similarly in more or less parallel veins or layers, separated by bdocks of black, lusterless material. This black material has been derived from pyrrhotite, representing the last stage of its breaking down before limonite is formed. Scattered in this matrix of arsenates sulphates and altered pyrrhotite - Th - - 75 - pyrrhotite are flecks of fresh unaltered chalcopyrite. These areas are the result of descending solutions. The nickel and cobalt sulphate and arsenate- bearing solutions are carried downward a short distance, to replace and oxidize the massive ore. Chalcopyrite resists these effects as long as pyrrhotite remains present. SUMMA RY * I. The ore occurs in a basic magma as an isolated mass, unrelated to contact of this magma with older rocks, to any shell of early peripheral solidifi- cation, or to any pre-mineral fault. The presence of other small bodies of similarly isolated magmatic con- centrations are indicated by the residual masses of com~ pletely oxidized material. The ore occurs in a mass of intrusive rock, composed of the "basic" minerals and a notable amount of pyrrhotite and magnetite. The variety of rocks present in this intrusion represent the stage of me gmatic differentiation reached by the molten magma during solidification. This differentiation produced, in the earlier stages, areas of more basic nature than average and resulting in a concentration of more acid constitu- ents and mineralizers in the final residue. - 75 = Conclusions. I. The disseminated magnetite and pyrrhotite are primary constituents of the basic magma. They have solidified from it afterthe silicate minerals were crystallized or partly crystallized. This conclusion is based on the distribution, mode of oc currence, tex- tural relations to the silicates and lack of any related secondary mineralization or alteration. Authors favoring the introduction of these opaque minerals by mineralizers, consider the hornblende as magmatic alteration product. A Study of the Magmatic Sulfid Ores" Rogers snd Tolman, Stanford University Publications, 1916. The author of this: paper can see no evidence of this in the rocks of the region under consideration. The hornblende appears to have formed from the melt as a primary mineral and not at the expense of ferromagnesian ° minerals previously crystallized. Certain occurrences of the disseminated sul- phides cannot be explained by the theory of introduction by mineralizers. The hornblende gabbro dikes are seen to be mineralized in extent equal to that of the rocks they invade. The dikes must be younger than this country rock and would have been exposed to mineral ization for a shorter period. 76 = Yet we find them equal, in the metallic constituents carried, to the invaded rock. Furthermore the dike cutting the ore carries the normal amount of sulphides. It is difficult to conceive by wheat process these minerals could have been introduced without enriching the ore neighboring the dike. That no such enpichment occurs here is proof the sulphides and magnetite carried by the dike is primary. 11. The deposit 1s a magmatic segregation of pyrrhotite, chalcopyrite and gersdorffite. This concentration has been modified by ascending alkaline solutions replacing the primary minerals and depositing smaltite, calcite and chlorite. The original ore body has formed by a process of liquation or limited miscibility similar to that ppocess by which the certain parts of the magma have become enriched in its basic constituents, olivine or rhombic pyroxene. There 1s no reason for believing the processes which affected the segregation of these minerals could not also have affected the segregation of the ore minerals. This manner of segregation is upheld by the occurrence of several isolated masses of sulphides segregated at certain points; the presence of euhedral and subhedral unaltered augite and hornblende included in the deposit; the absence of alteration products in the country rock bordering the deposit; the early period - 77 = — in which the deposit formed; the form of the mass; the absence of quartz, caleite or other solution minerals during the period of the formation of the primary minerals; the crystalline form of the Primary minerals and their textural relations. III. The minerals, pyrrhotite, chalcopyrite and gersdorffite have crystallized from the segregation in the order named. The pyrrhotite solidified, leaving the latter two minerals in a fluid condition and in in- terstit ial positions. Chalcopyrite next crystallized. Following this period strain and compression on the solidified portion caused a certain amount of redistribution of the still molten gersdorffite, forcing it into new positions and into cracks formed in the pyrrhotite. The gersdorffite attacked the pyrrhotite and to a greater extent the chalcopyrite. The amount of these minerals corroded and replaced has not been suf ficlently great to produce a material effect #&n the composition of the gersdorffite. These conclusions are based on: the crystalline form of the primary minerals; their mode of occurrence or textural relations; the absence of solution minerals in this stage of formation; the clean-cut nature of contacts; the occurrence of isolated blebs of chalcopyrite and gersdorffite included in pyrrhotite; the entire lack of similarity between the occurrence of the interstitial minerals undeniably of solution forme tion; the lack of - 78 - vein structure, concentric banding or other effects that normally accompany solution deposits. IV. The smaltite, with its associate gangue minerals has deposited from agcending alkaline solutions. These solutions originated in the still molten portion of the magma and have reached the ore body along fissures in the solidified shell. Fracturing of the ore allowed these minerals to penetrate it freely. The smaltite has probably been an original constituent of this mineralizing agent, which has taken into solution, while traversing country rock, the con- stituents from which calcite and chlorite were formed. That these minerals, smaltite, calcite and chlorite are formed as solution deposits, later than the magmatic ore minerals is a fact which cannot be denied. Their typical vein structure, concentric banding, lack of crystal cleavage, conformation to and control of pyrrhotite cleavage planes, their ramifying "aborescent" or dendritic form and the mineral species themselves are conclusive proofs of their origin from solutions. The points above outlined strongly emphasize that those minerals ascribed to magmatic segregation could not have been due to such agencies as produced these later modifications to the original deposit. - 79 = EE PRACTICAL CONCLUSIONS Amount and Tenor of Ore. The amount of "ore" present in this mine deposit is approximately 1600 tons. Although the data obtainable is such that this can be but an estimate it is believed this figure represents closely the tonnage available. No assays or analyses were made by the author to determine the tenor of the ore. Reports given by eastern firms on the analysis of this ore give L.34% and L.12% nickel and 2.4% copper U.5.8+8. Bull. 640 C, p. 77. F.C. Calkins on "An Ceccur=- rence of Nickel Ores in San Diego County, Cal." Silver and gold were not present and platinum was not looked for. No mention is made of the cobal% content. As several small bodies of "oré&" lie at or near the present surface and furthermore as segregation is known to have occurred, it is highly probable that other bodies exist. It is believed that not only nickel- bearing pyrrhotite bodies but magnetite bodies as well may be discovered. Owing to the magnetic properties of these minerals it is suggested their location may be discovered by careful magnetic surveys of the intrusive body. The size and delineation of deposits so discovered should be checked up by diamond drills. It is well within the range : of probability that an ore body of economic value may be so ; located. - 80 - i si riday Mine 250 level | : Faults \ | in=10 ft. Geology by ; = : acts Ta A WE Inman ; Dip and i / / Strike Sehist and | S Gnrerss Bagsic. /hlrusive Ore Horneblende Gabpro Pe grmal il e Fr iday Mine 200 level | in=10 f1. Geology by WE. Inman. Contacts Dip and strike Jehist~Gniess Bose /nfrasion Ore HHornblende Ga bb ro Huan lig 1 w He "9 "aly 3] Tg Tg] Hy gl 1 2 2 6 Geologic Map Vicinity of Friday Mine | Scale 4in-Imile Geology by ‘FS Hudson, WE. Inman. Legend Roads n Section [-—4—. corner A idg € ~UN % Stream Dry- wash |. - ~ 5 Mine ) Prospe ct x Contact \ ip, iP Strike of 3 wile Schisrosity ical : : > Schist and s / Grejss asammn : : 3 va > Boosie Bt bi : ; \ \ ntrusion. Er . : 1 KX ( rE. C - a pn == a 4 A S == * \ Jo/o02 : | @ : ) X & 7 : 7 { : = Tallys Bi Oo IZ : = / : 3 : Pa = Schillings 724 (, : ls & ; z © 1/9 ie : 0/06 ria pr” ous rz ; 0/27 ie 27/3 : ya 5 O//5 ! i Bi ) Ls { { 1 i f 0/30 a North Peck END OF TITLE