UC BERKELEY MASTER NEGATIVE STORAGE NUMBER 03-67.82 (National version of master negative storage number: CU SN03067.82) MICROFILMED 2003 UNIVERSITY OF CALIFORNIA AT BERKELEY LIBRARY PHOTOGRAPHIC SERVICE REPRODUCTION AVAILABLE THROUGH INTERLIBRARY LOAN OFFICE MAIN LIBRARY UNIVERSITY OF CALIFORNIA BERKELEY, CA 94720-6000 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. Rocca, B. T. The geology of the Helen Mine 1915 BIBLIOGRAPHIC RECORD TARGET University of California at Berkeley Library Master negative storage number: 03-67.82 (national version of the master negative storage number: CU SN03067.82) GLADIS NUMBER: 184777207G FORMAT : BK AD:990922/FZB LEVEL:b BLT:am DCF:a CSC:d MOD: FlL.:7 UD:030604 /MAP CP:cau L.:eng . INT: GPC: BIO: FIC: CON: ARCV: PC: PD:1915/ REP: CPI: FSI: T1.C: I1: 040 CUScCU 090 SbDISS.ROCCA.GEOL 1915 100 1 Rocca, B. T. 245 14 The geology of the Helen Mine. 260 $c1915. 300 ii, 43 leaves :5bill., col. maps ;$c29 om. 502 Thesis (B.S. in Geology) --University of California, Berkeley, May 1915. 610 20 University of California, Berkeley.S$bDept. of Geology and GeophysicsSxDissertations. 690 0 Dissertations, AcademicS$xUCBS$xGeology$y1911-1920. 700 1 Vander Leck, Lawrence. 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 THE GEOLOGY OF THE HELEN MINE. Submitted in partial fulfill- ment for the degree of B. S. in the College of Mines, and A. B. in the Department of Geology, College of Natural Seiences, LIBRARY COPY University of Califormia. by B. T. ROCCA, B. 8S. L. VANIER LECK, A. B. May 12, 1915. Introduction Index Map Illustrations of Topography Location Topography and Geography Geological Summary Formations (a) Sedimentary 1l. Franciscan sandstone 2. Franciscan chert (b) Igneous Rocks 1. Quartz, Hypersthene, Latite 2. Olivine Dishese 8. Olivine Basalt 4. Serpentine (e¢) Metamorphic schists (d) Slide The Vein Genesis Chemical Analysis Quicksilver Deposits of Pacific Coast History of Helen Nine Geological Map of Helen Nine Section Map Mep of Santa Maria Tunnel INTRODUCTION. The authors wish to acknowledge their thanks to Prof. A. C. Lewson, under whose supervision the work was done, also to Mr. Andrew Rocca, owner of the Helen Mine, who kindly allowed us the privilege of the use of the mine for study. Prof. E. S. Larsen we wish to thank for his help in the petrographic work. The following works were used as references:- Monograph XIII, U. 8S. G. S., Becker; Folio 193 and 163, U. 8. G. 8S. Geology of Angel Island.-Ransome, Bull. Dept. of Geology, U. C.; 12th and 13th Annual Reports of the U. S. 6G. 8. (Quicksilver); Quicksil- ver Deposits of Pacific Coast ,-Bull. State Mining Bureau. JILIN mn 1 iii AE uli J ith v | os \ Mt.Hanng Sha ah i iw wh 220m HE | preside 1% WW < RQ tr, a5 Ne oo" B a Moy 9 Hi Jo L Hil hd 6 x0 1, | HEH | l pit Miia IS ef ES yh wy 7 \ ” my \ pend Sf a es 2 00 Me PS cote F 2 QO) We i Hg = , a i, 58 ak, Spo. Cig Aji on W : Ie PY al I iin a N Ns To Wig? ys ySers ye rvs Hel pls SE eer Ao Kah a 0S EN | os, a CO 5 “sea ho or Gi \ 1 0 Hi il i 1 at 1 mim | i Wed ii al, ¥| Hi | Scale lingh = 2 Miles BT Rocca area maped L.vanderlLech : : 2 MAP OF NAPA, SONOMA, LAKE, AND YOLO COUNTY QUICKSILVER DISTRICTS. General view looking N. W. from Station 9, show- ing outerop of Vein on Red Hill on the right, and bare sandstone slope in the middle. View showing soft and hard material in the Vein. ER —— Generel view looking II.W. fron St. 24, showing growth of teama- rack on latite, and the scant vegetation on serpentine, on the left in back ground is the out- crop of Vein on Red Hill. View looking S. E. from below office, showing serpentine hill View at St. 9, showing contact between serpen- View of basalt flow. tine and vein. LOCATION. The HEIEN MINE is situated in Ieke County, California, two miles north-east of the summit of the Mayacmas Mountains. The summit forms the Sonome-Ieke county line, as well as the divide; the ILeke County side draining into Dry Creek a trib- utary of Putah Creek, and thence on into the Interior Val- ley of Califoxnia, while the south-west side drains into the Russian Rivex. The Index Mep will show more clearly the exact loce~- tion of the mine. Celistoge is the nearest railway termi- nus. A toll road leads from that place to Middletown, and a county road privately meintained leads to the mine seven miles distant. The highest peeks of the Mayacmes Mountains in this region, are Mt. St. Helena, Pine Mountain, and Cobb Moun- tein, all largely composed of light colored eruptive rocks, standing out prominently as the chief landmarks of this belt. TOPOGRAPHY AND GEOGRAPHY. The immeturity of the geomorphic development is shown by the many steep narrow canyons, and by the fact that many slopes are so steep that the heavy rains which prevail in the winter season prevent the formation of soil upon them. This absence of soil is most conspicuous on those slopes underlain by serpentine. These serpentine slopes are often absolutely barren, bluish in color, and can be recognized for miles. The underlying cause ig the lack of plant food in the rock. Wherever scent soil forms, the oxidation of the iron colors it & distinet red, showing plainly for some distance through its sparse covering of serub oek, tamarack, Juniper and manzanita. In all cases, the weathering is not uniform, large more or less rounded and slickensided masses of rock stending out like huge boulders. The lavas and tuffs are light in color, presenting a bleached esppearance, are partly decomposed near the surface, and support heavy growths of timber up to the highest peek where all soil is carried away as soon as formed. Pine, fir and tanbark oek predominate here though meny other trees grow in sbundence. Pine Mountain having served as a source of mining timber and wood since the Helen mine was reopened in 1900. A rich soil supporting dense growths of trees, is formed on the slopes of moderate angle. The slopes underlain by sandstone are more rounded, though cut by sharp canyons. They are preveilingly covered with dense underbrush, or grass, the boundary between grassy slopes and thick chamisal and chaparral being as clear cut es a hedge, and suggests in many cases local landslides, due to & more or less clayey material occurring in the sandstone. Lendslides are in some places quite large due to the steep slopes, and their approximate parallelism to. the dip of the sandstone, end the heavy reins. Near the mine one such slide has divided the outerop of the vein into two distinet parts, a noteble gap several hundred feet long having been cut out of the vein, end partly filled by the debris from the hills above. From all ap~- pearances this slide was about one and one half miles in length, and occurred quite recently, as two parallel ridges are still seen quite plainly on either side of the slide. | The silicified or chalcedonie vein is very hard and resistant, the outcrops being especially prominent. These are of many colors from white to black, and stained red or yellow with iron oxides. The so-called "vein matter” is very distinctive. The schistose rocks overlying the sandstone are herd, dense and resistant, showing bold outcrops as well as large blocks scattered over the country below. GEQLOGICAT SUMMARY. The oldest rocks of this belt exposed to view are of Frenciscan age, comprising messive sandstone, chert, and schist of varying composition. It might be well at this point to give a brief de- scription of the Frenciscen series. This series of which ( the sandstones, chert, schist and serpentine are a part, is the oldest known sedimentary of this part of the Coast Ranges. The sedimentery rocks rest unconformably upon the bed rock complex which is probably of Jurassic age. In the vicinity of San Francisco where it is best known the Franciscan series consists of the following kind of rocks. l. A medium coarse dark gray sandstone with some conglomerate and shales. 2. Rediolarian chert beds. 3. Igneous rocks chiefly serpentine and basalt. 4. Gleaucophane and various other similar sheists. 5. Lenses of limestone. The serpentine and basalt are intrusive into the for- mation over a very widespread area and form one of its most characteristic features. The age of the Frenciscen is not positively known. It is probably Jurassic, for a discussion see Folio 193 of the U., 8. G. 8. The particular area studied consists of massive sand- stone, a lececolithic serpentine intrusive mass, a smell olivine diabese intrusion into the sandstone, flows of latite presumably from Pine Mt., smell patches of chert, olivine besalt, end the uppermost a series of schists. The sendstone is messive, medium coarse grained, with a peculiar flaky character for a thickness of ten feet near the serpentine contact, clearly showing the intrusive charecter of the serpentine. The detail description and petrographic evidence will be given later, merely & gen- eral deseription at this time. The olivine diabase, much altered, oceurs as a small neck or plug eutting through the sandstone & few hundred feet south of the west end of the vein. It is very limi- ted in extent and of no particular interest. RA BS RR A small peteh of rediolarian chert end a similarx vateh of basalt rest upon the sandstone on the downthrow side of a rather large feult which foxms the henging wall of the vein. These formations are of interest as giving & hint as to the overlying formations before erosion had removed all trace of them except the small blocks faulted down and thus protected. The schistose rocks above the sandstone are quite thick, though partly removed by erosion. These schists are very complex in structure, composition, and vary greatly, but are for the most part composed of glauco- phene, aetinolite, chlorite, white mica, hornblende and titanite. A flow of latite occurs in thin patches overlying all the above formations, even covering the outerop of the vein on the east end. It has evidently been extruded lat- er than the formation of the vein, and is the latest vol=~ cenic rock encountered. The more or less irregular zone of altered and silici- fied serpentine on the foot wall side of the previously mentioned fault, which carries the mercury ore, will for the sake of brevity be referred to as a vein, though in & strict sense it does not possess all the characteristics of sueh. All the evidence seems to point to the deposi- tion of the cinnabar at & much later date than the perido- tite intrusion and its subsequent alteration to serpentine which subject will be discussed in detail later. FORMATIONS. A. SEDIMENTARY. 1. FRANCISCAN SANDSTONE. This is prevailingly a massive medium coarse grained rock, fairly hard and resistant weathering to buff colored ellipsoids. The structure is best shown in the vertical cross sections, but the bottom of the sandstone is not known. The sandstone is rather abundant in the vicinity of the mine, and besides the massive texture there are a few small inclusions of shale, and in other places pebbles, characteristically of igneous rock, or chert. These pebbles are not found in place, but occur extensively scattered over the sandstone areas. The sand- stone fragments are subangular to angular, showing little effect of being water worn. They are prevailingly com=- posed largely of sodie (plagioclase) feldspars, quartz, chert, and the following to a lesser degree; chlorite, orthoclase, fragments of an andesitic rock, magnetite, zircon, plates of biotite, apatite as inclusions in quertz and albite, pyrite, glaucophane, epidote, hematite flakes. Secondary calcite occurs as veining quite frequently. The shale is very fine grained and much the same composition. Glaucophene has been developed as & secondary mineral. The shele is bluish black and appears quite carbonaceous, but some of the dark color is evidently due to glaucophane. The sandstone at the irruptive conteet with the ser- pentine presents & striking difference to the massive coarse grained rock above described. The sandstone is rendered somewhat schistose, or slaty, breaking off in thin sheets or flakes, which are rather friable. The im- perfect cleavage is parallel to the contact of sandstone end serpentine. The extent of the metamorphism is slight being limited to a zone of perhaps ten feet in thickness, there losing its vague sheistose nature and péssing into messive unaltered sandstone cheracteristic of the Francis- can. The ever present albite twinning laminae of the sodie feldspar fragments clearly seen in the massive sandstone ig here perceived with difficulty. The extinction under eross nicols is undulatory, @s it is with the quartz greins as well. The mass of the rock is very fine grained and it is very difficult to determine the constituent min- erels. They are chiefly quartz, elbite, orthoelase, mag- netite, chlorite minerals, some evidently developed meta- morphically. This sandstone is very light in color, with faint greenish staining. Several slides of the sandstone on the fault contact with the altered serpentine and chalecedonic material com=- posing the vein were studied, both at the surface and where the Sente Marie tunnel cuts thru the hanging wall of the vein into the sandstone. A brief description of them will be given here and they will be referred to later in the study of the vein. The specimen from the surface contained albite, oligoelase, quartz, orthoclase, chlo=- rite, magnetite, biotite in hexagonal plates, zircon, py- rite, marcasite, a rhombic pyroxene chert, apatite and kaolin, cemented by a notable amount of magnesite, which apparently has replaced part of the sandstone. Fully one fourth of the rock is carbonate of magnesia as shown by its exceedingly high birefringence; white granular aggre- gates showing no cleavage, and the ordinary ray has an i : | : ; : A PS ET AR VB IS ATE a i index of refraction higher then calcite or dolomite cor- responding to magnesite. Cold hydrochlorie gcid does not cause it to effervesce, while hot acid does. A good reac- tion for megnesium is obtained chemically. This rock is ] seen to differ from the normal sandstone only in the addi- tion of iron sulphide and A carbonate. The under- ground sandstone at a depth of 150 feet on the hanging wall of the vein is seen to be identical with that of the surface, snowing thet the addition of magnesium carbonate and iron sulphides in the sandstone, evidently came from the serpentine mass before the fault had formed an imper- vious gouge. The igneous pebbles previously alluded to as oceur- ring in the Franciscan sandstone may well be described here due to their clastic nature and occurrence in the sandstone. Many verieties oceur, but the principal ones are & quartz porphyry, and a granodiorite. QUARTZ PORPHYRY.- These water worn pebbles very from one to eight inches in diesmeter, are slightly weathered on the outside, the phenocrysts standing out above the ground mass. The rock is hard and quite fresh in the center. The phenocrysts are lergely orthoclase, occur- ring commonly in groups of intergrown crystals. These are quite cloudy due to keolinizeation. The phenocrysts of quartz are less abundant. The ground mass is fine grained, composed of quartz end orthoclase. Some mag- netite occurs as an alteration product of an iron bear=- ing mineral, probably biotite. GRANODIORITE.- This is & medium coarse grained granitic rock, quite hard and fresh. Quartz and oligo~ clase are abundant, orthoclaese and hornblende quite abund- ant, and a scattering of apatite, magnetite and titanite make up the balance of the rock. 2. FRANCISCAN CHERT. The occurrence of Franciscéen radiolarien chert is limited to & small cap about fifty feet across, and of 8light thickmess. It is red colored, or black from man- genese oxide in cracks and seams, the layers of chert end interbedded shale being twisted and crumpled, as is typical of the cherts seen elsewhere. In thin section the chert is seen to be composed of a great number of trensparent forms of chalcedony closely packed in & red~- dish brown iron stained matrix of chalcedony. The color- less parts are of a variety of forms, chiefly cone shaped radiolaria and as spicules. B. IGNEOUS ROCKS. 1. QUARTZ HYPERSTHENE LATITE. This rock oceurs in the area mapped as & thin residual capping, covering the eroded surface of sandstone, schist, and the east outcrop of the vein. The sheet ex- tends to Pine Mountain, the upper half of the mountain which rises to a sharp crest being entirely of this vol= canic rook. Though there is no evidence of & crater, it seems probable that the mountain was the seat of local outpouring of lave, as the shoulders of the mountain on both sides are capped by the same white, bleached appear- ing lava, resembling in color white fire brick. The beds of tuff at the base of the mountain near the mine have evidently been pretty well leached, and the more clayey parts are used as fire clay. The rock: is known locally ag "fire clay rock? The rock is resistant enough to stend out boldly, though weathering rather rapidly at present. In thin seetion the large phenocrysts of quartz are seen to be corroded, due to magmetic resorption. The phenocrysts of plagioclase feldspar are clear and glassy, showing distinet zoning, the feldspars ranging from oli- goclase andesine at the center to albite on the periphery. Many are not zoned and are entirely albite. Phenocrysts of orthoclese are less common. The rhombic pyroxene hy- persthene occurs quite abundantly in clear almost coloxr- less elongated prisms. It is distinguished by its high indices of refraction, medium high birefringence, nega- tive optic sign (biaxial), parellel extinction, positive elongation, end slight pleochroism pele green parallel to ites length, reddish brown or pinkish at right angles to its longer dimension. Some enstetite occurs also show- ing magmatic resorption, lower birefringence and a posi- tive optical sign. Magnetite occurs in octahedral crys- tals. The ground mess is a fine grained or spongy appearing intergrowth of quartz and orthoclase, with per- haps some sodic feldspar. The phenocrysts of quartz and feldspar are in some instances intergrown, showing simul- taneous development. The magnetite and hypersthene are evhedrel. The essential minerels are quartz, both potash and soda feldspars, and the hypersthene a characterizing mineral. The classification as & quartz hypersthene le~ tite seemg to be justified, in preference to the more general term "andesite" formerly applied to the similar voleanies of Mt. St. Helena, described by Becker in Non~- ograph XIII, and by osmont in the publications of the Depertment of Geology of the University of California. It would seem that the volcanic rocks forming Pine loun- tain ere more acid in character then those of Mount St. Helene, though in &ll probability closely related. 2. OLIVINE DIABASE. This is intrusive into the Franciscan sandstone in the form of a neck perhaps thirty feet in diemeter, standing out rather prominently above the surrounding sandstone. It appears reddish brown colored due to weathering, and indeed it is quite difficult To get 8 fresh fracture on account of numerous irregular fract- ures. The fresher rock is green to greenish black in col- or. Under the microscope the greenish color is seen to be due to chlorite which makes up & large part of the rock, apparently being formed by the alteration of augite as interstitial material. Olivine is rather prominent, al-. tering on the edges, and along fractures to a greenish serpentine mineral. The centrel portions are still clear and glassy, with characteristic high relief and .birefrin-: gence. The crystal boundaries ere not developed. The plagioclase feldspar andesine shows a tendency towards idiomorphism, the twinning is rather indistinct as the crystals are cloudy from alteration, and chlorite stain- ing. Secondary quartz occurs in seam fillings and replac- ing some of the chlorite. This rock seems to be much the seme a8 the "Older Diabese"™ described by Fairbanks, U. S. G. S. Folio 163. TFeirbanks put the age of this formation as part Franciscan end Pre-Tertiary. 3. OLIVINE BASALT. The basalt occurs as & thin cap faulted down on the hanging wall side of the vein near the west end. It is quite limited in extent evidently the remnant of a fairly recent flow. It is almost black, looks quite fresh To J (vg 14 and is very hard. Columnar structure is but imperfectly developed at best. The constituent minerals are olivine, anorthite with inclusions of apatite and magnetite, enstatite, and magne- tite. The olivine shows perfect crystal form, but only the center is unaltered. The alteration product is greenish white, has one index below balsam, the other above, is neg- ative uniaxial, with & high birefringence. The index of the ordinary ray appears too low for magnesium carbonate, and the high birefringence would seem to preclude its be~ ing a chlorite mineral, though it resembles chlorite or serpentine. The ground mass is fine grained, composed of caleic feldspar and pyroxene. The essential minerals of the rock as a whole are very basic feldspar and pyroxene. Olivine is & characterizing mineral. 4. SERPENTINE. The serpentine appears to underlie the major portion of a belt meny miles long and several miles wide, probably in the form of & laccolithic intrusive mass. It is typical Coast Range serpentine, being composed of more or less rounded slickensided masses much harder then the : intervening material. The fracturing and slickensiding was due to the intermel forces set up in the peridotite mess by its hydration and conversion of the anhydrous megnesian silicate olivine to the hydrous silicate mineral serpentine. The serpentine forms the foot wall of the fault which limits the vein on the hanging wall side. The serpentine in the vein has been silicified or removed com- pletely, all gradations occurring. The serpentine distant from the vein, and unaffected by the agencies forming it will be deseribed here, and the silicified and carbonated zone will be described later under the heading "Vein". The freshest rock exposed in cuts and tunnels is black and messive in texture, excent for the rhombic PYy- roxene altering to bastite. With this exception, the rock as seen in thin section shows the characteristic mesh structure of fine fibrous chrysotile and more platy entigorite. Io olivine is left to-dey in the freshest rock found. It is interesting to note that a careful qualitative analysis of this rock failed to reveal any trace of mercury. Chromite was quite generally observed in small emounts as a brownish semitransparent minerel in thin sections. Metallic greins of magnetite were less common. Some sections of serpentine are wholly composed of retic- ulated masses of pale green aciculaer crystals of chrysotile. & y — TA more complete description of the Coast Kenge Serpen- tine can be found in Monograph XIII, U. S. G6. S., by Becker; and in Folio 193, U. S. G. S., by Lawson; also in Ransome's Geology of Angel Island, in the Bulletins of the Dept. of Geol. U. C. The massive variety is traversed by numerous veins of asbestos, these seldom being over one half inch thick. As alweys the fibkes are perpendicular to the walls of the sean. C. METAMORPHIC SCHISTS. The schists are very complex mineralogically, structurally, and genetically. They occupy & rather large area southwest of the mine, a comparatively small portion being within the area mapped. These schists are hard crystalline rocks, some very fine greined, others comparatively coarse. They are preveilingly bluish or greenish colored, depending upon whether glaucophane or chlorite and actinolite are most abundant. The gections studied with one exception were from the same horizon, and all came from a limited area, yet they differ great- ly in appearance, physicel characteristics and mineralog= ical meke~up. Overlying the unaltered Franciscan send- stone, it would seem that regional metamorphism had lite tle to do with their formation; and it is equally apparent that they are not intruded in this region. Some other explanation mudt be sought. 1. GLAUCOPHANE MICA SCHIST. This is a medium dark blue rock composed large- ly of potash or soda mica and pleochroic glaucophane. Chlorite is a decidedly minor constituent, as is also titanite as honey yellow aggregates. 2. ACTINOLITE GLAUCOPHANE SCHIST. This rock is a coarsely orystalline gray colored schist. Glaucophame and actinolite intergrowths are fre- quent, composed largely of curved fibres. A few crystals of pleochroic green hornblende, with its characteristic extinction angle and cleavage are occasionally seen. Ti- tanite occurs rether sparingly. A large part of the rock is composed of a rather soft greasy mineral, white in the hend specimen, but in thin section aimost color- less. When thick it has a Slight greenish tint. Its optical character is positive biaxiel. The birefrin- gence is exceedingly low, and it is seen to have one good cleavage. This does not correspond with any data in Weinschenk's tables, but there is a possibility that it is a chlorite mineral, of variable optical properties. 5. GLAUCOPHANE CHLORITE SCHIST. At all times the extreme fineness of grein of this rock renders its petrographic study most difficult. Hard, nearly black, dense and even grained, it possesses no schistosity, but is classed as a schist for lack of better terminology. It appears to be an altered igneous rock from the faint suggestion of diabasiec structure. The prevalence of pyrite, rather abundantly in finely disseminated crystals is notable. Assays yielded 40¢ 18 gold, end 4 oz. of silver per ton. Glaucophane is per- haps most abundant in fine blue pleochroic shreds, and also as a later formation in minute seams traversing the rock. The larger seems, though rare, are filled with quartz, including fibres of the metamorphic minerals. Chlorite is rather abundant, ectinolite less so. A few comparatively large augites are found sporadically sceat- tered throughout the rock. Terheps many more minerals are present, but are impossible of geternination. 4. QUARTZ ALBITE GLAUCOPHANE SCHIST. The schist occurring in a very small area at the east end of the vein is hard and almost slaty, break- ing off in sheets, characteristically polygonal in shape. It is deeply iron stained masking its true color. The méin mass of the rock is fine fibrous glaucophene, chlo- rite, and to a lesser extent a rhombohedral carbonate, al- ‘bite, magnetite, end rounded quartz grains, appearing eas if but partly metamorphosed or resorbed in some other min- eral by metamorphic action. Quartz seams occur occesion- ally. 5. ANPHIBOIE CHLORITE SCHIST. A compact deep green chloritic rock, with the amphiboles actinolite, tremolite, and pargasite, the lat- ter determined by its positive optic sign, and brownish green color. A rhombohedral carbonate occurs, apparently 19 as an alteration produet. Glaucophane is not seen in this rock, though it occurs so ebundantly in most of the Frenciscan schists. Much float of pure actinolite occurs, but none was found in place. The prisms are rather long, thick, curved and packed in the usual reticulated manner. D. THE SLIIBE. The previously mentioned slide which cuts the out~- crop of the vein into two parts is a mass of debris of all sizes and descriptions. Sandstone and schistose rocks are the chief constituents. Some of these are many feet high, rising out of a mass of smaller ones. Clay end soil cover the slopes at present in most places, but very poorly. THE VEIN. The vein is closely related to a rather large nor- mel fault, the strike of which is nearly northwest by southeast, and dip 45°to the south. The sandstone on the hanging wall of the feult has relatively gone down ver- tically 200 feet, and judging from the extent of the gouge this figure could well be exceeded. The horizon- tal component is not determinable, there being no groove ing along the fault plane to indicate the direction of movement. In all probability the successive movements were not in the same direction along the fault plane. On the surface, the fault can be traced the full length of the vein, some 2000 feet. Beyond the vein es- pecially on the east end, the fault eppeers to die out. The thickness of the fault gouge is in places most re- markable. In the Sente lMerie tunnel, 128 feet of gouge and brecciated material was passed thru, end the end not reached. In other tunnels a few feet of gouge was passed thru and then massive sandstone encountered, but it is quite likely that this sandstone was but & large block torn off and for some reeson partially protected. In one case this was definitely proven, thanks to a small but rich seam of cinnebar and native mercury following ea secondary fissure which cut thru the gouge for a few yards. | I : This gouge or hanging wall is coumonly referred to as the "elta™ or "black elta™ a term derived from the Spanish. The vein has no foot wall gouge, and it is impossi=- ble To mark the exact boundary whieh limits the vein on This side. At ell times it is most irregular. From the hanging wall the zone of silicificetion extends fairly uniform in character for distances horizontally varying from forty feet in places on the surface to three or four hundred feet in The Long tunnel. And on the surface above the Sante Merie tunnel in whet is mown as Red Hill, the outcrop is a few hundred feet in width. This zone though extremely irregular is nevertheless quite distinet. Then beyond it on the foot wall side, for perhaps five feet on an average, the vein matter passes into greatly altered and silicified serpentine, then into less altered serpentine with & few stringers of quartz; and finally into pure serpentine. This gradation is clearly seen in the crossecut tunnels, and is further brought out by chem- ical enalysis and petrogrephic study of & series of sam- ples. Within the vein itself, the gradation ceases. The hard chalcedonic rock, the end product of the alteration end silicification of the sexpentine, is found in irreg- uler masses throughout the vein, but occurs more frequently neer the henging wall. However large messes are found along the foot wall. The "vein matter” es it is usually referred to, or rquicksilver rock," is at all times largely composed of chalcedony, containing notable amounts of marcasite and pyrite, silicified serpentine, magnesite apperently es a later infiltration, quartz seams, some opal and smell amounts of bituminous metter, alkaline earth carbonates and sulphates. The physical properties are most varied, the rock ranging in hardness from chalcedony to soft clay- ey material which can be dug out with the fingers. In color from black to white, depending upon the amount of disseminated iron sulphides. A description of the lead- ing types may give & clearer idea of these totally dif=- ferent appearing rocks, formed by the same action and oc- curring in the same zone. Lerge masses of black chalcedonie rock are found throughout the vein, usually in more or less rounded and slickensided "boulders", extremely hard and brittle, and barren of cinnebar, except in the cracks and seams where it has been deposited by solutions following the forma- tion of the rock and its subsequent fissuring and fract- uring cesused by feult movements. The order of events is as follows: The peridotite intrusive altering to serpen- tine, further broke down into free silice and magnesia. The latter was apparently leached away, and contemporane- ously there occurred the addition of large quantities of finely disseminated sulphides of iron, chiefly marcasite. In thin section the black color of the cheloedonie rock is seen to be entirely due to the finely disseminated sul- phides. Many of these erystals are in the fom of elon- geted prisms, some rather short and stocky, others quite acicular. These are often grouped in clusters, and are evidently mostly marcasite. A few crystals appear iso- metric, brass yellow, and are distinetly pyrite. The proportion of marcasite to pyrite is impossible of deter- mination, but it appears that pyrite is almost neglible in comparison. The total per cent of a specimen was de- termined by determining the specific grevity, end then on the assumption that the rock was composed wholly of mer- casite of specific gravity 5.0 and chalcedony, specific grevity 2.60. On these assumptions from the determined specific gravity of 2.84, and simulteneous equations, the per cent of marcesite by weight equaled 10.0%, and by volume 5.48%. It is quite possible that silice also came in at this time along with the marcasite. Verious hydro- carbons ceme in at this period, as they are found to-day completely sealed up in & mess of chalcedonic rock. These hydrocarbons are usually viscous or even rubbery, usually brown or black and do not ignite readily. Others are al- most colorless, and quite liquid, flowing out of the cav- ities of the rock as soon &8 the rocic is cracked or broken. Following this period, the silicified matter was sub- jected to many movements along the hanging wall. The rock was shattered, and ground together until a distinet goug wes formed about many of the lerger fragments. Some of these gouges occur within the vein, parellel to the main fault plene and as much as a foot or two in viickuess. In extreme cases the vein looks much like & masonry struet- ure composed of rounded boulder like masses, with gouge material between. IT should be stated here that some of this souge wes formed later than the deposition of the | ¢innebar, being itself rich in cinnabar. This is the ex- ceptional case, however, as will be noted later. Lerge parts of the vein are quite massive in appear- ance and have suffered but slightly. However fractures have been produced extensively in all the rocks, but no movement. These fractures are at times large open seams, but usually mere crevices, and under the microscope can be seen numbers of minute fissures now completely filled with magnesite, chalcedony and occasionally cinnabar. The larger fractures are in two sets, one parallel to the fault plane, far the more prominent, and the other set making a low angle to the horizontal toward the foot wall. Iueh of the rock is shattered quite extensively, the cracks and crevices being in all directions, but the pre- 8 I veiling fissures are of the two systems above mentioned. There has heen movement along the fissures parallel to the fault plene. These slips largely control {the miner- elization. The deposition of cinnsbar clearly follows this period of crushing and fracturing occurring wholly in seans developed by dynemic agencies. Aft no place does the cinneber occur within the siliceous rock above de- seribed, but very frequently on the outside end in the numerous seams developed along fractures, and associated with later depositions of pyrite, marcasite, chalcedony, magnesite, quartz, and rarely barite and calcite. Thin sections of the black chalcedonic rock with the disseminated mercesite show an intricate system of microscopic fissures forming & network, and now filled with megnesite and chalcedony with an occasional speck of einnabar and mercesite. Some black metallic sulphide, presumably, occurs with the mercasite in the original rock, but to a very limited extent. It was not deter- mined. Assays of this rock for gold and silver revealea a trace of silver and $1.50 gold per ton. The gold is presunebly associated with the disseminated sulphides and if so, came in during the first period of activity. It is difficult to say whether this is exceptional or the meen velue, from the few assays made. Should the roasted ones from the furnace be amenable To cyanide treatment, an interesting economic problem might arise. The ebove deseribed rock is usually too hard to mine and rather low grade. Nuch of it is roasted however, af- ter sorting. The best stopes have been found in the com- reratively softer rock, largely in & black rock, rether Soft and elmost granular from the large amount of iron sulphides present. In cases perhaps half the rock will be mercasite, & little cinnsber end the balance opaline rock and magnesite. The large amount of sulphur present causes serious difficulties, metallurgical and otherwise. The fillings in the old stopes become so heated due to the oxidetion of the iron sulphide thet in & short time no further work can be done near them. The same rock piled upon the dump, charred and finally destroyed the wooden trestle supporting the ear treck. This rock in the furnece gives off such & volume of sulphur dioxide thet soon absorbs moisture and perheps oxygen forming very powerful acids. The morter of the brick condensers is soon attacked, and destroyed often causing a collapse of the brickwork arches, and even the walls. The softer bricks are also attacked. Another tyve of vein metter which is considered to be favoreble for cinnabar, though quite frequently bar- ren, is a light gray, medium herd rock streaked or spot- ted with sulphides. Oceasional traces of serpentine still 7 remein, some of the flaky antigorite, curved and distor- ted and some fibrous chrysotile. These are rare, as are also octahedrons of magnetite. Greenish stains of chro=- nium are more common, but unimportant. The amount of extremely fine grenular megnesite, chiefly in veining, is quite high, perhaps being 25%. Chalcedony and opal ere abundent. The proportion of megnesite, opal and chalcedony is by no means constant, wide variations oc~ curring, and also the amount of iron sulphides and ser- pentine vary within a narrow renge. Cinnabar when it does occur is in seams throughout the rocks, and not as a primery constituent. Neer the hanging wall of the vein vertically above the Sante Marie tunnel on the surface, there is & mas- sive bluish green rock, rether hard and silicified, which in thin section is seen to be & mass of fine fibrous | chrysotile closely compacted, with some mercasite, magne- tite, chalcedony, and & network of very small magnesium carbonate stringers. It carries no cinnebar, and is de~ seribed merely to show the extremely verieble nature of | the vein. A rich seem of cinnaber was found near the surface on the hanging wall of the vein, above the Santa larie tunnel. This seam was followed down the dip in a reking direction which near the level of the Sante Maria cer- ried it beyond the previously recognized hanging wall, and thru a zone of crushed carbonated rock, with occa~-- sional large masses of sandstone. At times this seam wes a mere stringer for several feet then it would widen out to several inches of pure cinnebar, and at the level of the Sante Maria it is several feet wide, very rich in cinnebar and especially rich in native quicksilver. A notable amount of iron sulphides occur associated with it, and pyrrhotite is especially abundant. This rock is too soft end frisble to study in thin section. A speci- men from nearer the surface contained about 10% cinnabar disseminated in & mass of medium grained magnesite. Smell amounts of iron sulphide, and chalcedony occur with & brownish green rather flaky mineral, badly decomposed which is epperently entigorite from ite low birefringence and negative optic sign. Apparently the magnesite and cinneber replaced the serpentine, if this mineral really is antigorite. The cinnabar and magnesite were evident- ly formed at the seme time, being intimately intermixed. One peculiarity is noticeable, meny of the cinnabar grains form a nucleus of magnesite, far more coarsely crystelline then the main mass of the rock. The reason for this is unexplained. The Red Hill end of the vein is characterized by masses of soft light colored, greasy material, locally called tale. This at times is quite rieh in ¢innaber, 29 either disseminated thru it, or in thin horizontal seams. These irreguler formations extend to the surfece from the Sante lMerie tunnel, and have been largely worked due to ease of mining and fairly constent emount of cinmabar. This white clay like material is pitted or spotted with green chromium steined specks. On exposure to the air it crumbles to a powder. The composition is largely mag- nesite and silica with some mercasite and cinnebar. The reason for its extreme softness and clayey character is not clear, as it occurs in irregular chambers, snd does not appear to be due to crushing. In driving the SANTA MARIA TUNNEL efter passing thru one part of vein, then barren serpentine, large masses of white quartz were encountered. This rock is given a white appearance and is fer from trensparent except in thin sections due to the large number of inclusions, both liquid and gaseous, meny ges bubbles being inclosed in liquid. This vein quertz is itself veined, and in these minute veins were formed, chiefly along the edges, elongated prisms of a colorless mineral, with a peculiar cross fracture, dividing it into sections. The index of refraction is high, ', birefringence quite high, elonga- tion negative, and extinction parallel. Due to the small- ness of the individual crystels it was impossible to de- termine the optic sign. The ore mineral far the most important is cinnabar, but in some instances native quicksilver is of more im- portance, occurring in rather large quantities at pres- ent along and in the henging wall of the vein in the Sente Maria tunnel. It is scattered profusely through- out the rather soft material of this offshoot of the main vein, often in large globules. It is associated with iron sulphides, prineipally mercasite and pyrrho- tite. The occurrence of the black sulphide of mercury metacinnabarite is extremely rare. The gangue minerals include the following: MAGNESITE, HARCASITE, HYDROCARBONS, CHALCEDONY, PYRITE, PROBABLY POSEPNYTE, OPAL, PYRRHOTITE, AND NAPALITE, QUARTZ, CERYSOTIIE, BLACK SULPHIIRE, CALCITE, ANTIGORITE, GYPSUM, MAGNETITE, BARITE, CHROMITE, Besides the above, oxidation caused by the cireu- lation of air in the openings forms epsomite, melanter- ite, limonite, a greenish chromium minersl (mariposite?) and free sulphur. These lists could probably be in- creased by careful study of all the many phases of the vein. GENESIS. Following the intrusion of the peridotite into the sandstone in point of time, ceme the hydration of the latter, and its alteration into serpentine. The absorp- tion of 10 =~ 13% of water was necessarily attended by en increase in volume, and the expansive force thus produced shattered, crushed and mashed the serpentine itself; and it is quite conceivable that the cumula- tive swelling of this large laccolithic mass caused meny fault movements in the adjacent and overlying for- mgtions. The normal fault along the present serpentine sendstone contact mey have had its inception at this time. Moreover it would seem that the present fault contect was formerly en intrusive or irruptive contact. The sendstone along the contact is for some little dis- tance thoroughly impregnated with magnesium carbonate whieh must have come from the serpentine, and just as surely could not have come from this source after any appreciable faulting had occurred. It is not at all unlikely that the magnesia in the serpentine was to some extent replaced by silica from the sandstone. An intrusion cutting across the stratification of the sed- imentary formetions would afford & line of weakmess 32 along the irruptive contect, which later developed into a rather large fault attributeble to the swelling of the serpentine. This theory offers a satisfactory explana- tion of the silicification of the vein and its corre- sponding loss of magnesia and is merely stated as a possibility. The decomposition of the serpentine in what is now vein matter gave use to a vast amount of chlecedony, opal, and silicified serpentine, all containing appre- ciable amounts of disseminated marcasite, and various hydrocarbons. All of these except the hydrocarbons could have easily been formed from the breaking down of serpentine, its loss of megnesia, and addition by waters circulating along the fault plane of sulphuret- ed waters to form the iron sulphides. The hydrocarbons probably were derived from the sandstone or some under- lying shale, but by what agencies is not known. After silicification was complete considerable movement took place along the fault, crushing end grind- ing part of the silicified material into a gouge, and shattering the main mass, forming a network of ecrecks, crevices and fractures. The brittle and comparatively strong rock in the zone of silicification was capable of mainteining many comparatively small seams, and it was these seams that were all importent as affording a 33 path for later solutions. These solutions of the second period rose from whatever their source may have been, and deposited in these basins, fractures and seams, the cin- nebar now mined, along with sulphides of iron, magnesite, - chalcedony and quartz. This period of mineralization is seperate and distinet in every particular from the silic- ification following the decomposition of the serpentine, and it appears difficult to conceive that the second period of activity was the dying stage of the first. No- where is cinneabar in the silicified rock first formed; always in the openings formed by its shattering. The origin of the later solutions cerrying the c¢in- nabar presumably as alkaline double sulphides in hot solutions, is seen to be little explained by observation- al evidence, yet many relations are seen that at least eliminate some of the possibilities. It is quite clear that some igneous rock, possibly related to the latite, was intruded into the region, which stimulated the flow of hot solutions. Within a radius of six miles, occur the geysers of Sonoma County, and meny hot springs in Lake County, some within & mile and a half of the mine. It is quite probable thet these springs bear some rela- tion to hot waters which formerly were active in form- ing the quicksilver deposits. Granting some late intrusion as a source of heat which would give rise to upward circulation of hot alkeline waters, it must next be determined where they derived their mineral content. Rising along the brecciated zone of silieified rock next the impervious hanging well, it would seem that these so~ lutions by reason of the fault were restricted within comparatively narrow limits, and all the roek within these limits, from all evidence was absolutely barren of mer- eury in any form. These solutions did not penetrate the serpentine along the footwall, this serpentine being quite impervious to-day. 4 fifty foot shaft filled with water was tepped by ean uprise a few years ago, the serpentine forming & water tight barrier until only a few inches separated the weter filled shaft and the uprise. From this, it would eppear highly impossible that solutions any sort could leach the ecinneber from the serpentine, provided it were minutely disseminated in it, which is not likely, judging from the careful qualitative tests made upon the fresh serpentine. It thus appears that all mineral content must have had the same source as the heated solutions, namely some late intrusion. CHEMICAL ANALYSIS. In order to ascertain the origin of the vein, and cinnebar, a series of analyses was made. First a qualitative analysis of a typical piece of unaltered serpentine, teken at a point 400 feet east of the vein and 10 feet below the surface of the ground. The following elements were found in abundance- silica, iron, aluminia, magnesium, traces of nickel and chromium were found. A special effort was made to discover any mercury, but no trace of that element was found. A petrographic description of this sample is given under the discussion of serpentine. A similer enelysis was made of a typical sample of the latite flow, in order to discover if it contained any mereury, but a negative result was obtained. The results of these two analyses seem to indicated, that at least in so fer as the Helen Nine is concerned, the cinnabar wes not concentrated by solutions Irom either the serpentine or latite. Then & series of quantitative analyses were made of a sample of surface serpentine, and four samples of the rock along the Santa Maria tunnel from station E to the henging wall. (See Map of Sante Maria Tunnel). 1 2 3 4 5 S10, 34.04 34.59 53.61 28.03 58.01 Ngo 36.10 34.70 15.83 26.23 20,03 Hy0 12.01 13.81 13.85 4,01 Trace Al50z 7.12 7.59 1.80 — TU COs Trace Trace Trace 10.00 5.01 FeO 9.37 9.17 15.40 30.52 18.02 “99.00 99.86 100.51 ° 101.0% 36 Semple No. 1, was & piece of fresh serpentine tak- en at & point 500 feet east of the vein and 10 feet below the surface of the ground. It is interesting to com- pare it with the results of the analysis obtained by Becker.* The Helen Mine Serpentine is lower in silica, higher in FeO and Al,0z, and lower in MgO, only a trace of Crg03 and NiO was found, and no MnO. Semple No. 2 was taken from St. B, Senta Maria Tun- nel, this sample is still in the unaltered serpentine. *Becker-lonogreph XIII U.S.G.S., gives two analyses of serpentine taken from the Sulphur Bank Mine, at a point 22 miles north of the Helen line. 510g 39.64 41.86 HoO 13.81 14,16 Al 20x 1.30 0.69 Cro 0x 0.29 0.24 Fe 7.76 4.15 Nio @ 3d Wap mea MgO 37.13 38.63 MnO 0.12 0.24 100.28 37 samples lo. 3 and 4 were taken between station E and the vein metter, No. 3 shows The increase in 810g and decrease in MgO. No. 4 was teken from & portion of the tunnel high in iron. No. 5 is a typical piece of the black chalcedonic vein matter. THE QUICKSILVER DEPOSITS OF THE PACIFIC COAST. The Quicksilver deposits of the Pacific Coast are found for the mein pert in the Coast Renges of Califor- nie, extending in & belt from Trinity County in the north to San Luis Obispo County in the south. The deposits of cinnsber are characteristically found in rocks of pre-cretaceous age, known &s the Fran- ciscen Series, consisting of sandstones, cherts, ser- pentine and basaltic intrusions. The cinnebar mines have been worked since 1850, and have been a great source of wealth to the state of caelifornie, at the present time these mines still pro- vide the greater part of the nerewey mined in the Unit- ed States. In the year 1913 the totel output from Cal- ifornie was 15,396 flasks, while the total output of the United States was 19,681 flasks. A flesk of guick- silver contains 75 pounds of metal, and varies in value at different time from $30.00 to $90.00, the average being about $40.00 per flask. In the year 1913 there were twenty producing mines in Celifornie. The principal output being from the New Idrie mine in Sen Benito County. The New Almaden and Guadalupe mines in Sente Clare County, and from scatter- ing mines in Sonome and Ieke Counties. Of these the 39 New Alameda mine, has long been the most famous quick=- silver mine in the western hemisphere, having been dis- covered in 1850, it has been worked continuously ever since, with a total output of $56,000,000.00. The un- derground workings are very extensive, being over one hundred miles in extent. The ore in this mine has been the richest yet discovered in California, yield- ing for a good many years over 36% metal, at the pres- ent time the ore has probably been exhausted, the only work done is in cleaning up old stopes and furnaces. The ore minerals of the Californias mines consist on of cinnabar, metecinnabarite and meture mercury, found characteristically in chambered veins of silicified serpentine, the one notable exception being at the Oat Hill mine in Napa County, where it is found as impreg- nations in Franciscan ssndstone. Ores that pay to mine sometimes run &s low &s 25% mercury. The richest ores have been found et the New Alameden and New Idria mines. where certain stopes run 36% metel. The average return at the present time is about 12 lb. of metal per ton. The silicified ser- pentine of the vein is a dense hard blue chalcedonie rock, carrying large amounts of sulphides of iron and known among the miners as "quicksilver rock.” The cinnaber is found in cracks, fissures and cavaties in the chalcedony. The principal gangue minerals are as & rule, chalcedony, quartz, mercasite, pyrite, magnesite, calcite and barite, and certein inelusions of mineral oil, Cinnabar is the principle ore, metacinnabarite and native mercury not being very common. The Califor- nia mines have not suffered mueh from the abundance of native mercury, the only large mine that has been forced to shut down on account of it, was the Socrates mine in Sonoma County, where the great abundance of free metal stopped work. Native mercury is elways looked upon as & bad sign by the miners, aside from the fact that it makes work dangerous, it usually indicates the end of the ore body. As to the genesis and origin of the California quicksilver deposits, nothing as yet can be definitely - said, though several hypotheses have been advanced. There are, however, certain facts that point to a common origin for these deposits of the Pacific Coast. lst. The mines of the quicksilver belt appear to run in par- allel lines elong zones of faulting and igneous activity. 2nd. Everywhere it is found in connection with serpentine and sandstone of Frenciscan age. 3rd. The cinnabar belt is characterized by & great number of hot sulphur springs. The following are two of the theories most general~ ly advanced as to the origin of the quicksilver deposits. 1st. Its common occurrence with serpentine seems to suggest that these serpentine intrusives may have contained minute quantities of cinnsbar scattered thru them, and then later intrusions of Pliocene age consist- ing of andesites and basalts may have set up eirecula- tions of hot alkaline waters, which concentrated the cinnebar, and deposited it in zones of fracture in the siliocified serpentine. Up to the present time no trace: 0f cinnebar in the unaltered serpentine rocks of the Coast Range has been reported. The second theory, and the one most generally accepted, is that the deposits are due to the hot sulphur springs, which carrying the cinnabar in solution from some unknown rocks of the basal complex, have deposited it in the Practured quick- silver rock. The true origin is till, however, an: open question. HISTORY OF HEIEN MINE.- The Helen Mine was located in 1864, and was worked for some ten years by Pushbacker & Co., with & production of about 1000 flasks. It wes then sold to the Americen Compeny in '75 for $100,000.00. This company operated until '79 and produced over 1000 flasks. Then the mine was dormant until 1900, when the present owner, Mr. Andrew Rocce, purchased the mine. Since that time, 3303 flasks have been shipped. A Pifty ton Scott furnace was erected in 1906 and since that time has been operated at irregular inter- vals, during the dry season. Under the present arrange- ments the excessive rainfall during the winter precludes the operation of the furnace, as & dry oné is required. Further the large amount of sulphide present gives off during the process of roasting large volumes of $0s. This combining with condensed moisture in the conden- sers, forms acids so strong that the brickwork, espec- ially the arches, soon collapse. MNany serious shut- downs have been thus occassioned. The extreme irregularity of the ore bodies, and the fact that they are small in comparison with the main mess of the vein, require a great deal of development work, which in the past has not kept pace with the ex- traction of ore in the summer months. However, the Lower or Long Tunnel is now being reopened and with the eid of compressed air drilling just installed, it is hoped that the operation of the mine will reach a more settled condition. Prior to the building of the furnace & bench of pipe retorts was operated on high grade ore for a con~- siderable period yielding several hundred flasks. The ore &8 now mined requires rough sorting in the mine. The ore is quite variable, but the average re- covered quicksilver is about 6f - 8F per ton. 0] Latite Slide Recent ba ; Basalv Terhary and Quaternary vein S erpenti ne SP. @ pr {2 ls: AR ik schist ~ Franciscan series Jurassic ? Radiolarian Chert Ss. | sandstone -— hoo BT AOCCA 1 Foo 1 +00 1914 CeEaLocy AND = |OOFT.— CONTOUR INTERVAL = |OFT. w SURVEY 5 260 TEPT.OF GEOLOGY UNIV. OF CAL. ONE IN. I So LVANDERLECK CEOLOGICAL MAF HHH Hil] pT HHI fH HELIN THT { 6) 7| g| 9 "10 11'12'13'1415 we 'g 3 3 vy 2 ez lg a 3, vl Lot | 1 {A in Lili I ! } / i Lid Recent Tertiary and Quaternary Serpentine Ven on Diabas Schist Jurassic ? Wi i i . i hl wr errs: ! i lei jd . | nt th i i Gi i i HE Yishun rr rte Ls ¥ [a wd f Sh alt 1 i i y i HE Hi DOCUMENT FILMED IN SECTIONS AE AA "lg Tg] el, gl Vg PTH ERE F RE HEH HTH ) 3 (22) HA Sec. DD. VE] ] E : o =| = z E ed E Z | H =1 i - | PL BR PRR - LELGENI Lv | law | [se] [be] [wr | [a] Sandstone Ragiolavian vein Diabase Serpentine Basalt Latte Shde Che a usA | SeC.B.B Sec.cC.C. — SecC.DD. SeC.EE. m : Sandstone Radiolarian Le] a | Ll, Lie] s fo Lt] sl. Tm — — a - SS — I ~ — ee — —— " _ i ss. A SeC.FF BT Roccd L. Vqnider Lect Si 1111] 31141 { | | FETE 112 1 | i HH i 1 "10 i ‘9 ibid fi 71" Ig] HTHE 1! METRIC PH | TT 2 11) 3 ull sn i @ ly 3g | labial f 8 | £ Hii ° Lihinlig b 1 ht 0,01, | | 3 iy) 9 Lid mouth of tunnel. / StA leo nN) \ > Heb ] NY oer xT A) 33! TAR 5 ew ap cra WEE RA ARI ARR . mouth of Gir shaft 0) Sty. SANTA MARIA TUNNEL HELEN NANIE peak Sins poft. LE GBND Ae Ce. rt ‘oe twa th ein serpentine hanging va | Cinnabar Soo B.T'Rocca L.vander Leck feo i ——- END OF TITLE