University of

Reno

Geology and Mineral Deposits of the

Northern Half of the Mt. Tobin Mining District,

✓ Pershing County, Nevada

P thesis submitted in partial fulfillment of the requirements for the degree of Master of Science,

by

Richard Michael Perry

Ppri 1, MINES UBRAJUC

T K e &

m

The thesis of Richard Michael Perry is approved;

University of Nevada

Reno

April, 1385

ii ABSTRACT

The Northern half of the Mt. Tobin Mining District, 45 miles south of Winnernucca in the , produced 1073 flasks of mercury and minor silver and gold from deposits located near the northern margin of a late Tertiary vo1cano-tect oni c g ra ben.

This graben is bounded to the north by a fault which juxtaposes complexly deformed sediments of the late

Paleozoic Havallah sequence with sediments and

Tertiary volcanics which fill the graben.

Two types of mineralization are present; <1) Tertiary epithermal mercury—gold-siIver mineralization which is structurally controlled by the graben-bounding fault and <£> stratiform volcanogenic silver mineralization in the

Havallah sequence.

Analyses of 171 samples of Tertiary mineralized rocks

indicate a vertical zoning of gold, silver, arsenic,

antimony and mercury in vein and fossil hot springs

deposits.

i i i ACKNOWLEDGEMENTS

The author is indebted to Larry Larson, Rich Schweickert and Dan Taylor for their critical reviews of this thesis.

The not so subtle humor and threats of Dr. Larson were an inspiration to the author during the writing of this manuscript.

Appreciation is also extended to Thomas Cudzilo,

District Manager of Nicor Mineral Ventures, Inc., Sparks,

Nevada, for approving funding for this thesis project. The

Mt. Tobin District was suggested as a thesis by Tom Kuhi,

Senior Geologist at Nicor. Bill Fuchs, also of Nicor, provided use of his ore microscope and many excellent suggest ions.

Special thanks go to my wife Lisa, who provided love, understanding, and moral support during the span of this project.

IV TABLE OF CONTENDS

□age ABSTRACT . i i i

ACKNOWLEDGEMENTS . .

LIST OF ILLUSTRATIONS

LIST OF TABLES

INTRODUCTION . .

PURPOSE ...... 1 GEOGRAPHY ...... 2 FIELD METHODS' AND LAB PROCEDURES...... 4 PREVIOUS WORK ...... 5 HISTORY AND PRODUCTION...... 7 GEOLOGIC SETTING...... 9

STRATIGRAPHY AND STRUCTURE ...... 12

SEDIMENTARY AND VOLCANIC UNITS...... 12 Havailah Sequence...... X•« o!— •J o Introduction and distribution, . . . . . X u_ Stratigraphic description...... IS Structure...... 19 Discussion of structural chronology. . . 27 China Mountain Formation ...... £8 Introduction and distribution. . . . . , £8 Stratigraphic description...... £8 Structure. 3£ Discussion of structural chronology. . . 36 Relation of Havailah to China Mountain structures ...... 36 Matches Pass Formation ...... 40 Introduction and distribution...... 40 Stratigraphic description. . , 40 Caetano ...... 42 Introduction and distribut ion...... 42 Strat i graph ic description...... 43 Structure...... 43 Andesite—Dacite Flows and Flow Breccias. . 43 Introduction and distribution. ■ • § - ■ 43 Strat1 graphic description...... 44 Structure...... 44 Fish Creek Mountains Tuff...... 45 Introduction and distr ibut ion...... 45 Stratigraphic description...... 45 Structure...... 46 ...... 46 Introduction and distribution...... 46 Strat igraphic description...... 48 Structure...... - * 48 V INTRUSIVE R O C K S ...... 49 Needle Peak Stock...... 49 Descript ion...... 49 Structure...... 49 Dikes arid sills related to Koipato Group . 51?. Descript ion...... 50 Diabase Dikes...... 52 Description......

TOBIN VOLCANO-TECTONIC GRABEN...... 54 Introduction ...... 54 Structure...... 54

ECONOMIC GEOLOGY

INTRODUCTORY STATEMENT 60

TERTIARY EPITHERMAL MERCURY-GOLD SILVER MINERALIZATION...... 60 Gold-Bearing Veins ...... > 60 Rockhouse adit ...... Quartz-Barite Veins with Silver and Copper Sulfides...... 69 Blue Lead mine ...... 69 Badger mine...... 73 Unnamed adits...... 75 Fossil Hot Spring Mercury Mineralization. 77 Mt. Tobin mine ...... 77 Last Chance mine ...... S3 North Fork mine...... as Unnamed prospect ...... 91 Origin of mercury deposits ...... 94 EXHALATIVE STRATIFORM SILVER MINERALIZATION . . 95 Queenstake prospect...... 95 Origin of mineralization ...... 96 GEOCHEMISTRY...... 101 Contour Maps of Metal Values ...... 101 Correlation of Metal Values...... 108 Scatter gr a m s ...... 110 Discussion of Geochemical Data ...... 111

CONCLUSIONS AND RECOMMENDATIONS. 119

REFERENCES CITED

APPENDIX ...... INDIVIDUAL SAMPLE ASSAYS

VI LIST OF ILLUSTRATIONS

Plate Pa5e

1. Geologic map of the Northern half of the Mt. Tobin district...... > in pocket

£. Cross sections...... in pocket

3. Sample location map ...... in pocket

Figure

i. Location Nap...... • ■ £. Stratigraphic Column...... 13 3. Outcrop of Havallah in North-Central Nevada 14 4. Photomicrograph of Havallah Argillite . . . 15 5a. Isoclinal Fold in Havallah ...... £1 o 5b. Isoclinal Fold in Havallah Chert...... L— u. 6. Photomicrograph of cleavage in Havallah . . £3 7. Pi Diagram of Fold in Havallah...... £4 8. Pi Diagram of Bedding Attitudes in Havallah £5 9. Contoured Pi Diagram ...... £6 HZi. Photomicrograph of China Mountain Formation T u f f ...... ^ . 30 11. Photomicrograph of China Mountain Formation Pebble Conglomerate ...... 31 l£a. Photomicrograph of Cleavage in China Mountain Formation Tuff ...... 34 l£b. Isoclinal Fold in China Mountain Formation. 34 13. Asymmetric F3 Fold in China Mountain Formation ...... 35 14. Pi Diagram of Bedding and Foliations in Ch ina Mounta in Format ion...... 37 15. Contoured Pi Diagram...... 38 16. Photomicrograph of Natchez Pass Biomicrite. 41 17. Photomicrograph of Fish Creek Mountains Tuff...... 47 18. Photomicrograph of Pyroxene basalt Flow . 47 19. Photomicrograph of Koipato Dike ...... 51 £0. Mao Showing East-West Volcano-Tectonic Depression in North—Central Nevada. .... 55 £1. Outcrop of gold-bearing quartz vein .... 61 ££. Polished section of gold—bearing quartz vein 63 £3. Geologic mao of Rockhouse adit ...... 64 £4. Photo of quartz vein underground at Rockhouse adit...... 66 £5. Thin section of quartz after calcite vein . 67 £6. Geologic map of Blue Lead mine...... 71 £7. Polished section of ore from Blue Lead mine 7£ £8. Geologic map of Badger mine ...... 74 £9. Geologic map of Unnamed adit...... 76 30. Geologic mao of Mt. Tobin mine...... 78 31. Geologic map of East workings ...... - - 81

vii d i d . * Geologic map of Snake Pit adit. .... 82

. . . • B 86 C j L j * Geologic map of Last Chance mine. • 34. Polished section of cinnabar from Last Chance mine ...... 87 35. Geologic map of North Fork mercury mine - - - 89 36. Mercury retort at North Fork mine . . . 90 37. Geologic map of Unnammed prospect . . . 92 38. Thin section of silicially altered tuff with hydrothermal barite ...... 93 39. Polished section of folded quartz stringer in Hava11ah argillite ...... 97 40. Geochemical contour map of gold .... 41. Geochemical contour map of silver . ■ . ■ ■ - 103 42. Geochemical contour map of arsenic. . . a a 104 43. Geochemical contour map of antimony . . ■ ■ * 105 44. Geochemical contour map of mercury. . . 106 45. Scattergram of gold vs. elevation . . . i 12 46. Scattergram of silver vs. elevation . . a a ■ 113 47. Scatterqram of arsenic vs. elevation. . B B B 114 48. Scattergram of antimony vs. elevation . a u B 115 49. Scattergram of mercury vs. elevation. . B B B 116 50. Relative values vs. elevations for gold silver, arsenic, antimony and mercury . . . H 117

LIST GF TABLES

i. Assay results from pyritic quartz veins . 62 65 CL a Assay results from Rockhouse adit . . . . 3. Assay results from Blue Lead Mine . . . . 70 4. Assay results from Badger Mine...... 75 cr 75 -J b Assay results from Unnamed adit. . . . . 6. Assay results from West workings. . . . . 81 7. Assay results from Snake Pit adit . . . . 81 6. Assay results from 1957 DMEA drilling at Mt. T.::>bin Mine. . . 84 9. Mercury production at Mt. Tobin Mine from 1936 to 1941...... 84 10. Assay results from Last Chance Mine . 85 i i. Assay results from North Fork Mine...... 88 12. Assay results from Unnamed mercury prospect 94 13. Assay results from Queenstake prospect. . . 96 14. Assay resuIts from strati form sulfide­ bearing bed in Hava11ah ...... 98 15. Correlation coefficient matrix for 196 samples of Au, Aq, As, Sb, Hg ...... 110

VI11 1

INTRODUCTION!

PURPOSE

The primary objective of this study was to map the

Northern Mt. Tobin district and each of the mines and prospects within the area to determine the relationship of mineralicat ion and alteration to the major structural features of the area— chief of which is a northwest trending vo1cano-tect on i c graben.

Along the northern margin of this graben mercury, gold, and silver mineralisation are known to exist. 'he gold-mercury geochemical association has been used to guide gold exploration in the Western United States since the discovery of the McLaughlin gold deposit in the Knoxville

Quicksilver district of California in the 197©’s. In addition, recent work oy Buchanan (±930) incicases fcwev e ± => a vertical zonat ion of certain elements in epithermal precious metal deposits and that mercury occurs near the tops of these systems.

The main emphasis of this thesis, therefore, will be to determine if there is a genetic relationship between the mercury, gold, and silver mineralization and to define the major ore controls for the district. GEOGRAPHY

The Northern half of the Mt. Tobin district is in

T.£8-£9N. , R.39-48E. of the Mt. Tobin and Buffalo Springs

15-rninute quadrangles, Pershing County, Nevada, approximately 73 kilometers south of Winnernucca in the

Central Tobin Range (fig.i). Relief exceeds 618 meters within the study area with elevations ranging from 1778 to

£388 meters above sea level.

A County-maintained dirt road in Golconda Canyon provides access to the western part of the study area. An unimproved dirt road up Bushee Creek canyon provides acces to the northern Dart of the district. Both of these roads can be reached by taking Grass Valley road south from

Winnernucca for approximately 73 kilometers. From the east an unimproved dirt road from Buffalo Valley anas at the mouth of Blue Lead canyon at a cattle watering trough. pr here the area must be accessed by foot.

The climate of the Tobin Range is typical of the

northern . Yearly rainfall is

approximately 15 centimeters in the valleys and up to 58

cent irnet ers in the mountains. Rain falls mostly in the

winter, but thunderstorms do occur in the summer months.

The study area often remains under snow from December to

March with average winter temperatures in the 8°to 18°C

range. Average summer temperatures are generally in the £ 3 4

Much of the study area is covered by Piny on pine and juniper, particularly where the underlying rock is andesite on the western slopes of the range. Sagebrush is common in the canyons and level areas where a soil layer is present.

Very little vegetation exists in areas above £10® meters.

Permanent spring-fed streams are present in Golconda,

Blue Lead, and Bushee Creek canyons (plate 1.). This water is potable and is used for irrigation by ranchers in the adjacent valleys.

FIELD METHODS AND LRB PROCEDURES

The study area was mapped during the summer of 1983 at a scale of 1:1£,808. Forty five days were spent surface mapping and sampling and another ten days were spent in underground mapping and sampling. Resistance during underground mapping was provided by Nicor geologists Paul

Dobak and Joe Foster. Standard Brunton compass triangulation methods were used to locate points on the map during surface mapping and Brunton and tape methods used for underground work.

Nicor Minerals provided color aerial photographs at a scale of 1:18,00® which were carried during mapping to

assist in interpretation. R total of 196 samples were

collected for geochemical analyses and 77 for hand specimen

study. Twenty six thin sections and seven polished sections

were made and studied by the author using a Nikon

petrographic and ore microscope. Other laboratory apparatus 5

used include a Norelco powder diffractometer and a fluid

inclusion stage. Samples were analyzed for gold, silver, arsenic and antimony by aqua regia digestion atomic

absorption. Samples containing greater than 1 PPM gold were

cross checked by fire assay methods. Mercury was analyzed

for by flameless atomic absorption. fill samples were

prepared and analyzed by Hunter Mining Laboratory in Sparks,

Nevada.

Pice dates (K-P!r) quoted in this report have been

recalculated where necessary to conform to new IUGS

constants (Dalryrnple, 1979).

PREVIOUS WORK

The Mt. Tobin mine was first mapped by R.J. Roberts and

Pi. E. Granger of the U. S. Geological Survey in 194®. The

author is indebted to the Office of Minerals Exploration

(OME), U. S. Geological Survey, for a copy of the original

geologic and topographic map of the mine which is included

with several modifications as figure 3® in this report.

The first geologic map of the Tobin Range was made by

S. W. Muller, H. G. Ferguson and R.J. Roberts as part of a

USGS regional geologic mapping program of the Sonoma one

degree sheet. The results of this program were published on

the maps of four 30—minute quadrangles (Ferguson and others,

1951a; 1951b; Muller and others, 1951; Ferguson and others,

1952; pl.l). The study area of this thesis lies within two

of these geologic maps— the Mt. Tobin and Mt. Moses quadrangles. This U. S. Geological Survey work was very successful at unraveling the pre-Tertiary structure and stratigraphy of a very complex area and remains to date as the standard by which the geology of northern Nevada is understood.

Two major orogenic events were proposed by Ferguson,

Muller and Roberts to explain the deformation of the

pre—Tertiary units in the Tobin Range. The first was a

Permian east-verqent folding and thrusting event which

deformed strata. The major structural feature

resulting from this event was termed the Golconda thrust.

The second was a event which thrust Paleozoic and

Triassic strata over rocks of the Golconda allochthon. The

major structural feature of this event was termed the Tobin

Thrust.

Two decades later, Burke (1373) mapped a portion of th

Southern Tobin Range just south of the study area of this

thesis. Burke’s mapping was done for the purpose of

re-evaluatinc the pre-Tertiary sedimentary and tectonic

history of the region. He concluded that large—scale

folding and thrusting of the Triassic strata did not exist

and therefore questioned the existence of the Tobin thrust.

Unpublished reconnaissance mapping by Burke (1371) of

the central Tobin Range which includes the area of this

study was used by Johnson (1377) in the compilation of the

Pershing County 1:250,000 scale geologic map. Except for

the unpublished map of the Mt. Tobin Mine by Roberts and 7

Granger mentioned above, this thesis contains the first detailed maps and descriptions of the mines, prospects, and geology of this district.

HISTORY fiND PRODUCTION

The following history of production in the district is derived mainly from Roberts (194c!) and Baily and Pheonix

(1944).

Cinnabar was first discovered in the district prior to

1918, however, the major producing mine— the Mt. Tobin mine— was not discovered until 1929. The original claims were called the Miner’s Dream group and were located by J.D and B.ft Thornton in the northwest 1/4 of Section 1, T.28M. ,

R.39E. The Thorntons, a father and son, intermittently explored the property and in 1938 installed a two—tube retort and commenced production. During the period

1938-1940 they produced a total of 45 flasks of mercury.

Sometime in early 1940 the property was sold to H. W. Gould &

Company who renamed it the Mt. Tobin mine. Gould installed a 22 ton per day rotary furnace and several buildings at a cost of $18,000 and commenced production on June 13, 1940.

The mine operated until March, 1942, when the higher grade surface ores were exhausted. During the time the mine operated, 9568 tons of ore were treated yielding 1073 flasks of mercury. The grade of the ores mined ranged from 2 to j>8

lbs./ton mercury with the average grade being 8.5 lbs./ton. 8

The Last Chance prospect, 1.6 kilometers northwest of the Mt. Tobin mine in the southwest 1/4 of Section 36,

T.29N. , R. 39E. , was located by the Thorntons in 1938. The property was optioned by H. W. Gould &• Company in 1940 and

100 tons of ore were mined, sorted, and treated in the Mt.

Tobin furnace. The grade proved to be too low and no work has been reported on the property since that time.

The North Fork prospect lies one kilometer west of the

Last Chance in the southeast 1/4 of Section 35, T.29N. ,

R.39E., and was located by Walter Low in 1942. Low produced one flask of mercury in 1942 using a retort at the Mt. Tobin property. The prospect was worked again in the late 1960’s and produced an unknown amount of mercury. ft five-tube retort and 12’ X 2’ rotary furnace left after the 1960’s mining were present on the property when the author mapped it in the summer of 1983.

There are numerous other mines and prospects in the study area for which there is no record of production. Two of these mines appear to have produced some ore and are worthy of mention. In the northeast 1/4 of Section 12,

T.28N. , R. 39E. , an exploration tunnel was driven from the bottom of the canyon to explore several quartz—calcite veins which crop out to the north. Underground mapping and sampling revealed gold mineralization in one stope of up to

0.15 oz./ton. The author named this the Rockhouse adit because the remains of a stone building can be found in the canyon below. The mine appears to have been worked in the 9

1910-1930 era.

The Blue Lead mine, at the bottom of Blue Lead Canyon in the southeast 1/4 of Section 32, T.29N. , R. 40E. , produced an unknown but small amount of silver ore from a quartz-barite vein. Silver was discovered in the Jersey

Valley district six miles southeast in the year 1874.

Vanderburg (1936) stated that considerable silver ore was shipped from the Jersey Valley mines between 1880 and 1910.

It is likely that some of this ore came from the Blue Lead mine.

Several valid claim blocks were present in the district

in 1983. Only one was actively being explored: Queenstake

Mining Company of Denver controlled claims covering an altered area of low-grade silver mineralization in Section

5, T.2SN. , R.40E.

GEOLOGIC SETTING

During the early Paleozoic the area of the

lied along the western margin of continental North America

and was the site of deposition of continental shelf

terrigenous detritus and carbonate (Stewart, 1980). m

Mississippian time siliceous oceanic rocks (siliceous

assemblage) were thrust eastward along the Roberts Mountains

thrust over rocks of the continental shelf (carbonate

assemblage) (Speed and Sleep, 1982). Roberts (1951) termed

this event the Antler .

To the west of the Antler orogenic belt, where the

study area of this report lies, eugeosynclinal sedimentation 10 occurred during - time with the deposition of chert, greenstone, argillite and of the Hava11ah sequence. Sometime during the Late Permian to

Early Triassic the siliceous and volcanic rocks of the

Havallah sequence were structurally emplaced along the

Boiconda thrust over the Roberts Mountains allochthon and

its partial cover of late Paleozoic shallow marine strata

(Speed and Sleep, 198E). Silberling and Roberts (ISbE)

termed this event the .

Following the ernolacernent of the Golconda allochthon,

the upper Lower Triassic Koipato Group was deposited in

North-Central Nevada (Stewart, 1980). The Koipato is a

largely volcanic unit consisting of a basal greenstone

(Limerick greenstone) overlain by presumably non-marine

silicic volcanic rocks (Rochester and Weaver rhyolites).

The China Mountain Formation is laterally equivalent to and

interfingers with the uppermost unit of the Koipato, the

Weaver rhyolite, and is found only in the Tobin Range and

northern (Nichols, 1971). The China

Mountain consists of tuffaceous volcanic rocks interbedded

with clastic sedirnentary rocks derived mainly from the

Sonoman h i gh1and.

Following deposition of the Koipato, the area was

covered by carbonate platform deposits of the Lower to Upper

Triassic Star Peak Group, which includes the Natchez Pass

, and a thick monotonous sequence of pelitic and

sandy strata known as the fluid Lang Syne Group (Burke and 11

Silberling, 1374).

The Luning-Fencernaker fold and thrust belt was active in Middle or Late Jurassic and Early time in northwest Nevada, and deformed rocks of the marine province, which includes the Koipato and Star Peak Groups, and rocks of the Golconda allochthon. The primary regionally extensive structures that formed during this folding and thrusting event consist of northeast-trending folds and associated thrust faults (Oldow, 1983).

During the mid to late Tertiary a 11© kilometer long east-west volcano-tectonic depression formed from the

Shoshone Range in the east to the area of this report in the

Tobin Range. About 17 million years ago extensional

faulting commenced and the Basin and Range province began to

form. This faulting is responsible for the present

morphology of the Tobin Range— a typical north—south

trending horst block bound on both sides by deep

alluvium-filled grabens. 12

STRATIGRAPHY AND STRUCTURE

SEDIMENTARY AND VOLCANIC UNITS

Exposed iri the study area are sedimentary and igneous rocks ranging in age from Paleozoic to Recent. The oldest unit that crops out, the Pennsy 1 vanian-Perrnian Hava 11 ah

Sequence, is in fault contact with other units along the northern margin of a volcano-tectonic graben. On plate one, it can be seen that the graben-boundiny fault trends in a northwest direction. Within the graben the Triassic China

Mountain Formation and Natchez Pass limestone crop out.

Tertiary volcanic units include several cooling units of ash flow tuff derived from nearby volcanic centers and andesite and basalt of local origin. Figure two is a composite stratigraphic column of rocks in the study area showing the relationships between each of the units.

Hava11ah Sequence

Introduction and Distribution— The Havallah Sequence crops out over a large area in north-central Nevada but its best exposures are in the Tobin and Sonoma Ranges and in the

Antler Peak quadrangle in Battle Mountain (fig. 3). Early work by Muller, Ferguson, and Roberts (1951a; 1951b) separated the Havallah into two distinct 1ithostratigraphic units— the Havallah and Pumpernickel Formations. The

Pumpernickel was considered to be the older of the two units and was described as consisting of greenstone, chert, argillite, and interbedded limestone and clastic rocks. The ____PALEOZOIC >k ---MESOZOIC >1< CENOZOIC — ^ ERA Finure Carboniferous-Permian-----?1<------T riassic------— Oligocene ------^M io.l? I Quat. I SYST. ______?.______300-900 m.------J t — ? — 4l20rtw4«-----240m.------*|42m.l9ml 30h.5l THICK. 2 . tairpi clm o nrhr M. oi District Tobin Mt. northern column of Stratigraphic m a m a • j

A A S a , n . : c ,< ■ . D .‘. .17.. Xl le ucnoiae bench gravels unconsolidatedOlder Unconsolidated^ recentfsajids jjnd_grayeL§ neiedct fos n fo breedas-Variably flow and flows Andesite-dacite aat flow Basalt el eeoe cnuae rcue e i flows. in set fracture developed conjugate Hell vran y esl-edd hoie tuff rhyolite densely-welded by overlain iil ciod, rcs n aastropods. and brachs crinoids, Visible welded devitrified gray to Tuff-TanCaetano andesite hornblende biotite and pyroxene, colored n dct fos /io fo breccias. w/minor flows flow dacite and hn Mn F.Ahntc uf cet n volcanic and chert tuff, Fm.-ADhanitic Mtn.China biomicrite crystalline Fm.-Gray, Pass Natchez F hoie uf Lcly bet beneath andesite. absent Locally tuff. rhyolite ebe ogoeae dct fos n mnr lime­ and minor flows dacite conglomerate,pebble Havallah sequence-Consists of of sequence-Consists Havallah ihlgc ybl fo Comoton symbols from (1962) RMP 3/85 Lithologic conglomerate and pebble chert ,argiilite, tn. uf ae oal flae. Commonly mercury deposits for foliated. host locally hydrothermallv altered, are Tuffs stone. conglomerate. pebble chert interbedded with hoie porphyry dikes. rhyolite greenstone. and argillite bedded chert, n district. in ietn. uprikl se.Msie n thinly Pumpernickel and assem.-Massive limestone. nrdd y rnt Sok n Koipato-related and Stock byIntruded s Cek ts Tf-o-edd ail tuff lapilli Tuff-Non-welded Mtns. Creek ish aalh se.Msie urzt, hny oedded thinly , assem.-Massive Havallah DESCRIPTION __

__

___ _ _

2 ___ itnt assemblan: distinct

___

___

___

1

3 14

Lunirr^- GOLCONDA Fence^aker THRUST ttft-ust Jj&iPlbelt w m m V p a i

TOBIN) THRUST

GOLCONDA t & m THRUST

Tobin volcano- tectnnic O'aben

TERTIARY AND GRANITIC QUATERNARY INTRUSIVE ROCKS

upper lower plate plcfe

TRIASSIC

PALEOZOIC

u i l ES

Figure 3. Extent of Havallah sequence (upper plate Paleozoic) outcrop in north-central Nevada. The map also shows the original concept of extent and geological relationships of the Golconda thrust fault. In general, both upper-plate and lower-plate Triassic rocks include the Koipato, Star Peak, and Auld Lang Syne Groups; upper plate Paleozoic rocks belong to the Havallah sequence; lower plate Paleo­ zoic rocks comprise all other Paleozoic rocks in the area. Approximate location of study area indicated, and Luning-Fencemaker thrust of Oldow (1983) shown in northwest corner of map. From Silberling (1975). 15

Havallah Formation was mapped as the younger of the two units and was differentiated from the Pumpernickel by the relative absence of greenstone and predominance of chert and quartzite. Contacts between the two formations were interpreted to be thrust faults, normal faults, and in some places depositional. It was also noted that these formations were intensely folded prior to deposition of the overlying Koipato Group.

Silberling and Roberts (1962) lumped the Pumpernickel and Havallah Formations into the Havallah sequence, but continued to recognize the conclusions of earlier workers that the Havallah was a separate 1ithostratigraphic unit of a younger age than the Pumpernickel.

While studying the structural fabric of the Havallah sequence in the ftntler Peak quadrangle, Miller and others

(1982) found that Radiolarian dates indicate age reversals in the Pumpernickel—Havallah succession. Their conclusions were that the Pumpernickel and Havallah were in thrust contact and that these two lithologies do not constitute a simple stratigraphic sequence, but are in fact 1ithotectonic assemblages formed during imbricate thrust faulting of

Sonoman (Permo-Triassic) age.

In summary, current understanding of the Havallah sequence indicates it can be divided into two 1ithotectonic assemblages— the predominantly greenstone Pumpernickel assemblage and predominantly chert-quartzite Havallah

assemblage— and the internal contacts between these 16 assemblages are stacked imbricate thrust faults.

Stratigraphic Description— Two distinct lithologic assemblages were found in the study area. The predominant assemblage, which is referred to on the geologic map (plate

1) as the Havallah, consists of tan to brown rnassive-bedded quartzite, green to black thinly-bedded (£.5-£5 cm.) chert with argillite partings, purple to brown argillite which sometimes grade into phyllites, chert pebble conglomerate, and thinly bedded (£.5-13 cm.) gray silty crystalline

1 imestone.

Quartzite comprises 43 percent of the unit and is commonly laced by cross-cutting quartz and calcite

stringers. The quartzite is most commonly interbedded with

limestone and forms bold outcrops. Excellent exposures of

thin1y—bedded chert are present in the study area, although

beds can rarely be traced for any distance. Chert is almost

always interbedded with argillite and together the two form

about 58 percent of the Havallah. Chert often contains

authigenic pyrite. Thin section studies reveal that the

material mapped as chert has recrystal1ized to form

microquartz, a finely crystalline mosaic with pin-point

extinction, and megaquartz, commonly with authigenic clays

and hydromicas forming between the quartz grains. Thin

sections of argillite reveal ill-sorted particles of quartz

and feldspar in a matrix of authigenic clays and chlorite.

The fissility of the argillite is evidenced by a spaced,

discontinuous alignment of fine-grained minerals and iron 1 oxides (fig.A). Chert pebble conglomerate comprises approximately 1 percent of the area of the Havallah and is interbedded with thinly bedded cherts. They conglomerate consists of well-rounded prolate chert pebbles in a siliceous matrix.

Limestone is more continuous in outcrop than any other lithology in the Havallah, primarily because it is an outcrop former and its gray color is a distinct contrast to the darker colors of other lithologies. Lens-shaped outcrops of thinly bedded, sandy, micritic limestone crop out throughout the unit. The are non-fossi1iferous and crystal1ine. One outcrop, in the northeast 1/4 of Section 31, T. £9IM. , R. 40E. , exhibited well-formed current ripple marks which indicated the section was upright.

The Pumpernickel assemblage consists of massive and thinly bedded chert with interbedded argillite and greenstone. The Pumpernickel does not commonly form bold outcrops and was mapped mainly on the basis of float. The

Pumpernickel cherts are similar in composition to Havallah cherts, the major difference being the lack of argillite

partings in some beds, which result in massive beds of chert

up to 3 meters thick. Approximately 10 percent of the

Pumpernickel is composed of green, chloritic greenstone

which forms oblate pillows with "eyes" of white chalcedony

filling 6 to 1£ millimeter vesicles. Syngenetic pyrite is

found within the greenstone or in beds adjacent to the 18

Figure 4. Photomicrograph of Havallah argillite showing SI spaced discontinuous cleavage. The cleavage domains are spaced every 0.5 mm and consist of quartz, il'iite and opaque oxides. Microlithons are composed of quartz, illite, aibite and opaque oxides. Voids at botton are oxidized pyrite of possible syngenetic origin. Plane light, E-W field of view is 1.4£ mm. 19 greenstone.

Steep slopes with deep incised valleys develop in rocks of the Havallah Sequence. Very little vegetation grows on the red, hernat ite-rich soils. Particularly noticeable is the absence of Pinyon pine and juniper which are common to other rock types in the area.

No attempt was made to measure the thickness of

Havallah Sequence. The base of the Havallah, the Solconda

Thrust, is nowhere exposed in the area and bedding can rarely be followed for any distance. Late Mississippian to

Early Permian ages have been obtained by Miller and others

(198£) from radiolarians in the Antler Peak area.

Structure— The structural fabric of the Havallah sequence in other areas has been described in detail by other authors

(Silberling and Roberts, 1962; Miller and others, 198£;

Snyder and Brueckner, 1983). The purpose of this section will be to describe the structural fabric of the Havallah exposed in the map area and compare this with the data obtained by other authors.

Thinly bedded cherts proved to be the only lithology

where fold styles could be studied and although folds were

not discernible in enclosing argillites or limestones, many

bedding attitudes were taken from these rock types. This

structural data was used to plot Pi diagrams for bedding.

In addition, several plots were also made by dividing the

Havallah into local structural domains in order to study

individual folds. Four phases of deformation (D1-D4) were 20 documented by the structural fabric of the Hava11ah exposed in the study area:

Dl. The earliest structures formed in the Havallah are bedding-parallel cleavages (Si) in argillites which are sometimes poorly developed in cherts. In hand specimen the argillites have a continuous cleavage; however, in thin section the cleavage domains are formed by spaced discontinuous alignment of hydromicas and are spaced every

0.50 mm (fig. 4). Another early feature, which is probably of diagenetic origin is Monroe stucture, which forms from crystallization of opal to cristobalite during compaction and dewatering (Snyder and Brueckner, 1984). Veinlets of megaquartz which commonly contain diagenetic pyrite probably formed in the argillites at this stage.

D£. Isoclinal F£ folds fold bedding and the SI bedding-parallel cleavages. These isoclinal folds have northeast to northwest trending axial planes that dip parallel to local bedding. These folds are isoclinal reclined plunging similar folds with amplitudes up to o meters and wavelengths up to 1 meter. Figures Sab are

photos of two of these folds in thinly bedded cherts.

D3. Open to tight upright and inclined plunging asymmetric

folds have folded the F£ isoclines. These ■J folds have

considerably larger wavelengths and amplitudes up to 13

meters— than the F£ isoclines. The axial planes of these

folds generally strike north—south and dip to the 21

Figure 5b,

Figures 5. 'isoclinal F£ fold in thinly beaded Havallah chert. Bedding in the chert is the result of argillite part ings. west— indicating they are east-vergent. Another D3 structure that may have formed during this time as a weak crenulation of the Si cleavage in argillites. This can be seen in figure fa where an S3(?) crenulation has deformed Si cleavage and a Dl (?) stage quarts veinlet.

D4-. Large anticlines and synclines (F4) evidence a possible fourth stage of deformation. These folds were not clearly evident in the field due to their large wavelengths— up to l.S kilometers— but were noticed when bedding attitudes were plotted on Pi diagrams for local structural domains (fig.

7). All of these F4 folds have north to northeast-trending axial surfaces. Resistant , cherts, and

limestones often form the tops of ridges and the less resistant argillites the eroded, talus-covered valley areas. Repetition of certain stratigraphic sequences of the more resistant lithologies which are dipping in a direction

consistent with folding were the criteria used to plot these

folds on the geologic map.

Figure 8 is a Pi diagram of bedding attitudes in the

Hava11ah and figure 9 is the corresponding contoured

diagram. Although there is a significant amount of

scatter— presumably due to the Did—D3 deformat ional

structures— it does appear that there are two girdles, eacn

having northeast—trending axial planes but with higelines

plunging in different directions. This is consistent with

the doubly-plunging folds that were mapped. 23

Figure 6. Photomicrograph pf argillite showing SI s paced cleavage and Dl stage quartz veinlet deformed by an S3 crenulation. Plane light, E-W field of view is 1.42 mm. 24 25 Figure 9. Contour diaqram of a 5,9% per 1% area bedding attitudes recorded in Havallah Sequence. Kalsbeek ne 4,7% per 1% area used. Based on 68 measurements. 3.5% per 1% area o 2.4% ner 1% area 27

Due to the relative paucity of outcrop in some areas arid large wavelengths of these F4 folds, their style cannot be described in much detail. In general, they have axial planes that strike from N. 10 E. to N. 50 E., dip near vertically and have hingelines that plunge from 30 to 40 degrees.

Discussion of Structural Chronology— The D1-D3 structures in the study area correlate with D1-D3 structures documented by

Snyder and Brueckner (1983) in exposures elsewhere in the

Tobin and Sonoma Ranges and Battle Mountain. The major difference is that these authors do not document the existence of major folds such as the F4 folds mapped in the study area, but instead attribute much of the deformation in the Havallah to imbricate thrust faulting. According to these authors the SI bedding plane foliation, F2 isoclines and F3 open to tight folds represent a continuous deformation under low temperature and pressure conditions which was occurring at the same time that other parts of the

Havallah were being deposited. Bedding plane thrusts which are documented by paleontological evidence near the sole thrust in the Antler Peak quadrangle presumably occurred during the D£!—D3 stages. Thrusts of large displacement,

such as those that separate Pumpernickel from Havallah-type

lithologies, represent the culmination of the Sonoma Orogeny

and emplacement of the Havallah sequence onto continental

North America. 28

The last episode of folding

China Mountain Formation

Introduction and Distribution— The China Mountain Formation was first named by Ferguson and others (135'c!) for exposures of conglomerate, sandstone, and impure dolomite found along the west side of China Mountain in the northern Tobin

Range. Ferguson considered the formation to be a thinner, more coarsely clastic equivalent of the Tobin and Dixie

Valley Formations found in the southern Tobin Range.

Because of the presence of volcaniclastic strata within it, Nichols (1971) considered the China Mountain to be part of the predominantly volcanic Koipato Group. No fossils have been found within the unit, but it is no younger than

late Early Triassic since it underlies the fossi1iferous

Tobin Formation in the southern Tobin Range. fit its type

locality the China Mountain is 400 feet thick.

Stratigraphic Description— The section of China Mountain 29 exposed in the study area consists of 75 percent aphanitic white to gray tuff, £0 percent chert and volcanic pebble conglomerate, 4 percent dacitic flows and <1 percent gray crystalline limestone.

Aphanitic tuffs originally consisted of quartz and

feldspar crystal fragments in a matrix of lapilli and ash

(fig. 10). Lithic fragments of chert and greenstone are commonly also present. Most of the original constituents have been altered to quartz and clay. Some of these tuffs

exibit a well-developed spaced bedding plane foliation which

gives it a "banded" appearance. Zircon is an accessory

mineral. The tuff does not form bold outcrops and because

of its white, earthy appearance can often be mistaken for

hydrothermally altered rock.

Chert and volcanic pebble conglomerate form bold

outcrops and are the most reliable lithologies for the

measurement of bedding attitudes. These pebble

conglomerates consist of poorly sorted, subangular,

fine-grained to cobble size fragments of chert and

intermediate volcanic rocks in a matrix of clastic fragments

and microquartz (fig. 11). Bedding thicknesses range from 3

to & meters and beds form bold, si 1iceous—looking outcrops

with a wide variation of colors. Thin section studies reveal

the conglomerates are rnatrix-supported, the pebbles are

bladed, and rnicrosty lol ites are present along pebble

boundaries. The conglomerates are not foliated and occur as

lenses interbedded with the aphanitic tuffs. 0 3 igure 10. igure 10. Photomicrograph of unaltered China Mtn. ormation aphanitic tuff. Rock has recrystal1ized to include zircon. Crossed polars, E-W field of view is 1.4£ believed to be relict pumice lapilli. Minor constituents mm. U Ll cryptocrystalline quartz and clay. Finer grained areas 31

Figure 11. Photomicrograph of China Mtn. Formation chert and volcanic peboie conglomerate. Conists of poorly—sorted subangular chert (ch) and volcanic (v) pebbles in a matrik of polycrystal1ine quarts grains and illite. Yellow brown mineral in center is siderite. Plane light, E-kJ field of view 1.4E mm. 32

One dacitic flow unit was identified within the China

Mountain in the Northwest 1/4 of Section 1, T.£8N., R. 39E.

The rock is a porphyritic volcanic flow which flowed over local bedding; it contains altered phenocrysts of K-feldspar and biotite. The K-feldspar has been mostly altered to a peculiar lime-green illite which gives outcrops of the mostly white to gray flow a distinct appearance. In thin section it can be seen that the rock has been hydrothermally altered and consists of quartz, illite, sericite Replacing biotite), and pyrite.

A 6 meter thick bed of gray, non-fossi1iferous crystalline limestone was mapped as part of the formation in the southeast 1/4 of Section 1, T. £SN. , R39E.

Much of the China Mountain Formation in the study area is fractured, faulted and hydrothermally altered, and as such does not lend itself to detailed stratigraphic descriptions. The formation appears white to tan in aerial photographs, develops a poor soil layer and supports some juniper growth. Total exposed thickness of the unit in this area is estimated at 300 to 900 meters, and it is in fault contact with the Havallah sequence along the northern margin of the volcano-tectonic graben. The China Mountain is the host unit for all of the mercury deposits in the study area.

Structure— Three phases of deformation are evidenced by the structural fabric of the China Mountain Formation: Dl. A locally-developed SI bedding plane foliation is present in China Mountain tuffs. In the classification of foliations by Borradaile (1982), this would be described as a spaced cleavage with parallel cleavage surfaces. Figure l£a is a thin section of the foliated tuff. The cleavage domains are spaced every 1 millimeter and consist of hydromicas and clay. The microlithons are composed of non-oriented quartz, clay and albite.

D£. Isoclinal F£ folds have folded the SI bedding plane foliation. These folds have axial planes parallel to the Si foliations and wavelengths of less than 1 meter. They are best seen in the foliated tuffs but occasionally can be recognized in non-foliated tuffs, and are not present in the pebble conglomerate. Figure l£b is a photograph of one of these folds.

D3. Upright and inclined tight to open asymmetric parallel folds with wavelengths up to 15 meters are the most common folds seen in the China Mountain Formation. These F3 structures fold SI foliations and F£ isoclines (fig 13).

The best exposure of these folds is in the northwest 1/4 of

Section 1£, T. £8N. , R.39E.; a convolute style of folding is present at this location. Field study of these F3 folds reveals that they they have north-trending axial surfaces which dip to the east.

Figure 14 is a Pi diagram of bedding and foliation attitudes recorded from the China Mountain and figure 15 is Figure l£a. Photomicrograph of spaced continuous cleavage in China Mtn. Formation tuff. fill original textures have been obliterated. Cleavage domains are composed of oriented quartz, illite and albite. Quartz and albite comprise the microlitons. Crossed polars, E-W field of view is 1.42 mm.

Figure l£b. Isoclinal F£ fold in China Mountain Formation tuff folding SI bedding-parallel cleavage. 35 36

the corresponding contoured diagram. One possible

interpretation of this diagram is that the F3 folds have

north-trending, east-dipping axial planes and nearly

horizontal hinge lines. Field observations of F3 folds

indicate this is probably the correct interpretation.

Discussion of Structural Chronology— fts with the rocks of

the Havaliah sequence, the lack of regional metamorphism

indicates these structures formed in a low temperature and

low pressure regime. The SI foliation and F£ isoclines are

present only locally in the tuffs; F3 folds appear to be

more pervasive in distribution and more likely represent

regionally extensive stresses.

The location of the China Mountain Formation along the

margin of a Tertiary volcano-tectonic graben casts some

doubt on the validity of using fold attitudes in trying to

unravel the Mesozoic tectonics of the area. The unit has

been faulted into juxtaposition with the Havaliah— and

presumably some rotation from its original position has

occurred.

' Relationship of Havaliah to China Mountain Structures The

relationship between structures in the China Mountain

Formation and Havaliah sequence are not clearly understood.

This is in part due to the fact that the China Mountain has

been faulted from its original pre—graben position; this

effectively eliminates the use of axial plane orientations

to correlate folds. 37 38 39

The D1 to D3 structures in the Hava11ah have been assigned an age of Sonoman or Permian to Early Triassic by

Snyder and Brueckner (1983). Johnson (1977) stated that rocks of the Koipato Group, which include the China Mountain

Formation, were deposited unconforrnably on Paleozoic rocks of the Havallah sequence. Since pebble conglomerates in the

China Mountain Formation contain chert derived from the

Sonoman highland (Johnson, 1977), it is concluded that the

China Mountain was not deposited until the Havallah was already emplaced along the Golconda thrust. Therefore, the

D1-D3 structures in the Havallah, if they are Sonoman, cannot be correlated with D1-D3 structures in the China

Mountain Format ion.

Oldow (1983) has documented a Middle or Late Jurassic to Early Cretaceous event which deformed Mesozoic rocks in northwestern Nevada, and refers to it as the

Luning-Fencemaker fold and thrust belt. The major features of this event are northeast—trending folds and associated thrust faults (fig. 35. North to northeast-trending F4

folds in the Havallah could be correlative with the northeast—trending folds Oldow described in Mesozoic rocks

in the Humboldt and East Ranges. The west—vergent Do folds

in the China Mountain Formation could likewise oe assigned to Luning-^encemaker deformation because, according to

Oldow, west—vergent folds and thrusts to the north in the

Sonoma Range (fig. 3) are part of this fold and thrust

belt. 40

Assuming the China Mountain has not rotated to any degree, the west-vergent folds could be correlative with oost-Bonoman west-vergent folds in the Havallah in the

Antler Peak area (Snyder and Brueckner, 1983) and in

Triassic units in the (Silberling, 1975). In the Sonoma Range the Clear Creek Thrust displaces Triassic strata in a westward direction. Silberling (1975) has established the age of this thrust as early to middle

Triassic.

Natchez Pass Formation

Introduction and Distribution— The Natchez Pass Formation was originally defined in the Mt. Tobin quadrangle by

Ferguson and others (1951a) for exposures at Natchez Pass in the East Range. The formation consists of massive carbonate rock with subordinate units of mafic volcanic rocks, terrigenous clastic rocks, and impure limestones.

Silberling and Wallace (1969) recognized the Natchez Pass

Formation in the Humboldt Range and assigned it to the Star

Peak Group of King (1878). The formation attains a total thickness of 760 meters in the Humboldt Range and has been

assioned an age of Middle to Late Triassic (Silberling and

Wallace, 1969).

Stratigraphic Description— An outcrop of Natchez Pass

Formation approximately 350 by 150 meters occurs m the

southernmost part of the study area. Here, the formation Figure 16. Photomicrograph of Natchez Pass Formation biornicrite showing fossil shell fragments. S-shaped fragment is cross section of brachiopod plicae. Other fragments include crinoid ossicles and gastropods. Crossed polars, E-W field of view is ■!. 42 mm. 42 consists of gray, partially crystallized fossiliferous limestone with visible crinoid ossicles replaced by chert.

The limestone is interbedded with lenses of chert pebble conglomerate for the extent of its outcrop. In thin section the limestone is a biomicrite containing greater than 50 percent shell fragments of gastropods, crinoids and brachiopods (fig. 16). This description matches that of

Burke (1973) for exposures of Natchez Pass just south of the study area.

The eastern contact of the Natchez Pass and Caetano tuff is a fault which is evidenced by outcrops of silicified limestone or "". This jasperoid extends out of the study area to the south for 1.6 kilometers where it is host to the Needle Peak fluorite prospect (Papke, 1975). No measurement of the thickness of the unit was attempted due to its limited outcrop.

Caetano Tuff

Introduction and Distribution— Originally named by Gilluly and Masursky (1965) for exposures in the northern Toiyabe

Range, the Caetano consists of welded ash flows and water-lain tuffs which reach a maximum thickness of £500 meters in a volcano-tectonic graben located 50 kilometers to the east of the Tobins in the Shoshone Range. ft potassium-argon determination on sanidine from the welded tuff yielded an age of 34.4 m.y. (McKee and others, 1971) volcano-tectonic graben. The unit consists of tan to gray welded tuff composed of £0 percent quarts, 15 percent sanidine, 10 percent volcanic lithic fragments, 1 percent biotite and 55 percent white earthy groundrnass. Thin section studies reveal that the groundrnass consists of devitrified ash shards and that some of the sanidine has been altered to clay. The Gaetano is highly fractured, often having limonite or quartz veinlets filling these fractures, and exhibits liesegang banding from weathering.

One cooling unit is present which is approximately 1£0 meters thick. The unit was only locally deposited within the volcano-tectonic graberi as indicated by its absence beneath the overlying andesite in some areas.

Structure— The Gaetano has been tilted steeply by complex normal faulting due to subsidence of the volcano-tectonic graben to the southwest. The maximum dip attitude recorded was 75 degrees.

Andesite—Dacite Flows and Flow Breccias

Introduction and Distribution— 'JncontormabIy overlying the

Gaetano tuff is an andesite—dacite unit first mapped by

Burke (1373) for exposures in the southern Tobin Range. The unit reaches a maximum thickness of £40 meters in the volcano—tectonic trough south of the study area where it has been described as consisting of lenticular flows, 44 agglomerates and a basal tuff unit. McKee and others (1971) obtained a potassiurn-argon date of 32.8 m. y. from sanidine in the basal tuff unit.

Stratigraphic Description— Andesite-dacite flows and flow breccias comprise the thickest volcanic unit found in the study area. Approximately 95 percent of the unit consists of pyroxene, hornblende and biotite andesite; dacite comprises 3 perc&rit and flow breccias 2 percent.

The andesites are variably colored in shades of gray, pink, green and brown and exhibit both fresh and highly weathered outcrops. A thin section from a relatively fresh outcrop shows 3G percent plagioclase of An40 (andesine) composition, 5 percent pyroxene (augite), 5 percent opaque oxides, 5 percent volcanic lithic fragments and 55 percent dark felty groundmass composed primarily of plagioclase.

The plagioclase phenocrysts exibit oscillatory extinction with both normal and reverse zoning.

Pinyon pine and juniper commonly grow best on soils developed on andesite. The unit forms more gentle, rolling topography than other units in the area and is found only within the volcano—tectonic graben where it thickens toward the center of the graben to the southwest. Total thickness of the unit is estimated at 240 meters.

Structure— Attitudes were taken at what was believed to be the bases of several of the flows. Assuming horizontal emplacement, these attitudes indicate the unit has been 45 tilted up to 63 degrees from horizontal; this is due to complex normal faulting from subsidence of the graben. ft well-developed set of conjugate cooling joints is present in the flow rocks.

Fish Creek Mountains Tuff

Introduction and Distribution— The Fish Creek Mountains tuff was erupted from a volcanic center in the Fish Creek

Mountains approximately 16 kilometers east of the study area. The unit fills a 64 to 32 kilometer diameter caldera with a tuff prism approximately 315 meters thick at its center (McKee, 137®). One single, probably composite ash flow sheet composed of densely welded crystal tuff locally with a thin base of non—welded lithic and lapilli tuff, makes up the unit in the Fish Creek Mountains. McKee (137®) described the unit as light gray to pink, crystal—rich densely welded rhyolitic ash flow tuff composed of about equal amounts of smoky quartz and sanidine and very few mafic phenocrysts. The ash flow spread only a short distance from its source and is found only in the Fish Creek

Mountains and southern Tobin Range.

R fission track date on zircon of 24.6+1.3 m.y. (early

Miocene) was obtained by McKee (1371). Outside of the Fish

Creek Mountains Caldera the tuff unit is rarely more than 3® meters thick.

Stratigraphic Description— Remnants of one cooling unit of the Fish Creek Mountains tuff is present in the study area. It consists of 9 to 12 meters of tan non-welded lithic and lapilli tuff overlain by 3 to 30 meters of pink to red densely welded crystal tuff. The unit is thickest nearest its source in the southeast part of the map area. The non-welded tuff contains rhyolite, andesite, silicified plant fragments and pumice lapilli in an ash matrix. It commonly has weathered to clay and is not an outcrop former. The densely welded tuff is quite conspicuous in that it forms bold outcrops of dense, blocky, glassy tuff with eutaxitic structures. Lithologically it consists of £5 percent sanidine, £5 percent quarts, 5 percent squashed pumice fragments, £ percent oxidized biotite, 1 percent twinned albite and 4£ percent matrix of glassy ash shards

(fig. 17). A sharp contact exists between the densely welded and non-welded members.

Structure— The tuff dips about 10 degrees to the southwest towards the center of the volcano—tectonic graben and unconformab1y over1ies the China Mountain, andesite—dacite and Havallah rocks.

Basalt

Introduction and Distribut ion— Burke (1973) mapped one srnax basalt flow overlying -Pliocene sediments 1.6 kilometers southeast of the study area. Several olivine basalt flows, cinder cones and dikes are found along the range front in the Fish Creek Mountains 16 kilometers to th east. Mo other or Pliocene to Recent extrusive Figure 17. Photomicrograph of Fish Creek Mountains densely welded rhyolite tuff. The tuff is composed of sanidme (s) , quartz

Figure IS. Pyroxene basalt flow. ftugite phenocrysts in center surrounded by a trachytic qroundrnass of labradorite, opaque oxides and black glassy groundrnass. Plane light, £-W field of view is 1.4£ mm. 48 rocks occur in the nearby area.

Stratigraphic Description— The unit consists of fresh black basalt composed of laths of plagioclase in a black glassy groundmass. In thin section it appears to be a tholeiitic basalt containing 50 percent plagioclase of Rn50

(Labradorite) composition, 8 percent clinopyroxene (augite),

£ percent opaque oxides and 40 percent glassy groundmass

(fig. 13). The rock has a trachytic texture indicating it was a flow.

The flow reaches its maximum thickness of 9 meters near the fault marking the margin of the volcano-tectonic graben

and thins to only several meters thick to the south toward the canter of the graben. This fact, together with its

localized areal distribution indicate the basalt is of local

origin and may be the extrusive equivalent of several

diabase dikes to the north in the map area.

Structure— Except where the flow is intersected by a fault

along the graben margin, the overali dip appears to be 10

degrees south— toward the center of the graben. This dip

probably represents original topography in that the basalt

flowed south. Needle Peak btock

Descript ion— ft medium-grained hypidiomorphic-granular biotite granite stock intrudes rocks of the Havallah

Sequence in the south-central part of the map area. The granite is composed of 65 percent feldspar, 30 percent quartz, 5 percent biotite and accessory zircon. Most of the feldspar has been altered to clay but the relict form of the ohenocrysts indicate they were probably orthoclase. Biotite phenocrysts have been pseudomorphically replaced by sericite. Pi contact met amorphic aureole 15 to 30 centimeters wide is intermittently present along the contact of the granite with the Havallah Sequence. Hornfelsic rock, epidote, and tremolite are present in this zone.

Structure— Dikes of Koipato rhyolite porphyry intrude the

granite in several places, indicating the age of the granite

to be pre—Koipato or pre—late Early Triassic. Since the

Havallah has been assigned an age of Late Mississippian to

Permian, the granite is probably Early Triassic. Triassic

granite and leucogranite has been mapped in the Granite

Mountain area £0 kilometers to the east in the East Range

(Johnson, 1977), and in the Humboldt Range (Wallace and

Tat lock, I960). In the East Range the granite intrudes

rocks of the Havallah sequence and Koipato Group. Wallace

and Tat lock (I960) believe the leucogranite in the Humboldt

Range to be the intrusive equivalent of rocks of the Koipato 50

Group. It is possible that the Needle Peak stock is an intrusive related to the Koipato Group but further work is needed to substantiate this conclusion.

Dikes and Sills Related to Koipato Group

Description— Gray to light orange rhyolite porphyry dikes, sills and pipe-like bodies intrude rocks of the Havallah sequence and the Needle Peak Stock. These intrusive rocks occur throughout the Havallah and range from 3 meters to several hundred meters in width. fit several locations the outcrops could be followed for several hundred meters beiove being lost in co11uviurn.

These dikes and sills form blocky, angular, resistant outcrops with phenocrysts of quartz and feldspar in a leucocratic groundrnass. In thin section the rock is composed of 4® percent altered feldspar phenocrysts up to 6 millimeters in diameter, 1® percent quartz phenocrysts up to

£ millimeters in diameter, 5 percent altered biotite and 45 percent clay-altered groundrnass (fig. 13). The majority of the feldspar appears to have been K—feldspar, which has now been altered to clay or in some cases replaced by twinned met amorphic albite. Primary biotite phenocrysts have been oxidized and replaced by sericite.

The contacts of these dikes and sills with Havallah rock is marked by i to £ inches of 1 irnonite-irnpregnated

country rock. Numerous bodies of rhyolite porphyry and leucogranite

in the Humboldt Range have been found to represent feeders 51

Figure 19. Photomicrograph of Koipato—related rhyuxite porphyry. Relict phenocryst of K—feldpar (k) at left h<*e been replaced by sericite, and biotite phenocryst (b) psuedomorphically replaced by sericioe. The qroundrnass is composed of cryptocrystal 1ine quarts and clay. The only original mineral constituents are quarts (q) phenocrysts and accessory sircon (not visible). trussed polars, E—W field of view is 1.42 mm. 52 for or to be intrusive relatives of the volcanic rocks of the Triassic Koipato Group. fis described by Wallace (1960), the rhyolite porphyry contains small ( <£ mm) phenocrysts of quartz and larger (1-5 mm) phenocrysts of K-feidspar, embedded in a vitreous appearing groundrnass.

Ferguson and others (1951b) mapped dikes of rhyolite porphyry intruding the Havallah Sequence in the Sonoma

Range. They noted also that these dikes in part follow folded thrust planes but at the time believed them to be of

Tertiary age. It is likely that these were Koipato-related feeders deformed along Mesozoic thrust faults.

The description of Ferguson and others for Koipato feeders in the Humboldt Range closely matches the rhyolite porphyry intrusions in the study area. The fact thai, whey do not intrude any of the Tertiary units and that they have undernone some low—grade metamorphism, producing twinned metamorphic albite, is solid evidence that they are not of

Tertiary age.

Diabase Dikes

Description— Three diabase dikes were mapped in the study area. Two of these crop out m an area of alteration and low-grade silver mineralization in the Havallah in the northeast 1/4 of Section b, T.'dSN. , R. 40E. , and one cuts across a fault block of the Needle PeaK Stock. Tne dikes are probably the intrusive relatives of the basalt fiow described earlier. 53

These dikes are brown to green, fine-grained and have

13 to £5 millimeter clay aureoles along contacts with other units. The rock consists of 60 percent plagioclase of Pln55

(Labradorite) composition, 30 percent clinopyroxene

(pigeonite), and 10 percent opaque oxides. They are holocrystal1ine with a subophitic texture. fill three of the dikes mapped have been partly hydrothermally altered along fractures. 54

TOBIN VOLCANO-TECTONIC GRABEN

Introduction— The principal structural feature of the study area is a northwest trending volcano-tectonic graben. The map area covers part of the northern margin of the graben and extends 1.6 kilometers southwest towards its center.

This graben was first described by Burke and McKee

(1973) as part of a 110 kilometer long volcanic depression that spans from the Cortez area in Lander County to the East

Range in Pershing County. Figure c!0 is Stewart and

Carlson’s (1976) map of this volcano-tectonic depression.

Faultinq along the northern edge of this graben is the primary structural control for Tertiary mineralization in the northern half of the Mt. Tobin district.

Structure— The margin of the graben is defined by northwest trending faults that have juxtaposed the Havaliah sequence

against China Mountain Formation and rocks.

Attitudes from slickersides found along several of these

faults indicate the faults dip from 50 to 60 degrees to the

southwest. Plate £ consists of three cross-sect ions across

the graben margin which show an en echelon pattern of

northwest trending faults. The major fault separating

Havaliah from China Mountain is characterized by a zone of

fault gouge from 3 to 15 meters wide which is highly iron

stained; springs occur along this fault in the canyon

areas.

Subsidence along the graben-bounding fault has produced

two structural features in rocks of the Havaliah sequence. Figure 20. East-west volcano-tectonic depression in north-central Nevada. Depression on the right believed to be source area for Caetano tuff. Depression on the left is Tobin volcano-tectonic graben. Original form of the 110 kilometer long feature has been obscured by formation of the Fish Creek Mountains Caldera and Basin and Range faulting. From Stewart and Carlson (1976). 56

The most prominent of these are low-angle normal faults that are marked by 1.5 to 3 meter thick zones of resistant, brecciated, silicified rock with wel1-developed siiekensides. Attitudes of these slickensides indicate movement down to the southwest coincident with that of the

graben. The area mapped as the Pumpernickel assemblage on the geologic map (plate 1.) is the hanging wall of this

Tertiary fault. Several outliers of the brecciated base of

the hanging wall are present to the north and east of the

main hanging wall fault block.

These low-angle faults were probably active during the

incipient formation of the graben, and most of the hanging

wall has since been eroded.

High—angle normal faults of minor displacement which

are sub-parallel to the major graben-margin fault are also

present in the Havailah.

The terrane within the graben is cut by many steep

faults of varying displacements. i-aults and fractures in

the China Mountain Formation are numerous and some have

provided the channelways for Tertiary hydrothermal fluids.

These faults are often marked at the surface by resistant

ribs of silicified rock.

Volcanic rocks were erupted upon the China Mountain

Formation south of its main area of outcrop along the graben

margin in the western half of the study area. these

volcanic units thicken toward the center i_n the graben whsr e

they attain a maximum thickness of approximately 61® meters 57

(Burke arid McKee, 1973).

Faulting and rejuvenation of topography occurred during subsidence of the graben. This is indicated by the fact that the older Gaetano tuff is not everywhere present beneath the andesite. In general, the dip angles of the volcanic units

increase with age, suggesting that faulting occurred during voleanism. The oldest Tertiary unit, the Gaetano tuff, dips

up to 75 degrees. The overlying andesite attains a maximum dip of 63 degrees, and the Fish Creek Mountains tuff has a

maximum measured dip of 10 degrees. The youngest volcanic

unit, the basalt, is very nearly in the same position as

when it was extruded. The ages of these volcanic units and

their relative dip angles provide data necessary to

reconstruct the tectonic history of the margin of the

vo1cano-tectonic graben.

ft general lack of relief in the middle Tertiary is

demonstrated by widespread distribution of individual ash

flow sheets and uniform stratigraphic sequences of ash flow

units from area to area in central Nevada (Stewart, 1980).

It is likely that the earliest subsidence of the graben

occurred some time prior to eruption of the baetano tuii as

the Gaetano is found only within the graben. ihe Caetano

originated from a source area in a volcano—tectonic graben

in the Shoshone Range 48 kilometers to the east according to

Gilluly and Masursky (1965). This probably formed a

continuation of the Tobin volcano—tectonic graben. ihis

relationship places a minimum age on the inception of the 58 graben of around 34 rn. y.

Continued subsidence of the graben led to faulting and tilting of the Mesozoic units and Caetano tuff. The andesite that overlies the Caetano reaches its maximum thickness in the Tobin volcano-tectonic graben (Burke, 1973) and was most likely extruded from a source within it. It is not found in the adjacent mountain ranges or in the volcano—tectonic graben in the Shoshone Ranee. Continued subsidence is evidenced by faulting and tilting of the o£ rn. y. old andesite. One cooling unit of the £4 rn. y. old Tish

Creek Mountains tuff was deposited in the graben. The distribution of outcrop of this ash flow unit indicates j.t was deposited nearly everywhere on what must have been a relatively flat topography that sloped gently to the east.

Pi small outcrop of the tuff overlying rocks of the Havallan

Sequence in the southeast 1/4 of Section S, T. £8N. , R.48E.,

gives some indication of the amount of subsidence in ^he

graben since the tuff was deposited. This small, in—place

outcrop lies 158 meters topographically higher than the

nearest outcrop of tuff within the graben. It is reasonable

to assume that the two outcrops were once connected and

later separated by displacement along the graben fault.

North-south Basin and Range faulting marked the end or

subsidence and obscured the relationship between the Tobin

volcano-tectonic graben and other volcanic depressions along

the 118 kilometer trend. In summary, the Tobin volcano-tectonic graben began to form sometime prior to or during the early Oligocene.

Maximum fault movement and subsidence occurred concurrently with extrusion and filling of the graben with an £40 meter thick section of locally extruded andesite. From the early

Miocene to the beginning of Basin and Range faulting at about 17 m.y. ago (Stewart, 1980), the graben subsided another 150 meters.

a total thickness for the volcanic units filling the graben is 400 meters. This would be the minimum amount of vertical subsidence in the graben; the actual amount could be significantly greater because an unknown thickness or

Triassic strata was downdropped beneath the graben, ano an unknown amount of erosion has reduced the thicknesses or units within the graben. 60

ECONOMIC GEOLOGY

INTRODUCTORY STATEMENT

Mineralization in the study area can be divided into:

syngenetic stratiform silver in the Havaliah sequence. The first type is structurally controlled along faults and fractures near the margin of the Tobin volcano-tectonic graben; the second type is found in Havaliah chert and argillite and is volcanogenic i n or i g i n.

TERTIARY EPITHERMAL MERCURY-GOLD-SILVER MINERALIZATION

Gold-Bearing Veins

Two types of veins were found to contain gold. One consists of gray to white pyritic quartz which crups out west of Needle Peak in the Needle Peak stock (plate 1)-

These veins transect the stock and parallel Koipato—related dikes. Both coarse and fine disseminated pyrite are present in the quartz, and boxworks of limonite after pyrite have formed at the surface. The veins appear to have formed along a zone of structural weakness at the Koipato-granite contact; vein thicknesses range from 0.3 to 1 meter and they pinch and swell along strike (figure c!l).

Several prospect tunnels and pits explore the veins, but it does not appear that any ore was produced. Table 1

lists the assay results from chip samples taken along these 61

Flours £1. Outcrop of gold-bearing quarts vein west or Meed1 e Peak at sample location 1884-0 (see plate cJ. !ne quarts veins are up to 1 meter wide, contain approximately 10 percent pyrite and occur adjacent to Koipato diKes. h caved adit lies just beneath this outcrop. 62 veins and plate 3 shows the location of these samples.

Table i. Assay results from samples of pyr itic quartz veins west of Needle Peak. Minus sign indicates less than detection limit. All values are in parts per million (PPM).

Sample =8 flu fig As Sb Hg 13839 6. 50 1.9 1£ -1 . 17 1S840 0. 10 1.8 810 170 . i£5 13347 0. 40 6» o 55 59 -78 19004 0. 03 1-6 190 35 a UjQ

Figure ££ shows the veins contain pyrite in a quarts gangue, and no gold can be seen.

Rockhouse adit— The second type of gold bearing structure consists of veins of quartz pseudomorphous after' calcite found in the area of the Rockhouse adit (plate 1). hi pure

£3, an underground map of the geology and workings of this mine, shows that the workings explore several of these veins which nave formed along north—south to N. 60t.. striking fractures in China Mtn. tuff and pebble conglomerate. The veins are 5 to 10 centimeters wide on the surface above the workings and widen to a maximum of 1 meter underground. ihe surface exposure of the veins is a calcite boxwork where quartz has pseudomorohically replaced the calcite.

Underground in the Rockhouse adit the same veins contain minor amounts of gold. Table £ lists the assay results for samples taken underground at the Rockhouse adit. 63

Figure ££» Photomicrograph of polished section of auriferous quartz vein at sample location 18839. The rock consists of pyrite along late stage fractures in white "bull" quartz. A sample of this rock contained 8.5 PPM (.19 oz./ton) gold, however, no visible gold can be seen. E-W field of view is 1.42 mm. 64

Figure 23 65

Table 2. Assay results from samples taken undergrcu at Rockhouse adit . Minus sign indica tes below detect ion limit. All results are in parts per rnilli

Sample # Au fig As 3b Hg 19013 1.450 1 . 6 21 5 2 19014 3. 700 3. 4 £9 6 3. 0 19015 0. 200 0. 2 44 5 1.2 19016 -. 025 0. 3 59 16 da U 19017 0. 030 0. 1 34 11 £« 3 19018 0. 035 0. 3 69 12 2.8 19019 3. 700 2. 4 £0 5 1 . 8 19020 0. 800 0. 7 5 1.5 19021 0. 215 0. 7 170 7 a. 5 19022 0. 060 0. 1 44 4 0. 6 19023 0. 065 0.2 79 6 2. 4 19024 1. 150 1.2 24 5 2. £ 19025 1. 150 1. 3 55 7 3. 0 19026 0. 550 i—i. 6 62 13 1.8

Figure £4 shows the largest of these veins found underground at sample location 19024 (fig. £3). Surround ing the bleached white quartz after calcite vein is a zone of limonite gouge. Sample 19024, from the center part of the vein, and sample 19025 from the limonite border , bot h contain similar amounts of gold and trace elements. XRD analysis indicates the vein consists entirely of quartz. in thin section the vein material (sample location 19024) consists of terminated "dogtooth" quartz crystals which have grown into the relict calcite voids (fig. 25). I he crystals contain abundant primary fluid inclusions. i-luid inclusion studies were done on a doubly polished section of this sample. Homogenization temperatures for 37 primary fiuid inclusions yielded a range of 190 to 252°C with a mean value of 237°C. Radiating bands of primary fluid inclusions are present in the quartz. Radiating textures like these are 66

Figure £4- Quartz pseudomorphous after calcite vein found underground at the Rockhouse adit at sample location 190£4. The vein is extremely soft and relict calcite rhombohedrons can be seen with the unaided eye. ft sample of the center part of the vein assayed 1.15 PPM (.033 oz./ton) as did a sample of the adjacent 1 imonite-rich selvage. 67

Figure 25. Photomicrograph of thin section of quartz pseudomorphous after calcite vein at sample location 19024. The relict rhornbohedral calcite cleavage planes are clearly visible. Terminated quartz crystals have grown outward from the calcite cleavage planes with their C-axes perpendicular to the planes. The tiny black specks within the quartz crystals are primary fluid inclusions which yielded homogenization temperatures of 19® to 252 degrees Centigrade. Crossed polars, E--W field of view is 1.42 mm. 68 considered to be evidence for boiling (Fahley, 1961).

The occurrence of veins of quartz pseudornorphically replacing calcite was noted by Pansze (1975) for hydrothermal veins in the Silver City district in Owyhee

County, Idaho, and in the Delamar district in Lincoln

County, Nevada (Callaghan, 1937). The following explanation, using the work of Pansze (1975) and Holland and

Malinin (1979), is proposed to explain the formation of these veins.

Calcite is less soluble at higher temperatures than at lower temperatures; quartz is less soluble at lower temperatures than at higher temperatures. Since calcite was the first mineral to form, it can be concluded that the hydrothermal solutions cooled with time or with increased distance from their source. Calcite is relatively insoluble above ££5°C regardless of the partial pressure of COS

(Ellis, 1959). fts the solution temperature dropped below

£00®C, the solubility of calcite increased and the solubility of quartz decreased so that quartz replaced calcite. The fluid inclusion data indicate that quartz formed at temperatures around £00®C. ‘he system must have been active at the lower temperature for some time as the calcite was completely replaced in the vein over a vertical distance of at least 80 feet.

Tuffs of the China Mountain Formation have been hydrothermally altered to a quartz-i1 1 ite-pyrite assemblage in the area of the Rockhouse adit. XRD and thin section 69 studies of altered arid unaltered China Mountain tuffs

indicate that quartz and illite were present prior to alteration and must have been in close chemical equilibrium with the altering solutions. The presence of pyrite— which has mostly oxidized to goethite— distinguishes the altered

from unaltered rock.

fts can be seen from figure £3 and table c!, the highest

gold values are found in the veins near the only stooe in

the workings. Some ore appears to have been removed from

this stope, but the volume removed appears to have been less

than 180 tons.

Boyleite, a blue-green acicular hydrous zinc-sulfate

mineral is present on the ribs in the area of samples

19020—£3. This mineral has formed in voids created during

minima and has therefore formed since the tunnel was

driven.

Quartz-Barite Veins With Silver find Copper Sulfides

Three occurrences of quartz—barite veins were mapped a^ong

Tertiary faults. These veins are found only in rocks of the

Hava11ah Sequence.

Blue Lead mine— The largest and most extensive quartz-barite

vein is at the bottom of Blue Lead Canyon in the southeast

1/4 of Section 3£, T.L9N.J R. 4®E. opiate 1). The diue t_ead

Mine explores a quartz vein which pinches and swells along a

normal fault separating Havallan argillite and a Koipato

dike. Figure £6 shows the mine was developed from at least 70 two levels, the lower of which is now flooded. The vein reaches a maximum width of 0.6 meters and consists mainly of quarts and sericite with visible pyrite, chalcopyrite, tetrahedrite-tennantite, and coveilite (fig. £7). This sample contains 925 PPM (£7 oz./ton) silver and 0.65 percent antimony, indicating that the mineral identified in polished section as tetrahedrite-tennantite is probably the antimony end member tetrahedrite. Since silver can substitute for copper in the tetrahedrite structure (Skinner, 1976) it is likely that the silver is contained in this mineral

( (Cu, Fe, Ag) 1£ Sb4 S13).

Table 3 lists assay results for samples taken in the

Blue Lead Mine. fill samples contained detectable amounts of silver and several contained traces of gold.

Table 3. Assay relults from samples taken at the Blue Lead Mine. Minus sign indicates below detection limit. All values are in parts per million unless indicated

Sample 4 Au Aq As Sb Hg 190£S 0. 030 68.0 97 £40 CL a E) 190£9 -. 0£5 £. 7 £9 70 0. 5 19030 0. 0£5 £6.0 39 £60 b 19031 0. 030 13. 5 3£ CL ub 3. 7 19036 -. 0£5 3. £ £8 75 1 . 6 16875(dump) . 110 9£5.0 550 . 65% 63. 0

Hypogene wailrock alteration is confined to the

foot wall Koipato dike rock and consists of quartz-sericite

crosscut by a pyritic quartz stockwork. The stockwork has

formed along a pre-existing conjugate fracture set; the

alteration extends up to 6 meters into the footwall

perpendicular to the vein. 71

Figure 26 72

Figure 27. Photomicrograph of polished section of ore from Blue Lead mine. Consists of primary pyrite (p), chaicopyrite (c), and tetrahedrite (t) in a quartz gangue. Secondary goethite (g) has formed around the pyrite and secondary coveilite (cv) around the tetrahedrite. A sample of this rock (#10875) assayed 325 PPM <27 oz./ton) silver and 0.65 percent antimony indicating a probable formula for the tetrahedrite of (Cu, Fe, Ag)12 Sb4 S13. E-W field of view is 1.42 mm. 73

The Blue Lead vein can be traced along strike to the south for approximately 60 meters and followed up the hill vertically for 12 rneters (plate 1 ). Over this distance the vein changes composition from the quartz-sulfide assemblage at the Blue Lead mine described above to a barite plus minor quartz and sulfide assemblage. ft sample of the vein where it is 0.6 meters wide and consists almost entirely of white vein barite with minor chalcopyrite—tetrahedrite (plate 2, sample #18876) assayed 33 PPk! (1 oz./ton) silver.

Badger mine— The Badger mine in the northwest 1/4 of Section

6, T.S8N. , R. 40E. , is similar to the Blue Lead but the vein is much smaller. Figure 28 is a geologic map of the underground workings and two adjacent prospect pits.

The mine is developed from one level along a normal fault which separates argillite and quartzite or the

Hava!lah Sequence. The mine is within 250 meters of the major graben—bounding fault system which juxtaposes Havallah

Sequence with units inside the Tobin voicano—tectonic graben. It is likely that these small faults at the Badger mine are genetically related to graben subsidence, as they are subparallel to the graben margin fault.

The Badger mine contains two veins which attain a maximum thickness of 5 centimeters and consist of barite, quartz and pyrite. Table 4 lists the results of assays from samples taken at the mine. Sample 19042 was a select grab of the barite vein from the dump. 74

BADGER MINE GEOLOGIC MAP OF UNDERGROUND WORKINGS SW1/4 OF NW 1/4 SEC.6 T.28N., R.40E.

PODS OF PYRITE MINERALIZATION IN HIGHLY CARBONACEOUS ARGILUTE 2 INCH VEIN OF QUARTZ-. ^C A V E D PYRITE-BARITE ALONG CARBONACEOUS ZONE ADJACENT SMALL FAULT - 1 9 0 4 5 / TO FAULT WIDENS TO 15’ f-CAVED SULFATE COMMON

19043 (CARB. ZONE) 19044 (FAULT) . QUARTZ STRINGERS AND MINOR PYRITE ALONG SMALL FAULT Ph 1-2* WIDE FAULT ZONE WITH BRECCIATED CLASTS _ OF QUARTZITE AND SULFIDES IN A C L A Y MATRIX; UNDERLYING 2-3* ZONE OF REMOBILIZED CARBON

QUARTZ. PYRITE ALONG FRACTURE IN BEDDING

/ / /

EXPLANATION

BEDDING Ph -PERMIAN HAVALLAH FORMATION MINERALIZED BED

FAULT

MINERALIZED FAULT ZONE

CARBONACEOUS ARGILLITE ROAD 0i__E§§!__ i V DUMP

BRUNTON & TAPE BY P.DOBAK/R.PERRY 8-4-83

Figure 28 75

Table 4. Assay results from samples taken at the Badger mine. Minus sign indicates below detection limit. fill results are in parts per mill ion.

Sample # flu Ag As Sb Hg 13803 —.025 2.2 37 £0 5. 5 16837 025 0. 2 340 v j 0. 3 13042 025 14. 5 i 5 66 6. 0 13043 025 0. 3 14 CL 1.8 13044 025 5 b v i 44 15 25. 0 13045 025 0. 8 48 6 3. 4

Pi distinct alteration zone is absent along the mineralized fault zone, however a zone of carbon is present

in the rocks below the fault.

Unnamed adits— two unnamed adits in the northwest 1/4 of

Section 7, T.£8N., R.40E., explore quartz and quartz-barite veins (Figure £3). The more extensive working in the southwest is approximately 10 meters topographically lower than the smaller adit to the northeast. The lower adit was driven to explore a narrow, 7 to 10 centimeter wide quartz vein which contains gold (table 5). The upper adit explores

a flat-lying barite-quartz vein with minor malachite. It

appears that neither working produced any ore.

Table 5. Assay results from samples taken at unnamed adit. Minus sign iridicates less than detection limit, All values are in parts per mill ion.

Sample# flu Ag As Sb Hg 13043 -0. 025 0. 2 -1 -i 1 . £ 13050 1.050 c!» CL 310 4 i. 3 UNNAMED ADIT GEOLOGIC MAP OF SURFACE AND UNDERGROUND WORKINGS SE 1/4 OF NW 1/4 SEC. 7, T.28N., R.40E.

UNDULATING BARITE-QUARTZ- MALACHITE VEIN 1-3 INCHES WIDE 1/4-1/2 INCH CALCITE VEINLETS ALONG \ FRACTURES \

19050- 3-4 INCH MINERALIZED VEIN OF: QUARTZ PYROPHYLLJTE LIMONITE f CLAY

1 INCH LIMONITE & •19049 CALCtTE GOUGE

1/2 INCH LIMONITE & CLAY GOUGE

1 O N

TERTIARY BASALT DIKE FAULT

—-' PROBABLE FAULT

TRIASSIC GRANODIORITE MINERALIZED VEIN

FRACTURE — w

w ROAD

Vtitff DUMP BULLDOZER CUT

METERS BRUNTON & TAPE BY P.DOBAK/R.PERRY 8-4-83

Figure 29 77

Fossil Hot Spring Mercury Mineralization

Several mercury mines and prospects are present near the graben-bounding fault system in the China Mtn.

Formation. This mercury mineralization is structurally controlled by faults and fractures and commonly occurs at the intersect ions of these structures.

Mt. Tobin mine— The Mt. Tobin Mine in the northeast 1/4 of

Section 1, T.£8N., R.39E, is the largest mercury deposit and has had the only significant production of any mine in the district. Figure 3® is a topographic and geologic map of the Mt. Tobin mine area done by Roberts and Granger in 194® when the mine was operating. The author has modified some of the geology on this map to conform to existing knowledge of map units in the area. The map also shows the location of several drill holes that were completed in 1957 under

DMEft contract (DMEfi, 1957).

The rocks at the Mt. Tobin mine consist of tuff and pebble conglomerate of the China Mountain Formation, fish

Creek Mountains rhyolite tuff and alluvium. Mercury mineralization is localized along faults and fractures mainly in the China Mountain Formation.

Three sets of fault systems were mapped; one set strikes N.ICE and dips 33 degrees east parallel to bedding.

These faults control mineralization at the west workings

(fig, 3®). The second fault set strikes N.5®—7®W. and dips steeply to the southwest; these faults control mercury EXPLANATION

Qal ALLUVIUM Qoa OLDER ALLUVIUM Qfg TERRACE GRAVELS |Tt Tr | FISH CREEK MTNS RHYOLITE TUFF Tw CHINA MTN. FM.

Ph HAVALLAH SEQUENCE

- "CONTACT

'INFERRED CONTACT

"Fa u l t o r f r a c t u r e

"P r o b a b l e f a u l t

'’'b e d d in g * PROSPECT <£PGLORY HOLE # DUMP STQPE 400 F««t 'y.___ PORTAL ANC ^ WORKINGS FIG . 30 i o CLAIM CORNER GEOLOGIC MAP METERS X Slog* 0 non* /•SPRING MT. TOBIN MINE ° ^ GEOLOGY by R.ROBERTS & E.GRANGER USGS 12AH 03 79 mineralization at the Snake Pit adit (Fig. 32). The third strikes northeast and dips steeply northwest.

The ore bodies were concentrations of cinnabar, chalcedony and minor pyrite found mainly in the pebble conglomerates where faults intersect (Roberts, 1942). The conglomerate appears to have been a more favorable host rock than the tuffs because it was more brittle and fractured more readily, creating permeability for the mineralizing solutions to pass. Faults, sealed by gouge, also aided in confining the solutions by preventing lateral migration.

The cinnabar is often found as a "paint" or coating in the matrix of the pebble conglomerates. The matrix of the

pebble conglomerates and the aphanitic tuffs have been hydrothermally altered to an i1 1 ite-quartz-pyrite assemblage adjacent to the primary solution channels.

Two ore bodies were mined at the Mt. Tobin mine. fit the East workings (figure 31) an ore body was mined from a

glory hole 45 meters long, 12 meters wide and 12 meters deep

which yielded 6,600 tons of ore from a body about 6 meters wide averaging 7.12 pounds of mercury per ton (Roberts,

1942). The ore was in pebble conglomerate between two

bedding parallel faults which are 9 meters apart. Cinnabar

paint is present in fractures along the sides of the glory

hole; manganese oxide is present in fractures and permeates

the rock near the fault zone. The proximity and

distribution of these manganese oxides indicate they were

deposited from hydrothermal solutions moving through the 80

EAST WORKINGS MT. TOBIN MINE GEOLOGIC MAP OF SURFACE AND UNDERGROUND WORKINGS SW 1/4 OF NE 1/4 SEC. 1 T.28H, R.39E.

2-5* FAULT ZONE WITH CNNABAR PAINT 1-2* ZONE OF CNNABAR PANT\

CINNABAR PAINT HANGING WALL INTENSELY SHALLOW SHAFT ILLITICALLY ALTERED, WITH STOPE BANDS OF UMONITE PARALLEL TO FAULT

TOPED UP 30* AT 5(T INCLINE

T-2* ZONE WITH CINNABAR PAINT AND UMONITE ALONG FRACTURES

ZONE BETWEEN FAULTS HIGHLY FRACTURED ANO BRECCIA TED; BRECCIA FRAGMENTS NCLUDE CHINA MTN. FM. TUFF/PEBBLE CONGLOMERATE ANO TERTIARY RHYOLITE TUFF.

ZONE IS SULFATE-RICH. WITH ABUNDANT REUCT PYRrTE PODS LOCALIZED ALONG INTESECTIONS OF SMALL FRACTURES

EXPLANATION

TRIASSIC CHINA MOUNTAIN FORMATION FAULT TlCM TUFF AND PEBBLE CONGLOMERATE

CNNABAR-BEARNG . FRACTURE

ILLITIC ALTERATION V * BRECCIATED AND FRACTURED

— — 19054 SAMPLE LOCATION

ILLITIC ALTERATION r----- ■- PIT WALL OF GLORY HOLE STORED 20-40' DEEP WITH 5-10% MANGANESE OXDES UNDERGROUND WORKING

METERS BRUNT ON ANO TAPE BY R. PERRY & J. FOSTER 8-9-63

Figure 31 81 fault zone. Table 6 is a list of the assay results from sampling at the East workings.

Table 6. Assay results from samples taken in the West working of the Mt . Tobin mine . Minus sign indicates below detection limit. All values are in parts per mill ion unless otherwise indicated.

Sample # flu ft 3 As 3 b Hg 19051 -0. 025 -0. 1 10 7 140 19052 -0.025 -0/1 37 9 5® 19053 -0.025 0. 1 £3 a 34 19054 -0.025 -0. 1 -5 53 19055 -0.025 -0. 1 —5 110 29

The West ore body was mined from a glory hole 36 meters

long, 15 meters wide and 6 meters deep. Approximately £,30® tons of ore averaging 1£.78 pounds of mercury per ton were mined (Roberts, 1942). The ore was localized in pebble conglomerate between two faults.

The Snake nr' x - jKt- adit is about 30® meters south of the

wor k i ng s (fig. 30) . This prospect produced a few ton5 of ore from a 15 centimeters wide vein along a fault that strikes northwest and dips 30. degrees to the south (DMEft,

1957). Figure 32 is a geologic map of the workings at the

Snake pit adit and table 7 lists the sample assays from this

prospect.

Table 7. Assay results from samples taken in the Snake Pit adit area. Minus sign indicates below detect ion limit. All va1 ue are in parts per m i1 1 i on unless otherwise indicated.

Sample # flu ftg^ As 5 b Hg 19047 -®.®£5 2 1® 36 17 19043 -®.®£5 0- 3 74® 37® 0. ®7% 82

SNAKE PIT ADIT GEOLOGIC MAP OF SURFACE AND UNDERGROUND WORKINGS NE 1/4 OF SE 1/4 SEC. 1, T.28N„ R39E.

MINOR SHJCA ASSOCIATED WITH CINNABAR ALONG 1-2* FRACTURE ZONES

/STOPED UP 20* « O • - / / 4 3 8 0 ^ PYRITE AND SULFATES ABUNDANT IN FRACTURE 60 1 9 0 4 8 ^ < o - 75 o ° °

CINNABAR PAINT LOCALIZED ALONG 1* FRACTURE ZONE ° / // ^ CINNABAR

■&CM

EXPLANATION

CINNABAR ANO PYRITE-BEARING TRIASSIC CHNA MTN. FORMATION FRACTURE

N0N-MNERAL1ZED FRACTURE

LLITICALLY ALTERED CARBONACEOUS TUFF BEDDMG CARBON CONTENT APPROXIMATELY 5% DUMP

CHERT AND GREENSTONE PEBBLE CONGLOMERATE ROAD E 3 WITH TUFFACEOUS MATRIX -19046 SAMPLE LOCATION 40 0 U> METERS BRUNTON ANO TAPE BY P. DOBAK & R. PERRY 8-4-63

Figure 32 83

The following was taken from unpublished DMEA report

#4715 on the 1957 exploration drilling program at the Tt.

Tobin mine;

DMEA drilling explored the zone of alteration from 5®® feet northeast to 6®® feet southwest of the East workings with £4 holes ranging in depth from 6® to 12® feet. The highest grade material was recovered from hole 11 near the south end of the explored zone where the interval 55 to 6® assayed ®. 8 pound of mercury per ton. The longest interval containing significant indications of ore was found in hole £0, also near the south end of the explored zone where the interval 65 to 75 feet averaged ®.5 pound of mercury per ton. In two other holes (S and £3) intervals of 11 and 5 feet averaged 1 pound or less mercury per ton. Although no ore was cut in any of the holes the intervals containing cinnabar are of the same order of magnitude as the ore bodies, and may well be in the fringes of ore bodies. A smaller alteration zone 6®® to 11®® feet southwest of the West working was also explored with D'fER drill holes. Five holes were drilled to depths of 6® to 8® feet. In two of these (15 and 16) the intervals from 1® to £® feet in depth averaged ®.1 pound or less mercury per ton. * Table S lists the results of 17 assays done in 1357 of rotary drill cuttings where pannings indicated that cinnabar was present in sufficient quantities to warrant sampling.

The total production from the Mt. Tobin mine from 1333 to 1941 was 9568 tons of ore which yielded 1073 flasks of mercury. The average grade of the deposit was 8.5 pounds mercury per ton. Table 9 shows the monthly mercury production from the mine from 1938 to 1941.

It appears that most of the shallow surface ores at the

Mt. obin mine have been removed, and the results of the

DMEA drillina indicate no ore of economic value is in sight.

Last Chance mine— The Last Chance mine s a m i1e northwest Table a. Assay results of samples of ro tary drill cuttings from 1957 DNEA drilling at Mt. Tobin mine. From unpublished DMLA file 4715.

Sample # Lbs. Interval Deser i ption Hg/ton feet 527 0. 1 75-78 Drill hole #8 526 <0. 1 78-80 Dr i 11 hole #8 529 <0. 1 80-81 Drill hole #8 530 0. 1 81-82 Drill hole #S 531 0. 2 82—83 Drill hole #8 5 c* <0. i 83-84 Drill hole #8 533 <0. 1 84-85 Drill hole #8 534 <0. 1 85-86 Drill hole #8 535 0. 8 55-60 Drill hole #11 536 <0. 1 60-65 Drill hole #20 537 0. 7 65-70 Drill hole #20 536 0. 3 70-75 Drill hole #23 539 <0. 1 70-75 Drill hole #23 540 <0. 1 10-15 Dr i 11 hole #15 541 0. 1 15-20 Drill hole #16 542 <0. 1 10-15 Dr i 11 hole #16 543 <0. 1 15-20 Drill hole #16

Table 9. Mercury production at the Mt. Tobin mine from 1938 to 1941. From Roberts (1942).

Year Tons of ore tirade Flasks treated Lbs./Ton Hg i938-40 500 6. 8 45 1940 2384 13. 5 June C.C. July 91 August 64 September 36 October C. iZ. November 75 December 91 3.941 6684 7. 1 January 73 February 91 March i 06 Apr i 1 58 May 80 J une 44 J u 1 y 47 August Li/b September 24 October 24 November 21 December c! A

TOTAL 9568 a. 5 1073 85 of the Mt. Tobin mine in Bushee Creek Canyon (plate 1).

Figure 33 is a geologic map of the mine and workings. The deposit was developed underground in foliated tuff and pebble conglomerate of the China Mountain Formation along the intersection of a northwest striking fault with northeast striking fractures. Cinnabar occurs in fractures and chalcedony veinlets and locally extends into the bedding plane foliations. Figure 34 is a polished section of cinnabar in a chalcedony veinlet at sample location 1S858

(fig. 33).

Wallrock alteration conists of an enveloping pattern with silicic alteration surrounded by illitic which is in turn enveloped by an argil lie assemblage.

Sometime after Roberts and Granger visited the property in 1942 the mine was opened by bulldozing and presently consists of a small glory hole. , Approximately 135) tons of ore were mined, sorted and processed at the Mt. Tobin furnace in 1943, but the grade was low and mining was discontinued (Roberts, 1942). Table 13 lists the assay results for samples taken at the Last Chance mine.

Table 13. Assay r■esults from samples t aken at the Las' Chance mer>cury mine. Minus sign indicates be 1 ow detect ion limit. All values are in parts per million unless otherwise indicated.

Sample # Au An nS Sb he 18857 -3. 35 3. 6 78 133 £93 18858 -3. 35 3. 4 £93 C. L 3. 34f. 19338 -3.3£5 -3. 1 47 3 0 a 0 A % 19339 -3.325 3. 5 163 53 S5 19343 -0.325 3. 5 123 133 3. 32% 19341 -3.325 -3. 1 £7 £3 13 86

Figure 33 87

FiQuire 34. Photomicrograph of polished section of cinnabar in a chalcedony veinlet in altered pebble conglomerate of the China Mountain Formation from the Last Chance Mine. -he cinnabar occurs as dispersed grains throughout a late stage fracture in the chalcedony and appears to have been the last mineral to form. E—W field of view is 1.4c! mm. 88

North Fork mine— The North Fork mine lies 0.8 kilometers northwest of the Last Chance just north of Bushee Creek

Canyon (plate 1). Figure 35 shows that the mine consists of several bulldozer cuts and a short tunnel developed along three intersecting faults in tuff and pebble conglomerate of the China Mountain Formation. Note that a slice of Fish

Creek Mountains tuff has been caught in and altered along the fault. This dates the fault and the alteration as post-Miocene.

Cinnabar occurs in pockets and veinlets adjacent to and along the faults where the rock has been sheared and fractured. Barite and cinnabar are present in a circular area of silicic alteration located at the intersection of two of the faults. The silicic alteration assemblage consists of quartz and dickite and the illitic assemblage consists of quartz and ill its.

A S-tube retort and 0.3x2 meter rotary furnace were present on the property in the summer of 1383 (figure 36).

From the size of the calcines dump it is estimated that 200 tons of ore were processed. Table li lists the assay results for samples taken at the North Fork mine.

Table 11. Assay results from samples taken at North Fork mercury mine. Minus sign indicates below detec­ tion limit. All values are in parts per million unless otherwise indicated.

Sample # Au A g As Sb He 19® 3 A -0.025 -0. 1 23B 53 59 19035 -0.025 -0. i 110 25 i 3 19036 -0. 0 2 5 -0. l 520 100 58 19037 -0.025 -0. 1 46 28 0. 0i 89

Figure 35 90

Figure 36. Six-tube mercury retort and rotary furnace present at North Fork mine in summer of 1983. Some quicksilver is present in the pan beneath the retort. Coal was used to heat the furnace. License plate on trailer indicates the equipment was worked as late as 1969. 91

Unnamed prospect— Figure 37 is a geologic map of a small prospect located between the Mt. Tobin and Last Chance mines

(plate 1). It was mapped because it contains visible cinnabar and is characteristic of alteration and mineralization in the China Mtn. Formation near the graben—bounding fault.

The prospect consists of several pits which explore silicified China Mtn. tuff and pebble conglomerate which has been hydrothermally breedated and contains visible cinnabar, pyrite and barite along fractures. Figure 38 is a photomicrograph of silicified China Mountain tuff which contains hydrothermal barite along secondary fractures.

Pyrite boxworks are present in several of the vugs created by breed at ion, which has occurred where two fractures intersect, resulting in silicified, angular clasts of tuff which have been rotated and recemented in a siliceous matrix. Liesegang banding is present in these silicified t uffs.

Surrounding this zone of silicic alteration is an area with a quartz stockwork which has developed along a pre-existing conjugate fracture set. Table 12 lists the assay results from samples taken at this prospect. 92

Figure 37 3 9

Iteration (quartz-i11ite-barite-jarosite). Crossed polars, —W field of view is i.4£ samplemm. location f-rorn 1905/. (s) ly replacingrelict (s) pseudornorphical primary a, biotite

in in fractures with barite. Oxidized pyrite (p) probably phenocryst. The iron sulfate jarosite (j) is also present

fracture. Sirefringent mineral at upper right is sericite alterationite-quartz-pyrite) (i11 preceded the silicic

tuff with hydrothermal barite

Table i£. ftssay results from samples takers at unnamed mercury prospect. Minus sign indicates below detection limit. fill values are in parts per million.

Sample # fiu fig fis Sb Hg 19057 -0.0£5 0. 3 £40 140 £00 19058 -0.025 1. 1 92 320 96 19059 -0.025 0. 4 390 190 £10 19060 -0.025 0. 9 300 92 65 19061 -0.0£5 0. 3 3£0 £10 95

The area around this prospect has many similar silicified zones of China Mtn. rock. Numerous faults on the hill north of the prospect have silicified ribs which have

1.5 to 3 meters of relief and mark the surface exposure of these faults. Barite is common in fractures in these silicified fault zones.

Origin of the Mercury Deposits— The ores were formed by mercury—bearing solutions which rose from depth along faults and spread throughout the fractured rock depositing cinnabar. The presence of opalite sinter boulders and float

in the area around these mercury mines and prospects

indicate some of the solutions reached the surface to form hot springs. From the location of several of these small opalite outcrops it is estimated that the cinnabar deposits are no more than 3 to 6 meters below the topographic surface along which they formed. 95

EXHAl ATIVE STRATIFORM SILVER MINERALIZATION!

Queenstake prospect— In the eastern 1/2 of section 5,

T.28N. , R. 40E. (plate 1), a lens of stratiform low-grade silver mineralization is present in interbedded chert and argillite of the Havallah sequence. This zone is 45 to 60 rneters wide, forms bold outcrops due to its siliceous composition, and crops out intermittently for 1200 meters along the limbs of a major Havallah F4 fold. As of August of 1903 the property was being prospected by Queenstake

Exploration of Denver, Colorado.

In outcrop a zone of silicic alteration is surrounded by a zone of argillic aIterat ion (plate 1). Brecciated zones, present in the silicically altered rocks, consist of angular fragments of chert and argillite cemented in quartz. Tiny (1mm) quartz stringers containing euhedral pyrite permeate the chert and argillite in the silicic altered zone.

The argillic zone is actually an i11 ite-quartz alteration assemblage and the siliceous zone consists of auartz, illite and a 1 bite.

Coarse and fine-grained pyrite are present in both alteration zones, and much of this pyrite has been oxidized to goethite forming limonite boxworks along fractures in the silicic assemblage.

Table 13 lists the results of samples taken from the

Queenstake prospect. Plata 3 shows sample locations. 96

Table 13. Assay resul ts from samples taken of 3 i i i c i c a Iterat ion zone at Queenstake prospect . Minsus si gn indicates below detect ion limit. All values are in parts per mi 11 ion.

Sample # Au Ag As Sb Hg 13877 0. 075 35. 0 140 140 2. 3 13830 -0.025 7. 3 65 55 0. 6 13388 -0.025 0. 5 160 18 0. 2 13339 -0.025 2. 0 260 23 0 a 18390 -0.025 i„9 57 1j. -1J. 0. 1 18391 0. 025 6. 3 120 55 0. 9 18392 0. 035 0. 5 43 10 1, 9

Several of the samples contain gold and silver values above detection limits. Chalcopyrite and were identified in outcrop in minor amounts, but analyses of base metal contents were not performed on any of the samples.

Thin section studies reveal that there are two stages of stringer quartz veinlets: the first consists of veinlets of quartz and albite, and the second, larger than (up to imrn) and crosscut the first, consist of quartz and pyrite.

Both of these veinlets have been deformed by tiny crenulations which also deform the SI bedding-parallel cleavage. Figure 33 is of a polished section of a sample from the quartz stringer zone showing pyrite and arsenopyrite in a folded quartz stringer veiniet.

Stratiform pyrite-bearing chert and argillite are present throughout the section of Havallah Sequence mapped in this report. Many of these occurrences were sampled and analyzed but only one other occurrence had any precious metal values. In the northeast 1/4 of Section 35, T23N.,

R33E., a one meter thick lens of argillite containing 10 97

Figure 39. Photomicrograph of polished section of folded quartz stringer in Havallah argillite. Dotted line marks axes of folded quartz stringer. The coarser grained slightly less reflective mineral, is pyrite (p) and the fine-grained more reflective mineral is arsenopyrite (a). The sulfides are found almost entirely within the quartz stringers and it appears that the large pyrite grain on the left has been fractured during folding. E-W field of view is 1.42 mm. 98 percent sulfides has been explored by a short tunnel. The lens contains pyrite and arsenopyrite in a quartz matrix, and is surrounded on both sides by greenstone. Table 14 lists the analytical results of two samples collected at this prospect.

Table 14. Assay results from samples collected at stratiform sulfide-bearing bed in Havallah Sequence. Minus sign indicates below detection limits. All values are in parts per million.

Samole# Au os As Sb Hg isass -0. 05 3. 3 £700 IS 0. 1 18863 0. 05 S. 4 5400 IS 1. 0

Origin of Mineralization— Several observations point toward an exhalative, volcanogenic origin for this type of mineralization. These observations, which are mostly structural, include the following: (1) the mineralization is stratiform, (£> the stratiform mineralization has been deformed by F4 (Triassie ?) folding and (3) the pyritic quartz stringers have been deformed by SI bedding parallel foliations and a later (possibly D£-D3) crenulation.

Since the pyritic quartz stringers formed prior to the earliest deformational structure (SI), and in the Havallah structure section it was shown that Sonornan-aqe deformation began very soon after deposition, it is concluded that the mineralization occurred sometime after deposition of the chert and argillite beds and before Sonoman age tectonism.

This places an implied age of Permian for this mineralizat ion 99

Iri add it ion to the evidence above, volcanogenic massive

sulfide mineralization is known to exist in the Havailah

fifteen miles northwest on the western side of the Tobin

Range at the Big Mike mine. The Big Mike deposit was a

high-grade, low-tonnage cupferiferous pyrite volcanogenic

massive sulfide ceposit which was mined in 1978 by Ranchers

exploration and Development Company. The ore body contained

188,888 tons of 18.5 percent copper ore hosted in a lens entirely within cherty carbonaceous argillite. Silver values from samples collected within the deposit ranged from

9.1 to ££ oarts per million (Rye and others, 1984). Primary mineralization at the Big Mike consisted of pyrite and quartz with lesser amounts of chalcopyrite and soarse sphalerite. Stringer mineralization consisted of veinlets or quartz, containing pyrite, carbonate, sericite, and some chalcopyrite and sparse sphalerite. Stringer mineralization is found in both the hanging and footwall of the deposit

(Rye and others, 1984). In addition, at least three phases of folding, which are similar in style and chronology to those mapped in the study area, affect rocks at the Big Mike deposit (Snyder and Brueckner, 1983). Rye and others (1934) classify the Big Mike as a Cyprus—type massive sulfide deposit.

The description of the stringer zone at the Big Mike deposit closely resembles the silicically altered zone mapped at the Queenstake prospect. In addition, the sulfide assemblage of pyrite, chalcopyrite and sphalerite are the 100

same and silver values are similar at both locations.

Lisina the Big Mike deposit as an exploration model, the

best possibility for locating massive ore at the Queenstake

prospect is down dip and to the west of the stringer zone where alteration may be concealed beneath the Pumpernickel hangingwal1 of a Tertiary low-angle normal fault (plate 1). 101

GEOCHEMISTRY

A total of 1S6 rock samples were collected. All of

these were taken at mines, prospects,or on mineralized or

altered outcrops. !his Pias toward geologic material that

is more likely to contain metal values is of course the

basis of exploration geology but precludes the use of any

type of random or grid statistical treatment of the data.

Statistics is the mathematical science of estimating

the parameters of a population by sampling members or parts of that population. In this case the population consists of

all of the altered and mineralized outcrops in the map area. The samples collected by the author are an attempt to estimate the parameters— in this case the gold, silver, arsenic, antimony and mercury contents— of this population.

Contour Maps of Metal values

In order to graphically exibit the g istribut ion of metal values a simple contouring method was employed

(figures 40—44). Fhe contours do not represent areas above contoured values, but rather represent areas where mineralized zones or structures contain concentrations of elements over a certain value. For example, in figure 40 the area inside of the 0.10 PPM gold contour does not uniformly contain rocks with over 0. 10 PPM gold, rather it represents an area where several vein structures that crop out contain gold values exceeding 0.10 PPM.

In a practical sense, this is a very efficient method of expressing the assay data in that the contour maps can be __

Figure 40. Geochemical contour mao of gold values from 196 samples. The total range'of values was <0.025 to 6.5 ppm. Fifty-eight of these samples were above the instrument detection limit of 0.025 ppm and 18 were above 0.10 ppm.

>0.10 PPM Gold

0.025 - 0.09 PPM Gold 103 104

Figure 42. Geochemical contour map of arsenic values based on 196 samples. The total range of values was <5 PPM to 5400 PPM. One hundred of these samples were above 50 PPM and 18 were above 500 PPM.

>500 PPM Arsenic

50 - 499 PPM Arsenic 105

Figure 43- Geochemical contour map of antimony values based on 196 samples. The total range of values was 1 ppm to 65OO ppm. Forty-eight of the samples.were above 50 ppm and seven were above 300 ppm.

>300 PPM Antimony

$0 - 299 PPM Antimony 106

Figure 44. Geochemical contour map of mercury values based on 196 samples. The total range of values was 0.12 to 1400 ppm. Seventy-five of the samples oon-tained greater than 10 ppm and 17 contained greater than. 100 ppm.

>100 PPM Mercury

10 - 99 PPM Mercury 107 compared with the structure and stratigraphy on plate 1 and conclusions can be made from these visual observations.

The most apparent observation is that except for silver, all of the major metal anomalies lie along a northwest trend adjacent to the graben-bounding fault system. It is also clear that most of the mineralisation is hosted by the China Mountain Formation.

The higher gold values were found in the canyon west of

Needle Peak in veins with quarts psuedomorphous after calcite and in quarts veins in the Needle Peak stock. The area within the 3.10 PPM contour in figure 42 outlines the extent of outcrop of these two types of gold-bearing veins.

Several single and multiple trace gold anomalies occur in hot springs mercury deposits in China Mountain rocks near the graben-bounding fault system. The Mt. Tobin, Last

Chance, North Fork and Uunnamed prospect each have at least one sample which contained a trace of gold.

There is a spatial association of silver with rocks of the HavaIIah sequence. The silver anomalies coincide with stratiform mineralisation at the Queenstake prospect and at the Blue Lead mine (Figure 41). Several single sample silver anomalies correspond to other prospects in the

Havallah, but it is noticeable that silver is relatively absent in the China Mountain hosted hot springs mercury deposits.

Arsenic anomalies are present in both Tertiary mineralization and stratiform mineralization in the Havallah 108

(figure 42). The most extensive of these correlates with

goId-Bearing quarts veins in the Needle Peak stock and on

the hill above the Rockhouse adit.

Antimony occurs in hydrothermally altered zones along

the graben-hounding fault and at the Blue Lead mine and

Queenstake prospect (figure 43). Antimony at the Blue Lead

mine is in the form of tetrahebrite. Elsewhere in the

Tertiary mineral i zat ion antimony corresponds to si 1 ideally

altered fault zones with hydrothermal barite.

Mercury corresponds directly to hydrothermally altered

rocks at fossil hot springs deposits and with areas

containing silicic alteration along fault zones (figure

44). Except for one anomaly at the Blue Lead mine— which

helps to tie the Blue Lead vein with the Tertiary

hydrothermal system— all of the mercury anomolies occur in

the China Mountain Formation. It is also noticeable that

many of the mercury anomalies correspond to topographic

higns.

Correlation of Metal Values

From the contoured geochemical data it can be seen that some areas anomalous in one element appear to correspond to anomalous areas of other elements— mercury, arsenic, and antimony, for example, appear to correspond in many areas.

Gold, however, does not appear to correspond closely to other elements.

In an effort to estimate the degree of interrelation between elements m each sample correlation coefficients 109

were calculated. The correlation coefficient is the ratio of the covariance of two variables to the product of their

standard deviations. Using gold and silver as an example, this would be:

Correlation Coefficient = r = covariance ______flu-fin S S flu flg

where S and 3 are the standard deviations of gold flu flg and silver, respectively, and the covariance is the joint variation of gold and silver about their common means.

Because the correlation coefficient is a ratio, it is a unit less number. Covariance may equal but can not exceed the product of the standard deviations of its variables, so correlation ranges from +1 to -1. fi correlation of +1 indicates a perfect direct relationship between two elements; a correlation of —1 indicates an inverse relationship. Between the two extremes is a spectrum of less than perfect relationships, including zero which indicates the lack of any sort of linear relationship

(Davis, 1973).

iable 15 is a correlation matrix between elements for samples taken in the study area. 110

Table 15. Correlation coefficient matrix for 19S samples collected in study area. Calculated using stepwise multiple regression program on SPSS.

fig 00068 As -.05641 .04351 Sb -.02218 .97552 .07894 Hg -.06341 .00720 .04504 .16976 flu flg fts Sb

The correlation coefficients for all pairs of elements

except silver and antimony indicate the lack of any linear

relationship. Silver and antimony, however, have a nearly

perfect direct relationship with each other that can in part

be explained by the fact that the highest silver and

antimony values are found at the Blue Lead mine where the

antimony-si1ver sulfide tetrahedrite has been identified.

Scattergrams

The contour maps (figs. 40-44) show that some elements

in the Tertiary mineralised area -are concentrated near topographic highs and some in the valley areas. This

indicates the possibility that there is a vertical sonat ion of metals within the study area. Numerous authors,

including Barnes (1979), have documented the vertical soning of certain metal elements in vein and hot spring hydrothermal systems, and attribute this soning to boiling

levels of the metal-carrying hydrothermal solutions.

According to Buchanan (1981) there is a restricted depth

interval which marks the tops and bottoms of precious metal ore horizons in volcanic hosted deposits that exibit evidence of boiling. Ill

If vertical zoning of metal elements in the study area can be demonstrated, this would lend evidence to the hypothesis that the hydrothermal fluids which formed the vein and hot springs deposits were once connected by open stuctural conduits. In order to test this hypothesis, scattergrarns of each element were plotted against the elevation where the sample was taken to see if there is any cluster of higher metal values at certain elevations.

Figures 46-50 are the scattergrarns for each of the five elements from samples taken only in Tertiary mineralized rocks.

The scattergrarns indicate definite vertical zoning of all of the elements. Curves were interpolated and a range for the anomalous values was estimated for each element.

Figure 51 is a composite of all of the curves and ranges for the five elements. The vertical distance between higher element concentrations can be determined using this figure by taking the distance between the relative peak curve values for each metal.

Discussion of Geochemical Data

The scattergram data strongly support the hypothesis that the hydrothermal solutions which deposited gold, silver, arsenic, antimony and mercury were connected by ooen structural conduits. Since the Tertiary alteration and mineralization parallels the margin of the Tobin volcano-tectonic graben, the graben—bounding fault system probably represents the primary structural conduit by which GOLD (parts per million) i.3<3 60 ♦ 0 .6 2 1.95 3.25 90 .9 3 * 0 .2 5 < 5.35 6. SO 6. Tertiary mineralized rock in Northern half of Mt. Tobin district TobinofMt.inhalf rockNorthern Tertiary mineralized F ». 55 • 65 gr 6 Satrrmo odv. lvto o 171 samplesoffor elevation gold vs. Scattergram of 46.igure 5800.00 __ .I * * I 1 ♦ ♦ I I I I I I I I I ♦ *-indicatesplotdataone I I-I I I I I I I I- ♦ 1 1 1

2*2° ♦ - (ACROSS) ELEV 00 .0 0 0 0 6 2 4 5 5 100 600. 0 00 6/00. 6000.00 0 .0 0 0 / 6 0 .0 6 500 0 .0 0 610 6100.00 AU 6200.00 * * 2 9 * \ 9 * 9 9 9 3*9 9 9 400 60.0 8 00 7000. 7200.00 0 .0 0 0 0 7 0 .0 0 680 6600.00 6400.00 I * \ •u ( 1 I I I I I 1 I I I I I 1 I I ! I I ELEVATION'(feet) < wtr+tj -niae 2dataplots2-indicates 1 00 .0 0 710 2

2 i i i i i i i l i i i i r i i i 7300.00 00 .0 0 0 4 7 7500.00 600 7800. 7600.00 7700.00 00 r\5 Figure 47. Scattergram of silver vs. elevation for 171 samples of Tertiary mineralized rock in Northern half of Mt. Tobin district.

(DOHN'l AG 1ACR0SS) £LEV 6900.00 <10.00 ££££;££__.££££?£° 12.no + 1 lb I H I I .00 \ I / I s A I I \ I 6.00 1 * l1 9 I * ♦ 3 *53 2*2 2 * $ * I 0 »* * 2 * 2 6 3 * ’ 7 6 7 2 7 * 2 * t * i ♦ I 5800.00 6000.00 6200.Oo" 6^00.00 6600.00 6800.00 7000.00 7200.00 7*00.U0 7600* 00 7 8 0 0 .0 0 ELEVATION (feet) *_ indicates one data plot 2-indicates 2 data plots ARSENIC (parts per million) 1080.00 2160.00 lt>2U.00 7 00 .0 0 270 00 .0 0 8 7 3 32AO.00 Tertiary mineralized rock in Northern half of Mt. Tobin district Tobinof inMt.halfNorthernrock Tertiary mineralized F A320.00 *863.00 5AQ. 00 5AOO.OO gr 4. ctega fasncv. lvto o 171 samplesfor elevation arsenic vs. Scattergramof 48.igure 5800.0 *♦o i i»/ i i i i * i ♦ i i i i i i - i ♦ ♦ r i I I I *-indicatesplotonedata I I I I I I ~ ♦ I I I ♦ I I 1 I ♦ I I I I I I 0_ 30 6300. 3 .0 0 0 3 6 0 .3 0 0 1 ^ .00_ 9 0 9 3 ^ / / (ACKUSS) ELEV (DOWN) AS * * 2 . 00 * * / * A 3 * 9 6 2 A 2 2 * / 00 ,0 0 0 2 6 * / - *81 c \ 400.00 6 2 6 o*37 1 * 1 6500. 7 00 .0 0 670 0 .0 0 6 0 5 + _ «• \ * -v LVTO (feet)ELEVATION N - — ♦ 9 2 2 f\ 3 2 2 * 6600.00 \ \ \ * * \ \ 6800.00 ♦ - v 2

N. 2 ♦ 6900.00 7000. 2 -niae 3data3-indicatesplots 7 200 0 0 * i * 2 7100,30 *I 1 I 1 I I I 1 1 I I 1 I I I I I 1 1 I 0 7AOo! .00 7300.00 00 7500.00 600 7800 0 8 7 7600.00 7 00 700. f o .00 ANTIMONY (parts per million) 1300.00 ?00 * 1?50.00 Z600.00 3250.00 i i 3250.00 3900.00 500 ♦ 5550.00 650.00 200 ♦ 5200.00 800 ♦ 5850.00 0 0 . 0 0 5 6 etaymnrlzdrc nNrhr afo t Tobindistrict.ofMt. inhalfrockNorthern Tertiary mineralized F igure 300 6000.00 5300.00 0

*-indicates one data plot*-indicatesonedata f-r * 1 1 I 1 I I I — I I I I I 1 * I 1 i [ I 1-I I 1 I I I 1 I 1 I * 49. V E L E ) S S O R C A ( T ( DO * N ) S3 S3 ( DO )* N ctega fatmn s eeainfr 171 samplesoffor elevation vs. antimony Scattergram of j-q lO(l 6300.00 0 . 0 0 3 6 hlOO.()l) + 2 6 2 0 0 .6' t o u 0 0 . 0 0 ELEVATION 2 < * y 2 / * / \ A l I Ir~' \ I I I I I 1 I A I 600 68 U0loO 6600.00

2<* 7*5*6

(feet) 700 000. 0 7300.JO 0 0 3 7 .00 0 0 L / 0 .0 0 090 b700<0u i 2 3 _ _ 22—* 2 ’ ------niae 2data2-indicates 7000.00 *------* J ------7200.00 7 * *7— ! ------7600.00 * ------2 plots 7500.OG . 0 0 6 7 0 7 0 0 0 , 3 0 00 * *♦ * 7/00.00 I I I ♦ I I I I ♦ 1 1 I I ♦ I i i 1 I I I I I ♦ I I I ♦ I 1 I I ♦ I 1 1 I I i ♦ c_n MERCURY (parts per million) SCAT t F L S C AT T LEb R 1120.01 ♦ Tertrary mineralized rock in Northern half of Mt. Tobin district?f TobinofMt. halfinNorthernrock Tertrarymineralized 2ri 0.0 5 200 ♦ 1260.01 F 1*0.05 6 0 * .0* 560 L < 1 0 0 . 0 ♦ 0 ’ *2 0.3 ♦ 700.03 8 ?80.02 ♦ Tc. gr 5. ctega fmruyv. lvto fr m fnr- elevationvs. Scattergramof 50. mercury igure m * . 0 0.02 RC 0 ^ ^ .06 0A 5800. k M OHAM * . I I ♦- I I - I i I I I 1 I I I I- I I t I I 1 I I I _ 00 indicatesplotdataone tiJOJ. JJ 6000*00 ClAI. IAt = */J l l l / d*>/0Ji = IJAft: (CRllATIU.N ( A C i\! j 5 t LS c) V QN HJ OQWN)( / 2* 0100.00 * * 6200.OO - -A- 3 ^ E L E V A T I O N J ° ( f / * * *• * *—• ** 2 ♦ * * 3927*55322 6600.JO 3 X ♦ * 3 \i 1 H \ -♦ 2 l 2 2 eet*)°U 700°-U0 "°°;o0 ; 2 L * * 3*“ 0 00 00: ^ “ . _ -niae 33-indicatesplotsdata

*7 ♦ 2 I 2 2 ' uo.oo 1 I 1 I I I I I I I I I I I I I 1 I 1 i I I I I I 1 I 1 I 1 I I I 1 I I I I I I I I l 1 I 1 I I ------300 70.0 7700.00 7*00.00 7300.00 ♦ ------♦ ------♦ ------2♦ -- 7600.00 ------♦ ------c ► ----- 7 ♦ ♦♦ * 600.00 ------. ♦ -1 -I ♦ 1 I 1 1 I I 1 I I ♦ I I i I ♦ I I I I ♦ 1 1 I 1 I I X ♦ I I I I ♦ I I I ♦ I 1 I I 1 RELATIVE VALUE s a s a s s 117 118

hydrothermal solutions ascended. The vertical zoning of

metals also -points towards the possibility that quartz veins

such as those at the Rockhouse adit represent the feeding

structures to the hot springs mercury deposits.

Tertiary silver mineralization occurs in the Hava11ah

Sequence at the Blue Lead mine some distance from the grsben

fault which controlled mineralization. Since the

relationship between the graben fault and the controlling

structure at the Blue Lead mine is uncertain, it can not be

concluded that mineralization at the Blue Lead is of the

same age and origin as that of the gold and mercury. This

is a possible explanation of why silver is vertically zoned above gold and all other elements.

Structural relationships indicate the hot spring deposits are of post-Early Miocene age, and the presence of intact sinter in the steep, erosional environment present in the area indicates the deposits are probably of a relatively recent age. Today’s topography may be a close reflection of that present during mineralization. 119

CONCLUSIONS AND RECOMMENDATIONS

The northern half of the Mt. Tobin District lies along the

northern margin of an 01igocene-Miocene age volcano-tectonic

graben which trends in an east-west direction through the

central Tobin Range.

The graben is bounded by a normal fault which

juxtaposes late Paleozoic Havallah sequence with Triassic

sediments and Tertiary volcanics which fill the graben.

Four episodes of deformation are evidenced by the

structural fabric of the Havallah sequence. The first three

episodes are believed to be related to thrusting during the

Triassic Sonoma Orogeny; the last episode produced major

north-trending plunging folds with amplitudes up to one

mile. These folds are believed to have formed during a

post-Sonoman Mesozoic deformational event, possibly the

uuning—Fencemaker fold and thrust event of Oldow (1SS3).

ihe major iriassic unit found within the graben is the

Lower iriassic China Mountain Formation, a clastic and volcanic unit which is part of the Koipato Group. Three

phases of deformation are evidenced by the structural fabric of the China Mountain. This deformation is of Mesozoic age but its relation to deformation in the Havallah is uncertain.

Two types of mineralization are present; (1) Tertiary epithermal mercury—gold—si 1ver found mainly in the China

Mountain Formation and (£> syngenetic stratiform silver m the Havallah sequence. 120

The Tertiary mineralization is structurally controlled

hy the graben-bounding fault system and consists of

gold-bearing quartz veins, si 1ver-copper bearing

quartz-barite veins and fossil hot springs mercury

deposits. The major production from Tertiary mineralization

was from the Mt. Tobin Mercury Mine, which produced 1073

flasks of mercury from 1938 to 1941.

From bottom to top, a vertical zoning of gold, arsenic,

mercury, and antimony is present in the Tertiary mineralized

rucks, indicating these elements are genetically related to

the same mineralizing event. Silver is found outside of the

graben in rocks of the Havallah Sequence and its relation to

the mercury-gold bearing system is uncertain.

Gold is found at the lowest elevation of any of the

metals in tightly structurally controlled epithermal veins,

ihe graben-bounding fault system represents the best structurally prepared zone for a bulk-mineable size gold deposit to be located. Since this fault dips 50 degrees to the southwest and the major gold anomoly in the area lies one-half mile to the southwest, it is concluded that this target would be too deep to explore.

Although there is abundant alteration and mercury, arsenic and antimony anomolies present along the margin of the graben, no other gold anomolies were found which would justify exploration drilling.

Similar Tertiary cinnabar-bearing mines and prospects are located in the southern half of the Mt. Tobin District 121 along the southern graben-bounding fault of the Tobin volcano tecuunic graben. Clastics and carbonates of the

Triassic Qsobb and Dun Glen Formations are present in this area and could provide more favorable host rocks than those found in the northern half of the district. Since the presence of gold in the Tertiary mineralising system has been proven by this work, it is recommended that exploration

'-'f the southern half of the district be conducted. 122

REFERENCES CITED

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Barnes, H. L., 1979, Soludiiities of ore minerals, in: Barnes, ed., Geochemistry of Hydrothermal Ore Deposits, End. Ed., New York, John Wiley and Sons, p. 404-460.

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Burke, D. B., 1973, Reinterpretation of the Tobin Thrust: Pre-Tertiary Geology of the Southern Tobin Range, Pershing County, Nevada: Stanford Univ., Stanford, Calif., Ph. D. thesis, 8£ p.

Callaghan, E., 1937, Geology of the Delamar District, Lincoln County, Nevada: Bull. Univ. Nev. voi. 31, no. 5.

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Ferguson, H. G., Muller, S. W., and Roberts, R. j. , 1951a, Geology of the Winnemucca■ quadrangle, Nevada, u. S. Geol. Survey Quadrangle Map •11.

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McKee, E. H. , 1971, Silberman, M. L. , Marvin, R. E. , and Obradovich, J. D., 1971, fl summary of radiometric ages of Tertiary volcanic rocks in Nevada and eastern California Part 1, Central Nevada: Isochmn/West no. p. 21-42. ’

Miller, E. L. , Kanter, L. R. , Larue, D. K., and Turner R. J., 1982, Structural fabric of the Paleozoic Golconada aj. lochthon, ftntler Peak quadrangle, Nevada: progressive deformation of an oceanic sedimentary assemblage: Jour. Geophysical Research, v.87, no. B4, p. 3795-3804. Muller, S. W. , erguson, H. G., and Roberts, R. J. , 1951, Geology of the Mt. Tobin Quadrangle, Nevada: U. S'. Geo Survey Quadrangle Map GQ-7.

Nichols, K. M, 1972, Friassic depositional history of China Mountain and vicinity, north-central Nevada: Stanford Uni v. anforti, Calif., Ph. D. thesis, 142 p. b:’ !rfctor'lc implications of a late Mesozoic p' 542-546 "tSt beit ir' northwesterri Nevada: Geology, v. 1

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^and^M-fi n5 Roberts, R. J. , Snyder, W. S. , Lahusen, G. L. , and Lotica, J. E., 1984, Textural and stable isotope h T the.Hi§ m k e Cupriferous volcanogenic massive s_u_.de deposit, Pershing County, Nevada: Econ. Geol. v. 79, no. 1, p. 124— 140.

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Skinner, B. J. , Luce, F. D. , and Makovicky, E. , 1967, Stuoies of the sulfosalts of copper. III. Phases ana 10r'S *" the system Gu-Sb-S: Econ. Geol. v. 67

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Wallace, R. E., Tat lock, D. B., and Silberling, N. J.,I960, Intrusive rocks of Permian and Triassic age in the Humboldt Range, Nevada, in: Geol. Survey Research I960, U. S. Geol. Survey Prof. Paper 400-8, o. B291-B293. SA.yssy 3 id w h s lynaiAiciNi

X IQNBddb’

921 SAMPLE ASSAYS

NOR': HERN HALF OF THE jvIT I OBIN DISTRICT

PERSHING COUNTY, NEVADA

Minus sign indicates below detection limit nil valaues are in parts per million.

SAMPLE # Au Ac As Sb He 18801 05 0. 4 770 150 118 18802 . 05 0. 3 410 65 18803 38 . 05 0. 3 570 15 40 18804 05 ~0. 1 80 10 13805 107 -■ 05 ~0. 1 2400 310 5. 5 18806 05 0. 2 1200 30 18807 IS 05 0. 3 1 200 690 400 18808 05 0. 4 210 60 18809 o o 43 05 L - 1— 37 20 18810 '- J n VwJ 05 0. 4 190 110 uuc r 18811 . 05 0. 3 170 170 18812 £3 . 05 0. 5 160 260 68 13813 05 0. 5 450 170 18814 100 . 05 0. 3 1900 190 148 18815 05 0. 4 210 60 18816 18 . 05 0. 1 57 24 6. 2 18817 . 05 0. 4 150 18818 16 i b 05 0. 2 11 43 18819 58 . 05 -0. 1 -5 9 241 18820 . 05 -0. 1 27 10 18821 58 05 0. 3 60 910 1400 18822 05 0. 5 120 330 18823 65 . 05 0. 5 400 220 220 18824 . 05 0. 2 100 86 18 18825 05 0. 5 80 6 18826 16 - S5 0. 2 150 30 14 18827 . 05 -0. 1 86 25 18828 11 . 05 0. 2 120 9 6. 0 18829 5. 00 3. 3 7 6 18830 3. 8 . 70 4. 1 30 4 3. 0 18831 05 0. 2 -5 __ 18332 0. 85 . 05 32. 0 540 79 38 18833 05 0. 4 190 -1 18834 0. 22 . 05 -0. 1 -5 i.i 18835 0. Si 05 0. 1 85 4 1.8 18836 ’! "j, ___-j 05 -0. 1 •I. s—< { / [ "T* u 18837 05 0. 2 340 18838 0. 35 . 05 1.4 70 -i 0. 23 18839 6. 50 ■1 •“ i 1.9 1 c. — i 18840 0. 17 . 10 1.8 810 170 18841 0. 25 . 05 3. 7 1000 31 11 18842 05 0. 2 410 15 18843 0. 98 05 0. 3 160 12 0. 62 128

SfiMj-'Lt ffc flu flc fls Sb He 13044 05 0. 2 970 40 6. 3 13645 05 C -0. 1 uJ cl 0. 18 16046 . 05 14. 0 610 73 ■jcr 18347 . 40 ~ 6. 5 55 59 18648 0. 76 05 -0. 1 24 12 18849 0. 12 05 0. 1 58 -1 18050 0. 21 05 0. 3 a -1 0. 65 18851 05 -0. 1 21 13 18852 12 05 -0. 1 -5 -1 i3 18853 05 -0. 1 —5 — 1 0. 88 18854 05 0. 1 -5 ~ X 18855 1 a 5 05 -0. 1 20 -1 2a 6 18856 . 05 0. 1 30 C. 18857 0 a 64 05 0. 6 78 100 290 18858 05 0. 4 290 2l 400 13859 ■ 05 0a 2 300 61 7? iX 18860 •uJ 05 0. 2 15 72 20 18861 05 “0. 1 —5 -1 18 18862 05 3a 9 2700 12 0. 09 18363 - 05 2. 4 5400 16 1.0 18864 _ •» 05 0. 2 42 -L 0. 68 18865 05 “0. 1 98 35 90 .18866 05 -0. 1 140 110 60 18867 05 ~0. 1 220 55 17 i 8868 05 -0. 1 490 66 40 18869 05 0. 1 83 C a d 6 5 18870 025 “0. 1 5 7 0. 08 18871 025 0. 1 —5 6 18872 0a 12 025 1-6 -5 13 0 a 86 18873 a 085 2. 3 26 ■ 20 18874 0. 51 “a 025 0.8 60 5 0. 32 18875 a 110 925. 0 550 6500 63 18876 025 33. 0 35 280 0a 61 18877 a 075 35. 0 140 140 1— M 18873 025 0. 3 20 -1 18879 0 a 08 “a 025 X m u J 19 8 0a 06 18880 “a 025 7. 3 65 55 0. 57 18881 “a 025 0. 1 —5 8 18882 0a 14 “ a 025 0. 1 -5 4 0a i7 18883 _cr 025 0-2 vJ -1 18884 0. 22 " a 025 0. 1 —5 5 18885 0. 07 “ a 025 0. 5 40 11 0. 63 18886 “ a 025 0. 2 73 -1 0. 16 18867 025 0. 1 _crU _ i i seas 0. 14 “ a 025 0a 5 160 18 0. 24 18889 a 065 2. 0 260 d 3 0. 30 18890 025 i. 9 57 ii 18891 0- 09 a 025 6. a 120 55 13892 0. 92 - 035 0. 5 49 10 18393 1.9 “ a 025 0. 1 17 10 0. 40 18894 “a 025 3. 6 4 1 00 35 18895 0-22 025 aJ. 3 580 68 0. 14 129

S A M P L E # H u f i g f i s S b H g

1 8 8 9 6 0 2 5 - 0 . 1 8 2 1 2 0 . 1 3 1 8 8 9 7 0 2 5 vi ■ - 5 — 1 0 . 5 8 1 8 8 9 8 . 0 2 5 0 . 2 4 8 1 0 . 3 2 1 8 8 9 9 0 2 5 0 N 6 1 6 0 8 1 . 8 1 8 9 0 0 0 2 5 0 . 1 1 7 0 2 0 c!„ 5

1 9 0 0 1 0 2 5 “ 0 . 1 5 0 wJ n O 1 9 0 0 2 0 8 5 0 . 1 1 u 6 2 . 9 1 9 0 0 3 . 0 3 0 0 . 3 6 5 4 1 3 1 9 0 0 4 . 0 8 0 1 . 6 1 9 0 3 5 0 a 3 8 1 9 0 0 5 “ a 0 2 5 “ 0 . 1 _ 1 3 1 •L 0 . 4 6 1 9 0 0 6 0 2 5 0 . 1 1 5 1 0 . 3 8 1 9 0 0 7 0 2 5 0 a 3 ... -J 1 7 0 . 3 7 1 9 0 0 8 0 2 5 0 . 1 7 - 1 0 . 5 1 1 9 0 1 1 . 0 2 5 0 a 3 8 5 6 3 . 2 1 9 0 1 2 . 1 8 5 0 . 7 5 7 4 3 a 4 -“i a —\ 1 9 0 1 3 1 . 4 5 0 l a 6 nr 1— X aJ i—1 a lH 1 9 0 1 4 3 . 7 0 0 3 . 4 2 9 6 3 a 0 1 9 0 1 5 . 2 0 0 0 . 2 4 4 5 1 . 2 1 9 0 1 6 - » 0 2 5 0 . 3 5 9 1 6 u 1 9 0 1 7 . 0 3 0 0 a 1 3 4 1 1 2 „ 3 1 9 0 1 8 . 0 3 5 0 . 3 6 9 1 2 2 a 8 1 9 0 1 9 3 . 7 0 0 2 . 4 rr 2 0 u 1 . 0 1 9 0 2 0 . 8 0 0 0 . 7 u lii 5 1 . 5 1 9 0 2 1 . 2 1 5 0 , 7 1 7 0 7 8 . 5 1 * 8 0 2 2 . 0 6 0 0 . 1 4 4 4 0 . 6 1 9 0 i 2 ' 3 . 0 6 5 0 a 2 7 9 6 c!o A- 1 9 0 2 4 i . 1 5 0 1 . 2 2 4 5 lla C 1 9 0 2 5 1 - 0 5 0 “7 1 . 3 5 5 c 3 a 0 1 9 0 2 6 . 5 5 0 2 . 6 1 3 l a 8 1 9 0 2 7 0 2 5 0 a 2 —5 3 0 a 6 4 1 9 0 2 8 . 0 3 0 6 8 . 0 9 7 2 4 0 8 a & 1 9 0 2 9 0 2 5 2 a 7 2 9 7 0 0 . 4 9 1 9 0 3 0 . 0 2 5 2 8 . 0 7 a 2 6 0 5 . 5 1 9 0 3 1 . 0 3 0 1 3 . 5 vi'iz! .c! 3 . 7 1 8 0 8 2 0 8 5 3 . 2 2 8 7 5 l a 6 1 9 0 3 4 0 2 5 - 0 . 1 2 3 0 5 3 5 9 1 9 0 3 5 0 2 5 0 . 2 1 1 0 i “J 8 5 a. -J 1 9 0 3 6 0 2 5 - 0 . 1 5 2 0 1 0 0 5 8 1 9 0 3 7 0 2 5 - 0 . 1 4 6 2 8 3 0 0 1 9 0 3 8 0 2 5 “ 0 . 1 4 7 3 3 4 0 0 1 9 0 3 9 0 2 5 0 a 5 1 6 0 5 3 8 5 1 9 0 4 0 0 2 5 0 a 5 1 2 0 1 0 0 8 0 0 1 9 0 4 1 0 2 5 - 0 a 1 2 7 2 0 1 3 1 9 0 4 2 0 2 5 1 4 . 5 1 5 6 6 6 . 0 1 9 0 4 3 0 2 5 0 . 3 1 4 CL 1 . 8 1 9 0 4 4 0 2 5 5 , 3 4 4 1 5 2 5 1 9 0 4 5 0 2 5 0 . 6 4 8 6 3 . 4 1 9 0 4 6 0 2 5 0 . 5 9 0 0 8 2 4 0 1 9 0 4 7 0 8 5 0 . 3 2 1 0 8 6 1 7 1 9 0 4 8 0 2 5 0 . 3 7 4 0 3 7 0 7 0 0 cr 1 9 0 4 9 0 8 5 0 . 2 •» ."*! v-J ~ 1 x u c 130

SAMPLE # flu Ag As Sb Hg

19050 1.050 C . n CL 310 4 1. 9 19051 025 -0. 1 10 7 140 19052 025 -0. 1 37 9 50 19053 025 0. 1 28 8 34 19054 025 -0. 1 -5 58 L j v J 19055 025 -0. 1 —5 11 0 29 19058 025 1.1 92 320 96 19059 025 0„ 4 390 190 210 19060 025 0. 9 300 92 65 190S 1 025 0. 3 320 210 95 19062 025 0. 1 110 vi 3. 0. 1.4 19063 "”** a i_ 0. 1 —5 5 025 -0. 1 55 10 3.. 3 19064 •t 19068 025 -0. 1 —5 A el • 19069 025 -0. 1 —5 el 9. 0 19070 025 0. 9 190 13 0. 21 19071 025 0. 2 L j C . a c l » u 19072 025 0. 1 30 %i 3-5 . 19073 0-25 0*8 320 55 14 19074 025 0. 1 66 1 8 14 -1 19075 - 085 0. 1 v ie . 92 19076 025 0. 1 12 — 1 5. 8 _t 19077 025 -0. 1 —5 0. 18 "i 19078 025 0. 1 31 9 1 a L . 19079 025 0. 1 67 20 be 6. 5 19079—A 1. 450 2. 8 220 20 19080 025 0. 1 —5 10 45 19085 025 0. 1 28 5 4. 5 19086 025 0. 1 10 7 3., 7 19087 025 -0. i 15 J. v J a J _ *» 19088 025 -0. 1 —5' A 0. 12 19089 025 0. 5 20 -1 0 a 45 19090 025 -0. 1 —5 — i 0. 06 19091 025 -0. 1 —5 l Z. h 6 19092 025 -0. 1 —5 •i 6. 7 19093 0.25 -0. 1 —5 c . 8. 1 19094 025 0. 5 93 — I 11 19095 — OIOS - Cl 45 1 17 19096 025 0. 1 7 e l 16 19097 025 0. 1 50 a 21 19098 025 -0. 1 —5 10 0. 69 19099 025 0, 1 —b 4 7. 2 19100 025 0. 2 840 19 88 19101 025 0. 1 230 55 16 ,7, o vz- 19102 ■ l—. w -0. 1 —5 — l 0. 51 19103 025 0* 8 230 16 17