Geology and Mineral 

Deposits of the Osgood 

Mountains Quadrangle 

Humboldt County, Nevada 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 431 
Geology and Mineral 

Deposits of the Osgood 

Mountains Quadrangle I 

Humboldt County, Nevada 

By PRESTON E. HOTZ and RONALD WILLDEN 

GEOLOGICAL SURVEY PROFESSION L PAPER 431 

Stratigraphy and structure of Paleozoic rocks, 

granitic intrusions, contact metamorphism, and 

deposits of tungsten, gold, and other minerals 

I 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1964 
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary 

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director 

The U.S. Geological Survey Library has cataloged this publication as follows: 

Hotz, Preston Enslow, 1913-

Geology and mineral deposits of the Osgood Mountains 

quadrangle, Humboldt County, Nevada, by Preston E. Hotz 

and Ronald Willden. Washington, U.S. Govt. Print. Off., 

1963. 

v, 132 p. Illus., maps (part col.) diagrs., tables. (U.S. Geological 

Survey. Professional paper 431) 

Part of illustrative matter fold. in pocket. 

Bibliography: p. 122-124. 

Hotz, Preston Enslow, 1913-

Geology and mineral deposits of the Osgood Mountains 

quadrangle, Humboldt County, Nevada. 1963. (Card 2) 

1. Geology-Nevada-Humboldt Co. 2. Ore:-deposits-NevadaHumboldt Co. 3. Mines and mineral resources-Nevada-Humboldt Co. 

I. Willden, Charles Ronald, 1929- joint author. II. Title: Osgood 

Mountains quadrangle, Humboldt County, Nevada. (Series) 

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 
CONTENTS 

Abstract __________________________________________ _ 

Introduction ______________________________________ _ 

Location, culture, and accessibility _______________ _ 

Physical features _________ _______ - ___ - _________ _ 

Climate and vegetation _________________________ _ Previous work _________________________________ _ 

Present work and acknowledgements _____________ _ Rock units ________________________________________ _ 

Rocks of Cambrian(?) and Cambrian age _________ _ 

Osgood Mountain quartzite _________________ _ 

Lithology of the Twin Canyon member ___ _ Preble formation ___________________________ _ 

Paradise Valley chert _______________________ _ 

Harmony formation ________________________ _ 

Rocks of Ordovician age ________________________ _ 

Comus formation __________________________ _ 

Valmy formation _________ .. ________________ _ 

Equivalence of the Comus and Valmy formations, and possible facies relationships ______ _ 

Rocks of Mississippian age ____ ___ _______________ _ 

Goughs Canyon formation __________________ _ 

Rocks of Pennsylvanian and Early Permian age ___ _ Battle formation ___________________________ _ 

Etc hart limestone __________________________ _ 

Adam Peak formation ______________________ _ 

Conditions of deposition of the Etchart 

limestone and Adam Peak formation ____ _ 

Rocks of Pennsylvanian(?) to Permian(?) age _____ _ 

Farrel Canyon formation ___________________ _ 

Intrusive basalt of uncertain age _________________ _ 

Intrusive igneous rocks of Late Cretaceous age ____ _ 

Granodiorite and related rocks ______________ _ 

Distribution ______________ -_- __________ _ 

Structural relations of the stock in the Osgood Mountains _____________________ _ 

Structural relations of granodiorite in the 

Hot Springs Range __________ _________ _ 

Age of the granodiorite ____ -_--- _____ ---_ Petrography __________________________ _ 

Chemical composition __________________ _ 

Marginal facies ________________________ _ 

Alteration of the granodiorite ___________ _ 

Chemical changes __________________ _ 

Comparison with other examples of 

hydrothermal alteration __________ _ 

Similar alteration of sedimentary rocks 

of the Harmony formation ________ _ 

Minor intrusive bodies __________________ --- _ 

Quartz diorite ______________________ -- __ 

Aplite and pegmatite ___________________ _ 

Dacite porphyry _______________________ _ 

Andesite porphyry _____________________ _ 

Alteration of the minor intrusives ________ _ 

Age.of the minor intrusives _____________ _ 

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Rock units-Continued 

Rocks of Tertiary age ___ ------------------------ Conglomerate _____________________________ _ 

Rhyolite tuffs __________ - - ------------------

Distribution ______ ____ ------------------ Petrography __________________________ _ 

Body of tuffaceous rock near Getchell mine ___ - Flows ____________________________________ _ 

Andesite flows of the southern Osgood 

Mountains, Dry Hills, and Hot Springs Range ______________________________ _ 

Olivine basalt on Soldier Cap ______ ______ _ 

Chemical composition of the Tertiary flows_ 

Age and correlation ___________ -""'------------

Rocks of Quaternary age ______ ------------------

Basalt flow near Comus station ______________ _ 

Older fan gravels _____ ----------------------

Talus-----------------------~------------- Alluvium _________________________________ _ 

Metamorphism ___________ --------------------------

Contact metamorphism and metasomatism ________ _ 

Contact metamorphism at Dutch Flat_ _______ _ 

Contact metamorphism in the Osgood Mountains-----------~------------------------

Metamorphism of the pelitic rocks _____ -_-_ 

Metamorphism of the carbonate rocks ____ _ 

Marble and silica ted marble ___ -------

Calc-silicate rocks __ ,__--- __ ----------

Tactite __________ - _----------------

Metamorphism of Paleozoic volcanic rocks_ 

Endomorphism of the granodiorite __ ----------

Structural geology ______________ --- - - --- --- - - - ---- - -

Folds in the Osgood Mountains __________________ _ 

Age of the folding __________________________ _ 

Thrust faults in the Osgood Mountains..:_----------

Valmy thrust plate _______ -------------------

Twin Canyon fault _________ -----------------

Adam Peak thrust _________ -----------------

Granite Creek thrust_ ____ -_-----------------

Peak 683 7 thrust ______ - _-------------------

Imbricate thrust zone in the Osgood MountainsPreble thrust plate_-_-- -----------------

Etchart Canyon thrust plate_------------

Harmony thrust plate __ -----------------

Goughs Canyon thrust plate __ "'" ---- ------

Farrel Canyon thrust_ ____ ---------------

High-angle faults in the Osgood Mountains--------

Anderson Canyon fault ___ -_-----------------

Village fault- __________ -_-_-- ---------------

Getchell fault _________ ------ ---------------

Ogee and Pinson fault ____ -------------------

Other high-angle faults _________ -_-_---------

Folds in the Hot Springs Range _____ - _-----------

Faults in the Hot Springs Range _____ -------------

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IV 

Structural geology-Continued 

Relation between the Hot Springs Range and the ~good ~ountains ___________________________ _ 

Origin of the ranges ____________________________ _ 

Interpretation of the structural relations and geologic 

historY------------------------------------------ Paleozoic history _______________________________ · 

Cambrian sedimentation ____________________ _ 

Cambrian diastrophism _____________ --------_ 

Ordovician sedimentation ___________________ _ 

Antler orogeny ____________________________ _ 

Late Paleozoic sedimentation ________________ _ 

Late Paleozoic or ~esozoic orogenic history _______ _ Cenozoic history _______________________________ _ 

Early Cenozoic history _____________________ _ 

Cenozoic diastrophism ______________________ _ 

~ineral deposits ___________________________________ _ 

Tungsten deposit$ in the ~good ~ountains _______ _ 

Deposits in. tactite _________________________ _ 

~ineralogy and paragenesis _____________ _ 

Form and structural relations ___________ _ 

Origin----------------·----------~----- Deposits in altered granodiorite ______________ _ Origin ________________________________ _ 

Gold-arsenic deposits in the ~good ~ountains ____ _ Distribution _______________________________ _ 

General features ___________________________ _ 

~ineralogy and paragenesis _________________ _ Gold _________________________________ _ 

Silver---------------------------------

Origin and classification of the deposit ________ _ Age of mineralization_ ______________________ _ 

Quicksilver deposits ____________________________ _ 

Gold-bearing quartz veins in the Hot Springs Range __ 

Gold-scheelite-cinnabar placer ___________________ _ 

Minor deposits of lead and copper _______________ _ Lead deposits _____________________________ _ 

Copper deposits ___________________________ _ 

Barite deposits in the Osgood Mountains __ -------- Silica _________________________________________ _ 

.Mining future of the region _____________________ _ 

CONTENTS 

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Mines and prospects _______________________________ _ 

Tungsten deposits _____________________________ _ 

History and production _____________________ _ 

Granite Creek mine __ ------ _____ ------- ____ _ 

Tip Top mine------------------------------ Marcus mine ______________________________ _ 

Pacific mine _______________________________ _ 

Valley View mine __________________________ _ 

Kirby mine _______________________________ _ 

Top Row pit ______________ --- __ --------- __ _ 

Riley and Riley Extension mines ____________ _ 

Tonopah mine ________________ --------------

Alpine (Porvenir) mine ________________ ------

Richmond mine _____ ---------- ____________ _ 

Mountain King mine _______________________ _ T.N.T. mine ______________________________ _ 

Section 5 (Marshall Canyon) pit _____________ _ 

Prospects in the canyon of ~good Creek _____ _ Gold deposits __________________________________ _ 

Getchell mine _____________________________ _ 

History and production _________________ _ Geology ______________________________ _ 

Ogee and Pinson mine ______________________ _ 

Other occurrences of Getchell-type gold deposits_ 

Gold-quartz veins in the Dutch Flat district ___ _ 

Quicksilver deposits in the Hot Springs Range _____ _ Dutch Flat mine ___________________________ _ 

Last Chance prospect ____ ------------------- K and K (Red Devil) prospect ______________ _ 

Lead-zinc deposits _____________________________ _ 

Richmond mine ___________________________ _ 

Silver Hill mine ___________________________ _ 

Unnamed prospect _________________________ _ 

Copper deposits __ -· ____________________________ _ 

Barite prospects _______________________________ _ 

Barium and Barum groups of claims ________ _ Other prospects ____________________________ _ 

References cited ___________________________________ _ 

Index ____________________________________________ _ 

ILLUSTRATIONS 

PLATE 1. 

2. 

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9. 

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u. 

[Plates are 1n pocket] 

Geologic map and sections of the Osgood Mountains quadrangle, Nevada. 

Geologic map and sections of the Granite Creek and Tip Top Mines. 

Underground workings of the Granite Creek mine. 

Geologic map and section of the Valley View mine. 

Geologic map and section of the Kirby mine. 

Geologic map and sections of the Riley and Riley Extension mines. 

Underground workings of the Riley and Riley Extension mines. 

Geologic map and underground workings of the Tonopah mine. 

Geologic map of the Alpine (Porvenir) mine. 

Geologic map of the Richmond and Mountain King mines. 

Surface map, sections, and composite level map of ore bodies, Getchell mine. 

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CONTENTS v 

Pue 

FIGURE 1. Index map of Nevada_______________________________________________________________________________ 4 

2. Photomicrographs of feldspathic sandstone of the Harmony formation_____________________________________ 16 

3. Point diagram of poles of 95 joints measured in granodiorite stock of the Osgood Mountains________________ _ 42 

4. Modal composition of granodiorite from the Osgood Mountains__________________________________________ 44 

5. Graph showing gain and loss of principal rock constituen'Gs by alteration of the granodiorite stock at Dutch Flat__ 4 7 

6. Rittman diagram showing p-values of volcanic rocks in the Osgood Mountains quadrangle___________________ 57 

7. Diagram of the k-ratio of volcanic rocks plotted against their Si02 content_________________________________ 57 

8. Calc-silicate rock cut by tactite at the Pacific mine pit____ ______________________________________________ 65 

9. Graph showing gain and loss of rock constituents in conversion of limestone to garnet-pyroxene tactite_ _ _ _ _ _ _ _ 68 

10. Views of the Granite Creek thrust fault_______________________________________________________________ 72 

11. View of the GetcheJl fault, Getchell mine______________________________________________________________ 75 

12. Thin section photomicrographs of scheelite in tactite_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 85 

13. Sketches of some tactite bodies_________________________________ _______________ ____ ____ ________________ 87 

14. Sequence of mineral deposition at Getchell gold deposit__________________________________________________ 90 

15. Map of the Dutch Flat district_______________________________________________________________________ 94 

16·. Index map of the Osgood Mountains tungsten deposits_____________ _______________________________ ______ 98 

17. Block diagram of the Pacific mine____________________________________________________________________ 102 

18. Geologic map of the T.N. T. mine__________________________ __ _________________________________________ 113 

19. Map of the Dutch Flat mine_________________________________________________________________________ 120 

TABLES 

Page 

TABLE 1. Precipitation and temperature data, Winnemucca, Nev., to 1957-------------------------------------- --- 5 

2. Chemical and spectrographic analyses of shale and limestone from the Preble formation ________________ -- __ -_ 11 

3. Modes of the Harmony formation______________________________________________________________________ 15 

4. Chemical analyses of sandstone of the Harmony formation_______________________________________________ 17 

5. Heavy minerals in limestones of the Harmony formation _____ .:___________________________________________ 18 

6. Analyses and norms of altered volcanic rocks from the Goughs Canyon formation ______________________ - _ _ _ _ 25 

7. Analysis, norm, and Niggli values of intrusive basalt of uncertain age _______ ________________________ ------ 41 

8. Modes of granodiorite from stock in the Osgood Mountains ______ ____________________________________ --__ 44 

9. Analyses, norms, and Niggli values of granodiorite________________________________________________________ 45 

10. Quantitative spectrographic analyses for minor elements in granodiorite____________________________________ 45 

11. Modes of marginal facies of granodiorite from stock in the Osgood Mountains _______________________ -------- 46 

12. Analyses, norms, and Nigg1i values for unaltered and altered granodiorite _________________________________ - 48 

13. Quantitative spectrographic analyses for minor elements in unaltered and altered granodiorite_________________ 49 

14. Analysis, norm, and Niggli values of typical altered intrusive dacite porphyry_______________________________ 50 

15. Analyses, norms, modes, and Niggli values of Tertiary flows in the Osgood Mountains quadrangle _________ ---- 55 

16. Quantitative spectrographic analysis of minor elements in volcanic rocks___________________________________ 56 

17. Analysis, norm, mode, and Niggli values of basalt near Comus station ________________________________ - __ -- 58 

18. Analyses of cordierite hornfels and schistose biotite hornfels_______________________________________________ 62 

19. Analyses of limestone and garnet-pyroxene tactite ______________________________________________________ - 67 

20. Production of tungsten ore, Osgood Mountains__________________________________________________________ 99 

21. Gold, silver, copper and lead production from the Getchell mine _______________________________________ -___ 115 

22. Gold mines and prospects in Dutch Flat________________________________________________________________ 118 
., 
GEOLOGY AND MINERAL DEPOSITS OF THE OSGOOD MOUNTAINS QUADRANGLE, 

HUMBOLDT COUNTY, NEVADA 

By PREsTON E. HoTz and RoNALD WILLDEN 

ABSTRACT 

The Osgood Mountains quadrangle is in north-central Nevada 

northeast of Winnemucca, the principal town in the region. 

The quadrangle includes two north-northeast-trending mountain 

ranges, the Osgood Mountains on the east and the Hot Springs 

Range on the west, which are separated by a narrow valley and 

are bounded on the east and west by broad alluviated basins. 

Large deposits of tungsten and gold have been mined in the 

northeastern part of the Osgood Mountains; small deposits of 

quicksilver, lead, zinc, and gold are known in the Hot Springs 

Range, and some prospecting has been done on barite deposits 

in the Osgood Mountains. Some quartzite beds are potential 

sources of silica. 

Paleozoic rocks exposed in the quadrangle include strata of 

Cambrian, Ordovician, Mississippian, Pennsylvanian, and 

Permian age. 

Four units of Cambrian and one of probable Cambrian age 

have been recognized. The oldest, the Osgood Mountain qual"'tzite of Cambrian(?) age, is exposed only in the southern part of 

the Osgood Mountains. Most of the formation is a relatively 

pure crossbedded quartzite with a few thin shaly partings. In 

places an impure quartzite unit, the Twin Canyon member, 

forms the upper part of the Osgood Mountain quartzite. The 

formation is unfossiliferous, but it grades upward into the 

Preble formation, which contains fossils of Middle and Late 

Cambrian age. The Preble formation, which also occurs exclusively in the Osgood Mountains, is predominantly shale but 

includes a few quartzite beds in its lower part and is composed 

of interbedded limestone and shale in the middle and upper 

part of the section. A new formation, the Paradise Valley chert 

of Late Cambrian age, is the next youngest unit, but its stratigraphic relations to the Preble formation are not known because 

it is restricted to a small area on the northwest side of the Hot 

Springs Range. The formation is predominantly chert but 

includes some thin beds of shale and limestone. On the basis of 

fossil faunas the Paradise Valley chert is correlated with the 

lower part of the Dunderberg shale in the vicinity of Cherry 

Creek and McGill, eastern Nevada. The uppermost Cambrian 

unit is the Harmony formation, which rests in depositional contact on the Paradise Valley chert. The Harmony makes up 

most of the Hot Springs Range .in the quadrangle and occupies a 

thrust plate in the Osgood Mountains. Feldspathic sandstone 

and shale are the predominant rock types of the Harmony formation, but the formation also includes some limestone and a little 

.chert. Trilobites of Late Cambrian age were found in the limestone at two widely separated places. 

Two Ordovician units having very different lithologies were 

mapped. The Comus formation of Early and Middle Ordo. 

vician age is predominantly an alternating sequence of dolomite, 

limestone, and shale, with subordinate amounts of chert, .siltstone, and tuffaceous ( ?) material. Sandstone and quartzite 

are conspicuously absent. In the Valmy formation of Early, 

Middle, and Late Ordovician age, chert and siliceous shale predominate. The Comus and Valmy formations are not in contact 

in this quadrangle, but from relations elsewhere the Comus is 

regarded as autOchthonous, whereas the Valmy is believed to 

have been brought into the area by thrust faulting. 

A formation of Early and Late Mississippian age, the Goughs 

Canyon formation, occupies a thrust plate in the Osgood 

Mountains. Its stratigraphic relations with other Paleozoic 

rocks are not known. The formation is composed mostly of 

altered volcanic rocks of medium to basic composition and coarsegrained fossiliferous limestone, and minor amounts of calcareous 

shale, siliceous shale, and chert. 

Strata of Middle Pennsylvanian to Late Pennsylvanian and 

Early Permian age rest unconformably on the older Paleozoic 

rocks in the Osgood Mountains. The beds include the Battle 

formation, a dominantly terrestrial conglomerate of Middle 

Pennsylvanian age (Atoka to Des Moines), which underlies and 

interfingers with the Etchart limestone of Middle Pennsylvanian 

(Des Moines or older) to Late Pennsylvanian or Early Permian 

(Missouri or "\\"olfcamp) age. The Etchart limestone is predominantly a sequence of limestone and sandy limestone, with 

some interbedded dolomite, minor amounts of calcareous shale, 

and lenticular beds of conglomerate. A clastic facies partly 

equivalent in age to the Etchart limestone, the Adam Peak 

formation, has been thrust over the Etchart limestone. The 

Adam Peak is chiefly shale, siltstone, dolomitic sandstone, and 

chert, but the formation includes some limestone and dolomite. 

A sequence of sandstone, shale, chert, and altered volcanic 

rock, the Farrel Canyon formation, crops out in the northwestern part of the Osgood Mountains. No fossils have been found 

in the Farrel Canyon formation, hence its stratigraphic position 

is uncertain ; but lithologically it resembles parts of the Pumpernickel formation of Pennsylvanian(?) age and the Havallah 

formation of Middle Pennsylvanian (Atoka) and Permian age 

which occur elsewhere in north-central Nevada. 

One large intrusive body of granodiorite cuts the Preble formation in the Osgood Mountains and three smaller stocks cut 

the Harmony formation in the Hot Springs Range. A leadalpha age determination of 69 · million years for the Osgood 

Mountains stock dates the granodiorite as very Late Cretaceous. 

Except for a slightly more mafic border facies in parts of the 

Osgood Mountains stock, the composition of the granodiorite is 

1 
2 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

very uniform. Alteration has affected a small area in the 

Osgood Mountains stock, however, and large parts of the smaller 

stocks of the Hot Springs Range have likewise been transformed. The alteration, which was accompanied by introduction of pyrite, resulted in albitization and sericitization of 

feldspars, destruction of biotite, and some addition of quartz. 

Small bodies of quartz diorite in the northern end of the Osgood 

Mountains show similar alteration effects. The granodiorite is 

cut by aplite dikes and small dikes and veinlets of quartz-feldspar pegm~tite. Thin tabular bodies of intrusive dacite porphyry are widespread in the Paleozoic sedimentary rocks of the 

Osgood Mountains. Probably the dikes are genetically related to 

the granodiorite, but their relative ages are uncertain; 

Remnants of formerly widespread volcanic rocks of Tertiary 

age (late Miocene(?) to middle Pliocene(?)) are scattered 

over the quadrangle in the lower parts of the Osgood Mountains 

and the Hot Springs Range. These are mostly andesitic and 

some basaltic flow rocks, locally underlain by tuffaceous rocks 

of rhyolitic composition. Some small remnants of conglomerates that are presumably of Tertiary age were also observed 

but are not shown on the map. 

Surficial deposits of Quaternary age have been divided into 

older fan gravels, talus, and alluvium. A basalt flow on the 

southern boundary of the quadrangle is also probably of Quaternary age. 

A conspicious aureole of contact metamorphism surrounds the 

Osgood Mountains granodiorite stock, and a small but well-defined halo of metamorphism surrounds the largest of the small 

stocks in the Hot Springs Range. In the Osgood Mountains, the 

contact metamorphic aureole is as much as 10,000 feet wide; the 

rocks involved were mainly shales and carbonate rocks of the 

Preble formation, although some other formations were also 

affected. The shales were transformed to hornfelses in which 

biotite, andalusite, and cordierite were formed. The carbonate 

rocks were converted to marble, light-colored calc-silicate rock, 

and dark tactite composed of garnet, pyroxene, other lime-silicate minerals, and the economically important tungsten-bearing 

mineral, scheelite. Paleozoic volcanic rocks were generally ~oo 

far from the intrusive body to be contact metamorphosed, but at 

one or two places there has been recrystallization and formation 

of plagioclase, pyroxene, actinolitic amphibole, and biotite. A 

narrow aureole of metamorphosed shale and feldspathic sandstone surrounds a small granodiorite stock ii;l the Hot Springs 

Range. The shale has been darkened and hardened, and where 

it is most intensely metamorphosed, andalusite and biotite have 

formed. Some endomorphism of the Osgood Mountains granodiorite stock has taken place along the contact by reaction between carbonate country rock and the intrusive. The granodiorite contains pyroxene as the principal mafic mineral instead 

of hornblende or biotite, sphene is plentiful, and orthoclase is 

somewhat more abundant. 

The main structural elements strike closely ,parallel to the 

northeasterly trend of the ranges. Within both ranges northon the west side of the range is the dominant structural feature 

of the northern two-thirds of the Osgood Mountains. Other 

thrust faults are exposed along the crest and east side of the 

range, involving many of the same rocks. A major thrust fault 

that probably is equivalent to the Roberts Mountains thrust 

fault, a major structural feature in north-central Nevada, is 

postulated to explain the occurrence of two Ordovician formations of different facies-the Valmy and Comus formationsin the same area. The Valmy is believed to have been carried 

in on a thrust plate. 

The rocks in the Osgood Mountains are also cut by northstriking high-angle longitudinal faults, which are more 

continuous and more important structurally than the high-angle 

cross faults. The age of most of the high-angle longitudinal 

faults is not known ; however, the Getchell fault on the east side 

of the range is younger than latest Cretaceous, and some of the 

longitudinal faults on the east side of the Osgood Mountains 

are range-front faults of late Tertiary age. 

The principal structural features of the Hot Springs Range 

are a series of asymmetrical, north-plunging, westward-overturned folds in the Paradise Valley and Harmony formations. 

The faults are normal vertical or high-angle faults in this part 

of the range ; they can be grouped into a north- to northeaststriking set and a northwest-striking set. Many of the faults 

cut the Tertiary volcanic rocks. 

The structural relation between the Osgood Mountains and 

Hot Springs Range is obscured by an alluvium-filled valley between the two ranges. Two possibilities suggested by the observable data are (1) that the Hot Springs Range is an autochthonous block on the west side of a major anticline whose crest 

is in the Osgood Mountains; or (2) that the Hot Springs Range 

is on the upper plate of a thrustfault. High-angle normal faults 

on the east side of the Hot Springs Range, which postdate the 

Tertiary volcanic rocks, may be the structural boundary between the mountain blocks. High-angle normal faults also 

bound the east side of the Osgood Mountains and the west side 

of the Hot Springs Range. 

Mining activity has been directed chiefly toward exploitation 

of tungsten and gold deposits in the Osgood Mountains. Active 

mining of tungsten ore began in 1942 ; by the end of 1955 more 

than 1,300,000 tons of ore containing more than 590,000 units 

of WOa had been produced. Between 1938 and 1950 production 

from the Getchell gold mine exceeded $16 million in value. A 

small production of quicksilver and gold has come from deposits 

in the Dutch Flat district in the Hot Springs Range. The placers 

at Dutch Flat have yielded gold valued at about $200,000. Leadsilver and copper deposits of minor importance are known but 

have yielded little or no production. Nonmetallic deposits include barite prospects in the Osgood Mountains and high-purity 

quartzite suitable as a source of silica. 

Tactites formed by metamorphism of limestone of the Preble 

formation adjacent to the granodiorite stock in the Osgood 

Mountains have been the main source of scheelite, the ore 

west-striking cross faults are about perpendicular to the north- . mineral of tungsten. Molybdenite has a sporadic distribution 

east structures. A major broad anticline involves chiefly the 

Osgood Mountain quartzite and Preble formation in the Osgood 

Mountains. This structure is concealed by younger thrust plates 

and unconformable Pennsylvanian strata in the northern part 

of the range, and by Tertiary volcanic rocks in the southern part 

of the range. The younger Paleozoic rocks are steeply tilted and 

tightly folded at many places ; much of the folding is related 

to thrust faulting. An imbricate thrust zone affecting rocks of 

Cambrian, Mississippian, and Pennsylvanian and fermian age 

in the tactite zone, and accessory amounts of pyrite, chalcopyrite, sphalerite, and galena are present. The tactites are generally tabular bodies parallel to the granodiorite contact. Many 

of the largest and most productive tactite bodies are situated 

in troughs and sharp reentrants in the granodiorite contact 

surfaces. 

The Getchell gold deposit is a gold-arsenic association in 

fractured rocks along the Getchell fault, a high-angle normal 

fault zone on the northeast base of the Osgood Mountains. 
iNTRODUCTION 3 

Gold is associated with the arsenic sulfides orpiment and realgar. This epithermal deposit was formed later than the tungsten deposits. 

Other gold deposits are on the western side of the Hot Springs 

Range near Dutch Flat, where gold-bearing quartz veins cut a 

small granodiorite stock and the surrounding sedimentary rocks 

of the Harmony formation. The history of mining from these 

small veins is unknown, but there is no evidence of any important production. 

Three small quicksilver deposits are known in the Dutch Flat 

district in the Hot Springs Range. The only recorded production, fro~ the Dutch Flat mine, has amounted to less than 2 

flasks per year since 1942. Cinnabar fills fractures in altered 

feldspathic sandstone and shale of the Harmony formation and 

occupies spaces between mineral grains in sandstone. 

Placer deposits at Dutch Flat contain significant amounts of 

gold, scheelite, and cinnabar. Economic recovery of scheelite 

and cinnabar has not been accomplished. 

Three small barite deposits are situated in the Osgood Mountains. None has had any commercial production, and only one 

appears to be a potentially commercial deposit. 

The principal mineral resources of the area are tungsten and 

gold. Although the reserves of tungsten have been reduced by 

high production since 1951, and most if not all of the ore that 

could be readily mined by open pits is gone, there remain important underground deposits of tactite that can be mined. It 

is very unlikely that new scheelite deposits will be discovered 

at the surface, but underground exploration might show important extensions of known ore bodies and possibly totally unknown 

deposits. There is a large reserve of gold-arsenic ore at the 

Getchell mine, but its exploitation must await more favorable 

economic conditions and technological improvements. Probably 

no important production of quicksilver can be expected from 

the known deposits, and the outlook for discovery of new resources of cinnabar is not good; but the placers at Dutch Flat 

might yield a moderate amount of quicksilver and tungsten as 

well as gold. Probably no more than token amounts of galena 

and sphalerite will ever be produced. Barite and possibly silica 

may eventually be produced in modest quantities. 

INTRODUCTION 

LOCATION, CULTURE, AND ACCESSIBILITY 

The Osgood Mountains quadrangle is in Humboldt 

County, north-central Nevada, between lat 41 °00' N. 

and 41 °15' N., and long 117°15' W. and 117°30' W. 

(fig. 1). 

No established towns are within the quadrangle, but 

Golconda (pop. 430) is about 3 miles south of the southern boundary. Winnemucca (pop. 2,847), the county 

seat and the most important town in the region, is about 

16 miles west of Golconda. Getchell townsite is a semipermanent community with modern facilities at the 

Getchell mine, but the population varies widely depending on the number of men employed in the mines and 

mill. A few scattered ranch houses are the only other 

habitations in the quadrangle. As in most rural areas 

of Nevada, mining and cattle ranching are almost the 

only means of livelihood. 

Main lines of the Southern Pacific Railroad and the 

Western Pacific Railroad run on parallel rights-of-way 

through the southeast corner of the quadrangle. Stations for both lines are located at Golconda. Red 

House, on the Southern Pacific less than 0.1 mile beyond 

the southeast corner of the quadrangle, is the main 

shipping point for the Getchell mine. 

The valley areas are readily accessible by automobile 

road from either south or north, but most of the travel 

is to and from the south where roads connect with U.S. 

Highway 40, which passes through Golconda. A good 

dirt road crosses the full length of the quadrangle from 

Golconda north through Eden Valley (pl. 1) to the 

Little Humboldt River; a side road branches off near 

Stone Corral and leads to the east side of Paradise 

Valley and the Dutch Flat quicksilver mine. The road 

along the east side of the Osgood Mountains to the 

Getchell mine connects with State Route 18, which 

leaves U.S. Highway 40 about 1 mile east of Golconda. 

It is paved for 13.5 miles to the junction in NW1,4 sec. 

20, T. 37 N., R. 42 E. where a good unpaved road (State 

Route 18) continues eastward to Midas and southeastward to Red House. The paved road is new and is not 

shown on the topographic map of the quadrangle, but 

it is about 1 mile east of and roughly parallel to the 

road that passes near Lone Butte and Hugh Bains 

ranch. The lower parts of several valleys in the ranges 

are accessible by poor roads and jeep trails, but the 

higher parts can be reached only on foot or horseback, 

except in the northern part of the Osgood Mountains 

where the steep Burma Road from the Getchell mine 

crosses the range and connects with the Eden Valley 

road via Anderson Canyon. All the tungsten mines in 

the Osgood Mountains are accessible by fair to good 

roads. 

PHYSICAL FEATURES 

Two mountain ranges-relatively short in comparison with many Nevada ranges-and a narrow intervening valley are the principal gross topographic features 

in the quadrangle (fig. 2). The Hot Springs Range 

trends north-northeast through the northwest part of 

the quadrangle and ends at the Little Humboldt River, 

approximately 12 miles beyond the north boundary. 

The Osgood Mountains, which are only about 24 miles 

long, commence at the Humboldt River about 2 miles 

south of the south boundary and continue through the 

southwest, central, and northeast parts of the quadrangle. The main part of the range terminates about 2 

miles beyond the north boundary, and some low hills 

extend about 8% miles northeast of the northeast 

corner of the quadrangle. The Hot Springs Range is 

flanked on the west by Paradise Valley, which drains 
4 

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:WASHOE 

I 

25 0 

GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

H U M B 

25 50 

•Manhattan 

P I N E 

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----------~~~-~-==~~~~-~=---------~----~~38~ 

ERALDAI 

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'"~~~~~~ FIGURm 1.-Index map of Nevada showing the location of the Osgood Mountains quadrangle. 
INTRODUCTION 5 

to the Little Humboldt River. Eden Valley lies between the Hot Springs Range and the Osgood Mountains; on the topographic map of the quadrangle only 

the northern part, which drains northward through 

Eden Creek to the Little Humboldt .River, is shown as 

Eden Valley, but the name is also applied locally to the 

southern part that drains southward to Humboldt 

River. The Osgood Mountains are bounded on the 

east by the broad alluviated valleys of Kelly Creek 

and the Humboldt River. The main drainage channel 

of northern Nevada, the westward-flowing Humboldt 

River, is slightly south of the quadrangle, except for 

a short loop that enters the extreme southern part near 

Comus railroad siding. West of Comus the river enters 

a narrow valley which separates the Osgood Mountains 

from the Edna Mountains to the southeast in the Golconda quadrangle. 

The general altitude of the valleys that border the 

ranges is from 4,500 to 4,700 feet. The crest of the 

Osgood Mountains gradually increases in altitude from 

approximately 5,750 feet at the south end to more than 

8,000 feet in the central and northern parts, and declines to 6,000 feet at the north boundary of the quadrangle. The Hot Springs Range is somewhat lower, 

ranging from a general crestline altitude on the order 

of 6,750 feet in the northern part to around 6,000 feet 

in the southern part. Average relief of the Osgood 

Mountains ranges from 1,250 feet ·to 3,500 feet above the 

basins, that of the Hot Springs Range is from 1,500 

feet to 2,250 feet. Adam Peak, in the central Osgood 

Mountains, is the highest point in the quadrangle; its 

altitude is 8,678 feet. The lowest part is in the southwest corner, where the alluvium-filled valley is about 

4,350 feet above sea level. Maximum relief, therefore, 

is more than 4,300 feet. 

The topography of the Osgood Mountains is more 

rugged and less uniform than that of the Hot Springs 

Range. In the Hot Springs Range rather uniform 

dissection has resulted in topography of monotonous 

aspect. Many short steep-sided canyons, each with a 

multitude of steeper subsidiary ravines and gullies and 

narrow smooth-surfaced divides, lead eastward or westward from the narrow north-trending crest to the alluvial aprons at the base of the range. The crest of the 

range east of Dutch Flat and extending southward for 

about 2 miles is a rather broad surface of gentle relief; 

but in general the canyons, ravines, and gullies and 

the slopes bocween them resemble their counterparts 

elsewhere in the range, and there is a general lack of 

eye-catching forms. The Osgood Mountains, on the 

other hand, have a considerably varied topography. 

In the southern part of the range the summit areas 

are commonly gently rolling surfaces which drop off 

abruptly to steep slopes below. The central and northcentral parts of the range have high na.rrow ridges, long 

relatively smooth steep slopes, some bold clifflike features, and several large valleys, amphitheaterlike at 

their heads, narrow and steeper toward the range front. 

The north end of the range is thoroughly dissected by 

many short ravines and gullies. The east front is fairly 

straight, and in the northern part several of the easttrending ridges are terminated with subtriangular facets; in the southern and central parts the mountain 

front is fairly steep but descends gradually into gentler 

pediment slopes veneered with gravel that grades into 

the valley alluvium. The west front is considerably 

more irregular and is marked by several reentrants and 

mountain spurs that project into the valley. 

CLIMATE AND VEGETATION 

Rainfall records for Winnemucca, Nev. (table 1), 

show that the annual rainfall averages 8.75 inches. 

Most of the precipitation is in the winter and spring, 

chiefly as snow during the winter and early spring 

months. Occasional thunderstorms bring some rain 

during the summer. 

The mean annual temperature is 49.1 °F (table 1). 

Summer days are warm and the nights cool. The winters are cold, the average temperature during December 

and January being below freezing. 

The Hot Springs Range and the Osgood Mountains 

are almost devoid of trees, except for a few aspens in 

the upper parts of some canyons. The most conspicuous vegetation is "sagebrush" and sparse grasses which 

are food for the range cattle. During the spring small 

flowering plants of many kinds are plentiful. 

TABLE I.-Precipitation and temperature data, Winnemucca, 

Nev., to 1957 

[U.S. Weather Bureau, Annual Summary 1957, v. 72, no. 13, p. 153-154] 

January ___________________________ _ February __________________________ _ ~arch _____________________________ _ 

ApriL __________ - _- _---------------- ~ay ___________________________ ___ _ June ______________________________ _ July _______________________________ _ August ____________________________ _ September _________________________ _ October ____________________________ _ November _________________________ _ December __________________________ _ 

Annual ____________________________ _ 

Years of record ____________ -_-_-_----

Average 

temperature 

(° F) 

27. 8 

34. 5 

39. 4 

46. 8 

55. 9 

64. 0 

74. 2 

69. 7 

59. 9 

48. 6 

37. 6 

30.0 

49. 1 

77 

A,verage precipitation (inches) 

0. 96 

1. 01 

. 86 

. 73 

. 84 

. 79 

. 31 

. 18 

. 34 

. 79 

. 84 

1. 00 

8. 75 

87 
6 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

PREVIOUS WORK 

No detailed geologic m·apping was done in the Osgood 

Mountains quadrangle until 1946 when S. W. Hobbs 

mapped the northern part of the Osgood Mountains 

as part of a study of contact metamorphism and 

tungsten deposits adjacent to the granodiorite stock.1 

Pre'7ously Hess and Larsen ( 1921, p. 300-304) briefly 

studied some of the tungsten deposits in the northern 

part of the Osgood Mountains, and Hardy (1941) published a short description of the geology of the Getchell 

gold deposit. The Dutch Flat placer deposit on the 

west side of the Hot Springs Range was first described 

by Smith and Vanderburg ( 1932). The quicksilver deposits in the Hot Springs Range were first described 

by Bailey and Phoenix in 1944. 

Eugene Callaghan and C. J. Vitaliano prepared 

planetable maps of some of the tungsten properties for 

the U.S. Geological Survey in 1940 as part of the Strategic Minerals Program; and during the summers of 

1943, 1944, and 1945, Hobbs and S. E. Clabaugh continued the study with revisions of Callaghan's and Vitaliano's maps and preparation of maps of the other deposits. The result of their work was published in 1946 

(Hobbs and Clabaugh, 1946) . Following World War 

II a detailed study of the gold deposit at the Getchell 

mine was made by Peter J oralemon. The results of 

his field and laboratory investigations are contained in 

a thesis 2 and a published article ( J oralemon, 1951). 

Mapping of adjoining areas by others greatly facilitat~d work in the Osgood Mountains quadrangle. Geologic maps accompanied by brief texts have been published on the Winnemucca quadrangle (Ferguson, 

Muller, and Roberts, 1951) southwest of the Osgood 

Mountains quadrangle, and the Golconda quadrangle 

(Ferguson, Roberts, and Muller, 1952) to the south 

and southeast. 

PRESENT WORK AND ACKNOWLEDGMENTS 

Work began in the field in July 1951 and continued 

during the summer months until August 1955. The 

areal geologic mapping was done on aerial photographs 

enlarged 2 X and was transferred by inspection each 

day to the topographic map. The original compilation 

was at a scale of 1 :40,000 and was replotted at 1 :48,000 

for reduction to the publication scale of 1 :62,500. 

Planetable rna ps were made of the surface workings of 

all the important tungsten deposits and adjoining areas, 

because rna ps of the same areas prepared earlier by 

Hobbs- and Clabaugh ( 1946) were outdated by later 

1 Hobbs, S. W., 1948, Geology of the northern part of the Osgood 

Mountains, Humboldt County, Nevada: Yale Univ. unpublished doctoral 

thesis. 2 Joralemon, Peter. 1949, The occurrence of gold at the Getchell mine, 

Nevada: Harvard Univ. unpublished doctoral thesis. 

intensive mining activity. The underground geology 

of the tungsten deposits was plotted on level maps furnished by the companies. Geologic maps of the quicksilver and gold deposits in the Hot Springs Range were 

made by tape-and-compass methods. 

Most of the geologic mapping and planetable work 

were done by Hotz and Willden. Assisting in the areal 

rna pping for short periods at various times were H. R. 

Craig, D. C. Laub, F. R. Shawe, and G. C. Simmons. 

Ing. A. Tellez, R., assisted in the planetable work during part of one season. The underground mapping of 

the tungsten deposits was done by the senior author 

with the help of his son, R. P. Hotz. 

The writers acknowledge the help and cooperation 

given by Royce A. Hardy, Keith Kunze, and W. J. 

Ne~an of the Getchell mine, and by Harry J. Trollope, engineer of the Riley mine (Union Carbide Nuclear Co.). The friendliness of the ranchers in the area 

did much to make the work pleasant and facilitated 

it in many ways. We are especially grateful to Mr. 

and Mrs. Ralph Smith, Mr. and Mrs. William Stevens, 

and Mr. and Mrs. Gene Christiansen for many courtesies received from them. 

In the field we profited greatly from visits and discussions with colleagues whose wider knowledge of 

Nevada geology supplemented our relatively meager 

experience in the region. H. G. Ferguson, whose pioneer work serves as a basis for most of the geological 

knowledge of northern Nevada, was often a helpful 

and inspiring visitor. We are indebted for paleontologic assistance, both in the field and in the office, to 

A. R. Palmer on the Cambrian faunas; to Josiah Bridge 

and R. J. Ross on Ordovician faunas; and to Helen 

Duncan, Lloyd Hen best, MacKenzie Gordon, Jr., and 

James Steele Williams on the Carboniferous faunas. 

ROCK UNITS 

Sedimentary rocks exposed in the Osgood Mountains 

quadrangle include strata of Cambrian ( ? ) , Cambrian, 

Ordovician, Mississippian, Pennsylvanian, Permian, 

Tertiary, and Quaternary age. The complete stratigraphic succession is nowhere exposed; in fact most of 

the units mapped in the Osgood Mountains do not occur 

in the Hot Springs Range. Nondeposition or erosion 

have left gaps in the record, and thrust faults have 

brought into contact rocks that were deposited in different areas and some that are of different ages. 

ROCKS OF CAMBRIAN(P) AND CAMBRIAN AGE 

Four units of Cambrian an'd one of possible Cambrian age are exposed in the Osgood Mountains quadrangle (pl. 1). Of these, the Osgood Mountain quartzite, the Twin Canyon member of the Osgood Mountain 
ROCKS OF CAMBRIAN (?) AND CAMBRIAN AGE 7 

quartzite, and the Preble formation are exposed only 

in the Osgood Mountains. The Harmony formation 

is exposed in both the Osgood .Mountains and the Hot 

Springs Range._ The Paradise Valley chert is found 

only in the Hot Springs Range. 

The unfossiliferous Osgood Mountain quartzite is the 

oldest unit exposed in the area. It is overlain by the 

Preble formation, which contains Middle and Upper 

Cambrian fossils. The Paradise Valley chert of Late 

Cambrian age is the next youngest unit, but its relations 

to the Preble formation are not known. The Paradise 

Valley chert is overlain by the Harmony formation, 

which contains fossils of Late Cambrian age. In the 

Osgood Mountains the Harmony formation is found 

only in the upper plate of a thrust, so its stratigraphic 

relations with units other than the Paradise Valley 

chert are unknown. 

OSGOOD MOUNTAIN QUARTZITE 

The Osgood Mountain quartzite was named by Ferguson, Muller, and Roberts (1951) for exposures at the 

south end of the Osgood Mountains in the Golconda 

quadrangle. This unit, which is composed predominantly of relatively pure quartzite, is widely exposed in 

the southern half of the Osgood Mountains. It contains in its uppermost part a discontinuous member 

characterized by interbedded shale and impure quartzite which has been mapped separately and called the 

Twin Cany011 member. The Twin Canyon member 

represents beds apparently transitional between the 

Osgood Mountain quartzite and the overlying Preble 

formation. 

DISTRIBUTION 

The Osgood Mountain quartzite is extensively exposed in the central and south-central part of the Osgood Mountains; it extends southwestward for a;bout 9 

miles from the latitude of Goughs Canyon and Hogshead Canyon to the southern part of the range, where 

it is covered by volcanic rocks of Tertiary age. Younger 

Paleozoic rocks overlap the quartzite on the north. In 

the south-central part of the quadrangle the quartzite 

is continuous across the range to the valleys on either 

side. South of the quadrangle, the formation is exposed 

west of Emigrant Canyon at the south end of the Osgood Mountains (Ferguson, Roberts, and Muller, 

1952), and in discontinuous areas along the east side 

of the Sonoma Range (Ferguson, Muller, and Roberts, 

1951). 

The Twin Canyon member of the Osgood Mountain 

quartzite, here named from typical exposures in Twin 

Canyon, SWJ.4 sec. 35, T. 38 N., R. 41 E., crops out in 

two narrow elongated belts on the east side of the Osgood Mountains. One belt, which is clearly lenticular, 

occurs in the southern one-fourth of the quadrangle in 

the low hills northwest of Lone Butte. This belt has a 

maximum exposed width of approximately 0.8 mile and 

a length of about 3.5 miles. It pinches out to the northeast along its strike. Its apparently abrupt termination to the southwest probably is due mostly to structural complications caused by faulting and folding. 

The member is exposed in a second belt on the southeast side of the main ridge of the Osgood Mountains, 

in the east-central part of the quadrangle. This belt 

is more than 3.5 miles long and extends from SW% 

sec. 10, T. 37 N., R. 41 E. to Hogshead Canyon in SW1Jt 

sec. 25, T. 38 N., R. 41 E. Its exposed width, which 

is controlled over most of its length by a reverse fault 

along its east boundary, is nowhere more than about 

0.4 mile. The belt pinches out gradually at its southwest end; it is overlapped by the Pennsylvanian Battle 

formation on the north. 

LITHOLOGY 

The bulk of the Osgood Mountain quartzite is composed of white, gray, pale-greenish-gray, pale-brown, 

and purplish-brown medium- to thick-bedded quartzite. 

Locally some pure white thin-bedded quartzite is exposed. Beds generally range in thickness from 1 to 10 

feet, though some beds or lenses may be as much as 50 

feet in thickness, and some strata in the thinly bedded 

varieties may be only a few inches thick. Crossbedding 

is characteristic of the quartzite in many exposures. 

The rocks are commonly massive and stratification is 

obscure, but many beds are separated by partings, a fraction of an inch to 1 or 2 inches thick, which are composed of platy fine-grained greenish-gray to light-brown 

micaceous quartzite and silty ( ~) quartzite. On the 

parting planes of some specimens sericitic mica is so 

abundant that the rock has a phyllitic aspect. Where 

platy partings are absent, bedding in the quartzite may 

be expressed by faint color variations or minor differences in lithology. 

Most of the quartzite is fine to medium grained and 

very uniform in composition. The quartz grains are 

subrounded to rounded and generally are well sorted, 

although in places a few noticeably larger grains are 

scattered through an even -grained finer matrix. · In 

some specimens individual grains are readily visible 

with a hand lens ; in others the grains are closely packed 

and indistinguishable from the interstitial siliceous cement, and freshly broken surfaces have a vitreous appearance. Here and there pebbly layers, a fraction of 

an inch to a few inches thick, are interbedded with 

otherwise uniformly even grained rock. The pebbles 

are white quartz, as much as one-fourth of an inch in 

diameter, set in a fine-grained sandy matrix. 
8 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

Most of the quartzite is light colored, but some beds 

are a distinctive dusky reddish purple owing to hematite in the matrix. Some of the light quartzite is traversed by purplish seams of hematite, and in a few 

places it contains small reddish-purple concentrations 

of hematite one-fourth of an inch in diameter. 

Microscopic examination shows that in typical specimens of quartzite more than 90 percent of the grains are 

quartz ; grains of chert and feldspar are rare. Other 

primary constituents are limited to a few detrital grains 

of "heavy" minerals including zircon and tourmaline 

most commonly, and some sphene. Most of the sphene 

has been altered to white opaque leucoxene( ~). An 

uncommon variety of quartzite containing a significant 

amount of feldspar was collected near Soldiers Pass 

(center NW~ sec. 20, T. 37 N., R. 41 E.). Approximately 10 percent of the grains is feldspar, of which 

orthoclase is the most common species, albite is less 

common, and grains of microcline are rare. The feldspar grains are partly replaced by sericite at the contact with quartz, and also in the body of the mineral. 

In addition the rock contains some flakes of muscovite. 

Mogt grains are rounded to subrounded, and the 

larger quartz fragments are well rounded; the smallest 

grains are subrounded and a few are subangular. The 

"heavy" accessory mineral grains are rounded to well 

rounded. The clastic grains are firmly bonded hy secondary quartz, which is in optical continuity with the 

quartz grains, so that in many specimens the original 

grains are impossible or difficult to distinguish and the 

rock appears to be an interlocking mosaic of quartz. 

Grain outlines are made visible in some specimens by a 

film of impurities such as sericite or hematite on the 

· interface between the quartz grains and the silica of 

the matrix. 

Sericite and small amounts of chlorite are common 

in some specimens and make up several percent of the 

rock. The sericitic and chloritic material occurs interstitially to the quartz grains. Sericite replaces quartz 

along some grain boundaries, indicating that the sericite is authigenic (Pettijohn, 1957, p. 305, fig. 77). 

Hematite is an important constituent in the matrix of 

some specimens; it forms films on the interface between 

clastic grains of quartz and the secondary quartz cement or is concentrated in small areas that appear 

megascopically as purplish spots. 

The thin shaly or phyllitic partings between quartzite beds ·are composed of angular to subrounded quartz 

grains loosely packed in a matrix of sericite, chlorite, 

and silica, which probably was originally silty material. 

In addition to quartz grains there are a few rounded 

grains of tourmaline and zircon. 

LITHOLOGY OF THE TWIN CANYON MEMBER 

The Twin Canyon member of the Osgood Mountain 

quartzite has a greater proportion of silty and shaly 

material than the rest of the formation. Shaly material in the formation below the Twin Canyon member is represented only by thin pa;rtings between quartzite beds, but in the Twin Canyon member the shale units 

are 100 or more feet thick. Beds of quartzite alternate 

with phy llitic shale; the beds of quartzite are thicker 

and more abundant in the lower part of the member, 

whereas shale predominates and the quartzite beds are 

thin in the upper part. 

In general the rocks are darker than the rest of the 

Osgood Mountain quartzite. The shales are dark 

greenish gray to gray and the interbedded quartzite 

ranges through greenish gray, light brown, and dusky 

red purple; some beds of quartzite ·are white to light 

gray. Dark purple quartzite is abundant in ·the northern belt of the Twin Canyon member. 

The Twin Canyon member is more prominently 

sheared than the rest of the Osgood Mountain quartzite. The less competent fine-grained units are almost 

everywhere sheared and are somewhat phyllitic. In 

many places the shaly units are badly contorted. 

Most of the quartzite in the Twin Canyon member is 

impure, though the unit contains some beds of clean 

quartzite. Much of the impure quartzite might be 

more properly classed as subgraywacke or quartzose 

subgraywacke (Pettijohn, 1957, p. 316-320). 

The impure quartzite is fine to medium grained and 

massively bedded; cro~pedded structures are not common. Even in hand specimens the impurity of the rock 

is apparent. Microscopic examination shows that some 

specimens contain as much as 48 percent sericitic and 

chloritic matrix material, which is greatly in excess of 

the amount of cementing silica. The fragments are 

in general no more angular than the grains in the purer 

kinds of quartzite, but the whole bulk of material has 

not been as cleanly washed, so that detrital grains are 

comparativ:ely loosely packed in the matrix. Quartz is 

the principal clastic constituent; plagioclase, potassium 

feldspar, and a few flakes of muscovite occur in minor 

amounts. Some lithic fragments, principally chert but 

also a few pieces of shale, are commonly present. The 

"heavy" mineral assemblage--zircon, toUTmaline, 

sphene, leuooxene, rutile, and magnetite--is the same 

as in the quartzite in the rest of the formation but is 

more abundant. Besides sericite and chlorite, the matrix of many specimens contains scattered irregular 

grains of hematite and a little magnetite. Probably 

the sericite and chlorite were mainly derived from the 

reconstitution of an original "clay" matrix, but in part 

they may be detrital. 
ROCKS OF CAMBRIAN (?) AND CAMBRIAN AGE 9 

The Twin Canyon member contains some purplish 

quartzite like that in the main part of the formation, 

and there are also some beds of very dark purplishblack quartzite that contain as much as 15 percent 

hemaHte in the matrix. Hematite occurs as finegrained structureless interstitial material, as oolitic 

forms in the m·atrix, and as shells around quartz grains. 

The principal bonding agent, however, is silica. The 

rock is well sorted and contains only a little sericite in 

the matrix ; detrital zircon and tourmaline are very 

rare. 

Some of the fine-grained rock interbedded with the 

quartzite is shale or silty shale, or their phyllitic 

equivalents, but much of it is very fine to fine grained 

silty sandstone that has platy parting parallel to the 

bedding. Fine flakes of sericite are plainly visible on 

parting surfaces of most specimens. Commonly, microscopic examination shows the rock to be composed of 

alternating very fine grained sandstone and chloritebiotite-sericite layers. The sandy layers contain, in addition to quartz, considerable chlorite, sericite, occasional pyrite ·and limonite, and some fragments of shale 

and chert. Grains of tourmaline and zircon can also 

be recognized. The biotite, which is a common constituent of the fine-grained silty sandstone and phyllite, 

may be partly detrital, though most of it appears to 

have formed later than the rest of the minerals. 

STRATIGRAPHY AND THICKNESS 

The Osgood Mountain quartzite is the oldest formation exposed in this part of northern Nevada. The 

formation is in conformable succession with the overlying Preble formation. The top of the Osgood Mountain quartzite is drawn at the top of the last quartzite 

above which the amount of shale exceeds the amount 

of quartzite. At most places this contact is easily established, but where the Twin Canyon member of the. 

Osgood Mountain quartzite is present the position of 

the contact is less certain. 

The Twin Canyon member is transitional between 

lithology of the Osgood Mountain quartzite and that 

of the-overlying Preble formation, a predominantly 

shale and limestone unit. The lower contact of the 

member commonly is abrupt and conformable, but in 

some places it seems to be gradational over a distance 

of a few feet. This contact is drawn at the base of the 

first prominent shale bed, above which there is an alternating succession of shale and impure quartzite. 

The upper contact with the Preble formation is arbitrarily drawn at the top of the last quartzite bed, above 

which the sootion is predominantly shale. Where the 

Twin Canyon member is missing, the upper contact of 

the clean Osgood Mountain quartzite with the shale of 

the Preble formation seems to be abrupt from the general field relations, but exposures are generally poor 

along the contact. 

The thickness of the Osgood Mountain quartzite is 

not known because the base of the formation is not exposed. The exposed thickness can be estimated, but 

without much certainty because the absence of distinctive lithologic units does not permit the working out of 

the structural complexities within the formation. Ferguson, Roberts, and Muller ( 1952) estimated more than 

5,000 feet of beds in the Golconda quadrangle. A similar thickness of beds is exposed in the Osgood Mountains quadrangle including the Twin Canyon member, 

which is 1,000 to 1,500 feet thick in most places and 

has a maximum thickness of 2,500 feet. 

AGE AND CORRELATION 

No fossils have been found in the Osgood Mountain 

quartzite, but the formation is in apparently continuous 

stratigraphic succession with the overlying Preble formation, which contains organic remains of Middle and 

Late Cambrian age. The lithology closely resembles 

that of the Prospect Mountain quartzite and other similar quartzites found at the bottom of Cambrian sections 

in other parts of the Great Basin. The Twin Canyon 

member, which indicates the beginning of an important 

change in conditions of sedimentation, was possibly similar in origin to the Pioche shale, which overlies the 

Prospect Mountain quartzite at some places. 

The Prospect Mountain quartzite is generally regarded as Lower Cambrian, and some believe that it 

may be in part Precambrian (Wheeler, 1943, 1948). At 

most places where the Prospect Mountain quartzite 

occurs, it underlies beds in which Lower Cambrian fossils are known. No remains older than Middle Cambrian have been discovered in the Preble formation 

above the Osgood Mountain quartzite, but because of 

its position beneath fossiliferous strata of Cambrian 

age, and the presence between these beds of strata apparently representing nearly continuous sedimentary 

deposition, we tentatively regard the formation as Early 

to Middle Cambrian in age, although it is officially considered to be Cambrian ( ? ) in age. 

CONDITIONS OF DEPOSITION 

The siliceous sediments of the Osgood Mountain 

quartzite and its equivalents elsewhere in the Great 

Basin represent the initial deposits of a widespread 

system of strata of Cambrian age laid down in a gradually encroaching sea (Deiss, 1941, p. 1089-1090, 1098; 

Wheeler, 1943, p. 1808-1811). These first accumulations represent detritus derived from a landmass that 

had been subject to a long period of subaerial decay. 
10 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

The purity of the quartzite, its thick-bedded and persistently cross-stratified character through several thousand feet of section indicate that it was deposited in a 

gradually sinking basin under persistently shallow water conditions where wave action was an effective sorting mechanism. Probably it represents deposits of 

sand in a shelf environment where offshore bars and 

spits were constru~ted not far from the gradually transgressing strand line. Under conditions like these the 

quartzite would almost certainly not be time-equivalent 

from one area to another. 

The beds of impure subgraywacke and interbedded 

shale that constitute the Twin Canyon member at the 

top of the Osgood Mountain quartzite represent a 

change in conditions of deposition. Possibly these 

sediments accumulated without much 'washing and reworking, although the occasional relatively thin beds 

of quartzite suggest that from time to time, but with 

decreasing frequency, the environment reverted to conditions such that sorting by wave action was effective. 

Possibly this change reflects an increase in rate of sedimentation brought about by accelerated erosion or reflects relatively rapid subsidence of the basin of deposition, or both. The common occurrence of ferruginous 

quartzite in the section is possibly related to oxidizing 

conditions on parts of the sea floor that permitted accumulation of iron oxide along with the detrital material. James (1954, p. 272) has suggested that hematite may be "* * * deposited as hydrated ferric oxide 

in shallow, well-aerated waters." 

PREBLE FORMATION 

The name Preble formation was given by Ferguson, 

Muller, and Roberts (1951) to an argillaceous and calcareous section overlying the Osgood Mountain· quartzite in Emigrant Canyon near Preble Station, Golconda 

quadrangle. Rocks belonging to the formation have 

been followed northward along strike from the type locality into the Osgood Mountains quadrangle, where 

they are economically important because of the tungsten 

deposits that have been formed in the limestones adjacent to a granodiorite stock. 

DISTRIBUTION 

The formation is on the southeast flank of the Osgood 

Mountains from the southern border of-the quadrangle 

to about Hogshead Canyon (pl. 1) . North of Hogshead Canyon it occupies a continuous belt in the main 

part of the range, partly interrupted by a granodiorite 

stock. The unit extends to slightly beyond the northern 

boundary of the quadrangle. Rocks of the Preble formation are also exposed in a small rectangular area in 

the lower part of Goughs Canyon and in small irregular-shaped areas in Goughs and Perforate Canyons on 

the west side of the range. The Preble formation is 

not present in the Hot Springs Range. 

The limestones within the formation have been 

mapped separately because of their importance as host 

rocks for the tungsten deposits. It can be said, in general, that the limestones of the Preble formation occur 

in a belt a mile or so wide in the easterly, stratigraphically higher part of the Preble, and a belt of phyllitic 

shale lies between the limestone belt and the underlying 

Osgood Mountain quartzite. Limestone is also the predominant rock type in a belt about one-fourth of a mile 

wide and ry2 miles long at the head of Farrel Canyon. 

Relatively thin discontinuous and lenticular limestone 

beds are found in the western part of the Preble outcrop at the north end of the quadrangle, in a section of 

predominantly pelitic rocks. The spatial and stratigraphic relations between the lim~tone in the southern 

and eastern part of the range and that in the north end 

of the range are not known because of structural complexities and metamorphism. 

LITHOLOGY 

Along the southeastern side of the Osgood Mountains, the Preble formation is dominantly phyllitic 

shale in its lower part and interbedded limestone and 

shale in its middle and upper parts. In the northern 

part of the quadrangle, the relative stratigraphic position of the beds is uncertain, but shale is more abundant 

than limestone except at the head of Farrel Canyon. 

The limestone along the northwest side of the Osgood 

Mountains occurs as long thin lenses within the shale; 

in Farrel Canyon the combined width of the limestone 

lenses exceeds that of the interbedded shale. 

The phy llitic shale is most commonly greenish gray or 

yellowish gray; less commonly it is yellowish brown. 

Weathered surfaces are lighter in general. A slaty 

cleavage has been developed in much of the formation, 

as a rule generally parallel to the bedding, though in 

places it cuts the bedding at a fairly large angle. Cleavage surfaces are generally coated with flakes of white 

or pale-colored mica. Some of the shale is calcareous, 

and some of it is rather siliceous and does not split 

readily, so that it breaks down on weathering into 

small rough-surfaood chips. In places where deformation has been severe, the phyllitic shale is intricately 

crinkled. Locally, .strong deformation has converted 

the phyllitic shale to a phyllite in which microscopic 

folia and porphyroblasts of yellowish-green biotite 

have been formed in a quartz-plagioclase-sericite rna-
ROCKS OF CAMBRIAN (?) AND CAMBRIAN AGE 11 

trix. Retrograde metamorphism has caused partial replacement of the biotite, particularly the porphyroblasts, by chlorite. In some specimens the phyllitic 

cleavage direction is crossed at a m'arked angle by a 

later more widely spaced strain slip cleavage (Williams, 

Turner, and Gilbert, 1954, p. 213) that deforms the 

earlier formed mica flakes and reorients them subparallel to the later cleavage direction. 

A chemical and a spectrographic analysis of shale 

from the Preble formation are given in table 2. 

TABLE 2.-Chemical and spectrographic analyses of shale and 

limestone from the Preble formation 

Chemical analyses 

[Samples were analyzed by methods similar to those described in U.S. Geol. Survey Bull. 

1036-C; P. L. D. Ellmore, K. E. White, S. D. 

Botts, P. W. Scott, analysts, U.S. Geol. 

Survey] 

2 3 

Si02---------- 53. 1 5. 8 2. 4 

Al20a--------- 26. 4 . 80 . 34 

Fe20a--------- 3. 0 . 43 . 10 

FeO__________ 5. 3 . 01 . 02 

MgO _ _ _ _ _ _ _ _ _ 1. 7 . 26 . 42 

CaO__________ . 19 52. 7 54. 9 

N a20 _ _ _ _ _ _ _ _ _ 1. 0 . 07 . 06 

K20__________ 3. 9 . 12 . 02 

Ti 02- _ _ _ _ _ _ _ _ _ . 87 . 04 . 02 

P20s---------- . 14 . 09 . 10 

MnO_________ . 11 . 00 . 01 

H20__________ 5. 1 . 01 . 02 

C02 __ ------ _ _ . 05 40. 1 42. 6 

1-------1------1------11 

Sum____ 101 100 101 

Sp. G. (lump)__ 2. 81 2. 58 2. 34 

(powder)____ 2. 86 2. 71 2. 70 

1. Phyllite from NE~ sec. 36, T. 38 N., R. 41 E. 

2. Limestone from NE~ sec. 1, T. 37 N., R. 41 E. 

3. Limestone from NE~ sec. 1, T. 37 N., R. 41 E. 

Spectrographic analysis 

[Harry Bast ron, analyst, U.S. Geol. 

Survey] 

Cu ______ 0. 002 

Pb _______ .004 

Mn ______ . 09 

Co_______ . 002 

NL ______ .007 

Ga _ _ _ _ _ _ . 002 

Or_ ______ . 01 

v ________ . oo7 

Sc _______ . 008 

La _______ . 02 

Ti_ ______ . 4 

Zr _______ . 009 

Be _______ . 0004 

Sr _ _ _ _ _ _ _ . 004 

Ba _______ . 1 

B ________ . 009 

Looked for but not found: Ag, Au, Hg, Ru, 

Rh, Pd, Ir, Pt, Mo, 

Re, Ge, Sn, As, Sb, 

Bi, Zn: Cd, Tl, In, Y, 

Yb, Tn, Nb, U, P. 

The above results have an overall accuracy of 

±15 percent. 

Because of its tendency to disintegrate rapidly the 

phyllitic shale does not form prominent outcrops, and 

areas underlain by shale have a relatively subdued topography. It is characteristic of these areas, however, 

that the overburden is not thick and the bedrock is 

exposed whenever there is a small rill or gully, or where 

a slope is oversteepened. 

A few beds of quartzite occur within the formation; 

however, they are almost entirely restricted to the lower 

shaly part. These beds, which stand up as bold outcrops because of their greater hardness, are relatively 

thin-mostly no more than a few tens of feet thickand probably lenticular, but they are persistent units 

that can usually be followed for many hundreds of feet. 

69Q-159 0-63-2 

Where the formation grades downward into the Twin 

Canyon member of the Osgood Mountain quartzite, 

beds of quartzite gradually become more abundant than 

shale. 

Limestone in the Preble formation is of several kinds, 

but all of it is dark bluish-gray on weathered and 

freshly broken surfaces. Most of the limestone is fairly 

well bedded, though in places it is massive. Some of it 

has a characteristic rhythmically bedded appearance 

that is not seen in limestone from the later Paleozoic 

formations in this area; beds of fine-grained limestone 

from 1j2 inch to 2 inches thick alternate with shaly partings that are mostly one-half an inch or less thick. 

Some of the limestone is platy and on weathering breaks 

down into small slabs that range from 1 to 3 inches 

in thickness. Much of the thicker bedded limestone 

is medium to coarsely crystalline and weathers to a 

rough surface. Some is cherty, with nodules and irregularly lenticular bodies of chert, 1 inch or so thick, 

scattered so mew hat irregularly through the rock. 

Some beds are rather sandy, and some show oolitic 

structure. In places, particularly where the limestone 

has been recrystallized, the rock is cut by a network of 

white coarsely crystalline calcite veinlets. Chemical 

analysis of two specimens of limestone from the Preble 

formation are given in table 2. 

STRATIGRAPHY AND THICKNESS 

The Preble formation conformably overlies the Osgood Mountain quartzite. In some places the lower 

shales rest directly on the quartzite; in other places 

the Twin Canyon member of the Osgood Mountain 

quartzite grades upward into the Preble formation. 

The top of the Preble is not exposed in the quadrangle. 

On the geologic rna p of the Golconda quadrangle (Ferguson, Roberts, and Muller, 1952), the Comus formation of Ordovician age is shown overlying the Preble 

formation with a depositional contact; but on the basis 

of new data obtained from a reexamination of the area 

by us with Ferguson, we now believe that this contact 

is a high-angle reverse fault. The contact between the 

Preble and Comus formations has also been mapped 

as a fault in the eastern part of the Osgood Mountains 

quadrangle. Elsewhere in the area the Preble formation is incompletely exposed because of burial beneath 

younger rocks or truncation by faulting. On the basis 

of fossil evidence it is known that. the Preble is older 

than the Paradise Valley and Harmony formations of 

Late Cambrian age, but there is no stratigraphic evidence for this relation because the formations occur in 

different parts of the quadrangle. 
12 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

Detailed studies of the stratigraphy and measurements of thickness cannot be made satisfactorily in the 

Preble, because the beds are tightly folded and the lithologic units ·are not sufficiently distinctive to serve as 

markers in working out the structural complexities 

within the formation. Probably the structure is also 

complicated by faulting; there is some minor thrusting 

along contacts between the shale and limestone beds. 

Some general lithologic subdivisions can be made, 

however, on the east side of the range. The lower part 

of the formation above the Osgood Mountain quartzite, 

or above the Twin Canyon member, is composed predominantly of phyllitic shale and siltstone with a few 

thin beds of quartzite and graywacke. Above this is a 

unit composed mostly of limestone with some interbedded and interfingering shale, and between the limestone unit and the Comus formation is another section 

of phyllitic shale. The lower shale probably ranges 

from 2,800 feet to 4, 700 feet in thickness; the intermediate limestone unit may be from 1,300 feet to as 

much as 1,500 feet thick; and there may be as much as 

1,500 feet of shale above the limestone. Following is a 

measured section of the predominantly limestone unit 

exposed on the ridge northeast of the lower part of 

Hogshead Canyon in the NE% sec. 1, T. 37 N., R. 41 E., 

and SE% sec. 36, T. 38 N., R. 41 E.: 

Thicknes8 

(ft) 

Slaty shale, greenish-gray, very fissile ___________ not measured 

Limestone, blue-gray, crystalline, rough-surfaced, thickbedded to massive; many white calcite veinlets and 

some sandy beds that contain organic fragments______ 250 

Cherty limestone, brown-weathering, rather badly sheared, 

very rough surfaced ; contains blobs and some veinlets 

of white calcite_____________________________________ 200 

Limestone, blue-gray, platy-weathering, thin-bedded; 

contains a little brown chert and some interbedded 

shaly limestone and greenish-gary phyllitic shale_____ 225 

Cherty limestone, blue-gray, rough-weathering, thickbedded to Inassive__________________________________ 75 

Limestone, bluish-gray, somewhat platy, slightly cherty__ 100 

Platy limestone, bluish-gray; and some interbedded phyllitic shale__________________________________________ 200 

Quartzite, brown-weathering___________________________ 10 

Phyllitic shale, greenish-gray-------------------------- 50 

Platy limestone, gray to purplish-gray; interbedded with 

calcareous shale____________________________________ 100 

Phyllitic shale, greenish-gray; thin calcareous shale and 

thin beds of limestone______________________________ 175 

Cherty limestone, gray-------------------------------- 110 

Total thickness of limestone section ______________ 1, 495 

Phyllitic shale, greenish-gray ; lenses of quartzite 

as much as 5 in. thick _______________________ not measured 

Ferguson, Roberts, and Muller (1952) reported: 

';l'hiclmess not determinable because of isoclinal folding and 

minor thrusting ; may exceed 12,000 feet. 

The present authors estimate that the section in the 

vicinity of Hogshead Canyon may be about 5,000 feet 

thick, but both the upper and the lower contacts are 

faults. 

AGE AND CORRELAITION 

The Preble formation has yielded several collections 

of fossils which have been reported on by A. R. Palmer, 

of the U.S. Geological Survey (1953, 1954, written 

communication). 

Four collections have been made from limestone beds on the 

southeast side of the Osgood mountains: 

Collection No. USGS 3136-00. East of center, SE%NElA, sec. 

1, T. 37 N., R. 41 E. 

Collection No. USGS, 1972-00. Extreme NElA,SEt_4SW% sec.1, 

T. 37 N., R. 41 E. 

Collection No. 1973-CO (field No. f54-W-7). On ridge in NE% 

SW1,4NW% sec. 12, T. 37 N., R. 41 E. 

Collection No. USOS 1506-00. 100 feet east of a prominent 

draw and about 100 feet above the main valley bottom, 

SE:J4NW% sec. 12, T. 37 N., R. 41 E. 

Collection 3136-CO had identifiable fossils only in the insoluble residue. Here, a scrap of acrotretid brachiopod that suggests Acrothele indicates a probable Cambrian age for the 

collection. 

Collection 1972--CO has a few scraps of trilobite pygidia that 

suggest an Ehmaniella-like trilobite. Trilobites of this type are 

difficult to identify even when fairly good material is present. 

The collection is probably Cambrian and possibly Middle Gambrian in age. 

Collection 1973-CO contains unusually well preserved Conchostracans, including one specimen possibly referable to Alttta primordiaZi.<J ( Linnarsson), a species known from near the MiddleUpper Cambrian boundary in Sweden. Scraps of unidentifiable 

silicified trilobites were present in the insoluble residue. 

Collection 1506-CO was made from a single piece of 

limestone float that probably came from the same stratigraphic position as 1973-CO. Palmer says of this 

collection : 

The fauna contains six genera of trilobites, inarticulate and 

articulate brachiopods, a snail and some interesting tentaculiteslike problematica. This extends knowledge of the distribution 

of early Upper Cambrian pre-Aphelaspis fossiliferous rocks 

more than 200 miles westward. 

The following trilobite genera are recognized : 

M eteoraspis 

Ooo.<JelZa? 

Tricrepicephalus 

Kingstonia 

M aryvillia? 

Pemphiga.<Jpis? 

A new species of the snail genus Strepsodiscus previously 

known only from early Upper Cambrian beds of Colorado is also present. 

The presence of MetE:orapis and Ooosella indieates a ('OlTelation to the lower part of the Orepicephalus zone of the standard 

Upper Cambrian faunal sequence. 

The unit from which this collection came isr equivalent in age 

to the Hamburg dololl\ite * • *. 
ROCKS OF CAMBRIAN (?) AND CAMBRIAN AGE 13 

Two collections of trilobites were made from thin limestone beds on the north west side of the range north of 

Anderson Canyon: 

Collection No. USGS 1372-CO. Northern part NW~NW~ sec. 

30, T. 39 N., R. 42 E. 

Kootenia sp. 

WimaneZla sp. 

Collection No. USGS 1378-CO. Eastern part 'SE~SE~ sec. 25, 

T. 39 N., R. 41 E. 

Kootenia? sp 

According to Palmer these two collections 

contain trilobites characteristic of rocks of lower Middle Cambrian age. The trilobites * * * are probably older than those 

collected from the "Secret Canyon" in the Mount Lewis ( Nevada) quadrangle. 

The fossil determinations thus indicate that the Preble 

formation ranges from lower Middle Cambrian to lower 

Upper Cambrian. Ferguson, Roberts, and Muller 

( 1952) reported finding linguloid brachiopods in limestone in the upper half of the Preble form·ation in 

Emigrant Canyon, Golconda quadrangle, which was 

the basis for assigning a Middle or Upper Cambrian age 

to the formation at the type locality. 

According to the faunal data, the Preble exposed on 

the southeast side of the Osgood Mountains is younger 

than the rocks mapped as Preble on the northwest side 

of the range. Stratigraphic rela;tions between the rocks 

in these two areas cannot be determined, but rocks on 

the northwest end of the range are predominantly 

shale, and the limestones are relatively thin and lenticular, so the section may be roughly equivalent to the 

shale in the lower part of the formation on the southeast side of the range. 

Lithologically the Preble formation does not closely 

resemble the known Cambrian from other parts of N evada. Faunally the limestone on the southeast side of 

the Osgood Mountains is correlated with the Hamburg 

dolomite of the Eureka district; and beds on the northwest side are probably somewhere below the Secret 

Canyon shale. 

CONDITIONS OF DEPOSITION 

The lower phyllitic shale of the Preble formation has 

been Shown to grade down into the Twin Canyon member of the Osgood Mountain quartzite, which marks a 

change in conditions of deposition from a nearshore 

environment to one of deeper water. farther from the 

land. The fine-grained clastic rocks in the lower part 

of the Preble, followed by a section in which limestone 

predominates, is in keeping with the general picture of 

a gradually encroaching sea in which deposition that 

began with the clean sands of the Osgood Mountain 

quartzite continued with essentially no interruption but 

with a gradual change to conditions of offshore deposition of mud and carbonate. 

PARADISE VALLEY CHERT 

The Paradise Valley chert is a new formation, here 

named for Paradise Valley, the large valley west and 

northwest of the Hot Springs Range. 

DISTRIBUTION 

The Paradise Valley chert is exposed along the west 

side of the Hot Springs Range in two narrow belts in 

the northwest corner of the quadrangle (pl. 1). The 

most extensive exposures are in sees. 27 and 28, T. 39 

N., R. 40 E.; to the south the belts become narrow .and 

disappear under alluvium in sec. 33, T. 39 N., R. 40 E.; 

these exposures do not extend much beyond the northern border of the quadrangle, but the formation is 

found farther north, about a mile north of Stewart Gap 

(Hot Springs Peak quadrangle). 

In general, the formation is not well exposed because 

of heavy soil cover. Chert forms fairly prominent outcrops, but in many places it can be followed only by 

fragments in the soil ; limestone and siliceous shale, 

which are interbedded with the chert, are generally 

poorly exposed. 

LITHOLOGY 

The Paradise Valley chert consists predominantly of 

chert, but it also contains minor amounts of siliceous 

shale and limestone. The chert is light to dark gray, 

light to dark brown, and black; it is well bedded but 

extensively fractured, so that it is difficult to get a large 

piece or fresh surface. Most of the beds are 2 inches to 

18 inches thick, but some beds are as thin as one-fourth 

of an inch and others as thick as 5 feet. Individual 

chert beds are separated by partings of siliceous shale. 

The siliceous shale partings are light gray or light 

brown. Siliceous shale also occurs as a few thin beds; 

the shale of the thin beds is usually light gray or green. 

Limestone occurs in small lenses and thin beds which 

can be followed for only short distances. It is dense, 

fine to medium grained, and fairly pure to slightly 

shaly. Fossils are found in the medium-grained 

slightly shaly limestone lenses and beds. 

The chert is composed of microcTysta1line quartz and 

many impurities consisting mostly of minute colorless 

to faintly greenish rods and fibers with parallel alinement, which appear to be chloritic and sericitic material 

probably derived from original argillaceous material. 

In addition there is a little limonitic material, some of 

which is pseudomorphous after pyrite. A few scattered small ovoid bodies of fine-grained quartz may 

represent the remains of organisms. The rock is cut 

by a multitude of veinlets of fine-grained quartz. No 

textures or structures were observed that would be in-
14 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

dicative of replacement of original tuffaceous material 

or limestone by silica. 

Microscopic examination of the limestone shows that 

it is uneven grained, grain size ranging from 0.05 mm 

to 1 mm, possibly because the rock has been partly recrystallized. It contains many fragments of fossils and 

a very few detrital grains. The detrital grains identified in thin section and by a study of the insoluble 

residue of the limestone include quartz and a little 

quartzite and chert, and "heavy" minerals. The heavymineral suite consists of colorless zircon, blue and green 

tourmaline, abundant monazite and xenotime, muscovite, leucoxene, ilmenite, rutile, magnetite, and hematite. 

Pyrite, which floods the heavy concentrate, is an authigenic constituent. 

STRATIGRAPHY AND THICKNESS 

The base of the Paradise Valley chert is not exposed 

and its stratigraphic relation to the Osgood Mountain 

quartzite and the Preble formation is not known. The 

contact with the overlying Harmony formation is depositional, but exposures are not good enough to be 

sure whether the contact is conformable or not. 

The full thickness of the Paradise Valley chert is 

not known because the base of the formation is not 

exposed. Estimates of the thickn·ess are further complicated by uncertainty as to the degree of unconformity with the overlying Harmony formation and by 

poor exposures that make it difficult to detect repetition of beds by faulting or tight folding. The exposed 

thickness on the west side of the Hot Springs Range 

is estimated to be about 300 feet, and the thickness 

north of Stewart Gap is estimated to be about 500 feet. 

AGE AND CORRELATION 

The Late Cambrian age of the Paradise Valley chert 

is well established by fossils collected from two localities, one of this quadrangle and one in the Hot Springs 

Peak quadrangle. 

Collections Nos. USGS 1370-CO, 1380-CO, 2901-CO. Ridge 

SlhNEJA,SE14, sec. 28, T. 39 N., R. 40 E., Osgood Mountains 

quadrangle. 

Collection No. USGS 1374-CO. Extreme NE%NWJA, sec. 31, T., 

40 N., R. 41 E. (Unsurveyed), Hot Springs Peak quadrangle. 

A. R. Palmer reports ( 1960, written communication) : 

collections 1370-CO, 1380-CO, and 2901-CO were made at the 

same locality by three different collectors at three different 

times. Because of the structural complexity and poor exposures, 

different limestone lenses including in part different faunas were 

sampled. 

Collection 1370-CO and most of 2901-CO contain the following 

trilobites : 

Aphelaspis sp. 

Agnostus inexpectans Kobayashi 

Glyptagnostus reticulatus reticulatus (Angelin) 

Olenaspella regularis Palmer 

Pseudagnostus sp. 

H omagnostus sp. 

Collection 1380-CO and one piece of collection 2901-CO indicate the presence of a slightly older fauna containing: 

Kingstonia cf K. spicata Lochman 

Orepicephalus sp. 

Deiracephalus sp. 

Collection 137 4-CO contains the following trilobites. 

GlyptagnoMt-ts reticulatus angelini (Resser) 

Agnostus cf A. inea:pecta;ns Kobayashi 

H omagnostus sp. 

Oheilocephalus sp. 

Aphelaspis sp. 

Olenaspella separata Palmer 

The Glyptagnostus-bearing faunas, in collection 1370-CO and 

1374-CO have been found in sections near Cherry Creek and 

McGill, Nevada, respectively. They characterize the lower beds 

of a nonresistant unit of interbedded limestones, siltstones, and 

shales that probably represents the Dunderberg shale. These 

faunas are older, however, than the oldest fossiliferous beds in 

the Dunderberg shale at Eureka. ·Trilobite assemblages equivalent to the oldest faunas of the type Dunderberg shale are 

found in the McGill and Cherry Creek sections about 200 to 250 

feet above the Glyptagnostus-bearing beds. 

HARMONY FORMATION 

The Harmony formation is a distinctive lithologic 

unit that was first described by Ferguson, Muller, and 

Roberts (1951) in the Winnemucca quadrangle. They 

tentatively assigned the formation to the Mississippian ( ~) on the basis of lithologic evidence and structural relations, an age assignment that was followed by 

Roberts ( 1951) in the Antler Peak quadrangle, where 

the Harmony is also exposed. Fossil collections from 

the Hot Springs Range and the Osgood Mountains have 

shown that the Harmony formation is of latest Cambrian age. 

DISTRIBUTION 

The Harmony formation is rather widely distributed 

in north -central Nevada. The type locality is Harmony 

Canyon in the northern part of the Winnemucca quadrangle, and rocks belonging to the formation are abundantly exposed in the Sonoma Range (Ferguson, Muller, and Roberts, 1951). The formation is also found 

on Battle Mountain 30 miles east of the Sonoma Range, 

and Gilluly has observed breccia blocks of Harmony in 

the Mount Lewis quadrangle 15 miles southeast of Battle Mountain. Rocks of the same distinctive lithology 

make up the bulk of the Hot Springs Range in the 

Osgood Mountains quadrangle; they can be followed 

northward into the Hot Springs Peak quadrangle, 

where they become covered by volcanic rocks of Tertiary age of alluvium south of the Little Humboldt 

River. 

Within the Osgood Mountains quadrangle, the Harmony formation makes up the bulk of the Hot Springs 
ROCKS OF CAMBRIAN (?) AND CAMBRIAN AGE 15 

Range (pl. 1), but in the Osgood Mountains it is confined to a rather narrow belt between two thrust faults 

on the west side of the range, extending for about 3 

miles from Goughs Canyon on the south to the ridge between the East Fork of Eden Creek and Cave Canyon 

on the north. 

LITHOLOGY 

The Harmony formation is composed predominantly 

of feldspathic sandstone with some interbedded shale 

and minor amounts of pebble conglomerate and clastic 

limestone. A basal shale member 75 to 150 feet thick 

is included within the formation in this quadrangle, 

though it has not been found elsewhere. 

Perhaps the most characteristic lithologic feature of 

the Harmony formation is the sandstone, which is very 

distinctive throughout the section. It is light brown to 

olive green and ranges in grain size from medium to 

coarse, some of it having a distinctly gritty appearance. 

Many specimens, especially the coarser grained and 

gritty varieties, are characterized by an abundance of 

prominent bluish-gray to milky-white grains of quartz, 

light-gray to milky-white grains of feldspar, and less 

abundant fairly large flakes of muscovite in a considerably finer grained greenish-brown matrix. The 

sandstone is generally thick bedded to massive-though 

some thin-bedded units are seen-and the beds are commonly separated by thin partings of shale half an inch 

to an inch thick. Many of the beds show graded bedding, which in some places is easily seen and in other 

places is difficult to recognize. The graded beds range 

in thickness from a few inches to several feet and are 

continuous along strike for as much as 1,000 feet. The 

lowermost part of some of the graded beds contain shale 

fragments; small-scale scour-and-fill structures, usually 

not very well developed, can be seen in the underlying 

shaly beds. Crossbedding was not seen in the sandstone. 

Microscopic examination of thin sections of the sandstone show that most specimens are poorly sorted and 

most of the grains are subangular to subrounded; a 

small percentage are angular or rounded fragments 

(fig. 2). Commonly, many of the grains show various 

degrees of etching, and some of the quartz grains have 

secondary overgrowths. The grains are tightly bonded 

by a matrix that is largely very fine sercite and chlorite 

but is also composed of very fine fragments of the same 

minerals that constitute the sand-size fraction of the 

rock. Sericite and chlorite probably formed from original clay, though some of the mica may be detrital. 

Some varieties of sandstone have a calcareous cement or 

contain secondary quartz in the matrix. 

Quartz and feldspar are the predominant mineral 

grains. Quartz accounts for from 70 percent to 80 percent of the grains, and the total feldspar ranges from 

approximately 10 percent to 18 percent. The quartz 

grains, including the coarsest sizes, are mostly fragments of single individuals, but some are composite 

grains with sutured interlocking borders; some are 

crowded with fine dust and liquid inclusions; nearly 

all grains are strained and show undulatory extinction. 

Some slides contain recognizable fragments of quartzite. The feldspar grains are mostly completely fresh. 

Both plagioclase and potassium feldspar are present; 

the ratio of plagioclase to potassium feldspar is about 

1 to 2. The plagioclase is a sodic variety, judging by 

its index of refraction and small extinction angles; 

orthoclase-commonly perthitic-and microcline are 

the potassium feldspars. 

The remainder of the detrital grains include apatite, 

zircon, sphene, leucoxene probably derived from sphene 

and ilmenite, tourmaline, epidote, magnetite, and rutile. 

Apatite is perhaps the most abundant, but two kinds 

of zircon are also present, a colorless and a pink variety. 

The colorless variety occurs as euhedral crystals and as 

well-rounded grains. The pink zircon is the more abundant and shows hardly any effects of abrasion, being 

in short prismatic crystals with pyramidal terminations. 

Pink zircon from sandstone of the Harmony formation 

in the Antler Peak quadrangle has been determined to 

be 958 million years old ( J a:ffe and others, 1959, p. 

130). 

Additional "heavy" mineral species are undoubtedly 

present but most of the sandstone is very difficult to 

break down to sizes that permit satisfactory separation. 

A specimen of calcareous sandstone was disintegrated 

with acid, however, and the following additional minerals were observed : monazite, dumortierite, cassiterite, 

ilmenite, pyrite, pyrrhotite. The grains of monazite 

are both rounded and euhedral; the dumortierite and 

cassiterite are euhedral or angular. 

Modal composition of some typical sandstone specimen are given in table 3. 

TABLE 3.-Modes of the Harmony formation 

[Volume percent. Tr, trace] 

2 3 

Quartz _____________________ 72 78 73 38 

Plagioclase _________________ 2 5 3 8 

Orthoclase and perthite_ _ _ _ _ _ 7 11 7 8 

Microcline _________________ 1 ________ Tr. 1 

Muscovite and biotite_______ 2 Tr. 1 1 

Accessory minerals ________________ ---------------- Tr. 

Matrix _______________ _____ 16.0 6 16 44 

1-3. Feldspatbic sandstone. 

4. Calcareous sandstone. 
16 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

A.. Grains range widely in size and angularity; some edgewise flakes of B . Loosely packed grains cemented by finely crystalllne calcite. 

muscovite in a matrix of quartz, sericite, and chlorite. 

0. Closely packed grains ranging widely in size, in a sericite matrix. D. A quartzitlc variety composed of tightly packed angular grains with 

almost no distinguishable cement. 

FIGURE 2.-PHOTOMICROGRAPHS OF FELDSPATHIC SANDSTONE OF THE HARMONY FORMATION. 

Unlabeled grains are mostly quartz; others are plagioclase (P), orthoclase (or), mlrocline ('ml), and flakes of muscovite (M). CrOBSed 

polarized light. 
ROCKS OF CAMBRIAN I(?) AND CAMBRIAN AGE 17 

The rock type corresponds to Pettijohn's (1957, 

p. 291) feldspathic sandstone, or to Gilbert's ("Tilliams, 

Turner, and Gilbert, 1954, p. 291-292) feldspathic 

wacke. 

The chemical composition of two specimens from the 

Hot Springs Range ( 1 and 2) and two from Battle 

Mountain ( 3 and 4) are shown on table 4. 

TABLE 4.-Chemical analyses of sandstone of the Harmony 

formation 

[Samples were analyzed by methods similar to those described in U.S. Geological 

Survey Bulletin 1036-C. Analysts (1, 2), H . F. Phillips, P. L. D. Elmore, K. E . White; (3, 4), K. E. White; H. F. Phillips, P. W. Scott, F. S. Borris, U.S. Geol. Sur- vey, Washington, D.C.] 

2 3 4 Avg. 

Si02------------- 78. 2 88.3 84. 4 78. 2 82.3 

Al20a-- __ - ---- ___ 11. 3 5. 9 7.0 9.0 8.3 FeO _____________ 1.0 . 16 1.0 2.0 1. 04 

Fe20a----- _______ 1.0 . 14 .7 .8 . 66 MgO ____________ . 82 . 14 . 72 1.0 . 67 CaO _____________ . 22 . 24 1.0 1.2 . 66 

Na20------------ 1.8 1.2 2.0 1.8 1.7 K2

0-- ___________ 2.0 1.5 . 66 2. 2 1.6 Ti02 ____________ . 52 . 32 . 25 . 36 .36 

P206------------ . 06 . 16 .11 . 10 .11 

MnO ____ ------- . 02 . 01 . 04 . 06 . 03 

H20+----------- 2.2 . 67 1.0 1.6 1.4 

H20- ___ ------- . 31 . 03 . 05 . 06 .11 

C02----------- __ . 05 . 05 . 82 . 64 

Sum ______ 100 99 100 99 99 

TotalS asS _____ 0.03 0.06 -------- -------- ------ Spgr (lump) _____ 1. 96 2.49 -------- -------- ------ Spgr (powder) ___ 2. 65 2.62 -------- -------- ------

Throughout most of the section a considerable amount 

of shale is interbedded with the sandstone. Shale is 

possibly one-fourth as abundant as sandstone, but no 

reliable estimates of the sandstone : shale ratio have 

been made. Except for the lower part of the section, 

shale ranges from partings less than 1 inch thick between sandstone beds to units as much as 100 feet in 

thickness. In the northwest corner of the quadrangle, 

the amount of shale increases downward toward the 

Paradise Valley chert contact until there are about 

equal amounts of shale and sandstone. The base of 

the formation is marked by a very persistent shale member 75 to 150 feet thick. 

The shale varies from light olive gray and dusky 

yellow to grayish red and dusky red; shades of olive 

gray and yellow predominate. The basal shale member, however, is characterized by an abundance of red 

beds, which constitute as much as one-half of the section. 

Pebble conglomerate occurs throught the exposed 

section of the Harmony formation, but it seems to be 

most abundant in the lower half. The pebbles range 

in size from 4 mm to more than 1 em; they seldom are 

as large as 2.5 em. Sorting is poor; the matrix generally is composed of granules 2 to 4 mm in m·aximum 

dimension and interstitial sand. The pebble conglomerate beds commonly show graded bedding. The pebbles consist of suhangular to subrounded quartz and 

microcline and minor amounts of chert and shale fragments. The shale fragments are usually confined to 

the lowermost part of conglomerate beds that rest on 

shale. 

Beds of limestone are distributed rather unevenly 

through the formation. Limestone is most abundant 

about 3,000 feet above the base of the formation, in the 

northwest part of the quadrangle. Several beds-possibly one or more repeated by folding and faultingare found at the south end of the Hot Springs Range 

south of the K and K quicksilver prospect and on the 

ridge west of the Last Chance quicksilver prospect. 

Three limestone beds crop out north of Mills Canyon 

in the southern part of sec. 4 and the NWl!.t, sec. 9, T. 

38 N., R. 40 E. The beds of limestone range from 

about 50 feet to 150 feet in thickness. Some seem to be 

lenticular without much lateral continuity; several, 

however, have been followed for many hundreds and 

even thousands of feet. The limestone ranges from 

medium light gray to light yellowish brown, and from 

fine to coarse grained. The light-gray fine-grained 

limestone commonly has some light-colored chert (light 

brown, dusky yellow green to gray) associated with it. 

Calcareous shale is abundant in the vicinity of Dutch 

Flat but is generally lacking elsewhere. 

The limestone has been recrystallized to varying degrees so that the original calcite grains are no longer 

visible. The limestone contains varying amounts of 

the same detrital grains that are constituents of the 

sandstone : quartz, smaller amounts of feldspar, a few 

flakes of mica, and some quartzite. Etching of the 

grains by reaction with the calcareous matrix has considerably modified their original shapes. Commonly 

some of the quartz grains are broken and veined with 

calcite. "Heavy" minerals obtained by separation of 

insoluble residues of the limestone are shown in table 5. 

The Harmony formation on the west side of the Osgood Mountains is in a relatively thin sheet between 

two thrust faults. Strong deform·ation by shearing 

has resulted in a unit characterized by highly sheared 

dark greenish-gray shale containing boudins, boulderlike knobs and blocks as much as 10 feet on a side, of 

feldspathic sandstone, grit, pebble conglomerate, and 

limestone. Some beds of feldspathic sandstone are continuous for 100 foot or more, and one sheared lenticular 

mass of coarsely crystalline gray clastic limestone contains fragments of fossils. 
18 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

TABLE 5.-Heavy minerals in limestones of the Harmony formation 

[Separations made in bromoform capable of floating pure calcite. Based on examination of -100 to +150 mesh size fractions. 

1. Sandy limestone 2. Limestone 

3. Shaly limestone •· 6; Limestone 

Pink Color- Blue Green 

F (flood) A (abundant) 

C (common) R (rare) Tr (trace) 

Weight percent >30 

1o-30 

5-10 

1-6 <1 (usually one or two grains)] 

Weight 

percent 

nonopaque 

Weight 

percent 

opaque 

minerSample No. zircon less tour- tour- Mon- Xeno- Hom- Musco- Biotite Garnet miner- Leuco- llme- Rutile Mag- Hema- Py- als in 

zircon maline maline azite time blende vite 

l _________________ R c C ----- ----- _____ F c 

als in xene nite netit.e tite 

total 

heavy 

minerals 

30 F c ----- c F 

rite total 

c 

heavy 

minerals 

70 

------1------------------------------------------------------ 2 _ _ _ _ _ _ _ _ _ _ _ _ Tr R Tr C _____ R _____ F c R 10 F A c c F 90 

------1------------------------------------------------------

3 ____________ A R R C _____ Tr Tr F c 10 F c ----- c F F 90 

------1---1---1·--1------------------------------ 4 ____________ C A R A R C _____ F ------ c 20 c F c c F 80 

------1---1------------------------·------------------ 5------------ Tr C _____ C _______________ F 

STRATIGRAPHY AND THICKNESS 

The Harmony formation rests on the Paradise Valley 

chert (pl. 1) in the northwestern part of the quadrangle 

on the west side of the Hot Springs Range. The contact is not visible, but evidence based on the distribution of float and scattered outcrops strongly suggests a 

conformable relation or only slight and perhaps local 

angular discordance between the two formations. 

Locally the contact may be a low-angle thrust fault of 

minor displacement due to tight folding and difference 

in competency between the rocks of the two formations. 

The stratigraphic relation between the Harmony formation and younger Paleozoic formations cannot be demonstrated in the Osgood Mountains or the Hot Springs 

Range, because the younger formations are in fault 

contact with the Harmony formation. 

The Battle formation of middle Pennsylvanian age 

rests unconformably on the rocks of the Harmony 

formation on Battle Mountain in the Antler Peak quadrangle (Roberts, 1951), and in the Edna Mountains 

(Ferguson, Roberts, and Muller, 1952); the Pennsylvanian and Permian Antler Peak limestone overlies the 

Harmony unconformably in the Sonoma Range (Ferguson, Muller, and Roberts, 1951). 

The stratigraphy of the Harmony formation could 

not he studied in any detail because the formation is 

structhrally so complex in most places. In the Hot 

Springs Range the base of the section is marked by a 

very persistent shale member, 75 to 150 feet thick, above 

which lies an uncertain thickness of sandstone with 

interbedded shale and small amounts of grit and pebble 

conglomerate. Limestone seems to be more common in 

the upper part of the section on the east side of the Hot 

F 70 R c ----- c c F 30 

Springs Range in this quadrangle, but elsewhere it is 

also found in beds that may be lower in the section. 

The total thickness of the Harmony formation is unknown because the top of the formation is not exposed 

and tight folding makes precise stratigraphic correlation impossible. The exposed thickness in the Hot 

Springs Range estimated from structure sections is 

more than 4,000 feet. Ferguson, Muller, and Roberts 

(1951) estimated a thickness of more than 5,000 feet at 

the type locality in the Winnemucca quadrangle, and 

more than 2,000 feet in the Golconda quadrangle. 

AGE AND CORRELATION 

Previous studies of the Harmony formation by 

Ferguson, Muller, and Roberts ( 1951), Ferguson, Roberts, and Muller (1952), and Roberts (1951) were in 

areas where, because of faulting, the relations to older 

formations were unknown, and the rocks were unfossiliferous ; the oldest rocks known to overlie the formation 

are of Early Pennsylvanian age. These relations and 

the observation that "beds of similar lithology [occur] 

in the Permian ( ~) Inskip formation and Permian Edna 

Mountain formation * * *" led Ferguson, Muller, and 

Roberts (1951) to"* * * suggest that an age not older 

than Mississippian is probable for the Harmony 

formation." 

In the Hot Springs Range the Harmony formation 

overlies the Paradise Valley chert and, therefore, is 

younger than that formation. Fossils have been found 

in discontinuous limestone beds or lenses in the sheared 

shale and sandstone of the Harmony formation in 

Goughs Canyon on the west side of the Osgood Moun-
ROCKS OF CAMBRIAN (?) AND CAMBRIAN AGE. 19 

tains. A. R. Palmer reports (1954, written communication) Collection No. USGS 1504-CO as follows: 

Two identifiable trilobites, Theodenisiaf sp., and Leiocoryphe? sp., were found. Similar trilobites have been described 

from boulders in the Levis conglomerates in Quebec and have 

most recently been considered to be upper Franconian (medial 

Upper Cambrian) to early Trempealeauan (late Upper Cambrian) in age. 

In 1960, Palmer (written communication) reported 

the following forms : 

Collection No. USGS 1807-00. Lens of sheared limestone in 

Goughs Canyon on the west side of the Osgood Mountains, 

North edge of ridge, NE~SW~SE~ sec. 22, T. 38 N., R. 41 E. 

Pseudagnostus sp. 

A.gnostus sp. 

H omagnostus sp. 

Of these he says, 

Protopeztura sp. 

Oonokephalina? sp. 

The presence of an olenid trilobite resembling Protopeltura, 

and Ooookephalina? sp indicates that this collection is probably 

Middle Late Cambrian (Franconian) in age. Associated agnostids could equally well indicate an early Late Cambrian age 

according to our present inadequate knowledge. 

The Harmony formation cannot be correlated lithologically with Upper Cambrian formations elsewhere 

in Nevada, but the fossil collections indicate that it is 

approximately equivalent with the Windfall formation 

(Nolan, Merriam, and Williams, 1956, p. 19-23) in the 

vicinity of Eureka, eastern Nevada. 

No fossiliferous beds have been found in the Harmony 

formation in the part of the Hot Springs Range that is 

within this quadrangle; however in the Hot Springs 

Peak quadrangle, about 2 miles north of Stewart Gap, 

fossils have been collected from limestone of the 

Harmony formation at two localities, and the following 

forms have been identified by A. R. Palmer ( 1953, 

written communication) : 

Collection No. USGS 1376-CO. Hot Springs Peak quadrangle, 

about 2 miles north of Stewart Gap road. About 0. 75 mile S. 

21 °30' E. from lat 41 °20' N., long 117°25' W., at north edge 

NE~ sec. 25, T. 40 N., R. 40 E. 

Briscoia? 

Ewrekia sp. 

Idiomesus cf. I. levisensis (Rasetti) 

Geragnostus? sp. Illaenurus sp. 

Homagnostus sp. Prosaukia? sp. 

Collection No. USGS 1375-00. Hot Springs Peak quadrangle, 

on ridge in NW corner SW~ sec. 30, T. 40 N., R. 41 E. (unsurveyed). 

Bilz.ingseUa sp. 

Dartonaspis sp. 

Eurekia? sp. 

Prosaukia? sp. 

Ptychaspis sp. 

Palmer ( 1953, written communication) states that the 

collections indicate a late Late Cambrian age approximately equivalent to the Windfall formation at Eureka, Nevada (Nolan, Merriam, and Williams, 1956, p. 

20). The fauna from collection 1375-CO is slightly 

older than the fauna from 1376-CO. 

ORIGIN 

The mineralogy of the sedimentary rocks indicates 

that the Harmony formation was derived from a terrane of acidic granitic-textured rocks with some quartzite or sandstone, or both. The 958 million year age 

for zircon in the formation in the Antler Peak quadrangle indicates that the source rocks were at least in 

part of Precambrian age. A rather minor amount of 

volcanic material and chert were also contributed from 

the source area. 

The material composing the bulk of the formation 

either has been transported no great distance or was 

carried in from far away by turbidity currents, as indicated by the predominance of angular grains, unabraded 

quartz overgrowths, and euhedral or angular heavy 

minerals. The basal shale unit is evidence of a source 

area of low relief from which the streams carried mud 

and silt. The overlying coarser clastic units with abundant fresh feldspar are evidence of rapid uplift of the 

source area with consequent vigorous erosion and rapid 

transportation and deposition. 

The environment of deposition is postulated to have 

been a rapidly subsiding basin in which the sandstone 

and shale were deposited below wave base. The graded 

beds probably were deposited at times of high seasonal runoff, possibly aided by turbidity currents generated when sediment-charged rivers entered the sea. 

The occasional beds of clastic limestone and red shale 

are indicative of shallow-water conditions that prevailed where sedimentation had nearly caught up with 

subsidence. The rare chert beds were probably formed 

as chemical precipitates during periods when clastic 

sedimentation was at a minimum, or by the metasomatic 

replacement of limestone, or perhaps by both processes, 

ROCKS OF ORDOVICIAN AGE 

Two formations of Ordovician age have been mapped 

in the Osgood Mountains quadrangle (pl. 1). These 

are the Comus and Valmy formations, which were originally defined in the Golconda and Antler Peak quad-' 

rangles, respectively (Ferguson, Roberts, and Muller, 

1952; Roberts, 1951). The two formations are not 

found in mutual contact in the Osgood Mountains quadrangle, so the relations between them are not clearly 

known; however, both formations contain Lower and 

Middle Ordovician strata. Regional studies suggest 

that the Comus formation was deposited virtually where 

it is found, and the Valmy formation, which was deposited somewhere to the west of its present outcrop 

areas, has been brought into the area on a thrust fault. 
20 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

COMUS FORMATION 

DISTRIBUTION' 

The Comus formation is exposed on the east side of 

the Osgood Mountains in a discontinuous belt about 

9% miles long, from the mouth of Hogshead Canyon to 

about 2 miles northeast of the Penson Ranch. The 

formation is separated from the type locality, as defined 

by Ferguson, Roberts, and Muller ( 1952), in the Edna 

Mountains by nearly 12 miles of valley fill and some volcanic flows. A more complete section is represented in 

the Osgood Mountains quadrangle, and the age of the 

rocks is somewhat better established by fossils. We 

propose, therefore, that the formation be redefined in 

terms of its lithology on the east side of the Osgood 

Mountains. 

Metamorphosed sedimentary rocks which we believe 

belong to the Comus formation occupy a tonguelike 

thrust plate overlying the Preble formation along the 

crest and eastern side of the range at the northern end 

of the Osgood Mountains. Two small klippen lie several hundred and a few thousand feet, respectively, west 

of the main sheet, in sec. 19, T. 39 N., R. 42 E. Faults 

also bound the sequence on the northeast and north 

where it is in contact with the Etchart limestone and 

rocks of the Farrel Canyon formation. 

LITHOLOGY 

The Comus formation along the east side of the Osgood Mountains is predominantly an alternating sequence of dolomite, limestone, and shale, with subordinate amounts of chert, siltstone, and tuffaceous ( ~) material. Sandstone and quartzite are conspicuously 

absent. 

The dolomite varies from grayish orange to moderate 

yellowish brown and from light gray to grayish black. 

Its composition varies from nearly pure dolomite to 

sandy and shaly dolomite, and calcareous dolomite grading into dolomitic limestone. The gray and dark-gray 

dolomite is commonly thick bedded to massive cut by 

a network of quartz veinlets and contains many lenses 

and nodules of chert. The upper part of the section 

contains a prominent intraformational conglomerate 

composed of platy fragments of medium dark-gray to 

grayish-black surgary-textured dolomite. The grayish-orange dolomite occurs as thick beds within a section of brown-weathering light-gray to grayish-brown 

platy sandy dolomite. 

Most of the limestone varies in shades of gray and 

some beds have a definitely bluish cast. It ranges from 

fairly pure limestone to shaly limestone and grades into 

dolomitic limestone and calcareous dolomite. Bedding 

is clearly defined at most places, and it ranges from 

thick bedded to thin bedded. Some limestone units contain interbedded chert and shale. Some limestone conglomerate has also been observed. 

The shale that is interbedded with the carbonate units 

is mostly gray, commonly with a tinge of green or greenish yellow. Most of it is well stratified and has a secondary cleavage that intersects the stratification from 

20° to 90°. At some places where the beds have been 

tightly folded, closely spaced intersecting cleavage 

planes have cut the shale into pencillike fragments. 

The section also contains a moderate amount of bluishgray siliceous shale, and some dark yellowish-green 

siltstone. 

Tuffaceous-appearing shale or siltstone is characteristic of the Comus formation in this area. The rock is 

grayish orange to dark yellowish brown, rather soft, 

and highly porous, as much as 30 percent of its volume 

occupied by small (0.05 mm) open cavities of irregular 

shape. It contains angular to subangual fragments of 

quartz and feldspar averaging 0.03 mm in greatest 

dimension, and wisps of sericite in an exceedingly fine 

grained groundmass composed of feebly birefringent 

cryptocrystalline material and scattered minute granules of clay and iron oxide. 

Nodules, lenses, and thin beds of dark chert are associated with the dolomite. Abundant dark chert has 

apparently replaced limestone and dolomite in an area 

of extensive faulting on the low hill south of the mouth 

of Hogshead Canyon. Here also, scattered bodies of 

barite replace the carbonate rocks and, to a lesser extent, 

thin chert lenses in the dolomite. 

The Comus formation on the thrust plate at the 

north. end of the Osgood Mountains includes phyllite, 

calc-silicate hornfels, recrystallized limestone, and subordinate amounts of dark recrystallized chert. Individual units have little resemblance to the unmetamorphosed sedimentary rocks of the Comus formation on 

the east side of the range, but their gross aspect indicates 

that originally the sequence was fine-grained calcareous 

or dolomitic siltstone, shale, and carbonate rocks, probably including limestone and dolomitic limestone or 

dolomite, and some chert. These rocks also have been 

intricately folded, probably because of thrust faulting. 

STRATIGRAPHY AND THICKNESS 

The only contacts of the Comus formation with other 

Paleozoic formations are fault contacts (pl. 1). Therefore, its stratigraphic position is established solely on 

its age as indicated by fossils. The Paradise Valley 

chert and the Harmony formations, which should be 

present between the Comus and Preble formations, have 

apparently been cut out by the high-angle fault that 

separates the Comus and Preble on the east side of the 

Osgood Mountains. This fault appears to be an exten-
BOCKS OF ORDOVICIAN AGE 21 

sion of the mineralized Basin-Range fault from which 

gold has been produced at the Getchell mine. At the 

type locality in the Golconda quadrangle the contact of 

the Comus and the Preble is a high-angle reverse fault. 

Stratigraphic units in the Comus formation cannot 

be correlated from one area to the next, because the outcrop areas are discontinuous and the carbonate units 

are lenticular, and because folding and, perhaps to a 

lesser extent, faulting cause apparent changes in the 

thickness of strata. Metamorphism has also made correlation more difficult. 

A generalized section of the Comus formation south 

of Granite Creek follows: 

Limestone, light-gray to grayish-brown, thin- to thickbedded ; a few thin shale beds and a few thin lenses 

(Jt) 

and beds of brown chert_ ____________________________ 700+ 

Dolomite, medium dark-gray to grayish-black, massive. 

Some grayish-brown to black chert beds. Conspicuous 

"fiat-pebble" intraformational conglomerate in upper 

part of the unit_ __________________________ 1, 000+-1, 200+ 

Shale, green to gray; some fine-grained tuff?; some siltstone; minor siliceous shale ___________________ 350-1, 050 

Dolomite, medium dark-gray to grayish-black, massive, 

extensively fractured; upper part interfingers with overlying shale; lenses and nodules of dark chert_ ________ 450+ 

Platy dolomite, brown-weathering light-gray to brownishgray, sandy; some beds of buff medium- to thick-bedded 

dolomite -----------------------------------~------- 200+ 

Limestone, light- to dark-gray, thin- to medium-bedded ; 

some interbedded shaly limestone and shale ___________ 450+ 

Shale and phyllite, light-gray to dark greenish-gray __ 10Q-600 

Fault contact with Preble formation. 

The exposed thickness of the Comus is, therefore, on 

the order of 3,200 to 4,600 feet. Ferguson, Roberts, and 

Muller (1952) estimated about 3,000 feet of beds at the 

type locality. 

AGE 

The age of the Comus formation has been established by collections of graptolites and a single trilobite 

mold. Two graptolite collections were made from 

shales that crop out on the small hill south of the mouth 

of Hogshead Canyon. Mr. Josiah Bridge (1952, written communication) reported on the graptolites as 

follows: 

Collection (field No.) H-7 -52. Osgood Mountains quadrangle, 

brick red tuffaceous shale from southern part sec. 12, T. 37 N., 

R. 41 E. (0.2 mile N. 25° E. from main barite quarry). 

One specimen contains a single, well-preserved fragment O.L 

Didymograptus similis (Hall). The second specimen contains 

at least two distinct forms, one of which may be identical with 

the above. They are, however, so badly distorted by metamorphism that not even a tentative identification can be made. 

D. similis is a Deepkill, or Lower Ordovician form, and if this 

identification is correct this fauna falls .somewhere between the 

two faunas listed by Ruedemann from Summit, Nevada (1947, 

p. 107). 

R. J. Ross, Jr., and W. B. Berry (written communication) examined another collection and identified specimens as follows (written communication, January 

1960) : 

Collection No. USGS 1072-CO (field No. H-83-51). Barite 

quarry, E. edge NW:JA,SE:JA, sec. 12, T. 37 N., R. 41 E., Osgood 

Mountains quadrangle. 

Olimaoograptus bicornis (J. Hall) 

sp. 

Diplograptus? sp. 

Orthograptus aff. 0. calcaratus Lapworth 

Age: Probably the zone of Olimacograptus bicornis. 

Ross and Berry (written communication, January 

1960) examined a small graptolite collection from a 

shale unit which overlies thin-bedded and massive chert 

in the thrust plate at the north end of the Osgood 

Mountains. 

Collection No. USGS 1373-CO (field No. F53-W-78). Just 

below crest of ridge in SE part SE:JA,SE:JA, sec. 30, T. 39 N., 

R.42E. 

Dicellograptus cf. D. divaricatus var. bicurvatus Rudemann 

cf. D. sextans (J. Hall) 

Unidentifiable scadent form 

Age : Probably zone of Olimacograptus bicornis. 

A single mold of a trilobite was found in beds that 

are at about the same stratigraphic position or slightly 

lower than those from which H-7-52 was collected. 

According to R. J. Ross, Jr. (1955, written communication), who reported on this fossil, the specimen is not 

good enough for certain identification, but it resembles 

Acerocare and Oyclognathus. He said that both"* * * 

are typically Upper Cambrian genera in the Baltic 

region but Acerocare has been reported in the lowest 

Lower Ordovician * * *" and that the specimen came 

from beds that may be "* * * a little lower stratigraphically than your H-83-51 [Coil. No. USGS 1072· (CO)] 

or H-7-52." 

The fossil evidence indicates that the Comus formation probably ranges in age from Early to Middle Ordovician, and may be as old as Late Cambrian. 

V .A;LMY FORMATION 

The type locality of the Valmy formation is about 

20 miles southeast of the Osgood Mountains quadrangle, 

on North Peak in the Antler Peak quadrangle. According toR. J. Roberts (oral communication) the formation consists of interbedded chert, quartzite, argillite, 

slate, and greenstone. He subdivided the Valmy into 

a lower and an upper unit totaling more than 8,000 feet. 

Only a few small areas of"V almy formation are known 

in the Osgood Mountains quadrangle, and we have interpreted these as remnants of a formerly much more 

extensive thrust sheet. 
22 GEOLOGY AND ~RAL DEPOSITS, OSGOOD MOUNT~S QUADRANGLE 

DISTRIBUTION 

Rocks assigned to the Valmy formation are exposed 

at two places along the east front of the Hot Springs 

Range, and in the low hills east of the Getchell mine 

(pl. 1). Only the westernmost end of the second locality is within the quadrangle. 

The Valmy formation on the east side of the Hot 

Springs Range is exposed on the hill west of Stone Corral and on the low hills just east of Box Spring, about 6 

miles north of Stone Corral. At both places the Valmy 

formation is in fault contact with the Harmony formation and Tertiary volcanic rocks and is covered on the 

lower parts of the slopes by alluvium. East of the Getchell mine, limestone of Pennsylvanian age is thrust 

over the Valmy formation, and the Valmy is probably 

thrust over rocks that belong to the Comus formation, 

although the trace of the thrust and the rocks on either 

side of it are covered by alluvium. 

LITHOLOGY 

The Valmy formation in the Hot Springs Range consists of chert, siliceous shale, quartzite, and some interbedded altered volcanic rocks. The Valmy east of the 

Getchell mine consists of greenstone and some interbedded limestone in the lower part of the section, overlain by siliceous shale and chert. 

The quartzite is light colored, ranging from almost 

white to, rarely, medium bluish gray. It is dense, medium grained, and exceptionally pure, containing 95 + 

percent quartz and 3 to 5 percent quartzite grains. The 

quartz and quartzite grains range from about 0.1 mm 

to 1 mm and average about 0.5 mm; they are rounded 

to well rounded but commonly show incipient development of interlocking borders. The interstitial material 

is recrystallized silica cement with a very small mount 

of fine mica shreds. Some of the quartz and quartzite 

grains contain crystals of apatite, zircon, and rarely, 

mica. No chert fragments or rock fragments other 

than the quartzite have been observed. 

Chert in the formation ranges from light gray to 

black and is thin bedded to massive. Some chert specimens show fine mica particles oriented in more or less 

parallel bands and small (0.2 mm) angular quartz 

grains with a cryptocrystalline silica cement, suggesting 

th:lit the chert originated by silicification of shale. 

Other specimens of chert contain dark fine-grained fragments with shardlike outlines and a few irregular clots 

of chlorite; these probably are silicified tuffs. Other 

specimens show no relict structures that might be indicative of origin. 

The siliceous shale is light gray, light brown, and light 

green. It commonly occurs as partings between chert 

beds, but it also forms beds as much as 2 feet thick interbedded with limestone and altered volcanic rocks. The 

siliceous shale is composed of very fine angular quartz 

fragments, fine-grained mica particles, very finely divided moderately birefringent material which may be 

mica or clay particles, and a cryptocrystalline silica cement. The grain size of most of the quartz and mica 

fragments is in the lower limit of the silt size range 

(smaller than 0.01 mm) and very few rocks are shale 

on the basis of grain size alone, but because of the shaly 

partings produced by the mica, the rocks are referred to 

as shale. 

Dark greenish-gray fragmental altered volcanic 

rocks are exposed east of the Getchell mine. Most of 

the rocks are composed of small fragments in a still finer 

grained groundmass, but in some places the rocks are 

composed of pieces of volcanic rock an inch or so across 

in a limestone matrix. Many of the fragments retain 

an original amygdaloidal or porphyritic structure. 

Much of the original texture of the rocks, however, has 

been destroyed by alteration. The rocks are now composed of masses of pale-green to bluish-green actinolitic hornblende; and the plagioclase, though retaining 

the former shape of phenocrysts, is recrystallized to a 

fine-grained mosaic of calcic oligoclase or possibly andesine. Some clear, more coarsely crystalline oligoclase 

occurs with actinolitic hornblende as cavity fillings. 

Some pale biotite occurs in scattered interstitial masses 

and as amygdaloidal fillings and partial replacements 

of plagioclase phenocrysts. In addition there is some 

clinozoisite and abundant secondary sphene and 

magnetite. 

Some altered volcanic rock is associated with the 

chert and siliceous shale in the outcrops west of Stone 

Corral. These are dense, green and gray, sheared rocks 

that no longer have much resemblance to igneous rocks. 

Some of these are composed almost wholly of contorted 

folia of chlorite and small amounts of magnetite and 

calcite veins. One specimen has a relict intersertal texture shown by kaolinite and illite derived from feldspar 

laths, montmorillonite derived from interstitial glass, 

and chlorite, calcite, and magnetite formed from ferromagnesian minerals. 

STRATIGRAPHY AND THICKNESS 

The stratigraphy and thickness of the Valmy formation in the Osgood Mountains quadrangle are poorly 

known because of the limited exposures, complex folding 

of the beds, and complete ignorance as to the top or 

bottom of the section. The two localities east of the 

Hot Springs Range cannot be correlated with each 

other, and they cannot be matched with the strata 

exposed east of the Getchell mine. 
ROCKS OF ORDOVICIAN AGE 23 

An east-to-west section on the hill west of Stone 

Corral consists of: 200 to 300 feet of sheared and mylonitized shale with a phyllitic appearance, known only 

from float; 100 to 150 feet of thick-bedded to massive 

quartzite (one unit of which, 25 feet thick, forms a 

persistent outcrop over a considerable length of the 

hill) ; 250 to 350 feet of poorly exposed interbedded 

dark chert, siliceous shale, altered volcanic rocks, and 

limestone; 400 to 500 feet of poorly exposed light-gray 

to black chert with siliceous shale partings and some 

thin beds of siliceous mylonitized shaly sandstone 

known mainly from float; about 50 feet of massive 

quartzite; and, finally, about 150 feet of chert and siliceous shale float, which is covered to the west. 

The total exposed section on the hill west of Stone 

Corral is 1,300 to 1,650 feet thick. The section at the 

northern locality, which is about 700 feet thick, cannot 

be matched with that at the southern locality. This 

implies a minimum thickness of nearly 2,000 feet for the 

formation as exposed in the quadrangle. 

The strata assigned to the Valmy east of the Getchell 

mine consist of greenstone, a little chert, and limestone 

in the western part of the exposed area, and interbedded 

chert and siliceous shale to the east. Top and bottom 

directions are not known, but the beds dip steeply in a 

general easterly direction, so that the greenstone section 

is apparently below the chert and siliceous shale. 

Possibly 3,000 to 4,000 feet of greenstone and about 2,000 

feet of chert and siliceous shale are exposed. The chert 

and siliceous shale closely resemble the Valmy on the 

east side of the Hot Springs Range but lack the beds of 

pure quartzite characteristic of the Valmy exposed 

there. 

In the Antler Peak quadrangle (Roberts, oral communication) the Valmy formation is 8,000 to 9,000 feet 

thick and can be divided into a lower and an upper unit; 

the lower unit measures more than 5,200 feet in 

thickness. 

AGE AND CORRELATION 

Graptolites collected from the Valmy formation in 

the Antler Peak quadrangle and in the northern Shoshone Range indicate that the age of the formation is 

of Early, Middle, and Late Ordovician age (Roberts 

and others, 1958, p. 2833). Some poor impressions of 

graptolites were found in the siliceous shales east of the 

Getchell mine, but these were useless for age determination ( R. J. Ross, 1955, written communication) ; however, clastic limestone interbedded with the greenstones 

in the same general area contains trilobites that were 

identified as very early Early Ordovician in age. The 

locality from which the trilobites were collected is east 

of the eastern boundary of the quadrangle, approximately 0.65 mile N. 46° E. from the mill stack at the 

Getchell mine on the south side of a low east-trending 

ridge (approximately SEl4 sec. 28, T. 39 N., R. 42 E.). 

R. J. Ross reported the following forms (1955, written 

communication) : 

Collection USGS D-151-00. 

Symphysurina cf. S. brevispicata Hintze 

cf. S. cleora (Walcott) 

sp. 

Hystricurus aff. H. cordai 

sp. 

Leiosteguim? 

Remopleuridiella? sp. (a single free cheek) 

Ross regarded the forms from the first collection as indieating equivalence with the lettered "B" zone of the 

Garden City formation and Pogonip group (Ross, 1951 ;. 

Hintze, 1952). According to him, none of the graptolites from the Valmy are as old as the "B" zone; but, 

as he points out, the lettered zones are based on trilobites in the eastern carbonate facies and almost no 

information is available about the corresponding graptolite zones. Beds from which these collections came 

may be equivalent to the Goodwin limestone of the 

Pogonip group in the Eureka, Nev., area (Nolan, Merriam, and Williams, 1956, p. 26-27), which is of Early 

Ordovician age and contains faunas showing relationships to faunas in the Garden City formation. 

The rocks on the east side of the Hot Springs Range 

are correlated with the Valmy on the basis of lithologic 

similarity, for no fossils have been found. The correlation is regarded as fairly sound, however, because the 

association of beds of highly pure quartzite with chert 

and siliceous shale is characteristic of the Valmy at its 

type locality. 

The lithology of the Valmy formation in the Osgood 

liountains quadrangle suggests that it be correlated 

with the lower member of the Valmy formation mapped 

by Roberts in the Antler Peak quadrangle. There the 

lower member is pure, generally light-colored quartzite 

and includes significant amounts of greenstone in addition to chert and siliceous shale; whereas the upper 

member consists principally of dark thin-bedded 

chert interbedded with dark shale, and only a little 

greenstone. 

The lower part of the Valmy is correlative . in part 

with beds to the east in Eureka County that were assigned by Merriam and Anderson ( 1942, p. 1694) to 

the lower part of the Vinini formation in the Roberts 

Mountains; the upper part of the Valmy is probably 

equivalent in age to the upper part of the Vinini as 

originally defined by Merriam and ... L\.nderson. 
24 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

EQUIVALENCE OF THE COMUS AND VALMY FORMA· 

TIONS, AND POSSIBLE FACIES RELATIONSHIPS 

The faunas contained In the Comus and Valmy formations are evidence that both formations are of Ordovician age; yet their lithologies are dissimilar and 

there is no doubt that they are different formations. 

Neither one, however, is like the dominantly carbonate 

lithology of contemporaneous rocks in eastern Nevada 

and western Utah. 

The Valmy formation is similar to the Vinini formation, which Merriam and Anderson (1942, p.1699-1701) 

recognized as a western clastic facies equivalent in age 

with Ordovician formations in the eastern part of 

Nevada where carbonate rocks are predominant. The 

Comus formation, however. has no lithologic equivalents 

in either the Valmy and Vinini or the carbonate formations, but it contains a mixture of fine clastic sedimentary rocks, chert, minor amounts of silicic tuff, limestone, and dolomite, and seems to have affinities with 

both the western and eastern facies formations. We 

are inclined, therefore, to regard it as a transitional 

facies (see p. 79) that was deposited in an environment intermediate between those in which the western 

and eastern facies originated. The implications that a 

transitional facies has for the depositional and structural history of the region are discussed on pages 70 

and 81 of this report, and have been published elsewhere (Roberts and others, 1958, p. 2816-2820). 

ROCKS OF MISSISSIPPIAN AGE 

A formation of Mississippian age is exposed on the 

west side of the Osgood Mountains and is here named 

the Goughs Canyon formation (pl. 2). The formation is on the upper plate of a thrust fault and is overlapped by a higher thrust and Tertiary volcanic rocks; 

its stratigraphic relations with other Paleozoic rocks 

are not known. The formation is composed mostly of 

altered volcanic rocks of medium to basic composition 

and coarse-grained fossiliferous limestone, with minor 

amounts of calcareous shale, siliceous shale, and chert. 

Rocks with a similar lithology in the northern part of 

the Hot Springs Range north of the Osgood Mountains 

quadrangle have been tentatively correlated with the 

Goughs Canyon formation by Willden, although he did 

not refer to them by that name. ' 

GOUGHS CANYON FORMATION 

DISTRIBUTION 

The Goughs Canyon formation is named for Goughs 

Canyon, near the center of the quadrangle on the west 

side of the Osgood Mountains; where the best fossil collections have been found. South of Goughs Canyon the 

formation is exposed in discontinuous remnants of a 

thrust plate for 1¥2 miles to the upper part of Perforate Canyon; to the north it ex·tends continuously 

for 5 miles to the north side of Farrel Canyon. The 

outcrop area is widest in East Fork of Eden Creek, 

where it is slightly over 1 mile wide, and it narrows to 

less than half a mile at Farrel Canyon. The formation 

is limited on the west by a northeast-trending normal 

fault near the mouth of Goughs Canyon, and by Tertiary volcanic rocks in the Dry Hills and near the mouth 

of East Fork of Eden Creek; north of East Fork of 

Eden Creek the Goughs Canyon formation is overridden by a younger thrust. The eastern and southern 

limit is the Goughs Canyon thrust fault. 

The meta volcanic rocks and interbedded limestones 

form prominent, nearly continuous exposures north of 

East Fork of Eden Creek, where the slopes are steep 

and rugged. Exposures are also good on the ridge 

north of Goughs Canyon, but in Goughs Canyon the 

slopes are gentler and the soil cover is fairly thick, so 

that outcrops are scattered and only the siliceous shale 

and chert and beds of limestone form good exposures; 

the altered volcanic rocks generally weather to thick 

soil. 

LITHOLOGY 

The Goughs Canyon formation is composed predominantly of altered volcanic rocks and interbedded limestone: approximately 60 percent altered volcanic rocks; 

30 percent limestone; and 10 percent calcareous sandstone, calcareous shale, siliceous shale, and chert. 

The volcanic rocks are easily recognized despite their 

altered condition, for they contain many of the characteristic structures and textures found in rocks of volcanic origin. The rocks are ,greenish gray, dark grayish green, and dusky yellow green where freshly brok~n; 

weathered surfaces are moderate to dark yellowish 

brown. In exposures the rocks are broken into many 

small polygonal blocks by closely spaced joints or very 

commonly are sliced by closely spaced parallel shear 

planes. Pillow stt'uctures are visible in some exposures, 

and the rocks in many places are obviously volcanic breccias which are composed of fragments that range from 

less than an inch in diameter' to blocks as much as a 

foot in greatest dimension. weathered surfaces of the 

fragments commonly have a pitted or vesicular appearance due to the leaching out of amygdular fillings of 

calcite. The fragments are firmly bonded by a finer 

grained matrix that in many places is calcareous. Some 

material is a mixture of volcanic rock fragments in a 

limestone matrix. 

The volcanic rocks are fine grained to microcrystalline; in fine-grained varieties gray plagioclase laths in 

a microcrystalline greenish-gray interstitial ground-
ROCKS OF MISSiSSIPPIAN AGE 25 

mass can be seen with a hand lens, and in some specimens small phenocrysts of plagioclase and relicts of 

pyroxene are visible, but a characteristic of these rocks 

is their generally nonporphyritic texture. Although 

the rocks are obviously altered, their original fabric has 

been preserved without any apparent distortion of flow 

structures and amygdules. The texture of the groundmass is typically pilotaxitic; phenocrysts of plagioclase 

and mafic minerals are uncommon. The plagioclase is 

sodic oligoclase in most specimens studied, though nearly pure albite was also identified. The feldspar is mostly hazy and contains many small inclusions of sericite, 

chlorite, and possibly some clinozoisite. Clear albite 

occurs as little pockets associated with magnetite veinlets in some rocks and as amygdule fillings in others. 

Chlorite and epidote are common constituents of the 

rock; some of the chlorite obviously is pseudomorphous 

after primary mafic minerals, possibly pyroxene. An 

unusual type has phenocrysts of fresh augite in a 

ground-mass of albitic plagioclase and abundant epidote. Actinolitic hornblende, presuma;bly an alteration 

product of pyroxene, is present in some specimens. 

Minor accessory minerals are fine-grained sphene, magnetite, and ·apatite; secondary leucoxene after sphene is 

also common. Quartz, calcite, and chlorite occur as 

amygdule fillings. Calcite is plentiful in some of the 

fragmental rocks as part of the matrix. 

Analyses of two specimens are given in table 6. 

Calcareous sedimentary rocks of the Goughs Canyon 

formation, including clastiQ limestone and calcareous 

sandstone and shale, are interbedded with the metavolcanic rocks. Limestone is the more abundant, but sandy 

and shaly rocks are common. In Goughs Canyon the 

limestone units are mostly less than 100 feet but more 

than 10 feet thick and are lens shaped and discontinuous. 

North of East Fork of Eden Creek however, the limestone units are several hundred feet thick and can be 

followed continuously for thousands of feet; outcrop 

widths vary considerably, partly owing to folding but 

mainly because of original variations in the thickness of 

the limestone. 

The limestone is medium to coarsely crystalline and 

gray to light gray where it is purest, but some of it contains considerable amounts of volcanic rock fragments 

which give it a greenish-gray color. In places the 

limestone is mottled gray and pinkish. Much of it is 

massive to poorly bedded; however, some is thinly 

bedded and some has a shaly parting. The limestone 

is locally fossiliferous; crinoid stems are abundant in 

some beds, corals and bryozoans are plentiful in some 

places and brachiopods in others. The fossiliferous 

units are highly lenticular, so that richly fossiliferous 

pods are surrounded by more or less barren limestone. 

TABLE 6.-Analyses and norms of altered volcanic rocks from the 

Goughs Canyon formation 

[Samples were analyzed by methods similar to those described in U.S. Geol. Survey Bull. 1036-0; P. L. D. Elmore, K. E. White, S.D. Botts, P. W. Scott, analysts, U.S. Geol. Survey] 

Chemical analyses Norms 

H-220-52 52-W-71 H-220-52 52-W-71 

Si02--------- 43. 9 60. 1 Q ___________ ------- 7.2 Al20a __ ______ 16. 8 15.5 Or ___________ 1.4 3.3 

Fe20a- __ _____ 2. 8 3.5 Ab __________ 24.3 60. 7 FeO _________ 7. 6 3.6 An __________ 30.8 7. 4 

MgO ______ -- 6. 2 3.0 c_- --------- ------- 0. 4 

CaO ________ - 10.8 3.2 Ne_ --------- 1.5 Na20 ________ 3. 2 6.5 Wo __________ 7. 6 

K20 __ --,.. ---- . 24 . 56 En __________ 4. 7 7. 4 Ti 02- ________ 2. 5 . 54 Fs ___________ 2.4 3.0 

P20s--- - ----- . 63 . 76 Fo __________ 7. 5 MnO ________ . 20 . 08 Fa __________ 4.2 

H20 __ - _--- __ 4. 8 1.8 Mt __________ 4. 1 5. 1 

002--------- . 07 . 57 IL __________ 4. 8 1.0 

Ap_ --------- 1.5 1.8 

Sum ___ 100 100 Cc __________ 0. 2 1.3 

Sp gr (lump)_ 2.87 2. 64 H20- --- ----- 4. 8 1.8 

Sp gr 

(powder) ___ 2. 96 2. 77 Sum _______ 99. 8 100.4 

Some of the best fossil collections have been from "hash 

beds" containing a rich mixture of coral, bryozoan, and 

brachiopod remains, many of them broken. These remains probably represent material that was reworked 

by turbulent water shortly after deposition, transported 

a short distance, and redeposited without much sorting. 

Some of the limestone and sandy limestone has a high 

content of volcanic material including small angular 

fragments of altered crystalline volcanic rock, plagioclase, chlorite, and epidote, with some chert. 

The shale and sandstone contain grains of quartz, 

flakes of colorless mica, and magnetite, and considerable 

amounts of chlorite and clayey material in the matrix. 

Calcite is a common constituent of some of these rocks 

but minor or lacking in others. 

Chert is not plentiful in the formation, but a few small 

lenticular beds of dark chert are interbedded with the 

limestone and altered volcanic rocks. However, on the 

south side of Goughs Canyon, apparently in a part of 

the section different from that exposed elsewhere, chert 

associated with fossiliferous limestone and altered volcanic rock is fairly abundant. The chert is thin bedded 

to moderately thin bedded, and much of it is pale olive 

and dusky yellow green. Some is also dark gray and 

moderate bluish gray. 

THICKNESS 

The exposed thickness of the Goughs Canyon formation in the Osgood Mountains quadrangle is uncertain 

because of complex folding but may be more than 5,000 

feet. How nearly this represents the total thickness is 

unknown because the formation is bounded above and 
26 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

below by thrust faults and is overlapped by later volcanic rocks and alluvium. For the same reasons the 

degree of completeness of the section where it is exposed 

in the northern part of the Hot Springs Range is unknown. The formation has not been recognized outside 

of these two areas. 

AGE AND CORRELATION 

The stratigraphic position of the Goughs Canyon 

formation is unknown because of thrust faulting, except 

that it is older than the Tertiary volcanic rocks which 

overlap it. Fossil evidence, however, establishes the 

age as probably Early and early Late Mississippian 

(Visean). 

A rather large collection of fossils has been obtained 

from the limestones interbedded with the altered volcanic rocks. The corals and bryozoa were studied by 

Helen Duncan, and the brachiopods by Mackenzie 

Gordon, Jr. Their findings are summarized in the 

following discussions. 

Collection No. USGS 19807-PC (field No. H-76-51). Cherry 

Canyon, southern part of SW:JA, sec. 11, T. 38 N., R. 41 E. 

The fossils collected are a peculiar type of caninoid 

coral which Miss Duncan referred to Timania ~. She 

said (written communication, 1952) : 

Timania is known mainly from the Upper Carboniferous and 

Permian of Russia. These American corals seem to be closer 

to Timania than to any other genus so far described ; however, 

they probably should be recognized as a distinct taxon. At 

present, the only definite information we have on the stratigraphic distribution of these corals in North America is their 

occurrence in the upper part of the Deseret and in the lower part 

of the Humbug formations of north-central Utah (East Tintic 

and Oquirrh Mountains). 

Certain other fossils in the Deseret fauna have Meramec 

affinities and suggest that the formation is assignable to the 

lower part of the Upper Mississippian. Furthermore, we generally find that in the west the larger caninoid corals, a category that includes these specimens, are much more characteristic 

of the Upper Mississippian than they are of the Lower Mississippian. For these reasons, it seems probable that this Nevada 

occurrence indicates that the coral-bearing rocks in Cherry 

Canyon are of early Late Mississippian age. 

Collection No. USGS 19808-PO (field No. H-77-51) Cherry 

Canyon, Osgood Mountains quadrangle. Oenter SW:JA, sec. 

11, T. 38 N., R. 41 E. Near locality of H-76-51, and from 

same limestone unit. 

Of this collection, Helen Duncan reported (written 

communication, 1952) : 

This lot contains a recrystallized tabulate coral identified as 

Michelinia?· sp. indet., and indications of indeterminate rhomboporoid bryozoans. These fossils are of Carboniferous types, but 

they are not particularly useful for precise correlation. From 

general observations on faunas in the region, such fossils are 

more likely to occur in the Upper Mississippian or in the Pennsylvanian than they are in the Lower Mississippian. 

Collection No. USGS 14206-PC (field No. B-13-52), Goughs 

Canyon, NW:JA,NW:JA, sec. 27, T. 38 N., R. 41 E. Bank north of 

main stream. 

Corals: 

Michelinia sp. 

Oyathaa:onia sp. 

Zaphrentites sp. 

Triplophyllites sp. 

Rhopalolasma n. sp. 

Permia? sp. 

Rylstonia sp. 

Trochophyllum sp. 

Zaphrentoid coral fragments, indet. 

Concerning this collection Miss Duncan said (written 

communication, 1953) : 

It was amazing to :find such a varied assemblage of coral 

genera in such a relatively small collection (less than 30 specimens). As I recall the corals were difficult to get out of the 

rock without breaking them, and we collected very few examples 

of the larger forms. I suspect that an even larger assortment 

of genera is to be found at this locality. At least two of the 

genera have not been reported as of 1953 in the United States. 

Rhopalolasma and Rylstonia were described from the Lower 

Carboniferous of Great Britain and are known only from the 

upper Tournasian and Visean of western Europe. Permia occurs in the Tournasian and Visean of Europe and Asia, and possibly in the Keokuk of the Mississippi Valley. Most of the corals 

in the collection came from a clastic limestone and were fairly 

well broken up before they were incorporated in the enclosing 

sediments. For this reason, the material is not entirely satisfactory for investigation or comparison with described species. 

The coral faunule certainly has a Mississippian aspect, but at 

this stage of investigation, it is impossible to suggest any precise correlation with the Mississippi Valley section or even with 

the Rocky Mountain section. Some of the corals suggest correlation with the upper Tournasian and the Visean of Europe 

and Asia. 

Bryozoa: 

Fistuliporoid bryozoans, genera undet. 

Stenoporoid bryozoans, genera undet. 

Fenestella, 2 or more species 

H emitrypa sp., possibly new 

Polypora sp. undet. 

Thamniscus.?, probably 2 species 

Ptilopora? sp. undet. 

Oystodictya ct. S. lineata (Ulrich) 

Rhabdomeson sp. undet. 

Miss Duncan (written communication, 1953) reported 

on the bryozoans as follows : 

One bed at this locality contains a diversified and fairly well 

preserved bryozoan fauna, which helps confirm the Mississippian age of the limestones and may eventually be significant in 

their correlation. The Hemitrypa may be a new species and is 

probably identical with the one in Collection USGS 14029-PC. 

The Oystodictya is close to or identical with a species that is 

abundant in the Keokuk and lower Meramec of the Mississippi 

Valley. On the other hand, the bryozoan Rhabdomeson has not 

been reported prior to 1953 in the Mif¥1issippian of this country. 

The genus was described on material from the Lower Carboniferous of England. The genus is rather common in our Pennsylvanian and Permian, but if it occurs at all in our type 
ROCKS OF MISSISSIPPIAN AGE 27 

Mississippian it has never been identified. As it is rather easy 

to recognize, I do not think it is very likely that it has escaped 

detection. Material for some of the other genera is scant. 

The following brachiopods were collected from the 

Goughs Canyon locality (USGS 14026-PC) and identified by Mackenzie Gordon, Jr.: 

Brachiopods : 

"Productus" (Setigerites?) atr. P. setiger Hall 

"Productus" (Linoproductus) sp. 

"Productus" (Avonia) sp. 

"Productus" f:!P· 

Schizophoria? sp. 

Spirifer atr. S. grimesi Hall 

Spiriter sp. 

Brachythyris atr. S. suborbicularis (Hall) 

Strophopleura n. sp. 

Gordon reported (written communication, 1953) : 

This fauna is a rather puzzling one, but it appears to be Mississippian in its general composition. The productid related to 

"P." setiger Hall is represented by poorly preserved specimens 

and is also reminiscent of the genus Dictyoclostus which has a 

fairly long range through the Carboniferous and Permian. The 

other productids likewise belong in genera that are long-ranging. The Spirifer related to S. g'rimesi Hall is indicative of 

Mississippian age, but in western America, Spirifers of this type 

may be found rather generally distributed through the Mississippian. The Brachythyris resembles a lower Mississippian type, 

but the genus ranges through a considerable part of the Mississippian. Perhaps the most interesting form in the collection is 

the single specimen I have identified as Strophopleura, a genus 

known at present only from Late Devonian and early Mississippian rocks. The species, however, appears to be a new one, and 

therefore there is no guarantee that it does not represent an 

extension of range of the genus. The other forms that I have 

not mentioned specifically have no additional stratigraphic implications. 

I have also conferred with Helen Duncan, who has studied the 

corals and Bryozoa from this collection. Some of them are 

bizarre types that are closer to European than to American 

forms. w·e both agree that this is not the sort of fauna with 

which we are familiar in other western localities (for example, 

in west-central Utah). There are enough genera, usually restricted to the Mississippian, among the corals, bryozoans, and 

brachiopods to suggest that this is indeed a Missisippian fauna 

and probably one well below the top of the Misissippian. I 

think that the best age determination we can give at present is 

that the lens containing the fauna is pre-Chester Mississippian 

in age. 

Subsequent work on Mississippian rocks and faunas 

in north-central Nevada has furnished a better frame 

of reference for dating collection No. USGS 14026-PC 

and for interpreting the age span of fossiliferous beds 

in the Goughs Canyon formation. Duncan and 

Gordon (written communication, 1961) stated : 

The fauna in collection No. USGS 14026-PC contains several 

corals and brachiopods that appear to be identical with genera 

and species found in the Mississippian rocks of western El.ko 

690-159~-8 

County, where the sequence of Early Mississippian faunas has 

been worked out (Gordon and Duncan, 1961). This particular 

assemblage fram the Goughs Canyon formation is clearly related 

to Elko County faunules that suggest early Osage age. 

CoHection No. USGS 14029 (field No. 52-W-16), SW:l4SE:l4 

SKI~ sec. 28, T. 38 N., R. 41 E. 

This collection contains one bryozoan, two corals, and a 

piece of crinoidal limestone with indeterminate fragments of 

corals and Bryozoa. The species identified are : 

Syringopora atr. S. surcu..laria Girty 

Lithostrotion atr. L. whitneyi Meek 

H emitrypa sp., possibly the same as the species from 

USGS locality 14026. 

Miss Duncan (written communication, 1953) said of 

this collection : 

The Syringopora has smaller, more widely separated, and evenly 

spaced corallites than the type of S. surcularia, which is very 

common in the Madison and equivalents in the West. I have 

seen comparable specimens from rocks that are supposed to be 

of post-Madison age but have not studied the material in enough 

detail to determine whether the variation is persistent enough to 

distinguish a subspecies. 

The Lithostrotion falls within the limits of L. tvhitneyi as it 

has been interpreted by various authors, but the corallites are 

smaller than those of the type. L. whitneyi occurs in the lower 

part of the Upper Mississippian in Utah. This specimen is also 

related to L. irregulare Phillips and L. scoticum Hill described 

from the Visean of Great Britain. 

The H emitrypa is probably an undescribed species, at least it 

does not appear to fit the description for any species described 

from the Mississippian of North America. This bryozoan is one 

of the few fossils that have so far been found at more than one 

locality in the Goughs Canyon formation. It is abundant in one 

bed at USGS locality 14206. 

A Mississippian age is certainly indicated by the fossils collected. H emitrypa is not known to persist beyond the Lower 

Carboniferous in the United States. The Syringopora is related 

to a common Madison species, but it is not known whether this 

particular variant has a restricted range. Certain lithostrotionoid corals (Lithostrotionella especially) occur in the Lower 

Mississippian, but the phaceloid lithostrotionoids appeared 

somewhat later. In Utah and Idaho, phaceloid forms such as 

the one in this collection characteristically are found in the 

Upper Mississippian, and we have tentatively considered that 

their appearance coincided approximately with the beginning of 

Late Mississippian (Meramec) time. However, corals of this 

type do occur in the uppermost part of the Mission Canyon and 

Redwall formations, and it may be that they first appeared in 

late Early Mississippian faunas in areas where environmental 

conditions were favorable. 

Helen Duncan (written communication, 1961} has 

contributed the following discussion on the age of the 

Goughs Canyon formation as a unit: 

When collections from the Goughs Canyon formation were 

first studied in 1952 and 1953, it was concluded that the 

faunal evidence pointed to a Late Mississippian age for the included fossiliferous rocks. The occurrence of T·imania? and I h' . phaceloid lithostrotionoid corals in some lots favors t Is assignment, though Gordon and I were very puzzled about the significance of the fauna collected at USGS locality 1420&--PC. Re-
28 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

cent work on the faunas from western Elko County (Gordon 

and Duncan, 1961) has clarified our ideas considerably. A vailable evidence suggests that the lenticular limestones of the 

Goughs Canyon formation carry faunas that range in age from 

late Early Mississippian (Osage equivalent) to early Late Mississippian (Meramec equivalent). The upper beds of the :fine 

clastic sequence in Elko County also contain phaceloid lithostrotionoids and other corals suggestive of Late Mississippian age 

although Timania? has not as yet been identified from the area. 

The corals obtained from the Inskip and Banner formations, 

though deformed and recrystallized, seem to belong to the same 

general faunal sequence. 

The Goughs Canyon formation is probably correlative with the Mississippian ( ~) Inskip formation of the 

East Range, Winnemucca quadrangle, Nevada, which 

was regarded by Ferguson, Muller, and Roberts (1951) 

as Permian ( ~) . The Inski p contains volcanic rocks 

and limestone that somewhat resemble rocks of the 

Goughs Canyon formation, and is now known to contain fossils of probable Late Mississippian age (Roberts, 

and others, 1958 p. 2847). Limestone of Late Mississippian age is common in the eastern part of the Great 

Basin (Nolan, '1935, p. 27-29; Gilluly, 1932, p. 25-26; 

Weller, 1948), but no precise correlations with the 

Goughs Canyon formation are possible. No reliable 

correlation with Oregon or California Mississippian 

rocks can be made. The Coffee Creek formation of 

central Oregon was determined by Merriam and Berthi,aume (1943, p. 149-151) to be"* * * Lower Carboniferous, roughly Visean, in terms of the British succession", and, according to Duncan .and Gordon, is probably a little younger than the Goughs Canyon formation. The faunal assemblages are different, however, 

and the Coffee Creek formation, which consists of lime-

. stone, argillaceous to sandy limestone, and calcareous 

sandstone but does not contain volcanic rocks. The upper part of the Baird formation in the Redding-Weaverville districts, California, is related faunally to the 

Coffee Creek formation (~ferriam and Berthiaume, 

1943, p. 163) and has volcanic material associated with 

the sedimentary rocks (Hinds, 1933, p. 92-93). 

CONDITIONS OF DEPOSITION 

The clastic limestones with their localized concentrations of fossils comprising several forms are evidence 

of a shallow marine environment where turbulent waters reworked unconsolidated calcareous sediment shortly after its deposition. Beds of dirty limestone and 

calcareous, argillaceous, and arenaceous rocks probably 

can also be attributed to a stirred-up limy sea · floor 

though locally, perhaps in deeper quieter basins, some 

fine-grained siliceous sediments accumulated. Some of 

the volcanic rocks were extruded in the sea, where they 

became brecciated on contact with the water and churned 

up and incorporated some of the limy deposits on the 

sea floor. Some of them may have formed shallow sills 

in the ocean sediments. Probably in places they built 

up piles that rose above the surface or were temporarily 

elevated above sea level by earth movements, and further extrusion took place subaerially, for there are thick 

sections with no indications that they were deposited on 

a sea floor. Explosive volcanism resulting in the deposition of tuffs seems to have been relatively minor. 

ROCKS OF PENNSYLVANIAN AND EARLY 

PERMIAN AGE 

Rocks ranging in age from Middle Pennsylvanian to 

Late Pennsylvanian or Early Permian rest unconformably on the older Paleozoic rocks in the Osgood Mountains (pl. 1) ; none are known in the southern end of 

the Hot Springs Range. Similar rocks elsewhere in 

north-central Nevada have been called the overlap assemblage (Roberts and others, 1958, p. 2821, 2838-2846). 

They represent sediments deposited in marine basins or 

on their margins following a late Paleozoic orogenic 

episode (Roberts, 1951; Roberts and Lehner, 1955, p. 

1661; Ferguson, Muller, and Roberts, 1951; Ferguson, 

Roberts, and Muller, 1952) that formed a highland area 

through central Nevada (Dott, 1955, p. 2288). Rocks 

of the overlap assemblage in this part of Nevada have 

become known as the Antler sequence (Roberts and 

others, 1958, p. 2839, 2841), which includes the Battle 

and Highway formations of Middle Pennsylvanian age, 

the Antler Peak limestone of Late Pennsylvanian and 

Permian age, and the Edna Mountain formation of Permian age. 

The dominantly terrestrial conglomerate of the Middle Pennsylvanian Battle formation rests unconformably on older Paleozoic rocks. It is overlain by limestone, and westward it wedges out and interfingers with 

limestone that also rests on older Paleozoic rocks. Ferguson, Roberts, and Muller (1952) named the limestone 

equivalent of the Battle formation in the Edna Mountains the Highway limestone; in the Antler Peak quadrangle, Roberts (1951) called the limestone above the 

conglomerate in the Battle, the Antler Peak limestone. 

Representatives of both the Highway and Antler Peak 

formations are present in the Osgood Mountains, but 

they cannot be separated on the basis of lithology; so 

they have been mapped as one unit, here designated the 

Etchart limestone. A clastic facies of the Etchart limestone, here named the Ad.am Peak formation, has been 

thrust over the Etchart limestone. The Edna Mountain formation does not occur in the Osgood Mountains 

quadrangle. 
ROCKS OF PENNSYLVANIAN AND EARLY PERMIAN AGE 29 

BATTLE FORMATION 

The Battle formation, which crops out in the central 

part of the Osgood Mountains, was named and defined 

by Roberts (1951) in the Antler Peak quadrangle, where 

it takes its name from Battle Mountain. The formation has subsequently been recognized as far west as the 

Edna Mountains in the northwest part of the Golconda 

quadrangle and as far east as the Shoshone Range, 

Mount Lewis quadrangle, but it is best developed at its 

type locality. Hague and Emmons (1877, p. 688) 

briefly mentioned this unit in the 40th Parallel report; 

and Lawson ( 1913, p. 328-329), describing it in some 

detail, regarded it as an ancient fan deposit for which 

he proposed the now common term, "fanglomerate" 

(Lawson, 1913, p. 329-330). 

DISTRIBUTION 

In the Osgood Mountains quadrangle the Battle formation is confined to the central and south-central parts 

of the Osgood Mountains (pl. 1). In most places the 

formation is overlain by younger strata, but midway 

down the eastern side of the range it occurs as gently 

dipping to nearly flat erosion remnants from which the 

higher beds have been removed. The crest of the ridge 

for 3¥2 miles south of Hogshead Canyon is composed 

of Battle formation, which in places has been tilted so 

that it forms prominent nearly vertical "ribs." Along 

the northern side of Hogshead Canyon, gently dipping 

Battle formation is very prominently exposed in steep 

cliffs rising above the Osgood Mountains quartzite (fig. 

lOA.). These cliffs are a prominent topographic feature that can" be recognized from far out in the valley to 

the southeast. Narrow, discontinuous exposures of 

steeply dipping conglomerate of the Battle formation 

also occur high up on the steep slopes west of Adam 

Peak, where the formation is partly cut out by a highangle reverse fault. A small remnant of conglomerate 

of the Battle formation resting on shale of the Preble 

formation forms steep cliffs on Lone Butte, east of the 

main range in the southern part of the quadrangle. 

Except for some small patches of conglomerate, the 

Battle formation is not found much farther west than 

the crest of the Osgood Mountains. Near the top of the 

range east of Goughs Canyon in the north-central part 

of sec. 26, T. 38 N., R. 41 E., the thick bed of conglomerate beneath limestone can be seen pinching out rapidly 

westward, and limestone rests directly on the Osgood 

Mountain quartzite. On the ridge in the north-central 

part of sec. 4, T. 37 N., R. 41 E., the conglomerate of the 

Battle for~ation also wedges out bene-ath limestone. 

LITHOLOGY 

In the Osgood Mountains the Battle formation is 

predominantly a poorly bedded boulder conglomerate; 

but at some places the upper part is composed of pebble 

conglomerate, some coarse-grained sandstone, and some 

interbedded white limestone in beds less than 10 feet 

thick that generally contain some sandy and pebbly 

material; and in a few places it contains minor amounts 

of interbedded red shale and sandstone. The conglomerate is composed almost entirely of fr3.ooments of 

Osgood Mountain quartzite, with only a few small 

fragments of chert. Most commonly the quartzite fragments are of boulder size, but they range from small 

pebbles about one-fourth of an inch in diameter to rare 

blocks 10 feet or more in diameter. In most places the 

fragments are firmly cemented in a quartzite matrix, 

which, being of much the same color and texture as the 

fragments of quartzite, may make it difficult to tell the 

fragments from the matrix, and in places it is difficult 

to distinguish the quartzite conglomerate from the Osgood Mountain quartzite. The matrix in some places 

is dark-reddish-brown to dark-purple sand and shaly 

material. The basal 2 or 3 feet of the formation at 

many places are composed of angular fragments of randomly oriented quartzite in a sand and shaly matrix. 

Where the underlying quartzite is thick bedded or 

massive, the angular fragments are few and as n1uch as 

several feet in diameter; where the quartzite is thin 

bedded, the fragments are abundant and not much more 

than 1 foot in greatest dimension. This basal zone 

grades upward, with no apparent break, into poorly 

bedded boulder conglomerate. 

STRATIGRAPHY AND THICKNESS 

The Battle formation rests unconformably on the 

Osgood Mountain quartzite in most places, and on the 

Preble formation locally. At some places where the 

beds have been steeply tilted, as along the crest of the 

range south of Hogshead Canyon, the contact with the 

older rocks is faulted but the faulting appears to be 

along the contact plane. The contact between the 

Battle formation and the Osgood Mountain quartzite 

over a distance of approximately 2 miles on the north 

side of Hogshead Canyon is nearly parallel with the 

contact of the Battle formation and the overlying 

Etchart limestone, and the Battle formation shows only 

small changes in thickness due to minor channeling of 

the underlying quartzite. Minor channeling is also 

visible at several other places in the range where the 

contact between the Battle and Osgood Mountain formations is well exposed. 

At its type locality in the Antler Peak quadrangle, 

Roberts ( 1951) noted that the lithology of the Battle 

formation changes upward from coarse conglomerate to 

pebble conglomerate with interbedded sandstone, shale, 

calcareous shale, and limestone. The Battle formation 

in the Osgood Mountains shows a similar succession at 
30 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

some places, though at others only coarse-grained conglomerate is present. On Lone Butte-sec. 34, T. 37 N., 

R. 41 E.-a boulder conglomerate approximately 60 

feet thick is overlain by limestone which at its base has 

thin interbeds of quartzite pebble conglomerate. In 

the Osgood Mountains, limestone generally rests directly on the older rocks; but in places there are patches 

of coarse-grained conglomerate beneath the limestone, 

and the base of the limestone commonly contains lenticular beds of coarse-grained quartzite conglomerate 

and pebble conglomerate. 

Owing to lenticularity and faulting, the thickness of 

the Battle formation varies considerably. In the 

Antler Peak quadrangle (Roberts, 1951) the maximum 

thickness of the Battle formation is more than 700 feet; 

but in the Osgood Mountains the m~ximum thickness 

exposed is approximately 400 feet, and at most places it 

does not exceed 100 feet. 

AGE AND CORRELATION 

The Battle formation has been established on fossil 

evidence as being of Middle Pennsylvanian (Atoka to 

Des Moines) age at its type locality in the Antler Peak 

quadrangle. At the type section the Antler Peak limestone of Late Pennsylvanian and Permian age overlies 

the Battle formation with a slight erosional unconformity. In the- Edna Mountains, northwest Golconda 

quadrangle (Ferguson, Roberts, and Muller, 1952), and 

at some places in the Osgood Mountains, the Battle 

formation is overlain by limestone of Middle Pennsylvanian (Des Moines or older) age. Ferguson regarded 

the Middle Pennsylvanian Highway limestone in the 

Edna Mountains as the offshore facies contemporaneous 

with the upper part of the Battle formation at Battle 

Mountain (Antler Peak quadrangle) . 

Strata of Late Pennsylvanian age, probably contemporaneous with the Antler Peak limestone, also rest on 

conglomerate of the Battle formation in the Osgood 

Mountains. Some conglomerate mapped as Battle formation in the Osgood Mountains may be as young as 

Late Pennsylvanian, however, because on the main ridge 

east o:f Etchart Canyon (SE1,4 sec. 4, T. 37 N., R. 41 E.) 

some thin beds of limestone containing fusulinids o:f 

Late Pennsylvanian age (Antler Peak limestone) are 

interbedded with coarse conglomerate. 

Gilluly (oral communication) has mapped conglomerates in the Shoshone Range (Mount Lewis quadrangle) that are correlated with the Battle :formation 

on the basis o:f lithologic similarity and their stratigraphic position beneath the Antler Peak limestone. 

In eastern Nevada and western Utah, parts o:f the Ely 

limestone are equivalent in age to the Battle and Highway formations ( Dott, 1955, p. 2282-2287). 

CONDITIONS OF DEPOSITION 

A. C. Lawson (1913) studied the conglomerate at 

Battle Mountain and concluded that it was the remnant 

o:f an alluvial :fan deposited under arid conditions in a 

region o:f bold relief. He, therefore, called it a ":fanglomerate," a term that has since had wide use in the designation o:f deposits which more or less come within Lawson's definition. Since Lawson's study, which presumably was confined to a limited area, the :formation has 

been examined and mapped at many places in northcentral Nevada, and although it seems very possible that 

parts o:f the Battle :formation were terrestrial deposits. 

much o:f it certainly is o:f marine orgin. In general, the 

basal parts o:f the :formation are poorly sorted and show 

some crossbedding, current bedding, channeling, and 

abrupt changes in lithology, whereas the middle and 

upper units contain a large proportion of marine beds. 

From our know ledge o:f the regional distribution and 

variations o:f the formation and the changes that are 

apparent within the Osgood Mountains quadrangle, we 

conclude that the Battle formation interfingered with 

carbonate marine strata at many places, a relationship 

that was first recognized by Ferguson (Ferguson, Roberts, and Muller, 1952) in the Edna Mountains in the 

northwestern part o:f the Golconda quadrangle. 

ETCH.A.RT LIMESTONE 

The Etchart limestone is a :formation composed predominantly of carbonate rocks exposed along the west 

side o:f the central part o:f the Osgood Mountains; it is 

named :for Etchart Canyon on the west side o:f the range 

in sees. 4, 5, and 8, T. 37 N., R. 41 E. (pl. 1), where the 

:formation is well exposed. It contains rocks o:f Middle 

Pennsylvanian age and Late Pennsylvanian or Early 

Permian age that are elsewhere assigned to the Highway (Ferguson, Roberts, and Muller, 1952) and Antler 

Peak (Roberts, 1951) :formations, respectively. The 

two formations are included in a single unit because we 

could not separate the Highway limestone from the 

Antler Peak limestone in the Osgood Mountains quadrangle on the basis of lithology. 

DISTRIBUTION 

In the Osgood Mountains quadrangle the Etchart 

limestone is almost entirely confined to the west side o:f 

the Osgood Mountains and an area north and east of 

the Getchell mine (pl. 2). It extends northeast beyond 

the quadrangle boundary about 4 miles. The formation is not exposed in the Hot Springs Range and has 

not been identified in the mountains :farther west in 

Humboldt County. It occupies two principal areas in 
ROCKS OF PENNSYLVANIAN AND EARLY PERMIAN AGE 31 

the Osgood Mountains : ( 1) on the southeastern side of 

Goughs Canyon, on the upper parts of Perforate Canyon, and in Etchart Canyon; and (2) in a narrow belt 

on the west side at the north end of the range, north 

of Anderson Canyon. Limestone beds are prominently 

exposed on the north side of Hogshead Canyon, where 

they lie with a northerly dip above conglomerate of the 

Battle formation and are terminated above by a thrust 

fault that brings in rocks of the Preble formation (fig. 

lOA). A limestone section is well exposed in the hills 

east of the quadrangle boundary, 2 or 3 miles northeast 

of the Getchell mine. Some of the same beds are poorly 

exposed in the low hills north of the Getchell mine, in 

the extreme northeast corner of the quadrangle. An 

isolated remnant caps the small hill known as Lone 

Butte, more than 1 mile east of the main range, where 

it rests on the Battle formation. 

LITHOLOGY 

The formation is predominantly a limestone and 

sandy limestone sequence with some interbedded dolomite, minor amounts of calcareous shale, and lenticular 

beds of conglomerate. Sandy and pebbly units and 

conglomerate are most common in the lower part, 

though higher beds may have some thin, pebbly members. The higher strata tend to have mo~e pure limestone and dolomite and commonly some calcareous shale. 

Bedding is thick and indistinct within most of the 

units; however, some are well bedded. In general, stratification is best defined by the boundaries between li-

~ thologic types. The lithology varies rapidly laterally 

as well as vertically, and individual units tend to be 

lenticular and discontinuous, so that it is impossible to 

make precise stratigraphic correlations between exposures in different areas. 

Much of the limestone-perhaps 50 percent or more--

is sandy. Although sandy limestone may occur anywhere in the section, it is more common in the lower 

part. Weathered surfaces are light brown to gray, the 

unweathered rock varies from very light gray to medium gray. The sandy limestone is medium to coarse 

grained and generally fairly well sorted, but some beds 

contain a few small pebbles mixed in with the sand. 

The majority of the sand grains are subangular to subrounded grains of quartz from 0.1 mm to 2 mm in size; 

many of the larger grains are quartzite. Most specimens 

contain a few grains of dark chert, and some contain 

occasional grains of fresh feldspar. The calcite matrix is medium grained, less commonly coarsely crystalline. Light-gray to light-brown well-rounded quartzite pebbles, whose size range from one-fourth of an 

inch to cobbles 5 inches in diameter, are scattered 

through the sandy limestone. The pebbles also occur 

in a few · thin beds which commonly are only one pebble 

thick. In places the sandy limestone is cherty. The 

chert is dark gray, weathers brown, and occurs as irregularly shaped lenses and elongated nodules parallel 

with the bedding. In places the chert is fairly continuous in beds no more than 1 or 2 inches thick. At 

several localities the limestone is cut by a network of 

thin quartz veinlets which, with the chert nodules, give 

it a very rough weathered surface. Poorly preserved 

fragments of bryozoans, corals, and brachiopods found 

in the sandy limestone are suitable for only approximate 

age assignments. 

The fairly pure limestone is thick bedded to massive, 

medium gray to light gray, and commonly distinctly 

granular. Some of it contains brown to black chert 

that is commonly nodular but locally forms interbedded 

layers a few inches to a few feet thick. Some calcareous 

and dolomitic reddish-brown siltstone and shale a few 

inches to a few feet thick are interbedded with the 

limestone. Most of the fossils have been found in the 

fairly pure limestone, where they are rather poorly 

preserved owing to transportation and abrasion prior to 

incorporation in the sediment; they are seldom found 

in sandy limestone. A very fine grained light-brownish-gray variety of limestone forms single massive beds 

about 10 feet thick at a few places in the formation. 

Dolomite and sandy dolomite are interbedded with 

the limestone. The dolomitic rocks characteristically 

weather moderate yellowish brown to light brown or 

yellowish gray but are greenish gray to medium gray 

on freshly broken surfaces. 

The beds of pebble conglomerate are reddish brown 

on a weathered outcrop and light gray to pale brown on 

a fresh surface. Individual beds are generally less 

than 10 feet and no more than 5 feet thick. Calcareous 

sandstone and, in places, a bed or two of quartzite 1 foot 

or less thick are interbedded with the conglomerate. 

Mostly, the conglomerate is composed of sub rounded to 

rounded, fairly well sorted pebbles and small boulders 

of light-gray to pale-brown and greenish medium- to 

coarse-grained quartzite that looks like the Osgood 

Mountain quartzite; small pebbles of dark chert are 

much less common. The matrix of the pebble conglomerates is brown sand or silica-cemented quartz sand. 

Some beds are identical in appearance with conglomerates of the Battle formation. 

The calcareous shale beds are thin, rarely exceeding 2 

or 3 feet in thickness. Some beds weather yellow 

brown or greenish gray and are brown to light gray on 

fresh surfaces; others are grayish red on both weathered 

and fresh surfaces. 
32 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

STRATIGRAPHY AND THICKNESS 

Along the crest of the Osgood Mountains south of 

Hogshead Canyon and east of the range crest, the 

Etchart limestone rests conformably or with slight erosional disconformity on conglomerate of the Battle formation. On the west side of the range the limestone 

sequence lies unconformably on folded Osgood l\Iountain quartzite at most places, because the Battle formation lenses out westward and is present only as scattered 

discontinuous lenses beneath the limestone. Thin beds 

and lenses of quartzite conglomerate that resemble the 

Battle formation occur in the lower part of the limestone sequence, and thin beds of limestone are known in 

the upper part of the Battle formation; so it is possible 

that the lower part of the Etchart limestone is locally a 

temporal equivalent of the Battle formation. 

No well-defined stratigraphic succession can be established, because of the lateral variations in lithology and 

lenticularity of units within the sequence. The rocks 

are involved in thrust faulting, which makes stratigraphic relations even more difficult to resolve. But in 

general, in the southern part of the Osgood l\Iountains 

the lower part of the formation-perhaps the lower 

one-fourth-is composed of light-gray to light-brown 

sandy and pebbly limestone containing thin beds and 

lenses of quartzite conglomerate and occasional thin 

beds of pure, fine-grained limestone. Following these 

beds are light-gray to light-brown, sandy, medium- to 

fine-grained limestone with only scattered quartzite 

pebbles or thin pebbly beds and some che.rty units. The 

upper part of the formation in many places is predominantly a medium-dark-gray, fine- to medium-grained, 

thick-bedded to massive, rather pure limestone containing some chert and some beds of dolomite and dolomitic 

limestone. In some places the highest beds are reddishbrown-weathering calcareous shale and siltstone, and 

some interbedded thin limestone units. 

In the southern part of the Osgood Mountains the 

maximum thickness of the Etchart limestone is about 

250 to 300 feet. On the west side in the northern part 

of the range there may be 1,000 feet of beds, although 

faulting and tight folding obscure the true thickness. 

In the northeast corner of the quadrangle the formation is separated from the underlying greenstone of the 

Valmy formation by a thrust fault; but probably it was 

originally deposited on the greenstone, for in places at 

the contact the limestone contains fragments of greenstone. The most complete and thickest section is 2 to 3 

miles east of the northeast corner of the quadrangle, 

where possibly more than 2,000 feet of beds are exposed. 

Here, at least 540 feet and probably about 1,400 feet of 

strata make up a dominantly carbonate- section that 

grades upward into a section more than 600 feet thick 

of interbedded calcareous shale, limestone, and dolomitic limestone. The individual units are not distinctive and probably they change rapidly laterally, so 

that no direct correlations can be made between here and 

the exposures in the northeast corner of the quadrangle. 

The measured sections are listed below : 

Measured section on isolated hill, SE¥4 sec. ~1, T. 89 N., R. 4~ E., 

approfeimately 1."1 miles N. 66° E. from mill stack at the 

Getchell mine. 

Tape-and-compass traverse: Thickness 

(ft) 

Limestone conglomerate, angular to subangular fragments of limestone of pebble to cobble size and 

pebbles of quartzite in calcareous and sandy 

matrix ---------------------------------------- 20 

Limestone, gray, massive, cherty------------------- 5 

Quartzite conglomerate, some pebbles of limestone, 

chert, and greenstone in sand matrix_____________ 8 

Dolomite, yellowish- and reddish-brown-weathering, 

thin-bedded, shelf-making________________________ 30 

Limestone, gray, rough-weathering; moderately well 

bedded, with very thin sandy laminre_____________ 10 

Limestone, tan, with dolomite laminre______________ 4 

Limestone, light-gray, prominent, cliff-making, roughweathering, massive, with scattered quartz 

pebbles ---------------------------------------- 11 

Dolomite, tan and gray, brown-weathering, wellbedded ; interbedded ribbed gray .limestone and 

medium-gray massive limestone__________________ 24 

Limestone, gray, shelf-making; some sandy and dolomitic layers____________________________________ 20 

Limestone, gray ; many thin brown-weathering dolomitic layers; cliff making; contains scattered isolated quartz pebbles. "Hash beds" of small smooth 

coiled and straightg astropods and brachiopod 

fragments ------------------------------------- Limestone, gray platy-weathering, sandy-----------

Dolomite ---------------------------------------- Limestone, light-gray, massive---------------------

Limestone, gray, moderately well bedded to shaly, 

sand to locally conglomeratiC--------------------

Dolomite, dark .... brown-weathering, shelf-making ____ _ 

Limestone, medium-gray, massive to thick-bedded; 

few sandy laminae ; contains abundant smooth 

coiled and straight gastropods and fragments of 

brachiopods ------------------------~--------

Limestone and dolomite, shelf-making, interbedded--

Limestone, gray, slightly ribbed, cliff-forming, massive to faintly bedded---------------------------

Limestone and dolomite, interbedded _____________ _ 

Limestone, gray, cliff-making, medium-grained; few 

sandy laminae --------------------------------- Limestone, medium-light-gray; many sandy laminae_ 

Covered ----------------------------------------- Largely covered, except for small outcrops of gray 

limestone with sandy layers---------------------

Total--------------------------------------

Possible thrust fault. 

14 

62 

12 

16 

47 

21 

19 

24 

9 

34 

12 

71 

25 

43 

541 

Greenstone of the Valmy formation _____________ not measured 
ROCKS OF PENNSYLVANIAN AND EARLY PERMIAN AGE 33 

Measured section on long ridge, in approa:. SE1f4 sec. 15 and NE 

14 sec. 22, T. 39 N., R. 42 E., approa:irnately 2 to 3 miles northeast from mill stack at the Getchell mine. 

Pace-and-compass traverse: Feet 

Limestone, dark-gray, thick-bedded, coarse-grained, 

sandy ; some thin lenticular chert beds____________ 110 

Covered : Dolomite and limestone ; brown-weathering, shaly _________ :________________________________ 35 

Largely covered: Pale-red-weathering shaly limestone and brown-weathering dolomitic limestone. 

Some g_ray cherty limestone______________________ 215 

Covered: Float of reddish and brownish shale_______ 162 

Covered : Pale red-weathering shaly limestone; some 

brown dolomitic shale___________________________ 100 

Limestone, pale-red-weathering, shaly, few thin medium-gray beds----------------------------------- 32 

Tape-and-compass traverse: 

Covered: Pale-red-weathering shaly limestone and 

thin medium-gray limestone beds----------------- 52 

Limestone, tan, thick-bedded_______________________ 154 

Covered: Brown sandy dolomite___________________ 30 

Limestone, medium-gray, thick-bedded to massive___ 73 

Limestone, gray, thick-bedded, somewhat sandy_____ 67 

Limestone, yellow- to brown-weathering, sandy; some 

interbedded gray limestone______________________ 67 

Covered: Same as above__________________________ 65 

Limestone, gray, cliff-forming, massive; some sandy 

laminae --------------------------------------- 12 

Covered: Platy limestone :float_____________________ 37 

Quartzite conglomerate____________________________ 4 

Limestone, gray, massive; some sandy laminae and 

1-ft chert beds__________________________________ 3 

Limestone, gray, sandy--------------------------- 55 

Limestone, cliff-forming, massive___________________ 60 

Covered: Limestone?------------------------------ 173 

Limestone, medium-gray, massive__________________ 14 

Covered: Limestone?------------------------------ 28 

Limestone, gray; sandy laminae____________________ 62 

Subtotal ---------------------------------------

Break in section; separation or possibly duplication 

betwe~n sections. 

Limestone, medium-gray, massive, sandy; thin sandy 

1,610 

laminae________________________________________ 26 

Limestone, light-gray, massive, slightly sandy______ 37 

Limestone, medium-gray, thick-bedded to massive; 

some thin dolomitic interbeds__________________ 76 

Covered : Brown fine-grained sandy dolomitic limestone------------------------------------------ 41 

Limestone, gray, massively bedded ; few thin interbeds of brown calcareous sandstone; 4-inch pebbly 

bed____________________________________________ 69 

Limestone and sandy limestone, gray, rather massive; 

sandy laminae and some chert___________________ 114 

Covered: Limestone?______________________________ 62 

Subtotal --------------------------------------- 425 

Total ----------------------------------------- 2,035 

Possible thrust fault. 

Greenstone of the Valmy formation------------- not measured 

AGE AND CORRELATION 

Collections of fossils show that the Etchart limestone 

ranges in age from ·Middle Pennsylvanian (Des Moines 

or Atoke) to Late Pennsylvanian or Early Permian 

(Missouri and Virgil or W olfcamp). 

In general, most of the collections of Middle Pennsylvanian age come from limestones in Goughs Canyon, 

where conglomerate of the Battle formation is missing 

or occurs only locally in thin lenses; collections from 

limestones resting on the conglomerate were determined 

to be of Late Pennsylvanian or Early Permian age. 

Exceptions to these generalizations were found, however, and Late Pennsylvanian fossils have been collected 

from beds near the base of the section that cannot be 

distinguished from strata containing Middle Pennsylvanian forms. 

Furthermore, much of the fossil material is abraded 

fragments which, with the lithology, indicate that they 

were introduced into the sediments as clastic particles 

and therefore are not necessarily of the same age as 

the enclosing rock. 

Several collections from the Etchart limestone in 

Goughs Canyon have yielded forms that were identified as Middle Pennsylvanian in age. Helen Duncan, 

James Steele Williams, and Mackenzie Gordon, Jr., of 

the Geological Survey made the fossil determinations. 

Miss Duncan reported on the bryozoans and corals, and 

Mr. Gordon and Mr. Williams studied the brachiopods. 

The following notes are taken from their reports on 

collections from the Etchart limestone in Goughs 

Canyon: 

USGS Oollection No. 19800--PC (field No. H-9-52). Goughs 

Canyon, hill near center NEY4 sec. 27, T. 38 N., R. 41 E. 

Medium dark-gray limestone containing bryozoan, coral, and 

a few brachipod remains. 

Miss Duncan reported the following forms (written communication, 1953) : 

Horn coral fragment, indet. 

Rhombotrypella sp. 

Fenestella sp. 

Polypora, 2 spp. 

Archimedes sp. indet. (1 fragment) 

Oy.<Jtodictya sp. 

Rhabdomeson sp. 

"Ascopora" sp. 

Of the bryozoans, she said (written communication, 

1953) : 

Oystodictya is extremely abundant at this locality, and Fenestella and Polypora are abundant in some beds. Very few examples of Rhombotrypella were found. The species of Oystodictya is considerably smaller than the one found in the 

Mississippian at the Goughs Canyon locality (USGS loc. 14206--

PC), and the Rhabdomeson in these lots is distinctly different 

from the species found in the Goughs Canyon formation or the 

one found in the Antler Peak limestone. The bryozoan called 
GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

"Ascopora" is also different from the Ascopora found in collections from the Antler Peak and from beds that I think are 

probably Antler Peak equivalents. The makeup of this bryozoan 

faunule is obviously quite different from that found in the 

Antler Peak limestone at its type locality or at Edna Mountain. 

I consider the fragment of Archimedes to be rather significant. 

In this country, the genus is confined to the Morrowan and older 

rocks in the central interior region, but it occurs in Middle 

Pennsylvanian rocks in north-central Utah (Oquirrh formation). 

In Russia it occurs in the Middle and Upper Carboniferous 

( Cn and Cm) and Permian but apparently not in older rocks. 

Of course, one cannot absolutely depend on the genus being restricted to the Middle Pennsylvanian of this region, but present 

knowledge of its occurrence suggests that these beds are likely 

to be of Middle Pennsylvanian age. 

Miss Duncan further stated (written communication, 

1961) : 

All described North American species correctly assigned to 

Oystodictya came from rocks that are older than Late Pennsylvanian ; and in 1953, it was generally assumed that the genus 

did not range above the Middle Pennsylvanian. More recent 

work on bryozoan faunules obtained farther south in Nevada 

has revealed that Oystodictya occurs in association with Early 

Permian fusulines. Inasmuch as we now have good evidence 

that the genus has a longer range than was previously thought, 

the occurrences of Oystodictya-like forms is faunal assemblages 

of Late Pennsylvanian and Early Permian age is not so anomalous. The Etchart limestone bryozoan faunule from USGS 

locality 1980!)...-PC seems to be older than the Late Pennsylvanian faunule known from the lower part of the Antler Peak 

limestone; how-ever, one cannot be certain on objective evidence 

that it is not Late Pennsylvanian. 

Mr. Williams (written communication, 1953) said: 

The collection contains a fragment of a brachiopod that might 

be a piece of M eekella ?, another fragment that is probably a 

Hustedi a? sp. indet., but that does not show the punctate structure, typical of the genus, an indeterminate Chonetes?, remains 

of a spiriferinoid · brachiopod and a fragment of a very large 

coarse-ribbed Dictyoclostus? sp. indet. The age is Carboniferous 

or Permian and the general assemblage looks to me to be of Late 

Pennsylvanian or Early Permian age, but I cannot be sure of 

which, if in fact either. The Hustedia does not seem to be the 

same species, H . pkosphoriensis Branson, that I found in the 

Edna Mountain. Whether it is another species of the same age 

or one of the species of Hustedia that occur in both the Upper 

or Middle PennsylV'anian or in older rocks, I cannot tell from 

the specimen. The large Dictyoclostus is of a general type 

that I would expect more to find in Upper Pennsylvanian or 

Lower Permian ; but it is represented by only a fragment and 

cannot be specifically identified, and a few instanc-es of the 

occurrence of somewhat similar forms in middle Pennsylvanian 

rocks are known. I would be inclined to defer to Miss Duncan's 

analysis of the significance of the Bryozoa as she seems to have 

more diagnostic material than I httve. 

Collection No. USGS 19815-PC (field No. 52-W-22). Southeast 

corner SW14NE1,4 sec. 27, T. 38 N., R. 41 E. Gray limestones 

containing brachiopod fragments. 

Oaninoid corals (fragments of a small species) . 

Stenoporoid bryozoan, sp. indet. 

Fenestellid bryozoans, genus and sp. indet. 

"Ascopora" sp. cf. species in collection No. 19809-PC. 

Other rhomboporoid bryozoans, indet. 

Oyatodictya? sp. indet. 

Helen Duncan (written communication, 1953) said : 

I am fairly certain that the bryozoan I am calling 'Ascopora' 

in this collection is the same species that occurs at USGS locality 19809-PC, where I think the rocks are of Middle Pennsylvanian age. This species is very small but quite distinctive, and 

it certainly is entirely different from the Ascopora I have identified in the Antler Peak. The fenestellids and the probable 

Oystodictya also are more suggestive of the fauna that is presumably of middle Pennsylvanian age than they are of the Antler Peak limestone fauna as now known. 

Collection No. USGS 19812-PC (field No. 52-W-27) SE corner 

W%SW34 sec.~. T. 38 N., R. 41 E. 

Fenestella sp. 

PoT!ypora, 2 sp. 

Oystodictya sp. 

Rhabdomescm sp. 

RhfYmboporaids, genera indet. 

Of this collection, Miss Duncan (written communication, 1953) said: 

This bryozoan assemblage contain~ species that appear to be 

identical with the species that are found in some other collections that are believed to be of Middle Pennsylvanian age. They 

are certainly very much like the bryozoans that were found at 

USGS locality 19809-PC. 

The strata that contain fossils suggestive of Middle 

Pennsylvanian age probably are equivalent to the 

Highway limestone which Ferguson (Ferguson, Muller, 

and Roberts, 1951) described in the Edna Mountains, 

northwest Golconda quadrangle. The Highway limestone contains fossils of Middle Pennsylvanian age, and 

Ferguson regards it as the offshore facies of the upper 

part of the Battle formation. 

Other beds, indistinguishable lithologically from 

strata containing Middle Pennsylvanian fossils, have 

yielded fossils that have been determined as Late Pennsylvanian, partly equivalent in age to the Antler Peak 

limestone. 

Collections of fusulinids from· two localities in the 

southern part of the range, where limestone either rests 

on Battle type conglomerate or is interbedded with it, 

were determined as Late Pennsylvanian by L. G. Henbest and R. C. Douglass (written communications 1952, 

1953, 1961) : 

Collection No. f-9471. North side of hill, east part, SW% sec. 

8, T. 37 N., R. 41 E. Rests on Battle type conglomerate. 

Olimacammina? sp. 

Endothyra or Endothyranella sp. 

Bradyina sp. (small, thin-shelled form) 

Ozawainella?? sp. 

W aeringella?? sp. 

Triticites sp. 

The preservation is very poor. The determination of the 

specimens of W aeringella·?? is extremely uncertain. The species 

identified as Triticites is determinable with fair assurance as 

to genus ; but the wall structure is poorly preserved, and it is 

barely possible but seemingly unlikely that it may actually represent a species of Fusulinella of Atoka (lower middle Pennsylvanian) age. 
ROCKS OF PENNSYLVANIAN AND EARLY PERMITAN AGE 35 

The species of Triticites is probably not older than the middle 

part of the Missourian and not younger than the earliest third 

of the Virgil. Early Virgil or late Missourian seems most likely. 

Permian age seems to be definitely ruled out. 

Collection No. f-9514a. From ridge a little east of center SE14 

sec. 4, T. 37 N., R. 41 E. Interbedded with conglomerate. 

The microfauna includes: 

Olimacammina sp. 

Bradyina sp. 

Tetrataa:is sp. 

Triticites sp. 

Mr. Douglass (written communication, 1961) believes 

that this collection is of Late Pennsylvanian age 

(Missouri) . 

Another fusulinid locality is a small remnant of limestone and conglomerate east of the Osgood range near 

the south border of the quadrangle. Henbest reported 

(written communication, 1955) : 

Collection No. f-12070a. Nevada, Osgood quadrangle; SW14 

NW14 sec. 8, T. 36 N., R. 41 E. ; approximately 600 feet southeast of powerline road. 

Endothyra sp. 

Bradyina sp. 

Globivalvulina? sp. 

M ille,rella-like foraminifer 

Schubertella or juvenarium of microspheric 

generation of Triticites ( ?) sp. 

Ozawainella sp. 

Triticites cf. T. secalicus (Say) 

Triticites aff. T. ventricosus (Meek and Hayden) 

According to Mr. Douglass (written communication, 

1961) this collection is also Late Pennsylvanian but 

younger than collection f-9514a, and represents Virgil 

equivalents. Neither f-951,4a nor f-12070a suggests 

Permian age. 

Two types of corals are also abundant at this locality 

(USGS 15778-PC)-a large caninoid and a syringoporoid. According to Miss Duncan (written communication, 1956) : 

The caninoids were broken up, decorticated, and eroded before deposition. They cannot be accurately identified but resemble generally the caninoids that occur in the Antler Peak 

limestone on Antler Peak and at other localities. Most of the 

horn corals collected are examples of these poorly preserved 

caninoids, but I found one specimen that I think probably belongs to the genus Gshelia. I do not recall having identified 

this genus in other collections from North America. The genotype came from late Upper Carboniferous (Cur) beds in Russia 

that are probably the temporal equivalent of rocks classed as 

Early Permian (Wolfcamp) in the United States. 

The syringoporoid corals are crudely silicified and their internal structures mostly destroyed. A few random tubes exhibit 

structures that indicate relationship with Syringopora, but the 

species in hand is certainly not Syringopora multattenuata McChesney, the species that has been found in the Antler Peak 

limestone at several places. At present this particular form of 

syringoporoid furnishes no good evidence on age of the beds. 

By themselves, none of the corals in this lot provide good objective evidence for dating the collection. However, comparable 

species have not been found in any collections that we know are 

Battle or Middle Pennsylvanian in the region, and the large 

caninoids do occur in the Antler Peak at several localities in 

association with the forms of fusulinids that were identified by 

Henbest in this collection. Therefore, the caninoids might be 

used as presumptive evidence that the rocks are Antler Peak 

equivalents. 

In Goughs Canyon a limestone bed a few feet above 

sandy limestone that rests on Osgood Mountain quartzite, and which is like beds from which Middle Pennsylvanian fossils were obtained, contains Late Pennsylvanian fossils : 

Collection No. USGS 19810-PC (field No. 52-W-20). Center, 

sec. 28, T. 38 N., R. 41 E. 

Bryoooans: 

Fistuliporoid sp. indet. 

Fenestella sp. indet. 

Polypora? sp. 

Penniretepora? sp. 

Oystodictya? sp. 

Brachiopods: 

WeZZerella? ct. W. osagensis (Swallow) 

Ambocoelia? sup. indet. 

Oleiothyridin-a? sp. indet. 

Chonetid brachiopod, gen and sp. indet. 

Hustedia, prob. 2 species, one which is close to H. 

phosphoriensis Branson. 

Miss Duncan (written communication, 1953) at first 

believed that the bryozoans were probably of Middle 

Pennsylvanian age, but on restudy of the collection said 

that she had seen the same sorts of bryozoans in collections (from elsewhere) known from other fossil evidence to be of Antler Peak age. Mr. Williams said 

(written communication, 1953) that although data 

from the brachiopods were insufficient to make a positive age reference, what data there are faintly suggest 

the possibility of Late Pennsylvanian or of Early Permian age. 

A collection of bryozoans from limestone above Battle type conglomerate was identified as probably of Antler Peak age by Miss Duncan (written communication, 

1953). 

Collection No. USGS 15777-PC (field No. 52-W-25). Just 

nol'lth of the saddle north of center, sec. 26, 26, T. 38 N., R. 41 E. 

The rock is dolomitic and the bryozoans are crudly silicified. 

One form is a rhomboporoid that suggests Rhabdomeson. Another specimen is a fenestrate type with a coarse network; the 

size of the branches suggest Polypora, but finer structures are 

destroyed and its generic identity cannot be proved. A third 

type is represented by cross sections that are comparable to 

those of the H ea:agonella I found in the Antler Peak limestone 

(Roberts' N unit). 

This meager and poorly preserved bryozoan assemblage is more 

like that found in the Antler Peak than like the fauna that occurs in the older rocks. 
/ 

36 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

Westward a few thousand feet, the thick conglomerate 

beneath limestone from which this collection came 

pinches out, so that along the strike, this limestone 

would lie with no distinguishable hiatus above limestone beds which rest on the Osgood Mountain quartzite 

and from which fossils identified as Middle Pennsylvanian have been collected. 

The limestone unit in the northeast corner of the 

quadrangle is continuous to the east with a thick section 

from which fossils definitely identified as Late Pennsylvanian to Early Permian have been collected. Here no 

Battle type conglomerate underlies the section and no 

Middle Pennsylvanian limestones have beenrecognized. 

The strata have been dated as equivalent in age to the 

Antler Peak limestone. 

Miss Duncan (written communication, 1956) reported 

on the bryoza: 

Collection No. USGS 15777-PO (field No. FH-22-54). From 

approximately 2.6 miles N. 37° E. from stack at Getchell mill; 

in NE14 sec. 18, T. 39 N., R. 42 E. Limestone, approximately 

550 ft. above base. 

This collection contained a large representation of very 

poorly preserved bryozoans. The following genera have been 

identified : 

H ea>agcmeUa ·sp. 

Rhomb·oporeZla sp. 

Rka1Jd()1'}1,eson sp. (abundant) 

Other indeterminate rhomboporoid bryozoans 

FenesteZla sp. 

Polypora sp. 

Septopora sp. 

Penniretepora sp. 

In general aspect this bryozoan assemblage suggests Late 

Pennsylvanian or Early Permian in this region. Coarse-meshed 

fenestrate genera, such as occur in this collection, appear to be 

especially characteristic of this faunal zone. The presence of 

HeaJagonella also is interpreted to indicate post-Des Moines age. 

Even without the supporting evidence provided by the brachiopods, reported on by Mackenzie Gordon on De'cember 15, 1955, I 

should have felt it was relatively safe to determine the collection as Antler Peak equivalent. 

Mr. Gordon reported (written communication, 19.55) 

the following forms : 

Spirijer ( Ohoristites?) sp. 

Neospirijer cf. N. teaJanus (Meek) 

The Spirifer resembles the species which is abundant in the 

lower part of the type Antler Peak section. The Neospirifer 

has been compared with Texas specimens of N. teaJanus from the 

Graham formation (Virgilian), Texas and looks close enough to 

be conspecific. 

A collection of mollusks from a nearby section, approximately 250 feet above the lower contact, was reported by E. L. Y ochelson and R. L. Batten (written 

communication, 1954) : 

Collection No. USGS 15381-PC (field No. FH-20-54. 1.7 miles 

N.66° E. of stack at Getchell Mill; SE14 sec. 27, T. 39 N., 

R.42E. 

The collection appears to be of Permian age, but the possibility of Permian? age cannot be ruled out. The following fossils 

have been identified: 

Plagioglypta canna (White) 

?Schizodus species indet. 

Bellerophontid species 

Glabrocingttlum new species 

Paleozoic scaphopods are poorly known, but Plagioglypta 

cawna is relatively common. To date it has been reported only 

in rocks of Permian age. There are no reports of the species 

in beds classified as ?Permian by the Survey, but the scaphopods 

of these have not been studied. 

The gastropod Glabrocinglum is relatively high spired and 

lacks reticulate ornamentation. These characters are suggestive of Permian rather than Pennsylvanian on the basis of our 

present knowledge of the genus and the specimens available for 

study. 

ADAM PEAK FORMATION 

A predominantly clastic sequence including shale and 

siltstone, dolomitic sandstone, chert, and limestone that 

overlies a coarse conglomerate along the west side of the 

Osgood Mountains has been separately mapped and 

named the Adam Peak formation for Adam Peak, the 

highest peak in the range. Fossil evidence indicates 

that the rocks are Late Pennsylvanian to Early 

Permian in age, though a younger age for the upper 

part of the unit is not definitely ruled out. 

DISTRIBUTION 

The Adam Peak formation occupies a belt approximately 2112 miles long on the high, western slope of the 

range west of Adam Peak, from the head of the East 

Fork of Eden Creek on the north to the ridge east of 

Goughs Canyon on the south (pl. 1). The formation 

also occurs as fault-bounded blocks along the crest of 

the range from Goughs Canyon to Perforate Canyon. 

The formation is on a thrust plate that overrides strata 

of the Etchart limestone at the south end of the northern belt and along the west side of ~he southern blocks. 

The northern belt is bounded on the west by a thrust 

plate of the Harmony formation. A belt of conglomerate mapped as Battle formation occurs with some interruptions along the east side of the belt. The conglomerate is in contact with the Preble formation along a steep 

reverse fault which in places cuts out the conglomerate 

and at the north end flattens into a thrust that carries 

the Preble above the Adam Peak formation. 

LITHOLOGY 

The Adam Peak formation is chiefly shale and siltstone, dolomitic clastic rocks, and chert but includes 

some limestone and dolomite. 

The shale and siltstone weather yellowish brown to 

olive gray and are light olive -gray to dark gray on 

freshly broken surfaces. Some of the shale is slightly 
ROCKS OF PENNSYLVANIAN AND EARLY PERMIAN AGE 37 

calcareous, much is slightly dolomitic, and some of the 

siltstone is dolomitic. The principal silt-size particles 

are quartz ; in addition, a few percent of chert fragments, less than_ 1 percent of fresh plagioclase, and a 

small number of grains of subrounded zircon and, less 

commonly, green tourmaline have been seen. Most of 

the matrix is too fine for positive identification, but it 

contains shreddy, colorless mica in abundance. Some 

specimens of the shale and siltstone have flat, twisted 

impressions on bedding planes that suggest worm 

trails. 

Distinctive sandstone and dolomitic sandstone make 

up more than 50 percent of the section wl).ere it is thick-

. est. Unweathered surfaces are medium dark gray, medium gray to olive gray, and light olive gray; the weathered rock is brown, generally pale yellowish brown. 

Grain size ranges from very fine to coarse, but in most 

exposures the rock is fine grained. On the whole, the 

size sorting is poor; but thin-section studies show that 

the sorting in some specimens is good. The fragments 

are angular to subangular and a few are subrounded. 

Grains of quartz and quartzite are most plentiful, with 

minor amounts of detrital chert and shale; a few small, 

subrounded to rounded grains of zircon and tourmaline 

are visible in all thinsections. The phosphate, collophane, is a characteristic constituent, and though present in most specimens examined, it does not amount to 

more than 2 to 3 percent, commonly less. It occurs as 

small, brown, weakly birefringent to isotropic pellets 

and irregularly shaped bodies in the matrix. Many 

specimens contain fine-grained apatite that seems to 

be inversely proportionate in amount to the amount of 

collophane, which suggests that it is reconstituted collophane. The clastic fragments are loosely packed but 

firmly bonded by the matrix, which is composed of 

microcrystalline silica and dolomite in various proportions, and a few percent of sericite. In some specimens, 

dolomite is the chief cement; in others, it forms scattered, individual rhombs. 

In the upper part of the section, chert is common. 

The chert is grayish black to brownish black and varies 

from massive to thin bedded; most commonly, it is massive to thick bedded. Some thin beds of dark-gray, 

brown-weathering dolomite, dark siliceous shale, and 

dolomitic sandstone are interbedded with the chert. 

Limestone occurs as thin beds and lenses that are 

commonly more or less sandy and may locally be pebbly. 

One thin bed in the lower part of the section is a darkgray bioclastic limestone composed predominantly of 

the broken remains of fusulinids and bryozoans. 

. Light-gray, commonly brown-weathering, fine-grained 

dolomite forms beds several tens of feet thick interbedded with dolomitic sandstone. 

STRATIGRAPHY AND THICKNESS 

The Adam Peak formation rests with apparent conformity on coarse-grained conglomerate of the Battle 

formation on the crest and west side of the Osgood 

Mountains. West of Adam Peak, where the section is 

most complete, the formation is divisible into three 

members: a lower member of interbedded shale, limestone, and dolomitic sandstone; a middle member of 

chert, dolomite, and interbedded shale and chert; and 

an upper member of dolomite and dolomitic sandstone. 

The beds dip steeply west and are locally overturned 

to the west, and although there is probably some unrecognized tight folding, the beds are generally younger 

to the west. 

The lower member is approximately 850 feet thick. 

Its lower part is predominantly shale and siltstone but 

includes thin interbeds and lenses of limestone; these 

rocks give way upward to predominantly dolomitic 

sandstone and shale. The middle member, about 950 

feet thick, is composed of about 700 feet of interbedded 

shale and thin-bedded chert, but dark, thick-bedded to 

massive chert prevails in the top 200 feet or so of the 

member. The upper member consists of fine-grained 

dolomite and dolomitic sandstone having an exposed 

thickness of about 300 feet; however, its true thickness 

is unknown because of cutting out by the overriding 

Harmony formation. Thus, the exposed section is on 

the order of 2,100 feet thick. 

AGE AND CORRELATION 

Fossils indicate that the Adam Peak formation is 

Late Pennsylvanian to Early Permian in age and is 

contemporaneous in part with the Etchart limestone in 

the Osgood Mountains and the Antler Peak limestone 

of the Battle Mountain region. 

A bed of bioclastic limestone approximately 250 feet 

above the base of the section west of Adam Peak contains fragments of fusulinids and bryozoans that have 

been identified as Late Pennsylvanian or Early Permian. Mr. Henbest reported (written communication, 

1953) on the fusulinids as follows: 

Collection F-9708 Nevada. Osgood Mountains quadrangle. 

On knob in center SW:J4SW% sec. 13, T. 38 N., R. 41 E. (field 

No. 52-W-48). 

Triticites sp. 

Schwagerina sp. (early form) 

Schwagerina sp. 

The fusulinid fauna in this clastic limestone is represented 

by numerous more or less fragmentary specimens and by a 

smaller number of entire specimens. The fauna is more nearly 

like that of the lower or middle part of the Wolfcamp than that 

in any later part of the West Texas section. It definitely represents a younger faunal stage than that of the Virgil (Pennsylvanian) but older than that in the upper (:Mill Canyon) and 

lower (Jory) quartzite members of the Havallah formation, 
38 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

Antler Peak area, recently reported to Roberts (that is, late 

Hueco or Leonard). 

Whether it correlates with the Antler Peak formation or not 

is very uncertain. One nearly entire specimen of Triticites in 

this collection resembles the small ventricose species of Triticites 

that characterizes the Antler Peak collections f9653 and . f9661, 

evidence of doubtful value for close correlation. 

Of the bryozoans, Miss Duncan said (written communication, 1953) : 

The bryozoan genera I am able to recognize in collection No. 

USGS 19814-PC (field No. 52-W-48) include the following: 

M eekoporella sp. 

H eaJag()'fl;ella? sp. 

Other nstuliporoids, genera undet. 

Stenodisous sp. (laminar form) 

Rhombotrypella sp. 

Stenoporoid bryozoan (incrusting ( ?) form) 

Fenestella sp. 

Rhombopora sp. 

Ascopora sp. 

This assemblage is characteristically found in rocks of Pennsylvanian and Hueco age. It certainly suggests some part of 

the Antler Peak to me. I have not seen any bryozoans from 

rocks we are sure are Edna Mountain formation and very much 

doubt that, if they do occur, they would be sufficiently well preserved to identify. The assemblage listed above does not look 

like any Phosphoria (with which the Edna Mountain is correlated) bryozoan faunule I have seen, and it does not resemble 

that of the Kaibab. Neither does the faunule correspond to the 

one that I think is possibly of Middle Pennsylvanian age in this 

part of Nevada. 

A collection of brachiopods and bryozoans was obtained from dolomitic sandstone in the upper part of the 

lower division of the Adam Peak formation. 

USGS locality 19816-PC (field No. H-44-52). SW*SW* sec. 

13, T. 38 N., R. 41 E., on ridge, brachiopods, Bryozoa, Oonularia ?, from brown weathering gray dolomitic sandstone. 

Mr. Williams wrote (written communication, 1953) 

concerning the brachiopods: 

This collection contains several large specimens of one or 

more species of a large productid, possibly belonging to the 

genus Juresania or to a closely related genus. It also contains 

indeterminate remains of one or two species of an undetermined 

type of productid, a fragment of a productid that is probably a 

linoproductid, and incomplete remains of a rhynchonellid or a 

terebratuloid brachiopod and of a large chonetid brachipod. 

Other brachiopods are represented by specimens that cannot be 

classified even as to type. Some crinoid columnals are in the 

collection. No conularias were seen. If present they may have 

been inadvertently destroyed by preparing. The conularias are, 

in general, not of very much use stratigraphically. 

Except for the specimens tentatively referred to Juresania, 

the shells have been so altered by replacement or broken or 

"skinned" .in freeing them from the matrix that even those retaining a fairly large portion of the shells do not have · enough 

of the ornamentation preserved to provide a basis for identification. The juresanias in this collection are very similar to ones 

I . have seen in the Antler Peak formation (and the accompanying fragmentary specimens do not dispute an Antler Peak age 

for the collection), but closely related species of Juresania occur 

in both younger and older rocks. The collection could be Antler 

Peak, but it could also belong to a younger or older part of the 

late Paleozoic section. 

The bryozoans from this collection were also in conelusive, according to Miss Duncan (written commu~ication, 1953) : 

This lot contains a few indicatioDB of twiglike bryozoans. 

The specimens are crudely silicified and not identifiable. In 

form they suggest some type of rhomboporoid. Bryozo·ans of 

this general group are common in the Antler Peak but unknown 

in the type Edna Mountain. Bryozoan evidence on the age of 

the rocks at this locality is entirely inconclusive, for rhomboporoids have a considerable range in the Paleozoic. 

The dolomitic sandstones and shales of the Adam 

Peak formation resemble the Edna Mountain formation 

of Permian age, which rests with an erosional unconformity on the Antler Peak limestone in the northern part of the Golconda quadrangle (Ferguson, Roberts, and Muller, 1952). The fossil evidence, however, 

precludes correlating the Adam Peak with the Edna 

Mountain formation. The Adam Peak is regarded as 

equivalent in age to part of the Etchart and .Antler 

Peak limestones and possibly represents a locally developed facies. 

CONDITIONS OF DEPOSITION OF THE ETCHART LDIESTONE AND 

ADAM PEAK FORMATION 

The variability of the Etchart limestone, its abundant 

content of clastic material, and its relations to the Battle 

formation are indicative of deposition in a shallowwater marine environment. The lower beds probably 

are the offshore marine equivalent of part of the Battle 

formation, but higher beds overlap the westward-thinning conglomerates of the Battle and represent the landward encroachment of the sea. A marine environment 

is also indicated for the Adam Peak formation, but in 

contrast to that of the Etchart limestone its basin of 

deposition received more sand and silt. The wide variation of these sedimentary rocks of Pennsy 1 vanian and 

Early Permian ·age indicate that they were laid down 

in environments that also differed widely from place to 

place, as might be expected in an archipelago. 

ROCKS OF PENNSYLVANIAN(P) TO PERMIAN(P) AGE 

FARREL CANYON FORMATION 

A sequence of sandstone, shale, chert, metavolcanic 

rocks, and small amounts of limestone in the northwestern part of the Osgood Mountains (pl. 1) is here named 

the Farrel Canyon formation. Farrel Canyon is on the 

northwest side of the Osgood Mountains, approximately 

1 mile south of Anderson Canyon, in the northeastern 
ROCKS OF PENNSYLVANIAN(?) TO PERMIAN(?) AGE 39 

part ofT. 38 N., R. 41 E., and the southeastern part of 

T. 3? N:, R. 41 E. The formation is not well exposed, 

and Its lithology and stratigraphic succession are poorly 

known. 

DIISTRIB'O'TION 

The Farrel Canyon formation extends along the west 

side of the Osgood Mountains from the ridge south of 

Cave Canyon to the north end of the range. It continues around the north end of the range, about 2 miles 

north of the quadrangle boundary, and continues for at 

least 3 miles in an east-northeasterly direction from the 

northeast corner of the Osgood Mountains quadrangle. 

Rocks of somewhat similar lithology are also known at 

the north end of the Hot Springs Range in the Hot 

Springs Peak quadrangle. In the Osgood Mountains 

the formation is ·bounded on the west and north by 

alluvium and Tertiary volcanic rocks. Thrust faults 

and high-angle reverse faults limit it on the east and 

south. 

LITHOLOGY 

The Farrel Canyon formation is an interbedded sequence of sandstone, chert, shale, siltstone, and some 

volcanic flow rocks and pyroclastics. Individual units 

are lenticular and variable. 

One of the most distinctive features of the formation 

is the sandstone, which may constitute 25 percent of the 

formation. It commonly is thick bedded and alternates with beds of shale and lenses of chert. Most of it 

is fine grained, some is medium grained, and some beds 

are pebbly in places. The sandstone is firmly lithified, 

tough, and hard to break with a hammer. Fresh specimens are medium gray to light brown, but weathered 

surfaces are pale yellowish brown to moderate brown 

and olive gray. Detrital grains chiefly of quartz and 

scattered fragments of gray to brown chert give the 

rock its characteristic appearance in hand specimens. 

Poorly sorted angular to subangular mineral and rock 

fragments are set in a matrix of mica, chlorite, clay, 

and silt-size quartz and feldspar, which ranges from 

30 percent to 55 percent of the rock. The coarser 

grains ~re chiefly quartz, some chert, a few grains of 

fresh feldspar, and, uncommonly, a few pieces of shale. 

Most of the quartz grains are single individuals, commonly strained, though a few are combined grains, 

possibly quartzite; the feldspar includes plagioclase 

and untwinned K-feldspar. Reaction between the 

grains and the matrix has corroded the grain boundaries. "Heavy" minerals amount to a small fraction 

of a percent and are mostly well rounded zircon-some 

clear, some of the pinkish "hyacinth" vnriety-and 

grains of magnetite and tourmaline. The matrix is 

composed of shreds of colorless mica (sericite), a pale 

greenish-brown to yellowish clay mineral (possibly 

nontronite or hydrobiotite), and very pale chlorite, plus 

silt-size quartz and feldspar. Some specimens contain 

a little carbonate, presumably calcite, in the matrix. 

Brown iron oxide stains the rock along minute fractures and along grain boundaries. The pebble conglomerate has a similar composition; however, most of 

the pebbles are chert and some quartzite, in a sandy 

matrix. The sandstone is classified as a lithic graywacke (Pettijohn, 1954, p. 363-364) or quartz graywacke (Gilbert, in Williams, Turner, and Gilbert, 1954, 

p. 292, 294) . 

Shale and siltstone are interbedded with the sandstone and chert in units that are seldom more than a 

few tens of feet thick. Most of these fine-grained 

clastic rocks are silty shale and siltstone that weather 

olive gray and are dark greenish gray, light brownish 

gray, and dark gray on fresh surfaces. Most specimens 

have a hackly fracture rather than a well-developed 

shaly parting. 

Chert may amount to 50 percent of the formation. 

Thick lenses are interbedded with the sandstone; some 

sections are mostly chert with some interbedded dark 

shale, and commonly chert is associated with altered 

volcanic flow rocks. In many exposures the chert is 

well bedded to thin bedded, individual strata ranging 

from 1 inch to 4 or 5 inches in thickness and having 

interbeds of sandy or silty shale 1 inch or less thick. 

In many exposures the chert is tightly and complexly 

folded. The generally thin-bedded nature of the chert 

distinguishes it from chert of the Goughs Canyon formation. It also has a lighter appearance than chert 

in most of the other formations, except the Valmy. 

Some of it is dark gray to black, but in many exposures 

it is a light brown, light brownish gray, light greenish 

gray, and greenish gray, and some is very light gray. 

Some of the chert was examined microscopically, and 

most specimens revealed nothing but cryptocrystalline 

silica with some faintly visible structure that suggested 

remnants of micro organisms, such as sponge spicules 

or spines of radiolaria, though one thin section showed 

an abundance of circular bodies that presumbly were 

radiolarians. A few specimens, however, contain material suggestive of volcanic origin, including angular 

to subangular quartz fragments, some fresh plagioclase 

and hazy, altered feldspar, plus many shreds of sericite 

and flakes of nontronite ( ~) in a matrix of cryptocrystalline silica. 

Altered volcanic rocks are interbedded with the chert 

at a few places. The units of volcanic rock seem to be 

no more than a few tens of feet thick, discontinuous, 

and probably lenticular. Volcanic rocks probably 
40 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

make up somewhat less than 25 percent of the formation. They are fine-grained to aphanitic nonporphyritic 

dark-gray, medium-gray, or greenish-gray rocks. 

Some are obviously fragmental evenin hand specimens; 

the clastic nature of others is only apparent :from thinsection study. 

Typical specimens of the flow rock have a microscopic intersertal texture and are composed of albitic 

plagioclase and interstitial chlorite and a brown clay 

mineral, possibly nontronite. Additional secondary 

minerals ·are sericite, leucoxene, and calcite. Presumably, these originally were flow rocks of intermediate 

composition, possibly andesites. The pyroclastic rocks 

were crystal-vitric tuffs and crystal tuffs. In some, 

relicts of original glass shards are visible, now devitrified ·and crystallized to an untwinned potassium feldspar (probably originally sanidine), in a cryptocrystalline groundmass of silica. Also embedded in 

the groundmass are crystal fragments of quartz plagioclase, untwinned mottled -appearing potassium feldspar 

that may have been sanidine originally, and minor 

amounts of sericite, some chlorite, and rare epidote. 

Other specimens contain crystal fragments and no relicts 

of shards. A few fragments of microcrystalline volcanic rock, quartzite, and chert were also .recognized. 

The mineral composition suggests that originally these 

pyroclastics. were of rhyolitic or dacitic composition. 

From the microscopic studies it is concluded that 

these ·volcanic rocks have been affected by low-grade 

retrogressive metamorphism, which may have been 

caused partly by deuteric alteration at the time of 

extrusion and deposition, and party by burial and involvement in subsequent diastrophism. 

In addition to the rocks that are obviously volcanic, 

some dark-gray, streaked, microcrystalline rocks that 

look like argillites in hand specimens probably are also 

of volcanic origin. They are fine grained and have a 

streaked or sheared appearance, and the individual components are difficult to resolve even with microscopic 

study. Mostly, they-'are composed of lenticular bodies 

of cryptocrystalline silica in a brownish mass of clay 

minerals, sericite, chlorite, and epidote, ·and may have 

been pyroclastic rocks that have been intensely sheared. 

~TRATIGRAPHY AND THICKNESS 

Neither the top nor the bottom of the Farrel Canyon 

formation is expo-Sed, and exposures are so poor that its 

structure and stratigraphy cannot be worked out. In 

the western belt, south of Anderson Canyon, there is 

a general succession from east to west of chert and interbedded metavolcanic rooks that grade westward and 

possibly upward - through interbedded chert, shale, 

and some sandstone-into a predominant-ly sandstone 

unit on the west. At the north end of the range, however, the formation seems to consist of interbedded 

chert, sandstone, and some shale, with no clearly recognizable succession of beds. The thickness of the forma.-

tion is unknow, but it seems likely that it is at least 

seveml thousand feet thick. Along the west side of 

the range the exposed thickness must be on the order 

of 3,000 to 4,000 feet, and perhaps twice this amount is 

represented by the exposures across the north end of 

the range. 

POSSIBLE AGE AND CORRELATION 

No fossils have been found in the Farrel Canyon formation, and its stratigraphic position relative to the 

other sedimentary rocks is unknown. Rocks of somewhat similar lithology exposed in the north end of the 

Hot Springs Range have yielded some rather poorly 

preserved fossils which range from Mississippian to 

Permian; however, experience has shown that longrange lithologic correlations in the western part of the 

Great Basin are hazardous. The formation contains 

rock assemblages that resemble parts of both the Pumpernickel ·and Havallah formations of the Sonoma Range 

(Ferguson, Roberts, and Muller, 1952) and Antler Peak 

quadrangle (Roberts, 1951). The Havallah formation 

ranges· in age from Middle Pennsylvanian (Atoka) to 

Permian. The Pumpernickel formation is Pennsylvanian(?) (R. J. Roberts oral communication). Without fossils and sound stratigraphic evidence, the age of 

the Farrel Canyon formation must remain unknown; 

however, it is tentatively assigned a Pennsylvanian(~) 

to Permian ( ~) age. 

INTRUSIVE BASALT OF UNCERTAIN AGE 

A small body of basaltic rock is exposed in the central 

part of sec. 20, T. 39 N., R. 42 E., in the northern part 

of the Osgood Mountains (pl. 1). Another body of 

similar size is also known beyond the quadrangle boundary in the southern part of sec. 18, T. 39 N., R. 42 E., 

in the Hot Springs Peak quadrangle. 

The fresh rock is dark gray to black, very fine grained 

to microcrystalline, and in places is slightly porphyritic 

and contains small plagioclase phenocrysts in an aphanitic groundmass. Locally, the rock has small amygdules 

as much as 3 mm in diameter. Plagioclase occurs in 

randomly oriented laths that average 0.2 mm in length, 

and in a few small (0.7-0.9 mm) phenocrysts. The 

plagioclase composition is uncertain, but its optical 

properties as determined from thin -section study suggest sodic oligoclase or albite-oligoclase. Fibrous palegreen actinolitic hornblende is interstitial to the plagioclase and also forms small squarish phenocrysts. Prob-
INTRUSIVE IGNEOUS ROCKS OF LATE CRETACEOUS AGE 41 

ably it is an alteration product of pyroxene. In addition, minute grains of magnetite are plentiful, and a 

little chlorite is present, mostly as partial replacements 

of the central parts of plagioclase phenocrysts. In 

some specimens the interstitial material is so fine grained 

that it cannot be clearly resolved with the microscope, 

but in one thin section it appeared to be a mixture of 

pale-brown biotite and minute rods of colorless actinolitic amphibole. Amygdules in some specimens are 

filled with quartz and rimmed with pale-brown biotite; 

in others, small amygdular bodies are filled with chlorite. Petrographically, the rock appears to be a basalt 

which has been subjected to low-grade metamorphism, 

with resultant change of the plagioclase to a sodic variety, and replacement of original pyroxene to actinolitic 

amphibole. Chemical analysis of a sample of the rock 

(table 7) also suggests that it was a basalt. This is 

indicated by the low silica content, absence of normative 

quartz, and negative qz value. The low CaO : N a20 

value, relatively high H 20, and moderate C02 reflect the 

low-grade metamorphism the rock has undergone. 

TABLE 7.-Analysis, norm, and Niggli values of intrusive basalt 

of uncertain age 

Northern Osgood Mountains; extreme SW~SE~ sec. 18, T. 39 N., R. 42 E., Hot 

Springs Peak quadrangle 

[Analyzed by methods similar to those described in U.S. Geol. Survey Bull. 1036-C; 

P. L. D. Elmore, K. E. White, S.D. Botts, P. W. Scott, analysts] 

Chemical analysis 

Si02--------

Ah0a_-------

Fe20a- _____ _ FeO _____ -- _ MgO _______ _ CaO _______ _ 

N a20 ______ _ 

K20- - __ - - - - TiO!!- ______ _ 

P20s-------- Mn0 _______ _ 

H20 ____ - _--

C02---------

50. 8 

14. 2 

2. 4 

11. 0 

5. 7 

5. 3 

4. 5 

. 06 

2. 1 

. 29 

. 18 

3. 0 

. 58 

Sum ______ 100 

Sp gr (lump)_ 2. 85 

(powder)___ 2. 91 

C.I.P.W. norm 

Q _______ _ 

Or ______ _ Ab _____ _ 

An _____ _ Wo _____ _ 

En _____ _ Fs ______ _ Mt _____ _ IL ______ _ 

Ap_--- -- Cc ______ _ 

H20- __ --

0. 5 

0. 3 

38.0 

18.4 

1.0 

14. 1 

14. 6 

3. 5 

4. 0 

0. 7 

1.3 

3. 0 

99.4 

Niggli values 

aL _ _ _ _ _ _ 21. 9 

fm_______ 51. 5 

c - - - - - - - - 15. 0 

alk _ _ _ _ _ _ 11. 6 

sL _ _ _ _ _ _ _ 133 

k________ . 986 

mg______ . 431 

c/fm_____ . 291 

cfalk_____ 1. 29 

qz _______ . -13 

Field relations indicate that the bodies of basalt are 

intrusive; they are essentially thick dikes that cut 

across the strike of the enclosing rocks. The body in this 

quadrangle intrudes the thrust plate of metamorphosed 

rocks of the Comus formation; the body in the adjacent 

quadrangle also intrudes these rocks and rocks of the 

Preble formation as well. The latter body apparently 

cuts the thrust fault between the Comus formation and 

the Preble formation; the body in section 20 of this 

quadrangle is terminated on the east by a high angle 

fault that is possibly of Tertiary age. The other body 

is cut by a dacite porphyry dike believed to be related 

to the Late Cretaceous episode of granitic intrusion. 

The available evidence suggests that these weakly metamorphosed basaltic bodies are hypabyssal intrusions of 

postthrusting pre-Late Cretaceous age and hence may 

be of Late Jurassic or Early Cretaceous age. 

INTRUSIVE IGNEOUS ROCKS OF LATE CRETACEOUS 

AGE 

GRANODIORITE AND RELATED ROC~S 

DISTRIBUTION 

The principal body of granodiorite is exposed on the 

eastern side of the Osgood Mountains in the northeastern part of the quadrangle (pl. 1). It extends from 

the ridge south of Granite Creek about to the Getchell 

mine; much of its eastern contact is near the range 

front, and its western contact is east of the crest of the 

range, except for a small area near the Burma Road 

where the contact extends several hundred yards west 

of the range crest. In general plan the body is a 

double stock consisting of two lobes joined by a narrow 

dikelike septum. The northern lobe, which is somewhat 

elongate, is about 3¥2 miles long and about 2 miles 

wide. The southern lobe has a nearly circular outline 

2 miles in diameter. The total exposed area of the 

stock is 7.7 square miles. A few dikelike apophyses 

extend from the stock for short distances, and north 

of the stock there are a few small isolated bodies that 

may be connected with the stock at depth. 

Some granodiorite is exposed east of the Getchell 

fault in the main gold pit (south pit) , in the school 

yard north of the mill, and granodiorite was encountered in excavations for the mill foundations. 

Three small bodies of granodiorite are exposed in 

the Hot Springs Range (pl. 1). The largest, which 

is in the little valley east of the Dutch Flat mine 

(NW% sec. 16, NElJ.t sec. 17, T. 38 N., R. 40 E.), has a 

nearly circular outline and is 0.35 mile in diameter. To 

the north, two smaller bodies are found west of the 

range crest in NWl!.t sec. 23 and SWl!.t sec. 26, T. 39 N., 

R. 40 E. All three bodies are considerably altered and 

the one east of the Dutch Flat mine has metamorphosed the adjacent rocks for a distance of 200 to 1,000 

feet from the contact. 

STRUCTURAL RELATIONS OF THE STOCK IN THE OSGOOD 

MOUNTAINS 

The Osgood Mountains granodiorite body has a 

well-developed joint pattern, which is illustrated by 

the point diagram, figure 3. Three major joint systems 
42 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

N 

. .. 

..... . , 

. . ·.• . ~----~------ .~ •• ~~~--------------~ E .. 

s 

. . . . :- .. . . 

. .. . 

FIGURE 3.-Point diagram of poles of 95 joints measured in granodiorite 

stock of the Osgood Mountains. Plotted on upper hemisphere. 

have been recognized : ( 1) one of the two most prominent systems strikes in a north to north-northeasterly 

direction and dips gently (average, 30°) west to northwest; (2) equally prominent is a northeast-striking 

system that dips steeply (average, 75°) southeast, nearly 

at right angles to the west-dipping joints; and (3) a 

less common system of west-northwest joints dips 

steeply north and south, or are vertical. 

No planar and linear structural elements can be seen 

in the granitic rocks. Even adjacent to contacts with 

the country rocks, no preferred orientation is apparent 

in the granodiorite. 

Both the eastern and western contacts of the stock 

dip eastward, but the eastern contact is less steeply 

inclined than the western, being parallel or nearly so 

to the dip 6f the sedimentary rocks, whereas the western contact is generally steeper than the bedding. The 

bedded rocks tend to wrap around the lobes of the 

stock and appear to have partly accommodated themselves to the boundaries of the granodiorite. In detail, 

however, the contact at many places sharply transects 

the bedding, and the north and south ends of the southern lobe and the south end of the northern lobe show 

markedly discordant relations. 

The contact relations can be best observed in tJhe mine 

workings and therefore more observations have been 

made along the eastern contact, where most of the tungsten deposits are located, than along the western boundary. Beginning at the north on the east side, at the 

Riley mine the general dip of the granodiorite contact is 

from 30° to 60° E., parallel to or slightly transecting the 

bedding in the limestone; the parallelism is not continuous, however, for the contact makes several sharp 

bends or jogs and cuts sharply across the bedding in 

some places (pl. 1) . Farther south at the Kirby mine, 

which is on the south end of the northern lobe of the 

stock, the contact is irregular and in general cuts across 

the north-trending structure of the sedimentary rocks . 

The contact mostly dips steeply east or is vertical; but 

at the main deposit in the western part of the mine area, 

the contact dips about 30° E. beneath eastward-dipping 

tightly folded limestone beds. At the Pacific mine on 

the north-striking eastern boundary of the southern 

lobe, the granodiorite-limestone contact, like the bedding, dips steeply east ( 60°), with the usual local 

parallelisms and discordant relations. At the Granite 

Creek mine on the south end of the southern lobe of the 

stock the contact trends generally east and west, with 

many ,local irregularities and stubby projections, and 

transects the sedimentary rocks; the contact dips southeast rather steeply in the mine workings. 

Direct observations cannot be made as easily on the 

west contact because of the ahsence of mine workings, 

except on the northwest side of the northern lobe. At 

the Richmond mine, the contact trends northeast across 

the general structure of the metamorphosed sedimentary 

rocks and is vertical. The contact at the Alpine mine 

in part cuts across the general sedimentary rock structure, but in the mine area it strikes parallel to the limestone and dips steeply eastward. Elsewhere on the 

western border the configuration of the contact and its 

relation to topography indicate that the contact dips 

steeply east. 

The stock in the Osgood Mountains is a downwardenlarging asymmetric eastward-dipping body (pl. 2, 

section B-B') as indicated from its contact relations. 

The steeply dipping, abruptly terminated southern contact and the absence of outlying bodies to the south 

suggest that the stock ends abruptly in this direction. 

The north end of the northern lobe extends out into 

the country rock in several dikelike apophyses, and 

north of the main mass some small plugs of granodiorite 

intrude the sedimentary rocks. In the low terrain 

north of Getchell the carbonate rocks of the Etchart 

limestone show widespread weak to moderate metamorphic effects. These data all suggest that the granodiorite has an underground extension to the north and may 

lie fairly close to the surface. The upward-converging 

contacts and the apparent gentle northward plunge of 

the crest of the stock suggest that the granodiorite body 
~RUSIVE IGNEOUS ROCKS OF LATE CRETACEOUS AGE 43 

is the upper part of a larger subjacent mass. The rough 

parallelism between the east and west boundaries and 

the enclosing sedimentary rocks is an indication that the 

shape of the visible part of the body was partly controlled by the structure of the sedimentary rocks. 

STRUCTURAL RELATIONS OF GRANDIORITE IN THE 

HOT SPRINGS RANGE 

The largest granodiorite body in the Hot Springs 

Range east of the Dutch Flat mine has outward-dipping 

steep contacts, judging from the shape at the surface 

and its relation to topography, and from data obtained 

by mapping mines and prospects. Except very locally, 

the contacts cut across the structure of the sedimentary 

rocks. Extensive hydrothermal alteration of the 

granodiorite, a metamorphic aureole from 200 to 800 

feet wide, and the many prospects and small mines 

within the body and around its periphery are an indica.-

tion that the body is a cupola or a pluglike mass that 

may be of offshoot from a larger body at depth. The 

smaller bodies of identical composition in the northern 

part of the range may also be offshots from the same 

body. 

AGE OF 'I'HE GRANODIORITE 

Relations to the country rocks indicate thJI,t the 

granodiorite is younger than Late Pennsylvanian or 

Early Permian and older than the Tertiary volcanic 

rocks. A lead-alpha age determination on zircon from 

the Osgood Mountains stock confirms this approximaw 

dating and gives an age of 69 million years, corresponding to Late Cretaceous time (Jaffe and others, 1959, 

p. 82) .a 

PETROGRAPHY 

The unaltered granodiorite has a rather uniform 

mineralogical composition. Some of the small pluglike 

bodies north of the stock in the Osgood Mountains 

differ slightly mineralogically, and in places along the 

contacts some different facies have been formed by reaction with wallrocks; but no important variations are 

found within the main bodies themselves. Except in 

a few places next to the contact, the granodiorite is 

free from inclusions. 

The granodiorite is predominantly an equigranular 

medium-grained light-gray to very light gray rock composed mostly of visible intergrown white feldspar and 

clear inconspicuous quartz, with a uniform sprinkling 

of dark minerals which closer examination shows to be 

mostly biotite, less abundant hornblende, and a few 

metallic grains of magnetite. An occasional grain of 

8 Specimen 54-W-48, granodiorite, north side of Julian Creek, north 

center sec. 17, T. 88 N, R. 42 E., Osgood Mountains quadrangle, Nevada. a per mllligram per hour, 378; lead (ppm), 10 and 1'1. 

690..159 0-63--4 

honey-colored sphene can be seen in most specimens. 

Much of the biotite is in little columnar books with a 

hexagonal cross section commonly as much as 3 mm in 

diameter. The hornblende is in stubby subhedral prisms 

which are generally less than 1 mm long. In places the 

granodiorite is slightly porphyritic, where euhedral to 

subhedral crystals of plagioclase a few millimeters long 

occur in a contrastingly finer grained groundmass. At a 

few places the granodiorite is stained yellowish orange 

by iron oxides, but rock in these areas is no different in 

mineralogy from unstained rock; the staining possibly 

is related to ·an old surface of deep weathering, from 

which iron-bearing surface waters percolated downward into the underlying rock. 

The microscope shows that the granodiorite is composed predominantly of plagioclase, orthoclase, and 

quartz, with biotite the most abundant mafic mineral 

and hornblende considerably less abundant but nevertheless consistently present. Magnetite, sphene, apatite, 

and, much more rarely, zircon are the remainder of the 

primary accessory minerals. Even the freshest rock 

contains a few secondary minerals, which include chlorite derived by alteration of biotite ·and, less commonly, 

hornblende, a little sericite and cloudy-looking clay minerals in some of the plagioclase, and a very few grains 

of epidote. Minute amounts of secondary sphene 

accompany some of the chloritized biotite. 

The plagioclase is subhedral to euhedral, but its crystal faces are corroded where it is enclosed by orthoclase 

and quartz. The crystals show pronounced oscillatory 

zoning except for the rims, which are progressively 

zoned; the boundaries between zones are somewhat corroded. Except for the more sodic rims, the plagioclase 

composition ranges from Ana1 to An4s, and the average 

is approximately An40 (andesine) ; the rims range from 

An2 5 to An1o (oligoclase). Orthoclase is completely anhedral and interstitial, for it, along with quartz, was 

one of the last minerals to crystallize; commonly it 

encloses small corroded plagioclase crystals. It is almost entirely free from perthitic inclusions. A little 

myrmekite occurs along some boundaries between orthoclase and plagioclase. 

Biotite, which is strongly pleochroic from reddish 

brown to golden yellow, commonly is partly altered to 

chlorite. Some of the mica plates poikilitically enclose 

small rounded grains of early-formed plagioclase. 

Many of the hornblende crystals are partly replaced by 

biotite and also show some alteration to chlorite. The 

hornblende is the common variety, pleochroic in yellowish green and greenish yellow. 

Magnetite occurs in anhedral grains which tend to be 

distributed in groups, though it is also in isolated grains. 
44 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

Apatite is in small euhedral crystals and tends to be 

more plentiful near magnetite. Sphene is in anhedral 

grains, though some typical diamond-shaped crystals 

are also seen. Zircon is extremely rare. 

Modal analyses of 10 specimens of the granodiorite 

are in table 8. The mineral composition agrees with 

Johannsen's (1939, v. 1, p. 141-161; table 38) classification of granodiorite (227P). The positions of the 

specimens in the granodiorite field are shown in 

figure 4. 

CHEMICAL CO:MPOSlTION 

The chemical compositions of four specimens of 

granodiorite are listed in table 9 with the computed 

norms and Niggli numbers. For comparison, N ockolds' 

(1954, p. 1014) average compositions of biotite granodiorite and granodiorite are included. 

Spectrographic analyses for minor elements in the 

same samples are listed in table 10. 

:MARGINAL FACIES 

A pyroxene-rich variant of this marginal facies occurs 

along the contact between gradiorite and marble, calcsilicate rock, or tactite. Both kinds may have been 

formed by endomorphic processes, but the evidence 

seems particularly good for the pyroxene-rich rock, 

which, therefore, will be described in a later section of 

the report on endomorphism of the granodiorite 

(p.681). 

ORTHOCLASE PLAGIOCLASE 

FIGURE 4.-Modal composition of granodiorite from the Osgood Moun·-

tains. Sketch shows specimen localities in stock. 

TABLE 8.-Modes of granodiorite from stock in the Osgood Mountains 

[In volume percent. Location of specimens shown on sketch map in fig. 4. Obtained from thin sections by the Chayes (1949) point-counter method and from stained slabs by the use of dot pattern (Jackson and Ross, 1956)] 

Specimen 

1 (A) t _________ _ 

2 (B) 1 _________ _ 

3 2 _____________ _ 

4 2 _____________ _ 

52 _____________ _ 

6 ______________ _ 

7 ______________ _ 

8 ______________ _ 

g ______________ _ 

10 2---'----------

Location 

Southeast side of Rocky Canyon, Osgood 

Mountains. NE~NW~ sec. 5, T. 38 N., R. 42 E. (75H53) _____________________ _ 

Point where Burma Road crosses crest of 

Osgood Mountains. Center NW~NE~ 

sec. 6, T. 38 N., R. 42 E. (53W81) __ _: __ _ 

Near center, sec. 5, T. 38 N., R. 42E. (H-5-

55)---------------------------------- N. part NE~ sec. 8, T. 39 N., R. 42 E. 

(H-2-55)-----------------------------

West of Ril~y mine, c. a. 50 ft. from contact SW~SW~ sec. 4, T. 38 N., R. 42 E. (H1-55)-------------------------------- South side of ridge between Granite and Osgood Creeks, Osgood Mountains. Northeast of center, sec. 19, T. 38 N., R. 42 E. 

(54W12)------------------------~---- North side Julian Creek. N. center sec. 17, T. 38 N., R. 42 E. (54W48) ___________ _ 

South side of ridge between Julian and Sum- mer Camp Creeks, Osgood Mountains. 

Near cente;r, SE~NE~ sec. 7, T. 38 N., R. 42 E. (54W16) ____________________ _ 

North side of ridge between Granite and Osgood Creeks, Osgood Mountains. Near NW~SE~NW~ sec. 19, T. 38 N., R. 42 E. (54Wl3) _____________________________ _ 

Granite Creek, N. Part NE~ sec. 30, T. 38 

N., R. 42 E. (H-34-55) _______________ _ 

Average ___ ----------------------------------------

t Letters refer to chem.iC:l.l analyses, table 9. 2 .From stained slabs. 

Potassium 

feldspar 

(orthoclase) 

Quartz Plagioclase Biotite Hornblende 

Accessories 

Nonopaque Opaque 

------------1------1-------1------

14 

16 . 

12 

18 

9 

7 

11 

12 

11 

12 

12 

26 

25 

27 

22 

16 

25 

24 

29 

23 

21 

24 

52 

49 

49 

49 

59 

56 

51 

48 

55 

54 

52 

6 

6 

13 

4 

15 

8 

12 

8 

7 

12 

9 

<O. 5 1 1 

1 2 1 

Tr _______________ _ 

7 -------- --------

<.5 

3 <.5 1 

5 1 .5 

1 1 . 5 

2 1 1 

1 -------- --------

1 1 1 
INTRUSIVE IGNEOUS ROCKS OF LATE CRETACEOUS AGE 45 

TABLE 9.-Analyses, norms, and Niggli values of granodiorite 

[Samples were analyzed by methods similar to those described in U.S. Geol. Survey Bull. 1036-C; P. L. D. Elmore, K. E. White, S.D. Botts, P. W. Scott, analysts, U.S. 

Geol. Survey] 

A B c D E F 

Chemical analyses 

SiOs. ----------------------- 67. 6 68.4 67.2 66.4 68.97 66.88 

AltOs----------------------- 16.8 16.8 16.0 16.6 15.47 15.66 

FesOs----------------------- 1. 3 1. 6 . 9 . 9 1.12 1. 33 

FeO------------------------ 1. 6 1. 4 1. 7 1. 4 2. 05 2. 59 

MnO. ---------------------- 0. 10 . 09 . 9 . 5 . 06 . 07 

MgO_ ---------------------- 1. 0 1. 2 . 92 . 94 1.15 1. 57 Cao________________________ 4. o 4. o 3. 3 3. o 2. 99 3. 56 

NasO. ---------------------- 3. 5 3. 5 3. 6 3. 9 3. 69 3. 84 

KsO •• ---------------------- 2. 8 2. 8 3. 2 3. 2 3. 16 3. 07 

Ti02------------------------ . 42 . 40 . 38 . 43 . 45 . 57 

P206------------------------ . 22 . 22 . 20 . 28 . 19 . 21 

HsO+---------------------- --------- --------- --------- 1. 3 . 70 . 65 

A B c 

C.I.P. W. nonns 

Q___________________________ 26.3 27.2 24.4 24.0 26.2 21.9 

Or__________________________ 16.7 16.7 18.9 18.9 18.9 18.3 

Ab-------------------------- 29.3 29.3 30.4 33.0 31.4 32. 5 An__________________________ 18.9 18.9 15. 6 13. 1 14.2 16.4 

En____________ ______________ 2. 5 3. 0 2. 3 2. 3 2. 9 3. 9 

Fs_______________ __________ _ 1. 4 . 66 3. 4 . 9 2. 2 2. 9 

n____________________ Kit·:======================== _______ t . ~6 76 ~: . 8 . 8 . 8 . 8 ~ 1: ~ t ~ 1: ~ ---i~9-- 1. 1 

AP-------------------------- . 34 . 3 . 3 . 67 . 4 . 5 Pr __________________________ --------- --------- --------- 2. 3 -------- -------- ---------------- Sum__________________ 99 100 98 99 99 99 

~~~~====================== ~~~~~~~~~ ~~~~~~~~~ ~~~~~~~~~ ----~::-- ======== ======== II---------....,...--~N_i...,...gg_li_va_l_ue_s.,...----,-----:----:---- aL.......................... 42.8 42 42. 7 45. 0 41. 1 32. 7 fm__________________________ 16. 6 17.9 16.3 16.3 19. 5 23.2 c____________________________ 18.4 18. 1 16.0 14. 4 14.3 15.8 

alk-------------------------- 22.2 22 25.0 25.9 25. 1 23.4 sL. __________________ ~------ 292 291 304 295 321 275 

k. -------------------------- . 349 . 349 . 370 . 351 . 37 . 348 

mg__________________________ . 391 . 428 . 384 . 377 . 40 . 391 

qz __________________________ 103 103 140 91 121 81 

Sum__________________ 100 101 99 100 100 100 

~£:~~~;~==~~~~~~~~~~~~ :::::~:: ::::~~:: ____ :~-- ---.~::-- ~=~~~~~~ ~~~~~:~~ (powder)__________________ 2. 69 2. 68 2. 68 2. 67 -------- --------

1 Includes gain due to oxidation of FeO. 

A. East side Osgood Mountains, SE side Rocky Canyon, NEUNWU sec. 5, T. 38 N., R. 42 E. (75H53). 

B. Osgood Mountains, where Burma Road crosses range. Center NWUNEU sec. 6, T. 38 N., R. 42 E. (53W81). 

C. Hot Springs Range, Dutch Flat district. Extreme west center NWUNWU sec. 16, T. 38 N., R. 40 E. (53W94). 

D. Hot Springs Range, Dutch Flat ~istrict. Bottom of gully, SWUNWUNWU sec. 16, T. 38 N., R. 40 E. (20H53). 

E. Nockolds' average biotite granodiOrite (Nockolds, 1954, p. 1014). 

F. Nockolds' average granodiorite (Nockolds, 1954, p. 1014). 

TABLE 10.-Quantitative spectrographic analyses for minor 

elements in granodiorite 

[Harry Bastron, analyst, U.S. Geol. Survey] 

Cu ___________________________ _ 

Mn_ .. ______ -------------------- Ga ___________________________ _ Cr ____________________________ _ v _____________________________ _ y ____________________________ _ 

Yb ___________________________ _ Ti ____________________________ _ Zr ____________________________ _ Sr ____________________________ _ Ba ____________________________ _ B _____________________________ _ 

A 

0. 0003 

. 03 

. 001 

. 0006 

. 007 

. 002 

. 0001 

.2 

. 007 

. 08 

. 1 

. 001 

B 

0. 002 

. 03 

. 001 

. 0008 

. 008 

0 

. 0001 

.2 

. 007 

. 08 

.2 

. 002 

c 

0. 002 

. 02 

. 001 

. 0006 

. 008 

0 

0 

.2 

. 007 

. 09 

.2 

0 

Looked for but not found: Ag, Mo, Co, Ni, P, Au, Hg, Ru, Rh, Pd, Ir, Pt, W, Re Ge, Sm, Pb, As, Sb, Bi, Te, Zn, Cd, Tl, In, Sc, Tb, Nb, Ta, U, Be, Li,_ Cs. ' 

The above results have an overall accuracy of ±15 percent of the value shown. 

A. East side Osgood Mountains, SE side Rocky Canyon, NEUNWU sec. 5, T. 38 

N., R. 42 E. (75H53). 

B. Hot Springs Range, Dutch Flat district. Extreme west center NWUNWU sec. 16, T. 38 N., R. 40 E. (53W94). 

C. Hot Springs Range, Dutch Flat district. Bottom of gully, SWUNWUNWU sec. 16, T. 38 N., R. 40 E. (20H53). 

At some places along the margin of the granodiorite 

stock in the Osgood Mountains a somewhat more mafic 

facies generally characterized by abundant hornblende 

has been recognized. The marginal zone is narrow; its 

width is seldom as much as 10 feet, more often 3 to 5 

feet, and locally only a few inches. 

The marginal facies is characterized by a slightly 

higher content of mafic minerals than in the normal 

granodiorite, less quartz, and less orthoclase, although 

the amount of potassium feldspar varies between rather 

wide limits. The grain size is about the same as in 

the granodiorite, and microscopic examination shows 

that texturally the rocks are the same. As in the 

granodiorite, the plagioclase is subhedral to euhedral 

and shows strong rhythmic zoning; the composition is 

from calcic andesine to oligoclase. Hornblende instead 

of biotite is the most abundant ma.fic mineral; in some 

specimens there is no biotite. Very locally, as in pit 2 

of the Kirby mine, biotite is the chief mafic mineral of 

the border facies. The hornblende is the common green 

variety and apparently the same as that which occurs 

in lesser amount in the granodiorite away from the 

border facies. The hornblende is in subhedral to 

anhedral prisms. Actinolitic hornblende (Z, very pale 

green; X, colorless; Zl\c 15°) is seen in some specimens where apparently it is an alteration product of the 

hornblende. Most biotite occurs in euhedra.I to subhedral c~ystals, but some partly replaces hornblende. 

Sphene is considerably more abundant in some of the 

marginal facies than in the normal granodiorite. Some 

of it is in small grains and trains of granules within 

chloritized biotite, but most of it is in relatively large 

irregular-shaped grains and euhedral crystals. Commonly it is a rather strongly colored variety and contains little areas within the larger grains that are 

markedly pleochroic from pink to colorless. 

Mild alteration effects are common in rocks from the 

marginal facies. Biotite and hornblende usually show 

some alteration to chlorite; plagioclase in some speci-_ 

mens is rather severely altered to sericite and subtranslucent gray finely divided clay minerals; in others 
46 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

the majority of grains are essentially fresh. Some 

calcite as veinlets and small interstitial masses is fairly 

common, and a grain or two of epidote can be seen 

in some thin sections. 

The modal composition of specimens of the marginal 

facies is given in table 11. 

TABLE 11.-Modes of marg1'nal facies of granodiorite from stock 

in the Osgood Mountains 

[In volume percent] 

Accessories 

Pot as- Plagio- HornSpecimen sium Quartz clase Biotite blende 

feldspar Nonopaque Opaque 

------------ 1 __________ 22 13 48 1 12 4 tr 2 __________ 20 16 48 - ·· ---- 12 4 tr 3 __________ 5 13 66 5 8 2 1 4 __________ 

5 __________ 12 15 59 4 11 ------ ------ 10 18 60 6 5 1 ------

1. Approximately 1 ft from contact with hornfels, west of Top Row Pit mine, SE~ 

NW~SW~ sec. 9, T. 38 N., R. 42 E. (54W18). 2. Zone 2-3 ft wide between granodiorite and pyroxene-bearing granite rock adjacent to contact. Pacific mine. (H-50--54). 3. Darker granitic rock near tactite. Getchell extension of Riley mine (H-58-55). 4. Approximately 3 ft from contact with tactite. Kirby mine, north side Julian 

Creek (54-W-26). 

5. Approximately 10ft from tactite contact. Tonopah mine (To--8-54). 

ALTERATION OF THE GRANODIORITE 

Most of the granodiorite of the Osgood Mountain 

stock and its outliers in the north end of the range is 

essentially free from alteration, except for minor effects 

such as partial chloritization of biotite and hornblende 

and slight sericitization of plagioclase. Approximately 

in the center of the northern lobe ( SW~ sec. 5, T. 38 

N., R. 42 E.), however, the granodiorite over an area 

of approximately one-fourth square mile has been modified by late magmatic solutions prior to final crystallization and altered by hydrothermal solutions after its 

consolidation. The small granodiorite stock at Dutch 

Flat and two smaller bodies farther north in the Hot 

Springs Range have also been rather extensively altered. 

The granodiorite in the Osgood Mountains is altered 

adjacent to some of the tungsten deposits and where 

it has been affected by solutions related to mineralization along the Getchell fault; these effects are described 

elsewhere in the report. The discussion here is limited 

to a consideration of the "internal" alteration in the 

Osgood Mountains body and at Dutch Flat. 

In the areas of alteration the granodiorite is stained 

reddish brown with iron oxide derived by weathering 

of pyrite. Much of the rock is finer grained than 

unaltered granodiorite and in places, particularly in 

the stock at Dutch Flat, has a porphyritic texture with 

feldspar and quartz in a finer groundmass of granular 

quartz and feldspar. In much of the rock, feldspar is 

dull gray and altered appearing, and white mica instead of biotite can be observed. Where alteration 

has been more severe, commonly along the periphery of 

the bodies, the granodiorite has been transformed to 

a soft, somewhat porous light-gray quartz-sericite rock 

with spots of brown iron oxide. 

In the areas of alteration the granodiorite has been 

affected by both late magmatic and postmagmatic 

changes. The late magmatic episode resulted in a 

peculiar texture that is responsible for the porphyritic 

appearance. At Dutch Fla·t most of the granodiorite, 

instead of having the usual granitic texture, is porphyritic with relatively large euhedral crystals of 

plagioclase, some anhedral quartz, and biotite books 

enclosed in a fine-grained equigranular groundmass 

of quartz and orthoclase. The plagioclase phenocrysts are generally more or less cloudy with kaolinitic 

material and are partly sericitized, though parts m'ay 

be quite fresh and in some specimens the plagioclase 

is unaltered or only slightly so. In the Osgood Mountains, little of the granodiorite in the zone of alteration 

is as clearly porphyritic as at Dutch Flat, but earlier 

crystallized plagioclase is partly replaced by orthoclase 

which, with small rounded bodies of quartz, forms a 

slightly finer grained interstitial groundmass. 

The porphyritic texture was formed partly by replacement, which is indicated by corrosion of the plagioclase phenocrysts by the groundmass, hut there is no 

evidence that the groundma:ss has formed by wholesale replacement of previously crystalline material. 

The plagioclase phenocrysts are all of a similar size and 

are like the plagioclase crystals in the normal hypidiomorphic granodiorite. Similar textures have been 

described at Ajo, Ariz., by Gilluly (1946, p. 29) who 

wrote that "* * * if the groundmass were entirely of 

replacement origin, the preservation of the major form 

of the plagioclase crystals would be inexpliooble." 

There is, furthermore, no indication that quartz and 

orthoclase have been added in excess of the normal 

amount in granodiorite. An alternative explanation 

suggested by Gilluly (1946, p. 29) is that equilibrium 

conditions suddenly changed prior to complete consolidation, and the earlier crystals were attacked by the 

residual liquid, but the replacement was quickly halted 

by the final crystallization. 

Postmagmatic changes in the granodiorite involved 

hydrothermal alteration effects similar to some of those 

that have been described by many geologists who have 

studied altered granitic rocks (Schwartz, 1939; 1947). 

In the rocks that have been hydrothermally altered, 

plagioclase has been albitized and strongly sericitized. 

The prominent zoning so characteristic of plagioclase 

in the unaltered granodiorite becomes faint or dis-
LNTRUSIVE IGNEOUS ROCKS OF LATE CRETACEOUS AGE 

I 

47 

appears, but in general the twinning is still visible; 

the composition becomes more sodic and approaches 

pure albite; the crystals are filled with sericite and 

minute blebs of kaolinite. Biotite is completely replaced by chlorite that contains blebs and chains of 

leucoxene and laminae of colorless to. slightly yellowish 

strongly birefrigent mica. Orthoclase remains relatively fresh, though it is slightly clouded with submicroscopic inclusions. Where alteration has been 

more severe, the feldspar, including orthoclase, is completely replaced. by sericite; and instead of chlorite, colorless mica 4 with interlaminated rutile and 

leucoxene marks the former place of biotite and also 

occurs as patches and sheaves in the groundmass, where 

in part it appears to fill small fractures and cavities. 

At a few places, commonly on the periphery of the 

alteration zones, the altered rock is heavily impregnated with late quartz that apparently has replaced the 

altered feldspar, and sericite 5 occurs as larger flakes 

and sheaves intergrown with the quartz. In the 

Osgood Moutains, near the southern boundary of the 

alteration zone but within the altered granodiorite, 

irregularly shaped masses of coarsely crystalline gray 

·to white quartz cut the altered rock. Some of the 

quartz is in terminated crystals .as much as 6 inches 

long and 4 inches in diameter, which include large 

crystals of pyrite an inch or more across. In one 

place-the Section 5 pit-the quartz contains some 

scheelite. In and adjacent to the Dutch Flat stock, 

gold-bearing quartz veins cut the altered granodiorite 

and country rock. 

The altered granodiorite contains a few percent of 

pyrite as small scattered grains. Its paragenetic relations are uncertain, but it seems to have been introduced 

either during the late magmatic stage or very early in 

the episode of postmagmatic alteration, for it is present 

jn rock that has been only slightly sericitized. Some 

pyrite also accompanied the late development of coarsely 

crystalline quartz in the Osgood Mountains alteration 

zone. 

CHEMICAL CHANGES 

Samples of altered granodiorite from Dutch Flat 

were chemically analyzed and are compared with unaltered rock in table 12. Gains and losses of chemical 

constituents in milligrams per cubic centimeter for the 

samples are graphically illustrated in figure 5. 

4 Examination under the microscope. shows that this mica bas a birefringenee (estimated 0.038) and index of refraction (b= 1.595 ± 0.003) 

like muscovite, but a smaller optic angle (5°-10° in many). X-ray powder diagrams have characteristics of muscovite. 

s Optical properties like those of muscovite (estimated birefringence 

0.038; index of refraction, 'b=1.595±0.003; 2V approximately 45°); 

X-ray powder diagrams also have lines characteristic for muscovite. 

1 

Si0 2 2 

3 

I 

Fe 2 

3 

1 

MgO 2 

3 

1 

CaO 2 

3 

500 1000 1500 2000 

MILLIGRAMS PER CUBIC CENTIMETER 

50 100 150 200 

MILLIGRAMS PER CUBIC CENTIMETER 

1. Unaltered granodiorite containing pyrite 

2. Albitized sericitic-chloritic facies 

3. Quartz-sericite facies 

FIGURE 5.-Graph showing gain and loss of principal rock constituents by alteration of the granodiorite stock at Dutch Flat. 

1, Unaltered granodiorite containing pyrite. 2, Albitizedserlcitic-chloritic facies. 3, Qua.rtz-sericite facies. 

Si02, Al20 3 , and Na20 remain fairly constant in the 

formation of the albite-sericite-chlorite facies but there 

is a significant loss of CaO and an important gain in 

K20. Loss of CaO and constancy of N a20 indicate 

that .albitization of the plagioclase is due to the breakaown of the more calcic plagioclase and removal of 

baO rather than an introduction of Na20. The inbrease in K20 is reflected in the formation of sericite, 

bhe sericite taking up Al20a and Si02 released by alterabon of the plagioclase while CaO set free by this 

;replacement was removed. Total Fe and Mg9 do not 

change appreciably in alteration of granodiorite to the 

albite-sericite-chlorite facies, but the analyses show a 

:marked increase in Fe20 3 and a concomitant decrease 

in FeO, reflected mineralogically by the presence of 

'chlorite in place of biotite and by iron oxide pseudomorphs of pyrite, which probably was more abundant 
48 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

TABLE 12.-Analyses, norms, and Niggli values for unaltered and altered granodiorite 

[Samples were analyzed by methods similar to those described in U.S. Geol. Survey Bull. 1036-C; P. L. D. Elmore, H. F. Phillips, K. E. White, analysts, U.S. Geol. Survey] 

Chemieal analyses 

Si02 ______________________ _ 

AI,03 _____________________ _ 

Fe20 3 _____________________ _ 

FeO ______________________ _ ~no _____________________ _ ~gO _____________________ _ CaO ______________________ _ 

N a20 _____________________ _ 

K20-----------------------

Ti0~---------------------­

P20s----------------------- H20 + ____________________ _ 

HC020- __ ------------------- 2 

______________________ _ 

66.4 

16. 6 

.9 

1.4 

.5 

. 94 

3. 0 

3.9 

3. 2 

. 43 

. 28 

1.3 

. 36 

. 69 

Sum_________________ 100 

Total Fe_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 1. 72 

Total S as S _________________________ _ s__________________________ .51 

so.________________________ . 2 

Sp gr (lump)_______________ 2. 62 

(powder) __ ------------- 2. 67 

2 

68. 5 

16. 5 

2. 0 

. 75 

. 08 

. 75 

. 90 

3. 7 

4. 0 

. 54 

. 33 

1.4 

100 

. 06 

. 05 

1. 98 

. 02 

3 

70.5 

18. 6 

. 85 

. 12 

. 02 

. 58 

. 15 

. 16 

5. 6 

. 48 

. 08 

2. 4 

. 06 

. 05 

100 

0. 69 

. 04 

2. 47 2. 29 

2. 69 2. 73 

2 3 

C.I.P. W. norms 

Q_________________________ 24.0 29.2 47. 1 

Or_________________________ 18. 9 23. 91 33. 36 

Ab________________________ 33.0 31.44 1.36 

An________________________ 13. 1 2. 50 -------- C _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 1. 9 5. 1 12. 1 

En_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 2. 3 1. 9 1. 4 

Fs_________________________ . 9 ---------- -------- ~ t- - ---------------------- 1. 4 . 93 --- - ---- n_________________________ . s 1. 06 . 30 

Pr _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 2. 3 _ _ _ _ _ _ _ _ _ _ _ ______ _ 

~IIi:---~===================== Ru _______________ ----- _ _ __ -----~~~-- _ __ ___ _ _ _ _ _ __ ___ 1: :~ _ _ _ _ . : ~5 03 

H20 ___ --- ____________ - _ _ _ _ 1. 3 1. 4 2. 4 

Sum_________________ 100. 57 

Niggli values 

al_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 45. 0 

fm_________________________ 16. 3 

C-------------------------- 14.4 alk _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 25. 9 

si__________________________ 295 

k__________________________ .351 

mg________________________ .377 

qz_________________________ 171 

99.55 

50. 0 

13.3 

4.9 

31. 8 

346 . 416 

. 422 

118 

99. 19 

67. 6 

7. 8 

1. 1 

23.4 

437 . 954 

. 667 

243 

1. Hot Springs Range, Dutch Flat. Bottom of gully, SWUNWUNWU sec. 16, T. 38 N., R. 40 E. Unaltered granodiorite containing pyrite. 

2. Hot Springs Range, Dutch Flat. Prospect in NWUNWU sec. 16, T. 38 N., R. 40 E. Albite-sericite-chlorite facies. 

3. Hot Springs Range, Dutch Flat. Adit, NWUNWU sec. 16, T. 38 N., R. 40 E. Quartz-sericite facies. 

in the sample of altered rock selected for analysis than 

it was in the unaltered sample. In the most intensely 

altered granodiorite, the quartz-sericite facies, there is 

a notable loss of Fe, MgO, CaO, and N ~0, but a 

further increase of K20. Si02 decreases slightly, but 

Al20a remains constant. 

Throughout the alteration, titania shows no appreciable change, reflected mineralogically by the formation 

of stable leucoxene and rutile from the breakdown 

of sphene and biotite in the original rock. P 20 5 is 

constant in the albite-sericite-chlorite facies, but is 

markedly leached away in the more severely altered 

quartz-sericite facies. 

COMPARISON WITH OTHER EXAMPLES OF HYDROTHERMAL 

ALTERATION 

The alteration of granodiorite at Dutch Flat and in 

the Osgood Mountains is remarkably similar to the 

hydrothermal alteration of quartz monzonite at the 

principal porphyry copper deposits in the southwestern United States, which has been summarized and compared graphically by Anderson (1950, p. 613-615, 617-

625), Anderson, Scholz, and Strobell ( 1955, p. 52-59), 

and Creasey (1959). Marked addition of 1{20 accompanied by loss of CaO and N ~0, with Si02 and Al20a 

remaining constant, are features common to this kind 

of alteration. MgO is generally leached, but in some 

examples it increases. Fe generally does not increase, 

and commonly is leached in the more altered facies. 

The main difference in the alteration in the Osgood 

Mountains quadrangle is that it was not accompanied by 

the introduction of chalcopyrite, whereas in the 

porphyry copper depo-sits introduction of chalcopyrite 

accompanied the stage of sericitic alteration (Schwartz, 

194 7, p. 351; 1955, p. 302). Spectrographic analysis 

(table 13) shows 0.002 percent copper in the unaltered 

granodiorite at Dutch Flat, and 0.00003 percent in a 

sample froni the northern lobe of the stock in the Osgood Mountains. The albite-sericite facies at Dutch 

Flat contains 0.005 percent, 2.5 times as much as the unaltered rock, and the quartz-sericite facies contains 

0.002 percent copper. In contrast, Anderson ( 1950, p. 

618; Anderson, Scholz, and Stobell, 1955, p. 55) reported 1.0+ percent copper and 2.4 percent chalcopyrite in the albitic facies of quartz monzonite at Bagdad. 

No chalcopyrite has been observed in the granodiorite 

at Dutch Flat or in the altered zone at the Osgood 

Mountains, and there are no indications that it was 
UNTRUS~ IGNEOUS ROCKS OF LATE CRETACEOUS AGE 49 

present and subsequently removed by supergene leaching. Sulfide metallization seems to have been restricted 

to the deposition of iron sulfide at an early stage in the 

alteration, possibly during or shortly following the late 

magmatic episode. Chalcopyrite is known only in some 

of the contact metamorphic scheelite deposits, where it 

may be later than the episode of alteration in the 

granodiorite. Possibly it is significant that the alteration zones in the granodiorite here are not zones of 

extensive fracturing. Mcl{instry ( 1955, p. 192-193) 

has emphasized that "porphyry copper" deposits "in all 

cases * * * are in thoroughly fractured ahd shattered 

rock * * *." 

TABLE 13.-Quantitative spectrographic analyses for minor clements 

in unaltered and altered granodiorite 

[Harry Bastron, analyst] 

2 3 2 3 

---1---1---·1---1---------

Cu _____ 0. 002 0. 005 0. 002 y ______ ------ 0. 002 ------ Ag_ _ _ _ _ _ _ _ _ _ _ . 0005 _____ _ Yb ___________ . 0001 _____ _ Mo _ _ _ _ _ _ _ _ _ _ . 0005 _____ _ La ___________ . 006 

Mn ____ . 02 . 02 .-001 TL _ _ _ _ 0. 2 . 2 0. 2 

N L _ _ _ _ _ _ _ _ _ _ . 0003 _____ _ Zr_ _ _ _ _ . 02 . 01 . 01 

Ga _____ . 001 . 001 . 001 Sr_ _ _ _ _ . 09 . 05 

Cr _____ .0006 .0008 .0007 Ba_ _ _ _ _ . 2 . 2 . 1 

v ______ .oo8 .oo8 .oo8 p ------ ------ . 1 B_ _ _ _ _ _ _ _ _ _ _ _ . 006 . 04 

Looked for but not found: Au, Hg, Rn, Rh, Pb, Ir, Pt, W, Re, 

Ge, Co, Sn, Pb, As, Sb, Bi, Te, Zn, Cd, Tl, In, Sc, Th, Nb, 

Ta, Nb, Ta, U, Be, Li, Cs. 

The above results have an overall accuracy of :!:: 15 percent of 

value shown. 

1. Unaltered granodiorite containing pyrite. 

2. Albite-sericite-chlorite facies. 

3. Quartz-sericite facies. 

SIMILAR ALTERATION OF SEDIMENTARY ROCKS OF THE HARMONY 

FORMATION 

Sandstone and shale of the Harmony formation have 

been altered locally for as much as half a mile from the 

granodiorite stock at Dutch Flat, at the Last Chance 

prospect in south-central sec. 33, T. 38 N., R. 40 E., 

and in the vicinity of the K and K quicksilver prospeet 

in the central part sec. 5, T. 37 N., R. 40 E., approximately 4 and 5 miles, respectively, from the stock. The 

alteration is very similar to the hydrothermal alteration 

that affected the granodiorite. In the zones of alteration, sandstone and shale have been more or less softened 

and converted to light-gray or white rocks composed 

principally of quartz, sericite, and kaolinite. Presumably the sites of alteration were localized by fractures 

that made the rocks accessible to fluids that caused the 

alteration, for the rocks are not affected everywhere 

adjacent to the granodiorite stock, but wherever quartz 

veins cut them alteration effects are apparent. Where 

the rock is altered and there are no quartz veins, there 

is abundant evidence of fracturing, and rocks at the 

Last Chance and K and K quicksilver prospects are 

altered where there has been fracturing and cinnabar 

mineralization. 

Where the rocks are altered they are noticeably softer 

than the unaltered shale and sandstone, but their sedimentary structures are preserved except where the 

rocks are crushed in fault zones. As a result of the 

alteration the rocks are bleached light gray to white, 

but in many places downward-percolating solutions 

have precipitated iron oxides which stain them shades of 

brown and yellow. 

Where feldspathic sandstone so typical of the Harmony formation has been strongly altered, the product 

is a rock composed of original quartz grains in a matrix 

of sericite, kaolinite,6 and silt-sized and smaller quartz 

grains. Former feldspar grains are barely discernible 

under the microscope, for they are composed of sericite 

and kaolinite like the matrix; plagioclase and potassium 

feldspar are equally affected by the alteration process. 

Siltstone and shale also have been converted to finegrained quartz-sericite-kaolinite rocks. 

Where the rocks are less severely altered, as indicated 

megascopically by their medium-gray color in contrast 

to the white or very light gray of ,the strongly altered 

rocks, the feldspar grains are cloudy with kaolinite and 

contain small amounts of sericite, the plagioclase more 

so than the potassium feldspar. The matrix between 

the grains in sandstone and the fine material in siltstone 

and shale is not much different than in unaltered rocks; 

some material of low birefringence that may be kaolinite 

can be seen, but biotite, where present, is unchanged 

except for slight bleaching. 

MINOR INTRUSIVE BODIES 

QUARTZ DIORITE 

Some small intrusive bodies mapped as altered granodiorite at the northern end of the Osgood Mountains 

in sec. 24, T. 39 N., R. 41 E., and sees. 19 and 30, T. 39 

N., R. 42 E., proved to be altered quartz diorite when 

petrographic studies were made of them in the laboratory. They are, however, probably related closely to 

the granodiorite, which they resemble except for the 

absence of potassium feldspar. Their alteration is like 

the alteration of the granodiorite in the northern lobe 

of the main stock and at Dutch Flat. Plagioclase is 

albitized and largely replaced by sericite, original biotite 

is replaced by chlorite, and some pyrite has been introduced, though in most specimens it has been replaced 

by iron oxide due to weathering. Unlike the altered 

e Confirmed by X-ray powder patterns of -2 micron fraction. 
50 GEQLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

granodiorite, this rock contains a few percent of calcite, 

which is interstitial and seems at least partly 3$0Ciated 

with the sericite. The quartz diorite is finer grained 

than the granodiorite, a~d some is slightly porphyritic. 

The bodies are small, som-e of them are dikes, and some 

are irregular in outline and have dikelike apophyses. 

The mode of occurrence as well as the generally finer 

grain size suggests that these small bodies may be hypabyssal intrusives. 

APLITE AND PEGMATITE 

Dikes of aplite cut the granodiorite, but are not 

abundant. They range in width from an inch or so to 

as much as 10 feet, but are more commonly on the order 

of 3 to 5 feet in width. These dikes usually are several 

tens of feet long, and some are more than 100 feet in 

length. The aplites are white even-textured mediumgrained rocks composed principally of quartz and feldspar with virtually no accessory mafic minerals. Microscopic study of several typical specimens shows ·that 

although some of the plagioclase crystals are subhedral, 

the texture is allotriomorphic, an intergrowth of anhedral plagioclase, orthoclase, and quartz. Orthoclase 

makes up 50 to 60 percent of the rock; quartz, 25 to 30 

percent; and plagioclase ( sodic ·andesine to sodic oligoclase) , 15 to 25 percent. The remaining few percent is 

biotite, chlorite, and sphene, with traces of zircon. 

Pegmatite dikes and veinlets composed of coarsely 

crystalline intergrowths of quartz, feldspar, and a little 

mica are much less common than aplite. 

DACITE PORPHYRY 

Thin tabular bodies of intrusive dacite porphyry are 

widespread in the Paleozoic sedimentary rocks of the 

Osgood Mountains and also intrude the granodiorite. 

They range from approximately 5 feet to 20 feet in 

thickness, but most of them are ·about 10 feet thick. 

Although relatively thin, the bodies are very persistent 

laterally, being continuous for many hundreds or even 

thousands of feet; one hody, approximately 1 mile south 

of Adam Peak, is continuous for more than 2 miles 

(pl. 1) . Some of the bodies are dikelike in the sense 

that they cut across the preexisting structure, but many 

are nearly flat to gently dipping sheets which have been 

intruded along the contact between Osgood Mountain 

quartzite and the Etchart limestone, or they lie within 

the Etchart a short distance above the contact. Similarly, a sheet of dacite porphyry has been intruded 

partly along the low-angle thrust fault between the 

Preble formation and the plate of metamorphosed rooks 

of the Comus formation at the north end of the Osgood 

Mountains. 

Typically, the intrusive drucite porphyry is an alteredappearing medium light greenish-gray porphyritic rock 

with dull white euhedrnl phenocrysts of felspar 2 mm 

to 6 mm in greatest dimension in a fine-grained dull 

groundmass containing chloritic remnants of original 

mafic minerals. On microscopic examination it is seen 

that the original plagioclase phenocrysts of most specimens are completely altered to sericite and sodic plagioclase containing unidentified clay minerals, carbonate, 

and some epidote, although a few contain unaltered 

cores of andesine to sodic labradorite that show twinning and strong oscillatory zoning. Other original 

hornblende and biotite phenocrysts, smaller than the 

plagioclase, are now chlorite pseudomorphs. A few 

small phenocrysts of quartz may be present. The 

groundmass is holoccystalline and composed of cloudy 

feldspar most of which apparent]y is plagioclase near 

sodic oligoclase or albite in composition, some orthoclase, subordinate interstitial quartz, and an abundance 

of sericite, chlorite commonly containing secondary 

sphene, carbonate, some epidote; apatite, and very little 

magnetite. Some specimens contain small miarolitic 

cavities 1 or 2 mm in diameter filled with quartz ·and 

less com.monly, calcite. 

A sa:mple of typical dacite porphyry from the long 

sheet that crops out on the northeast side of Goughs 

Canyon was analyzed (table 14). Its composition is 

very similar to the granodiorite (table 9) of the main 

stock except that it is slightly lower in Si02 and contains slightly more FeO. The relatively high H20+ 

and C02 content refloot the altered condition of the rock. 

The analysis strengthens the conclusion arrived at from 

the field relations and the petrography that these widespread thin tabular intrusive bodies are probably genetically related to the granodiorite intrusives. 

TABLE 14.-Analysis, norm, and Niggli values of typical altered 

intrusive dacite porphyry, Goughs Canyon: SE}(.SEY-t sec. 22, 

T. 38 N., R. 1,.1 E. 

[Samples were analyzed by methods similar to those described in U.S. Geol. Survey Bull. 1036-C: P. L. D. Elmore, K. E. White, analysts, U.S. Geol. Survey) 

Chemical analysis 

Si 02 - - - - -- - - Al20a-------- Fe203 ______ - FeO _______ _ MgO _______ _ 

CaO _______ -

N a20 _ - - -- -- K20_._- ----- Ti02--------

P20n-------- Mn0 _______ _ 

H20+---- -- 002---------

63.3 

16. 5 

1.6 

2.2 

1.7 

3. 7 

3.7 

2.9 

. 55 

. 26 

. 08 

2.0 

1.6 

100 

C.I.P. W. norm 

Q __ ------ c _______ _ Or ______ _ 

Ab ______ _ 

An ______ _ En ______ _ Fs ______ _ Mt _____ _ IL ______ _ Ap ______ _ Cc ______ _ 

H2o ____ --

24.4 

4.9 

17. 1 

31.3 

6. 6 

4.2 

1.9 

2.3 

1.0 

.6 

3.6 

2.0 

99.9 

Niggli values 

aL_______ 39.3 

fm_ _ _ _ _ _ _ 22. 8 

c-- - - - - - - 16. 0 

alk__ _ _ _ _ _ 22. 9 

sL_ _ _ _ _ _ _ 256 

k________ .340 

mg___ _ _ _ _ . 449 

q z- - - - - - - + 68 
ROCKS OF TERTIARY AGE 51 

ANDESITE PORPHYRY 

Some thin dikes of andesite porphyry were observed 

in the northern part of the Osgood Mountains but are 

not shown on the geologic map. They are much less 

plentiful than the dacite sheets. One of the most 

prominent bodies cuts granodiorite at the Riley mine 

and is exposed underground and at the surface on the 

slope west of the open cuts. Some dikes, which have 

been altered, are known to cut sedimentary rocks at the 

Getchell gold mine. 

The unaltered rock is dark gray to medium gray, 

fine grained, holocrystalline, and porphyritic, with 

prominent white phenocrysts of plagioclase, smaller 

randomly oriented prismatic crystals of hornblende, 

and, in some specimens, small biotite phenocrysts. Even 

in the freshest rock the plagioclase phenocrysts are 

mostly altered to sericite, but clear remnants show 

strong normal progressive zoning with oores of labradorite. The groundmass is fine grained and composed 

chiefly of plagioclase, hornblende, and biotite. The 

plagioclase is fresh and euhedral, and the squarish crystals have strong progressive zoning from cores of labradorite ( An6o) to andesine ( An4a) in the outer parts of 

the crystals, and very narrow rims of oligoclase ( An20 ). 

Hornblende and biotite in the groundmass as well as 

the phenocrysts are partly chloritized. The ~pecimens 

that were examined microscopically contain 1.5 to 2 

percent interstitial quartz in the groundmass. 

ALTERATION OF THE MINOR INTRUSIVES 

A characteristic feature of the hypabyssal intrusives, 

especially the dacite porphyry, is their widespread 

alteration. For the most part the alteration has been 

a mild saussuritization, accompanied by the chloritization of hornblende and biotite. These alteration effects 

cannot be attributed to the effect of heated solutions 

given off by the granodiorite, which is only locally 

altered. Furthermore, many of the intrusives are in 

unaltered sedimentary country rocks, whereas others 

cut rocks that have been metamorphosed by the granodiorite intrusive body. The alteration seems to have 

been the result of reactions peculiar to the hypabyssal 

intrusives themselv~in other words, an endomorphic 

process. 

In a study of alteration of sills on Loveland Mountain, Colorado, Singewald ( 1932, p. 27) concluded that 

because the sedimentary rocks show no sign of alteration comparable to that in the intrusive rocks the ' agents of alteration were probably contained in each 

intrusive magma or followed the same paths, and the 

alteration was an end phase of the igneous intrusion. 

There is no indication of fracturing that would have 

provided channels for the altering solutions other than 

those taken by the magma. The presence of miarolitic cavities in some specimens of dacite porphyry is 

an indication that after emplacement and prior to final 

crystallization the magma or the crystal mush contained hydrothermal solutions that presumably would 

have been capable of reacting with and altering earlier 

crystallized constituents. Perhaps, as Singewald 

( 1932, p. 27) postulated, late-stage solutions within the 

sills themselves were augmented by hyperfusibles from 

more deeply seated magma before complete consolidation in the conduits themselves. In the Ajo district, 

Arizona, Gilluly (1946, p. 83) discussed the possibility 

that similar alteration in andesite dikes may have resulted from ·the action of water in the sediments that 

was heated by the intrusives and actively penetrated 

them; however, such an explanation would not hold for 

dikes that cut the granodiorite, as at the Kirby mine. 

AGE OF THE MINOR INTRUSIVES 

Relations between the dacite porphyry and the 

andesite porphyry are not known, for neither has been 

seen cutting the other. The composition of the dacite 

porphyry suggests strongly that it is the hypabyssal 

intrusive equivalent of the granodiorite. An andesite 

dike cuts granodiorite at the Riley mine; therefore, 

the andesite is later than the crystallization of the 

granodiorite. Hobbs (1948/ p. 43) regarded the intrusive andesite as "* * * related to a much later phase 

of the same igneous activity * * *"that was responsible 

for the emplacement of the granodiorite, and J oral em on 

(1949,8 p. 25; 1951, p. 269) considered the andesite to 

be an early phase of volcanism of Tertiary age. The 

mineralogy of the unaltered andesite is quite different, 

however, from the andesite flows of Tertiary age elsewhere in the quadrangle, which contain olivine and 

pyroxene; the intrusive andesite contains hornblende 

biotite and zoned plagioclase, which suggests its consanguinity with the granodiorite. 

ROCKS OF TERTIARY AGE 

Remnants of a formerly more extensive cover of 

volcanic rocks are scattered over the quadrangle in the 

Hot Springs Range and in the lower parts of the 

Osgood Mountains (pl. 1). These are mostly andesitic 

flows, but in a few places the flows are underlain by 

stratified water-laid tuffs and rhyolitic welded tuffs. 

Some remnants of conglomerates that are presumably 

of Tertiary age are also found in the southern end of 

the Osgood Mountains and in the Hot Springs Range. 

7 See footnote 1, page 6. 8 See footnote 2, page 6. 
52 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

CONGLOMERATE 

Pebble conglomerate is poorly exposed at a few places 

in the low land east of the southern part of the Osgood 

Mountains in sees. 5, 6, a!!d 7, T. 36 N., R. 41 E., and 

sees. 1 and 12, T. 36 N., R. 40 E. Because of the smallness and scarcity of exposures, the conglomerate is not 

shown on the map; and the alluvium derived from it, 

which is characteristically an unconsolidated sand with 

pebbles of chert scattered through it, was not mapped 

separately from the Quaternary alluvium. The sandy 

aluvium with chert pebbles differs from alluvium along 

the stream courses, which contains abundant coarse 

debris of volcanic rock and quartzite. 

Pebbles of the conglomerate are mostly black, brown, 

tan, and green chert, and smaller amounts of gray 

quartzite. In addition, some fragments of gray and 

tan porphyritic silicic volcanic rock were also observed. 

The pebbles are mostly subangular, but they range 

from angular to subrounded, and from 2 to 3 mm to as 

much as 6 em in maximum dimension. A matrix of 

sand and opal cement binds the pebbles together fairly 

firmly, yet loosely enough so that pebbles can be broken 

free from the matrix without fracturing. 

Alluvial sand containing chert pebbles is also common 

on the west side of the Osgood Mountains at the south 

end of the range. In a ravine in SWI4SW% sec. 23, 

T. 37 N., R. 40 E., poorly consolidated gravel with 

pebbles of chert and some light-colored volcanic rock 

is exposed in a shallow shaft. The hill to the south 

and west is capped by andesitic flow rocks, which apparently overlie the gravel. 

Four small remnant patches of conglomerate that 

rest on the Harmony formation were discovered in the 

Hot Springs Range at widely separated localities: in 

the southern part of the range in center SEli.t, sec. 27, 

T. 38 N., R. 40 E., on the northeast side of a ridge slightly below exposures of lava; on the west side at two places 

on a ridge south of Dutch Flat in center NElJ.t and 

north of center SElM sec. 20, T. 38 N., R. 40 E., where 

it apparently underlies flow remnants; and north of Mill 

Creek, also on the west side of the range, on the ridge 

in SWli.t, sec. 3, T. 38 N., R. 40 E., where it occurs east 

of a down-faulted flow remnant. The fragments are 

subrounded to well-rounded pebbles, cobbles, and boulders. Many are obviously feldspathic sandstones and 

grits derived from the Harmony formation. In addition are plentiful pebbles of dark chert and clean finegrained white quartzite. Mostly, the conglomerate is 

not exposed but weathers down to a loose sandy soil 

with many pebbles and boulders. At the first locality 

mentioned, in the southern part of the range, however, 

~n estimated 25 to 30 feet of moderately well lithified 

conglomerate is visible in an old prospect shaft. 

RHYOLITE TUFFS 

DISTRIBUTION 

Tuffaceous rocks underlie the flow rocks at places in 

the south end of the Osgood Mountains and are exposed 

in some low ridges and knobs in the lowland east of the 

southern part of the range. Generally, the tuffaceous 

unit is covered by talus and soil wash from the steeper 

slopes above because it is thin and softer than the overlying flows. The tuffaceous rocks are probably discontinuous, and many of them are remnants of a unit that 

was formerly much more continuous and was largely 

removed by erosion before the flows were laid down. 

Bedded pumiceous tuffs are poorly exposed in some 

small ravines in SW1i.t,SW14 sec. 35, T. 37 N., R. 40 E., 

and NW% sec. 2, T. 36 N~, R. 40 E. A small exposure 

of tuff is found on the southeast side of the Dry Hills in 

the northern part of sec. 28, T. 38 N., R. 41 E. The 

only tuff known in the Hot Springs Range is in a small 

isolated outcrop in a gully below some andesite in NE% 

SW~~ sec. 21, T. 39 N., R. 40 E., in the extreme northwest corner of the quadrangle; elsewhere Tertiary andesite rests directly on the Harmony formation. 

Light-gray to greenish-gray fine-grained thinly stratified to massive welded rhyolitic tuffs make up parts of 

some small low ridges and knobs on the southeast side 

of the Osgood Mountains in sec. 6, T. 36 N., R. 41 E., 

and sec. 12, T. 36 N., R. 40 E. Characteristically, they 

have a very fine grained dense porcellaneous appearance, but they contain a few brilliant 0.5 to 1.0 mm crystal fragments of quartz and feldspar. Many pinpricklike open cavities are visible with a hand lens. 

PETROGRAPHY 

The pumiceous tuffs are commonly buff or light gray 

to white, and some are dark gray. They are more or 

less stratified and obviously fragmental. Microscopic 

examination shows that some are almost almost wholly 

composed of pumice and fragments of very fine grained 

vesicular to scoriaceous volcanic rock composed of glass 

and tiny laths of feldspar. Some contain discrete mineral grains in addition to volcanic rock fragments and 

pumice; a typical specimen contains fragments of orthoclase and sodic plagioclase, a little quartz, hypersthene 

and augite, hornblende, and small amounts of magnetite 

and zircon. 

The welded tuff is composed mostly of devitrified 

glass in which the original shard outlines are plainly 

visible. Welding has been only slight, for the shards 

are mostly undeformed and most of the vesicles show 

no flattening; yet there was some compaction while the 

glass was still in a hot, plastic condition, for the shards 

show slight tendencies to wrap around crystal fragments . . The crystal fragments, many of which show 
ROCKS OF TERTIARY AGE 53 

resorption by the groundmass, are quartz and orthoclase. 

The vesicular cavities are lined with finely crystalline 

tridymite and sanidine, and some contain a little brownish opal. 

BODY OF TUFFACEOUS ROCK NEAR GETCHELL MINE 

The north shaft at Getchell mine, approximately half 

a mile north-northwest of the mill site, was sunk in 

tuffaceous rock through a vertical distance of nearly 

300 feet. In the 600-level crosscut from the shaft, the 

tuff is in contact with. hornfels 180 feet west of the 

shaft, and the contact seems to be mostly vertical, 

though lagging of the walls and roof make observations 

difficult. Tuff is also exposed in the walls of a small 

room, excavated in the hillside for storage of fuse and 

dynamite caps, about 1,000 feet south of the shaft. We 

have not shown the tuff on the geologic map (pl. 1) 

because alluvium· and slope wash cover make it impossible to determine its true extent. Hobbs (1948,9 pl. 2) 

showed it as an elliptical area nearly 2,500 feet long 

and 1;250 feet wide elongate from north to south, and 

Joralemon (1951, fig. 3) showed a body of similar size 

but somewhat different shape. 

Bedding in the tuff could not be seen. Underground 

near the north shaft it is a structureless light-buff soft 

porous fine-grained rook containing small recognizable 

pumice fragments, a few flakes of biotite, and angular 

grains of quartz and feldspar. Some angular fragments 

of quartzite and shale as much as 1.5 inches across were 

also identified. Some blocks of granodiorite that range 

from a few inches to several feet in diameter are enclosed 

in the tuff in the small underground excavation south of 

the shaft. The blocks are subangular to subrounded 

and are considerably weathered. 

Hobbs (1948/0 p. 44-45) and Joralemon (1949,11 p. 

34; 1951, p. 269), in order to explain the relatively thick 

body of tuff with limited areal extent, regarded it as 

a roughly conical pipe formed by explosive volcanic 

action. Without more substantial evidence as to the 

form of the tuff body, however, we do not believe that 

this is its only explanation. Elsewhere in the region 

the tuff varies widely in thickness over short distances. 

Situated as it is near the front of the range, where 

undoubtedly more faults exist than are recognized at 

the surface, it seems likely that a downfaulted block of 

an originally more extensive tuff unit might have been 

preserved from erosion. We do not believe that the 

blocks of granodiorite in the tuff near the surface are 

necessarily fragments torn from the granodiorite by 

o See footnote 1, page 6. 

10 See footnote 1, page 6. 

u See footnote 2, page 6. 

volcanic explosion. Their form and rather strongly 

weathered condition suggest that the deposit may be a 

reworked tuff, possibly a mudflow that incorporated foreign fragments from the surface over which it moved. 

FLOWS 

Andesitic flows cover the southern one-fifth of the 

Osgood Mountains and extend about 2 miles southward 

into the Golconda quadrangle (Ferguson, Roberts, and 

Muller, 1952). Remnants of the same kind of rock 

are scattered north of this main area of flows for about 

2 miles. Flows of andesite also make up the Dry Hills 

on the west side of the Osgood Mountains, and remnants 

of similar flows lie along the east and west flanks of 

the Hot Springs Range and occur in small patches 

within the range. Basaltic lavas make up Soldier Cap 

on the west side of t~e Osgood Mountains. The general 

distribution of these flows suggests that the region was 

once more or less covered by volcanic rocks. 

Classification of these flow rocks is based on chemical 

analyses of typical examples. We have used a modification of the scheme used by Williams ( 1950, p. 234-235 ; 

Williams, Turner, and Gilbert, 1954, p. 43) to distinguish between andesite and basalt: lavas containing less 

than 54 percent Si02, with negative qz values and 

without normative quartz are classed as basalts; and 

rocks containing more than 55 percent Si02 and having 

high positive qz values are classed as andesites. 

ANDESITE FLOWS OF THE SOUTHERN OSGOOD MOUNTAINS, 

DRY HILLS, AND HOT SPRINGS RANGE 

The andesite flows are typically dark gray to black, 

but in some places where they are scoriaceous they are 

brick red ; however, black scoriaceous rocks are also 

common. Many of the flows have a platy fracture, but 

more commonly they break with smooth conchoidal 

surfaces. Some are massive, many contain a few 

vesicles, and some are highly vesicular or scoriaceous. 

Flow structures are not prominent, for the most part, 

but are shown here and there by the subparallel orientation of feldspar laths and elongation of vesicles. Commonly where the flow is highly vesicular it also has a 

twisted bulbous appearance with slightly ropy surfaces. 

In a few places cavernous forms have been seen. In 

some areas the soil above the flows contain many small 

flat chips of light-colored chalcedony, apparently 

derived from chalcedony-filled fractures. Some surfaces bear mammilary coatings of clear glassy, rarely 

somewhat iridescent, opal. 

The flow rooks are uniformly very fine grained to 

aphanitic. Some contain visible lathlike phenocrysts 

of plagioclase seldom more than 1 or 2 mm long and less 
54 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

than 1 mm wide, and less abundant millimeter-sized 

grains of olivine; aphanitic varieties generally have no 

prominent phenocrysts. The rocks also commonly contain glass. Texturally, therefore, most of them are 

hyalopilitic, although some are pilotaxitic and contain 

no glassy residue. Most are porphyritic, but the phenocrysts are commonly of microscopic size. 

Plagioclase, olivine, and orthopyroxene constitute 

phenocrysts and microphenocrysts within a groundmass 

of plagioclase laths, intergranular olivine, and both 

orthopyroxene and clinopyroxene, accessory magnetite, 

and, in some specimens, apatite, and glass. 

The plagioclase phenocrysts are commonly zoned and 

are somewhat more calcic (An57_62 ) than the groundmass laths (An55 on the average). 

Many specimens contain minor amounts of olivine, 

mostly as . phenocrysts but also in the groundmass as 

intergranular crystals between plagioclase laths; some 

varieties of andesite, however, contain no olivine. 

Measurements of optic angles suggest an olivine composition range from Fos9 to F012· 

Faintly pleochroic hypersthene is common in most 

specimens that ere examined microscopically but is 

absent from a few ; it occurs both as microphenocrysts 

and as minute'stubby grains in the groundmass. Compositions, as determined from measurements of the optic 

angle~ range from Enso to En85 • The interstitial clinopyroxene is generally too fine grained for reliable 

identification, but it appears to be an augite or diopsidic 

augite. 

Minute acicular crystals of apatite are plentiful in 

the gr<?undmass, and a percent or so of magnetite is 

found in most specimens as small scattered grains and 

as dust in the glass. ·The interstitial glass is dark brown 

and translucent to nearly opaque. Trace amounts of 

calcite have been observed in some specimens, which 

seems to have crystallized in an interstitial position in . 

the groundmass and not as cavity fillings. 

Analyses and model compositions of typical andesites 

from the area are given in table 15, Nos. 2, 3, and 4. 

Perhaps some of the flow rocks are more properly 

to be classed as basaltic andesites, though none that 

have been chemically analyzed fall into this category. 

Although texturally the same as the andesites, some 

that were examined microscopically contain slightly 

more olivine and pyroxene, the plagioclase may be somewhat more calcic, and the hypersthene and clinopyroxene tend to be somewhat c.oarser than in the andesites. 

Stubby crystals of the clinopyroxene occupy an interstitial position and in some specimens may have a subophitic relation to the ground~ass plagioclase. Optic 

angles ranging from approximately 44° to 47° and 

extinction angles (z/\c)from 40° to 43° suggest common 

augite. Clinopyroxene also occurs in some specimens 

as light-brown groups of subparallel needles, blades, 

and a few well-formed long prisms in the interstitial 

glassy material. The needlelike crystals are filled with 

opaque dusty inclusions of magnetite, which are less 

abundant in the stubby better developed crystals and 

appear to have been interrupted in the process of 

crystallizing from the interstitial liquid by chilling of 

the lava. Their optical properties are difficult to measure, but the optic angle is large (approximately 

60°), though variable, and the extinction angle z/\o is 

also large and variable. Magnetite (probably magnetiteilmenite) occurs as dust and minute grains and, in 

some specimens, as chainlike and elongate skeletal crystals. In contrast to the ~ndesite, acicular apatite crystals are very uncommon. A little calcite occurs interstitially in the groundmass of some specimens. The 

residual glass is brown and commonly dusty with opaque 

inclusions. In some specimens it is faintly anisoptropic due to slight devitrification. 

OLIVINE BASALT ON SOL,DIER CAP 

A pile of many relatively thin sheets of olivine basalt 

forms the prominent layered mesalike feature known as 

Soldier Cap north of Cave Canyon on the northwest 

side of the Osgood Mountains. The flows also cap a 

similar unnamed feature south of Cave Canyon and are 

present on two ridges north of Soldier Cap. The rock 

of these flows is petrographically quite distinct from 

the andesite in the Dry Hills to the south. The lower 

valley of the East Fork of Eden Creek separates the 

olivine basalt flows from the andesite, and the relative 

ages of the two volcanic units cannot be established. 

The contact of the lava pile with the underlying 

rock dips from 20° to 30° NW., whereas the flows 

themselves are nearly horizontal or inclined slightly 

westward, indicating the flows were extruded into an 

area of considerable relief. It is a puzzling fact that 

flows of similar composition have not been recognized 

elsewhere in the qhadrangle, and it is especially puzzling that they apparently do not cross the East Fork 

of Eden Creek into the Dry Hills and that the andesite 

in the Dry Hills is not found north of the creek. 

In the upper part of the olivine basalt pile, individual 

flows are easily recognized for they form prominent 

steplike cliffs a~d benches. In the lower part of the 

section, possibly because individual flows are thicker, 

the steplike topography is not developed and the flow 

members cannot be seen. The flows range from approximately 10 feet to 30 feet in thickness; the majority 

probably are around 15 to 20 feet thick. The total 

thickness of basalt is on the order of 1,250 feet. 
ROCKS OF TERTIARY AGE 55 

The upper parts of individual flows are highly vesicular; the central parts are dense and considerably less 

vesicular; and the lower parts of the thickest flows contain a few small cavities. Freshly broken surfaces of 

vesicular rock are medium gray, mottled with areas 

of light brownish gray; specimens of the more massive 

rock are medium dark gray. Weathered surfaces are 

brownish gray to moderate brown. In general, the 

color of the fresh rock is lighter than the andesite and 

balsaltic andesite elsewhere in the quadrangle. In hand 

specimens the rock is porphyritic with millimeter-sized 

phenocrysts of olivine and, very rarely, plagioclase laths 

in an aphanitic groundmass. 

The phenoorysts of olivine and plagioclase lie in a 

microcrystalline groundmass of plagioclase and intergranular pyroxene and olivine. All specimens contain 

magnetite and acicular apatite as minor accessories. 

A little interstitial brown glass occurs .in some specimens. All specimens contain a little biotite interstitial 

to the essential constituents and in places seemingly 

occupying microscopic cavities. Montmorillonitic clay 

occupies a similar position and commonly is associated 

TABLE 15.-Analyses, norms, modes, and Niggli values of Tertiary flows in the Osgood Mountains quadrangle 

[Analysts (1, 3), J. M. Dowd and Katrine White; (2, 4) P. L. D. Elmore and Katrine White, U.S. Geol. Smvey] 

2 3 4 

Chemical analyses 

Si02--------------- 50.6 57.6 58. 0 59.8 

Al20a-------------- 16. 3 15. 0 17. 0 16. 0 

Fe20a-------------- 6. 9 2. 0 4. 6 2. 4 

FeO_____________ __ 2. 4 6. 5 2. 6 3. 8 

Mn 0 _______ - _ _ _ _ _ _ . 16 . 18 . 12 . 15 

MgO _ - - __ - __ - _ _ _ _ _ 5. 6 2. 5 3. 1 2. 8 

CaO______________ 7.1 5. 5 5. 5 5. 0 

NaaO______________ 4. 0 3. 5 3. 9 3. 4 

KaO---- - - --- - --- - - 2. 1 2. 7 2. 8 3. 2 

TiOa- __ ----------- 1. 9 1. 9 1. 2 1. 0 

PaO&--------------- . 76 . 82 . 66 . 54 

lg_________________ 2. 0 1. 3 . 88 1. 1 

HaO+------------- --------- --------- -------~- --------- COa--------------- --------- --------- --------- ---------

Sum ________ _ 99.2 

2 

p-values and Rittman classification 

p-value (Rittman, 49. 5 55. 2 1953) ____________ (medium (weak 

alkaline) calcalkaline) 

Classification _______ B5 B5 

(Rittman, 1952) (olivine (trachy 

andesine andesite) 

trachybasalt) 

Modes (volume percent) 

3 4 

56.6 58. 0 

(weak (weak 

calc- calcalkaline) alkaline) 

B5 A5, FM 

(tra-chy 13 

andesite) (trachy 

andesite) 

Sp gr (powder) ____ _ 99. 8 

2. 82 

99. 5 

2. 73 

100.4 

2. 72 2. 69 Phenocrysts: 

Olivine________ 11 --------- --------- ---------

C.I.P. W. norms Pyroxene_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 1 ____ ----- 1 

Plagioclase_____ _ _ _ _ _ _ _ _ _ 3 --------- ------- --

Q _________________ --------- 11.5 10. 1 13. 3 Groundmass: Or_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 12. 2 16. 1 16. 7 18.9 AL _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 34. 1 29.3 33. 0 28. 8 

An________________ 20.3 17.2 20.6 18.9 VVo_______________ 4.3 1.9 1.6 0.9 En________________ 13. 6 6.2 7. 7 6.9 Fs _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _______ _ 7.4 --------- 3. 6 

Fo________________ .5 

Mt________________ --------- --------- --------- 2. 6 3. 0 5. 1 3. 5 

IL __ - - - ____ - _ _ _ _ _ _ 3. 6 3. 6 2. 3 2. 0 

Hm_______________ 5. 1 --------- 1.1 

Ap________________ --------- 1. 7 2. 0 1.3 1.3 

1-------1--------·1--------1--------11 

Sum_________ 98. 0 98. 2 

Niggli values 

aL _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 25. 2 

fm________________ 41. 2 

c_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 20. 0 

alk________________ 13. 7 

sL _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 133 

k_________________ . 253 

mg______ __________ . 534 

q z- - - - ------------ -22 

28. 8 

35.4 

19.2 

16. 6 

188 . 342 

. 343 

22 

99. 5 

31. 5 

32. 4 

18.5 

17. 6 

182 . 323 

. 448 

11.6 

98. 1 

32. 1 

31. 5 

18. 2 

18. 2 

206 . 382 

. 455 

33 

1. Olivine basalt from Soldier Cap, Osgood Mountains, sec. 2, T . 38 N., R. 41 E. (H5052.) 

Plagioclase_____ 59 27 72 61 

Pyroxene______ 17 2 13 11 

Olivine __ ------ 110 3 3 2 

Magnetite_ _ _ _ _ 7 2 7 3 

Glass __________ --------- 62 --------- 21 

Cristobalite____ 3 --------------------------- Apatite________ 1 Tr Tr Tr 

Biotite________ 1 --------------------------- Iron oxide_ _ _ _ _ 1 ____ - _- _- ______ - __ ---- -----

lndetermina te groundm~ss _______ - ______ -- ---- 5 1 

Sum ___ _ 100 100 100 100 

2. Andesite, Belmont Hill, Hot Springs Range, BE~ sec. 8, T. 38 N., R. 40 E. (53W95.) 

3. Andesite, west side southern end of Osgood Mountains, BE~ sec. 21, T. 37 N., R 40 E. (OM251.) 

f. Andesite, Dry Hills, BE~ sec. 20, T. 38 N., R 41 E. (76H53.) 

I Partly to wholly altered to lddingslte. 
56 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

with the biotite. Some small cavities are partly to 

wholly filled with opal; others contain, in addition to 

opal, a zeolite, feldspar, and commonly biotite. 

Olivine shows all stages of alteration to reddishbrown iddingsite and hematite. Phenocrysts are seldom 

completely altered, whereas the smaller interstitial 

grains in the groundmass are totally replaced by reddish-brown alteration products in most specimens. A 

less common type of alteration seen in the phenocrysts 

is the replacement of the olivine by serpentine and 

bowlingite along fractures. Some phenocrysts are 

crowded with grains of secondary magnetite. The 

phenocrysts are euhedral to subhedral and show virtually no resorption. Optic angle measurements indicate 

that the composition of the olivine ranges from Foss to 

F0g~~. 

Two kinds of plagioclase can be seen in the groundmass of many specimens. First, and most abundant, 

are euhedral to subhedral twinned and slightly zoned 

laths of labradorite ( Ans2-ss). Second, interstitial to 

the labradorite laths, are anhedral crystals that show 

wavy extinction, are commonly untwinned, and contain 

many inclusions of apatite needles. The refractive 

index (/3) of the interstitial feldspar is distinctly less 

than that of the labradorite laths-it ranges about 1.540 

and averages approximately 1.539-and has an optic 

angle of moderate size and positive sign. MacDonald 

(1942) described similar interstitial feldspar in H·awaiian lavas characterized by an abnormally small positive 

optic angle and with indices of oligoclase or andesine 

that he concluded was a potassic oligoclase or potassicandesine. Some feldspar that may be anorthoclase, as 

indicated by its abnormally small optic angle of negative sign and refractive index higher than that of orthoclase, is also associated with the interstitial plagioclase. 

The pyroxene, occurring exclusively as granules and 

s,tubby prisms in the groundmass, is mostly so small that 

its optical properties are very difficult to determine. It 

is a colorless to very faintly brown common augite. 

Some of the larger grains have the following characteristics: {3= 1.695, 2V ( +) =49° to 51°. 

The biotite, which is a common minor constituent in 

all specimens, is strongly pleochroic from reddish brown 

to very pale yellow, with observed optic angles near 29° 

on the average, refractive indices {3= 1.633 andy= 1.634, 

and strong dispersion r>v. Its position in interstitial 

cavities in the groundmass and in amygdules indicates 

that it is of late magmatic or hydrothermal origin. 

An analysis and the modal composition of the lava 

from Soldier Cap are given in table 15. 

CHEMICAL COMPOSITION OF THE TERTIARY FLOWS 

Table 15 lists the chemical compositions of fpur samples of flows together with modes, computed norms, and 

Niggli values; the results of spectrographic analysis 

for minor elements in three of the samples are given in 

table 16. On the basis of these few analyses, the alkalilime index-tha;t is, the Si02 yalue at which N a20 + 

K20 equals CaO-appears to be approximately 59, and 

the lavas belong to the calc-alkalic igneous rock series 

of Peacock's (1931) classification. Rittman (1953) has 

devised a system of calculation by means of which a 

number which he de..c;ignates as the p-value can be used 

to indicate the character of either a series or single 

rocks. Where only a few analyses are available, Rittman's method has an advantage over Peacock's classification because no variation diagram is needed to obtain 

the index. The p-values for the analyzed volcanic rocks 

of the Osgood Mountains quadrangle are given in table 

15 and shown on figure 6 (Nos. 1 to 4). Three of tlw 

analyzed samples (Nos. 2 to 4) have similar p-values 

which average 56.6 and according to Rittman's scheme 

are weakly calc-alkaline; these we regard as essentially 

contemporaneous and representative of the flows in the 

quadrangle with the exception of those at Soldier Cap. 

The basaltic rocks at Soldier Cap probably are a different series; for them p=49.5, medium alkaline. 

TABLE 16.-Quantitative spectrographic analyses of minor elements 

in volcanic rocks 

[Harry Bastron, analyst] 

1 2 3 1 2 3 

-- ----- Cu ______ 0.006 0.001 0.005 Yb _____ 0.0002 0.0004 0. 0003 

Mn _____ . 07 . 07 . 06 La _____ . 007 . 004 . 01 Co ____ __ . 003 . 001 . 001 Ti_ ____ 1.0 1.0 .6 

Ni_ _____ . 01 ------ . 003 Zn _____ . 01 . 02 . 01 Ga ______ . 001 . 001 . 001 Sr ___ __ . 1 . 05 . 07 

Cr_ _____ . 002 ------ . 002 Ba _____ .2 .2 .1 v _______ . 02 . 01 . 01 p ------ .2 .2 .2 

y _______ . 003 . 005 . 004 B ______ . 001 . 001 . 001 

1. Olivine basalt from Soldier Cap, Osgood Mounatins, sec 2, 

T. 38 N., R. 41 E. (H-5G-52). 

2. Andesite, Belmont Hill, Hot Springs Range, SEX sec. 8, 

T. 38 N., R. 40 E. (53-W-95). 

3. Andesite, Dry Hills, SEX sec. 20, T; 38 N., R. 41 E. (76-H-53). 

Looked for but not found: Au, Ag, Mo, Hg, Ru, Rh, Pd, Ir, Pt, W, Re, Ge, Sn, Pb, 

As, Sb, Bi, Te, Zn, Cd, Tl, In, Sc, Th, Nb, Ta, U, Be, Li, Cs 

The above results have an overall accuracy of ±15 pP-rcent the value shown. 

It is apparent from the analyses and the a.mount of 

normative orthoclase that these lavas have a relatively 

high K20 content compared to Si02. The high l{z0 

is also reflected by the naming of the analyzed rocks 

acco~ding to Rittman's ( 1952) proposed nomenclature 

of volcanic rocks, for they are cl~ssified as trachyandesite, trachybasalt, and rhyodacite (table 15) . Although 

these rocks do not contain any recognizable potassium 

feldspar, the microcrystalline and glassy interstitial 
ROCKS OF TERTIARY AGE 57 

residue has potentially the composition of orthoclase 

plus quartz; the potassic character of the flows on 

Soldier Cap probably accounts in part for the late 

interstitial potassic-oligoclase in those rocks. If, as was 

done by Merriam and Anderson ( 1942, p. 1724), the 

k-ratio is plotted against Si02 (fig .. 7), it is readily 

apparent that the Tertiary volcanic rocks (spec. 1 to 4) 

from the Osgood Mountains and Hot Springs Range, 

together with others from western Nevada, are intermediate between the potash-rich province of central 

and eastern Nevada and Utah, and the relatively lowpotash province of the Sierra Nevada and Cascade 

Range in California. 

The analyses bring out another feature worth noting; 

the andesitic la.vas have a relatively high content of 

Ti02. Presumably it is mostly in the form of titaniferous magnetite, for the pyroxenes do not have the 

purplish or brownish cast that typifies titaniferous 

varieties. It is also noteworthy that these rocks are 

exceptionally rich in bari urn (table 16) . 

AGE AND CORRELATION 

The age of the volcanic rocks and the conglomerate 

can only be determined as post-Paleozoic and pre0 

ro "' oz 

N f ~0 

~~ 

0 

E 

0.9 f0.8 t0.7 r0.6 r0.5 rEXPLANATION 

Utah and eastern Nevada 

X 

California 

+ 

Western Nevada 

® 

Osgood Mountains quadrangle + 

Quaternary from their relations with other rocks in 

this quadrangle, but the Tertiary age of similar rocks 

in adjoining areas has been firmly established. 

An 

0.7 

0.6 

0.£ 

0.4 

0.3 

0.2 

0.1 

0 

-0.1 

P= Si02 (An+ 0. 70) 

-+--......,..._-----'"1.:-----+------i------i A _ (AI- Alk) 

n_ (AI+Aik) 

-+-:..,---+c------':..,-+------i------i AI= 0.9 Al 2 0 3 

Alk=K20+1.5 Na 2 0 

45 50 55 60 65 70 

Percent SiO 2 

FIGURE 6.-Rittman (1953) diagram showing p-values of volcanic rocks 

in the Osgood Mountains quadrangle. Nos. 1 to 4 are Tertiary flow 

rocks, corresponding to same-numbered analyses in table 15; No. 5 is 

basalt near Comus station, table 17. 

x_ 

-

X 

-

+ 

~ + . + 

• + X + .x -f 

X+ •X X -" 

•• • ++ x•><. 

x+ + + x • +• . X • 

II 

~ 

0.4-- ----. _:. -·~-+- ·: -· -+-

®.3 2 + + 

-·~ -~:2~-- X + . X X X 

. 

x+ X +X X X 

X xx 

X 0.3 - + 

+ 

0.2 - X + X 

X X 

X + xx @)5 X 

X 0.1 - + XX 

X X X 

I X I 0 

45 50 55 

@) 

+ 

XX xx X X 

X X x+x 

X X X X 

X 

X 

X 

X X 

X 

I 

60 

Percent SiO 2 

X X 

X X 

X 

X 

X 

I 

65 

X 

X 

I 

70 

I 

75 

-

'j 

z: 

--v 

-

Q 

.; 

FIGURE 7.-Diagram of tbe k-ratio of volcanic rocks plotted against their 8102 content. (Taken from Merriam and Anderson, 1942, p. 1724, 

with some additional data.) Nos. 1 to 4 are Tertiary tlow .xock.s, corresponding to same-numbered analyses in table 15; No. 5 is basalt 

near Comus station, table 17. 
58 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

The tuffaceous rocks that underlie the andesitic 

flows are tentatively correlated with vitric tuffs and 

welded tuffs that constitute a widespread unit of late 

Miocene to middle Pliocene age in Nevada (Van 

Houten, 1956, p. 2814-2819). Similar beds at the north 

end of the Hot Springs Range yielded a transitional 

Miocene and Pliocene flora (VanHouten, 1956, p. 2805, 

fig. 2). The andesitic flow rocks that overlie the 

rhyolite tuffs are probably of early to middle Pliocene 

age (Nolan, 1943, p. 168-169; Van Houten, 1956, p. 

2816, fig. 6). The pebble conglomerate underlies the 

flows in at least one place, but its relation to the 

rhyolite tuffs is uncertain. Van Houten . ( 1956, p. 

2814-2819) reported that Paleozoic pebble conglomerates occur sporadically through the vitric tuff unit. 

Ferguson and others (1952) mapped gravels at the 

south end of the. Osgood Mountains that might be 

equivalent with the pebble conglomerates in this quadrangle, but he considered them to be of Quaternary age. 

RUCKS OF QUATEBNARY AGE 

Surficial deposits of Quaternary age in the OsgGO<i 

Mountains quadrangle have been subdivided into older 

fan gravels, older and younger alluvium, and talus. 

A flow of basalt that extends into the southern part of 

the quadrangle, west of Comus station, is also believed 

to be of Quaternary age. 

BASALT FLOW NEAR COMUS STATION 

The northern end of a basalt flow that was mapped 

in the Golconda quadrangle (Ferguson, Roberts, and 

Muller, 1952) extends about half a mile into the south 

end of the Osgood Mountains quadrangle, west of 

Comus st'ation on the Southern Pacific Railroad (pl. 1). 

Its physical relation to the other volcanic rocks in the 

quadrangle cannot be determined, but petrographically 

and chemically it is considerably different. It is tentatively believed to be of Quaternary age because it 

is considerably less dissected than the other flows and 

because it appears to have obstructed the course of the 

Humboldt River and caused it to flow around the end 

of the tongue of lava. The flow is tilted westward to 

northwestward at a small angle, possibly by normal 

faulting along its eastern edge. 

The rock is dark gray, very: fine grained to aphanitic 

with a vesicular and scoriaceous structure. It is texturally different from the flows in the Osgood Mountains 

and Hot Springs Range as it is typically basaltic 

with an intergranular to subophitic groundmass, a 

small amount of interstitial glass, and a few olivine 

and plagioclase phenocrysts. The chemical .composition (table 17) is also much different from that of the 

other flows. 

Olivine and plagioclase phenocrysts make up 6 percent of the total volume. The olivine ( 3 percent) is 

approx-imately Fo82 according to its optic . angle 

( 2V = 87°) . The plagioclase phenocrysts ( 3 percent) 

are labradorite to bytownite ( An53 to An111 ) • The 

groundmass, about 94 percent of the total volume, includes about 12 percent olivine and 45 percent plagioclase ( An47 to Anss) . Intersertal to subophitic clinopyroxene ( 27 percent) in the groundmass is pale 

greenish -!brown and non pleochroic augite (/3= 1.703, 

2V( +) =48°, r>v distinct). The rock also contains 

magnetite (3 percent) in small grains and rods, and 

interstitial brown glass ( 7 percent) . 

TABLE 17.-Analysis, norm, mode, and Niggli values of basalt near Comus station. Railroad cut west of Comus, S.EXS.EX sec. 10, T. 36, N., R. 41 E. (H-53-54) 

[Samples were analyzed by methods similar to those described in U.S. Geol. Survey Bull. 1036-C; P. L. D. Elmore, K. E. White, analysts, U.S. Geol. Survey] 

Chemical analysis Norm Mode 

SiO,_________ 48.6 Q _________ ------ Plagioclase___ 48 

AhOa-------- 15.4 Or________ 3.6 Pyroxene_____ 25 FetOa-------- 2. 9 AL_______ 21.1 Olivine_______ 17 FeO_________ 7.1 An ________ 29.0 Magnetite____ 3 NnO_________ . 16 Wo_______ 7. 2 Glass_________ 7 MgO________ 9.2 En ________ 17.3 

cao_________ 10.6 Fs________ 6.4 Na2o________ 2. 5 Fo________ 3. 9 K,o_________ .60 Fa________ 1.6 TiO,______ ___ 1. 4 Mt______ __ 4. 2 

Niggli values 

al_ -------- 20.1 fm________ 48.6 c__________ 25. 1 alk________ 6. 2 sL ________ 108 k__________ .137 

mg________ . 624 qz _________ -17 

P20s--------- . 24 ll __ ------- 2. 7 p-value (Rittman. H20+------- .54 Ap________ .6 (1953)=59.4 

COt---------- . 74 Cc_ ------- 1. 7 (weak calc- H,o_______ . 5 alkaline) --1-----1-- Rittman (1952) 

Sum_____ 100 ------------ 99.8 --------------- 100 classification: 

B~~~~~a'', 

Basalt. 

The chemical composition of a sample of the flow is 

included in table 17. According to Rittman's (1952) 

classification, the rock is a labradorite basalt; its p-value 

of 59.4 is slightly greater than that of the andesitic 

flows in the quadrangle, but like them its character 

is weak calc-alkaline in Rittman's ( 1953) system (fig. 

6) . It is the ·most mafic volcanic rock in the quadrangle. 

OLDER FAN GRAVELS 

Remnants of older fan gravels are scattered along 

the east side of the Osgood Mountains from Felix 

Canyon on the north to a point on the south about 2 

miles southwest of Lone Butte, and they are shown 

on the geologic map (pl.1). The deposits are fanglomerates like the more recent alluvial deposits along the 

front of the range. They are as much as 25 to 30 feet 

above the surrounding alluvium in most places, and 

their upper surface may be as much as 50 feet above an 

adjoining drainage channel. Unlike the conglomerate 

that is believed to be of Tertiary age ( p. 52), the 
METAMORPHISM 59 

younger deposits are generally coarser and poorly consolidated, hut the chief difference is in the character 

of the fragments. The older fan gravels have only 

locally derived fragments, while the deposits of Tertiary age contain much exotic debris. 

These older fan gravels apparently represent an extensive fanglomerate that once mantled bedrock along 

this part of the range. Accelerated erosion, perhaps 

caused by the slight uplift of the range along buried 

range-front faults, or lowering of the general base level 

resulted in deep incision of the gravels and their large 

scale removal by streams that issued from the range. 

TALUS 

Many slopes in the Osgood Mountains and Hot 

Springs Range are mantled with talus. No consistent 

criteria for mapping talus bodies have been followed, 

and only a few talus accumulations in the Osgood 

Mountains are shown on the geologic map (pl. 1). 

Generally, talus was mapped where it concealed critical 

structural elements such as faults and contacts between 

formations. In one or two places, however, it was 

mapped because it formed ·a large conspicous deposit. 

Most of the talus shown on the map is derived from the 

Osgood Mountain quartzite, although one prominent 

mass composed of volcanic rock is shown in the Dry 

Hills. Many other slopes underlain by volcanic rocks 

in both ranges are covered by talus,·which forms dark 

streaks that are most conspicuous, even from a long 

distance. 

ALLUVXUM 

Alluvium covers about 45 percent of the quadrangle. 

It includes alluvial fans on the gentle slopes at the 

foot of the ranges; the veneer of gravels that cover 

pediment surfaces, gravels, and sands along the streams; 

and finer sands, silts, and clays that are found farther 

out in the main valleys and along the flood plain of the 

Humboldt River. 

The thickness of the alluvium in the main valleys is 

not precisely known, but probably it is not less than 

several hundred feet in the axial parts. A well in 

Paradise Valley west of the northwest corner of the 

Osgood Mountains quadrangle is reported to have penetrated 800 feet of valley fill (Loeltz, Phoenix, and Robinson, 1949, p. 27). A well 400 feet deep was drilled 

6 miles east of Getchell mine to supply water for the 

mill; presumably it did not reach bedrock. A veneer of 

alluvial gravel covers pediment, slopes on the northwest 

and along much of the east side of the Osgood Mountains. The alluvial cover is less than 10 feet thick 

at many places but may be as much as 25 feet thick. 

690-159 0-63-5 

Alluvium of two ages can be recognized. An older 

alluvium occurs on the upper parts of the fans and 

much of the veneer on the pediments; it can also be 

seen where it forms terraces along some of the streams. 

The older alluvium has been incised by the present 

streams, and a younger alluvium occupies the stream 

channels .. / In the lower parts of the fans and out in the 

main intermontane basins the younger alluvium overlaps the older alluvial deposits. 

Near the mountains the alluvium is composed of 

coarse, bouldery to cobbly gravels intermixed with sand 

and silt; the material rapidly becomes finer toward the 

valleys. In the southeast corner of the quadrangle, 

the alluvium in the nearly flat part of the valley floor 

is silty, with only small local pebbly patches. Probably 

some of this fine material was deposited at times of 

flood by the Humboldt River. On the southwest side 

of the Osgood Mountains, south of Stone Corral, much 

of the alluvium, even fairly close to the mountain 

front, is composed at the surface of fine loose sand; 

rounded chert pebbles are locally abundant in the sand. 

Some of the sand obviously has been blown by the wind. 

It is possibly derived in part from fine sediments deposited to the west and southwest in Lake Lahontan. 

The eastern limit of Lake Lahontan was 2 miles or so 

east of Golconda (Russell, 1885, p. 31, pl. 46) and a 

small part of the shore would have lain in the southwest 

corner of the quadrangle, assuming that the original 

altitude of the Lahontan beach was 4,378 feet (Russell, 

1885, p. 101). Part of the material, as attested by the 

pebbles of chert, probably is reworked sand from the 

prevolcanic Tertiary conglomerate. 

METAMORPHISM 

CONTACT METAMORPHISM AND METASOMATISM 

A prominent metamorphic aureole surrounds the 

granodiorite stock in the northern part of the Osgood 

Mountains, and a small but well defined halo of metamorphism was formed around the small stock at Dutch 

Flat. A distinctive pattern has been used on the goologic map to show the distribution of metamorphic rocks 

around the stocks (pl. 1). Emplacement of the granodiorite bodies raised the temperature of the country 

rocks sufficiently to cause reorganization of the original 

constituents of the sedimentary rocks and crystallization of new minerals. For the most part these changes 

were attained without any addition of material from 

the granitic rock and are the result of reactions that 

took place between the original minerals of the rock 

through the medium of aqueous pore solutions, the water 

of which was supplied by the rock itself. Close to the 
60 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

contact, however, the metamorphosed rocks contain mineralogical, textural, and structural evidence that material has been added from the igneous body. The 

formation of the tungsten. deposits in the Osgood Mountains was an integral part of the metamorphic process, 

for they were formed by solutions of the same origin 

as those that caused the formation of tactites from limestones adjacent to the granodiorite. For purposes of 

description, however, the tungsten deposits are considered separately in the chapter on ore deposits. 

CONTACT METAMORPHISM AT DUTCH FLAT 

A narrow belt of metamorphosed rock surrounds the 

small stock of granodiorite at Dutch Flat, where the 

rocks affected by the metamorphism are shale and feldspathic sandstone of the Harmony fonnation. On the 

north and east sides of the stock the rocks have been 

metamorphosed for only about 200 feet from the contact ; on the south side metamorphic effects are recognizable for as much as 1,000 feet from the contact. The 

variation in width of the belt of metamorphism has no 

apparent relation to the structure of the sedimentary 

rocks or exposed shape of the stock. 

The first sign of metamorphism is a darkening and 

hardening of the shale and sandy shale of the Harmony 

formation. The microscope shows that there has been 

some recrystallization of the finer material in the rock 

and the formation of some chlorite and much finegrained muscovite. About 100 feet from the contact, 

spongy porphyroblasts of andalusite appear, as well as 

small flakes of biotite. Chlorite persists to within 50 

feet of the contact. Introduction of orthoclase is a 

fairly common phenomenon, not recognized in the metamorphosed shaly rock but observed in some of the sandstones near the granodiorite. The introduced feldspar 

occurs as irregularly shaped bodies in the matrix of the 

sandstone. Some clinozoisite accompanies the orthoclase, and some specimens contain carbonate veinlets 

with intergrown prehnite. 

CONTACT METAMORPHISM IN THE OSGOOD 

MOUNTAINS 

The granodiorite stock in the Osgood Mountains is 

surrounded by a metamorphic aureole that varies considerably in width, a variation that for the most part 

seems to be a reflection of the shape and form of the intrusive body. At the south end of the stock, where the 

contact presumably is steeply dipping to vertical, the 

zone of contact metamorphism is narrowest, measuring 

from less than 1,000 feet to 1,500 feet in width, though in 

a few places metamorphism extends somewhat farther, 

parallel to the structure of the sedimentary rocks which 

strike into the contact. North of the stock, however, 

metamorphic effects are noticeable as far as the quadrangle boundary, or nearly 10,000 feet from the outcrop 

of the main intrusive body, which has a decided prolongation in this direction and, as indicated by the 

presence of small outliers, probably is continuous beneath a relatively thin cover of country rock for perhaps 

5,000 feet north of the main exposure. The metamorphosed belt is from 2,000 feet to nearly 8,000 feet wide 

along the west side of the stock. On the east side, the 

width of the belt is uncertain because the rocks pass 

beneath alluvium and only a narrow strip of metamorphic rock is exposed. 

Most of the sedimentary rocks metamorphosed by the 

granodiorite in the Osgood Mountains are the shales 

and carbonate rocks of the Preble formation. The 

Comus formation, which is near the east side of the 

stock and on a thrust plate at the north end of the range, 

is also affected. Some of the other formations come 

within the metamorphic aureole but are so distant from 

the intrusive body that they hav:e been only slightly 

affected. As would be expected, the metamorphism has 

caused the formation of a considerable variety of rock 

types, containing several metamorphic minerals whose 

variations in composition and distribution depend partly on the composition of tl).e original rock, partly on 

the dist~nce from the intrusive body, and partly on the 

addition of substances by solutions derived from the 

granodiorite. In a general way, the metamorphic aureole is zoned with respect to the stock, for the products of 

the most intense metamorphism are at the contact between the stock and the country rock, and with increasing distance from the stock they grade rapidly into a 

less strongly metamorphosed zone of variable width 

that fades off gradually into unmetamorphosed country rock. Excepting the tactites formed from carbonate rocks at the contacts of the granodiorite, most of 

the metamorphism has been accomplished by reactions 

between the original constituents of the rocks with no 

addition of material and hence is designated isochemical 

metamorphism. Where the metamorphism has been 

accomplished by the addition of substances to form 

garnet-pyroxene tactites from the carbonate rocks, the 

process is designated allochemical silicate metamorphism (Holser, 1950, p.1072). 

METAMORPHISM OF THE PELITIC ROCKS 

Argillite and hornfels formed by the metamorphism 

of shale and siltstone belonging to the Preble and Comus 

formations are the most common metamorphic rocks 

that surround the granodiorite stock. In the outermost 

zone, the most obvious metamorphic effect in these finegrained sedimentary rocks is a hardening and loss of 

fissility commonly accompanied by a darkening of the 

rock. A faint foliation made visible by slight color and 
METAMORPmSM 61 

textural differences may be apparent in some specimens. 

These rocks are so fine grained that their mineral components are difficult to resolve even by microscopic 

study, but even at this early stage of metamorphism 

hiotite is visible as microscopically small flakes. This 

early biotite characteristically is pale and its pleochroic 

colors vary from light brown to very pale yellow. 

Sericite and quartz can also be recognized. 

The appearance of the minerals cordierite (2Mg0 

·2Alz0a · 5Si0z) and andalusite (Al2 0 3 • Si02 ) is indicative of a further increase in the degree of metamorphism 

of the pelitic rocks. Cordierite is more common than 

andalusite in the metamorphosed shale and siltstone of 

the Preble formation, but in the fine-grained sedimentary rocks of the Comus formation andalusite seems to 

have formed more readily than cordierite. Exceptions 

to this general rule are to be found, of course, and 

some hornfels contains both minerals. Undoubtedly, 

however, the tendency for one or the other to be formed 

reflects differences in the original sedimentary rock. 

Tilley ( 1924, p. 31) has pointed out that andalusite 

normally arises from the: metamorphism of kaolinbearing rocks, and if magnesia is abundant, generally 

in the form of chlorite, cordierite is formed. 

Cordierite appears in the pelitic rocks where the 

intensity of metamorphism is apparently only slightly 

greater than that which caused the formation of 

biotite. In fact, in many places cordierite and biotite 

seem to make their appearance simultaneously; however, biotite is found in rocks farther from the granodiorite than cordierite. In the Osgood Mountains 

cordierite is found in hornfels as much as 5,000 feet 

horizontally from the granodiorite, and in rocks of 

the appropriate composition it persists up to the 

contact. Its first appearance is commonly signalled 

megascopically in otherwise microcrystalline rock by 

minute ovoid spots that are somewhat lighter than the 

rest of the rock. Under the microscope these spots appear as relatively large anhedral cordierite crystals 

crowded with fine flakes of biotite and indeterminate 

fine groundmass material. The biotite-cordierite hornfels 'Persists without much change over most of the 

width of the contact aureole, though as the granodiorite 

is approached the cordierite porphyroblasts contain 

somewhat less included biotite and the biotite becomes 

perceptibly darker. 

In some of the rocks andalusite forms instead of 

cordierite. The shales of the Comus formation in several places east of the granodiorite body, for example, 

have been metamorphosed to hard microcrystalline 

dark-gray to black rocks in which small prismatic 

porphyroblasts of andalusite (commonly the variety 

chiastolite) can be recognized with the unaided eye. 

The andalusite is accompanied by muscovite instead of 

the biotite which is common in the cordierite hornfels. 

Some of the hornfels recrystallized from shales of the 

Prebel formation contain andalusite, with or without 

cordierite; in these rocks the andalusite forms anhedral 

spongy porphyroblasts that enclose minerals of the 

ground mass and is partly altered to matted aggregates 

of sericite. 

Within a few feet of the granodiorite contactgenerally less than 25 feet, most commonly 10 feet or 

less-the grain size of the hornfels increases and the 

metamorphosed rock has a granoblastic texture. Most 

commonly these hornfelses are biotite-cordierite-plagioclase-quartz assemblages, though some contain muscovite in place of the cordierite. Locally, hornfels close 

to the granodiorite contains orthoclase. In these rocks 

muscovite is not primary, though it may be present as 

a retrograde alteration product of andalusite or 

cordierite. Common assemblages of this type are 

cordierite(less commonly andalusite) -biotite-orthoclase-minor plagioclase-quartz. The biotite in those 

rocks that have been more strongly metamorphosed is 

typically dark and strongly pleochroic from moderate 

reddish brown to colorless. Plagioclase, which is 

rarely seen in the lower grade rocks, is in well-defined 

anhedral grains, mostly untwinned, and approximates 

andesine in composition. Cordierite in some specimens 

close to the granodiorite contact is partly to almost 

wholly altered to a low birefringent or isotropic substance (pinite?) and pale phlogopitic mica. The biotite in some specimens is partly altered to chlorite. 

Probably these mineral alterations are due to a lowering of the temperature following metamorphism and are 

to be regarded as retrograde metamorphic effects. 

Chemical analysis of a biotite-cordierite-plagioclasequartz hornfels is given in table 18. 

Microscopic study of the hornfels shows that the 

following minerals are commonly present in minor 

amounts: tourmaline, sphene, zircon, magnetite, and 

graphite. Tourmaline is perhaps the most widespread 

minor accessory, for nearly every thin section contains 

several grains. Most of the grains are subhedral prisms 

that are pleochroic in shades of yellow and yellowish 

brown, indicating a member of the dravite-schorlite 

series (magnesium-iron). Tourmaline has been reported elesewhere as an introduced mineral in contact 

zones; however, here it is a common detrital mineral 

in the unmetamorphosed sedimentary rocks, and as it 

is no more common in hornfels near the granodiorite 

than in the outer parts of the metamorphic aureole, it 

probably is an original constituent. Zircon, too, probably is carried over from the unmetamorphosed sedimentary rooks. 
62 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

TABLE lB.-Analyses of cordierite hornfels and schistose biotite 

hornfels 

[Samples were analyzed by methods similar to those described in U.S. Geol. Survey 

Bull. 1036-C] 

I 1 l 2 I 1 I 2 

Chemical analysis Spectrographic analysis 

[P. L. D. Elmore, K. E. White, S.D. [Harry Bastron, analyst, u.s. Geol. 

Botts, and P. W. Scott, analysts; U.S. Survey] Geol. Survey] 

Si02- _____ 63. 4 62. 9 Cu _______ 0. 003 0.004 

AbOa_ ---- 17.8 15. 8 Pb _______ . 002 2 nd 

Fe,Oa-- ___ 1.2 1.1 Mn _______ . 008 . 02 FeO ______ 3. 4 5. 2 Co _______ . 002 . 001 MgO _____ 3. 6 4. 9 NL _______ . 004 . 004 CaO ______ 1.1 2. 1 Ga _______ . 001 2 nd Na20 _____ 1. 5 1.5 Cr ________ . 006 . 007 

K20- ----- 4. 5 3.9 v ________ . 008 . 007 

Ti02--- ___ . 65 . 60 Sc ________ . 005 . 005 

P20s------ . 24 . 06 La _______ . 02 . 02 MnO _____ . 02 . 04 Ti_ _______ .4 .4 H20+ ____ 1.3 1.4 Zr ________ . 01 . 01 

002------ . 06 . 05 Be _______ . 0001 . 0001 Sr ________ . 002 . 003 Sum __ 99 100 Ba _______ .1 . 08 

Sp gr B ________ . 02 . 002 (bulk) __ 2. 57 2. 70 

Sp gr 

(powder) ____ 2. 69 2. 77 

Loss on ignition_ 1 2. 4 --------

Looked for but not found: Ag, Au, Hg, Ru, Rh, Pd, Ir, Pt, Mo, 

Re, Ge, Sn, As, Sb, Bi, Zn, Cd, Tl, In, Y, Yb, Th, Nb, U, P. 

1 Sample contained organic matter. 2 nd, no data. 

1. Cordierite hornfels from Top Row pit, near center SW}~ 

sec. 9, T. 38 N., R. 42 E.; 5 feet from granodiorite contact. 

2. Schistose biotite hornfels from Riley mine. 

An unusual type of metamorphic rock for this area, 

a fine-grained biotite-rich commonly schistose ro~k, 

occurs along the granodiorite contact at the Riley and 

the Riley Extension mines where it forms a continuous 

stratum ranging from 1 foot to 10 or 20 feet in thickness between the granodiorite and metamorphosed 

carbonate rocks. In hand specimens it is very fine 

grained, light brown with commonly a purplish hue, 

and although hard at most places where it is exposed 

underground-on surface exposures it commonly is soft 

and crumbly. Much of it has a visible foliation, but 

some lacks any apparent directional fabric. Under the 

microscope, textures are fine grained and range from 

granoblastic to schistose; the principal minerals are 

strongly colored red-brown biotite, muscovite, plagioclase, and quartz. 

Chemical analysis (table 18) shows that this rock is 

of about the same composition as the nonschistose 

biotite-cordierite-plagioclase-quartz hornfelses occurring next to the granodiorite contact elsewhere. Possibly it was formed by metamorphism of a shale bed 

under conditions of stress that promoted the development of a directional fabric and inhibited the formation or caused the destruction of cordierite or andalusite. Because of the persistence of the unit along the 

granodiorite contact, even where the contact cuts across 

the bedding, Hobbs (1948,12 p. 22; Hobbs and Clabaugh, 

1946, p. 75) concluded that this unit re.presented a 

metamorphosed · sheared zone in country rock adjacent 

to the granodiorite .. 

l'tiETAXORPHISJI. OF THE CARBONATE ROCKS 

Most of the carbonate rocks within the metamorphic 

aureole surrounding the granodiorite stock belong, like 

the peltic rocks, to the Preble formation. Carbonate 

rocks of the Comus formation and the Etchart limestone are generally farther from the stock and therefore, 

have been affected by the metamorphism to a lesser 

extent. 

The products of metamorphism of the carbonate rocks 

vary widely depending partly on their original composition and distances from the granodiorite, and partly 

on the extent to which materials have been added. At 

many places at the contact with the granodiorite, the 

carbonate rocks have been transformed to rocks which, 

from their mineralogical composition and structural 

relations, have surely resulted from the addition of some 

chemical compounds and the removal of others-principally C02. Away from the granodiorite contact, however, the relative importance of allochemical and 

isochemical metamorphism of the carbonate beds are 

not always easy to assess. Metamorphism has caused 

the formation of rocks which, given the proper amounts 

and kinds of impuritie&-such as Si02 and MgO-in 

the original sedimentary rock, could result from recrystallization without any addition of material, but with 

the loss of C02 and ~0. Addition of materials in the 

correct proportions, however, could equally well have 

caused the formation of the same kind of rocks. There 

is no certain way to tell whether or not there has been 

an introduction of material without detailed tracing of 

strata from their unaltered condition to their metamorphosed equivalents, accompanied by chemical analyses and careful measurements to determine changes 

in thickness of beds. 

Two well-defined metamorphic zones are commonly 

present where the carbonate rocks are in contact with 

the granodiorite; the tactite zone (Hess, 1919; Hess and 

Larsen, 1921, p. 251-253), composed of dark silicates 

that replace the carbonate rock; beyond the tactite, the 

zone of light-colored silicate rocks, commonly called 

calc-silicate rocks. The calc-silicate rocks in turn 

change outward into marble and silicated carbonate 

rocks. At some places a zone of marble separates the 

uSee footnote 1, page 6. 
METAMORPIDSM 63 

calc-silicate rocks from the tactite; in some places the 

tactite zone is lacking, and marble and calc-silicate 

rocks are in contact with the granodiorite. The marble 

and silicated carbonate rocks change outward into 

unmetamorphosed rocks through a zone of variable 

width around the stock. Small areas of more intensely 

metamorphosed rocks are found 3Jt a few places completely surrounded by weakly metamorphosed rocks. 

MARBLE AND BILICATED MARBLE 

The qest example of isochemical metamorphism of 

carbonate rocks is limestone that has recrystallized to 

marble. Some of the limestone beds.· that contained 

small deposits of impurities were recrystallized to marble containing various amounts of silicate minerals. 

Beds of pure limestone are recrystallized to mediumgrained, locally coarse-grained, marble around the borders of the granodiorite stock for as much as 5,000 feet 

from the contact. Limestone of the Preble formation is 

ordinarily dark gray, and though recrystallized it maintains its color until near the granodiorite contact. The 

gray marble is distinctly granular, its grain size av~raging about 0.2 to 0.4 mm. Near the stock, over distances ranging from a few tens of feet to several 

hundred feet, it is bleached to light gray or pure white, 

probably because of the removal of bituminous or carbonaceous matter which is responsible for the original 

dark color of the rock. In the outer part of the zone 

of bleaching, where removal of carbonaceous material 

is incomplete, the marble is streaked and mottled in 

gray and dark gray; locaiiy it is very friable and has a 

dark-gray or black sooty appearance, possibly representing local redeposition of carbonaceous material carried away from the bleached marble. Bleaching of the 

marble is accompanied by an increase in grain size to 

an average of 1 mm, in places coarser. Holser (1950, p. 

1069) noted a similar relation in the Philipsburg region, 

Montana, and concluded that"* * * bleaching is closely related to macrocrystallization * * *". 

Silicate minerals of metamorphic origin have been 

formed in some of the impure carbonate rocks as much 

as 5,000 feet from the nearest surface exposure of granodiorite. Most commonly, mild metamorphism of 

slightly impure limestone results in a recrystallized 

matrix of calcite containing a few percent of tremolite 

as small prismatic blades and fibers or larger megascopically visible sheaves or bundles of fibers, and with 

or without scattered grains of detrital quartz. Commonly the original bedding, if any, is well preserved 

and made visible by parallel layers of different grain 

size and mineral content. 

Shaly and silty limestones are recrystallized to finely 

layered rocks composed of alternating light-colored 

bands of calcite and tremolite, and darker, commonly 

greenish, laminae of diopside-quartz, diopside-quartzcalcite, and less commonly diopside-calcite-plagioclasequartz assembhiges. 

Diopside and wollastonite instead of tremolite are 

observed in the more intensely metamorphosed impure 

calcareous· rocks. Some of the purer slightly siliceous 

marbles are composed of calcite and wollastonite, but 

commonly wollastonite-bearing marble is found close 

to the granodiorite contact, where there is a strong possibility that the wollastonite has formed by the metasomatic introduction of silica. Light-brown isotropic 

grossularite 13 garnet accompanies the wollastonite at 

some places. 

CALC-SILICATE ROCKS 

Close to the granodiorite the carbonate rocks commonly are metamorphosed to light-colored calc-silicate 

rocks, which are mostly found closely associated with 

dark tactite. Calc-silicate rocks unaccompanied by tactite have been seen at a few places where limestones are 

in contact with granodiorite, but generally the two occur 

together. Similar rocks are mentioned in many published descriptions of contact metamorphic tungsten 

deposits, where they are commonly referred to as light 

silicate rocks or calc-silicate hornfels; these are the 

rocks of Hess' and Larsen's ( 1921, p. 251, 253) " zone 

of light-colored silicates." In addition, light-colored 

calc-silicate rocks are known at a few other places in 

the Osgood Mountains where no granodiorite is exposed. 

The calc-silicate rocks near the granodiorite constitute a clearly defined zone that generally is parallel to 

the contact of the intrusive body and closely parallel 

to the bedding of the adjoining sedimentary rocks. The 

calc-silicate zone is situated in several different ways 

with respect to the marble and tactite, but mining developments have shown that the relations at any giv~n 

locality tend to be the same throughout the deposit. 

At some places it lies between granodiorite and marble, 

in others it separates marble from the tactite zone, and 

in still other localities a belt of marble lies between the 

calc-silicate zone and tactite. No evidence of gradational relations between the calc-silicate zone and tactite 

has been seen; the contact between them is sharp. 

The calc-silicate rocks are typically well layered, 

commonly thinly layered. Many are composed of 

alternating light and dark layers than range from 

less than V2 inch to 4 inches in thickness; some of the 

layers may, in turn, be finely laminated within them-

:u1 Garnet associated with wollastonite in marble at the Riley Extension mine has a refractive index of 1.759 and a unit cell size of 11.86 A 

which indicate a high ratio of grossularite to andradite (Frietsch, 1957). 

Refractive index was measured by immersion methods ; unit cell was determined by X-ray powder methods using Cu radiation, geiger counter 

diffractometer, and' recording chart. 
64 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

selves. The layering is comp<>sitional and probably 

reflects bedding in the original sedimentary rock. Most 

of the rocks are so fine grained that microscopic exexamination is necessary to determine their mineral 

composition. 

Many of the calc-silicate rocks are composed of alternating light-gray to white layers interbedded with generally thinner greenish-gray layers. The light layers 

commonly are the softer, and on weathered surfaces 

they are depressed, whereas the greenish-gray layers 

form hard ribs. The light layers may fbe mostly marble, 

although usually they are composed of mixtures of 

calcite-wollastonite, wollastonite-diopsidic pyroxene, 

wollastonite-diopsidic pyroxene-gross u I a rite, and 

rarely, wollastonite-diopsidie pyroxene-idocrase. The 

greenish layers are composed of granoblastic assemblages of diopsidic pyroxene-plagioclase-quartz or diopsidic pyroxene-plagioclase-grossularite, less commonly diopsidic pyroxene-grossularite. 

Some calc-silicate rocks are hard microcrystalline 

hornfels with ·a light-gray porcellaneous appearance. 

These rocks have layers of more or less uniform hardness, but they -obviously are thinly layered to finely 

laminated. They are composed of microcrystalline 

granoblastic intergrowths of diopsidic pyroxene and 

plagioclase; some have wollastonite in addition. Megascopic layering is due to slight variations in the proportions of minerals, which may not be readily apparent 

under the microscope; dark-gray laminations in some 

specimens are caused by variations in amount of minute 

opaque grains, possibly carbonaceous material. 

~other variety of calc-silicate rock is light gray 

with brown himinations composed of idocrase and grossularite garnet. The light-colored layers are composed 

of interlayered calcite and wollastonite; subsidiary 

amounts of diopsidic pyroxene are associated with some 

of the wollastonite in some specimens. 

Calc-silicate rock at some places contains some interstratified dark biotite and cordierite hornfels in thin 

laminae or in layers an inch or so in thickness. 

The composition of clinopyroxene in some of the calcsilicate rocks was determined by measurement of the 

refractive index f3 and the optic angle, used in combination with Hess' (1949, pl. 6, p. 641) composition diagram for the diopside-hedenbergite series. In the light 

layers where wollastonite is the predominant mineral, 

the intergrown pyroxene is diopside, whose refractive 

index is ,8=1.676 and 2V=57°; in the greenish-gray 

layers it is salite-refractive index {3= 1.699 to 1.703. 

Two generations of pyroxene can be recognized in some 

specimens. For example, in one dominantly pyroxene 

rock, early fine-grained clear colorless diopside is replaced by co.arser dusty slightly greenish salite. 

Where garnet occurs in the calc-silicate rocks it is 

light brown, like that in silicated marble, and isotropic. 

Typical garnet from calc-silicate rock at the Pacific 

mine has a refractive index of 1.757, and unit cell of 

11.85 Ar which indicate grossularite (Frietsch, 1957). 

The light-colored calc-silicate rocks near the granodiorite contact, which are commonly associated with 

tactites and their acJCOmpanying scheelite deposits, were 

formed from well-bedded carbonate rocks. It is difficult, however, to say how much of the transformation 

was acoomplishad by heating rocks o£ the appropriate 

composition without addition of material, and how 

much of the metamorphism was due to metasomatic 

addition of some materials and loss of others. The 

interbedding of wollastonite and wollastonite-bearing 

carbonate layers with layers containing diopsidic pyroxene strongly suggests the metamorphism of interbedded impure limestone and dolomitic limestone. The 

thin layers of grossularite and idoorase in some calcsilicate rocks may originally have been aluminous shaly 

partings that reacted with adjoining calcareous layers. 

Field data suggesting that formation of the calcsilicate rocks was aided by addition of material, mostly 

silicia, are the occurrence of irregular-shaped replacement bodies of wollastonite in otherwise pure marble 

found at several places near calc-silicate rocks and the 

oommon close association of a zone of light-colored 

calc-silicate rooks with dark tactities, which have been 

formed by addition of material. There is some indication that the calc-silicate rocks were formed prior to the 

formation of tactite, which is certainly the result of 

large-scale addition of material, because at some places 

replacement veins of ta;ctite cut calc-silicate rock (fig. 

8). 

Some light-colored calc-silicate rooks have been 

formed elsewhere in the Osgood Mountains away from 

the main granodiorite contact. For some there is 

evidence of a granitic intrusive nearby or at shallow 

depth ; for others there is no direct evidence for the 

cause of the metamorphism, but it is assumed that the 

heat and solutions responsible came from a buried intrusive body nearby, or they traveled outward from 

granitic bodies along a favorable structure. 

In the extreme northeast corner of the quadrangle, 

part of the Etchart limestone has been metamorphosed 

to a calc-silica.te hornfels (pl. 1). In two irregularshaped areas, light-gray to white microcrystalline 

commonly porcel,anoous-appearing rock ·apparently 

overlies limestone that has not been much recrystallized. 

Because of its fineness of grain little can be seen in the 

rock, even with a hand lens, except for fibers of tremolite in some specimens and a faint layering in others. 

11' See footnote, p. 63. 
METAMORPmSM 65 

FIGURE 8.-Calc-silicate rock cut by tactite at the Pacific mine pit. 

gd, granodiorite; T, tactite; csr, calc-silicate rock. 

Under the microscope, however, the rock is seen to be a 

fine-grained ( 0.05 mm. average) crystalloblastic diopside-quartz-plagioclase rock, with a few percent of 

orthoclase, sphene, and some minute scattered grains of 

zircon. Some specimens contain a little tremolite and 

chlorite on the borders of small cavities containing 

calcite. 

PresumB~bly the calc-silicate hornfels· is metamorphosed calcareous or dolomitic siltstone and shale, 

which is interbedded with essentially unmetamorphosed 

limestone. The 31rea of hornfels is a mile or more from 

the main granodiorite stock, but one or two very small 

granitic bodies, not shown on the map, are exposed in 

the hornfels area. These and the rather extensive 

area of hornsfels suggest that an intrusive body underlies the area at no great depth. 

In the NElf<t sec. 25, T. 38 N., R. 41 E., a sandy 

dolomitic member of the Etchart limestone has been 

metamorphosed to a fine-grained diopside-q~artzplagioclase hornfels. Near by, some of the carbonate 

rock is recrystallized to tremolite marble. Here the 

hornfels can be related to the dikes and apophyses of 

granodiorite which intrude the rock. 

In the NE1,4 sec. 1, T. 38 N., R. 41 E., again a short 

distance below a thrust fault, in a "hot spot" a few 

yards square, limestone of the Preble formation has 

been metamorphosed to diopside-wollastonite-grossularite hornfels. Here the nearest outcrop of the main 

granodiorite stock is nearly half a mile to the east. 

TACTITE 

At many places where carbonate rocks have been 

intruded by granodiorite, a zone of dark silicate rock 

· has heen formed at the contact. This zone, commonly 

lying between the granodiorite and the zone of lightcolored calc-silicate rocks or marble, is the innermost 

zone of cont31ct metamorphism in the carbonate rocks. 

The general term, tactite (Hess, 1919, p. 378), is oommonly used to designate the dark silicate rock, though 

the term skarn has about the same meaning. In the 

Osgood Mountains, as in many other contact metamorphic tungsten deposits, most of the scheelite is contained in tactite, though not all the tactite carries 

scheelite. 

Unlike the zone of calc-silicate rock ·and marble, the 

limits of the tactite zone are clearly defined. Although 

it may be irregular, the contact between tactite and 

calc-silicate rook or between tactite and marble is 

abrupt and easily recognized. The inner limit between 

tactite and granodiorite is sharp and clean at many 

places, but it may be less abrupt where reaction and 

late stage alteration effects have resulted in a hybrid 

zone a few inches wide. 

The tactites characteristically are dark heavy rocks of 

relatively simple mineral composition. Mostly they 

range from fine to medium in grain, and commonly they 

are massive; but in many places a compositional layering can be seen that is parallel to the bedding in the 

adjoining carbonate and calc-silicate rocks. The predominant constituents are calc-silicate minerals, 

which may include garnet, clinopyroxene, actinolitic 

amphibole, epidote, and idocrase; but typically only 

one or two mineral species compose the bulk of the rock. 

Minor quantities of quartz and calcite are found in 

nearly every specimen. Perhaps the most common rock 

types are garnet-pyroxene tactites; almost monomineralic garnetites have been formed in many places; and 

garnet-actinolite tactites are commonly encountered. 

Less abundant types are nearly pure actinolite tactites, 

pyroxene-quartz rocks, and varieties in which epidote 

is a plentiful constituent. An uncommon variety of 

tactite of only local occurrence is composed p~ominantly of dark grayish olive-green pyroxene without 

garnet. 

Garnet of the tactites is dark reddish brown to dusky 

red, in contrast to the pale brown or honey-colored 

garnets of the silieated marble and calc-silicate rocks. 

The color also reflects the contrast in composition, for 

the garnet of the tactites contains substantial amounts 

of ferric iron-that is, the ratio of andradite ( 3Ca0 

· Fe20 3 ·3Si02 ) to grossularite (3Ca0· AlzOa ·3Si0z) is 

high. Garnets in contact-metamorphosed carbonate 

rocks commonly eontain very small amounts of FeO, 

MgO, and MnO (Kennedy, 1953, p. 15). The measurements of refractive index and size of the , unit cell as 
66 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

determined by X-ray measurements show that the ratio 

of andradite to grossularite is high (Frietsch, 1957). 

Refractive indea: 

1---------------------------------- 1.810-1.820 

2---------------------------------- 1.811 

3---------------------------------- 1.815 

4---------------------------------- 1.824 

5---------------------------------- 1.861 

Unit cell 

(A) 

11.92 

11.97 

11.89 

11. 95 

11. 95 

Almost without exception zoning is visible in the garnet, 

in some specimens both under the microscope and megascopically. The zoning is made apparent in part by 

color differences; the central parts of zoned crystals are 

commonly nearly colorless, indicating a lower iron content than the outer parts, which are colored in shades of 

of pale brown to yellow. Under crossed polarized light 

the garnet in most specimens is anisotropic, and the 

zoned structure is made strikingly apparent by narrow 

concentric zones of varying birefringence, ranging 

from 0 to about 0.008. No clearly defined association 

of isotropic or anisotropic garnet with particular kinds 

of tactite can be established, but there is some evidence 

that anisotropic garnet is a late-stage modification of 

the isotropic variety. Isotropic garnet occurs with unaltered pyroxene, and tactites in which it occurs lack 

epidote, quartz, and sulfide minerals, which are known 

to be late-stage minerals elsewhere in the tactite zone. 

Some confirmation of this apparent relationship was 

observed in a specimen of an isotropic garnet-pyroxene 

tactite where the garnet adjacent to a quartz-calciteepidote veinlet is slightly sheared and anisotropic. 

Clinopyroxene of the diopside-hedenbergite series 

occurs as dark grayish-green layers in garnet-pyroxene 

tactite and as small subhedral granules poikiliticaHy 

enclosed in the garnet. From the mutual boundary 

relations it is not clear that pyroxene is earlier than 

garnet, but in a few specimens garnet veinlets cut 

across the pyroxene layers. Viewed under the ~icroscope, the clinopyroxene is pale green to almost Golorless. Approximate compositions were determined from 

the refractive index {3 (Hess, 1949, p. 641) and measurement of the optic angle. From one specimen to another 

the clinopyroxenes range from salite to hedenbergite, 

but the composition in an individual sample is uniform, 

as evidenced by the constant optical properties. The 

refractive index f3 of the samples studied ranges from 

1.694 to 1.727, and 2V ranges from 59° to 62°, indicating 

a variation in the diopside: hedenbergite ratio of from 

approximately 30: 70 to 15: 85 (Hess, 1949, p. 641). 

In much of the tactite, clinopyroxene is partly or 

entirely uralitized. The alteration product is a fibrous 

pale-green pleochroic amphibole, probably near actinolite in composition. A little chlorite may accompany 

this secondary amphibole. An actinolite tactite composed of greenish-gray to dark greenish-gray matted 

fibrous actinolite has been formed in some places, presumably by the alteration of a pyroxene tactite. In 

some specimens the garnet is partly replaced by actinolitic amphibole. At ·a few places, principally at the 

Granite Creek mine, the pyroxene is replaced by a dark 

hornblende instead of actinolitic amphibole. The following optieal properties were observed in the hornblende: 2V=35° approx.; extinction Z/\a=l8° approx.; pleochroism, X=yellow, Z=dark blue green; 

dispersion, r< v strong. 

Coarsely crystalline ealcite in small amounts is found 

in nearly all the tactite. It fills interstices between garnet erystals, locally corrodes the crystal faces, and occupies zones in skeletal garnet crystals. Some calcite is 

intergrown with and partly replaces ·actinolitic amphibole, and, along with quartz, occupies veinlets that traverse the tactite. Its relations indicate that it was 

among the last minerals to form. 

The occurrence of epidote is sporadic. It is not found 

in most of the tactite; however, it is abundant at some 

localities and minor amounts are found in veinlets in 

some specimens. Textural relations indicate the epidote 

crystallized late, essentially simultaneously with calcite. 

Quartz, like calcite, is almost ubiquitous in the tactite; 

it fills veinlets and interstices, and replaces earlier 

formed minerals. It is clear and glassy, and much of 

it is fairly coarse grained. Rather commonly, the tactite next to the granodiorite contact is ·abundantly 

veined and extensively replaced by quartz over a zone 

a few feet wide. In these places the granodiorite, 

too, may be heavily impregnated with quartz. Relations with respect to calcite are not altogether clear, 

but the evidence indicates that, though some may be 

simultaneous with the introduction of calcite, the bulk 

of the quartz is later and, except for the sulfide minerals, 

is the last miner,al to erystallize. 

The tungsten ore mineral, scheelite, is an accessory 

constituent of low concentration in the tactite. Most 

commonly, it occurs as small discrete grains that range 

from 0.5 mm or less to a maximum of 1 or 2 mm across in 

the greatest dimension. Exceptionally, grains as large 

as 2 mm have been noticed in local concentrations. The 

relations of scheelite to other minerals of the tactite are 

discussed more fully in the section on mineral deposits 

(p. 84). The paragenesis affords evidence that ,scheelite was deposited during most of the episode in which 

tactite was being formed, and continued into the stage 

of late quartz deposition. 

Traces of idocrase are found in some of the tactite. 

Its relations to the other minerals is uncertain, but it 

occupies late veinlets in some specimens. 
METAMORPmSM 67 

The origin of taetite by replacement of marble and 

calc-silicate rocks is proved at many places by the field 

relations. Where it is found, it is always on or near 

the contact between granodiorite and the carbonate 

rocks; tongues and cr~cutting replacement bodies of 

tactite occur in the marble and calc-silicate rocks. It 

is difficult to assess the relative extent to which tactite 

has been formed by the replacement of marble rather 

than by replacement of light silicate rock. A some 

places the tactite and calc-silicate rocks are in contact, 

but original marble may have been completely replaced 

by tactite. At some places tactite obviously replaces 

marble. And examples of crosscutting replacement 

bodies of tactite in calc-silicate rock have been seen. 

Recrystallized but unsilicated marble may have been 

more susceptible to replacement by tactite because it 

was more permeable to the transforming solutions, 

whereas fine-grained calc-silicate rock would be less 

~asily replaced, though one might expect that the platy, 

well-bedded structure in most of the calc-silicate rocks 

would probably afford suitable avenues for the introduction of the metasomatizing fluids. On the other 

hand, unsilicated marble would be more reactive with 

respect to the fluids than the calc-silicate rocks. 

The consistent occurrence of tactite at or close to the 

granodiorite contact strongly suggests that temperature 

was an important controlling factor in the formation 

of tactite. It is to be expected that a steep temperature 

gradient outward from the granodiorite contact existed 

at the time of intrusion, and tactite formed where the 

temperature was highest-next to the granodiorite. The 

abrupt outer boundary of the tactite may also have been 

governed by the temperature distribution. Structural 

relations at the time of metamorphism were ·also important; that is, the rocks that were metamorphosed to 

tactite were situated so as to be available for reaction 

with the magmatic fluids when they were given off. 

These structural relations are discussed more fully in 

the section on tungsten deposits (p. 85). 

The chemical changes involved in the conversion of 

limestone to tactite are exemplified in table 19, in which 

the compositions of marble and garnet-pyroxene tactite 

are compared, and in figure 9, which affords a visual 

comparison of the amounts of constituents gained and 

lost in the transformation. As might be inferred from 

the prevalence of garnet and clinopyroxene in the tactite, silica, iron, magnesia, and alumina have been added, 

and large amounts of carbon dioxide and considerable 

calcium oxide have been subtracted. 

M:ETAl'tiORPHISl'tl OF PALEOZOIC VOLCANIC ROCKS 

Most of the volcanic rocks of pre-Tertiary age in the 

Osgood Mountains are beyond the metamorphic aureole 

TABLE 19.-Analyses of lime::Jtone and garnet-pyroxene tactile 

[Samples were analyzed by methods similar to those described in U.S. Geol. Survey Bull. 1036-C; P. L. D. Elmore, K. E. White, S.D. Botts, P. W. Scott, analysts, U.S. Geol. Survey] 

Limestone Tactite 

2 3 

Si02--------------------------- Al203 ________ - _- _- _- _- _--- _- _- _ 

Fe0 Fe20a-------------------------- __________________________ _ ~gO __________________________ _ Cao __________________________ _ l'razO _________________________ _ K 2

0 __________________________ _ 

Ti02 __________________________ _ 

P205---------------------------

~nO ____ - _- _- _- _____ - _- ___ - _- _ H20 __________________________ _ 

C02------------------------ ----

5. 8 

. 80 

. 43 

. 01 

. 26 

52. 7 

. 07 

. 12 

. 04 

. 09 

. 00 

. 01 

40. 1 

Sum________________ _ _ _ _ _ 100 

Sp gr (lump____________________ 2. 58 

Sp gr (powder)___________________ 2. 71 

Porosity (calc) __________ percent__ 9. 71 

2. 4 

. 34 

. 10 

. 02 

. 42 

54. 9 

. 06 

. 02 

. 02 

. 10 

. 01 

. 02 

42. 6 

101 

2. 34 

2. 70 

9. 63 

1. Limestone of Preble formation; NE~ sec. 1, T. 37N., R. 41 E. 

2. Limestone of Preble formation; NE~ sec. 1, T. 37 N., R. 41 E. 

3. Dark, layered garnet-pyroxene tactite, Pacific mine. 

42. 2 

4. 1 

12. 7 

5. 7 

5. 6 

26. 6 

. 17 

. 06 

.10 

. 21 

1.4 

. 95 

. 47 

100 

3. 36 

3. 52 

4. 54 

that surrounds the granodiorite stock. In the northern 

part of the range, however, some of the altered volcanic 

rocks have been metamorphosed by intrusion of the 

granodiorite. The metamorphism has not been very 

intense: recrystallization has been slight or negligible 

and original textures and structures are well preserved; 

but new minerals have been formed which are indicative 

of a higher metamorphic grade than that attained by 

the rest of the altered volcanic rocks. 

Volcanic rocks most affected by the contact metamorphism are part of the Farrel Canyon formation found 

in the low hills north of the quadrangle boundary. 

Some are exposed inside the quadrangle boundary in 

sec. 20, T. 39 N., R. 42 E. Megascopically, they look 

much the same as the other altered volcanic rocks-that 

is, dark greenish gray, hard, rough surfaced, and fine 

grained to microcrystalline. Original porphyritic textures with dull gray feldspar crystals can be recognized 

in some, and fragmental and amygdular structures are 

preserved in others. Seen under the microscope, however, they differ from the ordinary low-grade altered 

volcanic rocks in the absence or scarcity of chlorite 

and the presence of metamorphic pyroxene, actinolitic 

amphibole, and biotite. For example, in a fragmental 

volcanic rock of intermediate composition, porphyroblasts of colorless clinopyroxene have been formed in a 

Inicrocrystalline granoblastic groundmass of plagioclase 

and pyroxene; a flow rock, probably also of intermediate 

composition, has amygdules of crystalline calcite bordered by pale-green clinopyroxene set in a fine-grained 

groundmass of small cloudy plagioclase laths, inter-
68 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

1 

SiO 2 ~ ~"""'~~~~~~'*":""""'""""'~""'""'~""'"m+"""""'""~ 

1 

Fe 2 

3 

1 

MgO 2 

3 

1 

200 400 600 800 1000 1200 

AI203 2 ~~~.,..,.., 

3 ~~=±~--~----L_--~----~ 

1 

Ti0 2 2 

3 

100 200 300 400 500 

MILLIGRAMS PER CUBIC CENTIMETER 

10 

1 and 2. Unaltered limestone of Preble formation 

3. Garnet-pyroxene tactite 

MILLIGRAMS PER CUBIC CENTIMETER 

1400 

FIGURE 9.-Graph showing gain and loss of rock constituents in conversion of limestone to garnet-pyroxene tactite. 

stitial fine-grained pyroxene and minor sphene, actinolitic amphibole, and clinozoisite. An example of a 

metamorphosed more silicic volcanic rock has a relict 

porphyritic structure consisting of phenocrysts of 

granular quartz and subhedral to euhedral phenocrysts 

of sodic feldspar in a very fine grained groundmass of 

abundant light-brown biotite and nearly unresolvable 

granular feldspar and quartz. 

ENDOMORPHISM OF THE GRANODIORITE 

The marginal facies of the granodiorite (p. 44) exhibits endomorphic effects where the granodiorite ~s in 

contact with marble, calc-silicate rocks, or tactite. The 

reaction zone is narrow, most commonly 6 inches to 2 

feet in width, but may be as much as 10 feet or as 

little as a fraction of 1 inch. West of the Granite 

Creek mine, dikelike offshoots into limestone from the 

main body of granodiorite are entirely composed of 

granitic rock similar to that in reaction zones elsewhere. 

Megascopically, the rock of the reaction zone is greenish and has a granitic texture. In some places an abrupt 

gradation from granitic rock into the wallrock is 

visible, but elsewhere the contact is sharp, though microscopic examination of specimens taken across a megascopically sharp·contact shows gradation. The rock is 

characterized by diopsidic pyroxene as the principal 

--mafic mineral instead of hornblende or biotite. Most 

specimens that were examined microscopically also 

contain some hornblende and rarely biotite intergrown 

with pyroxene in such a way as to show that some of the 

pyroxene was formed by replacement of these earlier 

crystallized minerals. The clinopyroxene has two main 

variations of habit: on the granodiorite "side" the 

crystals are equant to subequant and intergrown with 

plagioclase and quartz; toward the contact it commonly 

is in anhedral, more or less rounded granules which are 

poikilitically enclosed by feldspar and quartz. The 

amount of pyroxene is variable but equals and commonly 

is more abundant than hornblende and biotite in the 

normal granodiorite. Quartz, plagioclase, and orthoclase make up the balance and bulk of the rock. Plagioclase is in subhedral to euhedral crystals, shows prominent normal zoning, alteration to gray translucent 

kaolinitic ( ~) material, some sericite, and in some specimens contains small granules of clinozoisite. The unaltered crystals range from An4o to Anso (andesine) ; in 

some specimens the plagioclase has rims of oligoclase 

(An22-An27 ) that have corrosive boundaries against the 

more calcic cores, which in some specimens are altered 

in contrast to fresh rims. Orthoclase and quartz are 

anhedral and interstitial; orthoclase encloses, corrodes, 

and partly replaces plagioclase in some specimens. The 

amount of orthoclase is generally the same as in the 

normal granodiorite-approximately 10 to 12 percentbut in some specimens it is more plentiful; in the rock 

that forms dikelike projections west of the Granite 

Creek mine it amounts to about 35 percent. Sphene, 

commonly in diamond-shaped crystals, is the most plentiful minor accessory; apatite is ubiquitous but not 

plentiful; and only trace amounts of magnetite are 

visible. 

Formation of the pyroxene-bearing granitic rock is 

attributed to enrichment of CaO in the granodiorite by 

mutual reaction of the solidifying magma with limestone at the contact, aided, perhaps, by limited physical 

incorporation of the wallrocks by the magma. The 

modification of the granodiorite in border zones adj acent to limestone is interpreted to be the result of reactions that took place as a consequence of the increase 

of CaO in the magma, which suppressed the formation 

of biotite and hornblende and caused diopsidic pyroxene 

to crystallize instead. Concomitantly, there was a loss 

of Al203 (Mg, Fe) 0, and Si02 to the wallrocks, where 

garnet and clinopyroxene crystallized. It seems unlikely, however, that the great volume of tactite and 

light calc-silicate rocks in the contact zones were formed 

by transfer of material from only the very narrow 

selvage on the border of the granitic body. The increased amount of orthoclase in some parts of the reac-
STRUCTURAL GEOLOGY 69 

tion zone is possibly due to release of K20 that normally 

would have been contained in biotite; Ti02 , freed by 

noncrystallization of biotite and hornblende, combined 

with the added lime to form sphene. 

Similar reaction products have been formed on the 

border of the Boulder batholith in Montana, according 

to Knopf (1957, p. 97-98). Others, including Eskola. 

(1914), Nockolds (1934), Joplin (1935) and Tilley 

(1949) have described pyroxene-bearing granitic rocks 

in selvages of normally biotitic and (or) horniblendic 

granitic rocks against carbonate rocks. All attribute 

the mineralogical changes in the granitic rock to the 

increase of lime in the granitic magma. Eskola ( 1914, 

p. 61) ascribed the crystallization of diop!>ide "* * * to 

the fact that the amount of alumina was insufficient to 

form anorthite with the lime present * * *" and the 

OaO combined with FeO and MgO that normally 

would have formed hornblende, to form pyroxene. 

Joplin (1935, p. 110-112) regarded diopside as forming 

from the (Fe, Mg)O that normally would form biotite 

and hornblende, the released K20 being free to form 

orthoclase in the contaminated rock, and the Ti02 

combining with CaO to fonn sphene. Tilley (1949, 

p. 88-92) showed that alumina was transferred from 

the granite at Skye, which led to the precipitation of 

an "* * * effectively non-aluminous member of the 

reaJCtion series (pyroxene) * * *" in place of the 

aluminous types, biotite and hornblende. 

STRUCTURAL GEOLOGY 

The pages that follow include rather detailed descriptions of the folds and faults that have deformed and 

displaced the rocks of the Osgood Mountains and the 

Hot Springs Range. The chapt~r concludes with an 

interpretation of the structure and geologic history and 

their relation to the regional geology. The internal 

structures and structural relations of the granodiorite 

are excluded from the discussion, for they have been 

described in a preceding section, and minor structural 

features related to ore deposition will be set forth in the 

chapter on mineral deposits. 

A glance at the geologic map (pl. 1) shows that the 

main structural trends in the Osgood Mountains and 

the Hot Springs Range are closely parallel to the trend 

of the ranges. In the central and south parts of the 

Osgood Mountains the bedding of the sedimentary 

rocks, axes of folds, and the major thrust and highangle reverse faults have a predominant strike near 

N. 50° E. The strikes of the main structural elements 

in the north half of the range gradually become more 

northerly and are virtually north -south in the north 

end of the range. In the Hot Springs Range, where 

the main structural features arre folds in the Harmony 

formation, the trends of the fold axes range from 

about north -south in the southern parrt of the range, to 

slightly east of north in the northwestern part. The 

granodiorite stock in the northeastern part of the Osgood Mountains is elongate in a north-northeasterly direction, the predominant structural trend in this part of 

the range. Within both rarnges steeply dipping, mostly 

vertical, northwest-trending cross farults cut the rocks 

nearly perpendicular to the northeast struetures. 

Locally, in both ranges, vertical or steeply dipping 

frontal faults parallel the ranges and are among the 

youngest structurnl features of the area. 

FOLDS IN THE OSGOOD MOUNTAINS 

Erosion of younger rocks has revealed a rather broad 

anticline in the Osgood Mountain quartzite and the 

overlying Preble :formation in the central and southcentral part of the range (pl. 1, sections B-B', 0-0'). 

The Preble formation is exposed in normal position on 

the west limb of the fold for a short distance near the 

mouth of Goughs Canyon; elsewhere the anticlinal 

structure is inferred from bedding attitudes in the 

Osgood Mountain quartzite. North of the northweststriking fault that crosses the range between Goughs 

Canyon and Hogshead Canyon, the fold is concealed beneath younger thrust phvtes and unconformably overlying strata of Pennsylvanian age. Tertiary volcanic 

rocks conceal the south end of the anticline. The surface trace of the fold axis is sinuous arnd tends to be west 

of the range crest in the south; in its northern part 

it is straighter and lies more or less along the crest 

of the rarnge. The axial plane is vertical or dips 

steeply westward. 

On the limbs of the anticline, beds in the Osgood 

Moruntain quartzite are markedly drag folded. The 

axial planes of the drag folds are steeply inclined east 

and west on the corresponding limbs of the major fold. 

The amplitude of most of the subsidiary folds is from 

a few foot to several tens of feet. 

Throughout most of the Osgood Mountains, the Paleozoic sedimentary rocks younger than the Osgood 

Mountain quartzite are steeply tilted and tightly folded. 

Mostly, however, it is impossible t<> recognize and trace 

any well-defined persistent anticlines and synclines, 

and much of this folding is related to the thrust faults, 

which cut and displace most of the younger strata. 

AGE OF THE FOLDING 

The deformation responsible for the development of 

the major anticline took place prior to deposition of the 

Lower Pennsylvanian beds. The Osgood Mountain 
70 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

quartzite, the Preble formation, and possibly some 

younger strata, were folded; the Preble formation and . ' 

any younger beds that may have been present, were 

eroded from the up arched fold; and then strata of 

Pennsylvanian age were deposited on the Osgood Mountain quartzite. Evidence for a second episode of deformation in post-Pennsylvanian time that caused 

minor in-folding of the quartzite and Pennsylvanian 

limestone on the limbs of the anticline is found at a 

few places. 

THRUST FAULTS IN THE OSGOOD MOUNTAINS 

A thrust zone along the west side of the range is the 

dominant structural feature of the northern two-thirds 

of the Osgood Mountains. Here, roc}rs of Cambrian, 

Mississippian, Pennsylvanian, and Permian age have 

been thrust over one another in a pattern resembling a 

large imbricate thrust, although the rather poor exposures and inability to trace the thrusts into other 

areas make it difficult to substantiate such an interpretation. Thrust faults are also exposed along the 

crest and east side of the Osgood Mountains, but here 

they are less numerous and their origin is more easily 

interpreted. Thrust faults have not been recognized 

in the Hot Springs Range within the Osgood Mountains 

quadrangle, although one was mapped in the northern 

part of the range by Willden (in press) and the Valmy 

formation on the east side of the range is believed to 

have been brought into the area on a major thrust fault. 

VALMY THRUST PLATE 

The Valmy formation is very different lithologically 

from its partially temporal equivalent, the Comus formation, and must have been deposited under altogether 

different conditions. The Comus formation is believed 

to be autochthonous or parautochthonous, and we have 

concluded that the Valmy formation has been brought 

into the area in the upper plate of a thrust. This thrust 

fault is concealed in the Osgood Mountains quadrangle 

because of downfaulting, but probably it is equivalent to 

the Roberts Mountains thrust fault (Merriam and 

Anderson, 1942, p. 1693-1706), which is one of the important structural elements of north-central Nevada 

(Gilluly, 1954; Roberts and others, 1958, 2817-2820, 

2850-2854). The Roberts Mountains fault is pre-Middle 

Pennsylvanian, probably Late Devoni·an or Early Mississippian (Roberts and others, 1958, p. 2852-2854). 

TWIN CANYON FAULT 

The Twin Canyon thrust is named for Twin Canyon 

on the east side of the Osgood Mountains, where it is 

well exposed. It crops out for about 4 miles between 

Hogshead Canyon at the north and Garden Spring 

(sec. 15, T. 37 N., R. 42 E.) at the south with an average strike of approximately N. 40° E. The fault dips 

southeastward and the angle becomes increasingly steep 

from south to north: north of Garden Spring the sinuous trace denotes a gentle dip; one-half mile south of 

Twin Canyon it dips approximately 35°; at Twin Canyon a dip of 65° was measured; and toward the north 

end of its outcrop it is nearly vertical. 

The Twin Canyon thrust fault is properly designated 

a thrust only in the area south of Twin Canyon; north 

of Twin Canyon it is a high-angle reverse fault. The 

upper plate or hanging wall is Osgood Mountain quartzite, which is thrust over Preble formation for approximately 1112 miles north of Garden Spring and which 

overrides the Twin Canyon member of the Osgood 

Mountain quartzite for the rest of the distance to Hogshead Canyon (pl. 1, section 0-0'). In the vicinity of 

Twin Canyon the rocks in the lower plate are folded 

into an asymmetric syncline whose axial plane dips 

southeast ; beds of the southeast limb of the syncline, 

which are adjacent to the fault, are overturned to the 

northwest in places. 

The displacement on the Twin Canyon is not accurately known, but a few thousand feet of movement 

would easily account for repetition of the Osgood Mountain quartzite over the Preble formation and the Twin 

Canyon member. The fault ·appears to have originated 

by fracturing along the attenuated common limb of 

an asymmetric syncline and anticline, with thrusting 

of the southwest limb of the anticline over the syncline 

caused by continued compressional deformation. The 

thrusting is olderthan Middle Pennsylvanian because 

the Battle formation has been deposited across the trace 

of the thrust in the southeastern part of sec. 3, T. 37 

N.,R.41E. 

ADAM PEAK THRUST 

The Adam Peak formation has been thrust over the 

Etchart limestone along the crest of the Osgood Mountains from the head of Perforate Canyon northward 

to the north side of the divide between Goughs Canyon 

and Hogshead Canyon. This thrust is named the Adam 

Peak thrust because the principal upper plate unit is the 

Adam Peak formation. The trace of the thrust can be 

only approximately delineated because it is concealed 

by thick overburden in most places. East of Goughs 

Oanyon the trace indicates that the fault is nearly flat 

lying or dips gently northeast. The western part of the 

contact in the SW% sec. 23, T. 38 N., R. 41 E., seems 

to be about vertical and probably is a high-angle fault 

that has intersected the thrust. North of the divide 
STRUCTURAL GEOLOGY 71 

between Goughs and Hogshead Canyons the Adam Peak 

thrust plate is overridden on the east by the Granite 

Creek thrust, and on the west by a thrust slice of Harmony formation (pl. 2, section B-B'). South of the 

divide, the Adam Peak thrust plate is bounded on the 

west by the trace of the Adam Peak thrust and on the 

east by a high-angle (probably normal) fault. This 

high-angle fault either marks the boundary between 

the Battle and Osgood Mountain formations or separates steeply dipping from gently dipping Battle. 

The structure in the Adam Peak plate has not been 

worked out in detail, but generally the beds in the Adam 

Peak formation are steeply inclined, whereas the 

Etchart limestone, below the thrust, is nearly horizontal 

or gently inclined. Some small tight folds, whose axial 

planes dip steeply west, have been recognized at a few 

places, and overturned beds dip steeply east at several 

places along the east boundary of the plate, where it 

is overridden by the Preble formation on the Granite 

Creek thrust. 

The likelihood of considerable horizontal displacement on the thrust is indicated by the approximately 

equivalent age of quite dissimilar units in the Adam 

Peak and Etchart formations. The Battle formation, 

however, underlies both formations and is to all appearances the same regardless of the overlying rock. 

GRANITE CREEK THRUST 

The Granite Creek thrust fault, so-named because 

it is well exposed in the head of Granite Creek (NE% 

sec. 25, T. 38 N., R. 41 E.), is a prominent feature on the 

geologic map and can be plainly seen in the field where 

it crosses the high part of the range north of Hogshead 

Canyon. In the northern part of sec. 25, T. 38 N., R. 41 

E., contorted and generally steeply dipping beds of the 

Cambri·an Preble formation have been thrust over gently northward-dipping strata of the Battle formation 

and Etchart limestone (fig. 10). Southward the thrust 

carries the Preble formation over the Osgood Mountain 

quartzite; northward it overrides the Adam Peak formation (pl. 2, section B-B') and in sec. 12, T. 38 N., R. 

41 E., it is overridden by the Harmony thrust plate. 

The abrupt changes in direction of the trace of the 

thrust fault north of Hogshead Canyon (pl. 2) are 

caused by intersection of a warped fault surface with 

the uneven surface of the ground. The fault surface 

dips approximately 20° N. where it crosses the spur 

that projects south into sec. 25 from the main ridge. 

In the head of Granite Creek the fault surface has an 

anticlinal warp that plunges northward, carrying the 

fault trace around through 180°; south from here the 

fault dips moderately to steeply eastward. Where the 

fault rises over the Adam Peak formation and crosses 

the main ridge it becomes steeper and, going through 

a right-angle turn, strikes northward and dips eastward 

approximately 35°. In the head of East Fork of Eden 

Creek another warp gives the fault surface a gentler 

dip, and carries the Preble across the Adam Peak 

formation. 

The edge of the fault plane is exposed in the head 

of Granite Creek and at a few places on the west side 

of the Adam Peak ridge. Wherever the contact can 

be seen it is sharp and tight, but with careful examination a thin seam of crushed rock can usually be found, 

and at some places the bedding in the rocks above the 

fault is considerably contorted. No marked brecciation 

of rocks above or below the fault has heel?: recognized. 

PEAK 6887 THRUST 

Along the crest of the Osgood Mountains near the 

north boundary of the quadrangle, a sequence of 

strongly deformed phyllite, hornfels, and thin-bedded 

recrystallized limestone of the Comus formation is 

thrust over the Preble formation. From its surface 

trace, it is estimated that the thrust dips approximately 

10° to 15° NE. Near the northern boundary of the 

quadrangle the plate is overridden by the Farrel Canyon 

formation and terminated by normal faults. 

In detail, the rocks of the Comus formation on the 

upper plate are rather strongly deformed, particularly 

the thin-bedded limestones which commonly are intricately crumpled; exposures are not abundant enough 

t<;> permit the structure to be fully worked out, but a 

synclinal fold plunging northeast is indicated by the 

plotted observations of bedding attitudes. The syncline 

seems to continue southwestward in the Preble formation. Fine-grained intrusive rocks are more plentiful 

in the sequence of rocks above the contact, and in places 

sheetlike intrusive bodies occupy the contact or occur in 

the upper plate close to the contact, indicating that the 

contact was a surface along which magma found relatively easy access. 

IMBRICATE THRUST ZONE IN OSGOOD MOUNTAINS 

A complex pattern of overlapping thrust plates is 

exposed along the west side of the Osgood Mountains. 

Individual plates are continuous north of Goughs 

Canyon, but to the south they are represented by generally isolated klippen of various sizes. The thrusts 

are approximately parallel: their traces trend northeast to north, and they dip gently to moderately west. 

The general parallelism of the faults and their pattern 

of distribution suggests that they may have moved 

essentially simultaneously. 
72 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

These faults in their approximate order of superposition from bottom to top are : the Preble, Etchart, Harmony, Goughs Canyon, and Farrel Canyon thrusts. All 

these faults are named after the dominant rock unit on 

their upper plate. 

PREBLE THRUST PLATE 

The Preble thrust is the lowermost of these thrusts. 

Its upper plate consists of exceedingly contorted 

phyllitic shale provisionally classified as Preble formation of Cambrian age. The thrust has overridden the 

Etchart limestone and, at a few places, the Osgood 

Mountain quartzite. The thrust plane locally is somewhat contorted, but in general it strikes northeast and 

dips gently northwest at a.n estimated 15° to 20°. The 

relatively thin thrust plate is estimated to be between 

100 and 300 feet thick where it intersects the surface. 

The Preble thrust plate has formed a sole for some of 

the higher thrusts in Goughs Canyon. 

A. North side Hogshead Canyc:m. Steeply inclined rocks of the Preble formation thrust over gently dipping strata of the Etchart limestone, 

which are underlain by conglomerate of the Battle formation and the Osgood Mountain quartzite. (£om, Osgood Mountain quartzite; 

£p, Preble formation; IPb, Battle formation; PIPe, Etchart limestone.) 

B. Granite Creek. Rocks of the Preble formation thrust over conglomerate of the Battle formation. ( £p, Preble formation; 

IPb. Battle formation.) 

Fiou&m 10.-VIEWS OF THE GRANITE CREEK THRUST FAULT. 
STRUCTURAL GEOLOGY: 73 

ETCHART CANYON THRUST PLATE 

The Etchart limestone has been thrust over several 

rock units in different parts of the Osgood Mountains. 

For convenience of description, all these overthrust 

blocks of Etchart, and some klippen of Battle formation, 

are collectively referred to as the Etchart thrust plate; 

although there is evidence that suggests this thrusting 

has occurred at different times. 

Several klippen of Battle formation and Etchart 

limestone .are exposed in the upper part of Goughs 

Canyon. Most of these rest on the Etchart limestone, 

but there is a thin sole of Preble formation intervening 

between some of the klippen and the underlying 

Etchart. These relations are particularly well exposed 

on a small hill in NE~4 sec. 27, T. 38 N., R. 41 E., where 

the Etchart limestone overrode a thin plate of Preble 

formation. The edge of the thrust plane is clearly exposed dipping northwest about 15°. It gradually cuts 

across strata of the upper plate, which are inclined 

somewhat more steeply in the same direction as the 

thrust, fault. Crumpling in the underlying shale next 

to the contact gives evidence that the thrust moved from 

northwest toward the southeast. A klippe of Etchart 

limestone rests on the Adam Peak formation on the 

ridge west of Adam Peak and two klippen rest partly 

on the Adam Peak across the trace of the Adam Peak 

thrust on the north side of Goughs Canyon. 

The Etchart limestone has been thrust on the Farrel 

Canyon formation on the west side of the range north 

of Anderson Canyon, and on the Valmy formation on 

the east side of the range northeast of the Getchell mine. 

On the west side of the range the Etchart thrust plate 

rests on the Farrel Canyon formation; whereas on the . ' east side of the range it has been overridden by the 

Farrel Canyon, presumably on the Farrel Canyon 

thrust. This relation can be used as evidence that the 

Etchart limestone has been involved in more than one 

period of thrusting, but we believe the Etchart limestone was first thrust into the area, coming to rest on the 

several different formations, and then the Farrel 

Canyon thrust broke across the earlier Etchart thrust 

plate, carrying part of the Etchart plate with it. 

HARMONY THRUST PLATE 

Next highest in this succession is the Harmony thrust 

plate, which has carried the Harmony formation of Late 

Cambrian age over the Adam Peak formation, autochthonous Etchart limestone, and thrust remnants of the 

Etchart limestone and the Battle formation. The fault 

strikes N. 40° E., dips northwest, and crops out for more 

than 3 miles northeast of Goughs Canyon. The dip is 

about 25° NW. where the fault trace crosses the ridge 

north of Goughs Canyon in SW% sec. 23, T. 38 N., R. 

41 E.; northward, the relation of the fault trace to 

topography indicates that the dip is in the same direction but somewhat steeper. The strata, lithologically 

like the type Harmony-feldspathic sandstone and grit, 

shale, and limestone-are highly deformed throughout 

all of the thrust sheet, and no pattern of folds can be 

resolved. The strike of beds is northeast and rather 

constant, but dips are highly variable. Where exposures are good the exceedingly deformed condition of 

the rocks can clearly be seen. The shale has been so 

squeezed that it appears crumpled and sheared and 

weathers out into small polygonal fragments which in 

places are pencil like. Beds of sandstone and grit, and 

less commonly limestone, commonly a foot to several 

feet thick, are interbedded with the shale, in which they 

have been rolled and twisted as if in a plastic mass. 

Many of the sandstone beds show a kind of structure 

that resembles "boudinage" ( Cloos, 194 7). The beds are 

broken across the bedding, and the relatively softer and 

more plastic shale has flowed into the fractures, separating the original beds into an alined series of disconnected blocks. Many of the sandstone "boudins" are 

separated from their original position and are seen as 

hard boulders embedded in a shale matrix. 

GOUGHS CANYON THRUST PLATE 

The plate of Harmony formation rocks is overridden 

by a still higher thrust sheet that carries the Goughs 

Canyon formation of Mississippian age. At its south 

end, in and near Goughs Canyon, the thrust rests directly on thin thrust sheets of the Etchart limestone and the 

Preble formation, and on autochthonous beds of the 

Etchart limestone. A small klippe of the Goughs Canyon formation laps over the Preble sheet on to the 

Osgood Mountain quartzite just north of center sec. 33, 

T. 38 N., R. 41 E., in the head of Perforate Canyon. 

North of Goughs Canyon, the thrust gradually overlaps 

the plate of Harmony formation rocks -and at its north 

end brings the Goughs ·Canyon formation into contact 

with the Preble formation. Westward the plate is covered by volcanic rocks of Tertiary age, and northward 

it disappears beneath a thrust plate of Farrel Canyon 

formation. The· trace of the thrust fault trends northeast in its southern two-thirds, and very slightly east of 

north at its northern end. On the south slopes of 

Goughs Canyon the pattern of the fault trace is evidence that the fault plane dips very gently north or 

northwest; north of Goughs Canyon the trace is relatively straight, indicating a steeper dip estimated by 

graphic methods as about 25 °. The fault is fairly well 

exposed on the north side of the East Fork of Eden 

Creek in north center sec. 14, T. 38 N., R. 41 E., where 

it dips approximately 40° NW. 
74 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

The beds on the upper plate persistently strike northeast and dip steeply west in the southern part of the 

thrust plate; north of the East Fork of Eden Creek 

the strike is nearly north-south and dips are variable, 

but generally steep. In the northern part of the thrust 

plate some tight folds were seen, but they were not 

mapped in detail; in the southern part of the plate 

poor exposures limit the observation of folding. The 

structures strike north and beds near the thrust fault 

are overturned to the west, but graphic reconstruction 

of folds suggests that farther from the thrust fault the 

anticlines and synclines have axial planes that dip 

steeply west. 

FARREL CANYON THRUST 

The Farrel Canyon thrust is the uppermost thrust 

in the zone of imbrication on the west side of the 

Osgood Mountains. The thrust is exposed from the 

head of Cherry Canyon to the north side of Farrel 

Canyon, where it overrides the Goughs Canyon formation and a small part of the Preble formation. The 

thrust is also exposed in the extreme northeast corner 

of the quadrangle where it overrides the Comus formation and the Etehart limestone. On the west side of 

the range the Farrel Canyon thrust is cut off by the 

high-angle Anderson Oanyon fault; on the northeast 

side of the range the thrust terminates against the 

Village fault, also a high-angle fault. North of Farrel 

Canyon the thrust is nearly flat; on the south side of 

the canyon it dips approximately 75° W., and farther 

south the pattern of the trace of the thrust suggests 

that the dip ranges from steep to gentle. The rather 

sinuous trace <>:f the thrust in the northeast corner of 

the quadrangle indicates that the thrust dips gently 

north. 

Strata in the thrust plate on the west side of the 

range are closely folded into a series of anticlines and 

synclines that strike mostly north; elsewhere, the 

Farrel Canyon forn1ation is too poorly exposed to give 

any indication of the structure, burt in most outcrops the 

beds are steeply inclined. 

HIGH-ANGLE FAULTS IN THE OSGOOD MOUNTAINS 

The rocks of the Osgood Mountains are broken by 

many steeply dipping or vertical faults which have two 

principal orientations, one northeast to north and the 

other northwest. The northeast faults ·are, for the most 

part, closely parallel to the trend of the formations and 

strike of the rocks and may be classed as longitudinal 

or strike faults. These are more oontinuous and more 

important structurally than the other set. The northwest-striking faults are classed as cross faults because 

their orientation is generally normal to the predominant 

structural trend. There is direct evidence that many of 

the faults are later than the thrusts ; there is no evidence 

that any preceded the thrusting. Age relations 

between the high-angle faults, however, are not complet~ly clear. At least one on the east side of the range 

near the Getchell mine is later than the granodiorite 

stock; there is no clear evidenoo that the others 

preceded or followed emplacement of the granodiorite. 

Some on the east side of the range probably should be 

regarded as range-front faults related to the basin-andrnnge system. The more prominent high-angle faults 

will be discussed in the following pages. 

ANDERSON CANYON FAULT 

The Anderson Canyon fault, named for a prominent 

canyon in the northwestern part of the Osgood Mountains, can be traced from Cave Canyon to the north 

boundary of the quadrangle. Phyllites of the Preble 

formation on the east side of the fault have been 

brought against the Etchart limestone at the north end 

of the range, the Farrel Canyon formation in Anderson 

Canyon, and limestone of the Preble formation in 

Farrel and Cave Canyons. The fault surface is not 

exposed, but the dip is known to be very steep or vertical 

from the straight trace of the fault. The relative displacement was down on the west side. The total displacement is not known, but a minimum displacement of 

1000 feet can be postulated on the supposition that the 

Etchart thrust plate once extended across the range. 

VILLAGE FAULT 

The Village fault is on the east side of the Osgood 

Mountains in the northeast corner of the quadrangle ; 

it is so named because it passes through the northeastern part of the village at the Getchell mine. In 

some ways it seems to be the eastern counterpart of the 

Anderson Canyon fault; it has a northerly trend on the 

east flank of the range and brings older rocks on the 

range side into contact with younger formations on the 

basin side. 

The Village fault can be followed southward from 

the north boundary of the quadrangle for nearly two 

miles; south of the village it is covered by alluvium. 

The fault strikes approximately N. 20° W. with only 

one minor offset within the quadrangle, and presumably, from the way it maintains its straightness regardless of topography, the fault is vertical. 

The apparent displacement is up on the west or 

range side of the fault and down on the east side. 

Thus, the older Preble £ormation and the metamorphosed Comus £ormation above it on the Peak 6837 

thrust plate west of the fault are brought into juxtaposition with younger rocks east of the fault, including 
STRUCTURAL GEOLOGY 75 

the Etchart limestone, the underlying Valmy formation and the overthrust Farrel Canyon formation. 

Here again, the total displacement is not known, but 

a minimum displacement of 1,000 feet can be postulated 

on the assumed offset of the Etchart thrust plate. 

GETCHELL FAULT 

A more or less continuous zone of faulting extends 

along the east side of the Osgood Mountains nea;r their 

base from about 1 mile north of Getchell mine to the 

mouth of Granite Creek, a distance of about 6 miles. 

The fault takes its name from the Getchell mine, which 

is on the fault zone. The Ogee and Pinson fault south 

of Granite Creek possibly is a southwestward continuation of the Getchell fault zone. 

Although the fault is m·ainly along the east front 

of the range, at most places it is not the boundary 

between bedrock and the alluvium-filled basin to the 

east. Bedrock is exposed in low hills for more than a 

mile east of the fault in some places. Throughout its 

length the fault, or fault zone, is generally parallel to 

the strike of the sedimentary rocks, though in detail 

at many places it transects the bedding at a small 

angle. Furthermore, where the sedimentary rocks tend 

to strike parallel to the eastern contact of the granodiorite stock, the fault, too, clearly bends eastward and 

outward around the bulging northern lobe of granodiorite, and less so east of the southern lobe. At several 

places where mining operations have exposed the fault 

(fig. 11), it dips east at moderate to steep angles; at 

the Getchell mine the fault dips 30° to 40° E. in its 

northern exposures, and 70° to 80° E. in the southern 

mine pits; farther south at the Riley mine the footwall 

break dips 49° E.; a parallel fault segment at the 

Pacific mine dips 45° E. Mining operations have also 

FIGURE 11.-View of the Getchell fault, Getchell mine. Looking 

south along ore zone in south pit. Footwall of Getchell fault, dipping 

east, on right. 

690-1~9 0--63--6 

shown that a zone of fracturing and brecciation as much 

as 500 feet wide lies above the generally well defined 

footwall break, and many subsidiary faults split off the 

main zone into the hanging wall and footwall. 

The Getchell fault is a zone of overlapping fractures. 

North of the Riley mine the rocks on both sides of the 

fault are shown on the map as Preble formation except 

near the mouth of Rocky Canyon, where granodiorite 

is on the footwall, and at the Getchell mine, where 

granodiorite is on the hanging wall. South of the 

Riley mine a fault separates rocks of the Preble formation from those of the Comus formation. Absence of 

exposures obscures the relations between the fault at the 

Riley mine and the fault to the south between the Preble 

and Comus formations; but it appears that, though the 

general zone of faulting may be continuous, the fault 

contact between Preble and Comus splits off from the 

main fault and possibly joins the Village fault somewhere between the Riley mine and the low hills of Comus 

formation to the east of the quadrangle. East of the 

Valley View mine the fault between Comus and Preble 

formations disappears southeastward beneath alluvium~ 

but a strong parallel fault with a wide breccia zone lies 

one-fourth of a mile to the west within the Preble formation and continues southward for a mile until it, 

too, is covered by alluvium. 

Near the mouth of Rocky Canyon, a mile south of the 

Getchell mine, the Getchell fault intersects the 

granodiorite contact, and for almost half a mile northward granodiorite forms the footwall. In the main 

mine pit south of the mill (South Pit) at the Getchell 

mine, granodiorite is exposed in the hanging wall next 

to the fault zone. It is also exposed east of the fault 

in an excavation for the primary crusher, and in a bank 

and on the playground of the school north of the mill. 

In the South Pit at the Getchell mine the footwall of 

the fault is well exposed. The footwall surface, 

highly polished in places, dips moderately to steeply 

east, and on it are prominent grooves or mullions that 

are horizontal or plunge northward at angles of a few 

degrees. At set of striae and slickensides caused by 

late movement cut across the nearly horizontal grooves 

at about 90°, and thus pitch down the dip of the footwall plane. Here, then, is evidence of strike-slip movement along the fault, succeeded by chiefly dip-slip 

movement. No stratigraphic data are available for determining the amount of movement along the fault, but 

indirectly the evidence suggests that the granodiorite in 

the hanging wall is a segment of the main body of 

grandiorite cut by the fault and displaced northward 

about 3,500 feet by a predominantly strike-slip leftlateral movement. The occurrence of bedrock east o:f 
76 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

the fault and relations of formations on opposite sides 

of the fault, the presence of gran diorite east of the fault, 

and the absence of topographic expressions such as welldeveloped scarps and triangular facets along the range 

fron~all indicate that the amount of late dip-slip 

movement was relatively small. 

Clearly, the Getchell fault zone is later than the 

granodiorite, and earlier than the episode of mineral deposition that formed the gold -arsenic deposits at the 

Getchell mine, which may have been in Tertiary time. 

Evidence of late normal displacement on the fault-in 

Quaternary or perhaps Recent time-is shown by the 

alluvium, which is as much as 25 feet thick a few hundred feet east of the fault and only a few inches to 1 or 

2 feet thick on the slope west of the fault. In a cut 

where Burma Road crosses the footwall fault, alluvium 

5 to 10 feet thick on the east side ends abruptly at the 

fault, and west of the fault the overburden is but a foot 

or so thick. 

OGEE AND PINSON FAULT 

The Ogee and Pinson fault takes its name from a 

small open-pit gold mine near the top of a ridge half 

a mile southwest of the mouth of Granite Creek. The 

fault is shown on the geologic map (pl. 1) as the contact between the Preble and Comus formations south of 

Granite Creek. Actually, clear evidence of a fault is 

seen only at the Ogee and Pinson mine, where a wide 

zone of brecciated hornfels and chert is exposed. To 

the southwest, from Felix Canyon to southwest of the 

mouth of Hogshead Canyon, the contact between the 

Preble and Comus is concealed by soil and alluvium. A 

fault contact is postulated in the concealed area because 

of evidence of faulting to the north and the absence of 

higher Cambrian strata betwen the Preble and Comus 

formations; however, the original distribution of the 

Paradise Valley chert and the HarmoiJ.y formation is 

poorly known, and they may never have been deposited 

here or may have been removed by erosion prior to. deposition of the Comus. In the Edna Mountains, 12 

miles to the south in the Golconda quadrangle, the 

Preble-Comus contact is a high-angle fault (p. 11). 

At least the northern segment of the Ogee and 

Pinson fault may be an extension or offshoot of the Getchell fault zone. It is on the general trend of the Getchell fault zone, has a wide brecciated zone at the Ogee 

and Pinson mine, and contains a low-grade ,gold deposit. 

OTHER HIGH-ANGLE FAULTS 

Many other steep faults have boon mapped in the Osgood Mountains. These faults and their effects are obvious from the geologic map (pl. 1), so individual faults 

are not described in detail. 

North west-striking faults in the central part of the 

Osgood Mountains are most conspicuous on the geologic 

map, for they trend chiefly at right angles to the northeast-trending structures and have caused many interruptions and offsets of the strata. Some of the faults 

can be followed for as much a8 11h miles, but most are 

less than 500 feet long. Although the dip of the faults 

cannot be measured in most places because of inadequate exposures, the relation of their traces to the topography is evidence that they are vertical or very steeply 

inclined. Normal dip-slip movement accounts for the 

apparent displacement of units relative to one another 

on opposite sides of the fault~a displacement indicating total movement of the faults of only a few hundred 

to, in one place, a thousand feet. 

Faults that strike slightly east of north, mostly diagonal to the regional structure, terminate some of the 

northwest faults. These, too, are steep to vertical 

faults, and the amount of displacement along them is 

similar to that on the north west faults. 

A few other steep minor faults have been mapped 

elsewhere in the Osgood Mountains, and most of them 

have either a northwest or north strike. Most of the 

steep minor faults obviously were formed later than 

deposition of the Pennsylvanian rocks, after the thrust 

faulting and later than the folding. 

FOLDS IN THE HOT SPRINGS RANGE 

Deformation chiefly by folding characterizes the comparatively simple structural unit of the Hot Springs 

Range in contrast to the complexly faulted Osgood 

Mountains. Inspection of the geologic map (pl. 1) 

shows many recorded measurements of bedding attitudes in the Harmony formation, which range widely in 

direction of strike and dip and are an indication of 

many intricate folds. Characteristically, the Harmony 

formation lacks persistent, distinctive lithologic units 

that can be easily followed and mapped, and by which 

the folds could be clearly delineated ; therefore, the true 

pattern of folds in the Hot Springs Range is not known. 

However, some folds can be recognized in the field from 

bedding attitudes and outcrop patterns, and by mapping 

some of the interbedded limestone members. In general, the structure is a series of north-plunging asymmetrical anticlines and synclines whose axial planes dip 

moderately east; some of the folds are isoclinal (beds 

on opposite limbs dip at equal angles in the same direction). On the northwest flank of the range, in the 

northwest corner of the quadrangle, the Paradise Valley chert, which underlies the Harmony formation, is 

exposed in two anticlines (pl. 1, section A-A') that 

probably are chiefly isoclinal. 
STRUCTURAL GEOLOGY 77 

By direct stratigraphic or structural relations the 

folding of the upper Cambrian rocks in the Hot Springs 

Range can only be determined to be later than Cambrian ·and earlier than Tertiary in age, for the oldest 

rocks that overlie the folded strata are volcanic rocks 

of Tertiary age. The small granodiorite bodies that intrude the folded rocks are of the same composition as 

the stock in the Osgood Mountains, which from age determinations by the zircon method is estimated to be 

Late Cretaceous in age. Probably the folding is, at the 

latest, earlier than late Cretaceous. 

FAULTS IN THE HOT SPRINGS RANGE 

Undoubtedly there are more faults in the Hot Springs 

Range than are shown on the geologic map. Evidence 

of faulting is common in many places, but without distinctive lithologie markers, most of the faults could not 

be mapped. 

All the faults shown in the Hot Springs Range are 

vertical or high-angle normal faults. The amount of 

movement on most of the faults need not have exceeded 

a few hundred feet to account for the relations between 

the rocks involved. With a few exceptions most of the 

faults shown can be grouped into two sets: those which 

strike north to northeast and those which strike 

northwest. 

North- and northeast-striking faults on the east side 

of the range have downfaulted, and therefore preserved 

from erosion, blocks of Tertiary volcanic rocks that 

formerly overlay the Harmony formation in the range. 

Similarly, near Box Canyon midway along the east side 

of the range, a downfaulted block of Valmy formation 

has been preserved from erosion. Probably the small 

patch of Valmy at Stone Corral is similarly preserved, 

although alluvium hides the contact with the Harmony 

formation. North- or northeast-striking faults are less 

prominent elsewhere in the range, except in the northwest corner of the quadrangle where northeast faults at 

the range front probably are responsible for repetition 

of the Paradise Valley chert. 

The major faults along the east front of the range all 

have the same kind of displacement, with the west or 

mountain side of the faults displaced upward relative 

to the east or valley side. In the vicinity of Box Canyon the block of Valmy formation rocks between the 

parallel faults is down relative to the western or range 

block but is up relative to the eastern block that preserves the volcanic rocks. Farther south, a narrow 

block of Harmony formation rocks with some remnants 

of volcanic rock has been lowered relative to the northwest side of the fault, and the block of volcanic rocks to 

the southeast has been further downfaulted. This step 

faulting is probably responsible for the major uplift of 

the range. 

Most prominent of the northwest-striking faults are 

those on the northwest side of the range that are chiefly 

at right angles to the folding and intersect and displace 

a belt of the Paradise Valley chert. Their southeastward extensions are recognizable in the field by offsets 

in thin limestone members of the Harmony formation. 

Many of the faults shown in the Hot Springs Range 

are certainly of Tertiary age or younger, for they transect the volcanic rocks. For some, such as the two 

prominent northwest faults in the northern part, there 

is no direct evidence of their age except that they are 

later than folds in the Cambrian rocks. Some faults of 

each set are known to cut volcanic rocks; so it seems 

probable that both sets are of about the same age. 

Some quicksilver deposits of minor importance are 

associated with faults whose relation to the faults shown 

on the map is not clearly known. Not shown are some 

small gold-bearing quartz veins in and surrounding the 

stock of granodiorite at Dutch Flat, which presumably 

are related to the intrusive body and were deposited in 

fractures formed during or soon after emplacement of 

the granodiorite. 

RELATION BETWEEN THE HOT SPRINGS RANGE AND 

THE OSGOOD MOUNTAINS 

An alluvium-filled valley separates the Osgood 

Mountains from the Hot Springs Range, concealing the 

boundary between the prevolcanic rocks of the two 

ranges. Interpretation of the concealed relations is 

difficult because the Paleozoic rocks of the two ranges 

are not alike, except for a thrust silver of the Harmony 

formation in the Osgood Mountains, and there is no 

clear structural continuity between the ranges. 

The Osgood Mountain quartzite and Preble formation beneath the thrust plates of Preble formation are 

interpreted to be autochthonous (for the most part, in 

the place where they were deposited). Shales of the 

Preble formation overlie the quartzite on the northwest 

flank of the fold near the mouth of Goughs Canyon. 

Here, then, is evidence that Preble formation may underlie the alluvium and volcanic rocks between the Hot 

Springs Range and the Osgood Mountains south of the 

Dry Hills. In the Hot Springs Range the Harmony 

formation rests depositionally on the Paradise Valley 

chert, which is younger than the Preble formation; but 

the nearest exposures of Paradise Valley and Preble 

formation are 8 miles a part, so their stratigraphic relations are entirely conjectural. The Harmony and Paradise Valley in the Hot Springs Range may be either autochthonous or allochthonous (brought from elsewhere 
78 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

to their present position). In the Sonoma Range (Ferguson, Roberts, and Muller, 1952) the Harmony formation occurs on thrust sheets and also in apparently autochthonous position beneath thrusts; at Battle Mountain -(Roberts, 1951) and in theMountLewisquadrangle 

(James Gilluly~ oral communication) the Harmony 

formation is thrust over Lower Cambrian and Ordovician rocks. 

Lengthy speculation on possible structural situations 

tha·t would explain the present relations between the 

two ranges is fruitless, but two possibilities that seem 

plausible should be mentioned briefly : ( 1) the Harmony 

formation and underlying Paradise Valley chert in the 

Hot Springs Range are in an autochthonous block on the 

west side of a major anticline or in a generally synclinal 

structure, modified by normal faulting along the flanks 

of the range; or (2) the Hot Springs Range is allochthonous and is on the upper plate of a thrust fault 

whose outcrop is concealed by alluvium in the valley. 

Evidence for the first possibility includes the ample 

room between. the two ranges for accommodation of the 

postulated structure, and the absence of a thrust beneath 

the Harmony formation or Paradise Valley chert in the 

Hot Springs Range. - Evidence for the second possibility is the position of the Harmony formation in thrust 

sheets at several places in north-central Nevada including the west side of the Osgood Mountains north of 

Goughs Canyon, and the lack of exposures in the Osgood 

Mountains of either the Paradise Valley chert or the 

Harmony formation in normal position. 

Clearly the present structural relations were established prior to the Tertiary erosion and subsequent volcanic activity. Much if not all the Hot Springs Range 

and at least the southern part and western slope of the 

Osgood Mountains were blanketed by volcanic rocks 

that were laid down on ·an uneven erosion surface cut 

into rocks that had the same general relationships that 

they have now. The northern, higher part of the Osgood Mountains may not have been covered by the volcanic flows, for it may have stood as a highland during 

the time of Tertiary volcanic activity. The flows in the 

Dry Hills and at Soldier Cap on the west side of the 

range may lie on the east side of an old valley that was 

established prior to the episode of volcanism, as suggested by the rather steeply inclined basal contacts that 

truncate the nearly flat or gently tilted flows and the 

rapid thickening of the flows westward. 

ORIGIN OF THE RANGES 

Evidence bearing on the origin of the present form 

of the Osgood Mountains, the Hot Springs Range, and 

the bordering alluvi.mn-covered valleys is largely circumstantial. Certain facts suggest, but do not prove, 

that faulting has been mainly responsible for delimiting 

the mountain blocks from the basins, but that some of 

the relief resulted from uplift by slight arching, possibly attende.d.by step faulting. 

Separation of bedrock in the mountains from alluvium in the basins by normal faults along the front of 

the ranges cannot be conclusively demonstrated. 

Nevertheless, the straightness of a mountain frontparticularly if it cuts across the strike of the rocksis commonly regarded as evidence of a range-bounding 

fault. Attention is drawn therefore to the east front 

of the Osgood Mountains, which is fairly straight from 

about the latitude of Lone Butte to Getchell mine, and 

more so between the mouth of Granite Creek and Getchell mine. The front is slightly oblique to the strike 

of the rocks in the range. Similarly, the east and west 

fronts of the Hot Springs Range are quite straight. 

High -angle faults along the east front of the Osgood 

~fountains are generally parallel to the range, but they 

seem to be structural elements of the range rather than 

the boundary between the range and the alluviated 

valley to the east, for low hills and pediment slopes lie 

between the range proper and the valley alluvium. 

Weakly developed facets on some of the spurs along the 

northern part of the east front of the range and steeply 

dipping striae on the Getchell fault are evidence of 

some uplift of the range along this fault, but other data 

cited previously (p. 75) indicate that perhaps the 

major movement on the fault was lateral. Other faults 

east of the present range front may have been responsible for the uplift, and the range front retreated by 

erosion to its present position. Some evidence supporting this hypothesis is provided by a northeast-striking 

fault that cuts through alluvium east of the range front 

in the southeast part of the quadrangle. Another possibility is that the range is bordered by step faults, and 

the foothills lying east of the Getchell and the Ogee and 

Pinson faults are part of a steplike block between the 

higher part of the range and the basin. 

The west front of the Osgood Mountains is very irregular, and presents no compelling evidence for a 

range-front fault. The west boundary of the Osgood 

Mountains block may, however, be more or less along 

the east side of the Hot Springs Range, where normal 

faults form the boundary between volcanic rocks 'on the 

valley side and older rocks to the w~ in the range. 

The flows on the east side of the Hot Springs Range 

and those on the west side of the Osgood Mountains are 

less than a mile apart in places and probably are continuous beneath the valley alluvium. 
INTERPRETATION OF THE STRUCTURAL RELATIONS AND GEOLOGIC IDSTORY 79 

Some relative upward movement of the Hot Springs 

Range must be postulated to account for the almost 

complete removal of volcanic rocks in the range in contrast to their preservation along the east foot of the 

range. The straightness of the front on both sides of 

the range is suggestive of a range bounded by faults. 

Some faults are known on both sides of the range: on 

the east side, relative upward movement of the range 

undoubtedly has taken place along the faults between 

volcanic rocks at the foot of the range and the older 

rocks, and extensions of these faults may be covered by 

alluvium; a normal fault probably occurs along the 

range front in the northwest corner of the quadrangle. 

Elsewhere, alluvium laps up on the range in many places 

without an abrupt change in slope, and the ridges are 

not faceted along the front of the range. However, the 

possibility that part of the uplift of the Hot Springs 

Range was accomplished by arching along the axis of 

the range, accompanied perhaps by step faulting, must 

also be considered. The flow remnants dip gently east 

and west away from the range crest toward the valleys, 

and many are bordered on one side by a normal fault. 

It can be seen from sections A-A' and B-B', plate 1, 

that the structural relief of the range as shown by the 

gently dipping flow remnants could have been satisfied 

by gentle arching. Similar evidence for origin of some 

of the ranges by upwarping has been found by Willden 

(in press) in Humboldt County. In the Santa Rosa 

Range volcanic rocks close around the north end of the 

range, with west dips on the west and east dips on the 

east side; in the Black Rock Range, also, volcanic rocks 

have gentle fold structures. 

INTERPRETATION OF THE STRUCTURAL RELATIONS 

AND GEOLOGIC HISrr<>RY 

The structural development of an area can be clearly 

understood only as part of the geologic history. Therefore, the following discussion, which attempts to interpret the structural position of the Osgood Mountains 

and Hot Springs Range in a regional framework, includes an interpretation of the geologic history founded 

on known structural and stratigraphic relations in this 

and neighboring areas. 

PALEOZOIC HISTORY 

In an earlier report (Roberts and others, 1958), which 

summarized the Paleozoic stratigraphy and structural 

history of north-central Nevada, it is,shown that most 

strata of early and middle Paleozoic age can be assigned 

to two main assemblages of contrasting facies, regional 

in extent, and that the facies have been brought together 

by thrust faults. In eastern Nevada the rocks are a 

carbonate assemblage that is composed mostly of limestone and dolomite but includes minor amounts of shale 

and quarzite. They were deposited in a shallow-water 

miogeosynclinal environment that covered much of 

western Utah and Eastern Nevada. West of long 116° 

to 117° and north of lat 39° in central and western 

Nevada, rocks of the same age are a siliceous assemblage 

composed dominantly of clastic sediments and chert, 

with intercalated volcanic and pyroclastic rocks. These 

rocks were deposited in a eugeosynclinal environment 

in western Nevada west of the shallow shelf seas. 

In the Osgood Mountains quadrangle, Cambrian 

rocks younger than the Osgood Mountain quartzite 

and the Comus formation of Ordovician age are characterized lithologically by a combination of siliceous, 

clastic, volcanic, and carbonate elements; that is, the 

lithology is neither distinctly a siliceous and volcanic nor 

a carbonate assemblage, but intermediate. Hence, the 

concept has developed that these rocks belong to a third, 

or transitional, assemblage. Taken individually, some 

transitional units resemble the carbonate assemblage 

and others the siliceous; but as a whole, a transitional 

siliceous-carbonate assemblage is recognizable. Boundaries between the assemblages probably oscillated 

back and forth across central Nevada, and locally 

deposits of one assemblage ·may have accumulated in 

a part of a basin characterized predominantly by 

another assemblage. 

The three assemblages were laid down in a broad 

north-trending geosyncline in north-central Nevada 

that persisted until the end of the Devonian (Nolan, 

1928, p. 158), when orogenic movements resulted in 

the emergence of a positive area that trended northnortheast medially across the state. This positive area, 

which was the locus of intense folding ·and faulting 

during the Antler orogeny in the late Paleozoic, has 

been called the Antler orogenic belt (Roberts, 1949, p. 

95; Roberts and others, 1958, p. 2851). 

CAMBRIAN SEDIMENTATION 

The geologic record in the Osgood Mountains quadrangle begins probably in Early Cambrian time with 

the deposition of clean sand in an advancing sea that 

extended over much of the present Great Basin. This 

sand, representing washed and reworked material derived from a low-lying deeply weathered landmass, 

accumulated to an unknown thickness probably amounting to several thousand feet and became the Osgood 

Mountain quartzite in this area. Gradually the sediment being deposited changed from clean sand to finer 

clastics and carbonate, which became the shale and limestone of the Preble formation. 
80 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

The record of Cambrian history after Preble time 

is interrupted in the Osgood Mountains, for the top of 

the Preble is not exposed and str31ta of Cambrian age 

later than the Preble formation are missing, except for 

a thrust sliver of Harmony formation. In the Hot 

Springs Range, however, the Paradise Valley chert is 

evidence that sediment31tion continued in the Late Cambrian with the deposition of chert, a little siliceous 

shale, and limestone, and later with coarse feldspathic 

sand that become the Harmony formation. 

CAMBRIAN DIASTROPHISM 

Aside from the initial downsinking that formed the 

geosyncline in which the sediments began to accumulate, the first clear event in the structural history is the 

evidence provided by the Harmony. form·ation that 

Precambrian crystalline rocks were exposed to erosion 

in the Late Cambrian. We do not know where the 

land was that furnished the feldspathic sands of the 

Harmony. It may have been near the site of depositior. 

or the sediments may have been transported a long way 

by turbidity currents. The episode of active uplift 

seems to have been of limited extent, for the Harmony 

formation is restricted to north-central Nevada· no . ' evidence of similar activity is found in Late Cambrian 

strata in eastern Nevada. Perhaps this was merely 

a local event, for there is no apparent angular discordance between the sediments of the Harmony formation 

and the strata of the underlying Paradise Valley chert. 

ORDOVICIAN SEDIMENTATION 

The geologic record is resumed in the Osgood Mountains with the Comus formation of Ordovician age, 

which provides evidence of continued deposition of fine 

clastics and carbonates in an environment that seems 

to have been intermediate between the miogeosyncline, 

represented by a predominantly carbonate section in 

eastern Nevada, and the eugeosyncline, where the chert, 

fine clastics, and volcanic rocks that characterize the 

Valmy and Vinini formations were deposited. 

Between Ordovician and late Early Mississippian 

time the record in this area is missing. The nearest 

positive evidence of marine deposition in the Silurian 

and Devonian is found to the east and southeast in the 

Tuscarora Mountains and northern Shoshone Range, 

where strata belonging to both western and eastern assemblages have been brought together by thrust faulting. The only Mississippian that can be dated with 

confidence in this part of Nevada is the assemblage of 

limestone, chert, and greenstone belonging to the Goughs 

Canyon formation of late Early to early Late Mississippian age, and it has been carried in from elsewhere 

on a thrust fault. In other words, in the Osgood Mountains, autochthonous strata between the Ordovician and 

Lower Pennsylvanian are missing, and there is no way 

of knowing whether this was an area of nondeposition 

after the Ordovician or whether the rocks were deposited and subsequently eroded or stripped off by 

thrust faults. 

ANTLER OROGENY 

A major orogenic episode that is recognized elsewhere in north-central Nevada is clearly expressed in 

the Osgood Mountains by an unconformity that separates the conglomerate of the Battle formation and the 

carbonate sediments of the Etchart limestone from the 

older Paleozoic rocks. In recent years this important 

structural event has come to be known as the Antler 

orogeny (Roberts, 1951), its name taken from Antler 

Peak on Battle Mountain where its effects are so well 

shown. In the Osgood Mountains the orogeny can only 

be dated as post-Cambrian-pre-Middle Pennsylvanian, 

for the Battle formation of Middle Pennsylvanian 

(Atoka) age is not known to rest on rocks younger than 

Cambrian. To the east in Eureka County however ' ' rocks as young as Devonian were involved in the orogeny 

(Roberts and Lehner. 1955; Roberts and others, 1958). 

The Antler orogeny was accompanied by thrust 

faulting on a grand scale, the first of several episodes 

of thrusting that took place in the Great Basin at 

various time between the late Paleozoic and early 

Tertiary. In this first episode great plates of siliceous 

clastic, and volcanic rocks of the siliceous as..~emblage, 

were sheared off, carried eastward, and thrust over 

rocks of the same age but of different lithologic character. Merriam and Anderson (1942, p. 1701-1706) 

showed that in the Roberts Mountains a great thrust 

fault, which they named the Roberts Mountains thrust, 

separates an eastern carbonate assemblage from a 

western assemblage of fine clastics, chert, and volcanic 

rocks. Gilluly (1954) recognized the thrust in the 

Cortez and Mount Lewis quadrangles, and Roberts and 

Lehner (1955) traced it northward through Eureka 

and Elko Counties approximately along the 116° 

meredian and showed that it passed into Idaho northeast of Rowland. Although Merriam and Anderson 

(1942, p. 1706) . suggested that the Roberts Mountains 

thrust may have been of Late Cretaceous or early 

Tertiary age-that is, part of Laramide orogenyKay (1952, p. 1270) reported that in the Toquima 

Range and Car lin Canyon the thrusting preceded deposition of Pennsylvanian sediments. A similar age 

for the thrusting was postulated by Dott ( 1955, p. 

2288 and fig. 11). Near Mountain City, conglomerate 

and limestone of Pennsylvanian age rest on a thrust 

sliver of rocks of the siliceous assemblage and also on 
INTERPRETATION OF THE STRUCTURAL RELATIONS AND GEOLOGIC HISTORY 81 

rocks of the carbonate assemblage (K. 0. Bushnell and 

J. R. Coash, oral communication cited in Roberts and 

others, 1958, p. 2·854). 

The Roberts Mountains thrust cannot be definitely 

recognized west of the Shoshone Range, but other 

thrusts on Battle Mountain, in the Sonoma Range, and 

in the Osgood Mountains quadrangle probably are 

contemporaneous with it. Thrust faults on Battle 

Mountain that are overlapped by the Battle formation 

(Roberts, 1951) probably are structurally higher than 

the Roberts Mountains thrust, for the Valmy formation of the western assemblage is in the block beneath 

the thrusts. The distribution of the Comus and Valmy 

formations in the Osgood Mountains quadrangleboth of Ordovician age but of different lithology-is 

the basis for postulating that a thrust fault contemporaneous with, if not an extension of, the Roberts Mountains thrust brought the two facies together. The 

Comus formation, believed to be an intermediate or 

transitional assemblage, is regarded as autochthonous 

or parautochthonous, for it is associated with the seemingly autochthonous Osgood Mountain quartzite and 

Preble formation of Cambrian age. Unfortunately, 

the structural relation of the Valmy formation is obscured by later normal faulting and poor exposures, 

but the interpretation made here is that it represents 

remnants of a thrust sheet of the siliceous assemblage 

that overrode the Hot Springs Range and Osgood 

Mountains. Some support for this structural interpretation is found on the east side of the Sonoma Rarige, 

where the Adelaide thrust (Ferguson, Muller, and 

Roberts, 1951) carries the Ordovician ( ~) Sonoma 

Range and Ordovician Valmy formations over Osgood 

Mountain quartzite and the Preble formation in the 

lower autochthonous block. 

LATE PA.:.LEOZOIC SEDIMENTATION 

Orogenic uplift in the late Paleozoic was accompanied by erosion and widespread deposition of sediments 

that overl.apped preorogenic rocks of the carbonate, 

transitional and siliceous assemblages and that have 

been designated the overlap assemblage (Roberts and 

Lehner, 1955, p. 1661; Roberts and others, 1958, p. 2821, 

2838). Rocks of the overlap assemblage in the Osgood 

Mountains quadrangle belong to the Antler sequence, 

which also occurs in parts of Battle Mountain, the Edna 

Mountains, and the Sonoma Range. 

In the Osgood Mountains, parts of the area were 

once more beneath the sea by Middle Pennsylvania 

(Atoka) time, and clastic marine limestone was deposited on an eroded surface that exposed rocks as old 

as the Osgood Mountain quartzite. Uplift continued 

locally, however, for the limestones grade into and interfinger with coarse conglomerates that must have been 

derived from a nearby rugged terrain. The thinning 

and disappearance of conglomerate of the Battle formation westward in the Osgood Mountains suggests that 

a highland lay nearby east of the present range, and a 

marine basin lay to the west. Most of the area was 

probably beneath the sea by Late Pennsylvanian (Missouri or Virgil) time and continued so into the Permian, because remnants of marine deposits represented 

by the Etchart limestone are found throughout northcentral Nevada as well as in the Osgood Mountains. 

Locally there may still have been uplift and erosio!l, 

which would explain why some conglomerates that are 

identical with the Battle formation contain interbedded 

limestone containing fossils of Antler Peak age; however, some of these conglomerates may be reworked 

early Pennsylvanian deposits. The variation in thickness and lithology of the Late Pennsylvanian and Permian deposits indicate that conditions of deposition 

and the kind and abundance of material being contributed differed considerably from place to place, suggesting an environment of many bays and straits, as in an 

archipelago. 

Marine deposition was interrupted in this region between Early and Middle Permian time, and the previously deposited sedimentary rocks were moderately 

deformed, uplifted, and subjected to erosion. In Edna 

Mountain (Ferguson, Roberts, and Muller, 1952), on 

Battle Mountain (Roberts, 1951; Ferguson, Roberts, 

and Muller, 1952), and in the Sonoma Range (Fer!:~­

son, Muller, and Roberts, 1951) there are erosional remnants of the dominantly clastic Edna Mountain formation, which was laid down in middle Permian (Word) 

time on an erosion surface cut on the Antler Peak limestone or, where erosion had completely removed the 

Pennsylvanian formations, directly on Cambrian and 

Ordovician rocks. The Edna Mountain formation has 

not been identified in the Osgood Mountains quadrangle, 

and if deposited it has been completely removed by 

erosiOn. 

LATE PALEOZOIC OR MESOZOIC OROGENIC HISTORY 

Following deposition of the Edna Mountain formation, the .rocks were again deformed during the Sonoma 

orogeny of late Permian age ( Silberling and Roberts, 

oral communication, 1961). The orogeny is well illustrated in the China Mountain area of the Golconda 

quadrangle where rocks of Pennsylvanian and Early 

Permian age have been folded and thrust faulted and 

are overlain unconformably oy the Koipato formation 

of Permian and Early Triassic age. Major structural 

events that have been assigned to the Sonoma orogeny 
82 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

include the Golconda thrust, a major thrust fault that 

has been traced throughout the region. 

The early Mesozoic history in the Osgood Mountains 

quadrangle is uncertain, because no Mesozoic rocks have 

been identified. The historical record was interrupted 

again after the Upper Pennsy 1 vanian and Lower Permian sedimentary rocks were deposited. Looking beyond the immediate area, however, we find that by the 

Middle Triassic marine deposits were being laid down 

in the area now occupied by the Sonoma Range and 

East Range (Ferguson, Muller, and Roberts, 1951), and 

sedimentation continued throughout the rest of the 

Triassic. So, presumably, this was a period of quiescence in the Osgood Mountains area too. Perhaps the 

Triassic sea covered all the region, but if sediments 

of Triassic age accumulated in the Osgood Mountains 

area they have been removed by erosion. 

An orogenic episode affecting all of north-central 

Nevada began in the Early Jurassic (Ferguson and 

Muller, 1949, p. 9, 13) and may have continued into the 

Cretaceous and locally into the early Tertiary (Willden, 

1958, p. 2396). In the Osgood Mountains the orogenic 

episode responsible for deformation of the post-Ordovician rocks cannot be dated closer than after the Late 

Pennsylvanian and Early Permian sedimentation and 

before the intrusion of granodiorite in Late Cretaceous 

time. The emplacement of granodiorite is believed to 

have been a significant part of the orogeny ; granodiorite in the Osgood Mountains is of Late Cretaceous age, 

according to lead-alpha determinations. 

The rocks in the Osgood Mountains quadrangle responded to the orogeny by moderate folding and extensive thrust faulting. Generally speaking, the late 

Paleozoic rocks beneath the thrusts were only moderately folded and some-for example, the Pennsylvanian strata in the prow-shapped bluffs a/hove Hogshead 

Canyon and those in the northeast corner of the 

quadrangle-have been tilted without marked folding. 

The close folding of the Cambrian and Ordovician 

rocks below the thrust is attributed mainly to earlier 

deformation, probably during the Antler orogeny. The 

strata on the major thrust plates are closely folded and 

may have been deformed during the Late Permian 

Sonoma orogeny as well as during the Mesdzoic orogeny. 

Several thrust faults attributable to late Paleozoic 

or Mesozoic orogenies have been recognized in the Osgood Mountains. Each thrust except the uppermost is 

overlapped or cut by a higher thrust. This relation in 

the eastern part of the range is probably an indication 

of successive pu]ses of thrusting, but in the west part of 

the range it probably represents relative movement between a stacked series of thrusts which in the main 

moved together. The lowermost of the eastern thrusts 

seems to be the one that brought the plate of Adam 

Peak formation, a clastic facies of Pennsylvanian and 

Permian rocks over beds of the Etchart limestone, a 

predominantly limestone facies of approximately the 

same age. The Granite Creek thrust was active next 

and carried Preble formation over conglomerate of the 

Battle formation, the Etchart limestone, and the Adam 

Peak formation. Judging by the crosscutting relations, the plates of the imbricate zone of thrusting on 

the west side of the range were brought into the area 

next, and the general coextensive distribution and parallelism of the thrusts suggest that they moved together, perhaps riding on a thin sole of shale of the 

Preble formation. Minor thrusts in the Etchart limestone in the Goughs Canyon region are believed to outline subsidiary plates sheared off the underlying fixed 

block by movement of the overlying sheets. The Farrel Canyon thrust is the highest plate of the imbricate 

thrust zone. The age of the Farrel Canyon formation, 

on the upper plate of the thrust, has not been firmly 

established, but it may be in part the correlative of the 

Havallah and or the Pumpernickel formations. In 

the Antler Peak (Roberts, 1961), Golconda (Ferguson, 

Roberts, and Muller, 1952), and Winnemucca quadrangles (Ferguson, Muller, and Roberts; 1951), the 

Havallah formation, a dominantly clastic facies of Middle Pennsylvanian and Permian age, and the Pumpernickel formation of Pennsylvanian age are part of a 

very extensive thrust plate that overrode the region on 

the Golconda thrust fault. Therefore, the Farrel Canyon thrust may be equivalent to the Golconda thrust. 

Possible evidence of a still later episode of thrusting is 

found on the west side of the Osgood Mountains north 

of Anderson Canyon, where the Etchart limestone is 

thrust over Farrel Canyon formation; however, we believe it just as likely that an earlier thrust plate of 

Etchart limestone was broken and carried on the Farrel 

Canyon thrust plate. 

In the northern part of the Hot Springs Range, 

north of this quadrangle, the Goughs Canyon formation overrides the Harmony formation on a thrust fault. 

Presumably thrust faults of late Paleozoic or Mesozoic 

age extended over the southern part of the range, too, 

but were removed by erosion. The deformation responsible for folding of the Harmony and Paradise 

Valley formations in the Hot Springs Range cannot be 

dated with certainty. Perhaps these rocks were deformed during the earlier Antler and Sonoma orogenies. However, they may have been folded in Mesozoic 

time. West ward -overturned Triassac rocks have been 

reported (Ferguson, Muller, and Roberts, 1951) be-
INTERPRETATION OF THE STRUCTURAL RELATIONS AND GEOLOGIC HISTORY 83 

neath thrust faults of Mesozoic age in the Sonoma 

Range. 

Possibly, although this cannot be proved, some of the 

high-angle faults were formed during the late Paleozoic and Mesozoic orogenies. Many of the northwesttrending faults that displace the Osgood Mountain 

quartzite and the rocks of Pennsylvanian and Permian 

age near the crest of the range in the south-central part 

of the Osgood Mountains may have been minor tear 

faults developed during the thrusting and folding; the 

northwest faults on the northwest side of the Hot 

Springs Range may be regarded similarly. Possibly 

some of the faults on which there was Cenozoic movement were also sitM . of earlier movement. 

The Mesozoic orogeny culminated in the Late Cretaceous with the intrusion of granodiorite in the Osgood 

Mountains and the Hot Springs Range. Some deformation attributable to emplacement of the granodiorite 

can be recognized adj ace.nt to the Osgood Mountains 

stock, but most contacts indicate that the intrusive 

bodies cut the rocks cleanly, without distortion. No 

special control of empla.cmnent of the major bodies by 

local structure is apparent, but the main stock in the 

Osgood Mountains is virtually conformable to the eastward-dipping Preble formation. Some minor dacite 

porphyry bodies, regarded as satellitic to the granodiorite, occur on or near the contact between Osgood Mountain quartzite and Etchart limestone, which may have 

guided emplacement of the intrusive to some extent. 

Similarly, other bodies are near or on the Peak 6837 

thrust fault in the north end of the range. Intrusion 

of the granodiorite was accompanied by transfer of 

heat and material that metamorphosed the adjacent 

country rocks, locally converted limestone beds to silicate rocks, and deposited minerals bearing tungsten, 

lead, zinc, and some copper and gold. Where some of 

the emanations accumulated in the high parts of partly 

solidified granodiorite they caused extensive modification of the earlier crystallized minerals. 

CENOZOIC HISTORY 

EARLY CENOZOIC HISTORY 

The history of the Osgood Mountains and the Hot 

Springs Range following the Mesozoic orogeny is incompletely recorded in the rocks, but during the earlier 

part of the Cenozoic period extensive erosion and 

terrestrial and lacustrine deposition seem to have been 

the main geologic processes in operation. Subsequent 

erosion has destroyed much of the evidence, but in a 

few places poorly consolidated sands and gravels are 

preserved beneath volcanic rocks that fell as ash and 

flowed as lava over a surface of low relief in the ranges. 

The episode of volcanism is recorded by rhyolitic tuffs 

and andesitic .and basaltic flows. The tuffs locally 

underlie later and more extensive andesitic flow rocks, 

which cannot be closely dated but which probably are 

of late Miocene to middle Pliocene age; a basalt flow 

at the south boundary of the quadrangle near the 

Humboldt River may be of Quaternary age. 

CENOZOIC DIASTROPHISM 

The last diastrophic episode, which came in the late 

Tertiary and extended into the Quaternary, is chiefly 

recorded by high-angle faults that displace the Tertiary 

volcanic rocks, and by uplift of the ranges. Other highangle faults in the ranges, many of which transect older 

structures, may also have formed during the late Cenozoic orogeny, although some that follow earlier structural trends may have had pre-Cenozoic movement. 

Uplift of the ranges probably was accomplished partly 

by displacement along north-trending faults near the 

present front of the ranges, but lack of direct evidence 

of boundary faults, except in a few places, makes a 

hypothesis of uplift by arching accompanied by some 

faulting attractive. Some range-front faults are buried 

beneath alluvium in the basins. At least one of the 

range-front faults, the Getchell fault, had an important strike-slip component of movement that may have 

been nearly as large as later dip-slip displacement. A 

few of the fractures provided channels for rising hydrothermal fluids that altered the wallrocks, and deposited 

metal-bearing minerals: arsenic and gold along the 

Getchell fault, and quicksilver in faults in the Hot 

Springs Range. Continuation of diastrophism into 

Quaternary time is expressed by faults that displace 

valley alluvium and by partly eroded older fan deposits 

that signify rejuvenation of drainage. 

Erosion consequent on uplift is largely responsible 

for the present topography in the ranges, though some 

remnants of an old surface of low relief are found at 

the crest of the ranges. Erosion has cut deeply into 

the ranges, obviously guided in many places by zones 

of weakness along high-angle faults. Detritus from 

the erosion of the ranges accumulated in thick deposits 

in the basins. 

MINERAL DEPOSITS 

Mining activity in the Osgood Mountains quadrangle 

has been directed chiefly toward exploitation of tungsten and gold deposits in the Osgood Mountains. A 

small production of quicksilver and gold has come from 

deposits in the Hot Springs Range. In addition, leadsilver and copper deposits of minor importance are 

known but have yielded little or no production. 
84 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

For purposes of description the metalliferous deposits are classified mainly according to their metal 

content and distribution. Each class has a distinctive 

mode of occurrence and, for the most part, is genetically distinct. Following is the classification adopood 

here: 

1. Tungsten deposits in the Osgood Mountains 

a. deposits in tactite 

b. deposits in altered granodiorioo 

2. Gold-arsenic deposits in the Osgood Mountains 

3. Quicksilver deposits in the Hot Springs Range 

4. Gold-bearing quartz veins in the Hot Springs Range 

5. Gold-scheelite-cinnabar placer in the Hot Springs 

Range 

6. Minor deposits of lead-silver and copper 

Nonmetallic deposits include three barite prospects in 

the Osgood Mountains and an unexploited quartzite 

bed of exceptional purity in the southeast part of the 

Hot Springs Range that might be used as a source of 

silica. ' 

TUNGSTEN DEPOSITS IN THE OSGOOD MOUNTAINS 

Tactites, which were formed by metamorphism of 

limestone, have been the main host rock for the scheelite 

that has been produced from mines in the Osgood Mountains. The tactioos that have been mined for their scheelite content a.re along the contact of the granodiorite 

stock where it has intruded limestone beds of the Preble 

formation. Minor amounts of scheelite have been produced from alteration zones and bodies of quartz in 

granodiorite; but such occurrences, though interesting, 

are of little past or future importance as sources of 

tungsten ore. 

The only tungsten mineral that has been recognized 

here is the calcium tungstaoo, scheelite. The ore is 

almost exclusively tactite that contains accessory 

amounts of scheelite and minor amounts of metallic 

sulfides. At some places scheelioo is also found in 

calc-silicate rock and granodiorite, but usually not in 

sufficient amount for the rock to be considered ore. 

In addition, at a few places scheelite occupies narrow 

seams and small pockets of intense alteration in granodiorite, and in the northern lobe of the stock coarsely 

crystalline quartz in a zone of altered granodiorite contains some scheelite. 

DEPOSITS IN TACTITE 

Scheelite is an accessory mineral of relatively low 

concentration in most of the tactite but is sufficiently 

plentiful at many places so that the tactioo can be 

mined for its tungsten content. The grade of most of 

the tactite mined ranges from approximately 0.3 percent to approximately 0.7 percent WOa, and the average 

grade of all the ore mined contained about 0.5 percent 

W03 • Tactite containing less than 0.3 percent WOa 

has been mined where the bodies are situated so that 

they can be mined in conjunction with material of 

higher grade. 

MINERALOGY AND PARAGENESIS 

Scheelite occurs in the tactite as small discrete subhedral to euhedral grains that range from less than 

0.5 mm to 2 mm along their greatest dimension. The 

scheelite grains commonly are scattered through the 

tactite as if they crystallized at the same time that the 

tactioo was formed ; in some specimenes the scheelite 

grains are enclosed in garnet and, less commonly, in pyroxene. On the other hand, at many places scheelite 

grains are distributed in thin stringers parallel to the 

tactite layering as if they were localized along zones 

of voids remaining after formation of the tactite; in 

some places the scheelite stringers extend out from veinlets of schelite or scheelite and garnet that cut across 

layered tactite (fig. 12B). 

Scheelite occurs in a variety of ways in the tactite. 

In some specimens it is interstitial to garnet and to 

garnet and other minerals (fig. 12A) ; in others, equant 

scheelite crystals occur in quartz-calcite veinlets; in 

others, scheelite replaces interstitial calcite along calcite-garnet boundaries. Anhedral grains of scheelite 

are enclosed in some epidote veins that cut tactite. 

Late-stage quartz commonly replaces tactite and granodiorite at their contact, and some of these quartz replacements contain rich concentrations of coarse scheelite crystals; however, a few of the replacements are 

barren or have a low scheelite content. Scheelite is 

associated with green actinolitic amphibole and calcite 

in an unusual variety of tactite that is represented by 

the west ore body in the Riley Extension mine and in 

lesser amounts elsewhere and that is possibly a late 

modification of a garnet-pyroxene tactite. 

The most plentiful gangue minerals of the tactite 

are the silicate minerals of the host rock, and calcite. 

In addition, metallic sulfides are erratically distributed 

in the tactite. The following sulfide minerals have been 

recognized: pyrite, chalcopyrite, molybdenite, sphalerite and galena. Hobbs ( 1948/5 p. 68, 7 4) has also reported bismuthi.nite, but none was recognized during 

this investigation. Most of the tactite and adjoining 

rocks contain no sulfides except pyrite, but locally all 

the above-mentioned sulfides are abundant, and commonly they occur together. 

111 See footnote 1, p. 6. 
MINERAL DEPOSITS 85 

FIGURE 12.-THIN-SECTION PHOTOMICROGRAPHS OF SCHEELITE IN TACTITE. PLANE POLARIZED LIGHT. 

A, Scheelite ($) and calcite (C) filling spaces between zoned birefringent 

garnets (G) and some epidote (E) on boundary between calcite and 

garnet. 

T;tctite at many places contains a few scattered grains 

of pyrite and locally it is permeated with , pyrite that 

may amount to as much as 10 to 15 percent of the rock. 

The crystals of pyrite range from less than 1 mm to as 

much as 2 em along an edge. Usually, lesser amounts 

of chalcopyrite accompany pyrite, but in some places 

the ratio is reversed. Molybdenite is not common, but 

small local concentrations have been observed in tactite 

close to the granodiorite contact, commonly attended 

by abundant epidote or fibrous uralitic amphibole and 

late-stage calcite. Sphalerite and galena are restricted 

in their distribution to small highly concentrated bodies 

at a few places close to the granodiorite-tactite contact. 

Sphalerite tends to be more plentiful than galena in an 

estimated ratio between 3:1 and 5:1. Variable amounts 

of pyrite and chalcopyrite accompany the sphalerite 

and galena. 

Aside from the specks of pyrite and chalcopyrite that 

are scattered through some of the contact rocks, the 

local concentrations of sulfides tend to be on or close 

to the granodiorite contact. Mostly, they are in the 

tactite or other contact-metamorphosed carbonate 

rocks; uncommonly, they are in the granodiorite next 

to the contact. Relations to the host rocks suggest that 

the sulfides occupy space made available by a combined 

filling of intercrystal boundaries and replacement of 

adjoining grains. No clearly defined veinlike fracture 

fillings of sulfides in the tactite were observed. The 

B, Garnet-pyroxene tactite cut by more coarsely crystalline irregularshaped veinlet of birefringent garnet, accompanied by grains of 

scheelite. Garnet (G), pyroxene (px), scheelite (S). 

relation of the sulfides to scheelite is obscure .at most 

places. Locally, concentrations of sulfides are attended 

by larger amounts of fine-grained scheelite. In a fa,w 

specimens, microscopic examination showed mutual 

relations strongly suggesting that formation of scheelite preceded the introduction of sulfides. 

FORM AND STRUCTURAL RELATIONS 

Most of the tactite bodies are tabular, though some 

are irregular in shape and discontinuous. They range 

from a few inches to as much as 35 feet in thickness, but 

the majority are between 5 and 15 feet thick; the thickness may vary along the strike and down the dip. 

Most of the tactite zones are fairly continuous along 

the strike, commonly for several hundred feet and in 

places for more than 2,000 feet, and they are continuous 

down the dip for hundreds of feet. The tactite bodies 

are parallel to the granodiorite contact; where the limestone strata are concordant with the contact, the tactite 

is parallel to the bedding; but where the limestone is 

discordant, the tactite also is discordant with the bedding, although locally concordant tongues of tactite 

may extend out along bedding into the wall rocks. 

The contacts are sharp and well defined on both the 

footwall and hanging wall. Some of the tactites end 

abruptly along strike or down dip by a sudden tapering, 

or bluntly with perhaps one or more stubby protuberances into limestone or calc-silicate rock. 
86 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

No markedly crosscutting tactite bodies of veinlike 

habit have been observed. At many places, however, 

a relatively thick body of tactite that otherwise terminates rather abruptly has thinner fingerlike extensions 

that suggest localization of tactite-forming solutions 

by fractures beyond the main part of the body. The 

tactite bodies are cut by high-angle faults on which 

the displacement is ordinarily relatively unimportant 

and measurable in a few tens of feet of normal and 

strike-slip movement. 

In many places the form and size of tactite bodies is 

directly related to the configuration of the granodiorite 

contact surface (fig. 13). The contact surface is not 

smooth but is corrugated with large-scale ridges and 

troughlike grooves. On rna ps and sections these irregularities are expressed in the trace of the contact 

as sharp, commonly right-angle changes of strike or 

dip. Mostly the corrugations are steeply inclined, but 

some troughs have a nearly horizontal axis. The thickest parts of several tactite bodies are in the troughlike 

grooves on the contact surface, and they become thinner away from the axial part of the structures. Where 

a body of tactite is continuous for several score or hundreds of feet along strike, the tactite is commonly thinner over slight outward bulges or broad ridges on the 

contact surface than on either side. In places where 

the contact is relatively smooth, tactite is localized at 

minor irregularities, whereas the smoother segments 

of the contact are barren even though limestone is available for replacement by tactite. The corrugations persist downward for as much as several hundred feet; 

underground development and mining have demonstrated that at several places they plunge steeply but 

at a different angle from the dip of the contact, and 

that the tactite bodies follow the plunge of the 

corrugations. 

On a larger scale, also, this correlative relation between tactite and the shape of" the granodiorite contact 

is generally valid. It is apparent from the map (pl. 

1) that most of the tungsten deposits are situated in 

sharp-angled reentrants of limestone along the granodiorite contact. 

ORIGIN 

The tactites are regarded as having formed from 

marble and calc-silicate rock by reaction with heated 

solutions whose source was the intrusive body of granodiorite. 'rhe solutions contained tungsten, so that some 

scheelite was formed simultaneously with the tactite, 

but scheelite deposition also continued from solutions 

that followed permeable avenues along the granodiorite 

contact after formation of the tactite. 

The distribution of tactite bodies in relation to irregularities in the granodiorite contact indicates that tactite was formed after the granodiroite was emplaced. 

The tactite bodies range in width along strike from 

many feet to a few inches with no correlative change 

in the bulk composition of the adjacent granodiorite, 

which may be evidence that the granodiorite at the contact was not directly responsible for the metamorphism 

of the limestone to tactite. If convection currents were 

operative, however, they might have obliterated changes 

in granodiorite at the contact. Channeling of solutions by troughlike structures along the contact would 

account for the fact that many tactite bodies are situated at reentrants and irregularities in the contact. 

Mining has shown that the tactite bodies are continuous 

downward along the contact and do not end as long as 

the Structure is favorable, which lends support to the 

hypothesis that the reacting solutions were guided along 

suitable structures. It seems likely that fracturing 

along the contact, perhaps caused by stresses consequent 

on emplacement of the stock or by cooling of the intrusive mass, may have controlled the permeability along 

the zone of replacement, but if so, the formation of 

tactite has obscured the evidence. 

The paragenetic relation of scheelite to the common 

tactite minerals cannot be decisively established, but 

the data suggest that some scheelite was deposited when 

the tactite was formed and that scheelite deposition continued during the waning stages of the magmatic 

episode. 

Deposition of scheelite after the tactite was formed 

required that the rocks in which it was deposited were 

permeable to tungsten-bearing solutions-either by 

reason of , voids that remained after alteration or by 

continued fracturing-and that the solutions were made 

available to the tactite. The sporadic distribution of 

scheelite in the tactites is explainable on the basis that 

the avenues by which tungsten-bearing solutions could 

enter were wholly or partly closed after the tactite 

formed. For example, one of the largest tactite bodies, 

at the Richmond mine, contains less scheelite on the 

average than any of the other tactites, and large volumes of it are essentially barren. Perhaps a better 

example is found in the underground workings of the 

Tonopah mine, where the central part of a thick tactite 

lens is barren and scheelite mineralization is confined 

to the borders next to the granodiorite contact. · 

Composition of the sedimentary rocks at the granodiorite contact also controlled the localization of the 

scheelite deposits, for although structural controls of 

permeability probably determined the sites that were 

accessible to tungsten-bearing solutions, scheelite as 
MINERAL DEPOSITS 87 

A c 

E F 

EXPLANATION 

Plans 

I 

I -

Granodiorite 

Tactite 

limestone and calc-silicate rock 

t 

Contact, showing direction of dip 

Section Fault, showing dip 

0 100 FEET Generalized strike and dip of beds 

FIGURE 13.-Sketches of some tactite bodies, showing typical shapes and relations to the granodiorite contact. 
88 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

well as the gangue minerals of the tactite host rock were 

formed by chemical processes. Limestone bodies at the 

contact were necessary for formation of tactite, and 

scheelite is essentia.lly restricted to tactite. It seems 

unlikely that all contacts against hornfels were completely sealed, or that the hornfels next to the contact 

was so free from fractures that the rocks were impermeable to the same solutions; yet no tactite or scheelite 

were formed, because the rocks were chemically inert 

with respect to the composition of the same fluids that 

reacted with marble and calc-silicate rocks elsewhere. 

The origin of the scheelite in the late quartz that 

came in along the granodiorite-tactite contact in places 

is puzzling. Not all of the late quartz contains scheelite, yet at places in silicified tactite, scheelite is unusually abundant. The quartz-forming solutions may 

have carried tungsten, but possibly earlier formed 

scheelite in the tactite was mobilized and reprecipitated with the quartz, or remained as a residual in 

bodies of replacement quartz. 

Although at some places scheelite is abundant where 

sulfide minerals are abundant, there is no concrete evidence that they were formed together. On the other 

hand, there is considerable paragenetic evidence that 

scheelite is earlier than the sulfides. Possibly some sites 

where scheelite was abundantly formed were also favorable for the deposition of sulfides. 

DEPOSITS IN ALTERED GRANODIORITE 

In the course of mining the tactite deposits, pockets 

and seams of scheelite have been discovered in the adjacent granodiorite at a few places. Most of the occurrences are too small to be of any economic importance 

except where they can be mined with the tactite. At 

the Mountain King mine, however, some seams in 

granodiorite were so rich that the scheelite was dug 

out by hand with a pick and collected in powder boxes. 

Typically, coarse scheelite crystals are embedded in 

somewhat porous, light-colored, soft masses of micaceous material. The . micaceous material is mostly 

muscovite, some pale-brown hydrobiotite, and small 

clear crystals of quartz. Microscopic crystals of apatite with smoky gray centers are fairly plentiful. The 

associated scheelite is in subhedral to euhedral crystals, 

some of tabular habit and som~ with octahedral form. 

They range from 1 mm to as much as 1.5 em in size. 

A few are clear and colorless, but most are gray, dusky 

yellow, and moderate yellowish brown. With ultraviolet light the yellowish, brownish and colorless crystals fluoresce blue, while the gray ones give off a bluishwhite light. The scheelite crystals are concentrated 

in the central part of ovoid pockets and in the middle 

of the seams. 

The micaceous, scheelite-bearing seams are approximately 2 to 4 inches wide. At the Mountain 1\::ing mine 

they are more or less parallel to gently inclined joints 

in the granodiorite, and may be localized along some 

of the joints, though some of the seams pass into the 

adjacent hornfels. Their dimensions are uncertain, 

but probably they are neither very long nor wide, for 

apparently they do not extend more than a few feet 

or a few tens of feet beyond the granodiorite contact. 

The micaceous pockets in granodiorite are along or 

within a foot or so of the contact. They are more or 

less ovoid and 6 to 10 inches in greatest dimension. 

Their internal surface is drusy with small singly terminated crystals ()f quartz. Some drusy cavities were 

seen that have a little white mica on the surface of the 

quartz crystals, but it is uncertain whether or not these 

cavities were originally filled with mica. The granodiorite is slightly altered for % to 1 inch next to the 

micaceous seams and pockets, chiefly by slight sericitization of plagioclase. 

An unusual deposit of scheelite in the altered zone in 

the central part of the northern lobe of the Osgood 

Mountains stock contains scheelite with coarsely crystalline quartz in the most intensely altered part of the , 

body. At t.he section 5 (Marshall Canyon) pit, crystalline quartz in soft, altered granodiorite ranges from 

crystals an inch or so long to huge bodies with intergrown individual crystals as much as 4 inches in diameter and 6 inches in length. Some of the quartz contains small subhedral crystals of scheelite. The scheelite seems to be intergrown with the quartz, some of it 

may be in fractures. Some, however, is within the 

quartz as intracrystalline phantomlike films, as if it 

were deposited during formation of the quartz. At 

places in the pit irregular-shaped masses of sericite rock 

are found, wJ?_ich are similar to the masses that contain scheelite in seams and pockets elsewhere. 

ORIGIN 

The relations between the deposits of scheelite in 

tactite and the scheelite that is in fractures and cavities at a few places in the granodiorite is not clearly 

established, but presumably they belong to the same 

general episode of mineralization. The association of 

sericite aggregates with the scheelite is indicative of 

the alkaline composition of the solutions that traversed 

the granitic rock, the sericite having been formed by 

alteration of the feldspar. Calcium necessary for precipitation of scheelite from an alkaline solution (Lovering, 1941, p. 269-271) could have been obtained from 

plagioclase in the granitic rock or possibly, as all occurrences are near or at the contact, it came from adj acent calcareous beds. Scheelite that is intergrown 
MINERAL DEPOSITS 89 

with quartz at the section 5 (Marshall Canyon) deposit 

indicates that the siliceous solutions depositing quartz 

in the sericitized granodiorite also contained some 

tungsten. 

GOLD-ARSENIC DEPOSITS IN THE OSGOOD 

MOUNTAINS 

The Getchell gold mine, which was developed and 

successfully mined on a large scale by open-pit methods, 

had brought considerable attention to the Osgood 

Mountains before active mining of tungsten deposits 

began. The gold deposits are situated along the 

Getchell fault near the base of the northeast side of 

the range. 

A few years before our study of the Osgood Mountains quadrangle, Peter J oral em on made a careful field 

investigation of the Getchell gold deposit and a detailed 

laboratory study of the ore. .Our work at the Getchell 

mine was limited to a few days study of geologic features exposed in the open pits, and a brief examination 

of part of the accessible underground workings. Most 

of the data contained in this section, including the maps, 

have been taken from Joralemon's J;'eports (1949 16 ; 

1951). 

DISTRIBUTION 

The gold-arsenic deposits are in fractured ro_cks along 

the Getchell fault zone and its possible southward extension, the Ogee and Pinson fault. The main deposit, 

however, is confined to a zone nearly 7,000 feet long at 

the northern end of the Getchell fault zone. Marginal 

gold ore is known to occur in the Getchell fault zone at 

the Riley tungsten mine, and material in a fault zone 

east of the Pacific mine-possibly an en echelon branch 

of the Getchell fault-contains goldY The Ogee and 

Pinson mine south of Granite Creek yielded some lowgrade gold ore from fractured chert and hornfels. 

Some realgar is also reported here by J oral em on 

(1949,17 p. 92), which suggests that this deposit belongs 

to the same episode of mineralization as the Getchell 

mine. 

GENERAL FEATURES 

Joralemon (1951, p. 270) has described the general 

features of the gold deposits as follows: 

The gpld ore bodies are sheet-like masses that lie along the 

various strands of the Getchell fault zone. They extend at 

least 7,000 feet horizontally and 800 feet down the dip, and vary 

in width from a few feet to more than 200, averaging about 

40 feet wide. The vein pattern, extremely complex at the 

surface, becomes simpler with depth and, deeper than 800 feet 

18 Joralemon, Peter, 1949, The occurrence of gold at the Getchell mine, 

Nevada: Harvard Univ., unpublished doctoral thesis. 11 Op. cit., p. 91. 

below the surface, all the branch veins apparently join to 

form a single persistent structure * * *. The veins consist of 

sheared and mineralized argillite [here called hornfels] and 

limestone cut by quartz and calcite veins and containing a 

soft, plastic gumbo that has replaced the sediments. The gumbo 

is the principal gold-bearer. 

He said further ( p. 273) : 

The gumbo, the important gold-bearer, is unusual in that while 

it appears to be a fault gouge, it actually consists of minute 

subhedral quartz crystals embedded in a nearly submicroscopic 

intergrowth of quartz and amorphous carbon. In places veins 

of gumbo several feet wide and parallel to the surrounding 

sedimentary rocks end abruptly against unsheared limestone or 

argillite. 

Joralemon (1951, p. 273) regarded the gumbo as having formed hydrothermally in two stages: 

First was the replacement of wall rock by fine-grained quartz 

to form a porous aggregate of subhedral quartz crystals in 

narrow bedding veins. In the second stage, carbon, probably 

derived from underlying argillite, was introduced into the 

porous quartz veins and was deposited interstitially to the 

quartz. * * * Those portions of the veins that contained the 

most gumbo * * * were the most permeable parts of the 

veins * * * and the later ·hydrothermal solutions were there 

concentrated. 

Open, vuggy structures are common, especially in 

some of the calcite and late quartz veins; uncommonly, 

some small vugs occur in the gumbo.18 In contrast, 

however, there is a"* * * nearly complete lack of certain common epithermal structures such as 'colloform' 

banding, crustification, and comb structure" ( J oralemon, 1951, p. 306). 

MINERALOGY AND PARAGENESIS 

Nonmetallic gangue minerals of the deposit in addition to quartz, calcite and carbon are sericite and 

chlorite, and distinctly minor and sporadic barite, gypsum, fluorite, and chabazite. Metallic minerals include 

pyrrhotite, pyrite, marcasite, chalcopyrite, arsenopyrite, orpiment, realgar, and very minor amounts of 

scheelite, stibnite, cinnabar, and magnetite. The precious metals are gold and silver. The paragenetic relations of the minerals and their relative abundances are 

diagrammatically illustrated in figure 14, modified from 

J oralemon ( 1951, p. 305). 

Concerning the distribution of the metallic minerals, 

Joralemon (1951, p. 273) said that pyrite and minor 

pyrrhotite are the earliest sulfides and occur in irregular porous masses in the ore shoots, whereas in the 

"outlying segments of the veins * * *" pyrite tends to 

be euhedral. 

Marcasite constitutes about 5 percent of the iron sulfides in the 

central channelways, but is rare or nonexistent in the outlying 

areas. It occurs as irregular shells or rims encircling earlier 

pyrite grains. 

a Op. cit., p. 58-62. 
90 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

EARLY T LATE 

Quartz::~;~~=::::::~~~----·- - Calcite 

Carbon 

Sericite-·----·-

Chlorite .... ----·--

Pyrrhotite --

Pyrite .... -•• - .. -···--·- JXrsenopyrite _ 

Chalcopyrite --~­

Orpiment-~ 

Realgar _ ....... -•• •-·-

Marcasite --..... ·-~·- Gold--------------~ 

Silver - _..,.•--~-

Scheelite --

Chabazite --

Barite --

Gypsum--

Fluorite --

Stibnite --

Cinnabar -

Magnetite --

FIGURE 14.-Sequence of mineral dt=:Wosition at Getchell g.old deposit 

(from Joralemon, 1951, figure 29). 

Chalcopyrite is present in extremely small quantities 

as grains embedded in the gumbo and as blebs in the 

pyrite.19 

Arsenopyrite is present in minute euhedral crystals and is 

almost entirely restricted to parts of the veins in andesite 

porphyry.-( J oralemon, 1951, p. 273). 

One of the most distinctive mineralogical features of 

the Getchell deposit is the association of the arsenic 

sulfides, orpiment and realgar, with the gold. J oraleman (1951, p. 273) said that they 

• * * are the most abundant of the metalliferous minerals and 

unlike pyrite, are entirely restricted to the areas within the 

veins that now contain noteworthy quantities of gold. Orpiment is apparently earlier than realgar and is found only in isolated pockets, characteristically occuring in low-grade sections 

of the veins * * * [where it] constitutes as much as 40 percent 

of the mineralized material and is veined and coated by realgar. 

Realgar occurs throughout the commercial ore bodies in amounts 

ranging from 1 to 10 percent. It shows such a consistent relation to gold that the presence of realgar is usually a strong indication of gooq values. 

Very fin~ly crystalline stibnite, commonly accompanied by ilsemannite, is restricted to a few isola:ted pockets 

and narrower pipelike bodies where orpiment, realgar 

and marcasite are also present. Cinnabar is very un10 Op. cit., p. 79. 

common but coats calcite and chabazite in a few branch 

veins. (Joralemon, 1951, p. 273-274). 

According to J oral em on ( 1951, p. 276) 

Magnetite is apparently the latest of the metalliferous minerals 

associated with gold, and is the one most closely related to gold. 

It occurs only in Jll!icroscopic particles and has been seen only in 

the gumbo and andesite. * * * It is so closely associated with 

gold that any polished sections containing a cluster of magnetite 

grains have also some gold close at hand, generally within a 

millimeter. 

According to Mr. Keith Kunze (oral communication, 

1957) the gold ore contains a few one-thousandths to a 

few one-hundredths of one percent wo3, and the tungsten minerals scheelite and hlibnerite have been identified in ore on which metallurgical tests had been made. 

J oralemon 20 noted that in the north end of the 600 

level scheelite veinlets 

* * * less than a millimeter wide cut the andesite porphyry 

along minor slips. In a 2-foot-wide band in the gumbo near 

the dike, it occurs as fracture-filling, crusts, and as minute 

disseminated grains closely related to realgar. * * * Other 

minor veinlets occur in the wall rock northeast of the turn 

in the gold vein. 

The nature of the oxidized gold ore that was produced from the open pits at Getchell mine is poorly 

known ; J oral em on did not describe it, and none was 

seen by the writer, for it was mined out and primary 

sulfide ore had been reached in the open cuts. According to Hardy's ( 1938, p. 31; 1940, p. 4) descriptions 

the oxidized ore was siliceous and formed prominent 

outcrops; much of the silica seems to have been of secondary origin, the pyrite and pyrrhotite were 

* * * oxidized to limonite and hematite, and the sulphides of 

arsenic have been oxidized to a soluble form and removed 

by meteoric waters. 

GOLD 

Concerning the distribution of gold at the Getchell 

mine, Joralemon (1951, p. 276-288) said that economic 

amounts of gold are restricted to the veins within the 

fault zone; however, the entire zone containing the ore 

bodies may_ be visualized as a block of submarginal goldbearing rock within which are downward-projecting 

rootlike: ore shoots. The snbeconomic parts of the veins 

between the richer shoots, and the wall rocks for as 

much as 400 feet on either side of the ore body contain 

0.01 to 0.08 ounce of gold per ton. The ore boundaries 

are economic and at the economic vein \Yall the gold 

content increases to more than 0.1 ounce per ton.21 

According to J oralemon's laboratory investigations 

(1951, p. 276-281) the bulk of the gold in the economic 

parts of the deposit is in microscopic particles that 

20 Op. cit., p. 84-85. 

21 Op. cit., p. 86. 
MINERAL DEPOSITS 91 

range from a fraction of a micron to nearly 1 mm, 

and the smaller grains are more abundant than the 

larger. He found that visible gold is sparsely disseminated through all the rock types but that most of it 

is intimately associated with the fine-grained quartz.:. 

carbon matrix of the gumbo. In the gumbo some of 

the gold is uniformly distributed in small isolated particles, but it also is concentrated in pods or lenses as 

much as 100 microns wide and several millimeters long 

and is intimately associated with magnetite and carbon. 

Inclusions of visible gold are also found in all the major 

sulfides of the ore zone, though the amount is probably 

less than in the gumbo. Of the sulfides, pyrite and 

marcasite are the principal hosts. To account for submarginal values found in the rocks outside the ore 

shoots, where there is essentially no visible gold, 

Joralemon (1951, p. 281-292) reasoned that the gold 

may be mainly in solid solution in pyrite and carbon. 

SILVER 

The gold: silver ratio in bullion assays varies from 

2:1 to 134:1 and averages 10:1 for the entire bullion 

production ( Joralemon, 1951, p. 294). Joralemon 

(1951, p. 294) observed microscopic metallic grains 

in the Getchell ore that he concluded were native 

silver, although the particles were so small that conclusive chemical tests were not possible. No other 

silver-bearing minerals have been recognized, nor does 

silver seem to occur, except very rarely, as electrum, . 

the natural silver-gold alloy. 

The following observations on the occurence and distribution of silver were made by Joralemon (1951, p. 

295-296) : 

In general the amount of silver in the ore varies inversely with 

the amount of gold. Extremely rich portions of the ore body 

contains less silver than the portions of average grade. * * * 

Native silver persists with no large decrease in amount to the 

deepest levels of the mine. * * * Silver particles show the 

same variations in grain size a's the gold particles. * * * Like 

gold, silver occurs in the carbonaceous matrix of the gumbo 

and in sulfides, particularly the porous pyrite-marcasite 

intergrowths. 

ORIGIN AND CLASSIFICATION OF THE DEPOSIT 

The general sequence of deposition of the minerals 

in the Getchell mine ore zone is illustrated in figure 14. 

Joralemon (1951, p. 299) concluded that: 

The changes in the nature of deposition with time were 

brought about largely by changing conditions of deposition. The 

changes were gradational and the minerals characteristic of the 

early stage were being deposited in the outlying areas at the 

same time that the late stage minerals were forming in the 

ore shoots. At the earliest stage of deposition at the known 

depth horizon, pyrite containing low-grade gold was deposited, 

with some quartz, calcite, sericite, and chlorite, near the major 

690-159 0-63--7 

channelways. As the flow of hot solutions continued, more and 

more heat was carried into the zones of mineralization, the 

intensity-character increased, pyrite and lean gold were deposited toward the centers of mineralization by replacement or 

re-solution of those minerals that had been stable during the 

earlier and feebler stages then and there existing. Realgar, 

marcasite, and the economically important gold, which latter 

was becoming richer with time, were deposited in the main 

channelways at about the same time that the solutions in the 

outlying portions of the veins and wall rock were depositing 

disseminated pyrite and included submicroscopic gold in noncommercial amounts. 

Joralemon (1951, p. 292) regarded the rootlike ore 

shoots as representing the sites of original channelways 

along which most of the gold-bearing fluids passed 

throughout the period of gold deposition : 

These richer shoots coincide with the zones of extensive development of gumbo, suggesting that even before gold deposition 

began, these areas were most permeable to the mineralizing 

solutions. 

The gumbo, being unconsolidated, was more permeable 

than the enclosing rock, and therefore afforded more 

favorable channels for transportation of the gold-bearing fluids. The intense shattering of rocks in the ore 

zone, the vuggy structures, the unconsolidated nature 

of the gumbo, and the relatively shallow blanket of 

richer ore with its rootlike downward projections suggest that the Getchell deposit was formed under a relatively shallow cover ( J ora]emon, 1951, p. 308). 

In many ways the Getchell deposit is similar to the 

epithermal gold-realgar deposits at Manhattan, Nev. 

(Ferguson, 1924), 150 miles to the south. Both have 

a high gold-silver ratio and abundant realgar and 

orpiment in addition to carbon, pyrite, stibnite, fluorite, 

and cinnabar; lead, zinc, and copper sulfides are very 

scarce or absent. D. E. 'Vhite. (1955, p. 143) and 

Joralemon (1951, p. 306) called attention to characteristics of the Getchell deposit that are similar to hot 

spring deposits at Steamboat Springs, Nev., where 

siliceous muds precipitated at shallow depth in the 

spring system contain small amounts of gold, and where 

cinnabar and aggregates of minute stibnite needles are 

also being deposited. 

The GetcheU ore bodies can be classed as epithermal 

deposits, and Joralemon (1951, p. 309) suggested that 

they may represent a gradation between the depositional environments of typical epithermal gold deposits 

and lower intensity stibnite, realgar and cinnabar 

deposits. 

AGE OF MINERALIZATION 

The episode of mineralization that formed the Getchell deposit is later than the emplacement and solidification of the granodiorite . stock of Late Cretaceous 
92 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

age, for the ores are localized in a fault zone that cuts 

the granodiorite. The deposit also is younger than 

andesitic dikes that postdate the granodiorite and have 

been mineralized in the ore zone. Alluvium of Recent 

and possibly Pleistocene age overlays the mineralized 

zone. On evidence from geologic relations in the immediate area, therefore, the mineralization is of Tertiary age. 

Indirect evidence suggests that the Getchell deposit 

may be related to a widespread episode of mineralization of late Tertiary age in Nevada. Ferguson ( 1929, 

p. 131-141) has suggested a classification for the precious metal deposits of Nevada based on the gold-silver 

ratios of the ores, which is supported by certain correlative features that indicate that the classification is valid 

from a genetic standpoint (Nolan, 1933, p. 625). In 

this classification, deposits in which the ratio of silver 

to gold is greater than 1 to 1 seem to be of Miocene (preEsmeralda) age whereas those in which gold exceeds 

the amount of silver are of late upper Miocene or 

Pliocene (Esmeralda and post-Esmeralda) age ( Ferguson, 1929, p. 131-136). The high gold-silver ratio of 

the Getchell deposits puts it in the second class, and 

the mineralogical peculiarities strongly suggest that it 

is genetically similar to the Manhattan deposit, which 

belongs to the later gold-rich deposits. 

QUICKSILVER DEPOSITS 

Three quicksilver deposits of minor importance are 

known in the southern part of the Hot Springs Range 

within the Osgood Mountains quadrangle (Bailey and 

Phoenix, 1944, p. 90-91). Other deposits in the northern part of the Hot Springs Range have also been dedescribed by Bailey and Phoenix (1944, p. 101-106) 

and by Willden (in 1963). 

- The deposits are small, and as of 1955 only one, 

the Dutch Flat mine, had produced more than a token 

amount of quicksilver. One other, the K and K mine, 

is a potential small producer. The third, the Last 

Chance mine, appears to be 'no more than a poor prospect. The average grade of the ore at all these properties is low, probably less than 10 pounds of quicksilver 

per ton of. ore and more nearly on the order of 5 to-6 

pounds per ton, althO'Ugh small shoots and highly restricted pockets of higher grade material have been 

found in the Dutch Flat and K and K mines. 

The deposits are in fractured altered feldspathic 

sandstone and shale of the Harmony formation. Cinnabar, the only ore mineral of mercury that has been 

recognized in the deposits, fills fractures and also occupies spaces between mineral grains in sandstone. In 

some fine-grained rocks disseminated subhedral cinnabar crystals that are several times larger than the 

average grain size of the rock may have been deposited 

by replacement. The gangue minerals of the altered 

host rocks are the quartz and sericite and minor amounts 

of vein quartz, pyrite, calcite, limonitic iron oxide, and 

jarosite. Paragenetic relations are not completely clear 

and the entire sequence of deposition is not represented 

in all the deposits. Cinnabar is later than quartz and 

pyrite, for cinnabar fills fractures that contain brecciated quartz with inclusions of pyrite. There is no 

evidence that any of the quartz succeeded cinnabar. 

Calcite was introduced after cinnabar, as it cements 

breccia zones containing cinnabar, and also veins and to 

a minor extent replaces cinnabar, and encrusts the walls 

of fractures and small cavities. Weathering processes 

caused oxidation of pyrite and stained the rocks with 

iron oxide and in places formed jarosite. 

Although the rocks that contain the cinnabar have 

been altered, the alteration is not necessarily closely related to cinnabar mineralization, for at most places the 

altered rocks are associated with gold-bearing quartz 

veins and contain no cinnabar. Mostly, the alteration 

has a direct spatial relation to the granodiorite stock 

at Dutch Flat, and is possibly a late-stage phenomenon 

of granitic intrusion in the region. 

GOLD-BEARING QUARTZ VEINS IN THE HOT SPRINGS 

RANGE 

Near Dutch Flat on the western side of the Hot 

Springs Range the small stock of granodiorite and the 

surrounding sedimentary rocks of the Harmony formation are cut by gold-bearing quartz veins on which 

prospects and a few small mines have been located. 

The gold deposits are in bodies of quartz in the 

granodiorite stock, on its periphery at the contact with 

the sedimentary rocks, and in the sedimentary rocks 

beyond the stock for approximately 2,000 feet northward and southward. The quartz· bodies range from 

veinlets to well-defined veins and occur in two ways: 

(1) in the sedimentary rocks along faults or fault 

zones that strike north-northeast to northeast and dip 

moderat~ly to steeply northwest or southeast and (2) 

in the granitic rock in fractures that strike north-northeast to north, dip gently to moderately west, and are 

parallel to a joint system in the granitic stock. Some 

of the prospects are on faulted zones with no quartz, 

but the larger properties were all developed on quartz 

bodies. 

Most of the quartz veins are from 3 inches to 2 feet 

thick, and. veinlets and stringers that range from less 

than 1 inch to 3 inches in thickness are plentiful. Veins 

as much as 5 to 8 feet thick are unusual, but were seen 
MINERAL DEPOSITS 93 

in a few places. The veins vary considerably in thickness and individual bodies are seldom continuous for 

long distances, but several discontinuous bodies may 

occupy a zone and constitute a minable "vein." The 

veins are parallel to the fractures that they occupy 

and obviously their emplacement was controlled by earlier fracturing. The veins have sharp clean walls, show 

all the features indicative of fracture filling, and give 

no evidence of replacement origin. Commonly they 

are brecciated and may be displaced by later faults. 

The quartz is white, except where stained by brown and 

yellow iron oxide,o and commonly is more or less vuggy. 

Small clear terminated prisms of quartz project into the 

cavities. Some specimens show comb structure. Only 

a few inclusions of wallrock in quartz were seen. 

The wallrocks adjacent to the fraotures and veins 

are more or less altered, whether they are granodiorite, 

sedimentary rocks of the Harmony formation, or hornfels formed from the sedimentary rocks at the granodiorite contact. Although the stock at Dutch Flat is 

somewhat altered everywhere, alteration is noticeably 

more intense where the granodiorite is fractured and 

veined by quartz. In the sedimentary rocks and hornfels, alteration is most intense close to the quart.z veins 

and to faults that have no visible quartz. The effects 

of the alteration are essentially the same in the granitic 

or sedimentary rocks and have resulted in the formation of sericite and kaolinite. The alteration effects are 

described in more detail on pages 46-49. 

Samples of vein material from three of. the properties 

we:re assayed for gold and silver, 22 and values ranging 

from a trace to 0.05 ounce of gold per ton and 0.3 to 

1.5 ounces of silver per ton were reported. The assays indicate a ratio of gold to silver of 1 to 3; these 

samples cannot be considered representative of the ore 

mined, but no other data on grade of the ore are a vailable. Small stopes in some of the mines indicate that 

parts of some veins contained small relatively highgrade ore shoots. Presumably the gold is free and 

occurs in the quartz; no gold-bearing minerals have been 

recognized. A specimen of qua.rtz containing visible 

gold in limonite-filled fractures was found by one of us 

on the dump of a shallow prospect shaft on the ridge 

southwest of the granodiorite stock. No silver minerals were recognized, and probaply the silver is contained in galena. · 

The quartz contains very minor amounts of the following metallic sulfide minerals: stibnite, galena, 

chalcocite(~), pyrite, sphalerite, and chalcopyrite. In 

addition veins in the mines at locations 4 and 5 (fig. 15) 

contain a few grains of scheelite at widely scattered 

22 Assays for the authors by Union Assay Office, Inc., Salt Lake City, 

Utah. 

places. Mostly, the sulfides are sparsely scattered 

through the quartz as individual grains 1 to 3 mm in 

maximum dimension, less commonly as irregular shaped 

bodies as much as 20 mm in size. Some sulfides occupy 

cavities in the quartz, and sulfides also occur along fractures. Stibnite is one of the commonest sulfides, and 

several large pieces of stibnite were found on the dumps, 

but none of comparable size were seen underground. 

Galena and light-brown sphalerite occur together. A 

gray metallic mineral uncertainly identified as chalcocite is' fairly common but occurs as exceedingly minute 

individual grains. Pyrite is also fairly common but 

seemingly not more plentiful than the other sulfides, 

and chalcopyrite is rare. The paragenetic relations of 

the sulfides to one another could not be satisfactorily 

determined, but all are later than the quartz. 

Distribution of the veins strongly suggests that they 

are genetically related to the granodiorite stock at Dutch 

Flat. The veins cut the granitic rock as well as the 

metamporphosed rocks that border the stock, which suggests the veins were formed after the stock was emplaced and had cooled sufficiently to solidify and 

maintain open fractures. The character of the veins 

and their accompanying minerals are indicative of intermediate or mesothermal conditions of formation, 

though the association of stibnite seems to mean that 

they were formed in an environment that approached 

the epithermal type. None of the veins is known to 

cut the closely associated volcanic rocks of Tertiary age, 

and the volcanic rocks are not affected by the alteration 

that modified the sedimentary rocks and intrusive body, 

which is further evidence that the veins ·were formed 

earlier than the volcanic episode. The: volcanic rocks 

rest on a surface that is only about 100 feet higher than 

the minimum altitude at which the roof of the stock 

may have been, and therefore it is assumed that a considerable thickness of rock which contained the veins 

was removed by erosion, for surely the stock was emplaced several hundred, possibly more than a thousand, 

feet below the surface. 

GOLD-SCHEELITE-CINNABAR PLACER 

Placer deposits at Dutch Flat on the west side of the 

Hot Springs Range (fig. 15) contain significant 

amounts of gold, scheelite, and cinnabar. The following description has been abstracted from an account 

published elsewhere by Willden and Hotz ( 1955). 

Placer gold was discovered in the area by F. G. Wendell 

in 1893 (Vanderburg, 1936, p. 94); cinnabar probably 

was also noted in the early placer operations. The 

original discovery of scheelite in the placer is not 

known, but scheelite was recovered along with cinna-
94 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

11J030' 

7 . N 

J: 

Base enlarged from part of Osgood Mountains 

quadrangle. Area west of quadrangle 

boundary from aerial photographs 

R. 40 E. 

Geology by P. E. Hotz and 

Ronald Willden, 1953 

EXPLANATION 

5I 

Alluvium Heavier shading indicates area most 

likely to contain profitable concentrations of placer gold, scheelite, 

and cinnabar 

Granodiorite 

D 

Harmony formation 

Contact, approximately located 

Fault 

Dashed where approximately located 

Strike and dip of beds 

.,rfiO 

Strike and dip of overturned beds 

90 -+-

Strike of vertical beds 

~ 

Mine 

X 

Prospect 

Numbers I through 17 are described 

in table 22. Dutch Flat mine 

described in text 

0 1000 2000 3000 FEET 

CONTOUR INTERVAL 100 FEET 

DATUM IS MEAN .SEA LEVEL 

FIGtrRJII 15.-Map of the Dutch Flat district. 

bar and gold in a small washing plant in 1952. The 

only published production figures are those given by 

Vanderburg ( 1936, p. 94) and Smith and Vanderburg 

( 1932, p. 55) for placer gold. Gold production in the 

first year after discovery was valued at about $75,000 

and the total placer production in the district at about 

$200,000, nearly all of which was recovered by working with rockers (Vanderburg, 1936, p. 94). 

Two types of placer deposits are present in the areas: 

stream deposits containing water-transported material, 

and slope-wash deposits containing material weathered 

from rocks in the immediate vicinity. The streamtransported material occurs in the bottoms of the larger 

canyons and on the alluvial fan below the mouth of 

Sodarisi Canyon (fig. 15). The stream deposits range 

in depth from 10 feet in the upper parts of the canyons 

to 35 feet at the mouth of Sodarisi Canyon, with an 

average depth of about 20 feet. The depth of the 

alluvial fan below the mouth of the canyon is known 

from a few scattered prospect pits to range from 12 

to 90 feet. 

The slope-wash deposits are found on both sides of 

El Paso Gulch to a height of as muoh as 50 feet above 

the creek bottom. The slope-wash deposits, as the term 

is used here, includes some stream-transported material 

which was left on the sides of the canyons as the streams 

cut down through bedrock. Some high assays reported 

from the slope-wash material are probably due to such 

~tccumulation of placer material from the stream channels. The slope-wash deposits range in depth from 5 

to about 25 feet, with an average vertical depth to 

bedrock of 12 feet. 
MINERAL DEPOSITS 95 

Sampling of the placer deposits has been sporadic 

and in general inadequate to delimit channels or pay 

streaks. Smith and Vanderburg (1932) report that 

the placer covers an area 8,000 feet long and 300 to 2,000 

feet wide. Twenty acres of this ground sampled in 

1904 (Vanderburg, 1936, p. 94) gave an average value 

in gold of 31 cents per cubic yard based on a price of 

$20.67 per ounce. Assays of the placer material give 

values of gold ranging from 20 cents to more than $1.00 

per yard (at $35 per oz.), mercury ranging from 12 to 

60 cents per yard based on the price of mercury in 

March 1954 ($185 per flask), and scheelite ranging 

from 60 cents to $2 per yard based on a price of $39 per 

20-pound unit of WOa (Willden and Hotz, 1955, p. 

666). Don B. Sebastian of San Francisco, Calif., had 

the property under lease in 1954. Preliminary samples 

of the alluvial fan and lower stream gravels, covering an 

area of about 50,000 square yards, indicate an average 

grade of $1.50 in combined gold, mercury, and tungsten 

based on the prices of the metals in August 1954 (mercury at $290 per flask) and a 60-percent W03 concentrate (Willden and Hotz, 1955, p. 666). Values up to 

$30 per yard for some of the slope-wash material have 

been reported, but such high values are probably a result of sporadic nuggets in the sample. 

Some of the scheelite is in quartz fragments, particularly in the slope-wash material. This association 

is regarded as an indication that at least part of the 

scheelite was de:rived from erosion of quartz veins, even 

though the quartz veins exposed in the mine workings 

carry very little scheelite. Calcareous shale and sandy 

limestone beds occur in the Harmony formation in the 

area, and possibly contact-metamorphic tungsten deposits in these calcareous beds were the source of part 

of the scheelite in the placer. A small amount of garnet in the placer lends some support to this idea, but no 

contact-metamorphic tungsten deposits are exposed in 

this area. 

The cinnabar grains range in size from minute dust 

to nuggets about 1 em in diameter. The larger grains 

are not single crystals of cinnabar but consist of aggregates of cinnabar, quartz, and feldspar. Cinnabar 

commonly makes up 70 to 80 percent by volume of the 

aggregates. It shows a closer correlation of grain size 

with distance of transport than either scheelite or gold. 

The larger grains are found only in the upper part of 

El Paso Gulch, whereas the material from the alluvial 

fan is rarely larger than 0.5 mm and is usually very 

fine grained, with average grain size smaller than 0.02 

mm. The shear zone of the Dutch Flat mine containing cinnabar provides an adequate source for the cinnabar found in the placer. 

The gold in the placer occurs as coarse angular grains, 

which are sometimes attached to a quartz matrix, and 

as fine angular free grains. Vanderburg ( 1936, p. 96) 

reported that the purity of the gold is 940 fine and 

states that the largest nugget found had a value of 

$180. A sample of gold from concentrates of slopewash material assayed by C. W. Hammond (written 

communication 1955) of the Nevada Mining Analytical 

Laboratory was 954 fine. The samples of placer material from the fan that were examined contained no 

gold. Of the many quartz veins known in the Dutch 

Flat district, those that were assayed contained some 

gold, and rich pockets of ore have been reported in some 

of the mines, so there is an adequate source within the 

district for the gold in the placer. 

Scheelite occurs as nearly equant grains that range 

in size from 0.05 mm to 1 em. The larger grains are 

found in the slope-wash material from the sides of El 

Paso Gulch and from stream deposits in El Paso Gulch 

above the junction with Sodarisi Canyon. Most scheelite grains in samples of the upper part of the alluvial 

fan are not more than 1 mm in size, and their average 

size is about 0.5 mm. The scheelite fluoresces blue 

white and is presumed to be free of molybdenum. 

Several other minerals are associated with the gold, 

scheelite, and cinnabar, especially in the fine size fractions of the placer concentrates. These are magnetite. 

ilmenite, hematite, zircon, and pyrite, with small 

amounts of hornblende, monazite, garnet, and augite. 

These minerals are scarce in the size fractions of concentrates larger than about 1 mm, but they become 

increasingly abundant in the fine-size fractions, until 

in the size fraction smaller than 0.1 mm, only 25 percent 

of the total heavy minerals consist of gold, scheelite, 

and cinnabar. 

The concentration of the minerals is largely due to 

the proximity of the placer deposits to the sources of 

the placer minerals. Greater distance of transportation 

of the minerals would result in progressive loss of cinnabar and, to a lesser extent, scheelite due to comminution of these brittle minerals by abrasive action during 

transport in the stream. 

MINOR DEPOSITS OF LEAD AND COPPER 

In addition to the minor amounts of copper, lead, 

and zinc that are associated with the tactite at many 

places, two small lead deposits and showings of copper 

mineralization of little or no economic importance are 

known in the Osgood Mountains and the Hot Springs 

Range. All are in Paleozoic sedimentary rocks and, 

except for a lead deposit at the Richmond mine, relatively far from exposures of granitic rock. 
96 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

LEAD DEPOSITS 

The only deposit that is reported to have had production is at the Richmond mine on the northwest side 

of the Osgood Mountains. Small seams-and bunches 

of galena accompanied by sphalerite, pyrite, chalcopyrite, and considerable scheelite occur in metamorphosed 

limestone ·and tactite close to the granodiorite contact. 

According to Hess and Larsen (1921, p. 303) the mine 

was operated for many years as a silver mine with a 

small production. Presumably the silver was in galena, 

because no other silver minerals have been recognized. 

The sulfide mineralization seems to have been an episode 

that was related to the deposition of scheelite, although 

apparently galena and sphalerite were formed later 

than the scheelite. 

In contrast, a small deposit of galena with subordinate amounts of sphalerite at the Silver Hill prospect 

at the south end of the Hot Springs Range is far from 

. any granodiorite intrusive body. This deposit is in a 

fault zone in sedimentary rocks of the Harmony for:tnation, and the sulfide minerals fill fractures and spaces 

between breccia fragments in the country rock. Supergene alteration of the galena and sphalerite and secondary deposition have formed some anglesite, cerussite, and hemimorphite, which accompany the primary 

minerals. 

COPPER DEPOSITS 

Some showings of copper mineralization in the Osgood Mountains have been explored by small pits and 

short adits where green stains in the rocks have attracted 

the attention of prospectors. The deposits are in calcareous and dolomitic rocks of various formations of 

Paleozoic age, and are generally several thousand feet 

beyond the granodiorite stock. None are known in the 

Osgood Mountain quartzite. . 

All the deposits consist of small seams and irregular 

bunches of chalcopyrite, usually with some pyrite, and 

some are associated with small amounts of galena. Vein 

quartz may or may not be present. Secondary copper 

minerals including malachite, chrysocolla, and rarely 

azurite, and green stains of indefinite mineral composition are also common. 

BARITE DEPOSITS IN THE OSGOOD MOUNTAINS 

Three small barite deposits are known in the Osgood 

Mountains. The largest is on the southeast side of the 

range, near the mouth of Hogshead Canyon. Barite 

is also exposed in a prospect pit approximately 2 miles 

to the northeast, near the Blue Bell mine at the 

mouth of Felix Canyon. A small deposit is on the 

northwest flank of the range north of Anderson Canyon. 

None of the deposits is known to have had commercial 

production of barite, and only the one. at the mouth 

of Hogshead Canyon appears to be a potentially commercial deposit. 

The deposits are geologically similar in several respects. They are relatively far from the granodiorite 

stock, ranging from 6,000 feet to as much as 15,000 feet 

from the nearest granodiorite contact. They replace 

dolomite and limestone chiefly, and chert to a lesser extent, in strata of Cambrian and Ordovician age; none 

are known in younger strata. Except for a little vein 

quartz locally, the harite seems to be unaccompanied by 

other ore or gangue minerals. Mostly the barite is dark 

gray, but some is gray to light gray. Commonly it is 

medium grained and equigranula.r, but it also occurs as 

globular or nodular concretions which have an internal 

radiating coarsely fibrous structure. Some aggregations of tabular crystals have crested surfaces where the 

crystals terminate on the outside of the nodules. The 

globular forms range from a few millimeters to as much 

as several centimeters in diameter; in places a carbonate 

bed may contain many scattered small separate globules 

of radiating barite. 

The age of the deposits cannot be clearly established. 

They are certainly later than the strata of Cambrian 

and Ordovician age which they replace. The small 

deposit near the Blue Bell mine is in an area where there 

has been some metamorphism and copper metallization 

that are probably related to the emplacement of granodiorite, but the relations of the barite to the copper and 

metamorphism are not known. Gianella ( 1940) has 

described similar barite deposits in Lander and Eureka 

Counties which he regards as of hydrothermal origin, 

and he suggests that they may range from Jurassic to 

late Tertiary in age. 

SILICA 

The Valmy formation west of Stone Corral contains 

a quartzite unit which consists of quartz in a silioa 

cement. The only deleterious constituents observed are 

traces of colorless mica and occasional minute grains 

of apatite and zircon. A chemical analysis of a random chip sample of the quartzite exposed in the low 

ridge west of Stone Corral is presented below : 

Si02 --------------- 99.6 ~02 --------------- 0.01 

AJ20a .00 --------------

Fe20a -------------- FeO ---------------

~gO --------------- CaO ---------------

Na20 ---------------

~0 ----------------

.20 

.08 

.04 

. 03 

.09 

. 01 

. 02 

P20; ---------------

MnO ----------·-----

II20 ----------------

002 ----------------

. 01 

.10 

.05 

Sum ----------- 100.24 

Sp gr (lump)-------- 2. 57 

Sp gr (powder)------ 2. 64 

[Analyzed by methods similar to those described in U.S. Geol. Bull. 

1036-C. ·Analysis by U. S. Geol. Survey] 
MINES AND PROSPECTS 97 

The quaTtzite bed is about 150 feet thick and is well 

exposed for approximately 3,000 feet along the strike. 

The exposure stands as much as 50 feet above the general ground level, is close to the east side of the low 

ridge, and could be quarried with relative ease. It is 

readily accessible by 10 miles of unpaved road from 

Golconda. 

MINING FUTURE OF THE REGION 

The main mineral resources that are known in the 

Osgood Mountains quadrangle are the deposits of tungsten ore and the gold-arsenic reserves in the Osgood 

Mountains. 

The reserves of tungsten ore contained in the Osgood 

Mountains scheelite deposits have been considerably 

reduced by the high production since 1951, and probably most if not all of the ore that was readily obtained 

by open-pit methods is gone. There remain, however, 

important known deposits that can be mined underground at the Pacific, Riley, Riley Extension, and 

Tonopah mines. From the available data it does not 

seem that proximity of the Getchell fault zone to these 

mines will limit the downward continuation of these 

tactite deposits. The dips of both the contact and the 

fault are in the same direction, and it appears. that the 

fault will not intersect the contact until much greater 

depths, if at all. Irregularities in the granodiorite 

contact, which can be defined by exploratory drilling, 

are probably the most important factors in determining 

the extent of known deposits or in predicting new ore 

bodies. At the Granite Creek mine considerable ore 

remained to be mined when the deposit was studied, but 

it was fairly clear that the bottom of the main deposit 

had been reached. 

Exploration of the underground continuation of tactites mined at the surface in the Tip Top pits west of 

the Granite: Creek mine may be profitable, and the steep 

slope and depth of the canyon should make these deposits exploitable by relatively short, direct adits. 

Similarly, additional reserves may lie beneath Pit 2 at 

the Kirby mine. 

The possibility of finding new scheelite-bearing tactite bodies at the surface where limestone is in contact 

with the granodiorite seems remote, for the area has 

been rathe-r thoroughly prospected. Tactite float is 

known, however, at a few places in the canyon of Osgood Creek, and possibly warrants some investigation 

(seep. 112). 

Exploitation of the gold deposit at the Getchell mine 

depends on the ability of an operator profitably to mine 

and extract gold from a low-grade ore whose high arse.nic content presents a difficult metallurgical problem. 

No other deposits of comparable size have been found 

along the Getcheii fault zone, although there has been 

considerable exploration along it by the Getchell company. Possibly the Getchell deposit, like other epithermal precious metal deposits, will become of lower grade 

with depth and hence completely uneconomic. 

It seems unlikely that any important production can 

be expected from the deposits of quicksilver in the Hot 

Springs Range, but the gold-scheelite-cinnabar placer 

at Dutch Flat might yield a moderate amount of quicksilver and tungsten as well as gold. Probably no more 

than token amounts of galena and sphalerite will be 

produced from the few small deposits of these minerals. 

Barite and possibly silica may eventually be produced 

from the area in modest quantities. 

MINES AND PROSPECTS 

TUNGSTEN DEPOSITS 

The tungsten deposits of the Osgood Mountains are, 

with a single exception, in metamorphic rocks on the 

contact of a stock of granodiorite in the northern part 

of the range. A small, economically unimportant deposit occurs within altered granodiorite in the cent:ral 

part of the northern lobe of the stock. The location 

of the deposits is shown on figure 16. Most of the 

deposits and the most productive mines are distributed 

intermittently along the east contact of the northern 

and southern lobes of the stock; a large deposit and 

some less important ore bodies are on the south contact 

of the southern lobe; some small deposits are on the 

west contact of both lobes. 

HISTORY AND PRODUCTION 

Scheelite was discovered in the Osgood Mountains in 

about 1916 (Hess and Larsen, 1921, p. 247) after the 

attention of prospectors had been directed toward contact-metamorphic scheelite deposits by the high prices 

paid for tungsten at that time and the establishment 

of tungsten mills near Lovelock, Nev., and Bishop, Calif. 

When Hess and Larsen made their reconnaissance 

examination of contact-metamorphic scheelite deposits 

in 1917 and 19l8, several tactites in the Osgood Mountains had been prospected for scheelite, and claims had 

been located, but no ore had been produced (Hess and 

Larsen, 1921, p. 301-304). Some of the deposits were 

on claims that had previously been prospected for 

copper and silver. 

Active development and production of tungsten ore 

from mines in the Osgood Mountains began in the summer and fall of 1942 during the general stimulation of 

production, increased prices, and a Federal purchase 
98 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

program brought about by increased demands for tungsten during World War II. The principal mines were 

·developed and mined by Getchell Mine, Inc., and U.S. 

Vanadium Corp. In 1942 the Getchell company remodeled its gold mill to enable milling and concentration 

of scheelite ores coming from their mines, and to treat 

ores from other properties on a custom basis. In 1945 

a mill was erected at the Riley mine by the Northern 

Nevada Mining Corp., but only a small amount of ore 

was treated until the mine and mill were purchased by 

U.S. Vanadium Corp. later in the same year. Active 

R. 41 E. 

36 

12 

13 

24 

25 

31 

' \MOUN,:,~': KING 

5 

33 

/ I 

RILE.Y _. X 

SECTIONS 

PIT 

EXTENSION 

MINI!J 

7 8 

\ 

0 1 MILE 

EXPLANATION 

~ 

Mine 

X 

Prospect 

_, 

I ,~;g; 

PIT 

16 

21 

28 

T. 39 N. 

T. 38 N. 

41° 10' 

FIGURE 16.-Index map of the Osgood Mountains tungsten deposits. 

development and mining continued in the district until 

the summer of 1945, when the demand for high domestic 

production of tungsten was lessened with the· termination of World War II. All except the Riley mine had 

ceased operation in July 1945, but the Getchell mill 

continued to process stockpiled ore into 1946. A small 

production of scheelite from the Riley mine was maintained until early 1948. 

From 1948 through 1950 the scheelite mines in the 

Osgood Mountains were idle. Then, in 1951 mining was 

resumed in response to a Federal purchase program, 

which raised the price of tungsten concentrates to $63 

per unit of W03 and was designed to stimulate domestic production of tungsten to supply the rapidly expanding consumption consequent on the increased use of 

tungsten carbide, especially for military purposes. 

Full-scale development and mining of the tactite deposits was still going on in 1954 and 1955 when they were 

examined by the U.S. Geological Survey. At that time 

Getchell Mine, Inc., owned and operated four of the 

producing mines, one was operated by U.S. Vanadium 

Corp. (later the Union Carbide Nuclear Co.), and two 

belonged to independent operators. All the ore mined 

in the district was milled and concentrated at the 

Getchell mill, the mill that was built at the Riley mine 

in 1945 having been previously dismantled. 

Table 20 is the recorded production from the Osgood 

Mountains tungsten deposits. 

GRANITE CREEK MINE 

Tactite has been mined at several places in Granite 

Creek along the south boundary of the Osgood Mountains granodiorite stock, on the steep south side of the 

canyon where the intrusive is in contact with limestone 

of the Preble formation. Most of the production h~ 

been from the Granite Creek mine; less important deposits west of the Granite Creek mine l;lave been mined 

from surface pits known collectively as the Tip Top 

mine. 

The Granite Creek mine is in the SW14 sec. 29, T. 

38 N., R. 42 E., (fig. 16) approximately one-half mile 

above the mouth of Granite Creek. The mine is easily 

accessible by a good unpaved road. 

The Granite Creek mine, owned by Getchell Mine, 

Inc., was first active in the fall of 1942 and continued 

in operation until the summer of 1944. A crosscut was 

driven on the 300 level to the tactite (pl. 3) and a drift 

was run along the strike (Newman,23 1955, p, 16), from 

which the tactite zone was stoped to the surface. Production during the period of slightly more than 2 years 

amounted to 88,000 tons of ore averaging 0.5 percent 

23 Newman, W. J., 1955, Tungsten mining at the Getchell mine: Nevada Univ., unpublished Mining Engineer thesis, 43 p., 5 figs., 3 tables. 
MINES AND PROSPECTS 99 

W03 (Hobbs and Clabaugh, 1946, p. 15). Mining was 

resumed in December 1950, and in 1951 a drift 1,700 

feet long with the portal at the canyon mouth was 

driven on the 500 level to intersect the ore body below 

the 300 level ( pls. 2, 3) . An intermediate level ( 400 

level) was then driven off raises from the 500 level (pl. 

3) and the ore bodywasstoped uptothe300level (Newman, 1955, p. 19-20). In 1955 mining was being actively pursued at all levels, and production for the 

!l/2 yoars from December 1950 through June 1955 exceeded 188,000 tons. Total production from 1942 was 

276,000 tons. 

The country rock at the Granite Creek mine (pl. 2) 

is limestone of the Preble formation which has been 

intruded by granodiorite. Mostly the limestone strikes 

from N. 40° E. to N. 60° E. and dips from 35° to 

60° southeast. Locally it departs from this general attitude and in places has been squeezed and tightly 

folded on a small scale, but no major folds have been 

recognized. Some minor faults were observed underground in the western workings on level 300 that dip 

steeply east or southeast along the limestone-granodiorite contact. In the mine the limestone is metamorphosed to calc-silicate rock, marble, and tactite. Tactite occurs along only part of the granodiorite-limestone contact, an indication that special conditions were 

necessary for its formation. The distribution of scheelite is almost entirely restricted to the tactite, though 

minor amounts are found in silicated limestone near 

the granodiorite contact. 

The gross trend of the granodiorite contact in the 

Granite Creek mine area is easterly, and the contact 

dips steeply south; but in detail it has irregularities 

and sends off dikelike apophyses southward into the 

country rock. The main scheelite-bearing tactite body 

at the Granite Creek mine is at the contact between 

limestone and granodiorite in the angle of a reentrant 

that is formed by a narrow granodior:ite offshoot on 

the west and broader ·protrusion on the east. Between 

the surface and the 300 level the granodiorite contact is 

TABLE 20.-Production of tungsten ore, Osgood Mountains 

Production, 1943--1945, Hobbs and Clabaugh, 1946, p. 14-27; Getchell-owned properties and Riley mine, 1950-1955, from owners; Richmond mine, 1954, Valley View mine, 

1951-1955, Mountain King and T.N.T. mine, compiled by U.S. Bur. Mines and published with permission of owners 

Property Year 

Avg. grade, Contained 

Tons of ore in percent units of WOa WOa 

Getchell Mine, Inc: 

Tip Top mine _______________________________________ 1954-55----------------------

Grani te Creek mine_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 1942-45 ___ - - - - - - - _ - - - - - - - - - - - 37,000 1 (0.3) 11, 100 

88, 000 .5 44,000 

December 1950-June 1955 _____ _ 188,000 . 5 94,000 

Pacific mine_________________________________________ February 1952-June 195n ______ _ Kirby mine _________________________________________ 1942-43 _____________________ _ 1952-53 _____________________ _ 

226, 700 .3 68,010 

32,000 . 43 13, 760 

34,550 . 43 13,820 Top Row pit_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 1954 _______________________ --

Riley Extension mine_________________________________ 1951-June 1955 _______ -- __ ---- Tonopah mine __________________________ _____________ 1950-June 1955 ______________ _ 

Alpine (Porvenir) mine_______________________________ 1943 _______________________ -- 1950-53 _____________________ _ 

2,800 (. 3) 840 

188,800 (. 3) 56,640 

19, 750 (. 3) 5, 925 

8,000 .5 4,000 

43, 700 (. 3) 13, 110 

---- Total ____________________ ______ _________________ ------------------------------ 869, 300 -------- 325,205 

Union Carbide Nuclear Co: 

(Formerly U.S. Vanadium Corp.) Riley mine __________________________________________ 1943-44______________________ 80,000 . 63 50,400 

1945_________________________ 8,500 . 70 5,950 

1946-48_ - - --- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 1952-June 1955_______________ 264,600 . 57 150,822 

Richmond mine ______________________________________ 1942-43______________________ 31,500 . 5 15,750 

1954_________________________ 2, 800 560 

.2 

Total ___________________________________________ ------------------------------ 387,400 -------- 223, 482 

1=====1 

Valley View mine ________________________________________ 1943-44 _____________________ _ 

1951-55-------------~--------

1, 500 (. 5) 750 

67, 300 .5 33, 650 1------ ---- Total ___________________________________________ ------------------------------ 68,800 -------- 34, 400 

1=====1 

T.N.T., Inc.: 

Mountain King and T.N.T. mines _____________________ 1951-55 __ -------------------- 18,650 .6 11, 190 1------

Total ___________________________________________ ------------------------------ 18, 650 -------- 11, 190 

Total, all mines _______________________________________________________________ _ 1, 344, 150 -------- 594,277 

1 Figures in parentheses are estimated average grade. 
100 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

troughlike, with the keel plunging approximately 50° 

S. 13 °E.; the trough is slightly overturned to the west, 

so that on the eastern side granodiorite overlies the tactite and metamorphosed limestone. The reentrant 

angle persists down to the 400 level, but the eastern 

side of the trough is very short. On the 500 level the 

contact, though somewhat concave southward, no longer 

has the reentrant angle and troughlike form. Development and drill-hole exploration underground indicate 

that the limestone in the reentrant is isolated from the 

main body of limestone by a narrow east-west granodiorite dike that cuts through the limestone a short 

distance south of the mine workings and is continuous 

with the granodiorite on each side of the reentrant. 

When the mine was examined in 1955, it appeared 

that the limestone was a downward-tapering roof pendant whose root lay not far below the 500 level. 

The form of the tactite deposit can be most clearly 

visualized from the map and sections through the mine 

shown in plate 3. The main tactite body was continuous from the surface to the 500 level, and lay in the keel 

and lower part of the troughlike structure. It varied 

considerably in width, ranging from 5 to 25 feet and 

averaging between 15 and 20 feet above the 400 level 

and approximately 10 feet below that level. It was 

most persistent in depth on the west side of the trough, 

where it was followed continuously from the surface to 

the 500 level, though between the 400 and 500 levels 

its length became considerably shorter. It was longest 

on the 300 level, whe·re it lay on both sides of the keel, 

and tapered towards the surface and in depth. The 

tactite body exposed in the 500 level workings is small 

and of irregular shape. 

The tactite parallels the granodiorite contact rather 

closely and tends to be most persistent and wider where 

the strike of the limestone and the granodiorite contact 

are parallel, although tactite was also formed on the 

300 level, where the contact is about perpendicular to 

the strike of the beds. The tactite terminates along 

strike by pinching or ending abruptly in blunt tongues 

or slightly interfingering contacts against calc-silicate 

rock and marble. In most places there is no obvious 

geologic reason for the termination, such as a sharp 

change in strike and dip of the granodiorite contact, 

change in lithology, or control by faulting. 

Underground drill-hole exploration of the block 

southeast of· the mine workings between the 300 and 

500 ·levels showed that some tactite containing scheelite 

occurs at the contact of limestone with an offshoot of 

granodiorite. The body probably is continuous with 

the tactite in the drift at the end of the southeast crosscut on the 300 level (pl. 3) and is present approximately 

130 feet southeast of the 400 level. The size and extent 

of the body is virtually unknown. 

Exploration southwest of the mine workings failed 

to discover tactite along the contact with the long southward-projecting dike of granodiorite on the 300 level. 

A short crosscut and drift west of the south west drift on 

the 300 level exposed a small body of tactite that is in 

a position similar to that occupied by a small mass 

of tactite exposed at the surface in the end of the reentrant of limestone between two granodiorite tongues 

west of the mine (pl. 2) . 

TIP TOP MINE 

Discontinuous bodies of tactite occur along the granodiorite-limestone contact on the south side of Granite 

Creek for about 2,000 feet west of the Granite Creek 

mine. Except for a little prospecting, the deposits 

west of Granite Creek mine were not worked until the 

summer of 1954 when Getchell Mine, Inc., commenced 

open-pit mining, which continued until June 1955. 

About 37,000 tons of ore was produced from three open 

pits, the bulk coming from two of them. The average 

grade of the material mined is not known. The two 

larger pits are shown on plate 2; a third one is on the 

crest of the ridge southeast of the upper pit shown 

on plate 2. The workings, called collectively the Tip 

Top pits, are in SEYt,SE% sec. 30, T. 38 N., R. 42 E. 

The country rock is granodiorite, and limestone and 

hornfels of the Preble formation. The sedimentary 

rocks strike N. 50° E. toN. 70° E. and dip 50° to 60° SE. 

Locally there is some minor folding but no large-scale 

folds have been recognized. The granodiorite contact 

trends west with many slight local variations in strike, 

and with some south-trending dikelike offshoots, from 

the Granite Creek mine to the middle pit of the Tip 

Top mine (pl. 2). At the west end of the area shown 

on the map (pl. 2) the contact assumes a southwest 

trend which continues to the crest of the ridge (Hobbs 

and Clabaugh, 1946, pl. 2). In its large-scale relations 

then, the granodiorite contact cuts across the strike of 

the sedimentary rocks, but locally the strikes of both 

are more or less parallel. Observations of the contact 

in the open cuts show that it dips southeast to south 

at about 60° to 70° ; where strike of the contact is 

parallel to the strike of the sedimentary rocks it dips 

more or less in conformity with the bedding. 

The limestone is recrystallized to marble, calc-silicate 

rock, and tactite adjacent to the granodiorite. The tactite bodies are discontinuous, occurring only where the 

granodiorite intrudes limestone; the hornfels contacts 

are barren. Limestone is recrystallized to marble for 

as much as several hundred feet from the contact;. calc-
MINES AND PROSPECTS 101 

silicate rock occurs sporadically along the contact and 

is confined to a zone within a few feet of the contact. 

At a few places limestone and marble near the contact 

are complexly crumpled. The tactite bodies are confined to the granodiorite contact and everywhere are 

next to the granodiorite, between the intrusive rock 

and the limestone. The tactite bodies are tabular and 

as long as 400 feet. The largest of those exposed in 

the open pits are about 6 feet thick, and they average 

about 4 feet; however, the mined-out parts may have 

been wider. 

The tactite is a brown garnet rock with accessory 

pyroxene and at places contains some coarsely crystalline calcite. The contact with granodiorite i~ sharp and 

clean, and that between tactite and limestone or its 

metamorphosed equivalents is also abrupt. At many 

places the granodiorite immediately adjacent to the 

contact is strongly impregnated with quartz, contains 

visible pyrite and chalcopyrite, is richer in dark minerals, and contains hornblende in addition to biotite. 

Narrow reaction zones and indefinite contacts between 

calc-silicate rock and pyroxene-bearing granitic rock 

are observable in places. In addition to scheelite, the 

tactite contains at places a little chalcopyrite and pyrite, 

and some is stained with green secondary copper minerals. The tungsten content of the tactite is not known. 

The tactite bodies in the Tip Top pits occupy parts 

of the contact that are relatively smooth. Limestone 

adjacent to the tactite bodies is not obviously different 

from that adjacent to barren parts of the contact, but 

the area is not well enough exposed to eliminate entirely compositional or structural variations in the host 

rock as factors of possible importance. It may be significant that the important tactite bodies seem to be 

situated at positions along the contact, where it closely 

parallels the strike of bedding in the limestone. 

MARCUS MINE 

The Marcus mine is 2 miles northwest of the Granite 

Creek mine in NE%,SW%, sec. 24, T. 38 N., R. 42 E. 

(pl. 1), at an altitude of approximately 7,250 feet. A 

rdad from the Granite Creek mine was built in 1955 

by Getchell Mine, Inc. Before 1955, the Marcus mine 

had been explored by several trenches and open cuts 

and two short adits, but no ore had been produced. In I 

,July 1955, Getchell Mine, Inc., commenced open-pit 

mining and when the property was visited in 1955 a 

few hundred tons of ore had been produced. 

The Marcus deposit is on the west eontact of the 

southern lobe of the granodiorite stock. The rocks adjacent to the granodiorite are argillaceous hornfels and 

interbedded limestone of the Preble formation (pl. 1). 

At the Marcus mine a bed of limestone is partly enclosed 

between the main body and a northwestward-projecting 

tongue of granodiorite. Tactite containing scheelite 

has been formed in limestone at the east contact of the 

granodiorite apophysis. Beyond the tactite the limestone is marbleized and eonverted to calc-silicate rock. 

The excavation made by Getchell Mine, Inc., was on 

a tactite body described by Hobbs and Clabaugh ( 1946, 

p. 27) as being 2 to 10 feet wide and at least 75 feet 

long. The tactite is a medium-grained garnet rock containing caleite, epidote, quartz, a little idocrase, and 

scheelite. Hobbs and Clabaugh (1946, p. 27) estimated the ore to contain approximately 1.7 percent 

W03 • A tactite body that is exposed in a . short adit 

downhill approximately 120 feet to the south may or 

may not be a continuation of the same body. Two small 

isolated exposures of tactite of lower grade, about 600 

and 1,000 feet north of the upper deposit, were also reported by Hobbs and Clabaugh (1946, p. 27) but were 

not seen during this later study. 

PACIFIC MINE 

The Pacific mine is at the front of the Osgood Mountains approximately three-f-ourths of a mile north of 

the mouth of Granite Creek, in eastern part sec. 29, T. 

38 N., R. 42 E. (fig. 16). An excellent graded dirt road 

from the property joins the main road to Getehell mine 

approximately 1 mile to the east, and also connects with 

the Granite Creek road to the south. 

Before 1951 the Pacific mine was a prospect with no 

recorded production. Hobbs and Clabaugh ( 1946, p. 

18-19) estimated a reserve of 40,000 tons of tactite containing 0.5 percent W03 , and predicted that larger 

masses of tactite would be discovered underground. 

From 1951 through 1956 the Getchell Co. mined more 

than 279,000 tons of tungsten ore from an open pit at 

the Pacific mine (Newman, 1957, p. 91). Ore was mined 

underground from two levels, and by early 1957 stopes 

from the upper level had broken through into the floor 

of the open pit at two places. As of July 1955, more 

than 4,500 tons of ore had been mined by underground 

methods. 

The Pacific deposit (fig. 17) is on the east contact of 

the southern lobe of the granodiorite stock. Limestone 

of the Preble formation that strikes north toN. 15° W., 

with an average dip eastward of a'bout 40°, is intruded 

by granodiorite. The contact trends generally north 

and dips 55° to 60° E, possibly becoming steeper with 

increased depth. Little unmetamorphosed limestone is 

to be found at the Pacific mine, as most has been metamorphosed to calc-silicate rock composed of interlayered diopside-plagioclase hornfels, calcite-wollasto-
102 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

nite rock, and some layers of marble. East of the 

carbonate unit is a zone of strongly crushed and sheared 

black hornfels, which is at least 600 feet wide where 

it is exposed in the adit of the lower or 300 level of 

the underground workings. The eastern part of the 

limestone and calc-silicate rock unit is also somewhat 

broken where it is exposed underground. The faulting 

is along a zone that seems to be en echelon with the 

southern extension of the Getchell fault zone. 

EXPLANATION 

Tactite 

Containing 5Citeelite 

---~z 

Limestone and marble 

Silicoted in port 

The scheelite deposit is confined to tactite, and the tactite is at the contact between granodiorite and calcsilicate rock, but tactite is not found everywhere that 

granodiorite intrudes- carbonate beds or their metamorphosed equivalent. The main tactite body is confined to a relatively short distance along the contact 

south of a hook-shaped southward projection of granodiorite which formed a trough that plunges steeply 

south. The tactite body was tabular, with its thickest 

FIGURE 17.-Block diagram of the Pacific mine. 
MINES AND PROSPECTS 103 

part near the trough, and became thinner and pinched 

out southward. It was mined down dip for approximately 550 feet to the lower level ( 300 level) of the underground workings; most of it was mined from an 

open pit. A smaller body of tactite was mined approximately 600 feet north of the main deposit where apparently another jog in the contact formed a trough 

that plunged steeply northeast. This body was mined 

out from the surface workings. 

VALLEY VIEW MINE 

The Valley View mine is in low hills at the east front 

of the Osgood Mountains in SE%,SE%, sec. 20, T. 38 N., 

R. 42 E. (fig. 16), near the mouth of Bunch Creek, and 

joins the property of the Pacific mine on the north. A 

good unpaved road 1.4 miles long connects the property 

with the main road to Getchell mine approximately 

5lj2 miles south of the Getchell Mill. 

According to Hobbs and Clabaugh (1946, p. 24) the 

property was originally prospected for silver and copper before scheelite was recognized in the district. Harold's Club Mining Co. of Reno, Nev., leased the property 

in 1943 and commenced mining tungsten ore, which, 

beginning in July 1943, was shipped to the Metals 

Reserve Co. stockpile at Getchell mine. Ore production 

between the summers of 1943 and 1944 was from underground workings that included a 225-foot adit along 

the contact zone south from Bunch Creek and more extensive workings along the contact north from the creek. 

The property had a relatively small production of approximately 1,500 tons during this period (Hobbs and 

Clabaugh, 1946, p. 24). From 1944 to 1950 the property was idle, but in 1951 mining operations were resumed by the Valley View Mining Co., les~es, and 

67,318 tons of ore whose average grade was 0.5 percent 

W03 was mined from 1951 through 1955. The ore was 

trucked to the Getchell mine, where it was milled on 

a custom basis. Total production from 1943 through 

1955 was approximately 69,000 tons. 

Between 1951 and 1955 some ore was mined from 

shallow open cuts in tactite along the contact south of 

Bunch Creek but the main operation ·was in the tactite 

north of the creek (pl. 4) . Here the ta-etite was mined 

in a deep narrow open cut that was more than 250 feet 

deep in the summer of 1955; the taetite body has been 

mined for a depth of nearly 300 feet down the dip. 

Country rocks at the Valley View mine are granodiorite, limestone, calc-silicate rocks, marble, hornfels, and 

a little biotite schist that have been formed by metamorphism of limestone and pelitic sedimentary rocks of the 

Preble formation by the granodiorite intrusive body. 

The tactite ore body is on or near the contact between 

granodiorite and limestone. 

The tactite is like that elsewhere in the district:r composed of. reddish-brown garnet and dark-green pyroxene; some is massive and some is composed of alternate 

layers of pyroxene with relatively coarse garnet and 

narrower layers of fine-grained pyroxene with little or 

no garnet. Scheelite occurs as grains a millimeter or 

less in diameter in the tactite. In the wall next to the 

bottom of the pit the tactite is veined by gray greasylooking quartz that encloses fragments of tactite and 

dark biotite-rich streaks. The quartz contains specks 

and veinlets of chalcopyrite and pyrite. In a crushed 

zone along the granodiorite-tactite contact in the north 

end of the pit, probably subsidiary to the fault along the 

west side of the open pit (pl. 4), tactite is altered to a 

porous crumbly rock composed of a soft dark-greenishyellow to moderate-greenish-yellow material, identified 

as a mixture of nontronite and quartz. Presumably the 

nontronite was formed by alteration of the tactite, for 

it veins, encloses, and apparently replaces garnet-rich 

tactite. Some jasperoid with cavities coated by finely 

crystalline quartz is associated with the altered rock. 

In the surface workings south of Bunch Creek a 

ta-etite layer is exposed between the granodiorite and 

limestone. In part, the surface workings reached to 

the depth of an old adit (not shown on pl. 4) that followed the layer southward. The layer averages 2lf2 to 

3 feet in thickness and is exposed for approximately 175 

feet at the surface. The main ore body was north of 

the creek, and as it was originally exposed at the surface 

it extended northward from near the portal of the north 

adit as a thin tabular body ranging from 2 to 7 foot in 

width for about 300 feet, where it expanded into an irregular-shaped body of mixed hornfels and tactite 200 

feet long and 50 to 100 feet wide (Hobbs and Clabaugh, 

1946, p. 25) . The inset in plate 4 taken from Hobbs' 

and Clabaugh's report (1946, pl. 7), illustrates the shape 

and extent of the tactite at the surface before open-pit 

mining began. Judging from the original surface expression of the tactite and its present distribution in the 

pit, the wide northern end of the tactite body plunges 

northeastward at about 50°, becoming narrower with increasing depth. From the relations visible in 1955, the 

main tactite deposit that was mined from the open pit 

was separated from the footwall granodiorite for most 

of its length by a layer of calc-silicate rocks and marble 

5 to 15 feet thick, and it was overlain by similar rocks. 

It was in contact with granodiorite only at its northern 

termination and south of the pit, where it narrowed 

from its maximum thickness. It is worth noting that 

the expanded part of the tactite is where the granodiorite contact makes an abrupt change in direction of 

strike from the somewhat irregular but generally northerly strike pursued in the southern part of the mine to 
104 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

a roughly easterly trend. The result is that the granodiorite contact changes from a generally concordant 

attitude with respect to the bedding of the sedimentary 

rocks to a strongly discordant relation, and the tactite 

was formed in a pocket partly enclosed by granodiorite. 

Two conspicuous faults are exposed in the walls of 

the main open cut. They strike slightly west of south 

and dip steeply east. The west fault cuts through 

granodiorite in the north face of the open cut, where 

it strikes approximately N. 10° W. and dips 60° E. 

Southward it is on the central contact between limestone 

and a tongue of granodiorite east of the limestone and 

tactite. In the north adit a wide faulted zone that is 

probably a continuation of the west fault forms the 

east wall of the tactite layer (Hobbs and Clabaugh, 

1946, p. 24). The tactite in the pit dips in the same 

direction as the fault but the angle of dip se~s to be 

about 10° less than the dip of the fault, and therefore 

the fault may limit the downward extent of the tactite 

(pl. 4, section A-A'). Possibly this part of the fault 

follows the original intrusive contact of the granodiorite tongue, but even so, the tactite may be limited 

in depth by convergence of granodiorite from the hanging wall and footwall sides. The east fault separates 

limestone and hornfels on the east from the granodiorite on the west in the pit. Its strike is essentially 

parallel to that of the west fault, but it is nearly vertical or dips steeply east. It is interesting to speculate 

that if the fault on the ea.st side of the pit intersects 

the granodiorite-tactite contact 'beneath the pit, there 

might be a down-faulted tactite body to the east at 

depth. Although the faults cannot be traced beyond 

their exposures in the open cut they are, judging from 

the strong crushing along them, probably persistent for 

considerable distances north and south of the mine. 

They are chiefly parallel to the strong zone of faulting 

along the east front of. the range and it seems reasonable to suppose that they are related in age and origin. 

North of the main open cut a blunt projection of 

granodiorite extends eastward across the north-trending sedimentary rocks. On the north side of the projecting granodiorite, where it is in contact with limestone, a zone of thin discontinuous tactite crops out for 

200 to 250 feet. One of the tactite bodies is explored by 

an adit 110 feet long, and is approximately 3 to 8 feet 

wide. Hobbs and Clabaugh (1946, p. 25) estimated the 

tactite along this zone to be 3 to 10 feet wide and to have 

a low tungsten content of 0.3 percent to 0.4 percent 

wo3. 

KIRBY MINE 

The Kirby mine includes three open-cut operations 

in NW~~ sec. 17, T. 38 N., R. 42 E. (fig. 16), in the 

valley of Julian Creek (also commonly known as Kirby 

Creek or Ranch Creek). Two of the open cuts are on 

the south side of the valley, and one is on the north side, 

near the bottom. They are easily accessible by 13t4 

miles of good dirt road that joins the main road to 

Getchell mine near the Riley mine. 

In 1917 the property, in part at least, was on claims 

held by Fayant and Blaine, and was briefly described 

by Hess and Larsen (1921, p. 301-302) as a potentially 

important scheelite prospect. The claims were subsequently relocated by Mr. Kirby and in 1942 the property was sold to Getchell Mine, Inc., which mined approximately 32,000 tons of tungsten ore containing 

more than 12,000 units of wo3 from underground and 

open-pit workings in a deposit south of the creek at an 

altitude of about 6,300 feet. The ore contained 

an average of 0.43 percent W03 (Hobbs and 

Clabaugh, 1946, p. 17). Mining ceased in the summer 

of 1943 and the property lay idle until 1952, when the 

Getchell company resumed mining and developed two 

smaller open -cut operations on deposits that are, respectively, lower down the south side of the valley, and 

near the valley bottom north of the creek (pl. 5) . The 

operations were closed down in 1953 after having produced 34,550 tons during this secondperiod of operation. Total production from 1942 to 1952 was 66,550 

tons. 

The tactite deposits of the Kirby mine area are on 

the southeast contact of the northern lobe of the granodiorite stock, near the narrow central waist of the stock 

(fig. 16). The granodiorite intrudes shale and limestone of the Preble formation (pl. 5), which have been 

metamorphosed to hornfels, marble, and calc-silicate 

rock. Tactite is restricted to the contact between granodiorite and limestone and is a scheelite-bearing garnetpyroxene rock like that found elsewhere in the district. 

The average strike of the sedimentary rocks is N. 50° 

E., and they dip moderately southeast. The contact of 

the granodiorite trends generally northeast, also, but is 

irregular and strongly discordant locally. Dikelike 

apophyses extend out into the sedimentary rocks from 

the main granitic body. It is clear from the map (pl. 5) 

that localization of the important tactite bodies is related to abrupt bends in the contact, which form reentrants of calcareous rocks in the granodiorite. 

The principal deposit of tactite, here called the No. 1 

pit, was in the southwest part of the Kirby mine area 

where the granodiorite contact makes a right-angle turn. 

This deposit has been essentially mined out. A pendantlike body of tactite projected downward into the 

granodiorite (pl. 5, section A-A') and tapered out 

westward beneath limestone that overlies the granodiorite. West of the No. 1 pit, thin tabular bodies of tactite probably not more than about 5 feet thick occupy 
MLNES AND PROSPECTS 105 

the gentle eastward-dipping granodiorite-limestone conl tact. They are nearly parallel to the slope of the htl1 

and therefore the wide prominent outcrops represeht 

only small volumes of ore. An attempt was made to 

strip and mine these thin bodies of tactite in 1943, bbt 

the operation was unprofitable and was abando~ed 

(Hobbs and Clabaugh, 1946, p. 18-19). Hobbs and C]abaugh ( 1946, p. 18) estimated 

* * * 1,500 tons of measured ore containing 600 units of \VOa, 

2,000 tons of indicated ore containing 900 nnits of WOa and 2,000 

tons of inferred ore containing 800 units of 'VOa 

from the tactite bodies on this hillside. 

A small tactite body is exposed in a small open cut approximately 450 feet southeast of the No.1 pit. The 1eposit is situated in a shallow reentrant of calc-silicate 

rock and hornfels in granodiorite. The tactite has been 

nearly all mined out, and a small lenticular body ~f 

mixed tactite and calc-silicate rock remains. The cou!ntry rock in the reentrant is mostly hornfels, and the volume of tactite probably is not large. 

During the operations in 1952-53 an open-pit mine, 

here called the No. 2 pit, was developed on a fairly lar~e 

body of tactite on the south slope of Kirby Creek 1 at 

an altitude of about 6,100 feet. The tactite body is taBular and dips approximately 60° SE., parallel to tJhe 

northeast granodiorite contact and discordant to dhe 

bedding of the limestone. Its widest part and northeast termination is where the granodiorite contact makes 

a short right-angle bend; here it is about 10 feet thi1,k. 

It wedges out gradually southwestward along strike 

and ends below the top of the cut, a horizontal distance 

of about 110 feet and about the same distance vertically. 

A septum of hard epidote-rich granitoid rock separaFes 

the tactite from the granodiorite footwall. Limestone in 

the hanging wall has been converted to calc-silicate rdck 

and marble. The granodiorite exposed in the loJ er 

east wall of the open cut contains many dark streJks 

rich in hornblende and biotite. that are arranged subparallel to the contact with the overlying sedimenta)r:v 

rocks. 

A tactite layer about 2 feet thick is in a small exposure of calc-silicate rock approximately 110 feet sout~ of 

the upper rim of the No. 2 pit. Bedrock between here 

and the open pit is concealed by soil and colluvium, hut 

probably this is an isolated body of tactite separ te 

from the tactite in the open cut. 

Tactite was also mined from a small open cut on the 

lower north slope of Kirby Creek, here called the N d. 3 

pit. This deposit was also situated at a right-ankle 

bend in the granodiorite contact. It is almost mi:ded 

out and only some thin remnants of the original body are 

left. The rocks intruded by the granodiorite re 

mainly hornfels with some calcareous interbeds, and 

limestone is subordinate. A little tactite has formed in 

the hornfels, presumably from interbedded calcareous 

layers, but the main deposit seems to have been a small 

body on the contact between granodiorite and limestone. 

The unreplaced limestone exposed in the pit is thickbedded to massive marble. Some of the remaining tactite contains much glassy quartz, some of which is 

coarsely crystalline. Some of the quartz contains 

scheelite. 

The tungsten resources of the Kirby mine area are 

definitely limited, and probably the major production 

from the area is past. Some tactite remains to be mined 

from the deposits west of the No. 1 open cut, but the 

amount is limited by the sheetlike form of the bodies, 

which are not expected to have much extension in depth. 

The steeply dipping tactite body exposed in No. 2 pit has 

a limited strike length. Its extension in depth is not 

known. Its position on the hill makes further openpit mining expensive, and underground development 

may be required to mine the body profitably. 

TOP ROW PIT 

The Top Row pit is on the east side of the Osgood 

Mountains, approximately 0.25 mile south of Summer 

Camp Creek in SW1j1 sec. 9, T. 38 N., R. 42 E. (fig.l6). 

It is at an altitude of approximately 5,750 feet and is 

situated on the southeast side and near the top of a small 

knob about 600 feet west of the road from Riley mine to 

Julian Creek and the Kirby mine. A short steep road 

makes the mine accessible from the Julian Creek Road. 

In June 1954, Getchell Mine, Inc., opened a pit on a 

small tactite body and mined approximately 2,800 tons 

of tactite. Because the tactite body is small, further 

development has not been undertaken. 

The tactite is on the east contact of the northern lobe 

of the granodiorite stock. . Argillaceous hornfels is the 

principal rock type in this area, but scanty amounts of 

thin lenticular limestone are interbedded with the argillaceous rocks. A small body of limestone in a reentrant 

angle along the slightly irregular granodiorite contact 

was replaced by scheelite-bearing garnet-pyroxene tactite. A little tactite is left, probably less than 25 feet 

long and 5 feet wide at the surface; other calcareous interbeds have been converted to calc-silicate rock that 

contains no scheelite. 

RILEY AND RILEY EXTENSION MINES 

The Riley and Riley Extension mines are in the northern part of sec. 9 and southern part of sec 4, T. 38 N., 

R. 42 E. (fig. 16), respectively, at the east front of the 

Osgood Mountains between Hansen Canyon on the north 
106 GEOLOGY AND MINERAL DEPOSITS_. OSGOOD MOUNTAINS QUADRANGLE 

and Summer Camp Creek on the south. Parts of the 

tactite deposit are east of the quadrangle boundary. 

Both properties are served by good dirt roads that join 

the main road to Getchell mine approximately onefourth of a mile to the east. 

· . The Riley mine, formerly known as the Dernan property, was prospected during World War I, but little if 

any tungsten was produced. J. E. Riley leased the 

property from heirs of the Tom Dernan estate in the 

fall of 1942, and developed and operated it as the Riley 

mine (Northern Nevada Mining Co.) until1945. About 

80,000 tons of ore averaging 0.63 percent W03 was 

mined from surface pits and sold to MetalsReserve Co. 

from June 1943 to July 1, 1944. A mill was constructed 

on the property and beginning in May 1945 about 8,500 

tons of ore, reported to average 0.70 percent W03 ore, 

were treated up to July 31, 1945 (Holmes, 1946, p. 3). 

In 1945 the United States Bureau of Mines conducted 

a diamond-drill exploration of the Riley mine, testing 

the underground extent of the ore to depths of 500 feet 

down the dip from surface exposures, and greatly enlarged the known reserves (Hobbs and Clabaugh, 1946, 

p. 21 ; Holmes, 1946). 

In October 1945, the U.S. Vanadium Corp. purchased 

the property and continued operation of the mine until 

1948. Production during this period is not known, although in 194 7 the mine was the second largest producer 

of tungsten concentrates in Nevada (Minerals Yearbook, 1947, p. 1191). The mine was idle from 1948 to 

August 1952, when mining was resumed by the same 

company. In 1955 the name of the property owners 

was changed to Union Carbide Nuclear Co. From 1952 

to June 1955, approximately 264,600 tons averaging 

nearly 0.5 percent WOa was produced from combined 

surface and underground operations. 

The northern extension of the Riley mine or body is 

on property owned by Getchell Mine, Inc., which began 

underground development and mining at the Riley Extension mine in 1951. By June 30, 1955, about 161,000 

tons of ore had been produced and mining and further 

development was still being actively pursued. In November 1953 a small open-cut mine was started in another ore body on the ridge south of Hansen Canyon at 

an altitude of about 6,000 feet. The operation ended 

in the summer of 1954 after approximately 27,800 tons 

of tactite averaging 0.5 percent W03 had been produced. 

Since mining started at the Riley mine in 1943, total 

combined production from the Riley and Riley Extension mines to June 1955 is estimated to have been more 

than 550,000 tons, not including the small open-cut 

operations at the Riley Extension mine. This, then, was 

the largest single tactite deposit in the district. 

Before 1952, the Riley mine was entirely a surface 

operation, and the ore was mined from a series of open 

pits. Since August 1952, mining has been conducted 

underground and continued from surface pits as well 

(pl. 6). Underground development and mining (pl. 

7) was initiated by driving an adit in the hanging wall 

on the 200 level, from which drifts were developed 

northward and southward on the ore. Tactite above 

the level was mined from shrinkage stopes. An inclined shaft was sunk down dip from the 200 level, and 

drifts .were driven on three levels from which stopes 

were developed to mine the ore. At the south end of 

the deposit a short incline was sunk from pit 4 in a 

northwest direction and a level and stope were developed to mine the underground continuation of the 

tactite in pit 3. 

Underground development of the Riley Extension 

mine by Getchell Mine, Inc., was started in 1951 on the 

northern continuation of the Riley mine tactite body 

(pl. 7). The underground workings are connected with 

the Riley mine on the 200 level and by stopes from the 

300 level and 400 sublevel. A 23,4-compartment vertical 

shaft was sunk to 183 feet, with a station 152 feet below 

the collar from which cross cuts were driven to the ore 

body and raises put up to the 200 level. 24 Intermediate 

levels were driven off these raises, from which shrinkage stopes were developed. In 1955 an inclined shaft 

was being sunk down dip from the 400 level to develop 

more ore at depth. 

The tactite deposits of the Riley and Riley Extension mines are on the east contact of the northern lobe 

of the granodiorite stock. Limestone and interbedded 

shale of the Preble formation have been intruded by 

the granodiorite. The Riley mine has one main tactite 

zone. Ore has been mined from three tactites at the 

Riley Extension mine: the main tactite, called the east 

vein, is an extension of that in the Riley mine; a second 

important underground ore body is west of and stratigraphically beneath the first; and a third was mined at 

the surface still farther west at the granodiorite 

contact. 

The granodiorite contact trends generally north, but 

it has abrupt changes in direction that, from south to 

north, carry it progressively farther west (pl. 6). North 

of pit 4 the contact strikes practically west approximately 400 feet to· pit 3. From pit 3 of the Riley mine 

north to the little valley west of the vertical shaft at 

the Riley Extension mine the general strike of the granodiorite contact is a few degrees west of north, and the 

dip is from 30° to 55° east, predominantly near 40°. 

Along this course the contact has several small sharp 

124 Newman, 1955, p. 22-23. 
MINES AND PROSPECTS 107 

bends. West of the vertical shaft the granodiorite ends 

in a blunt northward projection and the contact swings 

westward approxima.tely 900 feet and partly encloses 

a broad reentrant of sedimentary rocks between the 

projection and the main part of the granitic body. The 

sedimentary rocks strike generally south, dip moderately east and are for the most part parallel to the 

granodiorite contact, except locally where the granodiorite transects the structure. 

The sedimentary rocks tl!djacent to the granodiorite 

at the Riley mine are practically all limestone or metamorphic rocks derived from limestone; at the Riiey Extension mine a wide body of hornfels with some interbedded limestone occurs in the reentrant of sedimentary 

rocks where the granodiorite contact swings west. 

Some of the limestone is rather pure, thick bedded to 

massive, medium to coarse grained; much is impure, 

fine grained, and thin bedded. Metamorphism of the 

limestone near the granodiorite contact has formed marble, calc-silicate rock, and small bodies of wollastonite 

rock as well as the tactite that contains scheelite. The 

hornfels is dark and fine grained and has a more or 

less well defined platy parting. Close to the granodiorite contact it grades into a purplish or brownish 

fine-grained, commonly somewhat schistose biotitequartz-plagioclase rock. At many places in both mines 

a stratum of this schistose rock that ranges from a few 

inches to as much as 10 feet in thickness is the footwall 

between the tactite ore body and granodiorite. Schistose hornfels forms the hanging wall as well as the 

footwall of the "west vein" in the Riley Extension mine. 

The rock east of the limestone belt is dark gray, soft, 

and crumbly brecciated hornfels or argillite that marks 

a fault zone along the front of the range. 

Dikes of hard fine-grained dacite porphyry cut all 

the rocks at the surface and underground. 

The "east vein," a tactite zone mined in both the Riley 

and the Riley Extension mines, extends along the granodiorite contact for approximately 1,600 feet at the 

surface and on the 200 foot level (pis. 6, 7). Mostly 

it is between marble or calc-silicate rock and the underlying granodiorite or schistose biotite hornfels. The 

tactite includes reddish brown medium- to coarsegrained garnetite that locally contains some green 

clinopyroxene of the diopside-hedenbergite series, 

banded rocks composed of alternating .. reddish brown 

garnet and green clinopyroxene layers, and, less commonly, rocks composed almost wholly of green clinopyroxene with minor amounts of garnet. Locally, especially at the footwall contact but also extending well 

into the tactite zone, tactite is partly replaced and 

veined by irregular masses of gray glassy quartz. 

690-159 0-63-8 

Granodiorite also contains an rubundance of this late 

quartz where it is the footwall of quartz-rich tactite. 

Scheelite is almost completely restricted to the tactite 

and occurs as small discrete grains that are generally 

more plentiful in the garnetite and garnet-rich layers 

of garnet clinopyroxene rock than in the pyroxene layers or the pyroxene tactite. Scheelite is more abundant, 

coarser, and commonly has fairly w~ll defined crystalline forms in the quartz-rich tactite. The tactite contains a few small grains of pyrite and chalcopyrite at 

many places; concentrations of these sulfides in small 

masses, measurable in inches, locally constitute as much 

as 30 percent of the tactite. Generally the sulfide concentrations are in places where glassy quartz is abundant. The tactjte also contains small concentrations 

of molybdenite in places. Sphalerite, commonly accompanied by a little galena, is fairly common but not 

as plentiful as pyrite and chalcopyrite. 

The contacts of the tactite in the Riley mine and its 

continuation in the Riley Extension mine are sharp 

and definite. Even the hanging-wall contact is abrupt, 

and in places transects the ·bedding of the limestone or 

its metamorphosed equivalent. Generally, a zone of 

calc-silicate rock overlies the tactite zone and in contrast therewith has a highly variable thickness and 

indefinite outer limit. In some places pure marble or 

marble containing wollastonite adjoins the tactite zone 

and may lie between tactite and the zone of calc-silicate 

rocks. 

The most continuous body of tactite in this zone was 

in the northern part of the Riley mine and the Riley 

Extension mine where a roughly tabular mass has been 

developed and mined for approximately 800 feet down 

dip (pis. 6, 7). The tactite, which pinches and swells 

along strike and down dip, ranges from 2 or 3 feet to as 

much as 20 feet in thickness and is 10 feet thick on the 

average. 

At its north end the tactite ends rather abruptly by 

thinning and fingering out along the strike. Presumably the termination coincides with the ending of the 

apophysis of granodiorite that underlies the north end 

of the tactite zone, for limestone favorable for replacement is present where the tactite ends. At its south 

end the taotite thins down and ends where the granodiorite footwall swells eastward. The swell, which is 

between pits 1B and 10 at the surface (pl. 6), pitches 

northeastward in depth, thereby causing the tactite 

to terminate farther north at successively deeper levels 

in the Riley mine. On the 500 level of the Riley mine 

(pl. 7) the tactite is thin, and drill-hole data east of 

the tactite on the 400 level of the Riley Extension mine 

indicate that the body may be too narrow to mine eco-
108 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

nomically less than 100 feet below the level (pl. 6, sectionA-A'). 

The tactite bodies are less continuous in the southern 

part of the Riley mine, where they are localized by 

irregularities of the granodiorite contact. Sharp bends 

in the conta.ct form troughlike structures that plunge 

slightly north of east at an angle of about 40°. The 

thick parts of the tactite follow the troughs, while the 

thin or barren sections are on the ridges between the 

troughs where the contact bends outward (pl. 6). 

The granodiorite contact and the tactite are generally 

west of the Getchell fault zone, however, at the south 

end of the property in pit 4, granodiorite and the ore 

zone end against the fault. Northward the contact is 

progressively farther west of the fault. Underground 

there is no evidence that the ore north of pit 4 is cut 

off by the fault.; mostly the fault and granodiorite contact ha.ve nearly the sa.me eastward dip (pl. 6, sections 

0 -0' and D-D'). 

At the Riley Extension mine another tactite zone, 

called the "west vein" by the operators, was discovered 

underground approximately 125 feet west of and 100 

feet stratigraphically below the tactite that is the continuation of the Riley mine tactite (section A-A', pl. 6). 

This lower tactite does not crop out at the surface but 

possibly the limestone lens that is partly exposed on 

the hillside approximately 900 feet N. 70° W. of the 

shaft (pl. 6) is part of the same layer, which at 

depth is changed to tactite. The footwall is schistose 

biotite hornfels and the hanging wa:ll is calc-silicate 

rock and impure thin-bedded limestone. 

The tactite of the "west vein" is different from the 

tactite of the "east vein" and most other tactites in the 

area, for it is a greenish-gray massive fine-grained rock 

composed of matted pale-green actinolitic amphibole 

and calcite; a little typical garnet-pyroxene tactite is 

found in places but is not common. Grains of scheelite 

are scattered through the tactite, which also contains 

some small grains of pyrrhotite and chalcopyrite. The 

boundaries of the tactite zone are less definite than those 

of the garnet-pyroxene tactites elsewhere, and scheelite 

also is not as strictly confined to the tactite. During the 

underground mapping of the "west vein", it was difficult in many places to determine the limits of the ore 

without an ultraviolet lamp. 

The granodiorite apophysis that is below the "east 

vein" tactite in the Riley Extension mine overlies the 

hanging-wall rocks of the "west vein" (pl. 6, section AA') ; the main granodiorite body is west, south, and beneath the mineralized "west vein" zone. The granodiorite contact surface has, therefore, the shape of a 

broad northward-plunging trough. Presumably the ore 

was localized in the only available limestone above the 

trough and extended upward along bedding from the 

granodiorite and ended below the present surface. 

The small deposit mined in the open cut at the Riley 

Extension mine is in a limestone lens in hornfels near 

the granodiorite contact (pl. 6). The scheelite in 

garnetiferous tactite, and some is in pale-green amphibole tactite. The ore, which has been mostly mined out, 

appears to have been largely confined to a lens of massive limestone in a body of thin-bedded impure 

limestone. 

TONOPAH MINE 

The Tonopah mine, owned by Getchell Mine, Inc., is 

in the SWI4 sec. 33, T. 39 N., R. 42 E., on the northeast contact of the northern lobe of the granodiorite 

stock (fig. 16). The open pits are on the lower slopes 

of the range, approximately 600 to 1,200 feet west of the 

large South Extension pit of the Getchell gold mine. 

The portal of the underground workings is in the west 

wall of the gold pit. 

Mining at the _Tonopah property did not begin until 

1950. Before then, only the most northern pit had been 

opened in 1943 as a tungsten prospect (Hobbs and Clabaugh, 1946, p. 19). Hess and Larsen ( 1921, p. 304) 

mention the Jack mine, which may be the same as the 

Tonopah, where a body of tactite along the northeastern 

part of the contact was prospected for copper and lllOlyhdenum. Getchell Mine, Inc., started open-pit mining at the Tonopah in 1950 and produced 12,650 tons 

of tactite. The surface operations were idle when the 

property was exami_ned in 1955, but underground exploration and development were being carried on (pl. 

8). The underground operations began in 1953 when a 

500-foot adit, which was originally driven to explore the 

footwall of the gold-bearing zone, was extended to intersect the granodiorite contact. A small tactite body 

was encountered and mined from overhead stopes. A 

drift northward on the contact of a dikelike offshoot 

for approximately 400 feet failed to find minable tactite, so a crosscut was driven westward. The crosscut 

encountered a tactite body, which was being developed 

in 1955, that is the down-dip extension of an ore body 

that had been mined on the surface. By July 1, 1955, 

production from the underground workings had been 

7,100 tons of tactite. The total production from the 

surface and underground was 19,750 tons. 

At the Tonopah mine, granodiorite is intrusive into 

limestone and shale of the · Preble formation. Much 

of the limestone is impure and thin bedded and has 

interbeds of hornfelsed shale. The beds strike generally north to northeast and dip east, but locally they 

are distorted by small-scale complex folds. The granodiorite contact strikes approximately N. 50° W., dips 

moderately to steeply northeast, and cuts across the 
M~ES AND PROSPECTS 109 

bedding of the sedimentary rocks (pl. 8). In the 

southeastern part of the map area the contact has a 

more northerly strike and is mostly parallel to the bedding. Furthermore, in this southeastern area the 

granodiorite approaches the Getchell fault zone and is 

displaced by a minor fault related to that zone of faulting; a bit farther south, beyond the area of pl. 8, granodiorite is on the footwall of the main Getchell fault 

zone. 

The tactite is fine- to medium-grained pyroxene-garnet rock that commonly has a crudely defined color 

banding caused by variations in amounts of pyroxene 

and garnet in parallel laminae. Scheelite occurs in 

the tactite ~small grains, few of which are more than 

2 to 3 mm in diameter, that tend to be concentrated in 

narrow zones parallel to the rock layering. At a, few 

places tactite next to the granodiorite is impregnated 

with glassy gray quartz, and in some of these places 

the granodiorite is also silicified. The sulfide minerals, pyrite, chalcopyrite, and molybdenite, are much less 

common in the tactite than at some of the other deposits. 

Some green incrustations of a secondary copper mineral, possibly chrysocolla, coat fracture surfaces in tactite at some places in the pits. 

Limestone adjacent to the tactite has been converted 

to calc-silicate rock and maDble. The shale has been 

metamorphosed to fine-grained dark hornfels. 

Tactite is exposed in mine pits at the surface for 

approximately 1,000 feet along the granodiorite contact. In the exposures the tactite layer ranges from 1 

foot to as much as 15 feet in thickness, is parallel to the 

granodiorite contact, and is transverse to the bedding 

of the limestone. Mapping shows that tactite is discontinuous along the contact, and the tactite bodies 

appear to be separated by barren rock; but poor exposures preclude accurate delineation of the relations. 

Exploration at depth is not sufficient to clearly determine the form of the tactite, but from the available data 

the bodies seem to be tabular and continuous down dip, 

at least to the 500-level underground workings. The 

tactite bodies are not guided by any obvious strong 

structural controls; unlike most of the other deposits 

in the district, they are not localized at any pronounced 

bends in the granodiorite contact. A change in direction of the contact may, however, be responsible for 

the localization of the tactite1 body that was mined at 

at the south end of the 500 foot level and that is exposed 

in the southernmost of the main open cuts (pl. 8) . The 

wide tactite body exposed in the. west end of the 500 

foot level may be related to a change in dip of the granodiorite contact, for underground the contact dips 

steeply west, whereas at the surfa.ce it dips moderately 

northeast. 

ALPINE (PORVENIR) MINE 

The Alpine mine is near the crest of the Osgood 

Mountains at an altitude of about 7,600 feet in SW% 

sec. 6, T. 38 N., R. 42 E. (fig. 16). It is about 4 miles 

by road from the Getchell mine, and can be reached by 

a road that branches south from the Burma Road at 

the crest of the range. 

In 1943 the property was operated as the Porvenir 

mine by W. C. Rigg of Winnemucca, Nevada, and about 

8,000 tons of tactite averaging 0.5 percent WOs was 

mined 'from an open pit at the south end of the deposit 

(Hobbs and Clabaugh, 1946, p. 25) . The property was 

idle from 1945 until 1950, when Getchell Mine, Inc., 

resum'ed open-pit operations and produced 43,700 tons 

of ore. The property was inactive in 1954, but some 

tactite still remained in the pits. 

The mine (pl. 9 ). is on the west contact of the northern lobe of the granodiorite stock with rocks of the 

Preble formation. The granodiorite contact strikes approximately N. 30° W. and dips steeply east. Inasmuch 

as the contact-at least at the outcrop-dips toward the 

stock, the sedimentary rocks chiefly underlie the intrusive body. 

The host rock is a limestone unit in a predominantly 

hornfels area. The limestone, which is thin bedded and 

rather impure, has been converted to tactite or calcsilicate rock near the granodiorite contact. Contact 

metamorphism has affected the limestone as much as 

700 or 800 feet from the granodiorite contact and has 

resulted in bleaching and recrystallization of the purer 

carbonate layers; the impure layers are calc-silicate 

rock. The hornfels formed from shaly rocks is dark 

and commonly spotted with porphyroblastic cordierite. 

Near the contact it is a purplish fine-grained biotiterich hornfels. Much of the tactite that remains in the 

pits is composed of coarsely crystalline brown garnet 

with prominent prisms of epidote and fine-grained 

green actinolitic hornblende; some is mostly garnet 

with small amounts of calcite, and some is predominantly epidote and calcite, with subordinate amounts 

of actinolitic amphibole. Garnet-pyroxene tactite 

seems to be scarce but may have been more abundant in 

the material that has been mined. The tungsten content 

is reported to have ranged from 0.4 to 0.5 percent WOa, 

and some parts; contained more than 1 percent 'VOa 

(Hobbs and Clabaugh, 1946, p. 26). The tenor of the 

remaining tactite is not known. 

Tactite occurred intermittently for approximately 

1,300 feet along the contact, but the main production 

came from two pits, at the north and south ends of the 

property (pl. 9). The bodies were tabular or flattened 

lenses that lay parallel to the grartodiorite conta.ct. The 

tactite that remains in the open cuts ranges from ap-
110 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

proximately 3 to 20 feet in thickness. An erroneous impression of the amount of tactite remaining is obtained 

from the map, because the tabular tactite bodies are 

nearly parallel to the slopes of the hillside and the walls 

of 1he cuts. The depth to which the remaining tactite 

continues is uncertain. With favorable structural situations it could presumably continue in depth as far as 

the granodiorite is in contact with limestone. 

The tactite body that was mined in the South Pit 

is situated where the surface trace of the granodiorite 

contact makes a right-angle turn. In effect, the granodiorite surface forms an inverted trough that pitches 

steeply northeastward, and the tactite is in the trough, 

on the footwall side of the contact. A small tactite 

body has been exposed in a cut 100 feet or so north 

of the north rim of the South Pit, where the contact also 

makes another right-a.ngle turn. For approximately 

600 feet, to the North Pit, the granodiorite contact is 

straight and barren of tactite. The North Pit tactite 

body cannot be correlated with any very obvious structural feature, for the trace of the contact is essentially 

straight. A structural feature that may be at least 

partly responsible for localization of tactite in the 

North Pit is visible, however, in the south wall of the 

pit near the bottom, but is too small to be shown on 

the map. The tactite layer in the south wall is above 

a short, blunt, nearly flat-lying tongue of granodiorite 

that extends 10 feet or so into the footwall and, if continued along the strike, would form a narrow shelf or 

trough. 

RICHMOND MINE 

The Richmond mine in SW!Jt sec. 31, T. 39 N., R. 

42 E., is on the west side of the Osgood Mountains 

(fig. 16), in the upper part of Anderson Canyon at an 

altitude of approximately 6,500 feet. Two tactite deposits, on the east and west sides of the canyon, were 

mined from open cuts (pl. 10), and the deposit on the 

east side was also mined partly by underground workings. The property is accessible from the Getchell 

mine by Burma Road, a distance of approximately 5 

miles. 

Hess and Larsen (1921, p. 302-304) briefly described 

the property, which had been operated as a silver prospect up to the time of their examination. Sometime 

prior to the summer of 1942, U.S. Vanadium Corp. 

purchased the property and it was leased toW. C. Rigg 

of Winnemucca, Nevada (Hobbs and Clabaugh, 1946, 

p. 19). Between the summers of 1942 and 1943 more 

than 31,500 tons of taotite was mined from open-cut 

and underground operations on the east tactite deposit. 

The average tungsten content of the tactite was approximately 0.5 percent W03 (Hobbs and Clabaugh, 

1946, p. 20). The only reported activity on the west 

tactite deposit was open-pit mining, which was attempted from June to August 1954, but the operation 

ceased in August because the low tungsten content of 

the tactite made further mining unprofitable. Approximately 2,800 tons of ore with an average grade of 0.2 

percent W03 were mined during that period. 

The tactite deposits of the Richmond mine are on the 

north side of a blunt westward projection of the northern lobe of the granodiorite stock, at the contact of 

granodiorite with a wide bed of limestone in the midst 

of hornfels mapped as Preble formation (pl. 1). The 

contact strikes approximately N. 75° E. and is for the 

most part vertical. On the west side of the canyon in 

the southwest corner of the map area, the contact makes 

nearly a right-angle turn where a short protrusion of 

granodiorite extends northward (pl. 10). The limestone bed, bounded on the east and west by hornfelsed 

shaly rocks, strikes into the granodiorite. Tactite has 

been formed at the contact of granodiorite with the 

limestone and occurs on both sides of the valley; the 

larger tactite body is on the west side in a reentrant in 

the granodiorite. Bedrock is not exposed in the valley 

between the two tactite bodies, but the west body does 

not appear to continue east of the lower pit, and th(j 

east ore body is terminated· on the west by hornfels. A 

small exposure of hornfels on the west. side of the canyon suggests that limestone-and therefore, also tactite-does not underlie the covered area. 

The tactite bodies are tabular, and they strike and 

dip parallel to the granodiorite contact and are mostly 

perpendicular to the bedding of the limestone that they 

replace. Their outer limit is as clearly defined as at the 

granodiorite contact and is unrelated to the bedding. 

On the limestone side they are joined by a zone of calcsilicate rock and marble a few feet to a few tens of feet 

wide th~t grades into limestone. In this zone, bedding 

control is more evident, and layers of marble alternate 

with layers of calc-silicate rock. 

Characteristically, the tactite is a medium- to coarsegrained granular brown to greenish-brown garnetite 

with not much more than 10 to 15 percent of accessory 

minerals, including interstitial calcite, quartz, a little 

chlorite, and fibrous pale green amphibole. Fairly 

large grains of pyrite are locally plentiful in the east 

tactite body. Most conspicuous and characteristic is 

the absence of pyroxene, which is present in most other 

tactite bodies in the district. Locally the tactite contains considerable quartz, accompanied by epidote. 

At places on the granodiorite contact of the east tactite body small masses of quartz that contain pyrite, 

galena, and sphalerite as well as a few grains of scheelite replace the granodiorite and tactite. No sulfides were 

seen in the tactite as suggested by Hess and Larsen's 
MINES AND PROSPECTS 111 

( 1921, p. 30) statement that the "* * * silver ore is in 

considerable part on the limestone side of the contact 

zone * * *". 

The east tactite body was approximately 210 feet long 

and averaged nearly 30 feet in thickness (pl. 10; Hobbs 

and Clabough, 1946, p. 20, fig. 28). Although it is 

the smaller of the two, it has been the most extensively 

mined. It 'vas mined from an open cut and by underground methods in which stopes were developed to the 

surface. Some tactite remains in pillars and as thin 

remnants lying on the granodiorite contact surface. 

The underground workings were inaccessible in 1954, 

but Hobbs and Clabaugh ( 1946, p. 19-20) reported that 

they consisted of an adit 120 feet below the floor of the 

cut, and a sublevel below the open cut and 85 feet above 

the adit level. According to their report (1946, p. 20) 

* * * most of the ore body is cut out on the main adit level by 

fine-grained dike rock which takes the place of limestone at the 

contact, and little ore is indicated below the sublevel. The average tungsten content of the tactite was about 0.5 percent W03 • 

The west tactite deposit is about 300 feet long and 

from 30 to 140 feet thick. Although it is larger than 

the last deposit, its average tungsten content is so low 

that attempts to mine it profitably have been unsuccessful. The tactite is mostly an almost pure garnetite 

with sparsely distributed small grains of scheelite. 

Hobbs and Clabaugh ( 1946, p. 20) reported that in 

adits the greatest concentration of scheelite appeared to 

be at the contact with granodiorite; surface samples 

ranged from 0 to 0.58 percent wo3, but the distribution 

was very erratic, and more than half the samples contained less than 0.15 percent W03 (Hobbs and Clabaugh, 1946, plate 9). An attempt was made to mine 

the west body in open cuts during the summer of 1954, 

but the operation was abandoned after about 2,800 tons 

of tactite averaging 0.2 percent wo3 were produced. 

MOUNTAIN KING MINE 

The Mountain IGng mine is east of the Richmond 

mine, on land leased from the Southern Pacific Land 

Co. The claims were held by R. L. Taylor, M. V. 

Trvylor, K. Nielsen, and L. Thomas, members of a private company, T.N.T., Inc., which was operating the 

mine. The workings, which include three open cuts, 

are in SE~4 sec. 31, T. 39 N., R. 42 E. (fig. 16), on the 

upper western slope of the Osgood Mountains from an 

altitude of about 6,800 feet to the crest of the range at 

about 7,000 feet, and are easily reached from Burma 

Road, about 3.5 miles from the Getchell mine. The 

workings at the crest of the range are referred to in the 

report by Hobbs and Clabaugh (1946, p. 28, plate 1) as 

Ed Knight's claims. 

Mining of these deposits was started in 1951, and a 

small production was maintained that totalled about 

18,000 tons in June 1955. The tungsten content of the 

ore produced ranged from 0.4 7 percent to as much as 

0.85 percent wo3, and the weighted average is 0.6 percent wo3, slightly higher than the average grade of 

ore produced from other mines in the diStrict. The 

ore was trucked to the custom mill at the Getchell mine. 

In this area the granodiorite contact maintains the 

northeast strike it has at the Richmond mine, and conJ 

tinues with slight irregularities in its surface trace to 

the eastern part of the map area, where the strike becomes slightly more northerly (pl. 10). It dips southeast at steep to moderate angles. The argillaceous 

hornfels and interbedded limestone of the Preble formation, which are intruded by the granodiorite, have a 

more northeasterly trend than at the Richmond mine 

and hence are only slightly truncated by the intrusive 

rock. 

The sedimentary rocks adjacent to the granodiorite 

in this area are predominantly argillaceous hornfels 

but include some interbedded chert and thin interbeds of 

limestone and impure shaly limestone. Tactite is restricted to places where the granodiorite is intrusive 

into shaly limestone beds; the purer. limestone along 

the contact has been converted to marble containing 

some tremolite. The tactite zone at the easternmost 

mine pit on the ridge crest is only about 5 feet thick, and 

other layers only a few inches thick interbedded with 

hornfels are not shown on the map. These were originally thin limestone members interbedded with argillaceous and cherty rocks. The localization of the tactite bodies, other than proximity of favorable beds to 

granodiorite, seems to have been controlled by composition and bedding; they follow the bedding of the sedimentary rocks. In the two pits adjacent to Burma 

Road the tactite bodies are thickest next to the granodiorite and become narrower and pinch out northeastward along the strike of the beds. 

The tactites are brown garnetite containing sma11 

amounts of quartz. Scheelite grains are scattered 

through the garnetite and many are intergrown with 

the quartz. In places the tactite is cut by seams of 

greenish nontronite, which is an alteration product of 

the garnet. 

In the face of the open cut adjacent to Burma Road, 

on the east side, scheelite also occurs along seams which 

are parallel to a prominent close-spaced set of joints in 

the granodiorite that strike N. 10° E. and dip 28° W. 

The alteration occurs in the granodiorite and in the 

hornfels as well. In the granodiorite soft masses of 

white mica accompanied 'by chlorite, crystalline quartz. 
112 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

and tiny euhedral crystals of smoky apatite have been 

formed, and within it are local concentrations of crystalline scheelite. In places next to the altered zone there 

are cavities in the granodiorite as much as 6 in~hes long 

that are lined with quartz crystals. Where the seams of 

alteration cut the hornfels the rock is silicified, and it 

contains small amounts of fine-grained white mica, some 

minute crystals of smoky apatite, goethite, and limonite 

perhaps derived from pyrite, and in places incrustations 

of green secondary copper minerals. No concentrations 

of scheelite were observed in the alteration seams in 

hornfels. 

T.N.T. MINE 

The T.N.T. mine is on the east slope of the Osgood 

Mountains in the northern part of the range at an altitude of approximately 6,500 :feet in NWl,-4 sec. 32, T. 

39 N ., R. 42 E. (fig. 16), 0.9 mile due west of the Getchell 

mine. It is 1.2 miles by road from th~ Getchell mine, 

partly over Burma Road, and partly by a very steep 

mine road. · 

The mine is owned by T.N.T., Inc., and was started in 

July 1954, operated for only short time as an openpit operation, and discontinued in December the same 

year. The recorded production from August 4 to September 29 was approximately 600 tons of ore whose 

weighted .average grade was 0.87 percent vV03 • The 

ore was trucked to the custom mill at the Getchell mine. 

The workings consist of a small open cut and an explo~ation adit 345 feet long beneath the ore zone (fig. 

18). The exploratory adit and two diamond -drill holes 

were partly financed by the Defense Minerals Exploration Administration, a Federal agency. 

The mine is on the northwest contact of the northern 

lobe of the granodiorite stock where it begins to narrow 

rapidly. This part of the contact has a highly irregular surficial trace (pl. 1), and the deposit is in a prong 

of sedimentary rocks with granodiorite on three sides. 

At the deposit, the contact strikes northwest and dips 

steeply northeast. Rocks of the Preble formation, 

which are mostly argillaceous hornfels but include a few 

thin discontinuous beds and lenses of limestone, are intruded by the granodiorite. In general the sedimentary 

rocks strike northeast and because of close :folding they 

dip steeply west and east; at the mine, possibly because 

of disturbance by emplacement of the granodiorite, bedding attitudes diverge widely :from the general pattern. 

In contrast to deposits elsewhere in the district, scheelite at the T.N.T. mine is not in a well-defined garnetite 

tactite zone. A small lens of limestone about 100 feet 

long and 70 feet thick interbedded with argillaceous 

hornfels is partly metamorphosed to a clinopyroxeneplagioclase hornfels containing small masses and veinlets of sulfide minerals, mostly pyrrhotite and chalcopyrite, and lesser amounts of dark-brown sphalerite and a 

:few grains of galena. Part of the calc-silicate rocks contains small grains of scheelite in addition to the sulfide 

minerals; the scheelite grains are scattered through the 

rock and not necessarily associated with the sulfides. 

Scheelite is restricted to the calc-silicate rock but its distribution is not well defined; however, it does not seem 

to occur in the adjacent carbonate rocks that have been 

partly bleached and recrystallized. 

The small size of the limestone body and seemingly 

erratic distribution ·of scheelite preclude important production from the T.N.T. mine in the future. 

SECTION 5 (MARSHALL CANYON) PIT 

Exploratory pits were opened by Getchell Mine, Inc., 

in the summer of 1955 on a scheelite prospect near the 

head of Hansen Canyon, known locally also as Marshall 

Canyon, in SW% sec. 5, T. 38 N., R. 42 E. (fig.16). The 

operation was suspended after -a few . hundred tons of 

scheelite-bearing rock were produced. Previously the 

area had been prospected for silver. 

The prospect is near the center of the northern lobe of 

the granodiorite stock (pl. 1) , in the southern part of an 

area of sericitic alteration p. 46, 88). A few irregular-shaped bodies and 3- to 5-:foot veins of coarse glassy 

quartz cut the granodiorite in the southern part of the 

altered area. Some of the quartz is coarsely crystalline 

prisms. In places the veins contain cubes of pyrite as 

much as 4 to 6 inches on a side. In addition it contains 

erratically and generally sparsely distributed scheelite 

in subhedral to euhedral grains as much as 5 mm across, 

a :few larger crystals a few centimeters in dimension, 

and phantomlike films that coat intracrystalline surfaces in the quartz. In places a boxwork of iron-stained 

j asperoid and small quartz crystals contains a few crystals of scheelite as much as 1 em across. Sche~lite ap-. 

parently does not occur in the altered granodiorite but is 

confined to the quartz bodies. 

PROSPECTS IN THE CANYON OF OSGOOD CREEK 

On the south side of the canyon in NWl,-4 sec. 20, T. 

38 N., R. 42 E., the contact between granodiorite and 

limestone has yielded a little tactite float that contains 

a :few grains of scheelite, and in addition, irregularities 

in the contact deserve some attention. Small-scale exploration has also revealed a small amount of tactite that 

is low in scheelite on the north side of Osgood Creek 

where the granodiorite contact has a small irregularity, 

near the line between sees. 17 and 18, in SWl,-4 sec. 17, 

T. 38 N., R. 42 (pl. 1). This and the former locality 

were also mentioned by Hobbs and Clabaugh ( 1946, p. 
D 

Alluvium and colluvium 

Letter symbol used where formation 

beneath COYer is inferred 

ll} li· APPROXIMATE MEAN 

DECliNATION. 1963 

MINES AND PROSPECTS 

limestone 

Granodiorite 

EXPLANATION 

Calc-silicate rock 

Contains disseminated suHides and 

, scheelite 

- . 

. 

Calc-silicate rock 

Contains disseminted sulfides but locks 

scheelite 

Hornfels 

Massive sulfide replacement of 

hornfels 

Contains pyrrhotite, chokopyrite, 

pyrite, and sphalerite 

Contact 

Dashed where approximately located; 

dotted where concealed 

~ 

Strike and dip of beds 

7::) 

Cut 

gd 

~--++---11 r-------- ---

~ ~ II !I --~-

113 

/' -- 1 Mapped by P. E. Hotz and Ronald Willden 

50 0 50 100 150 FEET~---, PORTAL. OF ADIT 1954. Additions by R. M. Smith, 1955, 

L--'---'---'-----'---------1..----L----__J ' Alt 6420 ft and R. G. Reeves, 1956 Diamond-drill 

CONTOUR INTERVAL 20 FEET I I ~ ~------ holes No. 1 and No. 2 and part of adit 

DATUM ASSUMED ~!11/f!Tr" ~\\\\"'" completed on OMEA project 

FIGURE 18.-Geologic map of the T.N.T. mine. 
114 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

27). Tactite float is also known near the west contact 

of the southern granodiorite body east of Adam Peak, in 

eastern part NE% sec. 24 T. 38 N., R. 41 E. (pl. 1). 

This area is accessible from Granite Creek by a bulldozed road from the Marcus mine. 

GOLD DEPOSITS 

GETCHELL MXNE 

The Getchell mine is at the foot of the Osgood Mountains on the northeast side of the range (pl. 1). Mining operations have been carried on along a zone more 

than 7,000 feet long, most of which is in the western part 

of sec. 33, T. 39 N., R. 42 E.; parts of the zone are also 

in SW% sec. 28, SE% sec. 29, and NE% sec. 32, same 

township and range; at its south end the zone is in the 

northern part of sec. 4, T. 38 N., R. 42 E. The mine is 

26 miles north of Golconda via good blacktop and 

graded dirt roads, and 15 miles northwest of Redhouse, 

the nearest railroad station. 

HISTORY AND PRODUCTION 

The Getchell gold deposit was discovered in the fall 

of 1934 by two prospectors, Ed Knight and Emmet 

Chase, on the site of a prominent siliceous outcrop that 

had been known for many years but that had failed to 

yield any gold to those who previously had tested it by 

panning. Knight and Chase interested Noble H. Getchel1 in the prospect, and it was sampled and assayed. 

The assays showed that the samples contained between 

0.1 and 0.2 ounces of gold per ton and ~n equivalent 

amount of silver. Later that year Getchell purchased 

Knight's interest and called the prospect to the attention 

of Mr. George Wingfield. Wingfield bought Chase's 

share of the property early in 1935, and Getchell and 

Wingfield organized Getchell Mine, Inc., with Wingfield 

as president, Getchell as vice-president and general 

manager, and T. L. Wilcox as secretary-treasurer. The 

outcrops were prospected by several short adits that intersected from 60 feet to 90 feet of ore, and churn -drill 

holes showed that the ore extended to· at least 1,100 feet 

down the dip of the vein, and that the grade warranted 

further work. Therefore, developrrlent was continued 

with drill holes, adits, shafts, and drifts ( J oral em on, 

1949,25 p. 8). 

The following historical and production data were 

taken ·from the U.S. Bureau of Mines Minerals Yearbooks, 1938 to 1951, inclusive. :eroduction started in 

February .or March 1938 with ore mined from an open 

pit, and by theyear's end the Getchell mine had established itself as the leading mining enterprise in Hum-

,21> Joralemon, Pete~:, 1949, The occurrence of gold at the Getchell 

mine, Nevada: Harvard Untv., unpublished doctoral thesis. 

boldt County. The first dividend was declared in September of the same year. By 1939 Getchell mine was 

the leading gold producer in Nevada, a position that 

was maintained until 1943 when byproduct gold from 

the copper pits at Ely exeeded Getchell's output. The 

bulk of the production during the first five years was 

from oxidized ores, but as mining progressed more and 

more arsenic sulfide ores had to be treated. By September of 1943 the oxide ores were virtually exhausted and 

the ore had to be roasted before the gold was recovered 

by cyanida;tion. In 1941, however, a Cottrell electric 

precipitating unit had been installed to save the arsen_ic 

tha.t was liberated by roasting the sulfide ore, and In 

1943-45 when government wartime restrictions forced ' . the shutdown of many gold producers, Getchell mine 

was permitted to continue operation as a producer of 

"strategic" arsenic. In 1943 arsenious oxide was being 

produced at the rate of 10 to 25 tons per day from furnace fume. In 1945, however, gold production became 

increasingly difficult because of rising costs of labor and 

supply, and shortages of labor and material. On about 

May 1, 1945, mining of the gold ore was suspended and 

activities were confined to underground development, 

reconstruction and expansion of the plant, and metallurgical research. Discovery of additional sources of oxidized ore at the Getchell mine and at the Ogee-Pinson 

lease 7% miles south of Getchell enabled gold production 

to be resumed in 1948 and continued through 1950. In 

1949 the Getchell- plant was again an important gold 

producer and rose to second place in the list of Nevada 

gold operations. A description of the milling operation 

is given by Huttl ( 1950). In 1951, however; the Getchell mine gave up its gold operations entirely and converted its plant to treat tungsten ores. Following the 

close-down of tungsten production in 1957, plans for 

resuming the gold operations were being formulated; 

this depended on the solving of metallurgical problems 

involving separation of gold from the sulfide ores. 

The gold ore has been mined by power shovels from 

three large open pits developed along the fault zone. 

When operations ceased, open-pit mining had progressed to approximately 100 feet maximum depth 

below the original surface, and the oxidized ore was 

virtually exhausted. Considerable underground exploration and development have been carried out that include a vertical shaft (the S24 shaft), from which 

development work was conducted on the 800 and 1,000 

levels beneath the southern part of the South Extension 

pit; a 45° inclined shaft from the 400 level in No.4 tunnel, whose portal is in the west side of the South pit, and 

from which workings were developed on the 600 and 800 

levels; and the North shaft, which is connected with the 
MINES AND PROSPECTS 115 

600 level at the north end of the mine by a haulage drift 

700 feet long. Considerable underground exploratory 

and development work has been done on the 400 and 

600 levels at the north end of the mine preparatory to 

mining the north ore body. The North shaft and inclined shaft from No. 4 tunnel are connected by a drift 

on the 600 level approximately 2,800 feet long. 

Production data for the Getchell gold mine are inoomplete, but the available figures are presented in table 

21. The information has been obtained from yearly 

volumes of the Minerals Yearbook, except where noted 

in the table. According to J oralemon. 26 

* * * at the close of 1945 the mine had produced 428,571 ounces 

gold with a gross value of $15 million. Most of this production 

had come from three large open pits. 

TABLE 21.-Gold: silver, copper, and lead product1:on .from the 

Getchell mine 

Year Tons Gold Silver Copper Lead Total (ounces) (ounces) (pounds) (pounds) value 

------1-------------------

1938_ --------------- 159,857 23, 574 2, 964 ---------- ---------- $827, 006 1939_ --------------- 278, 975 49,288 2, 559 ---------- ---------- 1, 726,902 

194(}-41_ ------------ (1) ---------- ---------- - --------- ---------- ---------- 1942_ --------------- 295,624 46,625 8, 442 2, 600 6, 200 1, 638,608 

1943_ --------------- 257,572 35,047 10,603 64,000 5, 700 1, 242, 933 

1944_ - -------------- (1) ---------- ---------- ---------- ---------- ---------- 1945_ --------------- ---------- 10,752 2, 264 ---------- 4, 000 378,274 1946-47 _ ____________ None ____________________ ---------- ___________________ _ 

1948_ --------------- (1) ---------- ---------- ---------- ---------- ---------- 1949_ --------------- 151,695 18,785 2, 000 ---------- ---------- 2 656,038 

195Q________________ 153,516 ---------- ---------- ---------- ---------- 3 68Q, 992 

1 Production figures not available. 

'Eng. and Mining Jour., 1950, v . 151, no. 6, p. 122. a Gross yield Jan. 1 to June 30 (Mining Record, v. 61, no. 39, p. 1, Sept. 1950). 

GEOLOGY 

The gold deposits of the Getchell mine are in fractured rocks along the Getchell fault zone (pl. 11). 

Areal mapping has shown that the predominant country rocks of the mineralized zone are part of the Preble 

formation of Cambrian age. They include dark hornfels and lenticular bodies of thin-bedded limestone. 

Dikes of fine-grained andesite porphyry cut the sedimentary rocks. In the southern and central parts of 

the mine area granodiorite forms the walls of the fault 

zone, but does not seem to have been one of the host 

rocks for the ore. At the northern end of the mine 

area, in the vicinity of the North shaft, a somewhat 

conical body of rhyolite tuff lies east of the fault zone. 

On the west side of the faulted and mineralized zone 

the average strike of the sedimentary rocks is about 

parallel to the east contact of the granodiorite stock. 

Dips vary somewhat, but on the average the bedding is 

inclined about 50° E. At the north end of the mineralized zone, and beyond, the beds strike more northwest 

and west and dip northeast and north. 

East of the zone of faulting and mineralization the 

beds are mostly concealed by alluvium, and their struc-

• Op. cit., p. 9. 

ture is unknown. A few poor exposures suggest that 

the strata strike parallel to the fault zone. 

The Getchell fault zone is the dominant structural feature of 

the mine area [pl. 11]. It trends in a northerly direction and 

is composed of a persistent footwall strand dipping moderately 

eastward, with steeper, arcuate hanging-wall branches. 

(Joralemon, 1951, p. 270.) 

As discussed on pa.ge 75 there is evidence that the 

fault had a strike-slip movement with left-lateral displacement, which was followed by later normal movement. J oral em on ( op. cit.) believes that 

the steeper, hanging-wall branches were formed at that time 

[during the episode of normal movement] and occur above 

flexures in the footwall fault where the dip flattens * * *. 

The gold ore bodies are tabular deposits unlike veins 

in the usual s~nse, but because they are sheetlike bodies 

of mineralized rock whose form and distribution are 

related to fractures of the Getchell fault zone, they are 

most conveniently referred to as veins. The following 

descriptions are derived .from J oralemon's unpublished 

report 27 with some editorial changes by the present 

authors. 

The gold veins are localized almost entirely within the 

Getchell fault zone, lying against the footwall of the 

numerous echelon branches and the cymoid loops 

(McKinstry, 1948, p. 315-319). The ore bodies are 

lenticular or tabular in shape, and in places they swell 

to nearly 200 feet in width. Most of the veins are 

linked by relatively narrow, low-grade stretches along 

cymoid loops (pl. 11). Between junctures the, veins 

swell irregularly, rolling with the fault both vertically 

and laterally. The shapes of the veins are shown in 

the composite vein plan (pl. 11). 

At the south end of the mine the fault zone contains 

at least five veins. The largest vein persists throughout the South Extension pit. Near the surface it is 

steeply dipping to vertical, but in depth it joins the 

footwall branches of the fault zone and resumes the 

normal easterly dip (pl. 11, section A-A'). It appears 

to be the main vein on the surface, although it does not 

follow the major fault but is a wide steep hangingwall branch from the main fault to the west (pl. 11). 

The small vein between the two major ore bodies in the 

South Extension pit has a westerly dip. The main vein 

and this minor branch seem to lie along tension fractures formed, perhaps, by normal faulting. Two mineralized branches of the main fault lie west of the 

pit arid are not well exposed. Toward the north these 

footwall branches join and form the main vein exposed 

in the South pit. At the south end of the ·South pit, 

the strong vein that persists through the South Extension pit swings west and rejoins the main footwall vein. 

zr Op. cit., p. 50-55. 
116 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

In the South Extension pit, then, the major footwall 

fault is occupied by a minor vein from which arcuate 

hanging-wall veins branch and rejoin. 

In the South pit the vein structure is simple. One 

strong vein persists for 1,000 feet along the main footwall fault. It is bounded on the east by a zone of from 

2 to 50 feet of barren blue gouge. One small lenticular vein that lies 700 feet into the footwall from the 

main vein is not exposed at the surface (pl. 11, section 

B-B'). It dips steeply east and probably occupies a 

tension fracture. Drill holes prove that it i~ a discontinuous lens and does not join lat~rally with the main 

vein, either· to the north or to the south. 

The veins in the north end of the mine area are similar in form and disposition to those in the South Extension pit. At the surface in the North pit the main 

vein ends, and no northern continuation has been found 

although the northerly extension of the Getchell fault 

has been thoroughly explored. Underground workings bear out this observation. Although the main 

Getchell fault zone continues to the north without deflection it contains no vein. In this area, however, the 

major fault is no longer parallel to the bedding; 

rather, the sediments strike at angles from 50° to 80° to 

that of the fault. Underground workings have shown 

that the strong vein frays to the north, splitting into 

a series of minor veins developed along shears parallel 

to the bedding which with westerly strike departs from 

the main fault at a moderate angle. Here as in the 

South Extension pit, a persistent but narrow footwall 

vein swings toward the west, and from it wider, less 

persistent, arcuate hanging-wall veins branch and rejoin, thus surrounding a series of narrow wall-rock 

horses. Both in dip and in strike these veins are persistently lenticular and discontinuous. The northern 

part of the ore body contains three major hangingwall branches and several minor veins from 1 to 2 feet 

thick. 

The persistence of the veins with depth is poorly 

known. 28 Most of the hanging-wall branch veins in 

the South Extension pit join the main, footwall vein 

within 100 to 200 feet below the surface. Churn-drill 

holes show that the two major veins in the area 

of the South Extension pit persist as separate units to 

at least 700 feet vertically beneath the surfa.ce, but they 

appear to approach one another with depth because 

they are 350 feet apart at the surface and less than 100 

feet at a depth of 700 feet. At the north end of the 

mine, the veins also appear to unite with depth. 

• Op. cit., p. 54. 

Vein structure becomes simpler with depth, as several veins merge into one. But, as J oral em on 29 pointed 

out, there is no obvious reason why the vein structure 

should not persist to at least 1,000 feet vertically beneath the surface, or 1,500 feet downdip. 

J oral em on 30 noted the following facts concerning 

the distribution of the gold ore at the Getchell mine. 

The distribution of gold in economic amounts is similar to the distribution of realgar, and therefore realgar 

is commonly a good indicator of the . presence of gold 

ore at the Getchell mine. Gold is not present throughout the fault zone, but is restricted to the lenticular 

veins that generally occur along the footwall of the 

fault zone. The economic boundaries of the ore bodies 

are sharp, whereas the actual mineralogic boundaries 

are gradational. The wallrock for at least 100 feet and 

in places for as much as 400 feet from an ore body contains between 0.01 and 0.08 ounce of gold per ton, but 

farther out the wallrock contains only traces of gold. 

At the economic vein wall the gold content increases 

abruptly to more than 0.1 ounce of gold per ton; however, the increase in gold content at the vein wall is 

insignificant, as J oral em on 31 pointed out that a change 

in grade from 0.06 ounce to 0.12 ounce per ton, which 

is the difference between waste and minable ore, is a 

change in gold content of less than 0.0002 percent of 

the rock. 

Changes in attitude of the veins apparently have 

little effect in the gold content, but commonly the wider 

parts of the vein are the richer parts. · Gold occurs 

in the sedimentary rocks of the fault zone, in altered 

dike rocks, and in the gumbo. It almost always is more 

abundant in the gumbo than in the other rocks. 

Nearly every mineral of the ore is host for at least some 

of the gold. Pyrite, marcasite, and the carbonaceous 

matrix of the gumbo are the most important gold bearers, but gold also occurs sparsely in realgar, arsenopyrite, and coarse quartz. 

The gold ore bodies at the Getchell mine have been 

determined from exploration and development to occur 

for at least 7,000 feet horizontally and 800 feet downdip, and they range in width from a few feet to more 

than 200 feet with an average width of about 40 feet 

(Joralemon, 1951, p. 270). At the north end of the 

mine the ore bodies turn northwest from the main Getchell fault, more or less in conjunction with a bend in 

the strike of the sedimentary rocks, and end rather 

abruptly. At the south end the complex of branching 

veins becomes simpler with the joining of several 

29 Op. cit., p. 55. 

ao Op. cit., p. 86-94. 

81 Op. cit., p. 86-87. 
MINES AND PROSPECTS 117 

branches, and southward the ore body gradually tapers 

down to uneconomic proportions, though churn-drill 

hole exploration suggests that gold ore may lie as much 

as 500 feet south of the South Extension pit. 32 

From development and exploration data, J oralemon 33 (1951, p. 276, fig. 3) prepared -a longitudinal 

projection showing the distribution of the gold values. 

Of the vertical distribution he said: 34 

This projection indicated that the rich gold values become 

increasingly rare with depth. A section in the vein that extends about 150 feet down the dip from the surface is largely 

of richer than average ore, and much of it contains more than 

0.3 ounce of gold per ton. Deeper than 150 feet, the richer 

portions become rarer and, instead of covering large parts of 

the vein in a blanket like form as they do near the surface, 

they project downward in narrow, steeply pitching shoots. The 

ore shoots thus have the form of a shallow, extensive blanket 

with an irregular rootlike lower surface. The roots extend 

downward at least 300 feet along the dip of the vein from the 

surface, the great north ore body persists at least 900 feet along 

the dip of the vein and, at that depth, contains richer gold values 

than at any other place in the mine * * *. 

Much of the vein stuff between these roots is of lower but 

still mineable grade. This material, containing from 0.1 to 

0.3 oz gold per ton, persists to the deepest level o:t' exploration, 

decreasing only slightly in amount with depth. It may be 

expected to continue several hundred feet deeper before it 

pinches into roots similar to those of the richer but shallower 

ore shoots. 

Barren and uneconomic -vein material occurs in a large zone 

that separates the north ore bodies from the ore in the South 

pit, and again in the footwall veins west of the South Extension pit. 

OGEE AND PINSON MINE 

The Ogee and Pinson mine is on the south side of 

Granite Creek in the northern part of sec. 32, T. 38 N., 

R. 42 E., about 7¥2 miles south of the Getchell mine 

(pl. 1). From a small open pit, approximately 4,150 

tons of oxide ore assaying 0.186 ounce of gold was 

mined under a lease agreement in 1949, and treat:OO at 

the Getchell mill (Huttl, 1950, p. 62). Apparently 

some prospecting had been done previously on the 

. property. 

The property is on a fault that possibly is a southern 

continuation of the Getchell fault zone, or a branch of 

the same general system which separates rocks of the 

Preble formation from those of the Comus formation. 

The open pit from which the gold ore was mined is iri 

strongly fractured cherty rocks and possibly silicified 

hornfels, apparently east of the fault. According to 

Joralemon 35 irregular zones of low-grade ore occurred 

32 Op. cit., p. 00. 

aa Op. cit., p. 93-95, pl. 30. 

u Op. cit., p. 94-95. 86 Op. cit., p. 92. 

along bedding planes and minor fractures in argillite 

on the footwall of the fault, and realgar was reportedly 

found, though none is visible now. 

OTHER OCCURRENCES OF GETCHELL-TYPE GOLD 

DEPOSITS 

According to Joralemon 36 the wide shear zone exposed in the open cuts of the Riley tungsten mine contains "* * * several tens of feet of marginal gold ore." 

In addition, black, siliceous gouge is exposed in short 

adits and prospect pits a few hundred feet east of the 

quadra~gle boundary in sec. 4, T. 38 N., R. 42 E., north 

of Hansen (Marshall) Canyon, between the Riley Extension mine and the South Extension pit of the Getchell mine. Possibly this material also contains gold 

values, for it resembles material in the Getchell pits 

and at the Riley mine, but no assay data are available. 

J oralemon also reported that fault material exposed 

in a trench several hundred feet east of the Pacific 

mine contained"* * *nearly 0.1 ounce of gold per ton." 

GOLD-QUARTZ VEINS IN THE DUTCH FLAT DISTRICT 

Presumably most of the gold mines and prospects in 

the Dutch Flat district were located and worked after 

the discovery of placer gold in the district in 1893 (Vanderburg, 1936, p. 94), but their history is unknown. Excepting the Dutch Flat quicksilver mine, all the properties have been abandoned for several years. Their production is not known; the only published production 

data for the district are the figures given by Vanderburg ( 1936, p. 94) for placer gold and by Bailey and 

Phoenix (1944, p. 90) for quicksilver. The ruins of 

two small mills for recovery of gold from quartz remain. At a few of the mines the scarcity of vein quartz 

on the dump is out of keeping with the size of the underground workings, and suggests that the vein material 

was sent to a mill for treatment. 

The mines and prospects are situated in the granodiorite stock at Dutch Flat (pl. 1, fig. 15) and in rocks of 

the Harmony formation as far as half a mile north and 

south of the center of the stock. About 40 workings 

were visited. Most of these are no more than prospects 

with a short adit or pit that was dug on a fractured 

or altered zone; in many no . quartz was visible. Most 

of the properties warranted only a brief inspection, but 

a few that had more extensive workings were mapped 

with tape and compass. Except for one mine, the El 

Paso, we were not able to learn the names of the properties, as they are numbered on the map (fig. 15) and so 

listed in the description, table 22. 

ae Op. cit., p. 91. 
118 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

TABLE 22.-Gold mines and prospects in Dutch Flat 

Number on map (fig. 15) Location (T, 38 N., R. 40 E.) 

1 (El Paso mine)____ South center, NWXNWX sec. 16. 

2_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ NE?~NE% sec. 17 ______ _ 

3 _________________ NE corner sec. 17 ______ _ 

4 _________________ Near SWXSW?~ sec. 9 ___ _ 

5 _________________ W part NW% sec 16 ____ _ 

6__ _ _ _ _ _ __ _ _ _ _ _ __ _ SE%NE7~ sec. 17 _______ _ 

7 _- _________ - _ _ _ _ _ South center, NW% sec. 

16. 

8 _________________ South center, SW?~ sec. 9_ 

Geology 

Discontinuous broken quartz stringers in 4-ft 

fault zone striking N. 20° E. dip steeply west 

in altered sandstone and shale of Harmony 

formation. Stibnite in vein quartz. Sample 

from stope assays 0.05 oz gold, 1.5 oz silver 

per ton. 

North-striking, gentle westward-dipping quartz 

vein pinches downdip from 2 to 3 ft on upper 

level to 0 on lower level. W allrock is altered 

granodiorite. Sheared stibnite on dump, none seen underground. 

Granodiorite near portal, rest of workings in 

slightly altered to intensely altered hornfels 

of Harmony formation. Workings follow 

several faults containing coarse, vuggy quartz 

veins and stringers. ~uartz on dump con- tains some galena, pyrite, and chalcopyrite. 

Workings cross granodiorite contact with 

hornfels and · sandstone of Harmony formation. Some alteration. Very little quartz; 

most in prominent N. 50° E., 60° NW. fault zone in main adit. Traces of scheelite in 

quartz. 

Country rocks are altered granodiorite faulted 

against Harmony formation underground. A 

little quartz in veins near portal of long 

(south) adit and near its end contain traces of 

s<,heelite and chalcopyrite. 

Sandstone and shale of Harmony formation, 

altered in few plates, cut by nearly continuous 

northeast-striking fault zone containing discontinuous quartz veins and brecciated 

quartz. Sample assayed 0.02 oz gold, 0.4 oz silver. 

Shale and sandstone of Harmony formation, more or less altered. Northwest- to nort;heasttrending faults contain a little brecCiated 

quartz. Quartz on dump contains traces of 

sphalerite. Sample assayed trace of gold, 0.3 oz silver. 

Discontinuous quartz veins 2 in to 2 ft wide in 

N. 5° to 10° E., 55° NW, fault zone. Quartz 

is mostly in part of fault south of shaft, not 

much north of shaft. Quartz from dump 

contains small amounts or galena, sphalerite, 

and stibnite. 

9 _________________ Near center, SW ~ sec. 9_ Fault zone,N.50° E., 80° SE., containing quartz 

stringer in unaltered sedimentary rocks of 

Harmony formation. 

10_- -.------------- NW?~NWX sec. 16_ _ _ _ _ _ Vuggy, iron oxide-stained quartz vein 3 ft wide, 

strikes N. 10° E., dips 40° W. in altered 

granodiorite. Small amounts stibnite and 

pyrite in quartz. 

Workings 

Drift along fault zone, stoped 

to surface. 

Vein developed on two levels. 

About 345 ft of drifts and 

crosscuts. 

Three adits totaling about 340 

ft. No stoping. 

Two adits and a 75-ft winze. 

Lower adit (drift) 280 ft long, 

stoped above and below, 

with raise to short (65 ft) 

drift. Estimate more than 

1,000 tons removed from 

stopes, but dumps are small. 

Adit 450 ft long follows several 

fractures that contain quartz. 

150-ft-long inclined shaft to 

depth of 120 ft; five levels 

with total length of 300 ft. 

No important stoping. 

Adit 307 ft long. Drift 122 ft 

long perpendicular to adit 

follows fault. No stoping. 

Incline 25 ft long. 

ll ________________ Near line between NWX 

sec. 16, and NE?~ sec. 17. 

Altered granodiorite. No clear structure or Adit approximately 240 ft 

vein. long; vertical shaft 60 ft 

deep. 

12 ________________ Center, NEX sec. 17 _____ N. 35° E., 80° W. fault zone 4% feet wide in Inclined shaft 40 to 50ft deep. 

altered hornfels of Harmony formation; 4- to 

6-in. quartz vein. Quartz white, slightly 

vuggy; piece from dump contains visible 

particles of gold. 
MINES AND PROSPECTS 119 

TABLE 22.-Gold mines and prospects in Dutch Flat-Continued 

Number on map (fig. 15) Location (T. 38 N., R. 40 E.) Geology Workings 

13 ________________ SWHNWX sec. 16 _______ Quartz vein 2 to 6 ft wide in altered rocks of Two shallow shafts, short adit. 

Harmony formation. Vein strikes N. 10° E. 

to N. 30° E., dips 70° to 75° SE. 

14_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Approximately 300 feet 

southwest of No. 13. 

North-trending alteration zone in sedimentary Prospect pit, 40-ft incline, 

rocks of Harmony formation. Some narrow adits 45 ft and 285 ft long. 

veins and veinlets of crushed, white, vuggy 

quartz that contains traces of stibnite and 

pyrite. 

15_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Near south boundary, 

NEX sec. 17. 

Adit in altered sedimentary rocks of Harmony Adit 35ft long; 25-ft shaft. 

formation follows N. 10° E., 20° W. fault 

containing quartz veinlets. Shaft SJ.mk on breccia zone 3ft wide, N. 35° E., 80° W., that 

contains broken quartz. 

16 ________________ Near center, SEX sec. 17_ Fault strikes N. 40° E., dips steeply northwest, Couple of shallow pits; 45-ft 

in slightly altered sedimentary rocks of Har- adit. 

mony formation, and contains thin discontinuous quartz stringers. 

17 ______ --- _ _ _ _ _ _ _ _ 300ft east of no. 16_ _ _ _ _ Fault, N. 30° W., 10° NE. in slightly altered Adit 25 ft long. 

sedimentary rocks of Harmony formation. 

QUICKSILVER DEPOSITS IN THE HOT SPRINGS RANGE 

Three deposits of quicksilver are known in the Hot 

Springs Range within the Osgood Mountains quadrangle. They are included in the Dutch Flat ( Florence) district by Bailey and Phoenix ( 1944, p. 90-91), 

although only one of the properties is near Dutch Flat. 

DUTCH FLAT MINE 

The Dutch Flat mine is in the northern part NE14 

sec. 17, T. 38 N., R. 40 E. (pl. 1; fig. 15) on the west 

side of the Hot Springs Range near its base at an altitude of approximately 5,000 feet. The property is 

about 18 miles northeast of Winnemucca and 14 miles 

north of Golconda and is accessible by 19 miles of dirt 

road from the Southern Pacific and Western Pacific 

railroads and U.S. Highway 40 at Golconda. 

Cinnabar was probably noted in placer operations as 

early as 1893 (Vanderburg, 1936) but was not discovered in place until 1939. The Dutch Flat Mining Co. 

was organized by E. R. Rogers, Ed. Hazlett, and J. W. 

Tuft in September 1940, and ore was developed and 

mined from underground workings (Bailey and Phoenix, 1944, p. 90). Intermittent production since 1942 

has amounted to less than 2 flasks of quicksilver a year 

(Willden and Hotz, 1955, p. 663). 

The mine is on a fault zone that transects slightly 

metamorphosed shale and feldspathic sandstone of the 

Harmony "formation a few hundred feet west of a small 

stock of granodiorite. The fault zone strikes approximately N. 10° E., dips from 20° to 35° SE., and has 

an average width of about 5 feet over a length of 900 

feet. At the south end of the zone, shallow open -cut 

bulldozer operations have discovered only traces of cinnabar in altered sedimentary rocks and an altered dike. 

The main cinnabar mineralization seems to be in a small 

area at the north end of the fault zone, where about 

700 feet of underground workings have been developed 

to explore and mine the mineralized zone (fig. 19). 

In the underground workings cinnabar seems to be 

chiefly distributed in light-gray fine-grained altered 

hornfels that has been fractured and sheared. The 

cinnabar occurs as small disseminated grains, but at a 

few places small concentrations of cinnabar are visible, 

and some shear surfaces are coated with a thin film of 

cinnabar "paint". Some cinnabar obviously is in small 

discontinuous veinlets. It seems to be restricted to the 

light-gray altered rock, for none was seen in brown 

altered hornfels. The light-gray rock tends to be in 

the upper part of the fault zone adjacent to the hanging wall, though in places the full width of the fault 

zone is occupied by the light-gray altered rock. Locally the crushed rock has been impregnated with calcite cement which makes it more resistant than the surrounding material. Cinnabar is commonly plentiful in 

these calcite cemented masses, and pyrite is present in 

visible amounts. 

Bailey and Phoenix (1944, p. 91) estimated that the 

retorted ore averaged approximately 20 pounds of 

quicksilver to the ton. The ore zone has not been systematically sampled, but even at its northern end, where 

it is most strongly mineralized, it is unlikely that ore 

of this grade could now be mined consistently. The 
120 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADR,ANGLE 

NORTH INCLINE 

Small amount 

SOUTH INCLINE 

Caved and lagged tight> ----

Sheared and 

altered 

rock--.._ 

/ 27 

Stringers of cinnabar 

in 4 in. white gouge / 

Some 

cinnabar 

1ST LEVEL 

Cinnabar in back 

against fault 

gouge 

Cinnabar in gray 

altered rock 

Brown altered 

rock,no cinnabar 

20 LEVEL 

EXPLANATION 

~ 

Bottom of shaft 

---"lTo 

Fault, showing dip 

N Inclined shaft 

Chevrons point down 

~ C8J - - .J!O --=:.....----~ 

Tape·and-compa ss map by P. E. Hotz 

and Ronald Wil lden, June 1953 

1 

Vertical shaft Foot of raise Fault zone, showing dip 

l%l LSJ Shaft going above and 20 0 20 40 FEET 

below levels Head of raise 

FIGURE 19.-Map of the Dutch Flat mine. 

past history of the underground development and mining has shown that the ore shoots are small and discontinuous and considerable dilution of the ore with 

barren or low-grade material is unavoidable,' because 

of the narrowness of the ore zone. 

LAST CHANCE PROSPECT 

The Last Chance prospect is in NWlhSElh soc. 32, 

T. 38 N., R. 40 E., approximately 3.5 miles south of 

the Dutch Flat mine (pl. 1). It is at an altitude of 

approximately 5,000 feet on the east side and near the 

head of an unnamed westward -draining canyon near 

the south end of the Hot Springs Range. The prospect 

is accessible from the Dutch Flat-Golconda road by a 

barely passable road. The only known production was 

in 1941, when one flask of quicksilver was recovered 

from ore treated in the retorts at Dutch Flat (Bailey 

and Phoenix, 1944, p. 91). 

The property has 2 short adits and 2 shallow shafts 

that were driven to explore an alteration zone in sandy 

rocks of the Harmony formation. The rocks exposed 

in the adits are light-gray and brown soft altered sandstone and sandy shale with streaks of vermillion and 

brown iron oxide and veinlets of harder limonite. A 

few veinlets of white quartz cut the rock. No cinnabar 

is visible and none was obtained by panning a sample 

taken from one of the adits. 

The altered zone has an indefinite width of about 

20 feet. The zone trends slightly west of north, nearly 

parallel to the strike of the beds, which dip moderately 

to gently east. Alteration artd iron oxide stains were 

also seen in rocks which are exposed at the surface 

approximately 0.2 mile south of the prospect on the 

southwest side of the saddle at the head of the canyon 

and which may be a continuation of this zone. The 

alteration zone is not visibly related to faulting, how-
MINES AND PROSPECTS 121 

ever, it is parallel to the strike of a fault approximately 

400 feet to the west (pl. 1). 

K AND K (RED DEVIL) PROSPECT 

The K and K quicksilver property is at the south 

end of the Hot Springs Range in sec. 5, T. 37 N., R. 40 

E., at an altitude of about 4,800 feet pl. 1). It is easily 

accessible by 13.5 miles of dirt road from Golconda. 

Presumably this is the property referred to by Bailey 

and Phoenix (1944, p. 91) as the Red Devil prospect. 

Cinnabar was discovered here in 1941 on land owned by 

the Southern Pacific Railroad, from whom the property, consisting of about 197 acres, was purchased by 

Major Estridge of Winnemucca, Nev. An inclined 

shaft about 40 feet long was sunk immediately after 

the discovery but no production of quicksilver was recorded. A vertical shaft 20 feet deep on a ridge onehalf mile northeast of the incline may also have been 

sunk at this time. The property was acquired by Humboldt County after the death of Estridge, and Charles 

Kassebaum purchased it in Ju.ly 1950 from the county. 

Aside from deepening the incline a · few feet and doing 

some bulldozer work, the new owner performed no 

additional exploration or development work. However, a small gas-fired Rossi-type retort and condenser 

were installed in 1953; the dump from the incline was 

treated, and a small amount of quicksilver was obtained. In January 1955 the property was leased by 

Lilburn Davey and Cleto, Frank, and Chris Bengoa. 

They drove an adit 310 feet long and a raise from 

the adit to the incline shaft. During the summer and 

fall of 1955 the lessees erected a small jaw crusher, a 

5-stamp mill, and two concentrating tables at Stone 

Corral, about 21/z miles east of the mine, where they 

planned to concentrate the cinnabar prior to roasting. 

The country rocks are feldspathic sandstone, some 

shale, and a few thin limestone members-all of the 

Harmony formation. The prevailing strike of beds 

is north and the moderate dips are'>-east, but ·there is 

some evidence of close folding and disruption by faulting. The mineralized zone is about 200 feet east of a 

fault that strikes north and dips at a moderate angle 

east and has been traced for about 4,000 feet south of 

the mine shaft. In 1955 the mineralized zone had been 

explored by an inclined. shaft and an adit at the discovery site, but its length and continuity were unknown. 

Cinnabar occurs in a faulted · zone in soft altered 

feldspathic sandstone and shale. Where it is exposed 

in the adit the zone of alteration is about 90 feet wide. 

The rocks are most altered in the faulted zone, where 

cinnabar mineralization is also most intense. In the 

faulted zone the fractures strike from N. 10° W. toN. 

30° W. and dip from 35° to 80° E. Visible amounts of 

cinnabar occur in brecciated quartz and calcite veinlets along a faulted contact between sandstone and shale 

in the adit, and in a sublevel between the adit and inclined shaft. In the inclined shaft cinnabar grains 

are in fractured and altered rock, and some apparently 

barren altered rock yields fine-grained cinnabar when 

~rushed and panned. 

LEAD-ZINC DEPOSITS 

The lead-zinc deposits are at the Richmond mine in 

the northern part of the Osgood Mountains and the 

Silver Hill prospect at the south end of the Hot Springs 

Range. Neither has any recorded production. 

RICHMOND MINE 

Before development and operation as a tungsten property, the Richmond mine (pl. 1) inS~~ sec. 31, T. 39 

N., R .. 42 E., on the n·orthwest side of the Osgood Mountains was operated in a small way for many years as 

a silver mine. According to Hess and Larsen ( 1921, 

p. 303) small irregular bunches and lenses of quartz 

carrying some galena and considerable scheelite occurred on the limestone side of the granodiorite contact. 

The ore was mined from underground workings, the 

portal of which is in the upper part of Anderson Canyon. The original workings were later extended to 

develop and mine the tungsten ore. Specimens on the 

dump are like those found in places at the surface near 

the granodiorite contact and are composed of silicated 

limestone containing small seams and bunches of galena 

intergrown with smaller amounts of dark-brown sphalerite associated with pyrite, and some chalcopyrite in 

a gangue of milky quartz and coarsely crystalline 

calcite. 

SILVER HILL MINE 

The Silver Hill mine is at the south end of the Hot 

Springs Range on the west side of a small ravine in 

center SE~ sec. 5, T. 37 N., R. 40 E., 0.25 mile south-· 

east of the K and K quicksilver property (pl. 1). The 

workings consist of a short adit with a small stope, and 

a shallow vertical shaft to the north from which some 

short exploratory crosscuts and an inclined winze were 

driven. The adit and stope were driven on small westtrending mineralized fractures and brecciated zones in 

sandstone of the Harmony formation. 

Fine-grained galena and subordinate amounts of 

sphalerite and traces of chalcopyrite accompanied by 

some vuggy quartz fill the fractures and spaces between breccia fragments of country rock and earlier 

quartz with but slight replacement. Anglesite and 

cerussite which are formed by supergene alteration of 
122 GEOLOGY AND MINERAL DEPOSITS, OSGOOD MOUNTAINS QUADRANGLE 

the galena, partly replace galena and fill openings in 

it and the vein quartz and country rock. In places 

fractures in the wallrocks are filled and coated with 

white to greenish radiating aggregates of the secondary 

zinc mineral hemimorphite. 

UNNAMED PROSPECT 

A prospect whose name is not known is" on the east 

side of the Osgood Mountains on the south side of the 

ridge between Osgood and ,Julian (Kirby) Creeks, in 

NW1;4SW1;4 see. 17, T. 38 N., R. 42 E. The workings 

include an inclined shaft about 50 feet long and an open 

cut 20 feet long, which are in light-gray sugary-textured recrystallized limestone of the Preble formation. 

The prospect is approximately 600 feet from the narrow 

"waist" of granodiorite between the southern and northern lobes of the stock. No ore was seen in place, but 

some of the limestone on the dump contains a small 

amount of galena. 

COPPER DEPOSITS 

Some small exploratory cuts and adits have been 

made on showings of copper in the Osgood Mountains, 

but no important or even promising deposits have been 

discovered. None are known in the Hot Springs Range. 

BARITE PROSPECTS 

BARIUM AND BARUM GROUPS OF CLAIMS 

The principal barite deposit is covered by the Barium 

and Barum groups of claims, five in each, which almost 

cover a low hill at the east front of the Osgood Mountains in the eastern part sec. 12, T. 37 N., R.. 41 E. (pl. 

1) ~ near the mouth of Hogshead Canyon. The property, originally located by P. V. Sanders and W. M. 

Pettit in September 1940, is held hy the Baroid Division of National Lead Company. No recorded production of barite from the property has been made; the 

principal activity has been surface exploration and 

trenching done for assessment work. 

The country rocks are limestone, dolomite, shale, and 

black chert of the Comus formation of Ordovician age. 

On the eastern and southeastern slopes of the hilrthe 

rocks are mainly interbedded limestone, dolomite, and 

shale; the s~mmit area and western slope is black chert 

cut by veinlike bodies of brown jasper and quartz. The 

country rooks are contorted and are not well enough 

exposed to permit the structure to be clearly deciphered: 

at the largest open cut on the southeast slope of the hill, 

beds strike generally east-west and dip moderately to 

the south, whereas elsewhere in the area strikes are 

north and dips are moderately east or steeply west. 

Barite occurs mainly in the southeast area, where it 

replaces the carbonate rocks but not the shales. Locally, however, chert is also replaced by barite along zones 

of brecciation accompanied by jasper and veins of 

quartz. 

Some surface exploration has been done, mainly by 

means of shallow bulldozer cuts, but not enough to 

delimit clearly the extent of the mineralization. It has 

been shown, however, that barite deposits occur over 

· an area of about 20 acres. 

OTHER PROSPECTS 

A shallow prospect pit near the Blue Bell mine in 

north-central part NE14.NW1;4 sec. 5, T. 37 N., R. 42 E. 

(pl. 1), exposes interbedded limestones and shales of 

the Comus formation. The limestone in the pit is 

partly replaced by barite. 

A barite prospect known as the Thirsty Lode claim 

was located in May 1951 by Lyman Thomas and R.. L. 

Taylor, north of Anderson Canyon in extreme SW~ 

SW1;4 sec. 30, T. 39 N., R. 42 E. (pl. 1). Here, finegrained gray barite apparently replaces a limestone bed 

in the Preble formation. The bed strikes N~ 20° W. and 

dips 40° northeast; the thickness and strike length of 

the barite replacement is not known. 

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Anderson, C. A., Scholz, E. A., and Strobell, J. D., Jr., 1955, 

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Eskola, Pentti, 1914, On the petrology of the Orijarvi region in 

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163 p. 

---1929, The mining districts of Nevada: Econ. Geology, v. 

24, p. 115-148. 
REFERENCES CITED 123 

ll,erguson, H. G., and Muller, S. W., 1949, Structural geology 

of the Hawthorne and Tonopah quadrangles, Nevada: U.S. 

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Geol. Quad. Map GQ-11. 

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Frietsch, Rudyard, 1957, Determination of the composition of 

garnets without chemical analysis : Geol. foren. Stockholm 

Forhand., v. 79, no. 488, p. 43-51. 

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A 

Abstract_ ____________________________________ _ 

Accessibility _____ _____________ ___ ___________ _ 

Acknowledgments ___________________________ _ 

Adam Peak ____ ----------------------- __ ____ _ 

Adam Peak formation, age and correlation ___ _ 

conditions of deposition __________________ _ 

definition and distribution _______________ _ 

Page 

1 

3 

6 

37 

38 

36 rocks oL_________________________________ 36 

stratigraphy and thickness________________ 37 

structural relations_-----~---------------- 82 Adam Peak thrust_ ________________________ 28, 70,73 

Alluvium _________________________ ---------___ 59 

Alpine (Porvenir) mine, geologic map ________ pl. 9 

granodiorite contact__-------------------- 42 

tungsten deposits_________________________ 109 

Altitude ______ --------------_________ _______ __ 5 

Andesite flows, Osgood Mountains___________ 53 

petrographic description__________________ 54 

Anderson Canyon ____________________________ 31,73 

fault_ _____ _____ _______ -------------------- 74 

Andesite porphyry __ ------------------------- 51 

Antler orogeny_--------------------------- 79, 80,82 

thrust faulting of_________________________ 80 

Antler Peak limestone ____ _________ __ 28, 30, 36, 37,38 

Antler sequence of Roberts ____ --------------- 28,81 

Aplite and pegmatite_________________________ 50 

Argillite, metamorphic origin_________________ 60 

Arsenic, deposition along Getchell fault_______ 83 

Atoka time, events oL_______________________ 81 

B 

Barite deposits in Osgood Mountains_________ 96 

Barite prospects______________________________ 84 

Barium and Barum groups of claims __ T___ 122 

other prospects _______ --------------______ 1tt 

Basalt, intrusive, analyses____________________ 44 

Basalt flow near Comus station, analyses and 

petrographic description ___ _______ 55,58 

Battle formation _________ 28, t9, 31, 32, 36, 37, 71, 80,81 

age and correlation_______________________ 30 

conditions of deposition ____ -------------- 30 

distribution _______ --------_______________ 29 

klippen on________________________________ 73 

structural relations ____________________ 80, 81,82 

Battle Mountain region______________________ 37 

Berry, W. B., fossils identified by_ ----------- 21 

Bridge, Josiah, graptolites identified by_______ 21 

c 

Qalc-silicate rocks __ -------------------------- 62,63 

mineral assemblages______________________ 64 

Camhrian age, rocks of_______________________ 6 

diastrophism _____________ ---------------- 80 

sedimentation __ -------------------------- 79 

Carbonate assemblage, environment of deposition ___ ----------------_ _________ 79 

Carbonate rocks, metamorphism oL__________ 6t 

Cave Canyon, Harmony formation___________ 15 

Cenozoic historY------------------------------ 8S 

INDEX 

[Italic page numbers indicate major references] 

Chemical analysis, altered dacite porphyry __ _ 

granodiorite, Osgood Mts. stock _________ _ 

hornfels __ -------------------------------- intrusive basalt_ _________________________ _ 

sandstone, Harmony formation __________ _ 

Tertiary flows ___________________________ _ 

unaltered and altered granodiorite _______ _ 

volcanic rocks, Goughs Canyon formation_ Cinnabar ____________________________________ _ 

Page 

50 

45 

62 

41 

17 

55 

48 

25 

92 

grains oL __ ------------------------------ 95 

K and K prospect_ _____________________ 119,121 

placer ___ --------------------------------- 93 

Climate __ ------------------------------------ Comus formation ____________________ 19, tO, 41, 76,81 

age ____________________________________ 19, tl, 80 

distribution ____ ------------------________ SO 

equivalence to Valmy formation__________ 24 fault relation______________________________ 75 

lithology __ ------------------------------- tO 

measured section_________________________ 21 

metamorphism of. ________________________ 60,61 

metamorphism of carbonate rocks___ ____ 62 

rocks oL__________________________________ t1 

stratigraphy and thickness ___ ------------ tO 

structural relation _________ -------------__ 81 

thrust of__________________________________ 71 

Contact metamorphism __ -------------------- 59 

Dutch Flat_ __ ---------------------------- 60 

Osgood Mountains stock_________________ 60 

Copper deposits __ --------------------------- 96, 1tt 

minor ____ -------------------------------- 95, 96 

Culture. ___ -·---------------------- ____ _____ 3 

D 

Dacite porphyry_---------------------------- 50 

altered, analysis, norm, and Niggli values 

oL ___ ---------------------------- 50 Diastrophism, Cambrian_____________________ 80 

Cenozoic ___ ------------------------------ 83 

Douglass, R. C., fossils identified by __________ 34,35 

Dry Hills, andesite, analyses ___ -------------- 55,56 

andesite flows ___ ------------------------- 53,54 

faulting near------------------------------ 77 

Duncan, Helen, fossils identified by__________ 26, 

27, 33, 34, 35, 36, 37, 38 

Dutch FlaL--------------------------------- 5 contact metamorphism___________________ 60 

gold mines and prospects, location, geology, and workings________________ 118 

gold-bearing quartz veins ________________ 77,117 

gold-scheelite-cinnabar placer_____________ 93 

granodiorite alteration____________________ 46 

granodiorite body, metamorphic aureole._ 41, 59 

hydrothermal alteration__________________ 49 

mining future_--------------------------- 97 

quicksilver mine _________ ---------------- 3,119 

production._----------------------------- 92 

Dutch Flat mine area, granodiorite body----- 41 

Dutch Flat district, map_____________________ 94 

E 

East Fork Eden Creek __ ---------------------

East Fork Eden Creek area, Goughs Canyon 

Page 

36 

formation ____________ ------------- 25 

flow rocks________________________________ 54 

Eden ValleY---------------------------------- 5 

Edna Mountain formation_------------------ 28,38 

El Paso Gulch, slope-wash deposits ___________ 94, 95. 

Endomorphism, of granodiorite_______________ 68 

Erosion, Late Cambrian______________________ 80 

Etchart Canyon ______________________________ 30,31 

Etchart Canyon thrust plate _________________ 72,73 

Etchart limestone __________ 28,30,36,37,38, 73,80,81 

age and distribution______________________ 30 

Adam Peak thrust __ --------------------- 70 age and correlation_______________________ 33 

conditions of deposition___________________ 38 

faults in---------------------------------- 74 klippen of._______________________________ 73 

lithology_-------------------------------- 31 

measured sections_----------------------- 32,33 metamorphism ___________________________ 42,64 

carbonate rocks_______________________ 62 

stratigraphy and thickness.-------------- 3t structural relations __________ ____________ _ 80,82 

F 

Facies, relation to history--------------------- 79 

Farrel Canyon.------------------------------ 38 

Preble formation _________ ---------------- 10 Farrel Canyon thrust fault_ __________________ 72,74 

Farrel Canyon formation _____________________ 38,82 

chert __ ----------------------------------- 39 contact metamorphism oL_______________ 67 

distribution. __ --------------------------- 39 

lithology __ ------------------------------- 39 

possible age and correlation_______________ 40 

stratigraphy and thickness __ ------------- 40 

thrust oL.---------------------------- 71, 74,82 Farrel Canyon thrust fault_ __________________ 72,74 

Faulting, age of.______________________________ 78 

Faults---------------------------------------- 20,41 in Hot Springs range_____________________ 77 

thrust_----------------------------------- 19,22 

Fieldwork and mapping______________________ 6 

Flows_--------------------------------------- 59 

See also Andesite flows; Basalt flows; Tertiary flows. 

Folds, in Hot Springs range__________________ 76 

in Osgood Mtns __ ------------------------ 69 

Fossils identified_--------------------- 12, 13, 14, 19, 

20, 21, 23, 26, 27, 33, 34, 35, 36, 37,38 

G 

Garden Spring, Twin Canyon fault___________ 70 

Geologic historY------------------------------ 79 

Geosyncline, Early PaleozoiC----------------- 79,80 

Getchell area, metamorphism in-------------- 42 

125 
126 

Getchell deposit, age of mineralization ....... . 

features oL ...................... __ . ___ . __ 

gold. ________ . _______ ... __ .. _ ...... ____ .. . 

gold-arsenic, distribution and general 

features ...•... -------- ____ ..... . 

Page 

91 

90 

90 

89 

mineralogy and paragenesis •. ------------- 89 

origin and classification................... 91 

silver .... ____ ............................. 91 

Getchell fault •................................ 41, 75 

Getchell fault zone .... ----------------------- 75 

age relations •. ---------------------------- 76 gold-arsenic deposits along ________________ 83,89 

granodiorite alteration along______________ 46 

movement on .•.. ---------------------- 78, 79,83 

relation to granodiorite stock .. ----------- 75 

Getchell mine.------------------------------- 3, 75 

description .. ----------------------------- 115 

fault relations in-------------------------- 75,89 geology ______________ .. ________ .. _______ .. 115 

gold _______________ -------------------- 51, 89,90 

location, history, and production_________ 111, 

maps.------------------------------------ pl. 11 

mining future.--------------------------- 97 

silver ___ .. -----. __ .--•• --------. _____ .____ 91 

tuffaceous rock . .. ------------------------ 53 

Getchell mine area ... ------------------------ 31,41 fossils ...• ___ . ______ . __ . ____ ------ __ .______ 23 

Valmy formation.------------------------ 22,23 

Getchell townsite ... -------------------------- 3 

Golconda, Nev., access.---------------------- 3 

Golconda thrust, age .. ----------------------- 82 

Gold .. --------------------------------------- 8a 

Getchell mine.--------------------------- 90 

other Getchell-type deposits __________ 117 

mining, Hot Springs Range_______________ 83 

mining, Osgood Mts .... ------------------ 83 

Pacific mine area_________________________ 89 

placer_._.-------------------------------- 93, 95 

Gold mines and deposits, detailed descriptions 11;, 

See also Getchell mine; Ogee and Pinson 

mine; Dutch Flat; Riley tungsten 

mine. 

Gold mines and prospects in Dutch Flat._._. 118 

Gold-arsenic deposits, Osgood Mountains..... 89 

reserves .. --...... _____ .. ________ ....... __ . 97 

Gold-bearing quartz veins in Hot Springs Range ___________________ __ _______ 77, 9S 

relation to granodiorite stock ... ---------- 77,92 

Dutch Flat granodiorite stock____________ 47 

Gold-scheelite-cinnabar placer in Hot Springs 

Range . ... ------------------------ 9S 

Gordon, Mackenzie, Jr., fossils identified by__ 26, 

27, 33, 34, 36 Goughs Canyon ___________________________ 31, 35,69 

fault . ... ______________________ . ___ ........ 72 

fossils ..... ----------------------- ______ 18, 33, 35 

Harmony formation______________________ 15 

klippen ..... __ . ________________ ........... 73 

Preble formation .. ----------------------- 10 

Goughs Canyon area.------------------------ _ 36,50 

faulting .. ____ ---------------------------- 77 

structural relations.---------------------- 82 

Goughs Canyon formation ____________________ 21,39 

age....................................... 80 

age and correlation....................... 16 

chemical analyses and norms.------------ 25 

deposition................................ 18 

distribution .... -------------------------- 14 

faulting _____ ..........•................... 7S 

fossils ...... ------------------------------ 25 

lithology--------------------------------- e;, 

thickness ....... __ ........................ 15 

Goughs Canyon thrust fault ..........•.... 24, 72, 7!1 

Granite Creek................................ 41 

Comus formation......................... 21 

Granite Creek mine, description.............. 98 

endomorphic products.................... 68 

geologic map and sections................. pl. 2 

granodiorite contact...................... 42 

INDEX 

PageGranite Creek mine-Cont:nued 

mining future . --------------------------- 97 

underground workings.................... pl. 3 

Granite Creek thrust. ........................ 71,82 

Granodiorite, age ........................ ·..... J,!J 

analyses, norms, and Niggli values....... 45 

chemical composition..................... 44 

contact surface, relation to tactite bodies.. 86 

emplacement, age of...................... 82 

endomorphism ... ------------------------ 68 

lead-alpha age determination........ ..... 43 

marginal facies .... __ ___ ______ ------------ 41, 

modes ... ____ . __ .......................... 44 

petrography------------------------------ J,!J 

quantitative spectrographic anaLyses for 

minor elements ................... 45, 49 

structural relations, Hot Springs Range_. 4S 

tungsten deposits in...................... 88 

Granodiorite alteration.---------------------- 46 

analyses, norms, and Niggli values....... 48 

chemical changes......................... 1,7 

comparison with other examples.......... 48 

spectrographic analyses ................... 48,49 

Granodiorite and related rocks, distribution.. 1,1 

Granodiorite stock, Getchell fault relations... 75 

modes ........ ___ ............... _____ ..... 44 

structural relations....................... 1,1 

Great Basin, Prospect Mountain quartzite... 9 

H 

Harmony formation .......•...... 14, 36, 37, 71, 80,96 

age and correlation .• --------------------- 18 

age of folding.---------------------------- 82 

chemical analyses......................... 15 

distribution .... -------------------------- 11, 

fault......... ............................. 72 

folds ............... __ ..................... 69 

gold-bearing quartz veins ................. 92,93 

heavy minerals ........................... 15,18 

history .• --------------------------------- 80 

hydrothermal alteration.............. .... 49 

lithology. _______ ------------------------- 15 

metamorphism in........................ 60 

modal analyses........................... 15 

origin ..... -------------------------------. 19 

quicksilver in............................. 92 

stratigraphy and thickness_______________ 18 

structural relations ....................... 77, 78 

Harmony formation and Paradi!le Valley chert. 18 

Harmony thrust plate ........................ 72, 7!1 

Havallah formam~n Son.oma Range__________ 40 

Henbest, L. G., fossils identified by ....... 34, 35,37 

High-angle faults, history of.................. 83 

in Osgood Mts .... ------------------------. 7 4 

Highway limestone ........................ 28, 30,34 

History, Cenozoic .... ------------------------ 8!J 

late Paleozoic or Mesozoic. ............... 81 

Paleozoic ........... ___ ....... ___ ......... 79 

Hogshea,d Canyon ............................ 29,31 

barite deposit............................. 96 

Comus formation......................... 20 

fossils in.................................. 21 

Preble formation ........................ . 

measured section ... ------------------

Hogshead Canyon, Twin Canyon fault ...... . 

Hornfels, chemical and spectrographic analyses .............. ---.............. . 

metamorphic origin ........ --------------

mineral assemblages ................ _ ..... . 

Hot Springs Range .......... ................ . 

age of faulting.---------------------------

andesite :flows .... ------------------------

10 

12 

70 

62 

60 

61 

3,5 

77 

5S 

analyses .............................. 55, 56 

faults and fault blocks .................... 69,77 

folds in ................................ 69, 75, 76 

gold-bearing quartz veins................. 92 

granodiorite bodies....................... 41 

alteration ..... ------------------------ 46 

Page 

Hot Springs Range-Continued 

Harmony formation...................... 14 

Late Cambrian sedimentation............ 80 

lead and copper_ ... ---------------------- 95 

lead deposits.---------------------------- 96 

origin ............... -----..... ::: ........ ___ 78 

Paradise Valley chert ..................... 13,14 

pure quartzite............................ 84 

quicksilver deposits.--------------------- 91 

quicksilver mines and deposits.---------- 119 

relation of..------------------------------ 18 

structural relations of granodiorite........ J,S 

struct-qral relation to Osgood Mts ......... 77,78 

Tertiary conglomerate____________________ 52 

Valmy formation _________________________ 22,23 

volcanic rocks____________________________ 51 

Humboldt River----------------------------- 3, 5 

Intrusive basalt, uncertain age________________ 1,0 

Intrusive igneous rocks, late Cretaceous age.. 41 

minor ------------- ...... ----------------- 1,9 

J 

Joint systems in Osgood Mountains stock ..•. 41,42 

K 

K and K (Red Devil) quicksilver prospect.. 92,111 

hydrothermalalteration__________________ 49 

Kirby mine._-------------------------------- 45 

geologic map and section_------------- -- pl. 5 

granodiorite contact._____________________ 42 

Kirby mine, tungsten deposits________________ 104 

Klippen. __ . ______ . __ .• _________ . __ ._ ... __ .. __ 20 

L 

Last Chance prospect, hydrothermal alteration_ ... -------------------------- 49 quicksilver occurrence ___________________ 92,110 

Late Paleozoic or Mesozoic orogenic history .. 81-83 

sedimentation.--------------------------- 80, 81 

Lead, minor deposits_________________________ 95 

Lead-silver deposits______________________ _____ 96 

Lead-zinc mines and prospects, detailed descriptions ....• _. __ . ___ . __ . __ ._____ 1 It 

Little Humboldt River----------------------- 3 

Location of report area .. --------------------- 3 

Lone Butte.: .. ~- ----------------------------- ~31 

M 

Marble and silicated marble __________________ 62, 6!1 

Marcus mine, tungsten deposits______________ 101 

Marshall Canyon, scheelite ... ---------------- 89 

Section 5 pit, tungsten ------------------- 112 

Mesozoic orogeny, age .... ------~-----------~- 83 

Metamorphism _______ ... ___ ---... __ -----.--.- 59 

of carbonate rocks.----------------------- 61 

of Paleozoic volcanic rocks________________ 67 

of pelitic rocks •• -------------------------- 60 

zoning ________________ -------------------- 62 

Metasomatism .. ----------------------------- 59 

Mineral deposits .•... ----------------------~- 8!J 

Mineral resources, mining future ... ---------- 97 

Mines and prospects, alteration and age...... 51 

detailed descriptions _____________ ... ------ 97 

structural relations ... -------------------- 8S 

Mississippian age, rocks oL •. ---------------- II, 

Modes, of basalt. ... -------------------------- 58 

of Harmony formation •••. ---------------- 16 

of Osgood Mountains granodiorite........ 44 

of Tertiary flows ..•. ---------------------- 55 

geologic map ..... ------------------------ pl.lO 

scheelite ..... -------•. -------------------- 88 

Mountain King mine, tungsten deposits...... 111 
N 

Page 

Niggli values, altered dacite porphyry________ 50 

analyses, norms, and modes, of Tertiary 

flows._-----------------------· --- 55 

basalt. __ --------------------------------- 41, 58 

granodiorite_----------------------------- 45 

Tertiary flows____________________________ 55 

unaltered and altered granodiorite________ 48 

Norms, altered dacite porphyry______________ 50 

basalt. __ --------------------------------- 41, 58 

Goughs Canyon rocks____________________ 25 

Tertiary flows------------- --------------- 55 

unaltered and altered granodiorite________ 48 

granodiorite_----------------------------- 45 

0 

Ogee and Pinson fault. ___________________ _ 75, 76,89 

movement on ___ _________________________ 78,79 

Ogee and Pinson mine, description___________ 117 

gold-arsenic deposit_________ __ ____ ___ _____ 89 

Older fan gravels __ --------------------------- 58 

Olivine basalt, petrographic description ______ 55,56 

Soldier Cap area__________________________ 54 

Ordovician age, rocks oL --------------------- 19 

sedimentation._------------------------__ 80 

Orogeny, Antler------------------------------ 79,80 

Late Paleozoic or Mesozoic_______________ 81 

Mesozoic.-------------------------------- 82,83 

post-Early Permian and pregranodiorite 

thrust faulting____________________ 82 

Osgood Creek canyon, tungsten prospects____ 112 

Osgood Mountain quartzite._-------- 7, 29, 32, 36,71 

age and correlation__ _____________________ 9 

anticline in------------------------------- 69 

crossbedding in________________ ___ ____ ____ 7,10 

deposition_ ____________ _____ ______________ 9 

distribution ___ --------------------------_ 7 faults_____________________________ ________ 77 

stratigraphy and thickness ___ ------------ 9, 29 

Osgood Mountains _________________ 3, 5, 30, 32, 37,38 

andesite analyses ______ ___ ________________ 55, 56 

lithology ____ ----------------------------- 7 origin________________ _____________________ 79 

andesite flows____________________________ 58 

barite deposits, occurrence________ ________ 96 

barite prospects ____ ---------------------- 84 Comus formation _________ ________________ BO, 80 

copper mineralization______________ _______ 96 

folds and faults___________________________ 69 

gold-arsenic deposits______________________ 89 

granodiorite stock._.--------------------- 41 

alteration_____________________________ 46 

contact relations______ ________________ 42 

joints ___ ------------------------------ 42 

metamorphic aureole •• --------------- 59,60 

structural relations._----------------- 41,83 

structural trend ____ ------------------ 69 

Harmony formation_____________ ____ _____ 15 

high-angle faults _________________________ ._ 74 

See also Anderson Canyon fault; Village fault; Getchell fault; Ogee 

and Pinson fault. 

imbricate thrust zone_____________________ 71 

lead and copper_------------------------- 95 

lead deposits ___ -------------------------_ 96 

marginal facies of granodiorite stock__ _____ 44 

metamorphism ___ ------------------------ 61 

origin ___________________ ----------------- 78 

rocks exposed in__________________________ 7 

structural relation to Hot Springs Range__ 77, 78 

thrust faults______________________________ 70 

tuffaceous rock___________________________ 5~ 

tungsten deposits ___ ---------------------- 84 

in altered granodiorite________________ 88 

in tactite_____________________________ 84 

volcanic rocks __ -------------------------- 51 

INDEX 

p 

Page 

Pacific mine, analysis of tactite_______________ 67 

block diagram____________________________ 102 

calc-silicate rocks_________________________ 64 

description __ ----------------------------- 101 gold_____________ ________ __ _____ __________ 89 

granodiorite-limestone contact____________ 42 

known tungsten reserves_________________ 97 

tactite ________ ____________________________ 65,68 

tungsten deposits_______________ ____ ______ 101 

Paleozoic history _________ -------------------- 79 

Paleozoic volcanic rocks, metamorphism______ 67 

Palmer, A. R., fossils identified by_ 12, 13, 14, 19, 20 

--quoted_________________________________ 14 

Paradise Valley_----------------------------- 3 

Paradise Valley chert_ _________________ ___ 18, 76, 80 

deposition___________________________ _____ 80 

distribution ___ ____________ --------------- 13 

faulting of__------------------------------ 77 fossils____________________________________ 14 

heavy minerals in________________________ 14 

lithology ____ ----------------------------- 18 

stratigraphy and thickness_-------------- 14 

structural relations_______________________ 77 

age of folding __________ ._________ __ ________ 82 

Peak 6837 thrust______________________________ 71 

Pebble conglomerate, Tertiary __ ------------- 52 

Pelitic rocks, metamorphism oL____ _________ 60 

Pennsylvanian and early Permian age, rocks 

oL _ ------------------------------ ~8 

Pennsylvanian(?) to Permian('(} age, rocks of_ 88 

Perforate Canyon_--------------------------- 31 

Physical features ___ -------------------------- 8 

Placer deposits, assays and origin____________ _ 95 

Dutch Flat________________ _______________ 93 

production ___ ------------------------ 94 

Preble formation __________ ___ 7, 10, 31, 36, 41, 73, 76 

age and correlation_______________________ 1~ 

analyses, of limestone_____________________ 67 

of shale and limestone_--------------- 11 

anticline in_______________________________ 69 

correlation________________________________ 13 

deformation in __ ------------------------- 10,70 

deposition ________ ------------------------ 13 distribution ______________________________ 7,10 

faults in ______________________________ 74, 75,77 

fossils____________________________________ 1 ~ 

limestone from __ ------------------------- 11 

lithology _____ ---------------------------- 10, 36 

measured section________________________ _ 12 

metamorphism oL ________________ 60, 61, 63, 64 

metamorphism of carbonate rocks___ _____ 6~ 

origin __ ---------------------------------- 79 rocks exposed in _________________________ _ 

scheelite mining_------------------------- 84 

stratigraphy and thickness_______________ 11 

stratigraphic relations ___ ----------------- ~9 

structural relations __ --------------------- 81,82 

Preble thrust plate___________________________ 7~ 

Precipitation ___ ------------------------------ 5 

Previous and pre.sent work__________ _________ 6 

Pumpernickel formation___________ ___________ 40 

Q 

Quartz diorite_------------------------------- 49 

Quaternary age, rocks of.____________ __ _______ 58 Quicksilver _________________________________ -- 83 

Quicksilver deposits in Hot Springs Range___ 9~ 

association with faults___________ ___ ______ 77 

relation of mineralization to granodiorite 

stock _________________ ------------ 92 

Quicksilver mines and prospects in Hot Sp1 ings 

Range, detailed descriptions______ 119 

See also Dutch Flat mine; K and K prospect; Last Chance prospect. 

R 

Ranges, origin _____ ---------------------------

Red House, Nev _ ----------------------------

References cited ______ ------------------------

Relief.---------------------------------------

127 

Page 

78 

3 

JU 

5 

Rhyolite tuffs, distribution and petrography__ 51 

Richmond mine, geologic map ________________ pl. 10 

granodiorite contact..---~---------------- 42 

lead deposits and production_____________ 96 

lead-zinc deposits_________________________ 111 

tactite deposit---------------------------- 110 

tungsten deposits_____________ __ __________ 110 

Riley Extension mine, geologic map and sec- tion ______________ __ ______________ pl. 6 

known tungsten reserves.---------------- 97 

underground workings____________________ pl. 7 

Riley mine___________________________________ 51 

fault relation__ ___________________________ 75 

geologic map and section.---------------- pl. 6 

gold __________ ------- __ -----------------~- 89 

granodiorite-limestone contact____________ 42 

hornfels.--------------------------------- 62 

known tungsten reserves.---------------- 97 

underground workings____________________ pl. 7 

Rittman classification, Tertiary flows.------- 55 

Roberts Mountains thrust, age oL_._________ 80 

Rock units.---------------------------------- 6 

Rocky Canyon, Getchell fault zone___________ 75 

Ross, R. J., Jr., fossils identified by_--------- 21,23 

s 

ScheeJite __ ----------------------------------- 95 

in fractures and cavities__________________ 88 

in tactite ... ------------------------------ 84,85 

mineralogical occurrence and origin_______ 88 

placer deposits._------------------------- 93,95 

See also under Tungsten mines and 

deposits. 

Sedimentation, Cambrian____________________ 79 

Late Paleozoic____________________________ 81 

Sedimentation, Ordovician ... ---------------- 80 

Silica deposits.------------------------------- 96 

Siliceous assemblage, environment of deposition _______________ ---_----- _---- 79 

Silver, Getchell mine.------------------------ 91 Silver Hill lead-zinc mine ____________________ 96, 1~1 

Sodarisi Canyon, placer deposits ______________ 94,95 

Soldier Cap, basalt.-------------------------- 53 

olivine basalt.---------------------------- 54 

analysis.-----J---------------c·------ 55 

Soldiers Pass, quartzite_______________________ 8 

Spectrographic analyses_--------------------- 56 

of granOdiorite •• -------------------------- 45 

of hornfels-------------------------------- 62 

Stewart Gap, age and correlation_____________ 14 

Stone Corral area, silica_________________ ____ _ 96 

Valmy formation _________________________ 22,23 

structural relations------------------- 77 

Structural relations .. ------------------------- 69 

geologic history interpreted from__________ 79 

T 

T.N.T. mine, tungsten deposits-------------- 112 

host rock.-------------------------------- 88 

Tactite, chemical analysis____________________ 67 

mineralogy------------------------------- 84 

form and structural relations __ . __ ---- 85-86 

occurrence and mineral constituents ______ 64,65 

origin. _____ --------- _________ -- __ -------- 86 

scheelite content__________________________ 84 

tungsten ore grade________________________ 84 

Tactite bodies, relation to shape of granodiorite 

contact surface ____ --------------- 86 

Tactite zone.--------------------------------- 62,65 
128 

Page 

Talus.------- ____________ --------------- _____ 59 

Temperature _________ ------------------------ 5 

Tertiary age, volcanic rocks__________________ 7 

Tertiary flows, chemical composit:on _ _ ____ _ _ 56 

spectrographic analyses _____ -------------- 56 

Tertiary flows and Rittman classification_____ 55 

Tertiary rocks.------------------------------- 51-59 

age and correlation __ --------------------- 57 

Thrust faults.-------------------------------- 82 

in Osgood Mountains____________________ 70 

Tip Top Mine, tungsten deposits_ ____________ 100 

underground workings____________________ pi. 2 

Tip Top pits, mining future____ ______________ 97 

Tonopah mine, geologic map and underground workings ___ _______ _______ pl. 8 

known tungsten reserves ___ -------------- 97 

tungsten deposits_________________________ 108 

Top Row pit, analyses of hornfels____________ 62 

tungsten deposit__________________________ 105 

Topography, structural control oL _ ---------- 83 

Tuffaceous rock, Getchell mine area__________ 53 

Tuffs .• ---------------------- ____ _ ------------ 58 Tungsten deposits, access_____________________ 3 

index map-------------------------------- 98 

in Osgood Mountains-------------------- 84 

metamorphic origin______________________ 60 

INDEX 

Page 

Tungsten deposits in altered granodiorite_____ 88 

origin ____________ -----------------_-----__ 88 

Tungsten deposits in tactite ____ ______________ 65,84 

form and structural relations_____________ 85 

tactite, mineralogy and paragenesis_______ 84 

origin __________________ ------------------- 88 

Tungsten deposits, mines and prospects______ fJ7 

Tungsten mining, Osgood Mts__ _____________ 83 

Tungsten ore, production of, Osgood Mountains ____ ------------------------- 99 

reserves. __ --·----------------------------- 97 

Twin Canyon member of Osgood Mountain 

quartzite, exposures______________ 7 

shales in •• -------------------------------- 8 

lithology __ ------------------------------- 7, 8, 9 

Unconformity_------------------------------- 80 

u 

Uplift, late Paleozoic._ ----------------------- 81 

v 

Valley View mine, fault relations_____________ 75 

geologic map and section _________________ pl. 4 

tungsten deposits.------------------------ 103 

0 

Page 

Valmy formation ______________ 19, 11, 22, 73, 77, 80,81 

age and correlation__ _____________________ 18 

distribution. ____ -----------------~------- It 

equivalence to Comus formation__________ 14 

lithology ____ ----------------------------- II 

silica •• ----------------------------------- 96 stratigraphic section______________________ 18 

structural relations_______________________ 81 

Vegetation. ___ ------------------------------- 5 

Village fault.·-------------------------------- 74 

Vinini formation __ --------------------------- 80 

Volcanic rocks, contact metamorphism in____ _ 67 

See also Tertiary rocks. 

Volcanism, history oL----------------------- 88 

w 

Williams, James Steele, fossils identified by____ 33, 

34,37, 38 

Winnemucca, Nev _ -------------------------- a 

weather data __ __ '------------------------- 5 

y 

Yochelson, E. L., and Batten, R. L., fossils 

identified by ____ ----------------- 36 

z 

Zoning, metamorphic.----------------------- 61