Vol. 66, 1971, pp.

14-33

Gold-Bearing
Depositsin North-CentralNevadaand
Southwestern Idaho

R, nPri J. RO•E•TS,A•Tr•U• S. RADTKE,*ND R. R. CO*TS

With a section on
Periods of Plutonism in North-Central Nevada

MILES L. SILBERMAN AND EDWIN H. MCKEE

Abstract

Gold-bearingdepositsin north-centralNevadaoccurin a wide variety of geologic

environmentsrelatedto major stratigraphicand structuralfeatures. These environments
includepre-Tertiary sedimentaryand metamorphicrocks,granitic rocks, and volcanic
rocks of pre-Tertiary and Tertiary age which have been complexlydeformed. The
depositswere formedduring five principalintrusivemetallogenic episodes;the oldestis
Jurassic,two are Cretaceous,one early Tertiary, and the last, late Tertiary. Three
major epigenefic groupsof gold-bearing depositsare recognized:replacement deposits,
disseminated deposits,and veins. The replacement depositsmay be subdividedin order
of decreasing temperature of formationinto contactpyrometasomatic deposits,base-metal
deposits,
and peripheralgold-silverdeposits.The disseminated gold depositsseemto be
intermediatein mineralogy betweenthe peripheralreplacement deposits and low-temper-
atureveins,but differ in that they containonly minor amountsof silver. They are here
consideredto be a distinctgroup. The veinsare subdividedinto two classes:veins in
pre-Tertiary and graniticrocksand veinsin or associated with Tertiary volcanicrocks.
Contact pyrometasomaticdepositshave yielded significant production in only one
district, Battle Mountain (Copper Canyonand CopperBasin), where calc-hornfelscon-
taining pyrite, chalcopyrite,pyrrhotite, arsenopyrite,sphalerite, and galena was mined
as copper-gold
ore. Base-metal
replacement
deposits
occurat Eur4ka (silver-gold-lead-
zinc) and Copper Canyon (copper-goldand zinc-lead-silver). Peripheral gold-silver
depositsoccur at Eureka and Copper Canyon.
Disseminatedgold depositssuchas Carlin, Cortez, Getcheil,and Gold Acres, which
are relatively new discoveries,have yielded significant productionto date and have
excellentpotentialfor continuedlarge-scalefuture production. They are characterized
by generallylow-temperaturemineral assemblages which includepyrite, quartz, gold,
realgar,stibnite,cinnabar,sphalerite,and galena.
Gold-quartzveins in pre-Tertiary and granitic rocks generallycontainsulfideassem-
blagessimilar to thoseof the high-temperaturereplacementdeposits;medium-temperature
veins are characterizedby tetrahedrite, galena, sphalerite,and pyrite; low-temperature
veins by pyrite and galena and by stibnite-quartz. Veins in volcanicrocks or in base-
ment rocks just beneathare divisible into three types: argentite-quartz-adularia
veins
containingpyrite, gold, and sparsegalonaand sphalerite;argentite-quartz-adularia
veins
characterizedby pyrite, gold or electrum,argentite, naumannite,and lesser amountsof
base-metalsulfides;and stibnite-quartzveins containingargentiteand silver sulfosalts,
locally with adularia.

Introduction coveredduringthe last 40 years.at Getcheil,Gold

M•.TAn deposits in Nevada were subdividedby Acres, Carlin, and Cortez do not fit readily into the
Ferguson (1929) into two principalgroups,those schemeand somemodificationis required (Jorale-
associated with intrusive rocks and those with vol-mon, 1951; Ketner, in Gilluly and Gates, 1965;
canic rocks (Table 1). This classificationis still Roberts,1960, 1964, 1966; Hardie, 1966; Erickson
gold depositsdis- et al., 1966;HausenandKerr, 1968;Hewitt, 1968;
valid exceptthat the disseminated
Wells,Stoiser,andElliott, 1969). In addition,many
x Publicationauthorizedby the Director, U.S. Geological
Survey. new data on the structuralenvironment,geochronol-
14
 GOLD-BEARING DEPOSITS IN NEVADA AND IDAHO 15

ogy,and geochemistry
of the ore deposits
are avail- TABLE 1. Metallogenic Epochs in Nevada (Ferguson,1929)
able. Some of these new data will be summarized
I Deposits associatedwith intrusive rocks
here with particular emphasison the gold-bearing
A. Jurassicor Cretaceous B. Early Tertiary
depositsin north-centralNevada and southwestern Argentiferous quartz veins Base metals, silver
Idaho (Figs. 1, 4). In this report Roberts is re- and gold
sponsiblefor the geologicframework and sectionon I I Deposits associatedwith volcanic rocks
C. Pre-late Miocene D. Post-late Miocene
replacementdeposits;Roberts and Radtke for the Silver-gold deposits Gold-silver deposits
sectionon disseminated deposits;Coatsfor the sec-

OREGON IDAHO
42 ø 118 ø 117o 116 ø
42. 8lack Can
Mining Districts
1. Disaster
2. National
--81 l-- •McDermitt[ 43. Railroad
44. Rye Patch
3. Gold Basin
4. Mountain City i i
Moun
City y
45. Unionville
46. Lewis
47. Hilltop
5. larbidge
6. Alder
7. Edgemont I i
48. Lee
49. RubyValley
50. Sacramento
8. Aura
9. Charleston
11' Q12 51. SpringValley
10. Island Mtn
HUM OLDT 52. Rochester
11. Rebel Cr ELKO 53. Kennedy
12. ParadiseValley 54. McCoy
13. Lime Mtn
14. Cornucopia
ß-'.-'•ß
i Tuscarora
016 55. Bullion(Tenabo)
55a. Gold Acres
56. Willard
15. Shon
O17 i

o,,Getchel
'@;! idas ß
16. Rock Cr 57. Antelope
17. Awakening 58. lersey
023 59. Cortez
18. Tuscarora
Deeth
19. Midas 60. 8uckhorn
20. Warm Sprs 61. Mineral Hill
21. Dutch Flat 62. Table Mtn
22. Getcheil 410 . _ .024 • 63. Bald Mtn
23. Merfimac 64. White Cloud
24. TenMile Elko 65.Antelope
' 340' ,
25. Winnemucca
26. Bootstrap
33V• ,

I
• I
66. Diamond
67. Shade Run
27. Harmony
28. Golconda
35,,[ 68. 8ernice
69. Ravenswood
29. Iron Point
30. Lynn (Carlin)
31. Haystack 038 ',,, •: ' Mountain 043 ,,,'
70. Mount Hope
71. IXL
72. New Pass
32. Mill City 73. Alpine
33. Gold Run 74. Skookum
34. Maggie Cr
35. Sierra
EKSHIN'G
•
'
'
' /"
' 054
460
¸ 47 ' I '
, , 75. Eureka
76. Granite
77. Wonder
36. Washiki
37. Imlay 56 78. ReeseR (Austin)
38. Willow Cr 057 79. Birch Cr

.' ' ' •'•• • - • iold

39. Battle Mtn,
Copper Can.
Copper Basin
• Oortez
40. SMford 400
41. Star
ii
/' • L•NDER [ 065
O67/'
u•C•U•C•ltt
•n •J ,'" ' •U•A• , ( (yl•
• ,
, ;
EXPLANATION Modified after 8onham,(1967)Roberts,(1966)
Productionin ouncesof gold

0
O
O 10-1,000
1,000-10,000
10,000-100,000
• .I"•
,,"',
Town
Paved
highway
Secondary road
Au,
Ag
Sb/ Metallogenic
Hg,
province
boundary
Pb,
Zn
100,000-1,000,000
• U.S.
Highway /'Minor
Ag,
Au
50 MILES

O More
than
1,000,000
(•)State
Highway 0
! I

Fro. 1. Index map of north-centralNevada showinggold mining areas.

16 ROBERTS,
RADTKE,AND COATS

D A.H 0/.
• / ........ o• • WYOMING

?:.•.•; : C• ,

, J
0%',_.
"'.
Tonopah•pi•h•.
• .
I / Ba.,•._.•in
andRange
ß /C.r

%. i1•_•:
•) '",..,_:•Lo
s•e_
Province
boundary .........
g•• ARIZONA Los
Ve
0 100 200 MILES 0 100 200 MILES
I I I I I I

FIG.2. A, Map showingdistribution

of faciesin the Cordillerangeosyncline,
Cambrian throughDevonian
time.
B, Distribution
of faciesafter late Devonianto earlyMississippian
thrusting.

tion on veins; and Silberman and McKee for the deposition

of threeprincipalfaciesin northeasterly
sectionon age of plutonism. trendingbelts(Fig. 2A).: an easterncarbonate
facies
(miogeosynclinal)and a westernsiliceous and vol-
Structural and Stratigraphic Framework
canicfacies(eugeosynclinal),
separated
by a transi-
Precambrian Time tional facies. Depositionin these belts continued
The ore depositsof the Western United Statesare untilLateDevonian
time,whenit wasinterrupted
by
localized in a structural framework that formed in the Antler orogenythat lasteduntil Middle Penn-
Precambrian time and which has continued to de- sylvaniantime (Robertset al., 1958; Kerr, 1962;
velop till the presentday. The Precambrianstruc- Smith and Ketner, 1968).
tural tectonicevents developednortheasterly,east- During the Antler orogeny,in latestDevonianor
west, and northwesterlystratigraphicand structural earliest
Mississippian time,a greatglideplatemoved
trends (Roberts,1957, 1960, 1966, 1968; U.S. Geol. eastwardfrom the orogenicbelt into centralNevada.
Survey, 1968). The principal northeasterlytrend The plate was composed mostlyof eugeosynclinal
was paralleledby the Cordillerangeosyncline,which and transitional rocks and it overrode rocks of the
carbonate
formed in late Precambrian time and was a zone of facies,reaching
pointsalonga sinuousline
major subsidenceuntil Late Devonian time. East-from Eurekanearlyto Wells (Fig. 2B). Uplift
west orogenictrends along zones of Precambrian along northwest-trendingbelts at placesformed
deformationhave been recognizedin centralUtah; domesin Late Pennsylvaniantime; these domes
thesetrends have beenprojectedinto westernUtah were further accentuatedduring Mesozoic and
earlyTertiary intrusionand deformation,
and Nevada (Robertset al., 1965; Zietz et al., 1969), forminga
where they are recognizedin east-westalinements favorablestructuraland stratigraphic
environment
in
and uplifts and in block faulting. Northwesterly which gold-bearingdepositswere localized.
trendingfeaturesthat probablyfollow structuresof
Mesozoic and Tertiary Time
Precambrian origin include mineral belts charac-
terized by lines of fractures,domes,and faults. During early Mesozoictime north-central Nevada
Paleoxoic Time
was intermittentlycoveredby shallow seas; local
volcanismand plutonismin Permian and Early
The Cordilleran geosyncline,which came into Triassictime heraldedorogenyat the end of Jurassic
existencein late Precambriantime, was the site of (Muffler, 1964; Wallace and Tatlock, 1962; Wallace,
 GOLD-BEARING DEPOSITS IN NEVADA AND IDAHO • 17

Tatlock, and Silberling,1960; Wallace, Tatlock, Sil- bodiesappear to be distributedrandomlyin the re-
berling, and Irwin, 1969). Since then, the region gion, othersmay be structurallycontrolled. Thirty-
has been undergoinguplift and erosion. In late one of these plutons have been dated by the
Mesozoictime, block-faulting,accompaniedby igne- K.-Ar method, and their ages are consideredrepre-
ous intrusions and volcanic activity, ushered in a sentativeof the timesof major plutonism.
new regimewhich culminatedin the development of The grouping of ages indicatesthat plutonism
basin-and-rangestructure. The cycle began with occurredduring five periods in the Mesozoic and
the emplacementof intrusive bodies during late Cenozoic(Fig. 4). The oldest group of dates in
Eoceneand early Oligocenetime, followedsoonafter Jurassic (168 to 143 m.y. old), then follow two
by widespreadvolcanismthroughoutOligocene,Mio- Cretaceous groups(105 to 87 and71 to 68 m.y. old,
ceneand Pliocenetime. Block-faulting,which gave respectively),the next group is early Tertiary (40
rise to the presenttopography,was most intensein to 30 m.y. old) and the youngestgroup is late
Plioceneand early Pleistocene time. Tertiary (16 to 10 m.y. old).
Widespread tectonic activity including the em-
Metallogenic Provinces placementof large granitic bodieswest of central
Nevada may be divided into two major metallo- Nevadain the Sierra Nevadais reflectedby the plu-
genic provinces: a western one, characterizedby tons of the two older age groups in north-central
gold, silver, tungsten, mercury, and antimony de- Nevada. The oldestgroup of north-centralNevada
posits; and an eastern province, characterizedby plutonsare the sameage as parts of the Inyo and
lead and zinc depositswith minor silver and gold2 Yosemite intrusive epochs of the Sierra Nevada
(Figs. 1, 5) (Ferguson, 1920; Bateman, 1950; batholithas definedby Everndenand Kistler (1970;
Roberts, 1966). The boundarybetweenthe prov- Fig. 4). The older of the Cretaceousperiods of
incesis gradationaland roughlybisectsnorth-central plutonismin north-centralNevada is about midway
Nevada. Copper, tungsten, and molybdenum de- in age betweenthe Huntington Lake and Cathedral
positsoccurin both provinces. Range Sierran intrusive epochs of Evernden and
The ore depositsof the westernor preciousmetal Kistler (1970; Fig. 4), and a number of plutonic
rocks in the Sierra Nevada batholith have been dated
provinceoccur mostly in eugeosynclinal Paleozoic
and Mesozoicrocks (shale, chert, graywacke,vol- at about 100 m.y. as well. The younger Cretaceous
canicrocks,and minor limestone)and in overlying intrusive rocks in north-centralNevada (70 m.y.
Tertiary rocks. The eugeosynclinal rocks were de- old) correspondin age to early Laramide,as defined
positedon simaticoceaniccrust 5-10 km thick. The by Damonand Mauger (1966). The early Tertiary
ore depositsof the easternor base-metalsprovince (40 to 30 m.y. old) plutonsin north-centralNevada
occur mainly in miogeosynclinalcarbonate rocks are the same age as the start of Tertiary igneous
(limestone, dolomite, and minor shale) that were activityin the Great Basin (McKee and Silberman,
depositedon sialiccrust. 1970a,b). Plutonicrocksof Laramideand middle
The boundarybetweenthe two provincescoincides Tertiary age are not found in the Sierra Nevada,
broadly with the boundarybetweenmajor geosyn- suggesting that the two youngerperiodsof plutonism
clinal trends and with the frontal zone of the Roberts (70 m.y. and 40 to 30 m.y.) in north-centralNevada
are not related to Sierran intrusion but are related
Mountains thrust fault. The nature of these rela-
tionshipsis not clear, but processesrelated to geo- to geologicevents in the eastern Great Basin.
syndinal sedimentationand subsequentorogenyre- Large bodiesof plutonicrocksyoungerthan about
sulted in conversionof the upper mantle under the 30 m.y. old are not known in north-centralNevada,
geosynclineto continental crust with consequent but widespreadvolcanicrocksyoungerthan about 16
magmatismand volcanism during several epochs m.y. old probablyhave deep-seatedplutonic equiv-
(Bateman, 1950; Coatset al., 1965; Roberts, 1968). alents not exposedat the present level of erosion.
This youngergroup (16 to 10 m.y. old) shownin
Periods of Plutonism in North-Central Nevada Table 2 was defined by McKee and Silberman
In north-centralNevada (Fig. 3) there are ap- (1970a) from occurrencesin the SheepCreekMoun-
tain and northern ShoshoneRanges, and is repre-
proximately50 plutonsof coarse-grained equigran-
sentedby basalticandesiteto rhyoliteflowsand dikes.
ular to porphyriticquartz-monzoniteto granodiorite. A swarm of these dikes and flows also occurs in the
These bodies range from about 130 to less than 1
square kilometer in outcroparea. Although many CortezMountainsand RobertsMountains('Fig. 3).
Roberts and Coats consider that the five intrusive
• An exception to this pattern is the Ely district, which epochsin north-central Nevada also represent dis-
contains porphyry copper deposits; the gold content of the
ore is low, but the total productionis significantbecauseof tinct metallogenicepochs,and have so designated
the enormous tonnage of ore treated. them in Table 2. The replacementdepositswere
18 ROBERTS,
RADTKE,
ANDCOATS
Figure 3
118 ø
117' 116'

ELKO

0 10 . •0 80 40 EOMILES
I . I ' I ; i
 GOLD-BEARING DEPOSITS IN NEVADA AND IDAHO 19

Figure 3 (cont'd.) Table 2. Intrusive and metalloganic epochs in north-central Hevada

Age in m.y. Intrusive and Age span, m.y. Characteristic metals

Metellogenic epoch before present and source of data
1. OsgoodMountainspluton 90
2. GreggCanyonpluton 104
3. BuffaloMountainplutoniccomplex 146 159 16- 10 Gold, silver, mercury
4.StonyBasin
pluton 105r (Gilluly and Ma•ursky, 1965;
5. LeePeakpluton 150 V Late Tertiary (McKee and Wells, Stoiser, and Elloitt,
6. GraniteMountain(Hu•nboldt
Range)
plutonic
complex 30z $ilberman, 1970a) 1969; Schilling, 1965)
7.NewYorkCanyon
pl,u{0n' 69
8. TrentonCanyonpluton 87
9. CopperCanyonpluton 38 40- 30
10. ElderCreekpluton 37 Major base metals, gold,
11.Tobinpluton 153 IV Early Tertiary (Silberman et aZ., silver, antimony (Roberts,
12.McCoypluton 153 1969; McKee and f966; Wells, Stoiser, and
13. Hdltoppluton 38 Silberman, 1970a) Elliott, 1969)
14.GraniteMountain (ShoshoneRange)pluton 37
15 Gold Acresquartzmonzonite 99 71- 68
16. Goat Ridgepluton 35 III Late Cretaceous Tungsten, silver, gold.
17.Tenabopluton 38 (Thie Report)
18. Cain Creek pluton 155
19 Ravenswood pluton 71
20.SwalesMountainpluton 39 105- 87
21.Frenchie
Creek
plutonic
complex 'i433 153 II Cretaceous Tungsten, base metsis, gold
22.MillCanyon
pluton 150• (This Report) (Hotz and Willden, 1966)
23. Cortezdike 343' Wells andothers,1969
24. Cortez dike swarm -
25 IowaCreekpluton 68 168-143
26.GrassValleypluton 68 Tungsten, minor base metals,
I Jurassic minor silver and gold
27.Austinpluton 157
28.Walti pluton 33 (This Report) (Muffler, 1964; Coats et aZ.,
29.ClipperGappluton 151 1965; Coats, 1967; Gilluly
•0. Northumberlandpluton 154 and Masursky, 1965)
31.MountHopepluton 36'
32.WhistlerMountainpluton 1523
33. RubyHill 100
Intrusive
epochs
in north-central
Nevada epochs,but theprincipalgoldmetallization
mayhave
V• 16-10(Late
Tertiary) taken placeduring the fourth (40-30 m.y.). The
veins containedin granitic and pre-Tertiary rocks
IV '•':'-•'"•40-30(Early
Tertiary)
Ill "&'"'"'="•
71-68(Late
Cretaceous)
were mostly formed during the first three epochs;
the veins in volcanicrocks were formed during the
II • 105-87
(Cretaceous)
last two epochs.
I :v.• 168-143(Jurassic)
• undated
intrusive
body Mineral Belts

Note: The age of Grass Valley Pluton (No. 26) should Theprincipalgolddeposits
in north-central
Nevada
read 168 m.y., not 68 m.y. occur in mineral belts that trend northwestward and
FIG. 3. Plutons in north-central Nevada. Modified from northeastward
(Robertsand Lehner,1955; Roberts,
Map 30, Nevada Bureau of Mines by Roland V. Wilson and 1957,1966). The principalnorthwesterly
beltsthat
Richard R. Paul. K-At age and name of pluton listed.
have beenrecognizedare the Lynn-Railroad,Battle
Mountain-Eureka,Getcheil-National,and Lovelock-
formed during the first four of theseepochs;certain Austin; the northeasterly Shoshone-Jarbidgebelt
of the disseminatedgold depositsare also apparently cuts across the northwesterlytrends (Table 3;
associatedwith igneous rocks of the first three Fig. 5).

TERTIARY J CRETACEOUS JURASSIC

Start igneousJ Laramide

ofTerhary igneous
Southwest activity
Basin J Intrusive
epochs
ofSierra
Nevada
batholith
from
Evernden
&K•stler
(1970) J
activity•n centralNevada I &Range
Prov,nce I I
(McKee& Sdberman,1970) I (Damon
andMauJ•er,
1966)I 79-90 1o_•:12__[
! 132- 14s 16o- tso ,
Cathedral HunhngtonLake Yosemite InyoMountains
Range

4 -Gilluly (1967)
6- D. B. Tatlock written
30 -40 68-71 87- 105 143- 16• communication 1970
20-Coatsandothers(1965)
21-Armstrong (1970)

•////
'•\!
22-Armstrong(1970)
27-Armstrong(1970)
-Schilling(1970)
written communication

//
/ \ 5o 6o
/ 70 90 1• 11o 1• 1• 140 150 160 170 i'• MILLION YEAR5

1•0. 4.
20 ROBERTS, RADTKE, AND COATS
Table 3. Mineral belts in north-central Nevada

Mineral belt Basis for

and trend Geology Commodities recognition Source

Lynn-Railroad Paleozoic limestone, Au, Ag, Pb Alinement of windows Roberts and Lehner (1955); Roberts
N. 400-47 ø W. calcareous siltstone intrusive bodies and (1957, 1960); Hardie (1966);
districts; aeromag- Hausen and Kerr (1968); Roberts
netic data et ai. (1967).

Battle Mountain- Paleozoic chert, shale, Au, Ag, Cu Alinement of districts Roberts and Lehner (1955); Nolan,
Eureka limestone; calcareous Pb, Zn and intrusive bodies; Merriam, and Williams (1956);
N. 400-47ø W. conglomerate aeromagneticdata; Nolan (1962); Roberts and Arnold
geochemical data (1965); Roberts dtaZ. (1965);
Shawe (1965); U.S. Geol. Survey
(1968).

Getcheil-National Paleozoic chert, shale, Au, Ag, W Alinement of districts; This paper.
N. 250-30 ø W. limestone; calcareous aeromagnetic data
conglomerate

Lovelock-Austin Paleozoic chert, shale, Ag, Au, Pb, Alinement of districts; Roberts and Lehner (1955); Roberts,
N. 40 ø W. volcanic rocks; limestone W aeromagnetic data (1966); Ross (1953).

Shoshone-Jarbidge Paleozoic chert, shale, Barite, Au Alinement of district, Ketner •n Gilluly and Gates (1965);
N. 40ø E. volcanic rocks; Ag, Hg, W fracture zones, and Roberts (1966); D. R. Shawe (oral
Tertiary volcanic geosynclinal trends commun.,1966); Landwehr (1967).
rocks

The mineral belts have been defined from struc- in the upper plate of the RobertsMountainsthrust
tural, geophysical,
andgeochemicalevidence(Rob- fault, as alongthe Lynn-Railroadand Battle Moun-
erts,1966,p. 57). Structural is bestshown tain-Eureka belts. The northwest trends are con-
evidence
bythestrikingnorthwestward alinementof windows sideredto be of probablePrecambrianage,and may
have developedas a set of fracturesnormalto the
earliernortheast-striking
geosynclinal
trends. Shawe
•moOREGON •7o IDAHO•6o
(1965; U.S. Geol.Survey,1968,p. A30) considers
them to be strike-slipfaults. Geophysical
evidence
includes a series of broad aeromagneticanomalies
that follow a N40øW zone related to stocklike in-
ßtrusive bodies such as those of Lewis, Gold Acres,
and Hilltop districts (Roberts, 1966). Pertinent
geochemical evidenceis the isotopiccomposition of
lead in galenafrom depositsalongthe Battle Moun-
tain-Eurekaand Lynn-Railroadbelts. The ratiosof
leadisotopes of the two beltsare distinctlydifferent,
suggesting that the leadmay havebeenderivedfrom
different mantle sources(Arthur Pierce, oral com-
munication,1963).
The intrusive rocks in north-central Nevada fol-
low at leasttwo tectonictrends (Fig. 3): (1) north-
easterly,parallelto Cordilleran geosyncline trends,
40 ø
and (2) northwesterly, parallelto deep-seated frac-
ture systemswhich controlthe mineralbelts. A
possible
northeasterlyalinement of plutonsof groupI
extends from Austin (27 on Fig. 3) along the
ToiyabeRangeto the FrenchieCreekplutoniccom-
plex (21 onFig. 3); anotherlocalalinement
includes
plutonssouthwest of Greggpluton(2 onFig. 3). A
FIG. 5. Mineral belts in north-centralNevada modified, notablenorthwesterly alinementof plutonsof group
Roberts (1966). IV lies in the Battle Mountain-Eureka mineral belt.
 GOLD-BEARING
DEPOSITSIN NEVADA AND IDAHO 21
Table h. Gold-bearing deposits in north-central Nevada and southwestern Idaho

I. Replacementdeposits II. Disseminateddeposits III. Veins

Est. Est. Estß Veins in pre-Tertiarystra-Est. Veins associated with
T.øC T.øC T.øC tified rocks andplutons T. øC Tertiary volcanic rocks

15o
- *i I
•' • [ Stibnite-gold•' veins
Disseminated
golddeposits
* Stibnite-quartz'
(SQ)vein,,• •
(_+argentite,
polybasite,
I • (pyrite,
quartz,gold, • (+pyrite,
minor
galena)• • electrum,
minor cinnabar).
• realgar;
minor
stihnite, (Battle
Mountain)
Estß • • National)
Estßdepth
225-I ' 'i galena)
cinnabar,sphalerite,
(Carlin; Cortez; ]I depth
1,000-5,000
ft •• •• 1,000-B,000
ft
I Peripheral
gold I•
I Gold
deposits Acres)
Estß
depth
•I m••ciArgentite-a
2,000-5,000
depth
ft
1,000-h,000
ft
•c • (AAQ)
veins(_+naumannite,
(Jarbidge; Midas) Estß

? (pyrite,
gold,
argentif- • I •
minor
tellurides
)1 • Argentite-adularia-quartz
I•
I•cerous
BOO-- galena,
(Battle
•1 depth sphalerite,
Mountain)
Est.
B,000-10,000
ft •• Te.
sphalerite,
(TQ), •
trahedrite-quartz
galena,
rhodo-
• (AA)
veins
pyrite,
inpre-Tertiary
galena)
(Silver
•
•
veins (tetrahedrite, gold •
chrosite)
(Gold
Creek;
rocks (_+naumannite,
I • City;Tuscarora)
gold,
Estß
ß I Base
metal replacement
deposits(pyrite, argen-
• ReeseRiver)
2,000-5,000
ft
Estß
depth'•
•
depth
2,000-5,000
ft
•I •ß pyrite,
tiferous'galena,
arseno-
chalcopyrite,
•='• -•1
I• gold)
•1 siderite,
sphalerite,
(Battle
Mountain; I•
• Arsenopyrite-quartz
veins (AQ)
gold, I
(arsenopyrite,
•1 Eureka)
Est.depth
ß ß B,000-10,000
ft -•
• pyrite, galena,
ite) (Battle sphaler-
Mountain)
375-
s1• • Pyrometasomatic deposits
• Estß
depth
B,000-10,000
ft
.• (scheelite,
molybdenite, •
• pyrrhotite, bismuthinite
• arsenopyrite, pyrite,
• galena,chalcopyrite,
• sphalerite; gold in sul-
•50-- • Eureka)
fides)(Battle Mountain;
Estß depth
B,000-10,000

1Mineralassemblages
characteristic of eachgroupshownin parentheses;not all specieslisted are foundin eachdepositß
2Temperature
rangeof pyrometasomatic
deposits
fromRidge(1•6•, p. 1816-17)
B00ø-600øC.,
ParkandMacDiarmid,196•,p. 210.
SRange
of mesothermal
replacement
deposits
andveinsfromRidge(1969,p. 1817);Sawkins
(196•,p. 88B-919);
Roedder and
Creel(1965);Roedder
(1967);Meyer• •. (1969,p. 1•12); Helgeson
andGarrels(1968);Lovering(19•0).
•Rangesof peripheral deposits and low-temperaturestibnite-quartz and stibnite-gold veins using uppermesothermal
and
leptothermal
rangesfromRidge•969, p. 1817);Dickson
andTunell(1969,P. 1690);White(1967);Brow•e (1969).
•Ranges
of veinsin volcanic
rocksfromRidge(1969,p. 1817);near-s•rface
veinsfromWhite(19•5,p. 103-108,1•0-1•1);
White (1967); Browne (1969).
•Temperature
determinations
by U.SßGeolßSurvey
(1970,p. A7)andfromNashandTheodore
(1971),andRadtke(unpub.
dataon
Carlin and Cortez deposits)ß

Gold Deposits recognizedthat the isogeothermal

surfacesare curved
over intrusive bodies and along structural features
Classification
so that some estimatesof depth of formation may
On the basisof form and host rock, gold deposits need modification.
in north-centralNevadaand southwestern Idaho may
ReplacementBodies
be divided into three major classes:replacementde-
posits, disseminateddeposits,and veins. The re- Replacementbodieshave beenthe most productive
placementdepositsmay be subdividedinto pyrometa- ore depositsin north-central Nevada. They were
somatic deposits,base-metalreplacementdeposits, mostly discoveredin the 1860's and dominatedthe
and peripheral gold deposits. Carlin-type dissemi-Americanmining sceneduring the 1870-90 period.
nated gold depositsappearto be a distinctclassand The Eureka district leads in productionwith more
are treated here separately. The veins have been than $120 million, mostly in gold, silver, and lead.
subdividedinto veins in pre-Tertiary and granitic Battle Mountain is next with more than $20 million
rocks and veins in or associatedwith Tertiary vol- (Roberts and Arnold, 1965; Meisinger,1969), fol-
canic rocks. Characteristicsof these depositshave lowedby Cortezwith more than $13 million.
been summarized in Table 4 to show the inferred The replacementdepositsare generallyarranged
relationship in mineralogy and temperature and zonally around small stocksof quartz monzoniteor
depth of formation of one group to another. It is granodiorite. The central zone is characterizedby
22 ROBERTS,
RADTKE,AND COATS
outerzonesbeyondthe mainbase-metal deposits, and
thus far have yieldedonly small production. They
are of interest principallybecausethey are thought
to form a link betweensomebase-metaldepositscon-
'
' I
,,,ß'•
/'•Florida^
IJJS?•erC•ty 43'00, taining preciousmetals and the disseminatedgold
•ll o•an / O ß
Valley I • •,. deposits. The nature of this link will be discussed
in the sectionon disseminateddeposits.
Southwestern Idaho.•Gold-bearing replacement
depositson SouthMountainin southwestern Idaho
•int
• District
• OU•q/•S includepyrometasomatic and base-metalreplacement
bodies which are in Paleozoic(?) limestone and
shalecut by granodiorite(Lindgren,1900; Piper and
Laney, 1926; Sorenson,1927) (Fig. 6). The flanks
oJ- of South Mountain are overlappedon all sidesby
Tertiary volcanicrocks which concealthe relation-
i /
•
' k•Triangle shipof the Paleozoic (?) limestoneand relatedrocks
j . to Paleozoic rocks in other parts of Idaho and
j •OUJh
Mountain 42'45'- Nevada. The pyrometasomatic depositsassociated
with granodioriteon South Mountain containhigh-
i 0
I 5MILE8
I temperaturesilicatessuch as hedenbergite,ilvaite,
diopside,and garnet; the sulfidesare pyrite, chal-
FzG. 6. Index map of southeasternIdaho.
copyrite,arsenopyrite,sphalerite,and a little galena.
The replacementdepositswhich fringe the pyro-
metasomatic zones contain similar sulfide assem-
a pyrometasomatic
assemblage
of high-temperatureblages. All of thesedepositscontainsmall amounts
silicate and sulfide minerals. This zone is bordered
of gold and silver, but the principal gold-bearingore
by an innerenvelopeof base-metalreplacementbodies bodieswere found in the associatedveins (Sorenson,
containinggoldand silver,and gradesoutwardinto 1927,p. 40).
peripheralgold-silverdeposits. This zonalarrange- Battle Mountain district.--The Battle Mountain
ment has been noted at Eureka, Baffle Mountain, districtcontainsa full range of replacementdeposits,
South Mountain, and Cortez. includingpyrometasomatic, base metal, and periph-
The pyrometasomatic depositsrepresentthe high- eral. The principal productionhas come from the
est temperaturegold-bearingdepositsin the region. Copper Canyon and Copper Basin areas (Roberts
Ganguemineralsincludegarnet,hedenbergite, ilvaite, and Arnold, 1965).
diopside,wollastonite,zoisite,and related minerals; The district is underlain by silicic and volcanic
the ore minerals, which commonlyappear to have rocksof the upper plate of the RobertsMountains
been introducedlater than the silicates,includepyr- thrust (Scott Canyon,Valmy, and Harmony 'Forma-
rhotite, pyrite, arsenopyrite,chalcopyrite,and some tions) which was overlappedby late Paleozoicrocks
sphaleriteand galena. The goldcontentis generally (Battle Formation, Antler Peak Limestone,and the
low. Ore was mined from the pyrometasomatic Edna Mountain Formation) and overriddenby the
zoneat CopperCanyonand SouthMountainchiefly Golcondathrust plate. The ore bodies at Copper
for its base-metal content.
Canyon are mostly in the Battle Formation just
Replacementbase-metaldepositsin the Eureka belowthe Golcondaplate. The ore bodiesat Copper
and Cortez districtsare in dolomiteof early Paleozoic Basin are in the Battle Formation and the under-
age; the depositsin the Battle Mountain district are lying Harmony Formation.
in conglomerate and limestoneof late Paleozoicage. The CopperCanyonmine was workedin several
All thesedepositsare characterized by pyrite, arse- stages:in the 1860'sand 1870'shigh-gradecopper
nopyrite,pyrrhotite,and varying amountsof chal.- depositsalong faults were mined; in the 1930's
copyrite,sphalerite,and galena. Quartz and calcite through 1957 copper-goldore in undergroundwork-
are the principalgangueminerals. Many of the ore ings was milled by the InternationalCompanyand
bodiescontainsignificantamountsof silver and gold, CopperCanyonCompany;since 1967 copper-gold
and someore bodieswere mined principallyfor their ore from an opencutnorth of the undergroundwork-
precious-metalcontent. ings together with sulfide ore from Copper Basin
Peripheralgolddepositsassociated with base-metal hasbeenmilledby the Duval Corporation in a 5,000-
depositsoccur in the Eureka, Battle Mountain, and ton-per-dayplant at CopperCanyon.
Cortez districts. These depositsare generally in The ore mined in undergroundworkingsat Cop-
 GOLD-BEARING DEPOSITS IN NEVADA AND IDAHO 23

per Canyonwas mainly in calcareousconglomerate tite, pyrite, and pyrrhotiteoccursporadicallyin the

and hornfelsof the Battle Formation; adjacentto the tactite (Nolan, 1962, p. 46). The gold and silver
Copper Canyon stock these rocks were metamor- contentof this material has not been reported.
phosed to calc-hornfels. During later stages of The replacementore bodiesrange in form from
metallization the silicates were altered to chlorite irregular, chimneylikebodiesto podlikeand tabular
and clayminerals,and sulfidesincludingpyrite,pyr- bodies. The oresthat were minedduring the 1860's
rhotite, arsenopyrite, chalcopyrite,and minor sphal- and 1870's were mixtures of cerussite,anglesite,
erite and galenawere introduced. This ore ranged mimetite,plumbojarosite, calamine,smithsonite, mal-
in gradefrom 0.5 to 1 percentcopper,and contained achite, and iron oxides along with relict galena,
0.10 to 0.25 ouncesgold,and about1.5 ouncessilver sphalerite,pyrite, and minor quartz. During oxida-
to the ton. tion, iron, zinc, and sulfur were largely removed,
At Copper Basin, gold ore was found in the leavinglead,gold, and silver relativelyconcentrated.
Carissaand Copper King mines in metamorphosed Ore on the deeperlevelsis largelyunoxidized.
limestonebeds of the Harmony Formation and in The peripheral ore bodies in the Eureka district
overlying Battle 'Formation adjacent to intrusive on ProspectRidge are typifiedby thoseof the Wind-
bodies. This ore containsremnantsof garnet,diop- fall mine (Nolan, 1962, p. 44, 70; Nolan and Hunt,
side, epidote,pyrite, pyrrhotite, and chalcopyritein 1968, p. 989). These ores consistmostly of sanded
a groundmassof chlorite and clay minerals. The dolomiteand quartz veinscontaininga little limonite
copper in the ore' occurred mainly as supergene and the ferric arsenate, scorodite,derived from the
cuprite and chalcocite. About 9,100 tons of this oxidationof pyrite and arsenopyrite. Gold was pre-
ore was mined which averaged2.96 percentcopper sumed to occur as the native metal. Production from
and 0.49 ouncesgold and 2.15 ouncessilver to the 1908 to 1916 totaled 65,132 tons valued at $349,428.
ton. In additionto gold, the ore containedsmall amounts
BetweenCopperCanyonand CopperBasin, gold- of zinc, copper, and antimony; locally it contained
and silver-bearingveins are found in outer zones silver and lead. The metal content of these ores
beyond the base-metalreplacementbodies., These clearly differs from that of the central and inner
veins include the following mineral assemblages: zones,suggestingthat they formed in a cooleren-
pyrite-quartz containinggold and silver (Buena vironment.
Vista), stibnite-quartz(Antimony King) and a
quartz-telluride (Telluride) (Roberts and Arnold, Disseminatedgold deposits
1965). The disseminatedgold depositsare relative new-
At the White and Shiloh mine, silver-goldore was comersto the Nevadaminingscene. They may have
minedfrom peripheralreplacement bodiesand veins. been tested by the bonanza-seeking prospectorsof
The primary ore containedsmall amountsof pyrite, the late 1800's, but their comparativelylow grade
sphalerite,and galena,but wasminedprincipallyfor made them less attractive than the richer veins and
its silvercontent. The silverwasmostlyin galena, replacementdeposits. In addition, the gold was
but Whitehill (1873, p. 48) reportedwire silverand mostlytoo fine grainedto be recoveredin a pan and
,.,

pyrargyrite in the oxidizedore. couldbe detectedonlyby fire assay. Althoughearly

Eureka district.--The ore bodies at Eureka have day placer operationsin the vicinity of Carlin and
been describedby Curtis (1884), Nolan (1962, p. Cortez (Vanderburg, 1936, 1938, 1939) indicated
41-46), and Nolan and Hunt (1968, p. 966-991). the presenceof lode gold, no veinsof significantsize
Most occurin the EldoradoDolomite and Hamburg were foundin the disseminated gold deposits. Gold-
Dolomite of Cambrianage, which are cut by intru- bearingveinsat Tenabo,3 milesnorth of Gold Acres
sive quartz diorite datedat 100 m.y. by K-Ar. The open pit, and in the Lynn district, which were the
pyrometasomaticcentral zone at Eureka has not probablesourceof nearby placers,were workable
yielded significanttonnagesof ore, but surrounding only in the oxidizedzone. As workingsproceeded
replacementbodieshave yieldedore valued at more downward, costs rose, and the sulfide ores were
than $120 million, largely in gold, silver, and lead. generallytoo lean in gold for shipmentto smelters.
The averagegrade of 1,317,388tones mined from The disseminatedgold depositsbecameeconomic
1869 to 1901 was as follows:gold, 1.1 ounces;silver, followingthe increasein price of gold from $20.67
27 ounces;and lead, 17 percent. One depositsin to $35 an ounce in 1934. Gold Acres in 1936 was
the southernpart of the district on ProspectRidge the first depositto be put into production(Vander-
containmore gold than thosein the centralpart. burg, 1939, p. 39). Getchell followed in 1938
The pyrometasomatic (tactite) bodies consist (Joralemon,1951); during World War II produc-
mainly of garnet,diopside,tremolite,epidote,zoisite tion was stoppedfor severalyears, then resumedin
whichare alteredto chloriteand serpentine;magne- 1962through1967. Risingcosts,a fixed goldprice,
24 ROBERTS, RADTKE, AND COATS

and metallurgicalproblemsultimately made oper- are givenby Akright,Radtke,and Grimes(1969);

ationsunprofitableat Gold Acres and Getcheil. In at Gold Acres by Wrucke, Armbrustmacher, and
1961 the Carlin deposit,which was muchhigher in Hessin (1968); at Getchellby Ericksonet al.
grade, was discovered;operationsbegan in 1965 (1964); andat Cortezby Wells,Stoiser, andElliott
(Hardie, 1966). More recently,in 1968,the Cortez (1969).
mine was put into operation. The disseminated gold depositscontain rather
Currentproductionof goldfrom the disseminatedcharacteristicgold:silverratiosin the rangeof 9:1
depositshas raisedNevadato secondrank in gold to 30:1, which servesto set them apart from other
productionin the United States,after SouthDakota. gold-silverand silver-golddepositsin Nevada.
Other showsof disseminated gold mineralizationin Among the replacement depositsat Eureka, the
north-centralNevada are still being explored,and silver-goldratiowasabout27:1 (Nolan, 1962) and
it seemslikely that someof thesewill becomepro- at CopperCanyonit wasabout18:1; the veinsshow
ductivein future years. Only a small part of the more variation, ranging from 1:1 at National to
potentiallyproductivegroundhas been thoroughly 230:1 at Mountain City.
testedto date becausemost of the region is covered Coexistence of .the assemblagestibnite-realgar-
by thrustplates,volcanicrocks,andalluvium(Nolan, cinnabar as at Getchell and Carlin are uncommonin
1950; Roberts, 1966; Stewart and McKee, 1968; the Western States,but havebeenrecognizedlocally
Gott and Zablocki,1968). at Bingham,Utah, wherestibniteandcinnabarwere
The disseminated golddeposits thusfar discovered depositedduringlate-stagemetallization on upper
in north-centralNevada are spatiallyrelatedto the levelsin the U.S. and Lark mines (Rubright and
Roberts Mountains thrust fault. Ore bodies dis- Hart, 1968); in the Mercur area,Utah (Gilluly,
•932; Hewitt, 1968); and at the White Capsmine,
covered thus far formed in the thrust zone or within
a few hundred feet below it in carbonate rocks, Manhattan district, Nevada (Ferguson, 1924;
wherethe thrusthas beendomed. The Hewitt, 1968). Mercuryandantimonysulfides
especially also
thrust zone therefore appearsto exert an overall occurin hot springenvironments (White, 1955;
regionalcontrol. Roberts (1966), however,has SchoenandWhite, 1965; DicksonandTunell, 1968),
emphasized that threeothersignificantrequirements and a closerelationship betweendisseminated gold
must be met in order for an ore bodyto form: (1) depositsand hot springshas been suggested by
a sourcefor gold-bearingsolutions;(2) fractured Joralemon (1951)andbyHausen andKerr (1968);
andpermeable groundto permitaccess of solutions; this impliesthat the depositsformedat shallow
and (3) precipitants, suchas carbonateand(or) depths. Robertsand Coatsdo not supportthis
organiccarbon(Radtkeand Scheiner,1970), must implication,
butinsteadsuggestthatthedisseminated
be availablein a potentialore zone. The role each depositsformedat depthsgreaterthan 2,000 feet.
ore controlplayedapparently variedfrom depositto This figureis basedon restoration
of the rockunits
deposit. that are thoughtto havecoveredthe deposits at the
The geneticrelationship of the disseminatedgold time of formation in early Tertiary. Restorationis
deposits to thegold-bearing
replacement deposits,on complicated by post-ore volcanism and basin-and-
the one hand,and to the vein deposits,on the other, rangefaulting,but2,000feetseems to be a minimum.
is still uncertain. The disseminateddepositsare a For example,Nash and Theodore(1970) estimate
specialkind of replacement depositin that large that as much as 4,000 feet of cover may have been
amountsof carbonateare replacedby silica,but they erodedfrom the CopperCanyonarea followingem-
containmineral assemblages which more closelyre- placement of the intrusivebody (38 m.y.) and prior
veinsthan those to extrusionof the weldedtuff (33.6 m.y.; McKee
semblethoseof the low-temperature
of the replacement deposits.Unoxidizedoresin the andSilberman, 1970a)thatcovered the region. As-
Getcheiland Carlin depositsare characterizedby suming a constant erosionrate of '6 cm/1,000yr.,
pyriteandrealgar;in theCarlindeposit by cinnabar, whichJudson(1968) suggests is theaveragepresent
andin the rate for the United States,then as much as 2,400
stibnite,anda little galenaandsphalerite;
Cortezdeposit,by only vyrite and gold. meters(7,874 feet) couldhavebeenerodedsince
In additionto gold, significantamountsof other earlyOligocene time. Erosionwasalmostsurely
elementsWereintroducedduring ore devositioninto not constant,however,and a more realisticfigure
deposits. The most important would be from 2,000 to 4,000 feet.
all the disseminated
of these elementsare silica, iron, barium, arsenic, The Getchelldepositis spatiallyassociated
with
mercury,antimony,lead,zinc,copper,andtungsten. an intrusivebodyemplacedin the second
intrusive
Datacomparing theminorelement in fresh epoch
contents (105-87m.y.),andtheGoldAcresdeposits
hostrockswith that of oxidizedgoldoresat Carlin withanunexposedintrusive
bodyof thesameepoch
 GOLD-BEARINGDEPOSITSIN NEVADA AND IDAHO 25

(99 m.y.),3 but veinsin theTenaboandCortezareas of thesesignificant

orebodies.Basicinformation on
are associatedwith Oligocene intrusive bodies ofthe Getcheil,Carlin, Cortez, and Gold Acres gold
depositswill be summarizedbriefly below.
the fourth epoch (40-30 m.y.; Wells, ,Stoiser,and
Elliott, 1969; Wrucke, Armbrustmacher,and Hessin, Getchelldeposit.--Joralemon (1951), Hotz and
1968; Wrucke and Armbrustmacher,1969; Silber- Willden (1964), and Ericksonet al. (1964) have
man, Wrucke, and Armbrustmacher,1969). At describedthe Getchellgold mine in the Osgood
Gold Acres pyrite, arsenopyrite,sphalerite,and Mountains,north-central
Nevada,whichhasyielded
galenaare associatedwith altereddikesand tactitein more than 436,000 ouncesof gold valued at more
than$15 million(Bergendahl,
greenstone;sericitein the dikeshasbeendatedat 94 1964). The principal
m.y. (M. L. Silberman,written communication,orebodyextends alongtheGetchell
faultzone. The
gold metallizationin chert golddeposit
1970). The associated at Getchellisassociated
withtheOsgood
and shalenearby couldbe youngerthan this, how- Mountains stock, which has been dated by M. L.
ever, and may representan Oligoceneoverprinton Silbermanby the K-Ar methodas90 m.y. Tungsten
a highertemperaturepyrometasomatic metallization depositsalongthe marginof the stockare believed
of Cretaceousage. The reasonfor this speculation to be genetically
relatedto the stock(Hobbsand
is that the mineral assemblagecommonlyfound in Clabaugh,1946; Hotz and Willden, 1964). The
the disseminated gold depositshere and elsewhereis mineral assemblage
of the gold depositsappearsto
distinctly lower temperaturethan implied by the be distinctlylowertemperaturethanthe assemblage
tactite assemblageat Gold Acres. of the tungstendeposits,and the gold depositsare
Detailed discussionof the geochemistryof these considered by Robertsand Coatsto be considerably
typesof golddepositsandthat of individualdeposits younger,possiblyearlyTertiary. It shouldbe em-
in each group is beyondthe scopeof this paper. phasized that the gold deposititself has not been
Basic data on transport of gold in hydrothermal datedas yet, so thisconclusion is tentative.
solutionsweregivenby HelgesonandGarrels(1968) Joralemon(1951, p. 270-73) has described the
and by Helgeson(1969). The chemicalmodelpro- gold depositsin detail as follows:"The gold ore
posedby Helgesonand Garrelsfor vein depositsin bodiesare sheet-likemassesthat lie along the vari-
whichgold is carriedin acid solutionsas the aurous ous strandsof the Getchellfault zone. They extend
chloridecomplexat temperatures above175ø C also at least7000 feet horizontallyand 800 feet downthe
fits well for the disseminateddepositsat both Carlin dip, andvary in widthfrom a few feet to morethan
and Cortez (Radtke and Scheiner,1970). In the 200, averagingabout40 feet wide.... The veins
caseof disseminated depositsat Carlin, Gold Acres, consistof shearedand mineralizedargillite and lime-
and Getcheil,the typesand amountsof carbonaceous stonecutby quartzandcalciteveinsandcontaining a
materials in the host rocks were a dominant influence soft,plasticgumbothat hasreplacedthe sediments.
on gold deposition. The gumbois the principalgold-bearer.... [It] is
Silica is a ubiquitousconstituentin all types of unusualin that while it appearsto be a fault gouge,
golddeposits.In disseminated deposits,fine-grained it actuallyconsistsof minute subhedralquartz crys-
quartz was precipitatedalong with gold. Small talsembedded in a nearlysubmicroscopic intergrowth
jasperoidbodiescontainingwidely varying amounts of quartzand amorphous carbon .... "
of gold are presentin and near these deposits. Joralemon(1951, p. 273) suggested that the
Quartz makesup the bulk of the ganguemineralsin "gumbo" formedhydrothermally. Robertsconsiders
virtually all vein deposits. Although replacement that the "gumbo"is an alterationproductof car-
depositscommonlycontain only small amounts of bonaceousshale or argillite and chert of the upper
silicawith the ore, numerousbarren and gold-bearing plate of the RobertsMountainsthrust whichwas
quartz veins usuallyare locatedon the peripheryof caughtup in theGetcheil fault,andthatthe Getchell
these districts. The close association_
between gold golddepositis oneof the disseminated
typewhich
and quartz in many deposits,plus the dependence of was localizedin the upperplate rocksas well as in
silica solubilityon temperature,forms the basisfor carbonaterocksof the lower plate. The association
studiesof fluid inclusionsin quartz to gain informa- betweenquartz,organiccarbon,and gold is similar
tion on temperaturesand composition of gold-bearing to that noted at Carlin, Gold Acres, and other de-
solutions. positsin north-centralNevada.
Studiesof the disseminated gold depositsare still Many of the geologicand geochemical features
beingcarriedon by the U.S. GeologicalSurveyand of the Getchelldepositcloselyresemble thoseof the
by the miningcompanies.Many new data are being Carlin depositdescribed by Radtke and Scheiner
assembledwhich will lead to a better understanding (1970). Most of the gold in the unoxidizedcar-
bonaceousrocks at Getchell •ould not be concentrated
a The igneousrock yielding this date came from a drill
hole at about 500 feet below the open pit at Gold Acres. by ordinarymillingprocesses,
and the ore had to be
26 ROBERTS,RADTKE,AND COATS

roasted beforecyanidation; evidentlya significantstonewas apparentlynot involvedin this fold, indi-

amountof the goldwasassociated with organicmate- cating that the two units may be separatedby a re-
rial. The ores generallycontaina low-temperature verse fault. Roberts believes that the Roberts Moun-
mineralassemblage of quartz,gold,realgar,stibnite, tains thrust plate probablycoveredthe area at the
pyrite, and minor amountsof other sulfides. Small time of metallizationand may have exerted an im-
amountsof arsenopyritehave been recognizedlo- portantstructuralcontrolon ore deposition.In addi-
cally. Goldoresat Getchellare characterized by sig- tion, the Cortez district lies within the Battle Moun-
nificantlylarger percentagesof arsenic (mainly as tain-Eureka mineral belt that trends N35ø-45øW in
realgar) than any of the other disseminated deposits. this area; this belt apparentlylies alonga deep-seated
The distributionof gold within the OsgoodMoun- fracture zone which localized plutonic bodies in
tains stockwas studiedby Neuerberg(1966). He Mesozoicand Tertiary time and localizedore de-
found that the gold contentin the stockwas one or positsduring severalmetallogenicepochs(Roberts,
two ordersof magnitudegreaterthan for crustaland 1966; Robertset al., 1967).
graniticrocks,but did not establisha clear-cutspatial Gold ores of the Cortez depositare characterized
relationshipbetweenhigh.-goldzonesin the stockand by quartz, metallic gold, various iron oxides after
gold depositsalong the Getchellfault. pyrite, and small amounts of remnant carbonates
Cortez gold deposit.--The Cortez silver district and clays. Fine-grained gold is dispersedthrough
was discoveredin 1862, shortlyafter the discovery the oxidizedand hydrothermally alteredcarbonate
of the Austin district, and was productiveduring rocks. Coarsergrainedmetallicgold occursin small
severalstagesuntil the 1930's (Vanderburg, 1938; quartz veins and is intergrownwith partly oxidized
Gilluly and Masursky, 1965). The Cortez gold hydrothermalpyrite scatteredthroughthe hostrocks.4
mine,3 milesnorthof the old silvercamp,wasdis- Carlin deposit.--The Carlin gold depositis in the
coveredin 1965 following the discoveryat Carlin. northeastcorner of the Lynn window in the Tusca-
Ericksonand Marranzino (1961) and Ericksonet al. rora Range of northern Eureka County. Excellent
(1961, 1964) had been carrying on a program of descriptionsof the geologicenvironmentof the Carlin
geochemicalstudies in the Cortez district, but no depositare givenby Hardie (1966) and Hausenand
gold determinationswere made on the samples. Kerr (1968). Radtkeand Scheiner(1970) recently
After the discoveryat Carlin, somesamplesfrom the discussedthe geochemistryof gold deposition at
earlier program at Cortez were rerun for gold. Carlin. The Carlin mine was put into operationin
Anomalousamountsof gold were detectedin some. 1965. By January1, 1970,3,694,405tonshad been
of them; this led to resamplingof the areasby the milled and 1,218,497ouncesof gold recovered;ore
Geological Survey and the Cortez joint venture reservesare 6,251,000tonsaveraging0.253 ouncesof
group, which revealedthat ore of commercialgrade gold per ton.
might be present. Subsequentexploration during Gold ore bodies of the Carlin depositare in the
1965-68 resultedin the discoveryof 3.4 million tons upper part of the Roberts MountainsFormation,
of ore containingabout 0.30 ouncesof gold per ton. several hundred feet below the Roberts Mountains
The host rocks of the Cortez gold body are de- thrust. Although gold'isdispersed throughcertain
scribedby Gilluly and Masursky(1965), Elliott and intervals of carbonatehost rocks, suggestinglocal
Wells (1968), andWells, Stoiser,and Elliott (1969) stratigraphiccontrol,crosscuttingrelationsbetween
as altered calcareous siltstone and limestone of the
mineralizedzones and bedding,plus the geometric
Roberts Mountains Formation and limestone of the
relationshipbetweenmineralizedareas and certain
Wenban Limestone. These rocks are cut by intru- sets of high.-angle faults and intersections of fault
siveigneousrocksof Jurassicand early Tertiary age sets, indicate that structural controls are critical.
and overlain by Tertiary volcanicrocks. The ore Unoxidized gold ore bodies of the Carlin deposit
may be geneticallyrelatedto biotite-quartzporphyry are characterizedby gold-organic compoundsplus
dikes and sills of Oligoceneage (34 m.y.) that cut minor amounts of metallic gold, quartz, barite,
the Roberts Mountains and Wenban Formations in
realgar, pyrite, lesseramountsof various other sul-
the orezone,or to youngerigneousrocksin the area fide minerals includingstibnite,cinnabar,sphalerite
(Wells, Stoiser,and Elliott, 1969). and galena,plusremnantillite and carbonates.Near-
The zoneof gold metallizationis not controlledby
4 Radtke considers that most of the carbonaceous mate-
any obviousstructuralfeature,but it trendsnorth-
rials in the host rocks were destroyedeither by a processof
westward,parallelto the strike of the RobertsMoun- "weatheringoxidation" or by thermal metamorphisminduced
tains thrust at the mouth of Mill Canyon nearby. by igneousintrusion prior to gold mineralization. Thus, the
Wells, Stoiser,and Elliott (1969, Fig. 6) showthe influence of organic carbon on the deposition of gold at
Cortez was less than that at Carlin. Details of the genesis
ore body in a tight, overturnedfold in the Roberts of the Cortez ores will be discussedin a paper by Radtke,
iVIountains
,Formation;the overlyingWenban Lime- Scheiner,and Christ (unpublishedmanuscript).
 GOLD-BEARINGDEPOSITS IN NEVADA AND IDAHO 27.

surfaceore bodiesreflectingstrong oxidation and rocks, volcanic rocks, or both (Ferguson, 1929;
secondary alterationcontainmainlyquartz and illite, Nolan, 1933).
minor carbonatesand iron oxides, plus barite and Gold-bearingsulfideveins cut replacementbodies
extremely fine-grained metallic gold (Radtke and at Eureka and Battle Mountain, Nevada (Hill,
Scheiner,1970). 1915), and South Mountain, Idaho (Sorenson,
Gold Acres deposit.--TheGold Acres depositis 1927). Theseveinscontainrelativelyhigh-temper-
at the edge of the Gold Acres window on the east ature sulfideassemblages similar to thoseof the base-
flank of the Northern ShoshoneRange. From 1935 metal replacementdeposits.
to 1957 the mine yieldedabout2 million tons of ore A minor classof quartzveinsfoundin the older
from which about$10 million in gold was recovered. rocks includes those of massive texture, and with
Since 1961 the mine has been inactive. simple mineralogy,principally pyrite, sphalerite,
The ore depositsat Gold Acres are in the brecci- galena,and tetrahedrite. These veins have been
ated zone of the Roberts Mountains thrust and in found associatedwith many plutons (e.g., Gold
rocks above the thrust which have been cofnplexly Creek, Mountain City) but have not been economi-
broken by younger high-anglefaults. The ore oc- cally mineable.
currencethereforediffers significantlyfrom that of In two areas,veins in granitic plutonshave tex-
the Carlin and Cortez deposits,which are largely tures and mineral compositions suggesting that they
within the lower plate. The thrust zone at Gold are, in part, of later and shallowerorigin than the
Acres contains sheared and brecciated chert and pluton. Theseareasare MountainCity and Austin
shale of the upper plate, as well as fragmentsof (ReeseRiver), Nevada. At MountainCity, hydro-
lower plate limestone; in addition, it also contains thermal alteration of Tertiary volcanic rocks near
dikes of altered felsitic intrusive rock and tactite the gold-silverveins gives indirect evidencefor the
zoneswith podsand veinletsof pyrite,arsenopyrite, relative youth of the gold-silver veins. At Austin,
and a little sphaleriteand galena; accordingto Nevada, veins in the mineralized area, which is
Wrucke and Armbrustmacher (1969) the gold con- areally restricted comparedto the exposuresof the
tent of this materialis low. The quartzmonzonite, pluton of quartz monzonite,are made up largely of
as mentionedabove,has beendatedat 99 m.y. and vein quartz that Ross (1953, p. 58) recognizedas
sericitein thesheared zoneat 94 m.y. (M. L. Silber- beingformed in at leastthree stages. Rossregarded
man, written communication, 1970). Gold quartz chalcedonyand flamboyantquartz, which are areally
veins in the northern part of the Tenabo district restricted, as being possibleassociatesof Tertiary
nearbyare associated with Oligoceneintrusivebodies volcanic rocks which rest on the granitic rocks.
(Silbermanet al., 1969). Robertsbelievesthat the Pyrite is in large part contemporaneous with early
gold metallization at Gold Acresmay be relatedto milky quartz and rhodochrosite, but most other sul-
theseyoungerigneous bodies, andwassuperimposedfides,particularlythe silver.-richones,are relatedto
upon an older pyrometasomatic deposit. a later generationof fine-grainedquartz. The sulfide
Gold-bearingdisseminated ore is erraticallydis- minerals identified (Ross, 1953, p. 56) include
tributedwithinthe thrustzoneand alongfracture galena, sphalerite,chalcopyrite,arsenopyrite,pyr-
zonesand in felsite (Wrucke and Armbrustmacher, argyrite,stephanite, polybasite,enargite,and xantho-
1969). No simplepattern of the distributionof conite.
goldhasbeenworkedout; fragmentsof limestoneof The Austin and Mountain City vein systemsre-
the Roberts Mountains Formation in the thrust zone
semblein sulfidemineralogythe veinsof Silver City,
are of ore grade only where cut by veinsof iron Idaho. At Silver City, however,the veinsmay be
oxide. It thereforeseemsthat controlby fractures traced from the underlyinggranite pluton up into
dominatesover lithologiccontrol. An overall litho- the volcanic rocks.
logic control is neverthelesspossible,becausecom- Stibnite-quartzveins are found in an outer zone
minuted carbonate rock and carbonaceous material in surroundingreplacementdepositsand high-temper-
the thrustzoneare in 'a positionwherethey could atureveinsat Battle Mountain (Robertsand Arnold,
haveinfluenced the precipitation
of goldfrom hydro- 1965). They are alsofoundin the Mount Lewis and
thermal solutions. Hilltop districts(Lawrence,1962, 1963), wherethey
Veins
are associatedwith silver-gold veins that contain
argentite and silver sulfosaltsand are related to in-
Gold-bearingveins in north-central Nevada and trusive rocks of Oligocene age.
southwesternIdaho belongto two major groups, Other classesof veinsrelatedto Tertiary volcanic
thosethat cut only pre-Tertiary rocksand are related rocksare the low-temperatureveinscontainingpyrite,
to the replacementdeposits,and thosethat are re- gold (electrum), argentite,naumannite,pyrargyrite,
latedto volcanicrocksandthatmaycutpre-Tertiary proustite, and other sulfosaltsin a quartz-adularia
28 ROBERTS,
RADTKE,AND COATS
gangue,and the quartz-stibnite-gold
veins (National, naumannite, and silver sulfantimonides. The aver-
Nevada) (Lindgren, 1900; Hewett, 1964; Hewett age Au:Ag ratio was about 1:190 in the Trade
and Radtke, 1967). Dollar-Black Jack vein; the ore averaged0.246
In the followingdiscussion, veinstypicalof the ouncesgold and 47.2 ouncessilverper ton.
principalgroupswill be described;
the highertem- The veins at De Lamar, 4 miles west of Silver
perature veins will be describedfirst. City, are composed mostlyof lameliarquartzwhich
CopperCanyon.--TheSuperiorveinin the Copper cuts late Tertiary rhyolite (Lindgren, 1900; Piper
Canyonundergroundmine yieldedhigh-gradesec- and Laney, 1926, p. 106). The silver ore minerals
ondary copperore on the upper levels and sulfide are principallyargentite,naumannite,
polybasite,
and
ore belowthe 300 level (Roberts,1951; Robertsand related sulfides. Gold occursmainly as electrum.
Arnold, 1965). The ore mineralsincludepyrite, The ore averaged0.15-0.50 ouncesgold and 20-50
pyrrhotite, arsenopyrite,and sphaleritein quartz ouncessilver per ton.
gangue; this assemblageis similar to that in the re- National district.--Gold-silver quartz-adularia
placementbodies. Individual particlesof metallic veinsin the Nationaldistrictyieldedspectacular ores
gold in thesesulfideoresare not abundantevenunder in the period from 1908 to 1920 (Lindgren, 1915;
highmagnifications, and mostof it is probablyfinely Willden, 1964). Ore as rich as $135,000a ton was
disseminated in the sulfides,
especially pyrrhotiteand recorded;muchore wasvaluedat $20 a pound. The
pyrite. In a drill coreat CopperCanyonfree gold veins,which cut volcanicrocksof probableMiocene
was found in a pyrite-amethystine quartz veinlet. age, are mostlybandedand showexcellentradial or
This veinletmay well haveformedlate in the metal- comb structure. The principal sulfide was stibnite,
logeniccycleat a distinctlylower temperaturethan alongwith pyrite, and a little chalcopyrite,arsenopy-
the main ore phase. rite, sphalerite,andl galena; most of the gold and
Peripheralgold-silver deposits
in andnearCopper silver was in electrum, but, in addition, silver was
Canyonare characterizedby pyrite, quartz, and found as cerargyriteand pymrgyrite.
argentiferous galena(Robertsand Arnold,1965,p. farbidge.--TheJarbidgeminingdistrictwas dis-
B32), withminoramounts of sphalerite, arsenopyrite, coveredin 1909, and between 1910 and 1949 pro-
andtellurides. Thesedepositsare mostlyveinscon- ducedabout $10 million in gold and silver. Sub-
taining lenticular shoots of gold-silverore, but stantialproductionendedabout1937,and minorpro-
locallythe ore replacedfavorablebedsadjacentto duction continued through 1948 (Granger et al.,
the veins. The gold contentranged from 0.08 to 1957, p. 84). The silver-goldratio averagedabout
2.80 ouncesper ton and silver from 4 to 55 ounces 3tol.
per ton. All the productionof preciousmetals from the
$tibnite-quartz veinscontaining a little pyrite oc- Jarbidge mining district has come from quartz-
cur in the outerzoneof metallization betweenCop- adularia-bearingveins and lodes in the Tertiary
per Canyonand CopperBasin at the Apex and JarbidgeRhyolite, a thick sequenceof phenocryst-
AntimonyKing mines. These veins do not contain rich rhyolite flows, with minor tuff and weldedtuff.
muchgold,but are listedhereto showtheir placein In the mineralizedarea, narrow horsts of Prospect
the zonal scheme. A pocketof rich silver ore was Mountain(?) Quartzite of Cambrian age appear
minedduringthe early daysat the AntimonyKing, within the rhyolite terrane. The rocks underlying
but theseveinsare normallylow in preciousmetals. the quartzitehavenot beendisclosed by mining,but
Flint district, Idaho.--Gold-bearingveins in the 3 or 4 milesto the southwest, quartziterestsin thrust
Flint district (Fig. 6) are mostlycomposedof mas- contact on Paleozoic limestone (Coats, 1964, p.
sive white quartz, tetrahedrite,and other sulfosalts M21).
with arsenopyrite,pyrite, and chalcopyrite;the ore The age of the mineralizationhas not been deter-
averaged20-30 ouncesgold per ton. Other veins mined directly. Two K-Ar dates on the Jarbidge
in the district are mostly quartz and stibnitewith Rhyolitefrom nearbyareasare 16.8 (Coats, 1964,
tracesof silver; still othersare pyritic quartz veins p. Mll) and 15.4 m.y. (Everndenet al., 1964, p.
and native gold (Piper and Laney, 1926). 194). A samplefrom near the uppermostpart of
The Trade Dollar vein system,a half-mile south- the unconformably overlyingignimbrite(the Cougar
west of Silver City on Florida Mountain, cuts Point WeldedTuff) in the Owyheequadrangleabout
granodioriteon the lower levels,Tertiary basalt on 30 milesto the west, was datedby John Obradovich
intermediate levels, and overlying rhyolite on the as 12.2 m.y. (Coatsand Stephens,1968). The Cou-
upper levels (Lindgren, 1900; Piper and Laney, gar Point postdatesthe mineralization. As the min-
1926, p. 118). The veins are massiveand consist eralization is believed to be closely related to the
of comb quartz, adularia, and a little calcite. The
eruption of the late Miocene(?) JarbidgeRhyolite,
ore mineralsincludepyrite, nativegold, argentite, the mineralizationis alsoprobablylate Miocene.
 GOLD-BEARING DEPOSITS IN NEF'ADA AND IDAHO 29

The ore depositsin the rhyolitefollowsteeplydip- 1966. Altered and mineralized rocks are overlain
ping faults,trendinggenerallynorth to northwest;a unconformablyby rhyolite ignimbriteand andesite,
few have northeast trends. The gangue minerals, bothof whichpostdate
mineralization.Coats(1967,
in additionto quartz and adularia,includeearly cal.- p. 1) foundevidencefor the existenceof unexploited
cite (largelyreplaced),barite,fluorite,kaolinite,and parts of veinsbeneaththe later volcanicrocks. The
halloysite;ore minerals includepyrite, gold, argen- age of the mineralizationis not preciselyknown, but
tite, and naumannite(Schrader,1923, p. 50-52; the ignimbrite yielded sanidinethat was dated by
Davidson,1960). J. C. Von Essen (written communication, 1969) at
Mountain City ( Cope).MThe originaldiscoveries 15 m.y.
of silver-goldore in the MountainCity districthave The ore bodiesare sheetedzonesin andesite;they
beenshadedinto obscurityby the later productionof trendeastwardand dip steeplynorthward. Primary
copperore from the Mountain City Copper Com- mineralsare quartz, barite, pyrite, argentite,tetra-
pany's Rio Tinto mine. The copper depositsare hedrite, and possiblypyrargyrite. Comb structure
geneticallyunrelated to the silver-gold deposits is presentin the quartz veins. In places,silicified
(Coats and Shephens,1968). The proportionof countryrock was worked. The maximumgradeof
silverto gold in the bullionproducedfrom the veins mill-run ore reportedto Emmons(1910, p. 64) was
duringthe period1869-1932wasabout230 to 1. 400 ouncessilverper ton. Reworkingof the tailings
The gold and silver depositsof the Mountain City yielded0.13 ouncesof gold and 9 ouncesof silver
mining district are quartz veins,mostlyin a pluton per ton.
that rangesfrom granodioriteto quartzmonzonitein Tuscarora.--The Tuscorora district was discov-
composition.Near the southernmargin of the plu- ered in 1867. Placer gold was mined for a number
ton, veins cut Paleozoicsedimentaryrocks. In the of years,mostlyby Chinese;the total productionwas
centralpart of the pluton,near the town of Mountain about $700,000 (Nolan, 1936, p. 14) The lode
City, veins occur near, but not in, a narrow east- depositswere discoveredin 1871, and the recorded
trendinggrabenof rhyolitic rocks,which are hydro- productionthrough1941 (Granger et al., 1957, p.
thermally altered near the veins. 153) was 128,165 ouncesof gold and 7,138,684
After a long period in which these mines were ouncesof silver, for a silver-gold ratio of about 44
dormant,one, the Protection,was reopenedin 1946 to 1. Productionsince 1941 has been negligible.
and continuedto produceuntil 1948. Total ore pro- The bedrock in the mineralized area consists
duced during this 3-year period is estimatedat 2 chieflyof two types: (1) a beddedseriesof rhyolitic
thousandtons, averagingabout 40 ouncesof silver tuff and interbeddedandesiticflows, and (2) intru-
and three-quartersof an ounceof gold per ton. It siveandesitebodiesof irregular shape(Nolan, 1936,
seemslikely that two different epigenetictypes of p. 14). The beddedseries dips east or southeast
precious-metal depositsare presenthere at Mountain quite regularlybut is cut by many faults,mostlyof
City, oneconsisting of Cretaceouspyriticgold-quartz north to northeasttrend with indeterminatedip and
veins, which have not been mined but have con- displacement.Recentmappinghas shownthat the
tributedgoldto the placers,andthe otherof Tertiary Tuscarora district is boundedon the north by a
silver-goldveins, which have furnishedmost of the narrow horst of Valmy quartziteand chert; no ore
production. Sanidinefrom pumice,in an unaltered bodies seem to have been mined in it.
part of the rhyolitetuffs mentionedabove,was dated The age of the mineralizationat Tuscarorawas
by J. C. Von Essen(written communication, 1969) determinedby a K-Ar date on adularia from the
at 30 m.y. The mineralizationthat is spatiallyas- ModocVein (E. H. McKee, written communication,
sociatedwith the alterationof these rocks may be 1970) as 38 m.y.
any age younger than 30 m.y. Emmons (1910, p. 60) and Nolan (1936, p. 28)
Cornucopia.--Mining operationsat Cornucopiaex- recognizedtwo kinds of ore depositsat Tuscarora,
tendedfrom 1873 to 1882. Old tailingswere re- silver lodes and gold-bearingfracture zones. The
treatedin 1937--40. Total production(Grangeret depositsin the andesiteare relativelynarrow veins
al., 1957,p. 41) was $1,273,000. Silver-goldratio or lodes,thosein the beddedpyroclastics are wide
in the later productionwas68 to 1. Informationon and poorly definedbrecciatedzones. In the gold
the weight ratiosof silver-goldfor the earlier pro- deposits,the weightratio of silverto gold is 4 or 5
duction is unknown. to 1; in the silver lodesit is nearly 150 to 1. Nolan
The mineral depositsare in propylitizedandesite, consideredand rejectedas explanationsfor the dif.-
argillizednearthe veins(Lovering,1949). Primary ferencebothzoningand differentepochsof minerali-
structures in the wallrocks are unclear. Emmons zation; he believed that the lodes and veins in ande-
(1910, p. 64) reportedquartz-porphyryexposedin site were richer in silver because of more effective
the mine workings,but outcropswere not seen in supergene
enrichment,
whilethe silver-bearing
super-
30 ROBERTS,RADTKE,AND COATS

gene solutionswere removed or dissipatedin the (Rott, 1931, p. 16). Some calciteis early, and has
widefracturezonesin thebeddedpyroclastics. How- beenpartly replacedand removedby later vein-form-
ever, the materialminedin the mostsuccessful gold ing solutions. The veins and lodesare relatively
producer,the Dexter, was notablypyritic, where high grade, but narrow, extensive brecciatedzones
fresh (Emmons,1910, p. 61), and it is difficultto are low in grade. The metallicmineralsare pyrite,
understandwhy available silver should not have stromeyerite, and native gold, with tetrahedrite,
beenprecipitatedby this pyrite. Differencesin the proustite, chalcopyrite,and sphalerite much less
chemistryof the wallrockmay be responsible for common.

differencesin the silver-goldratio in the ores. Buckhorn.--The Buckhorn mine northeast of Cor-
The principalganguemineralsare quartz,adularia, tez is in siliceousshaleof Tertiary age which is over-
and calcite;the principalore mineralswere, accord- lain by andesiticflows (Roberts et al., 1964). The
ing to accountssummarizedby Nolan, argentite, workingsexplorean area 650 feet long, 245 feet
stephanite,proustire,pyrargyrite, pyrite, enargite, wide, and 120 feet deep which has yielded 39,024
arsenopyrite,bornite, chalcopyrite,sphalerite,and ouncesgold, 311,278 ouncessilver, and 319 pounds
galena. Secondaryhorn silverand nativesilverwere coppervaluedat $1,109,838. The ore bodyconsisted
common. The textures are simple, at least in the of pyritic siliceousbrecciazones,oxidizedto a depth
very low grade materialthat remains. Crude crusti- of 100 feet, that strike N5øW and dip 75øE; the
ficationand vuggy texturesmay be recognized. andesiteand shale adjacent to the ore were exten-
The grade of ore as mined ranged from $50 to sively argillized. Correlative andesitenear Tenabo
$200 per ton in the early daysof production,but fell hasbeendeterminedby K-Ar methodsto be 16 m.y.
to aslittle as$6 per ton in 1890for onemine (Nolan, old (McKee and Silberman,1970a).
1936, p. 31).
Gold Circle.--TheGold Circle (Midas) district Summary and Conclusions
was discoveredin 1907 (Emmon•s, 1910, p. 48). Gold-bearingdepositsin north-centralNevada be-
Mining essentiallyterminatedin 1942. Production long to three principalgroups:replacementand dis-
statistics
are summarized
by Grangeret al. (1957, p. seminateddepositsand veins which were formed
65). From 1908 to 1949 the Gold Circle district duringfive principalmetallogenicepochs,in the early
produced401,752 tons of ore containing126,726 Mesozoic, late Mesozoic, early Tertiary, and late
ouncesof gold and 1,630,268 ouncesof silver; the Tertiary. The replacementdeposits were mostly
averagegrade of the ore producedwas thus 0.314 formedduring the first four epochs;the disseminated
ouncesgold and 4.60 ouncesof silver per ton; the depositsare thoughtto have formed mostly during
silver-goldweight ratio was 12 to 88. During the the fourth epoch,althoughage data are availablefor
last years of production,the grade fell to about $5 only one deposit,Cortez; and the veins formed dur-
per ton. ing all five epochs.
The rocks in the known mineralized area are en- The replacementdepositsare zonally arranged
tirely Tertiary volcanicrocks. Emmons(1910, p. around intrusive centers: from the center outward
47) mentionedan outcropof shalylimestoneabout are central pyrometasomaticdeposits, outer base
5 milesfrom Midas; this has not beenverified,but metal and associatedgold and silver deposits,and
it suggests that the Midas districtmay be underlain peripheralgold deposits. The disseminated
gold de-
in part by rocksof the easterncarbonateassemblage.positsoccurin a uniqueenvironmentassociated with
The Tertiary volcanicrocks includepremineraliza- the RobertsMountainsthrust. They are character-
tion rhyolite and andesiteand postmineralizationized by low-temperaturemineral assemblagesand
rhyolite ignimbritesof the Cougar Point Welded may be geneticallyrelated to the replacementde-
Tuff, known to be as young as 12.2 m.y. in this posits,but if so,theyformedin coolerzones,possibly
region(CoatsandStephens,
1968,p. 1083). nearer the surface or on the flanks.
The ore depositsare veins, sheeted zones, and Exploratory programs in north.-centralNevada
breccia zones that follow faults in the volcanic rocks.
shouldbe directed towards testing zonesbelow the
These structures strike generally N30 ø to 60øW; disseminateddeposits for potential base-metal re-
the dip ranges from 65øNE to vertical, locally placementdepositsin favorable stratigraphicunits
steeplywest. and structural zones near intrusive centers. The
The age of mineralizationhas recentlybeendeter- major mineral belts are the most favorablezonesin
mined at 15.0 by K-Ar dating of adularia collected which to conduct exploratory programs for base-
by Dan Shawe (R. H. Marvin, written communi- metal depositsas well as disseminated deposits.
cation, 1968). The gold- and silver-bearingveins likewise may
The vein material is principallyquartz and altered be related to replacementor disseminated deposits,
wallrock, with minor amounts of calcite and adularia so favorable stratigraphicand structural zones be-
 GOLD-BEARING DEPOSITS IN NEVADA AND IDAHO 31

neath productivevein systemsshouldalso be care- ., and Stephens,E. C., 1968, Mountain City Coppermine,
Elko County, Nevada, in Ridge, J. D., ed., Ore Deposits
fully evaluated by geochemicaland geophysical of the United States, 1933-1967 (Graton-Sales volume),
methods. v. 2: New York, Am. Inst. Mining Metall. Petroleum
Engineers, p. 1074-1101.
Acknowledgments Curtis, J. S., 1884, Silver-lead depositsof Eureka, Nevada:
U.S. Geol. Survey Mon. 7, 200 p.
The writers are indebtedto many operatorsand Damon, P. E., and Mauger, R. L., 1966,Epeirogeny-orogeny
mining companyofficialsin north-central Nevada, viewed from the Basin and Range province: Soc. Mining
Engineers Trans., v. 235, p. 99-112.
especiallyR. B. FuRon,Frank McQuiston,Jr., R. L. Davidson,D. F., 1960,Seleniumin someepithermaldeposits
Akright,5 Mel Essington, Byron Hardie, Robert of antimony, mercury, and silver and gold: U.S. Geol.
Hilander,J. McBeth,and Perry West of Newmont Survey Bull. 1112-A, r•. 1-16.
Mining Corporationand Carlin Gold Mining Com- Dickson, F. W'., and Tunell, George, 1968, Mercury and
antimonydepositsassociatedwith active hot springsin the
pany; and to Dave Blake, Fred Howell, J. B. Mc- WesternUnited States,in Ridge,J. D., ed., Ore Deposits
Carthy,and A. E. Schiellof the Duval Corporation; of the United States, 1933-1967(Graton-Salesvolume),
v. 2: New York, Am. Inst. Mining Metall. Petroleum
and to Don Duncanand C. J. Purdy of the Cortez Engineers, p. 1673-1701.
Gold Company. In addition,geologists of the U.S. Elliott, J. E., and Wells, J. D., 1968,Anomalousconcentra-
GeologicalSurvey, includingT. J. Armbrustmacher, tionsof gold, silver, and other metalsin the Mill Canyon
area, Cortez quadrangle,Eureka and Lander Counties,
J. E. Elliott, J. T. Nash, T. G. Theodore, J. D. Nevada: U.S. Geol. Survey Circ. 606, 8 p.
Wells, and C. T. Wrucke, have furnished valuable Emmons,W. H., 1910,A reconnaissance
of somemining
unpublishedinformation. John Obradovichand J. campsin Elko, Lander, and Eureka Counties,Nevada:
U.S. Geol. Survey Bull. 408, 130 p.
C. Von EssencontributedmanyK-Ar'determinations Erickson,R. L., and Marranzino,A. P., 1961,Hydrogeo-
of intrusive and volcanic rocks. Published informa- chemicalanomalies,Fourmile Canyon, Eureka County,
tion is acknowledged
by citation. D.E. White, C. T. Nevada,in GeologicalSurvey research1961: U.S. Geol.
Survey Prof. Paper 424-B, p. B291-B292.
Wrucke, T. G. Theodore, and H. R. Cornwall re- , .., Oda, Uteana, and Janes,W. W., 1964, Geo-
viewed the manuscript;the authors acknowledge chemicalexplorationnear the Getchellmine, Humboldt
helpful suggestions County,Nevada:U.S. Geol.SurveyBull. 1198-A,p. A1-
and commentsmade by these A26.
men.
, Masursky,Harold, Marranzino,A. P., and Oda,
Uteana, 1961,Geochemical anomaliesin the upperplate
U.S. GEOLOGICAL SURVEY, of the Robertsthrustnear Cortez,Nevada,in Geological
MENLO PARK, CALIFORNIA, Surveyresearch1961: U.S. Geol. SurveyProf. Paper
August 21, 1970 424-D, p. D316-D320.
, , , --, and Janes,W. W'., 1964,Geochemical
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32 ROBERTS,RADTKE, AND COATS

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