Potassium-Argon ages of igneous rocks and alteration minerals associatedwith mineral deposits, western and southern Nevada and eastern CaliforniaL.J. Garside, H.F. Bonham Jr., J.V. Tingley, and E.H. McKeeIsochron/West, Bulletin of Isotopic Geochronology, v. 59, pp. 17-23

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17

POTASSIUM-ARGON AGES OF IGNEOUS ROCKS AND ALTERATION MINERALSASSOCIATED WITH MINERAL DEPOSITS, WESTERN AND SOUTHERN NEVADAAND EASTERN CALIFORNIA'

LARRY J. GARSIDEHAROLD F. BONHAM, JRJOSEPH V. TINGLEY

EDWIN H. McKEE

■) Nevada Bureau of Mines and Geology, Reno. NV89557

U.S. Geological Survey, Menio Park, CA 94025

Seventeen new potassium-argon ages on e i^aryand Mesozoic Igneous rocks andassociated with mineral deposits are repo e(fig. 1). Seven of the samples are frorn unal ereand include analyses of blotite, . roninnalrock material. These ages help establish 9framework for some mineral deposits o*" ® „fiu\ar\arock of a mineral deposit. Ten samples (ifour alunite, and one sericite) aremining districts and provide information gjtes.of alteration and possible mineralization ^The samples wele dated as part ot minoml re^umand geologic quadrangle mapping studies byNevada Bureau of Mines and Geology.

ANALYTICAL METHODS

The K-Ar sample preparation wasNevada Bureau of Mines and analyses wereNevada, Reno. Argon ygw laboratories,done in the U.S. Geologica standardMenIo Park, California. Analyse oalrympleisotope dilution P''0'^®'^"'^®t^®_:neral concentrationsand Lanphere (1969). The gpetic, electrostatij^were made using heavy-liq > y,,hole-rock samPand hand-picking procedure . jgachedwas ground to 80-100 were performedand HF solution. j^gion flameby lithium metaborate internal ®tecbnlquss. 'XgrSryses wars(Ingamells, 1970). 9 .^.^pe mass eP ggd

rperlence tss drs'^^minatlon ot the& ParK IdbamlSSy determined on the basis ofspectremeterK air. The constants used inmultiple an^ye^l^P,ion are those from the sub-the age eex

lAge determinations done under the U.S.Geological Survey-Nevada Bureau of Mines and Geology cooperative program.

commission on Geochronology (Steiger and Jaeger,1977).

1. RR-32 K-ArKate Peak Formation;andesite flow (39°33'35"N, 119°49'17'W; NEV4,NEV4 SWV4 NWV4 S35,T20N,R19E: N of Reno,Reno 7.5- quad.. Washoe County NV).data- KpO = 8.53%; ''"Ar = 1.7609 x 10mol/gm- 40Ar*/i:''0Ar = 0.643. Collected by. L. J.SS. Analyzed by. E. H. Vlfee.^^^Eroch riated flow overlies advanced argillicaTerailoTrn^re underlying AJtaPoj^^^^^^^^providing an "PP®^ g jg the midpoint ofthermal ®'^®''®^'®"' i^ate Peak ages of 12-16 Mathe known range of Kate Peak 9 ^g^e

must thus be at least 14 Jm. (tg.soM)Ma age on ^^VeSe P^ km to thetaken on t^e flank silberman, unpub.

data. -ifg Ma from the same areadetermination otlt^Sher ,'®2mat later period ot hydrothermal alterationf°T?emene oicidatlon). Similar alunite agesabout 11 Ma) are recorded from altered Tertiaryandesite in the northern Carson Range about 15km to the southwest (Russell and others. 1989).

(biotite) 14.3 ± 0.5 Ma

2. V-34 K-ArAlunite (39°33'52"N, 119°44'21"W; SEVa SEVaS28, T20N,R20E; NE of Reno in the Wedekindmining district. Vista 7.5' quad., Washoe County,NV). Analytical data-. K2O = 5.09%; '^^Ar* =1.1973 X 10"^° mol/gm; ̂°Ar*/I'*°Ar = 0.549.Collected by. H. F. Bonham, Jr. Analyzed byE. H. McKee. Comment Alunitic hydrothermalalteration of Alta Formation associated withmineralization at the Wedekind mining district.

[ISOCHRON/WEST, no. 59, May 1993]

18

OREGON IDAHO

DOUGLAS

HUMBOLDT

6

WASHOE

PERSHING

EUREKA .LANDER

1 Reno 12CHURCHILL

• 14 / WHITE PINE

LYON -

r

\MINERAL • 13

/\

ESMERALDA

LINCOLN

I

CLARK

Las VegasX

ARIZONA

NI

9 50 milesI Hi i' I "i—rH—I0 80 kilometers

descriptions in^he'texl.^"'"'''® collection sites for radiometric age-determinations in this paper. The numbers refer to

tISOCHRON/WEST, no. 59, May 19931

19

Extensive areas of quartz-aiunite alteration in theReno-Virginia City area have an age range of Ills Ma and are related to multiple hydrothermalevents. This Wedekind district alunite date iscomparable to an older group of ages from theVirginia City and Geiger Grade areas 25-40 krn tothe south (see Vikre and others, 1988). Alterationand mineralization of similar character to that atWedekind extends westward from the Wedekinddistrict for 20-25 km to the Peavine miningdistrict. If most or all of this hydrothermalalteration is approximately of thebest estimate of that age is 15-16 Ma, based onpresently available data (see the discussisample RR-32 above). ^ ̂ ̂ ̂

Homblende-biotite andesite (3|°35'29JN.119°59'5VW' NWV4 NW /4 NE /S19,T20N,R18E: NW fl^kVerdi 7.5' quad., Washoe County. N )•data: K^O = 8.10%: -Ar = j.mol/gm; 40Ar*/z:'»°Ar = 0.57 . commentGarside. Analyzed grfjcially resemblesThe andef Formation (and wasflows of the Kate ^ quad by SoeH^^mapped as such in the Reno N q

and Nielsen, 1980)^11 lies ongranodiorite (Bell and middle Miocenepresent at the "ase exposedsequence of andesite ̂ along the eastmainly to the west in discussion forflank of the Sierra '^® . ggquence is probablysample GD-1, below), Formation aridage equivalent to the of the Virginiaat least part of tt"® g sample V-205 is frorncity quadrangle. the eerapled unhthe basal part of th correlative of th® Kais not likely to u.3 Ma at thePeak, which ^/sampi® Manearest dated locality (sa ± o.5 Ma

K-Ar

A \/^lfiQ rk/Ki 119°56'53.5 W,Olivine basalt (39 S15T19N,R18E; E ofSWV4 NWV4 SE a Washoe County, NV).V^dh Verdi "Ar- XAnalyticel <«»i,^5^40Ar - 0.582^10-11 mol/gm: ̂ Ar/^ g h. McKee.L. J. G®''®'f'® dated basalt flow appears to beComment '"® , ̂̂g sandstone of Hunter Creek/"SllTn^Garside, 1987). Its stratlgraphicSonship to a Hemphillian flora (Axelrod, 1958)located just to the east (and interbedded with a

[ISOCHRON/WEST, no. 59, May 1993]

5.9-Ma andesite tuff,* Evernden and James, 1964)is uncertain; the basalt may be separated fromthe fossiliferous beds by an unrecognized fault.Possibly the basalt flow unit is the same as onereported to be 11.3 Ma (using new constants) byEvernden and James (1964); if so, the reason forthe age discrepancy is unknown.

(whole rock) 8.6 ± 0.3 Ma

5 AJ-1 K-ArAdularia (41°18'10"N, 118''00'00"W; NWi/4S36,T40N,R35E; main pit of the Jumbo (AustinJumbo) Mine, Awakening (Slumbering Hills)mining district. Awakening Peak and JacksonWell 7 5' quads., Humboldt County, NV).Analytical data: KgO = 14.45%; ̂ Ar* = 3.6157 x10-1° mol/gm; At* 11/^°At = 0.866. Collected by.R. j. Roberts. Analyzed by: E. H. McKee.Comment Quartz-adularia veins and stockworkscut sandstone and argillite of the Mesozoic AuldLang Syne Group (Calkins, 1938) at the mine,which is the major producer in the district. Iron-stained adularia rhombohedria, 1-3 mm indiameter are present in veinlets having open-soace textures. See also the comment on sampleQippoer (below) and Conrad and others (1993).°'® ^ (adularia) 17.3 ±0.5 Ma

K-Ar

6- fSe r41 °20'07"N, 118°03'05"W; C WU NV4cSi T40N,R35E; Sleeper Mine, Awakening/c1. mbering Hills) mining district, Jackson Well1 i"Tiad Humboldt County, NV). AnalyticalJ *<!■ K 6 = 8.62%: ""Ar* = 6.7156 x lO HWr'/S'^Ar = 0.246. Collected by D. E.Banta Analyzed by. E. H. McKee. Comment,wish and others (1991) and Conrad and others(1993) report th®t 5.4 Ma acid leaching (withAssociated opal-kaolimte-alunite deposition)occuTS along post-ore fau ts, and is thus laterthan the main-stage mineralization. They sugqesthat it may be shallow solfataric alterSassociated with a geothermal system tho

isiderably later than the main-staqe ooiA .leralization. The hypogene gold-silvp

eralization and a mineralized rhyoUte

associaitju w.... - system that icconsiderably later than the main-stage gqiq. ®mineralization. The hypogene gold-silvaeralization and a mineralized rhyoUte oornhthe mine are reported to be approximatJi . ^(Nash and Bartlett, 1991; Conrad and1993). This age is relatively close to the 17 'mineralization at the Jumbo Mine 5 wcniitheast Isee samole A. 1.1 ok to the

'5.4 + 0.2 Ma(alunite)!7. BlueMtn

Alunite (40°59'17"N, 118°07'45"\/\;.SEV4, S14.T36N,R34E ^®st tlanlf^*ank Of Blue

20

Mountain, Gaskell 7.5' quad., Humboldt County,NV). Analytical data: K2O = 1.68%; '"'Ar* =9.3342 X 10-12 mol/gm; '•"ArVS'iOAr = 0.151.Collected by. H. F. Bonham, Jr. Analyzed byE. H. McKee. Comment: The Blue Mountainprospect, located 35 km south of the SleeperMine, has gold and silver mineralization inTriassic metasedimentary rocks. Alunite at theproperty is probably associated with solfataricacid leaching, and thus apparently dates only thelatest hydrothermal alteration. The precious-metal mineralization is probably older, and maybe of more than one age. The alunite age is closeto an alunite age at the Sleeper Mine (sampleSleeper, above), and may record the same latergeothermal system.

(alunite) 3.9 ± 0.2 Ma

8 STONEH K-ArStonehouse porphyry body (40°49'53"N,117°12'07"W; SWV4 SWV4, S12,T34N,R42E; SEflank of Lone Tree Hill, Valmy 7.5' quad.,Humboldt County, NV). Analytical data: (biotite)K O = 8.73%; '*°Ar = 5.00678 x 10-1° mol/gm;40Ar'/T40Ar = 0.77; (hornblende) KgO = 1.082%;40Ar' = 5 70628 x lO'" mol/gm; lOArVs^OAr =n 42 Collected by. L. B. Gustafson. Analyzed by.F H McKee. Comment The biotite-hornblendemineral pair was separated from an unaltered^ranodiorite porphyry dike that closely resembles!her hvdrothermally altered dikes on Lone Treeuiii We interpret the dike to represent a late

of the mineralizing porphyry system. Thus,nne of the dike sets an upper limit onmtion and represents in a general way theof intrusion and mineralization. The

Sricitized dikes are believed associated with Pb-In and Zn-Cu skarn mineralization observed atthe Lone Tree Mine just to the west of Lone TreeHill (Bloomstein and others, 1993). The skarnmineralization is similar to other 36-Ma skarns inthe Battle Mountain area (Bloomstein and others,1993; Theodore, 1991). The mesothermal andepithermal gold mineralization at the Lone TreeMine is post-skarn, but otherwise undated. Theage determinations for the mineral pair do notoverlap within their error limits, and biotite(normally considered less retentive of radiogenicargon) has the older age. The reason for thisdiscrepancy is unknown.

/u ?.'°*'*®)39-4±1.2Ma(hornblende) 36.3 ± I.2 Ma

9. GD-t K-ArAlunite (39°38'43.6"N, 120°17'34"W; SWV4IMWV4, S27,T21N,R15E; approximately 300 m N

of the Antelope Mine in Antelope Valley, 3 kmSW of Loyalton, Sierra County, CA). Analyticaldata: KgO = 4.52%; ̂OAr* = 4.94492 x lO""mol/gm; i°Ar''/X''OAr = 0.191. Collected by. L. J.Garside, H. F. Bonham, Jr., and M. W. Brady.Analyzed by. E. H. McKee. Comment. Date oncoarse, hypogene alunite from quartz-alunitealteration of Tertiary andesite and dacite flows. Asample of alunite collected from near theAntelope Mine also yielded an age of 7.6 Ma (P.G. Vikre and E. H. McKee, unpub. data, 1993).Alteration is associated with enargite-gold typemineralization at the Golden Dome property.Similar mineralization is noted to the southeast inNevada in the Peavine, Wedekind, Castle Peak,Comstock Lode, and Ramsey districts. Andesiticrocks similar to the wall rock at Golden Dome aredated at 10.4 and 13.3 Ma at two localities 20and 10 km to the southeast and northeast,respectively (Saucedo and Wagner, 1992).Unaltered flows in the vicinity of the mineralizedarea are interpreted by Young and Cluer (1992)to be younger than the alteration. If thisinterpretation is correct, there are intermediate-composition flows in this area younger than 7.6Ma.

(alunite) 7.6 ± 0.2 Ma

10. R-3 K-Ar

Quartz and adularia (39°26'37.1"N, 119°22'41.2"W;SWV4 NWV4, S11,T18N,R23E; 1.5 km southeastof Ramsey townsite, Martin Canyon 7.5' quad.,Lyon County, NV). Analytical data: K2O =0.782%; i°Ar* = 1.21517 x lO'^ mol/gm;40ArV2:'iOAr = 0.072. Collected by: LarryMcMaster. Analyzed by. E. H. McKee. CommentQuartz-adularia alteration associated withprecious metal mineralization in the Ramseydistrict. An alteration age of 9.3 Ma is reportedon alunite from the district (Vikre and others,1988).

(adularia) 10.8 ± 0.3 Ma

K^Ar

Tuff of Axe Handle Canyon; moderatelyrhyolite vitric ignimbrite (39°45'31"N, 119°3825 'W,SEV4 S20,T22N,R21E; Pah Rah Range north orReno, Eraser Flat 7.5' quad., Washoe County.NV). Analytical data: (biotite) K2O = 8.18/o, Ar= 3.7789 X 10-1° mol/gm; - 0-758,(sanidine) K2O = 10.32%; ̂^Ar* = 4.5683 x 10mol/gm; lOAr'/Z^OAr = 0.984. Collected by. H. f-Bonham, Jr. Analyzed by: E. H. McKee.Comment The tuff is present as a local erosionaremnant below the tuffs of Whiskey Springs(Garside and Bonham, 1992) and it rests on

[ISOCHRON/WEST, no. 59, May 1993]

21

Mesozoic granodiorite. The age places a lowerlimit on the middle Tertiary section of ignimbritesin this region.

(biotite) 31.8 ± 1.0 Ma(sanidine) 30.5 ± 0.8 Ma

12. OG-54

Rhyolite ignimbrite (39°38'05"N, 119°25'59W:NEV4 NEV4 S6,T20N,R23E near mouth ofPierson Canyon, Olinghouse 7.5' quad., WashoeCounty, NV). Analytical data: K2O = 6 ^r= 1.09020 X 10'^^ mol/gm; ""Ar /2 Ar - 0.73.Collected by: L. J. Garside and H. F. Bon^ham,Jr. Analyzed by. E. H. McKee. Comment Thesample is from a vitrophyre at the top orhyolitic unit consisting of basa .and volcaniclastic sandstone overlam b^unwelded grading to welded ;h^ignimbrite. The rhyolitic unit 'Swith basalt flows of the forThe Pyramid sequence is athe predominantly f^ggtern Nevadain ,he Pyrannd LaKe area o. western Nwhich lies above 22- to u-Mabrites (and iccauy aboveAlta Formation), Reno-Virginia Citytion (oa. 12-16 l^a 'ba^,^a",° 83)%bout 1area - see ̂ ''<'6 fab q'q.54 ^ rhyolitekm to the east of lo Y ^ Barstovianair-fall tuff associate intercalated inor early Clarendonia f^Qp, that tuff isthe Bonham, Jr. and DJ.dated at 13.3 Ma (n- • ^ to the north,Axelrod, unpubl. basal flows of thein Fort Defiance ropagus Formation ofPyramid sequence ( Bonham, ^Axelrod [19^6] a^^nham, 1969, P^ 30are dated at 14-9^'^® i971. sample GKrueger Elsewhere in the Pyra^^R0674/NBM-AD^5^^ determinations onoSlhe'^yramid^e'quence-^^have a range sses ^ ^^^gger and Schilling,16 Ma (Bonharn, McKee, "'972, P^ )^1971- Silberman ̂ Q.^y aH ages discussedEvans and others. 198^J^ constants or haveabove are based constants (Dalryrnple,been converted t ptm1979). The young based on adjacentappears to be qu< ^gg.equivalent strata. Ifdates of suggests that the Pyramidcorrect, the a younger than heretoforesequence is^ may overlap in age Kate Peakvolcanism of the Reno-Virginia City area. The

Kate Peak Formation overlies the Pyramidsequence in the nearby Olinghouse miningdistrict, but has not been dated there.

(biotite) 11.7 ±0.4 Ma

13. 2699

Adularia (38°39'00"N, 117°31'30"W: NEV4 NEV4NWV4, S18,T9N,R40E; southern ShoshoneMountains east of the old camp of Golden, MountArdivey 7.5' quad., Nye County, NV). Analyticaldata: KgO = 14.92%; ̂^Ar* = 4.3108 x IQ-i"mol/gm; "OAr'/S^OAr = 0.914. Collected by J. V.Tingley. Analyzed by E. H. McKee. CommentThe sample is from a quartz-cemented breccia inthe footwall of a wide northwest-trending fracturezone in rhyolitic welded ash-flow tuff at the EastGolden Mine, Cloverdale mining district. Quartzand adularia crystals, along with clots of limoniteand minor manganese oxide, coat fracturesurfaces and line vugs in the brecciated, silicifiedrock All of the mineralized areas within theCloverdale district are located along a generalnorthwest trend which parallels the southwesternmaroin of the Peavine caldera (Snyder andHpalev 1983). The mining areas lie outside thedefined caldera margin, but mineraliza^tion is„®'L,ated to occur along structures related to theSS f acture zone of the caldera. A sample of

from the Golden King Mine yielded anadularia from ̂ g Ma reported by McKee andage or -John (1987). (adularia) 20.0 ± 0.6 Ma

K-Ar

ffLria (39°28'49"N, 118°04'59"W: SWV42wV4 SEV4, S30,T19N,R35E; northwest ofreiaer Gap in the northern Louderback Moun-tainl Wonder Mountain 7.5' quad., ChurchillCounty, NV). Analytical data: KgO = 7.68%- aoa.*= 2 5559 X 10-^° mol/gm; ̂ OArVl^OAr = q qSCollected by J. V. Tingley Analyzed by E hMcKee. Comment The sample is from an irreaularstriking vein that generally follows the northwptt"trending Gold King Group fault (SchraderGold King Mine, Wonder mining district vmaterial consists of vuggy, limonite-stained orcolored quartz and adularia, white aua'rt, 'specks of black silver sulfide. Northeast tquartz-adularia veins in this area have beenoffset by the major northwest-trendino 1both sets of structures cut the Wondnr rvf -of Schrader (1947). unit

[ISOCHRONWEST, no. 59, May 1993]

22

15. 3477 K-Ar

Adularia (39°03'52"N, 117°46'25"W: SEV4 SWV4NWV4 S24,T14N,R37E: south of Burnt CabinSummit in the northern Paradise Range, BurntCabin Summit 7.5' quad., Nye County, NV).Analytical data: KzO = 7.25%; "OAr* = 1.73229 x10-10 mol/gm; "OArVz^OAr = 0.77. Collected by.J. V. Tingley Analyzed by: E. H. McKee.Comment Sample was collected from a vuggyquartz-adularia vein exposed in a northeast-trending drift intersected by the upper adit ofthe Duluth Mine, Bruner mining district. Thedistrict is underlain by Tertiary volcanic rocks,chiefly silicic domes, plugs and irregularly-shaped intrusive bodies (KleinhampI andZiony, 1984). A sample of biotite rhyoliticporphyry from the Bruner Mine, located about 1mile northeast of the Duluth Mine, yielded abiotite age of 19.3 Ma by K-Ar analysis(KleinhampI and Ziony, 1984). Ore deposits inthe Bruner district are free-gold-bearing quartzveins that formed along fractures, faults, andbreccia zones in the rhyolitic volcanic rocks. Atthe Duluth Mine, vuggy, lenticular quartz-adularia veins occur along a wide, N20°E-striking sheeted, zone in brecciated, silicifiedrhyolite tuff. Breccia fragments are kaolinizedand cemented with quartz; cavities in thebreccia are lined with quartz and adulariacrystals and some crystals are stained amberby limonite and jarosite. Some quartz veinmaterial exhibits a lamellar texture believed torepresent pseudomorphic replacement ofcalcite by quartz.

(adularia) 16.5 ± 0.5 Ma

16. CHA-MIN K-ArSericitized granite porphyry (35°50'24"N,115°25'55"W; SWV4 SEV4 SEV4, 824,T24S,R57E; south of Keystone Wash in thesouthern Spring Mountains, Shenandoah Peak7.5' quad., Clark County, NV). Analytical data:

= 2.736984 IQ-^ mol/gm;, ̂. .. " 0*976. Collected by: H. F. Bonham,F Vi Gs^'side. Analyzed by.Dvritic csprtnv Sericite obtained fromcollected from^th granite porphyry

± 6 a?d" 89^that Intrudes rSKeystone thrust°?fh;Vetw S^^e ahou*two miles northeast of the Chaqulta iZe He.SS

(1931) and Aibritton and others (1954) observedthat the porphyry dikes and sills of the districtwere, in many cases, intruded along preexistingthrusts and that the porphyry intrusions precededdolomitization and the deposition of ore minerals.Many of the porphyry contacts, however, showevidence of continued movement subsequent tocrystallization of the porphyries (Hewett, 1931).See sample CP-HB below.

(sericite) 199.3 ± 6.0 Ma

17. CP-HB K-Ar

Granite porphyry of Crystal Pass (35°47'45"N,115<'25'09"W; SEV4 SWV4 SEV4, S1,T25S,R58E;one mile southeast of Crystal Pass, south of thetown of Goodsprings in the southern SpringMountains, Goodsprings 7.5 quad., Clark County,NV). Analytical data: KgO = 1.582%; ̂OAr* =4.571196 X 10-10 mol/gm; lOArVZ^OAr = 0.878.Collected by. H. F. Bonham, Jr., J. V. Tingley,and L. J. Garside. Analyzed by. E. H. McKee.Comment Hornblende was separated from anessentially unaltered hornblende granodioriteporphyry dike exposed near the head of a smallbasin southeast of Crystal Pass. This dike is oneof a number of related granitic porphyries havingsomewhat different mineralogies and textures.Intrusive rocks with ages in this range are knownonly from the Goodsprings district in southernNevada, but latest Triassic (and Early Jurassic)plutons of the Lee Vining intrusive epoch occur inthe central Sierra Nevada (Evernden and Kistler,1970), Inyo batholith (McKee and Nash, 1967),and nearTonopah (John and McKee, 1987; Johnand Robinson, 1989). The date obtained fromthis sample is comparable to (within the analytical reproducibility limits) the date obtainedfrom the sample of altered, mineralized porphyryfrom the Chaquita Mine and with dates reportedby Carr and others (1986) from the Yellow Pinesill (see sample CHA-MIN, above). If theKeystone thrust has a displacement of at least 10km (Burchfiel and others, 1974), the presence ofporphyry dikes in both plates of the thrust withina relatively limited area seems to preclude a pre-thrust age of intrusion. The zonation of metadeposits within the district, and the association ofthis zonation with the intrusive rocks (Hewett,1931) suggest that the deposits have not beendisplaced much by thrust faults, and probablyformed after thrust faulting. These dates thusprovide evidence that porphyry intrusion andmineralization in the Goodsprings district arecoeval and that both apparently postdate themajor period of thrust faulting.

(hornblende) 190.3 ± 6.0 Ma

USOOHRON/WEST, no. 59, May 1993]

23

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Albritton, C. C., Jr., Richards, A., Brokaw, A. L., and Reinemund, J. A. (1954)Geologic controls of lead and zinc deposits in the Goodsprings (YellowPine) district, Nevada: U.S. Geological Survey Bulletin 1010, 111 P-

Axelrod, D. I. (1956) Mio-Pliocene floras from west-central Nevada: Universityof California Publications in Geological Sciences, v. 33. p. 91-160.

Axelrod, D. I. (1958) The Pliocene Verdi flora of western Nevada: University orCalifornia Publications in Geological Sciences, V. 34, p. 91-15^

Bell, J. W. and Garside, L. J. (1987) Geologic map of the Verdi Q^^drangie,Nevada: Nevada Bureau of Mines and Geology Urban Series Map 4C3g.scale 1:24,000. „ . anri

Bloomstein, E., Braginton, B., Owen, R., Parratt, R.. '* l,.,Thompson, W. (1993) Geology and geochemistrygold deposit, Humboldt County, Nevada: Society for Mining.and Exploration. Inc.. Preprint 93-205 (Reno. Nevada meeting. Febru ry15-18, 1993), 23 p. , ,A/oehnP and

Bonliam. H. F.. Jr. (1969) Geology and mineral ® mineralStorey Counties. Nevada, with a section . qooIoov Bulletindeposits by K. L. Papke: Nevada Bureau of Mines and Geology

Burchfiel. B.'^C.. Fleck. R.. Secor. D. T.. Qgo,ogfc^^Sod of(1974) Geology of the Spring Mountains. Nevada. GeologAmerica Bulletin, V. 85, p. 1013-1022. Mflvada-Nevada

Calkins. F. C. (1938) Gold deposits of 3),Bureau of Mines Bulletin 30B (University of Nevada Bulletin.20 P- ^ . I, X/ A Drt K M and Zartman,

Carr. M. D.. Evans. K. V.. Fleck. R. J-. for movement on theR. E. (1986) Early Middle Jurassic "PP®^ , society of AmericaKeystone Thrust, southern Nevada: Geological SocietyAbstracts with Programs, v. 18, no. P* ' , j utterback, W. C.

Conrad, J. E., McKee, E. H., Rytuba, J^ J. ̂as^^. Nevada:(1993) Geochronology of the Sieepe emplacement of a silicicEpithermal gold-silver nnineralizatio 0.81-91.flow-dome complex: Economic Geo ogy. ^^^^._^^ old to

Dalrymple, G. B. (1979) Critical tables for cnew constants: Geology, v. 7, P- pggv potassium-argon dating: San

Dalrymple, G. B., and Lanphere, M. A. tFrancisco, W. H. Freeman Company.^o ^ of the

Evans, S. H., Jr., Moore, J. N- aad^ , san Emidio geothermal area.Pyramid sequence in the no. 31, p. 19-21-Washoe County, Nevada: Isoch potassium-argon dates a

Evernden, J. F., and James. G. T. of Science, v. 262. p.Tertiary floras of North America. mpnt of

P.. ... a W

Garside. L. J.. and Bonham. H. g^.. Walker UneSym^^^^^^^^^^Washoe County. Nevada, "®"°, Society of Nevada Special1992 spring field trip #2 9 geological Socie ymineralization and struc Goodsprings quad-Publication no. 15. p. 48. ^^g deposit o' "^ 172 p.

John. D. A., and McKee. e H^J^^g.ern part ofhn, u. A., anu ivio.w . ^16

John D A and Robinson. A. C. (1989) Rb-Sr whole-rock isotopic ages ofgranitic plutons in the western part of the Tonopah 1» by 2° quadrangle.Nevada: Isochron/West, no. 53, p. 20.

Kleinhampl. F. J.. and Ziony. J. I. (1984) Mineral resources of northern NyeCounty. Nevada; Nevada Bureau of Mines and Geology Bulletin 99B. 243

k-ruroer H W.. and Schilling. J. H. (1971) Geochron-Nevada Bureau ofiwne's K-Arage determinations, list 1: Isochron/West. no. 1. p. 9.

Mz-k-pp E H and Nash. D. B. (1967) Potassium-argon ages of granitic rocksin the Inyo batholith. east-central California: Geological Society of AmencaRi illptin V. 78, p. 669.

E H and John, D. A. (1987) Sample locality map and potassium-arnon aoes and data for Cenozoic igneous rocks in the Tonopah r by 2°^..aHranale central Nevada: U.S. Geological Survey Miscellaneous FieldSs Map. MF-18771, scale 1:250,000.h J T and Bartlett, M. W. (1991) Progress on studies of the geologicPttino of Miocene volcanic rocks at the Sleeper gold-silver mine,u hnldt County, Nevada, in Thorman, C. H., ed.. Some current research• i^otprn Nevada and western Utah by the U.S. Geological Survey: U.S.Geological Survey Open-File Report 91 -386, p. 1.

J T Utterback, W. C., and Saunders, J. A. (1991) Geology andNash, J Qf (he Sleeper gold deposits, Humboldt County, Nevada: anreport, in Raines, G. L., Lisle, R. E., Schafer, R. W., and Wilkinson,intenm p Geology and ore deposits of the Great Basin, Symposium

iloHinns- Geological Society of Nevada, Reno, p. 1063.o r McKee E. H., and Vikre, P. G. (1989) K-Ar ages from Nevada

aZistem California: IsochronAA/est. no. 52. p. 13.^ H G J and Wagner, D. L. (1992) Geologic map of the ChicoSau^eoa^^^^^ California: California Division of Mines and Geoiogy, Map 7A(Geoiogy). .y. Carson Sink area, Nevada: U.S. Geological Survey

Schrader. F. C. pOpen-File n^j-Kee. E. H. (1972) A summary of radiometric age

Silberman, M. jertiary volcanic rocks from Nevada and easterndeterminatio ^ggtern Nevada: Isochron/West, no. 4. p. 7.California—P p, l. (1983) Interpretation of the Bouguer gravity

Snyder, D. B.. an _ ' ̂ sheet: Nevada Bureau of Mines and Geologymap of Nevaoa.Report 38, 14 P- p L. (1980) Geologic map of the Reno NW

Soeller, S. A.. . Nevada Bureau of Mines and Geology Urban SeriesQuadrangle. .24,000.Map 4Dg. seal • '^ ̂ Dalrymple, G. B., Lanphere, M. A., and

Stacey. J- ̂ ̂ ^ w ngai) A five-collector system for the simultaneousCarpenter, N- • ̂ jsotopic ratios in a static mass spectrometer:measurement or ^ Spectromet/y and Ion Physics, v. 39, p. 167.International Jouf. ^ ̂ ^^ ̂ Subcommission on geochronology-

Steiger. R- use of decay constants in geo- and cosmochronoloqvconvention on ̂ "s^ience Letters, v. 36. p. 359.Earth and PlaneB-y g^gjggy gnd ore deposits of the Valmy and North

Theodore. T. G. 'gg„,g Mountain mining district. Nevada, in Thormanpeak current research in eastern Nevada and western Utah hwSe U.I.'Geolo^'^' U.S. Geological Sunrey Open-File Re^ g/-386.

Vikre,

[IIC7

J®®' P- i/iokee E- H.. and Silberman. M. L. (1988) Chranoloqv of>»• ° '!lafan'd igneous events in the western Virginia Ranoe u,

Young

ttydrothe^a ,|es. Nevada: Economic Geology, v 83 oand Cluer. J. K. (1992) The Antelope Valtey'p

jng. ̂ •. " a Tertiary acid sulfate system in Sierra Countv r r."®®®P° Steve, ed.. Walker Lane Symposium, 1992 sprino rCraig. P . nraa - nnrthp»rn WalL-A.- i _ PHnn fielH 4,.-

I.UI iw w y 11 ipvJOl Ul I) 1 y02 S

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hydrothermal a'^er^ionNevada: IsochronAA/est. no.

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mdebook. Reno area - northern Walker Lane minTr=i''®''^ '"P »2Stricture: Geological Society of Nevada Special Publication 0^15°^33.

[ISOCHRON/WEST, tio. 59, May 1993]

Geologic time chart referencesThe 1983 revision of this deologic time chart was prepared by the Geologic Names Committee for U.S. Geological Survey use. It supersedes tte

1980 chart. Numerical ages of chronostratigraphic boundaries are subject to many uncertainties besides the analytical prec^ion of the dabng. Theplacement of boundary stratotypes and the achievement of international agreements on these ages is a slow process subject to niuch revision andreview. Recent studies and revisions of the geologic time scale of especial interest are reported geologic meCox, P. G Llewellvn GAG. Pickton, A. G. Smith, and R. Walters, 1982: Cambridge University Press, 132 p.. The decade ofNoi^Amen^geology 1983 geologic time scale, by A. R. Palmer, 1983: Geology, v. 11, p. 503-504; and The chronology of the geological record, N. J. Snelling(ed.), 1985: Blackwell Scientific Publishers, The Geological Society, Memoir No. 10, 343 p.

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American Association of Petroleum Geologists, 1978, Studies in Geology6, 388 p.

Berggren, W. A., 1972, Lethaia, v. 5. no. 2. p. 195-215Berggren. W. A., Kent. D. V., van Couvering. J. A.. 1985, The Neo-gene—part 2, Neogene geochronology and chronostratigraphy,Snelling, N. J. (ed.). The chronology of.ttif seojos'"'well Scientific Publications, The Geological Society, Memoir No.

Evernden!/F°,' Savage, D. E., Curtis. G.American Journal of Science, v. 26^ P- , .J,:'-i „ ions 458

Geoiogicai Society of London, 1964, Quarteriy Journai, v. 120S, 458Lambert, R. S., 1971, Geoiogicai Society of London, Speciai Publica

tions 3, Part 1, p. 9-31. Cnollinn N I fed 1

^"Srchrligl^Sf^thtVeSaS

V. 36, p. 359-362.

Holocene-Plelstocene boundaiyHopkins, D. M., 1975, Geoiogy, v. 3, p. 10.

Pleistocenfr-Pliocene boundaryHaq, B. U., Berggren, W. A., and van Couvenng, J. A., 1977, Nature,

V. 269, p. 483-488. m Rortolani M. D., Bigazzi, G.,

SorsSt?.™and Ta^Ser!: R.".' K^Giornaie di Geologica Bologna, ser. 2,V. 42, no. 1, book II, p. 181-204-

Cita, M. B., 1975, Micropaleontology. orMcDougall,l.,andPage,R.W..19/:'-'"

lication 1, p. 75-84. . .|gg4 Nature, v. 201, p. 365^6/.Tongiorgi, E., and '''o"9'°o®''n^ishoo W- and Uiii-van Couvering, J. A.,1f2: Academic Press and Uni

Caiibration of hominid %47_271.versify of Toronto Press, P-

van Couvering, | A., ̂Oj®g'efggren, W-f • eth^dV^of^b^^^^van Couvering, J. A.'a concepts and f" nY: exclusive dis-and Hazei, J. E (ed^)' ̂ Hutchinson, & Ross,Stroudsburg, PA: Dowdtributor: Halstead Press.

1-30.Pub-

OiigocenoJoe^®^® 5;j"'J'^erican Association ofHardenbol, J-. ®?nnjsts®Sto^^^^ Journal of thepetroleum and Hunzg J-

n- paiBocene boundaryEocene-r ^ ^gf^enbol, J., and Obradovich, J.

%®®'l978^jJurn¥o&^^ N. R., 1978,"irna/offfSlogicaifg^^^°teol?gi&SoSeti of London, v. 135, p. 481-497.

Paleocen&-Cretaceous boundary

Lerbekmo, J. F., Evans, M. E., and Baadsgaard, H., 1979, Nature, v.279, p. 26-30.

Obradovich, J. D., and Cobban, W. A., 1975, Geological Associationof Canada, Special Paper 13, p. 31-54.

Late-Early Cretaceous boundary

Folinsbee, R. E.. Baadsgaard, H., and Gumming. G. L.. 1963, NationalResearch Council, Publication 1075, p. 70-82.

Obradovich, J. D., and Cobban, W. A., 1970, Geological Associationof Canada, Special Paper 13, p. 31-54.

Cretaceous-Jurassic boundary

Lanohere M A., and Jones, D. L., 1978, American Association ofPetroleum Geologists, Studies in Geology 6, p. 259-268.

Jurassic-Trlassic boundary

Armstrong, R. L., and Besancon, J., 1970, Eclogae Geologicae Hel-vetiae v. 63, no. 1, p. 15-28.

White W H Erickson, G. P.. Northcote, K. E., Dirom, G. E., andHarakal*. J.*E., 1967, Canadian Journal of Earth Sciences, v. 4, p.677-690.

Triasslc-Permlan boundary

\A/Phh A W and McDougall, I., 1967, Earth and Planetary ScienceLetters* 2, p'. 483-488.

Permian-Carboniferous boundary

u c I Miller J A., and Williams, S. C., 1970, IntemationalS'ngress'on Stratigraphy and Carboniferous Geology, 6th, Sheffield,1967: Compte Rendu, v. 2, p. 771-789.

Carboniferous-Devonian boundary1 Miiipr J A and Williams, S. C., 1970, IntemationalFitch, F. "'e, ''tinraDhyandC^^ 6th, Sheffield,Congress on Strangr ^ 771-789.

1967: Coh"?*® JL ..Qp vv., and Boflnger, V. M., 1966, GeologicalMcDougall, L.C0f^®™,,^jP ^ 77, p. 1075-1088.

Society of AtnenM A. J., Evolution and extinction rateTalent, J. publishing Co., Amsterdam, New York,

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'' Devonian-Silurian boundary■ Mapcer C. W.. Izett, G. A., Whittington, H. 8., Hughes

Ross, R. 3-.' D B Zaiasiewicz, J., Sheldon, P. R., Jenkins c'G. P.. J Bassett, M. G., Toghili, P., Dean, W. T. andJ., Cocks, L. H- jj g geological Survey, Open-file Report 78-yOtT 863-365-

Sllurlan-Ordovician boundary

od A rhurkin, M., Jr., and Eberlein, G. D 1977 .Lanphere, M-A-:,S"I,7'i. p. 15-24. ' GeologicalI^TT'jr Nae'ser.C.W., Izett, G. A.,Whittington H B u ,

Precambrian subilivisions

"^°6'p:3n-380°' BW«ln. ,, 9,Harrison, J. E., and Peterman, 2. E., 1982, American Ac.

Petroieum Geologists Bulletin, v. 66, no. 6, p. 80l-8o|Proteroioic subdivisions

James, H. L., 1972, American Association o1Bulletin, V. 56, p. 1128-1133. ''etroleum Geologts^g

Proteroioic-Archean boundawJames, H. L., 1978, Precambrian Research v 7

Afchean ^Goldich, S. S., and VHooden, J, L., 1975. .

\Nilliams, J.G.ieds.V Proceedings t miContence. p, 285-318,