Geochemistry and 

Potassium-Argon Ages of 

Plutonic Rocks in the 

Battle Mountain Mining District, 

Lander County, Nevada 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 798-A 

Geochemistry and 

Potassium-Argon Ages of 

Plutonic Rocks in the 

Battle Mountain Mining District, 

Lander County, Nevada 

ByTED G. THEODORE, MILES L. SILBERMAN, and DAVID W. BLAKE 

GEOCHEMISTRY OF THE PORPHYRY COPPER ENVIRONMENT IN 

THE BATTLE MOUNTAIN MINING DISTRICT, NEVADA 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 798-A 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1973 
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary 

GEOLOGICAL SURVEY 

V. E. McKelvey, Director 

Library of Congress catalog-card No. 73-600110 

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

Washington, D.C. 20402 -Price 65 cents domestic postpaid or 45 cents GPO Bookstore 

Stock Number 2401-00333 
CONTENTS 

Page 

Abstract -------------------------------------------------------------------------------------- A1 

Introduction -------------------------------------------------------------------------------- 1 

General geology of the Battle Mountain mining 

district -----------------------·------------------------------------------------------ 1 

Geology of the Copper Canyon area -------------------------------- 3 

Chemistry of the granodiorites ------------------------------------------------ 5 

Major elements ------------------------------------------------------------------ 5 

Minor elements ------------------------------------------------------------------ 10 

Biotite compositions ------------------------------------------------------------------ 11 

Altered granodiorite of the Copper Canyon area___________ 13 

Granodiorites of the Long Peak and Timber Canyon 

areas ---------------------------------------------------------------------------------- 16 

Page 

K-Ar ages -------------------------------------------------------------------------·----------- A17 

K-Ar analytical procedure and precision------------------------ 17 

Cretaceous granodiorite of Trenton Canyon ------------------ 18 

Tertiary granodiorite and altered granodiorite ------------ 19 

Samples collected outside the Copper Canyon 

area ---------------------------------------------------------------------------- 19 

Copper Canyon area -------------------------------------------------- 19 

Significance of the data ------------------------------------------------------ 20 

Summary -------------------------------------------------------------------------------------- 22 

References cited -------------------------------------------------------------------------- 22 

ILLUSTRATIONS 

Page 

FIGURE 1. Index map of north-central Nevada----------------------------·-·--------------------------------------------------------------------------------------------------------- A2 

2. Facies maps showing distribution of facies in the Cordilleran geosyncline, Cambrian through Devonian time, 

distribution of facies after Late Devonian and Early Mississippian thrusting, and the location of the 

Battle Mountain mining district --------------------------·------------------------------------------·-·····---········-·-·····-··-·--·----·--··-··-----·-············· 3 

3. Generalized geologic map of the Antler Peak quadrangle and Battle Mountain mining district-·······-·-···--···--·--·-······ 4 

4. Generalized geologic map of the Copper Canyon area........................................................................................................... 6 

5. Photomicrographs showing textures in the altered granodiorite of Copper Canyon .............................................. ........ 7 

6. Distribution of normative quartz, plagioclase, and orthoclase in 11 chemically analyzed specimens .................. ........ 7 

7. Distribution of Ca, Na, and Kin 18 specimens of plutonic rocks ·················-······························-························'············ 7 

8. Plots of K:Rb for average crustal rocks, "granitic" rocks, and five specimens of unaltered granodiorite.................. 11 

9. Photomicrograph of primary biotite from altered granodiorite ···--------··········--····-······························································ 13 

10. Relation among Mg, Fe+2 (Mn+2), and AI (Fe+3

, Ti) in biotites ---·-·····-······-····-·····································--·························· 15 

11. Photomicrograph of hydrothermal biotite from Battle Formation.................................................................................... 20 

12. · Effect of grain size on Ar retentivity ··········--···---·--···--·-··-·······--·················-·····················-··········-············-------···-·······-····-----···· 21 

TABLES 

Page 

TABLE 1. Analyses of intrusive rocks in the Battle Mountain mining district ................................................................................ AS 

2. Analyses for selected minor metals in plutonic rocks in the Battle 1\tlountain mining district ............................ ........ 12 

3. Abundance of minor elements in "granitic" rocks···········-···········-····-····-····-····-·····-·-·········-----------------··········--····-··············-··-- 14 

4. Compositions and structural formulas of biotites from granodiorite of the Copper Canyon, Long Peak, and 

Timber Canyon areas --····-·····---------·-·······-·-···-······-····················-·················--·······-··-··-····--··-··-······-······-·············-·······-········ 14 

5. X-ray d-spacings of 005 and 060 reflections, calculated unit cell volumes, and densities of biotites from 

granodiorite of the Copper Canyon and Long Peak areas -----······-····--···················-······················-·······-······-···----------- 15 

6. Sample locations and descriptions of K-Ar age-dated specimens from the Battle Mountain mining district.......... 17 

7. K-Ar analytical data-····-··-·····--------------·-········-···-······----············-······································-··--······-··-·-···--···-·····-··········--········-····- 19 

8. K-Ar ages of rocks from the Battle Mountain mining district···-··················-··············-·········-------··········----·--···-······-····-··· 19 

9. Effect of grain size on retentivity of argon, biotite from Snowbank stock, 2.9 km from contact with Duluth 

Gabbro Complex -···············-················--·····-···-·-······-··-·····-············--·-···--···-····--·············-············--····-·-····------··-·····--···-····--·· 21 

III 

GEOCHEMISTRY OF THE PORPHYRY COPPER ENVIRONMENT IN THE BATTLE MOUNTAIN 

MINING DISTRICT, NEVADA 

GEOCHEMISTRY AND POTASSIUM-ARGON AGES OF PLUTONIC 

ROCKS IN THE BATTLE MOUNTAIN MINING DISTRICT, 

LANDER COUNTY, NEVADA 

By TED G. THEODORE, MILES L. SILBERMAN, and DAVID W. BLAKE1 

ABSTRACT 

The Battle Mountain mining district is in Lander County, 

north-central Nevada, at the northwest end of the EurekaBattle Mountain mineral belt. The district is underlain predominantly by lower to upper Paleozoic sedimentary rocks, 

which occur in three major thrust plates and an interjacent 

autochthonous tectonic block. These rocks were intruded by a 

single Cretaceous (87million years) pluton and subsequently by 

a large number of stocks and dikes in the Tertiary from 41 to 

38 m.y. ago. Many of the intrusive rocks are inferred to have 

originally been granodiorites, now hydrothermally altered in 

varying degrees to more potassic K-feldspar-white mica-(biotite) assemblages. The altered plutons are chemically equivalent 

to quartz monzonites. These silicate alteration assemblages are 

commonly associated with economic sulfide deposits in the 

southern part of the district. In addition, increases in concentrations of Cu, Ag, Mo, and Rb in the intrusion at Copper 

Canyon during alteration followed increases of K20. 

At Copper Canyon, biotite K-Ar ages for an altered granodiorite associated with the nearby porphyry copper deposit 

average 38.22±0.23 m.y. The age of metallization in the porphyry copper deposit is 37.2o±O.Os m.y., as measured by wholerock K-Ar determinations. Hypogene sulfide veins that cut the 

intrusion establish the post-magmatic nature of most metallization. However, the measured 1-m.y. time interval between 

crystallization of coarse primary biotite and metallization may 

be a maximum value, resulting from the much finer grain size 

of the hydrothermal assemblage rather than from an actual age 

difference. During cooling of the ore, its retentivity of argon 

was probably less than that of the coarse primary biotites. 

INTRODUCTION 

The Battle Mountain mining district is in the Antler 

Peak quadrangle (15 min) and at the northwest end 

of the Eureka-Battle Mountain mineral belt-a northwest-southeast alinement of metal mining districts 

inferred to be localized by deep-seated Precambrian ( ?) 

1 Duval Corp., Battle Mountain, Nev. 

structural features (Roberts, 1966) (figs. 1 and 2). The 

district produces the most copper in north-central 

Nevada and includes the Copper Canyon porphyry 

copper deposit (Sayers and others, 1968) and additional potentially economic porphyry-type deposits. 

Over $13 million in copper, gold, silver, lead, and zinc 

was produced through 1961, mostly from the Copper 

Canyon area in the southern part of the district 

(Roberts and Arnold, 1965, p. B40). Noble (1970) estimated that proved copper reserves in the Battle Mountin mining district totaled $300 million before Duval 

Corp. began large-scale mining operations in 1967. 

This report serves three purposes: it (1) dates plutonism in the mining district, ( 2) describes the 

chronology of igneous activity and metallization at the 

Copper Canyon porphyry copper deposit, and (3) provides a basic geochemical framework (including data 

and interpretation) for more detailed studies of the 

Copper Canyon deposit (Theodore and Blake, 1973). 

Acknowledgments.-The cooperation of F. H. Howell 

and A. E. Shiell, Duval Corp., made possible those 

aspects of this study dealing with the Copper Canyon 

porphyry copper deposit. T. J. Armbrustmacher, R. J. 

Roberts, and C. T. Wrucke, all with the U.S. Geological 

Survey, helped to collect many of the samples. Chemical and spectrographic analyses were made in the 

laboratories of the U.S. Geological Survey. 

GENERAL GEOLOGY OF THE BATTLE MOUNTAIN 

MINING DISTRICT 

The Battle Mountain mining district is underlain 

predominantly by Paleozoic rocks that form a complex 

sequence of thrust plates (Roberts, 1964). Much of 

this part of Nevada was underlain by siliceous and 

Al 
A2 GEOCHEMISTRY OF PORPHYRY COPPER, BATTLE MOUNTAIN MINING DISTRICT, NEVADA 

f--- -----

• Quinn River 

Crossing 

) 

HOUMBOLDT 

OSGOOD 

MOUNTAINS --. 

Comus 

cc ,_,e<. '5 ~, ... 

(1) 

Cl 

c 

cc 

a: /

co e 

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e 0 It._. 

Rochester ..cE MOUNT TOBIN j ~·S CJ~ i .§§ • (Lovelock t; /liJ..;f 

MOUNT 

LEWIS 

COR~EZ 

Corte~ 

-

•Mountain City 

ELK 0 

\ 

\ 

\ 

\ 

\ 

\ 

MINERAL HILL f--- I - --- --- --- .....___ s\n~ (1) I Vcafson :S: ,' MOUNT MOSEs 

40° r-- ---- --- ----+--L-------+-----1.....--+-1 -+---+----+--+------------+--I ) 1 e GARDEN l 

\ 

CHURCHILL 

,-----n 

I Area shown on I 

I index map I 

~eno Manhattan E!y ! 

' Sono~ah .. Tybo 

1 "" Pioche• 

-.Beatty 1 ,e Las 

39° f-~-----------1,1----"' ~:~ 

( L A N D E R I Tonkin VALLEY \ \' "'k_ I ROBERTS CREEK e I 

l ~ r,.,ouNTAIN Summit ~..o I I 

~~ I \ 

\ I 

I • Austin 1EUREKA 

I 

--------j_- -------- _-( 

NY E 

0 20 40 MILES 

0 20 40 KILOMETERS 

FIGURE 1.-North-central Nevada. 

WHITE 

PINE 

•Hamilton 
GEOCHEMISTRY AND POTASSIUM-ARGON AGES, PLUTONIC ROCKS, LANDER COUNTY, NEVADA A3 

ioche ===! 

A ~Las 

'...yega~ 

B 

-,------ 1 

I I Winnemucca 

I e 

j Battle Mtn/~: ·.~ ~ \ mmtng dtsti'tct · ·:~j"· 

,\ 

.. ~ 

1\. IRe no '-, ...~· . Y. · ~t=Ely ~o.:.-

'," \ ... /., i ! ', \ 7 _(t 0" \ . ',"-,\Tonopah Pioche 

CALIFORNIA'~,, \) "-, Las 

' Vegas . 0 100 

Basin and Range 

Pr~~nce ~':~!Y-----

WYOMING 

I 

I 

UTAH \ 

Cedar City 

200 MILES 

I 

I 

\ 

I 

I 

\ 

I 

FIGURE 2.-Facies maps. A, distribution of facies in the Cordilleran geosyncline, Cambrian through Devonian time. B, 

distribution of facies after Late Devonian and Early Mississippian thrusting (Roberts and others, 1971) and the location 

of the Battle Mountain mining district (Roberts, 1966). 

volcanic rocks in the upper plate of the Roberts Mountains thrust (fig. 2), which moved volcanic rocks, chert, 

shale, and quartzite of early and middle Paleozoic age 

eastward over a lower plate consisting of carbonate 

rocks of an equivalent age (Roberts and others, 1958; 

Roberts, 1966). This thrust does not crop out in the 

mining district (Roberts, 1964), but it probably passes 

beneath the area at depths greater than about 1,400 m 

(Theodore and Roberts, 1971). In addition to rocks in 

the upper plate of the Roberts Mountains thrust, the 

district is underlain by rocks belonging to two other 

structurally higher major thrust plates, the Dewitt and 

Golconda plates, and an interjacent autochthonous 

block, the Antler sequence (fig. 3). 

About 35 stocks and dikes, each generally less than 

3 sq km in outcrop area, intrude this complex of tectonic blocks. They range from gabbros to granites, with 

quartz monzonites and granodiorites predominating. 

Complete descriptions of many of these rocks are 

included in the report by Roberts (1964). Texturally, 

many are hypidiomorphic-granular, although porphyritic facies are also common. As part of a broader 

regional investigation by Silberman, K-Ar age determinations were made on 14 mineral separates from nine 

different intrusive bodies in the Antler Peak quadrangle. Two whole-rock age determinations were made 

also on hydrothermal biotite-white mica-K-feldspar 

intergrowths from two pyrite- and chalcopyrite-bearing 

rocks in the Copper Canyon porphyry copper deposit. 

GEOLOGY OF THE COPPER CANYON AREA 

A 1,200-m-wide intrusive body crops out at Copper 

Canyon (fig. 4), in the southern part of the mining 

district. Drill holes into the body have shown it to be 

sill-like or laccolithic (Blake, 1971; Theodore and 

Blake, 1973). Peripheral to it, base- and precious-metal 

deposits are arranged in fairly systematic zones for a 

distance of about 8 km outward from the center 

(Roberts and Arnold, 1965). The Copper Canyon porphyry copper deposit (the east and west ore bodies) is 

in a central copper-gold-silver zone, just north and east 

of the intrusive body, primarily in conglomerate of the 

lower member of the Battle Formation (fig. 4) but also 

in sandstone of the Harmony Formation and tactite 

provisionally assigned to the Pumpernickel Formation . 

Locally, metamorphism and metasomatism of rocks 

belonging to the Pumpernickel Formation in the west 

ore body (fig. 4) produced anhydrous tactite silicate 

assemblages (Nash and Theodore, 1971), most likely 

concomitant with the intrusion's crystallization from a 

magma. The intrusive rock is predominantly porphyritic. A remnant "quenched" groundmass texture (fig. 

5A) has been detected in a few samples. We interpret 

inclusion of K-feldspar and quartz groundmass crystals 

along the margins of plagioclase phenocrysts (fig. 5A) 

as reflecting continued growth of the plagioclase 

(although more albitic) at hypersolidus conditions fol-
A4 GEOCHEMISTRY OF PORPHYRY COPPER. BATTLE MOUNTAIN MINING DISTRICT, NEVADA 

.. · .. ·. 

... 

.. :-.·:-.-.-· ... · .. -.··:. 

. . : .... · 

·.·· . . . . . . . . . . . . . . .. . : -~-.' : . ::--.· . . _.·.:·-·:··-.·:·· ... . ... :'·.··_·.-_: .. ··.··.·.-·:·-::-·.·: ... ·.-.· ·_._-:-.:·. : : •. . . . . . . ~: . . . . - . . . . . . . ·. -: : :- .. 

··.··:·.··.·.·.-:.::-:::.··· .· ... 

::_.·::::.· ·.-·:·.·.·: ... _ ........ ::·:_. . . . · .. ·: --·: ... ·.· ·:_.:·.:: 

. : . . . . . . . . . . . . . . . . . . ..... ~ --~ ....... :: ·:. ·.· : . : :- .·. 

. . .. · .. _: :'· . :-. · .... : .<· .. · .. .: . ·: ~ :_::.;: : .. ··: .. · -_:· ..... :··.··:'·:'· .. ·.·:. ._ ... ·_::·-·:.-

· .. ::-::·· 

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.. '•: ........ .. ·.-::·:-. •' 

. . . : : :- --~ : .. :· .· :~ .··. :.' · ... : : 

Geology modified from Roberts ( 1964, pl. 1) 

FIGURE 3.-Generalized geologic map of the Antler Peak quadrangle and Battle Mountain mining district, Lander 

County, Nev. Localities of chemically and (or) K-Ar analyzed samples also shown. Location numbers same as tables 

1 and 7. Localities 9-14, 17, 18 are shown in figure 4. 
GEOCHEMISTRY AND POTASSIUM-ARGON AGES, PLUTONIC ROCKS, LANDER COUNTY, NEVADA A5 

EXPLANATION 

LZJ 

Alluvium } 

ffi >- i-CC 

<(<( 

:::lZ 

0 

-

Basalt }

>- ·>- cc<(cc 

~a~ a: eeoc LJ.JOLJ.J 

1- 1-

w 

1-

<( 

Caetano 

-

Tuff 

Age 34 m.y. (McKee and Silberman, 1970) 

Welded tuff and pyroclastic rocks 

Granodiorite and altered granodiorite 

Age 38 to 41 m.y. (this report) 

D 

Granodiorite and quartz monzonite(?) 

Granodiorite 

~ of Trenton Canyon 

Age 87 m.y. (this report) 

Antler 

-

sequence 

Consists of Middle Pennsylvanian Battle Formation, 

the Upper Pennsylvanian and Lower Permian Antler 

Peak Limestone, and the Upper Permian Edna 

Mountain Formation 

UNCONFORMITY 

~ 

~ Havallah ~ sequence 

~ Consists of Pennsylvanian(?) 

1- Pumpernickel Formation 

~ and Middle Pennsylvanian 

z and Lower Permian Havallah 0 

(.) 

...J 

Formation 

GOLCONDA THRUST 

<I) 

::a 

>-

a: 

<( 

i= 

a: 

LJ.J 

1-

~(I) 

1-:::l 

LJ.JQ 

OCLJ.J 

uu 

z 

<(z 

-<( z_ 

<(2 

>a: 

....lLJ.J 

>-c.. 

Vlo 

zz 

~<( c.. 

8 w 

1-

<( 

...J 

a. 

w II- ~ ~ :s a: 

H { lm\tmttl } ~ : "8 Valmy Formation o 

-~ a. ~ 

~{ ~t.J;~mation ~ 15: ~ 5 :::::> ~ DEWITT THRUST ~ 

w 

0 

. . ........ ---- Thrust fault 

Dashed where approximately 

located; dotted where concealed or inferred. Sawteeth 

on upper plate 

(f.) 

1-

a: 

w 

co 

0 

a: 

Contact 

® 

vo 

~ THRUSTCONTACT 

~ 

Scott Canyon 

Formatwn 

BASE NOT EXPOSED 

High-angle fault 

Dashed where approximately 

'located; dotted where concealed or inferred 

Location and sample number referred to 

in tables 1, 5a, 5b, and 6 

z 

~ 

a: 

Cll 

2 

<( 

u 

lowing emplacement of the intrusion. Both the anhydrous metamorphic assemblages in the wallrock and 

much of the matrix in the intrusivetock subsequently 

were metasomatically recrystallized to an even finer 

grained (fig. 5B), highly sutured assemblage of quartzK-feldspar-white mica-(biotite). The average grain 

.size of the matrix is now about 0.01 mm. This superposition of potassic alteration on an earlier anhydrous 

contact assemblage was also recognized by Roberts and 

Arnold ( 1965, p. B26). Both the pluton and the porphyry copper ore zones are characterized by potassic 

alteration assemblages similar to those described by 

Creasey (1966) and Meyer and Remley (1967). Very 

little sulfide ore has been found in the altered granodiorite of Copper Canyon itself, although several of the 

samples collected for the K-Ar study contain pyrite, 

and the pluton is at the core of a broad pyritic halo that 

encompasses most of the southern part of the mining 

district (Roberts and Arnold, 1965; Theodore and 

Blake, 1969). The altered granodiorite is anomalously 

rich in copper, compared with unaltered rocks in the 

district (as described below) and rocks of similar composition elsewhere, but much of this copper is contained 

in altered plagioclase phenocrysts and is secondary, or 

supergene. 

There is further evidence in the rocks that alteration 

and metallization followed primary crystallization of 

the intrusive body. Fluid inclusions of the dense, brine 

type occur both in the ore zones and, especially, along 

microfractures through quartz phenocrysts in the intrusive rock (Nash and Theodore, 1971). These relations 

strongly suggest that most hydrothermal potassic alteration and attendant metallization took place after the 

intrusive rock had solidified. Nevertheless, metallization must have occurred soon after the body was 

emplaced, with magmatic heat as a possible driving 

mechanism. Additional petrographic descriptions of 

rocks from this intrusive body are included in the sections on the chemistry of the plutons and their biotites. 

CHEMISTRY OF THE GRANODIORITES 

MAJOR ELEMENTS 

Twelve samples (table 1) of intrusive rocks representing 11 different plutonic bodies from throughout 

the mining district were chemically analyzed for major 

and minor elements, and eight of these samples were 

dated by the K-Ar method. The samples include both 

fresh, unaltered rock and rock hydrothermally altered 

by fluids associated with the development of nearby 

hypogene sulfide deposits. 

Five analyses of unaltered rocks are similar to the 

"average biotite granodiorite, average hornblende-biotite granodiorite, and average granodiorite" of Nock-
A6 GEOCHEMISTRY OF PORPHYRY COPPER, BATTLE MOUNTAIN MINING DISTRICT, NEVADA 

0 1000 

0 250 

FIGURE 4.-Generalized geologic map of Copper Canyon area, Lander County, Nev., showing location of K-Ar age-dated and 

chemically analyzed samples. Geology modified from Roberts (1964) and Theodore and Blake (1973). Explanation same 

as for figure 3. 

olds ( 1954, p. 1014), listed in table 1 for comparison. 

However, our samples are slightly richer in MgOprobably reflecting the high magnesian content of biotites, as found in one of the intrusive bodies. Furthermore, the rocks are generally also slightly lower in 

Na20 than the three "average" granodiorite analyses 

of Nockolds (table 1). Finally, specimens 3, 4, and 15 

(all of which contain notable modal hornblende) are 

slightly richer in CaO than Nockolds' average for 65 

hornblende-biotite granodiorites. These analyses suggest slightly more modal hornblende in these three 

rocks than in Nockolds' "average hornblende-biotite 

granodiorite." 

The differentiation index (sum of normative orthoclase, quartz, and albite) for the five unaltered igneous 

rock specimens ranges from 61 to 75; the average is 67. 

The differentiation indices for N ockolds' ( 1954) "average biotite granodiorite, average hornblende-biotite 

granodiorite, and average granodiorite" are 67, 70, and 

73, respectively. Normative Q, Ab, An, and Or in 

molecular proportions for five unaltered specimens are 

included on the accompanying ternary diagram (fig. 6). 

The triangular plot indicates that these five unaltered 

specimens (collected from four widely separated intru-
GEOCHEMISTRY AND POTASSIUM-ARGON AGES, PLUTONIC ROCKS, LANDER COUNTY, NEVADA A7 

0.5mm 

0.5mm B 

FIGURE 5.-Textures in the altered granodiorite of Copper Canyon. A, Photomicrograph of "quenched" groundmass texture. 

Crossed nicols. P, plagioclase phenocryst; Q-F, quartz-Kfeldspar. B, Photomicrograph of hydrothermally altered rock 

from the granodiorite of Copper Canyon. Crossed nicols. B, 

primary phenocrystic biotite; RB, secondary recrystallized 

biotite; P, partly sericitized plagioclase phenocryst; Q-F, 

quartz-K-feldspar hydrothermally altered groundmass. 

sive bodies, fig. 3) form a fairly tight cluster of points 

within what Bateman (1961) defines as the granodiorite part of the diagram. 

On a triangular plot of Na, Ca, and Kin atomic proportions for all available chemical analyses of igneous 

rock specimens from the Battle Mountain district (fig. 

7), the unaltered and altered rocks appear to define 

two partially overlapping domains. Most of the effects 

of hydrothermal alteration are found in the matrix, 

where alteration is indicated by complexly recrystallized quartz, K-feldspar, and white mica intergrowths, 

with some newly grown hydrothermal biotites. Furthermore, magmatic plagioclase and K-feldspar phenocrysts are sericitized and "clouded" to varying degrees, 

Q 

EXPLANATION 

Sample number same 

as table 1 

Unaltered 

,;-, 

Altered 

Ab+An 10 35 Or 

Na 

FIGURE G.-Distribution of normative quartz (Q), plagioclase (Ab+An), and orthoclase (Or) in 11 chemicially analyzed specimens (table 1) of intrusive rocks 

from the Battle Mountain mining district, Lander 

County, Nev. Bateman's classification (1961). 

Ca EXPLANATION 

. Analysij from Robarts, 11964) 

0 

This report; sample number 

same as in table 1 

Altered specimen 

/// 

Domain of unaltered rocks 

Domain of altered rocks 

K 

FIGURE 7.-Distribution of Ca, Na, and K in 18 specimens 

of plutonic rocks (both altered and unaltered) from the 

Battle Mountain mining district. 

and hornblende is commonly partly altered to biotite. 

The most intensely altered rocks (specimens 17 and 

18, table 1 and fig. 7) are samples of two dikes, 4.5 and 

6.0 meters wide, emplaced into the Battle and Harmony 

Formations, respectively, in the east ore body of the 

Copper Canyon porphyry copper deposit. Eight of the 

nine altered specimens shown in figure 4 are from the 

general area of Copper Canyon; the remaining sample 

of altered rock (specimen 16) is from the Elder Creek 

area, at the north end of the mining district. The 
A8 GEOCHEMISTRY OF PORPHYRY COPPER, BATTLE MOUNTAIN MINING DISTRICT, NEVADA 

TABLE 1.- Analyses of intrusive rocks 

[·······, not detected or calculated; N .A., not analyzed. Biotite from Nos. 3-9 was subjected to K-Ar analysis for age 

Specimen and location number, same as table 7, and figs. 3, 4 Field number (MB-) 3 4 5 20 12 16 

Rapid rock chemical analyses (weight percent)4 

SiO, -------------------------------------------------------------------- AI,O, ................................................................. . Fe,O, ................................................................. . 

FeO -------------------------------------------------------------------- MgO ------------------------------------------------------------------ CaO ................................................................... . Na,O ................................................................. . K,O ................................................................... . H,o- .............................................................. .. H,O + ................................................................ . TiO, ................................................................... . 

P,o. ------------------------------------------------------------- ------- Mno ------------------------------------------------------------------ CO, ................................................................... . 

Total ..................................................... . SasSO, .......................................................... .. 

Q ....................................................................... . c ........................................................................ .. or ....................................................................... . ab ..................................................................... . 

an ---------------------------------------------------------------------- Normative an .................................................. . wo ..................................................................... . en .................................................................... .. fs ....................................................................... . mt ..................................................................... . il ....................................................................... . 

ap ---------------------------------------------------------------------- cc ------------------------------------------------------------------------

Total ..................................................... . 

AI ---------------------------------------------------------------------- Fm ................................................................... . c ....................................................................... . Alk ----------------------------------------------------------- --------- Si ....................................................................... . 

Ti ------- ------------------------------------------ --------------------- p ...................................................................... .. H ....................................................................... . K ....................................................................... . Mg ................................................................... . Q ....................................................................... . 

64.5 

15.4 

1.3 

2.7 

2.9 

4.7 

3.1 

3.2 

.43 

.87 

.46 

.11 

.06 

.09 

100 

19.7 

18.9 

26.3 

18.7 

(An..) 

1.4 

7.2 

3.2 

1.9 

.9 

.3 

.2 

98.7 

33.9 

28.4 

18.8 

18.9 

241.0 

1.3 

.17 

16.2 

.40 

.57 

65.6 

66.3 

15.2 

.62 

2.8 

3.0 

4.5 

3.0 

2.6 

.09 

1.0 

.54 

.10 

.05 

<.05 

100 

CIPWnorms 

23.7 

15.4 

25.4 

20.4 

(An..) 

.6 

7.5 

3.8 

.9 

1.0 

.2 

98.9 

Niggli numbers 

34.9 

28.5 

18.8 

17.8 

250.5 

1.6 

.16 

14.2 

.36 

.61 

87.1 

65.6 

16.2 

.81 

2.9 

1.8 

3.8 

3.4 

3.2 

.20 

.73 

.51 

.17 

.08 

<.05 

99 

21.8 

.8 

19.0 

28.9 

17.3 

(Anas) 

4.5 

4.0 

1.2 

1.0 

.4 

.2 

99.1 

38.6 

23.4 

16.5 

21.6 

265.2 

1.6 

.29 

12.5 

.38 

.46 

78.9 

6 

21 

64.4 

16.3 

.50 

3.0 

2.5 

4.1 

3.3 

3.0 

.00 

.91 

.58 

.11 

.08 

1.2 

100 

22.9 

3.2 

17.7 

27.9 

12.0 

(An,.) 

6.2 

4.3 

.7 

1.1 

.3 

2.7 

99.0 

Semiquantitative spectrographic analyses (weight perceut)6 

Ag ...................................................................... 0.00007 

B ------------------------------------------------------------------------ Ba ---------------------------------------------------------------------- Be ..................................................................... . Co ..................................................................... . Cr .................................................................... .. Mo ................................................................... . Nb .................................................................... .. 

Ni ------------------------------------------------------------------ Sc ..................................................................... . Sn ..................................................................... . Sr ................................................................. . v ....................................................................... . w ---------------------------------------------------------------------- y ------------------------------------------------------------------------ Zr ..................................................................... . Ga ..................................................................... . Yb ..................................................................... . La ..................................................................... . Ce ..................................................................... . 

Au .................................................................... .. Cu ..................................................................... . 

See footnotes at end of table. 

.15 

.00015 

.001 

.015 

.0007 

.005 

.0015 

.07 

.007 

.001 

.015 

.0015 

.00015 

0.1 

.00015 

.0015 

.015 

.0007 

.005 

.0015 

.07 

.01 

.0015 

.01 

.0020 

.00015 

Chemical analyses (ppm)1 

0.1 

.0002 

.001 

.002 

.001 

.0005 

.001 

.05 

.01 

.002 

.01 

.0015 

.0002 

0.07 <0.05 <0.05 

6.6 120. 7.6 

0.07 

.0002 

.001 

.01 

.003 

.0015 

.05 

.01 

.001 

.01 

.0015 .00015 

<0.05 

4.2 

7 

9 

68.4 

15.6 

.73 

1.7 

1.5 

3.6 

3.9 

3.0 

.09 

.75 

.35 

.08 

.03 

.10 

100 

24.0 

17.8 

33.1 

16.2 

(Ail:J,) 

.2 

3.7 

2.0 

1.1 

.7 

.2 

.3 

99.3 

40.0 

18.4 

16.8 

24.8 

297.1 

1.2 

.15 

12.2 

.34 

.53 

98.6 

0.15 

.0002 

.001 

.005 

.0007 

.001 

.0007 

.07 

.005 

.001 

.01 

.0015 

.0001 

<0.05 

4.8 

8 

19 

69.1 

15.0 

.43 

1.7 

2.2 

2.7 

2.1 

3.7 

.41 

1.3 

.38 

.07 

.03 

<.05 

99 

33.2 

2.8 

22.1 

17.9 

13.1 

(An..) 

5.5 

2.2 

.6 

.7 

.2 

98.3 

0.0007 

.0007 

.2 

.0003 

.0007 

.007 

.001 

.001 

.003 

.001 

.05 

.007 

.0015 

.015 

.0015 

.00015 

0.4 

900. 
GEOCHEMISTRY AND POTASSIUM-ARGON AGES, PLUTONIC ROCKS, LANDER COUNTY, NEVADA A9 

in the Battle Mountain mining district 

determination. Specimens 6, 8, 9, 12, and 16-18 were hydrothermally altered; Niggli Nos. were not calculated for them] 

Hornblende- 9 12 15 16 17 18 Biotite biotite Average 18 40 10 11 17 28 granodiori te1 granodiorite2 granodioriteS 

Rapid rock chemical analyses (weight percent)4 

70.5 64.0 62.5 70.5 66.9 67.2 68.97 65.50 66.88 

14.5 15.1 16.9 14.5 14.7 15.8 15.47 15.65 15.66 

1.0 2.0 1.6 .90 .92 1.2 1.12 1.63 1.33 

.16 3.1 3.4 1.0 1.6 1.5 2.05 2.79 2.59 

1.5 3.5 2.9 1.5 2.7 2.5 1.15 1.86 1.57 

.95 3.5 4.8 2.2 .29 .94 2.99 4.10 3.56 

2.1 1.5 3.3 2.1 .53 .93 3.69 3.84 3.84 

6.1 4.3 2.4 5.6 6.6 5.5 3.16 3.01 3.07 

.50 .44 .25 .26 .93 1.2 

1.5 1.5 .85 .84 2.2 2;5 .70 .69 .65 

.47 .51 .75 .43 .78 .47 .45 .61 .57 

.00 .16 .18 .07 .07 .14 .19 .23 .21 

.00 .02 .09 .00 .00 .01 .06 .09 .07 

<.05 <.05 .14 <.05 <.05 <.05 

100 100 100 100 98 100 100 100 100 

1.5 

CIPWnorms 

31.2 25.2 18.6 30.2 35.0 26.2 20.0 21.9 

3.2 2.0 .9 1.5 7.0 .7 

36.0 25.5 14.2 33.0 32.5 18.9 17.8 18.3 

17.7 12.7 27.9 17.8 7.9 31.4 32.5 32.5 

3.4 16.4 21.7 9.6 3.7 14.2 16.4 16.4 

(Aih&) (A!hs) (AI44) (A11a5) (A11a2) (A11a1) (Ana4) (Ana4) 

.9 

3.7 8.7 7.2 3.7 6.2 2.9 4.6 3.9 

1.3 3.2 3.8 .6 1.0 2.2 2.9 2.9 

1.2 2.9 2.3 1.3 1.7 1.6 2.3 1.9 

.9 1.0 1.4 .8 .9 .8 1.2 1.1 

.2 .4 .4 .2 .3 .4 .6 .5 

.3 .3 .3 

599.2 98.0 98.7 99.0 96.2 99.3 99.2 99.4 

Niggli numbers 

35.2 

29.9 

18.2 

16.7 

221.0 

2.0 

.27 

13.0 

.32 

.51 

54.1 

Semiquantitative spectrographic analyses (weight percent)6 

0.0002 0.0005 0.0001 0.0007 0.001 

.0007 .0007 .0007 --------·--- .15 .3 0.07 .07 .2 .5 

.0002 .00015 .0002 

.001 .002 .0015 .0003 .005 .0005 

.01 .02 .005 .007 .02 .015 

.003 .0005 .0003 

.001 .0007 .001 .0007 .0007 .0007 

.005 .005 .0002 .002 .007 .0015 

.001 .0015 .0015 .0007 .0015 .0015 

.0007 .0007 

.03 .05 .07 .05 .02 .03 

.01 .01 .01 .005 .01 .01 

.015 

.0007 .0015 .002 .001 .001 .003 

.01 .007 .015 .007 .01 .01 

.002 .002 .0015 .0015 .0015 .002 

.00001 .00015 .0002 .0001 .00015 .0002 

.003 .005 

.007 .01 

Chemical analyses (ppm)7 

0.1 N.A. <0.05 <0.05 0.3 N.A. 

1500. 990. 16. 460. 6600. 555. 

See footnotes at end of table. 
A10 GEOCHEMISTRY OF PORPHYRY COPPER, BATTLE MOUNTAIN MINING DISTRICT, NEVADA 

TABLE I.-Analyses of intrusive rocks in the 

Specimen and location number, same as table 7, and figs. 3, 4 Field number ( MB-) 

3 4 5 6 

21 7 8 20 12 16 9 19 

Chemical analyses (ppm)7-Continued 

Ph ..................................................................... . 14. 20. 20. 28. 

50. 

4.2 

6.9 

<LO 

20. 22. 

Zn ..................................................................... . 44. 140. 29. 43. 160. 

u ········································································ 2.3 3.6 4.7 2.4 4.3 

Th ..................................................................... . 8.0 8.2 7.2 9.6 6.9 

Hg ······································································ <1~ <1~ <1~ <LO <LO 

Rb ..................................................................... . 102 119 126 111 

540 

120 147 

Sr ..................................................................... . 640 590 490 570 414 

(Rb:Sr) ........................................................... . (.159) (.202) (.257) (.206) 

(223) 

(.211) (.356) 

(K: Rb) ........................................................... . (259) (220) (215) (222) (217) 

1 Average of 36 biotite granodiorites from Noekolds ( 1954, p. 1014). 2 Average of 65 hornblende-biotite granodiorites from Nockolds (1954, p. 1014). 3Average of 137 granodiorites from Nockolds (1954, p. 1014). 

4 Chemical analyses by rapid rock method; analysts: P. L. D. Elmore, Lowell Artis, J. L. Glenn, Gillison Chloe, J. Kelsey and Hezekiah Smith. Methods used are those described in Shapiro, L., and Brannock, W. W., 1962, Rapid Analysis of silicate, carbonate, and phosphate. ' 5 Includes 0.1 percent normative hematite. 

changes due to alteration, depicted diagrammatically 

in figure 7, primarily reflect potassic metasomatism 

-the K-feldspar, white mica (biotite) facies of Creasey 

(1966)- in the general area of the porphyry copper 

deposit at Copper Canyon (Roberts and Arnold, 1965; 

Nash and Theodore, 1971; Theodore and Blake, 1973). 

The trend shown by the altered rocks (fig. 7) is one of 

progressive leaching of CaO and addition of K20 concomitant with increasing intensity of potassic alteration. Alteration of specimen 6 (table 1; fig. 7) appears 

to have consisted primarily of groundmass recrystallization, with negligible addition of K20. 

From the data plotted in figures 6 and 7, we infer 

that, before alteration, the intrusive rocks at Copper 

Canyon were granodiorites. Truly unaltered specimens 

of these rocks have not been found at Copper Canyon. 

Modally the rocks are now quartz monzonites (Roberts, 

1964; Clement, 1964; Blake, unpub. data). To emphasize further the chemical contrasts between the altered 

and unaltered plutonic rocks, we have also shown in 

figure 6 plots of normative Q, Ab +An, and Or ratios in 

molecular proportions for the altered specimens analyzed. These plot as normative quartz monzonites and 

granites. Similar chemical contrasts between altered 

and unaltered intrusive bodies associated with porphyry copper deposits have been reported elsewhere 

(see Moore, 1970b). Creasey (1966, p. 52) found that 

the norms of unaltered porphyries associated with 

seven of the Arizona porphyry copper deposits cluster 

in the granodiorite field, near the granodiorite-quartz 

monzonite boundary. 

For each of the recognized intrusive sequences in the 

Sierra Nevada batholith, Bateman and Dodge (1970) 

found a systematic (almost linear) decrease in the 

K20: SiO:! ratio with decreasing SiO:!. They showed that 

KzO-SiO:! plots define trends that intersect zero K20 

at about 40-45 weight percent SiO:!. Similar K:!O-SiOz 

plots from the granodiorite analyses of Battle Mountain define a remarkably similar trend whose projection 

intersects zero K20 at about 45 weight percent Si02. 

However, chemical data available from plutons across 

much of north-central Nevada (M. L. Silberman, 

unpub. data) suggest a slightly different average trend 

for the region: zero K20 would be intersected at about 

50 weight percent Si02. 

MINOR ELEMENTS 

Trace elements in the plutons are typical of those 

commonly associated with granodiorites or potassicaltered granodiorites. The trace element contents of 

the specimens selected for rapid rock analyses are 

shown in table 1. As an aid to estimate better the areal 

variations of metallic trace elements in the stocks, concentrations across nine of the intrusive bodies (both 

altered and unaltered) are listed in table 2. The samples 

in table 2 were collected from localities spanning the 

entire exposed plutons. Each sample is a composite 

weighing a total of about 1 kilogram collected over an 

outcrop area of about 10 sq. m; sample group 6 (AEH926, AEH-927), however, represents composite drill 

core samples. 

Estimates by Vinogradov ( 1962) and Turekian and 

Wedepohl (1961) of average abundances of minor elements in selected rock types are shown in table 3. Compared with these estimates, unaltered granodiorite 

from the Battle Mountain mining district is generally 

poorer in Nb, Y, Zr(?), La, and Hg, and generally 

slightly richer in Sc. In addition, many of the granodiorite plutons display individual differences. The granodiorite of Trenton Canyon, for example, is richer in Cu 

and Mo. The granodiorite of the Elder Creek area is 

richer in Cu, Cr, and W. (W occurs as very sparse disseminated grains of scheelite.) Granodiorite of the 

Long Peak area is richer in Mo, and granodiorite of the 
GEOCHEMISTRY AND POTASSIUM-ARGON AGES, PLUTONIC ROCKS, LANDER COUNTY, NEVADA All 

Battle Mountain mining district-Continued 

Hornblende- 9 

18 12 

40 15 

10 

16 17 18 Biotite biotite Average 11 17 28 granodiorite granodiorite3 1 granodiorite2 

Chemical analyses (ppm)7-continued 

20. 

110. 

33. 

245. 

1.9 

6.0 

<LO 

140 

348 

17. 

59. 

1.7 

7.4 

<1.0 

14. 21. 18. 

26. 31. 39. 

9.0 

5.4 

<LO 

2.3 5.1 2.1 

6.6 6.3 15. <1~ <1n <1n 

215 87 121 274 175 

319 

(.675) 

570 

(.153) 

231) 

429 209 204 

(.403) 

(255) 

(.283) (1.31) (.857) 

(245) (382) (203) (261) 

6Analyst: Chris Heropoulos. Results are reported to the nearest number of the series 1, 0.7, 0.5, 0.3, 0.2, 0.15, .......... , which represent approximate midpoints of interval data on a geometric seale. The precision of a reported value is approximately plus or minus one series interval at 68 percent confidence. 

Looked for but not found: As, Au, Bi, Cd, Pd, Pt, Sb, Te, U, Zn, Ge, Hf, In, Li, Re, Ta, Th, Tl. Also looked for but not found in samples 12 and 18: Pr, Nd, 

Sm and Eu. 7 Au was determined by a combined fire-assay atomic absorption technique; analyst: Carroll L. Burton. Cu, Pb, and Zn were determined by atomic 

absorption spectroscopy; analyst, Carroll L. Burton. U was determined fluorimetrieally; analyst, Joseph Budinsky. Th was determined by instrumental neutron activation analysis; analysts: Carroll L. Burton and F. 0. Simon. Hg was determined speetrophotometrieally by a Penfield-dithizone method; analyst: Jesse J. Warr. Rb and Sr were determined by x-ray spectroscopy; analysts: B. P. Fabbi and L. F. Espos. 

Timber Canyon area is slightly richer in Cu. 

Additional data for whole-rock Ba, Rb, and Sr in the 

five unaltered granodiorites provide background levels 

with which to compare these elements in altered rocks 

(table 1). Ba concentrations are in the 700-1,500 ppm 

range; Rb, 87-126 ppm; and total Sr, 490-640 ppm. 

These Ba and Sr values are slightly higher than the 

tabulated crustal abundances for rocks of this composition (table 3). Also, the average K:Rb ratio for these 

five specimens (229) is nearly identical with that for 

crustal rocks (230) (Heir and Adams, 1964), and well 

within the range of reported K:Rb ratios for "granitic" 

rocks (fig. 8). Ba:Rb ratios for the five granodiorites 

are about 10, and Rb:Sr ratios are in the 0.153-0.257 

range. The geochemical data (table 1) for the unaltered 

granodiorites of Battle Mountain also indicate a direct 

relationship between silica content and both K20 and 

Rb. Furthermore, a K: Rb versus Rb: Sr variation plot 

for these unaltered granodiorites is consistent with the 

results obtained in plutonic rocks over a broad area of 

/ 

/ 

/ 

/ 

/ 

/ 

"' Altered granodiorites 

(this report) 

"Granitic" rocks 

(Heir and Adams, 1964,p. 286) 

FIGURE B.-Plots of K (in percent) : Rb (in ppm) for 

average crustal rocks, "granitic' rocks (modified from 

Heir and Adams, 1964),andfivespecimensofunaltered 

granodiorite from the Battle Mountain mining district. 

north-central Nevada (M. L. Silberman, unpub. data). 

Percentages of several minor elements in altered 

granodiorite of the Copper Canyon area are significantly different from those in the unaltered granodiorites. The altered rocks are enriched in Cu. However, 

because of the extreme mobility of Cu during supergene 

processes, it is very difficult to use these data to evaluate overall levels of Cu enrichment that occurred 

during potassic alteration in the granodiorites. The 

geochemical data (tables 1 and 2) also suggest that 

alteration resulted in widespread but relatively low 

level increases in Ag, Mo, and possibly B contents. The 

altered granodiorite of the Copper Canyon area 

(sample location 9, table 2) also appears to be somewhat more enriched in As and Zn than the other granodiorites. The altered granodiorite of the Iron Canyon 

area (sample location 6, table 2) contains relatively 

high concentrations of As (300 and 2,000 ppm). Also, 

increases in the Rb: Sr ratios of the altered rocks (table 

1) correlate remarkably well with increasing potassic 

alteration. (Compare table 1 with figure 6.) These 

results are not unexpected, as Rb closely follows K, and 

Sr follows Ca. K ( + Rb) was apparently added to the 

rocks during alteration whereas Ca ( + Sr) was lost. 

The most intensely altered specimen (17, table 1) 

appears to contain more than twice as much Rb as the 

unaltered granodiorites, and about one-third as much Sr. 

The average K:U ratio for all Battle Mountain 

plutonic rocks, altered and unaltered, is 1.1 X 104, about 

the same as for most igneous rocks (Heir and Rogers, 

1963; Tilton and Reed, 1963). The average K:U ratio 

for the seven altered rocks is 1.5 X 104 • 

BIOTITE COMPOSITIONS 

In an attempt to resolve ambiguities of age determinations on primary phenocrystic biotites in hydro-
A12 GEOCHEMISTRY OF PORPHYRY COPPER, BATTLE MOUNTAIN MINING DISTRICT, NEVADA 

TABLE 2.-Analyses for selected minor metals in plutonic rocks in the Battle Mountain mining district 

[Spectrographic analyses: Ag, Co, Cr, Cu, Mo, Ni, Pb. Results are reported in ppm to nearest number in the series 1, 0.7, 0.5, 0.3, 0.2, 0.15, 0.1, 0.07, .......... ; these numbers represent approximate midpoints of group data on a geometric scale; analyst, E. F. Cooley. Gold and zinc were determined by an atomic absorption technique; analysts, H. D. McBride and J. G. Viets. Antimony and arsenic were determined by a colorimetric technique; analysts, S. I. Hoffman, H. D. McBride, M. S. Rickard, and A. W. Wells. Mercury was determined instrumentally; analyst, C. A. Cortis ........... , not detected] 

Granodiorite of Trenton Canyon (Location No. 1 and 2, fig. 3) 

Sample No. 179 180 181 182 183 184 185 186 187 188 189 (AHW-) 

Ag .................... 1.0 1.0 <0.5 <0.5 <0.5 

As -------------------- <10 10.0 10.0 40.0 10 20 10 

Au .................... <0.02 <0.02 <.02 <0.02 .02 <.02 <.02 <.02 <.02 <.02 <.02 

Co ....................................... 5 10 10 5 5 5 5 5 5 5 5 

Cr -------------------- 5 10 10 5 5 5 <5 5 <5 5 5 

Cu .................... 50 50 50 100 70 100 70 100 30 50 100 

Hg .................... .02 .03 .02 .03 .04 .05 .06 .02 .28 .24 .22 

Mo .................................... <5 <5 <5 <5 7 5 <5 10 <5 70 70 

Ni ....................................... 10 10 5 10 5 5 5 5 5 5 5 

Ph .................... 10 20 20 20 10 10 <10 15 10 10 10 

Sh -------------------- <1 <1 <1 <1 <1 <1 <1 <1 <1 7 6 

Zn ....................................... 60 50 70 45 50 50 <25 45 55 <25 <25 

Granodiorite of Modoc mine area (Location No. 3, fig. 3) 

Sample No. 114 115 116 117 118 119 120 121 122 123 124 125 126 (AHW-) 

Ag ···················· 2.0 1.0 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 

As ...................................... 10 20 <10 <10 <10 10 

Au .................... .1 .1 .1 .12 .04 .02 .06 .06 .06 .28 .08 .06 .06 

Bi ....................................... 10 

Cr ......................................... 150 150 150 150 150 150 150 150 150 150 150 150 150 

Cu .................... 10 20 10 50 30 20 30 30 30 30 50 30 30 

Hg .................... .09 .04 .04 .03 .03 .03 .02 .03 .03 .02 .06 .03 .03 

Mo ..................................... <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 

Ni ...................................... 30 30 20 30 30 30 30 20 30 30 30 30 30 

Ph ....................................... 200 150 100 10 10 10 10 10 10 10 10 10 10 

Sh ......................................... 16 8 9 <1 <1 <1 2 <1 <1 <1 2 <1 <1 

Zn .................... 1500 2500 300 50 30 30 40 <25 30 30 65 75 75 

Granodiorite of Elder Creek area (Location No. 4, fig. 3) 

Sample No. 157 158 159 160 161 162 163 164 165 166 167 168 (AHW-) 

Ag .................... 2.0 5.0 3.0 1.5 

As .................... 20.0 60 20.0 10.0 20.0 10.0 10.0 10.0 80 120 40 

Au .................... .02 <.02 <.02 .02 0.02 .02 <.02 <.02 <.02 <.02 .02 <.02 

Bi ........................................ 10 

Cr ...................................... 200 <5 100 70 <5 100 150 150 70 50 50 70 

Cu .................... 50 20 100 100 30 50 50 50 200 500 200 200 

Hg .................... .02 .01 .04 .03 .03 .01 .03 .07 .02 .02 .03 .06 

Mo _______________ ,. __ 5 5 10 5 <5 10 5 20 20 5 20 5 

Ni -------------------- 50 10 20 20 5 20 20 20 20 15 15 20 

Ph .................... 30 10 15 20 <10 20 20 15 20 70 20 30 

Sh .................................... <1 12 <1 2 <1 <1 <1 <1 <1 <1 20 9 

w ................................... 150 200 100 50 100 

Zn .................... 40 <25 25 30 <25 40 40 30 30 30 200 50 

Granodiorite of Long Peak (Location No. S, fig. 3) 

Sample No. 210 211 212 213 214 215 216 217 218 219 AEH-9261 AEH-9271 (AHW-) 

Ag ·--················· 0.5 0.5 0.5 0.5 0.5 0.5 0.5 

A.s .................... 40.0 10.0 10 <10.0 60.0 <10 40 <10 20 300 2000 

Au .................... 0.02 .02 <.02 .04 <.02 .02 <.02 .06 .02 .02 .02 .06 

Cr .................................... 20 15 15 10 20 15 10 10 15 10 100 100 

Cu .................... 30 30 20 30 20 70 7(\ 20 20 20 100 50 

Hg .................... .03 .03 .02 .03 .01 .02 .02 .03 .02 .04 .06 .07 

Mo ................................... 15 5 5 10 5 20 10 15 7 <5 

Ni 10 20 10 15 15 15 10 10 10 10 70 20 

Ph:::::::::::::::::::: 15 10 15 20 20 30 20 20 30 20 200 150 

Sh ..................................... <1 <1 2 <1 1 <1 <1 <1 <1 <1 <100 <100 

Zn ....................................... 230 420 40 50 45 70 25 30 35 140 <200 <200 

Granodiorite of Timber Canyon area (Location No. 7 and 15, fig. 3) 

Sample No. 169 170 171 172 173 174 175 176 177 178 (AHW-) 

Ag ··················-· 0.5 0.5 0.5 

As ................................... 10.0 

Au .................... <0.02 .02 .04 <0.02 <0.02 <0.02 <.02 <0.02 <.02 <0.02 

Cr 15 20 30 30 50 20 20 20 30 20 

Cu :::::::::::::::::::: 50 200 200 100 70 50 70 50 50 50 

Hg .................... .02 .02 .03 .03 .05 .03 .04 .04 .04 .04 

Mo .................. <5 5 <5 <5 <5 <5 <5 <5 <5 <5 

Ni 10 10 10 10 10 10 10 10 10 10 

Ph:::::::::::::::::::: 20 20 20 20 15 30 30 20 30 30 

Sh ....................................... 1 2 <1 2 2 <1 <1 <1 <1 <1 

Zn .................... 55 55 75 45 55 55 55 60 70 55 
GEOCHEMISTRY AND POTASSIUM-ARGON AGES, PLUTONIC ROCKS, LANDER COUNTY, NEVADA A13 

TABLE 2.-Analyses for selected minor metals in plutonic rocks in the Battle Mountain mining district-Continued 

Biotite was separated from three different samples 

of altered granodiorite from the Copper Canyon area. 

Typically, these biotites are medium-grained (somewhat greater than 1 mm across), "hexagonal," redbrown plates that are optically homogeneous (fig. 9). 

The plates are single crystals and do not appear to have 

recrystallized during the later potassic alteration. 

Alteration of biotite phenocrysts more than 1 mm 

across is minimal; only a small number show thin rinds 

of bleaching with some marginal chloritization. Some 

of the smaller biotite phenocrysts are somewhat more 

pervasively bleached, with the concomitant development of very fine clusters of sphene. However, these 

more altered biotites were excluded from the final 

separates by size-sieving. Compositions and calculated 

structural formulas of the three biotites are shown in 

lmm 

FIGURE 9.-Photomicrograph of primary biotite from altered 

granodiorite of the Copper Canyon area. Plane polarized light. 

table 4. Implications for pressure-temperature stabilities of their compositions are discussed by Theodore 

and Blake (1973). The first of the three was separated 

from a hand specimen collected from a roadcut (fig. 4; 
A14 GEOCHEMISTRY OF PORPHYRY COPPER, BATTLE MOUNTAIN MINING DISTRICT, NEVADA 

TABLE 3.-Abundance of minor elements in "granitic" rocks 

[Reported in ppm] 

Felsic Inter- g ranites Granites 2 

Element mediate and r ocks 1 grano- Hig h Low diorites 1 calcium calcium 

Ag ········-··········· 0.07 0.05 0.051 0.037 

B ...................... 15. 15. 9. 10 . Ba --------····· ····· · · 650. 830. 420. 840. 

Be -------------------- 1.8 5.5 2. 3. Co ·····--········----· 10. 5, 7. 1. 

Cr -----------·······-- 50. 25. 22. 4.1 

Mo ·········--------- .9 1. 1. 1.3 

Nb ·················- 20. 20. 20. 21. 

Ni .................... 55. 8. 15. 4.5 

Sc ·····--------------- 2.5 3. 14. 7. 

Sn ············-------- 3. 1.5 3. 

v ············-·····---- 100. 40. 88. 44. 

w ·---················ 1. 1.5 1.3 2.2 

y ······------- -·-······ 34. 35. 40. 

Zr -----------········· 260. 200. 140. 175. 

Ga --------··········-- 20. 20. 17. 17. 

Yb ··------------------ 4. 3.5 4. 

La ···········-···----- 60. 45. 55. 

Ce ·----------····----- . 5 2 . 4. 

Au ·······-·······----- .004 .004 .004 

Cu ············-······- 35. 20. 30. 10. 

Pb ···················· 15. 20. 15. 19. 

Zn ···················· 72. 60. 60. 39. 

u ...................... 1.8 3.5 3. 3. 

Th .................... 7. 18. 8.5 17. 

Hg .................... .08 .08 .08 

Rb ···················· 100. 200. 110. 170. 

Sr ···················· 800. 300. 440. 100. 

Sb ···················· .2 .26 .2 .2 

1 Vinogradov, 1962. 2Turekian and Wedepohl, 1961. 

No.9). The other two were separated from composite 

drill core samples (about 100m below ground surface) 

from two different drill holes in the intrusive body. 

K-Ar age determinations were made on two of the biotites (Nos. 9 and 10, table 4), and the rock bulk chemistry was also determined for one (No. 9, tables 1 and 

4). Purity of the three analyzed biotite separates was 

visually estimated to exceed 99 percent. (No magnetite 

was observed in grain mounts of final separates.) However, the anomalously high Cu content (0.2 weight percent) of specimen 9 (table 4) suggests the presence of 

minute inclusions of chalcopyrite in this sample. If we 

then assume that about 0.18 (that is, 0.2- [0.03 + 

0.01] /2) weight percent Cu in this specimen is due to 

the presence of chalcopyrite (CuFeS"), the specimen 

must be contaminated by about 0.5 weight percent 

chalcopyrite, which implies, in turn, that the actual 

Fe"O" content of biotite in specimen 9 is about 0.2 

weight percent less than the reported value, because 

iron in chalcopyrite is in the Fe+3 state (Donnay and 

others, 1958). 

Limited optical and X-ray data were obtained from 

the biotites analyzed (table 4). Their strong pleochroic 

scheme (X < Y= Z) is typical of most biotites; optic 

axial angles are 0° or very nearly. This suggests the 

absence of interleaved polymorphs. We assume that 

the biotites belong to the single layer ( 1 M) polymorph 

of Hendricks and Jefferson (1939)-a polymorph comTABLE 4.-Compositions and structural formulas of biotites 

from granodiorite of the Copper Canyon, Long Peak, and 

Timber Canyon areas [Major elements shown in weight p ercent; analyses of Copper Canyon area by Sarah T . Neil, U.S. Geological Survey, using classical methods, and methods of Ingamells (1962, 1966), Suhr and .lngamells (1966), and Medlin, Suhr, and Bodkin ( 1969); analyses of Long Peak and Timber Canyon areas by P. Elmore, H. Smith, G. Chloe, J. Kelsey, and J . Glenn using rapid rock methods. Minor elements shown in weight percent; semiquantitative spec- trographic analyses by R. E. Mays and Chris Heropoulos, U .S. Geological 

Survey; results are reported in percent to the nearest number in the series 1, 0.7, 0.5, 0.3, 0.2, 0.15, 0.1, 0.07, .......... ; these numbers represent approx i- mate midpoints of group data on a geometric scale. The precision of a reported value is approximately plus or minus one interval about 68 per- cent of the time or two intervals 95 percent of the time. Elements looked for but not found: As, Au, B, Be, Bi, Cd, Ce, Ge, Hf, Hg, In, La, Li, Mo, 

Pb, Pd, Pt, Re, Sb, Sn, T a , Te, Th, Tl, U, W, Y, Yb, Zn. Structural formu· la s calculated on the basis of 24 ( 0 , OH, Cl, F) anions per formula unit. X,Y,-eZsOzo (OH, F, Cl), is assumed to be the general structural formula] 

Specimen and Copper Canyon area 

9 10 19 

Long 

Peak 

area loc. No. (figs. 3, 4) Lab No. Field No. M109678 M109679 M109681 5 W174693 

MB-16 

sio, .............................. .. AlzOa ............................ .. Fe,Oa .......................... .. FeO .............................. .. MgO ............................ .. CaO ............................. . Na,o ............................. . K.o .............................. .. H,O• ............................. . H,O ............................. . TiO, ............................ .. p,o, ............................ .. MnO ............................. . Cl ................................... . F ................................... . 

Cr.Oa ........................... . BaO .............................. .. v.o, ............................ .. Subtotal .......... .. Less O=F, Cl ............. . Total ................. . 

Ag .................................. Co . ................................. Cu ·································· Mo .................................. Nb .................................. Ni .................................. Sc .................................. Sr ·································· Zr ·································· Ga .................... 

Si. 

Al 1v }z t~~} 8.00 

Alvi 

ly Fe+ .181 3 .19 Ti .32 5.46 Mg 3.43 Fe+2 1.34 

Mn ........ J Ca }x .03} Na .03 1.69 K 1.63 

OH ................ 3.96} F ·················· .74 4.80 Cl ............. .10 

MB- 18 MB- 23 MB- 31 

Major elements 

37.81 

15.30 

1.69 

10.97 

15.72 

.21 

10 

8:73 

4.05 

.32 

2.93 

.18 

.02 

.4 

1.69 

.1 

.33 

.1 100.6 .75 99.8 

37.51 

14,70 .51 14.49 

15.12 .36 

,15 

9.12 

3.59 

.08 

2.69 

.32 

.09 

.5 

1.17 

.1 

.37 

.1 101.0 .61 100.4 

36.49 

15 79 

:as 14.49 

15.91 

.16 

.10 

8.48 4.11 .02 

2.91 

,21 

.04 

.4 

1.29 

.1 

.34 

.1 101.3 .63 100.7 

Minor elements 

0.0007 

.002 0.005 0.003 .2 .03 .01 

.003 

.003 .003 .003 .015 .02 .015 .005 .003 .003 .001 

.003 .005 

Structural formulas 

35.8 

14,6 .70 20.1 10.9 .68 

.15 

8.3 

3.8 

.00 

3.5 

.32 

.36 

.02 

.05 

99.3 

0.005 

.0007 

.003 

.003 

.001 

.0015 

.007 

.003 

~:m 8.00 tm8.oo tm 8.00 

"j '"j .171 .06 .04 .08 .30 5.71 .32 5.74 3.36 3.49 2:t~ f 5.81 1.80 1.78 2.59 .01 .01 .05 

.06} .03} .11} .04 1.83 .03 1.65 .05 1.79 1.73 1.59 1.63 

3.57} 4.03} 

:~:~:~} .55 4.25 .60 4.73 .13 .10 

Timber 

Canyon 

area 

7 W174694 

MB-9 

37.2 14.1 

2.7 

1'7.0 

11.5 

1.6 

.44 

7.6 

3.0 

.00 

3 4 

:28 

.34 

99.2 

tm 8.00 

"! .31 

2:~~ 5.84 

2.19 

.04 

.26} .13 1.88 1.49 

~:~~} 

mon to intrusive "granitic" rocks (Smith and Yoder, 

1956, p. 227; Dodge and others, 1969). From the 

method outlined by Wones (1963), cell volumes (table 

5) were first calculated using the biotites' X-ray dspacings of 005 and 060 reflections, the relation bla= 

y3 (Smith and Yoder, 1956) ,and calculated values of (3 

((3=180° - cos-1 (aM/3cM) ) 2 • The values calculated for 

specimens 9, 10, and 19 (table 4) are within 12' of arc 

of the 100°(3 value (Deer and others, 1962, p. 53) 

reported common to 1 M biotite polymorphs. 

2 a, b, a nd care unit translations in angstroms a long a crystal's lattice; the a ng le between a a n d c directions is {3. 
GEOCHEMISTRY AND POTASSIUM-ARGON AGES, PLUTONIC ROCKS, LANDER COUNTY, NEVADA A15 

TABLE 5.-X-ray d-spacings of 005 and 060 reflections, calculated unit cell volumes, and densities of biotites from granodiorite of 

the Copper Canyon and Long Peak areas [Ni-filtered Cu radiation C\Ka=l.54178A). Si (ao=5.4307 A, calibrated against diamond by Steve Huebner), internal standard. 1° and 0.010 slits. Oscillated 

2 cycles with interposed 180° rotation of unoriented smear mount. 1,4 o 2 8 per min scan speed] 

d (060) Cell volume1 Cell volume2 Calculated density3 Measured density 

(A) (A3) (A3) (&4/cc) (g/cc) 

9 ........ Copper Canyon ........ 2.014 1.541 489.8 489.9 2.946 2.945 ± 0.005 

10 ____________________ do ·-------·-----------2.015 1.543 491.2 494.4 3.009 2.990± .005 

19·------·--------·--- do --------------------2.015 1.542 490.6 493.0 2.985 2.970± .005 

5____________ Long Peak ____________ 2.017 1.545 493.0 498.8 3.085 3.049± .005 

GN (see text). 3From Vc= 10_~:oo (see text). 10-24 AVo lFrom Vc=a b c sin {J. 2 From oc 

However, there is some uncertainty regarding use of 

the 060 reflection as a measure of b, because of the 

possibility of an overlapping 331 reflection (Wones, 

1963, p. 1305). Accordingly, unit cell volumes were 

also calculated by the relation, 

GN Vc 10-24Ap~ 

where V c is the calculated cell volume in cubic angstroms, G the formula weight in grams, N the number 

of formulas per unit cell, A Avogradro's number, and 

p 0 the measured density in grams per cubic centimeter 

(Jackson and others, 1967, p. C26). Uncertainties 

( -+-0.005) in measured densities (table 5) primarily 

reflect density variations in the biotites. Nevertheless, 

the close agreement of the unit cell volumes calculated 

from the X-ray-determined d-spacings with those calculated from the formula weights and measured densities (table 5), seems to confirm the biotites' assumed 

polytype and the use of the 060 reflection as a measure 

of b. Lastly, the unit cell dimensions and densities 

(both calculated and measured) of the sample collected 

from the roadcut in the stock (No. 9, table 5) are all 

slightly less than those of biotites from drill holes in 

the pluton (Nos. 10 and 19, table 5). These differences 

may be due to higher concentrations of "oxybiotite" or 

ferric component in this biotite, because Wones ( 1963) 

has shown that the c axis of the unit cell contracts as 

"oxybiotite" increases. 

Structural formulas were calculated from the biotite 

analyses using the computer program described by 

Jackson, Stevens, and Bowen (1967). We assumed 24 

( 0 + OH + F + Cl) anions per formula unit and a minimum of eight cations in fourfold coordination as in the 

general trioctahedral mica formula. 

Interlayer, 12-coordinated cation positions are not 

fully occupied in these biotites. In fact, K, Ca, and Na 

fill only 1.65-1.83 of the available 2.00 sites. Of these 

filled positions, more than 95 percent are occupied by 

K. Ca and N a fill very few, as CaO and N a20 each make 

up less than 0.4 weight percent of the three biotites. 

The interlayer positions in these biotites have unusually 

low occupancy, compared with published structural 

formulas (Foster, 1960; Dodge and others, 1969; Lee 

and Van Loenen, 1970; Moore, 1970a) but are not outside the range others have reported. 

In the biotites from the intrusive body at Copper 

Canyon, octahedral Y group cations occupy from 5.46 

to 5. 7 4 sites, or over 90 percent of the 6.00 octahedral 

sites in the general trioctahedral mica formula (table 

4). Mg makes up about 60 percent of the total Y group 

cations in these micas, and Fe+2 about 30 percent. 

According to Foster's classification ( 1960), these biotites would all be termed magnesian biotites (fig. 10), 

although specimen 9 (table 4) is more intermediate 

between the magnesian biotite and phlogopite fields 

than specimens 10 and 19. Similar high Mg contents 

in biotites from the early-stage porphyry at the Ely, 

Nev., porphyry copper deposit suggested to Fournier 

( 1967, p. 71) a relatively high ratio of sulfur to oxygen 

fugacity during the magmatic stage. Lesser amounts of 

AI, Fe+3, Ti, and Mn fill the remaining occupied Y 

group sites of the Copper Canyon biotites. Ti02 contents and FezOg/ ( Fez03 + FeO) ratios for these biotites are comparable with those of other red-brown 

biotites (Hayama, 1959). 

Almost all AI occurs in the presumably filled, tetrahedrally coordinated Z group cation sites (table 4). 

Mg 

FIGURE 10.-Relation among Mg, Fe+ 2 (Mn+2), and AI 

Fe+3

, Ti) in biotites from the Battle Mountain mining 

district. Biotite classification from Foster (1960). 
A16 GEOCHEMISTRY OF PORPHYRY COPPER, BATTLE MOUNTAIN MINING DISTRICT, NEVADA 

And, in all three biotite specimens, OH, F, Cl anions 

total more than the four available positions-primarily 

an effect of the high F contents (more than 0.55 ions 

per formula) of these biotites. These biotites are much 

richer in F than biotites from the Sierra Nevada batholith (Dodge, Smith, and Mays, 1969). They are also 

slightly richer in F than magnesian biotite in latitic 

dike rocks in the Bingham mining district (Moore, 

1970a) and generally richer in F than biotites from the 

Snake Range, Nev. (Lee and Van Loenen, 1970). However, Foster (1960) in her extensive compilation of biotite analyses lists several biotites, with appropriate Mg 

contents, whose F concentrations are comparable to 

those at Copper Canyon. 

Compositions of phenocrystic biotites in the pluton 

at Copper Canyon, together with several other factors, 

may have helped to preserve them during metallization. 

Certainly the brine-type fluids ascribed to the metallization processes there circulated through much of the 

intrusion (Nash and Theodore, 1971). Quartz phenocrysts and groundmass quartz are abundantly filled 

with prominent postmagmatic fluid inclusions characterized by N aCl and KCl daughter mineral assemblages. Studies of fluid inclusions yielded filling temperatures in the 310°-380°C range in the east ore body. 

We suggest that some of the pluton's original biotite 

was preserved at these temperatures owing to a combination of several factors: 

1. The ferrous (Fe+ 2 ) nature of most iron in the original 

biotite. Fluids initially in equilibrium with pyrrhotite 

in the system Fe-S-0 at 250°C are typified by maximum oxygen fugacities of about 10-45 atm in a 

slightly acidic environment (Barnes and Czamanske, 

1967). Biotites similar in composition to those at 

Copper Canyon (table 4) probably crystallized initially at prevailing oxygen fugacities higher than that 

suggested by the later pyrrhotite assemblages (see 

below; W ones and Eugster, 1965). Accordingly, these 

biotites may have been "less reactive" to fluids with 

lower oxygen fugacities because their Fe was already 

reduced. Alternatively, subsequent removal of any of 

the biotites' buffers would stabilize the biotite to 

oxygen fugacities lower than those prevailing during 

its crystallization. 

2. Failure of Fe+z in the biotites in these samples to be 

sulfidized suggests domains of relatively "low" sulfur fugacity in the intrusive body at the magmatic 

stage, and also during the hydrothermal stage. The 

samples collected from the intrusion for this study 

are from the "least altered" appearing rock. This in 

turn implies that fluids with relatively high sulfur 

fugacities were not freely circulating. 

3. Reaction rates may have been lower at the temperatures prevailing during the bulk of the metallization. 

Perhaps the metal-bearing fluids were locally 

quenched by mixing with cooler ground waters. 

4. Locally high Mg/H ratios in the fluids. As pointed 

out by Rose (1970, p. 921), there are two critical 

ratios involved in potassic alteration: "***K/H high 

enough in the ore fluid to stabilize and form biotite or 

orthoclase, and in the case of biotite, Mg/H high 

enough to avoid removal of Mg." K-feldspar-quartz 

veins with hydrothermal vein chlorite do occur locally 

through the intrusion and in the porphyry copper 

deposit. 

GRANODIORITES OF THE LONG PEAK AND 

TIMBER CANYON AREAS 

Many of the K-Ar ages of plutonic rocks from the 

Battle Mountain district were determined from grain 

concentrates of medium-grained, euhedral to subhedral 

biotite, seemingly unaltered, yet set in rock samples 

hydrothermally altered to varying degrees. Chemical 

and X-ray study of biotites from unaltered granodiorites (the stocks at Long Peak and Timber Canyon) 

was therefore undertaken in order to learn more about 

the effects of hydrothermal alteration. These data have 

a bearing on the age determinations at Copper Canyon, 

where completely unaltered intrusive rocks have not 

been found. 

The main compositional difference between unaltered 

biotite from the granodiorite at Copper Canyon and 

biotite from the Long Peak stock is in MgO content 

(see fig. 10), and Mg/Mg+Fe+z distribution ratios 

between biotite and whole-rock analyses suggest that 

the differences shown in figure 10 may result from contrasts in original (prealteration) bulk chemical compositions, not from alteration. 

The overall fabric of the granodiorite at Long Peak is 

remarkably similar to that of the altered granodiorite 

of the Copper Canyon area. Phenocrysts of hornblende, 

plagioclase, and quartz (as much as about 6 mm 

across), and generally euhedral biotite laths and plates 

(about 1 mm across), are set in a groundmass of quartz, 

K-feldspar, and accessory minerals. Groundmass grains 

are about 0.2 mm across. The plagioclase crystals (calcic oligoclase to sodic andesine) are clear and complexly 

zoned in an oscillatory manner, with slightly more albitic rims. Quartz in the phenocrysts and groundmass is 

remarkably free of fluid inclusion and, most importantly, does not contain any brine-type fluid inclusions. 

Biotites are strongly pleochroic (X <Y ==Z), with optic 

axial angles close to 0°. They are reddish brown (Y ==Z) 

but a paler red than those from the intrusive body at 

Copper Canyon. In addition, they typically include 

sparse needles of rutile oriented parallel to the (001) 

cleavage direction, and about 1 percent of the biotite 

grains are partly rimmed by chlorite. 

Granodiorite of the Timber Canyon area is also 
GEOCHEMISTRY AND POTASSIUM-ARGON AGES, PLUTONIC ROCKS, LANDER COUNTY, NEVADA A17 

porphyritic, with groundmass grains about 0.01 mm 

across. Biotites from this intrusive body are dark 

brown (Y==Z), with a slight greenish hue. They also 

include minute rutile needles and some magnetite, and 

their optic axial angles are very nearly 0°. 

Structural formulas of both biotites (Nos. 5 and 7,. 

table 4) and unit cell dimensions of one (No.5, table 5) 

were determined as described in the preceding section. 

Cl and F contents of these biotites were not determined 

(because of sample size), and it is probably because 

these data were not available that the discrepancies in 

cell volumes and densities of sample 5 are as large as 

they are. 

Occupancy of the 12 coordinated cation positions by 

K, Ca, and Na in these biotites (Nos. 5 and 7, table 4) 

is about the same as in the biotites at Copper Canyon. 

However, octahedral Y group cation sites are slightly 

more fully occupied, and Mg makes up about 45 percent 

of the total Y group cations. Again, using Foster's 

( 1960) classification, these biotites are intermediate 

between Mg biotites and Fe+2 biotites (fig. 9). Moreover, the iron in these two biotites from the unaltered 

granodiorite samples is largely Fe+2 (table 4). This is 

especially so in the biotite from the stock at Long Peak, 

which is texturally very similar to the intrusive· body at 

Copper Canyon. Most AI in the biotites from the Long 

Peak and Timber Canyon intrusive bodies is tetrahedrally coordinated in the Z group cation sites (table 4). 

K-Ar AGES 

K-Ar ANALYTICAL PROCEDURE AND PRECISION 

Bulk rock samples were prepared for mineral separation by crushing and sieving to retain the 1-0.1-mm-size 

fraction. An electrostatic mineral separator, heavy 

liquids, and an inclined vibrating table were used to 

prepare the mineral concentrates for K-Ar analysis. 

The mineral concentrates were split with a Jones microsplitter, and separate aliquots were analyzed for Ar and 

K. The purity of mineral separates was usually 99 percent or better, with the exception of several separates 

whose biotites were partially chloritized. Detailed 

sample locations and purity estimates for the mineral 

separates are listed in table 6. Potassium analyses were 

TABLE 6.-Sample locations and descriptions of K-Ar age-dated 

specimens from the Battle Mountain mining district 

Loc. No. (figs. 3 Field and 4) No. 

L ...... MB-25 

Description 

Granodiorite of Trenton Canyon. SW%, sec. 24, T. 32 N., R. 42 E., from outcrop adjacent to road along Trenton Canyon. 

Sparse pyrrhotite along joint surfaces. 

Medium-grained hypidiomorphic-granular hornblende-biotite granodiorite. Very 

slightly porphyritic with some zoned 

andesine phenocrysts ranging up to 7 mm across. K-feldspar and plagioclase slightly 

to moderately sericitized, and brown bioTABLE 6.-Sample locations and descriptions of K-Ar age-dated 

specimens from the Battle Mountain mining district-Continued 

Loc. No. (figs. 3 Field and 4) No. 

2 ........ MB-26 

3 ........ MB-20 

4 ........ MB-12 

5 ........ MB-16 

6 ........ MB-21 

7 ........ MB-9 

Description 

tite (Y =Z) slightly chloritized. Accessory minerals: sphene, apatite, magnetite, 

zircon, allanite (trace), and epidote group 

(trace). 

Granodiorite of Trenton Canyon. SW%, sec. 24, T. 32 N., R. 42 E., from outcrop adjacent to road along Trenton Canyon. 

Medium-grained hypidiomorphic to 

xenomorphic-granular biotite-hornblende 

granodiorite. Slightly porphyritic with 

subhedral brown (Y =Z) biotite, and andesine phenocrysts ranging up to 6 mm across. K-feldspar and plagioclase slightly 

sericitized; biotite slightly chloritized. Accessory minerals: magnetite, zircon, apatite, sphene, epidote group, pyrrhotite 

(trace) and allanite (trace). 

Granodiorite of Modoc mine area. SW%, sec. 30, T. 31 N., R. 43 E. Fine-grained 

porphyritic hornblende-biotite granodiorite. Hornblende phenocrysts (averaging 

about 0.75 mm in their longest dimension), and dark-reddish brown (Y =Z) biotite phenocrysts (about 0.5 mm across) 

set in a predominantly quartz-K-feldspar 

matrix whose grains average about 0.02 mm across. Tabular euhedral to subhedral sodic labradorite phenocrysts (averaging about 1 mm in length but ranging 

up to 5 mm) sparsely altered to white 

mica. Accessory minerals: apatite, magnetite, zircon, pyroxene(?, trace), and 

chlorite (trace). 

Granodiorite of Elder Creek area. SE%, sec. 2, T. 32 N., R. 43 E.; from outcrop about 

500 feet from southwestern contact of 

intrusive body. Medium-grained porphyritic biotite-hornblende granodiorite. Biotite (red-brown, Y =Z), hornblende, plagioclase, and quartz phenocrysts (average 

about 2 mm across) set in a predominantly 

quartz-K-feldspar matrix whose grains 

average about 0.08 mm across. Biotite 

sparsely chloritized. Accessory minerals: 

hematite, sphene, apatite, magnetite(?), 

and zircon(?). 

Granodiorite of Long Peak area. NE%, sec. 26, T. 32 N., R. 43 E., from outcrop about 

15m below summit of Long Peak. Mediumto fine-grained biotite-hornblende granodiorite that is slightly porphyritic. Hornblende, quartz, and zoned plagioclase 

(calcic oligoclase to sodic andesine) 

phenocrysts (about 1 mm across) set in a quartz-K-feldspar-accessory mineral 

groundmass whose grains average about 

0.2 mm across. Reddish-brown biotites 

(Y =Z) include some rutile and are sparsely chloritized. Accessory minerals: 

zircon, apatite, magnetite, sphene, hematite, and pyrrhotite(?). 

Altered granodiorite of Iron Canyon area. NE%, sec. 23, T. 31 N., R. 43 E. Composite sample collected from porphyritic dike 

penetrated by DDH-2 (Theodore and 

Roberts, 1971) between 871.1 and 876.9 m below ground surface. Phenocrysts of 

quartz, plagioclase, and K-feldspar are unaltered, but the matrix has recrystal- lized to a sericite, quartz, and K-feldspar 

intergrowth. Accessory minerals: apatite, zircon, pyrrhotite, bornite, chalcopyrite 

(trace), calcite (trace), and ilmenite(?). 

Granodiorite of Timber Canyon area. NE%, sec. 15, T. 31 N., R. 42 E. Sample col-
AlB GEOCHEMISTRY OF PORPHYRY COPPER, BATTLE MOUNTAIN MINING DISTRICT, NEVADA 

TABLE 6.-Sample locations and descriptions of K-Ar age-dated 

specimens from the Battle Mountain mining district-Continued 

Loc. No. 

(figs. 3 Field and 4) No. 

8 ........ MB-19 

9 ........ MB-18 

10 ........ MB-23 

1L ...... MB-30 

12 ........ MB-40 

Description 

lected from outcrop about 50 m from 

perimeter of stock, in relatively leucocratic core area of compositionally zoned 

granodiorite. Medium- to fine-grained 

porphyritic biotite-hornblende granodiorite. Euhedral plagioclase, biotite (darkbrown, Y =Z), hornblende, and quartz 

phenocrysts (about 1 mm across) set in a chiefly quartz-K-feldspar matrix whose 

grains average 0.01 mm across. Accessory 

minerals: apatite, zircon, and magnetite. 

Altered granodiorite of Wilson-Independ- ence mine area. NW% sec. 28, T. 31 N., 

R. 43 E., sample from outcrop. Mediumgrained altered porphyritic granodiorite. 

Subrounded, partially resorbed quartz 

phenocrysts; biotite phenocrysts (about 1 mm across, and partially recrystallized); 

intensely sericitized plagioclase and Kfeldpar phenocrysts; all set in a quartzK-feldspar-white mica-biotite matrix 

(grains about 0.01 mm across). Accessory 

minerals: sphene, apatite, zircon, chlorite, 

and sulfides. 

Altered granodiorite of Copper Canyon area. SW% sec. 22, T. 31 N., R. 43 E. Hand 

specimen collected from roadcut in intrusive body, 50 m northeast of Duval's primary crusher. Medium- to coarse-grained altered porphyritic granodiorite. Quartz 

phenocrysts (up to 1 em across), variably 

sericitized plagioclase and K-feldspar 

phenocrysts, red-brown (Y = Z) biotite 

phenocrysts, quartz- K-feldspar- white 

mica-chlorite (trace) matrix. Biotite very 

sparsely chloritized with trace amounts 

of included chalcopyrite(?) (see text). 

Accessory minerals: zircon, sphene, apatite, hematite, magnetite(?). and sulfide. 

Altered granodiorite of Copper Canyon area. SW% sec. 22, T. 31 N., R. 43 E. Composite sample of nine drill core splits from 

depths of 74.7 to 131.1 m below ground 

surface. Rock typically coarse- to mediumgrained porphyritic altered biotite granodiorite. Quartz phenocrysts (subangular, 

locally recrystallized, up to 2 em across) ; 

moderately sericitized plagioclase phenocrysts; biotite phenocrysts (red-brown, Y 

=Z, tabular, averaging slightly greater 

than 1 mm long, sparsely chloritized); 

predominantly quartz-K-feldspar-white 

mica-biotite (trace) matrix whose grains are about 0.01 mm across. Accessory minerals: sphene, apatite, chlorite, amphibole 

(trace) , and sulfides. 

Altered granodiorite of Copper Canyon area. SW% sec. 22, T. 31 N., R. 43 E. Composite sample of eight drill core splits from 

depths of 57.9 to 86.9 m below ground 

surface. Rock description same as MB-23, 

except chlorite (trace) typically in nar- row veinlets and amphibole absent. 

Altered granodiorite sill. SE% sec. 21, T. 

31 N., R. 43 E. Composite sample of nine 

drill core splits from depths of 115.8 to 

123.4 m below ground surface. Intensely 

sericitized and pyritized porphyritic 

granodiorite. Remnant quartz, clouded 

plagioclase, and primary biotite phenocrysts set in a fine predominantly white 

mica matrix with minor pyrite. Primary 

biotite phenocrysts (0.5 to 1.0 mm across, 

red-brown Y =Z, and optically homogeneous) are only sparsely chloritized and 

TABLE 6.-Sample locations and descriptions of K-Ar age-dated 

specimens from the Battle Mountain mining district-Continued 

Loc. No. 

(figs. 3 Field and 4) No. Description 

sericitized. Some chlorite along veinlets. 

Accessory minerals: apatite, sphene, ru- tile, and amphibole (trace). 

13 ........ MB-6500 Metallized matrix of Battle Formation. 

14 ........ MB-52 

SW% sec. 22, T. 31 N., R. 43 E., hand 

specimen from 6500 bench of Copper Canyon porphyry copper deposit. Almost 

schistose facies of metamorphosed rock 

belonging to lower member of Battle Formation. Rock consists of very fine, 0.01 mm and less, intergrowths of hydrothermal red-brown (Y =Z) biotite, K-feldspar, quartz, pyrite, chalcopyrite, sericite 

(trace), and sphene(?}. Some relict plagioclase. 

Metallized matrix of Battle Formation. 

SW% sec. 22, T. 31 N., R. 43 E., description same as MB-6500. 

performed by Lois Schlocker (U.S. Geological Survey) 

by flame photometer using lithium metaborate fusion, 

the lithium serving as an internal standard. Argon 

analyses were performed in the U.S. Geological Survey 

laboratory in Menlo Park, Calif., using standard isotope 

dilution procedures (Dalrymple and Lanphere, 1969). 

A Neir-type, 6-inch, 60° sector, mass spectrometer and 

a Reynolds 4~-inch, 60° sector, mass spectrometer, 

both operated in the static mode, were used for mass 

analyses. Analytical precision of the reported ages is 

approximately 2 percent and is based on statistical 

analysis of a large number of replicate potassium analyses and duplicate argon analyses run during the course 

of earlier studies (McKee and Silberman, 1970; Silberman, unpub. data). Constants used are: 

A.e=0.585xl0-10 yr1 

A.f1=4.72xl0-10 yr1 

K40/K=1.22xl0-4 gm/gm 

The analytical data are tabulated in table 7. 

CRETACEOUS GRANODIORITE OF TRENTON CANYON 

The oldest K-Ar ages in the mining district, 87.2 and 

87.0 m.y. (million years) (Late Cretaceous), were 

determined for biotite from two samples of the granodiorite of Trenton Canyon (table 8, Nos. 1 and 2; fig. 3, 

Nos. 1 and 2). The samples (medium-grained biotitehornblende granodiorites) were collected approximately 

0.4 km apart and are within the porphyritic outer margins of the pluton that intrudes argillite and chert of 

the Pumpernickel Formation, chert of the Havallah 

Formation, and conglomerate of the Battle Formation. 

This pluton, with an outcrop area of about 2.5 sq km, is 

the largest exposed igneous body in the district. Sample 

2 has some pyrrhotite both as disseminated grains and 

as fracture coatings; the groundmass and phenocrysts 

appear to be unaltered. 

Following emplacement of the granodiorite of 

Trenton Canyon, there was a gap of about 46 m.y. in 
GEOCHEMISTRY AND POTASSIUM-ARGON AGES, PLUTONIC ROCKS, LANDER COUNTY, NEVADA A19 

TABLE 7.-K-Ar analytical data 

Location No., 

figs. 3, 4 Mineral WK!Oht Radiogenic Ar'• Ar'0 X 10_, Radiogenic Ar'0 

pe;~~nt molejgmX 10-1° K" Total Ar'• Age X10• yrs 

Outside of Copper Canyon area 

!.. .......... Biotite, 3 percent chlorite ( - 20+60 mesh)......................... 7.38 

2 ............ Biotite, <1 percent chlorite (- 20 + 140 mesh)................... 8.20 

9.729 5.219 0.791 87.2±1.7 

10.78 5.206 .762 87.0±1.7 

3 ............ Hornblende, <1 percent pyroxene ( -100 + 150 mesh) ..... .685 .4205 2.429 .232 41.1±1.4 

3 ............ Biotite, 2 percent chlorite, matrix (-50+ 150 mesh)....... 7.20 4.209 2.315 .622 39.2±0.8 

4 ............ Biotite, <1 percent chlorite ( -48+80 mesh)..................... 8.43 4.691 2.204 .663 37.3±0.7 

5 ............ Biotite, <1 percent chlorite ( -42+60 mesh) ................... 8.45 4.699 2.201 .739 37.3±0.7 

6 ............ Biotite, <1 percent sericite ( - 35+60 mesh)..................... 8.82 4.939 2.217 .601 37.5±0.8 

7 ............ Biotite, <1 percent adhering matrix ( - 80 + 100 mesh)... 7.78 4.532 2.307 .828 39.0±0.8 

7 ............ Hornblende, 10 percent biotite ( - 80+ 100 mesh) ............. 2.80 1.620 2.290 .799 38.8±0.8 

8 ............ Biotite, 1 percent chlorite (- 60 + 150 mesh)..................... 7.92 4.518 2.258 .787 38.2±0.8 

Copper Canyon area 

9 ............ Biotite, <1 percent chlorite ( - 60+ 100 mesh)................... 8.54 4.900 2.273 0.865 38.5±0.8 

lO ............ Biotite, no visible impurities ( - 40+80 mesh)................... 9.05 5.155 2.256 .820 38.2±0.8 

lL .......... Biotite, no visible impurities (-80 + 100 mesh)................. 9.38 5.318 2.246 .634 38.0±0.8 

12 ............ Biotite, 2 percent chlorite (-42 + 65 mesh)....................... 9.00 5.048 2.220 .782 37.6±0.8 

13 ............ Whole rock matrix of Battle conglomerate, biotite, 

sericite, K-feldspar, quartz, relict plagioclase 

(-100+150mesh).1............................................................ 9.51 5.283 2.200 .814 37.2±0.7 

14 ............................ do.1 .............................................................................. 2.55 1.411 2.195 .521 37.2±0.7 

1 Sample prepared by crushing to 60 mesh and settling sulfides in methylene iodide. Light fraction was reground to -100 + 150 and mixed thoroughly. 

TABLE 8.-K-Ar ages of rocks from the Battle Mountain 

mining district 

Location No. Name Mineral K-Ar age (figs. 3, 4) ( X 1 0' yr ) 

!.. .......... Granodiorite of Trenton Canyon ............ Biotite .............. 87.2 2 ............ Granodiorite of Trenton Canyon ............ Biotite .............. 87.0 

3 ............ Granodiorite of Modoc mine area .......... Hornblende1 .... 41.1 

3 ............ Granodiorite of Modoc mine area .......... Biotite1 ............ 39.2 4 ............ Granodiorite of Elder Creek area .......... Biotite .............. 37.3 

5 ............ Granodiorite of Long Peak area ............ Biotite .. ........... 37.3 6 ............ Altered granodiorite of Iron Canyon area.2 .•. ..••..•...•..•.•............. Biotite .............. 37.5 7 ............ Granodiorite ............................................. Biotite' ............ 39.0 7 ............ Granodiorite .............................................. Hornblende' 38.8 

8 ............ Altered granodiorite of Wilson- Independence mine area ....................... Biotite ........ 38.2 

9 ............ Altered granodiorite' of Copper 

Canyon area ............................................. Biotite(l) . ...... 38.5 

10 ............ Altered granodiorite' of Copper Canyon area ............................................. Biotite(II) ...... 38.2 ll ............ Altered granodiorite' of Copper 

Canyon area ............................................. Biotite (III) .... 38.0 12 ............ Altered granodiorite sill' 3 ...................... Biotite .............. 37.6 13 ............ Matrix of mineralized conglomerate, 

Battle Formation, Copper Canyon 

porphyry copper deposit.• ................... Whole rock (I) .. 37.2 

14 ............ Matrix of mineralized conglomerate, Battle Formation, Copper Canyon 

porphyry copper deposit.• .......... ........ Whole rock (II) 37.2 

1 Mineral pair from same bulk sample. 

'Drill core. •see text. • Biotite-K-feldspar-white mica-<Iuartz- (plagioclase) -bearing matrix sepa- rated from pyrite-chalcopyrite-rich rock specimen collected from 6500 bench. 

Copper Canyon porphyry copper deposit. Samples 13 and 14 are from differ- ent locations on the bench. 

the intrusive igneous record. All 14 remaining K-Ar 

ages on intrusive rocks in the district fall between 37 

and 41 m.y., placing them in the latest Eocene and 

earliest Oligocene(?) Epochs. Thus, the K-Ar ages in 

the district span a 50-m.y.-time interval from Late 

Cretaceous to late Eocene or early Oligocene (table 8). 

TERTIARY GRANODIORITE AND 

ALTERED GRANODIORITE 

SAMPLES COLLECTED OUTSIDE THE 

COPPER CANYON AREA 

Six intrusive bodies outside the Copper Canyon area 

yjelded K-Ar ages of 41.1 to 37.3 m.y. from biotite and 

hornblende mineral concentrates. K-Ar ages of 41.1 

m.y. and 39.1 m.y. were obtained from hornblende and 

biotite, respectively, separated from a sample of porphyritic biotite-hornblende granodiorite intrusive into 

chert and calcareous sandstone of the Havallah Formation at the Modoc mine, in the southern part of the 

district (No. 3, table 8 and fig. 3). Biotite separated 

from samples of porphyritic granodiorite intruding 

sandstone and arkose of the Harmony Formation in 

the upper plate of the Dewitt thrust, at Elder Creek, 

and at Long Peak (fig. 3, Nos. 4 and 5), both gave 

37.3-m.y. ages (table 8, Nos. 4 and 5). 

Medium-grained biotite (greater than 1 mm across) 

separated from a composite sample of a porphyritic 

granodiorite dike, intruding chert and argillite of the 

Scott Canyon Formation intersected in a drill hole, 

approximately 1,050 m beneath the present erosion 

surface (fig. 3, No.6), yielded a 37.5-m.y. age (table 8, 

No.6). Phenocrysts of biotite, quartz, plagioclase, and 

K-feldspar are unaltered in this sample, but the groundmass has recrystallized to an intergrowth of white mica, 

quartz, and K-feldspar. Ages of 39.0 and 38.8 m.y., 

respectively, were obtained from a biotite and a compos:lte hornblende-biotite concentrate separated from 

the core of a small porphyritic biotite-hornblende 

granodiorite stock intruding chert and quartzite of the 

Havallah Formation near the southwest corner of the 

district (fig. 3, No.7). Biotite separated from an altered 

granodiorite plug near the Wilson-Independence mine, 

about one-third km southwest of the main intrusion at 

Copper Canyon (fig. 3, No. 8), yielded an age of 38.2 

m.y. The remaining six K-Ar age determinations in the 

district come from the Copper Canyon area. 

COPPER CANYON AREA 

Biotites from the altered granodiorite of the Copper 

Canyon area have been described above. They gave 
A20 GEOCHEMISTRY OF PORPHYRY COPPER, BATTLE MOUNTAIN MINING DISTRICT, NEVADA 

K-Ar ages of 38.5, 38.2, and 38.0 m.y. (Nos. 9-11, table 

8 and fig. 4). 

An altered sill emplaced along the Golconda thrust 

was intersected in a drill hole (collared about 150 m 

north of the Copper Canyon intrusive body) at a depth 

of 116-125 m below ground surface. Feldspar phenocrysts and groundmass minerals of the sill are extensively altered to white mica, and the rock contains 

pyrite plus some chlorite, mainly along microfractures. 

Red-brown biotite plates are again optically homogeneous and contain minute amounts of quartz and magnetite. An age of 37.6 m.y. was obtained on biotite 

separated from a composite sample of the sill (No. 12, 

table 8 and fig. 4). 

Finally, two samples of metallized rocks from the 

Battle Formation were collected from the 6500 bench 

of the porphyry copper deposit at Copper Canyon. 

Attempts to obtain a clean biotite separate were not 

successful at first, because the grains are so small 

( <0.01 mm, fig. 11). However, a sample suitable for 

dating was acquired first by crushing the rocks to 60 

mesh and then by settling the sulfides in methylene 

iodide. The light fraction (which consisted of quartzbiotite-white mica and K-feldspar with some relict 

plagioclase) was reground to 100-150 mesh, thoroughly 

mixed, and then analyzed forK and Ar. The two separates varied in K content by a factor of 5, due to differing proportions of K-feldspar and quartz, but both 

yielded ages of 37.2 m.y. (Nos. 13 and 14, table 8 and 

fig. 4). 

SIGNIFICANCE OF THE DATA 

Metallization at Copper Canyon occurred during a 

hydrothermal stage that closely followed the emplacelmm 

FIGURE H.-Photomicrograph of hydrothermal biotite (Bio), 

K-feldspar and quartz (KQ), and pyrite and chalcopyrite 

(PC) from the Middle Pennsylvanian Battle Formation, 6500 

bench, Copper Canyon porphyry copper deposit. Plane polarized light. 

ment of the Copper Canyon intrusion. The hydrothermal fluid ( s) giving rise to the wallrock ore also 

were responsible for alteration and recrystallization of 

the groundmass of the intrusive body. The relative ages 

of granitic host rocks and porphyry-type copper 

deposits have been the subject of considerable investigation. Most of the studies that have been done using 

the K-Ar method have shown that the age of mineralization as determined on hydrothermal biotite or muscovite is the same within analytical uncertainty as the 

age of the granitic host rock (Creasey, in Anderson, 

1968; McDowell and Kulp, 1967; Livingston and 

others, 1968; Damon and Mauger, 1966; Laughlin and 

others, 1969). Damon and Mauger (1966, p. 106) summarized these relations in stating that the age data 

require that the processes of mineralization are 

restricted in time to the cooling history of the genetically 

associated porphyry. However, two recent detailed 

studies using the K-Ar method have indicated that the 

time interval between emplacement of granitic host 

rocks and some stages of mineralization may be large 

enough to resolve (Moore and Lanphere, 1971; Page, 

1971). The K-Ar age relations of the Copper Canyon 

intrusive body and ore deposits have some bearing on 

this problem. 

The data in table 8 show that the ages of the biotites 

in the intrusive body and the ages of the ore zone 

matrix overlap within the analytical uncertainty ( 0. 7 

m.y.) when individual age determinations are considered, essentially confirming the close relation in time 

between the intrusion and the ore deposit. However, 

when the results are averaged, the age of the intrusion 

is 38.22±0.023 m.y., and the age of the ore deposit, as 

measured by the age of recrystallization of the Battle 

Formation's matrix, is 37.20±0.06 m.y. The averages 

differ significantly at the 85-percent confidence level, 

according to the critical value test of Mcintyre ( 1963). 

The measured age difference between the intrusion and 

the ore deposit is thus statistically resolvable; however, 

it is premature to say that this age difference has 

genetic validity because of two problems in interpreting 

the ages. 

The first problem is whether the biotite ages from 

the intrusive body give a true picture of their age of 

magmatic crystallization at the exposed levels of the 

intrusive body. No unaltered samples of the intrusive 

rock were found during this study, and it might well 

be argued that the biotite ages were reduced by alteration from their true age. As described earlier, 310°-

3800C fluid-inc1usion temperatures were determined in 

the ore zones at the Copper Canyon porphyry copper 

deposit by Nash (Nash and Theodore, 1971). Study of 

Ar retention of biotite in contact metamorphic zones 

(Hart, 1964) has demonstrated that biotite loses Ar 
GEOCHEMISTRY AND POTASSIUM-ARGON AGES, PLUTONIC ROCKS, LANDER COUNTY, NEVADA A21 

at temperatures much lower than these. Converging 

lines of evidence at Battle Mountain, however, strongly 

suggest that the biotite ages of the Copper Canyon 

intrusive body give accurate estimates of its age of 

emplacement: 

1. The biotite K-Ar ages for the altered granodiorite of 

the Copper Canyon area are the same, within the 

analytical uncertainty, as the K-Ar ages from minerals of texturally similar rocks that are unaltered 

elsewhere in the district (table 8). The porphyritic 

granodiorite of the Long Peak area, for example, 

closely resembles granodiorite of the Copper Canyon 

area alid gives a K-Ar age of 37.3 m.y. 

2. Petrographic evidence suggests that some alteration 

may have occurred during late-stage crystallization 

of the intrusive body, when the temperatures would 

normally be high. Roberts and Arnold (1965, p. 11) 

suggested that the ore deposits formed during an 

alteration episode that could be considered a late 

hydrothermal phase of the igneous activity. Some 

cooling, however, of the primary biotites must then 

have continued after most of the alteration had 

ceased. 

Two other factors suggest that these biotites were 

not affected by the alteration in a way that might 

make them lose argon subsequent to cooling: 

3. The studied biotites are optically homogeneous and 

have apparently not recrystallized during the· alteration, the physical conditions for which must have 

been well within their stability field. 

4. Oxygen isotopic analysis of biotite sample 10 (table 

4) by James O'Neil of the U.S. Geological Survey 

gave a 8018 of + 7.17°/oo, which is within the range 

of normal magmatic biotite (James O'Neil, written 

commun., 1970). 

For these reasons, particularly the first, we conclude 

that the 38.2 m.y. age given by the biotites of the Copper Canyon intrusive body is an accurate estimate of 

their age of crystallization. 

The second problem concerning the genetic validity 

is in interpreting the ages of the matrix of the Battle 

Formation in the ore zone. The samples contain disseminated sulfides, and the metasomatic recrystallization of the matrix to a potassium silicate alteration 

assemblage took place during ore deposition. Ore deposition, however, appears to have occurred over a period 

of time, because both the intrusion and the ore zone are 

cut by similar quartz-K-feldspar veins that contain 

sulfides. Some time must have elapsed between intrusion and veining in order for the igneous rock to have 

sustained brittle fracture and for the fractures to have 

then become filled with the sulfide-bearing veins. As 

the ore zones are veined, fluids at temperatures possibly 

up to 400°C (see Theodore and Blake, 1973) must 

have circulated there. The very fine grained material 

dated (K-feldspar-white mica-biotite, 0.01 mm and 

less) would not retain Ar at these temperatures. A 

study of grain size versus Ar retentivity for micas was 

conducted by Hanson and Gast (1967), who compared 

K-Ar and Rb-Sr ages of samples of the Snowbank stock 

in Minnesota at varying distances from the contact 

with the Duluth Gabbro Complex, a lopolith. The 

stock, a granitic body of varying composition, is 

2.6 X 109 years old, and the lopolith is 1.05 X 109 years 

old. The effect of grain size of the biotite from one 

locality on the retentivity of Ar is illustrated in table 9 

(modified from Hanson and Gast, 1967, p. 1132) and 

figure 12. The data illustrate that the retentivity of Ar 

varies as a function of grain size. The maximum temperature at 2.9 km from the contact with the lopolith 

was estimated at about 450°C. The study also demonstrated that biotite lost Ar in a range of temperature 

from 500° to 350°C. A similar study of K-Ar ages in a 

TABLE 9.-Effect of grain size on retentivity of argon~ biotite 

from Snowbank stock~ 2.9 km from contact with Duluth 

Gabbro Complex (sample is 5240a) 

[Modified from table 4, Hanson and Gast (1967, p. 1132)] 

Grain size (mm) K-Ar age1 K-Ar age2 Fraction of 

-1.05 X 109 yr argon retained3 

1.8 ± 0.3 .......................... 2.07 X lOS yr 

.95± .28 ........................ 2.10 x lOS yr .41 ± .11 ........................ 1.90 X lOS yr 

.17± .04 ........................ 1.52 x 100 yr .41 (ground to 0.18) .... 1.91 x 109 yr 

1.02 x 109 yr 0.65 

1.05 x lOS yr .67 

.85 x 109 yr .54 

.47 x 109 yr .30 

.86 x 109 yr .55 

lApparent age of biotite from sample 5240a from Snowbank stock, 2.9 km 

from Duluth Gabbro contact. Age of emplacement of stock is 2.61X109 yr. 2 Age of Duluth Gabbro Complex=1.05 X 109 yr. The Duluth Complex was thus emplaced 1.56 X 109 yr after the Snowbank stock. a After emplacement of Duluth Gabbro Complex, at 1.05 X 109 yr b.p., 

fraction apparent age-1.05 X 109 yr. 

1.56X109 yr 

100 .------..-1----.,-1----.1----,1----, 

1- 75 - z 

w 

C,) 

a: 

w 

a. 

~ 

c· 

~50-

< ti:i 

a: 

z 

0 

c.::l 

a: 

< 25 r0 

.,,..., / 

--=~== 

+ I 

I 

I 

I 

f 

I 

I 

I 

I 

I 

0.5 

I I 

1.0 1.5 

GRAIN SIZE, IN MILLIMETERS 

-

-

I 

2.0 

FIGURE 12.-Effect of grain size on Ar retentivity of biotite 

from Snowbank stock intruded by the Duluth Gabbro 

Complex (from Hanson and Gast, 1967). 
A22 GEOCHEMISTRY OF PORPHYRY COPPER, BATTLE MOUNTAIN MINING DISTRICT, NEVADA 

contact metam"rphic zone adjacent to the Eldora stock 

in the Front Range of the Colorado Rockies indicated 

that biotite lost Ar in the temperature range 500°-

2000C (Hart, 1964) and also indicated a grain-size 

effect on the retentivity of Ar similar to that demonstrated by Hansen and Gast (1967). 

The temperatures in the ore zones at Copper Canyon 

were generally in the 300°-400°C range during the 

early stages of sulfide deposition, but it is difficult to 

compare the two cases of Ar loss mentioned previously 

to that at Copper Canyon because of the mixed nature 

and the metasomatic aspects of the biotite and K-feldspar assemblages dated in this study. The ore-zone 

matrix, because of its very fine grain size, probably lost 

Ar until the ambient temperature dropped to perhaps 

200°C, the lowest probable temperature for which Ar 

loss occurred in the contact zone of the Eldora stock 

(Hart, 1964). The coarse biotite of the Copper Canyon 

intrusive body, on the other hand, probably became 

closed to statistically significant Ar loss at some higher 

but again unknown temperature. 

The K-Ar age of the matrix of the Battle Formation 

thus measures the time at which this assemblage 

dropped below some low but unspecified temperature 

and, similarly, the age of the coarse biotites in the 

granodiorite measures the time at which its ambient 

temperature dropped below some higher value. The 

difference of 1 m.y. between the coarse biotites of the 

granodiorite and the fine-grained matrix of the Battle 

Formation, which is statistically resolvable, cannot 

therefore be interpreted as indicating that a comparable 

interval of time occurred between emplacement of the 

intrusion and the initiation of hydrothermal mineralization. The apparent age difference may simply be due 

to the grain-size effect,)Coarse biotite, or K-feldspar of 

grain size comparable to the coarse biotite in the intrusion, has not been found in the ore zone. K-Ar ages on 

such material would yield more accurate data on any 

time interval that may have occurred. 

At Bingham Canyon, Utah, Moore and Lanphere 

( 1971) found age relations similar to those of Battle 

Mountain between the magmatic biotite from unaltered 

parts of the Last Chance and Bingham stocks and 

hydrothermally recrystallized fine-grained aggregate 

biotite from altered rocks in the ore zone. They demonstrated that coarse, late-stage biotite deposited with 

quartz and sulfides on fracture coatings was younger 

(35.8+0.2 m.y.; average of two determinations on a 

single sample) than magmatic biotite from the Last 

Chance and the Bingham stocks (38.6+0.2 m.y. and 

37.6+0.1 m.y., respectively; both ages are averages of 

three samples). However, this age difference has much 

greater validity than that suggested by the K-Ar data 

at Battle Mountain, because the minerals are of comparable grain size. Their data suggest that the magmatic-hydrothermal system responsible for the igneous 

rocks and ore deposits of Bingham had a lifetime of 

about 3 m.y. We infer, however, the lifetime of the 

system at Battle Mountain to be less than 1 m.y. Suitable coarse-grained mate"'ial for K-Ar age determination in the ore zone might refine this estimate. 

The age relations of altered granodiorite of the Cor--

per Canyon area and ore deposits agree with the generalization made by Damon and Mauger (1966) that 

the processes of ore deposition in the porphyry-copper 

deposits are restricted in time to the cooling history of 

the associated igneous rock. 

SUMMARY 

Intrusive bodies were first emplaced in the Battle 

Mountain mining district during the Late Cretaceous 

( 87 m.y. ago). There was then a quiescent gap of about 

46 m.y. in the intrusive history, and intrusive activity 

finally culminated in late Eocene or early Oligocene 

time (41-38 m.y. ago). The magmatic composition of 

all these intrusions appears to be granodioritic-with 

remarkable major element chemical coherence across 

the entire district. Many of the intrusive bodies in the 

southern part of the district have been altered by fluids 

associated with hydrothermal sulfide deposits. Changes 

in concentrations of many minor elements reflect relative intensities of alteration. We infer no differences in 

major element chemistry before post-magmatic hydrothermal alteration between the intrusive body at 

Copper Canyon and intrusive bodies throughout the 

district not associated with economic copper deposits. 

However, primary magnesian biotites with most of 

their iron as Fe+2 have not everywhere been notably 

affected by the alteration. K-Ar ages of biotite in 

altered granodiorite of the Copper Canyon area are 

different from K-Ar ages in nearby disseminated ore, 

but this difference may be primarily a grain-size effect. 

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Barnes, H. L., and Czamanske, G. K., 1967, Solubilities and 

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batholith: Geol. Soc. America Bull., v. 81, p. 409-420. 

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