Geochemical and Geophysical

Anomalies in the Western Part

of the Sheep Creek Range

Lander County, Nevada

Geochemical and Geophysical

Anomalies in the Western Part

of the Sheep Creek Range

Lander County, Nevada

By Garland B. Gott and Charles J. Zablocki

G E 0 l 0 G I C A l S U R V E Y C I R C U l A R 595

Washington J 968

United States Department of the Interior STEWART l. UDALL, Secretary

Geological Survey William T. Pecora, Director

First printing I 968

Second printing 1968

Free on application to the U.S. Geological Survey, Washington, D.C. 20242

CONTENTS

Abstract ---------------------------------------- -------------------------------------------------------------- ---------------------------------------- ---------------------------------Introduction ___________________________________________ ---------------------------------------------------------------- -------------------- ---- -- ------------------- -------------Geologic environment ---------------------------------------------------------------------------------------------------------------------------------------------------------­Geochemical investigations ------------------------------------------------------ -----------------------------------------------------------------------------------------­

Materials sampled -------------------------------------------------------------------------------------------------------------------------------------------------------­Analytical procedure -------------------------------------------------------- ------------------------------------------------------------------ ------------------------Distribution of metals in the Paleozoic rocks ___ ------------------------------------------------------------------------ ----------- -----------------

Geophysical investigations ______________________ ------------------------------ ___________ -------------------- ------ ----------------- --- --------------- ------------Magnetic data -----------------------------------------------------------------------------------------------------------------------------------------------------------------Gravity data ------------------------------------------- ___________________________ ___________ -- ------------- --------------------------------------Resistivity data ---------------------------------------------------------------- ___________________________________ ------------------- -------- --------------------------

Conclusions -------------------------------------------------------------------------------------------------- -------------------------- -------- ----------------------------References --------------------------------------------------------- ________________________ --------------------------------------

FIGURE 1. 2.

3-10.

11. 12. 13.

14.

15.

ILLUSTRATIONS

Index map of Nevada showing area of this report __ _ ----------------- - ---------------Photogeologic map of part of the Sheep Creek Range showing sampled localities and area of

figures 3-10 _ _____________________ ________________ ------------------------- ------------------------- ----------------------Maps showing highest concentration at each locality sampled for:

3. Zinc _________________________________________ -----------------,------- ________________ -------------------------- _ -------------------------4. 5. 6. 7. 8. 9.

Arsenic ____________________________ _ Mercury _____________ _ Silver _ Lead ______ _ Copper Gold ___________________________ _

10. Tungsten _______________ ____ __________________ _____ __________ ---------------------------------------------Aeromagnetic map of part of the Battle Mountain quadrangle __ __ _ ____ ------------- -----------------------Aeromagnetic and generalized geologic map of the Rennox area _________ ----------- ----- -- ------- --------------Diagram showing comparison of magnetic data taken from aeromagnetic map (fig. 12) witl

model curve for the two-dimensional body shown _ -------------------- --------------------------------Diagram showing comparison of the simple Bouguer gravity values (fig. 12) with model curve

for the two-dimensional structure shown ______ _ _______________________________ ---------------- ---------------Generalized cross section (fig. 12) showing resistivity values of the various zones defined by the

electrical survey and the diagrammatic shape of the bedrock based on the magnetic and gravity models ___ ____________ _ _______________________________ ----------------------------------------------------

III

Page

1 1 3 3 3 3 3

12 12 15 15 16 17

Page

1

2

4 5 6 7 8 9

10 11 13 14

15

16

17

GEOCHEMICAL AND GEOPHYSICAL ANOMALIES IN THE WESTERN PART OF THE

SHEEP CREEK RANGE, LANDER COUNTY, NEVADA

By GARLAND B. GOTT and CHARLES J. ZABLOCKI

Abstract

Extensive geochemical anomalies are present along the west side of the Sheep Creek Range in Lander County, Nev. Anomalous concentrations of zinc, arsenic, mercury, silver, copper, lead, and to some extent gold, molybdenum, and antimony occur in iron-rich material along fracture planes and in quartz veins in Paleozoic formations.

After completion of the fieldwork involving both the geochemical and geophysical investi­gations a photogeologic base map was obtained from Knox-Bergman-Shearer, Photogeohgists, Denver, Colorado (fig. 2). Neither Knox­Bergman-Shearer nor the writers have h:td an opportunity to check this map in the field, but the map suggests the presence of structures related to the geochemical anomalies.

120° 116° 114°

A magnetic anomaly occurs over a pediment at the southern part of the range, close to one of the geo­chemical anomalies. Gravity and electrical resistivity measurements suggest that the magnetic anomaly is caused by an intrusive igneous mass rather than by a block of downfaulted basalt. A limited amount of shallow drilling would clarify the geochemical and geophysical data.

42°'~----------~~----------+-----~----~

INTRODUCTION A geochemical reconnaissance of the west

side of the Sheep Creek Range (fig. 1) was made by R. L. Erickson in 1965. Encouraging results from this survey prompted a more de­tailed investigation during the sumn1er of 1967. Anomalous concentrations of several metals were found throughout an area in which Paleo­zoic cherts and quartzites are exposed. These metals-zinc, arsenic, mercury, silver, lead, copper, gold, molybdenum, antimony, tungsten, and tellurium-occur in such great concentra­tions as to suggest that they constitute a dis­persion halo around or over a concealed mineral deposit. The outcrop belt of the Paleozoic rocks is limited to a narrow strip about 10 miles long on the west side of the range. The geo­chemical anomalies occur throughout this belt and may extend eastward under basalt and westward under alluvial cover.

Geophysical investigations were made in and around an anomalous magnetic feature pre­viously observed on an aeromagnetic map of this area. Results of these investigations sug­gest a shallow exploration target.

1

Elko

40° f

Ren! ~ jOA"'';" Eureka

Elyo

,~TY (

" 0 Tonopah 38°'

" 0 50 100 MILES

FIGURE 1.-Index map of Nevada showing area of this report.

I I

' I I

' I I

'

FIGURE 2.-Photogeologic map of part of the Sheep Creek Range, Lander County, Nev., showing sanpled localities and area of figures 3-10. Photogeology modified from map prepared by Knox-Bergman-She"'Ter, Denver, Colo., 1967.

2

GEOLOGIC ENVIRONMENT One of the major structural features in

north-central Nevada is the Roberts Mountains thrust fault (Roberts, 1964; Gilluly and Gates, 1965). This fault has thrust a western facies of Paleozoic siliceous rocks eastward over a carbonate facies of the same age. Ore deposits in many mining districts of this region are confined to the shattered and crushed rock along the thrust plane or to the carbonate rocks below the thrust plane.

The Paleozoic rocks that are exposed on the west side of the Sheep Creek Range are part of the western siliceous facies of the upper plate of the thrust fault. They consist of inter­bedded cherts and quartzites with some lime­stones and shales (fig. 2). The center of the range is capped by Tertiary basalt flows as much as 1,000 feet thick. Trains of basalt boulders derived from the basalt cap cover the Paleozoic rocks in many areas, and colluvial materials cover the lower slopes. A pediment thinly mantled by alluvium lies along the south­west base of the range.

Some of the interbedded chert and quartzite sequence was identified by R. J. Roberts (oral commun., 1967) as part of the Valmy Formation of Ordovician age, but other Paleo­zoic formations may also be present. In general the beds strike about N. 35° W. and dip about 45° NE. The exposed chert-quartzite sequence is probably several thousand feet thick.

The cherts are mainly gray and grayish brown although some are red, green, or gray­red mottled. The quartzite beds are predomi­nantly light gray and of high purity. Both the cherts and quartzites are highly brecciated and fractured.

Carbonate facies Paleozoic rocks are not exposed on the west side of the Sheep Creek Range, but on the basis of present knowledge of the structure in nearby areas, the Roberts Mountains thrust fault can be inferred to be present at depth in this area.

GEOCHEMICAL INVESTIGATIONS

MATERIALS SAMPLED

The principal objective of this investigation was to evaluate the possibility that metals were localized near the thrust plane in either the upper or the lower plate. Samples were col­lected, therefore, that seemed most likely to

3

represent introduced material such as vein quartz and iron minerals in fractures anc. vugs. An effort was made to include such mate.rial in all samples collected, but chert with iron oxide­stained fractures constitutes the bulk of the samples. Where more than one sample was collected at the same locality the highest value was used to construct the geochemical maps.

ANALYTICAL PROCEDURE

Gold, silver, and tellurium were dete~mined by a wet chemical method using atomic absorp­tion. Mercury was determined instrumentally by an atomic-absorption technique (Vaughn and McCarthy, 1964). Arsenic, antimory, and zinc were determined by wet chemical methods (Ward and others, 1963). The remairder of the elements were determined by a semi()uanti­tative spectrographic method (Wari and others, 1963).

DISTRlBI.:TION OF METALS IN THE PALEOZOIC ROCKS

Several metals occur in unusually high con­centrations along the outcrop belt of Paleozoic rocks. The most extensive anomalies are of zinc, arsenic, mercury, and silver (figs. 3-6). Lead, copper, and gold (figs. 7-9) are pre:;oent in highly anomalous concentrations but the anomalies are less extensive. Isolated an')malies of tungsten (fig. 10), antimony, moly~denum, and tellurium are also present. The principal concentrations of all the metals are with iron oxide on fracture planes and with vein quartz. The n1ost consistent anomaly for all the metals is, expectably, near the Snowstorm mira. (figs. 3-10).

The following comparison of the average crustal abundance of 11 metals with their con­centration in the Sheep Creek Range illustrates the magnitude of these anomalies:

A l'l'l'n!lc '''"''·eutratitul ill the l'fl !'lit's t'/'1181

(Jijl/11)

Zn ----------------180

Cu 170 Ph ----------------

116 As ---------------- 15 Mo ----------------

12.3 w ---------------- 11.0 Sb 11.0 Hg ---------------- :!.06 Ag ----------------

1.02 Au ----------------

3 .002 Te ----------------

1 .002 1 From Goldschmidt (1958 ). ~ From (C}reen ( 19:i9). 3 From Del'}razia anrl Ha~kin ( 1964).

Rau11e uj t'OIIt't'ufrntiol! in lilt' ,.;,'hi'CJI Creek Rauge

(J'Jiill)

<25 - 800 <10 - 15,000 <10 ->20,000 <10 - 1,500 <5 200

<50 - 1,000 1 >100

<.1 - 30 <.2 - 260 <.02- 1.3 <.1 - 17

T. 34 N.

T. 33 N

T. 33 N.

T. 32 N.

R.45E. R.46E.

ZINC (parts per million)

23 24 19 <25

0 25-99

0 100-199

25 30 ~ 200-399

• 400-800

F Float sample

36 31 ~ Paleozoic formations

6 5 4

12 7 8 9

15 13 18 17 16

22 19 20 21

27 26 30 29 28

34 35 32 33

3 2

5 4

0 2 MILES 0

FIGURE 3.-Zinc distribution, highest concentration at each locality.

4

R.45E. R.46E.

ARSENIC (parts per million)

23 24 19 <io 0

10-40

0 .50-00

25 30 ~ lOO-lOLJ

• 200 or greater Value given

T.

F Float sample

34 36 31 N.

Paleozoic formations

T. 33 6 5 4 N.

8 9

17 16

20 21

29 28

32 33

5 4

0 2 MILES 0

FIGURE 4.-Arsenic distribution, highest concentration at each locality.

5

R. 45 E. R. 46 E.

~ MERCURY

(parts per million)

23 24 19 ~~:: -~-,~· <O.l ~- . .2

0 ~. 0.1-0.49

0 0,5-0.99

Q 25 30 1.0-1. 9Q

• 2 or greater Value given

Float sample

34 35 36 31 ~ T. 34 Paleozoic formations

N.

T.

33 N.

1 6 5 4

8 9

17 16

20 21

29 28

T. 34 35 32 33

33

N.

T. 32 3 2 N.

5 4

0 2 MILES 0

FIGURE 5.-Mercury distribution, highest concentration at each locality.

6

T. 34 N.

T_ 33 N.

T. 33 N.

T. 32 N.

R. 45 E_ R. 46 E.

23 24 19

25 30

36 31

6

12 7

15 13 18

22 19

21 30

34 35

3 2 1

0 2 MILES 0

SILVER (parts per millwnJ

<<\'2

0 IJ.'2-U.LJ

• 'ill or greater Value given if>OO

F Float sample

PaleuzoiC formations

5 4

8 9

17 16

20 21

29 28

32 33

5 4

FIGURE 6.-Silver distribution, highest concentration at each locality.

7

R.45E R.46E.

~l

~~~ LEAD (parts per million)

s\r~<:9 2-3 24 19 do "2ooo· ·: .:Gl·. a} ... 0

~' '~ 10-4G

0 50-GG

Q

25 30 100-4GG

• 500 or greater Value given

F Float sample

T.

~ 34 36 31 N.

Paleozmc formations

T. 33 6 5 4 N.

8 9

17 16

20 21

29 28

32 33

5 4

0 2 MILES

FIGURE 7.-Lead distribution, highest concentration at each locality.

8

R 45 E. R.46 E.

COPPER (parts per million)

23 24 19 <70

0 70-149

0 150-499

'i)

25 30 500-999

• 27 1000 or greater Value given

f

Float sample

34 36 ~ T 31

34 Paleozoic formations N.

T.

33 N.

6 5 4

8 9

17 16

20 21

29 28

T. 34 35 32 33

33

N

T. 32 3 2 1 N.

5 4

0 2 MMS

FIGURE 8.-Copper distribution, highest concentration at each locality.

9

R. 45 E. R. 46 E.

GOLD (parts per million)

23 24 19" <0.02 0

0.02-0.049

0 0.05-0.0QQ

Q O.L-0.4Q

30 • 25 O.S-1 Value given if >L

F Float sample

~ Paleozoic formations

T. 34 36 31

34 N.

T. 33 N.

6 5 4

8 9

17 16

20 21

29 28

FIGURE 9.-Gold distribution, highest concentration at each locality.

10

R. 45 E. R. 46 E.

TUNGSTEN (parts per million)

23 24 19 <SO

• 50 or greater

~ Paleozoic formations

25 30

T. 34 36 31 32 33

34 N.

T. 33 N.

6 5 4

8 9

17 16

20 21

29 28

FIGURE 10.-Tungsten distribution, highest concentration at each locality.

11

It is not known whether or not the Paleozoic rocks in the Sheep Creek Range originally contained a metal content comparable to that of the earth's crust, but it appears that most of the elements listed have subsequently been locally enriched by very large factors.

The metals were probably introduced into the heavily fractured rocks by upward or laterally migrating solutions. The anomalies may repre­sent a dispersion halo above or around concealed mineral deposits, possibly located along or below the thrust plane or associated with a buried intrusive mass, or they may constitute the whole mineral deposit. Inasmuch as broken and crushed rock along the Roberts Mountains thrust plane is known to be a favorable host for ore deposits elsewhere, the possibility that mineral deposits exist along the thrust below the anomalies is at least reasonable. The geo­physical investigations indicate that the possi­bility of the existence of an unexposed in­trusive mass in the southern part of the area is also reasonable.

A geochemical association of arsenic, mer­cury, antimony, and tungsten with gold has been recognized in many of the ores of north­central Nevada (Erickson and others, 1966). Examples of ore deposits with this kind of association are the Getchell, Bootstrap, Carlin, and Gold Acres mines and the newly discovered gold deposit in the Corte,z area. The, similar geochemical association of metals on the west side of the Sheep Creek Range may be similarly significant.

GEOPHYSICAL INVESTIGATIONS

Aeromagnetic surveys of large areas in western and north-central Nevada have been flown as part of the U.S. Geological Survey's program of geologic investigations. Of timely interest is an aeromagnetic' map made from a 1967 survey of the Battle Mountain quadrangle (U.S. Geological Survey, 1968) ; part of this map is shown in figure 11. A local magnetic high near the Rennox railroad siding is super­imposed on a northeastward-increasing regional magnetic gradient. The prominent, high­amplitude magnetic anomaly shown in the northeast part of the map is related, in part, to basaltic rocks of Tertiary age that form the cap rock of the Sheep Creek Range. This

12

anomaly is an extension of the linear northwest­striking regional magnetic anorr.aly reported previously by Mabey (1966).

The local magnetic anomaly c~ntered near Rennox is over alluvium along the western front of the Sheep Creek Range. In amplitude and shape, the anomaly resembles the magnetic anomaly in the Cortez area 40 miles to the southeast (Mabey, 1965).

Subsequent geophysical inve;;-tigations-a low-level aeromagnetic survey, a gravity sur­vey, and electrical resistivity soundings-were made in and around the Rennox area to pro­vide some insight into the probable source of the magnetic anomaly.

MAGNETIC DATA

Two prominent magnetic features exist in the area of the low-level aeromagnetic survey (fig. 12). The feature at the southeast end is attributed to exposed basalt; basalt extends some distance southward beneath alluvial cover.

The magnetic anomaly near F.ennox, only partially surveyed, shows pronounced lineations on the north and east sides of the feature; the lineation along the east side coinci~es with the projection of the inferred fault O"l the photo­geologic map. The steepest magnetic gradient on the north side of the anomaly indicates a source less than a hundred feet below the surface. Magnetic material also eY.ists at shal­low depths immediately to the south of the Snowstorm mine and east of the irferred fault.

The Rennox anomaly does not fit a simple model of a normally magnetized. steep-sided body because no low (relative to background) is developed on the north and nor~heast sides. A model based in part on the gravity and electrical data (fig. 13) is a two~dimensional tabular body 1,500 feet thick and 3,750 feet long, having a minimum depth fron1 the surface in the vicinity of the fault of 750 feet and inclining to the southwest toward Rennox to a maximum depth of 1,500 feet.

The smaller amplitude anomaly east of the fault could not be attributed solely to a thin veneer of basalt boulders and fragments on the Paleozoic chert-quartzite seouence. The magnetic material probably is an intrusive mass in the Paleozoic bedrock.

2 3 4 MILES

EXPLANATION

-2000-

Magnetic contours Showing total intensity magnetic

field of the earth in gammas relative to arbitrary datum; x, location of recorded maximum or minimum intensity within a closure. Contour interval 10 and SO gammas.

Flight path Showing location and spacing of data

!v--Ja·~ :'=

" APPROXIMATE MEAN

CiFCLINATION, 1968

FIGURE H.-Aeromagnetic map of part of the Battle, Mountain quadrangle, Nevada, obtained from a fF~ht ele­vation of 9,000 feet above sea level. Aeromagnetic survey flown by R. W. Krizman; compilation supervised by C. L. Long.

13

40° 44'

-18"-

APPROXIMATf: MEAN

DECLINATION, 1968

EXPLANATION

--zoo-

Magnetic contours Showing total intensity magnetic

field of the earth in gammas relative to arbitrary datum; x, location of recorded maximum or minimum intenEity within a closure. Contour interval 10 and 50 gammas.

Flight path Showing location and

spacing of data

SNOWSTORM MINE rl~

0 5000 FEET ~1 --~~--~~--~f

FIGURE 12.-Aeromagnetic and generalized geologic map of the Rennox area, Nevada. Aerorr.11gnetics from flight elevation of 400 feet above ground. A-A', location and extent of profile discussed in text. Geologic symbols explained in figure 2.

14

100

/Observed magnetic field •

-50~------------------------------------------------------------------------~

Rennox Inferred fault (fi~. 12) A'

0 1500 3000 FEET

FIGURE 13.-Comparison of magnetic data taken from aeromagnetic map along line segment from Rennox to A' (fig. 12) with model curve for the two-dimensional body shown. Line of observation is 400 feet abovf~ ground. Magnetic susceptibility, 1.5 x 10-3 cgs (centimeter-gram-second system) units; total field, 5.45 X 10-4 gammas; inclination, 66°. Strike of model is 37o west of magnetic north.

GRAVITY DATA

A two-dimensional model which fits the ob­served gravity data taken along profile A-A' indicates the probable existence of two faults that displace the bedrock surface beneath the surficial cover (fig. 14). The smaller of the two faults is about 750 feet nor~heast of the fault inferred on the photogeologic map. Bedrock on the northeast side of the smaller fault prob­ably lies less than 100 feet below the surface, and bedrock on the downdropped side is about 750 feet below the surface. The larger fault near Rennox is probably a major Basin and Range fault with an approximate displacement of about 7,000 feet. It may be an extension of the fault along the west front of the Shoshone Range south of the Argenta Siding reported

15

by Mabey (1964) and corroborated by Erwin (1967).

RESISTIVITY DATA

The interpretation of six Schlumbe1·ger re­sistivity soundings made between Rennox and the Snowstorm mine supports some part:s of the gravity and magnetic models presented. Sound­ings 1 and 2 (fig. 15) indicate that a low­resistivity section (perhaps water-sr..turated alluvium) extends to a depth of at least 800 feet.

Soundings 3 through 6 indicate that the pedi­ment cover is only 15 to 35 feet thick on the northeast side of the fault. A second zone, about 500 feet thick, has a resistivity of about 50 ohm-meters at sounding 3, which gradually increases to about 140 ohm-meters at sounding 6. The values in this zone would normally be

0

~ -10 Bouguer H

:J ~ -20

A Rennox Inferred fault (fig. 12) A'

Or-------------~--------~-------------L~========------~~--1

~ 1.5 ~ 0 (/)

~ 3.0

(/) ~(7' -0.4-5 gm/cm3 ::::> = 0

R .5

i:=i .. ~

6.0

~ 7.5

0 1500 3000 4500 FEET I I I I

FIGURE 14.-Comparison of the simple Bouguer gravity values projected along A-A' (fig. 12) with model curve for the two-dimensional structure shown. Density contrast between the two bodies is -0.45 gmjcm~ (gram per cubic centimenter).

too low for competent chert and quartzite, which have rather low intergranular porosity. However, because the chert and quartzite in the area are highly brecciated and fractured, values such as these are not unlikely.

Perhaps the most significant result of these four soundings is an anomalously lower re­sistivity zone below 500 feet, extending to at least 1,000 feet. Resistivity values of about 20-30 ohm-meters in the bedrock would likely require the presence of some clay minerals with high ion-exchange capacity.

CONCLUSIONS

The source of the magnetic anomaly in the vicinity of Rennox was not resolved by the geo­physical studies made in the area. Although the simple straight-sided gravity and magnetic models presented might be suggestive of a block of basalt, the physical counterpart might

16

be quite different. The thickness of the mag­netic mass could be greater and itE shape more irregular than shown. The high-level aeromag­netic data suggest the magnetic n1ass extends almost a mile southwest of Rennox at a depth in excess of 6,000 feet. This configuration would suggest an intrusive mass. Further, the broad magnetic anomaly with smaller an1plitude east of the fault appears to be causei by an in­trusive mass. The anomalously low resistivity zone below 500 feet could result from clay alteration related to an intrusive b'1dy.

Because most of the anomalous rocks in­ferred from the geophysical data are at shal­low depths, a drilling program would effectively resolve the uncertainties. A drill hole near the steepest gradient shown on the n'lrth side of the magnetic anomaly should inter·cept the ig­neous rock within 100 feet from the surface.

Chert outcrop Inferred fault (fi~. 12) (Valmy Formatio1)

Rennox 0

~ 5060 140 OHM-METERS

~ <20<20 <30 <30

0 (/)

~ 1.5

~ ~ .. ~ 3.0

~

0 1500 3000 FEET

FIGURE 15.-Generalized cross section along line segment from Rennox toward A' (fig. 12) showing loc.ation of the resistivity soundings, (1-6), expanded in a N. 20° W. direction, with the resistivity values of the. various zones defined by the electrical survey and the diagrammatic shape of the bedrock based on the magnetic and gravity models shown in figures 13 and 14.

Similarly, a hole placed on the northeast side of the inferred fault about one-half mile south­west of the Snowstorm mine would determine the composition of the bedrock material. The juxtaposition of the geophysical and geochemi­cal anomalies in the vicinity of the Snowstorm mine further suggests that consideration should be given to an exploration program in that area.

REFERENCES DeGrazia, A. R., and Haskin, Larry, 1964, On the gold

content of rocks: Geochim. et Cosmochim. Acta, v. 28, no. 5, p. 559-564.

Erickson, R. L., Van Sickle, G. H., Nakagawa, H. M., McCarthy, J. H., Jr., and Leong, K. W., 1966, Gold geochemical anomaly in the 'Cortez district, Nevada: U.S. Geol. Survey Circ. 534, 9 p.

Erwin, J. W., 1967, Gravity map of Battle Mountain and adjacent areas, Lander, Pershing, and Hum­boldt Counties, Nevada: Nevada Bur. Mines Map 31.

Gilluly, James, and Gates, Olcott, 1965, Tectonic and igneous geology of the northern Shoshone Range, Nevada, with sections on Gravity in Crescent Val­ley, by Donald Plouff, amil Economic geology, by K. B. Ketner: U.S. Geol. Survey Prof. Paper 465, 153 p.

Goldschmidt, V. M., 1958, Geochemistry (ed. by Alex Muir]: London, Oxford Univ. Press, 730 p. [re­print of 1954 edition].

17

Green, Jack, 1959, Geochemical table of the elements for 1959: Geol. Soc. America Bull., v. 7"', no. 9, p. 1127-1184.

Mabey, D. R., 1964, Gravity map of Eureka Co•mty and adjoining areas, Nevada: U.S. Geol. Surrey Geo­phys. Inv. Map GP-415.

---1965, Gravity and aeromagnetic surveys, in Gilluly, James, and Masursky, Harold, G~ology of the Cortez quadrangle, Nevada: U.S. Geol. Survey Bull. 1175, p. 105-111.

---1966, Regional gravity and magnetic snomalies in part of Eureka County, Nevada, in Case his­tories of mining geophysics, volume 1 : Tulsa, Okla., Soc. Explor. Geophysicists, p. 77-83.

Roberts, R. J ., 1964, Stratigraphy and structut"e of the Antler Peak quadrangle, Humboldt and Lander Counties, Nevada: U.S. Geol. Survey Prof. Paper 459-A, p. A1-A93 [1965].

U.S. Geological Survey, 1968, Aeromagnetic m"~.p of the Battle Mountain and Dunphy quadrangles, Lander and Eureka Counties, Nevada: U.S. Geol .. Survey open-file report.

Vaughn, W. W., and McCarthy, J~. H., Jr., 1964, An instrumental technique for the determination of submicrogram concentrations of mercury in soils, rocks, and gas, in Geological Survey reseal'ch 1964: U.S. Geol. Survey Prof. Paper 501-D., p. D123-D127.

Ward, F. N., Lakin, H. W., Canney, F. C., ar1 others, 1963, Analytical methods used in geoche'llical ex­ploration by, the U.S. Geological Surv~y: U.S. Geol. Survey Bull. 1152, 100 p.

* U. S. GOVERNMENT PRINTING OFFICE : 196~ 0 - 326-027