GEOLOGICAL SURVEY CIRCULAR 596 

Preliminary Results of 

Geological, Geochemical, and 

Geophysical Studies in 

Part of the Virginia City 

Quadrangle, Nevada 

Preliminary Results of 

Geological, Geochemical, and 

Geophysical Studies in 

Part of the Virginia City 

Quadrangle, Nevada 

By Donald H. Whitebread and Donald B. Hoover 

GEOLOGICAL SURVEY CIRCULAR 596 

Washington J 968 
United States Department of the Interior 

WALTER J. HICKEL, Secretary 

Geological Survey 

William T. Pecora, Director 

First printing 1 968 

Second printing 1970 

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

Abstract ------------------------------------

Introduction --------------------------------

Acknowledgments ---------------------------

Page 

1 

1 

4 

4 

4 

4 

5 

5 

6 

Geophysical studies --------------------------

Induced-polarization surveys -------------

Electromagnetics ------------------------

Geochemical studies -------------------------

Cornwall Knob area ---------------------

Washington Hill area --------------------

References cited -----------------------------

Geology ------------------------------------ Alta Formation -------------------------

Kate Peak Formation --------------------

Lousetown Formation -------------------

Alteration ------------------------------

Structure -------------------------------

ILLUSTRATIONS 

FIGURE 1. Index map showing location of Virginia City quadrangle, Comstock Lode district, and limit:;' 

of the Cornwall and Washington Hill areas-------------------------------------------

2. Geologic map of Cornwall Knob area -----------------------------------------------------

3. Geologic map of the Washington Hill area ----------------------------------------------

4. Map of part of the Cornwall Knob area showing location of geophysical traverses and 

mercury distribution --------------------------------------------------------------- 5--7, Profiles showing induced-polarization data, Cornwall Knob area: 

8. 

9-10. 

11. 

12. 

13-17. 

18-23. 

5. Traverse 1 -----------------------------------------------·----------------------

6. Traverse 2 ---------------------------------------------------------------------

7. Traverse 3 --------------------------------------------------------------------- Contour map of induced-polarization values, Cornwall Knob area ------------------------·--

Profiles showing induced-polarization data, north end of Cornwall Knob area: 

9. Traverse 4 ----------------------------------------------------------------------

10. Traverse 13 -------------------------------------------------------------------- Slingram profiles south of Cornwall Knob -----------------------------------------------

Turam map of the Cornwall Knob area --------------------------------------------------

Maps showing distribution of metals in the Cornwall Knob area: 

13. Gold --------------------------------------------------------------------------

14. Silver ------------------------------------------------------------------------

15. Mercury ----------------------------------------------------------------------

16. Copper -----------------------------------------------------------------------

17. Lead ------------------------------------------------------------------------- Maps showing distribution of metals in the Washington Hill area: 

18. Gold --------------------------------------------------------------------------

19. Silver -------------------------------------------------------------------------

20. Mercury ----------------------------------------------------------------------

21. Bismuth ----------------------------------------------------------------------

22. Copper ------------------------------------------------------------------------

23. Lead --------------------------------------------------------------------------

m 

Page 

6 

6 

11 

13 

17 

18 

20 

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1 

2 

3 

7 

8 

9 

10 

11 

12 

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13 

14 

14 

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15 

16 

16 

17 

17 

18 

18 

19 

19 
• 
PRELIMINARY RESULTS OF GEOLOGICAL, GEOCHEMICAL, AND GEOPHYSICAL 

STUDIES IN PART OF THE VIRGINIA CITY QUADRANGLE, NEVADA 

By DONALD H. WHITEBREAD and DONALD B. HOOVER 

Abstract 

Geological, geochemical, and geophysical studies in 

the Comstock Lode district and adjoining parts of the 

Virginia Range near Virginia City, Nev., have resulted 

in recognition of two geophysical anomalies and several 

geochemical anomalies in an area north of Virginia City. 

The geophysical anomalies were found during an induced-polarization survey carried 0ut to aid in tracing 

the Comstock fault, the principal structure localizing 

the bonanza silver-gold deposits of the Comstock Lode 

district, in an area of intensely altered rock and alluvial 

cover about 5 miles north of Virginia City. Geochemical 

anomalies showing mercury in excess of 5 ppm (parts 

per million) were found in altered rocks along the Comstock fault near Cornwall Knob about 5 miles north of 

Virginia City and in the Washington Hill area, 6 miles 

farther north. 

INTRODUCTION 

The bonanza ore bodies of the rich and highly 

productive Comstock Lode district, in the Virginia Range near Virginia City, Nev. (fig. 1), 

were in altered andesitic volcanic rocks along 

the eastward-dipping Comstock fault. This 

fault can be traced for a few miles north of 

Virginia City, but farther north its location is 

obscured by intense alteration of the enclosing 

rocks and by alluvial cover. Geological, geochemical, and geophysical studies are underway 

to determine whether the Comstock fault persists to the north of where it is last recognized 

at the surface and, if so, to ascertain if possible 

its attitude, the relations between the fault and 

rock alteration and mineralization, and the potential for the occurrence of concealed ore deposits along its extension. 

The Virginia Range is one of several areas in 

western Nevada that contain epithermal deposits of gold, silver, and mercury in altered 

andesitic volcanic rocks. 

1 

The Comstock Lode district is one of the 

world's greatest precious-metal producers. 

From 1859 to 1940, the recorded production of 

silver and gold was $397,445,998 (Couch and 

Carpenter, 1943, p. 93-94; p. 133-136). The 

gold-silver ratio by weight was about 1 :40 

DWoehinttoft Hill ore a 

(1 .... 3) 

~1 Knob a<oa 

(fi9Uft 2) 

0 

FIGURE 1.-Index map showing location of Virginia 

City quadrangle, Comstock Lode district, and limits 

of the Cornwall Knob and Washington Hill areas. 
1.\:) 

Base from U.S. Geological Survey Geology by 

1:62,500 Virginia City, 1950 D. H. Whitebread, 1966-67 

~ !A 0 1 i'OliLE 

EXPLANATION 

1 B Q){ 

:iJ Alluvium and colluvium 

c 

(1)'0-u; ., 0 ' c 

., { CJ s:: ...... (1) 

0 "' (1) C) 

~ 0: 

""{ 

., ~ 

c-o~ 

~~~ ~ 0 

::E :::: 

p.. 

H 

~~ Lousetown Formation 

->oJ~i>J K<tte l'eak Formation 

Tki; intrusive r ocks 

Alta 

~ Formation 

Approximate contact 

--------

Fault 

Bleached 

~ 

~ rocks of 

the Kate Peak and 

Alta Formations 

Long-dashed where approximately lucate>d: 

short- dashed where indefinite or· infe tTt>d; 

dotted where conc ealed. l:lar a nd ball <on 

dow nth rnwn side 

__.._ -35 

Strike and dip of planar structure 

X 

Prospect 

FIGURE 2.-Geologic map of the Cornwall Knob area. 

,. 

~0:: 

t-<-< 

} ;z 

0:: >< 

C1 >< 

~ ~ :Soz 

t-<zO:: 

a::<.:~ 

~ t-< 

t-< ~ 

>< 0:: 

::: 

t-< 

0:: 

~ 

t-< 

C1 
(Nolan, 1933, p. 633). Argentite, gold, and polybasite occurred with sphalerite, galena, and chalcopyrite; gangue minerals were pyrite, quartz, 

and some calcite (Bastin, 1923, p. 44-45). Native silver locally replaced the argentite at shallow depths. Aguilarite, a silver sulfoselenide, 

was recognized in several specimens by Coats 

(1936, p. 532). 

The Castle Peak mine, about 7 miles north of 

Virginia City, has yielded more than 2,500 

flasks of mercury, and the Root mine, or Washington Hill prospect, 3 miles farther north, 

probably yielded a few flasks (Bailey and Phoenix, 1944, p. 184-187). At both localities, cinnabar occurs in intensely altered. andesite. 

The current geological studies, a part of the 

Heavy Metals program of the Geological Survey, have revealed several geochemical anomalies and two geophysical anomalies. Two areas 

in particular are attractive for further investigations: the Cornwall Knob area and the Washington Hill area, about 5 and 11 miles, 

respectively, north of Virginia City (fig. 1). 

The Cornwall Knob area is along the northern 

extension of the Comstock fault (fig. 2). The 

only indications of previous exploration in the 

area are widely scattered, shallow prospect pits. 

While using induced-polarization (IP) methods 

to aid in locating the northern extension of the 

Comstock fault in an area of altered volcanic 

rocks and alluvium, an anomalous area was 

found near Cornwall Knob. Geochemical sampling revealed high mercury values clustered 

near Cornwall Knob and about 1 mile south. 

Geological and geochemical studies here and in 

the Washington Hill area (fig. 3) have provided 

additional information on anomalous amounts 

of mercury reported by Cornwall, Lakin, N akagawa, and Stager (1967, p. Bll-B13). Mercury 

in excess of 6 ppm (parts per million) is distributed widely at Washington Hill, and in 

addition, many of the samples in a northeasttrending belt through the Root mine are high in 

mercury and also contain anomalous amounts of 

lead, silver, and bismuth. 

Geologic core drilling is planned to obtain 

further information on the nature of the IP 

anomalies and on the relation of the geochemical anomalies to rock alteration and possible 

mineralization. 

3 

R.Z1 E. 

Base from U ,S. Geological Survey Geology by 

1:62,500 Virginia City, 1950 · D. H. Whitebread, 1967 

0 lMILE 

EXPLANATION 

<=: 

]' Bleached rocks of the Kate Peak Formation 

~ Tkb; nonresistant bleached rocks composed chiefly ;;... 

.S of quartz and clay minerals 0:: 

P:: Tkl; resistant ledges of qu_artz of chalcedony, local ::S ~ alunite, and varying amount. of clay minerals ~ 

., Tko; opal or cristobalite ~ 

1::: 

'" " 

~ Kate -

Peak Formation 

Approximate contact 

X 

Prospect 

FIGURE 3.-Geologic map of the Washington Hill area. 
ACKNOWLEDGMENTS 

The cooperation of the Curtiss Wright Corp., 

on whose property the investigations were conducted, and the Duval Corp., which is engaged 

in geological studies in the area, is gratefully 

acknowledged. 

In the geophysical work described, G. I. 

Evenden, assisted by C. L. Tippens, was responsible for the gathering and compilation of the 

electromagnetic data. D. R. Schoenthaler, R.N. 

Babcock, and E. D. Seals assisted with the IP 

surveys. To these coworkers, we extend our ap~ 

preciation. 

GEOLOGY 

Thompson (1956) and Thompson and White 

(1964) have described the geology within the 

Virginia City quadrangle, and their geologic 

maps have been used extensively during the 

present investigation. The most detailed reports 

on the geology of the Comstock Lode district 

are by Becker (1882.), Gianella (1936), and 

Calkins ( 1944) . 

Volcanic rocks of Tertiary and Quaternary 

age cover most of the Virginia Range. The Alta 

and Kate Peak Formations are the most widespread and together with the Lousetown Formation constitute the bedrock in the areas of 

this report. According to Thompson and White 

(1964, p. A14-A15) the upper part of the Kate 

Peak Formation is probably of Pliocene age. 

Recent potassium-argon age determinations by 

J. C. Engels (written commun., 1968) show 

that part of the Kate Peak, the Alta, and the 

underlying Hartford Hill Rhyolite Tuff are of 

Miocene age. Triassic ( ?) metamorphosed sedimentary and volcanic rocks and Cretaceous 

granodiorite underlie the Hartford Hill Rhyolite Tuff. 

ALTA FORMATION 

The Alta Formation is the principal extrusive 

rock unit in the Comstock Lode district and was 

the host for the bonanza deposits; for several 

miles north of Virginia City it makes up much 

of the footwall block of the Comstock fault. The 

Alta consists mainly of andesitic flows and flow 

breccias, but where the rock is altered, the flows 

and breccias are difficult to distinguish. Calkins 

(1944, p. 12-15) described four members of the 

4 

Alta, but they were not recognized outside the 

Comstock Lode district. In the Cornwall Knob 

area (fig. 2), the Alta is principally mediumlight-gray hornblende-pyroxene andesite. More 

altered varieties are commonly shades of green 

or bluish gray, and some fresh varieties are 

dark gray. Phenocrysts of plagioclase 1-3 mm 

(millimeters) in length are conspicuous, and 

phenocrysts of hornblende, commonly 3-5 mm 

long, are more than 10 mm long in some places. 

The pyroxene is not readily visible in hand 

specimen. The Alta is cut by numerous dikes 

and other small intrusive bodies. Some of these 

younger rocks can be distinguished from the 

Alta by their textural differences or by the 

presence of biotite; others are nearly indistinguishable, owing to variations in the degree 

of alteration and other factors. 

KATE PEAK FORMATION 

The Kate Peak Formation is composed of 

flows, flow breccias, intrusive bodies, and tuff 

breccias; it ranges in composition from andesite 

to rhyodacite (Thompson and White, 1964, p. 

A13). Flows predominate within the areas of 

this report, although flow breccias are especially common north of Cornwall Knob (fig. 2). 

Flow banding is locally well developed but is 

quite variable in attitude. 

In the Cornwall Knob area, the most readily 

recognized varieties of the Kate Peak are porous to dense, medium-dark-gray, light-gray, or 

pale-red rocks with conspicuous phenocrysts of 

plagioclase 5 mm or more in length. Hornblende 

is the most common dark mineral and is present 

in all the specimens examined. Biotite occurs as 

large prominent books or scattered small flakes 

in some specimens and is absent in others. 

Where present, it can be used to distinguish the 

Kate Peak from the Alta. Pyroxene is plentiful 

in some specimens, but the small green crystals 

are difficult to detect with a hand lens. Hornblende, biotite, and pyroxene occur together in 

some specimens. Scattered phenocrysts of 

quartz are not uncommon. Hornblende-pyroxene andesite in the basal Kate Peak northwest 

of Cornwall Knob is characterized by smaller 

and less conspicuous plagioclase phenocrysts 

and by the absence of biotite. This rock closely 

resembles the underlying Alta and is locally 

indistinguishable from it. Several intrusive 
bodies of Kate Peak were mapped within the 

Alta, and some may be present within the 

areas shown as Kate Peak. In particular, a 

biotite-rich unit underlying the prominent hill 

on the west side of sec. 4 may intrude adjacent 

flows, but relations at the contacts are inconclusive. 

Outcrops of the Kate Peak in the Washington 

HiH area (fig. 3) are dense, dark-gray pyroxene-hornblende andesite in which the plagioclase phenocrysts are small and relatively 

inconspicuous. Pyroxene is more abundant than 

hornblende, and biotite is lacking. 

LOUSETOWN FORMATION 

The Lousetown Formation is made up of welldefined lava flows of medium-gray to dark-gray 

basalt and basaltic andesite. Individual flows 

range in thickness from about 5 to 30 feet and 

have vesicular tops. The flows exposed in the 

area of figure 2 came from a vent about 1 mile 

northeast of the map boundary. The Lousetown 

unconformably overlies the Kate Peak Formation, and in many places a few feet of fluviatile 

deposits separate the two formations. To the 

north, fluviatile and lacustrine deposits of the 

Truckee Formation underlie the Lousetown. 

Small grains of olivine and phenocrysts of 

green pyroxene are commonly visible in many 

flows, and in some places the alinement of 

plagioclase laths is pronounced. The attitude of 

platy parting and flow banding does not coincide with that of the gently inclined flows. The 

Lousetown shows none of the alteration that is 

typical of much of the underlying Kate Peak 

and Alta Formations. 

Potassium-argon dating of flows near the 

base of the type Lousetown Formation in the 

Virginia Range gave an age of 6.9 -+- 0.19 m.y. 

(million years) (Dalrymple and others, 1967, p. 

165). Birkeland (1963, p. 1456-57) correlated 

these flows with flows in the Truckee area that 

range in age from 1.2 to 2.3 m.y. Thus, the age 

of the Lousetown is considered to be Pliocene 

and Pleistocene. 

ALTERATION 

Propylitization and intense bleaching are 

widespread types of alteration in the Alta and 

Kate Peak Formations. The Alta Formation is 

generally more altered than the Kate Peak, and 

5 

prior to the regional studies of Th ~mpson 

(1956), the extensive alteration was coiJsidered 

to be restricted to the Alta and older rocks. 

Becker (1882, p. 81-90) first recogniz~d that 

the rock, earlier named propylite in th~ Comstock Lode district, was a variety of altered 

andesite rather than a distinct type of volcanic 

rock. The widespread propylitic alteration in 

the district was later described by Coats 

(1940), who redefined j>ropylitization as alteration characterized by epidote and albite replacing plagioclase and by chlorite, calcite, and 

epidote replacing ferromagnesian minerals. Altered rocks containing epidote were noted in 

the Alta and intrusive bodies of the Kate Peak 

in a few places along the west edge of f?:ure 2, 

but a less intense alteration, characterfzed by 

chlorite-calcite assemblages, is morE: widespread. The ferromagnesian minerals typically 

are thoroughly altered, but plagioclase appears 

fresh or only slightly altered. Weak alteration 

in much of the Kate Peak Formation is denoted 

by alteration of the hornblende. Zeolites are 

locally abundant in the Kate Peak Fo~mation 

near the Comstock fault south of Cornwall 

Knob. 

Calkins (1944) and Thompson (1956) mapped areas of intensely altered Alta and Kate 

Peak Formations as bleached rocks. Generally, 

the two formations cannot be distiiJguished 

where they have reached such an aqvanced 

stage of alteration. Typical bleached rocks are 

white to grayish yellow and are irr,~gularly 

stained by brown, red, and yellow iro"'l oxide. 

Fractures are commonly coated with dark iron 

oxide. The porphyritic texture of the original 

rock ordinarily can be distinguished except in 

the most intensely silicified varietie·s. Much of 

the bleached rock is relatively soft and does not 

form coherent outcrops. Kaolinite, quartz, and 

alunite are the most common constituents of 

the bleached rocks, but other clay n1inerals, 

pyrophyllite, jarosite, cristobalite, gypsum, and 

diaspore occur locally. More resistant altered 

rocks commonly contain a larger perce:'ltage of 

quartz or alunite. The proportions of silica minerals, alunite, and clay minerals vary vridely in 

resistant ledges like those delineated in figure 

3. The most resistant parts, however, are composed entirely of chalcedonic quartz. 
In the mines of the Silver City area, about 

3 miles south of Virginia City, the bleached 

rocks commonly grade downward into propylitized rocks peppered with small crystals of 

pyrite (Gianella, 1936, p. 53). At Virginia City 

and Gold Hill the intense bleaching apparently 

persisted as deep as the ore bodies (about 1,500 

feet), and Becker (1882) indicated that 

bleached rocks extend downward to the level of 

the Sutro tunnel. Thompson and White (1964, 

p. A28) reported that in a drill hole 4 miles 

north of Virginia City the bleached rock extends to a depth of 50-75 feet, where it grades 

downward into altered andesite with pyrite 

and zeolites. In the areas of this report, disseminated pyrite was found in only a few places 

in the Alta and the Kate Peak intrusive bodies, 

and in small dark-gray highly silicified pods in 

the bleached rock. Gianella (1936, p. 53) and 

Thompson and White (1964, p. A27) proposed 

that the bleaching is a near-surface supergene 

alteration due to the action of sulfuric acid produced when the pyrite was oxidized. At least 

part of the bleaching, however, probably is the 

result of hypogene alteration. 

STRUCTURE 

According to Thompson and White (1964, p. 

A35), the Virginia Range consists of tilted 

blocks bounded by normal faults. The Comstock 

fault, which can be traced for about 8 miles, is 

the principal fault in the range. Mine workings 

in the Comstock Lode district show that the 

fault dips eastward about 45 o. There the fault 

has an estimated throw of 2.,500-3,450 feet 

(Gianella, 1936, p. 85; Thompson, 1956, p. 66), 

but the throw may diminish to the north. 

Gianella (1936, p. 81-87) gave evidence for 

movement along the fault both before and after 

ore deposition. The fault can be traced north 

from Virginia City for about 5 miles, and 

spatial relations between the Alta and Kate 

Peak define the approximate trace of the fault 

as far north as the prospect pit about onefourth mile south of Cornwall Knob (fig. 2). Its 

position north of that point is inferred from 

geophysical data. The fault in the Lousetown 

Formation at the northeast corner of the map 

area, however, probably reflects later movement 

along a northward extension of the Comstock 

fault. The two faults east of Cornwall Knob de6 

veloped during a period of faultin~ and gentle 

tilting that occurred after the Lousetown flows. 

Prominent north- and east-trending resistant 

ledges in the Washington Hill area (fig. 3) may 

be alined along faults or fracture~ .. Thompson 

and White (1964, p. A26) suggested, however, 

that the ledges are erosional remnants of tabular zones in which nearly all con<;1tituents except silica have been removed. 

GEOPHYSICAL STUDIES 

Limited geophysical studies were made in the 

Virginia City quadrangle in conjunction with 

the more extensive geological n1apping and 

sampling program. Because the northern extension of the Comstock fault was of prime importance as a guide to further investigations, 

most of the geophysical work was concentrated 

in the region of Cornwall Knob (fig-. 2). One of 

the authors (Whitebread) has beer. able to map 

the Comstock fault as far north as a small prospect pit about one-fourth mile soutl· of the crest 

of the Cornwall Knob (fig. 2). Beyond this 

point, the fault trace was lost in an area of 

bleached rock and alluvial cover. Faults have 

been traced by IP surveys (Sumi. 1959), and 

this was considered as a possible way of tracing 

the Comstock fault. Thus IP and electromagnetic surveys were used in an atte~pt to trace 

the fault zone through this difficult area. 

Alteration zones appeared to b~ promising 

areas to study with IP surveys owing to the 

presence of clay minerals in the bleached outcrops and the gradation downward into propyli tized rocks with pyrite, as d a. scribed by 

Gianella (1936) and Thompson and White 

(1964). If the clay mineral content or pyrite 

content were high enough, it would be possible 

to map altered zones beneath tl·o. extensive 

Lousetown flows in the northern part of the 

quadrangle. 

INDUCED-POLARIZATION SURVFYS 

Colinear dipole-dipole electrode gt~ometry was 

used on all the IP traverses. Measurements 

were made in the frequency domain using BurrBrown models 97 40 and 97 41 equipment, with 

frequencies of 0.05 and 5.0 Hz (l·o.rtz). Data 

reduction was made in the convertional manner, with apparent resistivities computed in 

ohm-feet/271" (pa/211"), IP values in percent fre-
0 •0.1 1;1 0.1-0.99 

0 1.0-4.99 

• 5.0-9.99 

• ~10 

4 

Sample locality 

Showing mercury content 

in parts per million 

')( 

Prospect 

0 

EXPLANATION 

[~'_] 

APPROXIMATE M EAN 

DECLI NATION, 1968 

'h MILE 

J{ 

~{ 

lluvium and colluvium 

Lousetown ~ Formation 

QJ'O~ k 

g ~ QJ :>; 

~ ~{. ..... g Kate Peak 

~ ~ Formation r·· §,·.-fill ~ Bleached rocks of ~ the Kate Peak and fil 

~{- Alta Formations E-< o Alta 

:@ Formation 

1-------114 

Induced-polarization 

traverse 

_____ ...,E 

Slingram traverse 

FIGURE 4.-Map of part of the Cornwall Knob area showing location of geophysical traverses 

and mercury distribution. 

7 
BLEACHED ZONE EAST .. 

2 3 4 6 7 8 9 10 

30.0 36.3 33.8 ~248 26.3 28.5 

31 .5 ~I!$ I!$ 

32.6 28.6 

23.8 "'-. -'o 

n - 1 

n-2 

n -3 

EXPLANATION 

ELECTRODE CONFIGURATION 

n - 4 

nx ~ 

00.5 02.5 n -1 

z~ n -2 3 03.5 03.8 

n-3 

n-1 

n-2 

109 n-3 

n-4 

.., \,. 36.3 

~ ~ "" 

~ .... 03.6 

03 ~ 02 .93 

03.8 

160 

147 109 

r--'00 

( 69 

pa/21T 

MF 

'-.. / 

'-.. / '-.. / '-.. / 

Y Plotting point 

x = / eo " teet 

Frequencies: 0.05 and 5.0 Hz 

FIGURE 5.-Induced-polarization results, Cornwall Knob area, traverse 1. 

quency effect (PFE), and metal factor (MF) in 

reciprocal ohm-feet. 

A small, but well-defined, bleached area (fig. 

4) about one-half mile west of Cornwall Knob 

was selected as the first area to study. The 

bleached zone, alined in a north-south direction, 

is about 100 feet wide and 500 feet long. A 

shallow prospect pit on the north end of this 

zone contains some pyrite-bearing dark chalcedonic quartz and copper-stained altered rock. 

The pyrite, in euhedral crystals, is for the most 

part completely surrounded by silica. 

Owing to the small size of the bleached zone, 

a 50-foot dipole length was used on traverse 1 

(fig. 4) perpendicular to the long dimension of 

the zone. A weak anomaly, which correlates 

well with the outcrop of bleached rock, can be 

seen in both the resistivity and the PFE data 

plots (fig. 5). The anomaly is characterized by 

both higher resistivity and higher PFE. Both 

anomalous values, however, are only slightly 

higher than background, and the PFE is lower 

than would be expected from the pyrite present 

in the outcrop. Although the pyrite-bearing 

rock exposed in the prospect pit may not be 

representative of the rock mass sampled by the 

traverse, the close proximity (20 feet south) 

8 

makes this supposition doubtful. These data are 

consistent with an interpretation of a narrow 

altered zone containing principally silica and 

some pyrite and clay minerals. The extensive 

silicification as seen in the prospect pit could 

give rise to higher values of resistivity, and the 

pyrite, to higher PFE. The almost total insulation of pyrite grains by silica would explain the 

slight increase in PFE above background. 

Traverse 2 (fig. 4) was run just south of 

Cornwall Knob in an area of intensive alteration 

of both the Alta and Kate Peak Formations. 

The traverse, which was run from the unaltered 

Kate Peak on the east toward the Alta on the 

west, crossed the projection of the Comstock 

fault. The data from traverse 2 (fig. 6) shows, 

as on traverse 1, a small PFE anomaly, but 

associated with this is a broad zone of reduced 

resistivity. The metal factor anomaly is narrow, well defined, and suggests an east dip if it 

is assumed that a narrow tabular body gives 

rise to this anomaly. 

Interpretation of the resistivity data is difficult because of topographic variations on the 

traverse. The increase in resistivity at both 

ends, however, is real since the topographic effect would tend to decrease the apparent re-
EAST• 

3 4 5 6 7 8 9 10 II 12 

n-1 ')S-._~: 6.11 5.55 6.37 5.70 7.04 5.04 5.815-~6.54 6.-::; 

...... ~ 6.48 r". 5.13~.05 5~ 

EXPLANATION 

ELECTRODE CONFIGURATION 

-o.s> cP ~ 7.08~ ~ ~"~ " / 

n-1 02.3 02.1 02.3 03 9 03.1 

n-2 02.5~ 02 4 02.6 

01.9 

01.8 

" / " / " V / Plottino point 

x= / 100 " feet 

'NO n ;02.6 n-3 00.9-1 03.4~----

02.6 r.: 02.1 

20 

Frequencies: 0.05 on1 5.0Hz 

30 

n-1 

n-2 

n-3 

FIGURE 6.-Induced-polarization results, Cornwall Knob area, traverse 2. 

sistivity at these places. The regions of higher 

resistivity at the ends of the traverse correlate 

well with outcrops of unaltered rock. As observed on traverse 1, the frequency-effect 

anomaly was only slightly above background. 

The dipole length used in this traverse was 100 

feet, which in this location would give penetration below the expected water table. Thus, the 

depth of penetration was presumably greater 

than the depth of the zone of pyrite oxidation 

and acid-leaching effects. No noticeable change 

in either resistivity or PFE with depth can·be 

seen within the broad altered zone on this traverse. This may be indicative of a bleached zone 

shallower than the electrode spacing. A short 

series of measurements made along this traverse using 50-foot dipole separations and an 

n spacing of 1 showed no significant changes in 

resistivity or PFE in comparison to the 100-

foot, n = 1 values. 

Traverses 1 and 2 show the marginal utility 

of IP surveys for mapping of altered volcanic 

areas in this region. Where bleached rocks are 

exposed on the surface, no difficulty is experienced in mapping, but if the bleached rocks are 

buried under much cover, the low anomalous 

PFE values would make their detection difficult 

and require very careful surveying. This would 

9 

be especially true in most areas covered by alluvium where the presence of clay ninerals 

would result in low resistivities. The su""lerficial 

nature of the bleached rocks is suggested by the 

lack of a discernible layer on traverse 2. and by 

a shallow, low-PFE region associated V7ith the 

altered region on traverse 1. If bleaching, in 

contrast to propylitization, is due to surface 

oxidation of pyrite and not to hypogen~ alteration, then the depth of bleached rock is shallower than the electrode separation. This 

finding is in accord with that of Thomp~on and 

Sandberg (1958), who on the basis of gravity 

work concluded that the bleached zo-.,es are 

superficial. 

On traverse 2 a narrow PFE anomaly· stands 

out in the metal-factor plot. Because the 

anomaly coincides with the Comstock fault, if 

extended along strike from the south, and because no evidence for faulting exists in the rock 

on either side of the broad bleached zone, we 

believe this anomaly defines the fault zo..,e. This 

is further established by electromagnetic work 

described later. Since the results on tr~.verse 2 

offered some hope that IP surveys could be used 

to trace the Comstock fault, an effort W?S made 

to locate the fault farther north by this method. 

The remainder of the IP traverses in thi~ region 
10 

18.04 25.73 ~ 8.96 -o 10.76 7.61 8.03 8.10 8.25 10.16 n-1 ~ 

~~ ·~· ""~·· EXPLA~ATION 

n-2 9.03 

ELECTRODE CONFIGURATION 6.53 9.11 14.96 7.35 NR n-3 0.00 ,o, Ill~ t--.r--+- nx ---+-x---1 

n-4 6.05 6.15 ~ ~ 

NR NR 10.65 

~ 

16.05 

~ ~ " / 

" / 

" / 

" / 

~·~~~· n-1 03.6 04.9 05.4 02.8 Y Plotting point 

~~7 / " 03.5 06.5 x= 10" feet n-2 

Frequencies: 0.05 and 5.0 Hz 

01~ ~7 NR 06.8 ~ 

05.4 

n-4 04.7 06.7 NR NR 05.9 

~.,. "0 'b 

n-1 461 

n-2 392 

NR 

NR 

MF 

FIGURE 7.-Induced-polarization results, Cornwall Knob area, traverse 3. 

were made in an attempt to map the Comstock 

fault and to test for other faults in a nearby 

area of anomalous mercury values. 

Along traverse 3 (fig. 7), about 0.3 mile 

north of traverse 2, two narrow anomalous 

zones were discovered. The westermost anomaly 

is similar to that found on traverse 1, in that 

higher PFE values are associated with a zone 

of higher resistivity. A well-defined metal-factor anomaly is also indicated in this region. 

This anomaly coincides with projections from 

previous geologic mapping and is believed to be 

the most probable location of the Comstock 

fault. 

The less well defined anomaly near station 7 

on traverse 3 appears to be associated with a 

spur ridge branching east from the main crest 

of Cornwall Knob halfway between traverses 2 

and 3. Additional profiling in the area, however, 

was not dense enough to reveal the true nature 

of this anomaly. 

A frequency-effect map was made (fig. 8) for 

an n separation of 3, which shows the northeast-trending zone identified with the Comstock 

10 

fault. Additional traverses would be: desirable to 

unequivocably relate this zone to the Comstock 

fault, but in the absence of conflicting information, the present supposition is most tenable. 

This linear PFE anomaly dies out to the north, 

where conductive alluvium overlies the bedrock 

to greater depth. Extension of this trend along 

strike coincides with a fault cuttin,g the Lousetown Formation. This fault was ea:rlier mapped 

by Thompson (1956) but not identified by him 

as the Comstock fault. Becau~e Gianella 

(1936) found evidence for post mineralization 

movement along the Comstock faul\ this extension into the Lousetown is possible. 

Near the north end of the aref'. covered by 

the PFE map (fig. 8), a strong anomaly associated with the assumed fault zone was discovered. Profile data on traverse 4 (fig. 9) show 

a strongly anomalous zone with minimum depth 

of less than 100 feet and probable eastward dip. 

Here again the PFE anomaly is asr0ciated with 

a zone of slightly increased resistivity. A traverse with 200-foot dipole spacing and n separation up to 4 indicated no apparent depth limit 
FAULT? 

T ... lll. 2 3 

T.17N. 

R. E. 

N 

l 

EXPLANATION 

1-------42 

Induced-polarization traverse 

-5--

Contour of PFE values 

Contour interval 5 percent 

0 400 800 1200 FEET 

FIGURE B.-Induced-polarization (PFE) map, Cornwall 

Knob area. 

to this anomaly. The high PFE values are indicative of sulfide mineralization. 

In order to ascertain if high mercury values 

might also be associated with PFE anomalies, 

several profiles were run east of Cornwall Knob 

where particularly high mercury values were 

found. Traverse 13 (fig. 10) was made across 

a bedrock outcrop which showed greater than 

10 ppm mercury. A moderate PFE anomaly 

correlates well with the high mercury value in 

outcrop. Topographic effects on this traverse 

preclude an exact resistivity interpretation; 

however, the PFE values are again associated 

with a zone of slightly higher ·resistivity. The 

profile shows the anomalous zone to be virtually 

at the surface. 

11 

ELECTROMAGNETICS 

Slingram and turam electromagnetic n1ethods 

were tried in the Cornwall Knob area. One of 

the two slingram traverses (fig. 4, 87) crossed 

the Comstock fault zone one-fourth mile south 

of Cornwall Knob; the other (S3) was ru, along 

the road just south of Cornwall Knob,, along 

nearly the same ground as IP traverse 2. These 

traverses were made using a coplanar horizontal loop configuration with a 200-foot coil separation and station intervals of 100 fe~'~t. The 

frequency used was 1,800 Hz. 

The results of both traverses (fig. 11) show 

a distinct anomaly on crossing the pr-.,jected 

position of the fault just south of Cornwall 

Knob. On the east side, in the Kate Pe~.k Formation, a very low resistivity, flat-lying conductive layer is indicated. The presence of bl~ached 

or altered rock cannot be detected t~y this 

method, as there is no evident change in conductivity ~n passing through the several altered 

zones. Smaller anomalies could not be correlated 

with any surface geologic features. Because of 

the irregular terrain, noise was introduco.d into 

the real component through the inability to 

maintain coplanar coils. The noise may have 

masked more subtle conductivity chan.f?:es related to the alteration zone. The west side of 

each traverse shows less conductive roc1

· .. associated with the Alta Formation and r0ck of 

about the same resistivity as obtained trroughout the IP work ( 15 and 50 ohm-meter~) . No 

such clearly defined resistivity chan~~·~ was 

noted on the IP profiles, but as Hall of ( 1967) 

has pointed out, the two methods sam:ole the 

environment in decidedly different way~. The 

slingram anomaly is due to differences in electrical properties of the Alta and Kate Peak 

Formations and offers a relatively inexpensive 

means of verifying the fault trace south of 

Cornwall Knob. To the north of Cornwall Knob, 

the fault would be in the Kate Peak For1nation, 

and this method may not be as effective. 

A turam survey (Frischknecht, 195!') was 

conducted in areas where strong IP anomalies 

were found to see· if this method could supplant 

the more expensive IP surveys. The turam 

method has greater depth of penetration than 

the slingram method, which would be important 

in trying to get below the highly conductive 

alluvium in much of the region. All turmn trav-
EAST2 4 lS 6 II 

8.70 12.12 fl 7.lSO fl 10.62 8.91 9.90 ,o 13.14 -.;.. 16.6!5 17.23 n-1 

~81 ·~·" 13~ EXPLANATION 

ELECTRODE CONFIGURATION 

6.18 11.76 12.96 10.68 14.07 13.26 

12.24 10.38 1!5.00 11.16 13.02 12.00 ~··~ p0/271" "" / "" // 

"" / 

"" / n-1 04.3 05.0 06.8 08.6 08.0 07.8 05.3 0!5.3 06.3 YP1ottin9 point 

~L / 

05.2 14.9 14.8 x = IC\0 " feet 

Frequenciu: o.olS and lS.OHz 0!5.1 

07.lS 18 u···· 17.7 ~0 

493 413 907 810 898 788 

n-1 _........ 500 !568 n-2 666 

82!5 n-3 

n-4 874 1429 1133 

MF 

FIGURE 9.-Induced-polarization results,· north end of Cornwall Knob area, traverse 4. 

EASTn-1 

EXPLANATION 

ELECTRODE CONFIGURATION 

~ nx ~ 

" / " / " / " Y / Plottint point 

/"'-.. x= IC\0 feet 

Frequencies: 0.0!5 and !I.O:Hz 

FIGURE 10.-Induced-polarization results, north end of Cornwall Knob area, traversE: 13. 

12 
t--< 

z 

w 

u 20 0::: 

w 

0... 10 z 

w"' 

......J 0 ~ 

u 

VJ 

\ /' \ / \ / \ / 

\ / \_.,.-....... __ ...... --/ \ / \ I .... _ .... 

......J -10 ,_..,.,., ~ 

u 

~ 

COMSTOCK FAULT I 0::: -20 

w 

> TRAVERSE S7 

EXPLANATION 

t--< 

z 

w 

u 20 

Real componem 

0::: --------- w 

0... 10 

~ 

Imaginary comronent 

w \ I\ 

I I \ I I \ \ I \ I I \ 

~ 0 

u 

VJ 

......J -10 

0 200 .:tOO FEET 

L_I _ _.J..._I_----.~1 

\ I \ 1 

'-" \ I 

~ 

u \ I 

COMSTOCK FAULT ?I \ /~\_/ 

'-" 

~ -20 0::: 

w 

> 

TRAVERSE S3 (CENTRAL PART) 

FIGURE 11.-Slingram profiles south of Cornwall Knob. 

erses were made with horizontal coplanar coil 

configuration and 50-foot station intervals; an 

operating frequency of 500 Hz was used. 

The turam map (fig. 12) shows no distinct 

anomalies, but background noise is high and 

tends to mask any effect that may be coming 

from the source of the IP anomaly. The noise 

on all the turam traverses is attributed to variations in salinity and porosity in the bleached 

rock and alluvial fill, which make up a highly 

conductive surface layer. Hall of ( 1967) has previously reported difficulties with electromagnetic methods in semiarid regions where ioncharged ground water can cause anomalies 

indistinguishable from shallow sulfide bodies. 

Lines 20S and 28S show anomalies on the east 

end which may correlate with smaller IP anomalies found on the east side of Cornwall Knob. 

The IP profiles apparently show the trace of 

the Comstock fault as a zone of slightly higher 

13 

resistivity relative to surrounding rock. Increased polarizability results from the higher 

percentage of clay minerals or sulfides associated with this zone. Electromagnetic tecl'niques 

are not effective methods for tracing tr~ fault 

except where it divides different rock units such 

as the Alta and Kate Peak Formations. In these 

areas, the slingram technique appears to be an 

effective aid to mapping, but it would r()t distinguish the fault from a simple formati f)n contact. Neither electromagnetic nor IP n1ethods 

appear to hold much promise as mappir~ tools 

for locating bleached zones in the Cornwall 

Knob area. 

GEOCHEMICAL STUDIES 

Geochemical samples were collected in several 

areas of altered volcanic rocks in the Virginia 

Range. Most samples have been collected in 

areas underlain by bleached rocks in an r.ttempt 
N 

T.I8N. 

I 32 33 

T.t7N. 54 

R.2t£. 

EXPLANATION 

----24S 

Line of profile 

Quadrature component 

Real component 

0 400 800 1200 FEET 

FIGURE 12.-Turam map of the Cornwall Knob area. 

to determine whether trace-element distribution 

and abundance would be useful to define areas 

in which further exploration for concealed ore 

deposits might be warranted. 

Gold was determined by a wet-chemical 

method using atomic-absorption spectrophotometry. Mercury was determined by a mercury-vapor detector. Other elements were 

determined by six-step semiquantitative spectrographic analysis. The analysts for gold were 

W. L. Campbell, M. S. Rickard, T. A. Roemer, 

G. H. VanSickle, T. G. Ging, Jr., R. B. Tripp, 

and T. M. Stein; for mercury, W. L. Campbell, 

W. W. Janes, H. D. King, K. R. Murphy, and 

S. L. Noble; for silver, lead, copper, and bismuth, D. J. Grimes, E. L. Mosier, J. M. Motooka, E. E. Martinez, and K. C. Watts, Jr. 

14 

I 

R. 21 E. -+ 

29 0~ 0 

0 0 

28 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I I ----------+--------------~ 

32 0 

I 

4 0 0 0 

1 o o 0 10 0 

<ij og o 

el 

0 0 6 ~ 8 ~ 

0 o I 

I o o I 

o o o 1 T. 18 N. 

33 

--~----~+------~--------~ % t9 ° I T. 17 N. oo o I 

0 

• 

0 

0 so 

0 

oltP f 

Cb I o o I 

I 0 I 

I 

0 0 ·' I 

I o I 

0 

0 

0 • 

4 

0 0 0 

o • I ---------~---------------+-

I 

I 1 r" o I 

I 

~ ! I 

0 

0 

0 

0 lllltiLE 

EXPLANATION 

0 • 

<0.02 0.02-0.04 

Sample locality 

Showing gold content in parts per million 

FIGURE 13.-Gold distribution, Cornwall Knob area. 
I 

R. 21 E. -+ I 

I I 

I I 

I I 

I 28 I 29 

o ~ o I I o I I 0 

I I 

I I 

I I 

I I 

I I 

----------+--------------, 

32 • 

0 

I 

I 

~ 0 0 0 

o I o o 

I o 

~ os 0 

ol 

o I~ o ~ ~ I 

g 9 

0 o I 

I o I o o o 1 T. 18 N. 

33 

--~-----~+---------------r ~ ~. I T. 17 N. 

0 

o oo o I 

0 so 

0 

0 

0 oo I • o I ._ I 

o • I 

0 

I 

I 

o I o o I 

I 

I o I 

o o I 

0 

0 

0 0 4 

0 0 0 

---------+---------------~-

1 N I 

I I 

I f I I o I 

! I 

0 

0 

0 

0 1 MILE 

EXPLANATION 

0 ~ • • 

<0.5 0.5-0. 7 1.-1.5 15 

Sample locality 

Showing silver content in parts per million 

FIGURE 14.-Silver distribution, Cornwall Knob area. 

29 a» 

• 

R. 21 E. 

• 

• 

28 

I 

-+ I 

I 

I 

I 

I 

I 

I 

I 

I 

I I 

I I 

----------+--------------, 

32 • 

I 

I 

9 • 

• I ~ • .• I •• 

C\1 • 0 

ol ~ 

~ 1.,. ii# ~, I. 

! -t 

oOO I 

I o I o ~"' 1 T. 18 N. 

33 

--~-----~+---------------~ ~ liil I T. 17 N. I o ~ o I I 

o I I 

• too I I -. I I o • I ~~ I 

I 4 I 

I • ~ I 

I I 

0 ~I ~ ~ ~ I 

• ~I I 

I I 

"' I I o o I I ---------+---------------~-

1 N I 

I I 

I f I I o I 

! I 

0 

0 

0 

0 1 MILE 

EXPLANATION 

0 • • 

<0.1 0.1-0.99 1.0-4.99 ~5 

Sample locality 

Showing mercury content in parts per million 

FIGURE 15.-Mercury distribution, Cornwall Fnob area. 

15 
29 

R. 21 E. 

28 

I 

-+ I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I I 

----------+--------------, 

I 

~ . I rw o rwo 

rw I rw 

~ wi rw 

32 • J 33 

rw !Ill~ 

r;o~.i>~ 

rwf'O : 

"" o I o o o 1 T. 18 N. 

--~-----~+---------------~ 'b ri'rw I T. 17 N. 

0 

0 

o o o I o I 

w~~ I 

-.. I rw rw I 

0 

I 

I 

I o. I w 0 I 

I rw I o rw I 

0 w 4 

0 

---------+---------------~-

0 

0 

<20 

0 

1 N I 

I I 

I f I I rw I 

! I 

1 MILE 

EXPLANATION 

rw • • 20-70 100-150 >150 

Sample locality 

Showing copper content in parts per million 

FIGURE 16.-Copper distribution, Cornwall Knob area. 

16 

R. 21 E. -+ I 

I I 

I I 

I I 

I 28 I 

rwwP._ I I 

rw I I 

29 

I I 

I I 

I I 

I I 

I I 

----------+--------------, I 

I 

32 0 

• 

9 .. I .. 0 ,. .. .. I rw 

~ --= .. -.I ,. ~ -.-.~I s ., ~o I 

I ,. I 

.. .. .. I T. 18 N. 

33 

--~----~-+---------------r ~ ri*-. I T. 17 N. 

• 

• rw-. I o I 

• 

• s,. 

.~fiP I ~ I ,. ,. I 

I 

I 

rw I .. ,.1 

I 

I o I o ,. I 

0 0 

---------+---------------~-

1 · I 

I N I 

I f I I o I 

! I 

0 

0 1 MILE 

EXPLANATION 

0 .. • 

<20 20-70 100-200 

Sample locality 

Showing lead content in parts per million 

FIGURE 17.-Lead distribution, Cornwr~ll Knob area. 
R. 21 E. 

~ 

29 28 0 I 0 

0 0 

I 0 0 

01 (ilo 

I 0 0 I 0 

I 0 

0 

~ I oro 0 

• 0 0 0 0 ~ 

u v 0 

oo 0 0 0 0 0 0 ~ oo 0 w 0 00 0 0 0 

081# 0 0 T. 

32 033 0 e 19 0 

cf 0 0 ~ 

0 N. 0 0 

0 00 0 

0 0 

0 '\, 0 0 

._,o 0 w 0 0 

d 'boo 

w 0 cP 0 ~ w 

"' ~ 

0 0 0 I 0 N 

ROOT MINE1t~ I 

r 0 0 

oo 

~ %~ I 

I 0 I 5 I 

I 

0 * lMILE' 

EXPLANATION 

0 w • <0.02 0.02-0.07 0.30 

Sample locality 

Showing gold content in parts per million 

FIGURE 18.-Gold distribution, Washington Hill area. 

CORNWALL KNOB AREA 

Of 125 analyzed samples from the Cornwall 

Knob area, 58 were collected from outcrop, 21 

were from dumps of prospect pits, 38 were soil 

samples, and eight were iron-rich fracture fillings. Most of the samples were collected in areas 

underlain by bleached rocks that were apparently barren and unmineralized. The distribution patterns of gold, silver, mercury, copper, 

and lead are shown in figures 13 to 17. Where 

several samples of various types were collected 

at a single locality, the geochemical maps show 

the highest value obtained. 

17 

R. 21 E. 

0 

29 I • 28 0 

0 0 

I 0 0 

01 ~ 

I 0 

0 I 0 0 I 0 

I 010 ._ 0 0 0 0 0 0 .... ..,. 0 0 00 0 0 0 0 0 () 0 oo 0 0 0 0 0 0 0 

08tJP 0 0 

6' 32 0 0330 

0 0 -~ 0 0 0 

0 () 

0 00 0 

0 0 0 0 0 ~ 

0 lila• 

0 w 0 oc ow •• 

0 0 6> 0 

0 0 

Q _Q 

0 I 0 0 w N 

ROOT MINE~ I ~, i oO 0 0 

~ I ._ I 

5 I 

I 

I 

0 ~ lMILE 

EXPLANATION 

0 w • • <0.5 0.5-0.7 1-3 5-7 

Sample locality 

Showing silver content in parts per millio"l' 

FIGURE 19.-Silver distribution, Washington Hill area. 

Only a few scattered samples contained gold 

or silver in detectable amounts, but mer~ury is 

present in amounts of 1 ppm or more in 29 of 

the 84 sample localities. The high rr o.rcury 

values occur mostly in two clusters ak"'lg the 

Comstock fault, and the largest concentration 

is in the bleached rocks near CornwalJ Knob. 

The other cluster of anomalous mercury values 

in the NE~ sec. 5 also has four high (>1 ppm) 

silver values. No geophysical traverses were 

made here. The distribution of copper is similar 

to mercury but more widely scatterrrl. Unfortunately, the site of the IP anomaly northeast of Cornwall Knob is covered by alJuvium; 

T. 

19 

N. 
R. 21 E. 

.. 29 28 • 

I • • .. I .. .. '""I .. I 

""' .. I .. I .. .. I •<il • ~ 

• • • ... 0 • .., -- • •• ... • .. .. • • .. •• . ~ 

... • ""' • .. .. 

.. , .. • T. 

32 .33. i • ~ 19 • .. • .. .. N. 

• .. .. • .. • 0 

.. ... ""' ... 

""' 

~0 

.. • • ,; -... • II' • • ... • ... - •• .. I • N 

ROOT MINE 1tl I 

... ~ ""' ""' i c- I 

I • I 5 I 

I 

0 ~ I MILE 

EXPLANATION 

0 w • • <0.1 0.1-0.99 1.0-4.99 lS 

Sample locality 

Showing mercury content in parts per million 

FIGURE 20.-Mercury distribution, Washington Hill 

area. 

therefore, no samples were collected, and a comparison with other areas is not possible. 

WASHINGTON mLL AREA 

The distribution patterns of gold, silver, mercury, bismuth, copper, and lead in the Washington Hill area (fig. 3) are shown in figures 18 to 

23. Of 232 samples collected, 163 were from 

outcrops, 26 from dumps of prospect pits, 39 

were soil samples, and four were iron-rich fracture fillings. Because of the extensive colluvium 

that covers most of the slopes underlain by nonresistant bleached rocks, many of the samples 

18 

R. 21 E. 0 

29 • 28 0 

I 0 0 

·I 0 

•o 0 

I 0 0 I .. 0 I 0 p I O<b 0 

0 0 0 0 0 0 

J'll. ... 0 .... 0 

0 wo 0 0 0 

0 0 oo o'bo 0 

0 0 0 

08tl 0 0 

T. 

32 0 0330 c9 19 e 0 0 ~ 

0 N . 0 0 00 0 0 0 0 0 0 0 ~ 

.. 0 0 0 ~--· oc ~ .... c9 0 0 0 0 0 0 n 

000 0 I 

ROOT MINE r~tl I N 

0 0~ ~ _, I 

I l 

I 5 I 

I 

0 * I MILE 

EXPLANATION 

0 8 • .. <10 10-70 100-150 200-300 

Sample locality 

Showing bismuth content in parts per million 

FIGURE 21.-Bismuth distribution, W ~ shington Hill 

area. 

were collected along or near the ree·istant ledges 

delineated on the geologic map (fig. 3). The 

distribution patterns of the various elements 

therefore may be controlled to sor1.e extent by 

the outcrop patterns. Cornwall, Lakin, Nakagawa, and Stager (1967, p. B11-B13) reported 

the widespread anomalous mercury in the area. 

Figure 20 shows mercury values of 1 ppm or 

more in 75 of the 126 sample localities, and of 

these, 34 contain more than 6 ppm. High values 

for silver, bismuth, lead, and gold are mostly 

concentrated in a belt that trenis northeast 

through the Root mine. 
R. 21 E. R. 21 E. 

.. 0 

29 I • 28 • 29 • 28 ~ 

• 0 I 0 ~ 

I ~ ~ I ~ ~ 

~ ~ ~, ~ 

I ~ I ~ 

0 I ~ ~ I ~ 

~ ~ 

I ~ 

~ I ~ 

~ I ~~ ~ I 0 co 0 .. ~ ~ ~ 

~ ~ ~ • ~ ~ ~ ~ 

~ 

- v v 

0 ~ 

00 ~ ~ ~ 0 0 0 ~ •o 0 0 0 ~ 0 ~ ~~ 0 q,. 0 ~ 0 ~0 ~ 0

o 0 

0 

~ 0 ~ 0 ~ 0 

~~ ~ ~ 

~ 0 0 0 

T. T. 

32 101 33~ ~ 19 32 ~0 ~33 ° 8 ~ 19 ~ ~ lilib ~ 0 w CXb 

"' w N. 0 0 "' N. ~ 0 ~ 0 

~ 0. 0 ~ ~ 

~ "' 0 ~~ 0 0 

• ... ~ "' "' ~ ~ " 'ti~ 0 y ~ • w • ~ .,.~~ w 110. ~ 

~ 00 ~ "' ~ ~ ~ ~ 0 ~ 0 ~ 

"" "' ~ ,. 

0. w ~ I N •o w w I N 

ROOT MINE~~ I ROOT MINE')tl I 

oo ~ i ·\ •• ~ i ~ 0 (' ~ 0 I .r I 

I I • I • I 5 I 5 I 

I I 

0 '* lMILE 0 ~ I MILE 

EXPLANATION EXPLANATION 

0 "' • • 0 ~ • • <20 20-70 100-150 200-500 <20 20-70 100-200 300-5()(' 

Sample locality Sample locality 

Showing copper content in parts per million Showing lead content in parts per million 

FIGURE 22.-Copper distribution, Washington Hill area. FIGURE 23.-Lead distribution, Washington Hill area. 

19 
REFERENCES CITED 

Bailey, E. H., and Phoenix, D. A., 1944, Quicksilver 

deposits in Nevada: Nevada Univ. Bull., v. 38, no. 

5, Geol. and Mining ser. no. 41, 206 p. 

Bastin, E. S., 1923, Bonanza ores of the Comstock lode, 

Virginia City, Nevada: U.S. Geol. Survey Bull. 

735, p. 41-63. 

Becker, G. F. 1882, Geology of the Comstock lode and 

the Washoe district: U.S. Geol. Survey Mon. 3, 

422 p. 

Birkeland, P. W., 1963, Pleistocene volcanism and deformation of the Truckee area, north of Lake 

Tahoe, California: Geol. Soc. America Bull., v. 74, 

no. 12, p. 1453-1464. 

Calkins, F. C., 1944, Outline of the geology of the Comstock Lode district, Nevada: U.S. Geol. Survey, 

open-file rept. 

Coats, R. R., 1936, Aguilarite from the Comstock lode, 

Virginia City, Nevada: Am. Mineralogist, v. 21, 

no. 8, p. 532-534. 

---1940, Propylitization and related types of alteration on the Comstock Lode: Econ. Geology, v. 35, 

no. 1, p. 1-16. 

Cornwall, H. R., Lakin, H. W., Nakagawa, H. M., and 

Stager, H. K., 1967, Silver and mercury geochemical anomalies in the Comstock, Tonopah, and Silver Reef districts, Nevada-Utah, in Geological 

Survey research, 1967: U.S. Geol. Survey Prof. 

Paper 575-B, p. B10-B20. 

Couch, B. F., and Carpenter, J. A., 1943, Nevada's 

metal and mineral production ( 1859-1940 inclusive): Nevada Univ. Bull., v. 37, no. 4, Geol. and 

Mining Ser. no. 38, 159 p. 

Dalrymple, G. B., Cox, Allan, Doell, R. R., and Gromme, 

C. S., 1967, Pliocene geomagnetic polarity epochs: 

Earth and Planetary Sci. Letters, v. 2, no. 3, p. 

163-173. 

Frischknecht, F. C., 1959, Scandinavian electromagnetic 

prospecting: Am. Inst. Mining, Metall., and Petroleum Eng. Trans., v. 214, p. 932-9~7. 

Gianella, V. P., 1936, Geology of the Sil'T~r City district 

and the southern portion of the Comstock Lode, 

Nevada: Nevada Univ. Bull., v. 30, no. 9, 105 p. 

Hallof, P. G., 1967, The use of indue~ polarization 

measurements to locate massive s:ul~.fe mineralization in environments in which ETjf methods fail 

[abs.]: Canadian Centennial Conf. Mining and 

Groundwater Geophysics, Niagara Falls, Ontario, 

1967. 

Nolan, T. B., 1933, Epithermal precious--metal deposits, 

in Ore deposits of the Western States (Lindgren 

Volume) : New York, Am. lnst. Mining Metall. 

Engineers, p. 623-640. 

~umi, F., 1959, Geophysical exploratio:-1 in mining by 

induced polarization: Geophys. Prc~p., v. 7, no. 3, 

p. 300-310. 

Thompson, G. A., 1956, Geology of the Virginia City 

quadrangle, Nevada: U.S. Geol. Survey Bull. 

1042-C, p. 45-77. 

Thompson, G. A., and Sandberg, C. H., 1958, Structural 

significance of gravity surveys in th~ Virginia CityMount Rose area, Nevada and California: Geol. 

Soc. America Bull., v. 69, no. 10, p. 1269-1281. 

Thompson, G. A., and White, D. E., 1964, Regional 

geology of the Steamboat Spring~ area, Washoe 

County, Nevada: U.S. Geol. Surva.y Prof. Paper 

458-A, p. A1-A52. 

20 

1r U. S. GOVERNMENT PRINTING OFFIC:"' : 1970 0 - 399-661