Mineral Resources of the Bristol/ 

Granite Mountains Wilderness 

Study Area, San Bernardino 

County, California

U.S. GEOLOGICAL SURVEY BULLETIN 1712-C

Chapter C

Mineral Resources of the Bristol/Granite 

Mountains Wilderness Study Area, 

San Bernardino County, California

By KEITH A. HOWARD, JAMES E. KILBURN, 

ROBERT W. SIMPSON, TODD T. FITZGIBBON, 

DAVID E. DETRA, and GARY L. RAINES 

U.S. Geological Survey

CHARLES SABINE 

U.S. Bureau of Mines

U.S. GEOLOGICAL SURVEY BULLETIN 1712

MINERAL RESOURCES OF WILDERNESS STUDY AREAS: 

CENTRAL CALIFORNIA DESERT CONSERVATION AREA
DEPARTMENT OF THE INTERIOR 

DONALD PAUL MODEL, Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1987

For sale by the

Books and Open-File Reports Section

U.S. Geological Survey

Federal Center, Box 25425

Denver, CO 80225

Library of Congress Cataloging-in-Publication Data

Mineral resources of the Bristol/Granite Mountains 

Wilderness Study Area, San Bernardino County, 

California.

U.S. Geological Survey Bulletin 1712-C

Bibliography

Supt. of Docs. No.: I 19.3:1712-C

1. Mines and mineral resources California Bristol/

Granite Mountains Wilderness. 2. Geology Bristol/

Granite Mountains Wilderness. 3. Bristol/Granite

Mountains Wilderness (Calif.) I. Howard, Keith A. II.

Geological Survey (U.S.) III. Series.

QE75.B9 No. 1712-C 557.3 s 87-600062

fTN24.C2l [553'.09794'95l
STUDIES RELATED TO WILDERNESS

Bureau of Land Management Wilderness Study Areas

The Federal Land Policy and Management Act (Public Law 94-579, October 21, 

1976) requires the U.S. Geological Survey and the U.S. Bureau of Mines to conduct 

mineral surveys on certain areas to determine the mineral values, if any, that may be 

present. Results must be made available to the public and be submitted to the President 

and the Congress. This report presents the results of a mineral survey of part of the 

Bristol/Granite Mountains Wilderness Study Area (CDCA-256), California Desert 

Conservation Area, San Bernardino County, California.

CONTENTS

Summary Cl 

Abstract 1

Character and setting 1 

Mineral resource potential 1 

Introduction 2

Location and physiography 2 

Previous and present investigations 3 

Acknowledgments 3 

Appraisal of identified resources 3

Methods and scope of investigation 3 

Mining history 3

Reserves and identified resources 3 

Assessment of mineral resource potential 5 

Geology 5

Rock units 5

Faults and evidence of alteration 6 

Remote-sensing data on alteration 6 

Geochemistry 7 

Geophysical studies 8 

Mineral and energy resources 9 

Skarn, iron, and tungsten 9 

Hydrothermal silver 9 

Epithermal gold in fault breccias 9 

Oil and gas 9 

Limestone 10 

Perlite 10 

References cited 10 

Appendixes

Definitions of levels of mineral resource potential and certainty of

assessment 15

Resource/reserve classification 16 

Geologic time chart 17

FIGURES

1. Index map showing the location of the Bristol/Granite Mountains Wilderness 

Study Area, San Bernardino County, California C2

2. Mineral resource potential and generalized geology of the Bristol/Granite 

Mountains Wilderness Study Area, San Bernardino County, California 4

3. Map of the Bristol/Granite Mountains Wilderness Study Area showing mines 

and prospects, geochemical sample sites, quartz veins, and areas of 

altered rocks 7

TABLE

1. Mines and prospects in and adjacent to the Bristol/Granite Mountains 

Wilderness Study Area CIS

MINERAL RESOURCES OF WILDERNESS STUDY AREAS: 

CENTRAL CALIFORNIA DESERT CONSERVATION AREA

Mineral Resources of the

Bristol/Granite Mountains Wilderness Study Area,

San Bernardino County, California

By Keith A. Howard, James E. Kilburn, Robert W. Simpson, 

Todd T. Fitzgibbon, David E. Detra, and Gary L. Raines 

U.S. Geological Survey

Charles Sabine

U.S. Bureau of Mines

SUMMARY

Abstract

At the request of the Bureau of Land 

Management, 45,000 acres of the Bristol/Granite 

Wilderness Study Area (CDCA-256) were studied by 

the U. S. Geological Survey and the U. S. Bureau of 

Mines. In this report, the area studied is referred to as 

"the wilderness study area", or simply "the study area".

The wilderness study area is located 25 mi 

southeast of Baker, California. Two iron deposits total 

about 110,000 tons at 47 percent iron but are not large 

enough to constitute resources. The potential for 

undiscovered iron resources is low. There is low 

resource potential for undiscovered tungsten, silver, 

gold, lead, zinc, limestone marble, perlite, and oil and 

gas. Sand and gravel resources are present but more 

accessible supplies are abundantly available outside of 

the study area.

Character and Setting

The Bristol/Granite Wilderness Study Area 

(CDCA-256) lies in the Mojave Desert, near Baker, 

Calif. The study area occupies approximately 45,000 

acres and includes the rugged Granite Mountains and 

flanking lowlands on the north and west sides of the 

range (fig. 1). The Granite Mountains are composed of 

Mesozoic (63 to 240 million years before present (Ma); 

see Geologic Time Chart, appendix), plutonic, and 

metaplutonic rocks, with small pendants of calcareous

Paleozoic (240 to 570 Ma) strata (fig. 2). Tertiary (2 

to 63 Ma) igneous dikes, volcanic rocks, coarse 

sedimentary debris, and Quaternary (2 Ma to present) 

alluvium are present in the study area around the 

flanks of the range. There are no active mines in the 

study area.

Mineral Resource Potential

Skarns (formed where calcium-rich rocks have 

been metamorphosed) are favorable hosts for iron and 

tungsten deposits. Small deposits of magnetitehematite contain about 110,000 tons of ore averaging 

47 percent iron at the Iron Victory prospect and 10 

tons at 43 percent iron at the Comanehe mine (fig. 

2). Neither deposit is considered large enough to 

constitute a resource. The potential for undiscovered 

iron resources in the study area is low. Streamsediment samples contain tungsten, molybdenum, and 

the mineral scheelite (indicative of tungsten mineral 

occurrences in skarn rocks). The study area has a low 

potential for undiscovered tungsten resources.

An occurrence of silver at the Silver Lode mine 

adjacent to the wilderness study area is associated 

with sulfides and hydrothermally altered granite along 

fracture zones within a Cretaceous (about 75 Ma) 

pluton. Altered granite of the same pluton exposed 

within the study area adjacent to the Silver Lode mine 

has low potential for undiscovered hydrothermal silver 

and associated lead, zinc, and gold resources.

The study area has low mineral potential for 

undiscovered epithermal gold, limestone marble, 

perlite, and oil and gas resources. Sand and gravel are

C1
115° 50' 115° 40'

BRISTOL/GRANITE MOUNTAINS

WILDERNESS STUDY AREA

(CDCA-256)

Granite___

MOUNTAINS Cove I 2

r"sr't"" MARBLE '*"£_ ° 

MOUNTAINS i\*'

Figure 1. Index map showing the location of the Bristol/Granite Mountains Wilderness Study Area, San Bernardino County, California.

present, but more accessible supplies are abundantly 

available outside the study area.

INTRODUCTION

This mineral resource study is a joint effort of 

the U.S. Geological Survey and the U.S. Bureau of 

Mines. The history and philosophy of such joint 

mineral surveys of U.S. Bureau of Land Management 

Wilderness Study Areas were discussed by Beikman and 

others (1983). Mineral assessment methodology and 

terminology were discussed by Goudarzi (1984). See 

the appendix for the definition of levels of mineral 

resource potential and certainty of assessment. 

Studies by the U.S. Geological Survey are designed to 

provide a reasonable scientific basis for assessing the 

potential for undiscovered mineral resources by 

determining geologic units and structures, possible 

environments of mineral deposition, presence of

geoehemical and geophysical anomalies, and applicable 

ore-deposit models. The U.S. Bureau of Mines 

evaluates identified resources at individual mines and 

known mineralized areas by collecting data on current 

and past mining activities and through field 

examination of mines, prospects, claims, and 

mineralized areas. Identified resources are classified 

according to the system described by U.S. Bureau of 

Mines and U.S. Geological Survey (1980).

Location and Physiography

The Bristol/Granite Mountains Wilderness Study 

Area (CDCA-256) is located in the Mojave Desert of 

southeastern California, about 10 mi south of Kelso 

and 25 mi southeast of the town of Baker (fig. 1). The 

Union Pacific railway passes 7 mi north of the study 

area, and Interstate Highway 40 passes 3 mi to the 

south. Access to the study area is provided by dirt

C2
roads leading west from the Kelbaker Road. The study 

area encompasses most of the rugged Granite 

Mountains; elevations range from 1,890 ft at the 

northwestern corner of the study area to 6,786 ft at 

the range crest. The mountain range contains 

numerous springs and water seeps. The higher 

elevations and north-facing slopes are vegetated by 

pinyon pine, juniper, and various shrubs and grasses. 

Lower elevations and south-facing slopes are more 

sparsely vegetated by yucca, cacti, creosote, and other 

shrubs.

Previous and Present Investigations

The U.S. Bureau of Mines conducted a literature 

search and studied claims records of mining activity in 

and adjacent to the wilderness study area. Field 

examination of mines, prospects, claims, and 

mineralized zones was carried out in 1982, and 

seventy-four rock samples were collected and 

examined in the laboratory (Sabine, 1984). Previous 

reports of mineral occurrences are contained in Wright 

and others (1953), and reports written for the Southern 

Pacific Company (Bonham, 1959; Bonham and 

Cooksley, 1959; Gamble, 1959a, b; Oesterling and 

Spurck, 1964).

The U.S. Geological Survey assessed the mineral 

resource potential of the study area by integrating and 

interpreting geologic, geochemical, and geophysical 

data from existing sources and new investigations. 

Mineral evaluations of adjacent wilderness study areas 

were reported in Yeend and others (1984) and Miller 

and others (1985). Field mapping done in 1984 and 

1985 by K. Howard and T. Fitzgibbon provided most of 

the geologic information for the study area. 

Supplementary geologic mapping was provided by 

Charles Sabine, Lorie Cahn, and Helen Gibbons (all hi 

Stein and Warrick, 1979), by B.E. John (written 

commun., 1980), Bonham (1959), Bonham and Cooksley 

(1959), Gamble (1959a, b), and Miller and others 

(1982). A stream-sediment sampling survey conducted 

in 1984 provided geochemical data (Detra and Kilburn, 

1985). Areas of limonitic alteration were outlined by 

Raines (1983) as a result of his spectrographic study of 

Landsat images; some of the limonitic areas were field 

checked and sampled for geochemical analysis. In 

1983-1984, new gravity data were collected to 

supplement existing gravity data, and aeromagnetic 

data (U.S. Geological Survey, 1981) provided a basis 

for further geophysical interpretations. An aerial 

gamma-ray survey (Geodata International Inc., 1979) 

also provided useful data.

Acknowledgments

The authors wish to acknowledge Michael Miller, 

Steven Munts, Jerry Olson, and Michael Sokaski of the 

U.S. Bureau of Mines Western Field Operations Center, 

and D.H. Sorg, B.E. John, J.K. Nakata, J.E. Wright, 

S.E. Shaw, T. Gage, and J.A. Pitkin of the U.S. 

Geological Survey for assistance in field work and 

laboratory investigations.

APPRAISAL OF IDENTIFIED RESOURCES

By Charles Sabine, U.S. Bureau of Mines

Methods and Scope of Investigation

Preliminary work for this report included 

compilation of available geologic and mineral resource 

literature, production records, and U. S. Bureau of 

Land Management and San Bernardino County claim 

records. In the spring of 1982, mines, prospects, and 

areas containing active and lapsed claims in the study 

area were examined and sampled (table 1).

Seventy-four samples were collected in the study 

area. Chip samples were taken from mineralized 

structures and altered zones. Grab samples were 

collected from mine and prospect dumps. Samples 

were prepared for analysis at the U. S. Bureau of 

Mines Western Field Operation Center and analyzed 

for gold, silver, and other elements by fire-assay and 

atomic-absorption methods by a contract laboratory. 

At least one sample from each locality was analyzed 

by semi-quantitative spectrography for 42 elements, 

including gold, arsenic, copper, iron, lead, 

molybdenum, platinum, silver, tin, and zinc. 

Limestone samples were analyzed at the U.S. Bureau 

of Mines Reno Research Center. Results were 

presented by Sabine (1984).

Mining History

There has been very little mining activity and no 

production in the study area during the past 120 

years. The Comanche mine was first located in 1902 

and was known as the El Companche in 1925 and the 

Comanche in the 1950's. It was known as the 

Christopher in 1965. There were no claims on the 

property when it was examined in 1982.

Claims were located in the vicinity of the Silver 

Lode mine as early as 1902 when the property was 

known as the Pine Ridge mine. The Silver Queen Nos. 

1-4 claims were located in 1919, and the mine was 

known by that name thereafter. Most of the workings 

were developed during the 1930's. The Silver Lode 

Nos. 1 and 2 claims were filed in 1978, and the McCoy 

group of ten lode claims was filed in 1982.

Claims were located for iron in the vicinity of 

the Iron Victory prospect as early as 1912. The 

present claims were located in 1942 and patented 

January 26, 1956.

Reserves and Identified Resources

The Comanche mine and six prospects lie within 

the wilderness study area; the Silver Lode mine is 

adjacent to the study area (fig. 3). The Comanche 

mine is situated in a roof pendant consisting of 

magnesian marble. The marble contains 41 to 45 

percent calcium oxide and 14 to 16 percent magnesium 

oxide. About 10 tons remain from a 110-ton pod of 

magnetite that contained 42.5 percent iron. Less than 

50 tons remain from a mineralized fault breccia that 

averaged 2.5 percent copper and 0.3 oz/ton silver.

C3
115° 45'

APPROXIMATE BOUNDARY 

OF

BRISTOL/GRANITE MOUNTAINS

WILDERNESS STUDY

AREA (CDCA-256)

Figure 2. Mineral resource potential and generalized geology of the Bristol/Granite Mountains Wilderness Study Area, San Bemardino County, 

California.

The Iron Victory prospect explored lenses of 

magnetite and hematite that contain some 

chalcopyrite; they occur along a skarn zone in a 

marble roof pendant. About 110,000 tons of iron-rich 

rock, averaging 47.2 percent iron, are present. The 

largest lens contains about 30,000 tons of iron-rich 

rock. About 150,000 tons of magnesian marble, which 

averages 41.0 percent calcium oxide and 11.7 percent 

magnesium oxide, are also present in the roof pendant.

Silver, copper, lead, and zinc minerals are disseminated along altered joints and in quartz veins in 

granite at the Silver Lode mine (fig. 3). Analyzed 

samples contained as much as 0.12 oz/ton gold, 1.8 

oz/ton silver, 1.1 percent lead, 3.8 percent zinc, and 

0.3 percent copper (table 1). Mineralized zones in the 

workings are not considered to be resources, but they 

may indicate the presence of possible silver-lead-zinc

resources at depth.

Magnesian marble examined at the Comanche 

mine, Iron Victory prospect, and elsewhere in the study 

area contains too much magnesium oxide for 

commercial use other than as agricultural soil 

supplements or crushed stone. Transportation costs to 

existing markets would exceed the value of the rock.

Sand and gravel are abundant within the study 

area. However, more accessible supplies of these 

materials are abundantly available outside the study 

area. According to Yeend and others (1984), the U.S. 

Bureau of Mines considers the windblown sand of much 

of the Kelso Dunes dune field adjacent to the north 

side of the study area to be a source of marginal 

reserves of glass and feldspar sand, with byproduct 

magnetite and gold. Very little of this dune field 

extends into the study area.

C4
EXPLANATION

w

Ag

Au

Fe

Zn

Pb

Lst

Per

Area of low mineral resource potential with some 

evidence of resource forming processes. See 

appendix for definition of levels of mineral 

resource potential and certainty of assessment

COMMODITIES

Tungsten

Silver

Gold

Iron

Zinc

Lead

Limestone

Perlite

Qs 

Qal 

QTs

TV 

Kg 

Jg

TR g 

m

Pg

Oil and gas

DESCRIPTION OF MAP UNITS

Windblown sand (Quaternary)

Alluvium (Quaternary)

Fanglomerate and sedimentary breccia (Quaternary?

and Tertiary) 

Rhyolite dike (Miocene) 

Volcanic rocks (Miocene) 

Granite and granodiorite (Cretaceous) 

Granitoid rocks (Jurassic and Jurassic?) 

Granitoid gneiss (Triassic?) 

Marble, calc homfels, and skam Paleozoic and

Triassic(?) protoliths 

Granitoid rocks (Proterozoic) 

Contact

Fault Dotted where concealed 

Mine or prospect having mineral occurrence

Figure 2. Continued.

ASSESSMENT OF MINERAL RESOURCE POTENTIAL

By Keith A. Howard, James E. Kilburn, Robert W. 

Simpson, Todd T. Fitzgibbon, David E. Detra, and 

Gary L. Raines 

U.S. Geological Survey

Geology

Rock Units

The Bristol/Granite Mountains Wilderness Study 

Area contains rocks ranging in age from Paleozoic to 

Cenozoic (fig. 2). The Granite Mountains are largely 

underlain by Mesozoic plutonic rocks.

Several small pendants of metasedimentary rocks 

are part of the plutonic suite in the Granite 

Mountains. The metamorphosed strata are mainly 

marble, siliceous marble, dolomite marble, and calcsilicate hornfels. Some of the marble and siliceous 

marble can be lithologically correlated with the Bird 

Spring Formation (Pennsylvanian and Permian) and the 

Monte Cristo Limestone (Mississippian), which are 

exposed a few miles to the northeast in the Providence 

Mountains. The siliceous marble contains metamorphic 

wollastonite and phlogopite. Calc-silicate rock 

associated with the Paleozoic marble includes 

laminated calc-silicate hornfels that is tentatively 

correlated with Triassic strata exposed in the Little 

Piute Mountains (Miller and others, 1982). Skarns 

containing diopside, garnet, quartz, and epidote are 

associated with the calcareous rocks and are important 

for resource evaluation (fig. 3). Field relations suggest 

that the skarns formed mainly by intrusion of Jurassic 

diorite and felsic plutonic rocks. Triassic(?) and 

Cretaceous plutonic intrusions also may have 

contributed to skarn formation. Quartzite, schist, and 

metavolcanic rocks of unknown age occur as small 

bodies in the study area.

Plutonic rocks of the Granite Mountains can be 

divided into Triassic(?), Jurassic, and Cretaceous 

intrusive suites. The oldest of these suites consists of 

hornblende quartz diorite gneiss and hornblende quartz 

monzodiorite gneiss containing megacrysts of 

potassium feldspar 2-10 cm across. An inclusion of 

laminated calc-silicate hornfels within the augen 

gneiss suggests that it postdates Triassic(?) calcsilicate strata. The gneissic rocks also contain 

amphibolite inclusions and biotite-rich and diorite 

inclusions. A Triassic(?) age for the gneisses is 

suggested by cross-cutting Jurassic diorite and by the 

quartz-poor, potassium-feldspar-rich composition 

reminiscent of Triassic monzonite in the western 

Mojave Desert (Miller, 1977).

A wide variety of plutonic rocks belong to the 

Jurassic intrusive suite. Quartz monzonite 

characterized by medium-grained lavender potassium 

feldspar crops out along the east side of the Granite 

Mountains. The quartz monzonite is assigned a 

Jurassic age based on its close resemblance to Jurassic 

rocks in the eastern Mojave Desert as described by 

John (1981), D. Miller and others (1982, 1985), and 

Alien and others (1983). A heterogeneous unit of 

diorite and metadiorite gneiss has mutually intrusive 

relations with the quartz monzonite and intrudes the 

Triassic(?) augen gneiss. The diorite unit is 

heterogeneous in texture and composition, and much of 

it consists of fine-grained foliated metadiorite 

characterized by migmatitic wisps of leucocratic 

rock. The Jurassic quartz monzonite and diorite are 

intruded by several other plutonic rocks (here included 

in the Jurassic plutonic suite): fine-grained inclusionspotted quartz monzonite, medium-grained quartz 

monzodiorite, and syenogranite present in varying 

degrees on the north, west, and northeast sides of the 

Granite Mountains.

The Triassic(?) and Jurassic intrusive suites and 

older rocks are metamorphosed, foliated, and locally 

intricately folded throughout most of the Granite

C5
Mountains. The foliation strikes northeast to east, 

dips steeply, and is cut by small, east-striking mafic 

dikes of Late Jurassic or Cretaceous age. The crosscutting mafic dikes have been slightly distorted and 

cut by dikes of undeformed Cretaceous plutonic rocks.

The Cretaceous intrusive suite consists of a 

granodiorite pluton, a zoned pluton, and many granite, 

aplite, and pegmatite dikes. The granodiorite pluton 

forms a sheet-like mass in the western part of the area 

that dips west at moderate angles. The larger zoned 

pluton occupies the southeastern part of the study 

area. A discontinuous border phase of granodiorite is 

intruded by porphyritic monzogranite that forms a 

broad annular zone around, and gradational to, a 

central zone of nonporphyritic monzogranite (Sabine, 

1971). The zoned pluton yielded potassium-argon (KAr) dates of 70.9 to 74.5 Ma on biotite (R.F. Marvin, 

written commun., 1982; M.A. Pernokas, written 

commun., 1982; Miller and others, 1985) and U-Pb data 

on zircon that indicate a similar age (J.E. Wright, 

written commun., 1985).

Sabine (geologic map iii Stein and Warrick, 1979) 

found that the Mesozoic plutonic rocks are cut by 

west-northwest-striking rhyolite dikes. A Miocene age 

for the dikes is likely, based on the prevalence of 

Miocene volcanic rocks in the region. Miocene 

volcanic flows and tuffs of basaltic to rhyolitic 

composition crop out along the southwest border of the 

wilderness study area, where they are in fault contact 

with the Cretaceous zoned pluton. Rhyolitic flow 

rocks adjacent to the study area there are partly 

perlitic.

Tertiary fanglomerate and sedimentary breccia 

flank the north side of the Granite Mountains. They 

are locally in fault contact with Jurassic rocks. 

Deposits of Tertiary or Quaternary fanglomerate 

overlie Jurassic rocks in the northeast part of the 

study area and southeast of Granite Pass. Quaternary 

alluvium laps around the Granite Mountains; it forms a 

thin veneer over partly exposed pediment on the south 

border of the study area. Windblown sand deposits are 

present on the north side of the study area.

Faults and Evidence of Alteration

Faults are present on the periphery of the 

Granite Mountains, but the interior of the range 

contains few faults, in contrast to the adjacent highly 

faulted Old Dad Mountains (fig.2). However, the 

interior does contain a system of altered fracture 

zones that transect the pluton in the eastern and 

southeastern part of the Granite Mountains and define 

a crudely orthogonal pattern along east-northeast- and 

north-northwest-striking joint systems. Individual 

zones are as long as 3 mi and as wide as 0.5 mi. Within 

fracture zones, the granite is sheared, argillized, 

chloritized, and sericitized to varying degrees. 

Copper, lead, and zinc sulfides are disseminated in 

fracture zones at the Silver Lode mine. Quartz veins 

fill fractures in some zones, most notably in the 

Granite Cove area, where gossans also are present. A 

reddish gossan zone covering about one third of an 

acre also crops out high in the southern Granite 

Mountains at the headwaters of Budweiser Wash. A

quartz muscovite vein along one of the northwesttrending fracture zones, on the north side of 

Cottonwood Basin, was sampled in order to investigate 

the age of alteration. The muscovite yielded a K-Ar 

date of 68.0 ± 1.7 Ma (J.K. Nakata, written commun., 

1985). This date is close to the K-Ar dates (70.9 to 

74.5 Ma) on unaltered biotite in the pluton, and to the 

crystallization age inferred for the granite. These 

data indicate that the alteration closely followed 

crystallization of the granite; the alteration may have 

been deuteric or hydrothermal.

A normal fault at least 2 mi long on the 

northeast side of the wilderness study area north of 

Cottonwood basin dips 45-50° to the northeast. The 

fault zone is marked by sericitic breccia a few yards 

thick containing pyrite, and by rust-colored hematitic 

vein quartz. An adit more than 100 feet long was 

driven along the fault zone.

The trace of the Bull Canyon fault, a low-angle 

normal fault of late Tertiary age, skirts around the 

northern base of the Granite Mountains. The fault dips 

20-40° north and northwest, outward from the range. 

A zone of red to tan breccia and gouge, locally over 

300 ft thick, separates a chloritically altered footwall 

of Jurassic and Jurassic(?) plutonic rocks from 

chloritized and brecciated equivalents and Tertiary 

sedimentary breccia in the hanging wall. Striae 

measured at two localities trend in the northwest 

quadrant. The fault breccia, derived from local 

crystalline rocks, was previously interpreted as 

volcanic rock (Stein and Warrick, 1979). The breccia is 

locally calcareous and manganiferous but is more 

generally silicified. It contains brecciated white vein 

quartz, vuggy quartz, jasper, and limonitic boxwork. 

Outcrops of the altered breccia form a band 5 mi long 

in the northwest part of the study area (fig. 3). 

Prospect pits are present in the breccia, but direct 

evidence of mineral deposits was not observed.

West-to-northwest-striking rhyolite dikes in the 

southern Granite Mountains are bordered by 

discolored, brownish granite. At least one of the dikes 

follows an older quartz vein. Sabine (ni Stein and 

Warick, 1979) mapped several faults with similar 

strikes in the same area.

A major northwest-trending fault, the Bristol 

Mountains fault zone (Gamble, 1959a, b), separates the 

Granite Mountains from the Old Dad Mountains to the 

southwest. It juxtaposes Tertiary volcanic rocks of the 

Old Dad Mountains against Cretaceous granodiorite of 

the Granite Mountains. Where exposed in pediment 

adjacent to the southwest corner of the wilderness 

study area, the fault zone is a few feet wide and 

consists of reddish brecciated vein quartz, black 

calcite, and gouge. The fault dips northeast 70-80°. 

In the northern Bristol Mountains, 9 mi northwest of 

the wilderness study area, it dips moderately (50°) to 

steeply northeast (Davis, 1973). In both places, 

Mesozoic plutonic rocks in the hanging wall overlie 

Tertiary supracrustal rocks in the footwall, indicating 

reverse separation.

Remote-Sensing Data on Alteration

A remote-sensing study outlined areas in which 

rocks are discolored by limonite or other iron oxides

C6
115° 45'

 I 

BRISTOL/GRANITE MOUNTAINS

WILDERNESS STUDY AREA

(CDCA-256)

X Mine 

x Prospect

Patented claim

Geochemical sample and 

anomalous elements) 

Quartz vein

Area of altered rocks 

Skam

Figure 3. Map of the Bristol/Granite Mountains Wilderness Study Area showing mines and prospects, geochemical sample sites, quartz veins, 

and areas of altered rocks. Numbers refer to mines and prospects.- 1, unknown; 2, Comanche mine; 3, unknown; 4, Golden Legend Nos. 

1 and 2; 5, unknown; 6, Silver Lode mine; 7,unknown; 8, Iron Victory. Letters refer to anomalous elements: Ag, silver; Ba, barium; Bi, bismuth; 

Cd, cadmium; Cu, copper; La, lanthanum; Mo, molybdenum; Pb, lead; Sn, tin; W, tungsten, Zn, zinc.

(Raines, 1983). The discoloration can result from 

weathering of sulfide minerals or from other processes 

unrelated to alteration. Field reconnaissance 

determined that several discolored areas were not 

altered, but confirmed that skarn is present in lower 

Bighorn Basin, propylitically altered rocks occur along 

the Bull Canyon fault, and pegmatite occurs near the 

crest of the Granite Mountains (fig. 3).

Geochemistry

Reconnaissance geochemical sampling of stream 

sediments was conducted in the study area in 1984 for 

a geochemical survey. Twenty-eight samples were 

collected from drainages near range fronts that drain 

areas ranging from less than one to several square 

miles (see fig. 3). Samples were analyzed for 30 

elements by a six-step semiquantitative emission

spectrographic method (Grimes and Marranzino, 1968); 

analytical results are given in Detra and Kilburn 

(1985). Nonmagnetic heavy-mineral concentrates of 

stream sediments were particularly useful for 

assessing mineralization because they concentrate oreforming sulfide and oxide minerals. Further 

geochemical data comes from analyses of altered 

rocks sampled from inactive mine workings (Detra and 

Kilburn, 1985; table 1) and limonitic areas (G. Raines, 

unpub. data).

Tungsten anomalies are present in Bull Canyon 

and in stream courses that drain the ridge between 

Bighorn and Cottonwood basins (fig. 3). This ridge is 

capped by a large pendant of calcareous 

metasedimentary rocks. The tungsten is probably 

derived from skarn deposits associated with such 

pendants. Samples collected from stream channels 

that provide drainage of the east and west flanks of 

the ridge revealed abundant scheelite and calc-silicate

C7
minerals (relatively rare manganoan diopside being a 

minor component). Anomalous molybdenum, a 

common constituent of tungsten-bearing skarns, 

locally occurs coincident with tungsten anomalies.

A sample of altered rock collected from Bighorn 

Basin for the remote-sensing survey contained 

anomalous concentrations of silver, gold, bismuth, 

cadmium, copper, mercury, and zinc. Gouge from a 

shear zone in an adit at or near prospect No. 3 (fig. 3) 

contained anomalous concentrations of copper, lead, 

tin, and zinc. The presence of pyrite in this sample 

may explain iron oxide stains found within the shear 

zone. Five miles east of Bighorn Basin, in the area of 

the Bull Canyon fault, propylitically altered rocks 

contained anomalous concentrations of arsenic, 

cadmium, copper, molybdenum, and antimony. These 

elements are sometimes associated with epithermal 

deposits of gold.

Evidence of hydrothermal activity also exists on 

the south side of Cottonwood basin at or near the site 

of the Silver Lode mine (fig. 3, No. 6), where quartz 

veins with disseminated pyrite and minor veinlets of 

galena are evident. A geochemical sample composited 

from mine tailings contained anomalous concentrations 

of silver, barium, bismuth, cadmium, copper, lead, and 

zinc. This trace-element signature correlates with the 

sulfide assemblage of galena, chalcopyrite, sphalerite, 

and pyrite identified in the concentrate. Lasermicroprobe studies confirmed the presence of silver 

and bismuth in galena, and cadmium and copper were 

found to be integrants of sphalerite. Bornite and 

covellite were also reported at this locale by Gamble 

(1959b). Pegmatite samples collected about 4 mi east 

of the mine for the remote-sensing study contained a 

similar assemblage of elements.

Barium and lanthanum anomalies occur together 

in stream-sediment samples collected from Willow 

Spring basin near the southern edge of the wilderness 

study area (fig. 3). Barite was identified optically. 

Since most barite deposits in the region occur in veins 

and small stringers (Wright and others, 1953), it seems 

likely that the barium present in the concentrates in 

the study area has a similar origin. Geologic or 

geochemical evidence to indicate that the barite 

(barium) is associated with mineralized systems of 

economic interest has not been found. The rare-earth 

phosphate monazite, a common accessory mineral in 

granitic rocks, was identified in the optical study and 

probably is the source of the anomalous lanthanum.

Geophysical Studies

Aero magnetic data for the study area were 

extracted from a regional survey of the Needles 1° x 

2° quadrangle (U.S. Geological Survey, 1981), for 

which east-west flight lines were spaced 

approximately 0.5 mi apart and flown at a nominal 

elevation of 1,000 ft above the ground surface. The 

data obtained over the study area were reduced to the 

pole (Baranov and Naudy, 1964) to remove 

asymmetries in the magnetic anomalies and better 

define rock bodies with which the anomalies are 

associated. Some anomalies in the study area can be 

attributed to inconstant flight altitude above the 

rugged terrain.

Magnetic anomalies within the study area range 

from highs of about 300 gammas to lows of 

approximately -200 gammas. These anomalies are 

modest in amplitude by comparison with those 

occurring in adjacent mountain ranges. Two 

occurrences of magnetite noted by the U.S. Bureau of 

Mines, one a 20 ft by 30 ft pod at the Comanche mine 

and the other located in a skarn at the Iron Victory 

prospect, do not coincide with aeromagnetic 

anomalies, although the latter occurrence does lie near 

the southeast end of a moderate high over Triassic(?) 

gneissic rocks that are themselves moderately 

magnetic. Therefore, the magnetite bodies must be 

small; the aeromagnetic pattern does not suggest the 

presence of a large unseen subsurface accumulation.

A magnetic high over the mouth of Cottonwood 

basin in the eastern part of the study area is probably 

caused by Jurassic or Cretaceous igneous rocks 

exposed in the area. A series of magnetic lows located 

in the northern and northwestern parts of the study 

area lie over or are adjacent to the low-angle Bull 

Canyon fault. These low-intensity anomalies probably 

reflect topographic effects and natural variations in 

magnetite content of mostly unaltered plutonic rocks, 

although loss of magnetite in altered rocks may in part 

account for the lows. Changes in the patterns of 

magnetic anomalies across Budweiser Wash indicate 

that the northwest-trending Bristol Mountains fault 

zone is a major fault zone. Negative magnetic 

anomalies occurring along the trend of the fault zone, 

especially to the south of the Granite Mountains, could 

be caused by alteration; however, no evidence of 

mineralization was seen in adjacent parts of the study 

area that would account for it.

The regional isostatic gravity field appears in 

Roberts and others (1981). New gravity data collected 

in and near the study area by the U.S. Geological 

Survey in 1983 and 1984 were combined with existing 

data in order to prepare an isostatic residual-gravity 

map. The coverage is adequate for defining major 

structural boundaries and distinguishing geologic units 

of regional extent, provided that density contrasts 

exist.

Isostatic residual-gravity values range from a 

high of -10 mGal in the northern part of the study area 

over exposures of Jurassic gneiss to a low of-26 mGal 

in the south over Cretaceous granite. This relation is 

consistent with the distribution of gravity highs and 

lows over Jurassic and Cretaceous rocks in many of 

the neighboring ranges (for example, Miller and others, 

1985). A linear, northwest-striking gradient along the 

southwest side of the study area indicates that the 

Bristol Mountain fault zone juxtaposes unlike rocks 

with less dense rocks on the southwest side. Gravity 

values over alluviated areas at the northwest and 

northeast edges of the wilderness study area suggest 

that sedimentary fills are less than 1,000 ft thick.

An aerial gamma-ray survey (Geodata 

International, Inc., 1979) detected uranium levels 

above the normal background level over parts of the 

Granite Mountains. However, the anomalies correlate 

closely with flight altitude above terrain and not 

closely with geologic units. Flight altitude often 

greatly exceeded nominal during the aerial traverses 

of this rugged area, so terrain corrections and 

resulting anomalies may be unreliable. The gammaC8
ray-survey data are not considered to indicate the 

presence of significant uranium or thorium 

concentrations in the wilderness study area.

Mineral and Energy Resources

Geologic, geochemical, and geophysical data 

indicate that the Bristol/Granite Mountains Wilderness 

Study Area has low resource potential for tungsten, 

silver, gold, lead, zinc, limestone marble, perlite, and 

oil and gas. See the appendix for definition of mineral 

resource potential and certainty of assessment 

(Goudarzi, 1984). Figure 2 outlines areas of low 

potential for mineral resources for which there are 

indications that mineralization processes occurred.

Skarn Iron and Tungsten

Skarns, formed by contact metasomatism of 

calcareous strata, are favorable hosts for iron and 

tungsten deposits. Iron deposits at the Iron Victory 

and Comanche mines are probably similar in origin to 

other iron deposits in the eastern Mojave Desert, 

including the much larger Vulcan mine iron deposit 

located 8 mi northeast of the study area (Miller and 

others, 1985). Most such deposits occur at intrusive 

contacts of Jurassic plutons with carbonate rocks. 

Based on the lack of sharp aeromagnetic highs and the 

limited extent of carbonate rocks, no large iron 

deposits are thought to exist in the study area. Small 

undiscovered bodies of iron would not constitute 

resources now or in the foreseeable future. The 

mineral resource potential for iron is therefore 

considered to be low in areas where skarns are present, 

with a C certainty level.

Based on the presence of the tungsten-bearing 

mineral scheelite and anomalous concentrations of 

tungsten and molybdenum in stream sediments 

downstream from skarns, tungsten appears to be 

associated with skarns in the area. There has been no 

known exploration for tungsten in the study area. No 

tungsten minerals were seen in outcrop. The resource 

potential for tungsten in the skarns of the study area 

and downstream placers is considered to be low, with a 

C certainty level. Studies of the tungsten minerals in 

outcrop could improve the certainty of this 

assessment.

Hydrothermal Silver

The altered fracture zones (fig. 3) in and near 

the zoned Cretaceous pluton occupying the 

southeastern part of the study area (fig. 2) provide 

evidence of hydrothermal or deuteric fluids that may 

represent a mineralizing system. This alteration 

probably closely followed the emplacement of the 

pluton at several miles depth, and was formed at a 

moderate to low temperature, as indicated by the 

presence of quartz and quartz-muscovite veins, 

chloritized granite, and sulfides of copper, zinc, lead, 

and iron at the Silver Lode mine. In the area of the 

Comanche mine, the presence of iron-staining and 

copper- and iron-sulfide minerals in fracture zones

north of the pluton may be related to the same 

alteration event. Geochemically anomalous silver, 

barium, bismuth, cadmium, zinc, lead, and gold, and 

the presence of sulfides at the Silver Lode mine (just 

outside the study area) indicate that similar small 

occurrences of silver and associated zinc, lead, and 

gold may be present along adjacent zones of fractured 

and altered granite in the study area. Any such 

occurrences may be low-grade and even smaller than 

the occurrence at the Silver Lode mine. The mineral 

resource potential for hydrothermal silver and 

associated lead, zinc, and gold in two areas within the 

wilderness study area is considered to be low, with a C 

certainty level.

Epithermal Gold in Fault Breccias

Extensive iron-stained breccia along the Bull 

Canyon low-angle normal fault on the northwest flank 

of the Granite Mountains provides a potential 

environment for epithermal or low-grade hot-springtype gold deposits. The presence of limonite 

boxworks, iron-staining, jasper, and quartz veinlets 

suggests that alteration produced silica deposits and 

sulfide minerals; reconnaissance geochemical sampling 

shows anomalous concentrations of arsenic, cadmium, 

copper, molybdenum, and antimony. There is no direct 

evidence of gold or other mineral resources. 

Accordingly, the mineral resource potential for 

epithermal gold in the breccia is considered to be low, 

with a C certainty level. A thorough geochemical 

survey of the breccia would improve the certainty of 

assessment.

The fault zone north of Cottonwood basin on the 

east side of the study area also contains iron-stained 

vein quartz, and it has been prospected. No evidence 

of significant mineral deposits was observed, and this 

area therefore has a low resource potential for 

epithermal gold, with a C certainty level.

Two other areas have some indicators of a 

geologic environment possibly suitable for gold 

mineralization. However, after examination of these 

areas, described below, it was concluded that gold is 

less likely to occur in these areas than in the two areas 

described above. At the southwest boundary of the 

study area, the Bristol Mountains fault zone is present 

beneath alluvium. Iron-stained vein quartz occurring 

along the fault zone indicates the possibility of 

epithermal mineralization. It is unlikely that gold 

resources exist along the fault zone because the fault 

zone is narrow and lacks known mineral deposits where 

it is exposed close to the study area, and because no 

important deposits are known to exist where the fault 

zone is extensively exposed 10 mi to the northwest in 

the Bristol Mountains. Accordingly, the mineral 

resource potential for gold in these areas is low, with a 

C certainty level.

Oil and Gas

There is no potential for oil and gas within the 

crystalline rocks of the Granite Mountains. Cenozoic 

basin sediments north and northwest of the Granite 

Mountains provide a possible environment for oil and

C9
gas if the sediments are thick enough, but gravity data 

suggest that these sediments are less than 1,000 ft 

thick. Oil and gas resources are unlikely to be present 

unless the sediments are much thicker. The potential 

for oil and gas resources in areas underlain by 

Cenozoic materials is low, with a D certainty level.

Limestone

Limestone marble, if highly calcareous, can 

constitute a resource. At the Comanche mine and the 

Iron Victory prospect, marble is magnesian according 

to analyses by the U. S. Bureau of Mines; much of the 

marble elsewhere in the study area is siliceous. Highly 

calcareous marble may occur locally along the east 

border of the study area southeast of the Comanche 

mine, where several acres of white calcareous marble, 

probably correlative with the unmetamorphosed Monte 

Cristo Limestone, are present a few hundred feet 

outside the east border (NW section 36, T.9N., 

R.12E.). Metamorphosed Monte Cristo Limestone is 

mined elsewhere in the Mojave Desert. However, the 

Monte Cristo Limestone was not recognized within the 

study area, and so the mineral resource potential for 

limestone marble within a small area in the eastern 

part of the study area is low with a C certainty level.

Perlite

Perlite is present in Tertiary volcanic rocks in 

the Old Dad Mountains adjacent to the southwest 

corner of the study area. The Tertiary volcanic rocks 

are undoubtedly present in small areas beneath 

alluvium in the study area southwest of the Bristol 

Mountains fault zone (fig. 2). Perlite was not observed 

within the wilderness study area, but could be present 

under a veneer of alluvium southwest of the Bristol 

Mountains fault zone; therefore, the potential for 

perlite resources is low with a C certainty level.

REFERENCES CITED

Alien, C.M., Miller, D.M., Howard, K.A., and Shaw, 

S.E., 1983, Field, petrologic and chemical 

characteristics of Jurassic intrusive rocks, 

eastern Mojave Desert, southeastern California: 

Geological Society of America, Cordilleran 

Section, Abstracts with Programs, v. 15, no. 5, p. 

410-411.

Baranov, V., and Naudy, H., 1964, Numerical 

calculation of the formula of reduction to the 

magnetic pole: Geophysics, v. 29, p. 67-79.

Beikman, H.M., Hinkle, M.E., Frieders, T., Marcus, 

S.M., and Edward, J.R., 1983, Mineral surveys by 

the Geological Survey and the Bureau of Mines of 

Bureau of Land Management Wilderness Study 

Areas: U.S. Geological Survey Circular 901, 28

PBonham, H.F., Jr., 1959, Geology and mineral 

resources of Township 8 North, Ranges 13 and 14 

East, San Bernardino Base and Meridian, San 

Bernardino County, California: San Francisco,

Calif., Southern Pacific Company, unpub. report 

and l:24,000-scale map, 38 p.

Bonham, H.F., Jr., and Cooksley, J. Jr., 1959, Geology 

and Mineral resources of Township 9 North, 

Ranges 13 and 14 East, San Bernardino Base and 

Meridian, San Bernardino County, California: 

San Francisco, Calif., Southern Pacific Company, 

unpub. report and l:24,000-scale map, 22 p.

Davis, G.A., 1973, Geologic studies of the 

hypothesized Death Valley fault zone, in 

Southern California Edison Company, 

Information concerning site characteristics, 

Vidal Nuclear Generating Station, Vol. 5, 

Appendix 2.5-E, Attachment A, p. E-A-1 to E-A17.

Detra, D.E., and Kilburn, J.E., 1985, Analytical results 

and sample locality map of heavy-mineralconcentrate samples from the Bristol/Granite 

Mountains (CDCA-256) Wilderness Study Area, 

San Bernardino County, California: U.S. 

Geological Survey Open-File Report 85-510, 

scale 1:62,500, 8 p.

Gamble, J., 1959a, Geology and mineral resources of 

Township 8 North, Ranges 11 and 12 East, San 

Bernardino Base and Meridian, San Bernardino 

County, California: San Francisco, Calif., 

Southern Pacific Company, unpub. report and 

l:24,000-scale map, 22 p.

___1959b, Geology and mineral resources of Township 

9 North, Ranges 11 and 12 East, San Bernardino 

Base and Meridian, San Bernardino County, 

California: San Francisco, Calif., Southern 

Pacific Company, unpub. report and 1:24,000- 

scale map, 18 p.

Geodata International Inc., 1979, Aerial radiometric 

and magnetic survey Needles national 

topographic map, California and Nevada: U.S. 

Department of Energy Report GJBX-114 (79).

Goudarzi, G. H., 1984, Guide to mineral survey reports 

on public lands: U. S. Geological Survey, OpenFile Report 84-787, 41 p.

Grimes, D.J., and Marranzino, A.P., 1968, Directcurrent arc and alternating-current spark 

emission spectrographic field methods for the 

semiquantitative analysis of geologic materials: 

U.S. Geological Survey Circular 591, 6 p.

John, B.E., 1981, Reconnaissance study of Mesozoic 

plutonic rocks in the Mojave Desert region, in 

Howard, K.A., Carr, M.D., and Miller, D.M., eds., 

Tectonic framework of the Mojave and Sonoran 

Deserts, California and Arizona: U.S. Geological 

Survey Open-file Report 81-503, p. 48-50.

Miller, C.R., 1977, Early alkalic plutonism in the calcalkalic batholithic belt of California: Geology, 

v. 5, p. 685-688.

Miller, C.F., Howard, K.A., and Hoisch, T.D., 1982, 

Mesozoic thrusting, metamorphism, and 

plutonism, Old Woman-Piute Range, southeastern 

California, in Frost, E.G., and Martin, D.L., eds., 

Mesozoic-Cenozoic tectonic evolution of the 

Colorado River Region, California, Arizona, and 

Nevada (Anderson-Hamilton Volume): San Diego, 

Cordilleran Publishers, p. 561-581.

Miller, D.M., Click, L.L., Goldfarb, R., Simpson, R.W., 

Hoover, D.M., Detra, D., Dohrenwend, J.C., and 

Munts, S.R., 1985, Mineral resources and

C10
resource potential map of the South Providence 

Mountains Wilderness Study Area, San Bernardino 

County, California: U.S. Geological Survey 

Miscellaneous Field Studies Map MF-1780-A, 

scale 1:62,500, 29 p.

Miller, D.M., Howard, K.A., and John, B.E., 1982, 

Preliminary geology of the Bristol Lake region, 

Mojave Desert, California, in Cooper, J.D., 

compiler, Geologic excursions in the California 

desert: Geological Society of America 78th 

Annual Meeting, Cordilleran Section, Anaheim, 

California, 1982, p. 91-100.

Oesterling, W.A., and Spurck, W.H., 1964, Eastern 

Mojave and Colorado Deserts (part III), in 

Minerals for Industry, Vol. Ill: San Francisco, 

Calif., Southern Pacific Company, p. 99-108.

Raines, G.L., 1983, Preliminary map of limonitic 

alteration for portions of the Needles 1° x 2° 

quadrangle, Arizona and California: U.S. 

Geological Survey Open-file Report 83-421, scale 

1:250,000, 7 p.

Roberts, C.W., Jachens, R.C., and Oliver, H.W., 1981, 

Preliminary isostatic residual gravity map of 

California: U.S. Geological Survey Open-File 

Report 81-573, 5 sheets, scale 1:750,000.

Sabine, C., 1971, Plutonic rocks of the Granite 

Mountains, eastern San Bernardino, County, 

California: Geological Society of America 

Abstracts with Programs, v. 3, no. 2, p. 189.

___1984, Mineral investigation of the Bristol/Granite 

Mountains Wilderness Study Area, San Bernardino 

County, California: U. S. Bureau of Mines Open 

File Report MLA 28-84, 26 p.

Stein, B.A., and Warrick, S.F., eds., 1979, Granite 

Mountains resource survey: University of 

California Santa Cruz, Environmental Field 

Program Publication No. 1, 361 p.

U.S. Bureau of Mines and U.S. Geological Survey, 1980, 

Principles of a resource/reserve classification 

for minerals: U.S. Geological Survey Circular 

831, 5 p.

U.S. Geological Survey, 1981, Aeromagnetic map of 

the Needles 1° x 2° quadrangle, California and 

Arizona: U.S. Geological Survey Open-File 

Report 81-85, scale 1:250,000.

Wright, L.A., Stewart, R.M., Gay, T.E., Jr., and 

Hazenbush, G.C., 1953, Mines and mineral 

deposits of San Bernardino County, California: 

California Journal of Mines and Geology, v. 49, 

p. 49-259, with tabulated list of mines and 

mineral deposits.

Yeend, W., Dohrenwend, J.C., Smith, R.S.U., Goldfarb, 

R., Simpson, R.W., Jr., and Munts, S.R., 1984, 

Mineral resources and mineral resource potential 

of the Kelso Dunes Wilderness Study Area 

(CDCA-250), San Bernardino County, 

California: U.S. Geological Survey Open-file 84- 

647, 15 p.

C11

APPENDIXES

DEFINITION OF LEVELS OF MINERAL RESOURCE POTENTIAL 

AND CERTAINTY OF ASSESSMENT

Definitions of Mineral Resource Potential

LOW mineral resource potential is assigned to areas where geologic, geochemical, and geophysical 

characteristics define a geologic environment in which the existence of resources is permissive. This 

broad category embraces areas with dispersed but insignificantly mineralized rock as well as areas with 

few or no indications of having been mineralized.

MODERATE mineral resource potential is assigned to areas where geologic, geochemical, and geophysical 

characteristics indicate a geologic environment favorable for resource occurrence, where interpretations 

of data indicate reasonable likelihood of resource accumulation, and (or) where an application of 

mineral-deposit models indicates favorable ground for the specified type(s) of deposits.

HIGH mineral resource potential is assigned to areas where geologic, geochemical, and geophysical 

characteristics indicate a geologic environment favorable for resource occurence, where interpretations of 

data indicate a high degree of likelihood for resource accumulation, where data supports mineral-deposit 

models indicating presence of resources, and where evidence indicates that mineral concentration has 

taken place. Assignment of high resource potential to an area requires some positive knowledge that 

mineral-forming processes have been active in at least part of the area.

UNKNOWN mineral resource potential is assigned to areas where information is inadequate to assign low, 

moderate, or high levels of resource potential.

NO mineral resource potential is a category reserved for a specific type of resource in a well-defined area.

Levels of Certainty

t

U/A

UNKNOWN

POTENTIAL

H/B

HIGH POTENTIAL

M/B

MODERATE POTENTIAL

L/B

LOW

POTENTIAL

H/C

HIGH POTENTIAL

M/C 

MODERATE POTENTIAL

L/C

LOW

POTENTIAL

H/D

HIGH POTENTIAL

M/D 

MODERATE POTENTIAL

L/D

LOW POTENTIAL

N/D

NO POTENTIAL

B C 

LEVEL OF CERTAINTY

A. Available information is not adequate for determination of the level of mineral resource potential.

B. Available information suggests the level of mineral resource potential.

C. Available information gives a good indication of the level of mineral resource potential.

D. Available information clearly defines the level of mineral resource potential.

Abstracted with minor modifications from:

Taylor, R. B., and Steven, T. A., 1983, Definition of mineral resource potential: Economic Geology,

v. 78, no. 6, p. 1268-1270. 

Taylor, R B., Stoneman, R. J., and Marsh, S. P., 1984, An assessment of the mineral resource potential

of the San Isabel National Forest, south-central Colorado: U.S. Geological Survey Bulletin 1638, p.

40-42. 

Goudarzi, G. H., compiler, 1984, Guide to preparation of mineral survey reports on public lands: U.S.

Geological Survey Open-File Report 84-0787, p. 7, 8.

C15
RESOURCE/RESERVE CLASSIFICATION

ECONOMIC

MARGINALLY 

ECONOMIC

SUBECONOMIC

IDENTIFIED RESOURCES

Demonstrated

Measured

Res<

Mar 

Rest

Indicated

srves

ginal 

jrves

Demonstrated 

Subeconomic 

Resources

Inferred

Inferred 

Reserves

Inferred 

Marginal 

Reserves

Inferred 

Subeconomic 

Resources

UNDISCOVERED RESOURCES

Probability Range

Hypothetical Speculative

Major elements of mineral resource classification, excluding reserve base and inferred reserve base. Modified from U.S. Bureau of Mines 

and U.S. Geological Survey, 1980, Principles of a resource/reserve classification for minerals: U.S. Geological Survey Circular 831, p. 5.

C16
GEOLOGIC TIME CHART 

Terms and boundary ages used by the U.S. Geological Survey in this report

EON

Phanerozoic

Proterozoic

Archean 

pre-Ar<

ERA

Cenozoic

Mesozoic

Paleozoic

Late Proterozoic

Middle Proterozoic

Early Proterozoic

Late Archean

Middle Archean

Early Archean 

:hean 2

PERIOD

Quaternary

Tertiary

Neogene 

Subperiod

Paleogene 

Subperiod

Cretaceous

Jurassic

Triassic

Permian

Carboniferous 

Periods

Pennsylvanian

Mississippian

Devonian

Silurian

Ordovician

Cambrian

 -(3800?)- -

EPOCH

Holocene

Pleistocene

Pliocene

Miocene

Oligocene

Eocene

Paleocene

Late 

Early

Late 

Middle 

Early

Late 

Middle 

Early

Late 

Early

Late 

Middle 

Early

Late 

Early

Late 

Middle 

Early

Late 

Middle 

Early

Late 

Middle 

Early

Late 

Middle 

Early

_ _

AGE ESTIMATES 

OF BOUNDARIES 

(in Ma)

- 0.010

- 1.7

\j

S\M

 IP

_ cc

cm

- 96

1 OO

one

- -240

^<JV

*\Ort - ~330

 OCn

- 410

 4^R *too 

- 500

o/ u

- 900 

- 1600

 oenn

oUUU

- 3400 

 Accn 

'Rocks older than 570 Ma also called Precambrian, a time term without specific rank. 

Informal time term without specific rank.

C17
g

CO

TABLE 1. Mines and prospects in and adjacent to the Bristol/Granite Mountains Wilderness Study Area

Map 

no. Name Geology Workings Sa

o 

hj 

o

««J 

00 

Ui

t

o 

-p00

1 Unknown

2 Comanche mine

Unknown

Golden Legend 

Nos. 1 and 2

Unknown*

Silver Lode 

mine*

Unknown

Iron Victory

prospect

(patented)

Milky quartz vein, 1 ft thick and 100 ft 

long, in granodiorite.

Wedge-shaped pod of chalcopyritebearing magnetite 20 ft long, 3 ft 

thick, and 19 ft wide, replaced 

marble along the footwall of fault 

in upper adit. Pod originally contained 

about 110 tons, of which about 10 

remain. Interstitial malachite and 

azurite occur in zone of fault breccia 

40 ft long and 2 ft thick. Less than 

50 tons of mineralized breccia remain. 

Deposit is in 400-ft-long roof pendant 

of marble in diorite and quartz monzonite.

Green malachite stain on diorite at 

portal. No other mineralized structures.

Milky quartz veins, as thick as 7 ft and 

as long as 40 ft, in quartz monzonite.

Disseminated chrysocolla and pyrite in 

altered quartz monzonite.

Sulfides and secondary minerals containing 

silver, lead, zinc, and copper disseminated along altered joints in granite 

and in the quartz veins. Altered zones 

and veins range from less than 1 in. to 

1 ft thick; most are less than 6 in. 

thick.

East-northeast-trending zone of enechelon quartz veins in altered granite 

is more than 2,000 ft long. Individual 

veins as thick as 3 ft and as long 

as 100 ft.

Lenses of magnetite and hematite with 

some chalcopyrite occur in a 400 x 150- 

ft skarn zone in a roof pendant of 

marble in diorite and granite.

One 12- by 10-ft pit.

Two adits, one pit. Upper 

adit: 70 ft of drift, 

one stope open to surface, 

winze to lower level (unmapped), 

Lower cross-cut adit: 205 

ft long, no mineralized 

structures.

One adit, 104 ft long. 

One pit. 

One pit.

Two adits, 200 and 85 ft long, 

three shafts, five pits, and 

one trench.

One pit.

One cut, one pit,

One sample no sign

Two chip samples of 

iron; a grab sample 

10.7% iron, 0.86% c

Four chip samples a

average 2.5% copper 

0.3 oz/ton silver r

samples of marble c

and 15.6 and 13.8% 

Three samples no s

Three samples no s

One sample 0.115% 

0.09% lead, and 0.1 

Twenty-seven sample

and grab samples co

ton gold, 1.8 oz/to

1.1? lead, and 3.8% 

averaged 0.005 oz/t

silver, 0.02% coppe

zinc

Three samples no s

About 110,00 tons o

47.2? iron; the lar

contains about 30,0

tons of marble aver

MgO. Five samples 

limestone were coll

 Outside study area

00