Mineral Resources

Mount Nutt Wilderness Study

Mohave County, Arizona

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Chapter D

Mineral Resources of the

Mount Nutt Wilderness Study Area,

Mohave County, Arizona

By FLOYD GRAY, ROBERT C. JACHENS, 

ROBERT J. MILLER, ROBERT C. TURNER, ERIC K. LIVO, 

DANIEL H. KNEPPER, JR., and JOHN MARIANO 

U.S. Geological Survey

CARL L. ALMQUIST 

U.S. Bureau of Mines

U.S. GEOLOGICAL SURVEY BULLETIN 1737

MINERAL RESOURCES OF WILDERNESS STUDY AREAS: 

BLACK MOUNTAINS REGION, ARIZONA
DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, JR., Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

Any use of trade, product, or firm names

in this publication is for descriptive purposes only

and does not imply endorsement by the U.S. Government

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1990

For sale by the

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Library of Congress Cataloging-in-Publication Data

Mineral resources of the Mount Nutt wilderness study area. Mohave 

County, Arizona / by Floyd Gray ... [et al.].

p. cm. (U.S. Geological Survey bulletin : 1737) (Mineral 

resources of wilderness study areas Black Mountains region, Arizona 

: ch. D) Includes bibliographical references. 

Supt. of Docs, no.: I 19: 1737-D

1. Mines and mineral resources Arizona Mount Nutt Wilderness. 

2. Mount Nutt Wilderness (Ariz.) I. Gray, Floyd. II. Series. 

III. Series: Mineral resources of wilderness study areas Black 

Mountains region, Arizona: ch. D.

QE75.B7 no. 1737-D 557.3 s dc20 90-3813 

UN24.A6] [553 1 .09791'59] CIP
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 

Mount Nutt Wilderness Study Area (AZ-020-Q24), Mohave County, Arizona.

CONTENTS

Summary Dl

Abstract Dl 

Character and setting Dl 

Identified mineral resources D2 

Mineral resource potential D2 

Introduction D3

Area description D3 

Previous and present investigations D3 

Acknowledgments D5 

Appraisal of identified resources D6 

Methods D6

Mining and mineral exploration history D6 

Mines and prospects, mining claims and leases D6 

Reserves and identified resources D6 

Assessment of mineral resource potential D7 

Geology D7

Stratigraphy D7 

Structure D8

Brecciation and alteration D8 

Geochemical studies D9 

Methods D9 

Results D9

Geophysical studies D10 

Aeromagnetic data D10 

Gravity data D10 

Radiometric data D13 

Remote sensing D13 

Interpretation D13 

Results D13

Mineral and energy resource potential D14 

References cited D16 

Appendixes D19

Definition of levels of mineral resource potential and certainty of

assessment D20

Resource/reserve classification D21 

Geologic time chart D22

FIGURES

1. Index map showing location of Mount Nutt Wilderness Study Area, Mohave 

County, Arizona D2

2. Map showing mineral resource potential and generalized geology of Mount Nutt 

Wilderness Study Area, Mohave County, Arizona D4

3. Map showing aeromagnetic anomalies of Mount Nutt Wilderness Study Area, 

Mohave County, Arizona D12

4. Map showing areas of alteration minerals in Mount Nutt Wilderness Study Area, 

Mohave County, Arizona D15

TABLE

1. Analyses of altered rock samples in and near Mount Nutt Wilderness Study 

Area, Mohave County, Arizona Dll

Contents

Mineral Resources of the

Mount Nutt Wilderness Study Area,

Mohave County, Arizona

By Floyd Gray, Robert C. Jachens, Robert J. Miller, Robert C. Turner, 

Eric K. Livo, Daniel H. Knepper, Jr., and John Mariano 

U.S. Geological Survey

Carl L. Almquist 

U.S. Bureau of Mines

SUMMARY

Abstract

The Mount Nutt Wilderness Study Area (AZ-020-024) is 

located in the Black Mountains about 15 mi west of Kingman, 

Arizona. At the request of the U.S. Bureau of Land Management, approximately 27,210 acres of the wilderness study 

area was evaluated for mineral resources (known) and mineral resource potential (undiscovered). In this report, the area 

studied is referred to as the "wilderness study area" or simply 

"the study area;" any reference to the Mount Nutt Wilderness 

Study Area refers only to that part of the wilderness study area 

(27,210 acres) for which a mineral survey was requested. 

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

conducted geological, geochemical, and geophysical surveys 

to assess the identified mineral resources and mineral resource potential of the study area. Fieldwork for this report 

was carried out in 1987 and 1988. A gold resource totaling 

at least 56,000 troy oz has been identified at two sites in 

Secret Pass Canyon, less than 0.5 mi north of the study area. 

No other metallic mineral resources were identified inside the 

study area. An area near the center of the study area contains 

fire agate, a gem stone. On the basis of tonnage, site accessibility, and current production methods, this area is considered an indicated subeconomic fire-agate resource for the 

foreseeable future. Sand and gravel are present in the study 

area. An area surrounding the Tincup mine and including a 

small portion of the extreme north-central part of the study 

area has high potential for gold and low potential for silver, 

lead, and mercury. Three areas in the extreme northwestern, 

north-central, and southwestern parts of the study area have

Manuscript approved for publication, April 27, 1990.

moderate potential for gold and low potential for silver, lead, 

and mercury. A small area near the known fire-agate resource in the south-central part of the study area has low 

potential for fire agate. Large areas in the eastern and central 

parts of the study area have low potential for perlite and 

zeolite resources. The entire study area has no potential for 

oil and gas and no potential for geothermal resources.

Character and Setting

The Mount Nutt Wilderness Study Area is located 

just north of the town of Oatman, Arizona, approximately 

15 mi west of Kingman, Arizona (fig. 1). It is situated 

between Arizona Highway 68 and old U.S. Highway 66. 

The study area has a total relief of about 3,000 ft; the 

highest points in the study area are an unnamed peak 

(Benchmark Nutt, 5,216 ft) and Mount Nutt (5,062 ft). The 

benchmark lies approximately 1 mi northeast of Mount 

Nutt. These peaks are surrounded by precipitous cliffs, 

small mesas, rough slopes, and several steep-walled 

canyons, the deepest of which is Grapevine Canyon. The 

area is underlain by Proterozoic (see "Appendixes" for 

geologic time chart) granite and gneiss that is overlain by 

or in fault contact with Tertiary volcanic rocks and 

Holocene sand and gravel. Small late Miocene rhyolitic 

intrusive bodies cut the older Tertiary rocks in several 

places in the study area and are typically associated with 

localized alteration. Volcanic rocks in the study area are 

cut by numerous, dominantly north-trending high-angle 

normal faults. Dilatant zones resulting from the 

intersections of these faults or from curved fault planes 

served to localize any hydrothermal alteration and gold 

mineralization that may have occurred.

Mount Nutt Wilderness Study Area, Mohave County, Arizona D1
Identified Mineral Resources

A gold resource totaling at least 56,000 troy oz was 

identified by Fischer-Watt Gold Co., Inc., at two sites in 

Secret Pass Canyon, one site just east of the study area and 

the other less than 0.5 mi north of the study area. A block 

of mining claims was located near the center of the study 

area for fire agate, a gem stone. Hand-sorted specimens, 

averaging $30-100 per Ib and rarely $1,000 or more, have 

been extracted from the site. On the basis of a rough size 

estimate, current production methods, and site accessibility, 

this deposit will be an indicated subeconomic fire-agate resource for the foreseeable future. Sand and gravel in the 

study area have no qualities that would make them more 

valuable than abundant supplies available from established 

sources closer to existing markets.

Mineral Resource Potential

Geologic, geochemical, and geophysical studies 

show that the Mount Nutt Wilderness Study Area has an 

area with high potential for gold and low potential for silver, lead, and mercury in the north-central part of the study 

area. Three areas in the northwestern, southwestern, and 

north-central parts of the study area have moderate potential for gold and low potential for silver, lead, and mercury 

resources (fig. 2). That these areas are predominantly 

underlain by fractured, veined, and altered volcanic rocks 

suggests volcanic-hosted gold deposits may be present.

The areas are cut by mostly north- to northwest-trending 

faults with localized areas of thin, irregular stockwork 

veins consisting of calcite and minor amounts of quartz; 

limonite staining and localized illitic alteration characterize 

the stockwork. Anomalous concentrations of elements 

including barium, silver, and lead and smaller concentrations of mercury and arsenic were detected in stream sediments collected from drainages in these areas. Gold was 

consistently detected in rock samples from shears and fault 

zones within Secret Pass Canyon.

Occurrences of gem-quality fire agate have been 

reported from a locality in the south-central part of the 

study area within rhyolite flows, but the potential for 

undiscovered agate resources is low in the region surrounding the known deposit.

Zeolite and perlite occur locally in the upper part of 

the volcanic section associated with thick tuff intervals and 

rhyolite flows, flow breccias, and intrusive bodies throughout the study area. Large areas in the central and eastern 

parts of the study area underlain by these volcanic rocks 

have low potential for perlite and zeolite resources. 

However, the low grade and difficult access to these perlite- and zeolite-bearing beds in the study area would hinder development of these commodities.

The oil and gas resource potential of the study area 

was considered by Ryder (1983) to be low to zero. In this 

region, hydrocarbon source or reservoir rocks are limited to 

Tertiary and (or) Quaternary sedimentary basins that flank 

the mountain ranges. Within the study area, a Proterozoic 

schist, gneiss, and granite unit crops out or underlies expoAPPROXIMATE BOUNDARY

OF

MOUNT NUTT 

 TiNESSSTUD' 

(AZ-020-024)

FORT MOHAVE 

INDIAN RESERVATION

35

Figure 1. Index map showing location of Mount Nutt Wilderness Study Area, Mohave County, Arizona. 

D2 Mineral Resources of Wilderness Study Areas: Black Mountains Region, Arizona
sures of Tertiary volcanic rock at shallow depths. Therefore, there is no resource potential for oil and gas within the 

study area.

There is no potential for undiscovered geothermal 

energy within the study area because well temperatures (approximately 30 °C) from the surrounding area are average 

for this region of the Basin and Range province (Bliss, 

1983).

INTRODUCTION

This mineral survey was requested by the U.S. 

Bureau of Land Management and is the result of a cooperative effort by the U.S. Geological Survey and the U.S. 

Bureau of Mines. An introduction to the wilderness review 

process, mineral survey methods, and agency responsibilities was provided by Beikman and others (1983). 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 a 

system that is a modification of that described by 

McKelvey (1972) and U.S. Bureau of Mines and U.S. Geological Survey (1980). U.S. Geological Survey studies are 

designed to provide a scientific basis for assessing the 

potential for undiscovered mineral resources by determining geologic units and structures, possible environments of 

mineral deposition, presence of geochemical and geophysical anomalies, and applicable ore-deposit models. 

Goudarzi (1984) discussed mineral assessment methodology and terminology as they apply to these surveys. See 

"Appendixes" for the definition of levels of mineral 

resource potential and certainty of assessment and for the 

resource/reserve classification.

Area Description

The Mount Nutt Wilderness Study Area 

(AZ-020-024) covers approximately 27,210 acres in the 

desert highlands 15 mi west of Kingman and 8 mi east of 

the Colorado River. The terrain of the study area is rugged, 

rising from about 2,300 ft along the west side to sharp 

peaks above 5,000 ft with precipitous cliffs and rocky 

canyons. Grapevine Canyon is the deepest and most spectacular canyon and is over 1,000 ft deep at its east end. The 

Mount Nutt Wildernes Study Area lies in the Mohave 

desertscrub biome of the Warm-Temperate Desertland 

Biotic Community (Brown, 1982). The vegetation of the 

study area is dominated by the shrubs and cacti that are 

typical of southwest desert biomes. However, this study 

area also contains local areas of the Great Basin desertscrub 

biome. The dominant shrubs in the study area are Mohave

indicators, such as creosotebush (Larreo tridentata),v/hi\.e 

bursage (Ambrosia dwnosa), brittlebush (Enceliafairnosa), 

and all-scale (Atriplex polycarpa); the Yucca (Yucca spp.) 

is the characteristic Mohave tree that flourishes in the study 

area. The Mohave desertscrub is especially rich in ephemeral plants, many of which are endemic to the biome. 

Cholla (Opuntia spp.) and other cacti are well represented 

in the study area and are common in the large spaces between the shrubs. Many of these cacti are endemic to the 

Mohave biome. Local areas of the Great Basin desertscrub 

biome contain California juniper (Juniperus californica), 

sagebrush (Artemisia spp.), and Torrey joint-fir (Ephedra 

torreyana). The area contains several species of lizards, 

small mammals, and birds. Rattlesnakes and desert tortoise 

are native to the study area. Other wildlife including deer, 

bobcat, kit fox, cottontail, and jack rabbit inhabit the region; the northern part of the study area contains Bighorn 

sheep migratory/watering routes. The study area is easily 

accessible in the north by gravel roads from Arizona Highway 68, from the west by dirt roads off the Silver Creek 

road, and from the east by roads leading into Secret Pass 

Canyon from Sacramento Valley.

Previous and Present Investigations

Early reports on the geology and ore deposits of the 

Katherine and Oatman mining districts, which include parts 

of the study area, were given in Ransome (1923) and 

Lausen (1931). Thorson (1971a) described the stratigraphy 

and structure of volcanic rocks in the Oatman district. 

Clifton and others (1980) and W.P. Durning (written 

commun., 1980) modified the descriptions of Thorson 

(1971a). Recent studies on the geology and ore-deposit 

characteristics of the Oatman district were conducted by 

Smith (1984) and Dewitt and others (1986).

The U.S. Geological Survey carried out field investigations in the study area during 1987 and 1988. This 

work included geologic mapping at scales of 1:48,000 and 

1:24,000, geochemical sampling, geophysical surveys, and 

examining outcrops for evidence of mineralization. The 

geochemical survey used rock and stream-sediment 

samples (including a fine fraction and heavy-mineral concentrate) that were analyzed for 31 elements by semiquantitative emission spectrography. Arsenic, antimony, cadmium, zinc, and bismuth were analyzed by inductively 

coupled plasma-argon atomic-emission spectrometry. 

Gold was analyzed by electrothermal atomic-absorption 

spectroscopy and mercury by continuous-flow, cold-vapor 

atomic-absorption spectroscopy. Previously collected geophysical data, which resulted from regional gamma-ray, 

gravity, and magnetic surveys, were compiled and analyzed 

for this study. X-band side-looking airborne radar data and 

stereoscopic Landsat thematic mapper (TM) images were 

interpreted for structural fabric, major tectonic elements,

Mount Nutt Wilderness Study Area, Mohave County, Arizona D3
and potential areas of hydrothermal alteration using photographic techniques. Further details on analytical procedures undertaken for this resource assessment are given in 

the appropriate sections that follow.

The Mount Nutt Wilderness Study Area geologic 

map is generalized from mapping in the southern half by 

Thorson (1971a) and Clifton and others (1980) and the 

northern half from mapping done during the course of this

114° 23'

M/B 11 ] Au 

L/C Ag, Pb, Hg

H/C 11 ] Au _ 

L/C Ag, Pb, Hg

APPROXIMATE BOUNDARY

OF

MOUNT NUTT

WILDERNESS STUDY AREA

(AZ-020-024)

M/B [ 1 ] Au 

L/C Ag, Pb, H

L/C Per, Zeo

Gold ore 

^*s - 

M/B [ 1 ] Au

L/C Ag, Pb, Hg Goldroad

Figure 2. Mineral resource potential and generalized geology of Mount Nutt Wilderness Study Area, Mohave County, Arizona.

D4 Mineral Resources of Wilderness Study Areas: Black Mountains Region, Arizona
study (Floyd Gray and RJ. Miller, unpub. data, 1988; Gray 

and others, 1987). Altered and mineralized areas in the 

northern half were mapped in detail to characterize the 

extent and effect of hydrothermal activity in the study area. 

The U.S. Bureau of Mines carried out field investigations in 1987, including searches for mines, prospects, 

claims, and mineralized geologic structures (Almquist, 

1989). Ninety-two chip, grab, and select samples and one 

panned-concentrate sample were collected.

Acknowledgments

The authors would like to thank Robert Harrison of 

the U.S. Bureau of Land Management and Perry Durning 

of Fischer-Watt Gold Co., Inc., for their information regarding the geology and mining activity in the study area. 

In addition, the staff of the Kingman, Arizona Resource 

Area Office of the U.S. Bureau of Land Management 

provided logistical support, equipment, and facilities.

EXPLANATION

B 

C

Commodities

Au

Ag

F

Hg

Pb

Per

Zeo

Area having high resource potential (H) Tr

Area having moderate resource potential Tc 

(M)

Area having low resource potential (L) Ts

Mine having identified fire-agate resource

 See text for discussion Tm

Levels of certainty of assessment 

Data only suggest level of potential 

Data give good indication of level of potential

Gold

Silver

Fire agate

Mercury

Lead

Perlite

Zeolites

[ ] Deposit type

1 Epithermal gold deposits in volcanic and

volcaniclastic rock 

Map units

Qal Alluvial deposits (Quaternary) Mostly stream 

sand and gravel; includes fanglomerate; also 

includes minor amounts of eolian and lacustrine 

sediment. May also include scattered low-lying 

bedrock outcrops

Job Olivine basalt (Tertiary) Medium-grained, gray, 

granular to ophitic basalt with 1- to 3-mm 

phenocrysts of iddingsite (altered olivine)

Tmf Meadow Creek and Flag Spring Trachytes, 

undivided (Tertiary) Alkalic to subalkalic 

quartz latite flows, agglomerates, and flow 

breccias

Rhyolite (Tertiary) Rhyolitic flows, massive

domes, plugs, and associated breccias and tuffs 

Cottonwood unit of Thorson (1971a) (Tertiary) 

Rhyolite to alkali rhyolite flow domes and flow

breccias. May be correlative with unit Tr 

Sitgreaves Tuff (Tertiary) Volcaniclastic

sedimentary rock including conglomerate and

air-fall tuff 

Moss Porphyry (Tertiary) Rhyolite to rhyodacite

porphyry stock. Contains phenocrysts of

feldspar, quartz, and minor amounts of altered

biotite. Intrudes the Alcyone Formation of

Thorson (197 la, b) on west side of study area 

Trd Rhyodacite dikes and intrusive rocks (Tertiary) 

Argillically altered, limonite-stained intrusive

rocks; commonly contains altered plagioclase

and quartz phenocrysts 

Ta Antelope quartz latite unit of Thorson (1971a)

(Tertiary) Rhyodacite to rhyolite flows and

domes 

Tpa Porphyritic andesite (Tertiary) Porphyritic,

plagioclase-rich andesite flows and flow breccias 

Tg Gold Road Latite (Tertiary) Andesitic to dacite

flows, flow and vent breccias, and minor

amounts of lithic air-fall tuff 

To Oatman latite unit of Thorson (1971a)

(Tertiary) Dacite to andesitic basalt flows,

tuffs, and flow breccias 

Tal Alcyone Formation of Thorson (1971a,b)

(Tertiary) Rows, tuffs, and breccias of quartz

latitic composition 

Pg Granite, schist, and gneiss (Proterozoic)

 -- Contact Dashed where approximately located

Fault Dashed where approximately located; dotted 

where inferred

Mount Nutt Wilderness Study Area, Mohave County, Arizona D5
APPRAISAL OF IDENTIFIED RESOURCES

By Carl L. Almquist 

U.S. Bureau of Mines

Methods

In March 1987 the U.S. Bureau of Mines conducted 

a mineral investigation of the Mount Nutt Wilderness Study 

Area. This investigation included a review of literature, 

unpublished U.S. Bureau of Mines and U.S. Bureau of 

Land Management files, mining claim, and land-status 

records; contact with mineral interest holders; a field examination of the study area and vicinity; and an evaluation 

of sample analyses. Two U.S. Bureau of Mines geologists 

spent nine days in the study area and collected 92 chip, 

grab, and select samples and 1 panned-concentrate sample. 

The samples were analyzed by Chemex Labs, Inc., Sparks, 

Nevada. Gold content was determined by fire assay and 

neutron activation. Silver, arsenic, antimony, bismuth, 

cadmium, gallium, tellurium, copper, lead, zinc, and molybdenum contents were determined by inductively coupled 

plasma-atomic emission spectrometry. All analytical data 

are reported in Almquist (1989).

Mining and Mineral Exploration History

The Oatman mining district, Arizona's third largest 

gold producer, extends into the southwestern part of the 

study area. In the early 1860's, a gold-bearing ore shoot 

was discovered in a prominent quartz vein outcrop 2.5 mi 

west of the study area at the Moss mine (Almquist, 1989, 

pi. 1). Shortly after this discovery, other gold-bearing 

veins were located nearby to the east and southeast, but 

nearly 30 years passed before the largest gold mines of the 

Oatman district were opened. In the early 1900's, development work was started at the Tom Reed, United Eastern, 

and Gold Road mines, which were by far the most productive in the district. Ore production peaked in 1920 and then 

sharply declined in 1924 as gold ore grades decreased. 

Mining activity stagnated in the late 1920's, was revived in 

1933 when the gold price increased to $35 per oz, and 

ceased in 1942 (Ransome, 1923; Lausen, 1931; and 

Durning and Buchanan, 1984). Recorded production, from 

1870 to 1980, is 1,966,000 troy oz of gold, 1,147,000 troy 

oz of silver, and 60,000 Ib of copper from 4,073,000 short 

tons (st) of ore (Keith and others, 1983, p. 38-39). All the 

past-producing mines in the Oatman district are outside the 

study area.

More gold-bearing veins are present in the Union 

Pass mining district, which extends into the northern part of 

the study area at the mouth of Secret Pass Canyon. Discoveries in the district followed the Moss mine discovery at 

Oatman by about ten years, and mining activity coincided

with the main period of activity at Oatman, but on a smaller 

scale. The most productive past-producing mines in the 

district are all northwest of the study area. Recorded production, from 1868 to 1943, is 128,000 troy oz of gold and 

313,000 troy oz of silver from 704,000 st of ore (Keith and 

others, 1983, p. 52-53).

An unknown tonnage of gold ore, reportedly containing from 0.43-0.57 oz/st, was produced from the Tin 

Cup mine, which is in Secret Pass Canyon less than 0.5 mi 

north of the study area (Almquist, 1989, pi. 1; Westervelt, 

written commun., 1987). Recent exploration work 

(1984-1988) by Santa Fe Pacific Mining, Inc., and FischerWatt Gold Company, Inc., which included drilling, resulted 

in the identification of approximately 460,000 st of ore with 

a grade of 0.110 troy oz gold/st at the Tin Cup mine and 

approximately 108,000 st of ore with a grade of 0.053 oz 

gold/st at a nearby site, a total resource of about 56,000 

troy oz gold. As of early 1988, Fischer-Watt Gold Company was continuing its exploration efforts in the Secret 

Pass area (F.L. Hillemeyer, Fischer-Watt Gold Company, 

Inc., Kingman, Ariz., oral commun., 1988).

Mines and Prospects, Mining Claims and Leases

There are numerous prospect pits, shallow shafts, 

and adits inside the study area but no mines with a history 

of metallic mineral production. Large blocks of unpatented 

mining claims, located on gold-bearing vein deposits in the 

Oatman and Union Pass mining districts, extend from the 

north, west, and south into the study area (Almquist, 1989, 

pi. 1). Mining claims have also been located on a gemstone resource northeast of Mount Nutt, where fire agate 

was being mined on a small scale during the U.S. Bureau 

of Mines investigation.

Ryder (1983, p. 19) rated the study area as having 

zero to low potential for the occurrence of petroleum, on 

the basis of prevalent Proterozoic crystalline rocks and 

Tertiary volcanic rocks. Approximately 5,160 acres were 

under lease for oil and gas at the time of the U.S. Bureau 

of Mines investigation (Almquist, 1989, pi. 1).

Reserves and Identified Resources

Host rocks, structures, and some types of alteration 

associated with gold deposits in the Oatman mining district 

are present in the southern and western parts of the study 

area. Although these characteristics suggest the presence 

of ore deposits and there has been some prospecting in the 

study area, no ore deposits have been discovered. Element 

concentrations that could indicate the presence of metallic 

mineral resources were not detected in U.S. Bureau of 

Mines samples from prospects and altered outcrops inside 

the study area (Almquist, 1989, table 1 and appendix), but

D6 Mineral Resources of Wilderness Study Areas: Black Mountains Region, Arizona
these findings are not conclusive. In the Oatman mining 

district, most past-producing ore shoots are not exposed; 

their only surface expression is altered volcanic rock that 

gives no distinct geochemical anomaly (Durning and 

Buchanan, 1984).

The gold ore deposits recently identified by drilling 

in the Secret Pass Canyon area are on the Frisco Mine fault, 

which is traceable for more than 2 mi into the study area 

(Almquist, 1989, pi. 1; fig. 2). Gold was detected in all 

U.S. Bureau of Mines samples collected from workings in 

the Secret Pass Canyon area, with concentrations as high as 

0.880 and 0.354 oz/st (Almquist, 1989, table 1), but there 

are no known gold-bearing deposits in the study area.

Deposits that were mined on the Mossback, Gold 

Ore, and Gold Trail mine veins are not traceable at the 

surface into the study area (Almquist, 1989, pi. 1). The 

northwest-trending Mossback vein dips about 80° SW and 

appears to be fault-terminated at a point near the east 

boundary. The Gold Ore and Gold Trail mine veins trend 

toward the study area, but their trace is obscured by volcanic cover.

A block of mining claims near the center of the 

study area was located for fire agate. Hand-sorted specimens, valued at $30-$ 100 per Ib, are packed out from the 

remote site and sold in small quantities. Exceptional individual specimens reportedly sell for $1,000 or more (Tom 

Dodge, claimant, oral commun., 1987). On the basis of a 

rough size estimate, current production methods, and site 

accessibility, this deposit will be a subeconomic indicated 

fire-agate resource for the foreseeable future. Inferred 

subeconomic resources of sand and gravel in the study area 

have no qualities that make them more valuable than abundant supplies available from established sources closer to 

existing markets. Therefore, development is unlikely. No 

other industrial-mineral commodities are present in the 

study area.

ASSESSMENT OF MINERAL RESOURCE 

POTENTIAL

By Floyd Gray, Robert C. Jachens, Robert J. Miller, 

Robert C. Turner, Eric K. Livo, Daniel H. Knepper, Jr., 

and John Mariano 

U.S. Geological Survey

Geology

Stratigraphy

The Mount Nutt Wilderness Study Area is underlain 

by Proterozoic granite, schist, and gneiss and Tertiary 

volcanic and volcaniclastic rocks. Rhyolitic to rhyodacitic 

porphyries intrude the basement rocks and the lower to 

middle parts of the volcanic section. The geology shown

in figure 2 is modified from Thorson (197la), Ransome 

(1923), Clifton and others (1980), Dewitt and others 

(1986), and Floyd Gray and RJ. Miller (unpub. data, 

1988).

Proterozoic rocks are exposed in scattered areas 

along the east side of the Mount Nutt Wilderness Study 

Area and in a northwest-trending fault-bounded block as 

much as 2 mi wide in the Secret Pass Canyon area. These 

rocks consist of medium- to coarse-grained biotite granite 

to quartz monzonite, weakly foliated gneiss, and schist. 

The granitic rocks are commonly porphyritic with feldspar 

phenocrysts as large as 2 in. in diameter; some rocks have 

a rapakivi texture. The granitic rocks are hypidiomorphicgranular and consist of potassium feldspar (approximately 

55 percent), plagioclase (approximately 25 percent) and 

quartz (approximately 20 percent). They contain as much 

as to 6 percent biotite and nearly an equal amount of 

amphibole; they also contain minor amounts of magnetite 

and sphene locally. The feldspars in the granite, gneiss, 

and schist are slightly saussuritized, and they are typically 

altered to sericite and muscovite. Biotite is slightly altered 

to chlorite, and mafic minerals are partially replaced by 

iron oxide. The eastern contact of the Proterozoic rocks 

with the volcanic rocks is a depositional unconformity with 

the volcanic rocks dipping approximately 25-35° W. The 

western contact of the basement rocks and the overlying 

volcanic rocks is exposed just north of the study area and 

is an east-dipping low-angle normal fault.

The oldest volcanic rocks of the study area are basalt 

and basaltic volcaniclastic rocks within the Alcyone Formation of Thorson (197la, b), a sequence of mainly andesite and trachyandesite (subalkalic quartz latite) flows 

exposed just inside the west boundary of the study area 

(fig. 2). The trachyandesite flows are typically dark porphyritic rocks consisting of 65 percent groundmass and 35 

percent phenocrysts of sanidine, plagioclase, and biotite 

and minor amounts of pyroxene and quartz.

The middle volcanics unit of Thorson (1971a) unconformably overlies the Alcyone Formation. Units comprising the middle volcanics unit include the Oatman latite 

unit of Thorson (197 la) and the Gold Road Latite. The 

Oatman latite unit ranges in composition from dacite to 

andesitic basalt, but its average composition is subalkalic 

latitic andesite (Dewitt and others, 1986). The unit is 

composed of flows, flow breccias, and minor amounts of 

tuff and is exposed in the western part of the study area. 

The Gold Road Latite conformably overlies the Oatman 

latite unit and is composed of porphyritic subalkalic to 

alkalic flows and vent breccias; this unit is exposed 

throughout the study area.

The middle volcanics unit is intruded by the Moss 

Porphyry, a small stock exposed west of the study area 

(Thorson, 1971a). The unit's composition ranges from 

porphyritic tonalite and monzodiorite to granodiorite. 

Numerous silicic, porphyritic north west-trending dikes and

Mount Nutt Wilderness Study Area, Mohave County, Arizona D7
small sills similar to the Moss Porphyry are exposed in the 

northern part of the study area and suggest a more widespread intrusive episode that may include separate highlevel plutonic bodies (Floyd Gray and RJ. Miller, unpub. 

data, 1988).

The upper volcanics unit of Thorson (197la) unconformably overlies the middle volcanics unit and consists of 

the Antelope quartz latite unit of Thorson (1971a), Cottonwood unit of Thorson (1971a), Flag Spring Trachyte, 

Meadow Creek Trachyte, and the dominantly volcaniclastic 

Sitgreaves Tuff. In the north half of the study area, the 

upper volcanics unit is correlated with a thick sequence of 

rhyolite flows and domes, welded tuffs, and small silicic 

plugs. The Antelope quartz latite and Cottonwood units are 

dominantly flows and domes of subalkalic rhyodacite to 

rhyolite and rhyolite to alkalic rhyolite, respectively 

(Dewitt and others, 1986). The Flag Spring Trachyte and 

Meadow Creek Trachyte are quartz latite flows, agglomerates, and flow breccias. The Sitgreaves Tuff is a volcaniclastic unit that contains conglomerate and air-fall tuff with 

abundant lithic fragments derived from the upper volcanics 

unit.

The upper volcanics unit is unconformably overlain 

by flat-lying to gently east-dipping olivine basalt flows and 

interbedded conglomerate and silicic ash.

Although ages are available for several units in and 

near the study area, the details of the timing of Tertiary 

volcanic events remains unclear. Thorson (1971a) reported 

conventional potassium-argon (K-Ar) ages of 18.6+0.9 Ma 

(million years before present) and 19.2+0.9 Ma for the 

Gold Road latite and Antelope quartz latite, respectively. 

This apparent inversion of the stratigraphy can be accounted for in the analytical uncertainty of the ages or by 

assuming that one or both represent minimum ages. Dewitt 

and others (1986) obtained an Ar-Ar age of 18.8+0.1 Ma on 

hornblende from the Moss Porphyry. This body intrudes 

the Alcyone (lower unit) and is chemically similar to the 

Cottonwood unit. DeWitt and others (1986) suggested that 

the Moss Porphyry may be coeval with the upper volcanics 

unit. A uranium-lead age of 18+4 Ma for the Moss Porphyry (DeWitt and others, 1986) suggested that the intrusion was coeval with the main period of volcanism and not 

late Miocene, as was suggested by Thorson (197 la).

Ages from volcanic rocks in the northern part of the 

study area, correlated with the upper volcanic unit, are 

somewhat younger than the age reported by Thorson 

(1971a). Biotite from two samples of porphyritic andesite 

(unit Tpa, fig. 2) produced ages of 18.2+0.5 Ma and 

18.4+0.5 Ma (RJ. Miller, unpub. data, 1989). A silicic 

dike, tentatively correlated with the upper part of the upper 

volcanic unit, has a K-Ar biotite age of 17.1+0.5 Ma (RJ. 

Miller, unpub. data, 1988) suggesting that the upper volcanic unit may represent as much as 2 million years of 

volcanic activity. A brief quiescent period may have preceded eruption of mesa-capping basalts. This basalt is 

much thicker and more areally extensive south of the study 

area and has been dated by whole-rock K-Ar methods at 

15.8±0.5 Ma (RJ. Miller, unpub. data, 1988). No volcanic 

units overlie this basalt in the southern Black Mountains. 

Quaternary units unconformably overlie Tertiary 

volcanic and older crystalline rocks. Flanking some of the 

peaks are poorly sorted, semiconsolidated to unconsolidated locally derived terrace gravels. Closer to some of the 

mountains are talus slopes that obscure underlying geology. 

Widespread pediment surfaces are covered by older alluvium, and major drainage channels contain Quaternary 

alluvium.

Structure

Rocks within the study area are intensely faulted and 

tilted as a consequence of late Tertiary deformation related 

to extensional tectonism. The faults are generally north- to 

northwest-trending high-angle normal faults. The study 

area is divided into two areas that have different structural 

configurations. The south half of the study area (roughly 

from Mount Nutt south) is dominated by a large circular 

structural feature inferred to be a volcanic depression 

(Thorson, 197la; Clifton and others, 1980; Dewitt and 

others, 1986; Gray and others, 1987). This feature is older 

than the north- to northwest-trending fault set and is offset 

along them (Gray and others, 1987). The north half of the 

study area is dominated by north- to northwest-trending 

normal faults. The Tertiary volcanic cover is thinner in the 

northern part of the study area where a more closely spaced 

set of parallel faults is exposed. The general structural 

pattern suggests a faulted, southward-plunging horst cored 

by Proterozoic granitic rocks.

Brecciation and Alteration

Brecciation and localized alteration are coincident 

with Tertiary fault and fracture systems. The fault and 

fracture systems possibly served as conduits for circulating 

hydrothermal fluids driven by proximal rhyolitic magmatism. Zones of intensely brecciated rocks from 5 ft to about 

150 ft wide characterize most faults. Weak to moderate 

propylitic alteration is evident along more prominent normal faults with irregular zones of illitic alteration; minor 

silicification is locally present along these faults. Alteration is mainly present in the lower part of the volcanic 

section; young bedded air-fall tuff, silicic breccias, and 

rhyolite plugs are virtually unaltered. Near the Frisco Mine 

fault, propylitic alteration is common adjacent to the fault 

in both granitic and volcanic rocks. The granitic rocks are 

intensely fractured near the fault and host an irregular

D8 Mineral Resources of Wilderness Study Areas: Black Mountains Region, Arizona
stockwork vein system consisting of quartz, calcite, and 

minor amounts of fluorite. Volcanic rocks near the fault 

are propylitically altered and also are argillically altered in 

irregular patches.

Rhyolitic to rhyodacitic dikes in the northern part of 

the study area are limonite stained and pervasively argillically altered; the alteration resulted from acid fluid associated with the breakdown of pyrite. The dikes are bleached 

white with irregular reddish brown to yellowish tan patches 

created by limonite staining.

Moderate to intense argillic alteration is predominant 

in the eastern margin of the Moss Porphyry west of the 

study area. This silicic, high-level intrusion is typically 

bleached white to yellowish-brown or pinkish-white in this 

region.

Geochemical Studies 

Methods

A reconnaissance geochemical survey was conducted in the Mount Nutt Wilderness Study Area in the fall 

of 1986 and the spring of 1987. Reconnaissance surveys 

allow the evaluation of large areas for evidence of mineralization. Reconnaissance surveys are not designed to find 

individual deposits, rather the spacing of samples allows 

large areas to be subdivided rapidly at low cost into zones 

of favorable geochemical provinces and mineralized tracts. 

Minus-80-mesh stream sediments, heavy-mineral concentrates derived from stream sediments, and rocks were selected as the sample media in this study. Fifty-three sites 

were sampled for stream sediments and heavy-mineral 

concentrates and 27 rock samples were collected at 25 sites.

The stream-sediment samples were collected from 

the active alluvium in the stream channel length of approximately 50 ft. The stream sediments were sieved through an 

80-mesh screen and pulverized to a fine powder before 

analysis. The heavy-mineral concentrates were sieved 

through a 10-mesh screen and then panned until most of the 

quartz, feldspar, clay-sized material and organic matter 

were removed. The remaining light minerals were separated from the heavy minerals with heavy liquid (bromoform, specific gravity 2.8). Magnetite and ilmenite were 

removed from the resultant heavy-minerals fraction with a 

Franz Isodynamic electromagnetic separator; the remainder 

was separated into nonmagnetic and slightly magnetic fractions. The nonmagnetic fractions, which were used in this 

study, were ground to a fine powder before analysis. 

Stream sediments represent a composite of the rock and 

soil exposed upstream from the sample collection site. The 

heavy-mineral concentrate represents a composite of the 

heavy-mineral components of the rocks exposed in the 

drainage basin, which could include ore-forming and orerelated minerals. Analyses of the nonmagnetic fraction of 

the concentrate permits determination of the concentration 

of some elements that are not easily detected in bulk stream 

sediments. Rocks were collected from mineralized and 

unmineralized outcrops and stream float. Samples that 

appeared fresh and unaltered were collected to provide 

information on background geochemical values. Altered 

samples were collected to determine the suite of elements 

associated with the observed alteration or mineralization. 

The rocks were crushed and pulverized to a fine powder 

before analysis.

The heavy-mineral concentrates, stream sediments, 

and rocks were analyzed for 31 elements by direct-current 

arc, semiquantitative, emission spectrographic analysis 

(Grimes and Marranzino, 1968; Crock and others, 1983). 

The rocks were also analyzed for antimony, arsenic, bismuth, cadmium, and zinc by inductively coupled argon 

plasma-atomic emission spectroscopy (O'Leary and Viets, 

1986); for gold by atomic absorption (Thompson and others, 1968); and for mercury by cold-vapor atomic-absorption methods (Koirtyohann and Khalil, 1976). Analytical 

data and a description of the sampling and analytical techniques were compiled by J. Bullock (written commun., 

1989).

Results

A plot of the anomalous values from the minus-80 

mesh stream-sediment samples delineated an anomalous 

zone in the northwestern part of the study area. This zone 

is characterized by anomalous values for mercury (0.1-0.6 

parts per million, ppm), gold (0.05-0.1 ppm), arsenic 

(10-18 ppm), lead (as high as 200 ppm), zinc (as high as 

250 ppm), and barium (2,000-3,000 ppm). A second zone, 

in the southeastern part of the study area, is characterized 

by anomalous values for mercury (8-16 ppm) and molybdenum (as high as 15 ppm). A third zone delineated from 

this sample medium is in the east to northeast part of the 

study area and is characterized by anomalous values of 

mercury (as high as 12 ppm) and zinc (230-250 ppm).

Rock samples collected from altered volcanic rocks 

and altered silicic dikes in and adjacent to the north-central 

part of the study area yielded anomalous precious metal 

values (table 1). The rocks are characterized by anomalous 

values for gold of as much as 10 ppm (average value being 

approximately 1.43 ppm), silver (as high as 30 ppm), and 

mercury (as high as 84 ppm). Arsenic concentrations are 

weakly anomalous but low compared to the Sleeper and 

Buckhorn gold deposits (table 1).

Weakly anomalous concentrations of trace elements, 

(mercury, arsenic, antimony, and molybdenum) were detected in scattered, altered rocks in and adjacent to the 

northwestern part of the study area.

Mount Nutt Wilderness Study Area, Mohave County, Arizona D9
Geophysical Studies

Three types of geophysical data from western Arizona (magnetic, gravity, and radiometric) were compiled 

and examined to aid in the assessment of the mineral resource potential of the Mount Nutt Wilderness Study Area, 

Arizona. Detailed aeromagnetic and radiometric data are 

available along profile lines spaced about 1 mi apart. The 

sparsely distributed nature of the gravity data and the wide 

separation between aeromagnetic and radiometric profile 

lines make these data adequate for addressing the regional 

structural and tectonic setting of the study area but do not 

permit detailed statements about mineral resource potential 

at the deposit scale.

Aeromagnetic Data

An aeromagnetic survey of the study area and vicinity was flown in 1977 and compiled by Western Geophysical Company of America under contract to the U.S. Department of Energy as part of the National Uranium Resource 

Evaluation (NURE) program (U.S. Department of Energy, 

1979). Total-field magnetic data were collected along eastwest flightlines spaced approximately 1 mi apart at a 

nominal height of 400 ft above the ground surface. Corrections were applied to the data to compensate for diurnal 

variations of the Earth's magnetic field, and the International Geomagnetic Reference Field (updated to the month 

data were collected) was subtracted to yield a residual field 

that primarily represents the distribution of magnetite in the 

underlying rocks.

The magnetic field of the Mount Nutt Wilderness 

Study Area is dominated by numerous short-wavelength 

(1-3 mi in width), high amplitude (200-400 nanoteslas) 

anomalies that are characteristic of areas of rugged relief in 

magnetic volcanic rocks. The mafic volcanic rocks that 

primarily underlie regions of rugged terrain within the 

study area appear to be strongly magnetic and cause large 

anomalies. These anomalies result both from lateral variations of induced and remanent magnetization within the 

volcanic rocks and from variable separation between the 

magnetic sensor and the underlying rocks because a constant flight elevation could not be maintained above the 

ground surface. In contrast, the tuff units and rhyolitic 

rocks appear to be much less magnetic and cause magnetic 

lows. Most of these anomalies do not directly contribute to 

an understanding of the mineral resource potential of the 

study area.

Two pronounced magnetic lows, one lying mostly 

outside the study area along its southwest edge and another 

that straddles the northwest corner of the study area, suggest mineralization may have occurred. The southwestern 

low lies over the Oatman mining district and extends less 

than 1 mi into the study area (anomaly 1, fig. 3). This low

covers more than 15 mi1 and includes most of the deposits 

and claims in the district. The rocks encompassed by this 

low are significantly less magnetic than the igneous rocks 

in the surrounding area, probably as a result of hydrothermal alteration that destroyed the magnetite in the rocks. 

The northwestern low (anomaly 2, fig. 3) is situated over 

exposures of rhyolite that include a group of rhyolite plugs. 

This low may be related to alteration associated with the 

intrusion of the rhyolite plugs, but it also partly indicates 

the magnetic character of the rhyolite that elsewhere in the 

study area appears to be only weakly magnetic.

Gravity Data

Gravity data in the vicinity of Mount Nutt Wilderness Study Area were obtained from Mariano and others 

(1986). Gravity stations are scattered at 1-3 mi intervals 

outside the study area, but only 12 stations are located 

within the study area boundary and most are aligned along 

a northeast-trending profile that crosses the center of the 

study area. The observed gravity data, based on the International Gravity Standardization Net datum (Morelli, 

1974), were reduced to free-air gravity anomalies using 

standard formulas (Telford and others, 1976). Bouguer, 

curvature, and terrain corrections (to a distance of 103.6 mi 

from each station) at a standard reduction density of 2.67 g/ 

cm3 (grams per cubic centimeter) were made at each station 

to determine complete Bouguer gravity anomalies.

The Bouguer gravity field over the study area and 

surrounding region shows shallow-density distributions 

related to near-surface geology and deep-crustal density 

distributions that correlate with topography in a manner 

consistent with the concept of isostasy. To isolate that part 

of the gravity field that arises from near-surface density 

distributions, an isostatic residual gravity map was constructed from the Bouguer gravity data. The method used 

was removal of a regional gravity field computed from a 

model of the crust-mantle interface that assumes Airy-type 

isostatic compensation (Jachens and Griscom, 1985).

Measurements were made on hand samples collected 

from outcrops in or near the study area to determine the 

densities of the major rock types. Fifteen samples of 

Proterozoic basement rock yielded an average density of 

2.72±0.06 g/cm3 . Twenty-six samples of unaltered Tertiary 

volcanic rocks yielded an average of 2.51±0.12 g/cm3 , although this average should be used with caution because 

the density measurements on the volcanic rock samples 

showed considerable scatter.

The gravity field in the vicinity of the Mount Nutt 

Wilderness Study Area primarily shows the thickness of 

low-density Cenozoic deposits that overlie higher density 

Proterozoic basement rock. An elongate gravity low about 

4 mi wide and 6 mi long that is centered on Mount Nutt 

covers most of the study area. This low, which culminates

D10 Mineral Resources of Wilderness Study Areas: Black Mountains Region, Arizona
Table 1. Analyses of altered rock samples in and near Mount Nutt Wilderness Study Area, Mohave County, Arizona 

[All samples are either from altered volcanic rocks in fault and fracture zones or from altered, hematite-stained silicic dikes. Analyses by J. Bullock

and B. Anderson. N, not detected at detection limit (given in parentheses). --, not analyzed for. AH element concentrations measured in parts per 

million unless otherwise indicated. Au, gold; Ag, silver; Hg, mercury; As, arsenic; Sb, antimony; Cd, cadmium; Pb, lead; Zn, zinc; Mo, molybdenum]

Sample Number

WGT-3 

WGT-13

WGT-15 

WGT-21-7

WGT-30 

WGT-34 

WGT-35

WGT-37 

7M136A

7M136B 

7M136C

7M136D

7M136F 

7M137 

7M137B

7M137C 

7M137D 

7M137E

7M137F 

7G105-1 

7G105-2

7G105-3 

7G105-4 

7G105-5 

7G106-1

7G106-3 

7G 106-4 

7G106-5 

7G106-6 

*7G102-1

*7G102-2

*7G102-3

'7G102-4

*7G103

Au

3.10 

5.45

1.60 

0.60

0.40 

0.15 

0.75

0.05 

0.40

<0.05 

0.10

0.10

<0.05 

0.45 

<0.05

6.55 

<0.05 

0.10

0.05 

0.55 

0.25

3.35 

0.20 

<0.05 

4.30

0.40 

2.30 

1.65 

0.25 

2.10

2.30

1.10

10

0.07

Ag

1.5 

1

1.5 

0.5

2

10 

0.5

2 

0.7

N(0.5)

1

<0.5

N(0.5) 

0.5 

<0.5

5 

N(0.5) 

2

1.5 

0.7

1

1 

N(0.5) 

N(0.5) 

10

0.7 

15 

<0.5 

1 

5

20

1.5

5

30

Hg

72 

28

0.06 

0.52

0.02 

0.12 

0.02

0.06 

0.08

<0.07 

1.1

0.12

<0.02 

0.04 

0.38

0.08 

0.04 

0.06

0.72 

24 

0.96

0.02 

0.20 

<0.02 

84

0.12 

0.06 

0.02 

0.08 

2.9

9.2

0.48

1.2

0.12

As

12 

33

27 

50

48 

65 

70

45 

39

120 

21

72

<5 

96 

27

9 

16 

8

12 

10 

<5

21 

39 

<5 

1 1

47 

44 

44 

57 

38

<5

19

8

10

Sb

<2 

<2

<2 

<2

<2 

2 

<2

15 

<2

<2 

<2

<2

<2 

4 

<2

2 

<2 

<2

<2 

<2 

<2

<2 

<2 

<2 

<2

<2 

<2 

<2 

<2 

<2

<2

<2

<2

<2

Cd

0.7 

0.6

0.8

1.2

0.6 

0.6 

0.5

0.2 

0.4

1.8 

0.7

0.9

0.2 

1.9 

0.7

0.7 

0.7 

0.1

0.7 

0.7 

0.1

0.1 

0.2 

0.8 

0.4

1.2 

0.7 

0.4 

0.5 

0.8

<0.1

<0.1

<0.1

<0.1

Pb

30 

50

20 

20

50 

70 

30

50 

<10

N(10) 

<10

20

<10 

50 

10

N(10) 

50 

20

N(10) 

50 

20

15 

15 

30 

20

30 

50 

20 

30 

100

10

100

10

50

Zn

24 

54

39 

62

38 

40 

48

36 

42

31 

36

64

26 

87 

31

<2 

12

7

31 

26 

14

24 

27

71 

39

63 

55 

47 

53 

100

5

92

6

7

Mo

N(5) 

<5

N(5) 

<5

N(5) 

N(5) 

<5

N(5) 

15

N(5)

7

10

N(5) 

N(5) 

<5

20 

N(5) 

15

N(5) 

N(5) 

<5

N(5) 

N(5) 

N(5) 

<5

N(5) 

N(5) 

N(5) 

N(5) 

100

50

20

<5

100

Deposits

1 Sleeper 0.25 27 -- 340 130 -- 7 25 --

Analyses in parts per billion (ppb)

2Buckhorn 3

Buckhorn 4

Buckhorn 5

Buckhorn 6

Buckhorn 14

51.25

327.86

1686.67

1581.11

201.67

8.48

3.19

2.52

16.06

5.40

567.50

334.29

271.67

3002.22

490

55.75

142.86

227.67 1

1017.67

151.00

8.35

10.97

01.77

48.29

11.80

..

--

--

--

--

3

6.86

6.67

5.67

8

803.75

29.71

283

9.78

55.33

2

3.43

2

35.78

14.33

*Sample from rhyodacite dikes in study area. 

Means of surface-rock chemistry from Wood (1988, p. 300) 

2 Average values of altered basaltic andesite (3-6 samples) and silicified fanglomerate (14 samples) from Monroe and others (1988)

Mount Nutt Wilderness Study Area, Mohave County, Arizona D11
in values lower than -30 milligals (mGal), is bounded on 

the northeast by a gravity ridge having highest values of 

about -12 mGal and on the south and southwest by gravity 

highs of about -10 mGal. These highs are centered over 

outcrops of Proterozoic basement rock. Proterozoic basement rock is also exposed along the north boundary of the 

study area, an area where gravity values reach only about 

-18 mGal. An area with gravity values of about -22 mGal 

that bounds the low on the west is not associated with any 

Proterozoic basement exposures.

A northeast-southwest trending structural trough is 

implied by low gravity values and, on the basis of modeling, may contain as much as 1.5 mi of volcanic rock.

Using a density contrast of 0.2 g/cm3 between Proterozoic 

basement and Tertiary volcanic rock, gravity-modeling 

results indicate that the structural trough is bounded on the 

northeast by a Proterozoic surface that dips gently southwest and on the southwest by a near-vertical interface. 

Northwest-trending faults have been mapped in Tertiary 

rock immediately above the inferred near-vertical southwest boundary and these faults parallel the gravity gradient 

that defines the edge of the trough. Although the gravity 

data are sparse and do not accurately define the extent of 

the inferred vertical boundary, it appears to lie within the 

deepest part of the magnetic low over the Oatman mining 

district.

114°30' 114°25' 114°20'

MOUNT NUTT

WILDERNESS STUDY AREA

(AZ-020-024)

Figure 3. Aeromagnetic anomalies of Mount Nutt Wilderness Study Area, Mohave County, Arizona. Contour interval, 20 

nanoteslas; hachured in direction of magnetic low; anomalies labeled 1 and 2 are discussed in text.

D12 Mineral Resources of Wilderness Study Areas: Black Mountains Region, Arizona
Radiometric Data

Knowledge of natural radioelement distribution in 

the Mount Nutt Wilderness Study Area is based on an 

aerial gamma-ray spectrometry survey (U.S. Department of 

Energy, 1979) of the Kingman 1- by 2-degree quadrangle. 

The survey acquired gamma-ray data along 1-mi-spaced 

east-west flightlines at 400 ft above the ground for the 

eastern part of Kingman quadrangle. The line spacing 

represents about 15 percent coverage for the study area 

because an aerial gamma-ray system flown 400 ft above the 

ground effectively detects terrestrial gamma radiation from 

a swath 800 ft wide along a flightline. The coverage represents a reconnaissance sampling of the near-surface (0- to 

18-in. depth) distribution of the natural radioelements potassium (K), uranium (eU), and thorium (eTh). The prefix 

"e" (for equivalent) denotes the potential for disequilibrium 

in the uranium and thorium decay series.

Examination of 1:500,000 and smaller scale radioelement maps made from the aerial-gamma-ray data for the 

eastern part of the Kingman quadrangle indicates that the 

study area is characterized by radioelement concentrations 

of 2.0 to 3.6 percent K, 2.5 to 3.5 ppm eU, and 12.5 to 20.0 

ppm eTh. Relatively lower concentrations of 2.0 to 2.4 

percent K, 2.5 to 3.0 ppm eU, and 12.5 ppm eTh are present in the southern part of the study area, and relatively 

higher concentrations of 2.4 to 3.6 percent K, 2.5 to 3.0 

ppm eU, and 15 to 20 ppm eTh are present in the northern 

part. These concentrations likely reflect the distribution of 

the Proterozoic and Tertiary igneous rock that composes 

most of the bedrock of the study area. Generally, higher radioelement concentrations relate to more silicic rock, and 

detritus derived from it. The study area includes part of the 

Oatman mining district at its southwest side and part of the 

Union Pass mining district (fig. 2) at the northeast side of 

Secret Pass Canyon (fig. 1). The southwest side of the 

study area is in the area of lower radioelement concentrations, and the northeast side is in the area of higher radioelement concentrations. There is no evidence that these 

concentrations relate to the mineralization that occurred in 

the mining districts.

Remote Sensing

Digital image data acquired by the thematic mapper 

(TM) system on the Landsat-4 satellite (Scene I.D. 

40174-17383) were analyzed to detect and map areas that 

may contain hydrothermally altered rocks. The six bands 

of image data in the visible and near-infrared spectral bands 

were digitally processed to enhance spectral characteristics 

of minerals that commonly accompany alteration or are 

derived from the weathering of altered rocks. Those areas 

that have spectral characteristics suggesting the presence of 

alteration minerals were visually mapped on l:62,500-scale 

Applicon color ink-jet plots of the processed data.

The broad bands of the TM data allow two groups of 

minerals to be identified, but the minerals within each 

group cannot be distinguished from each other. Group 1 

minerals consist of the limonite minerals, particularly 

hematite, goethite, and jarosite. Hematite and goethite are 

not diagnostic of hydrothermal alteration because they are 

common weathering products of iron-bearing minerals in 

altered and unaltered rocks alike. However, concentrations 

of hematite or goethite that crosscut lithologic units do 

suggest alteration. Jarosite is diagnostic of hydrothermal 

alteration, regardless of whether or not it crosscuts lithologic units.

Group 2 minerals include the hydroxyl-bearing and 

(or) hydrated minerals (clay minerals, micas, gypsum, 

alunite, jarosite) and carbonates (calcite, dolomite). Although the minerals in Group 2 are not restricted to altered 

rocks, they are commonly important constituents of altered 

rocks or are derived from the weathering of altered rocks. 

Alteration halos of Group 2 minerals (micas and clay 

minerals), which can extend as far as 200 ft laterally from 

vein systems, (Durning and Buchanan, 1984) can be detected with remote sensing.

Interpretation

Visual interpretation of the masked TM color-ratio 

composite consists of identifying concentrations of Group 

1, Group 2, and jarosite (included in both Group 1 and 

Group 2 minerals) in the study area. In general, areas of 

alluvium identified on the basis of outcrop patterns in 

available geologic maps and photo interpretation of the 

images were excluded from consideration. The areas of 

potentially hydrothermally altered rocks were manually 

outlined by visual interpretation of the color-ratio composite image and the outlines were transferred to a 1:62,500- 

scale base map of the wilderness study area, which was 

used to compile figure 4.

Results

Areas that may depict hydrothermally altered rocks 

taken from the masked TM color-ratio composite image are 

shown in figure 4. Areas containing only Group 1 minerals 

are labeled "1"; those containing only Group 2 minerals are 

labeled "2;" and those containing both Group 1 and Group 

2 minerals (and (or) jarosite) are labeled "3". Areas of 

widespread, apparently low concentrations of minerals of 

these groups are labeled "D" for dispersed. Another area 

(labeled "A") may represent an illitically altered area 

(Durning and Buchanan, 1984). Mine dumps, mill tailings, 

and (or) discharge in nearby stream beds are labeled "d."

No pronounced alteration patterns within the central 

Oatman mining district just south of the wilderness study

Mount Nutt Wilderness Study Area, Mohave County, Arizona D13
area are visible on the TM data. Traces of veining (through 

linear alignment of mine dumps) can be seen, but they were 

not plotted on figure 4. Ransome (1923), Lausen (1931), 

and Durning and Buchanan (1984) described the variability 

of the veining and surrounding alteration halos; surface 

expression of some of the most productive veins is very 

limited. However, the Mossback mine is associated with 

area "A" on the TM image. Propylitic alteration in the 

Oatman district is also associated with Group 1 elements 

(limonite) due to weathering of pyrite.

Vegetation obscures only a small part of the rocks 

and soil in the study area. The areas of rugged topography 

in the study area, combined with the relatively low solarelevation angle at the time the TM data were acquired (25 

degrees), results in a small part of the study area being in 

deep to moderate shadow on the TM data. Vegetation and 

shadows, then, have only modestly limited the area of 

surface rocks and soil that could be spectrally analyzed for 

alteration minerals. A number of anomalous areas were 

identified and these anomalies, because of the masking 

effects of vegetation and shadows, may represent a part of 

slightly more extensive areas.

Four types of potential dispersed alteration were 

delineated within the study area. Within the dispersed 

anomalies, locally more intense concentrations are present.

(1) Group 2 and Group 3 elements are widespread on the 

west edge of the study area (fig. 4). Area "A" is 

described as a large area of illitic alteration by Durning 

and Buchanan (1984). The area just to the north 

appears to be a similar, though less intense, area of 

alteration possibly attributable to the underlying Moss 

Porphyry.

(2) Moderate to strong potentially altered areas (Group 1 

and Group 2) were delineated within the southern onethird of the study area (fig. 4). Some of the areas 

contain Group 2 cores. In general, the areas are 

located on south-facing slopes; shadows mask any 

characteristics of these elements on north-facing 

slopes.

(3) Group 1 elements are widespread in the northern onequarter of the study area (fig. 4). Weathering of one or 

more volcanic lithologic surfaces (volcanic flow rock?) 

possibly could be generating nonhydrothermal Group 1 

products. However, Group 3 elements are also present 

in this area.

(4) Combinations of type 2 and type 3 anomalies (above) 

occur in the middle of the study area (fig. 4). Areas of 

Group 1, Group 2, and combinations of Group 1 and 

Group 2 elements are localized within the more dispersed alteration. Local high concentrations of Group 

2 and Group 1 and Group 2 elements are present 

within the north-central region excluded from the study 

area. 

The relative importance of any one of the mapped

anomalies is difficult to evaluate; however, proximity to

areas of known alteration or mineralization is probably a 

good method for assessing the anomalies.

Mineral and Energy Resource Potential

An area in the extreme north-central part of the 

Mount Nutt Wilderness Study Area has high resource potential for gold and low resource potential for silver, lead, 

and mercury with a C certainty level. Three areas in the 

north-central, northwestern, and southwestern parts of the 

study area have moderate resource potential for gold with 

a B certainty level. These areas also have low potential for 

silver, lead, and mercury with a certainty level C. A small 

area in the south-central part of the study area has low 

potential, certainty level C, for fire agate. Large areas in 

the central and eastern parts of the study area have low 

potential for perlite and zeolite resources with a certainty 

level of C. The entire study area has no potential for oil 

and gas, certainty level D, and no potential for geothermal 

resources, certainty level D.

The results of this study show that there is high 

mineral resource potential for gold in the extreme northcentral part of the study area (fig. 2). A gold resource 

totaling at least 56,000 troy oz has been identified at two 

sites in the Secret Pass Canyon area. The main site (Tincup 

mine) is less than 0.5 mi outside the study area; the second 

site lies approximately 500 ft north of the study area. Most 

of the area is underlain by intensely faulted and fractured 

rocks that also extend into the wilderness study area. The 

fault structure is visible in the study area for over 2 mi. 

Altered, mineralized rocks exposed north of the study area 

are also present in the study area and are covered by unaltered silicic tuff and flows. The thickness of this unaltered 

cover increases southward. Geochemical data suggest that 

the area is characterized by low but anomalous levels of 

arsenic and mercury in stream sediments and lead and silver in heavy-mineral concentrates. The potential is interpreted to be high because composite chip material and rock 

samples of altered rocks consistently yield anomalous 

concentrations of gold and low but detectable concentrations of gold suite elements (table 1) (see Berger, 1986). A 

certainty level C is assigned to the area because the fault 

trace is generally well exposed, and the geochemical data 

suggest that mineralization occurred in the area. Moderate 

resource potential for gold exists in three areas in the extreme northwestern, northeastern, and southwestern parts of 

the study area (fig. 2). This potential is suggested by 

anomalous concentrations of mercury, lead, barium, and 

arsenic. Scattered anomalous concentrations of gold, 

molybdenum, and zinc detected in stream sediments suggest that mineralization occurred. The potential is moderate because alteration patterns defined by remote sensing, 

faulting, and the anomalous trace-element suite are similar 

to the known gold deposits in the area. A certainty level of

D14 Mineral Resources of Wilderness Study Areas: Black Mountains Region, Arizona
B is assigned to the areas because either potential host 

rocks are poorly exposed or examination of their surficial 

appearance suggests that they are only weakly altered and 

mineralized. Each of the areas mentioned above has a low 

potential for silver, lead, and mercury resources, certainty 

level C. The concentrations of these three elements are not 

large enough clearly to suggest the occurrence of potential 

resources of these commodities even as byproducts.

Perlite and zeolite minerals occur in the upper part of 

the volcanic sequence associated with welded tuff sequences and small rhyolitic plugs. This part of the sequence has a low potential for zeolite and perlite, certainty 

level C. Low grade and the lack of access to perlite and 

zeolite-bearing beds in the study area would hinder development of these commodities.

Ryder (1983) assessed the oil and gas potential of 

the study area as zero to low on the basis of extensive 

occurrences of Proterozoic schist and gneiss which make 

up the basement rocks of the wilderness study area and 

which are unsuitable hydrocarbon source or reservoir rocks. 

There is no resource potential for oil and gas, certainty 

level D, in the study area.

114°25' 114°20'

35° 

10'

35° 

05'

APPROXIMATE BOUNDARY

OF

MOUNT NUTT

^WILDERNESS STUDY AREA

(AZ-020-024)

2 MILES 

J

3 

A

D 

d

EXPLANATION

Group 1 minerals are hematite, 

goethite, and jarosite See 

text for discussion

Group 2 minerals are hydroxylbearing and (or) hydrated 

minerals (including clay 

minerals, micas, gypsum, 

alunite, and jarosite) and 

carbonates (calcite and 

dolomite) See text for 

discussion

Group 1 and 2 minerals

Illite (Duming and Buchanan, 

1984)

Dispersed occurrence of mineral 

group

Mine dumps and mine tailings

Figure 4. Areas of alteration minerals in Mount Nutt Wilderness Study Area, Mohave County, Arizona.

Mount Nutt Wilderness Study Area, Mohave County, Arizona D15
No geothermal resources were observed in or adjacent to the study area (Witcher and others, 1982; Muffler, 

1979). Although the study area contains numerous rhyolite 

and basalt intrusions and the study area is in a region 

judged to have undergone greater than normal heat flow 

during the Miocene to early Pliocene, the Miocene intrusions in the study area are small and the entire region had 

most likely cooled to near ambient temperatures by the 

early Pliocene. Therefore, there is no potential for geothermal resources, certainty level D.

REFERENCES CITED

Almquist, C.L., 1989, Mineral investigation of a part of the Mount 

Nutt Wilderness Study Area (AZ-020-024), Mohave 

County, Arizona: U.S. Bureau of Mines Open-File Report 

MLA 35-88, 20 p.

Beikman, H.M., Hinkle, M.E., Frieders, Twila, Marcus, S.M., and 

Edward, J.R., 1983, Mineral surveys by the Geological Survey and Bureau of Mines of Bureau of Land Management 

Wilderness Study Areas: U.S. Geological Survey Circular 

901, 28 p.

Berger, B.R., 1986, Descriptive model of hot-spring Au-Ag, in 

Cox, D.P., and Singer, D.A., eds., 1986, Mineral Deposit 

models: U.S. Geological Survey Bulletin 1693, p. 143-144.

Bliss, J.D., 1983, Arizona: Basic data for thermal springs and 

wells as recorded in geotherm: U.S. Geological Survey 

Open-File Report 83^27, 200 p.

Brown, D.E., 1982, Biotic communities of the American southwest-United States and Mexico, Desert Plants, v. 4, no, 1 4, 

342 p.

Clifton, D.G., Buchanan, L.J., and Durning, W.P., 1980, Exploration procedure and controls of mineralization in the Oatman 

mining district, Oatman, Arizona: Society of Mining Engineers of AIME preprint 80-143, 38 p.

Crock, J.G., Lichte, F.E., and Briggs, P.H., 1983, Determination 

of elements in National Bureau of Standards geological reference material SRM 278 obsidian and SRM 668 basalt by 

inductively coupled argon plasma atomic emission spectrometry: Geostandards Newsletter, no. 7, p. 335-340.

Dewitt, E., Thorson J.P., and Smith, R.C., 1986, Geology and 

gold deposits of the Oatman district, northwestern Arizona: 

U.S. Geological Survey Open-File Report 86-638, 34 p.

Durning, W.P., and Buchanan, L.J., 1984, The geology and ore 

deposits of Oatman, AZ: in Wilkins, Joe, Jr., ed., Gold and 

silver deposits of the Basin and Range province western 

U.S.A.: Arizona Geological Society Digest, v. 15, p. 

141-158.

Goudarzi, G.H., 1984 Guide to preparation of mineral survey 

reports on public lands: U.S. Geological Survey Open-File 

Report 84-787, 51 p.

Gray, Floyd, Jachens, R.C., Miller, R.J., and Mariano, John, 1987, 

An interpretation of the shallow crustal structure of the Black 

Mountains, northwest Arizona: computer-generated modeling and structural compilation [abs.], Geological Society of 

America Abstracts with Programs, v. 19, no. 7, p. 682.

Grimes, D.J., and Marranzino, A.P., 1968, Direct-current arc and 

alternating-current spark emission spectrographic field methods for the semiquantitative analysis of geologic materials: 

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

Jachens, R.C., and Griscom, Andrew, 1985, An isostatic residual 

gravity map of California A residual map for interpretation 

of anomalies from intracrustal sources, in Hinze, W.J., ed., 

The utility of regional gravity and magnetic anomaly maps: 

Tulsa, Okla. Society of Exploration Geophysicists, p. 

347-360.

Keith, S.B., Gest, D.E., DeWitt, Ed, Toll, N.W., and Everson, 

B.A., 1983, Metallic mineral districts and production in 

Arizona: Arizona Bureau of Geology and Mineral Technology Bulletin 194, 58 p.

Koirtyohann, S.R., and Khalil, Moheb, 1976, Variables in determination of mercury by cold vapor atomic absorption: 

Analytical Chemistry, v. 48, p. 136-139.

Lausen, C., 1931, Geology and ore deposits of the Oatman and 

Katherine districts, Arizona: Arizona Bureau of Mines 

Bulletin 131, 126 p.

Mariano, John, Helferty, M.G., and Gage, T.B., 1986, Bouguer 

and isostatic residual gravity maps of the Colorado River 

region, including the Kingman, Needles, Salton Sea, and El 

Centre quadrangles: U.S. Geological Survey Open-File 

Report 86-347, 6 sheets, scale 1:250,000, 1 sheet, scale 

1:750,000.

McKelvey, V.E., 1972, Mineral resource estimates and public 

policy: American Scientist, v. 60, p. 32-40.

Monroe, S.C., Godlewski, D.W., and Plahuta, J.T., 1988, Geology 

and mineralization at the Buckhorn mine, Eureka county, 

Nevada: in, Schaffer, R.W., Cooper, J.J., and Vikre, P.G., 

eds., Bulk mineable precious metal Deposits of the western 

United States, symposium proceedings: Geological Society 

of Nevada, p. 273-291.

Morelli, C.E., ed., 1974, The international gravity standardization 

net 1971: International Association of Geodesy Special 

Publication No. 4, 194 p.

Muffler, L.J.P., 1979, Assessment of geothermal resources of the 

United States 1978: U.S. Geological Survey Circular 790, 

163 p.

O'Leary, R.M., and Viets, J.G., 1986, Determination of antimony, 

arsenic, bismuth, cadmium, copper, lead, molybdenum, silver, and zinc in geologic materials by atomic absorption 

spectrometry using a hydrochloric acid-hydrogen peroxide 

digestion: Atomic Spectroscopy, v. 7, no. 1, p. 4 8.

Ransome, F.L. 1923, Geology of the Oatman gold district, Arizona: U.S. Geological Survey Bulletin 743, 58 p.

Ryder, R.T., 1983, Petroleum potential of wilderness lands in 

Arizona; in Miller, B.W., ed., Petroleum potential of wilderness lands in the western United States: U.S. Geological 

Survey Circular 902-C, p. C1-C21.

Smith, R.C., 1984, Mineralogy and fluid-inclusion studies of 

epithermal gold-quartz veins in the Oatman district, northwestern Arizona: Tucson, University of Arizona, M.S. thesis, 233 p.

Telford, W.M., Geldart, L.O., Sheriff, R.E., and Keyes, D.A., 

1976, Applied Geophysics: New York, Cambridge University Press, 960 p.

Thompson, C.E., Nakagawa, H.M., and Van Sickle, G.H., 1968, 

Rapid analysis for gold in geologic materials, in Geological 

Survey Research 1968: U.S. Geological Survey Professional 

Survey Paper 600-B, p. B130-B132.

D16 Mineral Resources of Wilderness Study Areas: Black Mountains Region, Arizona
Thorson, J.P., 197la, Igneous petrology of the Oatman district, 

Mohave county Arizona: Santa Barbara, University of California at Santa Barbara, Ph.D. dissertation, 189 p.

 1971b, Igneous petrology of the Oatman district, Mohave 

county Arizona [abs.], Dissertation Abstracts, v. 32, no. 8, 

p. 4677-B.

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. Department of Energy, 1979, Airborne gamma-ray spectrometer and magnetometer survey, Kingman quadrangle,

(Arizona, California, Nevada): U.S. Department of Energy 

Open-File Report GJBX 59 (79), v. 2, variously paged.

Witcher, J.C., Stone, Claudia, and Hahman, W.R., Jr., 1982, 

Geothermal resources of Arizona: Arizona Bureau of Geology and Mineral Technology Map 15-2, scale 1:500,000.

Wood, J.D., 1988, Geology of the Sleeper gold deposit, Humboldt 

County, Nevada: in Schaffer, R.W., Cooper, J.J., and Vikre, 

P.O., ed., Bulk mineable precious metal deposits of the 

western United States, symposium proceedings: Geological 

Society of Nevada, p. 300.

Mount Nutt Wilderness Study Area, Mohave County, Arizona D17

APPENDIXES
DEFINITION OF LEVELS OF MINERAL RESOURCE POTENTIAL 

AND CERTAINTY OF ASSESSMENT

LEVELS OF RESOURCE POTENTIAL

H HIGH 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 a high degree of likelihood for resource accumulation, where data support 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.

M 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 for resource accumulation, and (or) where an application of mineral-deposit models 

indicates favorable ground for the specified type(s) of deposits.

L 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 little or no indication of having 

been mineralized.

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

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

moderate, or high level of resource potential.

LEVELS OF CERTAINTY

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

B Available information only 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.

LU 

U 

C£

O 

CO 

LU

o

_! 

LU

5

A

U/A

UNKNOWN POTENTIAL

B

H/B

HIGH POTENTIAL

M/B

MODERATE POTENTIAL

L/B

LOW POTENTIAL

C

H/C

HIGH POTENTIAL

M/C

MODERATE POTENTIAL

L/C

LOW POTENTIAL

D

H/D

HIGH POTENTIAL

M/D

MODERATE POTENTIAL

I/O

LOW POTENTIAL

N/D

NO POTENTIAL

LEVEL OF CERTAINTY

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. 1258-1270.

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.

D20 Mineral Resources of Wilderness Study Areas: Black Mountains Region, Arizona
RESOURCE/RESERVE CLASSIFICATION

ECONOMIC

MARGINALLY 

ECONOMIC

SUBECONOMIC

IDENTIFIED RESOURCES

Demonstrated

Measured

Rese

Indicated

jrves

Marginal 

Reserves

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 McKelvey, V.E., 1972, Mineral 

resource estimates and public policy: American Scientist, v. 60, p. 32-40; and 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.

Mount Nutt Wilderness Study Area, Mohave County, Arizona D21
GEOLOGIC TIME CHART

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

EON

Phanerozoic

Proterozoic

Archean

pre-Archean2

ERA

Cenozoic

Mesozoic

Paleozoic

Late Proterozoic

Middle Proterozoic

Early Proterozoic

Late Archean

Middle Archean

Early Archean

PERIOD

Neogene

Subperiod

Tertiary

rSUCOfiCnG

Subperiod

Jurassic

Triassic

Permian

Pennsylvanian 

Carboniferous

Periods 

Mississippian

Devonian

Silurian

Ordovician

Cambrian

._._..____ f3ftnn?i- - .

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

ACE ESTIMATES OF 

BOUNDARIES IN 

MILLION YEARS (Ma)

 0.010

 1.7

 5

 3Q

 55

 66

1 OQ

 205

 -240

 290 

 -330

 360

 410

 435

*J\J\J

 '-570

j\j\j

 1600

 2500

 3000

 3400

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

informal time term without specific rank.

D22 Mineral Resources of Wilderness Study Areas: Black Mountains Region, Arizona
SELECTED SERIES OF U.S. GEOLOGICAL SURVEY PUBLICATIONS

Periodicals

Earthquakes & Volcanoes (issued bimonthly). 

Preliminary Determination of Epicenters (issued monthly).

Technical Books and Reports

Professional Papers are mainly comprehensive scientific reports of 

wide and lasting interest and importance to professional scientists and engineers. Included are reports on the results of resource studies and of 

topographic, hydrologic, and geologic investigations. They also include 

collections of related papers addressing different aspects of a single scientific topic.

Bulletins contain significant data and interpretations that are of lasting scientific interest but are generally more limited in scope or 

geographic coverage than Professional Papers. They include the results 

of resource studies and of geologic and topographic investigations; as well 

as collections of short papers related to a specific topic.

Water-Supply Papers are comprehensive reports that present significant interpretive results of hydrologic investigations of wide interest 

to professional geologists, hydrologists, and engineers. The series covers 

investigations in all phases of hydrology, including hydrogeology, 

availability of water, quality of water, and use of water.

Circulars present administrative information or important scientific 

information of wide popular interest in a format designed for distribution 

at no cost to the public. Information is usually of short-term interest.

Water-Resources Investigations Reports are papers of an interpretive nature made available to the public outside the formal USGS publications series. Copies are reproduced on request unlike formal USGS 

publications, and they are also available for public inspection at 

depositories indicated in USGS catalogs.

Open-File Reports include unpublished manuscript reports, maps, 

and other material that are made available for public consultation at 

depositories. They are a nonpermanent form of publication that may be 

cited in other publications as sources of information.

Maps

Geologic Quadrangle Maps are multicolor geologic maps on 

topographic bases in 71/2- or 15-minute quadrangle formats (scales mainly 1:24,000 or 1:62,500) showing bedrock, surficial, or engineering geology. Maps generally include brief texts; some maps include structure 

and columnar sections only.

Geophysical Investigations Maps are on topographic or planimetric 

bases at various scales; they show results of surveys using geophysical 

techniques, such as gravity, magnetic, seismic, or radioactivity, which 

reflect subsurface structures that are of economic or geologic significance. 

Many maps include correlations with the geology.

Miscellaneous Investigations Series Maps are on planimetric or 

topographic bases of regular and irregular areas at various scales; they 

present a wide variety of format and subject matter. The series also includes 71/2-minute quadrangle photogeologic maps on planimetric bases 

which show geology as interpreted from aerial photographs. Series also 

includes maps of Mars and the Moon.

Coal Investigations Maps are geologic maps on topographic or 

planimetric bases at various scales showing bedrock or surficial geology, stratigraphy, and structural relations in certain coal-resource areas.

Oil and Gas Investigations Charts show stratigraphic information 

for certain oil and gas fields and other areas having petroleum potential.

Miscellaneous Field Studies Maps are multicolor or black-andwhite maps on topographic or planimetric bases on quadrangle or irregular areas at various scales. Pre-1971 maps show bedrock geology 

in relation to specific mining or mineral-deposit problems; post-1971 

maps are primarily black-and-white maps on various subjects such as 

environmental studies or wilderness mineral investigations.

Hydrologic Investigations Atlases are multicolored or black-andwhite maps on topographic or planimetric bases presenting a wide range 

of geohydrologic data of both regular and irregular areas; principal scale 

is 1:24,000 and regional studies are at 1:250,000 scale or smaller.

Catalogs

Permanent catalogs, as well as some others, giving comprehensive listings of U.S. Geological Survey publications are available under 

the conditions indicated below from the U.S. Geological Survey, Books 

and Open-File Reports Section, Federal Center, Box 25425, Denver, 

CO 80225. (See latest Price and Availability List)

"Publkationsof the Geological Survey, 1879-1961" may be purchased by mail and over the counter in paperback book form and as a 

set of microfiche.

"Publications of the Geological Survey, 1962-1970" may be purchased by mail and over the counter in paperback book form and as a 

set of microfiche.

"Publications of the U.S. Geological Survey, 1971-1981" may be 

purchased by mail and over the counter in paperback book form (two 

volumes, publications listing and index) and as a set of microfiche.

Supplements for 1982,1983,1984,1985,1986, and for subsequent 

years since the last permanent catalog may be purchased by mail and 

over the counter in paperback book form.

State catalogs, "List of U.S. Geological Survey Geologic and 

Water-Supply Reports and Maps For (S tate)," may be purchased by mail 

and over the counter in paperback booklet form only.

"Price and Availability List of U.S. Geological Survey Publications," issued annually, is available free of charge in paperback booklet form only.

Selected copies of a monthly catalog "New Publications of the U.S. 

Geological Survey" available free of charge by mail or may be obtained 

over the counter in paperback booklet form only. Those wishing a free 

subscription to the monthly catalog "New Publications of the U.S. 

Geological Survey" should write to the U.S. Geological Survey, 582 

National Center, Reston, VA 22092.

Note. Prices of Government publications listed in older catalogs, 

announcements, and publications may be incorrect. Therefore, the 

prices charged may differ from the prices in catalogs, announcements, 

and publications.