Mineral Resources of the

Kofa Unit 4 North Wilderness Study Area,

Yuma County, Arizona

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Chapter K

Mineral Resources of the

Kofa Unit 4 North Wilderness Study Area,

Yuma County, Arizona

By DAVID R. SHERROD, DAVID B. SMITH, and 

M. DEAN KLEINKOPF 

U.S. Geological Survey

DIANN D. GESE 

U.S. Bureau of Mines

U.S. GEOLOGICAL SURVEY BULLETIN 1702 '

MINERAL RESOURCES OF WILDERNESS STUDY AREAS: 

SOUTHWESTERN AND SOUTH-CENTRAL 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

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

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For sale by the

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Library of Congress Cataloging-in-Publication Data

Mineral resources of the Kofa Unit 4 North Wilderness Study Area, Yuma 

County, Arizona / by David R. Sherrod... [et at.].

p. cm. (U.S. Geological Survey bulletin : 1702-K)

Includes bibliographical references, (p.

Supt. of Docs, no.: 119.3: 1702-K

1. Mines and mineral resources Arizona Kofa Unit 4 North 

Wilderness. 2. Kofa Unit 4 North Wilderness (Ariz.) I. Sherrod, 

David R. II. Series.

QE75.B9 no. 1702-K 557.3 s dc20 90-3797 

[TN24.A6] [553 1 .0979171] 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 of certain areas to determine the mineral values, if any, that may be 

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

the Congress. This report presents the results of a mineral survey of the Kofa Unit 4 North 

Wilderness Study Area (AZ-050-033), Yuma County, Arizona.

CONTENTS

Summary Kl

Abstract Kl

Character and setting Kl 

Identified resources Kl 

Mineral and energy resource potential Kl 

Introduction K2

Location, physiography, and access K2 

Present investigation K2 

Appraisal of identified resources K2 

Setting K2

Mining and leasing activity K2 

Methods of investigation K2 

Results K3

Assessment of mineral and energy resource potential K4 

Geology K4 

Geochemical studies K4

Methods of investigation K4 

Summary of results K5 

Geophysical studies K5 

Mineral and energy resources K6 

Gold, silver, lead, and zinc K6 

Zeolites K6 

Geothermal energy K6 

Other commodities K7 

References cited K7 

Appendixes

Definition of levels of mineral resource potential and certainty of

assessment K10 

Resource/reserve classification Kll

Geologic time chart K12

»

FIGURES

1. Index map showing location of Kofa Unit 4 North Wilderness Study Area, 

Yuma County, Arizona K3

2. Map showing mineral resource potential and generalized geology of Kofa Unit 4 

North Wilderness Study Area, Yuma County, Arizona K4

3. Bouguer gravity anomaly map of region including Kofa Unit 4 North Wilderness 

Study Area, Yuma County, Arizona K5

4. Total intensity aeromagnetic anomaly map of region including Kofa Unit 4 

North Wilderness Study Area, Yuma County, Arizona K6

Contents

Mineral Resources of the

Kofa Unit 4 North Wilderness Study Area,

Yuma County, Arizona

By David R. Sherrod, David B. Smith, and M. Dean Kleinkopf 

U.S. Geological Survey

Diann D. Cese

U.S. Bureau of Mines

SUMMARY 

Abstract

The Kofa Unit 4 North Wilderness Study Area 

(AZ-050-033) is located in Yuma County, southwestern 

Arizona. At the request of the U.S. Bureau of Land 

Management, 1,380 acres of the Kofa Unit 4 North 

Wilderness Study Area were evaluated for mineral resources 

(known) and mineral resource potential (undiscovered). 

Throughout this report, reference to the "Kofa Unit 4 North 

Wilderness Study Area" or to the "study area" refers only to 

that part of the wilderness study area for which mineral 

surveys were requested by the U.S. Bureau of Land 

Management.

Inferred subeconomic resources of zeolite are scattered 

throughout the west half of the study area. Large amounts of 

sand and gravel in the study area have no unique qualities 

that make them more valuable than vast quantities in the 

surrounding areas. The entire study area has low mineral 

resource potential for gold, silver, lead, and zinc, presumably 

associated with minor alteration along faults. Resource 

potential for zeolite ranges from high to unknown and is 

spotty in distribution because of localized zeolitization in 

altered tuff. Low resource potential for geothermal energy 

exists northwest of the range-bounding faults of the study 

area. The study area has no resource potential for oil or gas.

Yuma County, about 60 mi northeast of Yuma, Ariz. The 

Castle Dome Mountains are a rocky desert mountain range 

having relief as great as 2,000 ft. In the study area the 

relief is a little less than 700 ft. The mountains are underlain by Tertiary volcanic rocks that underwent a major 

episode of extensional deformation about 22 to 20 million 

years ago (see geologic time chart in "Appendixes"). 

Sedimentary basins that bound the range were created 

during this time and subsequently filled by coalescing alluvial fans.

Identified Resources

The study area has inferred subeconomic resources 

of approximately 733,000 short tons (st) of 60- to 98-percent combined zeolites (mordenite and clinoptilolite). 

Tests for this study show that these zeolites may have 

commercial value as water purifiers. Zeolites have been 

mined approximately 1,500 ft west of the study area boundary. Sand and gravel in the study area have no unique 

qualities that make them more valuable than those that are 

closer to markets in surrounding areas.

Mineral and Energy Resource Potential

Low resource potential for gold, silver, lead, and 

zinc is assigned to the entire Kofa Unit 4 North Wilderness 

Study Area. A high resource potential for zeolite is assigned to three small areas adjacent to demonstrated zeolite 

occurrences, and an unknown resource potential for zeolite 

 is assigned to other areas underlain by silicic lava flows or 

Manuscript approved for publication, April 29,1990. intrusions, which may include locally zeolitized, thin, interMineral Resources of the Kofa Unit 4 North Wilderness Study Area, Yuma County, Arizona K1

Character and Setting

The Kofa Unit 4 North Wilderness Study Area is in 

the northwestern part of the Castle Dome Mountains of
bedded lenses of tuffaceous rocks. There is low resource 

potential for geothermal energy on the valley side of rangebounding faults in the study area. The area has no potential 

for oil or gas.

INTRODUCTION

This mineral survey was requested by the U.S. 

Bureau of Land Management and represents 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 is 

provided by Beikman and others (1983). The U.S. Bureau 

of Mines evaluates identified resources at individual mines 

and 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 the 

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

Studies by the U.S. Geological Survey 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. Mineral 

assessment methodology and terminology as they apply to 

these surveys were discussed by Goudarzi (1984). See 

"Appendixes" for the definition of levels of mineral resource potential and certainty of assessment and for the 

resource/reserve classification.

Location, Physiography, and Access

The Kofa Unit 4 North Wilderness Study Area 

(AZ-05Q-033).is located about 30 mi south of Quartzsite 

and 60 mi northeast of Yuma, Ariz. (fig. 1), in the Basin 

and Range physiographic province of southwestern Arizona. The climate is arid, characteristic of the Sonoran 

Desert region of the southwestern United States and northern Mexico.

The study area lies along the steep, northwestern escarpment of the Castle Dome Mountains. Elevations range 

from about 1,500 ft on alluvial fans of the flanking La Posa 

Plain to nearly 2,200 ft at the top of the escarpment. 

Access is by secondary roads from U.S. Highway 95, 

which lies about 0.5 mi west of the study area.

inside and within about 1 mi of the study area boundary 

(Gese, 1989). Field studies by the U.S. Geological Survey 

for this assessment were conducted mainly in 1984 and 

1985 and included geologic mapping and geochemical 

studies. Rock and stream-sediment samples were collected 

to supply background geochemical information and to 

identify areas containing anomalous concentrations of 

economic or indicator elements (Adrian and others, 1986; 

Bagby and others, 1987).

APPRAISAL OF IDENTIFIED RESOURCES

By Diann D. Gese 

U.S. Bureau of Mines

Setting

The study area is about 13 mi north-northwest of the 

Castle Dome mining district and about 16 mi west of the 

Kofa district (fig. 1). Both districts, however, are centered 

on vein deposits restricted to metamorphosed Mesozoic 

sedimentary rocks (Keith, 1978). Such rocks are buried in 

the Kofa Unit 4 North Wilderness Study Area by at least 

3,000 ft of Tertiary volcanic strata (Grubensky and others, 

in press). Sand and gravel fill the few washes in the study 

area.

The zeolites mordenite and clinoptilolite are the only 

minerals of economic interest known to occur in the study 

area. The zeolites occur in devitrified greenish silicic tuff 

that crops out along the west boundary. The tuff forms thin 

lenses within a more widespread unit of thick silicic lava 

flows or shallow intrusions.

Mining and Leasing Activity

Zeolites have been mined by open-pit methods and 

stockpiled along the western boundary of the study area by 

the Yuma Zeolite Corporation of Phoenix, Ariz., as recently as February 1986. The mine was inactive and 

appeared abandoned as of April 1988. A group of lode 

claims staked for zeolites extends into the study area from 

the west in sees. 20 and 29, T. 2 S., R. 19 W. There has 

been no mining of precious metals or other industrial 

minerals from the study area, and there are no oil or gas 

leases or lease applications in the study area.

Present Investigation

In 1988, the U.S. Bureau of Mines conducted a 

survey of the study area that focused chiefly on the examination of known mines, prospects, and mineralized areas

Methods of Investigation

U.S. Bureau of Mines personnel collected 11 rock 

samples during 2 days of field work and analyzed them for 

zeolite mineral content. Samples containing more than 60

K2 Mineral Resources of Wilderness Study Areas: Southwestern and South-Central Arizona
percent combined zeolites were further tested to determine 

suitability for industrial uses. Complete analytical results 

for all samples are available for public inspection at the 

U.S. Bureau on Mines, Intermountain Field Operations 

Center, Building 20, Denver Federal Center, Denver, CO 

80225. Conventional methods were used to estimate area 

and thickness of the three zeolite deposits found in the 

study area (Gese, 1989). Tonnages were calculated by 

dividing the deposit volumes by a tonnage factor of 15.

Results

Three zeolite deposits in the study area contain inferred subeconomic resources totaling approximately 

733,000 tons of 60- to 98-percent combined zeolites.

Clinoptilolite and mordenite are the major constituents; 

quartz or secondary silica are minor. Laboratory tests 

provided to the U.S. Bureau of Mines indicate that the 

zeolites' ammonium-ion exchange capacity, important in 

treating radioactive and water wastes, is low, ranging from 

0.54 to 0.96 milliequivalents per gram (meq/g), whereas 

most commercial zeolites have exchange capacities of 1 to 

2 meq/g. Some of the zeolite samples are capable of 

purifying water containing 200 to 1,000 parts per million 

lead (Pb2+) to drinking water standards of less than 50 parts 

per billion lead. Additional testing might determine other 

uses for these zeolites.

All three deposits are suitable for open-pit mining 

because they are exposed at the surface and are as thick as 

25 ft. Potential distribution centers are located within 60 

mi, at either Yuma, Ariz., or Blythe, Calif.

115°00' 114°30' 114°00'

33° 

30'

33° 

00'

RIVERSIDE CO 

IMPERIAL CO

, APPROXIMATE BOUNDARY,

OF

KOFA UNIT 4 NORTH 

WILDERNESS 

STUDY AREA 

(AZ-050-033)

YUMA CO

ARIZONA

AREA OF MAP

MEXICO

Kofa National 

Wildlife Refuge

Figure 1. Index map showing location of Kofa Unit 4 North Wilderness Study Area, Yuma County, Arizona.

Mineral Resources of the Kofa Unit 4 North Wilderness Study Area, Yuma County, Arizona K3
ASSESSMENT OF MINERAL AND ENERGY 

RESOURCE POTENTIAL

By David R. Sherrod, David B. Smith, and 

M. Dean Kleinkopf 

U.S. Geological Survey

Geology

The Kofa Unit 4 North Wilderness Study Area, in 

the northern Castle Dome Mountains, is underlain by Oligocene and lower Miocene volcanic and volcaniclastic 

rocks (Grubensky and others, in press). These rocks consist mainly of silicic lava flows, shallow intrusions, and 

interbedded ash-flow tuff that were erupted from caldera 

sources in the Kofa and Castle Dome Mountains about 24 

to 22 million years ago (Ma) (Shafiqullah and others, 1980; 

Gutmann, 1981; Grubensky and others, 1986).

Normal faulting and sedimentation occurred simultaneously, beginning sometime after about 22 Ma (Sherrod 

and others, 1987). The region was extended 10 to 40 

percent, as indicated by strata in fault blocks that are tilted 

as much as 60°. Thick sequences of sand and gravel (in 

unit QTs, fig. 2) accumulated as large alluvial fans that 

filled grabens and buried the pediment slopes of mountain 

ranges throughout the area.

Except for zeolites, mineralization is unreported 

from the study area, and the Tertiary volcanic rocks elsewhere in the general area have only a few small zones of

alteration and iron oxide staining. In contrast, mines in the 

Kofa and Castle Dome mining districts have produced 

precious and base metals from vein deposits in metamorphosed Mesozoic sedimentary rocks. Within the study area, 

however, these rocks are buried beneath at least 3,000 feet 

of Tertiary volcanic rocks.

Some of the volcanic rocks were glassy because they 

cooled so rapidly upon eruption. Glass is inherently unstable, however, and through time the Tertiary glass has 

been converted to minerals, including zeolites and clays. 

Devitrification of glass, most extensive in silicic tuff (part 

of unit Tsf) adjacent to silicic lava or intrusions in the study 

area, has resulted in the zeolite deposits on the west edge of 

the Castle Dome Mountains in the study area.

Geochemical Studies

Methods of Investigation

Stream-sediment samples were collected from four 

sites in dry stream beds in the Kofa Unit 4 North Wilderness Study Area in 1985 as part of a more extensive U.S. 

Geological Survey mineral resource assessment study of the 

Kofa National Wildlife Refuge and its proposed additions 

(Adrian and others, 1986; Bagby and others, 1987). Minus80-mesh stream sediments and heavy-mineral concentrates 

derived from stream sediments were selected as the primary 

sample media in that study because they represent a com-

,114° 15' 114° 12'30"

APPROXIMATE BOUNDARY

OF | 

KOFA UNIT 4 NORTH ' 

WILDERNESS STUDY AREA 

(AZ-050-033)

1 MILE

EXPLANATION

Area having high mineral resource potential (H) 

I I Area having low (L) or unknown (U) mineral resource potential 

Levels of certainty of assessment

A Data are not adequate to determine level of potential

B Data only suggest level of potential

D Data clearly define level of potential

Commodities

Au Gold

Ag Silver

Geo Geothermal

QTs 

Tsf

Tt 

Tdg

Pb Lead

Zn Zinc

Zeo Zeolite

Geologic map units

Sedimentary deposits and rocks (Quaternary and Tertiary) 

Silicic lava flows and shallow intrusions (Miocene) Locally

includes thin lenses of tuff that have been converted to

zeolite minerals

Tuff and welded tuff (Miocene and Oligocene) 

Dacite of Gravel Wash (Miocene and Oh'gocene)

Contact Approximately located

Fault Dotted where concealed. Bar and ball on downthrown

side 

Strike and dip of bedding or foliation in welded tuff

Figure 2. Mineral resource potential and generalized geology of Kofa Unit 4 North Wilderness Study Area, Yuma County, 

Arizona. Geology generalized from Grubensky and others (in press). Topographic contour interval 40 ft.

K4 Mineral Resources of Wilderness Study Areas: Southwestern and South-Central Arizona
posite of rock and soil exposed in the drainage basin upstream from the sample site. Chemical analysis of the 

sediment samples helps to identify basins containing unusually high concentrations of elements that may be related to 

mineral occurrences. Heavy-mineral concentrates are a 

useful sample medium in arid environments or in areas of 

rugged topography, where mechanical erosion predominates over chemical erosion (Overstreet and Marsh, 1981; 

Bugrov and Shalaby, 1975; Zeegers and others, 1985). 

Analytical data, sampling methods, sample preparation 

procedures, analytical techniques, and sampling sites are 

presented in Adrian and others (1986).

The nonmagnetic fraction of one heavy-mineral-concentrate sample was analyzed for 31 elements 1 by 

semiquantitative emission spectroscopy. A nonmagnetic 

fraction concentrates ore and ore-related minerals such as 

pyrite, galena, cassiterite, sphalerite, chalcopyrite, stibnite, 

free gold, barite, and scheelite and thus permits determination of some elements that are not easily detected in bulk 

stream-sediment samples.

This method is imprecise for the low concentrations 

of some elements commonly used as pathfinders for precious metal mineralization. Therefore, the minus-80-mesh 

stream-sediment samples were analyzed by atomic-absorption methods, which have lower determination limits as 

follows (shown in parentheses for each element): antimony 

(2 parts per million, ppm), arsenic (10 ppm), gold (2 to 8 

parts per billion, ppb, depending on amount of sample 

available), mercury (0.02 ppm), silver (0.05 ppm) thallium 

(0.1 ppm), and zinc (5 ppm). It is impractical to analyze 

heavy-mineral concentrates by atomic absorption because 

the preparation of the concentrate results in too little sample 

material for reliable results by that method.

Summary of Results

Within the study area, a sample from one site contains 0.05 ppm gold in minus-80-mesh sediments; the 

heavy-mineral concentrate from the same site contains 

1,000 ppm lead and detectable arsenic (that is, arsenic was 

detected but below the limit of determination, 500 ppm). 

Geochemically, the Kofa Unit 4 North Wilderness Study 

Area lies within the "northern Castle Dome anomaly" as 

defined and discussed by Bagby and others (1987). That 

anomaly covers approximately the northern quarter of the 

Castle Dome Mountains and encompasses scattered anomalous concentrations of gold, thallium, and zinc in minus-80- 

mesh stream sediments and scattered anomalous concentra1Arsenic, antimony, barium, beryllium, bismuth, boron, cadmium, 

calcium, cobalt, chromium, copper, gold, iron, lanthanum, lead, magnesium, manganese, molybdenum, niobium, nickel, silver, scandium, strontium, thorium, tin, titanium, tungsten, vanadium, yttrium, zinc, and zirconium.

tions of tin, arsenic, silver, zinc, lead, antimony, and bismuth in nonmagnetic heavy-mineral concentrates.

Geophysical Studies

The geophysical data discussed here are from reconnaissance gravity and magnetic surveys of the region. The 

Bouguer gravity anomaly map (fig. 3) was compiled from 

U.S. Geological Survey digital gravity files. Control for 

the map consists of randomly spaced stations that average 

about 2 mi apart, but no control points are located within 

the study area. The study area lies near the south flank of 

a broad and deep gravity minimum. The lowest gravity 

value is negative 92 milligals near the center of the La Posa 

Plain. This low has been attributed to a subsided block, 

possibly resulting from caldera-forming volcanism in 

Miocene time (Bagby and others, 1987; Gutmann, 1981). 

Gravity modeling by C.L.V. Aiken (cited in Gutmann, 

1981) suggests that the area is underlain at about 5 mi 

depth by a silicic batholith.

The aeromagnetic anomaly map (fig. 4) is from a 

residual total intensity map of the Salton Sea 1:250,000- 

scale sheet prepared for the National Uranium Resource 

Evaluation program (LKB Resources, Inc., 1980). That 

survey was flown along north-south flightlines having 3-mi

114°20' 114°05'

10 MILES

Figure 3. Bouguer gravity anomaly map of region including 

Kofa Unit 4 North Wilderness Study Area (shaded block), 

Yuma County, Arizona. Contour interval 2 milligals; 

hachures indicate area of closed low; dots represent gravity 

stations. Compiled by Viki L. Bankey.

Mineral Resources of the Kofa Unit 4 North Wilderness Study Area, Yuma County, Arizona K5
114°05 !

10 MILES

Figure 4. Total intensity aeromagnetic anomaly map of 

region including Kofa Unit 4 North Wilderness Study Area 

(shaded block), Yuma County, Arizona. Contour interval 20 

nanoteslas; hachures indicate area of closed low. Dashes 

show flightlines. Data from LKB Resources, Inc. (1980).

line spacing and terrain clearance of 400 ft. The Kofa Unit 

4 North Wilderness Study Area lies along a north-south 

flightline and an east-west tie line. The magnetic anomaly 

map indicates that the study area is about 4 mi northwest of 

a large negative anomaly having an amplitude of 80 to 100 

nanoteslas. This and several other negative anomalies on 

the map may be explained by low magnetization in preTertiary rock units that underlie the volcanic rocks of the 

study area. The low magnetization may also result from 

alteration.

Mineral and Energy Resources

Gold, Silver, Lead, and Zinc

The entire study area has low resource potential, 

certainty level B, for the precious and base metals of gold, 

silver, lead and zinc. This assignment is based on anomalous concentrations in one of the four stream-sediment 

samples from the study area and on the position of the 

study area within the northern Castle Dome geochemical 

anomaly, a broad area characterized by scattered anomalous concentrations of gold, thallium, and zinc in streamsediment samples and erratic concentrations of tin, arsenic, 

silver, zinc, lead, antimony, and bismuth in heavy-mineral

concentrates (Bagby and others, 1987). The specific location and style of mineralization and alteration responsible 

for the anomalous concentrations is undefined on the geologic map of the mountains (Grubensky and others, in 

press), but presumably the metal concentrations result from 

alteration and minor mineralization along fault zones or are 

associated with small veins and iron oxide staining. The 

metals are probably mobilized from buried pre-Tertiary 

rocks, which are locally mineralized elsewhere in the 

region.

Zeolites

A high mineral resource potential, certainty level D, 

for zeolite is assigned to areas adjacent to three small 

demonstrated zeolite occurrences in silicic tuff. The scattered distribution of these areas probably reflects spotty 

zeolitization of rocks in the area. An unknown resource 

potential, certainty level A, for zeolite is assigned to the 

northern part of the study area, which is underlain by 

Tertiary silicic lava flows that may include unrecognized 

small deposits of zeolite.

Geothermal Energy

The Castle Dome Mountains are in the Basin and 

Range physiographic province, which is characterized by 

high regional heat flow. Heat-flow values of 101 milliwatts 

per square meter (mW/m2) were measured 30 mi north of 

the study area near Quartzsite, and values of 80 to 88 

mWm2 were measured 60 mi south near Yuma (Muffler, 

1979). A well at Stone Cabin, 1.5 mi north of the study 

area on U.S. Highway 95, intercepted water having a 

temperature of 44 °C at 1,020 ft depth (Witcher and others, 

1982). Several alluvial basins located 20 to 60 mi east of 

the study area are considered "favorable for the discovery 

and development of local sources of low-temperature (less 

than 90 °C) geothermal water" suitable for space heating, 

agriculture, and perhaps industry (Sammel, 1979). This 

water is heated by deep circulation along fault zones in 

areas of high regional heat flow. Conceivably, similar 

thermal conditions may exist in the La Posa Plain at the 

north edge of the study area, but the hydrology of the basin 

is unexplored. No igneous-related geothermal systems 

those in which water is heated by young shallow intrusions occur within 100 mi of the study area (Muffler, 

1979).

Aquifers of the La Posa Plain lie chiefly in Tertiary 

and Quaternary alluvial fill and are outside the study area. 

Low-temperature thermal fluids, possibly from the La Posa 

Plain, may be convecting near the major range-bounding 

fault in the study area. Therefore, a low resource potential, 

certainty level B, for geothermal energy is assigned to the

K6 Mineral Resources of Wilderness Study Areas: Southwestern and South-Central Arizona
area northwest of that fault along the west boundary of the 

study area (fig. 2).

Data about geothermal gradients and lithologic conductivity are insufficient to show that the study area lies 

within a locally enhanced zone of heat flow. Nevertheless, 

an encouraging view of geothermal resources was offered 

by Gutmann (1981), who relied on a broadly defined negative Bouguer gravity anomaly, the depth to the Curie isotherm, and an anomalously shallow (6-mi depth) electrical 

conductor as favorable indicators that valleys near the 

northern and central Castle Dome Mountains are niore 

attractive for geothermal development than surrounding 

areas. However, much of the evidence is sketchy and illdefined; see Gutmann (1981) for references.

Other Commodities

Sand and gravel are high-volume, low-unit-value 

commodities that require a local market for economic 

development. The occurrences in the Kofa Unit 4 

North Wilderness Study Area have no unique properties that make them more valuable than other deposits 

closer to markets.

The Kofa Unit 4 North Wilderness Study Area 

has no potential, certainty level D, for oil and gas 

resources. It is in a part of the Basin and Range 

physiographic province that was considered by Ryder 

(1983) to have low or zero potential for oil and gas. 

No tar or oil seeps, black shales, or other evidence of 

hydrocarbon source beds are found in the Tertiary 

volcanic rocks that underlie most of the study area. 

The Tertiary alluvial fill of La Posa Plain may have 

limited potential for gas, but these rocks are relatively 

thin where they abut the Castle Dome Mountains in the 

study area.

REFERENCES CITED

Adrian, B.M., Smith, D.B., Hill, R.H., Roemer, T.A., 

Vaughn, R.B., and Delaney, T.A., 1986, Analytical 

results and sample locality map of stream-sediment, 

heavy-mineral-concentrate, and rock samples from the 

Kofa National Wildlife Refuge, Yuma and La Paz 

Counties, Arizona: U.S. Geological Survey Open-File 

Report 86-199, 122 p.

Bagby, W.C., Haxel, G.B., Smith, D.B., Koch, R.D., 

Grubensky, M.J., Sherrod, D.R., and Pickthom, L.G., 

1987, Mineral resource assessment of the Kofa National 

Wildlife Refuge, Arizona: U.S. Geological Survey 

Open-File Report 87-609, 71 p.

Beikman, H.M., Hinkle, M.E., Frieders, Twila, 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 p.

Bugrov, V.A., and Shalaby, I.M., 1975, Geochemical prospecting <in the eastern desert of Egypt, in Elliott, I.L., 

and Fletcher, W.K., eds., Geochemical exploration, 

1974: Rexdale, Ontario, Association of Exploration 

Geochemists, p. 523-530.

Gese, D.D., 1989, Mineral resources of a part of the Kofa 

Unit 4 North Wilderness Study Area (AZ-050-033), 

Yuma County, Arizona: U.S. Bureau of Mines Mineral 

Land Assessment Open-File Report MLA-11-89, 16 p.

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.

Grubensky, M.J., Haxel, G.B., and Koch, R.D., in press, 

Geologic map of the Castle Dome Mountains, southwestern Arizona: U.S. Geological Survey Miscellaneous Investigations Map 1-2138, scale 1:62,500.

Grubensky, M.J., Sherrod, D.R., Koch, R.D., Pickthorn, 

L.B.G., and Bagby, W.C., 1986, Late Oligocene-early 

Miocene calderas in the Kofa area, southwestern Arizona [abs.]: Geological Society of America Abstracts 

with Programs, v. 18, no. 2, p. 111.

Gutmann, J.T., 1981, Geologic framework and hot dry rock 

geothermal potential of the Castle Dome area, Yuma 

County, Arizona: Los Alamos Scientific Laboratory 

Report LA-8723-HDR, UC-66b, 23 p.

Keith, S.B., 1978, Index of mining properties in Yuma 

County, Arizona: Arizona Bureau of Geology and 

Mineral Technology Bulletin 192, 185 p.

LKB Resources, Inc., 1980, National Uranium Resource 

Evaluation aerial gamma-ray and magnetic reconnaissance survey, Colorado/Arizona area, Salton Sea, El 

Centro, Phoenix, Ajo, and Lukeville quadrangles Final 

report: U.S. Department of Energy Grand Junction 

Office Report GJBX 12-80, v. 2, unpaginated, scale 

1:250,000.

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

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

Muffler, L.J.P., ed., 1979, Assessment of geothermal resources of the United States 1978: U.S. Geological 

Survey Circular 790, 163 p.

Overstreet, W.C., and Marsh, S.P., 1981, Some concepts and 

techniques in geochemical exploration, in Skinner, 

Brian, ed., Economic Geology 75th Anniversary Volume, New Haven, Conn., p. 775-805.

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

Arizona, in Miller, B.M., ed., Petroleum potential of wilderness lands in the Western United States: U.S. Geological Survey Circular 902, chapter C, p. C1-C22.

Sammel, E.A., 1979, Occurrence of low-temperature geothermal waters in the United States, in Muffler, L.J.P., ed., 

Assessment of geothermal resources of the United 

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

86-131.

Shafiqullah, M., Damon, P.E., Lynch, D.J., Reynolds, S.J., 

Rehrig, W.A., and Raymond, R.H., 1980, K-Ar geochronology and. geologic history of southwestern Arizona 

and adjacent areas: Arizona Geological Society Digest, 

v. 12, p. 201-260.

Sherrod, D.R., Pickthorn, L.B.G., Tosdal, R.M., Grubensky, 

M.J., and Koch, R.D., 1987, Major early Miocene extenMineral Resources of the Kofa Unit 4 North Wilderness Study Area, Yuma County, Arizona K7
sional deformation in southwestern Arizona and south- Geothermal resources of Arizona: Arizona Bureau of

eastern California [abs.]: Geological Society of Amer- Geology and Mineral Technology, scale 1:500,000. 

ica Abstracts with Programs, v. 19, no. 7, p. 841. Zeegers, H., Al Shanfari, S.M., Al Muflehi, Y.A., and

U.S. Bureau of Mines and U.S. Geological Survey, 1980, Letalenet, J., 1985, Aspects of regional geochemical

Principles of a resource/reserve classification for miner- prospecting in desert conditions, in Prospecting in areas

als: U.S. Geological Survey Circular 831, 5 p. of desert terrain: London, The Institution of Mining and

Witcher, J.C., Stone, Claudia, and Hahman, W.R., Sr., 1982, Metallurgy, p. 131-140.

K8 Mineral Resources of Wilderness Study Areas: Southwestern and South-Central Arizona
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.

o

QL

LU 

LJ 

DC

Z> 

O

en LU 

a: 

u_ 

o 

_i

LU

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

L/D

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. 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.

K10 Mineral Resources of Wilderness Study Areas: Southwestern and South-Central Arizona
RESOURCE/RESERVE CLASSIFICATION

ECONOMIC

MARGINALLY 

ECONOMIC

SUBECONOMIC

IDENTIFIED RESOURCES

Demonstrated

Measured

Rese

Indicated

;rves

Marginal 

Reserves

Demonstrated 

Subeconomic

Resources

i

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.

Mineral Resources of the Kofa Unit 4 North Wilderness Study Area, Yuma County, Arizona K11
GEOLOGIC TIME CHART

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

EON

Phanerozoic

Proterozoic

pre-Archean2

ERA

Cenozoic

Mesozoic

Paleozoic

Late Proterozoic

Middle Proterozoic

Early Proterozoic

Late Archean

Middle Archean

Early Archean

PERIOD

Neogene

Subperiod

Tertiary

r al eogen e

Ci tnrY»ri/~y"l

Jurassic

Triassic

Permian

Pennsylvanian 

Carboniferous

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 

MILLION YEARS (Ma)

 0.010

 1.7

 5

0 . 

OO

 55

66

96

100

 205

 -240

 290 

 -330

 360 

 410

juu

 '-570

j\j\j

 1600

 2500

J\J\AJ

 3400

 Arm 

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

informal time term without specific rank.

K12 Mineral Resources of Wilderness Study Areas: Southwestern and South-Central Arizona
Mineral Resources of

Wilderness Study Areas:

Southwestern and South-Central Arizona

This volume was published as separate chapters A-K

U.S. GEOLOGICAL SURVEY BULLETIN 1702
DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, JR., Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director
CONTENTS

[Letters designate the separately published chapters]

(A) Mineral Resources of the Table Top Mountain Wilderness Study Area, Maricopa and 

Final Counties, Arizona, by Jocelyn A. Peterson, Gary A. Nowlan, 

William F. Hanna, James A. Pitkin, and John R. McDonnell, Jr.

(B) Mineral Resources of the New Water Mountains Wilderness Study Area, La Paz 

County, Arizona, by David R. Sherrod, David B. Smith, Richard D. Koch, 

William F. Hanna, James A. Pitkin, and Michael E. Lane.

(C) Mineral Resources of the Signal Mountain Wilderness Study Area, Maricopa 

County, Arizona, by Royd Gray, Robert J. Miller, Jerry R. Hassemer, 

Daniel H. Knepper, James A. Pitkin, William F. Hanna, and Terry J. Kreidler.

(D) Mineral Resources of the Muggins Mountains Wilderness Study Area, Yuma

County, Arizona, by David B. Smith, Richard M. Tosdal, James A. Pitkin,

M. Dean Kleinkopf, and Robert H. Wood H. 

(E) Mineral Resources of the Baboquivari Peak and Coyote Mountains Wilderness

Study Areas, Pima County, Arizona, by Gary A. Nowlan, Gordon B. Haxel,

William F. Hanna, James A. Pitkin, Denny V. Diveley-White,

John R. McDonnell, Jr., and William Lundby. 

(F) Mineral Resources of the Woolsey Peak Wilderness Study Area, Maricopa County,

Arizona, by Jocelyn A. Peterson, Jerry R. Hassemer, Daniel H. Knepper, Jr.,

James A. Pitkin, William F. Hanna, and John R. McDonnell, Jr. 

(G) Mineral Resources of the Eagletail Mountains Wilderness Study Area, La Paz,

Maricopa, and Yuma Counties, Arizona, by Robert J. Miller, Royd Gray,

Jerry R. Hassemer, William F. Hanna, James A. Pitkin, Michelle I. Hornberger,

Stephanie L. Jones, and Michael E. Lane. 

(H) Mineral Resources of the Ragged Top Wilderness Study Area, Pima County,

Arizona, by Gary A. Nowlan, Jocelyn A. Peterson, James A. Pitkin,

William F. Hanna, and Terry J. Kreidler. 

(I) Mineral Resources of the Sierra Estrella Wilderness Study Area, Maricopa County,

Arizona, by William J. Keith, Richard J. Goldfarb, Viki L. Bankey,

Stephanie L. Jones, and Stanley L. Korzeb. 

(J) Mineral Resources of the Trigo Mountains Wilderness Study Area, La Paz County,

Arizona, by David R. Sherrod, Richard M. Tosdal, Robert B. Vaughn,

David B. Smith, M. Dean Kleinkopf, and Robert H. Wood II. 

(K) Mineral Resources of the Kofa Unit 4 North Wilderness Study Area, Yuma County,

Arizona, by David R. Sherrod, David B. Smith, M. Dean Kleinkopf, and

Diann D. Gese.



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