Mineral Resources of the Muggins Mountains 

Wilderness Study Area, Yuma County, Arizona 

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Chapter D 

Mineral Res.ources of the Muggins Mountains 

Wilderness ·st~Jdy Area, Yuma County, Arizona 

By DAVID B. SMITH, RICHARD M. TOSDAL, 

JAMES A. PITKIN, and M. DEAN KLEINKOPF 

U.S. Geological Survey 

ROBERT H. WOOD, II 

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 

in this publication is for descriptive purposes only 

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

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1989 

For sale by the 

Books and Open-File Reports Section 

U.S. Geological Survey 

Federal Center, Box 25425 

Denver, CO 80225 

Library of Congress Cataloging-in-Publication Data 

Mineral resources of the Muggins Mountains Wilderness Study Area, Yuma 

County, Arizona I by David B. Smith ... [et al.] 

p. em. - (U.S. Geological Survey bulletin ; 1702-D) 

Bibliography: p. 

Supt. of Docs. no.·: I 19.3:1702-D 

1. Mines and mineral resources-Arizona-Muggins Mountains Wilderness. 

2. Muggins Mountains Wilderness (Ariz.) I. Smith, David B. (David Burl), 

1948- . II. Series. 

QE75.B9 no. 1702-D 557.3 s-dc20 89-600092 

[TN24.A6] [553'.09791'71] 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 Muggins 

Mountains Wilderness Study Area (AZ-050-053A}, Yuma County, Arizona. 
CONTENTS 

Summary 

Abstract 

01 

01 

Character and setting 01 

Identified resources 01 

Mineral resource potential 02 

Introduction 02 ·~ 

Acknowledgments 03 

Appraisal of identified resources and known mineralized areas 03 

Mining and leasing activity 03 

Gold 03 

Uranium 04 

Sand and gravel 04 

Conclusions 04 

Assessment of mineral resource potential 04 

Geologic setting 04 

Geochemistry 04 

Results 08 

Geophysical studies D8 

Mineral resource potential of the Muggins Mountains Wilderness Study 

Area D8 

Gold 08 

Uranium D10 

Geothermal energy 010 

Oil and gas 010 

References cited D10 

Appendixes 

Definition of levels of mineral resource potential and certainty of 

assessment 014 

Resource/reserve classification D15 

Geologic time chart 016 

FIGURES 

1. Index map showing location of Muggins Mountains Wilderness Study Area, 

Yuma County·, Arizona D2 

2. Map showing mineral resource potential and geology of Muggins Mountains 

Wilderness Study Area, Yuma County, Arizona 06 

3. Map showing mines, prospects, oil and gas leases, and anomalous geochemical 

sample localities in Muggins Mountains Wilderness Study Area, Yuma County, 

Arizona 09 

Contents V 
Mineral Resources of the Muggins Mountains 

Wilderness Study Area, Yuma County, Arizona 

By David B. Smith, Richard M. Tosdal, James A. Pitkin, and M. Dean Kleinkopf 

U.S. Geological Survey 

Robert H. Wood, II 

U.S. Bureau of Mines 

SUMMARY 

Abstract 

At the request of the U.S. Bureau of land Management, 

approximately 8,855 acres of the Muggins Mountains Wilderness Study Area (AZ-050-053A) in southwestern Yuma 

County, Arizona, was evaluated for mineral resources 

(known) and mineral resource potential (undiscovered). In 

this report, the area studied is referred to as "the study area"; 

any reference to the Muggins Mountains Wilderness Study 

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

which a mineral survey was requested. Fieldwork for this 

report was conducted between 1983 and 1988. 

Nearly half the study area is covered by unpatented 

mining claims, but no patented mining claims exist. There 

are no identified resources of metallic minerals in the study 

area. 

The study area contains sand and gravel, and the potential for gold in placer deposits is moderate. A tract having 

moderate potential for uranium extends along the southeast 

boundary of the study area. The pot.ential for geothermal 

energy resources and oil and gas resources is low in the study 

area. 

Character and Setting 

The Muggins Mountains Wilderness Study Area is 

located in southwestern Yuma County, Ariz., approximately 6 mi northwest of Wellton and 25 mi northeast of 

Yuma (fig.1). The relief with rugged hills, steep-walled 

arroyos, and broad sandy washes is about 1,470 ft 

The oldest rock exposed in the study area is 

Proterozoic augen gneiss (see "Appendixes" for geologic 

time chart). Paleozoic and lower Mesozoic metasedimentary rocks are exposed in a narrow east-trending mylonitic 

Manuscript approved for publication April 3, 1989. 

shear zone (fig. 2). The Proterozoic through lower Mesozoic rocks are intruded by monzogranite and diorite of Jurassic(?) age. The upper Oligocene(?) and lower Miocene 

Kinter Formation unconformably overlies the crystalline 

rocks. The Kinter Formation is divided into two informal 

members, a lower member consisting of fine-grained sandstone, siltstone, and tuff and an upper member consisting of. 

coarse conglomerate, fanglomerate, and sandstone. Silicic 

volcanic flows, domes, tuff, and tuffaceous sedimentary 

rocks interfinger with the Kinter Formation at its margins. 

Middle Tertiary volcanism, sedimentation, and extensional deformation were contemporaneous in the area. A 

tectonic breccia lies between the basement rocks and the 

volcanic flows. Latite dikes intrude the breccia, overlying 

conglomerate and volcanic rocks, and the underlying basement rocks. Continued extension during the Tertiary broke 

the area into northwest-striking, southwest-tilted blocks. 

Unconformably overlying all the older rocks and structures 

are gravel, sand, and silt deposited on the· Gila River 

floodplain. 

Identified Resources 

The study area contains sand and gravel, but they have 

no unique qualities to make them more valuable than the 

vast quantities in nearby areas. 

There are no identified resources of metallic minerals 

in the study area although about one-half of the area is 

covered by unpatented mining claims. Over one-third of 

the study area is under lease for oil and gas, but the area is 

untested. 

The Muggins Mountains were frrst prospected in the 

1860's for placer gold and silver. In the 1950's, U.S. 

Atomic Energy Commission investigators found several 

scattered uranium occurrences in the Tertiary sedimentary 

rocks in the southeastern part of the range, outside the 

study area. 

Muggins Mountains Wilderness Study Area, Yuma County, Arizona 01 
Mineral Resource Potential 

The entire Muggins Mountains Wilderness Study Area 

has moderate potential for gold in placer deposits. This 

rating is based on gold anomalies in panned concentrates 

derived from stream sediments collected at five sampling 

sites within the study area and on the historical production 

of minor amounts of placer gold and silver from the 

Muggins mining district, which includes part of the study 

area. 

One small drainage basin along the southeast boundary 

of the study area has moderate potential for uranium. This 

potential is based on anomalous concentrations of molybdenum and lead in nonmagnetic heavy-mineral concentrates derived from stream sediments and anomalous concentrations of lead in minus-80-mesh stream sediments. 

These geochemical anomalies are similar to those downstream from a known uranium occurrence 0.5 mi east of the 

study area. 

The potential for oil and gas in the study area is low on 

the basis of unfavorable evidence for the presence of hya 

"' Q. 

~\.~ •\~~ ~ov MUGGINS PEAK 

~0 1424 ~ \.p 

0 

I 

Improved 

drocarbon source rocks. The study area has low potential 

for geothermal energy. 

INTRODUCTION 

This report presents an assessment of the identified 

resources and the mineral resource potential of 8,855 acres 

of the Muggins Mountains Wilderness Study Area 

(AZ-050-053A), Yuma County, Ariz. The term "study 

area" refers to that part of the total wilderness study area 

for which the U.S. Bureau of Land Management (BLM) 

requested a mineral survey. The study area is approximately 6 mi northwest of Wellton and 25 mi northeast of 

Yuma, Ariz. (fig. 1). The entire study area is located 

immediately south of the U.S. Army Yuma Proving 

Ground. Secondary roads from U.S. Highway 80 provide 

access to gravel and unimproved roads that, in tum, provide · 

limited access to the study area. 

The topographic relief in the study area is about 1,470 

ft and elevations range from about 200 ft near the south and 

west boundaries to 1,666 ft at the summit of Klothos 

\ 

\ 

I 

I \ I 

I tC 

'.('l;. I§· <(10, rn 

...:(ov. I~ 

'~ \g_ 

' I '-<o \ .c(O' '-

APPROXIMATE BOUNDARY 

OF 

MUGGINS MOUNTAINS 

WILDERNESS STUDY AREA 

(AZ-050-053A) 

' ...... ' \ 

2 MILES 

I 

,, 

I 

I 

I 

( 

\o 

\~ 

ENAI 

AREA OF MAP 

Figure 1. Index map showing location of Muggins Mountains Wilderness Study Area, Yuma County, Arizona. 

02 Mineral Resources of Wilderness Study Areas: Southwestern and South-Central Arizona 
Temple. Intermittent streams have dissected the area into 

an intricate pattern of rounded hills, flat mesas, and deep, 

steep-walled arroyos. Virtually all streams within the study 

area flow southward into the Gila River. The climate is 

arid with an average annual rainfall of approximately 3 in. 

at Yuma and 4-6 in. in the adjacent mountains (Hely and 

Peck, 1964). 

This mineral resource study is a joint effort by the U.S. 

Geological Survey (USGS) and the U.S. Bureau of Mines 

(USBM). The history and philosophy of such joint mineral 

surveys of BLM study areas are discussed by Beikman and 

others (1983). Mineral assessment methodology and terminology are discussed by Goudarzi (1984). Studies by the 

USGS are designed to provide a reasonable scientific basis 

for assessing the potential for undiscovered mineral resources by determining geologic units and structures, possible environments of mineral deposition, and presence of 

geochemical and geophysical anomalies. The USBM 

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, and mineralized areas. Identified resources are classified according to a system that is a 

modification of that described by McKelvey (1972). 

Acknowledgements 

R.B. Vaughn assisted with the reconnaissance geochemical survey. B.M. Adrian, T.A. Roemer, K.A. 

Romine, and P.L. Hageman conducted chemical analyses 

on all samples collected by the USGS. MJ. Grubensky 

compiled the geologic map. We also thank BLM personnel 

in Yuma, Ariz., for their helpful discussions and cooperation during this project. 

APPRAISAL OF IDENTIFIED RESOURCES AND 

KNOWN MINERALIZED AREAS 

By Robert H. Wood, II 

U.S. Bureau of Mines 

The USBM surveys and studies mines, prospects, and 

mineralized areas to appraise identified mineral resources. 

Identified resources, as defined by the U.S. Bureau of 

Mines and the U.S. Geological Survey (1980), are those 

whose location, grade, quality, and quantity are known or 

can be estimated from specific geologic evidence. They 

include economic, marginally economic, and subeconomic 

components (see .. Appendixes .. ). 

Personnel from USBM reviewed various sources of 

mineral information including published and unpublished 

literature. Mining claim and oil and gas lease information, 

current as of January 1987, was obtained from the BLM 

State Office in Phoenix, Ariz. Field study was concentrated on the examination of known mines, prospects, and 

mineralized areas inside and within 3 mi of the study area 

boundary; peripheral mineral occurrences were examined 

to determine whether they might extend into, or are similar 

to those within, the st~dy area. 

Thirty samples (5 rocks and 25 panned concentrates) 

were collected for analysis (Wood, 1988). Rock samples 

were collected at prospects. Panned-concentrate samples~ 

consisting of a concentration of heavy minerals from a 16-

in. gold pan heaped with minus-0.5-in. material, were collected from major drainages in and within 3 mi of the study 

area to obtain information regarding placer gold deposits. 

Analytical methods and results are discussed in Wood 

(1988). Complete analytical data are available for inspection at the U.S. Bureau of Mines, Intermountain Field 

Operations Center, Building 20, Denver Federal Center, 

Denver, CO 80225. 

Mining and Leasing Activity 

The study area is in the Muggins Mountains, which 

include the Muggins mining district. The total recorded 

district production of placer gold and silver, until the area 

was withdrawn for military purposes in 1942, was 2,748 

troy oz (ounce) of gold and about 500 troy oz of silver. 

Production data after 1981, when the study area was again 

opened to mining, are not available; however, there is 

evidence of recent placer mining in the study area. Gold 

placer deposits were mined in two areas: Vinegarroon 

Wash north of the study area and in washes draining southward from Muggins Peak, Klothos Temple, and Long 

Mountain inside the study area (fig. 2). Quartz veins in 

Proterozoic metamorphic and igneous rocks north of the 

study area were mined for gold, silver, and copper (Keith, 

1978). This type of lode deposit has not been reported in 

the study area. 

Uranium is the other element of economic interest in 

the Muggins mining district, although no uranium production has been reported. The nearest known uranium occurrence, the Red Knob prospect, is a stratabound occurrence 

about 0.5 mi east of the study area (Peirce and others, 

1970). 

According to BLM records as of October 1987, nearly 

half the study area was covered by unpatented mining 

claims (fig. 3); however, there are no patented mining 

claims in the study area. Over half the study area is covered by oil and gas leases (fig. 3) according to BLM records as of January 1987. 

Gold 

Placer gold was reported in washes and canyons draining southward from Muggins Peak, Klothos Temple, and 

Long Mountain. The gold occurs as partiCles as much as 

0.15 in. across and was probably derived from gold-bearing 

quartz veins in the Proterozoic gneiss, schist, and granite 

that crop out in the northern Muggins Mountains (Keith, 

1978; Wilson, 1933). Conglomerate and alluvium in the 

Muggins Mountains Wilderness Study Area, Yuma County, Arizona 03 
study area contain gneiss and granite clasts derived from 

the Proterozoic rocks. 

Gold was detected in panned-concentrate samples from 

four drainages in the study area and two drainages southeast of the study area (fig. 3). Of the samples containing 

gold, the concentrations range from a trace to 0.230 troy oz/ 

ton in the panned concentrate~ equivalent to about $0.75/ 

yd3 (cubic yard). Two of the samples, however, contain 

more gold; the values of samples 14 and 16 (fig. 3) were 

about $26.25/yd3 and $33.90/yd3, respectively (Wood, 

1988). Gold yield was calculated using a pan factor of 150, 

a gold price of $500/troy oz and was based on a screened 

(minus-0.5-in.) yd3 of gravel, estimated to represent between 25 percent and 50 percent of the gravel in place. 

The drainages containing gold· in the study area are 

small. Samples with the highest gold concentrations were 

from the shallow (about 1 ft deep), narrow (no more that 12 

ft wide) gravel deposits near the heads of the drainages 

(Wood, 1988). Low gold concentration~ detected in the 

generally wider and thicker gravels deposited downstream 

may represent either partial gold depletion by past placer 

operations or dilution by barren sediment. In some areas, 

a thick alluvial cover prevented sampling at bedrock, where 

placer gold is commonly concentrated. The higher gold 

concentrations in gravels near the heads of the drainages 

might be profitable for small, 2- to 3-person placer operations; however, these small quantities of gravel could not 

support a commercial mining operation. On the basis of 

samples taken at each of the two locations where high gold 

v(llues were indicated, we estimate that less than 20 troy oz 

of gold are contained in about 550 yd3 of gravel at sample 

site 14 (fig. 3) and less than 5 troy oz of gold are contained 

in about 50 yd3 of gravel at site 16 (fig. 3). 

Uranium 

There are no identified uranium resources in the study 

area. The Red Knob prospect, about 0.5 mi east of the study 

area, is the nearest known uranium occurrence (fig. 2). 

According to Smith and others (1984), this prospect occurs 

in the lower member of the Kinter Formation and is associated with a northwest-trending normal fault near an intrusive rhyolite dome. A 1.5-ft-thick silicified mudstone bed 

is exposed along a 15-ft-long trench at the portal of a 

collapsed and partly filled adit at least 35 ft long. 

Weeksite, a rare uranium silicate (Outerbridge and others, 

1960), calcite, chalcedony, mimetite, and vanadinite occur 

in the silicified mudstone bed. Wood (1988) reported that 

rock samples contain as much as 1,150 parts per million 

(ppm) lead, 295 ppm vanadium, 41 ppm uranium, 25 ppm 

molybdenum, and 1.8 ppm (0.05 troy oz/ton) silver. These 

subeconomic concentrations are contained in samples from 

the silicified mudstone bed at the Red Knob prospect. 

Only the upper member of the Kinter Formation is 

exposed in the study area. Geochemical studies by Smith 

and others (1984) indicate that a drainage basin inside the 

southeastern boundary of the study area may contain mineralized rock with a geochemical signature similar to that at 

the Red Knob prospect. Scintillometer readings taken 

along traverses in this drainage basin did not show values 

above background levels. 

Sand and Gravel 

The drainages and alluvial fans in the study area contain sand and gravel, which were being mined, possibly for 

use as local road surfacing material, near the southern tip of 

the study area during the USBM's field investigation (fig. 

3). Sand and gravel in the study area have no unique 

qualities to make them more valuable than the vast quantities available in nearby areas. 

Conclusions 

Placer gold was found in four drainages in the study 

area. High gold concentrations identified at the heads of 

two of the drainages might be profitable for small, 2- to 3-

person placer operations; however, the amount of gold in 

both drainages is probably less than 25 troy oz. This 

amount of gold would not support a commercial operation. 

Considerable additional work is needed to quantify the 

identified placer gold resource in the study area because the 

gold is irregularly distributed, partially buried by locally 

thick alluvium, and partly removed by past placer mining. 

A low-grade uranium occurrence, containing by-product subeconomic concentrations of lead and vanadium, is 

associated with faulting in the lower member of the Kinter 

Formation about 0.5 mi east of the study area. This 

member underlies the study area but is not exposed. There 

are no identified resources of uranium in the study area. 

The sand and gravel in drainages and alluvial fans in 

the study area have no unique qualities to make them more 

valuable than the vast quantities in nearby areas. 

ASSESSMENT OF MINERAL RESOURCE 

POTENTIAL 

By David B. Smith, Richard M. Tosdal, james A. Pitkin, and 

M. Dean Kleinkopf 

U.S. Geological Survey 

Geologic Setting 

The oldest rock in the Muggins Mountains is 

Proterozoic augen gneiss, which underlies the northwestern 

part of the range. Only a small part of this unit crops out 

in the study area (fig. 2). The augen gneiss in the northern 

part of the range is similar in age to other metaplutonic 

bodies in the region, which are of Proterozoic age, on the 

04 Mineral Resources of Wilderness Study Areas: Southwestern and South-Central Arizona 
basis of U-Pb (uranium-lead) ages on zircon (L.T. Silver in 

Olmstead and others, 1973, and in Dillon, 1976). In the 

Muggins Mountains, the augen gneiss is inferred to be part 

of the widespread anorogenic granite suite of Middle 

Proterozoic age found throughout the southwest (Anderson, 

1983; written commun., 1989). 

Paleozoic and lower Mesozoic metasedimentary rocks 

crop out in a narrow east-trending ductile sqear zone. 

There, chlorite phyllite and epidote quartzite are structurally overlain by chloritic calc-silicate rocks, white and blue 

marble, and orange dolomitic marble. These metasedimentary rocks are similar to other metamorphosed Paleozoic 

and lower Mesozoic sedimentary rocks in the lower Colorado River region (Hamilton, 1982; Leveille and Frost, 

1985), and their protoliths are probably correlative with the 

Supai, Kaibab, and Moenkopi Formations. However, in the 

Muggins Mountains their normal stratigraphic sequence is 

apparently inverted. 

Proterozoic through lower Mesozoic rocks are intruded 

by porphyritic monzogranite and less abundant diorite of 

Jurassic(?) age. These granitic rocks are the unmetamorphosed equivalents to the orthogneisses that host gold 

deposits at Picacho and Mesquite in southeastern California 

(Tosdal and others, 1985). In the Muggins Mo~ntains, the 

contacts of the Jurassic(?) monzogranite are mylonite and 

mylonitic schist that formed in ductile shear zones. The 

upper shear zone includes the inverted Paleozoic and lower 

Mesozoic section, which implies that the shear zones may 

be the remnant of a major structure. 

Sandstone, siltstone, conglomerate, and fanglomerate 

of the upper Oligocene(?) and lower Miocene Kinter Formation unconformably overlie the Jurassic(?) monzogranite 

unit. The Kinter Formation is divided into two informal 

members that are interbedded along their contact.. The 

lower member consists of fine-grained sandstone, siltstone, 

and white vitric tuff beds. Early Miocene camel fossils are 

reported from these rocks and 22.5±0.7 Ma (million years 

before present) and 24.2±1.2 Ma potassium-argon (K-Ar) 

ages on biotite were determined for two tuffs outside the 

study area (Lance and WOod, 1958; Shafiqullah and others, 

1980). The upper member of the Kinter Formation consists 

of conglomerate, fanglomerate, and minor sandstone that 

represent debris flows and alluvial fan deposits. 

Proterozoic augen gneiss is the dominant clast type, J urnssic(?) monzogranite is subordinate, and Tertiary volcanic 

clasts are minor. Silicic volcanic flows, domes, tuff, and 

tuffaceous sedimentary rocks are interbedded with the 

Kinter Formation. 

Field relations indicate that middle Tertiary volcanism, 

sedimentation, and extensional deformation were contemporaneous in the range. A tectonic breccia along the 

western part of the range lies between the basement rocks 

and the volcanic flows. The breccia grades upward into 

conglomerate and sandstone at. the base of the volcanic 

section. This type of breccia is common along detacqment 

faults that fringe the Gila River trough in the northern 

Mohawk Mountains (Mueller and others, 1982) and in the 

Baker Peaks (Pridmore and Craig, 1982) 30 mi and 20 mi 

southeast and east of the Muggins Mountains, respectively. 

Latiie dikes intrude the tectonic breccia, basement rocks, 

and overlying conglomerate and volcanic rocks. Evidence 

for a second episode of extensional tectonism in the range 

is provided by the rapid transition from the fine-grained 

lower member to the coarse-grained upper member of the 

Kinter Formation. The silicic volcanic rocks are interbedded with the upper member of the Kinter Formation. A 

final episode of extensional deformation broke the area into 

northwest-striking structural blocks that dip 10-30° SW. 

Quaternary gravel, sand, and silt unconformably overlie the older units. The youngest unit consists of unconsolidated silt and sand deposited on the Gila River floodplain. 

Geochemistry 

A reconnaissance geochemical survey was conducted 

in the Muggins Mountains Wilderness Study Area in 1983. 

The purpose of the survey was to evaluate the study area 

for evidence of mineralization; it was not designed to locate 

individual mineral deposits. The sample media and sample 

density were chosen to identify favorable geochemical 

provinces and mineralized districts; thus barren ground not 

favorable for mineral occurrences is eliminated and attention is drawn to the more promising areas (Levinson and 

others, 1987). 

Minus-80-mesh stream sediments and heavy-mineral 

concentrates derived from stream sediments were selected 

as the primary sample media because they represent a 

composite of rock and soil exposed in the drainage basin 

upstream from the sample site. Chemical analysis of sediments provides information that helps identify those basins 

that contain unusually high concentrations of elements 

which may be related to mineral occurrences. Jn addition, 

studies show that heavy-mineral concentrates deri~ed from 

stream sediments are a very useful sample medium in arid 

environments or in areas of rugged topography, where 

mechanical erosion is predominant relative to chemical 

erosion (Bugrov and Shalaby, 1975; Overstreet and Marsh, 

1981; Zeegers and others, 1985). In this study, the nonmagnetic fraction of the heavy-mineral concentrates was 

analyzed. In areas where mineralization occurred, this 

fraction represents a concentration of ore-forming and orerelated minerals such as pyrite, galena, cassiterite, sphalerite, chalcopyrite, stibnite, free gold, barite, and scheelite. 

This selective concentration of ore-related minerals permits 

determination of some elements that are not easily detected 

in bulk stream-sediment samples. 

Both stream sediments and heavy-mineral concentrates 

were collected at 48 sampling sites inside and within 3 mi 

of the study area boundary. Samples were collected. from 

active alluvium in first-order (unbranched) and secondMuggins. Mountains Wilderness Study Area,_ Yuma County, Arizona 05 
32"45' 

EXPLANATION 

Area having moderate mineral 

~ resource potential for uranium (M) 

D Area having low mineral 

resource potential (L) 

Levels of certainty of assessment 

B Data only suggest level of potential 

C Data give good indication of level of potential 

Commodities 

Au Gold 

U Uranium 

O,G Oil and gas 

Geo Geothermal 

X Prospect 

Figure 2. Mineral resource potential and generalized geology of Muggins Mountains Wilderness Study Area, Yuma County, Arizona. 

Polyconic projection. Geology by R.M. Tosdal, 1983 and 1987. Contour intervals 20 and 40 feet; intermediate intervals 5 and 10 

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

DESCRIPTION OF MAP UNITS 

Oal Alluvium (Quaternary)-Pale-brown, 

QTc 

11 

Trd 

Tc 

Tb 

Thu 

Thl 

Jm 

"40 

,628 

20 

unconsolidated silt and fine sand. Forms 

floodplain deposits of Gila River and floors of 

active washes 

Conglomerate and sandstone (Quaternary and 

Tertiary?)-Unconsolidated to poorly 

consolidated conglomerate, sandstone, and minor . 

amounts of siltstone 

Latite (Miocene)-Orange-weathered, banded gray 

biotite-latite dikes and plugs 

Rhyolite, latite, and dacite (Miocene)-Redbrown, brown, gray, and black rhyolite, 

rhyodacite, latite, and dacite flows, domes, and 

minor amounts of yellow and pink lithic-lapilli 

tuff, tuff breccia, and tuffaceous sandstone 

Conglomerate and sandstone (Miocene)-

Brown conglomerate, sandstone, minor breccia, 

and less-abundant orange tuff breccia, tuffaceous 

sandstone, and white tuff 

Breccia (Mlocene)-Angular fragments of 

monzogranite and diorite that grades from intact 

but completely shattered rocks to a crudely bedded 

sedimentary deposit with a sandy matrix 

Kinter Formation (Miocene and 

0 ligocene ?)-Conglomerate, sandstone, 

siltstone, and minor amounts of tuff; divided into: 

Upper member (lower Miocene and upper 

Ollgocene)-Poorly to moderately sorted and 

bedded conglomerate, fanglomerate, minor 

coarse-grained sandstone, and minor white tuff; 

grades into and interfmgers with sandstones of 

the lower member, locally includes white biotite 

tuff marker beds (t); maximum thickness is 3 m 

Lower member (lower Miocene and upper 

Oligocene?)-Well-bedded, well-sorted, tan, 

fine- to medium-grained sandstone, siltstone, 

and minor white tuff; locally includes white 

biotite vitric tuff marker beds (t); maximum 

thickness is 3 m 

Monzogranite (Jurassic?)-Gray, fine- to 

medium-grained biotite porphyritic monzogranite 

and minor amounts of diorite 

Marble and phyllite (Mesozoic and 

Paleozoic)-Chlorite phyllite and schist, 

epidote quartzite, quartzose marble, white, blue, 

gray marble, and orange dolomitic marble 

Augen gneiss (Proterozoic)-Coarsely 

porphyritic augen gneiss characterized by 

abundant pink potassium feldspar augen 

Contact-Dashed where approximately located 

Fault-Dashed where approximately located; dotted 

where concealed. Bar and ball on downthrown side 

Strike and dip of beds 

Strike and dip of foliation-Showing bearing 

and plunge of lineation 

Base from U.S. Geological Survey, 1 :24,000, Dome, 1955; ligurta, Wellton, 1965 (photorevised, 1982); 1 :62,500, Red Bluff Mtn., 1955. 

feet 

Muggins Mountains Wilderness Study . Area, Yuma County, Arizona 07 
order (below the junction of two first-order) streams. Eight 

rock samples were also collected for chemical analysis. 

Samples of unaltered rock were analyzed to provide information on geochemical background values. Samples at 

mines, prospects, and altered areas were taken to determine 

suites of elements associated with mineralization and alteration. Analytical data and a description of the sampling 

and analytical techniques are given in Smith and others 

(1984). Additional data were obtained by analyzing the 

minus-80-mesh stream sediments for gold by a graphitefurnace atomic-absorption method (detection limit, 0.002 

ppm). 

Results 

Only one anomalous area was delineated by the reconnaissance geochemical survey, and this area was delineated 

on the basis of only one sampling site. A small drainage 

basin along the southeast boundary of the study area contains anomalous amounts of lead (1,000 ppm) and molybdenum (300 ppm) in the nonmagnetic heavy-mineral concentrate and an anomalous amount of lead (100 ppm) in the 

minus-80-mesh stream sediment. This geochemical signature is similar to that of the drainage basin containing the 

Red Knob uranium prospect approximately 0.5 mi east of 

the study area (fig. 3). Nonmagnetic heavy-mineral concentrates collected from this drainage contain 1 ,500 ppm 

lead and 150 ppm molybdenum. 

Low-level anomalies of tin (20-200 ppm) and tungsten 

(less than 100 to 1,000 ppm) are contained in nonmagnetic 

heavy-mineral concentrates from scattered sampling sites in 

the northern two-thirds of the study area. The origin of 

these anomalies is uncertain, but we believe they are derived from silicic volcanic rocks rather than mineralized 

rocks. 

Geophysical Studies 

Reconnaissance gravity and aeromagnetic anomaly 

maps (U.S. Geological Survey gravity files; LKB Resources, Inc., 1980) provide some information on regional 

geology. The data lack sufficient" detail to delineate local 

structures and igneous intrUsions that might be associated 

with mineral deposits. 

The regional data on the Department of Energy's 

National Uranium Resource Evaluation (NURE). residual 

intensity magnetic anomaly map of the El Centro 1° by 2° 

sheet is based on 6-mi spaced traverseS flown at an average 

of 400 ft above the terrain (i.KB Resources, Inc., 1980). 

Only one east-west traverse cross.ed the study area. The 

magnetic intensity contours trend northeast to east across 

the study area with an average southeasterly gradient of 

about 10 gammas/mi. This gradient may be related to the 

Proterozoic augen gneiss mass northwest of the study area 

(fig. 2). The regional gravity contours trend northeast 

across the study area with a pronounced gradient to the 

southeast averaging about 4 milligals per mile (mGaVmi). 

This northeast-trending pattern coupled with the regional 

northeast- to east-trending magnetic anomaly patterns suggests that the central part of the study area may be underlain by northeast-trending lithologic boundaries or fracture 

zones, probably within the crystalline basement complex. 

An aerial gamma-ray survey conducted in the region as 

part of the NURE program (U.S. Department of Energy, 

1979) measured the near-surface distribution of the natural 

radioelements potassium, uranium, and thorium. The survey was flown on flightlines spaced 6 mi apart at 400 ft 

above ground level. An aerial gamma-ray system at this 

altitude effectively detects terrestrial gamma radiation from 

a swath 800 ft wide along the flightline. Results indicate 

that the Muggins Mountains Wilderness Study Area is 

characterized by radioelement concentrations of 2.5 to 3.5 

percent potassium, 4 to 6 ppm equivalent uranium, and 12 

to 14 ppm equivalent thorium. (The term "equivalent" 

denotes the assumption that uranium and thorium are in 

equilibrium with their daughter products.) These concentrations are controlled by the location of NURE flightlines 

relative to the study area; in this instance, one east-west 

NURE flightline crossed the study area. Despite the sparse 

control, the concentrations detected are reasonable background levels for the Proterozoic crystalline rocks, Tertiary 

volcanic rocks, and Tertiary(?) and Quaternary alluvium 

and colluvium of the study area. 

Mineral Resource Potential of the Muggins 

Mountains Wilderness Study Area 

This assessment of the mineral resource potential of 

the Muggins Mountains Wilderness Study Area draws upon 

different and diverse sets of geologic data. These include 

regional geology, geochemistry, geophysics, mineral occurrence maps, mining claim records, and the application of 

ore-deposit models to geologic terranes. These data were 

used to delineate favorable tracts within the study area and 

an estimate was then made of the level of resource potential 

and degree of certainty for each tract (fig. 2). Mineral 

resource potential refers to undiscovered mineral resources; 

the true test of an estimate of mineral resource potential is 

through active exploration. 

Gold 

Gold and minor amounts of silver have been produced 

from placer deposits in the Muggins Mountains Wilderness 

Study Area. Gold was detected in five panned-concentrate 

samples collected by the USBM in the south-central part of 

the study area south of the Muggins Peak and Long Moun-

. tain area and in. two concentrate samples collected southeast of the study area ·(fig. 3). Using graphite-furnace 

· 08 Mineral Resources of Wilderness Study Areas: Southwestern and South-Central Arizona 
atomic-absorption analysis of minus-80-mesh stream sediments, the USGS detected gold (0.006 and 0.004 ppm) in 

two samples southeast of the study area (fig. 3). No gold 

was detected by this method in samples collected within the 

study area. 

Wilson (1933) and Keith (1978) reported placer gold 

production near Klothos Temple in the northwestern part of 

the study area and in the headwaters of Vinegarroon Wash, 

32° 

42' 

30" 

EXPLANATION 

~ : : : : : :j Oil and gas leases 

• 0. 0 ••••• 

rzl] Unpatented mining claimshown only in study area 

:: ~ 4:::: 

• 

6

'

7 

Locality of gold-bearing pannedconcentrate sample 

40 * Locality of gold-bearing minus-80-

mesh stream-sediment sample 

X Prospect pit 

y Caved pit 

approximately 0.5 mi north of the study area, in addition to 

the area south of Muggins Peak and Long Mountain. This 

gold is deposited in an.cient bars on terraces above and in 

stream channels where the bedrock consists of conglomerate intercalated with lavas (Keith, 1978). The source of the 

gold in the placer deposits is reported to be gold-bearing 

quartz veins in Proterozoic gneiss, schist, and granite exposed north of the study area (Wilson, 1933; Keith, 1978). 

APPROXIMATE BOUNDARY 

OF 

MUGGINS MOUNTAINS 

WILDERNESS STUDY AREA 

(AZ-050-053A) 

Red Knob : : : : : 

prospect : : : : : : 

, __ xm ~X 

X Gravel pit 

~ Abandoned gravel pit 

X Placer mine 8 *40 

•• 26 

27 

AREA OF MAP 

X Abandoned placer mine 

0 1 MILE 

Figure 3. Mines, prospects, oil and gas leases, and anomalous geochemical sample localities in Muggins Mountains Wilderness 

Study Area, Yuma County, Arizona. 

Muggins Mountains Wilderness Study Area, Yuma County, Arizona 09 
The entire study area has moderate potential with certainty 

level C for gold in placer deposits (see "Appendixes" for 

levels of mineral resource potential and certainty of assessment). This rating is based on the distribution of past 

placer mining activity and the distribution of gold in 

panned-concentrate samples over a large part of the study 

area. Geologic -mapping and geochemical sampling for this 

report were not sufficiently detailed to delineate all alluvium that might contain placer gold. 

Uranium 

Exploration for uranium in the Muggins Mountains has 

been intermittent since the early 1950's. Uranium occurs in 

the Muggins Mountains as pods and disseminations in silicified mudstones adjacent to northwest-trending faults, in 

interlacing quartz stringers within dikes or sills, as disseminations in volcanic rocks and mudstone and sandstone 

beds, in association with copper carbonates and silicified 

wood fragments in mudstone beds, and in loosely consolidated conglomerates or talus deposits (Reyner and Ashwill, 

1955). Many of these relations suggest that the source of 

the uranium is tuffaceous lake sediments from which connate water and dissolved uranium were squeezed out during 

compaction. The uranium precipitated in a reducing environment created by carbonaceous lacustrine sediments 

(Keith, 1978). 

All the known uranium prospects in the Muggins 

Mountains are east of the study area. One such prospect, 

called the Red Knob claims by Reyner and Ashwill (1955), 

is about 0.5 mi east of the study area boundary in the lower 

member of the Kinter Foimation near an intrusive rhyolite 

dome. Weeksite, mimetite, calcite, vanadinite, and chalcedony occur within a highly silicified mudstone bed, 1 to 

3 ft thick, along the north side of a normal fault that trends 

northwest. Chemical analyses of rocks from this prospect 

show elevated concentrations of uranium (as much as 257 

ppm), lead (as much as 2,000 ppm), molybdenum (as much 

as 500 ppm), vanadium (as much as 300 ppm), and zinc (as 

much as 700 ppm) (Smith and others, 1984; Wood, 1988). 

Nonmagnetic heavy-mineral concentrates derived from 

stream sediments collected downstream from the Red Knob 

prospect contain anomalous amounts of lead (1 ,500 ppm) 

and molybdenum (150 ppm). One small drainage basin 

along the southeastern boundary of the study area contains 

similar anomalies of lead (1,000 ppm) and molybdenum 

(300 ppm) in heavy-mineral concentrates and a small lead 

anomaly (100 ppm) in minus-80-mesh stream sediments. 

A normal fault strikes northwest along the center of the 

stream channel (fig. 2). On the basis of the lead and 

molybdenum anomalies and the presence of the fault, this 

drainage basin has moderate potential, certainty level B, for 

uranium resources (fig. 2). However, a scintillometer survey taken along traverses in this drainage basin by USBM 

personnel in 1987 did not detect readings above background levels. 

Geothermal Energy 

Wilson (1933) reported a group of thermal springs on 

the northern bank of the Gila River near the southeastern 

margin of the Muggins Mountains approximately 9 mi east 

of the study area. The temperature of the water was reportedly 140 °F. However, no hot springs or other indications 

of recent geothermal activity are known within the study 

area. The geothermal energy resource potential of the 

Muggins Mountains Wilderness Study Area is low, certainty level B (fig. 2). 

Oil and Gas 

The study area is located within the structural depression known as the Gila trough, which contains as much as 

6,000 ft of lower to middle Tertiary sedimentary rocks. 

Ryder (1983) states that minor oil shows were reported 

from holes drilled in the Gila trough. He ranks the hydrocarbon potential of the trough as low, however, because the 

organic richness, reservoir quality, and thermal history of 

the sedimentary rocks are unfavorable for the generation 

and entrapment of significant volumes of hydrocarbons. 

Therefore, the Muggins Mountains Wilderness Study Area 

has low potential, certainty level B, for oil and· gas resources. 

REFERENCES CITED 

Anderson, J.L., 1983, Proterozoic anorogenic granite plutonism of 

North America: Geological Society of America Memoir 191, 

p. 133-154. 

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. 

Dillon, J.T., 1976, Geology of the Chocolate and Cargo 

Muchacho Mountains, southeasterrunost California: Santa 

Barbara, University of California, Ph.D. dissertation, 575 p. 

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

survey reports on public lands: U.S. Geological Survey OpenFile Report 84-787, 42 p. 

Hamilton, Warren, 1982, Structural evolution of the Big Maria 

Mountains, northeastern Riverside County, southeastern 

California, in Frost, E.G., and Martin, D.L., eds., MesozoicCenozoic tectonic evolution of the Colorado River region, 

California, Arizona, and Nevada: San Diego, Cordilleran 

Publishers, p. 1-28. 

Hely, A.G., and Peck, E.L., 1964, Precipitation, runoff, and water 

loss in the lower Colorado River-Salton Sea area: U.S. Geological Survey Professional Paper 486-B, 16 p. 

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

Arizona: Arizona Bureau of Geology and Mineral Technology 

010 · Mineral Resources of Wilderness Study Areas: Southwestern and South-Central Arizona 
Bulletin 192, 185 p. 

Lance, J.F., and Wood, P.A., 1958, New Miocene fossil locality 

fTom southwestern Arizona: Geological Society of America 

Bulletin, v. 69, p. 1694. 

Leveille, Gregory, and Frost, E.G., 1985, Deformed upper Paleozoic-lower Mesozoic cratonic strata, El Capitan, Sonora, 

Mexico [abs.]: Geological Society of America Abstracts with 

Programs, v. 16, p. 575. 

Levinson, A.A., Bradshaw, P.M.D., and Thomson, 1., 1987, Practical problems in exploration geochemistry: Applied Publishing Ltd., Wilmette, lllinois, 269 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, Report GJBX-12(80), v. 2, scale 1:500,000. 

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

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

Mueller, K.J., Frost, E.G., and Haxel, Gordon, 1982, Mid-Tertiary 

detachment faulting in the Mohawk Mountains of southwestem Arizona, in Frost, E.G., and Martin, D.L., eds., MesozoicCenozoic tectonic evolution of the Colorado River region, 

California, Arizona, and Nevada: San Diego, Cordilleran 

Publishers, p. 357-375. 

Olmstead, F.H., Loelitz, O.J., Irelan, Burdge, 1973, Geohydrology 

of the Yuma area, Arizona and California: U.S. Geological 

Survey Professional Paper 486-H, p. H1-H227. 

Outerbridge, W.F., Staaz, M.H., Meyrowitz, R., and Pommer, 

A.M., 1960, Weeksite, a new uranium silicate from the Thomas Range, Juab County, Utah: American Mineralogist, v. 45, 

p. 39-52. 

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

techniques in geochemical exploration: Economic Geology 

75th Anniversary Volume, p. 775-805. 

Peirce, H.W., Keith, S.B., and Wilt, J.C., 1970, Coal, oil, natural 

gas. helium, and uranium in Arizona: Arizona Bureau of 

Mines Bulletin 182, 289 p. 

Pridmore, C.L .• and Craig. Christy, 1982, Upper-plate structure 

and sedimentation of the Baker Peaks area, Yuma County, 

Arizona, in Frost, E.G., and Martin, D.L., eds .• MesozoicCenozoic tectonic evolution of the . Colorado River region, 

California, Arizona, and Nevada: San Diego, Cordilleran 

Publishers, p. 357-375. 

Reyner, M.L., and Ashwill, W.R., 1955, Preliminary report on 

uranium occurrences on the Yuma Test Station, Yuma 

County, Arizona: U.S. Atomic Energy Commission Administrative Report, 12 p. 

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-C, 22 p. 

Shafiqullah, Muhammad, 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. 

201-242. 

Smith, D.B., Tosdal., R.M., Adrian, B.M., and Vaughn. R.B., 

1984, Assessment of mineral resources in the Muggins 

Mountains Bureau of Land Management Wilderness Study 

Area (AZ-050-53A), Yuma County, Arizona: U.S. Geological Survey Open-File Report 84-662, 31 p. 

Tosdal, R.M., Haxel, G.B., and Dillon, J.T., 1985, Lithologic 

associations of gold deposits, southeastern California and 

southwestern Arizona [abs.]: Geological Society of America 

Abstracts with Programs, v. 17, no. 6, p. 414. 

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, NURE aerial gamma-ray and 

magnetic reconnaissance survey of portions of Colorado-Arizona area, Salton Sea, Phoenix, El Centro; Ajo, Lukeville 

quadrangles: U.S. Department of Energy, Report 

GJBX-12(80), v. 2. 

Wilson, E.D., 1933, Geology and mineral deposits of Yuma 

County, Arizona: Arizona Bureau of Mines Bulletin 134, 234 

p. 

Wood, R.H. ll, 1988, Mineral resources of a part of the Muggins 

Mountains Wilderness Study Area, (AZ-050-053A), Yuma 

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

MLA 11-88, 17 p. 

Zeegers, H., AI Shanfari, S.M .• AI Muflehi, Y.A., and Latalenet, 

I .• 1985, Aspects of regional geochemical .prospecting in 

desert conditions, in Prospecting in areas of desert terrain: The 

Institution of Mining and Metallurgy, London, p. 131-140. 

Muggins Mountains Wilderness Study Area, Yuma County, Arizona 011 
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. 

8 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. 

r 

..J 

< 

i= 

z 

LU 

1-

0 

Cl.. 

LU 

u 

~ 

:::J 

0 

V') 

LU 

~ 

u.. 

0 

..J 

LU 

> LU 

..J 

A 

U/A 

UN KNOWN POTENTIAL 

Abstracted with minor modifications from: 

B c 

H/B H/C 

HIGH POTENTIAL HIGH POTENTIAL 

M/B M/C 

MODERATE POTENTIAL MODERATE POTENTIAL 

UB uc 

LOW POTENTIAL LOW POTENTIAL 

LEVEL OF CERTAINTY ... 

D 

H/D 

HIGH POTENTIAL 

M/D 

MODERATE POTENTIAL 

UD 

LOW POTENTIAL 

N/D 

NO POTENTIAL 

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. 

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

IDENTIFIED RESOURCES UNDISCOVERED RESOURCES 

Demonstrated Probabi I ity Range 

Inferred 

Measured Indicated Hypothetical Speculative 

I Inferred I 

ECONOMIC Reserves Reserves 

I - I ----~---- r--------- -~-

MARGINALLY Marginal Inferred 

Marginal ECONOMIC Reserves Reserves ____ l_ ____ - I I r--------- -~-

SUB- Demonstrated Inferred 

Subeconomic Subeconomic 

ECONOMIC Resources Resources I I I 

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. 

Muggins Mountains Wilderness Study Area, Yuba County, Arizona 015 
GEOLOGIC TIME CHART 

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

EON ERA PERIOD EPOCH 

Quaternary 

Holocene 

Pleistocene 

Neogene Pliocene 

Cenozoic Subperiod Miocene 

Tertiary Paleogene Oligocene 

Subperiod Eocene 

Paleocene 

Cretaceous Late 

Early 

Late 

Mesozoic jurassic Middle 

Early 

Late 

Triassic Middle 

Early 

Permian Late 

Phanerozoic Early 

Late 

Pennsylvanian Middle 

Carboniferous Early Periods 

Mississippian Late 

Early 

Late 

Devonian Middle 

Paleozoic Early 

Late 

Silurian Middle 

Early 

Late 

Ordovician Middle 

Early 

Late 

Cambrian Middle 

Early 

Late Proterozoic 

Proterozoic Middle Proterozoic 

Early Proterozoic 

Late Archean 

Archean Middle Archean 

Early Archean 

--------------- - - - - - - - - - - - - - - - - - - - - - - - - - - (3800?)- - - - - - - - - - - - - - - - - -

pre-Archean2 

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

21nformal time term without specific rank. 

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

AGE ESTIMATES OF 

BOUNDARIES IN 

Ml LUON YEARS (Ma) 

0.010 

1.7 

5 

24 

38 

55 

66 

r--- 96 

138 

205 

-240 

290 

-330 

360 

410 

435 

500 

'-570 

900 

1600 

2500 

3000 

3400 

4550 
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 incl~de 

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 7 1/2- 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 7 1/2-minute quadrangle photo geologic 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 planimetri~ 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.) 

"Publications of 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 (State)," may be purchased by mail 

and over the counter in paperback booklet form only. 

"Price and A vallablllty 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. 
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