ner sou 

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Chapter C 

Mineral Resources of the 

Swansea Wilderness Study Area, 

La Paz and Mohave Counties, Arizona 

By RICHARD M. TOSDAL, ROBERT G. EPPINGER, 

H. RICHARD BLANK, JR., DANIEL H. KNEPPER, JR., 

ANDREA J. GALLAGHER, JAMES A. PITKIN, and 

STEPHANIE L. JONES 

U.S. Geological Survey 

GEORGE S. RYAN 

U.S. Bureau of Mines 

U.S. GEOLOGICAL SURVEY BULLETIN 1704 

MINERAL RESOURCES OF WILDERNESS STUDY AREAS: 

HAVASU REGION, ARIZONA 
U.S. DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, jR., Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

Any use of trade, product, or firm names 

·in this publication is for descriptive purposes only 

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

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1990 

For sale by the 

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 Swansea Wilderness Study Area, La Paz and 

Mohave counties, Arizona I by Richard Tosdal...[et al.]. 

p. cm.-(U.S. Geological Survey bulletin ; 1704--C) 

Includes bibliographical references (p. ). 

Supt. of Docs. no.: I 19.3:1704--C 

1. Mines and mineral resources-Arizona-Swansea Wilderness. 

2. Swansea Wilderness (Ariz.) I. Tosdal, Richard M. II. Series. 

QW75.B9 no. 1704--C 557.3 s--dc20 90--13858 

[TN24.A6] [553 '.09791 72] 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 the Swan sea Wilderness 

Study Area (AZ--050--015A), La Paz and Mohave Counties, Arizona 
CONTENTS 

Summary C1 

Abstract C1 

Character and setting C1 

Identified resources C2 

Mineral resource potential C3 

Introduction C3 

Location and physiography C3 

Previous work C3 

Methods of study C4 

Acknowledgments C4 

Appraisal of identified resources and known mineralized areas C4 

Methods of investigations C4 

Mining history C4 

Oil and gas CS 

Appraisal of sites examined CS 

Conclusions C6 

Assessment of mineral resource potential C6 

Geology C6 

Geochemistry C7 

Introduction C7 

Methods C7 

Results C7 

Interpretation C8 

Geophysical studies C9 

Aeromagnetics and gravity C9 

Remote sensing C14 

Radioelement distribution C1S 

Mineral resource assessment C16 

Base and precious metals C16 

Manganese C16 

Uranium and vanadium C16 

Oil and gas C17 

Sand and gravel C 17 

References cited C 17 

Appendixes C21 

Definition of levels of mineral resource potential and certainty of 

assessment C22 . 

Resource/reserve classification C23 

Geologic time chart C24 

FIGURES 

I. Index map showing location of the Swansea Wilderness Study Area, La Paz and 

Mohave Counties Arizona C2 

2. Map showing mineral resource potential and generalized geology of the Swansea 

Wilderness Study Area, La Paz and Mohave Counties, Arizona C10 

3. Geochemical anomalies from stream-sediment, heavy-mineral concentrate, and rock 

samples from the Swansea Wilderness Study Area, La Paz and Mohave Counties, 

Arizona C12 

4. Aeromagnetic anomaly map of the Swansea Wilderness.Study Area, La Paz and 

Mohave Counties, Arizona C14 

5. Bouguer gravity anomaly map of the Swansea Wilderness Study Area, La Paz and 

Mohave Counties, Arizona C1S 

Contents V 
VI Contents 

TABLE 

1. Summary statistics for elements found in anomalous concentrations in streamsediment and heavy-mineral concentrate samples in the Swansea Wilderness Study 

Area, Arizona C13 
Mineral Resources of the 

Swansea Wilderness Study Area, 

La Paz and Mohave Counties, Arizona 

By Richard M. Tosdal, Robert G. Eppinger, H. Richard Blank, Jr., Daniel H. Knepper, Jr., 

Andrea j. Gallagher, james A. Pitkin, and Stephanie L. Jones 

U.S. Geological Survey 

George S. Ryan 

U.S. Bureau of Mines 

SUMMARY 

Abstract 

The Swansea Wilderness Study area (AZ-05~01 SA) lies 

in the Rawhide and Buckskin Mountains, west-central Arizona, about 20 mi east of Parker, Ariz. At the request of the 

U.S. Bureau of land Management, mineral surveys of approximately 15,755 acres were done by the U.S. Geological 

Survey and U.S. Bureau of Mines to assess its mineral resources (known) and mineral resource potential (undiscovered). In this report, the study area refers to only that part of 

the wilderness study area for which a mineral survey was 

requested by the U.S. Bureau of land Management. 

Mining and prospecting activity has o·ccurred in or adjacent to the Swansea Wilderness Study Area in the Swansea, 

Mesa, and Owens mineral districts. Copper, silver, and lesser 

quantities of gold, lead, zinc, and manganese have been produced from mines in these districts. Metals have been recovered from deposits along the Buckskin-Rawhide detachment 

fault and subsidiary high- and low-angle normal faults (Swansea 

and Mesa mineral districts) and along northwest-striking highangle faults that cut mylonitic gneiss and schist (Owens mineral district). There are no identified resources in the 

study area. 

Moderate and high potential for base and precious metals (copper, lead, zinc, gold, silver) in the study area exists in 

areas along northwest-striking high-angle faults in the northern part of the study area, along high- and low-angle faults in 

the lower-plate terrane south of the Bill Williams River, and 

along the Buckskin-Rawhide detachment fault and its upperplate faults on the south, northeast, and northwest margins of 

the area; low potential exists in the south-central area. Part of 

Black Mesa in the northern part of the study area has high 

potential for manganese, whereas an area in the southeast 

Manuscript approved for publication, August 20, 1990. 

corner of the study area has low potential for manganese. 

Areas of low potential for uranium and vanadium are found 

in the Tertiary sedimentary and volcanic rocks in the northern 

and southeastern parts of the study area. The entire Swansea 

Wilderness Study Area has no resource potentia I for oil and gas 

and sand and gravel. 

Character and Setting 

The Swansea Wilderness Study area (AZ--Q50--015A) 

covers approximately 15,755 acres in La Paz1 and Mohave 

Counties, west-central Arizona~ about 20 mi east of Parker, 

Ariz. (fig. 1). The study area straddles the Bill Williams 

River, which divides the Rawhide Mountains on the north 

from the Buckskin Mountains on the south. Elevations in 

the study area range from about 600ft along the Bill Williams River to 1,600 to 1,700 ft at the highest point on 

Black Mesa, north of the river, and at the crest of the Buckskin Mountains south of the river. 

The study area lies in the northwest-trending belt of 

metamorphic core complexes in west-central Arizona (Rehrig 

and Reynolds, 1980). In these complexes, mid-crustal and 

deeper rocks were tectonically transported to the surface 

along shallow-dipping nonnal faults or detachment faults 

during a period of extensional tectonism in the late Oligocene and Miocene (Davis and others, 1980; Spencer and 

Reynolds, 1986; Davis, 1988) (see appendixes for geologic 

time chart). The detachment fault in the study area is the 

Buckskin-Rawhide detachment of Spencer and Reynolds 

(1986, 1989), which crosses the northern part of the study 

area and crops out discontinuously along the south border 

of the study area (fig. 2). The detachment fault divides the 

1 La Paz County was created by the Arizona Legislature effective 

January 1, 1983, from what was the northern half of Yuma County. 

Mineral Resources of the Swansea Wilderness Study Area, La Paz and Mohave Counties, Arizona C1 
bedrock geology of the area into two parts, an extended and 

highly faulted upper plate of Proterozoic, Paleozoic, Mesozoic, and Tertiary metamorphic, igneous, and sedimentary 

rocks, and a lower plate of Tertiary mylonite and mylonitic 

gneiss that was derived from Proterozoic, Paleozoic, Mesozoic, and Tertiary metamorphic, igneous, and sedimentary 

protoliths. Mylonitic deformation in the lower plate is considered to be a deeper level expression of, and slightly older 

than, brittle extensional faulting along the detachment fault 

and its upper plate (Davis, 1983; Spencer and Reynolds, 

1986; Howard and John, 1987; Davis and Lister, 1988). 

Sedimentary and volcanic rock deposition accompanied extension, and these rocks now crop out in the highly faulted 

upper plate terrane (Davis and others, 1980; Spencer and 

Reynolds, 1989). During the last stages of, or after the end 

of, the extensional deformation, high-angle faults cut the 

detachment terrane. Extensional deformation was followed 

by basaltic and locally silicic volcanism in the middle and 

late Miocene (Suneson and Lucchitta, 1983). These volcanic rocks are interbedded with locally derived sedimentary 

rocks that filled depressions within the extended terrane. 

The extensional fault system, associated syntectonic 

114•oo· 

Casteneda Hills 

I 

\ 

'% " \ 

\ 

basins, and younger high-angle faults are important controls on the distribution of mineral resources in the study 

area (Spencer and Welty, 1985, 1989). Mineral exploration 

in western Arizona and southeastern California has focused 

on these geologic terranes, and some deposits and prospects 

are known (Sherborne and others, 1979; Wilkins and 

Heidrick, 1982; Wilkinson and others, 1988; Spencer and 

others, 1988; Lehman and Spencer, 1989). 

Identified Resources 

Mining and prospecting activity has taken place in 

the Owens and Mesa mineral districts of Spencer and Welty 

(1989) located in the northeastern and northern parts of the 

Swansea Wilderness Study Area (fig. 2). Minor production 

of silver, gold, copper, lead, zinc, and manganese is recorded from these districts. The Swansea mineral district is 

immediately south and southwest of the study area and the 

Planet mineral district is west of the study area. Significant 

amounts of copper, silver, and minor gold have been produced from these districts (Spencer and Welty, 1989, p. 

\ 

\ 

\'0. 

~Co' / 

,..--'\."' 

\)\<'-/ / / 

£1 

~:;t 

/ / 

113°45' 

/ 

/ 

/ 

/ 

/ 

/ / 

APPROXIMATE BOUNDARY 

OF 

SWANSEA ,.."""" \ 

8 

AREA OF MAP 

To Parker To AZ 95 

// \ •WILDERNESS STUDY AREA / \ / \ 

' R-'lJ.v. 

I 'lftD/2 '- Mesa ~mineral district 

.......---~ \ A1QJ, .,/ \ .----·-. v'fVI'J ....,... / ......... :.<lJ\rs -· \ / Cleopatra "-. 

i mineral district \ 

\ ) ........ ___________ ,.. (.-., 

0 

~ ·...._X Black Burro 

<., ~ mineral district 

Alamo Dam ...0 ~ 

~0~ 0 /·---........ 

\ \ \ '-.J Alamo ·, __ ./ mineral 

/-......__ 

/ 

', ~ii~~~~ ~~~Ytt district 

.................... ('\-·-.'\. 

', '-................. / u~" f',~s BUCKSKIN '-~~0 

' \ 

SMILES ' \ 

\ 

\ 

\ 

Figure 1. Index map showing location of the Swansea Wilderness Study Area, La Paz and Mohave Counties, Arizona. Dashdot lines, approximate boundaries of mineral districts near the study area from Keith and others (1983a, b) and Spencer and 

Welty (1985, 1989). 

C2 Mineral Resources of Wilderness Study Areas: Havasu Region, Arizona 
224-225) (figs. 1 and 2). No identified resources are present 

in the study area. 

• 

Mineral Resource Potential 

Moderate, high, and low potential for base and precious metals (copper, lead, zinc, gold, and silver) exists in 

the Swansea Wilderness Study Area (fig. 2). These areas 

are located along high-angle faults in the northeastern part 

of the study area and along the Buckskin-Rawhide detachment fault and related upper plate faults in the northern and 

southern parts of the study area. Areas of high potential for 

these elements are defmed by favorable geologic and geochemical data in the study area and by past production from 

mines. Areas of high potential for manganese and low 

potential for uranium and vanadium are found in the Tertiary 

sedimentary and volcanic rocks in the northern parts of the 

study area. Low resource potential for manganese, uranium, 

and vanadium exists in the southeastern part of the study 

area. No resource potential for oil and gas resources exists 

in the study area. 

INTRODUCTION 

This mineral survey was requested by the U.S. Bureau of Land Management and is the result of a cooperative 

effort by the U.S. Geological Survey and the U.S. Bureau 

of Mines. An introduction to the wilderness review process, 

mineral survey methods, and agency responsibilities was 

provided by Beikman and others (1983). Goudarzi (1984) 

discussed mineral assessment methodology and terminology as they apply to these surveys. The U.S. Bureau of 

Mines evaluates identified resources at individual mines and 

known mineralized areas by collecting data on current and 

past mining activities and through field examination of 

mines, prospects, claims, and mineralized areas. Identified 

resources are classified according to a system modified from 

that described by McKelvey (1972) and U.S. Bureau of 

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

Survey studies are designed to provide a scientific basis for 

assessing the potential for undiscovered mineral resources 

by determining geologic units and structures, possible environmentS of mineral deposition, presence of geochemical 

and geophysical anomalies, and applicable ore-deposit 

models. See appendixes for the definition of levels of mineral resource potential and certainty of assessment and for 

the resource/reserve classification. 

Location and Physiography 

The Swansea Wilderness Study area (AZ-050--015A) 

covers approximately 15,755 acres in west-central Arizona, 

about 20 mi east of Parker, Arizona (fig. 1). The study area 

straddles the Bill Williams River, which separates the Rawhide Mountains on the north from the Buckskin Mountains 

on the south. Alamo Dam, 13 mi east of the study area, 

controls the flow of the Bill Williams River, and the water 

level is normally kept low, providing numerous fording 

points. The part of the study area north of the river is in 

Mohave County, and that part south of the river is in La 

Paz County. 

The main access to the study area is by Swansea 

Road east from Arizona Highway 95 south of Parker to the 

ghost town of Swansea, which is 1 mi south of the study 

area. Another access road extends east from Arizona Highway 95 along the south side of the Bill Williams River as 

far as Planet Ranch, where a branch road turns south to 

'intersect the Swansea Road. An unimproved pipeline road 

continues northeast from Swansea, skirting the southeast 

boundary of the study area to a ford across the Bill Williams River and then continues north near the eastern side 

of the study area. The study area also can be accessed by 

unimproved roads from the north, northeast, and southeast. 

A private inholding, a Railroad Grant issued in 1922, consists of sec. 7, T. 10 N., R. 15 W. and has no access. 

The vegetation of the study area is classified as 

Sonoran Desert scrub, and the main subdivision found in 

the study areas is the Arizona Upland subdivision (Brown, 

1982). The Arizona Upland subdivision is a shrubland or 

low woodland of legwninous trees with open areas of shrubs 

and cacti. Cacti are important in this subdivision, and 20 

species of cacti are largely confined to or best represented 

in the Arizona Upland subdivision. Major areas of the Lower 

Colorado River subdivision of the Sonoran Desert also are 

found in the study area, especially in the Buckskin Mountains. Locally common riparian areas and wetland meadows 

are found around seeps, streams and washes. The dominant 

shrubs and cacti include cholla (Opuntia spp.), saguaro 

(Carnegiea gigantea), creosote bush (Larrea tridentata), and 

littleleaf paloverde (Cercidium microphylum). 

Previous Work 

Early descriptions of the rock types and various mineral deposits in the Rawhide and Buckskin Mountains are 

found in Lee (1908), Bancroft (1911), and Jones and 

Ransome (1920). That part of the Rawhide Mountains east 

of the study area was mapped by Shackelford (1976, 1989). 

The region north of the Bill Williams River, including the 

northern part of the study area, was mapped by Suneson 

and Lucchitta (1979, 1983) and Suneson (1980). Osborne 

(1981), Woodward (1981), Wilkins and Heidrick (1982), 

and Spencer and Reynolds (1987) mapped the Tertiary rocks 

and structures in the area of Swansea mine and Copper 

Penny prospect Geologists from the Arizona Bureau of 

Geology and Mineral Technology have studied the geologic 

Mineral Resources of the Swansea Wilderness Study Area, La Paz.and Mohave Counties, Arizona C3 
setting of the mineral occurrences within the region (Keith, 

1978; Keith and others, 1983a, b; Welty and others, 1985; 

Spencer and Reynolds, 1986; Spencer and Welty, 1986, 

1989; Reynolds and Spencer, 1989; Spencer and others, 

1988, 1989) and their work has been invaluable during the 

course of this mineral resource investigation. Spencer and 

Welty (1989) defined mineral districts throughout the region, 

including the study area, and their district names are used 

in this report. 

Studies in the Planet and Swansea mineral districts 

by Wilkins and Heidrick (1982), Lehman and others (1987), 

and Lehman and Spencer (1989) demonstrated the ties between the varied structures in the extensional terrane and 

the base- and precious-metal deposits in the region. Based 

on this work, other areas outside the study area have been 

actively explored for precious- and base-metal deposits 

(Wilkins and others, 1986; Spencer and others, 1988; 

Wilkinson and others, 1988). A similar link between manganese deposits in the Artillery Mountains and uraniumvanadium deposits in the Date Creek Basin, some 30 mi 

east of the Swansea Wilderness Study Area, has also been 

proposed (Lasky and Webber, 1949; Sherborne and others, 

1979; Otton, 1981; Spencer and Welty, 1989; Spencer and 

others, 1989). Results of this work are applicable to the 

mineral resource potential of the Swansea Wilderness Study 

Area. 

Methods of Study 

The U.S. Geological Survey conducted detailed field 

investigation of the Swansea Wilderness Study Area in the 

winter of 1987 and 1988. This work included geologic 

mapping at a scale of 1:62,500, geochemical sampling, and 

the examination of outcrops for evidence of mineralization. 

Rocks and stream sediments were collected and analyzed 

for 35 to 37 elements by semiquantitative emission spectrography and for arsenic, antimony, bismuth, cadmium, 

gold, and zinc by atomic absorption methods. Regional 

gravity and aeromagnetic surveys were used in the assessment Landsat thematic mapper images were interpreted 

for evidence of hydrothennal alteration in the study area. 

Further details on each analytical procedure used for this 

resource assessment are given later. 

Acknowledgments 

This study was supported by the National Mineral 

Resources Assessment Program of the U.S. Geological Survey. Discussions with J.E. Spencer and SJ. Reynolds of the 

Arizona Geological Survey and Bruce Bryant of the U.S. 

Geological Survey improved our understanding of the geology of the area. A special thanks is extended to Diana 

Mangan for preparation of the figures and to Carol Ostergren 

and Nobie Amamoto for patiently overseeing the fmal publication of the bulletin. 

• 

APPRAISAL OF IDENTIFIED RESOURCES AND 

KNOWN MINERALIZED AREAS 

By George S. Ryan 

U.S. Bureau of Mines 

Methods of Investigation 

I 

A review of literature, maps, and unpublished material related to mineral occurrences and mining activities in 

or near the Swansea Wilderness Study Area was completed 

before any field work was undertaken. Master title plats 

and Bureau of Land Management records were checked to 

locate oil and gas leases and mineral claims in the study 

area. 

Two geologists conducted a 12-day field examination 

in the study area and vicinity. Thirty-seven samples were 

taken from adits, mines, prospects, and outcrops. All 

samples were analyzed for 32 elements by inductively 

coupled plasma-atomic emission spectrometry and for gold 

and silver by fire assay. Eighteen samples were assayed for 

barium and copper by the atomic absorption method, and 

five samples were analyzed for manganese using neutron 

activation methods. All analyses were done by the Chemex 

Lab, Inc., Sparks, Nevada. A summary of the geochemical 

data is available in Ryan (1989). The complete analytical 

data are available for inspection at the U.S. Bureau of Mines,' 

· Intennountain Field Operations Center, Building 20, Denver Federal Center, Denver, CO 80225. 

Mining History 

Early mining near the study area consisted of Indian 

diggings in thick hematite layers found at the Mineral Hill 

and Plapet mine areas, 6 to 8 mi west of the study area. 

Also, the "coyote holes" along copper carbonate horizons 

at Mineral Hill are ascribed to the Indians or possibly the 

Spanish (Paul Konow, oral commun., Mineral Hill prospector, 1988). Larger scale copper milling began at the Planet 

and Swansea districts in the 1860's and steady production 

was sustained during the 1880's. Later, the declining price 

of copper resulted in intermittent closing of the mines for 

several years at a time. · 

The southern part of the study area lies in the Swansea 

mineral district (fig. 1). The Mesa mineral district encompasses Black Mesa north of the Bill Williams River, and 

the Owens mineral district is in the northeastern part of the 

study area north of the Bill Williams River. Other mineral 

districts within 12 mi of the study area include the Planet 

C4 Mineral Resources of Wilderness Study Areas: Havasu Region, Arizona 
and Clara. Recorded production from all districts includes 

some 930 troy ounces (oz) of gold, 43,700 troy oz of silver, 

24,000 tons of copper, 32 tons of lead, less than 1 ton of 

zinc, and 300 tons of manganese ore at an unspecified grade 

(Keith, 1978, p. 67; Kreidler, 1986, p. 5; Spencer and Welty, 

1989, p. 224). The total production includes manganese 

ore produced during World War II from the Mesa Manganese 

Prospect on the northeast boundary of the study area (Ryan, 

1989). Although most mining had ceased by 1942, one 

unidentified mine produced copper until the 1970's (Keith, 

1978, p. 71). 

Placer gold has been produced from the Clara mining 

district, 4 mi southeast of the study area, and placer claims 

have been located northeast, east, and northwest of the study 

area. At the time of this investigation, no mining activity 

was being conducted in any of the areas. 

Though some exploration drilling has been conducted 

near the Swansea mine (fig. 2, No. 1) Copper Penny prospect, (fig. 2, No. 2), and in the Planet mineral district (fig. 

1) in the last 10 years (Wilkins and Heidrick, 1982; Lehman 

and others, 1987), no mineral development or production 

has resulted. As of July 1988, no mining claims had been 

staked in the study area and no exploration activities were 

observed. 

Oil and Gas 

Petroleum resources are considered to be nonexistent 

in the study area because of the middle Tertiary metamorphic and tectonic history. Ryder (1983, p. C-19) rates the 

oil and gas potential of the region of the study area as low 

because the organic content, reservoir quality, and thermal 

history of the rocks are not conducive to the generation or 

preservation of significant volumes of hydrocarbons. As of 

August, 1988, no active oil or gas leases were extant in the 

study area. 

Appraisal of Sites Examined 

In the study area, mineral production has taken place 

in the Owens mineral district north of the Bill Williams 

River. Elsewhere, prospect pits, bulldozer cuts, near surface 

slopes, adits, or shafts are found in the northern, west-central, and southwestern parts of the area (Ryan, 1989). Evidence of manganese and copper oxides and carbonate 

minerals in association with hematite or specularite are 

present locally. 

The Mesa Manganese prospect (fig. 2, No. 3) consists of two small adjoining stopes near the surface on the 

east side of Black Mesa in the northern part of the study 

area (Ryan, 1989). The manganese is in lenses in a megabreccia of Paleozoic limestone and quartzite that lies in the 

upper plate of the Buckskin-Rawhide detachment fault. It 

is estimated that about 150 tons of low-grade ore was removed during World War II. One sample of residual material at the entry to one of the stopes assayed 10.9 percent 

manganese oxide (MnO), whereas another sample, from a 

trench northwest of the slOpes, assayed 20.3 percent MnO. 

This last sample is probably more representative of the material that was mined (Ryan, 1989). Most samples from the 

prospect area contain minor silver and elevated concentrations of barium. 

A 265-ft-long exploration adit lies in a side drainage 

leading into the wash that drains from the area of the 

Swansea mine across the southeast comer of the study area 

and terminates at the Bill Williams River (fig. 2, No. 4). 

The adit is at the base of a rugged cliff in which no structure or minerals were observed. The adit crosses several 

moderately to steeply dipping faults that strike northwest 

and north (Ryan, 1989). Five chip samples were taken in 

the adit from crosscutting faults. Two samples from a 2-ftwide, hematite-stained, northwest-striking fault zone contain 0.015 troy ounces of gold per short ton (oz/st), 1,5IO 

and 4,500 part per million (ppm) of barium, 1,755 and 2,050 

ppm lead, and 2,400 and 3,930 ppm zinc (Ryan, 1989). 

These concentrations are considered typical of those found 

along the northwest-striking high-angle faults that cut the 

lower plate mylonitic gneisses. 

Caved adits, shafts, and prospect pits north of the Bill 

Williams River are in the Owens mineral district, located in 

the northeastern part of the study area. Many of the caved 

adits are probably less than 30-ft long, based upon the 

amount of subsidence and the dump size. At least one shaft 

in sec. 4, T. 10 N., R. 15 W. may account for some of the 

limited production of metals in the district The shaft is 

caved and inaccessible, but a sample taken from the site of 

a loading bin contains 3.6 weight-percent copper and less 

than 15 weight-percent iron. Other samples collected in the 

area of the shaft were from pits, caved adits, and outcrops 

containing copper carbonates and oxides and ubiquitous 

specularite. These samples contain elevated concentrations 

of copper and iron and some also contain about 1,420 ppm 

manganese (Ryan, 1989). One sample also contains 415 

ppm strontium and another sample from a caved adit contains 0.01 troy ounces per ton silver. 

Elevated concentrations of arsenic, barium, magnesium, lead, strontium, and zinc found in various samples 

throughout the study area are consistent with the suite of 

minerals noted at the older producing properties in the region (Harrer, 1964, p. 143; Ryan, 1989). Hematite or 

specularite is found at most of the workings examined. 

Chloritic alteration, noted as being typical of detachmentrelated lower-plate mineralization (Reynolds, 1980, p. 7), 

also was found at all of the workings examined in the study 

area except the Mesa Manganese prospect. The presence of 

oxide, carbonate, silicate, and sulfate minerals suggest that 

conditions during deposition were oxidizing and that the 

minerals probably formed at a shallow depth. More reduced, 

Mineral Resources of the Swansea Wilderness Study Area, La Paz and Mohave Counties, Arizona CS 
sulfide-rich assemblages may be present at depth (Wodzicki 

and others, 1982, p. 94). 

Quantities of sand and gravel are readily available 

along the Bill Williams River and its tributaries. However, 

the material in the study area has no unique characteristics 

that would make it more desirable than similar deposits 

outside the study area. The desert environment of southern 

Arizona provides numerous sources of similar material closer 

to population centers. 

Conclusions 

The Swansea Wilderness Study Area contains no 

identified metallic mineral resources. Mineral assemblages 

in the various samples taken in the study area are similar to 

those noted in epithermal deposits found in various structural settings in the Tertiary extensional terrane of Arizona, 

as described by Spencer and Welty (1989). These minerals 

suggest the possibility of unidentified subsurface occurrences. 

· The metamorphic rocks that underlie much of the 

study area and the lack of significant sedimentary basins 

preclude oil and gas resources. 

Sand and gravel in the study area has no unique characteristics that would make it more desirable than similar 

deposits outside the study area and closer to population 

centers. 

ASSESSMENT OF MINERAL RESOURCE 

POTENTIAL 

By Richard M. Tosdal, Robert G. Eppinger, H. Richard 

Blank, Jr., Daniel H. Knepper, Jr., Andrea J. Gallagher, 

and James A. Pitkin 

U.S. Geological Survey 

Geology 

The Swansea Wilderness Study area lies in the northwest-trending belt of metamorphic core complexes in westcentral Arizona (Rehrig and Reynolds, 1980). In these 

complexes, mid-crustal and deeper rocks in the lower plate 

were tectonically transported to the surface along shallowdipping normal faults or detachment faults during a period 

of extensional tec~nism in the late Oligocene and Miocene 

(Spencer and Reynolds, 1989). Hydrothermal fluid circulation and mineralization accompanied extensional deformation (Spencer and Welty, 1989). Seveial deposits in the 

region that were formed during the extensional deformation 

have been mined and explored for their base and precious 

metals and for manganese, uranium, and vanadium. The 

detachment fault in the map area is known as the BuckskinRawhide detachment fault of Spencer and Reynolds (1986, 

1989). It crosses the northern half of the study area and 

crops out discontinuously along the southern border of. the 

study area (fig. 2). 

The geology of the study area can be divided into 

three parts (fig. 2). The upper and lower plates of the 

Buckskin-Rawhide detachment fault compose two parts. The 

posttectonic rocks that include rocks deposited in depres- · 

sions within the extended terrane and modern alluvial deposits along washes and the Bill Williams River form the 

third. 

Part of the upper plate terrane consists of Proterozoic, Paleozoic, and Mesozoic igneous and metamorphic 

rocks that had complex geologic histories prior to extensional deformation in the Tertiary (Reynolds and Spencer, 

1989). Currently these rocks are fault-bounded and commonly intensely brecciated and fractured as a result of the 

extensional deformation. Within the fault-bounded blocks, 

thrust faults and folds of probable Cretaceous age complicate 

the stratigraphy of these rocks (Reynolds and Spencer, 1989). 

Tertiary volcanic and sedimentary rocks unconformably 

overlie the older rocks and make up the remainder of the 

upper plate terrane (Davis and others, 1980; Suneson, 1980; 

Suneson and Lucchitta, 1983; Spencer and Reynolds, 1986, 

1989). The Tertiary rocks were deposited during regional 

extension. 

The lower plate terrane consists of Tertiary mylonitic 

rocks derived from Proterozoic layered mafic, granitic, and 

pegmatitic gneiss and the Tertiary Swansea Plutonic Suite 

(Bryant and Wooden, 1989). These rocks are characterized 

by a subhorizontal mylonitic foliation and an accompanying northwest-trending elongation lineation. Mylonitic deformation in the lower plate is considered to be a deeper 

level expression of, and slightly older than, brittle extensional faulting along the detachment fault and the upper 

plate (Spencer and Reynolds, 1986; Howard and John, 1987; 

Davis and Lister, 1988). 

, During the last stages of, or after the end of, the 

extensional deformation, high-angle faults cut the detachment terrane. Some of these faults have reverse motion in 

areas east of the study area (Shackleford, 1976; Spencer, 

1989). Within the study area and elsewhere in the region, 

these faults were the sites of epithermal mineralization 

(Spencer and Welty, 1989). 

Posttectonic rocks are common north of the Bill Williams River and sparse south of the river. The rocks are 

here divided into two broad units. The older unit consists 

of subhorizontal volcanic and sedimentary rocks of Miocene 

age that were deposited in depressions within the extensional terrane. To the west of, and within, the study area, 

basalt is the most common posttectonic volcanic rock and 

typically erodes to form mesas (Suneson and Lucchitta, 1979, 

1983; Suneson, 1980). Black Mesa, north of the Bill Williams River, is one example. Less extensive younger megaporphyritic basalt of presumed late Miocene age is present 

C6 Mineral Resources of Wilderness Study Areas: Havasu Region, Arizona 
in the northern part of ilie study area and in adjoining areas 

where n~ fAlls prueovalleys (Sunesollll, 1980). Rlhyolli~e occwrs Rocaily and! foms mos~ of ahe Casteneda Hills nmmediateny north of ilie stMdy area (fig. 1; Sooesollll, 1980; Samesollll 

and! Lucchitaa, 1983). Conglomerate and! sandstone, composed! of nocaUy derived detritus, also are commollll and 

characterize ilie oRder post-detachment rocks south of ilie 

study area im tile Buckskin Mountains llllear Swansea. 

The younger posttectonic units consis~ of unconsolidated! to poorly consolidated sandstone and! conglomemte 

and alluvium of late Tertiary and! Quaternary age ilia~ 

unconformably overlie older rock units. These rocks were 

deposited in alluvial! fan and in fluvial! environments. Mynonitic rocks of tile Rower plate are a major source of 

detritus for iliese rocks. The sandstone and! conglomerate 

now crop out in moderately dissected fans and! as !terrace 

gravels above ilie modem washes. The alluvium is along 

the modem washes and in the larger valleys. 

A reconnaissance geochemical survey of the Swansea 

Wilderness Study Area was conducted in May 1988 to aid 

in abe mineral! resource evaluation. The principal geochemical! sampling media were stream sediments and heavymineral concentrates, collected a~ 55 sites within tile study 

area. A stream-sediment sample represents a composite of 

the rocks and! soils exposed in the drainage basirn. The 

nonmagnetic fraction of a heavy-mineral-concentrate sample 

is useful in detecting mineralized! areas because primary 

and! secondary ore minerals are commonly found in this 

fraction. The concentration of ore and! ore-related minerals 

in the heavy-mineral-concentrate sample facilitates determination of elements that are not easily detected in bulk 

stream sediments. Rock samples provide information on 

background metal concentrations in unaltered bedrock and 

information on anomalous metal suites in mineralized areas. 

This geochemicall survey was designed to locate altered, mineralized, or geochemically anomalous areas, but 

not to fmdl individual mineral deposits. Detailed follow-up 

geochemical studies in areas of anomalous metal concentrations found in this reconnaissance study were not undertaken. 

Stream-sediment and !heavy-mineral-concentrate 

samples were collected from active alluvial channels generally along frrst-order streams. Each heavy-mineral-concentrate sample was separated into magnetic, slightly magnetic, 

and nonmagnetic fractions using an electromagnet in the 

Raboratory. Nonmagnetic fractions were examined for mineralogical! content; nhese frnctions andlltlhe sXightlly magnetic 

heavy-minemll-concelllltmte fractions were pulverized! for 

chemical! anallysis, and! ltlhe maglllletic fractiollll was arclhivedl. 

Rock sampRes were examined microscopica!Ry and ilieirn 

plUlRverizedl for clhlemicall anallysis. 

Stream sOOimen~ and rock sampRes were anallyzedl for 

35 eRements, and! ilie heavy-mineraR concentrate samples 

were arnallyzedl for ilie same eRements and! pRattinum Mdl 

paiadl.iii.RID, al!R ll>y semiqwmtitative emissiollll specttrogrnplmy. 

Kllll adlditiollll, stream sedimellllts and! rocks were anaRyzedlll>y 

more sensitive atomic-all>sorptiollll meltlhods for arsenic, ll>ismMili, cadmiW111l, antimony, and! zmc. Stream-sediment and 

rock samples were ana.Ryzedl for Row-ReveR gold concentrations ( detectiollll Rim it 50 parts per lbiHiollll (ppb) for stream 

sediments, 2pp1b for rocks) by atomic absorption methods. 

Histograms showing lllhe genernll distributiollll and! rnnge 

of the data were constructed for selected elements. Boundaries between background! and anomalous element concernttations were chosen using histograms, percentiles, and 

average crustal abundances for elements givellll by Levmson 

(1980). AnalyticaR results and full descriptions of sampling 

and! analytical techniques are found! m Eppinger and others 

(1990a, b). 

Geochemical anomalies Rikely related to lithologic 

differences and! 00 mineralization were founcll n1rn samples 

from the study area. Anomalies possibly relate<ll oo mineralization are found in 6 areas in ilie study area and are 

shown in figure 3. Gold was detected fum only 1 llllorunagnetic 

heavy-mineral-concentrate sample and! in only 2 rock 

samples, in areas 1 and! 6, discussed! below. Anomalous 

concentrations of silver, copper, lead, zinc, arsenic, barium, 

bismuth, cobal~, iron, molybdenum, manganese, antimony, . 

tin, thorium, vanadium, and tungsten were fooodl irn samples 

from the study area Anomalous concentrations of metals 

in stream-sediment and heavy-minerall-concerntrate samples, 

their rnnges, and the threshold! values used m this study are 

listed in table 1. 

Two distinct geochemical suites that llikely represent 

two different rock types are apparent m the samples. One 

is a barium-nickel suite nrn stream-sedimen~ and! heavy-mi~rneraR-concentrate samples draining Miocene basalt Ollll Black 

Mesa. The other is a lanthanum-yttrhl!m-ruobium suite fum 

stream-sediment and! heavy-mineral-concentrate samples 

derived from wee Ra.rge areas in abe southern and! central 

parts of ahe study area. The latter association, commorn to 

granitic \terrains, nike!y represents granitic phases within tile 

lower plate crystalline rocks underlying ilie majority of lllhe 

study area. Sphene contains these elements (Deer and! others, 1962) and! is tile dominant mineral phase in heavymineral-concentrate samples rich in these elements. 
Samples from area 1 contain the highest concentrations found in this study for several metals, including arsenic, copper, molybdenum, lead, antimony, tin, vanadium, 

tungsten, and zinc. Other metals present in anomalous concentrations include silver, barium, bismuth, and elements in 

slightly anomalous concentrations include cobalt, iron, and 

thorium. Ore-related minerals identified in nonmagnetic 

heavy-mineral-concentrate samples include abundant fluorite and barite, lesser vanadinite, descloizite, and malleable 

lead, and trace amounts of pyrite, scheelite, and thorite. 

Both rock samples containing detectable gold are from this 

area (quartz vein, 2 ppb gold; siliceous mylonite, 20 ppb 

gold). The area is dominated by lower plate mylonitic 

rocks, though the Buckskin-Rawhide detachment fault and 

associated syndetachment breccias, carbonate minerals, and 

retrograde chlorite-rich gneisses are found locally (fig. 2; 

Spencer, 1989). Several small chrysocolla- and specularitebearing prospects and an adit in the south end of area 1 are 

near the detachment fault. 

Area 2 contains samples with anomalous concentrations of silver, arsenic, barium, cobalt, copper, lead, vanadium, tungsten, and zinc and slightly anomalous 

concentrations of molybdenum and thorium. Ore-related 

minerals identified in nonmagnetic heavy-mineral-concentrate samples include barite and fluorite, small amounts of 

vanadinite and chrysocolla, and trace amounts of wulfenite, 

pyrite, and scheelite. Bedrock in the area· is predominantly 

mylonitic gneiss. Cobbles of carbonate-rich, chloritic, and 

metasedimentary rocks common to the upper plate terrane 

and the areas adjoining detachment faults were observed in 

sampled drainages. These rocks crop out upstream from 

the major wash that crosses this area. 

Anomalous concentrations of metals in area 3 include 

barium, copper, iron, and vanadium and slightly anomalous 

concentrations of arsenic, cobalt, and molybdenum. Abundant fluorite, moderate amounts of barite, and trace amounts 

of pyrite, chrysocolla, cuprite, native copper, and malleable 

lead were identified in nonmagnetic heavy-mineral-concentrate samples. Lower plate mylonitic gneiss crops out 

throughout area 3. Northwest-trending, and locally mineralized, high-angle faults cut the gneiss. No detachment fault 

or upper plate rocks are known in the area (fig. 2). Cobbles 

of retrograde gneiss were observed locally, and chrysocollamalachite-epidote-specularite cobbles were observed in three 

drainag~s. Shafts and adits along high-angle faults are upwash from the geochemical sample sites in two of these 

drainages. Ryan (1989) reports anomalous copper, iron, 

manganese, and silver from the area of these shafts. 

~ilver, arsenic, and lead are found in slightly anomalous concentrations in stream-sediment and nonmagnetic 

heavy-mineral-concentrate samples from area 4, along with 

trace amounts of pyrite and malleable lead in nonmagnetic 

heavy-mineral-concentrate samples. Sparse chrysocolla and 

specularite are in the alluvium at one site. Lower plate 

mylonitic crystalline rocks throughout the area are cut by 

high-angle fractures and small faults. Many cobbles of 

lower plate gneiss in the washes are strongly chloritized 

and epidotized. 

Anomalous concentrations of metals in samples from 

area 5 include barium, iron, manganese, nickel, lead, vanadium, zinc, and slightly anomalous silver, arsenic, lead, antimony, and thorium. Abundant barite, small amo~nts of 

fluorite, and trace amounts of pyrite were observed in heavymineral-concentrate samples. Arroyos in area 5 drain the 

east side of Black Mesa, a west-dipping mesa capped by 

postdetachment Miocene basalt. Upper plate volcanic and 

sedimentary rocks crop out along the east flank of the mesa 

(fig. 2). Cobbles of sandstone, conglomerate, vein quartz, 

biotite gneiss, muscovite schist, and granitic rocks were 

observed in drainages. A manganese prospect is present in 

the area (Ryan, 1989). 

Samples from area 6 contain anomalous concentrations of gold, silver, barium, lead, tin, and thorium. Gold 

(700 ppm) and silver (70 ppm) were found in a single heavymineral-concentrate sample along the south edge of area 6. 

Abundant barite, and trace amounts of fluorite, pyrite, hematite pseudomorphs after pyrite, and paraschachnerite, a 

silver-mercury alloy, were observed in several samples in 

area 6. Bedrock in the area is almost exclusively Tertiary 

postdetachment basalt, although cobbles of lower plate 

mylonitic gneiss were observed in one drainage. 

Interpretation 

The strong anomalous concentrations of silver, arsenic, barium, copper, molybdenum, lead, antimony, tin, 

vanadium, tungsten, and zinc and slightly anomalous concentrations of bismuth, cobalt, iron, thorium, and gold and 

abundant ore-related minerals in heavy-mineral-concentrate 

samples from area 1 are likely related to mineralization 

associated with the Buckskin-Rawhide detachment surface, 

which crops out locally. The large extent of the geochemical anomaly relative to the mapped exposures of the detachment surface suggests that lower plate rocks are more 

mineralized here than elsewhere in the study area. A possible reason for more metal-rich lower plate rocks in area 1 

is that these rocks may be erosional remnants of a relatively 

metal-rich zone that enveloped a detachment fault. In this 

model, the detachment fault would have been present prior 

to erosion a short distance above the bedrock outcrops in 

the area. Mineralization in lower plate rocks within this 

envelope may result from replacement, dissemination, or 

fractUre filling in the lower plate gneisses immediately beneath the detachment fault, as described by Spencer and 

Welty (1989). 

The anomalous concentrations of silver, arsenic, 

barium, cobalt, copper, lead, vanadium, tungsten, and zinc, 

slightly anomalous concentrations of molybdenum and thorium, and the ore-related minerals observed in heavy-mineral-concentrate samples in area 2 are similar to those found 

C8 Mineral Resources of Wilderness Study Areas: Havasu Region, Arizona 
in area 1. The Buckskin-Rawhide detachment surface does 

not crop out in this area but crops out just outside the study 

area (fig. 2; Spencer, 1989). The carbonate-rich and chloritic gneiss observed in .alluvium from area 2 indicates the 

proximity of a detachment surface. The sources of these 

geochemical anomalies and ore-related minerals in area 2 

are likely similar to those postulated for area 1. 

The anomalous concentrations of barium, copper, iron, 

and vanadium, slightly anomalous concentrations of arsenic, 

cobalt, and molybdenum, and ore-related minerals in area 3 

are probably related to mineralized ground similar to that 

explored by shafts and adits in 2 of the 10 drainages included in the area. The anomalous concentrations of metals 

and ore-related minerals found within this relatively large 

area likely are due to a more widespread presence of mineralized rocks than the area presently indicated by known 

shafts and adits. The geochemical suite and ore-related 

minerals observed in area 3 are not so complete as those in 

areas 1 and 2, but nevertheless are likely the result of similar 

mineralizing processes during extensional faulting and subsequent high-angle faulting. 

Weakly anomalous concentrations of silver, arsenic, 

and lead in area 4 are probably due to mineralizing processes like those in areas 1, 2, and 3. However, the relatively low-level concentrations of these metals, coupled with 

the pa1,1city of ore-related minerals found in samples from 

area 4, suggest that mineralized rocks are not extensive at 

present levels of exposure. 

The anomalous concentrations of barium, iron, manganese, nickel, lead, vanadium, and zinc and the slightly 

anomalous concentrations of silver, arsenic, lead, antimony, 

and thorium in area 5 may have at least three origins. One, 

much of the bedrock in the area is of basaltic composition, 

which tends to be enriched in many of the above metals. 

Two, the anomalous concentrations of metals may result 

from the adsorption of the metals onto manganese and iron 

oxides, as both manganese and iron are found in anomalous 

concentrations in the samples. These absorbed metals may 

reflect mineralization related to the Buckskin-Rawhide detachment fault, as manganese has been mined in upper plate 

rocks in the region. Three, unrecognized epithermal deposits may be present in and along the detachment fault Pyrite 

and fluorite are found in heavy-mineral concentrate samples 

from this area, as they are in areas 1 and 2, where the 

detachment fault is proximal. 

Barite in area 6 is likely derived from extensive outcrops of basalt in the area. However, the elevated concentrations of gold and silver in one heavy-mineral-concentrate 

sample, anomalous concentrations of lead in another heavymineral concentrate, and the presence of tin, thorium, and 

trace amounts of fluorite, paraschachnerite, and pyrite in 

several heavy-mineral-concentrate samples from the area 

are problematic. These metals and minerals are not generally associated with basalt. Further studies are necessary to 

determine the origin of the anomalous elements, pyrite, and 

fluorite in samples from basalt in area 6. 

Malleable lead and paraschachnerite were observed 

in several heavy-mineral-concentrate samples, the fonner 

in samples from areas 1, 3, and 4, and the latter in samples 

from area 6. These occurrences are interpreted to be of 

anthropogenic origin and probably introduced during past 

mining activity from precious-metal recovery processes using mercury amalgamation and as solder from food cans or 

from lead shot 

Geophysical Studies 

Aeromagnetics and Gravity 

Aeromagnetic and gravity data for a region encompassing the Buckskin and Rawhide Mountains and including the Swansea Wilderness Study Area were compiled from 

available data sources. Two somces of aeromagnetic data 

were utilized: a survey of the Prescott, Arizona 1 o by 2° 

quadrangle flown in support of the National Uranium Resource Evaluation (NURE) program and a survey of the 

Needles 1° by 2° quadrangle, California and Arizona, flown 

for the USGS (Western Geophysical Company, 1979; U.S. 

Geological Survey, 1981). The NURE traverses were made 

on east-west headings at spacings of 1 mi and a nominal 

height of 400 ft above ground. The USGS traverses were 

similarly on east-west headings but at 0.5-mi spacings and 

a nominal drape height of 1,000 ft. Gravity data were 

obtained from files of the Defense Mapping Agency (DMA) 

through the National Center for Solar-Terrestrial and Geophysical Data (Boulder, CO 80303). No new geophysical 

field work was performed for the present investigation. 

The residual total-intensity aeromagnetic field for the 

800-mi2 region surrounding the Swansea Wilderness Study 

Area reveals three features pertinent to the study area (fig. 

4). One, a striking contrast in magnetic expression is evident between the postdetachment volcanic rocks, chiefly 

basalts, that produce intense short-wavelength anomalies 

and the rocks affected by the extensional defonnation that 

produce much more subdued and longer wavelength 

anomalies. The boundary between these two magnetic domains traces an arc across the region. The study area lies 

mostly east of the domain of short-wavelength anomalies. 

Two, in the terrane affected by the extensional deformation, 

the aeromagnetic data trace out long-wavelength, northeasttrending anomaly highs and lows that correspond approximately to the corrugations in the detachment terrane. In 

this terrane, the mylonitic rocks in the lower plate form the 

antiformal arches and the faulted rocks in the upper plate 

crop out in the synfonnal troughs (Spencer and Reynolds, 

1989). Metallic mineral deposits are most prevalent in the 

synfonnal troughs (Spencer and Welty, 1989). The magnetic highs crossing the study area overlie the mylonitic 

rocks in the lower plate, whereas the magnetic lows overlie 

Mineral Resources of the Swansea Wilderness Study Area, La Paz and Mohave Counties, Arizona C9 

/ 
34 

10' 

• D 

D 

B 

c 

D 

Ag 

Au 

Cu 

Mn 

Pb 

u 

v 

Zn 

1 

2 

3 

4 

Qal 

Qt 

Qs 

QTc 

Tm 

Tb 

Tc 

EXPLANATION 

Areas having high mineral resource potential (H) 

Areas having moderate mineral resource potential (M) 

Areas having low mineral resource potential (L) 

Level of certainty of assessment 

Data only suggest level of potential 

Data give good indication of level of potential 

Data clearly define level of potential 

Commodities 

Silver 

Gold 

Copper 

Manganese 

Lead 

Uranium 

Vanadium 

Zinc 

Mines, prospects, and adits 

Swansea mine 

Copper Penny prospect 

Mesa prospect 

Unnamed adil 

Geologic map units 

Post detachment rocks 

Alluvial deposits (Quaternary) 

Talus deposits (Quaternary) 

Sand and gravel (Quaternary) 

Conglomerate and sandstone (MJ,oce:ne)ll----4 

Megacryst basalt (Miocene) 

Basalt (Miocene) 

Conglomerate and sandstone (Miocene)L· Q· 0-.~:::y:;, 

Tvs 

Mzs 

Pzs 

g 

mg 

Upper plate rocks 

Volcanic and sedimentary rocks (Miocene and Oligocene?) 

Sedimentary and volcanic rocks (Mesozoic) 

Sedimentary rocks (Paleozoic) 

Granitic rocks (Mesozoic and (or) Proterozoic) 

Lower plate rocks 

Mylonitic gneiss, undivided (Tertiary, Mesozoic, Paleozoic, and Proterozoic) 

8 

AREA OF MAP 

__ Contact 

----- Fault-Dashed where inferred, dotted 

where coocealcd 

~ ... Thrust fault-Dotted where concca1cd; 

sawteeth on upper plate 

~ ·· · Buckskin-Rawhide detachment faultDotted where coocealed; ticks on upper 

plate 

Figure 2. Map showing mineral resource potential and generalized geology of the Swansea Wilderness Study Area, La Paz and Mohave Counties, Arizona. Base 

from U.S. Geological Survey 1 :62,500-scale Swansea and Casteneda Hills quadrangles, 1966. Contour interval 80 ft. Geology north of Bill Williams River is 

modified from Suneson (1980) and Shackelford (1976, 1989). Geology around Swansea and Copper Penny is modified from Spencer and Reynolds (1987). 

Geology of rest of area by R.M. Tosdal (1987) and modified from Spencer (1989). 
......... _.,,,,.,..,found in anomalous concentrations ~' 

Silver 

Arsenic 

Gold 

/;;- Mo Molybdenum:!/ 

Ni Nickel " 

Pb I...e:crl 

Sb Antimony 

Sn Tin 

V Vanadium 

W Tungsten 

Zn Zinc 

Fluorite content from nonmagnetic 

heavy-mineral concentrate 

0 Trace (<1 percent) 

0 1-20 percent D More than 20 percent 

Figure 3. Geochemical anomalies from stream-sediment, heavy-mineral-concentrate, and rock samples from the Swansea 

Wilderness Study Area, La Paz and Mohave Counties, Arizona. Elements and minerals in parenthesis denote slightly anomalous 

concentrations .. See text for discussion of anomalous areas 1-6. Contours are in feet. 

C12 Mineral Resources of Wilderness Study Areas: Havasu Region, Arizona 
Table 1. Summary data for elements found in anomalous concentrations in stream-sediment and heavymineral-concentrate samples in the Swansea Wilderness Study Area, Arizona 

[lower limits of analytical determination are shown in parentheses. N, not detected; l, detected but lower than 

determination limit; G, greater than upper determination limit;%, percent, n, number of determinations. Analyses are 

by emission spectrography except for elements with an "-a" suffix, which are by atomic absorption methods. Values 

are in parts per million unless noted otherwise.) 

Element Minimum Maximum 50th Threshold Number of samples 

percentile above threshold 

Nonmagnetic heavy mineral concentrates (11 = SS) 

Ag (1) N 70 N L 2 

As (500) N 1500 N L 3 

Au (20) N 700 N L 1 

Ba (50) 5000 G(lO,OOO) 1000 G(lO,OOO) 16 

Bi (20) N L N L 1 

Cu (10) N 7000 L 150 6 

Mo (10) N 100 N L 4 

Pb (20) N 15,000 50 100 15 

Sb (200) N 500 N L 2 

Sn (20) N 500 30 100 3 

Th (200) N 700 N 300 7 

v (20) 20 10,000 100 700 7 

w (50) N 200 N L 2 

Zn (500) N 5000 N L 3 

Weakly magnetic heavy mineral concentrates (11 = SS) 

Co (20) 30 300 100 200 8 

Cu (10) L 1500 100 500 9 

Fe (0.1%) 3% 50% 10% 30% 6 

La (100) N 2000 500 1000 12 

Mn (20) 700 5000 1000 5000 3 

Mo (10) N 30 L 15 7 

Ni (10) 30 1000 70 200 9 

Pb (20) 20 1000 70 150 10 

Th (200) N 300 L 200 4 

v (20) 70 700 200 500 3 

Zn (500) N 700 N L 1 

Stream sediments (11 = SS) 

Ag (0.5) N 1 N L 13 

As-a (5) L 21 9 15 8 

Ba (20) 200 2000 500 1500 6 

Cu (5) 7 500 30 70 10 

La (50) L 200 70 150 8 

Mo (5) N 5 N 5 3 

Nb (20) N 50 L 30 4 

Ni (5) 10 200 20 150 2 

Pb (10) 20 300 30 70 7 

.Sb-a (2) L 5 L 2 3 

v (10) 20 500 50 150 ,1 

y (10) 15 100 30 70 7 

Zn-a (5) 16 190 39 200 

Mineral Resources of the Swansea Wilderness Study Area, La Paz and Mohave Counties, Arizona C13 
the extended upper plate rocks. Three, northwest-trending 

gradients within the aeromagnetic data cut across the northeast-trending highs and lows. Where these gradients overlie 

bedrock, they correspond to the northwest-trending highangle faults, one of which crosses the southwestern part of 

the study area. These faults locally contain base- and precious-metal deposits, as in the Alamo and Owens mineral 

districts (Spencer and Welty, 1989) 

The complete Bouguer gravity anomaly field computed from about 165 stations of the DMA set and terraincorrected to 167 km (Hayford-Bowie zones A-0) for the 

region of the Buckskin and Rawhide Mountains is shown in 

figure 5. Across the area of the map is an unexplained 

nonuniform decrease in anomaly levels to the north-northeast. The steepest part of this gradient transects the study 

area. Superimposed on this gradient in the region are broad 

lows that roughly correspond to areas of Tertiary volcanic 

rocks in the upper plate of the detachment fault. 

Remote Sensing 

Digital image data acquired by the Thematic Mapper 

(TM) system on the Landsat-4 satellite (Scene I.D. 40174-

17383) were analyzed to detect and map areas that may 

contain hydrothermally altered rocks. The six bands of 

image data in the visible and near-infrared range were 

digitally processed to enhance spectral characteristics of 

minerals that often accompany alteration or are derived from 

the weathering of altered rocks. Visual interpretation of a 

vegetation-masked TM color-ratio composite consists of identifying concentrations of limonite (Group 1), hydroxylbearing and (or) hydrated minerals (Group 2), and areas 

where both groups of minerals occur together (Group 3). 

Identification of the different groups is based on the spectral 

responses of the different limonitic minerals in the TM bands 

(Hunt and Salisbury, 1971, Hunt and Ashley, 1977; Raines, 

1977). 

Figure 4. Aeromagnetic anomaly map of the Swansea Wilderness Study Area, La Paz and Mohave Counties, Arizona (shaded). 

Contour interval, 20 nanoteslas; hachured in direction of magnetic low. 

C14 Mineral Resources of Wilderness Study Areas: Havasu Region, Arizona 
That part of the Swansea Wilderness Study Area south 

of a line that projects continuously southwestward from 

Centennial Wash (fig. 2) contains a fairly uniform distribution of limonite or limonite-group minerals (Group 1). This 

area is also underlain almost entirely by subhorizontally 

layered mylonitic mafic and less common granitic gneiss in 

the lower plate of the Buckskin-Rawhide detachment fault. 

The limonitic minerals are inferred to be related to the distribution and weathering of the mylonitic gneiss and not to 

reflect hydrothermal alteration. 

Radioelement Distribution 

Natural radioelement distribution in the Swansea 

Wilderness Study Area was evaluated by examination of 

available data from an aerial gamma-ray spectrometric survey of the Prescott 1°. by 2° quadrangle (Western Geophysical Company, 1979). The survey acquired aerial 

gamma-ray spectrometry data along 1-mi-spaced east-west 

flightlines at 400 ft above ground level. Nine lines cross 

the study area and provide about 15 percent ground coverage, 

because an aerial gamma-ray system at 400 ft above ground 

level effectively measures terrestrial gamma radiation from 

a swath 800ft wide along flightline. The 15 percent coverage represents a reconnaissance sampling of the near-surface (0-18 inches depth) distribution of the natural 

radioelements potassium (K), equivalent uranium (eU), and 

equivalent thorium (eTh). The prefix e for equivalent denotes the potential for disequilibrium in the uranium and 

thorium decay series. 

Examination of preliminary radioelement contour 

FigureS. Bouguer gravity anomaly map of the Swansea Wilderness Study Area, La Paz and Mohave Counties, Arizona (shaded). 

All data reductions and terrane corrections employed a standard Bouguer density of 2.67 glcm3 and followed conventional U.S. 

Geological Survey procedures (for example, Cordell and others, 1982). Contour interval, 2 mGals; hachured in direction of 

closed low; circle, gravity station. 

Mineral Resources of the Swansea Wilderness Study Area, La Paz and Mohave Counties, Arizona C15 
maps that include the Swansea Wilderness Study Area indicates that differing radioelement concentrations characterize the northern and southern parts of the study area. 

Generally, in terranes where crystalline rocks predominate, 

higher radioelement concentrations relate to more silicic, 

more radioactive rocks and the detritus derived from them. 

Lower concentrations relate to less silicic, less radioactive 

rocks and detritus derived from them. The northern part of 

the study area has relatively lower concentrations of 0.5 to 

1.5 percent K, 2 to 4 ppm eU, and 10 to 15 ppm eTh, which 

reflect the presence of less radioactive Miocene basalt. The 

southern part has relatively higher concentrations of 1.5 to 

2.0 percent K, 4 to 6 ppm eU, and 15 to 20 ppm eTh, which 

reflect the presence of more silicic, more radioactive mylonitic gneiss. For the study area as a whole, the radioelement concentrations of 0.5 to 2 percent K, 2 to 6 ppm eU, 

and 10 to 20 ppm eTh are thought to be usual (not anomalous) levels for the rock types present. 

Mineral Resource Assessment 

The assessment of the mineral resource potential of 

the Swansea Wilderness Study Area draws upon regional 

geology, geochemistry, geophysics, mineral occurrence 

maps, mining claim records, and the available ore deposit 

models that ·are applicable to the geologic terrane in the 

study area. These data were used to delineate favorable 

tracts within the study area, and an estimate of the level of 

resource potential and degree of certainty for each tract was 

made using the criteria outlined in the appendixes. 

I Throughout this discussion, mineral· resource potential refers only to undiscovered mineral resources. 

Areas of potential for gold, silver, base metals, manganese, uranium, and vanadium resources are present in the 

study area. These are outlined on figure 2 and are discussed 

below. Applicable metallic ore deposit models for the study 

area include detachment fault-related base- and preciousmetal deposits (Wilkins and Heidrick, 1982; Wilkins and 

others, 1986; Spencer and Welty, 1986, 1989), stratabound 

and fault-controlled manganese deposits (Cox and Singer, 

1~86; Spencer and Welty, 1985), and stratabound uranium 

and vanadium deposits (Sherborne and others, 1979; Otton, 

1981; Spencer and Welty, 1985). · 

Base and Precious Metals 

Base- and precio~s-metal mines and prospects in and 

adjacent to the Swansea Wilderness Study Area have been 

worked intermittently since the late 1800's. The mineral 

occurrences are of epithen:nal origin. The min~s are developed in replacement deposits in carbonate racks and in 

epithermal veins in low- a,id high-angle faults in and above 

the Buckskin-Rawhide detachment fault (Swansea, Planet, 

and Mesa mineral districts) (Wilkins and Heidrick, 1982; 

Welty and others, 1985; Spencer and Welty, 1989). Other 

mines are developed along veins in high-angle faults in 

lower-plate mylonitic gneiss (Owens mineral district) 

(Spencer and Welty, 1989). 

Based on the known occurrences within the entire 

region, all areas along the high- and low-angle faults, particularly where reactive (carbonate) rocks are present, are 

assigned a moderate potential with a certainty level of C for 

gold, silver, copper, lead, and zinc. These areas are in the 

northern and southern parts of the study area (fig. 2). Geochemical data support this assignment. Areas of high potential with a certainty level of C for gold, silver, copper, lead, 

and zinc are assigned to areas adjoining known mineral 

occurrences. These areas include the Owens mineral district 

within the study area and the area in the southeast where 

the Buckskin-Rawhide detachment fa~t crops out (fig. 2). 

The central part of the study area is assigned a low potential 

with a certainty level of B for these elements. 

I Manganese 

Mines in the Mesa mineral district in the northern 

part of the Swansea Wilderness Study Area and to the east 

in the Black Burro, Lincoln Ranch, and Artillery mineral 

districts (fig. I) have produced manganese (Keith, 1978; 

Keith and others, 1983a, b). The manganese deposits are in 

upper plate Tertiary rocks either along high-angle faults or 

as stratabound deposits (Lasky and Webber, 1949; Spencer 

and others, 1989). Upper plate Tertiary rocks are present 

only in small areas in the study area. The area around the 

Mesa mineral district in the northern part of the study area 

is assigned a high potential for manganese with a certainty 

level of D based on the presence of anomalous concentrations of manganese and the evidence of local past production. 

Tertiary rocks in the southeastern part of the study 

area are assigned a low potential for manganese with a 

certainty level of C based on the presence of permissive 

rocks and structures (fig. 2). A moderate or high potential 

for this area is unwarranted because there is no evidence for 

any manganese in these rocks, either in outcrop or in the 

geochemical data. 

Uranium and Vanadium 

The Anderson uranium-vanadium mine in the Date 

Creek Basin, 30 mi east of the Swansea Wilderness Study 

Area, is in fine-grained sedimentary and volcanic rocks assigned to the middle Tertiary Chapin Wash Formation 

(Sherborne and others, 1979; Otton, 1981; Spencer and 

Welty, 1985). These rocks are broadly correlative with the 

upper plate Tertiary volcanic and sedimentary rocks near 

~ study area, though correlations between the two rock 

C16 Mineral Resources of Wilderness Study Areas: Havasu Region, Arizona . 
sections are uncertain (Spencer and Reynolds, 1989). The 

presence of pennissive rock units and anomalous concentrations of vanadium in heavy-mineral-concentrate samples 

indicate that these areas should be assigned a low resource 

potential with a certainty level of B (fig. 2). 

Oil and gas 

No resource potential exists for oil and gas in the 

Swansea Wilderness Study Area because of the lack of hydrocarbon-bearing rocks, because the generally thin sections of unmetamorphosed rock are structurally bounded at 

shallow depths and are underlain by mylonitic rocks that 

were metamorphosed at midcrustal depths, and because much 

of the exposed terrane is underlain at the surface by metamorphic rocks. 

Sand and gravel 

Quantities of sand and gravel are available in the 

Swansea Wilderness Study Area as unconsolidated to poorly 

consolidated alluvial deposits in washes and along the Bill 

Williams River. These deposits, however, contain no unique 

characteristic that make them more attractive than areas 

closer to population centers (Ryan, 1989). 

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ore in Arizona: U.S. Geological Survey Bulletin 710, p. 93-

184. 

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

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Keith, Stanley, Gest, D.E., and DeWitt, Ed, 1983a, Metallic mineral districts of Arizona: Arizona Bureau of Geology and 

Mineral Resources of the Swansea Wilderness Study Area, La Paz and Mohave Counties, Arizona C17 
Mineral Technology, Map 18, scale 1:100,00. 

Keith, Stanley, Gest, D.E., DeWitt, Edward, Woode Toll, Netta, 

and Everson, B.A., 1983b, Metallic mineral districts and production in Arizona: Arizona Bureau of Geology and Mineral 

Technology Bulletin 194, 58 p. 

Kreidler, T.J., 1986, Mineral investigation of the Cactus Plains 

Wilderness Study Area, La Paz County, Arizona: U.S. Bureau of Mines Open File Report MLA 64--86, 11 p. 

Lasky, S.G., and Webber, B.N., 1949, Manganese resources of the 

Artillery Mountains region, Mohave Cmmty, Arizona: U.S. 

Geological Survey Bulletin 961, 86 p. 

Lee, W .T ., 1908, Geologic reconnaissance of part of western 

Arizona: U.S. Geological Survey Bulletin 352, pp. 14-15. 

Lehman, N.E., and Spencer, J.E., 1989, Mineralization in the central parts of the Planet mineral district, northwestern Buckskin 

Mountains, in Spencer, J.E., and Reynolds, S.J., eds., Geology and mineral resources of the Buckskin and Rawhide 

Mountains, west-central Arizona: Arizona Geological Survey 

Bulletin 198, p. 215-222. 

Lehman, N.E., Spencer, J.E., and Welty, J.W., 1987, Middle Tertiary mineralization related to metamorphic core complexes 

and detaclunent faults in Arizona and California: Society of 

Mining Engineers Preprint 87-21, 9 p. 

Levinson, A.A., 1980, Introduction to Exploration Geochemistry, 

second edition: Applied Publishing Ltd., Wilmette, illinois, 

924p. 

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

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

Osborne, G.M., 1981, The structural geology of the Squaw Peak 

area of the Buckskin Mountains, Ywna County, Arizona: Los 

Angeles, California, University of Southern California, M.S. 

thesis, 164 p. 

Otton, J.K., 1981, Geology and genesis of the Anderson mine, a 

carbonaceous lacustrine uraniwn deposit, western Arizona; a 

summary report: U.S. Geological Survey Open-File Report 

81-780,24 p. 

Raines, G.L., 1977, Digital color analysis of color ratio composite 

Landsat scenes: Proceedings, Eleventh International Symposium on Remote Sensing of Environment, Ann Arbor, University of Michigan, p. 1463-1472. 

Rehrig, W.A., and Reynolds, S.J., 1980, Geologic and geochronologic reconnaissance of a northwest-trending zone of metamorphic complexes in southern and western Arizona, in 

Crittenden M.D., Jr., Coney, P.J., and Davis, G.H., eds., Cordilleran metamorphic core complexes: Geological Society of 

America Memoir 153, p. 131-158. 

Reynolds, S.J., 1980, Geologic framework of west-central Arizona: Arizona Geological Society Digest, v. 12, p. 1-16. 

Reynolds, S.J., and Spencer, J.E., 1989, Pre-Tertiary rocks and 

structures in the upper plate of the Buckskin detaclunent fault, 

west-central Arizona, in Spencer, I.E., and Reynolds, S.J., eds., 

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Mountains, west-central Arizona: Arizona Geological Survey 

Bulletin 198, p. 67-102. 

Ryan, G.S., 1989, Mineral investigation of a part of the Swansea 

Wilderness Study Area (AZ-050-015A), La Paz and Mohave Counties, Arizona: U.S. Bureau of Mines Open-File 

Report MLA 12-89, 19 p. 

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Shackelford, T.J., 1976, Structural geology of the Rawhide 

Mountains, Mohave County, Arizona: Los Angeles, University of Southern California, Ph.D. thesis, 176 p. 

--1989, Structural geology of the Rawhide Mountains, Mohave County, Arizona, in Spencer, J.E., and Reynolds, S.J., 

eds., Geology and mineral resources of the Buckskin and 

Rawhide Mountains, west-central Arizona: Arizona Geological Survey Bulletin 198, p. 15-46. 

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and Pavlak, S.J., 1979, Major uranium discovery in 

volcaniclastic sediments, Basin and Range Province: American Association of Petroleum Geologists Bulletin, v. 63, 

p. 621-646. 

Spencer, J.E., 1989, Compilation geologic map of the Buckskin 

and Rawhide Mountains, west-central Arizona, in Spencer, 

J.E., and Reynolds. S.J., eds., Geology and mineral resources 

of the Buckskin and Rawhide Mountains, west-central Arizona: Arizona Geological Survey Bulletin 198, plate 3, scale 

1:100,000. 

Spencer, I.E .• · and Reynolds. S.J., 1986. Some aspects of the middle 

Tertiary tectonics of Arizona and southeastern California, in 

Beatty, Barbara, and Wilkinson, P.A.K., eds., Frontiers in 

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---1989, Tertiary structure, stratigraphy, and tectonics of the 

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mineralized areas in parts of the Buckskin, Rawhide, 

, McCracken, and northeast Harcuvar Mountains, western Arizona: Arizona Bureau of Geology and Mineral Technology 

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the lower Colorado River trough, Arizona and California: 

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• 

Mineral Resources of the Swansea Wilderness Study Area, La Paz and Mohave Counties, Arizona C19 
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. 

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B c 

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HIGH POTENTIAL HIGH POTENTIAL 

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MODERATE POTENTIAL MODERATE POTENTIAL 

UB uc 

LOW POTENTIAL LOW POTENTIAL 

LEVEL OF CERTAINTY 

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HIGH POTENTIAL 

tvVD 

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. 

C22 Mineral Resources of Wilderness Study Areas: Havasu Region, Arizona 
RESOURCE/RESERVE CLASSIFICATION 

IDENTIFIED RESOURCES UNDISCOVERED RESOURCES 

Demonstrated Probability Range 

Inferred 

Measured Indicated Hypothetical Speculative 

I Inferred 

I 

ECONOMIC Reserves 

Reserves 

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

MARGINALLY Marginal Inferred 

Marginal · ECONOMIC Reserves Reserves 

I I ----~---- f----------f- -~-

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. 

Mineral Resources of the Swansea Wilderness Study Area, La Paz and Mohave Counties, Arizona C23 
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 Sub period Miocene 

Tertiary Paleogene Oligocene 

Sub period 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 

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - (3 800?)- - - - - - - - - - - - - - - - - - -

pre-Archean2 

1Rocks older than 570 Ma also called Precambrian, a time term without specific rank. 

21nformal time term without specific rank. 

C24 Mineral Resources of Wilderness Study Areas: Havasu Region, Arizona 

AGE ESTIMATES OF 

BOUNDARIES IN 

MILLION YEARS (Ma) 

0.010 

1.7 

5 

24 

38 

55 

66 

- 96 

138 

205 

-240 

290 

-330 

360 

410 

435 

500 

1

-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 mcl~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. 

Clr'culars 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 1n.- 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. 

011 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 bepur'chased 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. 

Selectedcoplesofamonthlycatalog "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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