Mineral-Resources of the 

Woolsey Peak Wilderness Study Area, 

MariCopa Co ty, Ari · 

ARIZONA 
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Chapter F 

Mineral Resources of the 

Woolsey Peak Wilderness Study Area, 

Maricopa County, Arizona 

By JOCELYN A. PETERSON, JERRY R. HASSEMER, 

DANIEL H. KNEPPER, JR., JAMES A. PITKIN, and 

WILLIAM F. HANNA 

U.S. Geological Survey 

JOHN R. McDONNELL, JR. 

U.S. Bureau of Mines 

U.S. GEOLOGICAL SURVEY BULLETIN 1702 

MINERAL RESOURCES 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 Woolsey Peak Wilderness Study 

Area, Maricopa County, Arizona I by jocelyn A. 

Peterson ... [et al.]. 

p. em. - (Mineral resources of wilderness 

study areas-southwestern and south-central Arizona ; ch. 

F) (U.S. Geological Survey bulletin ; 1702) 

Bibliography: p. 

Supt. of Docs. no.: I 19.3:1702-F 

1. Mines and mineral resources-Arizona-Woolsey 

Peak Wilderness. 2. Woolsey Peak Wilderness (Ariz.) 

I. Peterson, jocelyn A. II. Series. Ill. Series: U.S. 

Geological Survey bulletin ; 1702-F. 

QE75.B9 no. 1702-F 557.3 s-dc19 89-600026 

[TN24.A6] [553 1

.09791 ?3] 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 resource assessment of part of the Woolsey Peak 

Wilderness Study Area (AZ-020-142/144), Maricopa County, Arizona. 

/ 
CONTENTS 

Summary 

Abstract 

Fl 

Fl 

Character and setting Fl 

Identified resources and mineral resource potential Fl 

Introduction F2 

Appraisal of identified resources F4 

Mining history F4 

Energy resources F4 

Mineral appraisal FS 

Assessment of mineral resource potential FS 

Geology FS 

Geochemistry F6 

Geophysics F7 

Gravity and magnetic data F7 

Landsat thematic mapper images and interpretation F8 

Aerial gamma-ray spectrometry F8 

Mineral and energy resources F8 

Barite, copper, molybdenum, lead, zinc, silver, and gold in epithermal veins FlO 

Commodities associated with quartz monzonite FlO 

Placer gold and platinum-group elements FlO 

Other commodities FlO 

Energy resources Fll 

References cited Fll 

Appendixes 

Definition of levels of mineral resource potential and certainty of assessment Fl4 

Resource/reserve classification Fl5 

Geologic time chart Fl6 

FIGURES 

1. Index map showing location of Woolsey Peak Wilderness Study Area, Maricopa County, 

Arizona F2 

2. Map showing generalized geology and mineral resource potential of Woolsey Peak Wilderness Study Area, Maricopa County, Arizona F3 

3. Bouguer gravity anomaly map of Woolsey Peak Wilderness Study Area, Maricopa County, 

Arizona F7 

4. Aeromagnetic anomaly map of Woolsey Peak Wilderness Study Area, Maricopa County, 

Arizona F9 

Contents V 
Mineral Resources of the 

Woolsey Peak Wilderness Study Area, 

Maricopa County, Arizona 

By Jocelyn A. Peterson, jerry R. Hassemer, Daniel H. Knepper, Jr., 

james A. Pitkin, and Wi II iam F. Hanna 

U.S. Geological Survey 

john R. McDonnell, Jr. 

U.S. Bureau of Mines 

SUMMARY 

Abstract 

The part of the Woolsey Peak Wilderness Study Area 

(AZ-020-142/144) requested for mineral surveys by the U.S. 

Bureau of Land Management encompasses 61 ,000 acres in 

southwestern Arizona. Throughout this report, reference to 

the Woolsey Peak Wilderness Study Area or to the study area 

refers only to that part of the wilderness study area requested 

for mineral surveys by the U.S. Bureau of Land Management. 

Fieldwork was carried out during the spring of 1985 and the 

winters of 1986 and 1987 by the U.S. Bureau of Mines and 

the U.S. Geological Survey to appraise the known mineral 

resources and to assess the mineral resource potential (undiscovered) of the study area. Inferred subeconomic resources 

of common variety rock and sand and gravel are present in 

the study area, but there are no identified locatable resources 

within the area even though there are some claims along its 

boundary. The study area has low resource potential for 

barite, copper, molybdenum, lead, zinc, silver, and gold in 

epithermal veins in the southwest and southeast corners of 

the study area and in a small area about 1 mi northwest of 

Bunyan Peak. Quartz monzonite on the northeast side of the 

study area has low resource potential for rare-earth elements 

such as lanthanum and for thorium and uranium in accessory 

minerals such as monazite. These rocks also have low resource potential for quartz, mica, and feldspar as well as rareearth elements, thorium, and uranium in the numerous pegmatites that are present. The east edge of the study area has 

low potential for gold and platinum-group elements in placers. The entire study area has low potential for copper resources in porphyry deposits on the basis of its regional 

geologic setting; however, specific data suggestive of a possible porphyry copper deposit are not present. Pumiceous 

Manuscript approved for publication December 28, 1988. 

rocks in the southwest corner of the study area have moderate potential for resources of pumice and Apache tears, the 

latter being primarily a commodity sought by rock collectors. 

The entire study area has low potential for geothermal energy 

resources. The area is not considered favorable for the discovery of oil and gas. 

Character and Setting 

The Woolsey Peak Wilderness Study Area 

(AZ--020-142/144) is located about 15 mi northwest of 

Gila Bend, in southwestern Arizona (fig. 1). The area is in 

the Sonora Desert section of the Basin and Range physiographic province, a region of large mountain ranges separated by alluvium-filled valleys. The study area is underlain primarily by Tertiary volcanic rocks (see geologic time 

chart in appendixes) that overlie quartz monzonite and 

metamorphic rocks of Proterozoic or Mesozoic age. Pediments and basin margins are covered by gravels, and 

washes contain alluvium. 

Identified Resources and Mineral Resource 

Potential 

Other than inferred subeconomic resources of common 

variety rock and sand and gravel, no mineral resources 

were identified in the study area. Traces of gold, silver, 

copper, manganese, niobium, platinum, uranium, and zinc 

detected in quartz monzonite samples suggest that metallicmineral concentrations could be present. 

The study area has low resource potential for barite, 

copper, molybdenum, lead, zinc, silver, and gold (fig. 2) in 

epithermal veins in the volcanic rocks of the southwest and 

southeast comers of the study area and about 1 mi northwest of Bunyan Peak in an area underlain by pyroclastic 

Mineral Resources of the Woolsey Peak Wilderness Study Area, Maricopa County, Arizona Fl 
rocks and felsic and basaltic flows. The quartz monzonite 

on the northeast side of the study area has a low resource 

potential for rare-earth elements such as lanthanum and for 

thorium and uranium in accessory minerals such as monazite. There is also low resource potential for quartz, mica, 

and feldspar and for rare-earth elements, thorium, and 

uranium in numerous pegmatites within quartz monzonite. 

Alluvium at the east edge of the study area has low resource potential for gold and platinum-group elements in 

placers, presumably derived from the metamorphic rocks in 

that area. On the basis of its regional geologic setting, the 

entire study area has low resource potential for copper in 

porphyry deposits. However, specific data suggestive of a 

porphyry copper deposits were not found. The southwest 

corner of the study area has moderate potential for resources of pumice and Apache tears, the latter being primarily a commodity sought by rock collectors, in the 

pumiceous rocks of Painted Rock Dam. The entire study 

area has low potential for geothermal energy resources 

33"00' 

AREA 

8 OF MAP 

Yellow Medicine 

'Bulle 

Face 

'Mountain 

Oatman 

• Mountain 

113"00' 

Harqua 

because of the proximity of warm-water wells and young 

volcanic rocks. The area is not considered favorable for the 

discovery of oil and gas. 

INTRODUCTION 

This mineral survey was requested by the U.S. Bureau 

of Land Management (BLM) and is the result of a 

cooperative effort by the U.S. Bureau of Mines (USBM) 

and the U.S. Geological Survey (USGS). An introduction 

to the wilderness review process, mineral survey methods, 

and agency responsibilities was provided by Beikman and 

others (1983). 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, claims, and 

mineralized areas. Identified resources are classified 

according to a system that is a modification of that 

described by M.cKelvey (1972)and U.S. Bureau of Mines 

) 

I 

Signal / 

'Mountain 1 

Woolsey I 

Spring,' 

I 

,• ... 

\ 

~ ,-

4 MILES 

I 

~I ._o/ 

Webb ;,s.~l \ 

' Mountain .,.J! / \ 0 I I 

i$-~'1"' : 

I 

( 

J 

112"45' 

"""'APPROXIMATE 

BOUNDARY 

OF 

WOOLSEY PEAK 

WILDERNESS 

STUDY AREA 

(AZ-020-142/144) 

Figure 1. Map showing location of Woolsey Peak Wilderness Study Area, Maricopa County, Arizona. 

F2 Mineral Resources of Wilderness Study Areas: Southwestern and South-Central Arizona 
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OTb 

Tft 

Tpp 

Tpb 

Ts 

qm 

m 

EXPL ANATIO N 

Geologic terrane having moderate resource potential (M) for pumice and 

Apache tears 

Geologic terrane having low resource potential (L) for geothermal energy and 

for copper in porphyry deposits 

Geologic terrane having low potential (L) for metallic resources in epithermal 

veins 

Geologic terrane having low resource potential (L) for quartz, mica, feldspar, 

rare-earth elements, thorium, and uranium in granitoid rocks 

Geologic terrane having low resource potential for gold and platinum-group 

elements in placer deposits 

Description of map units 

Alluvium and pediment gravels (Quaternary and Tertiary(?)) 

Basalt (Quaternary and Tertiary) 

Felsic and intermediate flows and tuffs (Tertiary) 

Pumiceous rocks of Painted Rock dam (Tertiary) 

Pyroclastic rocks of Bunyan Peak (Tertiary) 

Clastic and tuffaceous sedimentary rocks (Tertiary) 

Quartz monzonite (Mesozoic or Proterozoic) 

Metamorphic rocks (Mesowic or Proterozoic) 

L/C Bar, Cu, Mo,} 

Pb, Zn, Ag, A u 

/ 

/ 

..- / 

--, \ 

\ 

Pa inted Rock 

mining district 

\ 

\ 

' \ 

\ 

Ag 

AT 

Au 

Bar 

Cu 

Geo 

Mo 

112°55' 

Commodities 

Silver 

Apache tears 

Gold 

Barite 

Copper 

Geothermal energy 

Molybdenum 

\ 

' ' ' ' .... 

Pb 

PGE 

Pum 

Qtz 

REE 

Th 

Zn 

Webb 

mining 

district 

' 0 1 2 4 5 MILES ' \ 

\ ' ' ' 

Levels of cenainty of assessment 

Lead B Data only suggest level of potential 

Platinum-group elements c Data give good indication of level 

Pumice of potential 

Quartz, mica, and feldspar 

Rare-earth elements ........_,..... Contact Thorium and uranium 

Zinc --... Fault 

112°50' 

~--

:..!---Detectron ~ _ J ~ : _ ~ claims - . 

I 

I ~-----

t I 

I I 

1 Pe~;atite 1 claims l------

APPROXIMATE BOUNDARY 

OF 

WOOLSEY PEAK 

WILDERNESS STUDY AREA 

(AZ-020-142/144) 

Figure 2. Generalized geology and mineral resource potential of Woolsey Peak Wilderness Study Area, Maricopa County, Arizona. 
and U.S. Geological Survey (1980). USGS studies are 

designed to provide a scientific basis for assessing the 

potential for undiscovered mineral resources by 

determining geologic units and structures, possible 

environments of mineral deposition, presence of 

geochemical and geophysical anomalies, and applicable 

ore-deposit models. Goudarzi (1984) discussed mineral 

assessment methodology and terminology as they apply to 

these surveys. See appendixes for the definition of levels 

of mineral resource potential and certainty of assessment 

and for the resource/reserve classification. 

The BLM requested mineral surveys on 61,000 acres 

of the Woolsey Peak Wilderness Study Area (AZ-020-

142/144) in southwestern Arizona. The area is located 

about 15 mi northwest of Gila Bend, Ariz. (fig. 1), in the 

Sonora Desert section of the Basin and Range physiographic province, where mountain ranges are separated by 

broad alluvia ted valleys. The Woolsey Peak study area is 

in the southeastern part of the Gila Bend Mountains. It is 

centered around the prominent Woolsey and Bunyan Peaks, 

where elevations are 3,170 and 2,418 ft, respectively. 

Elevations along the south boundary adjacent to the Painted 

Rock Dam are about 600 ft. The area can be reached by 

unimproved dirt roads from all sides, although access to the 

interior is poor. The vegetation of the study area is that of 

the Lower Colorado River Valley subdivision of the Lower 

Sonoran Desertscrub Biotic Community (Brown, 1982), the 

largest and most arid of the Sonoran subdivisions. The 

dominant shrubs in the area include creosotebush (Larrea 

tridentata), incienso (Encelia farinosa), and white bursage 

(Ambrosia dwnosa). Widely spaced throughout the area 

are the small paloverde trees: Littleleaf paloverde (Cercidiwn microphyllum) and blue paloverde (C. floridum) and 

their hybrids. Saguaro (Carnegiea gigantea) is the dominant columnar cactus in the area; big galleta (Hilaria 

rigida) is the large common grass growing in dense clumps. 

The Woolsey Peak study area has local populations of wild 

boar, or javelina (Dicoty/es gajacu). 

Published geologic material about the study area is 

scant, except for generalized discussions in papers concerned primarily with the water supply of the region (Ross, 

1922, 1923; Babcock and Kendall, 1948; Coats, 1952). 

Cheeseman (1974) reported on the mineral occurrences in 

the Webb mining district adjacent to the northern part of 

the study area. Heindl and Armstrong (1963) discussed the 

geology of the Gila Bend Indian Reservation southeast of 

the Woolsey Peak area. Concurrent with this study is a 

study of the Signal Mountain Wilderness Study Area directly adjacent to the north (Gray and others, in press). 

The USBM reviewed the literature related to mineral 

occurrences and mining activity near Woolsey Peak, examined mining claim information and land status plats from 

the BLM, and studied mineral information and production 

data obtained from USBM files and other sources. In 

addition, mines and prospects within 2 mi of the study area 

were surveyed, mapped, and sampled in 1985 (McDonnell, 

1986). 

The geology of the study area was mapped in 1986 and 

1987 by J.A. Peterson and R.J. Miller, assisted by S.L. 

Jones (Peterson and others, in press); J.R. Hassemer collected stream-sediment and rock samples for geochemical 

analysis in 1986. Geophysical interpretations are based on 

published data. 

APPRAISAL OF IDENTIFIED RESOURCES 

By John R. McDonnell, Jr. 

U.S. Bureau of Mines 

Mining History 

The Woolsey Peak Wilderness Study Area is not in 

any organized mining district, and no mineral production 

has been recorded from within its boundaries. It lies at the 

south boundary of the Webb mining district and is 1 mi 

northeast of the Painted Rock mining district (fig. 2). The 

Webb district produced a small amount of copper, silver, 

and gold from mineralized quartz veins and includes bismuth and barium occurrences. The veins are in Proterozoic 

schist and gneiss that were intruded by granite, diorite, and 

andesite. The Painted Rock district produced some copper, 

lead, molybdenum, silver, and gold from quartz and barite 

veins in Tertiary volcanic rocks. These districts are near 

the study area, but the mineralized veins are not known to 

extend into the area. 

Placer and lode mining claims are north, east, and 

southwest of the study area and extend slightly into it along 

the east boundary. Although no active mining was observed during the USBM' s field investigation, preparations 

were under way on the ST AMSCO and contiguous claims 

(fig. 2) for exploratory drilling for gold and platinum-group 

elements to begin in late 1986 (Scott Hazen, claimant, oral 

and written commun., 1985). No activity was observed, 

however, during USGS field work in January 1987. 

Energy Resources 

No oil or gas discoveries have been reported in the 

vicinity, but leases on Federal land are scattered in and near 

the study area. According to Ryder (1983), the petroleum 

potential of the region surrounding the study area is "low to 

zero" on the basis of data from published literature. He 

concluded that hydrocarbons could accumulate only in the 

sediment-filled basins of the region and that the reservoirrock depths are generally too shallow for maturation. The 

study area is underlain by plutonic and volcanic rocks, 

which generally do not form reservoirs. Any oil or gas 

accumulation in nearby sedimentary rocks would have 

migrated or been destroyed by tectonic and magmatic activity. 

F4 Mineral Resources of Wilderness Study Areas: Southwestern and South-Central Arizona 
No geothermal waters or leasing activity are known in 

the study area. However, Witcher and o~ers (1982) considered two nearby areas as favorable for the discovery and 

development of low-temperature (less than 100 °C) geothermal resources: one 4 mi to the east, and the other 12 

mi to the southeast at Gila Bend. No thermal springs or 

wells are known in the study area. 

No uranium or thorium has been produced from the 

study area, but geochemical reconnaissance data and 

nearby prospecting (McDonnell, 1986) suggest that uranium- and thorium-enriched rocks may be present. The 

National Uranium Resource Evaluation program collected 

and analyzed water and stream-sediment samples from the 

vicinity (Bennett, 1981). Several stream-sediment samples 

from drainages in the northeastern and southeastern parts of 

the study area contain uranium and thorium concentrations 

at or above the regional mean; however, the above-background levels of uranium and thorium for rocks in the 

eastern part of the study area are well within regional 

averages. 

A uranium-bearing pegmatite deposit was reported by 

Krason and others (1982, p. 98, 198) on the Detectron and 

Pegmatite claims (fig. 2). The report, based on correspondence from the claimant to the BLM, includes assay values 

from "representative samples" of the pegmatite that range 

from 0.085 to 0.12 percent uranium oxide (U3

0 8

) (BLM 

file data). Three samples collected across the pegmatite by 

the USBM contain 5.5-29 parts per million (ppm) 

(0.00055-0.0029 percent) U30 8• 

Mineral Appraisal 

Occurrences of gold, silver, lead, niobium, platinumgroup elements, tantalum, thorium, titanium, uranium, and 

yttrium have been reported in faults, pegmatite dikes, and 

quartz monzonite within 1 mi of the study area's east 

boundary (Krason and others, 1982; BLM file data; Scott 

Hazen, claimant, oral and written commun., 1985). 

Thirty-five chip, select, grab, and stream-sediment 

samples, including five from inside the study area, were 

collected by the USBM from workings and mineralized 

areas. Selected samples were analyzed by fire assay for 

gold and silver, by fire assay combined with inductively 

coupled plasma-atomic emission spectrometry (ICP) for 

gold, silver, palladium, and platinum, by atomic absorption 

spectrophotometry for lead, by X-ray fluorescence for 

niobium and tantalum, by ICP for copper, manganese, lead, 

and zinc, and by fluorimetric analysis for uranium 

(McDonnell, 1986). All samples were analyzed by 

semiquantitative optical emission spectrography for 40 

elements (McDonnell, 1986). Complete analytical data are 

available at the U.S. Bureau of Mines, Intermountain Field 

Operations Center, Building 20, Denver Federal Center, 

Denver, CO 80225. 

Samples from the faults and pegmatites in the quartz 

monzonite contain traces to low values of gold, silver, 

copper, lead, manganese, niobium, platinum, uranium, and 

(or) zinc. However, exposures were insufficient and the 

values too erratic to make resource estimates. 

Common variety rock and sand and gravel are abundant and can be classed as inferred subeconomic resources. 

These commodities have no unique features and adequate 

resources are available closer to markets. 

ASSESSMENT OF MINERAL RESOURCE 

POTENTIAL 

By Jocelyn A. Peterson, Jerry R. Hassemer, 

Daniel H. Knepper, Jr., James A. Pitkin, and 

William F. Hanna 

U.S. Geological Survey 

Geology 

The Woolsey Peak Wilderness Study Area is underlain 

by volcanic rocks of Tertiary and Quaternary age and by 

quartz monzonite and metamorphic rocks of Proterozoic or 

Mesozoic age (Peterson and others, in press). Many pediments in the study area are covered by gravel and the 

washes contain alluvium. 

Metamorphic rocks and quartz monzonite crop out 

primarily in the northeast quarter of the study area. The 

metamorphic rocks are schists derived from sedimentary 

and volcanic rocks. They contain mostly quartz, feldspar, 

an~ biotite and are found between the ST AMSCO and 

Pegmatite claims (fig. 2). There has been some prospecting 

along copper-bearing veins in the metamorphic rocks. 

Fine- to coarse-grained equigranular quartz monzonite 

crops out extensively along the east margin of the study 

area and at one locality along the north margin. It is 

composed of plagioclase, potassium feldspar, quartz, and 

either biotite or muscovite locally. The quartz monzonite 

is intruded by numerous pegmatites and has quartz veins 

and epidote veinlets. The pegmatites increase in abundance 

to the south, and prospecting has occurred where a copperoxide coating is seen on fracture surfaces and in small 

veinlets. 

A poorly consolidated sequence of clastic and tuffaceous sedimentary rocks is interbedded with volcanic 

units in the northeast quarter of the study area and in small 

exposures elsewhere. The sequence consists of a heterogeneous mix of thin beds of alternating clastic and tuffaceous 

sedimentary rocks and includes one thin andesite flow. 

These rocks may correlate with the Sil Murk Formation 

found about 6 mi southeast of the study area (Heindl and 

Armstrong, 1963). 

Mineral Resources of the Woolsey Peak Wilderness Study Area, Maricopa County, Arizona FS 
Peterson and others (in press) mapped six main volcanic units within the study area. Andesitic pyroclastic 

rocks that underlie Bunyan Peak in the west-central part of 

the study area form a heterogeneous sequence of large-clast 

flow breccia, flows, and crystal-lithic tuffs. Rhyolitic 

pumice breccias and minor interbedded rhyolite flows, 

presumably related to rocks in the Painted Rock Mountains 

to the south, crop out in the southwest corner of the study 

area. The breccias contain mostly pumice and some obsidian. In the north-central part of the study area, intermediate 

to felsic tuffs and flows are characterized by the presence 

of hornblende phenocrysts as well as feldspar and quartz 

phenocrysts in an aphanitic groundmass or matrix. The 

three basalt flows mapped by Peterson and others (in press) 

are combined as unit QTb in this study (fig. 2). The basalts 

are all similar texturally and compositionally and are distinguished primarily by stratigraphic position and degree of 

weathering, although weathering in the younger Tertiary 

basalt and the Quaternary basalt is similar. These basalts 

underlie much of the study area and form most of the 

prominent ridges. 

Gravels of Tertiary(?) and Quaternary age are widespread on the pediments adjacent to the mountain ranges. 

In the mountains, large areas of talus flank the basalt flows. 

Washes contain poorly sorted alluvium. 

The area has a generally northwest-trending structural 

grain seen in the orientations of many of the mountain 

crests, in the strike of many of the faults, and in the strike 

and dip of tilted volcanic rocks. This grain reflects the 

basin-and-range faulting that created the Gila Bend Mountains and other ranges of southwestern Arizona. Faults and 

foliation that developed in the older crystalline rocks do not 

follow the prominent regional trend and presumably predate its development. 

Geochemistry 

A reconnaissance geochemical survey of the Woolsey 

Peak Wilderness Study Area, conducted in 1986, includes 

the study area, the Webb mining district to the north, and 

the Painted Rock mining district to the south. The USGS 

collected 74 sieved stream-sediment samples, 64 nonmagnetic heavy-mineral-concentrate samples, and 19 raw-concentrate samples from first-, second-, and third-order 

stream drainages. Sample density was about one site for 

each square mile in the northwestern part of the area, where 

some rhyolitic intrusions are present, and in the eastern 

part, where Proterozoic or Mesozoic rocks crop out. In 

basaltic terrain, sample density was about one site for every 

2 mP, whereas broad alluvial fans were sampled about 

every 4 mF. In addition, 22 rock and 2 water samples were 

collected. Data from the National Uranium Resource Evaluation (NURE) program (Bennett, 1981) were also used in 

the geochemical evaluation. Most samples collected in that 

study are from outside the study area but provide regional 

geochemical information for uranium and thorium. 

In both the USGS and the NURE studies, stream-sediment material was seived to minus-100 mesh and the fine 

fraction was retained for analysis. Each nonmagnetic 

heavy-mineral concentrate sample was panned from a 

composite sample of stream sediment to an approximate 

composition of half dark-colored (heavy) and half lightcolored minerals by using standard gold-panning techniques. This concentrate was then processed further 

through a heavy liquid and a magnetic separator to obtain 

a nonmagnetic heavy-mineral concentrate for analysis. 

The raw-concentrate sample was obtained by panning 

another, somewhat larger, sample of stream sediment until 

the sample was reduced to nearly 100 percent heavy minerals. The resulting raw-concentrate samples ranged from 

15 to 65 grams (g) from most of the study area but were 

150 to 1,200 g from the east side. A small split of sample 

material weighing about 0.1 g was used for spectrographic 

analysis; the rest of the sample was analyzed for gold and 

platinum. Rock samples were crushed, pulverized, and 

analyzed. 

All sediment and rock samples were analyzed for 31 

elements by a semiquantitative six-step, direct-current arc, 

optical emission spectrographic method (Grimes and Marranzino, 1968). Rock samples were also analyzed for arsenic, antimony, bismuth, and cadmium by an inductively 

coupled plasma-atomic emission spectroscopic method 

(Crock and others, 1987). The minus-100-mesh stream 

sediments were analyzed for uranium and thorium by 

neutron activation method (Millard and Keaton, 1982) and 

for 40 elements by another inductively coupled 

plasma-atomic emission spectroscopic method (Lichte and 

others, 1987). Raw-concentrate samples were analyzed for 

gold and platinum by atomic absorption spectroscopy (J .R. 

Hassemer, undocumented method modified from Thompson and others, 1968, and Swider, 1968). 

Many of the elements analyzed are anomalous in one 

or more of the sample media. Antimony, cadmium, gold, 

and platinum-group elements were found in samples from 

mines and prospects adjacent to the study area. On the 

basis of geochemical data from rock samples collected at 

nearby mines and prospects, arsenic, barium, copper, lead, 

silver, and zinc are the best indicators that epithermal 

deposits could be anticipated in the study area. 

Raw-concentrate samples contain (1) anomalous 

concentrations of manganese and vanadium throughout the 

study area, (2) weakly anomalous concentrations of copper, 

cobalt, chromium, and nickel in the northern and central 

parts of the study area, and (3) weakly anomalous 

concentrations of niobium in the northern part. Because 

these concentrations are near those determined as 

anomalous, little significance is given to them unless other 

elements, or elements in other media, are also anomalous. 

These near-threshold-level anomalies most likely reflect the 

F6 Mineral Resources of Wilderness Study Areas: Southwestern and South-Central Arizona 
widespread alteration and mineralization in the Proterozoic . 

or Mesozoic rocks and the influence of rock types such as 

basalt. 

Nonmagnetic-concentrate samples from the east 

boundary and outside of the study area commonly contain 

anomalous thorium (500-2,000 ppm), possibly in accessory 

thorite or monazite in the quartz monzonite, tungsten 

(70-1,500 ppm) in scheelite, and yttrium in an undetermined mineral, possibly monazite. These anomalies suggest that the quartz monzonite and associated pegmatites 

are permissive for concentrations of various metallic commodities. Samples collected from quartz monzonite within 

the northeastern part of the study area did not yield anomalous concentrations of these elements. Some samples from 

the southeast comer have anomalous barium (5,000 to more 

than 10,000 ppm), bismuth (200 to more than 2,000 ppm), 

molybdenum (10-200 ppm), lead (200-1,500 ppm), and 

weakly anomalous tin (10-150 ppm). One rock sample 

collected from that area contains 15 ppm molybdenum, 300 

ppm lead, and less than 200 ppm zinc; another rock sample 

contains 150 ppm lead. These anomalies suggest that the 

crystalline rocks in the southeast comer of the study area 

have been overprinted by a weak hydrothermal system 

containing the anomalous elements. Stream-sediment 

samples collected just east of the study area show weakly 

anomalous concentrations of rare-earth elements (cerium, 

europium, and neodymium), which probably are contained 

in an accessory mineral weathered from the quartz monzonite. 

Rare-earth-element concentrations are also high in the 

west-central part of the study area northwest of Bunyan 

Peak. Anomalous arsenic (20 ppm), barium (1,400 ppm), 

copper (110 ppm), vanadium (220 ppm), and zinc (140 

ppm) were also found in one stream-sediment sample from 

this area, and arsenic (10 ppm) was found in another 

stream-sediment sample. The samples are from drainages 

that erode the pyroclastic rocks of Bunyan Peak and the 

nearby felsic volcanic rocks. Because samples from other 

streams draining these units do not have anomalous element concentrations, the geochemically anomalous samples 

must represent localized mineralization. 

Low-level arsenic (10 ppm) and lead (62 ppm) anomalies in stream sediment collected near the pumiceous rocks 

of Painted Rock Dam are probably related to the same hydrothermal system that formed epithermal veins in the 

volcanic sequence of the Painted Rock Mountains. However, in the study area these rocks are not visibly altered. 

No anomalous uranium was found in stream-sediment 

samples. Only a few samples exceeded 5 ppm uranium and 

none exceeded 10 ppm. Water samples from Woolsey 

Spring and Gable Well No. 2 did not exceed 2 parts per 

billion uranium. NURE results also indicate a lack of 

uranium anomalies (Bennett, 1981). A weakly anomalous 

uranium concentration (29 ppm) was reported for a pegmatite sample (McDonnell, 1986) collected near the southeast 

comer of the study area; however, a NURE sample collected about 1 mi downstream showed only 2.6 ppm uranium (Bennett, 1981). Thus, geochemical data do not 

indicate uranium deposits in the study area. 

Geophysics 

Gravity and Magnetic Data 

The Woolsey Peak Wilderness Study Area is covered 

by regional gravity (Lysonski and others, 1980a, b; Aiken, 

1976; Aiken and others, 1981) and detailed aeromagnetic 

(U.S. Geological Survey, 1987) surveys, collectively having sufficient resolution to define anomalies of a few 

square miles or larger. Contours of complete (terrain-corrected) Bouguer gravity anomalies are defined by about 25 

gravity stations, all of which are near the periphery of the 

study area (fig. 3). Contours of aeromagnetic anomalies 

are defined by horizontal gradiometer measurements made 

along 21 east-west flightlines spaced about 0.5 mi apart at 

a mean terrain clearance of 1 ,000 ft. The gradiometer data, 

derived from a triad of magnetometers mounted on the 

aircraft wingtips and tail, were used to produce a gradientenhanced total-field aeromagnetic anomaly map (fig. 4). 

The Bouguer gravity anomaly map (fig. 3) is dominated by a westward-increasing prominent gradient over 

the east half of the study area, a saddle-shaped high immediately west of this gradient, and a subtle low at the west 

end of the area. The gradient is inferred to be caused by 

0 

I 

2 3 4 MILES 

I I I 

Figure 3. Bouguer gravity anomaly map of Woolsey 

Peak Wilderness Study Area, Maricopa County, Arizona. 

Contour interval 2 milligals; hachures indicate closed 

areas of lower anomaly values. Dots represent gravity 

observation points. 

Mineral Resources of the Woolsey Peak Wilderness Study Area, Maricopa County, Arizona F7 
a crustal boundary that separates a broad terrane containing 

abundant low-density basin fill to the east from higher 

density, mostly buried metamorphic rocks to the west. The 

saddle-shaped high appears to be a residual anomaly, also 

associated with the metamorphic rocks, formed in relation 

to the neighboring low to the west. This low is associated 

with low-density gravel and alluvium. 

The magnetic anomaly map (fig. 4) is dominated by 

several clusters of large-amplitude short-wavelength highs 

in the east half of the study area, one small-amplitude longwavelength high in the southwestern part of the study area, 

and one large-amplitude low in the northwest comer. Magnetic measurements of nine unoriented (with respect to 

north) rock samples of mapped units indicate that five of 

the units are sufficiently magnetic to generate these anomalies. 

The clusters of magnetic highs in the east half of the 

study area are associated principally with exposed basaltic 

units and quartz monzonite. The arcuate anomalies suggest 

a geometry commensurate with volcanic vents. In the area 

of Woolsey Peak, the basalt is 1,500 ft thick, estimated on 

geologic parameters, which agrees well with the anomaly 

of 1,500 nanoteslas amplitude, which is what is expected 

from modeling using measured magnetization. Where 

exposed magnetic rocks lack anomalies, we may infer one 

or more alternatives: the rocks may be thin and weathered 

and contain felsic phases, or they may be unusually magnetized (for example, a reversed magnetization may effectively cancel an induced magnetization). In the study area, 

we infer that the principal causes are thin volcanic rocks 

and felsic phases in underlying plutonic rocks. The broad 

magnetic high in the southwestern part of the study area is 

probably caused by buried basalt. The broad magnetic low 

in the northeast sector is enigmatic. Because of its large 

amplitude relative to surrounding features, it is possibly 

caused by reversely magnetized mafic rocks that may represent feeders to part of the basaltic pile. 

Landsat Thematic Mapper Images and Interpretation· 

Two Landsat Thematic Mapper (TM) color-composite 

spectral images for evaluating potential hydrothermal alteration were prepared for this study: a color-infrared 

composite (CIR), and a color .. ratio composite (CRC), both 

at approximately 1:150,000 scale. The CIR was used as an 

indirect measure of the albedo (brightness) of the rocks 

associated with potential alteration targets; the only such 

targets seen on the resulting map are associated with relatively bright rocks. The CRC image indicates some general 

mineralogical characteristics of the rocks and soils of the 

area. 

Because much of the bedrock in the quadrangle is 

volcanic, many of the potential alteration targets may be 

associated with local volcanic processes or weathering 

rather than with mineralization. Areas of silicic alteration 

cannot be detected using this technique. 

Potential alteration targets occur in two clusters in the 

northern part of the study area. The westernmost cluster is 

associated with a pattern distinctive of limonite; the targets 

represent apparent local concentrations of limonite. The 

eastern cluster, about 1 mi east of Spring Mountain (fig. 1), 

shows the presence of limonite and minerals of the clay 

group. Field examination of these targets indicated that 

most of them lie within or enclose outcrops of clastic and 

tuffaceous sedimentary rocks that have not been hydrothermally altered. The TM spectral-image data did not locate 

any unknown potentially mineralized areas within the study 

area. 

Aerial Gamma-ray Spectrometry 

Aerial gamma-ray spectrometry measures the nearsurface Oess than 2 ft deep) distribution of potassium (K), 

uranium (eU), and thorium (eTh). The e (for equivalent) 

prefix denotes the potential for disequilibrium in the uranium and thorium decay series. Because the distribution of -

these elements is controlled by geologic processes, aerial 

gamma-ray measurements can be used in geologic mapping, mineral exploration, and understanding of geologic 

processes. 

The spectrometry data were obtained between 1974 

and 1981 for the NURE program of the U.S. Department of 

Energy (1979). Four flightlines, 400ft above ground level, 

covered the study area: lines approximately along the north 

and south borders and two lines between them. Spectrometry data that include the study area are presented on radioelement contour maps and color-composite image maps 

(Duval, 1983) at scales of 1:500,000 and 1:1,000,000. The 

data described below were derived from the NURE report 

for the Phoenix 1° by 2° quadrangle (U.S. Department of 

Energy, 1979). 

Radioelement maps that include the Woolsey Peak 

Wilderness Study Area show two distinct regions. In the 

eastern one-third of the study area, concentrations of 3 to 

3.5 percent K, 6 to 8 ppm eU, and 9 to 10 ppm eTh reflect 

the more radioactive quartz monzonite and metamorphic 

rocks. Concentrations of 1 to 1.5 percent K, 2 to 3 ppm eU, 

and 2 to 6 ppm eTh in the western two-thirds of the area are 

related to the less radioactive volcanic rocks and alluvial 

material. The concentrations are not anomalous for the 

rocks in the study area. Mapping of any concentrations is 

controlled by the location of the NURE flightlines, and the 

sparse flightline coverage of the study area precludes deriving specific information on mineral resource potential from 

the aerial gamma-ray data. 

Mineral and Energy Resources 

Several types of mineral deposits are adjacent or close 

to the study area, including copper, silver, and gold veins 

of the Webb mining district directly north of the area, 

copper-lead-molybdenum-barite epithermal vein deposits in 

F8 Mineral Resources of Wilderness Study Areas: Southwestern and South-Central Arizona 
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113°00' 11 2°55' 112°50' 

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Figure 4. Aeromagnetic anomaly map of Woolsey Peak Wilderness Study Area, Maricopa County, Arizona. Contour intervals 20 (light) and 100 (bold) nanoteslas; 

hachures point toward closed areas of lower magnetic intensity. Dashed lines represent flightline traces . 
the Painted Rock Mountains south of the area, and pegmatites and placer claims east of the area. Geologically 

similar parts of the study area are permissive for such 

deposits, but abundant mineralization was not seen during 

the reconnaissance field studies. 

Barite, Copper, Molybdenum, Lead, Zinc, Silver, and 

Gold in Epithermal Veins 

Two different kinds of epithermal vein deposits are 

present adjacent to the study area. The Webb district 

contains copper, silver, and gold veins in pre-Tertiary 

metamorphic rocks. The epithermal vein deposits in the 

Painted Rock Mountains are found in Tertiary volcanic 

rocks. Largest of the veins is at the Rawley mine where 

molybdenum, lead, and barite have been the primary 

commodities produced (Stewart and Pfister, 1960). Veins 

similar to those of the Webb district could be present in 

both the quartz monzonite and metamorphic rocks within 

the study area, and several veins containing chrysocolla are 

known to be present in the area. Geochemical evidence 

indicates that a hydrothermal system may have affected the 

southeast comer of the area, which is underlain by quartz 

monzonite. This area has a low resource potential for 

barite, copper, molybdenum, lead, zinc, silver, and gold, 

certainty level B. Rocks of the Painted Rock Mountains 

consist of rhyolitic pumice breccias and are exposed in the 

southwest comer of the study area. Although there was no 

visual evidence of epithermal veins, these rocks have a low 

resource potential for barite, copper, molybdenum, lead, 

zinc, silver, and gold in epithermal vein deposits, certainty 

level C, because of weak geochemical anomalies for lead 

and arsenic. An area about 1 mi northwest of Bunyan Peak 

has geochemical anomalies indicative of hydrothermal 

activity, so the area has low resource potential, certainty 

level B, for barite, copper, molybdenum, lead, zinc, silver, 

and gold in epithermal deposits. 

Commodities Associated with Quartz Monzonite 

Pegmatite dikes form pronounced light-colored linear 

features in the quartz monzonite in and southeast of the 

study area. They are composed primarily of quartz with 

subordinate muscovite and rarely feldspar. Some of the 

pegmatites elsewhere in Arizona have been mined for these 

minerals (Keith, 1974). This study area is south of the 

main region of pegmatites in Arizona, where complex and 

rare minerals have been found. Nevertheless, nearby prospects for uranium (McDonnell, 1986) suggest that the 

pegmatites or accessory monazite in the host quartz monzonite may contain anomalous amounts of uranium, thorium, and (or) rare-earth elements. The aerial gamma-ray 

data also suggest the presence of slightly higher concentrations of uranium and thorium in quartz monzonite on the 

northeast side of the study area. Therefore, in the northeastern part of the study area the resource potential is low 

for quartz, mica, and feldspar in pegmatites within the 

quartz monzonite, certainty level B, and is also low, certainty level B, for uranium, thorium, and rare-earth elements in both the pegmatites and the enclosing quartz 

monzonite. 

Placer Gold and Platinum-group Elements 

Placer claims adjacent to the study area are inactive, 

although there were plans to begin a drilling operation on 

one of them (McDonnell, 1986). There does not appear to 

have been production from any of these claims. Analyses 

of samples collected at claims east of the study area show 

low levels of gold, silver, niobium, platinum-group elements, and uranium. These elements probably weathered 

out of the quartz monzonite and metamorphic rocks adjacent to the placer accumulations. The source of the platinum is uncertain; it may have been derived from metasedimentary rocks that received the platinum as a depositional 

product from an unknown source. Numerous pediments in 

the study area are covered by a thin layer of gravel. Most 

of these gravels are derived from basaltic rocks, but, along 

the east border of the study area, pediment gravel and alluvium that are underlain by or adjacent to quartz monzonite 

could possibly contain minor accumulations of these elements. Therefore, pediments adjacent to older rocks along 

the east border of the study area have a low resource potential for gold and platinum-group elements in placer deposits, certainty level C. 

Other Commodities 

The Woolsey Peak Wilderness Study Area lies northwest of the major porphyry copper deposits of Arizona, but 

in recent decades new deposits have been found beneath 

pediments. No alteration characteristic of porphyry copper 

deposits was seen in the study area, but the crystalline 

rocks do have small copper occurrences. The study area is 

permissive, then, for a buried porphyry copper deposit on 

the basis of the regional geologic setting and has a low potential, certainty level B, for copper in porphyry copper deposits. 

Three of the rock units within the study area contain 

pumice lapilli, at least locally, although the pumice usually 

constitutes only a small amount of the total rock volume. 

Isolated occurrences of nearly 100 percent pumice are 

present in exposures of the clastic and tuffaceous sedimentary rocks (Ts) and the pumiceous rocks of Painted Rock 

Dam (Tpp) units. Small amounts of pumice from the 

pumiceous rocks of Painted Rock Dam have been removed 

from a pit just outside the southwest boundary of the study 

area. The rocks within this unit have a moderate potential 

for pumice, certainty level C. 

In addition to pumice, the rocks by Painted Rock Dam 

locally contain Apache tears, which are sought by rock 

collectors. According to several rock collectors we talked 

Fl 0 Mineral Resources of Wilderness Study Areas: Southwestern and South-Central Arizona 
to at the site, most of these particular Apache tears are 

rather small, but occasionally larger ones can be found. 

They are only known from one outcrop, but they may be 

present in other parts of the unit where obsidian is abundant. The pumiceous rocks of Painted Rock Dam (Tpp) 

have a moderate resource potential for Apache tears, certainty level C. 

Energy Resources 

The Woolsey Peak study area is surrounded by four 

sedimentary basins that contain warm-water wells and 

springs. These include the large Agua Caliente-Hyder area 

about 25 mi to the west, an area north of Cotton Center 

about 5 mi to the east, an area north of Gillespie about 15 

mi to the north, and a small area centered in Gila Bend 

(Witcher and others, 1982). Such sedimentary basins, 

however, are not in the study area. The relatively recent 

eruption of basalt from Woolsey Cone (Peterson and others, in press) suggests that above-average temperatures may 

be present beneath the area. Because there are no known 

hot springs or basins in the study area, however, the resource potential for geothermal energy is low, certainty 

level B. 

Although the area has some oil and gas leases 

(McDonnell, 1986), there have been no discoveries near the 

study area and Ryder (1983) rates the area as having low to 

zero potential. Because the study area is underlain by 

crystalline rocks and basalt, it has no potential for oil and 

gas resources, certainty level D. 

REFERENCES CITED 

Aiken, C.L.V., 1976, Analysis of gravity anomalies in Arizona: 

Tucson, University of Arizona, Ph.D. dissertation, 127 p. 

Aiken, C.L.V .• Lysonski, J.C., Sumner, J.S., and Hahman, W.R., 

1981, A series of 1:250,000 complete residual Bouguer 

gravity anomaly maps of Arizona: Arizona Geolo~ical 

Society Digest, v. 13, p. 31-37. 

Babcock, H.M., and Kendall, K.K., 1948, Geology and groundwater resources of the Gila Bend basin, Maricopa County, 

Arizona: U.S. Geological Survey open-file report, 20 p. 

Beikman, H.M., Hinkle, M.E., Freiders, 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. 

Bennett, C.B., 1981, Phoenix 1° x 2° NTMS area, California and 

Arizona, data report (abbreviated) for the National Uranium 

Resource Evaluation program: Prepared for the U.S. Department of Energy by E.l. duPont de Nemours and Company, 

Savannah River Laboratory, Aiken, SC, GJBX-315(81), 20 

p. 

Brown, D.E., 1982, Biotic communities of the American southwest-United States and Mexico: Desert Plants, v. 4, 342 p. 

Cheeseman, R.I., 1974, The geology of the Webb Mountain district, Gila Bend Mountains, Maricopa county, southwest Arizona: Flagstaff, Northern Arizona University, M.S. thesis, 

69 p. 

Coats, D.R., 1952, Gila Bend basin, Maricopa County, in Halpenny, L.C., and others, Ground water in the Gila River 

basin and adjacent areas, Arizona-a summary: U.S. Geological Survey open-file report, p. 159-164. 

Crock, J.G., Briggs, P.H., Jackson, L.L., and Lichte, F.E., 1987, 

Analytical methods for the analysis of geologic materials: 

U.S. Geological Survey Open-File Report 87-84, 35 p. 

Duval, J.S., 1983, Composite color images of aerial gamma-ray 

spectrometric data: Geophysics, v. 48, no. 6, p. 722-735. 

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

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

Report 84-787, 51 p. 

Gray, Floyd, Miller, R.I., Pitkin, J.A., Hanna, W.F., and Kreidler, 

T.J., in press, Mineral resources of the Signal Mountain 

Wilderness Study Area, Maricopa County, Arizona: U.S. 

Geological Survey Bulletin, 1702-C. 

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

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

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

Heindl, L.A., and Armstrong, C.A., 1963, Geology and groundwater conditions in the Gila Bend Indian Reservation, Maricopa County, Arizona: U.S. Geological Survey Water Sup-· 

ply Paper 164 7-A, 48 p. 

Keith, S.B., 1974, Index of mining properties in Pima County, 

Arizona: Arizona Bureau of Mines Bulletin 189, 156 p. 

Krason, J., Wodzicki, A., and Cruver, S.K., 1982, Geology, energy, and mineral resources assessment in the Kofa area, Arizona: prepared for U.S. Bureau of Land Management by 

Geoexplorers International, Inc., Denver, Colo., 207 p. 

Lichte, F.E., Golightly, D.W., and Lamothe, P.J., 1987, Inductively coupled plasma-atomic emission spectroscopy, in 

Baedecker, P.A., ed., Methods for geochemical analysis: 

U.S. Geological Survey Bulletin 1770, p. Bl-BlO. 

Lysonski, J.C., Sumner, J.S., Aiken, C.L.V., and Schmidt, J.S., 

1980a, Complete residual Bouguer gravity anomaly map of 

Arizona: Arizona Bureau of Geology and Mineral Technology, scale 1:500,000. 

---1980b, The complete residual Bouguer gravity anomaly 

map of Arizona (ISGN 71): Tucson, University of Arizona, 

Department of Geoscience, Laboratory of Geophysics, scales 

1:500,000 and 1:1,000,000. 

McDonnell, J.R., Jr., 1986, Mineral investigation of a part of the 

Woolsey Peak Wilderness Study Area (AZ--020-142/144), 

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

Land Assessment Open-File Report 46-86, 14 p. 

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

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

Millard, H.T., Jr., and Keaton, B.A., 1982, Precision of uranium 

and thorium determinations by delayed neutron counting: 

Journal of Radioanalytical Chemistry, v. 72, p. 489-500. 

Peterson, J.A., Miller. R.I., and Jones, S.L., in press, Geologic 

map of the Woolsey Peak Wilderness Study Area, Maricopa 

County, Arizona: U.S. Geological Survey Miscellaneous 

Field Studies Map MF-2044, scale 1:48,000. 

Peterson, J.A., Nowlan, G.A., Hanna, W.F., Pitkin, J.A., and 

McDonnell, J.R., Jr., 1988, Mineral resources of the Table 

Top Mountain Wilderness Study Area, Maricopa and Pinal 

Mineral Resources of the Woolsey Peak Wilderness Study Area, Maricopa County, Arizona Fll 
Counties, Arizona: U.S. Geological Survey Bulletin 

1702-A, 18 p. 

Ross, C.P., 1922, Geology of the Lower Gila region, Arizona: 

U.S. Geological Survey Professional Paper 129, p. 183-197. 

---1923, The Lower Gila region, Arizona, a geographic, 

geologic, and hydrologic reconnaissance with a guide to 

desert watering places: U.S. Geological Survey Water 

Supply Paper 498, p. 19-23, 157-159. 

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

Arizona, in Petroleum potential of wilderness land in the 

western United States: U.S. Geological Survey Circular 

902-C, p. C1-C22. 

Stewart, L.A., and Pfister, A.J., 1960, Barite deposits of Arizona: 

U.S. Bureau of Mines Report of Investigations 5651, 89 p. 

Swider, R.T., 1968, The atomic absorption determination of platinum in geochemical and mining samples: Atomic Absorption Newsletter, v. 7, no. 6, p. 111-112. 

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

Rapid analysis for gold in geological materials: U.S. Geological Survey Professional Paper 600-B, p. B 130-B 132. 

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, Colorado-Arizona area, 

Salton Sea, Phoenix, El Centro, Ajo, Lukeville quadrangles: 

U.S. Department of Energy, Report GJBX-12(80), v. II. 

U.S. Geological Survey, 1987, Aeromagnetic map of the Woolsey 

Peak-Dendora Valley area, southwestern Arizona: U.S. 

Geological Survey Open-File Report 87-333, scale 1:50,000. 

Witcher, J.C., Stone, Claudia, Rahman, W.R., Sr., 1982, Geothermal resources of Arizona: Tucson, Arizona Bureau of 

Geology and Mineral Technology, scale 1:500,000. 

F12 Mineral Resources of Wilderness Study Areas: Southwestern and South-Central Arizona 
APPENDIXES 
DEFINITION OF LEVELS OF MINERAL RESOURCE POTENTIAL 

AND CERTAINTY OF ASSESSMENT 

LEVELS OF RESOURCE POTENTIAL 

H HIGH mineral resource potential is assigned to areas where geologic, geochemical, and geophysical characteristics indicate a geologic environment favorable for resource occurrence, where interpretations of data 

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

indicating presence of resources, and where evidence indicates that mineral concentration has taken place. 

Assignment of high resource potential to an area requires some positive knowledge that mineral-forming processes 

have been active in at least part of the area. 

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

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

indicate reasonable likelihood for resource accumulation, and (or} where an application of mineral-deposit models 

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

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

define a geologic environment in which the existence of resources is permissive. This broad category embraces 

areas with dispersed but insignificantly mineralized rock, as well as areas with little or no indication of having 

been mineralized. 

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

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

moderate, or high level of resource potential. 

LEVELS OF CERTAINTY 

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

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 

-I 

<( 

i= 

z 

UJ 

1-

0 

c.. 

UJ 

u 

ea::::: 

:::) 

0 

V> 

UJ 

ea::::: 

u.. 

0 

-I 

UJ 

> UJ 

-I 

A 

U/A 

UNKNOWN POTENTIAL 

Abstracted with minor modifications from: 

8 c 

H/8 H/C 

HIGH POTENTIAL HIGH POTENTIAL 

M/8 M/C 

MODERATE POTENTIAL MODERATE POTENTIAL 

U8 uc 

LOW POTENTIAL LOW POTENTIAL 

LEVEL OF CERTAINTY 

D 

H/D 

HIGH POTENTIAL 

M/D 

MODERATE POTENTIAL 

L/D 

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. 

F14 Mineral Resources of Wilderness Study Areas: Southwestern and South-Central Arizona 
RESOURCE/RESERVE CLASSIFICATION 

IDENTIFIED RESOURCES UNDISCOVERED RESOURCES 

Demonstrated Probability Range 

Inferred 

Measured Indicated Hypothetical Speculative 

I Inferred 

I 

ECONOMIC Reserves Reserves 

I 1----------- I ----~----

Inferred 

-~-

MARGINALLY Marginal Marginal ECONOMIC Reserves Reserves ____ j_ ____ - 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. 

Mineral Resources of the Woolsey Peak Wilderness Study Area, Maricopa County, Arizona FlS 
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 

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

pre-Archean2 

1Rocks older than 570 Ma also called Precambrian, a time term without specific rank. 2 lnformal time term without specific rank. 

F16 Mineral Resources of Wilderness Study Areas: Southwestern and South-Central 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 
GPO 685-041 /9789 
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