Mineral Resources of the 

Cowboy Spring Wilderness Study 

Area, Hidalgo County, New Mexico

U.S. GEOLOGICALSURVEY BULLETIN 1735-F

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Chapter F

Mineral Resources of the 

Cowboy Spring Wilderness Study 

Area, Hidalgo County, New Mexico

by WILLIAM E. BROOKS, JERRY R. HASSEMER, 

JOSEPH S. DUVAL, and WILLIAM F. HANNA 

U.S. Geological Survey

DAVID C. SCOTT 

U.S. Bureau of Mines

U.S. GEOLOGICAL SURVEY BULLETIN 1735

MINERAL RESOURCES OF WILDERNESS STUDY AREASSOUTHWESTERN NEW MEXICO
DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, JR., Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

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UNITED STATES GOVERNMENT PRINTING OFFICE: 1989

For sale by the

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Library of Congress Cataloging-in-Publication Data

Mineral resources of the Cowboy Spring Wilderness Study Area, Hidalgo 

County, New Mexico.

(Mineral resources of wilderness study areas southwestern New Mexico ; 

ch. F) (U.S. Geological Survey bulletin ; 1735) 

Bibliography: p. 

Supt. of Docs, no.: I 19.3:1735-F

1. Mines and mineral resources New Mexico Cowboy Spring Wilderness.

2. Cowboy Spring Wilderness (N.M.) I. Brooks, William E. II. Series. 

III. Series: U.S. Geological Survey bulletin ; 1735.

QE75.B9 no. 1735-F 557.3 S [553'.09789'693] 88-607944 

[TN24.N6]
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 a part of the Cowboy Spring 

(NM-030-007) Wilderness Study Area, Hidalgo County, New Mexico.

CONTENTS

Abstract Fl 

Summary Fl

Character and Setting Fl 

Identified Mineral Resources Fl 

Mineral Resource Potential Fl 

Introduction F2

Investigations by the U.S. Bureau of Mines F3 

Investigations by the U.S. Geological Survey F3 

Appraisal of Identified Resources F3

Mining and Mineral-exploration History F3 

Assessment of Potential for Undiscovered Resources F3 

Geology F3 

Geochemistry F6

Introduction F6 

Analytical Methods F6 

Results F6 

Geophysics F7

Aerial Gamma-ray Spectroscopy F7 

Gravity and Magnetic Data F8 

Mineral and Energy Resources F9 

Metals F9 

Fluorspar F9 

Oil and Gas F9 

Geothermal Energy F9 

Recommendations for Future Work F9 

References Cited F9 

Appendix F13

FIGURES

1. Summary and index map F2

2. Geologic map F4

3. Bouguer gravity anomaly map F8

4. Aeromagnetic anomaly map F8

Contents

MINERAL RESOURCES OF WILDERNESS STUDY AREAS-SOUTHWESTERN NEW MEXICO

Mineral Resources of the

Cowboy Spring Wilderness Study Area,

Hidalgo County, New Mexico

By William E. Brooks, Jerry R. Hassemer, 

Joseph S. Duval, and William F. Hanna 

U.S. Geological Survey

David C. Scott

U.S. Bureau of Mines

ABSTRACT

The Cowboy Spring Wilderness Study Area 

(NM-030-007) is in the Animas Mountains in Hidalgo 

County, southwestern New Mexico. The 6,699-acre study 

area is about 15 mi (miles) north of the international border 

between the United States and Mexico. This area is sparsely 

populated and access to the study area is by light-duty roads 

leading to the study area and four-wheel-drive roads and 

trails within the study area.

No identified mineral resources, mines, prospects, 

mineralized areas, or mineral resources were found within 

the study area. Evaluation of geologic mapping, geophysical 

studies, and a reconnaissance stream-sediment geochemical survey indicate that the mineral resource potential for 

undiscovered metals, fluorspar, oil and gas, and geothermal 

energy in the Cowboy Spring Wilderness Study Area is low.

SUMMARY 

Character and Setting

The Cowboy Spring Wilderness Study Area 

(NM-030-007) is in Hidalgo County in southwestern New 

Mexico, about 15 mi north of the border between the United 

States and Mexico (fig. 1). At the request of the U.S. Bureau 

of Land Management, the 6,699-acre Cowboy Spring 

Wilderness Study Area was examined. For convenience, this 

area is referred to in this report as the "study area." The study 

area is accessible by light-duty roads leading to the study

Manuscript approved for publication December 16, 1988

area and four-wheel-drive roads and trails within the study 

area. Elevations range from 4,920 ft (feet) in the eastern part 

of the study area to 6,601 ft at Elephant Butte.

Cretaceous to Quaternary (see geologic time chart in 

Appendix) sedimentary rocks that include sandstone, 

limestone, and conglomerate are exposed just north of the 

study area and in a small area in the eastern part of the study 

area. Tertiary volcanic rocks are the chief rock types exposed 

in the study area. One of the rock units that is widely 

'distributed in the Animas Mountains and south of the study 

area may be as thick as 3,000 ft. These rocks are associated 

with a large volcanic structure known as the Cowboy Rim 

cauldron.

Identified Mineral Resources

No mineral resources were identified nor were any 

mines, prospects, or mineralized areas found within the 

study area. However, modest amounts of silver, gold, 

copper, and fluorrte were reported to have been produced 

from the Gillespie mine, approximately 1.5 mi northwest of 

the study area, and silver and lead were produced from the 

Red Hill mine, approximately 4 mi northeast of the study 

area. The mineralized rock formations at the Gillespie mine 

and the Red Hill mine do not crop out in the study area.

Mineral Resource Potential

Results of a stream-sediment geochemical survey 

yielded no evidence to indicate exposed mineralized rock in 

the study area. Similarly, a uniform gravity gradient and a low 

aeromagnetic gradient within the study area indicate little 

likelihood of the kinds of concealed structures that could be

Cowboy Spring Wilderness Study Area F1
108°45' 108°30'

Red Hill mine

o. 1 Forest Federal well

v/ Gillespie mine

APPROXIMATE BOUNDARY 

OF COWBOY SPRING 

WILDERNESS STUDY AREA 

(NM-030-00 7)

USA

MEXICO 5 MILES 

J

EXPLANATION

-^ Axis of Winkler anticline showing directions

of plunge

Geologic terrane having low mineral resource 

potential for all metals, fluorspar, oil 

and gas, and geothermal energy, all with 

certainty level C Applies to entire 

study area

LEVELS OF CERTAINTY

Data indicate geologic environment, 

indicate resource potential, but 

do not establish activity of 

resource-forming processes

Figure 1. Summary and index map showing mineral 

resource potential and location of the Cowboy Spring 

Wilderness Study Area, New Mexico.

favorable sites for mineralization. A moderately strong 

thorium anomaly is suggested by airborne gamma-ray 

spectroscopy, but no mineralized rock was found.

The mineral resource potential for undiscovered metals 

is low because the rocks within the study area show little 

evidence of hydrothermal alteration, silicification, or faulting.

Analyses of rock-chip and stream-sediment samples indicate 

no anomalous concentrations of metals.

The mineral resource potential for undiscovered fluorspar is low because of the absence of favorable host rock. 

Fluorspar occurrences near the study area are found in 

faulted and fractured Pennsylvanian and Permian Horquilla 

Limestone. This formation does not crop out within the study 

area.

The energy resource potential for undiscovered oil and 

gas is low because the wilderness study area is in a volcanic 

complex. The great thickness of the volcanic rocks (3,000 ft), 

combined with the distribution and effects of plutonic and 

volcanic centers, creates a difficult environment for 

petroleum accumulation. A well drilled 1.25 mi north of the 

study area on the Winkler anticline was dry.

The absence of hot springs and other surface 

indications of geothermal activity in the study area, combined 

with only marginally favorable geothermal gradients in wells 

outside the study area, give it a low potential for 

undiscovered geothermal resources.

INTRODUCTION

The Cowboy Spring Wilderness Study Area (NM030-007) is in the southern Animas Mountains 

northwest of Playas Valley in southwestern New Mexico. 

Light-duty roads provide access leading to the study area 

and four-wheel-drive roads and trails provide access 

within the study area. The study area is about 15 mi north 

of the international border between the United States 

and Mexico. Elevations range from 4,920 ft in the eastern 

part of the study area to 6,601 ft at Elephant Butte, a 

prominent feature found along Cowboy Rim (fig. 2).

This report presents an evaluation of the mineral 

endowment (identified resources and mineral resource 

potential) of the study area and is the product of several 

separate studies by the U.S. Bureau of Mines (USBM) 

and the U.S. Geological Survey (USGS). Identified 

resources are classified according to the system of the 

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

(1980), which is shown in the Appendix of this report. 

Identified resources are studied by the USBM. Mineral 

resource potential is the likelihood of occurrence of 

undiscovered metals and nonmetals, industrial rocks and 

minerals, and of undiscovered energy sources (coal, oil, 

gas, oil shale, and geothermal sources) and is classified 

according to the system of Goudarzi (1984) shown in the 

Appendix. Undiscovered resources are studied by the 

USGS.

An assessment of the mineral resource potential of 

the Cowboy Spring Wilderness Study Area was made by 

compiling geological, geochemical, and geophysical 

information from earlier published reports as well as 

from recent studies carried out by the USBM and USGS.

F2 Mineral Resources of Wilderness Study Areas Southwestern New Mexico
Investigations by the 

U.S. Bureau of Mines

During 1986, personnel from the USBM Intermountain Field Operations Center investigated the 

mineral resources of the Cowboy Spring Wilderness 

Study Area. Prior to field work, a review of publications 

on the geology, mineralization, and mining activity in and 

near the study area was completed. Field work included 

a search for mines, prospects, and mineral occurrences in 

the study area. Reconnaissance of the study area was by 

four-wheel-drive vehicle and foot traverse.

Two panned-concentrate samples were taken from 

Elephant Butte Canyon (fig. 2) and were analyzed for 

gold by fire assay/atomic absorption and for thirty 

additional elements by inductively coupled plasmaatomic emission spectroscopy. Results of analyses and 

sample localities are given in Scott (1987). Additional 

information is available from the Bureau of Mines, 

Branch of Mineral Land Assessment (MLA), Intermountain Field Operations Center, Box 25086, Denver, 

CO 80225.

Investigations by the 

U.S. Geological Survey

Geologic mapping, geochemical sampling, and 

geophysical studies were used to evaluate the mineral 

resource potential of the Cowboy Spring Wilderness 

Study Area in relation to the types of deposits likely to be 

found in this volcanic environment. Assessment of the 

mineral resource potential is based on Goudarzi (1984) 

(see Appendix).

Regional geologic maps that included the study 

area (Zeller and Alper, 1965; Erb, 1979) were used as 

part of this study. Remapping and sampling of the study 

area was done during 1987, and a geologic map of the 

study area was prepared (fig. 2).

During 1987, a stream-sediment geochemical 

survey of the Cowboy Spring Wilderness Study Area was 

conducted as part of the mineral resource evaluation.

APPRAISAL OF IDENTIFIED RESOURCES

By David C. Scott 

U.S. Bureau of Mines

Mining and Mineral-exploration History

As of April 1987, no patented or unpatented 

mining claims were on file with the U.S. Bureau of Land 

Management for any acreage in the study area. No 

evidence of any type of mining activity was found during 

the field investigation. The entire area is covered by oil 

and gas leases.

Although no mining districts are in the study area, 

the Red Hill (Gillespie) mining district is about 1 mi 

north of the study area. This district includes the 

Gillespie and Red Hill mines and the Winkler anticline 

(fig. 1). Prospecting in the district and the general region 

of the study area began in 1880 when lead- and silverbearing veins in Tertiary ash-flow tuff and Pennsylvanian 

and Permian Horquilla Limestone were found at the 

Gillespie mine. Most of the mineral production from the 

district came from the Red Hill mine from which 3,746 

tons of ore, yielding 1,019,500 Ibs (pounds) of lead and 

14,249 oz (ounces) of silver were produced (Elston, 

1965).

Production of fluorspar in southwestern New Mexico began in the 1880's, and the last significant 

production was in 1954 (Rothrock, 1970). More than 60 

percent of the crude fluorspar production for the period 

1909-1962 came from mines in the southwestern part of 

the state where only 42 percent of the deposits are 

located (Williams, 1966).

During the 1960's, several trenches and pits were 

excavated on fluorite-bearing outcrops on the Winkler 

anticline. The fluorspar occurs in concordant silicified 

limestone fault-breccia zones in both the Pennsylvanian 

and Permian Horquilla (Drewes and Thorman, 1980) 

and Cretaceous U-Bar Formations. In 1970-71, the 

Texas Lime Company conducted a fluorspar exploration 

project on the Winkler anticline. Approximately 150,000 

tons of rock containing 25-35 percent CaF2 (fluorite) 

were defined by drilling but no production is known 

(McAnulty, 1972).

No mines, prospects, or mineral resources were 

found in the study area. The Pennsylvanian-, Permian-, 

and Cretaceous-age sedimentary rocks that make up the 

Winkler anticline, which hosts silicified limestone faultbreccia zones containing fluorspar, are not exposed in the 

study area. If these rocks are present in the study area, 

they are buried by accumulations of Tertiary Gillespie 

Tuff. No silver-lead vein-type occurrences, such as those 

at the Gillespie and Red Hill mines, were found in the 

Tertiary rocks of the study area.

ASSESSMENT OF POTENTIAL FOR 

UNDISCOVERED RESOURCES

By William E. Brooks, Jerry R. Hassemer, 

Joseph S. Duval, and William F. Hanna 

U.S. Geological Survey

Geology

The Cowboy Spring Wilderness Study Area is in 

the Animas Mountains in southwestern New Mexico in

Cowboy Spring Wilderness Study Area F3
108°40' 108°37'30"

31°37'30"

31°35'

T 31 S 

T 32 S

Base from U.S. Geological Survey, 1:24,000, 1982 

Center Peak, Gillespie Mountain, Horse 

Mountain, Walnut Wells NE

1 MILE 

j

R 18 W R 17 W 

Geologic mapping by W.E. Brooks, 1987; 

assisted by Ruben Martmez

Figure 2 (above and facing page). Geologic map of the Cowboy Spring Wilderness Study Area.

F4 Mineral Resources of Wilderness Study Areas Southwestern New Mexico
CORRELATION OF MAP UNITS

Tbs

QTa 

Tp

Tcp

Tg

QTa

Tp

Tcp

Tg

Tbbc

Teh

Tbc

TKt

Km

Holocene to Miocene [} QUATERNARY

Tbb

>- Oligocene

Lower Cretaceous

TERTIARY

- CRETACEOUS

DESCRIPTION OF MAP UNITS

Alluvium (Quaternary and Tertiary) Unconsolidated sediment along watercourses and on slopes

Ash-flow tuff of the Park (Oligocene) Gray, rhyolitic, crystalpoor ash-flow tuff containing chatoyant sanidine (1 mm), 

quartz, minor plagioclase, and altered biotite; flattened 

white pumice is common. Locally has a thin (less-than0.5-m-thick) pyroclastic unit at base (unmapped). K-Ar 

sanidine dates of 27.8±0.6 (Elston and Erb, 1977) and 

29.6±0.6Ma(Erb, 1979)

Andesite of Center Peak (Oligocene) Gray andesite; porphyritic, contains hornblende (1.0 mm), also contains 

plagioclase, opaque minerals, and minor clinopyroxene. A 

well-sorted, crossbedded, pyroclastic lens occurs locally 

near the top and is less than 0.5 m thick

Gillespie Tuff (Oligocene) Pink to gray, rhyolitic, crystalrich ash-flow tuff; contains abundant quartz, sanidine, 

plagioclase, biotite (as much as 3 mm across), and minor 

clinopyroxene, hornblende, zircon, and opaque minerals. 

Abundant pumice. Vitrophyre exposed near center of section 15. K-Ar biotite dates of 32.1±0.7 (Elston and Erb, 

1977) and 32.9±0.7 Ma (Erb, 1979)

Tbbc

Teh

Tbs

Tbc

Tbb

TKt

Km

25

V V

Tuff of Black Bill Canyon (Oligocene) Pink to gray, 

rhyodacitic to quartz latitic, crystal-rich ash-flow tuff; contains plagioclase, biotite (1 mm), minor clinopyroxene, 

quartz, sanidine, zircon, and opaque minerals

Cedar Hill Andesite (Oligocene) Red to pink, oxidized 

andesite; porphyritic, contains plagioclase (as much as 5 

mm across); also contains clinopyroxene, rare biotite, 

hornblende, and opaque minerals. An intrusive contact is 

indicated by map relations in north part of sec. 14

Tuff of Bennett Spring (Oligocene) Red, quartz latitic ashflow tuff; contains quartz, biotite, and hornblende. Includes 

mudflow deposits. Massive cliffs (south part of sec. 11) at 

top of unit are composed of angular volcanic rock 

fragments 8-10 cm in diameter

Tuff of Bluff Creek (Oligocene) White to gray to tan, rhyolitic 

ash-flow tuff having variable lithic and crystal content. 

Locally may be hydrothermally altered. Contains plagioclase, quartz, sanidine, biotite, zircon, and opaque 

minerals. Conspicuous flattened pumice in some locations. 

Zircon fission-track date of 36.5± 1.8 Ma (Erb, 1979)

Bennett Creek Breccia (Oligocene) White to gray, bleached 

in places, contains blocks and large slabs of ash-flow tuff, 

sedimentary rock fragments, and andesite

Timberlake Fanglomerate (Tertiary) and Cowboy Spring 

Formation (Cretaceous) Cobble to boulder conglomerate containing fossiliferous limestone clasts; interbedded with sandstone and shale; clasts are as large as 

0.5 m. Maximum thickness 3,000 ft southeast of Cowboy 

Spring (Elston and Erb, 1977)

Mojado Formation (Lower Cretaceous) Brown to gray, wellsorted, fine-grained quartz sandstone; with interbedded 

shale

Contact

Fault Dashed where inferred; dotted where concealed; ball

and bar on downthrown side 

Strike and dip of compaction foliation

Vitrophyre 

Pyroclastic sand

the southern Basin and Range physiographic province. 

The study area was included in regional mapping by 

Zeller and Alper (1965) and described by Erb (1979) in 

a compilation of volcanic centers in Hidalgo County. 

Topography of the study area is dominated by a 500- to 

800-ft-high cliff known as Cowboy Rim.

Conglomerate, sandstone, and shale of the 

Cretaceous Cowboy Spring Formation and Tertiary Timberlake Fanglomerate of Zeller and Alper (1965) are the 

oldest rocks exposed in the study area. Less than a mile 

north of the study area fine-grained quartz sandstone of 

the Early Cretaceous Mojado Formation is exposed.

Tertiary volcanic rocks that include andesite, ashflow tuff, and heterogeneous breccia are the dominant 

lithology in the study area (Zeller and Alper, 1965). Of 

these units, the Gillespie Tuff is the most widespread.

Other less voluminous units include the Bennett Creek 

Breccia, the tuff of Bennett Spring, the tuff of Bluff 

Creek, the andesite of Center Peak, the Cedar Hill 

Andesite, the tuff of Black Bill Canyon, and the tuff of 

The Park.

The study area is within the Cowboy Rim cauldron 

(Elston and others, 1976; Erb, 1979). A thick rhyolitic 

ash-flow tuff, the Gillespie Tuff, filled the Cowboy Rim 

cauldron, and outflow from this cauldron is widely 

distributed in the southern and central Animas 

Mountains. South of the study area, the Gillespie Tuff 

may be as thick as 3,000 ft (Erb, 1979).

Faults in the study area have minor displacements. 

However, there are quartz veins and iron and manganese 

staining along a northwest-trending fault in the eastern 

part of the study area.

Cowboy Spring Wilderness Study Area F5
Geochemistry

Introduction

The geochemical investigation included both a 

reconnaissance stream-sediment study and a rock-chip 

study of altered material. The stream-sediment study 

served to test broad parts of the study area for possible 

metal enrichment; the use of different stream-sediment 

sample types served to test a range of mineralogical 

possibilities. The rock-chip study supplemented the 

geochemical reconnaissance by testing specific sites 

where appearance or structure indicated the possibility of 

trace element enrichment.

The reconnaissance stream-sediment survey of the 

Cowboy Spring Wilderness Study Area was conducted in 

the spring of 1987. The stream-sediment survey included 

not only the 6,699-acre study area but also included an 

area of known mineralized rock which includes the 

Gillespie mine (fig. 1). Thirty-three sieved streamsediment samples, 33 nonmagnetic heavymineral-concentrate samples, five paramagnetic heavymineral-concentrate samples, and eight panned heavymineral-concentrate samples were collected from first-, 

second-, and third-order drainages in and near the study 

area. Sample density in the study area is about one 

sample locality per square mile. Data from two panned 

heavy-mineral-concentrate samples collected in 

Elephant Butte Canyon by Scott (1987) were 

incorporated into this survey.

Also used in the geochemical evaluation of the 

study area were data from 14 rock samples collected 

along faults or from areas of altered rocks (Brooks and 

others, 1988). An additional seven rock samples were 

collected during the course of the stream-sediment 

survey. Three of the samples came from outside the study 

area, two from near the Gillespie mine to ascertain the 

suite of metals present there, and one from a possible hot 

spring occurrence southwest of the study area. Four 

samples were float samples having minor iron staining.

Analytical data, descriptions of analytical 

procedures, and sample localities are given in Brooks and 

others (1988) and Scott (1987).

Analytical Methods

The sieved stream-sediment samples were 

obtained by passing 1-2 Ibs of raw stream sediment 

through 80-mesh stainless-steel screens. The fine 

fraction was retained for analysis. Rock samples were 

crushed, pulverized, and then analyzed.

The nonmagnetic heavy-mineral-concentrate 

samples were collected by panning a composite sample of 

stream sediment to an approximate composition of half 

dark-colored (mostly heavy) minerals and half lightcolored (mostly quartz and feldspar) minerals. The 

sample size was the amount of material, minus large 

pebbles and cobbles, that filled a 14-inch-diameter gold 

pan. The partially panned concentrate was then 

separated into light and heavy fractions by immersion in 

bromoform (a heavy liquid having a specific gravity of 

2.8), and a magnetic separator was used to obtain a 

nonmagnetic heavy-mineral concentrate for analysis. A 

few of the concurrently derived paramagnetic heavymineral fractions were analyzed; the remainder were 

archived.

Panned heavy-mineral-concentrate samples were 

obtained by panning larger samples of stream sediment 

in a larger gold pan (16-inch diameter) until the sample 

was reduced to 100 percent heavy minerals. This larger 

sample size filled the 16-inch-diameter gold pan, a 

sample amount that is sometimes called the "standard 

pan." The recovered heavy-mineral samples, reflecting 

bedrock geology of the drainage basin sampled, ranged in 

weight between 17 and 415 grams. The heavier samples 

were collected within the study area. Dominant 

mineralogy of these samples was iron-oxide minerals, 

mostly leucoxene-coated, oxidized pseudomorphs of 

magnetite. A small portion of sample material, weighing 

about 0.1 gram, was analyzed spectrographically; the 

remainder of the sample was analyzed for gold and 

platinum.

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), for gold 

and platinum by an atomic absorption spectroscopic 

method (J.R. Hassemer, unpub. method), and for 

mercury by an atomic absorption spectroscopic method 

(Crock and others, 1987). The minus-80-mesh streamsediment samples were analyzed for uranium by an 

ultraviolet fluorescence method (O'Leary and Meier, 

1986).

Results

The results of the geochemical survey yielded scant 

evidence indicative of mineralization within the study 

area.

The terms "enrichment" and "anomalous" are 

used in the general sense to indicate samples of unusual 

composition, but the terms do not necessarily imply the 

presence of mineral deposits. The term "threshold" 

indicates a value or amount at which an element might be 

classed as anomalous for a given sample type. Specific 

values are not given for most stream-sediment samples 

because several different stream-sediment sample media 

are discussed.

F6 Mineral Resources of Wilderness Study Areas Southwestern New Mexico
Throughout the area covered by the geochemical 

survey there is a weak enrichment of beryllium and tin 

that is sometimes accompanied by lanthanum, thorium, 

and yttrium. This is a suite of elements that suggests that 

the source, if in fact present, for some of the felsic 

volcanic units might be classified as a geochemically 

specialized granitoid. Such bodies, and their extrusive 

equivalents, can be hosts for metal deposits. Arguing 

against such deposits, either exposed or near the surface, 

is the fact that, excluding the Gillespie mine area, only a 

few scattered anomalies of these metals were found.

The only anomalous concentration of gold detected 

outside the Gillespie mine area was in a nonmagneticconcentrate sample collected in lower Park Canyon. This 

sample also had an anomalous concentration of silver. 

Although the sample locality derives some sediment 

from the study area, most material comes from outside 

the study area. A more likely source for this gold and 

silver may be the Tertiary Walnut Wells Monzonite 

(more specifically the contact zone between the monzonite and adjacent wall rock), an intrusive plug exposed on 

the north side of Park Canyon (Zeller and Alper, 1965). 

The sample also contained anomalous threshold-level 

concentrations of beryllium and tin. Analysis of a 

paramagnetic-concentrate fraction from the same 

locality found only weakly anomalous amounts of cobalt 

and zinc.

Additional stream-sediment anomalies include a 

threshold-level molybdenum anomaly found near Lower 

Walnut Creek Tank and a threshold-level silver anomaly 

found in a tributary to Elephant Butte Canyon.

Although some specialized granitoid bodies are 

frequently hosts to deposits of radioactive elements, 

there is little indication for such deposits in the surveyed 

area. Uranium in sieved sediments did not exceed 3 ppm 

in any of the samples. Anomalous concentrations of 

thorium were found in none of the sieved-sediment 

samples and only at threshold levels in a few of the 

nonmagnetic-concentrate samples. An occasional 

thorium-rich mineral grain is likely to be found in most 

felsic rocks.

There is no geochemical evidence of exposed 

mineralized rock in the study area. Furthermore, there is 

little evidence for mineralized rock at depth beneath the 

study area on the basis of the geochemical model 

proposed by Watts and Hassemer (1987, 1988) for 

Tertiary volcanic centers in the neighboring Silver City 

1° X 2° quadrangle.

Additional evidence for the absence of 

mineralization at depth is the fact that fault zones, where 

tested, were essentially devoid of anomalous 

concentrations of any elements. Such zones would be 

expected to act as conduits for mineralizing fluids or for 

trace-element-mobilizing ground water. Of fourteen rock 

samples collected principally along faults and altered

areas (Brooks and others, 1988), one sample contained 

an anomalous amount of arsenic (300 ppm (parts per 

million)) and another contained threshold-level mercury 

(0.06 ppm). For comparison, two samples from the 

Gillespie mine area contained 0.3 and 1.2 ppm mercury, 

respectively. Two other samples collected outside the 

study area, between the study area and the Gillespie 

mine, contained only threshold-level silver (0.5 ppm).

Further negative evidence for mineralized rock at 

depth is found by applying zirconium: tin and vanadium 

:niobium ratios as criteria for distinguishing productive 

(as opposed to barren of ore) granitoid bodies (Beus and 

Grigorian, 1977, tables 20 and 21). Only one rock sample 

had a vanadiummiobium ratio that met the criteria.

In contrast to the study area, rock samples 

collected in this study from the Gillespie mine area had 

anomalous concentrations of gold (as much as 2 ppm), 

silver (2 ppm), arsenic (700 ppm), antimony (30 ppm), 

molybdenum (50 ppm) with bismuth (11 ppm), cadmium 

(5 ppm), and threshold-level zinc (110 ppm); platinum 

values were below the detection limit (0.001 ppm). Minor 

amounts of gold and copper have also been reported 

from the mine (Hazen Research, Inc., 1979). Streamsediment samples, in various media, also contained 

anomalous amounts of cobalt, copper, nickel, and lead. 

The threshold-level beryllium and tin anomalies found 

throughout the volcanic rocks are also present in the 

mine area. Tertiary quartz latite dikes are known to occur 

in the mine area (Zeller and Alper, 1965), and it is not 

known if they are the source of the beryllium and tin 

anomaly.

Fluorite was found in the nonmagnetic concentrate 

samples from the Gillespie mine area, but none was 

observed in any of the samples from the study area.

Most of the nonmagnetic-concentrate samples 

collected north and west of the study area had anomalous 

concentrations of barium due to the presence of the 

mineral barite. These concentrations reflect the presence 

of pre-Tertiary sedimentary rocks or rock fragments.

Geophysics

Aerial Gamma-ray Spectroscopy

From 1975 to 1983 the U.S. Department of Energy 

contracted for aerial gamma-ray surveys that covered 

almost all of the conterminous United States and much 

of Alaska. As part of this mapping project, data for New 

Mexico were compiled and processed to produce a series 

of l:l,000,000-scale maps that include the compositecolor maps by Duval (1983). From these maps the 

percent potassium (K), parts per million equivalent 

uranium (eU), and parts per million equivalent thorium 

(eTh) for the study area were estimated. The occurrence

Cowboy Spring Wilderness Study Area F7
or absence of anomalous radioelement concentrations 

was also noted. The definition of an anomaly requires 

that the K concentration and its ratios to the eU and eTh 

all be high values.

Moderate radioactivity (concentrations of 2.6-3.0 

percent K, 2.6-3.1 ppm eU, and 11.3-13.9 ppm eTh) was 

found in the study area. A moderate thorium anomaly 

covers most of the study area, as well as a large part of 

the surrounding area. This anomaly suggests some 

thorium enrichment in the exposed rocks but does not 

indicate mineralization. The uranium content is slightly 

enriched.

Gravity and Magnetic Data

The Cowboy Spring Wilderness Study Area is 

sparsely covered by gravity and aeromagnetic data, which 

are suitable only for regional interpretations (figs. 3 and 

4). Contours of complete (terrain corrected) Bouguer 

gravity anomalies are defined by 2 gravity stations near 

the study area (fig. 3) and 7 stations farther away from 

the study area (Cordell and others, 1982; Defense 

Mapping Agency Aerospace Center, 1974,1975). Aero108°40' 108°37'30"

F

108°40' 10B°37'30"

APPROXIMATE BOUNDARY 

OF COWBOY SPRING 

WILDERNESS STUDY AREA

PPROXIMATE BOUNDARY 

OF COWBOY SPRING _ 

WILDERNESS STUDY AREA

Figure 3. Bouguer gravity anomaly map of the Cowboy 

Spring Wilderness Study Area and vicinity. Contour interval, 

1 mGal; dots represent gravity stations.

Figure 4. Aeromagnetic anomaly map of the Cowboy 

Spring Wilderness Study Area and vicinity. Contour interval, 

50 nT; hachures indicate closed low; dashed lines indicate 

flight lines.

magnetic anomalies are defined by measurements made 

along 3 east-west flight lines spaced 3 mi apart at a 

nominal height of 400 ft above the terrain (Cordell, 1983; 

Texas Instruments, Inc., 1979).

A uniform gravity gradient crosses the study area 

and gravity values increase northeastward (fig. 3). This 

gradient forms the flank of a broad high which is centered 

a few miles north-northeast of the area. This high 

appears to be caused mostly by exposed and near-surface 

sedimentary rocks, including carbonate-rich rocks, which 

are higher in density than tuff and tuffaceous sediment 

that surround or abut them. The decrease in gravity 

values southwestward indicates a general thickening of 

the tuff units in that direction.

The aeromagnetic anomaly map (fig. 4) shows a 

broad high centered over the northwest margin of the 

study area. This high appears to be generated mostly by 

intrusive rocks of andesitic composition, partly exposed 

and partly buried beneath gravel and alluvial deposits. 

The low magnetic values over the central and southern 

parts of the study area indicate that most of the mapped 

tuff is relatively nonmagnetic. Local, more highly mafic 

phases of the tuff cause local increases of magnetic 

intensity.

F8 Mineral Resources of Wilderness Study Areas Southwestern New Mexico
Mineral and Energy Resources

Metals

Association of mineral deposits with mid-Tertiary 

volcanic centers in southwestern New Mexico (Elston, 

1970) suggests that the Cowboy Spring Wilderness Study 

Area, which is in the Cowboy Rim cauldron of Erb 

(1979), is an excellent exploration target. However, 

location of the study area in a complex volcanic center 

having a variety of flow rocks is only one of the attributes 

stated by Silberman (1982) that is associated with hotspring-type gold and silver deposits. Other important 

features, such as thermal spring activity, repeated 

fracturing and veining, and anomalous concentrations of 

gold, silver, and arsenic, are not present.

With the exception of the altered rocks and minor 

concentration of arsenic noted in one analysis of a sample 

taken near the fault in the eastern part of the study area, 

the volcanic rocks in the remainder of the study area have 

not been altered, silicified, or faulted. No anomalous 

concentrations of metals were found in analyses of 

stream sediment. Therefore, a low mineral resource | 

potential with certainty level C for all metals is assigned ' 

to the study area.

Fluorspar

The Cowboy Spring Wilderness Study Area is 

approximately a mile south of the Winkler anticline; 

where several fluorspar prospects are located, primarily 

in faulted Horquilla Limestone (Williams, 1966; McAnulty, 1972). The absence of outcrops of faulted 

sedimentary rocks, specifically the Horquilla Limestone, 

and the thickness of the Tertiary volcanic rocks found in 

the study area indicate that the occurrence of fluorspar 

within the study area is unlikely. Therefore, the mineral 

resource potential for fluorspar in the study area is rated 

low, with certainty level C.

Oil and Gas

The Cowboy Spring Wilderness Study Area is one 

of a cluster of twelve wilderness study areas in 

southwestern New Mexico rated as having a low potential 

for oil and gas resources (Ryder, 1983a; 1983b). All of 

the Cowboy Spring Wilderness Study Area is covered by 

oil and gas leases.

No oil and gas wells have been drilled in the study 

area, but in 1974-75 the KCM No. 1 Forest Federal well 

was drilled about 1.25 mi north of the study area on the 

Winkler anticline. The well penetrated the Earp 

Formation (Permian) and the Horquilla Limestone (Permian to Pennsylvanian) and bottomed in quartz monzonite at a total depth of 4,464 ft. No significant shows of oil

or gas were encountered during drilling and the well was 

classified as a dry hole (Thompson, 1977). The thickness 

of the volcanic rocks, as much as 3,000 ft (Erb, 1979), 

combined with the distribution and effects of plutonic 

and volcanic centers near the study area (Elston and Erb, 

1977) creates an unfavorable environment for petroleum 

accumulation.

The energy resource potential for oil and gas in the 

study area is rated low, with certainty level C.

Geothermal Energy

The study area is approximately 30 mi southeast of 

the Lightning Dock KGRA (Known Geothermal 

Resource Area) studied by Elston and others (1983) and 

is in a part of the Basin and Range province where the 

heat flow is known to be 2.0-2.5 HFU (heat flow units). 

However, there is no indication of a geothermal anomaly 

in either the Animas Valley to the west or in the Playas 

Basin to the east of the study area (Stone and Mizell, 

1977). In the KCM No. 1 Forest Federal well, an above 

normal geothermal gradient was measured but it may 

only indicate a marginal source of geothermal energy 

(Thompson, 1977). In addition, there are no hot springs 

or evidence of other geothermal activity within the study 

area. Therefore, the resource potential for geothermal 

resources is rated low, with certainty level C.

RECOMMENDATIONS FOR 

FUTURE WORK

Because of the altered rock, the anomalous 

concentrations of arsenic, and the threshold 

concentrations of mercury found in samples near the 

northwest-trending fault in the eastern part of the study 

area, detailed sampling in this area is suggested.

REFERENCES CITED

Beus, A.A., and Grigorian, S.V., 1977, Geochemical 

exploration methods for mineral deposits: Applied 

Publishing, Ltd., 278 p.

Brooks, W.E., Adrian, B.M., and Erlich, Olga, 1988, Analytical 

results and sample locality map of rock samples from the 

Cowboy Spring Wilderness Study Area, Hidalgo County, 

New Mexico: U.S. Geological Survey Open-File Report 

88-0211, 9 p.

Cordell, L.E., 1983, Composite residual total intensity aeromagnetic map of New Mexico: New Mexico State 

University Energy Institute, Geothermal Resources of 

New Mexico, Scientific Map Series, scale 1:500,000.

Cordell, L.E., Keller, G.R., and Hildenbrand, T.G., 1982, 

Complete Bouguer gravity anomaly map of the Rio 

Grande rift, Colorado, New Mexico, and Texas: U.S. 

Geological Survey Geophysical Investigations Map 

GP-949, scale 1:1,000,000.

Cowboy Spring Wilderness Study Area F9
Crock, J.G., Briggs, P.H., Jackson, L.L., and Lichte, F.E., 1987, 

Analytical methods for the analysis of stream sediments 

and rocks from wilderness study areas: U.S. Geological 

Survey Open-File Report 87-0084, 35 p.

Defense Mapping Agency Aerospace Center, 1974, World 

relative gravity reference network, North America, part 

2: Defense Mapping Agency Aerospace Center 

Reference Publication 25, with supplement updating 

gravity values to the International Gravity 

Standardization Net 1971, 1,635 p.

____ 1975, Holding, storage, and retrieval of gravity data: 

Defense Mapping Agency Aerospace Center, 

Publication RP-75-0003, 33 p.

Drewes, Harald, and Thorman, C.H., 1980, Geologic map of 

the Steins quadrangle and the adjacent part of the Vanar 

quadrangle, Hidalgo County, New Mexico: U.S. 

Geological Survey Miscellaneous Investigations Series 

Map 1-1220, scale 1:24,000.

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

spectrometric data: Geophysics, v. 48, p. 722-735.

Elston, W.E., 1965, Mining districts of Hidalgo County, New 

Mexico, in Fitzsimmons, J.P., and Lochman-Balk, C, 

eds., Guidebook of Southwestern New Mexico II: New 

Mexico Geological Society Sixteenth Field Conference, 

p. 210-214.

___ 1970, Volcano-tectonic control of ore deposits, 

southwestern New Mexico, in Woodward, L.A., ed., 

Guidebook of the Tyrone-Big Hatchet MountainsFlorida Mountains Region: New Mexico Geological 

Society Twenty-first Field Conference, p. 147-153.

Elston, W.E., Deal, E.G., and Logsdon, M.J., 1983, Geology 

and geothermal waters of Lightning Dock region, Animas Valley and Pyramid Mountains, Hidalgo County, 

New Mexico: New Mexico Bureau of Mines and Mineral 

Resources Circular 177, 44 p.

Elston, W.E., and Erb, E.E., 1977, Cenozoic volcano-tectonic 

setting of KCM No. 1 Forest Federal Well, Animas 

Mountains, Hidalgo County, New Mexico, in Thompson, 

Sam, III, compiler, Geology, petroleum source rocks, and 

thermal metamorphism in KCM No. 1 Forest Federal 

well, Hidalgo County, New Mexico: New Mexico Bureau 

of Mines and Mineral Resources Circular 152, p. 53-62.

Elston, W.E., Rhodes, R.C., Coney, P.J., and Deal, E.G., 1976, 

Progress report on the Mogollon Plateau volcanic field, 

southwestern New Mexico, No. 3 Surface expression of 

a pluton, in Elston, W.E. and Northrop, S.A., eds., 

Cenozoic volcanism in southwestern New Mexico: New 

Mexico Geological Society Special Publication No. 5, 

p. 3-28.

Erb, E.E., 1979, Petrologic and structural evolution of ash-flow 

tuff cauldrons and noncauldron related volcanic rocks in 

the Animas and southern Peloncillo Mountains, Hidalgo 

Co., New Mexico: Albuquerque, N. Mex., University of 

New Mexico Ph. D. dissertation, 286 p.

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

mineral survey reports on public lands: U.S. Geological 

Survey Open-File Report 84-787, 51 p.

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

and alternating-current spark emission spectrographic 

field methods for semiquantitative analysis of geologic 

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

Hazen Research, Inc., 1979, Consulting service at Mining and 

Milling Corporation of America, core-drilling program 

on the Winkler Anticline, Hachita, Hidalgo County, New 

Mexico: New Mexico Bureau of Mines and Mineral 

Resources Open-File Report 108, 32 p.

McAnulty, W.N., 1972, Winkler Anticline fluorspar, Hidalgo 

County, New Mexico: New Mexico Bureau of Mines and 

Mineral Resources Target Exploration Report E-3, 7 p.

O'Leary, R.M., and Meier, A.L., 1986, Analytical methods used 

in geochemical exploration, 1984: U.S. Geological Survey 

Circular 948, 48 p.

Rothrock, H.E., 1970, Fluorspar, in Woodward, L.A., ed., 

Guidebook of the Tyrone-Big Hatchet MountainsFlorida Mountains Region: New Mexico Geological 

Society Twenty-first Field Conference, p. 123-125.

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

New Mexico: U.S. Geological Survey Miscellaneous 

Investigations Series Map 1-1543, scale 1:1,000,000.

____ 1983b, Petroleum potential of wilderness lands in New 

Mexico: U.S. Geological Survey Circular 902-1, 33 p.

Scott, D.C., 1987, Mineral investigation of the Cowboy Spring 

Wilderness Study Area (NM-030-007), Hidalgo County, 

New Mexico: U.S. Bureau of Mines Open File Report 

MLA 68-87, 10 p.

Silberman, M.I., 1982, Hot-spring-type, large tonnage, lowgrade gold deposits, in Erickson, R.L., Characteristics of 

mineral occurrences: U.S. Geological Survey Open-File 

Report 82-795, p. 131-143.

Stone, W.J., and Mizell, N.H., 1977, Geothermal resources of 

New Mexico a survey of work to date: New Mexico 

Bureau of Mines and Mineral Resources Open-File 

Report 73, 123 p.

Texas Instruments, Inc., 1979, National Uranium Resource 

Evaluation aerial radiometric and magnetic 

reconnaissance survey of portions of Arizona-New Mexico, Mesa, Clifton, Tucson, Silver City, Nogales, and 

Douglas quadrangles: U.S. Department of Energy Grand 

Junction Office Report GJBX-23(79), 1,167 p.

Thompson, Sam, III, 1977, Subsurface geology and the 

petroleum-exploration significance of KCM No. 1 Forest 

Federal Well, Hidalgo County, New Mexico, in Thompson, Sam, III, compiler, Geology, petroleum source 

rocks, and thermal metamorphism in KCM No. 1 Forest 

Federal well, Hidalgo County, New Mexico: New Mexico 

Bureau of Mines and Mineral Resources Circular 152, 

p. 5-23.

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.

Watts, K.C., and Hassemer, J.R., 1987, Geochemical signatures 

of deep-seated targets in Tertiary volcanic centers, Arizona and New Mexico: 12th International Geochemical 

Exploration Symposium, Orleans, France, April 1987, 

Program and Abstracts, p. 43.

F10 Mineral Resources of Wilderness Study Areas Southwestern New Mexico
____ 1988, Geochemical and interpretive summary maps, 

Silver City 1° x 2° quadrangle, New Mexico and Arizona: 

U.S. Geological Survey Miscellaneous Investigations 

Series Map I-1310-E, scales 1:250,000 and 1:500,000.

Wengerd, S.A., 1970, Petroleum prospects in southwesternmost 

New Mexico, in Woodward, L.A., ed., Guidebook of the 

Tyrone-Big Hatchet Mountains-Florida Mountains 

Region: New Mexico Geological Society Twenty-first 

Field Conference, p. 91-104.

Williams, F.E., 1966, Fluorspar deposits of New Mexico: U.S.

Bureau of Mines Information Circular 8307, 143 p.

Teller, R.A., 1970, Petroleum geology of southwestern New 

Mexico [abs.], in Woodward, L.A., ed., Guidebook of the 

Tyrone-Big Hatchet Mountains-Florida Mountains 

Region: New Mexico Geological Society Twenty-first 

Field Conference, p. 87.

Zeller, R.A., and Alper, A.M., 1965, Geology of the Walnut 

Wells quadrangle, Hidalgo County, New Mexico: New 

Mexico Bureau of Mines and Mineral Resources Bulletin 

84, 105 p.

Cowboy Spring Wilderness Study Area F11

APPENDIX
DEFINITION OF LEVELS OF MINERAL RESOURCE POTENTIAL 

AND CERTAINTY OF ASSESSMENT

Definitions of Mineral Resource Potential

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 unlikely. This broad 

category embraces areas with dispersed but insignificantly mineralized rock as well as areas with few 

or no indications of having been mineralized.

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 a reasonable likelihood of resource accumulation, and (or) where an application of 

mineral-deposit models indicates favorable ground for the specified type(s) of deposits.

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.

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

moderate, or high levels of resource potential.

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

area.

Levels of Certainty

LU

LU

o

OC

o

CO 

LU 

OC

LU 

LU

U/A

UNKNOWN

POTENTIAL

H/B

HIGH POTENTIAL

M/B 

MODERATE POTENTIAL

L/B

LOW

POTENTIAL

H/C

HIGH POTENTIAL

M/C 

MODERATE POTENTIAL

L/C

LOW

POTENTIAL

H/D

HIGH POTENTIAL

M/D 

MODERATE POTENTIAL

L/D

LOW POTENTIAL

N/D

NO POTENTIAL

B C 

LEVEL OF CERTAINTY

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

B. Available information 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.

Abstracted with minor modifications from:

Taylor, R. B., and Steven, T. A., 1983, Definition of mineral resource potential: Economic Geology,

v. 78, no. 6, p. 1268-1270. 

Taylor, R. B., Stoneman, R. J., and Marsh, S. P., 1984, An assessment of the mineral resource potential

of the San Isabel National Forest, south-central Colorado: U.S. Geological Survey Bulletin 1638, p.

40-42. 

Goudarzi, G. H., compiler, 1984, Guide to preparation of mineral survey reports on public lands: U.S.

Geological Survey Open-File Report 84-0787, p. 7, 8.
RESOURCE/RESERVE CLASSIFICATION

IDENTIFIED RESOURCES

Demonstrated

Measured Indicated

Inferred

UNDISCOVERED RESOURCES

Probability Range

 (or) 

Hypothetical i Speculative

ECONOMIC

MARGINALLY 

ECONOMIC

SUBECONOMIC

1 

Reserves

I

Inferred Reserves

Marginal Reserves

Demonstrated 

Subeconomic Resources

Inferred 

Marginal Reserves

Inferred

Subeconomic

Resources

Major elements of mineral resource classification, excluding reserve base and inferred reserve base. Modified from McKelvey,1972, Mineral 

resource estimetes 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.
GEOLOGIC TIME CHART 

Terms and boundary ages used in this report

EON

Phanerozoic

Proterozoic

Archean 

pre-Ar

ERA

Cenozoic

Mesozoic

Paleozoic

Late Proterozoic

Middle Proterozoic

Early Proterozoic

Late Archeen

Middle Archean

Early Archean 

chean 2

PERIOD

Neogene

Subperiod

Tertiary

Paleogene

Cretaceous

Jurassic

Triassic

Permian

Pennsylvanian 

Carboniferous

Mississippian

Devonian

Silurian

Ordovician

Cambrian

 3800? -

EPOCH

Holocene

Pleistocene

Pliocene

Miocene

Oligocene

Eocene

Paleocene

Late 

Early

Late 

Middle 

Early

Late 

Middle 

Early

Late 

Early

Late 

Middle 

Early

Late 

Early

Late 

Middle 

Early

Late 

Middle 

Early

Late 

Middle 

Early

Late 

Middle 

Early

 -

BOUNDARY AGE 

IN 

MILLION YEARS

-0.010

- 1.7

- 5

1A

_ tit

CC

- 96

_ 1*}Q

OftC

-A, 240

-*> 330

_ Qcn

- 410

- 500 

-A, 570 1

- 1600

- 2500

-3000 

- 3400

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

1 Informal time term without specific rank.

*U.S. GOVERNMENT PRINTING OFFICE: 1989-673-047/86067
Mineral Resources of 

Wilderness Study Areas 

Southwestern New Mexico

This volume was published 

as separate chapters A-F

U.S. GEOLOGICAL SURVEY BULLETIN 1735

CONTENTS

[Letters designate the chapters]

(A) Mineral resources of the Gila Lower Box Wilderness Study Area, Grant and 

Hidalgo Counties, New Mexico, by Donald H. Richter, Viki A. Lawrence, 

Harlan Barton, William Hanna, Joseph S. Duval, and George S. Ryan.

(B) Mineral resources of the West Potrillo Mountains-Mount Riley and the Aden 

Lava Flow Wilderness Study Areas, Dona Ana and Luna Counties, New 

Mexico, by James E. Kilburn, Douglas B. Stoeser, David R. Zimbelman, 

William F. Hanna, and Diann D. Gese.

(C) Mineral resources of the Big Hatchet Mountains Wilderness Study Area, 

Hidalgo County, New Mexico, by Harald Drewes, H.N. Barton, W.F. Hanna, 

and D.C. Scott.

(D) Mineral resources of the Organ Mountains Wilderness Study Area, Dona Ana

County, New Mexico, by Steve Ludington, William F. Hanna, Robert L.

Turner, and Rodney E. Jeske. 

(E) Mineral resources of the Brokeoff Mountains Wilderness Study Area, Otero

County, New Mexico, by Samuel L. Moore, M. Dean Kleinkopf, Gary A.

Nowlan, and Patricia A. Corbetta. 

(F) Mineral resources of the Cowboy Spring Wilderness Study Area, Hidalgo

County, New Mexico, by William E. Brooks, Jerry R. Hassemer, Joseph S.

Duval, William F. Hanna, and David C. Scott.



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reflect subsurface structures that are of economic or geologic significance. 

Many maps include correlations with the geology.

Miscellaneous Investigations Series Maps are on planimetric or 

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

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

which show geology as interpreted from aerial photographs. Series also 

includes maps of Mars and the Moon.

Coal Investigations Maps are geologic maps on topographic or 

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

Oil and Gas Investigations Charts show stratigraphic information 

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

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

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

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

environmental studies or wilderness mineral investigations.

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

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

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

Catalogs

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

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

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

CO 80225. (See latest Price and Availability List)

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

set of microfiche.

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

set of microfiche.

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

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

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

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

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

over the counter in paperback book form.

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

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

and over the counter in paperback booklet form only

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

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

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

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

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

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

National Center, Reston, VA 22092.

Note. Prices of Government publications listed in older catalogs, 

announcements, and publications may be incorrect. Therefore, the 

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

and publications.