Mineral Resources of the

Petaca Pinta Wilderness Study Area,

Cibola County, New Mexico

U.S. GEOLOGICAL SURVEY BULLETIN 1734-H

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Chapter H

Mineral Resources of the

Petaca Pinta Wilderness Study Area,

Cibola County, New Mexico

By CHARLES H. MAXWELL, GARY A. NOWLAN, and

VI Kl BAN KEY

U.S. Geological Survey

BRIAN J. HANNIGAN 

U.S. Bureau of Mines

U.S. GEOLOGICAL SURVEY BULLETIN 1734

MINERAL RESOURCES OF WILDERNESS STUDY AREAS WEST-CENTRAL NEW MEXICO
DEPARTMENT OF THE INTERIOR 

DONALD PAUL MODEL, Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

Any use of trade names in this report is for descriptive purposes only and 

does not imply endorsement by the U.S. Geological Survey or the 

U.S. Bureau of Mines.

UNITED STATES GOVERNMENT PRINTING OFFICE: 1989

For sale by the

Books and Open-File Reports Section

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Library of Congress Cataloging-in-Publication Data

Mineral resources of the Petaca Pinta wilderness study area, Cibola County, 

New Mexico.

(Mineral resources of wilderness study areas west central New Mexico 

ch. H) (U.S. Geological Survey bulletin ; 1734-H) 

Bibliography: p. 

Supt. of Docs, no.: I 19.3:1734-H

1. Mines and mineral resources New Mexico Petaca Pinta Wilderness.

2. Petaca Pinta Wilderness (N.M.) I. Maxwell, Charles Henry, 1923- 

II. Series. III. Series: U.S. Geological Survey bulletin ; 1734-H. 

QE75.B9 no. 1734-H 557.3 s [553'.09789'91] 88-607942 

[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 value, if any, that may be present. Results 

must be made available to the public and be submitted to the President and the Congress. 

This report presents the results of a mineral survey of the Petaca Pinta Wilderness Study 

Area (NM-020-014), Cibola County, New Mexico.

CONTENTS

Abstract HI 

Summary HI 

Introduction H2

Investigations by the U.S. Bureau of Mines H2 

Investigations by the U.S. Geological Survey H2 

Appraisal of identified resources H2

Mining activity and oil and gas leases H2 

Resource appraisal H2

Assessment of potential for undiscovered resources H2 

Geology H2 

Geochemistry H6 

Methods H6 

Results H7 

Geophysics H7

Aeromagnetic data H7 

Gravity data H7 

Radiometric data H9 

Mineral and energy resources H9 

Metals H9 

Oil and gas H9 

Coal H9 

References cited Hll 

Appendix H13

FIGURES

1. Map showing the location of the Petaca Pinta Wilderness Study Area, Cibola 

County, New Mexico H3

2. Map showing geology and mineral resource potential of Petaca Pinta 

Wilderness Study Area H4

3. Aeromagnetic map of the Petaca Pinta Wilderness Study Area and 

vicinity H8

4. Bouguer gravity anomaly map of the Petaca Pinta Wilderness Study Area and 

vicinity H10

Contents

MINERAL RESOURCES OF WILDERNESS STUDY ARE AS-WEST-CENTRAL NEW MEXICO

Mineral Resources of the Petaca Pinta Wilderness 

Study Area, Cibola County, New Mexico

By Charles H. Maxwell, Gary A. Nowlan, anc/Viki Bankey 

U.S. Geological Survey

Brian J. Hannigan 

U.S. Bureau of Mines

ABSTRACT

In 1987 the U.S. Bureau of Mines and the U.S 

Geological Survey conducted investigations to appraise the 

identified resources and assess the mineral resource 

potential of 11,668 acres of the Petaca Pinta Wilderness 

Study Area (NM-020-014), Cibola County, New Mexico. 

These investigations showed that the study area contains no 

identified (known) metallic mineral resources but has inferred 

subeconomic resources of sandstone and sand. The 

wilderness study area has a low resource potential for 

undiscovered deposits of metals, including uranium, and has 

a moderate resource potential for the occurrence of oil and 

gas. There is no resource potential for coal.

SUMMARY

The Petaca Pinta Wilderness Study Area is located in 

Cibola County, west-central New Mexico, about 50 mi (miles) 

west-southwest of Albuquerque. The area is bordered on the 

west by the Laguna Indian Reservation and part of the north 

boundary abuts the Acoma Indian Reservation. The area 

consists of about 11,668 acres. The area is accessible from 

Interstate Highway 40 via State Highway 6, old U.S. 66, State 

Road 55, and unimproved ranch roads (fig. 1).

Petaca Pinta is a small (30 acres) mesa with nearvertical 300-ft (foot) cliffs of Jurassic-age and Cretaceous-age 

(see geologic time chart in "Appendix") sandstone overlying 

Triassic-age shale that forms steep slopes a mile or two wide 

and 1,000 ft high. The slopes are almost completely covered 

by landslides, only a few small outcrops of the underlying 

Triassic shale show through the landslide debris.

Manuscript approved for publication, November 16, 1988.

No mines or prospects were seen and no metallic 

mineral resources were identified in or near the wilderness 

study area. Large amounts of sand and sandstone in the area 

are classified as inferred subeconomic resources.

A reconnaissance geochemical survey of the area was 

conducted by the U.S. Geological Survey in 1987, and 

samples were collected at 22 sites on ephemeral streams. 

Analytical results show that very few anomalous 

concentrations of any element are present. Most samples 

contain amounts of elements near or below their average 

crustal abundance in shale and sandstone. Concentrate 

samples contain anomalous amounts of barium, strontium, 

and vanadium, probably all derived from a barite-rich zone 

that occurs throughout the region immediately below the 

unconformity at the base of the Upper Cretaceous rocks.

A broad positive gravity high east of the study area 

suggests that denser Pennsylvanian limestones are thicker 

and more widespread than indicated by surface mapping 

and existing boreholes. The study area is located on a steep 

gravity gradient along the west side of the positive anomaly.

A large C-shaped positive magnetic anomaly is present 

in the vicinity of the Petaca Pinta study area. The anomaly is 

caused by the magnetic source rock for the basalts in the 

region; the amplitude and shape of subsidiary anomalies 

suggest that the source of the basalts is deep and may be 

fault controlled.

No mineralized areas or occurrences of metallic 

minerals were found in the wilderness study area. No 

significant geochemical anomalies were found by streamsediment and concentrate samples, and no anomalous 

radioactivity was found by the study. The resource potential 

is low for any undiscovered deposits of metals, including 

uranium. The potential for the occurrence of oil and gas 

resources is moderate, especially along the eastern side of 

the area. There is no potential for coal resources as coalbearing units do not occur in the area.

Petaca Pinta Wilderness Study Area HI
INTRODUCTION

The Petaca Pinta Wilderness Study Area is located 

in Cibola County, west-central New Mexico, about 20 mi 

(miles) south of Laguna Pueblo and 50 mi westsouthwest of Albuquerque. The area is bordered on the 

west by the Laguna Indian Reservation; part of the north 

boundary is the Acoma Indian Reservation. The studied 

area consists of 11,668 acres.

The study area is accessible from Interstate 

Highway 40 by turning south on State Highway 6, west on 

old U.S. Highway 66, and south on State Road 55 for 

about 7 mi, west on an unimproved dirt track along a 

fence line for about 3Yi mi, then southwest about 13 mi 

on a private ranch road (fig. 1). There is no public access 

to the Petaca Pinta area.

A preliminary evaluation of the mineral resource 

potential of the Petaca Pinta Wilderness Study Area was 

prepared by the New Mexico Bureau of Mines and 

Mineral Resources in 1981 (Logsdon, 1981).

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 

USBM and USGS (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). It is classified according to the 

system of Goudarzi (1984) and is shown in the Appendix. 

The potential for undiscovered resources is studied by 

the USGS.

Investigations by the 

U.S. Bureau of Mines

A comprehensive literature search was made for 

information on mines, prospects, and mineralized areas, 

and Bureau of Land Management mining claim and oil 

and gas lease records were checked for claim and lease 

information pertaining to the study area. Foot and 

vehicle traverses were made in August 1987, in and near 

the study area in a search for mines and mineralized 

areas (Hannigan, 1988).

Investigations by the 

U.S. Geological Survey

The Petaca Pinta Wilderness Study Area was 

mapped previously by Maxwell (1979,1988a, b, in press)

at a scale of 1:24,000, and compiled at a scale of 

1:100,000 for figure 2. Geophysical data were evaluated 

by Viki Bankey, and gamma-ray spectroscopy data were 

prepared by J.S. Duval. Geochemical sampling was done 

in August 1987, by Gary A. Nowlan.

APPRAISAL OF IDENTIFIED RESOURCES

By Brian J. Hannigan 

U.S. Bureau of Mines

Mining Activity and Oil and Gas Leases

No mines or prospects were seen in or near the 

Petaca Pinta Wilderness Study Area during the field 

investigations. As of August 1987, Bureau of Land 

Management records show no mining claims in or near 

the study area, but oil and gas leases cover about 1,080 

acres in and within 1 mi of the study area.

Resource Appraisal

No metallic mineral resources were identified in or 

near the study area. Several oil and gas exploration wells 

have been drilled 8-26 mi from the study area but no 

commercial production exists within 55 mi of the study 

area. Carbon dioxide was reported from one well 6 mi 

north of the area. No exploration wells have been drilled 

within or in the immediate vicinity of the study area (U.S. 

Bureau of Land Management, 1986).

Massive beds of sandstone occur in the area, but 

visual inspection indicates that they are generally too low 

in silica content to be suitable for any industrial purpose 

other than crushed rock. Sand is present in the drainages 

of the area but contains no unusual or unique properties. 

There are no gravel deposits in the area. The sandstone 

and sand are classified as inferred subeconomic 

resources, and, because vast quantities of similar 

material are available throughout the region, it is highly 

unlikely that these resources would ever be developed.

ASSESSMENT OF POTENTIAL FOR 

UNDISCOVERED RESOURCES

By Charles H. Maxwell, Gary A. Nowlan,

and Viki Bankey

U.S. Geological Survey

Geology

Petaca Pinta is a small (30 acres) mesa rising 

steeply about 1,300 ft (feet) above the flat valley floor of 

Arroyo Colorado. The western boundary of the study

H2 Mineral Resources of Wilderness Study Areas West-Central New Mexico
R. 7 W. 107°30' R. 6 W. R. 5 W

107° 15'

I 9 N 

35°00'

I 3 N

I 7 N. 

34°45'

I B

T. 5 N

Acoma

Indian

Reservation

Acoma

Laguna Indian 

Reservation

Acoma

Indian

Reservation

Laguna

Indian

Reservation

-APPROXIMATE BOUNDARY OF 

THE PETACA PINTA 

WILDERNESS STUDY AREA

I (NM-020-014)_____

35'

108°

NEW MEXICO

 Gallup 

Grants 

P

 Santa Fe 

 Albuquerque

Las Cruces

10 MILES 

I

Figure 1 . Map showing the location of the Petaca Pinta Wilderness Study Area, Cibola County, New Mexico.

area is the edge of Blue Water Mesa, at about the same 

elevation as Petaca Pinta and dropping as steeply to the 

valley floor (fig. 2). The most striking features of the area 

are the near-vertical 300-ft cliffs of the mesas and the tier 

upon tier of landslide blocks extending from the cliffs to 

the valley floor. The slides cover slopes a mile or two 

wide and as much as 1,000 ft high, with only a few small 

outcrops of the underlying Triassic Chinle Formation 

showing through.

Much of the landslides are composed of large 

rotated and tilted blocks of sandstone and basalt which 

have broken away from the cliffs and slid down the slope 

on the underlying soft shale. Some of the slides, 

especially in the northern part of the study area, are 

chaotic piles of rock debris. The landslides were formed 

during an early wet period, which was followed by 

progressive changes in climate to the present-day arid 

conditions. During the wet period large amounts of water

Petaca Pinta Wilderness Study Area H3
percolated through the porous sandstones and basalt, many of the lower slides and filled the valleys to form

soaked and weakened the underlying shales, and broad flat floors. Parts of the slides were subsequently

produced the numerous slide blocks that migrated eroded away to expose the underlying shale,

downslope. Eventually, the slides stabilized and the Almost all of the bedrock underlying the study area

valleys became choked with alluvium which covered is Chinle Formation, brick red and reddish-purple shale,

107°30'

34°45'

APPROXIMATE BOUNDARY 

OF THE PETACA PINTA 

/WILDERNESS S

T.5N.

Figure 2 (above and facing page). Map showing geology and mineral resource potential of Petaca Pinta 

Wilderness Study Area.

H4 Mineral Resources of Wilderness Study Areas West-Central New Mexico
EXPLANATION OF MINERAL 

RESOURCE POTENTIAL

Geologic terrane having moderate resource 

potential for oil, natural gas, and carbon 

dioxide, with certainty level B Applies to 

entire wilderness study area

L/C Geologic terrane having low resource potential for metals, including uranium, and 

with certainty level C Applies to entire 

wilderness study area

N/D Geologic terrane having no resource potential 

for coal, and with certainty level D Applies 

to entire wilderness study area

Levels of certainty 

B Data indicate geologic environment and

suggest level of resource potential 

C Data indicate geologic environment and

indicate level of resource potential 

D Data indicate geologic environment and

clearly defines level of resource potential

CORRELATION OF MAP UNITS

Ql

Qb

Qbc

Tb

Kd

Qb

Qe

Qal

Ql

i ? 1 

Qbc

Tb

} Holocene 

Holocene and 

Pleistocene

Pleistocene

Ju

QUATERNARY

> Pliiocene

~\ Upper

J Cretaceous

J> TERTIARY 

\ CRETACEOUS

"1 Middle 1 

J Jurassic J

JURASSIC

\ Upper 

J Triassic

[ TRIASSIC

DESCRIPTION OF MAP UNITS

Qe Eolian deposits (Holocene) Recent windblown 

sand and silt in sheets and small longitudinal dunes

Qal Alluvium (Holocene) Silt and fine sand, locally 

a few coarse grains of sand and pebbles; 

includes local small landslide deposits and 

minor eolian deposits

Landslide deposits (Holocene and Pleistocene) 

Mostly toreva block slides of basalt or sandstone and shale which have slid over Triassic 

shale and mudstone, locally rock slides and 

mudflows of chaotic debris

Basalt flows (Pleistocene) Black to dark-gray, 

fine-grained, slightly porphyritic basalt with 

small phenocrysts of olivine and feldspar

Cinder cone, flow, and vent complex (Pleistocene) Red-brown and black basalt scoria, 

bombs, breccia, flows, and small basalt 

plugs

Basalt flows (Pliocene) On Blue Water Mesa 

and Petaca Pinta, continuation of flows from 

the southwest

Dakota Sandstone (Upper Cretaceous) Includes lower part of the Oak Canyon Member and the basal conglomeratic unit The 

Oak Canyon is composed of dark-gray silty 

shale and light-gray siltstone and sandstone, 

the basal unit is composed of light-gray to 

white medium- to coarse-grained sandstone 

and conglomerate with festoon crossbedding; basal conglomerate truncates underlying units

Jurassic units undivided (Middle Jurassic) 

Includes Zuni Sandstone, Wanakah Formation, and Entrada Sandstone in northwestern part of map area The unconformity at 

the base of the Dakota Sandstone truncates 

the Zuni near the mouth of Blue Water 

Canyon and truncates the Wanakah a short 

distance south of the study area The Entrada 

Sandstone is truncated by the Wanakah Formation southwest of Petaca Pinta. All three 

units are white to pale-brown sandstone, 

form very steep slopes to vertical cliffs. The 

Zuni and Entrada are eolian, the Wanakah 

is fluviatile

Triassic units undivided (Upper Triassic) 

Includes Rock Point Member of Wingate 

Sandstone and Chinle Formation. The Rock 

Point is truncated by the Entrada Sandstone 

in the northwestern part of the study area, 

and by the Wanakah just south of the area; it 

is composed of pale- to moderate-red siltstone and mudstone, unconformable with 

the underlying Chinle Formation. The Chinle 

is composed of grayish- red to reddish- purple 

shaley siltstone and mudstone, interbedded 

locally near the valley floor with light-gray 

and tan fluviatile sandstone lenses

Contact

Location of geochemical samples

Petaca Pinta Wilderness Study Area H5
mudstone, and sparse lenses of fine-grained sandstone. 

The uppermost 150 ft of the Triassic at Petaca Pinta and 

along the central part of the western boundary of the 

study area is red massive siltstone of the Rock Point 

Member of Wingate Sandstone (Maxwell, 1988a). It 

thins rapidly, both north and south, along the west 

boundary of the study area.

The thickness of subsurface units under the study 

area is inferred, projected from outcrops 15-20 mi east 

and from wells around the area 8-26 mi distant. The 

inferred thickness of Pennsylvanian rocks is projected to 

be about 1,200 ft in the Petaca Pinta area (Kottlowski, 

1961). However, if the gravity high at and east of the area 

(fig. 4) is due to a thick limestone section as postulated, 

then the Pennsylvanian rocks could be 2,000-2,200 ft 

thick but thinning rapidly to the west, as indicated by the 

steep gravity gradient. Wengerd (1959) postulated 

massive carbonate rocks, possibly of reef origin, across 

the break in slope between the Lucero basin east of the 

study area and the Zuni positive area to the west, the type 

of rocks that could produce the gravity anomaly. Biostromal limestones are prominent in outcrops 20 mi east of 

the study area. Permian rocks in the subsurface of the 

study area are probably about 2,200 ft thick, composed of 

about 550 ft of Abo Formation, 1,000+ ft of Yeso 

Formation, 200 ft of Glorieta Sandstone, and 450 + ft of 

San Andres Limestone (Baars, 1961). About 600 ft of 

Triassic rocks are exposed on the flanks of Petaca Pinta, 

and an additional 1,000 ft is probable in the subsurface, 

to the top of the San Andres Limestone.

Other units exposed near the top of Petaca Pinta 

and on the cliffs along the western boundary of the study 

area are shown on the geologic map (fig. 2) taken from 

Maxwell (1979,1988a, b, in press) as Jurassic undivided 

and Dakota Sandstone. The Jurassic units include 

Entrada Sandstone, Wanakah Formation, and Zuni 

Sandstone. The Entrada is white- to greenish-white 

eolian sandstone, 0-200 ft thick, grading at the base into 

about 10 ft of crossbedded pebble conglomerate. The 

basal conglomerate cuts into and across bedding of the 

Rock Point Member of Wingate Sandstone and the 

Chinle Formation and is truncated in turn by the basal 

conglomerate of the overlying Wanakah Formation, both 

at angles of about 30°. The Wanakah Formation, 0-80 ft 

thick, is white to pale-brown fluviatile sandstone with 

lenses of grayish-green siltstone and pale-brown pebble 

conglomerate. It is gradational into the overlying eolian 

Zuni Sandstone. The lower 10-20 ft of the Zuni is thinto massive-bedded fluviatile sandstone grading upward 

into white to yellowish-gray massive sandstone with 

large-scale eolian crossbedding. The Zuni is about 300 ft 

thick in the northern part of the study area and thins to 

about 20 ft at the south edge because of erosional 

truncation prior to deposition of the overlying Dakota 

Sandstone. The basal unit of the Dakota Sandstone is

light-gray to white, poorly sorted, fluviatile sandstone and 

conglomerate, with rounded to angular grains and 

festoon crossbeds. Basal conglomerate truncates 

underlying formations, with local channels that cut into 

underlying rocks as much as 50 ft; thickness is 10-100 ft. 

The overlying Oak Canyon Member of the Dakota is 

exposed on Petaca Pinta and along parts of Blue Water 

Arroyo and is composed of interbedded dark-gray silty 

shale, light-gray siltstone, and grayish-tan fine-grained 

sandstone.

About 10 ft of vesicular and porphyritic basalt and 

olivine basalt caps Petaca Pinta and the mesa along the 

southwestern boundary of the study area. The flows were 

dated at 3.5 m.y. (million years) by Baldridge and others 

(1987).

Quaternary basalt flows cap several low mesas 

around the study area, on the south, east, and north sides; 

none are within the area.

Geochemistry

A reconnaissance geochemical survey of the Petaca 

Pinta Wilderness Study Area was conducted in August 

1987. Samples of drainage sediment were collected at 22 

sites on ephemeral streams draining the study area and 

vicinity. Drainage-sediment samples represent a 

composite of material eroded from the drainage basin of 

the stream sampled; panned concentrates represent the 

heavy-mineral component found in the sediment load.

Methods

Two samples were collected at each site. One of the 

samples was air dried and screened through an 80-mesh 

(0.177 mm) stainless-steel sieve to obtain the streamsediment sample, which was then pulverized to minus100 mesh (0.149 mm) for analysis. For the second sample 

at each site, about 20 Ib (pounds) of sediment was 

collected and panned to remove most of the quartz, 

feldspar, clays, and organic matter. Treatment with bromoform (specific gravity 2.8) removed the remaining 

quartz, feldspar, and other lower density minerals. 

Finally, a magnetic separation removed the magnetite 

and any other strongly magnetic minerals to produce a 

concentrate sample. The concentrate samples include 

nonmagnetic ore minerals, iron and manganese oxides, 

ferromagnesian silicates, and accessory minerals, such as 

titanite, zircon, apatite, and rutile. Concentrate samples 

were also pulverized to minus-100 mesh for analysis.

The stream-sediment and concentrate samples 

were analyzed for 35 elements by semiquantitative 

emission spectrography. In addition, the concentrate 

samples were analyzed by emission spectrography for 

platinum and palladium. The stream-sediment samples

H6 Mineral Resources of Wilderness Study Areas West-Central New Mexico
were analyzed for uranium by fluorometry and for 

arsenic, bismuth, cadmium, antimony, and zinc by 

inductively coupled plasma spectroscopy. Analytical 

data, sample-site map, and references to analytical 

methods are presented by Bullock and others (1989).

Results

Results from the geochemical studies show that 

very few distinctly anomalous concentrations of any 

element are present. Most stream-sediment samples 

contain near or below the average crustal abundance for 

a mixture of sandstone and shale. A few samples contain 

concentrations of barium, cadmium, chromium, and 

vanadium slightly above average. One stream-sediment 

sample has a highly anomalous concentration of silver, 7 

ppm (parts per million), but other element 

concentrations in the sample were not anomalous, and 

the corresponding concentrate sample contained no 

detectable silver. The sample, however, was collected 

from a stream that drains the vicinity of a prominent zone 

of alteration in the Wanakah Formation and Zuni 

Sandstone. Small deposits of travertine in the upper 

levels of the alteration indicate that it was formed by 

warm spring activity; no other mineralization was 

observed in the area. Concentrate samples contain high 

concentrations of barium, strontium, and vanadium, and 

several contain detectable molybdenum. Only 1 of the 22 

concentrate samples contains less than 10,000 ppm 

barium; 17 contain greater than 10,000 ppm. These 

consistently high concentrations of barium, as well as the 

strontium and vanadium, are probably derived from a 

thin but regionally extensive barite-rich zone in the Zuni 

Sandstone immediately below the unconformity at the 

base of the Dakota Sandstone. The minerals were 

deposited from meteoric and ground water, probably 

mediated by organic material on the unconformity.

Even though altered rocks and a barite-rich zone 

are present in the study area, concentrations of elements 

other than barium, strontium, and vanadium, and the one 

anomalous silver concentration, are near the average 

crustal abundance for shale and sandstone.

Geophysics

Aer©magnetic Data

The total intensity aeromagnetic anomaly map (fig. 

3) was compiled from two separate surveys. West of 

107°30' W. long., the survey was flown at 8,500 ft 

barometric elevation along east-west flight lines spaced 1 

mi apart (U.S. Geological Survey, 1979). The 1975IGRF 

(International Geomagnetic Reference Field) field, 

updated to the month flown, was removed. East of

107°30' W. long., the survey was flown at 8,000 ft 

barometric elevation along east-west flight lines spaced 1 

mi apart (U.S. Geological Survey, 1975). This survey was 

upward-continued to 8,500 ft using the technique 

described in Hildenbrand (1983) and the 1975 IGRF was 

removed.

The aeromagnetic map (fig. 3) shows variations in 

the magnetic field that are associated with increasing or 

decreasing magnetic minerals in the rocks, measured as 

magnetic susceptibility. A change in magnetic 

susceptibility will often generate a magnetic high that 

may be an order of magnitude greater than an anomaly 

caused by significant offset in subsurface structure. This 

can limit structural interpretation but enhance 

separation of sources having different composition.

West of the study area the magnetic field is 

relatively undisturbed. A large 400 nT (nanoTesla), 

C-shaped positive magnetic anomaly is located in the 

Petaca Pinta area. Two local maxima, north and 

southeast of the study area, occur on this regional 

positive anomaly and are not correlated with mapped 

geology or topography. This anomaly is located on the 

southwestern end of magnetic terrane that trends 

northeast from the study area for 40 mi, is about 25 mi 

wide, and is spatially associated with a northeast-trending 

gravity gradient. The magnetic terrane is delineated by 

positive magnetic anomalies that are similar in shape and 

magnitude. These positive magnetic values are caused by 

the magnetic source rock for the Quaternary basalts that 

crop out in the region; their amplitude and shape suggest 

that the source is deep and may be fault controlled. 

Although a few of the highs are associated with 

outcropping basalt, others do not correlate with the 

mapped geology, and some mapped basalt outcrops show 

no associated anomalies. This inconsistency reflects 

varying source rock geometry or magnetization, or both.

Gravity Data

The Bouguer gravity map (fig. 4) was made from 

data for 106 stations extracted from the Defense 

Mapping Agency gravity data base. These stations were 

reduced using a density of 2.67 grams per cubic 

centimeter and terrain corrected at a radius of 100 mi 

from each station. The map shows variations in the 

gravity field that are associated with changing rock 

densities or structure. The gravity map often shows 

subsurface structural detail more clearly and is less 

weighted toward compositional changes than the 

magnetic anomaly map. However, the large station 

spacing (no closer than 2 mi and sometimes as great as 12 

mi) gives the gravity map only a regional character; the 

broad or deep features are enhanced and shallow, highfrequency anomalies are missing.

A broad, 20 mGal (milligal) gravity high located 15 

mi east of Petaca Pinta is centered over Pennsylvanian

Petaca Pinta Wilderness Study Area H7
35°00' 107°30' 107°15'

34° 30'

WILDERNESS STUDY APibA

Figure 3 (above and facing page). Aeromagnetic map of the Petaca Pinta Wilderness Study Area and vicinity.

H8 Mineral Resources of Wilderness Study Areas West-Central New Mexico
EXPLANATION OF SYMBOLS

Aeromagnetic contour Hachured where contours enclose magnetic low. Contour interval 

20 nanoTeslas

Flight line location (available for 1979 survey only) 

Boundary of magnetic terrane (see text)

limestone and shale. This high suggests that a thick 

section of the the denser Pennsylvanian sedimentary 

rocks is more widespread than appears on the surface 

and in the existing boreholes north and south of the study 

area. The study area is located on a 15 mGal north-south 

gravity gradient that marks the western extent of the 

large gravity high. A local positive deflection just east of 

the study area corresponds to a magnetic low and 

suggests a smaller feature, possibly a compositionally 

distinct source for some of the less magnetic basalts that 

crop out in the area.

Radiometric Data

Aerial gamma-ray spectroscopy is a technique that 

provides estimates of the near surface (0-20 in. (inches) 

depth) concentrations of percent potassium (K), parts 

per million equivalent uranium (eU), and parts per 

million equivalent thorium (eTh). Because the uranium 

and thorium measurements utilize radioactive daughter 

nuclei that are chemically distinct from the parent nuclei, 

the uranium and thorium are described as equivalent 

concentrations. These data (K, eU, eTh) provide us with 

a partial geochemical representation of the near-surface 

materials. For a typical aerial survey each measurement 

reflects average concentrations for a surface area on the 

order of 60,000 square meters to an average depth of 

about 12 in.

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

contracted for aerial gamma-ray surveys that covered 

almost all of the coterminous United States and much of 

Alaska. The flight line spacings of these surveys vary 

from 1 mi (rare) to 10 mi and are, in general, only 

suitable for producing regional scale maps.

As part of a State mapping project, the data for 

New Mexico were compiled and processed to produce a 

series of l:l,000,000-scale maps. These maps include the 

composite-color maps described by Duval (1983). These 

maps were examined to estimate the K, eU, and eTh 

concentrations for the wilderness area and the 

occurrence or absence of anomalous radioelement 

concentrations were noted. The definition of an anomaly 

requires that the element concentration as well as its 

ratios to the other two elements all be high values in the 

context of the map.

The Petaca Pinta Wilderness Study Area has 

overall low radioactivity with concentrations of 1.0-1.5 

percent K, 1.7-2.3 ppm eU, and 6-8 ppm eTh. There are 

no anomalies within or near the study area.

MINERAL AND ENERGY RESOURCES 

Metals

No mineralized areas or occurrences of metallic 

minerals were found in the wilderness study area. No 

significant anomalies were found by the stream-sediment 

and concentrate samples; the one silver-bearing sample 

was not substantiated by the concentrate sample, nor by 

the presence of commonly associated elements. Slightly 

anomalous concentrations of barium, strontium, and 

vanadium are probably related to a thin, regionally 

extensive, barite-rich zone in the Zuni Sandstone. 

However, barite does not constitute a resource. The 

wilderness study area has a low potential for the 

occurrence of metallic mineral resources, with a certainty 

level of C.

Aerial gamma-ray spectroscopy of the region 

indicated no areas of anomalous radioactivity within or 

near the wilderness study area. Results of analysis of 

stream-sediment samples for uranium ranged from 0.35 

to 1.10 ppm, somewhat less than the average crustal 

abundance for sandstone and shale. The study area has a 

low potential for the occurrence of uranium, with a 

certainty level of C.

Oil and Gas

The area is classified by the U.S. Bureau of Land 

Management (1986) as having a moderate potential for 

the occurrence of oil, natural gas, and carbon dioxide. No 

test wells have been drilled in or near the study area, but 

wells 8 mi or more north and south of the area indicate a 

rapid eastward thickening of the Pennsylvanian 

sedimentary rocks which have a potential for both source 

and reservoirs for oil and gas. Gravity data suggest that 

the Pennsylvanian section may be even thicker in and east 

of the study area than indicated by the drilling and may 

contain reef facies that are favorable for the 

accumulation of oil and gas. The wilderness study area 

has a moderate energy resource potential for oil, natural 

gas, and carbon dioxide, with certainty level B.

Coal

Coal-bearing units do not occur within or near the 

wilderness study area, either on the surface or projected 

into the subsurface. There is no potential for coal 

resources in the study area, with a certainty level of D.

Petaca Pinta Wilderness Study Area H9
3 5 "00' 107°30' 107°15'

34°45'

APPROXIMATE BOUNDARY 

OF THE PETACA PfNTA 

WILDERNESS STUD^ARtfA 

(NM-(320~014)

EXPLANATION OF SYMBOLS

^^T) Gravity contour Hachured where contours en- 

'1 close gravity low. Contour interval 2 milliGals

 Gravity station location 

Figure 4. Bouguer gravity anomaly map of the Petaca Pinta Wilderness Study Area and vicinity.

H10 Mineral Resources of Wilderness Study Areas West-Central New Mexico
REFERENCES CITED

Baars, D.L., 1961, Permian strata of central New Mexico: New 

Mexico Geological Society, 12th Field Conference, Albuquerque Country, p. 113-120.

Baldridge, W.S., Perry, F.V., and Shafiqullah, Muhammad, 

1987, Late Cenozoic volcanism in the southeastern Colorado Plateau I., Volcanic geology of the Lucero area, 

New Mexico: Geological Society of America Bulletin, 

v. 99, p. 463-470.

Bullock, J.H., Jr., Roemer, T.H., and Nowlan, G.A., 1989, 

Analytical results and sample locality map for streamsediment and heavy-mineral-concentrate samples from 

the Rimrock (NM-020-007), Sand Cayon 

(NM-020-008), Little Rimrock (NM-020-009), Pinyon 

(NM-020-010), and Petaca Pinta (NM-020-014) 

Wilderness Study Areas, Cibola County, New Mexico: 

U.S. Geological Survey Open-File Report 89-007.

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

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

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

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

Survey Open-File Report 84-787, 42 p.

Hannigan, B.J., 1988, Mineral investigations of the Rimrock 

(NM-020-007), Little Rimrock (NM-020-009), Sand 

Canyon (NM-020-008), Pinyon (NM-020-010), and 

Petaca Pinta (NM-020-014) Wilderness Study Areas, 

Cibola County, New Mexico: U.S. Bureau of Mines Open 

File Report MLA 13-88, 13 p.

Hildenbrand, T.G., 1983, FFTFIL: a filtering program based on 

two-dimensional Fourier analysis: U.S. Geological 

Survey Open-File Report 83-237, 30 p.

Kottlowski, F.E., 1961, Pennsylvanian rocks in north-central 

New Mexico: New Mexico Geological Society, 12th Field 

Conference, Albuquerque Country, p. 97-104.

Logsdon, M.J., 1981, Preliminary evaluation of the mineral 

resource potential of the Petaca Pinta Wilderness Study 

Area, Cibola County, New Mexico: New Mexico Bureau 

of Mines and Mineral Resources Open-File Report 161, 

45 p.

Maxwell, C.H., 1979, Geologic map of the East Mesa 

quadrangle, Valencia [now Cibola] County, New Mexico: 

U.S. Geological Survey Geologic Quadrangle Map 

GQ-1522, scale 1:24,000.

___ 1988a, Geologic map of the Cerro Del Oro quadrangle, 

Cibola County, New Mexico: U.S. Geological Survey 

Miscellaneous Field Studies Map MF-2033, scale 

1:24,000.

___ 1988b, Geologic map of the Marmon Ranch 

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

Geological Survey Miscellaneous Field Studies Map 

MF-2049, scale 1:24,000.

___ in press, Geologic map of the Broom Mountain 

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

Geological Survey Geologic Quadrangle Map GQ-1666, 

scale 1:24,000.

U.S. Bureau of Land Management, 1986, New Mexico 

Statewide Wilderness Study, vol. 2, Wilderness analysis 

reports, Appendix 11, 36 p.

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. Geological Survey, 1975, Aeromagnetic map of an area 

north of Albuquerque, New Mexico: U.S. Geological 

Survey Open-File Report 75-187, scale 1:125,000.

___ 1979, Aeromagnetic map of the Malpais area, New 

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

79-1644, scale 1:250,000.

Wengerd, S.A., 1959, Regional geology as related to the 

petroleum potential of the Lucero region, west-central 

New Mexico: New Mexico Geological Society, 10th Field 

Conference, West-central New Mexico, p. 121-134.

Petaca Pinta Wilderness Study Area H11

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

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

s

UJ 1

3</>

UJ

cc

UJ

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.

4<M2. 

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

ECONOMIC

MARGINALLY 

ECONOMIC

SUBECONOMIC

IDENTIFIED RESOURCES

Demonstrated

Measured Indicated

1 

Reserves

Marginal Reserves

Demonstrated 

Subeconomic Resources

Inferred

Inferred Reserves

Inferred 

Marginal Reserves

Inferred 

Subeconomic 

Resources

UNDISCOVERED RESOURCES

Probability Range

 (or) 

Hypothetical i Speculative

I

+

1

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

resource estimates and public policy: American Scientist, v.60. p.32-40, and U.S. Bureau of Mines snd U.S. Geological Survey, 1980. 

Principles of a resource/reserve classification for minerals: U.S. Geological Survey Circular 831, p.S.
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 Archean

Middle Archean

Early Archean 

:hean*

PERIOD

Quaternary

Tertiary

Neogene 

Subperiod

Paleogene 

Subperiod

Cretaceous

Jurassic

Triassic

Permian

Carboniferous 

Periods

Pennsylvanian

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

IB

- 55

__ cc

- 96

-. 1OQ

-A. 240

Z27v

 «j 330

oen

- 410

 500

.~ 570 1

- 900 

- 1600

-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: 1989-673-047/86068
Mineral Resources of Wilderness Study Areas 

West-Central New Mexico

This volume was published as 

separate chapters A-H

U.S. GEOLOGICAL SURVEY BULLETIN 1734

CONTENTS

[Letters designate the chapters]

(A) Mineral Resources of the Jornada del Muerto Wilderness Study Area, Socorro and Sierra Counties, New Mexico: by Donald H. Richter and Richard 

W. Saltus, U.S. Geological Survey, George S. Ryan, U.S. Bureau of Mines

(B) Mineral Resources of the Antelope Wilderness Study Area, Socorro County, 

New Mexico: by Donald H. Richter and Richard W. Saltus, U.S. Geological 

Survey, Stanley L. Korzeb, U.S. Bureau of Mines

(C) Mineral Resources of the Horse Mountain and Continental Divide Wilderness Study Areas, Catron County, New Mexico: by James C. Ratte, Richard 

W. Saltus, and Robert L. Turner, U.S. Geological Survey, Carl L. Almquist 

and Robert H. Wood, 2d, U.S. Bureau of Mines

(D) Mineral Resources of the Sierra de las Caiias Wilderness Study Area, Socorro County, New Mexico: by Samuel L. Moore, Robert L. Turner, and 

H.R. Blank, Jr., U.S. Geological Survey, Stanley L. Korzeb, U.S. Bureau of 

Mines

(E) Mineral Resources of the Little Black Peak and Carrizozo Lava Flow Wilderness Study Areas, Lincoln County, New Mexico: by Douglas B. Stoeser and 

Michael K. Senterfit, U.S. Geological Survey, Jeanne E. Zelten, U.S. Bureau 

of Mines

(F) Mineral Resources of the Sierra Ladrones Wilderness Study Area, Socorro 

County, New Mexico: by Samuel L. Moore, Michael S. Alien, and Carl L. 

Long, U.S. Geological Survey, John T. Neubert, U.S. Bureau of Mines

(G) Mineral Resources of the Rimrock, Sand Canyon, Little Rimrock, and Pinyon Wilderness Study Areas, Cibola County, New Mexico: by Charles H. 

Maxwell, Gary A. Nowlan, and Viki Bankey, U.S. Geological Survey, Brian J. 

Hannigan, U.S. Bureau of Mines

(H) Mineral Resources of the Petaca Pinta Wilderness Study Area, Cibola 

County, New Mexico: by Charles H. Maxwell, Gary A. Nowlan, and Viki 

Bankey, U.S. Geological Survey, Brian J. Hannigan, U.S. Bureau of Mines



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