Mineral Resources of the

Gila Lower Box Wilderness Study Area,

Grant and Hidalgo Counties, New Mexico

U.S. GEOLOGICAL SURVEY BULLETIN 1735-A

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NEW MEXICO -ii.., -- ' **#$***

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Chapter 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, and JOSEPH S. DUVAL 

U.S. Geological Survey

GEORGE S. RYAN 

U.S. Bureau of Mines

U.S. GEOLOGICAL SURVEY BULLETIN 1735

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

DONALD PAUL MODEL, Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

UNITED STATES GOVERNMENT PRINTING OFFICE: 1988

For sale by the

Books and Open-File Reports Section

U.S. Geological Survey

Federal Center

Box 25425

Denver, CO 80225

Library of Congress Cataloging-in-Publication Data

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

Hidalgo Counties, New Mexico.

(Mineral resources of wilderness study areas southwestern New Mexico ; 

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

Bibliography: p.

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

1. Mines and mineral resources New Mexico Gila Lower Box Wilderness. 

2. Gila Lower Box Wilderness (N.M.) I. Richter, Donald H. II. Series. 

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

QE75.B9 no. 1735-A 557.3 s [557.89] 87-600388 

[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 Gila Lower Box 

Wilderness Study Area (NM-030-023), Hidalgo and Grant Counties, New Mexico.

CONTENTS

Abstract Al 

Summary Al 

Introduction A2

Investigations by the U.S. Bureau of Mines A3 

Investigations by the U.S. Geological Survey A3 

Appraisal of identified resources A4

Mining and mineral exploration history A4

Caprock mining district A4 

Mines, prospects, mining claims, and leases A4 

Consolation mine A4 

Black Bob prospect A4 

Prospects within the study area A4 

Mineral and energy occurrences A4 

Sand and gravel A4 

Oil and gas A4 

Sand-casting tuff occurrence AS 

Assessment of mineral resource potential AS 

Geology AS 

Geochemistry AS

Analytical methods AS 

Results A8 

Geophysics A8

Gravity data A8 

Aeromagnetic data A10 

Aerial gamma-ray data A10 

Mineral and energy resources All 

References cited A12 

Appendix A15

FIGURES

1-5. Maps of the Gila Lower Box Wilderness Study Area and vicinity showing:

1. Mineral resource potential and identified resources A2

2. Location A3

3. Geology A6

4. Terrain-corrected Bouguer gravity anomaly contours A9

5. Filtered aeromagnetic anomaly contours All

Contents V

MINERAL RESOURCES OF WILDERNESS STUDY AREAS-SOUTHWESTERN NEW MEXICO

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, and Joseph S. Duval 

U.S. Geological Survey

George S. Ryan 

U.S. Bureau of Mines

ABSTRACT

The Gila Lower Box Wilderness Study Area 

(NM-030-023) is in Grant and Hidalgo Counties in 

southwestern New Mexico, 27 mi (miles) northwest of Lordsburg. Identified resources of manganese, which have been 

mined in the past, occur within 0.25 mi of the study area 

boundary, but none are known within the study area. There 

are no other identified resources. The study area has (1) high 

mineral resource potential for manganese in its eastern part, 

(2) moderate mineral resource potential for manganese in its 

western part, and (3) low mineral and energy resource 

potential throughout for other metals, gemstone, geothermal 

energy, and oil and gas (fig. 1).

SUMMARY

The topography of the Gila Lower Box Wilderness 

Study Area (location map, fig. 2) is dominated by a 200- to 

500-ft-deep canyon cut into the layered Tertiary (see 

geologic time chart in Appendix) volcanic rocks by the Gila 

River. The area is accessible by improved and unimproved 

dirt roads.

The rocks in the study area consist of layered Tertiary 

volcanic rocks and associated volcaniclastic rocks with a total 

thickness of more than 2,500 ft (feet). Some of the volcanic 

rocks are covered by younger alluvial deposits, but most 

bedrock exposures are good. Canador Peak, an andesitic 

dome, is the only known volcanic vent in the study area; the 

remainder of the volcanic rocks are from sources outside the 

study area. Geologic mapping outside the study area 

indicates that the volcanic sequence is underlain by 

sedimentary rocks of Cretaceous age that lie on Precambrian 

granite. Structurally, the area is tilted 5-20° to the northeast 

along northwest-trending normal faults that have offsets of

less than 500 ft. Faulting occurred during middle to late 

Tertiary time and is related to Basin and Range extension.

Identified resources of manganese are in shallow veins 

in the Caprock mining district (fig. 1), 2 mi to the southeast, as 

well as in veins only 0.25 mi east and north of the study area. 

The Caprock mining district produced 5,000 tons of 

manganese oxide in the 1950's. The ore is in discontinuous 

veins in volcanic conglomerate. The Consolation mine, 0.25 

mi east of the study area, produced 10,000 tons of ore from 

a fault zone. The Black Bob prospect, 0.25 mi north of the 

study area, has had no known production, although the 

property has a 75-ft-deep shaft.

Material from a discontinuous tuff bed that crops out 0.5 

mi northeast of the study area has been used by a local 

silversmith for sand casting. The tuff is not known to occur 

within the study area.

Sand and gravel deposits south of the study area have 

been used locally, but none have been mined in the study 

area.

A geochemical study found only one sample containing 

tin, barium, and chromium in anomalous amounts. Although 

this sample was collected within the study area, it actually 

represents sediment from a drainage largely outside the 

study area, and the anomalous values are assumed to 

represent rocks outside the study area.

Geophysical data do not indicate the presence of any 

mineral resources in the study area. However, the gravity 

data indicate the presence of a northwest-trending fault, 

related to Basin and Range deformation, in the southwest 

margin of the study area.

The Gila Lower Box Wilderness Study Area has a high 

mineral resource potential for manganese in its eastern part, 

and a moderate mineral resource potential for manganese in 

its western part, with certainty level C, based on the presence 

of manganese vein deposits nearby, as well as the presence

Gila Lower Box Wilderness Study Area A1
10B-55' 10B*50'

Consolation mine 

. 

N

\APPROXIMATE BOUNDARY OF THE 

6ILA LOHER BOX (NM-030-023) 

WILDERNESS STUDY AREA To

Caprock mining 

district

Hidalgo County

EXPLANATION

[Entire study area has a low mineral and energy resource potential for all metals (other than manganese), gemstone, geothermal energy, and oil and 

gas, with certainty level C]

C

M/C

Identified resources 

Manganese-vein mine

Manganese-vein prospect

Geologic terrane having high mineral resource potential for 

manganese in vein deposits, with certainty level C

Geologic terrane having moderate mineral resource potential 

for manganese in vein deposits , with certainty level C

Certainty level Data indicate geologic environment 

and resource potential but do not establish 

activity of resource-forming processes

+ Sand-casting tuff occurrence

 USBM sampling locality

X Prospect pit

 Unimproved dirt road

Figure 1. Summary map showing mineral resource potential and identified resources of the Gila Lower Box Wilderness Study 

Area and vicinity, Grant and Hidalgo Counties, New Mexico.

of suitable structures and bedrock exposures especially in 

the eastern part of the study area. The mineral and energy 

resource potential is low for other metals, gemstone, geothermal energy, and oil and gas, with certainty level C.

INTRODUCTION

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

USBM (U.S. Bureau of Mines) studied 5,835 acres of the 

8,555-acre Gila Lower Box Wilderness Study Area 

(NM-030-023) as requested by the BLM (U.S. Bureau 

of Land Management). In this report the studied area is

referred to as the "wilderness study area" or simply the 

"study area."

The Gila Lower Box Wilderness Study Area is in 

Hidalgo and Grant Counties in southwestern New 

Mexico, approximately 27 mi northwest of Lordsburg 

(fig. 2). Access to the study area south of the Gila River 

is provided by improved dirt roads that branch off U.S. 

Highway 70 about 13 and 19 mi northwest of Lordsburg, 

and by an unimproved dirt road off New Mexico State 

Highway 92 just south of the Gila River bridge. Access to 

the study area north of the Gila River is more difficult 

but may be obtained by an unimproved dirt road that 

extends east from New Mexico State Highway 92 just

A2 Mineral Resources of Wilderness Study Areas Southwestern New Mexico
109*00* 108*30'

Hidalgo County 

APPROXIMATE BOUNDARY 

OF THE 8ILA LONER BOX 

HILOERNESS STUDY AREA

Figure 2. Map showing location of the Gila Lower Box 

Wilderness Study Area, Grant and Hidalgo Counties, New 

Mexico.

north of the Gila River bridge. All the dirt roads can be 

difficult to travel during and after periods of inclement 

weather.

The wilderness study area is on the south slope of 

the Mogollon volcanic highlands, a transition zone 

between the southern Basin and Range physiographic 

province to the south and the Colorado Plateau to the 

north. The area's main physiographic feature is a 200- to 

500-ft-deep canyon cut into layered volcanic rocks of 

Tertiary age (15-35 m.y. (million years) old) by the Gila 

River. Uplands south of the river are characterized by a 

gently north-dipping alluvial plain that is locally transected by small canyons and arroyos. A few low hills 

protrude above the alluvial surface. Elevations range 

from 4,500 ft above sea level on the slopes of Canador 

Peak to about 3,800 ft where the Gila River flows out of 

the study area.

This report presents an evaluation of the mineral 

endowment (identified resources and mineral resource 

potential) of the Gila Lower Box Wilderness Study Area 

and is the product of several separate studies by the 

USBM and the USGS. Identified resources are classified 

according to the system of the USBM and USGS (1980), 

which is shown in the Appendix. 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), which is shown in the 

Appendix. The potential for undiscovered resources is 

studied by the USGS.

Investigations by the U.S. Bureau of Mines

The USBM investigation included, in 1984, a 

review of published material relating to the mineral 

resources and mining activity in and near the study area. 

Claim status was checked in the BLM claim files. Four 

rock-chip and two grab samples were taken (fig. 1). All 

samples were analyzed for gold and silver by fire assay. 

Copper, manganese, molybdenum, lead, and zinc were 

determined by inductively coupled plasma-atomic 

emission spectrometry. Results are discussed by Ryan 

(1985).

Investigations by the U.S. Geological Survey

Field investigations consisted of about two weeks 

of geologic mapping in 1985, geochemical sampling, and 

examination of mines and prospects to help determine 

potential deposit types. Geologic studies were aided by 

previous mapping in the area (D.C. Hedlund and T.L. 

Finnell, unpub. mapping, 1979, Canador Peak IVz' 

quadrangle, New Mexico). The lack of bedrock 

throughout large sections of the study area, especially 

south of the Gila River, together with the absence of 

locally derived alluvium rendered the geochemical 

investigation meaningless in a major part of the study 

area. Large-scale gravity and aeromagnetic maps of the 

wilderness study area and vicinity were prepared from 

gravity and magnetic data used in the USGS's mineral 

resource assessment of the Silver City 1° x 2° quadrangle, 

New Mexico and Arizona (Wynn, 1981; Klein, 1987). No 

new geophysical data were acquired for this resource 

evaluation.

Acknowledgments. Personnel of the BLM in Las 

Cruces, N. Mex., were extremely helpful in providing 

background information on the wilderness study area. 

Thanks are also due James C. Ratte, USGS, and William 

C. Mclntosh, a graduate student at New Mexico Institute 

of Mines and Technology, who accompanied D.H. 

Richter during the geologic investigations of the area and 

provided pertinent observations regarding some of the 

geology.

Gila Lower Box Wilderness Study Area A3
APPRAISAL OF IDENTIFIED RESOURCES

By George S. Ryan 

U.S. Bureau of Mines

Mining and Mineral Exploration History

Shallow manganese occurrences associated with 

hot-spring transportation and concentration are found in 

faults near the study area (Elston, 1960). Hot-spring 

deposits of opal and travertine, and minor amounts of 

manganese, are found in prospect pits within the study 

area (fig. 1), but none are economic.

No mines or claims are in the study area, but 

manganese was produced from mines within 0.25-2 mi of 

the study area boundary. All of the producing manganese 

zones are shallow, the deepest being 70 ft in the Caprock 

mining district (Gillerman, 1964). Secondary enrichment 

associated with hot-springs activity concentrated the 

manganese minerals (Elston, 1960). The low-grade 

manganese ore produced was upgraded by jigging to 

concentrates of 43 percent manganese oxide before 

shipping (Gillerman, 1964).

Caprock Mining District

The Caprock mining district, 2 mi southeast of the 

study area (fig. 1), produced 5,000 tons of manganese 

oxide from near-surface deposits in the 1950's, and is 

considered to have identified manganese resources. Ore 

minerals were mainly psilomelane and minor pyrolusite 

(Gillerman, 1964). The ore is in discontinuous sections of 

small fractures within a volcanic conglomerate.

Mines, Prospects, Mining Claims, and Leases

The Consolation mine, east of the study area, was 

sampled and the various workings in the Caprock mining 

district, southeast of the study area, were examined 

during this survey. The Black Bob prospect, north of the 

study area, was also sampled. Both the Consolation mine 

and the Black Bob prospect are considered to have 

identified manganese resources. A cluster of small 

prospect pits and trenches within the study area were 

examined and 3 samples were taken (fig. 1).

Consolation Mine

During the 1950's, about 10,000 tons of ore 

assaying 8-10 percent manganese was produced from the 

Consolation mine, Vi mi east of the study area. The ore 

was produced from an 8- to 14-ft-thick fault zone over a

N. 45° W. strike length of 120 ft (Gillerman, 1964). At the 

surface the footwall is a well-defined, 50-ft-high, nearvertical cliff in basaltic andesite. The hanging wall is in 

the Gila Conglomerate (Miocene to Pleistocene). Two 

samples taken at the north face of the surface slope 

assayed 5.6 percent manganese on the footwall part of 

the vein and 1.3 percent manganese on the hanging wall 

part. Discontinuous calcite and quartz veinlets within the 

mineralized zone are characteristic of the veins in the 

area. The Consolation mine vein does not project into the 

study area.

Black Bob Prospect

The Black Bob prospect is 0.25 mi north of the 

study area (fig. 1) in a thick unit of andesite flows. A 

75-ft-deep shaft inclined 78° SW., which was inaccessible 

at the time of this study, once provided entry to a 

12-ft-wide east-striking zone of argillized brecciated 

basalt and gouge containing disseminated psilomelane 

(Gillerman, 1964). A sample, taken from altered gouge 

near the top of the shaft, assayed less than 0.1 percent 

manganese. The extent of underground workings is not 

known nor is there any record of production. The east 

trend of the brecciated basalt zone parallels the northern 

boundary of the study area.

Prospects Within the Study Area

Several small pits and trenches in calcite- and 

quartz-bearing outcrops are found near the north end of 

the westernmost road within the study area (fig. 1). Two 

samples were collected at three of the pits; the highest 

manganese assay from these samples was 0.44 percent; 

no resources were identified. Joint planes and minor 

fractures were locally coated with quartz and calcite. The 

host rock is a volcanic conglomerate, the same as in the 

Caprock mining district.

Mineral and Energy Occurrences

Sand and Gravel

Unconsolidated terrace gravels are widely 

distributed south of the study area and have been a major 

local source of sand and gravel. The limited exposures of 

similar terrace gravels within the southern part of the 

study area are not readily accessible and therefore not 

likely to be developed.

Oil and Gas

No oil or gas wells have been drilled in the study 

area or in the immediate vicinity, and there are no oil and 

gas leases in the study area.

A4 Mineral Resources of Wilderness Study Areas Southwestern New Mexico
Sand-Casting Tuff Occurrence

A thin, discontinuous, ash-flow tuff (included in 

the Gila Conglomerate, unit QTg, fig. 3) crops out in 

Nichols Canyon, 0.5 mi northeast of the study area, and 

has been used by a local silversmith for sand casting (T.L. 

Finnell, USGS, oral commun., 1987). Prior to using this 

tuff the artist paid $2/lb in 1979 for a similar material. 

The tuff bed is about 1.5 ft thick and has a fairly small 

known outcrop area. There are no known outcrops of the 

tuff in the study area.

ASSESSMENT OF MINERAL 

RESOURCE POTENTIAL

By Donald H. Richter, Viki A. Lawrence, 

Harlan Barton, William Hanna, and 

Joseph S. Duval 

U.S. Geological Survey

Geology

The wilderness study area is along the southern 

margin of the Mogollon volcanic highlands, a very large 

and complex Tertiary volcanic province in New Mexico 

and Arizona. The area also lies at the north end of the 

Burro Mountains arch (Stacey and Hedlund, 1983), a 

structurally positive element during late Precambrian, 

Paleozoic, and most of Mesozoic time.

A sequence of layered volcanic rocks and 

associated volcaniclastic rocks of middle Tertiary age 

underlies most of the wilderness study area (fig. 3). 

Bedrock exposures are generally good except for some of 

the highlands south of the Gila River, which are locally 

covered by younger alluvial deposits. The layered 

volcanic and volcaniclastic rock sequence totals more 

than 2,500 ft thick. From oldest to youngest, it consists of 

(1) a 33-m.y.-old ash-flow tuff, (2) volcaniclastic rocks 

derived from an andesitic terrain, (3) two 28- to 30-m.y.- 

old ash-flow tuffs Oligocene Bloodgood Canyon Tuff 

and the tuff of Fall Canyon, (4) a series of andesitic to 

basaltic lava flows, which in part are as young as 21 m.y., 

and (5) a thick unit of conglomerate and coarse 

sandstone, the Gila Conglomerate, that was largely 

deposited after the cessation of eruptive volcanic activity. 

The base of this layered volcanic sequence is only 

observed locally on Canador Peak where it unconformably overlies a 35-m.y.-old andesite dome.

None of the volcanic rocks in the layered sequence 

appear to have been erupted from vents in or near the 

wilderness study area. The older ash-flow tuff is probably 

a caldera-related tuff from the Cliff eruptive center, 20 

mi to the northeast (Drewes and others, 1985). Both the

Bloodgood Canyon Tuff and the tuff of Fall Canyon are 

regional ash-flow tuff sheets (Ratte and others, 1984). 

The Bloodgood Canyon Tuff is related to the collapse of 

the Bursum caldera, 45 mi to the north; the tuff of Fall 

Canyon is from an undetermined location. The andesitic 

to basaltic lava flows were probably erupted from linear 

rift zones to the north of the study area. The andesitic 

dome of Canador Peak is the only volcanic vent known to 

occur in the study area. However, geologic and geochemical evidence suggests that this center is an 

unfavorable environment for ore deposition.

The volcanic rocks of the wilderness study area 

have high-potassium calc-alkaline affinities, typical of the 

rocks throughout the eastern margin of the Western 

United States orogenic belt (Ewart, 1979). They were 

erupted during extensional tectonism in the middle and 

late Tertiary in response to plate interactions along the 

western margin of the orogen.

No Paleozoic rocks are known to be present in the 

section underlying the wilderness study area. Based on 

geologic studies beyond the boundaries of the wilderness 

study area (D. C. Hedlund and T. L. Finnell, unpub. 

mapping, 1979), the Upper Cretaceous Virden 

Formation of Elston (1960), as thick as 1,800 ft, overlies 

a thicker section of Cretaceous marine and nonmarine 

rocks, including the Upper(?) Cretaceous Beartooth 

Quartzite and the Upper Cretaceous Colorado 

Formation, which were deposited directly on a Precambrian granitic terrain. The middle Tertiary volcanic and 

volcaniclastic rocks of the area overlie, at relatively 

shallow depths, nonmarine shale, sandstone, and pebble 

conglomerate of the Virden Formation.

Structures in the wilderness study area and 

surrounding region do not appear to be complex. The 

layered volcanic rocks are tilted 5-20° to the northeast 

along a series of northwest-trending, steeply dipping 

normal faults, with maximum offsets on individual faults 

probably less than 500 ft. The faults are mostly middle to 

late Tertiary in age, are related to Basin and Range 

extension, and some may reflect older pre-Tertiary 

structures.

Geochemistry

Analytical Methods

A reconnaissance geochemical survey was 

conducted in April 1985. Heavy-mineral concentrates 

derived from stream sediments were selected as the 

primary sample medium. The removal of most of the 

rock-forming silicates, clays, and organic material 

permits the determination of elements not generally 

detectable in bulk stream sediments by the analysis 

methods available. Some of these elements can be

Gila Lower Box Wilderness Study Area A5
A6 Mineral Resources of Wilderness Study Areas Southwestern New Mexico
CORRELATION OF MAP UNITS

Surficial deposits

Qa

Qac

Volcanic and sedimentary rocks

Tr

QTg

Tb

Ta

Tt

Ts

Tit

Tac

Tas

Holocene 

> Pleistocene

Pliocene 

Miocene

Oligocene

QUATERNARY

TERTIARY

=

57

CO

a

DESCRIPTION OF MAP UNITS

Qa Alluvial deposits (Holocene) Alluvium in active flood plain of Gila River and some major 

tributaries. Deposits range from fine silt to boulders. Maximum thickness may be as much as 

100ft

Qac Alluvial and colluvial deposits, undivided (Holocene and Pleistocene) Chiefly alluvium in 

extensive alluvial fans on upland surfaces above present stream levels. Includes talus and 

slopewash on valley walls and hillsides and pediment gravels locally. Chiefly sand and 

gravel. Maximum thickness about 200 ft

QTg Gila Conglomerate (Pleistocene, Pliocene, and Miocene) Consists of upper unit of weakly 

consolidated, interbedded silt, sand, and gravel, and a lower unit of moderately to highly 

indurated coarse sandstone and conglomerate. On Caprock Mountain, lower unit contains 

chiefly subangular to rounded clasts of Bloodgood Canyon Tuff and tuff of Fall Canyon 

(unit Tt) as much as 6 in. in diameter. Near the mouth of Nicholas Canyon, a thin discontinuous ash-flow tuff is interbedded in the silt and gravel. Maximum thickness of upper unit, 

about 400 ft; lower unit may be more than 300 ft thick

Tb

Tr

Ta

Tas

Tt

Ts

Tit

Tac

Basalt flows (Miocene) Dark-gray, slightly p

plagioclase in a fine-grained intergranula

opaque minerals. Whole rock, from flow 

yielded a whole-rock K-Ar age of about 2

mapping, 1979). Maximum thickness ab

Rhyolite plug of Red Hill (Miocene or Ol

sparsely porphyritic rhyolite containing ph

(1 percent), and biotite (traces) in a crypt

Andesite flows (Miocene and Oligocene) D

erately porphyritic lava containing as mu

intergranular to pilotaxitic matrix of feld

minerals. Probably gradational with (and 

Tb) Maximum thickness about 400 ft

Andesite sill (Miocene or Oligocene) Dark-

plagioclase (10-15 percent) and hornblen

intrudes sandstone beds of unit Ts. Maxi

Ash-flow tuffs (Oligocene) Consists of uppe

lower unit of tuff of Fall Canyon (30 m.y.

gray and densely welded. It is moderately 

percent), quartz (1-3 percent), and biotite 

Bursum caldera(Ratteand others, 1984), 

approximately 200 ft. The tuff of Fall Can

erately welded. It is crystal rich, containin

(9 percent), quartz (9 percent), and biotit

Source is undetermined. Maximum thickn

flow tuffs are locally separated by thin sa

Sandstone (Oligocene) Greenish-gray, thin

tic sandstone composed chiefly of andesi

Ash-flow tuff (Oligocene) Light-brownish-g

posed of a lower densely welded unit and 

are moderately crystal rich, containing cry

cent), and biotite and plagioclase (traces) 

K-Ar age of approximately 33 m.y. (D. C

1979). Source unknown but maybe relat

the study area. Maximum thickness abou

Andesite dome of Canador Peak (Oligoce

andesite, containing phenocrysts of hornb

microlites (30-40 percent) in a cryptocry

yielded a K-Ar age of approximately 35 

approximately26 m.y. (D. C. Hedlundand

has probably been reset. Maximum thick

Contact Known, approximate, and inferred

Fault Dotted where concealed Ball and bar 

Strike and dip of bedding and primary laye

> Figure 3. Geologic map of the Gila Lower Box Wilderness Study Area and vicinity. (Geology mapped by D.C. Hedlund and 
constituents of minerals related to ore-forming processes 

rather than rock-forming ones. These minerals include 

sulfide and oxide minerals such as pyrite (FeS2 ), galena 

(PbS), cassiterite (SnO2 ), sphalerite (ZnS), chalcopyrite 

(CuFeS2 ), stibnite (Sb2S3 ), and cinnabar (HgS). Other 

minerals concentrated in this medium are gold (Au), 

barite (BaSO4 ), and scheelite (CaWO4 ).

Fresh rocks were analyzed to provide background 

geochemical information. Altered and mineralized rocks 

from the vicinity of the Consolation mine were analyzed 

to provide information about the geochemical signature 

of the mineralizing system. Analytical data, sample sites, 

and a description of the geochemical sampling and 

analytical techniques are given in Barton and Day (1987).

Heavy-mineral-concentrate samples were collected 

at 19 sites from active alluvium in first-order and secondorder streams. Samples were composited across the 

stream channel. Rock samples were collected from three 

sites.

To produce the heavy-mineral concentrate, bulk 

stream sediment was sieved through a 10-mesh (2.0-mm) 

screen. Approximately 10 pounds of the minus-10-mesh 

sediment was panned to remove most of the quartz, 

feldspar, organic materials, and clay-sized material. The 

panned concentrate was separated into light and heavy 

fractions using bromoform (heavy liquid, specific gravity 

2.8). The light fraction was discarded. The material of 

specific gravity greater than 2.8 was separated further 

into three fractions (highly magnetic, weakly magnetic, 

and nonmagnetic) using a modified Frantz1 Isodynamic 

Separator. The nonmagnetic fraction was hand ground 

and saved for analysis.

Rock samples were crushed and then pulverized to 

minus 0.15 mm with ceramic plates prior to analysis.

The heavy-mineral-concentrate and rock samples 

were analyzed for 31 elements using a semiquantitative, 

direct-current arc-emission spectrographic method 

(Grimes and Marranzino, 1968).

Results

One heavy-mineral-concentrate sample was 

determined to contain anomalous tin (2,000 ppm (parts 

per million)), barium (5,000 ppm), and chromium (500 

ppm). The sample was from the major drainage flowing 

south between Canador Peak and Rimrock, a drainage 

from an area mostly outside of the study area extending 

2.5 mi north to the southern slopes of Black Mountain. It 

was sampled within the study area, near the confluence 

with the Gila River, 1.2 mi southeast of Canador Peak.

:Any use of trade names in this report does not constitute 

endorsement by the USGS.

The anomaly probably reflects the lithology of the 

Bloodgood Canyon Tuff and the tuff of Fall Canyon, 

which are exposed in the drainage basin on the slopes of 

Rimrock. No alteration or mineralization was observed 

in the study area, nor are there any exposures of the 

high-silica rhyolite associated with the Bursum caldera to 

the north, which contains high concentrations of tin as 

cassiterite (Ratt6 and others, 1984). No occurrence of 

mafic or ultramafic intrusive bodies are known as a 

source of the chromium.

Geophysics

The Gila Lower Box study area and vicinity (lat 

32°35' to 32°40' N., long 108°49' to 108°57' W.) are 

covered by regional gravity and detailed aeromagnetic 

surveys having sufficient resolution to define anomalies 

of one-third square mile or more in areal extent. Gravity 

data are in the form of a terrain-corrected Bouguer 

gravity anomaly map (Wynn, 1981), based largely on 

about 20 stations within or adjacent to the area of figure 

4. The geologic significance of the gravity map must be 

partly based on the relationships of anomalies to known 

source rocks outside of the map area. These relationships 

were studied by using the filtered aeromagnetic anomaly 

map of Klein (1983) and the areally extensive 

compilation of Cordell and others (1982). Aeromagnetic 

data are in the form of a filtered anomaly map (Klein,

1983), based largely on measurements made along 21 

east-west flight lines spaced 0.6 mi apart, at an average 

altitude of 1,500 ft above ground. Knowledge of rock 

density and magnetization (average dipole moment per 

unit volume) of units within the map area is based largely 

on measurements made in nearby areas (Bath, 1976; 

Klein and Johnson, 1983; Klein and Wynn, 1984), 

supplemented by a few measurements of the authors.

Gravity Data

The gravity data show four significant features in or 

near the area of figure 4, two highs and two lows, parts of 

which extend into the study area. A high centered 

northwest of the map area is inferred to be caused 

principally by Precambrian granitic rocks, which are 

known to have densities much higher than the average 

density of Tertiary volcanic rocks (Klein and Wynn,

1984). The high flattens southward for a distance of 4 mi 

over a region underlain by tuffs and flows, which are 

extensively covered by Quaternary deposits, and finally 

noses out over the andesite dome of Canador Peak. The 

source of this flattened part of the high and its southpointing nose is ambiguous. The feature may express a 

southward continuation of Precambrian granitic rocks at 

increasingly greater depth in the study area, but it is

A8 Mineral Resources of Wilderness Study Areas Southwestern New Mexico
108»55' 108*50'

32«40'

32°35'

APPROXIMATE BOUNDARY OF 

6ILA LOWER BOX 

WILDERNESS 

STUDY AREA

3 MILES

J

EXPLANATION

 0 Gravity contour Contour interval 2.5 milliGals. Arbitrary datum

H Gravity high

|_ Gravity low

A Gravity anomaly- Referred to in text

-j- Gravity station

Figure 4. Terrain-corrected Bouguer gravity anomaly map of the Gila Lower Box Wilderness Study Area and vicinity. 

(Data from Wynn, 1981.)

probably caused in part by intermediate volcanic rocks, 

such as the andesite, having densities higher than 

Tertiary volcanic rocks and adjacent Quaternary 

deposits.

In the southeastern corner of the map area, a small 

part of another high trends northwest over limited 

outcrops of volcanic rocks extensively covered by 

Quaternary deposits. Because this high extends northwestward to within a mile or two of the study area, its 

source is of interest. Gravity data outside of the map area 

(Klein, 1983) show that the high links with two other 

highs, one associated with an isolated exposure of Precambrian granitic rocks and the other with a larger 

complex of Mesozoic intrusive and volcanic rocks, about 

5 and 9 mi south-southeast of the southeastern corner of 

the map area, respectively. These associations of

Gila Lower Box Wilderness Study Area A9
anomaly to exposed rock imply that the hidden source 

within the map area is Precambrian granitic rocks, Mesozoic intrusive and volcanic rocks, or both.

A major low partly shown in the southwestern 

corner of the map area is associated with low-density 

basin-fill and alluvial deposits, which are inferred to 

reach their maximum thickness about 3 mi west of the 

southwestern corner of the map area. The steep, nearly 

linear gradient of the anomaly suggests the presence of a 

vertical fault presumed to be related to Basin and Range 

deformation and having a northwest-trending trace near 

the southwestern margin of the study area.

In the northeastern part of the map area, a low is 

part of another regional low associated with basin-fill and 

alluvial deposits, which are inferred to gradually increase 

in thickness southeast of the southeast corner of the map 

area. This feature may also be caused by a northwesttrending Basin and Range fault, but its occurrence and 

definition is less certain.

The four major gravity anomalies converge over a 

region including most of the study area, forming a saddle 

punctuated by a single contour closure marking a weak 

residual high ( A on fig. 4). Anomaly gradients within the 

study area are generally low, with no manifestation that 

specific volcanic rock units are appreciably lower or 

higher on average than others. The exception previously 

noted is that the andesite of Canador Peak appears to be 

a little denser than most of its neighboring volcanic rocks 

in the subsurface.

Aeromagnetic Data

Major long-wavelength magnetic anomalies are 

seen most clearly by using a filtered version of the 

aeromagnetic anomaly map (Klein, 1983, 1987), 

simulating regional features that would have been 

mapped had the aircraft flown higher at a constant 

elevation of IVi mi. Figure 5 illustrates that the northern 

part of the map area is magnetically high and that the 

southern part is magnetically low, except for a high in the 

extreme southeast corner of the map area.

The broad low band traversing the southern part of 

the map area covers most of the study area. The low 

gradient is likely due to increasing depths of basin fill to 

the southwest away from the volcanic terrane.

In the extreme southeast corner of the map area, a 

small part of a weak magnetic high is of interest because 

its subsurface source may extend northwestward to 

within a mile or two of the southeast margin of the study 

area. This high correlates with the regional gravity high 

previously discussed. Nine miles to the south-southeast 

of the study area, associations of paired magnetic and 

gravity highs with exposed rocks suggest that the buried 

source is likely to be magnetic Laramide intrusive and 

volcanic rocks.

Based on criteria developed by Richter and others 

(1986), the geophysical data are more useful for defining 

broad terranes of mineral resource interest than for 

delineating mineral occurrences in specifically targeted 

areas. For example, manganese vein deposits and goldsilver-base metal vein deposits characteristically occur 

along or near northwest-trending faults cutting Tertiary 

volcanic and related intrusive rocks. The geophysical data 

suggest the subsurface occurrence of one such fault, 

inferred to cut across the southwest corner of the map 

area a few miles west of the study area. However, the 

volcanic rocks, known to host such vein deposits, are not 

identifiable because of the overprinting generated by 

basalt and andesite. The basalt, because of its diverse 

magnetic character, seems generally to be more of a 

hindrance than help in using magnetic anomaly data for 

assessment purposes. The geophysical data, to within the 

limits that they can be interpreted, do not signal the 

occurrence of a subsurface terrane beneath the study 

area itself likely to contain mineral deposits.

Aerial Gamma-Ray Data

Aerial gamma-ray spectroscopy is a technique that 

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

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 data 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 15 square acres to an 

average depth of about 15 in.

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. The flight-line spacings of these surveys 

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

suitable for producing regional 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 study area, and the 

occurrence or absence of anomalous radioelement 

concentrations were noted. The definition of an anomaly, 

as used in this report, 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.

A10 Mineral Resources of Wilderness Study Areas Southwestern New Mexico
108°55' 108°50'

32 «40'

32°35'

APPROXIMATE BOUNDARY 

OF GILA LOWER BOX 

WILDERNESS STUDY AREA

3 MILES

J

EXPLANATION

 U Aeromagnetic contour Contour interval 25 nanoTcslas

H Aeromagnetic high

L Aeromagnetic low

Figure 5. Filtered aeromagnetic anomaly map of the Gila Lower Box Wilderness Study Area and vicinity. (Data from 

Klein, 1987.) Original data have been processed to show anomalies having horizontal dimensions greater than about 

2km.

The Gila Lower Box Wilderness Study Area has 

overall moderate radioactivity, with concentrations of 

2.3-3.0 percent K, 2.3-2.5 ppm eU, and 9-11 ppm eTh. 

There are no anomalies within or near the study area.

Mineral and Energy Resources

The mineral resource potential for manganese in 

the Gila Lower Box Wilderness Study Area is high in its 

eastern part and moderate in its western part, with

certainty level C. The study area has a low mineral and 

energy resource potential for all other metals, gemstone, 

geothermal energy, and oil and gas, with certainty level C. 

This statement is based on our available knowledge, as of 

September 1,1987, of the surface and subsurface geology 

of the area and its environs.

The middle Tertiary high-potassium calc-alkaline 

volcanic terrane of the western orogenic belt in 

southwestern New Mexico and southeastern Arizona 

provides a favorable geologic environment for a 

restricted variety of ore deposit types, namely: graniteGila Lower Box Wilderness Study Area A11
type molybdenum porphyry deposits, rhyolite-hosted tin 

deposits, epithermal manganese and fluorite veins, and 

some base-metal (copper, lead, zinc) and precious-metal 

(gold, silver) veins (Richter and others, 1986). Only the 

manganese vein deposits are expected to occur in the 

study area. These shallow, low-temperature deposits of 

manganese oxides and associated calcite and quartz are 

fissure fillings along fractures and minor faults, generally 

near larger faults. The presence of manganese vein 

deposits within 0.25 to 2 mi north, east, and southeast of 

the wilderness study area and the presence of favorable 

host rocks (volcanic rocks) and structures (faults) within 

the study area indicate (1) a high mineral resource 

potential for these deposits, with certainty level C, in the 

eastern part of the study area, where faults are present 

and bedrock is exposed, and (2) a moderate mineral 

resource potential for these deposits, with certainty level 

C, in the western part of the study area, where faults and 

bedrock exposures are less common. The mineral 

resource potential for all other metals in the study area is 

low, with certainty level C.

Gemstone material is found locally throughout the 

study area, but is more a mineralogical curiosity than a 

resource. Agate and chalcedony commonly fill vesicles 

and fractures in the andesitic to basaltic lava flows, and 

banded calcite (travertine) is present locally in small 

veins and fractures. The three shallow prospect pits at the 

end of an unimproved road (fig. 1) expose some banded 

calcite veins; however, the pits were probably dug in 

search of manganese. The study area has a low mineral 

resource potential for gemstone, with certainty level C.

Although there are numerous hot springs within 50 

mi of the study area and the Clifton Known Geothermal 

Resource Area is about 30 mi to the northwest, there are 

no known hot springs in the immediate vicinity of the 

study area and the area is not considered to have any 

significant geothermal potential (Muffler, 1979). 

Therefore the energy resource potential for geothermal 

energy is low, with certainty level C.

The energy resource potential for oil and gas in the 

wilderness study area is low (Ryder, 1982), with certainty 

level C. The study area, on the Burro Mountains arch, is 

not underlain by any measurable section of Paleozoic 

carbonate rocks that elsewhere in New Mexico are highly 

productive reservoir and source rocks. Subsurface 

Cretaceous rocks in the study area could conceivably 

have reservoir qualities, but their shallow depth beneath 

the Tertiary volcanic sequence and thinness of section 

are not favorable. No oil or gas wells have been drilled in 

the wilderness study area or general vicinity.

REFERENCES CITED

Barton, H.N., and Day, G.W., 1987, Analytical results and 

sample locality map of heavy-mineral-concentrate 

samples from the Lower Gila Box Wilderness Study Area

(NM-030-023), Grant and Hidalgo Counties, New 

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

87-294.

Bath, G.D., 1976, Interpretation of magnetic surveys in intermontane valleys of Nevada and southern New Mexico: 

U.S. Geological Survey Open-File Report 76-440, 37 p.

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.

Drewes, Harald, Houser, B.B., Hedlund, B.C., Richter, D.H., 

Thorman, C.H., and Finnell, T.L., 1985, Geologic map of 

the Silver City I°x2° quadrangle, New Mexico and 

Arizona: U.S. Geological Survey Miscellaneous 

Investigations Series Map 1-1310-C, scale 1:250,000.

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

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

Elston, W.E., 1960, Reconnaissance geologic map of Virden 

thirty-minute quadrangle: New Mexico State Bureau of 

Mines and Mineral Resources Geologic Map 15, scale 

1:126,720.

Ewart, A., 1979, A review of the mineralogy and chemistry of 

Tertiary-Recent dacitic, latitic, rhyolitic, and related salic 

volcanic rocks, in Barker, Fred, ed., Trondhjemites, 

dacites, and related rocks, no. 6 of Developments in 

Petrology: New York, Elsevier Scientific Publishing 

Company, p. 13-121.

Gillerman, Elliot, 1964, Mineral deposits of western Grant 

County, New Mexico: New Mexico State Bureau of 

Mines and Mineral Resources Bulletin 83, 199 p.

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

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

Open-File Report 84-787, 42 p.

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

and alternating-current spark emission spectrographic 

field methods for the semiquantitative analysis of 

geologic materials: U.S. Geological Survey Circular 591, 

6 p.

Klein, D.P., 1983, Description of slides showing aeromagnetic 

and gravity data for regional mineral exploration in 

Colorado, New Mexico, and Arizona: U.S. Geological 

Survey Open-File Report 83-703, 13 p.

____1987, Aeromagnetic map of the Silver City I°x2° 

quadrangle, Arizona and New Mexico: U.S. Geological 

Survey Miscellaneous Investigations Series Map 

I-1310-D, scale 1:250,000.

Klein, D.P., and Johnson, G.R., 1983, Density, porosity, and 

magnetic properties of rock specimens from 

southwestern Arizona: U.S. Geological Survey Open-File 

Report 83-808, 31 p.

Klein, D.P., and Wynn, J.C., 1984, Density, porosity, and 

magnetic susceptibility of rocks from the Silver City 

I°x2° quadrangle, Arizona and New Mexico: U.S. 

Geological Survey Open-File Report 84-17, lip.

Muffler, L.J.P., ed., 1979, Assessment of geothermal resources 

of the United States 1978: U.S. Geological Survey 

Circular 790, 163 p.

A12 Mineral Resources of Wilderness Study Areas Southwestern New Mexico
Ratte, J.C., Marvin, R.F., and Naeser, C.W., 1984, Calderas and 

ash-flow tuffs of the Mogollon Mountains, southwestern 

New Mexico: Journal of Geophysical Research, v. 89, no. 

BIO, p. 8713-8732.

Richter, D.H., Sharp, W.N., Watts, K.C., Raines, G.L., Houser, 

B.B., and Klein, D.P., 1986, Maps showing mineral 

resource assessment of the Silver City 1° x 2° quadrangle, 

New Mexico and Arizona: U.S. Geological Survey 

Miscellaneous Investigations Series Map I-1310-F, scale 

1:250,000.

Ryan, G.S., 1985, Mineral investigation of part of the Gila 

Lower Box Wilderness Study Area (NM-030-Q23), 

Grant and Hidalgo Counties, New Mexico: U.S. Bureau 

of Mines Mineral Land Assessment Open File Report 

74-85, 12 p.

Ryder, R.T., 1982, Petroleum potential of wilderness lands in 

New Mexico, in Miller, B.M., ed., Petroleum potential of 

wilderness lands in the Western United States: U.S. 

Geological Survey Circular 902, p. 11-132.

Stacey, J.S., and Hedlund, D.C., 1983, Lead-isotopic 

compositions of diverse igneous rocks and ore deposits 

from southwestern New Mexico and their implications 

for early Proterozoic crustal evolution in western United 

States: Geological Society of America Bulletin, v. 94, 

p. 43-57.

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.

Wynn, J.C., 1981, Complete Bouguer gravity anomaly map of 

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

U.S. Geological Survey Miscellaneous Investigations 

Series Map I-1310-A, scale 1:250,000.

Gila Lower Box Wilderness Study Area A13

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

LU

cc 

o

V)

LU

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-^2. 

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 

1

1

Marginal Reserves

Demonstrated 

Subeconomic Resources

Inferred

Inferred Reserves

Inferred 

Marginal Reserves

Inferred 

Subeconomic 

Resources

UNDISCOVERED RESOURCES

Probability Range

 (or) 

Hypothetical i Speculative

1 

1

1

4_1

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

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 Archean

Middle Archean

Early Archean 

:hean 2

PERIOD

Quaternary

Tertiary

Neogene 

Subperiod

Paleogene 

Subperiod

Cretaceous

Jurassic

Triassic

Permian

Carboniferous 

Periods

Pennsylvanian

Mississippian

Devonian

Si urian

Ordovician

Cambrian

 38007 -

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

la

- 55

- 66

- 96

- 205

-/v 240 

- 290

-~ 330

f 1RO

r 410

- 500 

K ~ 570'

- 900 

- 1600

- 2500

-3000 

- 3400

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

! Informal time term without specific rank.

*U.S. GOVERNMENT PRINTING OFFICE: 1968-0-573-047/66019

%,-^r^-;;|Ml^^U|*S1^^'; v^:K%,

' ' :; 1 ' " ! ^ -*:' '' v