Agua Caliente SEZ Mineral Resource Potential February 2015 

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CONTENTS 

NOTATION .................................................................................................................................... v 

SIGNATURE PAGE .................................................................................................................... vii 

EXECUTIVE SUMMARY ........................................................................................................... 1 

1 INTRODUCTION ................................................................................................................... 3

1.1 Purpose of Report ........................................................................................................... 3 

1.2 Legal Description of the Subject Lands ......................................................................... 3 

1.3 Methodology and Resources .......................................................................................... 4 

1.4 Locatable Minerals ......................................................................................................... 6 

1.5 Arizona Mineral Production ........................................................................................... 6 

1.6 Strategic and Critical Minerals ....................................................................................... 7 

2 BACKGROUND ..................................................................................................................... 9

2.1 Lands Involved ............................................................................................................... 9 

2.2 Land Status ..................................................................................................................... 9 

2.3 Physical Features and Access ......................................................................................... 9

3 GEOLOGIC SETTING ......................................................................................................... 11

4 MINERAL HISTORY AND RESOURCE POTENTIAL .................................................... 15

4.1 Locatable Minerals ....................................................................................................... 15 

4.2 Saleable Mineral Materials ........................................................................................... 17 

4.3 Leasable Minerals ......................................................................................................... 17 

5 SUMMARY .......................................................................................................................... 19

6 REFERENCES ...................................................................................................................... 21
Agua Caliente SEZ Mineral Resource Potential February 2015 

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FIGURES 

1 Location of the Agua Caliente SEZ ......................................................................................... 5

2 Geologic Map of the Agua Caliente SEZ .............................................................................. 12 

3 Map Showing Mines and Mineral Prospects near the Agua Caliente SEZ ........................... 16 

TABLES 

1 Strategic and Critical Nonfuel Minerals .................................................................................. 7 

2 Summary of Mineral Resource Potential for the Agua Caliente SEZ Proposed Land 

Withdrawal Area ................................................................................................................... 19 
Agua Caliente SEZ Mineral Resource Potential February 2015 

v 

NOTATION 

 The following is a list of acronyms, abbreviations, and units of measure used in this 

document. Some acronyms used only in tables may be defined only in those tables. 

GENERAL ACRONYMS AND ABBREVIATIONS 

AZGS Arizona Geological Survey 

BLM Bureau of Land Management 

DOI U.S. Department of the Interior 

GIS geographic information system 

IBLA Interior Board of Land Appeals 

I.D. Interior Department 

LR2000 Land and Mineral Legacy Rehost 2000 System 

MRDS Mineral Resource Data System 

P.L. Public Law 

ROD Record of Decision 

ROW right of way 

RMP Resource Management Plan 

SEZ Solar Energy Zone 

USC United States Code

USGS U.S. Geological Survey 
Agua Caliente SEZ Mineral Resource Potential February 2015 

vi 

UNITS OF MEASURE 

C Celsius 

F Fahrenheit 

ft foot (feet) 

km kilometer(s) 

km2 square kilometer(s) 

m meter(s) 

mi mile(s) 

MW megawatt(s) 

m.y. million years 
Agua Caliente SEZ Mineral Resource Potential February 2015 

vii 

MINERAL RESOURCE POTENTIAL 

OF PUBLIC LANDS LOCATED WITHIN THE 

AGUA CALIENTE SOLAR ENERGY ZONE 

IN YUMA COUNTY, ARIZONA 

LANDS INVOLVED 

Covering 2,560 acres of public land in Yuma County, Arizona 

T5S, R12W, sections 15, 17, 20, 22, 23, 26, 28, 29, and 33 

Gila and Salt River P.M. 

Prepared by: 

____________________________________________ 

Terri L. Patton, Geologist 
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MINERAL RESOURCE POTENTIAL 

OF PUBLIC LANDS LOCATED WITHIN THE 

AGUA CALIENTE SOLAR ENERGY ZONE 

IN YUMA COUNTY, ARIZONA 

EXECUTIVE SUMMARY 

 This report assesses the mineral resource potential of public lands located within the 

Agua Caliente Solar Energy Zone (SEZ) that have been identified for withdrawal from location 

or entry under the mining laws on behalf of the U.S. Department of Interior (DOI), Bureau of 

Land Management (BLM). The report was prepared in consultation with Mr. Jeff Garrett, 

Mining Engineer and Mining Law Program Lead (Arizona State Office). Mr. Matt Shumaker, 

Chief Mineral Examiner (Division of Solid Minerals), provided guidance on the content and 

format of the mineral resource assessments prepared for the original 17 SEZs (in 2012); his 

guidance was also followed in the preparation of this report. Mr. Lane Cowger, Project Manager 

(Arizona State Office), prepared the legal description for the SEZ. 

 There are no documented occurrences of locatable mineral deposits within the Agua 

Caliente SEZ. Most of the metallic minerals in the region are concentrated in the mountain 

ranges to the northwest. The nearest known occurrences of locatable minerals (copper ore) are in 

the Palomas Mountains about 5 mi (8 km) northwest of the SEZ. Placer gold occurrences are 

associated with gravels deposited in streams and washes that drain these mountains. Modern 

alluvial deposits below the SEZ are estimated to be greater than 1,600 ft (490 m) deep, although 

the local stratigraphy has not been well characterized. The potential for metallic (lode) minerals 

within the SEZ is low (level of certainty B).1

 And because there is no evidence (assay or 

evidence of past production) to suggest that placer deposits occur within or in close proximity to 

the SEZ, the potential for placer deposits within the SEZ is also low (level of certainty A). 

 The Agua Caliente SEZ is an area with a high potential for the occurrence of sand and 

gravel (level of certainty C). The SEZ is underlain by alluvial and basin-fill sediments; however, 

based on the absence of free-use permits or mineral materials contracts within the SEZ, the 

demand for these resources is assumed to be low. 

 There are no active oil and gas leases within the Agua Caliente SEZ, and there has been 

no history of oil and gas production within or near the SEZ or in the Yuma Field Office planning 

area (the only areas producing oil and gas are located in Apache County in northeastern 

Arizona). Although eight oil and gas leases covered most of the SEZ in the past, these leases 

 

1

 Definitions of mineral potential are from the mineral potential classification system outlined in BLM 

Manual 3031 (BLM 1985). Mineral potential ratings of low, moderate, or high are assigned where the geologic 

environment and inferred geologic processes indicate low, moderate, or high potential for accumulation of 

mineral resources. Levels of certainty are defined as follows: A – available data are insufficient to support or 

refute the occurrence of mineral resources; B – available data provide indirect evidence to support or refute the 

occurrence of mineral resources; C – available data provide direct but quantitatively minimal evidence to support 

or refute the occurrence of mineral resources; and D – available data provide abundant direct and indirect

evidence to support or refute the occurrence of mineral resources. 
Agua Caliente SEZ Mineral Resource Potential February 2015 

2 

were closed in 1980, 1986, and 1997. The SEZ is an area with low potential for oil and gas 

resources (level of certainty A). 

 There also are no known coal resources within the immediate region of the Agua Caliente 

SEZ (Palomas Plain); and although helium (a commodity associated with and extracted from 

natural gas) does occur in Arizona, all of the known occurrences are adjacent to the Defiance 

uplift in the northeastern portion of the state. Given the absence of active leases within or in 

close proximity to the SEZ and the absence of coal and oil and gas (and, therefore, helium) 

exploration and production activity in the Yuma Field Office planning area, the potential for coal 

and helium resources within the SEZ is low (level of certainty A). 

 There are no recorded salt (halite) deposits within or near the Agua Caliente SEZ; the 

only produced salt deposits in Arizona are in the Holbrook Basin on the Colorado Plateau, a few 

hundred miles to the northeast of the site, and in the Luke Basin just west of Phoenix. There has 

been no commercial production of potash on BLM-administered lands in Arizona; the nearest 

known occurrence is in the Holbrook Basin (BLM 2012). The potential for finding salt and 

potash resources within the SEZ, therefore, is low (level of certainty B). 

 The Agua Caliente SEZ is located in the Hyder area, a region of known or potential 

geothermal resources. Although there are no active or historical geothermal leases within the 

SEZ and there are no nominated lands for geothermal sale within the SEZ or in the immediate 

region, there are several low-temperature geothermal wells scattered throughout the area adjacent 

to the SEZ (on private land between the east and west parts of the SEZ) and within 10 mi 

(16 km) of the SEZ to the east, south, and southeast. The status of these wells has not been 

confirmed; however, given the projected temperatures within the basin and the presence of 

geothermal wells in close proximity to the SEZ, the potential for geothermal energy resources 

within the SEZ is moderate (level of certainty B). 
Agua Caliente SEZ Mineral Resource Potential February 2015 

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1 INTRODUCTION 

1.1 PURPOSE OF REPORT 

 The purpose of this report is to assess the mineral resource potential of 2,560 acres 

(10.4 km2) of public lands within the Agua Caliente Solar Energy Zone (SEZ) in southwestern 

Arizona, which the Secretary of the Interior may decide to withdraw from potentially conflicting 

uses through the issuance of a Public Land Order. If the order is approved, the public lands 

within the SEZ would be withdrawn, subject to valid existing rights, from location or entry under 

the mining laws, as follows: 

 New mining claims could not be filed on the withdrawn lands; however, valid mining 

claims filed prior to the date the lands were segregated (i.e., the date the withdrawal 

application notice was published in the Federal Register) would take precedence over 

future solar energy development right-of-way (ROW) application filings. 

 Withdrawn lands would remain open to mineral leasing, geothermal leasing, and mineral 

material and public land laws; the Bureau of Land Management (BLM) could elect to 

lease the oil, gas, coal, or geothermal steam resources, or to sell common-variety mineral 

materials such as sand and gravel, if the authorized officer determined there would be no 

unacceptable impacts on future solar energy development. These discretionary actions 

would comply with the management objectives outlined in the Yuma Field Office 

Record-of-Decision (ROD) and Approved Resource Management Plan (RMP) 

(BLM 2010). 

 Withdrawn lands would remain open to ROW authorizations and land leases or permits 

authorized under Section 302 of the Federal Land Policy and Management Act of 1976 

(FLPMA). These decisions would comply with the management objectives outlined in 

the Yuma Field Office ROD and Approved RMP (BLM 2010). 

1.2 LEGAL DESCRIPTION OF THE SUBJECT LANDS 

 The Agua Caliente SEZ is located in BLM’s Yuma Field Office planning area in Yuma 

County. Its full legal description is provided below: 

Gila and Salt River Meridian 

T. 5 S., R. 12 W., 

Sec. 15, S1⁄2NE1⁄4NE1⁄4, S1⁄2NW1⁄4NE1⁄4, S1⁄2NE1⁄4, S1⁄2NE1⁄4NW1⁄4, S1⁄2NW1⁄4NW1⁄4, SE1⁄4; 

Sec. 17, SE1⁄4NE1⁄4, SE1⁄4; 

Sec. 20, NE1⁄4, SE1⁄4NW1⁄4, E1⁄2SW1⁄4, SE1⁄4; 

Sec. 22, E1⁄2NE1⁄4, E1⁄2SE1⁄4; 

Sec. 23, W1⁄2; 

Sec. 26, N1⁄2NE1⁄4NW1⁄4, NW1⁄4NW1⁄4; 
Agua Caliente SEZ Mineral Resource Potential February 2015 

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Sec. 28, W1⁄2NE1⁄4, W1⁄2, W1⁄2SE1⁄4; 

Sec. 29, NE1⁄4, E1⁄2NW1⁄4, E1⁄2SW1⁄4, SE1⁄4; 

Sec. 33, NW1⁄4NW1⁄4NE1⁄4, N1⁄2NW1⁄4, NW1⁄4SW1⁄4NW1⁄4. 

The location of the SEZ is also shown in Figure 1. 

1.3 METHODOLOGY AND RESOURCES 

 The assessment presented in this report focuses on locatable mineral resources, including 

those classified as strategic and critical, in the vicinity of the Agua Caliente SEZ proposed land 

withdrawal area; it also includes a discussion of leasable minerals and commercial saleable 

mineral values. The conclusions concerning mineral occurrence and development potential 

follow the methodology outlined in BLM Manual 3031 (BLM 1985) and are based on a review 

of topographic maps; geologic maps; mineral resource maps and reports; the scientific literature 

on the geology and mineral resources of Arizona; and consultation with the Jeff Garrett, mining 

law program lead at the BLM Arizona State Office. No mapping or field sampling was 

conducted as part of this assessment. 

 Digital data for the geologic map in Figure 2 (pages 12–13) was obtained from the 

U.S. Geological Survey (USGS) (Ludington et al. 2007). The dataset was digitized from 

previously published geologic maps ranging in scale from 1:100,000 to 1:1,000,000. Detailed 

map unit descriptions for this map are based on the published state geologic map by 

Richard et al. (2000). The large-scale, folded map (Map 1) provided in the back of this report 

shows the public land survey system grid (township and range) and should be consulted to locate 

mines and landscape features discussed in the text. 

 The BLM’s Legacy Rehost System (LR2000; BLM 2015b) was queried on February 10, 

2015, for information on active and historical (unpatented) mining claims and various leases and 

permits, including oil and gas leases, coal leases, geothermal leases and land nominations, free 

use permits, and mineral materials contracts that were issued on public lands within and around 

the Agua Caliente SEZ proposed land withdrawal area. 

 Mines and mineral prospects and occurrences and their descriptions are those reported in 

the USGS’s Mineral Resource Data System (MRDS) (USGS 2014b; Lipin 2000) and 

supplemented with information provided by BLM and the open literature. The MRDS is a large 

database containing historical records of the USGS and the U.S. Bureau of Mines (which is now 

part of the USGS). These records are of variable quality and currency, so it is possible that some 

information will be found to be out of date (the revision and refinement of the database is an 

ongoing effort at the USGS). The mining activity map in Figure 3 (page 16) was prepared from 

the MRDS and is intended to provide a general picture of the location and nature of mining 

activity in the vicinity of the Agua Caliente SEZ. Refinements with regard to the status of 

particular mines are included in the text as warranted on the basis of conversations with BLM 

mineral specialists. 
Agua Caliente SEZ Mineral Resource Potential February 2015 

5 

FIGURE 1 Location of the Agua Caliente SEZ 
Agua Caliente SEZ Mineral Resource Potential February 2015 

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Geographic information system (GIS) data for mining districts in Arizona were not 

available; however, the mining districts originally listed in Keith et al. (1983a and 1983b) and 

Welty et al. (1985a, b) are easily identified as areas of clustered mining activity and are 

acknowledged in the discussion of locatable minerals for the SEZ (Section 4.1), as applicable.2

The Arizona Geological Survey (or AZGS, which consolidated with the Arizona Department of 

Mines and Mineral Resources in 2011) publishes maps and data on mines, prospects, quarries, 

and processing mills and plants by county and available at http://mines.az.gov/Publications/. 

1.4 LOCATABLE MINERALS 

 Under U.S. mining laws, minerals fall into three categories: locatable, leasable, and 

salable. Because these categories were created by acts of Congress, they do not fall into simple 

economic or mineralogical divisions. Creating an exact and thorough list of locatable minerals 

(e.g., those subject to appropriation by using mining claims) is therefore difficult. Metallic 

minerals (e.g., gold, silver, copper, mercury, aluminum, antimony, lithium, molybdenum, 

tungsten, uranium, vanadium, and rare earths) are considered to be locatable. Numerous 

uncommon varieties of nonmetallic minerals may also be locatable, depending on their chemical 

content, quality, uses, and characteristics, as well as certain associated economic and legal 

matters. These nonmetallic minerals could include barite, calcite, specialty clays, bentonite, 

diatomite, feldspar, some gemstones (e.g., opals and diamonds), gypsum, chemical-grade 

limestone, perlite, chemical-grade silica sand, specific types of stone, talc, zeolites, and specific 

and uncommon types of dolomite. The determination of the actual locatability of uncommon 

varieties of nonmetallic minerals and the validity of mining claims for them is complex and 

relies on Public Law (P.L.) 84-167 (United States Code, Title 30, Section 601 et seq. 

[30 USC 601 et seq.]) and applicable case law (e.g., U.S. v Kenneth McClarty, 17 Interior Board 

of Land Appeals [IBLA] 20, 1974 [81 Interior Department (I.D.) 472]) (Shumaker 2011). 

1.5 ARIZONA MINERAL PRODUCTION 

 Arizona’s nonfuel raw mineral production in 2009 decreased from its 2008 level by about 

34% (which had increased by about 7.8% from its 2007 level). From 2005 through 2008, 

Arizona had the highest total nonfuel mineral production in the nation; however, in 2009 (the 

latest year for which statistics are available), it dropped in rank to second, accounting for 8.8% of 

the total U.S. production value. Copper accounted for more than 73% of the state’s total nonfuel 

mineral production value (and 60% of total U.S. copper production) in 2009. The remaining 27% 

of Arizona’s total nonfuel mineral production value was from the production of molybdenum, 

construction sand and gravel, and portland cement. The reduction in Arizona’s total production 

value was attributed to a significant decrease in the production value of copper. Other significant 

decreases in production value occurred with sand and gravel, crushed stone, molybdenum, and 

portland cement. Concurrently, however, there were significant increases in the production 

values of lime, salt, zeolites, and industrial sand and gravel. In 2009, Arizona’s rank among other 

 

2

 The closest historical district to the Agua Caliente SEZ proposed land withdrawal area is the Neversweat District, 

located in T4S, R15 W, on the west side of the Palomas Mountains (Map 1). 
Agua Caliente SEZ Mineral Resource Potential February 2015 

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producing states in produced gemstones, zeolites, gold, and lime increased to first, fourth (among 

six states), ninth (among 11 states), and 10th (among 33 states), respectively (USGS 2014a). 

1.6 STRATEGIC AND CRITICAL MINERALS 

 Strategic and critical minerals are those minerals necessary for national defense and 

national security; for the nation’s energy infrastructure (e.g., pipelines or renewable energy 

production); to support domestic manufacturing, agriculture, housing, and telecommunications; 

or for the Nation’s economic security and balance of trade. Table 1 lists the nonfuel strategic and 

critical nonfuel minerals that are imported by the United States for its National Defense 

Stockpile, as authorized by the Strategic and Critical Materials Stock Piling Act 

(50 USC 98 et seq.). The recent National Strategic and Critical Minerals Production Act of 2013 

(H.R. 761) requires the U.S. Department of the Interior (DOI) and the U.S. Department of 

Agriculture to develop domestic sources of these mineral materials. Several of the minerals 

produced in Arizona are classified as strategic and critical minerals. These include beryllium, 

copper, manganese, tungsten, vanadium, and zinc. 

TABLE 1 Strategic and Critical Nonfuel Minerals 

Antimony Copper Platinum group 

Asbestos Diamonds (industrial) Quartz crystals 

Bauxite and alumina Fluorspar Rutile (titanium) 

Beryllium Graphite Silicon 

Bismuth Iodine Tantalum 

Cadmium Manganese Thorium 

Chromium Mercury Tin 

Cobalt Mica sheet Tungsten 

Columbian Nickel Vanadium 

 Zinc 

Source: CBO (1983). 
Agua Caliente SEZ Mineral Resource Potential February 2015 

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2 BACKGROUND 

2.1 LANDS INVOLVED 

 The Agua Caliente SEZ is located on public lands managed by BLM’s Yuma Field 

Office, Yuma County. The SEZ lies within sections 15, 17, 20, 22, 23, 26, 28, 29, and 33 of 

Township 5 south, Range 12 west (T5S, R12W), Gila and Salt River Principal Meridian. The 

original SEZ boundaries were revised to include buffers around major washes and to avoid 

several known archaeological sites and lands with wilderness characteristics. The northern 

portion of the original footprint was also removed to maintain the area of potential tortoise 

migration between the Palomas Mountains and Baragan Mountain (BLM 2012). The SEZ and 

various landscape features in the region are shown on the location map in the back of this report 

(Map 1). 

 As of June 2014, there were no pending solar project applications within the SEZ, and 

one pending solar project application (Pacific Solar Inv., Inc.) located within a 25-mile (40-km) 

radius (and to the northeast) of the SEZ. A 290-MW photovoltaic (PV) facility (NRG Energy) is 

located on private land adjacent to the SEZ; it came online in 2014 (BLM 2015a). 

2.2 LAND STATUS 

 According to the LR2000, accessed on February 10, 2015, there are no locatable mining 

claims or active mines within the Agua Caliente SEZ proposed land withdrawal area 

(BLM 2015b). 

 There are no free use permits or mineral materials contracts within the SEZ 

(BLM 2015b). The SEZ remains open for the disposal of saleable mineral materials (e.g., sand 

and gravel). 

 There are no active oil and gas leases within or around the Agua Caliente SEZ; however, 

most of the SEZ was leased for oil and gas in the past (a total of eight leases, closed in 1980, 

1986, and 1997) (BLM 2015b). (According to the Arizona Oil and Gas Conservation 

Commission, all of Arizona’s oil and gas development occurs in Apache County; see 

AOGCC 2013.) There are no active or historical salt, potash, coal, helium, or geothermal leases 

within the SEZ. The SEZ remains open for the discretionary leasing of these commodities. 

2.3 PHYSICAL FEATURES AND ACCESS 

 The Agua Caliente SEZ is located in an area that is sparsely populated with limited 

economic development. The surrounding area is predominantly agricultural (to the east and 

south) and undeveloped desert (to the north and west). The nearest major road access is 

Interstate 8, about 12 mi (19 km) south of the SEZ. A Yuma County road, Palomas Road, passes 

just to the south; it also provides access to the SEZ (BLM 2012). 
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3 GEOLOGIC SETTING 

 The Agua Caliente SEZ proposed land withdrawal area is located within the Palomas 

Plain, a northwest-trending, broad, alluvial (extensional) basin within the Basin and Range 

physiographic province in southwestern Arizona. The plain is bounded on the southwest by the 

Palomas Mountains (part of the Kofa-Tank Mountains complex). The Agua Caliente Mountains 

are about 7 mi (11 km) to the east of the SEZ; the Aztec Hills are about 11.5 mi (18.5 km) to the 

south. The SEZ lies between two ephemeral washes, the Hoodoo Wash to the west, and the 

Baragan Wash to the east, which discharge to the Gila River a few miles to the south (Figure 2). 

Several small washes intersect the SEZ. 

 Precambrian metamorphic rocks (schist and gneiss – Xm) and granite (Xg) are exposed 

in portions of the Tank and Palomas Mountains and in the Aztec Hills to the south (YXg), as 

shown in Figure 2. These rocks are highly faulted and fractured, and they are intruded by quartzdominated pegmatite dikes and veins. Most of the mineralization in the Palomas Mountains 

(chrysocolla, malachite, hematite, and quartz) is located along the northern margin of Tertiary 

granite and foliated granitic rocks (Tg) (Skotnicki and Ferguson 1994). Tertiary volcanic rocks 

(Tv) comprise the Agua Caliente Mountains and occur throughout the Tank and Palomas 

Mountains (Jones 1979). 

 Basin fill beneath the Palomas Plain is estimated to be about 8,850 ft (2,700 m) deep. The 

uppermost sediments consist of unconsolidated sand, gravel, silt, and clay that overly an older, 

more indurated sequence of arkosic sediments and fanglomerates. These older sediments are 

about 4,600 ft (1,400 m) thick and sit unconformably atop Tertiary sediments, volcanics, and 

volcanic detritus from pre-Tertiary bedrock. The basin itself is underlain by a basement complex 

of granite and undifferentiated metamorphic rocks (Jones 1979; Armstrong and Yost 1958; and 

BLM 2012). 
Agua Caliente SEZ Mineral Resource Potential February 2015 

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FIGURE 2 Geologic Map of the Agua Caliente SEZ 
Agua Caliente SEZ Mineral Resource Potential February 2015 

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FIGURE 2 (Cont.) 
Agua Caliente SEZ Mineral Resource Potential February 2015 

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Agua Caliente SEZ Mineral Resource Potential February 2015 

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4 MINERAL HISTORY AND RESOURCE POTENTIAL 

 This chapter assesses the mineral potential of 2,560 acres (10.4 km2) of public lands 

identified for withdrawal from location or entry under the mining laws. The purpose of the land 

withdrawal is to protect and preserve, for a 20-year period, the area known as the Agua Caliente 

SEZ, which is located 65 mi (104 km) northeast of the city of Yuma, and 60 mi (97 km) 

southwest of Buckeye in Yuma County in southwestern Arizona. Under the withdrawal, the 

lands would be closed to locatable mineral entry but would remain open for discretionary leasing 

for oil and gas and other leasable minerals and for the disposal of saleable minerals (see also 

Section 1.1).

 There has been no documented mining within the Agua Caliente SEZ proposed land 

withdrawal area. Mining activity in the immediate region has been limited to the historical smallscale mining of copper in the Palomas Mountains about 5 mi (8 km) to the west of the SEZ 

(Figure 3). Currently, there is no mining activity within or in close proximity to the SEZ, and 

there are no major active mines within Yuma County (USGS 2014b; AZGS 2011). 

4.1 LOCATABLE MINERALS 

There are no known locatable mineral deposits or prospects and no mining claims or 

active mines identified within the Agua Caliente SEZ proposed land withdrawal area 

(BLM 2015b). The nearest occurrence of locatable minerals is of copper ore (chrysocolla and 

malachite), historically produced from the Engles-Adams Mine in the south-central part of the 

Palomas Mountains, about 5 mi (8 km) to the west (in section 16 of T5S, R13W; see Map 1). 

Workings include several short tunnels and four deep shafts (30 to 100 ft deep); however, 

production records for the mine are not available. A copper prospect, identified in the MRDS as 

Rainbow and Valley, is also located in section 16 of T5S, R13W. Both occurrences are 

associated with quartz-feldspar porphyry and basaltic dikes in Tertiary granitic rocks (Tg); 

neither is considered economically significant (USGS 2014b; Skotnicki and Ferguson 1994). 

 The nearest mining district to the Agua Caliente SEZ is the Neversweat District, located 

on the west side of the Palomas Mountains (in T4S, R15W), some 16 mi (26 km) to the 

northwest of the SEZ (based on the historical mining districts delineated by Keith et al. [1983a] 

and Welty et al. [1985a, b]; see Map 1). The district produced lead, gold, copper, and silver. 

Mineralization is associated with middle Tertiary rhyolite and andesite dikes (Keith et al. 1983a). 

Several inactive small mines, most of which produced copper, silver, and gold (with some 

reports of mica, tungsten, and lead), are located in the Kofa Mountains (Kofa District) much 

farther to the northwest (in T1S and T2S, R17W) (USGS 2014b). Some of these mines are placer 

operations and coincide with gold placer districts identified by Wilson (1981). 
Agua Caliente SEZ Mineral Resource Potential February 2015 

16 

FIGURE 3 Map Showing Mines and Mineral Prospects near the Agua Caliente SEZ 

(Source: USGS 2014b) 
Agua Caliente SEZ Mineral Resource Potential February 2015 

17 

 The Agua Caliente SEZ crosses none of the historical mining districts delineated by 

Keith et al. (1983a), Welty et al. (1985a, b), or Wilson (1981), and there has been no hard rock or 

locatable mineral activity within or in close proximity to the SEZ. Modern alluvial deposits 

below the SEZ extend to a depth of at least 1,600 ft (490 m) (Richard et al. 2007) and are 

underlain by a thick sequence of Tertiary volcanics similar to those exposed in the adjacent 

mountains. Mineralization below the SEZ is unconfirmed; however, based on available geologic 

data, it would likely be very deep (below basin sediments) if present. Therefore, the potential for 

metallic (lode) minerals (e.g., copper, iron, gold) is low (level of certainty B). Several washes 

intersect the SEZ; however, there are no major streams running through it. And there is no direct 

evidence (assay or past production) to suggest that placer deposits (such as gold) occur within or 

in close proximity to the SEZ. Therefore, the potential for placer deposits within the SEZ is also 

low (level of certainty A).

4.2 SALEABLE MINERAL MATERIALS 

 Saleable mineral materials in the region are mainly sand and gravel, stone, and crushed 

stone. These commodities are produced by the Aztec Granite Quarry, about 11.5 mi (7.1 km) to 

the south in section 28 of T7S, R12W (see Map 1) (USGS 2014b). According to the LR2000, 

accessed on February 10, 2015, there currently are no active free use permits or mineral 

materials contracts within the SEZ (BLM 2015b). 

 The Agua Caliente SEZ is underlain by alluvial and basin-fill sediments and is, therefore, 

a high potential area for sand and gravel deposits (level of certainty C). However, based on the 

absence of free use permits or mineral materials contracts within the SEZ, the regional demand 

for these materials is assumed to be low. 

4.3 LEASABLE MINERALS 

 There are no active oil and gas leases within the Agua Caliente SEZ (BLM 2014b), and 

there are no active oil and gas leases within the Yuma Field Office planning area (BLM 2010). A 

total of eight leases covered most of the SEZ at one time; however, these leases were closed in 

1980, 1986, and 1997 (BLM 2015b). There has been no history of oil and gas production in 

Yuma County; the only areas of the state currently producing oil and gas are located in Apache 

County in northeastern Arizona (AOGCC 2013; Rauzi 2011). There also are no known coal 

resources within the immediate region of the Agua Caliente SEZ (Palomas Plain); the most 

extensive coal reserves are in Cretaceous rocks such as those in the Black Mesa and Pinedale 

Fields in northeastern and eastern Arizona (Peirce et al. 1970). Helium (a commodity associated 

with and extracted from natural gas)3

 does occur in Arizona; however, all of the known 

occurrences are adjacent to the Defiance uplift (trapped within the anticlinal structures of the 

Holbrook Basin and in the oil and gas fields near in the four corners region) in the northeastern 

portion of the state (Rauzi 2003). Given the geologic conditions dictating oil and gas, coal, and 

 

3

 Helium is not a leasable mineral but is included here because it is associated with oil and gas production (as stated 

in the Yuma Field Office RMP [BLM 2012]). 
Agua Caliente SEZ Mineral Resource Potential February 2015 

18 

helium development in the state and the absence of exploration and production activity in the 

Yuma Field Office planning area (and the absence of active leases within or in close proximity to 

the SEZ), the potential for oil and gas, coal, and helium resources within the SEZ is low (level of 

certainty A). 

 There are no recorded salt (halite) deposits within or near the Agua Caliente SEZ. 

Permian-age salt deposits in Arizona occur (and are produced) in the Holbrook Basin on the 

Colorado Plateau, a few hundred miles to the northeast of the site, and in the Luke Basin just 

west of Phoenix. Massive salt deposits are also known to occur in the Hualapai Valley north of 

Kingman (BLM 2012). There has been no commercial production of potash on BLMadministered lands in Arizona. The nearest potash deposit occurs in the Permian Supai 

Formation in the Holbrook Basin (BLM 2012). The potential for finding salt and potash 

resources within the SEZ, therefore, is low (level of certainty B). 

 The Agua Caliente SEZ is located in the Hyder area, a region of known or potential 

geothermal resources (BLM 2008; INEEL 2003; Jones 1979). According to the LR2000, there 

are no active or historical geothermal leases within the SEZ, and there are no nominated lands 

for geothermal sale in the immediate region (BLM 2015b). However, there are several lowtemperature geothermal wells scattered throughout the area adjacent to the SEZ (on private land 

between the east and west parts of the SEZ) and within 10 mi (16 km) of the SEZ to the 

northeast, east, and south (Figure 3; see also Map 1) (USGS 2014b). The status of these wells has 

not been confirmed. Jones (1979) estimates a normal temperature gradient of 35°C (95°F)/km for 

the basin, and projects temperatures of 200°C (392°F) at depths as shallow as 6,560 ft (2,000 m) 

in some places. INEEL (2003) places wells in the Hyder area in the ≥20°C (≥68°F) and ≤50°C 

(122°F) range. Given the projected temperatures within the basin and the presence of geothermal 

wells in close proximity to the SEZ, the potential for geothermal energy resources within the 

SEZ is moderate (level of certainty B). 
Agua Caliente SEZ Mineral Resource Potential February 2015 

19 

5 SUMMARY 

 Table 2 provides a summary of the mineral resource potential for the Agua Caliente SEZ 

proposed land withdrawal area. 

TABLE 2 Summary of Mineral Resource Potential for the Agua Caliente SEZ Proposed 

Land Withdrawal Area 

Mineral Category Mineral History/Background Mineral Resource Potential 

Locatable Minerals No known locatable mineral 

deposits or prospects; no mining 

claims or active mines. Nearest 

occurrences are in the Palomas 

Mountains (copper). 

SEZ does not cross historical mining 

districts. 

Metallic (lode) minerals – 

low (level of certainty B) 

Placer deposits – low (level 

of certainty A) 

Saleable Mineral Materials Materials in region include sand and 

gravel, stone, and crushed stone. 

No active free use permits or 

mineral contracts within SEZ; low 

regional demand. 

Sand and gravel – high (level 

of certainty C) 

Leasable Minerals Oil and gas leases covered most of 

the SEZ at one time; leases closed in 

1980, 1986, and 1997 (no active oil 

and gas leases). 

No known coal resources in the 

immediate region of the SEZ. 

No known helium resources in the 

immediate region of the SEZ. 

No known salt or potash deposits in 

the immediate region of the SEZ. 

SEZ is located in the Hyder area, a 

region of known or potential 

geothermal resources, but there are 

no geothermal leases within the SEZ 

and no nominated lands in the 

immediate region. Several test wells 

adjacent to the SEZ and in the 

vicinity. 

Oil and gas – low (level of 

certainty A) 

Coal – low (level of certainty 

A) 

Helium – low (level of 

certainty A) 

Salt, potash – low (level of 

certainty B) 

Geothermal – moderate (level 

of certainty B) 
Agua Caliente SEZ Mineral Resource Potential February 2015 

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