Nonfuel mineral resources in the United States-Mexico border region: A progress report on information available from the

A Progress Report on Information Available from the =:en~L tor Inter-American Mineral Resource Investigations (CIMRI)

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Books Books and Maps

Nonfuel Mineral Resources in the United States-Mexico Border Region-A Progress Report on Information Available from the Center for Inter-American Mineral Resource Investigations (CIMRI)

By Greta J. Orris, Norman J Page, John-Mark G. Staude, Karen S. Bolm, Marguerite Carbonaro, Floyd Gray, and Keith R. Long

For sale by U.S. Geological Survey, Map Distribution Box 25286, MS 306, Federal Center Denver, CO 80225

1. Location map showing the area defined as the U.S.-Mexico border region for this report........................

2-4. Sketch maps of the U.S.-Mexico border region and adjacent areas showing the distribution of-

5. Maps showing simplified geology and geologic provinces in and adjacent to the U.S.-Mexico border region..............................................................................................................................
6. Map showing generalized distribution of volcanic and plutonic rocks in and adjacent to the U.S.-Mexico border region..................................................................................................................... 10
7. Map of the U.S.-Mexico border region showing the number of Mineral Resources Data System records for sites containing metallic and industrial mineral commodities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

8-14. Maps of the U.S.-Mexico border region and adjacent areas showing the distribution of mines, prospects, and occurrences of-

10. Lead and (or) zinc and copper.......................................................................................... 14
11. Construction materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
12. Gypsum, zeolites, and diatomite . .. . . . . . . . . . . . . . . . . .. . . . . .. . . . . . . . . . . . .. . . . . . . . . . . . . . . .. . . . . .. . .. . . . .. . . . . .. . . . .. . . .. . . 17
13. Barite, fluorite, and celestite............................................................................................ 17
14. Clays, evaporite (halite or potash), sodium carbonate or sodium sulfate, and sulfur......................... 18
15. Historical events related to mining in the U.S.-Mexico border region.... .. .. . . .. . .. . . . . .. . .. .. . .. .. . .. . . . . .. . . . .. .. .. .. .
16. Some general sources of information on mineral resources of the U.S.-Mexico border region...................... 12
17. Mineral commodities produced within the U.S.-Mexico border region................................................... 13
18. Significant industrial mineral commodities used in agriculture, infrastructure, and environmental improvements in the U.S.-Mexico border region............................................................................................... 15
19. Lands known to be closed to mineral exploration and (or) development........................................
20. Major standard-gauge railroad routes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
21. Selected primary paved highways and roads.........................................................................
22. All metallic and industrial mineral commodities for which the Mineral Resources Data System included records as of May 1993 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
23. Gold and silver . . . ...... .. ...... ... . ... . .... .. .. .. .. .... ...... ...... ...... .. ...... .... ...... ..... .... .......... ..... ..... .. 14

Abstract........................................................................................... Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mining History of the Border Region. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Land Status and Infrastructure... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Geologic Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Data Sources and Collection.................................................................. Mineral-Resource Distribution................................................................ Discussion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 References Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

TABLES

m Nonfuel Mineral Resources in the United States-Mexico Border Region-A Progress Report on Information Available from the Center for Inter-American Mineral Resource Investigations (CIMRI)

By Greta J. Orris, Norman J Page, John-Mark G. Staude, Karen S. Bolm, Marguerite Carbonaro, Floyd Gray, and Keith R. Long

ABSTRACT

The exploitation of minerals has played a significant role in population growth and development of the U.S.- Mexico border region. Recent proposed changes in regulations related to mining in the United States and changes in mining and investment regulations in Mexico have led to increased mineral exploration and development in Mexico, especially in the border region. As a preliminary step in the study of the mineral industry of this area, the Center for Inter-American Mineral Resource Investigations (CIMRI) of the U.S. Geological Survey has compiled mine and occurrence data for nonfuel minerals in the border region. Analysis of this information indicates that a wide variety of metallic and industrial mineral commodities are present which can be used in agriculture, infrastructure, environmental improvement, and other industries. Therefore, mining will continue to play a significant role in the economy of this region.

INTRODUCTION

Increasing mineral trade and the prospect of a free trade agreement with Mexico (North American Free Trade Agreement) raise many mineral-resource issues specific to the U.S.-Mexico border area. A free trade agreement, along with current and anticipated favorable changes in the Mexican mining and investment codes and increasing regulation in the United States, could lead to a revival of the transborder mining industry that existed in the late 19th century (Martino and others, 1992). Urban, agricultural, and industrial growth along the border will likely accelerate under a free trade agreement, resulting in increased demand for development and improvement of the infrastructure and for goods which require minerals that can be supplied from either side of the border. Pressure is already mounting to clean up industrial contamination along the border, an effort that would create a strong local demand for minerals useful for the treatment of effluent and the storage of hazardous wastes.

Many borderlands geologists know that the mineral resources of the border area are able to support a substantial minerals industry that could meet the demands of an expanding economy and population. This report is for policymakers, corporate managers, borderlands specialists, and the general public, who may have scant knowledge of borderlands mineral resources and of the mineral-related policy issues. Information regarding resource limitations, such as water supply, prior land-use decisions, or lack of infrastructure, that may affect economic development of the border area is widely dispersed or unavailable. The Center for Inter-American Mineral Resource Investigations (CIMRI), which is part of the U.S. Geological Survey, is involved in a multiyear study to investigate the geologic, economic, and environmental aspects of the minerals industry in the U.S.-Mexico border region.

This report begins with a brief overview of the history of the border region as it relates to mineral-resource development. Sections on land status, infrastructure, geologic setting, and data sources lead to the summary of currently available mineral-resource data for the border region. Maps of mineral-commodity occurrences are included. The primary archive of data on mineral occurrences, prospects, and deposits utilized for this project is the Mineral Resources Data System (MRDS) of the U.S. Geological Survey, which is described below in "Data Sources and Collection."

For this report, the border region is defined to include parts of southern California, Arizona, New Mexico, and Texas on the U.S. side and the northern parts of Baja, Sonora, Chihuahua, Coahuila, Nuevo Leon, and Tamaulipas on the Mexican side of the border (fig. 1). The boundaries of the CIMRI study area were selected to include the major population centers away from the actual border and do not confonn to existing political boundaries. Major population centers play important roles in the transport, processing, marketing, and demand for mineral commodities.

Figure 1. Area defined as the U.S.-Mexico border region for this report. Area shaded.

MINING HISTORY OF THE BORDER REGION

From pre-Columbian through modem time, the border region has played a vital role in the settlement and development of western North America. The resources of the border region were first utilized by North American indigenous peoples, who mined a wide variety of materials (Forrester, 1969; Gerald, 1984). Turquoise, jet (gem material made of dense coal), opal, copper, and silver were mined for decorative uses. Coal was utilized as a fuel. Obsidian and other igneous rocks were mined to produce projectile points, mortars and pestles, grinding stones, stone axes, and a variety of other tools. Clay, asbestos, and other materials were used to make pottery. Salt was mined for use as a preservative and flavoring, and sodium sulfate for use as a purgative. Extraction of these mineral products established some of the early flows of resource materials from the border region to other parts of North America.

The Spanish Crown granted the right to mine in the New World in 1504; from the 16th century to the early 19th century, the Spanish explored for and then exploited the silver and gold resources of the border region (table 1). Mining was done under a variety of laws and regulations that affected claim sizes, mining rights, royalties, taxes, ownership, and the level of exploration and development. Exploration and mining in the study area were also affected by repeated conflicts between settlers and miners and native peoples until the late 19th century. Near the present U.S.- Mexico border, mines were operated only sporadically due to the threat of violence.

Early discoveries during the Spanish Colonial period include silver districts in Chihuahua such as Parra! (discovered about 1544), Batopilas (1632), and Santa Eulalia (1652) (Alvarez-Ruiz, 1983). These districts have produced for centuries and are responsible for the border region becoming one of the world's largest silver-producing areas. Many other mineral discoveries were made during the early Spanish Colonial period, including gold in the San Juan Bautista district, Sonora, in 1657 and silver along the Sonora-Arizona border in 1736 (Officer, 1991). In the north, salt was being produced in the Estancia Valley of New Mexico by the year 1650 to supply the silver-mining operations at Parra! in Chihuahua (Bachman, 1965).

The 19th century saw continuous expansion of mining in the border region and the identification of other metal resources still produced today. In 1803, the United States acquired rights to much of the land west of the Mississippi through the Louisiana Purchase, and its citizens began to rapidly spread westward. In 1810, Mexico revolted against Spanish Colonial rule. By the end of the revolution in 1821, much of the mining industry in the new country of Mexico was in shambles, and foreign investment was restricted.

Following the revolution, Mexico entered a period of nationalism where foreign control of mining and other industries was restricted and the flow of minerals across and within the border region was diminished. In 1926, Mexico prohibited any new foreign ownership of mines. This was followed by nationalization of certain mineral commodities and reservation of large tracts of land. In 1937, Mexico nationalized the railroads and, 1 year later, the oil industry.

Significant mineral discoveries continued to be made during the first half of the 20th century. Potash was discovered at Carlsbad, New Mexico (1925), and celestite in Coahuila (prior to 1942). Iron was discovered at La Perla, Chihuahua (1937). Minor amounts of iron, tungsten, nickel, and cobalt were extracted from the border region and sent to Allied Forces during World War II. After World War II, mining in the border region boomed as large low-grade copper, molybdenum, and gold resources, as well as other deposits, were more fully exploited.

In the second half of the 20th century, there has been a diversification of uses and exploitation methods for natural resources within the border region. As late as the 1950's, commodities such as celestite and fluorite (at Pico Etero, Coahuila, in 1952) became significant products of the region. Today natural resources flow across the border, and large amounts flow in and out of the border region. The Mexican government is reversing many of the nationalistic policies of the earlier part of the century. Revision of the mining regulations in 1990 allows foreign control of mining projects for 12 years, and investment policies have been liberalized in the last few years. These changes have large numbers of international mining firms, including Canadian and American companies, investing in mineral exploration and development in Mexico, especially in the border region. Historically, the role of minerals and other resources in the region has been significant. In the coming century, as international commerce becomes greater, resources in the border region should continue to play an important role in socioeconomic development.

LAND STATUS AND INFRASTRUCTURE

In natural-resource development, one of the more important issues is land status. Availability of land for mineral exploration and development influences costs associated with exploitation. In the United States, the Bureau of Land Management in the U.S. Department of the Interior is responsible for the survey of Federal lands and maintains public land records and records of mining claims. In the United States, national park, Wilderness, and Department of Defense lands are mostly excluded from mineral exploration and production, whereas most lands managed by the Forest Service (part of the U.S. Department of Agriculture) and the Bureau of Land Management are open to mineral exploration and development under Federal regulation. Exploration for and development of some commodities on Federal lands can be done only under Federal lease; leasing of mineral rights is under the aegis of the Bureau of Land Management. Indian- and State-owned lands have diverse regulations governing mining, but exploration is severely restricted on most Indian lands. With the exception of Texas, which contains State-owned and privately owned land almost exclusively, the U.S. portion of the borderlands study area consists largely of Federal and Indian lands (fig. 2). Taxes, royalties, and other fees are often partially determined by the land status and commodity.

In Mexico, land status and the system controlling mineral exploration and development provide a significant contrast. In Mexico, just as in the United States, national parks and military training grounds are excluded from mineral exploration. However, the land-governing system set up through the Federal and State governments delegates control to individual municipios. Municipios, like counties

Figure 2. Distribution of lands known to be closed to mineral exploration and (or) development in and adjacent to the U.S.-Mexico border region. Data from Paul G. Schruben (U.S. Geological Survey, unpub. data, 1993).

in the United States, have a governmental seat where mining documents are filed with the Agencia de Mineria. Municipio land is open to mineral exploration on a caseby-case basis, and agreements between the municipio government and individual companies are used to allocate mining lands. Most of the ranch land in the Mexico portion of the border region is privately held; the desert lands are typically government controlled. Taxes are paid to the State and Federal governments for all mining claims.

Figure 2 shows various types of land excluded from mineral exploration in the border region. More exact information on land status should be obtained from the U.S. Bureau of Land Management (address in table 2) or Mexican municipio offices.

Infrastructure plays a significant role in the ability of the borderlands to process and export mineral products. Infrastructure for the purposes of this report includes power sources and transportation routes. Power sources and facilities in the Western United States are shown on a map prepared by the U.S. Department of Energy (1992). Much like the U.S. railroad system, that in Mexico was constructed largely in the late 19th century and earliest 20th century. Although as much as 80 percent of the capital for this infrastructure development came from the United States (Martino and others, 1992), the railroads were nationalized in 1937. Figure 3 shows major standard-gauge railroad routes within and near the study area. Cross-border connections exist at various locations (fig. 3). The density of railroad lines in the southwestern part of the study area is low, and there is no rail service in Baja California Norte. Scheduling problems, lack of railcars, and other bottlenecks have led to truck rather than rail transport of ore in many Mexican mining operations (Martino and others, 1992). Recent decentralization of Mexican railroad operations has improved the speed and efficiency of the rail transport system; however, service to the rural areas has been diminished.

Over 65,000 kilometers (40,000 miles) of paved roads exist in Mexico (Martino and others, 1992), but most of them are in or near Mexico City; the density of paved roads in the border region is low (fig. 4). Nevertheless, trucking is the major transport mode in northern Mexico, operating largely on dirt roads. In Mexico, the mining industry relies heavily on truck transport. Paved roads link the United States and Mexico at 10 border cities, and the daily international truck commerce is valued in millions of dollars.

GEOLOGIC SETTING

The U.S.-Mexico border region extends 1,800 kilometers (1, 100 miles) and, for purposes of this discussion, can be divided into six geologic provinces (fig. 5) from east to

Figure 3. Major standard-gauge railroad routes in and adjacent 7, Hermosillo; 8, Douglas; 9, Albuquerque; 10, El Pasoto the U.S.-Mexico border region. Modified from Mexico Juarez; 11, Chihuahua; 12, Hidalgo del Parral; 13, PresidioSecretarfa de Comunicaciones y Transportes (1990) and U.S. Ojinaga; 14, Amarillo; 15, Del Rio-Villa Acuna and Eagle Geological Survey (1970). State names shown in figure l. Pass-Piedras Negras; 16, Monclova; 17, Monterrey; 18, LaredoSelected cities indicated by numbers: 1, Los Angeles; 2, San Nuevo Laredo; 19, Dallas-Ft. Worth; 20, San Antonio; 21, Diego-Tijuana; 3, Mexicali; 4, Phoenix; 5, Tucson; 6, Nogales; Brownsville-Matamoros; and 22, Houston.

west: (1) the Gulf of Mexico Coastal Plain, (2) Paleozoic and Mesozoic platform rocks, (3) an area of terrestrial volcanism, (4) an area of structural extension, (5) a transitional area between platform rocks and the area of extension, and (6) an accreted terrane. These provinces and their associated mineral commodities are briefly described below.

The Gulf of Mexico Coastal Plain is the easternmost geologic province and is composed of the Tertiary to Holocene sedimentary rocks of Texas, Tamaulipas, and Nuevo Leon shown on the simplified geologic map in figure 5A and geologic province map in 5B. These rocks are relatively undeformed and overlie Paleozoic basement. Significant mineral deposits in the Gulf of Mexico Coastal Plain include sulfur, evaporites, and clays.

To the west of the Gulf of Mexico Coastal Plain are platform rocks of Paleozoic and Mesozoic age in western Texas, New Mexico, southern Tamaulipas, Nuevo Leon, and Coahuila. These dominantly carbonate rocks overlie Precambrian basement. Paleozoic and Mesozoic sedimen-

western New Mexico and northeastern Arizona. Silver is the most important metal mined in the area of Paleozoic and .e

Mesozoic rocks, although lead-zinc-silver replacement deposits and small copper deposits have also been mined. This province is also a major source of celestite (which yields strontium), fluorite, and potash. Other industrial minerals produced from Paleozoic and Mesozoic platform rocks include barite, sulfur, and sodium sulfate.

In the central part of the study area, a third geologic province is formed by the largely terrestrial volcanic rocks of west-central New Mexico, east-central Arizona, western Chihuahua, and eastern Sonora. Major mineral products of this area include silver and some gold, copper, pumice, and perlite.

The fourth province is a zone of extension. This province, the Basin and Range, is composed largely of Tertiary volcanic rocks and intervening basin fill and extends from southeastern California southeast through most of Sonora and east-southeast through Arizona and New Mexico to westernmost Texas and eastern Chihuahua. The Basin and Range province is possibly the richest in mineral wealth. World-class porphyry copper and gold deposits are found in this environment. Other mineral products include barite, borates, clays, diatomite, evaporites, fluorite, lead, zinc, and zeolites.

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Figure 4. Selected primary paved highways and roads in and Diego; 3, Tijuana; 4, Mexicali; 5, Phoenix; 6, Tucson; 7, adjacent to the U.S.-Mexico border region. Modified from Nogales; 8, Hermosillo; 9, Albuquerque; 10, El Paso-Juarez; Mexico Secretarfa de Comunicaciones y Transportes (1990) 11, Chihuahua; 12, Hidalgo del Parral; 13, Presidio-Ojinaga; and Rand McNally (1989). State names shown in figure 1. 14, Amarillo; 15, Monclova; 16, Monterrey; 17, Dallas-Ft. Selected cities indicated by numbers: 1, Los Angeles; 2, San Worth; 18, San Antonio; and 19, Houston.

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Figure 5. Simplified geology (A) and geologic provinces (B) in and adjacent to the U.S.-Mexico border region. Modified from U.S. Geological Survey (1970) and Ortega-Gutierrez and others (1992). Geologic province boundaries dashed where uncertain.

Figure 6. Generalized distribution of volcanic and plutonic rocks in and adjacent to the U.S.-Mexico border region. Modified from U.S. Geological Survey (1970) and Ortega-Gutierrez and others (1992) .

DATA SOURCES AND COLLECTION

Figure 7. U.S.-Mexico border region showing the number of Mineral Resources Data System records for sites containing metallic minerals only (M), industrial mineral commodities only (I), and both metallic and industrial mineral commodities (B).

Figure 8. Distribution of all mines, prospects, and occurrences of metallic and industrial mineral commodities in and adjacent to the U.S.-Mexico border region for which the Mineral Resources Data System included records as of May 1993.

MINERAL-RESOURCE DISTRIBUTION

One of the goals of this study is to identify which resources occur within the study area and which need to be imported to supply border-region industries. In addition, minerals that might be exported from the region will be identified. The variety and number of occurrences of metallic and nonmetallic resources in the border region are extensive. These resources include precious and base metals and materials used in agriculture, infrastructure development, environmental improvement, and production of chemicals. Commodities produced in the study area are listed in table 3. Fuel materials (coal, uranium, oil, and gas) are prevalent in the border region but are not addressed in this study. Metals for producing steel, aluminum, and nonferrous alloys occur in minor amounts and are not available in the quantity necessary to support an extensive industry in the border region. Ferrous metals occur in a number of deposits and have supported an integrated steel plant at Monclova, Coahuila, in the recent past, but increased reserves would be needed to revitalize this plant (Martino and others, 1992). A major integrated steel plant continues to operate in Monterrey, Nuevo Leon, but is dependent on imported ores.

The distribution of major mines, prospects, and occurrences of gold and silver in the border region is shown in figure 9. The sites shown in this figure represent both placer and lode deposits where gold and (or) silver were listed as major commodities. The distribution of precious metals in the study area indicates that the western part of the area is more gold rich and that the southeastern part of the area is silver dominated. There are no reported major gold occurrences in Nuevo Leon, Tamaulipas, or Coahuila, although a few small occurrences have been reported. Precious metals, gold and silver, were the dominant commodities of interest in the border region until the mid-19th century, when lead, zinc, and copper deposits began to produce and eventually dominated metal production. In the 1970's and 1980's, gold again became the focus of mineral exploration on the U.S. side of the border and continues to be the main commodity of exploration interest throughout the study area. The change in regulations concerning exploration and mining in Mexico in 1990 has created an explosion of activity by foreign investors in precious-metal exploration in Mexico. Current opinion of the potential for undiscovered deposits in northern Mexico and the large gap between early exploitation and modem exploration indicate that the border region will continue to be a source of considerable precious-metal wealth in the foreseeable future.

With the discovery of base-metal deposits (lead, zinc, and copper) in the mid-1800's, the resource focus changed to the development of lead and zinc industries. The distribution of known mines, prospects, and occurrences where copper or lead and zinc are the main commodities is shown in figure 10. Lead and zinc deposits appear to be more abundant in the eastern part of the border region, particularly in Chihuahua, Coahuila, and Tamaulipas. These base metals have played a key role in mineral-resource development in the border region. By World War I, the border region had become a significant copper producer and, in fact, there was a copper boom spurred by the technology to recover copper from large tonnages of low-grade copper material. Mexico's copper production grew to be the 11th e

Figure 9. Distribution of major gold and silver mines, prospects, and occurrences in and adjacent to the U.S.-Mexico border region. Data from the Mineral Resources Data System.

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Figure 10. Distribution of major lead and (or) zinc and copper mines, prospects, and occurrences in and adjacent to the U.S .-Mexico border region. Data from the Mineral Resources Data System.

Table 4. Significant industrial mineral commodities used in agriculture, infrastructure, and environmental improvements in the U.S.-Mexico border region. [Industrial mineral commodities produced in the border region are listed in table 3. Some commodities used in the border region are produced there, and some are brought in. Data from the Mineral Resources Data System]

largest in the world by 1992, with nearly all the copper coming from the border region, and copper production in the United States made it the 2d largest producer in the world (Thompson, 1993). Most of the U.S. copper also comes from the border region. The U.S.-Mexico border region is one of the richest copper provinces in the world.

Many of the same mineral materials used in agriculture are also used for infrastructure development and environmental improvement (table 4). For example, limestone, gypsum, light-weight aggregate, and boron (from borates) all have applications in these three areas. Many other materials are used in two areas. Most of the materials are used in agriculture. Figure 11 shows the distribution of known mines, prospects, and occurrences of limestone (including marble and dolomite), light-weight aggregate (including perlite, pumice, vermiculite, and other volcanic materials), sand and gravel, and stone used as aggregate or building stone. The absence of data points for these materials in Baja California Norte and Sonora in the figure is probably a function of incomplete data collection and not a

X X X

a;

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en

X X X X

result of the geology. The gap in known occurrences of these commodities in southern Arizona coincides with an Indian reservation adjacent to military lands. These materials, although used mainly in infrastructure development, have other uses as shown in table 4.

border region is shown in figure 12. Their applications cross several areas of use, but they are generally important to environmental cleanup because of their absorbent properties. Lack of known occurrences of these commodities outside of Arizona, Nuevo Leon, and Coahuila is a reflection of incomplete data.

from celestite and fluorine from fluorite, and the distribution of these commodities is shown in figure 13. Included on this figure is the distribution of barite, which is used in drilling mud. Again, the apparent lack of barite, fluorite, and celestite deposits in California, Baja California Norte, western Sonora, and western Coahuila is probably a function of the incomplete data.

X X

Zeolite, gypsum, and diatomite distribution in the

The border region is a leading producer of strontium

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X X X

en

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Figure 11. Distribution of mines, prospects, and occurrences of construction materials in and adjacent to the U.S.-Mexico border region, including sand and gravel, limestone, light-weight aggregate (pumice, perlite, vermiculite), and stone for aggregate or building stone. Data from the Mineral Resources Data System.

Figure 14 shows the distribution of four disparate groups of industrial minerals: all clays, evaporite minerals (potash and (or) halite), sodium sulfate and sodium carbonate, and sulfur. Again, there are large gaps in the plot of occurrences in northern Mexico that are probably due to incomplete data.

Other materials and metals occur in the border region. Readers interested in the distribution of commodities not included in this publication should contact the U.S. Geological Survey offices listed in table 2.

DISCUSSION

Initial compilation of nonfuel mineral-resource data has thus far identified approximately 9,300 known deposits and occurrences in the U.S.-Mexico border region of precious metals, base metals, and mineral commodities used in infrastructure, agriculture, and environmental improvement. Preliminary assessment of the geological terranes implies that further exploration in northern Mexico could augment the known deposits of many industrial minerals, including zeolites and clays. The low density of existing road and railroad infrastructure in parts of northern Mexico could impede future resource development, especially the development of low-value industrial minerals and bulk construction materials such as aggregate and sand and gravel.

Investment capital for exploration and mining will probably accelerate its flow to Mexico. The reasons for this include the decreasing land area in the southwestern United States open to mineral exploration and exploitation, increasingly restrictive U.S. regulations, the extensive amount of land open to mining in Mexico, and favorable Mexican investment and mining regulations. Expansion of mining activities in Mexico will probably mean increasing flows of many minerals and materials from Mexico to the United States and Canada. However, known deposits of materials for environmental cleanup efforts are limited in northern Mexico, and, in the short term, these materials may be expected to flow southward. Iron and aluminum alloys will also have to be imported into the border region.

In the future, with increased exploration and financial investment, the border region is likely to experience significant growth. As this growth occurs, the demand for minerals for industry, infrastructure, housing, agriculture, environmental cleanup, and other uses will also increase. The ability of the border region to supply many basic minerals to industries within its boundaries and outside of its boundaries contributes to the prospect of a bright economic future. oo

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Figure 12. Distribution of mines, prospects, and occurrences of gypsum, zeolites, and diatomite in and adjacent to the U.S.-Mexico border region. Data from the Mineral Resources Data System.

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Figure 14. Distribution of mines, prospects, and occurrences of clays, evaporite (halite or potash), sodium carbonate or sodium sulfate, and sulfur in and adjacent to the U.S.-Mexico border region. Data from the Mineral Resources Data System.

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