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Figure 3. Distribution of U.S. Forest Service wilderness lands studied from 1964 to 1984 (from U.S. Geological Survey Professional Paper 1300).

and siltstones. An introduced (or epigenetic) suite of trace elements in some samples also is present. Concentrations of the introduced-suite elements are commonly very low in the wholerock samples, but they are enhanced many times in the insoluble residue samples. The introduced suite of metals and their relative abundances in the suite were found to be the same as those found in ores of the southeast Missouri lead-mining district. By “mapping” relative metal abundances as well as other relationships of the introduced metal suite and correlating this information with certain characteristics of the subsurface stratigraphy, the scientists discovered that the probable extent of the zone that contains basemetal deposits is significantly larger than originally thought. These results were used by the team of Geological Survey and Missouri Division of Geology and Land Survey scientists to identify three areas in the Rolla quadrangle that are highly favorable for the existence of base-metal resources. The team also estimated the quantity of lead, zinc, copper, silver, nickel, and cobalt resources in the quadrangle; for example, the cobalt present in deposits in the quadrangle is estimated to be as much as 30 million to 55 million pounds-equivalent to 2 or 3 years' U.S. consumption of this strategic metal.

Mineral Resources and Public Lands

A major summary of wilderness mineral potential was published in 1984. U.S. Geological Survey Professional Paper 1300, titled Assessment of Mineral-Resource Potential in U.S. Forest Service Lands Studied, 1964-1984, a two-volume, 1,183-page work, brings together the results of a 20-year program that was completed by the U.S. Geological Survey and the U.S. Bureau of Mines under the provisions of the Wilderness Act of 1964 and subsequent related legislation. The report summarizes our current knowledge of known mineral and energy resources and of the potential for the occurrence of undiscovered mineral and energy resources in about 45 million acres of Federal lands. This acreage is distributed in about 800 individual areas, chiefly in national forests (fig. 3).

About two-thirds of the areas studied contain zones favorable for the occurrence of one or more mineral commodities that include base and precious metals, strategic and critical minerals, and energy resources. Construction materials are plentiful in most

areas.

Land use planners seek a quantitative estimate of mineral resources so that

[blocks in formation]

the mineral-resource value of an area can be compared with the estimated values of competing land use possibilities. The development and application of quantitative regional resourceassessment techniques from AMRAP and CUSMAP are being done at the same time that the 20-year study of wilderness areas was being completed. The publication of Professional Paper 1300 presented a summary of subjective evaluations for each area studied and references to site-specific information about the mineral resources of designated wilderness, roadless, or study

areas.

In fiscal year 1984, several Geological Survey scientists tested a method for obtaining quantitative estimates of mineral-resource value by using computer simulation techniques, gradetonnage models of mineral deposits, and the results or referenced studies presented in Professional Paper 1300. The quantitative estimates, although limited to undiscovered resources of selected mineral deposit types in areas of California, Nevada, Oregon, and Washington, are a landmark result for subsequent debate on how to resolve land use conflicts.

ACCESSIBLE INFORMATION BASES-A FOUNDATION FOR BETTER UNDERSTANDING OF MINERAL RESOURCES

To maintain the information bases essential to the proper management of the Nation's mineral-resource position, the Geological Survey continually updates its files of minerals information. This includes information on commodities such as cobalt, chromium, and manganese that are strategic to our national defense but also includes information on construction materials-sand, gravel, building stone, and materials for cement manufacture-and phosphate rock, potash, and other materials used in fertilizers. Not only are these "nonstrategic" materials absolutely necessary to maintain our modern standard of living, but they also have a role in national security. One might ponder the relative importance of cobalt in a jet engine, the crushed stone in the

runway, and the agricultural products that sustain the pilot. The United States does not depend on imports for these "nonstrategic" materials, but the scarcity of exploitable sand and gravel deposits near many cities where industrial and residential developments have covered prime deposits points out the need for information on the location, quantity, and quality of mineral deposits.

Information about mineral deposits, occurrences, and related geologic features is obtained by several types of field and laboratory research on mineral resources. Examples include regional and topical mapping projects in the United States and other countries, some of which are done in cooperation with earth science agencies of State governments or foreign countries.

In order that maximum benefit is obtainable from this massive stockpile of mineral-resource data, the Geological Survey maintains the Mineral Resources Data System (MRDS) and the International Strategic Minerals Inventory (ISMI). Some of the plethora of information that is obtained from many diverse research activities is disseminated in a large number of Geological Survey publications, outside journals, and professional meetings; other information is confined to internal reports and files. Through the MRDS, some of this information is organized in a mineral deposit file so that researchers can request information by the geographic location, mineral commodity, or other attribute of the mineral information they seek.

By the nature of the diverse sources from which data are gathered for MRDS, coverage of regions or commodities is not uniform. To improve the comprehensiveness and comparability of data on major mineral deposits, the Geological Survey, along with several other countries, started the ISMI. Progress and activities of MRDS and ISMI during 1984 are described below.

Mineral Resources Data System

This system was started in 1972 as the Computerized Resource Information Bank (CRIB). The Mineral Resources Data

System (MRDS) evolved from the CRIB to become the primary storage system for descriptive and archived historical mineral data for domestic and international deposits.

It is now a major reference tool for Federal, State, and mineral industry scientists who seek information on commodity locations and associated geoscience data. New mineral data are received and entered into the system from a wide range of technical reporters, including Geological Survey regional and commodity specialists. All data in the MRDS are organized into records; each record represents a single mine, mineral occurrence, district, or region. The master file now contains over 64,000 records of mineral deposits and occurrences in the United States and more than 5,300 records for other countries. As the need for rapid access to comprehensive mineral data grows and many pressing mineral policy decisions are being made, the MRDS is being refined and streamlined to handle national and international needs.

International Strategic Minerals Inventory

The easily accessible mineral information stored in the MRDS requires a complementary, summary inventory to complete our present-day knowledge of domestic and international strategic and critical mineral resources and supplies. To satisfy this need, the International Strategic Minerals Inventory (ISMI) was initiated on the premise that, for many mineral commodities, a large proportion of current and near-future production (as much as 90–95 percent) is or will be from a relatively few major deposits and that good information on production, reserves, and identified resources of those major deposits will improve the basis for sound mineral policy decisions. The ISMI also is based on the realization that many industrialized countries maintain extensive global mineral commodity files and that a cooperative program with these countries would avoid a great deal of duplication of effort and greatly improve the quality and amount of information available to each country. The ISMI is supported by mineral-resource agencies of the United

States, Canada, West Germany, South Africa, Australia, and the United Kingdom, with the goals of gathering, analyzing, and publishing information on major deposits of selected mineral commodities. A working group made up of representatives of the agencies of participating countries meets on a regular basis, and a continuing compilation of deposit records of selected commodities is underway. The summary commodity reports for manganese, chromium, and phosphate were published in fiscal year 1984 as Geological Survey Circulars 930–A, 930-B, and 930-C. Compilations of data and summary reports for seven additional commodities-nickel, cobalt, graphite, vanadium, titanium, tungsten, and the platinum-group elements—are being prepared.

NEW CONCEPTS FOR MINERAL EXPLORATION AND ASSESSMENT

Basic research that increases our understanding of the descriptive characteristics of mineral deposits and the genetic processes by which they form is the foundation for continued advances in mineral exploration and mineral-resource assessment. Geological Survey research on the fundamentals of mineral resources includes field and laboratory studies of the geologic aspects of economic minerals, modeling studies of mineral-deposit systems, and geochemical and geophysical traits of hidden deposits.

Some types of field and laboratory studies that will have future applications in mineral exploration are geochemical investigations, such as the importance of the role of organic matter in the formation of ore deposits, and geophysical research, such as the development of a new geophysical instrument, called the "Co-Axial Loop, ExtraLow-Frequency Electromagnetic Sounder." This device can detect some sulfide mineral deposits at depths of more than one-half mile without interference from electrical conductors such as fences and electric powerlines.

Included in modelling studies is an emphasis by a large number of Geolog

ical Survey geologists with field mapping and other research experience in various types of mineral deposits to record systematically the chemical and mineralogical characteristics and to decipher the geologic environments of formation of many types of mineral deposits. Over 60 such models have been constructed; new models are being prepared, and existing models are being refined with new information. These descriptive mineral-deposit models and associated quantitative estimates of the size (tons and grades) and abundance of deposits gives the economic geologist broader knowledge to apply to resourceassessment problems. Comprehensive, consistent information about types of mineral deposits also is needed as input to an analysis system that was completed by Stanford Research Institute in 1980 under Geological Survey sponsorship. This study applied artifical intelligence, the area of computer science concerned with computational methods for tasks involving reasoning and perception, to questions of prospect evaluation, regional resource evaluation, and drilling site selection. A microcomputer-based version of this system, designated "muPROSPECTOR," recently has been developed to aid geologists in mineral-resource assessment. This year, the system was used to assess mineral resources in several geologic terranes of the SherbrookeLewiston 2-degree quadrangle in New England as part of CUSMAP.

Exciting new examples of these types of research that were of particular interest in fiscal year 1984 are paleothermal anomalies and models of disseminated gold deposits. Paleothermal studies, using fluid inclusions, fission tracks, and maturation of organic material, gave new clues that will help in locating concealed mineral deposits. Disseminated gold deposits recently have become the largest source of U.S. gold production and were major targets of 1984 industry exploration efforts in the United States.

Detection of Paleothermal Anomalies

Heat plays a role in the formation of some mineral deposits and, at the same

time, causes physical and chemical changes in rocks that surround the deposits. The region around a deposit may contain a subtle record of past temperatures that were higher than those associated with the surrounding rocks. This region, in which the rocks may have been heated millions of years ago, is called a paleothermal anomaly (fig. 4A) and is analogous to the visible alteration halo sought during traditional mineral exploration. To detect paleothermal anomalies, geologists have studied several geologic features that retain a record of past temperatures. Geological Survey researchers have been instrumental in the development and application of three promising techniques for the detection of paleothermal anomalies: fluid-inclusion studies, fission-track analysis, and organic maturation indices.

Fluid inclusions are small amounts of fluid that were trapped within mineral grains during crystallization or recrystallization (fig. 4B). These small (0.001to 0.01-millimeter) inclusions may contain separate liquid and vapor (bubble) phases as a result of cooling but can be reheated in the laboratory to determine the minimum temperature of the fluid at the time it was entrapped. Studies of fluid inclusions have been used for over a century to determine the temperature of mineral deposits at the time of their formation, but, recently, they have come into wider use in the search for paleothermal anomalies associated with ore deposits. Fluid inclusions provide information about the composition, pressure, and flow direction of mineralizing fluids. They record the paleothermal anomaly well beyond the zone of visibly altered rock through subtle differences in temperature and fluid composition relative to those of the fluid inclusions in the surrounding rock.

Fission-track dating is one of the newer tools used to identify paleothermal anomalies. Fission tracks are small paths of radiation damage caused by the spontaneous fission of uranium in some minerals (fig. 4C). The number of tracks present in a mineral crystal is proportional to uranium content and to the length of time since crystallization. These tracks can be partly to completely

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