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exploration and mineral-resource
assessment. Current Geological Survey
research programs have responded to
several of today's most pressing mineral-resource problems: (1) the availability to the United States of minerals from domestic sources, (2) the need for systematic, comprehensive mineral-resource and geologic information for land use planning and
mineral exploration, (3) the preservation of past knowledge so that it does not have to be rediscovered, and (4) the development of new tools and methods to explore for, assess, and increase our understanding of mineral resources and the processes that form them. These responses have provided continually updated summaries of available domestic resources of all mineral commodities, descriptions of the mineral resources on Federal land proposed for wilderness preservation or other landuse decisions, summary and storage of current mineral-resource information in accessible data bases, guidance for future research by identification of what we do not know, and the development of innovative methods to provide answers to as yet unknown resource problems. In a 1975 Congressional Research Service report about the U.S. Geological Survey, Dr. Allen Agnew noted that, since its inception, the Geological Survey has maintained scientific eminence and has produced valuable and forward-looking naturalresource programs that have made important contributions to the formulation of the Nation's mineral resource policies. Some of the significant results and current state-of-the-art mineral-resource investigations are described below.
Domestic Sources Of
Closer looks at some unconventional geologic environments offer exciting possibilities for new domestic sources of minerals. Three areas currently being studied by the Geological Survey are the midcontinent region, eastern Mesozoic basins, and the offshore areas included in the Exclusive Economic Zone. Investigations in these areas encompass a
wide range of mineral-deposit types but
have a special focus on strategic and
critical minerals. This term, strategic
and critical, is applied to those minerals which are essential to our Nation's economic well being and military security and for which domestic or secure foreign sources are not assured.
Strategic and Critical Minerals
Because favorable geological conditions for several types of concealed mineral deposits were identified in an earlier Geological Survey study of the Rolla, Missouri, area, a similar mineralresource study, focussed on a few mineral commodities but encompassing a larger region, was started in fiscal year 1984. An area embracing all or part of 12 States between 36 and 46 degrees north latitude and 88 and 100 degrees west longitude will be studied by the Geological Survey and State agencies using geologic mapping, geochemical sampling, and measurements by geophysical teams (fig. 1).
The development of new concepts and methods for the identification of concealed mineral deposits in heretofore untested, but possibly mineralized, locations has been stimulated by the depletion of mineral resources from deposits discovered near the surface. The midcontinent region is an example of this situation because, until recent times, the only known mineral deposits in that region were those that outcropped. The potential for the occurrence of additional very large and economically significant mineral deposits in the subsurface of this region is excellent. From 1978 through 1982, the State of Missouri accounted for 90 percent of the U.S. mine production of lead, 20 percent of its zinc, and smaller amounts of copper, silver, and cadmium. These metals are produced from vast deposits that are concealed under 800 to 1,200 feet of barren overlying rock.
Historically, mining interest in the midcontinent region has centered on the near-surface sedimentary rocks (limestones and dolomites), which contain deposits of lead and zinc and are called
migration is believed to be related to crustal collision that occurred about 300 million years ago. Research to determine the origin and the location of mineral deposits formed during these ancient events will aid in the discovery of new mineral resources.
Eastern Mesozoic Basins
Mesozoic rift basins, formed between 205 and 240 million years ago, are another potential domestic source of minerals, including nickel, cobalt, and platinum-group elements for which the United States presently depends upon imported supplies. In the Soviet Union, near the city of Norilsk, similar rift basins contain significant deposits of nickel, copper, and platinum metals. Mesozoic basins of this type also are considered to be potential hosts for uranium deposits.
Concurrent with the midcontinent studies, the Geological Survey is investigating 10 Mesozoic rift basins or subbasins that are exposed in a belt that extends from Massachusetts to South Carolina (fig. 1). Many more of these basins are buried onshore beneath coastal-plain sediments and offshore beneath the continental shelf. The goal of these field and laboratory studies is to identify and outline areas that are favorable for the occurrence of basemetal deposits. Descriptions of examples of each type of mineral deposit associated with rift-basin environments are prepared for use as comparative models. The models are important tools for identifying favorable terranes for mineral deposit occurrence.
Exclusive Economic Zone
The Geological Survey continues to investigate the mineral potential of the Exclusive Economic Zone (EEZ) that was declared by President Reagan on March
10, 1983. The Eez is the offshore area that extends 200 nautical miles beyond the shorelines of the United States and its territories and possessions. Oil and gas have been produced from portions of the United States EEZ, but the mineral resources of this large area (3.9 billion acres compared with the 2.3 billion
acres of total onshore area for the United States) are virtually unknown. Three types of offshore mineral deposits that are the subject of current investigations are marine heavy-mineral placer deposits, cobalt-bearing manganese crusts and nodules, and polymetallic sulfides.
Geological Survey researchers are examining the continental shelves of the United States for possible sources of heavy minerals, which are concentrated in placer sand deposits by the action of water currents, waves, and winds. Titanium minerals, monazite, zircon, cassiterite, gold, sillimanite, kyanite, andalusite, garnet, staurolite, corundum, phosphorite, and other heavy minerals have been identified or indicated on the Atlantic Continental Shelf, where initial investigations are taking place. The mineralogy and chemistry of new and archived mineral sand samples from the Atlantic offshore are being studied using methods that represent significant improvements in the tools of reconnaissance and in methods of sample preparation and analysis. Results of preliminary studies have shown high concentrations of heavy minerals in an offshore area of Virginia where onshore deposits contain relatively low heavymineral concentrations. These results, although limited to one area of the Atlantic Continental Shelf, indicate that exploration philosophies linking the best offshore target areas with high onshore heavy-mineral concentrations may not be as reliable as previously thought.
Recent studies suggest that cobaltbearing manganese crusts on the flanks
of seamounts and oceanic islands in the central Pacific Ocean may represent a significant mineral resource. Cobalt content ranges from about 0.4 percent for the deeper crusts to 1.2 percent on seamount tops shallower than about 7,500 feet. Some crust material dredged from a seamount about 160 miles
northwest of the U.S. territorial possessions of Palmyra Atoll and Kingman Reef contained 2.5 percent cobalt, more than twice the concentration indicated by earlier studies.
Deposits of polymetallic sulfides have received much publicity in such journals as the National Geographic, where photographs from the research submersible Alvin have been printed. Studies by the Geological Survey of sulfide deposits along spreading centers, such as the Juan de Fuca Ridge off the coast of Washington State, are designed to determine how these deposits are forming and to assess the mineral resources of these areas. This information will help scientists to understand the environments of deposition of similar onshore deposits and aid them in locating additional terranes that are favorable for the occurrence of sulfide-type deposits.
New understanding of the Nation's mineral endowment has been gained from the Geological Survey's systematic geologic and mineral-resource studies of l:250,000-scale quadrangles (an area ranging from 5,000 to 8,000 square miles) and of mineral-resource surveys done with the U.S. Bureau of Mines under legislative mandate in those areas included or proposed for inclusion in the National Wilderness Preservation System.
The systematic quadrangle studies are carried out under two programs: the Conterminous United States Mineral Assessment Program (CUSMAP) for the 48 conterminous States and the Alaskan Mineral Resource Assessment Program (AMRAP) for Alaska. These two programs are providing a modern, systematic mineral-resource assessment of areas that have indications of mineral resources, especially for strategic and critical minerals. Mineral resources of the quadrangles are assessed by using data gathered during coordinated efforts of teams of scientists doing
geologic mapping, geochemical sampling of rocks and stream sediments, and analysis of measurements from geophysical surveys and satellite imagery. By fiscal year 1984, 175,000 square miles had been assessed under Amrap, and 80,000 square miles under CUSMAP. Present plans call for approximately 600,000 square miles of Alaskan lands to be assessed by the year 2000 and for almost a million square miles to be assessed in the conterminous United States during the next several decades.
The responsibility of the Geological Survey and the U.S. Bureau of Mines to assess the mineral resources of certain public lands that are administered by the Bureau of Land Management and the Forest Service is a provision of the Wilderness Act (Public Law 88-577, September 3, 1964) and of subsequent related legislation. Under the Federal Land Policy and Management Act of 1976, the Geological Survey and Bureau of Mines have undertaken mineral surveys of Bureau of Land Managementadministered lands for which a preliminary determination of wilderness suitability has been made. The Bureau of Land Management has found that 23.2 million acres deserve further study for wilderness consideration. The mineral resources of 12 Indian reservations also are being assessed by the Geological Survey for the Bureau of Indian Affairs.
Mineral-resource assessments from the CUSMAP, AMRAP, and public land studies can be used along with information about other possible land uses (timber, agriculture, grazing, recreation, and various types of development) to plan land uses that are in keeping with the Nation's interests. In addition, the Geological Survey has, in the course of these assessment studies, developed new techniques and methods of resource assessment which are applicable to public and private lands and which provide a practical approach to the assessment of the mineral endowment of the national domain.
Some recent highlights of regional mineral-resource assessment studies are the completion of the Rolla, Missouri, quadrangle under CUSMAP and the publication of a summary of the public lands mineral-resource studies done over the last 20 years under the Wilderness Act mandate.
Mineral Resources of the
The Rolla quadrangle was chosen as one of the first quadrangles for study under CUSMAP because it contains known mineral occurrences and high potential for additional undiscovered occurrences of important minerals. The
quadrangle (an area of about 8,000 square miles) includes most of the southeast Missouri lead-mining district, an area which contains the largest lead reserves in the world (fig. 2). The important mineral deposits of this major district occur in geologic formations that extend beneath the surface for hundreds of miles to the north and west of this area. The Rolla quadrangle is thus an excellent field laboratory for the development of mineral-resourceassessment methods that can be used throughout regions where similar geologic environments suggest the existence of mineral deposits like those that occur in the Rolla quadrangle. The
studies in the Rolla quadrangle were
done in cooperation will) the Missouri Division of Geology and Land Survey.
During the Rolla study, an innovative geochemical technique was developed that has significant possibilities for subsurface exploration throughout the midcontinent and similar geologic regions. This technique is based on the
chemical and mineralogical analysis of whole-rock and insoluble residue samples of drill core in the sample library of the Missouri Division of Geology and Land Survey. The drill holes selected for the analysis are not industry proprietary, do not intersect economically significant mineralized ground, and, in most cases, are not located in the Old Lead Belt, the Viburnum Trend, or other known orebearing localities. The whole-rock samples from the drill core were used to determine an intrinsic suite of trace elements that reflects the types of rocks in the geologic formations in the drill cores—dolomites, limestones, shales.
Figure 2. Mineral-resource assessment of the Rolla 2-degree quadrangle, Missouri.