GMEG - Mineral Resources
Additional information about the scope of our work is available in U.S. Geological Survey Circular 1363
Natural systems consist of a variety of interrelated geologic, biologic, hydrologic, and climatic subsystems, each with their own set of processes that affect, and are affected by, other subsystem processes. In many cases today, anthropogenic subsystems also affect, and are affected by, natural processes. Center scientists have a diverse set of skills and capabilities that have been and can be applied to diverse geoscientific issues of importance to society and the economy. Our approach to any particular problem is to understand the operable processes and their interrelations and provide comprehensive products that allow for more informed land-management decisions. Center scientists are skilled in the collection and synthesis of new and existing data and in the use of those data to arrive at scientifically sound conclusions. The scientific specialties include, but are not limited to:
Center scientists have extensive experience throughout the entire country and many parts of the world, and have collaborated with many Federal, State, and local agencies, with various private sectors, and with foreign countries and organizations. Each scientific and societal issue requires a different combination of the scientific skills. As a result, the Center, with its breadth of capabilities, provides scientifically sound approaches to a wide range of issues.
Mineral Deposit Studies
Mineral deposit models are important in exploration planning and quantitative resource assessments for a number of reasons including: (1) grades and tonnages among deposit types are significantly different, and (2) many types occur in different geologic settings that can be identified from geologic maps. Mineral deposit models are the keystone in combining the diverse geoscience information on geology, mineral occurrences, geophysics, and geochemistry used in resource assessments and mineral exploration. Too few thoroughly explored mineral deposits are available in most local areas for reliable identification of the important geoscience variables or for robust estimation of undiscovered deposits—thus we need mineral-deposit models. Globally based deposit models allow recognition of important features because the global models demonstrate how common different features are. Well-designed and -constructed deposit models allow geologists to know from observed geologic environments the possible mineral deposit types that might exist, and allow economists to determine the possible economic viability of these resources in the region. Thus, mineral deposit models play the central role in transforming geoscience information to a form useful to policy makers.
The foundation of mineral deposit models is information about known deposits. The purpose of USGS Open-file report 2008-1155 is to make this kind of information available in digital form for porphyry copper deposits. The publication contains a computer file of information on porphyry copper deposits from around the world. It also presents new grade and tonnage models for porphyry copper deposits and for three subtypes of porphyry copper deposits and a file allowing locations of all deposits to be plotted in GoogleEarth. The consistently defined deposits in the file provide the foundation for grade and tonnage models included here and for mineral deposit density models.
Knowledge of the distribution, characteristics and origin of mineral deposits decreases our reliance on imported commodities and improves our abilities to evaluate the geochemical effects of mineral deposits and mines on the biosphere and hydrosphere. The U.S. Geological Survey has a long and distinguished history in assessing the mineral resources of the public domain, and that role remains active today. The Survey has an immediate and constantly recurring need to upgrade and maintain the capability of its staff to identify and assess areas favorable for mineral deposits. The method WMR scientists use in identifying undiscovered mineral resources was developed to explicitly express estimates of undiscovered resources and associated uncertainty in a form that allows economic analysis and is useful to decision makers. Yet much of the Western U.S. is covered by geologic units that conceal important mineral deposits. This cover formed prior to, during, and after deposit formation and consists of rocks, soils, and water. WMR scientists are working to specify and evaluate innovative methods of combining geologic, geochemical, geophysical, and mineral resources data with existing and new mineral deposit models to predict the possibility and probability of undiscovered deposits in these covered areas.
The Proterozoic eon (c.2500 to 600 million years ago) encompasses more than 40% of Earth's history, a time during which fundamental atmospheric and oceanic changes occurred, biological diversity increased, and modern-style plate tectonics evolved. A disproportionately large share of the world's metallic resources occur in sedimentary basins of this age. World-class lead-zinc-silver deposits found in eastern Australia, British Columbia, and Montana; copper-silver deposits of Zambia, Michigan, and Montana; banded iron formations located in Michigan, Minnesota, and Canada; and iron-oxide copper-uranium-gold-silver-rare earth element deposits like Olympic Dam, Australia are found in these basinal strata. Our approach is to look holistically at the sedimentary basin in which the ore deposits are found. Ultimately hoping to track the origin of the ore deposit components from their site of residence within minerals in the basinal strata into the ore fluids, follow the effects of the migrating ore fluids through the basin aquifers, and understand the processes that resulted in precipitation of the ore deposit from the ore fluids.
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Mineral and Energy Resource Studies
Robust quantitative mineral resource assessments require both comprehensive knowledge of the regional geology and the mineral deposits of the assessment areas, and detailed genetic models of deposit types used in the assessments. A comprehensive understanding of the geology, hydrothermal systems, and mineral resources of the Cascades arcs and central California Coast Ranges is essential for land-use managers to be able to plan for future multiple uses and for increasing reliability of the forthcoming National Mineral Resource Assessment. Areas to the east of the western Great Basin (including the Humboldt River Basin), as well as the Western Cascades arc in Oregon and Washington, recently have received comprehensive geologic and mineral resource investigations. However, mineral resource information for much of the northwestern Great Basin and Modoc Plateau south of the High Cascades in California and for the central Coast Ranges is not comprehensive or the existing data compilations are outdated, creating a critical gap in regional geologic and resource knowledge and databases.
Geologic maps provide the foundation for all earth science studies. The characteristics of the diverse geologic units influence the formation of mineral deposits, the degree of weathering, erosion, and thus slope stability, and the chemistries of both the soils and erosion products that come from those rocks. Geologic structures play important roles in the distribution of geologic units, the formation of metal-bearing veins, the migration and trapping of ground water or hydrocarbons (oil, gas), and the localization of earthquakes. Geologic maps that show these features guide other studies, ranging from remote sensing studies of mineral deposits to the evaluation of ground-water chemistry. New mapping often is needed in new study areas to provide the essential data needed for the other studies.
The Great Basin is one of the world's great metallogenic provinces and about 11% of the total world production of gold (approximately 74% of the United States production) is produced annually from this region, as well as additional silver and copper. Included within this region are some of the largest Au deposits in the world with a resource potential that exceeds 3,200 metric tonnes (100,000,000 ounces) of gold. The impact of these mines on local economies, on the nation's economic sustainability, and on our national balance of trade are profound, and will continue to be so well into the 21st century. WMR scientists focus on critical questions regarding the genesis of precious-metal deposits in this region in order to develop state-of-the-art mineral and geoenvironmental models used in crucial land-use planning decisions affecting federal lands in the west and in designing exploration strategies by the mining industry.
Cape- and ridge-associated marine sand deposits, which accumulate on storm-dominated continental shelves that are undergoing Holocene marine transgression, are particularly notable in a segment of the U.S. Atlantic Continental Shelf that extends southward from the east tip of Long Island, N.Y., and eastward from Cape May at the south end of the New Jersey shoreline. These sand deposits commonly contain sand suitable for shore protection in the form of beach nourishment. Increasing demand for marine sand raises questions about both short- and long-term potential supply and the sustainability of beach nourishment with the prospects of accelerating sea-level rise and increasing storm activity. To address these important issues, quantitative assessments of the volume of marine sand resources are needed. Currently, the U.S. Geological Survey is undertaking these assessments through its national Marine Aggregates and Resources Program.
Assessment of Oil and Gas in the Arctic - Scientists from the WMERSC assisted USGS Energy Resources Program scientists in completing an assessment of undiscovered conventional oil and gas resources in the Arctic region (all area north of the Arctic Circle line of latitude). Using a geology-based probabilistic methodology, the scientists estimated the occurrence of undiscovered oil and gas in 33 geologic provinces thought to be prospective for petroleum. To improve the understanding of the petroleum resources in this area, the USGS is undertaking a multi-year research effort, termed the Circum-Arctic Resource Appraisal (CARA), to produce a comprehensive, unbiased, scientifically determined estimate of undiscovered petroleum resources in the high northern latitudes. This research effort is being conducted in collaboration with several U.S. and international entities. When completed, the results from the CARA will provide the first publicly available petroleum resource estimate of the area north of the Arctic Circle in its entirety.
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Geologic, Tectonic, and Hydrologic Studies
Water demands from the lower Colorado River system are increasing with the rapidly growing population of the southwestern United States. To decrease dependence on this over allocated surface-water resource and to help provide for the projected increase in population and associated water supply in the Las Vegas area, water purveyors in southern Nevada have proposed to utilize the ground-water resources of rural basins in eastern and central Nevada. Municipal, land management, and regulatory agencies have expressed concerns about potential impacts from increased ground-water pumping on local and regional water quantity and quality, with particular concern on water-rights issues and on the future availability of water to support springflow and native vegetation. Before concerns on potential impacts to pumping can be addressed, municipal and regulatory agencies have recognized the need for additional information and improved understanding of geologic features and hydrologic processes that control the rate and direction of ground-water flow in eastern and central Nevada.
Some aquifers of the southwestern Colorado Plateaus Province are deeply buried and overlain by several impermeable shale layers, and so recharge to the aquifer probably is mainly by seepage down penetrative-fracture systems. Using gravity and aeromagnetic-anomaly data, together with surficial-fracture data WMR scientists recently mapped candidate deep penetrative fractures over a 120,000-km2 area on the Colorado Plateau south of the Grand Canyon and west of Black Mesa. The resulting distribution maps are an objectively obtained, repeatable dataset and a benchmark from which additional studies can begin. All correlations are presented in datasets that can be used as layers in a GIS to assist in land-use planning. The data archived in this study should facilitate future research such as optimal depth-to-basement calculations for the area studied, and additional analysis of the data with regard to deep recharge of aquifers.
In the Western United States, the Great Basin physiographic province contains a diverse assortment of world-class ore deposits. It currently (2006) is the world’s second leading producer of gold, contains large silver and base metal (Cu, Zn, Pb, Mo, W) deposits, a variety of other important metallic (Fe, Ni, Be, REE’s, Hg, PGE) and industrial mineral (diatomite, barite, perlite, kaolinite, gallium) resources, as well as petroleum and geothermal energy resources. Ore deposits are most numerous and largest in size in linear mineral belts with complex geology. Scientists have increased their understanding of relations between crustal evolution, fluid flow, and ore deposits in the Great Basin. Because of its substantial past and current mineral production, this region has been the focus of numerous investigations over the past century and is the site of ongoing research by industry, academia, and state agencies. A variety of geoinformatic tools was used to organize, reinterpret, and display, in space and time, the large amounts of geologic, geophysical, geochemical, and hydrologic information deemed pertinent to this problem.
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Geologic Hazards Studies
Hydrothermally-altered rocks are present on many active volcanoes in the High Cascades of the northwestern United States. Hydrothermal alteration can result in severely weakened volcanic structures that may be susceptible to failure and catastrophic landslides. It also can result in rocks with elevated levels of sulfur and potentially toxic metals that can be leached into surface and ground waters. Hydrothermal alteration occurs when rocks interact with hot fluids resulting in crystallization of hydrothermal minerals in the rocks. In active volcanoes, these fluids come from many sources, including degassing of magmas, heated ground waters, precipitation, or mixtures from all of these sources. Interaction with extremely acidic fluids produces rocks highly enriched in sulfur and potentially toxic metals and metalloids. This process has also formed important mineral deposits, including major world sources of copper, gold, and silver, and many large mineral deposits are associated with this part of Washington, Oregon, California, and Nevada. Results will be used to develop genetic models of ore deposition, the degassing of magmas, the hydrologic structure of volcanoes, and the contribution of rock-alteration effects to volcanic hazards.
Historic placer gold dredging in the flood plains of many rivers in the western US has modified river geomorphology and impaired salmonid spawning and rearing habitats. Large-scale river restoration projects in mining-impacted watersheds may mobilize mercury (Hg) from dredge tailings and increase Hg levels in fish. Knowledge of the processes that control Hg mobilization, methylation, and biotic uptake is needed to plan and manage river restoration programs so that Hg accumulation in fish is minimized. Study results have been used by the US Bureau of Reclamation in the Trinity River Restoration Project, and by the US Bureau of Land Management and US Bureau of Reclamation in the restoration of lower Clear Creek.
Lead-rich sediments, containing at least 1000 ppm of lead (Pb), and derived mainly from discarded mill tailings in the Coeur d'Alene mining region, cover about 60 km2 of the 80-km2 floor of the main stem of the Coeur d'Alene River valley, in north Idaho. Although mill tailings have not been discarded directly into tributary streams since 1968, frequent floods continue to re-mobilize sediment from large secondary sources, previously deposited on the bed, banks, alluvial terraces, and natural levees of the river. Thus, lead-rich sediments (also enriched in iron, manganese, zinc, copper, arsenic, cadmium, antimony and mercury) continue to be deposited on the floodplain. This is hazardous to the health of resident and visiting human and wildlife populations, attracted by the river and its lateral lakes and wetlands.
Coccidioidomycosis (Valley Fever) is a disease caused by the inhalation of the arthroconidia (spores) of Coccidioides immitis, a fungus that lives in the soils of southwestern United States. Although large numbers of people are exposed to the arthroconidia and are consequently infected, very few individuals contract the more serious forms of the disease. Earth scientists working in field areas where Coccidioides immitis is endemic have an increased risk of becoming infected. Because field operations often disturb the upper surface of the ground, they may inhale large numbers of arthroconidia. This also increases their risk of developing more severe forms of the disease. Any other occupations or activities that create dusty conditions in endemic areas also have increased risk of infection. Risk management strategies can lower the incidence of infection and also reduce the numbers of arthroconidia inhaled thereby decreasing the chances of developing more serious disease.
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The characteristics of various geologic settings commonly influence the biota living in those environments. WMR scientists have determined that pine trees favor soils with high potassium levels (such as those developed over granites), that threatened Burrowing Owls and endangered Desert Tortoises utilize nest cavities dug into semi-consolidated alluvial and lacustrine units, and that microbes responsible for Valley Fever reside in playa soils before those soils are transported by winds during dry periods. Identification of the geologic setting has been essential for the success of these studies, and future studies will rely on a foundation of high-quality geologic data.
There are approximately 11,000 abandoned hard rock mine sites in the western United States. At many of these sites, historical mining activities resulted in adverse impacts to the quality of water and sediment and to the health of humans and other plants and animals. Successful management of these ecosystems requires an understanding of the processes that are responsible for where, how much, and how easy plants, animals and humans are exposed to potentially toxic elements, such as arsenic, cadmium, lead, mercury, selenium, and zinc, in the environment.Such understanding is used to identify those pathways that have the greatest immediate and long-term impact on the environment. It is the scientific foundation for making decisions, developing strategy, and assessing mitigation and remediation alternatives by local, state, and other federal agencies charged with minimizing the environmental and health impacts of the elements.
The USGS Headwaters Province project in western Montana and northern and central Idaho was designed to provide geoscience data and interpretations to Federal Land Management Agencies and to respond to specific concerns of USDA Forest Service Regions 1 and 4. The project has emphasized development of digital geoscience data, GIS analyses, topical studies, and new geologic interpretations. Studies were designed to more completely map lithologic units and determine controls of deformation, magmatism, and mineralizing processes.
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GIS/Database Synthesis, Modeling, and Analysis
A relational database was created to prepare and organize geologic map-unit and lithologic descriptions for input into a spatial database for the geology of the northern Rocky Mountains, a compilation of forty-three geologic maps for parts of Idaho, Montana, and Washington. Not all of the information was transferred to and incorporated in the spatial database due to physical file limitations. This report releases that part of the relational database that was completed for that earlier product. In addition to descriptive geologic information for the northern Rocky Mountains region, the relational database contains a substantial bibliography of geologic literature for the area.
Scientists collect important data as part of their studies. These include information on the characteristics and distribution of geologic units and structures, the chemistry of rocks, mineral deposits, water, and soils, and the geophysical characteristics of surficial and deeper geologic features. All of these data are made available on–line for use by public and private sectors. These data sets can be used for a wide variety of mineral exploration, water quality, and human health investigations and issues. An example of one of those data sets is the Mineral Resource Data System (MRDS) containing mineral resource occurrence data covering the world, most thoroughly within the U.S. This database includes the records previously provided by the Mineral Availability System/Mineral Industry Locator System (MAS/MILS) which originated from the now defunct U.S. Bureau of Mines. MRDS is a large and complex relational database developed over several decades by hundreds of researchers and reporters.
The Database and Information Analysis staff fulfill a continued need for acquisition, creation, analysis, publication and archiving of digital spatial geoscience datasets for use by our staff and for our other customers who are requiring that data be provided in an Arc/Info GIS format. In addition, the DIA staff assist their colleagues in performing minerals-related assessments by utilizing the spatial analytical capabilities inherent in a geographic information system (GIS). Coordination of GIS activities reduces duplication of effort and encourages the creation of GIS centers of excellence. Standardization of GIS products will ease the merging of data for regional analysis. GIS products also need to be published in a timely fashion for use by land management agencies and the general public.
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