|Alkalic Porphyry||Alkalic porphyry systems form in oceanic and continental magmatic arcs and in continental rifts by similar processes from fluids exsolved from more fractionated alkalic plutons and stocks. Resulting ore deposits tend to be more enriched in Au, Te, Bi, and V.|
|Arsenide||Arsenide systems form in continental rifts where deep-seated, oxidized, metal-rich, metamorphic basement brines ascend to shallow levels. Native elements (Ag, Bi, As), Ni-, Co- and Fe-mono-, di- and sulf-arsenides precipitate by reduction as hydrocarbons, graphite, or sulfide minerals are oxidized to form carbonates and barite.|
|Basin Brine Path||Basin brine path systems emanate from marine evaporite basins and extend downward and laterally through permeable strata to discharge points in the ocean. Limestone is replaced by reflux dolomite at low temperatures and hydrothermal dolomite at high temperatures. Basin brines evolve to become ore fluids by scavenging metals from various rock types along gravity-driven flow paths. The mineralogy of the aquifers controls the redox and sulfidation state of the brine and the suite of elements that can be scavenged. Copper and Pb-Zn sulfide deposits form where oxidized brines encounter reduced S. Unconformity U deposits form where oxidized brines are reduced. Barium and Sr deposits form where reduced brines encounter marine sulfate or carbonate.|
|Carlin-type||Carlin-type systems occur in continental magmatic arcs, but are remote from subjacent stocks and plutons. Consequently, ore fluids consist largely of meteoric water containing volatiles discharged from deep intrusions. Ore fluids scavenge elements from carbonaceous pyritic sedimentary rocks as they convect through them. Gold ore containing disseminated pyrite forms where acidic reduced fluids dissolve carbonate and sulfidize Fe-bearing minerals in host rocks. Arsenic, Hg, and Tl minerals precipitate by cooling. Stibnite precipitates with quartz by cooling from Au-, As-, Hg-, Tl-depleted fluids.|
|Chemical weathering||Chemical weathering systems operate in stable areas of low to moderate relief with sufficient rainfall to chemically dissolve and concentrate elements present in various rock types and mineral occurrences by the downward percolation of surface water in the unsaturated zone. Chemical gradients cause different elements to be concentrated at different positions in the weathering profile and at the water table. Bauxite, Ni-laterite, and carbonatite laterite are restricted to tropical climatic zones; others form in temperate and arid climates. Dissolved U is reduced on carbonaceous material in lakes and swamps. Dissolved Mn precipitates at redox interface in lakes.|
|Climax-type||Climax-type systems occur in continental rifts with hydrous bimodal magmatism. Aqueous supercritical fluids exsolved from A-type topaz rhyolite plutons and the apices of subvolcanic stocks form a variety of deposit types as they move upward and outward, split into liquid and vapor, react with country rocks, and mix with ground water. The broad spectrum of deposit types results from the large thermal and chemical gradients in these systems. At deep levels, NYF pegmatites emanate from plutons.|
|Coeur d-Alene-type||Metamorphic dewatering of moderately oxidized siliciclastic sequences during exhumation with fluid flow along dilatant structures. Metasedimentary host rocks may contain basin brine path Pb-Zn and Cu ± Co deposits.|
|Hybrid magmatic REE / basin brine path||This hybrid system operates where CO2- and HF-bearing magmatic volatiles condense into basinal brines that replace carbonate with fluorspar ± barite, REE, Ti, Nb, and Be, as in the Illinois-Kentucky Fluorspar District and Hicks Dome.|
|IOA-IOCG||IOA-IOCG systems form in both subduction- and rift-related magmatic provinces. IOA deposits form as hot brine discharged from subvolcanic mafic to intermediate composition intrusions reacts with cool country rocks. Albitite U deposits form at deeper levels where brines albitize country rocks. IOCG deposits form on the roof or periphery of IOA mineralization at lower temperatures, often with involvement of external fluids. Polymetallic skarn, replacement and vein deposits occur outboard from IOCG deposits. Manganese replacement and lacustrine Fe deposits form near or at the paleosurface.|
|Lacustrine evaporite||Lacustrine evaporite systems operate in closed drainage basins in arid to hyper-arid climatic zones. Elements present in meteoric surface, ground, and geothermal recharge water are concentrated by evaporation. As salinity increases, evaporite minerals typically precipitate in the following sequence: gypsum or anhydrite, halite, sylvite, carnallite, borate. Nitrates are concentrated in basins that accumulate sea spray. Residual brines enriched in Li and other elements often accumulate in aquifers below dry lake beds. Lithium-clay and Li-B-zeolite deposits form where residual brine reacts with lake sediment, ash layers, or volcanic rocks.|
|Mafic magmatic||Mafic magmatic systems generally form in large igneous provinces (LIP) related to mantle plumes or meteorite impacts. Nickel-Cu sulfide ores with PGEs result from settling and accumulation of immiscible sulfide liquids in mafic layered intrusions and ultramafic magma conduits. In layered intrusions, Fe-Ti oxides, chromite and PGE minerals crystalize from evolving parental magmas and are concentrated by physical processes in cumulate layers. In anorthosites, Fe-Ti oxides ± apatite crystalize from residual magmas entrained in plagioclase-melt diapirs. In convergent settings, Alaskan-type intrusions with Fe-Ti oxides and PGE form from mantle melts.|
|Magmatic REE||Magmatic REE systems typically occur in continental rifts or along translithospheric structures. REE and other elements in mantle-derived ultrabasic, alkaline, and peralkaline (agpaitic) intrusions are enriched by fractionation and separation of immiscible carbonatite melts ± saline hydrothermal liquids. Exsolved magmatic fluids or heated external fluids may deposit REE and other elements in adjacent country rocks.|
|Marine chemocline||Marine chemocline systems operate where basin brines discharge into the ocean, resulting in increases in bioproductiviy that can produce metalliferous black shales. Changes in ocean chemistry (for example, oceanic anoxic events) and development of chemoclines result in chemical sedimentation of phosphate and Mn and Fe carbonates and oxides.|
|Marine evaporite||Marine evaporite systems operate in shallow restricted epicontinental basins in arid to hyper-arid climatic zones. Sabka dolomite and sedimentary magnesite form in coastal salt flats and lagoons. Elements present in seawater are concentrated by evaporation. As salinity increases, evaporite minerals typically precipitate in the following sequence: gypsum or anhydrite, halite, sylvite. Residual basin brines are enriched in conserved elements, such as Mg and Li. Incursion of fresh water or seawater can produce halite dissolution brines.|
|Metamorphic||Metamorphic systems recrystallize rocks containing organic carbon or REE phosphate minerals or U minerals. Crystalline magnesite forms by carbonation of peridotite.|
|Meteoric convection||Low-sulfidation Au-Ag deposits associated with mantle plume volcanic rocks form under relatively low oxygen and sulfur fugacities, have low base metal contents, and high Au/Ag ratios and Se contents. Low-sulfidation deposits along extensional fault zones that are not associated with proximal, coeval magmatic activity may be underlain by rift-related dikes and sills.|
|Meteoric recharge||Meteoric recharge systems operate where oxidized meteoric groundwater displaces reduced connate water in sandstone aquifers that often contain volcanic ash or in granitic intrusions or where such groundwater evaporates at the surface. As oxidized water descends through sandstone aquifers it scavenges U and other elements from detrital minerals and/or volcanic glass. Uranium and other elements precipitate at a redox front with reduced connate water, on carbonaceous material in the aquifers, or ferrous Fe minerals in granite, or at the surface in calcrete by evaporation. In ultramafic rocks, dissolved CO2 in meteoric ground water reacts with Mg-silicates to form magnesite, which may also precipitate in permeable sediment or rocks nearby.|
|Orogenic||Metamorphic dewatering of sulfidic volcanic and/or sulfidic carbonaceous and/or calcareous siliciclastic sequences during exhumation with fluid flow along dilatant structures. Iron minerals in host rocks are often sulfidized. Metavolcanic host rocks often contain volcanogenic seafloor sulfide deposits.|
|Petroleum||Nickel and V in porphyry complexes are the most abundant metals in plant and animal remains in source rocks and in derived petroleum. Helium is produced by radioactive decay of U and Th in felsic igneous rocks and siliciclastic rocks derived from them. It is released by magmatic heat and/or fracturing and accumulates in gas reservoirs below an impermeable seal.|
|Placer||Placer systems operate in drainage basins and along shorelines where there is either topographic relief and gravity driven turbulent flow of surface water or tidal- and wind-driven wave action. Placer systems concentrate insoluble resistate minerals liberated from various rock types and mineral occurrences by the chemical breakdown and winnowing away of enclosing minerals by the movement of water. The distribution of insoluble resistate minerals is controlled by their size, density and the turbulence of fluid flow.|
|Porphyry Cu-Mo-Au||Porphyry Cu-Mo-Au systems operate in oceanic and continental magmatic arcs with calc-alkaline compositions. Aqueous supercritical fluids exsolved from felsic plutons and the apices of subvolcanic stocks form a variety of deposit types as they move upward and outward, split into liquid and vapor, react with country rocks, and mix with ground water. The broad spectrum of deposit types results from the large thermal and chemical gradients in these systems.|
|Porphyry Sn (granite-related)||Granite-related porphyry Sn systems form in back arc or hinterland settings by similar processes from fluids exsolved from more crustally contaminated S-type peraluminous plutons and stocks. At deep levels, LCT pegmatites emanate from plutons. Resulting ore deposits tend to be poor in Cu and Mo and enriched in Li, Cs, Ta, Nb, Sn, W, Ag, Sb and In.|
|Reduced Intrusion-related||Reduced intrusion-related systems form in continental magmatic arcs by similar processes from fluids exsolved from calc-alkaline plutons and stocks that assimilated carbonaceous pyritic country rocks. Resulting ore deposits tend to be poor in Cu, Mo, Sn and enriched in W, Au, Ag, Te, Bi, Sb and As.|
|Volcanogenic Seafloor||Volcanogenic seafloor systems are driven by igneous activity along spreading centers, back arc basins and magmatic arcs. In spreading centers and back arc basins, seawater evolves to become an ore fluid by convection through hot volcanic rocks. In magmatic arcs, ore fluids exsolved from subvolcanic intrusions may mix with convecting seawater. Ore deposits form where hot reduced ore fluids vent into cool oxygenated seawater. Sulfides and sulfates precipitate in or near vents. Manganese and Fe precipitate at chemoclines over wide areas in basins with seafloor hydrothermal activity.|
Development of the dataset was funded by the U.S. Geological Survey Mineral Resources Program. The spatial data set and supporting tables were developed by 4 regional teams: Geology, Energy & Minerals Science Center (Reston, VA); Geology, Geophysics, and Geochemistry Science Center (Denver, CO); Geology, Minerals, Energy, and Geophysics Science Center (Spokane, WA and Tucson, AZ); and Alaska Science Center - Geology Office (Anchorage, AK). Database reviews and contributions were made by USGS personnel Heather Parks, Ryan Taylor, Carlin Green, Dan Hayba, Damon Bickerstaff, and Patricia Loferski. Alaska Division of Geological and Geophysical Surveys – Werdon, M.B. Arizona Geological Survey - Richardson, C.A. Arkansas Geological Survey - Cannon, C., Chandler, A., and Hanson, W.D. California Geological Survey - Bohlen, S., Callen, B., Gius, F.W., Goodwin, J., Higgins, C., Key, E.L., Marquis, G., Mills, S., Tuzzolino, A., and Wesoloski, C. Colorado Geological Survey - Morgan, M.L., and O'Keeffe, M.K. Connecticut Geological Survey - Thomas, M. Delaware Geological Survey - KunleDare, M., and Tomlinson, J. Florida Geological Survey - Means, H. Geological Survey of Alabama - VanDervoort, D.S., and Whitmore, J.P. Idaho Geological Survey - Berti, C., Gillerman, V.S., and Lewis, R.S. Illinois State Geological Survey - Denny, F.B., Freiburg, J., Scott, E., and Whittaker, S. Indiana Geological and Water Survey - Mastalerz, M., McLaughlin, P.I., and Motz, G. Iowa Geological Survey - Clark, R.J., Kerr, P., and Tassier-Surine, S. Kansas Geological Survey - Husiuk, F., Oborny, S., and Smith, J. Kentucky Geological Survey - Andrews, W.M., Harris, D., Hickman J., and Lukoczki, G. Maine Geological Survey - Beck, F.M., Bradley, D., Marvinney, R., Slack, J., and Whittaker, A.H. Maine Mineral and Gem Museum - Felch, M. Maryland Geological Survey - Kavage Adams, R.H., Brezinski, D.K., Junkin, W., and Ortt, R. Michigan Geological Survey - Yellich, J. Minnesota Department of Natural Resources - Arends, H., Dahl, D.A., and Saari, S. Minnesota Natural Resources Research Institute - Hudak, G.J. Minnesota Geological Survey - Block, A. Missouri Geological Survey - Ellis, T., Lori, L., Pierce, L., Seeger, C.M., and Steele, A. Montana Bureau of Mines and Geology - Gunderson, J., Korzeb, S.L., and Scarberry, K.C. Nevada Bureau of Mines and Geology - Faulds, J., and Muntean, J.L. New Mexico Bureau of Geology and Mineral Resources - Gysi, A., Kelley, S.A., and McLemore, V.T. North Carolina Geological Survey - Chapman, J.S., Farrell, K.M., Taylor, K.B., Thornton, E., and Veach, D. North Dakota Geological Survey - Kruger, N. Ohio Geological Survey - McDonald, J., and Stucker, J. Pennsylvania Geological Survey - Hand, K., and Shank, S.G. South Carolina Geological Survey - Howard, C.S., and Morrow, R.H. South Dakota Geological Survey - Cowman, T., Luczak, J.N., and Myman, T.J. Tennessee Geological Survey - Lemiszki, P. Texas Bureau of Economic Geology - Paine, J. Utah Geological Survey - Boden, T., Mills, S.E., and Rupke, A. Virginia Division of Geology and Mineral Resources - Coiner, L.V., and Lassetter, W.L. Washington Geological Survey - Eungard, D.W., and Skov, R. West Virginia Geological and Economic Survey - Brown, S.R., Dinterman, P., and Moore, J.P. Western Michigan University - Thakurta, J., Harrison, W., and Voice, P. Wisconsin Geological and Natural History Survey - Ames, C., Gotschalk, B., Lodge, R., Stewart, E.K., and Stewart, E. Wyoming State Geological Survey - Gregory, R.W., Lynds, R.M., Mosser, K., Toner, R., and Webber, P. U.S. Geological Survey - Anderson, A.K., Bickerstaff, D., Bern, C.R., Brady, S., Brezinski, C., Brock, J., Bultman, M.W., Carter, M.W., Cossette, P.M., Crafford, T., Crocker, K.E., Day, W.C., Dicken, C.L., Drenth, B.J., Emsbo, P., Foley, N.K., Frost, T.P., Gettings, M.E., Grauch, V.J.S., Hall, S.M., Hammarstrom, J.M., Hayes, T.S., Hofstra, A.H., Horton, J.D., Horton, J.W., Hubbard, B.E., Hudson, M., John, D.A., Johnson, M.R., Jones, J.V. III, Kreiner, D.C., Mauk, J.L., McCafferty, A.E., McPhee, D., Merchat, A.J., Nicholson, S.W., Ponce, D.A., Roberts-Ashby, T., Rosera, J., San Juan, C.A., Shah, A.K., Scheirer, D., Siler, D.L., Soller, D.R., Stillings, L.L., Swezey, C.S., Taylor, R.D., Thompson, R., Van Gosen, B.S., Verplanck, P., Vikre, P.G., Walsh, G.J., Woodruff, L.G., and Zurcher, L.
These geospatial data provide the locations of focus areas to be used for the planning and collection of geophysical, geological, and topographic (lidar) data pertaining to the Earth MRI study of critical mineral resources in the U.S. Focus areas are outlined solely on the basis of geology, regardless of political boundaries. Therefore, areas may include Federal, as well as State, tribal, and private lands, which may or may not be open to exploration and mining activities. These data are shared to meet open data requirements and are suitable for use in Geographic Information Systems (GIS) or other database and geospatial software used to derive maps and perform geospatial analyses.
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|Data format:||Vector Digital Data Set (Polygon)|