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map of hydrothermally altered rocks, Basin and Range, USA
Image of Plate 3C, Map Showing Hydrothermally Altered Rocks (Not Including Hydrothermal Silica-Rich Rocks), from Hydrothermal Alteration Maps of the Central and Southern Basin and Range Province of the United States Compiled From Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Data, by John C. Mars, USGS Open File Report 2013-1139.

Regional hydrothermal alteration maps compiled from remote sensing data (phyllic, argillic, propylitic, and silicic types) and regional geochemical datasets for the southwestern United States are now available in Geographic Information Systems format. Rock alteration and regional geochemical mapping have traditionally been used with geologic maps to define mineral exploration targets and as a guide to resource assessment, but these and other regional geophysical data, such as gravity and geomagnetics, have often not been thoroughly evaluated or integrated into mineral resource studies. We will use geospatial and statistical techniques to integrate remote-sensing, geochemical, and other regional geophysical data into new quantitative methods to map mineral resource prospectivity. The new quantitative methods will provide a basis for investigating problems such as

  1. identification and ranking of potential deposit sites;
  2. estimation of depth to covered potential deposit sites by effectively integrating datasets such as geomagnetics, ASTER alteration patterns, topography and drill core data;
  3. quantitatively determine uncertainty for datasets; and
  4. better integration of data compiled using quantitative methods into regional commercial exploration and mineral assessment projects. See our products.

The available geologic framework, remote-sensing coverage, regional geochemistry, and mineral deposit and prospect data for porphyry copper and epithermal-related mineralization in the southwestern U.S. will provide a well constrained study area to develop and test the new quantitative techniques. Digital datasets and geospatial-geostatistical algorithms that make up the new geospatial-statistical quantitative methods will be synthesized and compiled in a geographic information system that will allow for more efficient access and analysis of the data and assessment results. Thus, the new quantitative methods will enhance mineral assessments, regional mineralogical and tectonic studies, and exploration by effectively combining and using state-of-the-art remote sensing, geophysical and geochemical digital datasets to quantitatively identify and define potential deposit sites and map mineral resource prospectivity.


Project Activities

  • Regional mapping of hydrothermal alteration minerals and terrain analysis using ASTER data
  • Identification of potential porphyry copper targets based on alteration types and patterns using the ASTER hydrothermal alteration data and added to a GIS database
  • Investigation into using additional geochemical and geophysical datasets such as the National Soils Geochemical Database in the quantitative assessment
  • Synthesis of GIS-format hydrothermal alteration units, compiled from ASTER and surficial geochemical data, into the quantitative assessment by applying geospatial mineral potential mapping and assessment methodologies



Berger, B.R., Mars, J.C., Denning, P.D., Phillips, J.D., Hammarstrom, J.M., Zientek, M.L, Dicken, C.L., and Drew, L.J., with contributions from Alexeiev, D., Seltmann, R., and Herrington, R.J., 2014, Porphyry copper assessment of western Central Asia: U.S. Geological Survey Scientific Investigations Report 2010–5090–N, 219 p., 8 plates, and spatial data,

Mars, J.C., 2014, Regional mapping of hydrothermally altered igneous rocks along the Urumieh-Dokhtar, Chagai, and Alborz Belts of western Asia using Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data and Interactive Data Language (IDL) logical operators—A tool for porphyry copper exploration and assessment: U.S. Geological Survey Scientific Investigations Report 2010–5090–O, 36 p., 10 plates, and spatial data,

Mars, J.C., 2013, Hydrothermal alteration maps of the central and southern Basin and Range province of the United States compiled from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data (ver. 1.1, April 8, 2014): U.S. Geological Survey Open-File Report 2013–1139, 5 p., 13 plates, scale 1:1,300,000,


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