INTEGRATION OF REMOTE-SENSING ALTERATION MAPPING INTO NEW GEOSPATIAL-STATISTICAL, QUANTITATIVE MINERAL RESOURCE METHODS

Remote sensing data have traditionally been used with geologic maps to define mineral exploration targets, but have not been extensively integrated into regional-scale mineral resource assessments. Geospatial and statistical techniques were used to apply Advanced Spaceborne Thermal Emission and Reflection Radiometer Data (ASTER) remote-sensing data as a new method to map porphyry copper mineral resource potential in the southwestern United States. Assessments of four permissive tracts for undiscovered porphyry copper deposits (Jurassic tract, Northwest (NW) Laramide tract, Southeast (SE) Laramide tract, and Tertiary tract) were delineated using ASTER remote sensing, geochemistry, gravity and magnetic, lithologic, and deposit and prospects data. All permissive tract data were compiled in a geographic information system (GIS). Using this GIS, we applied new geospatial-geostatistical techniques to form the basis of new quantitative methods for analysis and visualization of tract data.

In previous assessment studies applying ASTER alteration mapping, sites that may be associated with porphyry copper mineralization based on a visual assessment of remotely sensed alteration types, patterns, and lithology were represented as point locations on a map. A more accurate, automated, method of compiling geometric properties and evaluating hydrothermal alteration sites using alteration areas (polygons) was developed for this study. Alteration density of argillic, phyllic, and propylitic units based on a 1 km diameter circle around each pixel was mapped using a low-pass filter. Alteration polygons were compiled from permissive lithologies for hosting porphyry copper deposits that contained alteration densities greater than 19%. Physical characteristics of each polygon were recorded and then ranked. Polygon scores were classified and color coded on maps in 3 groups, low (0-4), moderate (5-7) and high (8-22). In addition, alteration polygons that were not associated with known deposits or prospects were identified to signify an area that had potentially not been explored. The classified ASTER alteration polygons were particularly effective for showing areas of favorable alteration for porphyry copper deposits on regional scale tract maps.