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