USING ASTER REMOTE SENSING DATA IN A PORPHYRY COPPER ASSESSMENT

Advanced Spaceborne Thermal Emission and Reflection (ASTER) data were used to identify and characterize hydrothermal alteration patterns in Kazakhstan, Tajikistan, Uzbekistan and Kyrgyzstan as part of an assessment of undiscovered porphyry copper resources. ASTER data consist of three bands in the 0.52 - 0.86 micrometer wavelength region (VNIR); six bands in the 1.6 - 2.43 micrometer wavelength region (SWIR); and five bands of emitted radiation in the 8.125-11.65 micrometer wavelength region (TIR) with 15 m, 30 m, and 90 m resolution, respectively. Interactive Data Language logical operator algorithms were used to map Al-O-H, and quartz restrahlen spectral reflectance absorption features in hydrothermally altered rocks. Argillic and phyllic hydrothermally altered rocks were mapped using 225 scenes of ASTER data at 30 m spatial resolution, and hydrothermal silica-rich rocks were mapped in 150 scenes at 90 m spatial resolution.

The resulting ASTER hydrothermal alteration mineral map of the region typically consists of elliptical to circular patterns of argillic- and phyllic-altered rocks with minor amounts (< 10 percent) of hydrothermal silica-rich rocks. The shape of these ASTER alteration patterns in Kazakhstan are similar to hydrothermal alteration patterns of known porphyry copper deposits in the Central Iranian Volcanic Belt, which are consistent with predicted patterns in variably exhumed porphyry copper deposit models. Thus, matching similar ASTER alteration patterns to alteration signatures of known porphyry copper deposits provided a powerful tool for identifying the location and estimating numbers of undiscovered deposits over large areas over which the porphyry copper assessment was conducted.

A total of 302 potential porphyry copper sites were identified with the ASTER hydrothermal alteration maps, with 240 potential sites located in tracts permissive for porphyry copper mineralization. Mineral databases indicated that of the 240 potential porphyry copper sites selected using ASTER data, approximately 60 sites are associated with known copper mineralization. The 180 potential porphyry sites not associated with copper mineralization would not have been included in the assessment if ASTER data and analysis had not been used.