REGIONAL ALTERATION MAPPING FOR MINERAL ASSESSMENT IN THE LAKE BALQASH REGION OF KAZAKHSTAN USING ADVANCED SPACEBORNE THERMAL EMISSION AND REFLECTION RADIOMETER (ASTER) DATA

The U.S. Geological Survey is currently assessing porphyry copper deposits in Kazakhstan as part of a global mineral resource assessment. Eastern Kazakhstan contains copper deposits within deformed, Paleozoic magmatic arcs and backarc basins. This study illustrates the use of ASTER data for regional mapping of hydrothermally altered silicic, argillic and phyllic rocks typically associated with porphyry copper deposits, and to assess the number of undiscovered deposits in the region.

A regional ASTER alteration map was complied from over 150 ASTER scenes of the Lake Balqash region and consists of AST05 emissivity data and Level_1b radiance data converted to reflectance. Interactive Data Language logical operators were used with emissivity and reflectance data to map silicic-altered rocks and were also used with reflectance data to map argillic- and phyllic-altered rocks.

The ASTER alteration map typically illustrates known deposits such as the Qonyrat mine, as elliptical to circular patterns of argillic- and phyllic-altered rocks with minor amounts (< 10% of the total altered-rock cover) of silicic-altered rocks. Over 300 potential deposits were identified on the ASTER alteration map based on similar alteration types and patterns of known deposits. Physical descriptions of potential deposits were recorded in a GIS database using the ASTER alteration map, an ASTER image (R=4, G=6, B=8), an ores database, and a 1:1,000,000 scale geologic map. Physical characteristics of potential deposits include shape of alteration patterns, types and percentages of alteration, diameter of alteration pattern along the long axis, argillic and phyllic alteration density determined by a low pass filter, age, lithology, observed structure or landforms in the ASTER image, associated occurrences and deposits, and the permissive tract defined by the regional assessment. The database is used to show the number of potential deposits within a permissive tract by matching their physical characteristics to known deposits. For example, the Permian Carboniferous permissive tract was found to contain 7 potential deposits with physical characteristics similar to the Qonyrat deposit. Thus, this method provides a semi-quantitative analysis of additional undiscovered deposits using remotely sensed data in a mineral assessment.