Image processing for ASTER remote sensing data to map hydrothermal alteration zones in East Kazakhstan

Porphyry copper deposits are accompanied by extensive aureoles of hydrothermally altered rocks which make it possible to detect them on satellite images in the absence of vegetation. The study is devoted to using the Earth’s remote sensing data, particularly, satellite images from the Japanese sensor ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer), which are used to identify areas that are promising for the discovery of porphyry copper deposits and ore occurrences within the copper belt of Kazakhstan. The analysis of numerous publications that offer various methods for processing ASTER images for the interpretation of hydrothermally altered rocks accompanying porphyry copper occurrences showed that the most effective method for this region is the Crosta technique. The Crosta technique, unlike other methods, does not use primary bands, but their combinations are obtained by the principal components analysis method. Thus, the combination of the results of the principal components analysis with the use of index images and analysis of the geological map made it possible to identify areas of hydrothermally altered rocks in the study area. The described technique helps to predict promising areas for porphyry copper mineralization of varying degrees of reliability, associated with their hydrothermal processing.