Regional mineral mapping of island arc terranes in southeastern Mongolia using multi-spectral remote sensing data

摘要

Over the last few decades, many porphyry Cu deposits have been discovered in southeastern (SE) Mongolia. In particular, the Gurvansayhan and Mandalovoo island arc terranes, have high potential for ore deposits. Regional mineral mapping of these terranes using data from the Landsat Enhanced Thematic Mapper Plus (ETM+) and the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) have provided new geological information on the metallogenic province, revealing potential mineral deposits for future explorations. Iron oxides/hydroxides with high ETM (+) band 1/3 ratio values occur extensively in Quaternary deposits located at the boundary between the Gurvansayhan and Mandalovoo island arcs terranes and basins. The high average band ratios ( > 1.35) registered for the porphyry Cu and Au deposits and their occurrences are associated with iron oxidation which originates from the erosion and weathering of ore zones. Regional mapping of the island arc terranes using the ASTER shortwave infrared (SWIR) logical operators showed circular or semicircular alteration patterns which usually cluster along faults. The mineral assemblages mapped by the ASTER SWIR analysis in five major porphyry Cu districts can be divided into two types. The first type includes argillic, phyllic, and propylitic mineral assemblages, as exemplified by the Shuteen, Ikh Shankhai, and Oyu Tolgoi deposits. The second type of assemblage includes phyllic and propylitic mineral assemblages, as exemplified by the Kharmagtai and Tsagaan Suvarga deposits. Within the deposits of the first type, quartz was also mapped using the ASTER thermal infrared (TIR) mineral index. The difference between the two types may be related to the presence of a lithocap. The results of a field survey including spectral reflectance measurements in the Ikh Shankhai porphyry Cu district, showed a good correlation with the image analysis results.