Application of Spectral Analysis in Mapping Hydrothermal Alteration of the Northwestern Part of the Kerman Cenozoic Magmatic Arc, Iran

Abstract

The northwestern part of the Kerman Cenozoic magmatic arc (KCMA) contains many areas with porphyry copper mineralization. In this research, we used the advanced space-borne thermal emission and reflection radiometer (ASTER) and Enhanced Thematic Mapper plus (ETM+) images of this region to map the distribution of hydrothermally altered rocks, based on their mineral assemblages. The spectral measurements based on the spectra of field samples and on ASTER and ETM+ data, show dominantly Al-OH (sericite and clays) and FeO absorption features in the VNIR/SWIR spectral regions. Directed principal components analysis (DPCA), spectral angle mapper (SAM) and linear spectral unmixing (LSU) were performed on ASTER/ETM+ images to map zones of hydrothermal alteration and iron oxide/hydroxide minerals. The individual principal components (PC) images generated by DPCA reveal the distribution of individual alteration minerals such as sericite, illite, kaolinite, chlorite, and epidote. The best results, in terms of mapping the distribution of alteration, were obtained using the SAM and LSU methods; but the LSU method produced a more accurate map. The altered zones were sampled and then subjected to X-ray diffraction (XRD), laboratory spectral and chemical analyses. Microscopic studies of the thin sections were also conducted. Field observations reveal that more than 90% of the known copper mineralized localities occur within the interpreted alteration areas.