Mapping mineralogical alteration using principal‐component analysis and matched filter processing in the Takab area, north‐west Iran, from ASTER data

The Takab area, located in north‐west Iran, is an important gold mineralized region with a long history of gold mining. The gold is associated with toxic metals/metalloids. In this study, Advanced Space Borne Thermal Emission and Reflection Radiometer data are evaluated for mapping gold and base‐metal mineralization through alteration mapping. Two different methods are used for argillic and silicic alteration mapping: selective principal‐component analysis and matched filter processing (MF). Running a selective principal‐component analysis using the main spectral characteristics of key alteration minerals enhanced the altered areas in PC2. MF using spectral library and laboratory spectra of the study area samples gave similar results. However, MF, using the image reference spectra from principal component (PC) images, produced the best results and indicated the advantage of using image spectra rather than library spectra in spectral mapping techniques. It seems that argillic alteration is more effective than silicic alteration for exploration purposes. It is suggested that alteration mapping can also be used to delineate areas contaminated by potentially toxic metals.