ASTER-based remote sensing investigation of gypsum in the Kohat Plateau, north Pakistan

Abstract

Gypsum is an important industrial mineral, the demand of which has increased manifold over the years, especially due to growing cement industry. Considering the industrial significance of gypsum, we employed advanced space-borne thermal emission and reflection radiometer (ASTER) multispectral data to map gypsum outcrops in the Kohat area, northern Pakistan. Kohat area, also known as Kohat Plateau, is the western extension of the Himalaya fold–thrust belt, characterized by Eocene gypsum reserves at many places, striking generally in east–west direction. In the present research, an attempt has been made to map the outcrops of gypsum through several remote sensing mapping techniques. These techniques include band ratio 4 + 8/6, decorrelation stretch RGB-468 composite, Principle Component PC4 and thermal infrared bands 10, 11 and 12 used as sulfate index. All these methods have helped in discriminating the gypsum outcrops from surrounding various lithologies, illustrating that ASTER is a powerful tool to map different rocks units in arid, remote and inaccessible areas. Results were verified through field mapping at numerous selected stations within proposed study area, which were further confirmed through X-ray analysis of selected gypsum specimens. The results of the applied techniques were compared with each other to better asses and evaluate their effectiveness and accuracy. Overall, all the methods successfully mapped gypsum; however, PC4 results exhibit higher degree of accuracy compared to other methods.