Sub-pixel mapping of alunite and jarosite using ASTER data; a case study from north of Semnan, north central Iran

Abstract

A widespread series of volcanic rocks and younger intrusive bodies are exposed in the north and northeastern Semnan, north-central Iran. They show an intermediate to felsic composition which have undergone various types of alteration including alunite and jarosite. In this research, ASTER data were used for sub-pixel mapping of these typical minerals using the Mixtured Tuned Matched Filtering (MTMF) algorithm. The spectral properties of field samples were measured by an ASD spectroradiometer and their spectra were analyzed through a visual comparison to the USGS spectral library. However, the z-profile method was used for extraction of target spectra from pixels in which the occurrence of desired minerals were verified by other methods. The MTMF output results revealed pixels with the highest fractions of alunite and jarosite dominantly near the altered rhyolitic and andesitic tuffs as well as in adamelites. It is suggested that an integration of MTMF method and the ASTER data is a powerful approach for sub-pixel mapping of alunite and jarosite, which could be applicable in mineral exploration projects.