Integrating geologic and Landsat-8 and ASTER remote sensing data for gold exploration: a case study from Zarshuran Carlin-type gold deposit, NW Iran

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and the Landsat-8 data were integrated with geological data to map lithologic units, lineament features, hydrothermal alteration zones, and distribution of Fe3+-bearing minerals in the Zarshuran Carlin-type gold deposit. The dominant hydrothermal alterations related to the gold mineralization in the study area, consist of argillic, alunite, silicified, and decalcified alterations of carbonate host rocks. The alteration assem-blages are accompanied by ferric iron minerals such as jarosite and hematite. The red-green-blue (RGB) combination of bands 5, 2, and 1 of the ASTER sensor provides excellent criteria for the separation of the host rock lithologic boundaries, particularly for the Oligo-Miocene andesitic volcanic rocks covering the vast parts of the study area. The ASTER lithologic map derived from RGB combination of bands 5, 2, and 1 is represented by a set of lineaments in which both the thrust and normal faults were enhanced. The band ratios obtained by the Landsat-8 and the ASTER datasets have been effectively used to delineate the alteration halos characterized by kaolinite, alunite, quartz, and ferric iron minerals both in regional and local (the Zarshuran gold mine) scales. In addition, methods such as the principal component analysis (PCA) and the selective principal component analysis (Crosta) were exerted on the ASTER data to identify the hydrothermal alteration zones. The spectral angle mapper (SAM) algorithm using the ASTER data could better differentiate the various alteration (e.g., argillic, alunite, and silicified) zones existing in the study area. The matched filtering (MF) technique processed on the Landsat-8 data was applied to characterize the ferric iron minerals (jarosite and hematite) and separate the hydrothermal alteration zones as well. The integration and combination of various image processing techniques indicated that the alteration zones at Zarshuran are affiliated with normal faults within the carbonate host rocks and can be used for prospection mapping purposes in regional scale.