Mapping hydrothermal alteration and gold mineralization in west Ahar using ASTER and Landsat ۷

In this study, the capability of ASTER and Landsat ۷ ETM+ sensors for alteration mapping at a scale of ۱:۲۰,۰۰۰ and gold mineralization exploration in western Ahar, East Azerbaijan Province, Iran, was evaluated. The study area is composed of pyroclastic rocks, red to purple conglomerates, sandstones, and argillaceous limestones. The pyroclastic units, which host the gold mineralization zone, consist of alternating lapilli tuff, crystal–vitric tuff, lithic tuff, and volcanic rocks such as basaltic–andesitic lavas. To discriminate alteration zones and lithological units, advanced image processing techniques including band ratios, Principal Component Analysis (PCA), and Spectral Angle Mapper (SAM) were applied to the visible and near-infrared (VNIR) and shortwave infrared (SWIR) bands of the ASTER data. Band ratio techniques were also employed for processing Landsat ۷ ETM+ data. The remote sensing results were validated through field investigations, petrographic studies, and geochemical analysis of gold. In the ASTER imagery, false color composites (۴–۶–۸ and ۷–۲–۹) effectively discriminated argillic–sericitic alteration, while the band ratio (۱۴/۱۲) optimally enhanced silicic alteration. In the Landsat ۷ imagery, the false color composite RGB = B۳/B۱ – B۳/B۵ – B۵/B۷ was suitable for lithological discrimination, and the band ratio (۱/۳) effectively highlighted iron oxide alteration. The results confirm the effectiveness of the applied image processing methods in alteration mapping and identifying mineralization potentials, with gold grades ranging from ۰.۰۲۱ to ۳.۱۲۸ g/t in the study area.

کلیدواژه ها:

Advanced paceborne Thermal Emission and Reflection Radiometer (ASTER) ، Landsat ۷ ، Principal component Aaalysis ، Spectral angel Mmpper ، Gold mineralization.