MINERAL EXPLORATION WITH LANDSAT ETM+ AND ASTER DATA IN THE WADI BIDAH MINERAL DISTRICT, SAUDI ARABIA

Optimum combinations of bands and band ratios for orbital optical remote sensing data are used to find, map and evaluate massive sulfide deposits (MSD) in the Wadi Bidah Mineral District (WBMD) located between latitudes 20o and 21o N and longitudes 41o and 41o 30’ E in the Neoproterozoic Arabian Shield of Saudi Arabia. The WBMD contains stratabound MSD hosted by a group of felsic volcaniclastics. The MSD of the WBMD have surface expression in the form of iron-rich caps or gossans and zones of hydrothermal alteration, all having distinctive spectral signatures. The utility of Landsat 7 Enhanced Thematic Mapper Plus (ETM+) and the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data for mineral exploration are evaluated using data sets covering the WBMD. ASTER and ETM+ detect radiation in the visible and near infrared (VNIR), short wave infrared (SWIR), and thermal infrared (TIR) regions of the electromagnetic spectrum. ASTER has 14 bands with spatial resolutions of 15 m (VNIR), 30 m (SWIR), and 90 m (TIR). ETM+ has 8 bands with spatial resolutions of 15 m (Panachromatic), 30 m (VNIR and SWIR), and 60 m (TIR). Red-Green-Blue (RGB) color composite images are the most basic form of spectral analysis and deciding which combination of bands conveys the most information on the basis of visual analysis of a scene can be difficult and time consuming. There are 56 ETM+ band combinations and 364 ASTER band combinations. Therefore, band combinations are quantitatively evaluated using the Optimum Index Factor (OIF). The optimum band combinations for ETM+ and ASTER using the OIF were 8-6-2 and 12-5-3, respectively. A limitation of the OIF is that the best combination for conveying the overall information in a scene may not be the best combination for conveying specific information. A band ratio enhances compositional information, while suppressing other types of information about the Earth’s surface, such as differences in albedo or local topographic slope and constructed with reference to the spectral properties of lithologies present in the field area can be used to differentiate the deposits from the host rock.