Delineating alteration footprints from field and ASTER SWIR spectra, geochemistry, and gamma-ray spectrometry above regolith-covered base metal deposits-An example from Abra, Western Australia

Shortwave infrared (SWIR) field and laboratory reflectance spectra were used to identify and characterize mineral assemblages in regolith within a study area around the Abra base metal deposit. The Abra deposit is situated at 300-m depth from surface and hosted by weathered sedimentary rocks of the Mesoproterozoic Edmund Group of the Capricorn Orogen of Western Australia. The deposit contains a chlorite-siderite (±white mica) alteration halo delineated from drill core, surrounded with host rocks that are modally poor in detrital and metamorphic chlorite and white mica. Mineral assemblages identified from the regolith SWIR data, which were verified through XRD analysis and preexisting geochemistry data, were used to identify three schematic SWIR mineral domains in the regolith. These domains are (1) poorly crystalline kaolinite in an extremely weathered transported regolith, (2) well-crystalline kaolinite and muscovite in regolith overlying unaltered bedrock, and (3) phengite ± chlorite ± well-crystalline kaolinite mineral footprint in regolith overlying the Abra deposit and nearby base metal prospects. Furthermore, we identified that the mineral footprint detected from regolith samples can be traced in a combined potassium gamma-ray spectrometry and ASTER AlOH group composition map. The combined use of mineralogical and geophysical remote sensing data, and the strategically planned ground validation through mineralogical and geochemical sampling, proved to be a powerful and cost-effective exploration method for regional mapping of mineral footprints potentially related to sedimentary rock-hosted base metal.