Proximal and remote spectroscopic characterisation of regolith in the Albany–Fraser Orogen (Western Australia)

Abstract Vast parts of the Australian continent are prospective for precious and base metal mineralisation, but exploration is hindered by extensive cover of often deeply reaching regolith. New operational exploration methods are required that can help to characterise the cover and provide information about bedrock signatures. This paper shows how mineral mapping information from a combination of satellite multispectral Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) imagery and drill core hyperspectral profiling data (HyLogging™) can be used to unravel the regolith stratigraphy and to describe regional variations of regolith landforms, delivering important information for mineral exploration. The case study is located in the Neale tenements in the northeastern Albany–Fraser Orogen (Western Australia), which is prospective for Tropicana-style gold mineralisation. By interpretation of indicator minerals from hyperspectral drill hole logging data the regolith stratigraphy atop a metamorphic basement, comprising saprock, ferrugineous saprolite, kaolinitic saprolite, silcrete and transported cover, is recorded in cm-detail. Important mineralogical parameters extracted from the hyperspectral subsurface data and validated by XRD and FTIR, are 1) the abundance and type of iron oxides, 2) the abundance and crystallinity of kaolinite, 3) the abundance and composition of primary minerals, such as white mica, and 4) the abundance of quartz. The HyLogging™ data served as ground control points for mineral mapping information provided by CSIRO's ASTER Geoscience Products, which are a collection of mineral maps that highlight variations in the abundance, type or chemistry of selected mineral groups. Key ASTER Geoscience Products for regolith characterisation were the Ferric Oxide and AlOH abundance and composition images. The comparison of the surface with the subsurface data suggests three major different regolith landforms, including erosional, depositional and relict areas, which were used to generate a map showing transported versus relict and erosional areas. Erosional domains were mapped out in great detail, providing important information for exploration in saprolite dominated areas. Furthermore, source areas of transported material could be identified, which may help to understand the distribution of geochemical signatures collected during, for example, geochemical soil sampling projects.

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