Mapping talc mineralisation and associated alteration using airborne and satellite-borne spectrometry: A case study at Mt Fitton, South Australia

Abstract

The Mount Fitton talc deposit and associated alteration, located in the northern Adelaide Geosyncline, has been observed to have characteristic spectral signatures in the short-wave infrared and thermal infrared wavelength regions. In particular, reflectance and emissivity spectral measurements of field samples collected in the area have been shown to contain spectral absorption features diagnostic of talc, muscovite/white mica, chlorite, and amphibole minerals. Such minerals are products of the hydrothermal alteration associated with the formation of talc mineralisation. Spectral measurements of field samples also identified other minerals related to the host-rock composition, such as quartz, dolomite, calcite, magnesite and mica/illite. The distinct, and often unique, nature of these spectral signatures indicates the potential for mapping alteration and lithological units at Mount Fitton. Several airborne sensors and recently launched satellite-borne systems have acquired data in the Mount Fitton area, and these data have been processed to evaluate their ability to map the outcropping geology. In particular, the Mount Fitton test site has been used to test various remote-sensing systems with different spectral and spatial resolutions, wavelength ranges and viewing platforms, for their ability to provide useful exploration information, including the location and nature of hydrothermal alteration. Although airborne and satellite-borne multi-spectral systems successfully discriminated geological units and mineral groups, identification of talc and other alteration minerals without a priori information required hyperspectral sensors. It was also found that higher signal-to-noise, spectral resolution and access to different wavelength regions improved the mapping of talc and associated alteration. Spectrally derived mineral maps were found to provide useful supplementary information, which complements traditional airborne geophysical datasets, such as radiometrics or magnetics.