REMOTE SENSING: Geoscan airborne multi-spectral scanners as exploration tools for Western Australian diamond and gold deposits

Abstract

The use of remote sensing in mineral exploration has evolved from basic photo-geology to interpretation of more sophisticated satellite and airborne multi-spectral data sets. Although the mineral mapping capabilities of Geoscan airborne multi-spectral scanners have been demonstrated for well-exposed and arid terrains, the question remains as to their effectiveness in deeply weathered regimes such as Western Australia. Geoscan airborne multi-spectral data have been collected for a number of Western Australian mineral deposits and prospects. The applicability of the data to exploration for similar deposits, based upon a series of simple image-processing treatments derived according to the known reflectance spectra of associated alteration minerals, has been assessed. Spectral characteristics of ultramafic rock such as kimberlite or lamproite are recognisable at Blue Well, but not over the Aries kimberlite pipe which has a spectral response dominated by the reworking and removal of desert varnish from detritus derived from its surrounding sandstone host. Shear-zone-hosted gold mineralisation in the deeply weathered Yilgarn Block is characterised by spectral signatures related to the presence of sericite, silica and iron oxides. The same minerals and spectral variations are also apparent in Carlin-style mineralisation at Kazput Pool. In each example studied, simple image-processing treatments are used to enhance the spectral characteristics of the deposit. These signatures are dominated by the present-day surface mineralogy of the deposit and are the result of the interaction between hydrothermal and supergene alteration. In an exploration mode, a method has been successfully developed and cost-effectively applied for first-pass testing for the basic spectral criteria of each geological model, followed by more detailed spectral discrimination of key mineral assemblages and early geochemical follow-up.