Gamma-ray spectrometric and oxygen-isotope mapping of regional alteration halos in massive sulphide districts: an example from Panorama, central Pilbara Craton

The Panorama district, in the central Pilbara Craton (WA), is perhaps the best exposed, least deformed volcanic-hosted massive sulphide (VHMS) district in the world, and represents an ideal laboratory not only to study the genesis of such deposits but also to test the utility of exploration techniques. Recent studies there indicate that γ-ray spectrometric and whole-rock oxygen-isotope mapping effectively define regional- and local-scale alteration facies in VHMS districts. The application of simple K/Th ratios to γ-ray spectrometric data, acquired as part of AGSO's regional aeromagnetic survey of the Pilbara, defines a regional semiconformable zone of potassium depletion. This zone becomes transgressive below known deposits and prospects. Potassium depletion zones, which were detected remotely, correspond closely with zones of potassium mineral destruction mapped by Brauhart et al. (1998: Economic Geology, 93, 292-303). Similarly, oxygenisotope mapping highlights the same semiconformable and transgressive zones as areas of low δ¹⁸O.