Geophysical characteristics of some Proterozoic base-metal deposits in the Curnamona province of South Australia

Abstract

The Curnamona Province is a large body of Mesoproterozoic and Palaeoproterozoic crystalline rocks that straddles the South Australia-New South Wales border. Minor base-metal, gold and uranium mineralisation occurs through out the Province in South Australia, however, the area is significant because the rocks have affinities with those that host the giant Broken Hill lead-zinc-silver deposit across the border in New South Wales. Where the rocks of the Curnamona Province are at, or close to, the surface, there is excellent coverage by modern high-resolution aeromagnetic data. Magnetisation contrasts are marked, and detailed structural and stratigraphic mapping is possible, albeit limited by the geological complexity of the region. A prominent magnetic marker is associated with the Bimba Suite, a stratigraphic horizon where base-metal mineralisation tends to be concentrated. Using the aeromagnetic data, the prospective stratigraphy is easily traced for many hundreds of kilometres within the Willyama Inliers, in the south of the Curnamona Province. In contrast with the successful use of aeromagnetic data for geological mapping, geophysical methods designed to directly detect mineralisation, or the mineralised environment, have been somewhat less successful. Attempts to detect lead-zinc mineralisation at the Hunters Dam prospect, using EM methods, have been largely unsuccessful, although IP/resistivity surveys have successfully detected areas of anomalous geochemistry. However, prospective regions also contain barren sulphides and graphitic horizons. At the Mutooroo Mine, copper(-gold) mineralisation is associated with a deeply weathered shear zone. The mineralised zone is chargeable, and there is a broad zone of increased conductivity that is easily detected using time- and frequency domain EM, SP and IP/resistivity surveys. However, the conductivity contribution to these responses from sulphide mineralisation is probably negligible. Gravity and magnetic data allow lithological variations and geological structure to be mapped. At Dome Rock the prospective stratigraphy, and also possibly mineralisation within it, can be mapped using the IP method, and the local folding is clearly defined by modelling of these data. Resistivity and frequency-domain EM data are less useful. Copper mineralisation at the Parabarana prospect gives rise to weak responses in IP/resistivity surveys.