Towards 3D maps of alteration under cover: Regional constrained 3D inversion of potential field data from the Olympic Cu-Au province, South Australia

Abstract

Regional-scale constrained potential field inversions can be used to map rock types, alteration, and structure. This is particularly valuable when basement is obscured by younger cover. The methods outlined in this study have been applied to a 150 km × 150 km region around the giant Olympic Dam copper-uranium-gold deposit, where abundant haematite, sulphide, and magnetite alteration produce strong potential field signatures despite thick cover. The results are used to develop the first 3D map of magnetite and haematite/sulphide alteration for the Olympic Cu-Au province, and show that the alteration around known Cu-Au mineral occurrences can be detected using coarse regional-scale inversions. The provision of a reference model in the inversion formulation permits geological observations to be introduced into the inversion process to guide the inversion towards more geologically reasonable results. This allows hypotheses regarding 3D geological architecture to be rigorously tested for compatibility with potential field data. An iterative procedure of inversion followed by updating the reference model allows 3D maps of alteration and structure that are consistent with both the known geology and observed potential field data.