Cu-Au mineralisation in the Curnamona Province, South Australia: a hybrid stratiform genetic model for Mesoproterozoic IOCG systems in Australia

The Proterozoic Curnamona Province lies between two of the most endowed Cu-bearing mineral belts on the Australian continent – the Gawler Craton, which hosts the giant Olympic Dam iron oxide copper gold (IOCG) system, and the Mount Isa Inlier, which hosts the giant Mount Isa Cu system and IOCG belt of the Eastern Succession. This study focuses on Cu-Au deposits within the Proterozoic rocks of the Benagerie Ridge Magnetic Complex in the central Curnamona Province. The Benagerie Ridge is buried beneath Neoproterozoic and Phanerozoic cover sequences. We use drillcore and geophysical data to determine the structural architecture and structural controls of Cu-Au mineralisation in the Benagerie Ridge. The Portia and North Portia deposits are the most significant Cu-Au mineral deposits in the Benagerie Ridge and lie adjacent to an extensive regional redox boundary that separates lower magnetic units from upper non-magnetic units. The redox boundary is extensive throughout the Curnamona Province and is linked with mineralisation in the region. Significant chalcopyrite, bornite and molybdenite occur along bedding-parallel layers and shear structures. These factors support a strong lithological control on Cu-Au mineralisation at all scales. Deformation in the Benagerie Ridge involved the development of a D1 layer-parallel foliation (S1), which is overprinted by D2 recumbent folds and D3 upright folds. The deformation history is associated with the c. 1610–1580 Ma Olarian Orogeny. Overprinting of D2 structures during D3 has resulted in a type 2 interference pattern, which we have successfully mapped using aeromagnetic data. Several later phases of post-Olarian faults overprint F2 and F3 fold interference patterns, and have resulted in the remobilisation of some of the Cu-Au mineralisation. We propose that the stratiform Cu-Au mineralisation occurred prior to the onset of the Olarian Orogeny. Mineralisation is preserved within the thickened hinge zone of a similar-type F2 fold proximal to the hinge of an overprinting F3 fold, which we propose has enhanced mineralisation within the North Portia deposit. Consequently the identification of the redox boundary within F2 folds elsewhere in the Curnamona Province – particularly when located proximal to F3 fold hinges, which place the mineralised zones into structurally favourable locations – provide good targets for future mineral exploration.