Crustal evolution and exploration potential of Delamerian south-eastern South Australia

Abstract

The Delamerian Orogeny compressional tectonic system commenced at 514 ± 3 Ma and for approximately 24 Mys provided the necessary mechanisms for the generation of hydrothermal intrusives and mineralisation events throughout much of south-eastern South Australia. The Hillgrove Resources Kanmantoo Cu-Au mine located 50 km south-east of Adelaide, hosts Delamerian age mineralisation formed by hydrothermal activity related to a pluton at depth. Many additional Delamerian aged intrusives have been identified distal to the Kanmantoo deposit and are hypothesised to provide temporal and spatial constraints of additional, and potentially mineralising, Delamerian events. Using monazite, titanite and zircon U-Pb geochronology, this investigation has identified the date and locations of two magmatic stages and one minor stage within sampled Delamerian intrusive rocks of south-east South Australia. Pre-Delamerian Magmatism (~520 Ma) consisting of the previously documented Truro Volcanics suite occurs throughout pre-Delamerian passive margin. Syn-Delamerian Magmatism (~490 – 480 Ma) has been identified at two locations (55 km north-east and 224 km south-east of Kanmantoo) and is interpreted to have been emplaced during late peak metamorphism, D3. Post-Delamerian Magmatism (~471 Ma) is represented by one sample location and is interpreted to represent a magmatic stage occurring during the final minor stages of the Delamerian Orogeny, during post D3 extensional reactivation conditions. Pyrite and pyrrhotite mineralisation is present throughout the entire sample suite, particularly within sampled intrusions representing Syn-Delamerian Magmatism at the Kanappa drilling project (approximately 60 km north-east of the Kanmantoo deposit) and 224 km south-east of Kanmantoo. The samples from these two locations were formed during relatively late Delamerian D3 post peak metamorphism, indicating two regions of enhanced prospectivity.