Tectonic evolution and exploration potential for the Gawler Craton, South Australia

Abstract

Interpretation of newly acquired high-resolution aeromagnetic data, accompanied by reassessment of corresponding integrated geological data, establishes a complex Archaean to Mesoproterozoic tectonic history for the Gawler Craton in South Australia. A key outcome is the recognition of major tectonic events between 1540 and 1565 Ma and at ~1650 Ma that postdate the Kimban Orogeny. The northwest part of the craton was subjected to high-grade metamorphism at these times, whereas in the central part of the craton coeval deformation is focused within major shear zones. The proposed new name for this orogenic advent is the Kararan Orogeny, derived from the major crustal feature the Karari Fault. Deformation during the Kararan Orogeny was essentially contemporaneous with Hiltaba Suite and Gawler Range Volcanics magmatism and is a critical factor in the emplacement of copper-gold mineralisation. We propose that deformation associated with the Kararan Orogeny is related to continental collision between the eastern proto-Yilgarn Craton, in the northwest, and the central Gawler Craton-East Antarctic Craton (the Marson Continent) in the south. The Fowler Orogenic Belt is one of the most intensely deformed regions within what is a broad collisional zone, and together with adjacent less-deformed crust may host mantle-sourced Proterozoic nickel deposits. Although recognition of the Kararan Orogeny is significant to our new understanding of the craton, there is a long and complex record of events that commenced in the late Archaean. Each stratigraphic unit within the craton and the subsequent tectonothermal history are briefly summarised. Newly available data have been included as far as possible following on from Drexel et al. (1993). It is well known that the Gawler-Craton is host to the world-class Mesoproterozoic Olympic Dam Cu-U-Au deposit. The craton also has significant potential for the discovery of additional Cu-Au deposits related to acid volcanism and/or late-stage high crustal level granitic intrusives associated with altered and deformed Archaean and Palaeoproterozoic hosts. This potential is now being realised with application of the cost-effective calcrete sampling technique to detect anomalous gold. The discovery, in 1996, of shear-hosted gold in the central Gawler Craton within the Yarlbrinda Shear Zone has intensified exploration in those regions where Hiltaba Suite and Gawler Range Volcanics intrude shatterd basement. Exploration expenditure for Archaean gold has increased significantly following discovery of the Challenger gold prospect in June 1995. Gold mineralisation occurs in complexly deformed Archaean quartz-feldspar-garnet-cordierite gneiss. Many other calcrete-hosted gold anomalies remain to be tested within poorly exposed Archaean Mulgathing Complex, which also includes layered ultramafic sills and exposed komatiites. Show more