High spatial resolution heat flow mapping in South Australia: implications for the nature of the South Australian heat flow anomaly and geothermal and mineral resource exploration

Geothermal exploration activity in Australia over the last decade has highlighted the poor surface heat flow data coverage in this country. While data coverage remains poor, a previous attempt to characterise the heat flow field of South Australia (Neumann et al. 2000) described an “anomalous heat flow zone” in central South Australia. This region was not previously delineated by high spatial resolution heat flow data, but the work published here demonstrates that the “zone” described as the South Australian Heat Flow Anomaly (SAHFA; Neumann et al., 2000), is a region where anomalously high heat flow values are interspersed with low values, and there is significant lateral variation in surface heat flow over scales of tens of kilometres. This thesis addresses the following questions: • Is the SAHFA, as shown in Cull (1982) and defined by Neumann et al. (2000), a zone of blanket or even dominant high heat flow? • What is the true nature of the SAHFA when considered on a 10km lateral scale? • What are the possible reasons for the surface heat flow pattern in southeastern South Australia? The heat flow field is a fundamental parameter for characterizing the tectonic setting of a geological terrane because the magnitude of surface heat flow, Qs, can have a strong influence on the mechanical or rheological behaviour of crustal rocks. The distribution of Qs is also directly relevant to resource exploration, in that it is related directly to the distribution of heat producing elements (HPEs). These control the prospectivity for high geothermal gradients and geothermal energy, as well as potentially the locations of elevated concentrations of uranium. Closely spaced surface heat flow data clearly highlights the location of the Olympic Dam ore body, and would probably have aided previous explorers in the discovery of Prominent Hill. Surface heat flow mapping in southeastern South Australia revealed a surface heat flow distribution as complex and varied as the geology of the region itself. Two studies in that region demonstrated that, while there is slightly higher than average surface heat flow around some of the volcanic centres in the Newer Volcanics Province, heterogeneous basement heat production is a more likely explanation than remnant magmatic heat for the overall distribution of surface heat flow. A study was conducted to test the hypothesis that the Torrens Hinge Zone in South Australia was likely to be a region of high average geothermal gradients and thus prospective for geothermal energy. A heat flow drilling program designed to test the idea returned results that validated this hypothesis.