Australia does not have any active volcanic terrains or conventional volcanogenic geothermal resources, however Geoscience Australia estimates Australia’s potential Hot Sedimentary Aquifer (HSA) and Engineered Geothermal System (EGS) resources are equivalent to 26,000 times Australia’s annual electricity energy consumption (Geoscience Australia, 2019; Budd et al, 2008).
Fig 1. Predicted temperature at 5 km depth based mostly on bottom-hole temperature measurements in more than 5000 petroleum and water boreholes. Courtesy Geoscience Australia
South Australia is situated between the ancient Archaean Shield of Western Australia and the mobile orogenic belts of the eastern states. As a result of this tectonic setting, the geological record in South Australia has preserved a unique history of sedimentation from the Neoproterozoic to Ordovician, and from the Early Devonian to Tertiary. Underlying these sediments, South Australia has large regions of interpreted high crustal temperature and high heat flow associated with buried Mesoproterozoic granite intrusives at depths over 3 km, which form important geothermal exploration targets. In parts of the Cooper Basin for example, geothermal gradients reach 55–60oC/km, significantly higher than the average geothermal gradient of about 25 – 30oC/km.
The Gawler Craton (late Archaean-early Mesoproterozoic) and Curnamona Province (Palaeo-Mesoproterozoic) are two large complex basement terrains consisting of mafic and felsic igneous intrusions and volcanics, moderate to high grade metamorphics. Mesoproterozoic granites, felsic volcanics and gneisses in the Gawler Craton and Curnamona Province contain anomalously elevated uranium and thorium concentrations relative to global Proterozoic averages (Neumann et al., 2000) and generate high heat flows. For example, the Mesoproterozoic Hiltaba Suite hosts the Olympic Dam copper-gold-uranium deposit.
Regions of interpreted high crustal temperature and heat flow, which have been blanketed by sedimentary cover form the main exploration targets for geothermal energy in South Australia. Neumann et al (2000) defined the South Australian Heat Flow Anomaly (SAHFA) based on sparse regional heat flow data (Fig. 2). The SAHFA occurs through the eastern Gawler Craton, Delamerian Fold Belt and Curnamona Province and displays high average heat flow relative to Proterozoic or younger terrains on other continents – mean heat flow within the SAHFA is 92±10 µWm-2 compared to a continental average of 51-54 µWm-2 (Neumann et al, 2000).
Fig 2. Average surface heat flow map. Contouring produced using minimum curvature-bicubic interpolation on historical uncorrected heat flow data. Data points represent calculated heat flow measurements from individual drill holes.
Budd, A. R., Holgate, F. L., Gerner, E., Ayling, B. F. & Barnicoat, A. 2008. Pre-competitive geoscience for geothermal exploration and development in Australia: Geoscience Australia’s Onshore Energy Security Program and the Geothermal Energy Project. In: Proceedings of the Sir Mark Oliphant International Frontiers of Science Australian Geothermal Energy Conference, Gurgenci, H. and Budd, A.R. (eds), record 2008/18, Geoscience Australia, Canberra, 1–8. (last accessed 8 February 2018).
Geoscience Australia, 2019. Australian Energy Resources Assessment (online)
Neumann, N., Sandiford, M. and Foden, J. (2000). Regional geochemistry and continental heat flow: implications for the origin of the South Australian heat flow anomaly. Earth and Planetary Science Letters, 183; 107 – 120.