Earth Heat holds 100% interest in three geothermal exploration licences (‘GELs’) covering circa 3,850km² in South Australia, in an area of higher heat flow which is known as the South Australian Heat Flow Anomaly (‘SAHFA’). In addition, the Company currently has three further GELs on offer for grant which would bring the Company’s total tenement coverage in South Australia up to 13,000km². The SAHFA is a corridor through the eastern-central part of the Australian continent (Figure 1) where heat-producing rocks in the crust contain relatively high concentrations of radiogenic isotopes of uranium, potassium and thorium. The natural radioactive decay of these rocks produces high heat flow. A thick succession of sedimentary rocks contained within the Adelaide Geosyncline of South Australia represents an effective insulating blanket required to maintain high heat flow through units of high thermal conductivity in this part of the SAHFA.

The part of the Adelaide Geosyncline between Adelaide and Copley has attracted much interest from geothermal explorers recently, and the southeast corner of the ORROROO 1:250 000 geological map sheet has been identified by Earth Heat as highly prospective. Several prospects are contained within the compeight GELs where there is strong potential for Hot, Dry Fractured rocks (‘HDR’) and Hot Sedimentary Aquifers (‘HSA’).

Geological Background

The outcrop geology of the ORROROO 1:250 000 geological map sheet is dominated by the Neoproterozoic succession of the Adelaide Geosyncline
(Figure 2). This succession is represented by the Adelaide System that comprises four ascending time-rock units designated as the Willouran, Torrensian, Sturtian and Marinoan series (Mawson and Sprigg,1950; Sprigg, 1952) and is reproduced in Table 4.3 below. The style of folding on ORROROO is mainly of the concentric parallel type. Sedimentary units on the limbs of the folds are probably near theiroriginal thickness.

Faulting is closely associated with anticlines cored by diapiric sediments of the Willouran series. Radial faulting in the Yednalue anticline (Figure 3), is most likely related to diapiric intrusion during growth of the structure. Other mapped faults on ORROROO run along the hinge of anticlines that commonly emanate from diapiric cores. These were re-interpreted by Dyson (2002) as salt welds that were formed by evacuation of vertically emplaced diapirs. The best example of this type of diapiric structure is found at Oladdie Diapir, some 40 km northwest of the prospect areas, and represents the basis for an exploration model used by Earth Heat.

Heat Sources

Heat sources regionally are interpreted to be a result of radiogenic basement, and or local intrusives which may also have a radiogenic makeup. Regionally, most of the SAHFA is located in areas where the TMI magnetics shows a strong response, suggesting that where there is a magnetic anomaly, this may be coincident with high heatflows and therefore potentially a source of heat. In analogous areas that have been the subject of recent exploration, excellent results have been published by companies such as Torrens Energy Ltd over such anomalies. Figure 4 shows the inferred relationship and heatflow, via the existing granted Exploration Licences in the region.

Where the GELs currently held by Earth Heat will be investigating the connection between basement heatflow, through diapiric units, and into potential heat reservoirs, it will be greatly assisted by a series of magnetic anomalies which could be local intrusive heat sources (Figure 5).

These potentially local heat sources will augment the ‘natural’ radiogenic heatflow transported into the reservoir (from basement) and increases the likelihood that a commercial resource may exist.

East of the GELs, magnetic anomalies are likely to be associated with radiogenic granites, and this is supported by Uranium exploration in the area. Should the unit within the Earth Heat project area be similar in composition to its easterncompatriots, this further enhances the potential for a heat source in the area. This is strongly supported by the information compiled and published by Geoscience Australia on Radiogenic Heat Generation (Figure 6 & 7).

Figure 6

Granite occurence and OZCHEM sample heat production map (Budd, 2007).