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Stimulated by recent interest in oil shale as an alternative source of oil, exploration since 1978 has revealed that the Tertiary and Cretaceous oil shale deposits of Queensland are of considerable size and extent. Tertiary deposits contain inferred resources of oil totaling 2,400 × 106 m3 (15 billion bbls), based on average Fischer Assay yields of 60 to 80 L/t in situ, while Cretaceous deposits are perhaps one hundred times larger. However, 90% of the latter are too deeply buried to be extracted with existing technology. On present information, Jurassic, Permian, and Cambrian oil shale deposits do not appear to be of economic significance.
Cretaceous oil shales occur within the shallow marine Toolebuc Formation of western Queensland. This stratigraphic unit is thin (16 to 49 ft, 5 to 15 m) but exceedingly widespread. Tertiary oil shales, which range up to 1,970 ft (600 m) in thickness, formed in freshwater environments in several basins located in the eastern one-third of the state.
Oil shale deposits most likely to be exploited in the next decade are those of Tertiary basins close to the coast, which contain multiple seams of high oil yield, amenable to open-cut mining and with adequate supplies of water. The Condor, Rundle, Stuart, and Yaamba deposits are in this category. Mining feasibility studies of these and the Cretaceous Julia Creek deposits envisage open-cut mining and surface retorting on a large scale. Experimental retorting investigations are in progress. Extraction of oil from oil shales in areas remote from the coast probably awaits development of economic methods of in-situ retorting.
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