Record 2008/04
Diamonds, diamond indicator minerals and a review of exploration for diamonds in Queensland
Exploration for diamonds in Queensland has continued to be influenced by the South African approach, modified by the discovery of diamonds in lamproite in Western Australia. This approach is to explore for kimberlite and lamproite bodies using indicator minerals that are dispersed from these rocks by fluvial and colluvial processes.
Exploration for diamonds in Australia has increased since the discovery and exploitation of the Argyle Mine in Western Australia. The New South Wales Geological Survey has produced a digital data product on the prospects for diamond exploration in that State as have the Northern Territory Geological Survey (as a grouping of Microsoft Excel spreadsheets with data on diamond indicator minerals) and the Geological Branch of PIRSA in South Australia. As part of the Smart Mining Initiative (2006-2010), the Geological Survey of Queensland has compiled a database of micro-diamonds and diamond indicator minerals from open file company data in the Department of Mines and Energy's QDEX system. Much of the exploration for diamonds in Queensland has been patchy and has proceeded along with exploration for other commodities. There has been no commercial exploitation of diamonds in Queensland and only rare occurrences of microdiamonds have been reported.
This report also outlines the properties of diamonds and geological models for their formation. There appears to be a regional difference in diamond occurrences in Queensland, with the kimberlite and lamproite models favoured for the north-western regions of the State and the subduction (S-type model) favoured for the eastern coastal and sub-coastal zones, linked to Cainozoic alkalic basalt volcanism. Sapphire is commonly associated with diamonds in these areas. Studies in New South Wales indicate that diamonds do occur in economic quantities in alkali basaltic intrusions and further exploration in Queensland is warranted on diamond indicator minerals and their composition.
The main occurrences of microdiamonds have been in the Mount Isa region, where they have been reported from stream sediment samples. Microdiamonds have been found in the Stanthorpe, Proston, Herberton and Lakeland Downs areas of eastern Queensland.
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