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10 March 2000 – 00/60

Gold deposits in the Pilbara: old province, new potential

A new report released today by Geoscience Australia, presents strong evidence of a previously unidentified type of gold mineralisation in Western Australia's Pilbara region. The recognition of this potential new gold style may lead to a re-examination of the gold bearing properties of similar regions elsewhere in Australia.

The Hon. Warren Entsch MP, Parliamentary Secretary to the Minister for Industry, Science and Resources, welcomed the report, saying the data provided exciting new opportunities for gold exploration in the Pilbara. "These findings suggest many of Australia's ancient rocks may yield future gold deposits. This opens up an exciting new area of exploration for the Australian gold industry."

The Geoscience Australia's documentation of a number of epithermal vein systems in the Pilbara is good news for mining explorationists as the work indicates potential new styles of gold mineralisation in the region.

Epithermal veins are low temperature, low pressure hydrothermal deposits. They are often associated with rich gold deposits, like those located in the Philippines, Chile, PNG and New Zealand. Until the discovery in the Pilbara, epithermal deposits have generally been connected with young terranes, those younger than 500 million years, where high level deposits are more likely to be preserved.

The recognition of this type of mineralisation in the Pilbara is significant as epithermal veins were located in rocks two and a half billion years old. It is unusual for epithermal veins to be preserved in rocks of this age, as their high level position is usually eroded over thousands of millions of years.

The survey of the mineral characteristics of the Pilbara, commissioned by Geoscience Australia and the Geological Survey of Western Australia (GSWA) as part of the National Geoscience Mapping Accord (NGMA), will contribute to a rethinking of the epithermal properties of older rocks. The findings have implications for locating epithermal veins - and potential gold deposits - in other parts of Australia. This may lead to areas older than 500 million years being re-assessed for similar mineralisation.

The epithermal properties in the Pilbara have a number of interesting characteristics. The vein systems are related to a major change in the Pilbara geology, the onset of extension and the formation of the laterally extensive Hamersley Province, more famous for its iron deposits than for its gold bearing potential. The veins, which may be several kilometres long, are found in a variety of rock types including granite, mafic volcanic rocks, and low-grade metasedimentary rocks. It is likely that the overlaying volcanic rocks protected the epithermal deposits from environmental conditions and prevented erosion.

CMR 101