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Call for rethink on gold deposit formation

Posted December 22, 2015

New CSIRO research has questioned the accepted theory on how some gold deposits formed, highlighting that current geological models are not universally applicable.

Gold is typically found with sulphide minerals and many studies have inferred that the gold was transported through the crust dissolved in sulphur-bearing fluids and deposited when the fluids reacted with iron-rich host rocks.

CSIRO’s study of the Junction gold deposit in Western Australia suggests that it formed differently, because the low observed fluid to rock ratios would not have allowed enough fluid to pass through the host rocks to form a deposit of that size.

CSIRO geologist and lead author, Dr Mark Pearce said that their models raise serious questions on how gold is transported and deposited in the deep crust.

CSIRO research shows chemical reactions that may have occurred to form Junction gold deposit (gold shown in yellow).

CSIRO research shows chemical reactions that may have occurred to form Junction gold deposit (gold shown in yellow).

“Our models imply that the gold concentration levels that led to the formation of Junction would have been 10,000 times higher than what could have been dissolved and transported in a sulphurous fluid, so an alternative gold transporting agent is required.

“For instance, we’re finding that the key chemical reactions involved in creating a gold deposit are localised, often within a few millimetres of the gold grains rather than metre-wide alteration zones.

“While it doesn’t mean that existing geological models are always wrong, it does indicate that there are other geological processes at play that need to be identified to improve their accuracy.”

Dr Pearce and the team used CSIRO’s state-of-the-art Advanced Characterisation Facility in combination with advanced computer modelling to conduct a detailed microanalysis on the Junction gold deposit.

These advanced tools can be accessed by companies for more targeted minerals exploration and to better understand their prospects.

Dr Pearce is now studying what other geological processes influenced the formation of the Junction gold deposit and this work could be used to improve the accuracy of exploration models used by geologists around the globe.

Source: CSIRO

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