Gold digging

Researchers in the Research School of Earth Sciences and Department of Earth and Marine Sciences have niftily applied software used to model earthquakes to show where significant clusters of gold deposits might be located.

Professor Stephen Cox and Dr Steven Micklethwaite have applied what is known as stress transfer modelling to a number of gold fields, including Mt Pleasant near Kalgoorlie, to accurately predict where gold was found — and where it might still exist, based on fault data going back millions of years.

In an earthquake a fault ruptures, triggering lots of aftershocks. During these aftershocks water flows through the cracks created in the Earth’s crust, carrying tiny amounts of dissolved minerals, including gold. Deposits of gold are left in these cracks.

“This model works on the basis that if you can map where these ruptures occurred and judge the location of the aftershock activity, we can also predict where gold deposits built up,” Professor Cox said.

“Most gold deposits close to the Earth’s surface have been found,” Dr Micklethwaite said. “But gold deposits a little deeper in the Earth are still abundant, it’s just a matter of knowing where they are.”

The findings have attracted more than passing interest from mining companies, which could use this relatively inexpensive and reliable modelling system before drilling expensive cores (often upwards of $30,000 a core) to find the coveted metal.

“Essentially, this is an important addition to the tools geologists could use to make educated guesses about where gold might be,” Professor Cox said.

“Stress transfer modelling is now enjoying success in predicting the location of gold deposits around ancient fault systems; a result with important implications for our understanding of faulting and fluid flow, as well as the exploration for deposits presently hidden underground.”

Mostly, the researchers have tested their models in existing goldfields and compared their results to where the gold was found, with very accurate results (and an idea about where gold still might be found). The next step is to study a greenfield site — where there are the right faults and rock types, but no previous gold production.

Professor Cox and Dr Micklethwaite are also looking to apply the model to other sought after minerals. Their latest results were published recently in Geology, a journal of the Geological Society of America.