A golden quest

There is a wealth of gold deposits across the Australian continent, and finding the largest and richest is an expensive business. Now, a Monash geoscientist is using synchrotron radiation to discover why gold deposits form where they do in the hope that it may aid in gold exploration. PENNY FANNIN reports.

The Golden Mile at Kalgoorlie, Western Australia, is one of the richest gold deposits in the world. Now an open cut 'super pit', Kalgoorlie's mines have produced more than 50 million ounces of gold with a value of more than $26 billion in the past 110 years.

Going for gold: Dr Andy Wilde. Photo: Greg Ford

Gold prospecting has become big business in Australia, and finding the largest and richest gold deposits is crucial for success.

Dr Andy Wilde, a research fellow in the School of Geosciences, has been using synchrotron radiation to better understand the chemistry involved in gold deposition, in the hope that it will help in locating large and profitable gold mines not only in Australia but in other gold-producing countries such as South Africa.

Synchrotrons are large particle accelerators that create bright, pinpoint beams of light. These high-intensity light beams allow scientists to examine the structure of matter down to the level of atoms. The Australian Synchrotron, being built at Monash University's Clayton campus, is expected to be completed in 2007.

"Most gold deposits are formed when gold precipitates from hot water in the Earth's crust," Dr Wilde says. "Predicting where new gold deposits might be found partly involves understanding the chemistry of this water, including how much gold is in it.

"It's not enough just to find a deposit because there are several thousand gold deposits in Australia. Research has to address why some gold deposits are very large and rich, such as the Golden Mile near Kalgoorlie, and others are not real economic targets for mining companies."

Australia's gold deposits formed millions, even billions, of years ago, and one of the questions that needs answering is how much gold was in the waters below the Earth's crust when these deposits formed. Unfortunately, the waters dried up long ago.

But tiny samples of the water are trapped in some of the minerals that make up the gold deposits. By sampling these tiny droplets, called fluid inclusions, scientists can understand the nature of them.

"These are tiny samples from an ocean of water that circulated through the Earth's crust," Dr Wilde says. "Before synchrotrons, we could not analyse fluid inclusions for gold because we were looking for gold concentrations of parts per billion in samples that were extremely small."

But now that synchrotrons are accessible, Dr Wilde is trying to quantify the amount of gold in these inclusions and look at how the gold is chemically bound. He began his research in Chicago in March at a synchrotron called the Advanced Photon Source.

"By understanding the chemistry of the ore-forming solutions, I might be able to explain why some gold deposits are small and others large," he says.

Dr Wilde's research is a small but important step in understanding why gold deposits form where they do.

"If a correlation can be shown between high gold concentrations in the fluid inclusions and the size of deposits, then mineral exploration could involve sampling of fluid inclusions," he says. "But it's a very expensive technique, costing up to $4000 a day. Most companies probably could not afford it."

Action

For more information on the Australian Synchrotron, visit the Australian Synchrotron at Monash website. Dr Andy Wilde can be contacted on +61 3 9905 1140, or email andy.wilde@sci.monash.edu.au.