The achievements of an Australian scientist and his team whose research has so far contributed to the discovery of more than $5 billion worth of gold were today recognised with the award of a CSIRO Medal.

They are the pioneers of a geochemical exploration method that has resulted in the finding of more than 20 gold and other mineral deposits, mainly in Western Australia.

Team leader Dr Smith is the Director of the Cooperative Research Centre for Landscape Evolution and Mineral Exploration and a chief research scientist in CSIRO's Division of Exploration and Mining, based in Perth.

The team's revolutionary "halo" technique enables mineral explorers to pinpoint rich sources of gold and other minerals buried deep beneath a blanket of sand and gravel.

It has been a key factor in the discovery of the world-class Bronzewing and Plutonic deposits, as well as others at Jundee, Nimary, Turrett and Waroonga.

Though the principal gold finds have been made in the 3 billion year-old rocks of Western Australia's Yilgarn craton, the technique is now being taken up by mineral companies exploring in Africa, India and South America as well as elsewhere in Australia.

"The work began in the mid-1970s, which highlights the time it takes not only to do the research but also to demonstrate to the satisfaction of industry that it works," he says.

The ancient rocks which contain the gold deposits were heavily weathered over eons, forming a material called laterite, which contains minuscule traces of the gold.

The laterite formed the last 130 million years or so, preserves a dispersed "halo" of trace elements surrounding the original deposit. Using sophisticated analytical techniques Dr Smith found these haloes contained about 50 parts per billion of gold, becoming steadily richer the closer one came to the source.

"The gold deposit itself might be quite small in dimensions - a few tens of metres across and a few hundred metres long - but its geochemical halo is typically 100 to 500 times larger, usually a kilometre or so wide and 2-3 kms long," he explains.

"That gives a mineral explorer a very much greater chance of pinpointing the actual deposit, even though it may be completely invisible from the surface."

The technique is based on detecting traces of gold and trace levels of arsenic, antimony, bismuth, tin and molybdenum. It is now also being developed for diamond exploration.

"The laterite blanket is typically one to three metres deep. It looks just like a lot of gravel, very uniform and boring. Beneath it lies another 30-50 metres of deeply weathered rock. The ore deposits are not at all spectacular, in fact very hard to recognise at all."

"But when you penetrate the covering layers, a wonderful story starts to unfold."

The laterite blanket is in fact a leftover of a past great Greenhouse Effect, a period of warm climate, heavy rainfall and massive erosion which began about 130 million years ago, he explains. The haloes are fossil remnants of the original mineral source, frozen in time.

Deciphering these complex processes and then applying very sensitive analytical methods to detect the faintest traces of gold has given the minerals industry one of its most powerful exploration tools, now used by scores of companies.

Dr Smith attributes Australian success in discovering the halo technique partly to the nature of our landscape: its sparsely-vegetated surface gives scientists using aircraft and satellites a birds-eye view of geological structures and the processes at work.

"Brazil has exactly the same sort of processes going on, but you would simply never be able to map the surface relationships because you couldn't see through all the jungle," he explains.

The halo research which also won the team the 1994 Sir Ian McLennan Award, cost some $5 million for a return, so far, of more than $5 billion or one thousandfold, in discovered resources. Mining companies themselves have put an estimated $320m into associated exploration and development.

More information:
Dr Ray Smith, CSIRO, CRC LEME 08 9333 6272, 0419 900 159
Dr Ravi Anand, CSIRO,CRC LEME 08 9333 6736
Chris Priday, CSIRO 018 416 470, 07 3212 4444