July 2004
Australian geologists believe they can explain an unusually regular pattern of gold distribution in Western Australia, a finding they believe could improve predictions of where large gold deposits can be found.
Dr Roberto Weinberg, a senior lecturer in Monash's School of Geosciences, was part of the research team that investigated the regular gold distribution pattern in the 2.7 billion-year-old Boulder-Lefroy fault zone.
Four of Australia's richest known gold deposits, each endowed with more than 100 tonnes of gold, and including the 1800 tonne giant Golden Mile at Kalgoorlie, occur at 30-40 km regularly-spaced intervals along this fault zone.
"Despite the long history of gold exploration and hundreds of years of investigation, determining a predictable pattern of gold distribution has remained elusive," Dr Weinberg said. "This is because of the wide variety of factors involved in gold mineralisation."
Large gold deposits result when vast amounts of fluids carrying dissolved gold within the Earth's crust converge into narrow paths within the fault system.
Dr Weinberg collaborated with Dr Paul Hodkiewicz and Professor David Groves from the University of Western Australia on the research, which found that the major factor controlling gold endowment was variations in the direction of the fault zone.
Their research is published in the July issue of the international journal Geology.
"Every rock has tiny pores, and the fluid migrates through these. When there was seismic activity along the Boulder-Lefroy fault zone, parts of the fault dilated - increasing the size of the pores in the rock - while others contracted, depending on variations in the fault's direction," Dr Weinberg said.
"During such events, fluid migrated into the areas of dilation, and it is in these sections that rich gold deposition resulted."
The research team believes that the richness of the Boulder-Lefroy area is related to the existence of few, very effective zones of dilation along the fault zone, spaced at distances that maximised the catchment of gold-carrying crustal fluids.
"Large dilational sites along faults should be the focus of exploration, as they are obviously key determinants of gold mineralisation," Dr Weinberg said. "Within these broad dilational sites, other physical and chemical factors may control the further focusing of fluids and the precipitation of gold out of the fluids, but the dilational sites are a good starting point for exploration."
Contact:
roberto.weinberg@sci.monash.edu .au
Ph: +61 3 9905 4902 | 
