Researchers at the Parker Centre, with the support of five gold companies, are tackling the problem of "preg-robbing" gold ores. Improved understanding of preg-robbing is essential for increasing gold recoveries from these ores.

Preg-robbing of gold during cyanide leaching occurs when the leached gold is adsorbed by certain components of the ore. This prevents some of the gold being recovered, making gold extraction less profitable.

The research team aims to identify where the gold originally occurs in the ores, what mineralogical associations it has and where it goes when it is adsorbed after leaching.

Using sensitive surface techniques to analyse ore samples, the scientists have confirmed that the culprit component in preg-robbing is the carbonaceous (carbon-containing) material in these ores. Research has shown that the gold is adsorbed on the surface of the carbon as gold dicyanide.

Stockpile of preg-robbing ore at Stawell gold mine in Victoria,which has provided
some of the ore samples for the preg-robbing research.

Mineralogical characterisation of the ores has found that all the preg-robbing ores appear to contain sulphide minerals and all contain carbonaceous material. The nature of the carbonaceous material is being determined by chemical analysis. Metallurgical assessment of the ore samples by cyanide leaching tests is being undertaken to measure the extent of preg-robbing.

The team will attempt to tie the results from the three experimental approaches together, for example by looking for correlations between the degree of preg-robbing and the type of carbonaceous material. This research could lead to better tests for assessing the preg-robbing activity of an ore and new strategies to combat this robbery.

For further information, contact
Dr Jim Avraamides, tel: (08) 9360 6360, e-mail: avraamid@central.murdoch.edu.au

By Ros Dilworth, Communications Officer, the Parker Centre.
First published in Process Magazine.