Saturday, 25 October 2014
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X-ray technique may boost yield of gold mines

Australian gold mines could recover more of the precious metal following the deployment of an x-ray technique that rapidly and accurately detects gold in ore samples.

Working with Canadian company Mevex, CSIRO (Australia’s national science office) has conducted a pilot study that shows that gamma-activation analysis (GAA) offers the advantage of speed and accuracy over chemical analysis methods.

GAA works by scanning mineral samples – typically weighing around half a kilogram – using high-energy x-rays that activate any gold in the sample. The activation is then picked up using a sensitive detector.

According to project leader Dr James Tickner, CSIRO’s study showed that this method is two-to-three times more accurate than the standard industry technique ‘fire assay’, which requires samples to be heated up to 1200°C.

‘The big challenge for this project was to push the sensitivity of GAA to detect gold at much lower levels – well below a threshold of one gram per tonne,’ he said in a statement.

Last year, Australia produced over A$10bn worth of gold. Even if GAA only led to a five per cent improvement in recovery, that would be worth half a billion dollars annually to the industry.

Tickner said that a gold processing plant may only recover between 65 and 85 per cent of gold present in mined rock. Given a typical plant produces around A$1bn of gold each year, this means hundreds of millions of dollars worth of gold is going to waste.

‘Our experience suggests that better process monitoring can help reduce this loss by about a third,’ he said.

Tickner said that the other major benefit of GAA is that it is easily automated, allowing for much quicker analysis of ore samples.

‘Fire assay usually involves sending samples off to a central lab and waiting several days for the results. Using GAA we can do the analysis in a matter of minutes, allowing companies to respond much more quickly to the data they’re collecting.’

‘A compact GAA facility could even be trucked out to remote sites for rapid, on-the-spot analysis.’

Another advantage of GAA is that it is more sustainable as, unlike fire assay, it doesn’t require the use of heavy metals such as lead. It is also adaptable.

‘While most of the work we’ve done has been based on the gold industry, the technique can be modified for other valuable commodities such as silver, lead, zinc, tin, copper and the platinum group metals.’

Now that the research team has proved the effectiveness of the technique, their next goal is to partner with local and international companies in order to get a full-scale analysis facility up and running in Australia. They hope to achieve this within the next two years.


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