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Golden needles in rocky haystacks

By Pat, 6 September 2013 News

Gold nugget.

While gold can be found in large nuggets, it’s usually found in much smaller concentrations in ores.
Image: CSIRO

Imagine you have a massive pile of rocks. You think there might be gold in the rocks, not much, but enough to make some money. Now it might be easier to find out how much hidden gold there is.

Gold is really rare. In Australia, the ores with gold typically contain about one gram per tonne. This is a bit like trying to find a paper clip in a car, except the paper clip isn’t in one piece – it’s been broken up and spread all over the car.

Even at these tiny concentrations, it’s still worthwhile extracting the gold, given how valuable it is. Currently, Australian mines don’t extract all the gold from an ore. At best, they might extract about 85 percent. Monitoring the amount of gold in ore as well as processed material could help improve recovery.

The standard method for measuring the amount of gold in an ore is a long process and can take days. CSIRO recently announced it has developed a new way, in partnership with a Canadian company, Mevex.

The method uses a beam of high energy X-rays, which is shone onto a sample of ore. Gold atoms in the sample interact with the X-rays, and become excited. The excited gold atoms are radioactive, and emit another type of radiation called gamma rays. More gold in the sample means more gamma rays are emitted. By measuring the gamma rays emitted from a sample, it is possible to calculate the gold concentration.

This process promises to be faster and more accurate than current methods, and one day might be carried out on mine sites. Making advances in detecting gold will hopefully lead to more gold being extracted from ore, with less of the ore going to waste.

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