Science

Eureka! X-rays detect gold faster and more accurately

Eureka! X-rays detect gold fas...
X-rays can be used to detect pieces of gold somewhat smaller than this monster
X-rays can be used to detect pieces of gold somewhat smaller than this monster
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X-rays can be used to detect pieces of gold somewhat smaller than this monster
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X-rays can be used to detect pieces of gold somewhat smaller than this monster
A microscope image of the internal structure of a gold nugget
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A microscope image of the internal structure of a gold nugget

Every year, Australian mining companies discard hundred of millions of dollars worth of gold. They're not doing it on purpose, it’s just that the standard industry technique of scanning mineral samples isn’t sensitive enough to detect small traces of the precious metal. Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO) and Canadian company Mevex have tested a new technique using powerful X-rays that can detect these small trace amounts quickly and accurately.

The current industry standard used by mining companies for valuing gold ore is fire-assay, which is time consuming, requires the use of heavy metals such as lead, and involves heating samples to temperatures of up to 1,200° C (2,192° F). According to the CSIRO’s Dr James Tickner, gold processing plants will generally only recover 65 to 85 percent of gold present in mined rock using this method.

He points out that last year Australia produced over AUD$10 billion (approx. US$9.1 billion) worth of gold, with a typical plant producing around AUD$1 billion (approx. US$910 million) of gold annually. So improving the detection rate by even a few percent would allow the recovery of gold worth hundreds of millions of dollars.

Dr Tickner was the project leader of a pilot study that examined a new technique called gamma-activation analysis (GAA), which involves blasting mineral samples with high-energy X-rays like those used in medical imaging. The X-rays make the gold radioactive for a few seconds, which allows it to be picked up with a sensitive detector. The results of the study showed that GAA was two to three times more accurate than the fire assay method at detecting gold in a mineral sample.

Aside from its accuracy, Dr Tickner says GAA also offers other benefits. It is easily automated, offering the potential for a portable GAA facility about the size of a shipping container to be trucked to remote sites for on-the-spot analysis that takes just a few minutes to complete.

"Fire assay usually involves sending samples off to a central lab and waiting several days for the results,” says Dr Tickner. “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."

Dr Tickner adds that the technology could also be modified to detect other metals, such as silver, lead, zinc, tin, copper and platinum group metals.

The researchers hope to have a full-scale analysis facility up and running in Australia within the next two years. Dr Tickner told Australia’s national broadcaster, the ABC, that the technology would cost in the ballpark of AUD$3 to $4 million (US$2.7 to $3.6 million), meaning mining companies would see the system paying for itself in quick fashion.

Sources: CSIRO, ABC

3 comments
Dekarate
Does detecting minute quantities of gold equate the recovery of the same traces? You can detect gold in sea water, but it isn't economical to recover it.
Kim Holder
I wonder if this would ever be a practical technology for surveying asteroids (skipping several steps ahead...).
Ron Turpin
Sort of reinventing the wheel I think, but it is a good "wheel" which produces good results. If you Google TEFA ORTEC you will find a long list of files concerning the Tube excited florescence analyzer that was in production and sold all over the world in the '70's and '80's. ORTEC also produced a SEFA (source excited florescence analyzer) which did the same task but the TEFA was the preferred unit because you could turn off the radiation at the end of the test, making it a safer and less difficult unit to license for meeting the myriad of regulations that such units had to meed. A spin off from the TEFA was a Gold Analyzer, a hand held field unit that was used by mining groups in Africa to follow the gold seams deep in the mines. I did not find reference to the gold gun on my first Google search. That may be because the development was funded in part by a mining consortium so published articles may not be as readily available.