CSIRO Uses X-Ray Vi­sion To De­tect Un­seen Gold

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Pow­er­ful X-rays can now be used to rapidly and ac­cu­rately de­tect gold in ore sam­ples, thanks to a new tech­nique de­vel­oped by the Com­mon­wealth Sci­en­tific and In­dus­trial Re­search Or­gan­i­sa­tion (CSIRO) – a move that could save Aus­tralia’s min­er­als in­dus­try hun­dreds of mil­lions of dol­lars each year.

Work­ing with Cana­dian com­pany Mevex, CSIRO has con­ducted a pi­lot study that shows that gamma-ac­ti­va­tion anal­y­sis (GAA) of­fers a much faster, more ac­cu­rate way to de­tect gold than tra­di­tional chem­i­cal anal­y­sis meth­ods.

This will mean min­ing com­pa­nies can mea­sure what’s com­ing in and out of their pro­cess­ing plants with greater ac­cu­racy, al­low­ing them to mon­i­tor process per­for­mance and re­cover small traces of gold – worth mil­lions of dol­lars – that would oth­er­wise be dis­carded.

GAA works by scan­ning min­eral sam­ples – typ­i­cally weigh­ing around half a kilo­gram – us­ing high-en­ergy X-rays sim­i­lar to those used to treat pa­tients in hos­pi­tals. The X-rays ac­ti­vate any gold in the sam­ple, and 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 says.

Dr Tick­ner ex­plains that a gold pro­cess­ing plant may only re­cover be­tween 65% and 85% of gold present in mined rock. Given a typ­i­cal plant pro­duces around A$1 bil­lion 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 says.

Last year, Aus­tralia pro­duced over A$10 bil­lion worth of gold. Even if GAA only led to a mod­est 5% im­prove­ment in re­cov­ery, that would be worth half a bil­lion dol­lars an­nu­ally to the in­dus­try. Dr. Tick­ner says 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. By 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 great ad­van­tage of GAA is that it is more sus­tain­able – un­like fire as­say it doesn’t re­quire the use of heavy met­als such as lead.

It is also very 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.

A mi­cro­scope im­age of the in­ter­nal struc­ture of a gold nugget.

An 8 kilo­gram gold nugget

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