Gold standard in mineral analysis
Wednesday, 14 June, 2017
SA analytical instrumentation provider Chrysos is developing a gold analysis process that is said to be up to three times more accurate than conventional methods.
Known as PhotonAssay, the process uses high-powered X-ray machines to activate the gold in a given sample and measure the signal it gives off to quickly and accurately quantify how much gold is present. It was invented by CSIRO and helps to reduce the environmental impact of mineral processing, as it eliminates the need for toxic chemicals and lead.
“The challenge the [mining] industry has at the moment is that the current methods for analysing gold ore are not fast enough and require too much work,” Chrysos CTO and PhotonAssay founder James Tickner explained.
During the PhotonAssay procedure, a sample is put into a plastic screw-top jar weighing about half a kilogram. The jar is then placed on a conveyor belt inside Chrysos’s analysis machine. Different metals are counted atom by atom on the basis of the unique signatures produced after excitation using an X-ray beam.
“Our process itself is not new, but we have developed it further to be more accurate… It also has the potential to assess other metals as well like silver or copper,” Tickner said.
A series of trials by CSIRO researchers in Canada demonstrated the technology’s performance, with results showing that PhotonAssay will be able to measure samples with gold levels as low as 30 parts per billion. The level of precision depends on the amount of gold in each sample, but for high-grade samples, the accuracy was within about 1%.
Chrysos is now setting up its first production unit in Western Australia, working in partnership with mining company Ausdrill and analytical service provider MinAnalytical. Ausdrill’s COO of Australian operations, Andrew Broad, said the destructive nature of contemporary procedures such as Fire Assays and the speed of PhotonAssay led the company to partner with Chrysos.
“There are two major issues with how things are done now with Fire Assays — they are quite laborious and it is quite difficult to get skilled labour in that field and they take anywhere between 24–48 hours to get results, reduced to just minutes using PhotonAssay,” Broad said.
“Fire Assay is also very destructive, but with this [PhotonAssay] you can run further tests on a sample at a later date,” Broad continued. He said one of the main benefits of PhotonAssay was its reduced environmental impact because it eliminated the need for dangerous chemicals and lead, which are used in other competing technologies.
Ausdrill plans to set up its first unit in Perth, which is projected to be up and running in December. A second mine-site unit is planned for Kalgoorlie by the middle of next year. The company then hopes to export the technology to other projects in Africa.
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