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TOMRA’s ore sorting technology creates opportunity for Vista Gold

Published by , Editorial Assistant
Global Mining Review,

Vista Gold Corporation owns the Mt Todd project in Australia, which was acquired in 2006 and is one of the country’s biggest undeveloped gold resource and presented particular challenges.

“We had a desire to find a way to only be spending money to process the rock that had gold in it,” explained Fred Earnest, President and CEO of Vista Gold. “We started looking for ways that we could get rid of the non-mineralised host rock prior to the grinding circuit. The company looked at different technologies to address the issues at the Mt Todd project and contacted TOMRA Sorting Mining to find out about its sensor-based sorting technology.”

TOMRA invited the Vista Gold team to visit their testing facility in Germany with a sample from the project to see first-hand what could be achieved.

The test was an eye opener for Fred Earnest: “In every evaluation of new technology, we have “aha moments”. For us it was the day we were at the facility in Germany watching our rock be sorted on a production-scale machine. When we saw how fast it was happening, when we saw the product sorted and rejected, and when we were able to pick it up and look at it – we realised that this was not just a dream, this was real technology being applied at a production rate to our rock. All of a sudden, we realised that this was technology that would work for us at Mt Todd and that we needed to evaluate more seriously.”

After integrated TOMRA’s two-stage sorting solution in its flow sheet the system sorts 20 tph, using X-Ray transmission (XRT) technology to remove particles containing sulphide minerals and subsequently lasers to remove particles containing quartz and calcite.

The benefits of TOMRA’s solution to the Mt Todd project are two-fold. On the one hand, operating costs have been reduced: “We’re getting rid of material and we’re not spending money grinding rock that has no value,” explains Fred Earnest. On the other hand, gold recovery has improved: “We’ve been able to make design changes in the plant. Because we’re processing less material, we’re now able to do a finer size. With finer grind our gold recovery has gone up. This has resulted in improvements of grade by 10%. Our feed grade to the mill has gone up from 0.84 g/t to now 0.91g/t.”

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