Hitting Gold at Half the Price

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. The project, briefly operated in the 1990s, is known for having hard ore. This, and the fact that the project was operated previously, presented particular challenges for Vista Gold.
“We had a desire to find a way to only spend money to process the rock that had gold in it,” explains Fred Earnest, President and CEO of Vista Gold. “We started looking for ways to get rid of the non-mineralised host rock prior to the grinding circuit. We 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.”
Technology makes the case
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, “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 being sorted on a production-scale machine. When we saw how fast
it was happening, 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, but 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.”
Two stage sorting
Vista Gold has integrated Tomra’s two-stage sorting solution in its flow sheet at Mt Todd. The system sorts 20 tonnes per hour, 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 the 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 not spending money grinding rock that has no value,” explains Fred. 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%.”
Nina Gustmann
Tel: +34 91 415 30 20
Email: Nina.Gustmann@tomra.com