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 (Figure 1). 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 be spending money to process the rock that had gold in it,” explains 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 Sorting Mining, Langenfeld/Germany, 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 Earnest.
Following extensive testing, Vista Gold has integrated TOMRA’s two-stage sorting solution in its flow sheet at Mt. Todd. The system sorts 20 t/h, 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 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 0.91 g/t.”
What’s more, the savings in operating costs have paid for the improvements to the plant: “We’ve been able to achieve all of this on a capital-neutral basis. We’ve been able to incorporate the equipment for the sorting to add fine grinding equipment, all with the money that we’ve saved from the ball mills. And so, ore sorting has opened up a whole new window of opportunity for us with the Mt. Todd project. We’re very excited about what this technology means to the mining industry and specifically to our projects in the future. And we look forward to seeing this technology grow and become even more efficient and of greater value to us,” concludes Earnest.
TOMRA worked closely with Vista Gold’s team to identify the best solution for the Mt. Todd project – from testing rock from the mine at its facility in Germany, to analysing the situation at the project and advising on how its sensor-based sorting technology could fit in their operation to deliver the best results.
TOMRA Sorting Mining