Sorting benefits

INTEGRATING an ore sorting system into its flow sheet has helped a Northern Territory gold miner improve its anticipated grade 10% while cutting its expected operational costs.
Sorting benefits Sorting benefits Sorting benefits Sorting benefits Sorting benefits

Mt Todd ore being sorted.

Vista Gold Corporation has integrated a two-stage Tomra sorting solution into its proposed Mt Todd circuit.

The system sorts 20t per hour. It uses X-Ray Transmission technology to remove particles containing sulphide materials and then lasers to remove particles containing quartz and calcite.

Feed grade to the Mt Todd mill has gone up from 0.84 grams per tonne ton 0.91gpt.

Vista Gold president and CEO Fred Earnest said the sorting meant the miner would not be spending money to grind valueless rock.

"We've been able to make design changes in the plant," he said.

"Because we're processing less material we're now able to do a finer size."

That finer grind has led to a 10% gold recovery improvement.

"We've been able to achieve all of this on a capital-neutral basis," Earnest said.

"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."

Tomra worked with Vista Gold's team to identify the best solution for Mt Todd.

That included testing rock from the mine at its facility in Germany, analysing the situation at the project and advising how its sensor-based sorting technology could fit in the operation to deliver the best results.

Earnest said the people at the testing facility in Germany had been very accommodating.

"We've been able to be there on the floor, watching the test, looking at the results and asking questions," he said.

Indeed, visiting the testing facility proved to be any eye opener for Earnest.

He had been keen to find a way to improve efficiency and felt only processing the rock with gold in it was the best way forward.

The company looked at a range of technologies besides the Tomra sorting approach.

"In every evaluation of new technology we have ‘aha moments'," Earnest said.

"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 project sorted and rejected, and when we were able to pick it up and look at it we realised this was not just a dream, this was real technology being applied at a production rate to our rock.

"Suddenly we realised that this was technology that could work at Mt Todd and that we needed to evaluate more seriously."

According to the base case in its recent pre-feasibility study, Vista anticipates processing 17.75 million tonnes per annum of ore to produce 413,400 ounces.