Mill wheel grinding

ONE of the standouts of Western Areas’ December quarter highlights was its mill achieving record throughput of 161,218t of ore. That was achieved thanks to sorting some old ore.
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Trial ore sorting at Flying Fox being carried out last year.

Noel Dyson

Western Areas had about 168,000t of 1% to 3% nickel it had been stockpiling since 2007 at its Flying Fox mine.

It brought in Kalgoorlie company Ore Sorting Australia to go through those stockpiles and pull out as much ore as possible.

The process started with some of the ore being sent to Germany where Steinert conducted testwork on it to see if it could be sorted.

Those tests showed it could so OSA arrived on site with its combination crusher-sorter rig and started going through the piles.

The material was crushed down to 20mm particles by the crusher and then pushed through the OSA sorter, which used induction and x-ray sensors to sort the ore.

Western Areas managing director Dan Lougher told Australia’s Mining Monthly the end result was high grade product and low grade fines.

“We got about 83% nickel recovery,” he said.

“We wouldn’t have processed that nickel anyway until the end of mine life.”

At the end of the process Western Areas has about 2000t of low grade fines left.

Lougher said the Cosmos operation Western Areas bought from Jubilee Mines had an old ore sorter out the back of the mill but that was an old optical system and not as effective as the one Western Areas applied to its Flying Fox stockpile.

“I must admit the material, the reason it was lower grade was that the massive sulphide in it was smaller than what we put through the mill,” he said.

“It’s very good for ore sorting.

“That’s why you have to do that amenability testing to make sure the recovery is commercially viable.”

While the ore sorting has been a win for Western Areas in this quarter, it is the potential of the New Morning/Daybreak deposit that has Lougher excited.

The deposit has open pit potential, however, its ore does not take well to flotation – the main way Western Areas treats its ores.

“When you float this ore the recoveries are less than 50%,” Lougher said.

However, it seems to react quite well to heap leaching and Western Areas has been doing testwork on it at CSIRO.

The idea is the leach liquor would then be put through Western Areas’ Mill Recovery Enhancement Project, which is closing on commissioning.

The MREP is designed to take the tails stream from the treatment plant and retreat it using the miner’s own BioHeap leaching process. It will only take 5% to 8% of the tailings.

The size of BioHeap tanks Western Areas will be running, the MREP will be able to turn out about 1400t of nickel a year.

However, given the New Morning/Daybreak ore has already been leached, it would be put through the back end of the MREP.

“The back end of the plant gets a nickel sulphate solution,” Lougher said.

“We need to bring it back to a sulphide so we had sodium sulphide to it.”

Lougher said Western Areas would be able to get a premium for this product.

“Remember, when we put the material through flotation, we get 90% back anyway.”

Another benefit is the process Western Areas is putting the material through ties up any arsenic in it with iron to form a very stable mineral.

“We’re going to fast track it because it’s not a very difficult thing to start an open pit mine,” Lougher said.

AMM understands Snowden is putting together an open pit design for the operation.

“We’re doing the infrastructure design,” Lougher said.

“Between Spotted Quoll and Flying Fox we have power and water there.”

Lougher said the work the company was doing on New Morning/Daybreak could provide dividends down the track.

“There are potentially many other orebodies we have that have poor economics due to the high magnetics or poor flotation results” that the technology could be applied to, he said.