Tungsten Tailings

Tungsten Tailings

Tungsten Tailings

At the Macraes opencast gold mine in East Otago, a new mineral deposit is forming, tungsten ore left in tailings after the gold has been removed. The challenge is how to economically recover this strategic metal from its scheelite host, a call on NZIMMR’s metallurgists to crack the code.

The raw material for NZIMMR’s project team is a fine yellowish powder stored in a tailings storage facility at OceanaGold’s Macraes mine. These left-overs from gold mining and ore processing have been accumulating since large-scale production began at this high country site in 1990. The size of the prize is considerable – an estimated 185 million tonnes of tailings, containing 37,000 tonnes of tungsten, expressed as the trioxide, having an in-ground value exceeding $500 million. But to turn this resource into a mine will take a new direction in separating the scheelite from other rock components in the tailings, and first-stage processing of the scheelite.

Tungsten ore is also found at Macraes at the Round Hill pit where mining has ceased. OceanaGold is considering re-opening this pit to recover gold and scheelite, as a by-product.

Metallurgist Kirsty Hollis is leading the NZIMMR project, supported by Thomas Trott, also a metallurgist or minerals processing engineer. A literature review of OceanaGold’s testing results is underway. This will arm the preparation of a formal research proposal for NZIMMR Board approval.

Among the research, challenges are the low grade of the tungsten in the mine tailings, which by itself leads to a lower rate of recovery of tungsten from minerals processing. The aim is to achieve a 60% tungsten recovery rate. If successful, the NZIMMR work will deliver a product suitable to feed into a synthetic scheelite process OceanaGold is looking to develop for its ore.


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