PERTH (miningweekly.com) – Preliminary results from an expansion study of the Nullagine gold operation, in Western Australia, have pointed to the economic advantages of an alternative processing route for the 850 000 oz of fresh ore resources.

ASX-listed Millennium Minerals said on Tuesday that the new processing solution would involve integrating a flotation circuit capable of treating sulphide ores through the existing two-million tonne a year carbon-in-leach (CIL) plant.

This was compared with an initial plan to build a standalone flotation circuit capable of processing 0.5-million tonnes a year of sulphide ore.

The development of the new processing solution builds on the breakthrough earlier this year that demonstrated fresh ore from the Nullagine project is free-milling, and can be processed in the existing CIL plant, while also showing it can be successfully processed in a conventional flotation circuit.

CEO Peter Cash said that the processing results amounted to a significant breakthrough for the company with the potential to deliver a step-change in the growth profile at Nullagine.

“The identification of an integrated processing solution is a major step forward which puts in place the most important foundation required to complete the expansion study.

“The ability to process any ore type at Nullagine in the future as and when our mining schedule determines, will give us unparalleled ability to exploit the vast resource inventory across the project. It will also allow us to fast-track the development of new openpit and underground ore sources, which are currently being drilled.”

The plant modification was expected to cost between A$40-million and A$60-million, while processing costs for free-milling fresh ore are expected to be around A$19/t, compared with the current processing cost for oxide ore of A$17/t.

The processing costs for sulphide ore through the flotation circuit have been estimated at an average of A$27.50/t.

The sulphide ore will be sourced from openpit deposits, and from potential underground operations, with some 30 deposits at Nullagine remaining metallurgically untested and open at depth.

“We can now see a pathway to achieve our objective of establishing a 100 000 oz/y production profile at Nullagine with a five-year-plus mine life, establishing a long-term gold business which has a significantly greater scope than the current openpit oxide gold operation,” said Cash.

“This is an exciting development for the company which could underpin the future of Nullagine as a long-term openpit and underground mining operation.”