PERTH (miningweekly.com) – Gold miner Millennium Minerals on Wednesday reported that the Stage 1 sulphide plant expansion at its Nullagine gold project, in Western Australia, has delivered its first gold.

CEO Peter Cash told shareholders that all early results from the sulphide circuit had been very positive, indicating the potential to generate strong, profitable gold production from sulphide ore.

“The ability to cost-effectively process the high-grade sulphide ore sources at Nullagine has been a core component of Millennium’s growth plan over the past four years, and we are absolutely delighted to have successfully achieved this milestone.

The ultra-fine grind mills were commissioned earlier this month, and gold is now being recovered from the sulphide concentrate. The circuit has been commissioned using lower-grade ore, however it has demonstrated sufficient capacity to accommodate the increased sulphide content and higher concentrate volumes expected once processing of higher-grade ore starts.

The stockpiled concentrates, which currently stand at around 1 200 t, along with freshly generated concentrates, will now be fed back into the mill circuit for final gold recovery.

It is expected that the stockpiled concentrates will be processed over the next four to six weeks.

“The past 14 months have been a very capital-intensive period for the company where we have made significant investment in long-term growth initiatives including the sulphide plant expansion and the development of sulphide ore sources,” Cash said.

He noted that the capital investment has had an impact on production and cash flow over the past six months, however, Millennium was now moving into a period where it expected to see both production and cash flow increase strongly, with an expected return to positive cash flow by the end of July.

“It is also important to note that the Stage 1 upgrade to the processing plant is expected to have a positive impact on gold recoveries across both oxide and sulphide ore sources. To date, the Stage 1 upgrade has enabled us to recover up to 30% of the residual gold from our lower-grade tailings, with the uplift likely to be much greater from the higher-grade sulphide ores.

“We are also seeing a positive impact on recoveries from our traditional oxide ore feed.”

In addition to the concentrator and fine grinding circuit, the sulphide expansion will also include the installation of an in-mill oxidation process as the concentrate transitions from a pyrite-dominant to a blended pyrite/arsenopyrite ore, and a pressurized in-mill oxidation to facilitate processing of arsenopyrite-dominant ore.