PERTH (miningweekly.com) – Gold production expectations from the Gruyere joint venture (JV), in Western Australia, have been downgraded for the 2019 calendar year, on the back of a delay to the completion of the plant construction and commissioning.

JV partners Gold Road Resources and Gold Fields on Wednesday reported that first gold production from Gruyere was still on track for the June quarter; however, full-year production guidance has now been amended from between 100 000 oz and 120 000 oz, to between 75 000 oz and 100 000 oz for 2019.

The JV partners noted that the commissioning of the entire process plant flowsheet, particularly of the ball mill, would be delayed by more than a month.

The time frame for the completion of construction and commissioning of the ball mill has been extended, pending the resolution of process control design and installation. Once the ball mill is fully functioning, the design throughput of up to 1 000 t/h will be achievable.

Ore commissioning of the ball mill is currently expected early in the September quarter of this year, with ramp-up to take place over a six- or seven-month period.

“The delay in construction and commissioning is disappointing, however, the areas of the plant currently commissioned are performing strongly,” said Gold Fields executive VP Stuart Mathews.

“Additionally, mining continues to track ahead of plan and mined tonnes are closely aligned to reserve and grade control estimates, which sets Gruyere up for sustainable production once commissioning and ramp-up have been completed.”

Gold Road MD and CEO Duncan Gibbs added that as a global tier-one mine, the project remained within cost guidance, with the JV partners' confident of a successful ramp-up to nameplate capacity, as well as the long-term performance of the operation.

The project’s final capital cost forecast has remained unchanged at A$621-million, with all-in sustaining cost (AISC) for the period to the end of 2019 likely to be higher than previous guidance of between A$1 050/oz and A$1 150/oz on the back of the delay.

Once in full production, Gruyere is expected to average 300 000 oz/y of gold, with average AISC of A$1 025 oz over a 12-year mine life.