PERTH (miningweekly.com) – ASX-listed metals producer Oz Minerals has again downgraded its full-year copper production expectations, as the Prominent Hill mine, in South Australia, delivered lower-than expected results.

Oz Minerals on Monday lowered its copper expectations from between 82 000 t and 88 000 t for the financial year to end of December, to between 70 000 t and 75 000 t. The company initially targeted 80 000 t and 95 000 t of copper production, but said in April that it would not meet that target.

Gold production forecasts have remained unchanged at the already lowered forecast of between 120 000 oz and 130 000 oz.

The miner told shareholders that record volumes were mined at the openpit operation during the three months to September, as it re-entered the Stage 3 operation, following a previous overburden slip.

MD and CEO Terry Burgess noted that despite the record tonnes mined, the required face advancement was not achieved, and mining in areas at the eastern periphery of the orebody delivered lower-than-expected grades.

This saw production during the September quarter decline to 17 390 t of copper and 28 117 oz of gold, compared with the 17 379 t of copper and the 31 018 oz of gold produced in the June quarter.

“In order to ensure the most efficient and cost-effective mining operation in the pit, a decision has been taken to adjust the current 2013 production target in favour of mining in the long-term interest of the pit,” Burgess said.

He noted that according to this plan, mining would continue in the areas with lower grade, while Oz Minerals progressed to the most efficient mine plan, rather than attempting to mine ore in advance of plan.

C1 costs at Prominent Hill were also expected to increase during the full year, owing to the lower gold price, lower gold production and the lower payable copper. C1 cash costs were expected to reach around $1.90/lb to $2.05/lb.

Meanwhile, Oz Minerals continued its investigation into supplementing copper and gold production with a second underground mine beneath the Malu openpit mine, Burgess said.

Depending on the outcome of resource definition drilling and economic analysis, production from this area could start in late 2014.