OZ Minerals shares slumped more than nine per cent after it cut its copper production targets due to a continued slowdown in operations.
Copper production for 2013 is now expected to be around 70,000 tonnes to 75,000 tonnes, down from 82,000 to 88,000 tonnes.
Shares in Australia's third largest copper producer fell 41 cents, or 9.3 per cent, to $3.99.
OZ Minerals said it did not achieve its expected September quarter production levels of gold and copper at its Prominent Hill operation in South Australia following a landslip earlier in the year.
Managing director Terry Burgess said the company had now decided to adjust the current 2013 production targets in favour of a long-term approach.
"Mining is to continue in the areas with lower grade while we progress to the most efficient mine plan rather than attempting to mine ore in advance of plan," Mr Burgess said.
He expects mining unit costs to decrease as the company focuses on efficiency.
OZ Minerals produced 28,177 ounces of gold and 17,390 tonnes of copper in the September quarter.
Lower than expected grades of ore were returned as the company worked to remediate the damaged wall.
"This saw production lower than expected," OZ Minerals said in a statement.
Meanwhile, cash costs were $US2.058 per pound for the September quarter.
Gold production targets were unchanged at 120,000 ounces to 130,000 ounces.
Mr Burgess said a pre-feasibility study at Carrapateena is due to be completed in the first half of 2014.
Shares in OZ Minerals have almost halved over the past year as the price of gold and copper waned.
The company suffered a $268 million loss in the first half of 2013, due to a writedown of Prominent Hill following a landslip which hurt production during the June quarter.
The company said guidance for 2014 will be reported after the 2013 reserve statement is completed in December.
Keep reading - next article