TORONTO (miningweekly.com) – Vancouver-based Copper Mountain Mining on Monday said the damaged semi-autogenous grinding (SAG) mill transformer at its eponymous mine, was now fully repaired and reinstalled, which has allowed the concentrator to be back at full operation with one SAG mill and two ball mills operating as expected.

Copper Mountain said site maintenance personnel received the repaired transformer from the repair shop in Edmonton over the weekend, a full week ahead of the scheduled shipment date.

The repaired transformer had had all three sets of coils replaced and was inspected and certified as new by power and automation technology group ABB personnel and comes with a one year warranty.

"We were very pleased with operational results of running with only one ball mill. During the period in which the concentrator was operating with only one ball mill, site personnel were able to make modifications to the operation to minimise lost production, which included mining higher-grade material, decreasing the size of the SAG mill discharge screen to provide a finer size of ore being sent to the ball mill, which increased the ball mill's capacity,” CEO Jim O'Rourke said.

He added that the operational adjustments were “very effective” in that, during the period of running with just one ball mill, the concentrator achieved a 95.4% availability, averaged 1 207 t/h, had copper recoveries of 86.7%, and produced 12% more pounds of copper a day than in the first two weeks of May before the transformer failure.

"The operation with one ball mill clearly confirms that if we can increase tonnage through the SAG mill, the ball mill circuit will handle it. All data from operations during this period confirms that we could achieve 2 000 t/h at 92% operating time with both ball mills running,” O'Rourke said.

The exact cause of the failure was not yet determined and the three replaced coils were sent to ABB`s repair shop in Italy for further testing and evaluation.