TORONTO (miningweekly.com) – Vancouver-based Copper Mountain Mining on Thursday said production had ground to a halt after one of two transformers powering the motors of the semi-autogenous grinding (SAG) mill failed.

Copper Mountain said it expected production to restart on Saturday, after a transformer from the ball mill had been moved over and installed.

As part of the original design of the concentrator, the SAG mill and two ball mills have identical motors and transformers that are interchangeable in the event of a component failure.

The miner said one set of coils in a transformer had failed and that the supplier was evaluating the cause of the failure.

Owing to the transformers being specialised, Copper Mountain expected repairs to take about four weeks to complete, and during this time, production would be limited to about 1 000 t/h.

“Immediate metal production will be impacted, but all resources are being made available to minimise the impact,” CEO Jim O'Rourke said.

Copper Mountain this week also reported first-quarter results for the period ended March 31, reporting revenues of $55.1-million being 22% lower year-on-year, compared with $71-million a year earlier. Adjusted earnings per share were $7.8-million or $0.08 a share, down 60% from $19.2-million or $0.20 a share.

Production during the quarter totalled 14.2-million pounds of copper, 5 300 oz of gold, and 64 200 oz of silver. Sales for the quarter were 15-million pounds of copper, 5 800 oz of gold, and 69 200 oz of silver, generating a gross profit of $8.1-million for the quarter.

Copper Mountain owns a 75% stake in the Copper Mountain mine, in southern British Columbia, which is a joint venture with Mitsubishi Materials, from Japan.

Copper production during the first three months was below the average guidance for the year, but significant mill throughput improvements were achieved in the latter half of March, which should enhance production during the rest of the year.

The company’s TSX-listed stock slid almost 9% on Friday morning to C$1.53 apiece.