TORONTO (miningweekly.com) – British Columbia-based Copper Mountain Mining on Tuesday said copper production during the first three months of the year was below the average guidance for the year, but emphasised significant mill throughput improvements were achieved in the later half of March, which should enhance production during the rest of the year.

During the quarter ended March 31, the company produced 14.2-million pounds of copper, 5 300 oz of gold, and 64 200 oz of silver from its flagship Copper Mountain mine, in the south of the province.

The mine shipped 29 400 wet metric tonnes of concentrate containing about 15-million pounds of copper, 5 900 oz of gold, and 69 000 oz of silver, generating an estimated $62.3-million in gross revenue.

The mill processed a total of 2.2-million tonnes at an average grade of 0.349% copper.

The company said mining activities continued from the Pit 2 and Pit 3 areas according to plan and averaged about 170 000 t/d. During the quarter a total of 15.5-million tonnes of material was mined, including 4.3-million tonnes of ore and 10.4-million tonnes of waste. The projected life-of-mine strip ratio was 2:1, but higher in the early years.

MILL IMPROVEMENT

Mill throughput improved significantly after the scheduled maintenance shutdown in early March. The mill achieved a 93.3% availability during February and after a planned shutdown in early March, the mill achieved above budget availability of 92% to the end of the month, compared with an availability of 85.9% averaged during the first quarter.

Before the shutdown in early March, a contractor was engaged to crush a 70 000 t sample of the hardest Pit 3 ore to minus two inch. When the mill restarted on March 8, it treated the finely crushed sample and demonstrated that with pre-crushing, the semi-autogenous grinding (SAG) mill could achieve throughput rates above the designed 35 000 t/d.

The test confirmed that secondary crushing was an option to pursue to ensure stable and consistent increased long-term mill throughput rates for ore from all pit areas.

Immediately following the fine crush sample a test was completed with ore from high-intensity blasting and limited supplemental pre-crushing. This test also successfully demonstrated increased mill throughput and had provided a path for short-term tonnage improvements.

Cooper Mountain said it planned to continue to use high-intensity blasting that created more fines in the SAG mill feed and to continue having a contractor crush up to 10 000 t/d of minus two inch SAG mill feed.