Centerra partially restarts Mt Milligan mill

VANCOUVER (miningweekly.com) – Canadian midtier miner Centerra Gold has partially restarted its Mount Milligan operation, in British Columbia, after unexpectedly cold weather in December caused a water shortage, halting operations.

Toronto-based Centerra said in a statement on Monday that the mill is using a single ball mill to reduce water requirements.

The company cautioned that there may be sporadic commissioning downtime as the operation ramps up; however, mill operations are expected to achieve sustainable mill throughput levels of about 30 000 t/d by mid-February.

During the recent shutdown, Centerra completed several steps to increase the flow of water into the tailings storage facility (TSF) from which the Mount Milligan mill draws all of its water requirements for the milling operations. 

Such steps included adding pumps to existing water wells, increasing pump sizes to increase the flow rate, and drilling more wells. Current make-up water sources for the TSF are from normal surface run-off, groundwater wells internal to the TSF, and from base underdrain towers that access process water underlying the TSF. 

The company expects to restart the second ball mill in April, returning mill operations to full capacity, when more fresh water becomes available from surface run-off after the spring ice melt. The return of mill operations to sustainable levels, on one or both ball mills, is dependent on the performance of the make-up water sources and the overall water balance in the TSF.

As a further longer-term mitigation measure, Centerra has now received an amendment to Mount Milligan's environmental assessment certificate to allow pumping of water from a nearby lake, Lake Philip, and has received the additional related permits. The company expects to start drawing water from Lake Philip by the end of February.

The company expects to issue its 2018 full-year company-wide guidance on February 23.