Imperial Metals to resume 
Mount Polley operations

VANCOUVER — The B.C. Ministry of Energy and Mines has given Imperial Metals (TSX: III; US-OTC: IPMLF) permission to resume full production at its Mount Polley copper-gold mine, 56 km northwest of Williams Lake, B.C., nearly two years after an unprecedented breach at the site’s tailings dam and storage facility.

The new permit authorizes Imperial to process up to 22,000 tonnes per day of ore and use the repaired and strengthened tailings facility to store the waste and water generated from mining.

The decision came after a lengthy review by members of provincial agencies, First Nations, local governments, the community of Likely, the federal Department of Fisheries and Oceans, and Environment Canada. The review concluded that the reinforced tailings facility met engineering standards.

Steve Robertson, vice-president of corporate affairs for Imperial, tells The Northern Miner during a phone interview that the statutory decision marks a milestone for the company.

“We’ve been working towards this for a long time and it’s welcome news — not just for the employees, but for the local community who now have a bit more stability in the economy of the area,” he says. “It’s also been a great relief to the company considering the tough operating environment right now, as commodity prices have not been favourable.”

The rehabilitated Lower Hazeltine Creek channel upstream from Quesnel Lake, where tailings from the Mount Polley copper-gold mine spilled in the summer of 2014. Credit: Province of British Columbia.

The open-pit and underground operation was temporarily shut down after a breach occurred without warning along a section of the dam’s perimeter embankment in August 2014. The event sent 25 million cubic metres of mine waste and water flowing into the adjacent Polley Lake, through Hazeltine Creek, into Quesnel Lake.

An independent expert investigative and review report, released last January, stated the failure happened because the design of the original facility and subsequent raises did not consider the strength and location of an underlying clay unit.

Robertson says the company has spent $67.4 million on restorative work to date, which included building buttresses along the dam’s perimeter using 2.5 million tonnes of material.

“There was an investigation after the breach to make sure there was a clear understanding of the subsurface conditions below the dam,” he says. “With those results in hand, the engineers at Golder Associates have gone back and redesigned the facility with buttresses along most of its perimeter, and that has raised the factor of safety for the embankments.”

Imperial has also established an independent tailings review board and appointed a facility overseer at the site.

The company has operated the mine at half capacity since July last year, diverting any water or waste into the existing Springer pit while the tailings facility underwent repair.

Under the restricted permit, the company processed 11,958 tonnes per day, and produced 8 million lb. copper and 15,190 oz. gold between Aug. 5 and Dec. 31 last year.

Between Jan. 1 and the time of the spill the company processed 21,056 tonnes per day to produce 24.5 million lb. copper and 25,901 oz. gold.

Robertson says that with the new permit in hand, it’ll take “a couple of days to redirect the lines” from the Springer pit back to the facility, but will still “take some time” before the company can resume its normal mine plan.

“There’s still a lot of mineralization beneath the Springer pit, which was in the original mine plan. So we’ll look at ways to potentially get both the water and tailings out of the pit so we can access those resources,” he says. “At this time we’re going to continue mining the ore within the Cariboo pit and some higher-grade material from underground.”

Probable reserves at Mount Polley stand at 86 million tonnes of 0.3% copper and 0.3 gram gold per tonne for 560 million lb. copper and 838,100 oz. gold, assuming US$2.75 per lb. copper, US$1,250 per oz. gold and a US/CAD exchange rate of US95¢.

He says the company is submitting a long-term water management plan for the operation.

“We have a temporary permit to discharge water that’s been treated into Hazeltine Creek and Quesnel Lake, which is good for another year,” he says. “Over that time we’ll have the longer-term water management plan in place, and that will determine how we’ll go forward for the rest of the mine life.”

In an investigative review released last December, B.C.’s chief mine inspector deemed Imperial not liable for the geotechnical oversight that caused the dam to fail, but said that the company exercised “weak practices” towards the dam’s design and water management at site.

Investigations into the incident concluded that emergency actions could have been more effective if there was less water on the tailings pond.

The report recognized that Imperial had applied for a water discharge permit in 2006, but for “unknown reasons,” it wasn’t accepted by the Ministry of Environment until 2012.

Under the issued permit, Imperial couldn’t discharge enough water to ease the surplus and sought amendment with the ministry to approve higher discharge. The permit was amended in July 2014, one month before the breach occurred.

“We’re confident that we have very good information to work with because of the team we’ve put together to look at how we deal with water in the long-term,” Robertson says. “As long as we provide good-quality information and keep the local community and First Nation community engaged … I have great confidence we’ll move ahead on this permit in a timely matter.”

He emphasizes that research and monitoring at the site indicate the environment is recovering after the spill.

“Rehabilitation of the impacted areas has gone really well and based on the current test results, we expect no long-term adverse effects from the presence of tailings in the environment,” Robertson says.

Tailings are ground-up rock that has been stripped of ore-bearing minerals during milling and mineral processing. They are stored in ponds to prevent most oxidation of sulphides, which generates acid. At Mount Polley, mineralization is associated with a low-sulphur content and extensive calc-sodic alteration. The nature of the material prevents the tailings from becoming acidic, and thereby incapable of leaching significant residual metal.