VANCOUVER — It’s been over two and a half years since a catastrophic tailings dam failure paralyzed activity at Imperial Metals’ (TSX: III; US-OTC: IPMLF) Mount Polley copper-gold mine, 56 km northeast of Williams Lake, British Columbia. But now, with a long-term water management permit in hand and recent promising brownfield exploration results, the future of the open-pit and underground operation appears bright.
The last batch of results from a 6,700-metre underground drill program expanded porphyry-related mineralization at the project’s Martel zone to over 130 metres long, 170 metres high and 140 metres wide, with drill highlights including 124 metres of 1.6% copper and 0.25 gram gold per tonne gold. (A higher-grade intercept within the interval measured 18.9 metres of 2.5% copper and 0.66 gram gold.)
Martel is under the previously mined Wight pit and 400 metres from the recently developed and mined Boundary zone. The mineralization extends outwards into a series of discontinuous lenses known as the Green zone, where the latest intercepts returned 8.7 metres grading 4.4% copper and 1.95 grams gold.
Steve Robertson, vice-president of corporate affairs at Imperial, tells The Northern Miner the Martel and Green zones could improve the production profile of Mount Polley, which has a mine life until 2022 at last count.
“We’re really pleased with the results, and especially pleased with the dimensions and grades of mineralization,” Robertson says. “The mill is not terribly hungry … we have lots of mineralization to feed it in the current mine plan, but it’s hungry for high grade, and that’s what these zones could provide.”
Mount Polley produced 25.3 million lb. copper from 6.7 million tonnes of ore last year at an average throughput of 18,265 tonnes per day. The figures include underground mining at the Boundary zone, which supplied 315,000 tonnes of 1.3% and 0.79 gram gold before the reserves were exhausted.
Martel and Green were discovered through surface drilling in 2004, and subsequent work outlined measured and indicated underground resources of 6.3 million tonnes of 1.2% copper, 0.4 gram gold and 7.38 grams silver.
“Development crews moved in to develop the Wight pit and exploration was cut off. We haven’t been back to explore that area since we started drilling late last year,” he says. “We were halfway through development at Boundary, so we ran a drift down to Martel with the purpose of setting up drill rigs to test the zones from underground.”
When asked about possible mining scenarios for Martel and Green, Robertson says the zones may be more amendable to underground bulk-mining techniques like block caving.
“The zones are quite a bit bigger than the mineralization we exploited at Boundary, so the long-hole stoping method we used there might not be the most appropriate way of approaching this from a mining perspective. We may be able to look at lower-cost, bulk-mining underground methods, and that would lower our mining costs, and in turn decrease our cut-off grades so that we can mine more.”
Imperial plans to update the resource estimate and complete an economic study on the zones, but Robertson couldn’t specify when the work should be completed.
In the meantime, the company is advancing a long-term management plan for Mount Polley that was approved by B.C.’s Ministry of Environment on April 7. With the permit, Imperial can discharge treated water from the mine site directly into Quesnel Lake.
Imperial shares has traded in a 52-week range of $3.46 to $8.50 per share, and last closed at $6.12 per share. The company has 93.6 million shares outstanding for a 571.8-million market capitalization.