Hidden but Hot

The Mount Polley mine is located almost dead centre between B.C.’s Rocky Mountains and the Pacific Ocean, in the south-central part of the province 8 km southwest of the village of Likely and about 100 km northeast of Williams Lake.

In other words, it’s “out there,” but not so far “out” that it’s gone unnoticed. In fact, quite to the contrary, because the Mount Polley property has been on the radar since the early 1960s when its copper-gold deposit was first discovered from an airborne magnetic anomaly, and since then there has been a steady stream of explorers making their way to the area.

From the 60s and through every decade since, the Mount Polley deposit has been the focus of a number of companies, starting with Cariboo-Bell Copper Mines (which by 1970 had come under the control of Teck Corporation), through 1982 when E&B Explorations Inc. took control, to 1987 and the present day where Imperial Metals Corporation of Vancouver oversees the operation.

It’s been 25 years since Imperial Metals first got involved with the Mount Polley project and like most companies working on a property over that length of time, there have been periods when they have questioned their commitment to the project.

Like in 2001, for example, when metal prices dropped and they were forced to suspend operations and place the mine on care and maintenance after just four years (1997-2001) of production.

It was a true test of Imperial Metals’ commitment to the property. They did not abandon the site and for the next two years, continued to invest in exploration and by coincidence, when the markets returned in 2003, Imperial Metals had discovered a major new, high-grade ore zone at Mount Polley.

This combination of the improving markets and the discovery of more ore facilitated financing for the restart of mining and milling operations in early 2005 and it’s now projected the mine will be producing to late 2016. And that’s keeping the 375 people currently working there very happy.

It’s believed this mine-life projection would probably not have been made possible without Imperial Metals’ commitment to stepping out and discovering additional resources during the shut down between 2001-2003 and beyond.

During the first year of the hiatus (2001), the company drilled a total of 170 percussion holes for 9,421 m and 41 core holes of 6,696 m. Trenching and drilling continued in late 2003 and through 2004 amounting to 54,715 m over 187 holes, revealing a new zone of hydrothermal breccia mineralization over a 450 m strike length.

By early 2005, exploration emphasis shifted from definition drilling to property-wide exploration focused on the discovery of additional mineralization zones. The programs included surficial and geological mapping, prospecting, soil surveys, till and whole rock geochemical sampling, and percussion and diamond drilling.

Much of the drilling targeted numerous areas and underexplored tracts on the eastern and southern borders of the Mount Polley area.

The Mount Polley property covers 18,405 hectares, which consists of five mining leases totalling 1,867 hectares, and 43 mineral claims encompassing 16,538 hectares, and by the end of 2010, a total of 2,261 explorations holes were diamond drilled.

In 2010 alone, the drill program consisted of 44,823 m of diamond drilling over 108 holes in or marginal to known resources, including the property’s Springer, C2, Junction, Boundary, Pond and Southeast zones.

The Springer zone contains the bulk of Mount Polley’s remaining reserves, and has a planned ultimate pit depth of around 300 m. In 2010, two low-angle drill holes collared outside the Springer footprint indicated even deeper potential: SD10-99 intersected 202.9 m grading 0.35% copper and 0.26 g/t gold, and SD10-100 intersected 221.3 m grading 0.32% copper and 0.34 g/t gold, in each case about 70 m beneath the pit’s designed base.

Drilling is continuing in other zones peripheral to the Springer zone and the company is confident that there’s potential for pit expansion. In addition, ongoing underground exploration development of deep mineralization in other zones northeast of the Springer will test the viability of adding high-grade material to the mill feed by undergound mining, which would significantly enhance the mine’s outlook.

Last year (2010), 77% of the mill feed at the Mount Polley mine was supplied by the Springer pit, with the balance coming from the now completed Southeast and Pond zone pits.

Daily mill throughput in the fourth quarter of 2010 averaged 21,203 tonnes per day, with a total of 7,894,596 tonnes being milled for the year. The current reserve estimate for the Mount Polley Mine contains 309.1 million pounds of copper and 386,000 ounces of gold. Mineral Resource Measured and Indicated (as at January 1, 2011) was 45.8 million tonnes grading 0.306% copper, 0.262 g/t gold and 0.471 g/t silver.

Mount Polley is an open pit mine where ore is processed through a rod/ball/pebble mill circuit producing a copper/gold concentrate. The loading equipment is a combination of P&H 2100 shovels and loaders. The haulage fleet includes Caterpillar 777 and 785C trucks and the primary crusher has the capacity to accept material from a 150 tonne truck.

Planned production for 2011 includes 32.0 million pounds of copper, and 44,000 ounces of gold.

To make all of this happen, Imperial Metals is basically using the same mill that underwent care and maintenance almost 10 years ago but various components have been upgraded over the years to handle the increased capacities and to comply with safety rules and regulations, but by and large, it’s the same mill.

The milling and metallurgical process at the mine is a run-of-mill ore operation where ore from the open pits is dumped into the feed pocket of the primary gyratory crusher, equipped with a hydraulic rock breaker, to reduce the rock to a nominal 200 mm.

From there, crushed ore is discharged onto an apron feeder which feeds onto a conveyor to the coarse stockpile. Ore is reclaimed from underneath the stockpile by four vibrating feeders and conveyed to a vibrating screen.

In preparation for flotation, ore from the feed stockpile is conveyed to a grinding circuit, consisting of parallel rod mill/ball mill circuits and a pebble mill circuit. Crusher product is first fed to a rod mill, and then to a ball mill. Ball mill discharge is then pumped to cyclones, where the coarse particles are separated to return to the ball mill, while the finer particles proceed to the three pebble mills. Cyclones are again used to return oversize material to the mills, where the fines, now at the necessary size for mineral separation, are pumped to the flotation circuit.

Once in the flotation circuit, the valuable minerals are separated from the waste rock, producing the concentrate. Initial separation is done in a rougher/scavenger circuit, where the waste rock is discharged as tailings, which flows by gravity to the mine’s impoundment area. Rougher concentrate is further upgraded in a cleaner circuit to produce the final product, and cleaner tailings are recycled to the rougher/scavenger circuit.

Concentrate from the milling is dewatered in two stages. Settling reduces the water content to roughly 35-40%, while pressure filtration further reduces it to roughly 8%. The water removed is utilized as process water in the mill, and concentrate is stored in the load-out building and loaded on to 40 tonne trucks for shipping.

Another saleable product enhancing the performance of Mount Polley is magnetite, a significant constituent of the alteration mineralogy. A magnetite circuit was installed in the mill in 2010 to recover the mineral from the tailings, which is sold to coal mines for use in coal wash plants.

Year-round road access to the mine from Williams Lake is 15 km southeast of Highway 97 to 150 Mile House, 76 km north on Likely Highway past Morehead Lake, and then 12 km south on the unpaved Bootjack Access Road. T
ravel time is about 75 minutes.

Concentrates are trucked to facilities at the Port of Vancouver, then shipped to overseas smelters or sent by rail to smelters in North America. The principal market for copper concentrate is Asia.

The Mount Polley Mine may be somewhat hidden from the world by the shadows of the Rocky Mountains, but location isn’t a deterrent to Imperial Metals; at least it hasn’t been for the past quarter of a century and it doesn’t look like it’s going to be in the future either.