Mount Polley mine is a Canadian gold and copper mine located in British Columbia near the towns of Williams Lake and Likely. It consists of two open-pit sites with an underground mining component and is owned and operated by the Mount Polley Mining Corporation, a wholly owned subsidiary of Imperial Metals. In 2013, the mine produced an output of 38,501,165 pounds (17,463,835 kg) of copper, 45,823 ounces of gold, and 123,999 of silver. The mill commenced operations in 1997 and was closed and placed on care and maintenance in 2019. The company owns 20,113 hectares (201.13 km2) of property near Quesnel Lake and Polley Lake where it has mining leases and operations on 2,007 hectares (20.07 km2) and mineral claims on 18,106 hectares (181.06 km2). Mineral concentrate is delivered by truck to the Port of Vancouver. As of January 2020, Mount Polley's Proven and Probable Reserves were 53.8 million tonnes of ore grading 0.34% copper, 0.30 grams per tonne gold and 0.9 grams per tonne silver, equating to 400 million pounds of copper, 517,000 troy ounces of gold and 1.55 million troy ounces of silver. Mount Polley Mining Company reopened the mine in July 2022. Mount Polley Mining Company estimates that the reopening of the mine created 300 local jobs.
Mining operations When operating, the Mount Polley mine moves 80,000–90,000 tonnes of material per day from the mine. This contains 20,000 tonnes of ore. Mount Polley does not require high-skilled labour for operations and hires and trains from the local communities of Big Lake, Horsefly and as far away as Quesnel and Williams Lake. Most workers come from communities near the mine.
Minerals Mount Polley determines what qualifies as ore and what qualifies as waste using drilling and blasting. Ore is then sorted according to blast ball assays. High value sulfide ore is hauled to a crusher for processing at the on site plant. Chalcopyrite and bornite are the main copper-bearing minerals of value at the Mount Polley mine.
Processing
During operation, Mount Polley mine processes 20,000 tonnes of ore per day. The ore is sent for crushing, size reduction, and froth floatation.
Gold and copper During assaying, the value of copper and the value of gold in the ore is determined and a monetary value per tonne is placed on the material. When this value exceeds a particular threshold, workers start processing the material. Subsequently, the material is processed through a mill where the minerals get floated. In particular, the copper and gold minerals both float and are then concentrated. This process, called upgrading, creates a concentrated material that is approximately 23% copper. Gold is also captured in the concentrate.
Transportation Mount Polley ships material, concentrated by floating, by truck to Vancouver when it is sent overseas to buyers who then smelt and refine the material.
Staff During operation, Mount Polley runs four shifts. There is a day shift and a night shift each running twelve hours. Around 370 workers work these shifts seven days on and then get seven days off. About 50 staff include administrators, supervisors, warehouse operators, engineers, geologists, assayers, technical personnel, and human resources.
Care and maintenance shutdown and reopening On 31 May 2019, Mount Polley mine was put on care and maintenance status. Remediation work in the areas affected by the 2014 breach has been the focus of Mount Polley's staff from 2014 to 2019. While the mine's closure affected mining operations, it did not impact the ongoing environmental monitoring and remediation programs. Care and maintenance at the Mount Polley mine included management of the water treatment facilities and the operation of site water management systems, including pumps and ditches. Mount Polley monitors the stability of the tailings storage facility on a regular basis. Mount Polley employed 15 staff at the site while it operated in care and maintenance status. The company reopened mine operations in July 2022.
Geology The Mount Polley mineralization is classified as an alkalic porphyry copper-gold deposit. The deposits are located in the Quesnel trough, a Mesozoic volcanic arc in the Canadian segment of the North American Cordillera. Precious metal mineralization in the two Mount Polley deposits occur the felsic stock occurred during the Jurassic-Triassic period. The copper-gold mineralization occurs within crackle and inclusion breccias.
History
Pre-development Placer mining, the mining of stream beds for minerals, was common practice in the area since the mid nineteenth century. The Mount Polley ore deposit was discovered subsequent to an airborne magnetometer study completed by the Canadian government in 1964 which detected a significant reading for the surveyed map in the region of Polley Mountain. Investigating further, Karl Springer discovered an alkalic porphyry deposit there the same year. Quintana Resources prospected the area in 1976, discovering numerous copper float boulders but let their claim to the property lapse in 1978. In 1980, E&B Exploration optioned the property from Highland Crow, a subsidiary of Teck. Through the early 1980s, the potential for gold mining on the site was explored due to the rising global price of the commodity. The first feasibility study for the site was completed in 1991 and the first permits for developing the deposit were approved the same year. Financing from Imperial Metals however was not yet in place.
Mine opening In 1997, the Mount Polley mine opened with the Cariboo pit being the first site developed. The tailings storage facility was also constructed the same year. In 2010, the underground portion of the mine was built and operations expanded. During a mine closure between 2002 and 2005, a new location called the "Wight pit" was discovered in the northeast region of the site. The Wight Pit was named after former Mine Manager George Wight. The Wight pit is located 1.5 km northeast of the Cariboo and Bell pits and revealed the richest deposit on the site (10 million tonnes of .9% copper). The Wight Pit's distance from the Cariboo pit necessitated new permitting. Subsequent to the discovery of the Wight Pit, after additional underground mining, another site was discovered and developed called "Martel Zone". It was named after former Environmental Coordinator Ron Martel.
Mount Polley tailings pond breach
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