Mount Polley mine
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 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 of property near Quesnel Lake and Polley Lake where it has mining leases and operations on and mineral claims on. 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
, 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. 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
The Mount Polley mine's tailings facility experienced a dam breach and tailings spill that began 4 August 2014. The four square kilometre tailings pond spilled an estimated 25 billion litres of contaminated materials into Polley Lake, Hazeltine Creek, Quesnel Lake, and Cariboo River, a source of drinking water and major spawning grounds for sockeye salmon. Quesnel Lake is claimed to be the deepest fjord lake in the world, the third deepest lake in North America, and is the major tributary of the Fraser River.According to Mount Polley mine records filed with Environment Canada in 2013, there were “326 tonnes of nickel, over 400 tonnes of arsenic, 177 tonnes of lead and 18,400 tonnes of copper and its compounds placed in the tailings pond,” in 2012.
By 8 August the sized tailings pond had been emptied of the majority of "process water" from which the crushed rock solids, or "tailings", gradually settle out. The slurry of tailings and process water carried felled trees, mud and debris and wore away the banks of Hazeltine Creek which flows out of Polley Lake and continued into the nearby Quesnel Lake. The spill emptied the tailings pond and caused Polley Lake to rise by.
Effects of spill
Early reactions to the tailings spill expressed grave concern, but no fines or charges against Imperial Metals have been assessed.On August 6, two days after the breach, the British Columbia Ministry of Environment issued a Pollution Abatement Order to Mount Polley Mining Corporation. The company submitted an action plan for the Preliminary Environmental Impact Assessment, environmental monitoring. The company was required and did report weekly on the implementation of action plan measures.
A local state of emergency in nearby communities was initially declared in the interest of public safety with widespread water restrictions implemented and local equitable water distribution set up as a precautionary measure. Days later, some water use restrictions were removed for non-local residents, leaving a boiling water advisory, and narrowing the "Do Not Use" order to Polley Lake, Hazeltine Creek, and an area within of the shoreline sediment deposit, where Hazeltine Creek runs into Quesnel Lake. Initial tests at five testing sites of the second water test run indicated zinc levels above chronic exposure limits for aquatic life, although rainbow trout toxicity test results from water collected at Quesnel Lake near the mouth of Hazeltine Creek on August 5 and 6 showed water was not toxic to rainbow trout.
Some tourism businesses in the adjacent surrounding areas remained open. Because the affected water system is salmon-bearing, there was a temporary closure of part of the Chinook salmon fishery by Fisheries and Oceans Canada. Complaints were filed with B.C.'s privacy commissioner regarding the release of environmental assessments and dam inspection reports after journalists found a report from 2010 and assessments from 1992 and 1997 in the public domain, the B.C. government has withheld subsequent reports. Following the event, some First Nations activists held protests and set up blockades. Several local landowners and business operators affected by the spill have launched legal challenges to seek compensation for damages.
Investigation and cause of spill
On 18 August 2014, the British Columbia government ordered an independent engineering investigation into the pond breach and a third-party review of all 2014 dam safety inspections for every permitted mine's tailings pond in the province. The report found that the tailings dam collapsed because of its construction on underlying earth containing a layer of glacial till, which had been unaccounted for by the company's original engineering contractor.The report investigated whether the piezometers measuring the water pressure on the dam had been located correctly, as the last readings, 2 August 2014, did not show any changes in the water pressure. In 2010, Mount Polley Mining Corporation's engineering firm reported a crack in the earthen dam while working to raise it, and that piezometers were broken, which were later fixed.
In 2018, three engineers who worked on the tailings storage facility were charged by their professional association with negligence or unprofessional conduct.