Mount Polley Mine
On August 4, 2014 the tailings dam at the Mount Polley mine was breached. Since that time, the mill has been on care and maintenance. The tailings dam breach has resulted in the loss of production at the mine for an indeterminate period of time.
Imperial is incurring costs for rehabilitation and restoration. While the precise costs of rehabilitation and restoration are presently unknown, the Company believes these costs can be managed over time, given the underlying value of the Company's assets, convertible debenture financing, current sources of liquidity, insurance proceeds and the expected cash flow from the Red Chris mine. Options for the resumption of Mount Polley operations are being studied.
Mount Polley mining crews and others have been engaged in response and recovery activities, including securing the remaining tailings within the impoundment, collecting contact water, reducing the water level in Polley Lake, and cleaning up woody debris deposited in Quesnel Lake. A program of rehabilitation and restoration in the areas affected by the breach is underway.
For information on the rehabilitation and restoration progress, refer to Mount Polley Updates.
A geotechnical study is currently underway to determine the root cause of the tailings dam breach. The geotechnical work program includes mapping, geophysical surveys, drilling and test pitting. The expert review panel established by the Province of BC to investigate the root cause of the dam failure is to issue a report by January 31, 2015.
The Company recorded costs of $67.4 million ($43.8 million net of tax) in the September 2014 period related to the tailings dam breach. These costs include $20.3 million incurred for response and recovery as well as initial rehabilitation and restoration activities. The $67.4 million in costs also includes a $47.1 million provision for future costs related to the tailings dam breach, exclusive of estimated insurance recoveries. Insurance recoveries will be recorded when received.
Mount Polley Annual Production
|Jan 1-Aug 4 2014||2013||2012|
|Copper - lbs||24,489,725||38,501,165||33,789,600|
|Gold - oz||25,901||45,823||52,236|
|Silver - oz||74,770||123,999||116,101|
Mount Polley Planned Stock Piles (in gold)
Mount Polley Mill InfrastructureIn the Mount Polley mill, run-of-mine ore from the open pits is hauled to the crusher. The crusher has three stages of crushing involving five crushers, twenty conveyors and four sets of screens. The ore is dumped into the feed pocket of the primary gyratory crusher and the product is discharged to the grinding circuit at finer than approximately 20 mm particle diameter.
The grinding circuit consists of two parallel rod mill/ball mill circuits and a pebble mill circuit. Crusher product is first split between to two rod mills where it has water added to form slurries. The slurries are pumped to cyclones that classify the ore particles by size. The larger particles flow to feed the ball mills while the fine particles are discharged to the second stage of grinding: the pebble mill circuit. The ball mills are in "closed circuit", meaning that the discharge is pumped to the classifying units (cyclones) and the particles will not pass to the next grinding stage until they are fine enough to be classified as such. The second stage grinding circuit (the pebble mill circuit) also consists of mills, pumps and cyclones. Three pebble mills receive the coarse product from the cyclones, fed by pumps. The pebble mills are so named as they use pebbles (rocks obtained from the crusher) for grinding. Particles finer than 200 microns are then pumped as slurry to the flotation circuit.
The flotation circuit separates the valuable minerals from the waste minerals. The particle size reduction described above is imperative to separation as the mineral grains are very fine, with a mean diameter size of 50 microns. The valuable minerals, mostly in the form of sulphides, are separated from waste minerals (gangue minerals) by floating and being collected and upgraded or cleaned to produce a concentrate. Initial separation is done in a rougher/scavenger circuit, where the waste minerals are discarded as tailings (which flow by gravity to the tailings impoundment area). Rougher concentrate is further upgraded in a cleaner circuit to produce the final concentrate product. Cleaner tailings are recycled to the rougher/scavenger circuit.
The concentrate is dewatered in two stages. The thickener houses settling of particles and decanting of process water so that the settled particles forming a sludge has a reduced water content to roughly 35-40% water while pressure filtration further reduces water content to approximately 7.5%. The water removed is utilized as process water. The concentrate is stored in the load-out building and loaded on to 40-tonne trucks for shipping. Mount Polley's copper concentrate is then trucked to facilities at the Port of Vancouver, and shipped to overseas smelters. The principal market for Mount Polley concentrate is Asia. As of December 31, 2012 concentrate sales contracts were in place with three buyers for the purchase of Mount Polley copper concentrate. New concentrate sales arrangements are negotiated as required.
For additional information refer to the Company's Quarter Reports & Annual Information Form.
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