Mount Polley Mine
Mining in 2013 focused on the Springer Phase 3 and the adjacent Cariboo pit. The majority of ore feed was sourced from Springer Phase 3, and the bulk of stripping activities was in the Cariboo pit. Higher copper grade and improved recovery in 2013 resulted in 38.5 million pounds copper production, up 14% from 33.79 million pounds in 2012. Gold production was down due to lower gold grade being treated in 2013 compared to 2012. Both copper and gold recoveries were higher in 2013 as a result of the ore treated being less oxidized.
Mount Polley Annual Production
|Copper - lbs||44.0 M||38,501,165||33,789,600|
|Gold - oz||47,000||45,823||52,236|
|Silver - oz||120,000||123,999||116,101|
Mining in 2014 will continue to focus on the lower benches of the phase 3 Springer pit for ore feed, with approximately 250,000 tonnes of underground ore also being processed. Stripping activity will continue to focus on the Cariboo pit. Mill feed will transition to the Cariboo in the fourth quarter of 2014 as Springer Phase 3 is exhausted near year end.
Underground operations at the Boundary zone are scheduled to deliver approximately 700 tonnes of ore per day to the mill starting in April 2014. This higher grade underground ore is a key reason for the planned increase in copper production in 2014.
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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