Mount Polley is an alkalic porphyry copper-gold deposit. It lies in the tectono-stratigraphic Quesnel terrane or Quesnellia, which is characterized by a Middle Triassic to Early Jurassic assemblage of volcanic, sedimentary and plutonic rocks which formed in an island arc tectonic setting outboard of the ancestral North American continental margin. Mount Polley itself is a complex of alkalic intermediate porphyritic intrusions and related magmatic-hydrothermal breccias.

In the deposits, the degree of brecciation and associated hydrothermal alteration is usually a reliable guide as to grade. The transition from breccia into unbrecciated intrusion forming the ‘wall rock’ roughly corresponds to ore/waste contacts. There is relatively little post-mineralization dike dilution. Chalcopyrite is the dominant copper mineral, typically accompanied by pyrite; bornite is relatively uncommon in the centre of the MPIC. Here, copper sulfides occur as disseminations or veins and fracture coatings in brecciated intrusion, or they are disseminated in the matrix of breccias, in both cases precipitated along with alteration minerals. This is characteristic of the Springer, Cariboo/C2, and WX zones, and in the now mined-out Bell and Southeast zones. The only significant oxide mineralization in the MPIC is in the upper 100-150 m of the Springer deposit, but it is treatable by heap leach for copper extraction, and can be later milled for gold recovery. Mineralization has been traced by deep drilling in the Springer zone to a depth of around 900 m (from pre-mining surface).

In the north of the MPIC are much higher grade orebodies, namely the Northeast (mined in the Wight pit, 2005-2009) and Boundary zones, where copper grades can reach several percent per tonne and are currently supporting underground mining. Chalcopyrite and significant bornite form coarse-grained infill in breccias, and intense vein and microvein stockworks. As in the zones in the centre of the MPIC, gold and silver occur mainly as microscopic inclusions in the copper sulfides and in pyrite. Throughout Mount Polley, copper and gold typically occur in a roughly 1:1 ratio (in terms of copper percent versus gold in grams per tonne).

Mining Methods - conventional shovel, truck and open pit mine. With a developing underground mine.

Open Pit Mining Equipment
The current open pit mining operation at Mount Polley utilizes a conventional truck and shovel fleet with drilling and blasting prior to excavation. The fleet includes a mixture of diesel and electrically powered equipment for drilling, excavating and dewatering.

Material Handling
Ore mined from the pits is hauled to either the primary gyratory crusher located immediately adjacent to the mill or to nearby stockpiles.

Waste material at Mount Polley occurs in one of two types: non-acid generating waste (NAG), and potentially acid-generating waste (PAG). NAG/PAG designations are made on the basis of the neutralizing potential ratio (NPR) of a given material. This NPR is calculated by performing acid-base accounting (ABA) using carbon and sulfur assays from blasthole cutting samples. Sampling is performed on a one sample per 20,000 tonnes basis. All rock with an NPR less than 2.0 and a sulfur content greater than 0.1% is designated as PAG and stockpiled.

PAG waste is estimated to constitute approximately 27% of the waste tonnage in the life-of-mine plan. PAG waste, as a condition of operating permits, must be submerged for long-term storage at the end of mine life. As such, all PAG rock is selectively mined and temporarily stored in the Northwest PAG Stockpile. This stockpile will be rehandled into the exhausted pits at the end of mine life. NAG waste is hauled to either the southeast rock dump (SERD), or to the Tailings Storage Facility (TSF) for construction purposes.

Pit Slope Design Parameters
Bench heights in the Main Zone are 12m, while the Boundary Zone Pit will be mined with 10m bench heights in waste and 5m spilt benches in ore.

The strength of the overall rock mass around the pits is generally good with the exception of faults and late-stage mafic dykes which can be of poorer quality. Jointing in the rock mass is semi-consistent through different rock units, resulting in pit slope design criteria being dominated by the orientation of the pit face in question, and specifically how this open face interacts with the local jointing regime.

Pit wall design parameters employed for mining at Mount Polley are provided by Golder Associates Ltd., and are based on historical mining experience.

Underground Mining Methods
The Primary Underground mining method at Mount Polley is mechanized long-hole open stoping followed by backfill with cemented rock before mining the next stope.

The three noteworthy zones which are currently being mined or planned to be mined are; the Boundary, Halo and Zuke Zones. The majority of the Mineral Reserve base is contained in the Boundary Zone (81% of the 312,000 tonnes of underground Mineral Reserves).

Ore is crushed in three stages to produce a 16 mm product for the grinding circuit, which is stored in a 15,000 t stockpile. The crushing plant consists of one (1) 42” x 65” gyratory crusher, one (1) 7’ standard cone crusher, three (3) short head cone crushers and four (4) screen decks. Sized rock for the pebble mill is removed from the secondary crusher feed and stored in a 2,000 t surge pile.

In 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, crushed in three stages to produce a product at finer than 16mm for the grinding circuit.

The grinding circuit consists of two parallel rod mill/ball mill circuits and a pebble mill circuit. Crusher product is first split between two rod mills where water is added to form slurries. The slurries are pumped to hydrocyclones that classify the 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 (hydrocyclones) and the particles will not pass to the next grinding stage until they are fine enough to feed the pebble circuit. The second stage grinding circuit (the pebble mill circuit) also consists of mills, pumps and hydrocyclones. Pebbles obtained from the crusher are used as grinding media for grinding. The coarse particles classified by hydrocyclones reports to three pebble mills for further size reduction. The pebble mills are in “close circuit” and product that is sized at 65% finer than 200mesh is fed to the flotation circuit.

Mill and Processing Plant
The mill at Mount Polley was commissioned in June 1997. The mill uses conventional rod and ball mills with a flotation and dewatering circuit to produce a copper /gold concentrate. The mill has a capacity to process 17,800 to 22,000 tonnes per day (tpd) of ore depending on hardness. Mount Polley concentrates are trucked to facilities at the Port of Vancouver and then shipped to overseas smelters.

The flotation circuit separates the valuable minerals from the rest of the crushed rocks. With the addition of reagents, the valuable minerals, mostly in the form of sulphides, are separated by floatation and being collected and upgraded to produce a concentrate. Initial separation is done in a rougher/scavenger circuit, where the remaining minerals are discarded as tailings (which flow by gravity to the TIA). Rougher concentrate is reground in a regrind mill and further upgraded in a cleaner circuit to produce the final concentrate product. Clean ........