Mineralization at Copper Mountain is classified as an alkalic porphyry deposit. Although there are several areas that have been mined separately over time, both alteration and lower-grade mineralization occurs between these areas, and all mineralization is thought to be part of a large, single system.

As a generalization, mineralization at Copper Mountain consists of structurally controlled, multidirectional veins and vein stockworks, with peripheral disseminations. Mineralization had been subdivided into four types, as follows: 1) disseminated and stockwork chalcopyrite, bornite, chalcocite, and pyrite in altered Nicola and LHIC rocks; 2) hematite-magnetite-chalcopyrite replacements and/or veins; 3) bornite-chalcopyrite associated with pegmatite-like veins (coarse masses of orthoclase, calcite, and biotite); and 4)chalcopyrite-bearing magnetite breccias.

Each mineralization type can be found in all pit areas, but each pit is unique with respect to the relative quantities and character of mineralization type. Both mineralization and alteration demonstrate a zonation through the camp, though not in a manner typically associated with calc-alkaline porphyry deposits. Three main types of alteration have been defined: hornfels, sodic, and potassic, each with its own spatial and temporal distribution.

The Copper Mountain alkalic porphyry copper-gold camp is part of a northerly-trending Mesozoic tectonostratigraphic terrane termed the Quesnel Terrane (or Quesnellia). It comprises a volcanic arc with overlying sedimentary sequences, which were built on top of a deformed, oceanic sedimentary-volcanic complex (Harper Ranch and Okanagan sub-terranes). The Quesnel Terrane was formed off-shore of the southwest of continental North America and accreted with other terranes onto North America in late Mesozoic times (Monger et al., 1992). The Nicola Group, a thick (7,000 m), Late Triassic succession of volcanic, sedimentary, and coeval intrusive rocks (Preto, 1972, 1979), underlie most of southern Quesnel Terrane.

The Eastern Belt of the Nicola Group includes the oldest rocks in the Copper Mountain camp. Within the mine area, a clear stratigraphic succession has not been defined due to extensive faulting and alteration, and probable rapid facies changes within the volcanic rocks. Dark green to black augite-porphyry flows, breccias, and possible tuffaceous material composes most of the rock types exposed in the mine area. A very fine-grained, laminated unit, referred to as a volcanic siltstone (VSLT), forms a distinct horizon (or possibly a few horizons) in the mine area. The VSLT is usually grey, but can be pale green to mauve in colour, and resembles chert. However, whole rock analyses indicated approximately 50% SiO2, and the unit is interpreted to be water lain volcanic ash and silt.

The Copper Mountain Mineral deposits are classified as alkalic porphyry copper-gold deposits. The termrecognizes the alkaline nature of the intrusive rocks associated with mineralization, where silica content is low relative to the alkali metals, sodium, and potassium. The intrusive rocks almost always have porphyritic textures, and the deposits are bulk minable. There are, however, many features of alkalic porphyry deposits that set them apart from the better known calc-alkaline porphyry copper-molybdenum deposits.

Alkalic porphyry deposits are relatively rare globally, and British Columbia contains some of the best examples within the Quesnel Terrane. Three mines (Copper Mountain, Afton-Ajax, and Mount Polley) and several other deposits and prospects form an extensive belt, stretching northwards for more than 1,000 km, with similar age and mineralization characteristics, although each deposit has its own unique features.

Alkalic porphyry deposits are markedly different from their calc-alkaline cousins, even within the samemgeological terrane, and share more similarities with iron-oxide-copper-gold (IOCG) deposits of Australiamand Chile. The distinguishing features of the British Columbia alkalic porphyry deposits include:
•Multiple deposits within a camp area
•Mineralization temporally and spatially associated with alkaline or sub-alkaline intrusions
•Early, extensive, and widespread sodic-calcic alteration
•Focused potassic alteration spatially correlated with copper and gold (±silver) mineralization
•Limited or no quartz-sericite alteration
•Structurally-controlled emplacement of mineralization as breccias, fracture fill, veins, and disseminations within both the causative intrusions and surrounding country rock
•Generally low sulphide systems, leading to presence of lower sulphur copper minerals (bornite and chalcocite), and low pyrite relative to copper sulphide and iron oxide minerals
•Abundant late carbonate alteration (calcite veining).

The low-sulphur nature of the mineralization and abundant carbonate alteration in alkalic porphyry deposits results in mines that have much lower probabilities of producing acid-generating waste rock.

Mining at the Copper Mountain Mine is by conventional open pit methods, utilizing a 15-m bench height. The major components of this mining method are blasthole drilling, blasting, loading, and hauling. Pit walls are designed to geotechnical specifications and vary in slope angle depending upon lithology, alteration, and local ground conditions, with bench face angles of 70 degrees to 73 degrees, and berms of 9 m to 14 m, resulting in inter-ramp pit wall angles that range from 45 degrees to 52 degrees. Ramps are generally 33.5-m wide.

Mining is done on a 24 h/d, 7 d/week basis, and the mining rate varies from 150 kt/d to 200 kt/d, depending on haulage distances, ore:waste ratios, equipment availabilities, and other factors. The current long-term mine plan was generated from pit design phases based on the optimized pit shells and Mineral Reserve block models from the Copper Mountain Mine pit, Alabama pit, and the Ingerbelle pit.

The mine plan uses the optimized pit shell to generate a schedule that maximizes the use of the mining fleet and provides a balance between ore and waste rock movement with a steady supply of mill feed material. The overall CMM mine plan is similar to the plan originally envisioned in the 2009 Prefeasibility Study as a series of pushbacks on the existing pits. The sequencing of the pushbacks has been modified to provide better efficiencies in mining (strip ratio) and milling (ore hardness).

The Copper Mountain Mine mill uses a simple processing flowsheet composed of primary and secondary crushing, and semi-autogenous ball mill, pebble crushing (SABC) grinding, followed by a sulphide rougher/cleaner flotation circuit.

ROM ore is fed to a gyratory 60-in by 89-in Metso primary crusher. The dump pocket is located northeast and adjacent to Pit 2. Real-time sizing cameras and belt samples support that the product produced by this unit is consistently below 127 mm. A series of six conveyor belts moves primary crusher product to the secondary crusher, or directly to the mill feed stockpile if desired.

In August 2014, a double-deck screen and a XL2000 secondary cone crusher were commissioned as part of a throughput upgrade. This crusher is fed by a 500-t surge stockpile, and can produce 24 mm mill feed.

Together, the primary and secondary crushers operate at 80% operating time, and can produce enough finely crushed material to satisfy the current milling schedule within the mine plan, plus surplus material to be used for blast-hole stemming and as a crushed road base for mining operations.

The grinding circuit is designed as a traditional (SABC) flowsheet. The semi-autogenous grinding (SAG) mill is a 34 ft by 17 ft effective grinding length (EGL) dual pinion mill with 13.56 MW of installed power. This mill operates in a closed circuit with a 12 ft by 28 ft vibrating screen, where oversized ore reports to an FLS XL900 cone crusher, with product returning to SAG feed.

The SAG is followed by two 24 ft by 40 ft ball mills operating in parallel. The ball mills are also dual pinion with identical variable frequency drive and motor installations, the same as the SAG mill (12.7 MW original to 13.5 MW upgraded). The ball mills are currently rated for a lower installed power; however, they are scheduled to be upgraded in a similar manner to the SAG in 2019.

The ball mills product is sent to the rougher flotation circuit, where it is treated by two banks of five OK 160 m3 mechanically agitated tank cells. Rougher concentrate is pumped to a 14 ft by 28.5 ft regrind mill for further liberation.

Flotation and Regrind Circuits
In August 2018, a new flash flotation circuit was installed to process a portion of regrind cyclone underflow. This circuit comprises an SK240 flash flotation cell followed by a TC5 cleaner cell. The intent of the circuit is to remove coarse liberated material to final concentrate, creating additional rougher mass pull capacity, while preventing unnecessary overgrinding, which historically resulted in gold losses.

Regrind cyclone overflow is pumped to two, 3.7 m diameter by 12 m high column cells for upgrade to final concentrate. In February 2018, these column cells were upgraded with a dynamic sparger system intended to improve fine particle and overall unit metal recovery.

In July 2019, a new second cleaner flotation circuit was installed to process flotation column concentrate. This comprises three 1.9 m direct flotation reactor (DFR) cells. This increased the final concentrate grade from 25% to 28% Cu while maintaining current levels of cleaner circuit performance.

Tailings from these columns are sent to a bank of five TK-70 m3 cleaner-scavenger tank cells. Concentrate from these cells reports back to the regrind cyclone feed pump box for further liberation. Tailings from this bank is joined by rougher tailings and reports to the TMF.

By means of smaller pump upgrades, the installation of the flash circuit, and column cell sparger upgrades, the cleaner circuit capacity has improved, allowing for higher mass pull despite the increased throughput compared to the original flowsheet design.

Gold and silver are recovered as by-products in the final copper concentrate. The historical relationships indicate that recoveries of both metals have a relationship with copper recovery, supporting an association with chalcopyrite.

Concentrate Handling
The dewatering circuit comprises a 16 m diameter, high-rate concentrate thickener, followed by a concentrate storage tank with 24 hours of capacity and a filter press containing 62 plates, each plate measuring 1.5 m by 1.5 m. Filter cake concentrate drops into a storage shed with seven days of storage capacity. Concentrate is loaded into concentrate highway trucks and trucked to the port in Vancouver to be loaded onto vessels bound for Asian smelters.

The introduction of the flash circuit has provided the indirect benefit of additional filtering capacity by means of sending coarse material directly to the dewatering circuit. This coarse concentrate filters faster, and has allowed for more capacity at the dewatering circuit.