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 has its own spatial and temporal distribution.

The Copper Mountain alkalic porphyry copper-gold camp occurs in the eastern volcanic belt of the Nicola Group, where the volcanic strata are intruded by a suite of Early Jurassic alkalic dykes, sills, irregular plugs, and zoned plutons of the Copper Mountain suite (Cromwell, 2015; Milhalynuk, 2010; Woodsworth et al., 1992). Other than local contact effects from intrusion and alteration associated with mineralization, the stratified rocks are relatively fresh, having undergone zeolite to lowermost greenschist facies metamorphism and minimal deformation.

As with alteration, mineralization is variable throughout the mine area in both form and mineralogy. There is a transition of chalcopyrite-pyrite-magnetite assemblages in the north to chalcopyrite-bornitechalcocite assemblages in the south.

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.

The Copper Mountain Mineral deposits are classified as alkalic porphyry copper-gold deposits. The term recognizes 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. However, there are many features of alkalic porphyry deposits that set them apart from the better-known calc-alkaline porphyry coppermolybdenum deposits.

Mining at the Copper Mountain Mine is by conventional open pit methods, using 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 37 degrees to 52 degrees. Ramps are generally 33.5 m wide.

The mining schedule is based on operating 24 h/d, 365 d/a. The mine operations and mine maintenance departments’ shift schedules are planned to continue to be two 12-hr shifts per day, using four alternating crews.

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 Main pit, North Pit (Alabama), and the Ingerbelle pit. The mine plan uses the designed pit shells 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.

It should be noted that the ultimate pit, the LOM mine production schedule generated by CMMC for the years 2020 to 2041, and the LOM processing schedule generated by CMMC use only Proven and Probable Mineral Reserves (Measured and Indicated Resources converted).

Existing Crushing and Crushed Ore Stockpile
ROM ore is fed to a gyratory 60–89 Metso primary crusher. The dump pocket is located northeast and adjacent to the Copper Mountain Main Pit. Real-time sizing cameras and belt samples show that the product produced by this unit is consistently less than 127 mm. A series of six conveyor belts moves primary crusher product to the secondary crusher, with the option to go directly to the mill feed stockpile if desired.

In August 2014, a double-deck screen and an 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 40 kt/d, plus surplus material to be used for blast hole stemming and as a crushed road base for mining operations.

Grinding
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 pebbles report 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 (13.56 MW).

45 kt/d Expansion
This expansion will install a third ball mill, installed in parallel with the two existing ball mills, allowing for a throughput increase from 40 kt/d to 45 kt/d, and at the same time improving the grind size from 225 µm to 150 µm. The expansion will use existing site facilities and infrastructure to achieve higher performance, and generate additional payable metals at a reduced cost per pound produced.

65 kt/d Expansion
This expansion is an increase to the current site expansions, following installation of the secondary crusher in 2014 and the addition of Ball Mill #3 in 2021. The target grind size is selected based on optimal use of the available equipment.

The existing crushing circuit was analyzed using power calculations and the Metso Bruno V4.10 software tool. The existing 60–89 gyratory crusher and XL2000 secondary crusher were evaluated for power consumption and performance at the increased production rate. The existing MKII 60–89 primary crusher is fitted with a 600-kW motor and operates at 2,200 t/oph. The primary crusher is planned to be upgraded from the MKII to MKIII format ahead of the 65 kt/d project. This will allow for a 1000 kW motor, supporting the new duty point of 3,385 t/oph.

The existing XL2000 secondary crusher currently uses a short-head liner package to achieve the finest product possible for this size of crusher (24 mm) at 2,200 t/oph. The increase in tonnage will require coarsening this product to 38 mm. The existing 3.7 m x 7.3 m secondary crusher screen operates in an open circuit format, with undersize reporting directly to the product stream. At the increased throughput, the available area on this deck may generate a small (2%) reduction in screening efficiency. The current design uses a new, reinforced screen deck which fits in the current footprint, capable of sustaining the required higher throughput rate.

Due to the open circuit format of the secondary crusher, additional equipment will need to be installed to limit oversize material from reporting to the downstream HPGR. The HRC3000 will require a top size of 90 mm. A security screen will be installed on the secondary crushing circuit product to close this loop and limit the top size. Oversized material will report back to the surge pile feeding the secondary screen deck. As the current models indicate that the top size will be 68 mm, oversized material is to be expected only during upset conditions or starting and stopping of the circuit.

The initial phase of the 65 kt/d project evaluated common comminution technologies to find the best fit for the Copper Mountain mill (Ausenco, 2020). To increase throughput from 45 kt/d to 65 kt/d additional energy is needed at both the primary and secondary milling stages of the process. Three scenarios were examined for primary milling, which evaluated how to increase tonnage beyond what the existing SAG mill is capable of. The three scenarios are:
- Existing SAG mill with a new second SAG mill in parallel (Base case)
- Existing SAG mill with a new HPGR in parallel (Option 1)
- A single new large HPGR, capable of processing 65 kt/d (Option 2).

The 65 kt/d flowsheet plans for the installation of a fourth ball mill in the existing grinding area. This is a second 22 ft x 38 ft ball mill with 12.6 MW of installed power, identical to Ball Mill #3 being installed in 2021. All four ball mills are to operate in parallel. The two existing 24 ft x 40 ft, 13.56 MW ball mills will be designated as Line 1, while Ball Mill #3 and the newly added Ball Mill #4, both 22 ft x 38 ft, 12.6 MW, will be designated as Line 2. The HPGR screening plant will generate a 4 mm P80 product that will be pumped to the Line 1 and 2 splitter boxes for distribution to the mills.

The total installed power of the four ball mills in parallel will be 52.3 MW. At a nominal ball charge of 33% and critical speed of 78%, the four mills are expected to draw 46.7 MW of power at the pinion, allowing for a 165 µm product, assuming a 4 mm circuit feed size, and a BWi of 24 kWh/t. All four ball mills will be operated in an overflow format, with rubber liners and 75 mm media.

The fourth ball mill will be installed within the existing grinding bay, between Ball Mills #2 and #3. The existing regrind mill is currently at this location; however, the design assumes that this mill is demolished and replaced with Ball Mill #4. A new regrind mill will be constructed as part of the flotation expansion.

Rougher Flotation
The additional tonnage will require additional rougher flotation capacity. The existing 10x 160 m3 rougher flotation cells will treat half of the total mill throughput, while a new circuit comprising 5x 300 m3 flotation cells will treat the remaining half. These will be designated as rougher flotation Lines 1 and 2, respectively.

Rougher Flotation Line 2 will receive feed from the two existing ball mills, while Rougher Flotation Line 1 will receive feed from the two expansion ball mills. The new cells will be constructed inside the north flotation annex, a new building located at the northeast corner of the existing mill building.

The north flotation annex will be laid out so that rougher concentrate from both Rougher Flotation Lines 1 and 2 will launder by gravity to the regrind cyclone feed pump box. Tailings from Rougher Flotation Line 1 and Line 2 will collect at a new tails collection tank located at the existing Drop Tank 1 on the exis ........