The Gibraltar mine is a large calcalkaline copper-molybdenum porphyry deposit located about 10 km north of McLeese Lake, British Columbia, and hosted by tonalite of the Late Triassic Granite Mountain batholith.

The Gibraltar Mine is a bulk tonnage, low-grade copper-molybdenum deposit concentrated along hydrothermally altered shear zones within the Granite Mountain Batholith along the west slope of Granite Mountain. It is one of the lowest grade base metal deposits ever mined in British Columbia. It is also the first in the province to have the majority of its initial production from supergene ore.

Copper-molybdenum mineralized rocks at Gibraltar have been mined from four open pits, the Gibraltar East (093B 012), Gibraltar West (093B 007), Granite Lake (093B 013) and Pollyanna (093B 006) (Figure 4). The ore bodies mined form part of a semi-continuous, anastomosing mineralized shear zone up to 100 metres or more in thickness, that parallels the strike of the regional foliation. The shear zone and associated mineralization are affected by broad open folding and display a geometry similar to that described previously for the regional foliation. Sulphide mineralization develops within or marginal to the more schistose zones, and fades out into the more massive, less foliated quartz diorite, with mineralization confined largely to the foliation surfaces and narrow mineralized veinlets (Simpson, 1970). The best mineralization is found towards the center of the mineralized belt of schistose rocks. The main ore minerals are chalcopyrite, chalcocite (supergene) and molybdenite. Pyrite is common in both ore and peripheral alteration zones and also forms an extensive halo with a few percent pyrite that envelopes the mineralized shear.

The Gibraltar deposits have been developed using open pit mining methods since the commencement of mining on site in 1971.

Current and future mining operations will be carried out utilizing conventional open pit mining equipment. The waste and ore are mined utilizing five electric blast hole drills, five electric rope shovels, one large front end loader and 26 haul trucks. The main mining fleet is supported by a fleet of ancillary equipment including track and rubber tired dozers, motor graders as well as sand and water trucks. The reserve mine plan does not require the purchase of any additional mine production equipment.

The processing facilities at Gibraltar mine consist of two separate bulk sulphide concentrators, a dedicated molybdenum flotation plant, and a series of leach piles which feed a solvent extraction and electrowinning (SX/EW) facility.

Sulphide ore is processed at a design rate of 85,000 t/day through two bulk concentrators to produce a concentrate which contains both copper and molybdenum values. The bulk concentrate from both facilities is combined and processed through a single molybdenum flotation plant. The molybdenum concentrate from this plant is dewatered and bagged, and subsequently shipped to market. The tailings from this plant are the site’s final copper concentrate. This copper concentrate is dewatered and shipped in bulk to market.

Oxide ore from the mine is delivered to oxide leach dumps and heap pads. The Solvent Extraction and Electrowinning (SX/EW) plant is designed to extract copper from the pregnant leach solutions (PLS) collected from the site’s leach dumps and heap leach pad. Copper is extracted from the copper oxide ores by using a grid solution system to deliver an acid containing stream from the plant called raffinate to the leach dumps and heaps. As this acidic material passes through the leach heap, it extracts copper in the form of copper ions in this pregnant leach solution.

The PLS is delivered to the SX/EW plant via collection ditches, ponds and pumping where required. The process takes PLS and extracts the copper ions in three extraction mixer-settlers. The copper is extracted via a liquid ion-exchange reagent carried in kerosene. A chemical reaction selectively causes the copper to transfer to the organic phase. The loaded organic phase is separated and flows to a strip mixer-settler where the copper is transferred from the organic to the electrolyte. The electrolyte is filtered and heated before being passed through the electrowinning cells where the copper is plated out on stainless steel cathodes. Once a sufficient amount of copper has plated out of solution, the cathodes are removed from the cells, washed, and the copper sheets mechanically harvested. The resultant high quality cathode copper is bundled and sold.

The barren solution leaving the plant, raffinate, is pumped back to leach additional copper from the stacked ore.