Commodities: Copper (Cu) and molybdenum (Mo)
Location: 75 km northwest of Williams Lake, near the small town of McLeese Lake, BC.
Geology and Type of Deposit: Gibraltar is located in the Intermontane region of the Canadian Cordillera. The ore deposit is a low-grade copper-moly porphyry. It occurs in seven mineralized zones within a Late Triassic (204 +/- 6 Ma) diorite pluton. The ore minerals include chalcopyrite, molybdenite, bornite and cuprite. These minerals are scattered widely through the host rock, and are concentrated locally in shear zones and veins.
The Operation: This ore deposit was first discovered in 1910. Focused exploration in the 1960s led to the construction of the mine in 1972. It operated from 1972 to December 1993, when it shut down due to low copper prices. Mining resumed in 1994 and continued until early 1999 when low copper prices again forced the mine to cease operations.
Taseko Mines purchased Gibraltar Mine in 1999 and brought it back into production in 2004. Currently, 130,000 tonnes of ore are mined each day, 85,000 tonnes of which feed the mill. In 2016, Gibraltar Mines produced 123 million lbs. of copper, and 740,000 lbs. of molybdenum. Based on current production, and proven and provable reserves, the mine will continue operating until 2038.
Mining Method: Mining is carried out using conventional open pit methods. Blasting is done 2-3 times a week. Blasted ore is loaded by electric shovels into haul trucks that transport the ore about 2.4 km to a crusher near the mill. Waste rock is hauled to waste rock dumps. Rock that contains oxidized copper mineral ore is hauled out of the pit to a stockpile.
Processing: Crushed ore is conveyed into the mill at a rate of ~85,000 tonnes per day. The ore first enters the ball mill circuits which pulverize the ore to sand. From the ball mills, the slurry is piped into flotation cells which float a mixed copper and molybdenite concentrate, which is piped to a second flotation circuit where the molybdenite and copper concentrates are separated. These concentrates pass through a thickener before being dried. Tailings that settle out of the flotation cells are piped ~4.8 km from the mill to the man-made tailings pond. The water is returned to the mill to be reused again in the milling processes.
Refining Process: From 1986 until 1999, Gibraltar also operated a SX/EW (solvent extraction electro-winnowing) plant on site to recover cathode copper (99.99% pure) from copper oxide minerals, namely azurite, malachite, chalcocite and cuprite. The process involved dissolving these minerals in sulphuric acid with the help of naturally occurring bacteria in outdoor piles of waste rock, followed by electroplating the dissolved copper metal from the acid in the enclosed refinery building. Gibraltar's SX/EW plant produced 38,430 tonnes of cathode copper in 13 years. The facility was refurbished in 2007 and is once again producing copper cathode at a rate of 1.1 million kg per year.
Markets: Copper concentrate produced at Gibraltar is hauled 20 km by truck to MacAllister Siding on the BC Rail line, located ~6 km north of McLeese Lake. From there it is transported to Vancouver Wharves in North Vancouver, where it is loaded onto bulk carriers and shipped to Asian smelters. Some rail cars transport the concentrates to smelters at Horne Mine in Noranda, Quebec or the Kidd Creek Mine in Timmins, Ontario.
Community and Employment: Gibraltar is the second largest open pit copper mine in Canada, and employs 650 people. Most employees live in and around Williams Lake, BC.
Environmental Considerations: Gibraltar Mine lies in the heart of BC's Cariboo Chilcotin plateau, a high interior region of mixed coniferous forests and grasslands. It is home to many different types of wild animals, deer, moose, caribou, black bears, wolves, as well as livestock. Gibraltar's reclamation plan is to return the site for use as wildlife habitat and rangeland. Final details have not been mapped out, but so far grass and legume vegetative covers have been established on disturbed land to immediately control wind erosion and provide forage.
So far, 445 hectares out of the 1,860 hectares disturbed, have been reclaimed. Research continues to determine the most successful methods. Successful reclamation on inactive Waste Dump #6 over a 2-year period involved reducing the slope angle, capping with a glacial till overburden, and planting a combination of grasses and clovers. Once the vegetation protected the surface from erosion, test plots with 17 different of native shrubs and trees (e.g. maple, alder, Saskatoon Berry, birch, juniper) were established. A selection of other fast-growing grasses and other legumes were successfully used to rapidly re-vegetate sandy tailings and reduce wind erosion on the dam and edge of the tailings pond.
BCMEM's Gibraltar MINFILE profile.