Musselwhite is principally an underground gold mine and associated processing plant producing nearly a quarter of a million ounces of gold annually.
The mine is situated in northwestern Ontario, Canada and is 100% owned by Goldcorp Inc.
With existing mineral reserves, the Musselwhite Mine has an expected mine life through to 2018. Gold production for 2009 totaled 233,000 ounces.
Musselwhite began commercial production on April 1, 1997 and by 2001 had poured its one millionth ounce. Today, cumulative production exceeds 1.7 million ounces The area also has excellent exploration potential which may further extend the mine life.
Musselwhite is a fly-in operation with pick-up points in Thunder Bay, Pickle Lake and five northern communities. The mine employs approximately 450 employees and contractors. Musselwhite uses First Nation contractors to provide air transportation and camp services.
The Musselwhite mine is located on the southern shore of Opapimiskan Lake, 480 kilometres by air north of Thunder Bay in northwestern Ontario. The nearest town, Pickle Lake, is 103 kilometres by air to the south. The property consists of a combination of leases and mining claim units covering a total area of 17,548 hectares.
The site is accessed by road from Pickle Lake via the North Road (formerly Highway 808). Approximately 150 kilometres north of Pickle Lake a 43 kilometre all-weather road leads to the mine site. Personnel and some services are flown into the mine which is serviced by a 1,500 metre gravel airstrip.
Musselwhite mine is located within the Weagamow - North Caribou Greenstone Belt of the Sachigo Subprovince, part of the Archean Superior Province. The stratigraphy in the immediate mine vicinity is dominated by mafic volcanics, chemical sediments and felsic volcanics. External to the supracrustal sequences are a series of undifferentiated gneisses and granitoids. All lithologies within the immediate mine area have been metamorphosed at mid to upper amphibolite facies.
Mineralization is predominantly hosted within meta-chemical sediments (banded iron formations) and in particular within garnet-magnetite-grunerite facies meta-banded iron formations (locally termed the Northern Iron Formation). The location of mineralization is controlled by the intersection of D3 shears zones and D2 folded meta-banded iron formations. These geological controls result in mineralized shoots, which plunge at approximately 15 degrees to grid north, have a down dip extent of up to 150 m, down plunge continuation in excess of 1.5 kilometres, and across-lithology width of up to 10 m. Mineralized zones are characterized by abundant pyrrhotite, quartz flooding and, rarely, visible gold.
Mining & Operation
The mining plan for the T-Antiform deposit has evolved considerably from the final pre-construction feasibility study. It now consists of four phases, organized according to depth from surface.
Phase 1 production began in 1997, during which the majority of the mineral reserves from surface to the 275 meter level were mined out at a rate 2,700 tonnes per day.
Phase 2 production, consisting of mineral reserves between the 275 meter level and the 375 meter level, began in 2001. Supplemented by the remaining reserves above the 275 meter level.
Phase 3, consisting of mineral reserves between the 375 meter level and the 500 meter level, began production in July 2002. Development of this phase began in the final quarter of 2001 and continues into 2006.
Phase 4, consisting of the remaining mineral reserves in the T Antiform between the 500 meter level and the 675 meter level, commenced development during the second half of 2003.
Two mining methods are employed in the T-Antiform. Transverse stopes are developed where mining widths are greater than 15 m. Longitudinal retreat mining is employed in areas with widths less than 15 m. Rock mass quality within the deposit is generally good and free of strong jointing and faulting.
PQ Deeps Mining
The mining of the PQ Deeps reserves started during the Phase 4 production in the T Antiform. The PQ Deeps mining will occur between the 570 metre level and the 820 metre level. Mining methods are the same as those used on the T Antiform.
Development of the PQ mineral reserve began in 2003 and production commenced in September 2003. The rate of production from this zone is planned at 550 tonnes per day. The mining methods employed in the PQ zone are conventional long hole and sub level drifting with long hole stopes.
Development towards the Esker zone started in 2004. Production is to begin in late 2006 at a rate of 1,000 tonnes per day. Access development for the Esker zone provides additional benefits serving as part of a ventilation circuit for mining Phase 4 of the T Antiform reserves and the PQ Deeps.
Due to its location beneath the polishing pond and close to the shop and warehouse buildings, production from the Snoppy deposit was originally scheduled for late in the mine life.
Potable water is obtained from Opapimiskan Lake then filtered and chlorinated in a Class II water treatment plant. About 80% of the mill process water is taken from the tailings pond. The balance of the process make-up water is obtained from Opapimiskan Lake.
A 115 kV transmission line from Pickle Lake provides electric power. The line follows the existing highway and the access road to the mine site, for a total length of 190 kilometres. The camp and buildings are heated by propane. Mine ventilation air is also heated by propane to provide an acceptable working environment and to prevent freezing of underground installations.
The milling facility uses two-stage crushing to reduce ore to minus 19 mm and conventional two-stage rod-ball grinding to further reduce ore to 80% passing 106 microns. Two Knelson concentrators extract liberated gold particles that are treated in an Acacia Reactor in an intensive cyanidation process. A high-grade gold-bearing solution reports to electrowinning. Between 26% to 30% of the gold is extracted with this process.
Conventional whole-ore cyanidation is used to further extract gold from the ore. This leaching is done in four stirred-tank reactors. About 93% of the remaining gold is extracted. Gold is recovered from leach solution using activated charcoal or carbon in a six-tank CIP circuit. This process is 99.8% efficient. The tailings or residue from this process is washed with incoming reclaim water in a two-stage counter-current decantation circuit and then treated for cyanide removal using Inco's sulphur dioxide technology. The mill tailing product is discharged to the impoundment containing less than 1.5 mg/L cyanide.
Gold is removed from the gold-laden carbon in an elution column using a caustic-cyanide solution at high temperature and pressure. The resulting gold-bearing solution reports to electrowinning where gold is deposited onto stainless steel cathodes by electrolysis. The combined elution and electrowinning process is 99% efficient. Gold is washed from the cathodes, filtered, dried and melted in a furnace to produce gold metal. Overall, gold recovery from start to finish is 95.5%.