Summary:
From 1955 to 2008, after which the Copper Rand mill site closed, the Chibougamau mining district had produced a total of 55 Mt of ore containing 994,802 t of copper, 120 t of gold, 102 t of silver, and 72,066 t of zinc (Leclerc et al., 2017). Thus, the district is considered as the second largest mining district in the Québec portion of the AGB.
Mineral deposits of the Chibougamau area comprise the following (Guha et al., 1988; Pilote and Guha,2006):
- Synmagmatic Fe-Ti-V and Ni-Cu-platinum group element (PGE) mineralization in mafic-ultramafic layered intrusion;
- Volcanogenic Massive Sulphide deposits;
- Early polymetallic (Au-Ag- Cu-Zn-Pb) mineralization;
- Porphyritic Cu-Au ± Mo;
- Cu-Au veins in northwest-southeast and east-west shears (Chibougamau-type copper-gold); and
- Shear zone-hosted.
Corner Bay and Cedar Bay.
The Corner Bay and Cedar Bay deposits are examples of Chibougamau-type copper-gold deposits, which typically host massive to semi-massive pyrite-chalcopyrite-pyrrhotite-sphalerite-molybdenite sheared quartz veins. The main alteration assemblage consists of quartz, carbonate, sericite, chlorite, and K-feldspar with occasional albitization locally.
The Chibougamau-type deposits host copper-gold vein mineralization and are spatially associated with the Chibougamau Pluton, which hosts the Devlin deposit. The nearby DLC hosts the Corner Bay and Cedar Bay deposits as well as several other regional copper-gold deposits. They demonstrate several characteristics of “Magmato-Hydrothermal Systems”, including: 1) hydrothermal alteration located in and around an intrusion; and 2) oxidized, high-salinity fluids and the related alteration minerals, e.g., K-feldspar and magnetite. (Mathieu et Racicot, 2019).
Devlin.
Kavanagh (1978) first proposed that Devlin may represent a distinct, late Archean porphyry-like mineralization event. Guha et al. (1984) also suggested that Devlin was a near-surface expression of a porphyry system.
Devlin is a copper-rich veins-hosted deposit in a polygenic igneous breccia. These types of deposits are structurally controlled and occur in faults, fault systems, and vein-breccia zones. Vein copper deposits tend to be relatively small. Copper grades are typically 1% to 3% although some deposits contain greater than 10% copper. Two main sub-types are recognized: 1) associated with mafic intrusions (Churchill type); and 2) associated with felsic and intermediate intrusion.
The Devlin deposit falls into the felsic and intermediate intrusion sub-type along with deposits of the Rossland camp in British Columbia and the copper-gold deposits of the Chibougamau and Opemiska mining camps in Québec.
Felsic and intermediate intrusion copper deposits characteristically occur in subduction-related continental and island arc settings, typically in areas of high-level felsic and intermediate intrusions and particularly those related with porphyry copper deposits. The Devlin deposit is in a different geological setting as it was emplaced in an Archean intermediate intrusion.
Joe Mann.
The Joe Mann deposit is categorized as a greenstone-hosted quartz-carbonate vein deposit, a sub-type of lode-gold deposits. Greenstone-hosted quartz-carbonate vein deposits correspond to structurally controlled, deformed to folded deposits hosted in metamorphosed terranes (Dubé and Gosselin, 2007; Gaboury, 2019). They can coexist regionally with iron formation-hosted vein and disseminated deposits as well as with turbiditic-hosted quartz-carbonate vein deposits.
Greenstone-hosted quartz-carbonate vein deposits consist of simple to complex networks of gold-bearing, laminated quartz-carbonate fault-fill veins in moderately to steeply dipping, compressional brittle-ductile shear zones and faults with locally associated shallow-dipping extensional veins and hydrothermal breccias. They are hosted by greenschist and formed at intermediate depth in the crust (5 to 10 km). They are distributed along deformed greenstone terranes of all ages, but are more abundant and significant, in terms of total gold content, in Archean terranes (Robert and al., 1990).
Corner Bay and Devlin are located at the northeastern extremity of the Abitibi subprovince in the Superior province of the Canadian Shield and are examples of Chibougamau-type copper-gold deposits. The Abitibi subprovince is considered as one of the largest and best-preserved greenstone belts in the world and hosts numerous gold and base metal deposits.
The Corner Bay deposit is located on the southern flank of the Doré Lake Complex (DLC). It is hosted by a N 15° trending shear zone more or less continuous with a strong 75° to 85° dip towards the west. The host anorthosite rock is sheared and sericitized over widths of 2 m to 25 m. The deposit is cut by a diabase dyke and is limited to the north by a fault structure and to the south by the LaChib deformation zone.
The Corner Bay deposit consists of three main mineralized veins (subparallel Main Vein 1 and Main Vein 2 above the dyke, and Main Vein below the dyke that make up the bulk of the deposit, and four other parallel smaller veins (three West Veins and East Vein). The Corner Bay deposit has been traced over a strike length to over 1,100 m to a depth of 1,350 m and remains open at depth.
The mineralization is characterized by veins and/or lenses of massive to semi-massive sulphides associated with a brecciated to locally massive quartz-calcite material. The sulphide assemblage is composed of chalcopyrite, pyrite, and pyrrhotite with lesser amounts of molybdenite and sphalerite. Late remobilized quartz-chalcopyrite-pyrite veins occur in a wide halo around the main mineralization zones.
Devlin is a flat-lying, copper-rich veins-hosted deposit in a polygenic igneous breccia that is less than 100 m from the surface. The tabular bodies have been modelled as four nearly horizontal veins: a more continuous lower zone and three smaller veins comprising the upper zone. Mineralization is reflected as a fracture zone often composed of two or more sulphide-quartz veins and stringers. Thickness of the mineralized zones range from 0.5 m to 4.4 m. It has been diluted during modelling to reflect a minimum mining height of 1.8 m.
The Joe Mann deposit is characterized by east-west striking shear hosted veins that extend beyond 1,000 m vertically with mineralization identified over a 3 km strike length. These shear zones form part of the Opawica-Guercheville deformation zone, a major deformation corridor cutting the mafic volcanic rocks of the Obatogamau Formation in the north part of the Caopatina Segment. The gabbro sill hosts the Main Zone and the West Zone at the mine, while the South Zone is found in the rhyolite. These three subvertical E-W (N275°/85°) ductile-brittle shear zones are subparallel to stratigraphy and to one another, with up to 140 m to 170 m of separation between them. These shear zones are hosted within a stratigraphic package composed of iron-magnesium (Fe-Mg) carbonate and sericite altered gabbro sills, sheared basalts, and intermediate to felsic tuffs intruded by various felsic intrusions. The Joe Mann gold mineralization is hosted by decimetre scale quartz-carbonate veins (Dion and Guha 1988). The veins are mineralized with pyrite, pyrrhotite, and chalcopyrite disposed in lens and veinlets parallel to schistosity, and occasionally visible gold. There are some other minor, mineralized structures, e.g., North and South-South Zones, with limited vertical and horizontal extensions.