Summary:
The Casa Berardi Property is located in the northern part of the Abitibi Sub province, within the Superior Province of the Archean core of the Canadian Shield. The regional geology is characterized by generally east-west assemblages of isoclinally folded and variably foliated and metamorphosed mafic volcanic rocks, flysch-type sedimentary iron formations, graphitic mudrocks, and a large granodioritic to granitic batholith. Structurally, the Property is within the Casa Berardi Break, a 15km wide corridor of strain that RSI-M0206.22001 11 can be traced over 200km. The Casa Berardi Fault, which strikes east-west and dips 80° to the south, was active during this stage along an unconformity between graphitic sedimentary and volcanic units.
Three principal styles of mineralization have been recognized at Casa Berardi with gold occurring in: 1) quartz veins, 2) stockworks, and 3) banded iron formation. The mineralized zones are closely associated with the Casa Berardi Fault and are found on both sides of the fault. They are restricted to a 500m wide corridor that is folded and plunges slightly to the west.
The grade of gold mineralization associated with veins generally increases with increasing complexity. Quartz phases include: 1) early grey quartz, with abundant sulfide and fluid inclusions; 2) mosaic microcrystalline quartz associated with higher grades; and 3) late non-mineralized coarsely crystallized white quartz. Veins contain only 1% to 3% sulfides, predominately arsenopyrite and pyrite, as well as traces of sphalerite, chalcopyrite, pyrrhotite, tetrahedrite, galena, and gold. Arsenopyrite is the main goldbearing sulfide present in all veins of the Casa Berardi deposit. Stockworks represent nearly the same volume as the large quartz veins. Stockwork mineralization is generally sub-economic, unless they occur in close proximity to larger quartz veins. Gold-bearing banded iron formation is restricted to the highly sheared, brecciated, and altered ferruginous sedimentary units occurring north of the Casa Berardi Fault. Mineralization contains up to 10% chert-magnetite beds, and exhibits high sulfide content which consists of pyrite, arsenopyrite, traces of pyrrhotite, and little or no visible gold.
The Casa Berardi deposit can be classified as an Archean-age, sedimentary-hosted lode-gold deposit. Gold deposits of the Archean Abitibi greenstone belt predominantly consist of epigenetic disseminated and vein-hosted deposits, and syngenetic gold-rich massive sulfides (Robert, et al., 2005; Monecke, et al., 2017). The Casa Berardi gold mining camp contains different styles of mineralization within the same deposit including gold-rich massive sulfides, auriferous pyritic and carbonaceous phyllite and chert, and pyrite-arsenopyrite-gold-quartz veins.
STYLES OF MINERALIZATION
Intense folding and metamorphism, and faulting centered on the Casa Berardi Fault, created favorable ground conditions for the deposition of gold mineralization at Casa Berardi. Hydrothermal fluids accessed the fault zone, which was developed along a 30 Ma to 40 Ma unconformity between the mafic volcanics and the flyschtype sedimentary sequence, deposited the gold mineralization and altered the material in the fault zone to silica and clay.
VEINS
Gold mineralization is largely located in quartz veins, either in the form of multi-meter veins, small-scale veins, or veinlet networks. Veins are heterogeneous and contain a variable percentage of foliated enclaves exhibiting a laminated appearance. Veins are of different color, texture, and structure. Gold grades are generally correlated with increasing complexity. Different quartz phases have been recognized in mineralized veins to exhibit the following sequence:
Phase 1: grey quartz, with abundant sulfide and fluid inclusions, comprising more than 50% of mineralized veins;
Phase 2: mosaic micro-crystalline quartz occurring in higher grade portions of veins; and
Phase 3: non-mineralized coarsely crystallized white quartz which cuts the two other types.
The gold bearing vein filling is rarely massive, but often brecciated, micro-brecciated, or laminated. The fracture planes are rich in graphite and muscovite. Veins contain only 1% to 3% sulfides, predominately arsenopyrite and pyrite, as well as traces of sphalerite, chalcopyrite, pyrrhotite, tetrahedrite, galena, and gold. Arsenopyrite is the main gold-bearing sulfide present in all veins of the Casa Berardi deposit.
STOCKWORKS
Stockworks represent nearly the same volume as the large quartz veins. Stockwork mineralization is generally sub-economic, unless they occur in close proximity to larger quartz veins. Across the deposit, hanging wall stockworks are present in contact with important mineralized quartz veins. From 10% to 20% of the rock volume is composed of centimeter to decimeter-wide quartz veins with grades ranging from 1g/t Au to 10g/t Au. Veins of all textures and composition are concordant with host rocks. Foliated and finely bedded rocks are cut by concordant veins. Less deformed basalts or iron rich rocks subjected to alteration by carbonate-rich fluids, are cut by fracture-controlled vein sets.
At the deposit scale, the primary mineralized areas of the West and East mine have stockworks surrounding quartz cores. The stockworks are not limited to the main Casa Berardi Fault and can affect the total width as meter to decameter-wide mineralized subzones. In the primary mineralized areas of the West Mine, the stockwork extends laterally for 400m at a 50° western plunge.
In the East Mine, the overall mineralized system, including stockworks, extends laterally along the strike of the Casa Berardi Fault for 400m, reaching a depth of 800m down dip (Figure 6-5). The system crosses the Casa Berardi Fault at a low angle over 100m of strike length. Mineralization continues to the west on the south side of the Casa Berardi Fault and to the east on the north side of the fault.
GOLD-BEARING BANDED IRON FORMATION
Gold-bearing banded iron formation (BIF) is found in the 124-8, 124-1, and 116 zones of the Principal area, at the western extension of the East Mine pit in the 148-09 Zone, and at the extension of the East Mine area in the 160 Zone. These zones are restricted to the highly sheared, brecciated, and altered ferruginous sedimentary units occurring north of the Casa Berardi Fault. Mineralization occurs within meter to sub-meter quartz veins and RSI-M0206.22001 47 stockworks with up to 10% chert-magnetite beds, and exhibits high sulfide content which consists of pyrite, arsenopyrite, traces of pyrrhotite, and little or no visible gold. These sulfides have replaced the oxide rich layers which surround the quartz veins and the veinlet stockworks. Strong carbonate and chlorite alteration halos surround the quartz rich areas.