The Casa Berardi gold deposit can be classified as an Archean sedimentary-hosted lode gold deposit. Iron formations and iron rich sediments are present near the base of the sequence and appear on both sides of the Casa Berardi Fault zone. The presence of sulphur and iron in the environment is a factor which is highly favourable for gold mobilization.

Gold mineralization is essentially located in quartz veining, either in the form of plurimetric veins, small-scale veins, or veinlet networks. Veins are heterogeneous and contain a variable percentage of foliated enclaves showing a laminated appearance. Veins are of different colour, texture, and structure. Gold grades are generally correlated with increasing complexity. Different quartz phases have been recognized in mineralized veins to show the following sequence:
Phase 1: grey quartz, with abundant sulphides and fluid inclusions, comprising more than 50% of mineralized veins.
Phase 2: mosaic micro-crystalline quartz occurring in higher grade portions of veins.
Phase 3: non-mineralized coarsely crystallized white quartz which cuts the two others.

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 minor sulphides (1% to 3%), including mainly arsenopyrite, pyrite, and traces of sphalerite, chalcopyrite, pyrrhotite, tetrahedrite, galena, and gold. Arsenopyrite is the main gold bearing sulphide present in all veins of the deposit.

The granulometric distribution of gold is similar for all locations. According to petrographic compilations, 50% of the gold particles have an average diameter less than 30 µm, and approximately 3% are > 100 µm. The gold distribution inside the mineral assemblage varies slightly according to the mineralized zones. In the West Mine area and 113 Zone, the vein mineralization, which is related to the Casa Berardi Fault, shows that gold is mostly free and in contact with arsenopyrite grains (< 10 µm to 0.5 mm). Arsenopyrite is associated with sphalerite and tetrahedrite in clusters, joints, and in micro-brecciated areas. In the South West Zone, the Principal Zone, and some areas of the East Mine, where the mineralization is not related to the Casa Berardi Fault, the gold distribution is variable and depends on the amount of sulphides in quartz veins and host rocks. Fifty percent (50%) of gold grains that have been observed are inclusions in pyrite and arsenopyrite crystals.

In the West Mine, an albite-sericite assemblage is observed in metasomatized ultramafic dykes below the 400 m level. Those dykes, enclosed in graphitic mudrocks, are associated with the gold bearing quartz vein system. Sulphidation is an important part of the mineralization process in iron environments, such as the carbonated chert-magnetite iron formations and primary massive pyrite lenses in Zone 25-8, where magnetite is pervasively replaced by pyrite with coeval arsenopyrite crystallization.

Stockworks are the second style of gold mineralization in the deposit and represent nearly the same volume as the large quartz veins. The stockworks are low grade and largely unexploited. Across the deposit, hanging wall stockworks are present in contact with important mineralized quartz veins. Between 10% and 20% of the rock volume is composed of centimetre- to decimetre-thick quartz veins with gold values ranging from 1 g/t to 10 g/t. 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 heavily carbonated iron-rich rocks are cut by fracture-controlled vein sets.

At the deposit scale, the Principal Zone and the East Mine zone areas correspond to the stockworks surrounding quartz cores. The stockworks are not limited to the fault and can affect the total width of the deformation zone. They appear as a superposition of metre to decametre wide mineralization subzones.

In the Principal Zone, the stockwork extends laterally for 400 m at a 50° western plunge. In the East Mine, the mineralized system extends laterally also for 400 m, reaching a depth of 800 m down the dip (Figure 9-2). The system crosses the Casa Berardi Fault at a low angle over a 100 m stripe. Mineralization continues laterally westward on the south side of the fault and eastward on the north side of the fault.

The project consists of an underground mine and the East Mine Crown Pillar open pit mine. The underground mine has two shafts; the West Mine shaft reaching a vertical depth of 1096 meters, and the unused East Mine shaft located 4.3 kilometers to the east, and going down to a vertical depth of 379 meters. A system of declines and drifts connecting both shafts provide access and underground services to ore zones.

The underground mine at Casa Berardi is a trackless mine accessed by declines and a shaft, which produces approximately 2,300 tons of ore per day. The mining methods are longhole transversal stoping in 10 metres or more mineralization width, and longitudinal retreat stoping in narrower ore bodies. The mineralized zones put in reserves are of varying thickness, ranging from a few tenths of meters to 3 metres, which is the minimum mining width. Most of the hanging walls are sub-vertical (55° to 85°), with typically the graphitic Casa Berardi fault at the footwall.

Stripping and development of the EMCP pit is planned to take place over five stages. The first stage was completed in the first half of 2016, and processing of ore from the EMCP pit began in July 2016. Stripping and development has been ongoing. The EMCP pit, as currently designed, is a smaller scale operation using conventional open pit mining methods, and is expected to run for approximately 5.5 years of production. The average amount of material to be moved every six months is anticipated to be approximately 160,000 to 260,000 tons of ore, with variable quantities of waste.

The Principale Zone open pit, as currently designed, would be mined using conventional open pit mining methods. The Principale Zone open pit is expected to commence production after the EMCP pit is depleted and to run for approximately 4 full years of production. The average amount of material to be moved every six months is expected to approximate 450,000 tons of ore, with variable quantities of waste.

Ore is hauled by truck from the West Mine headframe complex to the crusher dump pocket. A reciprocating feeder under the dump pocket meters the ore into a jaw crusher. The ore is crushed to approximately 5.5" (140 mm), and fed to a semi-autogenous (SAG) mill.

The SAG mill operates in closed circuit with a sizing screen. The screen oversize material is returned to the SAG mill for further reduction, and the screen undersize is sent to primary and secondary cyclones.

Cyclone underflow is diverted and equally split to two parallel gravity circuits. Each circuit is comprised of a vibrating screen and a Knelson gravity concentrator. The gravity concentrates are leached in an intensive cyanidation reactor (Inline Leach Reactor, or ILR). The pregnant solution from the ILR unit reports to the surge tank and to the electrowinning circuit for gold recovery, and the tail reports to the discharge ball mill pump box.

Samplers cut representative CIL feed and tailings samples. Process air is added to each CIL tank. Cyanide solution is added to the first CIL tank as required.

Regenerated and fresh carbon is supplied by batch to the #7 CIL tank and advanced from tank to tank counter current to the slurry flow. Loaded carbon from the #1 CIL tank is pumped to a loaded carbon wash screen to remove any residual cyanide solution. Oversize carbon from the loaded carbon wash screen flows by gravity to a loaded carbon surge bin. The loaded carbon screen undersize returns to the # 1 or #2 CIL tank.

Loaded carbon from the surge bin is transferred to the stripping vessel. Hot barren solution is pumped through the stripping vessel to remove the gold from the carbon. The solution exiting the top of the stripping vessel is defined as a pregnant solution containing gold in solution. To maintain the required volume and strength of the barren solution entering the stripping vessel, caustic and cyanide are added as required.

After stripping, the carbon is transferred to a regeneration circuit where organic contaminants are removed from the carbon by heat in a carbon regeneration kiln. Carbon is discharged from the kiln into a quench tank. Quenched carbon is educted to the sizing screen. Fresh carbon from an attrition tank is also fed to the sizing screen.

Regenerated carbon is pumped to the #7 CIL tank to maintain the required carbon loading in the CIL circuit.

Pregnant solution from the CIL circuit, along with pregnant solution from the ILR unit, is fed to two electrowinning cells for gold removal. The solution exiting the electrowinning cells is returned to the process. The gold extracted from the solution is deposited on cathode plates. The gold is removed from the plates, filtered, and smelted in an induction furnace. The refined gold is poured into gold bullion moulds to form “doré” bars. These bars are shipped to a refiner for further upgrading.