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. 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, which is equipped with a static grizzly and a pneumatic hammer to break any oversize material. Ore passing the grizzly is screened again on the scalping screen. The oversize ore is fed to a jaw crusher and its discharge rejoins the scalping screen undersize. The crushed ore is stored in the ore storage bin.

Ore is conveyed from the storage bin to the semi-autogenous (SAG) mill. The SAG mill operates in closed circuit with the SAG screen. The SAG mill discharges into the SAG screen pump box and is pumped onto the SAG screen. The SAG screen oversize material is returned to the SAG mill for further reduction and the screen undersize flows to the primary cyclone pump box. The mill feed is sampled on the SAG screen undersize stream.

The ball mill operates in closed circuit with the primary and secondary cyclones. The ball mill discharges in the primary cyclones pump box. The primary cyclone pump box pulp is pumped to the primary cyclone for a first size separation. The totality of the primary cyclone underflow feeds the gravity circuit. The primary cyclone overflow discharges into the secondary cyclone pump box with the gravity concentrator tailings. The secondary cyclones pump box pulp is pumped to the secondary cyclones for the final size separation. The secondary cyclones overflow goes to the trash screen to remove debris and the underflow goes back to the ball mill. The trash screen oversize is sent to the tailings pump and the undersize feeds the production thickener.

The gravity circuit feed, coming from the primary cyclone underflow, is split to feed two parallel gravity circuits. Each circuit consists of a vibrating screen and a gravity concentrator. The screen oversize from each circuit reports back to the ball mill and the screen undersize feeds a gravity concentrator. The concentrator’s tailings are pumped to the secondary cyclones pump box. The gravity concentrate flows to an intensive cyanidation reactor (Inline Leach Reactor, or ILR) for leaching. To promote gold leaching and control the pH, oxygen peroxide, cyanide and caustic soda are added to the ILR unit from their respective tanks using dosing pumps. The high-grade pregnant gold solution from the ILR unit is pumped to the electrowinning buffer tank and the tailings report to the secondary cyclones pump box.

The production thickener is fed with the milled ore pulp coming from the trash screen. Mill water from the thickener overflows in the mill water tank. Process water coming from the tailings pond is added to the mill water tank depending on the demand. The thickener underflow is pumped to the first CIL tank. CIL feed is sampled on the production thickener underflow stream. A carbon- in-leach (CIL) circuit is used to recover gold instead of a carbonin-pulp (CIP) to hinder preg- robbing due to graphite in the ore and to maximize gold recovery by putting the gold in solution in contact with activated carbon immediately. The circuit comprises seven CIL tanks in series. The pulp overflows from the #1 CIL tank to the #7 CIL tank.

To provoke gold leaching, a cyanide solution is added to the #1 CIL tank and compressed air is added to each CIL tank. Gold is leached from the ore and adsorbed onto activated carbon. Carbon is added in the #7 CIL tank and is pumped periodically in counter-current fashion from the #7 CIL tank to the #1 CIL tank. Screens at the discharge of each CIL tank prevent carbon from overflowing from tank to tank with the pulp. The #7 CIL tank overflows onto a safety screen to recover any fugitive carbon. The safety screen undersize is sampled and goes to the mixing tank. Fine quicklime and copper sulfate are added to the mixing tank to prepare for cyanide destruction. Pulp from the mixing tank is pumped to the cyanide destruction tank in which sulphur dioxide and compressed air is added to destroy residual cyanide with agitation. The pulp is then pumped to the paste backfill plant or the tailings pond. Ferric sulfate is also added to this pump in order to reduce arsenic content in the solution.

The carbon, elution and electrowinning circuits operate in batches unlike the CIL continuous process. Loaded carbon is pumped periodically from the #1 CIL tank onto a washing screen. Loaded carbon from the washing screen falls into the loaded carbon tank while the pulp and residual cyanide solution return to the #1 or #2 CIL tank. When carbon collection is completed, loaded carbon is transferred to the acid washing tank. Hydrochloric acid is added in the acid washing tank and carbon is soaking for two hours to remove inorganic contaminants. When the acid wash is completed, the loaded carbon is rinsed with process water to return to a neutral pH before being transferred to the elution vessel. After elution, eluted carbon is screened and sent either to the calibrated carbon tank or the regenerating kiln. The calibration screen undersize is sent to the carbon fines thickener where flocculant is added. Carbon fines are recovered at the underflow, filtered using a filter press and bagged. At the regenerating kiln, the carbon is heated to burn organic contaminants. The kiln discharges in a quench tank and carbon is pumped back onto the calibration screen. Calibrated carbon is pumped back into the #7 CIL tank from the calibrated carbon tank. Fresh carbon is also added to the CIL circuit using the calibration screen after being quenched in an attrition tank. Carbon moves in the circuit using a water eductors system.

The elution circuit uses the ZADRA process. Caustic soda and cyanide are added to process water in the barren solution tank to prepare for elution. The barren solution is pumped through a heat exchanger and a water heater before arriving at the bottom of the elution vessel. Under the right pressure and temperatures conditions in the elution vessel, gold desorbs from the loaded carbon and dissolves in the elution solution. The pregnant solution flows out from the top of the elution vessel through the heat exchanger and cooling battery toward the electrowinning cells. The heat exchanger recovers heat from the pregnant solution to warm up the barren solution. The cooling battery completes the pregnant solution cooling to a safe temperature and pressure for electrowinning using process water at an ambient temperature.

Two electrowinning cells recover dissolved gold from the pregnant solution by deposition on its cathodes plates to form a gold sludge. Barren elution solution is pumped from the electrowinning cells to the barren solution tank. During an elution cycle, elution solution flows continuously through the circuit. A third electrowinning cell, in loop with the ILR buffer tank, is dedicated to the ILR gold solution. When an elution cycle is over, gold sludge is recovered from the electrowinning cells, filtered and dried before being smelted in the induction furnace and poured into gold dorés at the gold room.