The Casa Berardi gold deposit can be classified as an Archean age, sedimentary-hosted lode gold deposit. Gold deposits of the Archean Abitibi greenstone belt dominantly consist of epigenetic disseminated and vein-hosted deposits, and syngenetic gold-rich massive sulphides (Robert et al., 2005; Monecke et al., 2017).

Three main groups of minerals are found in the mineralized material at the Casa Berardi Mine; silicates (quartz, albite, muscovite), carbonates (siderite, ankerite and dolomite) and sulphides (pyrite and arsenopyrite with traces of chalcopyrite and pyrrhotite). There is also gold mineralization found in a graphitic mud rock formation along the Casa Berardi fault plane. The historical recovery data suggest that material classified as “quartz ore” and is dominantly silicates and carbonates have better recoveries than sulphide dominant material, particularly those that contain arsenopyrite. Carbon in graphitic argillite rock at or near the Casa Berardi Fault can be “preg robbing” and influence gold recovery.

STYLES OF MINERALIZATION
VEINS
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 color, 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 sulphides 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 greater than 100 µm. The gold distribution inside the mineral assemblage varies slightly according to the location of the mineralized zones. In the 113 Zone of the West Mine area the vein mineralization, which is spatially close to the Casa Berardi Fault, 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, parts of the Principal area, and some areas of the East Mine mineralization is more common where lenses are adjacent to the Casa Berardi Fault. In these structures 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.

Alteration halos with gold values of above 100 ppb and anomalous values of arsenic and antimony surround most of the mineralized zones along the Casa Berardi Fault. Those halos can be found up to five kilometers away, on both sides of the deposit.

STOCKWORKS
Stockworks are the second style of gold mineralization in the deposit and represent nearly the same volume as the large quartz veins. However, the stockworks are generally noneconomic; but are mined with quartz veins when they are economic. 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-thick quartz veins with gold values ranging from 1 g/t to 10 g/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 heavily carbonated iron-rich rocks are cut by fracturecontrolled vein sets.

At the deposit scale, the Principal area of the West Mine and the East Mine areas have the stockworks surrounding quartz cores. The stockworks are not limited to the main Casa Berardi Fault and can affect the total width of the deformation zone. as meter to decameter wide mineralization subzones.

In the Principal area of the West Mine, the stockwork extends laterally for 400 m at a 50° western plunge. In the East Mine, the mineralized system extends laterally for 400 m, reaching a depth of 800 m down the dip. The system crosses the Casa Berardi Fault at a low angle over 100 m of strike length. Mineralization continues to the west on the south side of the fault and to the east on the north side of the fault.

BANDED IRON FORMATION
The third type of mineralization is the Banded Iron Formation (BIF) hosted mineralization. This type of mineralization is found in the 125 and 127 zones of the Principal area , and in the 160 Zone at the eastern extension of the East Mine area. These zones are restricted to the highly sheared, brecciated, and altered ferruginous sediments occurring north of the Casa Berardi Fault. Mineralization occurs within metric to sub-metric quartz veins and stockworks with up to 10% chert-magnetite beds, and shows high sulphide content which consists of pyrite, arsenopyrite, traces of pyrrhotite, and little or no visible gold. These sulphides 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.

The ore at Casa Berardi is extracted using a combination of underground and open pit mining methods. The underground mines at Casa Berardi are trackless and are accessed by a combination of ramps and a production shaft. The mining method is longhole stoping using a combination of traverse and longitudinal orientations depending upon the widths of the zone. The combined ore production rate from the underground zones is in the range of 2,000 to 2,200 tons per day.

Open pit mining is used to extract near surface mineralization, both above the existing underground mining horizons and in areas without economic underground resources. At present, one open pit mine is in production and another is being developed. Three additional pits are anticipated. The combined ore production rate from the open pit zones is highly variable depending on the mining sequence and ore release rates. Open pit ore is fed to the plant roughly in equal proportion to the underground ore and any surplus is stockpiled.

Current reserves at the Casa Berardi mine comprise eight zones at the West Mine, spread over a moderate horizontal distance from each other and located at different mine elevations, plus open pit and underground areas at the East Mine. The 113, Lower Inter, 118, 121, 123, 124 (Principal underground and open pit), 134, and the West Mine Crown Pillar ("WMCP") open pit zones in the West Mine, and the 148 Zone (open pit and underground) and the 160 open pit in the East Mine comprise the bulk of the reserve tonnage. The zones are of varying thickness, ranging from over 50 meters to less than three meters, which is the minimum mining width. Most of the hanging walls are sub- vertical (55º to 85º) and exhibit similar wall characteristics with the exception of the Lower Inter Zone, which in a number of places has relatively shallow hanging wall configurations (less than 45º).

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 meters or more mineralization width with good access from nearby development, and longitudinal retreat stoping in narrower ore bodies or long distances from development infrastructure. Longitudinal methods have the advantage of lower waste development requirements; however, there is much less flexibility in sequencing and in access, should ground instabilities occur. Timely supply of both cemented and unconsolidated backfill plays a crucial role in controlling dilution and maintaining a short stoping cycle. We believe this mining method satisfies all of the geotechnical requirements and constraints and, as a non-entry mining method, has proven to be safe and reliable in similar operations. The mineralized zones put in reserves are of varying thickness, ranging from a few tenths of meters to 3 meters, 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. Production from the underground mine areas is currently planned to continue for approximately 4.5 years, with the amount of material to be moved every six months to average between 270,000 and 410,000 tons, with variable quantities of waste.

In early 2016, Hecla made the decision to construct the East Mine Crown Pillar ("EMCP") open pit, which is just west of the East Mine infrastructure. 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 have been ongoing, and the pit is being expanded to the west and is currently in the final stage of development. The EMCP pit, including the extension area, uses conventional open pit mining methods, and is expected to run for an additional approximately 3 years of production. The average amount of material to be moved every six months is anticipated to be approximately 330,000 tons of ore, with variable quantities of waste.

With the addition of new information, including from new pits, evaluation of the schedule for mining the other pits is ongoing. The current plan is as follows:

• The 160 Zone open pit, as currently designed, would be mined using conventional open pit mining methods. The 160 Zone open pit is expected to commence production after the EMCP pit is depleted and to run for approximately 3.5 years of production. The average amount of material to be moved every six months is expected to approximate 320,000 to 475,000 tons of ore, with variable quantities of waste.

• The Principal Zone open pit, as currently designed, would be mined using conventional open pit mining methods. The Principal Zone open pit is expected to commence production after the 160 Zone pit is depleted and to run for approximately 4.5 years of production. The average amount of material to be moved every six months is expected to approximate 700,000 tons of ore, with variable quantities of waste.

• The WMCP pit, as currently designed, would be mined using conventional open pit mining methods. The WMCP pit is expected to commence after depletion of the Principal Zone pit and to run for approximately 7 full year of production. The average amount of material to be moved every six months is expected to approximate 700,000 tons of ore, with variable quantities of waste.

• The 134 Zone open pit, as currently designed, would be mined using conventional open pit mining methods. The 134 Zone open pit is expected to commence production prior to depletion of the WMCP pit and to run for approximately 1 full year of production. The average amount of material to be moved every six months is expected to approximate 120,000 to 130,000 tons of ore, with variable quantities of waste.

CRUSHING
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.

GRINDING
Ore is conveyed from the storage bin to the semi-autogenous (SAG) mill. The SAG mill feed conveyor is equipped with a scale to monitor and control the ore supply to the SAG mill. Dry quick lime is added from a bin onto the SAG mill feed conveyor for downstream pulp pH control. Mill water is added to the mill feed to pulp the ore. 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.

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.

GRAVITY CIRCUIT
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 ........