The Croinor Gold Property is characterized by the presence of epigenetic gold mineralization. Epigenetic gold deposits exhibit a number of common parameters: a) they are mainly controlled by structural elements; and b) host rocks are physically and chemically altered by metasomatism (Rocheleau et al., 1997). According to Rocheleau et al. (1997), even if all stratigraphic units in the region carry gold mineralization, a direct association is frequently observed with synvolcanic and pre-orogenic intrusions (QFPs, diorite sills and dykes, Bevcon granodiorite pluton). The structural parameters seem common to all these gold deposits. Mineralized zones are associated with shear zones, faults, stress fractures and/or tectonic breccias (Rocheleau et al., 1997). Ductile-brittle and brittle deformation appear to be dominant factors controlling gold mineralization, as is the case for many other deposits in the Abitibi Greenstone Belt (Colvine et al., 1988).

Lode gold deposits occur dominantly in terranes with an abundance of volcanic and clastic sedimentary rocks of low to medium metamorphic grade (Poulsen, 1996). Greenstone-hosted quartz- carbonate vein deposits are a subtype of lode gold deposits (Poulsen et al., 2000). They correspond to structurally controlled, complex epigenetic deposits hosted in deformed metamorphosed terranes (Dubé and Gosselin, 2007).

Several types of veins have been identified by previous authors, including Chénard and Turcotte (2004). Gaborit (1988), who mapped the Croinor deposit outcrop in detail, observed two types: veins parallel to the main shear (“shear veins”) and subhorizontal tension veins. The veins are generally composed of quartz, tourmaline and carbonates with minor amounts of pyrite, chalcopyrite and native gold. The veins vary from a few centimetres to several metres in thickness and plunge weakly toward the east. Based on a structural analysis, Gaborit (1988) showed that the shear zones and both types of veins are related to the same phase of deformation. Moreover, Chénard and Turcotte (2004) also encountered mineralized tectonic breccias.

Shear veins
Chénard and Turcotte (2004) noted that the shear veins are oriented parallel to shears and range from a few centimetres to several metres in thickness. These veins consist of quartz, tourmaline and carbonate with very little sulphides. The percentage of pyrite does not exceed 3% and it seems to be closely associated with tourmaline. Tourmaline occurs in the form of fine millimetre-scale veinlets and/or needles. Gaborit (1988) claims to have locally observed native gold in quartz, generally near contacts with host rocks or with tourmaline and chalcopyrite (<1%) associated with the quartz. These veins show variable degrees of deformation. They are boudinaged, folded and brecciated. The wall rocks to the veins are regularly bleached and, occasionally, brecciated.

Brecciated quartz-tourmaline veins
Chénard and Turcotte (2004) described these veins to be metric to decimetric in thickness and composed of grey or milky white quartz with varying quantities of tourmaline veinlets and/or needles. They contain less than 20% altered and mineralized diorite fragments. These fragments are subangular and range from 1 cm to 1 m in size. The fragments are leached, silicified, pyritized and carbonatized (calcite, ankerite). They contain 1% to 15% fine- to coarse-grained auriferous pyrite (0.3 cm - 2 cm). Fuchsite is occasionally present in the fragments with pyrite. In veins containing only quartz, pyrite is generally absent, and few carbonates are present, while quartztourmaline veins contain small amounts of pyrite (<2%). Pyrite borders and/or is present inside tourmaline veinlets. There seems to be a close relationship between tourmaline, fuchsite and pyrite. The host rocks are usually leached and pyritized (<15% pyrite).

Quartz-tourmaline-carbonate veins
Chénard and Turcotte (2004) described these veins as ranging from 10 cm to 1 m in width. They are composed of white quartz, massive tourmaline and/or tourmaline veinlets and carbonates (calcite, ankerite). Tourmaline and carbonates are generally more abundant along vein wall rocks. The percentage of tourmaline is usually less than 35%. In most cases, these veins contain traces to 3% fine pyrite, often associated with tourmaline.

Quartz-tourmaline veinlets
Chénard and Turcotte (2004) described the quartz veins to be millimetric to centimetric, whereas the tourmaline veinlets are usually millimetric. The density of these veins varies from 1% to 10%. Milky white quartz veinlets contain less than 1% tourmaline. Pyrite is generally absent in these veins, but their wall rocks contain auriferous pyrite (1%–15%), especially in silicified zones. Elsewhere in the diorite, trace to 3% disseminated pyrite is observed. Quartz-tourmaline veinlets are often folded, boudinaged and discontinuous.

Tourmaline veins
Chénard and Turcotte (2004) noted that tourmaline veins are rarely observed. These veins are generally 1 m to 10 m thick. They consist of more than 80% massive tourmaline with less than 20% quartz. Tourmaline is massive but may occur in the form of veins and needles in the presence of quartz. In some cases, these veins may be brecciated and contain 5%–25% leached and pyritized diorite fragments. Fragments contain up to 15% fine- to coarse-grained pyrite, sometimes cubic. Associated with tourmaline, trace to 10% medium- to fine-grained pyrite is regularly present. In drill hole CR-02-78, Chénard and Turcotte (2004) saw an example of a metre-scale tourmaline vein. This vein returned gold grades up to 9.7 g/t Au.

Tension veins
Chénard and Turcotte (2004) noted that even though tension veins have been well documented around shear zones, their identification in drill core remains difficult. The only clue that can confirm the presence of tension veins is the fact that tourmaline and/or quartz grow perpendicular to the vein contacts. The tension veins were injected into subhorizontal low-angle tension fractures (Gaudreau et al., 1988). According to Gaudreau et al. (1988), these veins dip to the southeast, but Gaborit (1988) observed north-northeast dips. The veins are generally arranged en echelon (Gaborit 1988). The subhorizontal tension veins contain milky white quartz with very little carbonates and rare tourmaline. The veins are thin (less than 15 cm) and have a very short extension. The wall rocks are pyritized and contain 1% to 5% auriferous pyrite (Gaborit, 1988). Gaborit (1988) reports the presence of visible gold in these veins.

Tectonic breccia
Gaudreau et al. (1988) observed an association between the tectonic breccias and faults and/or reverse shear zones. These tectonic breccias contain angular, leached and pyritized diorite fragments, similar to host rocks and ranging in size from 1 cm to 50 cm. The quartz-tourmaline matrix represents up to 80% of the breccia volume. Diorite fragments are strongly silicified, sericitized and ankeritized. Fuchsite is visible in some fragments. The fragments contain 1% to 15% fine- to coarse-grained auriferous pyrite crystals or aggregates. Chénard and Turcotte (2004) characterized these breccias as the main gold- bearing structures within the Croinor Sill, where gold grades are the most consistent and may exceed 30 g/t Au in some cases.

Two mining methods are proposed to accommodate the geometry of the mineralization: sublevel long-hole retreat and conventional room and pillar.

Long-hole method
The long-hole stopes will be mined from 3-m-high levels at 15 m vertical intervals. For stope heights exceeding 13 m, the maximum stope panel was defined as 15 m long. It is assumed that only a small number of stopes will be backfilled and that some pillars will be left between panels and mining horizons. For stope heights of 13 m or less, longer stope panels were considered on a case by case basis.

The method consists of drilling and blasting 64 mm diameter holes in a pattern parallel to the walls. Holes are drilled upward or downward depending on the context.

The development sequence consists of accessing the mineralized zone and excavating a level cut in the mineralized zone. The mining sequence will require the excavation of a raise opening, which is either developed as a conventional raise or as a drop raise when a top access is available. Once development is completed, the mineralized zone is surveyed with precision for the preparation of the drilling and blasting pattern.

Room and pillar
In some areas, room and pillar was a technically better choice than long-hole due to the ore body angle lower than 43°. The proposed room and pillar stope configuration is based on typical industry practices for currently operating mines in deposits with similar vein geometry. The typical mining height will vary from a minimum of 1.8 m to a maximum of 3.0 m.

The room and pillar mining method entails the excavation of a series of rooms following the vein, leaving pillars or columns of rock in place to help support the mine roof. In conventional room and pillar mining, drilling is achieved using hand-held drill equipment and holes are loaded with explosives. Bolts and cables are then installed in the mine roof to ensure the roof is properly supported. The broken rock is scraped to either a raise or a draw point where it is taken with a LHD to be hauled to surface.

Toll milling was considered in the previous PFS (Poirier et al., 2014). Since then the issuer has acquired the Beacon Mill facility. This updated PFS is therefore based on processing ore at the Beacon Mill at an average production rate of 575 tpd.

The Beacon gold mill is situated 15 km east of Val-d’Or. The plant started operating in 1987. The flowsheet uses gravity concentration, cyanide leaching and the MerrillCrowe process to recover the gold.

The plant feed is first dumped on a heavy-duty grizzly. An impact hammer breaks the oversize rock directly on it.

The crushing circuit consists of a 32" by 42" jaw crusher that can be fed with ore of about 20" at a rate of 175 m3 /h to 200 m3 /h. The ore crushed to about 4" is sent to the screen that sends the -¾ fraction to the fine ore silos. The +¾ fraction is sent to the conical crushers. A standard 4 ft crusher and a 4 ft short head crusher are used.

The plant has two fine ores silos with capacity of about 1,000 t each. The silos feed the grinding circuit with a conveyor at a rate of 32 t/h.

The grinding circuit is composed of a primary rod mill of 8 ft by 12 ft and one ball mill of 8 ft by 12 ft. The rod mill runs in open circuit. The ball mill is currently set up to run with both mill discharges going to the same common cyclone.

The first ball mill will operate in closed circuit with the existing cyclone cluster which is composed of two cyclones, one unit of which would be in operation and one in standby. A portion of the underflow is sent to the gravity recovery circuit and the remainder is returned to the first ball mill. The cyclone cluster overflow is sent to thickener.

The gravity circuit is composed of one Knelson concentrator operating to recover free gold. One unit is considered sufficient for operation at 750 tpd. The Knelson concentrate is treated on a shaking table. The gold concentrate is then further treated in the refinery.

The supply of water to the grinding circuit will come from the reservoir with barren solution or mill solution.

The 35 ft diameter thickener overflow is fed into a buffer tank before the Merrill-Crowe precipitation circuit. The thickener underflow is fed into the first leaching stage.

The thickened pulp remains about 15 h in the first leaching stage before being filtered. There are two drum filters of 11'6" diameter per 16 ft long. During filtration, the cake is washed with sterile solution. After filtration, the cake is re-pulped to 50% solid and more with barren solution. This slurry is pumped into the second leaching stage.

The pulp stays about 15 h in retention in the second leaching stage before being filtered using two drum filters identical to those of the first stage. The cake is washed with barren solution.

The clarifier, is fed from the buffer tank, which purpose is to filter the solution of all these particles. The clarifier consists of large panels covered with a filter cloth on which is added a layer of diatomaceous earth which allows a total filtration of the solution.

The clarified solution is pumped through a deaeration tower, which remove the air dissolved in the solution, to precipitate the gold. To enable a better precipitation of the gold, a solution of zinc powder and a little of lead nitrate is added in the outlet pipe of the deaeration tower.

The gold precipitate passes through a filter press where it remains trapped while the sterile solution will be stored in the reservoir of sterile solution.

When the filter press is full, it is air dried and emptied to collect the precipitate which will be put in a drying oven and further melted at the refinery to obtain a gold doré.

The drying oven and furnace are also used to treat the shaking table concentrate. The doré ingots are stored in a safety vault.

After filtration, the 35% solid pulp cake is returned with water to the polishing pond before being pumped on to the tailings pump box. The cyanide remaining in the slurry will be naturally degraded in the tailing pond.