The Rainy River deposit is an auriferous VMS system (Pelletier 2016) with a primary syn-volcanic source and possibly a secondary syn-tectonic mineralization event.

At Rainy River, gold and silver are the dominant metals and the base metal (Cu-Pb-Zn) sulphides, although good indicators of the presence of gold, represent less than 10%, by volume, of the host rock. This is in contrast with other VMS systems that generally contain large amounts of base metals. However, there are exceptions, i.e., gold-rich VMS deposits that often contain modest amounts of base metals relative to gold (Mercier-Langevin et al. 2015 and references therein).

The Rainy River deposit occurs within a sequence of felsic to intermediate, calc-alkaline metavolcanic rocks which is bounded to both the north and south by a lower mafic volcanic sequence. This mafic sequence is intruded by the trondhjemitic Sabaskong batholith to the north. Felsic to intermediate rocks are intruded to the east of the deposit by the Black Hawk monzonitic stock. In the deposit area all rock units strike approximately east-west and dip to the south, subparallel to the main foliation recognized in the area.

The Rainy River deposit comprises eight distinct zones of gold and silver mineralization. The bulk of the gold mineralization at Rainy River is contained in sulphide and quartz-sulphide stringers and veins hosted by felsic quartz-phyric rocks.

ODM/17 Zone
The ODM/17 Zone is a series of east-west trending, south dipping lenticular sheets hosted within calc-alkaline dacites of the intermediate fragmental volcanic succession. The zone is cut by numerous NNE trending faults. The ODM/17 Zone has presently been defined over a strike extent of 1,600 m and to depths of 975 m. The true width of the zone is approximately 200 m.

Three styles of gold mineralization are observed in the ODM/17 Zone. Low grade intervals are characterized by tightly folded pyrite stringer veins and disseminated pyrite in sericite quartzchlorite altered host rocks. Moderate-grade intervals are characterized by tightly folded and foliation parallel pyrite-sphalerite and pyrite stringer veins, commonly associated with stronger silica and weak garnet alteration.

433 Zone
The 433 Zone is located approximately 500 m north of the ODM/17 Zone and hosted within strongly sericitized calc alkaline dacite rocks and lesser tholeiitic basalts. The 433 Zone comprises a cigar-shaped lens which plunges steeply south-west. This zone has a strike length of 325 m, a vertical distance of approximately 820 m, and a true width of up to 125 m.

Gold mineralization is similar in style to the ODM/17 Zone but with a number of minor differences:
- The 433 Zone is dominated by chlorite alteration of quartz-phyric host rocks as opposed to sericite in the ODM/17 Zone.
- Chlorite-pyrite altered heterolithic conglomerates occur within the 433 Zone.
- Chalcopyrite and chlorite are associated with high-grade quartz-pyrite-gold veinlets.

Footwall Silver Zone
The Footwall Silver Zone occurs in altered dacitic tuffs and tuff breccias immediately adjacent to a high strain zone at the northern contact of the ODM/17 Zone. This zone plunges to the south west in similar orientation to the ODM/17 Zone. It is hosted by centimetre scale sulphide-bearing quartz veinlets with common millimetre scale fracture filling to dendritic native silver inclusions. Sulphides contained within these veinlets, in order of frequency, comprise pyrite, sphalerite, chalcopyrite, and galena. Localized spessartine garnets have been noted. The presence of isoclinal folding of the veinlets suggest mineralization occurred prior to or synchronous with deformation. The zone is considered to genetically related to the ODM/17 Zone. The zone is composed of numerous lenses that range from 5 to 30 m wide, have strike lengths between 5 to 50 m and plunge extents between 300 and 600 m.

HS Zones
Several subsidiary zones of gold mineralization occur between the ODM/17 Zone and 433 Zone. The HS Zones comprise a series of small, discontinuous south-west plunging, flattened shoots of mineralization. Discontinuous, irregular low-grade gold mineralization is associated with chlorite-pyrite replacement of matrix in flattened, albitized, heterolithic pebble conglomerates. The zone has a strike length of 200 m and extends to a vertical distance of approximately 700 m.

The Western Zone
The Western Zone occurs near surface approximately 500 m north-west of the western extent of the ODM/17 Zone. It is composed of stockwork of discrete centimetre scale anastomosing, folded to linear quartz and quartz-carbonate veinlets. The Western Zone is hosted predominantly within strongly deformed intermediate volcanic fragmental units (analogous to those that host the ODM/17 Zone) and mafic volcanic flows in the immediate footwall (FW) and hangingwall (HW). The Western Zone comprises a series of discontinuous 5 to 10 m wide zones of mineralization which strike approximately south-east and dip south-west at approximately 50°. Individual zones encompass a strike length of between 50 and 500 m. Collectively these zones occur over an area of approximately 500 x 1,200 m. They have been defined to down-dip depths of approximately 60 to 500 m.

The CAP Zone
The CAP Zone is located approximately 200 m to the south of the ODM/17 Zone in both tholeiitic basalts and calc-alkaline dacite of the upper diverse mafic volcanic succession. The CAP Zone has been defined over a strike length of 400 m, up to 120 m wide and with a down-dip extent of 750 m. Mineralization in the CAP Zone is open below the modelled depth. Higher-grade gold mineralization is associated with deformed quartz-ankerite-pyrite shear and extensional veins hosted by quartz-ankerite-pyrite altered mafic volcanic rocks.

Intrepid Zone
The Intrepid Zone is located approximately 800 m east of the ODM/17 Zone within dacitic\ tuffs and breccias of the intermediate fragmental volcanic succession. The Intrepid Zone has been defined over a strike length of 410 m and to 450 m down-dip. The width of the zone is variable ranging between 10 m to 60 m.

High-grade gold and silver mineralization is associated with deformed quartz-pyrite-gold, quartz-pyrite-silver, or quartz-pyrite-gold-silver veinlets that overprint other mineralization styles. The gold-silver ratio is determined by their location within the base metal zonation.

34 Zone
The 34 Zone comprises magmatic nickel copper sulphide mineralization associated with precious metals (gold, platinum group metals) within a tubular, ~100 m thick, late-stage pyroxenite gabbro intrusion which cross cuts the ODM/17 Zone and post-dates the main gold mineralization event. The host pyroxenite-gabbro intrusion is unmetamorphosed, but locally altered into serpentine and talc. Magmatic sulphides vary from massive to net-textured and disseminated. Gold and silver mineralization occur within 5 to 50 m thick dislocated (and therefor discontinuous) north-east oriented pods over a strike length of 500 m with a down-dip plunge of 100 m.

Mining at Rainy River is currently conducted using open pit mining methods and will transition into a combined open pit and underground operation over the next two years, with underground production commencing in 2022. An average processing rate of approximately 25,800 tpd is scheduled over the LOM.

The open pit mine is a conventional truck and shovel mining operation, with a fleet of 220 t payload haul trucks combined with diesel powered hydraulic excavators and large front-end loaders (FELs) as primary loading units. The open pit operates at a peak mining rate of 151,000 tpd of ore and waste and has an overall strip ratio of 2.53:1 (waste:ore).

Haulage ramps were designed nominally at 33 m width and a maximum ± 10% grade, except for the bottom few benches where widths were permitted to be reduced to one-way traffic of 20 m and ± 12% grade.

The mine plan is executed to take advantage of the installed mine fleet productive capacity, allowing an elevated COG policy to be adapted, whereby higher-grade ores are preferentially sent to the mill for processing while lower grade ores are sent to stockpile for deferred processing. This results in an open pit mine life extending to Q1-2025 with stockpile rehandling occurring in parallel to the underground operations through to Q1-2028 to fulfill available process plant capacity.

The Rainy River underground mining operation is planned to extract ore from five portals and / or zones: ODM Main Zone, ODE East Zone, 17 East Upper Zone, 433 Zone, and Intrepid Zone.

Each of the underground zones is planned to be mined using one or both of the following mining methods:
- Blind uphole LLHOS without backfill (uphole). Uphole is a top-down mining method that does not require the use of backfill. The uphole stopes have a minimum mining width of 3 m, a maximum width of 15 m, and an overall average width of 7.5 m. The sublevels will be spaced at 20 m intervals (floor to floor) in all zones except for the Intrepid Zone, where the stope heights have been increased to 25 m. Upholes are mined in a longitudinal retreat sequence, with open stopes up to 48 m long separated by a minimum 8 m wide pillar.
- Downhole LLHOS with backfill (downhole). The downhole mining method is a bottom-up mining method that uses backfill. Downhole stopes are only used in the ODM Main Zone, where 90% of the stopes are planned as downhole and 10% are planned as uphole. The downhole stopes represent 32% of all projected stope tonnages for the underground LOM.

The Intrepid Zone is the only zone with an existing portal and has approximately 166 m of decline development currently executed. The portal is at 365 RL and planned stopes are located between 225 RL and 100 RL. The zone extends approximately 250 m horizontally and dips between 50° and 70°.

Crushing
The crusher consists of a 1,400 mm x 2,100 mm, 600 kW gyratory crusher. The crusher is designed for 220 t mine haul trucks to dump directly into the crusher feed pocket. Two dump positions on opposite sides of the crusher allow for simultaneous dumping. The capacity of the dump pocket is 330 t or approximately 1.5 trucks. The crusher is equipped with a hydraulic rock breaker for reducing oversized material and a mobile crane is available for crusher maintenance.

The crusher is designed to process 1,346 tph of ore with a F100 feed size of 1,050 mm, a F80 of 550 mm and an operating availability of 65%. The crusher operates with an open side setting of 120 mm to produce a P80 product size of about 120 mm. The crusher discharge surge pocket live capacity is 418 t or approximately 1.9 trucks. Ore is removed from the discharge surge pocket by a single 2,134 mm wide apron feeder, FE01, which discharges onto the 1,372 mm wide crusher discharge conveyor, CV10. The crusher discharge conveyor then transfers ore to the 1,372 mm wide coarse ore stockpile feed conveyor, CV 11. CV11 transports the ore to the coarse ore stockpile. CV10 is equipped with a weightometer to measure the crusher production rate and total ore processed. In addition, CV10 has a metal detector that shuts down the conveyor belt automatically, permitting the operators to extract the metal detected.

The coarse ore stockpile has a total capacity of 85,700 t and a live capacity of 19,000 t. Ore is drawn from the coarse ore stockpile by three apron feeders. The apron feeders discharge onto the 1,372 mm wide SAG mill feed conveyor, which is installed in a single reclaim tunnel beneath the stockpile. The SAG mill feed conveyor has a variable frequency drive (VFD) and delivers ore to the SAG mill feed chute. The SAG mill feed conveyor is equipped with a weightometer to monitor and control the SAG mill feed rate.

Primary grinding – SAG mill
The SAG mill is an 11.0 m diameter by 6.1 m long grate discharge mill with a dual pinion drive consisting of two 7,500 kW motors with VFDs. The surveyed mill feed is a F80 of 46 mm and the discharge transfer P80 size is estimated to be 2.8 mm. The mill is currently operating at 58% of critical speed to achieve a production rate of 1,050 – 1,350 tph. The design operating power at the pinions is 12,580 kW, which is approximately 84% of the installed power. The mill currently has a grate discharge of 70 mm pebble ports.

The mill discharge is fitted with a single deck horizontal vibrating screen with 10.5 mm openings to remove oversized pebble, ball chips and tramp steel. The SAG mill currently operates with a 10% - 14% solids (v/v) ball charge made up with 130 mm balls and a total charge volume of 25% (v/v). The maximum design ball charge is 16% (v/v) with a maximum design mill fill volume of 30% (v/v).

The oversized pebble is conveyed from the SAG mill discharge screen to a Raptor L500, 3.5 m x 4.0 m x 3.6 m, pebble crusher (cone crusher), with a 447 kW drive via three conveyors, CV31, CV32, and CV33. Two belt magnets followed by a metal detector are installed on CV32. If metal is detected, a two-way gate will be opened and the metal containing ore is bypassed to a reject bin. The nominal operating rate of the crusher is 238 tph, 25% of nominal mill feed, with a design operating power draw of 235 kW. The crusher reduces the ore to an approximate P80 of 13 mm. The crushed product is conveyed to the SAG mill feed conveyor transfer tower where it is either discharged onto the SAG mill feed conveyor and recycled to the mill or fed to a bypass conveyor, which feeds a pebble stockpile adjacent to the conveyor transfer tower. The pebble crusher circuit assists in achieving the planned throughputs when the ore becomes harder. The pebble crusher circuit has been commissioned recently. The pebble crusher will not be operated unless the ore is sufficiently hard.

Secondary grinding – ball mill
The ball mill is a 7.9 m diameter by 12.3 m long overflow mill with a dual pinion drive consisting of two 7,500 kW motors with VFDs. The typical mill feed has a F80 of 2,800 µm and the resultant product size is currently a P80 range of 90 µm - 110 µm. The mill operates at 75% of critical speed to achieve a production rate of 1,050 – 1,350 tph. The design operating power at the pinions is 12,360 kW, which is approximately 82% of the installed power of 15,000 kW. The slurry discharges from the mill through a trunnion magnet for steel removal and into the cyclone feed pump box.

The ball mill is operated with a target slurry density of 72% solids (w/w) and a circulating load of 300%. The maximum circulating load is projected to be 400%. The design ball charge is 32% (v/v) with a maximum design ball charge of 36% (v/v).

The process plant experienced initial operating and maintenance issues, but in 2019, Rainy River was consistently able to achieve daily plant throughputs in the 22,000 tpd - 24,000 tpd range. Throughput is programed to achieve approximately 25,300 tpd in 2020 with the LOM throughput averaging approximately 25,800 tpd.

The process flowsheet consists of the following unit processes:
• Gyratory crusher.
• Coarse ore stockpile, discharged through draw pockets by apron feeders.
• SAG mill feed conveyor.
• SAG mill.
• Pebble crusher.
• Ball mill.
• Gravity concentration of cyclone feed slurry.
• Intensive cyanide leaching of the gravity concentrate using an Acacia reactor.
• Pre-leach thickener.
• Cyanide leaching.
• CIP circuit.
• Cyanide destruction using the sulphur dioxide-air process.
• Carbon stripping using the Zadra process.
• Electrowinning of the eluent and gravity concentrate leach solution.
• Ca ........