Four (4) main styles of mineralization have been identified on the Rainy River Project:
- Moderately to strongly deformed, auriferous sulphide and quartz-sulphide stringers and veins in felsic quartz-phyric rocks (e.g., ODM/17, Beaver Pond, 433 and HS Zones);
- Deformed quartz-ankerite-pyrite shear veins in mafic volcanic rocks (e.g., CAP/South Zone);
- Deformed sulphide-bearing quartz veinlets in dacitic tuffs/breccias hosting enriched silver grades (e.g., Intrepid Zone); and
- Copper-nickel-platinum group metals mineralization hosted in a younger mafic-ultramafic intrusion (e.g., 34 Zone).

The gold mineralization is interpreted as a hybrid deposit type, consisting of an early gold-rich volcanogenic sulphide mineralization overprinted by shear-hosted mesothermal gold mineralization. Magmatic-hydrothermal copper-nickel-platinum mineralization occurs within the main auriferous zones and crosscuts the volcanogenic sulphide mineralization and the later mesothermal gold mineralization associated with the regional deformation.

The Rainy River Mine is an open pit and underground gold-silver mining project. The open pit mine is a conventional truck and shovel open pit mining operation, which utilizes hydraulic shovels and 220-tonne trucks as the primary mining equipment. The open pit mine operates at a rate of 180,000 tpd of ore and waste and has an overall strip ratio of 3.7:1.0 (W:O). The underground mine is a mechanized ramp access mine that will use long hole stoping to exploit the underground Mineral Reserves at a rate of approximately 2,300 tpd after 2021.

The final pit design includes 35 m ramp widths graded by 10%. The glacial till has slopes of 8:1 (H:V), and the harder rock zones vary with inter- ramps slopes of 40° to 54°, which results in overall slope angles ranging from 34° to 48°.

The mine rock stockpiles have sufficient capacity to accommodate the 402 million tonnes of waste required by the mine production schedule. There is also capacity for 15 million tonnes as backfill.

Waste dump designs are based on 20 m berms for every 50 m lift and face angles of 35°. Dumps are located within the economic zone boundary and at a distance of more than 100 m from the final pit design.

Mine production was scheduled to be carried out at a maximum mining rate ranging from 125,000 tpd to 180,000 tpd of total material. Stripping ratios are expected to average 3.69 over the LOM plan.

The open pit is scheduled to be mined out by 2026. Mill production will continue with underground and stockpile feed until 2032.

In addition to the open pit Mineral Reserves, there are Mineral Reserves at Rainy River amenable to underground mining. Underground Mineral Reserves have been identified in ten zones. Several of the zones are extensions of the open pit ore bodies while others are up to one kilometre from the open pit. The underground deposits exist from near surface to approximately 600 m below surface within an area approximately 2.8 km long and 0.9 km in width.

The ore grade mineralization occurs in subvertical horizons from three metres to 20 m thick. Widths over 15 m are rare and the weighted average thickness is eight metres. A three metre minimum width is used for Mineral Reserves. The ore zones generally dip at 60° or greater but can flatten locally to 45°. The planned mining method relies upon gravity ore flow along the footwall. In areas where the dip is less than 55° there is the potential for higher costs, higher dilution and/or higher ore loss than planned. As detailed stope planning information becomes available, footwall geometry is planned to be reviewed.

The selected mining method is long hole open stoping with longitudinal stopes. Stopes will be the width of the ore zone, with a minimum three metre width and sublevels will be located at 20 m to 30 m vertical intervals (floor to floor). Stopes will be mined in a longitudinal retreat sequence with open stopes up to 48 m long and with stopes separated by an eight-metre wide pillar. Sill pillars will be used as work platforms in top down mining and then recovered with the subsequent lift.

A four-kilometre long main 5.0 m x 5.0 m decline driven at a -15% gradient from the surface portal will provide access for personnel and equipment. The main decline will connect to independent internal production ramps that will service all levels in each mining area. Internal production ramps are of spiral configuration and will be generally driven at a -10% gradient to provide level access on each revolution. The ramps and ore development are planned to be typically 5.0 m x 5.0 m headings.

The Rainy River process facilities were designed to process 21,000 tpd or 7.67 Mtpa from the open pit and underground mines. The target production was originally 19,500 tpd from the open pit mine and 1,500 tpd from the underground mine. The present expansion will increase the plant throughput to 24,000 tpd in 2019 and 2020, followed by a ramp-up to 27,000 tpd in 2021 for the remainder of the LOM. The operating availability of the primary crusher is 65% and the operating availability of process plant is 92%.

The process flowsheet consists of the following unit processes:

• Primary gyratory crushing;
• Coarse ore stockpile, discharged through draw pockets by apron feeders;
• SAG mill feed conveyor;
• Primary SAG mill grinding;
• Pebble crushing;
• Secondary ball mill grinding;
• Gravity concentration of primary cyclone feed slurry using centrifugal concentrators;
• Intensive cyanide leaching of the gravity concentrate using an Acacia reactor;
• Screening of cyclone overflow prior to thickening to remove trash;
• Grinding circuit thickening;
• Cyanide leaching using eight tanks in series;
• Carbon in pulp gold recovery using seven tanks in series;
• Cyanide destruction using the SO2 (sulphur dioxide) air process in two tanks in series;
• Carbon stripping using the Zadra process;
• Acid washing of the carbon using hydrochloric acid;
• Electrowinning of the carbon eluent and gravity concentrate leach solution; and
• Casting of gold and silver bars in an induction furnace.