The 2025 technical report presents a preliminary economic assessment for processing O’Brien mineralized material through existing and new circuits at the Westwood complex on a toll milling basis.
Report context
The report, dated August 20, 2025, documents a preliminary economic assessment (PEA) for the O’Brien Gold Project. The processing strategy is based on testwork conducted for the PEA and a memorandum of understanding dated September 6, 2024, between Radisson Mining Resources Inc. and IAMGOLD Corporation to assess design criteria for processing O’Brien material at the Westwood complex. As of the report date, the processing route remains a proposed design, with several circuits new or existing but not yet operated on O’Brien feed.
Processing route
Overview
A testwork program was undertaken to determine the optimal recovery method for O’Brien mineralized material at the Westwood complex. Economic assessment of the testwork results indicated that gold separation through gravity concentration, flotation, flotation concentrate regrind, carbon-in-leach (CIL) and carbon-in-pulp (CIP) would provide the highest NPV and be compatible with the existing plant. The process design is based on toll milling campaigns, where the Westwood complex alternates between Westwood mine feed and O’Brien feed without concurrent processing. Design throughput is 3,000 t/d, with overall mill capacity utilization dependent on O’Brien mine production rate (1,160 to 2,000 t/d).
Process flowsheet
The flowsheet includes both existing and new circuits. Existing equipment comprises primary crushing, feed material storage, SAG and ball milling, gravity concentration and shaking table, pre-leach thickening, leach and carbon adsorption, pressure Zadra-type elution, electrowinning and smelting, carbon regeneration, cyanide destruction, and tailings thickening. New equipment consists of a rougher flotation circuit with regrind mill. A paste plant exists at Westwood but is not considered necessary for O’Brien material.
Crushing and grinding (existing)
O’Brien mineralized material is truck delivered to the run-of-mine pad (60,000 t storage), crushed via a 1.07 m by 1.22 m jaw crusher, and conveyed to milling feed bins. The grinding circuit comprises a 5.4 m diameter x 6.3 m EGL 2,000 kW SAG mill in closed circuit with a 3.5 m diameter x 4.9 m EGL 745 kW ball mill in closed circuit. Primary grind size (P80) is 75 µm.
Gravity recovery (existing)
A scalping screen feeds a centrifugal batch Knelson concentrator from secondary cyclone underflow. Concentrate is further upgraded on a vibrating table, with table concentrate sent directly to drying ovens and induction furnace for doré production. Gravity recovery is designed for 42% Au at 100% of new feed routed to gravity.
Flotation and regrind (new)
Four new flotation cells and a rougher conditioning tank will replace decommissioned cells. The conditioning tank is fed by secondary cyclone overflow at 25% w/w solids, with collectors and frother added. Concentrate mass pull is targeted at 10%. Concentrate reports to a new open-circuit regrind using an IsaMill, with cyclone overflow and ground product combined at 15 µm (P80) for primary leach feed. Flotation tailings report directly to secondary leach tanks.
Leach and adsorption (existing)
The circuit comprises two primary leach tanks, four secondary leach tanks, three CIL tanks, and five CIP tanks. Primary leach residence time is 10 hours; secondary leach/CIL/CIP combined residence time is 35.5 hours. Primary leach operates at 25% w/w solids with air sparging, hydrated lime to pH 10.5, and intense cyanide addition. Secondary leach receives both leached concentrate and flotation tails, with lime and cyanide added. Carbon is advanced counter-currently, with intertank screens retaining carbon; recessed impeller pumps transfer slurry between tanks and to the loaded carbon screen.
Electrowinning and gold room (existing)
Pregnant solution from elution is pumped through electrowinning cells with stainless steel mesh cathodes. Gold-bearing sludge is washed off, filtered, dried, mixed with fluxes, and smelted in an electric induction furnace to produce doré within a secure gold room.
Tailings and cyanide destruction (existing)
Leach residues are treated with an SO2/air process in two parallel reactors. A buffer tank (14 hours backfill plant capacity) maintains slurry for the backfill plant during current Westwood operations. For O’Brien material, tailings are not planned to report to the paste plant but to the existing tailings management facility. Compatibility of these facilities for O’Brien tailings was not reviewed.
Energy, water, and process materials
Fresh water is sourced from Bousquet River; no water balance was completed for this report, but water usage is not expected to differ significantly from current operations. The plant with new flotation and regrind will have an estimated nominal demand of 5.1 MW and annual consumption of 43 MWh/a. Additional installed power for regrind and flotation is about 1.8 MW.
Key reported parameters
| Parameter | Units | O’Brien |
|---|---|---|
| Plant throughput | t/d | 3,000 |
| Gold grade, design mill head | g/t | 4.9 to 6.9 |
| Crushing plant availability | % | 100 (de facto) |
| Mill availability | % | 100 (de facto) |
| Bond CWi, 75th percentile | kWh/t | 18.7 |
| Bond RWi, 75th percentile | kWh/t | 18.2 |
| Bond BWi, 75th percentile | kWh/t | 12.8 |
| SMC Axb, 25th percentile | – | 35 |
| Bond Abrasion Index | g | 0.39 |
| Material specific gravity | – | 1.58 |
| Primary crusher | – | Jaw, 1.07 m x 1.22 m |
| SAG mill | – | 5.4 m dia x 6.3 m EGL |
| SAG mill installed power | kW | 2,013 |
| Ball mill | – | 3.5 m dia x 4.9 m EGL |
| Ball mill installed power | kW | 745.7 |
| Primary grind size (P80) | µm | 75 |
| Fraction of feed to gravity | % of new feed | 100 |
| Gravity gold recovery | % Au | 42 |
| Total gold recovery (LOM) | % Au | 87.5 |
| Rougher residence time | min | 4 |
| Rougher mass pull | % | 10 |
| Concentrate pulp density | % w/w | 25 |
| Pre-leach thickener diameter | m | 27 |
| Pre-leach thickener underflow density | % w/w | 53 |
| Primary leach capacity | m3 | 772 |
| Primary leach residence time | h | 10 |
| Primary leach extraction, average | % Au | 80.8 |
| Secondary leach capacity | m3 | 5,545 |
| Secondary leach residence time | h | 26 |
| Secondary leach extraction, average | % Au | 80.6 |
| Carbon adsorption stages | – | 3 CIL + 5 CIP |
| Carbon adsorption capacity | m3 | 1,112 (CIL), 1,860 (CIP) |
| Adsorption tail solution, target | ppm Au | <0.1 |
| Primary leach NaCN addition | kg/t leach feed, concentrate | 15.6 |
| Secondary leach NaCN addition | kg/t leach feed, combined | 1.2 |
| Primary leach lime addition | kg Ca(OH)2/t leach feed, concentrate | 5.9 |
| Secondary leach lime addition | kg Ca(OH)2/t leach feed, combined | 0.5 |
| Elution method | – | Pressure Zadra |
| Carbon batch size | t | 4 |
| Detoxification residence time (per tank) | min | 45 |
| Detoxification tanks | – | 2 |
| Detoxification SMBS addition | g SO2/g CNWAD | 5.0 |
| Detoxification copper sulphate | g Cu/m3 | 21 |
| Detoxification lime addition | g Ca(OH)2/g SO2 | 1.0 |
| Detoxification discharge CNWAD, design | mg/L CNWAD | 1 |
| Tailings thickener diameter | m | 20 |
| Tailings thickener underflow density | % w/w | 53 |
Project website: https://radissonmining.com/obrien-gold-project/
Technical qualifications
The report states that tailings facilities have not been reviewed for compatibility with O’Brien tailings or assessed for required modifications. Discussions with IAMGOLD indicated milling scenarios should currently assume use of existing tailings facilities, but this is not based on an assessment of O’Brien tailings geochemistry. Reagent and consumable estimates were developed independently of IAMGOLD from review of existing equipment and technical reports, not from IAMGOLD information. A water balance for the Westwood complex was not completed. Future studies should review the Westwood complex electrical infrastructure in more detail to confirm sufficient capacity. The process design is based on a toll milling campaign basis, with availability considered as 100% during active toll milling, assuming no planned or unplanned maintenance occurs during O’Brien processing hours.
Source: O’Brien Gold Project, NI 43-101 Technical Report & Preliminary Economic Assessment, August 20, 2025.
