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.
Consolidated report summaries
The following former standalone pages about this operation were consolidated here in October 2026. They are retained for source traceability; dates and figures reflect each report’s own effective date and may be superseded by the current information above.
Inside the O'Brien Gold Project: A Deep Dive into the 3,000 tpd Gravity-Flotation-CIL Processing Circuit
Overview
Nestled in the prolific Abitibi greenstone belt of Quebec, Canada, the O’Brien Gold Project represents a significant revitalization of a historic mining district with modern mineral processing technology. Operated by Radisson Mining Resources Inc., this advanced-stage project is poised to leverage a unique toll-milling agreement with IAMGOLD Corporation to process its mineralized material at the existing Westwood complex near Rouyn-Noranda. The project centers on rejuvenating the former O’Brien Mine, which was historically Quebec’s highest-grade gold producer during its operation from 1926 to 1956. The current initiative involves processing approximately 3,000 tonnes per day of material with head grades ranging from 4.9 to 6.9 g/t Au through a sophisticated flowsheet that combines gravity separation, flotation, and carbon-in-leach technologies. This strategic approach eliminates the need for building a new greenfield processing facility, significantly reducing both capital expenditures and environmental footprint while accelerating the path to production. The project exemplifies modern mining innovation through its collaborative operational model and technically advanced recovery methods designed to achieve an impressive 87.5% life-of-mine gold recovery.
Key Process Stages
The O’Brien Gold Project employs a comprehensive mineral processing circuit that integrates both existing infrastructure at the Westwood complex with new specialized equipment. The flowsheet has been optimized through extensive metallurgical testwork to maximize gold recovery while maintaining operational efficiency and cost-effectiveness.
- Primary Crushing (Existing Equipment): Run-of-mine material from the O’Brien deposit is delivered by truck and stored on a 60,000-tonne capacity pad. A 1.07m x 1.22m jaw crusher reduces the material size before it is conveyed to milling feed bins. The crushing circuit operates at 100% availability during toll milling campaigns.
- Grinding Circuit (Existing Equipment): The comminution circuit consists of a 2,013 kW (2,700 hp) SAG mill (5.4m diameter x 6.3m EGL) in closed circuit with cyclones, followed by a 745.7 kW (1,000 hp) ball mill (3.5m diameter x 4.9m EGL). The circuit is designed to achieve a primary grind size of 75 μm (P80) at the design throughput rate of 3,000 tpd.
- Gravity Recovery Circuit (Recommissioned Equipment): The secondary cyclone underflow reports to a gravity circuit featuring a scalping screen and centrifugal Knelson concentrator operating in semi-batch mode. Gravity concentrate is further upgraded on a shaking table, with the final concentrate reporting directly to the gold room for drying and smelting. The circuit is designed to recover 42% of the gold through gravity methods.
- Flotation and Regrind Circuit (New Equipment): Secondary cyclone overflow reports to a new rougher flotation circuit consisting of four flotation cells and a conditioning tank. With a targeted mass pull of 10%, the flotation concentrate is reground to 15 μm (P80) in an IsaMill to liberate gold particles for subsequent leaching. Reagents include PAX, R208, and MIBC collectors and frothers.
- Leach and Adsorption Circuit (Existing Equipment): The reground flotation concentrate reports to primary leach tanks (10 hours residence time), while flotation tailings report to secondary leach tanks (26 hours residence time). The circuit includes three carbon-in-leach (CIL) and five carbon-in-pulp (CIP) tanks with a total adsorption residence time of 35.5 hours. Loaded carbon is advanced counter-currently for elution.
- Cyanide Destruction and Tailings Management (Existing Equipment): Tailings are treated using the SO2/air process (INCO) with a target discharge concentration of less than 1 mg/L CNWAD. Treated tailings are thickened to 53% w/w solids in a 20m diameter thickener before deposition in the existing Westwood tailings management facility.
- Electrowinning and Gold Room (Existing Equipment): Loaded carbon is eluted using a pressure Zadra system, with gold recovered from the pregnant solution via electrowinning. Gold sludge is smelted in an electric induction furnace to produce doré bars within a secure gold room facility.
Critical Data
The following table presents the key technical and operational parameters for the O’Brien Gold Project processing circuit, based on the NI 43-101 Technical Report and Preliminary Economic Assessment.
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Plant Throughput | 3,000 | tpd | Design capacity based on existing equipment |
| Mill Power (SAG) | 2,013 | kW | 5.4m diameter x 6.3m EGL mill |
| Mill Power (Ball) | 745.7 | kW | 3.5m diameter x 4.9m EGL mill |
| Target Primary Grind Size | 75 | μm (P80) | Achieved at design throughput |
| Target Regrind Size | 15 | μm (P80) | For flotation concentrate |
| Overall Gold Recovery (LOM) | 87.5 | % | Life of mine average |
| Gravity Gold Recovery | 42 | % | Design recovery to gravity circuit |
| Flotation Mass Pull | 10 | % | Target rougher concentrate |
| Primary Leach Residence Time | 10 | hours | For flotation concentrate |
| Secondary Leach Residence Time | 26 | hours | For combined material |
| Total Adsorption Residence Time | 35.5 | hours | CIL + CIP circuits combined |
| Additional Power Demand | 1.8 | MW | For new flotation and regrind circuits |
| Total Nominal Power Demand | 5.1 | MW | Complete circuit with new equipment |
| Annual Power Consumption | 43 | MWh/a | Estimated for operations |
| Sodium Cyanide Consumption | 3,023 | t/a | Estimated annual usage |
| Lime Consumption | 2,142 | t/a | Estimated annual usage |
Additional Interesting Data and Summary
The O’Brien Gold Project represents a innovative approach to modern mineral processing through its toll milling arrangement with IAMGOLD’s Westwood complex. This strategy provides significant advantages in capital cost reduction, accelerated timeline to production, and minimized environmental impact through the use of existing infrastructure. The processing circuit has been specifically designed to handle the unique characteristics of the O’Brien mineralization, which demonstrates variable competency with Bond work indices of 18.7 kWh/t (CWi), 18.2 kWh/t (RWi), and 12.8 kWh/t (BWi) at the 75th percentile.
From an environmental perspective, the project benefits from existing water management systems that source fresh water from the Bousquet River, though a comprehensive water balance was not completed for this preliminary assessment. The circuit incorporates robust cyanide destruction using the SO2/air process to meet strict environmental standards with a target discharge concentration of less than 1 mg/L CNWAD. Tailings management utilizes existing facilities at the Westwood complex, though the geochemical compatibility of O’Brien tailings with these facilities requires further investigation in subsequent project phases.
The economic assessment indicates strong viability for the project, with the combination of gravity separation, flotation, and CIL/CIP processing providing the highest net present value. The circuit design takes advantage of the coarse gold component through early gravity recovery, while the flotation circuit captures finer gold associated with sulfide minerals. The regrind of flotation concentrate to 15 μm ensures optimal liberation for maximum leach recovery.
Looking forward, the project demonstrates the growing trend of collaborative mining operations where companies leverage existing processing infrastructure to bring new deposits into production more efficiently and sustainably. This approach aligns with ESG principles by reducing the environmental footprint of mining operations and optimizing resource utilization. As the project advances to feasibility and production phases, it will contribute to Quebec’s position as a leading mining jurisdiction while providing economic benefits to the local community through employment and regional development.
Source: NI 43-101 Technical Report | Preliminary Economic | Project: Brien Gold Project | Date: June 2025
