This technical report describes the mineral processing facilities and gold recovery operations at the Eagle River Gold Mining Complex, including historical operating data and proposed future testwork.
Report context
Dated April 22, 2022, this technical report for the Eagle River Gold Mining Complex (ERC) in Canada presents the mineral processing methods, plant description, operating parameters, and gold recovery performance for two ore types: Eagle River Mine (ERM) and Mishi. The mill is permitted for up to 1,200 tonnes per day on a crushing basis, with current operating parameters of 862 t/d for ERM and 840 t/d for Mishi. The report includes historical operating data from 2020 and 2021, as well as proposed future modifications based on testwork.
Processing route
Overview
The mill processes two types of ore (ERM and Mishi) through a flowsheet comprising crushing, grinding, gravity concentration, leaching, Merrill-Crowe precipitation, and tailings filtration for dry stacking. The total ounces produced in 2021 was 101,402.89 oz and for 2020 was 90,278.17 oz.
Stockpiles and crushing circuit
Three ore pads for stockpiles separate ERM and Mishi ore. From the stockpile, a front-end loader deposits ore into the jaw crusher. Coarse ore is transported by conveyor to be classified on a double deck vibrating screen. Oversize material goes to secondary crushing (cone crusher in closed circuit with the vibrating screen) and is reclassified after size reduction. Undersize material is directed to the fine ore bin. Fine ore is transported from the fine ore bin by two conveyors to the primary ball mill, with the second conveyor fitted with a weightometer.
Grinding circuit
The grinding circuit consists of a primary ball mill followed by a secondary ball mill in closed circuit with hydrocyclones. The primary ball mill discharges into the cyclone pumpbox, and slurry is pumped to cyclones for classification. Process water is added to the primary ball mill and cyclone feed pumpbox to obtain the required cyclone feed density. Lime slurry is added to the cyclone pumpbox to target the pH for cyanide leaching and downstream Merrill-Crowe circuit. Cyclone undersize material reports to the secondary ball mill, which also discharges into the cyclone pumpbox. The cyclone overflow is sent to the vibrating trash screen, and via gravity, the slurry enters the thickener pumpbox to be pumped to the thickener feedbox.
Gravity circuit
The gravity circuit includes centrifugal concentration fed via a 2 mm guard screen. Feed to the gravity circuit is a portion of the cyclone feed, varied based on feed tonnage. The guard screen oversize material reports to the primary ball mill. The guard screen undersize material is fed to the centrifugal concentrator via gravity. Operation of the gravity concentrator is semi-batch, and the gravity concentrate is collected in a hopper and upgraded on a shaking table daily. The table concentrate is treated by magnetic separation and sent to the refinery for smelting into doré bars. The centrifugal tailings discharge into the cyclone pumpbox, and the shaking table tailings are pumped to the secondary ball mill feed by the shaker room sump.
Testwork from SGS showed that a higher percentage of gravity recoverable gold was available from the secondary ball mill circuit than just the primary ball mill circuit. A method of diverting the secondary ball mill circuit's slurry to the gravity concentrator is being devised to allow greater gravity gold recovery.
Pre-leach thickener and leaching
The thickener pumpbox receives the trash screen undersize material and is the location for sodium permanganate solution addition. Slurry is pumped to the thickener feed box, where flocculant and cyanide are added, and the slurry discharges into the thickener feedwell. The thickener underflow is pumped to the leach tanks, which are agitated and use compressed air sparging as a source of dissolved oxygen. The leach circuit consists of six tanks (with one tank on standby), and slurry flows via an upcomer by gravity displacement. The retention time of the leach circuit (36 to 38 hours) is sufficient for gold extraction from the solids for both ore types.
The discharge from tank 6 is filtered by two drum filters to recover the pregnant solution, which is sent to the thickener. The solids are washed and re-pulped with barren solution and pumped to the tailings circuit. The thickener overflow reports to a dirty pregnant solution tank. The dirty pregnant solution is treated by clarifiers to remove suspended solids.
Merrill-Crowe circuit
The suspended solids in the thickener overflow are removed by three clarifiers in parallel, with two operated and one on standby. The clarifiers are primed with Dicalite and Solka Floc before filtering the dirty pregnant solution to the clear pregnant solution tank. The clarified pregnant solution proceeds to two vacuum towers to remove dissolved oxygen. The de-oxygenated solution is transferred to a hopper to which zinc is added. Lead nitrate is added to the zinc hopper via a small barren solution tank. The solution proceeds to a sock press primed with Dicalite where the gold precipitate is captured, and the filtered solution is pumped to the barren solution tank. Two sock presses are operated in parallel with one on standby.
Tailings circuit
The discharge from the drum filters is pumped to the tailings building and then filtered by two additional drum filters to recover the solution, which is sent to the process water tank or thickener. The solids are washed with reclaim water and loaded onto a conveyor for dry stacking at the tailings facility.
Refinery
The refinery is a restricted entry facility with CCTV, concrete vault with a safe, a sock burner oven, and a furnace. Smelting is performed in a Wabi furnace using propane as fuel. Solids-laden press socks are burned to remove the cloth and inorganic filtration material. The furnace treats two concentrates to produce doré: shaking table concentrate and precipitation concentrate. These are separately mixed with smelting and oxidative reagents to produce doré of 80 to 94% gold content.
Cyanide detoxification
Cyanide is detoxified by addition of 50% hydrogen peroxide in solution phase. Hydrogen peroxide is added in the Reclaim Pond as needed based on the concentration of Weak Acid Dissociable and free cyanide. The hydrogen peroxide treatment scheme is effective because the mill operates a closed loop water balance, reducing the mass loading of cyanide requiring treatment.
Consumables and reagents
Reagent consumption values derived from 2021 processing data include sodium cyanide at 0.520 kg/t for gold leaching, hydrated lime at 0.786 kg/t for pH maintenance, and zinc dust at 0.086 kg/t for gold cementation. Grinding media consumption is 0.773 kg/t for the primary ball mill (3" media) and 0.593 kg/t for the secondary ball mill (1.5" media).
Key reported parameters
| Parameter | Unit | Eagle (ERM) | Mishi |
|---|---|---|---|
| Mill Availability (design) | % | 93.3 | 93.3 |
| Mill Availability (actual 2021) | % | 86.0 | 86.0 |
| Daily Mill Throughput (max, actual) | t/d | 1,027 | 1,061 |
| Daily Mill Throughput (average, actual) | t/d | 779 | 773 |
| Crushing Product Size, 80% Passing | inch | 9/16 | 9/16 |
| Grinding Product Size, 75% Passing | μm | 74 | 74 |
| Thickener Underflow Density | % | 55 | 55 |
| Leach pH range | – | 10.5-11.2 | 10.5-11.2 |
| Recovery – Gravity Circuit (average) | % | 43 | – |
| Recovery – Merrill-Crowe Circuit (average) | % | 88 | 94 |
| Recovery – Overall (average) | % | 97 | 83 |
| Daily Produced Ounce (average) | oz | 330 | 51 |
Project website: https://www.wesdome.com/English/operations/eagle-river/default.aspx
Technical qualifications
This technical report is based on the original document dated April 22, 2022. The operating parameters presented in Table 17-1 are for 2021 and 2022. The mill operates based on 93.3% availability; however, for 2021 the mill was available for 86% of the time due to a planned shutdown in August 2021. The mill flowsheet is shown in Figure 17-1 but the figure itself is not reproduced in this summary. Consumables and reagents values are derived from 2021 processing data only.
Source: Technical Report for the Eagle River Gold Mining Complex, Canada, April 22, 2022, Sections 1.15, 1.16, 1.17, and 17.
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.
Eagle River Mill: Process Description and Debottlenecking Plans for a Mature Gold Operation
The Eagle River Mine, an active underground gold operation in Ontario, is advancing processing upgrades through a 2025 debottlenecking study while maintaining its established gravity and Merrill-Crowe flowsheet.
The Eagle River Mine (ERM) is a producing underground gold operation located approximately 50 km west of Wawa, Ontario, Canada. The site is wholly owned by Wesdome Gold Mines Ltd. as part of the Eagle River Gold Mining Complex, which also includes the Eagle River Mill, the Magnacon underground mine, and the Mishi open pit mine. Both Magnacon and Mishi are no longer in production. Commercial production at ERM began in 1996. A Pre-Feasibility Study was commissioned in March 2025, with the technical report effective 31 December 2025. The operation processes gold ore through the Eagle River Mill, which is permitted for up to 1,200 t/d on a crushing basis and planned around 1,000 t/d.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Mill permit capacity | 1,200 | t/d | Crushing basis |
| Planned throughput | 1,000 | t/d | Not stated |
| Mill utilization | 90 | % | Design value |
| Daily mill throughput (design) | 900 | t/d | Design value |
| Daily mill throughput (nominal) | 770 | t/d | Nominal value |
| Crushing product size, 80% passing | 19 | mm | Lower screen, design value |
| Grinding product size, 75% passing | 74 | µm | Design value |
| Gravity circuit feed source | Not applicable | Not applicable | Cyclone feed |
| Thickener underflow density | 58 | % | Design value |
| Leach pH range | 10.5 – 11.2 | Not applicable | Design value |
| Gravity recovery (average) | 59.8 | % | Design value |
| Merrill-Crowe recovery (average) | 37.7 | % | Design value |
| Overall recovery (average) | 96.7 | % | Design value |
| Daily produced ounce (average) | 290 | oz | Design value |
| Sodium cyanide usage | 0.246 | kg/t | From 2021 data |
| Hydrated lime usage | 0.470 | kg/t | From 2021 data |
| Zinc dust usage | 0.059 | kg/t | From 2021 data |
| Grinding media 1.5 inch usage | 0.708 | kg/t | From 2021 data |
| Grinding media 3 inch usage | 0.642 | kg/t | From 2021 data |
| Hydrogen peroxide usage | 0.848 | kg/t | From 2021 data |
| Total tonnes processed (LOM) | 2,887 | kt | From process plan |
| Average feed grade (LOM) | 7.3 | g/t Au | Tonnage-weighted basis |
| Life-of-mine gold recovery | 95.7 | % | Metal-weighted basis |
| Contained gold (LOM) | 675 | koz Au | From process plan |
| Recovered gold (LOM) | 646 | koz Au | From process plan |
Overview
The Eagle River Mill is a conventional gold processing facility that integrates gravity concentration with cyanide leaching and Merrill-Crowe precipitation. The flowsheet includes three stockpile pads for grade blending, followed by two-stage crushing and two-stage grinding. A gravity circuit recovers free gold from a portion of the grinding circuit slurry. Leaching occurs in six mechanically agitated tanks arranged in series, with compressed air sparging for oxygen supply. Gold is recovered from pregnant solution by zinc precipitation in the Merrill-Crowe circuit, and tailings are filtered for dry stacking. Cyanide detoxification is performed using hydrogen peroxide addition to reclaim pond water, and the mill operates on a largely closed-loop water balance. In a 2025 debottlenecking study, the operation identified potential modifications to support increased throughput to a nominal 46 t/h and a 48.5 t/h design basis.
Key Process Stages
Material from the mine reports to three stockpile pads where it is blended by head grade before reclaim. A front-end loader feeds the run-of-mine bin. Two-stage crushing uses a primary jaw crusher and a secondary cone crusher in closed circuit with a vibrating screen. Screen undersize goes to the fine ore bin while oversize is conveyed to the cone crusher.
The grinding circuit pairs a primary ball mill with a secondary ball mill in closed circuit with hydrocyclones. Fine feed is conveyed to the primary mill. Discharge flows by gravity to the cyclone pumpbox where it combines with secondary mill discharge and gravity circuit tailings. Lime slurry is added at the pumpbox for pH control ahead of cyanidation. Slurry is pumped to classification, with a portion of the circulating load directed to the gravity circuit. Cyclone underflow returns to the secondary mill. Cyclone overflow passes through a trash screen to the thickener pumpbox.
A 2 mm guard screen protects the gravity circuit. Feed is a portion of the grinding circuit slurry. Screen undersize reports to a centrifugal concentrator operating on a semi-batch basis. Concentrate is upgraded on a shaking table and further treated by magnetic separation before smelting. Tailings from the concentrator and shaking table return to the cyclone pumpbox.
Potassium permanganate is added at the thickener pumpbox which receives trash screen undersize. Flocculant and cyanide are added at the thickener feedbox. Thickener overflow goes to the dirty pregnant solution tank. Underflow is pumped to the leach circuit. The existing leach circuit contains six mechanically agitated tanks in series. Slurry moves by gravity displacement through upcomers. Compressed air sparging provides dissolved oxygen. Discharge from the final leach tank goes to first-stage vacuum drum filters. One filter operates while one is on standby. Filter cake is washed, repulped with barren solution, and pumped to the tailings building.
Clarifiers operating in parallel remove suspended solids from thickener overflow. The clarifiers are precoated with Dicalite and Solka Floc. Clarified pregnant solution is de-aerated in vacuum towers before zinc addition. Lead nitrate is added as required for gold and silver precipitation. Precipitate is recovered by sock filtration. Filtrate goes to the barren solution tank.
Final tailings filtration occurs in the tailings building using two additional vacuum drum filters. One filter operates with one on standby. Filtrate returns to the mill solution system. Filtered tailings are washed with reclaim water and conveyed to the tailings management area for dry stacking.
The refinery treats two concentrate streams. Shaking table concentrate comes from the gravity circuit. Precipitation concentrate comes from the Merrill-Crowe circuit. Gold-bearing socks are burned to remove filter media. Gravity concentrate and precipitation concentrate are mixed separately with smelting and oxidizing reagents before furnace treatment. Doré typically contains 80% to 94% gold.
Cyanide detoxification uses 50% hydrogen peroxide addition to reclaim pond solution. Cyanide in tailings moisture reports to the reclaim pond through runoff. Peroxide oxidizes cyanide to cyanate, which decomposes through hydrolysis. The closed-loop water balance reduces net cyanide mass requiring treatment.
Additional Interesting Data and Summary
Metallurgical testwork completed in 2025 found that overall leach residence time of more than 90 hours is required to achieve gold recoveries above 96%. This exceeds the capacity of the existing six-tank circuit. The feed grade averages 7.27 g/t Au over the life of mine on a tonnage-weighted basis. Annual grades are front-loaded, at 11.77 g/t Au in 2026 declining to around 5 g/t Au by 2030. Forecast gold recovery ranges from 94.74% to 96.52%. The life-of-mine recovery is 95.70% calculated on a metal-weighted basis. ERM material has moderate-to-hard comminution characteristics with Bond Ball Mill Work Index values from 13.6 to 18.3 kWh/t. Laboratory gravity recovery was approximately 81.7%. Cyanidation testing achieved combined gravity and cyanidation recoveries between 98.74% and 99.79% in the 2025 program. That program found oxygen improved early leach kinetics but did not materially improve final recovery compared with air sparging. Finer grinding produced the highest final recovery but increased reagent consumption. Increasing cyanide above 400 ppm did not materially improve recovery, while reducing cyanide to 200 ppm lowered final recovery.
Key Processes
- Crushing: two-stage arrangement with primary jaw crusher and secondary cone crusher in closed circuit with vibrating screen
- Grinding: primary ball mill followed by secondary ball mill in closed circuit with hydrocyclones
- Gravity concentration: centrifugal concentrator with shaking table and magnetic separation
- Leaching: six mechanically agitated tanks in series with compressed air sparging
- Gold recovery: Merrill-Crowe precipitation with zinc dust and lead nitrate
- Tailings: two-stage vacuum drum filtration for dry-stack tailings
- Detoxification: hydrogen peroxide addition to reclaim pond for cyanide destruction
- Refining: separate smelting of gravity concentrate and Merrill-Crowe precipitate to produce doré
Source: Independent Technical Report for the Eagle River Mine, Ontario, Canada, 31 December 2025. Project website: Eagle River Mine
Wesdome Gold Mines Ltd. — Technical Report
Wesdome Gold Mines Ltd. — Technical Report
| Company | Wesdome Gold Mines Ltd. |
| Date | Unknown |
| Region | Canada |
| Commodities | Gold, Silver |
| Throughput | 1,050 tpd |
| Status | Operating |
Executive Summary
This section details the mineral processing and recovery methods for the Wesdome Gold Mines Ltd. operations. The company utilizes the former Magnacon mill, located 17 kilometres by road from the mine. The mill capacity was increased to 1,000 tonnes per day in 1999, with a practical limit of approximately 1,050 tonnes per day due to maintenance requirements, despite a permitted crushing capacity of 1,200 tonnes per day.
The mill employs the Merrill-Crowe process for gold recovery from Eagle River ore, supplemented by gravity concentration using a Knelson concentrator which recovers about 40% of the gold. The Merrill-Crowe process utilizes cyanide solution and zinc precipitation to produce doré bars containing approximately 80%-92% gold. By-product silver is recovered at a rate of one part for every six to ten parts of gold. Overall mill recoveries are around 95% for Eagle River ore and 87% for Mishi ore. The mill operates 24 hours per day, seven days a week.
Website: https://www.wesdome.com/English/overview/default.aspx
Report Date: Unknown
Region: Canada
Project Status: Operating
Commodity: Gold, Silver
Throughput: 1,050 tpd
Mine Life:
Mine Type:
Ore type:
