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.
