This report details the processing route and design parameters for the Sleeping Giant Mine, based on historical operations and a study for proposed operations.
Report context
The Sleeping Giant mine began operation in 1988 and was last operational in 2014. Since August 2016, the processing plant has been in operation, fed by ore from nearby mines. The report presents a processing plant study that forms part of a mineral resource estimate dated 2023.
Processing route
Crushing
The crushing circuit has two stages of crushing in closed circuit with a 6’x20’ double deck vibrating screen. Coarse ore from the 680-ton bin and fresh feed from the run-of-mine (ROM) pad are fed to a 24”x36” jaw crusher to reduce particle size from 45 cm to 10 cm. Product from the jaw crusher and two cone crushers are fed to the double-deck vibrating screen. The fines (≤1 cm) go to two 600-ton fine-ore bins. Material retained by the first deck feeds a 5/2 Standard (STD) cone crusher and material retained by the second deck feeds a 5/2 Short Head (SH) cone crusher.
Grinding
The grinding circuit has a primary rod mill in open circuit that receives the crusher circuit discharge, and two secondary ball mills in closed circuit with cyclones. The objective of the grinding circuit is to reduce the particle size of the crushed ore. Crusher circuit product is fed to an 8’x12’ rod mill for primary grinding before being sent to the cyclones (Linatex HSE-1820 R) for classification. The cyclones’ underflow is sent to two ball mills in parallel for further grinding. The ball mill discharges are recirculated to the cyclones. The cyclone overflow (D80 of 50 µm) is sent to the pre-leach thickener. Lead Nitrate is added in the grinding circuit to counter the negative effects of sulfides and to accelerate gold dissolution.
Pre-leach thickener and carbon in column
The objective of this circuit is to increase the percent solids of the grinding circuit product before being sent to the carbon-in-leach (CIL) circuit. A carbon-in-column (CIC) circuit is installed to recover gold in the pre-leach thickener overflow, but it is not in operation as no cyanide was added during the latest operation and is not planned to be added in the grinding circuit. The grinding circuit cyclone overflows feed a 45’ diameter pre-leach thickener. Lime is added to increase slurry pH. The slurry is thickened from 10% to 54% solids. The thickener underflow is sent to Preparation Tank #1. The thickener overflow is sent to the process-water tank. If required, thickener overflow can be sent to the CIC circuit, composed of four carbon columns, to recover gold in solution. CIC discharge is sent to the process-water tank. Carbon from CIC tank #1 is sent to the loaded carbon screen.
Leach, CIL and gold recovery
Thickener underflow is sent through one pre-aeration tank, two cyanidation tanks and four CIL tanks. Total leaching time of the leach and CIL circuits is 46 hours (at 35 t/h, 54% solids). Lime is added to increase slurry pH. Cyanide and air are added to leach the gold. Carbon is added to recover the gold in solution. The CIL tails from CIL tank #4 pass through a carbon safety screen before being pumped to the tailing storage facility. Once loaded with gold, carbon is screened and eluted. The pregnant solution is sent to the gold room for electrowinning, drying, and finally, smelting into gold bullion. Eluted carbon is regenerated in a kiln and reused in the CIL circuit. Carbon fines generated from the circuit are recovered in bags for further gold recovery.
Reagents and consumables
Major reagents utilised within the process plant are lime, sodium cyanide (NaCN), caustic soda (NaOH), lead nitrate, flocculant and a descaling agent. Expected annual reagent consumption for the study is: lime 137 t/y, sodium cyanide 93 t/y, caustic soda 47 t/y, lead nitrate 50 t/y, flocculant 2 t/y, and descaling agent 1 t/y. Activated carbon is fed through the carbon sizing screen from the carbon quench tank; oversize feeds the CIL circuit and undersize feeds the fine carbon circuit.
Key reported parameters
| Parameter | Value | Unit | Basis |
|---|---|---|---|
| Daily throughput | 350 | t/d | Design |
| Head grade – Au | 8.1 | g/t | Design |
| Recovery – Au | 96.7 | % | Model from mill performances |
| Ore moisture | 5.0 | % | Design |
| Pre-leach thickener underflow % solids | 54 | % | Design |
| Leach and CIL retention time | 46 | h | Design |
| Grinding circuit cyclone overflow D80 | 50 | µm | Design |
| Thickener feed solids | 10 | % | Design |
| Throughput range (historical, Sleeping Giant ore) | 34.0 – 37.9 | t/h | Historical operating data |
| Plant capacity (24 h/d) | 700 – 750 | t/d | Historical operating data |
| Estimated annual power consumption | 7.4 | GWh | Estimate from historical power consumption |
| Expected process water requirement (grinding circuit) | 280 – 330 | m³/d | Design |
Project website: https://www.abcourt.ca/projects/the-sleeping-giant-mine/
Technical qualifications
Gold recovery is based on a model developed from mill performances that predicts recovery based on head grade. There is no modification in plant throughput, equipment size, number of equipment or ore-feed that is expected to change this recovery model. The electrical energy requirements were estimated from historical power consumption when processing similar annual tonnage of Sleeping Giant ore. The capacity of the processing plant is higher than the current expected processing tonnage of 350 t/d on a 12-hour daily shift.
Source: NI 43-101 Technical Report and Mineral Resource Estimate for the Sleeping Giant Mine, Quebec, Canada, relevant sections.
