The proposed gold processing facility for the MacLellan and Farley Lake projects is designed as a staged conventional crushing, grinding, gravity recovery, carbon-in-pulp (CIP) leaching, and cyanide destruction plant producing gold-silver doré.
Report context
The preliminary economic assessment for the MacLellan, Farley Lake, Burnt Timber, and Linkwood properties, Lynn Lake Gold Camp, Manitoba, was prepared for Carlisle Goldfields Ltd. The processing section (Recovery Methods) describes a proposed gold-silver processing facility designed to ultimately process a nominal 2.63 Mt/a or 7.50 kt/d of gold-silver mineralization. The mill is planned to be built in two stages: the first stage will process 1.31 Mt/a or 3.75 kt/d, with the remaining equipment installed after four years to reach full capacity. This facility is expected to produce an average of 145,092 troy oz/a of gold over the life of mine and 198,763 troy oz/a of silver during the years when MacLellan is operational. Recoveries are based on 93.7% gold recovery from Farley Lake and 89.3% gold recovery from MacLellan, with approximately 60% silver recovery possible from the MacLellan mineralization.
Processing route
Process flowsheet development
The process flowsheet was developed based on the results of test work conducted by SGS in Vancouver, British Columbia and by Witteck in Mississauga, Ontario. The selected process flowsheet will produce gold-silver doré as the final product.
Crushing circuit
The process uses a conventional crushing and grinding circuit with screens and cyclones for size control. ROM material will be trucked from the open pit mine and dumped directly into the jaw crusher feed hopper or stored on a stockpile for later processing. Two 86 cm by 112 cm jaw crushers will reduce ROM material from less than 400 mm to 135 mm; one crusher will be installed prior to mill start-up and the second during the second stage. Primary crushing will operate 17 h/d to process 238 t/h in the first capital stage and 475 t/h in the second stage. A grizzly screen with hydraulic rock breaker will handle oversized material.
Secondary crushing will reduce material to 32 mm using one standard head cone crusher measuring 1.5 m in diameter, operated in open circuit with screens. The tertiary crushing circuit will reduce material to 8 mm using one short head cone crusher measuring 2.4 m in diameter. The fine mineralized material bin will have a capacity of 13,300 t with a live bottom feeder.
Grinding circuit
Fine grinding will take place in a wet ball mill in closed circuit with cyclones. One ball mill measuring 4.4 m diameter by 9.7 m with 4,500 kW will be installed when the plant first begins production, and a second ball mill will be installed when the plant is expanded. Fresh material will be added at 166 t/h during the first years and 332 t/h at final capacity. Process water will maintain 70% solids in the ball mill. The ball mill product size is 80% passing 84 µm with a recirculating load of 300%.
Gravity gold recovery
Free or gravity gold is recovered separately by a centrifugal concentrator (KC-QS48, 48-inch diameter or equivalent). Gold thus recovered is subjected to intense cyanide leach followed by electrowinning. The centrifugal concentrator will operate intermittently on undersize material from a sieve-bend screen that ensures no +2 mm material enters the concentrators. Gold concentrate will be transferred to an intense leach tank (ConSep Acacia CS1000 or equivalent) once sufficient material has been collected, with each batch taking approximately one day to collect. The leach will take place at 50°C with approximately 1,000 g/L of cyanide and LeachAid added. Pregnant leach solution will be treated in a dedicated basketless EW cell.
Leaching and pre-aeration
Ground slurry advancing to leaching is first thickened in a conventional bridge thickener with steel wall measuring 35.6 m diameter to increase density to 40% solids. The design includes one thickener for both trains. Thickener underflow then advances to pre-aeration tanks.
Pre-aeration tanks will be sparged with air or oxygen. Six tanks measuring 17.2 m diameter by 17.2 m height will be installed, with three installed in each capital stage. Pre-aeration time is 24 h. Lead nitrate may be added at up to 300 g/t. The pH will be adjusted to between 8.0 and 11.0 with lime.
Leach tanks will be installed as two identical trains of seven tanks each, with tanks measuring 16.4 m diameter by 16.4 m height. Leach circuit retention time is 48 h. Sodium cyanide will be added at 1.0 to 1.5 g/L NaCN. The pH will be adjusted to 10.5 to 11 with lime. All leach tanks will be sparged; the first two leach tanks may need to be sparged with oxygen.
CIP adsorption circuit
Activated carbon will be used to remove gold from the slurry in the CIP circuit. The circuit will consist of one or two trains of six agitated tanks in series, with tanks measuring 8.3 m diameter by 8.3 m height. The CIP circuit will use Kemix pump cells arranged on the same level in a carousel pattern. Carbon will have a stage-wise residence time of 38 h, while pulp will continuously flow through the circuit with a residence time of 1 h in each stage. Approximately 25 g/L of granular activated carbon will be added to the sixth stage. The batch movement of carbon will be about 9.7 t, processed over 38 h.
Gold elution and electrowinning
Gold will be recovered from the loaded carbon using the AARL elution process. Up to 100% of loaded carbon may be subjected to an acid wash using hydrochloric acid to remove calcium scale and adsorbed base metals. Carbon will be soaked in approximately 3% sodium cyanide and up to 2% sodium hydroxide for about 30 min, then heated to approximately 110 to 120°C and 70 to 100 kPa and eluted with six to ten bed volumes of high-quality deionized water.
Gold will be removed from the pregnant eluate using basketless EW cells. The EW circuit will have four 4.25 m³ cells installed in two stages. Gold will be loosely deposited on the EW electrodes and pressure washed to form gold-rich sludge. This sludge will be dewatered in a filter press and dried, then mixed with fluxes and smelted in a 125 kW induction furnace to produce gold-silver doré.
Carbon regeneration
Some or all of the carbon may be regenerated in an electrically fired rotary kiln to remove organic poisons and reactivate the carbon. The kiln will process carbon at 750°C for 30 min. Reactivated carbon will be quenched and screened before being returned to the barren carbon storage tank.
Cyanide destruction
The barren CIP tailings will be pumped to cyanide detoxification tanks where cyanide will be treated using the INCO sulphur dioxide and air process. SMBS will be added to slurry in the presence of copper from copper sulphate. Test work indicates that 140 min will be required for this reaction. Slurries thus treated typically have less than 5 ppm CN WAD. One cyanide destruction tank measuring 11.5 m diameter by 11.5 m height will be installed in each stage.
Reagent handling and storage
Reagents will include lime (delivered on 40 t trucks, slaked on site), sodium hydroxide (delivered in totes), flocculant (bulk bags), sodium cyanide briquettes (boxes or drums), hydrochloric acid (totes), SMBS (bulk bags), copper sulphate (bulk bags), activated carbon (bulk bags), and lead nitrate (sacks).
Key reported parameters
| Criteria | Unit | Value |
|---|---|---|
| First Stage Overall Plant Feed | t/d | 3,750 |
| Second Stage Overall Plant Feed | t/d | 7,500 |
| Operation Rate | d/a | 350 |
| Primary Crushing Availability (Both Stages) | % | 70 |
| First Stage Secondary and Tertiary Crushing Availability | % | 47 |
| Second Stage Secondary and Tertiary Crushing Availability | % | 94 |
| Plant Remainder Availability (Both Stages) | % | 94 |
| Bond Ball Mill Work Index (design) | kWh/t | 12.4 |
| Bond Abrasion Index (design) | 0.158 | |
| Specific Gravity Plant Feed | g/cm³ | 2.7 |
| Mill Feed Size, 80% Passing | mm | 400 |
| Primary Crushing Product Size, 80% Passing | mm | 135 |
| Secondary Crushing Product Size, 80% Passing | mm | 32 |
| Tertiary Crushing Product Size, 80% Passing | mm | 8 |
| Ball Mill Product Size, 80% Passing | µm | 84 |
| Ball Mill Recirculating Load | % | 300 |
| Pre-aeration Time | h | 24 |
| Leach Circuit Retention Time | h | 48 |
| CIP Circuit Retention Time (pulp) | h | 6 |
| CIP Circuit Retention Time (carbon) | h | 228 |
| Carbon Retention Time (stage-wise) | h | 38 |
| Head Grade (design) Au | g/t | 2.30 |
| Head Grade (design, MacLellan only) Ag | g/t | 4.36 |
| Design Recovery Au | % | 90.7 |
| Design Recovery Ag | % | 60.1 |
Project website: https://www.canadianminingjournal.com/news/gold-resource-initial-burnt-timber-estimate-includes-780-500-oz/
Technical qualifications
The design criteria are based on test work conducted by SGS and Witteck. The process flowsheet was developed based on the results of that test work. Provision should be made to sparge the pre-aeration tank with air or oxygen depending on the results of additional test work. All leach tanks will be sparged with air, but future test work may indicate that the first two leach tanks should be sparged with oxygen. Lead nitrate addition of up to 300 g/t depends on the results of additional test work on a representative sample of mill feed. The silver value is only included in the process plan for material recovered from MacLellan because the mining plan does not account for silver in the Farley Lake mineralization. Recoveries of 93.7% gold from Farley Lake and 89.3% gold from MacLellan are stated; the overall design recovery of 90.7% is provided in the design criteria.
Source: Preliminary Economic Assessment for the MacLellan, Farley Lake, Burnt Timber, and Linkwood Properties, Lynn Lake Gold Camp, Manitoba, Carlisle Goldfields Ltd., Section 17.0 Recovery Methods.
