Based on the February 27, 2020 effective-date Technical Report and Preliminary Economic Assessment for the Tiger Deposit, Rackla Gold Project, Yukon, Canada, this profile describes a proposed 1,500 t/d carbon-in-pulp processing plant designed to treat two distinct mineralisation types with markedly different recovery expectations.
Report context
The technical report documents a Preliminary Economic Assessment (PEA) for the Tiger Deposit within ATAC Resources Ltd.'s Rackla Gold Project in Yukon, Canada. The processing section (Section 17.0 Recovery Methods) presents a proposed plant design, not an operating facility. The report distinguishes clearly between oxide and sulphide mineralisation, each with its own gold recovery projection. Metallurgical performance projections are supplied on a yearly basis for a six-year mine life, based on test work described in Section 13.0 of the report. The authors recommend further test work for more accurate projections.
Processing route
Crushing and grinding
The proposed plant will receive run-of-mine material trucked from the proposed open pit to a ROM receiving pad. A loader reclaims stockpiled material to a loading hopper that feeds a mineral sizer, selected because the mill feed is anticipated to be soft with a significant amount of fines. The sizer reduces material to 80% passing approximately 120 mm at an average crushing rate of 200 t/h. The crushing circuit operates on day shift only and has a design availability of 75%.
Crushed product is conveyed to a 1,500-tonne live-capacity SAG mill feed surge bin. Material is reclaimed from the bin by belt feeder at a nominal 68 t/h onto a conveyor feeding the primary grinding circuit.
The grinding circuit comprises a SAG mill and a ball mill in closed circuit with classifying hydrocyclones. The SAG mill measures 4.27 m diameter by 2.59 m effective grinding length, driven by a 470 kW variable frequency drive. It is equipped with 40 mm pebble ports. SAG mill discharge passes through an integrated trommel screen with 9.5 mm slot openings; oversize is conveyed back to the SAG mill feed conveyor. The ball mill measures 3.35 m diameter by 4.42 m effective grinding length, powered by a 665 kW fixed speed drive. Two 200 mm hydrocyclones classify the combined SAG mill trommel undersize and ball mill discharge. The circulating load to the ball mill is approximately 200 to 300%. The hydrocyclone overflow,the final primary grind product,is 80% passing 75 µm at approximately 30% w/w solids. Grinding media are added manually on a batch basis; lime slurry is added to the mill for pH adjustment. A particle size analyser monitors operating efficiency. Provision is made for future addition of a pebble crushing circuit.
The design Bond Ball Mill Work Index is 10.0 kWh/t. Grinding and leach circuit availability is 92%, with nominal milling process rate of 68 t/h.
Cyanide leaching and carbon adsorption
Hydrocyclone overflow is screened to remove oversize, then flows by gravity to a 10-metre diameter high-rate leach feed thickener. Thickener overflow is pumped to the grinding circuit for reuse. Thickener underflow at 55 to 60% w/w solids is pumped to the head of the cyanide leach circuit. Dilution water from the leach residue thickener overflow and process makeup water reduces solids density to approximately 45% w/w for cyanidation.
The CIP circuit consists of six leach tanks and five CIP tanks. Each leach tank is 10 m diameter by 10 m high, equipped with agitator, insulated and located outdoors. The five CIP tanks are 7 m diameter by 7.5 m high, located inside the mill building, equipped with in-tank carbon transferring pumps and inter-stage screens. Total leaching retention time is 38 hours. Tanks are aerated by compressed air from two oil-free compressors (one operating, one standby). Activated carbon is added to the last CIP tank; loaded carbon leaves the circuit from the first CIP tank. Sodium cyanide is added to leach tanks; lime maintains slurry pH at approximately 10 to 11.
Loaded carbon from the first CIP tank reports to the carbon stripping circuit. Leach residue passes through a carbon safety screen to recover coarse carbon grains; screen undersize reports to the residue thickener before cyanide destruction.
Carbon stripping, electrowinning and refining
Loaded carbon undergoes acid washing with dilute hydrochloric acid to remove inorganic contaminants such as calcium scale, then fresh water rinsing, before transfer to the elution vessel. The modified Zadra pressure stripping process circulates heated barren solution through the carbon bed. Barren solution is heated by two heat exchangers,one exchanging heat with pregnant solution, the other using steam from a boiler. The solution flows up through the carbon bed; pregnant solution overflows near the top of the stripping vessel, is cooled by heat exchange with barren solution, and flows to a pregnant solution holding tank. The stripping circuit processes approximately 2.0 tonnes of loaded carbon per batch.
Pregnant solution from the elution system is pumped through electrowinning cells where gold deposits on stainless steel wool cathodes. Depleted solution returns to the barren solution tank for reheating and return to the stripping vessel, or is sent directly to the CIP circuit without heating. Cathodes are periodically cleaned to recover precious metal sludge. The sludge is pumped to a plate-and-frame filter press for batch dewatering; filter cake is oven-dried. Dried slimes are mixed with flux and melted at approximately 1,150°C in an induction furnace to produce gold bullion containing mostly gold with some silver and impurities.
Eluted carbon is dewatered on a stationary screen, then fed to an electrically heated rotary kiln for reactivation at 650 to 700°C in an inert atmosphere. Reactivated carbon is quenched in water, undergoes attrition treatment and screen washing, then is circulated back to the CIP circuit. Makeup fresh carbon is added as required and treated by attrition before use.
Residue treatment and tailings management
CIP circuit residues are pumped to a 10-metre diameter high-rate thickener to recover residual cyanide and water. Thickener overflow is returned to the leach feed box as dilution water. Underflow reports to the cyanide destruction circuit, which uses a sulphur dioxide/air oxidation process. Sodium metabisulfite provides the sulphur dioxide source; copper sulphate is added as catalyst as required; lime controls slurry pH. Two 6.0 m diameter by 7.0 m high oxidation tanks are used, with air provided for oxidation.
Treated leach residue flows by gravity to a tailings management facility (TMF) located northwest of the process plant. The residue storage pond is lined with geomembrane liners. Residue is covered with water to prevent sulphide mineral oxidation. Supernatant is pumped back to the grinding and cyanidation circuits for reuse.
Reagents
Reagents for CIP and gold recovery include hydrated lime, sodium cyanide, activated carbon, sodium hydroxide, and hydrochloric acid. Cyanide destruction reagents are sodium metabisulfite, copper sulphate, and hydrated lime. Flocculant and antiscalant are also used.
Solid reagents are diluted to 10% to 25% solution strength with fresh water in mixing tanks and stored in holding tanks before addition via metering pumps. Undiluted liquid reagents (hydrochloric acid and antiscalant) are added via individual metering pumps. Flocculant is prepared in a packaged system, diluted to 0.2% solution strength, and distributed to the leach feed thickener and leach residue thickener via metering pumps.
Water systems
A freshwater system supplies an 8.0 m diameter by 8.0 m high storage tank from a fresh water reservoir or boreholes for fire water, mill motor cooling, pump gland seal water, and reagent preparation. The freshwater tank is designed to remain full at all times providing at least two hours of firewater supply. Potable water from boreholes is treated by filtration and chlorination.
A process water system supplies grinding, CIP leaching, gold recovery, and cyanide destruction circuits. Leach feed thickener overflow and water reclaimed from the TMF are pumped directly to process circuits or to a 5.0 m diameter by 6.0 m high process water surge tank. Process water from the residue thickener overflow dilutes the leach feed thickener underflow.
Key reported parameters
| Parameter | Unit | Value | Basis |
|---|---|---|---|
| Nominal throughput (annual) | t/a | 547,500 | Design |
| Daily process rate | t/d | 1,500 | Design |
| Operating days | d/a | 365 | Design |
| Overall gold recovery, oxides | % | 90.5 | Design |
| Overall gold recovery, sulphides | % | 60.8 | Design |
| Average gold production | oz/a | ~44,500 | Projected |
| Average head gold grade | g/t Au | 3.82 | Mine plan average |
| Specific gravity, oxide | – | 2.4 | Ore characteristic |
| Specific gravity, sulphide | – | 3.4 | Ore characteristic |
| Primary crushing availability | % | 75 | Design |
| Primary crushing rate | t/h | 200 | Design |
| Primary crusher product P80 | mm | 120 | Design |
| Grind/leach availability | % | 92 | Design |
| Nominal milling rate | t/h | 68 | Design |
| Mill feed size (P80) | µm | 120,000 | Design |
| Primary grind size (P80) | µm | 75 | Design |
| Bond ball mill work index | kWh/t | 10.0 | Design |
| Leach method | – | CIP | Design |
| Leach retention time | h | 38 | Design |
| SAG mill dimensions (diameter x length) | m | 4.27 x 2.59 | Design |
| SAG mill drive power | kW | 470 | Design |
| Ball mill dimensions (diameter x length) | m | 3.35 x 4.42 | Design |
| Ball mill drive power | kW | 665 | Design |
| Hydrocyclone diameter | mm | 200 | Design |
| Trommel screen opening | mm | 9.5 (slot) | Design |
| Circulating load (ball mill) | % | 200-300 | Design |
| Leach feed thickener diameter | m | 10 | Design |
| Leach tank dimensions (diameter x height) | m | 10 x 10 | Design |
| CIP tank dimensions (diameter x height) | m | 7 x 7.5 | Design |
| Number of leach tanks | – | 6 | Design |
| Number of CIP tanks | – | 5 | Design |
| Cyanide destruction tank dimensions | m | 6.0 x 7.0 | Design |
| Carbon stripping batch capacity | t/batch | ~2.0 | Design |
| Carbon reactivation temperature | °C | 650-700 | Design |
| Induction furnace temperature | °C | ~1,150 | Design |
| Freshwater tank dimensions (diameter x height) | m | 8.0 x 8.0 | Design |
| Process water tank dimensions (diameter x height) | m | 5.0 x 6.0 | Design |
Project website: https://miningdataonline.com/property/1801/Tiger-(Rackla)-Project.aspx
Technical qualifications
This profile is based exclusively on Section 17.0 (Recovery Methods) of the Technical Report and Preliminary Economic Assessment for the Tiger Deposit, Rackla Gold Project, Yukon, Canada, effective February 27, 2020. The report is a PEA, not a feasibility study, and the processing plant described is a proposed design, not an operating facility. All process rates, recoveries, and equipment specifications represent design criteria or projections, not demonstrated operating results.
Gold recoveries are reported separately for oxide (90.5%) and sulphide (60.8%) mineralisation, based on test work described in Section 13.0 of the report. Yearly metallurgical performance projections range from 62.9% to 89.3% over the six-year mine life, showing varying proportions of oxide and sulphide feed, with an overall life-of-mine average of 80.8%. The report explicitly notes that further test work is recommended for more accurate metallurgical performance projections.
The mill feed is anticipated to be soft with significant fines content, leading to selection of a mineral sizer for primary crushing. No operating data exist for this configuration at this deposit. The report makes provision for future addition of a pebble crushing circuit but does not include it in the base design.
Source: Technical Report and Preliminary Economic Assessment for the Tiger Deposit, Rackla Gold Project, Yukon, Canada, effective date February 27, 2020, Section 17.0 Recovery Methods.
