The Brewery Creek Project is a proposed gold and silver heap leach operation in Canada's Yukon, designed to process 9,000 tonnes per day of mineralized material over an estimated 7.9-year mine life.
The Brewery Creek Project is a proposed open pit mining operation located in the Yukon, Canada, with a processing design based on cyanide heap leaching for gold and silver recovery. The project's Preliminary Economic Assessment, detailed in a January 2022 technical report, contemplates processing a mineral resource of 18.7 million tonnes at an established rate of 9,000 tonnes per day, resulting in an estimated project life of 7.9 years. A key aspect of the project's design is the reuse of the existing heap leach pad and associated ponds for processing newly mined material. This plan involves reclaiming previously leached material from the existing pad during the pre-production period to both recover residual values and prepare the pad for new stacking.
The processing facility is designed around a conventional recovery flowsheet. Material will be crushed in a three-stage closed crushing circuit before being stacked on the expanded leach pad. Gold and silver will be dissolved from the ore by cyanide solution percolating through the heap, and the resultant pregnant solution will be processed through a carbon adsorption circuit. Finally, the loaded carbon will be stripped, and the precious metal sludge will be treated in a mercury retort and smelted to produce the final doré product. The project design emphasizes established technologies and includes provisions for seasonal operation, water management, and reagent handling.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Mineral Resource | 18.7 | million tonnes | Basis for project life calculation. |
| Processing Rate | 9,000 | tonnes per day | Average design rate for crushing and stacking. |
| Project Life | 7.9 | years | Estimated based on resource and processing rate. |
| Crushing Production Rate | 9,000 | tonnes per day | Average |
| Crushing Operation | 12 hours/shift, 2 shifts/day, 7 days/week | – | Design criteria for crushing operation. |
| Annual Tonnage Processed | 2,475,000 | tonnes | Corresponds to the 9,000 tpd average. |
| Crushing Product Size | 19 | mm | 80% passing. |
| Crushing Availability | 75 | % | |
| Crushing Season | Late March – December | – | Approximately 275 days per year. |
| Maximum Heap Height | 60 | m | Over a 2 m material buffer above the liner. |
| Leach Cycle | 85 | days | Estimated from metallurgical test work. |
| Cyanide Concentration | 150 to 300 | ppm NaCN | Target cyanide concentration in barren solution. |
| Carbon Final Grade | < 160 | g/t carbon | Gold and silver content of stripped carbon. |
| Current Density | 50 | A/m² | Approximately, on anode surface. |
| Acid Wash pH | 1.0 – 2.0 | – | pH maintained during carbon acid wash. |
| Overflow Pond Volume | 98,400 | m³ | Existing pond required for relining. |
| Moisture Retention | 9.6 | % of Total Material Weight | Design criteria (TBC). |
| Expansion Capacity | 22 | million tonnes | Total capacity for expanded heap (cells 8, 9, 10). Not yet constructed. |
Project website: https://onemine.org/documents/viceroy-minerals-corporation-brewery-creek-mine-process-overview
Project website: https://www.merriam-webster.com/dictionary/unspecified
Overview
The Brewery Creek Project is centered on the reuse of an existing heap leach facility. The 2022 Technical Report details a plan to excavate previously leached material from the existing pad to create capacity for new ore and assumes that the existing composite liner, solution collection, and leak detection systems are intact and can be reused. The existing liner system is designed from top to bottom with a 1000 mm gravel overliner, a 1 mm PVC geomembrane, a 300 mm compacted low permeability silt soil liner, a non-woven geotextile, a 300 mm leak detection gravel fill, a 0.75 mm PVC geomembrane, and a 300 mm compacted low permeability silt soil liner. To ensure the liner system is not damaged during reclamation, the bottom two meters of material will not be excavated.
The project also includes plans to expand the leach pad with three additional cells (cells 8, 9, and 10), which have not yet been constructed. The process design considers a run-of-mine (ROM) pad with a primary jaw crusher in open circuit. Crushing will be accomplished in three stages, including the open circuit primary jaw crusher. All selected processes and equipment are established technologies used in gold and silver processing plants. A new solution collection trench is also part of the design to manage process solutions from the pad. The three existing ponds will be re-lined and used to handle excess solutions from the process. The overflow pond will be constructed with a new composite liner system from top to bottom, including a 2 mm HDPE geomembrane, a geonet, and 300 mm of recompacted existing silt soil liner.
Key Process Stages
The primary flow sheet begins with the crushing circuit, which consists of mobile, trailer-mounted equipment interconnected by transfer conveyors. Material from the ROM pad is fed to the primary crusher. After the primary crushing stage, material is reduced in a three-stage closed crushing circuit to 80% passing 19 mm. The crushing circuit is designed to process 9,000 tonnes per day with an overall availability of 75% and operates seasonally from late March through December. A metal detector is installed on the ROM conveyor to stop the conveyor and all upstream equipment if tramp metal is detected. A central PLC control unit allows for control and monitoring of all crushing equipment and the conveyor stacking system.
Following crushing, material is transferred to a crushed product stockpile. From there, it is reclaimed by one of two belt feeders and conveyed to the heap leach pad. The leach pad design uses a dynamic stacking system to distribute the material in lifts onto the pad. Once a lift has finished leaching and is sufficiently drained, a new lift can be stacked over the top, with a maximum planned heap height of 60 meters over the 2-meter material buffer. After a leach cycle of approximately 85 days, the residual leaching of the material occurs as leach solution from higher lifts percolates downward through the heap. The pregnant solution is collected in the lined ponds and pumped to the process plant.
The pregnant solution is processed through a carbon adsorption circuit, which consists of one column train of five cascade-type, open-top adsorption columns. Gold and silver are adsorbed onto activated carbon, which is moved counter-currently to the solution flow using eductors. Loaded carbon is then transferred to the stripping circuit. The carbon is first acid washed to remove organic scale, which is performed by maintaining a pH ranging from 1.0 to 2.0. After acid washing, the carbon is transferred to the stripping vessel, where gold and silver are desorbed from the carbon. This process uses a heated, pressurized eluant solution. The final stripped carbon gold and silver content is typically less than 160 grams per tonne of carbon.
The resulting pregnant eluant is processed in an electrowinning circuit. This circuit operates using steel wool cathodes and a current density of approximately 50 amperes per square meter of anode surface. The precious metal sludge deposited on the cathodes is periodically removed and processed in a refinery to produce the final doré product. Before smelting, the sludge is treated in a mercury retort to recover mercury values. The doré poured from the furnace represents the final product of the processing circuit. Slag produced from the smelting operation is periodically re-smelted on a batch basis to recover residual metal values.
Additional Interesting Data and Summary
The project's design incorporates robust safety and containment features. All cyanide distribution lines will use double-containment either by “pipe-within-pipe” or “pipe-over-liner” containment systems. The adsorption circuit has redundancy built in for the stripping process, as separated pregnant carbon can be stored in a tank for later processing. The project also defines specific precipitation data, assuming rainfall is collected at a rate of 100% for new stacked pad areas and 90% for the old spent heap. Snowfall and snowmelt data are provided in the report for process water balance calculations. The project design also includes an emergency direct-fired solution heater for the first year of operation to ensure heap performance during cold weather. Submersible pumps used in the ponds will be removed during winter months when the pond is expected to freeze.
The project's economic and technical viability is, in part, dependent on the successful reuse of the existing infrastructure. The design criteria for the expanded heap capacity of 22 million tonnes rely on the construction of cells 8, 9 and 10, which are not yet built. The existing overflow pond has been partially reclaimed and will require relining for use in planned operations. The design includes leak detection pipes for the new liner system. The project explicitly assumes that the existing liner, solution collection, and leak detection systems are intact. The process involves the use of a blend of reagents including sodium cyanide, which is mixed to produce a 2% by weight sodium hydroxide eluant solution. The concentrated cyanide is added by metering pumps to maintain the cyanide concentration in solution.
Key Processes
- Three-stage closed-circuit crushing (primary open circuit jaw crusher) to 80% passing 19 mm.
- Heap leaching with cyanide solution over an estimated 85-day cycle.
- Carbon adsorption in a five-column train (CIC circuit).
- Acid washing and pressure stripping of loaded carbon.
- Electrowinning (approx. 50 A/m²) to produce a precious metal sludge.
- Mercury retorting and smelting to produce final doré bullion.
Source: Brewery Creek Project , 2022 Technical Report, January 2022
Project website: Brewery Creek Project, 2022 Technical Report
