Coffee Gold Project Gold Recovery: Crushing, Heap Leach & ADR

Source: Unnamed_Company_48 (2026)

Critical Data

Overview

The Coffee Gold Project, located in the Yukon, Canada, employs a robust gold recovery process designed to treat 7.4 million tonnes per annum (Mt/a) with an average head grade of 1.25 g/t gold and an overall recovery rate of 77.5%. The project, supported by engineering firms including Hatch, JDS, and WSP, has undergone multiple design updates since 2018, with the latest internal study in 2024 refining the process for a nominal throughput of 26,909 tonnes per day. The recovery methods center on a two-stage crushing circuit feeding a conventional heap leach operation, followed by an Adsorption, Desorption, and Recovery (ADR) plant to produce gold doré. Crushing utilizes a primary gyratory crusher and secondary cone crusher to achieve a product size P80 of 50 mm. The crushed ore is stacked on a multi-lift heap leach pad where a dilute cyanide solution is applied via drip emitters. Pregnant leach solution (PLS) is collected and processed through a six-stage carbon-in-column (CIC) circuit. Loaded carbon undergoes acid washing, modified Zadra elution, and electrowinning to recover gold. A mercury retort and induction furnace produce doré bars. Winter conditions are mitigated by suspending stacking from January to March, heating barren solution, burying drip emitters, and housing the ADR plant in a heated facility. The process design meets Preliminary Economic Assessment (PEA) requirements and is recommended to advance to the next development phase.

Key Process Stages

• Stage 1: Two-Stage Crushing — ROM material at F80 of 619 mm is fed into a primary gyratory crusher (Superior MK-III 50-65 or equivalent) to achieve a P90 of ~145 mm. The product is conveyed to a coarse stockpile, then reclaimed and fed to a secondary cone crusher (MP800 or equivalent) closed with a sizing screen to produce a final product with P80 of 50 mm. Lime is added on a transfer conveyor to maintain pH. Crushing operates at 1,495 t/h average throughput, 18 h/d, 275 d/a, with a fine stockpile of 10,000 t capacity for temporary storage.
• Stage 2: Heap Leaching and Solution Handling — Crushed ore is conveyed via overland and grasshopper conveyors to a ridge-top heap leach pad with a capacity of 91.5+ million tonnes, stacked in five stages. Drip emitters apply barren solution containing ~200 ppm cyanide at pH 10.5–11.5. Solution percolates by gravity, dissolving gold. A boiler heats barren solution during winter; drip emitters are buried to maintain thermal integrity. PLS flows by gravity through a lined perimeter channel to two pregnant solution tanks in the ADR plant. Meteoric water is managed by lined event ponds with double LLDPE liners and leak detection.
• Stage 3: Carbon-in-Column (CIC) Adsorption — PLS from the storage tank (2-hour holding capacity) is pumped through a single train of six cascading carbon columns, each with 6.0 tonnes of activated carbon. A trash screen protects the columns. Gold is adsorbed onto carbon in counter-current flow. Overflow passes through a recovery screen to capture fines, then gravitates to the barren solution tank where NaCN, NaOH, antiscalant, and make-up water are added. Loaded carbon is withdrawn daily from the first column (6 t/day) and transferred to acid wash and stripping.
• Stage 4: Desorption and Elution — Loaded carbon undergoes acid washing with 3% HCl to remove inorganic foulants. Gold is then stripped using a modified Zadra elution process at 130–150°C and 400–600 kPag with a solution of ~1% NaOH and 0.1% NaCN. The pregnant eluate is cooled and gravity-fed to electrowinning. Stripped carbon is regenerated in a kiln at 650–750°C, quenched, and returned to the CIC circuit. Attritional losses are offset by fresh carbon addition.
• Stage 5: Gold Refining and Doré Production — Pregnant solution from elution flows to two electrowinning cells where gold is deposited on knitted-mesh steel wool cathodes. Loaded cathodes are power-washed to collect gold-bearing sludge, filtered to reduce moisture, and retorted to remove mercury. Retort residue is mixed with fluxes (borax, silica, soda ash) and smelted in an induction furnace to produce doré bullion and slag. Doré bars are stored securely and shipped off-site for final refining.

Additional Interesting Data and Summary

The Coffee Gold Project’s recovery methods are designed for robust performance in Yukon’s extreme climate. The heap leach pad, with a capacity of 91.5+ million tonnes, uses a composite liner system: a 2.0 mm LLDPE geomembrane over a geosynthetic clay liner (GCL) with an objective permeability of 5×10⁻⁹ cm/s. Event ponds employ double LLDPE liners with leak detection and recovery systems (LDRS) to contain meteoric water and prevent environmental release. The ADR plant processes PLS at 1,100 m³/h with a six-stage CIC circuit using 6-tonne carbon columns. Elution follows the modified Zadra process at 130–150°C and 400–600 kPag. Carbon regeneration operates at 650–750°C to maintain activity. Gold refining includes electrowinning with two cells, a mercury retort, and induction furnace smelting to produce doré bars. Reagent handling adheres to the International Cyanide Management Code (ICMC). Sodium cyanide briquettes, sodium hydroxide, hydrochloric acid, antiscalant, and hydrated lime are delivered and stored on-site. Power is supplied by four on-site generators in an N+2 configuration, with a peak summer demand of 9,500 KVA for the processing plant. Water is sourced from a well field near the Yukon River. The design, reviewed by WSP as the Qualified Person, is considered sufficiently developed for PEA level, with crushing equipment (gyratory and cone crushers) selected for reliability over mineral sizers. Winter mitigation strategies—including suspending stacking from January to March, heating barren solution, burying drip emitters, and housing the ADR plant in a heated, insulated facility—ensure year-round operation. The project’s economic significance is underscored by a 77.5% gold recovery rate from a 1.25 g/t head grade at a 7.4 Mt/a throughput. Future development phases will further refine the design to meet Yukon regulatory guidelines for mine waste management. Overall, the Coffee Gold Project’s recovery methods represent a conventional yet climate-adapted approach to gold extraction, with a clear pathway to advancing toward construction.

Key Processes: Heap Leaching, Cyanidation, Gravity Separation, Crushing

Target Commodities: Gold