Gunnison Copper Heap Leach SX-EW Recovery Process

Source: Gunnison Copper Corp (2026)
Website: https://gunnisoncopper.com/projects/gunnison-project

Critical Data

Overview

Gunnison Copper Corp. is developing the Gunnison Project in Arizona, a large-scale open-pit copper mining operation that integrates heap leaching with solvent extraction and electrowinning (SX-EW). The facility is designed to produce 175 million pounds per annum of LME Grade A copper cathode. The process begins with primary crushing of run-of-mine material to minus 6 inches using mineral sizers. A critical innovation is the material sorting plant, which uses optical detection to reject high-carbonate rocks that would otherwise consume excessive sulfuric acid, thereby reducing operating costs and improving leach kinetics. Approximately 60% of the crushed material bypasses sorting and is conveyed directly to the leach pad, while the remaining 40% is sorted to remove waste. The heap leach pad is constructed in four phases, ultimately covering 840.8 acres, with a lined system to collect pregnant leach solution (PLS). PLS, containing approximately 1.38 g/L copper, is fed to the SX plant where two parallel trains of mixer-settlers extract copper into an organic phase. The loaded organic is stripped with high-acid electrolyte, and the rich electrolyte proceeds to the electrowinning tankhouse. Copper is plated onto stainless steel cathodes, mechanically stripped, and packaged for shipment. The entire flowsheet is designed for high efficiency and environmental stewardship, including water recycling, covered stockpiles, and a planned sulfuric acid plant to supply acid for leaching. Gunnison Copper’s recovery methods are significant for their ability to process both oxide and sulfide mineralization, with sulfide enhancement planned from Year 10 onwards.

Key Process Stages

• Stage 1: Material Sorting and Pre-concentration – Run-of-mine material is crushed to minus 6 inches and conveyed to a material sorting plant. Feed is screened into three size fractions: coarse (+3″ to 6″), intermediate (+1″ to 3″), and fine (+3/8″ to 1″). Each fraction passes through dedicated optical sorters that detect and reject high-carbonate, low-copper rocks. Approximately 45% of sorter feed is rejected as waste, reducing acid consumption and upgrading the leach feed. Water sprays wash particles to enhance sensor performance.
• Stage 2: Primary Crushing and Screening – ROM trucks dump onto a stationary grizzly with 2.5 ft square openings; oversize is reduced by a hydraulic rock breaker. Grizzly undersize feeds two apron feeders supplying mineral sizers that achieve a P80 of approximately 6 inches. Crushed material can be stockpiled (24-hour surge capacity) or conveyed directly to the leach pad. A secondary cone crusher and triple-deck screens further classify material into fine (-3/8″), intermediate, and coarse fractions for sorting.
• Stage 3: Heap Leach Pad Operation – The leach pad is built in four phases (total lined area 840.8 acres) with a low-permeability soil liner and HDPE geomembrane. An overliner aggregate layer (4 ft thick) protects the liner and collects PLS via perforated pipes. Crushed material is stacked mechanically in 30 ft high lifts; total pad height is limited to 336 ft to prevent copper re-precipitation. Acidified raffinate is irrigated at 0.002 gpm/ft². Sulfuric acid consumption averages 53 lb/ton. PLS drains by gravity to the PLS pond.
• Stage 4: Solvent Extraction – PLS from the pond (1.38 g/L Cu) is pumped to two parallel SX trains, each with two extraction settlers and one strip settler. The organic phase (extractant in diluent) extracts copper from PLS; loaded organic is stripped with high-acid electrolyte in the strip settlers. Raffinate is re-acidified and recycled to the leach pad. The SX circuit achieves 92% copper extraction efficiency. Crud treatment separates solids, organic, and aqueous phases for recovery.
• Stage 5: Electrowinning and Cathode Production – Rich electrolyte from SX is filtered through anthracite-garnet filters and heated to 40–45°C before entering EW cells. DC current plates copper onto stainless steel cathode blanks (1 m x 1 m). Cathodes are harvested weekly, washed, and stripped mechanically. The product is LME Grade A copper, bundled in 2-3 ton packages. A hot water system provides trim heating; cobalt sulfate and guar are added to improve plating quality.

Additional Interesting Data and Summary

The Gunnison Project’s recovery methods incorporate several advanced features that enhance sustainability and economic viability. The material sorting plant, using optical detection, rejects about 45% of the feed rock as waste, significantly reducing sulfuric acid consumption. Acid consumption varies by formation, from 24 lb/ton (Lower Abrigo, Bolsa, Quartz Monzonite) to 70 lb/ton (Martin, Escabrosa, Horquilla), with an average of 53 lb/ton across the mine plan. This pre-concentration step also lowers the carbon footprint by minimizing acid production requirements. The leach pad is designed with a low-permeability soil liner (1×10⁻⁶ cm/s saturated hydraulic conductivity) and HDPE geomembrane to prevent groundwater contamination. Overliner aggregate (minus ¾ inch) protects the liner and facilitates PLS collection via a gravity drainage system. Water management is critical: wet screening uses water sprays, and drainage water is clarified and recycled, reducing make-up water demand. A molten sulfur burning sulfuric acid plant is planned on-site, providing acid for leaching and electrolyte make-up, and reducing transportation emissions. Environmental considerations include covered coarse material stockpiles to control fugitive dust and prevent wetting from precipitation. The SX-EW circuit produces LME Grade A copper, ensuring high market value. The electrowinning tankhouse uses stainless steel blanks and a semi-automatic stripping machine, operating continuously with weekly cathode harvesting. Crud treatment recovers organic and aqueous phases, minimizing waste. From Year 10 onward, sulfide-dominant material will be treated with an engineered enhancement process (not yet defined) that may include finer crushing, chemical additives, and aeration to improve sulfide oxidation and copper recovery. The leach pad is built in four phases totaling 840.8 acres, with Phase 1 (244 acres) constructed during initial mine development. Total earthworks include 4.0 million yd³ of cut and fill, 1.4 million yd³ of low-hydraulic-conductivity soil liner, and 5.4 million yd³ of overliner aggregate. The project represents a significant copper production facility in Arizona, with a design capacity of 175 million pounds per year, supporting local employment and the global copper supply chain. Future testwork will confirm the viability of enhanced sulfide heap leaching, potentially extending the mine life and improving overall recovery from the deposit.

Key Processes: Heap Leaching, Gravity Separation, Crushing

Target Commodities: Copper