Copper Cathode Production at Johnson Camp Mine via SX-EW

Source: Gunnison Copper Corp (2026)
Website: https://www.gunnisoncopper.com/projects/johnson-camp-mine-jcm

Critical Data

Overview

Gunnison Copper Corp. (GCC), through its wholly owned subsidiaries Excelsior Mining Arizona, Inc. and Excelsior Mining Holdings, Inc., operates the Johnson Camp Mine (JCM) located in Cochise County, Arizona, approximately 65 miles east of Tucson. This conventional open-pit, heap leach operation uses solvent extraction and electrowinning (SX-EW) to produce LME Grade A copper cathodes for global markets. The facility was originally established decades ago, with significant recent expansions including the construction of Pad 5, completed in 2025, which adds 44 million tons of leachable material capacity. A key technological advancement at the site is the Nuton Demonstration — an industrial-scale, engineered sulfide heap leach operation utilizing Nuton’s proprietary bioleaching technology. This nature-based process employs elevated-temperature biological oxidation using naturally occurring bacteria to accelerate the leaching of primary sulfides (mainly chalcopyrite) and enhance copper recovery. The integrated recovery flowsheet involves crushing and agglomeration of sulfide ores, stacking on a dedicated portion of Pad 5, gravity drainage of pregnant leach solution (PLS) to collection sumps, and pumping to the existing JCM SX-EW plant. The SX-EW circuit, designed for 25 million pounds of cathode copper per annum operating 365 days with 90% availability, extracts copper from the PLS at efficiencies up to 92%. The entire system, including solution ponds, acid storage, and a comprehensive containment system, underscores the site’s commitment to environmental compliance and operational excellence. The combination of traditional heap leaching for oxide/transition ores and innovative Nuton technology for sulfides positions Johnson Camp as a forward-looking copper producer in the American Southwest.

Key Process Stages

• Stage 1: Leach Pad 5 Construction and Management — Pad 5 covers approximately 8,000,000 ft² and was designed by WSP based on Glasgow Engineering’s initial design. It is oriented for gravity drainage of solutions to the eastern toe at 4,900 ft elevation. The pad includes a soil liner (12-inch clayey alluvial layer), HDPE geomembrane liner, containment berms, and a perforated leachate collection pipe system buried in 24 inches of overliner material (crushed Bolsa Quartzite, minus 1½” to plus ¾”). The overliner totals ~527,000 yd³, placed to ensure hydraulic conductivity standards. The pad is developed in four phases: Phase 1 hosts ROM oxide/transition material (mining commenced Q3 2025), Phase 2 hosts primary sulfides for the Nuton Demonstration, Phase 3 contains crushing/agglomerating equipment (later used for ROM or crushed material), and Phase 4 stores ROM/crushed material.
• Stage 2: Nuton Bioleaching Demonstration — Fresh sulfide material is crushed and agglomerated before being mechanically stacked using grasshopper conveyors on a separate portion of Pad 5 (Phase 2). The Nuton process relies on elevated-temperature biological oxidation using naturally occurring bacteria to oxidize sulfide minerals, particularly chalcopyrite. Aeration of the heap provides necessary oxygen. The presence of abundant pyrite generates ferric iron, enhancing chalcopyrite oxidation. Leaching parameters—irrigation rate, acid concentration, bacteria, and leach cycle time—are optimized via testing. The demonstration stacks sulfide material for three years and leaches for five years. PLS from the Nuton cells is combined with ROM PLS after sampling, then pumped to the JCM PLS pond for uniform grade feeding SX.
• Stage 3: Solution Management and Ponds — PLS from Pad 5 flows by gravity to a collection sump equipped with 400 HP vertical turbine pumps (2 operating, 1 standby) rated at 5,000 gpm. HDPE piping conveys PLS to the existing PLS pond. Raffinate is recirculated back to the leach pad via three 400 HP pumps. An emergency runoff pond (13,000,000 gallon lined capacity) was constructed in 2025 to contain overflow from heavy rain events, with a pump barge for return to the pad or evaporation pond. A 3,400 ft lined containment trench routes all process piping. Average sulfuric acid consumption is 40 lb/ton of material (ranging 20–70 lb/ton depending on formation).
• Stage 4: Solvent Extraction Circuit — The existing JCM SX circuit consists of two trains of mixer-settlers operating in series. Each train has two extraction settlers and one strip settler. PLS flows through both extraction settlers sequentially, contacting organic (extractant in petroleum diluent) counter-currently to transfer copper, achieving 92% extraction at PLS grades up to 2.6 g/L Cu. Loaded organic then contacts lean electrolyte in the strip pumper mixers, transferring copper to the aqueous phase. Stripped organic returns to extraction. Raffinate is re-acidified and flows to the Raffinate Pond. Rich electrolyte (strong electrolyte) proceeds to the tankhouse for electrowinning.
• Stage 5: Electrowinning and Cathode Handling — Rich electrolyte is filtered through anthracite-garnet filters to remove entrained organic and particulates, then heated to ~45°C via heat exchangers (using lean electrolyte return heat and a trim heater if needed). Heated electrolyte flows to commercial recirculation tanks and then to EW cells where copper is plated onto stainless steel cathode blanks. Cathodes are harvested weekly using an overhead bridge crane and strongback frame. Harvested cathodes are washed in Cathode Wash Tanks, then stripped from blanks using a semi-automatic stripping machine, sampled, weighed, and banded into 2–3 ton packages. The product meets LME Grade A specifications. Small electrolyte bleeds control impurity buildup.

Additional Interesting Data and Summary

Beyond the core recovery processes, Johnson Camp Mine incorporates substantial technical infrastructure and environmental controls. The leach pad’s containment system includes a 13,000,000 gallon lined emergency overflow pond and a 3,400 ft lined containment trench to manage non-storm water and process piping, complying with BADCT guidelines. The pumping system is designed for a total of 5,000 gpm each for raffinate and PLS, ensuring efficient solution circulation. Acid management involves three 2,500-ton sulfuric acid storage tanks (installed 2019) plus a smaller agglomerator feed tank added in 2025, with a new acid injection station installed between the SX-EW plant and solution ponds to acidify raffinate before return to Pad 5. Historical column test work indicates sulfuric acid consumption averages 40 lb/ton, with formation-specific ranges from 20 lb/ton (Pioneer Shale) to 70 lb/ton (Upper Abrigo). The Nuton Demonstration represents a significant sustainability initiative: by harnessing biological oxidation of pyrite, the process reduces net acid consumption and enhances copper recovery from challenging chalcopyrite ores. This aligns with broader industry trends toward lower-carbon, bio-based leaching technologies. Economically, the facility’s 25 million lbs/yr cathode output supports regional employment and copper supply chains, with product sold on the world market as LME Grade A. The Nuton demonstration (3-year stacking, 5-year leaching) will validate parameters for full-scale sulfide processing, potentially expanding the mine’s resource base. Future outlook includes potential expansion of Pad 5 beyond its current 44-million-ton capacity, scaling up of Nuton technology to treat all sulfide material, and continued optimization of leach kinetics through refined irrigation and aeration. The site’s significant infrastructure—including a tank farm with crud treatment (Tri-canter centrifuge), electrolyte filtration, and a semi-automatic cathode stripping machine—positions Johnson Camp as a modern, environmentally responsible copper producer in Arizona’s historic mining district.

Key Processes: Heap Leaching, Gravity Separation, Crushing

Target Commodities: Copper