Gunnison Copper Project – Processing Circuit Overview

Gunnison Project — 2026 Technical Report

Executive Summary

The Gunnison Project is an open-pit heap leach operation designed to recover copper from oxide, supergene, and sulfide mineralization. The process involves primary and secondary crushing, optical material sorting to reduce acid consumption, heap leaching with acidified raffinate, and solvent extraction-electrowinning (SX-EW) to produce copper cathode. The facility is currently in the development phase, with construction scheduled to begin in Years -2 and -1.

Processing begins with ROM material delivered to a primary crushing area equipped with a grizzly, hydraulic rock breaker, and mineral sizers to achieve a P80 of approximately 6 inches. Material is then screened and sorted using optical technology to reject high-carbonate waste rock, significantly reducing acid consumption. The sorted mineralized material is stacked on a leach pad and irrigated with acidified raffinate.

The pregnant leach solution (PLS) is collected and processed in an SX-EW plant with a design capacity of 175 million pounds per annum of copper cathode. The SX circuit uses mixer-settlers to extract copper into an organic phase, which is then stripped into an electrolyte for electrowinning. The project aims to utilize enhanced sulfide heap leaching technology starting in Year 10 to improve recovery from sulfide materials.

Website: https://www.gunnisoncopper.com/projects/gunnison-project

Report Date: 2026

Region: Arizona, USA

Project Status: Development

Commodity: Copper

Throughput: 

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Mine Type: Open Pit

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Gunnison Project — 2024 Technical Report

Executive Summary

The Gunnison Project Technical Report outlines the recovery methods for the Gunnison SX-EW plant, designed to produce 175 million pounds per annum (mppa) of copper cathodes. The operation utilizes an open pit-heap leach process where mineralized oxide, supergene, and sulfide material is placed on a leach pad. Oxide and supergene materials are irrigated with acidified raffinate, while sulfide material scheduled for Year 8 will undergo an engineered sulfide enhancement treatment to improve recovery kinetics.

The processing flow involves collecting copper-bearing Pregnant Leach Solution (PLS) from the leach pad and pumping it to the Solvent Extraction (SX) facilities. The SX circuit uses mixer-settlers to extract copper from the PLS into an organic phase, which is then stripped into a high-acid electrolyte. This electrolyte is fed to the Electrowinning (EW) cells where copper is plated onto stainless steel cathodes. The plant includes supporting systems for reagent storage, process control, and solution ponds to manage raffinate and PLS.

The leach pad is designed in three phases over the mine life, with a total area of approximately 893 acres. Construction involves specific liner systems and collection networks to ensure environmental containment. The process relies on sulfuric acid consumption ranging from 24 to 70 lbs/ton depending on the formation, with an average of 53 lb/ton. The final product is LME Grade A copper cathode, packaged for market shipment.

Reports

Concepts

Website: https://www.gunnisoncopper.com/projects/gunnison-project

Report Date: 2024

Region: Not Specified

Project Status:

Commodity: Copper

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Gunnison Copper Project — 2023 Technical Report

Executive Summary

The Gunnison Copper Project is a development-stage mining operation planned by Excelsior to recover copper using In-Situ Recovery (ISR) methods. The project is designed to be developed in three stages, utilizing a wellfield network of injection and recovery wells to leach oxide copper mineralization from the subsurface. Stage 1 utilizes the existing JCM plant to recover 25 million pounds per annum (mppa) of copper cathode, with Stage 2 and Stage 3 expanding capacity to an aggregate of 125 mppa.

The recovery process employs a conventional Solvent Extraction and Electrowinning (SX-EW) flowsheet. Acidified leach solution is injected into the mineralization, and the resulting Pregnant Leach Solution (PLS) is processed through mixer-settlers for solvent extraction. Copper is then plated onto stainless steel cathodes via electrowinning, producing cathode-quality copper with 99.99% purity. The facility is designed as a zero-discharge operation, utilizing evaporation ponds and a water treatment plant to manage excess solutions and comply with reclamation standards.

Operational details include a hydraulic control system to contain groundwater impact and a central piping corridor connecting the wellfield to the processing plant. The project emphasizes environmental management through the use of evaporation ponds, solids impoundments, and hydraulic control wells to maintain an inward hydraulic gradient. The process is expected to deplete a mineralized block in approximately four years, followed by rinsing of the formation.

Reports

Website: https://www.gunnisoncopper.com/news/news-2024/excelsior-mining-announces-name-change-to-gunnison-copper2024-11-12-143923

Report Date: 2023-02-22

Region: Arizona, USA

Project Status:

Commodity: Copper

Throughput: 

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Gunnison Copper Project — 2022 Technical Report

Executive Summary

The Gunnison Copper Project is a development-stage mining operation located south of I-10 in Arizona, designed to recover copper from oxide mineralization using In-Situ Recovery (ISR) methods. The project utilizes a conventional Solvent Extraction and Electrowinning (SX-EW) flowsheet to produce cathode-quality copper with 99.99% purity. The development is planned in three stages, leveraging existing infrastructure in Stage 1 and expanding capacity in subsequent stages to achieve an aggregate production capacity of 125 million pounds per annum (mppa) of copper cathode.

The recovery process involves injecting acidified leach solution into the subsurface through a network of injection wells, which dissolves copper from the oxide mineralization. The resulting Pregnant Leach Solution (PLS) is pumped to recovery wells and sent to the SX-EW plant. Solvent extraction uses mixer-settlers to transfer copper from the PLS to an electrolyte solution, which is then electrowon onto stainless steel cathodes in a tankhouse. The facility is designed as a zero-discharge operation, utilizing evaporation ponds and a water treatment plant to manage excess solutions and ensure environmental compliance.

Processing Profile

• Leaching: In-Situ Recovery (ISR) using injection and recovery wells
• Solvent Extraction: Mixer-settlers (Extraction and Strip settlers)
• Electrowinning: Tankhouse with stainless steel cathodes
• Water Treatment: Milk of lime neutralization, flocculating clarifier
• Evaporation: Mechanical evaporators in lined ponds

Website: https://www.gunnisoncopper.com/news/news-2024/excelsior-mining-announces-name-change-to-gunnison-copper2024-11-12-143923

Report Date: 2022

Region: Arizona, USA

Project Status: Development

Commodity: Copper

Throughput: 

Mine Life: 

Mine Type: In-Situ Recovery (ISR)

Ore type:

Gunnison Copper Project NI 43-101 Feasibility Study

Executive Summary

The Gunnison Copper Project is a feasibility study for a copper recovery operation utilizing In Situ Recovery (ISR) technology combined with Solvent Extraction and Electrowinning (SX-EW). The project is designed to recover soluble copper from subsurface oxide mineralization using a network of injection and recovery wells. The process produces cathode-quality copper with 99.99% purity, intended for sale on the world market.

Development is planned in three stages. Stage 1 utilizes the existing JCM plant to recover 25 million pounds per annum (mppa) of copper cathode. Stage 2 involves constructing a new 50 mppa SX-EW plant independent of the JCM facility. Stage 3 doubles the Gunnison plant capacity to 100 mppa, resulting in an aggregate capacity of 125 mppa. The project is designed as a zero-discharge facility with water treatment and evaporation ponds to manage process solutions.

The recovery process involves acidified leach solution injection into the mineralized formation, collection of pregnant leach solution (PLS), extraction of copper via mixer-settlers, and plating of copper onto cathodes in electrowinning cells. An optional sulfuric acid plant is planned for Stage 3 to generate onsite acid for leaching requirements, utilizing waste heat for power generation.

Website: https://www.gunnisoncopper.com/projects/gunnison-project

Report Date: 2017

Region: South of I-10

Project Status:

Commodity: Copper

Throughput: 

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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