Santa Cruz Copper Project: Heap Leach & SX/EW Processing Circuit Overview

Santa Cruz Copper Project — 2025 Feasibility Study & Technical Report

Company	Ivanhoe Electric
Date	2025-06
Region	Arizona, USA
Commodities	Copper
Mine Type	Underground
Throughput	22,000 tpd
Mine Life	24 years
Annual Production	76,000 t Cu
Status	Development

Executive Summary

The Santa Cruz Copper Project, located in Arizona, is the subject of a 2025 NI 43-101 Feasibility Study & Technical Report prepared by Ivanhoe Electric. The project involves the development of an underground mine designed to extract oxide and secondary sulphide ores for processing into LME Grade A copper cathode. The facility is planned to operate for approximately 24 years with a design daily stacking rate of 22,000 tonnes.

The processing plant utilizes a conventional heap leach and solvent extraction/electrowinning (SX/EW) flowsheet. Ore is crushed to sub-9.5 mm, agglomerated with sulphuric acid and sodium chloride, and stacked on an on/off pad for leaching. The resulting pregnant leach solution is processed through two parallel SX trains and recovered via an EW circuit with 124 cells. The design targets a life-of-mine total copper recovery of 92.2%.

Operational parameters indicate a life-of-mine ore production of 136 Mt with a design annual copper production of 76,000 tonnes. The project includes comprehensive solution management with lined ponds and a zero-discharge plan. Spent ore will be managed in dedicated piles, with approximately 50% processed for paste backfill. The process is designed to run 24 hours per day, 365 days per year.

Website: https://ivanhoeelectric.com/electric-metals/santa-cruz/

Report Date: 2025-06

Region: Arizona, USA

Project Status: Development

Commodity: Copper

Throughput: 22,000 tpd

Mine Life: 24 years

Mine Type: Underground

Ore type:

Santa Cruz Copper Project — 2025 Technical Report

Company	Ivanhoe Electric
Date	2025
Region	Arizona, USA
Commodities	Copper
Mine Type	Underground
Throughput	22,000 tpd
Mine Life	24 years
Annual Production	76,000 t Cu
Status	Development

Executive Summary

The Santa Cruz Copper Project is a feasibility study for an underground mining operation located in Arizona, designed to process oxide and secondary sulphide ores. The proposed processing facility utilizes a heap leach circuit followed by solvent extraction and electrowinning (SX/EW) to produce LME Grade A copper cathode. The design is based on conventional technologies and proven equipment, with a life-of-mine ore production of 136 Mt.

Operations are planned to run 24 hours per day, 365 days per year for approximately 24 years. The design daily stacking rate is up to 22,000 tonnes, with an overall copper recovery target of 92.2%. The process includes primary, secondary, and tertiary crushing, agglomeration with sulphuric acid and sodium chloride, and an on/off heap leach pad configuration.

Spent ore management involves paste backfill for approximately 50% of the material, with the remainder stored in dedicated piles. The facility includes seven leach cells, solvent extraction trains, and an electrowinning tankhouse. Water management is designed as zero-discharge, utilizing lined ponds and recycling systems to minimize environmental impact.

Website: https://ivanhoeelectric.com/electric-metals/santa-cruz/

Report Date: 2025

Region: Arizona, USA

Project Status: Development

Commodity: Copper

Throughput: 22,000 tpd

Mine Life: 24 years

Mine Type: Underground

Ore type:

Santa Cruz Project — 2023 Technical Report

Company	Santa Cruz Project
Date	September 2023
Region	Unknown
Commodities	Copper
Mine Type	Underground
Throughput	15,000 t/d
Mine Life	20 years
Status	Development

Executive Summary

This NI 43-101 Technical Report details the recovery methods and processing plant design for the Santa Cruz Project. The facility is designed to process 15,000 dry metric tonnes per day (t/d) at 94% utilization, with an operating range of 10,800 to 16,300 t/d. The mine is classified as an underground operation with a planned mine life of 20 years. The project is currently in the development phase, with equipment sizing based on ultimate plant production targets.

The processing flowsheet is a hybrid system designed to handle four distinct ore domains: Exotic, Oxide, Chalcocite, and Primary Sulfide. The plant utilizes a combination of whole ore agitated leaching for acid-soluble copper and conventional flotation for sulfide minerals. Comminution involves primary crushing, SAG and ball milling, and tertiary grinding using vertical stirred mills. The leach circuit includes five agitated tanks followed by counter-current decantation (CCD) thickeners.

Production targets include an annual copper cathode production of 32,000 to 61,400 tonnes and copper concentrate production of 14,000 to 35,100 tonnes. The plant incorporates Solvent Extraction and Electrowinning (SX-EW) for cathode production, achieving a combined copper recovery of 95.4%. Reagents include sulfuric acid, limestone, lime, and flotation collectors, with tailings managed in a storage facility and partially used for paste backfill in the underground mine.

Website: https://ivanhoeelectric.com/electric-metals/santa-cruz/

Report Date: September 2023

Region: Unknown

Project Status: Development

Commodity: Copper

Throughput: 15,000 t/d

Mine Life: 20 years

Mine Type: Underground

Ore type:

Santa Cruz Copper Project — 2025 Feasibility Study

Company: Not explicitly stated, but associated with Ivanhoe Electric.
Date: June 2025
Region: Arizona
Commodities: Copper

Executive Summary

The Santa Cruz Copper Project in Arizona is proposing an on/off heap leach process to recover copper from oxide and secondary sulphide ores. The pregnant leach solution (PLS) generated from the heap leach will be processed through an on-site solvent extraction (SX) and electrowinning (EW) circuit to produce LME Grade A copper cathode. The process design leverages established technologies and is based on extensive metallurgical testwork conducted on the project’s mineralized material.

The mine is planned for a life of approximately 24 years with a daily stacking rate of up to 22,000 tonnes. The processing facility includes crushing, agglomeration, heap leaching, SX, EW, and associated reagent preparation and water treatment. Key operational parameters include a heap leach feed particle size of sub-9.5 mm, an irrigation rate of 8 L/h/m², and an overall copper recovery of 92.2%. The mine is projected to produce 76,000 tonnes of copper annually.

Website: https://ivanhoeelectric.com/electric-metals/santa-cruz/

Report Date: 

Region: 

Project Status:

Commodity: 

Throughput: 

Mine Life: 

Mine Type: 

Ore type:

Overview

Nestled in the mineral-rich landscape of Arizona, the Santa Cruz Copper Project represents a significant and modern endeavor in the United States’ critical minerals strategy. Operated by Ivanhoe Electric Inc., this advanced-stage project is poised to become a major domestic supplier of high-purity copper cathode, a commodity crucial for the electrification of the economy and renewable energy technologies. Located in the renowned Arizona Copper Belt, the project leverages a substantial resource base estimated at 136 million tonnes of ore, with a life-of-mine plan extending over 24 years. The processing methodology selected for this deposit is a sophisticated, yet proven, heap leach combined with solvent extraction and electrowinning (SX/EW) circuit, designed specifically for the oxide and secondary sulphide ore types present. This approach was chosen for its efficiency, lower energy intensity compared to conventional concentrator-flotation-smelter routes, and its ability to produce LME Grade A copper cathode directly on-site. The project, as outlined in its recent NI 43-101 Feasibility Study, is designed for a substantial throughput of 22,000 tonnes per day, targeting an impressive overall copper recovery of 92.2%. The Santa Cruz project is not just another mining operation; it is a strategically important asset designed to address the growing domestic copper shortage with a focus on sustainability and operational excellence, making it a key project to watch in the coming decade.

Key Process Stages

The Santa Cruz Copper Project employs a meticulously designed mineral processing circuit that transforms run-of-mine ore into high-purity copper cathode. The flow sheet is a conventional yet optimized sequence of size reduction, agglomeration, leaching, and solution purification. The entire operation is designed for 24/7/365 operation, with specific annual operating hours allocated to different sections: 6,570 hours for crushing and agglomeration and 8,497 hours for the continuous SX/EW plant. The following bullet points detail each critical stage of this advanced copper processing circuit.

• Stage 1: Primary Crushing Run-of-mine ore, delivered to the surface via a Railveyor system at a size of sub-20 cm, is first fed to a vibrating grizzly feeder. A magnet and metal detector remove tramp metal before the ore enters a single C160 Jaw Crusher for primary size reduction. Grizzly undersize bypasses the crusher to improve efficiency.
• Stage 2: Secondary and Tertiary Crushing The primary crusher discharge combines with grizzly undersize and is fed to an MP1000 cone crusher operating in open circuit. The product then moves to a closed-circuit tertiary crushing stage featuring two parallel MP1000 cone crushers and two double-deck banana screens (3m x 6.7m). The circuit is designed to produce a final product size of 100% passing 9.5 mm, which is conveyed to truck loadout hoppers.
• Stage 3: Agglomeration and Stacking The crushed ore is trucked to the leach pad area where it is fed into one of two portable agglomeration drums. Here, key reagents are added: sulphuric acid (6 kg/t) and sodium chloride (1 kg/t) to facilitate particle bonding and enhance leaching kinetics. The agglomerated ore is then systematically stacked onto the on/off leach pad in a 6-meter-high single lift using a mobile conveyor system culminating in a radial stacker.
• Stage 4: On/Off Heap Leaching The leach pad consists of seven cells (each 130m x 640m), constructed with a composite liner system for environmental protection. Each cell undergoes a precise 265-day cycle: 36 days of stacking, 180 days of irrigation with raffinate solution at a rate of 8 L/h/m², and additional time for drainage and setup. Air is forced into the base of the heap via fans to aid in oxidizing secondary sulphides. Pregnant Leach Solution (PLS) reporting an average of 2,000 m³/h is collected and pumped to the SX plant.
• Stage 5: Solvent Extraction (SX) The PLS enters a two-train SX circuit. Each train consists of two extraction stages, two wash stages, and one strip stage. A specialized organic extractant selectively removes copper from the aqueous PLS in mixer-settlers. The copper-loaded organic is then stripped using lean electrolyte from the EW circuit, producing a rich electrolyte solution that is filtered to remove organic carryover before being sent to electrowinning.
• Stage 6: Electrowinning (EW) The rich electrolyte is pumped into an electrowinning tankhouse containing 124 cells, each holding 84 stainless-steel cathode blanks. Using two powerful rectifiers (67 kA / 287 V), an electrical current plates copper onto the blanks. The resulting LME Grade A copper cathodes are harvested, stripped, washed, bundled, and prepared for shipment.
• Stage 7: Spent Ore Management After leaching, spent ore is removed from the pad. Approximately 50% is transported to a paste backfill plant for use underground, while the remainder is trucked to one of two engineered, lined spent ore storage facilities for permanent disposal, following strict environmental guidelines.

Critical Data

The feasibility of the Santa Cruz Copper Project is underpinned by robust metallurgical testwork and detailed engineering, resulting in the following key performance indicators and design criteria.

Parameter	Value	Unit	Notes
Throughput (Stacking Rate)	22,000	t/d	Design daily stacking rate to leach pad
Life-of-Mine Ore Production	136	Mt	Total ore to be processed over 24 years
Target Grind Size (Crush Size)	9.5	mm (P100)	100% passing 9.5 mm after tertiary crushing
Overall Copper Recovery	92.2	%	Life-of-mine average recovery to cathode
Design Annual Copper Production	76,000	t/y	Target annual cathode production
Acid Consumption	6	kg/t ore	Sulphuric acid addition at agglomeration
Irrigation Rate	8	L/h/m²	Applied to the heap leach surface
Bond Work Index (Spent Ore)	14.9	kWh/t	For paste backfill design considerations
Crusher Work Index	4.0	kWh/t	For crushing circuit energy calculations

Additional Interesting Data and Summary

Beyond the core processing circuit, the Santa Cruz Copper Project incorporates several advanced features that highlight its modern design and commitment to sustainability. The project is designed as a zero-discharge facility, a critical aspect of its water management strategy in arid Arizona. Makeup water is sourced from a combination of grandfathered water rights and mine dewatering, with the latter being treated and also supplied to local agricultural users, showcasing a community-focused approach to resource sharing. The solution management system is extensive, comprising multiple lined ponds (Raffinate, PLS, SLS, and stormwater) sized to handle both process flows and a 100-year, 24-hour storm event, ensuring environmental protection.

The project’s energy footprint is a key consideration. The use of a heap leach-SX/EW process is significantly less energy-intensive than traditional smelting, and the design includes efficient crushing equipment with specific work indices well-characterized for accurate power forecasting. The electrowinning tankhouse is equipped with cell covers and mist suppression systems to minimize acid mist emissions and ensure worker safety, aligning with best practices for industrial hygiene.

Economically, the project is substantial, with a projected annual production of 76,000 tonnes of copper cathode, directly contributing to the US copper supply chain. The spent ore management plan is innovative, diverting half of the material to become paste backfill underground, which reduces surface waste storage requirements and improves the geotechnical stability of the mined-out voids. The detailed NI 43-101 report underscores the project’s viability and positions Ivanhoe Electric as a significant future player in the copper market, leveraging smart mineral processing technology to develop a high-quality deposit responsibly.

Source: NI 43-101 Technical Report | Feasibility | Project: including resource estimation on copper deposit | Date: June 2025

Further Reading

• Ivanhoe Electric Inc. | Santa Cruz
• Ivanhoe Electric’s Preliminary Feasibility Study for the Santa Cruz Copper Project in Arizona Defines a High-Quality Underground Mine with Average Annual Production of 85,000 Tonnes of Copper Cathode
• Santa Cruz Copper Project, USA
• New study gives Ivanhoe Electric’s Santa Cruz copper project $1.4B value
• Ivanhoe Electric tackles US copper shortage with Arizona project

Ivanhoe Electric's Santa Cruz Copper Project in Arizona is designed around an on/off heap leach and solvent extraction-electrowinning circuit. The feasibility study describes a 140 Mt, 24-year operation producing 76,000 t/y of copper cathode.

The Santa Cruz Copper Project is an underground mining project in Arizona held by Ivanhoe Electric Inc. The proposed operation will process oxide and secondary sulfide ores through an on/off heap leach and an onsite solvent extraction and electrowinning (SX/EW) circuit to produce London Metal Exchange Grade A copper cathode. As described in the September 29, 2026 feasibility study, the facilities will operate 24 hours per day, 365 days per year for approximately 24 years, processing 140 Mt of ore at a design stacking rate of up to 22,000 t/d. The study reports a life-of-mine total copper recovery of 92.3% and a design annual copper production of 76,000 t.

Critical Data

Parameter	Value	Unit	Notes
Life of Mine	24	y	Design
Life of Mine Ore Production	140	Mt	Design
Stacking Rate Design	22,000	t/d	Design
Plant Feed Grade, Acid-Soluble Copper	0.64	%	Life of mine
Plant Feed Grade, Cyanide-Soluble Copper	0.38	%	Life of mine
Plant Feed Grade, Residual Copper	0.05	%	Life of mine
Plant Feed Grade, Total Copper	1.04	%	Life of mine
Life-of-Mine Total Copper Recovery	92.3	%	Design
Design Annual Copper Production	76,000	t/y	Design
Heap Leach Feed Particle Size (F100)	sub-9.5	mm	Testwork
Heap Leach Feed Particle Size (F80)	6.4	mm	Testwork
Bulk Density for Stacking	1.51	t/m3	Testwork
Ore Solids Density	2.77	t/m3	Testwork
Sodium Chloride Addition to Agglomeration	0.4	kg/t	Testwork
Gross Acid Consumption	27	kg/t	Testwork
Net (Gangue) Acid Consumption	10	kg/t	Testwork
Irrigation Rate	8.0	L/h/m2	Testwork
Residual Moisture	6.0	wt %	Testwork
Concentration of Soluble Copper in Residual Moisture	0.35	g/L	Testwork
Bond Work Index of Spent Ore	14.9	kWh/t	Testwork
Crusher Work Index of Ore Average	3.8	kWh/t	Testwork
Abrasion Index	0.12	grams	Testwork
Crushing & Agglomeration Annual Operating Time	75	%	Design
Crushing & Agglomeration Annual Operating Hours	6,570	h/y	Design
SX/EW Annual Operating Time	95	%	Design
SX/EW Annual Operating Hours	8,322	h/y	Design
Heap Leach Cell Dimensions (full cell)	640 x 131.0	L x W (m)	Design
Heap Leach Cell Dimensions (half-cell strip)	640 x 65.5	L x W (m)	Design
Number of Cells	7 / 14	no.	Full cells / half-cell strips
Lift Height	8.0	m	Single lift only
Aeration Rate	0.15	Nm3/h/m2	Design
PLS / Raffinate Flow Rate (Average)	2,000	m3/h	Design
Secondary Leach Solution Flow Rate (Average)	1,300	m3/h	Design
EW Rectifier Output (maximum)	67 kA / 287 V	Not applicable	Design
Process Personnel	114	persons	Design
Not stated	Not stated	Not stated	Expected construction timing

Overview

The processing facilities at Santa Cruz include a crushed coarse ore stockpile fed from underground, secondary and tertiary crushing and screening, agglomeration, conveyor and stacker systems, heap leaching, solvent extraction, electrowinning, reagent preparation and distribution, raw water and water treatment, and compressed air. The process plant and refinery designs rely on proven technologies, established operating practices, and commercially available equipment. Metallurgical design parameters come from testwork conducted on mineralized material from the project.

Ore from the underground mine will be processed using the heap leach and SX/EW flowsheet. Spent ore will be removed from the on/off leach pad and either processed for paste backfill or placed in a spent ore storage facility. Approximately 50% of the spent ore will go to paste backfill. The on/off pad design allows each cell to be loaded, irrigated, and unloaded at different times.

Key Process Stages

Crushing

ROM ore will be crushed underground by a sizer and delivered to surface at sub-254 mm diameter via belt conveyor. Ore reports to the crushed coarse ore stockpile and is reclaimed through two apron feeders that discharge to a secondary vibrating screen. Oversize material transfers to a secondary cone crusher operating in open circuit. Secondary crushed material and secondary screen undersize combine and feed two tertiary vibrating screens. These are large banana-type, dual-deck screens. Screen undersize at 100% passing 9.5 mm is conveyed to fine ore hoppers that buffer the continuous crushing circuit. Tertiary screen oversize returns to the tertiary crushing feed conveyor. The tertiary circuit comprises two cone crushers in parallel.

Sodium chloride is added via screw conveyor based on a tonnage ratio to the conveyor to the fine ore hoppers. Salt arrives in bulk and is blown into a silo for storage. Dry-type dust collectors capture dust from crushing, screening, and conveying, with mist generators used where appropriate. The crushing circuit sits outdoors, and maintenance lifting uses a mobile crane.

Agglomeration

Fine ore from the tertiary screens is agglomerated in rotary drums. Sulfuric acid and raffinate or water are added to facilitate agglomeration. Feed to the drums is measured for ratio addition of reagents. Acid is trucked to the mobile agglomeration module and transferred to a day tank, from which a metering pump adds the desired amount to the drum.

Stacking

Agglomerated ore discharges onto a transfer conveyor feeding a series of grasshopper-type mobile conveyors. The final mobile conveyor feeds two self-propelled indexing conveyors in series, which feed a self-propelled mobile radial stacker. Full-size pad cells are retreat stacked as two half-cell strips in 65.5 m wide half-moon shapes.

Heap Leach Pad

The on/off heap leach pad is subdivided into seven cells, each approximately 130 x 730 m. Cells are loaded in two half-cell strips, each typically 65.5 x 635 m at the crest. End cells are slightly larger to account for exterior side slopes. An approximate 55 m-wide onloading corridor runs along the west side, and a 15 m-wide off-loading corridor along the east. Divider berms near the bases of full-size cells allow solution flow from each cell to be segregated for collection in either the pregnant leach solution (PLS) ponds or secondary leach solution (SLS) ponds.

The pad base is graded so solution flows east to west. A solution pipeline conveyance channel along the western edge delivers solution to the pond system. A containment berm surrounds the pad to retain solution and stormwater runoff.

Initial capital includes construction of the four northern full-size cells with perimeter offsets, corridors, and berms. The three southern cells will be added as operations require.

The liner system comprises a high-density polyethylene geomembrane over a geosynthetic clay liner over prepared native foundation materials or compacted grading fill. Above the liner sits a drainage system with perforated pipes at 6 m spacing in a 0.9 m thick drainage layer of select, processed ore or imported drainage fill. Pipes connect to a main collector pipe along the downstream edge of each cell. The drainage system is sized to convey the design irrigation rate of 8 L/h/m2 applied over the top surface area multiplied by 1.5 to account for potential changes in conditions or stormwater flows.

Pad stability was analyzed under static and pseudo-static loading conditions and meets the factor of safety criteria in the Arizona Mining BADCT Guidance Manual. Laboratory testing on project-specific materials such as spent ore and liner interfaces supplied engineering parameters for the stability models.

Solution Management

Solution is managed in lined ponds: a raffinate pond for depleted PLS from SX, north and south PLS collection ponds, north and south SLS collection ponds, and north and south solution overflow ponds for upset conditions and stormwater. The pond system is sized to contain normal operating inventory, pad drain-down during upsets, and stormwater. Water accumulating in overflow ponds is pumped to the SLS ponds to maintain stormwater storage capacity and mitigate environmental discharge.

Pond liner systems follow Prescriptive BADCT guidelines. The process solution pond liner comprises a UV-resistant HDPE geomembrane over a leachate collection and removal system with a geonet gravity-draining to a sump for leak monitoring, over another HDPE geomembrane, over a geosynthetic clay liner, over prepared native foundation or compacted fill.

The SLS ponds support extended leach cycles during secondary sulfide leaching by allowing select copper solutions to return to the top of the heap to promote higher copper extractions or higher solution grades. The facility is designed as a zero-discharge operation.

Heap Leach Process

Cells are retreat stacked east to west by radial stacker in 65.5 m half-cell half-moon shapes. The leach stack is a single lift at angle-of-repose, 8 m high. Ore is stacked at up to 22,000 t/d, and unloading considers a constant rate of 22,000 t/d. A typical interior half-cell strip takes approximately 25 days to stack.

Each half-cell strip cycles through stacking (25 days), piping connections, stacker relocation and ore curing (3 days), irrigation (220 days), solution drain-down, water rinse, water drain-down and piping removal (23 days), spent ore reclaim (25 days), and inspection and maintenance (26 days). An entire cell cycle takes approximately 320 days under design production rates and idealized cell sizing.

Cells are irrigated with raffinate or SLS. PLS reports to the solvent extraction circuit, and raffinate returns to the heap at 2,000 m3/h.

Secondary sulfides require oxygen for leaching. Air is supplied to each cell by two dedicated fans. Fourteen fans total, with 10 operating at any given time. Each pair of fans discharges to an air header. Air piping is installed in a layer of select, processed ore or imported drainage fill beneath the stacked ore, above the drainage system. The air tubes have perforated holes for distribution.

Spent Ore Management

After irrigation, spent ore remains on the pad for initial solution drain-down, water rinsing, and water drain-down, lasting approximately 23 days. Following irrigation piping removal, dozers, loaders, and grasshopper or link conveyors unload the spent ore, loading it into trucks along the eastern edge of the pad. Trucks transport it to the spent ore stockpile or the paste backfill plant. After removal, the pad is inspected and maintenance performed before the next cycle begins with stacking.

The spent ore stockpile sits east of the pad. It will hold all spent ore not used for paste backfill. Mobile equipment places the ore in lifts, expanding from north to south during operations.

The stockpile is underlain by an HDPE geomembrane on prepared foundation or compacted grading fill. A 1 m thick compacted protection layer of carefully placed spent ore covers the geomembrane. Portions of the stockpile near slope toes are compacted for stability. Lined collection channels around the stockpile receive seepage and runoff, conveying flow to the spent ore stockpile collection pond on the northern side, where it is evaporated or reused. Once production ceases, the stockpile will be covered and shaped for surface water management and long-term stability.

Solvent Extraction

In the SX plant, copper is selectively extracted from PLS in mixers using an organic extractant. Denser aqueous and lighter organic phases separate in settlers. The aqueous raffinate retains chloride, acid, and iron and returns to the heap via the raffinate pond. A washing stage removes residual aqueous entrained in the organic.

Copper-loaded organic is stripped using highly acidic lean-electrolyte from the electrowinning plant. Copper transfers at higher concentration to the electrolyte, forming rich-electrolyte delivered to EW for recovery as cathode.

The SX circuit comprises two parallel trains. Each train has two extraction stages, two wash stages, and one strip stage. Organic circulates through extraction, washing, and stripping. A surge tank with pumps for loaded organic sits between the final extraction stage and the first wash stage. Entrained aqueous drains from this tank and returns to the extraction circuit.

PLS is pumped through the two extraction settlers in series, countercurrent to stripped organic. Loaded organic enters a surge tank and is pumped through the wash stage to the strip settler. Water added to the wash stages removes high-chloride aqueous via dilution.

Lean-electrolyte feeds the strip stage, extracting copper to form rich-electrolyte. This stream enters a surge tank and passes through a coalescing column to remove most entrained organic. The partially cleaned rich-electrolyte is stored in another surge tank, then pumped through dual media filters to reduce entrained organic to approximately 5 ppm. These filters are periodically backwashed with demineralized water, which returns to the raffinate.

The electrolyte product enters an EW cell feed tank system, mixed with a portion of lean-electrolyte and reagents to form cell feed electrolyte. This is pumped to the EW circuit. The EW circuit requires a higher flowrate than the strip settler, so circulating cell return lean-electrolyte increases the flow.

Electrowinning

The copper electrowinning tank house uses cells with calcium-tin-lead rolled plate anodes and stainless-steel cathode blanks. Cathodes are harvested manually using an overhead crane and bail. Positioning devices on the crane and cells assist alignment. An industry standard automated stripping machine strips cathodes, and washed blanks return to the cells. Product cathode is bundled, sampled, weighed, labeled, and shipped.

Cells and the stripping machine sit within a building. Cells are individually covered to contain acid mist evolving from the solution surface. Covered cells provide a safe working environment and capture acid mist before release. Captured cell gases and aerosols are scrubbed prior to environmental release.

Reagents and Consumables

Sulfuric acid, guar, cobalt sulfate, extractant, diluent, and sodium chloride are used in the process. Reagent mix tanks include bag breakers and dust collectors where appropriate. Each reagent makeup area has independent containment and a dedicated sump. Bagged reagents are stored under cover in the site warehouse.

Consumption rates: sodium chloride at 0.4 kg/t ore, sulfuric acid at 9 kg/t ore, makeup water at 723 kg/t ore, guar at 0.20 kg/t cathode, cobalt sulfate at 0.40 kg/t cathode, extractant at 3.168 kg/t cathode, and diluent at 8.81 kg/t cathode. Primary crusher liners are 2 sets per year; secondary and tertiary crusher liners are 9 sets per year.

Raw Water and Air Supply

Makeup water comes from existing grandfathered Type 1 non-irrigation rights and mine dewatering. Mine dewatering reports to a surface pond for storage, sedimentation, and eventual discharge to agricultural end users. A portion of makeup water is used untreated in the process. Another portion is treated in a reverse-osmosis plant for wash settlers, reagent mixing, and the EW circuit. Mine dewatering provides sufficient supply for the life of mine.

A compressed air distribution system supplies process air primarily to the crusher area. Instrument air is included for instrumentation and controls.

Additional Interesting Data and Summary

The heap leach feed particle size is sub-9.5 mm at F100 and 6.4 mm at F80, with bulk density for stacking at 1.51 t/m3 and ore solids density at 2.77 t/m3. The abrasion index is 0.12 grams. Gross acid consumption is 27 kg/t with net gangue acid consumption at 10 kg/t. Residual moisture is 6.0 wt %, and soluble copper concentration in residual moisture is 0.35 g/L. Bond work index of spent ore is 14.9 kWh/t, while crusher work index averages 3.8 kWh/t.

The design includes a stockpile feeder with two apron feeders, one secondary crusher (MP1000), one secondary screen (3.6 m x 7.3 m inclined, double-deck, banana), two tertiary crushers (MP1250), two tertiary screens (4.2 m x 8.5 m inclined, double-deck, banana), one heap leach stacking system with groundline conveyor to mobile conveyors with radial stacker, two SX circuits with trains of two extraction, two wash, and one strip, one EW circuit with cells holding 84 cathodes each at 2.3 m2 per cathode, and two EW rectifiers with maximum output of 67 kA at 287 V.

The process personnel count is 114 persons.

Key Processes

• Underground sizer crushing of ROM ore
• Secondary and tertiary crushing and screening to 100% passing 9.5 mm
• Rotary drum agglomeration with sulfuric acid and raffinate or water
• Sodium chloride addition for leaching facilitation
• On/off heap leaching with single 8 m lift, 7 cells in 14 half-cell strips
• Aeration for secondary sulfide leaching with 14 fans, 10 operating
• Solvent extraction with two parallel trains, each with two extraction, two wash, and one strip stage
• Electrowinning with stainless-steel cathode blanks and automated stripping
• Paste backfill for approximately 50% of spent ore
• Spent ore stockpile with lined collection channels and collection pond
• Zero-discharge solution management with lined ponds
• Reverse-osmosis water treatment for wash settlers, reagent mixing, and EW circuit

Source: Feasibility Study & Technical Report, Santa Cruz Copper Project, Arizona, September 29, 2026. Project website: Santa Cruz Copper Project