The Los Azules Project will employ bio-heap leaching followed by solvent extraction/electrowinning to produce LME Grade A copper cathodes from crushed sulfide ore at an annual throughput ramping from 25 million tonnes to 50 million tonnes.
Report context
This technical report, dated 2025, describes the processing methodology selected for the Los Azules Project in San Juan Province, Argentina. The initial project phase targets 1.023 billion tonnes of ore at an average total copper grade of 0.453% Cu with a soluble copper content of 0.312% Cu over a 20-year mining life. The processing route employs hydrometallurgical recovery through bio-heap leaching of crushed ore followed by solvent extraction/electrowinning (SX/EW) to produce copper cathodes for sale to industry.
Processing route
Process selection rationale
The processing methodology selection considered several options based on the copper mineralization present at Los Azules. The deposit contains very little copper oxide mineralization but has a high secondary copper mineralization content (primarily chalcocite with some covellite and bornite) in the upper supergene portion. The deposit also has a low content of potential by-products common with some copper deposits (gold, silver, molybdenum). Conventional milling and concentration, studied in the 2017 PEA, and emerging technologies for processing primary copper mineralized ore below the supergene layer (primarily chalcopyrite with some bornite) were evaluated. The assessment favors bio-heap leaching from an economic and capital intensity perspective.
The hydrometallurgical approach aligns with environmental and social license strategies by lowering the project’s carbon footprint and reducing water usage by two-thirds or more compared to milling and concentrate production for downstream smelting.
Bio-heap leaching is described as a mature technology for sulfide copper deposits, commercially practiced for over 50 years. Comparable large commercial operations include Quebrada Blanca (Chile) and Zaldivar (Chile), which have employed similar processing strategies at high altitudes in the Chilean Andes.
A future Phase 2 project would target longer-term, deeper, predominantly primary sulfide copper mineralization using conventional sulfide milling and copper concentrate production for smelting or use of Nuton Technology.
Crushing, conveying and ore stacking
The three-stage crushing and screening system design considers a packaged design/supply delivery from Metso, featuring Metso's Foresight family of MP cone stations and semi-mobile primary gyratory (SMPG) stations. Capacities range up to 15,000 tonnes per hour. The design principle aims to reduce concrete works and build a modular plant focused on ease of installation and relocation.
The primary crushing process begins with haul trucks delivering blasted ore to a dump hopper, which discharges onto an apron feeder. A rock breaker handles large material. The apron feeder delivers ore into a Superior MK-III 60×110 primary gyratory crusher at an F80 of approximately 239 mm and throughput of 8,754 mtph, reducing material to a P80 of 145 mm. The primary crushed ore stockpile has a live capacity of eight hours.
From the stockpile, three apron feeders each transfer 2,918 mtph to the secondary crushing feed conveyor. Material passes through secondary screens where oversized material (P80 approximately 171 mm) goes to two secondary cone crushers (Standard MP-1250) while undersized material (P80 approximately 21 mm) reports to the tertiary crushing feed conveyor. Tertiary screening directs oversized material (P80 approximately 48 mm) to tertiary cone crushers (Short Head MP-1250), with undersized material (P80 approximately 14 mm) reporting to the tertiary product conveyor.
The system delivers crushed product at a P80 of 19 mm to the heap leaching systems.
Agglomeration and stacking
Crushed material is distributed to agglomerator feed bins and conveyed to rotary drum agglomerators (4.6 m diameter by 15.2 m long). Ore agglomeration uses acidified raffinate solution from the SX facility without a binder. The agglomerate moisture target is 5%-8% with feed ore moisture starting at approximately 3%. Acidified raffinate includes enough sulfuric acid to achieve a 6 kg acid per tonne ore initial cure addition as ore is stacked onto the leach pad.
The stacking system uses Terra Nova Technologies Standard Super Portable conveyor designs. Material flows through a series of self-driven mobile tracked conveyors to a telescoping radial stacking conveyor that retreats as layers of ore are placed according to the stacking plan.
Heap leaching process
Heap leach processing scales from 25 Mtpa (Year 1) to 50 Mtpa (Year 3). Crushed oxide and supergene material is stacked on a lined leach pad in 9 m to 10 m lifts to a maximum 150 m height over the lined area. Sulfuric acid raffinate (5-10 g/L H2SO4) is applied at an adjustable rate averaging 6 L/hr/m2 in the active leaching area, dissolving copper into pregnant leach solution (PLS) for processing through SX/EW. The system allows periodic rest cycles for pile aeration and to minimize PLS dilution.
Aeration to the leach pad uses ten high-capacity aeration blowers (10,000 CFM or 17,000 m3/hr) packaged in containers for relocation. Low-pressure air is fed to abandoned piping 2 or 3 layers below the top active layer.
Solvent extraction and electrowinning (SX/EW)
The SX/EW plant operates 365 days per year at 99% overall nominal availability. Total PLS flow is expected initially at 2,400 m3/hr, increasing to 4,800 m3/hr at the 50 Mtpa ore throughput rate.
Solvent extraction occurs across three extraction stages (two in parallel, one in series) followed by two stripping stages, configured across four trains (Trains A through D). Each train uses a series-parallel configuration with two extraction mixer/settler units in series plus a parallel mixer/settler, and two stripping mixer/settlers. Each SX train can process up to 1,821 m3/hr PLS flow in the base series-parallel configuration, with piping design allowing series, series-parallel, or all-parallel operation depending on PLS grade and required extraction reagent concentration.
The electrowinning circuit comprises four tankhouses, each with 80 cells constructed of polymer concrete containing 55 anodes and 54 cathodes per cell. Each cell has a hood for acid mist capture feeding off-gas scrubbers using raffinate. Direct current voltage of 2.2 V is applied at a nominal current density of 320 A/m2 (maximum 360 A/m2). Cathodes are harvested weekly via overhead cranes and mechanically stripped before being bundled into 2,000 kg to 2,005 kg stacks.
The facility produces a nominal 210,000 tonnes of LME Grade A copper cathode per year with a design maximum of 240,000 tonnes achievable by increasing rectifier current output and current density to 360 A/m2.
Sulfuric acid production
On-site sulfuric acid plants convert elemental sulfur into 98% sulfuric acid using commercially available elemental sulfur. The initial acid plant capacity is approximately 372,000 tonnes per year, with a second plant of similar size required as ore throughput increases. The technology considered is Ballestra S.p.A. on a design/supply basis, employing Elessent Clean Technologies MECS Double Contact Double Absorption (DCDA) technology achieving up to 99.93% conversion.
Sulfuric acid requirements are based on an average gross acid consumption of 18 kg of 100% acid per tonne ore leached. In the SX/EW process, 1.54 tonnes of sulfuric acid are regenerated for every tonne of copper produced, offsetting a portion of leaching acid requirements.
The acid plant cogenerates steam for electric power up to approximately 13.6 MW per module, offsetting 15-20% of site electricity demand. Waste heat is recovered and used in the SX/EW process.
Key reported parameters
| Parameter | Units | Value | Basis |
|---|---|---|---|
| Processing operating life | yr | 22 | Design |
| Mining operation | yr | 20 | Design |
| Ore feed quantity (Reserves) | Mt | 1,023 | Design |
| Total copper grade (average) | % | 0.453 | Design |
| Soluble copper grade (average) | % | 0.312 | Design |
| Ore throughput Year 1 | Mt/yr | 25 | Design |
| Ore throughput Year 2 | Mt/yr | 37.5 | Design |
| Ore throughput Year 3-LOM | Mt/yr | 50 | Design |
| Overall availability | % | 92 | Design |
| Recoverable copper mined (total copper basis) | % | 74.5 | Estimate |
| Heap leach process efficiency factor | % | 95 | Design |
| Copper recovery to cathode (total copper to cathodes) | % | 70.8 | Estimate |
| Copper cathode production LOM | kt | 3,279 | Estimate |
| Annual copper production Year 1-5 (average) | t/yr | 204,789 | Estimate |
| Annual copper production LOM (average) | t/yr | 148,175 | Estimate |
| Maximum annual copper production | t/yr | 233,000 | Estimate |
| Design factor | – | 1.15 x Nominal | Design |
| Crushed product P80 | mm | 19 | Design |
| Leach pad capacity (total) | Mt | 1,054 | Design |
| Initial Phase 1 pad capacity | Mt | 68.3 | Design |
| Acid consumption (gross) | kg/tonne ore | 18 | Design |
| Initial acid plant capacity | t/yr | 372,000 | Design |
| Peak process water consumption | m3/hr | 417.5 | Design |
| SX/EW nominal availability | % | 99 | Design |
| Nominal EW current density | A/m2 | 320 | Design |
| Maximum EW current density | A/m2 | 360 | Design |
| Nominal cathode production capacity | t/yr | 210,000 | Design |
| Maximum cathode production capacity | t/yr | 240,000 | Design |
Project website: https://www.mcewenmining.com/operations/los-azules/default.aspx
Technical qualifications
The qualified person believes the design criteria, processing methodology, facilities and equipment selections and descriptions are appropriate and consistent with other similar current operations and studies for similar projects. Given the mature and commercially proven nature of the processing technologies considered, large-scale piloting is deemed not meaningful or necessary. Equipment selections are based on vendor proposals/consultations and appropriate process modeling.
The report notes that bio-heap leaching is commercially practiced at comparable operations including Quebrada Blanca (Chile) and Zaldivar (Chile). These are provided as directly comparable larger commercial operations, not as historical operating data for the Los Azules Project itself. The report does not contain operating data from Los Azules testwork or pilot plants; all reported parameters derive from design criteria and metallurgical recovery estimates for lithologic types to be mined.
The sulfur supply strategy analysis was conducted by Ellzey Zissos & Associates, with a Monte Carlo simulation estimating a P80 landed cost of USD $315 per tonne for elemental sulfur delivered to Los Azules. Sulfur pricing inputs include inland transport rates provided by PSA on December 11, 2024.
Source: Los Azules Project , NI 43-101 Technical Report, 2025, Section 17.0 Recovery Methods (pages 17-333 to 17-357).
