This technical report presents a preliminary economic assessment for the Escalones copper project, based on a conventional sulfuric acid heap leach, solvent extraction, and electrowinning flowsheet designed for a 50,000-tonne-per-day operation.
Report context
The Escalones Copper Project PEA NI 43-101 Technical Report, dated March 22, 2022, describes a proposed processing facility for the Escalones project owned by World Copper Ltd. The report outlines a conceptual design for a conventional sulfuric acid heap leaching operation followed by solvent extraction and electrowinning to produce Grade-A copper cathode. The target production rate is 50,000 tonnes per day of mineralized material, producing an average of 52,000 annual tonnes of copper cathode (115 million pounds). The estimated average copper extraction from the mineralized material is 72.5%. The proposed operation would run on a 365-day-per-year, 24-hour-per-day basis.
Processing route
Run-of-Mine and Crushing
Run-of-mine (ROM) material would be trucked to a primary jaw crusher located reasonably close to the proposed open pit. The proposed jaw crusher has a 200-centimetre by 150-centimetre opening (79-inch by 59-inch) and a target closed side setting of 225 mm (8.8 inches), equipped with a 400-kilowatt motor (536 horsepower). The feed rate to the circuit is designed at 2,604 tonnes per hour (2,871 short tons per hour). A ROM stockpile would be located near the crusher to handle excess feed and maintenance bypass material, to be rehandled by a frontend loader.
Primary crushed material would be conveyed to the secondary crushing plant via a 3-kilometre-long series of conveyors (1.9 miles), all 137 centimetres wide (54 inches). The secondary crushing circuit consists of a vibrating double deck screen, 2.48 metres wide and 6.1 metres long (8 feet by 20 feet). The top screen opening is 125 mm (4.9 inches) and the bottom is 50 mm (1.97 inches). The target product is a P80 of 50 mm. Screen oversize reports to two standard 2.3-metre-diameter (7.5-foot) cone crushers, each 600 kilowatts (800 horsepower). Crusher discharge and screen undersize report to the crusher discharge conveyor, which feeds the 2-kilometre (1.2-mile) overland heap conveyor. Circuit sizing was performed using crushing plant simulators based on the projected average hardness of mineralization.
Heap Leaching
The crushed material would be delivered to the heap via a series of overland conveyors. A tripper conveyor located adjacent to the heap leach would transfer the crushed material to a series of grasshopper conveyors and ultimately to a stacking conveyor for placement on the heap.
The heap leach would consist of a suitable area lined with a solution containment system, typically a linear low-density polyethylene (LLDPE) liner with a rock over liner of sized material to facilitate drainage. Within this over liner would be placed drainage pipes to conduct leach solution to centralized collection ponds. Crushed material would be stacked in lifts on the lined pad by means of a slewing stacking conveyor. Lifts are targeted at 10 metres (32 feet) in height with a total heap height of 100 metres (328 feet). Once a suitable area has been stacked (cell), the cell would be irrigated with dilute sulfuric acid solution. Stacking would continue to advance, and each area irrigated with acid solution for a set period of time (primary leach cycle).
Leach material would be stacked for a sufficient period to allow enough surface area for irrigation. Irrigation would be provided by an emitter-type system designed to deliver up to 12 litres per hour per square metre (0.005 gallons per minute per square foot). During the primary leach, the heap would be placed under irrigation for approximately 120 days. After the primary leach, irrigation would be discontinued and advanced to the next cell. The subsequent lift will be placed on top of the previous lift, leaving a suitable setback from the previous crest. Rinsing will only occur during closure or once the heap reaches its ultimate height.
The copper leach solutions or pregnant leach solution (PLS) flow from the pad to the PLS sump or pond by gravity. Solution would be pumped from the sump to the solvent extraction circuit. Excess solution would be diverted to the PLS pond. Solution would be collected from each heap cell by a series of drainpipes under the heap that transport solution to perimeter piping. Storm water collected from the pad during heavy precipitation events can be diverted to an Event water pond and used as fresh makeup water.
Due to land and terrain constraints, two heap leach facilities (HLFs) are required, located close to each other in the main valley near the mine. The HLFs are designed as a hybrid valley fill making use of the steep terrain. The base of the heap leach facility is contoured by a series of plateaus vertically spaced to provide heap stability. The toe of the heap leach is constructed as a dam to provide both buttressing and solution storage. The majority of the PLS will be drawn directly from the heap leach toe, with excess reporting to the PLS or Event Pond. The HLFs are designed to hold the life-of-mine production (19.5 years), approximately 366 million tonnes (229 million cubic metres). Heap 1 is approximately 189 million cubic metres and Heap 2 is approximately 40 million cubic metres. Heap leach sizing, solution flows, and water balances were developed using heap leach modeling software.
Solvent Extraction
The PLS would be processed directly in the solvent extraction plant (SX), diverted to a dedicated pond, or recirculated to the heap. The SX plant is estimated to process approximately 3,500 cubic metres per hour of PLS. The initial design uses a two-stage extraction and a single-stage strip configuration. No wash stage has been included at this level, but it may be necessary if high chloride water is employed. The SX circuit consists of a series of extraction stages and a stripping stage using a conventional mixer or settler arrangement.
A Ketoxime-Aldoxime or a mixture such as LIX984N has been proposed, along with a diluent such as Shellsol D90 (isoparaffinic high flash point) as per typical copper SX configurations.
The loaded organic from the extraction stage would be transferred to the stripper vessel, producing a rich electrolyte solution for subsequent electrowinning. The copper-depleted raffinate from the extraction circuit would be recycled to the raffinate pond. Prior to electrowinning, the rich electrolyte would be purified to remove entrained organic through column flotation and filtration. The depleted raffinate solution would report to the heap leach raffinate pond or tank and be recirculated back to the heap after having the reagent levels adjusted (free acid).
Electrowinning
The electrowinning (EW) circuit consists of two parallel trains of 174 cells with 60 cathodes per cell. Four rectifiers will provide the necessary current for electrowinning. Specific reagents would be added to promote proper cathode growth and maintain suitable over-voltages. Purge streams would be utilized to maintain acceptable impurity concentrations.
The copper-depleted lean electrolyte would report back to the SX stripping circuit. Cathodes would be allowed to plate until they reach their harvest mass. They would be harvested by an overhead crane and washed prior to reporting to a mechanical stripper. The stripping machine would be semi-automatic and would operate in 12-hour shifts. Grade-A copper cathodes would then be sampled and bundled for shipment. Standard acid mist mitigation measures would be implemented through the use of specialized reagents and proper ventilation. Polypropylene spheres may also be employed for acid mist control.
Heap Leach Pad and Pond Design
The HLF consists of the following system components: heap leach pad, liner system, leachate (solution) collection system, storm pond, stormwater management system, and freshwater supply. To minimize capital expenditure, the heap leach pad has been designed in phases. The HLF would be constructed in three phases, with pad foundation preparation, liner installation, and collection piping advanced as the leach pad expands. The capacity of each stacking stage includes an initial three-year period plus two additional two-year periods. The initial HLF development (Phase 1) would also include the full development of the solution handling system, storm pond, and perimeter diversion ditches prior to commencing ore stacking and leaching.
The heap leach pad for HLF1 has an approximate final footprint area of approximately 2,000,000 square metres and for HLF2 of approximately 750,000 square metres. The heap leach pad is designed to be operated as a fully drained system with no leachate storage within the main HLF except for solution storage at the heap face dam. A minimum pad grade of 1 to 2% is required. As a result of limited space and terrain constraints, the HLF will require significant cut and fill to develop a series of plateaus in the hillside.
A liner system is planned to maximize solution recovery and minimize environmental impacts. The pad is designed to operate with minimal solution storage within the pad structure during normal operating conditions. A double liner system has been employed with two layers of synthetic material. The double liner system consists of a 0.5-metre-thick (1.6-foot-thick) over liner (38 mm [1.5-inch] minus with less than 10% fines content) using ore as the material, a 2 mm (80-mil) LLDPE geomembrane, a 0.3-metre-thick (1-foot-thick) compacted low permeability soil liner, a Leak Detection and Recovery System (LDRS), and a 1.5 mm (60-mil) LLDPE geomembrane. LLDPE was proposed for the geomembrane liner systems for the heap leach pad due to higher interface friction values, ease of installation in cold climates, good performance under high confining stresses, and higher allowable strain.
Development of the heap leach liner would be constructed in three phases, with pad expansions proposed after three years of initial production. The perimeter berm would be constructed as part of the liner tie-in around the perimeter of the pad footprint. A 0.3-metre-thick (1-foot-thick) bedding sand layer would be placed on the face of the confining embankment directly underneath the bottom geomembrane liner.
The solution collection system consists of lateral collection pipes, collection header pipes, main header collection pipes, and leachate collection sumps. The lateral collection pipes, spaced approximately five metres (16 feet) apart under the entire pad footprint, feed into collection header pipes, then into the main header positioned along the centerline of each heap leach pad cell. Two leachate collection ditches or pipes allow solution to flow by gravity.
The LDRS consists of a 0.3-metre-thick (1-foot-thick) sand layer embedded with 100-mm (4-inch) diameter perforated corrugated plastic tubing collection pipes. Any leakage recovered by the LDRS would be conveyed into the LDRS sump at the downstream toe of the HLF. The entire pad solution collection system is subdivided into multiple independently monitored areas (cells) separated by small berms.
Solution Storage
The Event Pond is designed to provide storage for excess leachate and runoff generated as a result of rainfall events or excess PLS. It is situated immediately down gradient of the HLF. The Event Pond is designed to contain the excess HLF leachate and surface runoff from the 1 in 100-year 24-hour storm event without discharge, with overflow designed to discharge the 1 in 200-year 24-hour storm event. Total runoff estimates for the 1 in 100-year 24-hour storm event are 152,477 cubic metres, with an additional 10% factor of safety giving 163,000 cubic metres. Solution stored in the Event Pond would be pumped back to the heap leach pad over approximately ten days.
The PLS pond will functionally be the heap leach itself. No dedicated PLS pond is envisioned for the project, with excess PLS reporting to the Event or Raffinate Pond. The Raffinate pond or tank requires approximately four hours of storage capacity. The heap leach is designed to contain up to 24 hours of solution, assuming a maximum irrigation rate of 15 litres per hour per square metre, with a capacity of approximately 105,948 cubic metres. The Raffinate tank or pond is designed with a capacity of approximately 17,658 cubic metres.
The engineered double liner system designed for the ponds uses the same design principles as the HLF pad liner system, consisting of a 1.5 mm (60-mil) HDPE geomembrane, a 0.3-metre-thick (1-foot-thick) low permeability soil liner, a geosynthetic geonet drainage layer, and a 1.5 mm (60-mil) HDPE geomembrane. It is recommended that HDPE geomembrane be used for the pond liner system rather than LLDPE, as HDPE has higher ultraviolet resistance.
The surface water management system consists of a series of ditches constructed around the perimeter of the HLF to intercept overland surface runoff, designed to convey the 1 in 100-year 24-hour duration storm event with a minimum freeboard of 0.3 metres, minimum ditch grade of 0.01 metre per metre, side slopes of 2H:1V, and trapezoidal channel shape.
Key reported parameters
| Parameter | Value | Units | Basis |
|---|---|---|---|
| Target production rate | 50,000 | tonnes per day | Proposed design |
| Annual copper cathode production | 52,000 (115 million pounds) | tonnes | Proposed design |
| Average copper extraction | 72.5 | % | Estimated |
| Primary jaw crusher opening | 200 x 150 | cm | Proposed design |
| Jaw crusher closed side setting | 225 | mm | Target |
| Jaw crusher motor | 400 | kW | Proposed design |
| Crushing circuit feed rate | 2,604 | tonnes per hour | Design |
| Secondary crusher diameter | 2.3 | metres | Proposed design |
| Secondary crusher motor | 600 | kW each | Proposed design |
| Target product size (P80) | 50 | mm | Target |
| Heap lift height | 10 | metres | Target |
| Total heap height | 100 | metres | Target |
| Irrigation rate | 12 | litres per hour per square metre | Design |
| Primary leach cycle duration | 120 | days | Design |
| Life of mine | 19.5 | years | Design |
| Total heap capacity | 366 | million tonnes | Design |
| Heap 1 capacity | 189 | million cubic metres | Design |
| Heap 2 capacity | 40 | million cubic metres | Design |
| SX plant PLS throughput | 3,500 | cubic metres per hour | Estimated |
| SX configuration | Two-stage extraction, single-stage strip | , | Initial design |
| EW cells per train | 174 | cells | Proposed design |
| Cathodes per cell | 60 | cathodes | Proposed design |
| HLF1 final footprint | 2,000,000 | square metres | Approximate |
| HLF2 final footprint | 750,000 | square metres | Approximate |
| Minimum pad grade | 1 to 2 | % | Required |
| Over liner thickness | 0.5 | metres | Proposed design |
| Over liner material specification | 38 mm minus, <10% fines | , | Proposed design |
| Primary geomembrane (pad) | 2 mm LLDPE | , | Proposed design |
| Secondary geomembrane (pad) | 1.5 mm LLDPE | , | Proposed design |
| Compacted soil liner thickness | 0.3 | metres | Proposed design |
| Lateral collection pipe spacing | 5 | metres | Proposed design |
| LDRS sand layer thickness | 0.3 | metres | Proposed design |
| LDRS collection pipe diameter | 100 | mm | Proposed design |
| Event Pond capacity (1 in 100-year storm) | 152,477 | cubic metres | Estimate |
| Event Pond capacity with safety factor | 163,000 | cubic metres | Design |
| Heap leach solution storage capacity | 105,948 | cubic metres | Design |
| Raffinate tank or pond capacity | 17,658 | cubic metres | Design |
| Pond geomembrane | 1.5 mm HDPE | , | Proposed design |
| Maximum irrigation rate (design assumption) | 15 | litres per hour per square metre | Design |
Technical qualifications
The report is a Preliminary Economic Assessment (PEA) prepared in accordance with NI 43-101 and is based on conceptual design. The flowsheet is described as conceptual. Circuit sizing was performed using crushing plant simulators based on projected average hardness of mineralization. Heap leach sizing, solution flows, and water balances were developed using heap leach modeling software. The report notes that further engineering will be required to ensure acceptable heap stability is established. No wash stage has been included in the SX design at this level, but it may be necessary if high chloride water is employed. The report specifies that the information presented represents proposed design parameters and estimated performance, not operating data from a currently producing facility.
Source: Escalones Copper Project PEA NI 43-101 Technical Report, March 22, 2022, Sections 17.0 through 17.15.
