The Cerro Quema project proposes a heap leach processing operation with ADR recovery, based on metallurgical testwork indicating amenability to cyanide leaching.
Report context
The Updated Cerro Quema Pre-Feasibility Study NI 43-101 Technical Report, dated January 2022, describes processing facilities for an open pit gold-silver project in Panama. The report presents a designed processing route based on metallurgical testwork developed by KCA and others. No historical operating data is reported as the project is in the pre-feasibility stage. The information below is derived from Section 17.0 Recovery Methods of the technical report.
Processing route
Crushing and conveying
Run-of-mine ore from the La Pava or Quema-Quemita open pits will be delivered to the primary crusher station in 41 and 55-tonne capacity haul trucks and dumped directly into the ROM dump hopper or stockpiled in a ROM stockpile. Stockpiled ore from the ROM stockpile will be reclaimed by a front-end loader and fed to the dump hopper as needed. The dump hopper is equipped with a stationary grizzly, and oversized rocks will be broken using a rock breaker.
The crushing plant includes an apron feeder, vibrating grizzly, primary jaw crusher, and crusher discharge conveyor. Ore will be fed from the ROM dump hopper to a vibrating grizzly feeder via an apron feeder. The vibrating grizzly feeder has parallel bars spaced 100 mm apart with grizzly oversize fed to the primary jaw crusher and grizzly undersize recombined with the jaw crusher product on the primary crusher discharge conveyor. The primary crusher will operate with a 120 mm discharge setting. The final crushed product will be 80% passing 105 mm.
The crushed product will be delivered to the heap leach pad area and stockpiled in a conical 26,000-tonne stockpile by a crushed product transfer conveyor and overland crushed ore stockpile feed conveyor. The crushed product transfer conveyor will be equipped with a belt scale and tramp metal electromagnet and metal detector. Water sprays will be located at all material transfer points to reduce dust generation.
The crushing circuit will operate 7 days/week, 24 hours/day, 365 days/year with an overall estimated availability of 75%.
Reclamation and conveyor stacking
Crushed ore will be reclaimed from the stockpile by two reclaim belt feeders to a reclaim conveyor in a tunnel below the stockpile. Pebble lime (CaO) for pH control will be added to the ore on the reclaim tunnel conveyor from an 80-tonne lime silo equipped with a bin activator, variable speed screw feeder and dust collector; lime addition will vary by pit and material type. Barren process solution will be added to the ore on the reclaim tunnel conveyor once the conveyor is over the lined leach pad containment area.
The heaps will be constructed in 8 m high lifts using a mobile conveyor stacking system. The conveyor stacking system includes ramp portable transfer conveyors, grasshopper portable transfer conveyors, a horizontal index feed conveyor, a horizontal index conveyor, and a 33.5 m long radial stacking conveyor capable of powered height adjustment, slewing and stacking to a height of 8 m. The maximum planned heap height is 80 m over the composite liner system, or 10 total lifts.
Heap leach facility design
The Heap Leach Facility (HLF) located in Quebrada Maricela will be a multiple-lift, single-use type leach pad designed to accommodate approximately 27.3 million tonnes of crushed ore. The 43.2-hectare HLF has been sized using an average stacked ore density of 1.5 tonnes per cubic meter and a maximum heap height of 125 meters. Ore will be conveyor-stacked at a rate of 10,000 tonnes per day in approximately 8-meter lifts with 9.2 meters wide benches between lifts to create an average overall ore slope of 2.5H:1V.
The HLF will be lined with a composite liner system consisting of a prepared subgrade, a 300 mm thick low-permeability soil bedding layer or a geosynthetic clay liner (GCL), overlain by a 2 mm single-side textured linear low-density polyethylene geomembrane liner. The HLF will be constructed in three phases providing a total lined leach pad surface area of approximately 41.9 hectares.
Leaching and solution application
Ore will be leached in a single stage using barren solution consisting of a dilute sodium cyanide solution. Barren solution will be pumped from the barren solution tank to the active leach site using a dedicated split-case horizontal centrifugal pump and applied to the heap by a system of drip emitters and/or wobbler sprinklers depending on water balance requirements. Barren solution will be applied at an average rate of 10 L/h/m². Concentrated cyanide will be added to the barren solution tank by metering pumps to maintain the cyanide in solution at 300-500 ppm NaCN. The barren solution tank is sized for 45 minutes of residence time at the ADR plant design flow rate of 734 m³/h. Antiscalant polymer will continuously be added to the leach solutions at an average rate of 10 ppm.
Pregnant solution containing gold and silver values from the heap drains by gravity to a pregnant solution pond. The pregnant solution pond will be equipped with two submersible pumps which will pump pregnant solution to the carbon adsorption circuit.
Adsorption, desorption and recovery
The adsorption facility will consist of one train of five up-flow, open-top carbon columns (CICs). Each column will be 3.76 m in diameter and 3.76 m tall and sized to hold 4.8 tonnes of carbon. Pregnant solution will be pumped to the adsorption-feed head-tank at a nominal flow rate of 611 m³/h and flow by gravity through the set of five carbon columns, exiting as barren solution.
Loaded carbon from the CIC will be stripped using a pressure Zadra desorption circuit in 2.5-tonne batches. During the desorption process, gold and silver will be continuously extracted by electrowinning from the pregnant eluate concurrently with desorption. The elution will operate at a temperature of 135°C and a nominal operating pressure of approximately 483 kPa (70 psig).
Gold sludge will be washed from the electrowinning cell cathodes, treated in a mercury retort operating at temperatures up to 650°C under vacuum, and smelted to produce the final doré product. A portion of the carbon will be thermally regenerated using a kiln after each strip to maintain carbon activity.
Solution treatment facilities
Water treatment facilities will be required for discharging impacted water from the mine site. Two main sources of impacted water are identified: the waste rock dump (WRD) area and the heap leach facility (HLF) area.
The HLF process solution treatment includes cyanide neutralization using sodium metabisulfite followed by treatment in a plant with reaction tanks, disc filtration, a Moving Bed Biofilm Reactor (MBBR), and a fixed film denitrification filter. The HLF solution treatment system has a design maximum flowrate of 80 m³/h with an average treatment rate of 15 m³/h.
The WRD active water treatment plant will treat contact water from the La Pava Pit, Quema-Quemita Pit and the Upper Chontal Waste Rock Dump. The WRD treatment plant has a design treatment rate of 320 m³/h with an average treatment rate of 95 m³/h. The WRD plant process will include pH adjustment, precipitation/solid removal, and biological MBBR nitrification and denitrification filter systems.
Passive treatment systems for both the WRD and HLF during closure will utilize equalization basins and biological anaerobic processes using submerged organic media (biocarbonate reactors), followed by wetlands.
Key reported parameters
| Parameter | Unit | Design Value | Testwork Basis |
|---|---|---|---|
| Annual processing rate | tonnes/year | 3,650,000 | Design |
| Crushing production rate | tonnes/day | 10,000 | Design |
| Crushing product size | % passing 105 mm | 80 | Design |
| Crusher availability | % | 75 | Design |
| Overall leach cycle | days | 70 | Metallurgical testwork |
| Gold recovery – La Pava oxide | % | 88 | Metallurgical testwork |
| Gold recovery – Quemita oxide | % | 86 | Metallurgical testwork |
| Gold recovery – La Pava mixed | % | 57 | Metallurgical testwork |
| Gold recovery – Quemita mixed | % | 62 | Metallurgical testwork |
| Silver recovery – La Pava oxide | % | 30 | Metallurgical testwork |
| Silver recovery – Quemita oxide | % | 15 | Metallurgical testwork |
| Silver recovery – La Pava mixed | % | 25 | Metallurgical testwork |
| Silver recovery – Quemita mixed | % | 10 | Metallurgical testwork |
| HLF total capacity | million tonnes | 27.3 | Design |
| HLF lined area | hectares | 43.2 | Design |
| Lift height | m | 8 | Design |
| Maximum heap height | m | 125 | Design |
| ADR plant design flow rate | m³/h | 734 | Design |
| NaCN concentration in leach solution | ppm | 300-500 | Design |
| Solution application rate | L/h/m² | 10 | Design |
| Pebble lime consumption | kg/tonne ore | 1.8 | Metallurgical testwork |
| Sodium cyanide consumption | kg/tonne ore | 0.19 | Metallurgical testwork |
| HLF water treatment max flow | m³/h | 80 | Design |
| WRD water treatment max flow | m³/h | 320 | Design |
Project website: https://orlamining.com/asset/cerro-quema/
Technical qualifications
The report states that testwork developed by KCA and others has indicated the Cerro Quema ores are amenable to heap leaching. The recovery methods and parameters presented are design criteria based on this metallurgical testwork. The report notes there is no historical operating data for the project as it is in pre-feasibility stage. Cement agglomeration was found not to be required through testwork. Metallurgical testwork showed minimal additional gold recovery improvement through finer crushing. The average estimated reagent consumptions for lime and cyanide were based on metallurgical testwork and will vary by material type.
Source: Updated Cerro Quema Pre-Feasibility Study NI 43-101 Technical Report, January 2022, Section 17.0 Recovery Methods.
