Lumina Gold's 2023 prefeasibility study for the Cangrejos gold-copper project in El Oro Province, Ecuador, makes a copper-gold concentrate and gold doré. Tailings are filtered and dry stacked.
The Cangrejos Gold-Copper Project NI 43-101 Technical Report on the Pre-feasibility Study was prepared by Ausenco Engineering Canada for Lumina Gold Corp., with an effective date of April 7, 2023 and an issue date of June 1, 2023. The plant ramps up in three phases. It treats 30 kt/d in Years 1 to 3 (10.95 Mt a year), 60 kt/d in Years 4 to 6 (21.90 Mt a year), and 80 kt/d from Year 7 to Year 26 (29.20 Mt a year). Life-of-mine head grades are 0.55 g/t Au, 0.10% Cu and 0.68 g/t Ag. Average recoveries are 85.0% for gold, 78.9% for copper and 54.0% for silver. The flowsheet was chosen for the deposit's variable mineralogy, grades and hardness, and for the staged ramp-up. Trade-offs covered throughput sizing, comminution equipment, saprolite and saprock processing, a molybdenum circuit and flotation configuration.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Report effective date | April 7, 2023 | Not applicable | Ausenco for Lumina Gold Corp. |
| Throughput | 30, 60 and 80 kt/d | Not applicable | Years 1–3, 4–6 and 7–26 |
| Head grade (LOM) | 0.55 g/t Au, 0.10% Cu, 0.68 g/t Ag | Not applicable | Design criteria |
| Recovery (LOM) | Au 85.0, Cu 78.9, Ag 54.0 | % | Average |
| Primary crusher | Gyratory, 1,200 kW, sized for 80 kt/d | Not applicable | P80 141 mm |
| Secondary crushers | Cone, 600 kW (duty and standby) | Not applicable | P80 70 mm |
| HPGR | 2.4 m x 1.5 m, 6,000 kW | Not applicable | Screen undersize P80 4 mm |
| Grinding | Two ball mills with cyclones | Not applicable | P80 90 µm; duplicated in Expansion 1 |
| Copper regrind | P80 40 µm (Years 1–3), 20 µm (Year 4+) | Not applicable | Ahead of three cleaner stages |
| Concentrate | Membrane filter presses to 9% moisture | Not applicable | 24 h filter feed tank |
| Leach | 1 leach + 6 CIL tanks, 24 h at 40% solids | Not applicable | L-CIL in Years 1–3, L-CIP from Year 4 |
| Elution | 5 t columns, strip at 130°C and 650 kPa | Not applicable | Electric strip heater |
| Cyanide destruction | SO2/air | Not applicable | Detox tails thickened and filtered |
Overview
A gyratory crusher sized for the final 80 kt/d feeds a coarse ore stockpile. Secondary cone crushers, an HPGR and two ball mills follow in the Initial Phase, and these are duplicated for Expansion 1. Expansion 2 reaches 80 kt/d with no new comminution equipment by coarsening the grind, while more flotation cells maintain recovery. Copper rougher concentrate is reground and cleaned in three stages with a cleaner scavenger, giving a copper-gold concentrate. Rougher tails go to sand flotation. The sand flotation concentrate and cleaner scavenger tails are thickened and leached for gold, with elution, electrowinning and smelting to doré. Sand flotation tails and detoxified leach tails are thickened and filtered for a dry stack tailings facility (DSTF).
Key Process Stages
Primary and secondary crushing. Run-of-mine ore is tipped directly into the gyratory dump pocket. Crushed ore is carried by apron feeder, a magnet and an overland conveyor to the stockpile. Crushing runs 6,507 hours a year (75%). Secondary screens and cone crushers in closed circuit send screen undersize at P80 36 mm to the HPGR feed bin.
HPGR. The HPGR runs in closed circuit with wet screens. Oversize can be diverted to an emergency stockpile during HPGR maintenance and reclaimed by front-end loader. Ore can also bypass the HPGR.
Grinding. Two cyclone clusters close the ball mills, which have a maximum capacity of 46 kt/d in the Initial Phase. Collector is added at the ball mill feed boxes. Cyclone overflow passes trash screens to rougher flotation.
Copper flotation. Rougher concentrate goes to two regrind cyclone clusters and a regrind mill. Three cleaner stages produce the final concentrate. Cleaner scavenger concentrate returns to regrind, and cleaner scavenger tails go to the pre-leach thickener.
Sand flotation. Rougher tails are cycloned. The overflow goes to the tailings thickener, and the underflow is conditioned and floated in sand rougher cells. The sand concentrate goes to the pre-leach thickener.
Concentrate handling. A high-rate thickener produces 65% solids underflow. Vertical membrane plate-and-frame presses discharge cake at 9% moisture to bunkers.
Leach, CIL and gold recovery. Pre-leach thickener underflow is leached in one leach and six CIL tanks, with carbon advanced counter-current. Loaded carbon is acid washed in a 5 t column. It is pre-soaked in caustic cyanide at 95°C, then stripped at 130°C and 650 kPa. Gold is electrowon, and the sludge is filtered, dried, fluxed and smelted to doré in an induction furnace. Carbon is regenerated in a kiln, sized and returned to the circuit.
Cyanide destruction and tailings. Leach tails are detoxified by SO2/air, pass a carbon safety screen and go to the tailings thickener. Final tailings are filtered to a cake for the DSTF, and the filter plant is expanded in each phase.
Additional Interesting Data and Summary
Gold recovery equipment (carbon adsorption, desorption, regeneration, electrowinning and smelting) is sized from the start for the Expansion 2 throughput and is not added to in later phases. The rougher stage mass pull ranges from 8.3% to 16.3%.
In summary, the 2023 Cangrejos PFS is a staged HPGR-ball copper flotation plant. It recovers gold both to the copper concentrate and by leaching the cleaner scavenger tails and sand flotation concentrate, and all tailings are filtered and dry stacked.
Key Processes
- Gyratory, secondary cone and HPGR crushing
- Ball milling to P80 90 µm
- Copper rougher flotation, regrind and three-stage cleaning
- Sand flotation of rougher tails
- Concentrate thickening and pressure filtration
- Pre-leach thickening, leach and carbon-in-leach (later carbon-in-pulp)
- Acid wash, pressure elution, electrowinning and smelting to doré
- SO2/air cyanide destruction
- Tailings thickening, filtration and dry stacking
Source: Cangrejos Gold-Copper Project, NI 43-101 Technical Report on the Pre-feasibility Study, El Oro Province, Ecuador, prepared by Ausenco Engineering Canada Inc. for Lumina Gold Corp., effective date April 7, 2023.
Earlier report summaries
Earlier versions of this profile, based on older technical reports, are retained below for source traceability. Dates and figures reflect each report’s own effective date and are superseded by the current information above.
Cangrejos Gold-Copper Project — 2022 Technical Report
This article summarizes the conceptual processing route, design criteria, and personnel requirements for the Cangrejos Gold-Copper Project as presented in the June 1, 2022 NI 43-101 Technical Report.
Report context
The Cangrejos Gold-Copper Project, located in Ecuador, is the subject of a Preliminary Economic Assessment (PEA) dated effective June 1, 2022. The processing information in this report is conceptual in nature, based on metallurgical test data and trade-off studies that evaluated alternative recovery processes and comminution circuits.
Processing route
Comminution and grinding
The conceptual flowsheet begins with primary crushing, where run-of-mine material is dumped into a primary crusher sized for 80,000 tpd. The primary crusher and overland conveyor structures are designed for that throughput, though conveyor drives are sized for 40,000 tpd and designed for quick change-out to support expansion.
Material is conveyed to a coarse material stockpile, then withdrawn by apron feeders to a double-deck banana screen. Screen oversize reports to two secondary cone crushers operating in parallel, with crusher discharge returned to the screen. Screen undersize feeds a log washer to remove clay that could hamper subsequent operations.
Log washer oversize reports to a washing screen, with oversize fed to a single HPGR with 3,200 kW dual drives (6,400 kW total). HPGR discharge is returned to the washing screen in closed circuit. Screen undersize is split to two ball milling circuits, each in closed circuit with hydrocyclones. Cyclone overflow has a particle size distribution of 80% passing 90 µm.
Bulk flotation and regrind
Ball mill cyclone overflow feeds the bulk rougher flotation circuit, comprising two sets of tank cells operating in parallel with approximately 30 minutes retention time. Reagents include potassium amyl xanthate (PAX), Aero Promotor 208 (A208), MIBC, and Dowfroth 250 (DF250).
Bulk rougher concentrate is reground in a Vertimill to P80 35 µm, then cleaned through three stages of cleaner flotation plus cleaner-scavenger flotation. Third cleaner concentrate feeds the bulk concentrate thickener.
Copper-molybdenum separation
Bulk concentrate thickener underflow is pumped to an agitated conditioning tank where sodium hydrosulfide (NaHS) depresses copper minerals. The conditioned slurry feeds the molybdenum flotation circuit comprising rougher flotation, five stages of cleaner flotation, and cleaner scavenger flotation. Fuel oil and MIBC are used as molybdenum circuit reagents. Fifth cleaner concentrate is the final molybdenum concentrate.
Sand flotation and CIL
Bulk rougher flotation tailings are classified in sand flotation cyclones. Cyclone overflow reports to final tailings; underflow feeds sand flotation cells. Sand flotation tailings combine with cyclone overflow to report to final tailings.
Sand flotation concentrate combines with bulk cleaner-scavenger tailings, passes through a trash screen, and feeds the CIL feed thickener. Thickener underflow is pumped to a pH conditioning tank where lime adjusts pH to approximately 11.0. Slurry flows by gravity through five CIL tanks in series, designed for approximately 24 hours total retention. Sodium cyanide is added to CIL tank one; process air is injected into all tanks to provide oxygen for leaching.
Fresh and/or regenerated carbon is added to CIL tank five and advanced counter-current to slurry flow. Loaded carbon from tank one is screened and collected in a holding vessel.
Cyanide detoxification and carbon regeneration
CIL tailings are detoxified using the sulfur dioxide-air process. Sodium metabisulfite provides sulfur dioxide, air is supplied by blowers, copper sulfate catalyzes the reaction, and milk of lime controls pH between 8.0 and 9.0. The circuit includes two agitated tanks designed for approximately 2.5 hours residence time.
Carbon stripping uses a batch system with a pressure strip vessel designed for 2 tonnes of carbon per cycle. Sodium cyanide and caustic soda are added to prepare strip solution, with a water heater and heat exchanger increasing operating temperature and pressure. Barren and pregnant solution tanks are included.
Pregnant solution is pumped through three electrowinning cells where gold and silver plate onto cathodes. A hydrochloric acid wash removes inorganic carbon contaminants, and an electric rotary carbon regeneration kiln removes organic contaminants. Stripped and regenerated carbon discharges to a quench tank, then passes through a carbon sizing screen before returning to CIL tank five. A carbon attrition tank prepares new carbon.
Cathodes are power washed; electrowinning sludge is filtered, dried, mixed with fluxes, and smelted in a gas-fired furnace to produce gold-silver doré for off-site refining.
Tailings handling
Detoxified leach tailings, sand flotation cyclone overflow, and sand flotation tailings combine in the tailings box and flow to two parallel tailings thickeners. Underflows feed a filtration plant with nine pressure plate and frame filters (eight operating, one standby). Dewatered tailings are conveyed to a dry stack tailings facility via overland conveyor, placed using portable conveyors and a stacker.
The CIL circuit nominally processes 10% of plant feed: approximately 4,000 tpd during the first five years and 8,000 tpd after expansion.
Reagents and plant support
Reagents include PAX, MIBC, fuel oil, milk of lime, NaHS, antifoam, sodium metabisulfite, copper sulfate, flocculant, and sodium cyanide. Utilities include fresh water, process water, fire water, air blowers, air compressors, standby power generation, and gland water.
Plant support systems include analytical and metallurgical laboratories, truck scale, hoists, cranes, pumps, automated samplers and analyzers, and process control systems with PLCs and control rooms.
Process personnel
Process staffing is based on four crews, with two crews working 12-hour shifts while two are off. Personnel include process management, metallurgists, shift foremen, operators, and maintenance staff, with expatriate roles for defined durations to train local employees.
Key reported parameters
| Parameter | Units | Value | Basis |
|---|---|---|---|
| Plant throughput, Years 1–5 | tpd | 40,000 | Production schedule |
| Plant throughput, Years 1–5 | Mtpa | 14.6 | Production schedule |
| Plant throughput, Years 6–25 | tpd | 80,000 | Production schedule |
| Plant throughput, Years 6–25 | Mtpa | 29.2 | Production schedule |
| Plant availability, primary crushing | % | 75 | ONIX |
| Plant availability, other | % | 92 | ONIX |
| Head grade Au | g/t | 0.556 | Production schedule |
| Head grade Ag | g/t | 0.7 | Production schedule |
| Head grade Cu | % | 0.10 | Production schedule |
| Head grade Mo | ppm | 20 | Production schedule |
| Specific gravity | g/cc | 2.7 | Plenge |
| Bond Ball Mill Work Index | kWh/t | 17.1 | FLS |
| Bond Abrasion Index | g | 0.3511 | FLS |
| Primary grind size P80 | µm | 90 | Plenge |
| Concentrate regrind size P80 | µm | 35 | Plenge |
| Bulk rougher flotation time | minutes | 12 | Plenge data, factored |
| Tailings thickener sizing | m²/tpd | 0.125 | Pocock |
| CIL retention time | hours | 24 | Conceptual design |
Project website: https://www.wheatonpm.com/portfolio/development-projects/cangrejos/default.aspx
Technical qualifications
The processing information is based on a conceptual PEA-level flowsheet derived from metallurgical test data and trade-off studies. No pilot plant or full-scale operating data are presented for the Cangrejos process. Reported throughputs, head grades, grind sizes, flotation times, and equipment counts are design criteria, not confirmed operating performance. Labor tables show staffing used as a basis for the PEA, including expatriate positions of specified durations. All costs referenced are inclusive of process operating costs presented in Section 21 of the source report.
Source: Cangrejos Gold-Copper Project – Ecuador, NI 43-101 Technical Report, effective date June 1, 2022, Section 17 Recovery Methods.
