This report describes the processing methods and metallurgical performance of the Loulo-Gounkoto gold complex carbon-in-leach plant as of March 2023, including current operations and proposed expansion.
Report context
This technical report, dated 17 March 2023, covers the Loulo-Gounkoto Gold Complex and its processing facilities. The report presents the existing carbon-in-leach (CIL) gold extraction plant with a throughput capacity of 5.0 Mtpa, which has progressively increased to a peak of 5.1 Mtpa. Historical operating data from 2014 to 2022 are provided, alongside proposed expansion plans scheduled to commence in 2027 and reach full commissioning by 2029.
Processing route
Current plant configuration
The Loulo processing plant uses a carbon-in-leach gold extraction process for free-milling ores. The circuit comprises conventional comminution, milling, classification, and CIL. A gravity gold recovery circuit was originally installed but has been decommissioned due to low yield and no material improvement on overall recovery. Test work on new ore materials continues to include gravity recoverable gold (GRG) tests to assess potential reinstatement.
The upgraded processing plant remains a conventional crushing, milling, CIL, and tailings disposal circuit processing an average of 605 tph.
Crushing
Hard rock is delivered to a tipping bin that can receive from two directions. The hard rock crusher plant consists of a primary gyratory crusher (FFE Minerals 1,300 mm by 1,750 mm) driven by a 450 kW electric motor. A tramp iron magnet is installed over the product conveyor, and a metal detector trips the conveyor if metal is detected.
The primary crusher operates at a rate of +700 tph, feeding secondary crushers in open circuit, then tertiary crushers in closed circuit. An additional metal detector is installed on the feed to the tertiary crushers. The secondary circuit consists of two Sandvik CS660 Hydrocone crushers, and the tertiary circuit consists of four CH660 Hydrocone crushing units, all powered by 315 kW electric motors. The final product from the tertiary crushers discharges onto a reclaim ore stockpile with a live capacity of approximately 40,000 t and a total capacity of approximately 115,000 t.
A separate facility for soft ore uses a tooth roll crusher (MMD 625, 3-tooth) driven by a 250 kW electric motor, feeding a separate stockpile area with product fed directly onto the ball mill conveyor feed.
Grinding and classification
The milling section produces a leach feed with approximately 75% passing 75 microns. The circuit comprises a ball mill operating as the primary mill (6.1 m diameter, 9.5 m effective grinding length) with installed motor power of 7,000 kW upgraded to 8,000 kW, in open circuit. Oversize scats are re-handled to the stockpile and re-crushed. Primary mill discharge feeds two parallel single-stage overflow-type ball mills (5.5 m diameter by 8.0 m EGL) with power rating of 4,500 kW each, operating in closed circuit with dedicated clusters of twelve 250 mm hydrocyclones (eight typically in use). An additional High Pressure Grinding Roll (HPGR) has been installed to treat scats at a rate of 100 tph. A scat conveyor system returns all mill scats to the primary mill via a cone crusher.
Leaching and adsorption
The CIL circuit consists of fourteen tanks operating in series, each with a nominal capacity of 2,500 m³, giving a retention time of approximately 40 hours. Cyclone overflow at 35% solids density is introduced onto a linear trash screen (0.7 mm by 0.7 mm apertures), with undersize going to the leach feed thickener. Thickener underflow at 50% solids by mass is presented as leach feed.
One pre-oxidation tank (CIL Tank 1) is equipped with six high-shear reactors (Aachen REA-400) upgraded with an additional high-shear reactor unit (Aachen REA-450). Cyanide is added into CIL Tank 2 and dosed automatically to control concentration around the desired value within ±2%, equipped with six high-shear reactors (Aachen REA-400) as part of the Aachen Assisted Leach system. An oxygen dispersion system with power mixers (EKATO) installed in Tanks 3 to 7 maintains optimal dissolved oxygen across the CIL circuit. The oxygen plant, operated by Air Liquide, supplies 64 tpd. Hydrogen peroxide is injected at the thickener underflow as required. Each CIL tank is fitted with a mechanically swept cylindrical inter-tank screen (0.8 mm) from CIL Tank 3 to the end of the circuit. Fresh carbon and regenerated carbon are introduced to tank fourteen and advanced counter-current to the pulp.
Elution and gold recovery
Loaded carbon is recovered from CIL tank 3 into the acid wash cone. After elutriation, it is acid-washed using 3% hydrochloric acid solution, followed by caustic neutralisation and water flushing. Rinsed carbon is transferred to one of two elution columns where caustic/cyanide solution is circulated at elevated temperature (135°C) and pressure using the Zadra process. Two parallel circuits operate from harvest through elution column, heat exchangers, to electro-winning cells in the gold room.
The pressure Zadra method uses a pressure strip vessel that reverses the chemical equilibrium of the adsorbed gold-cyanide complex on activated carbon, resulting in desorption. The batch process requires approximately eight to 16 hours to complete.
Eight electro-winning cells are installed for gold deposition. After a number of elutions, gold-loaded stainless steel mesh cathodes are removed and hosed down, with the collected sludge smelted after drying in electrically heated calcine ovens to produce doré bullion. Barren carbon is transferred to the adsorption circuit or to a horizontal gas-fired regeneration kiln operating at 700°C, then charged back into the CIL circuit.
Tailings thickening and paste preparation
Tailings from CIL tank 14 gravitate through a tails linear screen (0.8 mm by 0.8 mm) to the tails tank, then are pumped to the Intermediate Plant. This plant provides cyanide destruction together with arsenic fixing and two-stage cycloning to remove clay and fines. Coarse tailings are used for paste backfill; fine slimes are pumped to the tailings storage facility. The tailings pump station has two streams of four-stage pumps and a flow diversion valve, with a duty mild steel pipe for high throughput deposition and a standby HDPE pipe for low throughput operation. The tailings pipeline is a 450 mm diameter steel pipe. Recycled water from underground paste plants and tailings storage facilities targets 80% recycled water.
Reagents
Sodium cyanide is delivered as solid briquettes in bulk bags. Lime is delivered in powdered form in bulk bags and made into slurry. Flocculants are delivered in powder form. Caustic soda is dissolved in an agitated tank and pumped to the elution section. Hydrochloric acid is delivered in concentrated form. Oxygen is produced by six Pressure Swing Adsorption units supplying 64 tpd. Hydrogen peroxide is stored in 1 m³ plastic isotainers. Reagents are mixed in a dedicated area outside the security fence and pumped in as required.
Metallurgical test work
Extensive metallurgical test work campaigns demonstrated two distinct behavioural patterns. Ore composites from Gounkoto, Gara UG, and satellites have free-milling characteristics suitable for conventional CIL processing. Yalea UG ore exhibits a degree of refractoriness with resultant lower recoveries. The operation uses a mill feed blending strategy limiting the ratio of refractory gold and associated copper and arsenic mineralisation within the overall mill feed blend. Since 2014, multiple optimisation projects have increased throughput and improved recoveries. The expected throughputs and recoveries are based on historical metallurgical test work and actual operational performance.
Metallurgical testing at the Loulo processing plant covers all CIL process simulation tests on ore sources. The laboratory uses standard bottle roll test procedures for recovery test simulation to predict plant recovery ahead of mining. Historical predicted recovery versus actual plant recovery shows generally strong correlation.
Ore blending and recovery
The life-of-mine plan has an average processing plant recovery of 89.47%, predicted from blended feed proportions of 24% Yalea Underground, 24% Gara Underground, 27% Gounkoto (UG and OP), and 25% Loulo open pits. Copper and arsenic are assayed for all grade control drilling. The mine plan aims to maintain blended material with copper below 100 ppm and arsenic below 4,000 ppm.
Proposed processing plant expansion
A planned processing plant expansion scheduled to commence in 2027 will expand annual capacity to 6.2 Mtpa from 2029 onwards. The main expansion works, in parallel to the current flow sheet, will build an independent flow sheet of 4,200 tpd processing plant including:
- A complete secondary and tertiary crushing circuit in closed circuit with the screening plant to produce a sub-12 mm product
- A closed-circuit single-stage milling circuit comprising a 4.5 MW ball mill and a hydrocyclone cluster producing a P₈₀ of minus 75 micron
- A high-rate thickener capable of handling combined streams from existing and new processing plant streams prior to feeding CIL at a total of 18,400 tph throughput
- Additional three 2,500 m³ CIL tanks
- An upgrade of the current CIL circuit ancillary equipment and tailings handling facilities
The definitive feasibility studies and construction are planned to be completed prior to full commissioning in 2029. The objective is zero to minimal interruptions to current operations during construction.
Historical operating performance
The plant performed at stable availability and utilisation from 2014 to 2022. Disciplined preventative maintenance resulted in consistent availability above 95% in the past three years. Plant availability ranged from 92.95% (2019) to 97.07% (2017). Plant utilisation ranged from 97.20% (2018) to 99.68% (2021).
Specific energy consumption has stabilised at around 40 kWh/t, with the milling circuit consuming between 17 kWh/t to 22 kWh/t depending on ore feed blend and Bond Work Indices. The plant specific energy consumption currently sits at 40.8 kWh/t.
A 50% fresh water consumption step down occurred in 2018 through increased internal water recycling. A water treatment plant was installed to further improve recycling efficiency, with expansion planned during 2023. Underground dewatering as an alternative to river water for elution and gland water service is being explored.
Power supply from renewable energy is planned to expand from the existing 20 MW solar plant to 60 MW total capacity combined with battery energy storage. An additional 15 MW of thermal power generation units are being added to bring installed capacity to 88 MW.
Key reported parameters
| Parameter | Design / Planned | Historical Actual | Testwork Basis |
|---|---|---|---|
| Total ore to plant (annual, kt) | – | 4,543–5,154 (2015–2022) | – |
| Plant throughput capacity (Mtpa) | 6.2 (from 2029 expansion) | 5.0 (design); peak 5.1 | – |
| Expansion flow sheet capacity (tpd) | 4,200 (independent flow sheet) | – | – |
| Average mill feed rate (tph) | – | 605 | – |
| CIL retention time (hours) | – | ~40 | – |
| Leach feed grind size (P₈₀) | 75 micron (expansion) | ~75% passing 75 micron | – |
| CIL tanks (nominal capacity each, m³) | 2,500 (additional 3 tanks) | 14 × 2,500 | – |
| Combined CIL feed rate (tph) | 18,400 | – | – |
| Plant availability (%) | – | 92.95–97.07 (2014–2022); >95% (2020–2022) | – |
| Plant utilisation (%) | – | 97.20–99.68 (2014–2022) | – |
| Specific energy consumption (kWh/t) | – | ~40; 40.8 current | – |
| Milling circuit specific energy (kWh/t) | – | 17–22 | – |
| Overall gold recovery (%) | 89.47 (LOM plan average) | 90.32–92.70 (2015–2021); 91.2 (2022) | Bottle roll testwork |
| Power supply capacity (MW) | 88 (installed, planned) | 20 (existing solar); additional 15 MW thermal being added | – |
| Primary mill power (kW) | – | 7,000 upgraded to 8,000 | – |
| Ball mill power each (kW) | 4,500 (expansion) | 4,500 | – |
| Oxygen supply (tpd) | – | 64 | – |
| Recycled water target (%) | – | 80 | – |
| Copper in blend (target, ppm) | – | Below 100 | – |
| Arsenic in blend (target, ppm) | – | Below 4,000 | – |
Project website: https://www.barrick.com/English/operations/loulo-gounkoto/default.aspx
Technical qualifications
This report presents processing information from the Loulo-Gounkoto Gold Complex technical report dated 17 March 2023. The processing plant expansion project is subject to definitive feasibility studies and construction completion prior to full commissioning in 2029. Metallurgical performance predictions are based on historical test work and operational data. The life-of-mine recovery of 89.47% is predicted from blended feed proportions. Copper and arsenic targets are based on grade control and resource models. The SGS Loulo assay laboratory is accredited by SANAS for gold assay (Scheme Code: FAA50V10) with certificate valid until April 2024.
