Wahgnion Gold Operations — 2023 Technical Report

This report details the proposed processing plant design for the Wahgnion Gold Operations, based on metallurgical testwork and operating experience from analogous facilities.

Report context

The Wahgnion Gold Operations technical report, dated 2023, describes the proposed process plant design for a gold operation in Burkina Faso. The plant design is based on a metallurgical flowsheet constructed from well-proven unit operations, replicating various areas of the Sabodala process plant to achieve operational synergies. The design incorporates nominal processing capacities of 2.7 Mtpa for oxide ore and 2.0 Mtpa for primary ore, with targeted rates of 2.8 Mtpa and 2.1 Mtpa respectively based on higher plant availability assumptions drawn from Teranga's Sabodala operating experience.

Processing route

Primary crushing and stockpiling

Run-of-mine ore will be delivered by haul trucks directly from the pit to the primary crusher area, either tipped directly to the ROM bin or stockpiled by gold grade, oxidation, and lithology. A front-end loader will reclaim ore from stockpiles. A grizzly fitted to the ROM bin protects downstream equipment from oversize material, and a rock breaker will break oversize rocks on the grizzly or ROM pad.

A variable-speed apron feeder draws ROM ore at a controlled rate onto a vibrating grizzly, with grizzly oversize reporting to a single-toggle jaw crusher. The crusher product and grizzly undersize discharge onto the primary crusher discharge conveyor feeding the crushed ore stockpile. The designed crushed product P80 ranges from 100 mm to 140 mm based on differing weathering types.

The crushed ore stockpile has a live nominal capacity of 2,000 t. Under normal conditions, the crushing rate exceeds the withdrawal rate to the milling circuit. Crushed ore will be reclaimed by front-end loader into an emergency feed hopper when reclaim apron feeders are offline.

Grinding and classification circuit

The grinding circuit consists of a SAG mill in closed circuit with a pebble crusher and a ball mill in closed circuit with hydrocyclones (SABC configuration). Crushed mill feed is withdrawn from the stockpile by variable-speed apron feeders and conveyed to the SAG mill. Quicklime for pH control is added onto the mill feed conveyor from two lime silos via a variable-speed rotary feeder.

The SAG mill, equipped with a variable-speed drive capable of operating between 60% and 80% of critical speed, discharges over a vibrating wet screen. Screen oversize (pebbles and worn grinding media) reports to a pebble transfer conveyor. A magnet removes tramp steel, and a metal detector activates a diverter gate to prevent steel reaching the pebble crusher. The diverter gate also allows pebble bypass for recycle to the SAG mill or to enable pebble crusher maintenance during milling circuit operation. Crushed pebbles discharge to the SAG mill feed conveyor.

SAG mill discharge screen undersize is diluted with process water in the mill discharge hopper and pumped to the classifying hydrocyclone cluster. The cyclone overflow, at nominal 42% w/w solids, gravitates to a trash screen. Cyclone underflow returns to the ball mill feed chute. The ball mill uses a variable-speed drive for soft starting only, with no speed variation available during operation. The designed grind size is P80 of 106 µm. The design allows for a future gravity circuit fed from cyclone underflow.

Leach and carbon-in-leach circuit

The trash screen undersize gravitates to the leaching circuit comprising one leach tank and seven CIL adsorption tanks (eight stages total). Tanks are interconnected with launders for gravity flow. Each tank has a dual-impeller mechanical agitator, and each CIL tank is fitted with a mechanically swept wedge-wire intertank screen to retain carbon. All tanks have bypass facilities for removal during maintenance.

Sodium cyanide solution is metered from a ring main system into the CIL feed distributor box and tanks. Medium-pressure compressed air is distributed to the CIL section and sparged down agitator shafts to provide oxygen for leaching.

Primary and reactivated carbon returns to CIL Tank 8 and advances counter-current to slurry flow by recessed-impeller pumps. Slurry from the final CIL tank gravitates to a vibrating carbon safety screen before reporting to the tails thickener.

Elution and goldroom

Gold recovery from loaded carbon uses the Split Anglo American Research Laboratory (SAARL) elution circuit. Loaded carbon is recovered on a recovery screen and directed to a rubber-lined acid wash column, where 3% w/w hydrochloric acid solution is pumped up-flow to remove acid-soluble contaminants. After acid washing and water rinsing, carbon transfers to the elution column.

Strip solution (sodium hydroxide and sodium cyanide) is heated via an in-line heater and injected into the elution column base. Loaded carbon is pre-soaked in cyanide/caustic solution for 30 minutes before elution. Pregnant solution passes through electrowinning cells with stainless steel anodes and mesh cathodes, plating gold and silver over approximately five hours. The electroplated metals are washed from cathodes with high-pressure water, filtered, dried, and smelted with fluxes in a diesel-fired furnace to produce doré bars. Slag returns to the milling circuit.

Barren carbon transfers from the elution column to a dewatering screen and then to a horizontal carbon reactivation kiln feed hopper. Carbon is heated above 750°C in a steam atmosphere for 15 minutes for reactivation, then quenched and pumped to a carbon sizing screen before returning to the CIL circuit.

Tails thickening and disposal

CIL tails are thickened in a high-rate thickener with flocculant addition. Thickener overflow gravitates to a stand pipe and is pumped to the mill or to the process water pond. Thickener underflow is pumped to the tailings storage facility using single-stage centrifugal pumping. Tailings are deposited using peripheral discharge and cyclic spigot deposition to allow consolidation and drying.

Power and water supply

Site-wide electrical power is supplied from an owner-operated heavy fuel oil power station. The installed load is 18.1 MW (20.7 MVA), with maximum demand of 13.6 MW (15.7 MVA) and average demand of 11.2 MW (12.3 MVA). The maximum demand is based on load factors of 97% for the SAG mill drive, 95% for the ball mill drive, and 80% for most other areas.

Raw water is pumped from a water harvest dam or mine dewatering system to a raw water tank. Filtered water is produced through clarification, sand filtration, carbon filtration, and biocide dosing. Potable water from bore water undergoes sand filtration, micro filtration, ultra-violet sterilization, and chlorination. The process water system uses tailings storage facility decant return water with raw water make-up as required. A double-lined process water pond with leak detection is included.

Key reported parameters

Technical qualifications

The source attribution in the key process design criteria identifies four origins for the reported values: Teranga (advice from Teranga Gold Corporation), Lycopodium (experience or generally accepted practice), Testwork (metallurgical testwork conducted), and OMC (advice from Orway Mineral Consultants). The report states that the proposed plant design is based on a metallurgical flowsheet for optimum recovery with minimum operating costs, using unit operations well-proven in industry. The higher plant availability used for production scheduling was based on Teranga's operating experience with the Sabodala processing plant, which utilizes a similar flowsheet and processes similar ore types, rather than on the design criteria in Table 17-1.

The crushing plant mechanical availability of 85% (7,446 hours per year) was used only for equipment sizing determination, while the remainder of the plant assumes 91.3% (8,000 hours per year) supported by crushed ore storage and standby equipment. The design includes provision for future expansion beyond 4.0 Mtpa but no performance data, economics, or current operational status are provided.

Source: Wahgnion Gold Operations, Burkina Faso , Technical Report NI 43-101, 2023, Section 17 Recovery Methods.