Technical Report for the Yaramoko Gold Mine, Burkina Faso — 2023

This report summarises the design, configuration, and seven years of operational performance of the Yaramoko Gold Mine processing plant in Burkina Faso.

Report context

This technical report section, dated 2023, describes the recovery methods for the Yaramoko Gold Mine processing plant after seven years of production. The plant operated to its original design capacity until December 2018, when the completion of the Stage 2 Plant upgrade in January 2019 enabled an increase to the current throughput. The plant site is located at 315 metres above sea level, adjacent to the 55 Zone underground portal.

Processing route

Crushing circuit

The crushing circuit is fed with a front-end loader via the run-of-mine bin. The circuit is based on two-stage crushing (primary jaw and secondary cone) at 1,100 tonnes per day, with secondary crushing operated in open circuit at a design feed rate of 100 tonnes per hour and availability of 70 percent on a 24-hour-per-day operation. The crusher circuit produces a final product particle size of P80 of 20 millimetres. Feed control into the crushing circuit is via a variable speed feeder to a jaw crusher, with choke-fed secondary crushing operations maintained by a surge bin and variable speed feeder prior to the secondary crusher. The crushing circuit includes a belt magnet for tramp steel removal, a metal detector prior to secondary crushing, and a weightometer. Crushed product is received by an open stockpile with a live capacity of 810 tonnes.

Reclaim, grinding, and classification circuit

An apron feeder inside the stockpile tunnel reclaims crushed ore from under the stockpile and discharges onto the mill feed conveyor, which feeds the ball mill (4.2-metre diameter by 4.8-metre effective grinding length) at the designed feed rate of 50.2 tonnes per hour. An emergency vibrating feeder can be used when the main reclaim apron feeder is under maintenance. The mill feed conveyor is fitted with a weightometer and quicklime is dosed onto the conveyor to control process pH. Total mill feed consists of crushed ore (fresh feed), cyclone underflow (recirculating load), scats recycle, and dilution water. Grinding media addition is a manual process onto the mill feed conveyor.

The SAG mill operates with a ball charge of between 20 to 27 percent volume/volume and a maximum total load of 35 percent, with a pinion power draw of 996 kW. A variable speed drive is installed on the mill. The ball mill discharge product passes through a trommel screen, with oversize (scats) reporting to a bunker for recycling back into the mill feed via the emergency feeder. Trommel screen undersize discharges into a mill discharge hopper before being pumped to the classification cyclone cluster, with six cyclones installed (four duty, two standby). The cyclone overflow product size distribution is P80 passing 90 micrometres and reports to a trash removal vibrating screen before being fed to the leaching circuit.

Gravity recovery circuit

The gravity circuit operates on cyclone underflow, consisting of two centrifugal concentrators and two intensive leach reactors for treatment of gravity concentrate, treating 68 percent of the cyclone underflow. The coarse material (cyclone underflow) feeds two gravity scalping screens; material less than 2 millimetres from the gravity scalping screens passes through the two semi-continuous centrifugal gravity concentrators. Tails from the gravity concentrators and gravity screen overflow recombine to feed back into the mill. Each gravity screen treats 38 percent of the recycling load, while the remaining slurry is directed to the cyclone underflow boil box and returns to the SAG mill feed spout.

Gold concentrates recovered from the gravity concentrators are sent to two intensive leach reactors within the gold room, where the process batch leaches the gold into pregnant liquors. These pregnant liquors are pumped to storage tanks for electrowinning in dedicated electrowinning cells. Barren solution from the electrowinning cells is sent to the carbon-in-leach (CIL) circuit.

Leaching and adsorption circuit

The CIL circuit consists of one leach tank and seven adsorption tanks in series, which can be converted to eight adsorption tanks if required. Total leach residence time is 26.5 hours. Each tank is fitted with an agitator, pumping interstage screen (except Tank 1), and carbon transfer pump (except Tank 1), with oxygen or air sparging through the agitator shaft. The first three tanks utilise oxygen to increase leach kinetics while the remainder use air. pH correction is done by adding quicklime to the mill feed conveyor, with a caustic dosing point provided in Tank 1. Cyanide addition is to CIL tank 1 to a set point of 200 ppm free cyanide in solution.

Carbon is held in all tanks except the first tank and is batch transferred counter-current to the slurry flow. Carbon is transferred from CIL tank 2 (or 3) to the loaded carbon recovery screen for elution purposes. Tails from CIL tank 8 report to the carbon safety screen. The undersized product reports to an 8-metre diameter high-rate thickener from which the underflow is pumped in three stages (one pump train duty, one standby) to the tailings storage facility. Thickener overflow reports to a second 8-metre diameter high-rate thickener which acts as a water clarifier, with overflow gravity-fed to the process water tank.

Elution circuit and gold room

CIL carbon is batch treated in a 1.5-tonne split Anglo-American Research Laboratory (AARL) elution circuit. Loaded carbon is collected in the acid wash hopper where dilute hydrochloric acid solution is pumped to remove chemically bound impurities. Acid-washed carbon is loaded into the elution column, which is pre-heated via primary and secondary heat exchangers, with the primary heat exchanger heated by a diesel oil heater. Caustic soda and cyanide solutions are dosed into fresh water and introduced at 130 degrees Celsius. Eluted carbon is educted using raw water and reports either to CIL tank 8 or the carbon regeneration kiln. Carbon is reactivated by a diesel-fired regeneration kiln and discharges into a quench box reporting to Tank 8.

Elution pregnant solution is received in pregnant solution tanks. Caustic solution is dosed to give required conductivity levels for electrowinning. Pregnant solution is circulated through the electrowinning circuit with barren solution transferred back to the CIL. Cathodes are removed by hand and washed with high-pressure water to recover sludge, which is dewatered and dried in an oven. Fluxes are added to dried sludge prior to smelting in a furnace. Gold and slag are decanted into pouring moulds where gold doré is recovered. The gold sludge from the gravity circuit is refined separately from that of the elution circuit to allow for separate metallurgical accounting.

Reagents and consumables

Quicklime is delivered in 1,200 kg bags and dosed onto the mill feed conveyor. Sodium cyanide briquettes are delivered in 1-tonne bags and mixed with raw water to create a 30.5 percent w/w solution. Cyanide is supplied to all main plant dosage points via a ring main supply system. Caustic soda pearls are mixed with raw water to produce 25 percent w/w solution, with batch make-up every three days. Hydrochloric acid is delivered in 1,000-litre intermediate bulk containers and combined with water to create a 3 percent w/w solution for carbon acid wash cycles. Activated carbon is delivered in 500 kg bulk bags and added directly to CIL tank 8. Oxygen gas is manufactured on site using a pressure swing adsorption plant. Flocculant is prepared using an automated dry powder mixing plant.

Key reported parameters

Technical qualifications

The qualified person considers process requirements to be well understood, with seven years of operating history to support future assumptions. There is no indication that the characteristics of the material being mined will change, and therefore the processing and recovery assumptions applied for future mining are considered as reasonable for the life-of-mine plan. The plant is of conventional design and uses conventional consumables. The comminution circuit design was reviewed by Orway Minerals Consultants (WA) Pty Ltd in Perth, Australia, which confirmed the necessity of a secondary crushing circuit and recommended a ball charge of 20 to 27 percent volume/volume. The flowsheet design was completed by DRA (Pty) Ltd.

Source: Technical Report for the Yaramoko Gold Mine, Burkina Faso , 2023, section 17 Recovery Methods.