The Edikan gold plant, commissioned in 2011 and designed for 5.6 Mt/y nominal capacity, processes sulphide-associated gold ores through a flowsheet of crushing, grinding, gravity concentration, flotation, concentrate regrind, and carbon-in-leach (CIL) recovery.
Report context
This technical report addresses the Edikan gold plant processing facilities operated by Perseus Mining Limited. The plant has been in operation since commissioning in 2011, with annual production rates varying between 4.8 and 7.2 Mt/y since commencement of operations. A minor plant upgrade completed in late 2016 improved plant reliability and allowed a significant increase in mill run time. With the exception of Esuajah South ores, the majority of ores to be treated are from cutbacks in the existing AG and Fetish pits. Gold in all remaining pits is associated with sulphide minerals (pyrite and arsenopyrite) recoverable by flotation at coarse grind sizes (80% passing 212 µm), with concentrate ground finer (approximately 90% passing 45 µm) prior to cyanidation. There are no plans to upgrade the processing plant’s capacity.
Processing route
Crushing, stockpile and reclaim
Run of mine ore is delivered by 100 tonne class rear dump haul trucks or front end loader. Ore is crushed by an FLSmidth 1400 x 1600 TS gyratory crusher operating with a closed side setting of approximately 120 mm, fitted with a rockbreaker for oversize and rock bridging. Crushed product is drawn from the crushing chamber by a low profile feeder and conveyed to the crushed ore stockpile (COS). Mine life to date crusher run time is approximately 52%, sufficient to keep the mill operating at its 90% run time. The COS live capacity is 4-5 hours, supplemented by a further 4-5 days of ore side cast and reclaimed by mobile equipment. Ore is reclaimed from COS by four vibrating pan feeders onto the SAG mill feed conveyor. Oxide ore is fed via a separate ROM bin with static grizzly and apron feeder onto the oxide feed conveyor, a retrofit necessitated by rat-holing and bridging within the COS and packing of vibrating feeders when treating oxide material.
Grinding and gravity
The grinding circuit comprises a 14 MW (twin 7 MW pinion drive) single stage SAG mill, 34 ft diameter x 22 ft (flange to flange), operating in closed circuit with primary cyclones. New feed from COS and oxide circuit is conveyed into the SAG mill. The mill typically operates with a ball charge of 12-14% and total volume of approximately 30%, with power draw varying between 12 MW and 13.5 MW depending on lifter condition. Slurry passes over a vibrating screen to remove scats and pebbles, which are conveyed to a Sandvik CH660:02 pebble crusher (315 kW motor) for size reduction and returned to mill feed. Screen undersize is pumped to the primary hydrocyclone cluster (11 g-MAX 26-20 cyclones available, 6-7 operating at 60-70 kPa). Cyclone overflow (approximately 80% passing 212 µm) gravitates to flotation. Cyclone underflow returns to the SAG mill, with a substream split to feed twin Knelson KCXD48MS batch centrifugal gravity concentrators operating in parallel. Coarse particles (+3 mm) are removed on a 4.88 m long x 2.44 m wide horizontal vibrating screen prior to each Knelson, with scalping screen oversize directed to mill feed. Knelson concentrate is stored in the CS3000 Acacia reactor; Knelson tails return to mill feed. The Acacia reactor is placed on a leach cycle once per day, with gold-bearing solution pumped to electrowinning. Gravity circuit gold recovery is typically about 25% of new feed.
Flotation and thickening
Cyclone overflow gravitates to flotation, consisting of a small conditioning tank and seven 70 m³ Wemco smart cells in series. Reagents include activator (copper sulphate), collector (sodium isobutyl xanthate), and frother; naphthalene sulphonate is added only when carbonaceous material is noted in mill feed. Flotation is conducted at natural pH. Concentrate from each cell is collected and thickened in an 8 m diameter high-rate thickener (approximately 60% solids) and pumped to the regrind mill. Flotation tails are pumped to the flotation tailings storage facility. Automatic cross stream samplers are fitted at feed and tail ends for metallurgical accounting.
Concentrate regrind
Thickened flotation concentrate is pumped to the regrind circuit, consisting of a 600 kW ball mill (3 m diameter x 5 m flange to flange) operating in closed circuit with a cluster of 6 gMAX6 cyclones. Cyclone underflow returns to the mill; cyclone overflow (90% passing 45 µm) gravitates to the CIL circuit. The regrind mill typically draws 300 kW of power. Cross stream samplers are located on thickener underflow and regrind cyclone overflow.
Carbon-in-leach (CIL)
The CIL circuit comprises seven 166 m³ tanks operating in series, interconnected by launders with slurry flowing by gravity. Each tank is fitted with a MPSP 100 Kemix interstage carbon screen preventing activated carbon from flowing downstream. Lime is added to raise pH to approximately 11 to prevent HCN gas generation. Cyanide is added to dissolve gold; oxygen is provided by a PSA plant and supplemented by hydrogen peroxide. Activated carbon is added at the back of the circuit and moved forward by recessed impellor carbon transfer pumps counter-current to slurry flow. Loaded carbon is recovered in 4 tonne batches from the first CIL tank, washed with dilute hydrochloric acid to remove inorganic foulants, then subjected to a split AARL elution process. Pregnant solution is sent to electrowinning. Barren carbon is sent to the regeneration kiln for thermal reactivation before return to CIL. A trash screen is located prior to the first CIL tank. Tails from the last CIL tank flow over a carbon safety screen before being pumped to the calcine tailings storage facility. A cross stream sampler is located on CIL tails.
Goldroom
Electrowinning cells are located in the gold room. Gold concentrate collects on cathodes as pregnant solution from the gravity circuit and CIL elution passes through the cells. Gold concentrate is periodically removed, filtered, dried, and smelted to produce gold doré for shipment.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Nominal plant capacity | 5.6 Mt/y | Design |
| Annual production range | 4.8–7.2 Mt/y | Historical operating data |
| Primary crusher | FLSmidth 1400 x 2100 TS, 600 kW motor | Design |
| SAG mill | 34 ft dia. x 22 ft, 14 MW (twin 7 MW) | Design |
| Pebble crusher | Sandvik CH660:02, 315 kW motor | Design |
| SAG mill ball charge | 12–14% | Historical operating data |
| SAG mill total volume | ~30% | Historical operating data |
| SAG mill power draw | 12–13.5 MW | Historical operating data |
| Primary cyclone overflow grind | ~80% passing 212 µm | Design/testwork |
| Gravity concentrators | Knelson KCXD48MS (2 units) | Design |
| Intensive leach reactor | Consep CS3000 Acacia | Design |
| Gravity gold recovery | ~25% of new feed | Historical operating data |
| Flotation cells | 7 x 70 m³ Wemco smart cells | Design |
| Flotation pH | Natural | Design |
| Concentrate thickener | 8 m dia., high rate | Design |
| Regrind mill | 3 m dia. x 5 m, 600 kW | Design |
| Regrind mill power draw | ~300 kW | Historical operating data |
| Regrind cyclone overflow grind | ~90% passing 45 µm | Design/testwork |
| CIL tanks | 7 x 166 m³ | Design |
| CIL interstage screens | Kemix MPSP 100 (7 units) | Design |
| CIL pH | ~11 | Design |
| Esuajah South predicted recovery | 90% | Testwork (4–5% discount from laboratory testwork applied following review of actual vs predicted recoveries) |
Project website: https://perseusmining.com/edikan-mine/
Technical qualifications
The predicted plant recovery of 90% for Esuajah South ore represents a discount of 4–5% from laboratory testwork, applied following review of actual and predicted recoveries of several Eastern pits ores recently processed. The 2009 Edikan Definitive Feasibility Study flowsheet was based on gravity, flotation, concentrate regrind, and cyanidation, with metallurgical testwork using samples from all planned ore sources; Esuajah South ores were included in composite sample testwork but the only specific tests were limited to comminution work, with later testwork programs on Esuajah South specific samples. Testwork was undertaken on three bulk composites representing Primary West, Primary East, and Oxide/Transitional ore zones. Sufficient testwork determined that Esuajah South ore is compatible with the existing processing circuit, with ore blended with open pit ore for the life of the underground operation, making up only a small percentage of total feed. The mass pull to concentrate is marginally higher than currently experienced from open pit ore types but is not likely to be an issue given that ores will be a small fraction of total mill feed and there is currently excess capacity in existing regrind and CIL circuits. Electrical power comes from three sources: national grid, standby diesel power station, and a new contract gas fired power station, with the site transitioning from grid supply (with diesel backup) to a site-based contractor provided gas power station. Water is sourced from site surface collection points, pit water, and bore water; disused pits at Esuajah North and Fobinso contain water accessible in dry periods if required.
*Source: PERSEUS MINING LIMITED TECHNICAL REPORT, Section 17 Recovery Methods*
