The 2025 feasibility study describes a proposed 6 Mtpa to 7 Mtpa gold processing plant based on conventional crushing, grinding, gravity concentration, cyanide leaching and carbon‑in‑pulp recovery, supported by metallurgical testwork.
Report context
This NI 43-101 technical report, dated June 2025, presents the feasibility study for the Oko West Project. The proposed process plant design is based on standard metallurgical flowsheets to treat gold‑bearing ore via cyanidation to produce doré. The flowsheet is founded on metallurgical test work described in Section 13 of the report, industry standards and conventional unit operations.
Processing route
Comminution and grinding
Material from the open pit will be tipped directly into a primary gyratory crusher dump pocket, or placed on a run‑of‑mine pad for blending and emergency storage. A rock breaker will assist with oversize material. Crushed material discharges to a surge bin, then via an apron feeder and sacrificial conveyor (fitted with a belt magnet for trash metal) to a crushed material stockpile. The fresh rock stockpile has a live capacity of approximately 9 kt, equivalent to 12 hours of mill feed. Two reclaim apron feeders with variable speed drives control the reclaim rate to the grinding circuit; an additional apron feeder allows direct saprolite feed.
Reclaimed material feeds a 10.4 m diameter by 5.4 m effective grinding length SAG mill powered by 12,000‑kW dual pinion synchronous motors with variable speed drive. Process water maintains a 75% slurry discharge density. SAG mill discharge passes through a screen; undersize reports to the cyclone feed pump box. Screen oversize (scats and pebbles) is conveyed back to the SAG mill feed.
Slurry is pumped to a cyclone cluster of 18 hydrocyclones (11–14 operating, 4–7 standby) for classification. Cyclone overflow at a target P80 of 75 µm flows by gravity to trash screens ahead of leaching. The hydrocyclones are designed for a 350% circulating load. Cyclone underflow feeds a 7.3 m diameter by 11.5 m EGL ball mill with 12,000‑kW dual pinion fixed speed motors; ball mill discharge passes through a trommel screen, with undersize returning to the cyclone feed pump box.
Gravity gold recovery
A portion of the cyclone feed is directed to three centrifugal gravity concentrator units (KC‑QS48 or equivalent) located in a secured area. Feed slurry is screened at +2 mm; oversize returns to the cyclone feed pump box. Concentrator tailings also discharge to the cyclone feed pump box. Concentrate is periodically flushed and pumped to an intensive leach reactor (CS6000 or equivalent) for batch processing in 24‑hour intervals using sodium cyanide, caustic solution and a leach accelerant. Pregnant solution from the intensive leach reactor reports to the electrowinning circuit; residue is pumped back to the cyclone feed pump box.
Pre‑leach thickening and leaching
Cyclone overflow passes through two parallel trash screens then feeds a 46 m diameter pre‑leach thickener. Flocculant is added to promote solids settling. Thickener underflow at 42% w/w solids (high saprolite feed) or 45% w/w solids (fresh rock feed) is pumped to a leach circuit of seven 6,048 m³ tanks providing 36 hours total retention time. Oxygen is sparged into the leach tanks. Sodium cyanide is added for gold dissolution, and lime slurry maintains a pH of 10.5–11 to prevent hydrogen cyanide gas formation.
Carbon‑in‑pulp adsorption
Leached slurry flows by gravity to a CIP carousel circuit consisting of seven 7.5 m diameter by 12.2 m high tanks. Each tank has a pumping inter‑stage screen for retaining activated carbon. The carousel arrangement rotates feed and discharge points to simulate counter‑current carbon movement. Average carbon concentration is approximately 50 g/L. Once per day, loaded carbon is pumped to a loaded carbon screen, then transferred to acid wash. Tailings from the CIP circuit pass through a carbon safety screen; undersize reports to cyanide destruction.
Cyanide destruction
CIP tailings are treated in two 3,000 m³ mechanically agitated tanks using the conventional SO₂/O₂ process, providing two hours total retention time. Oxygen is sparged; lime slurry maintains pH of 8.5; copper sulphate is added as a catalyst; sodium metabisulphite provides the SO₂ source. The circuit is designed to reduce weak acid dissociable cyanide to less than 5 mg/L. Treated slurry flows by gravity to a tailings pump box for delivery to the tailings storage facility.
Carbon elution and regeneration
Loaded carbon is acid washed with hydrochloric acid to remove inorganic foulants, then stripped in two 10‑t split pressure Zadra elution columns. The elution cycle uses barren solution containing approximately 2.0% hydroxide and 0.2% sodium cyanide at 150 °C and 500 kPa. Heat recovery heat exchangers preheat incoming solution. Stripped carbon is dewatered and sized; oversize feeds an 800 kg/h diesel‑fired regeneration kiln (treating 10 t carbon per day). Regenerated carbon is quenched and stored prior to return to the CIP circuit. Fresh carbon is added to compensate for attrition losses.
Electrowinning and smelting
Pregnant solution from the elution columns is pumped to two electrowinning cells operating on a single‑pass basis to produce gold sludge. Pregnant solution from the intensive leach reactor is treated in a dedicated electrowinning cell with recirculation until all gold is deposited. Cathodes are manually washed; sludge is filtered, dried and batch smelted with flux in an electric furnace to produce doré bars.
Tailings storage and water recovery
Tailings from cyanide destruction are pumped to the tailings storage facility, where further natural cyanide degradation and dilution from rainwater occur. Reclaim water is pumped back to the process water tank via vertical pumps on a barge.
Key reported parameters
| Area | Criteria | Unit | Nominal Value | Basis |
|---|---|---|---|---|
| General | Annual throughput (blend with soft ores) | t/y | 7,000,000 | Design |
| General | Daily throughput (blend with soft ores) | t/d | 19,200 | Design |
| General | Annual throughput (fresh rock) | t/y | 6,000,000 | Design |
| General | Daily throughput (fresh rock) | t/d | 16,500 | Design |
| General | Crusher plant availability | % | 70 | Design |
| General | Process plant availability | % | 92 | Design |
| General | Design gold head grade | g/t | 1.58 | Design |
| General | Average fresh rock gold recovery – open pit | % | 94.0 | Design |
| General | Average fresh rock gold recovery – underground | % | 92.7 | Design |
| General | Average transition material gold recovery | % | 93.3 | Design |
| General | Average saprolite gold recovery | % | 95.0 | Design |
| Crushing & Storage | Crusher work index | kWh/t | 15.0–22.2 | Design |
| Crushing & Storage | ROM maximum size | mm | 910 | Design |
| Crushing & Storage | Crusher circuit product size (P80) | mm | 115 | Design |
| Grinding | SMC A×b (15th percentile) – fresh rock | – | 29.4 | Testwork |
| Grinding | Bond ball mill work index (85th percentile) – fresh rock | kWh/t | 16.4 | Testwork |
| Grinding | Bond rod mill work index (85th percentile) – fresh rock | kWh/t | 17.9 | Testwork |
| Grinding | Grinding circuit product size (P80) | μm | 75 | Design |
| Gravity | Gravity concentrators | – | 3 × KC‑QS48 or equivalent | Design |
| Gravity | Intensive leach reactor | – | CS6000 or equivalent | Design |
| Pre‑leach thickening | Thickener underflow density (high saprolite) | %w/w | 42 | Design |
| Pre‑leach thickening | Thickener underflow density (fresh rock) | %w/w | 45 | Design |
| Pre‑leach thickening | Solids loading | t/m²h | 0.6 | Design |
| Leach‑CIP | Leach residence time | h | 36 | Design |
| Leach‑CIP | Leach tanks | – | 7 | Design |
| Leach‑CIP | CIP carousel tanks | – | 7 | Design |
| Elution | Elution batch size (carbon) | t | 10 | Design |
| Cyanide destruction | Technology | – | SO₂/O₂ | Design |
| Cyanide destruction | Number of tanks | – | 2 | Design |
| Cyanide destruction | Total retention time | h | 2 | Design |
Project website: https://gmin.gold/oko-gold-project/
Technical qualifications
The processing section of this report is a proposed design based on metallurgical test work described in Section 13 of the source report, industry standards and conventional unit operations. No historical operating data from this project are presented. The report does not provide actual plant performance data, detailed economic analysis, ownership information, project status updates, or links to external sources. All flowsheet details, recoveries, consumptions and personnel numbers represent design criteria or estimates for the feasibility study only.
*Source: “Feasibility Study NI 43‑101 Technical Report, Oko West Project”, June 2025, Sections 1.17 and 17.*
