Overview
Nestled in the mineral-rich Kédougou Region of southeastern Senegal, the Diamba Sud Gold Project represents a significant and strategic development for mid-tier producer Fortuna Mining Corp. With an effective date of October 2025, this advanced-stage project is poised to become a cornerstone asset, leveraging a robust and well-understood mineral processing strategy to unlock economic value from a substantial gold resource. The project is designed to process both oxide and fresh (sulphide) material sourced from open-pit mining operations, targeting an average annual throughput of 2.0 to 2.5 million tonnes. This operational flexibility is key to managing the Life of Mine (LOM) feed schedule, which transitions from predominantly oxide material in the early years to a fully fresh ore feed later in the project’s life. The mineralization at Diamba Sud is characterized as free-milling with a very low proportion of gold locked in sulphides, making it highly amenable to conventional cyanidation treatment—a factor that simplifies the flowsheet and enhances project economics. Fortuna’s commitment to advancing Diamba Sud underscores its growth strategy in West Africa, a region renowned for its world-class gold deposits. The project’s technical design, detailed in a comprehensive report prepared by Fortuna’s senior technical team and external consultants, reflects a focus on simplicity, robustness, and operational efficiency, aiming to deliver strong gold recovery and sustainable production for years to come.
Key Process Stages
The Diamba Sud processing plant is engineered as a continuous, high-capacity operation following a classic gold recovery flowsheet. The design philosophy emphasizes reliability and ease of operation, incorporating modern control systems and equipment selections based on extensive metallurgical testwork. The circuit is designed to handle variable ore blends while maintaining target grind sizes and leach efficiencies. Below is a detailed breakdown of the primary process stages from run-of-mine (ROM) ore to gold doré bar production.
- Stage 1: Primary Crushing & Stockpiling: ROM ore with a maximum size of 900 mm is delivered to an adjacent pad. A front-end loader feeds a 162-tonne ROM bin, which discharges via an apron feeder to a primary single-toggle jaw crusher (C150 equivalent). The crusher reduces the ore to a suitable size for grinding. The crushed product is conveyed to a large, conical crushed ore stockpile with a total capacity of 19,000 tonnes, providing a crucial buffer (up to 76 hours of fresh feed) between mining and processing operations. Lime for pH control is added directly to the mill feed conveyor from a dedicated 100-tonne silo.
- Stage 2: Grinding & Classification (Single-Stage SAG Mill): Based on comminution testwork and modelling by Orway Mineral Consultants, a single-stage Semi-Autogenous Grinding (SAG) mill circuit was selected. An 8.53m diameter by 5.77m EGL SAG mill, powered by a 7.1 MW drive, receives feed from the stockpile. It operates with a 10-15% ball charge and a variable speed drive to adapt to changing ore characteristics. Mill discharge is screened, with undersize slurry pumped to a cluster of classifying cyclones. The cyclones produce a target overflow grind size of P80 106 µm for fresh ore (finer for oxides) for leaching, while the coarse underflow recirculates to the SAG mill at a designed circulating load of 333%.
- Stage 3: Gravity Recovery & Pre-Leach Thickening: To capture coarse, free gold early in the process, a gravity circuit treats a portion of the cyclone underflow. The slurry passes over scalping screens before feeding two 30-inch batch centrifugal concentrators. These units produce a high-grade concentrate, which is directly treated in an Intensive Leach Reactor (ILR) located in the gold room. Meanwhile, the cyclone overflow (the fine grind product) is sent through trash screens and into a leach feed thickener. This thickener increases slurry density to ~45% solids, optimizing conditions for the subsequent Carbon-in-Leach (CIL) circuit and reclaiming process water for reuse.
- Stage 4: Leaching & Adsorption (CIL Circuit): This is the heart of the gold dissolution and recovery process. Thickened slurry enters a train of seven large CIL tanks (each 12m diameter x 14m high), providing a total residence time of 24 hours. Cyanide and oxygen are added to the first tanks to dissolve the gold. Activated carbon, continuously moved counter-current to the slurry flow in the last six tanks, adsorbs the dissolved gold. Loaded carbon is removed from the second tank via a recessed impeller pump and screened out of the circuit. The now barren slurry (tailings) is pumped to the Tailings Storage Facility (TSF).
- Stage 5: Elution, Electrowinning & Smelting (Gold Room): Loaded carbon undergoes an acid wash to remove contaminants before being fed to a pressurized Zadra-style elution column. Here, a hot (130°C) caustic cyanide solution strips the gold from the carbon. The resulting pregnant solution is passed through electrowinning cells, where gold plates onto steel wool cathodes. The sludge from these cathodes, along with gravity concentrate from the ILR, is calcined and then smelted in an LPG-fired furnace with fluxes to produce the final product: gold doré bars. The stripped carbon is thermally regenerated in a kiln and returned to the CIL circuit.
Critical Data
The operational and design parameters for the Diamba Sud process plant are rooted in detailed testwork and engineering studies. The table below summarizes the key technical data that defines the circuit’s capacity, performance, and resource requirements.
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Design Throughput (Fresh Ore) | 250 | t/h | Nominal instantaneous feed rate (2.0 Mt/a) |
| Design Throughput (Oxide Blend) | 313 | t/h | For feed with ≥20% oxide (2.5 Mt/a) |
| SAG Mill Installed Power | 7.1 | MW | Variable speed drive, duty draw ~5.7 MW |
| Target Fresh Ore Grind Size (P80) | 106 | µm | Cyclone overflow product size |
| Target Oxide Ore Grind Size | ~75 | µm | Naturally finer, requires less grinding energy |
| CIL Leach Residence Time | 24 | hours | In 7 tanks at 45% solids density |
| Primary Crusher Capacity | 400 | t/h | At 70% availability on 24/7 schedule |
| Crushed Ore Stockpile Capacity | 19,000 | tonnes | Total capacity, ~3,000 t live capacity |
| Bond Work Index (BWi) – Fresh | 17.2 | kWh/t | Indicates medium hardness |
Additional Interesting Data and Summary
Beyond the core process stages, the Diamba Sud project design incorporates several noteworthy technical, environmental, and logistical elements that underscore its comprehensive planning. The plant will be powered by a dedicated on-site Heavy Fuel Oil (HFO) power plant, with electrical reticulation at 11kV and 415V across the site. A sophisticated Supervisory Control and Data Acquisition (SCADA) system, utilizing GE Fanuc RX3i PLCs and Citect SCADA software, will enable centralized monitoring and control from multiple locations, including the main CIL control room and crusher station, ensuring high levels of automation and operational efficiency.
Water management is a critical pillar of the project’s sustainability framework. The majority of process make-up water (70-85%) will be sourced from recycled supernatant water from the Tailings Storage Facility (TSF). Additional supply will come from a dedicated water storage dam filled by water harvesting, pit dewatering, and, as a contingency, abstraction from the Falémé River located 7 km east. Current modeling suggests river abstraction may not be necessary, highlighting a design focused on minimizing external water draw. The tailings and return water pipelines will be installed in a fully bunded and lined trench to mitigate environmental risk from potential leaks.
The reagent handling systems are designed for safety and efficiency. Cyanide is received in 1-tonne bulk bags, mixed into a 30% solution in a contained, bunded area, and dosed via a ring main. Lime, cyanide, caustic soda, hydrochloric acid, and flocculant storage are all sized to hold multiple days of supply, allowing for logistical flexibility, especially during Senegal’s wet season. The project anticipates significant reagent consumption differences between ore types, with lime use forecast at 10.5 kt/year for oxides versus only 0.7 kt/year for fresh ore.
Economically, the project is designed to transition smoothly through its mine life. The first year will process 1.78 million tonnes of oxide ore, leveraging its natural fineness and higher recovery potential. Years 2-4 will see a blended feed, gradually shifting to 100% fresh ore by Year 8. This phased approach allows the comminution circuit to be optimized for changing ore characteristics. With its robust, conventional flowsheet, strong water recycling ethos, and detailed execution planning, the Diamba Sud Gold Project is positioned as a technically sound and strategically important future producer for Fortuna Mining in West Africa’s burgeoning gold sector.
Source: Project: Diamba Sud Gold Project | Date: October 2025
