This report summarises the process design basis for the proposed Doropo Gold Project processing plant, covering a robust metallurgical flowsheet for processing oxide, transition, and primary ore types.
Article Body
The Doropo Gold Project, located in West Africa, is a proposed open pit mining operation with gold as the primary commodity. The processing plant design is based on a metallurgical flowsheet aimed at achieving optimum recovery with minimum operating costs. The flowsheet utilises unit operations well proven in industry, with equipment selection criteria focusing on suitability for duty, projected mine life, reliability, and ease of maintenance. The plant layout is designed to provide ease of access for operating and maintenance requirements while maintaining a compact footprint to minimise construction costs.
The Doropo gold plant will process a range of material types from the nine pits included in the current life of mine plan, encompassing oxide, transition, and primary ore with variable material characteristics and head grades. All ore types contain significant quantities of gravity recoverable gold.
The key project and ore specific design criteria that the plant design must meet include a nominal capacity of 4,000,000 tonnes per year of primary ore, a crushing plant mechanical availability of 80% (7,008 hours per year), and a mechanical availability for the remainder of the plant of 91.3% (8,000 hours per year). The design also requires sufficient automated plant control to minimise the need for continuous operator interface while allowing manual override and control when required.
A process design criteria document (2234-FPDC-001) has been prepared incorporating the engineering and key metallurgical design criteria derived from the results of PFS metallurgical testwork and comminution circuit modelling. The comminution circuit design has been based on the 85th percentile results of the PFS comminution testwork for the primary material. Comminution data was provided to Orway Mineral Consultants (OMC) for circuit modelling and mill sizing.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Plant throughput (primary ore) | 4,000,000 | t/y | Design criterion |
| Crushing plant availability | 80 | % | Equivalent to 7,008 h/y |
| Milling/CIL plant availability | 91.3 | % | Equivalent to 8,000 h/y |
| Design gold head grade | Not stated | g/t | Refer Table 17.1.4 |
| Gravity gold recovery | Not stated | % | Refer Table 17.1.4 |
| Design overall gold recovery | Not stated | % | Refer Table 17.1.4 |
| Primary grind size P80 | 75 | µm | Target for fresh ore |
| Oxide/transition grind size P80 | 106 | µm | Predicted when processing these ore types |
| Design blend throughput | 5.4 | Mtpa | When processing exclusively oxide/transitional ore |
| Crushing plant utilisation | Not stated | % | Refer Table 17.1.4 |
| Mill type | SAG/ball | Not applicable | Variable speed drive, 60–80% critical speed |
| Primary crusher type | Jaw crusher | Not applicable | Coarse crushed product |
| Primary crusher open side setting | Not stated | mm | Not stated |
| CIL tank volume | 4,000 | m³ | All tanks identically sized |
| LP air pressure | 300 | kPa(g) | For CIL and cyanide destruction |
| Raw water source | Water harvest dam | Not applicable | Refer Section 18.3 |
Project website: https://www.rml.com.au/assets/doropo-cote-divoire/
Overview
The proposed processing plant for the Doropo Gold Project is designed to handle a range of ore types with variable material characteristics and head grades. The flowsheet incorporates primary crushing, milling, gravity gold recovery, and carbon-in-leach (CIL) processing. The design basis includes a nominal throughput of 4,000,000 tonnes per year of primary ore, with the capability to process significantly greater throughput when treating less competent oxide or transitional material.
The comminution circuit design has been based on the 85th percentile results of the PFS comminution testwork for the primary material. The circuit comprises a primary jaw crusher, a semi-autogenous grinding (SAG) mill, and a ball mill. The SAG mill will be equipped with a variable speed drive capable of operating between 60% and 80% of critical speed.
Key Process Stages
The treatment plant design incorporates several unit process operations. Primary crushing is achieved with a jaw crusher to produce a coarse crushed product. Stockpiling provides crushed ore storage capacity, maintaining sufficient surge capacity to ensure mill feed supply during crushing plant maintenance or periods of reduced availability. The stockpile will provide approximately 24 hours of nominal plant throughput when processing oxide or transitional material.
The milling circuit includes a SAG mill and ball mill configured in a comminution circuit. Screen oversize from the milling circuit will return to the ball mill feed hopper for further processing. The grinding circuit is designed to achieve a target P80 grind size of 75 µm for fresh ore, with an increased grind size of 106 µm predicted when processing oxide or transitional material at higher throughput rates.
Gravity gold recovery is incorporated into the flowsheet to recover free gold. The gravity circuit is followed by a carbon-in-leach (CIL) circuit for gold recovery from the remaining leachable material. The CIL circuit comprises a series of tanks, each with a volume of 4,000 m³, all identically sized to provide the required leaching residence time.
Cyanide destruction is included in the process to treat tailings. Low pressure air blowers will be installed to provide LP air at 300 kPa(g) for the CIL and cyanide destruction circuits. Additional secondary air receivers will be located throughout the plant, including at the grinding area for the mills auxiliary equipment.
The processing plant includes a raw water distribution system. Raw water will be distributed throughout the processing plant for process use from a raw water tank and will be used as feedstock for potable and filtered water treatment plants. The primary raw water supply to the processing plant will be from the water harvest dam.
Tailings management includes a tailings storage facility (TSF). The supernatant water from the TSF, referred to as decant return, will be pumped to the process water pond for re-use in the plant. Any plant spillage that may contain cyanide will report to plant bunding which will overflow to the event drainage channel for capture in the TSF.
Additional Interesting Data and Summary
The plant design incorporates measures to ensure operational resilience. The mechanical availability of 91.3% for the milling and CIL plants is supported by crushed ore storage and standby equipment in critical areas. The crushing plant availability of 80% is lower, showing the surge capacity provided by the crushed ore stockpile.
The plant control system consists of a process control system (PCS) that will control process interlocks and PID control loops for non-packaged equipment. Vendor supplied packages will use vendor standard control systems. The control system includes a supervisory control and data acquisition (SCADA) system with redundant servers. All remote I/O nodes will be linked to the PLC via a PCS Ethernet network, supported over site fibre optic cabling between switchrooms, remote I/O modules, and key infrastructure buildings. Regulatory control loops will be provided for all key process circuits to provide optimal control. Status indication of process interlocks and selected mode of operation will be displayed on operator interface terminals.
The plant layout drawings have been developed based on an appropriate level of engineering effort required for a PFS. Due consideration for the interaction of operating and maintenance activities is captured in the overall plant layout. The final location of the plant site may be optimised further when detailed geotechnical assessments are completed during the DFS phase. The layout of the plant roads and equipment takes into account the need for ease of access for operations and maintenance.
The comminution consumables by ore type have been summarised and are used in the estimation of the processing operating cost. These consumables include grinding media, crusher liners, and other wear components specific to the oxide and primary ore types.
The process design incorporates specific consideration for the variable material characteristics of the ore types. The less competent oxide or transitional material enables the comminution circuit to operate at a throughput equivalent to 5.4 Mtpa when processing exclusively those ore types. This higher throughput capability is a key design feature that allows the plant to maintain gold production during the early years of the mine life when treating predominantly oxide ore.
Key Processes
- Primary Crushing: Jaw crusher sized to achieve a coarse crushed product, with a design availability of 80% (7,008 h/y) and open side setting as specified
- Crushed Ore Stockpile: Provides surge capacity with approximately 24 hours of nominal plant throughput when processing oxide or transitional material
- Milling: SAG mill with variable speed drive (60–80% critical speed) and ball mill in a comminution circuit, designed using 85th percentile PFS comminution testwork results
- Gravity Gold Recovery: Incorporated to recover free gold from all ore types
- Carbon-in-Leach (CIL): Series of identically sized 4,000 m³ tanks for leaching, with low pressure air at 300 kPa(g) supplied by blowers
- Cyanide Destruction: Treatment circuit for tailings, also supplied with LP air at 300 kPa(g)
- Tailings Management: TSF with decant return water pumped to the process water pond for re-use
- Raw Water System: Raw water tank distributes process water, with feedstock for potable and filtered water treatment plants
- Plant Control System: PCS with PLC controls, redundant SCADA servers, and fibre optic Ethernet network between switchrooms and remote I/O modules
Source: Doropo Gold Project , 2023 Pre-feasibility Study, 2023.
Project website: Doropo Gold Project, 2023 Pre-feasibility Study
