This technical report describes the proposed processing facilities for gold-silver doré production from the Da Tambuk mineralization using whole mill feed cyanide leach technology.
Report context
The East Africa Metals Inc. Technical Report and Preliminary Economic Assessment for the Da Tambuk Project, Adyabo Property, Tigray National Regional State, Ethiopia, dated 704-ENG.VMIN03019-01, presents recovery methods based on metallurgical test work performed at BCR (Vancouver Island, Canada) and project-related parameters provided by Tetra Tech and EAM.
Processing route
Proposed process flowsheet
The Da Tambuk processing facilities are designed to process at a nominal rate of approximately 200,000 t/a, or 550 t/d, of gold-silver bearing material from an underground mining operation to produce gold-silver doré product. The proposed flowsheet includes: conventional crushing and ball mill grinding with a cyclone for particle size classification; a centrifugal gravity concentrator in the grinding circuit to recover coarse and liberated gold particles, with a shaking table to upgrade the gravity concentrate before smelting; a six-stage carbon-in-leach (CIL) circuit for gold and silver extraction using sodium cyanide solution, with adsorption onto activated carbon; carbon acid washing, elution, electrowinning and smelting; carbon reactivation in a thermal kiln with attrition; cyanide detoxification of CIL tailings using a sulphur dioxide/air procedure; and tailings thickening for process water recovery.
Process water will be recycled from the tailings thickener overflow, supplemented with water recovered from the tailings containment facility. Fresh water will be used for reagent preparation, the gold-silver loaded carbon elution circuit, and water make-up as required.
Crushing circuit (proposed design)
The crushing circuit will reduce mined material from a nominal top size of 400 mm to a product size P₈₀ of 9.0 mm. The circuit will include: stationary grizzly, ROM dump bin, jaw crusher vibrating feeder, jaw crusher (75 kW), conveyor belts, belt magnet and metal detector, sizing screen, cone crusher (150 kW), belt scale, and crushed material surge bin. The jaw crusher will reduce feed to less than 100 mm. The sizing screen will operate with the cone crusher in closed circuit. Screen undersize will be conveyed to a mill feed stockpile, then to a ball feed surge bin with live capacity of 200 t.
Grinding circuit (proposed design)
The grinding circuit will reduce material to a final product size P₈₀ of 80 µm. Equipment includes: ball mill feed conveyor belt with weigh scale, ball mill (3.2 m diameter by 3.7 m long), mill discharge pumpbox, cyclone feed slurry pumps, classification cyclone cluster, and vibrating trash screen. New feed rate will be 25.5 dry t/h. Slurry density in the ball mill will be maintained at approximately 72% solids. Circulating load will be between 250 and 300%. A 30% split of cyclone underflow will be directed to the gravity concentration circuit. Cyclone overflow will proceed to the cyanidation circuit. Lime will be added to the ball mill for pH adjustment.
Gravity concentration and concentrate tabling (proposed design)
A nominal 30% portion of cyclone underflow will be directed to the gravity circuit. Feed will be screened to remove oversize and trash greater than 2 mm. The primary centrifugal gravity concentrator will operate continuously with flushes twice per hour. Concentrate will be collected in a holding tank over a full day. Gravity tailings will return to the grinding circuit. Concentrate will be upgraded on a shaking table as a daily batch process to a level suitable for direct smelting. Table tailings will return to the centrifugal concentrator head.
CIL circuit and gold recovery circuit (proposed design)
Cyclone overflow will be thickened in a high rate thickener to approximately 47% w/w solids. Thickener overflow will be reused as process water. Thickened slurry will feed into Tank No. 1 of six CIL tanks (each 7.0 m diameter by 7.7 m high) and flow sequentially to Tank No. 6. Carbon will be transferred counter-current from Tank No. 6 to Tank No. 1. Loaded carbon will be removed from Tank No. 1 for elution. Slurry pH will be controlled with lime slurry. Sodium cyanide solution will be added as required. Each tank will have mechanical agitation and air injection nozzles to maintain dissolved oxygen at less than 5 mg/L. Slurry residence time will be approximately 30 hours. Equipment includes carbon transfer air-lifts, interstage wedge wire screens, loaded carbon screen, and carbon safety screen. Carbon concentration will be maintained in each tank.
Cyanide detoxification and tailings thickening (proposed design)
CIL tailings will be treated to destroy weak acid dissociable (WAD) cyanide by a sulphur dioxide/air procedure. After treatment, WAD cyanide concentration is expected to meet regulatory requirements. Detoxified tailings will be pumped to a thickener for process water recovery.
Key reported parameters
| Criteria | Unit | Value | Basis |
|---|---|---|---|
| Nominal processing rate | t/a | 200,000 | Design |
| Nominal processing rate | t/d | 550 | Design |
| Operating days per year | d | 365 | Design |
| Crushing circuit utilization (one shift per day) | % | 75 | Design |
| Grinding, CIL and carbon circuits utilization | % | 90 | Design |
| Crushing circuit throughput rate | t/h | 73 | Design |
| Grinding and leaching process rate | t/h | 25.5 | Design |
| Ball mill feed size, 80% passing | µm | 9,000 | Design |
| Ball mill product size, 80% passing | µm | 80 | Design |
| Ball mill circulating load | % | 250–300 | Design |
| Bond ball mill work index, design | kWh/t | 16.0 | Testwork/inferred |
| Bond ball mill work index, average | kWh/t | 12.0 | Testwork |
| Mill feed material specific gravity | 2.83 | Testwork | |
| Mill feed moisture content | % | 2.0 | Testwork |
| Leach circuit retention time | h | 30 | Design |
| Head grade, design | Au g/t | 9.0 | Design |
| Head grade, average | Au g/t | 4.7 | Testwork/inferred |
| Anticipated recovery, design | Au % | 95.1 | Design |
| Anticipated recovery, average | Au % | 93 | Testwork/inferred |
Project website: https://eastafricametals.com/east-africa-metals-tsxv-eam-gold-exploration-mine-development-africa/
Design parameters are based on test work results from BCR and typical industry parameters for this type of process.
Technical qualifications
This report presents proposed design criteria and flowsheet descriptions based on metallurgical test work performed at BCR (Vancouver Island, Canada) and project-related parameters provided by Tetra Tech and EAM. No historical operating data are presented. No actual operating performance data, final process design, or detailed engineering specifications are provided. Recovery and performance values are described as anticipated or design values only. The document is a Technical Report and Preliminary Economic Assessment and does not represent a definitive feasibility study.
*Source: East Africa Metals Inc. Technical Report and Preliminary Economic Assessment for the Da Tambuk Project, Adyabo Property, Tigray National Regional State, Ethiopia, document number 704-ENG.VMIN03019-01, sections 17.0–17.2.4.*
