This technical report presents the proposed processing route for a nominal 500,000 t/a gold-copper operation based on metallurgical testwork and industry-standard design parameters.
Report context
This technical report and preliminary economic assessment concerns the Mato Bula Deposit, located within the Adyabo Property, Tigray National Regional State, Ethiopia. The processing facilities described are designed to process a nominal 500,000 t/a, or 1,400 t/d, of gold-copper-bearing material from an open pit mining operation. The report is dated as part of the technical documentation for East Africa Metals Inc.
Processing route
Crushing circuit
The crushing circuit is designed to reduce mined material from a nominal top size of 500 mm to a product size of 80% passing (P80) 10 mm. Run-of-mine (ROM) material is delivered by haulage trucks to a stationary grizzly, then passes through a vibrating feeder to a 93 kW jaw crusher. The jaw crusher reduces feed size to approximately 60 mm P80. Crushed material reports to a sizing screen; screen oversize feeds a 224 kW cone crusher in closed circuit. Screen undersize (approximately 13 mm passing) is conveyed to a 1,500 t capacity crushed mill feed surge bin.
The crushing circuit is designed to operate 16 h/d in two 8-hour shifts with a projected utilization of 75%. Design throughput is 116.7 t/h.
Grinding circuit
Single-stage ball mill grinding in closed circuit with classifying cyclones is proposed. A 4.2 m diameter by 5.3 m long ball mill receives new feed at approximately 64.8 dmt/h from the crushed mill feed bin. Process water maintains slurry density at approximately 72% solids. The ball mill operates at approximately 75% of critical speed.
The grinding circuit circulating load is projected at 250 to 300%. Cyclone overflow particle size target is 80% passing approximately 75 µm at approximately 35% solids. Lime addition is included for pH adjustment. Grinding balls are added to maintain mill power draw.
Gravity concentration circuit
A centrifugal gravity concentrator treats approximately 30% of the cyclone underflow stream. The gravity circuit feed is screened over a vibrating preparation screen to remove particles greater than 2 mm; screen oversize returns to the grinding circuit. Screen undersize feeds the centrifugal concentrator, which operates continuously and is flushed twice per hour. Concentrate is collected in a holding tank. A shaking table upgrades the gravity concentrate as a daily batch process; table tailings return to the concentrator and table concentrate is collected, dried, and stored for smelting.
Copper-gold bulk flotation circuit
Cyclone overflow from primary grinding flows to an agitated conditioning tank then to two stages of rougher flotation. The rougher circuit consists of eight 10 m³ tank cells. Rougher concentrate reports to the regrind circuit; rougher tailings proceed to pyrite flotation.
The rougher concentrate is reground by a 1.5 m diameter by 2.1 m long, 56 kW regrind ball mill in closed circuit with cyclones. Regrind product target is 80% passing approximately 35 to 40 µm.
The cleaner flotation circuit comprises three stages of cleaning plus a cleaner scavenger stage. First cleaner flotation uses three 3 m³ tank cells; second cleaner uses two 2 m³ tank cells; third cleaner is a column type cell. Cleaner scavenger concentrate returns to the regrind circuit. Third cleaner concentrate is the final copper-gold concentrate.
Cleaner scavenger tailings contain gold recoverable by agitated cyanide leaching and are directed to the gold-bearing pyrite dewatering circuit.
Concentrate dewatering
The final copper-gold concentrate is dewatered in a 2 m diameter high-rate thickener to approximately 60% solids, followed by a 64 m² automated plate and frame pressure filter shared with gold-bearing pyrite material. Final filter cake moisture target is 8 to 9%. Dewatered concentrate is conveyed to a concentrate storage shed before offsite transport.
Pyrite flotation and dewatering
Copper rougher flotation tailings are treated in a dedicated pyrite flotation bank of seven 10 m³ tank cells. The pyrite concentrate, combined with copper cleaner scavenger tailings, is dewatered in a 5 m diameter high-rate thickener and then filtered using the shared plate and frame pressure filter. Filter cake is trucked to the proposed nearby Da Tambuk cyanidation plant or other facilities for gold recovery by agitated cyanide leaching.
Pyrite flotation tailings constitute the final plant tailings.
Tailings dewatering and water system
Final tailings are thickened in a 15 m diameter tailings thickener to approximately 60% solids. Thickener underflow is pumped to the tailings storage facility (TCF). Thickener overflows from concentrate, pyrite, and tailings thickeners, together with recovered water from the TCF, are reused as process water. Fresh water is used for gland services, reagent preparation, gravity circuit fluidization, and process water make-up.
Reagent preparation
Hydrated lime is delivered in 1 t bulk bags or 40 t trucks and prepared as a 20% slurry. Solid and liquid collectors are delivered in sealed drums and added to flotation circuits at controlled rates as solutions of approximately 10 to 20% strength. Frother is added without dilution via metering pumps. Flocculant is prepared in a vendor-supplied facility at required concentration.
Air supply
Two air compressors supply plant and instrument air. A dedicated air compressor serves the plate and frame filters. Low pressure air blowers supply flotation cells.
Key reported parameters
| Parameter | Unit | Value | Basis |
|---|---|---|---|
| Nominal plant throughput | t/a | 500,000 | Design |
| Nominal plant throughput | t/d | 1,400 | Design |
| Operating days per year | d | 365 | Design |
| Crushing circuit utilization | % | 75 | Design |
| Grinding and flotation utilization | % | 90 | Design |
| Crushing circuit throughput rate | t/h | 116.7 | Design |
| Grinding and flotation process rate | t/h | 64.8 | Design |
| Ball mill feed size, 80% passing | µm | 10,000 | Design |
| Ball mill product size, 80% passing | µm | 75 | Design |
| Ball mill circulating load | % | 250–300 | Design |
| Bond ball mill work index, design | kWh/t | 12.0 | Testwork |
| Bond abrasion index, design | g | 0.25 | Testwork |
| Ore specific gravity | , | 2.80 | Testwork |
| Ore moisture content | % | 2.0–3.0 | Testwork |
| Head grade, design, gold | g/t | 7.5 | Testwork |
| Head grade, average, gold | g/t | 3.4 | Testwork |
| Head grade, design, copper | % | 0.50 | Testwork |
| Head grade, average, copper | % | 0.24 | Testwork |
| Copper recovery to flotation concentrate, LOM average | % | 93.0 | Testwork |
| Gold recovery to flotation concentrate, LOM average | % | 31.8 | Testwork |
| Gold recovery to doré (including gravity concentrate), LOM average | % | 54.6 | Testwork |
Technical qualifications
The report states that design parameters are based on metallurgical testwork performed at BCR and typical industry parameters for this type of process as provided by Tetra Tech. The report notes that the grinding mill was sized based on Bond Work Index test data measured by BCR and typical experience for the type of deposit. The flotation circuit was designed based on the results of metallurgical testwork by BCR. The report also states that typical industry standard plant design parameters were considered appropriate for this process design.
The report is a preliminary economic assessment and contains forward-looking statements regarding proposed facilities, including the nearby Da Tambuk cyanidation plant, which itself is described as proposed for development or other facilities. No operating data from a production facility at Mato Bula are presented in this section of the report.
*Source: Technical Report and Preliminary Economic Assessment for the Mato Bula Deposit, Adyabo Property, Tigray National Regional State, Ethiopia, Section 17.0 Recovery Methods.*
