First Quantum's 2016 technical report on Guelb Moghrein near Akjoujt describes a 4 Mtpa SAG and ball mill flotation plant with Knelson and Falcon gravity circuits, plus a magnetite recovery plant that was placed on care and maintenance.
The Guelb Moghrein copper-gold mine lies about 250 km northeast of Nouakchott near Akjoujt in Mauritania's Inchiri region. Mauritanian Copper Mines (MCM), a subsidiary of First Quantum Minerals Ltd, owns 100% of it. FQM bought an 80% interest in 2004, reached commercial production in 2006 and took full ownership in 2010. The technical report, dated 30 March 2016, covers an operating open pit with a flotation plant that ships copper-gold concentrate to offshore smelters, mainly in China. Plant capacity had grown from 2 Mtpa to 4 Mtpa since commissioning. A CIL plant commissioned in 2008 and a magnetite plant commissioned in 2015 were both idle because they were not economic at the time.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Plant capacity | 4 | Mtpa | Expanded from 2 Mtpa |
| Primary crusher | Allis Chalmers 42-65 | Not applicable | Gyratory, 80% below 130 mm |
| Dome stockpile | 7,000 | t live | Over 30,000 t total |
| SAG mill | 5.8 | MW | Outotec, commissioned 2014 |
| Ball mill | 4 | MW | Closed circuit with 6 cyclones |
| SAG feed rate | 500 to 550 | wtph | Typical |
| Flotation feed size | 75 | µm P80 | Screened cyclone overflow |
| Rougher cells | 6 | Not applicable | 150 m3 each |
| Copper recovery, plan | 87.5 to 92.2 | % | Life of mine schedule |
| Gold recovery, plan | 62 | % | Life of mine schedule |
| Life of mine plant feed | 29.9 | Mt | 0.76% Cu, 0.68 g/t Au |
| Concentrate bags | 2.1 | t | Twelve per 6 m container |
| Magnetite output when running | About 80 | tph | Above 69% Fe |
| Planned tailings, 2016 | 3.80 | Mt | TSF2 and TSF3 |
Overview
Ore from the pit and stockpiles is crushed, ground in an open circuit SAG mill and a closed circuit ball mill, and floated to a copper-gold concentrate. Gold is recovered by gravity at two points. A Knelson concentrator treats ball mill discharge in the grinding circuit. Falcon concentrators and a vertical regrind mill treat the first cleaner tailings. Both gravity concentrates join the flotation concentrate in the thickener. The concentrate is filtered on ceramic disc filters, bagged and trucked in containers to the port at Nouakchott.
The plant runs on a CITECT control system, an Outotec on-stream analyser covering twelve streams and an SGS flotation expert system commissioned in March 2016.
Key Process Stages
Crushing
Trucks tip into the dump pocket of an Allis Chalmers 42-65 gyratory crusher. Product at about 80% passing 130 mm is conveyed to a covered dome stockpile, and a second stockpile outside the dome can be fed by loader when needed. Two vibrating feeders under the dome reclaim ore onto a conveyor to the mill feed bin.
Grinding
An apron feeder and two transfer conveyors feed the Outotec SAG mill installed in 2014. It runs in open circuit at about 500 to 550 wtph on a mill weight set point of 240 to 260 t. The SAG discharge screen sends oversize to a small stockpile for loader reclaim or back to the mill feed conveyor. Undersize goes to the ball mill discharge sump, along with ball mill screen undersize and Knelson tailings. Six cyclones classify the slurry. Overflow passes linear trash screens to remove fibre, and underflow returns to the ball mill. Rejected steel from the ball mill goes to a bunker.
Copper flotation
The screened slurry at 75 µm is conditioned with sodium ethyl xanthate and frother and floated in six 150 m3 rougher cells in open circuit. Rougher concentrate passes six 50 m3 first cleaner cells and then seven 10 m3 second cleaners. A column cell and third cleaners, in three banks of two 3 m3 cells, complete the cleaning. Concentrate from the first three second cleaner cells can bypass straight to the thickener. Lime raises the pH in the cleaners to depress pyrrhotite.
Gravity gold on cleaner tailings
First cleaner tailings are pumped to two Falcon concentrators, whose gold concentrate goes to the concentrate thickener. Falcon tailings are classified in cyclones. The underflow is reground in a vertimill to free more gold and returns to the Falcons, while the overflow feeds the scavenger flotation circuit. The scavengers, one 150 m3 and six 50 m3 cells, send the first three cells' concentrate to the first cleaner and the rest back to rougher conditioning. Scavenger tailings join the rougher tailings.
Concentrate and tailings
A thickener and two disc filters dewater the combined concentrate, which is packed in 2.1 t bulk bags. Flotation tailings go to a tailings thickener and on to the storage facilities. TSF2 was commissioned in 2009 and TSF3 in 2015, both raised upstream with spigots. Decant water returns to the plant. By the end of 2015, the operation had placed about 5.5 Mt in the old TSF1, 17.3 Mt in TSF2 and 0.16 Mt in TSF3.
Additional Interesting Data and Summary
The magnetite plant was added in late 2014 and early 2015 to recover magnetite from the flotation tailings. Four rougher wet low-intensity magnetic separators, each with two drums, made a rougher magnetite concentrate. This was reground to 53 µm in a ball mill with cyclones, passed through reverse flotation in three 100 m3 cells, and cleaned in four triple-drum separators. The flotation concentrate went back to the copper-gold plant through the Falcon and vertimill circuit. The plant made about 80 tph of magnetite above 69% iron. After about 50,000 t, the fall in iron ore prices put it on care and maintenance. Test work was under way on a premium magnetite product for dense media coal washing.
The life of mine schedule feeds 29.9 Mt at 0.76% copper and 0.68 g/t gold. It yields about 204,200 t of copper and 407,500 oz of gold in concentrate. Copper recovery is planned at 92% in the early years, easing to 87.5% as grade falls, and gold recovery at 62% throughout. Water comes from a saline and potable bore field at Bennichab, about 70 km away.
Key Processes
- Gyratory crushing to a covered dome stockpile
- Open circuit SAG milling and closed circuit ball milling with cyclones
- Knelson gravity recovery in the grinding circuit
- Rougher flotation and three cleaning stages with a column cell
- Falcon gravity recovery and vertimill regrinding of cleaner tailings
- Scavenger flotation with recycle to cleaners and roughers
- Thickening, ceramic disc filtration and bagging of concentrate
- Magnetite recovery by magnetic separation and reverse flotation, idle since 2015
Source: Guelb Moghrein Copper Gold Mine, Inchiri, Mauritania, NI 43-101 Technical Report, 30th March 2016.
Project website: Guelb Moghrein Copper Gold Mine
