Guelb Moghrein mineralisation may be classed as a structurally modified iron ore copper gold (IOCG) deposit that is hosted in a coarse grained ferro-magnesian carbonate (FMC) unit. Copper and gold mineralisation is largely coincident with some evidence for elevated gold in the shallow mined out upper zones. The main sulphide minerals are chalcopyrite and pyrrhotite with magnetite becoming more abundant external to the sulphide bodies. The zones of mineralisation were strongly controlled by tectonic shearing and faulting which resulted in topographic expressions of the deposit in the form of two hills known as the Occidental and Oriental hills. Mineralisation below Occidental hill is considerably larger than that at Oriental, and dips by about 20 degrees to the south with a strike length close to 700 m and a dip extent of close to 1,000 m. The Occidental mineralised vertical width varies according to structural controls and ranges from a few meters to several 10’s of metres. The mineralisation below Oriental hill is limited to the shallow outcropping area of the hill and has an ellipsoid shape with a strike length of around 250 m and a width of about 100 m.

The FMC unit is the primary host of Guelb mineralisation and is comprised mainly of chalcopyrite and pyrrhotite within the un-oxidised zone. Other minerals include iron-cobalt-nickel arsenides and bismuth-gold-silver-tellurides. Gold is largely coincident and associated with chalcopyrite.

A shallow (<40 m) oxidised zone has resulted from surface weathering and oxidation of the deposits primary sulphide mineralisation. Commonly, the oxidised zone has minerals such as native copper, malachite, cuprite and chalcocite. Mineralisation of the carbonate units is suggested to be hydrothermal and associated with the D2 deformation event, which was subsequently deformed by faulting and thrusting of the D3 event. The siderite within the FMC is considered to have provided a reactant for the hydrothermal Cu-Au bearing fluids. Sulphide mineralisation is often better developed along the basal portions of the FMC and ranges from semi-massive to disseminated.

The topographic expression of the Guelb Moghrein mineralisation outcrops as two small hills of notable FMC gossans. The two hills are known as Occidental and Oriental, below which mineralisation is located as two distinctly different volumes. Occidental is characterised as a tabular shaped body dipping to the south by approximately 20 degrees and has a strike length of 650 m and dip extent of 1200 m. The width of Occidental mineralisation ranges from a few meters to 10’s of meters. In contrast the Oriental deposit is much smaller and is restricted as an ellipsoid shaped body immediately below the Oriental hill. Oriental has a strike length of 500 m and is approximately 200 m wide.

Mining at Guelb Moghrein is conventional open cast mining using hydraulic excavators and mechanical drive haul trucks. Mining is owner operated, with fully equipped training facilities for operators and maintenance workshops.

Waste is trucked onto waste dumps in the vicinity of the open pit, while ore is trucked to the Process Plant for direct feeding into the Primary Crusher or onto the Run-of-Mine (ROM) Pad.

On average, sufficient ore is exposed in the pit for one to two months feed to the plant; stockpiling and re-handling is minimized to maintain high efficiencies.

Processing at Guelb Moghrein is by conventional SAG milling followed by concentration by flotation. The process flowsheet also includes gravity concentrators in the milling circuit (Knelson concentrators) and flotation scavenger circuit (Falcon concentrators) for the recovery of gold. The final product is a copper concentrates averaging 22.5%Cu and 10 to15 g/t Au.

Since commissioning, the Process plant has undergone several changes with the most significant being the increase in throughput from 2 Mtpa to 4 Mtpa following the installation of a new Outotec SAG Mill (5.8 MW).

Crushing and grinding
Material from mining is received at the primary crusher feed dump pocket and feeds directly to the primary gyratory crusher which is an Allis Chalmers 42-65 unit. Product material from the primary crusher at a nominal size of 80% < 130 mm is conveyed to the covered dome stockpile with 7,000t live capacity and a total capacity of more than 30,000 t.

The primary SAG mill is a new Outotec mill that was commissioned in 2014 and is operated in open circuit. It is fed by an apron feeder from the feed bin via two transfer conveyors to the SAG mill feed chute The feed to SAG 1 is cascade controlled typically at about 500 wtph to 550 wtph on a mill weight controller set at 240-260 tonnes.

From SAG 1 the ground material discharges onto a vibrating screen. The oversize has provision to be routed to either a small stockpile area from where it is reclaimed by FEL or is conveyed back to the mill surge bin feed conveyor. The undersize from SAG 1 discharge screen passes into a sump and from there is pumped to the discharge sump of BM3.

The ball mill discharge sump is thus fed with SAG 1 discharge screen undersize, ball mill discharge screen undersize and tailings from the Knelson concentrator circuit. This material is pumped to a 6 cyclones cluster, whose overflow reports to linear trash screens, whilst underflow reports to the ball mill. The ball mill steel rejects report onto a conveyor then a bunker, where they are loaded out by FEL.

Flotation plant
Processing at Guelb Moghrein is by conventional SAG milling followed by concentration by flotation. The process flowsheet also includes gravity concentrators in the milling circuit (Knelson concentrators) and flotation scavenger circuit (Falcon concentrators) for the recovery of gold. The final product is a copper concentrates averaging 22.5%Cu and 10 to15 g/t Au.

Ore from the open pit mine and stockpiles is crushed, milled and then undergoes sulphide flotation to produce a copper-gold concentrate, which is shipped to offshore smelters (mainly in China).

Since commissioning, the Process plant capacity has been expanded from 2 Mtpa to 4 Mtpa with current management focussing on improving recoveries and costs.

Continued optimization of process automation (‘SGS Expert System’) and the gravity concentrators has resulted in improved metal recoveries even at lower plant feed grades. Work to ensure the processing rate can be maintained a ........