Concentrator

Underground ore stream

Ore from the underground block-cave mine - less than 200mm in size - is conveyed to two stockpiles, each feeding two separate, autogenous wet-grinding circuits. These in turn, each comprise a 9.75 meter-diameter tumbling mill rotated by 2 x 3.5 MW drives and mill daily throughput of up to 32 500 tonnes.

Large rocks impact, scrub and attrition against each other, reducing their size, which results in the liberation of the copper sulphide. Mill products are sized by vibrating screens to produce coarse feed to 2 x Ore Sorters which separate the copper bearing material and dolerite. Cyclone overflow particles finer than 0.3mm are pumped 1.5 kilometers to the secondary milling plant (SMP) where the ore is further milled to less than 0.15mm, using steel balls in up to five parallel 1.2 MW milling circuits to the cyclone. The coarse cyclone underflow product is recycled to the mills. Secondary milling is to improve liberation and recovery of copper on higher grade underground ore.

Conventional process route

There are 6 x conventional grinding sections of which 3 x sections (section 2, 3 & 4) have been decommissioned and the 3 x sections ( section 1, 5 & 6) are in operation. The operational sections 1, 5 and 6 process bottom deck material from Automills and excess underground material and surface material (old tap-off and smelter reverts/slag). Each section consists of 1 x rod mill, 2 x ball mills and 2 x classification cyclones, with the cyclone underflow recycled to the mill and overflow pumped to secondary milling plant, the SMP output at 80% passing 150 micron is pumped to the flotation tank cells.

Flotation

Since 2019 Concentrator advanced from Wemco flotation cells to tank flotation cells. The final milled product at 80% passing 0.15 mm is fed to the Tankcells Flotation Plant (TFP) with capacity of 1 745 t/hr, which is a counter-current circuit, where the copper is concentrated into the overflow of the rougher, cleaner and re-cleaner flotation stages. The underflow from re-cleaner and cleaner stages is recycled to the rougher cells for further copper extraction. Chemical reagents such as collector and frother are used during the flotation process. The final concentrate from the re-cleaner overflow is pumped to the Copper Filter Plant (CFP) for dewatering and drying, whereas the final tailings from rougher cells are pumped to the magnetic separation plant (stream 1) for magnetite recovery.

Dewatering

The Concentrate received from the flotation plant is thickened using 3 thickeners and dewatered using vacuum disc filters. The filtered concentrate is dried through a rotary drier to reduce the moisture content to around 7.5 - 8.5%. Dryer product is weighed by a belt scale and sampled before it is conveyed to the smelter receiving shed.