The copper-gold deposit is part of the Kanmantoo Trough, which is the youngest of a succession of extensional sub-basins developed within the Adelaide Geosyncline. The Kanmantoo orebody comprises three main mineralised zones: Main, O’Neil/Nugent and Emily Star. Each of the ore zones contains an oxide, transition and primary sulphide ore component.

The Main Zone is hosted by a garnet-andalusite-biotite schist within the Cambrian Kanmantoo Group. Copper mineralisation occurs as chalcopyrite within a complex series of northern trending steep northeast plunging pipes and lodes 3 to 80 m wide (Figure 5.4) (Resource Evaluations, 2006). Mineralisation is characterised by chalcopyrite, pyrrhotite and magnetite with lesser pyrite. In the Emily Star Zone, mineralisation is characterised by chalcopyrite and pyrite. Mineralisation in the O’Neil/Nugent Zone is associated with a garnet-chlorite hydrothermal alteration zone with quartz veining. In comparison with the other zones, the O’Neil/Nugent Zone is enriched in gold.

Sulphide becomes less common with distance from the ore zone indicating there is likely to be broad zones of non-sulphidic waste rock outside of the main mineralised blocks. Across the ML area, there is a distinct weathering zone of approximately 15 m depth that appears to be completely oxidised. This oxidised zone is an important source of non-acid-forming (NAF) material suitable for use in encapsulation of the potentially acid-forming (PAF) waste material.

Mining is undertaken using conventional open pit methods, i.e., drilling and blasting where required with truck and excavator for removal from the pit. Ore and waste rock is predominantly blasted using 9 to 12 m high benches and mined over passes or ‘flitches’.

Blasting is undertaken using ammonium nitrate/fuel oil (ANFO) or emulsion-based explosives, which are loaded into blastholes. Hole diameters vary from 89 to 165 mm, with up to 600 holes fired in each shot. Blasting is generally undertaken from 10 am to 3 pm. and is managed to meet the lease conditions, Australian standards (AS 2187.2:2006) and other advanced blasting practices. Blast holes are backfilled with stemming material to contain the explosion on initiation and hence reduce noise, dust and fly rock. Surface and downhole delays are used to minimise ground vibration. Electronic or non-electric (Nonel) signal tube is used for downhole and surface tie-ins to improve blast performance and reduce noise and air blast. Blasts are designed to ensure that there will be no adverse public health and/or nuisance impacts.

The processing facility has been designed to operate 24 hours a day, 365 days per year and treat approximately 2.4 to 3.2 Mtpa of ore, at a rate of 350 to 400 tonnes per hour. This processing rate may vary dependent on the optimisation of the plant. The ore contains on average 0.7% copper and copper recoveries of approximately 92 to 93% based on a fixed tail of 0.055% Cu are achieved. The plant produces an average of 80,000 tpa of copper-gold concentrate (with silver credits) for export, containing approximately 18,000 to 20,000 t of copper.

The processing facility comprises the following unit operations (Figure 5.6):

• Primary and secondary crushing.

• Coarse ore storage and reclaim.

• Grinding and classification.

• Copper flotation.

• Concentrate thickening, filtration, storage and dispatch.

• Tailings thickening and transfer to the TSF.

Process Description.

A schematic of the ore concentrating process is shown in Figure 5.6. Ore is reclaimed from the ROM stockpile by a front-end loader and fed into the crushing plant, which reduces the ore size from 900 to 150 mm. The crushing plant operates up to 24 hours per day. The crushed ore is stored on a coarse ore stockpile with a capacity of approximately 9,000 t.

Ore is recovered from the coarse ore stockpile and conveyed to the semi autogenous grinding (SAG) mill, where the ore particle size is reduced to 212 pm to enable the valuable copper and gold minerals to be released and recovered by froth flotation.

The flotation circuit comprises roughing, scavenging and cleaning stages. Flotation reagents (lime, collector, gangue depressant, sodium meta bisulphide and frother) are added in this circuit.

Copper-gold concentrate is thickened and then filtered by a pressure filter to produce a de-watered concentrate product with a moisture content of approximately 9%. Flotation tailings are thickened to a solids density of 55% or greater before being pumped to the tailings storage facility.