McArthur River Mine Zinc-lead-silver mineralisation occurs predominantly as ultrafine bedded parallel sphalerite and galena rich bands hosted by dolomitic and carbonaceous pyritic siltstones, graded beds and chaotic debris flow breccias.

The HYC mineralisation covers an area of about two km2 and has an average thickness of about 55 m. It is 1.5 km west of the Emu Fault and separated from the fault by the Cooley Dolomite Member of the Barney Creek Formation and the Western Fault Block.

The western margin of the deposit has been folded and eroded and the eastern margin is faulted against the Cooley Dolomite Member. The northern margin interfingers with sedimentary slump breccia derived from older McArthur River Group sediments to the north of the deposit. The southern margin, which has been down faulted by 100 to 200 m by the northeast trending Woyzbun Fault, is transitional into barren pyritic shale.

The deposit is divided into seven mineralised intervals referred to as orebodies. Orebodies comprise shale with lesser amounts of sedimentary breccia and tuff. Number 1 orebody is used to refer to an interval of weak silver-lead-zinc mineralisation hosted by nodular dolomitic shale in the footwall sequence. In addition, there is a broad interval of weak silver-lead-zinc mineralisation hosted by nodular dolomitic shale in the immediate hanging wall, along the eastern margin of the deposit.

The hanging wall sequence comprises interbedded dolomitic shale, sedimentary turbidite breccia and occasional tuff beds.

The Cooley Dolomite occurs along the eastern margin of the deposit. It comprises a fault bounded block of Teena and Mara Dolomite Members (older than the host to the mineralisation), which have incurred several episodes of brecciation. The Cooley Dolomite commonly hosts coarse-grained sphalerite and galena as veins, disseminations and breccia matrix.

The open pit excavation is being undertaken in six stages, with the first three targeting the shallowest ore. Conventional drilling, blasting, loading and haulage methods are used.

After blasting, the overburden is excavated in horizontal benches to expose the target ore, which we then remove for processing. Separating the ore and waste at the mining stage ensures a relatively pure ore is fed to the processing plant.

Excavators with up to 550 tonne capacity load 175-220 tonne haul trucks with ore or waste to be taken to stockpiles or the waste rock piles. The majority of the overburden rock from the open pit is stored at the North Overburden Emplacement Facility, or waste rock pile.

Crushing:
The ore is crushed down to rock sizes of 9 mm through three stages of crushing commencing with a jaw crusher, followed by secondary and tertiary crushing using cone crushers. After crushing, low grade ore moves through to the Heavy Medium Plant to upgrade the ore to the target process feed grades while high grade ore moves directly through to the primary grinding stage.

Primary grinding:
The ore then moves through a primary grinding circuit at a rate of around 550 tonnes per hour. This circuit consists of a 4 megawatt SAG Mill operating in open circuit followed by a 11.5 megawatt Ball Mill running in closed circuit with hydrocyclones. Through this circuit, the ore is slurried with recycled process water and ground to produce fine material of 80% less than 45 microns.

Refining the ore:
Ore is trucked from the open pit to the processing plant where it goes through three stages of crushing and screening, pre-concentration via heavy media separation followed by flotation, oxidative leaching and dewatering.

Flotation circuit:
The slurried ore is then passed onto the flotation circuit where the zinc and lead bearing minerals are separated from the non value minerals. Here, various reagents are introduced which attach themselves to the metal sulphide materials and enable them to be recovered from tanks as a froth. The zinc and lead bearing minerals are then recovered and upgraded to the desired product quality for the clients.

Pre-cycloning:
The concentrate material recovered from the first stage of flotation requires further upgrading. As such, this material is then pumped through a pre-cycloning stage to produce two products, a fine and a coarse material. The fine material is sent to conditioner tanks for further p ........