The McArthur River lead-zinc-silver deposit of northern Australia is the largest known stratiform sediment-hosted base-metal deposit.

The mineralisation of the McArthur River area of the 'Here's Your Chance' deposit covers around two square kilometres and is 55 metres thick. It comprises eight recognisable and discrete zinc and lead ore zones. The natural movement of the earth changes the orientation and angle of each zone over time, which complicates our mining process.

Zinc-lead-silver mineralisation occurs predominantly as ultra-fine bedded parallel sphalerite and galena rich bands hosted by dolomitic and carbonaceous pyritic siltstones, graded beds and chaotic debris flow breccia.

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.

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.

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 ........