The Prominent Hill iron oxide copper gold (IOCG) deposit is located in the northeastern portion of the Archaean to Mesoproterozoic Gawler Craton, South Australia. Copper-gold-silver mineralisation at Prominent Hill is mostly hosted within hematitematrix breccia containing fragments of sandstone, siltstone, dolostone, and mafic to intermediate volcanic rocks. Copper mineralisation occurs as disseminations of chalcocite, bornite and chalcopyrite in the matrix of the breccia. Mineralisation generally has a tabular geometry. Most but not all copper mineralisation is hosted in hematite breccia. Gold mineralisation is commonly coincident with copper mineralisation, but some zones of gold-only mineralisation do exist. Copper grades generally show better spatial continuity within hematite breccia than within other rock types. Barren dykes cross cut the mineralisation. Barren covering sediments overlie the mineralised basement rocks. The current maximum extent of the reported Mineral Resource is 2,600m (east-west) by 1,400m (vertical). Multiple lenses exist within a mineralised zone having a plan width (across strike) of approximately 300-400m. Only a subset of this mineralised zone has sufficient continuity of grade to have been reported as a Mineral Resource. The upper and lower limits of the reported Mineral Resource are 105m and 1,461m respectively below the pre-mining topographic surface.

The Prominent Hill Underground Mineral Resource is being mined successfully using sub-level open stoping (SLOS) with cemented fill. Access to the ore body and ore haulage is carried out via decline (ramp) system. Operations are performed by mining contractor.

On August 18, 2021, The OZ Minerals Board approved construction of a hoisting shaft at the Prominent Hill copper-gold mine in South Australia, paving the way for a mine life extension and throughput expansion.

Sinking of the shaft is expected to commence in the March quarter of 2022. Mining and installation of underground and surface infrastructure is scheduled for completion along with commissioning of the Wira shaft at the end of 2024, with nameplate capacity expected in H1 2025.

The shaft design comprises a 1,329 metre deep, concrete lined shaft with a diameter of 7.5 metres.

The company plans to reduce its underground loading fleet to eight vehicles, from nine after the shaft expansion, with its trucking fleet going from circa-14 to five, post-shaft.

Prominent Hill is an operating mine and has the majority of necessary infrastructure in place for its continued operation.

Two new primary ventilation fans were commissioned in Q2 2020. This is the third pair of primary ventilation fans installed at Prominent Hill.

A second paste fill plant was successfully commissioned in mid-2020 and is capable of providing cemented fill at a rate to support forecasted production rates.

Crushing and Grinding
Ore is hauled from the mine directly to the primary crusher or stockpiled on the ROM pad until such time as it can be processed. Mineralised waste is stockpiled separately to allow for future reprocessing should this be determined to be economically viable.

The ore is taken from the mine or reclaimed from the ROM stockpiles and tipped into the primary crusher, located adjacent to the ROM pad, where it is crushed to a size of less than 125 mm. The nominal crusher throughput is up to 3,600 tonnes per hour, approximately three times the throughput of the grinding circuit. The ore is then conveyed to the crushed ore stockpile. It is reclaimed from the bottom of the stockpile and conveyed to the semi-autogenous grinding (SAG) mill which operates in a closed circuit with a vibrating screen and pebble recycle circuit. Grinding balls at 125 mm are added including water inside the SAG mill to reduce the ore to micron size contained in a slurry form. Material that doesn’t pass through the 5 x 20 mm screen is recycled back to the SAG mill for further grinding. The slurry containing the fine material that passes through the 5 x 20 mm screen is combined along with the ball mill discharge to slurry feed the primary hydrocylone pack for classification. The primary hydrocyclone separates the material by size, where the overflow fines report to flotation, and the underflow coarse returns to the ball mill where 60 mm balls are added for further grinding. The SAG and ball mill operates in closed circuit with the primary hydrocyclone pack. Dust generation occurs during the dry stages of crushing and when transporting ore to the coarse ore stockpile (COS). Water sprays are used in the crusher pocket and at the discharge of the first conveyor (CV1) to manage the dust. The rest of the size reduction process (grinding) is a wet process where no dust is generated.

The SAG/ball milling circuit enables 80% of the material is sized to less than 125 µm, and becomes suitable for further processing.

The Prominent Hill processing plant has been operating since February 2009 and comprises a conventional crushing, grinding and flotation circuit to recover copper, gold and silver to produce a high-quality concentrate.

Optimisation studies indicate that the plant can be configured to run at 4 – 6 Mtpa for minimal capital expenditure. If necessary, lower throughputs can be processed in batches which provides the ability to process ore at a range of underground production rates.

The processing schedule has the plant operating at approximately 9Mtpa until 2025, depleting the remaining open pit gold, copper and marginal stockpiles. Following this, the processing plant will be fed from underground sources only.

PLANT
Rougher Flotation and Concentrate Regrind
In the flotation area, the primary hydrocyclone overflow enters the flotation process, passing through the rougher flotation cells. Rougher concentrate overflowing these cells, containing eleva ........