The Prominent Hill iron-oxide copper gold (IOCG) deposit is located in the north-eastern portion of the Archaean to Mesoproterozoic Gawler Craton, South Australia. Most of these deposits are thought to be genetically related to the Gawler Range Volcanic (GRV) – Hiltaba magmatic event which affected the central and eastern portions of the Gawler Craton around 1600-1580 million years ago. Copper-gold-silver mineralisation at Prominent Hill is mostly hosted within hematite-matrix 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.

The current maximum extent of the reported Mineral Resource is 2,700m (east-west) by 1,300m (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 123m and 1,399m respectively below the pre-mining topographic surface.

The Prominent Hill Open Pit Mineral Resource was fully depleted, with the Open Pit mining operations completed in March 2018.

Open pit ore stockpiled in previous periods began to be processed from Quarter 2 2018 following the closure of the Prominent Hill Open Pit.

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. The plant can process approximately ten million tonnes per annum subject to the ore blend.

The current life of mine schedule has the plant running at that capacity approximately eight to nine million tonnes per annum until the end of quarter one 2025 with a high proportion of stockpiled open pit gold and lower grade ore. On exhaustion of these gold and marginal ore stocks the plant will be fed with underground ore alone.

Optimisation studies indicate that the plant can be configured to run at four to six million tonnes per annum dependent on the blend of copper and gold ores for minimal capital expenditure. If necessary, lower throughputs can be processed in batches providing the ability to process ore at a range of underground production rates.