The deposit, hosted within a hydrothermal breccia, contains magnetite, quartz, biotite, chalcopyrite, pyrite, fluorite, gold, molybdenite, uraniferous minerals, and potassic feldspar. Additional gangue minerals include chlorite, calcite, dolomite, barite, apatite, muscovite, garnet, scapolite, sphene, rutile, and tourmaline (Ryan, 1998). Chalcopyrite is the main copper‑bearing mineral and, together with pyrite, represents the only significant sulphide phases. Sulphides constitute approximately 1–20% of the breccia matrix and occur as fine‑ to medium‑grained disseminations commonly associated with magnetite. Gold occurs predominantly (>98%) as native gold–electrum (65–95 wt% Au), with minor contributions from sylvanite and sulphide‑hosted gold. Gold precipitation is interpreted to have been closely associated with, but preceded some of the chalcopyrite deposition, as evidenced by the lower gold‑to‑copper ratios in late‑stage chalcopyrite‑rich veins. Although arsenic, fluorine, and uranium minerals are present, their concentrations are generally below deleterious thresholds (Evolution Mining, 2023). Processing at Ernest Henry Operations involves crushing, grinding, and flotation. Mined ore is crushed underground before being conveyed and hoisted to the coarse ore stockpile (COS). The grinding circuit consists of an 11 MW SAG mill (10.4 m Ø × 5.1 m) and a 5.5 MW ball mill (6.1 m Ø × 8.5 m), operating in a closed AB configuration with a cyclone cluster comprising three 800 mm Ø and five 650 mm Ø CAVEX cyclones. SAG mill discharge is screened on a 3 m × 9 m vibratory screen with 4–5 mm apertures. Screen oversize is returned to the SAG mill feed via conveyor belts, while the undersize combines with the ball mill product and is pumped to the primary cyclone pack. Cyclone underflow gravitates to the ball mill, and overflow reports by gravity to the rougher flotation circuit. The flotation circuit consists of a rougher train of 9x127 m³ Wemco SmartCells arranged in five banks, followed by three stages of dilution cleaning. Concentrate from the first rougher bank is directed to the third cleaner stage, while concentrate from the remaining four banks reports to the regrind circuit. The regrind circuit includes a 1 MW Vertimill operating in closed circuit with six GMAX15 cyclones. Regrind cyclone overflow feeds the first cleaner stage. Cyclone underflow can be directed to an SK240 flash flotation cell via a feed box, with the cell tailings returning to the Vertimill. The SK240 concentrate can be routed either to the final concentrate sump or to the third cleaner stage. The cleaner circuit operates in a counter‑current configuration, with concentrate progressing from Cleaner Stage 1 to Stage 2 to Stage 3. Dilution water is added to Stages 2 and 3. Cleaner Stage 1 consists of eight OK50 cells, while Stages 2 and 3 utilise eight and five OK16 cells, respectively. Tailings from Cleaner Stage 1 and the rougher circuit are combined and directed to a 55 m Ø tailings thickener. Thickened tailings are pumped to the tailings storage facility (TSF). Final concentrate from Cleaner Stage 3 is thickened in a 25 m Ø concentrate thickener before filtration in a 144 m² Larox pressure filter. The filtered concentrate is transported by road train to Glencore’s Mount Isa Copper Smelter.
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