RD1 drilled through 335m of flat-lying Proterozoic and Cambrian sediments before passing through an unconformity into haematite altered basement rocks. In theory the copper mineralisation was supposed to be in the overlying sediments but assays revealed fine-grained hypogene chalcocite in the basement. RD1 returned 38m @ 1.05%Cu, which was considered uneconomic at these depths at this time, but RD10 changed that with an intersection of 170m @ 2.12%Cu and 0.58kg/t U3O8 and is considered the “Discovery Hole”.

However, following initial underground development in 1985-1987, it became apparent that none of the mineralisation was stratabound and that it was hosted in a highly variable magmatic-hydrothermal breccia complex that displays multiple brecciation, diatreme intrusions, mafic and ultramafic dyke intrusions along with interpreted gravity collapse of high level volcanic edifice material. The deposit is considered to be a member of the Iron Oxide Copper Gold (IOCG) family of deposits and has a close temporal and spatial association with the Hiltaba Suite of granites, dated at 1590Ma and more specifically the more fractionated and oxidised Roxby Downs subsuite (1588Ma).

The main lithologies at Olympic Dam comprise a continuum of breccias starting at the periphery with granite clasts set in little haematite matrix progressing into the centre where the clasts are wholly haematite in a haematite matrix. The principal gangue minerals are haematite, sericite and quartz. Minor gangue minerals include; siderite, chlorite, fluorite and barite.

The dominant sulphide minerals are chalcopyrite, bornite, chalcocite and pyrite. Minor sulphides include; carrolite, cobaltite, galena, sphalerite and molybdenite. Other minerals of interest are; metallic copper, electrum, Ag-, Hg-, Pb-, Bi-selenides and tellurides. The uranium at Olympic Dam occurs mostly as uraninite, coffinite or brannerite with trace amounts in zircon, monazite, florencite and bastinite.

Ore mined underground is hauled by an automated train system to crushing, storage and ore hoisting facilities or trucked directly to the surface.

The Olympic Dam ore body begins about 300 metres below the surface and continues to a depth of more than 1 kilometre. The existing mining operation employs a sub-level open stope method of underground mining. The underground operation includes crushing stations, vertical ventilation shafts and an automated rail network, used to produce and transport crushed ore to the surface, where conveyors move the ore to the processing plant.

Olympic Dam has a fully integrated metallurgical complex with a grinding and concentrating circuit, a hydrometallurgical plant incorporating solvent extraction circuits for copper and uranium, a copper smelter, a copper refinery, including an electro-refinery and an electrowinning-refinery, and a recovery circuit for precious metals.

2 grinding circuits. Nominal milling capacity: 10.3 Mtpa. Flash furnace produces copper anodes, then refined to produce copper cathodes. Electrowon copper cathode and uranium oxide concentrate produced by leaching and solvent extracting flotation tailings. Gold cyanide leach circuit and gold room producing gold bullion.