Iron oxide copper gold ore deposits

Iron oxide copper gold ore deposits (IOCG) are important and highly valuable concentrations of copper, gold and uranium ores hosted within iron oxide dominant gangue assemblages which share a common genetic origin.

[4] Iron oxide copper-gold deposits are also often associated with other valuable trace elements such as uranium, bismuth and rare-earth metals, although these accessories are typically subordinate to copper and gold in economic terms.

Iron oxide copper gold (IOCG) deposits are considered to be metasomatic expressions of large crustal-scale alteration events driven by intrusive activity.

[8] IOCG deposits are usually associated with distal zones of particular large-scale igneous events, for instance a particular Suite or Supersuite of granites, intermediate mafic intrusives of a particular age.

IOCG mineralisation may accumulate within metasomatised wall rocks, within brecciated maar or caldera structures, faults or shears, or the aureole of an intrusive event (possibly as a skarn) and is typically accompanied by a substantial enrichment in iron oxide minerals (hematite, magnetite).

Although not exclusively Proterozoic, within Australia and South America a majority of IOCG deposits are recognised to be within Neoproterozoic to Mesoproterozoic basement.

The driving factor for the fluids movement in the upper crust is the present paleogeothermal gradients, as well as regional hydrothermal systems responsible for the alteration within these deposits.

[4] Ore minerals in IOCG deposits are typically copper-iron sulfide chalcopyrite and gangue pyrite, forming 10–15% of the rock mass.

Supergene profiles can be developed above weathered examples of IOCG deposits, as exemplified by the Sossego deposit, Para State, Brazil, where typical oxidised copper minerals are present, e.g.; malachite, cuprite, native copper and minor amounts of digenite and chalcocite.

IOCG ore deposits containing economic quantities (highly profitable) of both copper and gold originate from the Precambrian.

In better exposed terranes, prospecting for alteration assemblages and skarns, in concert with geochemical exploration is also likely to yield success.