page_title: Iron oxide copper gold ore deposits
section_title: Mineralogy and alteration
hierarchical_section_title: Iron oxide copper gold ore deposits / Mineralogy and alteration
caption_attribution_description: English: Chalcopyrite in hematised breccia, Prominent Hill, South Australia
context_page_description: Iron oxide copper gold ore deposits 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.
  These ore bodies range from around 10 million tonnes of contained ore, to 4,000 million tonnes or more, and have a grade of between 0.2% and 5% copper, with gold contents ranging from 0.1 to >3 grams per tonne. These ore bodies tend to express as cone-like, blanket-like breccia sheets within granitic margins, or as long ribbon-like breccia or massive iron oxide deposits within faults or shears.
  The tremendous size, relatively simple metallurgy and relatively high grade of IOCG deposits can produce extremely profitable mines.
  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.
  Some examples include the Olympic Dam, South Australia, and Candelaria, Chile, deposits.
context_section_description: 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.
  Alteration is a mixture of sodic-calcic (albite-epidote)  to potassic (K-feldspar) in style, and may vary from province to province based on host rocks and mineralising processes. Typically for large-scale hydrothermal systems, fluid types within IOCG systems show a mixed provenance of magmatic, metamorphic and often meteoric waters. Deposits may be vertically zoned from deeper albite-magnetite assemblages trending toward silica-K-feldspar-sericite in the upper portions of the deposits.
  Gangue minerals are typically some form of iron oxide mineral, classically hematite, but also magnetite within some other examples such as Ernest Henry and some Argentinian examples. This is typically associated with gangue sulfides of pyrite, with subordinate pyrrhotite and other base metal sulfides.
  Silicate gangue minerals include actinolite, pyroxene, tourmaline, epidote and chlorite, with apatite, allanite and other phosphate minerals common in some IOCG provinces (e.g.; North American examples), with carbonate-barite assemblages also reported. Where present, rare-earth metals tend to associate with phosphate minerals.
  When iron oxide species trend towards magnetite or crystalline massive hematite, IOCG deposits may be economic based on their iron oxide contents alone. Several examples of IOCG deposits (Wilcherry Hill, Cairn Hill, Kiruna) are iron ore deposits.
caption: Chalcopyrite in hematised breccia from Prominent Hill
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