IOCG Deposits_general Characteristics

Iron Oxide Copper Gold (IOCG) Deposits: general characteristics Roberto Perez Xavier ([email protected])  Departamento de Geologia e Recursos Naturais  Instituto de Geociências –  Universidade Estadual de Campinas (UNICAMP)  Campinas Campin as (SP) (SP) – Brasil 

IOCGs: their diverse and common features Cu sulphides, with or without wi thout Au, Au, spatially associated with abundant (>10%) magnetite or hematite, relative to the surrounding host rocks. Fe oxides with low Ti contents ( 100 Mt resources) = intracratonic settings near the margins of Archean or Paleoproterozoic cratons (e.g. Olympic Dam – Gawler; Carajás – Amazon).

IOCGs: their diverse and common features

Strong structural control at crustal to lithospheric scale: Major IOCG provinces at margins of lithospheric blocks, controlled by transcrustal structures.

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Regional structures and IOCG systems

Courtesy of Sovereign Metals Limited.

IOCGs: Associated magma compositions Vast majority are spatially and/or broadly coeval with significant magmatic events.

Compositions are highly variable: Subalkaline to alkaline, mafic to felsic magmatism.

Barton (2014)

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IOCGs: Associated magma compositions No specific magma composition related to deposits  # from porphyry and skarn Cu-Au deposits Felsic magmatism volumetrically dominant  association with A-type and I-type batholithic granitoids.

Some IOCG deposits display no apparent connection to magmatism (e.g., Wernecke – NW Canada)

IOCGs: host rocks Range widely  in some terrains, particularly in arc settings, the vast majority of rocks are igneous-affiliated (plutonic, volcanic, and volcaniclastic). In others, there is an abundance of (meta) sedimentary lithotypes with fewer igneous components (e.g., Cloncurry, Tennant Creek - Australia). Strongly reduced (carbonaceous) host rocks are scarce (e.g., important at Cloncurry - Australia).

Evidence for evaporitic environments and related materials, whether contemporaneous or older, is documented in most IOCG regions  genetic significance remains controversial.

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STYLES OF MINERALIZATION • Heterolithic breccias are the most common host to IOCG deposits. • Replacement bodies and skarn-like also common but difficult to recognize. • Veins typically present but subordinate. • Stratiform ore bodies exist but are less common.

Olympic Dam (Australia)

Ernest Henry (Australia) magnetite dominated 

Hematite dominated 

Salobo (Carajás -Brazil)

Magnetite - hematite dominated 

Alvo 118 118 (Carajás (Carajás -Brazil) Alvo -Brazil)

magnetite dominated 

Structurally controlled breccia, veins and/or replacement ore styles.

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IOCGs: Magnetite and hematitedominated deposits K-spar-altered metavolcanic breccia with magnetite-pyrite-chalcopyrite matrix

Magnetitedominated ore, Ernest Henry, Cloncurry District, Australia Hematite-sericite-quartz-chalcopyrite-pyrite breccia

Carrapateena, S. Australia, hematitedominated ore

Hematite--related mineralization Hematite

Olympic Dam, Australia

Skirrow 2010 Geoscience Australia

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Matrix--supported breccias Matrix

Replacement and chemical corrosion of host rock abundant in deep ore.

Ernest Henry Cloncurry (Australia)

Infill dominated ore with some replacement

Shallow ore from Ernest Henry

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Mineralogy and Geochemistry 

• Fe (magnetite, hematite, biotite, chlorite, Feamphibole, pyrite, pyrrhotite, siderite) 

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• U (uraninite, coffinite, brannerite)

• REE (florencite, bastnaesite, allanite, apatite, gadolinite)  

• P (apatite, monazite)

• Ba (barite), F (fluorite), CO2 (carbonates)  

• Mo, Ag, Bi, Co, Se, Ni

Abundances depend upon host rocks

Uranium in IOCGs Gawler Craton Olympic Dam Oak Dam Prominent Hill Cloncurry, Australia Ernest Henry Monakoff Other Cloncurry deposits Carajas, Brazil Igarapé Bahia Salobo Chile Candelaria/Punta del Cobre

U (ppm) 425 ~400 103 50 (up to 980) ~100