IOCG, Geology, Characteristics, World Ocurrences, Hydrothermal mineral assemblages...
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)
• 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
