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Chapitre D'ouvrage Année : 2022

Mineral systems with IOCG and affiliated deposits: Part 3 - Metal pathways and ore deposit model

Résumé

Metasomatic iron-oxide and alkali-calcic alteration systems form a wide range of iron-oxide copper-gold (IOCG), iron oxide apatite (IOA) and primary critical metal deposits. Economic resources include Ag, Au, Bi, Co, Cu, F, Fe, Mo, Nb, Ni, Pb, Pd, Pt, Re, rare earth elements (both heavy and light REE), U, V, W and Zn. Metal enrichments or byproducts include: Al, As, Ba, Cd, Rb, Sb, Sc, Se, Sn, Sr, Ta, Te, Th, Y and Zr. The ascent of voluminous saline to hypersaline fluid plumes in tectonically and magmatically active continental upper crust triggers these metasomatic systems. High disequilibrium between fluids and host rocks drives metasomatism and self-sustains the formation of consecutive iron-oxide and alkali-calcic alteration facies, each having distinct mineral assemblages and deposit types. This paper links alteration facies to the spectrum of deposit types using examples from the global districts examined in the companion Parts 1 and 2 papers and other contributions from this volume. The ascent of a metal-laden hypersaline fluid plume first triggers regional-scale albitization in the upper crust (Facies 1 with Na alteration and transitional Facies 1–2 with Na-Ca-Fe alteration). Barren albitite corridors develop above sub-volcanic intrusions and along fault zones, and skarn forms amongst albitite in the presence of carbonate rocks. These steps recharge the fluid plume with metals, volatiles and other elements through extensive decarbonation and dissolution of minerals from host rocks. Proximal to the thermal cores of the systems, metal-rich fluids outflowing from Facies 1 trigger the onset Facies 2 (high-temperature Ca-Fe) alteration under very high temperatures, reaching 800 to 900°C in the presence of coeval intrusions. Iron skarn (e.g. Middle-Lower Yangtze River Metallogenic Belt in China), IOA deposits (e.g. Southeast Missouri district, US) and their Fe-REE ± P, F, Nb or Fe-Ni variants also form at this stage, including REE ores formed through subsequent remobilization of primary REE endowment (e.g. Josette REE deposit, Québec). Crosscutting relationships between iron mineralization and albitite indicate that albitite precipitates first and is not linked to magnetite precipitation (e.g. Great Bear magmatic zone in Canada and the Middle-Lower Yangtze River Metallogenic Belt in China). Fluids outflowing from Facies 2 form a transitional Facies 2–3 HT Ca-K-Fe alteration. Precipitation of Co, Bi, Au (± Cu, Ni) may form cobalt-bismuth deposits rich in iron silicates, iron sulphides or iron oxides. Tungsten, initially deposited in earlier skarn, can be remobilized to form additional mineralized zones in which Sb, Se, and Te are potential byproducts (e.g. NICO deposit in Canada). In most systems, Facies 2 directly evolves to Facies 3 (high-temperature K-Fe), which marks the onset of extensive brecciation and formation of magnetite-group IOCG deposits (Ernest Henry copper-gold deposit in Australia, Sue Dianne Cu-Au-Ag deposit in Canada). Palladium and platinum are enriched in some biotite-rich magnetite-group IOCG deposits (Dahongshan Fe-Cu-Au-Ag-Co-Pd-Pt deposit in China). Facies 4 alteration consists of locally mineralized K-skarn and barren K-felsite breccia (commonly as haloes around IOCG breccias or within K-skarn). These alteration types may subsequently host polymetallic deposits (Punt Hill in Australia) or form components of magnetite-to-hematite group IOCG deposits (e.g. Candelaria Cu-Au-Ag deposit, Chile). Facies 5 alteration zones (low-temperature K-Fe and Ca-Mg-Fe and their Ca-F-Fe and Si-Fe ± Ba variants) host a wide range of polymetallic deposits, including 1) hematite-group IOCG deposits with Ag, Au, Cu and U resources and LREE mineralization (e.g. Olympic Dam Cu-U-Au-Ag deposit in Australia), and 2) an emerging group of iron oxide- to iron-poor deposits, including Au-Co, Mo-Re ± Cu ± Au and Au-Pb-Zn (e.g. Merlin, Mount Dore and Tick Hill deposits in Australia; Scadding deposit in Canada). Facies 6 (K, Si, Al) comprises epithermal mineralization and polymetallic vein systems (including late-stage ones). Syn-metasomatic magma emplacement, tectonic and volcanic activity, and mixing of external fluids with the main fluid plume can induce a cyclical build-up or telescoping of alteration facies as well as retrogression of higher temperature mineral assemblages. The overprinting of albitite corridors by Facies 3 and Facies 5 fluids may generate albitite-hosted U and Au-Co ± U deposits (e.g. Southern Breccia albitite corridor in Canada; Valhalla in Australia). Reactivation of systems via renewed fluid circulation driven by orogenesis, magmatism or burial periodically remobilize early metal endowments into mineralized veins and breccias; five element (Ag, As, Bi, Co, Ni, ± U) veins are an example of such processes. The paragenetic ore system model presented herein provides a framework to classify the variety of ore deposits encountered in these systems while providing effective and predictive mapping and exploration tools for IOCG and affiliated deposits, including their primary critical metal deposits. It also enables to better frame alteration facies and mineralization that are low in iron oxides but rich in iron silicates, iron carbonates and iron sulphides as well as those poor in iron within metasomatic iron and alkali-calcic (MIAC) systems.

Domaines

Géochimie
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Dates et versions

hal-04417964 , version 1 (25-01-2024)

Identifiants

  • HAL Id : hal-04417964 , version 1

Citer

Louise Corriveau, Jean-François F Montreuil, Eric G Potter, Olivier Blein, Anthony A de Toni. Mineral systems with IOCG and affiliated deposits: Part 3 - Metal pathways and ore deposit model. Corriveau, L.; Potter, E.G.; Mumin, A.H. Mineral systems with iron oxide copper-gold (IOCG) and affiliated deposits, Special Paper 52, Geological Association of Canada, pp.205-245, 2022. ⟨hal-04417964⟩

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