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TitleIOCG and affiliated deposits in tectonically active regions: impact on deposit types and structural attributes of ore systems
AuthorCorriveau, LORCID logo; Montreuil, J F; Potter, E GORCID logo
SourceSGTSG and SGSEG 2019 abstracts, Biennial Meeting of the Specialist Group for Tectonics and Structural Geology and the Specialist Group in Solid Earth Geophysics: convergence on the coast; by Glorie, S; Wise, T; Dutch, R; South Australia Department for Energy and Mining, Report Book 2019/00019, 2019 p. 2 Open Access logo Open Access
LinksOnline - En ligne (complete volume - volume complet)
Alt SeriesNatural Resources Canada, Contribution Series 20190281
PublisherGeological Society of Australia
MeetingSGTSG and SGSEG 2019: Biennial Meeting of the Specialist Group for Tectonics and Structural Geology and the Specialist Group in Solid Earth Geophysics; Port Lincoln, SA; AU; November 18-22, 2019
Mediapaper; on-line; digital
File formatpdf
Subjectseconomic geology; tectonics; structural geology; Science and Technology; Nature and Environment; mineral deposits; polymetallic ores; iron oxides; copper; gold; apatite; uranium; ore mineral genesis; mineralization; tectonic setting; tectonic evolution; structural controls; alteration; metasomatism; bedrock geology; structural features; fault zones; intrusions; fluid flow; fluid dynamics; metamorphism; deformation; zoning; thermal history
ProgramTargeted Geoscience Initiative (TGI-5) Uranium ore systems
Released2019 11 01
AbstractOre systems with polymetallic iron oxide copper-gold (IOCG), iron oxide-apatite (IOA), albitite-hosted uranium and affiliated deposits, including those of Canada and Australia, are characterized by a regular sequence of iron oxide and alkali-calcic alteration (IOAA) facies and breccia that defines the prograde metasomatic path of the systems. At the root of and across these systems, sodic metasomatism (facies 1) is regionally developed along tectonic and stratigraphic discontinuities, including fault zones, in the apical parts of and along intrusions, and in favourably reactive units. In areas of intense fluid circulation, the Na facies forms corridors of albitite that can extend several kilometres in strike. The preferential siting of albitite in discontinuities along which deformation tends to be partitioned, the residual porosity left in albitite by dissolution-reprecipitation, and their isotropic nature favour the formation of extensive breccia zones, fracture and fault networks, and damage zones. The enhanced permeability facilitates subsequent fluid flow and can serve as ground preparation for ore deposition. Facies 1 Na transitions into skarn (clinopyroxene/garnet), Na-Ca (albite-scapolite) and high-temperature Na-Ca-Fe (albite, amphibole, magnetite) alteration (facies 1-2) to zones of high-temperature Ca-Fe (amphibole, magnetite, apatite) alteration (facies 2). In carbonate-rich units, skarn forms early, and is replaced by the high-temperature Ca-Fe facies, hence the need to distinguish these two facies systematically. Facies 1 and 2 are the earliest and commonly deepest facies. They demarcate areas of interest at the regional scale and form the immediate host of iron oxide-apatite (IOA) deposits and some magnetite skarn bodies. Systems that evolve to high temperature K-Fe (magnetite-K-feldspar/biotite) alteration (facies 3), to K-skarn (clinopyroxene, garnet and K-feldspar) and K-felsite breccia (K-feldspar) (facies 4), and lower temperature K-Fe and Ca-Fe-Mg (sericite, K-feldspar, hematite, chlorite, carbonate) alteration (facies 5) can form polymetallic IOCG deposits that can include critical metal and uranium ores. IOA deposits hosted within systems that evolved to these latter facies commonly host REE that can be remobilized into REE ore-shoots during renewed magmatic or orogenic activity. Increasing intensity of facies 3, 4 and 5 is intimately associated with brecciation even outside of discrete fault zones. This contrasts with the systematic and structurally controlled brecciation of albitite that postdates sodic alteration. Copper sulphide precipitation is so systematic during facies 3 and 5 alteration that a genetic link is empirically clear even though sulphides precipitate in veins and as breccia infill. Low-temperature K±Al, Si, Ba or Fe assemblages (facies 6) form vein systems within, or epithermal lithocaps above, earlier facies and can lead to five-element vein and epithermal deposits. Synmetasomatic intrusive, tectonic and/or volcanic activity favours fluid mixing, cyclical build-up and telescoping of alteration facies. The tectonic or thermal telescoping of albitite within the field of facies 3 and 5 can lead to albitite-hosted U and Au-Co±U deposits. The prograde, retrograde, repeated or telescoped sequence of metasomatic reactions serve to map the metal pathways to ore and control metal precipitation, metal associations and the types of deposits formed in IOAA systems. The albitite corridors provide first order information on the geometry of the structures and discontinuities that formed the main fluid pathways, while the presence of facies 3 through 5 provides insights for defining and ranking their mineral favourability. Brittle to brittle-ductile deformation prevails across IOAA systems, which is a typical trait of many hydrothermal systems. However, ductile fabrics also form during the high temperature Ca-Fe alteration; their relationship should be carefully investigated and ductile fabrics not mistaken as evidence for orogenic overprints. The resulting paragenetic ore deposit model provides effective, predictive and globally applicable mapping and exploration tools for, and vectors to, IOCG and affiliated mineralization. In turn, the presence or absence of certain alteration facies at regional scale helps prognosticate the zonation of the system and possible fault zones that can offset certain components to a different crustal level.
Summary(Plain Language Summary, not published)
This abstract reviews some of the main outcomes of the Targeted Geoscience Initiative 5, project 1. Uranium systems, activity 2.1 Metal pathways and traps in polymetallic (U +/- Fe, Cu, Au, REE) metasomatic ore systems. It provides an overview of the metal pathways to a variety of deposit types within these large ore systems in tectonically active regions.

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