Authors / CoAuthors
Skirrow, R.G.
Abstract
Deposits of the iron oxide copper-gold (IOCG) family are diverse in composition, ranging from relatively reduced magnetite-rich to hematite-dominated oxidized styles that may contain major uranium resources. These variations reflect an interplay between multiple hydrothermal fluids with different properties and the varied host lithological settings, each of which ultimately relate to differences in the tectonic evolution of IOCG provinces. - Early Mesoproterozoic and late Paleoproterozoic terranes of southern Australia host the 7.7 Bt Olympic Dam Cu-Au-U deposit as well as numerous lesser known IOCG±U deposits and prospects. They represent the spectrum of magnetite- to hematite-dominated IOCG deposit styles. Magnetite-rich styles of IOCG alteration and mineralization occur in the eastern Gawler Craton and western Curnamona Province. These styles developed at mesozonal to epizonal crustal levels between ~1610 Ma and ~1575 Ma when the terranes were subject to low pressure - high temperature metamorphism and compressional deformation. Magnetite-rich alteration was spatially and temporally associated with high-temperature A-type granitoids of the Hiltaba Suite and with mafic magmas, although the magnetite-forming fluids show major chemical and isotopic contributions from non-magmatic sources. Magnetite-rich alteration varies between IOCG districts and includes biotite-albite or albite-clinopyroxene-actinolite or K-feldspar. Generally minor quantities of chalcopyrite, gold, pyrite and rare pyrrhotite occur in magnetite-rich alteration. - Higher grade IOCG ±U mineralization is associated with hematite-rich alteration (± sericite, chlorite, carbonate) which generally overprinted magnetite-rich assemblages and formed at epizonal crustal levels prior to ~1575 Ma. In the Olympic Dam district uplift and exhumation inferred between ~1595 Ma and ~1575 Ma resulted in superposition of hematitic ±U mineralization on magnetite-rich alteration. Brittle deformation structures and the temporal and broad spatial association of hematitic alteration with bimodal volcanism and alkaline mafic magmatism are consistent with an extensional setting, although supporting data are not yet comprehensive. - The switch from syn-orogenic mesozonal magnetite-rich IOCG formation to post-orogenic epizonal hematite-rich IOCG mineralization is suggested to reflect a change from compressional to extensional tectonism at ~1595-1590 Ma. Contrary to propositions of an 'anorogenic' setting for the Olympic Dam deposit, back-arc settings have been advocated recently. However, several features including the composition of the Hiltaba Suite and co-magmatic volcanics are inconsistent with typical backarc settings. Alternatively, intracontinental orogenesis was closely followed by extension and uplift. A possible driver was convective removal or delamination of thickened lithospheric mantle, triggered by convergence at distant plate margins. This model reconciles magma compositions and timing of volcanism with a switch from compression to extension.
Product Type
nonGeographicDataset
eCat Id
65621
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Custodian
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Cnr Jerrabomberra Ave and Hindmarsh Dr GPO Box 378
Canberra
ACT
2601
Australia
Keywords
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- External PublicationAbstract
- ( Theme )
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- alteration
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- economic geology
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- metallogenesis
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- mineral deposits
- ( Theme )
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- mineral exploration
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- AU-SA
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Earth Sciences
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- Published_Internal
Publication Date
2008-01-01T00:00:00
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geoscientificInformation
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Extents
[-35.0, -28.0, 132.0, 141.0]
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