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Maggie hays ni deposit / Geoffrey J. Heggie in Economic geology, Vol. 107 N° 5 (Août 2012) 

Public ISBD [article]  in Economic geology > Vol. 107 N° 5 (Août 2012) . - pp. 797-816 Titre : Maggie hays ni deposit : part 1. Stratigraphic controls on the style of komatiite emplacement in the 2.9 ga lake Johnston greenstone belt, Yilgarn Craton, western Australia Type de document : texte imprimé Auteurs : Geoffrey J. Heggie, Auteur ; Marco L. Fiorentini, Auteur ; Stephen J. Barnes, Auteur Année de publication : 2012 Article en page(s) : pp. 797-816 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : Komatiites  Ni  sulfide  ore  deposits  Transition  from  arc-  to  plume-dominated  magmatism Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : Komatiites occur in many Archean greenstone belts and host significant Ni sulfide ore deposits. Establishing the stratigraphy and the control that stratigraphy has on the emplacement and morphology of ultramafic magmatism is crucial in understanding Archean geodynamic environments and in targeting for Ni sulfide mineralization within these environments. The ~2.9 Ga Lake Johnston greenstone belt, in the southern portion of the Youanmi Terrane of Western Australia, contains komatiite flows and related subvolcanic intrusions, mafic volcanic rocks, felsic volcanic rocks, banded iron formation, and sedimentary rocks. The stratigraphic sequence is intact, preserving original sedimentary and igneous textures and contact relationships, despite being overturned and variably deformed. This study proposes that the lithostratigraphic succession and ultramafic intrusions identified within the Lake Johnston greenstone belt record a transition from arc- to plume-dominated magmatism, accompanied by the establishment of a banded iron formation-dominated sedimentary basin. It is proposed that the rheological contrast between the felsic volcanic unit and overlying banded iron formation acted as a stratigraphic barrier, trapping ascending ultramafic magmas. The stratigraphic barrier inhibited the upward ascent of ultramafic magma causing the development of a subvolcanic magma chamber. Magma trapped beneath the banded iron formation progressively inflated and spread out along the contact, until overpressuring breached the banded iron formation and magma escaped, forming the overlying extrusive komatiites. Both the geodynamic and lithologic transitions gave rise to favorable substrate rock units and an ideal tectonic setting for formation of komatiite-hosted Ni sulfide ores. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/5/797.abstract [article] Maggie hays ni deposit : part 1. Stratigraphic controls on the style of komatiite emplacement in the 2.9 ga lake Johnston greenstone belt, Yilgarn Craton, western Australia [texte imprimé] / Geoffrey J. Heggie, Auteur ; Marco L. Fiorentini, Auteur ; Stephen J. Barnes, Auteur . - 2012 . - pp. 797-816. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 5 (Août 2012) . - pp. 797-816 Mots-clés : Komatiites  Ni  sulfide  ore  deposits  Transition  from  arc-  to  plume-dominated  magmatism Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : Komatiites occur in many Archean greenstone belts and host significant Ni sulfide ore deposits. Establishing the stratigraphy and the control that stratigraphy has on the emplacement and morphology of ultramafic magmatism is crucial in understanding Archean geodynamic environments and in targeting for Ni sulfide mineralization within these environments. The ~2.9 Ga Lake Johnston greenstone belt, in the southern portion of the Youanmi Terrane of Western Australia, contains komatiite flows and related subvolcanic intrusions, mafic volcanic rocks, felsic volcanic rocks, banded iron formation, and sedimentary rocks. The stratigraphic sequence is intact, preserving original sedimentary and igneous textures and contact relationships, despite being overturned and variably deformed. This study proposes that the lithostratigraphic succession and ultramafic intrusions identified within the Lake Johnston greenstone belt record a transition from arc- to plume-dominated magmatism, accompanied by the establishment of a banded iron formation-dominated sedimentary basin. It is proposed that the rheological contrast between the felsic volcanic unit and overlying banded iron formation acted as a stratigraphic barrier, trapping ascending ultramafic magmas. The stratigraphic barrier inhibited the upward ascent of ultramafic magma causing the development of a subvolcanic magma chamber. Magma trapped beneath the banded iron formation progressively inflated and spread out along the contact, until overpressuring breached the banded iron formation and magma escaped, forming the overlying extrusive komatiites. Both the geodynamic and lithologic transitions gave rise to favorable substrate rock units and an ideal tectonic setting for formation of komatiite-hosted Ni sulfide ores. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/5/797.abstract

Maggie hays Ni deposit / Geoffrey J. Heggie in Economic geology, Vol. 107 N° 5 (Août 2012) 

Public ISBD [article]  in Economic geology > Vol. 107 N° 5 (Août 2012) . - p p. 817-833 Titre : Maggie hays Ni deposit : part 2. Nickel mineralization and the spatial distribution of PGE ore-forming signatures in the maggie hays Ni system, lake Johnston greenstone belt, western Australia Type de document : texte imprimé Auteurs : Geoffrey J. Heggie, Auteur ; Marco L. Fiorentini, Auteur ; Stephen J. Barnes, Auteur Année de publication : 2012 Article en page(s) : p p. 817-833 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : Ni  deposits;  Mineralization;  Ore  formation  Australia Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Maggie Hays Ni-Cu sulfide deposit, located in the ~2.9 Ga Lake Johnston greenstone belt of Western Australia, is hosted in a peridotitic to dunitic subvolcanic feeder that cuts felsic volcanic rocks and sedimentary units. Ore formation at Maggie Hays is attributed to assimilation of a sulfide-rich metasedimentary unit located above the subvolcanic feeder, which induced sulfide saturation within the feeder magmas. Massive and disseminated sulfides display chalcophile element fractionation trends indicative of in situ sulfide crystallization. Sulfide saturation and ore formation within the system generated enriched and depleted chalcophile elements ore-forming signatures in the silicate magmas. These ore-forming signatures are quantified as deviations from calculated background abundances and are spatially constrained to known mineralization within the system using a three-dimensional deposit model. Platinum group element (PGE) depletion and enrichment signatures occur approximately 300 m upstream from mineralization at the intersection of the feeder conduit and sulfide-rich sedimentary unit, interpreted to mark the point of sulfide saturation within the system. The magnitude of PGE enrichment increases with proximity to mineralization. PGE depletion signatures exhibit a more complex pattern, attributed to mixing between sulfide liquid, depleted silicate magma, and undepleted recharging magma. The study of the Maggie Hays mineralization and its host sequence demonstrates that enrichment and depletion of the highly chalcophile PGEs, relative to abundances expected in sulfide-undersaturated mantle-derived magmas, is a powerful exploration tool. Constraining the spatial distribution of enrichment and depletion signatures in the context of a robust volcanic, stratigraphic, magmatic, and metallogenic model allows for quantification of the size of Ni sulfide-forming systems and targeting of Fe-Ni-Cu mineralization in komatiite-bearing sequences. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/5/817.abstract [article] Maggie hays Ni deposit : part 2. Nickel mineralization and the spatial distribution of PGE ore-forming signatures in the maggie hays Ni system, lake Johnston greenstone belt, western Australia [texte imprimé] / Geoffrey J. Heggie, Auteur ; Marco L. Fiorentini, Auteur ; Stephen J. Barnes, Auteur . - 2012 . - p p. 817-833. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 5 (Août 2012) . - p p. 817-833 Mots-clés : Ni  deposits;  Mineralization;  Ore  formation  Australia Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Maggie Hays Ni-Cu sulfide deposit, located in the ~2.9 Ga Lake Johnston greenstone belt of Western Australia, is hosted in a peridotitic to dunitic subvolcanic feeder that cuts felsic volcanic rocks and sedimentary units. Ore formation at Maggie Hays is attributed to assimilation of a sulfide-rich metasedimentary unit located above the subvolcanic feeder, which induced sulfide saturation within the feeder magmas. Massive and disseminated sulfides display chalcophile element fractionation trends indicative of in situ sulfide crystallization. Sulfide saturation and ore formation within the system generated enriched and depleted chalcophile elements ore-forming signatures in the silicate magmas. These ore-forming signatures are quantified as deviations from calculated background abundances and are spatially constrained to known mineralization within the system using a three-dimensional deposit model. Platinum group element (PGE) depletion and enrichment signatures occur approximately 300 m upstream from mineralization at the intersection of the feeder conduit and sulfide-rich sedimentary unit, interpreted to mark the point of sulfide saturation within the system. The magnitude of PGE enrichment increases with proximity to mineralization. PGE depletion signatures exhibit a more complex pattern, attributed to mixing between sulfide liquid, depleted silicate magma, and undepleted recharging magma. The study of the Maggie Hays mineralization and its host sequence demonstrates that enrichment and depletion of the highly chalcophile PGEs, relative to abundances expected in sulfide-undersaturated mantle-derived magmas, is a powerful exploration tool. Constraining the spatial distribution of enrichment and depletion signatures in the context of a robust volcanic, stratigraphic, magmatic, and metallogenic model allows for quantification of the size of Ni sulfide-forming systems and targeting of Fe-Ni-Cu mineralization in komatiite-bearing sequences. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/5/817.abstract