Dépouillements

A special issue on archean magmatism, volcanism, and ore deposits / Patrick Mercier-Langevin in Economic geology, Vol. 107 N° 5 (Août 2012) 

Public ISBD [article]  in Economic geology > Vol. 107 N° 5 (Août 2012) . - pp. 745-753 Titre : A special issue on archean magmatism, volcanism, and ore deposits : part 1. komatiite-associated ni-cu-(PGE) sulfide and greenstone-hosted au deposits Type de document : texte imprimé Auteurs : Patrick Mercier-Langevin, Auteur ; Michel G. Houlé, Auteur ; Benoît Dubé, Auteur Année de publication : 2012 Article en page(s) : pp. 745-753 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : Archean  magmatism  Volcanism  Ore  deposits Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Archean, which represents more than a third of Earth’s history, contains some of the largest and richest ore deposits of the world. Numerous cratons of variable size and age have been mapped (Fig. 1) and others are still being discovered or delineated largely due to the widespread use of high-precision U-Pb geochronology. One of the specific characteristics of Archean cratons is the coexistence and juxtaposition of different and major styles of base and precious metals deposits formed at different times and crustal levels (Poulsen et al., 2000; Groves et al., 2005a; Robert et al., 2005). DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/5/745.extract [article] A special issue on archean magmatism, volcanism, and ore deposits : part 1. komatiite-associated ni-cu-(PGE) sulfide and greenstone-hosted au deposits [texte imprimé] / Patrick Mercier-Langevin, Auteur ; Michel G. Houlé, Auteur ; Benoît Dubé, Auteur . - 2012 . - pp. 745-753. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 5 (Août 2012) . - pp. 745-753 Mots-clés : Archean  magmatism  Volcanism  Ore  deposits Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Archean, which represents more than a third of Earth’s history, contains some of the largest and richest ore deposits of the world. Numerous cratons of variable size and age have been mapped (Fig. 1) and others are still being discovered or delineated largely due to the widespread use of high-precision U-Pb geochronology. One of the specific characteristics of Archean cratons is the coexistence and juxtaposition of different and major styles of base and precious metals deposits formed at different times and crustal levels (Poulsen et al., 2000; Groves et al., 2005a; Robert et al., 2005). DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/5/745.extract

Komatiite magmas and sulfide nickel deposits / Stephen J. Barnes in Economic geology, Vol. 107 N° 5 (Août 2012) 

Public ISBD [article]  in Economic geology > Vol. 107 N° 5 (Août 2012) . - pp. 755-780 Titre : Komatiite magmas and sulfide nickel deposits : a comparison of variably endowed archean terranes Type de document : texte imprimé Auteurs : Stephen J. Barnes, Auteur ; Marco L. Fiorentini, Auteur Année de publication : 2012 Article en page(s) : pp. 755-780 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : Komatiites  Archean  granite-greenstone  terranes  Host  rocks  Ore  depsits  Nickel  deposits Résumé : Komatiites are found in most Archean granite-greenstone terranes, but sulfide Ni mineralization associated with these rocks has a very biased distribution. The global endowment of sulfides Ni in Archean komatiites is overwhelmingly dominated by the Kalgoorlie terrane of the Eastern Goldfields Superterrane in the Yilgarn Craton. The question of whether the Kalgoorlie terrane komatiites possess any exceptional attributes which could explain this bias is addressed through an exhaustive compilation of geochemical data from this terrane and a number of others: the southeastern Youanmi terrane of the Yilgarn Craton; the eastern terranes of the Eastern Goldfields superterrane (Kurnalpi, Burtville and others); and the Abitibi greenstone belt of the Superior province. High MgO komatiite magmas, with MgO in the 25 to 30% range, are found in all the terranes sampled, but the proportion of these compositions appears to be higher in the Kalgoorlie terrane, and the abundance of strongly adcumulate olivine cumulates is much higher. Crustal contamination is apparently more extensive and advanced in the Kalgoorlie terrane than in all the others, but there is no systematic difference in the lithophile trace element (LILE) characteristics and degree of source depletion evident in the most primitive magmas from all the terranes. Consideration of variable-valency transition metals V and Cr indicates there are no systematic variations in oxidation state between the terranes and komatiites uniformly evolved close to the quartz-fayalite-magnetite buffer. Platinum-group element (PGE) variations imply that komatiites in all the terranes were emplaced sulfide undersaturated and were derived from sources with remarkably similar PGE contents. There is no evidence that the Kalgoorlie terrane magmas were in any way exceptional. The Forrestania and Lake Johnston Belts of the Youanmi terrane include the only known examples of Al-depleted komatiites hosting significant Ni sulfide resources, and they are also the only komatiites of this type that form adcumulate dunite bodies. The presence of adcumulate dunites, formed by high magma fluxes in central conduits, is the common feature between these belts and the Kalgoorlie terrane. Coupled with evidence for higher degrees of contamination in the Kalgoorlie terrane, and the availability of accessible crustal S sources, it appears that magma flux, rather than primitive magma composition, is the critical factor, and that craton-scale deep lithospheric structure is the ultimate control on the rate of magma supply between mantle source and crustal emplacement site. The Kalgoorlie terrane komatiites were emplaced at exceptionally high rates, giving rise to well-developed long-lived magma conduits, either lava tubes or subvolcanic channelized sills, which are interpreted to be the essential condition for forming large deposits. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/5/755.short [article] Komatiite magmas and sulfide nickel deposits : a comparison of variably endowed archean terranes [texte imprimé] / Stephen J. Barnes, Auteur ; Marco L. Fiorentini, Auteur . - 2012 . - pp. 755-780. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 5 (Août 2012) . - pp. 755-780 Mots-clés : Komatiites  Archean  granite-greenstone  terranes  Host  rocks  Ore  depsits  Nickel  deposits Résumé : Komatiites are found in most Archean granite-greenstone terranes, but sulfide Ni mineralization associated with these rocks has a very biased distribution. The global endowment of sulfides Ni in Archean komatiites is overwhelmingly dominated by the Kalgoorlie terrane of the Eastern Goldfields Superterrane in the Yilgarn Craton. The question of whether the Kalgoorlie terrane komatiites possess any exceptional attributes which could explain this bias is addressed through an exhaustive compilation of geochemical data from this terrane and a number of others: the southeastern Youanmi terrane of the Yilgarn Craton; the eastern terranes of the Eastern Goldfields superterrane (Kurnalpi, Burtville and others); and the Abitibi greenstone belt of the Superior province. High MgO komatiite magmas, with MgO in the 25 to 30% range, are found in all the terranes sampled, but the proportion of these compositions appears to be higher in the Kalgoorlie terrane, and the abundance of strongly adcumulate olivine cumulates is much higher. Crustal contamination is apparently more extensive and advanced in the Kalgoorlie terrane than in all the others, but there is no systematic difference in the lithophile trace element (LILE) characteristics and degree of source depletion evident in the most primitive magmas from all the terranes. Consideration of variable-valency transition metals V and Cr indicates there are no systematic variations in oxidation state between the terranes and komatiites uniformly evolved close to the quartz-fayalite-magnetite buffer. Platinum-group element (PGE) variations imply that komatiites in all the terranes were emplaced sulfide undersaturated and were derived from sources with remarkably similar PGE contents. There is no evidence that the Kalgoorlie terrane magmas were in any way exceptional. The Forrestania and Lake Johnston Belts of the Youanmi terrane include the only known examples of Al-depleted komatiites hosting significant Ni sulfide resources, and they are also the only komatiites of this type that form adcumulate dunite bodies. The presence of adcumulate dunites, formed by high magma fluxes in central conduits, is the common feature between these belts and the Kalgoorlie terrane. Coupled with evidence for higher degrees of contamination in the Kalgoorlie terrane, and the availability of accessible crustal S sources, it appears that magma flux, rather than primitive magma composition, is the critical factor, and that craton-scale deep lithospheric structure is the ultimate control on the rate of magma supply between mantle source and crustal emplacement site. The Kalgoorlie terrane komatiites were emplaced at exceptionally high rates, giving rise to well-developed long-lived magma conduits, either lava tubes or subvolcanic channelized sills, which are interpreted to be the essential condition for forming large deposits. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/5/755.short

District to camp controls on the genesis of komatiite-hosted nickel sulfide deposits, agnew-wiluna greenstone belt, western Australia / Marco Fiorentini in Economic geology, Vol. 107 N° 5 (Août 2012) 

Public ISBD [article]  in Economic geology > Vol. 107 N° 5 (Août 2012) . - p p. 781-796 Titre : District to camp controls on the genesis of komatiite-hosted nickel sulfide deposits, agnew-wiluna greenstone belt, western Australia : insights from the multiple sulfur isotopes Type de document : texte imprimé Auteurs : Marco Fiorentini, Auteur ; Steve Beresford, Auteur ; Mark Barley, Auteur Année de publication : 2012 Article en page(s) : p p. 781-796 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : Komatite-hosted  Ni-Cu-(PGE)  deposits  Ore  genetic  model  Volcanic  facies Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Agnew-Wiluna greenstone belt of Western Australia is the largest komatiite-hosted nickel sulfide belt in the world and contains two world-class Ni-Cu-(PGE) deposits and a host of smaller deposits. This study focuses on the broader scale geology of this greenstone belt in order to understand the key controls on the genesis of the komatiite-hosted Ni-Cu-(PGE) deposits, with specific focus on camp to district controls. We apply multiple sulfur isotopes to this geologic framework and conclude not only that the addition of crustal sulfur is a prerequisite for ore genesis in komatiite systems, but above all that the sulfur required to generate world-class deposits is most likely derived from barren volcanic massive sulfide lenses, which are spatially and genetically associated with felsic volcanic and volcaniclastic sequences that were emplaced coevally with large komatiitic sills and channelized lava flows. Multiple sulfur isotope data can be utilized in exploration at the deposit to district scales. At the deposit scale, the spatial pattern of mass-independent S isotope values (Δ33S) provides crucial insight into the identification of proximal high-grade and high-tenor ores in mineralized systems. In fact, sulfur data reflect the assimilation process that occurred upon komatiite emplacement, whereby hot turbulent magma thermomechanically eroded and assimilated exhalative sulfides spatially located close to vent with negative to near zero Δ33S values, whereas less turbulent flows interacted with distal sulfidic shales having Δ33S values above 0 per mil. Accordingly, the spatial variation of multiple sulfur isotope values in magmatic sulfides and associated host rocks may be utilized as a vector towards high-grade ores of poorly known systems. At the district scale, rather than ascertaining what controls the distribution of komatiite-hosted Ni-Cu-(PGE) deposits, the appropriate question to ask is what controls the distribution of country rock sulfides, considering that exhalative sulfides may be crucial to ore genesis in komatiite systems. We propose that felsic lava domes unambiguously mark their vents and can be directly mapped or inferred from gravity data. This work provides the first step in identifying district-scale control on komatiite-hosted Ni-Cu-(PGE) deposits. This is the scale that has high impact on exploration for new komatiite-hosted nickel sulfide belts globally. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/5/781.short [article] District to camp controls on the genesis of komatiite-hosted nickel sulfide deposits, agnew-wiluna greenstone belt, western Australia : insights from the multiple sulfur isotopes [texte imprimé] / Marco Fiorentini, Auteur ; Steve Beresford, Auteur ; Mark Barley, Auteur . - 2012 . - p p. 781-796. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 5 (Août 2012) . - p p. 781-796 Mots-clés : Komatite-hosted  Ni-Cu-(PGE)  deposits  Ore  genetic  model  Volcanic  facies Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Agnew-Wiluna greenstone belt of Western Australia is the largest komatiite-hosted nickel sulfide belt in the world and contains two world-class Ni-Cu-(PGE) deposits and a host of smaller deposits. This study focuses on the broader scale geology of this greenstone belt in order to understand the key controls on the genesis of the komatiite-hosted Ni-Cu-(PGE) deposits, with specific focus on camp to district controls. We apply multiple sulfur isotopes to this geologic framework and conclude not only that the addition of crustal sulfur is a prerequisite for ore genesis in komatiite systems, but above all that the sulfur required to generate world-class deposits is most likely derived from barren volcanic massive sulfide lenses, which are spatially and genetically associated with felsic volcanic and volcaniclastic sequences that were emplaced coevally with large komatiitic sills and channelized lava flows. Multiple sulfur isotope data can be utilized in exploration at the deposit to district scales. At the deposit scale, the spatial pattern of mass-independent S isotope values (Δ33S) provides crucial insight into the identification of proximal high-grade and high-tenor ores in mineralized systems. In fact, sulfur data reflect the assimilation process that occurred upon komatiite emplacement, whereby hot turbulent magma thermomechanically eroded and assimilated exhalative sulfides spatially located close to vent with negative to near zero Δ33S values, whereas less turbulent flows interacted with distal sulfidic shales having Δ33S values above 0 per mil. Accordingly, the spatial variation of multiple sulfur isotope values in magmatic sulfides and associated host rocks may be utilized as a vector towards high-grade ores of poorly known systems. At the district scale, rather than ascertaining what controls the distribution of komatiite-hosted Ni-Cu-(PGE) deposits, the appropriate question to ask is what controls the distribution of country rock sulfides, considering that exhalative sulfides may be crucial to ore genesis in komatiite systems. We propose that felsic lava domes unambiguously mark their vents and can be directly mapped or inferred from gravity data. This work provides the first step in identifying district-scale control on komatiite-hosted Ni-Cu-(PGE) deposits. This is the scale that has high impact on exploration for new komatiite-hosted nickel sulfide belts globally. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/5/781.short

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

Physical volcanology and genesis of komatiite-associated Ni-Cu-(PGE) mineralization in the C zone, bannockburn township, Ontario / V. Taranovic in Economic geology, Vol. 107 N° 5 (Août 2012) 

Public ISBD [article]  in Economic geology > Vol. 107 N° 5 (Août 2012) . - pp. 835-857 Titre : Physical volcanology and genesis of komatiite-associated Ni-Cu-(PGE) mineralization in the C zone, bannockburn township, Ontario Type de document : texte imprimé Auteurs : V. Taranovic, Auteur ; C. M. Lesher, Auteur ; M. G. Houlé, Auteur Année de publication : 2012 Article en page(s) : pp. 835-857 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : Komatiite;  Ni-Cu-(PGE)  deposits;  volcanology;  Ontario Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The C zone, located in Bannockburn Township approximately 30 km W of Matachewan, Ontario, is one of several komatiite-associated Ni-Cu-(PGE) deposits within the 2710 to 2704 Ma Tisdale volcanic episode of the Abitibi greenstone belt. The sulfides, host rocks, and country rocks are superbly exposed over a strike length of 150 m in glacially polished and hydraulically stripped outcrops and have been intersected in 53 diamond drill holes. The mineralized zone is up to 2.5 m thick and comprises (from base to top) massive to semimassive, net-textured, and disseminated sulfide facies characterized by a pyrrhotite-pentlandite-chalcopyrite-magnetite assemblage. The massive sulfide zone contains an anastomosing network of dextral and sinistral shears that are oriented broadly subparallel to the contacts with the footwall dacite and hanging-wall andesite. Some contacts with underlying dacites are sheared, but others are scalloped and bordered by skeletal-euhedral Fe-rich chromites and appear to be primary magmatic features. The footwall rocks grade from chloritized dacites within 20 to 30 cm of the contact into massive and brecciated plagioclase-phyric dacites farther away from the contact. The host unit is up to 8 m thick and comprises massive olivine porphyritic and ortho- to mesocumulate komatiite in the eastern and central parts and a texturally heterolithic komatiite breccia in the western part. The breccia is composed of subrounded to subangular clasts 1 to 30 cm in length that exhibit mainly fine (<2 mm) olivine porphyritic or fine (<1 cm) random olivine spinifex textures, within a fine-grained, locally spinifex-textured ultramafic matrix. The absence of evidence for a pyroclastic origin and the presence of a spinifex-textured matrix suggest that the breccia is autoclastic. The hanging-wall rocks are barren differentiated (spinifex/cumulate) komatiite flows (total thickness of the lithostratigraphic package ~22 m) and variolitic pillowed andesites (total thickness >80 m). The komatiitic sequence at the C zone is much thinner than most other sequences within the Tisdale volcanic episode and is oriented oblique to the NW trend of the regional stratigraphy, but all contacts appear conformable and all younging indicators are uniformly to the SSE, suggesting that the local sequence is intact. The C zone is similar in many respects to other type I (Kambalda-type) komatiite-associated Ni-Cu-(PGE) deposits in the Abitibi greenstone belt but differs by not being confined within a well-developed footwall embayment and in being partly hosted by komatiitic breccias. The C zone Ni-Cu-(PGE) mineralization appears to be hosted in the eastern part of the stripped exposure by a thin lava pathway and in the western part by breccias formed via lateral breakout and roof collapse. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/5/835.short [article] Physical volcanology and genesis of komatiite-associated Ni-Cu-(PGE) mineralization in the C zone, bannockburn township, Ontario [texte imprimé] / V. Taranovic, Auteur ; C. M. Lesher, Auteur ; M. G. Houlé, Auteur . - 2012 . - pp. 835-857. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 5 (Août 2012) . - pp. 835-857 Mots-clés : Komatiite;  Ni-Cu-(PGE)  deposits;  volcanology;  Ontario Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The C zone, located in Bannockburn Township approximately 30 km W of Matachewan, Ontario, is one of several komatiite-associated Ni-Cu-(PGE) deposits within the 2710 to 2704 Ma Tisdale volcanic episode of the Abitibi greenstone belt. The sulfides, host rocks, and country rocks are superbly exposed over a strike length of 150 m in glacially polished and hydraulically stripped outcrops and have been intersected in 53 diamond drill holes. The mineralized zone is up to 2.5 m thick and comprises (from base to top) massive to semimassive, net-textured, and disseminated sulfide facies characterized by a pyrrhotite-pentlandite-chalcopyrite-magnetite assemblage. The massive sulfide zone contains an anastomosing network of dextral and sinistral shears that are oriented broadly subparallel to the contacts with the footwall dacite and hanging-wall andesite. Some contacts with underlying dacites are sheared, but others are scalloped and bordered by skeletal-euhedral Fe-rich chromites and appear to be primary magmatic features. The footwall rocks grade from chloritized dacites within 20 to 30 cm of the contact into massive and brecciated plagioclase-phyric dacites farther away from the contact. The host unit is up to 8 m thick and comprises massive olivine porphyritic and ortho- to mesocumulate komatiite in the eastern and central parts and a texturally heterolithic komatiite breccia in the western part. The breccia is composed of subrounded to subangular clasts 1 to 30 cm in length that exhibit mainly fine (<2 mm) olivine porphyritic or fine (<1 cm) random olivine spinifex textures, within a fine-grained, locally spinifex-textured ultramafic matrix. The absence of evidence for a pyroclastic origin and the presence of a spinifex-textured matrix suggest that the breccia is autoclastic. The hanging-wall rocks are barren differentiated (spinifex/cumulate) komatiite flows (total thickness of the lithostratigraphic package ~22 m) and variolitic pillowed andesites (total thickness >80 m). The komatiitic sequence at the C zone is much thinner than most other sequences within the Tisdale volcanic episode and is oriented oblique to the NW trend of the regional stratigraphy, but all contacts appear conformable and all younging indicators are uniformly to the SSE, suggesting that the local sequence is intact. The C zone is similar in many respects to other type I (Kambalda-type) komatiite-associated Ni-Cu-(PGE) deposits in the Abitibi greenstone belt but differs by not being confined within a well-developed footwall embayment and in being partly hosted by komatiitic breccias. The C zone Ni-Cu-(PGE) mineralization appears to be hosted in the eastern part of the stripped exposure by a thin lava pathway and in the western part by breccias formed via lateral breakout and roof collapse. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/5/835.short

Postmagmatic variability in ore composition and mineralogy in the T4 and T5 ore shoots at the high-grade flying fox Ni-Cu-PGE deposit, yilgarn craton, western Australia / Jane E. Collins in Economic geology, Vol. 107 N° 5 (Août 2012) 

Public ISBD [article]  in Economic geology > Vol. 107 N° 5 (Août 2012) . - pp. 859-879 Titre : Postmagmatic variability in ore composition and mineralogy in the T4 and T5 ore shoots at the high-grade flying fox Ni-Cu-PGE deposit, yilgarn craton, western Australia Type de document : texte imprimé Auteurs : Jane E. Collins, Auteur ; Stephen J. Barnes, Auteur ; Steffen G. Hagemann, Auteur Année de publication : 2012 Article en page(s) : pp. 859-879 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : PGE;  high-grade  Flying  Fox  komatiite-hosted  Ni  sulfide  deposit;  Mineralogy;  Australia Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The high-grade Flying Fox komatiite-hosted Ni sulfide deposit, located in the Forrestania greenstone belt of the Archean Yilgarn Craton, Western Australia, is hosted in a deformed and metamorphosed volcano-metasedimentary succession. Postmineralization events have sheared and modified the texture and composition of the original massive sulfide ore, creating up to 11 distinct ore shoots including massive, stringer/vein, and breccia sulfides composed of pyrrhotite, pentlandite, chalcopyrite, and variable abundances of pyrite ranging up to 40 vol %. Nickel and platinum group elements (PGE) tenor variations were investigated in two ore shoots, T4 and T5. All mineralization styles show considerable variability in Ni tenor. PGEs show strong linear correlations between Ir, Os, Ru, and Rh, but poor correlation between Pt, Pd, and Cu. The normalized molar proportions of Fe, Ni, and S, projected into the Fe-Ni-S ternary system, show a distinct linear trend of pyrite addition to a typical primary magmatic composition and no correlation with mineralization style. The high pyrite content present throughout the Flying Fox ore is also associated with elevated Cu and As contents and is interpreted to be primarily due to the addition of pyrite from circulating Fe-, S-, Cu-, and As-enriched fluids creating pyrite-pentlandite intergrowths. Localized mechanical segregation of pyrite, sulfidation of pyrrhotite to pyrite, and oxidation of pyrrhotite to pyrite + magnetite has also contributed to these increased pyrite contents, although to a lesser extent. The addition and segregation of pyrite has diluted the Ni tenor, with no evidence to suggest chemical mobilization of Ni. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/5/859.short [article] Postmagmatic variability in ore composition and mineralogy in the T4 and T5 ore shoots at the high-grade flying fox Ni-Cu-PGE deposit, yilgarn craton, western Australia [texte imprimé] / Jane E. Collins, Auteur ; Stephen J. Barnes, Auteur ; Steffen G. Hagemann, Auteur . - 2012 . - pp. 859-879. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 5 (Août 2012) . - pp. 859-879 Mots-clés : PGE;  high-grade  Flying  Fox  komatiite-hosted  Ni  sulfide  deposit;  Mineralogy;  Australia Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The high-grade Flying Fox komatiite-hosted Ni sulfide deposit, located in the Forrestania greenstone belt of the Archean Yilgarn Craton, Western Australia, is hosted in a deformed and metamorphosed volcano-metasedimentary succession. Postmineralization events have sheared and modified the texture and composition of the original massive sulfide ore, creating up to 11 distinct ore shoots including massive, stringer/vein, and breccia sulfides composed of pyrrhotite, pentlandite, chalcopyrite, and variable abundances of pyrite ranging up to 40 vol %. Nickel and platinum group elements (PGE) tenor variations were investigated in two ore shoots, T4 and T5. All mineralization styles show considerable variability in Ni tenor. PGEs show strong linear correlations between Ir, Os, Ru, and Rh, but poor correlation between Pt, Pd, and Cu. The normalized molar proportions of Fe, Ni, and S, projected into the Fe-Ni-S ternary system, show a distinct linear trend of pyrite addition to a typical primary magmatic composition and no correlation with mineralization style. The high pyrite content present throughout the Flying Fox ore is also associated with elevated Cu and As contents and is interpreted to be primarily due to the addition of pyrite from circulating Fe-, S-, Cu-, and As-enriched fluids creating pyrite-pentlandite intergrowths. Localized mechanical segregation of pyrite, sulfidation of pyrrhotite to pyrite, and oxidation of pyrrhotite to pyrite + magnetite has also contributed to these increased pyrite contents, although to a lesser extent. The addition and segregation of pyrite has diluted the Ni tenor, with no evidence to suggest chemical mobilization of Ni. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/5/859.short

Mesoarchean epithermal gold mineralization preserved at upper amphibolite-facies grade, Qussuk, southern west Greenland / Adam A. Garde in Economic geology, Vol. 107 N° 5 (Août 2012) 

Public ISBD [article]  in Economic geology > Vol. 107 N° 5 (Août 2012) . - pp. 881-908 Titre : Mesoarchean epithermal gold mineralization preserved at upper amphibolite-facies grade, Qussuk, southern west Greenland Type de document : texte imprimé Auteurs : Adam A. Garde, Auteur ; Martin Whitehouse, Auteur ; Rasmus Christensen, Auteur Année de publication : 2012 Article en page(s) : pp. 881-908 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : Gold  deposits;  mineraliation;  upper  amphibolite  metamorphic  conditions;  Greenland Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Qussuk gold occurrence, located in southern West Greenland (North Atlantic Craton), is a flattened, transposed, and metamorphosed, 20 km long Au ± Cu system interpreted as an epithermal mineralization system of Mesoarchean age. The Qussuk mineralization is hosted in the 3.075 Ga volcanosedimentary rocks of a relict andesitic arc. The volcanic arc component is embedded in 3.06 to 3.0 Ga plutonic, predominantly tonalitic rocks and was gradually deformed and metamorphosed as the original arc matured into a microcontinent. Metamorphism culminated with a sillimanite-grade amphibolites-facies thermal event and mobilization of granite at around 2.995 to 2.975 Ga. The premetamorphic hydrothermal alteration associated with the mineralization includes acid leaching revealed by quartz-alumina rocks with very high rare earth element (REE) contents and Ga-Al fractionation, and subsequent reintroduction of LIL elements including K, Th, and U together with the mineralizing agents. Premetamorphic carbonate alteration is widespread but unrelated to the mineralized system. Complexly zoned zircon with igneous-hydrothermal-metamorphic histories and metamorphic monazite bracket the mineralizing event to 3.075 to 3.02 Ga (most likely >3.06 Ga) in age. The zoned zircons have volcanic/igneous, 3.075 Ga oscillatory zoned cores with igneous-type REE distributions, <3.07 Ga hydrothermal spongy growth phases, diverse REE distributions and abundant inclusions of quartz and biotite, and homogeneous metamorphic, 2.995 Ga rims. Geochronological, petrographical, and geochemical evidence demonstrates that the gold mineralization at Qussuk was formed prior to peak deformation and metamorphism. The Qussuk gold occurrence illustrates that epithermal gold deposits existed at the Archean, and that they can be preserved up to upper amphibolite metamorphic conditions, further highlighting the prospectivity of ancient high-grade cratons and volcanic belts worldwide for primary gold deposits. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/5/881.short [article] Mesoarchean epithermal gold mineralization preserved at upper amphibolite-facies grade, Qussuk, southern west Greenland [texte imprimé] / Adam A. Garde, Auteur ; Martin Whitehouse, Auteur ; Rasmus Christensen, Auteur . - 2012 . - pp. 881-908. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 5 (Août 2012) . - pp. 881-908 Mots-clés : Gold  deposits;  mineraliation;  upper  amphibolite  metamorphic  conditions;  Greenland Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Qussuk gold occurrence, located in southern West Greenland (North Atlantic Craton), is a flattened, transposed, and metamorphosed, 20 km long Au ± Cu system interpreted as an epithermal mineralization system of Mesoarchean age. The Qussuk mineralization is hosted in the 3.075 Ga volcanosedimentary rocks of a relict andesitic arc. The volcanic arc component is embedded in 3.06 to 3.0 Ga plutonic, predominantly tonalitic rocks and was gradually deformed and metamorphosed as the original arc matured into a microcontinent. Metamorphism culminated with a sillimanite-grade amphibolites-facies thermal event and mobilization of granite at around 2.995 to 2.975 Ga. The premetamorphic hydrothermal alteration associated with the mineralization includes acid leaching revealed by quartz-alumina rocks with very high rare earth element (REE) contents and Ga-Al fractionation, and subsequent reintroduction of LIL elements including K, Th, and U together with the mineralizing agents. Premetamorphic carbonate alteration is widespread but unrelated to the mineralized system. Complexly zoned zircon with igneous-hydrothermal-metamorphic histories and metamorphic monazite bracket the mineralizing event to 3.075 to 3.02 Ga (most likely >3.06 Ga) in age. The zoned zircons have volcanic/igneous, 3.075 Ga oscillatory zoned cores with igneous-type REE distributions, <3.07 Ga hydrothermal spongy growth phases, diverse REE distributions and abundant inclusions of quartz and biotite, and homogeneous metamorphic, 2.995 Ga rims. Geochronological, petrographical, and geochemical evidence demonstrates that the gold mineralization at Qussuk was formed prior to peak deformation and metamorphism. The Qussuk gold occurrence illustrates that epithermal gold deposits existed at the Archean, and that they can be preserved up to upper amphibolite metamorphic conditions, further highlighting the prospectivity of ancient high-grade cratons and volcanic belts worldwide for primary gold deposits. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/5/881.short

Geology, alteration, and origin of archean Au-Ag-Cu mineralization associated with the synvolcanic chibougamau pluton / Olivier Côté-Mantha in Economic geology, Vol. 107 N° 5 (Août 2012) 

Public ISBD [article]  in Economic geology > Vol. 107 N° 5 (Août 2012) . - pp. 909-934 Titre : Geology, alteration, and origin of archean Au-Ag-Cu mineralization associated with the synvolcanic chibougamau pluton : the brosman prospect, abitibi greenstone belt, Canada Type de document : texte imprimé Auteurs : Olivier Côté-Mantha, Auteur ; Réal Daigneault, Auteur ; Damien Gaboury, Auteur Année de publication : 2012 Article en page(s) : pp. 909-934 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : Au-Ag-Cu  Brosman  prospect;  geology;  mineralization;  Canada Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Au-Ag-Cu Brosman prospect is located in the Line Lake area on the northern limb of the Chibougamau anticline, in the northeast part of the Archean Abitibi greenstone belt. This prospect comprises a broad N-S, subvertical mineralized envelope formed in a synvolcanic fault-related environment. This envelope is at least 300 m long, up to 30 m wide, and is known to a depth of 950 m, where it remains open. It exhibits two contrasting mineralized zones that are representative of the varying styles of mineralization in the area. The Auriferous zone consists of both ubiquitous pyrite disseminations and Au-bearing silicate-sulfide veins in strongly fractured intrusive, effusive, and volcaniclastic rocks showing propylitic and chloritic alteration assemblages. The Polymetallic zone, on the other hand, is characterized by discrete, Cu-Ag-Au–rich magnetite-sulfide veins and lesser pyrite disseminations within distal propylitic and proximal potassic to sodic alteration zones. The Polymetallic zone is hosted by a chaotic assemblage of gabbro and tuff bodies interpreted as a talus megabreccia. Several lines of evidence, including the spatial distribution pattern and nature of the alteration and mineralization assemblages, metal associations, mass-balance calculations, pyrite composition, and crosscutting relationships are indicative of a preregional deformation, synvolcanic origin for the hydrothermal activity. Crosscutting relationships, alteration characteristics as well as whole-rock and LA-ICP-MS pyrite analyses reveal two stages of hydrothermal alteration and mineralization. Stage I consists of both ubiquitous disseminated pyrite, found in the Polymetallic and Auriferous zones, and contemporaneous magnetite-sulfide veins, restricted to the Polymetallic zone. Stage II is restricted to the Auriferous zone and corresponds to Au-bearing silicate-sulfide veins with characteristic vein-halo chloritic alteration overprinting Stage I alteration and mineralization. This hydrothermal activity is interpreted to have occurred concurrently with the development of the fertile, deeper magmatic-hydrothermal system related to the Chibougamau Pluton. Stage I hydrothermal activity, related to the early build-up of the volcanic sequence, formed a continuum of mineralization from discrete massive magnetite-sulfide veins to ubiquitous pyrite disseminations in a submarine talus megabreccia generated along synvolcanic faults. Afterward, a late Au-rich contribution to the hydrothermal fluids, possibly related to intermediate to felsic magmatism (the 2707.6 ± 1.4 Ma Line Lake stock), produced Stage II silicate-sulfide veins overprinting mineralization and alteration in favorably oriented and sustainably permeable fracture zones of the Auriferous zone. Overall, this study suggests that the Brosman prospect is a rare example of Archean polymetallic mineralization produced by a shallow subaqueous epithermal-style subsystem developed in a broader, fertile magmatic-hydrothermal arc setting. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/5/909.short [article] Geology, alteration, and origin of archean Au-Ag-Cu mineralization associated with the synvolcanic chibougamau pluton : the brosman prospect, abitibi greenstone belt, Canada [texte imprimé] / Olivier Côté-Mantha, Auteur ; Réal Daigneault, Auteur ; Damien Gaboury, Auteur . - 2012 . - pp. 909-934. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 5 (Août 2012) . - pp. 909-934 Mots-clés : Au-Ag-Cu  Brosman  prospect;  geology;  mineralization;  Canada Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Au-Ag-Cu Brosman prospect is located in the Line Lake area on the northern limb of the Chibougamau anticline, in the northeast part of the Archean Abitibi greenstone belt. This prospect comprises a broad N-S, subvertical mineralized envelope formed in a synvolcanic fault-related environment. This envelope is at least 300 m long, up to 30 m wide, and is known to a depth of 950 m, where it remains open. It exhibits two contrasting mineralized zones that are representative of the varying styles of mineralization in the area. The Auriferous zone consists of both ubiquitous pyrite disseminations and Au-bearing silicate-sulfide veins in strongly fractured intrusive, effusive, and volcaniclastic rocks showing propylitic and chloritic alteration assemblages. The Polymetallic zone, on the other hand, is characterized by discrete, Cu-Ag-Au–rich magnetite-sulfide veins and lesser pyrite disseminations within distal propylitic and proximal potassic to sodic alteration zones. The Polymetallic zone is hosted by a chaotic assemblage of gabbro and tuff bodies interpreted as a talus megabreccia. Several lines of evidence, including the spatial distribution pattern and nature of the alteration and mineralization assemblages, metal associations, mass-balance calculations, pyrite composition, and crosscutting relationships are indicative of a preregional deformation, synvolcanic origin for the hydrothermal activity. Crosscutting relationships, alteration characteristics as well as whole-rock and LA-ICP-MS pyrite analyses reveal two stages of hydrothermal alteration and mineralization. Stage I consists of both ubiquitous disseminated pyrite, found in the Polymetallic and Auriferous zones, and contemporaneous magnetite-sulfide veins, restricted to the Polymetallic zone. Stage II is restricted to the Auriferous zone and corresponds to Au-bearing silicate-sulfide veins with characteristic vein-halo chloritic alteration overprinting Stage I alteration and mineralization. This hydrothermal activity is interpreted to have occurred concurrently with the development of the fertile, deeper magmatic-hydrothermal system related to the Chibougamau Pluton. Stage I hydrothermal activity, related to the early build-up of the volcanic sequence, formed a continuum of mineralization from discrete massive magnetite-sulfide veins to ubiquitous pyrite disseminations in a submarine talus megabreccia generated along synvolcanic faults. Afterward, a late Au-rich contribution to the hydrothermal fluids, possibly related to intermediate to felsic magmatism (the 2707.6 ± 1.4 Ma Line Lake stock), produced Stage II silicate-sulfide veins overprinting mineralization and alteration in favorably oriented and sustainably permeable fracture zones of the Auriferous zone. Overall, this study suggests that the Brosman prospect is a rare example of Archean polymetallic mineralization produced by a shallow subaqueous epithermal-style subsystem developed in a broader, fertile magmatic-hydrothermal arc setting. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/5/909.short

Geology of the Archean Intrusion-Hosted la-grande-sud Au-Cu prospect, la grande subprovince, James Bay region, Québec / Patrick Mercier-Langevin in Economic geology, Vol. 107 N° 5 (Août 2012) 

Public ISBD [article]  in Economic geology > Vol. 107 N° 5 (Août 2012) . - pp. 935-962 Titre : Geology of the Archean Intrusion-Hosted la-grande-sud Au-Cu prospect, la grande subprovince, James Bay region, Québec Type de document : texte imprimé Auteurs : Patrick Mercier-Langevin, Auteur ; Réal Daigneault, Auteur ; Jean Goutier, Auteur Année de publication : 2012 Article en page(s) : pp. 935-962 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : Au-Cu  prospect;  calc-alkaline  intrusion;  mineralization;  archean  intrusions;  Quabec Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Archean La Grande and Eastmain domains of the La Grande subprovince in the James Bay region of northwestern Québec are the focus of renewed and extensive exploration as a result of recent major discoveries made in this region (e.g., ~8 Moz Au Roberto deposit). A number of significant Neoarchean Au ± base metal occurrences are present in the La Grande domain, including the La-Grande-Sud Au-Cu prospect (Zone 32, inferred resource of 4.2 million metric tons (Mt) at 2.1 g/t Au and 0.2 wt % Cu). The La-Grande-Sud Au-Cu prospect is hosted in the 2734 ± 2 Ma synvolcanic La-Grande-Sud Tonalite in the 2751 to 2732 Ma Yasinski Group volcanic rocks. The La-Grande-Sud Tonalite is a synvolcanic calc-alkaline intrusion emplaced in an arc-like tectonomagmatic setting. Timing relationships in mineralized zones as well as associated hydrothermal alteration zones support a pre- to early-D1 origin for at least a part of the mineralization in the La-Grande-Sud Tonalite. Deformation events were responsible for the overprinting of the early mineralization by auriferous shear zone-related systems associated with D2. Evidence for a pre-D2 and pre- to early-D1 alteration and mineralization system includes: (1) a broadly concentric pattern defined by the hydrothermal alteration assemblages within the La-Grande-Sud Tonalite, which suggests that the hydrothermal alteration was, at least in part, controlled by the geometry of the intrusion rather than by the D2 deformation; (2) the development of a weak biotite-bearing potassic assemblage (biotite-epidote-plagioclase-muscovite-calcite ± pyrite) that is gradually replaced outward from the center of the intrusion by a chlorite-bearing propylitic assemblage (chlorite-epidote-muscovite-plagioclase-calcite-pyrite), and locally overprinted by a sericitic alteration assemblage (muscovite-quartz-albite-chlorite-pyrite-carbonate), which represents the most intense alteration in the La-Grande-Sud Tonalite; (3) the presence of mineralized hydrothermal breccias along the margins of the intrusion; (4) deformed disseminated and stockwork-style Au-Cu sulfide mineralization consisting of pyrite, chalcopyrite, tennantite, arsenopyrite, pyrrhotite, Bi sulfosalts, and native Au ± Bi in the sericite, chlorite, and biotite facies alteration zones; (5) S1-parallel elongated tonalite clasts and sulfide veinlets in D2-folded and transposed hydrothermal biotite breccias; and (6) pyrite porphyroblasts that are elongated parallel to the S1 fabric (syn-D1 metamorphic recrystallization) and that were folded during D2. D2 was associated with the development of conjugate auriferous extensional quartz-tourmaline veins (orogenic-style veins) that were superimposed on the pre- to early-D1 intrusion-hosted mineralized system. Gold in these syn- to late-D2 veins could have been remobilized from preexisting mineralization (disseminated sulfides) or was related to a late (syn-D2) auriferous hydrothermal event. The intrusion-hosted Au mineralization of the La-Grande-Sud Au-Cu prospect illustrates that Archean synvolcanic intrusions, regardless of their size, can host a range of styles of alteration and mineralization, including both “early” and “late” mineralizing systems. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/5/935.short [article] Geology of the Archean Intrusion-Hosted la-grande-sud Au-Cu prospect, la grande subprovince, James Bay region, Québec [texte imprimé] / Patrick Mercier-Langevin, Auteur ; Réal Daigneault, Auteur ; Jean Goutier, Auteur . - 2012 . - pp. 935-962. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 5 (Août 2012) . - pp. 935-962 Mots-clés : Au-Cu  prospect;  calc-alkaline  intrusion;  mineralization;  archean  intrusions;  Quabec Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Archean La Grande and Eastmain domains of the La Grande subprovince in the James Bay region of northwestern Québec are the focus of renewed and extensive exploration as a result of recent major discoveries made in this region (e.g., ~8 Moz Au Roberto deposit). A number of significant Neoarchean Au ± base metal occurrences are present in the La Grande domain, including the La-Grande-Sud Au-Cu prospect (Zone 32, inferred resource of 4.2 million metric tons (Mt) at 2.1 g/t Au and 0.2 wt % Cu). The La-Grande-Sud Au-Cu prospect is hosted in the 2734 ± 2 Ma synvolcanic La-Grande-Sud Tonalite in the 2751 to 2732 Ma Yasinski Group volcanic rocks. The La-Grande-Sud Tonalite is a synvolcanic calc-alkaline intrusion emplaced in an arc-like tectonomagmatic setting. Timing relationships in mineralized zones as well as associated hydrothermal alteration zones support a pre- to early-D1 origin for at least a part of the mineralization in the La-Grande-Sud Tonalite. Deformation events were responsible for the overprinting of the early mineralization by auriferous shear zone-related systems associated with D2. Evidence for a pre-D2 and pre- to early-D1 alteration and mineralization system includes: (1) a broadly concentric pattern defined by the hydrothermal alteration assemblages within the La-Grande-Sud Tonalite, which suggests that the hydrothermal alteration was, at least in part, controlled by the geometry of the intrusion rather than by the D2 deformation; (2) the development of a weak biotite-bearing potassic assemblage (biotite-epidote-plagioclase-muscovite-calcite ± pyrite) that is gradually replaced outward from the center of the intrusion by a chlorite-bearing propylitic assemblage (chlorite-epidote-muscovite-plagioclase-calcite-pyrite), and locally overprinted by a sericitic alteration assemblage (muscovite-quartz-albite-chlorite-pyrite-carbonate), which represents the most intense alteration in the La-Grande-Sud Tonalite; (3) the presence of mineralized hydrothermal breccias along the margins of the intrusion; (4) deformed disseminated and stockwork-style Au-Cu sulfide mineralization consisting of pyrite, chalcopyrite, tennantite, arsenopyrite, pyrrhotite, Bi sulfosalts, and native Au ± Bi in the sericite, chlorite, and biotite facies alteration zones; (5) S1-parallel elongated tonalite clasts and sulfide veinlets in D2-folded and transposed hydrothermal biotite breccias; and (6) pyrite porphyroblasts that are elongated parallel to the S1 fabric (syn-D1 metamorphic recrystallization) and that were folded during D2. D2 was associated with the development of conjugate auriferous extensional quartz-tourmaline veins (orogenic-style veins) that were superimposed on the pre- to early-D1 intrusion-hosted mineralized system. Gold in these syn- to late-D2 veins could have been remobilized from preexisting mineralization (disseminated sulfides) or was related to a late (syn-D2) auriferous hydrothermal event. The intrusion-hosted Au mineralization of the La-Grande-Sud Au-Cu prospect illustrates that Archean synvolcanic intrusions, regardless of their size, can host a range of styles of alteration and mineralization, including both “early” and “late” mineralizing systems. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/5/935.short

Structural and stratigraphic controls on magmatic, volcanogenic, and shear zone-hosted mineralization in the chapais-chibougamau mining camp, northeastern Abitibi, Canada / François Leclerc in Economic geology, Vol. 107 N° 5 (Août 2012) 

Public ISBD [article]  in Economic geology > Vol. 107 N° 5 (Août 2012) . - p p. 963-989 Titre : Structural and stratigraphic controls on magmatic, volcanogenic, and shear zone-hosted mineralization in the chapais-chibougamau mining camp, northeastern Abitibi, Canada Type de document : texte imprimé Auteurs : François Leclerc, Auteur ; Lyal B. Harris, Auteur ; Jean H. Bédard, Auteur Année de publication : 2012 Article en page(s) : p p. 963-989 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : Chapais-Chibougamau  mining  camp;  mineralization;  Canada Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The structure and stratigraphy of the Chapais-Chibougamau mining camp in the Archean Abitibi greenstone belt of the Superior Craton, Quebec, Canada, is reevaluated from new aeromagnetic data, geochronology, and field studies to provide a framework for syngenetic and epigenetic mineralization. Mineralization in the Chapais-Chibougamau area is synvolcanic (volcanogenic massive sulfide (VMS)), synmagmatic (Fe-Ti-V, Ni-Cu, Au-Ag-Cu-Zn-Pb veins, Chibougamau-type Cu-Au veins), and shear zone hosted (including Opemiska Cu-Au veins subtype). VMS deposits occur within felsic volcanic rocks of tholeiitic affinity and mafic to felsic volcanic rocks of transitional to calc-alkaline affinity at the top of three volcanic cycles of the Roy Group. VMS deposits and early polymetallic veins (Au-Ag-Cu-Zn-Pb) are associated with NNW- to NNE-striking synvolcanic faults. Fe-Ti-V deposits occur within the Layered zone of the Lac Doré Complex, especially where it thickens in areas of interpreted synmagmatic faults. Subeconomic magmatic Ni-Cu deposits occur at the contacts of mafic-ultramafic or tonalitic intrusions. “Chibougamau-type” Cu-Au veins formed through magmatic-hydrothermal processes. They are cut by dikes that predate regional D2 deformation but are located within, and are deformed by, NW- and NE-trending D2 shear zones. Shear zone-hosted Au deposits are developed preferentially within regional E-W–trending deformation corridors and along NNE-striking sinistral shear zones while “Opemiska-type” Cu-Au veins occur within regional overturned anticlines in mafic sills of the Cummings Complex. U-Pb dating of detrital zircons provides maximum depositional ages for metasedimentary rocks of the Blondeau Formation of the Roy Group and the Stella Formation of the Opémisca Group (which unconformably overlies the Roy Group). The Blondeau Formation is <2721 ± 3 Ma, which is coeval to the age of the Windfall Member in the Urban-Barry Belt. Both show similar exploration potential as they host early polymetallic (Au-Ag-Cu-Zn-Pb) veins. The Stella Formation is <2704 ± 2 Ma and is unaffected by first generation folds, thus providing a time constraint for the earliest folding event (D1). This new age also indicates that sedimentation in the Chapais-Chibougamau area occurred earlier than for the Timiskaming-type assemblages in the southern Abitibi greenstone belt, but the structural setting and presence of alkaline intrusions suggests similar potential for syenite-associated Au deposits in the Stella Formation. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/5/963.short [article] Structural and stratigraphic controls on magmatic, volcanogenic, and shear zone-hosted mineralization in the chapais-chibougamau mining camp, northeastern Abitibi, Canada [texte imprimé] / François Leclerc, Auteur ; Lyal B. Harris, Auteur ; Jean H. Bédard, Auteur . - 2012 . - p p. 963-989. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 5 (Août 2012) . - p p. 963-989 Mots-clés : Chapais-Chibougamau  mining  camp;  mineralization;  Canada Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The structure and stratigraphy of the Chapais-Chibougamau mining camp in the Archean Abitibi greenstone belt of the Superior Craton, Quebec, Canada, is reevaluated from new aeromagnetic data, geochronology, and field studies to provide a framework for syngenetic and epigenetic mineralization. Mineralization in the Chapais-Chibougamau area is synvolcanic (volcanogenic massive sulfide (VMS)), synmagmatic (Fe-Ti-V, Ni-Cu, Au-Ag-Cu-Zn-Pb veins, Chibougamau-type Cu-Au veins), and shear zone hosted (including Opemiska Cu-Au veins subtype). VMS deposits occur within felsic volcanic rocks of tholeiitic affinity and mafic to felsic volcanic rocks of transitional to calc-alkaline affinity at the top of three volcanic cycles of the Roy Group. VMS deposits and early polymetallic veins (Au-Ag-Cu-Zn-Pb) are associated with NNW- to NNE-striking synvolcanic faults. Fe-Ti-V deposits occur within the Layered zone of the Lac Doré Complex, especially where it thickens in areas of interpreted synmagmatic faults. Subeconomic magmatic Ni-Cu deposits occur at the contacts of mafic-ultramafic or tonalitic intrusions. “Chibougamau-type” Cu-Au veins formed through magmatic-hydrothermal processes. They are cut by dikes that predate regional D2 deformation but are located within, and are deformed by, NW- and NE-trending D2 shear zones. Shear zone-hosted Au deposits are developed preferentially within regional E-W–trending deformation corridors and along NNE-striking sinistral shear zones while “Opemiska-type” Cu-Au veins occur within regional overturned anticlines in mafic sills of the Cummings Complex. U-Pb dating of detrital zircons provides maximum depositional ages for metasedimentary rocks of the Blondeau Formation of the Roy Group and the Stella Formation of the Opémisca Group (which unconformably overlies the Roy Group). The Blondeau Formation is <2721 ± 3 Ma, which is coeval to the age of the Windfall Member in the Urban-Barry Belt. Both show similar exploration potential as they host early polymetallic (Au-Ag-Cu-Zn-Pb) veins. The Stella Formation is <2704 ± 2 Ma and is unaffected by first generation folds, thus providing a time constraint for the earliest folding event (D1). This new age also indicates that sedimentation in the Chapais-Chibougamau area occurred earlier than for the Timiskaming-type assemblages in the southern Abitibi greenstone belt, but the structural setting and presence of alkaline intrusions suggests similar potential for syenite-associated Au deposits in the Stella Formation. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/5/963.short

Volcanic stratigraphy, geochronology, and gold deposits of the archean hope bay greenstone belt, Nunavut, Canada / Ross L. Sherlock in Economic geology, Vol. 107 N° 5 (Août 2012) 

Public ISBD [article]  in Economic geology > Vol. 107 N° 5 (Août 2012) . - pp. 991-1042 Titre : Volcanic stratigraphy, geochronology, and gold deposits of the archean hope bay greenstone belt, Nunavut, Canada Type de document : texte imprimé Auteurs : Ross L. Sherlock, Auteur ; Andrew Shannon, Auteur ; Manfred Hebel, Auteur Année de publication : 2012 Article en page(s) : pp. 991-1042 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : Archean  Hope  Bay  greenstone  belt;  Au  deposits;  gold  deposits;  volcanic  stratigraphy;  Canada Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Archean Hope Bay greenstone belt is located in the Bathurst Block of the northeastern part of the Slave Structural Province, a predominantly Archean, granite-greenstone-metasedimentary terrane. The greenstone belt is dominated by mafic volcanic rocks with less common felsic volcanic and volcaniclastic products and subordinate ultramafic bodies and metasedimentary rocks. Three main Au deposits have been defined in the greenstone belt, with a cumulative resource of over 10 million ounces (Moz) of Au, as of April 2007. The Hope Bay greenstone belt can be divided into a series of coherent panels of strata that tend to be fault bounded and collectively are used to construct a composite stratigraphic column of the belt constrained by U-Pb geochronology on felsic suites. The oldest felsic suite, the Flake Lake suite (ca. 2700 Ma), is a succession of felsic volcanic rocks that has a tholeiitic geochemical affinity, interpreted as a product of rift-related volcanism. Overlying this suite is a series of well-constrained calc-alkaline, mainly felsic volcanic rocks, which have ages of ca. 2690 Ma (Square Lake suite), ca. 2686 Ma (Windy felsic suite), ca. 2677 Ma (Koignuk suite), and ca. 2662 Ma (Clover Lake suite), all of which are interpreted as products of arc volcanism. The transition from rift- to arc-related volcanism divides the greenstone belt into upper and lower volcanic cycles with the transition occurring at about ca. 2690 Ma. The older cycle of volcanic rocks has a distinctive group of mafic rocks consisting of mafic pillowed flows which have an Fe-rich tholeiitic geochemical affinity which is not recognized in the younger volcanic cycle. These Fe-rich tholeiitic mafic volcanic rocks commonly show a spatial relationship to Au mineralization acting as host strata to the main Au deposits in the greenstone belt. The younger cycle ( Detrital zircon work was carried out for all the main sedimentary successions recognized in the Hope Bay greenstone belt. The detrital zircon results show that in each case the sediments were derived mainly from local sources, as very few anomalously old zircons were recognized. A conglomerate outcropping in the north part of the belt is dominated by locally derived material, with detrital zircon work supporting this interpretation. The three main Au deposits at Hope Bay are all associated with the older cycle of volcanic rocks, interpreted as products of rift-related volcanism. The structural setting of each deposit is different but each is related to D2 strain in structural and/or stratigraphic settings which provided dilational environments to localize auriferous vein-related mineralization or localized alteration and mineralization of favorable host lithologies. The older cycle of tholeiitic felsic and Fe-rich mafic volcanic rocks are rift-related volcanic products, which are time-equivalent to the Kam Group, in the Yellowknife Supergroup. Overlying these rocks are calc-alkaline felsic volcanic rocks and tholeiitic mafic volcanic rocks, which represent the transition to calc-alkaline arc-related volcanism, which correlates to the Banting Group of the Yellowknife Supergroup. Overlying the younger (ca. 2677 Ma) felsic volcanic rocks are a succession of conglomerates consisting mainly of locally derived clasts, representing collapse of the arc into a fluvial-dominated environment. This sedimentary succession is possibly equivalent to the regionally extensive Burwash Basin of the Yellowknife Supergroup. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/5/991.short [article] Volcanic stratigraphy, geochronology, and gold deposits of the archean hope bay greenstone belt, Nunavut, Canada [texte imprimé] / Ross L. Sherlock, Auteur ; Andrew Shannon, Auteur ; Manfred Hebel, Auteur . - 2012 . - pp. 991-1042. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 5 (Août 2012) . - pp. 991-1042 Mots-clés : Archean  Hope  Bay  greenstone  belt;  Au  deposits;  gold  deposits;  volcanic  stratigraphy;  Canada Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Archean Hope Bay greenstone belt is located in the Bathurst Block of the northeastern part of the Slave Structural Province, a predominantly Archean, granite-greenstone-metasedimentary terrane. The greenstone belt is dominated by mafic volcanic rocks with less common felsic volcanic and volcaniclastic products and subordinate ultramafic bodies and metasedimentary rocks. Three main Au deposits have been defined in the greenstone belt, with a cumulative resource of over 10 million ounces (Moz) of Au, as of April 2007. The Hope Bay greenstone belt can be divided into a series of coherent panels of strata that tend to be fault bounded and collectively are used to construct a composite stratigraphic column of the belt constrained by U-Pb geochronology on felsic suites. The oldest felsic suite, the Flake Lake suite (ca. 2700 Ma), is a succession of felsic volcanic rocks that has a tholeiitic geochemical affinity, interpreted as a product of rift-related volcanism. Overlying this suite is a series of well-constrained calc-alkaline, mainly felsic volcanic rocks, which have ages of ca. 2690 Ma (Square Lake suite), ca. 2686 Ma (Windy felsic suite), ca. 2677 Ma (Koignuk suite), and ca. 2662 Ma (Clover Lake suite), all of which are interpreted as products of arc volcanism. The transition from rift- to arc-related volcanism divides the greenstone belt into upper and lower volcanic cycles with the transition occurring at about ca. 2690 Ma. The older cycle of volcanic rocks has a distinctive group of mafic rocks consisting of mafic pillowed flows which have an Fe-rich tholeiitic geochemical affinity which is not recognized in the younger volcanic cycle. These Fe-rich tholeiitic mafic volcanic rocks commonly show a spatial relationship to Au mineralization acting as host strata to the main Au deposits in the greenstone belt. The younger cycle ( Detrital zircon work was carried out for all the main sedimentary successions recognized in the Hope Bay greenstone belt. The detrital zircon results show that in each case the sediments were derived mainly from local sources, as very few anomalously old zircons were recognized. A conglomerate outcropping in the north part of the belt is dominated by locally derived material, with detrital zircon work supporting this interpretation. The three main Au deposits at Hope Bay are all associated with the older cycle of volcanic rocks, interpreted as products of rift-related volcanism. The structural setting of each deposit is different but each is related to D2 strain in structural and/or stratigraphic settings which provided dilational environments to localize auriferous vein-related mineralization or localized alteration and mineralization of favorable host lithologies. The older cycle of tholeiitic felsic and Fe-rich mafic volcanic rocks are rift-related volcanic products, which are time-equivalent to the Kam Group, in the Yellowknife Supergroup. Overlying these rocks are calc-alkaline felsic volcanic rocks and tholeiitic mafic volcanic rocks, which represent the transition to calc-alkaline arc-related volcanism, which correlates to the Banting Group of the Yellowknife Supergroup. Overlying the younger (ca. 2677 Ma) felsic volcanic rocks are a succession of conglomerates consisting mainly of locally derived clasts, representing collapse of the arc into a fluvial-dominated environment. This sedimentary succession is possibly equivalent to the regionally extensive Burwash Basin of the Yellowknife Supergroup. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/5/991.short

Zircon alteration in wall rock of pamour and hoyle pond Au deposits, abitibi greenstone belt / D. A. Schneider in Economic geology, Vol. 107 N° 5 (Août 2012) 

Public ISBD [article]  in Economic geology > Vol. 107 N° 5 (Août 2012) . - pp. 1043-1072 Titre : Zircon alteration in wall rock of pamour and hoyle pond Au deposits, abitibi greenstone belt : constraints on timescales of fluid flow from depth-profiling techniques Type de document : texte imprimé Auteurs : D. A. Schneider, Auteur ; J. Bachtel, Auteur ; A. K. Schmitt, Auteur Année de publication : 2012 Article en page(s) : pp. 1043-1072 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : Quartz-carbonate-Au  vein  deposits;  abitibi  greenstone  belt;  Zircon  alteration Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : Quartz-carbonate-Au vein deposits in the Timmins-Porcupine gold camp, Abitibi greenstone belt, have equivocal protracted parageneses and formed during late to post-Kenoran (2750–2670 Ma) deformation and metamorphism. Secondary ion mass spectrometry (SIMS) U-Pb, δ18O, and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) rare earth element (REE) depth-profiling techniques were employed on unpolished wall-rock zircons to resolve temporal constraints on mineralization and hydrothermal fluid sources at Hoyle Pond and Pamour Mines. Depth-profiling techniques successfully uncovered <3-μm alteration domains in zircon rims based on Th/U, REE, and isotopic signatures, and rim 207Pb/206Pb ages are significantly younger than host-rock ages. Zircon alteration is from a complex interplay of recrystallization and localized dissolution-reprecipitation of the crystals during hydrothermal fluid flow. Alteration of Hoyle Pond and Pamour zircons at 2660 Ma correlates to intensely mineralized and deformed quartz-carbonate-Au shear veins, and this age represents peak fluid infiltration at the mines, coinciding with peak regional metamorphism. Subsequent zircon alteration correlating to thin, shallow-dipping and less altered or mineralized vein networks occurred at ca. 2640 Ma, and this age likely represents a late hydrothermal fluid pulse at the end of regional retrograde metamorphism. Protracted hydrothermal alteration along discrete zones within the camp continued into the Proterozoic. Zircon alteration occurs as light REE-enriched “rims,” and Th/U and 18O values of alteration domains suggest that the source had a limited crustal recycling component. Whereas the underutilized depth-profiling technique has resolved ~200 m.y. of continuous crustal evolution and fluid flow in the southern Abitibi, further investigation of the southern Abitibi is required to clarify the genetic relationship between ore mineralization and zircon alteration. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/5/1043.abstract [article] Zircon alteration in wall rock of pamour and hoyle pond Au deposits, abitibi greenstone belt : constraints on timescales of fluid flow from depth-profiling techniques [texte imprimé] / D. A. Schneider, Auteur ; J. Bachtel, Auteur ; A. K. Schmitt, Auteur . - 2012 . - pp. 1043-1072. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 5 (Août 2012) . - pp. 1043-1072 Mots-clés : Quartz-carbonate-Au  vein  deposits;  abitibi  greenstone  belt;  Zircon  alteration Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : Quartz-carbonate-Au vein deposits in the Timmins-Porcupine gold camp, Abitibi greenstone belt, have equivocal protracted parageneses and formed during late to post-Kenoran (2750–2670 Ma) deformation and metamorphism. Secondary ion mass spectrometry (SIMS) U-Pb, δ18O, and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) rare earth element (REE) depth-profiling techniques were employed on unpolished wall-rock zircons to resolve temporal constraints on mineralization and hydrothermal fluid sources at Hoyle Pond and Pamour Mines. Depth-profiling techniques successfully uncovered <3-μm alteration domains in zircon rims based on Th/U, REE, and isotopic signatures, and rim 207Pb/206Pb ages are significantly younger than host-rock ages. Zircon alteration is from a complex interplay of recrystallization and localized dissolution-reprecipitation of the crystals during hydrothermal fluid flow. Alteration of Hoyle Pond and Pamour zircons at 2660 Ma correlates to intensely mineralized and deformed quartz-carbonate-Au shear veins, and this age represents peak fluid infiltration at the mines, coinciding with peak regional metamorphism. Subsequent zircon alteration correlating to thin, shallow-dipping and less altered or mineralized vein networks occurred at ca. 2640 Ma, and this age likely represents a late hydrothermal fluid pulse at the end of regional retrograde metamorphism. Protracted hydrothermal alteration along discrete zones within the camp continued into the Proterozoic. Zircon alteration occurs as light REE-enriched “rims,” and Th/U and 18O values of alteration domains suggest that the source had a limited crustal recycling component. Whereas the underutilized depth-profiling technique has resolved ~200 m.y. of continuous crustal evolution and fluid flow in the southern Abitibi, further investigation of the southern Abitibi is required to clarify the genetic relationship between ore mineralization and zircon alteration. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/5/1043.abstract

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