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Affiner la rechercheVolcanic 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)
[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 Whole-rock and mineral composition constraints on the genesis of the giant hongge Fe-Ti-V oxide deposit in the Emeishan large igneous province, southwest China / Zhong-Jie Bai in Economic geology, Vol. 107 N° 3 (Mai 2012)
[article]
in Economic geology > Vol. 107 N° 3 (Mai 2012) . - pp. 507-524
Titre : Whole-rock and mineral composition constraints on the genesis of the giant hongge Fe-Ti-V oxide deposit in the Emeishan large igneous province, southwest China Type de document : texte imprimé Auteurs : Zhong-Jie Bai, Auteur ; Zhong Hong, Auteur ; Anthony J. Naldrett, Auteur Année de publication : 2012 Article en page(s) : pp. 507-524 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : Fe-Ti-V oxide ore deposit Whole rock Mineral composition China Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Hongge giant Fe-Ti-V oxide ore deposit is hosted by a layered intrusion located in the central part of the Emeishan large igneous province, SW China. The intrusion is relatively small in comparison with other typical oxide-bearing intrusions worldwide; it consists of a lower olivine clinopyroxenite zone, a middle clinopyroxenite zone, and an upper gabbro zone (herein referred to as the lower, middle, and upper zones). Most of the economic Fe-Ti-V oxide ore layers occur within the middle zone. The Hongge oxide ores are depleted in REE and enriched in Zr, Hf, Nb, and Ta as compared to the associated clinopyroxenites. This enrichment of elements that are compatible in titanomagnetite is consistent with the interpretation that the ores formed by accumulation of magnetite and ilmenite. As in the nearby coeval Panzhihua Fe-Ti-V oxide deposit described previously by others, mafic silicates in the Hongge deposit have much higher MgO contents than those in other oxide deposits associated with large layered intrusions in the world. This highlights the importance of relatively primitive parental magma becoming saturated in titanomagnetite at an early stage in the genesis of the giant Fe-Ti-V oxide deposits in the Emeishan large igneous province. Phase equilibrium constraints suggest that the parental magma of the Hongge deposit is similar to that of some of the most primitive high Ti basalts in the Emeishan large igneous province. The ferrobasaltic parental magma and the ferropicritic primary magma of the Hongge intrusion are similar in major and trace element composition to the ferropicritic-ferrobasaltic magma in the Pechenga belt, Kola peninsula, Russia. Depletion of incompatible trace elements in the oxide ores and associated rocks in the Hongge intrusion as compared to the coeval high-Ti basalts suggest that not all the magma involved in the development of the Hongge intrusion has been retained in the intrusion. The occurrence of multiple Fe-Ti oxide layers alternating with Fe-Ti oxide-bearing silicate layers within a single zone and the repetitive appearance of sulfides, olivine, and Cr-rich layers suggest that multiple pulses of magma were involved in the formation of the Hongge intrusion and related Fe-Ti-V oxide deposit. We propose that the middle zone of the Hongge intrusion was a magma stepwise flow-through system and that some of the liquid was lost to the peripheral lavas to form the basalt. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/3/507.short [article] Whole-rock and mineral composition constraints on the genesis of the giant hongge Fe-Ti-V oxide deposit in the Emeishan large igneous province, southwest China [texte imprimé] / Zhong-Jie Bai, Auteur ; Zhong Hong, Auteur ; Anthony J. Naldrett, Auteur . - 2012 . - pp. 507-524.
Economic geology
Langues : Anglais (eng)
in Economic geology > Vol. 107 N° 3 (Mai 2012) . - pp. 507-524
Mots-clés : Fe-Ti-V oxide ore deposit Whole rock Mineral composition China Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Hongge giant Fe-Ti-V oxide ore deposit is hosted by a layered intrusion located in the central part of the Emeishan large igneous province, SW China. The intrusion is relatively small in comparison with other typical oxide-bearing intrusions worldwide; it consists of a lower olivine clinopyroxenite zone, a middle clinopyroxenite zone, and an upper gabbro zone (herein referred to as the lower, middle, and upper zones). Most of the economic Fe-Ti-V oxide ore layers occur within the middle zone. The Hongge oxide ores are depleted in REE and enriched in Zr, Hf, Nb, and Ta as compared to the associated clinopyroxenites. This enrichment of elements that are compatible in titanomagnetite is consistent with the interpretation that the ores formed by accumulation of magnetite and ilmenite. As in the nearby coeval Panzhihua Fe-Ti-V oxide deposit described previously by others, mafic silicates in the Hongge deposit have much higher MgO contents than those in other oxide deposits associated with large layered intrusions in the world. This highlights the importance of relatively primitive parental magma becoming saturated in titanomagnetite at an early stage in the genesis of the giant Fe-Ti-V oxide deposits in the Emeishan large igneous province. Phase equilibrium constraints suggest that the parental magma of the Hongge deposit is similar to that of some of the most primitive high Ti basalts in the Emeishan large igneous province. The ferrobasaltic parental magma and the ferropicritic primary magma of the Hongge intrusion are similar in major and trace element composition to the ferropicritic-ferrobasaltic magma in the Pechenga belt, Kola peninsula, Russia. Depletion of incompatible trace elements in the oxide ores and associated rocks in the Hongge intrusion as compared to the coeval high-Ti basalts suggest that not all the magma involved in the development of the Hongge intrusion has been retained in the intrusion. The occurrence of multiple Fe-Ti oxide layers alternating with Fe-Ti oxide-bearing silicate layers within a single zone and the repetitive appearance of sulfides, olivine, and Cr-rich layers suggest that multiple pulses of magma were involved in the formation of the Hongge intrusion and related Fe-Ti-V oxide deposit. We propose that the middle zone of the Hongge intrusion was a magma stepwise flow-through system and that some of the liquid was lost to the peripheral lavas to form the basalt. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/3/507.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)
[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