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Extreme PGE concentrations in lower Cambrian acid tuff layer from the Kunyang phosphate deposit, Yunnan province, south China- possible PGE source for lower cambrian Mo-Ni-polyelement ore beds / Jan Pasava in Economic geology, Vol. 105 N° 6 (Septembre/Octobre 2010) 

Public ISBD [article]  in Economic geology > Vol. 105 N° 6 (Septembre/Octobre 2010) . - pp. 511-522 Titre : Extreme PGE concentrations in lower Cambrian acid tuff layer from the Kunyang phosphate deposit, Yunnan province, south China- possible PGE source for lower cambrian Mo-Ni-polyelement ore beds Type de document : texte imprimé Auteurs : Jan Pasava, Auteur ; Hartwig Frimmel, Auteur ; Luo Taiyi, Auteur Année de publication : 2011 Article en page(s) : pp. 511-522 Note générale : Economic Geology Langues : Anglais (eng) Mots-clés : PGE  concentrations  Kunyang  phosphate  deposit  Yunnan  province  China Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : A study of the platinum group element (PGE) distribution in various lowermost Cambrian rock types of the Kunyang phosphate deposit in south China revealed unusually high PGE concentrations (434 ppb Pt, 142 ppb Pd, 57.97 ppb Rh, <1 ppb Ru, and 0.14 ppb Ir) in a whole-rock sample of acid tuff that is interbedded with phosphorite. Stratigraphically above this unit is an Mo-Ni–polyelement (including PGE and Au) phosphatic and sulfidic black shale. The tuff consists of clastic glass fragments in a matrix of clay minerals (dominantly mixed-layer illite-smectite) and cryptocrystalline quartz with minor dolomite, phosphatic fragments and nodules, and rare pyrite. The clay-quartz fraction revealed elevated Ru (11 ppb) and Ir (1.4 ppb) concentrations, but a depletion in Pt (6.8 ppb), Pd (25 ppb), and Rh (0.35 ppb) relative to the whole rock. LA-ICPMS analyses of pyrite yielded high Ni values (up to 1,243 ppm) and in some grains also elevated Re (up to 576 ppb) and Pd (up to 190 ppb) concentrations. No PGE were detected in the phosphatic nodules. It is very likely that the PGE are in part bound to submicroscopic inclusions in pyrite and/or intermetallic phases bound to the clay fraction. Petrographic observations and isotope data obtained on paragenetically late dolomite veinlets, which yielded C and O isotope ratios that correspond to those of contemporaneous seawater (δ13C ranges −2.32 to −2.44‰ V-PDB, δ18O −10.07 to −9.94‰ V-PDB), do not indicate any hydrothermal overprint. Instead, pyrite formation is ascribed to diagenesis in the reduced environment of black shales, as supported by δ34S ratios obtained for pyrite between 6.31 and 7.54 per mil CDT and elevated Ni concentrations in the pyrite. If other acid tuffs in the region have similar anomalous concentrations of PGE, they could have played an important role in the origin of the slightly younger Mo-Ni–polyelement (including PGE and Au) phosphatic and sulfidic black shales in the Yangtze platform. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/105/6/1047.abstract [article] Extreme PGE concentrations in lower Cambrian acid tuff layer from the Kunyang phosphate deposit, Yunnan province, south China- possible PGE source for lower cambrian Mo-Ni-polyelement ore beds [texte imprimé] / Jan Pasava, Auteur ; Hartwig Frimmel, Auteur ; Luo Taiyi, Auteur . - 2011 . - pp. 511-522. Economic Geology Langues : Anglais (eng) in Economic geology > Vol. 105 N° 6 (Septembre/Octobre 2010) . - pp. 511-522 Mots-clés : PGE  concentrations  Kunyang  phosphate  deposit  Yunnan  province  China Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : A study of the platinum group element (PGE) distribution in various lowermost Cambrian rock types of the Kunyang phosphate deposit in south China revealed unusually high PGE concentrations (434 ppb Pt, 142 ppb Pd, 57.97 ppb Rh, <1 ppb Ru, and 0.14 ppb Ir) in a whole-rock sample of acid tuff that is interbedded with phosphorite. Stratigraphically above this unit is an Mo-Ni–polyelement (including PGE and Au) phosphatic and sulfidic black shale. The tuff consists of clastic glass fragments in a matrix of clay minerals (dominantly mixed-layer illite-smectite) and cryptocrystalline quartz with minor dolomite, phosphatic fragments and nodules, and rare pyrite. The clay-quartz fraction revealed elevated Ru (11 ppb) and Ir (1.4 ppb) concentrations, but a depletion in Pt (6.8 ppb), Pd (25 ppb), and Rh (0.35 ppb) relative to the whole rock. LA-ICPMS analyses of pyrite yielded high Ni values (up to 1,243 ppm) and in some grains also elevated Re (up to 576 ppb) and Pd (up to 190 ppb) concentrations. No PGE were detected in the phosphatic nodules. It is very likely that the PGE are in part bound to submicroscopic inclusions in pyrite and/or intermetallic phases bound to the clay fraction. Petrographic observations and isotope data obtained on paragenetically late dolomite veinlets, which yielded C and O isotope ratios that correspond to those of contemporaneous seawater (δ13C ranges −2.32 to −2.44‰ V-PDB, δ18O −10.07 to −9.94‰ V-PDB), do not indicate any hydrothermal overprint. Instead, pyrite formation is ascribed to diagenesis in the reduced environment of black shales, as supported by δ34S ratios obtained for pyrite between 6.31 and 7.54 per mil CDT and elevated Ni concentrations in the pyrite. If other acid tuffs in the region have similar anomalous concentrations of PGE, they could have played an important role in the origin of the slightly younger Mo-Ni–polyelement (including PGE and Au) phosphatic and sulfidic black shales in the Yangtze platform. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/105/6/1047.abstract

Lithospheric, cratonic, and geodynamic setting of Ni-Cu-PGE sulfide deposits / Graham C. Begg in Economic geology, Vol. 105 N° 6 (Septembre/Octobre 2010) 

Public ISBD [article]  in Economic geology > Vol. 105 N° 6 (Septembre/Octobre 2010) . - pp. 1057-1070 Titre : Lithospheric, cratonic, and geodynamic setting of Ni-Cu-PGE sulfide deposits Type de document : texte imprimé Auteurs : Graham C. Begg, Auteur ; Jon A.M. Hronsky, Auteur ; Nicholas T. Arndt, Auteur Année de publication : 2011 Article en page(s) : pp. 1057-1070 Note générale : Economic Geology Langues : Anglais (eng) Mots-clés : Lithospheric  Cratonic  Ni-Cu-PGE  sulfide  deposits Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The location of magmatic Ni-Cu-PGE sulfide deposits is related to lithospheric architecture, particularly that of the subcontinental lithospheric mantle (SCLM). At crustal levels, this relationship is manifest by a close proximity to craton and paleocraton margins. Deposits are associated with mafic-ultramafic rocks and many show a close spatial relationship with a coeval large igneous province (LIP). Metal quantities and tenors observed in deposits require segregation of a magmatic sulfide melt from a large volume of parental ultramafic melt. Generation of these parental melts requires melting of upwelling mantle rising to depths of 100 km or less. The timing and tectonic setting of deposits indicates that this most likely occurs when mantle plumes impact on the base of the SCLM and are channeled laterally to areas of thinnest SCLM, where they undergo decompression melting. Alternatively, the setting of some smaller deposits suggests that upwelling may be induced by syn-to post-collisional lithospheric delamination. Craton margins are generally zones of relatively thin lithosphere and are the focus of strain during regional tectonism, providing points of dilation along active translithospheric faults. These faults facilitate melt introduction into the crust. The craton margin zone of thin lithosphere and active faulting may be adjacent to a neighboring block of continental lithosphere (paleocraton margin) or adjacent to a flanking narrow marginal basin (underlain by asthenosphere). All deposits form during periods of active regional tectonism, most commonly under mildly compressional to transpressional conditions. These different settings and conditions may result in differing depths of melting and differing depths and degrees of crustal interaction. The latter is believed to be a key factor for the development of a metal-rich sulfide melt, which is ultimately emplaced in the deposit environment. These variations can account for the observed range of ore and host rock types. Most large deposits are associated with intracontinental settings or with (former) passive margins at the edge of small marginal basins. No significant deposits are associated with the margins of large oceans or with supra-subduction zone environments, possibly reflecting poor preservational potential or (with the latter) limitations to plume interaction with continental lithosphere. A craton-margin model for the genesis of magmatic Ni-Cu-PGE deposits is proposed. This model provides a framework for further examination of deposit-forming processes and also provides a coherent predictive framework for mineral exploration. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/105/6/1057.abstract [article] Lithospheric, cratonic, and geodynamic setting of Ni-Cu-PGE sulfide deposits [texte imprimé] / Graham C. Begg, Auteur ; Jon A.M. Hronsky, Auteur ; Nicholas T. Arndt, Auteur . - 2011 . - pp. 1057-1070. Economic Geology Langues : Anglais (eng) in Economic geology > Vol. 105 N° 6 (Septembre/Octobre 2010) . - pp. 1057-1070 Mots-clés : Lithospheric  Cratonic  Ni-Cu-PGE  sulfide  deposits Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The location of magmatic Ni-Cu-PGE sulfide deposits is related to lithospheric architecture, particularly that of the subcontinental lithospheric mantle (SCLM). At crustal levels, this relationship is manifest by a close proximity to craton and paleocraton margins. Deposits are associated with mafic-ultramafic rocks and many show a close spatial relationship with a coeval large igneous province (LIP). Metal quantities and tenors observed in deposits require segregation of a magmatic sulfide melt from a large volume of parental ultramafic melt. Generation of these parental melts requires melting of upwelling mantle rising to depths of 100 km or less. The timing and tectonic setting of deposits indicates that this most likely occurs when mantle plumes impact on the base of the SCLM and are channeled laterally to areas of thinnest SCLM, where they undergo decompression melting. Alternatively, the setting of some smaller deposits suggests that upwelling may be induced by syn-to post-collisional lithospheric delamination. Craton margins are generally zones of relatively thin lithosphere and are the focus of strain during regional tectonism, providing points of dilation along active translithospheric faults. These faults facilitate melt introduction into the crust. The craton margin zone of thin lithosphere and active faulting may be adjacent to a neighboring block of continental lithosphere (paleocraton margin) or adjacent to a flanking narrow marginal basin (underlain by asthenosphere). All deposits form during periods of active regional tectonism, most commonly under mildly compressional to transpressional conditions. These different settings and conditions may result in differing depths of melting and differing depths and degrees of crustal interaction. The latter is believed to be a key factor for the development of a metal-rich sulfide melt, which is ultimately emplaced in the deposit environment. These variations can account for the observed range of ore and host rock types. Most large deposits are associated with intracontinental settings or with (former) passive margins at the edge of small marginal basins. No significant deposits are associated with the margins of large oceans or with supra-subduction zone environments, possibly reflecting poor preservational potential or (with the latter) limitations to plume interaction with continental lithosphere. A craton-margin model for the genesis of magmatic Ni-Cu-PGE deposits is proposed. This model provides a framework for further examination of deposit-forming processes and also provides a coherent predictive framework for mineral exploration. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/105/6/1057.abstract

The timing and formation of platinum-group minerals from the creighton Ni-Cu-platinum-group element sulfide deposit, sudbury, Canada / Sarah A. S. Dare in Economic geology, Vol. 105 N° 6 (Septembre/Octobre 2010) 

Public ISBD [article]  in Economic geology > Vol. 105 N° 6 (Septembre/Octobre 2010) . - pp. 1071-1096 Titre : The timing and formation of platinum-group minerals from the creighton Ni-Cu-platinum-group element sulfide deposit, sudbury, Canada : early crystallization of PGE-rich sulfarsenides Type de document : texte imprimé Auteurs : Sarah A. S. Dare, Auteur ; Sarah-Jane Barnes, Auteur ; Hazel M. Prichard, Auteur Année de publication : 2011 Article en page(s) : pp. 1071-1096 Note générale : Economic Geology Langues : Anglais (eng) Mots-clés : Minerals  platinum  Metal  Element  sulfide  deposit  Canada Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : Platinum-group elements (PGE) are typically hosted in base metal sulfides and by platinum-group minerals (PGM) in Ni-Cu-PGE sulfide deposits. At Sudbury, it appears that the majority of PGE are hosted in PGM. In order to understand why this is the case we have investigated the origin of PGM from the 402 trough ore-bodies of the Creighton deposit located on the South Range of Sudbury. These predominantly pyrrhotite-rich sulfides, with low (Pt + Pd)/(Os + Ir + Ru + Rh) whole-rock ratios, represent cumulates of monosulfide solid solution (MSS) that crystallized early from the sulfide melt, collected in troughs and embayments at the base of the Sudbury Igneous Complex, and formed small pendants of ore in the footwall country rock. The majority of PGE (Ir, Rh, Pt ± Os, Ru) show a stronger affinity for the sulfarsenide phases than the cocrystallizing sulfide phases which are strongly depleted in these PGE. The precious metal mineralogy is dominated by PGE sulfarsenides (86%) with subordinate sperrylite (PtAs2: 9%), michenerite (PdBiTe: 5%), and electrum (AgAu2: 0.1%). These discrete minerals are predominantly hosted within pyrrhotite and pentlandite except, however, a large proportion of michenerite is hosted either entirely by silicates and/or juxtaposed against silicates. The PGE sulfarsenides are euhedrally zoned with an irarsite (IrAsS) core, an outer layer of hollingworthite (RhAsS), and a PGE-rich Ni cobaltite rim (CoAsS). Rhenium sulfides, some of which are Os bearing, are documented for the first time at Sudbury. Platinum-group minerals may crystallize directly from sulfide melt, form by exsolution during cooling of the base metal sulfides or recrystallize from them during metamorphism. We propose that zoned PGE sulfarsenides and sperrylite crystallized from a sulfide melt at high temperatures (1,200°–900°C) and were subsequently surrounded by MSS cumulates, even by disseminated sulfides, that crystallized from the now Ir, Rh, Pt ± Os, Ru-depleted immiscible sulfide liquid. The base metal sulfides recrystallized with secondary hydrosilicates at a late magmatic and/or hydrothermal stage (<540°C) at which time michenerite formed. The magmatic zoning of the PGE sulfarsenides was preserved during later deformation in shear zones but these PGM were corroded, fractured, and juxtaposed against silicates. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/105/6/1071.abstract [article] The timing and formation of platinum-group minerals from the creighton Ni-Cu-platinum-group element sulfide deposit, sudbury, Canada : early crystallization of PGE-rich sulfarsenides [texte imprimé] / Sarah A. S. Dare, Auteur ; Sarah-Jane Barnes, Auteur ; Hazel M. Prichard, Auteur . - 2011 . - pp. 1071-1096. Economic Geology Langues : Anglais (eng) in Economic geology > Vol. 105 N° 6 (Septembre/Octobre 2010) . - pp. 1071-1096 Mots-clés : Minerals  platinum  Metal  Element  sulfide  deposit  Canada Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : Platinum-group elements (PGE) are typically hosted in base metal sulfides and by platinum-group minerals (PGM) in Ni-Cu-PGE sulfide deposits. At Sudbury, it appears that the majority of PGE are hosted in PGM. In order to understand why this is the case we have investigated the origin of PGM from the 402 trough ore-bodies of the Creighton deposit located on the South Range of Sudbury. These predominantly pyrrhotite-rich sulfides, with low (Pt + Pd)/(Os + Ir + Ru + Rh) whole-rock ratios, represent cumulates of monosulfide solid solution (MSS) that crystallized early from the sulfide melt, collected in troughs and embayments at the base of the Sudbury Igneous Complex, and formed small pendants of ore in the footwall country rock. The majority of PGE (Ir, Rh, Pt ± Os, Ru) show a stronger affinity for the sulfarsenide phases than the cocrystallizing sulfide phases which are strongly depleted in these PGE. The precious metal mineralogy is dominated by PGE sulfarsenides (86%) with subordinate sperrylite (PtAs2: 9%), michenerite (PdBiTe: 5%), and electrum (AgAu2: 0.1%). These discrete minerals are predominantly hosted within pyrrhotite and pentlandite except, however, a large proportion of michenerite is hosted either entirely by silicates and/or juxtaposed against silicates. The PGE sulfarsenides are euhedrally zoned with an irarsite (IrAsS) core, an outer layer of hollingworthite (RhAsS), and a PGE-rich Ni cobaltite rim (CoAsS). Rhenium sulfides, some of which are Os bearing, are documented for the first time at Sudbury. Platinum-group minerals may crystallize directly from sulfide melt, form by exsolution during cooling of the base metal sulfides or recrystallize from them during metamorphism. We propose that zoned PGE sulfarsenides and sperrylite crystallized from a sulfide melt at high temperatures (1,200°–900°C) and were subsequently surrounded by MSS cumulates, even by disseminated sulfides, that crystallized from the now Ir, Rh, Pt ± Os, Ru-depleted immiscible sulfide liquid. The base metal sulfides recrystallized with secondary hydrosilicates at a late magmatic and/or hydrothermal stage (<540°C) at which time michenerite formed. The magmatic zoning of the PGE sulfarsenides was preserved during later deformation in shear zones but these PGM were corroded, fractured, and juxtaposed against silicates. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/105/6/1071.abstract

Controls on tellurium in base, precious, and telluride minerals in the panormos Bay Ag-Au-Te deposits, Tinos Island, Cyclades, Greece / Stylianos Tombros in Economic geology, Vol. 105 N° 6 (Septembre/Octobre 2010) 

Public ISBD [article]  in Economic geology > Vol. 105 N° 6 (Septembre/Octobre 2010) . - pp. 1097-1111 Titre : Controls on tellurium in base, precious, and telluride minerals in the panormos Bay Ag-Au-Te deposits, Tinos Island, Cyclades, Greece Type de document : texte imprimé Auteurs : Stylianos Tombros, Auteur ; Karen St. Seymour, Auteur ; Anthony E. Williams-Jones, Auteur Année de publication : 2011 Article en page(s) : pp. 1097-1111 Note générale : Economic Geology Langues : Anglais (eng) Mots-clés : Tellurium  Minerals  Tinos  Island  Greece Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : Tellurium-bearing base metal assemblages dominate the eight stages of mineralization in quartz ± calcite ± adularia ± illite epithermal Au-Ag-Te veins at Panormos Bay, Tinos Island, Cyclades. Tellurium-bearing sulfides and sulfosalts both preceded and followed the main, telluride-forming event (stage V). The complex stage V telluride assemblage was characterized by a sequence of early Ag-, middle Cu-, and late Au-bearing tellurides. There is textural evidence for epitaxial growth of the tellurides. Phase separation of carbon dioxide would have caused H2Te(g) to partition into a gaseous phase and resulted in pH neutralization. Due to rapid up-vapor transport, tellurium-bearing vapors probably supersaturated, condensed as droplets, and were resorbed into the ore-forming solution. These mechanisms enhanced local Te enrichment in the mineralizing liquid, above equilibrium, of ∑Te as H2Te(g) (i.e., log fH2Te(g) values of −0.5 to −1.5), and resulted in epitaxial growth of stage V tellurides. Epitaxy in the Panormos Bay case can be simulated by the Stranski-Krastanov crystal growth model. For supersaturation ratios with S values of 1 and 4, we predict an overall increase of the nucleation rate of tellurium and subsequent telluride precipitation. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/105/6/1097.abstract [article] Controls on tellurium in base, precious, and telluride minerals in the panormos Bay Ag-Au-Te deposits, Tinos Island, Cyclades, Greece [texte imprimé] / Stylianos Tombros, Auteur ; Karen St. Seymour, Auteur ; Anthony E. Williams-Jones, Auteur . - 2011 . - pp. 1097-1111. Economic Geology Langues : Anglais (eng) in Economic geology > Vol. 105 N° 6 (Septembre/Octobre 2010) . - pp. 1097-1111 Mots-clés : Tellurium  Minerals  Tinos  Island  Greece Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : Tellurium-bearing base metal assemblages dominate the eight stages of mineralization in quartz ± calcite ± adularia ± illite epithermal Au-Ag-Te veins at Panormos Bay, Tinos Island, Cyclades. Tellurium-bearing sulfides and sulfosalts both preceded and followed the main, telluride-forming event (stage V). The complex stage V telluride assemblage was characterized by a sequence of early Ag-, middle Cu-, and late Au-bearing tellurides. There is textural evidence for epitaxial growth of the tellurides. Phase separation of carbon dioxide would have caused H2Te(g) to partition into a gaseous phase and resulted in pH neutralization. Due to rapid up-vapor transport, tellurium-bearing vapors probably supersaturated, condensed as droplets, and were resorbed into the ore-forming solution. These mechanisms enhanced local Te enrichment in the mineralizing liquid, above equilibrium, of ∑Te as H2Te(g) (i.e., log fH2Te(g) values of −0.5 to −1.5), and resulted in epitaxial growth of stage V tellurides. Epitaxy in the Panormos Bay case can be simulated by the Stranski-Krastanov crystal growth model. For supersaturation ratios with S values of 1 and 4, we predict an overall increase of the nucleation rate of tellurium and subsequent telluride precipitation. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/105/6/1097.abstract

Geochronology and geochemistry of the MAX porphyry Mo deposit and its relationship to Pb-Zn-Ag mineralization, Kootenay arc, southeastern British Columbia, Canada / C. J. M. Lawley in Economic geology, Vol. 105 N° 6 (Septembre/Octobre 2010) 

Public ISBD [article]  in Economic geology > Vol. 105 N° 6 (Septembre/Octobre 2010) . - pp. 1113-1142 Titre : Geochronology and geochemistry of the MAX porphyry Mo deposit and its relationship to Pb-Zn-Ag mineralization, Kootenay arc, southeastern British Columbia, Canada Type de document : texte imprimé Auteurs : C. J. M. Lawley, Auteur ; J. P. Richards, Auteur ; R. G. Anderson, Auteur Année de publication : 2011 Article en page(s) : pp. 1113-1142 Note générale : Economic Geology Langues : Anglais (eng) Mots-clés : Geochronology  Geochemistry  Mineralization  Canada Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The MAX porphyry Mo deposit is located at the northern end of the Kootenay arc in southeastern British Columbia, Canada. Molybdenum mineralization is genetically related to the variably altered Trout Lake granodiorite stock, which has lithogeochemical affinities to the low fluorine, calc-alkaline, granodiorite-hosted porphyry Mo deposit type. Three molybdenite samples from early and late Mo-bearing veins yield Re-Os dates that overlap within analytical error, with a weighted average age of 80.3 ± 0.2 Ma. These dates are in close agreement with two 206Pb/238U weighted average zircon ages for phases of the Trout Lake stock at 80.3 ± 1.6 and 79.2 ± 1.0 Ma, indicating that crystallization of the stock and hydrothermal molybdenite formation were coeval and likely cogenetic. 40Ar/39Ar plateau ages for primary biotite in igneous dikes, secondary biotite in early potassic alteration, and muscovite in late phyllic alteration range from 80 to 76 Ma. The younger 40Ar/39Ar plateau ages may reflect unusually slow cooling of the magmatic-hydrothermal system or a late thermal disturbance. Pb-Zn-Ag vein deposits are common throughout the Kootenay arc and several such veins are located within and proximal to the MAX porphyry Mo deposit. The presence of rare molybdenite associated with sphalerite and argentiferous galena in some of these Pb-Zn-Ag veins suggests that they represent a late-stage event related to the MAX magmatic-hydrothermal system. Fluid inclusions in quartz from Mo and Pb-Zn-Ag veins are similar and can be divided into two compositional groups: type 1, aqueous liquid-rich fluid inclusions; and type 2, aqueous-carbonic liquid-rich fluid inclusions. Pressure-corrected (1.4–1.7 kbar) trapping temperatures of typical type 1 inclusions from Mo-bearing veins range from 430° to 460°C, and for Pb-Zn-Ag veins, from 335° to 365°C. The ranges of salinity (0–12 wt % NaCl equiv) in fluid inclusions from both vein types are almost identical, and type 2 inclusions from both vein types contain similar amounts of CO2 (avg XCO2 = 0.08) with traces of CH4. The similarity of chemistry in the two vein types suggests a genetic link between porphyry Mo mineralization and adjacent Pb-Zn-Ag deposits. However, muscovite from the alteration halo around a Pb-Zn-Ag vein within the MAX deposit yielded a 40Ar/39Ar plateau age of 72.2 ± 0.5 Ma. This date is significantly younger than the ~80 Ma age of porphyry magmatism and Mo mineralization, suggesting either that this event is in fact unrelated to porphyry Mo mineralization at 80 Ma, or that the K-Ar isotope system has been disturbed by a later thermal event. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/105/6/1113.abstract [article] Geochronology and geochemistry of the MAX porphyry Mo deposit and its relationship to Pb-Zn-Ag mineralization, Kootenay arc, southeastern British Columbia, Canada [texte imprimé] / C. J. M. Lawley, Auteur ; J. P. Richards, Auteur ; R. G. Anderson, Auteur . - 2011 . - pp. 1113-1142. Economic Geology Langues : Anglais (eng) in Economic geology > Vol. 105 N° 6 (Septembre/Octobre 2010) . - pp. 1113-1142 Mots-clés : Geochronology  Geochemistry  Mineralization  Canada Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The MAX porphyry Mo deposit is located at the northern end of the Kootenay arc in southeastern British Columbia, Canada. Molybdenum mineralization is genetically related to the variably altered Trout Lake granodiorite stock, which has lithogeochemical affinities to the low fluorine, calc-alkaline, granodiorite-hosted porphyry Mo deposit type. Three molybdenite samples from early and late Mo-bearing veins yield Re-Os dates that overlap within analytical error, with a weighted average age of 80.3 ± 0.2 Ma. These dates are in close agreement with two 206Pb/238U weighted average zircon ages for phases of the Trout Lake stock at 80.3 ± 1.6 and 79.2 ± 1.0 Ma, indicating that crystallization of the stock and hydrothermal molybdenite formation were coeval and likely cogenetic. 40Ar/39Ar plateau ages for primary biotite in igneous dikes, secondary biotite in early potassic alteration, and muscovite in late phyllic alteration range from 80 to 76 Ma. The younger 40Ar/39Ar plateau ages may reflect unusually slow cooling of the magmatic-hydrothermal system or a late thermal disturbance. Pb-Zn-Ag vein deposits are common throughout the Kootenay arc and several such veins are located within and proximal to the MAX porphyry Mo deposit. The presence of rare molybdenite associated with sphalerite and argentiferous galena in some of these Pb-Zn-Ag veins suggests that they represent a late-stage event related to the MAX magmatic-hydrothermal system. Fluid inclusions in quartz from Mo and Pb-Zn-Ag veins are similar and can be divided into two compositional groups: type 1, aqueous liquid-rich fluid inclusions; and type 2, aqueous-carbonic liquid-rich fluid inclusions. Pressure-corrected (1.4–1.7 kbar) trapping temperatures of typical type 1 inclusions from Mo-bearing veins range from 430° to 460°C, and for Pb-Zn-Ag veins, from 335° to 365°C. The ranges of salinity (0–12 wt % NaCl equiv) in fluid inclusions from both vein types are almost identical, and type 2 inclusions from both vein types contain similar amounts of CO2 (avg XCO2 = 0.08) with traces of CH4. The similarity of chemistry in the two vein types suggests a genetic link between porphyry Mo mineralization and adjacent Pb-Zn-Ag deposits. However, muscovite from the alteration halo around a Pb-Zn-Ag vein within the MAX deposit yielded a 40Ar/39Ar plateau age of 72.2 ± 0.5 Ma. This date is significantly younger than the ~80 Ma age of porphyry magmatism and Mo mineralization, suggesting either that this event is in fact unrelated to porphyry Mo mineralization at 80 Ma, or that the K-Ar isotope system has been disturbed by a later thermal event. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/105/6/1113.abstract

Cu-rich scales in the Reykjanes geothermal system, Iceland / Vigdís Hardardóttir in Economic geology, Vol. 105 N° 6 (Septembre/Octobre 2010) 

Public ISBD [article]  in Economic geology > Vol. 105 N° 6 (Septembre/Octobre 2010) . - pp. 1143-1155 Titre : Cu-rich scales in the Reykjanes geothermal system, Iceland Type de document : texte imprimé Auteurs : Vigdís Hardardóttir, Auteur ; Mark Hannington, Auteur ; Jeffrey Hedenquist, Auteur Année de publication : 2011 Article en page(s) : pp. 1143-1155 Note générale : Economic Geology Langues : Anglais (eng) Mots-clés : Reykjanes  geothermal  system  Sulfide  mineralogy  Cu  sulfides  Iceland Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : Seawater-dominated fluids discharge from the subaerial Reykjanes geothermal system, Iceland. There is a sharp pressure decrease in surface pipes at an orifice (throttle point), and Cu-rich scales deposit at this orifice that consist largely of bornite and digenite, along with sphalerite and other sulfides. The bornite and digenite form complex intergrowths with sphalerite and galena, accompanied by high concentrations of gold and silver (up to 590 ppm and 2.3 wt %, respectively). The precipitates form in response to rapid boiling (flashing) of the hydrothermal fluids due to the sharp decrease in pressure (~37–22 bars) at the orifice, downstream of the well-head. The boiling, and concomitant separation of the vapor phase, results in a temperature decrease from 252° to 220°C across this throttle over distances of centimeters. There is a nearly quantitative deposition of metals from solution compared to concentrations in reservoir liquids, resulting in formation of the metastable Cu-FeS solid solution, rich in silver and gold, plus sphalerite and galena. A high degree of supersaturation of metals in the quenched liquid is indicated by the very fine grain size of the sulfides and dendritic textures. Postdepositional cooling likely caused exsolution of bornite and digenite from the high-temperature solid solution; in addition, silver was expelled from the Cu-Fe-S solid solution and remobilized into late fractures in the scales, whereas the gold appears to have remained in solid solution or as submicroscopic inclusions in the bornite and digenite. The observed mineral assemblage at Reykjanes contrasts with that of sea-floor black smokers, despite similar fluid compositions. The sea-floor hydrothermal vents characteristically have Cu-rich linings composed predominantly of chalcopyrite, which is precipitated by a combination of conductive cooling of high-temperature (~350°C) hydrothermal fluids and mixing with seawater. The difference in sulfide mineralogy between the Reykjanes orifice scales, with Cu sulfides dominated by bornite and digenite, and many sea-floor vents may provide an indication of the subsea-floor mineralization where fluids boil before discharging at sea-floor vents. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/105/6/1143.abstract [article] Cu-rich scales in the Reykjanes geothermal system, Iceland [texte imprimé] / Vigdís Hardardóttir, Auteur ; Mark Hannington, Auteur ; Jeffrey Hedenquist, Auteur . - 2011 . - pp. 1143-1155. Economic Geology Langues : Anglais (eng) in Economic geology > Vol. 105 N° 6 (Septembre/Octobre 2010) . - pp. 1143-1155 Mots-clés : Reykjanes  geothermal  system  Sulfide  mineralogy  Cu  sulfides  Iceland Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : Seawater-dominated fluids discharge from the subaerial Reykjanes geothermal system, Iceland. There is a sharp pressure decrease in surface pipes at an orifice (throttle point), and Cu-rich scales deposit at this orifice that consist largely of bornite and digenite, along with sphalerite and other sulfides. The bornite and digenite form complex intergrowths with sphalerite and galena, accompanied by high concentrations of gold and silver (up to 590 ppm and 2.3 wt %, respectively). The precipitates form in response to rapid boiling (flashing) of the hydrothermal fluids due to the sharp decrease in pressure (~37–22 bars) at the orifice, downstream of the well-head. The boiling, and concomitant separation of the vapor phase, results in a temperature decrease from 252° to 220°C across this throttle over distances of centimeters. There is a nearly quantitative deposition of metals from solution compared to concentrations in reservoir liquids, resulting in formation of the metastable Cu-FeS solid solution, rich in silver and gold, plus sphalerite and galena. A high degree of supersaturation of metals in the quenched liquid is indicated by the very fine grain size of the sulfides and dendritic textures. Postdepositional cooling likely caused exsolution of bornite and digenite from the high-temperature solid solution; in addition, silver was expelled from the Cu-Fe-S solid solution and remobilized into late fractures in the scales, whereas the gold appears to have remained in solid solution or as submicroscopic inclusions in the bornite and digenite. The observed mineral assemblage at Reykjanes contrasts with that of sea-floor black smokers, despite similar fluid compositions. The sea-floor hydrothermal vents characteristically have Cu-rich linings composed predominantly of chalcopyrite, which is precipitated by a combination of conductive cooling of high-temperature (~350°C) hydrothermal fluids and mixing with seawater. The difference in sulfide mineralogy between the Reykjanes orifice scales, with Cu sulfides dominated by bornite and digenite, and many sea-floor vents may provide an indication of the subsea-floor mineralization where fluids boil before discharging at sea-floor vents. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/105/6/1143.abstract

Longevity of porphyry copper formation at Quellaveco, Peru / Richard H. Sillitoe in Economic geology, Vol. 105 N° 6 (Septembre/Octobre 2010) 

Public ISBD [article]  in Economic geology > Vol. 105 N° 6 (Septembre/Octobre 2010) . - pp. 1157-1162 Titre : Longevity of porphyry copper formation at Quellaveco, Peru Type de document : texte imprimé Auteurs : Richard H. Sillitoe, Auteur ; James K. Mortensen, Auteur Année de publication : 2011 Article en page(s) : pp. 1157-1162 Note générale : Economic Geology Langues : Anglais (eng) Mots-clés : Porphyry  copper  Geochronology  Peru Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : Metal introduction at the late Paleocene to early Eocene Quellaveco porphyry copper-molybdenum deposit in southern Peru spans several phases of quartz monzonite porphyry emplacement and is bracketed by a precursor granodiorite pluton and a late-mineral porphyry body that postdates essentially all copper introduction. Together, the U-Pb ages of zircons from these intrusive rocks show that 1.08 ± 0.58 m.y. elapsed between the precursor pluton and initiation of stock emplacement; the porphyry system was active intermittently for at least 3.25 m.y. (4.07 ± 0.82 m.y.); and at least three-quarters of the copper inventory was deposited in a maximum of 3.12 m.y. (2.51 ± 0.61 m.y.). Recent U-Pb zircon dating of several other major central Andean porphyry copper deposits, in combination with other isotopic techniques, suggests that 2.5- to 4-m.y. life spans are commonplace. The longevity of porphyry copper systems implied by these studies appears to reflect the protracted time gaps between the multiple intrusions that intermittently replenished porphyry stocks. Other precise isotopic methods (Re-Os, 40Ar/39Ar) typically document shorter life spans because it is more difficult, if not impossible, to date the full sequence of events involved in porphyry copper formation. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/105/6/1157.abstract [article] Longevity of porphyry copper formation at Quellaveco, Peru [texte imprimé] / Richard H. Sillitoe, Auteur ; James K. Mortensen, Auteur . - 2011 . - pp. 1157-1162. Economic Geology Langues : Anglais (eng) in Economic geology > Vol. 105 N° 6 (Septembre/Octobre 2010) . - pp. 1157-1162 Mots-clés : Porphyry  copper  Geochronology  Peru Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : Metal introduction at the late Paleocene to early Eocene Quellaveco porphyry copper-molybdenum deposit in southern Peru spans several phases of quartz monzonite porphyry emplacement and is bracketed by a precursor granodiorite pluton and a late-mineral porphyry body that postdates essentially all copper introduction. Together, the U-Pb ages of zircons from these intrusive rocks show that 1.08 ± 0.58 m.y. elapsed between the precursor pluton and initiation of stock emplacement; the porphyry system was active intermittently for at least 3.25 m.y. (4.07 ± 0.82 m.y.); and at least three-quarters of the copper inventory was deposited in a maximum of 3.12 m.y. (2.51 ± 0.61 m.y.). Recent U-Pb zircon dating of several other major central Andean porphyry copper deposits, in combination with other isotopic techniques, suggests that 2.5- to 4-m.y. life spans are commonplace. The longevity of porphyry copper systems implied by these studies appears to reflect the protracted time gaps between the multiple intrusions that intermittently replenished porphyry stocks. Other precise isotopic methods (Re-Os, 40Ar/39Ar) typically document shorter life spans because it is more difficult, if not impossible, to date the full sequence of events involved in porphyry copper formation. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/105/6/1157.abstract

An evaluation of the effect of copper on the estimation of sulfur fugacity (fs2) from phyrrhotite composition / Michael J. Mengason in Economic geology, Vol. 105 N° 6 (Septembre/Octobre 2010) 

Public ISBD [article]  in Economic geology > Vol. 105 N° 6 (Septembre/Octobre 2010) . - pp. 1163-1169 Titre : An evaluation of the effect of copper on the estimation of sulfur fugacity (fs2) from phyrrhotite composition Type de document : texte imprimé Auteurs : Michael J. Mengason, Auteur ; Philip M. Piccoli, Auteur ; Philip Candela, Auteur Année de publication : 2011 Article en page(s) : pp. 1163-1169 Note générale : Economic Geology Langues : Anglais (eng) Mots-clés : Copper  Sulfur  fugacity  Pyrrhotite Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : Pyrrhotite is commonly used to estimate the fugacity of sulfur in natural and experimental systems; however, in some instances, high-temperature pyrrhotites can incorporate copper to such an extent as to raise questions concerning the accuracy of the sulfur fugacities calculated on the basis of their composition. The equation of Toulmin and Barton (1964), which is commonly used to determine sulfur fugacity from the composition of binary pyrrhotite (Fe1−xS) solid solutions, can be modified to account for the presence of other phase components. Three methods of incorporating the concentration of copper in the equation of Toulmin and Barton (1964) were evaluated in light of data from experiments performed at 1,000°C, which yielded run-product pyrrhotites with 0.028 (±0.005, 1σ) to 5.75 (±0.06) wt percent copper. Mixtures of synthetic pyrrhotite and bornite were heated in sealed, evacuated silica tubes, which were internally divided into separate chambers by silica rods. As a result, pyrrhotite grains with a range of copper concentrations, as well as copper-free “reference” pyrrhotites, were equilibrated at a common sulfur fugacity. The discrepancy between sulfur fugacity calculated from “reference” pyrrhotite and copper-rich pyrrhotite, based on EPMA analyses, indicated a source of error and potential for disagreement between published accounts when different methods are used to address the presence of copper. The term NFeS in the equation of Toulmin and Barton (1964), calculated as XFeSpyrrhotite in the system FeS-S2, was replaced by terms that incorporated the effect of copper. Method 1: —copper was ignored. Method 2: —copper was treated as CuS0.5. Method 3: —copper was treated as CuS. Method 1 overestimated log fS2 (bars) by 0.25 (±0.08, 1σ) per wt percent copper. Method 2 resulted in consistent fugacity estimates regardless of the concentration of copper in pyrrhotite, and is the recommended method. Method 3 underestimated log fS2 by 0.3 (±0.2) per wt percent copper. These systematic errors are propagated into the calculation of oxygen fugacity based on magnetite-pyrrhotite coexistence, resulting in a correction factor of ~¼ log fO2 per wt percent copper by the use of either Method 1 or 3 in determining sulfur fugacity. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/105/6/1163.abstract [article] An evaluation of the effect of copper on the estimation of sulfur fugacity (fs2) from phyrrhotite composition [texte imprimé] / Michael J. Mengason, Auteur ; Philip M. Piccoli, Auteur ; Philip Candela, Auteur . - 2011 . - pp. 1163-1169. Economic Geology Langues : Anglais (eng) in Economic geology > Vol. 105 N° 6 (Septembre/Octobre 2010) . - pp. 1163-1169 Mots-clés : Copper  Sulfur  fugacity  Pyrrhotite Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : Pyrrhotite is commonly used to estimate the fugacity of sulfur in natural and experimental systems; however, in some instances, high-temperature pyrrhotites can incorporate copper to such an extent as to raise questions concerning the accuracy of the sulfur fugacities calculated on the basis of their composition. The equation of Toulmin and Barton (1964), which is commonly used to determine sulfur fugacity from the composition of binary pyrrhotite (Fe1−xS) solid solutions, can be modified to account for the presence of other phase components. Three methods of incorporating the concentration of copper in the equation of Toulmin and Barton (1964) were evaluated in light of data from experiments performed at 1,000°C, which yielded run-product pyrrhotites with 0.028 (±0.005, 1σ) to 5.75 (±0.06) wt percent copper. Mixtures of synthetic pyrrhotite and bornite were heated in sealed, evacuated silica tubes, which were internally divided into separate chambers by silica rods. As a result, pyrrhotite grains with a range of copper concentrations, as well as copper-free “reference” pyrrhotites, were equilibrated at a common sulfur fugacity. The discrepancy between sulfur fugacity calculated from “reference” pyrrhotite and copper-rich pyrrhotite, based on EPMA analyses, indicated a source of error and potential for disagreement between published accounts when different methods are used to address the presence of copper. The term NFeS in the equation of Toulmin and Barton (1964), calculated as XFeSpyrrhotite in the system FeS-S2, was replaced by terms that incorporated the effect of copper. Method 1: —copper was ignored. Method 2: —copper was treated as CuS0.5. Method 3: —copper was treated as CuS. Method 1 overestimated log fS2 (bars) by 0.25 (±0.08, 1σ) per wt percent copper. Method 2 resulted in consistent fugacity estimates regardless of the concentration of copper in pyrrhotite, and is the recommended method. Method 3 underestimated log fS2 by 0.3 (±0.2) per wt percent copper. These systematic errors are propagated into the calculation of oxygen fugacity based on magnetite-pyrrhotite coexistence, resulting in a correction factor of ~¼ log fO2 per wt percent copper by the use of either Method 1 or 3 in determining sulfur fugacity. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/105/6/1163.abstract

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