Dépouillements

Mineralogy and PTX relationships of the Archean Hannan South Au-Cu (Co-Bi) deposit, Kalgoorlie, Western Australia / Andreas G. Mueller in Economic geology, Vol. 107 N° 1 (Janvier/Fevrier 2012) 

Public ISBD [article]  in Economic geology > Vol. 107 N° 1 (Janvier/Fevrier 2012) . - pp. 1-24 Titre : Mineralogy and PTX relationships of the Archean Hannan South Au-Cu (Co-Bi) deposit, Kalgoorlie, Western Australia : Thermodynamic constraints on the formation of a zoned intrusion-related Skarn Type de document : texte imprimé Auteurs : Andreas G. Mueller, Auteur ; Louisa M. Lawrance, Auteur ; Janet Muhling, Auteur Année de publication : 2012 Article en page(s) : pp. 1-24 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : Au-Cu  (Co-Bi)  deposit  Thermodynamic  constraints  Australia Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Hannan South Au-Cu skarn deposit is located 12 km southeast of Kalgoorlie in the 2.7 Ga Eastern Goldfields Orogen of the Archean Yilgarn Craton, Western Australia. Two epidote-quartz-calcite-magnetite orebodies, controlled by the same reverse fault but separated by 450 m, occur in granodiorite porphyry: an Au-Cu skarn in the southeast (30 vol % calcite) and an Au-Co-Bi skarn in the northwest (5–10 vol % calcite). Both are interpreted as remnants of a single eroded body. Regional and skarn pressure estimates of 400 ± 150 MPa indicate formation at 14 ± 5 km paleodepth. Thermodynamic analysis of the silicate-calcite and oxide-sulfide assemblages constrains the temperature of the H2O-CO2 fluid to 480° to 530°C in the proximal SE skarn (0.5 wt % Cu, 0.35 g/t Au, 6 g/t Ag), and to 417° ± 32°C in the more distal NW skarn (<0.1 wt % Cu, 3.5 g/t Au, 1–2 g/t Ag). The oxygen fugacity of the fluid declined with temperature from log fO2 = −18 to −19 (at 500°C) in the southeast, defined by magnetite + rutile ± hematite and by iron-rich epidote (pistacite = 0.31), to log fO2 = −24 to −26 (at 415°C) in the northwest, defined by magnetite + rutile ± ilmenite and by low iron epidote (ps = 0.25). The high oxygen fugacity stabilized phengitic muscovite + magnetite and restricted the occurrence of biotite to the NW skarn front. The fugacity of total dissolved sulfur decreased with temperature from log fS2 = −3 to about log fS2 = −6.5 buffered by pyrite ± pyrrhotite. In the SE skarn, copper precipitated mainly as intermediate solid solution (iss, Cu = Fe), which exsolved inclusions of sphalerite, galena, and Ag-Bi alloy but retained elevated bismuth (≤1,600 ppm) and silver (≤1,800 ppm) during cooling and inversion to chalcopyrite. Minor gold and electrum (≤60 wt % Ag) precipitated together with chalcopyrite and pyrite. In the more distal NW skarn, fluid cooling and reduction caused the deposition of pyrite, minor cobaltite, native gold, and bismuth minerals leading to the large-scale enrichment of gold (3.5 ppm) and bismuth (130–240 ppm). While the SE skarn contains trace hessite, tetradymite, and aikinite, all stable to at least 540°C, the NW skarn contains abundant bismuth sulfosalts (krupkaite, pekoite, junoite, felbertalite, nuffieldite, cosalite) and tellurosulfides (joseite, aleksite). Cosalite is not stable above 425° ± 25°C. The zoned Hannan South skarn is part of a cluster of intrusion-related Au-Cu and distal Ag-Au-Pb-Zn deposits located within 60 km E to SE of the giant Golden Mile (>1,500 t Au) at Kalgoorlie, and part of a larger genetic group including the diorite-hosted Boddington porphyry skarn deposit (968 Mt at 0.11% Cu and 0.65 g/t Au). DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/1/1.abstract [article] Mineralogy and PTX relationships of the Archean Hannan South Au-Cu (Co-Bi) deposit, Kalgoorlie, Western Australia : Thermodynamic constraints on the formation of a zoned intrusion-related Skarn [texte imprimé] / Andreas G. Mueller, Auteur ; Louisa M. Lawrance, Auteur ; Janet Muhling, Auteur . - 2012 . - pp. 1-24. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 1 (Janvier/Fevrier 2012) . - pp. 1-24 Mots-clés : Au-Cu  (Co-Bi)  deposit  Thermodynamic  constraints  Australia Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Hannan South Au-Cu skarn deposit is located 12 km southeast of Kalgoorlie in the 2.7 Ga Eastern Goldfields Orogen of the Archean Yilgarn Craton, Western Australia. Two epidote-quartz-calcite-magnetite orebodies, controlled by the same reverse fault but separated by 450 m, occur in granodiorite porphyry: an Au-Cu skarn in the southeast (30 vol % calcite) and an Au-Co-Bi skarn in the northwest (5–10 vol % calcite). Both are interpreted as remnants of a single eroded body. Regional and skarn pressure estimates of 400 ± 150 MPa indicate formation at 14 ± 5 km paleodepth. Thermodynamic analysis of the silicate-calcite and oxide-sulfide assemblages constrains the temperature of the H2O-CO2 fluid to 480° to 530°C in the proximal SE skarn (0.5 wt % Cu, 0.35 g/t Au, 6 g/t Ag), and to 417° ± 32°C in the more distal NW skarn (<0.1 wt % Cu, 3.5 g/t Au, 1–2 g/t Ag). The oxygen fugacity of the fluid declined with temperature from log fO2 = −18 to −19 (at 500°C) in the southeast, defined by magnetite + rutile ± hematite and by iron-rich epidote (pistacite = 0.31), to log fO2 = −24 to −26 (at 415°C) in the northwest, defined by magnetite + rutile ± ilmenite and by low iron epidote (ps = 0.25). The high oxygen fugacity stabilized phengitic muscovite + magnetite and restricted the occurrence of biotite to the NW skarn front. The fugacity of total dissolved sulfur decreased with temperature from log fS2 = −3 to about log fS2 = −6.5 buffered by pyrite ± pyrrhotite. In the SE skarn, copper precipitated mainly as intermediate solid solution (iss, Cu = Fe), which exsolved inclusions of sphalerite, galena, and Ag-Bi alloy but retained elevated bismuth (≤1,600 ppm) and silver (≤1,800 ppm) during cooling and inversion to chalcopyrite. Minor gold and electrum (≤60 wt % Ag) precipitated together with chalcopyrite and pyrite. In the more distal NW skarn, fluid cooling and reduction caused the deposition of pyrite, minor cobaltite, native gold, and bismuth minerals leading to the large-scale enrichment of gold (3.5 ppm) and bismuth (130–240 ppm). While the SE skarn contains trace hessite, tetradymite, and aikinite, all stable to at least 540°C, the NW skarn contains abundant bismuth sulfosalts (krupkaite, pekoite, junoite, felbertalite, nuffieldite, cosalite) and tellurosulfides (joseite, aleksite). Cosalite is not stable above 425° ± 25°C. The zoned Hannan South skarn is part of a cluster of intrusion-related Au-Cu and distal Ag-Au-Pb-Zn deposits located within 60 km E to SE of the giant Golden Mile (>1,500 t Au) at Kalgoorlie, and part of a larger genetic group including the diorite-hosted Boddington porphyry skarn deposit (968 Mt at 0.11% Cu and 0.65 g/t Au). DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/1/1.abstract

Petrography, mineralogy, and geochemistry of the Nkamouna serpentinite / Gideon Lambiv Dzemua in Economic geology, Vol. 107 N° 1 (Janvier/Fevrier 2012) 

Public ISBD [article]  in Economic geology > Vol. 107 N° 1 (Janvier/Fevrier 2012) . - pp. 25-41 Titre : Petrography, mineralogy, and geochemistry of the Nkamouna serpentinite : implications for the formation of the cobalt-manganese laterite deposit, southeast Cameroon Type de document : texte imprimé Auteurs : Gideon Lambiv Dzemua, Auteur ; Sarah A. Gleeson, Auteur Année de publication : 2012 Article en page(s) : pp. 25-41 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : Nkamouna  serpentinite  Cobalt-manganese  laterite  deposit  Mineralogy  Cameroun Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Nkamouna Co-Mn-Ni laterite is an advanced exploration project located in southeast Cameroon. The deposit comprises a deep and complex laterite profile with high Co (~0.25 wt %) and Mn (1.33 wt %) contents, subeconomic Ni grade and a Ni:Co ratio of less than 3. This makes Nkamouna an unusual type of laterite deposit as it will be primarily mined for Co. The Co-Mn mineralization occurs at the interface between an overlying allochthonous felsic rock-sourced laterite and a lower in situ serpentinite-derived laterite. The serpentinite is massive with a nonpseudomorphic texture and consists of two genetically related phases: Serpentinite-I and Serpentinite-II. Serpentinite-I is characterized by antigorite, magnetite, quartz, ferritchromite, and magnesite, and Serpentinite-II by antigorite and magnesite. Both serpentinite types are extremely low in sulfides. Serpentinite-I is the dominant and oldest phase and was derived from a subcontinental mantle (pyroxene-rich) peridotite emplaced in the crust during the Pan-African orogeny. The Ni concentration in the serpentinite is variable (0.07–0.30%) and heterogeneously distributed, partly reflecting the present dominance of pyroxenes in the protolith. However, Ni is also hosted by magnetite and ferritchromite. The differential weathering of these Ni-hosting minerals is also responsible for the lower Ni grade of the deposit. Importantly, the serpentinite is depleted in Co and Mn and the enrichment of these elements in the laterite profile suggests that these elements may be derived from an exotic source. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/1/25.short [article] Petrography, mineralogy, and geochemistry of the Nkamouna serpentinite : implications for the formation of the cobalt-manganese laterite deposit, southeast Cameroon [texte imprimé] / Gideon Lambiv Dzemua, Auteur ; Sarah A. Gleeson, Auteur . - 2012 . - pp. 25-41. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 1 (Janvier/Fevrier 2012) . - pp. 25-41 Mots-clés : Nkamouna  serpentinite  Cobalt-manganese  laterite  deposit  Mineralogy  Cameroun Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Nkamouna Co-Mn-Ni laterite is an advanced exploration project located in southeast Cameroon. The deposit comprises a deep and complex laterite profile with high Co (~0.25 wt %) and Mn (1.33 wt %) contents, subeconomic Ni grade and a Ni:Co ratio of less than 3. This makes Nkamouna an unusual type of laterite deposit as it will be primarily mined for Co. The Co-Mn mineralization occurs at the interface between an overlying allochthonous felsic rock-sourced laterite and a lower in situ serpentinite-derived laterite. The serpentinite is massive with a nonpseudomorphic texture and consists of two genetically related phases: Serpentinite-I and Serpentinite-II. Serpentinite-I is characterized by antigorite, magnetite, quartz, ferritchromite, and magnesite, and Serpentinite-II by antigorite and magnesite. Both serpentinite types are extremely low in sulfides. Serpentinite-I is the dominant and oldest phase and was derived from a subcontinental mantle (pyroxene-rich) peridotite emplaced in the crust during the Pan-African orogeny. The Ni concentration in the serpentinite is variable (0.07–0.30%) and heterogeneously distributed, partly reflecting the present dominance of pyroxenes in the protolith. However, Ni is also hosted by magnetite and ferritchromite. The differential weathering of these Ni-hosting minerals is also responsible for the lower Ni grade of the deposit. Importantly, the serpentinite is depleted in Co and Mn and the enrichment of these elements in the laterite profile suggests that these elements may be derived from an exotic source. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/1/25.short

The early cretaceous Yangzhaiyu lode gold deposit, north China Craton / Jian-Wei Li in Economic geology, Vol. 107 N° 1 (Janvier/Fevrier 2012) 

Public ISBD [article]  in Economic geology > Vol. 107 N° 1 (Janvier/Fevrier 2012) . - pp. 43-79 Titre : The early cretaceous Yangzhaiyu lode gold deposit, north China Craton : a link between craton reactivation and gold veining Type de document : texte imprimé Auteurs : Jian-Wei Li, Auteur ; Zhan-Ke Li, Auteur ; Mei-Fu Zhou, Auteur Année de publication : 2012 Article en page(s) : pp. 43-79 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : Yangzhaiyu  gold  deposits  Gold  veining  China Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Yangzhaiyu gold deposit is one of numerous lode gold deposits in the Xiaoqinling district, southern margin of the North China Craton. Gold mineralization is hosted in Neoarchean to early Paleoproterozoic amphibolite facies metamorphic rocks and consists of auriferous quartz veins and subordinate disseminated ores in the vein-proximal alteration zone. Ore-related hydrothermal alteration is dominated by sericite + quartz + sulfide assemblages close to gold veins, and biotite + quartz + pyrite ± chlorite ± epidote alteration generally distal from mineralization. Pyrite is the predominant sulfide mineral, locally coexisting with minor amounts of chalcopyrite, sphalerite, and galena. Gold occurs mostly as free gold enclosed in or filling microfractures of pyrite and quartz and is also present in equilibrium with Au-bearing tellurides, mainly petzite and calaverite coexisting with hessite, tellurobismuthite, and altaite. Fluid inclusion studies suggest that gold veins were deposited at intermediate temperatures (175°–313°C) from aqueous or aqueous-carbonic fluids with moderate salinity (5–14 wt % NaCl equiv). δ34S values of sulfide minerals range mainly from 2.0 to 4.4‰, whereas auriferous quartz vein samples have δ18O values of 12.4 to 9.6‰, with calculated δ18OH2O values of 6.0 to 3.2‰. Gold-related pyrite grains yield elevated 3He/4He ratios (1.51-0.32 Ra) relative to crustal reservoirs and mantle-like 20Ne/22Ne and 21Ne/22Ne ratios (9.90-9.68 and 0.029, respectively). The stable and noble gas isotopes thus suggest deep-seated, most likely magmatic and mantle-derived, sources for the ore fluids, sulfur and, by inference, other components in the ore system. 40Ar/39Ar dating of ore-related sericite and biotite separates indicates two episodes of gold genesis at 134.5 to 132.3 and 124.3 to 123.7 Ma. The mineralization ages overlap zircon U-Pb ages of 141.0 ± 1.6 to 125.8 ± 1.4 Ma (2σ) for the Wenyu and Niangniangshan monzogranite Plutons and a number of mafic to intermediate dikes intruding these Plutons, all being proximal to the Yangzhaiyu gold deposit. The synchronism of gold genesis and magmatism provides additional weights of evidence for a magmatic derivation of ore fluids and sulfur. The geochronologic data also suggest that gold veining took place billions of years after the stabilization of the North China Craton and associated metamorphism in the Late Archean to early Paleoproterozoic. This contrasts sharply to lode gold deposits in other Precambrian cratons that formed predominantly in Late Archean to Paleoproterozoic, temporarily and genetically related to regional high-grade metamorphism and compressional or transpressional tectonism. Available data have demonstrated that the North China Craton was reactivated in the late Mesozoic, as marked by voluminous igneous rocks, faulted-basin formation, high crustal heat flow, and widespread metamorphic core complexes in the eastern part of the craton. It is thus suggested that the Yangzhaiyu gold deposit, together with other deposits of similar ages in the Xiaoqinling district, were products of this craton reactivation event. Lithospheric extension and extensive magmatism related to the craton reactivation may have provided sufficient heat energy, fluid, and sulfur required for the formation of the gold deposits. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/1/43.abstract [article] The early cretaceous Yangzhaiyu lode gold deposit, north China Craton : a link between craton reactivation and gold veining [texte imprimé] / Jian-Wei Li, Auteur ; Zhan-Ke Li, Auteur ; Mei-Fu Zhou, Auteur . - 2012 . - pp. 43-79. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 1 (Janvier/Fevrier 2012) . - pp. 43-79 Mots-clés : Yangzhaiyu  gold  deposits  Gold  veining  China Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Yangzhaiyu gold deposit is one of numerous lode gold deposits in the Xiaoqinling district, southern margin of the North China Craton. Gold mineralization is hosted in Neoarchean to early Paleoproterozoic amphibolite facies metamorphic rocks and consists of auriferous quartz veins and subordinate disseminated ores in the vein-proximal alteration zone. Ore-related hydrothermal alteration is dominated by sericite + quartz + sulfide assemblages close to gold veins, and biotite + quartz + pyrite ± chlorite ± epidote alteration generally distal from mineralization. Pyrite is the predominant sulfide mineral, locally coexisting with minor amounts of chalcopyrite, sphalerite, and galena. Gold occurs mostly as free gold enclosed in or filling microfractures of pyrite and quartz and is also present in equilibrium with Au-bearing tellurides, mainly petzite and calaverite coexisting with hessite, tellurobismuthite, and altaite. Fluid inclusion studies suggest that gold veins were deposited at intermediate temperatures (175°–313°C) from aqueous or aqueous-carbonic fluids with moderate salinity (5–14 wt % NaCl equiv). δ34S values of sulfide minerals range mainly from 2.0 to 4.4‰, whereas auriferous quartz vein samples have δ18O values of 12.4 to 9.6‰, with calculated δ18OH2O values of 6.0 to 3.2‰. Gold-related pyrite grains yield elevated 3He/4He ratios (1.51-0.32 Ra) relative to crustal reservoirs and mantle-like 20Ne/22Ne and 21Ne/22Ne ratios (9.90-9.68 and 0.029, respectively). The stable and noble gas isotopes thus suggest deep-seated, most likely magmatic and mantle-derived, sources for the ore fluids, sulfur and, by inference, other components in the ore system. 40Ar/39Ar dating of ore-related sericite and biotite separates indicates two episodes of gold genesis at 134.5 to 132.3 and 124.3 to 123.7 Ma. The mineralization ages overlap zircon U-Pb ages of 141.0 ± 1.6 to 125.8 ± 1.4 Ma (2σ) for the Wenyu and Niangniangshan monzogranite Plutons and a number of mafic to intermediate dikes intruding these Plutons, all being proximal to the Yangzhaiyu gold deposit. The synchronism of gold genesis and magmatism provides additional weights of evidence for a magmatic derivation of ore fluids and sulfur. The geochronologic data also suggest that gold veining took place billions of years after the stabilization of the North China Craton and associated metamorphism in the Late Archean to early Paleoproterozoic. This contrasts sharply to lode gold deposits in other Precambrian cratons that formed predominantly in Late Archean to Paleoproterozoic, temporarily and genetically related to regional high-grade metamorphism and compressional or transpressional tectonism. Available data have demonstrated that the North China Craton was reactivated in the late Mesozoic, as marked by voluminous igneous rocks, faulted-basin formation, high crustal heat flow, and widespread metamorphic core complexes in the eastern part of the craton. It is thus suggested that the Yangzhaiyu gold deposit, together with other deposits of similar ages in the Xiaoqinling district, were products of this craton reactivation event. Lithospheric extension and extensive magmatism related to the craton reactivation may have provided sufficient heat energy, fluid, and sulfur required for the formation of the gold deposits. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/1/43.abstract

Controls on the concentration of zirconium, niobium, and the rare earth elements in the thor lake rare metal deposit, northwest territories, Canada / Emma R. Sheard in Economic geology, Vol. 107 N° 1 (Janvier/Fevrier 2012) 

Public ISBD [article]  in Economic geology > Vol. 107 N° 1 (Janvier/Fevrier 2012) . - pp. 81-104 Titre : Controls on the concentration of zirconium, niobium, and the rare earth elements in the thor lake rare metal deposit, northwest territories, Canada Type de document : texte imprimé Auteurs : Emma R. Sheard, Auteur ; Anthony E. Williams-Jones, Auteur ; Martin Heiligmann, Auteur Année de publication : 2012 Article en page(s) : pp. 81-104 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : Ziconium  Niobium  Metal  deposit  Hydrothermal  alteration  Metal  minerals  Mineral  chemistry  Canada Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Thor Lake rare metal (Zr, Nb, REE, Ta, Be, Ga) deposits in Canada’s Northwest Territories represent one of the largest resources of zirconium, niobium, and the heavy rare earth elements (HREE) in the world. Much of the potentially economic mineralization was concentrated by magmatic processes. However, there is also evidence of autometasomatic processes and remobilization of Zr and REE by hydrothermal fluids. The deposits are situated at the southern edge of the Slave province of the Canadian Shield, within the 2094 to 2185 Ma alkaline to peralkaline Blachford Lake Intrusive Complex. A layered alkaline suite dominated by aegirine nepheline syenite occurs in the center of this suite of rocks and is considered to represent the youngest phase of the complex. Much of the rare metal mineralization occurs in two subhorizontal tabular layers, which form upper and lower zones of the Nechalacho deposit (formerly the Lake zone), and in which Zr is hosted primarily by zircon, Nb primarily by ferrocolumbite and fergusonite-(Y), and HREE by fergusonite-(Y) and zircon. The LREE are present mainly in monazite-(Ce), allanite-(Ce), bastnäsite-(Ce), parisite-(Ce), and synchysite-(Ce). Much of the HREE mineralization in the lower mineralized zone occurs in secondary zircon, which forms small (10–30 μm) anhedral grains in pseudomorphs after probable eudialyte. In the upper zone, zircon is a magmatic cumulate mineral, which was replaced locally by secondary REE-bearing minerals. Element distribution maps of zircon crystals in the upper zone indicate that the HREE were mobilized from the cores and locally precipitated as fergusonite-(Y) along microfractures. The light rare earth elements (LREE) were also mobilized locally from both primary zircon and inferred primary eudialyte. The occurrence of zircon in fractures, wrapped around brecciated K-feldspar fragments, and as a secondary phase in pseudomorphs are evidence of its hydrothermal origin and/or of remobilization of primary zirconium. A model is proposed in which injection of separate pulses of miaskitic and agpaitic magma resulted in the crystallization of an upper zone rich in zircon and a lower zone rich in eudialyte. Primary eudialyte was later altered in situ to zircon-fergusonite-(Y)-bastnäsite-(Ce)-parisite-(Ce)-synchysite-(Ce)-allanite-(Ce)-albite-quartz-biotite-fluorite-kutnahorite-hematite–bearing pseudomorphs by an inferred fluorine-enriched magmatic hydrothermal fluid. Zirconium, niobium, and REE in both the upper and lower zones were subsequently mobilized during multiple metasomatic events, which, for the most part, served to further enrich the primary layers in REE (albitization generally dispersed REE and high field strength elements (HFSE)) and created new secondary REE-bearing phases. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/1/81.short [article] Controls on the concentration of zirconium, niobium, and the rare earth elements in the thor lake rare metal deposit, northwest territories, Canada [texte imprimé] / Emma R. Sheard, Auteur ; Anthony E. Williams-Jones, Auteur ; Martin Heiligmann, Auteur . - 2012 . - pp. 81-104. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 1 (Janvier/Fevrier 2012) . - pp. 81-104 Mots-clés : Ziconium  Niobium  Metal  deposit  Hydrothermal  alteration  Metal  minerals  Mineral  chemistry  Canada Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Thor Lake rare metal (Zr, Nb, REE, Ta, Be, Ga) deposits in Canada’s Northwest Territories represent one of the largest resources of zirconium, niobium, and the heavy rare earth elements (HREE) in the world. Much of the potentially economic mineralization was concentrated by magmatic processes. However, there is also evidence of autometasomatic processes and remobilization of Zr and REE by hydrothermal fluids. The deposits are situated at the southern edge of the Slave province of the Canadian Shield, within the 2094 to 2185 Ma alkaline to peralkaline Blachford Lake Intrusive Complex. A layered alkaline suite dominated by aegirine nepheline syenite occurs in the center of this suite of rocks and is considered to represent the youngest phase of the complex. Much of the rare metal mineralization occurs in two subhorizontal tabular layers, which form upper and lower zones of the Nechalacho deposit (formerly the Lake zone), and in which Zr is hosted primarily by zircon, Nb primarily by ferrocolumbite and fergusonite-(Y), and HREE by fergusonite-(Y) and zircon. The LREE are present mainly in monazite-(Ce), allanite-(Ce), bastnäsite-(Ce), parisite-(Ce), and synchysite-(Ce). Much of the HREE mineralization in the lower mineralized zone occurs in secondary zircon, which forms small (10–30 μm) anhedral grains in pseudomorphs after probable eudialyte. In the upper zone, zircon is a magmatic cumulate mineral, which was replaced locally by secondary REE-bearing minerals. Element distribution maps of zircon crystals in the upper zone indicate that the HREE were mobilized from the cores and locally precipitated as fergusonite-(Y) along microfractures. The light rare earth elements (LREE) were also mobilized locally from both primary zircon and inferred primary eudialyte. The occurrence of zircon in fractures, wrapped around brecciated K-feldspar fragments, and as a secondary phase in pseudomorphs are evidence of its hydrothermal origin and/or of remobilization of primary zirconium. A model is proposed in which injection of separate pulses of miaskitic and agpaitic magma resulted in the crystallization of an upper zone rich in zircon and a lower zone rich in eudialyte. Primary eudialyte was later altered in situ to zircon-fergusonite-(Y)-bastnäsite-(Ce)-parisite-(Ce)-synchysite-(Ce)-allanite-(Ce)-albite-quartz-biotite-fluorite-kutnahorite-hematite–bearing pseudomorphs by an inferred fluorine-enriched magmatic hydrothermal fluid. Zirconium, niobium, and REE in both the upper and lower zones were subsequently mobilized during multiple metasomatic events, which, for the most part, served to further enrich the primary layers in REE (albitization generally dispersed REE and high field strength elements (HFSE)) and created new secondary REE-bearing phases. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/1/81.short

Multiple sulfur and iron isotope composition of magmatic Ni-Cu-(PGE) sulfide mineralization from eastern Botswana / Marco L. Fiorentini in Economic geology, Vol. 107 N° 1 (Janvier/Fevrier 2012) 

Public ISBD [article]  in Economic geology > Vol. 107 N° 1 (Janvier/Fevrier 2012) . - pp. 105-116 Titre : Multiple sulfur and iron isotope composition of magmatic Ni-Cu-(PGE) sulfide mineralization from eastern Botswana Type de document : texte imprimé Auteurs : Marco L. Fiorentini, Auteur ; Andrey Bekker, Auteur ; Olivier Rouxel, Auteur Année de publication : 2012 Article en page(s) : pp. 105-116 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : Sulfur  Iron  Ni-Cu-(PGE)  deposits  Magmatic  systems  Botswana Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : We report here high-precision multiple sulfur and iron isotope compositions for a series of mineralized samples from Ni-Cu-(PGE) sulfide deposits in the Archean Tati greenstone belt and the Phikwe Complex of eastern Botswana. Mineralized samples from the Phoenix and Selkirk Ni-Cu-(PGE) deposits in the Tati greenstone belt display slightly positive δ34S isotope values, ranging from 0.2 to 0.8‰ V-CDT. Δ33S values of sulfides at Phoenix and Selkirk are −0.01 to −0.08‰ V-CDT, suggesting either a dominantly mantle sulfur source or effective eradication of a crustal Δ33S anomaly through equilibration with large amounts of silicate melt. In the Selebi-Phikwe belt, a granite-gneiss terrane with abundant amphibolite lenses of either volcanic and/or intrusive nature, mineralized lower grade samples from the Phikwe, Phokoje, and Dikoloti Ni-Cu-(PGE) deposits have more variable δ34S values ranging from −3.1 to +0.3‰ and display significant mass independent anomalies (Δ33S values ranging from −0.89 to −0.27‰), suggesting that barren sulfides associated with distal or low-temperature sea-floor hydrothermal activity contributed sulfur to these deposits. Iron isotopes of sulfides from these deposits show a relatively small range of negative Δ56Fe values (−0.29 to −0.04‰), consistent with high-temperature fractionations in magmatic systems, with the exception of one sample from the Dikoloti Ni-Cu-(PGE) deposit of the Selebi-Phikwe greenstone belt, which shows a more negative δ56Fe value of −0.61‰, consistent with assimilation of sedimentary or hydrothermal sulfides rather than fractionations in high-temperature magmatic systems. Data from this study highlight the complexity and variability that characterize ore-forming processes in magmatic systems. We suggest that the presence of sulfur-bearing lithologic units in host rocks of mafic and ultramafic intrusions may not be essential toward the assessment of the prospectivity of a province to host orthomagmatic nickel sulfides. Geologic settings without any or little sulfur in the stratigraphy, which have been traditionally neglected in terms of their prospectivity, should thus be revisited and possibly reassessed considering the potential importance of external source of sulfur to generate ore deposits. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/1/105.short [article] Multiple sulfur and iron isotope composition of magmatic Ni-Cu-(PGE) sulfide mineralization from eastern Botswana [texte imprimé] / Marco L. Fiorentini, Auteur ; Andrey Bekker, Auteur ; Olivier Rouxel, Auteur . - 2012 . - pp. 105-116. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 1 (Janvier/Fevrier 2012) . - pp. 105-116 Mots-clés : Sulfur  Iron  Ni-Cu-(PGE)  deposits  Magmatic  systems  Botswana Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : We report here high-precision multiple sulfur and iron isotope compositions for a series of mineralized samples from Ni-Cu-(PGE) sulfide deposits in the Archean Tati greenstone belt and the Phikwe Complex of eastern Botswana. Mineralized samples from the Phoenix and Selkirk Ni-Cu-(PGE) deposits in the Tati greenstone belt display slightly positive δ34S isotope values, ranging from 0.2 to 0.8‰ V-CDT. Δ33S values of sulfides at Phoenix and Selkirk are −0.01 to −0.08‰ V-CDT, suggesting either a dominantly mantle sulfur source or effective eradication of a crustal Δ33S anomaly through equilibration with large amounts of silicate melt. In the Selebi-Phikwe belt, a granite-gneiss terrane with abundant amphibolite lenses of either volcanic and/or intrusive nature, mineralized lower grade samples from the Phikwe, Phokoje, and Dikoloti Ni-Cu-(PGE) deposits have more variable δ34S values ranging from −3.1 to +0.3‰ and display significant mass independent anomalies (Δ33S values ranging from −0.89 to −0.27‰), suggesting that barren sulfides associated with distal or low-temperature sea-floor hydrothermal activity contributed sulfur to these deposits. Iron isotopes of sulfides from these deposits show a relatively small range of negative Δ56Fe values (−0.29 to −0.04‰), consistent with high-temperature fractionations in magmatic systems, with the exception of one sample from the Dikoloti Ni-Cu-(PGE) deposit of the Selebi-Phikwe greenstone belt, which shows a more negative δ56Fe value of −0.61‰, consistent with assimilation of sedimentary or hydrothermal sulfides rather than fractionations in high-temperature magmatic systems. Data from this study highlight the complexity and variability that characterize ore-forming processes in magmatic systems. We suggest that the presence of sulfur-bearing lithologic units in host rocks of mafic and ultramafic intrusions may not be essential toward the assessment of the prospectivity of a province to host orthomagmatic nickel sulfides. Geologic settings without any or little sulfur in the stratigraphy, which have been traditionally neglected in terms of their prospectivity, should thus be revisited and possibly reassessed considering the potential importance of external source of sulfur to generate ore deposits. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/1/105.short

Genesis of the Touissit-Bou Beker Mississippi valley-type district (Morocco-Algeria) and its relationship to the Africa-Europe collision / Mohammed Bouabdellah in Economic geology, Vol. 107 N° 1 (Janvier/Fevrier 2012) 

Public ISBD [article]  in Economic geology > Vol. 107 N° 1 (Janvier/Fevrier 2012) . - pp. 117-146 Titre : Genesis of the Touissit-Bou Beker Mississippi valley-type district (Morocco-Algeria) and its relationship to the Africa-Europe collision Type de document : texte imprimé Auteurs : Mohammed Bouabdellah, Auteur ; Donald F. Sangster, Auteur ; David L. Leach, Auteur Année de publication : 2012 Article en page(s) : pp. 117-146 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : Touissit-Bou  Beker  district  Africa-Europe  collision Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Mississippi Valley-type deposits of the Touissit-Bou Beker district are hosted by a 25 m thick sequence of diagenetically and hydrothermally dolomitized carbonate platform rocks of Aalenian-Bajocian age. The sulfide mineralization consists principally of galena and sphalerite and occurs as open-space fillings of voids and moderate to massive replacement of the medium- to coarse-grained host dolostone. Five types of dolomite have been distinguished, two of which (D1 and D2) are of replacement origin, whereas HD1, HD2, HD3 occurring as open-space filling are of hydrothermal affiliation. Main ore controls include stratigraphy and lithology, carbonate dissolution, paleogeography, faults or faulted rocks, and availability of organic matter. Fluid inclusion data, along with Na-Cl-Br leachate, indicate that the ore-forming fluids correspond to evolved NaCl-CaCl2-KCl-MgCl2 basin-derived hot (100° ± 20°C) saline brines (>20 wt % NaCl equiv) that acquired their high salinities and Ca/Na ratios through evaporation of seawater, and subsequent dolomitization and fluid-rock interactions. Stable isotope data for replacement and hydrothermal dolomites are tightly clustered and overlapping, with δ18O and δ13C values from 20.5 to 21.2 and 0.2 to 0.7‰, respectively. Similarly, sulfides yield δ34S values between 11.2 and 1.9‰, whereas those corresponding to the nearby Triassic gypsum cluster yield around 14‰. Altogether, these isotopic compositions are consistent with a basinal-type fluid with reduced sulfur very likely being derived through thermochemical reduction of dissolved sulfate, resulting in metal precipitation, and carbon of mainly marine Aalenian-Bajocian carbonate origin with a minor biogenic component. 87Sr/86Sr values of replacement dolostone are similar to those of ore-related hydrothermal dolomites, ranging from 0.70746 to 0.70833 and from 0.70769 to 0.70828, respectively, and are different from those of the Visean rhyodacite (0.71849–0.72167). Lead isotope ratios (206Pb/204Pb = 18.319–18.390; 207Pb/204Pb = 15.620–15.680; 208Pb/204Pb = 38.452–38.650) of sulfides are consistent with Pb being derived from the Visean rhyodacite and associated volcaniclastic rocks. The intimate link between faults and mineralization suggests the strong possibility of brine flow along both ENE-trending regional-scale faults and NW-SW-trending local-scale faults. The data suggest that MVT mineralization was emplaced during the late Neogene-Quaternary (i.e., ca. 15–0 Ma), possibly as a result of subsurface gravity-driven fluid flow in response to the collision between the African and Eurasian plates. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/1/117.short [article] Genesis of the Touissit-Bou Beker Mississippi valley-type district (Morocco-Algeria) and its relationship to the Africa-Europe collision [texte imprimé] / Mohammed Bouabdellah, Auteur ; Donald F. Sangster, Auteur ; David L. Leach, Auteur . - 2012 . - pp. 117-146. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 1 (Janvier/Fevrier 2012) . - pp. 117-146 Mots-clés : Touissit-Bou  Beker  district  Africa-Europe  collision Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Mississippi Valley-type deposits of the Touissit-Bou Beker district are hosted by a 25 m thick sequence of diagenetically and hydrothermally dolomitized carbonate platform rocks of Aalenian-Bajocian age. The sulfide mineralization consists principally of galena and sphalerite and occurs as open-space fillings of voids and moderate to massive replacement of the medium- to coarse-grained host dolostone. Five types of dolomite have been distinguished, two of which (D1 and D2) are of replacement origin, whereas HD1, HD2, HD3 occurring as open-space filling are of hydrothermal affiliation. Main ore controls include stratigraphy and lithology, carbonate dissolution, paleogeography, faults or faulted rocks, and availability of organic matter. Fluid inclusion data, along with Na-Cl-Br leachate, indicate that the ore-forming fluids correspond to evolved NaCl-CaCl2-KCl-MgCl2 basin-derived hot (100° ± 20°C) saline brines (>20 wt % NaCl equiv) that acquired their high salinities and Ca/Na ratios through evaporation of seawater, and subsequent dolomitization and fluid-rock interactions. Stable isotope data for replacement and hydrothermal dolomites are tightly clustered and overlapping, with δ18O and δ13C values from 20.5 to 21.2 and 0.2 to 0.7‰, respectively. Similarly, sulfides yield δ34S values between 11.2 and 1.9‰, whereas those corresponding to the nearby Triassic gypsum cluster yield around 14‰. Altogether, these isotopic compositions are consistent with a basinal-type fluid with reduced sulfur very likely being derived through thermochemical reduction of dissolved sulfate, resulting in metal precipitation, and carbon of mainly marine Aalenian-Bajocian carbonate origin with a minor biogenic component. 87Sr/86Sr values of replacement dolostone are similar to those of ore-related hydrothermal dolomites, ranging from 0.70746 to 0.70833 and from 0.70769 to 0.70828, respectively, and are different from those of the Visean rhyodacite (0.71849–0.72167). Lead isotope ratios (206Pb/204Pb = 18.319–18.390; 207Pb/204Pb = 15.620–15.680; 208Pb/204Pb = 38.452–38.650) of sulfides are consistent with Pb being derived from the Visean rhyodacite and associated volcaniclastic rocks. The intimate link between faults and mineralization suggests the strong possibility of brine flow along both ENE-trending regional-scale faults and NW-SW-trending local-scale faults. The data suggest that MVT mineralization was emplaced during the late Neogene-Quaternary (i.e., ca. 15–0 Ma), possibly as a result of subsurface gravity-driven fluid flow in response to the collision between the African and Eurasian plates. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/1/117.short

Tectonic deformation and fluid flow / Tao Cui in Economic geology, Vol. 107 N° 1 (Janvier/Fevrier 2012) 

Public ISBD [article]  in Economic geology > Vol. 107 N° 1 (Janvier/Fevrier 2012) . - pp. 147-163 Titre : Tectonic deformation and fluid flow : implications for the formation of unconformity-related uranium deposits Type de document : texte imprimé Auteurs : Tao Cui, Auteur ; Jianwen Yang, Auteur ; Iain M. Samson, Auteur Année de publication : 2012 Article en page(s) : pp. 147-163 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : Uranium  deposits  Tectonic  deformation  Fluid  flow Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : Numerical experiments were carried out to investigate the fluid flow in typical Proterozoic basins that host unconformity-related uranium deposits. We have constructed a simplified conceptual model by integrating important features shared by the Athabasca, Thelon, and Kombolgie Basins. Based on this conceptual model, various numerical scenarios were designed to explore the interaction between fluid flow, heat transport, topographic relief, and tectonic deformation. Our modeling suggests that thermally driven free convection may develop in the thick sandstone sequence at a geothermal gradient of between 25° and 35°C/km during periods of tectonic quiescence, with a maximum velocity of about 1.0 m/yr. However, reactivation of preexisting basement structures and the generation of new faults suppressed free convection and led to deformation-dominated fluid flow or mixed convection, depending on strain rates. During compressive deformation, reduced brines in the basement may flow out along fractured zones and encounter uranium-bearing fluids in the clastic sequence to form sandstone-hosted deposits. In contrast, basement-hosted deposits are likely to form during extension, when oxidized basinal brines flow into faulted structures to interact with reduced minerals or fluids in the basement. Maximum flow rates are estimated to be up to ~7 and ~2.5 m/yr in the relatively high permeability fracture zone for compressive and extensional deformation, respectively, given a strain rate of 10−13 s−1 and a geothermal gradient of 30°C/km. In addition, the rate of pressure accumulation and dissipation is different in various geologic units depending on their hydrological properties and strain rates. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/1/147.short [article] Tectonic deformation and fluid flow : implications for the formation of unconformity-related uranium deposits [texte imprimé] / Tao Cui, Auteur ; Jianwen Yang, Auteur ; Iain M. Samson, Auteur . - 2012 . - pp. 147-163. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 1 (Janvier/Fevrier 2012) . - pp. 147-163 Mots-clés : Uranium  deposits  Tectonic  deformation  Fluid  flow Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : Numerical experiments were carried out to investigate the fluid flow in typical Proterozoic basins that host unconformity-related uranium deposits. We have constructed a simplified conceptual model by integrating important features shared by the Athabasca, Thelon, and Kombolgie Basins. Based on this conceptual model, various numerical scenarios were designed to explore the interaction between fluid flow, heat transport, topographic relief, and tectonic deformation. Our modeling suggests that thermally driven free convection may develop in the thick sandstone sequence at a geothermal gradient of between 25° and 35°C/km during periods of tectonic quiescence, with a maximum velocity of about 1.0 m/yr. However, reactivation of preexisting basement structures and the generation of new faults suppressed free convection and led to deformation-dominated fluid flow or mixed convection, depending on strain rates. During compressive deformation, reduced brines in the basement may flow out along fractured zones and encounter uranium-bearing fluids in the clastic sequence to form sandstone-hosted deposits. In contrast, basement-hosted deposits are likely to form during extension, when oxidized basinal brines flow into faulted structures to interact with reduced minerals or fluids in the basement. Maximum flow rates are estimated to be up to ~7 and ~2.5 m/yr in the relatively high permeability fracture zone for compressive and extensional deformation, respectively, given a strain rate of 10−13 s−1 and a geothermal gradient of 30°C/km. In addition, the rate of pressure accumulation and dissipation is different in various geologic units depending on their hydrological properties and strain rates. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/1/147.short

Volatility of Se and Te during subduction-related distillation and the geochemistry of epithermal ores of the western United States / James A. Saunders in Economic geology, Vol. 107 N° 1 (Janvier/Fevrier 2012) 

Public ISBD [article]  in Economic geology > Vol. 107 N° 1 (Janvier/Fevrier 2012) . - pp. 165-172 Titre : Volatility of Se and Te during subduction-related distillation and the geochemistry of epithermal ores of the western United States Type de document : texte imprimé Auteurs : James A. Saunders, Auteur ; Matthew E. Brueseke, Auteur Année de publication : 2012 Article en page(s) : pp. 165-172 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : Selenium  Tellurium  Hydrothermal  gold  deposits  Hydrothermal  silver  deposits  Epithermal  ores  Metal(loid)  distillation  United  states Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : Subduction, partial melting of mantle and magma generation, and ultimately magma degassing can lead to the preferential mobilization of volatile elements and compounds. Research indicates that devolatilization reactions in a subducted slab can cause the overlying mantle to be enriched in volatile ore-forming constituents (water, CO2, sulfur, metal[loid]s). This process of mantle enrichment plays an important role in subsequent magma generation and initiation of ore genesis. Furthermore, the relative volatility of metal(loid)s appears to play a role in the ultimate geochemistry of shallow (epithermal-epizonal) hydrothermal ores in the western United States. For example, there is a general west-to-east geographic zonation of Tertiary ores, from Se rich to Te rich. It is proposed that this geographic-geochemical zonation is the direct result of the higher geochemical volatility of Se as compared to Te. Previously, Au, Ag, Te, Se, Hg, As, Sb, and Tl have been referred to as the epithermal suite of elements. It is suggested here that their geochemical cycles are linked by their similar volatile behavior, through subduction, partial melting in the mantle, and subsequent magma degassing processes. Essentially, specific tectonomagmatic events that affected the western United States (e.g., Oligocene-Eocene magmatism in the Great Basin and southern Rocky Mountains, mid-Miocene magmatism associated with the inception of the Yellowstone hotspot in the Pacific Northwest) were distillation events that drove devolatilization of fertile mantle after the Laramide shallow-slab event. Furthermore, the metal(loid) volatility behavior likely occurs in other regions affected by subduction and may play a fundamental role in the metal endowment of these regions. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/1/165.short [article] Volatility of Se and Te during subduction-related distillation and the geochemistry of epithermal ores of the western United States [texte imprimé] / James A. Saunders, Auteur ; Matthew E. Brueseke, Auteur . - 2012 . - pp. 165-172. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 1 (Janvier/Fevrier 2012) . - pp. 165-172 Mots-clés : Selenium  Tellurium  Hydrothermal  gold  deposits  Hydrothermal  silver  deposits  Epithermal  ores  Metal(loid)  distillation  United  states Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : Subduction, partial melting of mantle and magma generation, and ultimately magma degassing can lead to the preferential mobilization of volatile elements and compounds. Research indicates that devolatilization reactions in a subducted slab can cause the overlying mantle to be enriched in volatile ore-forming constituents (water, CO2, sulfur, metal[loid]s). This process of mantle enrichment plays an important role in subsequent magma generation and initiation of ore genesis. Furthermore, the relative volatility of metal(loid)s appears to play a role in the ultimate geochemistry of shallow (epithermal-epizonal) hydrothermal ores in the western United States. For example, there is a general west-to-east geographic zonation of Tertiary ores, from Se rich to Te rich. It is proposed that this geographic-geochemical zonation is the direct result of the higher geochemical volatility of Se as compared to Te. Previously, Au, Ag, Te, Se, Hg, As, Sb, and Tl have been referred to as the epithermal suite of elements. It is suggested here that their geochemical cycles are linked by their similar volatile behavior, through subduction, partial melting in the mantle, and subsequent magma degassing processes. Essentially, specific tectonomagmatic events that affected the western United States (e.g., Oligocene-Eocene magmatism in the Great Basin and southern Rocky Mountains, mid-Miocene magmatism associated with the inception of the Yellowstone hotspot in the Pacific Northwest) were distillation events that drove devolatilization of fertile mantle after the Laramide shallow-slab event. Furthermore, the metal(loid) volatility behavior likely occurs in other regions affected by subduction and may play a fundamental role in the metal endowment of these regions. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/1/165.short

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