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Basin evolution and unconformity-related uranium mineralization / S. R. Beyer in Economic geology, Vol. 107 N° 3 (Mai 2012) 

Public ISBD [article]  in Economic geology > Vol. 107 N° 3 (Mai 2012) . - pp. 401-425 Titre : Basin evolution and unconformity-related uranium mineralization : the Camie river U prospect, paleoproterozoic Otish basin, Quebec Type de document : texte imprimé Auteurs : S. R. Beyer, Auteur ; K. Kyser, Auteur ; E. E. Hiatt, Auteur Année de publication : 2012 Article en page(s) : pp. 401-425 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : Paleoproterozoic  Otish  basin  Uranium  deposits  Camie  river  uranium  prospects  Quebec Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Paleoproterozoic Otish Basin, Quebec, hosts several uranium prospects that until recently remained underexplored and poorly understood. In this study, the Camie River U prospect, which shows similar characteristics to high-grade unconformity-related U deposits, is the focus of an integrated basin analysis in the western Otish Basin. Conglomerate and sandstone of the Indicator Formation, which were deposited in at least six depositional sequences, were affected by insignificant early diagenetic compaction and cementation. This allowed the formation of regional peak diagenetic aquifers, which became muscovite altered due to interaction with fluids having δ18O and δ2H values similar to those of seawater-influenced basinal brines at 250°C. U mineralization at Camie River occurred at 1721 ±20 Ma based on a 207Pb/206Pb date obtained by laser ablation of uraninite, which coincides with a phase of the Otish Gabbro intrusion that has been dated at ca. 1730 Ma. The intrusive event promoted circulation of U-bearing basinal brines, triggering U mineralization at several locations in the western Otish Basin. Interaction of basinal brines with the Otish Gabbro produced coarse-grained chlorite, tourmaline, and phengitic muscovite, which decreased the fluid-conducting capabilities of diagenetic aquifers and resulted in fault zone- and fracture-dominated fluid flow. Subsequent fluid alteration events produced limited U remobilization, sulfides, sudoite, and siderite between ca. 1670 and 1410 Ma based on mineral paragenesis and 40Ar/39Ar dates of muscovite. Metamorphic fluids having high δ18O values and temperatures around 300°C accompanied 1.2 to 1.0 Ga Grenville orogenesis and subgreenschist-grade metamorphism in the Otish Basin but were present at low water/rock ratios at Camie River and therefore produced little alteration. Post-Grenville uplift of the Otish Basin likely produced late, low-temperature alteration minerals that have been influenced by recent meteoric water, suggesting that the fault zones and fractures the minerals occupy remain as preferential fluid-flow pathways to the present day. Radiogenic Pb and the characteristic trace elements Mo + W + Nb have also preferentially dispersed from the mineralization along fault zones, fractures, and depositional sequence boundaries, and can be used to explore for Camie River-style U mineralization. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/3/401.short [article] Basin evolution and unconformity-related uranium mineralization : the Camie river U prospect, paleoproterozoic Otish basin, Quebec [texte imprimé] / S. R. Beyer, Auteur ; K. Kyser, Auteur ; E. E. Hiatt, Auteur . - 2012 . - pp. 401-425. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 3 (Mai 2012) . - pp. 401-425 Mots-clés : Paleoproterozoic  Otish  basin  Uranium  deposits  Camie  river  uranium  prospects  Quebec Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Paleoproterozoic Otish Basin, Quebec, hosts several uranium prospects that until recently remained underexplored and poorly understood. In this study, the Camie River U prospect, which shows similar characteristics to high-grade unconformity-related U deposits, is the focus of an integrated basin analysis in the western Otish Basin. Conglomerate and sandstone of the Indicator Formation, which were deposited in at least six depositional sequences, were affected by insignificant early diagenetic compaction and cementation. This allowed the formation of regional peak diagenetic aquifers, which became muscovite altered due to interaction with fluids having δ18O and δ2H values similar to those of seawater-influenced basinal brines at 250°C. U mineralization at Camie River occurred at 1721 ±20 Ma based on a 207Pb/206Pb date obtained by laser ablation of uraninite, which coincides with a phase of the Otish Gabbro intrusion that has been dated at ca. 1730 Ma. The intrusive event promoted circulation of U-bearing basinal brines, triggering U mineralization at several locations in the western Otish Basin. Interaction of basinal brines with the Otish Gabbro produced coarse-grained chlorite, tourmaline, and phengitic muscovite, which decreased the fluid-conducting capabilities of diagenetic aquifers and resulted in fault zone- and fracture-dominated fluid flow. Subsequent fluid alteration events produced limited U remobilization, sulfides, sudoite, and siderite between ca. 1670 and 1410 Ma based on mineral paragenesis and 40Ar/39Ar dates of muscovite. Metamorphic fluids having high δ18O values and temperatures around 300°C accompanied 1.2 to 1.0 Ga Grenville orogenesis and subgreenschist-grade metamorphism in the Otish Basin but were present at low water/rock ratios at Camie River and therefore produced little alteration. Post-Grenville uplift of the Otish Basin likely produced late, low-temperature alteration minerals that have been influenced by recent meteoric water, suggesting that the fault zones and fractures the minerals occupy remain as preferential fluid-flow pathways to the present day. Radiogenic Pb and the characteristic trace elements Mo + W + Nb have also preferentially dispersed from the mineralization along fault zones, fractures, and depositional sequence boundaries, and can be used to explore for Camie River-style U mineralization. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/3/401.short

Formation and evolution of the centennial unconformity-related uranium deposit in the south-central Athabasca basin, Canada / P. Alexandre in Economic geology, Vol. 107 N° 3 (Mai 2012) 

Public ISBD [article]  in Economic geology > Vol. 107 N° 3 (Mai 2012) . - pp. 385-400 Titre : Formation and evolution of the centennial unconformity-related uranium deposit in the south-central Athabasca basin, Canada Type de document : texte imprimé Auteurs : P. Alexandre, Auteur ; K. Kyser, Auteur ; D. Jiricka, Auteur Année de publication : 2012 Article en page(s) : pp. 385-400 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : Uranium  deposit  Athabasca  basin  Canada Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Centennial U deposit is situated in the south-central Athabasca Basin (Canada) and straddles the unconformity between early Paleoproterozoic to Archean metasedimentary and metavolcanic rocks and granitoids, and the clastic sediments of the Paleoproterozoic Athabasca Group. Although it has most characteristics of an unconformity-related uranium deposit, the Centennial deposit is atypical in that it is not directly associated with an electromagnetic conductor (there is a paucity of graphite in the basement) or with a major reverse fault zone; it is distal from a major fluid conduit (ca. 300 to 400 m from the Dufferin Lake Fault), has low Ni, Cu, Co, Zn, and Pb contents, and contains an unusually large amount (up to 5%) of secondary uranyl minerals. Additionally, a network of diabase dikes and sills is observed at Centennial, seemingly intruding the main U mineralization of massive uraninite, based on the relatively sharp contacts between the diabase dike and the high-grade U mineralization. The pre-U alteration assemblage at Centennial includes kaolinite, illite, and sudoite, which have been formed by fluids with isotopic and chemical compositions that are comparable with those from other sandstone-hosted unconformity-type U deposits in the Athabasca Basin. Pre-U illite-related fluids have δ18O of ca. 3‰ and δD of ca. −40‰, whereas pre-U chlorite-related fluids have δ18O between 1.7 and 4.3‰ and δD between −18 and 1‰. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U/Pb dating of the various U phases indicates that initial mineralization, represented by disseminated uraninite found directly to the north-northeast of the Centennial deposit, occurred at ca. 1.6 Ga. The main U mineralization, represented by massive and strongly altered uraninite, followed at an unknown time. A minor (<5%) unaltered uraninite formed from the local remobilization of the main massive uraninite at ca. 380 Ma. The main uranyl mineral, uranophane, formed last, at ca. 2 Ma. The recurrence of local U remobilization might have been facilitated by the persisting high permeability of the sandstones in the area due to the nearby Dufferin Lake Fault and to the emplacement of the diabase dikes. The usefulness of Pb isotopes for exploration is demonstrated at the Centennial deposit, with strongly radiogenic Pb isotope signatures close to the deposit and a common Pb signature observed at a distance of a few km from the deposit. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/3/385.abstract [article] Formation and evolution of the centennial unconformity-related uranium deposit in the south-central Athabasca basin, Canada [texte imprimé] / P. Alexandre, Auteur ; K. Kyser, Auteur ; D. Jiricka, Auteur . - 2012 . - pp. 385-400. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 3 (Mai 2012) . - pp. 385-400 Mots-clés : Uranium  deposit  Athabasca  basin  Canada Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Centennial U deposit is situated in the south-central Athabasca Basin (Canada) and straddles the unconformity between early Paleoproterozoic to Archean metasedimentary and metavolcanic rocks and granitoids, and the clastic sediments of the Paleoproterozoic Athabasca Group. Although it has most characteristics of an unconformity-related uranium deposit, the Centennial deposit is atypical in that it is not directly associated with an electromagnetic conductor (there is a paucity of graphite in the basement) or with a major reverse fault zone; it is distal from a major fluid conduit (ca. 300 to 400 m from the Dufferin Lake Fault), has low Ni, Cu, Co, Zn, and Pb contents, and contains an unusually large amount (up to 5%) of secondary uranyl minerals. Additionally, a network of diabase dikes and sills is observed at Centennial, seemingly intruding the main U mineralization of massive uraninite, based on the relatively sharp contacts between the diabase dike and the high-grade U mineralization. The pre-U alteration assemblage at Centennial includes kaolinite, illite, and sudoite, which have been formed by fluids with isotopic and chemical compositions that are comparable with those from other sandstone-hosted unconformity-type U deposits in the Athabasca Basin. Pre-U illite-related fluids have δ18O of ca. 3‰ and δD of ca. −40‰, whereas pre-U chlorite-related fluids have δ18O between 1.7 and 4.3‰ and δD between −18 and 1‰. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U/Pb dating of the various U phases indicates that initial mineralization, represented by disseminated uraninite found directly to the north-northeast of the Centennial deposit, occurred at ca. 1.6 Ga. The main U mineralization, represented by massive and strongly altered uraninite, followed at an unknown time. A minor (<5%) unaltered uraninite formed from the local remobilization of the main massive uraninite at ca. 380 Ma. The main uranyl mineral, uranophane, formed last, at ca. 2 Ma. The recurrence of local U remobilization might have been facilitated by the persisting high permeability of the sandstones in the area due to the nearby Dufferin Lake Fault and to the emplacement of the diabase dikes. The usefulness of Pb isotopes for exploration is demonstrated at the Centennial deposit, with strongly radiogenic Pb isotope signatures close to the deposit and a common Pb signature observed at a distance of a few km from the deposit. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/3/385.abstract