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Formation of sedimentary rock-hosted stratiform copper deposits through earth history / Murray W. Hitzman in Economic geology, Vol. 105 N° 3 (Mai 2010) 

Public ISBD [article]  in Economic geology > Vol. 105 N° 3 (Mai 2010) . - pp. 627-639 Titre : Formation of sedimentary rock-hosted stratiform copper deposits through earth history Type de document : texte imprimé Auteurs : Murray W. Hitzman, Auteur ; David Selley, Auteur ; Stuart Bull, Auteur Année de publication : 2011 Article en page(s) : pp. 627-639 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : Sedimentary  rock  Copper  deposits  Mineralization Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : Sedimentary rock-hosted stratiform copper deposits form by movement of oxidized, copper-bearing fluids across a reduction front that results in the precipitation of copper sulfides. Large-scale production of such oxidized fluids, as well as the formation of mobile hydrocarbons (oil) has probably been common since the formation of the first red beds in the Paleoproterozoic, and deposits of this type occur in rocks from the Paleoproterozoic to the Tertiary. However, supergiant deposits are currently recognized in only three basins: the Paleoproterozoic Kodaro-Udokan basin of Siberia, the Neoproterozoic Katangan basin of south-central Africa, and the Permian Zechstein basin of northern Europe. The paucity of data regarding the Udokan deposit makes understanding this system difficult in terms of Earth history events. Both the Neoproterozoic and the Permian were times of supercontinent breakup with major landmasses at low latitudes. This global tectonic framework favored the formation of failed rifts that subsequently became significant intracratonic basins with basal, synrift red-bed sequences overlain by marine and/or lacustrine sediments and, in some basins located at low latitudes, by thick evaporitic strata. The intracratonic setting of these basins allowed the development of a hydrologically closed basinal architecture in which highly oxidized and saline, moderate-temperature basinal brines were produced that were capable of supplying reduction-controlled sulfide precipitation over very long time periods (tens to hundreds of millions of years). The length of time available for the mineralizing process may be the key factor necessary to form supergiant deposits. However, examination of the absolute ages for the Kupferschiefer (Zechstein basin) and Katangan deposits allows speculation that other factors may also have been important. Both the Neoproterozoic and Permian were times of major glacial events. Glaciation may also be conducive for the formation of supergiant sediment-hosted stratiform copper deposits. Glacial periods correspond to magnesium- and sulfate-rich oceans that could have been responsible for additional sulfur in basinal brines developed during evaporite formation and would then be available during the long mineralization process. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/105/3/627.abstract [article] Formation of sedimentary rock-hosted stratiform copper deposits through earth history [texte imprimé] / Murray W. Hitzman, Auteur ; David Selley, Auteur ; Stuart Bull, Auteur . - 2011 . - pp. 627-639. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 105 N° 3 (Mai 2010) . - pp. 627-639 Mots-clés : Sedimentary  rock  Copper  deposits  Mineralization Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : Sedimentary rock-hosted stratiform copper deposits form by movement of oxidized, copper-bearing fluids across a reduction front that results in the precipitation of copper sulfides. Large-scale production of such oxidized fluids, as well as the formation of mobile hydrocarbons (oil) has probably been common since the formation of the first red beds in the Paleoproterozoic, and deposits of this type occur in rocks from the Paleoproterozoic to the Tertiary. However, supergiant deposits are currently recognized in only three basins: the Paleoproterozoic Kodaro-Udokan basin of Siberia, the Neoproterozoic Katangan basin of south-central Africa, and the Permian Zechstein basin of northern Europe. The paucity of data regarding the Udokan deposit makes understanding this system difficult in terms of Earth history events. Both the Neoproterozoic and the Permian were times of supercontinent breakup with major landmasses at low latitudes. This global tectonic framework favored the formation of failed rifts that subsequently became significant intracratonic basins with basal, synrift red-bed sequences overlain by marine and/or lacustrine sediments and, in some basins located at low latitudes, by thick evaporitic strata. The intracratonic setting of these basins allowed the development of a hydrologically closed basinal architecture in which highly oxidized and saline, moderate-temperature basinal brines were produced that were capable of supplying reduction-controlled sulfide precipitation over very long time periods (tens to hundreds of millions of years). The length of time available for the mineralizing process may be the key factor necessary to form supergiant deposits. However, examination of the absolute ages for the Kupferschiefer (Zechstein basin) and Katangan deposits allows speculation that other factors may also have been important. Both the Neoproterozoic and Permian were times of major glacial events. Glaciation may also be conducive for the formation of supergiant sediment-hosted stratiform copper deposits. Glacial periods correspond to magnesium- and sulfate-rich oceans that could have been responsible for additional sulfur in basinal brines developed during evaporite formation and would then be available during the long mineralization process. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/105/3/627.abstract

Geologic setting, sedimentary architecture, and paragenesis of the mesoproterozoic sediment-hosted sheep creek Cu-Co-Ag deposit, Helena Embayment, Montana / Garth Graham in Economic geology, Vol. 107 N° 6 (Septembre/Octobre 2012) 

Public ISBD [article]  in Economic geology > Vol. 107 N° 6 (Septembre/Octobre 2012) . - pp. 1115-1141 Titre : Geologic setting, sedimentary architecture, and paragenesis of the mesoproterozoic sediment-hosted sheep creek Cu-Co-Ag deposit, Helena Embayment, Montana Type de document : texte imprimé Auteurs : Garth Graham, Auteur ; Murray W. Hitzman, Auteur ; Jerry Zieg, Auteur Année de publication : 2012 Article en page(s) : pp. 1115-1141 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : Sheep  creek  Cu-Co-Ag  deposit;  mineralization;  Montana Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The northern margin of the Helena Embayment contains extensive syngenetic to diagenetic massive pyrite horizons that extend over 25 km along the Volcano Valley-Buttress fault zone and extend up to 8 km basinward (south) within the Mesoproterozoic Newland Formation. The Sheep Creek Cu-Co deposit occurs within a structural block along a bend in the fault system, where replacement-style chalcopyrite mineralization is spatially associated mostly with the two stratigraphically lowest massive pyrite zones. These mineralized pyritic horizons are intercalated with debris flows derived from synsedimentary movement along the Volcano Valley-Buttress fault zone. Cominco American Inc. delineated a geologic resource of 4.5 Mt at 2.5% Cu and 0.1% Co in the upper sulfide zone and 4 Mt at 4% Cu within the lower sulfide zone. More recently, Tintina Resources Inc. has delineated an inferred resource of 8.48 Mt at 2.96% Cu, 0.12% Co, and 16.4 g/t Ag in the upper sulfide zone. The more intact upper sulfide zone displays significant thickness variations along strike thought to represent formation in at least three separate subbasins. The largest accumulation of mineralized sulfide in the upper zone occurs as an N-S–trending body that thickens southward from the generally E trending Volcano Valley Fault and probably occupies a paleograben controlled by normal faults in the hanging wall of the Volcano Valley Fault. Early microcrystalline to framboidal pyrite was accompanied by abundant and local barite deposition in the upper and lower sulfide zones, respectively. The sulfide bodies underwent intense (lower sulfide zone) to localized (upper sulfide zone) recrystallization and overprinting by coarser-grained pyrite and minor marcasite that is intergrown with and replaces dolomite. Silicification and paragenetically late chalcopyrite, along with minor tennantite in the upper sulfide zone, replaces fine-grained pyrite, barite, and carbonate. The restriction of chalcopyrite to inferred synsedimentary E- and northerly trending faults and absence of definitive zonation with respect to the Laramide Volcano Valley Fault in the lower sulfide zone suggest a diagenetic age related to basin development for the Sheep Creek Cu-Co-Ag deposit. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/6/1115.short [article] Geologic setting, sedimentary architecture, and paragenesis of the mesoproterozoic sediment-hosted sheep creek Cu-Co-Ag deposit, Helena Embayment, Montana [texte imprimé] / Garth Graham, Auteur ; Murray W. Hitzman, Auteur ; Jerry Zieg, Auteur . - 2012 . - pp. 1115-1141. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 6 (Septembre/Octobre 2012) . - pp. 1115-1141 Mots-clés : Sheep  creek  Cu-Co-Ag  deposit;  mineralization;  Montana Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The northern margin of the Helena Embayment contains extensive syngenetic to diagenetic massive pyrite horizons that extend over 25 km along the Volcano Valley-Buttress fault zone and extend up to 8 km basinward (south) within the Mesoproterozoic Newland Formation. The Sheep Creek Cu-Co deposit occurs within a structural block along a bend in the fault system, where replacement-style chalcopyrite mineralization is spatially associated mostly with the two stratigraphically lowest massive pyrite zones. These mineralized pyritic horizons are intercalated with debris flows derived from synsedimentary movement along the Volcano Valley-Buttress fault zone. Cominco American Inc. delineated a geologic resource of 4.5 Mt at 2.5% Cu and 0.1% Co in the upper sulfide zone and 4 Mt at 4% Cu within the lower sulfide zone. More recently, Tintina Resources Inc. has delineated an inferred resource of 8.48 Mt at 2.96% Cu, 0.12% Co, and 16.4 g/t Ag in the upper sulfide zone. The more intact upper sulfide zone displays significant thickness variations along strike thought to represent formation in at least three separate subbasins. The largest accumulation of mineralized sulfide in the upper zone occurs as an N-S–trending body that thickens southward from the generally E trending Volcano Valley Fault and probably occupies a paleograben controlled by normal faults in the hanging wall of the Volcano Valley Fault. Early microcrystalline to framboidal pyrite was accompanied by abundant and local barite deposition in the upper and lower sulfide zones, respectively. The sulfide bodies underwent intense (lower sulfide zone) to localized (upper sulfide zone) recrystallization and overprinting by coarser-grained pyrite and minor marcasite that is intergrown with and replaces dolomite. Silicification and paragenetically late chalcopyrite, along with minor tennantite in the upper sulfide zone, replaces fine-grained pyrite, barite, and carbonate. The restriction of chalcopyrite to inferred synsedimentary E- and northerly trending faults and absence of definitive zonation with respect to the Laramide Volcano Valley Fault in the lower sulfide zone suggest a diagenetic age related to basin development for the Sheep Creek Cu-Co-Ag deposit. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/6/1115.short

Late paleoproterozoic to early mesoproterozoic tangdan sedimentary rock-hosted strata-bound copper deposit, Yunnan province, southwest China / Xin-Fu Zhao in Economic geology, Vol. 107 N° 2 (Mars/Avril 2012) 

Public ISBD [article]  in Economic geology > Vol. 107 N° 2 (Mars/Avril 2012) . - pp. 357-375 Titre : Late paleoproterozoic to early mesoproterozoic tangdan sedimentary rock-hosted strata-bound copper deposit, Yunnan province, southwest China Type de document : texte imprimé Auteurs : Xin-Fu Zhao, Auteur ; Mei-Fu Zhou, Auteur ; Murray W. Hitzman, Auteur Année de publication : 2012 Article en page(s) : pp. 357-375 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : Sedimentary  rock-hosted  strata-bound  copper  deposits  Yunnan  province  China Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : Sedimentary rock-hosted strata-bound copper deposits are widespread in the Kangdian region of the Central Yunnan and southern Sichuan provinces, southwest China. The deposits occur within weakly metamorphosed rocks of the late Paleoproterozoic to early Mesoproterozoic Dongchuan Group and are spatially associated with discordant breccia bodies that are interpreted as having formed from salt diapirs. The Tangdan deposit, the largest in the region, consists of stratiform and discordant orebodies predominantly hosted in dolostones immediately above hematitic sandstones and siltstones and in black shales above the dolostones. Host rocks for the deposit display a complex paragenetic sequence of alteration and mineralization. Early sodic alteration resulted in the growth of both albite and ferroan dolomite. Later potassic alteration resulted in the precipitation of potassium feldspar and locally biotite in argillaceous layers. Sulfide mineralization was temporally and spatially associated with silicification that postdated both sodic and potassic alteration. Textures suggest that silicification may have preferentially affected evaporite minerals in the dolostones. Copper sulfides form bedding-parallel disseminations, veinlets and, to a lesser extent, stockworks. Copper sulfides are dominated by chalcopyrite with lesser bornite and chalcocite. Hypogene chalcopyrite and bornite from the Tangdan deposit have δ34S values that range from −12.7 to +9.3‰ and cluster between −3 to +5‰. The values suggest derivation from Mesoproterozoic marine sulfates. The dolostone host rocks have relatively homogeneous C and O isotope values ranging from 0.2 to 1.3‰ δ13CV-PDB and from 19.1 to 22.4‰ δ18OV-SNOW. Carbonate minerals in quartz sulfide veins display both a trend toward lighter oxygen isotope values and a trend to significantly lighter carbon isotope values. The light carbon isotope values suggest involvement of organic carbon in the mineralizing process. Alteration and mineralization at Tangdan probably occurred via interaction of oxidized saline brines derived from the underlying red-bed sequence with partially to wholly lithified dolostones. Sulfide precipitation was likely due to both redox reactions and mineralizing fluid pH changes resulting from dolomite and sulfate dissolution. The styles of alteration and mineralization at the Tangdan deposit are similar to those observed in the Central African Copperbelt, particularly the dolostone-hosted orebodies in the Mines Series of the Democratic Republic of Congo. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/2/357.short [article] Late paleoproterozoic to early mesoproterozoic tangdan sedimentary rock-hosted strata-bound copper deposit, Yunnan province, southwest China [texte imprimé] / Xin-Fu Zhao, Auteur ; Mei-Fu Zhou, Auteur ; Murray W. Hitzman, Auteur . - 2012 . - pp. 357-375. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 2 (Mars/Avril 2012) . - pp. 357-375 Mots-clés : Sedimentary  rock-hosted  strata-bound  copper  deposits  Yunnan  province  China Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : Sedimentary rock-hosted strata-bound copper deposits are widespread in the Kangdian region of the Central Yunnan and southern Sichuan provinces, southwest China. The deposits occur within weakly metamorphosed rocks of the late Paleoproterozoic to early Mesoproterozoic Dongchuan Group and are spatially associated with discordant breccia bodies that are interpreted as having formed from salt diapirs. The Tangdan deposit, the largest in the region, consists of stratiform and discordant orebodies predominantly hosted in dolostones immediately above hematitic sandstones and siltstones and in black shales above the dolostones. Host rocks for the deposit display a complex paragenetic sequence of alteration and mineralization. Early sodic alteration resulted in the growth of both albite and ferroan dolomite. Later potassic alteration resulted in the precipitation of potassium feldspar and locally biotite in argillaceous layers. Sulfide mineralization was temporally and spatially associated with silicification that postdated both sodic and potassic alteration. Textures suggest that silicification may have preferentially affected evaporite minerals in the dolostones. Copper sulfides form bedding-parallel disseminations, veinlets and, to a lesser extent, stockworks. Copper sulfides are dominated by chalcopyrite with lesser bornite and chalcocite. Hypogene chalcopyrite and bornite from the Tangdan deposit have δ34S values that range from −12.7 to +9.3‰ and cluster between −3 to +5‰. The values suggest derivation from Mesoproterozoic marine sulfates. The dolostone host rocks have relatively homogeneous C and O isotope values ranging from 0.2 to 1.3‰ δ13CV-PDB and from 19.1 to 22.4‰ δ18OV-SNOW. Carbonate minerals in quartz sulfide veins display both a trend toward lighter oxygen isotope values and a trend to significantly lighter carbon isotope values. The light carbon isotope values suggest involvement of organic carbon in the mineralizing process. Alteration and mineralization at Tangdan probably occurred via interaction of oxidized saline brines derived from the underlying red-bed sequence with partially to wholly lithified dolostones. Sulfide precipitation was likely due to both redox reactions and mineralizing fluid pH changes resulting from dolomite and sulfate dissolution. The styles of alteration and mineralization at the Tangdan deposit are similar to those observed in the Central African Copperbelt, particularly the dolostone-hosted orebodies in the Mines Series of the Democratic Republic of Congo. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/2/357.short