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B Thomson - One of the best experts on this subject based on the ideXlab platform.
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Geochronology and tectonic setting of silicic dike swarms and related silver mineralization at Candelaria, western Nevada
Economic Geology, 1995Co-Authors: B Thomson, M Aftalion, R.m. Mcintyre, Clive Maitland RiceAbstract:The Candelaria mining district in central western Nevada preserves a record of tectonism, magmatism, and mineralization related to early Mesozoic development of the cordilleran magmatic arc. A deformed basement of Ordovician chert-phyllite (Palmetto complex) and its thin parautochthonous cover of Permo- Triassic marine clastic rocks (Diablo and Candelaria Formations) are structurally overlain, along the Pickhandle- Golconda thrust system, by ophiolitic tectonic melange forming the base of the Golconda allochthon. The total assemblage is cut by three overlapping swarms of silicic dikes comprising, from the oldest to the youngest: fine-grained, sparsely porphyritic calc-alkaline rhyolites; medium-grained, strongly porphyritic, high K calc-alkaline dacites; fine-grained calc-alkaline rhyolites. U-Pb zircon dating gives ages of 222 + or - 2 Ma for the older rhyolites, 192 + or - 3 Ma for the porphyries, and 196 + or - 24 Ma for the younger rhyolites. These swarms are products of the Triassic-Jurassic cordilleran magmatic arc, which developed under a long-lived, broadly extensional to transtensional tectonic regime, to generate a major intra-arc graben system characterized by voluminous caldera-related ignimbrites. The dike swarms possibly mark the site of an eroded caldera. The dacite porphyries are genetically associated with important sediment-hosted disseminated silver (-gold-base metals) mineralization, which occurs in thick tabular zones along the Pickhandle thrust and in a subparallel footwall structure--the lower Candelaria shear--which cuts reactive carbonaceous marly shales at the base of the Candelaria Formation. Mineralization occurs where the porphyries intrude the Pickhandle thrust and the lower Candelaria shear. The 192 + or - 3 Ma date for the dacites defines Candalaria as the oldest disseminated precious metal deposit in the Great Basin. There are similarities in tectonic setting, magmatic association, metal composition, and possibly, age between Candelaria and the Darwin-type Pb-Ag-Zn vein replacement deposits of southeastern California. Differences in host-rock composition and host-rock amenability to structural preparation may account for grade-tonnage differences between Candelaria (large, low grade; hosted by thin-bedded marly shales) and the Darwin-type deposits (small, high grade; hosted by more massive carbonate rocks). K-Ar ages for sericites from the hydrothermal alteration envelope at Candelaria range from 91 to 132 Ma (mid to Late Cretaceous). The discrepancy between these ages and those of the silicic dikes is attributed to regional-scale reheating and resetting of K-Ar isotopic systematics, related to development of the younger, crosscutting Jurassic-Cretaceous cordilleran magmatic arc. This arc generated the Sierra Nevada batholithic belt, which is represented locally by several small calc-alkaline granite porphyry stocks, dated at 84 to 97 Ma (K-Ar biotite), exposed within a few kilometers of Candelaria.
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The Candelaria silver deposit, Nevada — preliminary sulphur, oxygen and hydrogen isotope geochemistry
Mineralium Deposita, 1994Co-Authors: B Thomson, A. E. Fallick, A. J. Boyce, C. RiceAbstract:The pre-Cenozoic geology at Candelaria, Nevada comprises four main lithologic units: the basement consists of Ordovician cherts of the Palmetto complex; this is overlain unconformably by Permo-Triassic marine clastic sediments (Diablo and Candelaria Formations); these are structurally overlain by a serpentinitehosted tectonic mélange (Pickhandle/Golconda allochthon); all these units are cut by three Mesozoic felsic dike systems. Bulk-mineable silver-base metal ores occur as stratabound sheets of vein stockwork/disseminated sulphide mineralisation within structurally favourable zones along the base of the Pickhandle allochthon (i.e. Pickhandle thrust and overlying ultramafics/mafics) and within the fissile, calcareous and phosphatic black shales at the base of the Candelaria Formation (lower Candelaria ‘shear’). The most prominent felsic dike system — a suite of Early Jurassic granodiorite porphyries — exhibits close spatial, alteration and geochemical associations with the silver mineralisation. Disseminated pyrites from the bulk-mineable ores exhibit a δ ^34S range from — 0.3‰ to + 12.1‰ (mean δ ^34S = +6.4 ± 3.5‰, 1 σ , n = 17) and two sphalerites have δ ^34S of + 5.9‰ and + 8.7‰ These data support a felsic magmatic source for sulphur in the ores, consistent with their proximal position in relation to the porphyries. However, a minor contribution of sulphur from diagenetic pyrite in the host Candelaria sediments (mean δ ^34S = — 14.0‰) cannot be ruled out. Sulphur in late, localised barite veins ( δ ^34S = + 17.3‰ and + 17.7‰) probably originated from a sedimentary/seawater source, in the form of bedded barite within the Palmetto basement ( δ ^34S = + 18.9‰). Quartz veins from the ores have mean δ ^18O = + 15.9 ± 0.8‰ (1 σ , n = 10), which is consistent, over the best estimate temperature range of the mineralisation (360°–460°C), with deposition from ^18O-enriched magmatic-hydrothermal fluids (calculated δ ^18O fluid = + 9.4‰ to + 13.9‰). Such enrichment probably occurred through isotopic exchange with the basement cherts during fluid ascent from a source pluton. Whole rock data for a propylitised porphyry ( δ ^18O = + 14.2‰, δ D = — 65‰) support a magmatic fluid source. However, δ D results for fluid inclusions from several vein samples (mean = — 108 ± 14‰, 1 σ , n = 6) and for other dike and sediment whole rocks (mean = — 110 ± 13‰, 1 σ , n = 5) reveal the influence of meteoric waters. The timing of meteoric fluid incursion is unresolved, but possibilities include late-mineralisation groundwater flooding during cooling of the Early Jurassic progenitor porphyry system and/or meteoric fluid circulation driven by Late Cretaceous plutonism.
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The Candelaria silver deposit, Nevada — preliminary sulphur, oxygen and hydrogen isotope geochemistry
Mineralium Deposita, 1994Co-Authors: B Thomson, A. E. Fallick, A. J. Boyce, Clive Maitland RiceAbstract:The pre-Cenozoic geology at Candelaria, Nevada comprises four main lithologic units: the basement consists of Ordovician cherts of the Palmetto complex; this is overlain unconformably by Permo-Triassic marine clastic sediments (Diablo and Candelaria Formations); these are structurally overlain by a serpentinitehosted tectonic melange (Pickhandle/Golconda allochthon); all these units are cut by three Mesozoic felsic dike systems. Bulk-mineable silver-base metal ores occur as stratabound sheets of vein stockwork/disseminated sulphide mineralisation within structurally favourable zones along the base of the Pickhandle allochthon (i.e. Pickhandle thrust and overlying ultramafics/mafics) and within the fissile, calcareous and phosphatic black shales at the base of the Candelaria Formation (lower Candelaria ‘shear’). The most prominent felsic dike system — a suite of Early Jurassic granodiorite porphyries — exhibits close spatial, alteration and geochemical associations with the silver mineralisation. Disseminated pyrites from the bulk-mineable ores exhibit a δ34S range from — 0.3‰ to + 12.1‰ (mean δ34S = +6.4 ± 3.5‰, 1σ, n = 17) and two sphalerites have δ34S of + 5.9‰ and + 8.7‰ These data support a felsic magmatic source for sulphur in the ores, consistent with their proximal position in relation to the porphyries. However, a minor contribution of sulphur from diagenetic pyrite in the host Candelaria sediments (mean δ34S = — 14.0‰) cannot be ruled out. Sulphur in late, localised barite veins (δ34S = + 17.3‰ and + 17.7‰) probably originated from a sedimentary/seawater source, in the form of bedded barite within the Palmetto basement (δ34S = + 18.9‰). Quartz veins from the ores have mean δ18O = + 15.9 ± 0.8‰ (1σ, n = 10), which is consistent, over the best estimate temperature range of the mineralisation (360°–460°C), with deposition from 18O-enriched magmatic-hydrothermal fluids (calculated δ18O fluid = + 9.4‰ to + 13.9‰). Such enrichment probably occurred through isotopic exchange with the basement cherts during fluid ascent from a source pluton. Whole rock data for a propylitised porphyry (δ18O = + 14.2‰, δD = — 65‰) support a magmatic fluid source. However, δD results for fluid inclusions from several vein samples (mean = — 108 ± 14‰, 1σ, n = 6) and for other dike and sediment whole rocks (mean = — 110 ± 13‰, 1σ, n = 5) reveal the influence of meteoric waters. The timing of meteoric fluid incursion is unresolved, but possibilities include late-mineralisation groundwater flooding during cooling of the Early Jurassic progenitor porphyry system and/or meteoric fluid circulation driven by Late Cretaceous plutonism.
Clive Maitland Rice - One of the best experts on this subject based on the ideXlab platform.
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Geochronology and tectonic setting of silicic dike swarms and related silver mineralization at Candelaria, western Nevada
Economic Geology, 1995Co-Authors: B Thomson, M Aftalion, R.m. Mcintyre, Clive Maitland RiceAbstract:The Candelaria mining district in central western Nevada preserves a record of tectonism, magmatism, and mineralization related to early Mesozoic development of the cordilleran magmatic arc. A deformed basement of Ordovician chert-phyllite (Palmetto complex) and its thin parautochthonous cover of Permo- Triassic marine clastic rocks (Diablo and Candelaria Formations) are structurally overlain, along the Pickhandle- Golconda thrust system, by ophiolitic tectonic melange forming the base of the Golconda allochthon. The total assemblage is cut by three overlapping swarms of silicic dikes comprising, from the oldest to the youngest: fine-grained, sparsely porphyritic calc-alkaline rhyolites; medium-grained, strongly porphyritic, high K calc-alkaline dacites; fine-grained calc-alkaline rhyolites. U-Pb zircon dating gives ages of 222 + or - 2 Ma for the older rhyolites, 192 + or - 3 Ma for the porphyries, and 196 + or - 24 Ma for the younger rhyolites. These swarms are products of the Triassic-Jurassic cordilleran magmatic arc, which developed under a long-lived, broadly extensional to transtensional tectonic regime, to generate a major intra-arc graben system characterized by voluminous caldera-related ignimbrites. The dike swarms possibly mark the site of an eroded caldera. The dacite porphyries are genetically associated with important sediment-hosted disseminated silver (-gold-base metals) mineralization, which occurs in thick tabular zones along the Pickhandle thrust and in a subparallel footwall structure--the lower Candelaria shear--which cuts reactive carbonaceous marly shales at the base of the Candelaria Formation. Mineralization occurs where the porphyries intrude the Pickhandle thrust and the lower Candelaria shear. The 192 + or - 3 Ma date for the dacites defines Candalaria as the oldest disseminated precious metal deposit in the Great Basin. There are similarities in tectonic setting, magmatic association, metal composition, and possibly, age between Candelaria and the Darwin-type Pb-Ag-Zn vein replacement deposits of southeastern California. Differences in host-rock composition and host-rock amenability to structural preparation may account for grade-tonnage differences between Candelaria (large, low grade; hosted by thin-bedded marly shales) and the Darwin-type deposits (small, high grade; hosted by more massive carbonate rocks). K-Ar ages for sericites from the hydrothermal alteration envelope at Candelaria range from 91 to 132 Ma (mid to Late Cretaceous). The discrepancy between these ages and those of the silicic dikes is attributed to regional-scale reheating and resetting of K-Ar isotopic systematics, related to development of the younger, crosscutting Jurassic-Cretaceous cordilleran magmatic arc. This arc generated the Sierra Nevada batholithic belt, which is represented locally by several small calc-alkaline granite porphyry stocks, dated at 84 to 97 Ma (K-Ar biotite), exposed within a few kilometers of Candelaria.
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The Candelaria silver deposit, Nevada — preliminary sulphur, oxygen and hydrogen isotope geochemistry
Mineralium Deposita, 1994Co-Authors: B Thomson, A. E. Fallick, A. J. Boyce, Clive Maitland RiceAbstract:The pre-Cenozoic geology at Candelaria, Nevada comprises four main lithologic units: the basement consists of Ordovician cherts of the Palmetto complex; this is overlain unconformably by Permo-Triassic marine clastic sediments (Diablo and Candelaria Formations); these are structurally overlain by a serpentinitehosted tectonic melange (Pickhandle/Golconda allochthon); all these units are cut by three Mesozoic felsic dike systems. Bulk-mineable silver-base metal ores occur as stratabound sheets of vein stockwork/disseminated sulphide mineralisation within structurally favourable zones along the base of the Pickhandle allochthon (i.e. Pickhandle thrust and overlying ultramafics/mafics) and within the fissile, calcareous and phosphatic black shales at the base of the Candelaria Formation (lower Candelaria ‘shear’). The most prominent felsic dike system — a suite of Early Jurassic granodiorite porphyries — exhibits close spatial, alteration and geochemical associations with the silver mineralisation. Disseminated pyrites from the bulk-mineable ores exhibit a δ34S range from — 0.3‰ to + 12.1‰ (mean δ34S = +6.4 ± 3.5‰, 1σ, n = 17) and two sphalerites have δ34S of + 5.9‰ and + 8.7‰ These data support a felsic magmatic source for sulphur in the ores, consistent with their proximal position in relation to the porphyries. However, a minor contribution of sulphur from diagenetic pyrite in the host Candelaria sediments (mean δ34S = — 14.0‰) cannot be ruled out. Sulphur in late, localised barite veins (δ34S = + 17.3‰ and + 17.7‰) probably originated from a sedimentary/seawater source, in the form of bedded barite within the Palmetto basement (δ34S = + 18.9‰). Quartz veins from the ores have mean δ18O = + 15.9 ± 0.8‰ (1σ, n = 10), which is consistent, over the best estimate temperature range of the mineralisation (360°–460°C), with deposition from 18O-enriched magmatic-hydrothermal fluids (calculated δ18O fluid = + 9.4‰ to + 13.9‰). Such enrichment probably occurred through isotopic exchange with the basement cherts during fluid ascent from a source pluton. Whole rock data for a propylitised porphyry (δ18O = + 14.2‰, δD = — 65‰) support a magmatic fluid source. However, δD results for fluid inclusions from several vein samples (mean = — 108 ± 14‰, 1σ, n = 6) and for other dike and sediment whole rocks (mean = — 110 ± 13‰, 1σ, n = 5) reveal the influence of meteoric waters. The timing of meteoric fluid incursion is unresolved, but possibilities include late-mineralisation groundwater flooding during cooling of the Early Jurassic progenitor porphyry system and/or meteoric fluid circulation driven by Late Cretaceous plutonism.
Robert Marschik - One of the best experts on this subject based on the ideXlab platform.
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Early Cretaceous U–Pb zircon ages for the Copiapó plutonic complex and implications for the IOCG mineralization at Candelaria, Atacama Region, Chile
Mineralium Deposita, 2006Co-Authors: Robert Marschik, Frank SöllnerAbstract:Four of the major plutons in the vicinity of the Candelaria mine (470 Mt at 0.95% Cu, 0.22 g/t Au, 3.1 g/t Ag) and a dike–sill system exposed in the Candelaria open pit have been dated with the U–Pb zircon method. The new geochronological data indicate that dacite magmatism around 123 Ma preceded the crystallization of hornblende diorite (Khd) at 118 ± 1 Ma, quartz–monzonite porphyry (Kqm) at 116.3 ± 0.4 Ma, monzodiorite (Kmd) at 115.5 ± 0.4 Ma, and tonalite (Kt) at 110.7 ± 0.4 Ma. The new ages of the plutons are consistent with field relationships regarding the relative timing of emplacement. Plutonism temporally overlaps with the iron oxide Cu–Au mineralization (Re–Os molybdenite ages at ∼115 Ma) and silicate alteration (ages mainly from 114 to 116 and 110 to 112 Ma) in the Candelaria–Punta del Cobre district. The dated dacite porphyry and hornblende diorite intrusions preceded the ore formation. A genetic link of the metallic mineralization with the quartz–monzonite porphyry and/or the monzodiorite is likely. Both of these metaluminous, shoshonitic (high-K) intrusions could have provided energy and contributed fluids, metals, and sulfur to the hydrothermal system that caused the iron oxide Cu–Au mineralization. The age of the tonalite at 110.7 Ma falls in the same range as the late alteration at 110 to 112 Ma. Tonalite emplacement may have sustained existing or driven newly developed hydrothermal cells that caused this late alteration or modified 40Ar/39Ar and K/Ar systematic in some areas.
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origin of fluids in iron oxide copper gold deposits constraints from δ 37 cl 87 sr 86 sr i and cl br
Mineralium Deposita, 2006Co-Authors: Dave Banks, R. A. Cliff, Robert Marschik, Massimo Chiaradia, Antoine De HallerAbstract:The origin of the hypersaline fluids (magmatic or basinal brine?), associated with iron oxide (Cu–U–Au–REE) deposits, is controversial. We report the first chlorine and strontium isotope data combined with Cl/Br ratios of fluid inclusions from selected iron oxide–copper–gold (IOCG) deposits (Candelaria, Raul–Condestable, Sossego), a deposit considered to represent a magmatic end member of the IOCG class of deposit (Gameleira), and a magnetite–apatite deposit (El Romeral) from South America. Our data indicate mixing of a high δ 37Cl magmatic fluid with near 0‰ δ 37Cl basinal brines in the Candelaria, Raul–Condestable, and Sossego IOCG deposits and leaching of a few weight percent of evaporites by magmatic-hydrothermal (?) fluids at Gameleira and El Romeral. The Sr isotopic composition of the inclusion fluids of Candelaria, Raul–Condestable, and El Romeral confirms the presence of a non-magmatic fluid component in these deposits. The heavy chlorine isotope signatures of fluids from the IOCG deposits (Candelaria, Raul–Condestable, Sossego), reflecting the magmatic-hydrothermal component of these fluids, contrast with the near 0‰ δ 37Cl values of porphyry copper fluids known from the literature. The heavy chlorine isotope compositions of fluids of the investigated IOCG deposits may indicate a prevailing mantle Cl component in contrast to porphyry copper fluids, an argument also supported by Os isotopes, or could result from differential Cl isotope fractionation processes (e.g. phase separation) in fluids of IOCG and porphyry Cu deposits.
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Origin of fluids in iron oxide-copper-gold deposits: constraints from δ 37 Cl, 87 Sr/ 86 Sr i and Cl/Br
Mineralium Deposita, 2006Co-Authors: Massimo Chiaradia, Dave Banks, R. A. Cliff, Robert Marschik, Antoine De HallerAbstract:The origin of the hypersaline fluids (magmatic or basinal brine?), associated with iron oxide (Cu–U–Au–REE) deposits, is controversial. We report the first chlorine and strontium isotope data combined with Cl/Br ratios of fluid inclusions from selected iron oxide–copper–gold (IOCG) deposits (Candelaria, Raul–Condestable, Sossego), a deposit considered to represent a magmatic end member of the IOCG class of deposit (Gameleira), and a magnetite–apatite deposit (El Romeral) from South America. Our data indicate mixing of a high δ 37Cl magmatic fluid with near 0‰ δ 37Cl basinal brines in the Candelaria, Raul–Condestable, and Sossego IOCG deposits and leaching of a few weight percent of evaporites by magmatic-hydrothermal (?) fluids at Gameleira and El Romeral. The Sr isotopic composition of the inclusion fluids of Candelaria, Raul–Condestable, and El Romeral confirms the presence of a non-magmatic fluid component in these deposits. The heavy chlorine isotope signatures of fluids from the IOCG deposits (Candelaria, Raul–Condestable, Sossego), reflecting the magmatic-hydrothermal component of these fluids, contrast with the near 0‰ δ 37Cl values of porphyry copper fluids known from the literature. The heavy chlorine isotope compositions of fluids of the investigated IOCG deposits may indicate a prevailing mantle Cl component in contrast to porphyry copper fluids, an argument also supported by Os isotopes, or could result from differential Cl isotope fractionation processes (e.g. phase separation) in fluids of IOCG and porphyry Cu deposits.
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Age of Mineralization of the Candelaria Fe Oxide Cu-Au Deposit and the Origin of the Chilean Iron Belt, Based on Re-Os Isotopes
Economic Geology, 2002Co-Authors: Ryan Mathur, Robert Marschik, Joaquin Ruiz, Francisco Munizaga, Richard A. Leveille, Walter MartinAbstract:Re-Os isotopes are used to determine the age of iron oxide Cu-Au mineralization at Candelaria, Chile, and to explore possible genetic links with the batholithic intrusions in the area. Re-Os ages calculated from molybdenite are 114.2 ± 0.6 Ma and 115.2 ± 0.6 Ma, and they are interpreted to represent the age of mineralization. These ages are consistent with previously reported ages for biotite alteration that range from 114 to 116 Ma. An isochron calculated by Re/Os ratios from hydrothermal magnetite and sulfides constrains an initial 187 Os/ 188 Os ratio of 0.36 ± 0.10. The initial 187 Os/ 188 Os ratio for sulfide from Bronce mine, a small satellite of the Candelaria orebody, is 0.33 ± 0.01. These values are broadly similar to the calculated initial 187 Os/ 188 Os ratio for magmatic magnetite in nearby batholithic rocks that range from 0.20 to 0.41. The relatively radiogenic initial 187 Os/ 188 Os ratio represents a mixture of mantle and crustal components in the ores and batholitic rocks. The similarity in initial 187 Os/ 188 Os ratio of the ore and magmatic oxides suggest that the granitic plutons could be the source of metals in the Candelaria district. These data are consistent with the existence of a significant magmatic fluid component in the hydrothermal system as suggested by previously published work. In order to establish a regional perspective, we analyzed ore minerals from other Chilean deposits of the iron oxide (Cu-U-Au-rare earth elements [REE]) class. Magnetite from the Manto Verde iron oxide Cu-Au deposit has Os and Re concentrations of 11 to 17 parts per trillion (ppt) and 4 to 6 parts per billion (ppb), respectively. The initial 187 Os/ 188 Os ratio is approximately 0.20 and is similar to that of ore minerals from Candelaria and of the Early Cretaceous batholithic intrusions. These data indicate a similar metal source for the mineralization at Manto Verde and Candelaria. Magnetite from three magnetite-apatite deposits of the Chilean iron belt have Re concentrations between 0.8 and 3 ppb and Os concentrations between 11 and 76 ppt. Calculated initial 187 Os/ 188 Os ratios of these magnetites range from 1.2 to 8.4 and are distinctly different from those of the iron oxide Cu-Au deposits. The cause of the comparatively high radiogenic signatures in the magnetite-apatite ores is probably related to fluid interactions with (i.e., leaching) the surrounding sedimentary rocks during their genesis. In contrast to the iron oxide Cu-Au systems, the Os in magnetite-apatite ores could be derived from sedimentary rocks. This evidence suggests that predominantly basin-derived, nonmagmatic brines formed these magnetite-apatite deposits.
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the Candelaria punta del cobre iron oxide cu au zn ag deposits chile
Economic Geology, 2001Co-Authors: Robert Marschik, Lluis FontboteAbstract:Several iron oxide-rich Cu-Au(-Zn-Ag) deposits define an approximately 5-km-wide and at least 20-km-long belt along the eastern margin of the coastal batholith near Copiapo, Chile. This belt includes the large Candelaria mine and a group of middle- and small-sized mines in the Punta del Cobre district, which is located about 3 km northeast of the Candelaria deposit. Estimated geologic resources of the belt are on the order of 700 to 800 million metric tons (Mt) at 1.0 percent Cu. The ore occurs in veins, breccia, and stringer bodies, and in replacement bodies that are roughly concordant to bedding. The orebodies are hosted mainly by volcanic and volcaniclastic rocks of the Punta del Cobre Formation and, in places, also occur in volcaniclastic intercalations in the lower part of the overlying Early Cretaceous Chanarcillo Group. Most of the larger orebodies in the belt are located where northwest-trending brittle faults intersect the contact between massive volcanic and volcaniclastic rocks. These northwest faults and a major northeast-trending ductile shear zone control portions of the ore of the Candelaria deposit. Chalcopyrite is the only hypogene Cu mineral. The Cu-Au ore is characterized by abundant magnetite and/or hematite and by locally elevated concentrations of Ag, Zn, Mo, and light rare earth elements. The ore is hosted mainly in zones with biotite-potassium feldspar ± calcic amphibole ± epidote alteration at Candelaria. In the Punta del Cobre district, ore in the deeper parts of the deposits is similarly associated, whereas at shallow levels it occurs in zones of biotite-potassium feldspar, or albite-chlorite ± calcite alteration. Mineralization at Candelaria-Punta del Cobre took place under relatively oxidized conditions manifested by the formation of specular hematite. In parts of the district, the pseudomorphic replacement of early specular hematite by magnetite during the main iron oxide formation marks a shift toward more reduced conditions or higher temperatures. The bulk of the magnetite probably formed at temperatures of about 500° to 600°C. The main sulfide stage followed with formation of pyrite and chalcopyrite at temperatures of >470° to 328°C. Subsequent martitization of the magnetite points to a temperature decrease. Cooling of the hydrothermal system is also indicated by the homogenization temperatures of <236°C of saline fluid inclusions in late-stage calcite. Oxygen isotope combined with microthermometric data suggest that magmatic fluids or nonmagmatic fluids equilibrated with magmatic silicates were dominant during the main copper mineralization. Relatively light oxygen isotope signatures of fluids in equilibrium with late calcite suggest mixing with a nonmagmatic fluid (e.g., basinal brines or meteoric waters) during the late stages of hydrothermal activity. Sulfur isotope ratios of chalcopyrite, pyrite, pyrrhotite, and sphalerite from the Bronce, Candelaria, Las Pintadas, Santos, and Socavon Rampa deposits range from δ 34SCDT values of –0.7 to +3.1 per mil. This narrow range of sulfur isotope ratios near 0 per mil is consistent with sulfur of magmatic origin. Anhydrite from the Candelaria mine paragenetically overlaps with chalcopyrite. Fluid inclusions in this anhydrite homogenize between 340° and 470°C and it has δ 34SCDT values between 14.5 and 17.5 per mil. A Δ sulfate-sulfide value of 13.4 per mil for a sample with coexisting anhydrite and chalcopyrite is consistent with sulfide-sulfate fractionation at temperatures on the order of 400°C. Ore lead isotope signatures are homogeneous and similar to those of least altered volcanic host rocks and nearby intrusive rocks. Radiometric ages, including new 40Ar/39Ar ages for hydrothermal alteration at Candelaria, point to a main Cu-Au mineralization event at Candelaria-Punta del Cobre at around 115 Ma. The ages indicate that ore formation was broadly coeval with batholithic granitoid intrusions and with regional uplift. They further imply that the Cu-Au(-Zn-Ag) deposits formed at shallow crustal levels (<3 km). The stable isotope data, the presence of previously reported hypersaline CO2-rich fluid inclusions in the main Cu ore stage and saline fluid inclusions in late-stage calcite, the oxidized character of the first ore-fluid pulses, and the mineralization age coeval with nearby intrusive activity are consistent with, but not unequivocally evidence of, magmatic fluid contribution into the hydrothermal system.
Marina Bento Soares - One of the best experts on this subject based on the ideXlab platform.
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To be or not to be: The Hidden Side of Cargninia Enigmatica and Other Puzzling Remains of Lepidosauromorpha from the Upper Triassic of Brazil
Journal of Vertebrate Paleontology, 2020Co-Authors: Paulo R. Romo De Vivar, Agustín G. Martinelli, Pedro Henrique Morais Fonseca, Marina Bento SoaresAbstract:In this contribution, we re-describe the holotype (i.e., the posterior fragment of a left dentary with dentition) of Cargninia enigmatica from the Riograndia Assemblage Zone, Candelaria Sequence, S...
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A New Rhynchocephalian from the Late Triassic of Southern Brazil Enhances Eusphenodontian Diversity
Journal of Systematic Palaeontology, 2020Co-Authors: Paulo R. Romo De Vivar, Agustín G. Martinelli, Annie Schmaltz Hsiou, Marina Bento SoaresAbstract:We describe a new eusphenodontian, Lanceirosphenodon ferigoloi gen. et sp. nov., from the Upper Triassic (Norian) Riograndia Assemblage Zone (AZ) of the Candelaria Sequence (Santa Maria Supersequen...
Antoine De Haller - One of the best experts on this subject based on the ideXlab platform.
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origin of fluids in iron oxide copper gold deposits constraints from δ 37 cl 87 sr 86 sr i and cl br
Mineralium Deposita, 2006Co-Authors: Dave Banks, R. A. Cliff, Robert Marschik, Massimo Chiaradia, Antoine De HallerAbstract:The origin of the hypersaline fluids (magmatic or basinal brine?), associated with iron oxide (Cu–U–Au–REE) deposits, is controversial. We report the first chlorine and strontium isotope data combined with Cl/Br ratios of fluid inclusions from selected iron oxide–copper–gold (IOCG) deposits (Candelaria, Raul–Condestable, Sossego), a deposit considered to represent a magmatic end member of the IOCG class of deposit (Gameleira), and a magnetite–apatite deposit (El Romeral) from South America. Our data indicate mixing of a high δ 37Cl magmatic fluid with near 0‰ δ 37Cl basinal brines in the Candelaria, Raul–Condestable, and Sossego IOCG deposits and leaching of a few weight percent of evaporites by magmatic-hydrothermal (?) fluids at Gameleira and El Romeral. The Sr isotopic composition of the inclusion fluids of Candelaria, Raul–Condestable, and El Romeral confirms the presence of a non-magmatic fluid component in these deposits. The heavy chlorine isotope signatures of fluids from the IOCG deposits (Candelaria, Raul–Condestable, Sossego), reflecting the magmatic-hydrothermal component of these fluids, contrast with the near 0‰ δ 37Cl values of porphyry copper fluids known from the literature. The heavy chlorine isotope compositions of fluids of the investigated IOCG deposits may indicate a prevailing mantle Cl component in contrast to porphyry copper fluids, an argument also supported by Os isotopes, or could result from differential Cl isotope fractionation processes (e.g. phase separation) in fluids of IOCG and porphyry Cu deposits.
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Origin of fluids in iron oxide-copper-gold deposits: constraints from δ 37 Cl, 87 Sr/ 86 Sr i and Cl/Br
Mineralium Deposita, 2006Co-Authors: Massimo Chiaradia, Dave Banks, R. A. Cliff, Robert Marschik, Antoine De HallerAbstract:The origin of the hypersaline fluids (magmatic or basinal brine?), associated with iron oxide (Cu–U–Au–REE) deposits, is controversial. We report the first chlorine and strontium isotope data combined with Cl/Br ratios of fluid inclusions from selected iron oxide–copper–gold (IOCG) deposits (Candelaria, Raul–Condestable, Sossego), a deposit considered to represent a magmatic end member of the IOCG class of deposit (Gameleira), and a magnetite–apatite deposit (El Romeral) from South America. Our data indicate mixing of a high δ 37Cl magmatic fluid with near 0‰ δ 37Cl basinal brines in the Candelaria, Raul–Condestable, and Sossego IOCG deposits and leaching of a few weight percent of evaporites by magmatic-hydrothermal (?) fluids at Gameleira and El Romeral. The Sr isotopic composition of the inclusion fluids of Candelaria, Raul–Condestable, and El Romeral confirms the presence of a non-magmatic fluid component in these deposits. The heavy chlorine isotope signatures of fluids from the IOCG deposits (Candelaria, Raul–Condestable, Sossego), reflecting the magmatic-hydrothermal component of these fluids, contrast with the near 0‰ δ 37Cl values of porphyry copper fluids known from the literature. The heavy chlorine isotope compositions of fluids of the investigated IOCG deposits may indicate a prevailing mantle Cl component in contrast to porphyry copper fluids, an argument also supported by Os isotopes, or could result from differential Cl isotope fractionation processes (e.g. phase separation) in fluids of IOCG and porphyry Cu deposits.
