Metalogênese do Depósito de Cobre Cerro dos Martins, RS -Revisão e Geoquímica Isotópica de SR, S, O e C-
João Angelo TonioloMarcus Vinícius Dorneles RemusMoacir José Buenano MacambiraCândido Augusto Veloso Moura
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This paper presents the geology, chemical data, Pb-Pb zircon ages, sulfur, carbon, oxygen, strontium isotopes and fluid inclusions of Cerro dos Martins copper deposit. The deposit is hosted by the Neoproterozoic volcano-sedimentary sequence of the Camaquã Basin in the Rio Grande do Sul Shield, southern Brazil. The ores consist of a set of Cu-sulfide NW-trending veins and disseminations within of the Bom Jardim Group. Chalcocite and bornite are the main ore minerals, whereas carbonates, barite, quartz and hematite are the gangue. The volcanic host rocks show an alkaline affinity. An intrusive quartz-diorite body, also shown alkaline affinity, yield a 550±5 Ma zircon age (initial 87Sr/86Sr of 0,704), which is considered the minimum age of the copper mineralization. The δ34SCDT of sulfides ranges from –6.2 to +0.9‰. Hematite in the mineral paragenesis suggests oxidizing conditions, which would shift the original magmatic sulfur isotopic compositions (δ34S ~ 0‰) to negative values. Barite with δ34SCDT from +9.25 to +10.65‰ may also indicate oxidation due to mixing of a hot rising fluid with cold meteoric water. The δ13CPDB of calcite from gangue, in the range of – 1,90 to – 4,45% is interpreted as originated from mixing sources – magmatic and fluids contaminated by basement marbles. Studies on primary aqueous biphasic fluid inclusions show homogenisation temperatures with average of 215°C. Water in equilibrium with calcite from hydrothermal fluid show calculated values of δ O18 SMOW between 3 and 14‰, suggesting derivation from a magmatic source with some contributions from meteoric water. 87Sr/86Sr from these calcite show values between 0, 7068 – 0, 7087, typical from upper crust. Hence, the Cerro dos Martins copper deposit is interpreted to have had origin by a mixing between a magmatic-hydrotermal fluids related to the alkaline-shoshonitic, post-collisional magmatic event (595-550 Ma) of the Dom Feliciano Orogeny and basement rocks. Exploration models for copper deposits in this shield should consider the alkaline magmatism in the genesis of deposits.Keywords:
Paragenesis
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Breccia
Jinshachang Pb-Zn deposit,located in Yunnan province and the northwest of Sichuan-Yunnan-Guizhou(SYG) Pb-Zn-Ag multi-metal mineralization area,is mainly hosted in the Upper Neoproterozoic carbonate rocks of Dengying Group.The ore minerals mainly contain sphalerite and galena,and the gangue minerals mainly contain barite,fluorite and quartz.The δ34S values of sphalerite minerals are in the range between 3.6‰ and 13.4‰ with an average value of 5.7‰.The δ34S values of galena range from 6.0‰ to 9.0‰ with an average value of 7.1‰.Two δ34S values of barite are 34.8‰ and 34.5‰ and consistent with that of sulfate from the Lower Cambrian stratum,indicating that the sulfur of barite were derived from this stratum.Because the homogenization temperatures of fluid inclusions exceed the suitable temperature for bacterial sulfate reduction,therefore this process is not an efficient path for the production of reduced sulfur in this district.If sulfides were derived from the Cambrian stratum due to thermochemical sulfate reduction,sulfides in this deposit should preserve a minimum δ34S value of 14‰ which exceeding that of sulfide from Jinshachang deposit.Therefore,this process is not the only source of reduced sulfur.Considered the fact that the ore district is surrounded by basalts and δ34S values of sulfide related to magmatic activities are relatively low,the reduced sulfur of sulfide may be derived from magmatic activities.The δ34S values of sphalerite are higher than that of coexisting galena,indicating that sulfur isotopic composition in ore-forming fluid had partly reached equilibrium.The equilibrium temperatures calculated by using the δ34S values of surfur-bearing mineral pairs are consistent well with the homogenization temperature of fluid inclusions.
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The Jinshachang lead–zinc deposit is mainly hosted in the Upper Neoproterozoic carbonate rocks of the Dengying Group and located in the Sichuan–Yunnan–Guizhou(SYG) Pb–Zn–Ag multimetal mineralization area in China.Sulfides minerals including sphalerite,galena and pyrite postdate or coprecipitate with gangue mainly consisting of fluorite,quartz,and barite,making this deposit distinct from most lead–zinc deposits in the SYG.This deposit is controlled by tectonic structures,and most mineralization is located along or near faults zones.Emeishan basalts near the ore district might have contributed to the formation of orebodies.The δ34S values of sphalerite,galena,pyrite and barite were estimated to be 3.6‰–13.4‰,3.7‰–9.0‰,6.4‰ to 29.2‰ and 32.1‰–34.7‰,respectively.In view of the similar δ34S values of barite and sulfates being from the Cambrian strata,the sulfur of barite was likely derived from the Cambrian strata.The homogenization temperatures(T ≈ 134–383°C) of fluid inclusions were not suitable for reducing bacteria,therefore,the bacterial sulfate reduction could not have been an efficient path to generate reduced sulfur in this district.Although thermochemical sulfate reduction process had contributed to the production of reduced sulfur,it was not the main mechanism.Considering other aspects,it can be suggested that sulfur of sulfides should have been derived from magmatic activities.The δ34S values of sphalerite were found to be higher than those of coexisting galena.The equilibrium temperatures calculated by using the sulfur isotopic composition of mineral pairs matched well with the homogenization temperature of fluid inclusions,suggesting that the sulfur isotopic composition in ore-forming fluids had reached a partial equilibrium.
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Abstract. Primary fluid inclusions in quartz and carbonates from the Kanggur gold deposit are dominated by aqueous inclusions, with subsidiary CO 2 ‐H 2 O inclusions that have a constant range in CO 2 content (10–20 vol %). Microthermometric results indicate that total homogenization temperatures have a wide but similar range for both aqueous inclusions (120d̀ to 310d̀C) and CO 2 ‐H 2 O inclusions (140d̀ to 340d̀C). Estimates of fluid salinity for CO 2 ‐H 2 O inclusions are quite restricted (5.9∼10.3 equiv. wt% NaCl), whereas aqueous inclusions show much wider salinity ranging from 2.2 to 15.6 equivalent wt %NaCl. The 6D values of fluid inclusions in carbonates vary from ‐45 to ‐61 %, in well accord with the published δD values of fluid inclusions in quartz (‐46 to ‐66 %). Most of the δ 18 O and δD values of the ore‐forming fluids can be achieved by exchanged meteoric water after isotopic equilibration with wall rock by fluid/rock interaction at a low water/rock ratio. However, the exchanged meteoric water alone cannot explain the full range of δ 18 O and δD values, magmatic and/or meta‐morphic water should also be involved. The wide salinity in aqueous inclusions may also result from mixing of meteoric water and magmatic and/or metamorphic water.
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