O papel do metamorfismo e fases fluidas na genese da mineralização de cobre de salobo, provincia mineral de Carajas, Para

Orientador: Roberto Perez XavierDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de GeocienciasResumo: O depósito polimetálico de Salobo, Pará, é constituído principalmente por uma mineralização primária de Cu (Au, Ag, Mo), hospedada por formações ferríferas arqueanas da Sequência Salobo. As formações ferríferas tipo I (magnetita-fayalita-grunerita:!: biotita -hastingsita-almandina -greenalita- fluorita-apatita -alanita -turmalina-titanita-calcopirita -bornita-uraninita-grafita- ilmenita-molibdenita-cobaltita-saflorita -ouro) e tipo 2 (magnetita-almandina-grunerita-biotita:!: quartzo-turmalina -clorita - fayalita-apatita -alanita -zircão-grafita -bornita-calcosita- molibdenita-uraninita) foram submetidas a um metamorfismo progressivo de fácies anfibolito alto (650°C, 3 kbars, JO2 = 10-2°-10-18 bars), seguido por um evento metamórfico-hidrotermal de fácies xisto verde alto (347°C, temperatura dada pelo geotermômetro da clorita). A mineralização de Cu consiste de disseminações de bornita-calcopirita e bornita-calcosita, asssociadas a lentes ricas em magnetita. Durante a evolução metamórfica do depósito, sob condições de fácies anfibolito alto, é provável que a assembléia sulfetada tenha sido representada por uma solução sólida cúbica, rica em Cu (i.s.s.), em equílíbrio com a solução sólida da bornita. Em condições retrometamórficas de fácies xisto verde, a assembléia sulfetada evoluiu para calcopirita tetragonal, estável abaixo de 547°C, e bornita e calcosita, provenientes da decomposição da solução sólida da bornita, a temperaturas inferiores a 335°C. A associação do Au rico em Cu (6,98-1O,82%peso Cu) com cobaltita, sulfetos de Cu e veios de clorita, juntamente com o intervalo de temperatura de estabilidade do Au e cobaltita (T < 400°C), indica uma forte relação entre o evento metamórfico-hidrotermal de fácies xisto verde e os fluidos responsáveis pela remobilização do Cu e Au. O estudo de inclusões fluidas revelou a ocorrência de 2 tipos de inclusões: inclusões monofásicas carbônicas (C02 e < 10 moI % CH4) e inclusões aquosas, sub-divididas em aquosas de salinidade elevada (30,6-58,4% peso eq.NaCI) e de salinidade baixa a moderada (1,0-25,8% peso eq.NaCI). Os fluidos carbônicos são interpretados como fluidos gerados ou reequilibrados sob condições metamórficas de fácies anfibolito alto. A composição dos fluidos aquosos de salinidade elevada (pH ácido, JO2 = 10-3°-10-28 bars, LS =0, 1-0,01 molal) pode ser estimada em cerca de 45% em peso de NaCI e 5,3% em peso de MgCI2:!:FeCI2:!:CaCl2. As possíveis fontes destes fluidos dominantes durante o evento metamórfico-hidrotermal de fácies xisto verde incluem águas de formação, águas meteóricas, que tornaram-se altamente salinas por reações de hidratação retrógradas, ou magmáticas, constituindo os prováveis responsáveis pela remobilização do Cu e Au via complexos de CI-. Os fluidos de salinidade baixa a moderada são interpretados como soluções aquosas de origem externa, provavelmente águas meteóricas, que causaram uma diluição progressiva do fluido de salinidade elevada. As isócoras representando a variação composicional dos fluidos das inclusões aquosas salinas, combinadas com o geotermômetro da clorita, demonstraram que a deposição do Cu e Au ocorreu entre 334°-366°C e 3,7-1,4 kbars. A diminuição na aCI- gerada pela mistura de fluidos e o subseqüente resfriamento, provavelmente constituem os principais mecanismos de deposição dos metais no depósito de SaloboAbstract: The Salobo polymetallie ore deposit, Pará, eonsists of a primary Cu (Au, Ag, Mo) mineralization, hosted by Arehean iron formations of the Salobo sequenee. The type I (magnetite- fayalite- grunerite: tbiotite- hastingsite- almandine- greenalite-fluorite- apatite- allanite -tourmaline- titanite - ehaleopyrite-bornite-uraninite-graphite- ilmenite-molybdenite-eobaltite-saflorite-gold) and type 2 (magnetite-almandine-grunerite-biotite:t quartz-tourmaline-ehlorite- fayalite-apatite-allanite-graphite-bornite-ehaleosite-molybdenite-uraninite) iron formations underwent a progressive high amphibolite facies metamorphism (650°C, 3 kbars,JOz=1O-zo-1O-18 bars), followed by a greensehist facies metamorphic-hydrothermal event (347°C, given by the eh1orite geothermometry). The Cu mineralization is most1y formed by bornite-ehaleopyrite and bornite-ehalcosite disseminations, in association with magnetite-rich levels. During the metamorphic evolution of the ore deposit, under high amphibolite facies eonditions, the sulfide assemblage was probably represented by a Cu-rich eubic solid solution (i.s.s.), in equilibrium with a bornite solid solution. The evolution of the sulfide assemblage to tetragonal ehalcopyrite, stable below 547°C, and to bornite and ehalcosite from the separation of the bornite solid solution at 335°C, took plaee at the greensehist facies retrograde event. The assoeiation of the Cu-rich gold (6.98-10.82 wt% Cu) with eobaltite, Cu sulfides and ehlorite veins, together with the stability temperature range of Au and eobaltite (T < 400°C), indicates a strong relationship between the greensehist facies metamorphie-hydrothermal event and the fluids involved in the Cu and Au remobilization. Fluid inc1usion studies showed that two types of fluid inc1usions oeeur in the Salobo ore deposit: monophase earbonie inc1usions (COz e < 10 moI % CH4) and aqueous inc1usions, subdivided into high1y saline aqueous inc1usions (30.6-58.4 wt% eq.NaCI) and low to moderate saline aqueous inc1usions (1.0-25.8 wt% eq.NaCl). The earbonie fluids are interpreted as fluids generated or re-equilibrated under high amphibolite facies eonditions. The bulk eomposition ofthe high1y saline aqueous fluids (acidie pH,JOz=1O-3O-1O-z8 bars, ES=0.1-0.01 molal) is estimated around 45 wt% NaCI and 5,3 wt% MgClz:tFeClz:tCaClz. Those high1y saline fluids seem to be the responsible for both Cu and Au remobilization, via CI- eomplexes, during the greensehist facies metamorphie-hydrothermal event and probable sourees inc1ude formation waters, meteoric waters which beeame highly saline through retrograde hydration reaetions, and magmatie waters. The low to moderate saline aqueous fluids ean be interpreted as externally-derived solutions, probably meteorie waters, which eaused a progressive dilution of the high1y saline fluids. The bulk-density isoehores representing the eompositional range of the saline aqueous inc1usion fluids, eombined with the eh1orite geothermometry, demonstrated that Cu and Au deposition probably oeeurred in the range of 334° to 366°C and 3.7-1.4 kbars. The deereasing in the aCl-, eaused by fluid mixing, and the subsequent eooling, possibly are the main meehanisms for the metal deposition in the Salobo ore depositMestradoMetalogeneseMestre em Geociência

Re-Os and Pb-Pb geochronology of the Archean Salobo iron oxide copper-gold deposit, Carajás mineral province, northern Brazil

Rhenium-osmium ages were determined for two molybdenite samples and a Pb-Pb age was derived from bornite-chalcopyrite-magnetite at the Salobo iron oxide copper-gold deposit to determine the timing of mineralization and its relation to the nearby Old Salobo Granite. Rhenium-osmium dating of molybdenite spatially associated with copper sulfide minerals yields ages with weighted means of 2576±8 and 2562±8Ma. Removing the error multiplier introduced by the decay constant uncertainty, appropriate for comparing ages from the same isotopic system, these data convincingly argue for two temporally separated pulses of molybdenite deposition at 2576.1±1.4Ma (n=2) and 2561.7±3.1Ma (n=3). The 2576±8Ma age coincides with a previously published U-Pb age of 2573±2Ma for the Old Salobo Granite, suggesting that main stage ore formation may have been contemporaneous with granite magmatism. The slightly younger 2562Ma age most likely represents new molybdenite precipitation associated with the development or reactivation of local shear zones. Lead-lead stepwise leaching of copper sulfide minerals yields a less precise isochron age of 2579±71Ma, and supports an Archean age for the Salobo ores. This is the first documentation of an Archean iron oxide copper-gold deposit, and the Re-Os and Pb-Pb geochronology herein support 2580-2550Ma estimates for basement reactivation and regional granite magmatism associated with the development of brittle-ductile shear zone

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The treatment of comminuted fractures of the mandible is challenging due both to the severity of the injuries generally associated with this type of fracture, and the lack of consensus as to the most appropriate treatment method.There are two distinct approaches for treating comminuted fractures of the mandible: closed reduction with maxillomandibular fixation (MMF) - the oldest and classical treatment - and open operation and internal fixation. The morbidity rate of closed reduction is lower but, with the advent of modern anaesthesia and antibiotics, open surgery has become more frequent. Stable internal fixation (SIF) is acheived using plates, miniplates and/or screws. The advantage of this approach is that there is a more precise reduction of the fragments, with the possibility of early function by eliminating or reducing the time of MMF. This paper reviews the main advantages, disadvantages and differences between the two techniques

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The COVID-19 containment response policies (CRPs) had a major impact on air quality (AQ). These CRPs have been time-varying and location-specific. So far, despite having numerous studies on the effect of COVID-19 lockdown on AQ, a knowledge gap remains on the association between stringency of CRPs and AQ changes across the world, regions, nations, and cities. Here, we show that globally across 1851 cities (each more than 300000 people) in 149 countries, after controlling for the impacts of relevant covariates (e.g., meteorology), Sentinel-5P satellite-observed nitrogen dioxide (NO2) levels decreased by 4.9% (95% CI: 2.2, 7.6%) during lockdowns following stringent CRPs compared to pre-CRPs. The NO2 levels did not change significantly during moderate CRPs and even increased during mild CRPs by 2.3% (95% CI: 0.7, 4.0%), which was 6.8% (95% CI: 2.0, 12.0%) across Europe and Central Asia, possibly due to population avoidance of public transportation in favor of private transportation. Among 1768 cities implementing stringent CRPs, we observed the most NO2 reduction in more populated and polluted cities. Our results demonstrate that AQ improved when and where stringent COVID-19 CRPs were implemented, changed less under moderate CRPs, and even deteriorated under mild CRPs. These changes were location-, region-, and CRP-specific

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