EM - Escola de Minas

URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/6

Notícias

A Escola de Minas de Ouro Preto foi fundada pelo cientista Claude Henri Gorceix e inaugurada em 12 de outubro de 1876.

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2017 - 201942020 - 20212

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Autor: search.filters.author.Nogueira, Leonardo Brandão

Resultados da Pesquisa

Agora exibindo 1 - 6 de 6
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    Metallogenetic Mn-model of the Rhyacian-aged Buritirama Formation, Carajás domain (Amazon Craton).
    (2021) Salgado, Silas Santos; Caxito, Fabrício de Andrade; Silva, Rosaline Cristina Figueiredo e; Uhlein, Gabriel Jubé; Nogueira, Leonardo Brandão; Nalini Júnior, Hermínio Arias; Aranda, Ramon de Oliveira
    The Mn-bearing Buritirama Formation is composed of clastic and chemical metasedimentary rocks representing a Rhyacian platformal basin (ca. 2.18–2.06 Ga) that limits the northern border of the Archean-Paleoproterozoic Caraj ́ as domain with the Paleoproterozoic Bacaj ́ a domain in the southern Amazon Craton, northern Brazil. The Buritirama Formation is divided into three main stratigraphic units. The Lower and Upper units consist of a basal quartzite followed by carbonate–silicate rocks (marls), dolomitic marbles (dolostone) and minor biotite schist while the Intermediate Unit consists of Mn-carbonate rocks topped by a supergene Mn-oxide deposit (Cenozoic age). These rocks were deformed and metamorphosed during the Transamazonian event (ca. 2.06 Ga). Geochemical data from dolomitic marbles (Lower Unit) exhibit negative Ce anomalies, high Y/Ho ratios (ca. 48) and seawater-like REE + Y patterns that reinforce an open platform setting for the Buritirama basin. Positive δ13C values (+3.2‰ to +5.0‰ V-PDB) for dolomitic marbles are considered to be an expression of the Loma- gundi Carbon Isotopic Excursion. The metallogenesis of Mn-carbonate rocks is evaluated based on redox- sensitive trace elements (e.g. Zn and Ni), PAAS-normalized REE + Y patterns and δ13C values (− 2.56‰ to +0.15‰ V-PDB) and point out to a classical multi-stage redox-controlled Mn-model involving: i) a primary hydrothermal fluid source related to ocean vents and/or normal faults; ii) microbially-mediated reduction of Mn- oxides particles at the ocean bottom; and iii) reactions between Mn2+ and CO3 2− (organic matter and seawater related), giving rise to diagenetic Mn-carbonates. The Rhyacian age, Mn deposits, and presence of Lomagundi- like δ13C allows to correlate the Buritirama Formation with the Aguas ́ Claras Formation within the Caraj ́ as domain further south, thus establishing an important metalliferous event that was up to now largely overlooked within the southern Amazon Craton.
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    Recharge sources and hydraulic communication of karst aquifer, São Miguel watershed, MG, Brazil.
    (2020) Lucon, Thiago Nogueira; Costa, Adivane Terezinha; Galvão, Paulo Henrique Ferreira; Leite, Mariangela Garcia Praça; Madeira, Thiago José Augusto; Nogueira, Leonardo Brandão
    The main public water supply in the São Miguel watershed (MG, Brazil) comes from a well-developed karst region, where information about hydraulic communications between caves entrances, sinkholes, recharge and discharge areas are still unknown. The study aims to identify regional hydrogeological processes describing groundwater hydrochemical evolution, interactions between meteoric, surface and ground waters, recharge and discharge sources, and possible hydraulic communications for proper management of water resources. Geophysical data were analyzed and water samples (meteoric, surface, and groundwater) throughout the watershed were collected for stable isotopes (18O and 2 H) and major ions analyzes. Results indicated strong influences of regional geological structures in the karst water flow directions; high concentrations of major ions in the central region of the watershed are common; karstification processes and aquifer recharge are more active during the rainy season, while in the dry season the watershed is supplied by groundwater.
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    The fate of a Neoproterozoic intracratonic marine basin : trace elements, TOC and IRON speciation geochemistry of the Bambuí Basin, Brazil.
    (2019) Hippertt, João Pedro Torrezani Martins; Caxito, Fabrício de Andrade; Uhlein, Gabriel Jubé; Nalini Júnior, Hermínio Arias; Sial, Alcides Nóbrega; Abreu, Adriana Trópia de; Nogueira, Leonardo Brandão
    Neoproterozoic marine systems are associated with major paleoecological changes that took place in the Ediacaran and during the Ediacaran-Cambrian transition. During this timespan, the Bambuí basin located on east Brazil held a peculiar paleoenvironmental scenario. Due to its intracratonic evolution, the basin was partially disconnected from neighboring open marine systems. This setting raises a very interesting opportunity to understand how an isolated Neoproterozoic marine system evolved in contrast with typical (globally connected) open marine systems. To understand the paleoenvironmental changes that took place in the Bambuí basin, we investigate the pre-glaciogenic deposits of the Carrancas Fm and the post-glaciogenic mixed (shale-carbonate) successions of the Bambuí Group. Through the analysis of iron speciation, TOC, trace element and C-O isotope systematics, our study suggests a very complex environmental evolution. Firstly, our samples are marked by strong contamination of detrital continental material that can be related to an increased bioproductivity on both the Carrancas Fm. and lower Bambuí group stratigraphic units, and provenance data show that all studied sediments probably shared common source areas. Iron speciation data, Ce anomalies and RSE enrichments shows that lower Bambuí Group stratigraphic units were likely deposited in an open marine scenario featuring high bioproductivity in shallow waters and euxinic incursions in predominant anoxic/ferruginous bottom waters. On the other hand, upper Bambuí stratigraphic units register a marine evolution in a restricted scenario, where anoxic ferruginous conditions probably reached surface waters. Finally, our data show that the lack of oceanic connection prevented the re-supply of marine sulfate, RSE, bionutrients and ultimately of dissolved oxygen which may have decreased biological activity and probably hindered biological evolution, preventing the rise of a typical modern-like Cambrian ecosystem. In this sense, our data suggest that oceanic connectivity and proper re-supply of inorganic marine input were important features in the development of complex life in the EdiacaranCambrian environment.
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    Geochemistry and C and O isotope composition of carbonate rocks from Bemil and Lagoa Seca quarries, Gandarela Formation, Quadrilátero Ferrífero - Brazil.
    (2019) Nogueira, Leonardo Brandão; Oliveira, Vinícius Queiroz; Araújo, Letícia Pereira; Leão, Lucas Pereira; Ali, Arshad; Leite, Mariangela Garcia Praça; Nalini Júnior, Hermínio Arias; Banerjee, Neil R.
    Geochemical and isotopic (carbon and oxygen) compositions of Paleoproterozoic carbonate rocks of the Bemil and Lagoa Seca quarries – Gandarela Formation – Quadrilátero Ferrífero – Brazil, were determined. Few samples (12 out of 69) show relatively higher REE contents that are associated with strongly positive correlation with the immobile elements including Al, Ni, Th, Cr, Sc and Y coupled with a negative correlation between ΣREE and CaO, suggesting that the observed variations in the ΣREE values in these samples were controlled mainly by the input of terrigenous materials. The Eu and Ce anomalies (normalized by the PAAS) of the analyzed samples vary from 1.1 to 2.13 and 0.79 to 1.03, respectively for Bemil quarry samples and 0.74 to 2.7 and 0.32 to 0.99, respectively, for samples from the Lagoa Seca quarry. In the present study, Al2O3 content do not show significant correlation with Eu/Eu* (correlation coefficient r = 0.23). Hence the positive europium anomalies in these samples seem to have not been influenced by the amount of terrigenous materials in them. Y/Ho ratios range from 27 to 93 for Bemil quarry samples and 24 to 132 for samples from the Lagoa Seca quarry. Some samples have Y/Ho ratio more or less similar to chondritic values (∼28). High REE contents, non-seawater-like REE patterns, the large abundance of certain trace elements such as Sc, Th and Hf, high (La/Yb)sn ratios and low Y/ Ho ratios collectively suggest that few samples were mainly influenced by the incorporation of terrigenous materials. Most of the studied samples (38 out of 69) of the Bemil and Lagoa Seca quarries have δ18O (VPDB) values lower than −12‰, corresponding to carbonates that underwent changes by post-depositional processes. The δ13C values (0.69‰ to −4.46‰ and 0.07‰ to −6.18‰) of the majority of the analyzed samples, both of the Bemil quarry and the Lagoa Seca quarry, are similar to those marine carbonates of the same age (∼2.42 Ga). Samples that have δ13C values around −4‰ are likely to result from decarbonation reactions. Two samples (LS11 and LS12) may record glacial periods.
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    Elemental and stable isotopes geochemistry of Paleoproterozoic dolomites from Fecho do Funil Formation, Quadrilátero Ferrífero - Brazil
    (2017) Nogueira, Leonardo Brandão; Oliveira, Vinícius Queiroz; Leite, Mariangela Garcia Praça; Ali, Arshad; Sampaio, Geraldo Magela Santos; Abreu, Adriana Trópia de; Nalini Júnior, Hermínio Arias; Banerjee, Neil R.
    Geochemical and stable isotopic characteristics of thirteen samples taken from Paleoproterozoic Fecho do Funil Formation, Quadril atero Ferrífero, Brazil have been analyzed to investigate the depositional conditions and source of rare earth elements (REEs) in Cumbi quarry dolomites. The major oxides such as CaO and MgO show variable compositions ranging from 20 to 29 wt % and 14e21 wt % respectively in most of the samples. The contents of loss on ignition (LOI) are lower (26e42 wt %) than that of the pure dolomite (~48 wt %). These mass discrepancies are compensated by other oxides including Al2O3 (1.9 e18.7 wt %), Fe2O3 (1.2e6.1 wt %), and K2O (0.5e6.8 wt %) that had been incorporated into the dolomite samples by the contamination of terrigenous input. Further, SREE contents (20e101 ppm) display significant variation that also corroborate with contamination of studied samples by detrital materials. The regression lines of SREE against Al2O3 (R2 ¼ 0.96), Fe2O3 (R2 ¼ 0.65), Ni (R2 ¼ 0.94), Cr (R2 ¼ 0.95), Th (R2 ¼ 0.98), and Sc (R2 ¼ 0.98) show positive correlation which is probably associated with the input of terrigenous materials during the deposition of Cumbi quarry dolomites. On the other hand, a negative correlation between SREE and CaO combined with a large variation in Y/Ho (27e50) is also interpreted as the sea-water like REE patterns have been masked by the contribution of variable amounts of terrigenous materials in Cumbi quarry dolomites. All the dolomite samples analyzed from the Fecho do Funil Formation exhibit a subtle negative cerium anomaly (Ce/Ce* ¼ 0.85e0.95). The dolomites from Cumbi quarry e Fecho do Funil Formation show narrow variations in Eu anomalies (Eu/Eu* ¼ 1.02 to 1.25). The positive correlation between Eu with Zr, Th and Y supports the non diagenetic influence on this element (R2 ¼ 0.94, 0.98, 0.84 respectively). Eu contents, in this study show significant positive correlation with Al2O3 (R2¼0.96), suggesting the detrital origin. The d13CVPDB (þ6.0 to þ7.2‰) and d18OVPDB ( 10.9 to 10.4‰) values in our samples display a narrow range which are identical to those shown by successions, characterized by positive carbon excursions, deposited during the Lomagundi event. We infer that the elevated carbon isotope values of the Fecho do Funil dolomites likely reflect primary carbon isotope compositions.
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    Estudo geoquímico e isotópico de rochas carbonáticas das formações gandarela e fecho do funil – Quadrilátero Ferrífero - Brasil.
    (2018) Nogueira, Leonardo Brandão; Nalini Júnior, Hermínio Arias; Leite, Mariangela Garcia Praça; Nalini Júnior, Hermínio Arias; Rudnitzki, Isaac Daniel; Gandini, Antônio Luciano; Rios, Francisco Javier; Carvalho Filho, Carlos Alberto de
    Estudo geoquímico (elementos maiores, menores e traço, incluindo os ETRs) e isotópico (carbono e oxigênio) foi realizado em rochas carbonáticas das Formações Gandarela e Fecho do Funil, Quadrilátero Ferrífero - Brasil. A caracterização mineralógica das amostras de rochas carbonáticas selecionadas foi realizada utilizando técnicas como microscopia de luz transmitida e difração de raios X (XRD). As 82 amostras de rochas carbonáticas coletadas foram analisadas no ICP-OES (Agilent 725) para a determinação das concentrações dos elementos maiores e menores, enquanto que as concentrações dos elementos-traço, incluindo os ETR foram realizadas no ICP-MS (Agilent 7700). Análises isotópicas (δ13C, δ18O) foram realizadas utilizando a espectrometria de massas de razões isotópicas (IRMS; Optima Dual Inlet – Western University – Canadá; Delta V Advanced – DEGEOEM- UFOP). Para as amostras da pedreira do Cumbi (Formação Fecho do Funil), óxidos como CaO e MgO apresentaram composições que variam entre 20-29% e 14-21 %, respectivamente, na maioria das amostras. Essas discrepâncias de massa são compensadas por outros óxidos, incluindo Al2O3 (1,9- 18,7%), Fe2O3 (1,2-6,1%) e K2O (0,5-6,8%) que foram incorporados nas amostras pela contaminação por materiais terrígenos. Além disso, o somatório dos ETRs (20-101 ppm) apresenta variações significativas que também corroboram com a contaminação de amostras estudadas por materiais detríticos. Correlações positivas entre ΣETRs e Al2O3 (r = 0,96), Fe2O3 (r = 0,65), Ni (r = 0,94), Cr (r = 0,95), Th (r = 0,98) e Sc (r = 0,98) nas quais podem ser provavelmente associada à entrada de materiais terrígenos durante a deposição de dolomitos da pedreira de Cumbi. Por outro lado, uma correlação negativa entre ΣREE e CaO combinada com uma grande variação na razão Y/Ho (27-50) corroboram a hipótese de os padrões da água do mar terem sido mascarados pela contribuição de quantidades variáveis de materiais terrígenos. Todas as amostras analisadas da Formação Fecho do Funil exibem uma sutil anomalia negativa de cério (Ce/Ce * = 0,85 - 0,95). Os dolomitos da pedreira do Cumbi apresentaram estreitas variações nas anomalias de Eu (Eu / Eu * = 1,02 a 1,25). Os conteúdos de Eu neste estudo, indicam uma correlação positiva significativa com o Al2O3 (r = 0,96), sugerindo a origem detrítica desse elemento. Os valores de δ13CVPDB (+6,0 a + 7,2 ‰) e δ18OVPDB (-10,9 a -10,4 ‰) das amostras analisadas apresentam uma pequena variação e podem ser correlacionados à sucessões carbonáticas caracterizadas por excursões positivas de carbono depositadas durante o evento Lomagundi. Infere-se que os elevados valores de isótopos de carbono dos dolomitos da Formação Fecho do Funil provavelmente refletem composições isotópicas primárias de carbono. Poucas amostras analisadas da Formação Gandarela (pedreiras Bemil e Lagoa Seca) apresentaram teores de ETR relativamente mais elevados que estão associadas à correlações fortemente positivas com os elementos imóveis incluindo Al, Ni, Th, Cr, Sc e Y, juntamente com uma correlação negativa entre ΣETRs e CaO, sugerindo que as variações observadas nos valores ΣETRs nestas amostras foram controladas principalmente pela entrada de materiais terrígenos. A correlação positiva entre Eu e as proxies detríticos como Zr, Th e Y suporta a origem não-diagenética desse elemento. As razões Y/Ho variam de 27 a 93 para as amostras da pedreira Bemil e de 24 a 132 para as amostras da pedreira Lagoa Seca. Os altos valores encontrados para a maioria das amostras indicam que a maioria dos carbonatos analisados mantém as características da água do mar, enquanto algumas amostras analisadas apresentam valores da relação Y/Ho muito baixos (<30), indicando contaminação por materiais terrígenos. A maioria das amostras estudadas da pedreira Bemil apresentou δ18O menor que -12 ‰, correspondendo a carbonatos que passaram por mudanças nos processos pós-deposicionais. Em geral, amostras da pedreira Lagoa Seca apresentam valores de δ18O superiores às da pedreira Bemil, sugerindo melhor preservação. Em relação aos valores de δ13C, estes, na maioria das amostras analisadas, tanto da pedreira Bemil quanto da pedreira Lagoa Seca, parecem semelhantes aos encontrados em carbonatos marinhos da mesma idade (~ 2.42 Ga). Razões isotópicas de carbono menores que -2 ‰ provavelmente resultaram de reações de descarbonatação.