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.
Navegar
5 resultados
Resultados da Pesquisa
Item 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.Item 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.Item A new appraisal of sri lankan bb zircon as a reference material for LA-ICP-MS U-Pb geochronology and Lu-Hf isotope tracing.(2017) Santos, Maristella Moreira; Lana, Cristiano de Carvalho; Buick, Ian S.; Schmitz, Mark D.; Kamo, Sandra L.; Gerdes, Axel; Corfu, Fernando; Tapster, Simon; Lancaster, Penelope; Storey, Craig Darryl; Basei, Miguel Ângelo Stipp; Tohver, Eric; Alkmim, Ana Ramalho; Nalini Júnior, Hermínio Arias; Krambrock, Klaus Wilhelm Heinrich; Leite, Cristiano Fantini; Wiedenbeck, MichaelA potential zircon reference material (BB zircon) for laser abla tion-in ductively coupled plasma-mass spectrometry (LA-ICP-M S)U-Pb geochronology and Hf isotope geochemistry is described. A batch of twenty zircon megacrysts (0.5–1.5 cm3) from SriLanka was studied. Within-grain rare earth element (REE) compositions are largely homogeneous, albeit with somevariation seen between fractured and homogeneous domains. Excluding fractured cathodoluminescence bright domains,the variation in U content for all analysed crystals ranged from 227 to 368 lgg-1and the average Th/U ratios werebetween 0.20 and 0.47. The Hf isotope composition (0.56–0.84 g/100 g Hf) is homogeneous within and between thegrains – mean176Hf/177Hf of 0.281674 ± 0.000018 (2s). The calculated alpha dose of 0.59 3 1018g-1for a numberof BB grains falls within the trend of previously studied, untreated zircon samples from Sri Lanka. Aliquots of the samecrystal (analysed by ID-TIMS in four different laboratories) gave consistent U-Pb ages with excellent measurementreproducibility (0.1–0.4% RSD). Interlaboratory assessment (by LA-ICP-MS) from individual crystals returned results that arewithin uncertainty equivalent to the TIMS ages. Finally, we report on within- and between-grain homogeneity of theoxygen isotope systematic of four BB crystals (13.16‰ VSMOW).Item A vibrational spectroscopic study of the silicate mineral normandite – NaCa(Mn2+,Fe2+)(Ti,Nb,Zr)Si2O7(O,F)2.(2015) Frost, Ray Leslie; López, Andrés; Theiss, Frederick L.; Cipriano, Ricardo Augusto Scholz; Romano, Antônio WilsonWe have studied the mineral normandite using a combination of scanning electron microscopy with energy dispersive spectroscopy and vibrational spectroscopy. The mineral normandite NaCa(Mn2+,Fe2+)(Ti,Nb,Zr)Si2O7(O,F)2 is a crystalline sodium calcium silicate which contains rare earth elements. Chemical analysis shows the mineral contains a range of elements including Na, Mn2+, Ca, Fe2+ and the rare earth element niobium. No Raman bands are observed above 1100 cm 1. The mineral is characterised by Raman bands observed at 724, 748, 782 and 813 cm 1. Infrared bands are broad; nevertheless bands may be resolved at 723, 860, 910, 958, 933, 1057 and 1073 cm 1. Intense Raman bands at 454, 477 and 513 cm 1 are attributed to OSiO bending modes. No Raman bands are observed in the hydroxyl stretching region, but low intensity infrared bands are observed at 3191 and 3450 cm 1. This observation brings into question the true formula of the mineral.Item Evaluation of signal-to-background and Mg II/Mg I ratios as response for the optimization of rare earth elements determination by inductively coupled plasma optical emission spectrometry.(2012) Silva, Aline Kelly Guimarães; Lena, Jorge Carvalho de; Costa, Leticia Malta; Nascentes, Clésia CristinaElementos terras raras (ETR) fazem parte de um grupo peculiar de elementos químicos e sua determinação em amostras geológicas é importante e complexa, devido às baixas concentrações e problemas com interferências espectrais e não espectrais. Neste trabalho, planejamentos experimentais foram utilizados para otimizar as condições operacionais de um espectrômetro de emissão óptica com plasma indutivamente acoplado (ICP OES) para a determinação de ETR. A razão entre o sinal analítico dos ETR e o sinal de fundo (SBR) e a razão Mg II/Mg I foram avaliadas como respostas na otimização. De acordo com os resultados obtidos, três diferentes condições de operação foram selecionadas e classificadas como robusta, semi-robusta e melhor SBR. Limites de detecção (LOD), SBR e desvio padrão relativo de medidas de uma solução do branco (DPRbranco) foram determinados. Na condição semi-robusta (potência de 1250 W e vazão do gás nebulizador de 0,90 L min−1) foram obtidos LOD e DPRbranco mais baixos que nas outras condições estabelecidas.