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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6 resultados
Resultados da Pesquisa
Item LA-ICP-MS U–Pb dating of rutiles associated with hydrothermal mineralization along the southern Araçuaí Belt, SE Brazil.(2020) Santos, Maristella Moreira; Lana, Cristiano de Carvalho; Cipriano, Ricardo Augusto Scholz; Buick, Ian S.; Kamo, Sandra L.; Corfu, Fernando; Queiroga, Gláucia NascimentoThe presence of hydrothermal rutile enables the dating of mineralization related to hydrothermal processes. Refinement of the laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) technique is key to enabling the quick analysis of individual rutile crystals in high spatial resolution and dating of crystals with low U contents, as a prerequisite for the reliable characterization of hydrothermal deposits. For this study rutile crystals were selected from quartz and topaz veins that extend along the southeastern portion of the Araçuaí Belt, part of the long-lived (630 - 490 Ma) polyphase Brasiliano Orogen that formed during West Gondwana amalgamation. The purpose was to allow a systematic evaluation of in situ dating of hydrothermal rutile by LA-ICPMS. U–Pb ages from different rutiles range between 527 ± 6 Ma and 487 ± 5 Ma, indicating that different parts of the orogen were affected by episodic fluid flow under oxidizing conditions over a similar time interval. Our U–Pb dating results of rutiles associated with the Imperial Topaz mineralization in the Quadrilátero Ferrífero (southern portion of the São Francisco Craton, SE Brazil) constrains the age of those deposits to 500- 498 Ma, which is within the range of U–Pb ages of hydrothermal systems and mineralized zones previously reported for the region. The chemical composition of the studied hydrothermal rutiles, as determined by electron microprobe and LA-ICP-MS analysis, together with their U–Pb ages, suggests that the extensive fluid production required to form the hydrothermal deposits was generated from multiple sources. Fluid production was related to extensional collapse of the Araçuaí Orogen. The findings of this research clearly shows the utility of U–Pb rutile dating via LA-ICP-MS for geochronological study of a range of hydrothermal deposits.Item LA-ICP-MS U–Pb dating of rutiles associated with hydrothermal mineralization along the southern Araçuaí Belt, SE Brazil.(2020) Santos, Maristella Moreira; Lana, Cristiano de Carvalho; Cipriano, Ricardo Augusto Scholz; Buick, Ian S.; Kamo, Sandra L.; Corfu, Fernando; Queiroga, Gláucia NascimentoThe presence of hydrothermal rutile enables the dating of mineralization related to hydrothermal processes. Refinement of the laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) technique is key to enabling the quick analysis of individual rutile crystals in high spatial resolution and dating of crystals with low U contents, as a prerequisite for the reliable characterization of hydrothermal deposits. For this study rutile crystals were selected from quartz and topaz veins that extend along the southeastern portion of the Araçuaí Belt, part of the long-lived (630 - 490 Ma) polyphase Brasiliano Orogen that formed during West Gondwana amalgamation. The purpose was to allow a systematic evaluation of in situ dating of hydrothermal rutile by LA-ICPMS. U–Pb ages from different rutiles range between 527 ± 6 Ma and 487 ± 5 Ma, indicating that different parts of the orogen were affected by episodic fluid flow under oxidizing conditions over a similar time interval. Our U–Pb dating results of rutiles associated with the Imperial Topaz mineralization in the Quadrilátero Ferrífero (southern portion of the São Francisco Craton, SE Brazil) constrains the age of those deposits to 500- 498 Ma, which is within the range of U–Pb ages of hydrothermal systems and mineralized zones previously reported for the region. The chemical composition of the studied hydrothermal rutiles, as determined by electron microprobe and LA-ICP-MS analysis, together with their U–Pb ages, suggests that the extensive fluid production required to form the hydrothermal deposits was generated from multiple sources. Fluid production was related to extensional collapse of the Araçuaí Orogen. The findings of this research clearly shows the utility of U–Pb rutile dating via LA-ICP-MS for geochronological study of a range of hydrothermal deposits.Item Characterization of xenotime from datas (Brazil) as a potential reference material for in situ u-pb geochronology.(2018) Vasconcelos, A. D.; Gonçalves, Guilherme de Oliveira; Lana, Cláudio Eduardo; Buick, Ian S.; Corfu, Fernando; Cipriano, Ricardo Augusto Scholz; Alkmim, Ana Ramalho; Queiroga, Gláucia Nascimento; Nalini Júnior, Hermínio AriasThis study investigatesfive megacrysts of xenotime (XN01, XN02, XN03, XN04, and XN05) aspotential reference materials (RMs) for U-Pb geochronology. These crystals belong to a 300 g xenotimeassortment, collected from alluvial deposits in SE Brazil. Electron microprobe and Laser Ablation-InductivelyCoupled Plasma-Mass Spectrometry (LA-ICP-MS) analyses show that the selected crystals are internallyhomogeneous for most rare earth element, (REE, except some light REE) but are relatively heterogeneous forU and Th. The xenotime REE patterns are consistent with an origin from hydrothermal quartz veins in theDatas area that cut greenschist-facies metasediments and that locally contain other accessory phases such asrutile and monazite. High-precision U-Pb Isotope Dilution-Thermal Ionization Mass Spectrometry (ID-TIMS)analyses showed slight age heterogeneity for the XN01 crystal not observed in the XN02 sample. The twocrystals have slightly different average206Pb/238U ages of 513.4 ± 0.5 Ma (2 s) and 515.4 ± 0.2 Ma (2 s),respectively. In situ U-Pb isotope data acquired via LA-(Q,SF,MC)-ICP-MS are within the uncertainty of theID-TIMS data, showing homogeneity at the 1% precision of the laser ablation (and probably ion microprobe)technique. U-Pb LA-(MC, SF)-ICP-MS analyses, using XN01 as a primary RM, reproduced the ages of otherestablished RMs within less than 1% deviation. Other Datas crystals (XN03-05) also display a reproducibility inPb/U dates better than 1% on LA-ICP-MS, making them good candidates for further testing by ID-TIMS.Item The Diamantina monazite : a new Low‐Th reference material for microanalysis.(2018) Gonçalves, Guilherme de Oliveira; Lana, Cristiano de Carvalho; Cipriano, Ricardo Augusto Scholz; Buick, Ian S.; Gerdes, Axel; Kamo, Sandra L.; Corfu, Fernando; Rubatto, Daniela; Wiedenbeck, Michael; Nalini Júnior, Hermínio Arias; Oliveira, Luiz Carlos Alves deMost monazite reference materials (RMs) for in situ U-Pb geochronology are rich in Th; however, many hydrothermal ore deposits contain monazite that is low in trace element contents, including Th, U and Pb. Because of potential problems with matrix effects and the lack of appropriate matrix-matched RMs, such variations can bias dating of hydrothermal deposits. In this paper, we describe a polycrystalline low-U and low-Th Diamantina monazite from the Espinhac o Range, SE Brazil. It has a U-Pb ID-TIMS weighted mean 207Pb*/235U ratio of 0.62913 ± 0.00079, 206Pb*/238U of 0.079861 ± 0.000088 and 207Pb*/206Pb* of 0.057130 ± 0.000031, yielding a weighted mean 206Pb*/238U date of 495.26 ± 0.54 Ma (95% c.l.). In situ dates acquired with different methods (LA-(Q, SF, MC)-ICP-MS and SIMS) are within uncertainty of the ID-TIMS data. U-Pb LA-(Q, MC)-ICP-MS runs, using Diamantina as a primary RM, reproduced the ages of other established RMs within < 1% deviation. The LA-MC-ICP-MS analyses yielded homogeneous Sm-Nd isotopic compositions (143Nd/144Nd = 0.511427 ± 23, 2s; 147Sm/144Nd = 0.1177 ± 13, 2s) and eNd(495 Ma) of -18.7 ± 0.5 (2s). SIMS oxygen isotope determinations showed measurement reproducibility better than ± 0.3‰ (2s), confirming Diamantina’s relative homogeneity at test portion masses below 1 ng.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 An assessment of monazite from the Itambé pegmatite district for use as U–Pb isotope reference material for microanalysis and implications for the origin of the “Moacyr” monazite.(2016) Gonçalves, Guilherme de Oliveira; Lana, Cristiano de Carvalho; Cipriano, Ricardo Augusto Scholz; Buick, Ian S.; Gerdes, Axel; Kamo, Sandra L.; Corfu, Fernando; Marinho, Moacyr Moura; Chaves, Alexandre de Oliveira; Valeriano, Claudio de Morisson; Nalini Júnior, Hermínio AriasLarge quantities of monazite from different pegmatite bodies of the Itambe pegmatite district were investigated to assess their suitability as U–Pb and Sm–Nd isotope reference materials for LA-ICP-MS and to track the origin of a piece of theMoacyrmonazite (termed here Itambé), awidely used reference material for LA-ICP-MS U–Pb geochronology. Monazite fromthe largest pegmatite bodies in the district (the Bananeira, Coqueiro and Paraíso pegmatites) are Ce-monazite, with negligible amounts of the huttonite and brabantite components. They are homogeneous in major and trace elements, which makes them potential candidates as compositional reference materials. U–Pb LA-ICP-MS and ID-TIMS analyses yielded identical ages within error. Although the ID-TIMS ages (507.7 ± 1.3 (207Pb⁎/235U) and 513.6 ± 1.2 Ma (206Pb⁎/238U)) were reversely discordant, spot ages determined by LA-ICP-MS geochronology were concordant at ca 508 Ma. The Bananeiro monazite was assessed as a LA-ICPMS U–Pb primary reference material against other known reference materials (treated as unknowns). This approach successfully reproduced the previously published ages of the reference materials.MREE/HREE fractionation (ie, (La/Gd)N and (Gd/Lu)N values), Eu/Eu⁎ and the chondrite-normalized REE patterns suggest that the “Itambé” monazite aliquot is very similar to that fromthe Coqueiro pegmatite. This similarity is likewise apparent in their Sm–Nd isotope compositions. Moreover, the εNdi values of the “Itambé” monazite fragment (εNdi=−4.2) and those fromall the major pegmatites in the district, are distinct fromother reference materials (eg, Managountry; εNdi = −22.3) as well as gem-quality monazite from c. 490–520 Ma pegmatites from the Araçuaí Orogen, further to the south. The εNdi can provide a further distinction for tracing Brazillian gemquality monazite reference materials.