Navegando por Autor "RODRIGUES, Paulo Roberto Soares"

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Petrografia, geoquímica e geocronologia de diques máficos a félsicos da região de Água Azul do Norte, Província Carajás, sudeste do Pará
(Universidade Federal do Pará, 2015-10-08) RODRIGUES, Paulo Roberto Soares; LAMARÃO, Claudio Nery; http://lattes.cnpq.br/6973820663339281
In the Água Azul do Norte region, southeast of Pará, mafic to felsic dikes arise in razed area in the form of discontinuous ridges sectioning anorogenic granites and Archean country rocks. Preferentially they occur under NW-SE direction forming tabular subvertical bodies with thicknesses of up to 30m. Four groups were individualized: diabases, andesites, rhyolites and alkali-feldspar rhyolites. Geochemically, are basalts, basaltic andesites, andesites and rhyolites metaluminous to weakly peraluminous of tholeiitic affinity. In Harker diagrams diabase displays the lowest contents of SiO2 and TiO2 and the highest contents of FeOt, MgO and CaO, reflecting the mineralogical composition of these rocks predominantly formed by plagioclase and clinopyroxene. The andesites show intermediate TiO2, FeOt, MgO, CaO, Na2O and K2O values compared to diabases and rhyolites, similar to other andesite dykes already studied in the Rio Maria Domain (RMD). The dikes of alkali-feldspar rhyolite and rhyolite have higher and varied concentrations of SiO2. FeOt, Al2O3, MgO and CaO exhibit negative correlation, while K2O is positively correlated with the silica. Na2O, TiO2 and P2O5 have no clear correlation. The diabase dikes show sub-horizontal pattern of rare earth elements (REE), with light REE fractionation, enrichment of light REE (LREE) relative to heavy REE (HREE) and not too prominent to slightly negative Eu anomalies. Comparatively, the andesite dykes have more accentuated REE fractionation, greater enrichment of LREE compared to the HREE and more pronounced Eu negative anomalies. The rhyolite dyke displays moderate REE fractionation and negative anomaly of Eu, while the alkali-feldspar rhyolites show greater fractionation of REE and enrichment of LREE compared to HREE, besides strongly pronounced Eu negative anomalies. The presence of compositional gaps between groups of Água Azul do Norte dikes rule out the existence of a continuous magmatic series; the mafic magmatism, represented by diabase dikes, has not evolved to form the andesite. On the other hand, the dikes of rhyolite and alkali-feldspar rhyolite would be linked to the anorogenic A-type granite magmatism of approximately 1.88 Ga active in the RMD. The comparative study shows similarities between the Água Azul do Norte dikes and those of other areas of the RMD, suggesting a common origin.
Acesso aberto (Open Access)
Quartzo magmático e hidrotermal do depósito de ouro São Jorge, Província Aurífera do Tapajós, Pará: petrografia, microscopia eletrônica de varredura-catodoluminescência e implicações metalogenéticas
(Universidade Federal do Pará, 2015-12) SOTERO, Aldemir de Melo; LAMARÃO, Cláudio Nery; MARQUES, Gisele Tavares; RODRIGUES, Paulo Roberto Soares
Studies in crystals of quartz present in the mineral associations to the area of the São Jorge gold deposit, Tapajós Gold Province, southwest of the Pará state, identified four morphological and textural types (Qz1, Qz2, Qz3 and Qz4) by scanning electron microscopy-cathodoluminescence images. In the more preserved rocks of the Younger São Jorge Jovem granite, rich in amphibole and biotite (associations 1 and 2), anhedral crystals of magmatic quartz with high to moderate luminescence (Qz1) dominate. In the partly altered rocks (associations 2 and 3), post-magmatic to hydrothermal fluids affected the granite, and filled fractures in Qz1 and crystallized not luminescent (dark) Qz2. In the most intensely altered rocks (association 4), successive alteration, dissolution and recrystallization processes gave rise to typically hydrothermal zoned, subhedral (Qz3) and euhedral (Qz4) quartz crystals. Images by backscattered electrons and semiquantitative analysis by energy dispersive spectroscopy identified two generations of gold: Au1, enriched in Ag (4.3 to 23.7%) and associated to pyrite crystals; Au2, enriched in Te (1.1 to 17.2%) and included or associated to Qz4. The scanning electron microscopy-cathodoluminescence study provided important information that was preserved in the quartz structure. The morphological and textural evolution of this mineral in different stages shows the gradual action of the hydrothermalism in the rocks and minerals associations of São Jorge deposit. Gold mineralization of the deposit was chemically (energy dispersive spectroscopy) and paragenetically (pyrite, sphalerite and Qz4) characterized, and it can be divided into different generations or mineralizing events. The effectiveness of the methodology used in this study was established, allowing its application in studies of other hydrothermal deposits.