International Multidisciplinary Scientific GeoConference SGEM .., Jun 28, 2016
Castromil gold area is part of Durico-Beirdo mining district, located not far from Porto (Norther... more Castromil gold area is part of Durico-Beirdo mining district, located not far from Porto (Northern Portugal). Several generations of gold were distinguished in the district, two of them related with stages of remobilization of primary gold. A new generation of gold is described in this study. A set of penetrative shear surfaces, main shear ruptures and veins are concentrated in the vicinity of a tectonic contact between a cataclastic, weathered, porphyritic granite and regional metassedimentary to metavolcanic Silurian formations. In some structural domains of the granite, where pervasive argillic alteration showed a major heterogeneity, secondary and ore-minerals and para-crystalline materials were characterized by optical microscopy, XRD and SEM-EDS. The systematic of the mineralization stages reveal the following sequence: a pyrite and minor chalcopyrite in metapelite enclaves; b - phyllitic alteration of granite, related to a low sulphidation stage - main gold stage in veins early hydrothermal; c - phyllitic to argillic complex alteration of cataclastic pophyritic granite and augen leucogranite, related to crack-seal of earlier veins and late infill of chalcedony and comb-quartz remobilization of early sulphides and disseminated sulphide impregnation of host-rocks late hydrothermal; d - dissolution of previous feldspar and sulphide crystals followed by the coating, infill and replenishment of dissolution cavities and vugs oxidative evolution late hydrothermal to early supergenic; e - sequence of late oxidative stages producing assemblages, referred as AMORPHOUS FERRIC ARSENATES (AFA), AMORPHOUS IRON SULPHOARSENATES (AFSA) and HYDROUS FERRIC OXIDES (HFO) - late hydrothermal to early supergenic. There is a strong spatial correlation between the increment of Au mineralization and the geometric progress of dissolution and pseudomorphosis of earlier minerals (especially sulphides) and signs of BYO dispersion. The arsenopyrite alteration products in the area of Castromil are crystalline Fe (III) arsenates (scoroditinfo:eu-repo/semantics/publishedVersio
Abstract. Preceeding the main Hercynian Au-As-Sb metallogenic hy-drothermal event, metallic preco... more Abstract. Preceeding the main Hercynian Au-As-Sb metallogenic hy-drothermal event, metallic preconcentrations (Au, Sb, Pb) occurred during the sedimentation of the Paleozoic, namely in the Precambrian (?) and/or Cambrian layers bearing volcanic prints, in the volcano- ...
Cathodoluminescence (CL) studies were carried out on polished thin sections of different feldspar... more Cathodoluminescence (CL) studies were carried out on polished thin sections of different feldspar samples (from migmatites, granites, aplite-pegmatites and granitic aggregates) using a hot cathode CL equipment HC3-LM coupled to an optical microscope and to a spectrometer (SpectraPro 2300i and a CCD Pixis 400B detector and the software Winspec32) from the Faculty of Sciences of University of Porto. The system was operated at 14kV and a filament current of 0.18 mA. The samples were coated with a thin gold film using a Cressington 108 Auto device. Luminescence images were acquired during the CL analysis with an adapted digital video-camera (KAPPA PS 40C-285 (DX) with dual stage Peltier cooling) and an acquisition time between 351ms and 3,52s. The CL study, including imaging and spectrometry, proved to be an important tool to complement the feldspar petrography as it contributes to the identification of features not observed under optical microscope. The application of the Cathodoluminescence to feldspar allows distinguishing between potassic feldspar and plagioclase, differentiating generations of feldspar and displaying internal zoning and growth areas, among other. The spectrometry complements the CL imaging. It allows obtaining a qualitative level of emission intensity, which permits the interpretation of the nature of this luminescence in each feldspar. Bands shown in the spectra are related to the existing activator elements. In the present study, it was found an association of each feldspar to different spectra and respective colour. The plagioclases exhibit yellow or green luminescence. The activator element is Mn2+, showing a broad emission band between 550 – 570 nm specially detected on this type of feldspars, due to the replacement of K+ for Mn2+. The potassium feldspars have more or less intense blue colour associated with various activators elements: the activator element is Cu2+ showing a broad emission band between 420±5 nm. This emission band can be detected either in potassium feldspar or in plagioclases, but when associated with the blue colour, it indicates that it is a potassium feldspar. Spectra with a wavelength of 460±10 nm, associated to the element activator/synthesizer Ti3+, which is initially deposited as Ti4+, replacing Al, as temperature rise. The emission band with a wavelength of 860 nm correspond to the activator element Pb+, and occurs specially in potassium feldspar like adularia and orthoclase. The activator element Al - O - Al, show a broad emission band between 450-480 nm. This emission in CL is caused by the replacement of Al3+ and Si4+ in feldspars.
The Montalto Formation consists of a succession of slate, greywacke, quartzites, and polygenic co... more The Montalto Formation consists of a succession of slate, greywacke, quartzites, and polygenic conglomerates cropping out in the Durico-Beira area of northern Portugal. The formation is of interest because it contains mixed volcaniclastic sequences that record changes in marginal-marine depositional environments and because it is associated with regional tectonic and magmatic processes. The Montalto Formation can be divided into three lithological associations that record a shallowing-upward sequence.
4 páginas. Trabajo presentado en el VII Congresso Nacional de Geologia, Évora, Jun. 2006.-- Resum... more 4 páginas. Trabajo presentado en el VII Congresso Nacional de Geologia, Évora, Jun. 2006.-- Resumen extendido.[EN] The Geopark concept emerged during the nineties. Presently, the majority of the Geoparks are located in Europe in spite of the recent UNESCO challenge towards the implementation of new Geoparks in other continents. This work outlines a new project under development created to prepare a submission of the future “Arouca Geopark” (Aveiro District) to the European Geoparks Network.[PT] A figura de Geoparque surgiu, na Europa, nos finais dos anos noventa. Actualmente, a maior parte dos Geoparques entretanto criados encontra-se neste continente, apesar do desafio da UNESCO para o estabelecimento de Geoparques em todo o mundo. Neste trabalho apresenta-se, de modo breve, um projecto em curso que dará origem à candidatura do “Geoparque Arouca” (Distrito de Aveiro) à Rede Europeia de Geoparques.Peer reviewe
Zircons in three samples of the Cambrian Montalto Formation and “Tremadoc-Arenig Santa Justa Form... more Zircons in three samples of the Cambrian Montalto Formation and “Tremadoc-Arenig Santa Justa Formation of the Valongo Anticline in northwest Portugal were dated by U-Pb secondary ion mass spectrometry (SIMS). A rhyolite sample near the top of the Montalto Formation gave clusters of Lower Paleozoic (600 to 450 Ma) and Upper Carboniferous zircon ages (360 to 300 Ma), with one Paleoproterozoic age (~1750 Ma). The middle black chert sample, underlying the massive “Arenig” quartzites of the Santa Justa Formation, gave only two zircon ages of 827 Ma and 492 Ma. The uppermost volcanic sandstone, overlying the massive “Arenig” quartzites of the Santa Justa Formation, gave similar zircon ages to the lowermost sample, but with mostly Neoproterozoic ages (933 to 560 Ma). The youngest Upper Carboniferous age clusters are caused by zircon alteration or hydrothermal recrystallization during Variscan metamorphism. The oldest Neoproterozoic ages are detrital and represent erosion of regional baseme...
International Multidisciplinary Scientific GeoConference SGEM .., Jun 28, 2016
Castromil gold area is part of Durico-Beirdo mining district, located not far from Porto (Norther... more Castromil gold area is part of Durico-Beirdo mining district, located not far from Porto (Northern Portugal). Several generations of gold were distinguished in the district, two of them related with stages of remobilization of primary gold. A new generation of gold is described in this study. A set of penetrative shear surfaces, main shear ruptures and veins are concentrated in the vicinity of a tectonic contact between a cataclastic, weathered, porphyritic granite and regional metassedimentary to metavolcanic Silurian formations. In some structural domains of the granite, where pervasive argillic alteration showed a major heterogeneity, secondary and ore-minerals and para-crystalline materials were characterized by optical microscopy, XRD and SEM-EDS. The systematic of the mineralization stages reveal the following sequence: a pyrite and minor chalcopyrite in metapelite enclaves; b - phyllitic alteration of granite, related to a low sulphidation stage - main gold stage in veins early hydrothermal; c - phyllitic to argillic complex alteration of cataclastic pophyritic granite and augen leucogranite, related to crack-seal of earlier veins and late infill of chalcedony and comb-quartz remobilization of early sulphides and disseminated sulphide impregnation of host-rocks late hydrothermal; d - dissolution of previous feldspar and sulphide crystals followed by the coating, infill and replenishment of dissolution cavities and vugs oxidative evolution late hydrothermal to early supergenic; e - sequence of late oxidative stages producing assemblages, referred as AMORPHOUS FERRIC ARSENATES (AFA), AMORPHOUS IRON SULPHOARSENATES (AFSA) and HYDROUS FERRIC OXIDES (HFO) - late hydrothermal to early supergenic. There is a strong spatial correlation between the increment of Au mineralization and the geometric progress of dissolution and pseudomorphosis of earlier minerals (especially sulphides) and signs of BYO dispersion. The arsenopyrite alteration products in the area of Castromil are crystalline Fe (III) arsenates (scoroditinfo:eu-repo/semantics/publishedVersio
Abstract. Preceeding the main Hercynian Au-As-Sb metallogenic hy-drothermal event, metallic preco... more Abstract. Preceeding the main Hercynian Au-As-Sb metallogenic hy-drothermal event, metallic preconcentrations (Au, Sb, Pb) occurred during the sedimentation of the Paleozoic, namely in the Precambrian (?) and/or Cambrian layers bearing volcanic prints, in the volcano- ...
Cathodoluminescence (CL) studies were carried out on polished thin sections of different feldspar... more Cathodoluminescence (CL) studies were carried out on polished thin sections of different feldspar samples (from migmatites, granites, aplite-pegmatites and granitic aggregates) using a hot cathode CL equipment HC3-LM coupled to an optical microscope and to a spectrometer (SpectraPro 2300i and a CCD Pixis 400B detector and the software Winspec32) from the Faculty of Sciences of University of Porto. The system was operated at 14kV and a filament current of 0.18 mA. The samples were coated with a thin gold film using a Cressington 108 Auto device. Luminescence images were acquired during the CL analysis with an adapted digital video-camera (KAPPA PS 40C-285 (DX) with dual stage Peltier cooling) and an acquisition time between 351ms and 3,52s. The CL study, including imaging and spectrometry, proved to be an important tool to complement the feldspar petrography as it contributes to the identification of features not observed under optical microscope. The application of the Cathodoluminescence to feldspar allows distinguishing between potassic feldspar and plagioclase, differentiating generations of feldspar and displaying internal zoning and growth areas, among other. The spectrometry complements the CL imaging. It allows obtaining a qualitative level of emission intensity, which permits the interpretation of the nature of this luminescence in each feldspar. Bands shown in the spectra are related to the existing activator elements. In the present study, it was found an association of each feldspar to different spectra and respective colour. The plagioclases exhibit yellow or green luminescence. The activator element is Mn2+, showing a broad emission band between 550 – 570 nm specially detected on this type of feldspars, due to the replacement of K+ for Mn2+. The potassium feldspars have more or less intense blue colour associated with various activators elements: the activator element is Cu2+ showing a broad emission band between 420±5 nm. This emission band can be detected either in potassium feldspar or in plagioclases, but when associated with the blue colour, it indicates that it is a potassium feldspar. Spectra with a wavelength of 460±10 nm, associated to the element activator/synthesizer Ti3+, which is initially deposited as Ti4+, replacing Al, as temperature rise. The emission band with a wavelength of 860 nm correspond to the activator element Pb+, and occurs specially in potassium feldspar like adularia and orthoclase. The activator element Al - O - Al, show a broad emission band between 450-480 nm. This emission in CL is caused by the replacement of Al3+ and Si4+ in feldspars.
The Montalto Formation consists of a succession of slate, greywacke, quartzites, and polygenic co... more The Montalto Formation consists of a succession of slate, greywacke, quartzites, and polygenic conglomerates cropping out in the Durico-Beira area of northern Portugal. The formation is of interest because it contains mixed volcaniclastic sequences that record changes in marginal-marine depositional environments and because it is associated with regional tectonic and magmatic processes. The Montalto Formation can be divided into three lithological associations that record a shallowing-upward sequence.
4 páginas. Trabajo presentado en el VII Congresso Nacional de Geologia, Évora, Jun. 2006.-- Resum... more 4 páginas. Trabajo presentado en el VII Congresso Nacional de Geologia, Évora, Jun. 2006.-- Resumen extendido.[EN] The Geopark concept emerged during the nineties. Presently, the majority of the Geoparks are located in Europe in spite of the recent UNESCO challenge towards the implementation of new Geoparks in other continents. This work outlines a new project under development created to prepare a submission of the future “Arouca Geopark” (Aveiro District) to the European Geoparks Network.[PT] A figura de Geoparque surgiu, na Europa, nos finais dos anos noventa. Actualmente, a maior parte dos Geoparques entretanto criados encontra-se neste continente, apesar do desafio da UNESCO para o estabelecimento de Geoparques em todo o mundo. Neste trabalho apresenta-se, de modo breve, um projecto em curso que dará origem à candidatura do “Geoparque Arouca” (Distrito de Aveiro) à Rede Europeia de Geoparques.Peer reviewe
Zircons in three samples of the Cambrian Montalto Formation and “Tremadoc-Arenig Santa Justa Form... more Zircons in three samples of the Cambrian Montalto Formation and “Tremadoc-Arenig Santa Justa Formation of the Valongo Anticline in northwest Portugal were dated by U-Pb secondary ion mass spectrometry (SIMS). A rhyolite sample near the top of the Montalto Formation gave clusters of Lower Paleozoic (600 to 450 Ma) and Upper Carboniferous zircon ages (360 to 300 Ma), with one Paleoproterozoic age (~1750 Ma). The middle black chert sample, underlying the massive “Arenig” quartzites of the Santa Justa Formation, gave only two zircon ages of 827 Ma and 492 Ma. The uppermost volcanic sandstone, overlying the massive “Arenig” quartzites of the Santa Justa Formation, gave similar zircon ages to the lowermost sample, but with mostly Neoproterozoic ages (933 to 560 Ma). The youngest Upper Carboniferous age clusters are caused by zircon alteration or hydrothermal recrystallization during Variscan metamorphism. The oldest Neoproterozoic ages are detrital and represent erosion of regional baseme...
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