Browsing by Author "Silva, P.B."
Now showing 1 - 9 of 9
Results Per Page
Sort Options
- Contaminação de águas associadas a mineralizações de W de Fonte Santa, NE PortugalPublication . Antunes, I.M.H.R.; Gomes, M.E.P.; Neiva, A.M.R.; Silva, P.B.; Rodrigues, A.M.O.Na região da mina de Fonte Santa ocorrem filões de quartzo mineralizados em W, com scheelite, que cortam os quartzitos do Ordovícico Inferior e estão relacionados com a zona de cisalhamento de Moncorvo-Bemposta. Alguns filões com scheelite têm quartzo recristalizado e brechificado e sulfuretos, tendo sido explorados para W entre 1942 e 1982. As águas relacionadas com a mina da Fonte Santa são pouco mineralizadas, com condutividade eléctrica < 965 μ S/cm, e classificadas como de tipo misto. A maioria dos valores de pH (pH = 5.0 - 8.5) indicam que não há drenagem ácida significativa associada às actividades mineiras e os valores mais ácidos (pH = 3.4) foram obtidos numa lagoa da mina. Nas águas associadas com os filões mineralizados e antigas explorações foram encontradas concentrações elevadas de Fe e Mn que proíbem o seu consumo humano e utilização na agricultura.
- Geochemistry of Li-bearing aplite-pegmatite veins from Cabeço Queimado and associated rocks (Segura, Central Portugal)Publication . Antunes, I.M.H.R.; Neiva, A.M.R.; Silva, M.M.V.G.; Ramos, J.M.F.; Silva, P.B.At Segura area, two-mica granite, muscovite granite, granitic aplite veins and Libearing granitic aplite-pegmatite veins from Cabeco Queimado intruded the Cambrian schist-metagraywacke complex. Aplite veins also intruded both granites. Variation diagrams of major and trace elements of the granitic rocks show fractionation trends for: a) two-mica granite and Li-bearing aplite-pegmatite veins; b) muscovite granite and aplite veins. Least square analysis for major elements and modelling of trace elements indicate that: a) the Li-bearing aplite-pegmatite veins were derived from the two-mica granite by factional crystallization of quartz, plagioclase, potash feldspar and biotite; b) the aplite veins were derived from muscovite granite by fractional crystallization of quartz, plagioclase, potash feldspar and ilmenite, which is supported by the similar δ18O values. The increase of δ18O values from two-mica granite to aplite-pegmatite veins suggests that fractional crystallization was accompanied by assimilation of metasedimentary material (AFC process). The pegmatite veins are REL-Li pegmatites and belong to the LCT family. The occurrence of amblygonite-montebrasite, lepidolite, cassiterite, ferrocolumbite, manganocolumbite and microlite suggest that Li-bearing granitic aplite-pegmatite veins are highly differentiated.
- Geochemistry of minerals, waters and weathering from the Fonte Santa mine area (NE of Portugal)Publication . Gomes, M.E.P.; Antunes, I.M.H.R.; Neiva, A.M.R.; Pacheco, F.A.L.; Silva, P.B.The quartz veins containing scheelite from Fonte Santa mine area were exploited for W between 1942 and 1982. At the end of November 2006, a flood event damaged the dam land of Fonte Santa mine and metal content of water increased. Fonte Santa mine area cuts the quartzites close to the Fonte Santa muscovite granite. The granite contains quartz, microcline, albite, muscovite, chlorite, columbite-tantalite, volframite, W-ixiolite and ilmenite. The quartz veins contain muscovite, chlorite, tourmaline, scheelite, pyrrhotite, pyrite, sphalerite, chalcopyrite, galena, arsenopyrite, magnetite, jarosite, phosphates of Pb, Fe and Al. The waters related to the Fonte Santa mine are poorly mineralized, with electrical conductivity < 965 μS / cm, of mixed type or HCO3 - and SO4 2- types. These waters have Fe and Mn contents that forbid to use that for human consumption and agriculture. Sodium, Mg and K water contents are associated with the alteration of albite, chlorite and muscovite of country rock, while Ca is related to the W-bearing quartz veins.
- Geochemistry of waters associated with the old mine workings at Fonte SantaPublication . Gomes, M.E.P.; Antunes, I.M.H.R.; Silva, P.B.; Neiva, A.M.R.; Pacheco, F.A.L.The quartz veins containing scheelite from Fonte Santa mine cut the Lower Ordovician quartzites. A muscovite–biotite granite (G1) and a muscovite granite (G2), both S-type, crop out close to the Fonte Santa mine and are related to the Moncorvo–Bemposta shear zone. The most altered samples of G2 show intense muscovitization and microclinization and contain chlorite, columbite–tantalite, wolframite, W-ixiolite and Fe-oxides. The tin-bearing granites contain 18 ppm (G1) and 73 ppm (G2) Sn. The most altered samples of G2 correspond to a tungsten granite. The quartz veins contain muscovite, chlorite, tourmaline, scheelite, pyrrhotite, pyrite, sphalerite, chalcopyrite, galena, arsenopyrite, iron oxides, Fe sulfates, phosphates of Pb, Fe and Al. The Fonte Santa mine area was exploited for W between 1942 and 1982. At the end of November 2006, a flood event damaged the tailings dam of Fonte Santa mine, releasing contaminated material and increasing contaminant levels in water within the area of influence of the mine. The waters related to the Fonte Santa mine are poorly mineralized, with electrical conductivity of b965 μS/cm, and of a mixed type or HCO3 − and SO4 2− types. Most pH values (5.0−8.5) indicate that there is no significant acidic drainage in the region, as found in other areas. More acidic values (pH=3.4) were found in the mine's lagoon. Waters associated with mineralized veins and old mine activities have Fe and Mn concentrations that forbid their use for human consumption and agriculture. Natural Na, Mg and K water contents are associated with the alteration of albite, chlorite and muscovite of country rock, while Ca with the W-bearing quartz veins. Weathering agents are carbonic and sulphuric acids and the latter has a strong influence in areas draining fine-grained mine tailings.
- Geochemistry of waters associated with the old mine workings at Fonte Santa (NE of Portugal)Publication . Gomes, M.E.P.; Antunes, I.M.H.R.; Silva, P.B.; Neiva, A.M.R.; Pacheco, F.A.L.The quartz veins containing scheelite from Fonte Santa mine cut the Lower 10 Ordovician quartzites. A muscovite-biotite granite (G1) and a muscovite granite (G2), 11 both S-type, crop out close to the Fonte Santa mine and are related to the Moncorvo - 12 Bemposta shear zone. The most altered samples of G2 show intense muscovitization and 13 microclinization and contain chlorite, columbite-tantalite, wolframite, W-ixiolite and Fe-14 oxides. The tin-bearing granites contain 18 ppm (G1) and 73 ppm (G2) Sn. The most 15 altered samples of G2 correspond to a tungsten granite. The quartz veins contain 16 muscovite, chlorite, tourmaline, scheelite, pyrrhotite, pyrite, sphalerite, chalcopyrite, 17 galena, arsenopyrite, iron oxides, Fe-sulfates, phosphates of Pb, Fe and Al. The Fonte 18 Santa mine area was exploited for W between 1942 and 1982. At the end of November 19 2006, a flood event damaged the tailings dam of Fonte Santa mine, releasing 20 contaminated material and increasing contaminant levels in water within the area of 21 influence of the mine. The waters related to the Fonte Santa mine are poorly mineralized, 22 with electrical conductivity < 965 μS / cm, and of a mixed type or HCO3- and SO42- types. 23 Most pH values (5.0 8.5) indicate that there is no significant acidic drainage in the 24 region, as found in other areas. More acidic values (pH = 3.4) were found in the mine’s 25 lagoon. Waters associated with mineralized veins and old mine activities have Fe and Mn 26 concentrations that forbid their use for human consumption and agriculture. Natural Na, 27 Mg and K water contents are associated with the alteration of albite, chlorite and 28 muscovite of country rock, while Ca with the W-bearing quartz veins. Weathering agents 29 are carbonic and sulphuric acids and the latter has a strong influence in areas draining 30 fine-grained mine tailings.
- Geoquímica do granito, filões de quartzo com scheelite e águas da mina abandonada de Fonte Santa (NE de Portugal)Publication . Gomes, M.E.P.; Antunes, I.M.H.R.; Silva, P.B.; Neiva, A.M.R.Os filões de quartzo com scheelite da mina da Fonte Santa atravessam a formação do Quartzito Armoricano, do Ordovícico Inferior. A mineralização é de tipo “stockwork”, ocorre associada ao leucogranito sin-F3, da Fonte Santa, que aflora a 250 m a Sul do jazigo e relaciona-se com a zona de cisalhamento Moncorvo-Bemposta (Silva e Pereira, 2001). O leucogranito é de grão médio a fino, moscovítico, com foliação N80ºW, subvertical. Possui quartzo, microclina, albite, moscovite, turmalina, silimanite, zircão, apatite, e ilmenite. As amostras alteradas com microclinização e moscovitização intensa contêm clorite, columbite-tantalite, volframite, ixiolite rica em W e óxidos de ferro. É um granito peraluminoso, do tipo S, muito evoluído e estanífero com Sn > 44ppm (Silva, 2000). Alguns filões têm quartzo parcialmente recristalizado, por vezes brechóide, impregnado de sulfuretos preenchendo microfissuras e fracturas. A paragénese dos filões é constituída por quartzo, moscovite, clorite, turmalina, scheelite, pirrotite, pirite, esfalerite, calcopirite, galena, óxidos de ferro, sulfatos de Fe e fosfatos de Pb, Fe e Al. A mina da Fonte Santa foi explorada para W entre 1942 e 1982 (Triede, 2002). As águas associadas à mina da Fonte Santa, são pouco mineralizadas, com condutividade específica < 150 μS/cm, de tipo misto, bicarbonatadas ou sulfatadas. A maioria dos valores de pH (5.0 e 9.2) indicam que não há uma drenagem ácida significativa na região, tal como encontrado noutros locais (e.g., Antunes et al., 2002). Os valores mais ácidos (pH: 3.4-3.5) foram encontrados na lagoa da mina.
- Mineralogia dos filões aplito-pegmatíticos litiníferos da região de SeguraPublication . Antunes, I.M.H.R.; Neiva, A.M.R.; Silva, M.M.V.G.; Silva, P.B.Na região de Segura, os filões aplito-pegmatíticos litiníferos Variscos instruíram o Complexo Xisto-Grauváquico, Câmbrico. Os filões pegmatíticos são do tipo REL-Li e incluem-se na família dos pegmatitos LCT. A ocorrência de lepidolite, montebrasite, microlite, cassiterite e minerais do grupo da columbite primários sugerem um elevado grau de diferenciação nestes filões. A montebrasite primária é heterogénea e a lacroixite secundária ocorre nas suas zonas enriquecidas em Na. A cassiterite é zonada com alternância de zonas escuras e zonas claras e possui Mn > Fe, o que é raro. As zonas escuras são fortemente pleocroicas, com zonamento oscilatório, e possuem teores mais elevados de Nb e Ta do que as zonas claras. As inclusões de moscovite, apatite, ferrotapiolite, ixiolite e microlite foram encontradas em ambas as zonas da cassiterite, mas as exsoluções de ferrocolumbite, ferrocolumbite manganífera e manganocolumbite ocorrem nas zonas escuras.
- Petrogenetic links between lepidolite-subtype aplite-pegmatite, aplite veins and associated granites at Segura (central Portugal)Publication . Antunes, I.M.H.R; Neiva, A.M.R.; Ramos, J.M.F.; Silva, P.B.; Silva, M.M.V.G.; Corfu, F.In the Segura area, Variscan S-type granites, aplite veins and lepidolite-subtype granitic aplite-pegmatite veins intruded the Cambrian schist-metagraywacke complex. The granites are syn D3. Aplite veins also intruded the granites. Two-mica granite and muscovite granite have similar ages of 311.0 ± 0.5 Ma and 312.9 ± 2.0 Ma but are not genetically related, as indicated by their geochemical characteristics and (87Sr/86Sr)311 values. They correspond to distinct pulses of magma derived by partial melting of heterogeneous metapelitic rocks. Major and trace elements suggest fractionation trends for: (a) muscovite granite and aplite veins; (b) two-mica granite and lepidolite-subtype aplite-pegmatite veins, but with a gap in most of these trends. Least square analysis for major elements, and modeling of trace elements, indicate that the aplite veins were derived from the muscovite granite magma by fractional crystallization of quartz, plagioclase, K-feldspar and ilmenite. This is supported by the similar (87Sr/86Sr)311 and δ18O values and the behavior of P2O5 in K-feldspar and albite. The decrease in (87Sr/86Sr)311 and strong increase (1.6‰) in δ18O from two-mica granite to lepidolite-subtype aplite-pegmatite veins, and the behaviors of Ca, Mn and F of hydroxylapatite indicate that these veins are not related to the two-mica granite. The occurrence of amblygonite–montebrasite, lepidolite, cassiterite, columbite-(Fe), columbite-(Mn) and microlite suggests that lepidolite-subtype granitic aplite-pegmatite veins are highly differentiated. Montebrasite shows a heterogeneous Na distribution and secondary lacroixite was identified in some montebrasite areas enriched in Na. Unusual Mn > Fe cassiterite is zoned, with the alternating darker zones being strongly pleochroic, oscillatory zoned, and containing more Nb and Ta than the lighter zones. Inclusions of muscovite, apatite, tapiolite-(Fe), ixiolite and microlite are present both in lighter and darker zones of cassiterite. It shows exsolutions of columbite-(Fe), columbite-(Mn,Fe) and columbite-(Mn), particularly in darker zones.
- Weathering and hydrochemistry associated with the old mine workings at Fonte Santa (NE Portugal)Publication . Gomes, M.E.P.; Antunes, I.M.H.R.; Pacheco, F.A.L.; Neiva, A.M.R.; Silva, P.B.Weathering and hydrochemistry associated with the old mine workings at Fonte Santa (NE Portugal)