M.E.P. Gomes
University of Trás-os-Montes and Alto Douro
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Featured researches published by M.E.P. Gomes.
Chemie Der Erde-geochemistry | 2002
M.E.P. Gomes; A.M.R. Neiva
Abstract Three Hercynian highly peraluminous tin-bearing granites define a sequence ranging from muscovite-biotite granite to muscovite granite. Tin-bearing quartz veins are genetically related to this sequence. Variation diagrams of most major and trace elements of granites, biotite and muscovite show fractionation trends. Least squares analysis of major elements and modelling of trace elements indicate that the muscovite-biotite granite M2 and the muscovite granite M3 were derived from the slightly porphyritic muscovite-biotite granite magma M1 by fractional crystallization of plagioclase, K-feldspar, biotite and quartz. The granite magma M1 was originated by partial fusion of peraluminous metasedimentary crustal materials. The magmatic fractionation was responsible for the increase in Sn contents of granites and their micas. Biotite has higher Sn content than coexisting muscovite. However, muscovite retains a higher percentage of the total granite Sn content, up to 99 % of the {uscovite granite. The very rare magmatic cassiterite present in muscovite granite M3 confirms the tin enrichment of magma. In the sequence, the melt temperature decreases from 765 to 735 C, P H 2 O decreases from 4 to 3 kb, and the F content in melt increases. Feldspars reequilibrated at 567–329 °C.
European Journal of Mineralogy | 2008
A.M.R. Neiva; M.E.P. Gomes; João M.F. Ramos; Paulo Bravo Silva
Granitic aplite-pegmatite sills intruded a granodiorite-granite and a biotite ≈ muscovite granite from Arcozelo da Serra (Gouveia, Portugal). A muscovite > biotite granite also crops out in the area. Variation diagrams of major and trace elements of the rocks show fractionation trends for a) granodiorite-granite and muscovite > biotite granite; b) biotite≈muscovite granite and aplite-pegmatite sills. REE patterns and δ 18 O of rocks, anorthite contents of plagioclases, Ba contents of potash feldspars, major elements and Li of biotites and muscovites confirm the two series. Least squares analysis of major elements and modelling of trace elements indicate that aplite-pegmatite sills were derived from biotite ≈ muscovite granite magma by fractional crystallization of quartz, plagioclase, potash feldspar and biotite. This mechanism is responsible for the Sn enrichment of aplite-pegmatite sills and Sn is retained in micas. Electron microprobe analyses of columbite-tantalite crystals from aplite-pegmatite sills show oscillatory, progressive and reverse zonings, which are characterized by the behaviours of eight elements and Mn/(Mn+Fe) and Ta/(Ta+Nb) ratios. Oscillatory zoning is mainly attributed to faster crystal growth than Nb, Ta, Fe and Mn can diffuse through liquid, while reverse zoning is due to nucleation and growth of evolved oxide cores and back-reaction of them with the more primitive bulk magma. Other samples of aplite-pegmatite sills show late zoned micas, consisting mainly of a Li-bearing muscovite core and a composition between zinnwaldite and trilithionite for the rim. However, alternating compositions of these two micas with relics of primary muscovite also occur. Late micas are derived from a phase melt enriched in F and Li.
Mineralogical Magazine | 2000
M.E.P. Gomes; A.M.R. Neiva
Abstract The tin-bearing muscovite granite from Ervedosa contains unzoned primary muscovite. This Hercynian S-type granite was hydrothermally altered at the stanniferous quartz vein walls and contains three types of muscovite: (1) very small unzoned muscovite replacing albite; (2) small unzoned hydrothermal muscovite replacing K-feldspar and quartz; and (3) zoned subhedral muscovite. In the zoned muscovite, the core has a composition similar to that of magmatic muscovite from the unaltered granite, while the rim has a composition similar to that of hydrothermal muscovite replacing K-feldspar and quartz in the altered granite. The rim corresponds to a late overgrowth richer in the celadonitic component than the core. Infiltrated mineralizing fluids reacted with biotite and K-feldspar of the unaltered granite. We interpret the rim of muscovite to have precipitated from these solutions.
Ecotoxicology and Environmental Safety | 2016
I.M.H.R. Antunes; M.E.P. Gomes; A.M.R. Neiva; Patrícia Catarina Sanches de Carvalho; A.C.T. Santos
The mining complex of Murçós belongs to the Terras de Cavaleiros Geopark, located in Trás-os-Montes region, northeast Portugal. A stockwork of NW-SE-trending W>Sn quartz veins intruded Silurian metamorphic rocks and a Variscan biotite granite. The mineralized veins contain mainly quartz, cassiterite, wolframite, scheelite, arsenopyrite, pyrite, sphalerite, chalcopyrite, galena, rare pyrrhotite, stannite, native bismuth and also later bismuthinite, matildite, joseite, roosveltite, anglesite, scorodite, zavaritskite and covellite. The exploitation produced 335t of a concentrate with 70% of W and 150t of another concentrate with 70% of Sn between 1948 and 1976. The exploitation took place mainly in four open pit mines as well as underground. Three lakes were left in the area. Remediation processes of confination and control of tailings and rejected materials and phytoremediation with macrophytes from three lakes were carried out between 2005 and 2007. Stream sediments, soils and water samples were collected in 2008 and 2009, after the remediation process. Most stream sediments showed deficiency or minimum enrichment for metals. The sequential enrichment factor in stream sediments W>Bi>As>U>Cd>Sn=Ag>Cu>Sb>Pb>Be>Zn is mainly associated with the W>Sn mineralizations. Stream sediments receiving drainage of a mine dump were found to be significantly to extremely enriched with W, while stream sediments and soils were found to be contaminated with As. Two soil samples collected around mine dumps and an open pit lake were also found to be contaminated with U. The waters from the Murçós W>Sn mine area were acidic to neutral. After the remediation, the surface waters were contaminated with F(-), Al, As, Mn and Ni and must not be used for human consumption, while open pit lake waters must also not be used for agriculture because of contamination with F(-), Al, Mn and Ni. In most waters, the As occurred as As (III), which is toxic and is easily mobilized in the drainage system. The remediation promoted a decrease in metals and As concentrations of soils and waters, however the applied processes were not enough to rehabilitate the area.
Chemie Der Erde-geochemistry | 2002
A.M.R. Neiva; M.M.V.G. Silva; M.E.P. Gomes; T.F.C. Campos
Abstract In nine Portugese peraluminous Hercynian granitic series of differentiation, Cr, V, Sc and Ba decrease, whereas Nb, Zn, Sn, Li, Rb and Cs increase in the sequence of micas crystallization. Commonly equilibrium was not attained for trace elements between coexisting primary biotite and muscovite. Correlations of Cr, V, Nb, Li, Rb and Cs were found for biotite-muscovite pairs. The same correlation has a different slope in distinct series due to distinct degree of fractional crystallization, but also to solid-liquid reequilibration during late-magmatic evolution, as suggested by regression lines, which do not generally pass through the origin. Most trace elements partition in favour of biotite, while Sn, Sc, Sr and Ba prefer muscovite. These micas probably crystallized simultaneously as suggested by intergrowths. The partition ratio for Cs is one series is similar to that found experimentally.
Periodico Di Mineralogia | 2012
R. J. S. Teixeira; A.M.R. Neiva; M.E.P. Gomes
At Braganca region, northeastern Portugal, accessory chromian spinels and magnetite occur in serpentinites and steatitic rocks and rarely in tremolite asbestos and chloritites. The chromian spinels h ave a large range in composition, which is related to serpentinization and other subsequent alteration processes such as steatization. Four varieties of zoned chromian spinels were distinguished: 1- zoned crystals with a Cr-rich hercynite core and a ferrian chromite rim in serpentinite from Donai; 2- zoned crystals with an aluminian chromite core and a ferrian chromite rim in steatitic rock from D onai; 3- zoned aluminian chromite crystals showing a rim richer in Fe 2+ and poorer in Mg than the core, found in Donai tremolite asbestos; 4- zoned chromian magnetite crystals showing a rim richer in Fe 3+ and poorer in Cr than the core, in serpentinites and steatitic rocks from Sete Fontes and Soeira/Pena Maquieira. Unzoned aluminian chromite crystals were found in Donai chloritite. Magnetite from the Donai serpentinite and steatitic rocks from Sete Fontes and Soeira/Pena Maquieira has a composition c lose to the ideal formula.
Lithos | 2009
A.M.R. Neiva; Ian S. Williams; João Farinha Ramos; M.E.P. Gomes; M.M.V.G. Silva; I.M.H.R. Antunes
Journal of Geochemical Exploration | 2010
M.E.P. Gomes; I.M.H.R. Antunes; Paulo Bravo Silva; A.M.R. Neiva; Fernando António Leal Pacheco
Lithos | 2005
M.E.P. Gomes; A.M.R. Neiva
Environmental Earth Sciences | 2013
L.M.O. Martins; M.E.P. Gomes; L. J. P. F. Neves; Alcides Pereira