M.M.V.G. Silva

Geochemistry of enclaves and host granites from the Nelas area, central Portugal

Abstract Tonalitic, granodioritic and monzogranitic enclaves occur in the Hercynian peraluminous porphyritic biotite granite and biotite–muscovite granite from the Nelas region. Some variation diagrams show linear trends, but others show dispersion. The enclaves generally have closely similar isotopic signatures to those of the host granites. They contain xenocrystic plagioclase with the same composition as phenocrysts of the host granite, and have biotite as the sole ferromagnesian phase with a composition typically similar to that of the host granite. However, some cores of enclaves have biotite slightly chemically distinct from that of rims. The modelling of major and trace elements of granodioritic enclaves and hybrid host granite indicate that they result from simple mingling/mixing between a tonalitic magma and the host granite magma. Microgranular enclaves are thus interpreted to be globules of a more mafic magma probably from an enriched mantle source. Partial equilibration has been achieved between these enclaves and the host granite.

The mineralized veins and the impact of old mine workings on the environment at Segura, central Portugal

Abstract At Segura, granitic pegmatite veins with cassiterite and lepidolite, hydrothermal Sn–W quartz veins and Ba–Pb–Zn quartz veins intruded the Cambrian schist–metagraywacke complex and Hercynian granites. Cassiterite from Sn–W quartz veins is richer in Ti and poorer in Nb and Nb+Ta than cassiterite from granitic pegmatite. Wolframite from Sn–W quartz veins is enriched in ferberite component. The Sn–W quartz veins contain pyrrhotite, arsenopyrite, sphalerite, chalcopyrite, stannite, matildite and schapbachite and the Ba–Pb–Zn quartz veins have cobaltite, pyrite, sphalerite, chalcopyrite, galena and barite, which were analyzed by electron microprobe. The presently abandoned mining area was exploited for Sn, W, Ba and Pb until 1953. Stream sediments and soils have higher concentrations of metals than parent granites and schists. Sn, W, B, As and Cu anomalies found in stream sediments and soils are associated with Sn–W quartz veins, while Ba, Pb and Zn anomalies in stream sediments and soils are related to Ba–Pb–Zn quartz veins. Sn, W, B, As, Cu, Ba, Pb and Zn anomalies in stream sediments and soils are also related to the respective old mining activities, which increased the mobility of trace metals from mineralized veins to soils, stream sediments and waters. Stream sediments and soils are sinks of trace elements, which depend on their contents in mineralized veins and weathering processes, but Sn, W and B depend mainly on a mechanic process. Soils must not be used for agriculture and human residence due to their Sn, B, As and Ba contents. Waters associated with mineralized veins were analyzed by flame atomic absorption spectroscopy (FAAS) and ICP-AES have high As, Fe and Mn and should not be used for human consumption and agriculture activities. The highest As values in waters were all related to Sn–W quartz veins and the highest Fe and Mn values were associated with the Ba–Pb–Zn quartz veins. No significant acid drainage was found associated with the old mine workings.

A RECOMBINANT ANTIGEN RECOGNIZED BY FASCIOLA HEPATICA–INFECTED HOSTS

This work reports the detection of specific immunoglobulins (Ig) against rFh8, a recombinant Fasciola hepatica adult worm excretion–secretion antigen, in sera from experimentally (rabbit, Wistar rat, cattle, and sheep), or naturally (human) infected hosts. In the case of laboratory experimental models the study revealed significant differences between rabbits, which recognized the recombinant antigen all along the infection, and Wistar rats, which showed high anti-rFh8 Ig levels only for a short period of the infection. Available sera from experimentally infected cattle and sheep, as well as sera from naturally F. hepatica–infected humans, also contained significant levels of Ig against rFh8, suggesting that Fh8 was produced by F. hepatica at a very early stage of infection in all hosts so far analyzed and that the rFh8 antigen could be used as a tool for the diagnosis of F. hepatica infections.

Assessment to the potential mobility and toxicity of metals and metalloids in soils contaminated by old Sb–Au and As–Au mines (NW Portugal)

The main purpose of this study is to assess arsenic and antimony availability in soils, as well as Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn availability in soils derived from the schist–metagraywacke complex close to old Sb–Au mines and in soils developed from Ordovician slates and close to an old As–Au mine in Portugal. The availability was determined using a European certified sequential extraction procedure (BCR). The results demonstrated that metalloids are not readily bioavailable, because they are mainly associated with the residual fraction. Arsenic and antimony proportions in exchangeable fractions are up to 3 and 1%, respectively. However, arsenic is up to 24% in oxy-hydroxide fractions, while antimony is up to 4% in them, demonstrating the highest bioavailability of arsenic compared to that of antimony, as metalloids are weakly bound to the soils in that fraction. Therefore, arsenic tends to be more toxic than antimony in all soils studied. However, the pseudo-total contents show that both metalloids are above the Italian and Dutch guidelines. Therefore, if physico-chemical changes occur arsenic and antimony will show higher potential environmental risk than evidenced by Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn.

Geochemistry of the granites and their minerals from Paredes da Beira-Penedono, northern Portugal

Abstract Seven types of Hercynian peraluminous muscovite-biotite granites (T 1 -T 5 ) and muscovite granites (T 6 and T 7 ) occur in the Paredes da Beira-Penedono area. Microscopically they show some small metasomatic effects (e.g., microclinization of plagioclase, sericitization of feldspars, small chloritization of biotite, small amounts of late-stage white mica and kaolinization of microcline). Three different types of white mica (muscovite, sericite and late-stage white mica) can be chemically distinguished in a TiMgNa diagram. Variation diagrams of major and trace elements and elemental ratios of granites and muscovites show trends of fractionation from the muscovite-biotite granites to the muscovite granites. Least-squares analysis of major elements and modelling of trace elements indicate that the muscovite granite T 7 might have been derived from the muscovite-biotite granite magma T 1 by fractional crystallization of quartz, K-feldspar, plagioclase, muscovite, biotite and ilmenite. Elemental variation diagrams of granites, biotites and muscovites also suggest trends of fractionation: (a) from the muscovite-biotite granite T 1 to the muscovite-biotite granite T 4 ; (b) in the muscovite-biotite granite T 5 ; (c) in the muscovite granite T 6 . However, the small metasomatic effects make it difficult to test fractional crystallization. The granite T 5 has a large range of composition from the least to the most silicic samples, similar to the variation of compositions of the granites in the sequence T 1 → T 4 . The granite T 1 and the least silicic samples of the granite T 5 would have their origin in two distinct pulses of granite magma, and probably have originated by partial melting of metasedimentary materials. Emplacement of granite magmas took place at ∼ 700°C and 4 kbar. They were completely crystallized at ∼ 450°C and slightly metasomatically altered at ∼ 370°C. log ( f H 2 O f HF ) is smaller in the muscovite granites than in the muscovite-biotite granites. log ( f H 2 O f HCl ) increases and log ( f HCl f HF ) and log ( f H 2 O f HF ) decrease in the sequence T 1 → T 4 of muscovite-biotite granites.

Geochemistry of gold quartz vein walls from Jales (northern Portugal)

Abstract The long hydrothermal quartz veins from Campo de Jales (northern Portugal) have been exploited for Au and form the main Portuguese Au deposit. Au and electrum occur included in sulfides, sulfosalts and quartz and in thin veinlets along fractures with sulfides, while Ag occurs in electrum, argentite, galena and most of the sulfosalts. The Campo gold quartz vein cuts mainly the Hercynian peraluminous medium- to coarse-grained porphyritic seriate two-mica granite and also the pre-Ordovician biotite-muscovite-andalusite schist with sillimanite. At 1–0.5 m from the vein the granite is altered into a porphyritic muscovite-biotite granite, while adjacent to the vein, up to 0.5 m, it is a muscovite granite. At 3 m from the vein the mica schist shows some metasomatic effects, but it is transformed into a biotite-muscovite-brunsvigite schist at 2 m from the vein and into a mica schist enriched in muscovite and sulfides adjacent to the vein in a zone of 0.1–0.5 m up to 1 m from the vein. There are progressive increases in SiO2, Fe2O3, K2O, H2O+, S, As, Sn, Sb, Cu, Pb, Rb, Au, a negative Eu anomaly and progressive decreases in TiO2, FeO, MgO, CaO, Cl, Li, Sr, Th and all REE with increasing degree of hydrothermal alteration of granite. K2O, F, S, Rb and Cs progressively increase, while FeO, CaO, Zr and Sr progressively decrease with increasing degree of hydrothermal alteration of mica schist. At the direct contact with the vein the granite and mica schist show enrichment in K2O, Fe2O3, H2O+, Sn, Rb, S, As, Zn, Sb, Cu, Pb and Au, and impoverishment in TiO2, MgO, FeO, CaO, Na2O, Cl, Cr, V, Nb, Li, Ni and Zr, which gives information on the ore-forming fluids. The hydrothermal alteration of granite increases with depth, but seems to decrease with increasing distance from the granite-schist contact. The mineral data are used to show the evolution of hydrothermal alteration at the vein walls and to write the representative reactions of hydrothermal alteration. The unaltered granite was emplaced at ∼ 3 kbar and 690°C and fO2 of 10−18 bar, but was completely crystallized at 460–600°C. It was hydrothermally altered at 200–400°C and log ( f H 2 O f HF ) and log ( f HCl f HF ) increase and log ( f H 2 O f HCl ) decreases during the alteration. The mica schist was hydrothermally altered at ∼ log ( f H 2 O f HF ) and log ( f HCl f HF ) .

Geochemistry of soils, stream sediments and waters close to abandoned W–Au–Sb mines at Sarzedas, Castelo Branco, central Portugal

ABSTRACT In the Sarzedas area, central Portugal, the Cambrian schist–metagreywacke complex predominates and is intersected by W–Au–Sb quartz veins and Sb–Au-bearing felsitic dykes, which were exploited for W, Au and Sb at the Gatas–Santa and Pomar–Galdins mines. The soils from the Gatas–Santa and Pomar–Galdins areas contain up to 11 000 and 21 600 ppm Sb, respectively. In the Sarzedas area, the stream sediments contain up to 840 ppm Sb. Only some surface waters contain Sb, which reaches 2.6 mg l−1. The waters have pH values of 5.5–7.3; they are neutralized by carbonate intercalations in the schist–metagrawacke complex. The mine wastes contain ferberite and sulphides, and have goethite and ferrihydrite coatings, which have up to 8.10 wt% Sb2O5 and 2.26 wt% As2O5 and contain inclusions of stibnite, arsenopyrite and pyrite. The highest Sb and As concentrations in soils, stream sediments and surface waters are related to the mineralized veins and dykes and mine wastes. The good correlation between W, Sb and As contents in soils from Gatas–Santa and good correlation coefficients for W–Sb, W–Pb and Sb–Pb in stream sediments from Gatas–Santa and Pomar–Galdins are due to the weathering of ferberite, stibnite, arsenopyrite and galena from mineralized veins and dykes and mine wastes. Soils, stream sediments and waters from the Sarzedas area are contaminated, which is consistent with findings for comparable effects in historical Sb mine sites elsewhere in Europe and Australasia, but the Sarzedas waters contain the highest Sb concentration and the lowest As concentration.

Geochemistry of Coexisting Biotite and Muscovite of Portuguese Peraluminous Granitic Differentiation Series

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.

Metal and metalloid leaching from tailings into streamwater and sediments in the old Ag–Pb–Zn Terramonte mine, northern Portugal

Tailings deposited over the Castanheira, a stream which flows through the old Ag–Pb–Zn Terramonte mine area, showed a great potential environmental risk due to sulphide weathering, facilitated by the tailings–water interaction. The high concentrations of Al, Fe, Pb and Zn in the tailings are associated with the exchangeable, reducible and sulphide fractions and suggest sphalerite and pyrite occurrences. Oxidation of pyrite is responsible for the low pH values (3.38–4.89) of the tailings. The water from the Castanheira stream is not suitable for human consumption due to high concentrations of SO42−, Mn, Al, Cd, Ni, and Pb. The lowest concentrations of metals and metalloids were detected in downstream stretches of the Castanheira. However, As, Fe and Zn in deeper sediments tend to increase downstream. Significant concentrations of trivalent forms of arsenic were detected in water samples. In downstream stretches of the Castanheira, some free ions (Fe2+, Mn2+ and Zn2+) also predominate and the water is saturated with ferrihydrite, goethite, hematite, lepidocrosite and magnetite.

Estimated Background Values of Some Harmful Metals in Stream Sediments of Santiago Island (Cape Verde)

Marina M. S. Cabral Pinto1,2,3, Eduardo A. Ferreira da Silva1, Maria M. V. G. Silva2 and Paulo Melo-Goncalves4 1University of Aveiro, Department of Geociences, GeoBioTec Research Center, Aveiro 2Geociences Center, University of Coimbra, Coimbra 3Department of Environmental Sciences, University Jean Piaget Cidade da Praia, Santiago Island 4Department of Physics and Centre for Environmental and Marine Studies (CESAM) University of Aveiro, Aveiro 1,2,4Portugal 3Cape Verde