RM - Artigos em revistas internacionais
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- Mineralogy and metasomatic evolution of distal strata-bound scheelite skarns in the Riba de Alva Mine, Northeastern PortugalPublication . Gaspar, L. Miguel; Inverno, Carlos
- The effect of unconfined mine tailings on the geochemistry of soils, sediments and surface waters of the Lousal area (Iberian Pyrite Belt, Southern Portugal)Publication . Silva, Eduardo Ferreira da; Fonseca, Edmundo Cardoso; Matos, João Xavier; Patinha, Carla; Reis, P.; Oliveira, J. M. Santos
- O reordenamento da actividade extractiva como instrumento para o planeamento regional : Vila Viçosa, PortugalPublication . Falé, Patrícia; Henriques, Paulo; Carvalho, JorgeO Anticlinal de Estremoz-Borba-Vila Viçosa, situado em Portugal na região do Alentejo, está integrado na denominada Zona dos Mármores e é o grande centro da actividade extractiva dos mármores. Esta zona tem características excepcionais de exploração mineral. No entanto, existem alguns condicionalismos geológicos, uma desorganização do espaço devido ao material não comercializado e acumulado em escombreiras, e a preocupação cada vez maior na exploração sustentada deste tipo de recurso mineral, fazendo desta zona uma área preferencial para o estudo de metodologias que auxiliem o reordenamento do sector extractivo. Tendo em mente a necessidade de compatibilização da actividade mineira com a preservação ambiental nas políticas de ordenamento territorial, este trabalho visa apresentar alguns indicadores geológicos e ambientais, imprescindíveis a um reordenamento das explorações de mármore permitindo a melhoria do uso e organização do espaço, a protecção do ambiente e o aumento da qualidade de vida.
- U-Pb geochronology of felsic volcanic rocks hosted in the Gafo Formation, South Portuguese Zone : the relationship with Iberian Pyrite Belt magmatismPublication . Rosa, Diogo; Finch, A. A.; Andersen, T.; Inverno, Carlos
- Exergy cost of mineral resourcesPublication . Rosa, Rui Namorado; Rosa, DiogoMineral deposits are considered as natural capital whose value can be assessed in exergy terms. Historical industry experience provides evidence that exploitation of mineral deposits and the beneficiation of ores are essentially energy intensive. The persisting decline of the grade of the developed deposits demands increasing exergy replacement and processing costs. The results demonstrate how far processed ores and concentrates are from ideal behaviour, and technologies from reversibility conditions. The exploitation of mineral resources of declining quality for mineral commodities imply a long time trend of increasing mass and exergy inputs spent per unit product output, in line with a law of ‘diminishing returns’ on invested exergy.
- The positive environmental contribution of jarosite by retaining lead in acid mine drainage areasPublication . Figueiredo, M. Ondina; Silva, Teresa
- Indium-carrier minerals in polymetallic sulphide ore deposits : a crystal chemical insight into an indium binding state supported by X-ray absorption spectroscopy dataPublication . Figueiredo, M. Ondina; Silva, Teresa; de Oliveira, Daniel Pipa Soares; Rosa, Diogo
- Geochemistry of stream sediments southwards of the SW Variscan suture in Portugal (Guadiana and Chança river basins) : insights into element anomalies of variable origin and intensityPublication . Luz, Filipa; Mateus, António; Matos, João Xavier; Gonçalves, M. A.Stream sediment samples were collected in the Trindade–Chança region at 1034 sites for mineral exploration purposes during 1996–97. Concentrations of Cu, Zn, Pb, Co, Cr and Ni are high enough in most sample sites to allow data assessment by multi-element anomaly definition and threshold computation using the area concentration multifractal model technique. The regional threshold values are 20, 45, 30 and 15 ppm for Cu, Zn, Pb and Co respectively. Anomalies for Cu, Zn, Pb, Co, Cr and Ni are delimited by first order local threshold values at 40, 94, 70, 21, 37 and 42 ppm. The main anomalies are clustered to the east-southeast of the surveyed region and reflect mixed contributions from a variety of sources, namely different volcanic units with local contributions from pelite rocks, contamination from old (abandoned) mining activities and hydrothermal mineralisation controlled by different fault zones.
- Natural nanomaterials : reappraising the elusive structure of the nano-sized mineral ferrihydrite through X-Ray absorption spectroscopy at the iron K-edgePublication . Figueiredo, M. Ondina; Silva, Teresa; Veiga, JPFerrihydrite is natural ferric oxyhydroxide occurring exclusively nanocrystalline. With ideal formula 5 Fe2 O3 . 9 H2 O, ferrihydrite is quite abundant in sediments, weathering crusts and mine wastes, being characteristic of red pre-soils formed by loose weathered rock plus mineral debris (regoliths) and commonly designated as “2-line” or “6-line” on the basis of the broadened maxima observed in the X-ray diffraction pattern. Synthetic nanocrystalline “6-line” ferrihydrite was recently studied through methods based on atomic-pair distribution functions disclosing the possible occurrence of icosahedral clusters formed by twelve octahedra centred by an inner tetrahedron, all filled by Fe 3+ ions. However, Mössbauer studies were inconclusive about the existence of 4-coordinated iron, thus suggesting that the tetrahedral cation may well be Si4+. In view of such structural uncertainty, a XANES study at the Fe K-edge was undertaken on ferrihydrite from a regolith to ascertain the occurrence of tetrahedral iron. Comparison with data collected from well crystallized iron oxide and hydroxide minerals where Fe 3+/2+ ions occur in octahedral and tetrahedral coordination is described and the results so far obtained are discussed, showing that supplementary study is needed on the elusive structure of ferrihydrite.
- Decorative 18th century blue-and-white portuguese tile panels : a type-case of environmental degradationPublication . Silva, Teresa; Figueiredo, M. Ondina; Barreiros, M. Alexandra; Prudêncio, Maria IsabelDecorated glazed ceramic tiles are used as an ornamental art, constituting an important cultural heritage whose preservation is mandatory. Environmental conditions are responsible for the degradation of exposed ancient tile panels originating various pathologies, related to the development of microorganisms. This is the case of a valuable 18th century blue-and-white Portuguese tile panel called “Cura do Cego,” belonging to the collection of the National Tile Museum (MNAz), where green stains are nowadays observable in the glaze. A prospective diagnosis of this green tarnishing was the aim of the present work. Small tile fragments were directly irradiated using nondestructive techniques: X-ray fluorescence spectrometry with a wavelength-dispersive system (WDXRF) for chemical characterization of the tile glaze and X-ray powder diffraction (XRD) to assess the phase constitution of both the glaze and the ceramic body. A destructive technique (scanning electron microscopy with energy-dispersive system (SEM/EDS)) was applied to tentatively infer the chemical changes induced in the glaze by the green staining and also to characterize the morphology of the microorganisms associated to this staining. The obtained results are reported and discussed, as a preliminary step for testing an innovative nondestructive decontamination technique applying gamma radiation, particularly suitable for overcoming such tile pathologies.