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.
- Decision criteria for the exploration of ornamental-stone deposits: Application to the marbles of the Portuguese Estremoz AnticlinePublication . Falé, Patrícia; Carvalho, Jorge; Henriques, Paulo; Luís, GabrielABSTRACT: Ornamental stones are almost ready-made raw materials with a high economic value for the building-construction industry. The discovery of new near-surface deposits, the very low exploitation efficiency, the huge amounts of wastes produced, and the land-use accessibility conditions are the main challenges that the extractive industry for this mineral resource is facing nowadays. Research on advanced geological exploration tools and methodologies is needed to reply to those challenges. During the process of geological ornamental-stone deposits exploration, the unique and decisive criteria that should be considered are its dimensions, homogeneity, and fracturing state. Lithostructural geological mapping and in situ fracturing surveys are the basic indispensable tools for their field assessment. By applying these criteria and tools to a marble-rich area in the Portuguese Estremoz Anticline and a step-by-step numerical evaluation of the qualitative geological parameters, the delimitation of the best target areas for exploitation or environmental rehabilitation has been effectively mapped.
- 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.