Browsing by Author "Luz, Filipa"
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- Cu- and Za-soil anomalies in the NE border of the South Portuguese Zone (Iberian Variscides, Portugal). Identified by multifractal and geostatistical analysisPublication . Luz, Filipa; Mateus, António; Matos, João Xavier; Gonçalves, M. A.Extensive Cu- and Zn-soil geochemical data in the Albernoa/Entradas–S. Domingos region (NE border of the Iberian Pyrite Belt, South Portuguese Zone) were examined to separate anomalies from background using the concentration–area fractal model. Distribution patterns of Cu and Zn concentrations in soil are primarily influenced by bedrock. The regional threshold values of Cu- and Zn-soil contents over metasedimentary sequences are 20–25 and 20–60 ppm, respectively, becoming 30–50 and 20–90 ppm, respectively, when metavolcanic rocks are present. The first-order threshold values for Cu are 80–90 ppm in soils over metasediments and 70–80 ppm in soils over sequences bearing metavolcanics. For Zn, the first-order threshold values are 40–80 and 90–100 ppm in soils over metasediments and metavolcanic rocks, respectively. Metasediments and metavolcanics comprising significant sulphide disseminations are outlined by Cu- and Zn-soil values above 100 and 300 ppm in soil, respectively. On the basis of these results, Alvares and Albernoa/Entradas areas emerge as the first priority targets for exploration. The observed non-coincidence of Cu- and Zn-soil anomalies in soil in the area could reflect difference in element dispersion during weathering, they mostly indicate distinct metal sources related to the original composition of different rock types or to chemical changes developed during Variscan deformation/re-crystallization path. The established regional baseline data can be used as reference for environmental studies.
- Geochemical exploration and assessment of environmental impacts in the Portuguese sector of the Iberian Pyrite BeltPublication . Batista, Maria Joao; Mateus, A; Matos, João Xavier; Gonçalves, Mário A.; Figueiras, Jorge; Abreu, Maria Manuela; Luz, FilipaABSTRACT: This work intends to briefly report the history and application of geochemical exploration techniques in the Iberian Pyrite Belt (IPB). The use of geochemistry in IPB for exploration purposes started in 1950s. Together with geophysics, the soil geochemical exploration surveys performed over several decades were responsible for important discoveries such as Carrasco and Feitais ore-bodies. However, the continuous development of analytical methods and the progress in data processing/modelling led to significant changes in the planning of sampling surveys, and their specific objectives, as well as in the accuracy of geochemical anomalies definition and corresponding interpretation. As a consequence, the number of samples involved in each survey was significantly reduced, but the chemical elements analysed with improved detection limits were considerably extended; additionally, geochemical anomalies were better resolved. Notwithstanding this evolution, data obtained in early soil geochemical surveys (notably by the Serviço de Fomento Mineiro) are still useful in the development of preliminary approaches at a regional scale. Over the years, many studies were made for exploration and environmental assessments, the most relevant of them reported in this chapter. Natural distributions of chemical elements were also identified in these studies as background (if pristine conditions are present) or baseline (depending how disturbed is the area covered by the sampling survey) values. Large part of IPB was, and still is, subjected to poly-metallic mineral exploration or mining, being also the focus of environmental evaluation and/or remediation projects on particular areas that, being the target of long-lasting human intervention, represent paradigmatic case-study examples. The exploration and exploitation works carried out by national and foreign private companies were, and still are, very important for innovative achievements in IPB along with copious contributions from the Portuguese R&D public institutions. Presently, LNEG possesses a vast quantity of geochemical data that can be provided for companies that wish to start their activity in the IPB; some of these datasets are compiled to a unique integrative map also presented in this work. Stream-sediments geochemistry, hydrogeochemistry and lithogeochemistry (of outcropping rock and drill-core samples) represent also important sources of geochemical data in regional or detailed studies over specific target areas in the IPB. However, these techniques are beyond the scope of the present paper which aimed at providing a general overview of the importance of soil geochemistry studies in the current knowledge of the IPB.
- Geochemical exploration and assessment of environmental impacts in the Portuguese sector of the Iberian Pyrite BeltPublication . Batista, Maria Joao; Mateus, António; Matos, João Xavier; Gonçalves, M. A.; Figueiras, Jorge; Abreu, Maria Manuela; Luz, FilipaABSTRACT: This work intends to briefly report the history and application of geochemical exploration techniques in the Iberian Pyrite Belt (IPB). The use of geochemistry in IPB for exploration purposes started in 1950’s. Together with geophysics, the soil geochemical exploration surveys performed over several decades were responsible for important discoveries such as Carrasco and Feitais ore-bodies. However, the continuous development of analytical methods and the progress in data processing/modelling led to significant changes in the planning of sampling surveys, and their specific objectives, as well as in the accuracy of geochemical anomalies definition and corresponding interpretation. As a consequence, the number of samples involved in each survey was significantly reduced, but the chemical elements analysed with improved detection limits were considerably extended; additionally, geochemical anomalies were better resolved. Notwithstanding this evolution, data obtained in early soil geochemical surveys (notably by the Serviço de Fomento Mineiro) are still useful in the development of preliminary approaches at a regional scale. Over the years, many studies were made for exploration and environmental assessments, the most relevant of them reported in this chapter. Natural distributions of chemical elements were also identified in these studies as background (if pristine conditions are present) or baseline (depending how disturbed is the area covered by the sampling survey) values. Large part of IPB was, and still is, subjected to poly-metallic mineral exploration or mining, being also the focus of environmental evaluation and/or remediation projects on particular areas that, being the target of long-lasting human intervention, represent paradigmatic case-study examples. The exploration and exploitation works carried out by national and foreign private companies were, and still are, very important for innovative achievements in IPB along with copious contributions from the Portuguese R&D public institutions. Presently, LNEG possesses a vast quantity of geochemical data that can be provided for companies that wish to start their activity in the IPB; some of these datasets are compiled to a unique integrative map also presented in this work. Stream-sediments geochemistry, hydrogeochemistry and lithogeochemistry (of outcropping rock and drill-core samples) represent also important sources of geochemical data in regional or detailed studies over specific target areas in the IPB. However, these techniques are beyond the scope of the present paper which aimed at providing a general overview of the importance of soil geochemistry studies in the current knowledge of the IPB.
- Geochemistry of soils and stream sediments in the NE border of the Iberian Pyrite Belt : implications to mineral explorationPublication . Luz, Filipa; Mateus, António; Matos, João Xavier; Gonçalves, Mário Abel Carreira
- 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.