Mineralogical controls on mine drainage of the abandoned Ervedosa tin mine in north-eastern Portugal |
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| Institution: | 1. Czech Geological Survey, Geologická 6, 152 00 Prague 5, Czech Republic;2. University of Namibia, Faculty of Earth Science, Department of Geology, Private Bag 13301, Windhoek, Namibia;3. Czech Hydrometeorological Institute, Air Quality Protection Department, 14306 Prague 4, Czech Republic;4. Institute of Geochemistry, Mineralogy and Mineral Resources, Charles University in Prague, Faculty of Science, Albertov 6, 128 43 Prague 2, Czech Republic;1. Institute of Water Sciences and College of Engineering, Peking University, Beijing, China;2. Shaanxi Key Laboratory of Comprehensive Utilization of Tailing Resources, Shangluo University, Shaanxi, China;3. CSIRO Land and Water, Private Bag No. 5, Wembley, WA 6913, Australia;4. School of Environmental Science and Engineering, South University of Science and Technology of China, Shenzhen, China;5. Department of Geological Science, University of Alabama, Tuscaloosa, AL, USA |
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| Abstract: | The Ervedosa Mine, in north-eastern Portugal, has Sn-bearing quartz veins containing cassiterite and sulphides that cut Silurian schists and a Sn-bearing muscovite granite. These veins were mined for Sn and As2O3 until 1969. Cassiterite, the main Sn ore, has alternate lighter and darker growth-zones. The darker zones are richer in Fe, Nb, Ta and Ti, but poorer in Sn than the adjoining lighter zones. Exsolution blebs of ferrocolumbite, manganocolumbite, Ti ixiolite, rutile, ilmenite and rare wolframite were found in the darker zones. Arsenopyrite is the most abundant sulphide and contains inclusions of pyrrhotite, bismuth, bismuthinite and matildite. Other sulphides are pyrite, sphalerite, chalcopyrite and stannite. Secondary solid phases consisting mainly of hydrate sulphate complexes of Al, Fe, Ca and Mg (aluminocopiapite, copiapite, halotrichite, pickeringite, gypsum and alunogen, meta-alunogen) occur at the surface of the Sn-bearing quartz veins and their wall rocks (granite and schist), while oxides, hydroxides, arsenates and residual mineral phases (albite, muscovite and quartz) occur in mining tailings. Toxic acid mine waters (acid mine drainage AMD), which have high conductivity and significant concentrations of As, SO4 and metal (Cu, Zn, Pb, Fe, Mn, Cd, Ni and Co), occur in an area directly affected by the mine. Surface stream waters outside this area have low conductivity and a pH that is almost neutral. Metal and As concentrations are also lower. Stream waters within the impact area have an intermediate composition, falling between that of the AMD and the natural stream waters outside impact area. Waters associated directly with mineralised veins must not be used for human consumption or agriculture. |
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