Title: Mineralogical controls on mine drainage, Ervedosa mine, Northern Portugal
Abstract: At Ervedosa, tin-bearing quartz veins with cassiterite and sulphides cut Silurian schists and quartzites and a Sn-bearing muscovite granite. The veins were exploited at Ervedosa, socalled Tuela mine, for tin (Sn) and arsenic trioxide (As2O3), until 1969. The veins fill faults related to the Hercynian movements along a dextral N30°W shear zone and belong to three paragenetic stages separated by faulting. Euhedral to subhedral crystals of cassiterite are generally <10 mm across or associated in round masses with a diameter of 10 cm. The cassiterite shows alternating parallel darker and lighter zones and the darker zones show exsolved columbite, titanian ixiolite, W Ti ixiolite, niobian rutile and very rare wolframite and ilmenite. Arsenopyrite is the most abundant sulphide and has inclusions of pyrrhotite, bismuth, bismuthinite and matildite. It is replaced by pyrite, chalcopyrite, sphalerite and stannite. At the tin-bearing quartz veins and their granite and schist walls, there are supergenic solid phases consisting mainly of hydrated sulphates of Al, Fe, Mg and Ca (alunogen, metaalunogen, aluminocopiapite, copiapite, halotrichite, fibroferrite, pickeringite and gypsum), while oxides, hydroxides, phosphates, arsenates and residual mineral phases (albite, muscovite and quartz) occur in mining tails. The aim of this study is to compare the acid mine drainage (AMD) with the granitic rock drainage using data collected during winter. The waters at the mining site are toxic and affected by AMD (pH=3.1-3.5), with high condutivity (130726 μS/cm) and significant metal concentrations (As=3-8μg/l, Cu=410-415μg/l, Zn=1919-8370μg/l, Fe= 922-11200μg/l, Ni= 26-95μg/l and Co= 49-118μg/l), while in the superficial granitic waters outside the mine influence the pH measured is close to neutral (pH=5.5-7), with low condutivity (28-35 μS/cm) and metal concentrations are lower (As=0.3-3μg/l, Cu=7-22 μg/l, Zn=108-147μg/l, Fe=50-411μg/l, Ni=6-9μg/l and Co= 0-3μg/l). Waters associated with mineralised veins should not be used for human consumption and agriculture activities. This research was carried out in the programme of Geosciences Centre, University of Coimbra. Formation and transformation of schwertmannite in acid-minedrainage deposits of the Chinkuashih mining area, northern Taiwan
Publication Year: 2005
Publication Date: 2005-05-01
Language: en
Type: article
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