Geochemistry of soils, stream sediments and waters close to abandoned W–Au–Sb mines at Sarzedas, Castelo Branco, central Portugal

Abstract

ABSTRACT In the Sarzedas area, central Portugal, the Cambrian schist–metagreywacke complex predominates and is intersected by W–Au–Sb quartz veins and Sb–Au-bearing felsitic dykes, which were exploited for W, Au and Sb at the Gatas–Santa and Pomar–Galdins mines. The soils from the Gatas–Santa and Pomar–Galdins areas contain up to 11 000 and 21 600 ppm Sb, respectively. In the Sarzedas area, the stream sediments contain up to 840 ppm Sb. Only some surface waters contain Sb, which reaches 2.6 mg l −1 . The waters have pH values of 5.5–7.3; they are neutralized by carbonate intercalations in the schist–metagrawacke complex. The mine wastes contain ferberite and sulphides, and have goethite and ferrihydrite coatings, which have up to 8.10 wt% Sb 2 O 5 and 2.26 wt% As 2 O 5 and contain inclusions of stibnite, arsenopyrite and pyrite. The highest Sb and As concentrations in soils, stream sediments and surface waters are related to the mineralized veins and dykes and mine wastes. The good correlation between W, Sb and As contents in soils from Gatas–Santa and good correlation coefficients for W–Sb, W–Pb and Sb–Pb in stream sediments from Gatas–Santa and Pomar–Galdins are due to the weathering of ferberite, stibnite, arsenopyrite and galena from mineralized veins and dykes and mine wastes. Soils, stream sediments and waters from the Sarzedas area are contaminated, which is consistent with findings for comparable effects in historical Sb mine sites elsewhere in Europe and Australasia, but the Sarzedas waters contain the highest Sb concentration and the lowest As concentration.