Geochemistry of waters associated with the old mine workings at Fonte Santa (NE of Portugal)

DOI:10.1016/j.gexplo.2010.05.001The quartz veins containing scheelite from Fonte Santa mine cut the Lower 10 Ordovician quartzites. A muscovite-biotite granite (G1) and a muscovite granite (G2), 11 both S-type, crop out close to the Fonte Santa mine and are related to the Moncorvo - 12 Bemposta shear zone. The most altered samples of G2 show intense muscovitization and 13 microclinization and contain chlorite, columbite-tantalite, wolframite, W-ixiolite and Fe-14 oxides. The tin-bearing granites contain 18 ppm (G1) and 73 ppm (G2) Sn. The most 15 altered samples of G2 correspond to a tungsten granite. The quartz veins contain 16 muscovite, chlorite, tourmaline, scheelite, pyrrhotite, pyrite, sphalerite, chalcopyrite, 17 galena, arsenopyrite, iron oxides, Fe-sulfates, phosphates of Pb, Fe and Al. The Fonte 18 Santa mine area was exploited for W between 1942 and 1982. At the end of November 19 2006, a flood event damaged the tailings dam of Fonte Santa mine, releasing 20 contaminated material and increasing contaminant levels in water within the area of 21 influence of the mine. The waters related to the Fonte Santa mine are poorly mineralized, 22 with electrical conductivity < 965 μS / cm, and of a mixed type or HCO3- and SO42- types. 23 Most pH values (5.0 8.5) indicate that there is no significant acidic drainage in the 24 region, as found in other areas. More acidic values (pH = 3.4) were found in the mine’s 25 lagoon. Waters associated with mineralized veins and old mine activities have Fe and Mn 26 concentrations that forbid their use for human consumption and agriculture. Natural Na, 27 Mg and K water contents are associated with the alteration of albite, chlorite and 28 muscovite of country rock, while Ca with the W-bearing quartz veins. Weathering agents 29 are carbonic and sulphuric acids and the latter has a strong influence in areas draining 30 fine-grained mine tailings