Arsenic and metals transport processes in surface waters from the mining district of Taxco, Mexico: Stable isotopes application

Abstract

Water isotopic ratios 18O/16O, 2 H/H and 34S/32S in dissolved sulfates were measured to determine sulfur provenance and dominant processes of transport, and, distribution of As and metals in surface waters in the mining district of Taxco. Zinc, Cd, Cu, Fe, Pb and As were analyzed in river and stream waters located nearby mine tailings. ?18O and ?D values (dry season) showed a lower slope (?D = 3.998 * ?18O ? 29.02) than the Global Meteoric Water Line (GMWL, ?D = 8 * ?18O + 10) indicating an evaporation process. In the rainy season, the slope (?D = 6.109 * ?18O ? 9.69) approximates to the GMWL showing an input of meteoric water to rivers. ?34S values in dissolved sulfates vary from ?6.8 to +2.2 (dry season) and from ?5 to ?0.6 (rainy season), indicating a sulfur source from sulfides oxidation and erosion. Clustering analysis showed that rivers and streams conditions are very similar to those of the tailings in the dry season, but not in the rainy season, with exception of TX3. This similitude exhibits the significance of seasonal changes in weathering and washing off processes from tailings, with further transport by runoff into surrounding water bodies. Variation in metal concentrations (dry and rainy seasons) indicates two-coupled processes: 1) discharge-erosion and 2) proportional dilution. Plot of ?18O vs ?34S confirms weathering of material from the basin and tailings with a wide and heterogeneous pattern in the dry season, while in the rainy season results indicate erosion and mixing of particles.