Mining waste acting as a precursor of environmental stress in sediments

Abstract Waste generated by mineral extraction is globally associated with environmental disturbances due to its deleterious effect on water resources. However, research focused on the influence of mine tailings resulting from the extraction of semi-precious stones on fluvial systems is still incipient in the environmental literature. From this perspective, this study quantified the average concentrations of major oxides present in the fine fractions of the sediment samples from the Várzea river, in the State of Rio Grande do Sul, southern Brazil, using wavelength dispersive X-ray fluorescence spectrometry. This region is acknowledged as the largest rock amethyst mining area in the world. Additionally, geochemical indices were established to characterize potential sources of production, maturity, degree of weathering, and sediment pollution. To evaluate the influence of mine tailings on the Várzea river sediments, the contents of Al2O3, Fe2O3, MnO, P2O5, CaO, SiO2, K2O, CuO, ZnO, and TiO2 major oxides present in sediment samples were determined and compared to the local background values; the values varied significantly (p < 0.05), classifying them as polluted and medium polluted. Also, the sediment samples with evident characteristics of extreme chemical weathering consist mainly of clay minerals and mafic igneous rocks, and similarities were found between sediment samples and tailings from the mineral extraction zone. The Principal Component Analysis and the cluster analysis also suggest the existence of three distinct mineral oxide groups, differentiating the zones leaving and upstream the mining zone from the other sampling points.