Contamination of surface waters by mining wastes in the Milluni Valley (Cordillera Real, Bolivia) : Mineralogical and hydrological influences

摘要: This study is one of very few dealing with mining waste contamination in high altitude, tropical-latitude areas exploited during the last century. Geochemical, mineralogical and hydrological characterizations potentially harmful elements (PHEs) surface waters sediments were performed Milluni Valley (main reservoir water supply La Paz, Bolivia, 4000 m a.s.l.), throughout different seasons 2002-2004 to identify sources sinks, control parameters. PHE concentrations greatly exceeded World Health Organization guidelines for human consumption. The acidic conditions, which resulted from oxidation sulfide minerals waste, favoured enrichment dissolved PHEs (Cd > Zn » As >> Cu ∼ Ni Pb Sn) downstream mine. Stream lake sediments, bedrock showed highest content area. With exception Fe, derived specific (Fe, pyrite; Zn, Cd, sphalerite, As, arsenopyrite, Cu, chalcopyrite, Pb, galena, Sn, cassiterite), but was responsible availability. Most extremely mobile (As Fe Cd wastes pH oxyhydroxides mainly explained contrasted availability (mostly labile fractions) (associated Fe-oxyhydroxides). Unexpectedly, significantly attenuated by organic matter sediments. Hydrological conditions highly influenced behaviours major PHEs. During wet seasons, diluted meteoric waters, whereas increased due dissolution sulfides unstable tertiary that formed dry seasons. particularly obvious at beginning season contributes flushes element transport downstream. altitude area compensates tropical latitude, rendering geochemical behaviour contaminants similar temperate cold regions. These results might be representative processes ore deposits located Andes plateau, their influence on within upper Amazon basin. Although activities this region stopped 10 years ago, impact quality remains a serious environmental problem.