Abstract
Mine wastes from the La Aurora mine in the state of Guanajuato were generated by the flotation process and placed in four tailing dumps on the local stream while the plant operated. Given that these wastes contain toxic elements, it is important to establish their impact on the quality of several surrounding natural sources of water that are considered potential drinking water supplies. This study identified four water source types, in which the contents of arsenic (As), mercury (Hg), and thallium (Tl) were exceeded, according to international guideline values for drinking water quality. The first type of aqueous sample corresponded to leachates produced by rainwater infiltration in tailings and water–mineral waste interactions. The second type corresponded to surface water along the Xichú and La Laja Streams, and the third and fourth types involved two groundwater well samples and spring samples, respectively. The Chiquito Stream was used as a reference area that had not been impacted by the mine wastes. The isotopic signatures associated with δ34Ssulfate and δ18Osulfate compositions from the El Ojo de Agua spring are similar to those of the Santa María River and are different from those of the mine waste leachates. This study shows evidence of the presence of As in the El Ojo de Agua spring, which results from dissolution of secondary mineral phases that were produced by alteration of the mine wastes, which then migrated along the Xichú Stream system until reaching the spring. These As-bearing fine particles are prone to dissolution when in contact with this water source. Principal component analysis revealed that the observed As, Tl, and Hg can be attributed to weathering of the mine wastes. However, the results suggest that a natural contribution of these elements could be associated with rainwater–igneous rock interactions.
Highlights
In the absence of adequate control and containment measures, these wastes undergo alteration processes when exposed to environmental conditions [4,7,8]. Some of these abandoned mine waste dumps (AMWDs) that are rich in Pyrite produce acid mine drainage (AMD) via sulfide oxidation processes, and the produced leachates are typically highly acidic and have high concentrations of potentially toxic elements (PTEs), which primarily include arsenic (As), lead (Pb), mercury (Hg), and thallium (Tl) [1,7,9,10,11]
Based on the chemical and physicochemical parameters measured and, mainly through the principal component analysis (PCA) statistical tool, a water quality classification of the different collected samples was proposed, resulting in four water samples classified as uncontaminated (W1, W2, EG, and ES), three as slightly–moderately contaminated (R1, CA, and GA), and the rest of the samples classified as highly–extremely contaminated, including a potential source of drinking water in the region, i.e., the El Ojo de Agua spring
The isotopic compositions of δ18 Osulfate and δ34 Ssulfate allowed the identification of three processes of sulfate fluxes in the study area that correspond to (1) the oxidation of mineral sulfides; (2) the precipitation of secondary sulfate mineral phases produced by AMWD weathering; and (3) sulfate dissolution from evaporites contained in the El Abra Formation
Summary
In the absence of adequate control and containment measures, these wastes undergo alteration processes (physicochemical or biological) when exposed to environmental conditions (precipitation, flood, evaporation, desiccation, solar radiation, drought, and wind) [4,7,8]. Some of these AMWDs that are rich in Pyrite produce acid mine drainage (AMD) via sulfide oxidation processes, and the produced leachates are typically highly acidic and have high concentrations of potentially toxic elements (PTEs), which primarily include arsenic (As), lead (Pb), mercury (Hg), and thallium (Tl) [1,7,9,10,11]. It is important to Toxics 2021, 9, 307 discern whether the presence of these elements is natural or associated with the leachates coming from the AMWDs at the inactive mine known as La Aurora in the Xichú mining district (XMD)
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