Caracterización geoquímica y mineralógica de la contaminación natural en un nacedero ubicado en la cuenca alta del Río Negro, municipio de Fómeque, Cundinamarca

Abstract

The project aimed to characterize natural water contamination at a spring located in the upper basin of the Negro River, in the municipality of Fómeque, Cundinamarca, through geochemical and mineralogical analysis of rocks, precipitates, and water. The research involved a literature review, fieldwork, and laboratory analysis. Rock and precipitate samples were collected for characterization via X-ray fluorescence (XRF), X-ray diffraction (XRD), and petrographic analysis. Additionally, physicochemical water parameters and concentrations of dissolved metals, sulfates, and other anions were evaluated at two sampling points. The results revealed differences in the system's hydrogeochemical conditions. The first point showed a pH of 3.25, an iron concentration of 160.85 mg/L, and sulfate levels of 1,265.42 mg/L, whereas the second recorded a pH of 6.23, iron at 68.90 mg/L, and sulfates at 726.55 mg/L. Mineralogical characterization identified pyrite in the rock, as well as mineral phases associated with iron oxides and hydroxides, clays, quartz, and secondary sulfates. These findings indicate that the natural oxidation of sulfide minerals—particularly pyrite—is a fundamental process driving acidity generation, the mobilization of chemical elements, and the formation of ferruginous precipitates responsible for the reddish coloration observed at the spring. It is concluded that the evaluated system represents naturally occurring acid rock drainage, primarily associated with the Macanal Shale Formation.