Geochemical dynamics of an acid drainage system: the case of the Amarillo River, Famatina (La Rioja, Argentina)

LECOMTE., K.L., MAZA, S.N., COLLO, G., Y DEPETRIS, P.J.

ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH

SPRINGER HEIDELBERG

Lugar: HEIDELBERG; Año: 2017 vol. 24 p. 1630 - 1647

0944-1344

Amarillo River (Famatina range, Argentina, ~29° S and ~67° W) is unusual because acid mine drainage (AMD) is superimposed on the previously existing acid rock drainage (ARD) scenario, as a Holocene paleolake sedimentary sequence shows. In a markedly oxidizing environment, its water is currently of the sulfate-magnesium type with high total dissolved solids concentrations (>5 g L-1 in ARD). At the time of sampling, the interaction with the mineralized zone and remnants of mining labors, determined an increase in some elements (e.g., Cu ~3 to ~45 mg L-1; As ~0.2 to ~0.5 mg L-1). Dissolved concentrations decreased significantly by dilution (i.e., mixing with circumneutral waters), and by precipitation of neoformed solids and subsequent metal sorption (~700 mg kg-1 As, 320 mg kg-1 Zn). Downstream, most metals exhibited a significant attenuation (As 100%, Fe 100%, Zn 99%). Chemical weathering of field rocks partially neutralized water acidity. PHREEQC-calculated saturation indices (SI) indicated that Fe-bearing minerals, especially schwertmannite, were supersaturated throughout the basin. All positive SI increased through the input of circumneutral water. PHREEQC inverse geochemical models showed throughout the middle and lower basin, that about 4.5 mmol L-1 of neoformed minerals were precipitated. The modeling exercise of mixing different waters yielded results with a >99% of correlation between observed and modeled data.