Natural factors and mining activity bearings on the water quality of the Choapa basin, North Central Chile: insights on the role of mafic volcanic rocks in the buffering of the acid drainage process

摘要: This contribution analyzes water chemical data for the Choapa basin, North Central Chile, period 1980–2004. The parameters considered are As, Cu Fe, pH, EC, SO\(_{4}^{-2}\), Cl − 1, and HCO\(_{3}^{-1}\), from samples taken in nine monitoring stations throughout basin. Results show rather moderate contents of Cu, with exception Cuncumen River Auco creek, explained by influence huge porphyry copper deposit Los Pelambres presence mining operations, respectively. When compared against results obtained previous researches at neighboring Elqui river which host El Indio Au–Cu–As district, a much reduced grade pollution is recognized Considering effect acid rock drainage (ARD)-related on fine fraction sediments both basins, differences recorded even more striking. Although deposit, headwaters between one two orders magnitude bigger than Indio, stream former exhibit significantly lower those latter. A main factor may explain these smaller degree H + -metasomatism rocks where mafic andesitic volcanic presenting propylitic hydrothermal alteration dominant. fact contrast highly altered most them have lost their potential to neutralize ARD.