Weathering behavior and metal mobility of tailings under an extremely arid climate at Jinchuan Cu-Ni sulfide deposit, Western China

A detailed mineralogical and geochemical study of a sulfide tailings impoundment was carried out in Jinchuan Cu-Ni sulfide deposit in western China. Since 1963, the tailings impoundment has been exposed to weathering in an extremely arid climate with dry-warm seasons. Samples from different depths of two boreholes, each located in the center and border of the impoundment, were analyzed to evaluate the oxidative weathering behaviors of the tailings. The obvious shift of Cu and Ni from the sulfide fraction to more mobile forms, increasing trend of SO42 − in the shallow of the tailings and decreasing trend of Fe content in sulfide fraction, show direct signs of sulfides oxidation, especially in the upper part of the tailings impoundment. Besides the upward migration of Ca2 + and SO42 − under the strong evaporation in hyper-arid climate, the heavy metals of Cu and Ni are retained by the in-situ adsorption and/or co-precipitation with secondary Fe3 + precipitates. These secondary minerals are poorly crystalline and unstable. So, for sulfide tailings with a simultaneous large production of carbonates and under extremely arid climate, acid pollutants can be avoided but heavy metal pollution from the windblown dust of secondary minerals is the key pollution source that should be taken seriously.