Geochemical and mineralogical characterization of tailings of the Dexing copper mine, Jiangxi Province, China

The Dexing copper mine is the largest open pit copper mines in Asia, with mining and beneficiation history stretching back more than half a century; consequently it has large amounts of ore tailings. The mineralogy, chemical composition and distribution of elements in the impounded tailings are of great significance to the future utilization and reclamation of the tailings ponds. In total, 1400 tailing samples from 35 drill cores were collected from the 1 tailings pond at the Dexing copper mine. All samples were analyzed to determine their chemical composition. The particle size, XRD, pH and sequential extraction fractions of selected samples were determined. The silt-size fraction dominates the grain-size distribution. Quartz and sericite are the most abundant gangue minerals in the tailings, with medians of 54.3 and 23.7%, respectively. 3D modeling of the tailings pond suggests that the distribution of particle size, minerals and elements is mainly controlled by the gravitational separation during tailings discharge. Silica, Cu, Mo and Ti are enriched in the dam area of the tailings pond, whereas Al2O3 and K2O are enriched in the impoundment area. The potential Cu, Ti and sericite reserves in the tailings pond were estimated at 38 149 tons, 142 175 tons and 8.15 million tons, respectively. The tailings are not significantly oxidized and so their environmental risk is low under the present circumstances. Their weak alkalinity and presence of carbonate minerals provide the tailings buffering capacity to weak acids. Sequential extraction data suggest that the mobility of elements in the tailings pond is low; however, about 6040 tons of Cu, 428 tons of Zn, 252 tons of Mo, 145 tons of As and 66 tons of Pb, may be released if the physicochemical conditions change and the tailings become acidic.