Assessment of the acid mine drainage potential of waste rocks at the Ak-Sug porphyry Cu–Mo deposit

• Published in: Journal of geochemical exploration 2015-10, Vol.157, p.1-14
• Main Authors: Abrosimova, Natalya, Gaskova, Olga, Loshkareva, Alexandra, Edelev, Alexey, Bortnikova, Svetlana
• Format: Article
• Language: English
• Subjects: Acid generation potential; Mine drainage prediction; Neutralization potential; Waste rocks
• ISSN: 0375-6742; 1879-1689
• DOI: 10.1016/j.gexplo.2015.05.009

This investigation was conducted using waste rock materials from the Ak-Sug porphyry Cu–Mo deposit, which is located in the northeastern region of the Tuva Republic in Russia. To predict the formation of acid mine drainage, the waste rocks were investigated using X-ray fluorescence with synchrotron radiation spectroscopy (XRF-SR), X-ray diffraction analysis (XRD), microscopy, and aqueous leaching and intensive oxidation experiments. In addition, the sulfide and carbonate contents were determined to calculate the net acid potential. The waste rock materials were generally low potential sources of acid mine drainage. Only 26% of the rock samples produced acidic effluent following long-term storage. In the results that were obtained from the complete oxidation of the waste rocks, the drainage solutions that were generated had elemental concentrations that exceeded the following MPC (Maximum Permissible Concentrations): Fe — 560 times; Cu — 43 times; Mn — 23 times; Mo — 20 times; As — 50 times; Cd — 19 times; Sb — 17 times; Se — 7.5 times; and Co — 4.5 times. Arsenic was of particular concern in the waste rocks due to its high concentrations, with more than 50% of the samples containing arsenic at concentrations of more than 10g/t and with a maximum concentration of 450g/t. Arsenic can leach rapidly in neutral and sub-alkaline solutions (which were dominant in the aqueous extracts of the investigated rocks). The change of the element species in solutions was shown by the WATEQ4F calculations. Occurrences of sulfate complexes of the elements resulted in higher concentration of Al, Fe and Mn in the solution. The most environmentally hazardous species Me(H2O)62+ of copper, zinc, and cadmium begins predominate in drainage solutions during a long storage of the sulfide-containing wastes. WATEQ4F equilibrium calculations indicated that in acidic solutions the partial dissolution of the hydroxides and oxides of Al, Fe, and Mn, and the substantial desorption of the potentially toxic elements from their hydrated surface and crystal lattice will occur. These results will be used for modeling and designing waste dumps, which could prevent acid production. •The waste rocks of the Ak-Sug deposit were generally not potential sources of AMD.•50% of the samples contain As at 10g/t (maximum content is 450g/t).•Me(H2O)62+ species of Cu, Zn, Cd begins predominate in acid drainage solutions.•Dissolution of Al, Fe, Mn phases and desorption of metals occur in acid solutions.