Geochemical Behavior of Mine Tailings and Waste Rock at the Abandoned Cu-Mo-W Azegour Mine (Occidental High Atlas, Morocco)

The abandoned Azegour mine is located in the High Atlas Mountains of Marrakesh (Morocco), and was mined for Cu, Mo, and W. About 850,000 t of waste rocks and tailings were deposited on the surface and have been exposed to weathering for 40 years. The remaining acid-producing potential (AP), acid-neutralizing potential, and geochemical behavior of the Azegour Cu-and Mo-rich tailings were investigated. The tailings were found to contain 9.6-19 wt% sulfur, mostly as sulfate (gypsum, anhydrite, and jarosite) while the waste rocks contain less (1.25-6.58 wt%) sulfur. The waste rocks and tailings contain 0.21-9.24 wt% Mo and 0.003-2.78 wt% Cu. The gangue is mostly composed of quartz, talc, chlorite, pyrophyllite, actonolite, clinoptilolite, and alusite. Lead, zinc, cobalt, arsenic, titanium, and nickel are also present. The calcium, which is mainly expressed as calcite, gypsum, scheelite, and powellite, is present at higher concentrations in the waste rocks (18-22 wt% Ca) than in the tailings (4.7-8.6 wt% Ca). Static ABA determinations showed that the Azegour mine wastes still have high AP, 38-205 kg CaCO3/t in the waste rocks and 46-387.7 kg CaCO3/t in the tailings. This was confirmed in weathering cell tests, where the Azegour tailings leachate had a pH range of 1.98-3.19 and high concentrations of SO4 (468-45,400 mg/L), Ca (230-675 mg/L), Fe (3-55,900 mg/L), Mn (0.1-1,430 mg/L), and Cu (2.3-9,000 mg/L). The Mo concentrations were high (35 mg/L) during the two first weeks of kinetics tests; W concentrations were below the 0.005 mg/L detection limit.