The geochemistry of Co and Cu in the Kafue River as it drains the Copperbelt mining area, Zambia

Samples of the dissolved (<0.45 μm) and suspended (>0.45 μm) phases have been collected in the Kafue River during a 1-year cycle. Within the mining area, the concentrations of Co, Cu and S in the river occasionally increase more than 100 times compared to concentrations upstream from the mining area. The highest concentrations of dissolved Cu (3.4 μM) and Fe (4.2 μM) are found during high water discharge, probably indicating a washout of leached weathering products from spoil heaps. High levels of Co appear to originate from one point source, the location where the Co ore is treated. In the Kafue River, secondary Mn- and Fe-rich particles are formed, on which Co and Cu, respectively, are enriched. The elements associated to secondary Fe and Mn particles are enriched at the sediment surface in the river due to redox processes. Hence, secondary particles and sorbed trace elements may be resuspended and transported further downstream in the river system. However, very high concentrations of Cu (1%) and Co (0.1%) in the sediment are caused by primary sulphides.