Copper isotopic record in soils and tree rings near a copper smelter, Copperbelt, Zambia.

The copper (Cu) content and isotopic composition were studied in soils and in pine tree rings at locations close to and far from the Cu smelter, located at Kitwe, Zambia. The soil in the remote area contained 25-75mgkg Cu, whereas the soil close to the smelter contained 207-44,000mgkg Cu. The δCu at the remote area and close to the smelter varied in the range -0.40 to -0.11‰, and -0.44 to 0.01‰ respectively. The δCu of the surface soil at both profiles (-0.44 to -0.40‰) is similar to the isotopic composition of the concentrates processed in the smelter (-0.75 to -0.45‰), i.e. both locations are affected by Cu ore dust. The increase in the δCu in the direction towards the centre of the profile is caused by the oxidative dissolution of Cu(I) from ore minerals, during which heavier Cu is released. In deeper parts of the profile, there is a slight decrease in δCu because of easier mobilisation of the lighter isotope. The tree rings at the two locations differ in the total contents and isotopic composition. At the less contaminated site, the Cu contents equal 0.4 to 1.1mgkg while, at the polluted site, the Cu contents vary in the range 3 to 47mgkg. Whereas, at the less contaminated location, the tree rings are substantially enriched in lighter Cu (δCu=-0.76 to -2.2‰), at locations close to the smelter the tree rings have an isotopic composition (-0.31 to -0.88‰) similar to that of the contaminated soil or processed ore. The isotopic compositions of the tree rings close to the smelter are affected particularly by interception of dust containing Cu ore. The δC in tree rings demonstrate the interconnection of acidification and Cu mobility.