Chemical sterilisation and vetiver grass performance on gold tailings dump chrono-toposequences at Muriel mine, Zimbabwe

Land pollution at gold mine dumps requires sustainable rehabilitation. A study was conducted at Muriel gold mine, Zimbabwe to investigate the integrated effects of dump age, topographic position and soil depth on chemical degradation and vetiver grass ( Vetiveria zizanoides ) performance. The triplicated experiment was set up as a split-split plot, where the fresh dump, old dump and reference site were the main treatments; topographic position (upper, middle, lower) was the sub treatment and soil layer (0-20cm, 20-50cm) was the sub-sub treatment. Samples collected from soil layers were analysed for total lead(Pb), zinc(Zn) and iron(Fe), pH and salinity. Irrigated vetiver growth was monitored over 12 weeks through measuring changes in height, rooting depth and shoot numbers. The old dump was acidic (pH = 4.30 ± 0.207); fresh dump alkaline (pH = 8.32 ± 0.142) and reference site was neutral (pH = 7.9 ± 0.09). Salinity was highest in the 20-50cm layers on old dump lower slopes due to salt concentrating processes of: evaporation, metal dissolution and translocation of cyanidation effluents. Total Pb, Zn and Fe concentrations were highest (p < 0.05) at the old dump; lower (p < 0.05) in the 0-20cm layers and differed (p < 0.05) in the order: upper < middle < lower slope. Soil Zn and Pb concentrations exceeded safe limits at lower slope positions of both dumps. Vetiver growth parameters were 1.5-3 times higher (p < 0.05) on the reference site compared with the dumps. Sterilisation of gold dumps was determined by chemical transformation and translocation processes on the landscape. Expeditious biological rehabilitation of dumps is recommended to evade unsuitable conditions created by rapid acidification.