DISTRIBUTION PATTERNS OF CONTAMINANTS IN THE MOGALE GOLD TAILING DAM; CASE STUDY FROM SOUTH AFRICA

The exposure of mine wastes such as tailings dams, waste rocks to oxidation and leaching has been the source of heavy metal release into the environment and its impacts has led to growing researches to alleviate the threat posed. This study assessed the magnitude of possible leachable metals, its distribution and associations and predicted the AMD load discharge over time, from Mogale’s tailings dam into the environs in Randfontein area, Witwatersrand Basin, South Africa.

Fifty-one tailings dam samples were analysed for their mineral and multi-elements contents. Petrography studies was done by X-Ray Diffraction (XRD) technique to determine the mineralogical composition. X-ray fluorescence (XRF) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) techniques were used to determine the multi-elements content in the tailings dam samples. The dataset were evaluated using multivariate statistics, Geographical Information Systems (GIS) and geochemical mass balance techniques.

From the results, the tailings dam lithology was grouped into four distinct layers. The layers are composed of varying proportions of quartz, muscovite, pyrophyllite, gypsum, jarosite, delhayelite?, hematite, pyrite and clinochlore based on the XRD results. The uppermost oxidized layer is siliceous and contains the highest SiO₂ (87.32%) contents, which is accompanied by the lowest contents in Tot/S, U, As, Zn, Ni, Co, and Cu. A downward decrease in SiO₂ (76.39%) contents occurs, coupled by an increase in Fe₂O₃, Tot/S, U, As, Zn, Ni, Co, and Cu, reaching maximum contents in layer 3. Layer 4 is the least weathered horizon.

The cluster analysis grouped the samples into four sub-clusters based on the variation in SiO₂ and Al₂O₃ contents. Factor analysis (83.542% total data variance) related the seven controlling factors of element distribution to the occurrence in ore elements (sulphides), silicates, mining additives and refractory minerals. Elements of the same origin show a similar concentration trend down hole in the GIS interpolation analysis. The geochemical mass balance showed variable gain and loss of oxides and trace elements within each layer. Based on the variation patterns of the Tot/S contents and other mobile elements, about 0.164kg/tonne/yr(±0.02) of the tailings materials are leached yearly. Layer 1 is the most altered.