The environmental impact of gold mine tailings footprints in the Johannesburg region, South Africa

Gold mining in South Africa resulted in vast volumes of tailings, which have been deposited in impoundments. Poor management of most of the tailings dams resulted in the escape of seepage, adversely affecting soils and water quality. Some tailings dams have been partially or completely reclaimed leaving contaminated footprints. These zones pose a serious threat to the underlying dolomitic aquifers. In this study, the footprints of seven selected sites situated near Johannesburg have been investigated. It was found that the topsoil is highly acidified and only a minor portion of contaminants is bioavailable. However, phytotoxic contaminants such as Co, Ni and Zn could complicate rehabilitation measures as they limit the soil function. In addition, soil samples contain trace element concentrations, which often exceed background concentrations in soils. As a result, the depletion of buffer minerals and the subsequent acidification could result in the long-term remobilization of large quantities of contaminants into the groundwater. Soil management measures such as liming are required to prevent the contaminant migration from the topsoil into the subsoil and groundwater as well as to provide suitable recultivation conditions to enable future land use.AB: Resume Les exploitations d'or en Afrique du Sud s'accompagnent de la production de grands volumes de dechets stockes dans des digues a steriles. Un controle insuffisant de la plupart de ces digues a steriles a pour consequence des fuites qui affectent la qualite des sols et des eaux souterraines. Quelques digues a steriles ont ete partiellement, ou totalement remises en etat, laissant cependant des taches de contamination. Ces zones representent une menace serieuse pour les aquiferes dolomitiques sous-jacents. Dans cette etude, les taches de contamination de sept sites selectionnes pres de Johannesburg ont ete etudiees. On a trouve que le sol de surface est fortement acidifie et seulement une faible proportion de polluants est bien degradable. Des polluants toxiques pour la vegetation, tels que cobalt et nickel, pourraient compliquer les mesures de rehabilitation dans la mesure o ils alterent les fonctions d'epuration des sols. De plus, les sols contiennent des concentrations d'e1ements traces, qui depassent souvent les concentrations regionales des zones non polluees. En consequence, la liberation de mineraux tampons et l'acidification resultante pourraient conduire a une remobilisation, sur le long terme, de