Metals retention after weathering of a sulphide ore body: unexploited gossan versus mine tailings.

Numerous studies have highlighted the fact that the bioavailability of potentially toxic trace elements (PTTE), such as As, Cd, Cr, Cu, Ni, and Pb, is strongly related to the redox state and chemical form. Since dissolved forms of trace elements are the most bioavailable, the issue of greatest concern is to define the conditions under which these elements may be remobilized in solution up to levels higher than those recommended by National agencies as e.g. the Environmental Protection Agency (EPA). In order to understand and then ideally to prevent trace element mobilization, the characterisation of the contaminant sources, i.e. the solid fraction, is crucial