Metal deportment in Pb-Zn mine wastes from a historic tailings pond, Plombières, East Belgium

•In-depth characterisation of different mine waste materials from the same tailing pond.•Sources of metals of interest (Pb and Zn) are different mineral and slag phases.•Low abundance of Pb/Zn phases causes a nugget effect.•The chemical heterogeneity of slags exacerbates the nugget effect.•The approach is applicable to different mine waste deposits around the globe.