Soil metal pollution from former Zn–Pb mining assessed by geochemical and magnetic investigations: case study of the Bou Caid area (Tissemsilt, Algeria)

International audienceAbstractFormer zinc and lead mines that have beenoperating for half a century are located in the massif of BouCaid (Tissemsilt, Algeria). Hazardous heavy metals emit-ted from the mines are abundant in the surrounding soil andcause strong metal pollution in the region. This paperinvestigates the extent of lead and zinc mine activityderived pollution by characterizing both magnetic andgeochemical properties of samples collected in the vicinityof the mines. The results of the magnetic study show thecoexistence of magnetic minerals such as magnetite,hematite and goethite. Analyses on surface soils andweathered rocks suggest that hematite and goethite haveore-related lithogenic origins. Magnetic susceptibilityshows a positive correlation with lead content when presentin low-to-medium concentrations (\*500 mg/kg). Athigher lead concentrations, there is no correlation withmagnetic susceptibility. The relationship between magneticsusceptibility and zinc content is not straightforward. Theseobservations are explained by the higher affinity of Pb toiron oxides at lower pollution levels and their preferentialbonding to carbonates when Pb and Zn contents areextremely high, as demonstrated by Iavazzo et al. (J Geo-chem Explor 113:56–67,2012) in a study of former Zn–Pbmine in Morocco. Based on the general features of thespatial maps of field-measured magnetic susceptibility,mass-specific magnetic susceptibility, Pb and Zn contents,it is concluded that field magnetic measurements provide agood qualitative proxy of pollution spread out of themining galleries, while laboratory measurements afford amore detailed investigation of the links between iron oxi-des and the main heavy metals in the ore