Distribution of Metals in Vadose Zone of the Alluvial Plain in a Mining Creek Inferred from Geochemical, Mineralogical and Geophysical Studies: The Beal Wadi Case (Cartagena-La Union Mining District, SE Spain)

The assessment of metals dispersal in polluted mining areas is a very complex issue, usually needing data from several analytical techniques in a joint approach. The present work focuses on the impact of the mining activity on lowlands alluvial plain sediments from an ephemeral creek, their role as source or sink of pollution and the spatial distribution of metals within the zone. In-depth distribution of elements (As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, S, Ti and Zn) coming from mining activities was investigated by using X-ray fluorescence techniques and their mineralogical form using X-ray diffraction. A 2-D electrical resistance tomography field survey was carried out throughout at the creek bed to interpret the potential relationships between chemical, mineralogical and geophysical parameters. The application of leaching procedure (DIN 38414-S4 test) allows us to know the sediment's heavy metals hazard and their potential mobility when changing redox conditions. From the results it was found that redox process of sulphur and the presence of carbonate influence the distribution of metals along the profile. In the present work, the precipitation of carbonates seems the most important process, especially for elements such as Zn and Mn. Secondary precipitation of sulphides enables the trapping of metals at sulphur-rich levels.