The study of rare earth elements in farmer's well waters of the Podwiśniówka acid mine drainage area (south-central Poland)

The principal objective of the current study was to elucidate the potential influence of acid mine drainage (AMD) pond on neighboring farmer's wells in the Podwiśniówka area (south-central Poland), using North American Shale Composite (NASC)-normalized rare earth element (REE) concentration profiles. The well waters generally displayed a distinctly positive Eu anomaly similar to that of parent rocks and AMD sediment. In contrast, the AMD pit pond water exhibited the typical roof-shaped NASC-normalized REE concentration pattern with a strong positive Gd anomaly. The low pH (mean of 2.9) of this pond water is induced by oxidation of pyrite that occurs in quartz veins and rocks exposed in the abandoned Podwiśniówka quarry. The principal source of REEs in turn is a crandallite series of aluminum–phosphate–sulfate (APS) minerals (gorceixite with florencite and Ce-bearing goyazite) that prevail in most clayey shales. These data indicate that the REE contents of the AMD pit pond and well waters are linked to bedrock mineralogy and lithology, but not to pyrite mineralization. The diverse REE patterns of NASC-normalized REE concentrations of the AMD and well waters may suggest complex sorption and desorption processes that occur at the rock–water interface influenced by different pH, Eh, temperature, and other factors. This is evidenced by a presence of strong positive Ce anomaly in the rocks, a lack of Ce anomaly in the AMD water and sediment, and the dominant negative anomaly of this element in the well waters. Variations in correlation coefficients (r 2) of REE concentrations between the rocks and the well waters may also result from a different contribution of quartzites, clayey shales, or tuffites to the REE signal of well waters as well as from mixing of shallow groundwater with infiltrating rainwater or meltwater with different REE profiles.