Geochemical anomalies for the determination of surface stream sediments pollution: case of Sierra de Cartagena-La Unión mining district, Spain.

This work explores the ability of the Spanish Geochemical Database to identify the existence of polluted stream sediments due to the presence of abandoned mine wastes. The mining district of Sierra de Cartagena-La Unión has been used as test area. A total of 18 abandoned tailings facilities were selected and samples were taken for analysis of the content in potential toxic elements. The results were contrasted with geochemical background values in order to identify which geochemical elements could entail anomalies potentially reflected in the Spanish Geochemical Database. For the study area, As, Cd, Pb, and Zn have been identified as potential toxic elements which can be used as geochemical indicators of sediment pollution processes originated in abandoned mine wastes. Furthermore, the correlation between Cd and Zn allows them to be considered as the best indicators of potential sediment contamination. The study of anomaly thresholds, through the analysis of accumulated frequencies of the contents of these elements in the sediments of the Spanish Geochemical Database, allows identifying sediments that may have been contaminated. A Mann-Whitney test contrasting the data of tailings, polluted sediments, and non-polluted sediments has been performed in order to verify differences among these types of samples. In addition, a geospatial analysis has demonstrated a very close relationship between contaminated sediments and the presence of mining wastes upstream. This methodology can be applied to any other mining region, to recognize the possible influence of pollution processes derived from the presence of abandoned mine wastes taking advantage of existing geochemical databases.