Rare earth elements in mineral waters in Serbia

The systematically varying properties and generally coherent and predictable behavior of rare earth elements (REE) make them potential tracers for studying water/rock interaction and weathering processes. In this work, a compilation and analysis of REE data in mineral and thermal waters were performed, focusing on their content and distributions in different hydrogeological systems, to quantify the natural REE variability and to discuss the controlling factors of REE concentrations. Quantitative challenges presented by multiply censored data were addressed with nonparametric and multivariate statistical methods. Considering a regional character of the research the application of Q and R mode Hierarchical Cluster Analysis with spatial analysis was an important approach for meaningful interpretation of large data set. An efficient approach to analyze differences between obtained HCA groups (clusters) was using a plot of reference-normalized concentrations. The results showed that REE data along with anomalies of Ce and Eu and inter-element ratios were good indicators of the aquifer lithology (hydrogeological systems formed in granitoid and volcanic rocks of various age, two main types of hydrogeological basins, and carbonate aquifers). The important mechanisms controlling REE migration in water were hydrochemical conditions in aquifers. The significance of the applied statistical analyses was represented by defining specific hydrochemical fingerprints of identified hydrogeological systems with distinct geochemical characteristics where REE showed the necessity of understanding of complex geological and hydrogeological settings, geodynamic evolution, and hydrogeochemical processes in fluid flow systems.