Rare earth element contents in high pCO2 groundwaters of Sakhalin Island (the Far East of Russia)

The geochemistry of rare earth elements in cold, high pCO(2) mineral waters was studied through the sampling of springs and boreholes of Sakhalin Island (the Russian Far East). The main common features of studied waters are the Na-Cl-HCO3 hydrochemical type, high TDS (6-20 g/L), alkaline pH (6.2-7.4), and reducing environment (-195 to +62 mV). The North American Shale Composite-normalized patterns of groundwaters exhibited a heavy REEs enrichment with high positive Eu anomalies. Both, positive and negative Ce anomalies were detected in CO2-rich mineral waters. The distinct positive Eu/Eu* in waters indicates water-rock interaction processes and positive Ce/Ce* corresponds to reducing conditions. The various processes responsible for negative Ce anomaly in reducing environment are described.