GEOCHEMISTRY OF Na-HCO3 GROUNDWATER AND SEDIMENTARY BEDROCKS FROM THE CENTRAL PART OF THE SIKHOTE-ALIN MOUNTAIN REGION (FAR EAST OF RUSSIA)

Abstract

New data on major element, trace and rare-earth element (REE) contents of groundwaters and sedimentary bedrock in the Lastochka Spa in the Primorye region of far eastern Russia, together with previous stable isotope data (δD, δ13C(TIC), and δ18O), allow elucidation of the origin and evolution of groundwater from the spa. The sedimentary bedrock in this area is mainly highly-permeable sandstone. Dominant minerals are K-feldspar, quartz and plagioclase, and secondary minerals are calcite, limonite, sericite and kaolinite. Bedrock samples are enriched in light REE (LREE) and depleted in heavy REE (HREE) and samples where calcite fills the fractures have positive Eu anomalies. Two types of groundwater issue from spring and wells in the study area: fresh water with low mineralization (TDS up to 0.4g/L) and high pCO2 water with high mineralization (TDS up to 4.7g/L). Isotopic data indicate that both types of groundwater are meteoric in origin having a short residence time. Groundwaters are characterized by enrichment of HREE in comparison with LREE and a positive Eu anomaly. Mass balance calculations are consistent with albite dissolution, with or without CO2 of deep-seated mantle origin as the dominant factor controlling the chemical composition of the groundwater.