Rare earth element geochemistry of groundwater from a deep seated sandstone aquifer, northern Anhui province, China

Abstract

Deep coal mines in northern Anhui province, China, provide opportunities for tracing the distribution and fractionation of rare earth elements (REEs) in deep seated environments. Major ions, as well as REE concentrations were measured in groundwater from a sandstone aquifer located between –400 and –280 m. Our results indicate that this groundwater consists of Cl·HCO₃-Na or Cl·CO₃-Na water types with warm temperature (30.1–31.4 °C), circumneutral pH (7.27–8.61) and high levels of total dissolved solids (TDS = 1306–2165 mg/L). Concentrations of REEs in groundwater are high as expressed by their Nd concentrations (0.0086–0.018 μg/L). Except for weak heavy REEs (HREE) enrichment relative to light REEs (LREE), the similarity of REE distribution patterns between groundwater and aquifer rock indicate that enrichment of REEs is considered to be controlled by aquifer rock, as well as by their minerals, whereas the fractionation of REEs is controlled by HREE enriched minerals and, to a lesser extent, by inorganic REE complexes. Ce anomalies normalized to Post Archean Average Shale (PAAS) and aquifer rock are weak, which probably reflect the contribution of reduced conditions in combination with pH, rather than a signature of aquifer rock.