Major, trace and rare earth elements geochemistry of geothermal waters from the Rehai high-temperature geothermal field in Tengchong of China

Abstract

Major and trace elements geochemistry of high-temperature geothermal waters are important for understanding the subsurface transport and transfer of mass during groundwater circulation. The major constituents and trace elements, including rare earth elements, are discussed to reveal the source of elements and the hydrogeochemical processes occurring in the geothermal waters in the Rehai high-temperature geothermal field in Southwest China. Neutral-alkaline bicarbonate geothermal waters and acid sulfate waters are observed in Rehai due to different genesises. The bicarbonate waters contain higher concentrations of Na, K, Cl, HCO3, Li, Be, F, Sc, Ti, V, Cr, Ga, Rb, Nb, Sb, Cs, W, Tl, Zr and Si and less SO4 than the sulfate waters. The hydrogeochemical analyses show that the recharge of magmatic fluids, mixing with cold water and water-rock interaction affect the concentration of the elements. The geothermal waters and host rock REE chondrite-normalized patterns and the Eu anomalies are inherited from the host rock signature. Negative Ce anomalies may result from oxidative scavenging process of Ce and/or adsorbtion by the precipitation of Fe oxyhydroxides. T, TDS, pH and Fe/Mn minerals all affect the REE concentrations of geothermal waters. Calculations of REE speciation show that in the alkaline waters, Ln(CO3)2- is the major speciation. In the neutral waters, Ln(CO3)2- and LnCO3+ are the main speciation. In the weak acid waters, LnCO3+ is the main speciation and LnSO4+ are the major speciation in the strong acid water.