Geochemical interpretation of long-term variations in rare earth element concentrations in acidic hot spring waters from the Tamagawa geothermal area, Japan

The rare earth elements (REE) concentrations in the waters of Obuki hot spring, Tamagawa geothermal system, Akita Prefecture, Japan, have been determined in order to investigate their long-term variations over a 30-year period. The temporal patterns of REE and SO42− concentrations are synchronous. Leaching experiments using source rock demonstrated that the relatively high REE concentrations in the waters were likely the result of dissolution of near-surface rocks by the acidic waters. The non-magnetic mineral group, enriched in light rare earth elements (LREE) and Eu(II), is easily attacked by the acid solution. The LREE will be selectively dissolved from the non-magnetic mineral group when the SO42− concentration is increased by SO2 derived from magmatic gases.