Geochemical behavior of rare earth elements associated with hydrothermal alteration: Implication for the migration and retardation of Am and Cm in hydrothermal system

Abstract

  Rare earth element (REE) contents of hydrothermally altered dacitic and basaltic rocks in the Kuroko mining area were analyzed. It was found that geochemical features of REE (Light REE/Total REE ratio, La/Sm ratio, Eu anomaly) are related to K₂O index (= K₂O / (K₂O + Na₂O + CaO + MgO) × 100) and oxygen isotopic composition (δ¹⁸O). This relation indicates that LREE (light rare earth element) did not remove from the rocks to hydrothermal solution and were probably added to the rocks from hydrothermal solution at and near the site of hydrothermal ore deposition. This geochemical behavior of LREE which are considered to be chemical analogue elements for Am and Cm suggests that Am and Cm would not remove from the high level nuclear waste glass if the hydrothermal solution ascent to the disposal site and contacted with the high level nuclear waste.