The mobility of rare-earth elements during hydrothermal activity: A review

Abstract

The mobility of the rare-earth elements (REE) during hydrothermal activities is increasingly documented. Geological and experimental evidence suggests that REE may be mobile in solutions rich in F-, Cl-, HCO3 -, CO3 2-, HPO4 2-, PO4 3-, or in combinations of the above ligands, even though little has been known about which ligand or which combination is most effective in mobilizing REE. The fractionation of REE resulting from hydrothermal activities is inconsistent. One set of field data implies the preferential mobility of the light rare-earth elements (LREE), whereas another set of field observations indicates the dominant mobilization of the heavy rare-earth elements (HREE), and some theoretical prediction is contradictory to the field evidence. The Eu anomalies due to hydrothermal activities are complex and plausible explanation is not available. The existing experimental approaches dealing with REE are not adequate for explanation of REE behaviour in aqueous solutions. Systematic experimental approaches are suggested.