Hydrothermal redistribution of rare earth elements in Toki granitic rock, central Japan

Distribution of rare earth elements (REEs) in granitic rock has been studied to clarify the migration behavior of REEs in granitic rock during alteration. The altered and unaltered rock samples were collected at Toki granitic rock, central Japan. The concentrations of REEs in rock samples were measured by the neutron activation analysis. The concentrations of the light REEs (LREEs) in the altered rock samples were higher than those in the unaltered ones. In contrast, the concentrations of heavy REEs (HREEs) in the altered rock samples were approximately the same as those in the unaltered ones. XRD patterns show that clay minerals were not present in the unaltered rock samples, but were in the altered ones. Both the altered and unaltered rock samples contain apatite, zircon and xenotime, which contain REEs as minor components. Carbonate minerals, calcite, CaCO ₃, bastnaesite, (LREE)(CO ₃)F, and parisite, Ca(LREE) ₂(CO ₃) ₃F ₂ were observed only in the altered rock samples. Calcite filled veins in the altered samples, and bastnaesite and parisite occurred with calcite. Bulk concentration of calcium in the altered rock are higher by a factor of two than those in the unaltered ones. It is concluded that both light REEs and calcium have migrated with hydrothermal solution, and precipitated as carbonate minerals.