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

Distribution of rare earth elements (REEs) in granitic rock has been studie d to clarify the migration behavior of REEs in granitic rock during alterat ion. The altered and unaltered rock samples were collected at Toki granitic rock, central Japan. The concentrations of REEs in rock samples were measu red by the neutron activation analysis. The concentrations of the light REE s (LREEs) in the altered rock samples were higher than those in the unalter ed ones. In contrast, the concentrations of heavy REEs (HREEs) in the alter ed rock samples were approximately the same as those in the unaltered ones. XRD patterns show that clay minerals were not present in the unaltered roc k samples, but were in the altered ones. Both the altered and unaltered roc k samples contain apatite, zircon and xenotime, which contain REEs as minor components. Carbonate minerals, calcite, CaCO3, bastnaesite, (LREE)(CO3)F, and parisite, Ca(LREE)(2)(CO3) F-3(2) were observed only in the altered ro ck samples. Calcite filled veins in the altered samples, and bastnaesite an d parisite occurred with calcite. Bulk concentration of calcium in the alte red 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 hydrother mal solution, and precipitated as carbonate minerals. (C) 1998 Elsevier Sci ence B.V. All rights reserved.