Precise determination of REE for sedimentary reference rocks issued by the Geological Survey of Japan

抄録

In order to obtain precise rare earth element (REE) compositions of sedimentary reference rocks issued by the Geological Survey of Japan (JSd-1, -2, JSl-1, -2, JLk-1), we analyzed their REEs by inductively-coupled plasma mass spectrometry (ICP-MS) using methods employing both acid digestion (HF-HClO₄) and carbonate fusion (Na₂CO₃-H₃BO₃). Analytical precision of these methods was estimated by analyzing JB-1a and BCR-1 with the same procedure. Analyses of these two reference rocks show good reproducibility and close agreement with compilation values, except for Ho in JB-1a and Tm in BCR-1. CI-normalized REE patterns of JB-1a and BCR-1 compilation values show deviations for Ho and Tm, respectively, from the smooth patterns. Therefore, the compilation values of those elements may be somewhat in error. After acid digestion of JSd-1, -2, JSl-1, -2 and JLk-1, 2-40% of total REEs were remained in the residues, i.e., secondary fluorides and/or undigested minerals. However, subsequent carbonate fusion effectively recovered the remained REEs. Analytical results by this study show relatively good agreement with compilation values, except for Pr, Ho, Er and Tm, and smooth REE patterns normalized to CI-chondrite. The REE patterns of compilation values show anomalous deviations of Pr, Ho Er, and Tm, suggesting that compilation values of these elements may be in errorneous. This study emphasizes that combined method of acid digestion and alkali fusion is an effective method for recovering REEs in sedimentary rocks for bulk REE determination.