SECONDARY-ION MASS-SPECTROMETRY ANALYSIS OF RARE-EARTH ELEMENTS IN GRANDITE GARNET AND OTHER SKARN RELATED SILICATES

A quantitative secondary ion mass spectrometry (SIMS) analytical metho d is presented for determining rare earth element (REE) abundances in similar to 60 mu m spots in calcic (grandite) garnet and other skarn-r elated silicate minerals. Grandite REE patterns are different from pyr alspite ones, being enriched in light rare earth elements (LREE) with respect to heavy rare earths (HREE). In SIMS this attribute requires b oth energy filtering and deconvolution of the HREE spectrum for interf ering LREE monoxides. Quantification was done by SIMS analyses on four Ca-Al silicate glasses with well-characterised REE levels. REE analys es done by this method are in good agreement with ICP-MS data on simil ar similar to 1 g samples. SIMS analysis of NIST glass standard SRM 61 3 confirms the accuracy of the method. Useful analyses can be made on mineral samples with extremely low REE abundances, down to 10 % of cho ndritic levels.