Chemical Characterisation of Natural Ilmenite: A Possible New Reference Material

Seven ilmenite (FeTiO3) megacrysts derived from alnöite pipes (Island of Malaita, Solomon Islands) were characterised for their major and trace element compositions in relation to their potential use as secondary reference materials for in situ microanalysis. Abundances of thirteen trace elements obtained by laser ablation ICP-MS analyses (using the NIST SRM 610 glass reference material) were compared with those determined by solution-mode ICP-MS measurements, and these indicated good agreement for most elements. The accuracy of the LA-ICP-MS protocol employed here was also assessed by repeated analysis of MPI-DING international glass reference materials ML3B-G and KL2-G. Several of the Malaitan ilmenite megacrysts exhibited discrepancies between laser ablation and solution-mode ICP-MS analyses, primarily attributed to the presence of a titano-magnetite exsolution phase (at the grain boundaries), which were incorporated solely in the solution-mode runs. Element abundances obtained by LA-ICP-MS for three of the ilmenite megacrysts (CRN63E, CRN63H and CRN63K) investigated here had RSD (2s) values of < 20% and therefore can be considered as working values for reference purposes during routine LA-ICP-MS analyses of ilmenite.