Rhenium-Osmium Isotope Measurements of Geological Reference Material BIR-1a: Evaluation of Homogeneity and Implications for Method Validation and Quality Control

To evaluate the homogeneity of geological reference material BIR-1a (basalt; United States Geological Survey, USGS) for Re-Os isotopic studies at the 0.2-1.0g test portion size level, sixty-three precise measurement results of Re and Os mass fractions and isotope amount ratios were obtained over an 18-month period. These data reveal that the reference material has higher Re (0.691 +/- 0.022ngg(-1), 2s, n=63) and lower Os mass fractions (0.343 +/- 0.089ngg(-1), 2s, n=63) than UB-N (serpentinite, CRPG) and is homogeneous in Os-187/Os-188 isotope amount ratio (0.13371 +/- 0.00092, 2s, n=63) at the 0.2-1.0g test portion size level. The results are essentially consistent with previous views indicating that BIR-1a gives precise measurement results for Re-Os isotope amount ratio measurements at the 1g test portion size level (Ishikawa etal., Chemical Geology, 2014, 384, 27-46; Meisel and Horan, Reviews in Mineralogy and Geochemistry, 2016, 81, 89-106). Based on these new Re-Os data and previous studies, we propose BIR-1a as a useful reference material that can be used in method validation and quality control and interlaboratory comparisons for studies dealing with mafic geological samples at test portion sizes of >0.4g.