High Precision Sr‐Nd‐Hf‐Pb Isotopic Compositions of USGS Reference Material BCR‐2

The Lamont‐Doherty Earth Observatory radiogenic isotope group has been systematically measuring Sr‐Nd‐Pb‐Hf isotopes of USGS reference material BCR ‐2 (Columbia River Basalt 2), as a chemical processing and instrumental quality control monitor for isotopic measurements. BCR ‐2 is now a widely used geochemical inter‐laboratory reference material (RM), with its predecessor BCR ‐1 no longer available. Recognising that precise and accurate data on RMs is important for ensuring analytical quality and for comparing data between different laboratories, we present a compilation of multiple digestions and analyses made on BCR ‐2 during the first author's dissertation research. The best estimates of Sr, Nd and Hf isotope ratios and measurement reproducibilities, after filtering at the 2 s level for outliers, were 87 Sr/ 86 Sr = 0.705000 ± 11 (2 s , 16 ppm, n = 21, sixteen digestions, one outlier), 143 Nd/ 144 Nd = 0.512637 ± 13 (2 s , 25 ppm, n = 27, thirteen digestions, one outlier) and 176 Hf/ 177 Hf = 0.282866 ± 11 (2 s , 39 ppm, n = 25, thirteen digestions, no outliers). Mean Nd and Hf values were within error of those reported by Weis et al . (2006, 2007) in their studies of RMs; mean Sr values were just outside the 2 s uncertainty range of both laboratories. Moreover, a survey of published Sr‐Nd‐Hf data shows that our results fall within the range of reported values, but with a smaller variability. Our Pb isotope results on acid leached BCR ‐2 aliquots ( n = 26, twelve digestions, two outliers) were 206 Pb/ 204 Pb = 18.8029 ± 10 (2 s , 55 ppm), 207 Pb/ 204 Pb = 15.6239 ± 8 (2 s , 52 ppm), 208 Pb/ 204 Pb = 38.8287 ± 25 (2 s , 63 ppm). We confirm that unleached BCR ‐2 powder is contaminated with Pb, and that sufficient leaching prior to digestion is required to achieve accurate values for the uncontaminated Pb isotopic compositions.