A new digestion and chemical separation technique for rapid and highly reproducible determination of Lu/Hf and Hf isotope ratios in geological materials by MC-ICP-MS

A new digestion procedure and chemical separation technique has been developed for measurement of Lu/Hf and Hf isotope ratios that does not require high-pressure bombs or use of HF or HClO4 acids. Samples are digested in dilute HCl or HNO3 after flux-fusion at 1100 degreesC in the presence of lithium metaborate. High field strength elements (HFSE) and rare earth elements (REE) are separated from this solution by co-precipitation with iron hydroxide. The dissolved precipitate (in 2 mol l(-1) HCl) is loaded directly onto a standard cation exchange column which separates remaining sample matrix from the heavy REE (Lu+Yb), and the middle-light REE and HFSE (Hf). The middle-light REE and individual HFSE are then separated (10.5, 9 and 6 mol l(-1) HCl) using a miniaturized column containing TEVA spec resin which provides a REE-, Ti- and Zr-free Hf cut. This chemical separation scheme can also be readily adapted for isotopic analysis of the Sm-Nd system and/or the other HFSE (Ti, Zr). Total procedural blanks for this technique are <100 pg and < 2 pg for Hf and Lu, respectively, even when digesting large (0.5 g) samples. We present data from replicate digestions of international rock reference materials which demonstrate this technique routinely reproduces Lu/Hf ratios to < 0.2% (2s) and Hf-176/Hf-177 isotope ratios to < 30 ppm (2s). Moreover, the technique is matrix-independent and has been successfully applied to analysis of diverse materials including basalts, meteorites, komatiites, kimberlites and carbonatites. The relative simplicity of this technique, coupled with the ease of digestion (and sample-spike equilibration) of large difficult-to-dissolve samples, and the speed (2 days) with which samples can be digested and processed through the chemical separation scheme makes it an attractive new method for preparing samples for Lu-Hf isotopic investigation.