Implementation and experience of using methods for analyzing the isotopic composition of Sm and Nd, Rb and Sr in rock samples at the Geoanalitik Center for Collective Use

Abstract

Research subject. AGV-2 and BHVO-2 geochemical reference materials for studying the Sm, Nd and Rb, Sr isotope systems along with various rocks and mineral samples. Materials and Methods. An analysis of the isotopic composition of Sm, Nd and Rb, Sr was carried out using Neptune Plus and Triton Plus mass spectrometers. Aim. To implement analytical techniques for the isotopic composition of Sm and Nd, Rb, and Sr in various rock and mineral samples using two types of multicollector mass spectrometers – inductively coupled plasma NeptunePlus and thermal ionization TritonPlus (Thermo-Fisher), as well as a description of the procedure of processing experimental data and the experience in using techniques at the “Geoanalitik” shared research facilities of the IGG UB RAS for the period 2015-2023. Results. The analytical techniques implemented included (1) column chromatography using various ion-exchange resins, optimised for the ratio of labour costs/quality of analytical results; (2) the measurement of isotope ratios using two types of mass spectrometers; (3) the correction of mass bias of isotope ratios and the determination of Sm and Nd, Rb, and Sr concentrations by the isotope dilution method using 149Sm+150Nd and 85Rb+84Sr spikes. Testing of the techniques was carried out using the AGV-2 and BHVO-2 geochemical reference materials; their metrological characteristics were presented. When using TritonPlus, the reproducibility (BHVO-2, n=60) of measurements of 143Nd/144Nd, 147Sm/144Nd isotope ratios and Sm and Nd concentrations are ±0.000020, ±0.0004, ±1.3 and ±0.4, respectively; indicators of correctness of determining the ratios 143Nd/144Nd and 147Sm/144Nd – 0.001 and 0.25% and concentrations of Sm and Nd – 2%; the reproducibility (BHVO-2, n=63) of measurements of 87Sr/86Sr, 87Rb/86Sr isotope ratios and concentrations (Rb and Sr) are ±0.0025%, ±1.5%, ±2%, respectively. The uncertainty of a single measurement of the 143Nd/144Nd and 87Sr/86Sr isotope ratio, represented by the standard error of the average single measurement in the sample, does not exceed 0.0025%. Conclusions: the results obtained for the geochemical reference materials are in satisfactory agreement with those provided in the GeoReM database, as well as with the certified values provided by the United States Geological Survey (USGS). The described analytical techniques are used at the “Geoanalitik” shared research facilities of the IGG UB RAS to analyse various rock and mineral samples. The work presents a number of experimental results obtained, which are subsequently used in geochronological applications.