Development of two novel natural calcite reference materials for enhanced in situ elemental and Sr isotopic analysis

Abstract

In situ trace-elemental and Sr isotopic compositions of calcite have become powerful tools to unravel detailed geological processes. However, the accuracy of such analyses is contingent upon the availability of appropriate reference materials, particularly for carbonates with low strontium concentrations. Herein, the homogeneity of Sr isotopes and trace elements of two natural calcites, BZS and WS-1 with low and moderate Sr content (212 and 598 μg g⁻¹), was evaluated through a large number of LA-(MC-)ICP-MS analyses. The result demonstrated that both BZS and WS-1 have homogeneous Sr isotopic compositions with mean ⁸⁷Sr/⁸⁶Sr values of 0.71181 ± 0.00013 (2SD, n = 183) and 0.70872 ± 0.00009 (2SD, n = 184), respectively. These values are consistent with the solution-based MC-ICP-MS measurements, which yield mean values of 0.71181 ± 0.00001 for BZS and 0.70872 ± 0.00003 for WS-1. Additionally, BZS displays uniformity in trace elements of Mn, Sr, Y (RSD <10%) and all REEs (RSD <20%), while WS-1 shows homogeneous Mg, Mn, and Sr (RSD <10%). Notably, their low Rb/Sr ratios (<0.0002) and Yb and Er contents (<2.70 μg g⁻¹ and <2.86 μg g⁻¹, respectively) further indicate that these materials have limited isobaric interference of ⁸⁷Rb and negligible interference of doubly charged Er²⁺ and Yb²⁺ in Sr isotope analyses. Consequently, BZS and WS-1 could be considered as potential natural calcite reference materials for accurate in situ elemental and Sr isotopic analyses in low-Sr carbonates.