Sphalerite and Zinc Metal Nugget Reference Materials for In Situ Zinc Isotope Ratio Determination Using fsLA-MC-ICP-MS

This study examined the micro-homogeneity of zinc isotope composition of the NIST SRM 683 and NBS 123 reference materials using femtosecond laser ablation multi-collector inductively coupled plasma-mass spectrometry (fsLA-MC-ICP-MS). NIST SRM 683 and NBS 123 are homogeneous in Zn isotope composition based on numerous measurements performed on twenty chips and four mounts of sphalerite using solution nebulisation (SN)-MC-ICP-MS and fsLA-MC-ICP-MS. The mean delta Zn-66(JMC-Lyon) values of NIST SRM 683 and NBS 123 determined by SN-MC-ICP-MS were 0.11 +/- 0.02 parts per thousand (2 standard deviation (2s), n = 100) and 0.16 +/- 0.02 parts per thousand (2s, n = 62), respectively. The mean delta Zn-66(JMC-Lyon) values determined by fsLA-MC-ICP-MS analyses for NIST SRM 683 and NBS 123 were 0.12 +/- 0.05 parts per thousand (2s, n = 200) and 0.16 +/- 0.05 parts per thousand (2s, n = 212), consistent with the bulk isotope compositions within uncertainty. The in situ measurement precision for NIST SRM 683 and NBS 123 was better than 0.06 parts per thousand (2s), suggesting NIST SRM 683 and NBS 123 are suitable to serve as microanalytical reference materials for Zn isotope measurement. Zinc isotopic compositions of Zn-rich materials were also determined using fsLA-MC-ICP-MS under wet/dry plasma conditions. Their delta Zn-66(JMC-Lyon) values were in agreement with those obtained by SN-MC-ICP-MS analysis, suggesting that fsLA-MC-ICP-MS is suitable to measure Zn isotopic ratios in Zn-rich materials. Thus, this method could potentially analyse spatially resolved Zn isotope compositions at the mineral or even sub-mineral scale, such as to address the process of ore formation or Zn redistribution in near-surface environments.