A new working reference material for cassiterite oxygen isotope microanalysis

Cassiterite is the principal ore mineral for tin, and its oxygen isotope is a promising proxy to trace the origin and evolution of ore-forming fluids, which requires precise and accurate oxygen isotopic analysis. Secondary ion mass spectrometry (SIMS) is a powerful tool for oxygen isotope analysis, especially when samples bear complicated textures, but matrix-matched reference materials are critical for accurate microanalysis. The only available matrix-matched reference material for cassiterite oxygen isotope analysis is Yongde-Cst, and more reference materials are required. Here, we report Piaotang-Cst as a potential working reference material for cassiterite oxygen isotope microanalysis. Our extensive SIMS microanalysis confirmed that Piaotang-Cst is relatively homogeneous, with an average two standard deviations (2SD) of 0.49‰ (n = 626). The δ¹⁸O_VSMOW value of Piaotang-Cst is 5.33 ± 0.07‰ (2SD, n = 5) as determined by a conventional fluorination isotope ratio mass spectrometer. We also demonstrated that there is no measurable matrix effect caused by the variable contents of trace elements for cassiterite oxygen isotope microanalysis. We proposed that the Piaotang-Cst can be used as a working reference material for monitoring the external reproducibility and accuracy of SIMS analysis.