Improved Pb-Free Sn-Bi Alloy Mounting Technique For Ion Probe U-Pb Analyses Of Zircon

: Zircon, a common U-rich accessory mineral occurring in terrestrial and extraterrestrial rocks, serves as a crucial tool for unraveling the temporal and geochemical clues on geologic events that have taken place on Earth and other planetary bodies. Zircon water content analysis has been advanced in the past three years via a novel sample preparation method using Sn-Bi alloy as a mounting material. Here, we present an improved Pb-free Sn-Bi alloy material for mounting samples and investigate whether the alloy mounts are suitable for in situ U-Pb dating. The secondary ion mass spectrometry (SIMS) U-Pb dating results show that the count rates of 204 Pb for zircon standards in the alloy mount are less than 0.01 cps/nA, and the calculated U-Pb and Pb-Pb ages of zircon standards are consistent with the recommended values within analytical uncertainties. Our results indicate that the alloy material used in this study is a good mounting material for U-Pb dating. Therefore, we recommend that this Pb-free Sn-Bi alloy material can be applied to mount geological samples for water abundance and U-Pb systematic analyses.