In situ U-Pb dating of cassiterite by LA-ICP-MS without a matrix-matched standard

In situ cassiterite U-Pb dating is an efficient method to directly determine the formation age of Sn-polymetallic deposits due to its simple pretreatment, high spatial resolution, high cost-efficient and fast analysis speed. The application of this method, however, is constrained by the influence of matrix effect and the lack of standard reference materials. In this study, the U-Pb age of cassiterite standard and unknow cassiterite samples were determined using different carrier gas and aux gas (N-2, water vapor). Zircon was used as the external reference material for the calibration of element and isotope fractionation, Tera-Wasserburg diagram method and Pb-207 method were used to correct the common lead. The results show that the introduction of N-2 and water vapor during measurement can improve the sensitivity of U and Pb. Under different gas conditions, the age obtained from three different types of cassiterite samples were consistent with the previous report values within error, and no obvious matrix effect was found. This study shows that it is possible to use zircon as external standard for in situ LA-ICP-MS U-Pb dating of cassiterite.