U–Pb dating of single-grain uraninite by isotope dilution thermal ionization mass spectrometry

Abstract

Uraninite can be used to measure U–Pb ages due to its high uranium and low common lead content. Accurate in-situ U–Pb dating of uraninite by secondary ion mass spectrometry (SIMS) or laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) requires a matrix-matched external standard as a result of the different Pb/U fractionation behavior in varied matrices. However, being lack of the suitable uraninite standard, in-situ U–Pb dating technique of uraninite is hardly carried out in many laboratories. In this paper, a method with a detailed analytical procedure is proposed for U–Pb age determination of single-grain uraninite by isotope dilution thermal ionization mass spectrometry (ID-TIMS). This method not only avoids the difficulty of looking for the ideal uranium mineral standards because of no need to make matrix effect calibration, but also gives high precision ages with a small amount of sample used (<1 μg), which provides a basis for in-situ ID-TIMS U-Pb dating of uraninite on the rocks or thin sections.