GX-5 calcite: a new matrix-matched reference material for in-situ LA-ICP-MS carbonate U–Pb geochronology

Abstract

In situ laser ablation U–Pb dating of carbonate minerals has emerged as an important geochronological tool, providing direct temporal constraints for hydrocarbon accumulation, mineral exploration, and tectonic processes. However, the limited availability of matrix-matched reference materials significantly restricts analytical accuracy, precision, and broader interlaboratory application. In this study, we present GX-5, a calcite reference material collected from a massive calcite vein. GX-5 is characterized as homogeneous low-Mg calcite with high uranium content (mean = 6.09 µg g⁻¹) and low common lead composition (mean f₂₀₆ = 4.75%), making it suitable for in situ LA-ICP-MS U–Pb geochronology. A total of 79 analytical sessions yield a lower intercept age of 78.64 ± 0.1 Ma (2S, MSWD = 5.8, n = 168, 8810 tests). Independent isotope dilution multi-collector inductively coupled plasma mass spectrometry (ID-MC-ICP-MS) analyses define a U–Pb age of 78.88 ± 0.15 Ma (2S, MSWD = 1.07, n = 8), with an initial ²⁰⁷Pb/²⁰⁶Pb value of 0.896 ± 0.039. The agreement between in situ and solution-based results demonstrates the isotopic homogeneity and age stability of GX-5. Owing to its abundant material supply, elevated uranium content, and consistent long-term analytical performance, GX-5 is proposed as a reliable matrix-matched reference material for in situ carbonate U–Pb dating.