Lithium Isotopic Composition of GSR Series Rock Reference Materials and Their Reliability as Quality Control Standards

Rock reference materials serve as benchmarks for inter-laboratory isotopic data comparison and for monitoring data accuracy and precision. In recent years, the internationally used United States Geological Survey (USGS) series rock reference materials have faced challenges including rising prices, inventory shortages, and long procurement lead times, limiting their widespread application in routine analyses. Chinese national rock reference materials have long lacked high-precision lithium isotopic reference data, preventing them from fully playing a role in international comparisons and daily quality control. To promote the application of reference materials and provide quality control benchmarks with higher accessibility and broader lithological coverage, this study employed multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS) to determine the Li isotopic compositions of 16 national rock reference materials (GSR series). The selected reference materials cover major rock types from ultramafic to felsic compositions, ensuring lithological representativeness of the dataset. Results show that the δ⁷Li values of the GSR series range from −3.0‰ to 13.9‰, while those of the USGS series range from −0.1‰ to 7.0‰, demonstrating that the GSR series has advantages over the USGS series in both lithological coverage breadth and isotopic composition span. Comparison with published data confirms that the analytical reproducibility of most GSR reference materials is better than 0.5‰, indicating good homogeneity. This study demonstrates that the GSR series rock reference materials possess the reliability and applicability as benchmarks for inter-laboratory Li isotopic data comparison. They can serve as important supplements to the USGS series, providing stable and accessible domestic quality control options for geochemical laboratories, reducing import dependence, and supporting Li isotopic tracing of geological processes.