Columbite SN3: A New Potential Reference Material for U‐Pb Dating by LA‐ICP‐MS

Abstract

Columbite‐tantalite LA‐ICP‐MS U‐Pb dating is a fast and useful method to determine the age of rare‐metal deposits and fingerprint the provenance of columbite‐tantalite ore concentrates. Accurate LA‐ICP‐MS U‐Pb dating requires matrix‐matched reference materials. We analysed three columbite‐tantalite samples (SN3, HND and RL2) from China using ID‐TIMS and LA‐ICP‐MS to assess their potential as reference materials for in situ U‐Pb dating. Coltan 139 and these three columbite‐tantalite samples with variable compositions yielded internally consistent LA‐ICP‐MS U‐Pb ages when using each other for calibration and the weighted mean 206Pb/238U ages are comparable to respective ID‐TIMS ages. Composition‐dependent U‐Pb fractionation seems to be insignificant under the LA‐ICP‐MS conditions used. Sample SN3 has a low percentage of heterogeneity for 206Pb/238U ages (4%) with low common Pb contributions (f206 < 1%) and shows a good potential in calibrating unknown samples as primary reference material for LA‐ICP‐MS analysis. Samples RL2 and HND have altered sections characterised by high LREE contents, flat LREE patterns and old 206Pb/238U apparent ages, and are not suited as reference materials. The low 207Pb/206Pb intercepts for samples RL2 and HND lack geological meaning but provide strong evidence that the disturbed U‐Pb systematics with anomalous apparent 206Pb/238U ages is a secondary feature.