Accurate and precise in situ U–Pb isotope dating of wolframite series minerals via LA-SF-ICP-MS

Abstract

We present an analytical protocol for in situ U–Pb isotope dating of wolframite series minerals [(Fe,Mn)WO₄], the main ore mineral for tungsten, by LA-SF-ICP-MS. Precision and accuracy of the protocol was intensively assessed using our newly developed well-characterized U–Pb wolframite reference material. The tungsten oxide interference on Hg and Pb was investigated in detail. The matrix effect between ferberite and hübnerite during laser ablation was thoroughly examined for wolframite series minerals with a different Mn/(Mn + Fe) ratio. The closure temperature of wolframite, with respect to the U–Pb system, was evaluated. The application of eleven wolframite samples, with ages from ∼1780 Ma to ∼26 Ma, robustly demonstrated the feasibility of our approach. Most studied wolframite series minerals yielded U–Pb concordant or subconcordant ages. Samples with a relatively high U content and negligible common Pb content typically had a ²⁰⁶Pb/²³⁸U age precision of ca. 1%. The new in situ data agree well with published cassiterite or wolframite ages from the same locations. LA-SF-ICP-MS, with the advantages of high sensitivity, rapidity, and relatively low cost, as well as moderate spatial resolution (i.e., 32 or 44 μm) that is sufficiently high to avoid sulfide inclusions, is the method of choice for in situ wolframite U–Pb microanalysis.