Direct dating of hydrothermal tungsten mineralization using in situ wolframite U-Pb chronology by laser ablation ICP-MS

摘要

The wolframite series may contain relatively high U and low common Pb contents, and thus has been used for direct U-Pb dating of hydrothermal W mineralization. In this paper, we present in-situ laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) analysis of U-Pb isotopes and trace elements of wolframite crystals from the giant Yaogangxian and Piaotang W deposits in the extensive Nanling metallogenic belt, South China. The objective of this work is to directly constrain the timing of hydrothermal W mineralization in these two deposits. Wolframite crystals from both deposits show textural evidence for two generations. Early wolframite (Wol-1) has higher Fe and lower Mn contents relative to those in the late wolframite (Wol-2). Uranium is correlated positively with Nb5+, tetravalent (Ti, Sn, Zr, Hf), and trivalent (Sc, V, Y, REEs) cations in all wolframite samples, suggesting that the incorporation of U into wolframite is controlled by the coupled substitution mechanisms. The early and late wolframite domains from the Yaogangxian deposit yielded U-Pb ages of 159.1 +/- 2.0 Ma (2 sigma; MSWD = 0.7) and 153.7 +/- 0.7 Ma (2 sigma; MSWD = 0.5), respectively. Similarly, two wolframite generations from the Piaotang deposits yielded U-Pb ages of 159.5 +/- 1.3 Ma (2 sigma; MSWD = 0.3) and 152.1 +/- 0.9 Ma (2 sigma; MSWD = 0.5). The obtained U-Pb ages confirm two successive episodes of hydrothermal W mineralization at similar to 159 Ma and similar to 153 Ma in the Yaogangxian and Piaotang deposits. This study demonstrates the potential of U-Pb dating of wolframite by LA-ICPMS and highlights its importance for directly dating hydrothermal ore-forming processes.