LA-ICP-MS U[sbnd]Pb geochronology of wolframite by combining NIST series and common lead-bearing MTM as the primary reference material:Implications for metallogenesis of South China

Abstract

Direct dating of W and WSn deposits by wolframite is more reliable relatively to gangue mineral and important for understanding their timing and genesis. However, such analysis still lacks of homogeneous wolframite standard recently. Due to containing considerable and variable common lead, and inhomogeneous in different grains, the wolframite sample of MTM, which is a promising candidate reference material proposed by previous studies, is not suitable as a primary standard for wolframite UPb dating by LA-ICP-MS using the normal normalization method as zircons. In this contribution, a modified normalization method is established for wolframite UPb dating, in which NIST612 or 614 and MTM are used for correction of PbPb and UPb ratios, respectively. Wolframite UPb dating are performed on the Langcun, Xihuashan, Piaotang, Shamai W or WSn deposits and the Baiganhu ore district, the obtained lower intercept 206Pb/238U ages are comparable with the ages from syngenetic molybdenite, cassiterite, muscovite and the genetically related granites, as well as wolframite by water vapor-assisted ns-LA-ICP-MS UPb dating method. The results of this analysis demonstrate that the robust age for W mineralization can be determined by LA-ICP-MS UPb dating of wolframite using this modified calibration method. Mineralization ages of 125–130 Ma by directly dating of metal minerals for the Langcun W, Jianfengpo Sn and large-size Xianglushan W deposits confirm that there exists an important WSn mineralization event in this period. The close temporal and spatial correlation indicates the granites and W-Cu-Mo-Pb-Zn-Sn mineralization have a genetic relationship with each other and are resulted from the same tectonic-magmatic-hydrothermal events during 140 to 120 Ma in South China.