Geochronological framework and ore genesis of the Tiantangshan Rb-Sn-W deposit, northeastern Guangdong, south China: Constraints from cassiterite and monazite U-Pb dating

Abstract

The newly discovered Tiantangshan Rb-Sn-W deposit in the northeastern Guangdong is one of the largest Rb deposit in China. The deposit is hosted by volcanic rocks and characterized by hydrothermal mineralization of Rb and Sn-W, with minor Rb mineralization of granitic K-feldspar alteration. In this study, we conducted LA-ICP-MS U-Pb dating of cassiterite and monazite to constrain the ore-forming ages of Sn and Rb. Two stages of cassiterite (Cst) are developed in the wolframite-cassiterite quartz vein, and the Cst I and Cst II yielded weighted mean 206Pb/238U ages of 133.9 ± 2.0 Ma and 133.2 ± 1.6 Ma, respectively. Monazites from biotite quartz vein yielded weighted mean 206Pb/238U ages of 134.2 ± 1.8 Ma and 132.7 ± 1.1 Ma. Combined with previous studies, a geochronological framework of volcanic eruptions (ca. 137 Ma), alkali feldspar granite (ca. 136 Ma) and Rb-Sn mineralization (134 to 133 Ma) for the deposit was established. Thus, the Rb-Sn-W mineralization is genetically related to the alkali feldspar granite and a volcanic-intrusive connection. Most Rb resources of the deposit are hosted by hydrothermal biotite in biotite quartz vein and related biotite alteration of volcanic wall rocks. Meanwhile, the K-feldspar alteration of the alkali feldspar granite displays higher Rb contents (1992–2092 ppm), stronger REE tetrad effect and lower Zr/Hf, Nb/Ta and Y/Ho ratios than the unaltered granite, indicating important involvement of hydrothermal fluids in this type of Rb enrichment. In combination with recent age data, the Tiantangshan deposit, with Yanbei and Taoxihu in the southeastern Jiangxi, are related to the numerous Sn deposits in southeastern Guangdong, which together form an early Cretaceous Sn metallogenic belt in South China. The early Cretaceous Sn belt was formed under an extensional environment likely due to the roll back of the subducted paleo-Pacific plate. The Tiantangshan deposit is indicative of Sn and related rare-metal exploration potential in the early Cretaceous volcanic basins in adjacent areas.