In situ LA-ICP-MS U–Pb geochronology and trace element analysis of hydrothermal titanite from the giant Zhuxi W (Cu) skarn deposit, South China
The Zhuxi W (Cu) skarn deposit is the largest W deposit in the Jiangnan porphyry–skarn tungsten belt in South China, and is also among the largest deposit of this type in the world. Titanite is a common mineral in the Zhuxi deposit, and occurs in three textural settings: titanite I associated with retrograde-altered exoskarn with weak mineralization; titanite II in retrograde-altered endoskarn with disseminated Cu ore; and titanite III from altered granite with disseminated W ore. Here, we present LA-ICP-MS U–Pb data on the three types of titanite which show 207Pb-corrected weighted mean 206Pb/238U ages of 148.1 ± 7.4 Ma (n = 25, MSWD = 0.22), 148.9 ± 1.5 Ma (n = 28, MSWD = 0.37), and 149.9 ± 1.3 Ma (n = 31, MSWD = 0.28), respectively. These ages are consistent with the previously reported ages of the ore-related granite. The coeval nature of the W and Cu ores suggests that the W and Cu ores formed synchronously, and are associated with the granitoids. The Ce and Eu anomalies in the three types of titanite record redox fluctuation during the mineralization process, and suggest variable contamination of the magmatic-hydrothermal system by reduced carbonate wall-rock that contains abundant carbonaceous matter. Our study demonstrates that hydrothermal titanite commonly occurring in reduced-type W skarn deposits has potential for isotopic dating and in constraining the redox conditions for the mineralization process.