Geochemical Characteristics, U-Pb Age, and Hf Isotope of Zircons from Muscovite Granite in Aotou Sn Deposit, Eastern Nanling Range, South China

The Jiulongnao W–Sn ore field in the eastern Nanling Range is characterized by large-scale early Yanshanian magmatic activity and W–Sn mineralization. In recent years, increasing attention has been given to the close relationship between Indosinian magmatic activity and Sn mineralization. The Aotou quartz vein-type Sn deposit is unique for only Sn mineralization without W during the Indosinian period. Seventeen thin-to-thick cassiterite–quartz veins are densely distributed in Ordovician metasandstone and slate, and these veins extend down to the top of the concealed granite. However, both the diagenetic age and the petrological characteristics of the concealed granite remain unclear. This contribution shows that the Aotou muscovite intrusion is a highly fractionated S-type pluton, characterized by a peraluminous, high-K composition, enrichment in LREEs, and depletion of Ba, Sr, Ti, and Eu. In this study, LA–ICP–MS zircon U–Pb dating of the concealed muscovite granite yields emplacement ages of 238.7 ± 1.0 Ma and 225.4 ± 0.9 Ma, indicating that at least two stages of magmatic intrusion occurred in the Triassic, with the diagenetic environment transitioning from a compressional setting to an extensional setting. The εHf(t) values during the two stages are −0.98 to −0.95 and −0.98 to −0.96, and the TDM2 values are 1.78–2.08 Ga and 1.78–2.06 Ga, indicating that two-stage magma was derived from the late Paleoproterozoic lower crustal materials. Comprehensive analysis reveals that the second stage of Indosinian magma intrusion (232–225 Ma) in the Jiulongnao ore field is closely related to Sn mineralization, and the northern Wenying pluton has good prospecting potential for quartz vein-type Sn(–W) deposits.