Geochemistry and U–Pb Zircon Geochronology of Granite at the Pilok Sn–W Deposit, Thailand: Implications for Late Triassic Tin Metallogenesis

ABSTRACT The Pilok Sn–W deposit in western Thailand is hosted by peraluminous S‐type granites that intruded Silurian–Devonian metasedimentary rocks. This study presents whole‐rock geochemistry, zircon U–Pb geochronology, and trace element data to constrain the timing of emplacement, petrogenesis, and regional metallogenic processes. Two granite types occur in the deposit: biotite–muscovite granite and tourmaline–biotite–muscovite granite, both showing high SiO 2 (72.6–75.2 wt%) and Sn (12.8–27.4 ppm) contents, strongly peraluminous characteristics (A/CNK = 1.20–1.38), pronounced negative Eu anomalies (Eu/Eu* = 0.13–0.27), and elevated Rb/Sr ratios (14.1–22.6), indicating extensive fractional crystallization. Zircon textures and chemistry of the host granites reveal four distinct types: Types I and II zircons displaying magmatic oscillatory zoning and heavy REE‐enriched patterns, and Types III and IV zircons showing hydrothermal characteristics with LREE enrichment in chondrite‐normalized REE patterns. U–Pb dating of magmatic zircons from four granite samples yielded 206 Pb/ 238 U ages of 208 ± 5.3 to 212 ± 1.5 Ma, synchronous with the granites in the Late Triassic tin metallogenic belt in Southeast Asia. Ti‐in‐zircon thermometry indicates crystallization temperatures of 698°C–829°C (average 754°C), and trace elements of zircon indicate strongly reduced conditions (ΔFMQ: −0.8 to −4.5, average −1.9), which were favorable conditions to retain Sn 2+ in a residual melt. REE patterns of zircon suggest a magmatic to hydrothermal transition, recording late‐stage fluid exsolution that mobilized Sn and W. The combination of Late Triassic ages, S‐type peraluminous geochemistry, extreme fractional crystallization, and reduced magmatic conditions can be used as criteria for identifying tin‐fertile granites in the Sibumasu Terrane and other terranes with similar tectonic settings.