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 SiO2 (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 206Pb/238U 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 degrees C-829 degrees C (average 754 degrees C), and trace elements of zircon indicate strongly reduced conditions (Delta FMQ: -0.8 to -4.5, average -1.9), which were favorable conditions to retain Sn2+ 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.