Geology, geochemistry, and zircon U-Pb geochronology of the Nanthila and Pedet granites in the Myeik Sn-W district, Tanintharyi region, southern Myanmar

Abstract

Critical metals, particularly tin and tungsten, are essential to global economic development and modern civilization. The Southeast Asian Tin Belt, extending 2800 km, represents the world’s most significant W–Sn metallogenic belt. This belt includes four metallogenic provinces: the Main Range Granitoid Province, the Northern Granitoid Province (North Thailand Migmatitic Province), the Eastern Granitoid Province, and the Western Granitoid Province), with ore assemblages predominantly associated with Phanerozoic intrusions. The Western Granitoid Province of southern Myanmar hosts numerous W-Sn mineralized granitoids, among which we investigated the Nanthila and Pedet granitic plutons in the Myeik Sn-W district. The study area consists primarily of the Carboniferous-Permian Mergui Group and Early Tertiary granitic rocks. The petrogenesis, tectonic setting, magmatic evolution, and the age of the Nanthila and Pedet granitic intrusions remain poorly constrained. This contribution reports field observations, petrographic studies, whole-rock geochemical analyses, in-situ U-Pb zircon dating, Lu-Hf isotopic data, and mineral chemistry analysis. Petrographic and geochemical data reveal that both plutons exhibit high SiO₂ (74.63–76.43 wt%), low CaO (0.62–0.73 wt%) and MgO (0.02–0.13 wt%) contents, elevated 10000*Ga/Al ratios (2.94–3.67), mildly peraluminous nature (A/CNK < 1.1), and high-K calc-alkaline affinity. They show high HFSEs concentrations (Y: 8.1–14.8 ppm, Nb: 25.3–40.4 ppm, Th: 41.9–103 ppm, and U: 19.8–29.7 ppm) and moderate to high melting temperatures (zircon: 731–806 °C; apatite: 709–813 °C). These characteristics align with highly fractionated aluminous A₂-type granites, displaying “V” type REE distribution patterns with pronounced negative Eu anomalies. The Sn-related granitic magmas likely originated from the partial melting of clay-rich felsic crustal sources under reduced conditions and high temperatures in a post-collisional tectonic setting. Magmatic zircons from six granitoid samples yielded Concordia ages of ∼ 50.78 ± 0.47 Ma to 51.46 ± 0.43 Ma (Eocene period). The ¹⁷⁶Hf/¹⁷⁷Hf ratios (0.282271 to 0.282541), negative εHf(t) values (−7.18 to −16.74), and two-stage crustal model ages (T_DMC) (1.58–2.01) indicate derivation from Neoproterozoic continental crust. These findings highlight the potential of the Nanthila and Pedet areas for further geological investigation and mineral exploration, suggesting they could be promising sites for new reserves.