Tectonic and metallogenic implications of W-Sn related granitoid rocks in the Kawthaung-Bankachon area, southernmost part of Myanmar: Constraints from petrology, geochemistry, and U-Pb zircon geochronology

Granitoid rocks are widely distributed along the N-S trending tectonic belts encompassing Myanmar, Thailand, Peninsular Malaysia, and Indonesia and these granitoid rocks are host to the world's largest deposits of tin-tungsten, in terms of both production and reserves. The investigated study area belongs to the southernmost part of the Central Cretaceous-Eocene granitoid belt of SE Asia in the border region of Myanmar and Thailand within the Sibumasu or Shan-Thai Terrane. The granitoid units in the area are biotite granite, muscovite-biotite granite, porphyritic biotite granite, and diorite which occur locally as dykes. All granitic rocks in the area are recognized in the High-K calc-alkaline series and show a high abundance of Cs, Rb, U, Th, K, Pb, Nd, Zr, and Sn. Based on the major oxide composition and tectonic discrimination diagram, all granitoid rocks in the area fall in the peraluminous, S-type granite category and within the Post-Orogenic Granite and Post-Collisional Granite fields. Radiometric dating by LA ICP-MS U-Pb zircon method yielded the ages of 78.97 ± 0.63 Ma (biotite granite), 79.59 ± 0.76 Ma (muscovite-biotite granite), and 79.14 ± 0.91 Ma (porphyritic biotite granite) and 49.48 ± 0.83 Ma for the biotite granite from the Yadanabon W-Sn deposit. According to the zircon U-Pb ages, the timing of the granitoid intrusions of the Kawthaung-Bankachon area is the Campanian (Late Cretaceous) to Eocene. The magmatism and W-Sn mineralization in the area is attributable to the Indian Ocean subduction and collision between the west Myanmar Terrane and the Sibumasu Terrane.