Geochemical characteristics of biotites in granites from the south-central Myanmar and tin mineralization potentials of those granites

The south-central Myanmar is an important segment of the Southeast Asian tin belt. The region is relatively rich in tin resources. However, due to the constraints of complex geological conditions and limited mineral exploration degrees, the assessment of tin metallogenic potential of granites in the area remains unclear. In this study, by using electron probe microanalysis (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis, we have systematicslly investigated the characteristics of major and trace elements of biotites in granitic intrusions, which are spatially close to tin deposits and contemporaneous with the tin mineralization, in the south-central Myanmar, and have made a comparative study with characteristics of biotites in typical ore-related granites from the Bwabin and Sintok districts in order to evaluate the tin metallogenic potential of the studied granitic intrusions in the region. The results show that biotites in granites of the study area are generally rich in Fe (TFeO=18.82%~28.36%) and poor in Mg (MgO=0.76%~10.59%). Specifically, biotites from the Kalonta, Myeik, Bwabin, Dawei, and Sintok granites are classified as aluminous-rich, Mg-poor siderophyllite. In contrast, those from the Kyaikto and Padatchaung granites are relatively Mg-rich ferrobiotite. Geochemical discrimination indicates that the Myeik, Kalonta, and Dawei granites, together with the peripheral granites of the Bwabin district and ore-related granites, all belong to the crust-derived S-type granite, whereas the Kyaikto and Padatchaung granites are characterized with the mixed crust-mantle sources. The results of biotite thermobarometry, fitted by using the machine learning algorithms, suggest that granites in the area have magmatic temperatures varying from 743 ℃ to 837 ℃ and pressures varying from 408 MPa to 580 MPa, corresponding to magmatic depths varying from 14.7 km to 20.9 km. Biotites of the Myeik, Kalonta, Dawei, and ore-related granites are characterized with high F contents, low K/Rb, high Rb/Sr and low IV(F/Cl) values, and enriched in Fe2+, reflecting that those biotites were formed in the F-rich, highly fractionated and reduced granitic magmas which are favorable for the tin enrichment. By comparison, the Kyaikto granite has relatively low Sn metallogenic potential due to the constraints of some unfavorable factors such as its Sn-poor source, relatively high oxygen fugacity, and low F content. In contrast, the Padatchaung granite is generally lack of favorable tin metallogenic factors altogether, with the lowest. Tin metallogenic potential. The various indicators of granites in the peripheral area of the Bwabin deposit vary between those of ore-bearing granites and those of barren granites, suggesting that those granites have moderate tin metallogenic potentials. Overall, particular attention should be paid to the Dawei−Myeik area in the southern Myanmar for the future tin exploration in Myanmar. This study provides new geochemical evidences for understanding the petrogenesis of regional granites and the associated tin metallogenic regularities in the south-central Myanmar.