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In hydrothermal tin (Sn) systems, it remains unclear whether cassiterite precipitates from reduced or oxidized fluids. To resolve this issue, the geochemistry of magmatic garnet and cassiterite separated from fractionated muscovite-garnet granite in the Paleocene Bawapin Sn W deposit was systematically investigated. CaO contents in Mn-rich garnet (spessartine) decrease from core to rim in single crystals and are negatively correlated with MnO/(MnO + FeO) ratios. These features suggest that garnet CaO content may be a good differentiation index for granitic magma evolution. Moreover, the Sn content in Mn-rich garnet increases with increasing Ca content and then decreases sharply at Ca contents of approximately 4300 ppm. Combined with evidence of Ta-rich magmatic cassiterite, the decreasing Sn content likely reflects the crystallization of magmatic cassiterite from the more evolved Sn-rich melts under oxidized conditions (ƒO 2 > ΔFMQ +1.5), in contrast to the reduced characteristics of the less-fractionated biotite monzogranite (ƒO 2 = ΔFMQ - 0.5). Late-stage oxidation might be attributable to fluid exsolution in the water-rich and Fe-poor granitic melts. This further indicates that hydrothermal cassiterite could precipitate in exsolved Sn4+-bearing fluids without Sn oxidation. This conclusion may provide a new perspective to our understanding of granite-related hydrothermal Sn systems worldwide. • The Paleocene muscovite-garnet granite has the characteristics of more evolved melt. • CaO content in Mn-rich garnet may be a good differentiation index of granitic magma evolution. • Sn variation in garnet and crystallization of magmatic cassiterite indicate late-stage oxidation in granitic melt. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Molybdenite Re–Os and zircon U–Pb ages indicate the Dapingba Mo–W deposit formed at Cretaceous (∼119 Ma and ∼114 Ma). • Cassiterite U–Pb ages of ∼60 Ma suggest the Bawapin and Kalonta Sn–W deposits in southern Myanmar formed at Paleocene. • Molybdenite Re–Os age for the Shangalon porphyry Cu–Au deposit indicates that this deposit formed at Eocene (∼39 Ma). • A comprehensive Mesozoic-Cenozoic tectono-magmatic and metallogenic model in Myanmar are proposed. Abstract It is well known that there are many Sn–W–Mo and Cu–Au metal resources in Myanmar. However, the absence of precise mineralization ages for these deposits significantly hinders to understand the close genetic relationship among metallogeny, ore-bearing intrusions, and tectonic evolution. In this study, two groups of consistent molybdenite Re–Os and zircon U–Pb ages indicate that the Dapingba Mo–W deposit in northern Myanmar (Tengchong terrane) formed at Early Cretaceous (∼119 Ma and ∼114 Ma). The Dapingba ore-bearing granitic magmas were mainly derived from melting of ancient Tengchong crust on the basis of zircon Hf isotopic compositions (εHf(t) = −9.3 to 2.5). Moreover, the first reported cassiterite U–Pb ages of ∼60 Ma for the Bawapin and Kalonta Sn–W deposits in southern Myanmar (western Sibumasu terrane) suggest that the two deposits formed at Paleocene. Whereas the precise molybdenite Re–Os age for the Shangalon porphyry Cu–Au deposit in the West Burma terrane indicates that this deposit formed at Eocene (∼39 Ma). Importantly, combined with previous studies on tectonic evolution and magmatic petrogenesis in Myanmar and southwest China, a comprehensive Mesozoic-Cenozoic tectono-magmatic and metallogenic model are proposed. Two periods of Early Cretaceous (∼120–114 Ma) and Late Cretaceous (∼75–70 Ma) crust-derived felsic melts and related Mo–Sn–W deposits from the Tengchong and western Sibumasu terranes likely formed in a continental arc during subduction of the Meso- and Neo-Tethys oceanic lithosphere, respectively. Subsequently, Paleocene-Eocene (∼60–50 Ma) Sn–W deposits and coeval ore-bearing granites in the western Sibumasu terrane possibly formed during roll-back of the Neo-Tethys oceanic slab. After ∼50 Ma India–Asia collision, Eocene (∼41–39 Ma) porphyry Cu–Au (West Burma terrane) and Sn–W deposits (western Sibumasu terrane) likely formed during the Neo-Tethys oceanic slab tear and break-off in a collisional setting. Whereas Miocene (∼19–14 Ma) high sulfidation epithermal Cu deposit in the West Burma terrane possibly formed in an arc setting during oblique subduction of the Indian oceanic lithosphere. [ABSTRACT FROM AUTHOR]

• MnO content of biotite is a good index of granitic magma differentiation. • Magma differentiation is a dominant factor for Sn enrichment. • Cl variations of biotite suggest fluid exsolution in fractionated granitic melts. • Ore-forming fluids have exsolved from late-stage more fractionated and F-rich magmas. Hydrothermal Sn ± W deposits are commonly formed by ore-forming fluids that exsolved from water-saturated granitic magmas. However, the timing of fluid exsolution and its influence on volatiles and ore-forming elements still remain confused. For this purpose, geochemical and O H isotopic compositions of biotite from Late Cretaceous-Eocene granitic intrusions in the Sibumasu terrane (southern Myanmar) are presented. MnO content of biotite is a well negative correlation with the amount of biotite and whole-rock (La/Yb) N ratio, indicating that it could be a good index of granitic magma differentiation. Cl content of biotite from Paleocene granite shows an increased first and subsequently decreased trend with increasing MnO content (0.71–2.36 wt%), suggesting Cl enrichment by magma evolution and depletion by late-stage fluid exsolution. Fluid exsolution is also supported reduced Li contents of biotite and O H isotopic compositions of residual magmatic water equilibrated with high-MnO biotite (δ18O = 7.0 to 8.8‰ and δD = −114 to −93.5‰). All studied biotite grains from Late Cretaceous granite have low Cl contents (0.01–0.11 wt%), decreased Li with increasing MnO contents, and residual magmatic water-like O H isotopic values (δ18O = 6.9‰ and δD = −105‰), indicating that their host granitic melts had undergone fluid exsolution. Importantly, a positive correlation between Sn and MnO contents in biotite suggests that magma differentiation is a dominant process for Sn enrichment. No depletion of Sn by fluid exsolution likely caused by low salinity fluids exsolved from Cl-poor granitic melts, which were estimated by low Cl contents of biotite (<0.2 wt%). The reduced Nb and Ta contents in high-MnO biotite possibly resulted by fractionation of Nb/Ta-bearing minerals during late-stage magma evolution. Moreover, ore-forming fluids equilibrated with hydrothermal muscovite from Sn-bearing quartz veins have consistent O H isotopic compositions (δ18O = 6.8–7.0‰ and δD = −61.9 to −90.2‰) with magmatic water, suggesting that ore-forming fluids probably exsolved from more evolved granitic melts with strong Sn and F enrichment. [ABSTRACT FROM AUTHOR]

There is a strong controversy about the petrogenesis of tourmaline nodules and their relationship with coeval tourmaline-bearing granites, which are commonly associated with magmatic-hydrothermal rare metal deposits (e.g., Sn, Nb, and Ta). In this study, tourmaline is extensively distributed in tourmaline-bearing nodules (NT-type), pegmatite (PT-type), and fine-grained granitic dyke (GT-type), which are hosted by the Late Cretaceous Nattaung biotite granite (Myanmar). Zircon U Pb dating results (~71 Ma) indicate that PT- and GT-types tourmaline-bearing magmatic rocks formed synchronously with biotite granite. All tourmalines have alkali group and schorl composition with Mg/(Mg + Fe) ratios of 0.03–0.45 and Na/(Na + Ca) ratios of 0.73 to 1.00. NT-type tourmaline shows high Nb/Ta ratios and V and Sr contents, indicating that they were likely crystallized from B-rich melts early immiscible with less evolved granitic magmas. PT- and GT-type tourmalines probably formed in aggregated B-rich melts that continuously separated from more evolved granitic magma, supported by their low Nb/Ta ratios and V and Sr contents. In addition, the studied tourmaline displays a slight variation of B isotopic compositions (δ11B values ranging from −12.2 ± 0.7‰ to −14.9 ± 0.4‰), likely resulted by Rayleigh fractionation of tourmaline. Their light B isotopic values are consistent with those of average continental crust, also revealing that the Nattaung granite was mainly derived from partial melting of the ancient Sibumasu crust. Importantly, late-stage PT- and GT-type tourmalines have higher Sn, Zn, Nb, and Ta contents than early-stage NT-type tourmaline, suggesting that the evolved B-rich magma could be one precursor to produce Sn-Nb-Ta-Zn deposits associated with extensive tourmaline in the world. Unlabelled Image • Three types of tourmaline are distributed in Cretaceous Nattaung granite. • All tourmalines were crystallized from B-rich immiscible melts. • Slight variation of B isotopic values resulted by Rayleigh fractionation of tourmaline. • B-rich magma may be one precursor for Sn-Nb-Ta-Zn deposits worldwide. [ABSTRACT FROM AUTHOR]

Subduction of the Indian continental lithosphere in the eastern Tibet-Himalaya orogenic belt remains unclear. Newly reported zircon U-Pb ages in this study indicate that the Shangalon intermediate-felsic magmatic rocks in northern Myanmar formed at Eocene-Oligocene (∼ 40–32 Ma). They have calc-alkaline to shoshonitic characteristics, LREE-enriched patterns, enrichments in LILE (e.g., Rb, Cs), and depletions in HFSE (e.g., Nb). Obviously, they show the higher initial Sr and lower Nd-Hf isotopic compositions (87Sr/86Sr i = 0.7054–0.7082, εNd(t) = −5.3 to −0.4, and εHf(t) = −3.4 to 10.8) than Cretaceous arc-related mafic-felsic rocks in the West Burma terrane. A positive correlation between Nd isotopic compositions and SiO 2 contents indicates that the Eocene Shangalon diorite and andesite with the lowest εNd(t) values (−5.3 to −4.0) likely derived from a mantle source contaminated by the subducted Indian continental lithosphere. Coupled with regional coeval OIB-like mafic melts and high temperature metamorphism, the Eocene-Oligocene Shangalon magma might have formed in the Neo-Tethyan oceanic slab break-off setting after the India-Asia collision. In addition, Eocene granodioritic rocks have the adakitic features, which possibly resulted by fractional crystallization of hornblende. The hornblende-dominated crystallization in the Shangalon ore-bearing granodioritic rocks is well consistent with magma evolution of H 2 O-rich melts, which play an important role in the formation of the Eocene Shangalon porphyry Cu-Au deposit. • The Shangalon magmatic rocks in northern Myanmar formed at Eocene-Oligocene (∼ 40–32 Ma). • Eocene intrusions were derived from a metasomatized mantle by the Indian continental lithosphere. • The Shangalon intrusions formed in a slab break-off setting after the India-Asia collision. [ABSTRACT FROM AUTHOR]

• Zircon U–Pb dating shows that granites in southern Myanmar formed in Late Cretaceous–Eocene. • The granites belong to fractionated I-type magmas and derived from the Sibusima crust. • The granites formed during subduction of the Neo-Tethyan oceanic lithosphere. • Fractional crystallization and fluid exsolution are the fundamental processes for Sn metallogeny. The geochronology, petrogenesis and tectonic setting of granites associated with tin–tungsten mineralization in southern Myanmar remain unclear. This work presents whole-rock geochemical, Sr–Nd isotopic, and zircon U–Pb and Hf isotopic data for felsic intrusions in the Sibusima terrane. Zircon U–Pb dating indicates formation in the Late Cretaceous–Early Eocene (~84–48 Ma) and suggests that these intrusions likely represent a southward extension of the coeval magmatic belt in the Tengchong terrane. Primarily classified as high-K calc-alkaline, the granites show strong enrichments in large ion lithophile elements (e.g., Cs, Rb, and K), depletions in Nb, Ta, P, and Ti, and negative Ba and Sr anomalies on primitive mantle-normalized diagrams. P 2 O 5 , CaO, Al 2 O 3 , MgO, TiO 2 contents, and Nb/Ta ratios decrease with increasing SiO 2 contents, possibly consistent with evolution trends in fractionated I-type granitic magmas. In addition, these intrusions display a wide range of negative ε Nd (t) (−14.6–−5.5) and zircon ε Hf (t) values (–22.7–5.7), suggesting a dominant Sibusimacrustal source with a minor mantle contribution. Notably, the Eocene and a few Paleocene granites show more contribution of mantle material based on higher ε Nd (t) (−8.5–−5.5) and zircon ε Hf (t) (−11.0–−3.2) values. Large variations in zircon Hf isotopic compositions within an individual Eocene granitic intrusion (e.g., −15.2–5.7) and corresponding biotite-rich enclave (−17.8–0.2) likely indicate magma mixing. Considering the spatial-temporal distribution of magmatism in the West Burma and Sibusima terranes, the studied Late Cretaceous–Eocene felsic magmas likely formed in a continental arc setting during normal subduction (~100–60 Ma) and subsequent roll-back of the Neo-Tethyan oceanic lithosphere (~60–50 Ma). Additionally, most of granites have the elevated Sn with increasing Rb/Sr ratios, and decreasing TiO 2 contents and Nb/Ta ratios, suggesting Sn enrichment is primarily controlled by magmatic fractionation. Meanwhile, Sn and Li depletions in some granites deviate from the magmatic evolution trend, likely as a result of fluid exsolution. The exsolved Sn-rich fluids could have made a genetic contribution to hydrothermal Sn mineralization in southern Myanmar. [ABSTRACT FROM AUTHOR]