Ages and genesis of W-Sn and Ta-Nb-Sn-W mineralization associated with the Limu granite complex, Guangxi, China

The Limu granite complex spans three granitic stages, forming the largest Indosinian Ta-Nb-Sn-W ore field in South China. There includes quartz-vein Wsbnd Sn (type-1) mineralization associated with second-stage granite, as well as Ta-Nb-Sn-W mineralization associated with third-stage granite including quartz-feldspar-vein (type-2), pegmatite dike (type-3), and disseminated (type-4) mineralization. To elucidate the magmatic evolution and genesis of these types of mineralization, we obtained muscovite ⁴⁰Ar/³⁹Ar ages, zircon LA-ICP-MS Usbnd Pb ages, and Lusbnd Hf and Nd isotopic, trace-element, and geochemical compositions of the Limu granite complex. The Limu granites are peraluminous (A/CNK > 1.1) with negative ɛNd(t) values (-8.5 to -9.7) and T_DM2 ages of 1780-1685 Ma, suggesting that they were derived mainly from partial melting of Paleoproterozoic basement. Remnants of Caledonian zircons (429.4 ± 5.6 Ma) indicate Caledonian granite melting in the source. Low Zr/Hf (<13) and Nb/Ta (<5) ratios and the tetrad effect in rare-earth-element patterns of the second- and third-stage granites indicate that the magmas were highly evolved and underwent late-stage exsolution of fluids. Muscovite from type-1 ore yielded an ⁴⁰Ar/³⁹Ar age of 213.7 ± 1.1 Ma. Two hydrothermal zircons and two muscovite samples from third-stage granite containing type-4 mineralization yielded similar Usbnd Pb ages of ca. 203 Ma and ⁴⁰Ar/³⁹Ar ages of ca. 208 Ma, respectively. We conclude that type-1 mineralization was formed at ca. 214 Ma and was hydrothermal in origin, whereas Ta-Nb-Sn-W mineralization was formed at ca. 208-203 Ma and was of magmatic-hydrothermal origin. Mantle-derived heat from a long-lived magma chamber was essential for the high-temperature anatexis that formed Ta-Nb-Sn-W-rich melts, with the combined effects of crustal thickening during the Indosinian Orogeny, local delamination, asthenospheric upwelling, and deep faulting facilitating the continuous supply of heat.