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

Abstract

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 WSn (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 UPb ages, and LuHf 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 TDM2 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 UPb 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.