Genesis of the Wuzhutang Granite and Associated W–Sn–Be Mineralization in the Xuebaoding Mining Area, Sichuan Province, China

Abstract

The Xuebaoding W–Sn–Be mining area, located in the Songpan–Garze orogenic belt in western China, is known for producing large, colorful, euhedral crystals of scheelite, cassiterite, and tabular beryl. Zircon LA-ICP-MS U–Pb dating of the Wuzhutang granite yields a concordia age of 218.96 ± 2.1 Ma, and a weighted mean 206Pb/238U age of 218.98 ± 1.12 Ma. Cassiterite LA-MC-ICPMS dating of the quartz vein bearing beryl, cassiterite, and scheelite, yields a concordant age of 213.5 ± 1.7 Ma. These observations indicate that magmatic activities and mineralization on the western side of the Zibaishan dome occurred during the late Indosinian, prior to their occurrence on the eastern side of the dome, reflecting the fact that the granite may have undergone two epochs of magmatic evolution and metallogenic processes. Geochemical analysis revealed that the Wuzhutang granite has relatively high A/CNK (average: 1.05) and differentiation index (DI; 81.16~85.88) values, and that they are enriched in W, Sn, Be, Li, and Cs. Unlike the Pukouling and Pankou granites, the Wuzhutang granite contains a certain amount of plagioclase and relatively high contents of Ba (633~1007 ppm) and Sr (334~411 ppm). Sr–Nd–Pb isotope values (87Sr/86Sr(t) = 0.70747–0.70865, εNd(t) = −6.35 to –4.34, 206Pb/204Pb = 18.186–18.3, 207Pb/204Pb = 15.556–15.592, and 208Pb/204Pb = 38.268–38.432) indicate a Mesoproterozoic basement origin for the Wuzhutang granite. We suggest the three granites belong to a peraluminous magma system and were derived by partial melting of the upper crust, the magma of the Wuzhutang granite originated from a deeper source and exhibits a lower degree of differentiation than that of the Pankou and Pukouling granites.