Introduction The Sn and W mineral deposits in

Introduction The Sn and W mineral deposits in southern China were historically suggested to have formed as part of one mineralizing event (Hsu, 1943), although the W ores are mainly distributed in the eastern part of southern China, whereas most Sn deposits are in the western part (Chen et al., 1989; Chen and Zhu, 1993; Pei et al., 2001; Wang, 2010). Through extensive geochronological investigations during the past 20 years, the majority of the W deposits, some with significant Sn concentrations, in southern China (also called Nanling region) were proven to have formed at ca. 160–150 Ma (Mao et al., 2004, 2007; Hua et al., 2005a,b; Hu et al., 2012), and in an intraplate geodynamic environment, although essentially it Ubenimex is associated with the convergence of the Yangtze Block and Cathaysian Block (Mao et al., 2008a,b, 2013; Hu et al., 2012). But, the most economically significant of the Sn-dominant deposits, which mostly distribute in southeast Yunnan and Guangxi Provinces in the western part of southern China, including several world class deposits (i.e., Gejiu, Dachang and Dulong) are not part of Jurassic W ± Sn event. This regional Sn ± W metallogeny and its geodynamic setting in Late Cretaceous has remained poorly understood. Furthermore, several recent studies have pointed out that northeastern Vietnam, with similar Sn ± W deposits, is tectonically a part of the South China Block (Fig. 1a) (Sanematsu and Ishihara, 2011; Morley, 2012; Li et al., 2012; Goldfarb et al., 2014; Romer and Kroner, 2016). Through comparison of geological and geochronological data from the Sn deposits in southeastern Yunnan and northeastern Vietnam, we discovered that the Sn mineralization occurred ca. 98–78 Ma. Thus a preliminary understanding is that the Sn deposits in the southeast Yunnan and northeast Vietnam region are formed contemporaneously in Late Cretaceous and may share a same geodynamic setting.
Brief regional geological outline The studied area is underlain by rocks of the Youjiang Basin (also called Nanpanjiang Basin) (Sanematsu and Ishihara, 2011; Mao et al., 2013; Cheng et al., 2013a,b). The southern boundary of the basin is the Red River Fault Zone (Fig. 1). Stratigraphically, five lithological units, some metamorphosed, have been recognized in this region, namely: (1) Precambrian gneiss, granulite, schist, and migmatite, with minor slate, limestone, sandstone, carbonate, and dolomite distributed in the northwestern part of the basin, which is a part of the Kangdian Massif (Li et al., 2013); (2) Cambrian to Silurian terrigenous and carbonate sedimentary rocks, deposited in a shallow marine environment (Roger et al., 2000); (3) Devonian to Permian strongly folded limestone, siliceous limestone, and terrigenous rocks; (4) Lower to Middle Triassic turbiditic sediments that include conglomerates, sandstones, tuffaceous sandstones, siltstones, and shales, with a large amount of intercalated carbonate (Chen et al., 2014); and (5) Quaternary sedimentary deposits distributes in the southeastern part of northeastern Vietnam (Fig. 1b). Plutons with ages from Proterozoic to Mesozoic have intruded parts of the sedimentary succession (Fig. 1b). Proterozoic granite is mostly developed in the Vietnam side of the basin (Li et al., 2013). Paleozoic, mainly Silurian, granites are exposed in the Song Chay massif that lies on the boundary between China and Vietnam. They include an augengneiss derived from a porphyritic monzogranite emplaced at 428 ± 5 Ma (Roger et al., 2000), and the Phan Ngame orthogneiss dated at 438.7 ± 3.5 Ma. Permian to Triassic plutons include the Phia Bioc granite and the Cao Bang mafic intrusive rocks. The Phia Bioc granite is porphyritic and undeformed, contains microdioritic enclaves, and yielded zircon LA-ICP-MS U–Pb ages scattered from 247 Ma to 242 Ma (Roger et al., 2012). Late Cretaceous igneous rocks are widespread throughout the basin margin. Gabbro, syenite, mafic enclaves, mafic dikes, porphyritic granite, and equigranular granite in the Gejiu district in southeastern Yunnan yield ages from 85 to 78 Ma (Cheng et al., 2013a,b). Various types of granites in the Bozhushan stock yield ages from 87 to 84 Ma (Cheng et al., 2010; Li et al., 2013). The Laojunshan complex of southeastern Yunnan, which contains porphyritic granites, equigranular granite, and granite porphyry, yield ages from 89 Ma to 83 Ma (Feng et al., 2013). The Pia Oac leucocratic monzonitic granite of northeastern Vietnam yields zircon U–Pb SIMS and LA-ICPMS ages of 94–87 Ma (Wang et al., 2011a,b; Roger et al., 2012). A group of Sn–W polymetallic deposits distribute around these late Cretaceous granitic plutons. A detailed geological description on these deposits has been complied in Appendix 1.