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  • br Late Cretaceous magmatism mineralization

    2018-11-14


    Late Cretaceous magmatism–mineralization geochronological frameworks in southeast Yunnan and northeast Vietnam The tin polymetallic mineralization and related igneous rocks in the western South China Block have attracted some interests in past decades (Tu et al., 1984; Xie et al., 1984; 308 Geological Party, 1984; Wu et al., 1984; Wu and Liu, 1986; Luo, 1995; Mao et al., 2008a,b). However, the pioneering data are controversial as it indicates that these igneous rocks and ore deposits mostly formed during the WP 1130 cost to Late Oligocene (Wang, 1983; Yan et al., 2005). Another aspect, previous studies on the geology and timing of the Sn–W polymetallic deposits and related tectono-magmatic activities in northeast Vietnam were relatively limited, which led the understandings on the ore genesis and regional metallogeny are limited. Fifteen high precise SHRIMP or LA-ICP-MS zircon U–Pb dating results, comprising ages of the gabbro, mafic microgranular enclaves (MMEs), syenite, mafic dykes, porphyritic granite and equigranular granite, demonstrate that all the igneous rocks in the Gejiu district formed between 78 Ma and 85 Ma (Cheng and Mao, 2010; Cheng et al., 2013a,b) (Appendix 3). Another 13 Ar–Ar muscovite/phlogopite dating results on different mineralization styles in the Gejiu district ranging from 77 Ma to 95 Ma. These similar ages between intrusions ore deposits indicate a genetic relationship between mineralization and magmatism. Cheng et al. (2010) and Li et al. (2013) reported the ages of three phases from Bozhushan granitic intrusions in SE Yunnan province are 86.5 ± 0.5 Ma, 87.5 ± 0.7 Ma and 87.8 ± 0.9 Ma. As mentioned before, the Bozhushan granitic complex is considered to be genetically associated the periphery Ag–Sn–W polymetallic mineralization (Appendix 1), including the Bainiuchang Ag–Sn deposit. Laojunshan is another Sn–W polymetallic ore related large granitic complex in SE Yunnan province (Fig. 1b). Three samples collected from Nanyangtian W polymetallic deposit, which locates in the eastern side of the Laojunshan complex, representing three phases of the Laojunshan granites yield ages of 87.2 ± 0.6 Ma, 86.8 ± 0.4 Ma and 85.9 ± 0.4 Ma, respectively (Feng et al., 2013) (Appendix 1). Li et al. (2013) analyzed the LA-ICP-MS zircon U–Pb ages of granites from Dulong Sn–Zn deposit, which locates in the western part of the Laojunshan complex (Appendix 1), yielding 84.3 Ma to 91.7 Ma. These results are consistent with the data reported by Liu et al. (2007), which are ranging from 86.9 Ma to 92.9 Ma. For the timing of mineralization in this district, Liu et al. (1999, 2000) reported the sphalerite Rb–Sr age of Dulong deposit is 76.7 ± 3.3 Ma to 79.8 ± 9.11 Ma, and Liu et al. (2007) further analyzed the TIMS cassiterite U–Pb age of 82.0 ± 9.6 Ma. The above data are consistent with the new molybdenite ReOs and muscovite Ar–Ar dating results presented in this study (Appendix 2). All these data suggest the late Cretaceous is a major mineralization and magmatism period in the Laojunshan complex and periphery areas. Late Cretaceous magmatic and mineralization ages have been reported in the northeast Vietnam in recent years. Wang et al. (2011a,b) reported the age of the Tinh Tuc Sn–W deposits in the east of Piaoac pluton in northeast Vietnam is 93.9 ± 3.0 Ma. By using of TIMS and LA-ICP-MS zircon U–Pb and mica Ar–Ar methods, Roger et al. (2012) and Chen et al. (2014) reported the ages of Piaoac granite are ranging from 83.5 Ma to 90.6 Ma. Another example in northeast Vietnam is the Nui Phao W polymetallic ore district (Fig. 1b), Sanematsu and Ishihara (2011) analyzed the ore-related granites by mica 40Ar39Ar method and obtained four ages, which yielding from 81.5 ± 0.3 Ma to 82.8 ± 0.3 Ma. These two ages are quite consistent and are believed to represent the solidification of granite and the formation of associated Sn–W mineralization occurred in the Late Cretaceous (Sanematsu and Ishihara, 2011).