Abstract:Miao’ershan- Yuechengling batholith, located in the north Guangxi, is a multi- aged composite granite pluton, including Neoproterozoic, Caledonian, Indosinian and Yanshanian granites. Granites in this region are related to several large tungsten (W)- depositsformed in the Caledonian and the Indosinian, such as the Niutangjie W- (Sn) deposit, the Jiepai W- Cu deposit and the Yuntoujie W- Mo deposit. Additionally, Yanshanian niobium- tantalum mineralization is found in the Gedongping district in the Yuechengling. Douzhashan pluton located in the middle of the Miao’ershan, is mainly composed of two- mica granites. In this study, we also found (tourmaline- bearing) muscovite granites which contain abundant Nb- Ta- W oxides in the Douzhashan drill- holes. We studied these samples in detail to further understand the multi- aged mineralization in the Miao’ershan- Yuechengling batholith and investigate the ore- forming processes of different types of deposits. The granitic samples from drill- holes include fine- grained (tourmaline- bearing) muscovite granites and two- mica granites.The (tourmaline- bearing) muscovite granite intrudes into two- mica granite which occurs as the main granite body. Detailed mineralogical studies show that the (tourmaline- bearing) muscovite granite contain various rare- metal minerals, such as columbite- group minerals, ilmenorutile, and cassiterite found in the muscovite granite, and complex Nb- Ta- W oxide mineral aggregates, including columbite- group minerals, wolframixiolite, qitianlingite, and wolframite found in the tourmaline- bearing muscovite granite. Morever, we also found some tourmaline- bearing stockworks which contain abundant scheelite grains in muscovite granite. U- Pb data of magmatic cassiterites (219±4 Ma) suggest that the mineralization occurred during the Indosinian. Combined with petrological observations and trace element composition of muscovite, it is found that the tourmaline- bearing muscovite granite is enriched in tungsten and thus contains higher abundance of the Nb- Ta- W oxide minerals. With the progressive enrichment of boron- rich fluid, scheelite and wolframite precipitated in the late- stage tourmaline- bearing stockwork. Compared to the two- mica granites, the (tourmaline- bearing) muscovite granites contain higher Na and P, but lower K, Ti, Fe, and rare earth element concentrations with more obvious tetrad effect. Additionally, they also have higher rare- metal elements such as Nb, Ta, W, and Sn concentrations (up to 56×10-6, 40×10-6, 547×10-6 and 89×10-6, respectively) and lower Nb/Ta and Zr/Hf ratios (as low as 14 and 112, respectively). These characteristics of whole- rock geochemistry show the (tourmaline- bearing) muscovite granites are more evolved than those two- mica granites. In addition, compared to selected Indosinian two- mica granite and muscovite granite related to the W mineralization in Miao’ershan- Yuechengling batholith, the tourmaline- bearing muscovite granite in the Yuntoujie W deposit share similar characteristics with the Douzhashan (tourmaline- bearing) muscovite granite. It is inferred that the potential Nb- Ta mineralization locally could be found in the Yuntoujie W deposit.
