Mineralogical Characteristics And Genesis Mechanism Of Xuebaoding W-Sn-Be Deposit, NW Sichuan Province

The Xuebaoding deposit is located in the northern region of Longmenshan, Sichuan Province, China. Situated in the merged area of the western Yangtze Block, Songpan-Ganze and Qingling Orogenic Belts, it is well known for its giant crystals with diameters up to 10cm. The typical ore vein can be distinguished into three Parts from granite to marble as host rocks with various mineral assemblages bearing W, Sn and Be.In the previous studies, views of ages, type, rocking-forming minerals and genesis of granites which provide ore material for mineralization differ. Also, distribution of veins, alternations and evolution of minerals are not clear. Furthermore, only fluid inclusions in minerals such as homogeneous temperature and oxygen ore carbon isotopes were provided. Therefore, origin of ore-forming fluids, deposit of ore materials and occurrence of ore deposits are not clear. In this study, genetic mineralogy and systematic Prospecting Mineralogy were employed to study various minerals in veins and granites. From the view of Chronology, Rock Geochemistry, Petrology, Crystal Chemistry, the mechanism of Xuebaoding deposit was discussed.It is hypothesized that both plutons represent an extremely fractioned and strongly prealuminous rare-metal granite system, rich in volatile and alkali elements with. On the one hand, exolution of large amounts of alkali elements and volatile elements lowing in solidus resulted in fractional crystallization sufficient to account for the high concentration of Li, Rb, Cs, Nb, Ta, W, Sn and Be. The 40Ar/39Ar age spectrums indicate that Pukouling and Pankou granites were emplaced at 200.6±1.3 Ma and 193.7±1.1 Ma, respectively. Morphology, chemical content, crystal structure and isotopes of beryl, scheelite, cassiterit, muscovite, fluorite and apatite were determined40Ar/39Ar step heating analyses of muscovite derived from the beryl-muscovite assemblage indicate mineralization at Part I began at 195.6±2. 5 Ma and is at least 5 Ma older than mineralization ages obtained at Part III, indicating that mineralization continued at least 5 Ma, partially explaining the occurrence of the giant crystals.It is inferred that ore material is from Pankou and Pukouling granites while ore-forming fluids evolved from magma. During the evolution of ore-forming fluids, meteoric water was fluxed. Also, organic material also was mixed with ore-forming fluids which facilitate the occurrence of the deposit.