Genesis of highly fractionated granite and associated W-Sn-Be mineralization in the Xuebaoding area, Sichuan Province, China
ORE GEOLOGY REVIEWS（2021）
Abstract
The Xuebaoding W-Sn-Be deposit in the Songpan-Garze Orogenic Belt of western China contains coarse-grained W-Sn-Be-F-P-bearing minerals, and has been the subject of several previous geochronological, petrographic, and ore-forming fluid studies. However, the genesis of the deposit, including the Pankou and Pukouling granites and associated W-Sn-Be mineralization has remained unclear. In this study, geochemical and Sr-Nd-Pb isotope analyses of both Pankou and Pukouling granites were performed revealing high A/CNK values (>1.09) and alkali contents (8.16-13.01 wt%), and are enriched in W, Sn, Be, B, F and volatiles. Sr-Nd-Pb isotope values of 87Sr/86Sr(i) = 0.67-0.73, epsilon Nd(t) = - 11.49 to - 23.19, 206Pb/204Pb = 18.710-19.908, 207Pb/204Pb = 15.647-15.708, and 208Pb/204Pb = 38.434-38.929 were determined. The samples contain 30-35 vol% muscovite and no hornblende. In addition, the granites have high Be (6.73-1681 ppm), Sn (28.9-200 ppm), and W (2.07-54.1 ppm) contents, and the host marble has low and variable Be (0.05-0.21 ppm), Sn (0.23-0.82 ppm), and W (0.20-2.37 ppm) contents. Further, three types of tourmaline were identified as associated with the magmatic-hydrothermal stage of the granites, with B isotope values of - 11.21%o to - 13.65%o, also indicating a metasedimentary origin for the granites. All these results indicate that the Pankou and Pukouling granites show highly fractionated S-type characters, derived by partial melting of metasedimentary rocks. Thus, the W-Sn-Be mineralization was closely related to the evolution of such highly fractionated granites in Xuebaoding.
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Key words
Highly fractionated granite,B isotopes,W-Sn-Be mineralization,Sichuan Province,S-type granite
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