Porphyry copper deposits are usually associated with high-Sr/Y granitoids. The Miocene Gangdese porphyry copper belt in southern Tibet is also associated with high-Sr/Y granitoids, which also formed wolframite mineralizations. Why some coeval high-Sr/Y granitoids formed Cu deposits (Cu granitoids) whereas others formed W mineralizations (W granites) remains unclear. We attempt to address this issue by studying the magma sources and properties, analyzing magmatic zircons, biotites and apatites in theses granites, and combing this information with previously published bulk-rock and zircon isotopic data. In-situ chemical analyses of magmatic zircon, biotite and apatite suggest that the properties of the magmas that produced the Cu granitoids and W granites were significantly different. Zircon ΔFMQ values of the W granites are much lower than those of the Cu granitoids, suggesting a more reduced magma for W mineralizations. Water content of the W granites (7-9 wt.%) seems to be lower than that of the Cu granitoids (10-12 wt.%). This is suggested by the low zircon Ce/Nd and (Ce/Nd)/Y ratios and high Dy/Yb ratios in the W granites. Biotite and apatite from the W granites generally have lower Cl contents than those from most Cu granitoids. Moreover, SO3 content in apatite from the W granites is also lower than that from the Cu granitoids. These data agree with the genetic environment suggested by previously published isotopic data. Bulk-rock Sr-Nd and zircon Hf isotopes indicate that the Cu granitoids were mainly sourced from juvenile lower crust. In contrast, the source of W granites was contaminated with the old Lhasa terrane basement. Our results highlight the role of magma oxygen fugacity and volatile components in controlling metal variations in high-Sr/Y granitoids. Combinations of magmatic zircon ΔFMQ and Ce/Nd, (Ce/Nd)/Y and Dy/Yb ratios, and apatite and biotite SO3 and Cl contents, can be used to discriminate W granites from Cu granitoids in the Gangdese metallogenic region, and hence granitoids potentially hosting W versus Cu ore deposits.

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