Mineralization age and magmatic origin of the Pujue Cu-polymetallic deposit in the western Gangdese belt: Implication for regional exploration.

The castern segment of the Gangdese tectono-magmatic belt hosts many giant and large porphyry copper deposits, while the western segment (west of 87 degrees E) of the belt is typically lacking of such type of deposits. However, the key factors controlling mineralization differences between the castern and western segments are still poorly understood. To address this issue, this paper investigates geology, geochronology and geochemistry of the newly-discovered Cu-Mo polymetallic deposit at Pujue in westem Gangdese. Zircon U-Pb LA-ICP-MS dating in this study shows that sample of the mineralization-associated granite porphyry has of 23.6 +/- 0.4Ma, and one sample of the post-mineralization quartz monzodiorite has an age of 16.4 +/- 0.3Ma. Molybdenite Re-D dating yields an isochron age of 24.4 +/- 0.3Ma, which is identical to crystallization age of the granite porphyry and can represent age o Ku-Mo mineralization. Both the granite porphyry and quarta moruodiorite exhibits gopchemical features of I-S type granites; in addition the elevated St/Y (27.57-49.62) and (La/Yb) (20. 18-40.37) ratios of the two suite of rocks also indicate their adakitic affinity. In combination with their goochemical features such as enrichment in LILE and depletion in HFSEa and relatively enriched S/Sr), (0.708014-0.708192), 8 (1) (-7.7-7.5) and (1) (-28-2.9) isotopic compositions, we propose that the granite porphyry were derived from partial melting of amphibolite facios lower crust modified by Noe-Tethys Ocean subduction, with different degree of involvement of ancient crustal material. Water-rich and oxidized nature of the granite porphyry magma reflected by high zircon AFMQ (-0.8-3.2) and low Ti-in-zircon temperature (564-677 degrees C degrees C) was resulted from high fractionation. In contrast, the post-mineralization quartz monzodiorite sourced from thickened eclogite-facies lower crust. In summary, the presence of the Pujue Cu-Mo polymetallic deposit in the western Gangdese implies that the western Gangdese has potential to produce water-rich and high /0, magma and associated magmatic-hydrothermal deposits even if it has significant amount of ancient crustal material