Abstract:

The Baishan porphyry Mo deposit is located in the SanchakouBaishan porphyry coppermolybednum belt, which is hosted in the eastern part of KangguerHuangshan ductile shear zone in eastern Tianshan, NW China. In this paper, SIMS U-Pb dating and in situ Hf isotope of zircons from the deep granite porphyry in Baishan deposit were systematically determined, so that we can constrain the petrogenesis and formation age of the granite porphyry emplaced in Baishan, and can reveal the geodynamical setting of the rockforming process of Baishan porphyry Mo deposit. Zircon SIMS U-Pb dating indicates that the magmatic activities in Baishan occurred at 229.7±3.2 Ma. Combined with the molybdenite ReOs isochron age (225229 Ma) reported by previous researchers, it is concluded that mineralization of the Baishan porphyry Mo deposit occurred in Triassic which is the same period as that of the rock formation. In situ Hf isotopic analyses of zircons that had previously been dated by SIMS yielded positive εHf(t) values ranging from +8.3 to +12 and the crustal model age ranging from 556 Ma to 758 Ma. Combined with the regional geological evolutionary history and isotopic data in this paper, we propose that the deep granite porphyry in Baishan deposit was formed in an intracontinental extension setting in the Late Triassic and the magma might be originated by partial melting of a juvenile lower crust.

Key words: Baishan porphyry Mo deposit, zircon SIMS U-Pb dating, zircon Hf isotope