矿床地球化学国家重点实验室知识库

The Bilihe gold deposit in Inner Mongolia is situated in the Central Asian Metallogenic Domain. Its major ore body II is a porphyry-type body, spatially and temporally associated with granodiorite porphyry and granite aplite. In this study, the timing of gold mineralization is precisely constrained by using the zircon U-Pb dating for pre-mineralization intrusions and the molybdenite Re-Os dating for later molybdenite veins. Furthermore, zircon lif-O isotope analyses have also been carried out to decipher the nature of primary magma. Zircon U-Pb dating shows that the granodiorite porphyry and the granite aplite were emplaced at 269 +/- 2 Ma and 270 +/- 2 Ma, respectively, indicating the gold mineralization occurring no earlier than 269 Ma. Meanwhile, molybdenite veins are developed within the fractures and commonly cut across the auriferous veins. Thus, combined with a molybdenite Re-Os isochron age of 268 +/- 1 Ma, the gold mineralization in the Bilihe deposit can be precisely restricted to ca. 269 Ma. Zircon epsilon(Hf) (t) values are mostly positive (1.6-11.3), along with high 5180 values of 6.20-7.63%o, suggesting a mixed source between mantle materials and ancient continental crust (such as the Bainaimiao Group) for the Bilihe magma. It is also supported by the presence of the captured detrital zircons in these intrusions. Given a universally metallogenic environment for porphyry gold deposits, a thicken crustal setting related to the collisional intermission of the Paleo-Asian Ocean is favored to interpret the formation setting of the Bilihe deposit.