Abstract:

         The Bangpu Mo-Cu polymetallic deposit is one of the typical large-scale porphyry deposits which lies in the eastern Gangdese metallogenic belt, Tibet. Its major  ore elements are molybdenum and copper, and its accompanying elements are lead and zinc. A monzonite granite-porphyry whole-rock Rb-Sr isochron age of (13.88±0.38) Ma with MSWD=1.7 was obtained which represents the crystallization age of the rock. Furthermore, a pyrite Rb-Sr isochron age of (11.0±1.5) Ma with MSWD=3.5 was obtained for Mo and Cu bearing ores which represents the age of later episode of Mo-Cu mineralization. Combining with the zirconSHRIMP U-Pb age （13.9±0.3） Ma and laser micro-probe 40Ar-39Ar age （13.9±0.9） Ma, it is shown that the rock-forming and ore-forming ages are mutually consistent. The molybdenum and copper mineralization lasted about 3 Myrs. The inital 87Sr/ 86Sr valu（0.706538~0.709190） and mantle composition percentage (Pm) (4.03%~ 51.65%) indicate that the primary magma might be derived from the mantle, and emplaced in the Gangdese extensional setting 14 Myrs ago. The mantle magma was interacted with crustal dioritic magma and contaminated by crustal materials during its ascending process. But generally speaking, the magma source was mainly mantle-derived.

Key words: Rb-Sr isochron, monzonite granite-porphyry, pyrite, Mo-Cu polymetallic deposit, Bangpu of Tibet