Re-Os Dating for Molybdenite from Qulong Porphyry Copper Deposit in Gangdese Metallogenic Belt,Xizang and Its Metallogenic Significance

Qulong deposit located in Gangdese granitoid batholite in the eastern Gangdese metallogenic belt is one of typical porphyry-type copper deposits. High precise dating of Re-Os for molybdenite determined the mineralization age of Qulong copper deposit. The Re-Os model ages for 6 molybdenite samples are from 15. 99 Ma to 16. 74 Ma, with variety less than 1 Ma. According to the best-fit calculation of 6 samples, Qulong deposit yielded a 187Re-187Os isochron age of 16. 41 + 0. 48 Ma(2σ error, MSWD=1. 5) , identical to the Re-Os model ages. Those date of Qulong deposit are consistent with the mineralization ages (14 Ma±) of the porphyry-type copper deposits in Gangdese belt. The date of mineralization age of the porphyry-type copper deposits in Gangdese belt shows that the copper mineralization occurred in the period from 16 Ma to 14 Ma, in a short session with time limit no more than 2 Ma, and implies the speciality of paroxysmal mineralization. The deposits occurred during eruption of potassic lava and east-west extension of the crust in Xizang (Tibet). The geochemistry characteristics of the copper-bearing porphyries and the space-time adhere to potassic lava and to south-north trending extensional structure system indicate that the porphyry-type copper deposits in Gangdese belt are controlled by the evolution of the Himalayan-Tibet collision orogen and tectonomagmatism under the collision belt, which implies the dynamic setting of paroxysmal mineralization of porphyry-type deposits in Gangdese belt.