摘要
We present new Re8211;Os molybdenite age data on three porphyry Cu8211;Mo8211;Au deposits (Yulong, Machangqing, and Xifanping). These deposits are associated with the Himalayan adakitic magmatism that occurred in a continental collision environment, controlled by large-scale Cenozoic strike-slip faults in the eastern Indo8211;Asian collision zone. Three distinct episodes of Cu8211;Mo8211;Au mineralization are recognized. At Yulong, Re8211;Os isotopic data of four molybdenite samples from sulfide-quartz veins in the quartz8211;sericite alteration zone yield an isochron with an age of 40.1±1.8 Ma (2σ), coincident to a zircon sensitive high-mass resolution ion microprobe (SHRIMP) age of 40.9±0.1 Ma for the host monzogranite. The molybdenite Re8211;Os dates, together with K8211;Ar, Rb8211;Sr, U8211;Pb, and 40Ar/39Ar dates on the pre- and intra-ore porphyries, suggest that Cu8211;Mo8211;Au mineralization formed during the late stage (∼40 Ma) of regional porphyry magmatism, but hydrothermal activity probably lasted to at least ∼36 Ma. At Machangqing, molybdenite Re8211;Os data from the K8211;silicate and quartz8211;sericite alteration zones yield an isochron with an age of 35.8±1.6 Ma (2σ), which is identical to the zircon SHRIMP and bulk-rock Rb8211;Sr ages (35∼36 Ma) of the host granite, but older than bulk-rock K8211;Ar dates (31∼32 Ma) for associated Au-bearing quartz syenite with advanced argillic alteration. At Xifanping, five molybdenite samples from the K8211;silicate alteration zone yield the youngest Re8211;Os isochron age in the area, at 32.1±1.6 Ma (2σ). The Re8211;Os molybdenite dates here are younger than K8211;Ar ages (33.5∼34.6) for hydrothermal biotite and actinolite. There is a positive correlation between the absolute age of the deposits and their Cu and Au reserves in the eastern Indo8211;Asian collisional zone. Episodic stress relaxation probably caused multiple magmatic intrusions, which most likely resulted in three episodes of Cu8211;Mo8211;Au mineralization in the eastern Indo8211;Asian collision zone.