Himalayan Cu–Mo–Au mineralization in the eastern Indo–Asian collision zone: constraints from Re–Os dating of molybdenite

• Published in: Mineralium deposita 2006-05, Vol.41 (1), p.33-45
• Main Authors: Hou, Zengqian, Zeng, Pusheng, Gao, Yongfeng, Du, Andao, Fu, Deming
• Format: Article
• Language: English
• Subjects: Absolute age; Cenozoic; Geology; Mineralization; Plate tectonics; Quartz; Rocks
• ISSN: 0026-4598; 1432-1866
• DOI: 10.1007/s00126-005-0038-2

We present new Re-Os molybdenite age data on three porphyry Cu-Mo-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 Indo-Asian collision zone. Three distinct episodes of Cu-Mo-Au mineralization are recognized. At Yulong, Re-Os isotopic data of four molybdenite samples from sulfide-quartz veins in the quartz-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 Re-Os dates, together with K-Ar, Rb-Sr, U-Pb, and ^sup 40^Ar/^sup 39^Ar dates on the pre- and intra-ore porphyries, suggest that Cu-Mo-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 Re-Os data from the K-silicate and quartz-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 Rb-Sr ages (3536 Ma) of the host granite, but older than bulk-rock K-Ar dates (3132 Ma) for associated Au-bearing quartz syenite with advanced argillic alteration. At Xifanping, five molybdenite samples from the K-silicate alteration zone yield the youngest Re-Os isochron age in the area, at 32.1±1.6 Ma (2σ). The Re-Os molybdenite dates here are younger than K-Ar ages (33.534.6) 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 Indo-Asian collisional zone. Episodic stress relaxation probably caused multiple magmatic intrusions, which most likely resulted in three episodes of Cu-Mo-Au mineralization in the eastern Indo-Asian collision zone.[PUBLICATION ABSTRACT]