DIAGENETIC AND MINERALIZATION AGES FOR THE PORPHYRY COPPER DEPOSITS IN THE GANGDISE METALLOGENIC BELT, SOUTHERN XIZANG
LI Guangming~1 and RUI Zongyao~2 (1. Chengdu Institute of Geology and Mineral Resources, Chengdu, SC 610082, China; 2. Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China.)
Recent examination and assessment about the porphyry copper deposits in Gangdise metallogenic belt, southern Xizang have revealed that these porphyry copper deposits are highly prospective. Several methods have been used for the isotopic dating of the Qulong, Tingong and Chongjing porphyry copper deposits, which gives out a diagenetic age of 17.58±0.74Ma (single-zircon dating of SHRIMP), a mineralization age of 15.99±0.32Ma (Re-Os isochron dating) and an alteration age ranging between 12.00Ma and 16.5Ma (K-Ar dating).The mineralization age is in general agreement with the alteration age. It can be seen that the diagenetic and mineralization age for the porphyry copper deposits in Gangdise metallogenic belt is noticeably later than the age for the collisional granitic intrusive rocks in this belt. The authors contend that the porphyry copper deposits in the study area were formed in a post-collisional extensional tectonic setting, and closely related to the delamination of the mountain roots of the orogenic belts and the uplifting of the Qinghai-Xizang Plateau.