Zircon SHRIMP U-Pb dating of porphyry vein from the Jiama copper polymetallic deposit in Tibet and its significance

The Jiama copper polymetallic deposit is an important ore deposit with a super-large scale in the Gangdese metallogenic belt of Tibet. Re-Os dating of molybdenites occurred in skarn, porphyry and hornfels has indicated the metallogenic period of Cu-Mo mineralization during 17Ma to 14Ma, whereas the research on its age of diagenesis is rather lack, especially for the porphyry veins as south-north distributed outcrops. In this paper, two samples of slightly mineralized porphyry rocks: granite porphyry (sample JM52-0) and granitic diorite porphyry (sample JM52-46.7), have been collected from the No. 52 adit in Qianshan of the mining area. Through zircon SHRIMP U-Pb dating at the first time, their 206Pb/238U -207Pb/235U concord ages are 14.2±0.2Ma and 14.1±0.3Ma, respectively. The ages from the zircon SHRIMP U-Pb dating in this paper mean the crystallization age of magmatic zircon representing the south-north distributed granite and granitic diorite porphyry outcrops. The diagenesis age of this type porphyry veins is at the same period of ore-bearing porphyry intrusive event related to the south-north normal fault system and rift zone in Gangdese(18~12Ma). Diagenesis and mineralization age of the Jiama copper polymetallic deposit shows the similar period for metallogenesis and diagenesis, which is similar to other porphyry-skarn type ore deposits in the east part of the Gangdese metallogenic belt with a strong concentration of mineralization during 17~14Ma, indicating the magmatic-tectonic events in Miocene in the Gangdese and the genesis relationship between Cu-Mo mineralization and hydrothermal process in Jiama.