Abstract: The occurrences,morphology of zircon,geochemistry and geochronology of andesite sampled from the upper section of cretaceous Bima formation emerged in Nuri mining area of Shannan,Tibet were analyzed in detail through the field macroscopic description,cathodoluminescence images of zircon and LA-ICP-MS to zircon.The results showed that Bima formation andesite has a comformable contact with underlying Mamuxia formation volcanic rock.The cathodoluminescence images of zircons showed that the zircon have better crystal form and clearer oscillatory band with ratio of w(Th)/w(U) greater than 0.1,which indicated that the zircon is a typical magmatic origin rock.Zircon with the U-Pb concordant age of 92.04±0.71 Ma（MSWD=0.74）belongs to the late Cretaceous epoch which represents the ore-forming time of Bima formation andesite,also represents that the eruptions of Sangri Group volcanic rock lasts from late Jurassic epoch to the late Cretaceous epoch.The accurate zircon U-Pb chronology evidence greatly constraints the activity time of Sangri Group arc volcanic rocks.Meanwhile,it implies that the Nuri deposit suffer from many large-scale and sustaining magmatic activities since the late Jurassic epoch.

Key words: Sangri group, Andesite, Bima formation, Zircon U-Pb dating