The Fule copper deposit is located in the western part of the Lhasa terrane. Cu mineralization is mainly developed in the tuff，which belongs to the Pana Formation of the Linzizong Group, coexisting with a large amount of hydrothermal muscovite. In this paper, the age of the hydrothermal muscovite was determined by using 40 Ar- 39 Ar method. Results shows that the plateau age is 77. 0±0. 8 Ma (MSWD=5. 8), corresponding with an isochron age of 76. 1±1. 3 Ma (MSWD=4. 1), indicating that the mineralization was formed in the Late Cretaceous and the age of ore- bearing tuff should be older than 77 Ma. Thus, the Fule tuff cannot be classified as the Eocene Pana Formation volcanic rocks. The geochemical composition of ore- bearing tuff shows that it belongs to calc- alkaline and metaluminous series and is geochemically enriched in Rb, Ba, Th, U and K, while depleted in Nb, Ta, Zr and Ti, showing the characteristics of is land- arc volcanic rocks. In addition, the geochemical composition of tuff also shows the characteristics of high Sr and low Y, with some properties of adakite. Based on the geochronology and rock geochemistry, we proposed that the ore- bearing tuff of the Fule copper deposit should not belong to the Pana Formation, and that it was formed at Late Cretaceous by partial melting of the New- Tethys ocean slab during the low- angle or flat- slab subduction.