Abstract:Baogutu porphyry copper deposit is located in the west Junngar, Xinjiang. The ore-forming processes are colsely associated with the late Carboniferous intermidate-acidic intrusions. The intrusion III-2, located in the south of the mine, is mainly composed of quartz diorite (porphyry) and diorite, with a small amount of proxeney diorite. With the characteristics of wholly mineralized and low grade, the intrusion is an ideal sample for investigation of the nature of the ore-forming magma. Early stage euhedrae amphiboles from quartz diorite have a high Mg# (0.72-1.00). The oxygen barometer based on amphibole compositions provides logfO2 values varing from ?NNO+1.4 to ?NNO+2.6, which is in the variation range of ore-bearing intrusions from porphyry copper deposits wordwild. Zircons from quartz diorite are characterized by high REE content (338ppm ~ 959ppm) and moderate Ce4+/Ce3+(29.55 ~ 89.50) and Eu/Eu*ratios (0.32 ~ 0.47), which are in the overlapping portion of ore-bearing and ore-barren intrusions from porphyry copper deposits. These data indicate that the oxygen fugacity of the ore-forming magma of the Baogutu intrusion III-2 are relatively high, which is benificial to the dissolution and migration of metal elements, and also facilitate to the formation of poyphyry copper deposits.