Abstract: The recently discovered Baxi porphyry copper deposit is located in the Qiongheba ore−concentration area in East Junggar, Xinjiang. The ore−bearing porphyry are mainly composed of quartz diorite, quartz monzodiorite and granodiorite. Zircon U−Pb dating yielded two similar late Early Carboniferous ages of 337 Ma for quartz diorite and granodiorite. Quartz diorites and granodiorites are high SiO₂, CaO, Al₂O₃, and low K₂O contents, belonging the calc−alkaline, aluminum−weakly peraluminous. They are rich in LREE and LILE, such as Nb, Ta and Ti with weak negative Eu anomaly and high Sr and low Y contents, showing arc granitic characters with some Adakite futures. Combined with the regional research, we suggest the diorites and granodiorites in the Baxi porphyry copper deposit formed by partial melting of former subduction arc with magmatic mixing and following crystallization differentiation during the tectonic transition period from subduction to post−orogenic setting in Late Paleozoic. Porphyry copper deposits also formed in this period. In other words, except the Silurian−Devonian large−scale metallogenic stage, Carboniferous is also an important metallogenic stage in the Qiongheba area. It indicates that we should more attention on Late Paleozoic post−collision porphyry deposits in mineral exploration in northern Xinjiang and adjacent areas.