The Jiama deposit is one of super large-sized deposits with high grade and one of the most explored and studied deposits in the Gangdese metallogenic belt of Tibet. Because the South-Pit segment host large-sized skarn Cu-Pb-Zn ore bodies with high-grade, it has been given priority to mining. However, its diagenesis, mineralization and the relationship with main segment are still unclear. Based on detailed borehole logging and field geological evidences, it is determined that the mineralization is related to intermediate-felsic porphyries. The high-precision U-Pb dating of ore-bearing granodiorite porphyry yields the age of 15.5±0.3 Ma, which is consistent with the Re-Os age of molybdenite (15.23±0.22Ma). As the important part of Jiama polycentric complex mineralization model, the skarn ore body in South-Pit segment is mainly distributed on the contact between marble and hornfels. The skarn should be the result of Miocene magmatism and destroyed by the slide nappe fault and secondary faults. For the future exploration in South-Pit, more attention should be paid to the study of alteration and mineralization of ore-bearing porphyry and skarn, and to the locating of the ore-related fluid center.