1. Xi'an Center of Geological Survey, China Geological Survey, Xi'an 710054, China; 2. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China

Guaishishan mafic-ultramafic complex in Beishan region of Gansu is a copper-nickel mineralized basic rocks. Their geochemical data show that theMg^# of basic rock is 74, and the Mg^# of ultrabasic rock is 84-90, which indicates the primary magma and early cumulation in characteristics. The total content of rare-earth and trace elements is low in ΣREE, the chondrite-normalized REE distribution pattern is slightly right enriched, and with 0.99-1.95 (La / Sm) _N , 1.13-2.96 (La / Yb) _N , 1.16-2.37 (Ce / Yb) _N , 0.93-1.02 (δEu) and 0.91-0.95 (δCe) in contents. Combining with the tectonic setting analysis of the rock, the authors consider that the mafic-ultramafic complex was produced in the active continental margin environment, and aged in Devonian with SHRIMP U-Pb dating. The subduction activity in Beishan area of Gansu in Paleozoic might continue to Devonian, in which the spinel peridotite in upper mantle partially melted in this process, and the rising magma was not contaminated significantly so that formed this copper-nickelmineralized mafic-ultramafic complex in Guanshishan.