Abstract: In order to study the ore-forming potential of mafic-ultramafic rocks with Cu-Ni sulfide in Dashantou, Beishan,Gansu Province, we have conducted the field investigation and comprehensive comparison, and made the following achievements : (1) the Dashantou rock was emplaced in Precambrian middle-deep metamorphic clastic rocks and gneissic granite, and is characterized by many episodes of magmatism. Early stage was dominated by the fine-grained gabbro rock foundation and the olivine, gabbro-two pyroxene peridotite mafic ultramafic rocks become dominant in later period. Rocks were differentiated obviously, and the Cu-Ni mineralization of lherzolite completely (Cu content 0.08%-0.46%, Ni content 0.2%-0.37%); (2) The major and trace elements have the characteristics of arc ultramafic basic magma (such as lack of high field intensity elements Nb, Ta, Ti, Hf , Y and P, enrichment of large ion lithophile elements Ba, Rb, Th, U, K and La); (3) Magnetic anomaly and rock surface mineralization are uniform. The results of electric conductivity show that the mineralization in deep rock is better.(the maximum value of the magnetic field strength 600nT, apparent polarizability (ηs) shows a maximum value of 7.5%-12.1% ); (4) the geochemical characteristics are similar to those of Jinchuan, Kalatongke, Hongqiling deposit, and the Heishan deposit in Gansu Provice. Therefore, Dashantou is expected to become the Cu-Ni sulfide deposit with reserve scale not less than that of the Heishan deposit.

Key words: copper and nickel sulfide;basic ultrabasic rock;Beishan;Gansu Province