A series of mafic-ultramafic plutons are distributed in the southern margin of Altay folded belt and many of them are associated in space and time with Cu-Ni sulfide deposits. As geologists are divided in opinion on the genesis of the mafic-altra-mafic rocks, the genesis of mineralization is still a problem of much controversy. Some chalcopyrite, pyrrhotite and pentlandite samples were collected from the No.1 and No.2 intrusions of the Cu-Ni sulfide ores inthe Karatungk deposit to carry out Re_Os dating and tracing of ore_forming materials. The two groups of measured points defined isochronal ages of 282.5±4.8 Ma and 290.2±6.9 Ma with the initial 187Os/188 Os rates being0.256 3±0.003 7 and 0.272 1±0.005 3, respectively. The data show that theore-forming age is later than that of the Early Carboniferous rocks which host the mafic-altramafic intrusions, and is corresponding to the extension stage. They share the same mineralization time with the extensively developed shear zone type gold deposits. The ages are also similar to the alkali-rich granitoids developed in the southern margin of Altay folded zone and the northern margin of the Junggar folded belt. Their initial 187Os/188 Os values and γOs values of 202.23～1 061.59 and 195.07～473.24 indicate that large quantities of crustal substances were mixed with the Cu-Ni sulfide metallogenic system in the ore-forming process. 