Abstract: The Lawu ore deposit is located in Damxung County of Tibet and within the Shenzha-Pangduo Cu-Ag-Pb-Zn-Au ore-forming belt in the Gangdise metallogenic district. A 187Re-187Os isochron of 309±31 Ma was obtained for samples of pyrrhotite from the Lawu district,with the initial value being 187Os/188Os, γOs values and Re/Os ratios being 0.51±0.12, 306.90~880.29 and 20.46~80.46, respectively. In combination with the field geological and stable isotopic features, the Lawu ore deposit is considered to have been formed in Late Carboniferous Laigu period, and the ore-forming materials were probably derived from the mantle and severely contaminated by the crust, thus forming a sedex skarn ore deposit.