Abstract: Located on the northwestern margin of the North China Craton, Siziwang Banner belongs tectonically to Bayun Obo mar-ginal rift. It is about 100km away from the north of Solonker suture. A mafic-ultramafic belt is exposed in central Inner Mongolia, in EW extension roughly 300km long and 30km wide, comprising a favorable metallogenic belt for Cu-Ni (PGE) sulfide deposits. Many Cu-Ni (PGE) deposits (ore spots) have been found here including the Xiaonanshan Cu-Ni (PGE) deposit. The Xiaonanshan intrusion consists of gabbro and belongs to the tholetiitic series in petrochemical composition. Most of the rocks are relatively en-riched in large ion lithophile elements (Rb, Ba, U, Pb) and depleted in high field strength elements (Nb, Ta, Ti), exhibiting right-in-clined linear REE patterns with LREE enrichment relative to HREE. LA-ICP-MS U-Pb dating of zircons from Xiaonanshan orebearing gabbro yielded an age of 272.7±2.9Ma, indicating that the pluton should be the Mid-Permain intrusion. According to the re-gional geology, combined with the geochemical features, it may be inferred that the intrusion may be associated with intraplate tec-tonic setting