Abstract: Langan District in Suzhou City of Anhui Province locates at the southeast part in north China,primary diamond is found in the basic rock in recent years,two strongly weathered residual type diamond orebodies are delineated,and diabase is the main carrier of diamond,this is the first time in China for finding primary diamond in the basic rock,great breakthrough has been gained,after mineral reserves review,the small scale can be reached. According to the prospecting achievements of Langan District,the geological characteristics of diamond deposit,the geological conditons and genesis of the diamond deposit are studied.The results show that:①genesis of the primary diamond deposit is a new genetic type which mainly have relationship with diabase rock mass in Laozhai Mountain,this is not same as the traditional concept that the ultrabasic kimberlite and potassium－magnesium lamprophyre are different from the ore－forming parent rocks of diamond deposit,basic rock is the main carrier of diamond deposit;②the relevant geological conditions of diamond mineralization are mainly for long term stable archean craton in North China Platform,gentle sedimentary cover,development of deep major dislocation and secondary dislocation system,diabase rock mass in the Laozhai Mountain,large number of indicative minerals, effect of weathe〖BP(〗〖BP)〗〖LM〗ring and residue etc.;③metallogenic genesis of the original diamond deposit in Langan Distric may be capture causes,which can be discribed that after the formation of primary diamond,it is captured in the rising process of basic magma formed in the deep mantle near asthenosphere,and it is quickly carried to the surface through Tanlu fracture zone and its secondary fault zone,the diamond deposit in Langan District is the outcome of multi－stage and multi－period development.

Key words: Primary diamond ore, Diabase, Basic rock, Metallogenic geological condition, Deposit genesis