Abstract:Most major diamond deposits are located in North China Craton (NCC). Now large number of micro-diamonds from alkalic basic rocks were sorted in south of NCC (at northen Jiangsu & Anhui province). This was a new type of diamond that differs from the kimberlite and lamproite types. In this research, these diamonds were tested and analyzed by FTIR. Most diamonds contain isolated nitrogen (C center), while A few contain nitrogen pairs (A centers) and nitrogen aggregates (B centers), in which Y center (1145~1150 cm-1) is associated with C center, indicated that these diamonds are mostly of natural Ib, Ib/IaA and IaAB types, of which Ib is the dominant. Nitrogen is the most common substitutional impurity in diamonds and is present in numerous combinations of nitrogen ± vacancy centres. The content of N in diamonds from this area is generally not high. Through the calculation of IaAB diamond’s FTIR data, it is believed that the mantle residence times of the IaAB diamond is about 550 Ma, and the diamond record the temperature is about 1225 ℃, derived from depth of 150 km. The large number of Ib type diamonds from this area indicates that the diamonds were rapid uplift out of the diamond stability field when they were still “young”, so most of isolated nitrogen were preserved, not aggregated to A centers.