In the Bayan Obo area, there is a unique large rock complex composed of an alkaline-carbonatite complex (H8), carbonatite dykes, sedimento-volcanic series (H9), shallow intermediate-basic dykes and breccia peri-dotite. The carbonatite (H8) , the host rock of the super-large Bayan Obo Nb-Fe-REE Deposit, has long been erroneously assumed to be sedimentary dolomites. A comprehensive comparative study suggests that the car-bonatite is quite similar to the igneous carbonatite dykes in this region and other carbonatites in the rest of the world and quite different from the micrite mound at Sailinhuodong and dolomite in the typical sedimentary sec-tion. Thus, the host carbonatite of the deposit is actually a typical alkaline-carbonatite complex. In the CaO-MgO-(FeO + Fe2O3 + MnO) diagram, the carbonatite falls into two regions, i. e. , a calcic carbonatite repre-sented by calcite carbonatite and a magnesian carbonatite represented by ferrous dolomite or ankerite carbon-atite. The magmatic composition of the former belongs to the Ca-Fe series and that of the latter Mg-Fe series, both having an evolutionary tendency of Fe enrichment.A statistics of main igneous carbonatites (excluding sodic carbonatite) in the world also shows two indepen-dent rock types and two magmatic series. This suggests that carbonatite have an intrinsic lithogenic and metal-logenic specialization, which is independent of locality, age and occurrence. The host carbonatite originally may be subhorizontal sills and later changed into a synformal fold due to syntectonic deformation. It is inferred that there is a deep magmatic passage between the main and east ore bodies.The recognition and description of basalt in H9 put new constraint on its nature of formation and offer a new understanding on the origin of K enrichment in the K-rich slate, that the K enrichment is a fenitization mainly represented by the K-Na metasomatism accompanying the host carbonatite.