Geochemical exploration has been gradually transformed from qualification into quantification. Based on previous research results, the authors put forward two methods, i.e., areal productivity integration and 3D geological blocks, to calculate the resources of concealed ore bodies in old diggings, which are characterized by lack of exploration engineering and deep burial. With the prediction of Mo resources in the Chengmenshan ore deposit as an example and the geological body rich in Mo as the calculation object, and according to the Mo geochemical halo formation in different cross-sections in combination with the characteristics of 3D ore deposit, the authors estimated Mo resources at the shallow part (the first space 0~-500 m) and the depth (the second space -500 m~-1 000 m) of the mining area. The calculation results show that the resources estimated by these two methods at the shallow part are consistent with actual estimations, but the 3D geological blocks method is better in predicting the resources at the depth.