Abstract: The black rock series are well developed in North Daba mountains of Southern Shaanxi,where the geochemical anomalies of Ag,Mo,V,As and Sb elements have been delineated. Although the geochemical anomalies of Ag element often have largescale and high strength,with the characteristics of a ring shaped, but the prospecting work of Ag deposit has no breakthrough.On the basis of analyzing and researching the newly discovered silver body in black rock series of this area, the cause of geochemical anomalies of Ag elements has been discussed in this paper. The results suggest that, ①The LujiapingFormation of Lower Cambrian(black shale, siliceous rocks) is the initial concentration of Ag element. Ag serves as the same group with Mo and V elements in the black rock series, all of them had experienced the same enrichment process, showing the deposition characteristics of deep-sea cold water. ②Secondary leaching is the main mineralization for stacking and enrichment of Ag element.The secondary leaching were easily happened in some favorable zones within the geochemical anomalies of Ag element to form the silver deposit.