Baiguoyuan Silver-Vanadium deposit is hosted by the Upper Sinian Doushantuo Formation black shales that were rich in Ag (up to 250ppm) and V (V2O5 up to 2. 484 weight percent). Studies on geochemistry and organic geochemistry show that the black shales contain amount sapropelic organic matter deriving from marine plankton and their DOP (degree of pyritization) values is very high, greater than 0. 70, indicating a euxinic bottom water environment. The marine transgression during the early Early Sinian was responsible for the formation of the black shales rich in Ag and V and organic carbon. The sea level rise during transgression made the water cloumn thicker and a oxic-anoxic-euxinic three-storeyed structure of water cloumn formed. Marine organisms collecting Ag and V from sea water and were deposited on the surface of sediment covering by euxinic bottom water. Within such a euxinic condition, organic matter would be decomposed rapidly by reducing bacteria; however, Ag and V appeared inactive in a reduced euxinic environment rich in H2S and they might be obserbed by residual organic matter, clays or Fe, Mn oxide/hydroxide, or surface-complexed with pryite formed in the early diagenesis. After a long sedimentation peroid, the balck shales that were rich in both Ag, V and organic matter formed.