Spatial and Temporal Variation and Mineralization Model of the Sinian Phosphorus-bearing Sequences in Central Guizhou Province

The phosphorus accumulation basin in central Guizhou province was developed on the basis of sedimentary basement of Nantuo Formation.During the transgression period of early Doushantuo Formation,the phosphate bearing upwelling from eastern deep ocean flooded into the semi-closed bays of central Guizhou in Fuquan,Weng'an,Kaiyang and Wenquan,where collophane synchronous was deposited.After that the central Guizhou old land uplifted rapidly and the original semi-closed bays transformed into highbeach.The previous cellophane layer was broken and leached by turbulent waves and ultimate formed sand-sized phosphorite ore bed.The disconformable contact between phosphorite deposits and overlying or underlying strata in Kaiyang indicated that the phosphorite ore beds suffered exposure and leaching.As the southeastern area of central Guizhou old land was outer continental shelf,the phosphorus was difficult to assemble in seawater and only thin and poor grade phosphorite ore bed was deposited in the area.During Dengying period to Early Cambrian,most areas of Guizhou turned into open shallow marine facies,but areas like Zhijin which was located in western of central Guizhou old land was relatively deep sea lagoon facies,the phosphate bearing upwelling flooded into these areas and formed low grade phosphorite ore bed.Based on the temporal and spatial variation analysis of sedimentary facies and the contact relation of layers in the Sinian phosphorus-bearing sequences,the authors proposed a mineralization model which explains the phosphogenesis event in central Guizhou.