Analysis of controlling factors for the deposition of thick phosphorite of the Doushantuo period in the Weng′an area, Guizhou, China

The Weng′an area in Guizhou Province is a major accumulation zone of sedimentary phosphorite of the Doushantuo Formation in the Ediacaran period. Phosphorite layers a and b were generally deposited there. In some local areas, the thicknesses of phosphorite layers are nearly 50 meters, indicating that those areas are of significant economic value and considerable potential for phosphorite exploration. However, there is still a lack of in-depth research on the controlling factors of the formation of extremely thick phosphorite. In order to better understand the mineralization laws and the constraints of the sedimentary environment of this type of phosphorite deposits, in this paper, we have conducted a detailed field geological investigation of some typical sections including the Yingshang, Chuanyandong and Dengke sections in the Weng′an area, and have studied the sedimentary characteristics and paleogeographic environment of the deposit. The results show that the extremely thick phosphorite was mainly formed in the subsiding area of the bay environment. The key controlling factors for the deposition of the extremely thick phosphorite are the large thickness of the phosphorite-bearing strata and interlayers, and the continuous deposition occurred in the hanging wall and footwall of the phosphorite layer. However, when there are phenomena of sedimentary discontinuities, breccias, intense silicification, and thin dolomite interlayers among the phosphorite-bearing strata, the hanging wall, and footwall, there is no deposited extremely thick phosphorite layer. This understanding provides an important theoretical basis for the study of the sedimentary laws of the extremely thick phosphorite in the Weng′an area and its exploration prediction.