Study on the difference of water-bearing capacity of fault-controlled dolomites in Dengying Formation of a mining area in central Guizhou and its significance of water control

The central region of Guizhou Province enjoys global fame of its areas with large-scale production rich in phosphorus. For a long time, the phosphate rock resources in this area have provided a reliable guarantee for the domestic economic development. At present, this region has also become an important raw material base of phosphate rocks and a production base of fine phosphate chemicals in China. After decades of mining, phosphorus mines in this area have gradually changed from open pits to underground ones and from shallow to deep, and thus the hydrogeological conditions of deposits become increasingly complex. Dengying Formation, the main aquifers of phosphate rocks, is composed of dolomite with the water-bearing medium of solution pores and cracks. It is a water-bearing formation comprised of pure carbonate rocks with medium to high water abundance. Consequently, the high cost of mine drainage has imposed a heavy burden on mining enterprises. In addition, mine water inrush has severely threatened the exploitation safety of phosphate rock resources in this region. Therefore, it is very important to research the characteristics of water abundance of the Dengying Formation. The phosphate mine of Dawan, a water-filling deposit with deeply covered karst, is located on the western flank of the Baiyan anticline. The high bearing capacity of groundwater and complicated hydrogeological conditions of Dengying Formation are representative and typical in the Baiyan anticline area. Due to the super large scale and high grade of phosphate ore resources, the phosphate mine of Dawan was listed as a key project of mineral resource exploration in Guizhou Province in 2020. During the exploration work, a large amount of geological data was obtained through surface surveys, geophysical and hydrological logging, drilling, and hydrogeological experiments. In this paper, a study on the water abundance of the Dengying Formation of the deposit has been conducted based on the data from the exploration of the phosphate mine as well as the anatomy of typical mining areas. The research results show that the phosphate mine in Dawan is a karst deposit with water-filled roof, and the lithology, structure and fracture structure of the Dengying Formation in the water-filled layer are the main factors controlling the water-filling condition of the deposit. With an obvious distribution law, the water content and permeability of Dengying Formation present obvious characteristics of "plane partition" and "vertical stratification". In the plane of exploration area, there is a significant difference in water abundance of the Dengying Formation near and far from the structural area. The differences in fault properties also result in different water abundance of the Dengying Formation. In the vertical direction, there is a weak permeable layer with poor water content and relative water resistance in the middle and lower parts of the Dengying Formation. The waterproof design of mine based on the characteristics of water abundance in Dengying Formation is of great significance to ensure the safe production of the phosphate mine in central Guizhou, and to reduce the cost of mining drainage.