Abstract:The rock salt deposit in Huanggang subdepression is a large rock salt producing area discovered by Shandong Institute of Geological Sciences in recent years. It is predicted that the total resources of rock salt deposit will exceed 24 billion tons. On the basis of summarizing the exploration results of rock salt deposits in Huanggang subdepression, sedimentary geological characteristics, metallogenic regularity and lithofacies distribution of rock salt deposits in the area have been preliminarily summarized and analyzed in this paper. The rock salt deposit is located in the middle section of Dawenkou formation of Guanzhuang group in Paleogene. The lithology is the interbedding of dark gray mudstone, silty mudstone, gray white gypsum mudstone and halite. It is a set of shallow lake saline lake sedimentary formation containing halite and gypsum. Its cap rock is Neogene Huanghua group and Quaternary. The occurrence form of rock salt mine is simple, and it occurs in layers with stable occurrence. Its strike is close to EW direction and inclines to S direction with gentle dip angle, generally less than 3 ° and 10 ° near local faults. There are 31 layers of exposed rock salt ore in the area. The burial depth is 1079.75~1730.86m, average thickness of single ore bed is 0.25~24.64m, maximum thickness of single layer is 53.96m, cumulative average thickness is 175.45m, and average grade of NaCl is 44.11%~96.08%. The accumulated maximum thickness of single hole is 320.23m, which is the largest thickness controlled by single hole in Shandong so far. The mineral composition of rock salt ore is relatively simple, the main salt minerals are halite and anhydrite, and the impurity minerals are mainly clayey minerals. The main chemical group of the ore is NaCl, followed by CaSO4, and the content of other components is very small. The ore structure is mainly medium and coarse-grained anisotomorphic to semi-idiomorphic granular structure, and the ore structure is mainly massive structure. The rock salt ore can be divided into two natural types: crystalline massive rock salt ore and gypsum rock salt mixed with rock salt ore, and the industrial type of ore is preliminarily determined as gypsum halite ore. The basin of Huanggang subdepression is a set of shallow lacustrine and salty lacustrine facies, which roughly reflects the evaporation deposition process of desalination, concentration and desalination of saline water bodies. In the plane, it is preliminarily divided into two lithofacies distribution areas: halite lithofacies area and gypsum mudstone facies area. The halite lithofacies area is close to the local sedimentary center of the salt forming basin, and thick rock salt deposits are developed. It is showed that the salt bearing strata in the southwest of Huanggang subdepression are inclined to the south, and the regional gravity data show that the area is close to local sedimentary center of the basin, so it has great prospecting potential for rock salt deposits. The rock salt deposit in the area is thick, pure in quality and moderate in buried depth. Geological conditions for the construction of salt cavern gas and energy storage are preliminarily evaluated, and the development and utilization prospect of the deposit is broad.
