## 2 Overview of the Mining Area
### Introduction to Geology and Hydrogeology of the Mining Area  
The main strata impacting coal-bearing strata mining in the Xinhua mining area, arranged from old to new, include the middle Permian Maokou Formation (P\({}_{2}\)m), the upper Permian Longtan Formation (P\({}_{3}\)_l_), the Changxing Formation (P\({}_{3}\)_c_), the lower Triassic Yelang Formation (T\({}_{1}\)_y_), and the Maocapu Formation (T\({}_{1}\)_m_), as well as the Quaternary (Q). The coal-bearing strata predominantly consist of the Permian Longtan Formation (P\({}_{3}\)_l_).  
The mining area is located on the west wing of the Jinsha Qianxi syncline, and the overall strata exhibit a monoclinic structure, with local undulations forming a secondary fold structure. Furthermore, during exploration and production activities, only one fault structure with a drop \(>\) 30 m was exposed near the southwest boundary of the mining area (within the Jinsha Longfeng Coal Mine scope). Subsequently, various coal mines have encountered small faults with varying drops. The strata within the mining area exhibited dip angles in the range of 65-155\({}^{\circ}\), with dip angles in the range of 0-27\({}^{\circ}\), with an average of 5-10\({}^{\circ}\).  
The Longtan Formation (P\({}_{3}\)_l_) in the mining area constitutes a coal-bearing stratum primarily composed of gray and dark gray, thin to moderately thick layers of siltstone, sandy mudstone, and mudstone. It is interbedded with fine sandstone, calcareous mudstone, and 4-7 layers of limestone and mudstone. It contained 12-15 layers of coal and 2-6 layers of minable coal seams. Notably, the 4\({}^{\overline{\pi}}\), 9\({}^{\overline{\pi}}\), and 15\({}^{\overline{\pi}}\) coal seams serves as the main mining coal seams in most mines, with the 5\({}^{\overline{\pi}}\) coal seam being the most minable, exhibiting a thickness ranging from 0.45 m to 5.55 m and an average of 1.68 m. The thickness of the 9\({}^{\overline{\pi}}\) coal seam varies from 0.59 m to 9.95 m, with an average of 2.77 m. The coal seam is positioned 39.70 m-76.22 m away from the Changxing Formation limestone, with an average of 53.31 m (Figure 2).  
Figure 1: Map of the Xinhua mining area.  
The main aquifers within the mining area include the Triassic Yelang Formation Yulongshan section (T\({}_{1}\)y\({}^{2}\)) limestone, the Permian Changxing Formation (P\({}_{3}\)c) limestone, and the Permian Maokou Formation (P\({}_{2}\)m) limestone. The limestone within the Yulongshan section of the Triassic Yelang formation (T\({}_{1}\)y\({}^{2}\)) served as the main aquifer, exhibiting a thickness range of 176.62-248.3 m and an average of 211.92 m. The karst development of this aquifer varied significantly, making it a weak-strong aquifer with abundant water. The Shabaowan section (T\({}_{1}\)y\({}^{1}\)) served as a water barrier between the Yulongshan limestone and the coal-bearing strata below, with a thickness range of 7.45 m-211 m and an average of 14.91 m. The coal-bearing strata of the Longtan Formation (P\({}_{3}\)l) served as weakly rich and impermeable layers. The aquifers directly filling water into the coal-bearing strata of the Longtan Formation were the overlying Changxing Formation limestone and the underlying Maokou Formation limestone. The limestone of the Changxing Formation (P\({}_{3}\)c), in contact with the Longtan Formation strata, varied in thickness in the range of 17.85 m-61.72 m, with an average thickness of 39.00 m. The karst was underdeveloped, functioning as a weakly water-rich aquifer. Furthermore, during mining activities targeting coal seams 9\({}^{\#}\) and above, the Changxing Formation limestone aquifer emerged as the primary aquifer influencing mine safety. The analysis of exploration data from various coal mines within the area indicated a third type of mineral deposit exploration, with the first type being karst water-filled deposits with simple hydrogeological conditions.  
Figure 2: Comprehensive bar chart of coal-bearing strata in the Xinhua mining area.