Characteristics and coal-controlling effects of structures in the Zhundong coalfield

The coal controlling of structures is critical to mining safety. However, few studies have been conducted on the structures of the Zhundong coalfield according to existing data. To ensure safe and efficient coal mining, it is necessary to conduct a study targeting the geological conditions for the coal mining of the coalfield. This study investigated the structural characteristics of the Zhundong coalfield. Based on the statistics of the fault structures, this study quantitatively characterized the structural complexity of the coalfield using fractal dimension, explored the current structural characteristics and tectonic dynamic genesis of the structures in Zhundong coalfield, and analyzed the influences of the structural characteristics on the geological conditions for coal mining. The results show that the faults in the Zhundong coalfield are dominated by normal faults and include a few large-scale strike-slip faults. As shown by the quantitative characterization of the structural complexity, the regional structures in the coalfield mostly have a fractal dimension of 0.5‒0.9, indicating that the Zhundong coalfield has a complex tectonic framework. The eastern Junggar Basin primarily underwent the Late Hercynian, Indosinian, Yanshanian, and Himalayan tectonic movements. After the formation of Jurassic coal seams, the north-south and northeast compressive stresses during the Yanshanian significantly transformed the coalfield. Moreover, the tectonic framework of the Zhundong coalfield was roughly formed after the Yanshanian tectonic movement. Controlled by multistage tectonic evolution, multiple typical coal-controlling structures have been formed in the Zhundong coalfield. Specifically, the synclinorium folded structures determine the tectonic framework of the Kalameili piedmont depression zone. For the coal-controlling imbricate thrust structures, their hanging walls are severely denuded and have poor coal-bearing properties, the coal measures on the foot wall are well preserved, and the coal seams are cut by the thrust faults on both sides. Moreover, the coal seams of the imbricate thrust structures have complex engineering geological conditions at fault boundaries, which increase the mining difficulty. The nappe structures cause the vertical recurrence of coal measures, increasing the difficulties with coal prospecting in the exploration of the coalfield. The nappe structures generally develop in parts with high in-situ stress, and the concentration of tectonic compression stress is prone to cause dynamic disasters in mines during coal mining. Therefore, it is necessary to develop corresponding mining modes for coal seams with different structural styles.