Discovery and prospecting significance of gravity sliding structures in the Lutang coal-bearing series graphite ore district

Objective  Previous exploration and research data indicate that the structure of the Lutang Mining Area belongs to the Rutang–Shatian synclinorium. The coal-bearing strata are the upper member of the Upper Permian Longtan Formation. The Qitianling granite pluton intrudes on the eastern flank, and the coal seams near the intrusion have undergone contact metamorphism into coal-measure graphite. The maximum buried depth of the orebody does not exceed elevation 0 m. However, huge discrepancies have emerged between structural interpretations based on mine exposures and the actual occurrence range of ore beds.

Methods  The author led a technical team to conduct in-depth development of geological data, leading to a new understanding of the structural features of the mining area. Using surface reconnaissance, roadway mapping, sampling and testing, geological mapping and other methods, the geometric, kinematic and dynamic characteristics of gravitational gliding were studied.

Results and Conclusions  Through a series of analyses and comprehensive studies, inferential understandings were proposed: a gravity sliding structure (F₁) sliding from east to west is developed on the eastern flank of the mining area. The overlying system is a synclinorium confirmed by years of exploration and development, while the underlying system constitutes the concealed segment of the regional Rutang–Shatian synclinorium, which hosts a large coal-measure graphite deposit in an area previously unexplored and unstudied. Subsequent prospecting and exploration work in 2024 yielded more definitive insights into F1, the concealed segment of the Rutang–Shatian synclinorium, and its ore-bearing potential. F1 is a gravity sliding structure that resembles a klippe in plan view and is spoon-shaped with an upward-warping end in cross-section. The concealed area forms an asymmetric tight syncline with a steep western limb and gentle eastern limb, hosting “thick, multiple and high-quality” coal-measure graphite orebodies with a maximum buried depth exceeding −400 m elevation. Research on the Rutang gravity sliding structure has revised the regional structural distribution pattern in southern Hunan, explored its formation mechanism, established a spoon-shaped gravity sliding structure-controlled mineralization model, and predicted coal-measure graphite resources in the concealed area. These novel understandings are of great guiding significance for geological prospecting and strategic importance for mines in the declining production stage.