Analysis of structural surface stability in the Panlong lead-zinc mine and engineering implications

 [Objective] The Panlong lead-zinc deposit, an important polymetallic deposit in the central Guangxi region. The increasing depth brings challenges related to high in-situ stress and structurally complex rock masses. Instabilities along structural planes have become a major geotechnical hazard. However, current understanding of the interplay between fracture geometries and stress fields remains limited. This study aims to evaluate the stability of structural surfaces at depth and their implications for safe mine development. [Methods] High-resolution data on fracture orientation and spacing were obtained through ultrasonic borehole television imaging in boreholes SK1 and SK2. Hydraulic fracturing tests were used to determine the magnitude and orientation of in-situ stresses. Stress tensor transformation and the Coulomb friction criterion were applied to estimate shear and normal stresses on structural planes and assess their slip tendency under current stress conditions. [Results] The rock mass in the Panlong mine contains steeply dipping structural planes predominantly oriented NW–NNW and NE–NEE. Cluster analysis revealed three dominant fracture sets, reflecting tectonic control from nearby faults. Furthermore, in-situ stress measurements between 500～850 m depth show S_H = 28.29～44.69 MPa, S_h = 19.46～27.09 MPa, and S_v = 14.50～22.68 MPa. The lateral stress coefficients k_H and k_h average 2.07 and 1.28, respectively, indicating a horizontal compressive regime with S_H oriented NW–NNW. Analysis of borehole breakouts and drilling-induced fractures supports the NW–NNW orientation of maximum horizontal stress. Subsequently, a total of 2,948 structural planes were analyzed. Slip tendency evaluation based on slip tendency (T_s = 0.2～0.4) shows that fractures with T_s > 0.20 are primarily distributed at depths less than 550 m. Steeper fracture planes (40°～75°) exhibit a high slip potential, indicating a higher likelihood of shear slip. NW–NNW-oriented planes exhibit both high density and high slip potential, especially when fracture aperture exceeds 10 mm. [Conclusion] It is found that the structural planes in the Panlong mine are characterized by steep dips and strong orientation clustering, primarily NW–NNW and NE–NEE, reflecting significant tectonic control. The in-situ stress regime is governed by horizontal compression, which favors the activation of reverse faults. This aligns with observed fracture development and supports the role of tectonic faults in stress field evolution. NW–NNW-oriented fractures, particularly those with low slip tendency and wide apertures, pose the highest risk for shear reactivation under current conditions and require targeted monitoring and support. Furthermore, structural planes in shallow zones (<550 m) present higher slip potential than deeper zones, emphasizing the need for depth-specific design strategies. [Significance] The findings provide a detailed understanding of structural plane behavior under deep mining conditions and provides scientific support for roadway layout optimization, support system design, and hazard mitigation.