3-D gravity inversion of the deep spreading pattern of rock bodies and its control on lead-zinc deposits, Qingchengzi, Liaodong, China

The Liaodong Qingchengzi ore district, a representative magmatic-hydrothermal lead-zinc system in northeastern China, is characterized by the Late Triassic Shuangdinggou (zircon U-Pb age 224 Ma) and Xinling (225 Ma) granitic intrusions, which exhibit congruence in lithology, age, and tectonic setting, as evidenced by their shared emplacement along the same NE-trending Erdaogou fracture zone, implying a concealed subsurface connection that may have governed ore-fluid pathways. Despite this, the characteristics and influence of this deep-seated link remain unresolved. This investigation employs the isolation forest algorithm for gravity data analysis. Compared with the Z-score and local outlier factor methods, the isolation forest method more effectively suppresses isolated noisy measurements while preserving the overall geometry of the Bouguer gravity anomalies, as indicated by cleaner anomaly patterns and reduced directional Kriging interpolation errors. Kriging interpolation was implemented to refine spatial continuity (root mean square error = 0.0552). Trend surface analysis facilitated the isolation of local gravity anomalies, thereby improving the delineation of concealed structures. A 3-D University of British Columbia−Geophysical Inversion Facility (UBC-GIF) gravity inversion model, spanning 28.8 × 37.6 × 5 km, reveals a “bridge-like” high-density connector at a depth of ∼2200 m, linking the two bodies and coinciding with the NE-trending Erdaogou fracture and the spatial distribution of lead-zinc mineralization. Interactive profile inversion along profiles A−A′ and B−B′ constrained the basal depth to ∼4500 m, with a root mean square misfit of <0.194 mGal between the observed and calculated gravity anomalies. These findings substantiate a persistent deep connection, with the Erdaogou fracture acting as a conduit for magma intrusion and hydrothermal fluid migration. The observed “connectivity-fracture-fluid” coupling mechanism provides novel geophysical evidence for mineralization processes within the Liaoji Rift and supports the exploration of concealed ore deposits in analogous geological settings.