Metallic ore deposits are generally formed through magmatic intrusions, followed by metamorphism. The geological structures in such regions are often complex, with mechanical parameters exhibiting significant variability. These characteristics dictate the need for refined geological modeling and heterogeneous mechanical parameters for rock mass stability analysis to ensure reliability. Therefore, this paper proposes a novel method for rock mass stability analysis. The method fully leverages high-density drilling data from the mine and introduces an intelligent rock quality designation (RQD) identification technique, facilitating characterization of the spatial heterogeneity of rock mass RQD. Building on this, laboratory experiment data and in situ measurements are integrated, and the Hoek–Brown criterion is employed to achieve a refined characterization of heterogeneous rock mass mechanical parameters. This method allows for a realistic inversion of in situ rock mass mechanical conditions, overcoming the limitations inherent in assigning uniform parameters. Finally, the computed rock mass mechanical parameters are assigned to the refined computational model to conduct rock mass stability analysis. Taking the Jiangfeng Iron Mine, with its complex geological conditions, as an example, this method enables the accurate evaluation of the rock mass stability, determines the feasibility of joint mining, and calculates the appropriate thickness of the isolation pillars, effectively mitigating safety risks in mining operations. This method provides a valuable reference for the rock mass stability analysis of underground joint mining operations for similar mines.