Study on heterogeneity of deep geothermal gradient and thermodynamic response mechanism in Sanshandao Gold Mine

As the exploitation depth of global deep mineral resources continues to increase, the geothermal hazards induced by the geothermal gradient effect have become a key challenge restricting the safe and efficient mining of deep mines. The Sanshandao Gold Mine, a typical deep mine in China, was taken as the research object. Through multi-scale thermal parameter-based dynamic borehole coupled monitoring technology, the heterogeneity characteristics of the deep geothermal gradient and its thermodynamic response mechanism were systematically analyzed. Combined with the regional geological background and structural features of the engineering area, the influence patterns of stratigraphic lithology, tectonic activity, and magmatic intrusion on the distribution of the geothermal gradient were revealed. The results indicate that the constant temperature zone of the Sanshandao Gold Mine is located at a depth of 30–70 m, with a stable temperature of 13 ℃–15 ℃. The temperature in the increasing temperature zone exhibits a segmented linear increase with depth, following a linear fitting relationship of t = 0.027h + 4.922 5. A significant rise in the geothermal gradient to 0.028–0.030 ℃/m is observed within the depth range from −1 100 to −1 700 m, while a slight decrease to 0.024–0.026 ℃/m occurs in the deeper section（from −1 700 to −2 000 m）. The predicted rock temperature at −2 000 m depth can reach 58.9 ℃. Further analysis shows that differences in lithological thermal conductivity are the primary driver of vertical heterogeneity in the geothermal gradient, while magmatic activities and regional tectonic background exacerbate gradient anomalies through heat flow redistribution. This study provides a theoretical basis and technical support for the prevention and control of geothermal hazards and the assessment of geothermal resources in deep mines.