Application of wide-field electromagnetic method for favorable target optimization in the Heishan granite geothermal area of Yunnan Province

The Heishan geothermal area is positioned above the sole Yunnan–Tibet high-temperature geothermal belt, where huge geothermal energy resources are available. Utilizing the characteristics of large exploration depth, extensive coverage, and high precision of the wide-field electromagnetic method, four survey lines were deployed, totaling 29.8 km, to enable a comprehensive analysis of the granite structure and fault distribution. The results indicate that the rocks within the area can be vertically divided into a granite basement and a fractured layer. Moreover, three different zones of resistivity were identified: the granite basement zone has a resistivity range of 2500–20000 Ω m, whereas the compressional shear zone and the secondary fault zone have a resistivity range of 750–2500 Ω m, and the extensional fault zone and the main fault zone have resistivity values below 750 Ω m. The Heishan-Hejian fault and the fault zone formed during its right-lateral strike-slip process, as well as the controlled area of the Qianmaihe fault, are all favorable targets. Of these, the Qianmahe fault possesses a larger-scale heat-conducting and water-controlling structure. In addition, in the secondary fault-controlled area extending to the west, the zone between F2’ and F4 exhibits renewed tectonic activity, suggesting a greater potential for geothermal resources.