Application of comprehensive geophysical exploration technology in geothermal exploration of the Foping dome

The Foping area, a geological dome in southern Shaanxi Province, has long been a geothermal blank zone. To explore the deep structural characteristics and stratigraphic configurations of the dome and preliminarily delineate the accumulation range of geothermal water, this study arranged the wide-field electromagnetic method (WFEM) and soil radon measurement profiles in the Foping area. Through field data collection, processing, and inversion, the electrical structural characteristics of the Foping area within a burial depth of 4 000 m were obtained. A new understanding was proposed accordingly: the Foping area develops multiple nappes from northwest to southeast, with the northern and southern sections dominated by thrusting and gliding, respectively. Its overall structural style is manifested as an antiform centered around Foping County. A continuous low-resistivity anomaly zone, occurring in the deep part, is associated with the roof detachment fault and the fracture zones formed in the central and lateral parts during rock intrusion. These faults create conditions for the downward migration and storage of groundwater. The superposition of thrusting rock fragments has led to well-developed fractures between rock fragments and pores, vugs, and fractures in brittle rocks such as marbles and quartzites, constituting the space for the occurrence of geothermal water. Based on objective factors such as local industrial planning, economic development, and road conditions, drilling work was conducted in Jiaochangba Village, Changjiaoba Town, 2.5 km north of Foping County, along the west bank of the Jiaoxi River. The completed well reached a depth of 2 002 m, producing geothermal water with a temperature of 35 ℃ at a flow rate of 392 m³/d. This achievement breaks through the traditional concept that the Foping dome contains no or little water. Therefore, this study provides actual data for exploring the geological structural characteristics and hydrogeological conditions in the Foping area, as well as a reliable basis for basic geological theory research.