Genetic mechanism of geothermal resources in the Gaoyang geothermal field and adjacent areas

As a green and renewable energy，geothermal energy plays an important role in solving the haze prob?lem northern China. Gaoyang geothermal field，near the Xiong’an New Area，is rich in geothermal resources. It is located in the Jizhong depression of the Bohai Bay basin，hosts strata of Jixian System andChangcheng System of Mesoproterozoic and Paleoproterozoic，in which the Wumishan Group of Jixian System is the main strata with reservoirs. The buried depth 3,600 m of the top of karst reservoir is considered as the boundary of the thermal field. The main body of the geothermal field is located in Gaoyang sub-uplift and Lixian slope, and covers a small area of the Baoding depression and Shaoyang depression. The Gaoyang geothermal field lies in an area of the karst reservoirs top surface with high temperature，where the temperatures of the middle and northern part of Gaoyang sub-uplift，the western boundary，and the junction area of Lixian slope and Shaoyang depression reach 120 ℃, while that of southern part of the geothermal field and the middle and eastern part of the Lixian slope is lower than 100 ℃. Overall the temperature contours of buried hill geothermal reservoirs exhibit an elliptic shape with a long axis in NNE direction. In hydrochemistry, geothermal water of Wumishan Group of Jixian System in the Boye area is of Cl-Na type，with solubility about 5,000 mg?L-1 and content of Cl-（2，300 mg?L-1） that is obviously higher than Xiongxian，Rong Cheng and other areas，while the solubility of SO42-（123-133 mg?L-1）is higher than Xiongxian，Rongcheng and Bazhou，and lower than the Tianjin and Liangxiang geothermal fields. This shows that the Jizhong depression belongs to a different geothermal system with the Tianjin and Liangxiang areas. The conceptual model of the Gaoyang geothermal field suggests that the atmospheric precipitation of the Taihang Mountains to the west is the supply of groundwater and the piedmont faults of the Taihang Mountains connect the surface water with reservoirs. Atmospheric precipitation flows through piedmont faults，the Hengshui fault，Anguo fault，Baichi fault，Chu’an fault and unconformities，and migrates to the Gaoyang sub-uplift，Lixian slope and Shenze sub-uplift where traps form. The fluid is heated by heat convection during the process of flowing through faults and bedrocks，forming the Gaoyang geothermal field which has a great potential of exploration and exploitation.