Genetic model of Gujishan anticline geothermal system and prediction of potential areas in Western Hills of Beijing

There is no natural hot spring outcropped in the uplift area of Beijing Western Hills (Xishan). In the past several years, geothermal water temperatures ranging from 40℃ to 49℃ were discovered through drilling of thermal water boreholes one after another in Gujishan anticline. However, the research on geothermal origin has not been carried out yet. Geological, hydrogeological and geochemical studies show that hot rock reservoir is the karst fissure water developed in dolomite rock of Wumishan Group, Jixian System. The water geochemical type is HCO₃-Ca·Mg, neutral-to-weakly alkaline, micro hardness and fluorine fresh geothermal mineral water, which is named Xishan Gujishan geothermal field primarily. In this paper, the authors put forward the geothermal genetic model, and the analytical results show that the heat source is the radioactive element decay heat from the concealed acid granite pluton at the deep dome in Yanshanian period. It is of the layer carbonatite hot reservoir type located in uplifted mountain area different from the common geothermal systems of convective type developed in heat conducting faults. Based on dome structure and Yanshanian magma characteristics, the authors preliminarily predict that the domes like Xiaweidian dome in Beijing Western Hills have conditions for the formation of geothermal system, and they can be regarded as the advantage potential areas.