Abstract: The Subei Basin was enriched with medium-low temperature geothermal resources. This paper selected one representative area of the Subei Basin where one proven middle-temperature geothermal well and a hot-dry-rock verification hole were found as the study area. We employed the geochemical information carried by the geothermal fluid to have knowledge of the basic characteristics of deep geothermal reservoirs and the formation of geothermal resources at different depths. Results showed that the dominant cation in the geothermal fluid in the study area was Na+, however, the anion was of composite ion type, mainly Cl-. There was a good positive correlation beween Na+, TDS and Cl-. The calculation results of geothermal reservoir temperature were 73.8-145.1℃ estimated by the cations and silica geothermometer. In addition, the deep circulation depth of geothermal fluids in the Huangdang geothermal field was estimated to be 2.1 km. Through quantitative calculation, the elevation of recharge area for the geothermal fluids has been estimated from 203.5 m to 418.5 m. The 14C age of the geothermal fluid corrected by Bayesian algorithm showed an increasing trend from west to east, which was related to the direction of runoff of the geothermal fluid. The recharge area might be located in Zhangbaling Hilly area along the Xuyi Laozi Mountain, Mingguang city as well as Chuzhou city on the southwest side of the study area. The hydrogen and oxygen isotopic composition of the atmospheric precipitation in the recharge area was relatively consistent with that of the geothermal fluids, which further demonstrated the rationality of the inference of recharge elevation. According to the circulation depth of geothermal fluids, circulation period（or revised age of the Huangdang geothermal field）, recharge elevation, geothermal reservior temperature, and logging results, the mineralization model of the Huangdang geothermal field in Baoying county was established for the first time.

Key words: Subei Basin, geothermal fluid, geothermal reservoir temperature, geochemistry, Huangdang geothermal field