Abstract: Tangshan hot spring is one of the four great spa resorts of China. We conducted a systematic study to explore the genesis mechanism through a graphical method using a plot of dissolved silica versus enthalpy and a hydrogeochemical investigation, for the purpose of further exploration and sustainable use of the geothermal resources of this regon. The thermal reservoir temperature has been estimated to be 90°C, and the hydrochemical and isotopic compositions of the karst-geothermal water are different from those of the karst-cold water, pore water and surface water. Moreover, a higher temperature occurs in a deeper geothermal well than in a shallower well and less cold water is mixed in a deeper than a shallower well. Based on these data, a genesis model of the Tangshan hot spring has been postulated to be a low-medium temperature geothermal system of a convective type. The recharge area is located in the Tangshan mountain (known as Nanjing-Zhenjiang Ridge) as well as the Maoshan Ridge situated in the east of Jurong Basin, with a water circulation depth at 2.6~2.9 km. The geothermal water flows upward in Tangshan hot spring area through the Tangshan-Dongchangjie Fault in the intersection zones of the NW-and NE-striking faults.

Key words: Tangshan hot-spring area;karst-geothermal water;reservoir temperature;genesis model;Low-medium temperature geothermal system of convection type