Abstract:

Laozishan is a typical geothermal field in Subei Basin. We conducted a systematic study to explore into the genesis mechanism through heat flow measurement and hydrogeochemical investigation, for the purpose of further exploration and sustainable use of the geothermal resources. Results show that the background heat flow is 63.9 mW/m², and the hydrochemical and isotopic compositions of the thermal water are different from those of the shallow groundwater and surface water. Based on these data, the genesis model of the geothermal field has been postulated to be a low-medium temperature geothermal system of convective type. The recharge area is located in the Zhangbaling to the Xuyi mountain chain with a distance of about 60 km to the south of the geothermal field. The reservoir  temperature of the geothermal field has been estimated to be 73-120 ℃, with a water circulation depth of  2 350-4 200 m. The water age is about 7 800 a.The thermal water flows upward in Laozishan area in the intersection zones of the faults striking NNE-SSW and NW-SE.

Key words: Subei basin, Laozishan, geothermal fields, genesis model, low-medium temperature geothermal system of convective type