Hydrogeochemical Characteristic and Formation of the Xiangcheng Ranwu Hot Spring in Sichuan Province.

Taking the observation spring (Xiangcheng Ranwu hot spring ) in Xiangcheng, Sichuan as the research object, we collect water samples from observation spring and other nearby hot springs and analyze the main chemical ions compositions, trace elements and hydrogen and oxygen isotope compositions to study water cycle characteristics and formation mechanism of the hot spring. The results show that, the hot spring hydrochemical type is Na-HCO₃, and belongs to medium temperature, alkaline, low salinity hot spring and contains B, Li, Ba and other trace elements. Ions in hot springs are mainly dissolved from silicate minerals in surrounding rock during water-rock interaction. The stable hydrogen and oxygen isotopes (δ¹⁸ O and δD) composition indicates that the main source of the recharge for the hot spring is precipitation. According to the result of Si-enthalpy model, the geothermal reservoir temperature of the hot spring is 275*C and circulation depth of hot spring is 5. 3 km. The ratio of mixing cold water with hot water is about 84% -- 86 % which calculated by Si-enthalpy equation method. The genetic model of Xiangcheng Ranwu hot spring is that groundwater receives recharge from infiltration of precipitation m the mountain area, undergoes deep circulation and obtains heat from heat flow and flows up to the surface along the Xiangcheng fault, at the same rime mixed with shallow cold water. Finally, exposing in the river valley as a medium hot spring. We relocated earthquakes in the study area by the "multistage" method. The results suggest that the focal depth that located near the hot spring is deeper than geothermal water circulation depth, which indicate that the geothermal cycle can weaken the fault strength and control the seismic activity around the Xiangcheng hot spring. Based on above results, we can conclude that Xiangcheng Ranwu hot spring plays an important role in earthquakes formation in this area and is suitable for further geochemical observation of earthquake precursor. [ABSTRACT FROM AUTHOR]