Hydrogochemical Characteristics And Formation Mode Of The Five Thermal Springs In Lushan County,Henan

Thermal springs are used because of their special temperature and solublecomponents, which distinguishes them from the common water resources. The fivethermal springs which lie in Lushan County, Henan Province have a long history, andhave the characteristics of centralized distribution. They also contain multiple traceelements which gives them therapeutic values. In recent years, however, thereconnaissances and study of geothermal resources in this area lags far behind thespeed of exploitation. It is necessary to carry out a comprehensive and systematicstudy of the hot springs.The five thermal springs in Lushan County were selected as the research objectsin this paper, and they were studied systematically by using geological, geophysicaland geochemical methods. First of all, geological methods were used to detail thetectonic background and small tectonic environment in the research area; Secondly,geophysical methods were used to clarify the temperature field, geothermalbackground of geological structure patterns and the earth background heat flow value.Thirdly, on the basis of sampling in the research area and testing the samples,hydrogeochemical including environmental isotope methods were used to detail thehydrogeochemical features which explained the questions of where the supply sourcearea were, how much the thermal storage temperature were and so on. Finally, on thebasis of above researches, the genetic model of Lushan five thermal springs wereestablished which laid the foundation for the exploration and development ofgeothermal resources in this area.The research results of this paper showed that there was a close relationshipbetween the five thermal springs and Checun-Lushan crack and the latter not onlycontrol the formation and exposure of thermal springs, but also affected thetemperature field; The terrestrial heat flow value in the study area changed between45mW/m²and50mW/m², which is lower than the average heat flow value ofsouthern North China Plain. The five thermal springs had the same general waterchemical types, namely HCO₃·SO₄-Na type or SO₄·HCO₃-Na type. The value of eachcomponent between the five thermal spings changed little and the value of F-andH₃SiO₃were relatively more, which indicated that the components of the spings allcame from leaching the surrounding rocks. Hydrogen and oxygen isotopic data show that the underground hot water in the study area was recharged by precipitation whichran off the mountain area which were located north west and south study area. Therecharge elevation changed between900meters and1200meters. The reservoirtemperature was about90celsius by calculating using SiO₂geothermometer.The type of geothermal system of the five thermal springs in the study area waslow medium temperature geothermal system of convective type. Its geneticmechanism could be summarized as follows: In normal regional geothermalbackground, the precipitation in the north, west and south mountain infiltrated andsupplied the underground hot water. Running along the fracture zone ofChecun-Lushan crack, the underground water flew down and arrived about3500meters deep where they were heated to90celsius by the deep-seated heat source,driving by the pressure difference between recharge area and discharge area. At thesame time, the constantly heated groundwater leached the surrounding rocks andacquired the chemical compositions in them. In the discharge area, the undergroundhot water was controlled by the NE trend faults and moved upto the earth’s surface,forming the thermal springs.