Hydrogeochemical characteristics and genesis of the low geothermal resources in Pingquan of Hebei
Chengde municipality in Hebei province has abundant geothermal resources,but the study on the resources in the subordinate Pingquan area are quite limited,therefore,comprehensive hydrochemical study on the formation processes of geothermal waters is essential for the geothermal resources exploitation in the Pingquan area.Based on the water quality indicators of geothermal and cold waters,this paper employed the methods of ionic ratios,isotopic analysis,the geochemical temperature scale and the silica-enthalpy model to delineate the hydrochemical characteristics of geothermal waters.Furthermore,the study analyzed the storage conditions and the recharge sources,and employed a quantitative assessment of the thermal storage temperature,cold water mixing ratio,and depth of thermal cycling in the study area.The results showed that the hydrochemical type of geothermal waters in the area was HCO3-Ca·Mg.The principal recharge source for the geothermal waters was atmospheric precipitation,comprising a mixture of ancient and modern groundwater undergoing slow deep circulation.The thermal storage temperature in the area ranged from 65.9 to 74.5℃,with a cold water mixing ratio of 79%.And without the mixing of cold water,the deep thermal storage temperature could reach 125℃.The geothermal waters in Pingquan were recharged by atmospheric precipitation,which infiltrated deep underground along water-conducting fractures and zones.These waters were continuously heated by the Earth's geothermal flux and stored in well-developed fracture zones.Driven by hydrostatic pressure and thermodynamic forces,it ascended through fracture zones and lithological contact zones,mixing with cold waters in the shallower parts of the crust to form low temperature geothermal resources.
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