Hydrogeochemical characteristics and genesis of Gaofeng geothermal fields in Hainan province
Data in chemistry,isotope and geothermal field in the study area were used to analyze the chemical characteristics of surface water,shallow subsurface cold water and geothermal water,and the recharge sources and age of geothermal water,and estimate the temperatures of geothermal reservoir,the mixing proportion of cold water and the circulating depth of the hot water in the Gaofeng geothermal fields.The results show that geothermal groundwater belongs to the lysofiltrational type of continental sedimentation.The geothermal groundwater is recharged by the atmospheric precipitation at the elevation of 1 133～1 215.8 m which run into the depth along the fault zone and heated by the terrestrial heat flow.The geothermal reservoir formed by the warm water in the stripped rocks of high porosity and high permeability the along fractured zones.The geothermal waters are mainly upwelling along stripped structure fractured zones near the intersection of F1 and F2.In the process of upwelling,the hot water is cooled by the cold water and discharged from the surface by artesian hot wells and thermal springs.The hydrochemical types of geothermal water are Cl-Na,Cl∙HCO3-Na,Cl∙HCO3∙SO4-Na;the highest content components are Cl-and Na+suggesting the characteristics of high-temperature hot water source from the deep.Good linear relations between Sr,Na+,Li+,Mg2+,Br,K+and Cl-reflects the geochemical characteristic of same source.The content of metasilicic acid and fluorine reaches the quality standard of physiotherapy hot mineral water and can be called fluoro-silicon thermal mineral water.The test results of 3H is under 2 TU indicating the geothermal water samples belongs to the ancient water formed before 1953,which are verified by the 14C test age of 9 530～10 830 a,corrected age of 8 462～9 802 a by the Vogel calibration model.The proportion of cold water mixing is 0.82 by graphical method of SI-enthalpy model and the calculated the temperature of reservoir is 154℃by the multi-mineral equilibrium diagram method and SiO2 geothermal scale method.The depth of the atmospheric precipitation circulation is 3 705 m.Analysis on the temperature field characteristics found that the in flection point of drilling temperature-depth line is well correlated to the stripped structure fractured zones with high porosity and high permeability,where the convection is stronger than the other section in the borehole.Therefore,Gaofeng geothermal field is a regarded as a middle and low temperature geothermal field of convection system.
geothermal waterhydrogeochemical characteristicsgeothermal temperaturegeothermal water agetemperature fieldreservoirs
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