Geochemical Characteristics Of Geothermal Fluids In Chabu Geothermal Field,xietongmen County,tibet

As a global new energy,geothermal resources will play an irreplaceable role in the future.High-temperature geothermal resources have been discovered in the Chabu geothermal field,but the research on the origin of the thermal fluid in the Chabu geothermal field is still unclear,which limits the subsequent development and utilization of geothermal resources.Clarifying the origin of geothermal fluids in the Chabu geothermal field will help to analyze the tectonic evolution law of the central and southern Qinghai-Tibet Plateau.This paper summarizes previous studies and found that the research on the genetic mechanism of geothermal fluids in the Chabu geothermal field remains at the geophysical method to discuss the tectonic evolution.Therefore,this paper integrates geophysical and geochemical means,and on the basis of existing research,takes the thermal fluid as the starting point,and constructs the genetic mechanism model of the Chabu geothermal fluid.This paper discusses the attribution of the heat source of the Chabu geothermal field through the study of geothermal water chemistry,hydrogen and oxygen isotopes of geothermal water,geothermal gas chemistry and sinter chemistry.Based on the results of geophysics,geothermal geology and geochemistry,a conceptual model of the genetic mechanism of geothermal fluids in the Chabu geothermal field is preliminarily constructed,and the genetic evolution mechanism of the deep thermal fluids in the Chabu geothermal field is briefly explained.The main conclusions are as follows:1.The origin of the Chabu geothermal fluid has roughly gone through three main processes;the deep melt is infiltrated and adiabatically cooled along the fault to the parent geothermal fluid(350°C);the parent geothermal fluid is infiltrated and mixed along the fault by the melting water of ice and snow and atmospheric precipitation Magma water is formed,and the magma water continuously expands and rises when heated,and continuously dissolves and filters the minerals of the surrounding rock and absorbs the radioactive elements of the surrounding rock to generate heat to form a thermal storage(maximum 220.2°C);the geothermal water in the thermal storage is driven by the density difference.The hot water does not experience mixing or is mixed with different proportions of shallow water,and the temperature of the thermal fluid exposed on the surface is different(up to 86.5?).It is speculated that the depth of geothermal water circulation ranges from 6.53 to 4.82 km,the supply source is atmospheric precipitation and ice and snow melt water,and the supply height is more than 5880 meters.2.The chemical type of hot water is HCO₃·Cl-Na·K type,followed by Cl·HCO₃-Na·K type,which is weak alkaline water.Chabu geothermal water is rich in metaboric acid,metasilicic acid,fluorine,lithium and other trace elements,which meet the concentration and naming standards of hot mineral water,and have great medical development value.It is estimated that the total amount of geothermal energy stored in thermal storage solids and fluids can provide 86.5MW,the heat stored in the water body of the Chabu geothermal field can provide 73.24MW,and the heat stored in the rock can provide 13.26MW.The chemical analysis of the Chabu sinter components shows that the average grade of cesium in the Siliceous sinter of the Chabu geothermal field is 0.17%,which exceeds the industrial grade;the Cs content in the Chabu geothermal water is tested,and the average grade is 0.537‰.The comparison found that the enrichment of cesium in Siliceous sinter was 332 times that in geothermal water on average.The cesium ore in the Chabu geothermal field can be mined using the principle of colloid enrichment.3.Use the relationship between ⁴He/²⁰Ne and R/Ra to determine the ratio of the crust-mantle source of the geothermal field heat source.The⁴He/²⁰Ne value in the Chabu geothermal gas is 2784.5,and the R/Ra value is 0.0449;the ⁴He/²⁰Ne value in the atmosphere is 0.326;the average R/Ra value in the crust is 0.02,and the R/Ra value in the mantle is 8.The relationship between ⁴He/²⁰Ne-R/Ra is drawn,and the results show that:the Chabu geothermal gas helium mainly comes from the crust,and the maximum ratio of mantle source is calculated to be 5.6‰;the source of the geothermal gas reveals the properties of the heat source of the geothermal field.The heat source of the Chabu geothermal field is mainly from the crust,mixed with a mantle-derived heat source of 5.6‰.According to the isotopic analysis results of geothermal gas,it is inferred that the magma heat source is the melt in the crust,that is,the partial melt of the crust is the main heat source of the geothermal field,mixed with a very small amount of mantle-derived heat sources.