Ganzi-Yushu Fault Ganzi-Dengke Section Hot Spring Hydrogeochemical Characteristics

As a sustainable green energy source,geothermal heat is of great significance to social and economic development and the protection of the ecological environment.The Ganzi-Yushu fault Ganzi-Dengke segment belongs to the eastern margin of the Qinghai-Tibet Plateau and is located in the tropical northwest of the western Sichuan.,The hydrothermal activity is strong,and the hot springs are distributed along the fault NW-SE.Studying the geochemical genetic model of the hot springs in the Ganzi-Dengke section of the Ganzi-Yushu fault can provide theoretical basis and technical support for the development and utilization of geothermal resources in the Ganzi and Dege areas.This paper takes the hot springs in the Ganzi-Dengke section of the Ganzi-Yushu fault as the research object,combined with the topic selection of the"Xianshuihe fault zone hot spring resources survey"project,based on previous research results,collects and organizes the hot spring related data in the research area,and conducts in the wild In the investigation and sampling work,24 groups of hot springs were selected as the research object.Using the geothermal geological background of the Ganzi-Dengke section,the control effect of the Ganzi-Yushu fault on the hot spring was analyzed.Hydrochemical characteristics,isotope characteristics and hydrogeochemical processes have proposed the genesis model of the hot springs in the Ganzi-Dengke section of the Ganzi-Yushu fault.The following results have been obtained:(1)The distribution of hot springs in the study area is mainly controlled by the Ganzi-Yushu fault zone.The Ganzi-Yushu fault zone is a block boundary fault with strong tectonic activity and the cutting depth has reached the lower crust.The formation provides a good channel for water and heat conduction.The heat source of hot springs in the study area is mainly the frictional heat generated by the high-temperature local melt in the middle-lower crust and the Ganzi-Yushu fracture.The thermal storage of hot springs is mainly Triassic sand slate type pore-fracture thermal storage,Quaternary pore thermal storage and Yanshanian granite fracture thermal storage.(2)The main cation in the hot springs in the study area is Na⁺,followed by Ca²⁺,and the main anion is HCO₃^-.Na⁺mainly originates from the dissolution of albite,Ca²⁺is mainly affected by the mixing of shallow cold water;HCO₃^-is controlled by the dissolution of carbonate.The chemical types of hot spring water are mainly HCO₃-Na,HCO₃-Na·Ca and HCO₃-Ca.Of the trace components,most of the hot springs in the study area have high Si O₂ content,showing the characteristics of high-temperature geothermal systems;the stable isotope characteristics of hydrogen and oxygen indicate that the sources of hot spring replenishment in the study area are mainly atmospheric precipitation and ice and snow melt water.The relationship diagram of Cl^-/(Cl^-+HCO₃^-)shows that the water-rock interaction of the hot springs in the Ganzi-Dengke section is low.The triangular diagrams of Na-K-Mg and Cl-SO₄-HCO₃ indicate that the hot springs were mixed by shallow underground cold water during the formation process.(3)The thermal storage temperature calculated by the quartz and quartz vapor loss Si O₂ geothermal temperature scale is relatively stable,most of which is between60?130?;silicon enthalpy graphic method shows that the proportion of cold water mixed is 19.96%?89.47%,the proportion of cold water The heat storage temperature is larger from 53.11 to 223.68?;the cation Na-K-Ca geothermal temperature scale corrects the Ca²⁺ion content to obtain a heat storage temperature of 71.76?203.72?.By comparing the calculation results of different geothermal temperature scales,the thermal storage temperature range of the hot spring in the study area is 60?210?.(4)The genesis model of hot springs in the study area can be summarized into three stages:(1)mineral dissolution during groundwater infiltration,(2)reduction and warming of groundwater,(3)rise and exposure of hot springs.The first stage is mainly mineral dissolution and cation exchange,forming shallow cold water with cations mainly Na⁺and anions mainly HCO₃^-;the second stage is mainly the redox of SO₄^2-and H₂S,from groundwater to the crust In the process of deep migration,groundwater is continuously heated to extremely hot geothermal water;at the end of this stage,hot water begins to rise to the surface.Due to the sudden decrease of temperature and pressure,flash steam of geothermal water occurs CO₂ and H₂S gases escape,and HCO₃^-in underground hot water decomposes.In the early stage of ascent,geothermal water with mainly cations as Na⁺and anions as SO₄^2-,high p H,and low salinity is formed;The mixing effect of hot water,due to the difference in environment and the mixing ratio of cold water,forms hot springs of different water chemistry types.