Geochemical Characteristics And Genesis Of The Western Sichuan Light Mineralized Hot Spring

The western Sichuan Plateau is located on the collision zone between the Indian Plate and the Eurasian Plate.It belongs to the Mediterranean-Himalayan tropical eastern branch and has abundant geothermal resources.On the basis of collecting and arranging the"Hengshan Mountain Hot Springs","Research Report on the Influence of High Temperature and Hot Water in the Moxi Fault Zone on the Pressure Steel Tube Tunnels of the Wandong Hydropower Station in Luding County"and related literatures on the hot spring water chemistry and field investigations.Comparing the relationship between the temperature of the spring mouth and the TDS of the hot springs in the western Sichuan Plateau,it is found that when the mineralization degree of the hot spring is as low as a certain degree,the salinity and the temperature of the spring mouth show a good linear relationship.This paper takes this as a breakthrough,combined with the topic selection of the"Shuishuihe Fault Zone Hot Spring Resources Survey"project,based on the geothermal background of western Sichuan,collects statistics on the relevant hot springs in western Sichuan,and conducts field surveys in the field to select the hot springs in the western Sichuan Plateau.The hot springs with the increase of the temperature of the springs,the least increase in the degree of mineralization,and the linear relationship between the salinity and the temperature of the springs?a total of10 groups,here in after referred to as“Western Sichuan Light Mineralized Hot Springs”?are used as research objects,comprehensively utilizing geothermal geology and hydrogeography.Analytical methods such as chemical and hydrochemical isotope analysis were carried out to analyze the hydrogeochemical characteristics,isotopic characteristics and water-rock processes of the western Sichuan mineralized hot springs,and to study the genetic model of geochemistry.The main findings of this paper are as follows:1.The distribution of the western Sichuan mineralized hot springs is mainly controlled by the Ganzi-Litang deep fault zone,the Dege-xiangcheng fault zone and the Maotangba active fault zone,and some hot springs are formed in the Indosinian-Yanshanian composite granite bedrock.In the crack.The Ganzi-Litang deep fault zone is a lithospheric fault with strong tectonic activities and a cutting depth that has reached the upper mantle.This provides a good heat conduction and water guiding channel for the formation of the western Sichuan mineralized hot spring.The heat source of the western Sichuan mineralized hot spring is mainly a local melt with a relatively high temperature within a depth range of 15 to 30 km.The heat storage is mainly the structural heat storage in the Indosinian granite body fissure and the Triassic sand slate and carbonate rock layered heat storage.According to the estimation of the thermal storage temperature of the western Sichuan demineralized hot springs,most of the western Sichuan mineralized hot springs belong to the high-temperature hydrothermal system;under the strong cold-hot water mixing,the low-temperature geothermal system can also form a very low salinity.Light mineralized hot springs.2.The chemical composition of the demineralized hot spring water in western Sichuan is dominated by Na⁺,Ca²⁺,HCO₃^-and SO₄^2-.Na⁺is mainly derived from the dissolution of albite,and Ca²⁺is derived from the mixing of shallow underground cold water.HCO₃^-is derived from carbonic acid.Salt dissolution and deep organic decomposition;SO₄^2-is derived from the oxidative decomposition of metal sulfide minerals and the redox of H₂S gas.Among the trace components,most of the Chuanxi light mineralized hot springs have higher CO₃^2-and H₂SiO₃,and Cl^-/HBO₂ and Cl^-/F^-correspond to a good linear relationship,indicating that the hot springs are formed by shallow underground cold water.The effect of mixing.The relationship between hydrogen-oxygen stable isotope and atmospheric rainfall line indicates that the western Sichuan light mineralization hot spring is mainly caused by the infiltration of atmospheric precipitation.3.The geochemical genetic model of the low-mineralized hot springs in the western Sichuan high-temperature hydrothermal system is divided into?1?groundwater-mineral dissolution/precipitation stage,?2?groundwater reduction and warming stage,and?3?geothermal water rising and exposed stage.In stage?1?,the dissolution of minerals such as albite,potassium feldspar,and anorthite is mainly caused by the dissolution of cations and cation adsorption,and the formation of cations is mainly Na+,and the anion is HCO₃^-based shallow underground cold water;2)SO₄^2--H₂S redox is dominant.During the cycle,the shallow underground cold water gradually increases temperature and transforms into high temperature hot water;at the end of the stage,geothermal water begins to travel along the dominant channel.Shift,due to sudden decrease in pressure and temperature,the geothermal water flashes and vaporizes,CO₂ and H₂S gas escape in large quantities,and HCO₃^-in geothermal water decomposes.In the initial stage of geothermal water rise,cations are formed with Na⁺as the main anion.Low-mineralized geothermal water with SO₄^2-as the main,high pH and very low salinity;?3?Mainly combined with cold-hot water mixing,and shallow mineralized geothermal formed at the end of stage?2?During the process of rising and falling water,due to the changes in geological environment conditions and the mixing and proportion of shallow underground cold water,it is possible to form demineralized geothermal water of different water chemistry types.4.The low-temperature hydrothermal system in western Sichuan is mainly composed of two groups of light mineralized hot springs in Xiangcheng County.In fact,the measured temperature is low,and the heat storage temperature is estimated to be only about 56.2°C.Both groups of hot springs are exposed in the Upper Triassic thick layer of limestone strata,and the water chemical composition content is characterized by calcium-rich magnesium and sodium-poor potassium.The hot spring water source comes from the precipitation of the nearby mountain body.The atmospheric precipitation is infiltrated along the secondary faults near the hot springs,and the runoff is heated by the thick layer of limestone in the Triassic system,and the secondary faults at the front end of the migration direction move upwards.It is mixed with shallow underground cold water to form a low-temperature hot spring with a low salinity of HCO₃-Ca type neutral?6<pH<7.5?.To carry out the geochemical characteristics and genesis of the low-temperature and high-temperature hot springs in western Sichuan,to enrich the geothermal theory,reveal the deep tectonic thermal evolution environment and water-rock interaction process,and supplement and enrich the understanding of the underground hot water circulation system in the region.It has important theoretical and practical significance.