Study On The Characteristics And Causes Of High Temperature Hydrochemistry In Litang Geothermal Field In Western Sichuan

The western Sichuan area is located in the Dianchuan area,one of the four hot spring dense zones in the country,and is located at the collision boundary between the Eurasian plate and the Indian ocean plate.The geothermal resource reserves are extremely rich,The high-temperature geothermal especially in the Batang block and Ganzi-Litang in the Jinsha River fault and the Litang block of the fault zone shows the most concentrated distribution.There are various types of water and heat display of natural high-temperature hot springs in the block,including hot springs,boiling springs,fountains,boiling fountains,geysers,jet holes,etc.This article focuses on a series of studies on hydrochemical characteristics,isotope characteristics and genetic analysis of high-temperature groundwater in the Litang block,which can not only reveal the deep geothermal process in the area,but also have important reference significance for the future development and utilization of local geothermal resources.The geothermal water temperature in Litang area is between 54 and 84°C,with a pH value of 6.73 to 8.2,an overall alkaline environment and a total dissolved solids TDS of 202.8 to 1618 mg/L.The main cations are K⁺,Na⁺and Ca²⁺,and the main anions are Cl^-,SO₄^2-and HCO^-.Through Aqua Chem software analysis data,it is concluded that the water chemistry types of the two geothermal fields in the Litang block are both HCO₃-Na type.In addition,the contents of both H₂SiO₃ and F^-in geothermal fluids are relatively high,and become the mark components of geothermal water,and the contents of Li⁺,Sr²⁺,and HBO₂ are relatively high,which may be leached and dissolved during the process of water-rock interaction.The role is related to the volatilization of gas components during magma formation.The characteristics of the two stable isotopes?D and?¹⁸O show that the source of high-temperature groundwater replenishment in the Litang area is mainly atmospheric precipitation,and a small part is glacial melt water,and the?¹⁸O isotope has obvious“oxygen drift”phenomenon.It is preliminarily calculated that the recharge elevation of the Kahui geothermal field is about 5292m,and the recharge zone temperature is about-15.7°C;while the recharge elevation of the Geza geothermal field is about 4904m,and the recharge zone temperature is about-11.7°C.According to the two methods of Na-K-Mg triangle diagram and multi-mineral equilibrium diagram,it is found that the fluid minerals in geothermal water have not yet reached the saturation state;using the silicon enthalpy equation method,the cold water mixing ratio of the Kahui geothermal field is about 58%to 68%In the meantime,the mixing ratio of cold water in the Gezha geothermal field is about 48%to 72%,most of which exceed 50%,and the mixing ratio is large.The results of the silicon enthalpy equation method are selected as the calculation results of the thermal storage temperature.The thermal storage temperature of the Kahui geothermal field is between 155 and195°C,which is a high temperature geothermal field,and the thermal storage temperature of the Gezha geothermal field is between 148 and 176°C,which is a medium-high temperature geothermal field.Using the conventional formula:Z=G(T_z-T₀)+Z₀,the circulation depth of the Kahui geothermal field is calculated to be 3212?4052m,and the circulation depth of the Gezha geothermal field is 3065?3653m,all of which belong to deep circulation springs.Based on the above results,combined with the existing geological structure,stratigraphic lithology and other data,a conceptual model of the genetic mechanism of high-temperature geothermal water in the Litang block is proposed to provide a scientific basis for the future development and utilization of geothermal resources in the area.