Study On The Formation And Evolution Mechanisms Of Underground Thermal Bittern In Yanjing County Of Tibet

The thermal underground bittern is a kind of liquid mineral resources, of which the formation is controlled by geology, hydrology, climate and other various factors. Until now, systematic research are lacked of in most scattered area except the plenty research of Sichuan Basin bittern, such as the natural bittern spring located along the river banks of Lancangjiang in Yanjing county of Tibet. Such more than 50 bittern springs are kinds of typical deep circulated Cl-Na water which the temperature is between 25～62.5℃and TDS between 25～86g/L. Therefor, the research of the bittern spring, including its and mechanism of formation and evolution, would provide the research example of thermal underground bittern and importance for special underground liquid in complex geological environment.This dissertation has taken the natural brine spring appearring in Yanjing county as the study object. Through detailed field survey and analysis of regional geology information, the distributing distributing and geological feature of spring drainage have been verified. The circle evolution mechanisms of the brine spring and its origin type as well as water replenishment, runoff, and excretion. have been analyzed by analyzing the hydrochemistry characteristic and the isotope characteristic test results of thermal underground bittern. The achievements are as following:1,The drainage geological condition of bittern spring in Yanjing county are controlled by the lack of Jurassic mudrock cutting by Lancangjiang valley and vertical open cracks developped in Yanjing-Sishui anticline.2,According to the calculation of geochemistry scale of bittern spring, the geothermal temperature reach to 101.6～109.2℃and cycle depth are 3247～3561m. Deep calculation provides the heat for bitter spring.3,High TDS was due to the water-rock interaction between underground water and salty stratum. As the circle depth and the distributing characteristic of salty stratum, T₃j and T₃b have been regarded as the circle stratum.4,The analysis of Hydrogen and oxygen stable isotopic characteristic indicated that the bittern spring origin from atmospheric precipitation, at the elevation between 3920 to 4980m. Considering the distributing characteristic of circle stratum, the mountain area in Luoni county matches the replenishment altitude and the salty stratum.5,Radioactive isotope of ³H and ¹⁴C characteristic indicate that, The bittern spring is ancient groundwater which circles in the stratum depth for more than 35000 years. The water circulates very slow that is advantageous for lixiviation with adjacent formation medium under the deep, high-pressured and high temperature environment, which is one of the most important reason for the high TDS in bittern spring.