Mineral Precipitation Sequence And Spout Deposition Mechanism Of Dagunguo Hot Spring,Tengchong,Yunnan

The terrestrial thermal spring sinter is the reflection of the silicon-rich geothermal fluid on the surface.It records the paleontology,paleohydrology and paleoenvironment information in the hydrothermal environment.It plays an increasingly important role in the reconstruction of regional paleoclimate and paleoenvironment.The preserved microbial characteristics are of great significance for the study of early earth and extraterrestrial organisms,and have become one of the important signs of ore prospecting in recent years.In this study,the hot spring water and its surrounding sinter in the Tengchong Rehai area were used.Based on the analysis of the properties of the hot springs and natural sinter,combined with isothermal evaporation experiments,the mineral precipitation sequence and spout deposition mechanism of the same type of hot springs in this area were discussed.According to field observation and laboratory experiment,the Dagunguo hot spring of Rehai is a high-temperature chlor-alkali hot spring with a maximum water temperature of 96?to 97?and a p H of about 8.The hot spring water is Na-Cl-HCO₃ silicon-rich water.Its main ion components are HCO₃^-,Cl^-,Na⁺,Si⁴⁺,followed by K⁺,B³⁺,Li³⁺,CO₃^2-,SO₄^2-,etc.,and the content of metal ions such as Ca²⁺,Mg²⁺,Al³⁺is extremely low.Sinter in the Dgunguo hot springs are mainly composed of opal-A,exogenous quartz,silicified microorganisms,natural sulfur and a small amount of calcite.The whole is a laminated structure and grid structure sediment.Opal-A is a round sphere or a beaded continuum under the microscope,and the diameter of the pellet varies from 0.18-2?m;the silicified microorganisms are mainly filamentous and rod-shaped,showing low diversity,with a length of about 20?m and a cross-sectional diameter of between Around 2?m,a large number of microorganisms formed a microbial mat;a large amount of elemental sulfur and the mutual layers of sulfur-rich and sulfur-depleted layers were observed.Isothermal evaporation experiments use a constant temperature?84??water bath and hot spring pre-concentrated water to evaporate.The solid precipitated from the solution during evaporation is mainly composed of halite,trona and amorphous Si O₂.Halite is produced in granular and thin shell shape,trona is mainly produced in plate and fiber form,and amorphous Si O₂ is mainly produced in sheet form.In addition to the above main minerals,irregular sylvite,granular calcite and annular thenardite can also be observed in the evaporated samples.Through the comprehensive analysis of the liquid and solid samples collected in the experiment,we think that the main mineral precipitation evolution sequence of the Dagunguo hot spring is amorphous Si O₂?rhalite?trona?sylvite,accompanied by calcite,thenardite,sodium bicarbonate and other minerals in the process.Combining the properties of Dagunguo hot spring and sinter with the results of isothermal evaporation experiments,we found that there are significant differences between the two in terms of amorphous Si O₂ forms,other mineral components,and microbial effects,indicating that the deposition of chlor-alkali high-temperature hot springs in the area is affected by many factors.By comparing and summarizing the various influencing factors of the formation of sinter and the characteristics of the hot springs in the Rehai region,we have obtained the jet deposition mechanism of the chlor-alkali high-temperature hot springs in the Tengchong Rehai geothermal area.The formation of sinter in the Rehai area is affected by a variety of environmental factors and human factors.In the hot spring water continuously flowing through the area,from the high temperature phase of the vent?>75??,the proximal slope?65-75??,and the mid apron pools?45-65??,to the low-temperature distal apron?<45??,the botryoidalis sinter under water develop,acicular and columnar sinter,lamellar and/or reticular sinter,and columnar stromatolitic sinter formed respectively.In the area where the hot spring water flows intermittently,plate-shaped sinter with ripples and cracks are mostly deposited on the top,the bottom is mostly breccia with siliceous debris.According to the chemical composition of the fluid,this area may exist the symbiosis of sinter and salt sinter.The study on the deposition mechanism of chlor alkali high temperature hot spring in the geothermal area of Tengchong Rehai provides modern examples and rich research contents for the comparative sedimentology study of ancient and modern Continental hydrothermal jet activities,and provides basis for deepening the understanding of hot spring water chemistry and jet deposition mechanism.