Hydrochemical Characteristics Of Spring And Potassium-prospecting In Changdu-lanping-simao Basin, Southwestern China

There are a large number of springs in Sanjiang tectonic belt,but the source of solute,geochemical evolution characteristics and circulation models of springs have not been proved up to now.This thesis systematically discussed the element and isotopic geochemical characteristics(?¹⁸O,?D,?¹¹B)of springs in the study area(Changdu-Lanping-Sioma Basin),aiming to better understand the solute source and c evolution characteristics of spring water,thus establishing the circulation model of the spring.From 2014 to 2015,the research group collected 51 spring samples(33 salt springs,5 cold springs and 13 hot springs)in the Changdu-Lanping-Simao saline belt.The main hydrochemical type of springs in the study area is chloride,and the minor type is sulfate and carbonate.The main source of solute in springs is dissolved by stone salt,followed by dissolution of sulfate and carbonate.this is also consistent with the salt formation from Jurassic to Paleogene(red layer dominated,mixed gypsum/anhydrite,argillaceous limestone and salt rock).the carbonate mineral saturation index and the relationship between SO₄^2-/Ca²⁺and Mg²⁺/Ca²⁺show that the springs dissolve a large amount of calcite and dolomite,and the magnesite saturation index of the Leiwuqi spring is greater than zero.The ternary diagram of Ca-SO₄-HCO₃ shows that the salt springs in Yanjing,Tibet is affected by deep Ca-Cl type water,and the salt springs in the study area dissolve a large amount of buried gypsum/anhydrite.The Tengchong geothermal water is close to the HCO₃ end,which is caused by the dissolved sediment rock and carbonate rock.According to previous studies,the dissolved sulfates in springs in the study area are Marine origin.In terms of elemental geochemical characteristics,the source of solute and water chemistry of the spring water in the study area is similar to that of Tibet Yanjing,Yangbajing and Qinghai Nangqian groundwater,and there is a large difference between the Tengchong-Baoshan-Lincang geothermal water.The B-isotope geochemical characteristics of springs in the study area show that B in spring water is mainly caused by the dissolution of marine carbonate,without the influence of crust-derived magmatic rocks and deep mantle.However,B in Tengchong-Baoshan-Lincang geothermal water is mainly originates from the dissolution of crust-derived magmatic rocks,and there are differences in B sources.The high?¹¹B value of salt springs in the study area compared with hot springs may be caused by the following three reasons:the separation of liquid and vapor in hot springs,the weak water rock interaction of hot spring water,and the carbonate deposition caused by CO₂ release.Comprehensive comparison of geothermal water in the geothermal system of the world shows that the spring water in the study area is a typical terrestrial origin,and the Cl/B ratio of rock salt leaching is significantly higher than that in other geothermal systems in the world.India,the Dead Sea in Israel,the Izu Peninsula in central Japan and the geothermal water in northern Taiwan are marine origin,and B is derived from seawater.The B in waters from the terrestrial origin depends on the geological background and the type of surrounding rock.The B in springs of the study area is mainly derived from the B-surround rocks(magmatic rocks and marine carbonates)of the shallow crust origin,non-deep mantle and marine causes.The comparison shows that B source in the study area is consistent in the Tibetan geothermal zone,the Nangqian basin,while the geothermal water B in western Yunnan is a product of the combined interaction of crust and mantle.Comprehensive analysis of the springs hydrochemistry and?¹⁸O,?D values in the study area,found that the spring water in the study area is mainly from the recharge of atmospheric precipitation or snow-melt water,and experienced a strong water-rock interaction.The?¹⁸O and?D values have obvious elevation and latitude effects,and to estimate the elevation of the recharge zone,the temperature of the recharge zone,the temperature of the heat storage,and the depth of the circulation in springs from the study area.Finally it is concluded that spring water circulation theory model in the study area:atmospheric rainfall or snow melt water flowing through the surrounding formation(rock salt,Marine carbonate and Marine sulfate),and the deep circulation with the tectonic fracture,and the heat source provided by the mantle.The circulation depth of salt springs is much deeper than that of cold springs and hot springs.Salt springs has experienced more sufficient water rock interaction than cold and hot springs.The transport channel,the heat source and the recharge source of the Tengchong-Baoshan-Lincang geothermal water are consistent with the spring water in the study area,and there are differences in the lithology of the surrounding rock(carbonate rocks mixed with siltstone and volcanic rocks).By analyzing the elements and chlorine isotope geochemical characteristics of the springs in the study area,and the dissertation discussed the spatial distribution characteristics about elements,potassium characteristic coefficients and?³⁷Cl values.Combined with previous research results,the potassium prospective area in the study area was redetermined,it is found that the concentration of salt spring water in the Changdu Basin is stronger than that in the Lanping and Simao Basin.The Changdu Basin can be used as the next prospective area for potassium.Leiwuqi,Gongjue may be a evaporation center,which is supposed to have been concentrated to the late stage,and can be used as a prospective area for potassium in the Changdu area.The prospects for finding potassium in the Lanping area are:Nuo Dengcun,Shangjing,Shangxiaojing,Dajing,Tian'anjing,and Shundangjing.The prospective area for finding potassium in Simao area is Naguohe Village,Xiaojing Village and Dajing Village.The results showed that the Cretaceous potassium-bearing evaporates involving Changdu,Lanping-Simao basins are the genesis of“Marine source continental facies”.This indicated that the formation of those evaporates is related to the intrusion and recharge of seawater in the continental environment.This is consistent with that a new metallogenic model of seawater migration and metamorphism in multistage basins.