Sedimentary Characteristics And Distribution Of Trace Elements Of Nitrate Deposit In Wuyongbulake Salt Lake,Xinjiang

Nitrate resources are widely used in industry and agriculture.The large-scale nitrate deposits are mainly distributed in the extremely arid regions,such as Atacama Desert of Chile and Turpan-Hami Basin of Xinjiang.Domestic and overseas scholars have done a lot of research on the geological characteristics,formation mechanism and comprehensive utilization of resources,and so on,for nitrate deposits.They have achieved some important research results,but still have controversies on the interpretation of nitrate origin and formation mechanism.A complete theoretical system of nitrate mineralization has not been established.There are many types of nitrate deposits in Xinjiang,and its formation mechanism varies with different types.The K-rich intercrystalline brine deposit of Wuyongbulake is the largest liquid Nitrate Deposit in Xinjiang.Scholars have studied the geological characteristics,salt forming stage,source supply and microtopography of nitrate deposits,they also have controversies on the ore-forming processes and origin of nitrate.The sedimentary characteristics of salt minerals and distribution characteristics of NO₃^-etc ions in different sedimentary sites of K-rich nitrate deposit are studied insufficiently,and also the distribution of trace elements,the characteristics of brine geochemistry etc,in Wuyongbulake.Based on the previous research,this thesis analyses the sedimentary characteristics,distribution of major and trace elements,brine and its simulated evaporation experiment of nitrate deposit in Wuyongbulake Salt Lake.Some main conclusions are as follows:?1?The main salt minerals in the salt crust are gypsum,thenardite,glauberite,halite,blodite,niter,etc.The evolution process of the Wuyongbulake Salt Lake is a typical“cattle-eye”evolution according to the change of mineral assemblage and sulphate minerals?glauberite and blodite?precipitation in different sedimentary sites.In the process of Wuyongbulake Salt Lake evolution,deposition is from the south and north to the center of lake and from the west to east.The content of the main and trace ions in different sedimentary sites of salt crust and brine samples changed greatly and partially.Through analysis,we think that it affected by the process of source supply and controlled by dissolution migration of local topography.?2?The simulated evaporation experiment of Wuyongbulake brine can be divided into ten salt precipitation stages:gypsum?halite is saturation?,halite,halite and bloedite,halite and hexahydrite,halite and sylvite and kainite and niter,halite and sylvite and carnallite,halite and carnallite,halite and carnallite and pentahydrite,halite and carnallite and starkeyite,bischofite.The content of ions in the process of niter precipitation decreases distinctly,the reason is unclear.By comparing the salt mineral assemblage of salt crust and simulated evaporation experiment,We think that arid environment plays an important role in the formation-transformation of salt minerals and the enrichment of nitrate.?3?The concentrations of K⁺,Ca²⁺,Na⁺,Mg²⁺,Cl^-,SO₄^2-in the salt crust have the potential trend of migration and enrichment from the alluvial fan to the center of salt lake.The highest concentration of NO₃^-in salt crusts that lie on the middle and upper of alluvial fan,is 4.35%,obviously higher than that of the front of alluvial fan and the center of salt lake.?4?The content of Na⁺and Cl^-in brine is abnormally high,the ratio of r _Na/r _Clis0.45 and r _Ca+Mg/r _HCO3+SO4is between 0.3 to 1.6.The result of r _Na/r _Clindicates that the brine of Wuyongbulake Salt Lake is the residual brine that formed by evaporation deposition,and r _Ca+Mg/r _HCO3+SO4indicates that Ca²⁺and Mg²⁺are mainly from the dissolution of silicate minerals and those minerals containing calcium and magnesium in the surrounding stratum.It shows that the sedimentary cations mainly come from the weathering-leaching of surface rocks.?5?The formation mechanism of K-rich nitrate deposit in Wuyongbulake Salt Lake is complex,which is affected by topography,source supply,climatic conditions and biological processes etc.Nitrate is mainly affected by the biological effect in the middle and upper of alluvial-proluvial fan with the process of enrichment and mineralization.Nitrate from various sources is transported to the sedimentary area,and then it is transformed into brine with high TDS through strong evaporation and concentration intensely.Thereafter,with a series of complex physical and chemical processes,the K-rich salt lake nitrate deposit of Wuyongbulake was formed.These conclusions obtained in this study has a practical significance for further explore the formation mechanism of K-rich intercrystalline brine Nitrate Deposit and the comprehensive exploitation and utilization of nitrate resources,and also plays a supplement and improvement role in the metallogenic theory of nitrate.