Study On Stable Isotope Geochemical Characteristics And Metallogenic Process Of Nitrate Salt Lakes

Sedimentary nitrate deposits can be divided into salt flats type and salt lake type based on their genesis.Currently,there is more research on the nitrogen source of sedimentary nitrate deposits,and it is unanimously believed that the nitrogen source is mainly from the atmosphere.The research on salt flats type nitrate deposits is relatively deep,but there is a lack of research on salt lake type nitrate deposits.There are significant differences in nitrogen and oxygen isotopes between salt flats type and salt lake type nitrate deposits in the Kumish Basin,and the salt lake type nitrate minerals are mainly potassium nitrate,while the salt lake type nitrate minerals are mainly sodium nitrate.Based on the above problems,this paper collected ice and snow melt water samples,groundwater samples,spring water samples,brine samples and solid nitrate samples in the Kumish Basin,and carried out nitrogen,oxygen and boron isotope analysis and hydrochemical characteristics analysis on the above samples to reveal the recharge relationship between the study area and surrounding water bodies and further explore the mineralization model of salt lake type potassium nitrate deposits,and obtained the following conclusions:1.The results of nitrogen and oxygen isotopes of nitrate minerals indicate that the nitrogen and oxygen isotopes of salt flats type nitrate minerals in the alluvial fan of the Kumish Basin are of atmospheric origin,while the salt lake type nitrate minerals in Wuyongbulak have higher nitrogen isotope composition and lower oxygen isotope composition compared to the salt flats type.The oxygen isotope composition of the water around the salt lake in Uyongbluk is much lower than that of atmospheric nitrate.After analyzing boron isotope and hydrochemical composition,it was found that in addition to the melting water of ice and snow in the South Tianshan Mountains,there is also groundwater in the Kumish Basin.These two types of water migrated to the Wuzong Spring water in their respective independent forms to converge,and then supplied to the Uyongbluk salt lake area in the form of mixed water.During the migration of water body,salt minerals in the stratum are dissolved and filtered to transport minerals for the study area.The nitrogen and oxygen isotopes of recharged water body and atmospheric nitrates are different from salt marsh nitrates under the action of microbial denitrification.2.The results of continuous sedimentation and complete separation evaporation experiments on the underground brine of Wuyongbulak Salt Lake at 25℃show that the main nitrate mineral in the continuous sedimentation and complete separation evaporation experiments is potassium nitrate.During the full separation evaporation experiment,due to the large precipitation of halite in the early stage consuming a large amount of sodium ions,the percentage content of potassium ions in the later stage brine is much higher than that of sodium ions,leading to the precipitation of potassium nitrate（KNO₃）as the main substance.Potassium nitrate precipitates in the range of brine specific gravity between 1.3481 and 1.3539;During the continuous deposition evaporation experiment,due to the retention of salt minerals that had previously precipitated during each evaporation stage,the re dissolution of halite resulted in an increase in the content of sodium ions in the later brine,resulting in the precipitation of both potassium nitrate and sodium nitrate.The amount of potassium nitrate precipitation was about twice that of sodium nitrate,and sodium nitrate precipitation occurred in the range of brine specific gravity between 1.3393 and1.3418,and potassium nitrate precipitation occurred in the range of 1.3393 to 1.3483.3.Under extremely arid climate conditions,atmospheric nitrate deposits in the basin accumulate over a long period of time,replenishing the ore-forming elements in the leached strata of water bodies and enriching them in the low-lying salt lake areas.Through strong evaporation and capillary action,salt precipitation and mineralization occur on the surface.In salt lake type nitrate deposits,due to the supply of ice and snow melt water,groundwater,etc.,the ore-forming brine contains more potassium ions.During the evaporation process of the brine,a large amount of sodium ions are consumed due to the precipitation of halite,resulting in a much higher concentration of potassium ions than sodium ions in the later stage of the brine.As a result,salt lake type nitrate deposits are mainly composed of potassium nitrate minerals.