Geochemical Characteristics And Genesis Analyses Of Saline Springs In The Kuqa Basin,Xinjiang

The worldwide potash deposits are extremely unevenly distributed with chiefly locating in Europe,North America,Central Asia,and Southeast Asia.In China,potash deposits are rare with limited distribution in basins belonging to the Tethyan domain.The Tarim Basin,located in the eastern Tethyan domain in western China with well developed thick evaporites?including carbonate,gypsum,halite,etc.?,which has been suggested by previous experts as the potential target area for exploration of potash deposits.The Kuqa Basin?KB?,located in the northern part of the Tarim Basin is regarded as the most potential potash-seeking area.Saline springs are widely developed in the KB.Though lots of research have been carried out on these springs,current research does not fully evince the origin of saline springs and the controversies on the origin of evaporate sediments of the Jidike Formation are still existed.In addition,circulation processes and evolution involving saline springs have not yet to be carefully elaborated.Herein,during 2015-2019,totally 30 saline springs and 11 river water samples were collected in three secondary structural belts including the Que Le structural belt?QL?,Western Qiulitage structural belt?WQ?and Eastern Qiulitage structural belt?EQ?from west to east of the KB.Experiments including major and trace?Sr,Br?ion concentrations,H-O-Sr isotopes and tritium values have been conducted successively.In combination with previously published hydrogeochemical and isotopic?H-O?data in the same area,this study aims to systematically discuss the origin and the water circulation process of saline springs in the KB.The major methods and conclusions are listed as follows:1.It is found that the main hydrochemical type of these spring waters are Na-Cl type,and the chloride type?Valyashko's classification?as the dominant water type in the study area.The results show that the origin of salinity was dominated by dissolving halite minerals.Each structural belt exhibits slightly different in terms of the origin of mineral solutes.The origin of mineral solutes in the QL is the dissolution of halite,carbonate and gypsum,while the origin of mineral solutes in the WQ and EQ is the dissolution of halite and gypsum only.2.By analyzing the hydrochemistry and?¹⁸O,?D values of the springs,it is found that the saline springs are recharged by the atmospheric precipitation or snowmelt water of surrounding alpine region.Meanwhile,it is considered that the distributive characteristics of oxygen isotopes in the saline springs are not only correlated with leaching halite from the recharge water,but also with the intense evaporation after the drainage of the saline springs to the surface.The?¹⁸O and?D values exhibit obvious elevation and temperature effects,which can be used to estimate the depth of the circulation of saline springs in the study area.The mean depth of QL,WQ and EQ were5.65km,4.82km and 5.38km,respectively.3.It is suggested that the ⁸⁷Sr/⁸⁶Sr values of the saline springs of the KB are mostly close to the value of a mixture of marine and terrestrial sources,showing a mixed origin.Meanwhile,the ⁸⁷Sr/⁸⁶Sr ratios gradually increased from the QL?west?to EQ?east?,which indicates the growing mixing of the terrestrial sources water.The saline springs of QL exhibit lower ⁸⁷Sr/⁸⁶Sr ratios and higher TDS indicating the mixture of seawater or marine evaporate sources.The saline springs of WQ are more likely close to the mixture of marine and terrestrial sources.The saline springs of EQ have been caused by mixing of the terrestrial sources.4.At last,comprehensive comparison of general chemical compositions and the characteristics of stable H-O-Sr isotopes and radio-tritium values of the saline springs,in combination with the formation lithology and geophysical results?Magnetotellurics?,systematically discussions on the origin and the water circulation of saline springs were conducted.The recharge source of the saline springs mainly comes from atmospheric precipitation or snowmelt water of alpine region,followed by recharge of partial hydrothermal Ca-Cl type water.Lots of high and steep thrust faults were well-developed in the KB due to the complicated tectonic evolutions,which served as favorable conduits for conducting groundwater circulation.Specially,the lithological characteristics of conglomerate provide a good medium for the recharge and discharge of the saline springs.Consequently,the precipitation or river waters can easily infiltrated under tectonic fractures conditions from the source area to the discharge area and circulated deeply into the earth,dissolving salty minerals along the way and returning to the surface along the fault.The findings provide scientific basis for the better understanding of the possible saltwater origin and circulation process of the saline springs in the Kuqa Basin.