Study On Origin Of Potassium-bearing Brine In Sandy Gravel Bed Of Heibei Concave In Qaidam Basin

Potassium salt is one of China's short mineral resources,which is closely related to agricultural safety.The Qaidam Basin is rich in potassium resources,it is important to study the hydrochemical characteristics of saline lakes and rivers in Qaidam Basin,and geological characteristics of potassium deposit in Heibei concave,which is in the west of Qaidam Basin.Heibei concave,located on the west of Qaidam Basin,which is 34 km long from west to east,11 km wide from north to south,is an important prospect area to find potassium resources.This paper detailed summary of regional geological features,sedimentary characteristics of salt layers and hydrogeological characteristics,and study the salt mineral resources features,spatial distribution of brine resources,ore body characteristics and brine hedrochemical characteristics.For comprehensive utilization of mineral reouces of the brine of Heibei concave,summer and winter natural evaporation of brine was carry out in Golmud.In this paper,hydrochemical charactersitics of rivers and lakes and B,Li,K contents in water was studied,the author discussed the distribution of B,Li and K and the classification of carbonate lakes,sodium sulphate subtype lakes,magnesium sulphate subtype lakes and chloride type lakes.This article mainly studies the foiling issues:(1)Regional salt formation geological characteristicsWith effects of the neotectonic movement and the arid and semi-arid climate,the Qaidam ancient lake divided to several smaller lakes,the lake gradually change from the freshwater to brackish water lake,to saline lake,finally Dalangtan Salt Playa.The salt materials in Dalangtan were of multiple sources,which include weathered chemicals from surrounding mountains,residual ancient lake water,deep oilfield water and geothermal water.In the dry and cold climate,the salt lake area is reduced,the salt lake brine concentration increases,and the salt deposits increase.In the wet and humid period salt lake desalination,lake area increases,brine concentration decreases,salt deposits decreased,debris sediment increased.(2)Hydrogeological characteristicsIn Heibei concave,different groundwater types in different lithofaces.The pore water is deposited in gravel layers of the Lower Pleistocene alluvial fan,the intercrystalline brine in salt layers of the Middle Pleistocene.The structure and geomorphic conditions determine the storage space of groundwater and the occurrence of groundwater.High mineralization brine distribution is concentrated.In Heibei concave,the brine types show regular distributions.There are manly two types of brine,one is magnesium sulphate subtype,which is distributed in the south of the study area,another is chloride type,which in the western part.Heibei concave is in the north west of Dalangtan playa,the groundwater is basically in a state of stagnation,.The salt layers sedimented in the Early Pleistocence to Holocene,meanwhile,the potassium-rich brine formed.During the wet period,the sand and gravel layers sediment,and the pore water formed.When the potassium-rich brine mixed with the pore water,resulting in magnesium sulfate subtype water,then,when the deep oilfied water flows along fractures in gravel layers,the chloride type water formed.(3)Potassium deposit features in Heibei concaveThe potassium mineral deposit in Heibei concave is mainly composed by brine potassium,both in the preservation of solid and liquid.Among the mineral,the brine minerals contains potassium chloride,sodium chloride,magnesium chloride,magnesium sulfate and boron oxide etc.,and polyhalite makes up the major solid minerals.According to the survey,there are two polyhalite layers(named respectively of Z4 and Z3),two magnesium halite layers(Mg4 and Mg3),two mirabilite layers(M4 and M3),two layers of halite(S4 and S3),which are respectively located in Qp3 and Qp2.There are two layers of brine mineral,namely W3 and W2.The former one is located in several layers in Qp2,including coarse-middle sized salt,fined salt containing silty,and it is surveyed that in W3,The salinity value is larger than 300g/L,the grade of KCI is larger than 1%,it contains little water and the hydrochemical type is Magnesium sulfate subtype.The latter one(W2)is characterized that the salinity value is about 300g/L,and the grade of KCI 0.5%,the aquosity is middle-upper,and the hydrochemical type is chloride type,distributed among the middle-sized silts,silty-fine sand,sand-gravel and dpebbly sandstone in Qp1.(4)Hydrochemical features of the saline lakes in Qaidam BasinAccording to the Krakow-Valak classification,there are four types of lake in Qaidam basin,including chloride type,magnesium sulfate subtype,sodium sulfate subtype and carbonate type,among which sulfate type contains sodium sulfate subtype and magnesium sulfate subtype,the former the main.It is found the saline lakes in Qaidam tend to be desalting in recent years.Through the analysis of the samples acquired in saline lakes and rivers,we learn that hydrochemical types vary from carbonate to sodium sulfate to magnesium sulfate to chloride with the water flowing from source to the lake,at the same time,the salinity and potassium amount have the tendency of rising.Based on the analysis of the concentration and the coefficient of boron and potassium,it shows that the distribution of boron and potassium have the symmetry between east and west.Most of them come from the mud volcano in north of Qilian mountain and the deep-sourced hongshui river in south of the Kunlun mountains.The two elements are mainly enriched in the Da Qaidam-Xiao Qaidam lake zone and the east and the west Jinaer lake zone.With the comparison of the potassium distribution among different valleys,it shows that the content and the coefficient of potassium in Golmud river is not higher than others.(5)Experimental study of natural evaporationThrough the evaporation experiment of shallow brine in Heibei concave in summer and winter,we conclude the sequence of evaporation and crystallization and the characteristic of the precipitation.The subject shows that the quality of potassium halite and potassium compound obtained from experiment in summer is better than in winter,and therefor it is recommended that mineral processing should mainly occur in summer.At first in winter the brine is evaporated naturally until the point of the separation of sodium,then continues to be naturally distilled in summer to get potassium halite and potassium compound.the coefficient of specific evaporation is recommended to be based on the data from experiment in summer.Picromerite can be acquired from potassium compound in the way of flotation;and the potassium halite can be mixed to produce camallitite,then potassium chloride by flotation.