The Characteristics Of Fluid Inclusions In Salt Minerals And The Paleoenvironment Study Of Mengyejing Potash Deposit,Yunnan

Mengyejing Potash Deposit at Jiangcheng,Yunnan,is located in the southeastern of Lanping-Simao Basin.And it is also located in Sanjiang tectonic belt,which is interacted by the India plate,the Eurasian plate and the Tethys Oceanic plate.It is an unique ancient solid potash deposit in China.However,the previous researches of homogenization temperature study in halite inclusions were less,and the paleotemperature of brine is still unclear during the potassium formation period.In order to study the characteristics of mineralogy and paleoenvironment,the paper focuses on field geological investigation,sample collection,thin section identification,X-ray diffraction(XRD),inclusion temperature and H,O isotope of inclusions analysis method by selecting eight typical cross-sections,which altitudes range from 670m to 535m.Based on field geologic investigations,there are five lithologic rocks in this mining area.They are white salt,grey potash,orange potash,greyish green boulder clay salt and brownish red boulder clay salt rocks.The XRD result shows that the Mengyejing Potash Deposit belongs to chloride type(the major minerals are halite,sylvite and small amounts of carnallite).In addition,other minerals are sulfate mineral(anhydrite),carbonate minerals(magnetite,dolomite and calcite),authigenic minerals(quartz,specularite and pyrite)and clay minerals(illite and chlorite).Combining with the development of inheritance fractures,the Mengyejing Potash Deposit may link with the western Tethys Sea through fractures or has the possibility of recharge from original storaged brine in Jurassic Zhangkezhai Formation.The homogenization temperatures of primary halite fluid inclusions for pure liquid phase and H,O isotope are tested in saline rock.The homogenization temperatures of the halite fluids inclusions are at a range of 21.8??48.2?.The ?18O values of the inclusions in potash rock are between 2.8‰-8.2‰,with an average of 4.9‰;the ?D values in potash rock are between-79.6‰?-64.2‰,with an average of-71.3‰.The ?18O values of the inclusions in salt rock are from 1.9‰ to 4.3‰,with an average of 3.1‰;the ?D values of the inclusions in salt rock are from-86.5‰ to 64.4‰,with an average of-73.8‰.Both of them indicate that the paleoenvironment is warm during the salt-forming period.According to the homogenization temperature increasing from halite layer to sylvite layer,the paleotemperature of water is gradually elevated.The oxygen isotope appears shift positively from the upper part of sylvite layer to the middle part.It means that the hot outside water body superposition and replenishment is possible,which is consistent with the highest temperature in the middle part of sylvite layer.The average homogenization temperature in halite rock and in potash rock is 25.7? and 30.4? respectively.So the deposition temperature from the potash rock is relatively higher than that from the salt rock.It indicates that the potash rock deposits after the halite rock,which is consistent with the process of brine crystallization and precipitation.Therefore,salt minerals are deposited in a thermal environment.Extensively and continuously,the evaporation is an important effect to the sylvite enrichment and mineralization...