| Mengyejing potash deposit at Jiangcheng of Yunnan is located in the southeastern of Lanping-Simao basin,which is the unique ancient solid potash deposit in China.However,previous research of geochemical features of the deposit was less,and the genesis of the deposit was still unclear.Three typical sections of 628m tunnel or 640m tunnel were selected as studying areas.The characteristics of mineralogy,petrology and geochemistry(including the major elements,trace elements and hydrogen and oxygen isotope)were studied by XRD,ICP-OES,ICP-MS,IRMS.The results show that major mineral components were the chloride type salt minerals,include halite,sylvite,and a small amount of carnallite.In addition,other components include anhydrite,magnesite,dolomite,calcite,quartz,specularite,pyrite,illite,chlorite and apatite.The salt rock is mainly composed of halite(83.39%).The potash rock is mainly composed of sylvite(17.55%)and halite(69.64%).The carnallite rock is mainly composed of carnallite(29.34%),sylvite(40.34%)and halite(25.44%).The average value of KCl in the brownish red boulder clay salt rock is 83.39%,and it was formed at relatively high concentration brine under oxidation condition.However,the average value of KCl in the greenish grey potash rock is 11.88%,and it was formed at concentrated brine with normal evaporation.The average value of KCl in the greyish green boulder clay potash rock is 19.00%,and it is formed at high concentration brine with a under reducing condition.In the potassium-rhythmic layering,the brownish red boulder clay salt rock,the greenish grey potash rock,the greyish green boulder clay potash rock deposit from bottom to top in turn,which show that the brine concentrated gradually.The content of Li,Rb,Cs,Sr,Br,I,B in all rocks has similar distribution.And Br.Rb have the most closely relationship with the potassuim salt mineral.The Br value is in range of 143×10-6?1886×10-6,the Br×103/Cl value is in range of 0.28?4.72,and the Rb value is in range of 0.14×10-6?165.00×10-6.They had a positive correlation with the content of KCI,show that the content decreased with the concentration of brine.And they are in the range of the theoretical contents of salts from seawater,show that potassium sources is maily derived from sea water.The 8D values of inclusions in salt rocks are from-86.50‰ to-44.9‰,with an average of-70.6‰,and the ?18O values of inclusions in salt rocks are from +1.9‰ to +8.2‰,with an average of +4.2‰.The ?D values and the ?18O values of inclusions in salt rocks are close to that of magmatic water.It is suggested that the ore forming brine is probably mixed with some deep Brine.In summary,Mengyejing potash deposit is a set of seawater-derived but terrestrial deposit. |
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