STUDY ON THE CONTROLLING STRUCTURE OF SALT DEPOSIT IN VIENTIANE PLAIN,LAOS

The salt deposits in Vientiane Plain occurrence in Palaeocene Tagong Formation.The main Kalium-bearing minerals are carnallite and a little of sylvinite.During mineralization period,the Tagong Formation and salt deposits were controlled by NW-trending boundary faults and Tagong syncline.After mineralization period,the salt deposits were controlled by fold(salt syncline and salt anticline).The salt deposits formed broad and gentle fold under the horizontal stress.Inside syncline,deposition rate is relatively quickly and the thickness of clastic rocks upper salt seam is relatively large.On anticline,the thickness of clastic rocks upper salt seam is relatively thin.There are large density differences between salt deposits and clastic rocks,and the thickness of clastic rocks in the anticline is different from the one in syncline,so the salt deposits form differential loading.The salt deposits in syncline happened plastic flow towards anticline by larger loading.Thus the salt deposits in anticline become thicker,salt anticline form.The thickness of salt deposits in syncline becomes smaller.Thickness of the salt deposits in anticline is often great;its burial depth is shallow.The strata over anticline are often incomplete.With the salt anticline far development,the potash deposits pierce upper mudstone and expose oneself to relatively freshwater surroundings to suffer corrosion.