Mineralogical characteristics and sedimentary envrionment significance of water-insoluble minerals in potash deposits of Vientiane Basin of Laos

The potash-bearing deposit was located in the Vientiane Basin of Laos where exists one of eastern Tethys metallogenic belt. The water-insoluble of Thongmang mining area in this basin were selected as carrier, through leaching and analysis, showed the water-insoluble minerals mainly include anhydrite, boracite, hilgardite, carbonate, quartz and muscovite, in which anhydrite, boracite and muscovite were dominant minerals. Mineralogical and morphological analyses of the water-insoluble minerals from different borehole-derived potash mineral strata have elucidated the evolution process of brine salt formation and restore the paleo-potassium deposit environment. The water-insoluble minerals revealed that the sedimentary environment in the late stage of salinity belongs to the shallow water disturbing environment. Accompanied by the fluvial influx and the influence continued, under the strong influence of terrestrial water body in the late salt-forming period, the evolution process of salt-forming brine will inevitably be affected. And the displacement of sedimentary center occurred during the metallogenic stage. Thus, this studies show that the characteristics of the water-insoluble can be used to retrieve the evolution process of brine salt formation and refect environment changes of the paleo-potassium deposits. In a word, the characteristics of water-insoluble minerals can provide effective information indicating the changes of sedimentary environments at the late stage of brine evolution.