Bieletan, the main area for solid potassium deposits in the Qarhan Salt Lake, is the principal mining region for brine exploitation and potash production. This study investigates the sedimentary characteristics of minerals after dissolution in the Bieletan area, focusing on borehole S2T3 in the northeast production area of Senie Lake. Using XRD, SEM, chemical element analysis, salt mineral identification, and physical parameter analysis, we identified polyhalite, carnallite, and sylvine as the main potassium minerals in the postliquefaction strata. Sylvine, the dominant component, exhibits the widest distribution and highest content in the 2320 cm core of S2T3. Sedimentary characteristic analysis reveals that polyhalite in the 1700~2200 cm layer is mostly of primary origin, formed during the penecontemporaneous sedimentary stage and coexisting with halite in the shape of bamboo flakes, petal, and velvet ball. Conversely, polyhalite in the 1000~1700 cm layer originates from epigenetic replacement. The layers with the highest carnallite content in the northeast Senie Lake are located at 1000~1700 cm and the upper 300 cm, providing valuable reference for selecting target regions for liquefaction in the next step. Furthermore, the 300~500 cm layer, characterized by the highest content of epigenetically replaced polyhalite currently forming, offers crucial materials and insights for subsequent polyhalite development and research.