|Abstract:The Mahai Salt Lake is located in the Saishiteng Sag in the north-central part of the Qaidam Basin. The large-scale solid-liquid conversion mining of Holocene solid potash in the northern section of the mining area has been operating stably for nearly ten years, providing important potash fertilizer production. This paper intends to ascertain the types and occurrence characteristics of low-grade solid potash minerals at the current stage in the northern section of the Mahai mining area, and carry out analysis and testing work such as mineral thin slice identification, energy spectrum scanning electron microscopy and X-ray powder crystal diffraction, which are suitable for water-soluble mining. Provide a basis for sustainable development. The research found that: (1) Polyhalite is concentrated in the 70-79 exploration line, with primary and epigenetic metasomatic genesis occurring, and the former dominates. The primary polyhalite is flake, fibrous, granular, fibrous radial and petal-like aggregates; the metasomatic polyhalites are disseminated and felt-like with the appearance of gypsum. (2) Carnallite is mostly distributed in the 67-70 exploration line, and it is molten, other-shaped granular, and crack-shaped. Symbiosis with salt, polyhalite, sylvine and other minerals. (3) sylvine is only concentrated in the 72 exploration line. It is an euhedral-subhedral cubic monomer, which is symbiotic with minerals such as carnallite, polyhalite, and bischofit. (4) According to the analysis of the occurrence characteristics of polyhalite in the Mahai Salt Lake, the cause may be that the climate is dry and cold, the water supply in the basin is reduced, and the lake water shrinks and concentrates on a large scale. The K+ and Mg2+-rich magnesium sulfate subtype brine in the southeastern part of the mining area is mixed and doped with the Ca2+-rich chloride-type brine of Niulang Zhinu Lake, forming a potassium-magnesium-calcium sulfate-type polyhalite potassium salt mineral. In the process of high-salinity chloride brine migration and penetration to the southeast concentration center, it is evaporated and concentrated to form chloride-based carnallite, potash and other minerals in the northwest of the study area. (5) It is necessary to formulate a corresponding solid-liquid conversion plan based on the occurrence characteristics of polyhalite.