Abstract: This research project is a key component of the Special Projects for Exploration and Exploitation of Deep Earth Resources launched in 2017 and supported by the national 13^th“Five-Year”Key Research and Development Plan. It is led by the Institute of Mineral Resources, Chinese Academy of Geological Sciences and China Geological Survey involving 10 major research centers from the Ministry of Natural Resources, Chinese Academy of Sciences, Ministry of Education and large state-owned oil companies, as well as several research groups, for collaborative innovation research that fully reflects the close integration of production, research, learning and application. This research focuses on the key scientific issues of potassium formation in Mesozoic (Triassic, Jurassic) marine environments and late stage transformation in the eastern Tethys, and the ‘migration-differentiation-convergence’ mineralization mechanism of deep potassium-rich brines in Qaidam Basin, northern Qinghai-Tibetan Plateau. The key technical problems of the project are the ‘dual complexity’ high-precision seismic imaging technology for deep potassic salt deposit and the logging identification and seismic prediction technologies for deep potassium ore bed (potassium-rich brine layer). Taking the major potassium-bearing areas of western Qaidam Basin and northeastern Sichuan Basin as the foothold of the ore base, and also considering other potassium-bearing basins, the research program is designed to establish the 3D geological and metallogenic models, improve the theory of potassium formation in both marine and continental environments, and establish a complete technical system for the exploration of potassium deposits no deeper than 3000 meters. So far, comprehensive evaluation of deep potassium resources potential and anomalous verification drilling have been carried out, which led to the discovery of a large potassium resource base and 3-4 favorable target areas for potassium deposits. We have finally made the breakthrough in deep potassium ore prospecting and improved the prospects for greater potassium reserves. It is worth emphasizing that only by focusing on domestic exploration, and breaking through in marine environment to find large-scale soluble solid potassium salt deposits in ancient marine evaporite strata in large and medium-sized superposed basins in central and western China, can we fundamentally reverse severe shortage of potassium resources in China. It is gratifying to see a series of new metallogenic theories and prospecting discoveries have been made for marine potassium salt deposits in China after nearly 10 years of hard work. The innovative ‘two-storey’ potassium formation model put forth in southwest Yunnan points to a new direction for the exploration of Jurassic marine potassium salt deposits, and the discovery of a new type of Triassic marine soluble polyhalite potassium ore in Xuanhan area, northeastern Sichuan, leads to a new research field and direction for the exploration of potassium deposits in the Sichuan basin. In the Kuqa area of Xinjiang, a sylvine ore bed with a depth of more than 5000 m has been discovered to show substantial progress in the marine potassium deposit prospecting in this area. And in northern Shaanxi, the ‘W-type double bottom pot’ potassium formation model contributed to the discovery of a thick sylvine mineralization section in the Ordovician marine salt basin, a new important progress in exploring potassium salt deposits formed in the ancient epicontinental sea. Presently, we are at the dawn of breakthroughs in ore prospecting for marine soluble potassium salt deposits in China. The main direction for exploration of potash salts deposits in China in the 14th “Five-Year” and beyond will be to achieve substantial breakthroughs in this field thus to build several large marine potassium salt resource bases, through greater investment and more in-depth research on the basis of the aforementioned new discoveries.

Key words: potassium, eastern segment of Tethys, regularity of ore formation, deep profiling, marine potassium formation, new type polyhalite potassium, resource base