Characteristics and origin of a new type of polyhalite potassium ore in the Lower Triassic Jialingjiang Formation, Puguang area, northeastern Sichuan Basin, SW China

A new type of polyhalite potassium ore (NTPPO) was found in the Lower Triassic Jialingjiang Formation, NE Sichuan Basin, SW China. It is water soluble, therefore can be exploited using the water-solution method, and is of great potential of economic value and research significance. Based on cores, thin sections, energy spectrum and SEM analyses, its microfeatures, macrofeatures and origin are discussed, and a genetic model is established to provide a scientific basis for future evaluation, prediction and exploration of potassium ore in the Sichuan Basin. It is proposed that the NTPPO was caused by storm activities: (1) the storm broke the original sedimentary polyhalite–gypsum beds, whose fragments were transported into the salt basin with high content of K+ and Mg2+; (2) in the basin, the polyhalite continued to be formed from gypsum by metasomatism with K- and Mg-rich brine; (3) during diagenesis, under high temperature and high pressure, K–Mg-rich brine from halite continued to replace anhydrite (or gypsum) to form polyhalite.