Abstract
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.
Highlights
Polyhalite is used as a high-quality soil-friendly chlorinefree fertilizer, which is rich in potassium and magnesium, and is good for growing crops (Chen 1999; Zheng et al 2018)
This paper mainly focuses on microfeatures and macrofeatures of the new type of polyhalite potassium ore (NTPPO) and analyzes its genesis in order to provide a scientific basis for future prospecting, prediction and evaluation of polyhalite in the Sichuan Basin
5 Discussion The theoretical origin of polyhalite and previous research results suggest that metasomatic polyhalite forms in two ways: (1) it forms from K+- and Mg2+-rich brine reacting with calcium sulfate; or (2) it forms from Ca2+and SO42−-rich fluids reacting with salt minerals containing potassium and magnesium, such as sylvite or carnallite
Summary
Polyhalite is used as a high-quality soil-friendly chlorinefree fertilizer, which is rich in potassium and magnesium, and is good for growing crops (Chen 1999; Zheng et al 2018). The polyhalite from the Triassic in the Sichuan Basin exhibits the widest distribution and the highest degree of enrichment, with a (2021) 10:4 easy to be exploited via the water-solution method, which greatly reduces its mining cost; this deposit has great potential economic value. This polyhalite is considered as a new type of polyhalite potassium ore (hereinafter called the ‘NTPPO’, Zheng et al 2018). The latter is further divided into: (1) parasyngenetic metasomatic polyhalite, that is, in the late stage of evaporation, polyhalite forms through reaction between concentrated brine with high K+ and Mg2+ concentrations and previously precipitated calcium sulfate salts (such as gypsum and sodium sulfate) (Yuan 1974); and (2) postdiagenetic metasomatic polyhalite, formed by metasomatism of potassium- and magnesium-rich brine transported through structural cracks into contact with calcium sulfate salts, such as gypsum or anhydrite (Yuan 1974; Liao et al 1984)
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