The giant potash deposit on the Khorat Plateau is one of the most promising targets for exploitation of potassium salts. So far, many researches and geologic survey have been conducted on the giant potash deposits. Hence, it is necessary to make an overall review on the potash deposits. The potash deposit on the Khorat Plateau was formed during the Middle to Late Cretaceous, during which seawater was enriched in Ca²⁺ and depleted in SO₄^2- compared with those of modern seawater. In addition to seawater, continental water and hydrothermal fluids could have affected the evaporite basins. The seawater was probably derived from Tethys ocean, and the brine should have evaporated to some extent before entering into the basin systems based on the evidence of absence of carbonates and unproportionate sulphate compared with chloride salts. The paleo-climate during Middle to Late Cretaceous was characterized as high temperature and extremely arid environment, which is favourable for deposition of potassium-magnesium saline minerals. The major saline minerals are of anhydrite, halite, carnallite, sylvite and, tachyhydrite, with trace amounts of borates. The resources of the potash deposit on the Khorat Plateau could be approximately as much as 400×10⁹ t of carnallite and 7×10⁹ t of sylvite. The evaporite sequences have been deformed and altered by postdepositinal processes, including tectonic movements and chemical alteration. Salt domes were formed in the postdepositional processes. Based on the analyses of geophysical surveys and drilling projects, high-quality sylvinite ores are commonly found at the flanks of those salt domes due to incongruent dissolution of carnallite. The future potential prospecting areas for the high-quality sylvinite ores would be on the edges of the Khorat Plateau.

Evaporites are widely distributed within continental “red beds” in the Lanping–Simao Basin, west Yunnan, China. Sr (Strontium), S (Sulfur), and O (Oxygen) isotope compositions have been measured on 54 sulfate or/and sulfate-bearing samples collected from Lanping, Nuodeng, Jinggu, Mengyejing, Baozang throughout the Lanping–Simao Basin. The ⁸⁷Sr/⁸⁶Sr ratios of all samples (0.708081 to 0.710049) are higher than those of contemporaneous seawater, indicating a significant continental contribution to the drainage basin. Sulfates in the Lanping Basin have higher ⁸⁷Sr/⁸⁶Sr ratios (0.709406 to 0.710049) than those (0.708081 to 0.709548) in the Simao Basin. Nevertheless, the δ³⁴S values of gypsums (13.4‰ to 17.6‰) in Lanping and Baozang fall within the range of Cretaceous seawater. Gypsums from a single section in Baozang have trends of decreasing δ³⁴S values and increasing ⁸⁷Sr/⁸⁶Sr ratios from base to top, indicating continental input played an increasingly significant role with the evaporation of brines. High δ³⁴S values (20.5‰ to 20.7‰) of celestites in Lanping are probably caused by bacterial sulfate reduction (BSR) process in which ³⁴S were enriched in residual sulfates and/or recycling of Triassic evaporites. The reduced δ³⁴S values of gypsums (9.5‰ to 10.4‰) in Nuodeng could have been caused by oxidation of sulfides weathered from Jinding Pb-Zn deposit. The complex O isotope compositions indicate that sulfates in the Lanping–Simao Basin had undergone sulfate reduction, re-oxidation, reservoir effects, etc. In conclusion, the formation of continental evaporites was likely derived from seawater due to marine transgression during the Cretaceous period. Meanwhile, non-marine inflows have contributed to the basin significantly.

The origin of Middle Jurassic evaporites in the Qamdo Basin is still controversial because palaeontological studies have reported that they have both marine and continental characteristics. The ⁸⁷Sr/⁸⁶Sr ratios of the gypsum in the Middle Jurassic Dongdaqiao Formation in the Qamdo Basin range from 0.707602 to 0.708163, which are higher than that of contemporaneous seawater. Model calculations suggest that continental water prevailed over seawater during the precipitation of these evaporites. However, the majority of the gypsum samples have δ³⁴S values of 15.3‰ to 16.3‰, which are consistent with that of contemporaneous seawater. This range of values (15.3‰ vs. 16.3‰) was likely caused by S isotope fractionation during evaporation because the δ³⁴S values and Sr contents are negatively correlated. The δ³⁴S values of the other three gypsum samples are 20.0‰, 20.5‰, and 20.8‰, which are significantly higher than that of Middle Jurassic seawater. The trace element compositions and scanning electron microscopy (SEM) observations indicate that these elevated δ³⁴S values were caused by bacterial sulphate reduction (BSR). The Sr and S isotope systematics of the gypsums from the Dongdaqiao Formation demonstrate that the parent brines from which the evaporites precipitated were marine based with a large quantity of continental input. A comparison of the lithologies and Sr isotope compositions of the Middle Jurassic sequences in the Qamdo and Qiangtang Basins revealed that the Qiangtang Basin was mainly recharged by Jurassic seawater, while the Qamdo Basin was primarily recharged by continental water with some seawater-derived overflow from the Qiangtang Basin.

Bromine contents of a 17-cm halite core from drilling hole of K203 in the Khorat Basin were analysed at 1 cm intervals (17 samples in total). The Br contents range from 99 to 184 ppm with a rapid variation. The K/Mg ratios of halite samples are tens of times higher than those of primary halite fluid inclusions. There is no positive correlation between Mg and Br contents, suggesting that fluid inclusions impose very little or negligible influence on Br contents of halites. The Br contents are not controlled by potash minerals either because the SEM examination shows no potash minerals and there is no relationship between K and Br contents. The Br contents of halite are thus primarily controlled by the Br concentrations of parent brines. The rapid variation of Br contents of halite within this section suggests a shallow saline pan wherein the giant Khorat evaporites were formed. This is contradictory to previous Br profiles of the Lower Salt Member which showed relatively stable and continuously increasing trends. The shallow saline pan model evidenced by high-resolution Br profile is consistent with sedimentary facies and salt mineral textures.