Genetic Mechanism of the Late Cretaceous Potassium Salt Deposit on the Khorat Plateau: Insights from the H-O-Cl Isotopic Constraints of Evaporite Minerals

Halite and sylvite samples from depths between 71.85 m and 83.85 m display δ37Cl values ranging from -0.31‰ to +0.67‰ (mean: +0.20‰) and from -0.87‰ to +0.75‰ (mean: +0.03‰), respectively. The H-O isotopic signatures indicate that the carnallite was derived from the Late Cretaceous seawater that underwent extreme evaporation and subsequent mixing with meteoric water. Meanwhile, Cl isotopic data indicate a marine depositional environment for the Late Cretaceous potassium deposit.

The sylvite metasomatism may be derived from the structural movement, and the non-marine inputs also contributed to the deposition of the potassium salt deposit. Combined with the previous studies, the metallogenetic stages of the potassium salt deposit in the Khorat Plateau have been divided into four stages: 1) original evaporation and deposition stage; 2) carnallitite metasomatic leaching stage; 3) structural metasomatic leaching stage; and 4) final deposition stage.

These isotopic constraints provide new insights into the formation of the Late Cretaceous potassium salt deposit on the Khorat Plateau.