Evidence of sulfur isotope about the sedimentary environment of new type of polyhalite potassium ore in the northeast Sichuan Basin

The δ 34 S curve of sulfate from Members V–IV of the Jialingjiang Formation of the Sichuan Basin in the Early Triassic (T 1 j 4−5 ) is highly consistent with global marine sulfate, and their trends are also similar, showing that the Early–Middle Triassic evaporites in the Sichuan Basin are comparable with those of the Early–Middle Triassic global evaporites and that the massive polyhalite deposit of the Early–Middle Triassic in the Sichuan Basin is related to global events, seawater composition and climate conditions. The sulfur isotopes of anhydrite with different symbiotic minerals at certain depths are steadily distributed, and the sulfur isotopes are not affected by recrystallization of gypsum (anhydrite). During the deposition of the Jialingjiang Formation, the Xuanhan–Dazhou area was the salinization center, accumulating a lot of the early residual brines with high δ 34 S values. In section V of the Jialingjiang stage, the volume of seawater entering the northeastern Sichuan Basin was integrally limited by basin uplift, the ancient Luzhou–Kaijiang uplift, and seawater with a low δ 34 S value slowly entered the Xuanhan area, leading to a gradual reduction in the δ 34 S value in the secondary basin until the basin was completely closed. Thus, the sulfur isotope value of sulfate from T 1 j 4−5 in the ZK001 core gradually decreased (from 33.65 to 30.69 ‰) and then remained steady at 30.14 + 0.35 ‰, and the δ 34 S value of marine sulfate was slightly higher than the global average. The δ 34 S composition of the anhydrite sample from the Zk001 core is stable, and no abnormal fluctuation is found at the bottom of the new type of polyhalite potassium ore, implying that the provenance and sedimentary environment have not changed. The polyhalite fragment in the new type of polyhalite potassium ore is a kind of “non-in situ” polyhalite.