Origin and Formation Mechanisms of Potassium- and Lithium-Rich Brines in the Triassic Strata of Northeastern Sichuan Basin, South China

The northeastern Sichuan Basin hosts deep brines with unusually high concentrations of potassium (K) and lithium (Li). This study examines deep brines abundant in K and Li in northeastern Sichuan Basin. Brine samples from Well ZK601 underwent comprehensive analysis for major elements, trace elements, and Sr isotopes. Lithium content in core samples correlated with regional brine reservoir features. Brine samples showed a salinity range of 354.6–363 g/L, with varying contents of Na⁺ (101–106 g/L), K⁺ (28.92–34.84 g/L), Cl⁻ (202.1–206 g/L), Br⁻ (2110–2980 mg/L), and Li⁺ (169.5–204.5 mg/L). The ⁸⁷Sr/⁸⁶Sr ratio in brine was 0.708324. Li notably increased post-green bean rock deposition in 71 core samples. The ratios are as follows: Br × 10³/Cl is 10.24, K × 10³/Cl is 169.13, nNa/nCl is 0.74, and SO₄ × 10³/Cl is 0.49. These brines likely originated from ancient seawater, evolving via rock interactions during burial, notably enriching K and Li through gypsum dehydration. Geochemical traits and Sr isotopes affirm ancient seawater origin, stressing continual water–rock interactions. The volcanic activity contributed significantly to lithium enrichment, consolidated during later burial stages. Brine reservoirs, mostly in formations like dolomite within the Jialingjiang Formation, associate closely with fractured zones. Structural traps define distribution, while fault systems govern enrichment. Accumulation mainly occurs in fractured zones, reflecting a mineralization model of seawater origins, metamorphism, filtration, and structural enrichment. In summary, our model outlines a transformation from seawater origins to structural controls enriching K and Li in deep brines in northeastern Sichuan Basin.