Objective China is rich in insoluble potassium mineral resources, especially in the Wanshan area of Guizhou Province. However, the occurrence state and enrichment mechanisms of potassium in potassium−bearing shales remain poorly understood.

Methods We focus on the potassium−bearing shales in the Wanshan area of Guizhou Province, conducting systematic mineralogical and elemental geochemical analyses to evaluate potassium enrichment processes and utilization potential.

Results In potassium−bearing shales, potassium primarily occurs in an ionic form within microcline (42.43%~74.22%), followed by illite (<25.27%), with minor amounts present in illite−smectite mixed−layer minerals (<5.10%). The ratios of Al/(Al+Fe+Mn), Fe/Ti, (Fe+Mn)/Ti, MnO/TiO₂, U/Th, La_N/Ce_N, and La_N/Yb_N, along with the K₂O/Na₂O−SiO₂/Al₂O₃, SiO₂−K₂O/Na₂O, SiO₂−Al₂O₃, and Cr−Zr diagrams, as well as the rare earth element (REE) distribution patterns, collectively indicate that the potassium−bearing shales were formed in a passive continental margin, with sedimentary materials primarily derived from terrigenous debris. The Al₂O₃/TiO₂ ratios in the potassium−bearing shales range from 21.37 to 30.17 (average 25.28), and the Sc/Th ratios range from 0.85 to 1.20 (average 1.08), indicating a source material derived from felsic rocks. The values of U/Th, authigenic U, δU, V/Cr, Ni/Co, and V/(V+Ni) consistently indicate that the potassium−bearing shales were formed in an oxidizing environment. The CIA values and ICV values of potassium−bearing shales are 60.78~71.04 (average 64.99) and 1~1.72 (average 1.18), respectively, reflecting that the sedimentary material has undergone moderate weathering.

Conclusions Integrated A−CN−K diagram and mineralogical composition of rocks indicate that potassium metasomatism, involving the replacement of plagioclase by K−feldspar during weathering, significantly promoted potassium enrichment. Potassium resources in potassium−bearing shales are difficult to utilize effectively in the short term. However, with future increases in potassium demand and advancements in extraction technology, they may hold significant potential for utilization.