Occurrence state, enrichment mechanism and resource potential of potassium in potassium-bearing shale in the Wanshan area, Northern Guizhou, China

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.