Potassium enrichment mechanism and controlling factors in Cambrian black shale from eastern Guizhou, China

Potassium is a critical mineral resource for global agricultural security. Besides soluble potash salts, insoluble potassium resources hosted in black shale series represent an important alternative potash mineral resource. Extensively developed Cambrian potassium-rich black shales occur in the Wanshan District of Tongren, eastern Guizhou Province, southwestern China. They have K₂O contents ranging from 8% to 11% and prospective reserves exceeding 5 billion tons. However, the potassium enrichment mechanism and its controlling factors in the potassium-bearing shales of this region remain unclear currently. Therefore, this study presents petrographic and elemental geochemical analyses of two representative sections in Wanshan, Tongren, Guizhou. The results indicate that potassium-rich felsic terrigenous detritus in the northwestern study area was transported to a passive continental margin setting, and deposited under restricted, suboxic to anoxic-dominated water conditions. The sedimentation-diagenesis stage underwent potassium metasomatism — a process that promoted the transformation of aluminous clay minerals into illite, eventually leading to the formation of potassium-bearing shales with K-feldspar and other minerals as the major potassium-bearing phases. This study provides a scientific basis for understanding potassium enrichment in the Cambrian black shales of eastern Guizhou and offers a valuable reference for exploring and developing potassium resources.