A tuff interlayer in deep potash-bearing salt rocks and its implication for potash mineralization in the Simao Basin, southwestern China.

The lithology and genesis of a dark grey clastic interlayer first encountered within the deepest potassium-rich salt body in the Simao Basin, southwestern China, were analysed. Analyses of the petrography, mineralogy, and element geochemistry of the layer revealed that (1) the layer contains quartz crystals with gulf corrosion edges and explosion cracks and angular volcanic ash-sized glasses; (2) the main mineral components of the crystal fragments are chlorite, illite, biotite, quartz, anhydrite, gypsum, magnesite, pyrite, molybdenite, clinopyroxene, and zircon; (3) the rare earth element patterns, Zr/TiO and Nb/Y diagrams as well as boron content all indicate a volcanic origin for the layer. Based on these observations, the layer is suggested to be an altered tuff associated with various volcanic fragments dominated by chlorite and formed after alteration of a parent tuff in an alkaline, salty, and low-temperature water body.