We present petrology and geochemistry of the largest single known banded iron formation in the world.

Dominant rock types are oxide BIF, silicate–carbonate–oxide BIF with minor stilpnomelane mudrock and stilpnomelane-rich tuffaceous mudrock.

Submarine hydrothermal input and fine-grained pyroclastic detritus were the main sources to the seawater.

Dominant volcanic sources were likely felsic of composition.

Dispersed stilpnomelane represents diluted ash material that interacted with Fe-rich seawater prior to deposition.