The paragenesis, textures, and chemical compositions of secondary hematite in regional potassic altered rhyolites, four IOA deposits, the sedimentary iron deposit at Pilot Knob and the Boss IOCG deposit in SE Missouri were determined and compared to primary magnetite from the IOA and IOCG deposits. Magnetite is composed of elements characteristics of mafic to intermediate intrusions whereas hematite is enriched in elements characteristic of felsic igneous rocks. These results suggest that magnetite formed from fluids discharged from mafic to intermediate composition intrusions. Hematite precipitated from fluids discharged from felsic intrusions or fluids that evolved in caldera lakes. Hematite in the sedimentary iron deposit at Pilot Knob formed in an evaporative caldera lake with fluid inputs from felsic intrusions.