Regional geologic and petrologic framework for iron oxide +/- apatite +/- rare earth element and iron oxide copper-gold deposits of the Mesoproterozoic St. Francois mountains terrane, southeast Missouri, USA .

This paper provides an overview on the genesis of Mesoproterozoic igneous rocks and associated iron oxide ± apatite (IOA) ± rare earth element, iron oxide-copper-gold (IOCG), and iron-rich sedimentary deposits in the St. Francois Mountains. The Missouri iron orebodies are magmatic-related hydrothermal deposits that, when considered in aggregate, display a vertical zonation from high-temperature, magmatic ± hydrothermal IOA deposits emplaced at moderate depths (ca. 1-2 km), to magnetite-dominant IOA veins and IOCG deposits emplaced at shallow subvolcanic depths. The shallowest parts of these systems include near-surface, iron oxide-only replacement deposits, surficial epithermal sediment-hosted replacement deposits, synsedimentary ironstone deposits, and Mn-rich exhalite deposits. Alteration associated with the IOA and IOCG mineralising systems of the host volcanic rocks dominantly produced potassic with lesser amounts of calcic- and sodic-rich mineral assemblages. No deposits are known to be hosted in granite, implying that the mineralising systems were operative during a relatively short, postvolcanic period yet prior to intrusion of the granitoids. Mineral chemical, fluid inclusion, and stable isotope data from new studies record the effects of metasomatic fluids that interacted with crustal reservoirs such as volcanic rocks or seawater.
This paper provides an overview on the genesis of Mesoproterozoic igneous rocks and associated iron oxide ± apatite (IOA) ± rare earth element, iron oxide-copper-gold (IOCG), and iron-rich sedimentary deposits in the St. Francois Mountains. The Missouri iron orebodies are magmatic-related hydrothermal deposits that, when considered in aggregate, display a vertical zonation from high-temperature, magmatic ± hydrothermal IOA deposits emplaced at moderate depths (ca. 1-2 km), to magnetite-dominant IOA veins and IOCG deposits emplaced at shallow subvolcanic depths. The shallowest parts of these systems include near-surface, iron oxide-only replacement deposits, surficial epithermal sediment-hosted replacement deposits, synsedimentary ironstone deposits, and Mn-rich exhalite deposits. Alteration associated with the IOA and IOCG mineralising systems of the host volcanic rocks dominantly produced potassic with lesser amounts of calcic- and sodic-rich mineral assemblages. No deposits are known to be hosted in granite, implying that the mineralising systems were operative during a relatively short, postvolcanic period yet prior to intrusion of the granitoids. Mineral chemical, fluid inclusion, and stable isotope data from new studies record the effects of metasomatic fluids that interacted with crustal reservoirs such as volcanic rocks or seawater.