Crustal architecture beneath the southeast Missouri (USA) Mesoproterozoic Iron-Oxide province from geophysical models

Results from three-dimensional (3-D) density and magnetic susceptibility models provide tectonic-scale geophysical constraints on crustal architecture underlying the Mesoproterozoic iron province in southeast Missouri, USA. The iron province contains one iron oxide-copper gold (IOCG) and several iron oxide-apatite (IOA) +/- rare earth element (IOA +/- REE) deposits within 1.48 to 1.44 Ga rhyolites and intermediate to mafic composition igneous rocks of the mostly concealed St. Francois Mountains terrane. The geophysical models cover over a 900 x 900 km area; susceptibility distributions are calculated within a volume defined by the Cambrian erosion surface and the Moho. Density distributions are constrained by these surfaces, but extend from sea level to 50 km depth. The models show that the iron deposits occur along the edges or in the center of caldera structures underlain by partly coincident dense and magnetic domains interpreted as intermediate to mafic composition intrusions in the middle and lower crust. Several such calderas are associated with known iron deposits, whereas others highlight the potential for new areas of IOCG and IOA REE mineralization. A major crustal boundary, demarcated by Nd isotopic data, coincides with abrupt density and susceptibility boundaries that extend to the mantle.