Cratonic tectonic controls of Late Precambrian iron deposits and Mississippi Valley-type deposits in the Central United States

Abstract

Middle Proterozoic age iron, light rare-earth apatite, copper deposits are exposed in the St. Francois Mountains in a larger alkalic granite and rhyolite terrane that is favorable for the occurrence of world-class deposits of the Olympic Dam type. The Precambrian age structural network of lineaments cut the Proterozoic rocks above where movement has been revived in post-Precambrian time including both Paleozoic and Mesozoic age rocks. The Mississippi Valley-type of deposits in Paleozoic-age rocks are located at the crests of domes (Central Kentucky and Central Tennessee districts), or faulted collapsed domes (Illinois-Kentucky) on half-domes (Upper Mississippi Valley and Tri-State districts), or they surround Precambrian islands in an open oval in fault zones and facies changes where shales, carbonate rocks and sandstones pinch out (Southeast Missouri). Some ores were deposited as veins in faults, as replacements in adjacent permeable beds, in cryptovolcanic breccia (part of Illinois-Kentucky), or in fault zones adjacent to and above Precambrian rift valleys (eastern northern Arkansas and parts of the Illinois-Kentucky districts). In the Central States major structures of repeated uplift and subsidence are crossed by a complex system of intersecting structural lineaments that form a cratonic network across the large domes, basins and rift valleys. The lineaments trend northwest, northeast, east and north. Some are curved and many have a strike-slip component of movement