Sedimentary manganese and iron mineralization in the St. Francois mountains magmatic-hydrothermal iron district; Southeast Missouri.
Though carbonate-clastic sequences within the middle-Proterozoic
St. Francois igneous terrane are quite rare, manganese and iron
mineralization at Cuthbertson Mountain, Missouri, is found within a
sedimentary section of limestone and siltstone that is intercalated within rhyolitic tufts. The limestones are laminated and contain
stromatolites, first reported by Stinchcomb (1976). The siltstones are
arkosic, have very angular grains, and apparently represent immature
volcanic sediments. Manganese minerals predominate over iron (hematite)
and include pyrolusite, psilomelane/cryptomelane, hausmanite, and
braunite. The manganese mineralization occurs mainly as nodules within
the sedimentary section, and both Mn and Fe minerals exhibit colloform
textures. Within this terrane we have described a number of banded iron
formation deposits that appear to have formed in shallow, restricted
basins, which were fed by iron-rich hot springs. The Cuthbertson
Mountain deposit appears to have been formed in a similar setting, but
one where hot springs were delivering manganese to the basinal waters.
* Dudley, M.A. and J.L. Nold. Department of Earth Science, Central
Missouri State University.