Book excerpt: The southeast Missouri and Illinois-Kentucky districts are two of the most important mineral districts in the country in terms of variety of minerals produced, mineral output, and mineral potential. Both districts lie on faulted structural uplifts within the covered shield area of the Central States. Complex fault lineaments intersect in each district and are major structural controls. Two fault zones, the Ste. Genevieve and Cottage Grove, form connecting links between districts. The iron deposits of southeast Missouri are in rocks of Precambrian age; but the lead, zinc, barite, copper, cobalt, and pyrite deposits of southeast Missouri, and the fluorite, zinc, barite, lead deposits of Illinois-Kentucky, are all in the domed and faulted thin cover of Paleozoic rocks.