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The mineral deposits of the Illinois-Kentucky fluorspar district are the major source of domestic fluorspar; they also contain significant amounts of lead, zinc, barite, cadmium, and germanium, and some silver. Barite, strontium, and a small amount of copper are present, but mostly these are not recovered. The ores contain approximately 9.9 tons (9 t) or more of lead and 55 tons (50 t) or more of zinc per 1, 102 tons (1 ,000 t) of fluorite. The cadmium, germanium, and silver are contained chiefly in the sulfide minerals sphalerite and galena. The major structural features of the region are a broad arch which trends northwestward, ending at Hicks dome, and a system of horsts and grabens that cross the arch and trend northeastward to eastward. Mineral deposits belonging to four structural types are known: (1) veins, which are along normal faults related to the horsts and grabens; (2) bedded deposits, which are found in horsts; (3) solution-slump breccias, which extend downward below some bedded deposits; and (4) diatremes, which are related to the Hicks dome structure. The structural ore control of the first three types is the intersection of faults and other fissures with certain beds of Mississippian limestone. The mining area, about 540 square miles (1 ,400 km 2), is nearly coextensive with the area of outcrop of these beds of limestone. The area of mineral potential is approximately doubled in size by projecting the favorable beas outwara rrom the mining area and downdip off the flanks and the end of the arch. Many square miles of area having mineral potential within the structural framework defined here are unexplored. In addition, the mineral potential of the diatremes has been largely unrecognized. These facts, coupled with a substantial production from the area, indicate a large mineral potential in the region.

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