| Basis for focus area |
Focus area outline of the Illinois-Kentucky Fluorspar District from Denny, Goldstein and others (2008). |
| Identified resources |
Historical production of fluorite, lead, and zinc (Pinckney, 1976). |
| Production |
Since 1880 the area has yielded more than 9,500,000 tonnes (8,600,000 t) of finished fluorspar concentrates of all grades, 80% of the total U.S. production (Grogan and Bradbury, 1968). |
| Status |
Past mining and one currently operating mine. |
| Estimated resources |
Nearly all the deposits of the region contain large amounts of fluorspar and differ significantly from other major deposits in the Mississippi Valley district, which are mined mainly for lead and zinc minerals. |
| Geologic maps |
Denny, Nelson and Devera (2008), scale 1:24,000; Martin and others (2007), scale 1:100,000. |
| Geophysical data |
Adequate Rank 1 aeromagnetic and radiometric coverage collected as part of Earth MRI Phase 1 (McCafferty and Brown, 2020a). |
| Favorable rocks and structures |
Major fault systems; Paleozoic carbonates. Most of the barite veins are in the Carters limestone, but some veins also are in the overlying and underlying limy rocks. The limestones are locally sandy, shaley, or dolomitic. Most of the deposits are within 20 miles of the junction of DeKalb, Smith, and Wilson Counties, but others are in Rutherford, Cannon, Williamson, Trousdale, and Putnam Counties. |
| Deposits |
Old Jim mine (MRDS dep_id: 10242273), Huston mine, Patrick mine, Hickory Cane mine (MRDS dep_id: 10218611). |
| Evidence from mineral occurrences |
MRDS. |
| Geochemical evidence |
Fluorite, REE, and beryllium reported in drill core cuttings; LREE enrichment (see Anderson, 2019). Old Jim mine, Huston mine, Patrick mine, Hickory Cane mine all contained high-grade Zn ores. Davis-Deardorf mine reported crude ore 50-60% CaF2, 12-14% Zn, 3-5% Pb. Concentrate contained 0.33% Cd and enough Ga to adversely affect further processing of the Zn concentrate. Lead concentrate contained 7.38 oz/t Ag. Minerva mine was a major producer of fluorite. In 1945 the Minerva No. 1 mine mill feed averaged 35% CaF2 and 4.2% Zn (Weller and others, 1952); Zn concentrates averaged 1% Cd and 0.25% Ge (Grogan and Bradbury, 1968). |
| Geophysical evidence |
New airborne magnetic survey shows elongate high amplitude magnetic anomalies associated with Permian dikes. Circular, high amplitude magnetic highs occur over Arkoma Dome, Coefield anomaly and several other inferred ultramafic igneous centers associated with dikes (McCafferty and Brown, 2020a). |
| Evidence from other sources |
Exploration industry interest. |
| Comments |
Unusual mineral deposits in this district are related to igneous dikes and intrusions similar to Hicks Dome (Illinois), an igneous intrusive carbonatite complex. These deposits contain a wide spectrum of mineralization, including fluorite, REE, beryllium, and zinc. In addition to Hicks Dome, other alkalic intrusives occur within the district, including the Coefield Ultramafic Complex (Kentucky). It is possible that the Coefield Complex (and perhaps other magnetic anomalies identified as igneous rocks) may contain diamonds. |
| Cover thickness and description |
Exposed to thin cover. |
| Authors |
Albert H. Hofstra, Warren C. Day, Anne E. McCafferty. |
| New data needs |
Mapping (Phase III); Geophysics (Phase I-II); Geochemistry (Phase III). |
| Geologic mapping and modeling needs |
Detailed geologic mapping to follow on new high resolution geophysical survey. |
| Geophysical survey and modeling needs |
Entire district has been flown with modern and uniform coverage for magnetics and radiometrics in 2019. |
| Digital elevation data needs |
Lidar adequate. |
