| Basis for focus area |
Focus area for the Hicks Dome intrusion, a nearly circular uplift about 12 km in diameter that was a result of explosive and intrusive igneous activity. The mineralized intrusive center of alkaline ultramafic dikes, plugs and diatreme breccias produced ~1,200 m of structural doming of Paleozoic sedimentary rocks. |
| Identified resources |
Unknown; confidential industry estimates. |
| Production |
Unknown. |
| Status |
Current exploration. |
| Estimated resources |
Confidential. |
| Geologic maps |
Denny, Nelson and Devera (2008), scale 1:24,000; Denny and others (2010), scale 1:24:000; Denny (2011), scale 1:24,000; Denny and Counts (2009), scale 1:24,000. |
| 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 |
Mineralized breccias are spatially related to the center of Hicks Dome. |
| Deposits |
Hicks Dome deposit (MRDS dep_id: 10193390; USMIN Site_ID: IL00002). |
| Evidence from mineral occurrences |
MRDS; USMIN; confidential industry data. |
| Geochemical evidence |
Moorehead (2013) includes detailed geochemical analyses of the Hicks Dome deposit. |
| Geophysical evidence |
Deposit occurs along the southern edge of a steep northwest-trending gradient associated with an elongate magnetic high. The magnetic high is called the south central magnetic lineament, which trends for several hundred km across southern Illinois and Missouri. |
| Evidence from other sources |
Exploration interest. |
| Comments |
Carbonatite breccias (diatremes?) at Hicks Dome are dike-like intrusives containing angular to sub-rounded clasts of country rocks in a matrix of igneous carbonatite. Breccia dikes are in a roughly radial pattern across the domed structure. Mineralization is largely confined to the central area of the dome and includes fluorite, barite, sphalerite, and galena (most common and confined within breccias); bertrandite (beryllium silicate) in two breccia bodies; and brockite (calcium thorium yttrium phosphate) and florencite (cerium aluminum phosphate) in a third breccia. Abnormal amounts of thorium, REE, and niobium were measured in breccia cuttings from a test well near the center of the dome (Bradbury and Baxter, 1992). REE minerals are secondary phases that most likely resulted from hydrothermal alteration-replacement by magmatic-hydrothermal fluids. A fertile (LREE enriched) lithospheric metasomatized mantle likely sourced the Hicks Dome carbonated alkaline silicate magma that, during emplacement, domed and brecciated the Paleozoic strata, expelled magmatic-hydrothermal fluids, and generated a F-REE mineralizing fluid with abundant carbonate. Igneous activity at Hicks Dome is genetically related to F-REE-base metal mineralization hosted by diatreme breccias, and likely contributed fluorine to the connate brines responsible for the F-base metal mineralization of the surrounding Illinois-Kentucky Fluorspar District (Moorehead, 2013). |
| Cover thickness and description |
Drill core at depths of 1,600 to 2,944 feet encountered zone of brecciated fluorite and REE minerals. |
| Authors |
Anne E. McCafferty, Gina Lukoczki. |
| New data needs |
Geochemistry (Phase III); Mapping (Phase I); Geophysics (Phase I-II). |
| Geologic mapping and modeling needs |
Mapping underway. |
| 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 or in progress. |
