| Basis for focus area |
Permian dikes, sills, and diatremes related to Hicks Dome, Arkoma Dome and Coefield anomaly in southern Illinois and northwestern Kentucky (including Omaha, Wildcat Hills, cottage Grove, Will Scarlet, Williams, Grant, and Clay Lick intrusions) (Maria and others, 2019). |
| Identified resources |
None; however, historical production of fluorspar, lead, and zinc in the Illinois-Kentucky Fluorspar District could be related to this igneous activity. |
| Production |
None. |
| Status |
None. |
| Estimated resources |
None. |
| 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 |
Permian alkaline, ultramafic carbonate-rich rocks (some within the larger structure of the Reelfoot Rift-Rough Creek Graben, at times fault-related). |
| Deposits |
None. |
| Evidence from mineral occurrences |
None. |
| Geochemical evidence |
Anderson (2019) reports on REE and F mineralogy and geochemistry of ultramafic rocks from surface samples and drill core analyses. Maria and others (2019) described the mineralogy, and trace, whole rock, and isotopic geochemistry of ultramafic rocks across the Midwest Permian ultramafic district. |
| 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 |
Numerous Permian igneous dikes, sills, and pipes are present underlying southeastern Illinois and northwestern Kentucky. Some of these intrusions outcrop on the surface while others were identified in the subsurface in drillholes and newly acquired aeromagnetic data. The igneous intrusions have been identified as ultramafic lamprophyres, specifically as minette (Moorehead, 2013), alnöite (Denny and others, 2017; Maria and others, 2019), and aillikite (Maria and others, 2019) based on their diverse mineralogical and geochemical characteristics. Rare earth minerals have been identified in the igneous rocks of the Midwest Permian Ultramafic District suggesting that a carbonatite phase may be present in the alkaline complex (for example, Moorehead, 2013; Denny and others, 2017). |
| Cover thickness and description |
Exposed to thin cover. |
| Authors |
Anne E. McCafferty. |
| New data needs |
Mapping in progress (EMRI Phase 3), Rank 1 geophysics (EMRI Phase 1-2) complete, Geochemistry in progress (EMRI Phase 3). |
| 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 (complete or in progress). |
