Pennsylvanian Phosphate, Black Shale, Underclay

Region Central, South Central
Mineral systems
Deposit types
Other minerals

Information leading to the delineation of this focus area

Basis for focus area All states listed here have Pennsylvanian black shales, but the nature of the rocks are different across this large focus area. Some parts of the Pennsylvanian are phosphatic, whereas others are not; thus the prospectivity for critical minerals from this mineral system is variable for states listed here. Areas of interest are the subcrop and outcrop of the Pennsylvanian. Pennsylvanian black shales are frequently phosphatic and organic rich. Pennsylvanian age units include: Below Tiawah Limestone (Scammon Formation), Above Tiawah Limestone (Scammon Formation), Above Mineral Coal Bed and below limestone bed in Robinson Branch Formation, Oakley Shale Member (Verdigris Formation), Excello Shale, Binkley Shale Member (Little Osage Formation), Anna Shale Member (Carbondale Formation), Lake Neosho Shale Member (Altamont Limestone), Nuyaka Creek Shale Member (Lost Branch Formation), Tacket Formation, Mound City Shale Member (Hertha Formation), Hushpuckney Shale Member (Swope Limestone), Stark Shale Member (Dennis Limestone), Quivra Shale Member (Dewey Formation), Muncie Creek Shale Member (Iola Formation), Eudora Shale Member (Stanton Formation), Heebner Shale Member (Oread Formation), Queen Hill Shale Member (Lecompton Formation), Larsh-Burroak Shale Member (Deer Creek Formation). Iowa's Pennsylvanian section has multiple black phosphatic shales. Focus areas in which Pennsylvanian black shales will be assessed are to be distributed across participating states. Areas of interest are the subcrop and outcrop of the Pennsylvanian.
Identified resources Unknown.
Production None.
Status Unknown.
Estimated resources Remains undocumented (Emsbo and others, 2015). No estimated phosphate and REE resources. Spotty occurrences in Pennsylvanian shales that are moderately enriched in REE.
Geologic maps Horton and others (2017), scale 1:500,000.
Geophysical data Inadequate coverage; majority of the area is Rank 4 and 5, whereas central Illinois, southwest Indiana, and eastern Ohio are Rank 3. Some rank 3 in southwestern Missouri.
Favorable rocks and structures All black shales are of interest, particularly those deposited at or near marine chemoclines; Pennsylvanian Desmoinesian and Missourian shales.
Deposits Deposits and occurrences from Chernoff and Orris (2002) and MRDS.
Evidence from mineral occurrences MRDS; data on phosphates in Chernoff and Orris (2002).
Geochemical evidence No past production, but V, REE, and some Total Organic Carbon and redox sensitivity trace element data are available from the following strata: Cherokee Group-Verdigris (Kansas, Oklahoma), Veale, Carrier Mills, Mecca Quarry shales (Illinois, Indian, Kentucky); Marmaton Group-Anna, Excello, Little Osage, Lake Neosho, and Oakley shales; Pleasonton Group-Nuyaka Creek; Kansas City Group-Tacket shale interval (under revision by the Kentucky Geological Survey); Hushpuckney, Muncie Creek, Stark, Portersville, and Upper Salesville shales; Lansing Group-Eudora; Shawnee Group; Ames/sub-Ames and Heebner shales. Marmaton Group: Kidder and Eddy-Dilek (1994), Hatch and Leventhal (1997), Kidder and others (2003); Pleasanton Group: Kidder and Eddy-Dilek (1994), Kidder and others (2003); Kansas City Group: Hatch and Leventhal (1992), Kidder and Eddy-Dilek (1994), Cruse and others (2000), Kidder and others (2003), Cruse and Lyons (2004), Yang and others (2017); Lansing Group: Cruse and others (2000), Kidder and others (2003); Shawnee Group: Kidder and others (2003).
Geophysical evidence Downhole spectral gamma-ray logs show an increase in U relative to Th and K for numerous black shales in Kansas. These data are also proxy for high TOC and V.
Evidence from other sources Internal Kansas Geological Survey has TOC data for some shale localities.
Comments Pennsylvanian black shales are frequently phosphatic and organic rich. Analyses of Pennsylvanian-aged phosphoritic shales in the United States demonstrate that these strata are often enriched in REE (Emsbo and others, 2015; also see list of references provided under Geochemical Evidence Header). High concentrations of V are similarly observed in association with phosphate, in addition to strata containing high-TOC (total organic carbon) that were deposited under slow rates of deposition (Breit and others, 1989). Spectral gamma ray analyses of phosphatic black shales also show elevated U, owing to the binding of U to organic material. For example, in Kansas, black phosphatic shales are known to contain up to 29.5% TOC. In Indiana, marine black shale often have more than 15% TOC and U content reaching 300 ppm (Mastalerz and others, 2019). Given these data, some Pennsylvanian black shales are prime candidates for the analysis of REE, V, and U. Iowa Geological Survey has 8 cores (1970s coal project) and 100s of water wells with cuttings into the Pennsylvanian.
Cover thickness and description Interested in partially exposed (zero cover) phosphate units and currently mined units in deposits In Iowa, Quaternary cover ranges from 0 to 200m thick; some Cretaceous cover in western part of the state. Polygon shows the extent of subcrop and outcrop.
Authors Poul Emsbo, John D. Horton, Stephan Oborny.
New data needs pXRF and ICP-MS (as needed) elemental analyses of core and outcrop with uniform use of USGS approved standards. Variable standards were used in previous studies. Improved chronostratigraphic control via biochemostratigraphic (for example, conodont and Ccarb) methodologies is also needed to verify the correlation of shales between basins. In some cases, numerous black shales exist within single long-ranging biozonations. Such long ranging biozonations limit complete chronostratigraphic constraint required for precise modeling of these deposits.
Geologic mapping and modeling needs Distribution and isopach thickness of phosphate units. Geochemical analysis of REE content of francolite and P2O5 content of phosphate units to document spatial and stratigraphic variability.
Geophysical survey and modeling needs High resolution aeromagnetic and aeroradiometric coverage needed.
Digital elevation data needs Variable lidar quality; some complete, some planned/funded, some inadequate.