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Upper Devonian Phosphate

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Region Central, South Central
States
Mineral systems
Deposit types
Commodities
Other minerals

Information leading to the delineation of this focus area

Basis for focus area Extent of Upper Devonian phosphorites from strata of large but incompletely known extent in the Chattanooga, New Albany and Ohio Shales (Emsbo and others, 2015). Emsbo and others (2015, 2016b) showed francolite is highly enriched in HREE. Upper Devonian "New Albany Group" and equivalents host thick shale deposits, several of which are phosphatic (Emsbo and others, 2015). In Iowa, the Famennian Shales (English River Formation, Grassy Creek Formation, Saverton Formation) are thick and can contain phosphatic lags. Polygon shows the extent of known subcrop and outcrop.
Identified resources Identified resources of uranium (Chattanooga Shale, Tennessee). Historical production of phosphate (Tennessee).
Production Unknown.
Status Past mining of phosphate in Tennessee.
Estimated resources Estimated reserves of U in the Chattanooga Shale within the Highland Rim and Cumberland Plateau provinces in Tennessee range from 19,500,000 to 39,000,000 tons (Stockdale and Klepser, 1959). This estimate is for the entire Chattanooga Shale and not specific to phosphate intervals.
Geologic maps Horton and others (2017), scale 1:500,000; Osborne and others (1989), scale 1:500,000; Harris and McMaster (1965), scale 1:63,360; Causey (1963), scale 1:63,360; Warman and Causey (1962), scale 1:63,360; Causey (1965a), scale 1:63,360; Moore and Harris (1962), scale 1:63,360; Causey (1961), scale 1:63,360; Harris and others (1962), scale 1:63,360; Daniel and Hastings (1960), scale 1:63,360; Malmberg and Sanford (1963), scale 1:63,360; Sanford (1967), scale 1:63,360; Drennen (1961), scale 1:63,360; Causey (1965b), scale 1:126,720; Causey (1965b), scale 1:126,720; Faust (1984), scale 1:126,720; Neathery, Clarke and Szabo (1969), scale 1:126,720; Neathery, Clarke and Szabo (1969), scale 1:126,720; Tew (1986), scale 1:126,720; Chaffin and others (1976), scale 1:126,720; Mies (1991), scale 1:126,720; Neathery and others (1973), scale 1:126,720; Rheams (1990), scale 1:126,720; Rheams (1986), scale 1:126,720; Chaffin (1976a), scale 1:126,720; Dean (1993), scale 1:126,720; Rheams (1981), scale 1:126,720; Chaffin (1972), scale 1:126,720; Dean (1995), scale 1:126,720; Daniel (1976), scale 1:126,720; Chaffin (1976b), scale 1:126,720; Dean (1992b), scale 1:126,720; Rheams (1993), scale 1:126,720; Raymond and Gilbert (1984), scale 1:126,720; Beg and others (1978), scale 1:126,720; Thomas and Drahovzal (2012), scale 1:24,000; Chaffin and Szabo (1975a), scale 1:24,000; Chaffin and Szabo (1975b), scale 1:24,000; Szabo and Chaffin (1982), scale 1:24,000; Szabo (1975a), scale 1:24,000; Chaffin and Szabo (1975c), scale 1:24,000; Szabo (1975b), scale 1:24,000; Osborne and others (1998), scale 1:24,000; Raymond, Osborne and others (2003), scale 1:24,000; Osborne and others (2019), scale 1:24,000; Rindsberg and Osborne (2001), scale 1:24,000; Irvin and others (2006), scale 1:24,000; Rindsberg and others (2007), scale 1:24,000; Irvin (2012), scale 1:24,000; Osborne (2006), scale 1:24,000; Irvin and others (2002), scale 1:24,000; Ward and Osborne (2000), scale 1:24,000; Guthrie (1994), scale 1:24,000; Irvin (2008), scale 1:24,000; Ward and Osborne (2004), scale 1:24,000; Irvin and Thomas (2018), scale 1:24,000; McMaster (1965a), scale 1:24,000; Thomas and Irvin (2013), scale 1:24,000; Thomas and Osborne (2011), scale 1:24,000; Raymond (2005b), scale 1:24,000; Ward and Osborne (2006), scale 1:24,000; Osborne (1996), scale 1:24,000; Irvin (2009b), scale 1:24,000; Irvin and Thomas (2017), scale 1:24,000; Rindsberg and others (2003a), scale 1:24,000; Raymond (1999), scale 1:24,000; Rindsberg (2004a), scale 1:24,000; Irvin (2015a, b), scale 1:24,000; Osborne (2004), scale 1:24,000; Osborne (1995), scale 1:24,000; Raymond (2003), scale 1:24,000; Raymond (2005c), scale 1:24,000; Osborne and Brewer (2006), scale 1:24,000; Osborne and Irvin (2002a, b), scale 1:24,000; Dinterman (2010a, b), scale 1:24,000; Osborne and Irvin (2002a, b), scale 1:24,000; Osborne and Thomas (2013), scale 1:24,000; Thomas and Ward (2013), scale 1:24,000; Bearce and Osborne (2004), scale 1:24,000; McMaster (1965b), scale 1:24,000; Raymond (2013), scale 1:24,000; Irvin and Osborne (2004), scale 1:24,000; Osborne and Thomas (2018), scale 1:24,000; Dinterman (2009), scale 1:24,000; Irvin (2010), scale 1:24,000; Rindsberg (2004b), scale 1:24,000; Rindsberg and others (2003b), scale 1:24,000; Irvin and others (2005), scale 1:24,000; Osborne (2008), scale 1:24:000; Bearce and others (2003), scale 1:24,000; Thomas and Irvin (2016), scale 1:24,000; Thomas and Irvin (2017), scale 1:24,000; Irvin and Osborne (2000), scale 1:24,000; Osborne and Rheams (1998), scale 1:24,000; Osborne and Irvin (2018), scale 1:24,000; McKay (2016), scale 1:24,000; Osborne (2010), scale 1:24,000; Cook (2018), scale 1:24,000; Osborne and Irvin (2019), scale 1:24,000; Cook (2019), scale 1:24,000; Osborne (2011), scale 1:24,000; McKay (2015), scale 1:24:000; Jackson and others (2016), scale 1:24,000; VanDervoort (2019), scale 1:24,000; VanDervoort (2018), scale 1:24,000; Jackson and others (2017), scale 1:24,000; Irvin and others (2000), scale 1:24,000. Nearly all of the 1:24,000 scale geologic maps in Tennessee have been completed where the Chattanooga Shale crops out.
Geophysical data Rank 1 aeromagnetic data available for much of the area in Minnesota and Iowa; Inadequate Rank 3-5 in most other areas (for example, Missouri, Tennessee).
Favorable rocks and structures Upper Devonian; Phosphatic siltstone ("bone bed"), ooidal ironstone and phosphorite.
Deposits Deposits and occurrences listed in Chernoff and Orris (2002). Tennessee: Gordonsburg district, Swan Creek district, Leatherwood district, Baptist Branch district, Perry County district.
Evidence from mineral occurrences MRDS; Chernoff and Orris (2002); Emsbo and others (2015).
Geochemical evidence Upper Devonian phosphorites contain francolite with startlingly high concentrations (18,000 ppm ΣREE, 7000 ppm ΣHREE) (Emsbo and others, 2015).
Geophysical evidence No data.
Evidence from other sources No data.
Comments Polygon shows the extent of the subcrop and outcrop only. In Iowa there are 100s of water wells with cuttings and few core that may intersect strata of interest. In Tennessee the phosphate deposits (referred to as "blue rock phosphate") associated with this focus area tend to be confined to the uppermost part of the Mississippian-Devonian Chattanooga Shale (Hardin Sandstone) and the overlying Lower Mississippian Maury Formation. Thickness varies from a few inches to 4 feet.
Cover thickness and description Interested in partially exposed (zero cover) phosphate units and currently mined unites in deposits. Large outcrop area, beyond that thickness varies widely including bedrock and glacial cover. In Iowa, cover thickness increases westward beneath younger sedimentary rocks.
Authors Poul Emsbo, John D. Horton, Ryan J. Clark, Patrick McLaughlin, Peter J. Lemiszki.
New data needs Alabama: Geophysical data are likely to be helpful but there is limited precedent for detailed geophysical surveys in this environment. Surface geologic mapping and geochemical analyses are likely to be very helpful. Iowa: Mapping the Famennian beyond the outcrop belt. All states-geochemistry.
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 aeroradiometric surveys needed to create anomaly maps as phosphate is also highly enriched in uranium.
Digital elevation data needs Lidar variable; some complete (for example, Arkansas), some inadequate.