Cretaceous-Paleocene coals, underclays, and interbeds

Region West, Rocky Mountains
Mineral systems
Deposit types
Other minerals

Information leading to the delineation of this focus area

Basis for focus area There is a lack of widespread, comprehensive data on the trace element composition of these coals units and associated beds like underclays and partings. Modern research of trace element geochemistry in coals and underclays has resulted in promising discoveries of elevated levels of REE and other critical minerals (Tetra Tech, Inc., 2018; Yang and others, 2020; Current Earth MRI projects are led by West Virginia Geological and Economic Survey and Kentucky Geological Survey).
Identified resources Historical and current coal production. Secondary production of coal clinker for aggregate. Historical production of uranium from South and North Dakota.
Production North Dakota: ~350,000 pounds of U3O8 from lignite; South Dakota (1956-1968): 600,000 pounds of U3O8 from lignite (Pool, 2017).
Status Past and current mining. Coal is currently mined in Powder River Basin (Montana and Wyoming), Rock Springs (Wyoming), Bull Mountain Basin (Montana), and Kemmerer (Wyoming) areas. Lignite is currently being mined in the Williston Basin (Montana) for electricity and industrial uses.
Estimated resources No data.
Geologic maps Love and Christiansen (1985), scale 1:500,000; Vuke and others (2007), scale 1:500,000; Martin and others (2004), scale 1:500,000; Murphy (2007), scale 1:360,000; Vuke and others (2001), scale 1:100,000.
Geophysical data Inadequate aeromagnetic and aeroradiometric coverage.
Favorable rocks and structures In Wyoming the focus area includes coal-bearing formations from Cretaceous and Paleogene periods -- the Adaville Formation, Almond Formation, Fort Union Formation, Frontier Formation, and Rock Springs Formation, among others. In Montana only the Fort Union Formation was included. In North Dakota focus area includes bedded uraniferous lignite deposits are in the Paleocene sandstone and lignite from the Fort Union Formation/Group.
Deposits In North Dakota over 35 properties report U production from lignite; the largest producer was the Frank Lease which produced 108 tU (Pool, 2017).
Evidence from mineral occurrences International Atomic Energy Agency (2020b); U.S. Environmental Protection Agency (2006).
Geochemical evidence Analysis of coal and bounding beds from a core of Fort Union Formation (Anderson coal seam) in the Powder River Basin reports Total REE values between 100.1 to 1572.1 ppm (Bagdonas and others, 2022). The USGS COALQUAL dataset includes trace element data on coals from across Wyoming; some of these samples report Total REE of 139.6 ppm (Bragg and others, 1997) and a mean Total REE+Y of 76.9 ppm from Wyoming coals. Analyses of spring waters from the Arikaree Formation in the Ekalaka Hills (Montana) indicate that U is being leached from this formation and transported by ground water (Gill, 1959).
Geophysical evidence No data.
Evidence from other sources Critical minerals in coals and underclays is an active area of research, particularly in the Illinois and Appalachia regions. This includes projects funded through DOE-NETL and USGS Earth MRI. Some of these studies have shown that inorganic components and rocks bounding coal beds (particularly underclays and partings) may be a promising source of critical minerals, including REE, Sc, and Y (Hower and others, 2020; Tetra Tech, Inc., 2018; Yang and others, 2020).
Comments The USGS COALQUAL dataset does not include analyses of the roof or floor beds bounding coal seams, which have been shown to have higher levels of REE than the associated coal seam (Tetra Tech, Inc., 2018; Yang and others, 2020). Additionally, according to Lin and others (2018), Wyoming is under sampled in the COALQUAL database, and so the Wyoming dataset may not comprehensively represent the true range of compositions of coals in Wyoming. In North Dakota, blanket-type mineralization ranges from 100 to 700 ppm U, with irregular higher grade pods from < 0.1 to 0.29% U3O8, and in South Dakota grades range from 0.1 to 0.4% U3O8 for mined lignite with maximum values up to 2.8% U3O8 (Dahlkamp, 2010). Uranium-bearing lignite beds 1.5 to 8 feet thick with about 0.005% U occur in massive coarse-grained sandstones in the upper part of the Fort Union Formation of the southern part of the Ekalaka Hills, Carter County, Montana. There was U/Ge/Mo commercial exploration in North Dakota as recent as 2008 when 400 exploration holes were drilled in Slope and Billings counties.
Cover thickness and description Surface exposures are common. Overburden can range from zero to thousands of feet, but typically within 500 ft of the surface.
Authors Kelsey S. Kehoe, Jay A. Gunderson, Susan Hall, Ed Murphy, Levi Moxness, Ned Kruger, Laurel G. Woodruff, Darren J. Johnson.
New data needs Geochemical analyses.
Geologic mapping and modeling needs 1:24:000 scale surface mapping needed; 3D subsurface modeling of ore bodies in North Dakota.
Geophysical survey and modeling needs Mostly inadequate Rank 5 airborne magnetic and radiometric coverage, but unclear if high resolution data would be useful.
Digital elevation data needs Lidar in progress most places; inadequate in many areas.