The Williston Herald had an article on this back in December, 2017:
Of 352 rock samples analyzed from the area, 277 averaged 120 parts per million total rare earth elements. That is twice the published average for U.S. coal, according to North Dakota Survey Geologist Ned Kruger.
See "Rare Earths in Coal" at dmr.nd.gov, Winter, 2017:One of the samples was at 603 ppm, which was twice the potential economic threshold identified by Department of Energy in its grant funding requirements, and it was the fifth highest recorded in the nation for coal. Overall, the samples ranked in the top 20 of coal samples nationwide.
Maintaining reliable sources of rare earth-containing raw materials, the vast majority of which are currently produced in China, is critical to each of the industries and manufactured products mentioned above.
New sources must be identified and developed to ensure an adequate supply of these important metals is available today and for the technological advances of the future. Recent publications indicate the potential of coal deposits for the recovery of rare earths as by-products of mining and combustion.
In particular, lignite has been highlighted owing to its potential for higher concentrations of rare earths and because there are existing techniques for extracting rare earth metals from the low-ranking coal.
The North Dakota Geological Survey is in the process of acquiring data on the quantity of rare earth elements present in the lignite beds and adjacent materials via sample collection from their exposures in the badlands region of southwest North Dakota. Goals of the program are to identify coal seams in which rare earths are concentrated beyond that found in average coal deposits, identify positions within a coal body where rare earths are most apt to be concentrated, and to spot trends in the data that may signal condition sets under which enrichment of rare earths is more likely to have occurred. Approximately 275 samples have been collected from 26 locations throughout Billings, north-central Slope, eastern Golden Valley, and southern McKenzie Counties [i.e., the same area as the Bakken]. To date, 100 of these samples representing 12 sample locations have been analyzed. The lignite beds found at and near the surface in this region were deposited 55-60 million years ago along with claystone, siltstone, and sandstones of the Bullion Creek and Sentinel Butte Formations.They are doing the similar studies in Pennsylvania.
- China produces more than 85 percent of the world's rare-earth elements, and the U.S. produces the second most at just over 6 percent, according to the USGS
- ammonium sulfate was [found to be] both environmentally friendly and able to extract the highest amount of REEs. Extracting 2 percent of the available REEs would provide an economic boon to companies
- in their study, the team also identified the locations within the coal seam that contained the highest amounts of REEs. Often the highest concentration is found in the poorest quality coal [that is, lignite]
- "You find some REEs in the coal itself, but the highest concentration is in what we call the coal shale, or the top layer of a coal seam. Knowing this, we can further target our operations to be more efficient," [a spokesman] said.