Geologists find elevated critical minerals in ND
BISMARCK – The N.D. Geological Survey has developed a comprehensive exploration model for lignite coals and organic-rich mudstones enriched in critical minerals, according to an announcement Monday by Lynn Helms, director of the North Dakota Department of Mineral Resources, and State Geologist Ed Murphy.
This model is based on the recent discovery of a 30-foot-thick interval of rocks containing elevated concentrations of many critical minerals, some of which can be significantly enriched. This brightly colored rock unit is called the Bear Den Member of the Golden Valley Formation, which is typically present in upland areas, covering 340 square miles spread across seven counties in west-central North Dakota. It extends north of New Town and into the White Earth area in Mountrail County on its northern end.
This discovery is documented in a just-released 90-page report: “ND Geological Survey Report of Investigation no. 133,” available for free download on the DMR – Geological Survey website.
Critical minerals are commodities defined by the U.S. government as essential to the economic or national security of the United States. They are increasingly vital components of modern technologies, especially the electronic components needed for an electrified energy infrastructure and advanced defense applications. There is little or no production of critical minerals in the United States, and domestic manufacturers depend on steady supplies from foreign countries. Most of the global supply of the more valuable, heavy rare earths currently comes from South China.
Sampling by the N.D. Geological Survey since 2015 has identified elevated critical mineral concentrations scattered throughout the Williston Basin. This sampling project has produced one of the most detailed datasets of coal enrichment in North America through the analysis of over 1,700 samples from more than 300 sites across western and south-central North Dakota. Although these samples represent only a tiny fraction of the state’s estimated 25 billion tons of lignite reserves, the geochemical results from them have already offered new insights into the occurrence and origins of promising critical minerals, especially the rare earth elements.
Contrary to what their name implies, rare earths are present in many types of rocks and sediments, but these metallic elements rarely concentrate into ores that can be economically mined. The U.S. has historically only developed one such deposit, the Mountain Pass mine in California, but it won’t be able to meet future domestic demand for rare earths. Igneous ores at Mountain Pass and other major mines are mostly enriched in the “light” rare earths, resulting in overproduction and low prices for some elements and ongoing global supply shortages for others. These hard rock sources can also harbor large amounts of the radioactive contaminant thorium, making the ores expensive to refine.
Coal and coal ash generally contain much lower overall concentrations of rare earths, but with comparatively cheap mining costs, low amounts of thorium and a higher proportion of the more valuable heavy rare earth elements.
Samples of thin lignite coals and organic-rich mudstones from the lower Bear Den Member contain up to 2,570 parts per million rare earth elements, believed to be the highest spot concentration yet reported from a North American coal and far exceeding the threshold of 300 parts per million considered potentially economic.
The N.D. Geological Survey has already identified a handful of other weathering zones in the Williston Basin, which will be the subject of future reports. One of those, located 1,000 feet stratigraphically below the Bear Den Member, also contains elevated concentrations of critical minerals and has been used to supply enriched lignite to the University of North Dakota’s Institute for Energy Studies for research on critical mineral extraction technologies.