The North Dakota Geological Survey has drafted a report that provides a road map to explore lignite coal and organic-rich mudstone that contains enriched critical minerals.
The report, released earlier this spring, is the latest in a series of studies by state geologists exploring the extent of rare earth minerals and other critical minerals — including lithium, which is used in rechargeable batteries for electric vehicles — that officials believe could be the foundation for a new mining and processing industry in North Dakota.
"We've been finding high concentrations of critical minerals," said Ed Murphy, the state geologist. "The problem has been finding them consistently along the same horizon."
Critical minerals such as copper, lithium, nickel, cobalt and rare earth elements are essential components in many rapidly growing clean energy technologies — ranging from wind turbines and electricity networks to electric vehicles. Demand for these minerals is expected to grow quickly as the transition to clean energy accelerates.
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State officials hope private companies will use the report to do explorations of their own, which could produce additional discoveries and provide the beginnings of a critical mineral industry in the state.
The concentrated tiny quantities of minerals embedded within millions of tons of lignite could contain billions of dollars of commercial-grade rare earth and other critical minerals, Lynn Helms, director of the North Dakota Department of Mineral Resources, has testified before legislators .
The exploration began in 2015 examining an 1,800-foot thick layer containing lignite coal and organic-rich mudstone in the valley of the Little Missouri River, located within the Williston Basin, which geologists now have narrowed to a 30-foot thickness that contains the richest known deposits.
The brightly colored rock formation is called the Bear Den Member of the Golden Valley Formation, found in upland areas covering 340 square miles across west-central North Dakota.
Critical minerals, which include rare earth minerals, are deemed essential by the U.S. government to the country's economic and national security. They often are provided by countries, including China, that aren't necessarily friendly to the U.S.
North Dakota researchers have analyzed more than 1,700 samples from more than 300 mineral outcropping sites across western and south-central North Dakota — a tiny fraction of the state's estimated 25 billion tons of lignite reserves.
Critical mineral deposits containing concentrations of 300 parts per million or more are considered economic to mine. Samples from thin lignite coals and organic-rich mudstone from the lower Bear Den Member contain up to 2,570 parts per million in rare earth elements — which the North Dakota Geological Survey believes to be the highest spot concentration yet reported from North American coal deposits.
Concentrations of several critical minerals were sometimes found in the same samples, including cobalt, gallium, germanium and lithium.
Although lignite is a low-grade coal, it holds promise as a source of critical minerals because of its ability to easily absorb rare earth minerals that are relatively accessible, potentially making extraction comparatively low-cost and environmentally friendly, according to the North Dakota Geological Survey assessment.
The rich deposits are found within what geologists call the Paleocene-Eocene thermal maximum, a formation resulting from a period of intense weathering — a process of breaking down rocks and minerals from exposure to the atmosphere — dating back 56 million years, when coal was deposited in subtropical rivers, lakes and swamps.
The mineral-rich Bear Den Member lies beneath layers of rock and sediment, including a thick layer of kaolinite, a clay that is used by Hebron Brick to manufacture bricks.
Rich deposits have been found on land owned by the U.S. Forest Service, North Dakota trust lands and private property in McKenzie, Dunn, Mercer, Stark and western Morton counties, Murphy said.
The North Dakota Geological Survey used a skid-steer loader to excavate 44 tons of material from a site on state trust land to provide to researchers at the University of North Dakota College of Engineering and Mines.
Initially, state geologists were finding that less than 20% of samples were greater than the 300 parts per million considered economic to mine. But within the enriched 30-foot layer 60% to 69% of samples were above that threshold, which Murphy called a "pretty big jump."
"That number has stayed consistent," he said.
That suggests to Murphy that North Dakota has abundant, viable deposits that could be mined for critical minerals.
"I think we've got areas that we can focus on," he said, with a road map sparing the need for companies to "drill randomly," enabling companies to speed-up exploration. "I think that's the big story."
Besides exploration for critical minerals, "companies are also waiting for the processing side" to enable commercial development, Murphy said.
The North Dakota Legislature has funded the Geological Survey's exploration for rare earth and other critical minerals, and pending legislation would provide another $500,000 to keep the work going, which Murphy hopes will yield information that will entice companies.
Murphy said the minerals could be mined using strip mining similar to conventional lignite mining or using "in situ" mining, which involves leaving the ore where it is in the ground, and recovering the minerals from it by dissolving them and pumping the solution to the surface where the minerals can be recovered.
Researchers at UND's Institute for Energy Studies are working to develop ways to mine and process rare earth and critical minerals on a commercial scale from North Dakota lignite.
The UND institute recently received a grant of $8 million from the U.S. Department of Energy for engineering and cost studies that could result in a $250 million plant to process critical minerals, if the UND project is selected.
"There's work left to be done to prove and really firm up the economics," said Dan Laudel, a chemical engineer and director of UND's Institute for Energy Studies. He called the North Dakota Geological Survey's work "exciting."
"It looks like they're starting to put together pieces of the puzzle," by pinpointing rich deposits, he said.
His team has been working on extracting rare earth and critical minerals from Falkirk, Coteau, Coyote Creek and Center lignite mines, where equipment already exists to mine the material at industrial scale. "So it's much cheaper to get access to a feedstock because of that," Laudel said, although he added that richer critical mineral deposits can be found elsewhere.
"We have found economic grades in the existing mines," he said.
The U.S. Department of Energy is mounting a big push to source rare earth and other critical minerals domestically, to avoid supply disruptions and to decrease dependence on other countries.
"These materials are just too important for our economy today," and are needed for the transition to cleaner energy and other uses, Laudel said.
"The discovery and description of these deposits are important steps in the development of a comprehensive exploration model for the coal and mineral industry, with the potential to one day reduce the necessity of critical mineral imports, a strategic vulnerability of the United States," the North Dakota Geological Survey said in a statement.