A new study by the Wyoming State Geological Survey has identified dozens of possible sources of rare earth metals in Wyoming in addition to deposits in the Bear Lodge Mountains that a company already has targeted for mining.
State geologists gathered and analyzed 335 rock samples from around Wyoming over the past year, making use of $200,000 appropriated by the Legislature.
The geologists picked out promising spots to sample based on the type of geological formations known to hold rare earths. They also went to places where others previously documented rare earths.
They took quick "grab samples" of no more than a few pounds of rock from each place, opting for a quick look at many locations instead of deep study of a handful of spots.
"A grab sample is a semi-educated guess," Geological Survey geologist Robert Gregory said Tuesday. "That's not near enough to characterize a deposit. But it can identify anomalies."
The geologists also analyzed 67 previously gathered samples. They found numerous deposits in just about every region of the state, with rare earths finds concentrated in the Medicine Bow, Sierra Madre and Laramie mountains of southern Wyoming and the area of the Granite Mountains in central Wyoming.
Rare earths are a group of about 16 obscure metals. Several, such as neodymium and lanthanum, are critical to manufacturing things such as wind turbines and hybrid cars. Rare earths also are necessary for high-tech military hardware including guided missiles.
China supplies about 95% of the global rare earths market, although a possible new source could be the Bear Lodge Mountains just north of Sundance, in northeast Wyoming. There, Lakewood, Colo.-based Rare Element Resources proposes what could be only the second significant rare earths mine in the United States after a Molycorp, Inc., mine at Mountain Pass in southeastern California.
The mine would be located in Black Hills National Forest. In May, the U.S. Forest Service agreed to conduct an environmental impact statement—a large-scale study—of the company's mining proposal, according to the company.
"We would hope officially to start the process in the next few weeks. And then we're probably looking at two years," said Robbin Lee, director of investment relations for Rare Element Resources.
After mining the rare earths ore, the company would refine it into rare earths at a plant it proposes to build in the Upton area about 30 miles to the south.
The Wyoming State Geological Survey didn't study the Bear Lodge deposits because of the considerable analysis already done there by Rare Element Resources. Follow-up study could show whether any of the deposits the Geological Survey examined contain enough rare earths to be profitably mined, Gregory said.
Promising formations included pegmatites—remnants of underground magma pockets that took longer to cool than surrounding magma—around Tie Siding, south of Laramie. Rare earths can become concentrated in pegmatites because rare earths don't readily solidify as magma hardens.
"The last, remaining liquid phase of the rock becomes enriched in these minerals," Gregory explained.
Ancient streambeds long ago buried and cemented in strata also can hold concentrated rare earths. The Geological Survey documented such "paleoplacer" rare earths in the northern Bighorn Mountains.
Despite their name, rare earths aren't rare but tend to be widely dispersed in the Earth's crust, making them difficult to mine profitably.
Global rare earths prices peaked in 2011 as China reduced exports. Prices have fallen off substantially since.