Rare Earth Elements (REE) are not particularly rare within the earth’s crust. However, economically mineable concentrations of them are. Even the two least abundant REE, Thulium (Tm) and Lutetium (Lu) are 140 to 180 times more common than gold.
Minor amounts of REE-bearing minerals were reported in Wyoming as early as the 1930s. Early exploration generally focused first on uranium and thorium, while REE represented what geologists considered an interesting association. Most early REE studies identified the potential for REE occurrences but did not produce detailed analyses due to high analytical costs. Modern technology has significantly reduced the cost of high quality, detailed analyses.
Prior to the 1990s, the United States produced sufficient REE for domestic use. Low prices and overproduction from the mid-1990s through 2003 closed most mines and plants outside of China. Since 2004, China has supplied 90 to 97 percent of the world’s REE, while in 2010 the United States produced none. In 2012, China still produced 97 percent of the world’s rare earths. Substitutes for many REE applications are available but they tend to be inferior. Alternative technologies and recycling of REE may help reduce market demand over the next few years. However, high-technology REE applications are diverse and expanding, driving increasing technological, economic, and strategic needs in the United States. Compounding supply problems, China drastically reduced its REE exports beginning in 2010, and hiked export taxes to a range of 15 to 25 percent. These actions resulted in a scramble for these resources in the rest of the world. In 2012, China continued to restrict the world supply of rare earths.
Slow economic conditions worldwide during 2012, combined with more efficient material usage, resulted in a decline in United States REE imports from 7,790 tons in 2011 to 5,700 tons in 2012. The economic slowdown also resulted in a decline in prices for most REE products, in the aftermath of significant price increases during 2011. The value of refined REE imported by the United States decreased from $802 million in 2011 to $615 million in 2012.
The largest known REE deposits occur in China, Australia, and North America, with much smaller reserves found in India, Brazil, Malaysia, and South Africa. Production has been dominated by China, with additional production from Australia, India, Malaysia, Russia, and Thailand. China's reserves are the largest. Estimates project that the country has the largest percentage worldwide of REE reserves at about 36 percent, compared to the United States at about 13 percent. The Commonwealth of Independent States (Azerbaijan, Armenia, Belarus, Georgia, Kazakhstan, Kyrgyzstan, Moldova, Russia, Tajikistan, Turkmenistan, Uzbekistan, and Ukraine) controls about 19 percent, followed by Australia with more than 5 percent and India with 3 percent.
China's state-owned mines kept rare earth prices artificially low during most of the past 15 years, which drove other suppliers out of business. The United States had the expertise but lacked the manufacturing infrastructure to refine rare earth oxides to metals. Rebuilding the U.S. REE supply chain has begun, but could take as long as 15 years to complete.
Current Production in the United States
The only current REE producer in the United States is the Molycorp mine, producing from a carbonatite at Mountain Pass, on the border of California and Nevada. Molycorp’s production has been from previously mined and stockpiled material. However, completion of their ongoing expansion and modernization project is expected to produce approximately 19,000 tonnes (21,000 tons) of REO equivalent per year, beginning in 2013. The company plans to increase production to 40,000 metric tonnes of REO per year when justified by demand, product pricing, capital availability, and financial returns.
REE minerals and deposits are often classified as either Light Rare Earth Elements (LREE) or Heavy Rare Earth Elements (HREE). However, since both types usually occur together, the designation is often a statement relating to the economic dominance of either the light or the heavy elements. LREE deposits are the most common and HREE are generally more valuable than LREE. Molycorp’s Mountain Pass deposit, for example, is dominated by LREE. These light rare earths also dominate the Bear Lodge deposit; however, increased HREE grades in the northern and western portion of the project area have been identified in recent exploration.
A 2010 study by the U.S. Department of Energy addressed the supply of critical minerals in the United States. The agency used the term critical as a measure of importance to the economy, availability of clean energy, and risk of supply disruption. Among other minerals and elements addressed, the agency considered five REE, (Dy, Nd, Tb, Eu, and Y) as the most critical in the short term future of the United States.
According to the U.S. Geological Survey, REE projects currently being investigated for exploration or development in the United States include the Bear Lodge deposit in Wyoming; Bokan, Alaska; La Paz, Arizona; Diamond Creek, Idaho; Lemhi Pass, Idaho and Montana; Pea Ridge, Missouri; Elk Creek, Nebraska; Thor, Nevada; and Round Top, Texas.