RARE EARTH ELEMENTS - HISTORY, POLICY, AND ORE DEPOSITS

Although the discovery of rare earth elements (REE) dates back more than two centuries their emergence as an essential component of many modern technologies, such as cell phones, flat screen TVs, electric vehicles, energy-efficient lighting, and wind power, is a relatively recent event. This long history is due in part to the similar chemical behavior of REE that makes them difficult to separate from each other and from their natural host ores and this in turn leads to their relatively high prices, up to thousands of dollars per kg. The United States once was largely self-sufficient in REE, but now obtains the majority of its REE from foreign sources, mostly from China. This is part of a larger trend; in 2012 the U.S. was 100 percent dependent on foreign suppliers for 18 mineral commodities and more than 50 percent dependent on foreign sources for 41 mineral commodities. This has led to concern about the possibility of supply disruptions of mineral commodities variously termed critical or strategic.

Recently, the White House Committee on Environment, Natural Resources, and Sustainability convened several working groups to guide development of a national critical minerals policy, focusing on identifying which minerals are critical for U.S. interests, what sources of information are available, and what long term research and development strategies can help the U.S. deal with future supply constraints. In the 112th Congress there were 9 bills introduced that addressed various aspects of REE, and several of these bills have been re-introduced in the 113th Congress.

For REE a useful exploration model starts with first principles of ionic charge and radius to track the enrichment of these elements through magmatic, hydrothermal, and supergene processes. Specific magmatic suites such as alkalic rocks and carbonatites, and alteration assemblages such as K feldspar and fenitization can be indicative of prospective geologic terranes for primary deposits. Secondary deposits form by either mechanical transport to form placers or chemical weathering to form residual deposits such as the ionic clay deposits of SE China that currently supply much of the world’s heavy REE.