RARE EARTH ELEMENTS - HISTORY, POLICY, AND ORE DEPOSITS
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.