Rare Earth Elements: A Review of Production, Processing ...

Rare Earth Elements Review Section 3 – Life-Cycle Stages of Rare Earth Elements Mines
Placer Mining
Placer deposits are accumulations of mineral or metal-bearing alluvial sediments that have accumulated in
depressions or stream beds. Placer mines are not considered hardrock mining because the REE ore is
recovered from unconsolidated alluvial or colluvial deposits; however, these mines are often grouped with
hardrock mines for regulatory purposes because the REE host minerals can present the same processing
challenges as those mined directly from a rock ore body.
Placer mining includes the classic image of a gold miner using a pan or a sluice box. Larger and more
modern operations may excavate an open-pit or tunnel into ancient riverbed sediments. Excavation might
be achieved using water pressure (hydraulic mining), excavation or tunneling equipment, or dredging
equipment that is used to mine ore-bearing sediments from stream beds or depressions. Native gold
deposits, uranium, thorium, zirconium, and mineral ores for REMs are examples of placer ore deposits
that occur in the United States. More REE mineral ores have been discovered associated with placer
deposits in the United States than any other deposit type (see Table 3-1 and Appendix B). The Vero
Beach mine in Florida and the Old Hickory mine in Virginia are examples of placer mines that had
produced REEs as a by-product of zirconium mining in the past. The Old Hickory mine continues to
operate, but currently is not producing REE-containing minerals (ILUKA Resources, Ltd, 2007). Placer
deposits containing monazite REE-mineral ores are typically associated with higher concentrations of
minerals containing radioactive elements, which has deterred production from these deposits in the United
States.
Prospective Mine Types by State
A general summary indicating the number of potential rare earth mining sites (i.e., potential resources)
that have been documented in the United States is summarized in Table 3-1. Data were summarized from
the table in Appendix B, which was compiled from a combination of sources, but is principally from
information available from the U.S. Geological Survey. The table is presented not to suggest that every
known deposit will be exploited, or that there is potential viability for the rare earth resources that occur
at these locations. It is provided simply to assist stakeholders in these states gain an awareness of the level
of known occurrences of REE resources. Other deposits and mine sites likely exist or are being explored
that were not identified or included in Appendix B; however, the following table gives a general idea of
types of mines that might be found or developed in each state. It should be noted that this information is
very general; no aspects of the mine sites have been verified, and the current condition of the mines listed
is largely unknown. Actual data were available for some existing mines, but the mine type for a few of the
mines listed was inferred from the deposit types or information found on the Internet; approximate counts
are shown in parentheses.
In large part, the table illustrates that the majority of discovered REE deposits, documented in the
information sources found, would be mined as placer deposits or from aboveground open pit mine types.
Neither the Molycorp or Pea Ridge mines, previously discussed, that are being developed and are near
production stage are the more common placer deposit (i.e., dredge type mining) operations, but rather the
Molycorp mine is an aboveground mine and the Pea Ridge mine is an underground mine. As previously
discussed, the feasibility and viability of a deposit depend on a number of complex variables.
3-17