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

Rare Earth Elements Review Section 3 – Life-Cycle Stages of Rare Earth Elements Mines
3. Life-Cycle Stages of Rare Earth Mineral Mines
The increasing importance of REMs for the manufacture of modern devices upon which society has become
reliant, along with uncertain supplies (see Section 2), is encouraging exploration and development of new mining
sites. While REMs are an important resource needed to sustain our modern technologies, the waste footprint and
environmental impact from REM mining operations is expected to be as significant as current mining practices for
metals and minerals. The requirements, regulations, and financial obligations and assurances for a new mine are
usually complex and take years of planning. The economic feasibility of discovered deposits must be proved, and
environmental effects to the local communities and habitat also must be evaluated to determine feasibility. The
process of exploration, development, and construction typically required before mining can begin may exceed 10
years. Except for a few locations, known rare earth deposits in the United States are generally considered small
to medium reserves. This section presents a discussion of the typical process steps used in developing a new
rare earth deposit and the associated mining wastes that typically would result. It is not expected that the mining
stages of a rare earth mine would be different than other hardrock or metal mining operations. Except for the
radioactivity of uranium and thorium, the potential REM waste emissions would be generally comparable to a
typical hardrock mine.
Mining operations produce a variety of solid materials that have the potential to cause environmental
contamination and require long-term remedial actions and operation and maintenance. The largest mines
may generate more than a billion tons of solid wastes that may cover areas exceeding a thousand acres,
and smaller operations still must handle and dispose of
quantities of materials that can affect large areas (U.S.
EPA, 2003). Most deposits of REE ores in the United
States would be expected to require mining operations
that likely would produce far less quantities of solid
wastes than the largest operating mines. An example
of an existing REE mine in the United States that
would be considered a large mining operation, is the
Molycorp Minerals rare earth mine in Mountain Pass,
California (see sidebar). It would be expected that rare
earth mineral mining operations developed in the
United States would be similar to other large hardrock
and placer mines that recover minerals containing
primary metals (e.g., gold, silver, copper, zinc, lead).
As examples, the mass of selected types of individual
REE-containing ore deposits occurring in the United
States is estimated by the USGS to be the following:
� 0.2 million tons (approximate average) for
thorium-rare earth vein deposits
(Armbrustmacher et al., 1995)
� 3.5 to 450 million tons for low titanium iron
oxide deposits containing REE, with a median
quantity of 40 million tons (Foose, 1995)
� 6.6 to 331 million tons for minable carbonatite
ore deposits (Modreski et al., 1995).
These rough quantity estimates are based on known
deposits, as characterized in geochemical deposit
models prepared by the USGS; other deposit models
may also exist other than those found and reviewed
and that provide additional estimates. Averages for the
3-1
The Scale of an Existing REE Mine
in the United States
The largest rare earth minerals mine in the
United States is Molycorp Mineral’s Mountain
Pass rare earth mine and site, which occupies
2,222 acres of land in San Bernardino County,
California. The mine started operation in 1952,
operating as an open pit lanthanide mining,
beneficiation, and processing facility. The period
of greatest ore production was from 1965 to 1995.
Mining activities ceased in 2002, but minor milling
activity continued to process stockpiled ore; and
full-scale ore production may resume in 2012.
When mining activities ceased, the open pit was
1,500-feet wide by 400-feet deep. Overburden
materials were held on site, and numerous
process water, tailings, and product storage ponds
were also operated.
Remaining REE reserves (relative to a 5
percent cutoff grade) at the Mountain Pass mine
are estimated to exceed 20 million tons. The
average REE content in the bastnasite mineral ore
is approximately 9 percent. The remaining gangue
minerals (calcite, barite, and dolomite) in the
carbonatite igneous rock body make up
approximately 91 percent of the ore-containing
rock. The expected overburden produced is
estimated to be 104 million tons, which will be
stored at two existing storage piles. These storage
piles will together cover approximately 315 acres
within 30 years of the proposed period of
operation through 2042 and represent
approximately a 120 percent change over current
stockpiles accumulated between 1950 and 2002.
California Regional Water Quality Control
Board, Lahontan Region (2010)