Rare earth elements (REE) have been mined in North America
since 1885, when placer monazite was produced in the southeast USA. Since the 1960s, however,
most North American REE have come from a carbonatite deposit at Mountain Pass, California, and
most of the world's REE came from this source between 1965 and 1995. After 1998, Mountain Pass
REE sales declined substantially due to competition from China and to environmental constraints.
REE are presently not mined at Mountain Pass, and shipments were made from stockpiles in recent
years. Chevron Mining, however, restarted extraction of selected REE at Mountain Pass in 2007. In
1987, Mountain Pass reserves were calculated at 29 Mt of ore with 8.9% rare earth oxide based on
a 5% cut-off grade. Current reserves are in excess of 20 Mt at similar grade. The ore mineral is
bastnasite, and the ore has high light REE/heavy REE (LREE/HREE). The carbonatite is a moderately
dipping, tabular 1.4-Ga intrusive body associated with ultrapotassic alkaline plutons of similar
age. The chemistry and ultrapotassic alkaline association of the Mountain Pass deposit suggest a
different source than that of most other carbonatites. Elsewhere in the western USA, carbonatites
have been proposed as possible REE sources. Large but low-grade LREE resources are in carbonatite
in Colorado and Wyoming. Carbonatite complexes in Canada contain only minor REE resources. Other
types of hard-rock REE deposits in the USA include small iron-REE deposits in Missouri and New
York, and vein deposits in Idaho. Phosphorite and fluorite deposits in the USA also contain minor
REE resources. The most recently discovered REE deposit in North America is the Hoidas Lake vein
deposit, Saskatchewan, a small but incompletely evaluated resource. Neogene North American placer
monazite resources, both marine and continental, are small or in environmentally sensitive areas,
and thus unlikely to be mined. Paleoplacer deposits also contain minor resources. Possible future
uranium mining of Precambrian conglomerates in the Elliott Lake-Blind River district, Canada,
could yield by-product HREE and Y. REE deposits occur in peralkaline syenitic and granitic rocks
in several places in North America. These deposits are typically enriched in HREE, Y, and Zr.
Some also have associated Be, Nb, and Ta. The largest such deposits are at Thor Lake and Strange
Lake in Canada. A eudialyte syenite deposit at Pajarito Mountain in New Mexico is also probably
large, but of lower grade. Similar deposits occur at Kipawa Lake and Lackner Lake in Canada.
Future uses of some REE commodities are expected to increase, and growth is likely for REE in new
technologies. World reserves, however, are probably sufficient to meet international demand for
most REE commodities well into the 21st century. Recent experience shows that Chinese producers
are capable of large amounts of REE production, keeping prices low. Most refined REE prices are
now at approximately 50% of the 1980s price levels, but there has been recent upward price
movement for some REE compounds following Chinese restriction of exports. Because of its grade,
size, and relatively simple metallurgy, the Mountain Pass deposit remains North America's best
source of LREE. The future of REE production at Mountain Pass is mostly dependent on REE price
levels and on domestic REE marketing potential. The development of new REE deposits in North
America is unlikely in the near future. Undeveloped deposits with the most potential are probably
large, low-grade deposits in peralkaline igneous rocks. Competition with estabished Chinese HREE
and Y sources and a developing Australian deposit will be a factor.