2
New Mexico. Previous reports compared the concentration
of REE and critical minerals in coal (whole-rock basis) to
adjacent sedimentary rocks within the San Juan and Raton
Basins. This report examines the concentration of REE and
other critical minerals in the ashed coal remaining after the
coal sample is burned. Measuring REE and critical minerals
in the ash-basis approximates the REE in the fly or bottom
ash remaining after coal is burned at a power plant, where
REE and critical minerals could be leached from the coal
ash.
GEOLOGY
The San Juan Basin is a predominant Laramide (Upper
Cretaceous–Early Tertiary age) structural basin in northern
New Mexico and southern Colorado (Figure 1) that host
and produced important energy and mineral resources,
including coal, uranium, petroleum, and gas (Figure 2, 3).
Stratigraphic units in the San Juan Basin dips inward from
the highlands towards the center of the basin, creating a
trough-like feature. San Juan Basin has three major coal-
bearing units: Crevasse Canyon, Menefee, and Fruitland
formations in 26 coal fields (Table 1).
Coal is mined in New Mexico and fuels electrical gen-
erating plants in New Mexico and Arizona. Coal mining
on a significant scale began in New Mexico in 1862, when
U.S. Army troops from Fort Craig opened the Government
mine in the Carthage field (Socorro County) to supply coal
for smithing at Forts Seldon, Bayard, and Stanton. Coal
mining continued to expand in the 1880s throughout New
Mexico supplying the railroads with fuel. Three surface
mines remain in operation today El Segundo, Lee Ranch
and Navajo. New Mexico is 12th in coal production in U.S.
in 2020, with production at approximately 10,249,000
short tons. However, production is decreasing because of
mine closures due to closure of coal-fired electrical generat-
ing plants. New Mexico is 15th in estimated recoverable
coal reserves in U.S. (65 million short tons of recoverable
reserves at mines and 6,719 million short tons estimated
recoverable reserves in the basin).
Coal is a sedimentary rock that is composed of more
than 50% by weight of organic material and is formed by
the compaction of decaying plant material deposited in
ancient peat swamps or mires. Coal is readily combustible
and is burned for fuel. Several factors beside the thickness
and quality of the coal determine whether a coal deposit
is economic: 1) geologic characteristics, 2) the technology
available for extraction, 3) distance to a market, and 4)
available transportation network. Throughout the history
of mining coal in New Mexico, these factors have changed.
Coal also contains minerals that are noncombustible and
do not burn. These minerals could contain REE and other
critical minerals that could be recovered from coal mining
or from the coal ash remaining after the coal is burned for
electricity. In the future, the concentration of critical min-
erals, including REE could be a factor in producing coal
deposits.
METHODS
Sample collection
Different sampling strategies were employed based upon
the purpose of each sampling task (McLemore and Owen,
2024). Several types of samples were collected: composite,
Figure 1. Structural features of the San Juan Basin and
adjacent areas. Chaco Slope is the area south of the Central
Basin, starting approximately at the subaerial exposure of
the Pictured Cliffs Sandstone (from Hoffman, 2017)
New Mexico. Previous reports compared the concentration
of REE and critical minerals in coal (whole-rock basis) to
adjacent sedimentary rocks within the San Juan and Raton
Basins. This report examines the concentration of REE and
other critical minerals in the ashed coal remaining after the
coal sample is burned. Measuring REE and critical minerals
in the ash-basis approximates the REE in the fly or bottom
ash remaining after coal is burned at a power plant, where
REE and critical minerals could be leached from the coal
ash.
GEOLOGY
The San Juan Basin is a predominant Laramide (Upper
Cretaceous–Early Tertiary age) structural basin in northern
New Mexico and southern Colorado (Figure 1) that host
and produced important energy and mineral resources,
including coal, uranium, petroleum, and gas (Figure 2, 3).
Stratigraphic units in the San Juan Basin dips inward from
the highlands towards the center of the basin, creating a
trough-like feature. San Juan Basin has three major coal-
bearing units: Crevasse Canyon, Menefee, and Fruitland
formations in 26 coal fields (Table 1).
Coal is mined in New Mexico and fuels electrical gen-
erating plants in New Mexico and Arizona. Coal mining
on a significant scale began in New Mexico in 1862, when
U.S. Army troops from Fort Craig opened the Government
mine in the Carthage field (Socorro County) to supply coal
for smithing at Forts Seldon, Bayard, and Stanton. Coal
mining continued to expand in the 1880s throughout New
Mexico supplying the railroads with fuel. Three surface
mines remain in operation today El Segundo, Lee Ranch
and Navajo. New Mexico is 12th in coal production in U.S.
in 2020, with production at approximately 10,249,000
short tons. However, production is decreasing because of
mine closures due to closure of coal-fired electrical generat-
ing plants. New Mexico is 15th in estimated recoverable
coal reserves in U.S. (65 million short tons of recoverable
reserves at mines and 6,719 million short tons estimated
recoverable reserves in the basin).
Coal is a sedimentary rock that is composed of more
than 50% by weight of organic material and is formed by
the compaction of decaying plant material deposited in
ancient peat swamps or mires. Coal is readily combustible
and is burned for fuel. Several factors beside the thickness
and quality of the coal determine whether a coal deposit
is economic: 1) geologic characteristics, 2) the technology
available for extraction, 3) distance to a market, and 4)
available transportation network. Throughout the history
of mining coal in New Mexico, these factors have changed.
Coal also contains minerals that are noncombustible and
do not burn. These minerals could contain REE and other
critical minerals that could be recovered from coal mining
or from the coal ash remaining after the coal is burned for
electricity. In the future, the concentration of critical min-
erals, including REE could be a factor in producing coal
deposits.
METHODS
Sample collection
Different sampling strategies were employed based upon
the purpose of each sampling task (McLemore and Owen,
2024). Several types of samples were collected: composite,
Figure 1. Structural features of the San Juan Basin and
adjacent areas. Chaco Slope is the area south of the Central
Basin, starting approximately at the subaerial exposure of
the Pictured Cliffs Sandstone (from Hoffman, 2017)