1
25-058
Minimum Concentrations of Critical Minerals for Exploration—
How Good Is Good Enough?
Richard E. Otoo
New Mexico Institute of Mining and Technology,
Socorro, NM
Virginia T. McLemore
New Mexico Bureau of Geology and Mineral
Resources, Socorro, NM
Evan J. Owen
New Mexico Bureau of Geology and Mineral
Resources, Socorro, NM
ABSTRACT
Disruption in critical minerals supply chains has resulted
in the evaluation of various types of mineral deposits for
critical minerals potential. Much of the study on critical
minerals focuses on occurrence and characterization, but
little research has addressed what concentrations of criti-
cal minerals in a mineral deposit are required to make an
exploration target into an operating mine. Understanding
the cut-off grades of ore deposits being actively mined is
one criterion to determine if concentrations in an explo-
ration target are high enough. Cut-off grade is defined as
the minimum amount of mineral contained in a ton of ore
that is sent to the processing plant. Among many factors,
cut-off grade depends upon the size and type of the deposit
and mining operation, the processing technique, and mar-
ket prices. This research does not aim to define cut-offs for
determining if a mineral deposit is economic. Rather, it
defines estimates of concentrations of critical minerals that
could be considered good enough for further exploration.
For example, ~2% total rare earth oxide (TREO) is the cut-
off grade for Mt. Pass carbonatite, but 500 ppm TREO
could be an exploration target for coals.
INTRODUCTION
According to United States Geological Survey (USGS), a
critical mineral is one that is essential to the economic well-
being of a nation and whose supply may be disrupted due
to geological, geopolitical, or environmental factors (Nassar
et al., 2020). For example, rare earth elements (REEs) are
critical to the production of electrical vehicles (EV) motors
as well as wind turbines, yet the global share of China rose
to over 95% in 2010 (IEA, 2021), since when its pro-
duction quota has fallen to nearly 70% in 2023 (Statista,
2023). This and similar situations with many of the critical
minerals raise deep global concerns about supply chain vul-
nerabilities (Bauer et al., 2011).
Critical minerals find uses in the production of renew-
able energy, electronics, agricultural products, and com-
mon household items (McLemore, 2020). As consumption
and demand for critical minerals keep rising, efficient
exploration strategies for assessing the viability of mineral
deposits are necessary to ensure sustainable supply. One key
approach is the application of cut-off grade as a fundamen-
tal concept in mineral exploration projects. Cut-off grade
refers to the minimum concentration of minerals required
to justify further exploration efforts based on factors such
as, type and size mineral deposit, mining and processing
technologies, associated by-products/co-products and the
market price of these minerals.
Typically, economic cut-off grades are used to deter-
mine whether a mineral deposit can be mined profitably.
However, this paper focuses on preliminary cut-off grades
needed to establish whether critical minerals within a
deposit are high enough to justify further exploration and
detailed evaluations. By comparing mineral deposit grades,
size, production and extraction technology, and other eco-
nomic factors with established and active mines, explora-
tion teams can estimate cut-off grades that justify further
exploration.
CRUSTAL ABUNDANCE
Crustal abundance refers to the average concentration of an
element within the Earth’s crust. Concentrations of com-
mon elements may be expressed in percent, while trace ele-
ments are usually expressed in parts per million (ppm) or
even parts per billion (ppb). In mineral exploration, crustal
abundance values serve as way to compare how enriched
or depleted a particular element is within the Earth’s crust.
25-058
Minimum Concentrations of Critical Minerals for Exploration—
How Good Is Good Enough?
Richard E. Otoo
New Mexico Institute of Mining and Technology,
Socorro, NM
Virginia T. McLemore
New Mexico Bureau of Geology and Mineral
Resources, Socorro, NM
Evan J. Owen
New Mexico Bureau of Geology and Mineral
Resources, Socorro, NM
ABSTRACT
Disruption in critical minerals supply chains has resulted
in the evaluation of various types of mineral deposits for
critical minerals potential. Much of the study on critical
minerals focuses on occurrence and characterization, but
little research has addressed what concentrations of criti-
cal minerals in a mineral deposit are required to make an
exploration target into an operating mine. Understanding
the cut-off grades of ore deposits being actively mined is
one criterion to determine if concentrations in an explo-
ration target are high enough. Cut-off grade is defined as
the minimum amount of mineral contained in a ton of ore
that is sent to the processing plant. Among many factors,
cut-off grade depends upon the size and type of the deposit
and mining operation, the processing technique, and mar-
ket prices. This research does not aim to define cut-offs for
determining if a mineral deposit is economic. Rather, it
defines estimates of concentrations of critical minerals that
could be considered good enough for further exploration.
For example, ~2% total rare earth oxide (TREO) is the cut-
off grade for Mt. Pass carbonatite, but 500 ppm TREO
could be an exploration target for coals.
INTRODUCTION
According to United States Geological Survey (USGS), a
critical mineral is one that is essential to the economic well-
being of a nation and whose supply may be disrupted due
to geological, geopolitical, or environmental factors (Nassar
et al., 2020). For example, rare earth elements (REEs) are
critical to the production of electrical vehicles (EV) motors
as well as wind turbines, yet the global share of China rose
to over 95% in 2010 (IEA, 2021), since when its pro-
duction quota has fallen to nearly 70% in 2023 (Statista,
2023). This and similar situations with many of the critical
minerals raise deep global concerns about supply chain vul-
nerabilities (Bauer et al., 2011).
Critical minerals find uses in the production of renew-
able energy, electronics, agricultural products, and com-
mon household items (McLemore, 2020). As consumption
and demand for critical minerals keep rising, efficient
exploration strategies for assessing the viability of mineral
deposits are necessary to ensure sustainable supply. One key
approach is the application of cut-off grade as a fundamen-
tal concept in mineral exploration projects. Cut-off grade
refers to the minimum concentration of minerals required
to justify further exploration efforts based on factors such
as, type and size mineral deposit, mining and processing
technologies, associated by-products/co-products and the
market price of these minerals.
Typically, economic cut-off grades are used to deter-
mine whether a mineral deposit can be mined profitably.
However, this paper focuses on preliminary cut-off grades
needed to establish whether critical minerals within a
deposit are high enough to justify further exploration and
detailed evaluations. By comparing mineral deposit grades,
size, production and extraction technology, and other eco-
nomic factors with established and active mines, explora-
tion teams can estimate cut-off grades that justify further
exploration.
CRUSTAL ABUNDANCE
Crustal abundance refers to the average concentration of an
element within the Earth’s crust. Concentrations of com-
mon elements may be expressed in percent, while trace ele-
ments are usually expressed in parts per million (ppm) or
even parts per billion (ppb). In mineral exploration, crustal
abundance values serve as way to compare how enriched
or depleted a particular element is within the Earth’s crust.