7
Estimation of Combined Uranium and Thorium
Content with a Scintillation Counter
Using the method described in the methods section,
U+Th content can be estimated using a handheld scintilla-
tion counter. The “specific activity” of a subset of samples
(n=12) with known U and Th concentrations from three
deposits were correlated with their combined U and Th
content (Figure 10). The resulting plot shows a very strong
positive correlation (R2=0.9361), demonstrating that this
method may be reasonable for estimating the combined U
and Th content of unknown samples. Like the estimation
of Zr from Hf, the equation from the line of best fit is used
to extrapolate combined U and Th content from “specific
activity.” The method has a sensitivity of around 30 ppm
U+Th with the setup used here, though this could likely be
improved upon by shielding the scintillation counter with
lead to reduce the background radiation. The results from
this experiment are shown in Table 2 and estimate that
one sample contains over 2000 ppm U+Th. This method
was also tested to see if it could reasonably estimate the
total REE content of mineralized samples. Of the 12 sam-
ples investigated, this method overestimated two samples
(FLAT13 and SAN56) by over five times the lab-deter-
mined total REE content and underestimated one sample
(Hog17) by nearly 50%. While not as reliable as estima-
tions of U+Th, this method may still have merit, especially
if developed from samples from only one deposit, where
the proportions of heavy minerals may be more consistent.
PRELIMINARY CONCLUSIONS
New Mexico’s heavy mineral sandstone deposits are worth
reinvestigating for their critical mineral potential, as the
Figure 10. XY plot of “specific activity” versus combined U
and Th showing a very strong positive correlation
economics of these commodities may change in the future.
The use of handheld scintillation counters greatly aids in
determining the extent of mineralized sandstones, as well as
selecting high grade samples, due to the U and Th content
of monazite and zircon, minerals found in relative abun-
dance in these deposits. Whole-rock and trace element
geochemical data show expectedly high values of critical
minerals such as TiO2 (29.4%), total REE +Y (1.4%), Zr
(1%), and Hf (0.16%). C1 Chondrite-normalized dia-
grams show distinct light REE enrichment, slight heavy
REE enrichment, and prominent negative Eu anomalies.
Normalizing these samples to the Average Upper Crust
for Sedimentary Rocks standard shows slight heavy REE
enrichment and strong negative Eu anomalies. Hf can be
used to accurately estimate Zr content for samples that pass
the upper limit of detection of most trace element analysis
suites (10,000 ppm Zr). Combined U and Th content can
also be accurately estimated in mineralized sandstones by
using a handheld scintillation counter to determine “spe-
cific activity,” subtracting the background radiation value
from a sample’s radioactivity and dividing by its mass.
The estimation of total REE using “specific activity” is less
accurate, but might find use when working with samples
from a single deposit. Future work will involve sampling
other heavy mineral sandstone deposits in New Mexico and
investigating the mineral chemistry of monazite and zircon
in mineralized sandstones.
ACKNOWLEDGMENTS
This report is part of on-going studies of mineral resources
in New Mexico, supported by the New Mexico Bureau
of Geology and Mineral Resources (NMBGMR), Nelia
Dunbar, Director and State Geologist. Current research is
funded through a DOE grant, Carbon Ore, Rare Earth,
and Critical Minerals (CORE-CM) Assessment of San Juan
River-Raton Coal Basin, New Mexico, DE-FE0032051.
Any persons wishing to conduct geologic investigations on
the Navajo Nation must first apply for and receive a permit
from the Minerals Department, P.O. Box 1910, Window
Rock, Arizona 86515, phone (928) 871-6588. Thanks to
students of the NMBGMR Economic Geology group for
assisting with sample handling.
REFERENCES
[1] Dow, V.T., &Batty, J.V., 1961, Reconnaissance of
Titaniferous Sandstone Deposits of Utah, Wyoming,
New Mexico, and Colorado. US Department of the
Interior, Bureau of Mines.
Estimation of Combined Uranium and Thorium
Content with a Scintillation Counter
Using the method described in the methods section,
U+Th content can be estimated using a handheld scintilla-
tion counter. The “specific activity” of a subset of samples
(n=12) with known U and Th concentrations from three
deposits were correlated with their combined U and Th
content (Figure 10). The resulting plot shows a very strong
positive correlation (R2=0.9361), demonstrating that this
method may be reasonable for estimating the combined U
and Th content of unknown samples. Like the estimation
of Zr from Hf, the equation from the line of best fit is used
to extrapolate combined U and Th content from “specific
activity.” The method has a sensitivity of around 30 ppm
U+Th with the setup used here, though this could likely be
improved upon by shielding the scintillation counter with
lead to reduce the background radiation. The results from
this experiment are shown in Table 2 and estimate that
one sample contains over 2000 ppm U+Th. This method
was also tested to see if it could reasonably estimate the
total REE content of mineralized samples. Of the 12 sam-
ples investigated, this method overestimated two samples
(FLAT13 and SAN56) by over five times the lab-deter-
mined total REE content and underestimated one sample
(Hog17) by nearly 50%. While not as reliable as estima-
tions of U+Th, this method may still have merit, especially
if developed from samples from only one deposit, where
the proportions of heavy minerals may be more consistent.
PRELIMINARY CONCLUSIONS
New Mexico’s heavy mineral sandstone deposits are worth
reinvestigating for their critical mineral potential, as the
Figure 10. XY plot of “specific activity” versus combined U
and Th showing a very strong positive correlation
economics of these commodities may change in the future.
The use of handheld scintillation counters greatly aids in
determining the extent of mineralized sandstones, as well as
selecting high grade samples, due to the U and Th content
of monazite and zircon, minerals found in relative abun-
dance in these deposits. Whole-rock and trace element
geochemical data show expectedly high values of critical
minerals such as TiO2 (29.4%), total REE +Y (1.4%), Zr
(1%), and Hf (0.16%). C1 Chondrite-normalized dia-
grams show distinct light REE enrichment, slight heavy
REE enrichment, and prominent negative Eu anomalies.
Normalizing these samples to the Average Upper Crust
for Sedimentary Rocks standard shows slight heavy REE
enrichment and strong negative Eu anomalies. Hf can be
used to accurately estimate Zr content for samples that pass
the upper limit of detection of most trace element analysis
suites (10,000 ppm Zr). Combined U and Th content can
also be accurately estimated in mineralized sandstones by
using a handheld scintillation counter to determine “spe-
cific activity,” subtracting the background radiation value
from a sample’s radioactivity and dividing by its mass.
The estimation of total REE using “specific activity” is less
accurate, but might find use when working with samples
from a single deposit. Future work will involve sampling
other heavy mineral sandstone deposits in New Mexico and
investigating the mineral chemistry of monazite and zircon
in mineralized sandstones.
ACKNOWLEDGMENTS
This report is part of on-going studies of mineral resources
in New Mexico, supported by the New Mexico Bureau
of Geology and Mineral Resources (NMBGMR), Nelia
Dunbar, Director and State Geologist. Current research is
funded through a DOE grant, Carbon Ore, Rare Earth,
and Critical Minerals (CORE-CM) Assessment of San Juan
River-Raton Coal Basin, New Mexico, DE-FE0032051.
Any persons wishing to conduct geologic investigations on
the Navajo Nation must first apply for and receive a permit
from the Minerals Department, P.O. Box 1910, Window
Rock, Arizona 86515, phone (928) 871-6588. Thanks to
students of the NMBGMR Economic Geology group for
assisting with sample handling.
REFERENCES
[1] Dow, V.T., &Batty, J.V., 1961, Reconnaissance of
Titaniferous Sandstone Deposits of Utah, Wyoming,
New Mexico, and Colorado. US Department of the
Interior, Bureau of Mines.