rare earth elements in Wyoming

entirely on descriptions of field relations provided
by Love (1964).
I-80 On-ramp Area, Exit 91, East of Green
River, NW¼SE¼ sec. 23, T. 18 N., R. 107 W.,
Sweetwater County
Mudstone and limestone of the Wilkins Peak
Member crops out at this location between the
on-ramp and east-bound driving lane of I-80. The
units exposed here match the descriptions of horizons
6 through 10 on Lulu claim #2 (Love, 1964),
which include UPZ 2 and UPZ 2a. UPZ 2 is
hosted within a green, blocky, calcareous mudstone
(Sample 20120928JC-A) about 1 m (3 ft) below
the base of the overlying tan to gray, thin-bedded
to laminated marlstone. UPZ 2a is hosted within a
green, blocky, calcareous siltstone and shale (Sample
20120928JC-B), about 1 m (3 ft) below the
overlying tan, slabby, dolomitc marlstone. Neither
of these samples is significantly enriched in REE or
other elements of economic interest.
Lulu claims, NE¼SW¼ sec. 10, T. 17 N., R.
106 W., Southern Sweetwater County
In this area, the uppermost Tipton Shale Member
and lower Wilkins Peak Member of the Green
River Formation are exposed. The Tipton Shale is
composed of a brown to gray, well-indurated oil
shale. The lower 3 m (10 ft) of the Wilkins Peak
Member consists of marly, sandy siltstone, and
marly shale (horizons 2 and 3 of Love, 1964). UPZ
1 is hosted in the upper 2 m (6 ft) of horizon 4,
which includes a lower gray to red, irregularly bedded,
blocky, slope forming, dolomitic marlstone
with a white powdery fracture coating mineral
(Sample 20120928JC-E). Horizon 4 also includes
an upper gray to brown, interlayered sandy siltstone
and marlstone (Sample 20120928JC-C).
A blocky, green mudstone to siltstone (Sample
20120928JC-D) that may contain UPZ 2 or 2a
crops out about 15 m (50 ft) above horizon 4; this
layer is similar to the two rock units of samples
20120928JC-A and 20120928JC-B. REE enrichment
is not present in any of these samples, but
all three are enriched in lithium, five to 6.5 times
crustal abundance.
South Firehole Canyon, NW¼SE¼, sec. 20, T.
16 N., R. 106 W., Southern Sweetwater County
At South Firehole Canyon (fig. 22), Love (1964)
reported the presence of UPZs 1, 2, 2a, 3, 3a, and
possibly 4, with up to 0.016 percent eU, 0.009
percent uranium and 10.56 percent P 2 O 5 in UPZ
2a. The Wilkins Peak Member here is similar to
the section described by Love (1964) at Lulu claim
#2, except that beds 2 through 6 (Love, 1964) are
replaced by about 12 m (39 ft) of resistant ridgeforming,
gray to tan, platy to fissile, dolomitic
siltstone, with thin interbeds of non-resistant
mudstone and shale. This unit exhibits lateral variations
in color, including bright red and rusty areas.
Background radioactivity at the site was 56 cpm.
About 3 m (10 ft) above the base of the Wilkins
Peak Member is a radioactivity anomaly up to 2.5
times the background (140 cpm). The anomaly
is within gray to tan (weathered), thin-bedded
(about 1 cm or 0.4 in) to fissile, limonite-bearing
dolomitic siltstone (Sample 20121129JC-A); the
stratigraphic position of the anomaly is equivalent
to bed 4 (table 19, Love, 1964, Measured Section),
which contains UPZ 1. Bedding at the sample site
strikes 295˚ and dips 4˚ SW.
A radioactivity anomaly up to 2.3 times background
(130 cpm) occurs within bed 7 (table 19),
about 15 m (50 ft) above the base of the Wilkins
Peak Member. Bed 7 consists of green, slope forming
interbedded mudstone and shale. The radioactivity
anomaly is associated with UPZ 2, which is
hosted in a layer of green, weakly calcareous shale
(Sample 20121129JC-B), about 0.5 m (20 in)
below the base of bed 8, which is composed of gray
to tan, fissile, dolomitic siltstone.
Uraniferous phosphatic zone 2a, hosted in bed 9
(table 19), is associated with a radioactivity anomaly
up to 10.6 times background (590 cpm) about
19 m (62 ft) above the base of the Wilkins Peak
Member. Bed 9 consists of green, slope forming,
interbedded mudstone and shale; UPZ 2a occurs
within green, blocky, noncalcareous mudstone
(Sample 20121129JC-C), about 0.5 m (20 in)
below the base of the gray to tan fissile calcareous
siltstone of bed 10 (fig. 23).
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