rare earth elements in Wyoming

distinct horizons (plus one unit within the underlying
Tipton Shale Member), and four uraniferous
phosphatic zones (UPZs) in the NE¼SW¼ sec.
10, T. 17 N., R. 106 W. (table 19). The UPZs in
the lower part of the Wilkins Peak tend to be more
enriched in uranium and phosphate (up to 0.15
percent uranium and 18.2 percent P 2 O 5 ) than
those higher in the member. Scarce, dark green to
black, REE-bearing carbonate minerals within the
Wilkins Peak Member include burbankite, mckelveyite,
and ewaldite (Milton and others, 1965;
Milton, 1971). Love (1964) noted the presence
of REE-bearing minerals in his UPZs 1, 2, and
57
2a (numbered from the bottom), as well as in a
trona bed. The lower UPZs commonly host greater
than 0.1 percent REE, but the enrichment is not
homogenous and significant lateral variation is
observed (King and Harris, 2002).
UPZs are not lithologically distinct from the surrounding
rocks and are best identified through the
use of radiation detecting equipment. A Geiger
counter was not available during sampling of the
I-80 on-ramp and Lulu claims (see below); therefore,
field identification at those sites was based
table 19. Measured section of the lower part of the Wilkins Peak Member of the Green River
Formation by Love (1964), Lulu claim #2, southwest of Rock Springs.
Bed Description
Thickness
(m) (ft)
14 Oil shale, dark-brown, laminated, hard; weathers white; UPZ 3 0.15 0.5
13 Shale, gray, soft, fissile 3.35 11.0
12 Gray, very hard, massive, medium-grained sandstone; weathers rusty
brown; out crops as ledge that breaks into angular blocks that are
conspicuous down slope; regionally identifiable, known as the Firehole
bed.
0.12 0.4
11 Shale, claystone, and siltstone, gray to greenish-gray, chippy;
moderately hard, but forms slope
4.88 16.0
10 Dolomitic marlstone, tan, slabby, hard, fissile; forms ledge 0.61 2.0
9 Claystone and silstone, green, blocky, slightly radioactive near top;
UPZ 2a occurs about 1 m below the top, but is not lithologically
distinct
2.74 9.0
8 Dolomitic marlstone, tan, hard, slabby, fissile; weathers gray; forms
ledge
1.52 5.0
7 Claystone and silstone, green, blocky; forms slope; UPZ 2 occurs
about 1 m below top, but is not litholigically distinct
3.35 11.0
6 Shale and marlstone, greenish-gray, hard, fissile; forms slope 1.52 5.0
5 Dolomitic marlstone, gray, hard, thin-bedded, fissile; weathers tan;
interbedded with gray, soft, fissile calcareous shale; forms slope
broken by thin ledges
9.14 30.0
4 Dolomitic marlstone, bluish-gray; weathers rusty brown at top; top 1.5
m forms widespread hard brown ledge that comprises most radioactive
part of UPZ 1
2.44 8.0
3 Shale, gray, marly, soft, fissile 0.91 3.0
2 Marly sandy siltstone, gray, hard slabby, fissile; weathers brown,
forms weak ledge; base of Wilkins Peak Member
1.83 6.0
1 Oil shale, dark brown, fissile, thin bedded; weathers gray; top of
Tipton Shale
4.3+ 14+