rare earth elements in Wyoming

Mud creek, nW¼nE¼ sec. 19, t. 44 n., r.
91 W., Washakie county
The black sands in the Mesaverde Formation just
north of Mud Creek were described by Houston
and Murphy (1962), with some details added by
King and Harris (2002). The titaniferous black
sandstone occurs in the uppermost part of the
basal sandstone of the Mesaverde and has a maximum
thickness of 2.3 m (7.5 ft) and an exposure
width of about 460 m (1,500 ft). Houston and
Murphy (1962) reported that the heavy mineral
suite contains 5 percent zircon. Another sample,
collected by Madsen (1978), contained 500 ppm
lanthanum.
Recent samples collected from the upper part of
the Mesaverde outcrop, about 0.5 km (0.3 mi)
northeast of the 1962 and 1978 samples, showed
no REE enrichment. These apparently were
stratigraphically higher in the formation than the
titaniferous black sandstone described by Houston
and Murphy (1962). Sample 20120731WS-G is
a dark brown, fine- to medium-grained, iron-rich,
discontinuous sandstone about 0.9 m (3 ft) thick.
Its dark color is mostly due to surface coatings.
This iron-rich sandstone is overlain by a thick,
white, cross-bedded sandstone near the top of the
Mesaverde Formation (Sample 20120731WS-F)
that also showed no REE enrichment.
dugout creek, nE¼sW¼ sec. 11, t. 44 n.,
r. 89 W., Eastern Washakie county
The titaniferous black sandstone in the Dugout
Creek deposit is in the upper part of the basal
Mesaverde Formation and is radioactive in some
outcrops. The black sandstone crops out across
several sections and its thickness varies from about
0.9 to 7.6 m (3 to 25 ft), but averages 3.0 to 4.6 m
(10 to 15 ft) (Houston and Murphy, 1962). This
is the most extensive exposure of Mesaverde black
sandstone in Wyoming.
Zircon makes up 5 percent of the total heavy
mineral content of the black sandstone here and
monazite accounts for 1 percent. Uranium content
reportedly varies from 0.001 to 0.021 percent eU,
depending on which earlier investigation is cited
(King and Harris, 2002). Madsen (1978) reported
one sample that contained 312 ppm lanthanum.
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A recent WSGS sample from this location (Sample
20120731WS-H) consists of fine- to mediumgrained,
dark-brown to purple and orange, crossbedded
sandstone about 0.9 m (3 ft) thick that
overlies a yellowish brown sandstone. The darkbrown
sandstone outcrop is about 0.40 km (0.25
mi) in length at this locality. A similar layer is
noted about 1.6 km (1 mi) to the north and appears
to be continuous for 0.4 to 0.8 km (0.25 to
0.5 mi). Several prospect pits are found near the
sample site. Sample 20120731WS-H is 12 percent
TiO 2 and slightly enriched in scandium, yttrium,
niobium, and all of the REE except dysprosium
and holmium. The LREE, ytterbium, and niobium
are enriched to greater than five times crustal
abundances.
Lovell, secs. 7 and 12, t. 55 n., r. 95 W.,
northwestern big Horn county
This slightly radioactive, titaniferous, black sandstone
deposit averages 0.9 m (3 ft) thick, with a
maximum thickness of 1.2 m (4 ft). The outcrop
extends along an 11˚ SW dipping hogback for 914
to 1,524 m (3,000 to 5,000 ft) (King and Harris,
2002). Houston and Murphy (1962) reported zircon
in the heavy mineral fraction, but no monazite.
A sample from this deposit by Garrand and others
(1982) showed 50 ppm lanthanum, greater than 20
ppm niobium, 40 ppm yttrium, 200 ppm zircon,
and 8 ppm cU 3 O 8 (20 ppm eU 3 O 8 ). Madsen
(1978) reported 316 ppm lanthanum in a sample
from this deposit.
A recent WSGS sample (20120801WS-A) from
the Lovell deposit represents a dark brown to
purple, thin-bedded, fine-grained sandstone up to
1.2 m (4 ft) thick. Analysis of this sample showed
more than 3 percent TiO 2 and weak enrichment in
the LREE, gadolinium, and niobium.
other Potential Paleoplacers
frontier formation
Frontier Formation, Spring Gap, SE¼NW¼ sec.
30, T. 16 N., R. 117 W., Uinta County
Madsen and Reinhart (1982) reported up to 1,000
ppm lanthanum, 80 ppm yttrium, less than 100