rare earth elements in Wyoming

samples 20110824WS-C and 20110824WS-D
were high in uranium. Some of the other samples
showed slightly elevated LREE values, but they did
not exceed five times average crustal abundances.
WSGS sampling demonstrated the presence of
significant REE concentrations, particularly the
LREE, associated with thorium-bearing monazite
investigated by the USBM/AEC in 1952.
Sample 20110824WS-A is an iron-stained and partially
white-banded, cross-bedded, coarse-grained,
arkosic sandstone and conglomerate representative
of the bottom of the Flathead in what appears to
be a paleochannel cut between low outcrops of Precambrian
granite and a mafic dike. Only thorium
within this sample was slightly elevated.
Sample 20110824WS-C is a poorly cemented,
limonitic layer in the basal Flathead Sandstone,
collected an unknown distance above the contact
with Precambrian crystalline rocks. The sample was
collected just below a coarse conglomeratic layer
exposed in the west side of an old north-trending
exploration trench about 6 m (20 ft) deep. LREE
values were significant in this sample and HREE
and yttrium values were also elevated.
Sample 20110824WS-D was collected near the east
side of the same trench as Sample 20110824WS-
C and about 18 m (60 ft) further south. It is a
coarse, limonitic, quartz pebble conglomerate
(fig. 14) representative of the layer above sample
20110824WS-C. It showed the greatest concentration
of REE and thorium of any sample taken
in the area. HREE and yttrium values were also
elevated in this sample.
Sample 20110824WS-E is a purple, iron-rich
sandstone and conglomerate collected about 6
m (20 ft) higher in the Flathead than sample
20110824WS-D, and at the west end of an easttrending
trench, west of the trench from which
samples 20110824WS-C and 20110824WS-D
were collected. This sample hosted elevated LREE
values, but none exceeded five times average crustal
values. Thorium, however, was notably higher at
more than 15 times average crustal values.
45
Sample, BM11211-A, taken from the middle part
of the Flathead on the lower southwestern slope of
Bald Mountain showed no anomalous REE, but
had slightly elevated thorium values.
Sample 20110824WS-F was collected from the east
end of an old exploration trench, about 43 m long
by 8 m wide by 4 m deep (140 x 25 x 12 ft). The
basal Flathead exposed in this trench is a heavily
iron-stained, partly limonitic, coarse sandstone to
conglomerate with some very angular clasts. Common,
non-magnetic, rounded black pebbles, up
to 1.27 cm (0.5 in) diameter, found here crushed
easily to a limonite-brown powder, which x-ray
diffraction showed to be goethite [Fe 3 (OH)]. The
raw sample contained 2,309 ppm REE, more than
10 times background crustal values. This would
be an estimated TREO of about 0.27 percent. The
sample was particularly enriched in La, Ce, Pr, Nd,
and Sm. Although not as high, values for Eu, Gd,
Tb, Dy, and Ho are elevated as well. The sample
also contained more than 65 times average crustal
abundance of thorium.
Sample 20110824WS-G was collected from
excavated material near the center of a 70 m long
by 1.2 m wide by 1.2 m deep (230 ft x 4 ft x 4 ft)
trench. The sample comprised iron-stained and
limonitic sandstone and conglomerate from the
lower part of the Flathead. It contained nine times
average crustal abundance of thorium, but did not
show REE significantly above background crustal
values (table 14, p. 41).
Sample 20110824WS-B is from a Precambrian
mafic dike in brecciated and rehealed contact with
the surrounding granitic rocks. The dike protrudes
through part of the lower Flathead. The sample
showed slightly elevated LREE values in the dike,
which may have contributed to the later Cambrian
paleoplacers.
Quaternary alluvial placers in drainages flowing
away from the Bald Mountain area are reported
to host higher gold values than those found in the
Flathead (Hausel, 1989), probably due to further
concentration of the paleoplacers. These placers
are also reported to host monazite (Wilson, 1951;