rare earth elements in Wyoming

lbs) for 1957 and 450 kg (1,000 lbs) for 1958
(King and Harris, 2002).
The euxenite was reported by Houston (1961) to
be metamict to the extent that it gave no x-ray diffraction
pattern. His x-ray fluorescence studies of
the euxenite showed, in order of decreasing abundance,
the presence of Nb, Y, Fe, Ta, U, and Zr.
These were accompanied by minor amounts of Pb,
Mn, Zn, Er, Eu, Ac, Ho, Ti, Th, Sm, and Rn. King
and Harris (2002) suggested that the euxenite crystals,
reported to be up to 7.6 cm (3 in) long, might
have been misidentified and were probably samarskite
or niobium-rich, yttrium-bearing tantalite.
X-ray fluorescence of monazite from the Platt mine
showed, in order of abundance, Ce, Nd, Y, Th, and
La. These were accompanied by minor amounts of
Pr, Sm, and Gd. Although phosphorus is a major
constituent of monazite, its presence could not
figure 9. Samples of the Big Creek – Platt pegmatites. A, Sample
20120917JC-A. B, Sample 20120917BW-A.
31
be shown by the type of analysis used (Houston,
1961).
A 1980 DOE report (Adams and others, 1980)
described both euxenite and allanite in several
samples from the Platt pegmatite. Sample analyses
in that report did not show any lanthanum,
or yttrium concentrations higher than average
crustal values. Scandium exceeded five times its
average crustal value at 200 ppm. No other REE
were evaluated in samples from the Platt pegmatite
(Adams and others, 1980).
The Platt Mine pegmatite dike trends approximately
50˚. A sample collected for this investigation
(Sample 20120917JC-A) is composed of muscovite
granite pegmatite dominated by quartz, microcline,
and perthite, with moderate plagioclase,
and hematite with limonite staining. It contains
minor garnet, dendritic pyrolusite, epidote alteration,
and a glassy black mineral, possibly euxenite
or columbite-tantalite (fig. 9a). The
dike intrudes granitic gneiss (Sutherland
and Hausel, 2005) with minor
biotite; banding in the gneiss trends
342˚, and dips 59˚ E. Analysis
of sample 20120917JC-A shows
enrichment in lutetium and ytterbium
greater than five time crustal
abundances; HREE are slightly
enriched above crustal abundances.
The sample is also enriched in niobium
and tantalum. The analyzed
values in this sample are a minimum
estimate for concentrations in this
pegmatite dike because the relatively
high silica content of the sample
suggests dilution by excess quartz.
When the analysis is normalized to
the global average silica content of
granite, 72.04 percent, (Blatt and
Tracy, 1996) Er, Lu, Tm, Yb and Y
are enriched above five times crustal
abundance, as are niobium and tantalum
(table 8). The high niobium
and tantalum concentrations suggest
that euxenite or columbite-tantalite
may be present within the pegmatite.