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2008 annual meeting – Spruce Pine Mining District: Little Switzerland, North Carolina
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A NOTE ON URANIUM MINERALS FROM THE
SPRUCE PINE AREA, NORTH CAROLINA
Richard Warner 1 , Stephen Poterala 2 and Chris Fleisher 3
1 Department of Environmental Engineering & Earth Sciences, Clemson University, Clemson, SC 29634-
0919
2 Department of Materials Science & Engineering, Pennsylvania State University, University Park,
PA 16802
3 Department of Geology, University of Georgia, Athens, GA 30602-2501
INTRODUCTION
Uranium minerals are often found in granitic pegmatites, where they nearly always occur
as minor constituents of insufficient quantity to be mined (Page, 1950). Their occurrence
in this geologic setting is a consequence of the fact that uranium behaves as an
incompatible element in magmatic systems. The size and charge of uranium ions make
their substitution for major ions in common silicate minerals difficult, with the result that
uranium is concentrated at the felsic (e.g., granitic) end of magmatic differentiation series
(Rogers and Adams, 1969; Krauskopf and Bird, 1995). Thus, the mean uranium content
of igneous rocks ranges from 0.8 ppm in mafic rocks to 4.0 ppm in granite (Rogers and
Adams, 1969; Plant and others, 1999). The separation of a water-rich fluid phase both
promotes the growth of exceptionally coarse crystals, characteristic of pegmatites, and
further concentrates uranium, such that some pegmatites eventually crystallize one or
more uranium-rich minerals.
The uranium minerals occurring in pegmatites include both primary (i.e., magmatic)
minerals and various secondary minerals. Chief among the primary uranium minerals is
the simple oxide, uraninite (UO 2 ). It typically is associated with muscovite-rich
pegmatites (Page, 1950). Also important are uranium-bearing multiple oxide minerals
(Frondel, 1958): these are principally niobate-tantalate minerals and often contain
significant amounts of the rare earth elements (REE). Samarskite is the most common
example, and may contain 10-20 weight percent UO 2 . Other primary uranium-bearing
minerals include the REE-phosphate, monazite, and silicate minerals such as zircon and
allanite. The latter minerals, though more abundant in pegmatites, generally contain
much less uranium (usually far below 1 weight percent UO 2 ). A wide variety of
secondary minerals, of variable water content, are derived from the partial or complete
alteration of uraninite and other primary uranium minerals. Gummite, uranophane,
autunite and torbernite are but a few of the many secondary minerals that can be formed
(Page, 1950; Frondel, 1958).
Pegmatites of the Spruce Pine mining district have long been known to host uraninite and
related uranium minerals and constitute one of the principal occurrences of such minerals
in the eastern United States (Ross and others, 1931). Allen (1877) reported chemical
analyses of samarskite and hatchettolite (a niobate-tantalate mineral belonging to the
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