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2008 annual meeting – Spruce Pine Mining District: Little Switzerland, North Carolina
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similarity between the Maw Bridge pegmatite and the Spruce Pine pegmatites. The
pyrochlore-group mineral at Maw Bridge is more Ti-rich, hence analyses plot in the
betafite field rather than the microlite or pyrochlore fields (Figure 6). Concentrations of
uranium in the niobate-tantalate minerals are roughly comparable at the two sites, the
largest difference being that betafite from the Maw Bridge pegmatite has notably higher
uranium than uranoan pyrochlore from McKinney mine (Table 5).
CONCLUSIONS
The results of our study indicate that pegmatites in the Spruce Pine district contain, in
order of decreasing uranium content, the following uranium minerals: uraninite, clarkeite,
fourmarierite, uranophane, samarskite-(Y) and uranoan microlite, plumbopyrochlore, and
fergusonite. Clarkeite, uranophane and fourmarierite are alteration products of primary
uraninite, whereas samarskite-(Y), uranoan microlite, plumbopyrochlore and fergusonite
are primary niobate-tantalate minerals. The chemical signature of the uranium minerals
analyzed in this study reinforces the affiliation of the Spruce Pine district pegmatites with
the NYF (niobium, yttrium plus REEs, and fluorine) family of granitic pegmatites
(Černý, 1991; Ercit, 2004). That is, the niobate-tantalate minerals taken as a whole are
characterized by Nb > Ta and high Y+REE, while appreciable amounts of F are present
in Ca-rich uraninite. Under the recent pegmatite classification scheme of Černý and Ercit
(2005), the Spruce Pine pegmatites belong to the muscovite – rare-element (MSREL)
class, specifically, subclass MSREL-REE. Muscovite, of course, is one of the two
principal economic minerals of the Spruce Pine district. Other minerals typical of this
subclass are fergusonite, samarskite, and monazite, while the minor elements Be, Y,
REE, Ti, U, Th, and Nb-Ta characterize its geochemical signature (Černý and Ercit,
2005). The metamorphic environment typical for this subclass is moderate to high P,
amphibolite facies, consonant with the Paleozoic metamorphism experienced by the Blue
Ridge of western North Carolina (Adams and Trupe, 1997).
ACKNOWLEDGEMENTS
We express our gratitude to Ruth Sponsler of Burnsville, North Carolina, for showing us
around various mine localities in the Spruce Pine district and for her contagious
enthusiasm for finding and collecting radioactive minerals. We also thank Dr. Donald
Van Derveer of Clemson University for obtaining X-ray diffraction patterns on two
uraninite samples.
REFERENCES CITED
Adams, M.G. and Trupe, C.H., 1997, Conditions and timing of metamorphism in the Blue Ridge thrust
complex, northwestern North Carolina and eastern Tennessee: in Stewart, K.G., Adams, M.G., and Trupe,
C.H., eds., Paleozoic structure, metamorphism, and tectonics of the Blue Ridge of western North Carolina:
Carolina Geological Society Annual Field Trip Guidebook, p. 33-47.
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