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2008 annual meeting – Spruce Pine Mining District: Little Switzerland, North Carolina
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exploited Spruce Pine minerals. White mica from archaeological sites in the midwest is
attributed to the Spruce Pine deposits. Historically, mining activity was concentrated in
the pegmatitic rocks that are common in the Spruce Pine Mining District. The very coarse
grain size (cms to 10's of cms) of some feldspar and mica allowed for hand separation of
these phases. The need for mica during World War II focused attention on the micabearing
pegmatites in the United States. Hundreds of mica mines operated in the Spruce
Pine District during WWII (Lesure, 1968). The search for mica prompted an intensive
geologic mapping program in the Spruce Pine District by the U.S. Geological Survey
(USGS) aimed at increasing the production of mica for the war effort. Dick Jahns, a
pioneer in the modern studies of pegmatites, headed the USGS effort in the Spruce Pine
District for nearly two years. The author was fortunate to spend several days visiting
Spruce Pine pegmatites with Dick during this study (1978) and his guidance and
experience was invaluable. Development of flotation techniques for separation of
feldspars, mica and quartz in the 1940's resulted in a shift in mining from pegmatitic
granitoids to open pit mining of the coarse-grained granitic plutons, a practice that
continues today.
Quartz was initially a waste product at Spruce Pine. The high purity and coarse grain
size of quartz from Spruce Pine allowed for some specialized uses, such as production of
high-purity glass used for the 200 inch mirror for Mt. Palomar telescope (Olson, 1944),
but most of the quartz was not used. The white sand traps at the Augusta National Golf
Course in Georgia were filled with quartz sand from Spruce Pine. Ultra high purity
quartz from Spruce Pine is currently used in the production of silica glass used in the
processing of silicon chips for the electronics industry.
Spruce Pine Pegmatites
Granitic rocks of the Spruce Pine plutonic suite are typically coarse-grained. Pegmatitic
granitic rocks at Spruce Pine are very coarse-grained. Jahns (1955) applied the term
pegmatite to rocks that are “at least in part very coarse grained ... (with) extreme textural
variations, especially in grain size”. Using this definition, there are two types of
pegmatite bodies in the Spruce Pine District based on the nature of the pegmatite - host
rock contact. Dikes, lenses and sills of pegmatitic granitoid rock that have sharp contacts
with the metamorphic rock intrude parallel to the foliation of the host rock. Dikes vary in
width from 10's of cm to 10's of m. Individual dikes can be traced for 3 km along strike
(Olson, 1944). Irregular pegmatitic pods and dikes with gradational contacts to the host
granitic plutons represent the second type of Spruce Pine pegmatite. Dimensions
(diameter or thickness) vary from one to 100's of meters. Pegmatitic and coarse-grained
granitoid rocks have very similar chemical and mineralogic compositions suggesting a
genetic link (Olson, 1944).
Most of the Spruce Pine pegmatites are unzoned (Lesure, 1968). Those with zoning have
a fine-grained margin of quartz, plagioclase, and K-feldspar; an intermediate zone of
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