ELEMENTAL COMPOSITION AND SPECTROSCOPIC ANALYSIS OF THE SPRUCE PINE PEGMATITE AT CRABTREE MINE, NORTH CAROLINA, WITH A FOCUS ON INCLUSIONS

Located in the Blue Ridge mountains of western North Carolina is the Spruce Pine mining district. Of 10 mining districts in the region, Spruce Pine is the most productive. The associated pegmatites in the area are derived from an extremely low iron leucogranite, dubbed “alaskite” for its snowy white appearance (due to an abundance of feldspar). As such, the Spruce Pine district has been the country’s principle source of feldspar for nearly 100 years. Despite the economic utility of these pegmatites, very few studies have investigated Spruce Pine geology.

Of particular interest in this study is the exposed pegmatite at Crabtree Emerald mine in Spruce Pine. Abundant coarse microcline, sodic plagioclase, and black tourmaline occur with accessory biotite, garnet, golden beryl, and emerald. A major portion of this study will be devoted to understanding the petrologic significance of quartz inclusions in both types of beryl and feldspar. The golden beryl forms rare crystals throughout the pegmatite, whereas the emeralds are located within the pegmatite but near the contact with the altered country rock. Near the contact with the pegmatite the country rock is altered to biotite ± tourmaline.

Important textures and mineral relationships identified in thin section under the petrographic microscope include perthitic microcline, coarse intergrowths of tourmaline and microcline, and quartz inclusions, which are common in crystals of emerald, golden beryl, and feldspar. These observations are verified under the scanning electron microscope, which is also paired with EDS technology to obtain elemental compositions and spectroscopic data.