Mineralogy of the peraluminous Spruce Pine plutonic suite, Mitchell, Avery, and Yancey Counties, North Carolina
Veal, William Brian
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The Spruce Pine plutonic suite consists of numerous Devonian (390-410 ma) peraluminous granitic plutons, dikes, sills, and associated pegmatites. The mineralogy of pegmatites and host granodiorites from seven locations was studied to determine the extent of fractionation of the pegmatites relative to the granodiorite. Garnets in the plutons are almandinespessartine and some display epitaxial overgrowths of grossular garnet. Similar garnets are found in the pegmatites. Pegmatitic muscovite contains several percent iron and is compositionally similar to muscovite from the host granodiorite. Feldspars in the granodiorites and pegmatites are compositionally similar (plagioclase Ab69-98; k-feldspar Or95-98). The lack of compositional variation between minerals in pegmatites and host granodiorites indicates the pegmatites were not the result of extreme fractionation and indicates that pegmatite mineralogy can be used to characterize the mineralogy of an entire granodiorite body.