Mica deposits of the Blue Ridge in North Carolina

Lesure, F.G.

doi:10.3133/pp577

Cited by 8 publications

(5 citation statements)

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“…Tappen and Smith 2003) or even extreme fractionation in the case of one pegmatite that contains spodumene, pollucite, amazonite, and fluorite (Wise and Brown 2009). However, well over 95 percent of the pegmatites are simple garnet-muscovite pegmatites, lacking in more exotic minerals (Lesure 1968). The lack of evidence for fractionation begs the question, why are pegmatitic rocks so abundant in the Spruce Pine granitoids?…”

Section: Mineral Compositionsmentioning

confidence: 99%

“…Most of the Spruce Pine granitic rocks show some evidence of post-magmatic recrystallization related to deformation (Lesure 1968). Feldspar and mica grains have bent and broken twin and cleavage planes.…”

Section: Spruce Pine Granitoid Rocksmentioning

confidence: 99%

“…Garnet ages are by Sm-Nd, hornblende ages are by Rb-Sr and Ar-Ar, muscovite dates are by Ar-Ar. Ages of the Spruce Pine pegmatites are shown over the top of the histogram and include U-Pb ages on uraninite (Aldrich et al 1958) and zircon (Johnson et al 2001), Rb-Sr wholerock isochrons on pegmatites (Kish 1983(Kish , 1989, and K-Ar dates on muscovite as compiled by Lesure (1968). Below the histogram is the model for deformation (F 1 , F 2 , F 3 ) and metamorphism (M 1 , M 2 , M 3 ) in the Spruce Pine area as proposed by Butler (1973).…”

Section: Geological Backgroundmentioning

confidence: 99%

“…Very fine-grained muscovite formed in the finegrained mortar texture between larger grains of feldspar and quartz. Grains of epidote, garnet, and biotite occur as flattened inclusions within the sheets of coarse-grained muscovite books (Lesure 1968 celadonitic component (5-6 weight percent Fe and c. one percent Mg; Tab. 3).…”

Section: Muscovitementioning

confidence: 99%

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Mineralogy and petrogenesis of pegmatites in the Spruce Pine District, North Carolina, USA

Swanson¹,

Veal²

2012

J. Geosci.

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Granitic rocks (mainly granodiorites) of the Spruce Pine Plutonic Suite occur as small plutons and numerous pegmatite bodies intruded into amphibolite-grade schists and gneisses of the Ashe Formation. Intrusion ages range from 377 to 404 Ma and are near the peak of amphibolite-facies metamorphism in the country rocks. The granodiorites have a mortar texture with coarse (~ 1 cm) grains of feldspar, quartz and muscovite enclosed in a finer grained matrix of the same phases. Large (10-30 cm) crystals of perthitic K-feldspar and plagioclase occur in the granodiorite. Pegmatites occur within the granodiorite and as isolated intrusions within the country rocks. Contacts between pegmatites and host granodiorites range from sharp, cross-cutting to completely gradational. Some of the plutons contain up to 50 % pegmatite. Pegmatite mineralogy is similar to the granodiorites; major amounts of feldspars and quartz, accessory amounts of muscovite, garnet, and epidote. Secondary minerals, formed by subsolidus recrystallization, include epidote, muscovite, quartz, and grossular garnet. A few of the pegmatites are more fractionated and contain tourmaline and beryl. Compositions of feldspars, muscovite, and garnet show some regional variation, but are generally similar for pegmatites and associated granodiorite. About half of the pegmatites are unzoned. Zoning in the pegmatites is simple with a quartz core, an intermediate zone of graphic granite, plagioclase and muscovite and an outer finer grained zone that locally shows mineral layering parallel to the contact. The abundance of pegmatitic textures relative to granitoid textures in the Spruce Pine Plutonic Suite is related to the depth of crystallization. Spruce Pine granitoids crystallized at depths of 20-30 km (0.7 to 1.1 GPa ) based on feldspar thermobarometry and experimentally determined melting relations. Skeletal crystals of quartz and feldspar along with plumose muscovite clusters are common in the Spruce Pine pegmatites. Water content of magmas at such high pressures can be high. The subtle transition from granitic to pegmatitic texture so common at Spruce Pine (and in other deep-seated systems) was probably related to the development of zones of water-enriched magma and delayed nucleation in the hydrous melts. Deformation (evidenced by mortar texture) of the Spruce Pine Plutonic Suite was related to later regional deformation.

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Section: Mineral Compositionsmentioning

confidence: 99%

Section: Spruce Pine Granitoid Rocksmentioning

confidence: 99%

Section: Geological Backgroundmentioning

confidence: 99%

Section: Muscovitementioning

confidence: 99%

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Mineralogy and petrogenesis of pegmatites in the Spruce Pine District, North Carolina, USA

Swanson¹,

Veal²

2012

J. Geosci.

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“…5b). Considering the major-element components, the most Zn enriched gahnite from the two studied localities has compositions similar to a low-Zn population of gahnite from the highly evolved LCT Alto Mirador pegmatite in the Borborema Pegmatite Province (Soares 2004;Soares et al 2007), the LCT Jemaa pegmatite in Nigeria (Batchelor and Kinnaird 1984), the Burleson Mica mine in the muscovite-rare-element class Spruce Pine District, North Carolina (Lesure 1968;Spry and Scott 1986b), pegmatites from China (Li et al 1999), and LCT pegmatites from the Separation Rapids area, Ontario (Morris et al 1997;Dunlop 2000), and they likely reflect a similar intermediate degree of evolution of their parent melts (Fig. 5b).…”

Section: Comparison With Pegmatite Gahnite Worldwide and Relative Degmentioning

confidence: 97%

Melt evolution in felsic dikes inferred from the composition of gahnite in two new occurrences, Pala Chief and Elizabeth R composite dikes, California

2016

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We report the occurrence and composition of gahnite ([Zn,Fe,Mg,Mn]Al 2 O 4 ) in aplites of the Pala Chief and Elizabeth R layered pegmatite-aplite dikes, Pala District, California, and the significance for felsic melt evolution. The aplite is characterized by alternating bands of white, finegrained plagioclase + quartz + muscovite +/− black tourmaline and thin laminations defined by concentrations of reddishbrown garnet (Bline rock^). Accessory gahnite occurs as extremely fine-grained (50-250 μm) green to bluish-green crystals. Gahnite compositions in both occurrences are similar and defined by end-member ranges Ghn 83.5-90.9 Hc 8.7-15 Spl 0-1.4 . Zinc contents in gahnite are high (36.7-39.5 wt.% ZnO for Pala Chief, 37.2-40.2 wt.% ZnO for Elizabeth R), the MgO and MnO contents are negligible (< 0.7 wt.%), and Fe is the main substitution present (< 6.9 wt.% FeO). Gahnite is chemically zoned and characterized by higher Zn (< 2 wt.% ZnO) and lower Fe, Mg, and Mn contents in rims compared to cores, which shows the substitution mechanism, and reflects fast growth during melt evolution via fractional crystallization followed by fast cooling. Compositional variations are greater within individual crystals than among crystals and between laminations, which indicate a homogeneous melt at the aplite scale. Compared with the composition of gahnite from pegmatites worldwide, the studied gahnite reflects a moderate degree of melt evolution. This study confirms the incompatible character of Zn in evolving pegmatite-aplite melts and shows the usefulness of gahnite as a petrogenetic indicator. Because gahnite is a resistant mineral, surficial findings of gahnite with very low Mg contents and Zn contents similar or higher than those measured here may indicate a source of granitic pegmatite-aplite.

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Muscovite, Phlogopite and Vermiculite Deposits

Shmakin¹

1982

The Development Potential of Precambrian Mineral Deposits

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Mica deposits of the Blue Ridge in North Carolina

Abstract: Kyanite-rich gneiss and schist are abundant in certain linear belts 3-8 miles wide and 20-40 miles long.

Cited by 8 publications

References 18 publications

Mineralogy and petrogenesis of pegmatites in the Spruce Pine District, North Carolina, USA

Mineralogy and petrogenesis of pegmatites in the Spruce Pine District, North Carolina, USA

Melt evolution in felsic dikes inferred from the composition of gahnite in two new occurrences, Pala Chief and Elizabeth R composite dikes, California

Muscovite, Phlogopite and Vermiculite Deposits

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