“The oldest rocks in the area consist mainly of para- schists of low to medium rank and restricted higher rank sillimanite schist. The entire series has been at least double folded. The most apparent are tight north to north- east trending folds. These have been intruded in the northern part of the area by a batholithic body of granitic composition, a granitic stock, a pegmatitic granite, a granitic sill-like body and different types of pegmatite dikes and sills. The youngest intrusions are a series of northeast trending basic dikes and sills. A major easterly trending transverse fault and a series of smaller faults of almost east-west trend are the main fault trends in the area. They are younger than all bodies above.
Pegmatites are very abundant and vary in size, shape, texture, and mineralogy. They are more numerous in the north than the south and invade all rock types except the younger basic intrusions.
A new classification of the size, shape, and texture of pegmatites is proposed. The size and shape of any individual pegmatite body is identified by two values, namely, the length X width (LXW) value and the length/width (L/W) ratio. Because of the extreme variation in texture of the pegmatite bodies a classification based on a geometric scale is proposed. Both mega- and microscopic sizes applicable to field and laboratory studies are included.
Five different mineralogioal types of pegmatites are recognized: magnetite granite, graphic granite, tourmaline granite, garnet granite, and biotite granite.
Both concordant and discordant types of pegmatites are present. A few of the concordant varieties show a rough zoned character, but layering is characteristic of the discordant and many of the concordant varieties. The layering may result from textural and/or compositional variations. Coarse and very coarse bands alternate with fine and very fine ones. Also distinct mineralogic variations are common in these different bands. Fine-grained red garnet-rich bands characterize a good percentage of the pegmatites in the area. These colored bands are of great help in determining the internal structure of such bodies.
The pegmatites are believed to be of magmatic origin. The temperature of the magmatic fluids, the content of volatiles, and the confining pressure as well as the chemical composition are thought to have varied greatly for the different pegmatite types of the area.
Beryl is the most important economic mineral known to date. The very coarse tourmaline granite pegmatites are the most important host for beryl. Coarse perthitic bands and massive quartz bands in the tourmaline garnet granite pegmatites and the garnet granite pegmatites offer some promise as hosts for beryllium minerals.
The district is now under active exploration”—Abstract, pages iii-iv.
Proctor, Paul Dean, 1918-1999
Brownlow, Arthur H.
Rupert, Gerald B., 1930-2016
Legsdin, Adolph, 1899-1969
Geosciences and Geological and Petroleum Engineering
M.S. in Geology
Missouri School of Mines and Metallurgy
x, 102 pages, 2 plates
Fremont County, Wyoming
© 1963 Hassan A. El-Etr, All rights reserved.
Thesis - Open Access
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Link to Catalog Record
Etr, Hassan A., "Pegmatites of the Anderson Ridge quadrangle, Fremont County, Wyoming" (1963). Masters Theses. 7626.