PEGMATITES OF THE MIDDLETOWN AREA, CONNECTICUT
The pegmatites of the Middletown area in Connecticut have been mined almost continuously for feldspar and muscovite mica since about 1865. Pegmatites in this and other areas have recently become the subject of renewed interest because they are the potential source of beryl. From 1948 to 1950 the Geological Survey studied and mapped the pegmatites in an area of about 58 square miles near Middletown. The primary objectives of the mapping were to determine beryllium resources of tbe Middletown area and to ascertain relations of beryl-bearing pegmatites to non-beryl-bearing pegmatites and to type of wall rock. Wore than 330 concordant and diacordant pegmatites were examined within the mapped area. The pegmatites cut the metasediments of the Bolton schist of pre-Mississippian(?) age and, in ascending order of sequence, mafic gneisses, the Glastonbury granite gneiss, Maromas granite gneiss, and Monson gneiss. The position of these formations in the stratigraphic column cannot be determined with accuracy; their maximum age is indicated by their relation to the pegmatites, which have been dated by uraniumand thorium-lead ratios as about 260 million years old, presumably Mississippian. The pegmatites are composed essentially of penthite, quartz. plagioclase, and muscovite. The common accessories are tourmaline, beryl, garnet, and biotite. The pegmatites have been divided into four groups based on the content of plagioclase feldspar: those with less than 40% of plagioclase, with and withuut beryl; and those with more than 40% of plagioclase, with and without beryl. About 42% of the pegmatites contain more tham 40% plagioclase, and 58% of them contain less than 40% of plagioclase. (auth)
- Research Organization:
- Originating Research Org. not identified
- NSA Number:
- NSA-13-004598
- OSTI ID:
- 4282577
- Journal Information:
- U.S. Geol. Survey Bull., Vol. Vol: 1042-Q; Other Information: 2 illus. Orig. Receipt Date: 31-DEC-59
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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