Connecticut pegmatites

Region East, Northeast
Mineral systems
Deposit types
Critical minerals
Other minerals

Information leading to the delineation of this focus area

Basis for focus area Two polygons are included for the two areas of pegmatite. Cameron and others (1954) included the Anderson pegmatite as part of the Middletown district. Bradley and others (2016) locate Anderson (41.5934, -72.5401) and Branchville (41.268, -73.4393) (datum is not given in publication). Focus area may contain polymetallic vein deposits, such as the Roxbury Iron mine.
Identified resources Historical production of beryllium (beryl), feldspar, lithium (lepidolite), and mica.
Production Production values for sheet mica and feldspar at 5400 tons/yr after 1927 until the end of WWII for an individual site. Production estimate for beryl is 26 tons between 1942-1945 (Bannerman and others, 1968).
Status Past mining.
Estimated resources Unknown.
Geologic maps Eaton and Rosenfeld (1972), scale 1:24,000; Rodgers (1985), scale 1:125,000; Lundgren (1979), scale 1:24,000; London (1989), scale 1:12,000; Dale and Gregory (1911), scale 1:500,000.
Geophysical data Inadequate Rank 4 aeromagnetic and Rank 5 aeroradiometric coverage.
Favorable rocks and structures 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 (Stugard, 1958).
Deposits Mt. Tom beryl prospect (MRDS dep_id: 10067779), Hale-Walker beryl prospect and feldspar mine (MRDS dep_id: 10067600), Anderson mica mines and Swanson litha mine (MRDS dep_id: 10105453), Strickland-Cramer feldspar-mica quarries (MRDS dep_id: 10067599), Bordonaro beryl prospect (MRDS dep_id: 10067597), Hale pegmatite quarry (MRDS dep_id: 10067594), Sawmill beryl quarry (MRDS dep_id: 10240541), Gotta-Walden feldspar prospect quarry (MRDS dep_id: 10105450), Branchville mica mine (MRDS dep_id: 10068106).
Evidence from mineral occurrences MRDS; Bradley and others (2016); Connecticut Geological Survey files.
Geochemical evidence The pegmatites are composed essentially of perthite, quartz, plagioclase, and muscovite. The common accessories are tourmaline, beryl, garnet, and biotite (Stugard, 1958).
Geophysical evidence Unknown.
Evidence from other sources Unknown.
Comments In the Middletown district, the Anderson No. 1 mica mine (Swanson mine) was worked for lithia from lepidolite during WWI, but none was sold. The Anderson No. 1 mine is one of the Anderson-Bailey group of mica mines (Stugard, 1958). The shape of the focus area includes the Mt. Tom beryl prospect and the Sawmill Beryl Quarry. There also are a number of MINDAT sites in this focus area. About 70 pegmatite quarries and prospects are recorded for the Middletown district in Connecticut State Survey files. The Middletown and southwest Connecticut areas are geographically defined and surround documented beryl-producing pegmatite operations. Focus area has been enlarged eastward and northward to surround 13 beryl quarries, most notably Branchville, Roebling, Woodbury, Bridgeport, and East Village.
Cover thickness and description Exposed at the surface.
Authors Nora K. Foley, Dwight C. Bradley, Anjana K. Shah, Gregory J. Walsh, Bernard E. Hubbard, Margaret A. Thomas.
New data needs Geologic mapping, geophysics.
Geologic mapping and modeling needs Mapping of pegmatites. Bethel quadrangle (Branchville) is unpublished at 1:24,000 scale. Middle Haddam quadrangle (Anderson) has a published preliminary map at 1:24,000 scale.
Geophysical survey and modeling needs High resolution aeromagnetic and aeroradiometric data can assist with framework geology such as structural features and contacts.
Digital elevation data needs Lidar complete.