Charles Davis Mine, Groton, Grafton County, New Hampshire, USAi

Regional Level Types
Charles Davis Mine	Mine
Groton	Town
Grafton County	County
New Hampshire	State
USA	Country

The Charles Davis mica mine (pl. 1, no. 24) is in the town of Groton 0. 7 mile N. 73 ° W. of the village of North Groton. To reach it from North Groton follow the North Groton-Cheever road northwest 0.6 mile to a mine access road on the left; follow the access road southwest 0.2 mile to the mine. The property is owned by Paul Glover of Bath, N. H. Mineral rights are leased by the Strafford Mining Co., Bristol, N.H.

An opencut 100 feet long, 12 to 18 feet wide, and 15 feet deep was made prior to 1920. Work by the Strafford Mining Co. began in December 1943 and continued until July 1944. The present opencut is about 150 feet long, 10 to 30 feet wide, and 40 feet deep near the southwest end. The northeastern half of the cut apparently contains considerable backfill. Open-pit mining methods were used and waste rock was removed by a bucket on an aerial tramway. About 1,350 tons of rock was removed from the cut between December 1943 and July 1944. The mine was mapped by Glenn W. Stewart and Norman K. Flint in June 1943 (fig. 62) and periodic visits were made to it by E. N. Cameron and Stewart.

The pegmatite is exposed for about 300 feet along strike. At the southwest end it narrows to 4 inches, but in the main part of the pit it averages 14½ feet thick. It appears to be a lens essentially parallel to the foliation of the wall rock. Minor rolls along the east edge suggest that the pegmatite plunges 40°-50°.

The wall rock, part of the Littleton formation, is a quartz-sillimanite schist that strikes N. 35° E. and has a dip ranging from vertical to steeply east. Sillimanite crystals 1 inch long and a ¼ inch thick are abundant in it. In some places along the contact the schist contains many small tourmaline crystals but generally a very fine-grained dense band of recrystallized schist, 3 to 4 inches thick, occurs at the contact.

The pegmatite has a well-defined border zone and a core. The border zone, 3 to 8 inches thick, is composed of fine-grained quartz, muscovite, and minor plagioclase, tourmaline, and garnet. The core is composed of plagioclase, quartz, perthite, muscovite, minor biotite, secondary chlorite, and accessory tourmaline, beryl, and pyrite. Small anhedral crystals of lazulite are scattered in the core. Several quartz bodies, 2 by 7 feet or less, also occur in the core.

Sterrett reported that mica was most abundant near the hanging wall and E. N. Cameron, on his first visit, noted a similar occurrence. However, the mica along the hanging wall was soon mined out and most of the mica recovered in 1944 occurred as disseminated books. The pegmatite adjacent to a small roll near the bottom of the pit, on the southeast wall, had a slightly higher mica content than the central parts of the pegmatite. Mica was also slightly more. abundant near the margins of the quartz bodies.

The muscovite has a medium rum color, is ruled, stained, relatively hard, and flat. Most of the books average 4 by 4 inches but a few are 10 by 12 inches. Some are intergrown with biotite. The muscovite contains numerous inclusions of magnetite(?) or pyrite(?) and small tourmaline crystals.

Satisfactory quantities of mine-run mica were recovered during 1934-44, but because of structural defects the mica yielded only small sheet. The mine is still capable of producing considerable quantities of small-sized sheet mica.