Anderson No. 1 Mica Mine, East Hampton, Middlesex County, Connecticut, USAi

Regional Level Types
Anderson No. 1 Mica Mine	Mine
East Hampton	Town
Middlesex County	County
Connecticut	State
USA	Country

The “mine” is a small cut somewhat filled in with soil and leaves; around it are piled heaps of white quartz and lepidolite. Lepidolite forms more than half of all the material removed from the pit, and large blocks of the pure mineral occur. It varies somewhat in texture and appearance. Some masses are composed of bright small scales of a beautiful deep purple-pink color, intergrown with fine platy cleavelandite stained yellow brown by iron, the contrast in colors yielding very showy specimens. Other coarser scaly masses are pale lavender to gray in color and much of the material shows small spheres up to the size of a pea composed of folia of grayish lepidolite embedded in white cleavelandite.

The only other abundant mineral in the pegmatite is quartz which is crystalline milky white, and resembles common vein quartz. Potash feldspar is entirely absent. Cleavelandite albite occurs in masses of white plates and these contain bunches and masses up to several inches across of a flesh red to brownish red material resembling massive garnet, which upon analysis proves to be triplite. The triplite will be more fully described in another paper. In places the triplite has oxidized to a black manganese oxide, which stains the cleavelandite. Occasional crystals of muscovite, which occur in the cleavelandite, are penetrated by flat opaque crystals of green tourmaline.

The Paul Anderson farm on the east side of the Hurd Park Road a mile south of Hurd Park and 5 miles south of the village of Cobalt is on the side of a ridge several hundred feet high. At the top of the ridge a metamorphic pegmatite 50 or 60 feet wide and 300 feet long follows the strike of the ridge and the gray mica schist, about north and at the south end stands 15 or 20 feet above the general contour.

Some quarrying was done near the north end of the pegmatite a good many years ago. At this point the pegmatite is largely quartz in which are buried mixed masses of a beautiful purple lepidolite and cleavelandite, some of which follow distinct cracks in the quartz and are 10 to 12 inches in diameter. Much of the lepidolite is in globular radial aggregates ranging from less than 1/4 inch to 3/4 inch in diameter. Possibly 4 or 5 tons of lepidolite more or less mixed with cleavelandite and quartz have been thrown in a pile. All came from an excavation about 20 feet long 6 to 10 feet wide and 4 to 6 feet deep.
A visual estimate from the spectrographic pattern of the lepidolite gave K2O, 5.0; Na2O, 1.0; Li2O, 5.0; Rb2O, 3.0; Cs2O, 1.0; and for a piece of microcline the estimate was K2O, 5-10.0; Na2O, 5.0; Li2O, not determinable; Rb2O, 2.0; Cs2O, 0.1.

Some green and blue black tourmalines are distributed through the pegmatite, and a little triplite edged round by lepidolite and blue tourmaline was found. From surface indications alone this appears to be next to Black Mountain, Maine, the largest lepidolite deposit seen in New England; but even so, remembering the erratic nature of pegmatitic deposits, no prediction as to further quantities can be made.

Considerable work has been done for mica between the lepidolite bearing portion and the east wall of the pegmatite. An excavation 30 by 50 feet and more than 20 feet deep (the bottom was covered with water when visited in April, 1942) has been dug but only one small chunk of lepidolite could be seen in the walls and none was found in the dump.

A number of large pegmatites outcrop to the north and east on the top of the ridge, but no lithium minerals were seen in them.

The Anderson No. 1 mica mine, formerly known as the Swanson lithia mine, lies in the town of East Hampton, 0.4 mile N. 35° W. of Haddam Neck village. It is one of the Anderson-Bailey group of mica mines...

The pegmatite was first prospected before 1920 (Shannon, 1920, p. 82-84). From June to December 1941, and from May 1943 to March 1944, the Connecticut Mica & Mining Co., Portland, Conn., operated the mine. When the mine was abandoned the workings consisted of a vertical pit 52 feet deep and 10 to 15 feet wide. Two drifts, 50 and 30 feet long, were driven northward and eastward, respectively, from the bottom of the pit. When operations ceased, the northern drift was about 10 feet longer than shown on the accompanying map (fig. 126)...

The pegmatite is a very irregular body about 30 feet thick and at least 90 feet long. It seems to strike northward and to have a moderate eastward dip. Apparently its south end is in the workings. In part the pegmatite is concordant with the foliation of the eastward-dipping wall rock (medium-grained hornblende gneiss of the Bolton schist), in part it is sharply discordant.

The pegmatite consists of the following units:

1. Border zone, quartz-[albite] plagioclase pegmatite 4 to 8 inches thick. Consists of fine-grained quartz and [albite] plagioclase with accessory black tourmaline, biotite [annite], and muscovite. The zone is cut by numerous fractures that are perpendicular to the contacts. The fractures are coated with films of pyrite.

2. Wall zone, quartz-[albite] plagioclase-muscovite pegmatite, 1 to 6 feet thick. Consists of coarse quartz, blocky [albite] plagioclase, muscovite and accessory tourmaline and garnet. The muscovite books are 2 to 18 inches broad and ¼ to 4 inches thick.

3. Intermediate zone, quartz-cleavelandite pegmatite, 5 to 25 feet thick. Consists of coarse quartz (in masses 6 feet in diameter), cleavelandite, muscovite and scattered large anhedral crystals of [microcline] perthite. Mica books 3 inches in average diameter occur in places adjacent to the quartz masses. Black and green tourmaline and green beryl (rare) are accessory minerals.

4. Quartz pegmatite, as much as 10 feet thick, consisting of coarse milky to smoky quartz. Occurs typically as a hood-shaped body adjacent to the lepidolite-cleavelandite unit and, at most places, above it. It also forms pods enclosed in the intermediate zone.

5. Lepidolite-cleavelandite unit, 5 to 10 feet thick. Fine- to medium-grained lepidolite (pink to violet to gray) with subordinate cleavelandite, quartz, and accessory dark green apatite and green tourmaline. The principal lepidolite-cleavelandite body seems to be an elongate ellipsoid at least 35 feet long whose long axis pitches S. 60° E. at an angle of about 30°. It is exposed only in the southern portion of the pegmatite but apparently a similar body was mined in the pit northwest of the vertical pit. Either this unit or the quartz unit may be the true core of the pegmatite.

The wall zone is thickest along the hanging wall in the northern drift. The content of sheet in the mica is low, and the books seem to be poorest in quality in the thickest parts of the zone. Cross fracturing, ruling, reeving, and limonite-staining are the most common defects. Shearing, probably of small displacement, has occurred along the hanging wall in the northern drift, and mica there is badly fractured.

Some blocks of virtually pure lepidolite have been obtained from the pegmatite, but most is probably too heavily intergrown with cleavelandite and quartz to be of value. It is estimated that 15 to 20 tons are in sight in the workings and that 40 tons are stockpiled on the surface.

The pegmatite seems to end southward in the workings and it may not persist for more than 100 feet north of the northern drift, so probably total reserves of mica are not large. Experience has shown that only a small percentage of sheet can be recovered from the crude mica, because of the structural defects of the books and the limonite-staining.