approximately
to the schistosity of the gneiss. By pinching and swelling the deposit
cuts the schistosity of the inclosing rock in one place and is
conformable with it in another. In the two connected open cuts the
pegmatite is over 20 feet wide, but pinches down to 6 feet at the
surface in the passage between the two cuts and widens to 10 feet at a
depth of about 10 feet below the surface. Where the pegmatite pinches
down in this passage it cuts across the bedding of the gneiss in part,
and in part the gneiss bends around the bulging shape.
The
texture of the "vein" rock is variable, but chiefly rather coarse. The
quartz occurs in large segregations of coarse smoky to gray grains. In
places it occurs in translucent to nearly clear masses several inches
across. Two varieties of feldspar were observed, gray orthoclase or
microcline crystals 2 feet thick and smaller masses of albite 3 to 4
inches across. Black tourmaline crystals are plentiful, some with good
crystal form. Biotite is present in quantity, and some of it is
intergrown with the muscovite. The muscovite is of good quality,
splitting well and having a fine clear rum color. Crystals were seen
around the workings which would yield perfect plates 2| by 3 inches and
2 by 4 inches. Beryl occurs rather plentifully, the greater part being
opaque, but some is clear with fairly good colors. It is not possible
to judge what quantity and quality of beryl were obtained when the mine
was in operation, but the following material was found on the dumps and
in the pegmatite: Well-formed opaque to translucent pale
yellowish-green and bluish-green crystals as much as 2 inches thick, a
few crystals with transparent portions showing the same colors that
would cut into small gems. The character of this material would
indicate that much larger clear beryl may be expected.
Another
prospect for gem beryl and mica was opened by the Columbian Gem Mining
Co., on one of the summits oi the northern part of Springfield
Mountain, about half a mile northeast of the Franklin Playter mine, 1\ miles
S. 40° W. of Grafton. Over 200 feet of open-cut and trench work with a
shaft and considerable stripping of vein outcrop have been made on the
summit of the mountain at an elevation of 1,750 feet above sea level.
The open cuts range from 10 to 25 feet wide and 5 to 15 feet deep. The
shaft is filled with water. No work has been done for a few years, but
at the time of examination (October, 1914), four buildings, in good
repair, a quantity of material suitable for punch and scrap mica, and a
few rough beryl crystals had been left at the mine.
The
country rock is quartz-mica gneiss in which the mica consists of both
biotite and muscovite. The gneiss is strongly banded and has been much
folded and crumpled so that definite strikes and dip could not be
measured. It has been cut by pegmatite and associated granite in
several directions, some of the pegmatites showing s.teep to nearly
vertical walls and others apparently lying nearly flat or with low
dips. The relations seem to be those of the nearly vertical dikes
acting as feed channels for the flatter beds. The granite associated
with the pegmatite is chiefly fine-grained biotite granite and merges
into the pegmatite. The texture of the pegmatite is variable, ranging
from a granite-like rock to masses in which there are orthoclase
crystals a foot thick, quartz segregations 3 feet across,
