stones
the color may be fine and deep, but defects, such as cracks,
cloudiness, or silky inclusions, are prominent. Still other gems of
paler color but containing only very slight flaws, if any, are found.
The total yield of selected rough emeralds in 1912 is placed at 2,969
carats, with an estimated value of $12,875. This material should yield
about 800 carats of cut gems with a greatly increased value, probably
$25 a carat or more. Retail values for some of the better emeralds
range up to $200 a carat, and one fine stone weighing a fraction over 2
carats was sold for $200 at wholesale value.
Prospecting
and development of the deposit and separation of emeralds from the
matrix have been carried on under the direction of Lovat Fraser, of New
York. The deposit lies in a hill with moderate slope northwest and
north, and has been opened by numerous pits, crosscut trenches, and
open cuts within a distance of about 100 yards in an east and west
direction. The principal development is the cotton-boll pit at the
place of original discovery. In November, 1912, this consisted of an
open cut of irregular shape about 75 feet long in an east and west
direction and 10 to 25 feet deep with a shaft or pit several feet
deeper in the bottom. A tunnel 15 feet long was run in from the east
end o"f the cut and a crosscut trench 160 feet long extended north from
the bottom of the pit for prospecting, drainage, and to facilitate
mining. Other pits and trenches, both east and west, have been made
close to the cotton-boll pit. A track about 250 feet long with a mine
car is used in the big crosscut trench to carry vein material and waste
rock to their respective dumps near a branch north of the mine. Later
developments have been reported by Mr. Fraser, which consist of a deep
pit about 90 feet south Of east and a deep crosscut trench about 200
feet east of the cotton-boll pit.
The
general geology of the region and of the emerald deposit was discussed
in this report for 1911, but a brief summary is here given in order
that the notes on later developments may be more easily understood.
The region is composed of mica, garnet, kyanite, graphite, and
hornblende gneisses and schists cut by granite, pegmatite, diorite,
gabbro, hypersthenite, and other ferromagnesian rocks. The strike of
the rock formations is va'riable between east-west and north-south
where the strata are tilted, but over large areas they are essentially
flat, with many small rather gentle folds.
The
emeralds occur in pegmatite cutting hornblende hypersthenite. Olivine
gabbro is closely associated with the hypersthenite either as a
magmatic segregation from it or as a separate mass east of the
cotton-boll pit. Ferromagnesian rocks closely allied to the hornblende
hypersthenite occur at other localities in the region. The common
constituents of these rocks are pale-green hornblende, light-brownish
hypersthene, olivine, augite, biotite, pleonaste, magnetite, and a
little pyrite and pyrrhotite. By weathering, a rock resembling
chloritic soapstone is produced. Diorite, broken up by a later
intrusion of biotite granite, surrounds the hornblende hypersthenite
at the emerald mine. The granite also cuts the hypersthenite, and has
become more basic near the contact with it and with the diorite by a
partial absorption of those rocks. Pegmatite bodies cut the hornblende
hypersthenite in various directions, but the majority have an easterly
strike. Some of these have been found grading into 'pegma-titic granite
or coarse granite, and it is probable that the pegmatites are closely
associated with the granite masses near the emerald
