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Fax: 704-721-4657 Website: www.reedmine.com Email: [email protected]
9621 Reed Mine Road Midland, NC 28107 Phone: 704-721-4653
Drilling and Blasting
Reed Gold Mine State Historic Site
Blasting had been developed by the Chinese prior to
1,000 A.D. Yet, the first instance of blasting in rock
excavation occurred in 1627. Kasper Wiendl placed
blasting powder in cracks within a rock and detonated
it using slow match, a loosely spun cord with salt pe-
ter.
By 1683, a rock drill was developed in Saxony. The
drill consisted of a steel rod with a star-shaped bit at
one end. This drill was held against the rock face and
turned after each blow with a sledgehammer. This
form of drilling is termed “double jacking” because
two Cornish miners, or “jacks,” would drill the holes.
The drilled holes were 1-1/2 inches wide and 18 inches
deep. Clay, sand or rolled tin lined the holes to pre-
vent the black powder from becoming damp and use-
less. A prescribed amount of powder was inserted
using a hollow tube. The loaded hole needed to be
capped with wood (plug shooting) or more commonly
clay (stemming). A trail of black powder over boards
led to the charge. A stem connected the flame to the
powder. Once the charges were ready, everyone ex-
ited the mine except the blaster, who would light the
various fuses, confirm that each fuse was burning cor-
rectly, and then leave. A safety fuse, developed by Wil-
liam Bickford of Cornwall in 1831, replaced this
method. This fuse was similar to rope and had a black
powder-filled core.
A pneumatic, or air-powered drill, replaced slow and
laborious double jacking. Ascanio Sobrero invented
nitroglycerin in 1846 to be used instead of powder,
but it proved to be extremely dangerous. Nitroglyc-
erin soaked into Fuller’s earth or sawdust and pack-
aged in waxed paper rolls called dynamite (developed
in 1867), however, was a lasting improvement.
Gold: The Mechanics of Mining
Reed Gold Mine State Historic Site
www.reedmine.com
The coolest place in North Carolina is a hole in the ground!
Developed in Mexico, and also called a “drag mill,” the
arrastra, is similar to a Chilean mill. The stones turn in
a circle around a center post. However, on the ar-
rastra these stones were dragged over a flat surface,
with the ore between the base and the drag stones,
rather than inside a trough. Often the arrastra was
used on ore that had already been through the early
stamp mills, to crush it more finely.
Because they were simpler, easier to build, and
cheaper, arrastras became more popular than the chil-
ean mill by the 1930s. Both arrastras and chilean mills
were slow compared to stamp mills.
Chilean Mills
The chilean mill usually featured two stone wheels
perhaps five or six feet in diameter (called runners)
that rotated around a shaft set into a circular stone
base. The base contained ore, water, and mercury.
Heavy wheels broke the ore into fine particles. The
base or “bedstone” had a circular trough cut into the
top. The vertical runner stones were held in place by a
wooden frame. This frame was attached to a center
post that was turned by a series of gears using either a
steam engine or horse (or mule) power. The stones
would circle the base seven to ten times per minute.
The stones, fashioned by stone masons, were difficult
to repair or adjust. This made them rather expensive
and eventually led to the widespread use of the ar-
rastra in place of the chilean mill.
The chilean mills located on Upper Hill at Reed Gold
Mine were able to grind two tons of ore in 24 hours.
The ore was broken up with sledge hammers, sent
through a stamp mill, then shoveled into the mill
trough. The trough was lined with mercury and had a
constant flow of water to insure maximum amalgama-
tion. It is not known how chilean mills came to North
Carolina, but by the 1830s this type of mill was the
primary means of recovering gold used throughout the
state. They remained popular through the mid-1800s.
Arrastras Stamp Mills
The stamp mill is a modification of the ancient technique
of breaking ore by the use of a mortar and pestle. Early
European mills were constructed of wood, with stone
stamps, and were bound together with rawhide and
wooden pins. The only major change in the stamp mill
during the next three centuries was the substitution of
iron for stone in the stamp heads and mortar.
Miners would deliver ore to the mill house where is was
crushed into pieces one to two inches in diameter. The
ore was then released into the hopper at the stamp mill
itself. By 1895, newer stamp mills could have been
equipped with automatic feeders that passed ore into the
mortar at a measured rate.
The ore would be mixed with water, under the crushing
action of the stamps. Starting around 1890, miners placed
mercury in the mortar box, as well as on the copper or
silver amalgamation plates, to catch the released gold. A
brass or tin screen was placed across the front of the
mortar box to prevent excessively large particles of ore
from escaping.
Amalgamation plates were placed in the mortar box and
on a table sloping away from the discharge of the mill.
The plates were coated with mercury and held gold sepa-
rate from the water-rock mixture that flowed over them.
The plates were scraped regularly and the amalgam was
saved. With proper cleaning and a suitable grade of ore, a
miner might recover a fair percentage of the free (non-
sulfured) gold in the water-rock mixture. A five-stamp
battery might crush five tons of ore in 12 hours. Though
faster than chilean mills or arrastras, stamp mills were
not necessarily more efficient. If the correct degree of
fineness could not be maintained, finer gold might simply
float away with the tailings, while ore that was too coarse
would not obtain enough contact with the mercury for
amalgamation (process of bonding gold with mercury). In
the 1930s stamp mills were replaced by ball mills.
Top: Arrastra Bottom: Apron table and mortar box of Stamp Mill. Chilean Mill