Year: 1876

How Mass Copper Is NIined.--The Difficult


ties Attending the Work. - 10,


The largest continuous mass of copper
which has been taken out of the mines
of the Lake Superior region was proba-
bly, that from the Minnesota In 1857,
which is variously stated as weighing
420 tons and 470 tons. Its length was
about forty-fve feet, its breadth OF
height twenty-five feet, and its greatest
thickness eight feet. All such masses
are very irregular and ragged in thei,
form and thickness, thinning out gradu.
ally from foot to few inches, and
struggling through the vein until they
connect with other large masses. This
was the character of a mass found in
the Phoenix mine, one of the oldest on
the lake, which mass altogether weighed
some six hundred tons. But this was
really a series of masses more or less
connected by strings of metal, yet nc
one large part of it weighed, sngly, over
two hundred tons. A similar series Of
masses, weighing about six hundred
tons, was extracted from the Minnesota.
Some of the Phoenix masses we're fon1
or five feet thick of solid copper. The
Cliff mine has yielded masses weighing
from one hundred to one hundred and
fifty tons in one piece. One of forty
tons was taken out this year, besides
numerous blocks weighing from one to
eight tons. This mine and the Central
are now yielding mass copper In abun'
dance. ~ = l,a


It is of course impossible to pick, OF
to drill, or to break out such huge mass
es of solid metal, when they are found
by drifting upon the course of the vein.
The method is as follows: The miner
picks out, or excavates, narrow passage
or chamber upon one side OF the mass,
laying it bare as far as possible over its
whole surface. It is usually firmly held
by its close union with the vein stuff, OF
by it's irregular projections, above, be-
low and at the end. If it then cannst
be dislodged by levers, the excavation Of
chamber is commenced behind the
mass, and this excavation is made large
enough to receive from five to twenty OF
more kegs of powder. In one instance,
in the Cliff mine, a charge of twenty-one
kegs of powder threw down two huu-
dred tons of copper Bags of sand are
used for tamping, and the drift is closed
up by barricade of refuse and loose
dirt. After such blast the drift is, OF
course, charged with foul air, and it can
not be safely entered for hours after
wards. If entered too soon, men lose
all strength in their limbs, and fall
down.


The huge masses of copper dislodged
in this way are too large to be handled
and got to the surface. They have to be
cut up. The copper cutters are called IN,
and the mass is marked off In squares or
blocks of suitable size. Copper cutting
is distinct art, and requires considera-
BILE skill and experience. Ordinary min
ers, however skillful they may be, can
not cut up copper without long training.


The tools are simply narrow chisels
and striking hammers. The chisels are
shaped like the parting tools OF turner's.


They are made of fiat bars of half inch
steel, about two inches wide and eigh-
teen inches long. They are chamfered
each way like cold chisel, to form the
cutting edge. This edge is made q little
longer than the thickness of the bar.


The cutter holds the chisel and two men
strike it. A thin slice or chip Of copper
is in this way cut out in narrow chan.


Eel across the mass Of copper. The
operation is repeated until the narrow
cut, but little over half an inch wide,


has been carried through the mass. The
chips cut out in this way are long, mar
row strips of copper only about half as
long as the groove from which they
are taken, the metal being condensed


and thickened by the force of the blow.


This work is necessarily slow and te-


dious, and it costs $12 per square foot
by contract. At this price, the cutters


make So per day.-Scie'atitfc american.