The copper era. (Clifton, Graham County, Ariz.) 1899-1911, 1910-07-29

about 13 cubic yards of bro ken rock
in shift of nine hours. Tally men,
stationed on elevated positions so as
to command a view of the working
aud dumping places. count the cars,
which are conspicuously numbered
and credit them to the respective
workmen. Certain parts of the mine
do not permit of this system, but so
far as it is possible the work is ar
ranged on this basis.
With the grade of ore mined, the
economic limit to the opencut method
is four tons of overburden removed
to develop one ton of ore. Weather
conditions in Arizona are favorable
to open work on account of the dry
climate and mild winters.
STOPPING WITHOUT TIN1BERs.
Where an oreshoot has been proved
in depth and is covered by heavy
overburden of waste underground
mining is employed. The ground in
most cases stands well without tim
bering; slopes up to IS feet in width
having been worked without diff
Guilty. In ore of moderate hardness,
the mode of working is as follows:
On the lowest level on which the
ore is exposed, the oreshoot is open
ed to its full width and length.
When the shape of the orebody has
been determined, raises are made
from the roof of the stope to the sur
face, the number depending on the
dimensions OF the stOpe. The ore is
then mined to d hight of 20 feet
above the j, vel md Il timbered road
way with the necessary chutes and
ladderways erected. The oyer burden
of waste is now milled down the
raises and leveled off, filing the slope
and forming a compact working floor,
Is feet above the level.
The ore is afterward broken by
overland stopping in ascending slices
Is to % feet high: depending on the
condition of the roof. AS each slice
is removed; the overburden is milled
down for filling material and to pro-
vide the next working floor. When
all the overburden has been utilized
in this manner, the back of ore re-
naming is gained by opencut or
milling method. The cost of break
ing the ore in stopping is necessarily
higher than in opencut work, but the
more economical removal of oven
burden compensates for this increase.
When the ore is hard and stands
exceptionally we'll the method of ex-
traction is vertical. A raise is made
to the top of the ore and extended to
the surface or to an upper working
for air. At a hight of 80 feet above
the level, mining is started from the
raise outward, the floor being always
left sloping so that the ore will run
directly into the chute. When the
extremities of the ore have been
reached or the roof is as wide as will
stand with safety, the bench forming
the floor of the stope is now mined.
Deep hole, charged with black pow
der, are used ond the ore is broken
as freely as in opponent work. The
slower action of the black powder
does not jar and weaken the roof OF
the stope to the stope of the same
degree as the rapid action of dyua-
mite.
When the first bench, so feet in
hight, has been worked out, the chute
and ladderway are timbered to with
in feet of the roof and the stope i,
filled with waste from the surface;
the filing material is leveled and the
next block of ore above is attacked
in a similar manner.
STOPPING WITH SQUARE SETS.
In some parts of the mine, the ore
is too soft and fria BILE to permit OF
any system of STOPPING without the
use of timbering is employed in such
cases to support the roof aud walls.
The slopes are kept full of waste t.
within one set of the back of ore:
timbered chutes and ladderways
alone being left open The waste is
obtained from the surface workings
and is distributed from a small chute
placed in one Garner of the stope.
This position of the chute is advisa-
BILE as by commencing the mining OF
each floor from this point, the filling
can be kept close to the working
breast withot interfering with the
shovelers.
Every floor is worked as rapidly as
the worhing faces allow, to avoid ex-
cessive weight settling on the tim
bers. The timbering is arched to
compensate for the sinking of the
sets in the center of the stope due to
the greater weight of roof. This is
accomplished by introducing one
floor of sets, the posts of which step
upward inches to the center of the
stope, and descending in like man
ner to the opposite wall. Should this
arch effect at any time be lost by ex-
cessive weight, causing the timbers
TO settle, or by the loosening of the
side blocking, another floor of special
posts is put in to restore it.
The sets employed consists of d