The Wallace miner. [volume] (Wallace, Idaho) 1907-current, 1920-01-08

4
ends OF the caps, without regard to
the posts underneath. The square
set" is used where the weight Is a side
pressure.
| After about three floors have been
mined, or about 80 feet, vertical dis
lance, this section is filed up with
waste rock, usually from development
work or from waste raises; then the
same stopping operation is continued
above
In the back -fill' method no tim
bers are used above the first floor. the
work being carried on directly on the
fill of waste rock instead Of on tim
beers as described in the foregoing
methods. In this system one cut or
bench, six to nine feet in vertical
height is carried horizontally through
the stope, and the filling follows d.
rectly behind the mining operation.
/ The "rill' system Is practically the
same as the 'iback-flll" method, ex-
cept that instead of the mining oper-
atoms being carried horizontally, they
are carried at about the angle of re-
pose, the action of gravity being util-
lied to move the ore to the chute and
also to refill with waste rock.
The 'timbered- rill" is used where
the character of the ledge matter
overhead requires support to prevent
its dropping in; otherwise, the prn-
ciple is the same as the "rill." Smaller
timbers can be used than in "stull-
sets" because as each cut is taken
is made below, and not more than 10
feet of wall Is left exposed at one
time.
The "shrinkage" method consists of
set in height to leave passageway and
ore loading space beneath. Ore chutes
are placed 50 that cars can be loaded
by gravity. only enough ore Is drawn
creased volume of broken ore, caused
by blasting from the solid ore In
place and to give the miners working
space above. The operation is con-
the ore Is broken in the stope. This
eliminates the necessity of timbering
and leaves the ore ready to be drawn
when wanted.
Practically all the stopping or actua,
ore breaking, is done overhead. by
drilling upward holes" at an average
of IS degrees from horizontal and
blasting down slices OF ore from
above, This operation continues up
ward from one level to the next.
Use Water leyners.
Air-feed machine drills are general
lily used with rs or ~ Inch cruciform
drill steel, both with and without wa
tel spray attachment. Compressed
air under about So pounds pressure is
delivered to these drills.
In drifting and prosecuting" the
water Leyner type machine drill is
used almost exclusively, with an oc-
casional exception where the recipro.
eating piston machines are used. Thu
water Leyner type machine uses 1 u :
inch round hollow drill steel, through
the center of which air and water are
forced to the bottom of the drill hole
to eject cutting and allay the dust
Bore holes of approximately 2-inch
diameter at the collar, tapering to
about Y inches at the bottom, are
drilled to an average depth Of from
five to six feet. Holes are spaced
about two feet apart this spacing
varying, Of course, to suit the char
acter of the material blasted and the
width of the stope. No springing or
chambering Of bore holes is DONE but
they are usually loaded about two
thirds full of dynamite and no lamp
ling material or stemming is used. The
advantages of tamping are generally
conceded, but the difficulty Of secur-
ling suitable material and of forcing
the miners to use it, is the probable
reason why tamping is not common
practice.
The primer cartridge is loaded near
the last with one or more cartridges
of dynamite on top, except where the
character of the rock is such that, the
blasting of one hole might cut off the
upper part Of another, making ii ne
cessary to put the primer nearer the
bottom. Several methods of making
primers are followed. A hole large
enough to receive the blasting cap is
punched straight into the end Of a
dynamite cartridge, or at an angle In
the side about the middle of the car
fridge. Another method is to punch
hole diagonally through the car
fridge near the end, drawing the cap
and fuse through this hole and insert
ing the cap into another hole punched
in the side. In this latter method
there is danger of ignlting the dyna-
mite from side splitting Of the fuse.
Slope Blasting.
In stope blasting. gelatin dynamites
OF 80, 80 and 40 per cent strengths are
used almost exclusively. The usual
practice, in loading the dynamite, is
to split the paper cartridge shells
llengthwise with a knife, and push
each cartridge into the bore hole with