120

gravels were reached by breaking out from the bedrock very great pressure
developed and heavy runs of water, mud, and gravel occurred, which
drowned out the pumps, although the shaft was equipped at different times
with several sets of pumps of various designs, having a maximum capacity
of 3,000 gallons a minute. In some of the drives heavy oak timber and
steel rails were used for timbering, and an air lock, designed to withstand a
considerable pressure, was placed in the main tunnel, but proved of little
value, because as long as the ground was undrained the heavy pressure
continued and apparently the ground could not be drained by pumping
under the conditions which obtained. Attempts to mine the ground by
drifts from the hill-shaft tunnel continued until 1902 when a “gravel”
shaft was started on Willow River flat 160 feet below the line of bore-holes.
The shaft was equipped with two 18-inch Cornish pumps actuated by a
water-wheel and with one steam pump. A drain tunnel, which tapped
the shaft at a depth of 15-5 feet, was run for 1,100 feet. The shaft was
then sunk to bedrock and continued a few feet into the rock. A tunnel,
the floor of which was 91 feet 3 inches below the collar of the shaft, was
driven to intercept the channel and mining of the channel gravels begun.
No serious difficulty was met with in draining the ground, although no
mining could be done during the freshet and about two months pumping,
starting about July 1, were required to drain the ground each year. Mining
could then be carried on during the autumn and winter. Once the ground
was drained there was very little pressure in the face or overhead in the
drifts to contend with. During these operations about forty sets were taken
out, but it was soon found that the deepest part of the channel was at least
11 feet below the level of the floor of the tunnel and, therefore, could not
be mined. The main tunnel from the hill shaft was about 4 feet lower at
its end than the tunnel from the gravel shaft. It was then decided to
deepen the main or gravel shaft and, as the depth of the deepest part of the
channel was not definitely known, it was decided to deepen it 25 feet in
order to be certain that the lowest part of the channel could be reached.
The method of deepening the shaft was designed by Laurent Muller, who
was appointed mine manager after the death of F. C. Laird, in 1906, and
the shaft deepening was accomplished under his directions in 1906 and 1907.
The chief difficulty to be contended with in deepening the shaft was that
the two 18-inch Cornish pumps, the pump columns of which rested on
bedrock in the two pumping compartments, were working nearly to capacity
in order to keep the mine free of water. To overcome this difficulty clay
puddle was placed outside the shaft timbers in the lower part of the shaft
and around the pump chambers. This cut off most of the water coming
from the bedrock. The water coming from above was caught in a trough
around the outside of the shaft and carried to the pump chambers. The
main compartment was thus rendered nearly dry and sinking could proceed
in it. Sinking was then carried to the full depth, another trough with clay
puddle around it being placed lower down and the water from the trough
pumped to the upper chamber by athird smallpump. Raises the full size of
the shaft were then made from the bottom and as the flow of water had
decreased because of the clay puddling and because of a tunnel driven from
the bottom carrying off some of the water, it was found possible to divert
nearly all the water to one pump, and to lower the other and place it in