336 THE DIAMOND MINES OF SOUTH AFRICA
this
mine is only about one-half that of the Kimberley mine. The following
work is being done with the view of preventing them. A tunnel is being
driven around the mine at the hard rock (melaphyre) level, about 380
feet from the surface, in order to take up the water which flows into
the open mine below the shale. Tunnels are also being driven on the
1000-foot level on the south and east sides of the mine, which will be
continued until they meet. Diamond drills are at work making holes
between levels, with the view of tapping the water. Everything feasible
will be done to free De Beers mine from the plague of water as
perfectly as it has been done at Kimberley mine. The problems are not
the same, however, for in Kimberley mine the debris had followed down
as the blue ground was extracted, and had left the hard rock more or
less exposed to view, and one could see in places where the streams of
water flowed into the open mine; but in De Beers no hard rock has been
exposed until lately, and one must grope in the dark, as it were, to
find out where the water enters the open or worked-out portions of the
mine.
The
pumping plants for freeing the mines from water have kept pace fully
with the advance in the hoisting plants. For the service of De Beers
mine, a new pumping engine was erected at the rock shaft in 1889. This
is a compound surface-condensing engine made by James Simpson &
Company, of London. Its high-pressure cylinder is 14-3/64 inches
diameter, and its low pressure, 21 inches, with a stroke of 30 inches,
It is capable of developing 120 horse-power. With this engine an
average of nearly 6000 gallons an hour was readily drained from the
mine from the start, and no difficulty was experienced in lifting over
8000 gallons an hour at times. The cost of pumping is largely offset by
using the water drained from the mine for washing the pulverized blue
ground. By combining this supply with that obtained from surface
reservoirs, enough water was obtained for the use of the concentrating
plants, except in very dry seasons. For the Kimberley mine a Cornish
pumping plant of 400 horse-power, from designs by the late Mr. L.I.
