and
the air current was increased to 45,000 cubic feet per minute. In the
Kimberley mine the influx of air per minute is 25,500 cubic feet.
Temperatures
At De Beers, with temperature of the air on the surface 790
F., the temperature ranges from 75° to 77° in the tunnels leading to
the mine on the 1000, 1200, and 1400-foot levels. The temperature of
the air as it leaves the mine on the 800-foot level is 840.
The temperature of the mud after a mud rush was on one occasion 85 ° F.
Temperatures at Kimberley mine in the 1200-foot tunnel were, for the
air, 71°.5; for the rock, 72°.1 ; for the large spring of water 78°.9
F. The quantity of water flowing from this spring, which is about 600
feet from the crater, is 3500 gallons an hour. The temperature in the
working galleries on this level is 870.
Springs of water on the 1520 and 1840-foot levels gave 83°.8 and 81°.9
respectively, the water in the lower level being the cooler.
The Output of Blue Ground
The
table of statistics (Appendix V) gives the amount of blue ground
produced from De Beers and Kimberley mines since the formation of the
De Beers Consolidated Mines Limited. In the same table of statistics
will be found the average cost of production per load. It will be seen
that the lowest cost was for the year ending June 30, 1894 -- 6s, 6.8d
per load. This includes all charges from the mining of the ground to
the delivery of the diamonds to the valuators. All mine charges,
including shaft-sinking, tunnelling, etc., are charged to current
expenses. It is interesting to note in the same table the greatest
output of each mine through a single shaft for various periods of time.
The maximum amount of blue ground produced in one year was 1,746,240
loads from De Beers mine for the year ending December 31, 1897. This
ground was raised from a depth of 1000 feet from the beginning of the
year until June 14, when winding commenced from the 1200-foot level.
