Reopening of South African Mines
It
was decided to reopen two mines of the De Beer's group, the Premier
Mine, Pretoria and the - New Jagersfontein. Dewatering is going on and
they are expected to produce in 1948 at the earliest. Belgian Congo is
the World's largest producer, but 90% of it is industrial material.
Treatment of ore
In
the early years the blue ground or the ore from the mine was left in
open fields called depositing floors for weathering. The rock
gradually softened and became friable. The larger pieces were broken by
sledge hammers. The material thus broken up was taken to the crushing
and washing plants for concentration. This practice is no longer in
vogue. The ore, nowadays is directly crushed and washed as soon as it
is received from the mines. The following processes are employed to win
the diamond from the ore:—
(a) Crushing and washing; (b) Jigging; (c) Greasing or automatic sorting; and (d) Cleaning and evaluating.
(a) Crushing and washing.—The
crushed material is passed into the washing machines, consisting of
large pans or shallow tanks about 14 ft. in diameter. Water flows into
these pans, the mixture is well stirred, which causes a mechanical
separation of the heavier and lighter material and also eliminates 99%
of the lighter material.
(b) Jigging.—The
concentrates from washing are passed through screen and sized, and then
passed on to the jigs and pulsators, where further concentration is
effected by gravity. The concentrates from the jigs were first hand
sorted, but now the greaser has taken its place.
(c) Greasing or automatic sorting.—'This
method came into force in 1896. It was found that grease sticks most
tenaciously to diamond than to any other mineral in the
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