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SOUTH AFRICAN DIAMONDS
crushers, set very finely, and then through the second and final set of rotary pans where the operation is completed.
In
many cases, instead of using crushers, the blue ground is spread out on
"weather floors" which cover from four to five thousand acres and is
left exposed to sun and rain until it crumbles and disintegrates, the
process being hastened by harrowing with steam ploughs; this may
require a period of six months or a year. The disintegrated ground is
then brought back in the trucks and fed through perforated cylinders
into the washing pans. The heavy minerals are then passed over sloping
tables smeared with grease to which practically all the diamonds
adhere. The diamonds are won by scraping off the grease and melting it.
The other minerals are washed away and shaken to and fro under a stream
of water which effects a second concentration of the heaviest material.
The
average yield per wagon load of 1,600 pounds of blue ground containing
16 cubic feet averages about one-eighth carat of diamonds or one and
one-half grains per ton, which may or may not be of good color.
In
twenty-five years the diamond did more to build a new empire than the
pioneers of the most vigorous and tenacious races the earth has ever
known had succeeded in doing in over three hundred years.
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