DIAMOND MINES OF SOUTH AFRICA 269
May,
1906, when it was opened, to the end of December, showed a profit,
after paying all the expense of prospecting, developing, mining
operations and registration, of £39,045 from 20,406 carats found.
One
of the most important processes in winning diamonds from the matrix is
the weathering. The " blue " of nearly all dry diggings is refractory.
It is about as hard as sandstone. It was found, however, that exposure
to the weather crumbled it so that it could be washed without further
preparation. Level pieces of ground hardened by heavy rollers were
enclosed convenient to the mines, tracks laid, and the blue as it was
taken out of the mine, was loaded on cars and carried to these
depositing floors or " Floors " as they are called, where it was spread
and left exposed to the weather. According to the nature of the blue,
which varies in hardness, it takes from two to twelve months to make it
sufficiently friable for the washers. An abundance of rain with hot
sunny days intervening, hastens the process, and if rains fail, the
miners sometimes water and harrow it. That there may be no interruption
to the work of the washers, it is customary to keep sufficient blue on
the floors at all times for two seasons' work. If the work of mining
were at any time suspended, a mine could nevertheless turn out a full
year's supply of diamonds, after the mine was shut down. In 1906 the De
Beers mines had 8,300,000 loads on the floors.
When
the blue is sufficiently weathered, it is put on trucks and taken to
the washing machines, where it is agitated with water, and forced
through a series of revolving cylinders perforated with holes one inch
in diameter. Lumps which resist the process are returned
