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African Diamonds.
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the
rocks, and so force open the channels which we recognize as the
"pipes." The vapour rushing up these pipes might tear the shales and
other rocks forming the walls, and thus give rise to fragmentary
materials to be caught in the uprising pasty magma, producing as it
cooled a brecciated mass. The pipes have thus become filled with a
medley of materials, partly brought up from great depths, and partly
due to the disintegration of the local rocks. But the Diamonds which
give supreme value to the breccia have been formed in a deep-seated
laboratory under the pipes, where carbon has crystallized from a
saturated bath of iron, under prodigious pressure, and with
inconceivable slowness.
In
the early days of Diamond-mining in South Africa, the ground in these
volcanic necks was worked as quarries, or open casts, and the material
was hauled up by means of aerial wire ropes. Much inconvenience however
was experienced as the diggings grew deeper, especially by the heavy
falls of the surrounding shales, or "reef," which tended to slip in
large masses into the workings. Moreover, the shales contained
iron-pyrites, which occasionally ignited spontaneously, with disastrous
results.
An
entirely different system of working was therefore introduced at the
Kimberley Mine, and this was soon followed at De Beers. Shafts were
sunk at a convenient distance from the pipes, and successive galleries
driven into the Diamond-bearing ground, as in the ordinary system of
underground mining. The rock is brought down by drilling and blasting,
and is run in trucks to the bottom of the shaft, up which it is hoisted
in skips running on steel rails and worked by a steam winding-engine.
The mines are fitted with all modern improvements, such as electric
lamps and telephones connecting the different centres of work.
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