rich
deposit is a wash from another source, and that the diamonds contained
therein are due to the concentrating action of ages and may have no
connection whatever with the underlying rock. It does not follow that
rich alluvial diamond diggings betoken rich diamond-bearing pipes. It
has been shown that the top layer of clayey red earth in the
(Transvaal) Premier Mine is rich in diamonds, that the yellow earth
below it is comparatively poor, and that the yield of the blue ground
is either unknown, or if known to those interested, has not been made
public. The yield of the Premier Mine is said to be phenomenal, but a
study of the published figures will show that the method adopted for
calculating the yield of the ground is unique in South African diamond
mining. At Kimberley practically all the top ground from De Beers
Premier Mine was sent to the washing machines and the total yield of
diamonds was divided by the total number of loads sent to the machines.
In the Pretoria District, it is authentically reported that the ground
is first sorted in the mine before being loaded and a very considerable
portion of the ground is rejected. This is quite the proper course to
pursue, for it would be useless to wash stones and waste. The good
ground is then loaded into trucks and sent to the washing machines. The
ground which passes through the one and a half inch mesh of the
cylinder screens goes into the pans ; the remaining portion, consisting
of coarse lumps and clay, is rejected. The yield of the ground is based
upon the results of the fine ground onlv. By this means of calculating,
the yield per load of original ground is doubled or trebled. Mention is
made of this so that the reader may see how results of yield are
obtained in different localities.
