|
PRINCIPAL SOUTH AFRICAN MINES 305
rock.
It has one great advantage over the De Beers mines, in that the rim
rock is very firm, and therefore is not liable to fall as the shale
formations of Griqua-land, about Kimberley, do. The contour of the
surrounding surface also is favorable both to the drainage of the
mine, and the storage of water by easily constructed dams.
The
Premier crystals have a peculiar laminated appearance. Many of them
also have an oily luster, and are quite blue. There are also many false
colors. Nevertheless some are of the finest quality and color. It is a
mine which yields the extremes. The percentage of bort and large
crystals of gem material is greater than from any other mine. The
immense Cullinan was of exceptional purity. All the stones cut from it,
ranging from five hundred carats down, are flawless.
In
the beginning, the Premier washings gave extraordinarily large
results; nearly one and a half carats to the load. (16 cubic feet,
equivalent approximately to a ton, now constitute a load.) The average
of June, 1903, was 1.45; of July, 1.47; but from that time the yield
steadily declined, the average to October 31 being 1.29. The highest
average for any month in 1904 was .92; the lowest .62. The highest in
1905, .85; the lowest .26. The highest in 1906 was .35 and the lowest
of average material .27. The yearly average since the opening of the mine and the value per carat is as follows:
|
||
|
|
||
|
|
||
|
|
||