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GEMS AND PRECIOUS STONES.
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1049
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£22,183
in value over 1909. The Premier diamond mine continues to be the
principal producer, but several other mines and the alluvial diggings
at Christiana contributed to the output.
Orange Free State.1—The
total production of diamonds in the Orange Free State (formerly Orange
River Colony) during the fiscal year ending June 30, 1910, amounted to
787,614 carats, valued at £1,525,707, as compared with 654,319 carats,
valued at £1,048,607, in 1909. The principal output came from the
Jagersfontein, Koffy-fontein, Voorspoed, Roberts, Victor, and a few
other mines, but the alluvial diggings along Vaal River contributed
1,653 carats, valued at £6,983. At the mines 8,027,487 loads of blue
ground were washed, yielding 10.19 carats of diamonds per 100 loads of
ground. The yield per 100 loads washed was less than in 1909, but the
average value obtained per carat was greater. The value of the diamonds
from the alluvial diggings averaged more than twice as much as those
from the mines. Among the largest diamonds found in the alluvial
diggings was one of 38 carats, valued at £250, and another of 24
carats, valued at £272.
BELGIAN KONGO.
The discovery and occurrence of diamonds in Belgian Kongo has been described by Sydney H. Ball.2
A few stones were found both in the tributaries of Lualaba River, and
in that river itself by prospectors of the Tanganyika Concessions Co.
during the years 1G06 to 1910. These diamonds were found in gravels and
the concentrates with which they were associated contain garnet,
diopside, diallage, biotite phlogopite, olivine, zircon, wollastonite,
aragonite, calcite, and goyazite. A rock similar to kimberlite is
reported to occur in the Kundelungu Plateau, east of the diamond
localities, cutting red sandstones of "Permo-Carboniferous" age.
In
1906 American and Belgian capitalists took over a mining concession in
Belgian Kongo under the name Societe internationale forestiere et
miniere du Congo. One small diamond of fine quality was found by a
prospector near Mai Munene in Kasai River. Work was recommenced in 1911
and many diamonds were found. At one place, about 55 miles northwest of
Mai Munene 240 stones were found in two weeks by one man. So far
diamonds have been found fcr a distance of about 75 miles along Kasai
River, and in the lower parts of its tributaries. They occur in riffles
or potholes in the river bed or in sands along their banks and are
locally abundant. Some of the gravel has a rather weak limonite cement.
The majority of the stones are well crystallized. The common forms are
octahedrons with some dodecahedrons and a few trisoctahedrons. Curved
faces, etching, and twinned crystals are common. A large percentage of
the stones are white, the others are mostly yellow and off-color, but
some deep-yellow, topaz, and apple-green stones occur. Associated
minerals are gold, quartz, cyanite, magnetite, zircon, ilmenite,
feldspar, mica, garnet, epidote, rutile, and hematite, in addition to
carnelian, chalcedony, agate, jasper, chert, diorite, schist, and
granite pebbles.
' Seventh Ann. Kept. Mines Dept. Orange Free State, 1910. > Eng. and Min. Jour., Feb. 3,1912.
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