upon it. which is reviewed by Mr. John Plummer in the Mining World of October 21. 1905.a
Mount
Werong is one of the peaks of the mountain range, some 4.000 feet high,
which separates the fertile coast region from the arid interior. In the
beds and ravines of the streams that drain the ridge much of the drift
gravel is found washed down and redeposited, and here occurs gold, with
zircons and sapphires, abundant but small, and also this
large diamond, and another found some years ago, and valued at £5. The
sapphires have undoubtedly come from the decomposed basalt overlying
the drift, as none have been found in the drift itself. The diamond Mr.
Fittnmn refers to the drift; but he also recognizes the possibility of
its having come from the basalt, in view of the discovery of one or
more diamonds in the somewhat related dolerite at Copeton. This new
locality is some 300 miles south of the Inverell and Biugara region.
NOTES ON THE DIAMOND.
Russian experiments in crushing carbons used in diamond drills.—Prof.
Alex. M. Mitinsky. of the Mining Academy of St. Petersburg, Russia, is
carrying on a very interesting series of experiments in crushing the
carbons used in diamond drills." The rate of advance of a diamond drill
increases with the pressure up to a point where the diamonds are likely
to break. Here the limit is reached, beyond which an economic loss is
involved by greater pressure. The object of this investigation was to
determine this limit, which had not before been done, and which is of
course a very important practical question.
There
has been hitherto a remarkable difference in the practice of European
and American operators in work of this kind. The former have generally
followed an empirical rule of applying a pressure of 2 kilograms per
square centimeter on the bottom of the drill, which is equivalent,
with ordinary tools, to 1 kilogram per square millimeter on the
diamonds. American drillers have used far higher pressures, as much as
50 or 60 kilograms per square centimeter; by the same ratio this would
give 25 to 30 kilograms per square millimeter on the stones set in the
drill.
Professor
Mitinsky. assisted by Mr. S. Woisslaw, the pioneer of diamond drilling
in Russia, selected a number of carbons and subjected them to pressure
tests. This was done by placing each stone between two metal plates, a
harder one representing tiie rock and a softer one representing the
tool. These were connected with a very sensitive
press and recording apparatus, with a maximum load of one metric ton.
Different metals and different grades of steel were tried, and tile
half-sum of the areas of the impressions made in the two plates, in
each test, was taken as the cross-section area of the diamond that had
been pressed into them for calculation of the force exerted per square
millimeter of the stone. The first test was to the limit
of the press, one metric ton, without breaking, and the determination
was 54.:! kilograms per Square millimeter. The second stone, a small
one. broke at a calculated pressure of 80.0 kilograms per square
millimeter. Three other tests had an average of (iS kilograms as the
breaking limit, the lowest being 50 kilograms.
These experiments, Professor Mitinsky thinks, show clearly that the pressure on drilling
tools can safely be much increased with corresponding advantage in
results, and that the Americans, although far in advance of the
Europeans, have yet been operating well within the limit of practical advantage.
After
these tests Mr. Woisslaw directed his workmen to disregard the risk of
breakage and to use' the highest pressure attainable with their
machinery.
