22 MINING IN CALIFORNIA AND NEVADA.
gaining
correct and reliable knowledge of the country beneath and ahead of past
explorations in our mines, they cannot be surpassed, after the method
of working them is once understood and has been mastered. As regards
the cost of boring by means of these mining diamond drills, I found in
the regular official vouchers that in California the total expenses
varied from 90 to 108 cents per foot, in which amount, however, all
expenses were charged together, with interest on original
purchase-money (for each drill about £400). At the Comstock lode, a
great number (the California United and Virginia Consolidated companies
employ alone from eight to ten drills continuously) of mining drills
are at work testing the ground in every direction, and the actual value
of these mines are to a great extent gauged by the results obtained by
their assayers from the " cores " obtained in boring. Owing to the
higher rate of wages and other requisites prevailing at these
celebrated mines, boring would cost about 50 per cent, more per foot
than in California.
Remarks respecting the Use of Power and Diamond Drills.
In
California, I found that the miners had already found it necessary to
alter their usual style of working, in consequence of the introduction
of the power drills; in the stopes especially, a number of holeB would
thus be drilled to the best advantage from 4 to 10 feet deep each;
those near the foot wall would be charged and fired first, leaving the
others for a similar procedure, but fired eventually and simultaneously
with strong charges of black prismatic powder. This would not bring
down any ore, owing to the depth and strength of the holes—merely
"cracking" the ore; these holes would then again be charged with
nitro-glycerine explosives, which on ignition would throw down the
whole stope to the full depth of the holes and in large blocks.
With
the mining diamond drills, which are destined to work very
advantageously on Bendigo and other mining districts, great advantages
may be achieved in the way of saving expense in nearly all kinds of
mining operations, because, in cases where valuable ore bodies or
auriferous quartz has been discovered by means of these drills, it
becomes necessary to follow up such discoveries, and as the character
of the country has been proved by means of the " cores" obtained in
boring, contracts may be let or miners employed at wages for this work,
without spending too much money for that class of work on account of
the knowledge obtained of the nature of the strata about to be driven
or sunk into. The tapping of new lodes is frequently attended by bursts
of water interfering with other works in the mines through their sudden
submersion, but these clear bore holes will effect a gradual drainage,
and thus new ground would be opened much quicker, and more room found
for miners in less time than this would take by miners " beating" the
hand drills.
VENTILATION.
Besides the "blowers," ue., a
kind of centrifugal pump on the "Root's" principle, by means of which
the impure air in deep and hot mines is forced out by wholesome air,
their ventilation is also effected by drawing the depraved air from
such workings.
One
instance, which came under my notice at a mine near Nevada City, in
which the unwholesome air was successfully removed from the bottom of
