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MINING IN CALIFORNIA AND NEVADA.
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Section II.—Mining Operations.
SINKING SHAFTS.
The
methods for sinking shafts in connection with lodes and the vertical
shafts examined call for no special remark, but, in cases where the
underlay of lode is followed like the Idaho Company, the main shaft of
which measures 20 feet long by 6 feet wide in the clear of timber, and
is divided into four compartments, a considerable saving of time and
expense was obtained by, firstly, using one of the compartments
exclusively for the " sinkers," and providing a " tub " specially for
their use in removing the debris to the surface by means of a
separate drum at the winding engine ; secondly, it was found to be more
expeditious and cheaper on the whole to sink a smaller shaft in
advance, say 100 feet deep, then open out to the full size and put in
the permanent timber from the bottom, widen out to full size of main
shaft whilst rising above the bottom sets until the above-mentioned
space was secured in the ordinary way. That this operation was effected
in a superior manner, I found after numerous inspections, and that the
sinking was of a satisfactory speed from the fact that this company
sank that large shaft, measuring 23 feet long by 9 feet wide, " outside
of timber," to a depth of 1,000 feet, in five years and eight months.
When it is borne in mind that the hard schist at the hanging wall and
the continuously swelling serpentine at the foot wall necessitated
continual repair, and a complete system of " false sets " to keep up
the sides, the actual time consumed would appear reasonable as. well as
the expense per foot, viz., 100 dollars, inclusive of all material,
labor, engine work, fuel, and interest.
The
American boards of directors or trustees controlling mines go very
systematically to work, and they require their mine superintendents to
furnish the board with complete written estimates of every kind of
permanent work, so that they may possess always a knowledge of what
amount of expense within a given time is required to carry on the
operations necessary, whereby a continuous opening of the ground is
effected. In this connection it should also be stated that in place of
written reports of what has been done during the past month—all
retorting and payments are made monthly to save time—a comprehensive
set of tables are printed, which are filled up under various heads by
the superintendent, chief engineer, amalgamator, assayer, surface
manager, and foreman of shifts, as the case might be, filed for
reference and comparison, and are always ready for use in future.
Returning
to the shaft named: the squared frames of spruce pine, 15 inches thick
and joggled, are placed every 4 feet, thus making the " studdles " 2
feet 9 inches in length each; and in this case, owing to the angle of
underlay it has been found requisite to stay diagonally their shaft
timber both above and below the various " stations " or plats. Iron
rails, from 30 lbs. to 40 lbs. per yard, are laid on and secured to the
foot-wall frames, and they form two or three lines of tramway to the
bottom, the cages with trucks travelling upon same by means of flange
wheels provided for each cage. In this case the cages have been
furnished with a movable bottom working on a strong hinge, which
adjusts itself to any angle of underlay or to the level bottom of each
plat. Cast-iron rollers are fixed between the rails in order to save
the trailing rope from chafing, and the working of underlay shafts
appears in some cases to be advantageous, because they avoid expensive
crosscuts for the lode, as with vertical shafts; but for other reasons
the latter are preferred, inasmuch of the danger in the angles of
underlay, which cause the cages to jump the rails and cause accidents
and delay.
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