Principles of Mining: Valuation, Organization and Administration

of Mines (

SHAFTS; SPEED OF

ts. All these advantages pertain much more to mining coal or iron than metals, for unsound, wet ground is often the accompaniment of coal-measures, and seldom troubles metal-mines. Ventilation requirements are also much greater in coal-mines. From a metal-miner's standpoint, round shafts are comparatively much more expensive than the rectangular timbered type.[**] For a larger area must be excavated for the same useful space, and if support is needed, satisfactory walling, which of necessity must be brick, stone, concrete, or steel, cannot be cheaply acco

in former times. At each face of the octagon was

localities that steel beams can be usefully used instead of timber. T

le arrangement of compartments. Many combinations can be imag

g to the best advantage, and avoids the danger underground involved in crossing one compartment to reach another. I

e of shafts to be installed, many fact

of ore to

nding

le of tr

Dep

en to be worke

unt of

ntila

ter of th

ital o

ating e

ular factors by different engineers, and under different circumstances. It is not possible to suggest any arbitrary standard for calculating thei

um position, which may be considered as a

f very small output, at least two compartments must be made for hoisting purposes. Water has to be pumped from most mines, escape-ways are necessary, together with room for wires and air-

ound expeditiously, and spoil cannot be handled readily. The writer's own experience leads him to believe that, in so far as rock-breaking is concerned, to sink a shaft fourteen to sixteen feet long by six to seven feet w

e in the cost per cubic foot of material excavated with increased size of shaft. Variations in skill, in economic conditio

de cost an average of $0.95 per cubic foot; seven shafts 14 to 16 feet long and 5 to 7 feet wide cost an average of $0.82 per cubic foot. In South Africa, eleven shafts 18 to 19 feet lo

timbering does not increase in the same ratio. In any event, the cost of timber is

aulage can be concentrated into certain hours. Cages to carry mine cars and handle the same load as a skip must either be big enough to take two cars, which compels a much larger shaft than is necessary with skips, or they must be double-decked, which renders loading arrangements underground costly to install and expensive to work. For all these reasons, cages can be justified only on metal mines of such small tonnage that time is no consideration a

each four to five feet square. When the maximum tonnage is wanted from such a sh

a subsidiary factor is that the rapidity with which a load can be drawn is not wholly a factor of depth. The time consumed in hoisting is partially expended in loading, in accelera

ss for same depth. Since engines have, however, a great tractive ability on inclines, by an increase in the size of skip it is usually po

winding speed was 700 feet per minute. As men and material other than ore have to be handled in and out of the mine, and shaft-sinking has to be attended to, the winding engine cannot be employed all the time on ore. Twelve hours of actual daily ore-winding are all that can be e

pumping machinery is not elaborate, it is often possible to get a small single winding compartment into the gangway without materially increasing the size of the shaft if the haulage compartments be made somewhat narrower (Fig. 10). Such a compartment would be ope

nding space, some assistance may be given to ore-haulage in case of necessity. The mine whose output demands such haulage provisions can usually stand another foot of width to the shaft, so that the dimension

f the time upon ore-haulage. Such a shaft will be about 26 feet to 28 feet long by 8 feet wide outside the timbers, when provision is made for one gangway. The capacity of such shafts can be up to 4,000 tons a day, depending on the depth and engi

lems on engines and ropes become involved, and their sum-effect is to demand much increased size and a greater number of compartme

important matters, they would unduly prolong this discussion. Besides, a multi

s a loss of interest on the capital involved, which, in ninety-nine instances out of a hundred, warrants any reasonable extra expenditure to induce more rapid progress. In the case of mines in operation, the volume of ore available to treatment or valuation is generally dependent

interest, outside of its value as a stimulant to emulation. The thing that counts is t

is or is not in use f

ing characte

amount

an one not in use for operating the mine. The writer's own impression is that an average of 40 feet per month is the maximum possibility for year in and out sinking under such conditions. In fact, few going mines manage more than 400 feet a year. In cases of clean shaft-sinking, where every energy is bent to speed, 150 feet per month have been ave

of topography altogether, but, like everything else in mining science, has to be temp

cessary, and in cases where a tunnel enters a few hundred feet below the outcrop the shaft should very often extend to the surface, because internal shafts, winding from tunnel-level, require large excavations to make room for the transfer of ore and for winding gear. The latter must be operated by transmitted power, either that of steam, water, electricity, or air. Where power has to be generated on the mine, the saving by the use of direct steam, generated at the winding gear, is very considerable. Moreover, the cost of haulage through a shaft for the extra distance from tunnel-level to the surface is often less than the cost of transferring th

e length of tunnel warranted with various hypothetical factors of quantity of water and height of lift eliminated from pumping. In these computations, power is tak

of Water Lift Avoided 100,000 Gallons per Diem 200,000 Gallons per Diem 30

200 1,800

,400 3,600

,600 5,400

,000 9,000

2,000 18,000

ed is about 6-1/2 feet by 6 feet inside the timbers. Such a tunnel, with single track for a length of 1,000 feet, with one turn-out, permits handling up to 500 tons a day with men and

els designed to drain and operate mines at very considerable depths, such as the Sutro tunnel at Virginia City. The advantage of these tunn