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FAG . 13.—Standard FIG. 14.—Flat See also:round Rope. Rope. (From The Colliery Engineer, May 1897.) carrying the grooved sheaves over which the hoisting See also:ropes ,pass, is known as the See also:head-See also:gear (fig. 15). In See also:Great See also:Britain and her colonies it is also called the poppet-head or See also:pit- Hesdgear head See also:frame; in the See also:United States head-frame or gallows-frame. Though it is small and See also:simple in construction for See also:light See also:work, for heavy hoisting at high speeds massively framed towers, often 8o to Poo ft. in height, are built. See also:Steel frames are more durable than those of See also:wood, and have become See also:common in nearly all See also:mining countries, especially where See also:timber is scarce. A See also:German See also:design is shown in fig. 16. The head-gear is often combined with ore-bins and machinery for breaking and sizing the lump ore previous to shipment to the reduction See also:works. Cages, See also:running in guides in the See also:shaft, are used for raising the cars of See also:mineral to the See also:surface (fig. 17). They may have one, two or more decks, usually carrying one or two cars on each See also:deck. Multiple-deck cages are cages . s and Skip rarely employed except for deep shafts of small See also:cross-See also:section or when the mine cars (tubs) are small, as in many parts of See also:Europe. In many mines the mineral is raised in skips (fig. 18), filled from cars underground and dumping automatically on reaching the surface. Skips are sometimes of very large capacity, holding 5, 7, and even Io tons of ore; such are used, for example, in several shafts at See also:Butte, See also:Montana, in the See also:Lake See also:Superior See also:copper See also:district, and in See also:South See also:Africa. Fig. 18 is a small skip; the upper See also:illustration showing position for dumping. The See also:lower cut is of a skip for either ore or See also:water; See also:note See also:valve in bottom. Hoisting buckets or kibbles are employed for small See also:scale work or temporary service, such as raising the material blasted in sinking shafts. They hold from a few See also:hundred pounds up to 1 ton. In hoisting from great depths the See also:weight of the rope, which may exceed that of the cage and contents, produces excessive See also:variations in the load on the See also:engine difficult to See also:deal with. Moreover, the limit of See also:vertical See also:depth at which rope of even the best quality will support its own weight only, with a proper margin of safety, is, say, ro,000 to 12,000 ft.; and with the load the safe working limit of depth would be reached at 7000 to 8000 ft. A number of and See also:silver mines. Wellman- See also:Chalmers Co., See also:Milwaukee, Seaver-See also:Morgan Co., See also:Cleveland, See also:Wisconsin, makers. See also:Ohio, makers. shafts in South Africa, the United States and elsewhere, are already approximating depths of 5000 ft., a few being even deeper. Ropes of tapering section may be used for great depths, but are not satisfactory in practice.' See also:Stage hoisting is applicable to any depth. Instead of raising the load in one lift from the bottom of the shaft, one or more intermediate A full discussion of this subject is given in Trans. Ins. See also:Min. and Met., vol.. xi.dumping and loading stations are provided. Each stage has its own engine, rope and cage. The variations in engine load are thus reduced, and incidentally hoisting See also:time is saved. In shallow mines the men use the See also:ladder-way in going to and from their work. This is sometimes the See also:case also for considerable depths. It is more economical Rflgootster}ng ngand to See also:save the men's strength, however, by raising men. and lowering them with the hoisting engines. At mines with vertical shafts this is a simple operation. Cages of the See also:size generally used in See also:metal mines will hold from ten to fifteen and occasionally twenty men. The time consumed in lowering the men is shortened by the use of cages having two or more decks. These are common in Europe, and are sometimes employed in the United States and elsewhere in mines where the output is large and the shafts deep and .of small cross section. While a shift of men is being lowered the miners of the preceding shift are usually raised to the surface in the ascending cages, the entire shift being thus changed in the time required for lowering. Nevertheless, in very deep and large mines the time consumed in handling the men may make serious inroads on the time available for hoisting ore. At a few mines See also:special See also:man-cages are operated in See also:separate compartments by their own engines for handling See also:part of the men, and for tools, supplies, &c. For inclined shafts, where the mineral is hoisted in skips, the operation of raising and lowering men may not be so simple. Even a large skip will hold but a few men, the See also:speed is slower, and more time is required for the men to get into and out of the skip than to step on and off a cage. Moreover, skips are rarely provided with safety attachments, so that the danger is greater. When the shafts are deep and the number of miners large man-cars are sometimes employed. These are See also:long frames on four wheels, with a See also:series of seats like a section of a See also:theatre See also:gallery. Ordinarily 4 or 5 men occupy each seat, the See also:car accommodating from 20 to 36 men. Such cars are in use at a number of deep inclined shafts in the Lake Superior copper district, where the depths range from 3000 to 5000 ft. or more. At a few mines (since safety catches cannot be successfully applied to man-cars) these conveyances are raised and lowered by separate engines and ropes. To replace the ore-skip expeditiously by the man-car when the shifts are to be changed a See also:crane is often erected over the shaft mouth. At the end of a shift the ore-skip is lifted from the shaft track—the hoisting rope being uncoupled—and the man-car put in its See also:place and attached to the rope. This See also:change may be made in a few minutes. Formerly, at many deep See also:European mines, and at a few in the United States, men were raised by means of "man-engines." A man-engine consists of two heavy wooden rods (like the rods of a Cornish pumping plant), placed Maa- Gngtnes. parallel and See also:close to each other in a special shaft compartment, and suspended at the surface from a pair of massive walking beams (or " bobs "). The rods are caused to oscillate slowly by an engine, one rising while the other is falling. Thus they move simultaneously in opposite directions through a fixed length of stroke, say from ro to 12 ft. At intervals on the rods are attached small See also:horizontal platforms, only large enough to accommodate two men at a time. As the rods make their measured strokes one of the miners, starting from the surface, steps on the first See also:platform as it rises to the surface landing And is then lowered on the down stroke. At the end of the stroke, when his platform comes opposite to a corresponding platform on the other See also:rod, he steps over on to the latter during the instant of See also:rest See also:prior to the reversal of the stroke, descends with the second rod on this down stroke, steps again at the proper time to a platform of the first rod and so on to the bottom. The men follow each other, one by one, so that in a few minutes all the rod platforms in a deep shaft may be simultaneously occupied by men stepping in unison but in opposite directions from platforms of one rod to the other. Meantime, the men quitting work are ascending in a similar way, as there is See also:room on each platform for two men at a time when passing each other. Man-engines were long used, but are now practically abandoned in both Great Britain and the United States, and few remain in any of the mining regions of the See also:world. Their first cost is great and they are dangerous for new men, as they require See also:constant alertness, presence of mind, and a certain knack in using them. See Trans. Inst. Min. and Met. xi. 334, 345, 380, &e.; also Eng. and Min. Jour. (See also:April 4, 1903), pp. 517 and 518. Surface Handling, Storage and Shipment of Minerals.—To mine ore or See also:coal at minimum cost it is necessary to work the mine plant at nearly or quite its full capacity and to avoid interruption and delays. When the mineral is transported by See also:rail or water to concentration or metallurgical works for treatment, or to near or distant markets for See also:sale, See also:provision must be made for the economical loading of railway wagons or vessels, and for the temporary storage of the mineral product. For See also:short periods the mineral may remain in the mine cars, or may be loaded into railway wagons held at the mine for this purpose. Cars, however, are too valuable to be used in this way for more than a few See also:hours, and it is usual to erect large storage bins at the mine, at concentration works and metallurgical establishments, in which the mineral may be stored, permitting cars, wagons and vessels to be quickly emptied or loaded. In mining regions where (water transportation is interrupted during certain months of the See also:year the mineral must be stored underground, or in great stock-piles on the surface. In coal mining the See also:market demand varies in different seasons, and surface storage is sometimes necessary to permit See also:regular work at the mines. For coal, See also:iron ore and other cheap minerals, See also:mechanical handling by many different methods is used in loading and unloading railway wagons and vessels, and in forming the stock-piles and reloading the mineral therefrom. (See CONVEYOR and Docxs; also G. F. Zimmer, Mechanical Handling of Materials, and See also:Engineering See also:Magazine, xiv. 275, xx. 157 and xxi. 657.) Mine Drainage.—A mine which has been opened by an adit See also:tunnel or See also:drift drains itself, so far as the workings above the adit level are concerned. In many mining regions long tunnels have been driven at great expense to secure natural drainage. Under See also:modern mining conditions drainage tunnels have lost much of their former importance. Taking into See also:account the See also:risk attending all mining operations, which make necessary large See also:interest and See also:amortization charges on the cost of a tunnel, it will in most cases be advisable to raise the water to the surface by mechanical means. Drainage channels are provided, usually along the See also:main haulage roads, by which the water flows to a sump excavated at the See also:pump shaft. In See also:driving mine passages that are to be used for drainage, care is taken to maintain sufficient gradient. Siphons are sometimes used to carry the water over an undulating grade and thereby save the expense of a deep See also:rock cutting. As the larger part of the water in a mine comes from the surface, the cost of drainage may be reduced by intercepting this surface water, and See also:collecting it at convenient points in the pump shaft from which it may be raised at less cost than if permitted to go to the bottom. Water may be raised from mines by buckets, tanks or pumps. Wooden or steel buckets, holding from 35 to 200 gallons, are employed only for temporary or See also:auxiliary service or for small quantities of water in shallow shafts. Tanks operated by the main hoisting engines, and of capacities up to 1 500 gallons or more, are applicable under several conditions: (I) When the shaft is deep, the quantity of water insufficient to keep a pump in regular operation, and the hoisting engine not constantly employed in raising mineral, the tank is worked at intervals, being attached temporarily to the hoisting rope in place of the cage. (2) For raising large volumes of water from deep shafts pairs of tanks are operated in See also:balance in special shaft compartments by their own hoisting engine. With an efficient engine the cost per See also:gallon of water is often less than for pumping. (3) For clearing flooded mines. As the water level falls the tanks readily follow it while at work, whereas pumps must be lowered to new positions to keep within suction distance. Self-acting tanks are occasionally built underneath537 the platforms of hoisting cages. Mine pumps are of two classes: (r) those in which the driving engine is on the surface and operates the pumps by a long See also:line of rods passing down the shaft, commonly known as the Cornish See also:system; (2) See also:direct-acting pumps, in which the engine and pumping cylinders See also:form a single unit, placed close to the point underground from which the water is to be raised. Cornish pumps are the See also:oldest of the See also:machines for draining mines; in fact, one of the earliest applications of the old Woolf and See also:Newcomen engines in the 18th See also:century was to pumps for deep mines. The engine works a massive See also:counter-balanced walking-See also:beam from which is suspended in the shaft a long wooden (or steel) rod, made in sections and spliced together. Attached to the rod by offsets are one or, more plunger or bucket pumps, set at intervals in the shaft. All work simultaneously, each raising the water to a tank or sump above, whence it is taken by the next pump of the system, and finally discharged at the surface. The individual pumps are placed several hundred feet apart, so that a series is required for a deep shaft. The speed is slow—from 4 to ro strokes per minute—but the larger sizes, up to 24 in. or more in See also:diameter by ro or 12 ft. stroke, are capable of raising millions of gallons per See also:day. Cornish pumps are economical in running expenses, provided the driving engine is of proper design and the disadvantages incurred in conveying See also:steam underground are avoided. Their first cost, however, is high and the cumbersome parts occupy much space in the shaft. Direct-acting pumps, first introduced (1841) by an See also:American, See also: See also:Hydraulic pumping engines, while not differing essentially from steam pumps, must have specially designed valves in the See also:power cylinder on account of the incompressibility of water. They can be used only when a See also:supply of water under sufficient pressure is available for power. Centrifugal pumps, constructed with several stages or sets of vanes, and suitable for high lifts, have been introduced for mine service. When mine water is See also:acid the working parts of the pump must be lined with or made of See also:bronze or other non-corrosive material; or the acid may be neutralized by adding See also:lime in the sump. See also:Ventilation.—The air of a mine is vitiated by the presence of large See also:numbers of men and animals and of numerous See also:lights, each of which may consume as much air as a number of men. In mining operations See also:explosives are used on a large scale and the See also:powder gases contain large quantities of the very poisonous See also:gas, See also:carbon monoxide, a small percentage of which may cause See also:death, and even a See also:minute percentage of which in the air will seriously affect the See also:health. In addition to these See also:sources of contamination the air of the mine is frequently charged with gas issuing from the rocks or from the mineral See also:deposit. For example, carbon dioxide occurs in some mines, and See also:hydrogen sulphide, which is a poisonous gas, in others. In coal-mines we have to deal with " See also:fire-See also:damp " or See also:marsh gas, and with inflammable coal dust, which form explosive mixtures with air and frequently See also:lead to disastrous explosions resulting in great loss of See also:life. The gases produced by such fire-damp or dust explosions contain carbon dioxide and carbon monoxide in large proportion, and the See also:majority of the deaths from such explosions are due to this " after-damp " rather than to the See also:explosion itself. The terrible effects of fire-damp have led to the See also:adoption of elaborate systems of ventilation, as the most effective safeguard against these explosions is the dilution and removal of the fire-damp as promptly and completely as possible. Very large volumes of air are necessary for this purpose, so that in such mines other sources of vitiation are adequately provided against and need not be considered. In metal mines, however, artificial ventilation is rarely attempted, and natural ventilation often fails to furnish a sufficient quantity of air. The examination of the air of metal mines has shown that in most cases it is much worse than the air of crowded theatres or other badly ventilated buildings. This has a serious effect on the health and efficiency of the workmen employed, and in extreme cases may even result in increased cost of mining operations. The ventilation of a mine must in See also:general be produced artificially. In any case whether natural or artificial means be employed, a mine can only be ventilated properly when it has at least two distinct openings to the surface, one an intake or " downcast," the other a See also:chimney serving as an " upcast." Two compartments of a shaft may be utilized for this purpose, but greater safety is ensured by two separate openings, as required by See also:law in most mining countries. The air underground remains throughout the year at nearly the same temperature, and is warmer in See also:winter and cooler in summer than the outside air. If the two openings in weight of the inside and outside air due to difference in temperature causes a current, and in the winter months large volumes of air will be circulated through the mine from this cause alone. In summer there will be less See also:movement of air and the current will frequently be reversed. In a mine with shafts opening at the same level, natural ventilation once established will be effective during See also:cold See also:weather, as the down-See also:cast will have the temperature of the outside air, while the upcast will be filled with the warm air of the mine. In summer this will occur only on cool days and at See also:night. When the temperature of outside and inside air becomes equal or nearly so natural ventilation ceases or becomes insignificant. In a mine with two shafts a ventilating current may result from other conditions creating a difference in the temperature of the air in either shaft—for example, the cooling effect of dropping water or the See also:heating effect of steam pipes. Natural ventilation is impracticable in See also:flat deposits worked by drifts and without shafts.
Ventilation may be produced by heating the air of the mine, as for example, by constructing a ventilating See also:furnace at the
bottom of an air shaft. The efficiency of such venerating ventilating furnaces is See also:low, and they cannot safely Furnaces.
be used in mines producing fire-damp. They are sometimes the cause of underground fires, and they are always a source of danger when by any See also:chance the ventilating current becomes reversed, in which case the products of See also:combustion, containing large quantities of carbon dioxide, will be See also:drawn into the mine to the serious danger of the men. On account of their dangerous See also:character furnaces are prohibited by law in many countries.
See also:Positive blowers and exhausting apparatus of a. great variety of forms have been used in mines for producing artificial
ventilation. About 185o, efficient ventilators of the Venttilatorsrl.
Me centrifugal type were first introduced, and are now ilato
the See also:discharge connecting with the mine air-way; in the more generally used exhaust See also:fan the inlet is connected with the air-way, the fan discharging into the See also:atmosphere. Among the exhaust fans most widely employed is the Guibal. Many others have been introduced, such as the See also:Capell (fig. 19), Rateau,
(From Mines and Minerals, See also: The Waddle may be instanced as an example of the open fans. Slow-speed fans are sometimes of large dimensions, up to 3C and even 45 ft. diameter, discharging hundreds of thousands of cubic feet of air per minute. Occasionally, at very gassy and dangerous collieries, two fans and driving engines are erected at the same air shaft, and in case of See also:accident to the fan in operation the other can be started within a few minutes. Opposed to the See also:motive force producing the air current is the frictional resistance See also:developed in passing through the mine workings. This resistance is equal to the square of the velocity of the current in feet per minute, o fAiration multiplied 'by the See also:total rubbing or See also:friction surface of Air of the air-ways in square feet and by the coefficient of friction. The latter, determined experimentally, varies with different kinds of surfaces of mine workings, whether rough or smooth, timbered or unlined; it ranges from o.00000000r872 to o•000e000arq lb per sq. ft., the latter being the value usually adopted. A certain pressure of air is required to maintain circulation against the resistance, and for a given See also:volume per minute the smaller and more irregular the mine openings the greater must be the pressure. The pressure is measured by a " water-See also:gauge " and the velocity of flow by an " See also:anemometer." The power required to circulate the air through a mine increases as the See also:cube of the velocity of the air current. To decrease the velocity, when large volumes of air are required, the air passages are made larger, and the mine is divided into sections and the air current subdivided into a corresponding number of See also:independent circuits. This splitting of the air not only lessens the cost of ventilating, but greatly increases its efficiency by permitting the circulation of much larger volumes, and has the added See also:advantage that the effect of an explosion or other accident vitiating the air current is often confined to a single See also:division of the mine, and affects but a small part of the working force. The See also:adjustment of the air currents in the different splits is affected by regulators which are placed in the return air-ways, and See also:act as throttle valves to determine the volume of air in each case. The circulation of air in any given division of the mine is further controlled and its course determined by temporary or permanent partitions (" brattices "), by the erection of stoppings, or by the insertion of doors in the mine passages and by the use of special air-ways (see COAL). In devising a system of ventilation it is customary to subdivide the workings so that the resistance to the ventilating current in each split shall be nearly equal, or so that the desired amount of air shall be circulated in each without undue use of regulating appliances which add to the friction and increase the cost of removing the air. In addition to this it is desirable to take advantage of the natural ventilations that is, to circulate the air in the direction that it goes naturally, as otherwise the resistance to the movement of the air may be Natural to the mine are at different levels the difference Ventilation. almost universally employed where the circulation of large volumes of air is necessary, as in collieries. The typical mine fan consists of a shaft upon which are mounted a number of vanes enclosed in a casing; the air entering a central See also:side inlet is caught up by the revolving vanes and thrown out at the periphery by the centrifugal force thus generated. " Open-running " fans have no peripheral casing, and discharge freely throughout their entire circumference; in " closed " fans the revolving part is completely enveloped by a See also:spiral casing opening at one point into a discharge chimney. Fans either force air into or exhaust it from the mine. The inlet opening of the pressure fan is in See also:free communication with the outside air, greatly increased. So far as possible, vitiated air is led directly to the shaft instead of passing through other workings; for example, mine stables when used are placed near the upcast shaft and ventilated by an independent split of the ventilating current. Deep Mining.—There has been much See also:speculation as to the depth to which it will be practicable to push the work of mining. The special difficulties which attend deep mining, in addition to the problems of hoisting ore and raising water from great depths, are the increase of temperature of the rocks and the pressure of the overlying strata. The deepest mine in the world is No. 3 shaft of the Tamarack mine in See also:Houghton See also:county, See also:Michigan, which has reached a vertical depth of about 5200 ft. Three other shafts of the Tamarack See also:Company, and three of the neighbouring See also:Calumet and Hecla mine, have depths of between 4000 and 5000 ft. vertical. The See also:Quincy mine, also in Houghton county, has reached a vertical depth of nearly 4000 ft. In See also:England are several collieries over 3000 ft., and in See also:Belgium two are nearly 4000 ft. deep. In See also:Austria three shafts in the silver mines at Prizbram have reached the depth of over moo metres. At See also:Bendigo in See also:Australia are several shafts between 3000 and 4000, and one, the See also:Victoria See also:Quartz mine, 4300 ft. deep. In the See also:Transvaal See also:gold region (South Africa), a number of shafts have been sunk to strike the See also:reef at about 4000 ft. In most cases the deposits worked are known to extend to much greater depths than have been reached. The possibility of hoisting and pumping from great depths has been discussed, and it remains now to consider the other conditions which will tend to limit mining operations in depth—namely, increase of temperature and increase of rock pressure. Observations in different parts of the world have shown that the increase of temperature in depth varies: in most localities the rise being at the See also:rate of one degree for 50 to 100 feet of depth; while in the deep mines of Michigan and the See also:Rand, an increase as low as one degree for each 200 ft. or more has been observed. In the Comstock mines at See also:Virginia See also:City, See also:Nevada, it is possible to continue mining operations at rock temperatures of 130° F. In these mines a constant supply of pure air, about moo cub. It. per minute, was blown into the hot working places through light iron pipes. The air issuing from these pipes was dry and warm, and served to keep the temperature of the air below 120°, at which temperature it was possible for men to work continuously for See also:half an See also:hour at a time, and for four hours in the day. In some places work was conducted with rock temperatures as high as 158° F., with air 135° F. In these very hot drifts the fatality was large. In the Alpine tunnels, where the air was moist and probably not as pure as in the Comstock mines, great difficulty was experienced in prosecuting the work at temperatures of 90° F. and less. The mortality was large, and it was believed by the See also:engineers that temperatures over 104° would have proved fatal to most of the workmen. Deep mines, however, are generally dry, so that in most cases it will be possible to realize the more favourable conditions of the Comstock mines. Assuming an initial mean temperature of 5o° F., and increments of one degree for Too and for 200 ft., a rock temperature of 130° will be reached at 8000 to 16,000 ft. In many deep mines to-day " explosive rock " has been encountered. This See also:condition manifests itself, for example, in mine pillars which are subjected to a weight beyond the limit of See also:elasticity of the mineral of which they are composed. Under such conditions the See also:pillar begins to yield, and fragments of mineral fly off with explosive violence, exactly as a specimen of rock will splinter under pressure in a testing See also:machine. The flying fragments of rock have frequently injured and sometimes killed miners. A similar condition of See also:strain has been observed in deep mines in different parts of the world—perhaps due to See also:geological movements. Assuming a weight of 13 cub. ft. to the ton, then at 6500 ft. the pressure per sq. ft. will be 500 tons, and at 13,000 ft. T000 tons; and as the mineral is See also:mined the weight on the pillars See also:left will be proportionately greater. At such pressures all but the strongest rocks will be strained beyond their limit of elasticity. At depths of See also:I000 ft.and less some of the softer rocks show a tendency to flow, as exhibited by the under-See also:clay in deep coal-mines, which not infrequently swells up and closes the mine passages. In the Mont Cenis tunnel a bed of soft See also:granite was encountered that continued to swell with almost irresistible force for some months. The pressure developed was sufficient to crush an arched lining of two-See also:foot granite blocks. Similar swelling ground is not infrequently met with in metal mines, as, for example, in the See also:Phoenix copper mine in Houghton county, Michigan, where the force developed was sufficient to crush the strongest timber that could be used. In very deep mines this flowing of soft rock will doubtless add greatly to the difficulty of maintaining openings. What may happen in some cases is illustrated by the curious form of accident locally known as a " bump," which occurs in some of the deep coal-mines of England. In one instance (described by F. G. Meacham, Trans. Fed. Inst. M.E: v. 381), the force developed by the swelling under-clay See also:broke through and lifted with the force and suddenness of an explosion a lower See also:bench of coal 8 ft. thick in the bottom of a gangway 12 ft. wide for a length of 200 ft., throwing men and mine cars violently against the roof and producing an air-See also:wave which smashed the mine doors in the vicinity. It is apparent that the combined effect of See also:internal See also:heat and rock pressure will greatly increase the cost of mining at depths of 8000 or 10,000 ft., and will probably render mining impracticable in many instances at depths not much greater. Mine See also:Administration.—In organizing a mining company it must be recognized that mining is of See also:necessity a temporary business. When the deposit is exhausted the company must be See also:wound up or its operations transferred to some other locality. Mining is also subject to the risks of ordinary business enterprises, and to additional risks and uncertainties See also:peculiar to itself. The vast majority of mineral deposits are unworkable, and of those that are developed a large proportion prove unprofitable. In addition mining operations are subject to interruption and added expense from explosions, mine fires, flooding, and the caving-in of the workings. To provide for the repayment from earnings of the See also:capital invested in a mining See also:property and expended in development, and to provide for the depreciation in value of the plant and equipment, an amortization fund must be accumulated during the life of the mine; or, if it be desired to continue the business of mining elsewhere, a similar fund must be created for the See also:purchase, development and equipment of a new property to take the place of the See also:original deposit when that shall be exhausted. If, for example, we assume the life of a given mine at ten years and the rate of interest at 5 %, it will be necessary that the property shall See also:earn nearly 13% annually—viz., 5% interest and 8 % for the See also:annual See also:payment to the amortization or the reserve fund. To See also:cover the special risks of mining, capital should earn a higher interest than in ordinary business, and if we assume that the sinking-fund be safely invested, we must compute the amortization on a lower basis than 5 %. Assuming, for example, the life of the mine at ten years as before, and taking the interest to be earned by the amortization fund at 3%, and that on the investment at to%, we shall find that the annual income should amount to 18.7% per year. These simple business principles do not seem to be generally recognized by the investing public, and mines, whose earning capacity is accurately known, are frequently quoted on the stock markets at prices which cannot possibly yield enough to the purchaser to repay his investment during the probable life of the mine. Mine Valuation.—The value of any property is measured by its annual profits. In the case of mining properties these profits are more or less uncertain, and cannot be accurately determined until the deposit has been thoroughly explored and fully developed. In many instances, indeed, profits are more or less uncertain during the whole life of the mine, and it is evident that the value of the mining property must be more or less speculative. In the case of a developed mine its life may be predicted in many cases with See also:absolute certainty—as when the extent of the mineral deposit and the volume of mineral can be measured. In other cases the life of the mine, like the value of the mineral, is more or less uncertain. Further, both time and See also:money are required for the development of the mining property before any profit can be realized. Mathematically we have thus in all cases to compute See also:present value on the basis of a deferred as well as a limited See also:annuity. The valuation of mines then involves the following steps: (T) The sampling of the deposit so far as developed, and See also:assaying of the samples taken; (2) The measurement of the developed ore; (3) estimates of the probable amount of ore in the undeveloped part of the property; (4) estimates of probable profits, life of the mine, and determination of the value of the property. Where the deposit is a regular one and the mineral is of fairly See also:uniform richness, the taking of. a few samples from widely separated parts of the mine will often furnish sufficient data to determine the value of the deposit. On the other See also:hand in the case of uncertain and irregular deposits, the value of which varies between very wide limits, as, for example—in most metal mines and especially mines of gold and silver—a very large number of samples must be taken—sometimes not more than two or three feet apart—in See also:order that the See also:average value of the ore may be known within reasonable limits of See also:error. The sampling of a large mine of this character may cost many hundreds of pounds. This applies with even greater force to estimates of undeveloped portions of the property. If the deposit is regular and uniform, the value of undeveloped areas may sometimes be predicted with confidence. In the majority of instances, however, the estimates of undeveloped ore contain a large See also:element of uncertainty. In order to determine the probable profit and life of the mine a definite scale of operations must be assumed, the money required for development and plant and for working capital must be estimated, the methods of mining and treating the ore determined, and their probable cost estimated. Where the deposit is uncertain and the element of risk is large, we must adopt a high rate of interest on investments of capital in our computations of value—in some cases as high as to, 15 or even 20 %. Where the deposit is regular and the future can be predicted with some degree of certainty, we may be justified in adopting in some cases possibly as low as 5 %. The interest on the annual contribution to the sinking-fund or its See also:equivalent should be reckoned at a low rate of interest, for such funds are assumed to be invested in perfectly safe securities. See also:Allowance must be made for the See also:period of development during which there are no contributions to the sinking-fund and within which no interest is earned on invested capital. Mining See also:Education.—It is necessary to have the work directed by men thoroughly See also:familiar with the characteristics of mineral deposits, and with wide experience in mining. For the purpose of training such men special See also:schools of mining engineering (ecoles See also:des mines, Bergakademie) have been established in most mining countries. A student of mining must receive thorough instruction in See also:geology; he must study mining as practised in different countries, and the metallurgical and mechanical treatment of minerals; and he should have an engineering education, especially on mechanical and See also:electrical lines. As he is called upon to construct lines of transport, both underground and on the surface, works for water-supply and drainage, and buildings for the handling, storage and treatment of ore, he must be trained to some extent as a See also:civil engineer, As a See also:foundation his education must be thorough in the natural and See also:physical sciences and See also:mathematics. In addition there have been established in many countries schools for the education of workmen, in order to See also:fit them for See also:minor positions and to enable them to work intelligently with the engineers. These miners' schools (Bergschule, ecoles des mineurs) give elementary instruction in See also:chemistry, physics, See also:mechanics, See also:mineralogy, geology and mathematics and See also:drawing, as well as in such details of the See also:art of mining as will best supplement the See also:practical See also:information already acquired in underground work. The training of a mining engineer merely begins in the schools, and mining graduates should serve an See also:apprenticeship before they accept responsibility fcr important mining operations. It is especially necessary that they should gain experience in management of men, and in the conduct of the business details, which cannot well be taught in schools. Accidents.—Mining is an extra-hazardous occupation, and the catastrophes, which from time to time have occurred, have caused 1900 OC ATII ARIDGE agencies to enforce their authority. While in some cases these See also:laws are unnecessarily stringent and tend to restrict the business of mining See also:Kiss on the whole they have had the effect of reducing greatly the loss of life and injuries of miners where they have been well enforced. This is evident from fig. 20, which shows the number of men killed in the coal and metal mines of Great Britain for a series of years. As will be seen from this See also:diagram the most serious source of death and injury is not found in mine explosions, but in the fall of rocks and mineral in the working places. This danger can be reached only in small degree by laws and inspection; but the safety of the men must depend upon the skill and care of the miners themselves and the See also:officers in See also:charge of the underground work. Great loss of life and injury occur through the See also:ignorance, carelessness and recklessness of the men themselves, who fail to take the necessary precautions for their own safety, even when warned to do se. Mining laws have proved chiefly serviceable in securing the introduction of efficient ventilation, the use of safety-lamps, and of proper explosives, to lessen the danger from fire-damp and coal-dust in the coal-mines, the inspection of machinery for hoisting and haulage, and prevention of accidents due to imperfection in design or in working the machinery. Fire-damp and dust explosions are caused by the presence of marsh-gas in sufficient quantity to form an explosive mixture, or by a mixture of small percentages of marsh-gas Explosions. and coal-dust, and in some cases by the presence of coal-dust alone in the air of the mine. Explosive mixtures of marsh-gas and air may be fired by an unprotected light. But when coal-dust is present, and little or no marsh-gas, an initial explosion —such as is produced by a blown-out shot—is required. To guard against explosions from this cause it is necessary to use explosives in moderate quantities and to see that the blast-holes are properly placed, so that the danger of blown-out shots may be lessened. In dry and dusty mines the danger may be greatly lessened by sprinkling the working places and passages, and the removal of the accumulated dust and See also:fine coal. Where large quantities of fire-damp are present, safety-lamps of approved See also:pattern must be used and carefully inspected daily. The use of matches and naked lights of any See also:kind must be prohibited. To lessen the danger from blasting operations the use of special safety explosives is required in Great Britain and some European countries. The use of such explosives decreases to some extent the danger from dust explosions; but experiment shows that no efficient explosive is absolutely safe, if used in excessive quantity, or in an improper manner. Absolute See also:security is impossible. as is proved by the many and serious disasters under the most stringent laws and careful regulations that can be devised. Mine fires may originate from ordinary causes, but in addition they may result from the explosion of fire-damp or from the accidental See also:lighting of jets of fire-damp issuing from the coal. Mine Fires. In some mining districts the coal is liable to spontaneous combustion. A fire underground speedily becomes formidable, not only in coal but also in metal mines, on account of the large quantity of timber used to support the excavations. Underground fires may sometimes be ,extinguished by direct attack with water. The difficulty of extinguishing an underground fire in this way is, however, very great, as on account of the poisonous products of combustion it is impossible to attack it except in the See also:rear, and even there the men are always in great danger from the reversal of the 0 49 ^~~®~~~~^~~~~~~~~ 111101 RR: r' m `mi 1,111 POI El IN II El i i IIAITIMIM I~i~'M .PH -,II i I III L 11111111 PH Ii P 1111 Ltd ii I II 111111 !II Ii P11 111:11111111 IyI 111 III' II 1I I ,III See also:Ili 'i ll I II 11 i i~ r# 111® fllI II See also:ICI II! Ili trot VI I I III :11 I'I ,III Al IMO 'II1' II11 .X19 iii ilia 11.i1J ~ I I ICI II' III! 1~ 1 lil 1873 1875 1876 187.7 1878 0[A 1000 1879 118 80 1881 1882 1883 1884 1885 1886 1887 1888 1889 1890 1891 1892 1893 1894 1895 1896 1897 1898 1899 27$ 250 22$ 2411 1.7$ 1.50 I.2$ 1 •oe .75 •5a .25 .00 250 2.25 2.00 I.75 1.50 125' ,.00 .75 • 50 I or R u p1ooR FALLS or GROUND[' SHAFT ACCIDENTS OMISCEDERGROUND LLANEOUS 00N• SURFACE ..y"'-ALC ACCIDENTS. IN AND ABOUT MINES. Additional information and CommentsThere are no comments yet for this article.
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