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FAG

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Originally appearing in Volume V18, Page 540 of the 1911 Encyclopedia Britannica.
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FAG. 13.—Standard FIG. 14.—Flat round Rope. Rope. (From The Colliery Engineer, May 1897.) carrying the grooved sheaves over which the hoisting ropes ,pass, is known as the head-gear (fig. 15). In Great Britain and her colonies it is also called the poppet-head or pit- Hesdgear head frame; in the United States head-frame or gallows-frame. Though it is small and simple in construction for light work, for heavy hoisting at high speeds massively framed towers, often 8o to Poo ft. in height, are built. Steel frames are more durable than those of wood, and have become common in nearly all mining countries, especially where timber is scarce. A German 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 works. Cages, running in guides in the shaft, are used for raising the cars of mineral to the surface (fig. 17). They may have one, two or more decks, usually carrying one or two cars on each deck. Multiple-deck cages are cages . s and Skip rarely employed except for deep shafts of small cross-section or when the mine cars (tubs) are small, as in many parts of 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 Butte, Montana, in the Lake Superior copper district, and in South Africa. Fig. 18 is a small skip; the upper illustration showing position for dumping. The lower cut is of a skip for either ore or water; note valve in bottom. Hoisting buckets or kibbles are employed for small scale work or temporary service, such as raising the material blasted in sinking shafts. They hold from a few hundred pounds up to 1 ton. In hoisting from great depths the weight of the rope, which may exceed that of the cage and contents, produces excessive variations in the load on the engine difficult to deal with. Moreover, the limit of vertical 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 silver mines. Wellman- Chalmers Co., Milwaukee, Seaver-Morgan Co., Cleveland, Wisconsin, makers. 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.' 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. 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 time is saved. In shallow mines the men use the ladder-way in going to and from their work. This is sometimes the case also for considerable depths. It is more economical Rflgootster}ng ngand to 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 size generally used in 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 special man-cages are operated in separate compartments by their own engines for handling 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 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 long frames on four wheels, with a series of seats like a section of a theatre gallery. Ordinarily 4 or 5 men occupy each seat, the 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 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 place and attached to the rope. This change may be made in a few minutes. Formerly, at many deep 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 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 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 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 rod, he steps over on to the latter during the instant of rest 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 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 world. Their first cost is great and they are dangerous for new men, as they require 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. (April 4, 1903), pp. 517 and 518. Surface Handling, Storage and Shipment of Minerals.—To mine ore or 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 rail or water to concentration or metallurgical works for treatment, or to near or distant markets for sale, provision must be made for the economical loading of railway wagons or vessels, and for the temporary storage of the mineral product. For 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 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 year the mineral must be stored underground, or in great stock-piles on the surface. In coal mining the market demand varies in different seasons, and surface storage is sometimes necessary to permit regular work at the mines. For coal, iron ore and other cheap minerals, 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 Engineering Magazine, xiv. 275, xx. 157 and xxi. 657.) Mine Drainage.—A mine which has been opened by an adit tunnel or 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 modern mining conditions drainage tunnels have lost much of their former importance. Taking into account the risk attending all mining operations, which make necessary large interest and 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 main haulage roads, by which the water flows to a sump excavated at the pump shaft. In 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 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 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 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 balance in special shaft compartments by their own hoisting engine. With an efficient engine the cost per 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 line of rods passing down the shaft, commonly known as the Cornish system; (2) direct-acting pumps, in which the engine and pumping cylinders form a single unit, placed close to the point underground from which the water is to be raised. Cornish pumps are the oldest of the machines for draining mines; in fact, one of the earliest applications of the old Woolf and Newcomen engines in the 18th century was to pumps for deep mines. The engine works a massive counter-balanced walking-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 diameter by ro or 12 ft. stroke, are capable of raising millions of gallons per day. Cornish pumps are economical in running expenses, provided the driving engine is of proper design and the disadvantages incurred in conveying 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 American, Henry R. Worthington, are made of many different designs. Typically they are steam pumps, the steam and water cylinders being set tandem on the same bed frame, generally without fly-wheel or other rotary parts; they may be single cylinder or duplex, simple, compound or triple expansion, and having a higher speed of stroke are smaller in all their parts than Cornish pumps. For high heads the water cylinders, valves and valve chambers are specially constructed to withstand heavy pressures, water being sometimes raised in a single lift to heights of more than 2000 ft. Condensers are always required for underground pumps. Sinking pumps, designed for use in shafts in process of sinking, are suspended by wire ropes so as to be raised before blasting and promptly lowered again to resume pumping. Electrically driven pumps, now widely used, are convenient and economical. Mine pumps of ordinary forms may be operated by compressed air, and air-lift pumps have been successfully employed. Hydraulic pumping engines, while not differing essentially from steam pumps, must have specially designed valves in the power cylinder on account of the incompressibility of water. They can be used only when a 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 acid the working parts of the pump must be lined with or made of bronze or other non-corrosive material; or the acid may be neutralized by adding lime in the sump. Ventilation.—The air of a mine is vitiated by the presence of large numbers of men and animals and of numerous lights, each of which may consume as much air as a number of men. In mining operations explosives are used on a large scale and the powder gases contain large quantities of the very poisonous gas, carbon monoxide, a small percentage of which may cause death, and even a minute percentage of which in the air will seriously affect the health. In addition to these sources of contamination the air of the mine is frequently charged with gas issuing from the rocks or from the mineral deposit. For example, carbon dioxide occurs in some mines, and hydrogen sulphide, which is a poisonous gas, in others. In coal-mines we have to deal with " fire-damp " or marsh gas, and with inflammable coal dust, which form explosive mixtures with air and frequently lead to disastrous explosions resulting in great loss of life. The gases produced by such fire-damp or dust explosions contain carbon dioxide and carbon monoxide in large proportion, and the majority of the deaths from such explosions are due to this " after-damp " rather than to the explosion itself. The terrible effects of fire-damp have led to the 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 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 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 law in most mining countries. The air underground remains throughout the year at nearly the same temperature, and is warmer in 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 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 cold weather, as the down-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 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 heating effect of steam pipes. Natural ventilation is impracticable in 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 furnace at the bottom of an air shaft. The efficiency of such venerating ventilating furnaces is 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 chance the ventilating current becomes reversed, in which case the products of combustion, containing large quantities of carbon dioxide, will be drawn into the mine to the serious danger of the men. On account of their dangerous character furnaces are prohibited by law in many countries. 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 discharge connecting with the mine air-way; in the more generally used exhaust fan the inlet is connected with the air-way, the fan discharging into the atmosphere. Among the exhaust fans most widely employed is the Guibal. Many others have been introduced, such as the Capell (fig. 19), Rateau, (From Mines and Minerals, March, loos.) Schiele, Pelzer, Hanarte, Ser, Winter, Kley, and Sirocco fans. 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 accident to the fan in operation the other can be started within a few minutes. Opposed to the motive force producing the air current is the frictional resistance 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 total rubbing or 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 volume per minute the smaller and more irregular the mine openings the greater must be the pressure. The pressure is measured by a " water-gauge " and the velocity of flow by an " anemometer." The power required to circulate the air through a mine increases as the 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 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 advantage that the effect of an explosion or other accident vitiating the air current is often confined to a single division of the mine, and affects but a small part of the working force. The adjustment of the air currents in the different splits is affected by regulators which are placed in the return air-ways, and 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 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 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 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 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 Houghton county, Michigan, which has reached a vertical depth of about 5200 ft. Three other shafts of the Tamarack Company, and three of the neighbouring Calumet and Hecla mine, have depths of between 4000 and 5000 ft. vertical. The Quincy mine, also in Houghton county, has reached a vertical depth of nearly 4000 ft. In England are several collieries over 3000 ft., and in Belgium two are nearly 4000 ft. deep. In Austria three shafts in the silver mines at Prizbram have reached the depth of over moo metres. At Bendigo in Australia are several shafts between 3000 and 4000, and one, the Victoria Quartz mine, 4300 ft. deep. In the Transvaal gold region (South Africa), a number of shafts have been sunk to strike the 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 rate of one degree for 50 to 100 feet of depth; while in the deep mines of Michigan and the Rand, an increase as low as one degree for each 200 ft. or more has been observed. In the Comstock mines at Virginia City, 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 half an 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 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 condition manifests itself, for example, in mine pillars which are subjected to a weight beyond the limit of elasticity of the mineral of which they are composed. Under such conditions the 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 machine. The flying fragments of rock have frequently injured and sometimes killed miners. A similar condition of strain has been observed in deep mines in different parts of the world—perhaps due to 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 mined the weight on the pillars left will be proportionately greater. At such pressures all but the strongest rocks will be strained beyond their limit of elasticity. At depths of I000 ft.and less some of the softer rocks show a tendency to flow, as exhibited by the under-clay in deep coal-mines, which not infrequently swells up and closes the mine passages. In the Mont Cenis tunnel a bed of soft 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-foot granite blocks. Similar swelling ground is not infrequently met with in metal mines, as, for example, in the 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 broke through and lifted with the force and suddenness of an explosion a lower 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-wave which smashed the mine doors in the vicinity. It is apparent that the combined effect of internal 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 Administration.—In organizing a mining company it must be recognized that mining is of necessity a temporary business. When the deposit is exhausted the company must be 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 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 capital invested in a mining 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 purchase, development and equipment of a new property to take the place of the 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 earn nearly 13% annually—viz., 5% interest and 8 % for the annual payment to the amortization or the reserve fund. To 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 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 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 present value on the basis of a deferred as well as a limited annuity. The valuation of mines then involves the following steps: (T) The sampling of the deposit so far as developed, and 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 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 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 order that the average value of the ore may be known within reasonable limits of 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 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 equivalent should be reckoned at a low rate of interest, for such funds are assumed to be invested in perfectly safe securities. Allowance must be made for the period of development during which there are no contributions to the sinking-fund and within which no interest is earned on invested capital. Mining Education.—It is necessary to have the work directed by men thoroughly familiar with the characteristics of mineral deposits, and with wide experience in mining. For the purpose of training such men special schools of mining engineering (ecoles des mines, Bergakademie) have been established in most mining countries. A student of mining must receive thorough instruction in 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 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 civil engineer, As a foundation his education must be thorough in the natural and physical sciences and mathematics. In addition there have been established in many countries schools for the education of workmen, in order to fit them for minor positions and to enable them to work intelligently with the engineers. These miners' schools (Bergschule, ecoles des mineurs) give elementary instruction in chemistry, physics, mechanics, mineralogy, geology and mathematics and drawing, as well as in such details of the art of mining as will best supplement the practical information already acquired in underground work. The training of a mining engineer merely begins in the schools, and mining graduates should serve an 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 laws are unnecessarily stringent and tend to restrict the business of mining 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 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 officers in charge of the underground work. Great loss of life and injury occur through the 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 fine coal. Where large quantities of fire-damp are present, safety-lamps of approved pattern must be used and carefully inspected daily. The use of matches and naked lights of any 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 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 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 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 Ili 'i ll I II 11 i i~ r# 111® fllI II 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.
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