{ "system": "GoGuides Verified Text", "api_version": "verified-text-v1", "status": "ok", "response_type": "verified_text_record", "source_key": "britannica_1926", "source_title": "Encyclopaedia Britannica (1926)", "license_code": "public_domain", "attribution": null, "license_url": null, "chunk_id": "1926:mining:bb56d0c79d5a", "title": "MINING", "section": null, "hash_alg": "sha256", "hash_sha256": "edb1d88376997f8cf998dee6227d3d1510551e1911321a09b354e3a18856aad0", "normalizer": { "name": "ggnorm", "version": "1.0" }, "verified_text": "since roto there has not been much change or development in the methods of working as applicd to the extraction of mineral ores and other substances from veins and stratified deposits. this is, perhaps, more particularly the case in regard to coal and stratified deposits than of metalliferous ores occurring in veins. the development in respect of the former lies chiefly in the direction of the machinery used in the mines and its application, more particularly at the working face, and especially that used in the getting and transporting the coal at the faces. | in the working of metalliferous veins, while the standard meth- ods of extracting the ore by overhand or underhand stoping have changed little, a more definite classification than existed formerly has grown up respecting the application of these methods to given local conditions. comparatively thin veins, with a steep pitch (dip), are developed by a series of drifts (levels), and above each of these overhand stopes are opened for extracting the ore, the working being advanced upward. the broken ore is run through chutes (mills or passes) to the level below, in which it is conveyed in trams by hand or mechanical power to the shaft or through an adit (tunnel) to the surface. for thicker veins, especially those with a steep dip, underhand stoping is occasion- ally employed, the advance being forward and downward toward the haulage level. in the case of flat veins or of bedded deposits breast-stoping is used, the details of which much re- semble those of underhand stoping. in all of these methods, the roof of the deposit (hanging wall) is supported by pillars of ore, by props, balks of timber (stulls), by “ square-set ” timbering or by masses of waste ore and rock (filling) carried by stulls. sometimes stopes are completely filled with waste. 926 shrinkage stopes.—there area variety of overhand stopes which have been more widely employed than formerly for both narrow and wide steeply dipping veins. in these stopes the broken ore accumulates until the stope is complete, thus making artiticial support for the walls of the stope unnecessary. since rock when broken increases in bulk, from 25 to 40°% of the ore is drawn from the stope as it advances to leave room at the top for the miners, who stand on the broken ore while drilling. this method is applicable only to those cases where the inclination and width of the vein are great enough to allow of the broken ore sliding down freely to the stope floor (footwall). finally, after all the ore has been drawn off, the stope is allowed to cave in or is filled with waste. in principle, the shrinkage stope is identical with the “ battery-breast,”” commonly used in fairly thick coal seams, when the pitch exceeds about 35° to the horizontal. caving systems.—the prototype of these, long employed in certain british iron mines, is known in the haematite iron ore mines of lancashire and cumberland as the caving system. in the united states caving was first used for the soft iron ores of northern michigan. more recently, it has been extensively ap- plied to the iron deposits of the mesabi district, minnesota, and to some large copper deposits in the south-west of the united states. the chief requisites for the successful application of caving methods are: (1) massive deposits of relatively cheap minerals; (2) ore-bodies of large horizontal dimensions, overlaid by a capping varying in character from earthy soil or glacial drift to firm rock; (3) large-scale work. ‘there are three distinct methods: top-slicing, block-caving and sub-level caving. the salient features of all are: (a) horizontal subdivision of the ore-body into floors; (#) subdivision of each floor into small slices or blocks which are mined separately; (¢) delivery of the broken ore through chutes to the haulage-ways below and thence to the shafts; (d) as the ore is removed, the overlying capping must gradually cave in and settle. the period 1910-25 was marked by a wider application of the slicing and caving methods, especially for large low-grade deposits of disseminated copper ore. more deposits of this type have been developed and worked in recent years than ever be- fore, many variations in details being introduced to suit the dimensions of the ore-body, its depth below the surface and the character of ore and of the super-incumbent strata or capping. all this has brought a more definite understanding of the ap- plicability and limitations of the caving systems, as determined by existing local conditions. some prominent examples of the newer mines, in which differ- ent forms of slicing and caving have been adopted, follow. inspiration mine, arizona.—the ore-body is a massive deposit of disseminated sulphide of copper (calcopyrite), containing about 100,000,000 tons of low-grade ore, and overlaid by a valueless cap- ping, 30 to 350 ft. thick. a variation of the caving system is used, known as ‘ block-caving.” the ore-body is intersected at vertical intervals of 150 {t. by main haulage levels, connecting with the yy capping f crvaler a day ¢ ycs pa (3 wea ka sevefapment raises yo” drawing raises 1 : ‘ % = s * “ye \" dritt holes in dr ift c) ** blasting drift (driven aubsequent to oy ) 4) 100 200 300 400 500 feat fic. i. a) haulage drift f) sublevel. development drift la a ” winding shafts (fig. 1). above the haulage levels are long chute- raises, inclined at 50° to the horizontal, from which numerous short secondary raises (‘‘ finger-raises ’’) are driven to a system of sub- level drifts, 35 ft. apart vertically and 50 ft. horizontally. the ore developed by the sub-!evel drifts is thus divided into small “ blocks,” mining which are undercut and broken up by blasting out the supporting pillars between the drifts. vhe broken ore is drawn down through the branching finger-raises underneath, into the main raises and thence to the haulage levels, the flow being coantrealled by gates. as the upper part of the ore-body is thus removed, the capping caves in on top of the solid unmined ore below. (for full details, see 7'rans, amer. inst. mining fing,, vol. 55, p. 218: vol. 59, pp. 299, 305; vol. 66, p. 127.) block-caving, similar to that of the inspiration mine, is also used by the ohio copper co., bingham, utah, and the nevada consolidated copper co., ely, nev. «lrisona copper co.—a top-slicing method (fig. 2} is applied to large bodies of soft ore, carrying 2 to 4% copper. a main haulage original surface z 7 sy, y arms as lp ae 8 ly ~ 4 bars \". z cpe es dls! aee h- =; ao oor a ei eee diba ete ete se tea : i 0 gt oak op ae > z pigs eh ere son oe sig hg eke be ; ts bit to rt 3 ~ pap solas , 11 c) w 8 6. 9 3 v easstg tes ed eg yr thu vast e///7 7, tes sill pds let sarr haaige revel sgcgeesvy longitudinal section vertical cross section fic. 2. road is driven near the bottom of the ore-body, and above it are intermediate working levels, 50 to 60 ft. apart vertically. these comprise a rectangular system of trammming drifts and cross-cuts, from which chute-raises are made into the ore above at 25 ta 30 ft. intervals. starting from the tops of these raises, horizontal slices of ore, 7 to 15 ft. thick, are blasted out and the broken ore is run down through the raises to the tramming level. thence it is conveyed to the nearest main raise, connecting with the haulage road below. (for details of the slicing operations and the manner in which the overlying capping caves in as the successive slices are removed, see 18.532.) these modifications of top-slicing consist chiefly in making raises from the intermediate tramming levels at short intervals, to minimise the labour cost of handling the ore mined in the slices. in one of the arizona copper co.'s mines a further saving has been effected by omitting the tramming levels and the small raises from them. a main drift is driven longitudinally through the axis of the ore-body, just below the roof or capping, and from it, at right angles, cross- cuts, 40 ft. apart, to the walls. the pancls or blocks of ore between the cross-cuts are sliced back from the walls of the ore-body towards the main drift. on each side of the latter a pillar is left; which is finally sliced back from its end, in completing a floor. while one floor is being mined, the next, 11 ft. below, is in preparation. this method of panel slicing has recently been adcepted successfully in the hlerman gold mine, california. the vein dips 45° to 60°, and the pancls are laid out at an inclination of 52°, across the ore-body. top- slicing is also use| in many massive deposits of low-grade copper ore; for example: cumberland-ely, nev.; cananea, mexico; miami, ariz.; bingham, utah; and mines of the calumet & arizona mining co., arizona, at the last-named property, the older caving method has been replaced by a modification called the mitchell top-slicing system, found economical in reducing the shovelling required. other varrations.—in a number of important mines working large ore-baclies, spectal conditions have been dealt with by combining two or more of the methods referred to above. examples are to be found in the mines of the braden copper co., chile; new jersey zinc co., franklin, n. j.; utah copper co. (boston mine); ray consol, cop- per co., ariz.; homestake gold-mining co., s.d., and the de beers mining co., south africa. in most cases, operations begin by shrink- age stoping, after which the intervening pillars are mined by top- slicing, block-caving or sub-level caving, the object aimed at being the getting of as high a total tonnage extraction as possible, that is, obviating loss occasioned by leaving ore in permanent pillars or through mixture with waste material. stripping superficial ore deposits. —this old mode of attack- ing shallow deposits of large horizontal area was oftener resorted to in the period roro-25 than previously, and was applied to deeper ore-hodies than formerly were considered capable of being mined by stripping. stundard methods —standardisation of methods of working when practicable probably promotes efficiency and economy of mining operation. seams of coal and some regular bedded deposits of the base metals, owing to their comparative uniformity of geological occurrence, can be worked to a greater degree by standardised methods than most metallifcrous deposits, which vary greatly in their physical characteristics. a notable instance to the contrary is perhaps that of the banket deposits of the rand, transvaal, which are in the nature of highly inclined beds of conglomerate. (sce the useful discussion by c. a. mitke, “mining methods of the united verde extension mining com- pany, arizona,” trans. amer. tust. mintug engs., vol. 61, p. 188.) in the three years 1922-5 a ‘‘ committee of one hundred ” of the amer. inst. mining engs. (comprising 13 sub-committees) collected and published descriptions of the mining methods in the principal districts of the united states. it was planned to classify these data, with a view still further to standardise mining practice for the different kinds and shapes of ore deposit. in many mining operations there is a stronger tendency toward standardisetion of details. thus, some mining companies have adopted standard “rounds” of holes for shaft-sinking, drifting, cross-cutting, raising and stoping. the foremen are furnished with instruction sheets which specify the position, depth and charge of explosive for each hole. the miners are required to follow these instructions instead of doing their work in accordance with their own individual ideas. the adoption of such methods has been assisted by the greater attention now given to what may be termed efficiency engineering. many large mines have “ efficiency engineers,” who study in detail the performance of both men and machinery, thus improving the quality and amount of work done. in great britain too, quite lately, attention is being directed in some enlightened quarters to the psychological side of mining with a view to ensuring greater efficiency. directed toward this end also are the movements inaugurated by several mining companies to instruct their employees in the best methods of doing their work, thus, an education department is maintained by the phelps-dodge corp., of new york, which oper- ates a number of mines in the southwest of the united states. lec- tures are delivered to the miners on practical mining topics, followed by examinations. the north butte mining co., of montana, has also standardised the details of many underground operations, the cost of these education departments is considerable, but is amply justified by the results. a wholesome spirit of rivalry is encouraged amongst the miners and their ambition is aroused; hence, better work is done, the morale of the whole force is raised, and better rela- tions are established between the employces and the mine manage- ment. the principles of standardisation have also been increasingly applied to the design of mining appliances and machines. blasting —explosives for blasting rock and ores underwent considerable change in composition during 1915-25, and tests have supplied valuable data respecting the disruptive and propulsive forces and the sensitiveness of the types and grades of dynamite, leading to a better understanding of their suitability for different kinds of service. explosives for coal-mines, especially those in which dangerous gases occur or which are dry and dusty, must be so constituted that ordinary charges will not produce a flame of sufficient intensity and duration to ignite explosive mixtures of gas and air. these comprise the tested “permitted explosives,” lists of which are published in coal- mining countries and revised from time to time, to keep them up to date. in europe their use under certain conditions—condi- tions which exist in the majority of the coal mines—is required by law. in the united states the lists appear in publications of the bureau of mines. the bureau can only recommend them, though legal requirements exist in some of the states. “ permitted explosives ’ have certain characteristic ingredi- ents: (a) ammonium nitrate; (6) salts containing water of crys- tallisation, which, being liberated and vaporised by the heat of explosion, reduces the flame temperature; (c¢) organic nitrate other than nitro-glycerine, ¢.¢g., nitro-starch; (d) nitro-glycerine, mixed with free water or an excess of carbon. it was formerly assumed that nitro-glycerine compounds and other detonating explosives were not suitable for collieries, because, due to market requirements, excessive shattering of coal is undesirable (except for coke-making); but low-strength, ‘* short-flame ” dynamites 927 are now being satisfactorily used. while no explosive can be absolutely safe in gassy mines, those in the “ permitted ” lists are relatively safe. the standard tests vary as between countries; that of the united states, which is now given, is less drastic than that operative in great britain. in the u.s.a. an explosive is accepted for the list when a charge of 680 gm. (14 ib.) does not ignite gas or coal-cust; it is not accepted if a charge of 250 gm. does cause ignition. in 1912 the permitted list of the u.s. bureau of mines comprised 96 kinds and grades of safety ex- plosive; in jan. 1924 the number had increased to 158, many being almost identical in composition. the united states is the largest user of “* permitted explosives ” in the world, the quantity consumed having more than doubled in ror2-25. blasting methods in the united states have been improved by the introduction of ‘f delay action ” electrical fuses. in work like tunnelling (cross measure or stone drifting) and shaft-sinking, where rounds of charged holes are best fired in volleys, these special fuses save time, as the miners need not return to the working place after each volley to prepare for the next. the en- tire round is wired, as if all the holes were to be fired simultane- ously, and there is but one application of the current. the groups of holes explode successively, in the desired order and at intervals of about one second, by using ‘‘ no-delay ”’ fuses for the first group and “‘ first-delay ’”’ and “‘ second-delay ” fuses for the following groups. in british coal-mining, volley firing of charges is not permitted by the laws regulating the industry. construction of delay fuses —the platinum bridge in the cap shell, between the terminals of fuse wires, is not embedded in the fulminating charge itself, so as to explode it directly, but ignites a short piece of slow-burning ordinary fuse, which in turn ex- plodes the fulminate. the delay interval depends on the length of ordinary fuse used. another new device for the same purpose is the electric fuse-igniter. a special electric cap contains a small charge of fine-grain black powder, beyond which is a piece of ordinary fuse, with a cap on the end to be placed in the dynamite cartridge. for blasting with black powder, no cap is put on the ordinary fuse. mine hygtene-——improvements made in the years 1910-25 were chielly in five directions: (1) better ventilation of mine workings; (2) enforcement of dust-prevention regulations and of regulations requiring the adulteration of coal-dust in the mine by the admixture therewith of inert dust; (3) introduction of new types of blasting explosives, so constituted as to minimise the quantity of deleterious gases evolved; (4) adoption of precautions with the object of producing more perfect combustion of explo- sives, and the consequent reduction or prevention of the forma- tion of the poisonous carbon monoxide; (5) study and better understanding of special miners’ diseases and their treatment. (see industrial welfare.) ventilation formerly, artificial ventilation by fans or blowers was provided only for collieries, to dilute and sweep out gases emanating from the coal and surrounding strata. in recent years, mechanical ventilators have been increasingly applied in the ventilation of metalliferous mines also. about the year 1902 the high mortality amongst the miners of some districts, especially on the rand, south africa, began to attract attention. investigation showed that acute lung trouble (‘‘ miner's phthisis \"’ or silicosis) is caused by inhaling dust from drilling in dry silicious rock or ore. in 1t903 a government commission was appointed to study the conditions in the transvaal gold-mines, their report led to a demand for better ventilation of the mine workings, and the adeption of water-spraying devices to allay the dust arising from the operation of drilling. revised and more stringent regulations were enacted in 913. other governmental investigations were made in cornwall and the ganister mines of the midlands, england, australia and new zealand, and in the united states by the bureau of mines, in 1911 one of the large gold-mining companics in the transvaal, the rand mines (ltd.), estabhshed a department of sanitation, to deal in general with miners’ living and working conditions and diseases. the department's activities now cover a large number of the mines of the district, employing between 55,000 and 65,000 men, and marked benefits have resulted from this important movement, which is gaining in strength. tests of the gases from blasting explosives have revealed the extent to which they may vitiate mine air. one pound of g28 standard dynamite produces about to cu. ft. of gas, which, due to incomplete detonation, often contains 25 to 30% of carbon monox- ide. since, for safety, this actively poisonous gas should be diluted to about o-o1 of 1%, it is evident that natural ventilation cannot always be relied upon, and mechanical ventilators have been installed for many metalliferous mines. several new types of high explosives have recently been introduced, so compounded that they produce much less carbon monoxide (co) and methane .(ch,) than the standard (“ straight ”) dynamites. they are therefore particularly useful in poorly ventilated mine workings, as headings where, in order to secure ventilation (in coal mines), bratticing or air pipes are necessary. furthermore, there has been increased insistence on the use of high-strength caps or detonators, since imperfectly detonated explosives of all kinds produce an excessive amount of carbon monoxide. explosions in coal afines.—advances have taken place in the appliances for fighting mine fires, in the modes of preventing and dealing with gas and dust explosions in collicries and in the design of safety lamps. coal dust explosions are generally much more serious in bituminous than in anthracite mines. most ex- plosions in anthracite mines are of gas, sometimes aided by pres- ence of dust. many investigations of coal-dust explosions have been made tn europe since 1880, but some of the phenomena attending their initiation and propagation have long been im- perfectly understood. since professor galloway (afterwards sir william galloway) first drew attention, about 1880, to the dangers arising from coal dust and the brothers atkinson (inspectors of mines) wrote their book on colliery explosives, sir william garforth, after the altofts explosion in yorkshire, described the arresting effects of stone-dust on the explosive blast, and thereafter the mining association of great britain established a plant near altofts for carrying out large scale experiments and did excellent work. eventually the ifome office took over the plant and, transport- ing it to eskmeals in cumberland, added to it and extended the scale of the experiments. the results of the elaborate work of the tome office commit- tees, extending over the period 1910-4, was published before the world war, and after the wara comprehensive set of regulations was established by the british govt. for the purpose of re- ducing the accumulations of coal-dust in the mine and render- ing such dust as remains uninflammable by reason of the admix- ture of inert and innocuous dust in stated proportions and of a specified fineness. experiments were also carried out at the lievin testing station in france, commencing in 1907, and later in belgium and in germany, and by the u.s.a. bureau of mines at their testing plant and brunton experimental mine, near pittsburgh (since 1909). amongst the facts demonstrated are:— (a) the blasting of a single hole, charged with long-flame ex- plosive (gunpowder or high explosive), may cause the ignition of coal- dust; (b) respecting the initiation of an explosion, if enough dry coal- dust is present, it is immaterial whether the air at the point of origin is quiescent or moving in either direction; (¢) quantitics of dust as small as 14 oz. per cu. ft. of space (or 1 lb. per linear ft. of an ordinary roadway in the mine) will propagate an explosion; (¢) in presence of sufficient dust, an explosion may be produced at will in a roadway, even when the roof, sicles and floor are wet to the touch owing to the presence of dry dust on the timbers, etc.; (e) the force of a coal-dust explosion usually increases in violence as it is propagated through a mine working and may reach its maximum after travelling 500 to soo {t. from the place of origin; (f) pressures as high as 120 |b. per sq. in. have been measured at right angles to the direction of movement of an explosion, the pressure in the line of advance being doubtless much greater. stone-dust barricrs—stone-dust barriers, for checking or preventing the propagation of coal-dust explosions, were devised by j. taffanel and modified by g. s. rice, of the u.s. bureau of mines, but constitute a doubtful safeguard. they consist of scries of wide shelves, set across the mine gangway near the roof, each loaded with rock-dust. the shelves are tripped mechani- cally by the advance force waves of an explosion, being set to operate at certain air velocities produced by the explosion. from two to three tons of rock-dust are thus discharged in a dense cloud, in front of the advancing explosion wave, and, mixing with mining the coal-dust-laden atmosphere of the gangway, prevent propa- gation of the explosion. it would appear that the only really safe precaution to take is the thorough admixture with the coal-dust of the fine stone-dust. it was until quite recently considered that the presence of 30% of inert dust secured safety, but the most recent experiments of professor wheeler, of the british mines department of safety of the mines’ research board, shows that this may prove insufficient with coal-dust of high volatile content, and that as much as 50% or more may be necessary in some cases. great interest in “stone dusting’? is now being manifested in mining circles. see the publications issued by the british mines department and the u.s. bureau of mines, bull. no. 225 (1924). gas helmets, ctc —gas helmets and oxygen breathing-appara- tus, long used in mine rescue work, have undergone consider- able improvement in point of construction, though no new principle can be said to have been evolved. winding eengines—dpower plants (frequently hydroelectric except in the case of great britain) have been established in many mining districts, and supply electric current at cheaper rates than are possible for equivalent steam power. flectric- driven winding engines are consequently used in much greater numbers than formerly and in great britatn, though electricity is seldom obtainable from water power, electric hoists have increased in use at collieries which have in some instances established large power plants, ¢.g., at powell duffryn colliery in south wales. the control mechanism of electric winders is so perfected that these engines are as manageable as the best steam winding engines. the large variations in load, unavoidable in winding operations, and very disadvantageous for electric trans- mission of power, are successfully dealt with by the “ equalising systems ” of winding or hoisting, the first of which, the siemens- ilgner, was introduced just previous to 1906. modifications of it, based chiefly on the mode of control, are the westinghouse and the ward-leonard. the design and operation of all of these devices are based on the principle that, when a motor receives electric current, it will deliver mechanical power; conversely, when driven by mechanical power, the motor becomes in effect a generator and furnishes electric current. the alternating cur- rent usually supplied to a mine is first reduced to about 500 volts and then goes to a motor-generator set, comprising a shunt or induction motor, which drives a direct-current generator and a heavy fly-wheel, all on a common shaft. this set is in constant motion, though not at constant speed. from the generator the current gocs to a winding engine motor, which drives a pair of drums on the drum shaft. at the beginning of a winding cycle, the winding engine motor receives current from the motor-generator set; but, after the descending cage has reached a point where the trip can be completed by the weight of the rope, the winding engine motor is driven by the drum, and therefore supplies current to the genera- tor of the motor-generator set. thus, part of the recovered power is stored in the fly-wheel, while the remainder is expended in driving the induction motor as a generator, thercby causing it to deliver current to the external circuit or power service. the fly-wheel cuts down the peaks of the load curve. since rors, a number of these plants have been erected; they are costly and suitable only where the hoisting is nearly continuous and high peak loads are heavily penalised in the power service. underground haulage-—yor locomotive haulage, the electric trolley system was in 1925 still first in importance, though the use of this system is not permitted in gassy and dusty coal- mines in great britain; next to this were the compressed-air locomotives, very rarely used in great britain, if at all. storage- battery locomotives, though invented many years ago, were rarely used until about torr and in 1925 were employed to a lim- ited extent only in the mines of the united states and the con- tinent of europe; their use in british coal mines is at the present time under consideration and a prize was recently offered for a safe and practical locomotive. their construction is simple, and, as they carry their power with them, they have the advantage of being able to operate mining wherever a rail track is laid, without the necessity of erecting a trolley wire. they are best suited to short distance haulage and light service, as for gathering individual tubs or cars from the working places and making them up into trains or sets on the main haulage roads, or what is termed “ secondary haulage.” - the maximum speed is about five miles per hour and easy track gradients are necessary. their chief disadvantage is high first ~ pops 35555 sss le wee eo et sot id as a a oes 9g elta eee : 4a ‘ i is reales 2 ieee * 3 ii srp “3 s°a 7.2