The New International Encyclopædia/Mining

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MINING. The art of obtaining from the earth the metallic ores and other useful minerals in an economical and profitable manner. The earliest metals employed by man were those found in the native state. Gold is the most widely distributed of these, and has been mined and utilized from very remote times. Meteoric iron was also known and utilized by many ancient peoples, and the native copper of Lake Superior was extensively mined and utilized by the aborigines of America. As, however, the knowledge of metals increased and civilization advanced, the ores, or metals in combination, were recognized and utilized and mining proper began. Reference is made to mining in the Bible, and other ancient records prove that the Phœnicians navigated the seas as far as Cornwall, England, in order to obtain tin ores for the manufacture of bronze. The Romans had extensive mines for iron ore in the island of Elba that are still in operation. They also worked the great copper veins at the Rio Tinto, Spain, and the timbering left by them is still visible. The mines at Laurium, Greece, were famous in ancient times for their yield of silver. From the old mining districts of Cornwall and from the Erzgebirge (Ore Mountains) and the Harz Mountains in Germany miners have gone all over the world, and under their tuition the mining practice of to-day has grown up in all the newer districts.

Problems in mining to-day may be grouped into those relating to: (1) mining geology; (2) mining engineering; (3) mechanical engineering; and (4) metallurgy. The problems of each group overlap to some extent those of the other groups, but the division adopted serves for a general consideration of the subject of mining. In this article particular attention will be devoted to mining as involving the problems of mining engineering and mechanical engineering. These problems embrace the operations of discovering and locating mineral deposits, of opening the earth and excavating the ores, of transporting the ores to the surface, and of handling mechanically the ores during their metallurgical treatment. As, however, the handling of the ores preparatory to and during the processes involved in extracting the metals is of a different nature than mining proper and is frequently done at places far from the mines, these operations are considered in the article on Ore-Dressing and in the section devoted to Metallurgy in the articles on the various metals and the adjunct articles there mentioned.

Prospecting. The search for and location of deposits or veins of metal-bearing ores is called prospecting, and the men who perform this kind of work are called prospectors. The first procedure in prospecting a tract of land suspected to contain mineral wealth is thoroughly to traverse it and to note carefully the familiar indications of the presence of minerals. These indications are often numerous in kind for each mineral and they also vary for different minerals. Generally speaking, coal, gypsum, salt, and similar minerals occur in unaltered deposits, that is, in rocks which have not undergone metamorphism, while the metallic minerals are found in rocks that have undergone more or less metamorphism. These are among the broad indications of the presence or absence of certain minerals. The geological age of the rocks is in respect to certain minerals a pretty certain indication whether these minerals are likely to be found or not. For example, the bulk of the coal deposits of the world has been found in rocks of the Carboniferous age; they exist in rocks of subsequent ages, but almost never in rocks of preceding ages. Referring to specific indications, the prospector for coal will search for traces of smut or coal dust in the streams and water-worn banks, and for the presence of outcropping seams.

The presence of iron is indicated by mineral springs and rust-like stains of earth and rock. The presence or absence of vegetation may also indicate the existence of minerals; for example, a bed of phosphate rock is commonly indicated by a line of luxuriant vegetation and the outcrop of a mineral deposit by a lack of vegetation. Beds of magnetic iron are frequently located by their attraction for the magnetic needle. Placers are fragmental deposits from water in which the heavier minerals have been concentrated in certain portions, usually next the underlying or bed rock. When prospecting for placers the prospector examines the country for the presence of any existing or ancient watercourses in which deposits of placer material are likely to have been formed. Metallic gold and precious stones occur frequently in placers. In prospecting for petroleum, natural gas, and bitumen, the surface indications looked for are springs of petroleum oil and naphtha; porous rocks saturated with bitumen or cracks in slate and other rocks filled with the same material; springs, pools, or creeks showing bubbles of escaping gas or an iridescent coating of oil.

The presence of a mineral deposit having been established, the next procedure is to determine its extent and richness. The richness of the ore is determined by assaying average samples. (See Assaying.) To determine the thickness of the veins or beds and their lateral extent, borings are sunk at more or less close intervals and records taken of the continued presence of the ore vein and of its thickness. These coupled with a geological survey of the region give fairly reliable data as to the quantity of ore and its location with respect to the ground surface. Upon these data the miner estimates the value of the deposit and decides whether it will pay to work it or not.

If the deposit is located on Government land, a ‘claim’ of variable size, according to the laws of the country or district, is staked out, and when this is opened up sufficiently to have necessitated the expenditure of a certain specified sum of money, a permanent title can be obtained. In the Western States of the United States claims usually extend 1500 feet along the vein, and either 150 feet or 300 feet on each side of it. The owner can then follow the vein where it leads him between the vertical planes of his end lines. The outcrop is called the apex. As, however, veins are so irregular and obscure underground, great uncertainty may arise as to title, and expensive litigation may ensue. For these reasons many authorities consider it better practice to adopt square claims, say 1500 feet on each side, conveying the rights to all the ore lying vertically beneath them. This is the practice in Western Canada and is practically so in most Eastern States of the United States, where title to the land, unless special reservations are made, carries title to the mineral rights. In some States, notably New York, and in many foreign countries, the State claims peculiar and special proprietary rights to deposits of useful minerals. Much variety also prevails in America in the size of claims other than for deep mines. Gold-hearing placers, for instance, have special sizes depending on local regulations; they may be very small in rich diggings or of great extent where large hydraulic enterprises are necessary.

Mining. The methods of mining differ according to the form and geological relations of the mass of ore or other minerals to be won. If the mass is of considerable size and extent and lies on the surface, one method is necessary; if it is a relatively flat and very widely extended bed, as in the case of most coal seams, another must be adopted; and if a steeply inclined, but relatively thin, and extended, tabular sheet of ore is to be removed, it may be to great depths, still a third. A mine resembles a huge well, and it is in the keeping of it free from water, in the support of the walls when the ore has been removed, in the ventilation, and in the cheap and quick removal of the broken rock and ore, that the difficult problems arise. They often demand the highest grade of engineering skill and courage. The development of modern hoisting machinery, of rock drills operated usually by compressed air, of high explosives, especially dynamite, and of cheap and efficient means of transportation both on and under the surface, has been the cause of our great modern advances and has made possible operations beyond the reach of our forefathers. Electricity is finding one of its principal fields in mining to-day, and as it proves a very cheap and convenient method of transmitting power down the shafts and through devious passages, it has great possibilities. Water-power, even at a distance from the mine, can often be employed to generate it, and notable economy introduced.

The methods of mining will be briefly outlined under the topics—A. Surface deposits; B. Underground deposits: (1) Flat; (2) Highly inclined or vertical.

Surface Deposits. When a mass of some useful material, metalliferous or otherwise, is found on or near the surface, the first step is to uncover it. This is technically known as stripping, and the overlying worthless material is called the burden. If the burden is soft earth or gravel, it is removed with the pick, shovel, and wheelbarrow or by a steam-shovel and small tram-cars, operated by horses, mules, or locomotives. In quarries of building stone, the decomposed rock is blasted out and removed. When the useful mineral is exposed, its most favorable position is on a hillside, because then the pit or open cut will drain itself, and the ore or rock will have the grade favoring its transportation in removal. If the pit is in level or depressed ground, pumping usually becomes an immediate and heavy charge on the work. In either case the operations of extraction are carried on by benches or terraces. A slice of convenient thickness is taken off by the first party or machines, and when they have advanced far enough a second is started, and so on as many as there may be room for. The outcrops of many large but inclined veins of ore have been worked in this way in their early development, but it places subsequent underground operations at a disadvantage, because it exposes them to the weather. Open cuts are the simplest form of excavation, but, as just stated, the men and machinery are subjected to all the inclemency of the seasons, and usually in winter have to cease work entirely. One form of surface mining remains to be mentioned, and that is the method which has been developed, especially in California, for working auriferous gravels. (See Gold.) Water is brought often from a great distance and with heavy fall, and is then directed through large nozzles, called ‘giants,’ against the bank to be removed. This is washed away and the gold is separated from the moving rock material. The destructive power of a swift and large stream of water directed against a bank is almost beyond belief until seen. The method is economical where the topography favors it, and profit is realized when the gold averages but a few cents per cubic yard.

Underground Deposits. In the winning of the useful minerals from underground deposits complications are introduced which are not met in open cuts. The overlying rock is always to be supported as long as that portion of the mine is being operated or is used as a passageway. This may require the leaving of much of the useful mineral as pillars to support the overhanging wall or roof, or the use of heavy timbering or even of masonry. Ventilation also becomes an important item, and all these charges, it must be appreciated, have to be borne by the product before any profit is realized.

The mining of metallic ores and minerals occurring in flat or slightly inclined beds or deposits does not differ materially from the methods pursued in the mining of coal (q.v.).

Almost all metal mining is concerned with steeply inclined beds, veins, and irregular masses. In the past history of the earth, especially in mountainous regions, and where eruptive rocks have come up from the depths below, cracks of greater or less size have been formed in the solid rocks, and often in numbers. Up through these have come waters, as a rule at elevated temperatures and charged with minerals. Where they have brought in metallic ores they have often deposited them in the fissures, along with more or less barren material called gangue, and in this way have produced ‘veins’ or ‘lodes.’ Where, coming through a crack as a channel of supply, they have met some soluble rock like limestone, they have often replaced it with valuable ore, the limestone acting like a precipitant upon the dissolved metals. If a porous rock has been met the solutions have at times impregnated it with ore. Ore bodies of great size and of more or less irregular character have thus resulted, and problems of varying degrees of complexity are met by the mining engineer in developing them. The ore is seldom uniformly distributed throughout a vein or other deposit, but, on the contrary, occurs in rich portions called chutes or bonanzas, with intervening spaces of barren ground. It is advisable therefore to keep the mine well opened up ahead of actual extraction of ore, so as to average the rich and lean portions and make the enterprise a permanent one. Veins often fork and send off stringers into the walls; they pinch and swell along their length and depth. They usually run out at their ends into small ramifications and finally cease. They may be cut off sharply by other cross-fractures and disturbances. They extend to considerable depths, having been followed in some cases as deep as 3000 feet or more.

As a typical case by which to illustrate the usual methods of procedure, we may assume that a vein has been located on the surface, that it extends a considerable distance, say a half-mile or mile, and dips at 60 degrees into the earth. Test pits and shallow shafts have indicated its value. The engineer, in opening a new deposit like this, would select as suitable a place as possible for his surface works, such as engine house, ore bins, and dump for waste rock, all in connection with a spot where the vein showed good ore. He would then sink a shaft or slope on the vein, and if it held good, would start drifts or levels at each 60 to 100 feet of descent. As soon as a level had advanced some distance from the shaft, say 100 feet or more, another party would be started near the shaft, working on the vein in the roof of the level. At first propped up on timbers, they would excavate a space, and clear away a working face, so that while the level was being driven ahead they could follow a short distance back, taking off a slice. Now in order that the loose rock and ore that are blasted down should not block the passageway, timbers would be set across the top of the level as at first run. The timbers called stulls would fit into sockets in the walls and on them would be laid rough plank or lagging, with taps or little hatchways at intervals for tapping out into cars the ore that would be blasted down upon them. This method is called ‘overhand stoping,’ and is the one usually adopted. When the first party of stopers had advanced far enough to warrant it, a second, and later a third, would be set at work following them up on other and higher slices. As soon as the levels had gone some distance, another shaft would be sunk to connect with them, not alone for hoisting, but to afford ventilation after blasting and for a safe line of escape for the men in case of accident.

Another method somewhat different from overhand stoping is sometimes adopted that is called underhand stoping. Suppose levels one and two had advanced some distance from the shaft, a small connecting shaft is then cut between them called a winze. It may be opened by sinking from the upper level or by an upraise from the lower. After it is cut, a party may begin on the upper level, and drilling in its floor may blast away the vein into the winze and allow it to fall to the level below to be removed. They may take off a vertical slice of the vein in this way, and gradually work each way from the winze. The upper level must then be kept passable with a floor of timber.

As these inclined shafts deepen and the vein is found to be rich and permanent, it is often advantageous no longer to use the inclined shaft, but rather to go out from the vein into the hanging wall on the surface, and sink a vertical shaft that will intersect the vein at some desirable depth. Above this point connections are made with the levels by crosscuts through the hanging wall, and below it by cross-cuts through the footwall. Vertical shafts are always to be preferred, on account of the greater ease and speed of hoisting, but in a new enterprise the safer rule is to follow the ore until its quantity is proved. Variations on the above simple methods are introduced by the character of the wall-rock and the size of the ore body. If the wall-rock is bad, and tends to scale off and impede the workings, it must be propped up with heavy timbering. If the vein is thick, the timbers are built up either rough or squared, and so mortised at the ends that they fit together like the edges of a cube, six feet on the side. Others fit in with them, each stick entering into the four adjacent cubes, and in the end a framework of timber of great strength is built up. As soon as possible this is filled in with waste rock, which finally settles down and is practically as solid as the original vein. Unless precautions are observed in connection with keeping the walls firm and immovable, they may settle and do great damage both to surface buildings and underground workings.

In the Lake Superior iron mines producing soft ore, that lies under a too heavy burden of gravel to warrant stripping, a system has been adopted called the ‘caving system.’ The ores of this character on Lake Superior lie in great troughs or elongated basins. A shaft is sunk in the rock beyond the limits of the ore and drifts at various levels are run out into it. From the uppermost level upraises are made to the top of the ore and minor drifts extended to its outer limits. Light timbering and lagging protect the miner, who then at these outer limits begins to mine out the ore on each side of the end of his drift, letting the burden gradually cave in to the place whence the ore is taken. By multiplying these drifts in every direction all the ore is removed, and the burden, closing in all the time, keeps the mine shut and the miners protected from the weather. In the end a great pit results, sunk in the natural surface.

In small mines no particular system of timbering or taking out the ore is necessary, especially if the wall-rock is firm. Beyond the general plan of shafts and levels the workings follow the ore, and, without much systematic exploration, blast it and remove it to the surface. The objection to this method is that when the known rich spots are exhausted, further operations until more ore is located are all dead work, yielding no return and often causing the enterprise to shut down. In large mines where the wall-rock is firm, great excavations may be made with no timbering whatever.

If the vein or series of veins outcrop on a hillside, either parallel with its surface or crossing the neighboring valley, the ore may be won by adits or tunnels run in on a slight up grade. Such a tunnel will automatically drain all the portions of the vein above it and will make it an easy matter to take out the ore, which is merely loosened and sent down to the tunnel in winzes and shoots. But the portions below the tunnel will of necessity be reached by shafts from it and will require pumping. For this reason, unless the advantages of a tunnel are very great, most engineers prefer a vertical shaft at as early a stage in the mine as possible, because it is so easy and convenient to handle ore quickly and cheaply by vertical hoisting. Nevertheless some long and famous tunnels have been excavated in former years to drain important veins.

In the handling and transportation of ore underground, important problems are met in large works. It is accomplished in the levels by small cars, usually built of boiler plate to withstand the pounding that they receive, and these are pushed along by men on light tracks to the shaft. The operation is called tramming. If the shaft is vertical the ears are run directly on the cage, and hoisted to the surface, where they are dumped and returned. Large mines may have cages with two or even three decks, bringing thus two or three tram-cars at a trip. If the shaft is inclined, the tram-cars are dumped at the landing of the level into a car in the shaft that is open at the end instead of at the top. This is called a skip and its track is the skipway. The skip dumps automatically at the top of the shaft. In small mines an iron bucket is used instead of a skip or cage, but as soon as the output becomes at all large, buckets have to he abandoned. The transportation of the miners up and down deep shafts is also an important matter. They may, and as a rule do, ride on the skips, cages, or buckets used for the ore, special trips being made for them. Ladders, except for shallow depths, are no longer used in good practice unless in emergencies, as the climbing is too slow and exhausting.

In all mines one of the most dreaded things is fire. The forests of underground timber in many old workings make it a very dangerous accident, and even when in shaft houses at the entrances it often entails disastrous consequences on the men below. In coal mines there is the added danger of explosions and even of combustion of the coal. It is more and more customary, therefore, to locate boilers and engines in separate buildings from shaft houses, and to use every precaution against an outbreak.

In the organization of the force of miners the relations of employer and employed in mines are somewhat different from those of operations on the surface. The men are distributed as individuals and small parties in places more or less scattered and beyond regular superintendence. It is therefore often customary to let out work by contract rather than by day wages. A fair price is offered, based on experience, and usually estimated by the cubic yard or fathom of ore or rock excavated, and a party of miners organize and assume the contract. Active and energetic men do well under these circumstances, but as a rule the prices soon adjust themselves to about a fair average. The company furnishes supplies of explosives, drills, timber, etc., to the men at rates agreed upon. It also has a mine foreman, with subordinates to see that the work goes on satisfactorily, and at the end of each month the surveyor or engineer or superintendent measures up the work. In case the owners lack capital, or the vein is pockety and not adapted to systematic work in the large way, the ‘tribute’ system may be adopted. The parties of men then lease a certain block of ground and mine at their own expense and risk, paying to the owners a graded percentage of the value of the ore. If the men strike rich ore they realize high returns, but if it proves lean and low-grade they may actually lose. Old miners who know a mine thoroughly may often thus work to a great advantage. Owners of small capital sometimes get a new mine developed by leasing it to a party of practical miners for a percentage of the ore values for a limited time period. In this way the ore body is opened up without expense to the owners, but the leasers, who take the risks, naturally reap the lion's share of the profits. The relations of employers to men in remote settlements are also peculiarly close. The mining company of necessity furnishes houses, supplies, and all necessaries of life.

The production of the metals and useful minerals the world over has increased remarkably. Nowhere has the advance been more pronounced than in the United States, which is the foremost of mining nations, leading, in 1902, in the production of iron and steel, copper, gold, silver, mercury, coal, salt, and petroleum. Of the other more prominent metals and minerals, Spain is the chief producer of lead, Germany of zinc, and Russia of platinum.

For statistics and further information, consult the separate articles on the various metals.

Bibliography. The Transactions of the American Institute of Mining Engineers contain many papers relating to mining. Additional ones may also be found in the Engineering and Mining Journal (New York); The Mineral Industry (New York); Mines and Minerals (Scranton); the Engineering Magazine (New York); Mining and Scientific Press (San Francisco); Trautwine's Engineers' Pocket-Book (New York, 1902) contains many valuable data grouped for easy reference, and among other works may be mentioned H. M. Chance, “Coal-Mining,” Report AC., Pennsylvania Geological Survey; R. Peel, Coal-Mining (Philadelphia); E. H. Davies, Machinery for Metalliferous Mines (London); F. A. Abel, Mining Accidents and their Prevention (New York); A. Serlo, Leitfaden zur Bergbaukunde (Berlin); Barringer and Adams, The Law of Mines and Mining in the United States (Boston); The Coal and Metal Miners' Pocket-Book (Scranton, Pa., 1900); Foster, A Text-Book of Ore and Stone Mining (Philadelphia, 1900); Stretch, Prospecting, Locating, and Valuing Mines (New York, 1902); Wilson, Hydraulic and Placer Mining (2d ed., New York, 1903); Ihlseng, A Manual of Mining (3d ed., New York, 1901); Miller, Field Book of Practical Mineralogy (New York, 1901).