Page:The New International Encyclopædia 1st ed. v. 13.djvu/614

MINING. 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.

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.

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 .) 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.

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 (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