Mining
the processes whereby minerals are obtained from their natural localities beneath the surface of the earth, and the subsequent operations by which many of them must be prepared for the purposes of the metallurgist. The art has been practiced from the remotest times. The coal mines of England are mentioned as early as 853 and the discovery of the Zwickau coal mines was made in the 10th century. In the 12th century the coal mines at Lüttich began to be exploited and in the 13th century the coal deposits at Newcastle, Wales, and Scotland were discovered. In the course of the 19th century, after the invention of the steam engine and the smelting of iron by means of coal and coke, mining was marvellously developed.
Coal has been discovered in Australia, New Zealand, Borneo, China, and Japan.
Great Britain has larger deposits than any other country in Europe. Next to these in amount of output are the coal mines of Belgium and France. In Germany those along the Rhine and in Westphalia, and in Saxony, Bohemia, and Silesia, are of great importance. Various machines have been invented with a view to lessen the labor and expense of under-cutting coal seams. They work with compressed air or electricity, some on the principle of the reciprocating rock drill, while others have the cutters arranged on the periphery of a rotating disk, or on a traveling pitchchain. The coal, when broken down, is placed in wagons and drawn by horses, mules, traction rope, locomotive, or trolley, to the bottom of the shaft and raised to the surface.
The actual mode of working the coal distri varies greatly in every district. trict. By the post-and-stall, or bord-and-pillar, or room-and-pillar, or (in Scotland) stoopand-room, method the first stage of excavation is accomplished with the roof sustained by coal; in the long wall method the whole of the coal is allowed to settle behind the miners, no sustaining pillars of coal being left. This when well pla planned is the safer both as regards facility of ventilation and liability to accidents from falls. In Pennsylvania anthracite beds, which are mostly highly inclined, the workmen often work on the coal broken down in driving the "breast" upward; this broken-down coal being drawn off from below at intervals to give the workmen room to work. When breast has been extended upward to its MINING full length the broken-down coal is all removed. Later when the breasts in one section of the mine are all worked out the sustaining pillars between them are "robbed" or removed, allowing the roof to fall.
In working metalliferous veins horizontal galleries termed "levels" are driven by the lode usually 50 to 100 feet apart.
They are rarely perpendicularly above one another, as they follow the inclination of the vein. The levels are connected by means of small shafts, termed "winzes." Represented on a vertical plane, the vein will thus be seen to be cut up into pillars which are worked by the method of "stoping." In underhand stoping, the ore is gradually worked away downward from the floor of one level, the ore and worthless mineral being taken out through the level next below. This method is especially adapted for working any valuable ores, as the loss is small. The overhand method, in which the miners stand on timber platforms and break down the mineral above them, is more economical, so far as cost of excavation is concerned; but the loss of ore is greater than by underhand stoping, and hence it is best adapted for the working of low-grade ores.
Placer Gold-Mining. - Many deposits of gold ores, as those first worked in California and those of the Klondike, are in the gravel or sand in the present or ancient stream beds. Such deposits are called "placers." In working these deposits in the beds of existing streams, the course of the stream may be deflected by a dam and sluice, and the water of the stream utilized for separating the gold from the gravel which may be dug from the stream bed. In the case of larger streams, mechanical dredges remove the material from the bottom, which after separation of the gold is returned to the stream bed. In the old placers which are abandoned stream courses, generally above water level, hydraulic mining is resorted to. A stream of water from 6 to 12 inches in diameter and under the pressure caused by a head of several hundred feet is directed on the hillside where the old placer outcrops and rapidly washes it away. The material thus removed is sorted by the same water and the gold separated.
The progressive legislation in connection with mines has proved beneficial in diminishing the proportion borne by the accidents to the number of miners employed. Great improvements have recently been made in sinking shafts, safety lamps, underground haulage, MINING ENGINEERS coal-cutting machinery, worked by compressed air and electricity, and pump ing apparatus. Better methods of sorting, picking, and washing coal have been adopted. Good progress has also been made in the application of steel girders as props and bars, and in reducing the cost of coal consumed at collieries. By means of forced draught and better mechanical stoking much coal practically unsalable has been utilized to great advantage. But by far the most appreciable good that has been done in connection with mining in recent years has been the scientific investigations carried on by the BUREAU OF MINES (q. v.) respecting the causation and prevention of explosions in coal mines, and improved means recommended and adopted to diminish, if not minimize, these disasters, where many lives have been lost and much valuable property has been destroyed.
In England and Ireland the crown has the right to all mines of gold and silver; but where these metals are found in mines of tin, copper, iron or other baser metal, then the crown has only the right to take the ore at a price fixed by statute. In Scotland gold mines belong to the crown without limitation, and silver mines when three-halfpence of silver can be extracted from the pound of lead.
As a general rule, in the United States as well as in Great Britain, whoever is the owner of freehold land has a right to all the mines underneath the surface, for his absolute ownership extends to the center of the earth; but under special grants and contracts it is not uncommon for one person to be owner of the surface of the land and another to be owner of the mines beneath; or several persons may be owners of different kinds of mines lying one above the other in different strata. On the public lands of the United States, a title or license may be obtained by any citizen from the general land office at Washington, at the rate of $5 per acre of surface pre-empted.