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 de termined by assaying average samples. (See As SAYING.) 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, accol•ding to the laws of the country or distriet. is staked out, and when this is opened up sufficiently to have necessitated the expenditure of a certain speCith.d sum of money, a permanent title con be obtained. In the Western States of the United States claims usually extend 15(1f1 fect along the vein. and either 15f1 feet or 300 feet on each side of it The owner can then follow the rein where it leads him be tween the vertical planes of his end lines. The outcrop is called the apex. As. however. veins are so irregular and obscure underground. great uneertainty 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, convey ing the rights to all the ore lying vertically be neath them. This is the practice in Western Can ada and is practically so in most Eastern States of the United States, where title to the• land, un less speeial 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. Aluch variety also prevails in America in the size of claims other than fur deep mines. (old-bearing placers, for instatice, have special sizes depending on local i011, ; they may he very small in rich diggings or of great extent where large hy draulic enterprises are neees:ary.
Alix IN G. The methods of Tinning differ ac cording 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 ease of most coal seams, another must be adopted; and if a steeply inclined, but relatively thin, a ml extend ed, tabular sheet of ore is to be removed, it may be to great depths, still a third. A mine resem bles a huge well. and it is in the keeping of it free from water, in the support of the wall: 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 (mirage. The development of modern
hoisting machinery, of rock drills operated usual ly by compressed air, of high explosives, especial ly dynamite, and of eheap and ellicie•nt 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 real•]] 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 possibili ties. 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 he briefly outlined under the topics—A. Surface deposits: 13. Under ground deposits: ( ) Flat; (2) Highly inclined or vertical.
Dr•ieOstTs. When a mass of sonic use ful material, metalliferous or otherwise. is found on or near the surface, the first step is to uneov er it. This is known as stripping. and the overlying worthless material is called the buril,a. if the burden is soft earth or gravel, it is removed with the pick. shovel, and wheel barrow or by a shinin-shovel and small train-cars, operated by horses. or hu-onitives. in quarries of building stone. the decomposed rock is bliisted Mr and removed. When the useful mineral is exposed. its most favorable position is on a hillside, beeause then the pit or open cut will drain and the ore or rock will have the grade favoring its transportation in re moval. if the pit is in level or depressed ground. pumping usnally liecomes an immediate and heavy charge on the work. In either ease the operations of extraction are carried on In• henehes or terraces. A slice of convenient thickness is taken off by the first party or machines, and when they have advanced far enough it second is started, and so on as many as there may be room for. The outcrops of many large but inclined veins of (ire have been worked in this way in their early development, but it places subsequent underground operations at a disadvantage, he e•ause 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 (hweloped, espe cially in California. for working auriferous gravels. (See tIoui.) 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.