The Business of Mining / A brief non-technical exposition of the principles involved in the profitable operation of mines

by Arthur J. Hoskin

By a tunnel has been intended any (approximately) horizontal passageway driven from the natural surface. Objection to this use of the word rests in the strict definition of a tunnel, which states that it must have both ends open to the natural surface of the earth, as for example, an irrigation or a railroad tunnel. A level passageway which has but one end open to daylight is not properly spoken of as a tunnel. In mining practice, practically every horizontal opening of this nature is open at only one end, and it is an adit rather than a tunnel. If the precaution of speaking of it as a "mining tunnel" is observed, very well, for this may be taken to be an expression synonymous with adit. The latter term is, however, shorter and more correct.

For the sake of a uniform usage, the following definitions are proposed. Their use will conform with the usages of those well-informed persons who adhere to correct speech.

A shaft is a truly vertical mine passage which may, or may not, be sunk in or along an ore or a coal body.

An incline is any mine passage which occupies a sloping position and which may, or may not, maintain a uniform inclination throughout its length. It may be sunk along, or in, a pitching vein or seam and it may thus conform to the irregularities of the dip of such body. It is neither horizontal nor vertical. Such an inclined passage following a seam of coal is known as a slope.

It sometimes happens, especially in coal mining, that a sloping passageway is driven through barren rock either to get at known bodies by the shortest means or to establish uniform grades for tracks. In a strict sense, these are not inclines or slopes, for they do not even approximately follow, nor parallel, bodies of value. The miner's term for such an opening is rock slope.

An adit or mining tunnel is a horizontal opening driven from the surface. If it be driven along an ore body, as a vein, it is properly called a vein adit; if it is driven across barren country to intercept presumed or known bodies, it is spoken of as a crosscut adit. All adits must be given a small amount of grade for drainage necessities.

Before getting underground we should consider what is required in the way of opening our mine; what is positively known about our body of coal or ore; and what conditions are liable to confront us later on. We must consider the type of ore body; character of material to be extracted; average thickness and hardness of the body; desired tonnage; power facilities; probable surface and underground drainage to be maintained; and dozens of other things which only the experienced man will think of and appreciate. The right kind of a manager will know that he cannot afford to overlook such points.

Every case involves different contingencies, and therefore extreme forethought must be given to the subject before deciding upon any particular kind of an opening into the ground for mining purposes. This remark does not apply to such openings as prospect drill-holes, openings which are not for mining purposes, but for exploitation. Assuming that sufficient data are known concerning the property to warrant the expenditures incident to the making of a mine, the question remains as to the best way of proceeding.

It is a well-established fact that it is much cheaper to drive an adit than to sink a shaft of equal transporting capacity. It is also cheaper to drive an adit than to sink an incline. If the topography is such that an adit can be driven into or beneath an ore body and thus expose it from a low elevation, the temptation is strong and along lines of good practice to do so. If the country is quite flat or nearly so, or, if the surface is such that, while rough, an adit of reasonable length cannot be driven to tap the valuable mineral and handle it economically, then it is good practice to decide upon a shaft mine.

An adit will not only be cheaper, foot for foot, than a shaft or incline, but, if given the proper, slight grade, it will afford a natural drainage outlet for all subsequent workings above its level. The cost of pumping, as already suggested, may be a considerable item and it may be a deciding factor in favor of an adit when this form of opening is possible.