Part 5

_Machinery_ is usually purchased at centres of mining supplies and manufactures. San Francisco, Los Angeles, Salt Lake City, Denver and Chicago are the principal _rendezvous_ in the West for mining men in need of machinery. Mexico City is, similarly, the outfitting point for the mines of southern Mexico. The United States holds the supremacy of the world in the matter of equipping mines and mills, large orders of American-made mining machinery being shipped to even the antipodes.

The nearer a property is to a depot of supplies, the less is bound to be the cost of getting goods onto the ground. It is this last item--the delivery of goods--that must be recognized as a very pertinent, and sometimes a critical, factor upon the cost side of mining accounts. Mines that are remote or in rugged countries are frequently dependent upon animal transportation. In some cases, machinery going to the mines must be so built that it may be taken apart into small portions suitable for loading upon the backs of horses or burros, or even, in the Andes, upon the frail llamas.

Operations, if planned to be conducted for a long term of years and therefore warranting the installation of large and expensive plants, should be based upon the holding of extensive ore-bearing ground. Here enters the notion of the _shape and size of a mining property_.

With some kinds of mining ground, the best form for the holdings would probably be a compact, approximately equilateral tract, covering a reasonably large acreage. This would be the case with ores that occur in sedimentary beds, for instance, where it is advisable to have the mining plant centrally located so as to work expeditiously the entire area. This would apply to a region like the Cripple Creek District, which contains innumerable veins running in all directions but displaying no outcrops.

In other instances, the most desirable shape might be long, narrow strips so laid off as to contain the strikes of persistent lodes or veins, as those of the wonderful Comstock Lode region. It is not acreage that counts here so much as lineal extent.

In the Transvaal, land is held in rectangular blocks. The first owners of the ground took it up for agricultural purposes. This same statement is also true of the mining properties in the Joplin District of Missouri and Kansas.

In the case of the South African properties, every company has definite boundaries to which operations may be planned. Hence it is possible for the management to so plant any mine as to operate it at a given rate for a predetermined life of the enterprise. The work is planned to maintain a certain output that will exhaust the ore bodies in just so many years, and all the equipment may thus be purchased with the forecast that it will serve its purpose and perform its economic share within the prescribed time.

This notion will be more readily understood when we consider the various types of ore bodies. With properties wherein there is no possible way of predicting the number, size, and worth of discoverable ore bodies, the life is wholly problematical and it is therefore difficult for a manager to decide how much he should expend in the initial equipment.

X

MINE OPENINGS.

In every new mining project, there is much to be considered concerning the expediency of opening up through shafts, inclines or adits. More attention has lately been given to this subject than formerly. There are very good reasons for the selection of any one of these kinds of mine openings.

The words shaft, incline, and tunnel have been handled with careless meanings by mining men. It is time that some definitions be accepted so that everybody will use these terms with the same meanings.

A shaft has loosely been any steep opening sunk through the ground. An incline--sometimes spoken of also as an incline shaft--has been taken to mean an opening resembling a shaft, but not very steep and not approaching verticality. Right here, there has been too much latitude of speech and it has entailed the necessity of many awkward explanations.

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.

Furthermore, an adit will obviate the installation and use of hoisting machinery, and thus there may be maintained a greater efficiency in the operating expense of the mine than would be possible with a shaft.

Again, it is a simpler and cheaper matter to maintain a mining tunnel in working shape than it is a shaft, particularly in bad ground. By the settling or "working" of the ground, a shaft may be thrown perhaps but slightly out of alignment and annoying interferences will be experienced in hoisting, especially when rapid and uninterrupted hoisting is necessary to maintain the desired output. While the same amount of disturbance does take place in an adit, it is an easy matter to readjust track grades while continuing regular haulage operations.

The timbers, in the case of either a shaft or an adit, will require occasional renewal, but the expense of such repairs is less in adits than in shafts or inclines, while the delay to other operations of mining, in the case of the adit, will be inappreciable.

Topography has been referred to above, but it must be again briefly mentioned. There are some places in which ore bodies extend to, or exist at, such depths that adits could not be projected to get beneath enough of the ore to warrant their construction. An adit mine is not a practicable thing in a flat country like Nevada or the Rand, but in the rough country of the San Juan it is the customary kind of a mine. In the very early days of Comstock Lode mining, shafts were sunk by each of the hundreds of companies. Before a great while, the advantages that would accrue from having a deep "tunnel" became evident, and the famous Sutro Tunnel, with its historic, checkered career, was driven. Although it loomed up like a gigantic undertaking for that period, the immense prospective or future value of it could not be denied.

The following relative advantages of the several types of mine mouths are in addition to those already given and are worth consideration:

With an incline, the value of a tabular deposit is determined as work progresses; the course and dip of the body will be known at all depths along the incline; the body may be explored from the incline in both directions, simultaneously, with a resulting doubling of the development and production; all, or nearly all, the material removed is "vein stuff" and its value may repay the sinking expenses; there is no losing of the ore body unless a geological fault is met.

With a shaft, more rapid hoisting is possible than with an incline; the timbering labor is less than in the case of an incline, but greater than in the case of an adit; with ground containing ore bodies in irregular masses and at no uniform intervals, vertically or horizontally, stations and levels may be started wherever desirable; the crosscuts which are usually necessary to reach the bodies may disclose otherwise unknown bodies.

With a vein adit, the vein is prospected as work advances; the ore removed may pay its own way, as it were; the drainage is automatic; ore is transportable from the mine by haulage rather than by hoisting; the ore in place is above the level and will handle itself to the outgoing passage by gravity.

With a crosscut adit, in addition to the last three advantages noted for the vein adit, there is bound to be exploration of the ground upon at least one side of the known body; there will generally be easier haulage because of the straighter track, since an adit driven along a vein will conform to the geological irregularities and the track is bound to be more or less crooked.

Without counting upon the doubtful success of the numerous propositions in tunneling machines, but judging only from past experiences, we may say that a shaft will cost about three times as much as a "tunnel" of equal transporting capacity. If the ground is wet, the discrepancy in first costs becomes much larger. In a remote region, with difficult transportation of machinery and fuel, it may be better to drive and use a long adit rather than a shallow shaft. An adit will transport more product than will a shaft of equal dimensions.

An adit may be driven to intercept a shaft and to serve as a sort of artificial surface, as it were, and thus save expenses in pumping and in hoisting up to the original collar of the shaft at the surface of the ground.

No matter how crooked an incline may be, it is possible to hoist ore in conveyances known as skips, although the hoisting may be necessarily somewhat slow. These same conveyances are useful for lowering and hoisting men, and the parody, "Men go down to the mine in skips," here finds its significance. The usual hoisting conveyances used in shafts are known as cages. They usually produce less friction than do incline skips. A skip in an incline must travel upon a track, while a cage, somewhat resembling a passenger elevator, has no wheels, but slides upon guides. However, an incline skip, because of the inclination of the passage, does not exert the same dead weight upon the cable and hoisting engine and hence these parts of the equipment may be made correspondingly lighter. Skips for shafts are similar to cages in their lack of wheels.

Complete estimates of probable future requirements should be made before a shaft is sunk. When it becomes necessary to enlarge a single-compartment shaft to one with two compartments, the expense has been found to exceed one-half the original cost of sinking; while, to convert a one-compartment shaft into a three-compartment shaft costs fully three-fourths of the original sinking expense. Approximately the same ratios of cost will hold in the case of enlarging inclines.

Character of ore sometimes influences the selection of the kind of passageway. Some high grade, brittle ores must not be dumped nor handled repeatedly, since values are lost in the "fines." Iron and copper ores will not probably be injured by any amount of dumping. Coal should be handled as few times as possible. In view of this fact, other things being equal, adopt that system that will injure the ore or coal the least.

As a rule, workmen are safer in tunnels than in shafts, since there is little danger from objects falling any great distance. Tiny bits of rock have been known to kill men in shafts. On the other hand, there is less liability of injury from falls of large rocks in shafts than in adits. Roof falls are a very prolific source of mine accidents.

The workmen of neighboring mines will often be able to give much valuable information as to the proper procedure in opening a new property. For instance, water levels, amounts and kinds of gases that may be expected, the nature of the wall rocks, and other pertinent points may be learned by interviewing the men who are employed in adjacent mines. Still better information may be obtained by personal visits to the underground workings of the nearby mines. In this connection, one must not permit himself to be unduly influenced by the prejudices or hobbies of the neighboring operators or their employés if there is reason to suppose that such notions are contrary to good practice.

Due consideration must always be given to the selection of some method of opening up what might be supposed will never amount to a great mine, so that, should subsequent disclosures exceed expectations, enlargement of the scale of operations can be advantageously effected. Always bear in mind that legitimate mining is just as much a commercial enterprise as is any other kind of business. The utmost concern for financial showings must be constantly borne in mind. Select a scale of operations consistent with the known--not the hoped-for--bodies of coal or ore; but have a certain feature of elasticity about the plans that may take care of future increase in business if found desirable. Do not "over-plant." Never plant, at all, _prematurely_. It is better to postpone the installation of the equipment until some specific facts are available. Many companies have met defeat in the exhaustion of capital through the purchase and installation of elaborate plants which were never warranted.

After a mine is once opened and preparations have all been perfected to operate upon a certain scale of output, it is quite essential that exploitation and production be maintained without material fluctuations, if the greatest economy is to be attained. Exploitation, _i.e._, development work, must be kept well in advance of actual mining operations to assure plenty of working space for the extraction of the normal output.

XI

TYPES OF ORE BODIES.

It has been necessary, a number of times in this discussion, heretofore, to make mention of kinds of ore bodies. It is well, at this time, to get some fixed ideas concerning the leading types of bodies of minerals which are extracted as ores.

Because of the laxity in type differentiation which has prevailed among miners and writers, the same geologists who have framed definitions of ore, have also defined the various types of ore bodies. The definitions, having been accepted by the leading mining geologists and engineers of the present day, it is well for us to fall into line and to agree with the authorities in such matters.

A _vein_ is a _single, ore-bearing fissure_, generally, though not necessarily, with at least one well-defined wall.

When we run across a tabular-shaped deposit of ore that looks as though it may have been put into a pre-existing fissure or chasm, the chances are that it is a vein. But a vein must not be confounded with a dike. A dike is a filling that has been injected, while molten or fluid, into an open passageway or rupture across rocks, or into an opening which it created for itself. A little examination of the material should tell, to even the novice, whether or not the substance is of plutonic origin. The filling of a vein is not eruptive, at all. Veins have been filled from circulating aqueous solutions, by slow depositions, that have occupied very long periods.

A vein may be any thickness, since a fissure may have been opened to any width. Hence, a vein may be as thin as a sheet of paper, or it may be a hundred feet across. However, it is true that some wide veins have resulted by a sort of enlargement from original thin seams. Very few of the notable wide veins of the world are believed to have been created by the filling up of chasms originally as wide as the present ore bodies. But, in all cases of real veins, there were original fissures, fractures or crevices which acted as channels for circulating solutions that contained the materials which were left to make the vein matter.

A _lode_ is an _assemblage of veins_ so closely spaced that the ground between the veins becomes, in places, ore-bearing, and the entire width of the aggregation becomes an ore body.

A zone of sheeted rocks like schist or slate, if sufficiently mineralized to warrant mining, would be a lode. Sometimes, in certain districts, the earth's crust has been subjected to many approximately parallel, closely-spaced fractures, and by the subsequent filling of these cracks, with the accompanying corrosion of the walls and their replacement by ore, extraction of the entire mass of rocks across a considerable distance will be found to yield a profit. Any such body is a lode.

In the Cripple Creek District, the ground is criss-crossed in every direction by tiny fissures which have resulted from the contraction of the country rock, just as a bed of mud is fissured in the process of drying up after a rain. Wherever these fissures are found in aggregates that are closely spaced and in which a majority of the cracks have a general trend so that the whole assemblage can be readily worked as one mass, this whole body of fractured rock may be found worth mining and it will then constitute a lode. It may be mentioned here that the so-called ore of this district is not really ore according to the accepted definition. The true ore, the filling of these innumerable, tiny cracks, really constitutes but about five per cent. of the material that is shipped as ore, but which is principally the "country rock" broken down with the small volume of ore.

In _legal_ phraseology, the word lode has come to include all sorts of ore bodies. When the word is thus used, in a legal sense, it should not be confused with the strictly technical meaning.

It has been the fashion for prospectors to dilate upon the fact that they have located "true fissure veins." This expression, formerly on the tongues of most mining men in districts possessing veins at all, is now obsolete and hence should be placed in the discard. There can be no such thing as an "untrue" vein nor an "untrue" fissure. Neither can there be any vein without a fissure. Therefore, if there is any vein, it must be a real or true vein. Accordingly, the verbiage is to be discouraged. The intention of a miner, in using this pet phrase, has been to convey the impression that his vein extended downward, indefinitely; there having arisen a notion that some veins are rather superficial and liable to "peter out" at slight depths, while others--the kind he invariably has located--persist both in size and value to extreme depths.

There are districts in which are found short fissures, generally confined to certain horizons in sedimentary rocks, such as the limestones of the great Mississippi Valley, from which are mined lead and zinc ores. These are called "gash veins." These are always readily recognized and there is not the slightest excuse for confusing them with the fissures which are common to other kinds of rock formations.

A _bed_ or _blanket vein_ is the term applied to any nearly flat deposit conforming to the bedding. Such a body of ore must be in a sedimentary series of rocks. Coal bodies are all of this type. Many bodies of iron ore are also of this type.

A _chimney_ is an ore body which has not the tabular form of a vein but is rudely elliptical in outline, horizontally, and with a very considerable vertical extent. A _stock_ is a similar body but it is of still greater irregularity of boundary.

These bodies are usually the filling of extinct volcanoes or geysers, and therefore they are presumed to extend to very great depths. The diamond mines of Kimberly, Africa, are of this type and the ore is a sort of hardened geyserite or mud in which are enclosed the precious gems. In Custer County, Colorado, the ore body of the Bassick Mine is a conglomerate of rounded boulders of all sizes cemented together, somewhat like concrete, by the materials which really carry the values. This mass occupies an ancient volcanic neck or throat of a geyser, probably the latter. The main portion of the Cripple Creek District is the crater of a great prehistoric volcano. It might be called a great chimney, but custom seems to limit the use of the word chimney to a smaller body such as might be included in a single mining property.

A _mass_ is a deposit whose irregularity of shape is so great that it cannot be recognized as belonging to any of the types already mentioned. Masses conform to no rules as to shape or size. They are usually the result of a chemical dissolving of the original barren rocks with a simultaneous or subsequent substitution of valuable materials. There are many instances of ores that have been deposited, molecule by molecule, replacing equal volumes of the previous rock, much upon the order of the petrifaction of wood. Again, there are immense masses which are believed to have accumulated in caves already dissolved out of the containing rocks.