Mines are discovered in many ways. One hears much about prospecting, and since this is a practice which is rapidly changing from a mystical to a scientific basis, a few considerations will here be in order.
Persons who have lived in mining communities are familiar with two types of prospector, the roving and the settled. Somehow, when we think of the former, there comes to mind a bearded, roughly clad man, usually accompanied by a "jack" and both packing the outfit consisting of a few tools, a pan, some blankets, a gun, and a supply of "grub." If we have in mind the other type of prospector, we imagine him as living an isolated life in a log cabin up in the hills, spending his daytime in putting in a few, short drill-holes and blasting down a ton or two of usually worthless rock in a "tunnel" or shallow shaft, confident that each succeeding shot will disclose a treasure.
Both of these types represent the utmost in optimism. These men endure many hardships and privations, they can have little converse with other humans, often they can see no provisions for the next day; in fact, they receive few of the benefits of modern civilization—if we except the food-preserving features. Still, a typical, old-style prospector keeps on with absolute faith that fortune will smile tomorrow. We must reach the conclusion that these uneducated men are led on by subtle beliefs which, to a technically-trained man, seem like the rankest folly. They are diviners, dreamers. They are disappearing now and, a generation hence, there will be but memories of them. They are giving way to successors of a different type.
The newer kind of prospector is well educated, and, perchance, he is rather youthful. His chances of success are many times those of the man he supplants. Why? Because he is taking advantage of the work that has been done by all former prospectors. He is guided by theories deduced from observations through ages, and he has the advice of the best contemporary men of experience in matters of geology as applied to mining. In other words, he is a scientific prospector.
The prospector of today has a general understanding of mineralogy and geology; he must have knowledge of mining methods, so that he may know whether a deposit, once found, can be exploited at a profit; he must be ready to account for all discovered mineral bodies, and he must be capable of applying theories to actualities.
There are so many metals and minerals sought for the markets of the world today that we see there are many fields of study and practice open to prospectors. It is not the purpose here to explain the details of scientific prospecting, for the study of this one subject would, in itself, fill a volume. The object of the above remarks is to draw to the attention of the economist the propriety (amounting almost to a necessity) of giving heed to the findings of the educated, trained searcher for mineral bodies, in preference to those of the illiterate man who has furnished themes for artists, narrators, and dramatists, because of his quaint characteristics.
Some writers have classified mineral discoveries into Search, Chance and Adventitious.
Search discoveries, being the rewards of earnest seeking, it is not surprising that, under the past guide of notions and mysticism, the percentage of such discoveries has been small. Under the new order of things, with science as a guide, the percentage is growing and, in the future, this kind of discovery will undoubtedly strongly outnumber the others.
Chance discoveries are those that are made purely without premeditation. They have been a dominant factor in the mineral development of the past. The discovery of gold in California came about through the noticing of shiny, yellow flakes of metal in a ditch leading to a saw-mill. The great iron mines of the Mesabi Range were found by the ore clinging to the roots of an overturned tree. The Wallaroo copper mine, the greatest in Australia, was discovered by the green minerals brought to the surface in the excavations of a wombat. The famous Sudbury nickel-silver ore bodies were disclosed when making a railroad cut on the Canadian Pacific Railroad. The Reddington quicksilver mine, in California, was similarly opened in a cut for a wagon road. The mining of silver at Catorce, Mexico, followed the discovery of shining silver nuggets in the camp-fire of a native, who had camped right upon a rich outcrop. The Kimberly diamond mines are said to have been disclosed by the burrowings of an ichneumon, which fetched a brilliant stone to the sunlight.
Adventitious finds are such as occasionally occur when, while really searching for, or actually mining, one metal, discovery is made of a different metal, or possibly the same metal is found in an entirely different kind of ore. The Comstock lode of Nevada was originally a search gold discovery, the gold having been sought and found by two prospectors with ordinary gold pans. In their working to recover gold, a black mineral and a yellow sand were discarded from the pans and rockers. Curiosity of one man resulted in the identification of these two minerals as ores of silver which henceforth were held as valuable as the native gold. The Anaconda mine, at Butte, Montana, was located, and for some time worked as a silver proposition; but the values gradually changed with depth from silver to copper, until now silver is only a valuable by-product. The rich lead-silver ores of Leadville were discovered as adventitious to the operation of the rich gold placers in California Gulch. A heavy, troublesome rock which accumulated in the sluices, much to the disgust of the miners, turned out to be cerussite, a fine ore of lead. This same district now produces in commercial amounts gold, silver, lead, iron, zinc, copper, and manganese. The Treadwell mine on Douglas Island, Alaska, was first worked as a placer and the values were found to extend downward into the underlying rock in a place which proved to be an immense deposit of eruptive, gold-bearing ore.
As the old-fashioned, venturesome kind of prospecting has but recently been crowded off the scene by the better, scientific kind, let us not overlook the great discoveries that were made in the past before we had applied "organized common sense" to such a field of activity. Those original prospectors were searchers, hunters. They had no guides, but they did accomplish a great deal, and their discoveries were rewards for diligence and hard labor which were, to a great extent, often misdirected.
The process of acquiring title to mining property may be viewed from a number of points. Such property is real estate and, as such, it may be bought and sold or otherwise transferred exactly the same as farms or city lots.
The United States has constructed an elaborate system for the disposal of its public lands to individuals, under various classifications, such as homestead, desert land, timber and stone, timber culture, coal, placer, and lode claims. Different rules apply to the filing upon, improvement and patenting (acquiring deed from the Government) of these various kinds of claims. The character of the lands in the public domain is decided by the surveyors who execute contracts from the General Land Office for subdividing or staking the country off into townships and sections, according to our American system. In the return of each surveyor's notes, he recommends the sale of the land according to his judgment as to its highest value. There has naturally been a good deal of erroneous conception upon these points, with the result that, often, land has been later shown to be entirely different in its character from the classification given to it by the contracting surveyor; for the qualifications of such a person are not always of a high grade, when it comes to geological questions. And yet, on the whole, the scheme has worked out well and much fraud against the Government has been prevented by the rigid practice.
The Government prices for some of the various classes of land have been as follows: agricultural, $1.25 per acre; coal, $10 per acre when the land was not closer to a railroad than 15 miles, and $20 per acre when it lay within this limit; placer, $2.50 per acre; lode, $5 per acre. These have been the prices demanded for the land only; the payment of these amounts, in many cases, has constituted a small fraction of the expense of securing the original deeds from the Federal Government.
Coal lands may be located very much the same as a homestead, with the exception that residence upon the ground is not required, nor are improvements essential. In cases of dispute as to priority of location, the land office will recognize those claimants who have expended the greater amounts in improvements. One citizen may locate but one claim of 160 acres.
Since April 10, 1909, the Government has been disposing of its public coal lands under a classification that takes note of many details. The kind, grade, thickness, and purity of coal; the number of workable seams; the depth; the features of local supply; transportation facilities; and the average prices at which similar private tracts are held, are among the items recognized in the classification. Probably no two tracts will be sold at the same rate. In general, the new prices are higher than the flat prices that formerly prevailed and some pieces of land are now estimated as high as $175 per acre. In every case of application to purchase coal land, hereafter, the area in question will undergo inspection by Government experts and a price will then be assessed. This law is being severely opposed as being unreasonably severe, and its amendment may be looked for.
Placer lands were formerly permitted to be taken up in any shape, the boundary stakes being placed upon the ground in such a manner as to include only the desirable area, which is usually of an alluvial nature along some valley or gulch. This practice has been forbidden, however, and a locator is now obliged to take up his land in quadrilateral tracts conforming to the subdivisions of the so-called Public Survey. By this rule, it is permissible to file upon land which is laid off into lots of not less than 1/16 of a quarter section—or ten acres—and a claim may be composed of such lots as lie contiguously and which may thus be considered as one complete workable area. The claims are often of zigzag or L shapes, but the locator is enabled, at the extra expense of subdivision surveying, to avoid filing upon, and paying for, much ground that he feels is not desirable in a placer claim. The Government does not survey public domain into smaller tracts than quarter sections of 160 acres each, so that in the taking up of placers it often involves a great deal of expense to carry the subdivisions upon the ground into sufficient detail to ascertain the location of boundary corners.
One person is entitled to as many placer claims as he desires. Each claim of a single individual may contain not to exceed 20 acres and, as said, it must be of one continuous area. Associations of citizens to the number of eight may unite in the location of 160 acres, which will then be held in equal and common interest by the several locators. The restraint placed upon greed in the matter of locations, either placer or lode, lies in certain expenses entailed in work or improvements upon the land before patent may be issued and the legal requirement of the performance of labor upon each claim amounting to $100 per annum. Also, it is required that bona fide values be disclosed upon the ground. For each 20 acres located under the placer laws of the United States, not less than $500 worth of improvements must be made before the issuance of a patent.
The legal (not the technical) definition of lode land covers all grounds containing deposits of ore in its natural and original place of deposit. Under the laws, therefore, a citizen may file upon a tract of land to include a vein, lode, mass, chimney or any other form of ore body. The laws were framed at a time when miners were familiar only with the steep, tabular forms, synonymously termed veins or lodes in their nomenclature, and there were introduced features which time and progress in geological investigations have proved to be entirely unsuited to the needs of locators in many districts.
Our statutes provide that a lode claim may not exceed an area of 20,662 acres, this being the area of a parallelogram 1,500 feet long by 600 feet wide. The intention is to permit a discoverer to lay off a "lode line" along the outcrop of his vein for a distance of 1,500 feet and, at each end, to measure off, at right angles, a distance of 300 feet each way, merely as assurance that he covers the entire thickness of his lode. Since the surface contours of rugged country will crook the outcrop of a dipping plane (such as we may imagine a vein to be) the laws were constructed to permit a claim being laid off with angles or bends in the boundaries so that the outcrop might be kept closely along the middle of the claim.
The above dimensions and area are the maximum permissible under the Federal laws. The Government does not say that claims may not be less in extent, anywhere, nor does it prevent states, counties or even mining districts from making further limitations. In most of the western mining states and territories that have applied the mining law, the full maximum is allowed; but in Colorado no claim is legal if it exceeds a width of 300 feet, while in four counties of the same state claims have been restricted in width to 150 feet. By legislative enactment, since September 1, 1911, claims in all counties of Colorado are permitted to be taken up 300 feet in width. The citizens or miners of any new district, in any state or territory, may elect to limit claims to any size less than the maximum granted by the statutes and such a decision will be recognized by courts as binding upon all comers. This is an example of the rights of custom in establishing common law. In all shapes and widths of lode claims, there is now the rigid restriction that the two end-lines must be laid off exactly parallel.
A Gilpin County, Colorado, Scene
A Gilpin County, Colorado, Scene,
Showing the Prize, Gunnell, Concrete, Gold Collar, and Eureka Mines.
The laws of our country contemplate the right of any locator of a vein to follow such vein down upon its dip, even if it extends beyond vertical planes passed through the side boundaries. The vertical planes through the end-lines, however, may not lawfully be penetrated in the extraction of ore bodies. The application of this doctrine of "extra-lateral rights" has led to innumerable controversies that have crippled many worthy mining enterprises. The inevitable habit of different veins to intersect, branch, unite, and in many other ways to cause complications, has served no purpose but to delay operations, cause legal warfare and embitter neighbors. So unjust have been courts' decisions in interpreting the lax laws that various mining districts have taken unto themselves the prerogative of deciding for themselves what is justice to all concerned; and we therefore find that many "camps" have unwritten laws under which claimants are restrained in their underground operations, to the ground contained between vertical planes through all boundaries, whether end or side. This is obviously the only fair plan, and it is hoped that, whenever the legislators at Washington get time to give to the matter the attention it deserves, our nation will be favored with a revision of this and a number of other objectionable mining laws which have retarded the industry. Ours is the only country having laws permitting extra-lateral rights and, upon this score, we are criticized by all foreigners.
The Canadian government appears to leave the framing of mining laws to the several provincial governments. Ontario and Quebec have very good and simple laws relative to mining claims. In some respects the laws of the two provinces are similar. For example, in each province a claim must be laid out as a subdivision of the usual public survey and is normally 40 acres in extent. Again, no prospecting or locating may be done except by persons holding so-called miners' licenses or miners' certificates, which cost $5 to $10 per year. No extra-lateral rights are recognized.
In Ontario, a patent may be applied for any time within 3-1/2 years of the date of certificate of record, and the land is purchased outright by the payment of $3 per acre. The patent thus obtained conveys no rights to timber or water on the property. In Quebec, patents are never issued and mining claims are held by a sort of lease, as it were. A license to hold a mining claim costs a flat fee of $10, plus an extra fee of one dollar per acre. At times, arrangements are made for holding and working mining property upon a 3 per cent royalty basis.
The Mexican laws permit the location of any number of claims by individuals. A locator is required to employ an expert (perito) to make a careful survey of his claims (pertinencias), which are taken up in rectangular form. Measurements are according to the metric system, and the unit of area is the hectara, which is the area of a square with 100-meter (328-feet) sides, and is equivalent to 2.471 acres. The government's sale price for mineral ground is 5 pesos (about $2.50) per hectare, or approximately one dollar, United States money, per acre. The unit size of a claim is a hectare, and it thus comes about that the words pertinencia and hectara are used somewhat synonymously.
Under United States laws, the owner of agricultural land, if he has not committed perjury in perfecting his title, will hold all minerals which may be disclosed subsequently to the granting of his deed. The proof of false representations will rescind any such patent and the ground will revert to the Government and be again open to location.
In the surveying and laying off of mineral claims for patent purposes, the United States laws require the claimant to put the work into the hands of a mineral surveyor. Such a surveyor may usually be engaged in any mining district and he will hold a commission from the Department of the Interior authorizing him to do this sort of work. He will have passed certain examinations as to his capabilities and he will have filed bonds in the sum of $5,000 for the faithful performance of his duties to both the Government and his client. He receives no compensation from the Government, and each claimant may make such terms with him as are equitable. He must hold no interest, directly or otherwise, in the property he surveys, nor is he permitted to file upon any mineral land. If he undertakes a case for a client his duties require him to survey the boundaries of every other mineral claim which may be contiguous to, or conflicting with, the one in question, and his maps must accurately show all such claims. His notes will contain sufficient data to accurately convey the exact location, the chief topographical features, the conflicts with all other locations, the position, and description of all mining improvements, and many other details which will be required in the final purchase of the land from the Government. The surveyor's fee will vary from $50 to possibly $200 for a single claim, much depending upon the nature of the survey, whether simple or difficult, and upon local financial conditions and competition.
After the filing of the mineral surveyor's notes and plats with the Surveyor-General, critical examination of the documents is made, and if they are found to conform with all requirements, the case is "approved" and it may then pass to the local land office of the district. Next begins a publication period of sixty days, during which opportunity is offered the public to enter objections to the issuance of a patent, either for reasons of conflict or because of fraud. If no such adverse proceedings are instituted, the patent will follow, in due time.
The ultimate expense of securing a patent to a claim of, say, the maximum area will not be less than $225, and it may run as high as $300 if in a region difficult to survey or if there are a good many conflicting surveys.
A mineral surveyor is prohibited from acting as attorney for the claimant in presenting his claims before the Land Office, so an attorney's fee must be added to the above rough estimates. As a matter of fact, although the surveyor does not nominally appear as the attorney, in many a case it is he who makes out all of the documents to be then signed by an attorney in fact. The laws are faulty in this respect. The lawyer recognizes this fact and he asks the surveyor to make out the many legal forms; for who is so fully cognizant of the property and the desires of the claimant as the surveyor who has become intimately acquainted with the premises, its workings, its desirable features and everything concerned with the adjustment of conflicts? It is to be expected that he could best protect the claimant's interests, and it is wrong to retire him at this very critical time prescribed by a foolish law. The fee of an additional man in the case is an unjust burden upon the client. Land Office officials have recognized this fact. They know that the best documents reaching their offices are those prepared by mineral surveyors.
Different writers hold the following slightly different definitions of a placer: One says, "a placer is a surface accumulation of minerals in the wash of streams and seas," while another writes that a placer is "a place where surface depositions are washed for valuable minerals, such as gold, tin, tungsten, gems, etc." One definition conveys no notion of the operations of mining, but is merely geological, while the other involves the thought of the recovery of values.
No matter how or where found, placers were all originally of surface deposition. They are now found in gulches, cañons, valleys, ocean and lake beaches, glacial drifts, and sometimes beneath eruptive flows. Such placers as occupy the courses of streams are spoken of as gulch, valley, bar, and bench placers. The meanings of the first three names are obvious. By a bench placer is understood a deposit that was originally the bed of a stream, but which, in the course of time, has been cut down, or through, in such a manner as to leave a shelf or bench of the "wash" hanging up some distance above the present base of the gulch or valley.
When such deposits that have been covered by lava flows are disclosed and worked, they go by the name of "buried placers." They are, by no means, uncommon, and typical "drift mines" of this sort are operated in California and New Zealand. They present the novelty of working alluvial deposits under cover of solid rocks, and they thus conform to one of the early definitions of a mine, as previously given. Since the workings of such subterranean placers are generally confined to an approximately horizontal zone, the mine passages, to a certain degree, resemble those of a coal mine.
Placer deposits, being of a secondary nature, the materials are not in the place nor form of the original components. The gravels and sands, together with the valuable contents, probably originally existed in some solid forms such as rocks or massive minerals. The primary structures, in the course of ages and by atmospheric agencies, have been disintegrated and carried by gravity and flowing water to lower levels. The finer the decomposed material, the further it has been transported.
If the original rocks carried gold, the flakes of the metal, being of high specific gravity, would tend to settle to the bottom of the channels and to be carried shorter distances than would the lighter, non-metallic particles. The finer the gold, the more evenly will it be distributed in the bed of gravel. Likewise, placers near the heads of gulches, as a rule, carry coarser gold than those farther down stream.
The valuable materials found in placers must, of necessity, be those that possess the property of resisting corrosion and disintegration. The minerals and metals are, therefore, of a very permanent character.
Every find of "values" in a placer is unquestioned evidence that somewhere, above the present deposit, there originally existed primary depositions containing the valuable metals or minerals. The trail can frequently be traced back to them. These so-called "mother lodes" are not necessarily rich. In the case of gold, for instance, these original deposits of ore may not carry the metal in coarse enough particles to be visible and yet the placers may contain nuggets. There are numerous theories proposed to account for this observed phenomenon, but we will not discuss them here. The fact remains that nuggets have been actually produced artificially in flowing water under conditions similar to Nature's.
The methods of prospecting and working placer ground have undergone many improvements, but there are still many men practicing the primitive ways of a generation ago. The use of devices of simple construction and for operation by muscular effort is still familiar in many regions; and there are good miners who cling to such practice in the belief that it is the cheapest and truest way in which to ascertain the values of wash deposits. Also, there are many placers of limited areas and irregular shapes that cannot be well handled in any other manner.
With a "pan," a man can wash, in ten hours, not over one cubic yard of dirt; and to accomplish this amount of washing the ground must be very loose and favorable. An ordinary ten-hour day's work is about 100 pans. This is equivalent to about one-half of a cubic yard, which is the unit of volume in all placering operations. One may thus readily arrive at the cost of carrying on operations in this way. A cubic yard of ordinary placer dirt is the equivalent of less than two tons. A batea is the Mexican equivalent for the American iron gold pan. It is a sort of broad, conical, wooden bowl and its capacity is not equal to the pan.
A "rocker" or "cradle" is a trough on rockers somewhat like the old-fashioned child's cradle. In using it, a stream of water is caused to flow into the device which has been nearly filled with gravel and the miner gives it a rocking motion that causes the contents to classify or stratify according to the laws of specific gravity. The valuable particles, being the heaviest, will settle to the bottom, whence they may be subsequently removed. A "long tom" is an inclined, narrow box set stationary with a constant stream of water entering at the upper end. Gravel is also shoveled into the device at the same point. The process is more continuous than the preceding ones, the values accumulating at the bottom of the lower end, while the upper layers of gravel are carefully removed by skimming with shovels. The work will keep two men busy and the capacity is correspondingly greater. With a long tom, two men will ordinarily handle about five or six cubic yards in ten hours.
Whenever deposits of a broad area, with considerable and uniform depth, are thought to be valuable, it has become a practice to prove their value by "prospect drilling." This is a mechanical method and one form of apparatus employed is of the churn-drill type common throughout oil and coal regions. With these portable machines, holes are put down to bed-rock at intervals across the ground. As they are sunk, the holes are cased with iron pipes, the drillings are carefully saved and washed, and the values are estimated for each foot of descent. From the summation and averages obtained from all the holes, a very fair knowledge of the ground's worth can be obtained.
Intensive placering is now the order of things and the marvelous increase in the use of dredges attests the success which these "gold ships" have attained. It is very interesting to watch the operations of these huge boats loaded with ponderous machines, especially when they are installed in inland regions or up in high mountain gulches. Yet numbers of them are thus in steady use. Wherever suitable beds with a tolerably uniform size of boulders and gravel are found, dams are built to retain the flows of streams until ponds are created of sufficient size to contain and float the barges.
Dredges of Yuba Consolidated Goldfields, Hammonton.
Dredges of Yuba Consolidated Goldfields, Hammonton, California.
Continual improvements are being made in the construction of these mammoth machines with a view to economy in operations that will result from greater capacities. All costs of placering are reckoned per cubic yard washed. Costs have been rapidly dropping during the past decade until now some companies, with extensive operations, are handling dirt at not to exceed three cents per cubic yard for excavating, washing, wasting the refuse, maintenance, repairs, labor, taxes, interest on investment, and the depreciation of equipment. Such figures will hold good only under very favorable natural conditions of ground and climate such as prevail in California; they have not been attained in the frigid regions of Alaska nor in the torrid South American interior. In view of the wonderful improvements brought forth by mechanical engineers, it is improper to deny that the future will bring still further reductions in placer costs. On the contrary, the signs are good for material reductions.
Dredges are very costly in their installation. They are usually designed to handle so many thousands of cubic yards per day. It has been stated, as a fair but rough rule, that "bucket" dredges will average, in initial cost, one dollar for every cubic yard the boats will handle per month. Thus, if a dredge of this type is built to treat fifty or seventy thousand cubic yards in a month, working steadily, the costs will be respectively $50,000 or $70,000. Other types of dredges, known as the "dipper" and the "suction," will cost less than the bucket type, but have not gained general usage.
"Hydraulicking" is extensively practiced. This term signifies the working of placer deposits by water which is conducted through flumes and pipe-lines and, by means of nozzles called "giants" or "monitors," is directed, in huge jets, against the banks of gravel. These banks or walls are thus torn down and, by the same water, the loosened, disintegrated materials are caused to flow into and through long, wooden, box-like troughs known as "sluices." The floors of these sluices are paved with ribs, cleats or other obstructions termed "riffles" whose function it is to retard and collect the heavy particles which may, later, during the process of cleaning up, be removed as the valuable product. The word "sluicing" is frequently used quite synonymously with hydraulicking.
Costs of this latter sort of placering are considerably higher than those of dredging; but there are many deposits not adapted to dredging operations that may be nicely worked by sluicing, so that there will always be a field for this scheme. Average costs are difficult to obtain since it happens that most of the companies now operating hydraulically are secretive in their accounts. More labor is entailed, more time is required, greater delay is occasioned in cleaning up, and the amount of water used is much greater. Where water is abundant, this last item need not be considered. It is well to remember that even a very large dredge, while requiring a continual and large flow of water through its devices, can still operate with just the water in which it floats, this water being pumped and used repeatedly; whereas, in the case of hydraulic mining, the water may be used but once and, consequently, there must be a large supply and at a good head or pressure.
But, in spite of these disparaging points, we find instances in which, under peculiarly favorable conditions, hydraulicking has been carried on at very low figures. E. B. Wilson says: "The yield of the gravel at North Bloomfield was 7.75 cents per cubic yard; the cost of mining, 4.1 cents per cubic yard. The yield per cubic yard of gravel at La Grange was 10.19 cents, the cost of mining, 6 cents. The costs of mining at these two mines would analyze about as follows: Labor, 60 per cent; supplies, 17 per cent; water, 13 per cent; office, 10 per cent. Ground carrying but 3.99 cents per cubic yard has been worked at a profit at the first mine. With such a small margin to work on, it is evident that skill and executive ability must be provided from the pipemen up." It is claimed that an Idaho mine was worked profitably with less than two cents value in the dirt, but this is to be regarded with some doubt.
The Snowstorm Placer, Fairplay, Colorado.
The Snowstorm Placer, Fairplay, Colorado.
A typical Hydraulic Mine.
There are large deposits in the arid portions of the globe where water for working is not obtainable. To meet such conditions, numerous inventions continue to be placed upon the market. These devices are all planned in such a way as to use very little or no water. If water is required at all, the machines are expected to use it repeatedly. The machines are built to effect the segregation of the precious contents gravitationally, electrostatically, pneumatically, and by amalgamation with mercury. It is too early to say how successful such devices will prove in commercial operations. Because some of them have not "made good" does not mean that genius will not yet cope with the situation; and we look into the future to see large operations efficiently and economically conducted by dry placer machinery. There are now no authentic figures obtainable upon this question of dry placering costs.
Some mention has been already made of open mining. The greatest development of this sort of mining has come about since the application of the modern steam shovel to the excavation of ore. This practice was an American innovation and it is being adopted throughout the world wherever natural conditions will warrant.
Within the past few years, immense bodies of iron ore have been discovered in northern Minnesota and the adoption of these immense, mechanically operated shovels has worked such economies in the mining of this kind of ore that entirely new cost figures have been established and tonnages are being produced which, a few years ago, would have seemed unbelievable. There are about a dozen mines of this "open pit" type that have each produced over a million tons of ore per year in a season that must cease with the close of navigation on the Great Lakes. One mine has shipped over three million tons a season.
At the Utah Copper Company's mine in Bingham Cañon, Utah, a great deposit of low grade, copper-bearing eruptive rock is being handled upon a steep mountain-side by this same scheme. This ore averages a little less than two per cent. in copper, but so economical is the handling of it in such vast amounts that a neat profit is made above all mining, transportation and milling charges. When the red metal sells at thirteen cents per pound, the gross value of this ore is about $5.20 per ton. This mine has maintained an output of ten thousand tons or more per day over long periods.
A famous gold mine in Queensland, Australia—the Mount Morgan—is also being worked by steam shovel methods. The deposit is here in the form of a small mountain and the operations are gradually razing this landmark to the level of the surrounding plains.
The mining of low-grade gold ores by open-pit methods has taken hold in America, and an example of the practice may be found at the Wasp No. 2 mine in the Black Hills. According to published accounts of the operations of this company, all of the costs of mining and treating the ore amount to only $1.02 per ton. The ore body is a bed of quartzite lying nearly flat, and averaging in the neighborhood of only $2.50 per ton in gold, the only mineral of value. The recovery of this metal is at the rate of between 75 and 80 per cent. efficiency, or about $2 from each ton. The net profit is therefore close to one dollar per ton. This very modern scheme of mining has been made possible through the recent advances made in the cyanidation of ore, and it is going to pave the way for many more such mining plants.
Steam Shovels and Churn Drills, Copper Flat, Ely.
Steam Shovels and Churn Drills, Copper Flat, Ely, Nevada.
The Nevada Consolidated Copper Company has conducted vast mining operations "in the open" at Ely, Nevada, by the use of 95-ton shovels having a capacity of two and one-half cubic yards per dip. One shovel has handled as high as 2,800 cubic yards (the equivalent of about 5,500 tons) in nine hours; but this must be recognized as an exceptional run, and cannot be taken as an average. The ore has a thickness of about 200 feet and covers many acres. As in the majority of such properties, there is here a large amount of "overburden" to be removed and disposed of before the ore can be excavated. This process of uncovering the ore body by the removal of the overburden is called "stripping." The cost per ton of ore mined is said to average 55 cents.
In an open mine there must be maintained a system of continually changing tracks placed upon grades (sometimes rather steep) and with sharp curves. With multiple switches, numbers of small locomotives are kept busy pulling and pushing up and down the tracks with their strings of loaded cars and replacing the "loads" with "empties." When such operations are upon a mountain-side, a very beautiful panoramic view may be had from the opposite side of the gulch.
Generally, the ore material is disintegrated to some extent. In some cases, it will actually crumble down before the advance of a steam shovel. In other mines, it is necessary to drill large holes which are loaded and blasted.
It is becoming more and more important for the active mining man to post himself upon the methods and economies of this latter-day mining practice. The development of this open or surface mining has introduced entirely new economic ideas. With no costs for timbering of mine passages, for ventilation, or for hoisting, and with a very material decrease in manual labor per ton mined, immense masses of rocks are now really ore, although a few years ago they were nothing but lean, country rock.
In consequence of the success attained by the pioneers in this kind of mining, there has been created a demand for properties possessing large deposits of low grade ore that is workable on this intensive scale. Copper properties have been holding a prominent place recently and stockbrokers carry regular lists of "Porphyries," this nickname having been coined to cover the companies operating in the low grade porphyry ores of the Western United States. Not all of these porphyry companies will use surface mining methods. Some companies in the Globe District of Arizona have started extensive underground schemes for mining large tonnages very cheaply by "caving" methods.
The word "exploitation" is used by many mining men and engineers to signify a plan of so opening up ore deposits as to render the contents removable. The same persons use the word "mining" to mean the operations involved in the actual extraction of the ore exploited. It is sometimes difficult to draw any line between the meanings of these two words for, as handled by different men, with varying shades of intention, they are sometimes synonymous. Thus, if exploiting an underground mine, which carries ore right from the surface, means developing the mine in such a way as to provide for a large, steady production, it is difficult to see why the ore taken out in this process cannot be said to be "mined."
By "dead work" is usually meant that work of opening up a mine which will put or keep it in a producing condition but which does not supply any remuneration in the shape of ore (or coal). Again, as used by some men, there is little distinction between this work and exploitation. There may, however, be lines reasonably drawn between these three terms, and therefore the following definitions are proposed:
Dead work is such work as is necessary to develop an ore body, but it does not produce any ore. It may be prosecuted for drainage or ventilation purposes or for creating passage-ways for men and products.
Exploitation is also work performed in opening up or developing a property, but it does not contemplate the value of the extracted materials which may, or may not, be of any commercial importance. Indeed, much ore might be extracted during work which was carried on merely to define extents or boundaries of ore bodies. In this last supposition, the original sense of exploration is brought out and this should serve to fix the definition clearly in mind.
Mining may be restricted to mean the methods and work involved in the profitable production of the mine's ore (or coal). The term would not be used to cover operations of shaft-sinking, tunneling, and the like, unless such work be in the valuable materials. Mining may be said to begin whenever there is produced an output upon which there is some profit. Exploitation may be in valuable ground. If so, we may say that mining is in progress during the exploitation. The driving of levels or drifts in an ore body—or of entries in a bed of coal—produces the valuable products of the mine, and we may, therefore, consider that mining is taking place.
The driving of a crosscut through barren rock to reach an ore body is dead work; but the driving of a drift or level in a vein is either exploitation or mining. Dead work produces no ore. Exploitation may, or may not, produce ore. Mining must produce ore.
Throughout all of the above and the following discussion of this chapter, the reader should bear in mind the point that the word "coal" may be substituted for the word "ore" without altering the substance of the definitions or the conclusions.
Before a mine is opened up, the economist-manager will consider many items. In the first place, care must be exercised in the examination of the title to the property. A mineral property may have passed through the most complicated kind of transfers of fractional interests in the title, just as is true with ordinary real estate. The abstract must be traced back clear to the issuance of patent from the Government, and then on back to the original location. With an undeveloped property (a prospect), this precaution is essential to estop any possible pretensions to ownership, by outside parties, in case the ground subsequently turns out to be exceptionally valuable. It has often been the case that no obstructions from any adverse claimants have been met until owners have, in good faith and at great expense, developed splendid mines. Then suits for possession or partial ownership have been instituted, sometimes with marked success for the plaintiffs. There are persons who make it a special line of business to examine titles to mining property, and it is economy for the average manager to employ such experienced men to attend to these matters.
Topographical considerations will hold a place in the study preceding the opening of a new mine. The nature of the surface of the property and the surrounding country will largely influence in the selection of the proper site for the mine's mouth. Neglect upon this point has been a common cause of failure in mining operations.
A mine opening must be away from all dangers of snow-slides, rock-slides, cloud-bursts and deluges from overflowing streams or breaking dams. It may make a difference in the mine's ventilation as to which direction the prevailing winds blow and therefore upon which side of a hill the mouth be opened.
Transportation facilities must be given due thought. If means are not already at hand, one must inquire into the feasibility of constructing some form of carrier; and here, again, will enter the question of the surface's contour. If a railroad is out of question, possibly an aerial tramway may be constructed. These modern conveyances stop at no obstacles of surface configuration and are dependent only upon the necessity of having the point of delivery lower in altitude than the point of loading at the mine. With some of the modern improvements in these installations, mine products are being transported up-hill as well as down-hill through the application of power. In mining regions, it is generally the case that the mines, themselves, are above the settlements in which are the railroads or treatment plants, so that the mine products will transport readily by the natural force of gravity.
Climate holds an important place in the economics of mining. The working of very rich pieces of ground may prove a losing proposition in some portions of the world where the climatic conditions are such as to render operations possible during only a very small portion of the year. Extremes of heat or cold, malaria or other pestilential obstacles, long rainy seasons with floods, and the hostility of native humans, beasts or insects have accounted for the abandonment of seemingly attractive mining projects.
The question of labor must be given due thought. It is true that the best miners on earth are Americans. We do not deny that many of our miners are of foreign birth, but the fact remains that they perform better and more intelligent service than do their fellow countrymen who have not been adopted into our country. Our men are in demand in the mining development of foreign countries. An American mine manager will always experience dissatisfaction while endeavoring to get, from natives in foreign parts, the same efficiency that he is accustomed to receive from the miners "at home." He may be paying a good deal less per capita for such labor, but he finds he is actually paying more per ton of output.
Even within a single country, there are notable differences in the worth of labor. The natives of some of the Mexican states are far preferable to those of other states. Within the United States, there may be discerned material differences between the efficiencies of the citizens of various sections, when it comes to mining. One cannot procure as competent miners in some of the agricultural states as in the typical mining states. This is but to be expected. For instance, there are deposits of lead ore in the "moonshine" regions of Kentucky which have never been successfully worked, and the real cause of failure, in the writer's belief, lies in the inability of superintendents to obtain real miners either in that region or from the outside. The residents will never become miners; outsiders will not enter for work under existing sociological conditions.
The question of unionism is sometimes held by managers as a deciding one when debating the opening of a mine. While there are those who will broadly denounce such organizations, there may be found other and just as successful mine operators who declare that the effects of union control over their miners are beneficial to their companies' interests. Probably the greatest objection to unionism raised by operators is that they resent the dictation that accompanies the inauguration of union rules in their mines. The owners and managers prefer to run their own business to suit themselves. Some managers are so imbued with this conviction of their own rights that they will refuse to open up mines or, if they are operating, they will close down their mines before they will submit to the demands made upon them by the union officials.
On the other hand, there are mine managers who prefer the presence of some central, labor-controlling body; for they believe that the men who belong to such a large federation or organization will, and do, have less complaint to make and therefore work more freely than is the case with the independent laborers. The argument is that these union men are satisfied because they feel that their interests are being looked after with a sort of attention that they, individually, could not give.
This is not a place to discuss the crimes that have been laid at the doors of both the labor organizations and the mine owners' associations. It is safe to assume that wrong has probably been done by both sides. But it is furthermore right to believe that most of the crimes were not authorized, nor recognized, by the officers or the majority of members of either side. Individual members must not be taken as averages of the membership in any kind of civil, social or political organization.
It seems entirely wrong that politics should enter into the considerations of a mine manager whose operations are apparently so apart from affairs of state; but the fact remains that there are places where mining operations cannot be carried on without the good will of certain officials of the state or national governments. It is not advisable to enter into any compromising terms to gain privileges for carrying on any legitimate business for there are other, better ways, generally, of attaining the justice that is deserved.
One must not omit to investigate the sources of supply for all the needs of a mine and its camp. There are many kinds of materials needed to keep a mine going. Fuel, machinery, timber, water, food for men and beasts, lumber, and all household furnishings and necessities must come from some markets or natural sources. It behooves the cautious manager to see that all these things may be had in ample amount and at figures which will not prove annihilating to his business.
In Utah, there are mines which have all their timbers framed in and shipped from the forests of Oregon, the sawing and framing being done before shipment to save on freight. The fir of Oregon is shipped to distant Australia for mining purposes. The arid camps of Nevada get their supplies of timber from the sister state, California. The Michigan mines are fortunate in being in a lumber region. Colorado's metal mines are more favored in the matter of timbers than are the coal mines of the same state. Most of the coal mines are upon the barren plains, while the metal mines are chiefly in the wooded mountains.
Mill of the Pittsburg-Silver Peak Gold Mining Co., Blair.
Mill of the Pittsburg-Silver Peak Gold Mining Co., Blair, Nevada.
Water may be too scarce for the needs of a mine or its community. There may not be sufficient to supply boilers or a mill, or for the domestic purposes of the workers. On the other hand, water may be so abundant in the mine workings as to prove a deterrent factor in profitable operation. With shaft mines, having deep workings and low grades of ore, if water must be delivered mechanically, the costs for such drainage are frequently prohibitive of mining. Some mines, in arid regions, have been fortunate in striking such flows of underground water that it has been possible to operate mills right at the mines. In this way, the cost of water hoisting has been more than compensated in the milling benefits which, in turn, have decreased freights and treatment charges.
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.
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.
Mills and Shaft House of Daly West Mine, Park City, Utah.
Mills and Shaft House of Daly West Mine, Park City, Utah.
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.