« PreviousContinue »
Perhaps the most correct method of procedure would be, to first describe the varieties of gold ores, their usual position, their characteristics, and attendant phenomena, together with their chemical constituents, and some observations upon their formation, such as may be drawn from actual observation and close examination.
But practical utility being my aim, and as the various ores are to a great extent well understood by those who are working them, I shall defer this part of the subject until after the appliances have been fully treated upon, and then take it up, in the hope of presenting the whole subject to the miner and general reader, in a plain and simple manner, which, if it does not present any new truths, will at least bring together, in a collated form, many of those already known.
Leaving, therefore, the description of mining and of the ores, I would, before entering upon that of the varied machinery, state a few important facts and principles, that during the working of the ore must never be lost sight of.
1st. Regularity and uniformity of “feeding," or supplying the machinery with ore, must be rigidly observed.
If the ore at any portion of the work is crowded into the · machinery, without a due regard to the quantity that is to be regularly supplied to it, it follows that either the crushing or the amalgamation must be proportionably imperfect. If, in the crushing department, the ore will be passed through the crusher, not reduced to that extreme state of disintegration, which is requisite to liberate the minute particles of gold contained in it. This point has been fully borne out in my own experience, and corroborated by that of all practical operators with whom I have corresponded or conversed upon the subject. Numerous author. ities to substantiate this rule could be quoted; but that of Hocheder in his valuable experiments, is directly to the point. He found that regularity was essentially requisite. That care was necessary that the ore was not passed over the works too coarsely ground; as when such was the case, much of the gold was washed away in the grains of the ore. He says, " The quantity of coarse stamped jacotinga (ore) which is rolling over the skins, into the river, attracted my attention, and I separated a portion of it from the fine stamped jacotinga, by means of a sieve, and caused the coarse grains to be pounded to a fine state, which showed, by washing, very good samples of gold. But the coarse grains with their contents are lost.” In the amalgamating department the quantity of ore, if too great, will prevent that direct contact of the gold and mercury, so necessary to produce the desired amalgam, and consequently much of the gold will be lost by being washed away. If, on the other hand, the quantity of ore be deficient, valuable time will be sacrificed and an undue wear of machinery will be produced. The gold, in this case,
will, much of it, be washed away by the quantity of water being disproportioned to the amount of ore. The flouring of the mercury will also be greatly increased, entailing an additional loss, if the supply of ore is insufficient. As I have already brought Hocheder forward as a witness, with his experiments, I will avail myself of his able scrutiny once more. He found that from forty to fifty per cent. of the gold was lost by being stamped to too fine a powder; as by this means “the smallest particles of gold, stamped nearly to the state of slime, and which lose the action of specific gravity, will alone amount to from twenty to twenty-five per cent.; which is never to be gained by any means of separation founded on mechanical principles.”
2d. The "feeding" must be slowly performed.
Gamboa, on "amalgamation,” states to this purport, in regard to slow manipulations.-In Guanaxuato, where the matrix is hard, and the ore finely disseminated through it, and more pains are taken in this operation, it is not usual to allow the charge to exceed six or seven quintals; to grind which, four and twenty hours are employed, and sometimes, if the ore be rich, as much as eight and forty hours.
A great advantage is derived from reducing the ore to the fine powder thus obtained, as appears from the analysis of the residue of the amalgamating process; and that it would be highly advantageous to the other districts to follow the example
of Guanaxuato. Hocheder also insists upon slowly operating the ores. My own experience was to this effect; I was using a new crusher, Bullock's Quartz Crusher," and supposed that all that was necessary was to crush as fast as possible, and rush the slime through the amalgamating apparatus. I crushed the quartz rock at the rate of from two to two and a half tons per hour, but I obtained no gold. I supposed that the large amount of mercury used was not "charged," as the point of saturation it must reach before it will yield amalgam, is termed, and worked on until I was sure that it was so; I then continued to pass the slime through as rapidly as ever; but obtained no gold." This was to me a mystery ; assays proved the ore to be rich; panning showed it to be so; particles of gold were visible in much of the ore, but when it was operated upon the precious metal disappeared. I then began to work more slowly, and found reason to be encouraged; and continued the slow movement until I had brought down the crushing action to the capacity of the amalgamating force employed, and the result of the last experiment tried upon one ton of ore, which gave fifty-six dwts. of amalgam, proved that the work must be slowly performed.
3d. A state of rest must be allowed to the ore, as frequently as can be done, during the manipulation.
4th. While in that state of rest, a continued showering of water-drops should be maintained from a moderate elevation,
upon the surface of the water in the tanks containing the slime.
By allowing the slime when washed from the crusher to fall into tanks of sufficient capacity to retain one or two days' work, it will be found that this state of rest will facilitate the deposit of the particles of gold, and prevent much of the loss, which results from allowing the water to pass through the whole process, in one continuous stream, thereby carrying away much of the gold suspended in it before it has time to subside to the bottom of the current.
The fact is well known that gold leaf is easily wafted away by a very light current of air ; if the gold can thus be suspended in so light a fluid as the atmosphere, it certainly can easily be washed in a current of the more dense fluid, water, and more particularly, if that water should be rendered still less fluid, by the intermixture of large proportions of earthy materials. The tendency of gold, when in minute particles, to float upon the surface of water, may very easily be shown, by finely dividing a small portion of gold left upon a smooth card, and gently blowing the particles from the card upon the surface of water; or by filing a small quantity of gold over the surface of water; or by placing a small quantity of water in a basin, and so inclining it that only a portion of the bottom shall be covered by the water; then, allowing the filings to fall upon the uncovered portion, and so turning the basin that the water shall gently flow over that portion upon which the filings have fallen. These simple experiments will readily prove that gold will float away upon the water, unless the utmost care is used to prevent such an occurrence. By freely wetting the fingers, or, better still, a whis -broom, and sprinkling the water drops off upon the water upon which the gold is floating, the advantage of this vertical agitation of the water will be instantly apparent.
It is in this state of rest that the tine particles, mentioned by Hocheder, as quoted under the first rule, as "never to be gained by any means of separation founded on mechanical principles," are, most of them, at least, to be saved.
5th. In all horizontal rotary motion the discharge of slime should be from the centre.
When the slimes enter machinery of this character, their specific gravity causes them to fall at once to the bottom; there the centrifugal force of the rotary motion, either of the bowls themselves, or of the appliances contained in them, forces them to the circumference, and produces an under current in the same direction, and a tendency for the slime to accumulate near to the outer rim of the aparatus. The under-current is necessarily counterpoised by an upper current from the exterior to the centre. Nothing but the lightest particles can float along this gen. tle current across the apparatus, without sinking beneath the sur
face, before they pass the entire distance. Consequently only the lightest sands can pass away. By this plan little or no loss can ensue from the floured mercury, as it must sink and be recombined with the fluid metal.
6th. Fresh, clean water should be introduced at each stage of the amalgamation.
The object of this arrangement is so obvious that it requires but brief explanation. After each state of rest, the slime will have to be removed by band from the tanks, and fed into the machinery; it here becomes necessary that the water should be as free as possible from any admixture of foreign matter, to allow the specific gravity of even the most minute particles of gold to have its full effect; which it could not do were the same water, as had already been once used, to be again operated with.
Considering the ores then as already at band for operating upon, the first step in the process will be to reduce them to that state of division by which the gold can be most easily separated from the accompanying rock; this is accomplished by
CRUSHING. The crushing of gold ores has been endeavored to be effected in as many various ways as there were minds to plan the mechanical arrangement. It has appeared as if every man that ever heard of a gold mine, immediately believed himself to be the only person capable of constructing the reqnisite machinery for the successful operation of the ore. Men have placed them. selves before their tables, and spreading out their drawing instruments, have elaborated upon the smooth surface of the Bristol-board or their drawing-paper, most beautiful specimens of human ingenuity, developing in the ablest manner the highest perfection of mechanical principles, and producing ornamental delineations of gold-working appliances, which, when patented, constructed, purchased, transported and placed upon the mines, were found worthless, futile, and useless. They lost sight of the important fact, that some experience was a necessary ingredient to combine with their calculations; they forgot the homely adage that “Necessity is the mother of invention, and consequently have produced works that are now scattered broadcast over the mining districts, which serve only as monuments of folly and illdirected labor. To crush gold ores, which usually are of siliceous formation, requires heavy, ponderous machinery, the mere weight of which, passing over the quartzose rock, reduces it to a powder. No elaborate combination is involved in this requirement. The machinery must be massive, simple, and of such construction, that the portions most liable to wear away by the friction of the ore, can be easily replaced; too strong in its parts to break under the powerful pressure to which it is subject, and made of such permanent material that no exposure to the changes of cli
mate or weather can sensibly affect it. It should be sufficiently capable to perform all the work that may be required of it to do; that is, if twenty, thirty, or even fifty tons of ore per each twenty-four hours, can be raised from a mine, the crusher should be able to fully pulverize it. The machinery should always be sufficient to control the mine. If not adequate for this purpose an accumulation of ore must ensue, or a retarding of the successful development must occur. It is owing to the failure of so many inefficient machines, that much of the doubt and discredit now attached to mining operations has arisen. It is seldom that an actual practical test has been made of the machines before they are offered for sale; the whole merit which they are said to possess is purely theoretical. The only way to prove any machine is not upon a ton or two of ore under the most favorable circumstances of working, but to place it upon the mine, and with the work before it, see if it can be made to execute it. No other test should ever be accepted. Too often the merits of the machines have been extolled with all the force that language and imagination could command; and could they have accomplished a moiety of the “immense advantages,” which were claimed for each, as its own peculiar value, they would almost have gathered the golden grains from a barren sand, or have created them from the ingredients of a solid rock, utterly devoid of metallic pre
The uninitiated have credited these tales of marvel, and have eagerly paid their good dollars for bad stock. And now, without stopping to discriminate between their own folly connected with illegitimate mining, and sound common sense, and true economical mining, they class all mineral operations under the censorious title of " humbug!" From the feeling thus engendered and promulgated, capital which else would be invested in mining properties, seeks other channels, to the detriment of the true mining interest of the country. There is no branch of industry, from the advancement of which the capitalist can de: rive more pecuniary emoluments than from that of mining; legitimate, economical, well-directed mining. From the little knowledge which I have been able to gather of the mineral resources of our country, I can foresee that ere the close of the next half century, the mining interest of the United States is destined to be the most important resource of national wealth. It is therefore with emotions of pain that I see these worthless specimens of machinery palmed oil upon a class of men, who, with a laudable ambition of availing themselves of mechanical aid in the prosecution of their labors, and by their very eagerness to progress
, are easily deceived by the plausible and falsely termed merits of the invention. Every such machine that is placed upon a mining location is an additional clog and hinderance to the prosperity of that mine individually, and to the mineral welfare of the entire country. How, ask the mining managers, are we