ore is not uniformly distributed, but occurs in pockets, and sometimes a vein which has yielded a large bonanza at one time may be worked for several hundred feet without yielding more than a very moderate amount of silver. Still, although the silver is not continuous throughout, yet, in the vein above alluded to, the old workings show a continuous body of ore, varying from 3 to 10 or 12 feet in width, and to a depth (these statements are made from memory, and not from notes) of over 200 feet. The present tunnel has cut eight large veins, all bearing silver, and by judicious working of these veins, following the indications of rich ore, new deposits may be constantly opened, so that once such a district is developed it may be as successfully worked as if there were but one vein with a continuous body of ore. The Mexicans were not prudent miners. If a large and rich deposit was opened they worked it out as rapidly as possible, not providing by dead work on other veins for the time when their bonanza should be exhausted.

It has been said that galena and zinc-blende accompanied the silver. These minerals, taken in connection with a lively appearance of the calcite, and the presence of arsenical iron, are the miner's guides. By their occurrence he judges where to look for the silver, and an experienced man can follow them up, until from a merely promising rock he proceeds to the silver itself. The country-rock is diorite, very hard and tough near the mouth of the tunnel, but becoming more tractable further in, and always changing decidedly when near a vein. Occasionally the diorite, in a somewhat altered state, and mixed with calcite, forms the vein-rock, as is the case in the largest and richest vein now worked in the tunnel; but invariably, wherever pay rock occurs, there the silver is found with the above accompanying minerals.

As regards the method and expense of mining and reducing the ore, the following facts are given, taken from notes furnished the writer, during a twelvemonths' stay in Batopilas, by the superintendent of the company, who is also the vice-president.

The cost of mining per ton, including all dead work, such as running the front of the tunnel, prospecting, &c., is $33; the actual cost of extracting the silver-ore, including necessary drifts, and the work on all the veins yielding silver in paying quantities, is $8 per ton. Hauling to the works, on donkeys, about half a mile, 62 cents per ton. In another article other details of mining expenses and methods will be given.

The ore is sorted into three classes: first class, value $2,500 and upwards perton; second class, value $1,000 to $2,500; third class, all under $1,000, averaging perhaps $250.

The third-class ore is dumped at the stamps, the better ore is kept in a store-room and weighed out. All the ore is crushed in a battery of three small stamps, weighing about 300 pounds each, with a fall of 9 inches, and a capacity of 8 tons per twenty-four hours. The ore falls through a screen with five-eighth inch slits, and is then charged in the arrastra. The lumps of silver are separated by the screen, cleaned by hand, and, with the larger lumps of pure silver from the mine, refined with the retort silver. The stamps are run by a horizontal water-wheel, which will be described under the arrastra. This latter apparatus it is unnecessary to describe. Suffice it to say that it is a large Mexican arrastra, 9 feet in diameter, with two stone mullers or runners, weighing 600 to 800 pounds each. The wheel that runs it is, however, peculiar. The arrastra is built on the top of a pile of masonry in a deep pit. In the center of the arrastra rises a shaft, revolving on a pivot which rests in a plate raised a little above the bed of the arrastra, and from this shaft horizontal arms project beyond the rim of the arrastra. From

these arms descend rods which support a horizontal wheel, that thus revolves around the arrastra a few inches above the bottom of the pit. In the periphery of this wheel, at intervals of 6 inches, are inserted rectangular floats, slightly concave, and set up edgewise, as if to receive the water from a tangential, horizontal chute. These floats are called cucharas, (spoons,) and hence these arrastras are called arrastras de cuchara as distinguished from the arrastra de mula. The water acts on this wheel solely by its momentum acquired while descending very rapidly through a tapering chute, having a fall of 8 feet, with a length of 12 to 15 feet. It is very evident that there is a great loss of power here, but as the works are supplied with a superabundance of water by a ditch, and the three arrastras are capable of reducing all the ore required, this makes little difference. These arrastras are universally employed in Mexico when water-power is at hand. Such a wheel, with a diameter of 20 feet, will carry the two runners of the arrastra as fast as four stout mules, which could not work more than eight hours per day, and it runs the battery of stamps as above stated.

From the stamps the ore is taken to the arrastras, into each of which a ton, more or less, according to the size, is charged at once. A few buckets of water are thrown in, just enough to give the mass a certain consistency, which is very essential to the proper conduct of the grinding process. If there is too little water, the ore is raised up and pushed forward by the mullers, without being ground; if there is too much water, it packs beneath the mullers. Water is from time to time added to preserve the proper consistency of the ore, and after the operation has been carried on about eight hours sufficient quicksilver is added to amalgamate all the silver in the ore. Generally the arrastra is charged with one ton per day of the third-class ore, requiring some 25 pounds of quicksilver, and after three days' run, or whenever the amalgamator thinks proper, rich ore is added, requiring proportionally more quicksilver, for the purpose of getting a suitable amount of amalgam collected in the arrastra, preparatory to cleaning up. Some hours after adding the quicksilver the amalgamator takes a portion of the charge out in a horn spoon, washes it, and thus judges whether there is the proper amount of quicksilver present. These assays are regularly made, but, after a little experience with any ore, he soon learns to gauge the amount of quicksilver very closely.

Every morning, after the silver appears to be thoroughly amalgamated, a large excess of water is added and the arrastra kept in motion for four to six hours; the heavier particles then settle, the amalgam separates from the fine ore, and after the machine has been at rest for a short time, the water is run off, carrying with it all of the finely ground and desilverized ore. The coarser grains of ore, not yet sufficiently reduced, remain and are ground with the next charge. The tailings thus obtained are very poor-so poor that the most experienced men in the place are unwilling to pay $3 per ton for them, with the object of extracting the silver on the patio. They contain nearly all of the galena, zinc-blende, and arsenical iron of the ore, a very little quicksilver and amalgam, and any arsenical silver (ruby silver) that may occur, with the exception of a trace that stays in the amalgam, either owing to its density or to native silver adhering to it. Most of the sulphuret of silver, being less brittle, and therefore not so easily reduced to powder, settles to the bottom of the arrastra and is taken out with the amalgam, in which it is plainly visible after washing. The rich tailings, removed after the rich silver-ore has been added, and just before a clean-up, are more valuable, and are saved for concentration or treatment on the patio.

As regards the quicksilver required in this part of the process, it is found that ore containing coarse silver needs less than ore with fine silver, in proportion to the amount of silver.

When the rich tailings have been run off, the top layer of coarsely ground ore is removed with iron scrapers and reserved for the next charge. Then the amalgam is scraped up and carried in wooden bowls (bateas) to the washing-tank. This amalgam seems, to the superficial observer, scarcely anything more than coarse sand and slime, but, on adding to a suitable amount of it, in a shallow wooden bowl, the proper quantity of quicksilver, and washing it, stirring and rubbing it constantly with the hand, the clean amalgam is obtained. The dirt thus removed from it is rich and is reserved for concentration by washing on the plane-table. About 10 per cent. of the quantity of quicksilver already employed in the arrastra is added to the amalgam in this process of cleaning. A small portion of amalgam from the finer-grained silverores is sometimes very carefully washed, the black silver (sulphuret) being removed by grinding the amalgam on a stone and washing it thoroughly, and the resulting very pure amalgam, after straining, is retorted carefully, and furnishes the bullion used in paying expenses. It is even purer than the refined silver cast into bars.

The clean amalgam is now strained in canvas cloths, and this is the most tedious part of the process. As the amalgam is at present retorted a very firm amalgam is required, so that it is not found sufficient to strain the amalgam in large bags by merely twisting them with a stick, but the quicksilver must be thoroughly pressed out from small balls, not over 2 to 2 inches in diameter, by squeezing and rubbing them in the canvas with the hands. The coarseness of the silver, which is frequently present in nails, renders the separation of the quicksilver impracticable by any other means yet tried; from the very finegrained amalgam obtained on the patio the quicksilver is much more easily expressed. Probably if some other system of retorting were introduced this part of the process might be made less laborious. The strained amalgam is charged into quicksilver-flasks, from which the bottom has been removed. About 65 to 70 pounds of amalgam are introduced, and then the flasks are set aside to allow as much of the quicksilver to drain off as possible, and also to harden the amalgam. In a day or so, or as soon as four of these flasks are ready, they are removed to the retorting-furnace, where they are set on end over holes in a slab which forms the bottom of the furnace. There is nothing to prevent the amalgam from falling out of the flasks except four narrow strips of iron set into the mouth of the flask; the amalgam never runs out when the fire is properly managed. Other quicksilver-flasks, open at each end, are placed below the holes in the bottom of the furnace, their lower ends being beneath the surface of water in a tank which lies under the furnace. After luting the lower ends of the amalgam-flasks with clay and ashes there is thus no outlet for the quicksilver except into the water, where it condenses. A charcoal fire is slowly kindled around the flasks and they are thus retorted. This simple furnace, universal in that part of Mexico, has supplanted the old copper-bell apparatus, but is itself susceptible of great improvement.

We have now followed the silver as far as the refining process. It is evident that whatever loss of quicksilver may have resulted is purely mechanical. There is no chemical action in the arrastra, nor is any needed. Consequently the loss of quicksilver is small. A careful account is kept of it, and the result shows only three-quarters of an ounce lost per marc (eight pounds) of silver produced.

The retort-silver is refined in a small reverberatory furnace, built of adobes and fed with wood, which can receive a charge of 600 pounds of crude bullion. This charge is worked off in four hours. A little litharge and lead are added to remove the impurities, sulphur, arsenic, lead, iron, and, possibly, a very little zinc which is present as zinc-blende, and carbonate of soda and borax are also used as fluxes. The loss is 7 per cent. on the crude bullion, and consists, to some extent, of silver and quicksilver; the amount has not been exactly ascertained, but is, doubtless, very small, as the silver is ladled out very rapidly when refined. It is cast into bars weighing about 70 pounds each, which assay .988 of silver on the average.

The slags from the refining-furnace, with the concentrated tailings or slimes from the tanks for washing amalgam, and sometimes other secondary products, are occasionally smelted in a small shaft-furnace, with addition of galena, and the resulting lead is used in refining the retort silver.

An experienced amalgamator, who was working up some of the ordi nary tailings from the every-day run of the arrastras, furnished the writer with the following facts relative to their treatment on the patio. The Mexicans sometimes make the operation pay, especially when the ores contain other ores than native silver, because they employ their peons, whose labor costs very little.

The tailings were made into a heap (torta) containing 100 cargas, (about 16 tons,) and to this were added 720 pounds of salt, which was thoroughly mixed in, with water enough to keep the whole at a proper consistency. The next day 50 pounds of magistral (in this case sulphate of copper) were added and thoroughly incorporated. The third day 100 pounds of quicksilver were added and the whole left standing one day. Then every other day the mass was thoroughly mixed by driving mules about in it, in the usual way, and this operation, called the repaso, repeated until, by assays in the horn spoon, it was shown that the heap had been properly amalgamated, or was rendida. This requires more or less time, according to the temperature, the size of the heap, the nature of the ore, &c., and the whole operation requires great experience and care. When it was found that the heap was ready for washing, 25 pounds of quicksilver were added, with plenty of water, and the whole thoroughly mixed. In this operation of the patio there is a chemical action; the loss of quicksilver is necessarily large, and in this particular case amounted to 25 per cent. of the original amount charged. The resulting silver from the retort showed .990 fine. The amount obtained from the heap of 16 tons of tailings was only $145, leaving a loss of $5 on the expenses, not counting the amalgamator's time, and showing conclusively that simple amalgamation of native silver-ores, in the arrastra, is as effective and cheap a treatment as it is possible to employ, in the absence of an important proportion of combined ores, as sulphuret, chloride, or arsenical ores, and in a country so difficult of access as the interior and mountainous portion of Mexico.

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CHAPTER XV.

THE REDUCTION OF SILVER-ORES IN CHILI.

This chapter was prepared at my request by Mr. James Douglas, jr., of Quebec, a gentleman whose high professional standing, and personal acquaintance with the subject, entitle his statements to respect.

The silver mines of Chili extend from its northern far toward its southern limits, the two last-discovered minerals happening to be those of Caracoles, in the debatable ground between Chili and Bolivia, and San Carlos in south latitude 36°. But the most prominent mines heretofore worked have been in the Department of Copiopó, and there are to be found the only extensive and scientifically managed establishments for the reduction of silver-ores. All through the central provinces, however, but especially in the neighborhood of Arqueros, the landscape is often enlivened by a pretty little mill, consisting of a single light stone trapeze, turned by a rude turbine attached to the vertical shaft beneath the mortar, and a single Freiberg barrel or open tub amalgamator. They work up two or three cwt. a day of tractable ores, but never touch the more refractory. In Copiopó, on the other hand, the most difficult ores are treated; the machinery is very perfect; and the extraction of the silver as thorough as in any mills in the world.

There are seventeen establishments on or near the Copiopó River which work up the ores from the three minerals of Chañareillo, Lomas Bayas, and Tres Puntas; but the three mills owned by Messrs. Escobar & Ossa, in which the patent process of Herr Krähnke is used, do more proportionately than any of the others.

In these establishments calcination is not employed. The different ores are mixed accurately in given proportions-the chlorides and native silvers of Chañareillo, with the polybasite of Lomas Bayas and the base metals of Tres Puntas. The refractory ores, however, largely preponderate, as the pure silver-ores are yearly becoming scarcer. The broken ore is sampled by falling from a hopper, accurately placed above the apex of a pyramidal cone, from the angles of which protrude partitions. The stuff which collects in each compartment is resampled separately in like manner, till by repeating the act a perfectly accurate sample is obtained. As the hopper and the pyramid are carefully protected from wind by being incased in canvas, no dust escapes, and thus the error, which for merly resulted from the difficulty of always taking up proper portions of dust and coarse ore in sampling with the shovel, has been remedied. This error was found to be so great (for the ores there are always absolutely dry) that more silver has, at the end of the ycar, been obtained from the furnace than was supposed to have been put into the mill.

The grinding is done altogether in the trapezes or Chilian mills; but these have been perfected in all their details. In Messrs. Escobar & Ossa's mill in the town Copiopó there are three double trapezes. Each wheel weighs 60 cwt. and is of metal. An automatic feed delivers the ore from a hopper, filled twice in the twenty-four hours. The three trapezes reduce to impalpable powder 12 tons in the twenty-four hours.

The pulp is received in slime-pits, whence it is carefully shoveled and allowed to dry by exposure to the air, every precaution being taken to prevent the lumps from breaking up. When perfectly dry, the cakes are ready for the barrels; of these there are five, arranged in a row, and