Sluice (mining)

“ The stones used are cobbles, six or eight inches through at the greatest diameter, and usually flattish. A good workman will pave eight hundred square feet of sluice-box with them in a day; and after the water and dirt have run over them for an hour, they are fastened very tightly by the sand collected between them. In large sluices, wooden riffle-bars are worn away very rapidly—the expense amounting sometimes, in very large and long sluices, to twenty or thirty dollars a day ”

“ When he awakes next day several feet of the soil have fallen down over the logs, and this he has to hoist. It is at this stage that the windlass worked by his companion, or partner, demonstrates its value. In a very short time all the gravel that the fire has thawed out is hoisted to the surface, and added to the dump, where it must remain until the warmth of summer shall have thawed the streams and permitted sluicing.
MINER'S GOLD PAN.
A sluice is really nothing more nor less than a trough, open at the top, in which the gold is sorted from the lighter gravel and dirt by running water. ”

“ More water is required for piping down banks than for washing the dirt; and often the sluice is almost idle for want of dirt, while the water, after being thrown against the hillside, runs away without doing any service at washing. Blasting, therefore, by loosening the earth, enables the hydraulic miner to have an abundant and regular supply of dirt in his sluice, at an expense much less than the cost of manual labor to dig the bank down with pick and shovel. ”

“ In hydraulic claims, all the dirt is washed; in all other kinds of claims, such dirt as contains no gold is thrown to one side, or "stripped off." "Hydraulic mining" is the highest branch of placer mining; it washes more dirt, and requires more water, and a larger sluice, than any other kind of mining. The number of men employed in a hydraulic claim, however, is usually small, from three to six, the water doing nearly all the work. In some claims a man is constantly employed with a heavy sledge-hammer in breaking up large stones, so that the pieces may be sent down the sluice. ”

“ Sometimes the upper part of the sluice is made steeper so as to dissolve the dirt, and the lower part has a small grade to catch the gold. The clayey matter of ordinary pay-dirt is fully dissolved in a sluice two hundred feet long with a low grade, so the use of the boxes beyond that length is merely to catch the gold. There are claims however in which the clay is so extremely tough that it will roll in large balls more than a quarter of a mile through a steep sluice with a large head of water, and come out at the lower end scarcely diminished in size. ”

“ Ordinarily the sluice runs only during daylight, but in some claims the work continues night and day. Cleaning up occupies from half a day to a day, and therefore must not be repeated too often, because it consumes too much time. In some sluices the cleaning up does not occur until the riffle-bars have been worn out or much bruised by the wear of the stones and gravel. ”

“ And, lastly, the sluice begat the jet, or hydraulicking proper, which is at present the highest effort of placer-mining. We thus reverse the primitive process which carried the wash-dirt to the water; we now carry the water to the wash-dirt. In California I found the miners washing down loose sandstones and hillocks of clay, passing the stuff through sluices, and making money when the gold averaged only 9d. and even 4d. to the ton. A man could work under favourable circumstances twenty to thirty tons a day. ”

“ The sluices emptying into it furnish both dirt and water, and in the dirt there is always a large amount of fine gold, as is plainly proved by the fact that some of the tail-sluices have paid large profits to their owners. Tail-sluices are always large, long and paved with stones; and sometimes they are double, so that one side may be cleaned up while the other continues washing. In a branch of the Yuba there is, or was not long since, a tail-sluice twenty feet wide. ”

“ The lower or riffle-box is 12 feet long by 3 feet wide, with a fall equal to that of the trough and a sufficient depth to keep the material and water from spilling over the sides. It should have four riffles. For this means of saving the gold, to work satisfactorily, the metal must be coarse and the water plentiful.
SLUICE BOXES.
Every sluice is an inclined channel through which flows a stream of water, carrying away all the lighter matter thrown into it, and separating it from the heavy. ”

“ Of course economy and convenience of working require that the sluice should be near the level of the ground, and as that may be steep or level below the claim, the grade of the sluice must to some extent conform to it. There are thus a multitude of points to be taken into consideration in fixing the grade of a sluice; but a fall of less than eight or more than twenty inches, in a box of twelve feet, would be considered as unsuitable for the board-sluice. ”

“ Often legs are broken; still more frequently the pipemen have warning, and escape in time. When men are buried in the falling dirt, the water is used to wash them out. In some claims, the pipe will tear down more dirt than the sluice can wash; in other claims, the sluice always demands more dirt than the pipe can bring down. In the latter case, blasting may be used to loosen the dirt, or the miners may undermine the bank, leaving a few columns of dirt for support ”

“ However, smelters were developed in 1866 for treatment of these sulfides, and gold, silver, lead, and copper were recovered. Gradually, as the gold was worked out, silver and lead became the important products of the mines.
Sluicebox mining was a common sight near the early gold camps, where primary recovery was from placer deposits or decomposed quartz and sulfide veins. ”

“ There are no falls of earth, as in coal mines, for the rock-salt is extremely tenacious, and the miners never undermine it but blast it, which is a much safer operation. The two great dangers to which rock-salt mining is exposed, though they rarely result in loss to human life, are the falling in of the mine bodily, or of the shafts and neighbouring earths, and the breaking in of brine either at the head of the top-rock shaft or from old mines, long disused, and full of brine. ”

“ Where the salt deposits are composed of a mineral that is white, odourless, and practically pure, as in the Wieliezka system and the mines of Rumania, and particularly if labour is abundant and cheap, and the industry is a monopoly of the State, rock-salt mining will always hold its own. ”

“ The dirt having been filled with water, the miner catches the pan at the sides, raises that part toward his body, and lowers the outer edge a little, and commences to shake the pan from side to side, holding it so that all the dirt is under water, and so that a little of the dirt can escape over the outer edge. The earthy part of the dirt is rapidly dissolved by the water, assisted by the shaking of the pan and the rolling of the gravel from side to side, and forms a mud which runs out while clean water runs in. ”

“ Rough gold smelting on the mine is effected with a flux of borax, carbonate of soda, or, as I have often done, with some powdered white glass. When the gold is smelted and the flux has settled down quietly in a liquid state, the bulk of the latter may be removed, to facilitate pouring into the mould, by dipping an iron rod alternately into the flux and then into a little water, and knocking off the ball of congealed flux which adheres after each dip. This flux should, however, be crushed with a pestle and mortar and panned off, as, in certain cases, it may contain tiny globules of gold. ”

“ Each compartment is provided with a loose metal bottom pierced with holes to admit the dust; the true bottom below it has cross-riffles, and above it are bars or gratings to catch the coarser stones. These sluices are mounted on trestles, and the latter are disposed upon a slope determined by the quantity of water: the average fall or grade may be 1 to 50. In Australia four men filling a 'Long Tom,' or raised box-sluice, will remove and wash twenty-four cubic yards of ground per day. When the ore is fine, mercury may be dropped into the upper end of the sluice ”

“ The court distinguished this process from smelting, and decided that it is, in practice, a part of mining. It is a step, the court reasoned, in the extraction of the ore from the mine, and the separation of the ore from the rock enclosing it. Roasting ore, therefore, is preparation for smelting, but not smelting, which, according to all of the definitions, is something more than melting,-it is obtaining the metal by heat and such reagents as develop it. Roasting is done crudely in the open air by burning wood and ore mingled in a pile. Smelting is the function of an organized plant. ”

“ Of course, some are very rich, while others are so poor that it does not pay to work them.
The sand and gravel from the placer-mine are hauled to water, and there the metal is washed out. This is called panning, and is spoken of as panning out “rich” or “poor.”
In the sluice or gulch mine the men dig the dirt into the water and mash up the clods, throw out the stones, etc., and the dirt all washes down{324} while the metal sinks to the bottom. When there is considerable on the bottom, the stream is turned and the gold is taken up, put in troughs, and washed out as in placer-mines. ”

“ Ground sluices are natural gullies, answering the purpose of wooden sluices in localities where water is abundant for short periods only, and the construction of permanent sluices would not be judicious. In river mining, the current of a stream is turned aside, and sluices are erected in its bed for washing the dirt there accumulated. ”

“ Whether with a pan, a cradle, or a sluice, the only thing that enables a miner to separate the gold from the worthless dirt is that the gold is smaller and heavier. But suppose the gold dust is so fine as to be invisible, it will be so light as to wash away easily; if it is in fine flakes, the flakes will almost float. All that light gold would be lost in the dirt that flows out of the bottom of the sluice, the tailings, as they are called. ”

“ THE MULATOS MINE SALTING SCHEME All sorts of methods of salting mines, even to the injection, with a hypodermic needle, of strong solutions of mineral salts into a mining engineer's carefully sealed sample bags, have been worked. The most honest, careful, and expert mining engineers have been deceived time and again, and salted right under their own eyes. Even a bland Chinee may be fooled. Take the instance of the Mulatos Mine: The bunch of Chinamen who proposed to buy it insisted on a mill-run test on fresh-mined ore, taken out BY THEMSELVES, for a five-days' run. ”

“ But the mining of the upper bed of salt by man does not account for the subsidences here recorded. The name of the dangerous miner is "water." When water reaches the upper bed of salt it dissolves it as water does snow. Water can take in 26 degrees of salt and no more, and then it is called brine. Underneath Northwich is a sea of brine which lies on the top of the upper bed of salt rock. From this brine white salt is made by a process of evaporation, and that is why all over Northwich you see numbers of pumping stations which pump up the brine as fast almost as it is made. ”

“ To assist its attrition, a rill of water keeps it constantly wet, and it is carried by a small gutter into the fore pit, where it makes its first settlement, the lighter particles running forwards with the water into the middle pit, and thence into the third, where what is called the slime, settles. From these pits the ore is carried into a large vat, called the keeve, where it is washed and rendered clean enough for the smelting house. Most of the tin mines now working have steam engines, the advantages of which have proved a great benefit to the proprietors of them. ”

“ Where skins are used, as in Brazil, they may be dried and beaten over a cloth, placed to receive the fallen particles. Sluice washing is generally carried on during the day only; but when water is abundant and cheap, the work may be continued throughout the whole twenty-four hours. The sluices are cleaned up once a week, or more seldom, according to the rate at which gold and amalgam accumulate. ”

“ The roof of a mine is held up by columns of salt which are left in position for that purpose, but they frequently give way and the buildings above them are wrecked.
The coarser kinds of rock-salt are still taken out in lumps. You may often see pieces in the Cheshire fields which farmers have put there for cattle to lick. For salt contains health-giving properties, and salt-mining is not injurious to health as coal-mining is. Brine baths have been made at Nantwich for people suffering from certain diseases. ”

“ There is only a hole in the ground, where mining is carried on in much the same manner as in other kinds of mines. The shaft is sunk and lined with timbers to keep the dirt from falling in, just as in other mines. In working salt mines, however, water is almost as bad as earth, and therefore a layer of clay is put between the timbers and the earth. There are the usual galleries and pillars, with roof and floor of salt. The workmen try to get the salt out in lumps or blocks as far as possible, and so they bore in drill holes and then blast with dynamite or powder. ”