Pillar (mining)

“ Passing through the entrance, the mine gradually widens underground to a depth of 1062 feet. The chief mass of ore is 600 feet broad on its upper surface, greatly narrowing as it descends to a depth of 1200 feet. Round it are other similar deposits. As the copper pyrites are deposited generally on the circumference of the outer shell of these masses, which are of a very irregular outline, the mining operations are carried on in a perfect labyrinth of winding passages and galleries, situated at various depths, and supported either by pillars or walls. ”

“ The placer miner throws the dirt into the water, which then does the work; whereas the pulverizing of rock is a nice operation, requiring constant attention. Quartz requires a mill and water-power; placer dirt is washed in a simple sluice. Dirt containing ten cents in the cubic yard may pay the hydraulic miner, but the quartz miner must have a hundred times as much in a cubic yard of vein stone, or he cannot work. The placer gold, when freed from the baser material surrounding it, is much of it in coarse particles, which are easily caught by their specific gravity ”

“ The process of mining coal is a combination of boring and digging. Shafts are sunk, levels are driven, and drains are carried off, by the help of picks or pickaxes, wedges and hammers, the rocks being also sometimes loosened by blasting with gunpowder. In searching for coal, a shaft is sunk through the uppermost soft stratum, and the rock is then bored, by striking it continually with an iron borer terminating in an edge of steel, which is in the mean time turned partly round; and, at proper intervals, a scoop is let down to draw up the loose fragments. ”

“ The copper was found in the capping, but as they gained in depth they became more and more valuable for their tin. Some of the Cornish mines are three-quarters of a mile in depth. Very lately tin has been discovered and mined in vast quantities in the Straits Settlements, India. As it is found in the streams the expense of mining is very light, and it is killing the European mines. The Cornish miners put their tin ore on a shovel when they wish to test it. The sample is first crushed fine and a few skillful shakes get rid of all the gangue, leaving behind the tin and wolfram. ”

“ The gold yield will undoubtedly continue to fall, but to what point and at what rate no one can know. I believe that in 1870, the yield will not exceed thirty millions of dollars.
Placer Mines.—Placer mines are divided into many classifications. The first and most important is into deep and shallow. In the former the pay-dirt is found deep, twenty feet or more beneath the surface; in the latter, near the surface. The shallow or surface diggings are chiefly found in the beds of ravines and gullies, in the bars of rivers, and in shallow flats; the deep diggings are in hills and deep flats. ”

“ The Oroya-Brownhill Mine, in western Australia, has had ore that carried a value of about $22 per ton and from it a profit of about $15 per ton was made. In the Cripple Creek District, ores that run above $30 per ton are considered high grade. This means that [126] the average rich ore shipments of the district have a gold content of about 1-1/2 ounces per ton. The expenses of mining, freight, and treatment will probably total close to one-half the gross value, or about $15 per ton. ”

“ In view, then, of these reasons, it is proper to decide that mining is a term broad enough to cover the operations of extracting coal and metallic ores from the ground and of preparing them for shipment or metallurgical treatment.
Coal is always coal, no matter in what thickness of deposit it is found. It may not be minable coal because in thin seams or because so intercalated with layers of slate or "bone," that the mine's mixture, or so-called "run of mine," is not salable. ”

“ Rock and earth on the one hand, and metal and ore on the other, are filled into buckets separately and drawn up to the open air or to the nearest tunnel. If the shaft is not deep, the buckets are drawn up by a machine turned by men; if it is deep, they are drawn by machines turned by horses.
It often happens that a rush of water or sometimes stagnant air hinders the mining; for this reason miners pay the greatest attention to these matters, just as much as to digging, or they should do so. ”

“ When the coal seam thins out so rapidly that the floor and roof come nearly together, this state of things is called a pinch, or squeeze, though the latter term is more properly applied to the settling of the roof rock after the coal has been mined out. The inequalities of a coal seam that have now been mentioned, although perhaps but a small portion of those that are daily met with in the process of mining, are neverthless characteristic of the whole. ”

“ 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. ”

“ The ore, on being extracted from the mine, is placed in the hands of "Pĕpĕnădōrĕs," men and women, who break all the larger pieces with hammers, and, after rejecting those in which no metallic particles are contained, divide the rest into three classes, called, in mining language, "Ăzōguĕs," and "Ăpŏlvillādŏs," "Buenos" or "Ordinarios." The "Ăzōguĕs" are the inferior ores, in which the matrix contains but a thin sprinkling of silver. As this increases, it becomes "Apolvillado ordinario," ”

“ Placer tin deposits on the Ringarooma River (Derby district) supply about 1,000 tons of tin concentrates a year. The principal placer mines are the Pioneer and Briseis. Near Gladstone, placers and lode deposits carrying tin and tungsten are worked. At the Anchor mine, in the Blue Tier district, a tin-bearing granite averaging one-half per cent. tin is worked, but mining has not been profitable. The Renison Bell, Dreadnought-Boulder and Montana mines, in the North Dundas field, are in slates cut by dikes of quartz porphyry. Zinc, lead, and iron sulphides are important in the lodes. ”

“ Round vertical shafts are largely applied to coal-mines, and some engineers have advocated their usefulness to the mining of the metals under discussion. Their great advantages lie in their structural strength, in the large amount of free space for ventilation, and in the fact that if walled with stone, brick, concrete, or steel, they can be made water-tight so as to prevent inflow from water-bearing strata, even when under great pressure. ”

“ When the engine-pit is sunk, and the lodgement formed, a mine is then run in the coal to the rise of the field, or a cropping from the engine-pit to the second pit. This mine may be 6 or 8 feet wide, and carried either in a line directly to the pit bottom, or at right angles to the backs or web of the coal, until it is on a line with the pit, where a mine is set off, upon one side, to the pit bottom. This mine or gallery is carried as nearly parallel to the backs as possible, till the pit is gained. Fig. 836. represents this mining operation. A is the engine-pit. ”

“ It not being possible to point out where the ancient river beds lie, smothered as they are by hundreds of feet of overlying drift, lava, and other later deposits, the only feasible plan is a series of boring with the diamond drill.
When gold has been discovered the finder must act with the greatest prudence, for even gold may be bought too dear. The surest test is a mill run, that is passing 10 to 50 tons through all the operations of crushing, milling, roasting, amalgamating, etc., and so ascertaining what returns are likely to be obtainable when the deposit is worked on a commercial scale. ”

“ 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. ”

“ Pure gold is soft, and the point of a knife will scratch it deeply. Pounded in a mortar, the pulverized mineral should be passed through a cheese-cloth screen stretched over a loop of wood. If the course contains much pyrite, it must be roasted before washing in the pan and amalgamating. Sample well, weigh out two pounds, put it in a black iron pan, with four ounces of mercury, four ounces of salt, four ounces of soda and a half gallon of boiling water. Stir with a green stick, and agitate until the mercury has been able to reach all the gold. ”

“ In mining, let us observe, the whole round of work consists in separations which bring masses from bigness to smallness, again and again. First of all the solid walls and floors are broken up by pick, or drill, or powder, or all together. Iron ores as hoisted to the surface of the earth are taken to breakers which crush them into pieces suitable for the blast furnace. When the ores carry gold, copper, lead, or tin, this crushing is followed by stamping to facilitate the final process by which metal is separated from worthless rock. ”

“ A similar sacrifice in the shape of pillars is often necessary to support the surface, either to avoid injury to valuable structures or to prevent a flooding of the mine. As already noted large pillars must always be left to protect shafts, adits and the more important mine-passages necessary for drainage, ventilation and the haulage of mineral. In the early history of mining there was but little attempt at systematic development and working, and the mines were often irregular and tortuous. ”

“ The blow-pipe is especially useful, though to the skilled assayer often unnecessary. The ore is first powdered, and any metallic flakes picked out and tested separately. A fair sample must be selected, otherwise all the work will be thrown away and the result be valueless.
The next step is weighing the ore and the reagents. Moisture is drawn off by heating in a crucible, a low heat being sufficient. Roasting will eliminate sulphur, antimony, arsenic, etc., and must take place in a flat dish, so that the air may have free access. The powder should be stirred frequently. ”

“ This is neither milling, metallurgy, nor ore dressing, but is more properly called Sorting. It is one of the operations connected with mining. Milling may be either ore dressing or metallurgy.
In the operations of placering, there is a simultaneous excavation of a deposit and an extraction of the valuable contents. In this case, shall we call the process mining or metallurgy? If it is a gold [15] placer, one may see the recovery of the metallic values. Here, the usage of the majority of practical mining men will uphold us in always speaking of the work as mining. ”

“ If local conditions are favourable and the management good, some mines have paid well with a yield of from 11⁄2 to 4 dwts. of gold per ton of ore; but others have not paid with much higher yields in test crushings. Great judgment is required in selecting the best possible site for the class of crushing machinery decided upon. The crusher should be as high as can be managed so as to give a good clear run for the tailings and room for the concentrators and amalgamators, &c., below the copper plates and blanket strakes. Solid, strong foundations are essential ”

“ Should copper be suspected, roast the powdered ore and mix with an equal quantity of salt and candle grease or other fat; then cast into the fire, and the characteristic flame of copper—first blue and then green—will appear. This test is better made at night.
Coal. Coal is often more valuable than gold, and the prospector should be prepared to estimate the value of any seams he may come across during his travels. The following is a very rough but wonderfully effective test for coal. Take a clay pipe, pulverize your sample, weigh off twenty pennyweights, and place it in the bowl of the pipe. ”

“ The trituration is effected by revolving the stone in a large cylinder together with a number of steel balls of various sizes, the attrition of which with the rock quickly grinds it to powder of any required degree of fineness.
More mines have been ruined by bad mill management probably than by bad mining, though every experienced man must have seen in his time many most flagrant instances of bungling in the latter respect. ”

“ Mining for gold alone is divided into two general classes: that which seeks the metal from the solid rock or quartz, and that which finds it in sand, gravel, or soil. The former process is the universal and familiar one of all rock mining, following the rich veins into the bowels of the earth with pick and powder, crushing the rock and separating the infinitesimal atoms of metal from the dusty, powdered mass. ”

“ If the fumes rise rapidly, the muffle is too hot. On the other hand, dense, falling fumes show the temperature is too low. Lead that is poor in silver stands the highest heat without vitiating the assay.
When the material in the cupel "freezes," i.e., the absorption by the cupel stops, reject the assay and try again, giving more heat or more lead.
Gold. Practically, the metal most prospectors seek is gold. It is so enormously valuable and constitutes so very small a percentage of any ore, that care must be taken or it may escape detection and be lost. Panning is the miner's method. ”