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advance allow average beds bench blasting block body bottom breaking breast broken capping carried cars cause caving cent chutes close coal connected cost covered cross-cuts deposits depth direction distance drawn drift drill driven dump entries Example excavation explosive face fall floor foot four gives ground hard heading height holes horizontal iron keep length less loaded lower machine means method mill miners mining necessary orebody panel parallel pillars pipe placed possible posts powder practice present pressure raises reached removed rock roof seam sets shaft shovel shown side slicing slope soft space square sets started stope sufficient surface taken thick timber tons track underground upper usually varying vein vertical wall waste wide width
Page 295 - ... some of them are exposed on three sides only, than on many blocks opened up on four sides in veins where the ore-bodies are of the bunch'y and erratic type which we must recognize to be, after all. by far the most frequently encountered? Even the "possible ore
Page 298 - Southwest, examined by me, it was required to ascertain the minimum available ore that must be found by prospecting operations to warrant the capital expenditure required to inaugurate production on a given scale. The unknown factors were hence Q and t, and the known were estimated from the collected data to be : G == $40,000; M = $56,000; P = $39,000; p = $10,000; W = $15,000; y = 100 tons; d = 300 days; u = $3; R = 0.15; r = 0.06; b = 2 years.
Page 114 - This does away with a large amount of shoveling, and the ore thus left is ultimately obtained through the stopes from the next lower level. " When the ground-floor has been cut out, the work of stoping upon the ore is immediately begun. The roof of the stope is arched, thus serving the double purpose of supporting the back, and offering a better surface for the attack of the machine-drills. The ore is shot down in large, thin slabs, so that the shock of falling, combined with that of the blasting,...
Page 300 - ... has a value of its own, not less real, though it be less authoritative, than the rigorously demonstrated certainty. In other words, I venture to believe that the discussion, by exact methods, even of more or less uncertain data, is a valuable check upon the hasty sentimental or temperamental general impressions which often claim the authority of conclusions. Such a check is the more important, because mauy mining investors are tempted to overlook the essential proposition that a mine is " a candle,...
Page 300 - ... metallic ores. In reply to this probable criticism, I beg to offer the following observations : 1. There are, in fact, besides collieries, more mines than we commonly realize, the actual reserves of which can be measured, and the probable or potential reserves estimated. Among such I might instance many quarries, massive ore-bodies already explored by boring, etc. To all such cases, mathematical formulas of valuation are directly applicable. 2. With regard to the very large number of metal-mines,...
Page 63 - ... in other cases the men will move a few feet away and drive another hole, experience having shown that a very short distance will usually be sufficient to avoid a boulder. The hole is started through the drier top soft ore or nodules on the surface, a little water is poured in, the bit lifted and driven down by the combined strength of two men, and then turned in the ore. The work is a combination of churning and boring. Every few feet the tool is lifted, the ore adhering to the bit is cleaned...
Page 114 - ... for the miners. It has been found that one-third of the broken ore can be drawn off while the stope is being worked, and the surface of the broken ore kept within working distance of the back. In other words, by the above methods, two-thirds of the ore broken must be left in the stope, and cannot be drawn off until the stope is worked up to the next higher level and finished. In the Treadwell mine the slate-horse forms a natural division between the stopes of the north and the south orebodies.
Page 300 - ... foregoing may be plausibly questioned, at least as regards all mines other than collieries, for which the quantity of available reserves can be estimated with a degree of confidence and precision not usually attainable in mines of the metallic ores. In reply to this probable criticism the author begs to offer the following observations : 1.
Page 225 - It happened frequently, after breaking through to the loose ground above, that clean diamondbearing ground would run down as fast as it was removed for weeks or months at a time. The galleries would at times become blocked with large pieces of blue ground, which had to be blasted, and then a further run of blue ground would follow. When the blue ground was worked back toward the center of the crater, larger boulders or fragments of basalt which had come down through the loose reef from the surface...