Gold ore

“ The ore may present visible metallurgical difficulties which make it unprofitable in any event. A gold ore may contain copper or arsenic, so as to debar cyanidation, where this process is the only hope of sufficiently moderate costs. A lead ore may be an amorphous compound with zinc, and successful concentration or smelting without great penalties may be precluded. ”

“ Gold is always found as a metal, never as an ore, and the separation from the accompanying vein-stone with which it is mixed mechanically, is much more simple and easy than the reduction of the argentiferous ores in which the silver is chemically combined with base substances, for which it has a strong affinity. Chemical knowledge and chemical processes are more necessary in mining for silver than for gold; and while all auriferous quartz is of the same kind, and may be treated in the same manner, there are many different kinds of silver ores, each of which requires a peculiar treatment. ”

“ The region so long remaining almost unknown, has suddenly become the desired bourne for men and women of all classes. It has always been known that its mineral resources were fine, and gold has been found there in small quantities, but the hardships endured in getting it from the soil were too great in proportion to the amount, but a new impetus to the labors of the gold seeker has been given by the discovery of the precious metal in such large quantities that thousands have rushed to this field eager to dig for the yellow ore. ”

“ An American scientist has just concluded a very interesting and suggestive experiment. He took a crushed sample of rich ore from Cripple Creek, which carried 1,100 ozs. of gold per ton, and digested it in a very weak solution of sodium chloride and sulphate of iron, making the solution correspond as near as practicable to the waters found in Nature. The ore was kept in a place having a temperature little less than boiling water for six weeks, when all the gold was dissolved, except what would be equal to one ounce per ton. ”

“ The richest ore, worth from one to four ounces per ton, occurs in irregular patches and bands very small in comparison with the bulk of the ore stuff, which varies in value from two to seven pennyweights per ton. The average value of all the ore treated by the Chontales Mining Company, up to the end of 1871, has been about seven pennyweights per ton, and during that time small patches have been met with worth one hundred ounces of gold per ton. The gold does not occur pure, but is a natural alloy of gold and silver, containing about three parts of the former to one of the latter. ”

“ A high-grade ore, in which there is a large proportion of gold, may be worth a good deal less, if it is more difficult to work and less easy of access. The richest gold-field in the world, that of the Rand, in South Africa, which gives one-third of the total gold output of the world, is of an ore so poor that a forty-niner would have turned up his nose at it, and the machinery, even of thirty years ago, could have done nothing with [Pg 200] it. Nearly all the big mines of to-day are winning wealth out of low-grade ore. ”

“ Sometimes it is ’bedded in quartz when the ore, as it is called, has to be mined and then crushed in a stamp mill to get the gold out; more often it is found as free gold, dust and grains and bits of pure gold mixed with the dirt when it must be panned, that is, put in a pan and the dirt washed away and then the gold, which is the heaviest, falls to the bottom of the pan, and again,” he lowered his voice to make what he was about to tell them more impressive, “nuggets of gold are picked up from bits the size of a pea to chunks as large as my fist! ”

“ Though the original condition of the ore was doubtless sulphide, it now contains, as the result of oxidation, hematite, limonite, magnetite, malachite, azurite, chrysocolla, cerussite, wulfenite, chloride of silver, manganese oxide, and metallic gold. The value of the ore lies principally in the gold contained, though in one portion of the ore body, near its eastern end, rich chloride of silver ore is found, with but little gold. The physical appearance of the ore is no criterion of its gold contents, as two pieces, with identically the same characteristics, will differ widely in value. ”

“ There remain the stringers in which gold alone is sometimes found, in the vicinity of rivers and streams, or in swamps. If upon the soil being removed, many of these are found, composed of earth somewhat baked and burnt, as may sometimes be seen in clay pits, there is some hope that gold may be obtained from them, especially if several join together. But the very point of junction must be pierced, and the length and width searched for ore, and in these places very deep shafts cannot be sunk. ”

“ Most silver ores are easily recognisable, and readily tested by means of the blowpipe or simple fire assay. Sometimes the silver on being tested is found to contain a considerable percentage of gold, as in the great Comstock lode in Nevada. Ore from the big Broken Hill silver lode, New South Wales, also contains an appreciable quantity of the more precious metal. A natural alloy of gold, termed electrum, contains 20 per cent. ”

“ Then there was another process, by which ores were roasted, and mixed with salt, and placed in barrels having certain machinery, for separation and amalgamation. So perfect was this system that a very minute portion of metal was left in the ore. The heat, dews, wet, and the magnetic state of the atmosphere, all played a part towards the extraction of the metal from the ore. They might say this process was very rough, but if it saved the gold, what mattered it? ”

“ During the wet season water percolates freely from the surface down through the lodes, and the gold set free by the decomposition of the ore at the surface must be carried down into it, so that in the course of ages, during the gradual degradation and wearing away of the surface, there has, I believe, been an accumulation of the loose gold in the upper parts of the lodes from parts that originally stood much higher, and have now been worn away by the action of the elements. ”

“ This belt contains the largest deposit of gold that has ever been found in one place, and its gold content probably equals that of all the other known gold fields of the world combined. The ore is not exceptionally high grade, but can be economically treated in large quantities. ”

“ Quartz ores should yield $6 to the ton in order to pay.
To test pyrites for gold, reduce a given quantity to powder and wash as before; then roast the residue at a red heat. Upon cooling, add quicksilver and treat as just{97} described. Pyrites should yield $1 of gold to the bushel of ore to be profitable.
Native silver often contains gold. To separate them, carefully flatten the alloy with a smooth hammer on an anvil, and then boil it in strong nitric acid in a glass flask for about ten minutes. ”

“ In really successful mining it is in the last degree important that the mode of extraction of metals in the most scientific manner should be thoroughly understood, but as a general rule the science of metallurgy is but very superficially grasped even by those whose special business it is to treat ore bodies in order to extract their metalliferous contents, and whether in quartz crushing mill, lixiviating, or smelting works there is much left to be desired in the method of treating our ores. ”

“ Go into any of the great mining works of central Germany, and you may see acres covered by machinery ingeniously constructed to clean, break, and sort, and ultimately deliver the ores into trucks or direct into the furnace, and the whole under the supervision of a youngster or two. When a parcel of ore arrives at any of the works, say Freiberg or Clausthal, it is carefully assayed by three or four different persons and then handed over to practical experts, who are expected to produce the full amount of precious metal according to assay ”

“ In testing a gold mine with a view to purchase, it should be remembered that as a rule the intersections of leaders or small veins with the main ore body are usually the richest portions of the lode. This the experienced prospector knows, and generally his shafts and cuttings are made at such points. For the ordinary mining investor, when inspecting with a view to purchase, these are places to avoid if endeavouring to form a correct estimate of the value of the ore in bulk. ”

“ The ore contains free gold, which is extracted by the simple process of stamping and amalgamation, and refractory values, extracted by the cyaniding process. Several hundred tons of ore are treated thus in Deadwood and its environs daily, and its stamp mills are exceeded in size only by those of the Treadwell mine in S.E. Alaska, and by those on the Rand in South Africa. ”

“ Ferdinand Fitzgerald, of the famous 'African Times.' When its directors inform us that 'twenty ounces of gold lately arrived from a neighbouring mine, the produce of stamping of twenty-five tons of ore, similar to that of Tamsoo-Mewoosoo,' they may not have been aware that the produce in question was worked from the alluvial drift discovered, about the end May 1881, in the north-western corner of the Swanzy estates. ”

“ The precious ore, bought by the middlemen, a peculiar race, from the wild tribes of the far interior, appears in the shape of dust with an occasional small nugget; the traders dislike bars and ingots, because they are generally half copper. We have now everywhere traced the trade from Gambia to the Gold Coast, and we may fairly conclude that all the metal comes from a single chain of Ghauts subtending the maritime region. ”

“ A third group of metals have coloured rusts, e.g., silver, copper, and iron. A fourth group never rust, such as gold and platinum, which occur as metals in the gangue, not as ore from which the metal is produced. In the case of the other metals it is an advantage that they are found in the rust or ore condition, as they can be manufactured much more easily than native metal. ”

“ Of late years, however, the theory of gold occurrence by deposition from mineral salts has been accepted by all but the “mining experts” who infest and afflict the gold mining camps of the world. These opine that gold ought to occur in “pockets” only (meaning thereby their own) .
Recently Professor Joseph Le Conte, at a meeting of the American Institute of Mining Engineers, criticised a notable essay on the “Genesis of Ore Deposits,” by Bergrath F. Posepny. The Professor’s general conclusions are:
1. ”

“ This appliance, working somewhat slowly, swings on rockers from side to side, and is usually employed in mills where, owing to the complexity of the ore, difficulties have been met with in amalgamating the gold. Riffles are provided and even very fine gold is sometimes effectively recovered by their aid.
The Frue vanner will, as a rule, act well when the pulp is sufficiently fine. It is really a adaptation of an old and simple apparatus used in China and India for washing gold dust from the sands of rivers. ”

“ The silver ore of Esmeralda and Coso is a sulphuret of silver, nearly all the veins having the same material, though the amount of it scattered through the vein-stone differs greatly in different lodes. In some veins there is much free gold, that is, little specks of metallic gold which can be separated from the other material in the same manner that gold is separated from auriferous quartz. ”

“ The process of extracting gold from lode stuff and tailings by means of cyanide of potassium is now largely used and may be thus briefly described:—It is chiefly applied to tailings, that is, crushed ore that has already passed over the amalgamating and blanket [96] tables. The tailings are placed in vats, and subjected to the action of solutions of cyanide of potassium of varying strengths down to 0·2 per cent. These dissolve the gold, which is leached from the tailings, passed through boxes in which it is precipitated either by means of zinc shavings, electricity, or other precipitant. ”

“ The gold coinage of Great Britain and Australia for 10 years has been as follows:
The exports of domestic gold from the United States during the year ending Dec. 31, 1873, amounted to $55,178,229 in coin, and $12,754,257 in bullion.—Gold Mining. Gold occurs principally in metallic form, as threads, scales, spangles, films, grains, monometric crystals, nuggets, &c. Such native gold always contains from 1 to 40 per cent. silver, and often also small quantities of iron, copper, mercury, palladium, platinum, or iridium. Gold ores proper are rare; the undoubted species are tellurides. ”

“ Set any one to talk about himself, instead of about other people, and you will have a seam of the precious mental metal opened up to you at once; only ore, most likely, that needs much smelting and refining; or it may be, not gold at all, but a metal which your mental alchemy may turn into gold. ”

“ All other gold ores are considered poor, because the earth or stone too far outweighs the gold. A vein which contains a larger proportion of silver than of gold is rarely found to be a rich one. Earth, whether it be dry or wet, rarely abounds in gold; but in dry earth there is more often found a greater quantity of gold, especially if it has the appearance of having been melted in a furnace, and if it is not lacking in scales resembling mica. The solidified juices, azure, chrysocolla, orpiment, and realgar, also frequently contain gold. ”

“ Another reason for anticipating further increase in the production of gold is found in our better knowledge of gold ores, and of the conditions under which gold occurs in Nature. Until the discovery of the Cripple Creek district the occurrence of gold as tellurid in deposits of large extent and value was practically unknown. ”