Ore (mineral)

“ The ore used is the common sulphuret, with a foliated, glittering and cubical fracture. It occurs with scarcely any adhering gangue. Cubical masses of it are found, at some of the diggings, which are studded over with minute crystals of calcareous spar. These crystals, when examined, have the form of the dog-tooth spar. This broad, square-shaped, and square-broken mineral, is taken from east and west leads, is most easy to smelt, and yields the greatest per centum of lead. It is estimated to produce fifty per cent. ”

“ The production of ore which occurs in the upper parts of the veins, furnishes us with the saline ores; for here the water, air and earth are principally active. In the upper depths are found most frequently the oxygenized metals, or as they are called mineral spars, as spathic-iron, malachite, calamine, lead-spar, pyromorphite, &c. ”

“ The manner in which metallic substances are distributed through the earth's crust, and more especially the phenomena of those nearly vertical and tabular masses of ore called mineral veins, from which the larger part of the precious metals used by man are obtained,—these are subjects of the highest practical importance to the miner, and of no less theoretical interest to the geologist. ”

“ Perhaps no other portion of the earth's surface is so rich in mineral resources as that which has been covered by these observations, and nowhere else is to be found as great a variety of ore deposits, or those which illustrate as well their mode of formation. This is so true that it maybe said without exaggeration that no one can intelligently discuss the questions that have been raised in regard to the origin and mode of formation of ore bodies without transversing and studying the great mining belt of our Western States and Territories. ”

“ To find the number of cubic feet per fathom of matter in a vein, multiply its thickness in inches by 3. Great care is requisite in estimating the ore in a vein or the amount of mineral in sight. Very clever men often make grave mistakes in such calculations.
A MAKE-SHIFT FLUX.
Rough smelting may be done with powdered white glass, though either borax or carbonate of soda is better. As soon as the gold is melted and the flux fluid and still, remove the bulk of the flux with an iron spoon, and pour the metal into a clay mould. Crush the flux for gold. ”

“ Ores of this type usually contain lead (galena) , zinc (sphalerite) , and iron (pyrite) minerals; many contain manganese and cadmium; some contain cobalt and nickel; but few carry gold, silver, copper, or antimony. Deposits of this type are of world-wide distribution, and many are extensive and commercially important. The greater purity of the ore and the simplicity of treatment (particularly [264] for the ores in the oxidized zones) , caused them to be exploited first and most extensively, and to dominate formerly the world production of lead. ”

“ Percentage of iron is of course an important factor; but an ore in which the iron is in the mineral hematite is more valuable than one with an equivalent percentage of iron which is in the form of magnetite. Substances present in the ore in minor quantities, such as phosphorus, sulphur, and titanium, have a tendency to make the iron product brittle, either when it is cold or when it is being made, so that excessive amounts of these substances may disqualify an ore. Excessive quantities of silica, lime, or magnesia may make the ore undesirable. ”

“ The stamps crush the ore to a fine sand more easily and rapidly than could be done by any other method. Water is kept running over the ore, and as fast as it is crushed sufficiently fine for the particles to pass through a wire screen, the water with which they are mixed is allowed to flow over large plates of copper which have been coated with quicksilver. The latter mineral has an attraction for gold, and so catches and holds most of the particles, no matter how small they are. ”

“ To the natural resources of the soil add the enormous mineral wealth hidden but a few feet below the surface, and wonder grows to amazement. Coal fields surpassing in extent all the remaining fields in the world; iron ore sufficient to stock the world with iron and steel for the next thousand years; copper of the finest quality; zinc, lead, salt, building stone and timber, all in quantities sufficient for a population a hundred times as great. ”

“ When the miner hoists his ore [1] to the surface, the contained metal may be either in the native uncombined state, as, for example, native gold, native silver, native copper, or combined with other substances forming minerals of more or less complex composition, as, for example, telluride of gold, sulphide of silver, sulphide of copper. In both cases the valuable mineral is always associated with minerals of no value. ”

“ The mineral resources also include nearly every variety required for manufacturing industries. In the production of the two minerals which constitute the basis of modern manufactures, coal and iron, the United States ranks foremost, and, indeed, produces nearly a third of the world's output of each. Moreover, the deposits of these minerals, together with deposits of limestone, which is needed in fluxing the iron ore, are frequently found in the same locality. ”

“ Although many of these grains are wholly copper black, they are occasionally only depositions of the mineral upon specks of carnelian, chalcedony, or agate, or are more frequently composed, in part, of what is apparently an imperfect steatite. The ore is so connected with, and so much resembles in color the rock, of which it may be said to be a constituent part, that they might easily, during a hasty examination, be confounded. ”

“ When our mining experts discover a mineral belt containing precious metals or copper, iron, lead, nickel, platinum, cobalt, quicksilver, manganese or any other ore used in manufactures and the arts, the first thing we do is to sink a shaft on the most likely ore chimney and at every one hundred feet in depth we run levels to develop it and if we continue to find ore as we go down and the ground requires drainage, we survey for a drainage tunnel that will drain the mine at the greatest depth, even if we have to run a tunnel ten miles. ”

“ Iron, manganese, aluminium and tin differ from the rest of the metals in their original occurrence in the oxidized form, whereas the others with the exception of gold, platinum, and possibly copper, in their first precipitation in ore-bodies are in the form of sulphides or related compounds. Only by subsequent changes, characteristic of the upper parts of the deposits, do they pass by oxidation into the minerals of the second group. ”

“ Seldom, however, do the processes go far enough in nature to produce an ore which can be used directly without some further mechanical sorting. Ore minerals concentrated in placers are those which resist abrasion and chemical solution during the processes of weathering and transportation, and which have a density sufficiently high so that they are partially sorted out and concentrated from the accompanying quartz and other minerals. ”

“ There are many naturally-existing mineral mixtures in the crushing of which a similar result occurs in a very marked degree; and, indeed, there are none which do not show the peculiarity more or less, because the constituents of an ore are never of exactly the same degree of hardness. When the worthless parts are the softer and therefore have the greater tendency to "slime," the ore is very readily dressed to a high percentage by means of water. ”

“ Rich ore bodies frequently occur on the borders of igneous dikes, and in fissures and cavities in igneous rocks, but the process by which they have been formed is similar to that leading to the concentration of mineral matter in metamorphic rocks, and will be referred to later. ”

“ In iron ore, the metallic oxide or carbonate makes up nearly the whole rock; in gold ore, the metal is the merest incidental constituent, from the petrologic point of view.
Concentration.—The essential fact in the formation of ores is the unusual concentration of the metal. There are vast quantities of all the metals disseminated through the rock substance of the earth and even throughout the hydrosphere, but they do not constitute ores because they have no economic value. They become ores when concentrated in accessible places to a workable richness. ”

“ The ore is found in detached pieces and solid masses, in beds, in red clay, accompanied by sulphate of barytes, calcareous spar, blende, iron pyrites, and quartz. The ore is of that kind called, by mineralogists, lead-glance, or galena, and is the sulphuret of lead, of chemistry. As it is dug up or quarried from the adhering spar, it presents a very rich appearance. It has a [Pg 171] broad, glittering grain, of a lead-gray colour, which passes into a bluish shade. The ore is easily broken by the blow of a hammer, and may be pounded to a fine powder, still preserving its glittering appearance. ”

“ The ore deposits are usually discovered by the cherty masses of silicious rock, which, being harder than the limestone, stand out from its weathered surface in bunches and small, vein-like masses. Often in 77 breaking the cherty rocks, stains of copper carbonate are found, and from such rock silver, and sometimes gold, is obtained. Numerous shafts, cuts, and tunnels have been made on these claims, twenty or more in number, and in every one ore of good grade has been found, although the quantity is usually small. ”

“ Lead, iron, coal, gypsum, manganese, zinc, antimony, cobalt, ochre of various kinds, common salt, nitre, plumbago, porphyry, jasper, chalcedony, buhrstone, marble, and freestone, of various qualities. The lead and iron ore are literally exhaustless, and of the richest quality. To say there is probably iron ore enough in this region to supply the United States with iron for one hundred thousand years to come, would not be extravagant. Here, too, is water power in abundance, rapid streams, with pebbly beds, forests of timber, and exhaustless beds of bituminous coal. ”

“ After discovering an ore of some valuable metal, it is essential to ascertain if its quantity and state of combination will justify an adventurer in working the mine, and smelting its products. The metal is rarely found in a condition approaching to purity; it is often disseminated in a mineralizing gangue far more bulky than itself; and more frequently still it is combined with simple non-metallic substances, such as sulphur, carbon, chlorine, oxygen, and acids, more or less difficult to get rid of. ”

“ A metalliferous rock is spoken of as an ore when it contains metallic minerals (or in some cases non-metallic minerals, such as sulphur) in such quantities and mixtures as to make possible their profitable extraction. The metal contained in an ore is sometime found in its elemental form, as in the case of gold or platinum, but more frequently as a sulphur compound, or as an oxide carbonate or silicate. Often several different forms of one metallic element are found in the same deposit and several metals are often found together. ”

“ After being thus freed from the admixture of other minerals, the ore is usually roasted or burned, to drive off any traces of sulphur it may contain; it is afterwards heated to redness with blind coal or culm, and a small portion of lime, when the melted metal separates from the dross, and runs into cavities prepared for its reception. It is afterwards refined by being remelted, and other impurities separated, which either sink or float on the surface. The purest metal is yielded by the ore called stream-tin, which is smelted with charcoal instead of coal. ”

“ It is the centre of a district very rich in minerals, obtained from a narrow stretch of crystalline schists underlying the Tertiary deposits. Iron ores (60 to 70% of iron) , copper ores, colours, brown coal, graphite, slate, and lithographic stone are obtained—nearly 2,000,000 tons of iron ore annually. ”

“ The ores when dug from the mine are generally stamped into powder, then “roasted,”—that is, made hot, and kept so for some time to drive off water, sulphur, or arsenic, which would prevent the “fluxes” acting properly. The fluxes are substances which will mix with, melt, and separate the matters to be got rid of, the chief being charcoal, coke, and limestone. The ore is then mixed with the flux, and the whole raised to a great heat; as the metal is separated it melts, runs to the bottom of the “smelting furnace,” and is drawn off into moulds made of sand ”

“ Iron ore, tin, copper and tungsten are extracted from the earth, refined, put to some use or wasted as the case may be, but they are gone. They may be replaced by other minerals. Through geological ages they may redeposited in the earth's crust. ”

“ Ore-deposits are but a special phase of the rock-forming processes already discussed. They have peculiar interest because of their industrial value. An ore is simply a rock that contains a metal that can be profitably extracted, though for convenience the term is used more broadly to include unworkable lean ores and ore material. The metal need not preponderate or form any fixed percentage of the whole, for the criterion is solely economic and not petrologic. A gold ore rarely contains more than a very small fraction of one percent. ”

“ These ores have some sulphur in them, and are therefore baked in ovens to remove it. They yield about 50 per cent. of iron. A geologist some time ago reported upon the ore banks that there were thirty millions of tons of ore in sight above the water-level, being over three times the amount taken out since the workings began in the eighteenth century. The deposits extend to a depth of several hundred feet under the surface, thus indefinitely multiplying the prospective yield. ”