Mineral deposit

“ While boring is sometimes adopted for prospecting irregular and steeply inclined mineral deposits of small area, the results are obviously less trustworthy than under the conditions named above, and may be actually misleading unless a large number of holes are bored. Incidentally, bore-holes supply information as to the character and depth of the valueless depositions of earth or rock overlying the mineral deposit. Such data assist in deciding upon the appropriate method for, and in estimating the cost of, sinking shafts or driving tunnels for the development and exploitation of the deposit. ”

“ The size of the blocks or the distance between the main passages is determined mainly by considerations of convenience and economy in excavating and handling the mineral, and by the possibility of supporting the roof long enough to permit the excavation of the mineral without unnecessary risk or expense. In metal mining, when the workable portions of the deposit are small and separated by unworkable areas, the levels serve also the purpose of exploration, and in such cases must not be so far apart as to risk missing valuable mineral. In coal-mines main entries are often 100 yds. ”

“ A vein of cobalt ore a, which is rich only in the grayish-white sandstone (weisse liegende) , traverses and deranges all the beds wherever it comes.
Of working mines by fire.—The celebrated mine worked since the tenth century in the mountain called Rammelsberg, in the Hartz, to the south of Goslar, presents a stratified [851] mass of ores, among the beds of the rock which constitute that mountain. The mineral deposit is situated in the earth, like an enormous inverted wedge, so that its thickness (power) , inconsiderable near the surface of the ground, increases as it descends. ”

“ Mechanical erosion of preëxisting mineral deposits or rocks and their transportation, sorting, and deposition are responsible for the placers of gold, tin, tungsten, platinum, and various precious stones, and for certain iron sands and conglomerates. Sands, sandstones, shales, and certain clays and bauxites also belong in this group. These deposits may be formed under air or under water, and under various climatic and topographic conditions. During the process of formation the minerals of differing density are more or less sorted out and tend to become segregated in layers. ”

“ With increasing depth subterranean water becomes more and more sluggish in its movements and more and more highly charged with minerals dissolved from the rocks above. At such depths it deposits these minerals in the pores of rocks, cementing their grains together, and in crevices and fissures, forming mineral veins. Thus below the zone of solution where the work of water is to dissolve, lies the zone of cementation where its work is chemical deposit. A part of the invisible load of waste is thus transferred from rocks near the surface to those at greater depths. ”

“ Mineral Resources.—Numerous mineral deposits have been discovered, but little has been determined with respect to their value. Sub-bituminous coal is widely distributed. That near the surface is generally poor in quality and the difficulties of deep mining may be great because of folds and faults in the rocks. ”

“ Mine à La Motte has also proved an extensive deposit, and is still unexhausted. New Diggings, Shibboleth, and Richwoods, are among the discoveries of later date, which have yielded very large quantities of ore. But the mode of mining in the diluvial soil must exhaust it of its mineral contents, and direct miners, in after years, to the true position of the ore, in the calcareous rock. So long as the search continues in the soil, the business will partake of the uncertainty which now attends it, and which renders it rather an object of temporary enterprise, than a fixed employment. ”

“ The irreplaceable character of our mineral deposits, together with the tendency for large industrial interests to monopolize minerals. has greatly stimulated the conservation of these resources. A valuable step forward has been the reclassification of public lands to allow of special treatment of lands containing mineral deposits. Coal is still used lavishly, but nine tenths of our original deposits are still in existence. ”

“ The development of soils by weathering should not be regarded as a special process of rock alteration, unrelated to processes producing other mineral products. Exactly the same processes that produce soils may yield important deposits of iron ore, bauxite, and clay, and they cause also secondary enrichment of many metallic mineral deposits. ”

“ When, therefore, adjacent or underlying excavations cause earth movements in a neighbor's property, litigation is likely to ensue and the geologist is likely to be called in. The long-wall method of coal mining, extensively practiced in certain parts of the United States, is slowly withdrawing support from the ground overlying the coal seams, resulting in damages to surface structures and in some cases to overlying mineral deposits. ”

“ The country rock is a coarse hornblendic biotite granite. The vein has the usual character of mineral deposits, swelling at times to a width of 8 feet, and then contracting to much less. The highest grade ore is found in 44 the narrower portions, where it is sometimes almost pure tin oxide, running as high as 70 per cent. The vein matter does not consist wholly of tourmaline, but contains quartz grains scattered through it in about the same proportion as in the granite. ”

“ Others are not convenient to markets, and still others have no present commercial use. In years to come, however, changes may occur that will make it practical to mine, process, and use some of these resources. Furthermore, some other mineral deposits that are now being utilized in a limited way may have greater future use. The Illinois Geological Survey continues to study the location, character, and composition of many such mineral materials and is alert for the development of new uses. ”

“ Many mineral deposits have been found because they outcrop at the surface; the discoveries may have been by accident or they may have been aided by consideration of geologic factors. There are still vast unexplored areas in which mineral deposits are likely to be found standing out at the surface. For much of the world, however, the surface has been so thoroughly examined that the easy surface discoveries have been made, and the future is likely to see a larger application of scientific methods to ground where the outcrops do not tell an obvious story. ”

“ The fact that no such limits were imposed on veins of coal or other minerals or metals indicates, not that the act was intended to be confined to the minerals enumerated in § 2, since that would be a clear restriction upon the words 'valuable mineral deposits' in the 1st section, but that these particular metals stood in special need of limitation and protection. ”

“ In the country immediately north are mineral deposits including copper, silver, free gold and mica. South, is a rich mountainous country where galena and free milling quartz are mined. Much English capital is invested in timber and mines in the region. ”

“ In the Missouri lead and zinc districts the ore deposits occur near the surface, the depth of the present working seldom exceeding 150 or 200 feet, and, as nearly as can be judged, have been formed by the downward transfer of mineral matter through the process of solution and recrystallization, as the surface of the land has been lowered by chemical and mechanical denudation.
Many of the rich silver-mines of the Pacific mountains occur in fissures and cavities in sedimentary rocks, mainly limestone. ”

“ Of far the greatest importance of all the ore-bodies in troughs are the iron ores of the Lake Superior region, now the most productive of all the iron-mining districts. In a series of sedimentary formations, generally of Huronian age, and with associated eruptives, there occur strata consisting of a cherty iron carbonate, which were probably originally marine deposits akin to glauconite. They rest upon relatively impervious rocks, and are often penetrated by basaltic dikes. ”

“ The enriching minerals have been introduced in solution, and the solvent has found its way through the rock because of its natural character, and not because geological movements have opened it. Porous sandstones are one of the most common cases. Deposits of silver ores have been extensively mined at St George in southern Utah, consisting of films of argentite and cerargyrite, which have been precipitated upon fossil leaves, sticks, and in the sandstone itself. ”

“ In the judgment of the writer, the phenomena presented by the Leadville ore deposits can be as well or better accounted for by supposing that the plane of contact between the limestone and porphyry has been the conduit through which heated mineral solutions coming from deep seated and remote sources have flowed, removing something from both the overlying and underlying strata, and by substitution depositing sulphides of lead, iron, silver, etc., with silica. ”

“ By the erosion of the igneous rocks the metals have been distributed among sedimentary strata, and even the sea has taken into solution an appreciable amount of gold and other metals, but in this widely diffused condition they are wholly useless to man. The concentration which has made them available is due to the interaction of many agencies. Earth movements fracturing deeply the rocks of the crust, the intrusion of heated masses, the circulation of underground waters, have all cooperated in the concentration of the metals of mineral veins. ”

“ Evidently the development of sediments from igneous rocks has involved the destruction of much of the feldspars and ferro-magnesian silicates, and the building from the elements of these destroyed minerals of more quartz, white mica, clay, dolomite, calcite, chlorite and limonite. The composition of the minerals of the sedimentary rocks is such as to indicate that the constituents of the air and water have been added in important amounts to accomplish this change of mineral character. ”

“ Replacement implies the precipitation of the ore and gangue, molecule by molecule, in the position of the original minerals but without, as in pseudomorphs, the necessary reproduction of crystalline forms. Some waterway must of course introduce the ore-bearing solutions, but it may be slight compared with the great size of the resulting ore-bodies. Lead and zinc ores, often carrying some silver, are those most widely distributed, as they were also the earliest recognized in deposits of this character. More than any other metals their association with limestone is pronounced. ”

“ By the term 'placer claim,' as here used, is meant ground within defined boundaries which contains mineral in its earth, sand, or gravel; ground that includes valuable deposits not in place, that is, not fixed in rock, but which are in a loose state, and may in most cases be collected by washing or amalgamation without milling. By 'veins or lodes,' as here used, are meant lines or aggregations of metal embedded in quartz or other rock in place. ”

“ About two-thirds of our gold is obtained from the placers, and one-third from the quartz.
A mine is defined and generally understood to mean "a subterraneous work or excavation for obtaining metals, metallic ores or mineral substances;" but this definition does not apply to our placer mines, which are places where gold is taken from diluvial or alluvial deposits. Most of the work is not subterraneous; it is done in the full light of day. ”

“ 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. ”

“ 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. ”

“ Mineral products formed by sedimentary processes include sandstones, limestones, and shales, used as building stone and road materials; certain sedimentary deposits of iron, like the Clinton ores of the southeastern United States and the Brazilian ores; important phosphate deposits; most deposits of salt, gypsum, potash, nitrates, etc.; comparatively few and unimportant copper deposits; and important placer deposits of gold, tin, and other metals, and precious stones. With the aid of organic agencies, sedimentary processes also account for the primary deposition of coal and oil. ”

“ Several of the mines in the mineral soil have been traced down into the rock, and have been pursued through apertures, closing and expanding in the manner of true veins. In the numerous cases where the rock has put a stop to further mining, and it has exhibited no signs of ore, it may be supposed that the ore has been moved, by diluvial force, from the original position of the mine, and been finally deposited, with the soil, upon unmetalliferous portions of the rock. ”