Mineral exploration

“ Not the least important application of geology to slides is in relation to deep mining operations. While the mining geologist has been principally engaged in exploration and development of ores, he is now beginning to be called in to interpret the great earth movements caused by the sinking of the ground over mining openings. For instance, the long-wall method of coal mining has resulted in a slow progressive subsidence of the overlying rock, affecting overlying mineral beds and surface structures over great areas. ”

“ These figures taken at face value are alarming; but the earth offers such huge possibilities for further discoveries that the life of oil reserves above indicated is likely to be considerably extended. At many times in the history of the mineral industry the end has apparently been in sight for certain products; but with the increased demand for these products has come increased activity in exploration, with the result that as yet no definite end has been approached for any one of them. ”

“ For oil and lead, on the other hand, the reserves now known have a life of comparatively few years, but the possibilities for successful exploration make it probable that their life will be greatly extended. Notwithstanding this tendency to lengthen the exhaustion period, the limits of mineral resource life are still small as compared with the life of the nation or of civilization,—and the fundamental desirability of conservation is not materially affected. ”

“ Annual production figures are only to a very partial extent an indication of the distribution of the great reserves of mineral resources. For instance, there are enormous reserves of coal in China which are not yet utilized to any large extent. The minerals of South America and Africa are in a very early stage of [Pg 66] development. The total world reserves will of course not be known until exploration and development of the world's resources are complete—a time which will probably never come. ”

“ For many mineral commodities the amounts now actually in sight will not last long, but the possibilities of extension and discovery are so great that a long future availability of these commodities can be counted upon with reasonable safety.
The present shortages in oil, tin, and other minerals mentioned may be only temporary. There is a large part of the world still to be explored, and the present reserves merely mark a stage in this exploration. Nevertheless, the ratio of reserves and discovery on the one hand to accelerated use on the other gives cause for much concern. ”

“ 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. ”

“ Origin of Mineral Deposits As a Factor in Exploration
In exploration, the geologist is keen to ascertain the origin of the mineral deposit. This is often a source of wonder to the layman or "practical" man, and the geologist may be charged with having let his fondness for theory run away with him. A widespread fatalistic conception is expressed in the Cornishman's dictum on ore, "Where it is, there it is." ”

“ It is true that the vast amount of war-time exploration and development, as well as the thoroughgoing investigations of the utilization of various minerals, have led to better knowledge of the mineral resources and their possibilities. It is also true that the war required a much more exhaustive census of mineral possibilities than ever before attempted. The immediate and direct effect of the war, however, was the intensive use of mineral resources without careful regard to cost, grade, or many other factors which determine their use in peace times. ”

“ The availability of minerals and mineral materials are essential for economic growth, national security, technological innovation, and the manufacturing and agricultural supply chain. (3) The exploration, production, processing, use, and recycling of minerals contribute significantly to the economic well-being, security and general welfare of the Nation. ”

“ The government of the United States has opened the public mineral lands to exploration for the precious metals, and, as a reward to the successful explorer, grants to him the right to extract and possess the mineral within certain prescribed limits. ”

“ In reality, more mines are found by careful prospecting than are ever given to the world by sheer accident. More and more is science turning prospector, and men go carefully, reading [30] geologic formations, following volcanic breaks and mineral outcroppings. Your desert prospector may eat with his knife and forget to take off his hat in the house, but he can talk you blind on intrusions and sedimentary deposits and the dips, angles and faults of certain mineral formations he knows. ”

“ 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. ”

“ Again, the Earth’s surface is covered with at least four-fifths water at depths ranging from one to five miles, including the millions of springs, lakes and rivers on land, to say nothing of the inexhaustible quantities of water encountered in the aforesaid boring and mining operations.
The deepest explorations in mines are the salt mines of Poland, the Calumet and Hecla copper mines and Comstock Lode. These have all been on trail of some mineral deposit formed by some remote work of Nature in the undefinable past, when volcanic or other influences in Nature’s laboratory left their deposit. ”

“ A great mineral country is usually marked by the outcrops of the veins being persistent in their courses and traceable for many miles, though very probably many breaks may occur in these outcrops. The rocks associated with great ore bodies are lime, porphyry, granite, shales, slates, quartzites, and diabase. Fragments of mineral and gangue, known to the miners as float, may be littered over the hills and encumber the courses of the stream. ”

“ The central cores of many of the now deeply eroded ranges consist of granite and other similar rocks, and are surrounded by sedimentary beds which range in age from the oldest stratified rocks now known to the youngest. Igneous rocks in great variety and in all forms incident to an extruded or volcanic and intruded or plutonic origin are present. The many disturbances that have occurred have led to the formation of mineral veins and the impregnation of rock masses with ores of various kinds—such as gold, silver, lead, copper, etc.—which have been mined with great success at many localities. ”

“ The treasures of commercially valuable ore-deposits have been hid by nature whimsically throughout the earth, here and there, by no rule of geography or latitude, and with a great disregard of equality. A nation’s needs or desires for mineral wealth have no stated relation to its actual mineral possessions ”

“ 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. ”

“ As the gold is found in quartz rock, and only to a small extent in gravel or other alluvial deposits, the mining requires capital, and will be carried on by companies. It will be carried on quickly, and so quickly with the aid of the enormously improved scientific appliances we now possess, as to exhaust at no distant period the mineral which the rocks contain. ”

“ For instance, manganese moves from three principal sources to four or five consuming centers. Chromite moves from two principal sources; tungsten also from two. Even for certain commodities which are widely distributed and move in large amounts, the concentration of movement is rather marked; for instance, the world movement of coal is controlled by England, the United States, and Germany. In other words, although the world movement of mineral commodities is widespread and exhibits many complex features, most of the individual minerals follow two or three salient lines of movement. ”

“ Missing from the lists of the most abundant minerals and rocks, are the greater part of the commercially important mineral resources—including such as coal, oil, gas, iron ore, copper, gold, and silver,—implying that these mineral products, notwithstanding their great absolute bulk and commercial importance, occur in relatively insignificant amounts as compared with the common rock minerals of the earth. ”

“ With respect to the products of the mines in general and particularly if the term be liberally interpreted, to include all inorganic products of the earth, it may be said that they as a group represent one of the most important of physical factors in the modern progress of nations. Leaving coal entirely aside, it still remains true that the tremendous development of every phase of modern industry, from the cultivation of the soil to the most complex manufacturing process, has become possible only through the constantly increasing employment of mineral products. ”

“ Should any of them, perchance, from curiosity or interest, descend into these dark recesses of the earth, they are prepared to discover only a few insulated objects, which they may think strange or possibly hideous; but they cannot recognize either the symmetrical disposition of mineral bodies, or the laws which govern geological phenomena, and serve as sure guides to the skilful miner in his adventurous search. It is by exact plans and sections of subterraneous workings, that a knowledge of the nature, extent, and distribution of mineral wealth, can be acquired. ”

“ The Mines.—No country can ever become great in industry unless it has ready access to minerals, especially iron and coal. It was the possession of iron and coal in great quantities that served to make England during the nineteenth century the industrial leader of Europe. Various regions of the United States possess these great stores of mineral wealth and have made good use of them. There is one great difference between mineral resources and other natural resources, namely, that when minerals are once taken from the earth there is no way of renewing them. ”

“ Placers are detrital or fragmental sediments containing the ore in mechanical fragments, which are derived from the erosion and transportation of solid-rock veins or lodes, sometimes called the "mother lode." During the process of transportation and deposition there is more or less sorting, because of differing density of the mineral fragments, resulting in the segregation or concentration of the ore minerals in certain layers or channels. Gold, because of its weight, tends to work down toward bedrock, or into scoured or excavated portions of stream channels. ”

“ 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. ”

“ 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. ”

“ I am, however, firmly of opinion that this extensive range, which presents many features in common with the Sierras of California, offers to the geologist a rich field for research, and to the miner a probable El Dorado where, I believe, great treasure will be brought to light in years to come. It is more than likely that the whole of this extensive mountain range will be found upon examination to be rich in all the mineral products common to geological formations of a like kind, and that not only gold but other minerals will be found. ”

“ 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. ”