Английский язык для направления гороное дело. Облова И. Учебное пособие СанктПетербург 2020 удк 811. 111 (075. 8) Ббк 81. 2Англ я73 О18
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Sedimentary Rocks Sedimentary rocks represent one of the three major groups of rocks that make up the crust of the Earth. Most sedimentary rocks have originated by sedimentation. They are layered or stratified. Thus, stratification is the most important characteristic of sediments and sedimentary rocks. It is necessary to note that the processes which lead to the formation of sedimentary rocks are going on around us. Sediments are formed at or very near the surface of the Earth by the action of heat, water (rivers, glaciers, seas and lakes) and organisms. Sedimentary rocks form a very small proportion by volume of the rocks of the Earth’s crust (only 5%), but about three quarters of the Earth’s surface is occupied by sedimentary rocks. It means that most of sedimentary rocks are formed by sediments, accumulations of solid material on the Earth’s surface. The thickness of the layers of sedimentary rocks can vary greatly from place to place. They can be formed by the mechanical action of water, wind, frost and organic decay. Such sediments as gravel, sand and clay “can be transformed into conglomerates, sandstones and clay schists as a result of the accumulation of materials achieved by the destructive mechanical action of water and wind. Mechanical sediments can be unconsolidated and consolidated. For example, gravel, sand and clay form the group of unconsolidated mechanical sediments, because they consist of loose uncemented particles (grains). On the Earth’s surface we also find consolidated rocks, which are very similar to the loose sediments whose particles are firmly cemented to one another by some substance. The usual cementing substances are sand, clay, calcium carbonate and others. On the other hand, chemical sediments are the result of deposits or accumulations of substances achieved by the destructive chemical action of water. The minerals such as rock salt, gypsum and others are formed through sedimentation of mineral substances that are dissolved in water. Sediments can also be formed by the decay of the remains of organisms, by the accumulation of plant relics. They are called organic sediments. Limestone, peat, coal, mineral oil and other sediments may serve as an example of organic sediments. The most principal kinds of sedimentary rocks are conglomerate, sandstone, siltstone, shale, limestone and dolomite. Many other kinds with large practical value include common salt, gypsum, phosphate, iron oxide and coal. Igneous Rocks Igneous rocks have crystallized from solidified magma. Igneous rocks can be classified in a number of ways and one of them is based on mode of occurrence. They occur either as intrusive (below the surface) bodies or as extrusive masses solidified at the Earth’s surface. The grain size of igneous rocks depends on their occurrence. The intrusive rocks generally cool more slowly than the extrusive rocks and crystallize to a larger grain size. The coarser-grained intrusive rocks with grain size of more than 0.5 mm called plutonic or abyssal are referred to as intrusive igneous rocks because they are intruded into older pre- existing rocks. Extrusive or volcanic rocks have even finer grains, less than 0.05 mm and are glassy. Exposed igneous rocks are most numerous in mountain zones for two reasons. First, the mountain belts have been zones of major deformation. Second, uplifts in mountain belts have permitted plutonic masses to be formed. Extrusive igneous rocks have been formed from lava flows which come from fissures to the surface and form fields of volcanic rocks such as hyalite (гиалит), basalt, as well as volcanic ashes and dust, tuff, etc. As a rule, these rocks of volcanic origin cool rapidly and are fine-grained. It is interesting to note that basalt is the most abundant of all lava types. It is the principal rock type of the ocean floor. Igneous rocks are rich in minerals that are important economically or have great scientific value. Igneous rocks and their veins are rich in iron, gold, zinc, nickel and other ferrous metals. Metamorphic Rocks Metamorphic rocks compose the third large family of rocks. “Metamorphic” means “changed from”. It shows that the original rock has been changed from its primary form to a new one. Being subjected to pressure, heat and chemically active fluids beneath the Earth’s surface, various rocks in the Earth’s crust undergo changes in texture, in mineral composition and structure and are transformed into metamorphic rocks. The process described is called metamorphism. As is known, metamorphic rocks have been developed from earlier igneous and sedimentary rocks by the action of heat and pressure. The role of water in metamorphism is determined by at least four variable geologically related parameters: rock pressure, temperature, water pressure, and the amount of water present. Many of the metamorphic rocks consist of flaky materials such as mica and chlorite. These minerals cause the rock to split into thin sheets, and rocks become foliated. Slate, phylum, schist and gneiss belong to the group of foliated metamorphic rocks. Marble and quartzite are non-foliated metamorphic rocks. The structure of metamorphic rocks is of importance because it shows the nature of pre -existing rocks and the mechanism of metamorphic deformation. Every trace of original structure is of great importance to geologist. Metamorphic rocks represent the oldest portion of the Earth’s crust. They are mostly found in the regions of mountain belts where great dislocations on the Earth once took place. Mineral Deposits Minerals that make up rocks are defined as inorganic substances which occur naturally and have a definite chemical composition and physical properties which vary within known limits. The major properties are colour, crystal form, hardness, cleavage and others. Cleavage is one of the most diagnostically useful mineralogical properties which can be found throughout the mineral. Minerals of use to man can be grouped into two broad categories: 1) metals, such as aluminium, copper, gold, silver, iron, tin, platinum, chromium, nickel, lead and zinc, and 2) non-metallic minerals, such as diamonds, salt, limestone, cement, sulphur, and asbestos. When minerals occur so that they can be worked at a profit they are called ore deposits. Mineral deposits are seldom equally rich throughout. Economic minerals are those which are of economic importance and include both metallic and non-metallic minerals. Most minerals consist of several elements. Such elements are oxygen, silicon, titanium, aluminium, iron, magnesium, calcium, sodium, potassium and hydrogen. They make up more than 99 per cent by weight of all the rock-forming minerals. Of these, aluminium, iron and magnesium are industrial metals. The other metals are present in small quantities, mostly in igneous rocks. For example, iron is one of the most abundant metals in the Earth’s crust. There are three important classes of iron deposits: deposits associated with igneous rocks; residual deposits and sedimentary deposits. Iron deposits associated with igneous rocks are usually small but very rich bodies either of hematite or magnetite. Large concentrations have been successfully mined in Pennsylvania (the USA) and in the Russian Federation. Residual deposits of iron minerals are formed wherever weathering occurs. Iron deposits formed this way are very widespread. It should be stressed that the residual deposits were among the first to be exploited by man. Sedimentary iron deposits make up most of the world’s current production. As the essential component of every variety of steel, iron is obviously the most important of all industrial metals. It has played a large part in the development of our modem civilization. Iron ores are mainly used for producing cast iron, steel and ferro-alloys. From a scientific point of view, iron’s most important property is that it becomes magnetized. The magnetic iron ore is the main wealth of the Kursk Magnetic Anomaly (KMA). Iron fields are worked by surface mining which is more economical. But the KMA is rich not only in iron ores. Its deposits contain bauxite, phosphorite, cement, sand and clays. Prospecting Mining activities include prospecting and exploration of a mineral deposit through finding, proving, developing, extracting and processing the ore. That is why it is possible to divide the mining activity into three phases: 1) before mining which involves prospecting and exploration required to locate, characterize and prove a potential ore body; 2) mining which refers to actual coal or ore extraction. Extraction processes include underground or surface mining and dredging; 3) after mining which involves processing and preparing the raw ore for the end product. Before a mineral deposit can be worked, that is, before it can be extracted from the Earth for use by man, it must first be found. The search for economically useful mineral deposits is called prospecting. To establish the quality and quantity of a mineral deposit, the type of country rock, etc. means to prove it and this process is called proving. Prospecting and proving are only two different stages of mining geological exploration; the latter includes drilling and driving of openings. Last century prospectors looked for visible evidence of mineralization on the surface of the Earth. To recognize valuable minerals, it was necessary to know their various distinctive physical properties. For example, gold occurs in nature as a heavy malleable yellow metal. Galena, the most important mineral containing lead, is dark grey, heavy and lustrous. The first ores of iron to be mined were deposits of magnetite, a black heavy mineral capable of attracting a piece of iron. As the deposits of mineral that cropped out at the surface were mined, the search for additional supplies of minerals took place. The science of geology was used to explain the occurrence of ore deposits. The aim of geological prospecting is to provide information on a preliminary estimation of the deposit and the costs of the geological investigations to be made. It also indicates whether it is available to continue the exploration or not. Prospecting work includes three stages: 1) finding signs of the mineral; 2) finding the deposit; 3) exploring the deposit. General indications of the possibility of exposing this or that mineral in a locality can be obtained by studying its general topographical relief, the type of ground and its general natural conditions. Thus, in mountainous regions where fissures were formed during the process of mountain formation, ore minerals could be expected in the fissure fillings. Certain deposits are found only in a particular type of ground. Coal seams, for example, are found in sedimentary formations mainly consisting of sandstones and shales. Veins, on the other hand, are found in crystalline (igneous) rocks, and the type of country rock usually determines the type of minerals. At present, prospecting methods to be used are as follows: 1) Surface geological and mineralogical prospecting such as panning. 2) Geophysical, geochemical, geo-botanical prospecting. 3) Aerial photography with geological interpretation of the data to be obtained is highly effective from aircraft or helicopter. Besides, successful development of space research has made it possible to explore the Earth’s resources from space by satellites. In modem prospecting the methods mentioned above are used together with the study of geological maps. General Information on Mining As has been said, mining refers to actual ore extraction. Broadly speaking, mining is the industrial process of removing a mineral-bearing substance from the place of its natural occurrence in the Earth's crust. The term "mining" includes the recovery of oil and gas from wells; metal, non-metallic minerals, coal, peat, oil shale and other hydrocarbons from the earth. In other words, the wo± done to extract mineral, or to prepare for its extraction is called mining. The tendency in mining has been towards the increased use of mining machinery so that modern mines are characterized by tremendous capacities. This has contributed to: 1) improving working conditions and raising labour productivity; 2) the exploitation of lower-grade metal-bearing substances and 3) the building of mines of great dimensions. Mining can be done either as a surface operation (quarries, opencasts or open pits) or by an underground method. The mode of occurrence of the sought-for metallic substance governs to a large degree the type of mining that is practised. The problem of depth also affects the mining method. If the rock containing the metallic substance is at a shallow site and is massive, it may be economically excavated by a pit or quarry-like opening on the surface. If the metal-bearing mass is tabular, as a bed or vein, and goes to a great distance beneath the surface, then it will be worked by some method of underground mining. Working or exploiting the deposit means the extraction of mineral. With this point in view a number of underground workings is driven in barren (waste) rock and in mineral. Mine workings vary in shape, dimensions, location and function. Depending on their function mine workings are described as exploratory, if they are driven with a view to finding or proving mineral, and as productive if they are used for the immediate extraction of useful mineral. Productive mining can be divided into capital investment work, development work, and face or production work. Investment work aims at ensuring access to the deposit from the surface. Development work prepares for the face work, and mineral is extracted (or produced) in bulk. The rock surfaces at the sides of workings are called the sides, or hi coal, the ribs. The surface above the workings is the roof in coal mining while in metal mining it is called the back. The surface below is called the floor. The factors such as function, direct access to the surface, driving in mineral or in barren rock can be used for classifying mine workings. Methods of Working Bedded Deposits Underground The method of working (or method of mining) includes a definite sequence and organization of development work of a deposit, its openings and its face work in certain geological conditions. It depends on the mining plan and machines and develops with their improvements. A rational method of working should satisfy the following requirements in any particular conditions: 1) safety of the man; 2) maximum output of mineral; 3) minimum development work (per 1,000 tons output); 4) minimum production cost and 5) minimum losses of mineral. Notwithstanding the considerable number of mining methods in existence, they can be reduced to the following main types: 1. Methods of working with long faces (continuous mining); 2. Methods of working with short faces (room-and-pillar). The characteristic feature of the continuous mining is the absence of any development openings made in advance of production faces. The main advantage of long continuous faces is that they yield more mineral. Besides, they allow the maximum use of combines (shearers), cutting machines, powered supports and conveyers. The longwall method permits an almost 100 per cent recovery of mineral instead of 50 to 80 per cent obtainable in room-and-pillar methods. The basic principle of room-and-pillar method is that rooms from 4 to 12 metres wide (usually 6-7) are driven from the entries, each room is separated from each other by a rib pillar. Rib pillars are recovered or robbed after the rooms are excavated. The main disadvantage of shortwall work is a considerable loss of mineral and the difficulty of ventilation. In working bedded deposits methods of mining mentioned above may be used either with stowing or with caving. In Russia, Germany (the Ruhr coal-field), France and Belgium nearly all the faces are now long ones. In Britain longwall faces predominate. The USA, Canada, Australia and to some extent India are developing shortwall faces and creating the machines for them. In these countries shortwall faces are widely used. In Russia the thick seams are taken out to full thickness up to 4.5 m thick if they are steep, and up to 3.5 m thick if they are gently sloping or inclined. In the Kuznetsk coal-field long faces are worked to the dip with ashield protection, using amethod proposed by N.Chinakal. In shield mining coal is delivered to the lower working by gravity so that additional haulage is not required. It should also be noted that in Russia hydraulic mining is widely used as it is one of the most economic and advantageous methods of coal getting. New hydraulic mines are coming into use in a number of coal-fields. Hydraulic mining is developing in other countries as well. The aim of hydraulic mining is to remove coal by the monitors (or giants) which win coal and transport it hydraulically from the place of work right to the surface. It is quite obvious that the choice of the method of mining will primarily depend on the depth and the shape and the general type of the deposit. Mining Thick Seams Longwall retreating is one of the primary methods of mining in many coal mining areas. There is a high degree of mechanization, and mine safety is receiving an increasing amount of emphasis. Thick seam coal mining is important in Russia. Many high-quality coal seams exceed 35 metres (12 feet) in thickness — the normally accepted classification for a thick seam (although this varies in different countries). Some of these thick seams are of key importance in major mining basins. Seam thickness is the most significant factor which is taken into account in mining practice. The increasing strata movement with increasing seam thickness requires not only specialized extraction techniques, but also highly specialized ground control and support methods. This is certainly true of the coal basins where coal seams are gassy and the majority of coal is liable to spontaneous combustion. Coal seams occur at a depth of between 350 and 710 metres (1,150 and 2,330 feet). Longwall retreating is the primary method of mining at the collieries with more than 98 per cent of the total output. Application of a mining method with the coal face being advanced down the dip is steadily expanding; shortwall pillar extraction with power loaders is being successfully employed. Coal faces and development headings are equipped with instruments for automatic gas protection and centralized telemonitoring of methane content. Data on gas conditions in development headings which are particularly dangerous from the viewpoint of methane content, and in all coal faces are transmitted to the mine dispatcher's control panel. In order to reduce gas content in mine workings, extensive use is made of preliminary gas drainage of the coal seams, gas drainage of roofs to be caved and also of the goaf. The main trend in mine transport is towards high-capacity automatic conveyer systems. In underground workings transport of men and materials is by high-capacity electric locomotives; in incline roadways, by ropeways, floor-mounted haulage and up-to-date hoisting installations. The mining district is usually developed by mine shafts. The mining method is longwall retreating along the strike and down the dip. The mining area is divided into two blocks east and west. In the eastern block, the panels are mined down the dip, in the western block, mining takes place along the strike. The faces are 200 metres long and operate along the strike of the seam. Sandstone forms the immediate roof and floor of the seam. Each face is mining a 3.5-metre thick section of coal, and a 0.5 to 0.8 metre thick pillar (band) of coal is left between two panels to form the roof of the lower face. Each face is equipped with a double-ended dram shearer. The drams are 1.8 metres in diameter and a 0.6-metre web of coal. The leading dram cuts the top section of the face, and the trailing dram cuts the bottom section. Water jets are fitted to the drams for dust suppression. Coal passes along the face on the armoured face conveyer to the crasher installed at the main gate end of the conveyer, which reduces the size of the coal before it is delivered to a beam stage loader in the main gate. The faces are operated on two production shifts and one maintenance shift per day. Each face is supported by shield supports. It should be stressed that special attention is paid to underground methane drainage. The methane is pumped through pipes first to the tail gate and then through the mine gate to the upcast shafts and then to the surface, where it is used for heating. Two sensors for continuously monitoring the emission of CH4 are situated in the top panel, one in the main gate, and the other in the tail gate. These are placed 20 metres in front of the face. The control room at the mine's surface automatically monitors and records CH4 emissions throughout the mine. In coal face and development operations, use is made of current forecasting of the liability to sudden outbursts, that is establishing dangerous and non-dangerous zones. All coal faces are equipped with mechanized complexes, comprising power loaders. In underground haulage roadways, use is made of high-capacity belt and apron conveyers. Coal is hoisted to the surface through two skip shafts. Monorails are widely used on levels for transport of materials and equipment to coal faces and development headings. Some of production processes are automatic. An Overview of the Mining Industry According to the broadest definition, mining includes discovering, extracting and processing of all nonrenewable resources up to the point at which they are used for fabricating or for producing energy. This broad definition includes the energy minerals such as coal, petroleum and natural gas; refined or processed metals such as copper, steel and the ferroalloys; and nonminerals such as diamonds, phosphate and potash. A much narrower definition of mining includes only crude or nonprocessed mine products, such as mineral ores and coal, and excludes petroleum and natural gas. We deal mainly with the major metals from the exploration and mining stages to the processing stage from which they are normally marketed for use in manufacturing. The production of useful minerals involves several stages that are generally carried on by large mining firms, although small mining operations may engage in the initial stage. The first stage is exploration of areas identified by geological reports as possessing potential mineral resources. Modern exploration methods are quite sophisticated and include geological, geochemical and geophysical investigation; three-dimensional sampling by core drilling or other methods; laboratory analyses, including ore treatment, concentration, and recovery tests; and economic appraisal. The objective is to discover and evaluate an orebody that can be economically exploited. Geochemical exploration is used to measure the chemical properties of the area surrounding the deposit in order to delineate abnormal chemical patterns that may be related to potentially economic mineral deposits. Geophysical investigations employ electronic equipment that can detect contrasts in such physical properties as specific gravity, electrical conductivity, heat conductivity, seismic velocity and magnetic susceptibility. Where much of the bedrock is concealed, telegeologic or remote sensing techniques measure various geologic properties from aircraft or satellites. Exploration is commonly carried on by teams of specialists that include geologists, geochemists and geophysicists. There are different levels of exploration beginning with regional geologic mapping of areas up to 50,000 square km (20,000 square miles) and ending with intensive investigations of orebodies by means of numerous drillings to obtain bulk samples which are then metallurgically tested to determine the dimensions and character of the orebody. If the results of exploration activities suggest that an economical deposit has been found, the second stage involves engineering and economic evaluations of the mining project. It is on the basis of this study that companies decide whether to go ahead with a mining project; the study may also be reviewed by prospective lenders. The feasibility study for a large mining project may be quite costly, running to $25 million or more in some cases. The total cost of exploration and the feasibility study for a large mine may run to $50 million or more. It is uncertain whether a profitable mine will be constructed until all the stages have been completed. In the initial exploration stage, several million dollars may be spent with less than a 10 per cent chance of a successful outcome. The third stage is the construction of the mine, the metallurgical plant, and infrastructure. There are two basic types of operations to extract mineral ores: open-pit or surface mining, and underground mining. An open-pit mine is largely a quarrying operation that handles a large volume of material. Such mining involves drilling and blasting the ore and hauling it out of the pit in large trucks with capacities ranging up to 200 tons, or in ore trains. The ore is hauled to crushers and then to the metallurgical plant. In underground mining, shafts are dug into ore deposits below the surface, from which ore is drilled, blasted and removed through underground passages to the surface. Iron, bauxite and copper ores are extracted by means of open-pit mining, while lead, zinc, silver and gold are largely extracted by underground mining. There are also some underground copper mines. Economies of scale in open-pit mining permit the mining of relatively low-grade ores. As much as 100,000 tons of ore per day containing less than 1 per cent metal are extracted in the larger open-pit operations. Higher ore grades are necessary for underground mining to be profitable. One recent advance in mining and processing of lower-grade ores is in situ mining. In situ mining may be defined as the extraction of metals from ores located within a mine (broken or fractured ore, caved material, slag heaps, etc.). These materials represent an enormous potential source of all types of metals. Large mines involve huge capital outlays running to a billion dollars or more. The mining complexes usually include concentration of ores for production of concentrates with 25 per cent or higher metal content. In the case of copper, large mine complexes include plants for smelting copper or for producing copper metal by hydrometallurgical methods, but in the case of other metals such as gold, lead, zinc, tin and iron, metal is produced in separate plants which may or may not be owned by the mining company. The degree of processing that usually takes place at the mine differs widely among metals, but refining the product for market ing to fabricators nearly always takes place in separate plants that refine the products of several mines. As is known, modern methods of processing are dense medium separation, jigging and froth floatation. Operations prior to coal preparation include: blending, screening, crushing, dewatering and others. The aim is to get clean coal for metallurgical plants, etc. Since mines tend to be located far away from developed areas, infrastructure is often a substantial proportion of capital cost. It is frequently necessary to provide sources of power and water, as well as highways, railroads and port facilities. In addition, the mining company may be responsible for constructing living quarters for workers and their families and for providing education and other public services required by the mining community. Appendix III |