Geological prospecting is the first step in finding the ore. It is initiated by a study of geological maps and reports, if such exist. Work is directed to regions where the geological conditions are favourable for mineralization. In search for primary deposits, intrusive igneous bodies should be sought, as they may be a source of mineralizing solutions. Features that show the presence of mineralization, such as fissures, faults, shear zones or drag folds, should then be looked for and followed. If limestones are intruded by or lie near intrusives or are cut by fissures, they should receive careful attention. If deposits are known in the area, the mineral habit of the region can then be utilizaed. Oxidized areas are sought to see if there are any croppings that can tell a story of the character and abundance of pre-existing sulfides.
Geophysical exploration may sometimes accompany the geological prospecting. At present, man’s inventiveness culminated in the development of scientific instruments and methods whose foundation is physics and mathematics. The chief methods used for exploration of oil and metals are as follows: magnetic, electrical, electromagnetic, gravimetric, seismic, radiometric.
In connection with exploration boring is sometimes used for the follownig reasons: for location of minerals covered by soil, rock or water; to search for extensions on strike or dip of known orebodies; to search for parallel orebodies; for location of faults and waterbearing strata; for detailed exploration of orebodies for estimating tonnages and values. Boring from the surface is best suited to large deposits of fairly uniform grade such as masses or beds dipping less than 50°. Boring is not always the cheapest method of exploration, and may not furnish all the desired information. In such cases trenching, test pitting, shaft sinking or drifting is used.
Trenches are confined to shallow soil; the economic limit of depth is about 6-7 ft. Test pits are used for alluvium too deep for trenches. They are applicable for depths to 100 ft; yet for depthhs over 30 to 50 ft. and in water-bearing ground test pits may be less suitable than boring methods.
Accurancy of sampling depends largely upon the character of the material drilled. Diamond drills give accurate samples in hard rock where core rocovery is complete. Accurate samples are also obtainable by churn drills in fine-grained unconsolidated material where casing piping can be driven ahead of the drill bit or sand pump. Soft, broken formations which cave in the hole are most difficult to sample. Cores are more satisfactory than churn-drill sludge for determining geological details.
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NOTES:
· fault - сброс, сдвиг;
· shear zone - зона узкого ступенчатого сброса, зона разрыва;
· drag fold - вторичная складка;
· dip - падение залежи, уклон;
· boring - бурение (скважины);
· trenching - рытье котлована;
· test pitting - разведочные работы в карьере;
· shaft sinking - проходка ствола;
· drifting - проведение штрека;
· churn drill sludge - шлам (грязь) ударно-канатного бурения.
Text 6. MINING EQUIPMENT
The scraper is most widely used in mines both for underground and open-pit operations for loading cars and transporting ore or waste for a short distance. There are two main types of scrapers – the open and the box type. The capacity of scrapers varies with the type of scraper used, the physical characteristics of the material handled, and the average rope speed.
For open-pit mining power shovels are widely used. Under normal conditions about 25 power shovels may be employed in a pit, having a bucket capacity of 4 to 8 cu. in. and loading into 50-ton mine cars or into trucks when trackless mining is used.
Apart from the above, every day sees the introduction of new mining equipment for some special use or for combined operations underground, and at the present time but little work is done by hand.
In coal mining longwall cutters are used which make a horizontal cut in the solid coal to a depth determined by conditions, in order to assist in breaking down the coal by subsequent use of explosives or other means. The cut can be made at any level between the roof and floor of the seam, but is generally made at floor level by an undercutter. The cut is made by specially shaped picks fitted to an endless chain running at a speed of between 350 to 500 ft/min and the cutter is hauled along the floor by a wire rope coiled around a suitable drum.
There are many types of cutters available designed to fit specified conditions. A new mining machine which does all labour-consuming operations in development of drifts for manganese mining has been built at Dnepropetrovsk Mining Institute, in the Ukraine. The machine is designed for heavy duty in the mines of Nikopol manganese ore basin. It will break up rock, load it into trolleys, and at the same time put up concrete props. In one month this machine prepares 600 meters of drift.
Loading in all the major working in metal mines is usually done by means of mechanical rail-mounted overhead loaders or crawlermounted loaders in trackless mines. They are fitted with a 1/2-cu. yd. bucket which swings completely over for discharge into the mine cars. This machine is fit for headroom between 7 ft. 6 in. to 8 ft. 6 in., discharge heights varying from 4 ft. to 6 ft. The entire unit weighs just over 3 1/2 tons and is powered by three reversible compressed-air motors, which have an average overall consumption of approximately 240 cu. ft. per minute at 90 lb. per sq. in. (psi).
A novel type of a mucking machine and a truck all-in-one is announced by an American company. This Transloader is a high-speed trackless transport: it can move up to 20 miles per hour either direction with round trip 1,600 ft. On shorter hauls the tonnage ranges up to 2 tons a minute. On longer hauls tonnages range down to 1 ton a minute. The Transloader is operated by only one man, mucking and hauling in the development and production work. Neither the Transloader nor its operator are ever idle.
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NOTES:
· power shovel - механическая лопата, экскаватор;
· trackless mining - ведение горных работ с безрельсовым транспортом;
· longwall undercutter - длиннозабойная врубовая машина;
· rail-mounted overhead loader - разгружающая через себя погрузочная машина на рельсовом ходу;
· crawlermounted loader - погрузочная машина на гусеничном ходу;
· mucking machine - машина, убирающая руду или породу (из забоя), разгружающая руду или породу в вагонетки.
