1. Surface mining is more expensive than underground mining.
2. Strip mines are used when the ore is of low grade, meaning that the amount of metal per cubic meter or kilogram of rock is small, and disseminated, meaning that the metals are distributed throughout large volumes of rock rather than being concentrated in veins.
3. A particularly destructive form of alluvial mining is hydraulic mining, in which pressurized water is used to wash away large amounts of sand and gravel.
4. Alluvial is similar to strip mining in that the overburden above a tabular coal deposit is removed. Instead of being stockpiled and used to restore the original topography, however, the overburden is used to fill adjacent valleys.
5. Although mountaintop mining is an inexpensive method of mining coal in mountainous areas, the filling of valleys can have negative environmental impacts.
6. The size of open-pit mines, which often take decades to excavate, makes it economical to reclaim the pits by filling them with rock.
Exercise 7. Refer to the text and complete the sentences below:
1. Because the strip mines consist of shallow excavations, the overburden can be economically
2. Coal mining accounts for about half of all surface mining, extraction of
3. In order to prevent the sides of the pit from collapsing, open-pit mines must be continually
4. Open-pit mines are used when the ore is of low grade, meaning that the amount of metal per cubic meter or kilogram of rock is , and disseminated, meaning that the metals are distributed throughout large volumes of rock rather than being concentrated in...
5. Instead of being stockpiled and used to restore the original topography, however, the overburden is used to fill...
6. Although mountaintop mining is an inexpensive method of mining coal in mountainous areas, the filling of valleys can have
7. Alluvial mining is a form of surface mining used to recover heavy minerals such as gold from sand and gravel beds, including stream beds, known as
8. In some cases these deposits can be removed by agitating the sand and gravel in simple pans.
9. A more sophisticated and efficient way of separating placer minerals from the sand and gravel is
10. As sand and gravel is shaken in the sluice box, lighter sand grains are and heavier metals are...
11. Dredges are used in other large-scale alluvial
Exercise 8. Make dialogues. Discuss different kinds of mining, their characteristic features, their advantages and disadvantages.
TEXT 6 (A). HEAVY MACHINERY.
Exercise 1. Listen to the text twice and do the following tasks:
Heavy machinery is needed in mining for exploration and development, to remove and stockpile overburden, to break and remove rocks of various hardness and toughness, to process the ore and for reclamation efforts after the mine is closed. Bulldozers, drills, explosives and trucks are all necessary for excavating the land. In the case of placer mining, unconsolidated gravel, or alluvium, is fed into machinery consisting of a hopper and a shaking screen or trommel which frees the desired minerals from the waste gravel. The minerals are then concentrated using sluices or jigs. Large drills are used to sink shafts, excavate stopes and obtain samples for analysis. Trams are used to transport miners, minerals and waste. Lifts carry miners into and out of mines, as well as moving rock and ore out, and machinery in and out of underground mines. Huge trucks, shovels and cranes are employed in surface mining to move large quantities of overburden and ore. Processing plants can utilize large crushers, mills, reactors, roasters and other equipment to consolidate the mineral-rich material and extract the desired compounds and metals from the ore.
