Деловой английский язык. Енютина А.А. - 26 стр.

                                       26


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                   для студентов специальности 130403
                 "Открытые горные работы" (№№ 18–22)

                                    TEST 18

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                         Open-cast (open pit) mining

      Open-cast mining is the process of surface mining in which large quantities
of mineral-bearing rock are scooped out to produce, in effect, a very large hole,
with terraced sides. The largest, in Bingham Canyon, USA, is 1.5x1.6 miles x
0.5 mile deep.
      Two basic types of open-cast mining are quarrying, in which the rock is cut
unto large blocks and usually transported away from the site in this form, and
metal mining, where the large quantities of rock are ground to the powder on
site and the metal-bearing minerals are removed. In this way, large quantities of
poor ores may be processed in order to obtain relatively small amounts of the
valuable minerals. This method also leaves a very large amount of useless
ground-up rock.
      Open-cast mining is used for the recovery of deposits, which are situated
close to the earth surface and have the gentle dipping. It is generally considered
that open pit mining is more advantageous than underground mining in:
      • (higher) productivity of labor;
      • (greater) production;
      • (lower) cost of mining;
      • (better) recovery;
      • (better) grade control;
      • (better) flexibility of operation;
      • (better) safety;
      • (better) working environment.
      When mineralization in an open pit mine extends to a greater depth, the
rapidly increasing amount of overburden imposes economic limits beyond
which mining must be abandoned. Under such circumstance, the mining op-
eration is usually converted from open pit to underground mining.