A Dragline is a
special machine used for stripping the overburden from the coal. These
machines stand more than 21 metres from the ground to the top and the steel
boom measures more than 60 metres in length. The overall weight of a dragline may be as
much as 2,030 metric tonnes, or equivalent to the weight of 300 elephants. In Saskatchewan,
the open pit method has been used to mine several metallic minerals.
Open cuts are
worked progressively deeper until the economic limit is reached, or the material
of value runs out. They are wider at the upper rim than at the pit bottom, to
ensure safety, and to provide a gradual spiral roadway for trucks and other
equipment. Vertical holes are repeatedly drilled 21 metres or more in depth
along the levels, which are called benches. After blasting, the broken ore is
loaded onto trucks and hauled up the twisting access road for treatment.