Opencast mining, also called "opencut mining," or "open pit mining," is based on the principle of
continuous conveying, employing large earth-moving machinery such as the
Big Muskie walking dragline to mine the
coal,
iron ore or
phosphates at the surface rather than underground. Opencast mining may include
multi-seam mining, where two or more coal seams are excavated. The advantage of opencast mining, as opposed to underground, mining is that it is generally easier, cheaper, safer and quicker to bring
onstream (into production).
Opencast mining of coal is carried out as these giant machines; including the bucket-
wheel excavator,
stripping shovel,
steam shovel, slusher and walking dragline; strip away the
overburden until the
coal seam is reached. This form of mining often employs the use of
mud caps, or other explosive devices to periodically break up the deposit of ore using this conventional
drill-and-blast method. The drill-and-blast method may be
single-row blasting involving driling, charging and firing a single row of holes along the opencast face; or
multiple-row blasting which involves multiple blasts often in a square pattern along the opencast face.
The overburden can then be removed in trucks or by railway to the
processing mill. The coal once extracted is then transported to a area to be sorted, broken and cleaned using
coal benefication techniques. Crushing usually involves the use of a
push feeder,
jaw crusher,
rotary breaker, discard bins and conveyors. Once processed the ore is graded for sale.
During the opencast mining process terraces, or benches are formed along the earth often leaving ugly gaping holes, often the overburden is backfilled to mined out areas on a continuous basis. Once the coal runs out the area is either abandoned, used for a landfill, or returned to its orignal state through
reclaimation.
A panoramic view of an opencast mine can be seen at:
http://zbyszek.strefa.pl/panoramy/kopalnia/me.html