Rabu, 24 Desember 2008
Sublevel stoping is a mining method in which ore is blasted from different levels of elevation but is removed from one level at the bottom of the mine. Before mining begins, an ore pass is usually drilled from a lower to a higher elevation. Jumbos selectively drill holes into the roof of the drift and fill them with explosives. When the roof is blasted, loose rocks, or muck, fall through the drilled ore pass. A scoop tram or Load Haul Dump (LHD) vehicle transports the muck to another ore pass where it falls to a crusher before being elevated (raised) to the surface. As the muck is taken out, more drilling of the now higher roof continues. The roof is blasted till it is so high that it cannot be reached by a jumbo. Then a jumbo working in a higher elevation drift is used to intersect the stope. After blasting, the ore falls down to the lower drift where scoop trams or LHDs can drive in to load the muck and dump it at an ore pass. Drilling and blasting continues until the stope is completely excavated. Once the stope is completely hollowed out, it is backfilled from the bottom, up. The backfill material used can be a mixture of sand and rocks, waste rock with cement, or dewatered mill tailings (rejected low grade ore from processing, usually fine and sandy). The backfill material must have a lot of strength to support the roof of the empty stope.
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