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MINE ACCESS Underground Access Accessing underground Ore can be achieved via a decline (ramp), Vertical Shaft or Adit .
Declines are often started from the side of the high wall of an Open Cut mine when the ore body is of a payable grade sufficient to support an underground mining operation but the strip ratio has become too great to support open cast extraction methods. Ore Access Levels are excavated horizontally off the decline or shaft to access the ore body. Stopes are then excavated perpendicular (or near perpendicular) to the level into the ore. DEVELOPMENT MINING VS. PRODUCTION MINING There are two principle categories of mining, development mining and production mining. Development mining is composed of excavation almost entirely in (non-valuable) waste rock in order to gain access to the orebody. There are five steps in development mining: remove previously blasted material (muck out round), drill rock face, load explosives, blast explosives, and support excavation. Production mining is further broken down into two methods, long hole and short hole. Short hole mining is similar to development mining, except that it occurs in ore. There are several different methods of long hole mining. Typically long hole mining requires two excavations within the ore at different elevations below surface, (15m-30m apart). Holes are drilled between the two excavations and loaded with explosives. The holes are blasted and the ore is removed from the bottom excavation. VENTILATION One of the most important aspects of underground hard rock mining is Ventilation . Ventilation is required to clear toxic fumes from blasting and removing exhaust fumes from diesel equipment. In deep hot mines ventilation is also required for cooling the workplace for miners. Ventilation raises are excavated to provide ventilation for the workplaces, and can be modified to be used as escape routes in case of emergency.The main sources of heat in underground hard rock mines are Virgin rock tempreture, Machinery, Auto compression and Fissure water although other small factors contribute like people breathing, inefficiency of machinery and blasting operations. GROUND SUPPORT Some means of support is required in order to maintain the stability of the openings that are excavated. This support comes in two forms, local support and area support. Area Ground Support Area ground support is used to prevent major ground failure. Holes are drilled into the back (ceiling) and walls and a long metal bar (or Rock Bolt ) is installed to hold the ground together. There are several different styles of area ground support.
Local Ground Support Local ground support is used to Prevent smaller rocks from falling from the backs and walls. Not all excavations require local ground support.
STOPE AND RETREAT VS. STOPE AND FILL Stope and Retreat reaches surface at the Ridgeway underground mine.]] Using this method, mining is planned to extract rock from the stopes without filling the voids, this allows the wall rocks to cave in to the extracted stope after all the ore has been removed. The stope is then sealed to prevent access. Stope and Fill Where large bulk ore bodies are to be mined at great depth, or where leaving pillars of ore is uneconomical, the open stope can be filled with backfill, which can be Cement and rock mixture, a cement and Sand mixture or a cement and Tailings mixture. This method is popular as the refilled stopes provide support for the adjacent stopes, allowing total extraction of economic resources. MINING METHODS
ORE REMOVAL In mines which use rubber tired equipment for coarse Ore removal, the ore is removed from the stope (referred to as "mucked out" or "bogged" ) using Center Articulated Vehicles (referred to as boggers or LHD for Load, Haul, Dump ). These pieces of equipment may operate using Diesel or electric engines and resemble a low-profile Front End Loader . The ore is then dumped into a truck to be hauled to surface (in shallower mines). In deeper mines the ore is dumped down an ore pass (a vertical or near vertical excavation) where it falls to a collection level. On the collection level it may receive primary crushing via jaw crusher. The ore is then moved by Conveyor Belts , Trucks or occasionally Trains to the Shaft to be hoisted to surface in buckets or skips and emptied into bins beneath surface headframe for Transport to the mill. In some cases (eg; the Nifty copper mine) the underground primary crusher feeds an inclined conveyor belt which delivers ore via an incline shaft direct to surface. The ore is fed down ore passes, ith mining equipment accessing the ore body via a decline from surface. TRIVIA
HARDROCK MINING TERMS
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