After mining, the support e. The cavity closure is either partial, for shallow mining, or complete, for deep level mining. Harraz Presentation Mining Methods 8 9. Harraz Presentation Mining Methods 9 Harraz Presentation Mining Methods 10 Harraz Presentation Mining Methods 11 From the 19th century onward, various other explosives, power-tools, and machines came into use.
As mining progresses the stope is often backfilled with tailings, or when needed for strength, a mixture of tailings and cement. In old mines, stopes frequently collapse at a later time, leaving craters at the surface. They are an unexpected danger when records of underground mining have been lost with the passage of time.
These include the incline of the deposit whether it is flat, tilted or vertical , the width of the deposit, the grade of the ore, the hardness and strength of the surrounding rock, and the cost of materials for supports i. Harraz Presentation Mining Methods 12 Figure shows stoping a narrow vein mining orebodies may be only half a meter wide Prof. Harraz Presentation Mining Methods 13 Stoping then takes place from these levels.
Harraz Presentation Mining Methods 14 Harraz Presentation Mining Methods 15 This allows for greater recovery as less ore is left behind in pillars. Harraz Presentation Mining Methods 16 Figure from Hartman and Mutmansky, Note the control of ventilation, i. Harraz Presentation Mining Methods 18 Figure shows Room and Pillar is designed for mining flat, bedded deposits of limited thickness. Figures from Hartman and Mutmansky, Front benching Vertical benching Benching of thicker parts of orebody Prof.
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Harraz Presentation Mining Methods 19 Harraz Presentation Mining Methods 20 Figure showing cut and fill mining method. Remove ore in horizontal slices, starting from a bottom undercut and advancing upward. As each horizontal slice is taken, the voids Opens are filled with a variety of fill types to support the walls. Harraz Presentation Mining Methods 21 Note: Drift and Fill is similar to cut and fill, except it is used in ore zones which are wider than the method of drifting will allow to be mined.
In this case the first drift is developed in the ore, and is backfilled using consolidated fill. The second drift is driven adjacent to the first drift.
This carries on until the ore zone is mined out to its full width, at which time the second cut is started atop of the first cut. Harraz Presentation Mining Methods 22 Harraz Presentation Mining Methods 23 Harraz Presentation Mining Methods 24 Figure 9: shows Square-set stoping Prof.
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Harraz Presentation Mining Methods 25 It has largely been replaced by mechanized methods but is still used in many small mines around the world. A portion of the broken ore is allowed to accumulate in the stope to provide a working plat form for the miners and is there after withdrawn from the stope through chutes. Harraz Presentation Mining Methods 26 In this manner, the stope is mined horizontally from one end to the other. Harraz Presentation Mining Methods 27 For this reason the blasted dirt is designed to fall into a supported drawpoint or removed with Tele Remote Control LHD.
Harraz Presentation Mining Methods 28 For the blastholes to successfully extract the ore material they must be able to fire into a void in front. This method works well in larger stopes however requires both access to top and bottom of stoping block, raise bore's work most effectively between 45o and 90o. Can be done as downhole and fired in multiple lifts 15m rise in 3 lifts of 5m to minimise chance of blast failing or as uphole in one single firing. This method works well for shorter raises between 45o - 90o, however is prone to freezing and remedial drilling is possibly required to extract slot to full height.
This method has the advantage of giving geological and geotechnical teams further analysis of the stoping block prior to mining. Harraz Presentation Mining Methods 29 Stage 1 Stage 2 Prof. Harraz Presentation Mining Methods 30 Harraz Presentation Mining Methods 31 It recovers the mineral in slices along a straight line that are repeated to recover materials over a larger area.
Since the mineralization is in the form of a sheet that extends over a wide area, the drifts can usually be arranged in a schematic network pattern. The haulage drifts are prepared in the seam itself. The distance between two adjacent haulage drifts determines the length of the longwall face. Top Gate Bottom Gate Face Longwall mining method includes drivage of two long roadways in coal and joining them at the end by a perpendicular drivage forming a face. Longwall General Layout Prof.
Harraz Presentation Mining Methods 32 Harraz Presentation Mining Methods 33 Figure shows "Slim-size" machines including drill rigs, jumbos, and 2 m3 bucket LHDs, are available for working in drifts as narrow as 2 m. Harraz Presentation Mining Methods 34 Longwall Mining Prof. Harraz Presentation Mining Methods 35 In coal mining, a mechanized cutting device is run along the length of the coal face. Temporary support near the working face: often hydraulic props. Harraz Presentation Mining Methods 36 Harraz Presentation Mining Methods 37 Longwall Mining Machine It's designed to let the roof fall behind it, and mines out big rooms in which the roof almost immediately collapses, leaving only a small entryway and the metal barrier that protects the longwall unit.
Harraz Presentation Mining Methods 38 Figure shows another continuous miner in an underground coal mine. Fig 12a: Passageway Figure 12b: A typical panel is m long by m wide Mechanized cutting machineon a longwall coal-mining face.
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Harraz Presentation Mining Methods 40 Harraz Presentation Mining Methods 41 Stope face with temporary support Deep level gold mining, South Africa Prof. Harraz Presentation Mining Methods 42 Harraz Presentation Mining Methods 43 Ultimately, the ground surface on top of the orebody subsides. Caving i. Subsidence of the surface normally occurs afterward. Harraz Presentation Mining Methods 44 After math of a rockburst in a deep-level tunnel showing complete tunnel closure. Rockbursts underground, causing injury and death in deep level mines.
Harraz Presentation Mining Methods 45 The bottom is V-shaped to funnel the blasted material into the draw-points. The ore in the stope is blasted, collected in the draw-points, and hauled away. Continued mining results in subsidence of the surface, causing sink holes to appear. Ultimately, the ground surface on top of the orebody subsides Fig. Harraz Presentation Mining Methods 46 Harraz Presentation Mining Methods 47 Figure shows Continued mining results in subsidence of the surface, causing sink holes to appear.
Figure shows sublevel caving is used to mine large orebodies with steep dip and continuation at depth. Harraz Presentation Mining Methods 48 The method has application, for example in sulfide deposits and underground kimberlite diamond mining. However, some mines start as block cave operations e. Rio Tinto is considering a deep at the Resolution deposit to the east of Phoenix. Harraz Presentation Mining Methods 49 The drawbells serve as a place for caving rock to fall into. As ore is removed from the drawbells the orebody caves in providing a steady stream of ore. Hydraulic fracturing has been applied to preconditioning strong roof rock over coal longwall panels, and to inducing caving in both coal and hard rock mines.
Surface subsidence can be a problem….???.
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Harraz Presentation Mining Methods 50 Figure shows application of the Block caving to large, deep, low- grade deposits Figure shows hundreds of draw points to take broken ore in a large block cave operation www. Harraz Presentation Mining Methods 51 Caving rock falls into the drawbells. As ore is continuously removed from the drawbells, the orebody continues to cave spontaneously, providing a steady stream of ore. If spontaneous caving stops, and removal of ore from the drawbells continues, a large void may form, resulting in the potential for a sudden and massive collapse and a potentially catastrophic windblast throughout the mine e.
Harraz Presentation Mining Methods 52 Block-cave mining: Mud-rushes —an under-reported hazard Mud-rushes are sudden inflows of mud from ore drawpoints or other underground openings , in block-cave mines that are open to the surface. Considerable violence, in the form of an airblast, is often associated with mud-rushes. Mud-rushes are under-reported hazardous occurrences that have occurred frequently in mines in South Africa, as well as in Chile and Western Australia, and have caused fatalities Butcher et al.
Mud is produced by the breakdown of rock in the near-surface muckpile in the presence of rainwater. Kimberlite rock on diamond mines is particularly susceptible to weathering by rainwater. Harraz Presentation Mining Methods 53 Figure shows Effect of Mineral extraction upon displacement of country rock and surface as well as rock displacement in mining.
Techniques in Underground Mining : Selections for Underground Mining Methods Handbook
The rock displacement zone include:- "a caving zone" within which the displacement is accompanied by the fault and destruction of layers and the separation of lumps and blocks from the solid; "a cracking zone" which is an area of rock discontinuity and cracks; "a smooth-displacement zone" wherein rock features plastics deformation without discontinuities. The earth's surface area which experienced displacement is called a "trough". Effect of Mineral extraction upon displacement of country rock and surface This phenomenon is called "Displacement of rock".
Displacement causes smooth subsidence of the earth's surface without ruptures, or abrupt subsidence with considerable movements, caving and collapses. Workings and voids formed after extraction of mineral gets filled with time by the caving rock so that the rock over the deposit may deformed and subside. Harraz Presentation Mining Methods 54 Stope and Retreat vs.