Jim Dowling - Mining Engineer

 

 

UNDERGROUND MINE PLANNING: An introduction to practical mine planning for small and medium sized mines

 

"Underground Mine Planning" by Jim Dowling

 

 

FIGURES

Figure  1.1   Stripping ratio worsening as ore reserve thins
Figure  1.2   Stripping ratio worsening as ore reserve deepens
Figure  1.3   Stripping ratio worsening as pit slope angles decrease
Figure  1.4   Stripping ratio worsening as pit deepens
Figure  2.1   Steep, narrow and continuous ore deposit
Figure  2.2   Steep, narrow and discontinuous ore deposit
Figure  2.3   Stockwork or vein swarm
Figure  2.4   Steep, wide or massive ore reserve
Figure  2.5   Deep, thin and flat reserve
Figure  2.6   Flat reserve – thin or thick
Figure  2.7   Volcanic pipe
Figure  2.8   Example of a non-uniform, arbitrary shaped ore reserve
Figure  3.1   Typical underground layout with a vertical shaft
Figure  3.2   Typical underground layout with an inclined shaft
Figure  3.3   Typical underground layout with a surface decline
Figure  3.4   Typical underground layout with an adit from surface
Figure  3.5  Typical deep underground layout with two vertical shafts and a sub vertical shaft
Figure  3.6   Layout with two vertical shafts and a decline extension
Figure  3.7   Layout with one or more vertical shafts and a surface decline
Figure  3.8   Layout with two surface declines
Figure  3.9   Layout with two shafts and an internal decline
Figure  4.1   Location of a shaft in relation to a dipping orebody
Figure  4.2   Defining the shaft pillar in relation to a flat dipping orebody
Figure  4.3   Shaft pillar in relation to a flat orebody
Figure  4.4   Shaft pillar in relation to a dipping orebody
Figure  4.5   Drift pillar protecting the drift when the reserve is flat dipping
Figure  4.6   Location of shafts – topographic effects
Figure  4.7   Shaft cross sections
Figure  4.8   Sinking to ultimate depth in Yr. 1, total cost, say, £100 million
Figure  4.9   Sinking in two stages, total cost, say, £150 million
Figure  5.1   When close reserves become exhausted, mines have to develop further to access more remote areas
Figure  5.2   When mineral reserves occur in areas of environmental importance, mines may need longer developments to reach them
Figure  5.3   When mines need to increase production, for example to combat a fall in metal price, more development is necessary to access more remote reserves
Figure  5.4.1   Cross section of development for exploration, showing footwall and hangingwall drives, lode drive and diamond drilling (D/D)
Figure  5.4.2   Plan view of development for exploration, showing footwall and hangingwall drives, lode drive and diamond drilling
Figure  5.5   Cross section of a typical single track metal mine development showing track and services
Figure  5.6   Main types of mine development
Figure  5.7   Options of cross section shapes for mine developments
Figure  5.8   Key gradients in mining
Figure  5.9   Ventilation raises to surface are features on long, shallow level developments – perspective view
Figure  5.10   Ventilation raise to level above – perspective view
Figure  5.11   Main level development using two headings – perspective view
Figure  5.12   ‘In Seam’ development using three headings – perspective view
Figure  5.13   Main level development of a steep vein showing crosscuts, lode drives and footwall drives in cross section
Figure  5.14   Main level development of a steep vein showing crosscuts, lode drives and footwall drives in plan view
Figure  5.15   Main level development of a steep vein without using footwall drives in cross section
Figure  5.16   Main level development of a steep vein without using footwall drives in plan view
Figure  5.17   Cross section showing crown and sill pillars protecting the lode drive from stoping activity
Figure  5.18   Plan view and cross sections showing a ‘mini’ footwall drive with drawpoint crosscuts
Figure  5.19   Boxhole raising from a footwall drive
Figure  5.20   Diamond drilling from a footwall drive
Figure  5.21   Longitudinal section showing conventional raising and some techniques to make it safer and easier
Figure  5.22   Main level development of a steep vein with an isometric view illustrating the main level vertical interval
Figure  5.23   Cross section of a flat dipping vein
Figure  5.24   Cross section showing why steep dipping veins require greater vertical intervals between levels
Figure  5.25   Longitudinal section showing the effect of pay shoot plunge angle on vertical level interval in a steeply dipping structure. In this case, the pay shoots are horizontal, plunge angle is 0° so main levels will be closer together to pick-up the lower pay limits
Figure  5.26   Longitudinal section showing the effect of pay shoot plunge angle on vertical level interval in a steeply dipping structure. In this case, the pay shoots are vertical, plunge angle is 90° so main levels can be spaced further apart
Figure  6.1   Typical mine transport system
Figure  6.2   Methods and haul distances for inbye rock handling and main haulage
Figure  6.3   Grizzly installed on an ore pass
Figure  6.4   Plan View of grizzlies for different rock types
Figure  6.5   Grizzly bars splayed outwards in the direction of rock flow to minimize blockages and the correct way to use scrap rail track for the same reason
Figure  6.6   Grizzly bar sections for important locations, the top surface wears but continues to be the narrowest gap to reduce choking
Figure  6.7   Isometric view of a scraper (slusher) winch
Figure  6.8   Isometric view of scraper (slusher) buckets
Figure  6.9   Downhill scraping disproportionately improves power usage and carrying capacity
Figure  6.10   Simple scraping in a narrow heading
Figure  6.11   Scraping a wide heading with multiple rock anchors
Figure  6.12   Scraping a wide heading with two rock anchors and a chain
Figure  6.13   Scraping a wide heading with a three drum scraper
Figure  6.14  Scraping a long heading with two scraper buckets
Figure  6.15   Snapped rope protection for the winch operator – isometric view
Figure  6.16   Removing ore from a stope with boxholes and chutes
Figure  6.17   Removing ore by driving a loader into the stope
Figure  6.18   Removing ore from a stope with drawpoints
Figure  6.19   Drawpoint spacing affects stope height
Figure  6.20   Isometric view of a typical tracked drawpoint as used at small metal mines – approximate dimensions and geometry
Figure  6.21   Isometric view of a trackless drawpoint
Figure  6.22.1   Drawpoint cone variations
Figure  6.22.2   Mechanical feeder option
Figure  6.22.3   Dipping crosscut option
Figure  6.22.4   Isometric view of a wide vein drawpoint
Figure  6.22.5   Drawpoint developed from the lode drive
Figure  6.22.6   Longitudinal section of a scram drift
Figure  6.22.7   Cross section of a scram drift
Figure  6.23   Three likely positions for rock passes in a metal mine
Figure  6.24   Typical features of an ore pass
Figure  6.25   Storage at an underground coal mine
Figure  6.26   ‘Cousin Jack‘ manually operated chute
Figure  6.27   Modern mechanically operated chute
Figure  6.28   More intricate chute for difficult conditions with control chains
Figure  6.29   Plan view of endless rope system
Figure  6.30   Plan view of main and tail
Figure  6.31   Direct rope haulages
Figure  6.32   Manually operated side tipping mine car
Figure  6.33   Mechanically tipped side tipping mine car
Figure  6.34   Mechanically tipped bottom discharge mine car
Figure  6.35   Storage battery locomotive with a removable battery
Figure  6.36   Overhead trolley electric locomotive
Figure  6.37   Diesel locomotive
Figure  6.38   Trackless diesel dump truck
Figure  6.39   Trackless scooptram / LHD (Load Haul Dump)
Figure  6.40   General layout of a conventional underground belt conveyor
Figure  7.1   Hoisting terminology
Figure  7.2   Cylindrical drum winders – isometric views
Figure  7.3   One full winding cycle for a drum winder with one rope and one conveyance starting at the shaft bottom
Figure  7.4   One production cycle for a drum winder with one rope and one conveyance. There is one unit of production, when the loaded conveyance is hoisted up the shaft
Figure  7.5   One full winding cycle for a drum winder with two ropes and two conveyances in balance. There are two units of production per cycle
Figure  7.6   Power demand for cylindrical drum winding using only one drum, one rope and one conveyance. The constant speed power reduces as the conveyance nears the surface because the rope is getting shorter and thereby lighter
Figure  7.7   Power demand for cylindrical drum winding using two drums, ropes and conveyances. The single conveyance graph is shown in the background for comparison. Peak power is lower because the conveyances are balanced. The constant speed power reduces as the conveyance nears the surface because the descending rope starts assisting the winder after halfway
Figure  7.8   Power demand for cylindrical drum winding using two drums, ropes and conveyances and a balance rope. The constant speed power remains constant as the only out of balance load is the mineral
Figure  7.9   The left hand sketch shows two conveyance hoisting from the lower level. Underground loading and surface tipping occur at the same time. The right hand sketch shows one conveyance at the intermediate level and the other hanging in mid-shaft – this one is then raised to surface independently by declutching the other one. Now two sided hoisting can begin from the intermediate level
Figure  7.10   Blair winder
Figure  7.11   Non-cylindrical drum winders
Figure  7.12   Friction hoists – isometric views
Figure  7.13   Examples of shaft cross section layouts
Figure  7.14   Isometric of a two deck cage, doors removed for clarity
Figure  7.15   Popular type of skip, shown in loading position on the left and discharging on the right
Figure  7.16   Section showing the important features of skip hoisting (left) and car and cage hoisting (right)
Figure  7.17   Typical crushing and skip loading station. The right hand drawing in bold shows the usual enlarged shaft side position. The left hand drawing shows a crusher station remote from the shaft, connected to the skip loading bins via a small drive and belt conveyor, if weak ground conditions make this alternative necessary
Figure  7.18   Spillage handling facilities at the bottom of a skip hoisting shaft are essential
Figure  8.1   Stable water table when mining starts
Figure  8.2   When pumping commences underground, in permeable strata, a ‘Dewatered Cone‘ (Cone of Depression, Drawdown Cone) is formed
Figure  8.3   Stable dewatered cone in permeable ground
Figure  8.4   When strata is impermeable mines can be remarkably dry, working successfully undersea, for example
Figure  8.5   Longitudinal section. It is often preferable, when mining under an aquifer, to almost eliminate subsidence by partial extraction thus saving on pumping costs
Figure  8.6   Longitudinal section. Forming a barrier pillar as protection from flooded old workings will reduce pumping cost and minimise the risk of accidental connection, but some reserves are lost
Figure  8.7   Standpipe for cover drilling and grouting
Figure  8.8   Injecting grout via a standpipe
Figure  8.9   Longitudinal section showing a schematic pumping layout
Figure  8.10   Schematic section of a main pump station. Note the settlers are always kept full, the clean water sump levels can vary
Figure  8.11   Schematic plan view of a main pump station. Note there are two settlers, each can feed either of two clean water sumps. This allows all parts of the pump station to be drained, cleaned out and maintained
Figure  8.12   Development approaching a potential inrush hazard under the protection of cover drilling
Figure  8.13   Schematic section showing development approaching flooded old workings. If the two old mines did not close at the same time, any connections between them may be sealed with timber dams
Figure  8.14   The first mine has been successfully drained and holed into. The mining company think they have drained all the water. They have not considered the possibility of a catastrophic inrush
Figure  8.15   The dams fail
Figure  9.1   Isometric of a stope of given size within a steeply dipping vein
Figure  9.2   Mines usually have several, sometimes many, stopes
Figure  9.3   Pattern of uneven production rate over the life of a shrinkage stope
Figure  9.4   Pattern of even production rate over the life of a room and pillar panel
Figure  9.5   Plan view of stoping a steep vein illustrating 10% dilution
Figure  9.6   Plan view of stoping a steep vein illustrating 91% recovery
Figure  9.7   Leaving some strong ore unmined to avoid excessive dilution
Figure  9.8   Payability example of a 1000 m longitudinal section of a steeply dipping vein; payability is 55%
Figure  9.9   High grade areas permit higher grade production in hard times
Figure  9.10   Grades varying horizontally are best for gravity methods, such as shrinkage, producing a continuous blend of high and low grade ore
Figure  9.11   Grades varying vertically are the worst for gravity methods such as shrinkage; stoping produces periods of low grade ore followed by periods of high grade. Methods which mine horizontally, such as sub level stopes, will perform better, producing a constant grade of blended high and low grade ore
Figure  9.12   Plunge angle of a pay shoot within a narrow dipping vein
Figure  9.13   How the shape of an orebody can affect Sublevel Open Stoping operations
Figure  10.1   Plan View of arterial ‘In Seam’ development in a room and pillar mine
Figure  10.2   ‘In Seam’ development using four headings showing ventilation and conveyor belt transport
Figure  10.3   Generalised plan view of a room and pillar mining panel
Figure  10.4   Plan view of a room and pillar mining panel commencing from the main development
Figure  10.5   Plan view of a trackless room and pillar mining panel
Figure  10.6   Plan and section view of a trackless twin boom drill rig
Figure  10.7   Plan and section view of a crawler mounted roadheader loading a shuttle car
Figure  10.8   Isometric view of a pillar in a room and pillar mining panel showing some ‘Rules of Thumb’
Figure  10.9   Plan view of common pillar shapes in room and pillar mining
Figure  10.10   Plan view of steep seam room and pillar mining
Figure  10.11  Seam section of an evaporite deposit mined in three passes by room and pillar
Figure  10.12   Seam section at a silica sandstone mine showing the mining height limited by support and quality requirements
Figure  10.13   Plan view of a  panel with 9 main headings
Figure  10.14   Plan view of a room and pillar panel showing the determination of panel width from no. of main headings
Figure  10.15   Plan view of part of a room and pillar panel used to calculate percentage extraction
Figure  10.16   Plan and cross section of pillar extraction on the retreat in a room and pillar panel
Figure  10.17   Plan view of room and pillar mining using a Continuous Miner (JCM) and a bridge conveyor
Figure  10.18   Cross section view of room and pillar mining using a  Continuous Miner (JCM) and bridge conveyor
Figure  10.19   Stoping in steep vein mines, before the introduction of trackless equipment, could only be started from main levels, from the top downwards or, more often, the bottom up
Figure  10.20   Trackless equipment can mine on gradients up to 1 in 6, creating many more points from which to start stoping, called ‘Sub Levels’
Figure  10.21   Selection of trackless vehicles used underground – the core of ‘trackless mining’
Figure  10.22   Plan view of straight and zig-zag ramps, showing crosscuts to the vein and strike direction. Note that in plan view the straight ramp is not parallel to strike direction unless the vein is vertical
Figure  10.23   Plan view (left) and isometric view (right) of a spiral ramp (by permission of the Wheal Jane Group)
Figure  10.24   Cross sections of straight, zig-zag and spiral ramps in the footwall of a steeply dipping vein showing ramp, crosscuts and sublevels
Figure  10.25   Longitudinal sections showing a straight, zig-zag and spiral ramp with crosscuts to the vein
Figure  10.26   Longitudinal section, cross section and plan view of a zig-zag ramp with level turns
Figure  10.27   Longitudinal and cross section of SLOS showing sublevel development from the ramp to the stop position – in this case a rib pillar
Figure  10.28   Longitudinal section of SLOS showing slot raising and drawpoint development
Figure  10.29   Longitudinal section of SLOS showing longholes and mining direction
Figure  10.30   Longitudinal section options for SLOS stope faces
Figure  10.31   Cross sections showing different sublevel orientations for differing vein conditions
Figure  10.32   Isometric view of longitudinal SLOS in a medium to narrow vein
Figure  10.33   Isometric view of transverse SLOS in a wide vein
Figure  10.34   Plan view of SLOS panel system in a massive deposit
Figure  10.35   Longitudinal section of SLOS showing the formation of rib pillars
Figure  10.36   Longitudinal section of SLOS showing the formation of waste pillars
Figure  10.37   When a straight ramp is used, awkward pillars are left where mining stops when stoping retreats back to the ramp crosscuts
Figure  11.1   Relationship between output rate/mine life and NPV
Figure  11.2   Relationship between cut-off grade and NPV
Figure  11.3   The best and worst strategies to mine an ore reserve in terms of mining cost
Figure  11.4   The best and worst strategies to mine an ore reserve in terms of grade
Figure  11.5   Some aspects of an ore reserve which may affect cash flow and therefore mining sequence, to optimise NPV. This sketch could be a plan view of a flat-dipping seam or, equally, a longitudinal section of a steeply dipping vein
Figure  11.6   Schematic showing how short term planning may prejudice future operations
Figure  11.7   It is often obvious that mining should logically be divided into two or more ‘strategic’ zones
Figure  11.8   More detailed study can then determine the best detailed phasing of each zone to maximise NPV
Figure  11.9   Ideal extraction sequence for a simple ore reserve, flat-dipping,  with uniform grade and cost structures – perspective view
Figure  11.10   Ideal extraction sequence for a simple ore reserve, steeply  dipping, with uniform grade and cost structures – perspective view
Figure  11.11   Perspective view of a reserve with three distinct zones defined by number of years of production and annual cash flow generated
Figure  11.12   Perspective view of the reserve showing the extraction sequence which results in the highest NPV of £4.99 m

 

 

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