Topic 6: Underground Mining Methods Cut-and-Fill ...

Topic 6: Underground Mining Methods  Cut-and-Fill stoping

Hassan Z. Harraz [email protected] 2014- 2015

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Outline of Topic 6:      

Introduction Application of Cut-and-Fill (C & F) stoping The activity cycle of the (C & F) method Stages of the production cycle of the C & F method Sequences of extracting ore bodies Filling in C & F Method  About filling of stopes  Functions of filler  Types of fillers  Advantages and disadvantages of the C & F method

We will explore all of the above in Topic 6. Prof. Dr. H.Z. Harraz Presentation Cut & Fill stoping

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Introduction Method in which ore is removed at horizontal slices generally upwards. The ore is drilled, blown up and removed from the stope. The resulting empty after the ore to be removed, is filled with a filler ("backfill"). The filler serves as a support for the sides of the stope, and as a platform for the devices when the next slice is mined. It is a recommended method, for example, where iron ore and / or waste are slightly relevant, which restricts the size of underground excavations and allows little time between the removal and the deposition of the mineral filler.

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Cut & Fill stoping

Introduction  It is one of the more popular methods used for vein deposits and has recently grown in use.  It is an expensive but selective mining method, with low ore loss and dilution.[3] (i.e., allows selective mining and avoid mining of waste or low grade ore).  Is relatively expensive and therefore is done only in high grade mineralization (Because the method involves moving fill material as well as a significant amount of drilling and blasting).  It is a method of shorthole mining used in steeply dipping or It is preferred for orebodies with irregular ore zones and scattered mineralization.  It requires working at face (which is less safe than longhole stoping).  It is used: in mining steeply dipping orebodies in stable rock masses (primarily in steeply dipping metal deposits),  in strata with good to moderate stability, and comparatively high grade mineralization.  either fill option may be consolidated with concrete, or left unconsolidated.  Generally uses no cement  Bottom up mining method: Remove ore in horizontal slices, starting from a bottom undercut and advancing upward.  Moderate production rates.  Good resource usage.  Not stress friendly.  Moderate ground support  Ore is drilled, blasted and removed from stope.  The ore is mined in slices: As each horizontal or slightly inclined slice is taken, the voids (Opens) are backfilled with a variety of fill types to support the walls (i.e., the fill can be rock waste, tailings, cemented tailings, or other suitable materials). {(note: The fill serves both to support the stope walls and provide a working platform for equipment when the next slice is mined)}.

Introduction Ore is drilled, blasted and removed from stope

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. (i.e., the fill can be rock waste, tailings, cemented tailings, or other suitable materials).

Figure showing cut and fill mining method.

Introduction  Because the method involves moving fill material as well as a significant amount of drilling and blasting, it is relatively expensive and therefore is done only in high grade mineralization where there is a need to be selective and avoid mining of waste or low grade ore.  It is practiced both in the overhand (upward) and in the underhand (downward) directions. i) Overhand (upward) cut and fill o is applied to ore lies underneath the working area and the roof is backfill. o involves a work area of cemented backfill while mining ore from the roof. ii) Underhand (Downward) cut and fill ore o is applied to ore lies beneath the working area and the roof is cemented backfill. o ore overlies the working area and the machines work on backfill.

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.

Application of Cut-and-Fill (C & F) stoping The C & F method is required when:  Ore Zones are irregular in shape and orientation.  Ore Is high grade and dilution control is critical.  The Need contacts between ore and waste are structurally critical but not readily visible.  The Waste rock is weak.  Ore Zones are large, but Their rock quality is weak.  Localized Underground stability is required.  Surface Disturbance must be minimized.  The Value of the ore makes recovery of economically viable support pillars.  The Reduction of surface waste storage is important.  The Need exists to advance the working platform for the upward mining of the ore body.

Prof. Dr. H.Z. Harraz Presentation Cut & Fill stoping

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The C & F method In mining C & F generally upward (overhand) advances; there is a least common variant C & F underhand - where the feed is from the top down.

C & F advancing bottom up 


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overhand C & F


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The activity cycle of the C & F method involves the following steps: a) drill-blast of a horizontal slice of ore, typically with three or four feet thick, removed the roof of the stope; b) loading and transport of ore, mechanically removed from the stope for orepass, and then to a lower horizon of transportation; c) removal of loose fragments ("cuttlefish") by the detonation and placement support / reinforcement ceiling; d) filling the floor of the stope (backfilling) with a layer of composite material varied and equal in thickness ore disassembled ceiling.


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Stages of the production cycle of the C & F method :


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The workers perform all the activities of the production cycle in the newly opened roof of stope. So, for the method to be successful, one must control the behavior of the rock on the outskirts of the stope. This is done in several ways: by controlling the dismantling of the roof, using reinforcement / support for openings and using the stope backfill.

Use of roof bolts in C & F


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Control ceiling by cable bolts :

Sequence of use :


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C & F method is versatile (there are different configurations of extraction) applied to bodies of different geometries (shafts, inclined tabular or massive deposits) can be divided into separated by vertical pillars and horizontal blocks.

Horizontal Pillar (i.e, Floor pillar) separating stopes 


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Sequences of extracting ore bodies ... View topic in 3.4.2 : Underground Mining Methods: engineering fundamentals

and international case studies. W.Hustrulid, R.Bullock, SME, 2001.


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C & F with overhand stopes separated by vertical pillars, in this case made with backfill:


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C & F overhand with ramp and stope access orepass located in the footwall:


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The method applies to deposits with dipping 35o to 90o, in deep or shallow bodies. Stopes may have a width ranging from 4 to 40 m. The filler allows to work in the presence of enclosing a low resistance. The ore should, however, have moderate resistance to high.

Thick body being mined in plan and in section 


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Different geometries of openings in thick ore bodies (seen in section).


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Narrow body being mined: plan view (left) And section (right).

Fig 1


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The C & F is a laborious method, requiring high value for the in situ ore. Some dilution is expected, which occurs when the backfill is loaded with ore in the stope (usually done by loading LHD's). Moreover, the method provides selectivity and flexibility, allowing good control of ore contents and disposal in the stope, sterile material. Also allows to follow irregular bodies during mining, due to the high degree of selectivity of the drill-blast sequence There are several benefits from an environmental standpoint, using the backfill. The integrity of the host rocks allows less affect the hydrogeology of the mined area. The possibility of subsidence at the surface is quite limited. Reduce the tailings storage areas on the surface because they can be taken back to the stopes, as backfill


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Variant of the C & F: Avoca method


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Filling in C & F Method About filling of stopes:  filling is done during the production cycle (and not after complete evacuation of the stope, as in SLS);  Hydraulic filling (water and sand particle size = hydraulic sand-fill) is the most common, containing 60 to 70% solids and requiring deposition techniques and special drain;  the filling with hydraulic sand-fill, the distribution for the stopes is done by piping;  The stope is filled almost to the ceiling height;  backfill needs to be the strongest, is added to the cement mixture;  When the water is drained, a good base for moving mining equipment while it is formed in the upper slice stope;  the backfill, traffic person is prevented for a few hours and the vehicle for several days.


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Filler Models


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Filling Functions of filler:  -preserve access to the stope;  avoid dilution of ore;  avoid subsidence on the surface;  serve as a working platform for workers in mining the next horizontal slice; The time of placing the backfill is critical because it must take the original load was exerted on the ore.


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Types of fillers

 Additional information on "backfill": read articles  Underground Mining Methods: engineering fundamentals and international case studies. W.Hustrulid, R.Bullock, SME, 2001, cap. 69. Prof. Dr. H.Z. Harraz Presentation Cut & Fill stoping

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Types of fillers 1) Hydraulic fill (also called slurry or sand fill)

2) Paste fill

3) Rock Fill Prof. Dr. H.Z. Harraz Presentation Cut & Fill stoping

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Advantages of the method  It is a versatile method and can be adapted to the ore bodies from any geometrical shape  Investments are moderated to implement the method  minimizes subsidence  High recovery and low dilution (selective method)  Waste can be taken to the basement, avoiding surface contamination

Disadvantages  Due to the high cost of mining, is only applicable in ores of high value;  Requires hand labour intensive and more specialized;  The activity of filling complicates the production cycle, causing reduction in production;  There are risks of instability in mass if the backfill is not properly sized and applied. Prof. Dr. H.Z. Harraz Presentation Cut & Fill stoping

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