Underground mining method; Shrinkage stoping, Ascending method of mining, Advantages and Disadvantages, Vertical Crater Retreat stoping, Introduction, Application, Developmental sequence of stopes, Production, How Cratering Works

1. Hassan Z. Harraz
hharraz2006@yahoo.com
2014- 2015
This material is intended for use in lectures, presentations and as
handouts to students, and is provided in Power point format so as to
allow customization for the individual needs of course instructors.
Permission of the author and publisher is required for any other usage.
Please see hharraz2006@yahoo.com for contact details.
Topic 5: Underground Mining Methods
 Shrinkage stoping
 Vertical Crater Retreat stoping
Prof. Dr. H.Z. Harraz Presentation
Shrinkage & VCR stoping

2. Outline of Topic 5:
 Shrinkage stoping
 Ascending method of mining
 Advantages and Disadvantages
 Vertical Crater Retreat stoping
 Introduction
 Application
 Developmental sequence of stopes
 Production
 How Cratering Works
Prof. Dr. H.Z. Harraz Presentation
Shrinkage & VCR stoping
2
We will explore all of the above in Topic 5.

3. Method stopes
configuration in which the
ore is removed at horizontal
slices from bottom to top.
Of the ore is left detonated
accumulated until the stope
is completely mined. The
fragmented ore is then
totally removed.
Shrinkage stoping
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4. Shrinkage
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5. Shrinkage
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6. Ascending method of mining
 The ore is dismantled temporarily used as filler to support the walls
of the stope and working platform for the miners.
 Overall the drilling is done on the ore disassembled using hand
drills (jacklegs).
 The ore dismantled remains within the block until it reaches its
upper limit. Because of blistering, 30-40% should be removed by
kicking or drawpoints to make room for the next disassemble.
 The space between the ceiling and ore dismantled dismantling is
1.8m to 2.2 m.
 The Shrinkage is typically used in vertical or subvertical bodies
with a thickness between 2 and 20 m. The bodies of higher power,
the blocks can be arranged transversely.
 The entries are made for miners from side to block chimneys.
 Depending on the mechanical properties of the rock, the distance
between levels ranging from 30 to 90 m 30-100 m between side
pillars. The drawpoints are arranged every 7-10 m.
Prof. Dr. H.Z. Harraz Presentation
Shrinkage stoping
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7. Advantages:
 Allows plowing narrow bodies.
 Low cost of development
 Simple equipment for drilling and loading.
Disadvantages:
 Ore disassembled remains the filler.
 The control of ore grade can be difficult.
 It is a method for high production.
 Security problems of staff working within the stope.
Prof. Dr. H.Z. Harraz Presentation
Shrinkage stoping
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8. 6) Vertical Crater Retreat (VCR) stoping
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9. VCR - Vertical Crater Retreat

10.  Vertical Crater Retreat (VCR) or Vertical Retreat Stoping:
configuration method in stopes where drilling large diameter is used to
detonate horizontal slices of ore, leading them to the base of the block
being mined. The method progresses vertically, as successive slices
of ore are detonated.
 Vertical Crater Retreat (VCR) uses parallel, vertical, descending and
spherical concentrated loads to fragment the ore (disassemble by
cratering) drilling;
 The advance of the stope is disassemble from the bottom up;
 The ore is recovered at the bottom of the block;
 Part of the mineral remains in walk through serving as stope support.;
Introduction
Prof. Dr. H.Z. Harraz Presentation
VCR stoping
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Application
 Sharp dip in bodies (same conditions as those
considered for Sublevel Stoping method).
 Requires less stability of the host rock;
 Stopes may receive the backfill after extraction.

11. Developmental sequence of stopes...
 Galleries transport are dug along the ore body
at the level of drawpoints;
 Arrangement drawpoints is created in the
lower portion of the stope;
 Stope is highlighted (undercut);
 Top Access (overcut) is excavated to allow
drilling and loading of explosives.
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Prof. Dr. H.Z. Harraz Presentation
VCR stoping

12. Production
 Drilling from the top level.
 The detonation dismantle slices upward from the bottom of the block.
 It is enough removed to make room for the next disassemble ore.
 Geometry of the explosive charge:
L: D ≤ 6: 1 (length: diameter)
 Drilling is large diameter (DTH or top hammer - 100 to 165mm) and preferably vertical;
 The method enables a reduction in development compared to SLS
 do not need to slot the initial stope
 Longer drilling
 The charge ratio fragmentation of ore and are larger than the blasthole stoping
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 High production rates; good recovery.
 Appropriate mechanization.
 Safe method with good ventilation.
Advantages
Prof. Dr. H.Z. Harraz Presentation
VCR stoping

13. The technique of vertical cratering (VCR) might be used to:
 Create initial slot in SLS;
 Fabricate raises;
 recover pillars
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Prof. Dr. H.Z. Harraz Presentation
VCR stoping

14. VCR - How It Works
 Uses cratering theory:
 Developed by Livingston 1962
 Charges 1 to 6 x hole diameter
 Placed at optimum distance from surface
 Loaded from top of hole
 Gravity moves rock down:
 Away from hole
 Providing a new face
 Holes drilled form development
heading(s) down to development
 Large diameter
 Accurate
 Blasting progresses upwards in layers
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Prof. Dr. H.Z. Harraz Presentation
VCR stoping

15. How Cratering Works
N = E W1/3
Where:
N is the critical distance
(maximum for cratering);
E is a constant for a given
explosive-rock combination;
W is the weight of the explosive
charge.
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Prof. Dr. H.Z. Harraz Presentation
VCR stoping

16. Best Efficiency at 0.58 N.
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Prof. Dr. H.Z. Harraz Presentation
VCR stoping

17. Loading
• Lower plug and tie off
• Drop rock to seal plug
• Sand stemming
• Load explosive
• Sand stemming above
 Drops out of hole
after blast
• Alternate use water
above
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Prof. Dr. H.Z. Harraz Presentation
VCR stoping

18. Luosavaara Mine Example
165 mm Holes 100 m depth max deviation 1m.
ANFO 3.3 x 4 m staggered pattern
Max size required 0.75 m ; K50 12-14 cm
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Prof. Dr. H.Z. Harraz Presentation
VCR stoping

19. Luossavaara Tests
19Prof. Dr. H.Z. Harraz Presentation
VCR stoping