2 - classification
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Classification of
UndergroundMining
Methods
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Over the years three factors have contributed to the evolution of
mining methods:
-Ground support, timber, fill, bolts, cables, and a combination of
these
-Developments in drilling and blasting techniques
-Mechanization or the advent of new equipment
CLASSIFICATION OF MINING METHODS
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Classification ofUnderground
Mining Methods
Slides 8-9 - Source:
Morrison R.G.K. (1976)A Philosophy of Ground Control. Department of Mining and
Metallurgy Engineering, McGill University.
Morrison Method
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Ground ControlGroup A Rigid Pillar Support
Group B Controlled Subsidence & Sequential LongwallGroup C - Caving
Ore WidthNarrow (< 3m)
Narrow to Wide (1.5 30m)Wide (>30 m)
Strain EnergyGroup A strain energy under controlGroup B increased strain energy and rockburst risk
Group C ground failure is a requirement
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Group A Rigid Pillar Methods
Pillar supported stopes, usually low costs methods, have their
widest applications with the stronger rocks at shallow depth
where strength-stress ratios provide adequate factors of safety.
Group B Longwall Methods
The use of longwall accepts the incompetency of rocks under
prevailing stress conditions, but takes advantage of the fact that
all rocks at the point of incipient failure and permit safe
operating conditions for a limited time at the working face.
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Group C Caving Methods
Caving is deliberately induced. If an unsupported undercut of
sufficient height to permit caving rather than subsidence is
extended beyond certain limiting dimensions which depend onthe stress pattern and the rock type, caving, predictable or
otherwise, can be expected to follow. The progress of caving
will depend on drawing off (shrinking) caved rock to eliminate
support above the undercut and when necessary extending the
undercut.
Caving is predictable over a specified undercut and results in
caved material which can be passed economically through
drawpoints below the undercut.
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Classification ofUnderground
Mining Methods
Euler De Souza MethodPlease review paper De Souza, E. and Archibald, J.F. (1987)
Rock Mass Classif ication as an Influence in Mine Design
Operations, Mining Science and Technology, 6, pp. 1-8.
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Stoping
Method
Block
Caving
Cut andFill
Sub level
Caving
Shrinkag e
Room and
Pillar
Sub level
Open
Orebod y Shape Orebody
Thic kness (m)
Orebody
Plunge
massive tabular non
regular10 30 100 20 - 50
0 0
Orebody Geometry vs. Mining Method Selection Chart
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Rock Mass Classification vs. Mining Method Requirements
Roc k Class
Q Index
Block
Caving
Cut and
Fill
Sub level
Caving
Shrinkag e
Room and
Pillar
Sub level
Open
.001
P1
P1 - - -- -- -
- -
Exc ep tionally Poor Fa ir Good
.01
P2
P2 Extrem ely Poor
Hang ing Wall
Very Good
.1
P3
P3 Very Poor
Orebody
Extrem ely Good
1
P4
P4 Poor
Footwall
Exc ep tionally Good
4
F
F
10
G1
G1
40
G2
G2
100
G3
G3
1000
G4
G4
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Unit Mining Cost Comparison for Selected Mining Methods
Mining
Method
Block
Caving
Sublevel
Caving
Sublevel
Open
Room and
Pillar
Shrinkage
Cut and
Fill
Low
Unit Mining Costs
Med ium High
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Case Example
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Case Example
Step 1. Suitable Methods Based on Orebody Geometry
sublevel openCut and fill
Shrinkage
Sublevel caving
Step 2. Suitable Methods Based on Rock Mass Classification
200-350 m - Q = 40-300 - sublevel stoping
350-400 m - Q = 10-100 - shrinkage stoping
Below 400 m - Q
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Underground Mining Methods
Selective Mining Methods
hrinkage Stopingut and Fill Stoping
Under-cut and FillRoom and Pillar StopingResuing
quare Set Stoping
tull Stoping
Bulk Mining Methods
Longhole Stoping
Sub-Level Open Stopingertical Crater Retreat StopingSub-Level CavingBlock CavingLongwall
PanelSolution Mining
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1. Stull stoping
Stull stopingis a method that uses systematic
or random timbering (stulls) placed between the
foot and hanging wall of the vein. This method
requires that the hanging wall and often the footwallbe of competent rock as the stulls provide the only
artificial support. This type of stope has been used
up to a depth of 1,000 m (3,500 ft) and at intervals
up to 3.5 m (12 feet) wide.
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2. Room & PillarRoom and pillar mining is commonly done in flat or gently dipping
bedded ores. Pillars are left in place in a regular pattern while the
rooms aremined out. In many room and pillar mines, the pillars are taken
out, starting at the farthest point from the mine haulage exit,
retreating, and letting the roof come down upon the floor. Room
and pillar methods are well adapted to mechanization, and are
used in deposits such as coal, potash, phosphate, salt, oil, shale,
and bedded uranium ores.
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3. Shrinkage StopingShrinkage stoping is a flexible mining method for narrow orebodies that need
no backfill during stoping. Successive horizontal slices of ore, usually about 3
m (10 feet) high, are taken along the length of a stope, in a manner similar tocut-and-fill. The ore is removed from the stope through drawpoints at the
bottom horizon spaced about every 7.5 meters (25 feet) along strike. Just
enough ore is left in the place to provide a floor from which to work when
taking the next cut.
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4. Sub-Level StopingSublevel stoping is a method in which ore is blasted from different levels of
elevation but is removed from one level at the bottom of the mine. Before
mining begins, an ore pass is driven from a lower to a higher elevation.Jumbos drill holes into the back of the sublevel. When the back is blasted, ore
falls through the ore pass. As the ore is taken
out, more drilling of the now higher back
continues. The back is lasted till it is so high
that it cannot be reached by a jumbo. Then ajumbo working in a higher elevation sublevel is
used to intersect the stope. After blasting, the
ore falls down to the lower sublevel where
scoop trams can drive in to load the ore and
dump it at an ore pass. Drilling and blasting
continues until the stope is completely
excavated. Once the stope is mined out, it is
backfilled from the bottom, up.
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Longhole Stoping
This stoping technique uti lizes both vertical and angled dri ll
holes drilled downward from the overcut drift to elevationsslightly above the undercut drift. Arrays of holes are drilled
across the full width of each stope such that they will create
a vertical slice of ore when loaded and blasted. For
production, a side slot running the full stope width, must
first be drilled and blasted (often by slot raising) to create a
void into which blasted ore can initially expand and drop.
Slices of ore, extending the full height and width of the
stope, are blasted and caused to drop into the drawpoints.
With progressive blasting, successive vertical slices of orewil l be broken and the ore wil l be mined proceeding from
one end of the stope to the other.
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Avoca
Avoca is a longhole retreat method which uses fill walls to
provide support to the adjacent longhole stope. Extraction isfrom bottom up. The method allows for ground control using a
combination of cable bolts and backfill, whilst allowing the
extraction of high tonnages in comparison to conventional cut-
and fill systems.
Drilling is done from the overcut. A remote controlled scoop is
used to muck ore from the stope. Backfill is dumped into the
stope from the overcut. When the level is completed, the next
level up is commenced working off the fill from the previous
level.
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Alimak Raise Mining
Alimak raise mining is a longhole method primarily intended for
steeply inclined narrow vein orebodies. The main access is
gained by driving a raise up dio along the center of the stope
hanging-wall. Horizontal production drilling is then achieved
from the raise climber. The method results in very low dilution,
has low development costs and enables quick and direct oreproduction as the development work is mainly carried out in ore.
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Vertical Crater Retreat
This stoping technique uti lizes vertical dri ll holes which aredrilled from overcut drifts to elevations slightly above the
undercut horizon at the bottom of each stope. Parallel
arrays of vertical holes are drilled across the full width of
the stope. When production blasting occurs, charges at the
bottom of all holes, across the full width and length of thestope, are simultaneously detonated. Blasted horizontal
slices of ore are dropped into drawpoint points. With
progressive blasting, successive horizontal slices of ore
wil l be broken as stope ore is mined upwards. VCRproduction thus proceeds from the bottom of the stope
upwards.
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5. Fil ling & Pillars
6. Unit Supports & Pillars
7. Pillar Recovery Fill8. Pillar Recovery Unit Supports
C t d Fill
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Cut and FillThis method consists of blasting the ore by successive horizontal
lift and extracting from the stope all the ore as the breaking
occurs. The mucking of the ore is done with a scraper or loadertowards a chute, generally developed in the backfill. The void
then created is filled with material that can differ from one mine
to the next, such as sand, gravel, ore residues. The backfill put inplace serves as a floor while supporting the walls.
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9. Longwall & Filling
10. Longwall & Unit Supports
Longwall is a form of coal mining where a long wall
(about 250-400 m long typically) of coal is mined in a
single slice (typically 1-2 m thick). The longwall panelis typically 3-4 km long and 250-400 m wide. The gate
road along one side of the block is called the
maingate, the road on the other side is called the
tailgate. The end of the block that includes thelongwall equipment is called the face. The other end
of the block is usually one of the main travel roads
of the mine.
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11. Top Slicing
A method of stoping in which the ore is extracted by
excavating a series of horizontal (sometimes inclined)
timbered slices alongside each other, beginning at the
top of the orebody and working progressively
downward; the slices are caved by blasting out thetimbers, bringing the capping or overburden down
upon the bottom of the slices that have been previously
covered with a floor or mat of timber to separate the
caved material from the solid ore beneath.Succeedingly lower slices are mined in a similar
manner up to the overlying mat, which consists of an
accumulation of broken timbers and lagging from the
upper slices and of caved capping.
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14. Panel Mining
Panel mining uses a moveable roof support to hold upthe overburden while coal is removed. Then the
support is moved allowing the overburden to collapse.
In longwallmining, two long tunnels are cut, up to
1.6 km (1 mile) long and 180 m (600 feet) apart. The
seam of coal between is cut away and loaded onto
conveyor belts. Shortwallmining is similar but uses
shorter tunnels. Shortwall costs less, but is lessproductive.
16 Bl k C i
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16. Block CavingBlock Caving is a mining method in which ore is allowed to
collapse due to its own weight in a controlled fashion into
chutes. Block caving is usually used to mine large orebodiesthat have consistent grade throughout.A thick block of ore is
undercut by removing a slice of ore. The unsupported block
of ore breaks and caves under its own weight. The broken
ore is drawn off from below as the caved mass falls due togravity.
S l ti Mi i
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Solution Mining
Solution mining is the extraction of the valuable
components from a mineral deposit using an aqueousleaching solution. Evaporites represent a broad classof water-soluble minerals (salts). Commerciallyimportant evaporites include halite; sylvite, silviniteand carnalli te; magnesium chloride; sodiumbicarbonate; trona; and magnesium oxide. Solutionmining involves injecting a solvent into the pay zoneof the deposit through a cased borehole. Forevaporites, the solvent is hot water, which forms brineas the soluble minerals dissolve. The brine is broughto the surface via the casing system in the same or
another borehole and sent to a processing facility forrecovery by the controlled crystallization of the
desired product, followed by dewatering and drying.
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Mining Methods
Rules of Thumb
Source: McIntosh Engineering
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Method Selection - A f latly dipping ore body may be mined
us ing Blasthole when the height of ore exceeds 100 feet(30m); otherwise, it is mined Room and Pillar.
Inclination - Ore will not run on a footwall inc lined at lesshan 50 degrees from the horizontal.
Inclination - Even a steeply dipp ing ore body may not bedrawn c lean of ore by gravity alone. A s ignificant portion of
he broken ore will inevitably remain ( hang ) on the footwall.If the d ip is less than 60 degrees, footwall draw points will
reduce, but not eliminate, this loss of ore.
Stope Development The number of stopes developed
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Stope Development - The number of stopes developed
should normally be such that the p lanned daily tonnage can
be met with 60% to 80% of the stopes. The spare stopes arerequired in the event of an unexpected occurrence and may
be required to maintain uniform grades of ore to the mill. Thisallowance may not be practical when shrinkage is applied to
a sulfide ore body, due to oxidation.
Stope Development - In any mine employing backfill, there
must be 35% more stoping units than is theoretically requiredto meet the daily call (planned daily tonnage).
Ore Width - Blasthole (longhole) Stoping may be employedfor ore widths as narro w as 3m (10 feet). However, th is
narrow a width is only practical when there is an
exceptionally good contact separation and a very uniformdip.
Ore Width - Sequence problems are not like ly in the case of a
massive deposit to be caved if the horizontal axes are more
han twice the proposed draw height.
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Footwall Drifts - Footwall drifts for blasthole mining shouldbe offset from the ore by at least 15m (50 feet) in good
ground. Deeper in the mine, the offset should be increased to23m (75 feet) and for mining at great depth, it should be not
less than 30m (100 feet).
Dilution - A ton of ore left behind in a stope costs you twice
as much as milling a ton of waste rock (from dilution).