2 - classification

8/13/2019 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).

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