QUESTION 1

CASE 1: ASSUME TONNNAGE OF 25Mt AND DILLUTION of 5%
5
Dilution of 5% => 100 𝑥25𝑀𝑡, = 1,25𝑀𝑡
Recovery => 25 – 1,25 Mt, => = 23,75Mt

CASE 2: ASSUME TONNNAGE OF 40Mt AND DILLUTION of 15%
15
Dilution of 5% => 100 𝑥40𝑀𝑡, = 3,75𝑀𝑡
Recovery => 40 – 3,75 Mt, => = 36,25Mt
𝟐𝟑, 𝟕𝟓𝑴𝒕 < 𝟑𝟔, 𝟐𝟓𝑴𝒕
QUESTION 2
Room and pillar Mining
This method is suitable for the extraction of horizontal to near horizontally Deeping coal seams. The
method involves the use of conventional drilling and blasting (drilling, charging, blasting, ventilate,
scoop, haul and bolt.) of rocks or Continuous Mining through continuous miners (break, load, haul and
bolt) or a combination of both to extract seams in a series of panels.
Each Panel extraction is done by a regular array of rooms and pillars of defined shape. Pillars are bands
of ore intentionally left behind to serve as roof support for the working panel. The size of each panel
pillar depends on the extraction ratio but also on geotechnical conditions.
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Long wall mining
Just as room and pillar, they are suitable for horizontal to near horizontal coal seams. They are suitable
for shallow deposits due to pressure constrains, they are highly mechanized with automated variants.
They have the highest production rates for coal mining. In this method development of panel headings
is by continuous miners or conventional drill and blast method.
Extraction is done by mechanical shearers in panels which cut coal face in a forward (advance) or
backward sense (retreat) manner, armored chain conveyors then convey ore to stage loader crusher
to be hauled by conveyor belt from panel.
Each panel is separated from neighboring panel and Main headings by barrier pillars, each panel is
made of a main and tail gate. They serve as entrance and exit into working panel but also for ventilation
in intake and return of fresh and exhaust air.
Short wall Mining
This is a hybrid of long wall with room and pillar mining. Face extraction can be by retreat or advance
method of Long wall mining, while haulage is partly done by mobile shuttle cars.
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QUESTION 3
1) Geometry of deposit.
This entails size shape depth of deposit. These factors determine the suitability of a mining method to
another in terms of economics, safety and environmental feasibility.
2) Geotechnical considerations.
This includes all geotechnical aspects linked to deposit such as RMR, joints, fractures, RQD,
Permeability etc… resulting from geotechnical studies.
3) Geology of mineral deposit.
The geology and structural control of mineralization. These involves aspects as faults, fracture, folds
of mineralization and their interrelation. This discriminates one method from another.
4) Social and Environmental aspects.
The environmental and social impact of a mining project are capital as they can affect the feasibility of
the project. Subsidence a case of environmental impact of some underground mining method if
located near habitats can render the project unfeasible. A second case can be the rejection of a project
because of the negative social impacts such as immigration, traditional customs.
5) Productivity or Mining Rate.
The production rate can discriminate from ore method to another i.e. some methods cannot sustain
high production rates compared to others.
6) Automation and Mechanization
Some mining methods enable the chance of automation and mechanization of operations.
7) Safety
The safety of operations is an important aspect of a method compared to another and need to be
assessed for each case.
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QUESTION 4
QUESTION 5
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Essentially 3 cases arise when with the multiple level room and pillar method.
i.
Case 1: Upper layer or seam is being mined before lower level.
This will result in high abutment pressure at the foot of left over pillar of the upper mined seam. The
high pressure zone created as a result of this will cause instability zones on the roof of lower level.
Remedies:
ii.
Columnize pillars when mining lower level i.e. Vertically align upper and lower level pillars.
Mine lower level with long wall mining technique.
Leave little or no pillar at upper level.
Avoid driving entries under high pressure zones
Case 2: lower seam mined first then upper seam follow
There is the creation of high tensile stress zones which may result in subsidence problems.
Remedies:
-
Columnize pillars of mining levels i.e. Vertically align upper and lower level pillars.
Avoid driving entries under high tensile zones
iii. Case 3: lower and upper seam mined together.
Instability linked to differential advance of workings
Remedies:
-
Columnize pillars of mining levels
-
Avoid driving entries under high tensile and high pressure zones
QUESTION 6
-
CAVABILITY:
The cavability of the deposit is critical in mine design of block caving. Caving initiation and sustainability
are determined by the extent of capability of the rock mass. The parameter used to illustrate the
cavability is the hydraulic radius HR, this is the ratio of the area of the cave zone to the perimeter of
cave. HR for cave initiation and sustain are determined by geotechnical studies.
The for mentioned studies will determine The frequency and orientation of the various fracture sets,
RQD, RMR are used for this. As requirements a minimum of three orthogonal fracture sets are needed.
Mine layout and production scheduling are clearly dependent on this parameter as the extent of block
must satisfy the ratio.
-
FRAGMENTATION:
Fragmentation here refers to the size in which ore will break, this is important in the design of layout
and extraction operation. Larger size will imply lead to increase size of draw points and draw point
spacing and the method of block caving. An accurate prediction of fragmentation is therefore
necessary to achieve good mine planning layout.
QUESTION 7
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Sulphide minerals such as Chalcopyrite galena Pyrhotite etc turn to oxidize when exposed to air or
water. Oxidation leads to the coating of ore particles and reduces recovery during mineral processing.
The mining and processing method therefore needs to take this into account.
When mining if potions of oxidized ore can be distinguished, selective mining can be done and each
treated separately. The latter situation may be found in cases were an ancient water table existed and
a clear demarcation exist between levels.
When this cannot be done the treatment method need to be adapted to take into consideration both
phases for maximum recovery. Porphyry Mines have seldom cases as these.
Methods for sulphide oxide treatments can be Roasting, Sulphidizing, sulfuric or Iron salt solvent Etc.
Methods of mining can be by open pit or by underground mining (bloc caving, shrinkage stopping, VCR
…).
QUESTION 8
QUESTION 9
ROOM AND PILLAR MINING
This is the extraction of Horizontal to near Horizontal ore from underground through a mosaic of
rectangular rooms leaving behind pillars of ore that serves as roof support of extraction panels. This is
to prevent roof sinking of working panel. Mining can be done either by continuous miners or by
conventional drill and blast method of mining.
LONGWALL MINING
This is the mining of relatively flat ores with weak strength with the use of mechanical shearers.
Continuous haulage is done by chain conveyors to crusher before moving to ore passes. it involves
sectioning of ore into panels each having a twin entry and exit gate used for service of man power,
equipment and ventilation. Main gate is used in the case of ventilation for the intake of fresh air while
tail gate for return of exhaust air.
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Both methods are similar in that they are suitable for flat deposit or slightly inclined deposits. Main
heading development in both methods are similar i.e. the use of conventional drill and blast or
continuous miners for their development. The differences in this methods in terms of productivity,
safety, economics and environmental feasibility are summarized in the table below.
N°
Productivity
Operations
Safety
Environment
Haulage system
Depth
LONGWALL
ROOM AND PILLAR
Highest productivity rates
Averagely good
Highly mechanized
Labor intensive
Automation reduces risk
Susceptible to caving
Less safe
Reduced caving
Conveyors
LHD, Conveyors and Shuttle cars
Feasible for shallow depths
Feasible at high depths
QUESTION 10
SHRINKAGE STOPPING.
This is an underground stopping method used to extract Thin (1.5 -30) m steeply Deeping hard rock
ore having relatively competent hanging and footwalls. It is an overhand mining method were strips of
ore is broken into a stope and the broken ore serves as floor for working next strip. Due to swelling, at
least 35% of blasted rock need to be extracted at draw points, before each successive round can be
started to provide space for operations.
Development of shrinkage stopping starts with the sinking of vertical shafts at the footwall side of the
ore body, haulage dive parallel in direction of ore strike are developed on the footwall side. Crosscut
to ore body are developed from haulage level to intersect ore body at bottom of ore. An extraction
drive is developed to intersect each crosscut at the bottom of ore.
Parallel raises are developed by drill and blast method at vertical limits of stopes to serve as manway.
Initially an undercut level is drilled and blasted, roof of extraction level is blasted and ore mucked partly
from draw points in crosscuts. Once sufficient ore has been mucked overhand mining can continue on
roof of undercut.
Advantages of shrinkage stopping
-
Can easily be adapted for narrow veins.
Backfilling not necessary
Good recovery and low dilution
Steady constant flow at draw points
Minimum ground support needed
Disadvantages of shrinkage stopping
-
Require steep dip to operate
Ore and walls need to be strong
Labor intensive method
0nly 35 % of blasted ore can draw from draw point per blasted sequence
QUESTION 11
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I.
INDIVIDUAL DRAWPOINT
Controlled mucking at individual draw points is done in sublevel caving in other to ensure dilution is
reduced to a maximum and ensure a uniform flow through draw zone. Measures to ensure this is
effective are:
-
II.
Mucking is done in a sequential manner from left to right of mucking face at draw point to
ensure uniform flow.
Draw point is designed to enable free flow of all fragmentation size so as to avoid blockage of
draw points causing discontinuous supply of ore draw points.
Mucking must ensure cutoff of draw point is reached to avoid dilution through mucking of
waste material or under extraction by leaving behind of valuable ore. This can be achieved by
sampling or visual control in situations where ore rock and waste can visibly be distinguished.
GROUPE OF CLOELY SPACED DRAWPOINTS.
Controlled mucking while taking into account a group of evenly spaced draw points is important just
as in the previous case to minimize dilution from draw zone. The following must be done:
-
Muck all draw points in a sequence starting from draw point to the next to enable even flow
of material in draw zone.
In case of over extraction of a particular draw point do not catch up by trying to extract other
draw points as this will lead to dilution of ore body by wall rock
Regular sampling or observation at mucking draw point to determine cutoff of draw point.
QUESTION 12
Long wall retreat and advance variants are similar in that they both lead to the production of a goof,
they have the same final configuration ie main gate tail gate chain pillars and barrier pillars as well as
Ventilation system. the difference resides in the direction of operations.
While retreat long wall method extract seam by retreat mining towards Main Headings Advancing
method makes extraction by advancing from Main Headings. Another different worth mentioning is
that because of these configurations Long wall top caving method can only be practiced in the retreat
configuration.
QUESTION 13
CASE 1
𝑤
R1 = 1 − (
);
𝑤+𝐵
𝑤: 𝑃𝑖𝑙𝑙𝑎𝑟 𝑤𝑖𝑑𝑡ℎ
{ 𝐵: 𝐸𝑛𝑡𝑟𝑦 𝑠𝑝𝑎𝑛 }
𝑅: 𝐸𝑥𝑡𝑟𝑎𝑐𝑡𝑖𝑜𝑛 𝑟𝑎𝑡𝑖𝑜
W = 20; B = 5;
20
R1 = 1 − (20+5) 𝑥 100 ; 𝑅1 = 36%
CASE 2
𝑅2 =
𝐴𝑟𝑒𝑎 𝑜𝑓 𝑜𝑟𝑒 𝑒𝑥𝑡𝑟𝑎𝑐𝑡𝑒𝑑 (𝐴𝑚)
; {𝐴𝑠𝑠𝑢𝑚𝑒𝑑 𝑈𝑛𝑖𝑓𝑜𝑟𝑚 𝐻𝑖𝑔ℎ𝑡}
𝑇𝑜𝑡𝑎𝑙 𝐴𝑟𝑒𝑎 𝑜𝑓 𝑜𝑟𝑒 𝑏𝑒𝑓𝑜𝑟𝑒 𝑒𝑥𝑡𝑟𝑎𝑐𝑡𝑖𝑜𝑛(𝐴𝑡)
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{
Am = At − Ap(total pillar Area)
}
𝐴𝑝 = 𝐴1 + 𝐴2 + 𝐴3
𝐴1: 𝑅𝑖𝑏 𝑝𝑖𝑙𝑙𝑎𝑟 𝑎𝑟𝑒𝑎 𝑝𝑒𝑟 𝑝𝑎𝑛𝑒𝑙;
{
}
𝐴2 ∶ 𝐴𝑟𝑒𝑎 𝑜𝑓 𝑐ℎ𝑎𝑖𝑛 𝑝𝑖𝑙𝑙𝑎𝑟𝑠;
𝐴3: 𝐴𝑟𝑒𝑎 𝑜𝑓 𝑏𝑎𝑟𝑟𝑖𝑒𝑟 𝑝𝑖𝑙𝑙𝑎𝑟.
𝐴1 = (40𝑥3000)
𝑨𝟏 = 𝟏𝟐𝟎 𝟎𝟎𝟎𝒎²; 𝐴3 = (40𝑥300); 𝑨𝟑 = 𝟏𝟐𝟎𝟎𝟎𝒎²
A2? Chain pillar Total area.
We know that R1 above can also be written as:
𝑅1 =
𝐴2
;
𝐴𝑟𝑒𝑎 𝑜𝑓 𝑔𝑎𝑙𝑙𝑒𝑟𝑖𝑒𝑠 𝑝𝑙𝑢𝑠 𝑝𝑖𝑙𝑙𝑎𝑟𝑠
𝐴𝑟𝑒𝑎 𝑜𝑓 𝑔𝑎𝑙𝑙𝑒𝑟𝑖𝑒𝑠 𝑝𝑙𝑢𝑠 𝑝𝑖𝑙𝑙𝑎𝑟𝑠 𝑖𝑠 = 2𝑥(10 + 20)𝑥3000 ; = 180 000𝑚²
Thus 𝐴2 = 180 000 𝑥 .36
𝑨𝟐 = 𝟔𝟒 𝟖𝟎𝟎𝒎²
𝑨𝒑 = 𝟔𝟒 𝟖𝟎𝟎𝒎𝟐 + 𝟏𝟐𝟎 𝟎𝟎𝟎𝒎𝟐 + 𝟏𝟐 𝟎𝟎𝟎𝒎²;
𝑨𝒑 = 𝟏𝟗𝟔 𝟖𝟎𝟎 𝒎²
Am = At − Ap(total pillar Area) ;
At = 3000 x 400 m2 At = 1,200 000 m²
𝑨𝒎 = 𝟏 𝟐𝟎𝟎 𝟎𝟎𝟎 − 𝟏𝟗𝟔 𝟖𝟎𝟎 𝒎²
Am = 1 003 200 m²
𝑅2 =
1 003 200
1 200 000
𝑹𝟐 = 𝟎. 𝟖𝟑
QUESTION 14
-
Split and fender pillar recovery
This is a retreat Mining pillar recovery method which entails the use of continuous miners and roof
support to extract strips of seam in a sequential retreating manner.
In this method Continuous miner start by splitting pillar into two, then the side walls are extracted in
a series of diagonal (fender) strips while retreating from gob. In this method unlike other Mining
methods for pillar recovery prior to start of operations, temporary support need to be established.
The support is achieved by use of breaker post. They are placed at entries to gob and along pillars to
be recovered. Roof bolts may be added if deemed necessary. This method is suitable for single split
pillar entry, were continuous miner needs to recover without support. This condition makes that the
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minimum fender width is about 2,6m and max is 3,9m while the width of spilt varies between 3m and
6m.
This method of pillar recovery apart from the afore mentioned conditions need that the roof shows
relatively high strength capabilities else it cannot be applied. Also multiple split can be applied in the
case of larger pillar size but extra support need to be given and roof stability conditions need to be
established.
QUESTION 15
-
SHRINKAGE STOPING.
VERTICAL CRATER RETREAT
SUBLEVEL CAVING.
SUBLEVEL STOPPING
This is an underground mining method suitable for thin ore bodies which can’t be mines by other
methods (1.5-30m). They are best applied to steeply Deeping ore bodies with relatively competent
hanging and footwall. The angle of repose must be less than inclination of ore body to ensure gravity
flow.
The methodology involves sinking a shaft or driving a decline at the footwall side of ore to the desired
depth. Developing horizontal drives parallel to strike at bottom of planed stope to be used for haulage.
Driving crosscuts to intersect ore body at bottom from haulage level and top from access ramp of
desired stopping height. Horizontal drives parallel to strike are driven in ore from wall of crosscut at
even intervals to link successive crosscut to form two vertically parallel horizontal drives within the ore
body. Lateral raises are developed joining top and bottom drives within ore.
An undercut is developed within the ore above roof of lower level drive by roof drilling and blasting to
create the funnel shape to serve draw points. The upper level is used for long hole blasting i.e. long
holes are drilled on floor of drive and blasted to be mucked at draw points in crosscuts.
Blasting operations are done in a retreating manner and raise can go to more than one level which can
be operated simultaneously.
QUESTION 16
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Dry sand and rock fill:
This is the filling of stopes with dry sand or sand sized rocks or course rocks. Transport underground
sand sized material can be through gravity by vertical raises or bore holes. LHD method using FEL and
Trucks can be used for coarser materials. Placed material need compaction to reach its final optimum
density.
This later fore mentioned case is a disadvantage in cases where stope is narrow and does not enable
easy access to equipment. Another dis advantage is that coarse rock contains voids and fill is not
complete, however this method remains suitable in cases where mine does not have processing unit
to reduce rock size to sand size. Example where this method was used is the Cannon Mine in
Wenatchee Washington USA.
UNCEMENTED HYDRAULIC FILL:
This is the hydraulic placement of sand fills in stopes with the use of hydraulic pumps. The material is
deslimed before it can be used as it potentially can cause liquefaction. Once material is in place
drainage needs to be done given the high volumes of water pumped for fill to reach its optimum
density.
The advantage of this method is that it enables uniform fill of stope, on the other hand it’s not selfsupporting, need regular maintenance in pipping infrastructures due to wear. Also due to drainage
requirements optimal density requirements are reached after a longer period than dry fill method.
Example of Mine using this method is the UNTERBREIZBACH OF WERRA OF THE K+S KALI GmbH Mine.
CEMENTED HYDRAULIC BACKFILL:
Used where hydraulic fill required to be self-supporting. It involves the addition of cement to hydraulic
fill, frequently used where adjacent blocs need to be mined. Sand is first de-slimed before mixed.
Mixtures vary depending on the required strength.
The main advantage of this method is that it provides high cohesive strength and enables pillar
recovery, cement flows more uniformly than uncemented hydraulic fill, as setback, cement provides
fines which causes slow drainage. Example of such Mine is the WOLFRAM Mine Mittersill.
PASTE FILL.
This is a high slurry with a solid content of about 75-80% by mass, it has high viscosity, placement is by
slurry pumps. The Viscosity of pulp is a disadvantage as fluid is prone to sedimentation in pipes. Little
drainage is required in this method and fines need not be removed. Example in use is the George
Fisher Mine at Mt Isa.
PNEUMATYIC STOWING.
Used when hydraulic Filling has drawbacks or less efficient. Cases where this may occur can be when
handling of large quantities of water is undesirable or cases where we have relatively flat deposits
where tight roof may be required in which case it’s difficult to achieve with hydraulic filling method. In
this method a defined particle size material is pneumatically projected at high velocity using high
pressure pumps.
QUESTION 17
CUT AND FILL STOPING:
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Stopping method in which horizontal slices of or are mined and backfilling done before mining of next
vertical slice. This method is suitable for irregularly shaped ore bodies dipping at about 45° and more
where angle of inclination exceeds angle of repose. Depending on the vertical sense of progression cut
and fill mining can be grouped under Underhand or overhand, Variants of this methods include:
-
Overhand cut and fill stopping (which will be described here)
Post-pillar stopping
Undercut and fill stopping
Drift and fill stopping
Overhand cut and fill stopping:
Here horizontal slices (thicknesses of about 1.8 to 5m) of ore are extracted from roof by conventional
drill and blast method, previously backfilled floor serves as working platform of successive sequences.
Backfilling is essentially by cemented hydraulic fills, in case of uncommented materials top of bottom
fill is done using cement fill.
In a sequential manner, operations begin with driving of access ramps to lowest level by the drill blast
haul cycle, start extraction of lower layer to a convenient height, backfill partly, develop height of ramp
and start first overhand drilling and blasting of roof or breast stopping. If rock shows instabilities bolting
is done or timber square set supports are used.
QUESTION 18
Ore Recovery: This is the percentage of ore that is extractable from an overall ore body by a given
method of extraction. Sampling to determine recoverable ore can be by either core drilling, drives,
reverse circulation drilling pitting, gama sondes or a combination of these methods.
Dilution: This is ore contamination with gangue material or wall rock during extraction. Sampling for
dilution can be by Channel sampling, Chip sampling, Grab sampling, XRF’S, bulk sampling or any
combination of this methods.
QUESTION 19
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AVOCA MINING: This is long hole mining with delayed backfilling. The development of this method
starts with the driving of two parallel drives along strike of orebody. The lower level is used for mucking
while upper level for drilling long holes in stope, blasting and backfilling.
In the development phases access ramps are created linking ore body to upper levels, horizontal upper
and lower drives are done, sectioning ore to desired stopping height, long holes are drilled vertically
on floor of upper level after raising a vertical slot between levels. Bands of ore are blasted and mucking
can start at the lower level from draw point.
Extraction operations are done in a retreating manner while once considerable ore has been extracted
backfilling then follows from opposite side of stope. Gab separating backfill material and blasting are
predefined so as to limit dilution.
QUESTION 20
i.
Drill and blast method
Undercut: This is the creation of an undercut or slot with a cutting machine on the face to be blasted.
Drilling: drilling of a regular designed pattern of drill holes using a drilling machine.
Charging: Loading holes with explosives to defined hole height, stemming,
Blasting: Connecting holes to each other and then to booster and blast.
Ventilation: wait till all exhaust fumes are ventilated.
Mucking: Haul rock fragments from face and clean face
Support: Shotcrete or bolt roofs if necessary in case of underground works.
ADVANTAGES
-
Applicable to both soft rock and hard rock operations
High flexibility and selectivity during operations
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-
Low dilution ratios.
DISADVANTAGE
-
Cyclical operations require larger cycle time per production cycle
Lesser production capacity
Not suitable for thin coal deposits dew to mining heights
Lower extraction ratios compared to long wall mining except when introducing pillar recovery.
ii.
Continuous miner method
The cycle of operations consists essentially of two operations:
Cutting and Loading: this is done by the continuous miner. Here a cylindrical drum with cutting bids
rotate and cuts through ore while simultaneously loading falling material either to shuttle cars to be
conveyed to crusher unit; or the ore is loaded directly to flexible conveyor.
Bolting: This involves the use of mobile bolters to support roofs of newly cut areas.
ADVANTAGES
-
Higher productivity with lesser entries;
Suitable for thin coal deposits;
Safer in methane environments;
Low dilution and suitable for multiple coal seams;
Lesser workers per production panel as it Need little support operations.
DISADVANTAGES
-
Limited by depth;
Higher operating cost.
QUESTION 21
a1 = 20m ,
a2 = 22.5m,
b1 = 5m,
b2 = 4.5m
Recovery Ratio. (R)
=
𝑅=
;
𝐻𝑥𝐴𝑚
𝐻𝑥𝐴𝑡
𝑅=
𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑜𝑟𝑒 𝑒𝑥𝑡𝑟𝑎𝑐𝑡𝑒𝑑
𝑇𝑜𝑡𝑎𝑙 𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑜𝑟𝑒 𝑏𝑒𝑓𝑜𝑟𝑒 𝑒𝑥𝑡𝑟𝑎𝑐𝑡𝑖𝑜𝑛
𝐴𝑚
𝐴𝑡
𝐴𝑚 = 𝐴𝑡 − 𝐴𝑝
H: Height or ore thickness; Am Area of mined ore, At Total area of ore body, Ap : Area of pillar
Ap = 20x22.5 Ap = 450m²;
At = (a1 + b1)x(a2 + b2);
Am = 2531.25m2 − 450m2 ;
At = 2531.25m²
Am = 2081.25m2 ;
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𝑅=
2081.25
2531.25
𝑅 = 0.82;
𝑅 = 82%
QUESTION 22
TRANSVERSE: This is the direction perpendicular to strike or length of ore body or parallel to ore width.
LONGITUDINAL: Direction parallel to strike of orebody.
QUESTION 23
Advantages of Backfilling.
-
Enables the extraction of irregular ore bodies
-
Enables extractions where surrounding wall is weak
-
Minimizes surface subsidence
-
Enables the recovery of support pillars
-
Provides a working platform were overhand mining needs to be used.
QUESTION 24
STOPE: This is an underground excavation done in an orebody for ore extraction
OVER HAND MINING: mining done in a bottom top wise direction with drilling done on the roof or wall
of workings
UNDER HAND MINING: Extraction of Ore in a Top down direction with drilling done on floor or side of
stope.
EXTRACTION RATIO: this is the ratio of the volume of ore extracted from an orebody to the volume of
ore originally in place.
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GRADE: This is the concentration of a mineral in a rock or an ore body.
CROWN PILLAR: This is a rock mass separating an underground stope to surface.
Sill PILLAR: Rock mass separating two levels of stopping.
ORE PASS: Vertical or Inclined Raises Used for the movement of ore between two vertical levels in a
mine.
SLOT RAISE: this is a vertical or inclined raise cut through rock to create face for blast rounds in an
underground blasting.
QUESTION 25
CHAIN PILLAR: Section of ore used as support pillars for entry galleries of extraction panels in room
and pillar, long wall or short wall mining
BARRIER PILLAR: Pillars or sections of ore left or unmined used or serving as support and separating
development headings from panel.
CROWN PILLAR: This is a rock mass separating an underground stope to surface.
Sill PILLAR: Rock mass separating two levels of stopping.
RIB PILLAR: Section of rock mass separating two stopes laterally.
STRENGHT BASED PILLAR DESIGN METHOD.
This method is a means to estimates a safety factor based on stress and strength values of pillar. The
starting point being an estimated extraction ratio arbitrarily selected.
From the tributary method of estimation pillar stress is a function of the extraction ratio so, knowing
the depth one gets the equivalent pillar stress value
Or
Here R is the extraction ratio, these are just illustrative a more generalized formula is proposed by Coat
(1981)
PILLAR STRENGTH
Bienwaski or Munro approximates these values as shown below
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Facto of safety F:
𝐹𝑜𝑠 = 𝑃𝐼𝐿𝐿𝐴𝑅 𝑆𝑇𝑅𝐸𝑁𝐺𝑇𝐻⁄𝑃𝐼𝐿𝐿𝐴𝑅 𝑆𝑇𝑅𝐸𝑆𝑆
Acceptable values of 2 is common for Main headings and 1.8 to 1.1 in Pillar recovery. If the value
computed does not correspond to that required, then pillar parameters can be changed until value is
obtained.
QUESTION 26
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ADVANTAGES OF REEF LONGWALL MINING
-
Better recovery
Higher production rates
Safer and greater stability
Low cost of operation
Development and production can be done at the same time
Can accommodate a variety of roof types.
QUESTION 27
PUNCH LONGWALL
Punch long wall mining is a high wall mining technique employed to near horizontal coal deposits which
cannot continue to be extracted by surface mining method.
Development is similar to long wall mining and entails driving entry galleries just as in long wall mining
but this time around only two parallel drives per panel. Crosscut is developed at the extreme end of
the drives, shearers mobile hydraulic supports and chain conveyors installed on working face and
retreat mining can commence and stops somewhere near entrance of drives to leave a barrier pillar.
Adjacent panels are repeated next to previous ones but ensuring to leave a rib pillar to separate
previously mined goof. This method is highly productive compared to long wall mining with low cost
of operation and higher recovery and rates of return.
Punch Mining Estimated production rates compared to, conventional long wall mining is 5 - 8 Mt/year
to 3 - 4Mt/year.
QUESTION 28
Long wall top caving:
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This is a variant of long wall mining which takes into account the limitations of conventional long wall
mining. This method is applied for the mining of the thick coal seams (>5m). The method operates in
a similar manner as Long wall mining.
The method makes use of modified hydraulic roof supports. This supports are equipped of flipper at
its back end which help in collecting extra caved ore in the goof. Apart from this modification. All other
procedures stay same but for the use of chain conveyors to transport ore located at both front and
behind of foot of roof support. The general configuration of two entries is not changed and extraction
maintained by retreat mining.
Other equipment not mentioned but in use are Shearer for ore breakage and feeder breaker for
crushing ore before transferred to conveyor.
QUESTION 29
Square set stopping:
this is an underground stopping method used in case where ore is very weak and cannot support itself
as well as wall rock. This method makes use of timber support arranged as the name says in a square
set pattern. Extraction is slow with low production rates as only small square portions of ore are
extracted at a time. This method is commonly used in the extraction of weak ore bodies with weak
walls.
During developments, ore is blasted and falls down by gravity in shuts where they are hauled at the
lower level. The square sets need to be developed immediately to support workings. Lagging of top or
sides of blasted stopes can be done if necessary as well as cement backfilling. It is a labor intensive and
highly skilled method so ore need to be profitable before any further investment into the method.
QUESTION 30
i.
Under Cut level
Undercut drifting: This entails horizontal drives below ore body in precise location vertically above
haulage drifts. Crosscut drives linking main drives to section undercut level into blocks in preparation
for long hole operations.
Long hole operations: This is the drilling of horizontal holes across or vertical holes along roof of drives
to angles of 45° to 90°, loading them and blasting sections of ore to create a slot which will enable
caving to begin. Apart from angle requirements other major requirements in development of undercut
are:
- Evenly spaced drill patterns as determined by hole size and powder factor requirements.
- Proper alignment of underlined workings.
ii.
Production Level
LHD System (example DOZ copper-gold mine in Indonesia): This are drives driven in ore body at even
spacing parallel to each other. Located below undercut and above haulage drives. The operations here
are:
-
LHD operations done by front end loaders from draw points to ore passes.
Drilling and blasting of large ore fragments
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GRIZZLY System (example Andina Copper Mine Chili): For this system production level corresponds to
the Grizzly level. The major operations carried out here are:
-
Ore sizing form draw points, Ore coming from undercut falls on grizzly rails where the can be
sized or classified and transferred by gravity through ore passes to haulage level.
Other operation is secondary ore fragmentation through mobile hammers before gravity
transfer to haulage level.
SLUSHER System: Production level is equivalent to the slusher level. Major operations carried out here
include:
- Ore slushing, this entails shlusher scraping of ore to ore pass to haulage level.
- Occasional drilling and blasting of large ore or rock fragments.
iii.
Ventilation level
The ventilation level in the case of small mines makes use of haulage levels and production levels for
intake and return of exhaust air. When volume of workings gets large an extra ventilation level is
constructed or driven between production and haulage levels with raises linking the haulage level.
The major operation is ventilation though it can also be used for access to haulage level for
maintenance purposes.
iv.
Transportation level.
This is the haulage level where the essential operation is ore haulage but also maintenance transport
logistics such as rail tracks as well ventilation.
QUESTION 31
Air blast is a hazardous situation that occurs when a void is created between mass of falling rock and
fallen rock within an open stope under extraction. The sudden detachment of a slab of ore from roof
of stope leads to the compression of air and development of high speed air and high pressure
differences in surrounding environment which can be source of unwanted accidents.
This phenomenon is not easily predictable in terms of engineering. Mitigative measures can be the
installation of air obstruction walls. An example of this phenomena occurred is in the North park Mine,
Australia November 24th 1999.
QUESTION 32
Conventional drill and blast method of room and pillar.
This makes use of conventional drill and blast cycle tin panel production of coal, Due to ventilation
constrain this method requires a minimum of 3 entries One for air intake the other for return air and
the last for coal haulage. Number of entries can exceed 13 as long as extraction and safety conditions
are met.
Continuous Mining method of room and pillar.
In the continuous mining method of room and pillar a minimum of 4 entries are required this is
because the use of shuttle cars to the movement of coal need use of an extra entry for the rotation
of shuttle cars during loading and unloading.
Methods of transportation.
Front end loader, shuttle cars, Conveyors, Train wagons, Trucks.
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QUESTION 33
Over break: Volume of excess rock produced by excavation from designed volume. This can result from
poor design, poor ground conditions, wrong explosive use, SYSMIC effect of blasting in soft rock
conditions.
Under break: this is when the volume of rock excavated is less than designed or expected value. They
result from wrong design of blast plan or excavation method.
Mitigative measures: presplitting, proper investigation of rock properties, proper blast design.
QUESTION 34
𝑇𝑜𝑛𝑛𝑎𝑔𝑒 = 𝑉𝑜𝑙𝑢𝑚𝑒 𝑥 𝑆𝐺 ;
𝑇𝑜𝑛𝑛𝑎𝑔𝑒 = 140𝑥15𝑥350 𝑥 3.6 =>
𝑻𝒐𝒏𝒏𝒂𝒈𝒆 = 𝟐. 𝟔𝟒𝟔𝑴𝒕
𝑻𝒐𝒏𝒏𝒂𝒈𝒆 = 𝟏𝟎% 𝒙 𝟐. 𝟔𝟒𝟔 𝑴𝒕 =>
𝑻𝒐𝒏𝒏𝒂𝒈𝒆 = 𝟎. 𝟐𝟔𝟒𝟔𝑴𝒕
a) Lead Pb
Tonnage
Mill recovery
𝑻𝒐𝒏𝒏𝒂𝒈𝒆 = 𝟗𝟎% 𝒙 𝟎. 𝟐𝟔𝟒𝟔 𝑴𝒕 =>
𝑻𝒐𝒏𝒏𝒂𝒈𝒆 = 𝟎. 𝟐𝟑𝟖𝟏𝟒𝟎𝑴𝒕
b) Zinc Zn
Tonnage
𝑻𝒐𝒏𝒏𝒂𝒈𝒆 = 𝟏𝟓% 𝒙 𝟐. 𝟔𝟒𝟔 𝑴𝒕 =>
𝑻𝒐𝒏𝒏𝒂𝒈𝒆 = 𝟎. 𝟑𝟗𝟔𝟗𝑴𝒕
Mill recovery
𝑻𝒐𝒏𝒏𝒂𝒈𝒆 = 𝟖𝟓% 𝒙 𝟎. 𝟐𝟔𝟒𝟔 𝑴𝒕 =>
𝑻𝒐𝒏𝒏𝒂𝒈𝒆 = 𝟎. 𝟑𝟑𝟕𝟑𝟔𝟓𝑴𝒕
c) Silver Ag
Tonnage
𝑻𝒐𝒏𝒏𝒂𝒈𝒆 =
𝟏𝟐𝟎𝒈
𝒙 𝟐. 𝟔𝟒𝟔 𝑴𝒕 =>
𝒕
𝑻𝒐𝒏𝒏𝒂𝒈𝒆 = 𝟑𝟏𝟕. 𝟓𝟐 𝒕
Mill recovery
𝑻𝒐𝒏𝒏𝒂𝒈𝒆 = 𝟔𝟎% 𝒙 𝟑𝟏𝟕. 𝟓𝟐 𝒕 =>
𝑻𝒐𝒏𝒏𝒂𝒈𝒆 = 𝟏𝟗𝟎. 𝟓𝟏𝟐 𝒕
d) Gold Au
Tonnage
𝟐𝒈
𝒙 𝟐. 𝟔𝟒𝟔 𝑴𝒕 =>
𝒕
𝑻𝒐𝒏𝒏𝒂𝒈𝒆 = 𝟓. 𝟐𝟗𝟐 𝒕
𝑻𝒐𝒏𝒏𝒂𝒈𝒆 = 𝟔𝟎% 𝒙 𝟓. 𝟐𝟗𝟐 𝒕 =>
𝑻𝒐𝒏𝒏𝒂𝒈𝒆 = 𝟐. 𝟔𝟒𝟔 𝒕
𝑻𝒐𝒏𝒏𝒂𝒈𝒆 =
Mill recovery
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