mining material

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MI 31003 Underground Metal Mining Methods
Lecture Notes
K.UMAMAHESHWAR RAO
Chapter 1
Salient features of Indian Mining Industry
1. The major contributors of mineral in the country are:
Table1. Share of key mining states on India’s mineral resources (Ministry of Mines, Government of
India; Ministry of Coal, Government of India, Indian Bureau of Mines, Centre for Monitoring Indian Economy -2006)
State Coal% Iron ore% Bauxite% Manganese
%
Lead-Zinc % Chromite
%
Jharkhand 29% 14% - - - -
Orissa 24 17 51 35 - 98
Chhattisgarh 16 10 - - - -
MP 18 - - 10 - -
AP (old) 7 7 21 - 1 -
Rajasthan - - - - 90 -
Karnataka - 41 - 29 - 1
Total 84 89 72 74 91 99
2. India produces about 87 minerals that include 4 fuel minerals, 3 atomic minerals, 10
metallic minerals, 47 non-metallic minerals and 23 minor minerals (including
building & other materials). India occupies a dominant position in the production of
many minerals across the globe.
3. There are close to 3000 mines in India. As per the records of 2010-11, of 2928 mines,
573 were fuel mines, 687 were mines for metals, and 1668 mines for extraction of
non-metallic minerals. Of the total number of about 90 minerals, the three key
minerals are coal, limestone and iron ore. There are 560 Coal mines (19% of total
number), 553 limestone mines (19% of total number) and 316 iron ore mines (11 % of
total number) bauxite (189), manganese (141), dolomite (116) and Steatite (113).
India ranks 3rd in coal production, 3rd in limestone production and 4th in iron
ore production, in the world as of 2010.
Table 2 .India’s Production Rank across Key Minerals – 2010 (Ministry of Mines, Government of
India; Ministry of Coal, Government of India, Indian Bureau of Mines, Centre for Monitoring Indian Economy -2006)
Mineral Application Total
Production
(‘000 tonnes)
India’s global
rank in
production
Coal Power, steel, cement 5,37,000 3rd
Limestone Cement, iron & steel, chemical 2,40,000 3rd
Iron ore Iron and steel 2,60,000 4th
Bauxite Transport vehicles, packaging, construction
materials
18,000 4th
Barite Oil and gas, paints, plastics 1,000 2nd

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Chromite Steel, dye & pigments, preservatives, refractory appli
cations
3,800 2nd
Zinc metal Iron & steel (galvanization), communication
equipment –as alloys)
750 4th
Managanese Iron & steel, packaging ( as alloy with
aluminium)
1,100 5th
Lead metal Paints 95 6th
Copper Electronics , architecture, alloys 161 10th
Aluminium Transport vehicles, packaging, construction 1,400 7th
4. Amongst the BRIC countries (Brazil, Russia, India and China), India is the least
developed in terms of per capita mineral consumption. As India’s per capita GDP
increases, its mineral consumption will grow at a rapid pace in line with the growth
witnessed in other emerging markets like China and Brazil.
5. Problems of sustainability of Indian mining industry:
 Regulatory challenges:
There is no guarantee of obtaining mining lease even if a successful exploration
is done by a company. The mining licenses are typically awarded on a first
come first serve basis in principle but there is no transparent system.
 Inadequacy of infrastructure: The inadequacy of infrastructure is related to
the absence of proper transportation and logistics facilities. Many of our mining
areas are in remote locations and cannot be properly developed unless the
supporting infrastructure is set up. For example, the railway connectivity in
most key mining states is poor and it has inadequate capacity for volumes to be
transported which adds to the overall supply chain cost. The government
foresees that steel production capacity in the country by the year 2025 will
increase to 300 million tonnes per annum. This would require Indian Railways
freight capacity to be around 1185 million tonnes, for only steel and its raw
material requirements.
 Environmental clearance: A large percentage of mining proposals has failed to
get environmental / forest clearance from the Ministry of Environment and
Forests, Government of India.
Over and above these regulations, the mining companies also need to take the
local communities along, to ensure that they have the support of the ‘local’ side
for their projects. As a result, several projects are impacted with challenges by
way of opposition from local communities / NGOs, difficulties in land
acquisition, denial of clearances from the governing bodies, etc. A few instances
of some of the major projects that have been impacted in recent past are as
follows:

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a) Pohang Steel Company (POSCO’s) US$ 11 billion investment plan:
strong opposition from local people over land acquisition.
b) Vedanta’s proposed US$ 1.7 billion bauxite mining project in Odisha:
opposition by local community and eventual withdrawal of the forest
clearance
c) Utkal alumina project, which was a US$ 1 billion joint venture between
M/s. Hindalco (India) and Alcan (Canada) to mine and refine bauxite:
delayed by more than a decade due to challenges in land acquisition
d) Uranium Corporation of India Ltd., UCIL’s two mining projects worth
US$ 200 million and US$ 225 million in Meghalaya and Andhra
Pradesh respectively: opposition from local communities and
organizations on the grounds of likely effects of radiations on human
health and environment
6. Non-metallic mineral: The resource base of industrial / non-metallic minerals in
India is adequate except for Rock Phosphate, Magnesite and Ball Clay, for which the
estimates show decreasing reserves. In fact, country is deficient in fertilizer minerals
and heavily depends upon imports. Based on the industry these minerals find use in,
they are grouped under four categories
A. Fertilizer Minerals
1. Rock Phosphate 3. Sulphur and Pyrites
2. Potash
B. Flux and Construction Minerals
4. Asbestos 7. Gypsum
5. Dolomite 8. Wollastonite
6. Fluorspar 9. Non-cement grade limestone
C. Ceramics and Refractory Minerals
10. Quartz and other silica minerals 15. Pyrophyllite
11. Fireclay 16. Kyanite
12. China clay and Ball clay 17. Sillimanite
13. Magnesite 18. Vermiculite
14. Graphite 19. Non-metallurgical bauxite
D. Export Potential Minerals
20. Barytes 23. Mica
21. Bentonite 24. Talc, Soapstone and Steatite
22. Fuller’s Earth

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7. Mining of granite, marble, sandstone of building material quality (Chunar sandstone),
slate, barite, etc.; are classified under small scale mining sectors in the country
Chapter 1
1.0 Formation of ore deposits/ ore genesis
1.1 Introduction
The geological environment, the earth s has been subjected to various activities and as a
consequence it undergoes a cyclic change through a number of stages such as :
1. Erosion and planning (running down of mountains)
2. Weathering Stage, formation of sedimentary rocks
3. Sedimentary stage. burial in the deep crust –
4. Plutonic stage. When molten rock solidifies within pre-existing rock, it cools slowly,
forming plutonic rocks with larger crystals.(Plutonic – meaning deep underground; it
refers to the hydrothermal process where igneous rocks are formed by solidification at
considerable depths)
5. Orogenic stage –a stage characteristic of forces or events leading to large structural
deformations (folding, faulting, mountain building and igneous intrusions) of earth
lithosphere (crust & uppermost mantle) due to tectonic activity.
2. Concepts of Genesis of Ore
Ore genesis theories generally involve three components: source, transport or conduit, and
trap. The genesis of ore deposit is divided into internal (endogenic) and external (exogenesis)
or surface processes. More than one mechanism may be responsible for the formation of an
ore body.
 Source is required because metal must come from somewhere, and be liberated by
some process
 Transport is required first to move the metal bearing fluids or solid minerals into the
right position, and refers to the act of physically moving the metal, as well as
chemical or physical phenomenon which encourage movement
 Trapping is required to concentrate the metal via some physical, chemical or
geological mechanism into a concentration which forms mineable ore.
The various theories of ore genesis explain how the various types of mineral deposits form
within the Earth's crust. Ore genesis theories are very dependent on the mineral
Syngenetic - A deposit formed at the same time as the rocks in which it occurs.
Ex. Banded Iron Formation

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Epigenetic- A deposit introduced into the host rocks at some time after they were deposited
Ex. Valley-type Deposits
GENESIS OF ORE DEPOSITS
Origin Due to Internal Processes
Magmatic
Segregation
Separation of ore minerals by fractional crystallization during
magmatic differentiation.
Settling out from magmas of sulfide, sulfide-oxide or oxide melts
which accumulate beneath the silicates or are injected into country
rocks or extruded on the surface.
Pegmatitic
Deposition
Crystallization as disseminated grains or segregations in
pegmatites.
Hydrothermal Deposition from hot aqueous solutions of various sources.
Lateral Secretion
Diffusion of ore and gangue forming materials
from the country rocks into faults and other structures.
Metamorphic
Processes
Pyrometasomatic (skarn) deposits formed by replacement of wall
rocks adjacent to an intrusive.
Initial or further concentration of ore elements by metamorphic
processes.
Origin Due to Surface Processes
Mechanical
Accumulation
Concentration of heavy minerals into placer
Sedimentary
Precipitation
Precipitation of certain elements in sedimentary environments.
Residual Processes
Leaching of soluble elements leaving concentrations of insoluble
elements.
Secondary or
Supergene
Enrichment
Leaching of certain elements from the upper part of a mineral
deposit and their reprecipitation at depth to produce higher
concentrations.
Volcanic Exhalative
Process
Exhalations of sulfide-rich magmas at the surface, usually under
marine conditions.
2.1 Spatial Distribution of Ore Deposits
It is considered that in certain periods of geological time scale, the deposition of a metal or
group of metals was pronounced; and also that specific regions of the world possess a notable
concentration of deposits of one or more metals.
Mineral deposits are not distributed uniformly through the Earth's crust. Rather, specific
classes of deposit tend to be concentrated in particular areas or regions called metallogenic
provinces.

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2.2 Mode of Formation
As hot (hydrothermal) fluids rise towards the surface (magma charged with water, various
acids, and metals in small amounts) through fractures, faults, brecciated rocks, porous layers
and other channels (i.e. like a plumbing system), they cool or react chemically with the
country rock.
Some form ore deposits if the fluids are directed through a structure where the
temperature, pressure and other chemical conditions are favourable for the
precipitation and deposition of ore minerals. The fluids also react with the rocks they are
passing through to produce an alteration zone with distinctive, new minerals.
2.2.1 Characteristic types of hydrothermal ore formations
Cavity Filling
The hydrothermal fluid fills in the cavities within the country rock and based on the shape of
solidified ore mineral several names have been attributed to the ore body shape, such as:
The cavity filling deposits are loosely termed as vein deposits Eg. gold, silver, copper and
lead-zinc. Veins range in thickness from a few centimeters to 4 meters. They can be several
hundreds of meters long and extend to depths in excess of 1,500 meters.
The process of cavity filling has given rise to a vast number of mineral deposits of diverse
forms and sizes. The Vein deposits resulting from cavity filling may be grouped as follows:
 fissure veins, ( it is a tabular ore body that occupies one or more fissures: two
of its dimensions are much greater than the third)
 shear zone deposits, ( thin sheet like connecting openings of a shear zone)
 stock-works, (interlacing network of small ore bearing veinlets traversing a
mass of rock.
 saddle reefs,
 ladder veins, and
 replacement veins or veinlet’s

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Fig .1 Various fissure veins: (A). Chambered vein; (B). Dilation veins; (C).Sheet veins;
(D). En-echelon vein (E). Linked vein
Fig.2 (a) Stockwork
Fig.2(b). Stockwork of a sulphide ore body

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Fig 3(a) Saddle reef
Fig.3(b). Bendigo Goldfield, Victoria, Australia

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Fig Ladder vein deposit.
Ladder veins are short, rather regularly spaced, roughly parallel fractures that traverse dikes
(tabular bodies of igneous rock). Their width is restricted to the width of the dike, but they
may extend great distances along it. Ladder veins are not as numerous or important as fissure
veins.
Questions:
Q1. What are the salient features of Indian Mineral industry?
Q2. Discuss the challenges of sustainability of Indian Mineral Sector?
Q3. Describe the geological processes involved in the formation of mineral resources.
Q4. Explain the characteristics and geometry of hydrothermal ore formations?
Q5. Geometric Measures of an Ore body
 Axis of ore body: line that parallels the longest dimension of the ore body.
 Pitch (Rake) of ore body: angle between the axis and the strike of the ore body

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ORE DEPOSITS and the Tectonic Cycle

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Lecture 2:Economic analysis for the assessment of viability of a
mineral resources sector
The first step of assessment whether a mineral deposit under consideration is viable under the
existing techno-economic conditions is to prepare a detailed feasibility report of the mining
project
Feasibility Report
A feasibility study is an evaluation of a mineral reserve to determine whether it can be mined
effectively and profitably or not. It includes the detailed study of reserve estimation, mining
methods evaluation, processing technique analysis, capital and operating cost determination
and the process effect on environment.
The feasibility study can be considered into two stages: prefeasibility studies and detailed
feasibility. Both stages are similar in term of content. The difference exist in the accuracy and
time required to perform the studies.
Detailed Feasibility Report:
This is the most detailed study to evaluate whether to proceed with the project. It is the basis
for capital estimation and provides budget figures for the project. It requires a significant
amount of formal engineering work and accurate within 10 - 15%.
Steps for a feasibility study
1. Geology and Resource: This is the step where drilling and sampling works is
performed. Various methods are available for drilling based on the soil and
mineral properties. The drill samples are prepared for the assay in order to
determine the minimum, maximum and average ore grade and these figures are
used to make the reserves estimation.
2. Mine design and Mineable Reserve: This is the step where most economic way of
mining is developed. Mine planning, model development, operation models and
cost analysis are performed and thus the mineable reserve is estimated based on
the economy.
The major steps for the mine development are:
 mine access (surface/underground),
 conveying system (especially in UG mines),
 backfill requirement,
 ore haulage, ventilation,
 Selection of mining equipment and justified against the performance and
economy.
 disposal of tailings generated.
3. Mineral processing facility: Sampling must be carried out to ensure that the
samples used in the mineral beneficiation processes are real representative of the
ore body. Some major characteristics of the ore body is determined prior to the
development of the plant design which includes Grinding work indices, feed size,

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settling characteristics, filtration characteristics etc.
Sometimes a mineral processing tests are performed in order to determine the
amenability of the given ore to different concentration technologies. The major
processes that are looked at are:
 Crushing and grinding,
 Concentration (Sizing, Gravity or Flotation)
 Dewatering (Mechanical or filtering)
 Chemical extraction (especially for gold)
When these tests are completed, based on the test results the basic material flow
sheet is developed. This helps in the selection of the equipment selection and the
stages of processing.
These data are used to estimate the amount and grade of concentrate, middling
and tailings that are used to search potential customers and revenue earned.
4. Tailings disposal: Tailing disposal system plays a crucial role in order to get the
mine permit. Mostly the tailings didn't place any major challenges. But, if the
tailings have hazardous or toxic materials like cyanide, mercury etc. in it, then the
disposal system must be effective in order to reduce the harmful effect on the
environment and society.
5. Infrastructure development: This section includes the civil and major earthworks
required to start the production. The office, labs, storage units, plant buildings,
mining equipment shelters etc. are included in the infrastructure.
6. Power supply: Determining the power source, power line distribution, total power
required and the power cost are the major things to be looked into in this step.
7. Water: Most of the plant processes are water based, so, the estimation of water
requirement plays an important role in the feasibility studies.
8. Environmental impacts: For a project to be permitted by any government, an
environmental clearance is required. In order to get the clearance, the
environmental impacts need to be studied. The important aspects are acid mine
drainage, cyanide management, and other toxic material controls (Arsenic,
mercury, sulfur etc.)
9. Other key parameters: Support facilities, maintenance, transport cost of man and
material, labor cost, site access (road facility or construction, fly in fly out,
marine etc.), social impacts are also need to be studied and the steps for social
responsibility.
10. Cost estimation: Based on the entire above-mentioned steps, capital and operating
cost for each unit is estimated. It included all the costs for mine equipment,
process equipment, construction costs etc.

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11. Financial Evaluation: This is the stage where the project is evaluated based on the
economy. The total cost and expenses are looked against the expected revenue
gained from the selling of final products and by-products.
The key financial indicators examined to determine the viability of the project
include Net Present Value (NPV) and the Internal Rate of Return (IRR). Annual
cash flow need to be estimated over the entire life of the project, from
construction to reclamation phase, based on clear and realistic capital
expenditures mine and mill operating costs, employee wages and sales revenue.
12. Sensitivity Analysis: A sensitivity analysis is then carried out to determine the
impact of variation in metal price, operating cost, metal recovery, metal grade,
and capital cost on the overall project NPV and IRR values.
The viability of the mine project is established by all these stages and if based on these
considerations if mine is feasible, then the next stage of actual development occurs.
Design elements of Underground Metal Mine (UMM)
The following constitutes the elements of underground metal mine design
1. Mineral resources and reserves i.e. mineral inventory
2. Cut-off grade
3. Production rate and mine life
4. Price of the mineral
Classification of Mineral resources
Of all the aspects of mining operations, the ore deposit and its characteristics is the only
aspect which is unalterable. Therefore the viability of a mining project is dependent on the
knowledge of mineral resource.
Geologists distinguish between mineral resources and reserves. The term resource refers to
hypothetical and speculative, undiscovered, sub-economic mineral deposits or an
undiscovered deposit of unknown economics. Reserves are concentrations of a usable mineral
or energy commodity, which can be economically and legally extracted at the time of
evaluation.
• Mineral resources is the name given to minerals which contain elements such as gold,
silver, copper, lead, zinc, iron, aluminum, nickel, molybdenum etc., as well as fossil
fuels, like oil, natural gas, and coal
• Mineral reserves are concentrations of various minerals and it is a geological term.
Whether a mineral deposit is also an ore deposit depends on its economic value.
• "Ore deposit" is therefore an economic term of a mineral deposit.
Mineral inventory (stock ) is commonly considered in terms of resource and reserve.

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Fig 1 Classification of Mineral Resources
Fig.2 Losses of various types in an u/g. metal mine
In terms of the mining project a mineral resource is divided into three categories as follows:
 Geological resource (QG)
 Mineable or workable reserves(QW)
 Commercial reserves (QC)
INFERRED
SUB-ECONOMIC
RESOURCES
DEMONSTRATED
SUB-ECONOMIC
RESOURCES
INFERRED
MARGINAL
RESERVES
MARGINAL
RESERVES
INFERRED
RESERVES
RESERVES
SPECULAT
IVE
HYPOTHETI
CAL
INDICATED
MEASURED
PROBABILITY RANGE
INFERRED
DEMONSTRATED
UNDISCOVERED
RESOURCES
IDENTIFIED RESOURCES
Economic
Marginally
Economic
Sub-
Economic
Economic
Feasibility Certainty Of Existence

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Fig 2 . Reserve Classification
𝑄𝑊 = 𝑄𝐺 − 𝑄𝑁𝑊 (𝑄𝑁𝑊 = 𝑞𝑢𝑎𝑛𝑡𝑖𝑡𝑦 𝑜𝑓 𝑛𝑜𝑛 − 𝑤𝑜𝑟𝑘𝑎𝑏𝑙𝑒 𝑟𝑒𝑠𝑒𝑟𝑣𝑒𝑠)
𝑄𝐶 = 𝑄𝑊 − 𝑂𝐿 (𝑂𝐿= various unavoidable losses of ore reserve in
pillars, etc)
Cut-Off Grade:
 Cutoff grade can be defined as the minimum grade of metal present in the mine which
could be mined economically. Cut-off Grade can be used to separate two courses of
action i.e. mine or to dump. The grade of mineralized material below cut-off grade is
classified as waste whereas the material above cutoff grade is classified as ore.
 The cut-off grade is extremely crucial with respect to economical, production and
geological parameters of the mine. Too high a grade can reduce the mineral recovered
and possibly the life of the deposit whereas too low a cut-off would reduce the
average the average grade ( and hence profit) below an acceptable level.
 Cut-off grade can be classified into two basic categories namely fixed cut-off grade
and the variable cut-off grade.
 The fixed cut-off grade assumes a static cut-off for the life of the mine while the
variable cut-off grade assumes dynamic cut-off maximizing the mine present value.

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 Professor Lane outlined three distinct stages in amine operation namely ore
generation (mining), concentration (milling), and refining.
 The various factors which are essential for assessing cut-off grade for mining
operations are the type of ore resource/reserve present, extent of mine development or
present day cost development of mine, cost of drilling, mucking and transportation,
present value of revenues to be obtained from selling the ore, net cash flows have to
be considered.
 For each of the stage as mentioned, there is grade at which cost of extracting the
recoverable metal equals the revenue from the metal. This is commonly known as
break-even grade. If the capacity of the operation of an operation is limited by one
stage only, the break-even grade for the stage will be the optimum cut-off grade.
Where an operation is constrained by more than one stage optimum cut-off grade may
not necessarily be beak-even grade. In such a case balancing the cut-off grade for
each pair of stages need to be considered as well.
Fig. Influence of cut-off grade on mining design parameters

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Fig. Optimum Mine Production rate
Categories of resources based on degree of assurance of occurrence
Identified (Mineral) Resource: Are the specific bodies of mineral-bearing material whose
location, quantity, and quality are known from specific measurements or estimates from
geological evidence. Identified resources include economic and sub-economic components.
To reflect degrees of geological assurance, identified resources can be divided into the
following categories:
Measured: Are the resources for which tonnage is computed from dimensions revealed in
outcrops, trenches, workings, and drill holes, and for which the grade is computed from the
results of detailed sampling. The sites for inspection, sampling, and measurement are spaced
so closely, and the geological character is so well defined, that size, shape, and mineral
content are well established.
Indicated: Are the resources for which tonnage and grade is computed from information
similar to that used for measured resources, but the sites for inspection, sampling, and
measurement are farther apart or are otherwise less adequately spaced. The degree of
assurance, although lower than for resources in the measured category, is high enough to
assume continuity between points of observation. Demonstrated: A collective term for the
sum of measured and indicated resources.

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Inferred: Are the resources for which quantitative estimates are based largely on broad
knowledge of the geological character of the deposit and for which there are few, if any,
samples or measurements. The estimates are based on an assumed continuity or repetition for
which there is geological evidence. This evidence may include comparison with deposits of
similar type. Bodies that are completely concealed may be included if there is specific
geological evidence of their presence.
Categories of resources based on economic considerations.
Economic: This term implies that, at the time of determination, profitable extraction or
production under defined investment assumptions has been established, analytically
demonstrated, or assumed with reasonable certainty (see guideline iii).
Sub-economic: This term refers to those resources which do not meet the criteria of
economic; sub-economic resources include Para-marginal and sub-marginal categories.
Para-marginal: That part of sub-economic resources which, at the time of determination,
almost satisfies the criteria for economic. The main characteristics of this category are
economic uncertainty and/or failure (albeit just) to meet the criteria which define economic.
Included are resources which could be produced given postulated changes in economic or
technologic factors.
Sub-marginal: That part of sub-economic resources that would require a substantially higher
commodity price or some major cost-reducing advance in technology, to render them
economic.
Some definition related to mineral resources:
• Ore is a naturally occurring, in-place, mineral aggregate containing one or more
valuable constituents that may be recovered at a profit under the existing techno-
economic indices. In metal mines, the amount of ore is usually expressed in tons
(metric ton =1000kg),
• Grade is a measurement of the metal content of ore.
• The grade of precious metal ore is usually measured in grams per tonne. The grade of
ore bearing other metals is usually a percentage (the weight for weight proportion of
metal in the ore).
• The grade of ore from a mine changes over time. Mining of a lower grade is likely to
incur (other things being equal) a higher cost per unit weight of extracted metal.
The most important factor in the profitability of a mine is usually the price of the
metal that it produces.
• Dilution is the result of mixing low-grade material with high-grade material during
material production, generally leading to an increase in tonnage and a decrease in
mean grade relative to original expectations.
Reserves of minerals are difficult to determine as the value and costs of extraction and
metallurgical treatment and transportation costs determine whether the resource are
potentially economic. Because of these uncertainties, mineral, mineral exploration is a
program that raises even more uncertainties.

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Lecture 3
3.0 Mine development
Opening a new mine is an expensive, time-intensive operation. Most mines must operate for
years to cover initial start-up costs, the period of capital investment for mine development
without any return on the investment is known as gestation period Mining is the process of
extracting valuable minerals from the earth. Mining involves a number of stages which occur
in a sequence. This sequence of stages is known as the mining sequence. The mining
sequence covers all aspects of mining, including: prospecting for ore bodies, analysis of the
profit potential of a proposed mine, extraction of the desired materials and, once a mine is
closed, the restoration of all lands used for mining to their original state.
3.1 Sequence of a mining enterprise
The mining sequence is divided into six stages. Each stage represents a certain period in the
life of a mineral deposit. The stages, ordered chronologically from earliest and following the
order in which they occur, include:
1. Exploration - gather data about potential mineral deposits and acquire the rights to
harvest those mineral deposits
2. Evaluation - determine which mineral deposit has the most profit potential
3. Mine Development - construction of a mine or mines
4. Production - operation of the mine or mines
5. Closure demolition of the mine or mines and rehabilitation of all lands used for
mining
Mine develop involves construction of various types of openings within the rock mass It is
therefore important to identify the importance of different types of mine openings on the
basis of their specific role in the entire term or life of the mine. Based on these criteria all the
mine openings are categorized into three types of openings, such as:
 Main access to the deposit, which connects the surface and the ore body is also the
called the primary development opening.
 Net-work of the openings like the levels, cross-cut, raise & winze, etc. – secondary
opening; which is the access to the stope
 Source of the ore (stope) also termed the tertiary opening.
The role of primary opening is to provide an access to the deposit from the surface and
therefore the life of these openings is as much as the life of the mine. The secondary
openings are next important development openings in terms of the life. The life term of a
stope, the tertiary opening, is the shortest compared to any other opening of the mine.
The primary development is creation of a main access from the surface to underground, such
as shaft, incline, decline, adit etc., and any development which generates a network of
openings connecting the main access and the main production zone (stope) are called the

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secondary developmental works. For example, levels, raises & winzes, ore pass, cross-cuts,
ore chutes, u/g electrical sub-station & mechanical workshop, first aid room, etc., are
categorized as secondary development openings. A stope, which the place of main zone of
mine production comes under tertiary development
3.2 Stages of Mine Development
3.2.1 Primary Development – access to the deposit
Access to the ore deposit is first operation, which establishes the entry to the mine. For an
underground metal mine, the modes of entry to a deposit are: adit, incline, decline, a vertical
shaft, inclined shaft. Based on the geometry, strike & dip dimensions of the ore deposit, and
depth one or more combinations of different modes of access is decided. Once the deposit is
accessed, in order to commence the mine excavation of ore, various types of constructions
within the rock mass are needed for various engineering purposes. Some of these openings
are vertical, inclined, parallel to the strike and along the dip etc. The shape and the cross
section of the excavation depend primarily on the target production, purpose of the opening
(transportation, ventilation, water outflow, etc.,), nature & stability of the rocks type, the
period of service.
Permanent access and service openings, as shown in the above figure, are expected to
meet rigorous performance specifications over a time span approaching or exceeding the
duration of mining activity for the complete orebody. For example the service shaft must be
capable of supporting high speed operation of cages and skips continuously. Ventilation
shafts and airways must conduct air to and from stope blocks and service areas. Main haulage
drives must permit the safe, high speed operation of loaders, trucks, ore trains and personnel
transport vehicles. In these cases, the excavation are designed and equipped to tolerances
comparable with those on other areas of engineering practice. The mining requirement is to
ensure that the designed performance of the permanent openings can be maintained
throughout the mine life. The magnitudes of the mining induced perturbations at any point in
the rock medium surrounding and overlying an orebody are determined, in part, by the nature
and magnitude of the displacements induced by mining in the immediate vicinity of the
orebody.
3.2.1.1 Selection of a suitable access to the deposit
The decision of selecting the suitable access to the deposit, between a vertical shaft and an
incline is based on the following factors:
 depth of ore deposit, size and shape of ore body,
 surface topography,
 geological condition of the ore and overlying rock mass ( it also includes the strength
condition of ore body as well as the surrounding rock type.
 time for development,
 method of mining (stoping)
 cost and choice of material handling system.

21. 21
Incline is not suitable for a deep seated ore body. Because with the increase in the depth of
ore body the haulage distance, at the required gradient, increases enormously and
proportionately the cost of material handling also increases. The cost of maintenance of the
inclined roadway increases. Though the rate of advance for incline/decline/drift are better
than sinking a shaft, with the advent of modern mechanized methods of shaft sinking can give
higher advance rates. Fully loaded ore trucks can travel up the incline and can travel straight
to ore dump. For shaft mine cars are to be loaded on a level via an ore pass and chute and
hauled to shaft. This system is not as flexible as trucks. However when a complete cost study
is made the use of inclines is never economical for deeper ore deposits.

22. 22
Fig . A-E different modes of access to deposits
Fig. Cross-section of a service shaft
Adit

23. 23
Source:
Surface
&
UG
excavations
Ratan
.R.
Tatiya
2013

24. 24
3.2 Secondary development
There are two categories of secondary development; first type is development in the nearest
proximity of the stope, like the stope access levels and the second type of development is
concerned to a stope or in-stope development. The in-stope development such as drill
headings and slot raises, horizontal and vertical openings for personnel access to stope, and
ore drawpoints from the stope. The life of drill headings, slot raises, draw points, sill & crown
is limited to life of the stoping. The openings, such as haulage levels and ore passes which are
developed near stress filed zone of a stope orebody rock. Their operation life approximates
that of adjacent stoping activity.
3.2.1 Levels and Level Interval
Level is an opening developed along the strike direction of an ore deposit and is driven with
zero to near zero (1 in 200) gradient. It is considered as the secondary mine development
operation of an underground metal mine, because it opens out the extent of mineralization
and thus a level offers a scope for a detailed evaluation of grade of the mineral deposit. Every
single underground mine developmental operation is a capital intensive and there is a
significant degree of risk, because any increase in the length of development openings could
augment high capital expenditures. In this respect mine development, involving levels and
their interval is an important operation. The levels also offer the service of transportation, for
men and material, from the shaft to the production site. Of the many factors influencing the
selection of a suitable level interval, the important factor is to facilitate quick disposal of
broken ore from the workings
3.2.1.1 Level intervals
Underground mining of ore deposits is necessarily worked with multiple levels. A level
interval is selected which lead to lowest overall mining cost for the mine development and
exploitation plan chosen. Number of factors affects these costs and some of them are
following:
• geological and natural conditions of the deposit and country rock
• method of mining
• development layout
• method of drivages of openings
• life of openings, mine life
• other financial considerations
The selection of optimum level interval is usually dependent on the development cost
(construction, supporting). Generally development cost increase with the number of main
levels required whereas exploitation cost as well as convenience of access for the miners
decrease with increasing number of levels. From the point of view of cost, a long interval
between levels is desirable. However in case of high grade ore deposits preclude higher level
intervals. The levels are placed at a closer interval to avoid missing high grade ore bodies.

25. 25
Speed of stoping and character of ground are related factors. Levels interval should be such
that stopes are completed and abandoned within the time that they can be kept open without
undue maintenance cost. In order to determine optimum level interval calculations of
development and exploitation cost for different assumed level intervals are made and plotted
graphically and the lowest overall mining cost point gives the optimum point as shown in
figure below. The current trend with mechanized high production method is to have fewer
levels with large level intervals and supplemented by less cost sublevels as required by the
stoping method adopted.
Fig Determination of optimum interval between levels for a hypothetical multi-level mine
Fig. Sublevel Open Stope
Exploitation
Development

26. 26
Fig. Stope developmental openings, ore draw points, slusher drifts.
3.3 Parameters considered in the design of stopes- tertiary openings
A stope, as shown below, is the site of ore production in an orebody. The set of stopes
generated during ore extraction usually constitutes the largest excavations formed during the
exploitation of the deposit. The stoping operation, that is, ore mobilization form it’s in situ
setting and its subsequent transportation from the mine void, forms the core of the mine
production process. In order that the stoping operations are safe it is essential to assess rock
performance within the orebody, and in the rock mass adjacent to the orebody. It ensures the
efficient geomechanical and economic performance of the individual stopes, and of the mine
as a whole. The size of stopes is large relative to all the other mine excavations. Therefore the
location, design and operational performance of other excavations connecting the stope and
the main access play a dominant role.
3.4 Raising Methods
3.4.1 Manual raising method
This is a simple and most common method adopted in majority of the metal mines.
The unit operations followed in the construction of a manual raise are:
 drilling and blasting
 mucking and transportation
 erection / construction of a manual platform or also known as scaffold
The workers stand on a platform or scaffold made of timber planks supported in stulls
or iron bars fitted into the footwall. The clamps used for supporting the platform are made in
standard lengths out of old rails.
Drilling & Blasting: Jackhammers / stoppers are used for drilling either wedge pattern or burn
cut pattern holes of 32 mm diameter and 1.5m deep. Before each round is blasted the
platform is dismantled. Immediately after blasting, compressed air is forced to the working
faces to remove the fumes of blasting. In longer raises sometimes a blower with a flexible air
duct is installed. Access to the faces is by a ladder way.

27. 27
Mucking & Transportation: The muck (ore if the raise in driven within the orebody, or a
waste rock if the raise is placed in foot-wall rock) based of ore or waste rock are trammed by
a mine car to the nearest grizzly.
Construction of a scaffold: The stoppers can reach a height of 2m and it facilitates the
construction of scaffold after every two rounds of drilling and blasting. The scaffold is
advanced regularly so as to maintain necessary head room at the face. The broken rock rolls
down by gravity. The scaffold is constructed by fixing steel bars into the holes drilled in the
side walls
Limitations: A simple but a very tedious method and has a limitation of comfortable raising
operations upto 15m. Careful checking and dressing down of the loose rock by skilled
workers before allowing workers to go up is essential At Jaduguda mine of UCIL where
this method of open raising was adopted for a number of stopes, the longest raise driven
was 90 m at 450 inclination.
Fig. Manual Raising method
3.4.1.1 Two compartment method
This method of raising is adopted for vertical or very steep raises only. After initial
excavation from the lower level on the direction of the raise for 2m the raise is divided into
two compartments and the follows a conventional driving methods
Raising with shallow holes is started by cutting out a recess at the bottom level, from which
subsequent operations are performed. Work is done from stage 1. After firing a round of
holes the stage rests on two or three stulls 2 temporarily set into holes made in the walls of
the raise. It consists of wooden planks laid over the stulls. Holes 3 are drilled from the stage

28. 28
by means of stoppers. After the drilling is completed the drilling equipment and the tools are
removed from the face and the holes are charged with explosives. Before firing, the ladder
way 4 of the raise is covered by inclined wooden planks 5 which guide the broken rock away
into rock, while standing under protection of the stage. Then the timber sets are erected and
the working stage is transferred closer to the face. As the face advances, the ladder
compartment is extended and equipped with ladders. Rope ladder 7 connects the upper
segment with the working stage.
The raising cycle comprises the following operations:
 inspection and dressing down of loose rocks,
 timbering extending the ladder way,
 construction of the working stage and drilling,
 removing the working stage,
 charging and firing of the blast holes, and
 clearing the smoke.
One of the drawbacks of the method of raising by firing shallow holes is the need for
performing a number of subsidiary tasks (like building the stages and ladder ways, their
extension, and repairs, etc.).
Fig. Fig. Two compartment method

29. 29
3.4.2 Mechanized Raising
Raising and winzing is one of the common development operations in underground metal
mines. These are vertical or sub-vertical connections between levels and are generally driven
from a lower level upward through a process called raising. An underground vertical opening
driven from an upper level downward is called a winze.
Raises with diameters of two to five metres and lengths up to several hundred metres are
often are developed either by manual and or mechanized methods, depending upon the size
and the extent of mechanization of a mine. The openings so created may be used as ore
passes, waste passes, or ventilation openings.
Earlier raising was done by manual method which was time consuming and hazardous.
Developments of raise climbers and raise boring machines have made the process faster and
safer.
The unit operations such as drilling blasting, mucking and erecting the support and surveying
for marking the centre line of a raise are done manually. The raising is done either dividing
the available area into two-compartments or a single chamber.
 height of raising is limited specially by conventional and raise climbers ladder
climbing and making platform is hazardous in conventional method
 potential hazard of rock falling
 surveying is difficult
In mechanical raise climber most of these difficulties are avoided and the most popular to this
kind are:
1. Jora raising method
2. Alimak raise climber.
3. Raising by long hole drilling
4. Raise borers
3.4.2.1 Jora raising method
Jora raising method is suitable only for the condition when two levels are available for
connectivity by a raise. The method consists of drilling a large diameter hole at the centre of
the intended raise to get through into the lower level (Fig. below). From the upper level a
cage is suspended using a flexible steel rope that can be hoisted up and down using a winch.
There is a working cabin also known as Jora cabin. The Jora cabin is provided with a sturdy
working platform on top of it, it is from this platform that the drill operators make the drill
holes.
Drilling: Usual practice is to follow parallel hole pattern and the central hole is used as a
relief hole. A stopper is used for drilling the holes of 34 mm diameter. Before blasting the
entire jora cabin is lowered to the lower level.

30. 30
Limitations:
1. One of the main limitations is that two levels are essential and arrangements are made
in both the levels.
2. The need to drill large diameter central hole for the hoisting rope.
3. Slow and a tedious operation.
4. Rate of advance is low.
1- Winch for rope; 2- winch skid; 3- drilling platform; 4- hoist rope;
5- Jora cabin; 6- steel rope; 7- Hole reel; 8- Drill hole for steel rope
3.4.2.2 Raising by Large Diameter Blast Holes
Top level
Bottom level

31. 31
Fig. Raising by Large Diameter Blast Holes
3.4.2.3 Alimak Raising:
Alimak raising is a mechanised blind raising method. It was introduced in mines way
back in 1957 and over the time it has proved to be economical, flexible, and a safe method of
raising for as long as 900 m. It can be used for vertical and inclined raises.
The machine along with a cage runs up and down on a guide rail that incorporates
rack and pinion gear mechanism (Fig. below). The guide rails are in segments and fastened to
the rock by rock bolts. They are extended as the raise advances.
The drilling operation is carried out standing on the platform after charging the holes
the cage is taken down at to a safe place for blasting the face. After the fumes clearance the
cage goes up again and guide rail extension is done. The blasted muck is removed.
Fig. Rack-and-pinion gear mechanism

32. 32
Alimak raising provides the safest of all entry methods involving the least risk to the
miner and can excavate safely through all types of ground conditions supporting the face after
each blast is taken ensuring the integrity of the excavation during all stages of development.
The Alimak raising system ensures fast mobilisation, minimal preparation, is flexible,
accurate, economical and very cost effective even over short distances. Even multiple raises
with directional changes in the raise of up to 90° can be carried out easily making this method
the ideal choice for ore passes, crusher chambers, split level ventilation raises or any difficult
excavation profile.
Alimak raise climbers are widely being used to drive shafts and raises in Mount Isa
mine Australia. Importantly the longest Alimak raise developed to date in these mines is
more than 1000m in length.
Fig. Preparatory work for installation of Alimak raise climber
Cycle of Operation
Step -1(Fig. a) –Drilling; Drilling is undertaken from the drill deck on top of the raise
climber, which is sized to suit the size, shape and angle of the raise. Drill machine is jack
hammer for drilling a 34 mm diameter and 2 m long blast holes. Burn-cut parallel blasting
patter in the common pattern used for raise blasting.
Step -2 (Fig b)-Loading: When drilling is completed the face is charged with explosives
along with MSD & HSD delay detonators. Of all the rounds, perimeter round is very

33. 33
important in raise blasting, and smooth blasting techniques are followed to contain over-
break.
Step-3 (Fig c)- The Alimak climber is then lowered to the bottom of the raise and into a
station for protection before the blast is triggered from a safe location.
Step-4: Ventilation: The Alimak system provides for efficient post blast ventilation and a
powerful air/water blast effectively dislodging loose rock from the freshly blasted face
making ready for re-entry.
Figure Steps of operation in Alimak raising method.

34. 34
This method has the following advantages:
 permits driving of long raises
 personal are well protected in a cage under the platform
 the miners work from the platform that can be easily adjusted for convenient height
 timbering is avoided and stability can be increased by rock bolting if necessary
 no danger from falling of rock pieces
However the cost and other arrangements required cannot justify this for short raises. Figure
above shows complete cycle of raising.
Special feature of Alimak raise climbers:
A. Drive Units:
The raise climber is developed with three kinds of drive units: air driven, electrically driven,
and diesel/hydraulically driven.
Of the different types of Alimak raise climbers, compressed air driven raising is very
common in the country, followed by diesel operated raise climbers are popular.
Air Driven:
In the air driven raise climbers, compressed air comes through a hose. An automatic winch or
reel winds the hose up and down as per the movement of the alimak in the raise construction.
The air motors are effective for raising up to 200m length.
Electrical drive:
Electric are not common in mines, however they have a capacity of driving about 1000m long
raises. The longest vertical raise for ventilation shaft at the Densison mines, Ontario, Canada,
in 1974 [SME-UMM Hand book].
Diesel / Hydraulic drive:
Diesel operated Alimak raises climbers are also common after the compressed air driven
machines. However there is a risk of excess air pollution due to diesel operated machines
underground. The diesel/hydraul;ic driven raise climber can drive more than 1000 m long
raises in one step.

35. 35
The figure above gives the scope and limitation of various types of Alimak raise climbers.
B. Safety features
For the types of Alimak raise climbers the following safety features make them more
adoptable in mines;
 Over speed control system; the permitted speed limits on descent are 0.9m/s, if the
climber exceeds this speed limit the automatic braking system stops the climber to
further descend.
 The rack-and-pinion gear plates are wielded to the guide rails thus ensure a guided
manoeuvring of the climber up and down the raise.
 The cross section of a guide rail is as shown in the figure below
(a) (b)
Fig (a). Cross-section of a guide rail; (b). Rack-and-pinion mechanism

36. 36
 The air, water supply is provided through the ports within the guide rail,
approximately 25m3
/min air supply is provided continuously at the face point. This
facilitates the operators with fresh air at the working face. There is a provision to
increase the air quantity as per the requirement.
 Telephone communication between the face crew and the bottom crew is provided by
an insulated wire passing through one of the ports in the rail.
 Blasting cable also runs through the port within the rail.
 A canopy is also provided for the safety of the face workers while scaling down the
loose material from the roof.
C. Initial guide rail sections
The guide rails for negotiating the curves are special made in angular sections, 80
, 250
, 250,
250
, 80
and having a radius of 2.3 ~3 m for vertical raises. The brow point is the point where
the cross cuts terminates into a vertical raise (Fig below), is slashed at 450
to accommodate
the circular guide rail segments.
RAISE BORING METHODS
Raise-Boring
In this system, the pilot hole is drilled down to a lower level in the mine or civil project. Once
the pilot hole connects to the lower access level in the rock, the drill bit is removed and a
reamer or raise head is attached and the reamer is rotated and pulled upwards. The broken
rock falls to the lower level by gravity. This system operates with the drill string in tension
and this provides the most stable platform.
Brow

37. 37
Figure. Raise Boring
Down-Reaming
In this system, the pilot hole is drilled downwards until it connects to a lower access level.
The drill string (all drill rods, stabilizers and cutting bits) is retrieved and then a reamer is
pushed downwards. The cuttings flow down the previously drilled pilot hole. This method
uses drill string in compression and usually stabilizers must be installed to eliminate the
potential of the drill string buckling.
Figure: Down Reaming method of raise boring

38. 38
Box-Holing
The most difficult raise method, known as Box-Hole excavation. It is to drill a pilot hole to
any level up from the raise borer. Once the desired length is achieved the drill string is
retrieved, and a reamer attached and pushed upwards. The broken rock falls down the
enlarged hole onto a special collection chute attached to the top of the raise borer. This
technique has been largely used to replace ladder rises, which completes the box-hole using
conventional methods. Ladder rise excavation is very dangerous
.
Figure. Box-holing method of raising.
ADVANTAGES OF BORED RAISES
 Raise boring offers several advantages over the conventional drill and blast method.
The most important are safety, speed, physical characteristics of the completed hole,
labour reduction and cost reduction. The safety factor in raise drilling cannot be over
emphasized. No men are exposed to the danger of rock fall from freshly blasted
ground or to the continual use of explosives, with their fumes and inherent danger of
misfires. Raises can be safely drilled in ground that would be extremely hazardous, if
not impossible, to drive by conventional methods.
 A hole drilled by Raise Boring Machine can generally be completed in a fraction of
the time required for conventional methods. The bored raise, with its firm undisturbed
walls, is more adaptable to use as ventilation and rock passes. As conventional
methods require a relatively large opening, it has become customary to drive raises
larger than actually required for ore and rock passes, a fact that long experience has
borne out. The advantage of smooth walls in ventilation raises is well known.

39. 39
 Raise boring will not only reduce labour requirements by achieving a higher advance
per day but, along with another technological advances, will have the tendency to
attract a higher level of skilled labour to the mining industry.
 Last, and probably most important from the long-range viewpoint, is cost reduction.
Although, it is true that the direct cost of conventional raises, especially short ones,
may currently be less in many cases, labour and material costs are continually
escalating and therefore their costs increasing. Skilled conventional miners, always in
short supply, are not required to operate a Raise Boring machine. Improved raise
drills, drilling techniques, pilot bit and cutters are lowering the cost of machine
excavated (RBM) raises. Less total manpower, less rock to handle, less construction
time and increased safety all add up to less costs and earlier projects.
Shaft Station
Underground mining operations involve deployment of different types of heavy duty rock
excavation and transportation machines. Some are electric power driven, others are diesel
operating machines. There are a few specialized openings such as bunkers, pumping station,
electric sub-station etc., at the bottom of the main shaft, and it is the horizon where the
vertical shaft intersects with horizontal openings. This is known as the shaft station.
The shaft station serves as the principal terminus of all underground and surface operations.
Those related to materials handling involve: skip loading pockets, retention bunker;
ventilation arrangements; pumping stations; electrical sub-stations; underground mechanical
shop / workshop; first aid centre & rest rooms etc.
The design considerations depend on the number of shafts within the station, type of deposit,
mode of materials handling in the mine and in the shaft, water inflow, ventilation
requirements, mining equipment, etc.
Fig. Standard shaft station layouts

40. 40
a-with circular mine traffic; b- with shuttle traffic; c- loop like layout of shaft staion;
1- Main shaft; 2- service shaft
Shaft station is an aggregate of working located in the immediate vicinity of the shaft. These
are provided to afford connection between a shaft and the different levels in a mine. Their
primary use is to tenable men and material to be delivered at the different working horizons
and for raising the ore. The size of the station will depend on the size and amount of material
that it will be required to accommodate.
Generally the longer the life of a mine and larger the output the shaft station becomes more
complex. Some of the factors that are considered for design of shaft station are:
 Type of deposit
 Mode of material handling in the mine
 Hoisting of ore in the shaft
 Water inflow and ventilation
 Mining equipment
Shaft stations related to the material handling are skip loading pockets, retention bunkers
pump chamber, explosive storage chamber, locomotive room and sometimes primary
underground crusher. These chambers are important link in the extraction process, transport
etc. They are located near the main or auxiliary shaft because of their functions.
The first group of chambers includes explosive storage, pump house, miners’ rest room
where as locomotive repair and clearing, dispatcher rooms are related to the transport. The
construction of shaft station chamber is made by conventional drilling and blasting method
taking into consideration of ground conditions. These chambers are properly supported by
bolting, grouting etc.
Question
Explain with a neat sketch a shaft with skip hoisting system for a production level of say,
1200 tpd . Show the surge bin, loading pocket, measuring hopper excavated and installed in
the shaft station label the sketch ?
Answer
The shaft stations in hard- rock mines for material handling arrangement will have the
following:
1. Skip loading pockets,
2. Retention bunkers
3. Pump chambers
4. Main power station
5. Explosive storage chamber
6. Locomotive room
7. Mechanical & electrical workshop
8. Dump (ore/waste) chamber – with bunker & u/g crusher.

41. 41
9. Arrangements for the type of ore/waste transport system ( eg: belt; train)
1- Access drift to waiting room; 2- basement for two-level traffic and swinging platforms;
3- Basements for pushers and barrages (blocking cars); 4- a slot for control equipment
Fig. Inset of cage shaft with three levels to step in and out for crew.
The size of the inset of a cage shaft depends on the width and number of cages being hoisted
on this level, number of decks in cages, and length of the supplies to be delivered. Depending
on the skip loading system and horizontal transportation arrangements, there could be the
following sets of openings for loading facilities:
1. For rail transport :
a. Dump(tippler) chamber or unloading ramp (for Granby cars), batchers chambers( this
for accommodating a batch or a train of mine cars), skip chamber
1-Skip chamber; 2- batcher chamber; 3.- tippler chamber; 4- basement of shifting mechanism; 5- basement of
braking system; 6- drive slot; 7- electrical equipment slot; 8- ventilation slot.
Fig. Connection of production skip shaft with the opening of loading system for rail transport system.

42. 42
b. Dump(tippler) chamber or unloading ramp (for Granby cars), retaining bunker, loading
devices chamber, batchers chambers( this for accommodating a batch or a train of mine
cars), skip chamber
1- Skip shaft; 2- skip chamber; 3- batchers chamber; 4- switches chamber 5- loading chamber; 6- retaining bunker; 7-
distribution chamber; 8- distribution ramp; 9- drift for clearing away jams; 10- chute
Fig Connection of production skip shaft with the openings of the loading devices for horizontal rail transport.
c. For belt transport: unloading chamber, retaining bunker, loading chamber, batchers
chambers( this for accommodating a batch or a train of mine cars), skip chamber
1. Skip shaft; 2- skip chamber; 3- belt scale ; 4- retaining bunker; 5- unloading chamber.
Fig. Connection of production skip shaft with the opening of loading devices for horizontal belt
transport system.

43. 43
Lecture 4- Stope Development
Once the economic extraction of ore body is ascertained, the step follows next is
development and preparation stope for extraction or ore. The development of an ore drift
(cross-cut) will confirm the thickness (extent of orebody) and continuity of the ore body and
enable the planners to finalize stope design.
Different development configurations and construction arrangements are possible for ore
body geometry. The stope preparation involves development of haulage level and sill-level.
This approach allows the development of draw points (figure below)
Fig Plan view of development of ore and footwall drives.
Draw points are developed at the bottom of open stopes as an inverted cone by drilling and
blasting. Their form is determined by the way in which the ore is to be loaded.
A large chute can be used to load ore from a main ore pass into a dump truck or smaller
chutes can be installed on each of several ore passes along a level to load directly into mine
cars.
Figure shows ore loading chutes. Chutes cause production holdups if they become blocked by
large pieces and to exclude the large pieces from coming to chute, ore is fed through grizzly
which has a grating made up of steel bars. Lumps which do not fall through grizzly are
broken with hammer of pneumatic pick.
Fig. Ore loading chutes

44. 44
The figure below shows a typical draw point configuration for LHD/Shovel loading draw
point. In this configuration the draw points are usually 10m long and driven perpendicular to
the haulage-way to facilitate ore loading into mine cars. The interval of draw points is around
10m apart. The dimensions of these draw points are selected considering the ease of loading.
The draw point around the mouth or the entrance of the stope requires a lower back to
establish a brow that will prevent ore from spreading too far into the draw point.
Fig. LHD/ Rocker shovel draw points
T
Plan view of the draw point with track system of transportation

45. 45
Fig. Cross section of a draw point configuration-track system of transportation
Another form if scram (also known as scraper) driven draw point. Ore is broken in the stope
and gravitates down into the drive. A scraper bucket is used in the drive to scrape ore and
drop it down through a grizzly down a mil hole into mine cars. Figure shows a scram driven
draw points and mill holes. Another from is to load ore from a stope by a mucking machine,
figure showing LHD draw points.
Fig. Scram drive points and ore draw points
In some mines construction of individual draw points for open stopes in not carried out. The
stope bottom is percussive drilled from the draw point level and blasted into a continuous v-
shape. Broken ore is loaded out from the bottom drive as it comes down. It is still necessary
to drive a raise to form an initial cut-off slot. Figure shows v-shaped draw point. A sill pillar
is left horizontally around and above the level drive to protect them and provide height to
develop draw points. As stopes are worked upwards to meet the level above a horizontal
crown pillar is left below the level above to stope them from collapsing.
Stope development thus includes haulage drifts cross cuts drifts, chutes and draw points,
raises. The size of the development is dependent on the equipment and winning methods to
be used. Minimum development requirements for a typical ore body include a drift from the

46. 46
main haulage to the ore body, raising into the ore body, driving the stope sill and finally
installing draw points and chutes.
Fig Draw point

47. 47
Fig . Mechanised ore loading methods
Ore pass system
Ore passes are underground passageways for the gravity transport of broken ore, waste rock
from one level of a mine to a lower level. Inclination of ore pass varies widely within a range
of 450
-900
, and most common angles are 700
and cross sections are mostly circular. Besides
transport of ore it also sometimes serves as a storage which is required for efficient mines
operation. Ore pass length range from 10 m to 200m or more
The components of ore pass system include: (1). a raise connecting two or more levels, (2).
Top-end facilities for material size and volume control such as grizzles, crusher and (3).
bottom end structures to control material flow.
Unlined ore pass may be located in country rock (FW) but some mines are lining ore-passes
with steel fibred-reinforced shotcrete. The bottom of the ore-passes at the haulage level
usually contains a loading chute equipped with pneumatic / hydraulic operated gates. The ore
is loaded in to tubs and a train of tubs then dump the ore in the main ore-pass which is usually
located at a haulage shaft.

48. 48
Fig. Schematic of an ore-pass: tip section; discharge zones.
In mechanized stopes the ore is removed from the stope by LHD units and is dumped at the
stope ore pass for handling at the lower level from where it is transported and dumped in the
main ore pass. The main ore pass are developed within the ore body rock or within the ore
body peripheral rock. Their operational life approximates that of adjacent stoping activity and
in some cases the excavations may be consumed in the stoping process.
Proper design of ore pass requires that the broken ore, waste rock will flow when the outlet is
activated. The flow process is driven by gravity and resisted by friction and cohesion. Proper
design will see that their malfunctions of ore pass operations are to be prevented: failure to
flow resulting in hang-ups and failure to flow over the entire cross-section of the ore pass
referred to as piping. The other important design consideration is the stability of ore pass
walls.
Ore pass construction
Ore pass systems are an integral part of the materials handling system in the majority of
underground mines. Ore passes are developed using either mechanical (raise borer) or drill
and blast techniques (Alimak, conventional raising and drop raising). The conventional
manual method of raising is slowly being replaced by Alimak raising. In Quebec mines,
Alimak raising was used in 63% of driven ore passes while only 3% were raise bored. The
dominance of Alimak driven passes over raise bored passes in Quebec mines is attributable to
several causes. It ensures a reasonable degree of safety for the miners, while still allowing the
installation of support. Furthermore, the ability to drive the Alimak pass from a single access

49. 49
(as opposed to raise boring, which requires that both the bottom and top accesses be
developed) and a strong expertise of local mining contractors are also contributing
factors.Conventional and drop raises represent 29% and 5% of the sections, respectively (Ref:
Ore pass practice in Canadian mines by J. Hadjigeorgiou, J.F. Lessard*, and F. Mercier-Langevin; The
Journal of The South African Institute of Mining and Metallurgy vol. 105 Dec. 2005). The dominance of
Alimak raising is attributed to several reasons. It ensures a reasonable degree of safety for the
miners, while still allowing the installation of support. Furthermore, the ability to drive the
Alimak in blind raises (as opposed to raise boring, which requires that both the bottom and
top accesses be developed) and it provides comfortable working environment at the face.
Table Case example of U/G mines of Lead & Zinc Quebec, Canada
(Ref: Ore pass practice in Canadian mines by J. Hadjigeorgiou, J.F. Lessard*, and F. Mercier-Langevin; The Journal of The South African
Institute of Mining and Metallurgy vol. 105 Dec. 2005).
Ore pass section length

50. 50
There is an inherent relationship between the type of excavation method and section length.
Typically, sections excavated by drop raising or conventional rising are shorter than sections
driven by Alimak or raise borers.
There are several practical and financial considerations that influence the selection of an ore
pass length. If, for example, an operation aims to minimize its capitalized development, it
will end up driving short ore pass sections, going from one level or sub-level to the next,
concurrently as the various levels are entering into production. Quite often a mine that
experienced problems when driving and operating long sections will subsequently opt for
shorter sections when constructing new ore and waste passes. An excavation of greater length
is more likely to intersect zones of poor ground. It also has a higher potential for problems
and is harder to bypass. Longer sections may also result in higher material flow velocity in
passes operated as flow-through.
Ore pass section inclination
Ore pass inclination varies between 45° and 90°, with an average inclination of 70°. The
choice for a particular inclination is dictated by the need to facilitate material flow. Shallow
sections may restrict flow, especially if a high proportion of fine material is present, while
steeper excavations result in higher material velocities and compaction. It should be noted
that all vertical sections are shorter than 100 m. Generally steep ore passes (80º ± 8.3º) are
advantageous because it ensures continuous material flow and limit hang-up occurrences.
Ore pass section shape
The majority of excavated ore passes are square or rectangular. Circular sections are usually
associated with raise boring methods but in some instances, circular sections were excavated
using Alimak. In most cases, the main factor indicating the choice between a rectangular and
a square section is local mine experience. Circular shape was used based on anticipated
higher stress regimes. It is of interest to note that a review of ore pass surveys reveals that
under high stress, and with material flowing in an ore pass, a design circular shape is not
maintained for long (in unlined ore passes). Ore pass size is an important factor influencing
material flow. This is reflected in empirical guidelines linking the potential for hang-ups with
ore pass size and material size. A common dimension of 2.0 m is widely used, however there
are some mines where a relatively larger cross-sectional dimension of 2.5 ± 0.6 m have also
been adopted.
Finger raises
Finger raises are used to funnel material into a pass intersecting two or more production
levels. Typically, a finger raise is a square opening with a smaller cross-sectional area than
the rock pass it feeds. The most common dimensions for a finger raise are 1.5 and 1.8 m.

51. 51
Screening of oversize material
Oversize material dumped into the passes may lead to blockages or interlocking hang-ups.
This can be avoided by either instructing the mucking crew or by installing the necessary
infrastructure to restrict the entrance of the oversize material.
The mechanical method of retaining oversized material at the mount of an ore-pass is by the
installation of a grizzly. Sometimes mucking crews can be ‘persuasive’ in trying to push the
block through the bars with the bucket. This practice damages both the bars and the scoop.
Broken and missing bars are often the result of this practice. In addition, the intrusion of a bar
in the ore pass can lead to severe obstruction further down the system. Grizzlies are the best
to keep big blocks out of the passes. Grizzlies require less maintenance than scalpers.
Reinforcement
Resin-grouted rebar constitutes the most popular reinforcement type for ore pass systems.
Nevertheless, the most recently developed excavations are reinforced by resin grouted short
cable bolts. An ore pass section is considered to have ‘failed’ if it had expanded to twice its
initial volume as recorded in the original layout.
Ore pass problems
Analysing the causes of degradation is a complex process due to the potential interaction of
several mechanisms. There is a relationship between the material unit weight and the degree
of observed degradation of the walls of the ore pass. A qualitative assessment of the dominant
degradation mechanisms include: structural failures facilitated by material flow; scaling of
walls due to high stresses; wear due to impact loading caused by material flow; wear due to
abrasion and blast damage caused by the hang-ups clearing methods.
Wall damage attributed to impact loading is most often localized at the intersection of finger
raises to the ore pass. It is most probable that the presence of structural defects in the rock
mass accentuates the influence of impact loading, resulting in more pronounced degradation.
The use of ‘rock boxes’ can reduce impact damage but in most cases impact damage is
localized on the ore pass wall facing the finger raise. Abrasion rate depends on the
abrasiveness of the material and the ore pass walls’ resistance to abrasion.
Blockages
Blockages are the most commonly encountered type of flow disruption in ore pass systems.
Flow disruption near the chute may be due to blocks wedged at the restriction caused by the
chute throat. Another source of problems is caused by the accumulation of fine or ‘sticky’
material in or near the chute, on the ore pass floor. This reduces the effective cross-sectional
area and results in further blockages.
Material flow problems

52. 52
Some types of material flow problems are reported in every mine operating an ore pass
system. Sometimes the transfer of coarse material can result in hang-ups due to interlocking
arches, while the transfer of fine material results in hang-ups due to cohesive arches,
Hang-ups
Restoring material flow is a priority in operating mines. There are several methods to restore
the material flow in case of a material hang-up with in the ore pass and they can be classified
as those that employ water and those that rely on explosives,
Most hang-ups lower than 20 m are brought down by attaching explosive charges on wood or
aluminium poles used to push the charge up to the hang-up. As a last resort, holes drilled
toward the hang-up can be driven and explosive charges set inside the hole, near the supposed
hang-up location. If the location of the hang-up is not clearly identified, it may take more
than one attempt to restore flow.
Cohesive hang ups are difficult to dislodge using explosives. Some operations resort to
blowing compressed air through a PVC pipe raised up to the hang-up location or dumping a
predetermined amount of water from a point above the hang-up. All mines have strict
procedures about the use of water in order to avoid the risks of mud rushes.
Fig. Hang-ups in an ore pass due to (a) interlocking; (b). cohesion arching,

53. 53
Fig. . Damage zones in an ore pass.
ORE PASS DEGRADATION DUE TO IMPACT
(ref: Influence of finger configuration on degradation of ore pass walls K. Esmaieli Université Laval, Quebec City, Canada J. Hadjigeorgiou
University of Toronto, Toronto, Canada; ROCKENG09: Proceedings of the 3rd CANUS Rock Mechanics Symposium, Toronto, May 2009 ;
Ed: M.Diederichs and G. Grasselli)
In ore pass systems gravity movement of rock includes rolling, sliding and inter fragment
collision. The interaction of moving material and ore pass walls can result in the development
of wear and/or impact damage zones. Wear is associated with the particles rolling and sliding
along a surface resulting in the scouring of the wall surface. Damage attributed to impact
loads can be caused by single falling boulders in the ore pass, a stream of rock or a large mass
of material, Iverson et al. (2003). The mechanical properties of the rock mass along the ore
pass wall can influence the extent of damage. Stacey & Swart (1997) note that wear of ore
pass walls is greater in weak rock material and in the presence of stress scaling. If the ore
pass is located in a rock mass with structural defects the action of moving material can
initiate further wall degradation, including falls of ground. Ore pass wall damage, induced by
impact, is one of the most important mechanisms of ore pass degradation. This paper reports
on-going work, using numerical models, on the influence of material impact for several ore
pass and finger raise configurations.
Figure above illustrates a typical finger raise - ore pass configuration. Hadjigeorgiou et al.
(2005) report that, in Canadian underground mines, finger raises have cross section
dimensions of 1.5 m x 1.5 m and 1.8 m x 1.8 m. The fingers are linked to ore passes of larger
cross section dimensions. A well designed finger raise can minimize the ore pass wall
damage and maximize ore pass longevity. Current practice is often based on empirical rules
which quite general and may not always be appropriate for site specific conditions. Empirical
guidelines recommend an inclination of 60o
for finger raises in order to ensure free flow of
rock fragments in the finger raise. This recommendation may not be valid for all the

54. 54
conditions. The finger raise inclination influences the motion and interaction of rock
fragments flowing in the ore pass and the resulting load on the ore pass wall. If the finger
raises are steep this will result in higher impact velocity on the ore pass walls. On the other
hand if the finger inclination is shallow material flow is slow and can result in hang-ups. A
steeply inclined finger raise results in narrower pillars at the intersection of the ore pass and
finger raise which are more susceptible to stability problems. Consequently an operational
design will use a finger raise inclination that will minimize impact load on the ore pass wall
while maintaining material flow in the finger.
It has been demonstrated that particle impact velocity and kinetic energy increase with finger
raise inclination. The impact duration decrease with increase of finger inclination. These
observations can be used to evaluate different options of finger inclination for any particular
ore pass inclination. The analysis clearly demonstrated that the choice of intersection angle
has a significant influence on the resulting impact loads on the ore pass wall and the location
and magnitude of damage to the ore pass. The highest impact loads were reported for
intersection angles of 1400
and 1450
.
Q. Explain the gravity ore transportation methods in u/g metal mines
Fig. Ore pass system in Mount Isa Copper Mines –Australia (Ref.L.J.Thomas Intro. to mining)

55. 55
Lecture 5 Factors influencing the selection of a suitable stoping method
The following factors are considered in selecting a suitable method of stoping operation.
1. Mining excavations and their importance in terms of the life term of a mine
2. Rock mass response to stoping activity
3. Spatial distribution of the ore-body
4. Disposition and orientation
5. Size
6. Geomechanical setting
7. Ore body value and spatial distribution of value
8. Engineering environment.
1. Mining excavations and their importance in terms of the life term of a mine
The three types of openings are employed in the mine operation, these are the ore sources, or
stopes, the stope access pathways, or the levels, cross cuts; and the main mine service
openings – shafts, inclines, declines, or adits. The geomechanical performance of these
different types of openings is specific to the function of the opening. Based on their function
and the life term of these openings, they are categorized as:
 Primary openings - shafts, inclines, declines, or adits, these are the permanent
openings in comparison to the other two types
 Secondary – levels, cross cuts, raises & winzes, drifts, etc., - these are semi-
permanent openings, their life terms is relatively less compared to the primary
openings.
 Tertiary openings: stopes or the source of ore – the main production zone. The life
term of the stopes is the shortest of the three above openings.
Stopes:
A mine has a large number of stopes therefore; a set of stopes constitutes the largest
excavation underground. The stability of stopes is controlled not only by the orebody strength
condition but also on the strength of the peripheral rock (HW and FW) the principles of stope
layout and design are integrated with the set of engineering concepts (like the rock
mechanics) and physical operations (such as mine transportation of the ore and waste) which
together compose the mining method for an orebody.
It is a commonly held belief amongst underground mine planning and design engineers
that in a sub-level open stoping mine, the bigger the stopes – up to the geotechnical limits –
the greater will be the production rate and hence, the more cost efficient the mine. This paper
shows that this can be a fallacy – it is usually true for the individual stope but may not be true
for the mine when considered as a system of inter-related stopes.
In a fixed size orebody there is a limit in the production rate achievable which in turn is
related to the number of active stopes, in the sense that the stopes are in some phase of the
stope development cycle (preparation, production, filling or curing) at a given time frame.
Once this limit is reached, there are no more stopes that can be brought into production. This
is a physical constraint, which places a limit on the production rate achievable for the stoping

56. 56
system. However, this constraint, the number of stopes, can be changed. This can be
accomplished by either altering stope size or cut-off grade.
Fig. Division of the ore body into active workable stopes based on grade value
Fig. Longitudinal section of a mine

57. 57

58. 58
2. Rock mass response to stoping activity
The extraction of mineral resources involves rock excavations of different shapes, sizes, and
orientation based on the purpose for which the excavation is made. And it is obvious on the
creation of an opening (stope / drive) the state of equilibrium in the surrounding rock is
disturbed and the redistribution of the induced stresses is dependent on the type of rock mass,
size of the opening and method of excavation.
The dimensions of ore bodies of mining significance typically exceed hundreds of meters in
at least two dimensions. During excavation of an orebody, the spans of the individual stope
excavations may be of the same order of magnitude as the orebody dimensions. The
performance of the host rock mass during mining activity can be easily measured in terms of
the displacements of orebody peripheral rock. It is clear from the studies of stresses around
mine openings, the zone of influence is usually taken as 3dm, where dm is the minimum
dimension of the opening. The zone of influence is considered as the near field zone and the
zone outside this is termed the far field zone.
The rock mass response to stoping operations is dependent on the inherent strength of the
rock. Therefore on the basis of its response, a rock mass can be categorised into a class of
competent (strong and self-supporting) and in-competent (weak and crushing & crumbling
type of rocks). There are many rock types which fall in between these two extremes.
Therefore there can be stoping methods which are self-supporting, and a few stoping methods
need some artificial supporting and lastly there can be some which cannot be supported, such
stopes are left to crumble and cave down.
Fig. Rock mass response to mining
 The supported methods of working can succeed only if the induced stresses are less
than the strength of the near-field rock. Caving methods can proceed where low states
Underground mining methods
Pillar supported Artificially supported Unsupported
Room &
Pillar
Sublevel
Long hole
Open
stoping
Cut-and-Fill Shrinkage VCR Sub Level
Caving
Block
caving
Magnitude of displacement in country rock
Strain Energy storage in near-field rock
Rock mass response to Mining

59. 59
of stress in the near field can induce discontinuous behaviour of both the orebody and
overlying country rock, by progressive displacement in the medium.
 In supported methods, since the strength of the rock mass in higher, they exhibit the
ability to store more strain energy in comparison to the caving methods.
 For caving method prevents the accumulation of strain energy by continuous
dissipation of pre-mining energy by fracturing.
 Fully supported stopes may completely depend on natural support in the initial
stoping phase, using ore body remnants as pillar elements. In the early stages of pillar
recovery, various types of artificial support may be placed in the mined voids, to
control local and regional rock mass displacements. In the final stages of pillar
recovery, pillar wrecking and ore extraction may be accompanied by complete failure
of the adjacent country rock. This change in the state from one geomechanical basis to
another can have important consequences on the performance of permanent openings
and other components of a mine structure. This indicates that the key elements of a
complete mining strategy for an orebody should be established before any significant
and irrevocable commitments are made in the pre-production development of an
orebody.
3. Spatial distribution of the ore-body
This property defines the relative dimensions and shape of an orebody. It is related to the
deposit’s geological origin. Ore bodies described as seam, placer or stratiform (strata-bound)
deposits are of sedimentary origin and always extensive in two dimensions. Veins, lenses and
lodes are also generally extensive in two dimensions, and usually formed by hydrothermal
emplacement or metamorphic processes. In massive deposits, the shape of the orebody
is more regular, with no geologically imposed major and minor dimensions. Porphyry
copper ore bodies typify this category. Both the orebody configuration and its related
geological origin influence rock mass response to mining, most obviously by direct
geometric effects. Other effects, such as depositionally associated rock structure, local
alteration of country rock, and the nature of orebody–country rock contacts, may impose
particular modes of rock massbehaviour.
4. Disposition and orientation
These issues are concerned with the purely geometric properties of an ore body, such as its
depth below ground surface, its dip and its conformation. Conformation describes orebody
shape and continuity, determined by the deposit’s post-emplacement history, such as episodes
of faulting and folding. For example, methods suitable for mining in a heavily faulted

60. 60
environment may require a capacity for flexibility and selectivity in stoping, to accommodate
sharp changes in the spatial distribution of ore.
5. Size
Both the absolute and relative dimensions of an ore body are important in determining an
appropriate stoping method. A large, geometrically regular deposit may be suitable for
mining using a mechanized, mass-mining method, such as block caving. A small deposit of
the same ore type may require selective mining and precise ground control to establish a
profitable operation. In addition to its direct significance, there is also an interrelation
between ore body size and the other geometric properties of configuration and disposition, in
their effect on mining method.
6. Geomechanical setting
The geo-mechanical setting includes:
 Rock material properties such as strength, deformation characteristics (such as
elastic, plastic and creep properties) and weathering characteristics.
 Rock mass properties are defined by the existence, and geometric and mechanical
properties, of joint sets, faults, shear zones and other penetrative discontinuities.
 The pre-mining state of stress in the host rock is also a significant parameter.
In addition to the conventional geomechanical variables, a number of other rock material
properties may influence the mining performance of a rock mass. Adverse chemical
properties of an ore may preclude caving methods of mining, which generally require
chemical inertness. For example, a tendency to re-cement, by some chemical action, can
reduce ore mobility and promote bridging in a caving mass. Similarly, since air permeates a
caving medium, a sulphide ore subject to rapid oxidation may create difficult ventilation
conditions in working areas, in addition to being subject itself to degradation in mechanical
properties.
Other more subtle ore properties to be noted are the abrasive and comminutive properties of
the material. These determine the drillability of the rock for stoping purposes, and its particle
size degradation during caving, due to autogeneous grinding processes. A high potential for
self-comminution, with the generation of excessive fines, may influence the design of the
height of draw in a caving operation and the layout and design of transport and handling
facilities in a stoping operation.
In some cases, a particular structural geological feature or rock mass property may impose a
critical mode of response to mining, and therefore have a singular influence on the
appropriate mining method. For example, major continuous faults, transgressing an orebody
and expressed on the ground surface, may dictate the application of a specific method, layout
and mining sequence. Similar considerations apply to the existence of aquifers in the zone of

61. 61
potential influence of mining, or shattered zones and major fractures which may provide
hydraulic connections to water sources. The local tectonic setting, particularly the level of
natural or induced seismic activity, is important. In this case, those methods of working
which rely at any stage on a large, unfilled void would be untenable, due to the possibility of
local instability around open stopes induced by a seismic event. A particular consequential
risk under these conditions is air blast, which may be generated by falling stope wall rock.
7. Orebody value and spatial distribution of value
The monetary value of an orebody, and the variation of mineral grade through the volume of
the orebody, determines both mining strategy and operating practice. The critical parameters
are average grade, given various cut-off grades, and grade distribution. The average grade
determines the size and monetary value of the deposit, since the market price for the mineral
changes with time and demand.
The significance of dilutions of the ore stream, arising, for example, from local failure of
stope wall rock and its incorporation in the extracted ore, is related to the value per unit
weight of ore. In particular, some mining methods are prone to dilution, and marginal ore
may become uneconomic if mined by these methods. Grade distribution in an orebody may
be uniform, uniformly varying (where a spatial trend in grade is observed), or irregular
(characterized by high local concentrations of minerals, in lenses, veins or nuggets). The
concern here is with the applicability of mass mining methods, such as caving or sublevel
stoping, or the need for complete and highly selective recovery of high-grade domains within
a mineralized zone. Where grade varies in some regular way in an orebody, the obvious
requirement is to devise a mining strategy which assures recovery of higher-grade domains,
and yet allows flexible exploitation of the lower-grade domains.
Engineering environment
8. Engineering Environment
A mining operation must be designed to be compatible with the external domain and to
maintain acceptable conditions in the internal mining domain. Mine interaction with the
external environment involves effects on:
 Local groundwater flow patterns, changes in the chemical composition of
groundwater,
 Possible changes in surface topography through subsidence. In general, caving
methods of mining have a more pronounced impact on subsidence than supported
methods.
 Mine gases such as methane, hydrogen sulphide, sulphur-dioxide, carbon dioxide or
radon may occur naturally in a rock mass, or be generated from the rock mass during
mining activity.

62. 62
In fact, stope backfill generated from mill tailings is an essential component in many mining
operations. Specific mining methods and operating strategies are required to accommodate
the factors which influence the mine internal environment.
Problems
Q1. Discuss the effects of rock mass response to stoping?
Q2.Explain how rock mass movement due to stoping affect ore dilution in different
stoping operations?
Answer:
Dilution is defined as the low grade (waste or backfill) material which comes into an ore
stream, reducing its value. By-and-large, dilution control may be more difficult in the caving
methods where displacements of large magnitudes within the host rock are experienced.
Artificially supported mining methods rely on achieving close control of the performance of
the rock mass surrounding a stope. Cut and fill relies on passive support from the applied
backfill, while shrink and VCR stoping use the broken ore as a temporary support for the
stope walls. Shrinkage stopes can be susceptible to external dilution due to time dependent
failure of the exposed walls, while excessive damage (external dilution) to the stope walls can
be experienced during VCR mining, specially when used for pillar recovery.
The success of naturally supporting methods such as sublevel open stoping (for large tabular
and massive ore-bodies) relies on achieving large stable and mostly unsupported stope
boundaries. The stand-up time before backfill support is introduced as well as support
provided by cable bolting is also an important factor controlling stability.
(Source of information: Ernesto Villaescusa)
Q3.What technical information is needed for preliminary mine planning?
Answer:
Many details must go into the planning of underground mine and information must come
from several sources. Geological, structural, and mineralogical information must first be
collected and combined with data on resources and reserves. This information leads to the
preliminary selection of a potential mining method and sizing mine production.
The following information should be gathered during the exploration phase and passed on to
the mine evaluation team of the mine development team. The information is:
 Property location and access
 Description of surface features
 Description of regional, local, and mineral deposit geology
 Review of exploration activities
 Tabulation of potential ore reserves and resources

63. 63
 Explanation of ore-reserve calculation method
 Description of company’s land position
 Description of the company’s water position
 Ownership and royalty conditions
 History of the property
 Any special studies by the exploration team
 Any social issues or environmental issues that have surfaced while exploration was
being completed.
Q4. What specific planning is required related to physical properties of the ore body
and surrounding ground?
Answer:
The physical nature of the extracted rock mass and the rock mass left behind are very
important in planning many of the characteristics of the operating mine. Four aspects of any
mining system are particularly sensitive to rock properties.
(a). the competency of the rock mass in relation to the in situ stress existing in the
rock determines open dimensions of unsupported roof unless specified by
regulations. It also determines whether additional support is needed.
(b). When small openings are required, they have a great effect on productivity,
especially in harder materials for which drill and blast cycles must be used.
(c). The hardness toughness and abrasiveness of the material determines the type
and class of equipment that can extract the material efficiently.
(d). If the mineral contains or has entrapped toxic or explosive gases, the mining
operation will be controlled by special provisions in mine regulations.

64. 64
Chapter 5 Mining Methods
The emphasis is confined to the relations between working method, the rock mass conditions
essential to sustain the method, and the key orebody properties defining the scope for
application of the method. The mining methods commonly employed in industrial practice
are classified as shown below. Other mining methods, mostly of historical or local
significance, such as top slicing or cascade stoping, could be readily incorporated in this
categorization. The gradation of rock performance, ranging from complete support to induced
failure and granular flow, and in spatial energy change from near-field storage to far-field
dissipation, is consistent with the notions discussed earlier.
Classification of stoping methods based on the strength of the rock mass
A. Naturally supported stopes
1. Open stoping with pillar supports
a. Room-and-pillar stopes
 Room-and-pillar with regular pillars
 Room-and-pillar with irregular pillars
2. Open stopes
a. Sub-level open stoping
b. Large Diameter Blast Hole stoping (Long hole stoping)
B. Artificially supported stopes
3. Shrinkage stoping
a. With pillar (post pillar)
b. Without pillars
c. With subsequent back filling
4. Cut-and-fill stoping
a. Horizontal cut-and-fill stoping
b. Post pillar cut-and fill stoping
5. Vertical Crater Retreat – with back filling
6. Square set stoping
C. Caved stopes
7. Sub-level caving
8. Block caving
A summary of factors for each U/G mining method, including the suitable orebody
geometries, orebody grades, orebody and country rock strengths, and depths are shown in
Table 1.

65. 65
Table 1: Summary of geotechnical factors for each underground mining method
Method
Class
Method
Relative
magnitude of
displacements
in country
rock
Strain
energy
storage
in near
field rock
Suitable
orebody
geometry
Suitable
orebody
grade
Suitable
orebody,
country rock
strength
Suitable
depth
Pillar
supported
Room-and-pillar Very low
Very high Tabular,
maximum
dip 55°
High
Both strong
and
competent,
low frequency
of cross
jointing in
roof
Shallow
Pillar
supported
Sublevel open
stoping
Very low Very high
Massive or
steeply
dipping
stratiform,
regular
boundary
Moderate
Must be
sufficient to
provide stable
walls, faces,
and crown for
stopes
Variable
Artificially
supported
Cut-and-fill Low High
Veins,
inclined
tabular,
massive;
35-90° dip
High;
variable
with lenses
is
acceptable
Competent
orebody, can
be weaker
country rock
Shallow
or deep
Artificially
supported
Bench-and-fill Low High
Narrow
vein
mining
High
Competent
orebody, can
be weaker
country rock
Shallow
or deep
Artificially
supported
Shrink stoping Moderate Moderate
Narrow
extraction
blocks;
veins,
inclined;
tabular,
massive
High;
variable
with lenses
is
acceptable
Competent
orebody (and
resistant to
crushing), can
be weaker
country rock
Shallow
or deep

66. 66
Artificially
supported
VCR stoping Moderate Moderate
Minimum
3 m width
orebody;
veins,
inclined
tabular,
massive
High;
variable
with lenses
is
acceptable
Competent
orebody (and
resistant to
crushing), can
be weaker
country rock
Shallow
or deep
Unsupported Sublevel caving High Low
Steeply
dipping ore
bodies
High
enough to
sustain
dilution
(perhaps
>20%)
Reasonably
strong
orebody rock
enclosed by
weaker
overlying and
wall rocks
From
shallow
to deep
Unsupported Block caving Very high Very low Large ore
bodies
where
height
>100 m
High
enough to
sustain
dilution
Rock mass of
limited
strength, with
at least two
prominent
sub-vertical
and one sub-
horizontal
joint set
Shallow
or deep
1. Naturally Supported Method- Room-and-Pillar Mining
A mining method based on natural support seeks to control the rock mass displacements
through the zone of influence of mining, while mining proceeds. This implies maintenance of
the local stability of the rock around individual excavations and more general control of
displacements in the near-field domain. (Ref: Brady & Brown1993).
Conditions
• Ore strength: weak to moderate
• Host rock strength: moderate to strong
• Deposit shape: massive; tabular
• Deposit dip: low (< 35 degrees), preferably flat
• Deposit size: large extent – not thick
• Ore grade: moderate