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English’s lecture for open pit mine speciality
LESSON 1
ROCK TYPES
Rocks are divided according to their origins, into three groups: the igneous,
metamorphic, and sedimentary rocks.
1.1 – Igneous rocks:
Igneous rocks are formed when hot, molten rock material called magma
solidifies. Magmas are developed either within or beneath the Earth’s crust, that is,
in the mantle. They comprise hot solutions of several liquid phases, the most
conspicuous if which is invariably a complex silicate phase. Thus, the igneous
rocks are principally composed of silicate minerals. Furthermore, of the silicate
minerals, six families, the olivines, the pyroxenes, the amphiboles, the micas, the
feldspars, and the silicate minerals, are quantitatively by far the most important
constituents.
The magmas which are generated when melting occurs in the mantle or crust are
named primary magmas. They tend to be basaltic in composition and represent the
parent mineral from which secondary or derived magmas may arise due to
differentiation and contamination. Differentiation is brought about due to the fact
that different minerals crystallize at different temperatures so that an order of
crystallization can be distinguished. When those minerals which crystallize at high
temperatures have formed, the composition of the remaining magma is changed.
This process, known as fractional crystallization, can produce different types of
rock from the original magma. Magma becomes contaminated when country rock
is incorporated into it. This can alter its composition. Evidence of contamination is
exhibited, for example, by the presence of fragments of country rock, termed
xenoliths, which have not been completely assimilated by the host magma.
It would appear, however, that most granitic rocks are developed by other
processes, that is, granitization and and anatexis. Granitization is a process by
which solid rocks are converted to rocks of granitic character without passing
through a magmatic stage. Anatectic processes, on the other hand, lead to the
remelting or rocks. Such rocks frequently have a mixed or hybrid appearance. They

have been termed migmatites.
Igneous rocks maybe divided into intrusive and extrusive types according to
their mode of occurrence. In the former type, the magma crystallizes within the
Earth’s crust, whereas in the latter it solidifies at the surface, having been erupted
as lavas and/or pyroclasts from a volcano. The intrusions may be further subdivided
on a basis of their sire, into major and minor categories: the former are developed
in a plutonic (deep-seated) environment. About 95% of the plutonic intrusions have
granite – graodiorite composition, and basaltic rocks account for approximately
98% of the extrusives.
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1.2- Metamorphism and metamorphic rocks:
Metamorphism rocks are derived from pre-existing rock types and have
undergone mineralogical, textural, and structural changes. The latter have been
brought about by changes which have taken place in the physical and chemical
environments in which the rocks existed. The processes responsible for changing
give rise to progressive transformation which takes place in the solid stage. The
changing conditions of temperature and not/or pressure are the primary agents
causing metamorphic reactions in rocks. Individual materials are stable over limited
temperature – pressure conditions which means that when these limits are exceeded
mineralogical adjustment has to be made to establish equilibrium with the new
environment. Grade refers to the range of temperature under which metamorphism
occurred.
When metamorphism occurs there is usually little alteration in the bulk chemical
composition of the rocks involved with the exception of water and volatile
constituents such as carbon dioxide. Little material is lost and gained and this type
of alteration is described as an isochemical change. By contrast, allochemical
changes are brought about metasomatic processes which introduce or remove
material from the rocks they affect. Metasomatic changes are brought about by hot
gases or solutions permeating through rocks.

Two major types of metamorphism may be distinguished on the basis or
geological setting. One type is of local extent whereas the other extends over a
large region. The first type includes thermal or contact metamorphism and the latter
refers to regional metamorphism.
1.3 Sedimentary rocks:
The sedimentary rocks form an outer skin on the Earth’s crust, covering three
quarters of the continental areas and most of the sea floor. They very in thickness
up to 10 km. Nevertheless they only comprise about 5 % of the crust.
Most sedimentary rocks are of secondary origin in that they consist of detrital
material derived by the breakdown of pre-existing rocks. Indeed it has been
seriously estimated that shales and sand-stones, both of mechanical derivation,
account between 80 and 95 % of all sedimentary rocks. Certain sedimentary rocks
are the products of chemical or biochemical precipitation whilst others are of
organic origin.
The composition of a sedimentary rock depends: (i) on the composition of the
parent material and the stability of its component minerals; (ii) on the types of
action. The least stable minerals tend to be those which are developed in
environments very different from those experienced at the Earth’s surface. In fact
quartz, and to a much lesser extent, mica, are the only common constituents of
igneous and metamorphic rocks which are found in abundance in sediments. Most
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of the others ultimately give rise to clay minerals. The more mature a sedimentary
rock is, the more it approaches a stable end product and very mature sediments are
likely to have experienced more than one cycle of sedimentation.
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LESSON 2
GEOLOGICAL STRUCTURES
The two most important features which are produced when strata are deformed

by earth movement are folds and faults, that is, the rocks are buckled or fractured,
respectively. A fold is produced when a more or less planar surface is deformed to
give a waved surface. A fault represents a surface of discontinuity along which the
strata on either side have been displaced relative to each other. Such deformation
principally takes place due to movements along shearing planes. When these are
small and numerous, flexuring and folding result, which if they are few and large,
they cause faulting.
2.1-Fold
There are two important directions associated with folding, namely, dip and
strike. True dip gives the maximums angled at which a bed of rock is inclined and
should always be distinguished from apparent dip (Fig 2.1). The latter is a dip of
lesser magnitude whose direction can run anywhere between that of due dip and
strike. Strike is the trend of a fold and is orientated at right angles to the true trip; it
has no inclination (Fig 2.1).
Folds are wavelike in shape and vary enormously in size. Simple folds are
divided into types – anticlines and synclines (Fig 2.2). In the former the beds are
convex upwards, whereas in the latter they are concave upwards. The crustal of an
anticline is the line which joins the highest parts of the fold whilst the trough line
runs through the lowest parts of a syncline (Fig 2.2). The amplitude of a fold is of a
fold in the horizontal distance from crest to or trough to trough. The hinge of fold is
the line along which the greatest curvature exists and it can be either straight or
curved. However, the axial line is another term which has been used to describe the
hinge line. The limbs of folds occur between the hinges, all folds having two limbs.
The axial plane of a fold is commonly regarded as the plane which bisects the fold
and passes through the axial or hinge line.
The interclimb angle, which is the angle measured between the two projected
planes from the climbs of the fold, can be used to assess the degree of closure of a
fold.
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Fig 2.1- Dip and strike: orientation of cross-hatched plane can be expressed as
follows: strike 330
0
, dip 60
0
toward 240
0
.
Fig 2.2- Block diagram of a non-plunging overturned anticline and syncline,
showing various fold elements.
2.2 Faults:
Faults are fractures in crustal strata along which the adjacent rock has been
displaced. The amount of displacement may vary from only a few tens of
millimeters to several hundred kilometers. In many faults the fracture is a clean
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break but in others the displacement is not restricted to a simple fracture but is
developed throughout a fault zone.
The dip and strike of a fault plane can be described in the same way as are those
of a bedding plane. The angle of hade is the angle enclosed between the fault plane
and the vertical. The hanging wall of a fault refers to the upper rock surface along
which displacement has occurred, whilst the foot-wall is the term given to that
below. The vertical shift along a fault plane is called the throw, whilst the term
heave refers to the horizontal displacement. Where the displacement along a fault
has been vertical, then the terms down throw and up throw refer to the relative
movement of strata on opposite sides of the fault plane.
A classification of faults can be made on a geometrical or a genetic basis, and as
such can be based on the direction in which movement has taken place along the
fault plane, on the relative movement of the hanging and foot-walls, on the attitude
of the fault in relation to the strata involved, and on the fault plane is used to

distinguish between faults, then three types maybe recognized:
+ Dip-slip faults;
+ Strike-slip faults;
+ Oblique-slip faults.
Fig 2.3 – Types of faults: (a) normal fault; (b) reverse fault; (c) wrench or
strike-slip fault; (d) oblique-slip fault; FW: footwall; HW: hanging wall; AB:
throw; BC: heave;
ϕ
: angle of hade.
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LESSON 3
EXPLORATION – GEOLOGICAL ASPECTS
3.1 The stages of exploration.
There are two main phases of exploration – reconnaissance and target
investigation each of which can be divided into stages.
A successful program is always marked by an increase in the favorability of the
area explored in advancing from one stage to the next; this progression is usually
accompanied by a reduction in the size of the favorable area. A complete
exploration sequence, sometimes referred to as full sequence, begins with the
appraisal of large regions for the purpose of selecting those permissive of the
occurrence of mineralization of interest. This appraisal is followed by detailed
reconnaissance of these favorable regions in search of target areas, each with
characteristics permissive of the occurrence of a mineral deposit of interest. These
target areas are investigated in detail, first on the surface, and, if warranted, then by
three-dimensional physical sampling. This latter stage is often called physical
exploration; but the techniques commonly used at that stage, such as drilling,
trenching and shaft sinking, are sometimes also used in previous reconnaissance
stages, especially in areas where targets.
The expression “physical exploration” is therefore best used for any physical

sampling technique at any stage of exploration.
The examination of mineral prospect, the most common exploration approach in
the past, usually involves only the last two stages and sometimes only the last one.
The search for a new one deposit within a known and geologically-mapped mining
district involves only the last two stages, whereas the search for a new body in a
virgin geologic environment involves at least the last three stages and often the full
sequence.
3.2 Planning for success in exploration.
Three essential ingredients are needed to find an economic mineral deposit:
ideas, money, and luck. Good ideas in exploration result from the imaginative
application to new situation of experience, practical and theoretical knowledge, and
sound judgment. Ideas and money are of course the results of human intelligence
and energy. Luck is the leverage of unknown, unforeseen events and factors on the
outcome of an activity, i.e., by transforming uncertainties into risk.
A risk is always related to known factor that can be foreseen, measured within
limits. Thus the role of luck as an ingredient of exploration success can be
controlled by scientific planning, organization, and performance.
3.2.1 Exploration methods and techniques.
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Methods and techniques do not find economic mineral deposit; they only assist
in the discoveries. They have value only if actually related to an objective and/or
working exploration hypothesis; the disciplines of geology, geophysics,
geochemistry, and land acquisition suggest many useful methods and techniques
that can be combined into successful exploration but, taken singly these disciplines,
methods and techniques are not exploration.
In the selection of any exploration method or technique, one must always make
sure that effectiveness, which is doing the right things with regard to the objectives,
governs efficiency which is doing these things well. Once effectiveness is assured
by proper selection of a given method or technique, then its efficiency can be

evaluated in term of detection ability versus costs. Similar studies can be conducted
either graphically, or empirically or mathematically for cost exploration techniques.
3.2.2 Need for planning flexibility
Because exploration is dealing with the unknown and because in spite of the
best possible predictive efforts, the exploration specialist copes with natural
occurrences which are highly unpredictable, the plans and the choice of methods
must be reviewed continuous by as new results are obtained. The exploration
manager must be on the alert to avoid rigidity in methodology; he should always
insist on in intelligent adaptation and flexibility. This should be done, however
without losing sight of objectives, while at the same time taking advantage of lucky
and unexpected discoveries.
3.3. Organizing for success in exploration.
Traditionally, prospecting has been an individual type of endeavor. In modern
times exploration tends to become a managed business activity. Whether in a
prospector working on his own, or in an exploration geologist or geophysicist
working for a firm, the chief qualities which make for success in exploration are
personal characteristics which include imagination, physical endurance, tenacity of
purpose, daring or willingness to assume risk and uncertainty and to make the best
possible decision without having all the facts, and knowledge-assimilated
experience.
Exploration groups should try to retain all the good elements and characteristics
of the entrepreneur’ spirit while taking advantage of the strengths of orderly
organization. The successful exploration group must combine the strength of both
enterprise and avoid the weaknesses of each bureaucracy.
An important aspect of organization of exploration group is the absolute
necessity of limiting the levels of authority to minimum in order to speed up
decisions and actions. This is critical because of the unavoidable geographical
decentralization of exploration efforts. This decentralization of authority through a
minimum number of levels will increase the personal requirements for know how
and will favor the development of a strong sense of personal accountability at

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levels of organization. Thus, a geographically and administratively decentralized
exploration group will be able to have a strong structure but without unnecessary
rigidity, and it will operate with flexibility but not in a chaotic manner. This is a
climate favorable to exploration success.
3.4 Exploration method and requirements for planning a new surface mine.
Many mines fail economically because inadequate information was obtained
before deciding to open them up. Thorough exploration work at the stage of three-
dimensional sampling allows realistic estimates of costs and profitability and,
therefore, informed decisions about opening a mine at any future time.
During the last stage of exploration, the only stage common to all successful
ventures, reliable estimates of reserves, including qualitative features of grade and
tonnage, must be developed with a minimum amount of work and at a minimum
cost. In all cases, the samples on which the estimates are based constitute a very
small fraction of the deposit. For instance, the core of a wire-line hole in a square-
shaped area 200 ft on the side represents only 1/2,000,000 th of the area. If the
squares is 500 ft on the side, only 1/15,000,000 th. In recent years, statistics have
been successfully applied to all aspects or target sampling. This approach is
becoming more and more important for low-grade metal deposits where the
valuable mineral is only a very small fraction of the rock: for instance, about 1/500
th by volume in the case of molybdenum deposits, much less for open pit gold
deposits. Thus drilling and sampling programs are critical aspects of most
exploration ventures.
3.4.1 Planning a drilling program
After detailed surface investigation of a target area has pointed to the possible
occurrence of a mineral deposit, one of the most critical decisions to be made is the
choice of the best three dimensional sampling technique to be used. This decision
can usually be made effectively after simple comparisions of volume, quality, and
costs of samples obtained with alternative techniques. The most likely geometry,

continuity, depth, hardness, fracturing and mineralogy of the expected deposit are
the controlling factors in evaluating each possible technique. In generally drilling is
the method used on targets. If the decision is to drill. The kind of drilling to be done
will depend on the factors mentioned above as well as the expected grade and grain
size of mineralization, minimum acceptable recovery, ground water conditions,
amount of barren rock above the deposit, etc.
A three-dimensional target investigation by drilling can usually be divided into
three steps:
1, “Information drilling” to verity qualitatively the working hypothesis about the
expectable deposit which has been developed during the detailed reconnaissance
and detailed surface targets of exploration.
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2, “Outline drilling” to determine in an approximate way the main dimensions
and characteristics of the deposit.
3, “Sampling drilling” to determine the qualitative and qualitative parameters of
the deposit with enough accuracy to allow reliable economic appraisals. Drilling
may have taken place precious to this fourth stage of exploration, especially in the
case of reconnaissance drilling; but such drilling is done usually for stratigraphy
and structural environment information precious to the definition of a target area.
3.4.2 Sampling
Before the results obtained from one sample are applied to large area of
influence, one must take all necessary precautions to insure that the recovered
sample - core, cutting, sludge, blast samples, car samples - is representative of the
material sampled. Before physical tests, mineralogical studies, and chemical
analyses are made, each sample must be prepared to sent to laboratories. They are
truly representative of the whole sample. Proper sample preparation is very precise
operation which must be continuously controlled with the most stringent
instructions and procedures as reviewed recently by Davis. Specifically, the
determination of minimum weight and maximum particle size of samples necessary

to obtain representative chemical analyses has been much enlightened by the work
of Pierre Gy. The chemical and physical determination can be investigated
statistically as to precious but as to accuracy, the average of the most frequently
occurring values must be relied on. The need for check assays check determinations
must be emphasized continuously during a detailed sampling program. Specific
gravity of material sampled is an often slighted physical property which
nonetheless is critical in tonnage estimates.
3.4.3 Reserves, mineral dressing, valuations.
The exploration project manager must prepare reserve estimates using all
available samples. He should, therefore, be acquainted with shortcut methods of
calculation and with the modern computer methods for estimating reverses of ore,
magical material and waster, and for determining stripping ratios. Traditional
approaches to reverse calculations have been presented by Patterson and King, and
a volume - estimating method using contoured maps has been described by Hughes.
The applications of statistics to reverse estimates have been investigated by Hazen,
Zimmer and Hewlett, and many other workers as recently reviewed by Weis.
Some material can be marketed in their crude stage as soon as removed from the
ground, but most require some postmine treatment before they can be sold. The
feasibility of transforming certain mineralized rocks into a marketable product or
concentrate through mineral dressing, including physical and chemical treatments,
must be investigated as soon as it is established that ore - grade rock has been
found and more many be discovered with additional exploration. These tests should
be directed to the type of deposit and the physical and chemical characteristics of
the materials that require preparation and/or concentration. Such tests are essential
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for determining in a preliminary fashion likely treatment, flowsheet, approximate
concentration costs, recoveries, and marketable product. The exploration geologist
can assist the mineral dressing specialist with this problem before the amenability
tests are made by determining mineralogic and textural characteristics of

mineralized rock as described by Amstutz for metallic deposits and specifically for
porphyry copper ores by Clemmer and Richard.
Reserve estimates and the results of mineral dressing tests are used by the
exploration manager to make preliminary economic evaluations of each deposit and
to determine whether surface mining is a real possibility.
3.4.4 Factors affecting the planning of a surface mine.
Political, social, and legal factors are discussed elsewhere in this volume. The
geographical and geological factors that are the most critical in determining
feasibility or surface mining are:
1, Topography and ground conditions as they relate to shape stability in surface
mine, cost of mining and removing waste overburden, bench height and location of
dumps, tailings disposal, location and feasibility of leaching dumps.
2, Water problems as they relate to the possible need for depressing ground
water level below bottom of the mine, pit slope stability, and tailing dam stability.
3, Weather and seasonal variations as they relate to surface mining during
winter, rainy season, ete.
As much information as possible should be obtained at mineral cost during the
detailed surface investigation stage; the outstanding problems should be
investigated in increasing detail and more conclusive answers should be obtained at
whatever justifiable cost, as the possibility or a surface mine turns into a reality.
Detailed, large scale topographic maps with close - spaced contouring are
indispensable in defining likely places for dumps, tailings dams, and ponds, and is
estimating volumes of waste rock to be stripped. Detailed geologic mapping,
especially lithologic and structural mapping, is necessary in predicting stability of
the pit slopes as shown by Lacy and Coater. Detailed mapping may also provide
information needed to predict water loss at sites for dump leaching. Studies of ore
grade distribution and lithologic variations are necessary in determining the
optimum height of pit benches to obtain satisfactory ore extraction and minimum
dilution. Careful structural logging of drill cores can also give elements for
predicting slope stability, rock breaking costs, and crush ability; petrographic and

mineralographic studies will give clues to grind ability, the fineness of grind
required and expectable recoveries. Soil mechanics tests can assist in establishing
safe slopes in overburden.
Detailed investigation of water flow in surface drainage is essential in
measuring the availability and suitability of water for process and domestic use.
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LESSON 4( 5 )
PIT PLANNING
4.1 Concepts of open pit mine planning.
An open pit mine is an excavation made in the earth’s surface for the purpose of
extracting ore. To get at the ore, it is usually necessary to also excavate large
quantities of waste. The selection of physical design parameters and scheduling of
the ore waste extraction are complex engineering decisions of enormous economic
significance.
The elements to be discussed in this paper consist of two phases: technically
devising a scheme or set of alternative scheme, and then evaluation and selection of
the best scheme.
Open pit mine planning must be correlated to all phases of a mining operation.
The factors that must be considered in planning an open pit mine are numerous and
must reflect the characteristics and surrounding conditions of a particular ore body.
Therefore, only an outline of the subject can be presented here to aid the planning
engineer in pointing out procedures that are generally applicable to pit design.
In planning an open pit mine the pertinent elements that must be included are:
assays, geology tonnage and area extent of ore reserves, topography, mining
equipment, economic factors of operating costs, capital expenditures, profit, type of
ore, pit limits stripping ratio, rate of production*+, pit slopes, bench heights road
grade, ore metallurgical characteristics, hydrological condition, property line, and
marketing considerations.
4.2 Open pit and underground methods.

The controlling factors that determine the choice of mining method between
open pit operation and underground methods are mining cost and ore recovery and
dilution. In an open pit operation, mining cost includes the cost of removing the
waste overburden and waste in the slopes of the pit. The ratio of waste to ore is
therefore the controlling factor in the comparative cost of mining an ore body by
open pits, underground methods.
Example 5.2, assume an underground mining cost of $ 2.00 per ton of ore for a
particular ore body. Assume open pit mining cost at $ 0.30 per ton for ore removal
and $ 0.35 per ton for waste removal. The indicated stripping ratio for an open pit
operation that results in a break - even cost differential between the two mining
methods is determined as follows:
Underground mining cost/ton ore - Open pit mining cost/ton ore
Open pit stripping cost/ ton waste
Substituting:
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Break-even stripping ratio = [$2.00 - $0.30]/[$0.35] = 4.86 waste: 1 ore.
Only that past of the ore body where the stripping ratio does not exceed 4.86
waste: 1 ore should be mined by open average resulting from inclusion of ores
recoverable at lower ratios from on selection of the open pit and higher ratio from
another section. In all cases it must be the highest allowable ratio. It is the ratio at
the final pit limit, i.e.…, the last cut from top to bottom of the final pit face.
In most pit designs, the overall stripping ratio is much lower than the allowable
maximum limiting ratio. Higher ratios than the overall stripping ratio usually obtain
in the early years of operation and lower stripping ratios in the early of operation.
4.3. Stripping ratio
To develop a pit design requires the establishment of the break-even stripping
ratio. This ratio is applied only at the surface of the final pit and must not be
confused with the overall ratio which is always less, otherwise there would be
profit to the operation. The break - even stripping ratio is determined by the

formula:
Break - even stripping ratio =
astecost/ton w Stripping
orecost/ton production - ore value/toneRecoverabl
Where production cost is the total of all costs to the refined metal, exclusive of
stripping cost. Ratio must be developed for variations in the grade of ore and
market price of the end product.
Where advisable, a minimum profit factor can be included in the break-even
stripping ratio formula:
Break-even stripping ratio =
astecost/ton w Stripping
ore) profit/ton Minimum orecost/ton n (productio - ore value/toneRecoverabl +
4.4 Ultimate pit slope
After fixing the allowable stripping ratio, the final pit slope must be determined.
Degree of slope is a critical factor, but unfortunately is the most difficult to
determine particularly in the initial staged of pit design. To minimize the overall
stripping ratio, the slope should be as steep a possible and still remain stable.
Geological structure such as joint and slip planes, faults, rock strength…are key
factors. There should be analyzed as completely as possible from geological
information available.
Time and the presence of water are also elements of slope stability. Drainage
should be provided for surface waters. Underground waters must also be deal with
in a manner to relieve build-up of water pressure. A typical method is to drive
drainage drifts.
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The time element must be considered. Many comparatively will stand for
periods of several months or even years. In such cases, mining plans should be
designed to remove waste as rapidly as possible and recover the ore so made
available. The pit should be designed to a conservative slope angle for the ore to be

removed and fixed at the economical stripping ratio. In actual practice, a steeper
slope can be attempted over a short period of time. Should be steeper slope show
signs of failing, stripping operations can be resumed to the designed flatter slope.
4.5 Operating pit slopes
Another element of long - range pit planning is ample operating room to permit
most economical mining practices. Tight bench room effects a minimum stripping
ratio but result in costly as well as hampering drilling and blasting operations. The
modern rotory drill require wide benches. Size of blast is also governed by bench
room. Shovel and haulage operations are also facilitated by ample working room.
This means flat fit slopes in contrast with the final pit slope that must be as steep as
possible to minimize the overall stripping ratio. Working - slope stripping ratio
must accordingly be much higher than the overall ratio in the early mining stages.
To minimize high stripping ratios during the early years of mine life, operating
slope should be as steep as possible and, at the same time, provide ample bench
room for optimum operating efficiency. This requires detailed studies of the room
required for the size of equipment selected for a given pit. In a rail haulage pit,
operating room must be provided for a trolley line, railroad track, and shovel.
Room must also be provided for drilling and blasting sequence and for track and
trolley shifting sequence. In a truck haulage pit, operating sequences are simple but
more bench room is required to provide for passing of trucks and for easy spotting
of trucks at the loading shovel.
The relationship of equipment size, bench spacing, and operating room
requirements to working slope is developed on Fig 5.1 which illustrates mining
bench room requirements for large equipment in a truck haulage pit. A 15 -cu yd
shovel shown loading into 85-ton trucks, double spotted. The indicated minimum
width of the operating berm is 110.3 ft from crest to toe. At the indicated bank
height of 40 ft, the overall working slope is:
[110.3 + 3]/40 = 3.5 horizontal to 10 vertical or about 16
0
For most pit, such as flat slop can not be tolerated of resulting high stripping

ratios.
To increase the working slope, several levels must be worked in group. This is
illustrated in Fig.5.2. Assume the operating slope should not be flatter than 24
0
30’.
The desirable operating room for the foregoing large equipment should be
somewhat in excess of the indicated minimum of 110.3 ft or about 115 ft as shown
in Fig 5.2.
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To accomplish this, five 40ft levels must be worked as a unit. This provides
room for carrying on 80 ft shoved cut down level by level. With the 35 ft remnant
berm on the intermediate level, the required operating room of 115 ft is maintained.
If the grouping of the five levels into one shovel operating unit results in a required
shovel output in excess of its capacity, the level grouping can be cut to four and the
intermediate bench remnant width can be reduced to 26ft. This however, reduces
the operating room from 115 to 106 fit. If it is desirable to maintain the 35 ft bench
remnant with, the shovel cut can be reduced by 71 ft, as illustrated in fig 5.3.
These examples serve to show the kind of pit planning that must be done to
develop optimum operating slopes, which should be as steep as possible and
consistent with desirable operating room.
4.6 Bench height
Selection of bench height is governed by the size of the loading and drilling
equipment to be employed. The maximum digging height dimension on a mining
shovel is the prime guideline used to establish bench height. As a general rude, an
increase in bench height is desirable for the following reasons:
a, Drilling efficiency:
A greater bench height reduces set up time per ton drilled. In addition, for a
given drill pattern, the sub-grade drilling and explosives are prorated over a greater
tonnage. The greater the difference in bench height, the greater the cost saving.

Two remaining factors with regard to drilling should be considered. As drill hole
diameter is increased, as is the trend in the industry today, then to maintain the
proper blast geometry, the bench height should increase.
b, Shovel efficiency:
The second aspect of increasing bench height is to improve overall shovel
productivity. Normally the number of rows a blast can be drilled while still
maintaining.
For a given blast hole diameter and explosive type, the broken reserves that can
be generated in front of a shovel are directly proportional to the bench height. An
increase in broken reserves will reduce the frequency of blasting and should reflect
in a reduction in shovel delays incurred by the reduces moving requirement.
In addition, the higher muckpile reduces the amount of moving requires to
maintain digging while loading trucks.
The Bucyrus-Erie series of Q-M shovels ranging from a 150B up to 295B,
equipped with standard boom lengths, can safety operate in bench heights of 38
feet to 50 feet respectively. If a greater bench height is desired, an optional long
range boom is usually available, which could permit safe operation in benches to
height of 75 feet.
By comparison, loaders of equivalent bucket capacity to this shovel series can
safely operate in benches with heights ranging from only 15 ft to 30 ft.
15 Department of Surface mining
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4.7 Ultimate haul road
Open pit mines require at least one haul road, and sometimes more depending
on the ore body configuration to mine the deposit to ultimate depth. There are three
prime considerations in constructing an ultimate haul road:
1. Grade;
2. With;
3. Location.
The grade of the haul road is best determined from the truck performance charts

with respect to speed and braking. A general rule, the best road grade lies in the
range of 8% to 12% allowing for normal rolling resistance. Where climatic
conditions are severe (i.e. freezing rain, excessive snow or rain), the tendency is to
reduce the grade.
Road width again is determined by the type of haulage unit selected. The
general rule is to use a haul road width not less than 3.5 times the width of the
haulage unit. This value should be slightly increased on road curves. Remaining
details, such as road material size crowning, ditching, culverts and supper-
elevation of curves should conform to normal road construction standards.
Location of ultimate haul road systemis perhaps the most difficult task. There
are two aspects to locating an ultimate haul road. The first aspect is the timing in
which th ultimate haul road will be established. Ideally thi road should be
established as soon as possible to avoid the construction of temporary. The ultimate
haul road mormally border the bench limit on each horizon as the pit progresses in
depth.
Location of the ultimate haul road would be on the footwall side of the bit
wherethe road could be established immediately to accommodate the ore mining
progression. If the access to the pit was on the hanging wall, then several temporary
haul roads would be required or considerable advance stripping would be required
locate the ultimate haul road of the hauging final pit wall boundary.
5.8 Mining and stripping sequence
Developing an optimum sequence for the removed of ore and waste from an
open pit is complex engineering and economic problem. Because of the vast
amount of data which has to be analyzed and very large number of options
possible, it is not usually practical to find the optimum solutions manually.
Workable solutions, which meet prescribed condition, can be found but these are
not necessarily the best available solutions.
Computers are beginning to play a major role in this field because they can
perform the analysis required to find optimum solutions within a reasonable time
frame. The computer software required to perform the analysis is highly complex.

Large corporation with central engineering facilities often have programs on file
that suit their general conditions. When using a computer program to develop a
16 Department of Surface mining
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mine design, it is crucial that the programmer is aware of all constraints and
objectives the design should seek. Someone that has an intimate knowledge of the
mechanics of the computer computations and of the practical mining problems
involved is needed to evaluate the result.
1. Basic concepts.
Following are four distinct examples of mining and stripping schedules. The
first two are extreme cases used for illustrative purposes only. (Declining stripping
and increasing ratio method).
a, Constant stripping ratio method:
This method attempts to remove the waste at a rate approximated by the overall
stripping method. The working slope of the waste faces starts very shallow but
increases as mining depth increases until the working slope equals the overall pit
slope. The method from an advantage and disadvantage point of view is a
compromise that removes the extreme conditions of the former two stripping
methods outlined. Equipment fleet size and labor requirements are relatively
constant.
b, Phased mining sequence (Fig 5.4)
In actual practice the best stripping sequence for a large orebody would be one
in which the stripping rate was low initially and towards the end of the life of the
mine. This has the following advantages:
1, A good profit can be generated quickly to assist the cash flow.
2, The labor and equipment fleet can built up to maximum capacity over period
of time.
3, The labor and equipment requirements decrease gradually towards the end of
mine.
4, Distinct mining and stripping areas can be operated simultaneously, allowing

for flexibility in planning.
5, The number of mining and stripping faces required is not unduly large.
6, In large ore body, the mining and stripping phases are sufficiently wide to
provide good mining condition.
Figure 5.4 Phased mining stripping
The example shown is more or less an overturned syncline type ore body with a
distinct hanging wall and footwall. Note the major berm left at the bottom of the
phase 1 ore removal. This berm should be approximately 100 ft wide to allow
should clean up spillage from the phase II stripping area, caused by blasting.
If the waste material were sufficiently weak so that heavy blasting with much
displacement was not required, this berm could be eliminated.
Figure 5.5 the relationship between present value and various mining
sequences
17 Department of Surface mining
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Each mining-stripping option generates a unique cash flow. In figure 6.5, option
1 would be typical of a program in which stripping as postponed in the early years,
option 3 involves a large stripping program in the early years and option 2 is a
compromise typical of a phased stripping sequence. The present value of property
is highly influenced by the stripping sequence. The sequence which maximum the
present value of the ore body, while maintaining efficient mining conditions and
equipment demands, is the optimum sequence.
The optimum ultimate pit boundary is the one which maximizes the profit
generated by mining the ore body. This relationship is shown for a typical cross
section in figure 5.6.
Fig 5.6 the relationship between ultimate pit depth and net profit.
LESSON 6
STRIPPING METHOD
6.1 Selection of stripping method
The size of an orebody and the distribution of values within that orebody

normally will limit the variety of economical stripping methods which need to be
considered. Much may depend upon the selectivity required in the mining due to
the relationship between ore and overburden, as well as character of the overburden
itself.
The following factors concerning the geologic nature and environment of an
orebody, as well as production requirements, must be determined before any
selection of equipment is made:
1, The size of the orebody and distribution of the values within that orebody. Is
the ore massive or scattered, bedded or disseminated, thick or thin?
2, The nature of the overburden to be moved. Is it a hard dense rock, bedded
rock (thin or thick), friable material, earth, sand, clay, march…?
3, The character and significance of geologic structure associated with the ore
occurrence. Are there water bearing formations with resulting water disposal
problems?
18 Department of Surface mining
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4, In considering the nature of the overburden, including its alternation products,
the physical or chemical conditions which, when combined with anticipates climate
conditions, may render certain equipment inoperable during unfavorable seasons.
5, The life and expected production rate of the operation. Is the production to be
continuous or intermittent?
6, The calculated capacity of, and haulage distance to, each disposal area.
7, The future use of the equipment. It is to be utilized to mine the orebody as it
is developed, or is it to be used for stripping only? What is the effect of ore
blending requirement on equipment size when it this also to be used to mine ore.
The character of the terrain at and in the vicinity of the orebody and proximity
of the ore body to waste disposal areas will greatly influence the cost of stripping
and the selection of equipment. Both flat and mountainous environments have their
advantages and disadvantages when selecting the stripping methods most suitable
for a particular ore body. The possible need to reclaim the land following mining

may be necessary if legislative trends continue. Such conditions may strongly
influence equipment choices because of the need to retain waste material adjacent
to the mine site for ease of reclamation.
Unit capacities of earth moving equipment have increased tremendously in
recent years. In 1966 many trucks were in use in the 60 to 110 ton range, and
shovel with capacities ranging from 8 to 15 Cu yds per bucket were coming into
common usage. Dragline with 85 Cu yd bucket capacities were available. Bucket
wheel excavators with capacities ranging form 1,000 to 14,450 loose Cu yds were
reported in operation. Scrapers with 80 ton capacity were being utilized, as were
front - end bucket loaders capable of handing from 15 to 20 yds. With such a
variety of equipment available, the selection of a stripping method becomes a
problem requiring careful analytical method.
Bulldozers, motograders, service trucks, drilling and blasting equipment, skip,
and conveyor belts are representative of the many type of auxiliary equipment that
may be needed, depending on the method of stripping chosen.
In the selection of a stripping method preliminary considerations, such as type
of material to be moved, accessibility, size of job, volume per day, and type of
power available at the site, will usually narrow the field to one ore two possibilities.
These should then be examined in detail using standard cost analysis techniques. A
listing of the attributes of the various types of equipment available should help
refine the selection possibilities.
Excavators
Shovels: 1. Can give high production
2. Can handle all types of material including large blocky material.
3. are limited to fairly rigid operating conditions.
19 Department of Surface mining
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4. Require supporting equipment for waste disposal except in some
strip mining.
Draglines:

1. Have the ability to dig well above and below grade.
2. Can function under less rigid operating conditions than shovels.
3. Are only 75 to 80 % as efficient in production as a shovel of
comparable size due to less precise motions?
4. May or may not require supporting waste haulage equipment.
5. Are normally used fore handling unconsolidated and softer material,
but large units can handle blasted rock.
Scrapers:
1. Have excellent mobility.
2. Are limited to fairly soft and easily broken material for good
production, although they can handle broken material up to about
24 in, in size.
3. Usually require pushers to assist in loading.
4. Usually are operated without supporting disposal equipment where
the distance to the dump area does not exceed one mile.
Bucket-Wheel-Excavators:
1. Must be operated under very rigidly engineered conditions.
2. Have very high capital cost.
3. Are limited to fairly easy digging.
4. Are capable of high production rates.
5. Require auxiliary disposal systems.
Haulage equipment
Bulldozers:
1. Are economically limited to a fairly short operating radius of about 500 ft.
2. Require good roads to minimize tire costs.
3. Are fast but are economically limited to an operating radius of approximately
one mile.
Trucks:
1. Require good roads to minimize tire costs.
2. Can negotiate steep ramps.

3. Are usually limited by economics to an operating radius of about 2. ½
miles.
4. Are very mobile.
Trains:
20 Department of Surface mining
English’s lecture for open pit mine speciality
1. Are high volume, long distance, low-unit-costs carriers.
2. Track requires careful conformity to engineering specifications.
3. Have a high initial capital cost.
4. Cannot handle adverse grades much greater then 3 %.
5. Can handle coarse, blocky material.
Conveyors:
1. Are high volume, long - distance, low - cost carriers.
2. Are difficult and costly to move.
3. Have a high initial capital cost.
4. Can haulage steep adverse grades (up to about 40%).
5. Require material broken into fairly small pieces for good belt life.
Some of the principal factors affecting the cost of open pit mining are the size of
the operation, the kind of material mined, and the distance it is moved. As a rule,
the cost per ton tends to decrease with increase production, large equipment
(assuming it is run full time), decreasing haulage distance, and easier handling
material. There are many other factors, of course, which enter the cost picture.
The variations for drilling, blasting, and loading generally amount to only a few
cents per ton. Haulage, on the other hand, not only accounts for a substantial potion
of the direct mining cost but also is most variable single cost item.
The major haulage systems are rail, conveyor, truck, and scraper, skips and
pipelines are additional, but limited systems. Costs vary according to distance,
although not indirect proportion. In general, rail is cheapest for very long hauls,
conveyors for long hauls, trucks for short hauls, and scrapers for very short hauls.
If analysis points to only a small difference in costs between two or more

proposed stripping systems, the consideration of post - stripping equipment uses
many points to the better choice.
5.2 Shovel - truck stripping
The shovel - truck combination is commonly selected for one or more of the
following reasons:
1. The overburden is rock - which breaks into large angular pieces.
2. There is limited access room.
3. Hauls involve short steep grades.
4. Extreme mobility is required.
5. Haulage is of medium length.
5.3 Shovel - train stripping
The use of trains as the haulage unit for a stripping operation should be
considered when the following conditions exist:
21 Department of Surface mining
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1. The operation will last long enough to amortize the high initial investment.
2. The haul is long (in established rail system the average haul is usually more
than two miles).
3. Grades can be held to a minimum, usually not to exceed about 4% in favor of
a load and about 3 % adverse to a load.
4. The rigidly engineered haulage system will not seriously impair the progress
of the stripping.
5. The material to be hauled is in a large, rough and block form.
When the aforementioned conditions occur, the use of rail haulage should be
carefully investigated because of the very favorable operating costs obtainable.
Operating costs of from less than 1 cent to 3 cents a ton - mile are not uncommon.
Rail haulage is particularly suited to large, high-tonnage, long-term operation.
There are copper mines in the Western United States which more rock in the range
of 50 million tons a year or more with their rail complexes.
5.4 Rippers and scrapers

The development of large and more powerful tractors and scrapers, as well as
special steels for ripper points, has made ripping and scraping a competitive
method of stripping under favorable conditions of overburden.
A method of seismic testing has been developed that permits more accurate
prediction of the pipability for various type of material. Materials which cannot be
ripped in situ may be stripped economically by combining light blasting with
ripping.
Use of a second tractor to push the ripper has been successful in extending the
range of the ripper-tractor combination in tough ground. Sandstone, lime stones,
and shale have been ripped at costs substantially lower than blasting costs for the
same material. Production rates vary from go to 450 yds per hour depending on the
hardness of the material, the effect of material size upon the disposal unit, and the
length of haul. Scrapers cannot handle as large rock fragments as can large shovel.
The advantage of using the ripper-scarper method where applicable is in its
versatility; scrapers can move to an area quickly, build their own roads or ramps,
and have their own power source. Efficient operation of system depends upon
having skillful scraper operations, a factor which must be considered especially
when starting a new operation.
The ripper-scraper combination is especially effective where the job is small,
where access is limited, and where power source are lacking. This equipment is
frequently leased, rather than purchased, thus minimizing initial capital
requirements.
5.5 Bucket-wheel excavators
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Large bucket-wheel excavators have been built in the last decade in an attempt
to lower costs by application of continuous mining principles to the stripping of
overburden.
Recently improved components have permitted the use of these machines
increasingly tougher material. Slates, shales, and sandstone, as well as earth, have

been removed successfully by bucket-wheel excavator. Controlled blasting to
reduce even harder material to pieces small enough to be handled by the wheels
gives these machines even wider scope.
Wheels up to 60 ft in diameter carrying buckets up to 5 yds in capacity are
presently in use. Turning at speeds of 500 to 1000 ft per minute, they mine the
bank, dumping the cutting on a ladder conveyor which in turn loads a fixed cutting
leading to the dump area or to a transfer point for final disposal by truck, train, or
conveyor system.
Smaller, shorter bucket wheels, some mounted on robber tires, have been
developed for smaller jobs and will produce from about 500 to 2000 Cu yd per
hour.
Careful consideration of auxiliary disposal system is imperative in order that the
high production rates of these wheels may be effectively utilized.
The bucket wheel application at the Nchanga Mine in Zambia is an excellent
example of this stripping method.
1. Location: Nchanga Consolidate Copper Mines, L.td; Zambia.
2. Start of Mining: Stripping started 1955; bucket wheel excavator installed
1958.
3. Topography: relatively flat with low relief.
4. Material: Alluvial overburden.
5. Objective: to remove approximately 100 million Cu yd of overburden 100 to
800 ft thick.
6. Production: 500,000 Cu yd per month.
7. Haul: 13,000 ft against grade.
8. Stripping method: Bucket-wheel, excavator loads 48-in. Conveyor belt
system to dumps. Portable bench conveyor feeds permanent pit conveyor
which feeds portable conveyor or dumps. Mobile stacking conveyor builds
dump.
9. Comments: shovel - to - truck and shovel - to - train haulage used prior to
installation of bucket excavator. Limited Shovel - to - truck - to - conveyor

operation is still in use.
5.6 Selection of number and capacity of equipment:
The selection of number and capacity of loading and haulage machines is based
on pit design, production rate, and desired flexibility. Ultimate pit slope and design
23 Department of Surface mining
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are functions of rock and ore characteristics, water conditions, cutoff, grade,…
Production rate is controlled by the market, which determines inventory and
shipping levels. Size and number of loading and haulage machines are indirectly
proportional to each other. As the capacity of machines increases, the number of
machines needs decreases.
In choosing a size of a loading unit, the depth and shape of ore body will
determine the waste-to-ore ratio, which govern the total amount of material to the
moved in given time. For any given shovel (or other loading mechanism) size,
production rate depends upon cycle time, digging characteristics of various shovel
makes, and machine availability. Cycle time is a function of pit layout and machine
design. Perhaps the most important factor in choosing shovel size is the desired
flexibility. If the ore grade is extremely variable throughout the ore body,
management may want to be able to mine from more faces simultaneously. In this
case the number of loading machines will go up and the capacity of each will go
down. If the ore grade, and ratios are constant throughout, fewer machine could
given better costs and logistics. Once the size is selected, the number of loading
machines can be determined.
Example: selection of equipment
Suppose a 5-cu yd loading machine has been chosen. Its cycle depend upon
digging characteristics of the ore, bench height, ete. Suppose this cycle time is 30
sec. Thus, the machine can produce about 8 to 10 bank yards every minute. Now a
35-ton truck size (with a 25-cu yds body) is under consideration. Cycle
characteristics are as follows:
Load time-5 bucket, a bucket: 0.5 minute 2.5 minutes

Haul time 2.0 min
Position at dump 0.15 min
Dump time 0.35 min
Return time 2.05 min
Position at shovel 0.2 min
Total cycle time 7.25 min
Time at shovel 2.70 min
Number of truck required to keep shovel busy:
7.35 min/2.70 min = 2.7
Use 3 trucks, with some waiting time.
Haul time depends upon haulage distance, haulage profile, and truck operating
characteristics. Time at shovel includes load and position times. Other factors
entering into this problem could include shovel and truck operating factors, need
for spares, etc. Also it is likely that the various times will vary, these random
variations possibly conforming to some kind of probability distribution. In this case
24 Department of Surface mining
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some of the newer techniques of operation research, discussed later in this chapter,
can be used to help select numbers and sides of loading and haulage.
The following is an example of selection of mining equipment for “A” coal
mine.
1. Possible system and system combination
The mining equipment for an open cast mine can be divided into two categories,
according to the working methods. Bucket wheel excavation (BWEs) belong to the
first category, namely continuous mining equipment. The BWE can operate in coal
as well as in waste, as far as cutting forces and material properties permit. The
second category, i.e. discontinuous mining equipment, includes hydraulic and rope-
shovel-excavator, front end-loaders and scrapers. Such machines can also be used
for both waste removal and coal extraction. Two types of hauling equipment are
available to transport coal and waste and are categorized in the same manner;

continuously operating, such as belt conveyors, and discontinuously operating,
such as dump trucks and scapers.
For “A” coal mine, the application of bucket wheel excavator was contemplated
first. Due to their satisfactory selectivity, BWEs are especially suitable for waste
removal as well as for coal extraction. However, BWEs can only be applied
effectively if they are combined with belt conveyors as haulage equipment. As
elaborated further on this chapter, BWES had to be discarded due to the fact the at
in pit belt conveyors could be applied efficiently for both coal and in pit waste
haulage.
Scarpers were also considered to remove the upper overburden and mine coal,
but were dismissed because of the great transport distances that occur and the
deteriorating effect which high precipitation during the rainy season. All of these
factors would have a negative impacts on the scrapers output and therefore make
them uneconomic as main mining transport equipment for “A” coal Mine.
The application of front-end loaders is a further alternative for coal extraction
and waster removal. In comparison to other loading equipment, front end loaders
are low in price, low operating weight and highly mobile. However, the waste is to
be removed directly from the face without pre-blasting, front end loaders are
unsuitable because of their limited break-out force. In addition, difficult soil
conditions occurring frequently during the rainy season cause a considerable loss of
productivity. Nevertheless, front-end loaders are favored in mining practice as a
loading for blasted or/and piled material.
Hydraulic or rope-operated shovel are another excavating equipment option.
Due to the kinematics of the rope shovels, it is not possible to horizontally
penetrate into the strata in the upper part of the mine wall, e.g for the purpose of
selectivity excavating waste and coal. In addition, rope shovel are less mobile than
hydraulic shovels. The operating weight of the rope shovel is approximately twice
25 Department of Surface mining