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LESSON 1ROCK TYPES

Rocks are divided according to their origins, into three groups: the igneous,metamorphic, and sedimentary rocks

The magmas which are generated when melting occurs in the mantle or crust arenamed primary magmas They tend to be basaltic in composition and represent theparent mineral from which secondary or derived magmas may arise due todifferentiation and contamination Differentiation is brought about due to the factthat different minerals crystallize at different temperatures so that an order ofcrystallization can be distinguished When those minerals which crystallize at hightemperatures have formed, the composition of the remaining magma is changed.This process, known as fractional crystallization, can produce different types ofrock from the original magma Magma becomes contaminated when country rock

is incorporated into it This can alter its composition Evidence of contamination isexhibited, for example, by the presence of fragments of country rock, termedxenoliths, which have not been completely assimilated by the host magma

It would appear, however, that most granitic rocks are developed by otherprocesses, that is, granitization and and anatexis Granitization is a process bywhich solid rocks are converted to rocks of granitic character without passingthrough a magmatic stage Anatectic processes, on the other hand, lead to theremelting or rocks Such rocks frequently have a mixed or hybrid appearance Theyhave been termed migmatites

Igneous rocks maybe divided into intrusive and extrusive types according totheir mode of occurrence In the former type, the magma crystallizes within theEarth’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 havegranite – graodiorite composition, and basaltic rocks account for approximately98% of the extrusives

1.2- Metamorphism and metamorphic rocks:

Metamorphism rocks are derived from pre-existing rock types and haveundergone mineralogical, textural, and structural changes The latter have beenbrought about by changes which have taken place in the physical and chemicalenvironments in which the rocks existed The processes responsible for changinggive rise to progressive transformation which takes place in the solid stage Thechanging conditions of temperature and not/or pressure are the primary agentscausing metamorphic reactions in rocks Individual materials are stable over limitedtemperature – pressure conditions which means that when these limits are exceededmineralogical adjustment has to be made to establish equilibrium with the newenvironment Grade refers to the range of temperature under which metamorphismoccurred

When metamorphism occurs there is usually little alteration in the bulk chemicalcomposition of the rocks involved with the exception of water and volatileconstituents such as carbon dioxide Little material is lost and gained and this type

of alteration is described as an isochemical change By contrast, allochemicalchanges are brought about metasomatic processes which introduce or removematerial from the rocks they affect Metasomatic changes are brought about by hotgases or solutions permeating through rocks

Two major types of metamorphism may be distinguished on the basis orgeological setting One type is of local extent whereas the other extends over alarge region The first type includes thermal or contact metamorphism and the latterrefers to regional metamorphism

1.3 Sedimentary rocks:

The sedimentary rocks form an outer skin on the Earth’s crust, covering threequarters 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 detritalmaterial derived by the breakdown of pre-existing rocks Indeed it has beenseriously estimated that shales and sand-stones, both of mechanical derivation,account between 80 and 95 % of all sedimentary rocks Certain sedimentary rocksare the products of chemical or biochemical precipitation whilst others are oforganic origin

The composition of a sedimentary rock depends: (i) on the composition of theparent material and the stability of its component minerals; (ii) on the types ofaction The least stable minerals tend to be those which are developed inenvironments very different from those experienced at the Earth’s surface In factquartz, and to a much lesser extent, mica, are the only common constituents ofigneous and metamorphic rocks which are found in abundance in sediments Most

of the others ultimately give rise to clay minerals The more mature a sedimentaryrock is, the more it approaches a stable end product and very mature sediments arelikely to have experienced more than one cycle of sedimentation.

LESSON 2GEOLOGICAL 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 togive a waved surface A fault represents a surface of discontinuity along which thestrata on either side have been displaced relative to each other Such deformationprincipally takes place due to movements along shearing planes When these aresmall 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 andstrike True dip gives the maximums angled at which a bed of rock is inclined andshould always be distinguished from apparent dip (Fig 2.1) The latter is a dip oflesser magnitude whose direction can run anywhere between that of due dip andstrike Strike is the trend of a fold and is orientated at right angles to the true trip; ithas no inclination (Fig 2.1)

Folds are wavelike in shape and vary enormously in size Simple folds aredivided into types – anticlines and synclines (Fig 2.2) In the former the beds areconvex upwards, whereas in the latter they are concave upwards The crustal of ananticline is the line which joins the highest parts of the fold whilst the trough lineruns through the lowest parts of a syncline (Fig 2.2) The amplitude of a fold is of afold in the horizontal distance from crest to or trough to trough The hinge of fold isthe line along which the greatest curvature exists and it can be either straight orcurved However, the axial line is another term which has been used to describe thehinge 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 foldand passes through the axial or hinge line

The interclimb angle, which is the angle measured between the two projectedplanes from the climbs of the fold, can be used to assess the degree of closure of afold

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 beendisplaced The amount of displacement may vary from only a few tens ofmillimeters to several hundred kilometers In many faults the fracture is a clean

break but in others the displacement is not restricted to a simple fracture but isdeveloped 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 planeand the vertical The hanging wall of a fault refers to the upper rock surface alongwhich displacement has occurred, whilst the foot-wall is the term given to thatbelow The vertical shift along a fault plane is called the throw, whilst the termheave refers to the horizontal displacement Where the displacement along a faulthas been vertical, then the terms down throw and up throw refer to the relativemovement of strata on opposite sides of the fault plane

A classification of faults can be made on a geometrical or a genetic basis, and assuch can be based on the direction in which movement has taken place along thefault 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 todistinguish between faults, then three types maybe recognized:

LESSON 3EXPLORATION – GEOLOGICAL ASPECTS3.1 The stages of exploration.

There are two main phases of exploration – reconnaissance and targetinvestigation each of which can be divided into stages

A successful program is always marked by an increase in the favorability of thearea explored in advancing from one stage to the next; this progression is usuallyaccompanied by a reduction in the size of the favorable area A completeexploration sequence, sometimes referred to as full sequence, begins with theappraisal of large regions for the purpose of selecting those permissive of theoccurrence of mineralization of interest This appraisal is followed by detailedreconnaissance of these favorable regions in search of target areas, each withcharacteristics permissive of the occurrence of a mineral deposit of interest Thesetarget areas are investigated in detail, first on the surface, and, if warranted, then bythree-dimensional physical sampling This latter stage is often called physicalexploration; but the techniques commonly used at that stage, such as drilling,trenching and shaft sinking, are sometimes also used in previous reconnaissancestages, especially in areas where targets

The expression “physical exploration” is therefore best used for any physicalsampling technique at any stage of exploration

The examination of mineral prospect, the most common exploration approach inthe 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 miningdistrict involves only the last two stages, whereas the search for a new body in avirgin geologic environment involves at least the last three stages and often the fullsequence

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 imaginativeapplication to new situation of experience, practical and theoretical knowledge, andsound judgment Ideas and money are of course the results of human intelligenceand energy Luck is the leverage of unknown, unforeseen events and factors on theoutcome of an activity, i.e., by transforming uncertainties into risk

A risk is always related to known factor that can be foreseen, measured withinlimits Thus the role of luck as an ingredient of exploration success can becontrolled by scientific planning, organization, and performance

3.2.1 Exploration methods and techniques.

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/orworking exploration hypothesis; the disciplines of geology, geophysics,geochemistry, and land acquisition suggest many useful methods and techniquesthat 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 makesure 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 beevaluated in term of detection ability versus costs Similar studies can be conductedeither 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 thebest possible predictive efforts, the exploration specialist copes with naturaloccurrences which are highly unpredictable, the plans and the choice of methodsmust be reviewed continuous by as new results are obtained The explorationmanager must be on the alert to avoid rigidity in methodology; he should alwaysinsist on in intelligent adaptation and flexibility This should be done, howeverwithout losing sight of objectives, while at the same time taking advantage of luckyand unexpected discoveries

3.3 Organizing for success in exploration.

Traditionally, prospecting has been an individual type of endeavor In moderntimes exploration tends to become a managed business activity Whether in aprospector working on his own, or in an exploration geologist or geophysicistworking for a firm, the chief qualities which make for success in exploration arepersonal characteristics which include imagination, physical endurance, tenacity ofpurpose, daring or willingness to assume risk and uncertainty and to make the bestpossible decision without having all the facts, and knowledge-assimilatedexperience

Exploration groups should try to retain all the good elements and characteristics

of the entrepreneur’ spirit while taking advantage of the strengths of orderlyorganization The successful exploration group must combine the strength of bothenterprise and avoid the weaknesses of each bureaucracy

An important aspect of organization of exploration group is the absolutenecessity of limiting the levels of authority to minimum in order to speed updecisions and actions This is critical because of the unavoidable geographicaldecentralization of exploration efforts This decentralization of authority through aminimum number of levels will increase the personal requirements for know howand will favor the development of a strong sense of personal accountability at

levels of organization Thus, a geographically and administratively decentralizedexploration group will be able to have a strong structure but without unnecessaryrigidity, and it will operate with flexibility but not in a chaotic manner This is aclimate favorable to exploration success.

3.4 Exploration method and requirements for planning a new surface mine.

Many mines fail economically because inadequate information was obtainedbefore 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 successfulventures, reliable estimates of reserves, including qualitative features of grade andtonnage, must be developed with a minimum amount of work and at a minimumcost In all cases, the samples on which the estimates are based constitute a verysmall 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 thesquares is 500 ft on the side, only 1/15,000,000 th In recent years, statistics havebeen successfully applied to all aspects or target sampling This approach isbecoming more and more important for low-grade metal deposits where thevaluable 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 golddeposits Thus drilling and sampling programs are critical aspects of mostexploration ventures

3.4.1 Planning a drilling program

After detailed surface investigation of a target area has pointed to the possibleoccurrence of a mineral deposit, one of the most critical decisions to be made is thechoice of the best three dimensional sampling technique to be used This decisioncan usually be made effectively after simple comparisions of volume, quality, andcosts of samples obtained with alternative techniques The most likely geometry,continuity, depth, hardness, fracturing and mineralogy of the expected deposit arethe controlling factors in evaluating each possible technique In generally drilling isthe method used on targets If the decision is to drill The kind of drilling to be donewill depend on the factors mentioned above as well as the expected grade and grainsize 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 intothree steps:

1, “Information drilling” to verity qualitatively the working hypothesis about theexpectable deposit which has been developed during the detailed reconnaissanceand detailed surface targets of exploration

2, “Outline drilling” to determine in an approximate way the main dimensionsand characteristics of the deposit.

3, “Sampling drilling” to determine the qualitative and qualitative parameters ofthe deposit with enough accuracy to allow reliable economic appraisals Drillingmay have taken place precious to this fourth stage of exploration, especially in thecase of reconnaissance drilling; but such drilling is done usually for stratigraphyand 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 ofinfluence, one must take all necessary precautions to insure that the recoveredsample - core, cutting, sludge, blast samples, car samples - is representative of thematerial sampled Before physical tests, mineralogical studies, and chemicalanalyses are made, each sample must be prepared to sent to laboratories They aretruly representative of the whole sample Proper sample preparation is very preciseoperation which must be continuously controlled with the most stringentinstructions and procedures as reviewed recently by Davis Specifically, thedetermination 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 investigatedstatistically as to precious but as to accuracy, the average of the most frequentlyoccurring values must be relied on The need for check assays check determinationsmust be emphasized continuously during a detailed sampling program Specificgravity of material sampled is an often slighted physical property whichnonetheless is critical in tonnage estimates

3.4.3 Reserves, mineral dressing, valuations.

The exploration project manager must prepare reserve estimates using allavailable samples He should, therefore, be acquainted with shortcut methods ofcalculation and with the modern computer methods for estimating reverses of ore,magical material and waster, and for determining stripping ratios Traditionalapproaches 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 theground, but most require some postmine treatment before they can be sold Thefeasibility of transforming certain mineralized rocks into a marketable product orconcentrate through mineral dressing, including physical and chemical treatments,must be investigated as soon as it is established that ore - grade rock has beenfound and more many be discovered with additional exploration These tests should

be directed to the type of deposit and the physical and chemical characteristics ofthe materials that require preparation and/or concentration Such tests are essential

for determining in a preliminary fashion likely treatment, flowsheet, approximateconcentration costs, recoveries, and marketable product The exploration geologistcan assist the mineral dressing specialist with this problem before the amenabilitytests are made by determining mineralogic and textural characteristics ofmineralized rock as described by Amstutz for metallic deposits and specifically forporphyry copper ores by Clemmer and Richard.

Reserve estimates and the results of mineral dressing tests are used by theexploration 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 Thegeographical and geological factors that are the most critical in determiningfeasibility or surface mining are:

1, Topography and ground conditions as they relate to shape stability in surfacemine, cost of mining and removing waste overburden, bench height and location ofdumps, tailings disposal, location and feasibility of leaching dumps

2, Water problems as they relate to the possible need for depressing groundwater level below bottom of the mine, pit slope stability, and tailing dam stability

3, Weather and seasonal variations as they relate to surface mining duringwinter, rainy season, ete

As much information as possible should be obtained at mineral cost during thedetailed surface investigation stage; the outstanding problems should beinvestigated in increasing detail and more conclusive answers should be obtained atwhatever justifiable cost, as the possibility or a surface mine turns into a reality.Detailed, large scale topographic maps with close - spaced contouring areindispensable in defining likely places for dumps, tailings dams, and ponds, and isestimating volumes of waste rock to be stripped Detailed geologic mapping,especially lithologic and structural mapping, is necessary in predicting stability ofthe pit slopes as shown by Lacy and Coater Detailed mapping may also provideinformation needed to predict water loss at sites for dump leaching Studies of oregrade distribution and lithologic variations are necessary in determining theoptimum height of pit benches to obtain satisfactory ore extraction and minimumdilution Careful structural logging of drill cores can also give elements forpredicting slope stability, rock breaking costs, and crush ability; petrographic andmineralographic studies will give clues to grind ability, the fineness of grindrequired and expectable recoveries Soil mechanics tests can assist in establishingsafe slopes in overburden

Detailed investigation of water flow in surface drainage is essential inmeasuring the availability and suitability of water for process and domestic use

LESSON 4( 5 )PIT PLANNING4.1 Concepts of open pit mine planning.

An open pit mine is an excavation made in the earth’s surface for the purpose ofextracting ore To get at the ore, it is usually necessary to also excavate largequantities of waste The selection of physical design parameters and scheduling ofthe ore waste extraction are complex engineering decisions of enormous economicsignificance

The elements to be discussed in this paper consist of two phases: technicallydevising a scheme or set of alternative scheme, and then evaluation and selection ofthe 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 andmust 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 planningengineer 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, miningequipment, economic factors of operating costs, capital expenditures, profit, type ofore, pit limits stripping ratio, rate of production*+, pit slopes, bench heights roadgrade, ore metallurgical characteristics, hydrological condition, property line, andmarketing considerations

4.2 Open pit and underground methods.

The controlling factors that determine the choice of mining method betweenopen pit operation and underground methods are mining cost and ore recovery anddilution In an open pit operation, mining cost includes the cost of removing thewaste overburden and waste in the slopes of the pit The ratio of waste to ore istherefore the controlling factor in the comparative cost of mining an ore body byopen pits, underground methods

Example 5.2, assume an underground mining cost of $ 2.00 per ton of ore for aparticular ore body Assume open pit mining cost at $ 0.30 per ton for ore removaland $ 0.35 per ton for waste removal The indicated stripping ratio for an open pitoperation that results in a break - even cost differential between the two miningmethods is determined as follows:

Underground mining cost/ton ore - Open pit mining cost/ton ore

Open pit stripping cost/ ton wasteSubstituting:

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 4.86waste: 1 ore should be mined by open average resulting from inclusion of oresrecoverable at lower ratios from on selection of the open pit and higher ratio fromanother section In all cases it must be the highest allowable ratio It is the ratio atthe 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 allowablemaximum 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 strippingratio This ratio is applied only at the surface of the final pit and must not beconfused with the overall ratio which is always less, otherwise there would beprofit to the operation The break - even stripping ratio is determined by theformula:

Break - even stripping ratio = Recoverable value/tonStrippingorecost/ton w-productionaste cost/ton oreWhere production cost is the total of all costs to the refined metal, exclusive ofstripping cost Ratio must be developed for variations in the grade of ore andmarket price of the end product

Where advisable, a minimum profit factor can be included in the break-evenstripping ratio formula:

Break-even stripping ratio =

aste cost/ton w Stripping

ore) profit/ton Minimum

ore cost/ton

n (productio -

ore value/ton

e

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 todetermine particularly in the initial staged of pit design To minimize the overallstripping 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 keyfactors There should be analyzed as completely as possible from geologicalinformation available

Time and the presence of water are also elements of slope stability Drainageshould 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 drivedrainage drifts

The time element must be considered Many comparatively will stand forperiods of several months or even years In such cases, mining plans should bedesigned 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 beremoved and fixed at the economical stripping ratio In actual practice, a steeperslope can be attempted over a short period of time Should be steeper slope showsigns 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 permitmost economical mining practices Tight bench room effects a minimum strippingratio but result in costly as well as hampering drilling and blasting operations Themodern rotory drill require wide benches Size of blast is also governed by benchroom 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 aspossible to minimize the overall stripping ratio Working - slope stripping ratiomust 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, operatingslope should be as steep as possible and, at the same time, provide ample benchroom for optimum operating efficiency This requires detailed studies of the roomrequired 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 andtrolley shifting sequence In a truck haulage pit, operating sequences are simple butmore 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 roomrequirements to working slope is developed on Fig 5.1 which illustrates miningbench room requirements for large equipment in a truck haulage pit A 15 -cu ydshovel shown loading into 85-ton trucks, double spotted The indicated minimumwidth of the operating berm is 110.3 ft from crest to toe At the indicated bankheight of 40 ft, the overall working slope is:

[110.3 + 3]/40 = 3.5 horizontal to 10 vertical or about 160

For most pit, such as flat slop can not be tolerated of resulting high strippingratios

To increase the working slope, several levels must be worked in group This isillustrated in Fig.5.2 Assume the operating slope should not be flatter than 24030’.The desirable operating room for the foregoing large equipment should besomewhat in excess of the indicated minimum of 110.3 ft or about 115 ft as shown

in Fig 5.2

To accomplish this, five 40ft levels must be worked as a unit This providesroom for carrying on 80 ft shoved cut down level by level With the 35 ft remnantberm 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 theintermediate bench remnant width can be reduced to 26ft This however, reducesthe operating room from 115 to 106 fit If it is desirable to maintain the 35 ft benchremnant 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 todevelop optimum operating slopes, which should be as steep as possible andconsistent 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 agiven drill pattern, the sub-grade drilling and explosives are prorated over a greatertonnage The greater the difference in bench height, the greater the cost saving.Two remaining factors with regard to drilling should be considered As drill holediameter is increased, as is the trend in the industry today, then to maintain theproper blast geometry, the bench height should increase

b, Shovel efficiency:

The second aspect of increasing bench height is to improve overall shovelproductivity Normally the number of rows a blast can be drilled while stillmaintaining

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 Anincrease 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 tomaintain 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 38feet to 50 feet respectively If a greater bench height is desired, an optional longrange boom is usually available, which could permit safe operation in benches toheight of 75 feet

By comparison, loaders of equivalent bucket capacity to this shovel series cansafely operate in benches with heights ranging from only 15 ft to 30 ft

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 threeprime considerations in constructing an ultimate haul road:

Road width again is determined by the type of haulage unit selected Thegeneral rule is to use a haul road width not less than 3.5 times the width of thehaulage unit This value should be slightly increased on road curves Remainingdetails, 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 Thereare two aspects to locating an ultimate haul road The first aspect is the timing inwhich th ultimate haul road will be established Ideally thi road should beestablished as soon as possible to avoid the construction of temporary The ultimatehaul road mormally border the bench limit on each horizon as the pit progresses indepth

Location of the ultimate haul road would be on the footwall side of the bitwherethe road could be established immediately to accommodate the ore miningprogression If the access to the pit was on the hanging wall, then several temporaryhaul roads would be required or considerable advance stripping would be requiredlocate 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 anopen pit is complex engineering and economic problem Because of the vastamount of data which has to be analyzed and very large number of optionspossible, it is not usually practical to find the optimum solutions manually.Workable solutions, which meet prescribed condition, can be found but these arenot necessarily the best available solutions

Computers are beginning to play a major role in this field because they canperform the analysis required to find optimum solutions within a reasonable timeframe The computer software required to perform the analysis is highly complex.Large corporation with central engineering facilities often have programs on filethat suit their general conditions When using a computer program to develop amine 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 themechanics of the computer computations and of the practical mining problemsinvolved is needed to evaluate the result.

1 Basic concepts.

Following are four distinct examples of mining and stripping schedules Thefirst two are extreme cases used for illustrative purposes only (Declining strippingand increasing ratio method)

a, Constant stripping ratio method:

This method attempts to remove the waste at a rate approximated by the overallstripping method The working slope of the waste faces starts very shallow butincreases as mining depth increases until the working slope equals the overall pitslope The method from an advantage and disadvantage point of view is acompromise that removes the extreme conditions of the former two strippingmethods outlined Equipment fleet size and labor requirements are relativelyconstant

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 themine 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

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 toprovide good mining condition

Figure 5.4 Phased mining stripping

The example shown is more or less an overturned syncline type ore body with adistinct hanging wall and footwall Note the major berm left at the bottom of thephase 1 ore removal This berm should be approximately 100 ft wide to allowshould clean up spillage from the phase II stripping area, caused by blasting

If the waste material were sufficiently weak so that heavy blasting with muchdisplacement was not required, this berm could be eliminated

Figure 5.5 the relationship between present value and various mining

sequences

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 acompromise typical of a phased stripping sequence The present value of property

is highly influenced by the stripping sequence The sequence which maximum thepresent value of the ore body, while maintaining efficient mining conditions andequipment demands, is the optimum sequence

The optimum ultimate pit boundary is the one which maximizes the profitgenerated by mining the ore body This relationship is shown for a typical crosssection in figure 5.6

Fig 5.6 the relationship between ultimate pit depth and net profit.

LESSON 6STRIPPING METHOD6.1 Selection of stripping method

The size of an orebody and the distribution of values within that orebodynormally will limit the variety of economical stripping methods which need to beconsidered Much may depend upon the selectivity required in the mining due tothe relationship between ore and overburden, as well as character of the overburdenitself

The following factors concerning the geologic nature and environment of anorebody, as well as production requirements, must be determined before anyselection of equipment is made:

1, The size of the orebody and distribution of the values within that orebody Isthe 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, beddedrock (thin or thick), friable material, earth, sand, clay, march…?

3, The character and significance of geologic structure associated with the oreoccurrence Are there water bearing formations with resulting water disposalproblems?

4, In considering the nature of the overburden, including its alternation products,the physical or chemical conditions which, when combined with anticipates climateconditions, may render certain equipment inoperable during unfavorable seasons.

5, The life and expected production rate of the operation Is the production to becontinuous 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 oreblending 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 strippingand the selection of equipment Both flat and mountainous environments have theiradvantages and disadvantages when selecting the stripping methods most suitablefor a particular ore body The possible need to reclaim the land following miningmay be necessary if legislative trends continue Such conditions may stronglyinfluence 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 inrecent years In 1966 many trucks were in use in the 60 to 110 ton range, andshovel with capacities ranging from 8 to 15 Cu yds per bucket were coming intocommon usage Dragline with 85 Cu yd bucket capacities were available Bucketwheel excavators with capacities ranging form 1,000 to 14,450 loose Cu yds werereported in operation Scrapers with 80 ton capacity were being utilized, as werefront - end bucket loaders capable of handing from 15 to 20 yds With such avariety of equipment available, the selection of a stripping method becomes aproblem 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 thatmay 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 ofpower 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 Alisting of the attributes of the various types of equipment available should helprefine 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

4 Require supporting equipment for waste disposal except in somestrip 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 ofcomparable 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 goodproduction, 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 wherethe 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 approximatelyone 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:

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 ofthe 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 handlingmaterial There are many other factors, of course, which enter the cost picture.The variations for drilling, blasting, and loading generally amount to only a fewcents 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 andpipelines 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 moreproposed stripping systems, the consideration of post - stripping equipment usesmany points to the better choice

5.2 Shovel - truck stripping

The shovel - truck combination is commonly selected for one or more of thefollowing 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 beconsidered when the following conditions exist:

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 morethan 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 becarefully 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 asspecial steels for ripper points, has made ripping and scraping a competitivemethod of stripping under favorable conditions of overburden

A method of seismic testing has been developed that permits more accurateprediction of the pipability for various type of material Materials which cannot beripped in situ may be stripped economically by combining light blasting withripping

Use of a second tractor to push the ripper has been successful in extending therange of the ripper-tractor combination in tough ground Sandstone, lime stones,and shale have been ripped at costs substantially lower than blasting costs for thesame material Production rates vary from go to 450 yds per hour depending on thehardness of the material, the effect of material size upon the disposal unit, and thelength 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 itsversatility; scrapers can move to an area quickly, build their own roads or ramps,and have their own power source Efficient operation of system depends uponhaving skillful scraper operations, a factor which must be considered especiallywhen 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 isfrequently leased, rather than purchased, thus minimizing initial capitalrequirements

5.5 Bucket-wheel excavators

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 ofoverburden

Recently improved components have permitted the use of these machinesincreasingly tougher material Slates, shales, and sandstone, as well as earth, havebeen removed successfully by bucket-wheel excavator Controlled blasting toreduce even harder material to pieces small enough to be handled by the wheelsgives these machines even wider scope

Wheels up to 60 ft in diameter carrying buckets up to 5 yds in capacity arepresently in use Turning at speeds of 500 to 1000 ft per minute, they mine thebank, dumping the cutting on a ladder conveyor which in turn loads a fixed cuttingleading to the dump area or to a transfer point for final disposal by truck, train, orconveyor system

Smaller, shorter bucket wheels, some mounted on robber tires, have beendeveloped for smaller jobs and will produce from about 500 to 2000 Cu yd perhour

Careful consideration of auxiliary disposal system is imperative in order that thehigh production rates of these wheels may be effectively utilized

The bucket wheel application at the Nchanga Mine in Zambia is an excellentexample of this stripping method

1 Location: Nchanga Consolidate Copper Mines, L.td; Zambia

2 Start of Mining: Stripping started 1955; bucket wheel excavator installed1958

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 beltsystem to dumps Portable bench conveyor feeds permanent pit conveyorwhich feeds portable conveyor or dumps Mobile stacking conveyor buildsdump

9 Comments: shovel - to - truck and shovel - to - train haulage used prior toinstallation of bucket excavator Limited Shovel - to - truck - to - conveyoroperation 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

are functions of rock and ore characteristics, water conditions, cutoff, grade,…Production rate is controlled by the market, which determines inventory andshipping levels Size and number of loading and haulage machines are indirectlyproportional to each other As the capacity of machines increases, the number ofmachines needs decreases.

In choosing a size of a loading unit, the depth and shape of ore body willdetermine the waste-to-ore ratio, which govern the total amount of material to themoved in given time For any given shovel (or other loading mechanism) size,production rate depends upon cycle time, digging characteristics of various shovelmakes, and machine availability Cycle time is a function of pit layout and machinedesign Perhaps the most important factor in choosing shovel size is the desiredflexibility If the ore grade is extremely variable throughout the ore body,management may want to be able to mine from more faces simultaneously In thiscase the number of loading machines will go up and the capacity of each will godown If the ore grade, and ratios are constant throughout, fewer machine couldgiven better costs and logistics Once the size is selected, the number of loadingmachines can be determined

Example: selection of equipment

Suppose a 5-cu yd loading machine has been chosen Its cycle depend upondigging characteristics of the ore, bench height, ete Suppose this cycle time is 30sec Thus, the machine can produce about 8 to 10 bank yards every minute Now a35-ton truck size (with a 25-cu yds body) is under consideration Cyclecharacteristics are as follows:

Load time-5 bucket, a bucket: 0.5 minute 2.5 minutes

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 operatingcharacteristics Time at shovel includes load and position times Other factorsentering into this problem could include shovel and truck operating factors, needfor spares, etc Also it is likely that the various times will vary, these randomvariations possibly conforming to some kind of probability distribution In this case

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” coalmine

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 thefirst 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 Thesecond category, i.e discontinuous mining equipment, includes hydraulic and rope-shovel-excavator, front end-loaders and scrapers Such machines can also be usedfor both waste removal and coal extraction Two types of hauling equipment areavailable 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 contemplatedfirst Due to their satisfactory selectivity, BWEs are especially suitable for wasteremoval as well as for coal extraction However, BWEs can only be appliedeffectively if they are combined with belt conveyors as haulage equipment Aselaborated 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 wastehaulage

Scarpers were also considered to remove the upper overburden and mine coal,but were dismissed because of the great transport distances that occur and thedeteriorating effect which high precipitation during the rainy season All of thesefactors would have a negative impacts on the scrapers output and therefore makethem uneconomic as main mining transport equipment for “A” coal Mine

The application of front-end loaders is a further alternative for coal extractionand waster removal In comparison to other loading equipment, front end loadersare 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 areunsuitable because of their limited break-out force In addition, difficult soilconditions occurring frequently during the rainy season cause a considerable loss ofproductivity Nevertheless, front-end loaders are favored in mining practice as aloading 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 horizontallypenetrate into the strata in the upper part of the mine wall, e.g for the purpose ofselectivity excavating waste and coal In addition, rope shovel are less mobile thanhydraulic shovels The operating weight of the rope shovel is approximately twice

that of the hydraulic shovel at identical digging capacities Rope shovels weredeveloped with the intention of applying them as immobile equipment.

The kinematics of the hydraulic shovel enable a crowd motion into the mineface above the machine’s working level Thus, material layers can be wonseparately from higher parts of the face providing for good selectivity whenexcavating coal and waste in alternating sequence In addition, the hydraulic shovelcan also pick up material below the working level and provides for high break-outforces

Further advantages of hydraulic shovel are procedures of loading transportequipment The bucket flap, which is the front part of the bucket, can be openedand shut in a controlled motion, whereas the floor flap of the bucket on a ropeshovel opens abruptly and completely Through the control valve of the hydraulicshovels it is possible that, first of all, fine material can be emptied onto a truckbody before large lumps follow Thus, the truck body is handled with care Inaddition, the material can be dispersed over the truck body so that the loadingcapacity of the trucks can be optimally utilized Finally, it is pointed out thathydraulic shovels can be rebuilt to hydraulic backhoes for loading below levelwhich is not the case with rope dippers For all of these reasons, hydraulic shovelswere selected for coal and waste excavation in the “A” coal mine

When selecting the equipment required to transport the waste to the dump, twomeans of transport were considered: continuously hauling belt conveyor systemscombined with spreaders or discontinuous haulage by trucks

From an economic viewpoint, using belt conveyors for in pit haulage anddeposition of overburden by spreaders in open cast mines necessitates adequatebench lengths to avoid frequent belt conveyor relocations following the mineadvance In the “A” coal mine, such a requirement can only be met in first andsecond area which has a sufficient pit with, but an operating life approximately fouryears If the period of four years is compared with the usual working life of aconveyor/spreaders overburden system amounting to approximately 25 years, itdoes not appear viable to procure spreaders and belt conveyors just for first andsecond area Hence, belt conveyor and spreaders had to be discarded

From an operational viewpoint, the combination of belt conveyor and spreaderdoes not offer any decisive advantages Especially because of flexibility required tooffer the frequently altering hauling distances between mine and dump, rear dumptruck and the articulated dump truck The later has become more important over thelast years as if offers several special advantage for mine operation For example, itenables a very small turning radius which is significant for the lay out of thetransport road as well as for the manoveuring around the loading equipment Inaddition, its ability to negotiate bends is good due to the fact that the springsuspension system is positioned for apart from the center of the axle, the axles areindividually typed and they have a low gravity point which is advantageous in

difficult terrain However, only few manufactures are on the standard type reardump truck is sufficiently proven in would-wide application and has therefore beenselected for the Than Thung-Yen Tu Mine.

For coal haulage discontinuous haulage system was selected, i.e the coal will beextracted by hydraulic shovels and hauled by the standard-type rear dump truck to amine stockpile or/and to coal crushing plant The reason trucks were selected forhaulage instead of belt conveyor is their higher flexibility which enable them toadjust more easily to changes in haulage routes and distances

2 Selection equipment

The mine plan for the “A” coal Mine Project is designed to provide a continuousand secure supply of coal at a minimum cost A truck - shovel mining method wasselected to achieve this objective A truck mining method using medium sizedequipment has several advantages i.e.:

* Truck shovel equipment is suited to local technology and is more manageablefor employee training

* Truck shovel mining method are flexible and can be easily adapted tochanging mining conditions such as drainage, highwall stability, coal quality,increased coal sales and geological conditions that are more accurately defined byfuture drilling

* Truck shovel mining methods do not required a large infrastructure at the start

of operations The mine equipment fleet can be increased or decreased in size as thestrip ratio changes Capital investment can be spread over the mine life Thisprocedure reduces the initial capital investment required before coal productioncomments

* The wrong type or size of equipment may be purchased at the start ofoperations A change in equipment selection can easily be made at a later datewithout adversely affecting the capital requirements Other mining systems do notprovide flexibility in changing the equipment selection during the life of the mine.Hydraulic shovel with a service weight of 65 t and a bucket capacity of 4.0 m3

were selected for coal extraction and waste removal

A 26 tonne trucks were selected for this project The shovel will require 4 cycles

to load a truck during the waste operation and 5 cycles during coal extraction.Furthermore, trucks of this size offer better manoeveur ability under the aspect ofprevailing adverse weather conditions which entail soft and muddy excavator andspoil benches

3 Description of Mining equipment

Major equipment

For its lifetime, the “A” coal mine was planned to be equipped with anextraction and haulage system consisting of a shove/truck combination for wasteremoval and coal operation.

Under the prevailing conditions, such a combination will guarantee themaximum possible degree of flexibility, i.e adjusts ability to the coal extractionwaste removal, haulage and dumping with frequent relocations involves

Auxiliary Equipment

Various auxiliary units are required in the mine to support the main equipmentand to ensure a smooth, high capacity operation Their task is to improve theworking condition of the main equipment on the working benches and to developand shape the inside and outside dump Furthermore, this equipment is required forthe maintenance of haul roads and for other work in connection with the open pitauxiliary

LESSON 6DRILLING6.1Principles of drilling

Introduction

The purpose of production drilling is to provide the cavity for placement of theexplosives For the vast majority of surface mines, however, drilling and blastingare prerequisite to excavator and essential to the production cycle

Drilling is also used in surface mining for purposes other than providingblastholes It finds application during exploration for obtaining samples and duringdevelopment for drainage, slope stability, foundation testing etc

Drilling is the most common means of rock penetration, the operation of placing

a directed hole in rock Closely akin to drilling for exploitation purposes is thecutting or freeing of dimension stone in quarrying

A variety of rocks may be encountered in drilling They are ore or water isusually of less consequence in selecting a drilling method than how resistant theyare to penetration and how they occur geologically The same drill may be used in

overburden and in ore - but different methods may be required in the same mine forvariations in ore.

Likewise, both consolidated and unconsolidated materials may have to bedrilled While soils and other loose material do not require blasting, on occasionthey may have to be penetrated by a drill when they overlie rock, or when they can

be partially moved by explosives economically The latter practice is termed

“explosives stripping”

Classification of method.

A classification of drilling method for surface or nay other kind of mining can

be made on several bases These include size of hole, method of mounted, and type

of power The scheme considered the most logical to employ is on the basis of form

of rock attack; or made of energy application

1/ Mechanical attack

The application of mechanical energy to rock can be performed basically in onlytwo ways by percussive or rotary action Combining the two results in a hybridmethod termed rotary-percussion

2/ Thermal attack

Although other principles are known and could be employed, the only method

of thermal penetration having practical application today is flame attack with jetpiercer or channeler

3/ Fluid attack

To produce a directed hole with a fluid from an external source, jet action orerosion appears to be most feasible, but application is limited Monitors have beenused for over a century to mine placer deposit and more recently for hydraulicmining of coal, gilsonite, and other consolidated of relatively low strength

4/ Sonic attack

Sometimes referred to as vibratory drilling, this method as presently conceived

is a form of high-frequency percussion Attractive but not presently commercial,actuation of sonic devices by hydraulic, electric, or pneumatic means is possible

5/ Other attack

While some attempts to employ other forms of energy have been made, theremaining methods must be classified as in the hypothetical or research category atpresent

Theory of penetration

1/ Operating components of system

There are three main functional components of a drilling system:

a, Drilling (source)

b, Rod (transmitter)

c, Bit (applicator)

The three main components are related to the utilization of energy by the system

in attacking rock in the following ways:

a, The drilling is the prime mover, converting energy from its original from(fluid, electrical, pneumatic, or combustion engine drive) into mechanical energy toactuate the system

b, The rod (or drill steel, stem, or pipe) transmits energy from the prime mover

or source to the bit or applicator

c, The bit is the applies of energy in the system, attacking rock mechanically toachieve penetration

In commercial drilling machines, much attention of late has been focus onreduction of energy losses in transmission This had led to the introduction ofdown-hole drills, both of the large percussion variety and the rollerbit rotory(electro and turbodrill) type, which replace mechanical energy transmission withfluid or electrical transmission

Phases of rock drilling:

A drilling system must perform two separate operations, in order to achieveadvance into rock: 1 fracture of material in the solid and 2 ejection of the debrisformed The first phase is, course, actual penetration, while the second is cuttingremoval Both affect drilling and drill performance but are distinct and separatephases of process

Mechanics of penetration

There are only basis ways to attack rock mechanically-percussion and and the four classes of commercial drilling methods, discussed below, theseprinciples or combinations of them

rotation-Causing rock to break during drilling is a matter of applying sufficient stresswith a tool to exceed the strength of the rock This resistance to penetration to rock

is termed its drilling strength; it is not equivalent to any of the well-known strengthparameters

By far the most common percussion drill in use today is hammer drill In thisdrill, the piston or hammer reciprocates in a cylinder and strikes the drill steed.There are two basic operating principles in the action of the percussion hammerdrill

First is the principle that makes the piston reciprocate in the cylinder, andsecond is that which makes the drill steel and bit rotate In all drills, pistonmovement is effected by a self-acting valve that admits compressed air at theproper instant, first to one end of the cylinder and then to other end Rotation of thedrill steel is accomplished by one or four methods: automatic rifle bar rotation,integral independent rotation, external independent rotation, integral independentrotation, external independent rotation, and manual rotation.

Most percussion hammer drills in use today are rifle-bar rotated and includejackhammers, drifters of all size, and most underground mining drills.Jackhammers are generally classified by weight in these categories: 15-Lb, 25- to40-Lb, 40- to 50-Lb, and 50- to 65-Lb tools Drifters are classified by cylinder boresize and include the following: 25/8, 22/4, 3, 31/2, 4, 41/2, 45/2, 43/4, 5, 51/4, 51/2 and 6 in.Figure 1 shows a typical, rifle-bar rotated, reserve rotation, large bore drifted.Machines of this class are designed to drill 21/2- to 9 in diameter holes up to 100 ft

in depth Drill rates vary from 30 to 60 ft per hr in granites and trap rocks and 70 to

150 ft per hr in limestones

Integral, independent – rotation drill are those that the piston in the samemanner as a hammer drill but depend on separately driven rotation mechanism torotate the steel Figure 2 is an example of the construction in use today This class

of drill is manufactured in bore sizes of 4, 41/2, 43/4, 5 and 51/2 in These machines aredesigned to drill 21/2 to – 6-in- diameter holes at rates and depths comparable totheir rifle-bar rotated counterparts

The drill illustrated in fig.3 has rotation motor located at the front of the drill.Variations in construction mount the air motor at the rear of the drifter, and onemanufacturer augments rifle-bar rotation with a front-end drive air motor Allindependent-rotation drills permit the sections of drill steel without cycling thepiston

An example of the externally rotated, independent-rotation drill is the hole drill shown in Fig 4 It has no built in rotation, and the piston strikes directly

down-on the bit Since the hammer follows the bit in the hole, no energy is lost throughlong lengths of the drill steel Drill speeds in deep holes are higher than thoseattainable with any other type of percussion drill Rotation of the drill is suppliedfrom an external source, and compressed air to operate the drill and clean the hole

is passed through the drill stems that connect the drill to mounting Various sizesare available which can drill holes from 31/2 to 9 in diameter

A relatively new method of drilling in use today which promises higher drillspeeds is the rotary-percussion method There are two types: rotary percussion withpercussion bit and drifter-type drill, and rotary percussion with roller bit and down-hole drill

Compressed air is almost the universal power source for all percussion drills

2/ Physics of the percussion tools

The total theoretical power output of a percussion drill is given by the followingequation:

Power output 3/2 31//22 1/2

W

B A P



Where: P is pressure on working face of piston, in psig

W is weight of piston, in Lb

A is area of face of piston, in in2

S is length of stroke of piston, in in

3/ Hole cleaning

The majority of percussion – drilling machines in surface mining usecompressed air as a hole-cleaning medium Attempts are made to achieve hole-cleaning velocities in excess of 3,000 fpm For the vertical lifting or rock particleshaving a specific gravity of 3.0 and less, the necessary velocity is given by theequation:

V=13,300(S(S1))D3/2



Where: V is air velocity, in fpm

S is specific gravity

D is diameter of rock particles, in in

The necessary compressed air requirement to achieve good hole cleaning ispound as follows:

Q =

144

) a A (

Where: V is air velocity, in fpm

A is area of hole cross section, in in2

a is area of drill rod cross section, in in2

Q is free air exhausted, in cfm

Down- hole drills provide velocities in excess of 4,000 fpm since their usepermits large cross-sectional drill steel The large-bore drifters present a differentoperating problem, since in most instances the drill steel must be handledphysically and steel section is limited due to weight

Wet drilling is not common in surface mining operations Water flushingreduces drilling speed up to 10%, and most operators drill dry A relatively newmethod of dust control is being used widely This is water mist or “detergent”drilling In this method, small amounts of water are introduced in the drill blowerair stream, and the dust particles are agglomerated and brought to the hole collar aspellets

6.2.2 Types of bits and steel

There are three general classes of drill bits used in percussion drilling: crossbits, chisel bit, and “button” bit Chisel bits are used frequently in undergroundmining operations on the jackhammer class of drills They are not effective in thelarger hole sixes All present bits in use are the sintered carbide, cutting-edge bitwhich is made in an “X” or cross design The “button” bit is a relatively new design

of drill bit that is being introduced by several manufactures This is a percussion bitwith a flat drilling place, mounted with carbide spheres similar to the buttons in ahard-rock roller bit

Energy applied to the bit by the stem is from the rotating action and thrust

2/ Cutting action

Rotary bits remove the rock by either a rubbing-abrading action, a scraping action, a spalling action, a chipping action, is usually some combination ofthese Sufficient thrust must be provided so that stresses included by the teeth aresufficient to overcome the compressive strength of the rock, but some rock failure

plowing-in its weaker tensile mode The action of the teeth on rollplowing-ing-cutter bits can beunderstood by imagining a gear being forced to roll on rock under a heavy load.Higher thrust loads provide deeper tooth penetration and, greater rock removalefficiency and lower drilling costs

Thrust force is obtained by the weight of the tools above the bit and by coupling

to these tools a part of the weight of the drill rig through hydraulic cylinders, cable,

or chain pull down

6.3.2 Type of drills

1/ Rigs

Drill rigs are mounted on trailers, truck and crawlers Most drag-bit drills aretruck mounted as are many medium-sized rigs for rolling-cutter bits The heavy rigsand many of the medium-sized digs for rolling cutter bits are crawler

Most primary blasthole drilling is vertical, but some is inclined or horizontal.There are a variety of horizontal drills in use; horizontal drills equipped with rollingcutters are uncommon Also uncommon are drills which more than one hole at atime

The application of horizontal drills is mainly in drilling coal overburden Bothdrag bits and rolling-cutter bits can be use for drilling inclined, vertical, orhorizontal holes.

2/ Hole cleaning

Air circulation may be used to clean holes for drag or rolling-cutter bits Air istransmitted from the compressor through a standpipe and hose into the rotating drillstem through a swivel at the top of the stem

3/ Power

The power source may be a gasoline engine, diesel engine, or electric motor.Power is required for tramming, rotating, hoisting, thrusting, leveling, dustcollecting, and operating air compressor Compressors are the largest continuingpower consumer, often using as much as a few hundred horsepower Rotating mayrequire 50 to 150 hp, but most rigs will require less than 75 rotary hp expect forpeak loads Hoisting, dust collecting, and thrusting require less than 25 hp

On most rigs the same motor or engine is used for more than one service

4/ Bits

Drag-bit bodies are casting or forging in which the cutting blades, sometimescalled bits, can be replaced when dull Rolling-cutter bits are made in four generaltypes for soft, medium, hard, and very hard formations The rolling cutters are steeland are specially processed to give them a hard carburized surface and tough innercore The three rolling cones on rolling-cutter bits for softer formations havelonger, more widely spaced teeth with more tooth hard facing than those for harderformation

6.3.3 Application

1/ Size

Rolling-cutter and drag are made in diameters up to 26 in Some special bits,more than 20 ft in diameter, have been made for special purposes other thanblasthole drilling The most popular size for surface mining are 6 to 9 in, althoughthe size range of those in use is form 4 to 15 in the 97/8- and 121/2- in rolling-cutterbits are the most common sizes in those mines where bits longer than 9 in are used

2/ Depth

Rotary methods are used for the deepest oil well drilling- to more than 25,000 ft.Most surface mine, primary blasthole are less than 60 ft deep, and many extendonly 30 to 40 ft There are a new surface mines or quarries where the face or benchheight is as much as 600 ft, and blastholes this deep are drilled by rotary rigs Atthose rate surface mines where holes more than 100 ft deep are used Mostblasthole drilling rigs are equipped with automatic-feed

3/ Utilization

Smooth walls and relatively straight holes are provided by rotary drilling Thisfacilities loading packaged explosives but is less important in loading the free-flowing type of explosives The straightness of the holes is important to achievebottoming of the hole on a predetermined plan An absolutely straight hole isdifficult to achieve with any small-diameter rock drilling method, and a few inchesdeviation per 100 ft must be expected.

6.3.4 Performance

1/ Drag bits.

Drag bits may be used in clays, soft and medium-soft shale, sandstone, limestone, or their equivalent in drillability Penetration rates vary form 60 ft/hr inthe firmer materials to 600 ft/hr in soft shales

soft-2/ Rolling-cutter bits

Rolling –cutter bits will penetrate hard formations such as granites, trap rock,very hard cooper ores, hard iron ore, and taconite at 17 to 30 ft/hr hard limestones,domolites, medium hard iron and cooper ores, and very and very hard sandstonescan be penetrated at 30 to 80 ft/hr penetration rates in clays, shales, softsandstones, and soft ores may be 100 to 300 ft/hr, and are often restricted more bythe ability of machine to remove the cuttings than by the ability of bit to penetrate

3/ Production

Moves and rig setups are required frequently in surface mine drilling Othernon-penetrating time is used add stem where required and for routine maintenance.These non-drilling operation will amount to about 30 % of total rig time Shiftproduction drilling rate will be about 70% of the penetration rate times the number

of hours per shift

Table 6.1- Typical hole spacing and performance data

Formation Hole diameter, in Spacing, ft Average drilling rate, ft/hrBituminous coal

“ 77/8 20×20 40

Rotary drills in shales and limestones often average 800 ft per shift A machine

at one operation produces over 200,000 ft of hole per year

4/ Rotary speed and thrust

Drag bits should be rotated at 25 to 50 rpm in soft material and 15 rpm or lower

in harder materials These bits require low thrust in soft material; and in verticaldrilling in soft materials, the weight of the tools is sufficient When drag bits areused in more resistant material, thrust of from 1,000 to 2,000 Lb/in of bit diameter

is desirable

Under blasthole drilling conditions with rolling cutter bits thrust up to 8,000 Lb/

in of bit diameter may be required Thrust for these bits is discussed in detail in thenext article

The penetration per revolution of rolling-cutter bits, with changes in rotaryspeed is constant when all other conditions remain the same This does not holdtrue in deep holes where drilling muds are used In such deep well drilling, thepenetration per revolution decreases with an increase in rotary sped, but this isunimportant in shallow blasthole work where air is used to clean the hole.Penetration rate in laboratory conditions is directly proportional to rotary speed.There is some indication that under field blasthole drilling conditions, there is aslight decrease in penetration per revolution as rotary speeds are increased but thismay be significant

Bearing wear per revolution on rolling-cutter bits is independent of the rotaryspeed If penetration per revolution is proportional to rotary speed, then bit bearinglife should not be shortened by increasing rotary speed At those mines where there

is a decrease in penetration per revolution, bearing life should be expected todecrease in direct proportion to the decrease n penetration per revolution

The most important, adverse effect of high rotary on rolling-cutter bit life is intooth wear Tooth wear per revolution increases rapidly on a new bit with anincrease in rpm There is an increase in tooth wear an partially dull bits withincreased rpm, but the wear increase is less than on a new bit On one test, the wearper revolution on a new bit at 300 rpm was 6 times that at 50 rpm When the bitwas partially dull, the wear per revolution at 300 rpm was 1.5 times that at 50 rpm.Total bit life was reduced by one-haft when the rotary speed was 300 rpm asopposed to one run at 50 rpm Bit life was reduced to one-third that at 50 rpm when

a bit was run at 500 rpm

It is quite clear from above that higher rpm will provide faster penetration at theexpense of bit life This usually produces higher costs per foot of hole in blastholedrilling, particularly in those formations where bit cost is a large part of the totaldrilling cost There are some indications that it is desirable to have a slight increase

in rpm as the bit dulls

The optimum rpm for rolling-cutter bits must be determined at each operation

by test This optimum usually will be between 50 and 100 rpm A rotary speed ofless than 50 rpm is used frequently to start the hole

5/ Bit life

Bit life of drag bits in soft formations is often excess of 1,000 ft Since the sevenreplaceable bits (cutter) for 6- in bodies and eleven for 8- in bodies cost than $ 2.00each, bit cost per foot of hole is only a few mils Steel-tooth, rolling-cutter bits inpopular sizes cost in excess of $100 and in soft materials will make more than10,000 ft In medium-hard formations- too hard for drag bits- the rolling-cutter bitpenetration will be rapid, but bit life will decline to a few thousand feet In harderlimestones, dolomites, and sandstones, and in some of the softer but hard ore, steel-tooth, rolling-cutter bit life may fall to the 500-to-1000 ft range When the material

to be drilled appears to be in the very hard class, such as hard granite trap rock, andthe harder ores where conventional steel-tooth bit life is in the 500 ft range, rolling-cutter bits with sintered tungsten carbide inserts must be considered

6.3.5 Selection

1/ Size

When the selection of a drill is to be made, the maximum height of overburden

or bench height will have been established The terrain will be known The burden(distance of drillhole from the edge or face of the bench), spacing (distancebetween blasthole), inclination of hole, and hole diameter for the necessaryexplosive charge also will have determined, the procedure for this determination isdiscussed in the section on blasting

2/ Thrust

The rig should be capable of applying thrust of 4,000 to 8,000 Lb/in of diameterdepending on the size of bit to be used Weight per inch of bit diameter willincrease with increase in bit diameter The following table show maximum thrustfor hard rock drilling

Table 6.2 Maximum thrust for hard rock drilling

3/ Circulation

Those rigs using air circulation should provide enough air to produce an annulusvelocity (the upstream velocity of air between the drill stem and the wall of the hole) or5,000 fpm for rock having a specific weight up to 200 Lb/cu ft in place Three thousandfpm annulus velocity is considered a minimum For heavier materials, this velocity should

be increased; some iron ore operations use 9,000 fpm for damp, heavy material

The air volume required on a rig with round drill stem can be determined by:

) d D ( V 0054 , 0 14

4

V ) d D (

2 2

D is diameter of hole, in in

D is outer diameter of drill pipe, in in

Thus, QC = 27.272.(D2-d2), for 5000 fpm velocity, and for a square drill stem,

144

) y D 78 0 (

V Q

2 2 C





Where: y is width of square drill stem, in in

Most compressors on drill are two-stage and deliver air at 70 to 100 psi Single-stagecompressors or high-pressure blowers delivering air at about 40 psi are also quite common.Air pressure should be maintained above 30 psi at the bit For mining operations at highelevations, a check should be made as to whether the rated capacity of compressor at thatelevation is adequate

LESSON 8BLASTING7.1 Fragmentation principles.

7.1.1Factors important to rock fragmentation.

The efficacy of explosives as tools for rock fragmentation lies in their ability to deliveralmost instantaneously large amounts of energy to a limited portion of the rock When anexplosive charge is detonated in a drill hole, its energy is released in a very small fraction

of a second in the iron of gas at extremely high pressure and temperature The mechanics

of the transfer of this energy to the rock and the resulting breakage are complex and not

completely understood Factors that have been identified as important to fragmentationprocess may be grouped in three categories: explosive parameters, charge loadingparameters, and rock parameters.

a/ Explosive parameters.

Explosive parameters known to influence breakage are density, detonation velocity,detonation impedance, detonation pressure, gas volume, and available energy Detonationpressure is probably the best indicator of an explosive ability to break solid hard rock.Detonation pressure is roughly proportional to the product of density and the square of thedetonation velocity The relative ability of different explosives to their pressure to stress in

a given rock is function of their detonation impedances Detonation impedance is theproduct of density and detonation velocity

The volume of gas released in explosive detonation undoubtedly is of importance, atleast in the later of breakage, and is probably of major importance in blasting weak ornaturally fractured rock The energy available to do work in an explosive detonation,essentially what is called “strength” of an explosive, has long been used as a measure ofbreaking ability In a gross way available energy and detonation pressure go hand in hand;however, explosives having an unusual detonation product, or releasing their at a relativelyslow rate because of non-ideal detonation, may produce pressures that are quite differentfrom another explosive of the same energy Both experiment and practice have shown thatavailable energy by itself is not satisfactory for predicting breakage

b/ Charge loading parameters.

 Charge loading parameters, primarily diameter, length, stemming, decoupling,type of initiation, and point of initiation, play an important role in thefragmentation process, often overshadowing the explosive parameters Indeed,for some explosives the charge diameter, the degree of confinement, and the type

of initiation, directly influence the explosive parameters For example, blow acertain limiting diameter, detonation velocity may decrease with decreasingcharge diameter Thus, charge of different diameters within this range are for allintents and purposes different explosives, even though their chemicalcompositions are that performance, as measured by strain-producing ability,diminishes with decreasing diameter to an even greater extent than would beexcepted from the decrease detonation velocity

The physical coupling between explosive charge and the rock has a very significanteffect on the breakage Experimental measurement of the effect that decoupling, defined asthe ratio of the diameter of the hole to the diameter of the charge, has on explosiveperformance are summarized in Fig … The amplitude of motion produced in the rock isapproximately inversely proportional to the 1,5 power of the decoupling As an example,using a 3-inch charge in a 6-inch hole instead of completely filling a 3-inch hole with thesame amount of explosive results in a three fold reduction in amplitude For thoseexplosives having detonation velocities and pressures that depend on confinement, theapparent effect of decoupling will be even greater because the detonation pressure of the

explosive pressure of the explosive will decrease with increasing decoupling chargegeometry, usually defined by the initiated are additional loading parameters central to thebreaking process, particularly in the case of the long cylindrical charges usually employed

in quarry that changing the diameter Length and point of initiation for a charge of a giveexplosive can produce larger differences in the peak strain in the rock than using explosivewith a considerably different detonation pressures

c/ rock parameters.

Rock parameters that need to be considered in understanding the fragmentation processinclude density, propagation velocity, characteristics impedance, energy absorption,compressive strength, tensile strength, variable and structure Density is widely used as ageneral indicator of the difficulty to be expected in breaking a rock, with the densermaterials requiring explosives with high detonation pressures However, less dense, moreporous rocks seem to absorb energy in ways that make desirable fragmentation quitedifficult

The velocity with which stress waves propagate in the rock (usually equal to the somevelocity) is important, first because it affects the distribution in space and time of the stressimposed on the rock by the detonating explosive, and second because it is a measure of theelasticity of the rock Characteristics impedance, the product of density and velocity, is auseful rock parameter for analyzing the transfer of energy from the detonation wave in theexplosive to the stress wave in the rock

Compressive and tensile strength properties are sometimes used to classify rock withregard to ease of breaking with explosives A common characteristic of rock that is crucial

to the fragmentation process is a high ratio of compressive strength to tensile strength Thisratio ranges from ten to hundred, most rocks being very weak in tension Because itmeasures the susceptibility of a rock to tensile failure by stress pulse reflection, the ratio ofcompressive strength to tensile has been defined as the blastability coefficient

Another important characteristic of rock is its variability Unlike ordinary engineeringmaterials, most rock is neither homogeneous nor isotropic The degree of variation of rockproperties with position and with direction is important in blasting In highlyinhomogeneous rocks a large spread in fragmentation results can be expected Effects onanisotropy on breakage have long been recognized

Changes in water content and in situ stress fields can contribute to rock variability.Increased water content seems to reduce energy absorption and thus makes explosivebreakage easier

7.1.2 Rock fragmentations zones

When an explosive charge is detonated in a drill hole, the effect on the surrounding rock

is like that of an immense hammer blow, shattering the rock immediately surrounding thehole and imposing large stresses over a broad area beyond

There are three major divisions, the explosion cavity where the originating process is ahydrodynamic one associated with the detonation of the charge, the transition zone wherethe pressure or stress is rapidly reduced by processes that may include shock waves, plastic