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nd easy way to get information about the mineralization but samples are less representative than in channel sampling for this reason this method should not be used for quantitative ore reserve calculations chip samples are taken by chipping over the whole area or a portion of the face for example using a grid laid out on the face of an exposed outcrop where a line is sampled rock chips are taken over a continuous band across the exposure approximately 15 cm wide using a sharp pointed hammer or an air pick this band is usually horizontal and samples are collected over set lengths into a cloth bag usually 15 cm by 35 cm and equipped with a tie to seal it at sigma mine val d or canada rock chips are taken at intervals of 0 25 0 5 m along horizontal lines marked on the face each line is spaced at 0 75 m from its neighbor and provides between 3 5 and 5 0 kg of material which is sent for assay annels 1991 a general requirement is to collect small chips of equal size or in some cases coarser lumps at uniform intervals over the sampling band or area the distance between any two points horizontally or vertically must be the same on any one face and can vary with the character of the ore the recommended number of points depends on the variation of the ore 12 15 for uniform to highly uniform deposits 20 25 for nonuniform deposits and 50 100 if mineralization is extremely uneven peters 1978 the possibilities for unintentional or intentional bias due to variable chip sizes and the oversampling of higher grade patches or zones are high effort should be made to keep relatively constant sample volume proportional to the widths of the ore and care must be taken to collect approximately the same size chips across the zone being sample chip points should also be as regularly spaced as possible often a composite sample is commonly obtained to establish the average grade of the ore present 4 2 4 3 grab sampling grab sampling is usually performed as the inexpensive and easy option but it is the least preferred sampling method and consisting of already broken material fig 4 9 the method involves collecting large samples from the stockpile at a face or at a drawpoint or from the trucks or conveyor belts transferring the mineralization from these points the accuracy of this sampling method is frequently in doubt and sampling bias is known to be large care must be taken that the sampler is not selective and does not tend to select only large or rich looking fragments some correlation usually exists whereby the larger fragments are enriched or depleted in the critical component of value impartiality is rather difficult to achieve unless rigorous precautions are taken and this is one of the disadvantages of the method storrar 1987 however if the grab sample is composed of enough fragments and if taken over a large enough area it can sometimes represent the grade of the mineralization in that area thus in disseminated or

massive deposits where the ore limits are outside the available site a composite of several pieces from a freshly blasted face can be the most successful sample in general grab sampling is not considered reliable since many independent variables can affect this type of sampling process for example if the ores occur in the softer fraction and a proportional amount of the resulting fines are not sampled the results are clearly erroneous because of the lack of significant dimension and the commonly biased collecting procedure grab sampling can neither be used to volumes estimation nor utilized in mineral deposit evaluation it is commonly accepted that the value of a grab sample is only applicable to the aliquot that was assayed thus a grab sample from a stockpile gives information just on the sample itself and is unsuitable for any accounting purposes the main problem is that the material in stockpiles or the material loaded into trucks is rarely sufficiently mixed to be representative of the block of ground from which it was drawn also material collected will be from the surface of the pile and rarely from its interior annels 1991 grab sampling works better in more homogeneous low nugget effect mineralization types such as some disseminated base metal deposits while in heterogeneous high nugget effect types e g gold especially if coarse gold is present strong bias is expected dominy 2010 in brief nugget effect means error one of the greatest problems with grab sampling is related to the size of the sample that is needed being the amount of individual samples ranging between 1 and 5 kg these few kilograms of sample that are obtained over a pile are therefore commonly inadequate which leads to a large error in most cases it is likely that tons of materials are required for each sample one approach to stockpile sampling is that employed at the gold mines in val d or quebec where the string and knot method is used according to annels 1991 the broken ground from each blast at the face is transported to surface and spread over a concrete pad three of four strings with knots at 0 5 m intervals are then placed over the pile at 3 m intervals and at each knot a sample is taken and its weight recorded along with the position of the knot each sample is assayed and the result weighted by the relevant weight to obtain the overall grade 4 2 4 4 bulk sampling bulk sampling is a usually utilized term to outline the method of the removal of large quantities of ore for the purpose of testing mineral contents before taking a decision to develop a mine an explorer can extract a bulk sample of the material to be mined for further metallurgical or chemical testing and refinement of the proposed mining procedures thus bulk sampling is carried out only in a much evolved exploration if making the decision to mine is required bulk samples are also used for developing beneficiation flow sheet and maximizing the r

ecovery efficiency in mineral processing moreover in parallel with the bulk sampling and geological appraisal work the geomechanical and mining features of the mineral deposit commonly can be studied in more detail extraction of a bulk sample e g 100 tons commonly involves excavation of a small pit or underground operation samples are dispatched for analysis in strong bags or in steel drums the primary purpose is to collect a representative sample and to reliably determine the grade for comparison with the resource estimate this aspect is essential for advanced mineral projects with a nugget problem e g gold mineralization therefore an integral part of a bulk sampling program is the verification of the geological interpretation used for a resource estimate for example where the grades of diamond drill core or reverse circulation drilling chips are suspect due to poor drilling conditions a typical bulk sampling and sample preparation protocol relies on several stages of comminution each followed by mass reduction through splitting fig 4 10 while expensive bulk sampling provides relatively cheap insurance against a failed mine investment as part of a pre feasibility or feasibility study many minerals and metals especially industrial minerals also require testing for the quality of the concentrate or mineral produced in these cases large scale samples of the concentrates or products may be needed by the customer 4 2 4 5 pitting and trenching if the soil is thin in a mineralized area the definition of bedrock mineralization is commonly carried out by the examination and sampling of outcrops however in locations of thick cover it is imperative a sampling program using pitting or trenching or drilling in these methods heavy equipment is utilized to clear surface soil and expose the bedrock hereafter trenches or pits are excavated into the rock to expose ore zones for sampling fig 4 11 despite their relatively shallow depth pitting and trenching have several benefits in comparison with drilling such as the comprehensive geological logging that can be delineated and large and undisturbed samples obtained pits and trenches can be dug by bulldozer excavator or even by hand being excavators commonly much quicker inexpensive and environmentally less harmful than bulldozers in general pitting and trenching can often be regarded as special cases of bulk sampling the advantages of pits and trenches are that they permit the accurate sampling of mineralized horizons and they facilitate the collection of very large samples which is particularly important in the evaluation of some types of mineral deposits such as diamondiferous or gold deposits if the terrain is unfavorable for trenching or if greater depth of penetration is required drilling techniques must be employed in some cases the pit can be sunk not including wall support but correct safety procedures are crucial if there is any possibility o

f the sides caving or of rocks being moved from the sides macdonald 2007 pitting is usually employed to test shallow extensive flat lying bodies of mineralization being buried heavy mineral placers an ideal example in tropical regions thick lateritic soil constitutes optimal conditions for pitting and if the soil is dry pits to 30 m in depth can be safely extracted the sinking of 1 m diameter pits through the overburden into weathered bedrock has been a standard practice in central africa where exposure is poor due to the depth of weathering circular pits 5 10 m apart are sunk to depth of 10 15 m along lines crossing the strike of geochemical anomalies to allow the geologist to cut sampling channels in the pit wall and to identify the bedrock type structure and mineralization if present annels 1991 pitting is a slow labor intensive exercise and the depth of penetration can be limited by a high water table the presence of gas co2 h2s or collapse due to loose friable rubble zones in the soil profile and hard bedrock with regard to trenches they are commonly utilized to expose steep dipping bedrock buried below shallow overburden being useful for further channel sampling where bulk sample treatment facilities are not available fig 4 12 excavated depth of up to 4 m is common in trenches and they can be cut to expose mineralized bedrock where the overburden thickness is not great 5 m most trenches are less than 3 m deep because of their narrow width 1 m and their tendency to collapse although expensive diamond drilling has many advantages over other sampling techniques in that 1 a continuous sample is obtained through the mineralized zone 2 constant volume per unit length is maintained this is very difficult to achieve in both chip and channel sampling 3 good geological mineralogical and geotechnical information can be obtained as well as assay information 4 problems of contamination are minimal for the core has good clean surfaces where contamination does exist the core can be easily cleaned using water dilute hci or industrial solvents and 5 drilling allows samples to be taken in areas remote from physical access annels 1991 these methods are now utilized routinely especially for evaluation of large ore where profuse data are needed from what would otherwise be inaccessible parts of a deposit mining geologist tends to play only a supervisory role in chip channel and grab sampling in a mine but a direct involvement in the logging and assaying of drill cores will be essential either solid rock core or fragmented or finely ground cuttings are brought to surface by drilling and sampled for assay fig 4 13 cuttings are either sampled invariably by machine as it reaches the surface or piled up that must be later subsampled samples are collected at depth intervals of 1 m or more depending on the variability of the mineralization in this sense the quantity of cuttings

from a single drillhole can be huge and the sampling problem is not unimportant sinclair and blackwell 2002 drill cuttings generally can be generally reduced in mass by riffling to generate samples of handy size for further subsampling and analysis in this sampling method it is essential that as much of the mineralization as possible for a specific drilled interval is obtained the rc drill recovers broken rock ranging from silt size up to angular chips a few centimeters across the total mass of cuttings produced in each drilled interval is then collected from the cyclone and the material should be routinely weighed being the common weigh of a 1 m interval of about 25 30 kg in diamond drilling core recovery should be 80 or more for an accurate evaluation although even at this level of recovery it is needed to establish whether losses are random or whether specific types of mineralization or gangue are lost preferentially yielding a systematically biased result once the core has been brought up from underground it should be washed and then examined to ensure that all the sections of core fit together and that none have been misplaced or accidentally inverted in the box after the core is in the correct order the core recovery is measured throughout the mineralized interval and where losses have occurred an attempt is made to assign these to specific depth ranges in the core boxes core is commonly split along the main axis one half being maintained for geologic information and the rest generating material for analysis the decision to utilize mainly half or quarter fig 4 14 as a sample for assay is based on the requirement for a sample size adequate to overcome any nugget effects in general half core split lengthwise is the most common amount taken for assay core splitting can be done with a mechanical splitter or with a diamond saw fig 4 15 being sawing the standard and preferred way to sample solid core thus the core is sawn lengthways into two halves using a diamond impregnated saw the diamond saw also gives a flat surface on which the mineralization can be examined with a hand lens and on which intersection angles of bedding or vein contacts can be measured with ease evaluation of grade distribution and estimation of overall grades are the first quantitative analyses of the grade data and are basic tools to provide inputs to the resources reserve estimation the grade of ore on a portion of a mine or on an entire deposit is estimated by averaging together the assay returns of the samples that have been taken the process involves basically two methods of estimation weighting techniques and statistical techniques mean median geometric mean and sichel s t estimator the first ones are commonly applied to estimation of grades in drillholes whereas statistical estimators of grade require the samples are randomly but uniformly distributed throughout the area being evaluated and that the values are far e

nough apart to be independent variables 4 3 1 weighting techniques grade estimations involving assay intervals in drillholes are enough for a general estimate of a potential mineral deposit in the early steps of prospection one of the most frequent calculations is to compute a grade value for a composite sample e g the average grade of a channel sample from data intervals of several lengths developing a weighted average for unequal sample lengths and or widths thus each sample grade in an intersection of a deposit can be weighted in a variety of ways annels 1991 the first is simply by length weighting in which the sum of the products of intersected length and grade are divided by the sum of the intersected thickness this method can be expressed mathematically as follows g frac displaystyle sum i 1 n left g i times l i right displaystyle sum i 1 n left l i right where g indicates weighted grade n is the number of samples combined and g i and l i are the grades and lengths of each sample respectively sometimes a thickness grade metal accumulation values is computed and utilized to estimate minimum mining width all these calculations assume that there is no significant difference in the specific gravities of different types of material and thus that equal volumes represent equal weights the assumption is usually not far from the truth but if certain portions of the ore body consist of material that is considerably heavier or lighter than the average it can be necessary to weight the samples not only for volume but for specific gravity it often occurs in vein deposits where massive sulfide and disseminated mineralization are present together so previous equation should be modified as follows g frac displaystyle sum i 1 n left g i times l i times s g i right displaystyle sum i 1 n left l i times s g i right where sg i is specific gravity of each sample precise application of the principle of weighting for specific gravity would require specific gravity determination for each sample a practice which is not common and ordinarily is hardly warranted in some ores the specific gravity is closely related to the assay value so that it is feasible to construct a curve based on a limited number of determinations and then read off the specific gravity corresponding to any given metal content another weighting method is the frequency weighting it was originally developed for the evaluation of the reserves of witwatersrand gold ores watermeyer 1919 it requires the production of a frequency histogram or curve from a large assay data base which is assumed to be representative of the deposit from which the intersection has been made for each assay value g i obtained during the sampling the corresponding frequency of occurrence f i is read off and used to weight the assay as follows g frac displaystyle sum i 1 n left g i times l i times f i ri

ght displaystyle sum i 1 n left l i times f i right very high assay values which only occur infrequently are thus assigned a very low frequency weighting factor and their tendency to bias the overall grade is reduced for this reason this technique is applicable where abnormal assays outliers are present see sect 4 2 3 raw data in a mineral deposit are usually matched in such a way as to generate composites of roughly similar support being composites combinations of samples the term compositing where used in mineral resource evaluation is applied to the process by which the values of adjacent samples are matched so that the value of the longer intervals can be evaluated thus compositing is a numerical process that includes the estimation of weighted average grades over larger volumes than the original samples sinclair and blackwell 2002 hustrulid et al 2013 data are composited to standard lengths to due to many reasons such as 1 reduce the number of samples 2 provide representative data for analysis where irregular length assay samples are present 3 bring data to a common support for example to combine drill core samples of different lengths to a general length of 1 m 4 reduce the effect of isolated high grade data 5 produce bench composites that is composites extending from the top of a bench to the base in an open pit such composites are especially helpful if two dimensional evaluation procedures are utilized in benches 6 incorporate dilution e g in mining continuous height benches in an open pit exploitation 7 provide equal sized data for geostatistical analysis after compositing the composited drillhole dataset is commonly validatedsince compositing is linear in nature a substantial smoothing effect reduction in dispersion of grades results because compositing is equivalent to an increase in support it should be considered that compositing can also be performed for values of variables other than grade downhole composites are computed using constant length intervals that generally start from the collar of the drillhole or the top of the first assayed interval these composites are used where the holes are drilled at oblique angles 45 or less to the mining benches and bench composites would be excessively long noble 2011 bench compositing has the advantage of providing constant elevation data that are simple to plot and interpret on plan maps for large and regular mineral deposits where the transition from ore to waste is gradual the compositing interval is often the bench height and fixed elevations are selected this bench compositing is nowadays the procedure most generally utilized for resource modeling in open pit mining hustrulid et al 2013 in the process of compositing the starting and ending points of each composite is recognized and the value of composite grade is estimated as a weighted average by matching the samples included within these limi

ts fig 4 22 in the case of a sample that crosses these limits only the part of the sample that falls within the mineralization is included in the calculation if density is extremely variable for example in massive sulfides compositing must be weighted by length times density by product components are both economically and technologically valuable minor elements that are obtained from the ores of the main metals these components are generally present in ppm ranges whereas the main metals occur within percent ranges in the mineralization for instance germanium occurs in zinc ores gallium in bauxites indium in zinc copper or tin ores tellurium in copper ores hafnium in zirconium ores and tantalum in tin ores moreover many high technology commodities currently are mostly provided by product commodities three types of commodities can be defined and classified according to the relative value of each commodity jen 1992 thus the principal metal product of a mine is the metal with the highest value of output in refined form from a particular mine in a specified period a co product is a metal with a value at least half that of the principal product and a by product is a metal with a value of less than half that of the principal product by products are subdivided into significant by products which are metals with a value of between 25 and 50 that of the principal product and normal by products which are metals with a value of less than 25 that of the principal product evaluation of coproducts and by products usually is carried out by methods similar to that of the main component e g inverse distance weighting or kriging see the next headings in these cases each estimate of the products is calculated regardless of the other with the tacit assumption that no important correlation is present among the different products being the estimation procedure time consuming and costly in other cases these estimation processes can be carried out indirectly if a strong correlation among the coproducts and by products to the principal component is present consequently many multi mineral deposits are generally valued planned and operated on the basis of equivalent grades box 4 3 equivalent grades the prediction of grade and tonnage in a mineral deposit is an essential problem in mineral resource estimation the classical approximation to this issue is to calculate the mineral grade for quantities significant to the mine planning and base the recoverable resource estimation on those calculations rossi and deutsch 2014 the process of calculating a mineral resource can only be carried out after the estimator is convincing of the robustness of the factors that justify the evaluation process from choice of method of sampling to sales contract specifications in this sense ore estimation is the bridge between exploration where successful and mine planning king et al 1982 thus the geological

data must be sufficiently complete to establish a geological model and this itself must have internal consistency should explain the observed arrangement of lithological and mineralogical domains and should represent the estimator s best knowledge of the genesis of the mineral deposit glacken and snowden 2001 in summary regardless of the method used all estimates start with a comprehensive geological database primarily derived from drilling without detailed high quality geological and geochemical data a resource estimate cannot be considered valid the estimation procedure is not only a mere calculation but also a process that includes assumption of geological operational and investigational information all estimates should have the best possible geological input combined with well thought out statistical or geostatistical treatment no purely mathematical estimate should be accepted the calculations therefore form only part and not necessarily the most important part of the overall procedure it is common practice in exploration to begin with economic evaluations as early as possible and to update these evaluations in parallel with the physical exploration work in an early stage the geologist has only a tentative idea about expected grades and tonnages based on the initial geological concept and early concrete indications through observations from trenches or a limited number of drillholes this early idea about grades and tonnages can be called grade potential and tonnage potential wellmer et al 2008 in this sense the four cs character of mineralization continuity calculation and classification are the basis for the correct estimation of ore resources or reserves owens and armstrong 1994 4 5 1 drillhole information and geological data the essential data needed for resource estimation are derived from drillhole information it includes detailed logs of the rock types and mineralization and geochemical and assay data for all samples that were collected it also includes survey data for each drillhole it is critical that the locations in 3 d space of the mineralized zones are known moreover the shape form orientation and distribution of mineralization in a deposit must be known with sufficient confidence to estimate the grade and tonnage of mineralization between drillholes regarding the geological model it obviously should support the distribution of mineralization achieved by sampling a geological model involves examining cross sections long sections plan maps and 3 d computer models of the deposit the resource estimation process includes definition of ore constraints or geological domains analysis of the sample data and application of a suitable interpolation technique in general less than one millionth of the volume of a deposit is sampled and grades and other attributes must be estimated in the unsampled region which is a high risk process in summary knowledge of the geology of the mi

neral deposit is a prerequisite to any reliable computation an incorrect model for the deposit will lead to incorrect resource estimate stevens 2010 this understanding involves space location size shape environment country rock overburden and hydrology mineral chemical and physical characteristics of the raw material as well as average grade and distribution of valuable and gangue minerals popoff 1966 the method used to calculate the ore reserve estimation will change according to the type of commodity type of mineral deposit geometry distribution and homogeneity of the ore mode of data collection among others but conceptually the steps to be taken will be always the same as expressed in the previous formula it should also be borne in mind that ore reserve statement is an estimate not a precise calculation all formulas for computing volumes tonnage and average factors are approximate because of the irregular size and shape of the ore body errors in substituting natural bodies by more simple geometric ones geologic interpretation assumptions and inconsistency in the variables accuracy of the results usually depends more on geologic interpretation and assumptions rather than on the method used fig 4 28 resources or reserves of the same category computed by different methods and based on the same data usually differ slightly in fact if sampling spacing could be sufficiently close estimation would be a matter of simple arithmetic this is almost the situation for example in grade control process see chap 5 where samples are separated 3 or 5 m each other in other words the closer the sample spacing the less important the procedure of ore estimation the sparser the data the more critical the procedure not only quantitatively but also qualitatively because of the greater dependence on subjective assumptions king et al 1982 a variety of procedures have been developed to estimate the tonnage and grade of mineralization in a deposit the methods can be grouped into two categories classical and geostatistical methods classical methods involve commonly the use of section and plan maps whereas geostatistical methods involve complex computer driven 2 d and 3 d statistical techniques to estimate tonnage and grade the utilization of geostatistical methods involves a further complexity in calculation all based upon the theory of regionalized variables described by the french mathematician georges matheron in the early 1960s these methods use the spatial relationship between samples as quantified by the semivariogram to generate weights for the calculation of the unknown point or block values the standard technique of geostatistics was called kriging by matheron in honor to the south african mining engineer danie krige and the type most frequently utilized is the variants of ordinary kriging namely linear kriging techniques classical also called traditional geometric or conventional est

imation methods can be used to assign values to blocks e g polygonal or inverse distance methods and they are commonly utilized at early stages of a mining project these techniques are not particularly reliable but can offer an order of magnitude resource calculation they are also utilized to check the results obtained using more complex geostatistical estimation methods the classical methods have stood the test of time but because of the uncertainties and subjectivities involved in assigning areas of influence they are now largely superseded by geostatistical techniques for the past three decades which are described in the following section however these classical methods are still applicable in many situations and can well produce an end result superior to that possible by a geostatistical method critical assessment for the use of geostatistical kriging should always be undertaken before dismissing the classical methods too often attempts to apply kriging are based on the use of mathematical parameters that have not been adequately tested or proven perhaps due to time or information constraints geostatistical methods will only work satisfactorily if sufficient sampling is available to allow the production of a mathematical model adequate to describe the nature of the mineralization in the deposit under evaluation otherwise it is much better to apply one of the classical methods classical and geostatistical methods for reserve estimation in a single deposit are complex to apply with skewed distribution mineralization variables that include grade ore body thickness and grade thickness and need sophisticated data processing wang et al 2010 the problem lies in the presence of local outliers or anomalies which produce great effects on the estimation process and the need for replace these outliers 4 5 5 classical methods classical or traditional methods utilize analytical and geometric procedures and constitute a deterministic approach the method aims to establish discrete geological boundaries to the mineralization both in mineral exploration and exploitation that are directly related to a sampling grid for resource reserve computations a mineral deposit is converted to an analogous geometric body composed of one several or an aggregate of close order solids that best express size shape and distribution of the variables construction of these blocks depends on the method selected some methods offer two or more manners of block construction thus introducing subjectivity in such a case a certain manner of construction is accepted as appropriate preferably based on geology mining and economics popoff 1966 numerous methods of reserve computations are described in the literature some are only slight modifications of the most common ones depending on the criteria used in substituting the explored ore bodies by auxiliary blocks and on the manner of computing averages for variables classical methods ca

n be classified into six main types 1 method of sections 2 polygonal method 3 triangular method 4 block matrices 5 contour methods and 6 inverse distance weighting methods fig 4 31 these methods do not consider any correlation of mineralization between sample points nor quantify any error of estimation all of them are empirical and their use depends mainly of the experience of the user selection of a method depends on the geology of the mineral deposit the kind of operation the appraisal of geologic and exploration data and the accuracy required time and cost of computations are often important considerations the purpose of reserve computations is one of the most important considerations in selecting a method for preliminary exploration the method should best illustrate the deposit the operations and permit sequential computations and appraisal on the other hand time consuming procedures must be avoided if reserves are being computed for prospective planning the system of mining or the problem of selecting one can influence the preference a certain method of computation can facilitate more than others the design of development and extraction operations owing to technical and economic factors such as mining by levels average grade or different cutoff grades a careful analysis of geology and exploration should be made to select the best method of estimation in general the method or combination of methods selected should suit the purpose of computations and the required accuracy it should also best reflect the character of the mineral deposit and the performed exploration in a complex or irregular deposit it is advisable to use two or more methods for better accuracy and self confidence average of these methods can be accepted as a final result or the values of one method can be considered as a control of others thus the use of two or more methods to compute reserves for the same deposit is common practice various methods can be also applied for different parts of a body depending on the geology mine design type and intensity of exploration workings and category of reserve computations a second method can often be used for control of the computations made by the principal method so that no crude errors can occur a common example of combined methods is where one method is applied to outline and divide the mineral body into blocks and another to determine the parameters of each block 4 5 5 1 cross sectional methods if a deposit has been systematically drilled on sections according to a regular grid reserve calculation will be based on cross sections along these lines the cross sectional methods are based on a careful consideration of the geology of the mineral deposit and the developing of a correct geological model that is essential for good resource estimates stevens 2010 it is possible to distinguish two variables of the standard method vertical sections or fence used mainly in exp

loration and horizontal sections or level used in mining although there are many geometric possibilities in the traditional cross sectional method the area or ore in a given cross section is calculated e g with a planimeter counting squares or through simpson s rule and the volume of the ore body is commonly computed using as a solid figure two consecutive cross sections and the distance between them fig 4 32a project evaluation is the process of identifying the economic feasibility of a project that requires a capital investment and making the investment decision torries 1998 much care and perhaps multiple evaluation methods are required to obtain results on which to base mineral investment decisions mineral investments show certain characteristics that differentiate them from other types of investment opportunities such as the depletable nature of the ore reserves the unique location of the deposit the existence of many geologic uncertainties the significant time needed to place a mineral deposit into production the commonly long lived nature of the operation itself and the strong cyclical nature of mineral prices this decrease in flexibility obviously increment the risk of mining projects compared to other types of investment opportunities the term risk has many meanings in the mining world but a broad definition of risk is the effect of uncertainty on objectives iso 31000 2009 risk management principles and guidelines it can be used by any organization regardless of its size activity or sector deeper in the subject rudenno 2012 selects up to seven differences between resource and industrial companies 1 volatility of share prices share price volatility for resource stocks has historically been greater than for industrials 2 exploration a unique feature of the mining industry is the need to explore in order to find and define an economic resource on which a mining project can be built 3 finite reserves any mineral resource has a finite volume and therefore will have a finite life industrial companies are in theory able to operate for an indefinite length of time once they have a raw material supply and a market for their product 4 commodity price volatility resource stocks are exposed to greater external commodity price volatility than most industrial stocks since most of the world s major exporters of raw mineral commodities are price takers rather than price makers 5 capital intensity the mining industry by its very nature is capital intensive being the high level of expenditure due to exploration economies of scale isolation and power and water factors 6 environmental protection of the environment is important for both industrial and resource companies but mining cycle environmental impacts see chap 7 are clearly more intensive and harmful in mining projects 7 land rights although industrial based companies can be faced with problems related to land right

s they are not as exposed as mining companies which are often involved in exploration on land not covered under freehold title moreover the effects of time greatly influence the value of a mineral project as they do any other long lived investment because many mineral procedures are cyclical and the issues to forecast prices and expenditures poses special problems in calculating and planning mineral projects labys 1992 time also affects mineral projects in several ways that are not always present in other investment opportunities for example the first higher grade ore mined increases early profits but diminishes the average grade of the rest of the ore thus reducing the global life of the mine moreover it is impossible to establish the right amount or grade of material to be mined until the deposit is depleted this is related to geologic certainty only statistical estimates of the reserves and economic certainty it is almost impossible to determine reserves since future prices cannot be forecast accurately torries 1998 in summary the use of adequate project evaluation techniques is more important in the mining industry than in many other industries this is because the mining projects are extremely capital intensive and require many years of production before a positive cash flow commences and their life is much longer compared to other industries it is important to keep in mind the dynamic nature of project evaluation numerous projects compete for the same scarce resources at any given time changes in the budget evaluation criteria or costs or benefits of any of the competing projects can change the evaluation results and ranking for any single project under consideration three levels of geological engineering economic studies are commonly applied by the mining industry the scoping study the preliminary feasibility pre feasibility study and the feasibility study depending on the context each of these types of study is sometimes generally referenced as a feasibility study the two important requirements for these types of studies especially feasibility reports are as follows 1 reports must be easy to read and their information must be easily accessible and 2 parts of the reports need to be read and understood by nontechnical people hustrulid et al 2013 once a resource estimate has been completed a decision will be made to either to shelve the project to continue drilling on the project with the hope of increasing the resource or to proceed with a preliminary economic assessment or pre feasibility study these studies build upon the resource estimate by designing a mine around the deposit and undertaking economic analysis of the viability of a mining operation each study builds upon the earlier study by increasing the detail and level of rigor the primary goal for determining the feasibility of a mineral property is to prove that the mining project is economically feasible if it is designed an

d operated properly the terminology for each stage of feasibility study is very varied and there is no agreed standard for quality or accuracy thus it is very common to refer it as scoping studies pre feasibility studies and feasibility studies it is convenient to use this terminology although the study process is iterative and several increasingly detailed pre feasibility studies can be undertaken before committing to the final feasibility study some of these steps are usually overlapped but this is improbable to reduce the time involved in this sense it is not rare to spend about 15 years between the beginning of the prospection program and the start mine production moon and evans 2006 the studies range from the lowest level of certainty scoping to the highest level of certainty feasibility and show increasing levels of detail and expense associated with their completion only the final feasibility study is considered to have sufficient detail to allow a definitive positive or negative decision for corporate and financial purposes however it is important to note that production of a final feasibility study report does not in itself mean that a project is viable or that the project will be one that will attract project finance often these project stages are required to be undertaken in line with international codes such as jorc or ni 43 101 see chap 1 to determine what is required and includes their associated confidence levels regarding the cost of these studies they vary substantially depending on the size and nature of the project the type of study being undertaken the number of alternatives to be investigated and numerous other factors for this reason some estimated data are offered in each type of study pre feasibility and feasibility studies involve establishing several key components of a mining operation including mine design processing methods reclamation and closure plans and cash flow analysis these are referred to as the modifying factors under the international reporting standards mine design involves determining the mining methods annual and life of mine production equipment needs and personnel requirements processing methods are the methods and equipment needed to concentrate mineral or recover metal from ore commonly presented in a flow sheet diagram that outlines the steps the ore will go through from the time it leaves the mine until the final product is produced reclamation and closure plans are part of the overall mining operation and must be factored into the mine and mill design as well as the cash flow analysis it represents the detailed economic assessment of the proposed mine and will be taken in detail in next section cash flow analysis may be very complex and generally include the capital costs table 4 16 the operating costs table 4 17 taxes and royalties and the revenues generated by the sale of products this type of study provides a first pass examination

of the potential economics of developing a mine on a mineral deposit though a scoping study is useful as a tool it is neither valid for economic decision making nor sufficient for reserve reporting the evaluation is conducted by using mine layouts and factoring known costs and capacities of similar projects completed elsewhere the study is directed at the potential of the property rather than a conservative view based on limited information and it is commonly performed to determine whether the expense of a pre feasibility study and later feasibility study is warranted at this stage mineralogical studies will identify undesirable elements and other possible metallurgical issues it is also common to explore different options for mining and processing the deposit in order to choose the most promising methods for further study scoping study usually takes a few weeks to a few months to complete and cost usd 20 000 to usd 200 000 stevens 2010 or 0 1 0 3 expressed as a percentage of the capital cost of the project rupprecht 2004 the major risk at this stage is that a viable mining project is abandoned due to an inadequate assessment for this reason it is paramount that expert people are implicated in the study the intended estimation accuracy is usually 30 35 though some companies accept 50 ni 43 101 defines a pre feasibility study as a comprehensive study of the viability of a mineral project that has advanced to a stage where the mining method has been established and an effective method of mineral processing has been determined and includes a financial analysis based on reasonable assumptions of technical engineering legal operation economic social and environmental factors and the evaluation of other relevant factors which are sufficient for a qualified person acting reasonably to determine if all or part of the mineral resource can be classified as a mineral reserve one of the most important aspects of a pre feasibility study is that a mineral resource cannot be converted to a mineral reserve unless it is supported by at least a pre feasibility study it is common that the results of the pre feasibility study can be the first hard project information which is seen by corporate decision makers and investors the aim of the pre feasibility study is to evaluate the various options and possible combinations of technical and business issues to assess the sensitivity of the project to changes in the individual parameters and to rank various scenarios prior to selecting the most likely for further more detailed study moon and evans 2006 there are many reasons for carrying out a pre feasibility study being the most important as follows a as a basis for further development of a major exploration program following a successful preliminary program b to attract a buyer to the project or to attract a joint venture partner c to provide a justification for proceeding to a final feasibility study and d as

a means to determine issues requiring further attention rupprecht 2004 for these reasons especially the second one the pre feasibility study must be carefully prepared by a small multidisciplined group of experienced technical people and its conclusions should be heavily qualified wherever necessary being the assumptions realistic rather than optimistic thus the pre feasibility study represents an intermediate step between the scoping study and the final feasibility study requiring a high level of test work and engineering design at the end of a pre feasibility study geological confidence is such that it is suitable to publicly disclose ore reserves from measured and indicated resources and any other mineral resources that can become mineable in the future with further study these studies tend to achieve an accuracy within 20 30 in a pre feasibility study economic evaluation see the following headings is utilized to assess various development options and overall project viability the results of the study are used to justify expenditure on gathering this additional information and the considerable expenditure needed to carry out the final feasibility study on a substantial project in a pre feasibility study the details of the processing methods will be based on initial metallurgical studies of the mineralization of the deposit table 4 18 rather than solely on standard industry methods accordingly pre feasibility studies can include washing milling and numerous other techniques designed to prepare the material for sale and distribution to customers the feasibility study is the last stage needed to establish if a mine is economically viable for this reason it is much more detailed and costly than the previous two study types the objective is to remove all significant doubt and to present relevant information about referenced material as well as to verify and maximize the value of the preferred technical and business options identified in the previous pre feasibility study for this reason a full feasibility study must prove within a reasonable confidence that the mining project can be operated in a technically sound and economically viable manner capital and operating costs are evaluated to an accuracy between 10 and 15 covering realistic eventualities based on the level of engineering completed in these studies the product price is the most important single variable and yet the most difficult to predict the feasibility study should determine ore reserves as per standard definition e g ni 43 101 samrec or jorc scale of the project construction budget and schedule for the project cost estimate for operating and capital contingencies table 4 19 market estimates table 4 20 cash flow studies and risk analysis rupprecht 2004 sensitivity analyses are carried out to establish the major factors that can impact upon the reserve estimate table 4 21 this will help quantify the risk associat

ed with the reserves which at this stage will fall within the company s acceptable risk category often financial institutions utilize independent consultants to audit the resource reserve calculations moon and evans 2006 the defined mine plans in a feasibility study is based on measured and indicated geologic resource which would become proven and probable reserves at this stage consultation and negotiation with local community groups landowners and other interested parties will proceed to the point of basic agreement full feasibility studies cost in the neighborhood of one to a few million dollars stevens 2010 or 0 5 1 5 of the capital cost of the project rupprecht 2004 and can take 1 2 years to complete this type of study is usually undertaken by engineering consulting firms with expertise in various aspects of mine design and development mineral extraction is the procedure of excavation and recuperation of mineralization and associated waste rock from the crust of the earth to derive a profit this mineralization generates the essential metal and mineral products used by present society mining is where all the hard rock time and cost of exploration evaluation financial analysis permitting and construction pay off thus extraction is the culmination of the preceding stages although extraction focuses on production it is accompanied by some exploration and development work which should continue until the end of the mine s life the process of planning a mine can be reduced to a network of interrelated systems that are tied together by a common philosophy of mine planning the resource being mined is to be extracted in a safe fig 5 1 efficient and profitable manner bise 2003 increasing mining costs declining average ore grades environmental considerations and improved health and safety awareness are some of the main challenges facing the mining industry in the last decades wetherelt and van der wielen 2011 in this extraction procedure mineralization is obtained from the ground using surface and or underground mining methods in surface mining soil and rocks overlying the mineral deposit are removed prior to extract the mineralization which is exploited from the surface these soil and rocks are left in place in underground mining being the mineralization extracted using a network of shafts and adits mines range in size from small underground operation producing a few hundred tons of mineralization per day to very large surface mines such as the escondida mine chile fig 5 2 which produces near 250 000 tons per day of copper gold and silver ore and greater amount of waste being in terms of production the largest world copper mine whatever the investment activities or metal prices the amount of metal produced every year in global mining is fairly stable and increasing slowly but steadily total volumes of rock and ore handled in the global mining industry amount to approximately 40 000

millions of tons per year roughly 50 are metals coal about 45 and industrial minerals account for the remainder the capability of the earth to meet these rocks and minerals demand is not truly a matter of resources since they are clearly there but rather a matter of price and cost hustrulid and fernberg 2012 the answer to this question will be determined by the ability of mining and mineral processing technology to stay ahead of demand growth randolph 2011 during the development and extraction stages of mining significantly similar unit operations are commonly used leaving aside the mining method selected these steps contributing directly to mineral extraction are called production operations and conform globally to the production cycle this employs unit operations that are normally grouped into rock breakage and material handling the basic production cycle in mining consists of drilling blasting loading hauling in addition to the operations of the production cycle certain auxiliary operations must be commonly performed thus mines require compressed air electrical power mine ventilation mine dewatering or pumping and backfill distribution for instance in a common day a typical underground mine uses a greater mass of ventilating air than ore the deeper the mine the more air to be moved for this reason it is essential to ensure that all the workings in the mine are kept free of blasting fumes and dust finally modern mine designs have to incorporate underground garages fueling stations and repair areas 5 2 surface mining vs underground mining the method chosen for extraction of the mineral deposit defines the third stage in the life of the mine being the selection of the method the key decision to be made in mine development it must take into account many factors and can have to be refined and changed over time for example it can be logical for a large copper deposit to be mined first by the open pit surface method then by block caving underground method and finally by solution mining method the fundamental rule of extraction is to choose a mining method that combines the singular features of the mineral deposit being extracted and the environment to perform the general lowest cost and return the maximum profit hartman and mutmansky 2002 some deposits are mined completely with surface methods while others can only be worked underground if an ore body is located very deep surface mining obviously is not a viable method these deposits commonly display geological and mineralogical characteristics that require more selective ore extraction in some cases especially in areas of high construction density it is almost impossible to obtain permits for new surface mines this is the case of quarries for aggregates in large metropolitan areas of many developed countries to solve this problem the unique possibility is to develop underground quarries the issue arises where the deposit is

located at depth that is amenable to either surface or underground mining methods if an ore body is large and spreads from surface to great depth mining process starts near the surface and then extraction continues by underground mining of the deeper parts of the ore body utilizing a ramp from the lower part of the pit fig 5 3 the increasing cost of extract waste at greater depths is one of the major factors in deciding when to transition from surface to underground mining of a given deposit where choosing between surface and underground methods there are many factors both quantitative and qualitative that must be evaluated to select the mining method some of the factors that must be considered include a size shape and depth of the deposit b geological structure and geotechnical conditions c productivities and machinery capacities d availability of experienced work force e capital requirements and operating costs f ore recoveries and revenues g safety and injuries h environmental impacts during and after the mining i reclamation and restoration requirements and costs and j societal and cultural expectations nelson 2011 for example if the mineral deposit lies horizontal it is commonly mined through either surface or underground mining methods but not both instead for a steeply dipping vein or massive deposit that outcrops on the surface and extend very deep the best strategy is often to mine at first using surface methods and then changing to underground mining in fact the ore to waste ratio is the principal feature in the choice between surface and underground mining although both methods have benefits and drawbacks surface mining is usually a more profitable method than underground mining in terms of daily production tonnage surface mines are almost always larger than underground mines producing the same commodity this is because surface mines must extract much higher waste rock whereas many of the underground mines extract the same mineral more selectively and with less dilution with all other conditions equal surface mining is normally regarded as preferable because of lower development costs quicker start up time and lower number of accidents the underground mining environment is recognized as being more hazardous than the surface environment underground mining is generally more expensive than surface mining since it is more capital intensive surface mining is also preferred because it does not need to extract an excessive amount of waste rock to access the ore in an underground mine a significant amount of infrastructure must be installed before mining begins in which that large capital investment is often necessary before production can start the development of a large underground mine can take as many as 5 10 years interest costs during this time will therefore be high and can comprise 30 40 of the pre mining capital requirements before mining can start howeve

r for large tonnage production capital and operating costs are commonly higher for surface mines in these cases a dual feasibility study must be performed comparing the surface option to the best underground mining option in all circumstances capital costs increase and operating costs decrease with increasing production tonnage the time between overburden removal and the mining of the product mineral in surface mines should be as short as possible to optimize overall cash flow otherwise high preproduction development costs are produced and the interest costs during development are high and represent a significant portion of the pre mining capital requirement before mining can start nelson 2011 the dominance of surface operations icmm 2012 fig 5 4 is based on the amount of rock handled many times mainly the removal of overburden which is often drilled and blasted thus by necessity the surface operations are larger than the underground ones moreover as a result of economy of scale mining design and equipment have drastically increased in size in the last decades although this strategy cannot always be advantageous consequently a number of large mining companies pursued a strategy of owning and operating large scale world class mines typically in the form of large surface mines although the depth at which surface mines can be developed is limited based on the previous commented factors the selection of the best mining method for a given deposit including the choice between surface and underground mining is a complex process involving the analysis of many interrelated variables these variables are not only technical but they include consideration of environmental social and political conditions and constraints and of the time and expense required to obtain the government permits the process is usually iterative in nature looking at many possible approaches and determining how all the variables interact with each other mining companies and consultants commonly use detailed and sophisticated models these models incorporate all the technical and financial data to provide exhaustive output including items such as mine and mill production direct and indirect costs taxes and royalties and cash flow and risk analysis once a mining method has been chosen the process has not finished because other decisions need to be made such as the specific underground method that will be used or the pit configuration for the surface mining selected among many others in this case the main goal is to maximize ore recovery and minimize removal of waste rock in the most economic safe and environmentally sound manner stevens 2010 5 2 1 stripping ratio one of the methods to describe the geometrical efficiency of a surface mining operation is with the term stripping ratio box 5 1 stripping ratio in pit design and scheduling is an essential parameter the stripping ratio commonly increases with the depth of the pi

t and determines the economic limit of the surface mine thus an increase in the stripping ratio can render the deeper ore uneconomic to mine by surface mining but economic to mine to underground methods the stripping ratio for metal mines is usually between 1 1 and 3 1 but can exceed 10 1 in mines with high grade ore stripping ratios greater than 20 1 occur in some coal mines stevens 2010 5 2 box 5 1 5 2 stripping ratio moving waste material and overburden to recover the ore is known as stripping therefore stripping ratio a key statistic for mining companies and almost universally used represents the amount of uneconomic material or waste rock that must be removed to extract one unit of ore or profitable material the stripping ratio in fig 5 5 an open pit with an ore body dipping is the ratio between abc and bdec for instance a stripping ratio of 5 1 or simply 5 means that it must be mined five times more amount of waste than ore the ratio is commonly expressed as cubic meters cubic meters tons tons or even in cubic meters tons for some minerals if the waste and ore have the same density it is obviously the same to estimate the stripping ratio in cubic meters cubic meters or in tons tons a wide variety of other units is sometimes used such as overburden thickness coal thickness or cubic meters thermal unit in coal mining operations the ratio of the total amount of waste to the total amount of ore in an entire mine or from the start of mining up to the moment of the present calculation is defined as the overall stripping ratio a stripping ratio can also be calculated over a much shorter time span such as 1 year and this can be referred to as the instantaneous stripping ratio where the instant in this case is 1 year hustrulid et al 2013 thus instantaneous stripping ratio is the real relation of the removed waste volumes and the mineral exploited in the pit during a certain and definite period of time the instant could be defined as a longer or shorter period for example the instantaneous stripping ratio for a day in which the mine extracted 5000 tons of waste and 2000 tons of ore will be 2 5 the pit slope angle plays an important role in the estimation of the stripping ratio steeper slope angles common in competent rocks allow for a lower stripping ratio the stripping ratio of a deposit may be used at least partially to evaluate how profitable it may be for instance a project with a very high strip ratio likely will not be profitable that is because a high strip ratio means that the unwanted material is much greater than the amount of ore that can potentially be extracted making it too expensive to mine conversely a project with a low strip ratio will probably have good prospects for profitability obviously since the waste rock must be also drilled blasted and hauled out of the pit and this process does not produce any revenue minimizing the stripping ratio is critical from an economic viewpo

int as a result mining companies calculate strip ratios for open pit projects well before they enter development and production and seek out projects with relatively low strip ratios 5 2 2 dilution moving to a larger scale of operation means less selectivity hence more dilution dilution refers to the waste material that is not separated from the ore being both mined together as a rule dilution varies between 5 and 30 this waste material is sent with the mineralization to the processing plant consequently dilution increases tonnage of ore while decreasing its grade increasing operating costs in the mill by incrementing the tonnage of material to be milled underestimating dilution can involve a significant risk to a project for example a 10 error in copper grade can generate a shift of 60 in the net present value of a project parker 2012 under existing economic conditions maximum mining efficiency can be defined as 0 dilution at 100 extraction of the mineral being mined in many projects it is common to undertake a global dilution such as 5 for massive deposits and 10 for tabular deposits ebrahimi 2013 dilution can be estimated as the ratio of the tonnage of waste mined and sent to the mill to the total tonnage of ore and waste combined that are milled being usually expressed in percent format thus if 100 tons of waste rock are mined with 900 tons of ore and all being sent to mill dilution is calculated to be 10 factors affecting dilution can be divided as deposit related and mine operation related the first are inherent features of the resource and comprise lithology structural geology grade distribution dip thickness and general shape of deposit factors related to mine operation include the mining method mine geometry mining direction equipment size and the skill of operators there are two types of dilution planned or intentional and unplanned or unintentional in underground mining planned dilution is usually caused by the design of the stope to improve and stabilize the geometry of the ore due to its irregular shape unplanned dilution is usually caused by overbreak of wall rock especially at the hanging wall ore waste boundary generally it is of the order of 10 but values exceeding 40 have been recorded annels 1991 it is almost impossible and costly to eliminate dilution in practice some amount of dilution is practically unavoidable in most underground mining operations scoble and moss 1994 however selective underground mining methods such as sublevel stoping result in a lower rate of dilution than bulk mining methods wellmer et al 2008 in surface mining dilution can vary in a single mine for different benches and zones dilution can also be classified as internal or external fig 5 6 in the context of using a block model to estimate resources dilution happens in two different parts sometimes within a mining block there are waste inclusions or low grade pockets of o

re that cannot be separated and they are inevitably mined with the block this is called internal dilution and it is difficult if not impossible to avoid external dilution sometimes called contact dilution refers to the waste outside of the ore body that is mined within the mining block this type of dilution can be controlled using adequate equipment and mining practices external dilution is of somewhat less significance in large deposits with gradational boundaries in comparison with small deposits because the diluting material can be a small proportion of the mined tonnage and contains some metal possibly near the cutoff grade sinclair and blackwell 2002 the local accuracy of external dilution estimate depends on the quality of the geologic model 5 3 surface mining surface mining which is the extraction of mineralization from the ground in mines open to the surface can be mechanical or aqueous extraction the former predominates whereas the latter cannot be employed unless there is sufficient water quantity available there is a great variation in detail in surface mining but only some basic techniques are employed being the terminology more easy to understand than in underground methods thus there are four main mechanical extraction methods to obtain minerals from the ground 1 open pit mining 2 strip opencast mining 3 quarrying mining and 4 auger mining in turn aqueous extraction can be varied dredging hydraulic mining in situ leaching and evaporite processing the subdivision of the mechanical extraction methods is clearly related to the commodity mined because open pit mining is used basically in metals and diamonds fig 5 7 quarrying and mining extract industrial minerals and rocks such as crushed and dimension stone and strip and auger mining are methods mainly applied to coal deposits open pit and strip mining are the two most dominant surface mining methods in the world accounting for approximately 90 of the surface mineral tonnage the advantages and disadvantages of one type of surface mining versus another are often related to the equipment used and the associated costs and benefits derived from their use bohnet 2011 strip mining has the greatest choice of equipment e g bucket wheel excavators whereas open pit loading equipment is usually matched with haul trucks that can be loaded in four passes in this sense the life of a mining project is an essential factor to select the most suitable mining method some practical and useful formulas can be provided to estimate the life of a mining project being the most used those described by taylor 1977 considering a wide range of ore body sizes and shapes the extraction rates seemed proportional to the three quarter power of the ore tonnage and the designed lives were proportional to the fourth root of the tonnage thus taylor s rule can be formulated as a simple and useful guide that states the nature of open pit mining requires

the application of sound geotechnical engineering practice to mine design and general operating procedures thus the nature of the geotechnical environment and the resultant geomechanics during excavation is one of the primary influences on mining it defines where to commence mining in the first place the choice of mining method the design of the mine layout monitoring strategies and the need for ground control measures during and subsequent to mining understanding the various mining constraints as a result of the nature of the geotechnical environment becomes a key mining consideration throughout the entire life of the project frith and colwell 2011 it is clear that the information gained from geotechnical investigations notably provides valuable information for mine design but also assists with the development of mineral resource estimate and ultimately ore reserve estimate geotechnical design monitoring and stabilization of an open pit mine are ultimately a matter of economics balancing the benefits and costs of stabilization against the costs and implications of a slope failure pine 1992 wyllie and mah 2004 the geotechnical aspects that must be correctly considered during the design operation and abandonment of an open pit excavation are the following 1 local geological structure and its influence on wall stability 2 shear strength of the rock mass and its geological structure 3 a proper analysis of rainwater inflow surface drainage pattern groundwater regime and mine dewatering procedures and their influence on wall stability over time 4 analysis of open pit wall stability for the projected geometry of the pit 5 appropriate drilling and blasting procedures to develop final walls fig 5 8 6 appropriate methods of open pit wall monitoring over a period of time to determine wall stability conditionsin surface mining slope angles are strongly linked to the geotechnical nature of the overburden or waste the less competent the overburden the lower the slope angle must be to maintain an adequate stable and safe pit wall as the slope angle decreases the amount of overlying material that needs to be removed to access each ton of mining product increases and in turn increases the mining cost as early as possible in the mine feasibility assessment process it is crucial to understand and fully consider the interrelationship between the local geotechnical environment and the mining process effective ground control is achieved by the successful management of four basic disciplines in an open pit mine geology planning geotechnical and production 5 3 1 1 geotechnical design process the geotechnical design process for open pit slopes regardless of the size of the pit or materials mined shall adopt the following strategic approaches a site investigation b formulation of a geotechnical model for the pit area c division of the model into geotechnical domains and design sectors d slope des

ign and stability assessment for the geotechnical domains design sectors and e design implementation and definition of monitoring requirements hoek and bray 1981 5 3 1 1 1 site investigation site investigation is the procedure by which geotechnical and all other relevant information that can influence the design construction and performance of the open pit mine slopes is acquired information collected during a site investigation program in the development of a project includes information about the mining history topography geomorphology climate drainage physical geology geological structure tectonic evolution lithology rock mass properties hydrogeology and other relevant items to the project for instance understanding the cause of the variation in rock mass quality is essential in addition to the classification ratings other geotechnical factors can be also defined and questions about these models commonly help to increase the knowledge of the rock mass variability pattern some examples of these critical parameters that are usually interrogated in the modeling process are given in table 5 1 the geotechnical model is the keystone in the design of an open pit mine the construction of the geotechnical model is an evolving process through the various development levels of an open pit mine in many projects sufficient data to compile a detailed model would only be available at the feasibility or construction stages at earlier stages such as scoping or pre feasibility studies a geotechnical model containing much less detail can only be possible box 5 2 geotechnical model data compiled in the four models geological structural rock mass and hydrogeological are utilized to develop the geotechnical model this is a stepway procedure of including subsequent layers of individual data sets into a 3 d solid model applying computer based modeling tools the geological model which displays the rock type limits within the mine is the beginning point and constitutes the first layer of the geotechnical model the layers of other information e g rock mass weathering structural data hydrogeological information among others can then be attached as aforementioned the readiness of a supportive geotechnical model is the essential basis for all slope designs 5 3 1 1 box 5 2 5 3 1 1 geotechnical model the availability of a comprehensive geotechnical model is the fundamental basis for all slope designs and it comprises four component models 1 the geological model 2 the structural model 3 the rock mass model and 4 the hydrogeological model guest and read 2009 several computer based modeling tools are available for the development of 3 d geotechnical models these tools permit visualization and construction of comprehensive models that can include geological and structural information ore grade distributions groundwater distributions and a variety of geotechnical details additional information in t

he geotechnical model includes climate surface drainage and regional seismicity the geotechnical model comprising the four components must be in place before the subsequent steps of setting up the geotechnical domains allocating design sectors and preparing the final slope design can start the purpose of the geological model fig 5 9 is to permit 3 d visualization of the material types that will be present in the pit slopes different material types often have different strength characteristics which require due attention and consideration in the process of pit slope design the model should describe the regional and mine site geology and provide clear and unambiguous information on location and extent of different material types it should represent a broader view of the geology of the deposit including the surrounding waste rock focusing on the engineering aspects this model differs somewhat from that required by mine geologists whose focus is primarily on mineralization read and keeney 2009 the aim of the structural model is to describe the orientation and spatial distribution of the discontinuities that are likely to influence the stability of pit slopes these discontinuities can be divided into two groups a large structural features such as folds and faults that are widely spaced and continuous along strike and dip across the entire mine site major structures and b closely spaced joints cleavage and faults etc that typically do not extend for more than two or three mining benches minor structures the rock mass model represents the engineering properties of the rock mass it comprises the various material types and structural defects in which the open pit slope will be excavated the rock mass properties including the properties of the intact pieces of rock the structures that cut through the rock and the rock mass itself these properties govern the performance of the slope and therefore the design approach in a slope constructed in hard rocks failure could occur along geological structures which are considered as pre existing planes of weakness in relatively weak materials such as weathered or soft rock failure can propagate through the intact material and or along geological structures therefore it is essential to determine the engineering properties in the various geological units present in a pit slope regarding the presence of groundwater in a pit slope it can have significant negative effects on its stability in the case of open pit mines excavated within weak materials such as clay or completely weathered rock pore pressures play a significant role on the stability of pit slopes high pore pressures reduce the effective stresses with concomitant reduction in shear strength of both soil rock material and rock mass this could lead to instability in the pit slope high water pressures also reduce shear strength of structural defects in unweathered strong rock leading to structurally contr

olled instability groundwater can also create saturated conditions and lead to water ponding inside the pit which in turn can lead to unsafe working conditions other problems that could result from saturated conditions or standing water in the pit include loss of access to all or part of the pit difficulties in the use of explosives for rock blasting and reduced efficiency in the mining equipment thus it is essential to develop a good groundwater model at early stages of any open pit mining project so that effective control measures can be designed and implemented to minimize the adverse effects of the groundwater regime in open pit mines excavated below the groundwater table dewatering or depressurization can be necessary for the abovementioned reasons kroeger 2000 beale 2009 5 3 1 1 3 geotechnical domains and design sectors before the slope design and stability analysis can start the pit is split into several geotechnical domains each with its own geotechnical features that are distinct from those of its neighbors fig 5 10 these features will define the stability based on the orientation of pit slopes the amount geotechnical domains significant to pit wall design can change depending on the characteristics of the mine thus several domains can be necessary to outline a large mine excavated in a complex geotechnical environment the geotechnical slope design is the process of determining the optimum slope angles and dimensions for open pit mines designing a geotechnical model is one issue but implementing the information it includes to the slope design is another guest and read 2009 in open pit mining there is a general tendency to increase the slope angle as an attempt to decrease the stripping ratio which in turn can originate higher return on investment however an increase of the slope angle decreases the stability of the slope and it could lead to safety implications and higher operating costs due to slope failures thus the slopes must be constructed to an optimum angle without compromising both safety and economics regarding the design acceptance a slope in mining is defined as stable if the forces resisting the potentially shearing sliding or toppling mass of material on the slope are greater than the forces driving the mass the ratio of the resisting forces to the driving forces is termed the factor of safety fos and has been the basis of stability acceptance criterion for many engineering applications where fos 1 the slope is considered to be in a state of limiting equilibrium while if fos 1 the slope is considered to be theoretically stable there are no strict criteria that specify the acceptable fos but for static loading conditions values of 1 2 2 0 are commonly used depending on the type of slope and its importance 5 3 1 1 5 implementation of the slope design the implementation of the design typically involves minimizing unnecessary damage to slopes during blasting excavation c

ontrol and scaling groundwater and surface water control as well as installation of ground support and reinforcement these measures are added to the production cost but they are required to improve stability for example poor blasting procedures near mine slopes can originate loose rock on slope faces and batter crests overbreak in the slope face and cumulative depletion in the strength of rock mass in which the slope is developed performance monitoring of open pit walls is required to check the geotechnical parameters and assumptions utilized to design the existing walls to assure that any potential falls of ground are identified previous to them becoming harmful and to set correct plans where ground movements are detected 5 3 1 2 slope monitoring in an active excavation slope monitoring is crucial in predicting and preventing slope failures and when failure is imminent mitigating the effects of a slope failure a comprehensive slope stability monitoring program reduces the risk of major production delays or even sterilization of part of a reserve permanently as a consequence of slope failure moreover it ensures overall safety of personnel and equipment in operation wetherelt and van der wielen 2011 another situation in which pit slope monitoring is essential is the presence of active underground workings in close proximity to an open pit mine crown pillar failure or caving related subsidence can permanently cease surface excavation activities slope stability monitoring techniques can be divided into surface and subsurface monitoring techniques wyllie and mah 2004 surface monitoring techniques include visual survey direct measurement techniques prism monitoring laser systems and radar systems fig 5 11 direct measurement techniques include crack width meters tilt meters and other similar devices subsurface monitoring techniques include time domain reflectometry borehole probers extensometers and inclinometers these techniques rely on measurement of changes of the inclination or other characteristics of a borehole that could indicate deterioration of stability additionally seismic monitoring techniques can be used these rely on geophones registering acoustic emissions associated with failure events the most cost effective approach to slope stability monitoring is generally a combination of several of these techniques where they are used to complement one another for instance laser systems or prism monitoring can be used to determine overall stability of pit slopes and identify possible failure zones if instability of a slope is detected extensometers or radar systems can be used for more precise determination of movement in this area a last important consideration in slope stability is the presence of groundwater piezometers are the main tool for determining groundwater level these together with rain gauges can act as an early warning system and serve as a basis for adjustment the rate of wat

er extraction from dewatering wells to prevent groundwater induced failures 5 3 2 surface production cycle the surface production cycle of unit operations for metal and many nonmetal mines commonly consists of drilling blasting loading and hauling fig 5 3 open pit mining deals with the extraction of topsoil and overburden blasting of ore and the transportation of material using a system of shovels or excavators and haul trucks once the haul trucks have been loaded they transport the material out of the mine to a dumping location where the material will either be stored or further processed the trucks then return into the mine and the cycle repeats itself note that each of the unit operations cannot begin its handling of the mineral product before the previous unit operation has completed his work 5 3 2 1 equipment selection in the last 50 years mining equipment and especially trucks have progressively increased in size and capacity because experience has demonstrated that larger equipment has diminished total cost by enhancing productivity in big mines to date in terms of productivity the mining industry continues to adhere to the bigger is better mentality in mine operations drills loading machines and haul trucks comprise the major cost items box 5 3 equipment selection problem the increasing size of mining equipment has occurred in parallel with the addition of new technologies that have brought noticeable changes in the mining industry in the last 20 years an example of these new technologies is the dispatching and global positioning systems for fleet management such as the dispatch system modular mining systems inc which provides optimization of the truck locations in real time thus decreasing truck queuing and shovel hang time fig 5 13 this process is accomplished with sensors integrated into the vehicle design loading or excavating is the third main stage in the production cycle of a mine these terms are not synonymous but they are commonly used interchangeably however the term loading is commonly utilized to indicate that the material is placed in a haulage device once the rock has been fractured by drilling and blasting loading process begins mining systems can generally be classified as continuous or cyclic continuous excavation systems used in surface mining include bucket wheel excavators and bucket chain excavators or dredges commonly applied to brown coal mining for power generation essentially large volume surface mining operations cyclic excavation systems include shovels hydraulic excavators draglines and wheel loaders that are applicable for a large range of operational scales commodities and surface mining configurations because all loading tools in cycling excavation systems perform basically the same function they load trucks differences lie in features such as capacity mobility flexibility life and support requirements the choice of loading unit is de

pendent on the minimum number of active works areas ore selectivity and total production and blending requirements continuous excavation systems are generally matched to continuous transport systems such as belt conveyors or pipelines there could be also applications where continuous excavation could be matched to cyclic transport with mining trucks but operational life or production rate cannot justify investment in continuous transport cyclic excavator systems can be adapted to continuous transport systems particularly for large scale long life deep open pits where waste and ore transported on conveyors generally after crushing to conveyable size is the best economic solution most often cyclic excavation systems are matched to cyclic transport systems typically conventional loading equipment loading mining trucks excavation equipment can be evaluated in terms of productivity metric tons per hour and efficiency cost per metric ton important factors in achieving acceptable productivity and efficiency from excavators are matching the trucks to excavator sizes ideally three or four loading passes selecting the right excavator for the bench height and providing enough working space for the excavator and trucks to operate hustrulid et al 2013 5 3 2 2 1 bucket wheel excavators the bucket wheel excavator bwe is the most powerful tool for mining in unconsolidated and soft rock fig 5 14 it is commonly used in coal seam mines reaching daily outputs of up to 250 000 m3 bwe combines three parts of the mining process in one machine extraction loading and transportation to the conveyor the in pit conveyor system then transports the excavated material to the dumping site or stockpile for purposes of comparison bwe is a high capital low operating cost that has limited flexibility and can operate through a limited range of applications with sensitivity to geological variance humphrey and wagner 2011 these machines are highly customized and vary in design more than do any other mining machines to the extent that nearly every machine is almost unique they are very robust in design and consequently very long lived although very expensive due to the associated conveyors bwe requires linear flat floored mining faces that advance in straight or radial patters for this reason major application of this equipment has historically been large lignite mines in mines of medium to large size the principal loading equipment is the shovel it can be hydraulic or electrical and bucket sizes range from 15 to 70 m3 the electrical cable shovel or rope shovel fig 5 15 continues to be the primary loader of selection for large open pit mines although initially costly these machines have the productivity ruggedness and longevity required by mining operations to reliably load broken rock into large trucks for haulage to processing plants or waste dumps over the life on an operation the dependence on the trailing cable

somewhat limits mobility its handling can be facilitated with the utilization of special cable handling trucks the advantages of electrical cable power are the effective use of power the credibility of the system and the monitoring equipment hustrulid et al 2013 the productivity and unit cost efficiency demanded of the mining industry have resulted in substantial increases in electrical cable shovel size in the last decades shovel capacities have grown tenfold in the past 50 years in the 1960s a typical shovel had a 4 5 m3 bucket to load a 30 ton truck actually machines with as large as a 70 m3 bucket load trucks of 400 tons or more compared with rope shovels hydraulic shovels have less reach so they move more often but they travel at higher speed and do not require assistance with a trailing cable or cable bridge the growth of loader machines has led to a new delineation in the loader market with wheel loaders predominant at the lower range of bucket capacity hydraulic shovels in the middle range and electrical shovels at the upper end of bucket capacity 5 3 2 2 3 hydraulic excavators for hydraulic excavators face shovel fig 5 16 and backhoe configurations are available face shovel configurations are preferred in harder rock and with higher rock faces whereas backhoe configurations allow for more selective digging and faster cycle times hydraulic excavators can be diesel or electrically driven they are somehow similar to hydraulic shovels and even both terms are often used interchangeably draglines fig 5 17 are self contained systems that load and transport material to a dump point they are highly productive comparatively low in operating cost and labor requirements and extremely robust consequently they have very long lives commonly 30 40 years because of their high productivity and capability of direct disposal of material draglines are favored for area mining see section strip mining in areas of flat lying tabular geology with high production requirements the most common application for large draglines is overburden removal in coal mining having up to 125 m3 bucket size the bucket is pulled by a dragrope over the face toward equipment itself hence the name dragline in most basic dragline operations the machine removes overburden material to uncover ore that is the most recent in a series of parallel adjacent pits narrow and relatively long overburden material from the current pit is placed in the previous adjacent pit from which product has been removed by auxiliary equipment wheel loaders are used in soft to hard formations and are forthcoming with small bucket size of 0 5 20 m3 these units are commonly wheel mounted but a few models are also offered with crawler mounting for their use in problematic terrain large wheel loaders are often favored as support loading equipment because of mobility advantage they can more readily clean up small quantities of batter trimmings wheel

loaders can be applied as prime loading equipment where mobility in pit blending and multi material selectivity are major issues particularly in shallow open pit operations such as lateritic ores bauxite mining and the like hardy 2007 more recently developed or upgraded large wheel loaders have the advantage of faster digging cycles that more closely approach a rope or hydraulic shovel 5 3 2 3 hauling equipment the fourth and last stage of the production cycle in a mine is haulage hoisting is the term used where essentially vertical transport is accomplished in surface mining works truck haulage is the biggest factor in the operating costs forming from 50 to 60 of the global costs ercelebi and bascetin 2009 off highway trucks they must be translated as well as other mining equipment fig 5 18 in a special tow truck transport medium have dominated haulage in surface mining operations for many years some decades ago a few mines worldwide utilized rail haulage and it is still being used an essential feature to be considered in terms of rail transportation fig 5 19 is the requirement to ensure almost completely horizontal track placement this status has largely restricted opportunities to employ this type of haulage the application of rail haulage only has economic sense if the distance transported is appropriately long czaplicki 2009 longer haulage distances in many large pits availability problems with haul trucks and improvements in technology have revived interest in in pit crushing and conveying ipcc since mineral and waste transportation costs include the greatest amount of surface s mine working costs in pit crusher and a conveyor belt instead of truck transport can reduce this cost aspect mainly where pits have become deeper this system uses a crusher sizer unit to process material from a cyclic loader to a size that is suitable for conveyor transport extending the application of around the pit conveyor systems to include consolidated waste and overburden humphrey and wagner 2011 ipcc fig 5 20 is preferred for the material handling transportation system where long term planning is possible the in pit crushers systems developed and operated to date have varying degrees of mobility ranging from fully mobile units to permanently fixed plants which resemble traditional in ground plants there are many advantages of ipcc as compared to truck haulage some of them among other are the following a cost by shortening the haulage distance between the loaders and crushing plant is reduced b other costs such as operating costs associated with fuel tires and lubricants or labor costs are reduced c safety risks are reduced d belt conveyors can traverse grades of up to 30 versus approximately 10 12 for trucks e co2 emissions are greatly reduced and f conveyors are more energy efficient than trucks and require less skilled labor for maintenance utley 2011 whether ipcc i

s economically viable is a function of production duration of the operation and the distance and vertical lift of the haulage route over the years off highway trucks also called mining trucks or haul trucks are primary means by which both ore and waste are transported in large open pit mines mining trucks haul the material from the loader to a dumpsite in simplest terms a haulage truck is a container the body on drive wheels the amount of material transported per cycle relies on the size of the container used the trucks have capacities ranging from less than 40 tons per load to 400 tons per load in large trucks such as caterpillar 797 and liebherr t 284 or 450 tons per load in belaz 75710 haulage truck capacity is usually measured on the basis of weight rather than volume to prevent overloading it must not be forgotten that loading capacities are measured in volume in this sense the speed at which the truck can transport the material is inversely proportional to its capacity rigid frame haul trucks fig 5 21 have dominated haulage in mining operations although articulated dump trucks have proven to be a viable alternative the truck drive systems can be broadly divided into mechanical drive with automatic transmission and electric drive ac or dc in which the engine drives a generator that powers the electric motor used for traction electric drive is currently becoming the predominant type because of its superior drive performance ease of maintenance and cost advantages made possible by rapid advances in technology because haulage costs are very high a thorough understanding of truck haulage is imperative most mines are designed to minimize the travel distance between the loading unit and the crusher in order to reduce the number of trucks in the fleet decrease wear on the truck and limit the round trip time for each load two important tasks must be undertaken for the proper use of haulage trucks first the trucks must be matched in size to the excavator second the number of trucks in the fleet must be matched to the haulage layout so that the system produces in a near optimal manner 5 3 2 3 2 wheel tractor open bowl scrapers one of the oldest concepts of bulk material handling is the wheel tractor or open bowl scraper fig 5 22 today it is the only machine that can self load haul and dump with a single operator mobility and flexibility are key characteristics of this type of equipment which makes it ideal for small short life mining projects its capability to remove and place material in controlled lifts makes it the machine of choice for topsoil relocation in reclamation operations auxiliary operations consist of all activities supportive of but not contributing directly to the production of ore since this unit operations do not generate incomes there is a tendency in mining organizations to assign them a staff function and a low priority however efficient operations depend largely on au

xiliary operations many of these operations common to mining are classified as supportive on the extraction function but others are associated with development and reclamation operations two examples of auxiliary operations equipment are the track dozers and the motor grades 5 3 2 4 1 track dozers large track dozers are extremely common in all mining operations they are designed to move the greatest amount of material in the most efficient way and generally are used for both utility and production work utility work includes tasks that support a mine s main production fleet such as dumpsite preparation and cleanup bench preparation road creation stockpile work and reclamation these machines can also develop production works such as excavation and to rip in situ or blasted material from one area to another track dozers are complex machines due to their variety of mechanical electrical and hydraulic systems all fitted into a compact design most of the industry commonly uses the smaller size of track dozers because of their lower operation costs and flexibility 5 3 2 4 2 motor graders in good road conditions trucks run faster and more safely fuel costs are lower and tire damage is reduced as truck maintenance is since loaders and haul trucks are responsible for producing ore motor graders fig 5 23 generate a clear impact on how productively these machines can operate especially in their role in haul road maintainability thus they are some of the most productive and productivity enhancing machines on site motor graders are designed to meet the specialized requirements of large mining operations they help to create and maintain constant grade and proper drainage by using the blade incorporated in the machine skillfully it is also possible with motor graders to finish a slope finally since dust in a mining operation presents one of the most visible and invasive operational constraints a haul road dust prevention system is essential to avoid dust lift off fig 5 24 open pits can be in the form of inverted truncated or circular cones where the radius of each circular bench decreases with depth figs 5 7 and 5 25 thus mining occurs in successively narrower benches in order to maintain safety and stability inside the mine it is important to note that each successive bench in the mine is smaller than the last one developed which causes the depth of the pit to be mined is determined by the size and location of the first cut or bench in stratiform deposits shallow and large open pits can be designed in the shape of footprints with steep sides and flat bottoms however some pits can be very deep up to 1 km the objective is to extract both metallic and nonmetallic ores while dumping overburden and tailings at a dedicated disposal site outside the final pit boundary open pit is utilized where the ore body is typically pipe shaped vein type steeply dipping stratified or irregular iron copper fig 5

25 and gold mineralization together account for most of the total open pit excavation volume in the world application of this mining method to coal is less common many features define the size and shape of an open pit and these must be correctly understood and utilized in planning of any open pit operation the importance of each factor is based on the particular project but the following are the key characteristics affecting pit design geology grade and localization of the mineralization extent of the deposit topography property boundaries bench height pit slopes road grades mining costs processing costs metal recovery marketing considerations stripping ratios and cutoff grades armstrong 1990 5 3 3 1 1 open pit geometry mining geometry is a dynamic rather than a static concept because the different geometries are very important so that the needed economic result revenue and costs is realized to evaluate the large number of possibilities the utilization of computers has become invaluable in open pit mining the ore body and the associated waste are extracted from the top down in several horizontal layers of similar thickness called benches fig 5 25 thus benches are the main extraction components in an open pit mine and possibly the most distinguishing feature they are crucial in an operation as they accommodate the active drilling and blasting and excavation areas each bench has an upper and lower surface separated by a distance equal to the bench height thus the bench height is the vertical distance between the highest point of the bench crest and the lower point toe fig 5 26 in general all benches in an open pit have the same height but geological conditions can dictate the opposite there are several types of benches a working benches which are in the process of being mined b inactive benches the remnant of working benches left in place to maintain pit slope stability and c safety or catch benches with a purpose of collecting the material which slides down from benches above constituting one of the busiest areas of an open pit working benches have to accommodate large excavators and dump trucks as well as the muck pile formed after a blast therefore maintaining the quality of a suitable working surface is vital to ensure acceptable safety and productivity levels at an active excavation in addition to leaving the safety benches berms or piles of broken materials are often constructed along the crest to form a ditch between the berm and the toe to catch falling rocks a berm is also a horizontal shelf or ledge at the ultimate pit wall slope the design of all these components is controlled by the geotechnical configuration of the slope several features can influence the selection of bench dimensions this includes ground competence existence of water presence of geological disturbances e g faults joints bedding planes and cutting height of the excavator tatiya 2

013 bench height decision is essential since once this value is determined the rest of the dimensions in the open pit follow consequently one of the most usual bench heights in large open pits is 15 m hustrulid et al 2013 although for smaller pits the value might be 12 m or less a common guideline is that the bench height must be matched to the loading equipment regarding the bench width it varies according to equipment size and the type of bench working benches should at least be wide enough to accommodate the turning radius of the largest haul truck plus the width of the safety berm bench width commonly ranges from 30 m to several hundred meters hustrulid et al 2013 recommended the following steps where considering bench geometry 1 mineral deposit characteristics such as total tonnage and grade distribution dictate a certain geometrical approach and production strategy 2 the production strategy yields daily ore waste production rates selective mining and blending requirements and number or working places 3 the production requirements lead to a certain equipment set fleet type and size 4 each equipment set has a certain optimum associated geometry 5 each piece of equipment in the set has an associated operating geometry 6 a range of suitable bench geometries results 7 consequences regarding stripping ratios operating vs capital costs slope stability aspects etc are evaluated 8 the best of the various alternatives is selected in turn the slope of the pit wall is one of the major elements affecting the size and shape of the pit the pit slope helps to determine the amount of waste that must be moved to mine the ore it is usually expressed in degrees from the horizontal plane the global height from the toe to the crest is the overall pit slope thus the overall pit slope angle can be established as the angle calculated in degrees constituted while joining the toe of the lowest bench to the crest of the top most bench of a pit where benches achieved their ultimate final designs slope angle is clearly an essential parameter that has meaningful economic impact if the slope angle is too steep the pit walls can collapse if it is too shallow excessive waste rock must be removed the exposed subvertical surfaces of the benches are called the bench faces they are described by the toe the crest and the face angle it can vary considerably with rock characteristics face orientation and blasting practices normally bench faces are mined as steeply as possible in most hard rock open pits the face angle ranges approximately from 55 to 80 mining starts with the top bench and after a sufficient floor area has been exposed extraction of the next layer can start in most mines the top few benches are commonly formed by soil and overburden material pre stripping is the term used to refer the removal processing of these materials the entry to the pit is generally defined utilizing a ra

mp or road that can be spiral around the pit or situated on one side of the pit with switchbacks at each end it is important to note that haul roads and ramps connect the benches allowing equipment to move freely about the pit and for ore and waste to be hauled out of the pit thus haul roads constitute a key element of an open pit mine haul roads can significantly impact pit angles and stripping ratios depending on the adopted design and geometry as such sound haul road design and management can play a significant positive influence on the safety record profitability and environmental impact of a mine wetherelt and van der wielen 2011 the width and steepness of the haul road or ramp are based on the type of equipment to be placed fig 5 27 according to the location and use haul roads are generally around 3 3 5 times wider than the largest truck size on two way straights for one way haul roads a width of 2 2 5 times that of the largest truck size is generally enough any change in the road width will directly affect the overall pit wall slope and increment drastically the stripping ratio particularly in deep open pit mines bozorgebrahimi et al 2003 in mining overburden refers to all unprofitable material that needs to be excavated to access an ore deposit if overburden is encapsulated between two layers of ore it can be referred to as interburden overburden forms by far the largest volume of material produced by most open pit mines in which concerns material handling there are three important differences between ore and overburden a overburden is not beneficiated and will generally not generate any revenue b overburden tonnages almost invariably exceed ore tonnages in an open pit mine and c the rock mass characteristics are often different from that of the ore the first two points imply that handling of overburden and related costs should be kept to a minimum furthermore overburden can contain sulfides or other substances that are potentially damaging to the environment consequently selection of the most suitable site for the overburden embankment involves a trade off between handling costs related to overburden disposal and the environmental impact of the overburden at a particular site to minimize costs related to the handling of overburden it is often blasted to a coarser fragmentation than ore and in many cases excavated and hauled by larger capacity equipment the overburden removal system should be in harmony with the mine planning of the future unless this and the other factors influenced by overburden removal schemes are carefully considered operation can suffer in efficiency and costs aiken and gunnet 1990 minimizing costs involves selecting and overburden embankment site in close proximity to the mine where the environmental impact is as small as possible preferably this site is close to the projected final pit limit at the same or at lower elevation than excavation to minimize up

slope haulage costs with these considerations in mind optimization of overburden management at a mine site can have considerable positive influence on the environmental impact and economic viability of a mine wetherelt and van der wielen 2011 topsoil is the near surface portion of the material lying above the ore so that it has sufficient agricultural nutrients to support varying degrees of vegetation growth it is included sometimes in the overburden although the differences are clear both are not ore but the topsoil has an essential end use depending of climate topography and bedrock geology the layer or layers of soil can be just a few centimeters deep or extend to several meters in depth in many operations topsoil storage is required for reclamation purposes at the end of the mine life thus soil and growth media are commonly stockpiled on the mine site for further use in reclamation to replace topsoil as it originally existed on mined areas requires that each layer be carefully excavated and placed in an area of easy recovery in some cases separate storage of different topsoil and subsoil layers can be necessary to ensure quality of the material depending on the duration of topsoil storage revegetation and erosion control can be required because of the unconsolidated nature of the topsoil it often requires different excavation techniques as topsoil is generally free digging scrapers bulldozers front end loaders and small hydraulic excavators are the most common equipment used in topsoil removing bulldozers can be used for pushing materials onto piles for further excavations by front end loaders or hydraulic excavators alternatively they can support scraper operation by ripping soil haulage distance is an important consideration in choice of equipment at short haul distances scrapers and bulldozers are the best option whereas a more conventional excavator truck haulage operation tends to be more economical at longer haul distances wetherelt and van der wielen 2011 5 3 3 1 3 open pit design and optimization the management of a large open pit mine is a huge and complex tax especially for long lived mines thus one of the most important economic inputs of an open pit is the calculation of the final pit limit it is the consequence of mining the amount of material that originates the global maximum benefit while fulfilling the operational needs of safe wall slopes cacceta 2007 the ultimate pit limit evidently gives the size of the mine at the end of its life this limit of the open pit must be set at the planning stage and defines many significant features such as the amount of mined mineralization the metal content and the amount of waste other similar terms for this concept are pit outline or pit contour predictably the size geometry and location of the ultimate design of the pit are important in planning tailing areas waste dumps access roads concentrating plant and all other surface faci

lities the open pit mine design issue is thus to decide the blocks of a mineral deposit to extract to maximize the total profit of the mine while fulfilling digging constraints on pit slope and those that enable underlying blocks to be extracted only after blocks on top of them the ultimate pit only exists if mining stops that is up until that time its final form is uncertain consequently the utilization of the term final pit is discouraged whittle 2011 5 3 3 1 3 1 open pit design there are many ways of designing an ultimate open pit differing by the size of the mineral deposit the features of the data and the accessibility of computer mining software see chap 8 as a rule two methods can be broadly outlined manual or hand methods and computer methods the manual or hand design method is rarely used nowadays because computers are used worldwide and relatively inexpensive software is available a complete description of this technique is shown by annels 1991 regarding the computer methods the growth of their use in the last two decades has enabled to handle huge amounts of data and to study more pit alternatives than with manual methods in computer methods again two groups can be defined computer assisted hand methods and automated methods or computer methods stricto sensu in the first the calculations are done by the computer under the direct guidance of the technician in the automated methods the software program designs the ultimate pit limit based on a given group of economic and physical constraints without assistance of the technician these methods are called in a general sense optimization methods and they obviously use different mathematical algorithms to perform the ultimate pit regardless of the method used in designing the open pit it is necessary to set up values of the physical and economic parameters the final pit limit will mean the maximum limit of all material matching these criteria thus the material included in the pit will find two objectives a a block will not be mined unless it can pay all costs for its mining processing and marketing and for stripping the waste above the block and b for conservation of resources any block meeting the first objective will be included in the pit armstrong 1990 the result of these aims is to establish the design that will maximize the total profit of the pit in terms of the physical and economic parameters applied as these parameters change the pit design can also change pit design relies on preliminary analysis consisting of 1 an ore body model in which the deposit is discretized into a grid of blocks each of which consists of a volume of material and the corresponding mineral properties 2 the value of each block which is determined by comparing market prices for ore with extraction and processing costs and 3 a geometric model of the deposit newman et al 2010 amankwah 2011 being the block model produced in a variety of way

s depending on the structure of the ore body this block model can consider millions of blocks based on the size of the deposit and the blocks the block dimensions are dependent on the physical characteristics of the mine such as pit slopes dip of deposit and grade variability as well as the equipment used however the block sizes should reflect the selective mining unit smu to be used if the ore blocks have heights equal to the bench height or to some exact fraction of them then it is an easy matter to locate bench faces to enclose as much ore as possible annels 1991 the raw material grade especially in metal mines is susceptible to the dimensions of mining blocks e g bench height and therefore the size of the equipment for example in a mine with erratic spatial ore distribution e g many gold deposits the dimensions of the mining block size have a dramatic impact on the ultimate pit value and must be determined very precisely the smallest mining unit or selective mining unit smu is the smallest block inside which ore and waste cannot be separated and grade estimates are utilized to maximize the pit value in fact the determination of mineral resources and or reserves from a block model needs the selection of a block of smu size the second step is carried out computing based on tonnage and grade data an estimated profit of extraction for each block in the model the ore body model is utilized to define the ultimate pit limits that are the limits of the deposit up to which it is economic to extract based on the financial metallurgical and geotechnical information the net profit of each block is calculated this type of block model is commonly referred as economic block model in the third step a geometric model is performed based on slope angle computations these angles are determined by the structural composition of the rocks and change depending on the location and depth if it is possible to fix the block values and the slopes an optimal outline can be determined it is clear that an increment of the values of the blocks generates an increase in the size of the optimal pit while an increment in slopes means the optimal pit gets deeper 5 3 3 1 3 2 open pit optimization optimum pit design is done by utilizing mining software that either uses the floating or moving cone method or the lerchs and grossmann algorithm lerchs and grossmann 1965 the lerchs and grossmann algorithm guaranties the optimality with respect to defining the pit limits that maximize the undiscounted profit while floating cone routine is heuristic and can give suboptimum results for this reason lerchs and grossmann algorithm is the most used method in optimization software programs whereas moving cone method is commonly integrated in low cost software box 5 4 lerchs and grossmann algorithm the moving cone is the simplest method for determining the optimal pit shape being also the most widely utilized of the heuristic al

gorithms since it is very easy to program and simple to understand in this method the optimum pit is a combination of groups of removal cones of blocks main problems of the method include the following a the final pit design relies on the sequence in which reference blocks are chosen and b many reference blocks might need to be chosen and the associated value of the cone computed to achieve a reasonable although not even necessarily optimal pit design annels 1991 aside from the algorithm used by the software package e g moving cone lerchs and grossman milawa korobov and others the aim of an optimization mining software is to generate the most cost effective and most profitable open pit design from a block model of an ore body new algorithms are described recently many of them related to environmental constraints including ecological costs of open pit mining such as prevention and restoration costs or cost of carbon emission from energy consumption e g xu et al 2014 5 3 3 1 3 box 5 4 5 3 3 1 3 lerchs and grossmann algorithm in the optimization of open pit mine design the lerchs and grossmann algorithm is the industry standard helmut lerchs and ingo grossman s paper 1965 optimum design of open pit mines outlined an algorithm based on graph theory that could help planners determine the ultimate limits of an open pit mine in three dimensions at that time most computers were incapable of performing the large quantities of iterative calculations required by the method for this reason a 2 d algorithm was also described this method provided a first approximation to an optimal pit as it only considers data on one section at a time ignoring data on adjacent sections though effective on sections the 2 d algorithm lost its optimized quality where sections were combined therefore lerchs and grossmann were the first to put forward a method to solve the open pit mine optimization problem the aim was to design the contour of a pit that maximizes the difference between total mine value of the extracted ore and the total cost of extraction of ore and waste materials in essence the algorithm works by flagging certain blocks as strong meaning that they are planned to be mined blocks that are not strong are labeled as weak meaning that there is no current plan to mine them a block is considered to be strong if it belongs to a group of linked blocks known as a branch with a total positive value initially each block is a separate branch and thus only the blocks with a positive economic value are strong lerchs and grossmann indicated that where a check through all the arcs does not detect any possible strong to weak connection then those blocks which are labeled as strong constitute the optimal pit being the first step of this process to generate the optimal ultimate pit the second step is to create nested pits within the ultimate pit by changing the capacities of the arcs between the nodes of the gr

aph this process is termed pit parameterization in the third step the nested pits are combined to obtain a pushback design and later on a production schedule is added pushbacks are generated by combining nested pits so as to maximize the net present value of the pit design pit limit and pushbacks in 1986 the whittle 3 d open pit optimization package was launched by whittle programming pty ltd this package utilized the lerchs grossman algorithm in a commercial software application for the first time therefore the lerchs grossman algorithm was the first optimization method used to design large open pits in reasonable time and it is still used in mining optimization software as the industry standard to find the optimal pit in 1987 whittle 4 d was released incorporating time risk and optimizing around npv and incorporating sensitivity analysis for long term planning 5 3 3 1 3 3 production scheduling production scheduling of the open pit mines is a difficult and complex optimization problem it can be outlined as the sequence in which ore and waste of the pit are extracted over the lifetime of the mine and the time gap in which every material is to be extracted the main goal production scheduling is to maximize the total discounted profit from the mine subject to a variety of physical and economic constraints in the process a set of nested pits is generated starting with the ultimate pit contour by varying the economic parameters cacceta 2007 this process assumes an a priori discretization of time into periods and a priori definition of production capacity in each time period to determine the time of extraction for each block a subgroup of nested pits from those calculated in the sequencing step is selected for instance in fig 5 28 the blue area the smallest pit is the one that represents the best value that is possible in the early stages of mining as it is the pit that would still be valuable even under the worst economic conditions i e a low commodity price the green largest pit represents the pit with the longest life under the best economic conditions each of these pits is called a pushback or phase chiscoine et al 2012 by changing the commodity price for instance from a low value to a high value it is possible to originate an increasing size number of pits and a diminishing average value per ton of mineralization included in the open pit since the smallest size open pit covers the highest valued ore the production is scheduled by extracting smallest pit first followed by the production in larger pits the incremental mining from the smallest pit to larger pit is commonly referred to as pushback mining table 5 2 shows an example of pushback values for a production schedule strip mining or opencast mining is a surface method that resembles open pit mining opencast mining seems to be a more descriptive generic term for the method hartman and mutmansky 2002 it is used for large tab

ular flat lying mineralization that is close to the surface although a range of commodities such as phosphate bauxite tar sands manganese and even industrial materials from quarries have been recovered by this method the most common deposits worked by strip mining are coal deposits fig 5 33 the main difference between strip mining and open pit mining lies in the overburden disposal in strip mining overburden is dumped directly onto mined out panels rather than outside the final pit boundary as typical of open pit mining this process is commonly established in one unit operation and carried out by a single machine therefore this method offers an additional advantage of utilizing the same land which is taken up by the deposit for locating the waste rock and hence a minimum land degradationbackfilling of strip mining is often economically feasible and desirable as part of the concurrent reclamation requirements in open pit mining this procedure generally cannot take place until the extraction is completed even then the very high cost of filling the pit with all of the waste rock extracted at the end of the mine life would seriously jeopardize the economy of the mining project therefore strip mining is characterized by its method of waste material movement which is placed almost entirely inside the pit thus strip mining includes a progressive and quick process of reclamation each mined cut is reclaimed arranging the waste rock overburden and fertile medium from the next cut to the mined strip and then revegetating the disturbed land in this method an initial cut is made on the subcrop called the boxcut and the overburden is placed on a natural surface updip of the subcrop line the exposed material e g coal is mined out and successive cuts or strips are taken to progress the mining downdip with the overburden from each strip placed inside the previous mining void thus waste rock recasting goes at the same time with mineralization mining that enables high production rate and almost continuous muck flow under appropriate conditions in the case of coal seams individual strip geometry is typically from 30 to 100 m wide and to the economically recoverable basal coal seam final landforms in strip mines can range from voids whose batters have been regraded to voids that have been fully backfilled to the original topographic levels strip mining is unique in that the drill and blast process itself can be employed as an overburden removal process as the overburden is to be placed into the mined out void immediately adjacent certain pit configurations and operating methodologies lend themselves to cast blasting cast blasting is where a powder factor and delay design are selected to purposely cause the fractured rock mass to heave in the direction of the mined out void with large quantities of overburden up to 30 resting in the final position it therefore requires no further handling by mining equipment

this is a particularly economical method of overburden removal strip mining is a bulk earthmoving operation making use of large scale mechanized equipment this enables high productivity and low mining charges allowing extraction of even low grade and deep seated mineral deposits with higher values of the stripping ratio tatiya 2013 thus the use of highly productive equipment such as bucket wheel excavators and high capacity belt conveyors is feasible dragline equipment supplemented by truck and shovel systems are also observed in strip mines in this method stripping ratios can be relatively high and slope angles can be steep largely due to the relatively low overall height of these slopes carter 2011 the two main variations of strip mining are area mining and contour mining area mining is performed on moderately flat terrain with flat lying seams mining cuts are made in straight parallel panels advancing across the property contour mining fig 5 34 is usually carried out in mountainous terrain with cuts located on the contours of the topography quarrying is the extraction of rock e g industrial minerals and rocks from the ground as such the geology of a country or region determines where a quarry is located quarries are very similar in design and operation processes to open pit mines commodities mined in quarries include aggregates dimension or natural building stone raw materials for portland cement and lime manufacture clays for bricks and tiles and many other especially industrial minerals e g calcite talc feldspars and silica sand in crushed stone for aggregates the excavated rock is crushed screened and separated into different size fractions for subsequent sale and use since the products are usually of relatively low value and for local markets they are transport cost sensitive hence wherever possible quarries of crushed stone are located as close as possible to the market e g a big city if site investigations for a new quarry of aggregates either sand and gravel or crushed stone are carried out local factors to study include depth of overburden size of reserve water table dewatering is sometimes necessary rock type visual impact landscaped amenity banks must be constructed and or large number of trees planted the presence of roads and railways close to the plant and distance to the market special measures are required to minimize adverse environmental impacts such as noise from drilling vibrations from blasting and dust from crushing and screening to the neighboring areas natural building stone quarries are also common examples of this type of surface mining although with some specific characteristics thus the majority of dimension stone quarries are conducted according to a regular bench design the rock is commonly cut in the quarry using diamond wire other techniques such as explosive splitting or flame jet burner are sometimes used in hard rocks e g g

ranite although flame jet burner damages the rock to a considerable depth the marketable dimension blocks obtained by drill and shear techniques are then transported to the factory where the blocks are again cut and sliced in different sizes and shapes in this type of quarries bench faces are commonly vertical due to the good geotechnical features of the rocks these products are frequently high value in comparison with crushed stone for aggregates for this reason they can be transported and sold worldwide as building stone an example are the alabaster panel windows used in the cathedral of los angeles usa since the raw material to obtain the panels was previously mined near zaragoza spain and then transported to the usa 5 3 3 4 auger mining auger mining fig 5 35 is a comparatively low cost method of coal mining it starts in the west virginia coalfields usa in the 1940s being in use today e g the usa and australia auger mining is used on mountainous terrain and needs a surface cut extraction of overburden and a fraction of the coalbed to enable the auger access to the bed the auger method involves boring horizontal or near horizontal holes in a face of the coal and loading the coal extracted by the auger it is usually utilized to add value at contour or strip mines where the overburden becomes too great to be economically extracted in a determined pit design it is also applied where the terrain is too steep for overburden removal because retrieval of coal using underground methods can be unfeasible or unsafe or to extract a proportion of the coal left from underground methods in case of physical constraints auger mining is usually the only choice to increment the amount of coal produced this method uses large diameter drills mounted on mobile equipment to bore into a coal seam fig 5 36 holes are horizontally drilled at regular intervals to depth of as much as 300 m and with diameters of up to 2 m where the hole is mined to its defined depth the auger equipment is translated laterally 1 or 2 m and another hole is drilled aqueous extraction encompasses several methods that are used in special circumstances they have in common the use of water or a liquid solvent as the basic component in the mining process either by hydraulic disintegration or physicochemical dissolution examples of these methods are dredging fig 5 37 hydraulic mining in situ leaching and evaporite processing dredging is the most common method of large scale mining of placers which involves the extraction of the unconsolidated materials from a body of water without the use of explosives or any other significant means of rock breaking force bullock et al 2011 this method is particularly suitable if adequate water supply is available and the mining operation can comply with the applicable environmental regulations modern dredges can produce between 600 and 1500 tons per hour the dredging process is usually performed fr

om a floating vessel called a dredge which can include many processing facilities the concentration of minerals is performed using jigs cyclones spirals and shaking tables see chap 6 the body of water used for dredging can be natural or human made dredges are often classified by method of excavation and material transport mechanical dredges are those that mechanically excavate and transport the mineral hydraulic dredges also called suction dredges are designed to transport the mineral in slurry form using water as the transport medium the valuable minerals or metals obtained with this method are meaningful gold diamonds cassiterite heavy mineral sands box 5 5 heavy mineral sands dredging and precious stone hydraulic mining fig 5 39 or hydraulicking is a method of mining placer deposits that was utilized in the past but actually is not applied due to environmental issues it is a low cost method to extract large amounts of unconsolidated material in this method a high pressure stream of water is directed against a bank to undercut and cave it the loosened particles are then washed and transported by gravity to a concentrating device in situ mining is the extraction of the meaningful elements of a mineral deposit without physical removal of the solid material bates and jackson 1987 it is commonly carried out by dissolving the mineral in an adequate liquid that is later removed for recuperation of the needed constituent in situ mining includes in situ leaching solution mining to extract water soluble salts brine extraction sulfur extraction using the frasch process and others in situ processes could potentially deliver the highest goal a zero environmental footprint the application of commercial scale in situ leaching to sedimentary uranium deposits has been around since the 1960s albanese and mcgagh 2011 being copper gold and silver deposits other common examples of minerals mined by this method surface leaching commonly uses heap leaching of mineral values the key to successful leaching of uranium is the identification of suitable below water table sedimentary deposits in which uranium is confined in permeable rocks by impermeable layers thus the process leaves the ore in the ground and recovers uranium by pumping a leachate solution into boreholes drilled into the deposit the pregnant solution from the dissolved minerals is then pumped to the surface regarding solution mining it is likely to be more economical and is inherently safer than conventional underground mining it will increase in the future as more effective reagents are developed and application methods are improved solution mining is used to the exploitation of easily dissolved materials for instance sodium and potassium bearing evaporates or sulfur and has also been applied to the extraction of uranium ores hosted in porous sandstone in a wider sense coal gasification by underground combustion can be included in

this type of surface mining a good example of this technique is the extraction of natural sodium sulfate in glauberite mines of spain box 5 6 glauberite solution mining the mining method employed begins with removal of overburden in an approximate 100 100 m pool that is then drilled and blasted over the whole area a system of wells is then developed and water is injected to the glauberite body and recirculated being the mineral dissolved the rich sodium sulfate brine obtained is pumped and sent to an evaporation plant where the brine is converted later into high quality anhydrous sodium sulfate salt in evaporite evaporation operations the valuable minerals are produced from a saline solution by evaporation in a closed basin halite potash and trona are typical examples of this category the minerals can be recovered by conventional mining operations or by solution mining in the latter case recovery is often accomplished by evaporation of the water from brines in solar ponds fig 2 50 thus saline solutions are pumped into large shallow ponds to allow the water to evaporate being essential a warm and dry climate evaporation conditions volume of solution to be processed and the expected low rainfall in the area are commonly the major parameters of concern in this type of mineral extraction hartman and muntmansky 2002 mineral deposits can be so close to the surface that their extraction by surface methods can easily be carried out in contrast some mineral deposits occur so far from surface that only underground mining is allowed besides these contrasted situations there are some deposits that start at surface or near surface and continue to great depth in such vertically extensive ore bodies a combination of both surface and underground methods could result in a higher net profit than only one bakhtavar 2013 within this transition zone it is necessary to consider issues such as the production rate or the economic and risk features because these factors can decide the open pit to underground mining point that is the best for the project however as the costs of underground mining can be many times that of surface mining only moderate to high grade deposits can be mined by underground methods below an open pit accurate estimation of the depth in mines where both methods are utilized is of significant interest bakhtavar et al 2009 the point at which economic considerations define the change from open pit to underground method is referred to as transition depth to take the decision of where to end the open pit method and begin the underground method is referred to as the transition problem and it has originated some attention in the literature since the 1980s box 5 7 venetia transition surface to underground mining this combination of initial surface mining and further underground mining is called sequential mining it is selected on the basis of the ore deposit geometry dimensions shape

and depth rock characteristics and conditions productivity capacities of machineries capital requirements operating costs investments amortization depreciation ore recovery safety and environmental aspects among other aspects it is important to keep in mind that extension of an open pit with a new pushback often involves removal of millions of tons of material generating huge capital investment thus decisions to expand or deepen an open pit instead a transition to underground mining required extreme care detailed planning and modeling before reaching the transitional depth of the mine is essential as many problems can arise influencing the production flow fig 5 42 it is important to bear in mind that only moderate to high grade mineral deposits can be mined using a combination of surface and underground mining because the costs of underground methods are commonly many times that of surface methods after feasibility of underground mining has been proved timing of transition to underground mining must be decided there are two major considerations for this decision first it is important to maintain continuity of the operation because underground mining should supplement and eventually take over production from the open pit without major permanent changes in tonnages of ore shipped to the mill differences between the open pit and underground ore grade and composition can complicate this issue second while a smooth transition requires a production overlap neither of the two operations should compromise the safety of the other wetherelt and van der wielen 2011 the main issues to be evaluated in determining the optimal transition depth are the availability of feed feed grade and resource utilization impact consequently there is a range of parameters that can be checked to estimate the sensitivity of the optimal transition depth it is important to specify the ultimate depth of an open pit mine as early as the planning stage considering economic efficiency of underground mining of the remaining mineral reserves later on ordin and vasilev 2014 the optimization of the transition depth is also a complex topic it is defined as the process of determining what part of the ore body e g what blocks in a block model should be mined by open pit what parts should do by underground methods and when they should be extracted so that operation can maximize the long term npv of the project the problem of optimizing a simultaneously producing open pit and underground mine plan is really complex and for a current technology an iterative process must be embraced in attempts to establish the optimal solution to consider the transition depth as an essential issue a number of algorithms were developed in the last two decades e g nilsson 1982 bakhtavar et al 2009 ordin and vasilev 2014 among many others the solution uses the lerchs grossman algorithm floating cone technique dynamic programming neural net

work etc and based on these methods different software packages are widely used e g datamine vulcan minesight and gemcom thus the open pit to underground transition problem is one of the hot topics in the mining industry that has not been mathematically solved since there is not a mathematical algorithm that can successfully optimize the transition depth by considering the life of the mine schedule of both open pit and underground all together due to the complexity of the problem and its size often the transition depth is defined by considering the open pit and the underground separately defining the transition depth by comparing the costs of these two mining methods the economics of the mining project cannot be optimized in terms of the net present value of the project the underground development work and the value of the underground mine are not properly considered therefore the costs and the value of the overall project cannot be correctly estimated where correctly defined the transition depth can significantly enhance the discounted net present value of the mining project traore 2014 the final design of the combination surface mining underground mining frequently includes a crown pillar left in place while underground mining is developed fig 5 43 the height of the crown pillar is commonly established equal to the maximum width of stopes to be extracted promptly beneath underground mining consists of the extraction of material in excavations below the earth s surface fig 5 44 this type of mining employs its own and distinctive nomenclature thus fig 5 45 shows the main terms commonly used to describe underground working and other aspects of underground mining underground mining exists where a surface mine becomes cost prohibitive to operate by different reasons a the ratio of extracted waste to ore becomes too high b waste storage space is insufficient c pit walls fail d environmental considerations outweigh extraction benefits and e environmental or social factors limit the viability of surface mining in such cases underground mining can be the only choice for a given deposit however it is important to note that the economic feasibility of an underground operation depends on more or less the same economic studies as an open pit mine if the appeal of surface mining lies in its mass production and minimal cost capabilities the attraction of underground mines derives from variety of ore deposits that can be mined and the versatility of its methods to meet conditions that cannot be approached by surface mining moreover underground mining is a method with less environmental impact to gain the access to a mineral deposit in contrast it is usually more expensive and involves greater safety risks than surface mining in general an underground mine is more complex and generally more expensive than a surface mine because the development openings of an underground mine can be consid

erably more costly than surface mining on a tonnage basis the social economic political and environmental factors of underground mining are often quite different from those of surface mining a more skilled labor force can be required financing can be more difficult because of increased risk and subsidence can become the most important environmental concern hartman and muntmansky 2002 in underground mining overburden extraction to gain access to mineralization is kept to a minimum being this access obtained by tunnels or shafts thus there is only a small amount of waste rock generated development waste and consequently limited excavation and relatively small openings are necessary for most underground mines the waste can even be useful since it can be used as backfill in the mine underground mines are generally utilized to exploit high grade deep mineralization usually with mining production rates lesser than 20 000 tons per day for instance a 10 000 ton mining production rate is a typical production of highly mechanized and large capacity underground mines a particular case should be block caving underground method since it can achieve mining production rates much greater than 20 000 tons per day in addition the use of smaller equipment in underground mining means production rates that are obviously much lower than at a surface mine in terms of ore tonnage underground mining is relegated to a secondary role for many commodities however it is possible to assume that underground mining will continue to play an important role in supplying mineral resources in the future with many large underground mines in operation around the world underground mining methods are always selected below 1000 m depth because it becomes difficult in a surficial exploitation to maintain the stability of a 1000 m high rock slope large tabular mineral deposits with long vertical or horizontal dimensions or mineralization lying more than 300 m below the earth s surface are commonly mined utilizing underground methods as well in this sense mponeng and tautona fig 5 46 gold mines located in south africa are currently the two deepest mines in the world respectively mponeng exploits at depths of between 2400 and 3900 m and tautona sinks to depths of between 2900 and 3480 m obviously geotechnical features of the ore and waste rocks are essential to develop a safe underground mine thus the main goals of geotechnical consideration in underground mine design independently of the mining method applied are a to ensure the overall stability of the complete mine structure defined by the main ore body mined voids ore remnants pillars and adjacent country rock b to protect the major service openings and infrastructure throughout their design life c to provide safe access and working places in and around the centers of ore production and d to preserve the mineable condition of unmined ore reserves brady and brown 200

6 the characteristics of the ore body itself constitute the basis to the geotechnical study including the thickness and orientation of the mineralization the ore and rock strength the distribution of mineralization within the ore body and the depth of mineralization and surface conditions thus geotechnical data are needed to decide 1 most economical method of excavating ore and waste rock 2 pillar sizes and extractions ratios 3 features to control the subsidence and 4 where to locate the accesses to the mine as early as possible in the mine feasibility assessment process it is essential to understand and fully consider the interrelationships between the local geotechnical environment and the mining process fritz and coldwell 2011 there are important benefits linked to an early prioritization of geotechnical evaluation and impact on underground mine planning regarding the hydrogeological conditions groundwater commonly concerns upper areas of a shaft and must be controlled by grouting to prevent water from entering the shaft with deeper level mining and higher overburden pressure it is very important to give geomechanical validation to engineering decisions to be in accord with the ground conditions collapse of mine structures rock bursts and higher cost of ground control and mine support directly influence mining productivity instability of such structures results as a rule in severe accidents and long term suspension of production up to mine closure which causes social tension and high economic loss for this reason geomechanical monitoring in underground mineral mining to evaluate the stress state and properties of rocks is of paramount importance therefore a monitoring program should be implemented in order to get better understanding of the rock mass deformation mechanisms this geomechanical monitoring structure can be outlined utilizing a package of instrumental fig 5 47 visual and numerical methods for the evaluation of mechanical condition and its alteration in rocks and in structural components of mines the information support of monitoring systems is based on instrumental and theoretical methods allowing a acquisition of reliable source data on natural stress state and mechanical properties of rock masses b determination of mechanisms of change in the stress strain state of structural elements in the course of deformation under natural or induced forces and c experimental analytical justification and estimation of limit state criteria in rocks and other materials concrete backfill baryshnikov et al 2014 the uncertain geotechnical environment in which an underground mine operates is among the prime reasons for geotechnical accidents accidents in the form of roof collapse fallouts uncontrolled caving etc can lead to loss of lives and machinery along with substantial ore loss and loss in productivity for instance one of the worst underground mine accident in the worl

d was the so called mufulira disaster recorded in zambia in 1970 when 89 miners died due to flooding the accident took place in the morning of 25 september 1970 when half of the mine was flooded because mud and water from the slime dam seeped through cracks in an old slope causing a section of the overhanging wall to give way thus the mud and water rushed into the eastern section of the mine and flooded all shafts below 500 m geotechnical risk assessment at early stages such as mine design can even help to make changes in the design for example the use of support methods in risky areas of the mine the risk assessment process can be defined into four sections hazard identification tool risk assessment approaches risk assessment parameters and risk representation tool mishra and rinne 2014 once a geotechnical risk assessment is completed the result should be analyzed to test if the risk must be mitigated or completely avoided for example switching to a different method or abandoning the area geotechnical risk assessment process in a mine should be subjected to continual improvement through feedbacks from the mine and via lessons learned during every assessment to summarize the methodology for the implementation of a rock mechanics program can include the following steps 1 site characterization definition of hydromechanical properties of the host rock mass for mining 2 mine model formulation conceptualization of site characterization data 3 design analysis selection and application of mathematical and computational schemes for study of various mining layouts and strategies 4 rock performance monitoring measurement of the operational response to mining of the host rock mass 5 retrospective analysis quantification of in situ rock mass properties and identification of dominant modes of response of mine structurean underground mine has different components that ensure the extraction of ore and the safety and movement of people and equipment therefore each mining method requires different underground infrastructure such as access drifts to sublevels drifts for longhole drilling loading drawpoints and ore passes together they form an intricate network of openings drifts ramps shafts and raises the mine requires three groups of physical plant installations the surface plant the shaft plant and the underground plant the first consists of a variety of facilities to provide the mine with necessary services such as access roads and parking transportation facilities power and water supply service and maintenance buildings mineral processing plant bulk storage and waste disposal facilities for air water and solids the shaft plant includes the facilities installed for material handling of ore and associated waste and the means of transport of miners and material it generally incorporates systems for ventilation drainage power supply and communications regarding the underground plant it cove

rs various installations to make the system work efficiently and safely including storage bins loading pockets power distribution equipment underground maintenance facilities and numerous other installations that provide auxiliary services to the underground operationsmine ventilation is one of the most important facilities of underground mining air quality in mine workings is an area of particular concern to the underground development it must be maintained at an acceptable health standard a continual and adequate supply of fresh air must be made available to working areas underground mines use networks of fans gates and surface openings to move fresh air into the mine and remove exhaust air high pressure fans on surface extract exhaust air through the upcast shafts and ventilation doors control the underground airflow passing fresh air through active work areas as most of the infrastructure is located on the footwall side of the ore body the fresh air is normally channeled via the footwall toward the hanging wall from where the exhaust air is routed to the surface nord 2007 it is particularly important to clear the air after an underground blast because harmful gases such as carbon monoxide or oxides of nitrogen can build up a good ventilation system will rapidly clear the air around a blast as blasting reduces the concentration of oxygen in the air underground development openings which are designed so that the ore bodies are easily accessible and transportable after excavation usually can be ranked in three categories by order of importance in the overall layout of the mine 1 primary or main openings e g shaft or slope 2 secondary or level or zone openings e g drift or entry and 3 tertiary or lateral or panel openings e g ramp or crosscut the construction of underground openings is specialized and expensive and consequently this phase of mine development has become increasingly mechanized and efficient in order to reduce costs a number of initial decisions related to the primary development openings of a mine must be made early in the mine planning stage and include the type number shape and size of the main openings factors to influence this decision include the depth shape and size of the deposit the surface topography the geological conditions of the ore body and surrounding rock the mining method and the production rate among others sometimes underground development openings double for exploration purposes and vice versa those openings driven in advance of mining can provide valuable exploration information and afford suitable sites for additional exploration drilling and sampling likewise openings driven for exploration purposes can be utilized to develop the deposit some shafts and drifts would almost certainly serve subsequently to open up the deposit 5 5 2 1 underground access the access method to underground works is an important aspect of underground mine development

and operation because it is required for people equipment and ventilation as well as for transporting ore to the surface underground mines usually have several access points with different objectives such as a ramp for equipment and personnel and a shaft for transporting ore out of the mine and form ventilation there are generally three methods of accessing an underground mine shaft adit and decline or ramp the shaft remains the mine s main artery and downward development is by ramps to allow access for the machines a decline ramp from surface can facilitate machine movements and transport of people and materials it can also be used for ore transportation by truck or conveyor eliminating the need for hoisting shafts 5 5 2 1 1 shafts a shaft is a vertical excavation in which elevators are used to transport people and ore in and out of the mine it is used where the deposit is located deep within the ground most shafts are divided into a number of compartments each with a different use for example one compartment for moving people a second for skipping ore to the surface and other compartments for ventilation and electrical infrastructure the main factor to establish the shaft size is the estimation of reserves in the sector to be mined by the shaft thus the ore body size will define the rate of mining and this will determine the tonnage ore and waste to be hoisted the number of persons and the material to be moved in a given shift figure 5 50 show de beers venetia mine in south africa with two headgears one is the production shaft used to lift kimberlite containing diamonds and waste rock the second is the production services shaft used to transport employees and equipment in and out of the underground mine because shafts are essential in the general planning of mine development their localization is commonly predetermined being this position changed where adverse geotechnical conditions are identified ground conditions and water bearing structures also govern the ultimate localization of shafts the decision to locate the shaft is critical if the terrain is moderately flat because the process to develop a shaft is very expensive and only a vertical shaft well located with respect to the ore deposit will be helpful later in the production work thus the correct configuration of the shafts will provide optimum operational benefit the shaft can be rectangular circular or elliptical in profile although almost all hard rock underground mines commonly have circular section shafts because this shape generates a correct geometry for airflow and suitable rock support characteristics 5 5 2 1 2 raises raises are steeply inclined openings linking the mine sublevels at several vertical elevations they are normally placed near the stopes employing specialized cyclic or continuous operations specific applications of bored raises are transfer of material ventilation personnel access and ore production incli

nation varies from 55 which is the lowest angle for gravity translation of blasted rock to vertical with cross sections from 0 5 to 30 m2 since manual excavation of raises is a very dangerous job the raise boring machine is currently utilized for boring ventilation raises ore passes and rock fill passes it provides safer and more efficient mechanized excavation of circular raises up to 6 m diameter because this method eliminates the need of explosives raise boring is the procedure of mechanically boring a vertical or inclined shaft between two or more levels in conventional raise boring a downward pilot hole is drilled to the target level by the raise boring machine where the bit is removed and replaced by a reaming head fig 5 51 the machine then reams back the hole to final diameter rotating and pulling the reaming head upward the cuttings fall to the lower level and are removed by any convenient method the capital cost of a raise boring machine is high but the return on investment is very worthwhile advantages of raise boring are that miners are not required to enter the excavation while it is underway no explosives are used a smooth profile is obtained and manpower requirements are reduced above all an operation that previously was classified as very dangerous can now be routinely undertaken as a safe and controlled activity an adit is a horizontal excavation that is used in mountainous areas where the ore body is located near or above the valley floor this type of development is the most difficult to design in certain aspects being commonly considered only where topographic relief is considerable in this opening the ore and waste can be taken down and out of the mine at minimal operating cost all the horizontal openings are developed by a process called drifting or tunneling the traditional method of performing this operation is to drill and blast the face load the material into a haulage device and then provide support and ventilation to the newly advanced face thus drilling and blasting are the standard excavation method for drifting the exceptions to the use of blasting are underground mines in relatively soft rock such as coal and salts where the rock can be removed without the need for blasting stevens 2010 in addition using explosives in underground coal mines creates a significant safety hazard because methane gases and dust associated with the coal can ignite 5 5 2 1 4 declines a decline or ramp is a tunnel fig 5 41 usually sunk at a low slope angle 20 dip the design of declines is considered as one of the main issues in underground mine development they are straight spiraled or a combination of both ramp access is the common selection in shallow ore bodies especially where the mineralization is near horizontal a ramp from surface can facilitate machine movements and transport of people and materials it can also be used for ore transportation by truck or conveyor elimina

ting the need for hoisting shafts ramps are sizing to include machines that pass through or operate inside space must incorporate a rational margin for clearance walkways ventilation ducts and other facilities cross sections vary from 2 2 m 2 5 m in mines with a low degree of mechanization to 5 5 m 6 0 m where heavy equipment is used nord 2007 in many mines the decline is used to transport ore to the surface through a conveyor belt being associated with grade limits for instance if utilized for conveyor belt haulage only the maximum grade of the decline could be from 15 to 25 depending on material to be conveyed 5 5 3 underground load and transportation the fragmented ore is removed from the mine by loading it called mucking in underground terminology onto transportation equipment and hauling it out of the mine the load haul and dump processes are carried out using a load haul dump lhd truck hence its name also known as scooptram lhd units are commonly used to move ore from the stope to a crushing plant or waiting truck to be transported to the surface they are adequate for small and large tunnels chambers and stopes in ramps and adits the lhd will dump its load onto a haul truck or onto a conveyor for transportation to the surface in mines with a shaft the lhd will commonly dump its load directly into an ore pass where the ore will fall near the bottom of the shaft into a crusher from there it will be hoisted or skipped to the surface for long ramp operations the lhd truck combination generates lower operating costs than lhd alone being considered on any haul more than 500 m in length lhd or scooptram can be used with remote control technology which utilizes a transmitter and radio receiver to control and monitor the operations of the lhd another possibility to transport the ore in underground mines is where a continuous miner is utilized to cut soft materials continually where drilling and blasting are not required the focus of the operation is the continuous miner fig 5 53 this machine consists of a central body to carry all other components mounted on some type of drive mechanism to provide mobility and a cutting head usually rotating drums equipped with tungsten carbide teeth that cut into the rock an internal gathering system then loads the broken ore onto an onboard conveyor and it feeds onto a shuttle car or articulated hauler which takes the product to an optional mobile belt feeder if present the feeder puts the product onto a conveyor belt which in turn carries the ore to the surface rock support is the term utilized to outline procedure and materials used to enhance the stability and maintain the load bearing capacity of rock near to the limits of an underground mine thus the primary aim of support processes is to conserve the intrinsic strength of the rock mass so that it becomes self supporting rock support is essential in underground workings for both the safety and

the productivity of the mine it is still the bottleneck in the working cycle in underground mining the selection of the support type installed in an underground excavation is based on the extent of the zone of loosened or fractured rock surrounding the excavation the support of excavations is commonly classified as primary or secondary the former is applied during or immediately after extraction to ensure safe working requirements during further excavations whereas the latter is applied as any additional support or reinforcement at a later stage support can also be separated into active or passive active support e g tensioned rockbolts means a predetermined load to the rock surface at the same time of installation while passive support steel arches is not installed with an applying load and develops its load as the rock mass deform more commonly used surface rock support methods are rockbolts and grouted cables as active rock supports and mesh shotcrete and steel sets as passive rock supports mechanically anchored rockbolts are probably the earliest type of rock reinforcement utilized in underground operations to prevent major ground failure fig 5 54 moreover they are yet the most usual way of rock reinforcement utilized in mines worldwide in this method holes are drilled into the roof and walls and long metal bars are inserted to hold the ground together point anchor or expansion shell bolt is a metal bar of 20 25 mm in diameter and 1 4 m in length and as the bolt is tightened the expansion shell located at the top end expands and the bold tightens holding the rock together haldar 2013 tensioned rockbolts are most useful to retain loose blocks or wedges of rock near the surface of the excavation rockbolts can be substituted by cable bolts fig 5 55 grouted with cement they are utilized to bind large masses of rock in the hanging wall and around large excavations being much larger than standard rockbolts e g between 10 and 25 m long the main advantage of these cables is that they are installed in openings with very low headroom grouted cables are very effective in applications such as the reinforcement of ore or waste passes grouting serves two main purposes in rockbolt installations first it bonds the bold shank to the rock making it an integral part of the rock mass and enhancing the interlocking of the components of the rock mass second grouting offers protection against corrosion for this reason rockbolts installed for long term use must be grouted regarding the passive rock supports the installation of mesh on the backs and sidewalls of an excavation is a method that can largely remove unintended fall of small rocks however this type of support system is not developed to support large static or dynamic loads in this case it can only be utilized in combination with other components such as rockbolts and grouted cables to constitute a global integrated system there is a great variety

of mesh forthcoming but the three major types are welded wire mesh 10 10 cm openings chain link mesh and nonmetallic mesh galvanized or nonmetallic mesh is recommended where corrosive conditions exist sprayed concrete gunite or shotcrete fig 5 56 has a long history of being used as a surface support in mines there are two application methods for sprayed concrete dry mix and wet mix having each type its special utilization in surface rock support the present tendency is to utilize fiber reinforced shotcrete or fibercrete it forms actually a very versatile support technique with the addition of microsilica to the mortar mix the mixture coats 50 100 mm thick layers on the roof and walls anticipating smaller fragments from falling there are many different underground methods that have been developed to respond the needs of differing geometry and the geotechnical features of the host and surrounding rock these underground mining methods called stoping by the american miners are difficult to classify rationally since each method depends not only on ore body geometry but also includes other considerations such as ground conditions hydrology grade distribution the presence of structures e g faults or dykes scale of operations economic factor availability of labors and materials equipments as well as environmental considerations the reason why the choice of a method is crucial is that it largely governs the type and placement of the primary development openings if disturbance of the surface due to subsidence inevitable with caving methods and possible with other methods is anticipated then all the access openings must be located outside the zone of fracture bounded by the angle of draw the angle of draw is the angle between a vertical line drawn upward to the surface from the edge of the underground opening and a line drawn from the edge of the opening to the point of zero surface subsidence the larger the angle of draw the wider will be the area on the surface in which subsidence should be present to show the significance of ground support underground mining methods can be classified in three main types based on the extent of support required a methods generating openings that are naturally supported or requiring minimum artificial support b methods requiring substantial artificial support and c caving methods in which failure of the back roof is inherent to the extraction process underground mining method can also be separated in selective and bulk methods the former are utilized to recover ore without dilution whereas the latter are used to extract large tonnages of ore with low cost evidently selective methods are more expensive per ton of rock extracted than bulk methods but the revenue per ton of ore is greater selective methods typically apply to narrow precious metal vein deposits and high grade base metal veins such as those hosting lead and zinc whereas bulk methods are used for

mining low grade large ore bodies which cannot be extracted profitably using selective mining methods in this section the goal is to summarize briefly the main characteristics of the major underground mining methods according to the first classification ground support the unsupported methods fig 5 58 of mining are generally utilized to mine mineral deposits that are roughly tabular plus flat or steeply dipping and are commonly related to high competent ore and waste rock they are termed with this name since they do not utilize any type of artificial element to help in the support of the openings however a great number of roof bolting and localized support measures are commonly needed in room and pillar method a classical unsupported method the support of the roof is generated by natural pillars of the mineral that are left standing in a systematic configuration supported mining methods need important amount of artificial support to keep stability in openings as well as systematic ground control throughout the mine they are utilized in mines with ground conditions ranging in competency from moderate to incompetent in fact the supported method is basically used where the other two types of methods unsupported and caving are not appropriate cut and fill stoping is the most typical of these methods and is utilized in steeply dipping metal deposits the third group caving methods is varied and involves induced controlled or massive caving of the ore body and or the overlying rock the mining workings are defined to collapse with intentional caving of the ore and or host rock subsidence of the surface normally occurs afterward two methods of this group widely applied due to their high productivity are longwall mining and block caving room and pillar is the most classical unsupported method figs 5 59 and 5 60 it is planned for mining of flat bedded deposits of limited thickness normally showing an inclination that does not exceed 30 examples are sedimentary deposits such as limestone or sandstone containing lead salt layers phosphate some base metal deposits box 5 8 rudna copper mine limestone magnesite and dolomite this method recovers the mineralization as completely as possible in open stopes called rooms leaving pillars of ore to support the hanging wall hence the name room and pillar but without jeopardizing working conditions and personal safety the dimensions of rooms and pillars depend upon factors such as the stability of the hanging wall and the ore the thickness of the deposit and the rock pressure in this respect the stability of the ore and the hanging wall is a flexible concept increasing the number of pillars and reducing the room width can compensate for poor ground conditions but ore recovery is sacrificed since a larger portion of the ore body is left to support the back although it is not common sometimes areas of waste can be utilized as pillars in this method the o

re is blasted and the material loaded in the room where it was extracted and transported to a point where it will flow either by gravity or mechanical means to a central gathering point to be taken out to the mine this is because the direction of excavation angle of dip is below that which would cause the dry material to flow by gravity to a drawpoint or gathering point the loose rock is then translated by dump trucks or lhd vehicles to the surface for waste disposal or processing in the case of mineralization in thin ore bodies loading points can be necessary for transferring ore from loader to hauler as all activities are carried out on one or very few levels covering a large area there are many faces available at any time so high equipment utilization is possible thus this method of extraction is well adapted to mechanization all tunnels are excavated by drilling and blasting and the production rate ranges from 500 to 35 000 tons per day being the recoveries of extraction obtained in mining in advance as high as 85 in soft rock deposits such as salt or coal seams drilling and blasting are not required and the valuable mineral is extracted using machines such as continuous miners mineralized heights greater than about 6 m are commonly operated by multiple passes barren rock originated during extraction can be easily disposed in the mined voids rooms and pillars are commonly disposed in regular configurations to simplify planning design and operation being designed with circular or square pillars and elongated walls dividing the rooms mining the ore body creates large openings where machines can travel on the flat floor since personnel works continuously under exposed roof close observations of the performance of roof and pillars are needed rockbolts are used extensively as rock reinforcement usually the pillars remain after mining is complete and they are not recovered because it is difficult and expensive however where all the ore in the openings has been mined and translated to the surface in a second phase of this method several pillars can be mined out prior to abandoning the stope this is because they still have valuable grade content in this case some pillars must be left standing to maintain active support for the hanging wall it is common in this method to collapse the rock mass into the rooms sometime after the extraction process has finished the main advantages of the room and pillar method are the high degree of flexibility and the high degree of mechanization since many aspects of the mining cycle are repetitious it is a very selective mining system leaving waste material on pillars being also relatively inexpensive it can be operated in multiple fronts and does not require much anticipated development regarding the disadvantages the method requires maintenance of the roof and eventually the pillars the loss of ore in pillars and the need of significant capital investment for extensiv

e mechanization if the method progresses in depth the tension in the open space increases significantly supported methods are commonly utilized in mines with weak rock structure and cut and fill fig 5 65 is certainly the most common of these methods box 5 10 efemcukuru gold mine for many years it was probably the main mining method used in underground metal mines especially those in poor ground conditions it is frequently applied in vein deposits where the vein is moderately to steeply dipping with considerable vertical extent although the method is readily adaptable to almost any ore body the ore body however must be accessible at both top and bottom as well as at regular intervals throughout vertical extent in general the cut and fill method is preferred for vertical or subvertical mineral deposits at great depths or within relatively weak rocks that need support mine planning and supervision are concerned with the geotechnical properties of the fill and their effects on mine and stope stability it is preferred for ore bodies with irregular shape and disseminated mineralization where high grade sections can be mined separately leaving the low grade mineralization in the stopes cut and fill method is a relatively labor intensive technique needing that the value of the ore body be high therefore it is carried out only in high grade ore where there is a need to be selective and avoid mining of waste or low grade mineralization offering better selectivity than sublevel stoping and vertical crater retreat mining the method is very flexible since multiple activities can be performed at the same moment for instance drilling in one level while other levels are being filled cut and fill mining excavates the ore in horizontal slices usually 2 5 3 m thick starting from a bottom undercut and advancing upward the ramps are excavated to link the surface to the underground rock mining can also proceed with slices mined downward and the fills form the roof for each subsequent cut because the miners in the stope work under freshly blasted areas the amount of ground control must be great since the volume of rock that is broken during one section of mining is relatively small and the amount of nonproductive work required is high this resulted in limited productivity for the stope the production from the stope can be quite cyclical because the nonproductive work must be done on a regular basis waterland 1998 the ore is drilled blasted loaded and removed from the stope which is then backfilled with deslimed sand tailings from the mineral processing plant or waste rock carried in by lhd from development drives the fill serves simultaneously to support stope walls and as a working platform for mining the next slice in modern cut and fill operations the fill is distributed by hydraulic means as a slurry cement is sometimes mixed in to provide harder and more durable support characteristics as no rib pillars are le

ft most of the ore can be recovered with a minimum of waste dilution in this method the development is minimal before mining starts and the equipment investment is relatively small it is a selective mining method that can also be used to reduce dilution the main disadvantages of the method include the following a ore production is cyclical b the method is labor intensive and required skilled miners c it is not as suited to mechanization as other methods so there is lower productivity and d the personnel must work under freshly blasted ground which creates a safety problem caving methods rely on the rock breaking into pieces that are small enough to be retrieved from the deposit and to flow into a recovery location without blasting all the ore although longwall mining is a classical caving method sublevel caving and block caving are the most characteristic caving methods they are bulk mining techniques with high production rates that approach or equal those of a medium sized open pit mine there is little or no opportunity for selective mining parts of the ore body so they are only used in large tabular deposits with a uniform and generally low value ore stevens 2010 as an example both methods are commonly used for massive low grade porphyry copper deposits where the stripping ratio for an open pit mine is too high or the deposit is too deep for surface mining 5 5 5 3 1 longwall mining longwall mining fig 5 67 is a classical underground mining method being practiced worldwide to mine thin bedded soft rock deposits with uniform thickness and large horizontal extent particularly coal seams fig 5 68 not all soft rock ores are suited for longwall mining which works best in laterally extensive flat lying deposits that are primarily free of discontinuities such as faults coalbeds deeper than 300 m are usually extracted by longwall mining because the room and pillar method would require the use of much larger pillars to support the roof reducing thus the amount of coal that can basically be extracted since a long face about 100 m or more defines the method hence the name longwall mining longwall mining requires and ore body dip of less than 20 with a reasonably uniform distribution of grade over the plane of the ore body the original application of sublevel caving fig 5 70 was in ground so weak that it would collapse even in small headings where the support was recovered cokayne 1998 sublevel caving can be adapted to large ore bodies with steep dip and continuity at depth the hanging wall has to fracture and collapse following the cave and subsidence of the ground surface above the ore body has to be tolerated caving needs a rock mass where both ore body and host rock fracture are under monitored conditions as the mining extracts rock without backfilling the hanging wall carries on caving into the voids thus continuous mining results in subsidence of the surface where sinkholes can be

produced sublevel footwall drifts must be stable requiring only occasional rockbolting the ore body is usually divided into sublevels with close spacing at approximately 8 15 m vertical intervals depending on the plunge of the deposit each sublevel is developed with a regular network of parallel drifts that penetrate the complete ore section development to prepare sublevel caving stopes is extensive as compared to other mining methods and mainly involves driving multiple headings to prepare sublevels ore is fragmented using blastholes drilled upward in fans from these headings since the ore is blasted against the caved waste explosive consumption is very high ore is extracted selectively with a lhd operating in the drill heading this vehicle transports the rocks to an ore pass where they are elevated to the surface waste dilution in sublevel caving is relatively high ranging from 15 to 40 and ore losses can be 15 25 depending on local conditions fernberg 2007 thus in this method the ore must be of sufficient grade to accept the high dilution arising from entrainment of barren country rock in the mineralization dilution is of less influence for ore bodies with diffuse boundaries where the host rock contains low grade minerals there is always a place for the machines to work which integrates mechanization into efficient ore production consequently the method is well suited for a high degree of automation and remote operations with corresponding high productivity the method generates important disturbances of the ground surface imposing some possible limitations on its applicability from considerations of local topography and hydrology 5 5 5 3 3 block caving if the ore is wide and steep enough block caving fig 5 71 would be selected because the cost is normally lower than that for sublevel caving this method sometimes called an upside down open pit is applied mostly to large massive ore bodies in which areas of sufficient size can be removed by undercutting so that the mass above will cave naturally where adequately used this method offers a lower mining cost per ton than any other underground technique tobie and julin 1998 box 5 12 cullinan diamond mine it is applicable only to very large ore bodies in which the vertical dimension exceeds about 100 m the rather unique conditions limit block caving applications to certain mineral deposits such as iron mineralization low grade copper and molybdenum ores and diamond kimberlite pipes fernberg 2007 block caving is based on gravity combined with internal rock stresses to fracture and break the rock mass caving is induced by undercutting the block by blasting destroying its ability to support the overlying rock thus gravity forces act to fracture the block continued pressure breaks the rock into smaller pieces to pass the drawpoints where the ore is handled by lhd loaders or trains fig 5 73 this method is therefore distinguished from

all other commented previously in that primary fragmentation of the ore is carried out by natural mechanical processes thus the elimination of drilling and blasting has advantages in terms of ore body development requirements and other direct costs of production as fragmentation without drilling and blasting is uneven a substantial amount of secondary blasting and breaking can be expected at the drawpoints in this type of underground mining the rock size and the rate at which rock passes through the drawpoints as well as continuously controlling the stability of the mine are essential where the ore block breaks up successfully and the extraction is carried out evenly from all of the drawpoints block caving becomes a low cost high productivity method with good ore recovery and moderate inflow of waste dilutions risks are high but the result can be extremely favorable this method is often used to convert an open pit operation into an underground mine where surface production can continue while the underground infrastructure is prepared in fact the block caving method generates production rates that can approach those of an open pit e g 100 000 tons per day as aforementioned in open pit mining section effective methods for modeling and optimizing the layout of open pit mines have been understood in a long time e g lerchs grossman 1965 although the underground mine design issue is more complex and less restricted than the open pit problem it has similar potential for optimization a meaningful issue in designing a global framework for the optimization of an underground mine is that there is a broad range of mining methods so that each mineral deposit has a comparatively specializing solution thus there will never be a simple procedure similar to that which is present for open pit mining however by decomposing the design problem into tractable subproblems such as infill drilling design stope definition topological network design and decline design highly effective though non globally optimal solutions can be found alford et al 2007 infill drilling can be improved through optimization of drillhole pattern and optimization of the physical infill drilling program development the latter can be managed as a network optimization matter where the aim is to optimize the cost of drilling in combination with the cost of drives and infrastructure to support the drill stations brazil et al 2003 in stope optimization the different variables can be decreased to dimensional restrictions on the minimum and maximum stope size suitable stope shape and orientation and pillar width in narrow and steeply dipping deposits the first choice is the width of ore to be extracted this diminishes the stope optimization issue from a 3 d to a 1 d optimization issue mine development network design and its optimization can be approached representing the mine using a weighted network model which is coordinated according to the coord

inates of the mine finally the decline design can also be optimized by using a network model the ultimate goal of the process is to cover the design of the drilling program cutoff grade objectives stope definition infrastructure development and mine scheduling in one comprehensive model alford et al 2007 regarding mining software for underground mine optimization there are several options in the market for instance datamine offers several programs for the strategic planning of underground mining operations for instance mineable shape optimizer mso generates optimized stope fig 5 74 designs to maximize the value of recovered ore within the given ore body geometry and design constraints being other tools mineable reserves optimizer mro and mine layout optimizer mlo drilling and blasting are the most cost effective method to mining mineral resources from the earth they comprise the first two stages in the production cycle of a mine and the most common method of rock breaking most surface mines excluding those operations that extract soft rock require the rock to be fractured using explosives prior to be loaded onto haul trucks reliable procedures for rock blasting are well established in mining engineering practice drilling and blasting outcomes cause great impact on different processes of a mine being essential to find the right combination of drill pattern explosives and blast design to contribute to the economic achievement of the global mining process the primary objectives in rock blasting are the fragmentation of rock masses and moving these rock masses to reduce the mechanical work required thus rock breakage utilizing explosives implicates drilling blastholes loading the borehole with explosives fig 5 75 and then detonating the explosive in each hole rock breakage is taken into account as the most essential feature of production blasting because of its immediate impacts on the cost of drilling and blasting of the rock and on the economics of loading hauling and crushing in general the discontinuities in the rock mass which includes bedding jointing and partings are the main items that dictate how a rock fragments the closeness of the separation of these determines the maximum block size in the pile of broken material consequently the effect of blasting is to reduce the size distribution of those preblast blocks lusk and worsey 2011 knowledge of the fragmentation mechanisms is essential to develop accurate techniques for extracting rock quickly the major elements of the fragmentation process in rock blasting include shock gas production extension of fractures and rock mass movement when properly initiated commercial explosives are quickly translated into gases at high temperature and pressure following detonation high pressure gases compress and beak the material surrounding the explosives the liberated energy by the explosive can be separated into two principal ty

pes the shock energy and the heave or gas energy the shock energy causes the conditioning of the rock and initiating mechanisms that originate fractures as for the gas energy or heave energy it is generated in the later expansion of the explosives into the crack pattern of the material once a fracture network is developed the gas is able to expand into the network both spreading the fracture process and causing movement of the rock 5 6 1 blasthole drilling the hole produced for filling explosives is the so called blasthole and the procedure of drilling such holes is the so called blasthole drilling most boreholes drilled for mine production are blastholes for explosives the machine utilized for drilling the hole is called blasthole drill or merely a drill fig 5 76 blastholes are drilled one after the other commonly hundreds then charged and blasted more or less at the same time the holes are drilled to a depth just below the bench height defined in the planning process of the mine in order to improve blasting operations the driller has to measure and log the conditions of all holes measure while drilling mwd is an optional instrumentation that logs a number of parameters at requested intervals while drilling such as hole depth penetration rate percussion rotation pressures and many others this information obviously provides interesting inputs for the analysis of the rock properties utilizing the mwd information it is probable to define the ideal blasting and obtain a uniform breakage of the rock by adjusting an individual hole charging and blast design from this choices can be taken about the most adequate type and quantity of explosive charge to situate in a per blasthole or optimizing the inter hole timing detonation design of diverse decks and blastholes in comparison with the other objectives of drilling such as waterwells or mineral exploration blasthole drilling shows some peculiarities a the holes are drilled at the same location b blastholes are very near to each other and they are drilled in rock masses that have a high degree of uniformity c they are shallow in depth and drilled in the same environment d no testing is done in blastholes except for grade control see sect 5 7 and e blastholes are always straight gokhale 2011 for the best overall blasting result the drillhole needs to follow a designed path along its entire length while drilling deviation should be avoided as far as possible geological conditions are a major cause of in hole deviation during drilling but deviation can also result from faulty setup hole alignment as well as bad collaring the main consequences of hole deviation are a uncontrolled fragmentation of blasted material b possible misfires due to intersecting holes firing at undesirable intervals c excessive burden and spacing between adjacent blastholes d secondary breaking leading to higher costs for loading haulage and crushing and

e uneven bench floors resulting in higher equipment maintenance costs using positioning lasers angle indicators and guide tubes will aid operators to control and manage deviation chinedu 2015 according to the way of rock attack blasthole drilling is performed by two primary methods percussive and or rotary drilling in percussive and rotary drilling e g top hammer drilling the rock is broken by a combination of rotation of the bit and high frequency percussive impacts transmitted by the bit to the rock these impacts create shock waves that move from the bit to the rock mass through the cutting edges or points on the bit as a consequence cracks are created in the material and produce rock chips the primary difference between rotary drilling and the rest of methods is the lack of percussion being the tricone bit the preferred to most rotary applications in rotary drilling the drill bill is rotated by applying torque at the end of the drill string which results in removal of chips from the face of the hole the drill forces the bit into the material mass strongly being transmitted to the rock mass by means of the cutting points of the drill bit in both methods cuttings are extracted from the hole using a circulating fluid bottom up main factors controlling the choice of drilling method are most importantly the continuity of operations the diameter and depth of the hole and the features of the rocks to be drilled selecting the correct method is essential in mining because the blasthole drilling commonly continues for many years and blasthole drills especially developed for a method are to be obtained before starting the process there are certain limitations to each method of drilling the effectiveness of top hammer methods decreases quickly as further drill rods are attached to achieve greater depth in surface mining holes deeper than 30 m with a top hammer is complex because of the energy lost at the connections of the drill rods rotary drilling is still the main technique to drill 230 mm diameter or greater up to 450 mm actually fig 5 76 another benefit of this type of drilling is that rotary rigs are big enough to operate a long tower that allows drilling of the complete bench height in a single operation at the largest open pit mines rotary units are drilling 20 m deep holes in a single pass fox 2012 5 6 1 1 percussive drilling the percussive method using a top hammer is mainly utilized to drill hard rock for hole diameters up to 140 mm being the principal advantage the high penetration rate in sound solid rock conditions the percussive impact is delivered by either pneumatic or hydraulic pressure percussive drills were originally powered by compressed air but hydraulically powered drills have supplanted pneumatic ones since the mid 1970s rostami and hambley 2011 the advantages of hydraulic drills over pneumatic drills are the fewer moving parts and the significantly higher penetrat

ion rates in the dth method the hammer is located immediately behind the bit and compressed air activates the hammer which impacts directly to the bit this eliminates the already commented loss of impact in joints being a more efficient mechanism of percussive drilling dth method is a reliable way to drill in hard to soft rocks and competent to broken or abrasive to nonabrasive rocks it is also an easy way to produce deep straight holes with minimum deviation and a very good hole wall stability even in fissured rocks dth is preferentially applied to drilling holes for different objectives on small surface and underground mines bits for hammer percussion drills come in various shapes e g chisel or button button bits are preferably used in harder rocks and the shape of the buttons is selected based on the application and the type of rock to be drilled underground drilling is usually carried out by using percussion drilling with holes up to 115 mm according to the underground mining method selected the holes can be guided in many directions the holes are usually established horizontally or vertically being drilled in a symmetrical pattern recent significant technological advances in underground drilling include the use of computer controlled equipment and remote access drilling rigs for underground mining applications can be divided into face drilling and production drilling face drilling is performed by mobile rigs equipped with drills mounted on one boom or multiple booms such as two boom jumbo fig 5 77 which can work on face of the tunnel roof side and floor the number of booms and drills depends on the opening dimensions and rock mass properties the number of holes to be drilled per blast round and the number of faces to be drilled in a shift rostami and hambley 2011 for instance penetration rate in underground blastholes can be considered to vary inversely with the rock strength other variables being equal in hard rock metal mining two boom or three boom jumbos are used whereas in soft rock mining for example limestone two boom or single boom drill jumbos are common multiboom jumbo drills can be programmed to drill the desired blasthole patterns automatically through coordination with an automated surveying and guidance system the system simultaneously monitors the drilling parameters and optimizes the control parameters although drill jumbos were historically powered by compressed air since the late 1970s electric hydraulic and diesel hydraulic units have almost completely supplanted the older pneumatic units in underground metal mines ring drilling production drills are used to drill the long inclined or vertical blastholes used in sublevel stoping sublevel caving and vertical crater retreat mining in such operations drilling can include not only long production blastholes but also ground support installation such as primarily cable bolts 5 6 1 2 rotary drilling it is important to

bear in mind that rotary drills can display two methods of drilling although the majority of the machines work as pure rotary drills driving tricone or fixed type bits tricone bits rely on crushing and spalling the rock this is carried out by transferring downforce to the bit while rotating to drive the teeth commonly tungsten carbide type into the rock as the three cones rotate around their respective axis producing cuttings of rock the softer the rock the higher the rotation speed most drilling functions are hydraulically driven once the cuttings of the rock are created they must be evacuated commonly with compressed air if the cuttings are not removed from the hole the bit will be eroded because of the abrasiveness of the rock chips in most rotary blasthole drills cuttings are lifted between the wall of the hole and the drill rods by compressed air the compressed air is also needed to dissipate the heat mainly originated by friction between cones and the rock two types of drilling bits drag bits and tricone bits fig 5 78 are utilized but since their intended direction introduction in the early 1900s tricone bits have been the traditional type of bits used in rotary drilling they remain the most popular bits for blastholes ranging from 150 to 450 mm in diameter bit selection is based on hole size and depth rock type and operational requirements most rotary drills are diesel powered for good mobility the most important advance in drilling equipment since 1990 has been the development of computer controlled drilling systems these systems automatically locate and collar the holes based on a preprogrammed blast round design and incorporated real time monitoring and optimization of the drilling to ensure that the blasthole is exactly located and is drilled to the right depth gps hole navigation has been developed this navigation system utilizes antennas mounted on the tower rest and radio antennas on the cab to produce a correct bit position 5 6 2 explosives an explosion is a physical or chemical process in which energy is liberated in just a short time it is commonly accompanied by formation of a great amount of hot gas there are many types of explosions mechanical nuclear electrical or chemical in this section only chemical explosions originated by decomposition or very quick reaction of a substance or a mixture are considered thus an explosive is a substance or mixture of substances which when started using heat impact friction or shock undergo rapid chemical transformation releasing tremendous amounts of energy in the form of heat gases at high temperature and shock the energy released by an explosive is used in mining to rock fragmentation and displacement the majority of explosives used in modern mines are manufactured using fuels oxidizings sensitizers energizers and subordinate substances behaving as stabilizers thickeners or flame retarders regarding the two main compon

ents an oxidizing is a chemical which provides oxygen for the reaction whereas a fuel is the component that reacts with oxygen to produce heat for a chemical to be considered an explosive it must produce quick expansion and liberation of heat fast reaction and request to initiate the chain of reactions to understand the different concepts the distinction between deflagration and detonation is required these are the two distinct types of rate of reaction detonation takes place when the rate of reaction in the explosive product clearly exceeds the speed of sound creating a shock wave the speed of detonation for commercial explosives ranges from 1500 to 9000 m s which is much higher than the speed of sound table 5 3 on the contrary deflagration is a process where the reaction takes place at much lower rates than the speed of sound so that no shock wave is produced in the explosive material deflagrating explosives include black power which burn relatively slowly and generate comparatively low blasthole pressure whereas detonating explosives such as penthrite are characterized by superacoustic reaction rate and comparatively high blasthole pressure the speed of propagation is based on the intensity of heat with which the procedure initiated and how quickly and how much oxygen the burning process needs thus explosives can be classified as high explosives e g nitroglycerin and low explosives e g black powder high explosives detonate and require a detonator while low explosives deflagrate and do not require a detonator low explosives cause heavy push or powerful lift of the surrounding material but do not cause a shatter high explosive substances decompose very quickly through detonation under particular situations to develop a large volume of gases extraordinarily high amount of heat and quickly translating shock waves in atmospheric gases when the explosives detonate they mainly originate common and harmless chemical compounds such as water carbon dioxide and nitrogen with subordinate harmful gases such as nitrous oxide carbon monoxide ammonia and methane this is because the majority of explosives are chemicals constituted by carbon hydrogen oxygen and nitrogen it is important to note that nitrogen is presumably the most essential component of a chemical to achieve the explosive nature explosives can also be classified according to their sensitivity as primary secondary and tertiary sensitivity of an energetic material can be seen as the quantity of power that the material requires to absorb to achieve a specific probability of making an explosive reaction matyas and pachman 2013 thus the most sensitive energetic substances are primary explosives less sensitive are secondary explosives and very insensitive are tertiary explosives primary explosives e g mercury fulminate lead styphnate and lead azide can be specified as materials that respond to stimuli like shock impact friction fla

me etc and pass from the state of deflagration at high rate of burning to detonation they are also called initiating explosives being used in the manufacturing of detonators detonating fuses and boosters secondary explosives are relatively insensitive to heat shock or friction and they are also termed base explosives the most typical example of secondary explosives is pentaerythritol tetranitrate petn or penthrite secondary explosives have a high rate of detonation and commonly require a small device including small amount of primary explosive for their detonation these substances are utilized in the production of detonators and constitute their base charge tertiary explosives also called blasting agents are very insensitive to shocks and they cannot be reliably detonated by a limited amount of primary explosive therefore the detonation device contains a small quantity of secondary explosives tertiary explosives are commonly used in mining and construction operations the most commonly utilized tertiary explosive is anfo acronym of ammonium nitrate and fuel oil near 80 of mining blasts are carried out utilizing this explosive besides the above classifications explosives are also ranked based on other parameters such as their consistency packaging cartridge versus bulk or their chemical nature the latter include two groups those classed as substances that are explosive and those that are explosive mixtures for instance black powder 5 6 2 1 properties of explosives properties of the explosives are relevant because they are the ultimate reasons for their choice obviously the ingredients of the explosives influence directly on many of their properties such as resistance to water detonation speed or cost the utility of an explosive can only be defined where the properties are completely understood the properties of explosives are summarized in table 5 4 gokhale 2011 being some of them briefly described below velocity of detonation is a measure of the speed at which the detonation front moves for example along an explosive column it is the most important property of an explosive two explosives with same strength but different velocity of detonation can perform quite differently in a blast the velocity of detonation depends on components of the explosive density accomplished when the blasthole is charged blasthole diameter type of confinement the presence of cavities in the rock mass rock mass temperature and temperature originated at the initiation element of the detonators that are utilized for firing the explosive in general the higher the velocity of detonation the better will be the shattering effect and rock fragmentation process some military explosives have velocities of detonation reaching up to 10 000 m s or more but velocities of detonation of explosives used in mining rock blasting range from 2000 to 7000 m s 5 6 2 1 2 strength strength of an explosive means the energy r

eleased by unit weight weight strength or unit volume bulk strength of the explosive the energy of an explosive shows the ability of the explosive to do work the strength is commonly well correlated to density and detonating velocity as well as heat and gas volume released in the detonation of the explosive the global energy liberated by an explosion can be separated into two main components shock energy and bubble energy the former is generated by the shock wave which moves from the place of its origination as a strain wave and the latter is produced by the heat developed by the chemical reactions included in the detonation process it is complex to estimate the strength of explosives in terms of absolute units several tests allow the effect of the strength of an explosive to be monitored easily offering indications of the strength of an explosive with respect to the strength of a common explosive which is considered as 100 nowadays taking anfo as standard thus strength expressed in terms of such an indicator is called relative strength high strength is required to shatter the hard rocks but the utilization of high strength substances in soft and fractured rocks will be wastage of the excessive energy produced by this explosive 5 6 2 1 3 density density of the majority of commercial explosives is in the range of 0 5 1 8 g cm3 a dense explosive liberates more energy per volume unit because increasing density leads to an increase in velocity of detonation and detonation pressure thus dense explosives are very useful to break hard rocks primary explosives are usually manufactured as crystalline or powdery material with low densities and large specific surface where higher pressures are used to achieve higher densities the compaction process is reflected in the density of the explosive a phenomenon called dead pressing can occur leading to a material which is hard to ignite and if ignited only burns without detonation matyas and pachman 2013 therefore pressing a primary explosive to a point where it loses its capability to detonate is not desirable for example the optimum density range for ammonium nitrate is between 0 8 and 1 0 g cm3 in general it is desirable to press explosives to densities as close to the critical density as possible explosives are supplied by the manufacturers in different densities to control the total energy released in a blasthole 5 6 2 1 4 sensitivity sensitivity of an explosive is an estimation of the ease with which it can be detonated since explosives utilized in older days e g nitroglycerin were very sensitive and exploded without reason today explosives utilized for rock blasting are far less sensitive and have become far safer naturally a perfect explosive to be utilized in rock blasting should be very insensitive so it does not detonate in all the storing or transportation processes nevertheless if the sensitivity of the explosive is too low the detonation

within a blasthole can be interrupted if there are gaps or obstacles among the charges 5 6 2 1 5 water resistance water reduces the effectiveness of an explosive largely since one or more ingredients of the explosive can be dissolved in water and becomes ineffective in low temperature regions the water can cool a water resistant explosive to such a low temperature that a much higher detonation energy is required to ensure its detonation gokhale 2011 the water resistance of explosives varies considerably according to some results of tests performed on samples the manufacturers define water resistance of the explosive as excellent very good good limited or poor the water resistance of an explosive is essential because the blasting process can often take place in wet conditions as an example emulsions have excellent water resistance heavy anfo has some water resistance and anfo has poor or negligible water resistance 5 6 2 2 types of industrial explosives industrial or commercial explosives are designed produced and utilized for commercial applications rather than for military purposes the principal explosives utilized in mining are generally multicomponent type containing fuel oxidizer and in many cases a sensitizer as well fuel is used to burn and generate heat the oxidizer accelerates the process of burning and where high energy output is required a sensitizer is supplemented to the explosive mixture from an industrial viewpoint four main groups of explosives used in mining blasts can be considered 1 dynamites 2 blasting agents 3 slurries and water gels and 4 emulsions according to the federation of european explosives manufacturers the us and europe explosive consumption in 2014 was about 3 600 000 tons with anfo products representing the more consumed group in the market 5 6 2 2 1 dynamites the original dynamite made by alfred nobel was a mixture of nitroglycerine and kieselguhr diatomaceous earth the kieselguhr absorbed the oily nitroglycerine and the mixture became quite insensitive to shock thus it could be used far more safely than nitroglycerine over the years formulations of dynamite have changed but nitroglycerine has still remained the main detonating component there are three basic types of dynamites according to their consistency granular powdery gelatine and semi gelatine they are offered in cylindrical paper cardboard or plastic cartridges gelatine dynamites are powerful explosives nitroglycerin 92 and or nitroglycol ammonium nitrate and nitrocellulose 8 with a detonation velocity ranging from 4300 to 7500 m s and generating high shattering capability sensitivity to initiation by cap or detonating cord is very good and density water resistance and detonation pressure are high gelatine dynamites fig 5 79 can be utilized as the principal explosive component where high density and energy are needed or as a primer for anfo dry blasting agent is a

term used for components of an explosive that they themselves are not defined as explosives but when mixed together they constituted a mixture that can explode a dry blasting agent is a granular mixture of solid oxidizer commonly ammonium nitrate into which a liquid fuel or propellant is absorbed thus the ammonium nitrate serves as the oxidizer and the fuel oil as the fuel in surface mines the most commonly used dry blasting agent is anfo box 5 13 anfo anfo ammonium nitrate and fuel oil is formed by mixing ammonium nitrate 94 with fuel oil 6 a mix that gives maximum energy and velocity of detonation around 3660 m s even after mixing these two components the final product remains fairly dry since the percentage of fuel oil in the mix is very small and it is absorbed in the pores of the small granules prills of ammonium nitrate because of their insensitivity anfo cannot be detonated by a detonator and it should be detonated by a primer of high explosive e g one or two cartridges of dynamite with detonator anfo is supplied basically as poured or packaged where the quantity of explosives is high e g large open pit mines anfo is supplied in separate component containers on a truck mechanically mixed at the worksite and poured into blastholes hence it is also called bulk anfo where the requirement of the mine is low for example in small quarries anfo is usually supplied in nylon bags figure 5 80 shows the anfo loading operation using nylon bags poured anfo proves more effective than the packaged form as it fills the entire cross section of the blasthole whereas the package leaves a gap between the walls of the blasthole and external diameter of the package gokhale 2011 if a blasthole has a significant quantity of groundwater seeping into it it cannot be charged by poured anfo in such cases anfo is premixed and packed into thick cylindrical plastic bags sealed at both the ends charging a blasthole with packaged anfo is very tedious and time consuming advantages of anfo are their safety ease of loading and low price in the free flowing form they have a great advantage over cartridge explosives because they completely fill the borehole regarding disadvantages there are two disturbing aspects about the use of anfo in large surface mines the first is the quick evaporation of diesel oil the second is the high solubility of ammonium nitrate in water where atmospheric temperature and humidity are high it becomes essential to add extra fuel in the anfo mix to take care of the degree of evaporation likely up to the time of detonation in respect of solubility in water if humidity of the atmosphere is high the ammonium nitrate being highly hygroscopic absorbs a large quantity of water and becomes less effective in the process in this context it is worth noting that after about 9 water content the anfo mix becomes insensitive and fails to detonate if anfo mix contains aluminum

as a sensitizer such mixture is called alanfo it is particularly useful for blasting hard rock masses being 10 15 the most commonly used percentage of aluminum in alanfo 5 6 2 2 3 slurries and water gels the explosives that include more than 5 water by weight are called wet blasting agents slurry explosives water gels and emulsions fall within this category slurries are made from ammonium nitrate partly in aqueous solution they are fluid pumpable and miscible with water these types of explosives were invented to avoid anfo explosives issues such as no water resistance low density and limited energy options thus these substances are waterproof and are commonly the preferred selection in an environment where the blastholes stay wet slurry explosives are forthcoming in highly viscous paste bulk slurry as well as in cartridge form they cost more than other commercial explosives such as anfo bulk slurries can be pumped into a blasthole through tubes connected to a truck fig 5 75 slurry density ranges commonly from 1 10 to 1 25 g cm3 water gel explosives a special form of slurry explosive include meaningful quantity of water and split oxidizer and fuel elements generating a mixture that is less sensitive than water free nitroglycerin dynamites water gels are made up of oxidizing salts e g ammonium nitrate calcium nitrate or sodium nitrate and fuels e g ethylene glycol aluminum or oil dispersed in a continuous liquid phase physical sensitizers such as air plastic or glass bubbles can be also mixed with the gel the density of most water gels ranges from 1 0 to 1 35 g cm3 in the last years water gels and emulsions have almost completely replaced dynamite 5 6 2 2 4 emulsions emulsions fig 5 81 are explosive materials that contain substantial amount of oxidizers dissolved in water droplets surrounded by a fuel that is unable of blending or mixing the ratio of oxidizer to fuel in an emulsion is typically 9 1 an emulsifying agent e g sodium oleate stabilizes the water in oil emulsion against liquid separation dispersed gas can be included into the emulsion matrix for density control ranging from 0 68 to 1 36 g cm3 thus voids in the form of microballs or by chemical gassing of the composition make the emulsion more sensitive emulsion explosives show excellent water resistance are moderately insensitive to temperature changes have high energy and develop very good efficiency and flexibility of use the performance of the emulsion explosives makes them as superior products compared to the available slurry based explosives in rock blasting many additional items are required besides the main explosive these components are commonly called accessories the main items in a blast are a booster cartridge a primer cartridge initiation transmission line itl and detonators of these the primer and booster are used to amplify the energy released by the detonation of the detonator the explosi

ve cartridges are mainly formed by pentolite although other explosives such as dynamites water gel slurries or emulsions are also utilized in primer or booster cartridges since these types of explosives have been already explained this section is devoted to aspects related to detonators including blasting instruments such as testing or initiating instruments 5 6 2 3 1 initiation transmission line an initiating device located at a very great distance for the sake of safety always detonates a primer cartridge it is therefore crucial to transmit the pulse through a line called the initiation transmission line itl the more common used itl in blasting is probably the detonating cord fig 5 82 which transmits a detonation wave it is made up of a plastic tube with 3 5 mm outside diameter and being usually filled with penthrite 10 15 g m thus the velocity of detonation is about 6500 m s with very high shock energy since anfo needs a great initiating effect throughout its charge column detonating cord can fulfill this requirement perfectly some similar device is igniter cords which are cord like in appearance last option of initiation is a signal or shock tube fig 5 83 which transmits a signal from the detonating cord to the delay detonator in the hole signal tube can be initiated by an electric detonator and transmits a low energy signal at 2000 m s from one point to another this initiation system is not violent compared to detonating cord and is hence much safer to use it is also recommended in zones where electric detonators are not desirable to be used a detonator is commonly referred to as an initiating device since it begins the detonation procedure in a blasthole they are compact devices that are manufactured to safely initiate and control the efficiency of larger explosive charges box 5 14 detonators 5 6 2 3 box 5 14 5 6 2 3 detonators a detonator consists of a metal tube fig 5 84 usually 5 5 7 5 mm in outer diameter and variable length depending upon whether it is instantaneous or delay type it incorporates a primer explosive e g lead azide and a secondary explosive such as penthrite or pentolite these explosives can be initiated by electrical or shock energy from an external source with such sensitive explosives detonators become sensitive and are more prone to accidental detonation these characteristics make them the most dangerous explosive products in industrial applications thus they must be stored transported handled and used according to set procedures there are three types of detonators based on the source of energy used for starting detonation in the detonator electric non electric and electronic in turn they can be instantaneous or with a delay element built into them the delay element is in the form of a small tube filled with densely packed pyrotechnic material commonly used delays are either from short delay series or long delay series electric detonators cause

the initiation of detonation by an electric current passed through the detonators by electric wires they have an outer aluminum copper or steel shell that contains primary and secondary explosives insulation material two wires and a delay element if applicable the current heats up a high resistance wire that ignites a fusehead similar to a match the resulting flash ignites a delay element which in turn burns the primer charge that detonates the base charge or secondary explosive the simplest and better way to connect electric detonators is in series because if one or more detonator connections are faulty then the entire circuit will not fire this eliminates the possibility of having explosive in the broken rock after blasting in a parallel circuit each detonator is independent of the others moreover connection in series allows the entire circuit to be tested for continuity and resistance the electric delay detonators are manufactured as two varieties long half second delay detonators and short millisecond delay detonators long delay or period detonators are available in several numbers with a nominal half second time interval between each delay short delays detonators present delay intervals much shorter varying from 8 to 100 or more milliseconds anyway delays available can differ from manufacturer to manufacturer 5 6 2 3 non electric detonators non electric detonators are fired by detonating cord instead of electricity a non electric detonator consists of a plastic shell filled with primary explosive secondary explosive and a delay if applicable and a certain length of detonating cord this system is frequently used for blasting a large number of holes it is able of introducing delays of millisecond intervals between holes or rows of holes the delay intervals also change depending on the manufacturer but always in milliseconds e g between 15 and 700 ms or between 75 and 1000 ms the use of these delays can produce advantages such as easy and safe to handle better fragmentation and reduced ground vibration the system finds its applications in surface and underground metalliferous mines 5 6 2 3 electronic detonators the difference between electronic and electric detonators is the replacement of the pyrotechnic delay element by a microchip most electronic detonators consist of wires a detonator shell that looks similar to electric and non electric detonators a microchip a capacitor and a primer charge base charge similar to electric and non electric detonators at firing time the blasting machine sends out a code to initiate the electronic timing devices within the detonators since electronic detonators utilize microchip technology to provide delays for blast designs it allows for much greater accuracy in firing times thus the negligible variation in the electronic delays means that the firing pattern will consistently be the same for each blast resulting in uniform blast results banda and rh

odes 2005 each detonator has its own time reference but the final delay time is determined through the interaction between the detonators and the computerized blasting machine before their firing shortest delay time is 1 ms but detonators are extremely precise to the extent of 0 2 ms this electronic initiation system is considered the safest among all the initiating systems it can be tested in the field without causing actual detonation electronic detonators cannot be initiated by a conventional blasting unit nor can they be activated without entering proper security codes however electronic detonators are still susceptible to initiation by lightning fire and impact of sufficient strength therefore as all other detonator types they must be properly transported stored and handled as an explosive 5 6 2 4 blasting instruments blasting instruments can be broadly classified into two main groups testing instruments and initiating instruments regarding the testing instruments every circuit must be completely checked prior initiating the blast besides this the area of blasting must also be surveyed for extraneous current if electric detonators are utilized for this purpose two very commonly instruments are used blaster s multimeter and blaster s ohmmeter the first is utilized to measure voltage resistance and current in various parts of the blasting circuit the second is sometimes preferred because it is more accurate than multimeters for measure of resistance for instance to ensure that the electric detonator circuit has continuity initiating instruments produce an action that leads to detonation of the detonator in the main explosive an initiating device naturally depends upon the itl used for the blasting circuit there are many different types of initiating devices initiators used for initiating the detonation of electric detonators or exploders fig 5 85 have the capability of imparting electric current to the blast circuit another initiating device is the detonation wave initiator in which a detonation cord transmits a detonation wave finally electronic blast initiator is utilized to compose a computer program listing that controls the complete blast including detonation sequence delay intervals etc it includes also protection to overvoltages electrostatic discharge and unauthorized use as the detonator requires a specific coded signal to fire blast design is the most crucial step in drilling and blasting first and foremost blast design is an iterative process where important factors such as the required fragmentation production and muck pile shape are used as a starting point for determining optimal drillhole diameter depth and inclination subdrilling explosive type and detonation timing moreover operating costs of both the mine and the processing plant are directly related to the fragmentation achieved during blasting bhandari 1997 the aim of a good blast design is to spread the e

xplosives throughout the rock mass such that the rock breakage generates the desired result the rock blasted is easily mobile by the excavation equipment and the procedure originates minimal adverse environmental effects e g flyrock high air blast and ground vibrations distribution here is considered a combination of blast pattern and explosive density blast modeling programs and other tools such as high speed photography or computer software to calculate fragmentation distribution have significantly aided engineers in accurately simulating and analyzing different blast designs the most common blasting method in surface mining is bench blast being the bench height the starting point for blast design fig 5 86 in bench blasting parallel holes are blasted in each round in large numbers it is of huge importance to have a proper delay between each row and even between individual holes in each row the bottom charge from where the initiation normally starts requires well packed explosives of higher blasting power than is needed in the column charge a charge of explosives in a blasthole in the form of a long continuous unbroken column stemming materials are used to top off the blastholes to provide confinement it corresponds to the cross sectional width of the borehole fig 5 86 the blasthole diameter is generally chosen in accordance to the depth of the excavation shallow excavations commonly utilize smaller diameter holes than deeper operations the selection of the hole diameter in the blast design is based on the geology of the blast site primarily the jointing and bedding of the formation which is the only factor that cannot be changed the desired fragmentation and economics must also be considered large diameter blastholes are less suitable in strong massive rock where minimal broken rock movement is required or where it is essential to monitor blast vibrations larger blasthole diameter commonly reduces costs for drilling primers and initiators however smaller blasthole diameter gives better distribution of energy in the rock mass since blasthole diameter is directly related to bench height a good rule of thumb is that bench height in meters is equal to blasthole diameter in millimeters divided by 15 in surface mining practice the rate of drilling and rate of removal of the blasted rock must match thus the diameter of blastholes is loosely related to the capacity of the shovel bucket a free face is a rock surface exposed to air that generates room for expansion upon fragmentation it is sometimes also termed open face forward displacement of blasted rock takes place if a blast shoots to a free face fig 5 87 free faces are necessary because some movement of the rock mass is crucial to enable for crack propagation moreover increased movement assists crack propagation and improves fragmentation in some cases free faces can be limited to avoid dilution in the mineralization vertical blastholes a

re commonly utilized in surface open pit metal mines since drilling accuracy is greater and angled blastholes are more difficult to set up and drill some drills even do not have an angled drilling capability in free face blasting vertical front row blastholes often leave variable and excessive burdens between the top and bottom of the charge causing hard and immovable toe toe in bench blasting is the excessive burden measured at the floor level of the bench it is common to prevent adequate breakage and movement of the toe using some angled blastholes in front rows however excessive blasthole angles can cause problems spacing and burden are related to blasthole diameter depth rock type and charge length spacing is the distance between adjacent boreholes in a row fig 5 86 in bench blasting the distance is measured parallel to the free face and perpendicular to the burden being burden the distance from the borehole and the nearest free face or the distance between boreholes measured perpendicular to the spacing fig 5 86 spacing can be somewhat dependent on the timing but is most often a function of the burden the presumption of from 1 to 2 times the burden is a correct starting point for establishing the spacing of a blast to be initiated simultaneously in holes in the same row with respect to burden the proper burden dimension to utilize in any given individual blast can be calculated by taking into account hole diameter relative rock density table 5 6 gokhale 2011 and the explosive that will be incorporated in the blast a burden too small can result in excessive air blast and flyrock on the contrary a burden too large can result in improper fragmentation toe problems and excessive ground vibrations the assumption of 25 35 times the hole diameter can be a good approximation for establishing the burden dimension subdrilling fig 5 86 is the procedure of drilling boreholes below floor level to assure breakage of rock to working elevation subdrilling is also the length of the explosive charge that lies beneath the designed bench floor level some operations range from 0 2 to 0 5 times the burden or 5 8 times the diameter of the hole it is good practice to drill always a certain extra distance especially in blasting massive rocks where there is no adequate horizontal bedding plane to maintain floor grade the subdrill part is usually backfilled with drill cuttings or other stemming material for its part decking is the separation of the explosives column in a blasthole into two or more parts with stemming between them this procedure is commonly utilized to decrease either the charge load per hole the quantity of explosives detonated per delay or both it should be 6 times the hole diameter for dry holes and 12 times the hole diameter for wet holes 5 6 3 6 stemming stemming is the inert material located in a borehole on top fig 5 89 of or between separate charges of explosive material it is uti

lized for confining explosives or to separate charges of explosives in the same borehole stemming improves fragmentation and rock displacement by reducing premature venting of high pressure explosion gases to the atmosphere dry granular materials such as sized crushed stone or drill cuttings are used for stemming appropriate stemming chip size lies in the range of 10 of the blasthole diameter inadequate stemming creates more flyrock surface overbreak noise and air blast fig 5 90 optimum stemming length depends mainly on blasthole diameter stemming material and surrounding rock properties stemming column is usually 0 5 1 3 times the burden being a correct approach for its height the value of 0 7 times the burden delay blasting is the method of initiating explosive boreholes or rows of boreholes at predefined time intervals utilizing mainly delay detonators the sequence in which blastholes are initiated and the time interval between successive detonations play a major role on global blast efficiency this enables the blastholes closest to the open excavation to detonate and translate rock into the open space first the blastholes behind the first holes then can translate rock horizontally into the new open space thus the burden on each blasthole requires time to move after the detonation to generate an effective free face dependent blastholes then fire toward this new free face developed during the blast therefore the first consideration to establish delay intervals is the availability of free faces the efficiency of production blasts can only be optimized where charges detonate in a controlled sequence at suitable discrete but closely spaced time intervals there are two main types of delay in a blast pattern these are the hole to hole delay and the row to row delay the optimum hole to hole delay is 4 5 ms per meter of burden for designing delay times needed for maximum rock breakage the row to row delay to provide good movement and fragmentation is a minimum of 3 ms per meter of burden obviously these values depend on many factors such as rock mass properties blast geometry explosive characteristics initiating system environmental constraints or the desired result fragmentation muck pile displacement and profile etc 5 6 3 9 blast design to protect pit walls if blast is not well designed overbreak can contribute to pit wall instability therefore it is important to optimize but not minimize overbreak especially as blasts approach the designed wall of the pit the successful application of overbreak control blasting techniques reduces not only the quantity of rock to be removed but it lessens the hazard and cost of rockfalls it can also reduce the need for pit wall support cushion blasting postsplitting and presplitting are the three more important blasting methods utilized to produce stable final walls cushion blasting is the simplest and least expensive smooth wall blasting technique it is a

lso the most versatile and useful method of the three techniques mentioned a cushion blast is a pit wall blast in which back row blastholes contain lighter charges than the production blastholes and are drilled in a correspondingly small pattern cushion blastholes have generally the same diameter as the production blastholes in front of them the charge weight for the cushion holes is commonly reduced by about 45 both burden distance and blasthole spacing are also reduced by about 25 cushion blastholes should detonate in a delayed sequence after the more heavily charged blastholes in front of them this method is utilized without pre or postsplitting where the rock is strong or only minor reductions in damage are needed or for forming pit walls with relatively short lives hagan and bulow 2000 postsplitting is frequently used in conjunction with cushion blasting it consists of drilling a row of parallel closely spaced blastholes with a suitable burden to spacing ratio about 1 25 1 along the final face these blastholes are charged with light well distributed charge which is fired after the production blastholes in front of them have detonated this produces a sound smooth face with minimal damage presplitting requires a row of parallel closely spaced blastholes drilled along the design excavation limit the blastholes are then charged lightly and detonated simultaneously before the blastholes in front of them firing of the presplit charges splits the rock along the designed final face producing an internal surface to which the later firing blastholes in front of them can break presplitting rarely gives impressive results in closely fissured rock comparatively postsplitting gives considerable reduction in damage in massive rocks but the final face is rarely as sound as that produced by presplitting in closely fissure rocks however the final face formed by postsplitting is sounder than that produced by presplitting because the optimum spacing of postsplit blastholes is larger than that for presplit blastholes the cost of postsplitting is usually lower 5 6 4 underground blasting as in surface mining a well designed blasting process and right execution are crucial components for successful underground mining thus bad blasting procedures can generate a very negative impact on the economics of underground mining holmberg et al 2001 development of tunnels shafts raises stopes caving and other underground openings is performed by means of blasting rounds fig 5 92 the design of underground blasting rounds can utilize two types of rounds those with one free face and those with more than one free face single face rounds are utilized in development openings tunnels shafts raises as well as in room and pillar longwall and shrinkage stoping methods of mining multiple face rounds are indispensable for open stopes sublevel caving and large in diameter tunnels that use benching methods sometimes the de

sign of multi face rounds is similar to that of surface blasting types of patterns of holes fig 5 93 mainly vary in the configuration of breaking in holes which are utilized to generate a first free face toward which the blast is further directed otherwise the rock will be projected outward into the openings which can damage infrastructure these patterns can be broadly classified as angled cuts or parallel cuts if breaking in holes is put at an angle to the axis of the working face the patterns of holes are known as angled cut wedge cut is an example of angled cuts and it is particularly suited to large sized drifts which have well laminated or fissured rocks blastholes are drilled at an angle to the face in a uniform wedge formation so that the axis of symmetry is at the center line of the face the void into which rock broken by the blast can expand is generally achieved by a wedge cut the cut displaces a wedge of rock out of the face in the initial blast and this wedge is widened to the full width of the drift in subsequent blasts each blast being fired with detonators of suitable delay time hole placement should be carefully preplanned and the alignment of each hole should be accurately drilled other hole patterns of angled cuts in underground mining are diamond cut drag cut or fan cut firing sequence for a typical parallel hole pattern includes contour or perimeter holes that are fired simultaneously with light explosives and bottom holes or lifters which are fired last to shake up the muck pile in burn cut included in the group of parallel hole cuts a series of parallel holes are drilled closely spaced at right angles to the face one hole or more at the center of the face are uncharged the so called burn cut when the shock waves are reflected at these empty holes the rock is shattered and subsequently blown out by the escaping gases thus there is a specific geometrical relationship between the diameter of empty holes and the spacing between the empty and charged holes in a given rock which performs essential conditions of breakage tatiya 2013 since all holes are at right angles to the face hole placement and alignment are easier than in other types of cuts this method is particularly suitable for the use in massive rock such as granite or basaltdangers of blasting procedures can arise from generation of harmful gases throw of rocks in the air pollution by dust vibrations generated in the ground mass and propagation of air shock waves air blast is an airborne shock wave that originates from the detonation of explosives regarding the ground vibration where an explosive is detonated in a blasthole a pressure wave is originated in the surrounding rock mass and as the pressure wave travels from the borehole it generates seismic waves by displacing particles flyrock and elevated air blast levels indicate inadequate confinement whereas elevated ground vibrations suggest excess confinement

excessive flyrock air blast and ground vibration all indicate inefficient utilization of explosive energy rostami and hambley 2011 on the other hand improper translation stored and handling may be also very harmful initial production planning commonly depends on exploration information plus smaller amount of information coming from other sources e g surface trenches however prior to mining a program of grade control sampling is generally carried out to define the boundaries of ore and waste blocks and where possible ore and waste blasted separately thus grade control is essential for most mining operations the grade control or ore control process involves predictive delineation of the tons and grade of ore that will be recovered by mining accurate grade control is essential to the economics of any mine mistakes at this step are expensive and irreparable and can be quantified in terms of cash flow losses and incremented operational costs every year rossi and deutsch 2014 thus the correct knowledge of grade distribution and optimizing mining selectivity through grade control is crucial to attain the mine plan it is essential that mill feed be kept as close as possible to that called for in the original design specification of the mill and concentrator thus one of the main purposes of grade control is to ensure that material being fed to the mill is of economic grade as well as minimizing ore loss and dilution large fluctuations in grade can be minimized by blending ores from different benches or parts thereof or from different stopes therefore a well managed record database is important for effective grade control and blending this allows for continuous feed through elimination of fluctuations resulting in homogenized feed grade grade control requirements and practices are largely dependent of the commodity first the commodity price controls the implications of ore loss and management has to justify the extra expenditures relating to selective extraction second the increased mill performance due to lower dilution must justify any additional actions required during the mining processes last the style of mineralization often commodity specific dictates whether grade control is geared more toward ore waste discrimination or it is focused on grade and stockpile control e g davis 1992 wetherelt and van der wielen 2011 modern grade control has the aim of minimizing errors in the classification of material types in a mining process but not only ore versus waste but also the allocation of different types of rocks based on grade deleterious material content physical properties or mineralogy moreover the resulting ore grade misclassification is responsible for severe reconciliation problems it is worthy important to remind that true block grades are never known before to mine and therefore must be estimated thus if the classification of ore type based on the true but unknown block grade is differ

ent from the ore type based on the estimated block grade then the ore type of the block is misclassified grade control is performed at the mine on a daily basis fig 5 94 the potential of grade control for improved profits is large for example in a 10 million ton per year copper mine better grade and control procedure that generate an enhancement in average grade from 0 41 cu to 0 42 cu increment gross annual income by about 5 millions of us considering copper official prices at lme in january 2016 although grade control procedures may differ widely it usually consists of sampling and assaying to establish the amount and position of the mineralization to define the valuable ore areas grade control generally entails sampling and assaying of blasthole cuttings followed by estimation of ore control block model grades often blasthole samples are not as useful as samples produced from exploration or rc drillholes but the comparatively huge amount of blasthole samples forthcoming will minimize the influence of the error of a single blasthole sample in some cases grade control can also involve the sampling of truck or shovel loads to ensure that rock is assigned to the correct stockpile or waste dump annels 1991 grade control should always be seen as a complex process in which at least three basic aspects must be considered a data collection and quality b grade control model to determine ore and waste boundaries and c operational procedures and constraints including mining methods and mining practices rossi and deutsch 2014 since grade control depends on a large number of samples the estimation data to define the grade model can be carried out applying classical methods such as inverse distance or nearest point methods or geostatistical techniques kriging nowadays grade control practices have evolved from paper based recording methods to computerized three dimensional modeling and geostatistical simulations 5 7 1 open pit grade control in an open pit operation grade control involves sampling of blasthole cuttings produced by drills and classification of bench reserves into ore low grade and waste material or into various metallurgical types the final and irreversible decision as to what is ore and what is waste is generally made on a daily basis blasthole samples are obtained on closely spaced grids fig 5 95 according to blasting requirements the use of blastholes can be contentious for different causes including sampling quality and disagreements of its grade distribution compared to the exploration drillhole grade distribution consequently classical blasthole sampling has gained an extraordinarily poor reputation for the last five decades due to the introduction of many sources of bias in the procedure pitard 2008 some of these biases are due to the type of drilling machine that is used and are nearly unsolvable others are due to the sampling tools used often unsatisfactory furthermore

there is commonly an unsolvable time logistic problem in blasthole sampling the miner wants that the ore grade control was carried out in 2 or 3 days at most but not enough time is allowed for samplers preparation facilities laboratory and resources department to perform an accurate job the amount of sampling fig 5 96 is constrained by both practical limitations and cost considerations but random sampling errors can be large if sample volume is too small there are different sampling methods to choose from including different grid patterns and spacings although all sampling methods incur errors in open pit operations possibly the most typically utilized method to forecast in situ grades is the arithmetic average of the forthcoming blastholes thus a block model is developed commonly with the block size similar to the blasthole spacing and the predicted block grade is the arithmetic average of the blastholes that fall within the block many times the blocks are relatively large with respect to the average distance between sample points which is unjustifiable and a major source of inaccuracies because the data density is generally sufficient to justify much smaller blocks thus smaller blocks would lead to better definitions of ore and waste boundaries in underground mining mining methods are insufficiently flexible and therefore there is no chance for ore and waste definition at the time of extraction in these situations grade control can be based on infill drilling and completed at the time of defining the stopes to be extracted any failures that can take place at this situation are not only irreparable but also cannot be balanced by other types of errors as it is in some cases with resource calculations rossi and deutsch 2014 grade control can involve mapping and sampling of stope faces sampling of tramcar loads or drawpoint muck piles broken rock at a recently blasted face jackhammer cuttings or diamond drill cores samples are measured off along the stope at specified intervals and marked on the face the process is laborious and includes to extract the marked sample by chipping an exact rectangle from the solid rock face and to ensure at the same time that all the rock fragments are collected it is the geologist s job to guarantee that mining is closely following the mineralized zone and that overbreak during stoping is kept to a minimum annels 1991 at big gossan mine skarn type deposit an open stope paste backfill underground mine in papua indonesia the major objective in the grade control drilling program is to identify the grade boundary in certain levels to guide the mine planning in preparing the stope shape as well as the stope access development haflil et al 2013 this program is designed in a fanlike drilling pattern so that the drilling covers the stope and also 40 m above and 40 m below the targeted stope using a diamond drilling the drilling design is usually from the footwall towar

d the hanging wall of the mineralization detailed logging is conducted to gather better knowledge of the formation mineralization and alteration boundary thus ore waste boundary is defined based on the chalcopyrite mineral content and the ore type is classified based on skarn mineral content sampling interval is also determined using those boundaries as a guide sampling is done continuously along 3 m intervals prior to splitting crushing and assaying of the core the core is measured on its rock mechanical properties geotechnical logging includes specific gravity rqd and point load tests assay testing covers five elements cu au ag pb zn and the assay data is systematically stored in a drilling database standard qa qc sampling practices include duplicate samples blank samples and certified standard samples for every fifteenth sample a grade control block model or short range block model is constructed for short term and stope mining purposes this block model is created on 2 5 m 2 5 m 2 5 m block from 5 m drill core composite lengths and includes data from the updated grade control drilling this short range block model is used as a guide in determining the metal tonnage a stope produced stope reconciliation see next section is conducted after all material from the stope has been mined out grade and tonnage reconciliation compares the grade and tonnage from the planned stope based on the short range block model versus the grade and tonnage using the present stope shape determining the dilution is also a main part in the reconciliation process by utilizing the short range block model it is possible to predict the expected grades and tons to be produced in a stope daily grade to mill and stope reconciliation are based on data produced from this model 5 7 3 grade control and reconciliation predictions of grades in grade control process have a number of common characteristics across all mineralization and mining types from small low production rate metalliferous underground mines to large world class open pits a abundant geological data that can have only minimal relevance or cannot be used b abundant sampling data that can be of relatively poor quality e g have significant sampling errors and c production pressures requiring fast interpretation of the data and rapid prediction of the ore blocks for this reason besides ore waste rock discrimination and assigning metallurgical grades to material grade control provides a basis for reconciliation of mill production figures geostatistical models and pit production tonnages and grades davis 1992 box 5 15 reconciliation reconciliation is the process of comparing predictions to actual production regular reconciliations will be required between the estimated mining grades the grades indicated from stope bench sampling and those reported by the mill fig 5 97 it is essential that this is undertaken so that modifications can be made t

o sampling practice or to the methods or parameters used to calculate grade tonnage or contained metal annels 1991 in fact reconciliation will increasingly become the benchmark by which mining company performance is judged based on comparing actual production with predictions promises in a mining industry context reconciliation equates to the comparison of an estimate a mineral resource model a mineral or ore reserve model or grade control information with a measurement survey information or the official production usually from the processing or treatment plant reconciliation does not of itself generate errors but it can identify the net impact of the errors in the process it is not necessarily the determining test as to whether the mine is successful a mine may be profitable even if it is based on a poor mineral resource a poor ore reserve which includes mine planning practices or poor mining or processing practices shaw et al 2006 therefore the most useful concept of reconciliation is that of ore reserve prediction to grade control prediction to mining production to milling production the basic aims of reconciliation are a to measure performance of the operation against targets b to confirm grade and tonnage estimation efficiency c to ensure valuation of mineral assets is accurate and d to provide key performance indicators in particular for grade control predictions morley and moller 2005 thus reconciliation of resource and reserve models grade control models mine production data and plant tonnage and grade are one of the most vital functions in the mining cycle reconciliation can also highlight any issues in the reserve to production process and in the stockpiling systems minimizing the difference between planned versus actual production will improve business performance consequently the implementation of a reconciliation system often generates a range of benefits such as lowering costs improving efficiency enhancing the accuracy of estimates and saving capital in the simplest case the shareholders want to see a comparison between the annual net revenue for the mine compared to the predictions made to them at the end of the feasibility study defining this question more tightly they want to know there are comparisons of production against predictions for ore and metal produced over consistent volumes and time periods reconciliations should be consistently monitored over time a successful predictive approach can deteriorate due to changes in geology ore type sampling procedures grade control methods mining methods milling controls etc lack of systematic reconciliation means that there are no controls to monitor the predictions and this can result in wrong use of the resource and profit objectives not being met shaw et al 2006 it is useful to know that the mill is receiving the predicted ore at a lower than expected grade even while there is still uncertainty a

s to whether this is due to problems with the ore reserve due to data interpretation or estimation with the grade control due to similar errors plus ore loss and dilution with mining due to deviations from the plan or with milling due to sampling errors or losses similarly it is useful to know that production is exceeding predictions since this can mean the grade control process the mine plan and the revenues are all suboptimal society needs mining industry since products derived of this activity improve our wealth and quality of life and allow society to growth in parallel new technologies that help to minimize human impact on the earth s environment require metals and other mineral products stevens 2010 however the environmental impacts of mining are perhaps part of the price that humankind has to pay for the benefits of mineral consumption because some environmental degradation due to mining is unavoidable in the recent past mining was carried out with little concern for its effects on the environment resulting often in significant environmental damage as political and cultural norms evolved and new legal requirements were enacted almost all major mining companies adopted rigorous policies and procedures for sustainability community engagement and environmental risk assessment and mitigation these companies apply such policies throughout their operations many of which are worldwide up to date many mining companies work actively to remediate environmental damage caused by historic mining operations in areas where they developed operations and or have current activities thus environmental considerations are an important part of the modern mining industry they must be included in all project plannings and feasibility studies must account for the influence of environmental considerations on project schedules and costs nelson 2011 it is clear today that a zero harm environment is achievable and that all fatalities occupational diseases and injuries are preventable the mining industry has followed the same trend as our society big mines affect surrounding environment similar to other industrial operations in the second half of the twentieth century the mining industry developed a better understanding of its impact on the environment today mines are designed developed operated and closed in an environmentally sound manner and considerably effort is put into continually improving environmental standards stevens 2010 consequently the mining industry has changed in the last decades it is not the industry it was 100 50 or even 30 years ago modern mines operate under modern laws that place far greater importance on environmental protection and use knowledge and technologies that limit the impact of a mine on the environment moreover the modern mining industry also considers the environment in a broader context than in the past today it is not just about the physical environment but also th

e social and economic environment in which a mine operates therefore the policy makers and organization conducting the mineral development must foster the social well being of the people living in the mining areas mines must have the support of the communities and countries in which they operate in order to be successful this support is garnered ensuring high standards of environmental stewardship haldar 2013 large mining operations affect surrounding communities flora and fauna land and water similar to other major industrial operations the extent to which mining becomes an environmental impact depends largely upon the number of people that a mine affects high quantities of waste are a consequence of most mining and quarrying operations although the major part of this waste is inert and nonhazardous disposal is often a space problem at least in densely populated areas since economic growth cannot take place without mineral raw materials the rational conclusion is that the exploitation of mineral resources is not the problem but it must be developed in a green and modern execution pohl 2011 obviously the larger the size of a mining operation the larger the impact is likely to be because it will produce more waste occupy more land and have a greater number of buildings old mining works commonly dumped wastes without interest for their physical or chemical stability and the disposal of waste has led to the pollution of surface streams and groundwater moreover urban areas have suffered subsidence damage by underground mining thus although the mining companies generally showed a lack of concern for the environment this does not indispensably mean that society was not aware of the environmental issues that could be generated with mining for example in 1306 a royal proclamation prohibited the use of coal in london for domestic and industrial purposes because of the nuisance caused by smoke but it proved impossible to enforce in addition agricola 1556 commented the environmental issues generated by mining such as the devastation of fields and the contamination of streams the greater awareness of the importance of the surrounding environment has led to tighter regulations being implemented by many countries to lessen the impact of mining operations the concept of reclamation of a site after mining works has entered definitely in the country laws thus in most developed countries mining is closely regulated now and environmental impacts are increasingly being controlled modern mines are bound by present environmental legislations that are becoming strict in the developed world in this sense it is important to remember that there is legacy of older operations in most countries worldwide many of which have been abandoned therefore there is a combination of modern impacts the impact of current mining in developing countries is still more marked matched with ancient legacies due to the above mining comp

anies are carrying out considerable efforts to decrease the environmental impact of mine works and diminish the footprint of their operations throughout the mining cycle including working to reclaim ecosystems post mining to achieve this objective many mining companies have developed their own codes of practice to assure that mining operations do not so significant harm to their surroundings all mines have a finite life and once the ore is extracted the mine will close and the mine site will be reclaimed to a productive natural state thus generally the final step in the operation of mine works is closure and reclamation the procedure of closing a mine and recontouring fig 7 1 revegetating and restoring the water and land features to the previous configuration closure and reclamation plans are part of mine planning and environmental assessment and must be in place prior to mine development before the incorporation in the 1970s of mine closure requests and best practices in the laws mines were commonly abandoned fig 7 2 thus mine land reclamation and closure planning are actually needed by regulatory agencies worldwide and they are frequently a part of the environmental impact assessment procedure carried out in many countries regarding the financial assurance requirements of a closure and reclamation plan it is the responsibility of the mining company to pay for closure and reclamation costs to avoid mine abandonment mining companies are ever more requested to supply financial warranty in the form of a deposit or bond to governments and communities as a guarantee that the resources to meet closure needs will be available in a perfect world mine works only finish their activity if the mineral resources are exhausted and a mine closure planning is gradually implemented however in the real world mines extract reserves not resources and the grade and tonnage of reserves change daily based on the commodity price mineralization grades geotechnical issues and other features that can produce the closure before the calculated reserves have been wholly mined in these cases the reputation of the mineral industry is dependent on the legacy it leaves the reasons why mine works close preterm are numerous including low commodity prices or high expenditures reducing grade of the mineralization unfavorable geotechnical conditions policy changes social or community influences and many others this closure position previous the entire extraction of the mineralization can generate important issues for the mining enterprise the community and the regulator commonwealth of australia 2006a the concept of community is usually used in the minerals industry to describe those who live in the geographic region of an operation either in defined settlements or dispersed settings a mine closure plan including physical rehabilitation and socioeconomic aspects must be an integral portion of the project life cycle and should

be determined so that a the future public health and safety are not compromised b the after use of the site is beneficial and sustainable to the affected communities in the long term and c the adverse socioeconomic impacts are minimized and socioeconomic benefits are maximized ifc 2007 moreover the closure plan is a dynamic document that must be constantly updated to express variations in mine development and operational planning as well as the environmental and social conditions closure and post closure planning should incorporate adequate aftertreatment and continuous monitoring of the mine site the duration of post closure monitoring can be organized on a risk basis however site features commonly need a minimum period of 5 years following closure or longer whether an operation has 10 or 50 years of operational life remaining implementing closure plan into the mining business originates a great value for both the company and the wider community for this reason mining companies must involve governments communities of which they are part and other stakeholders in closure planning to achieve a successful closure outcome external mining stakeholders such as local communities conservation groups and biodiversity advocates are becoming more and more sophisticated about the outcomes of good and bad closure planning practices bingham 2011 planning for a successful closure is a complex multidisciplinary task that is essential to minimizing long term risk for the mining company the environment and the affected stakeholders assessing closure risk requires a systematic structured evaluation thus the risk assessment forms the basis of the closure plan and cost estimates the focus of the closure risk assessment will be to establish an acceptable risk profile for the company and all other stakeholders upon completion of the closure project to address closure planning issues and meet business objectives to manage risk it is necessary to assure that closure planning is wholly integrated in the core business of the asset bingham 2011 additionally the detail and accuracy of closure plans must change through the life cycle of the asset starting out as conceptual and progressively becoming more detailed over time 7 1 2 1 1 closure objectives closure objectives establish the closure results for the mining project and must be realistic and attainable they can form the requirement to restore a site to its original state and rehabilitating the site to a condition compatible with the surrounding terrain these goals are designed in accordance with the suggested post mining land use s and are as precise as possible to afford a specific indication to the government and the community on what the proponent commits to attain at closure timing and the methods to achieve these objectives are through the life of the asset life cycle is commonly very specific for example some of mines may not enable for any concurrent or prog

ressive reclamation during the operating stage since the disturbed areas are in constant utilization during the mining works while other mining operations e g several types of coal mines display generally the possibility to carry out reclamation activities during the life of the asset the environmental protection authority of western australia summarizes the main closure objectives of a mining project 1 landforms constructed waste landforms will be stable and consistent with local topography constructed tailings storage facilities will be nonpolluting and non contaminating and toxic or other deleterious materials will be permanently encapsulated to prevent environmental impacts surface water bodies shall not be left in mining voids unless the operator demonstrates there will be no significant environmental impact e g salinization reduction in water availability toxicity algal problems attraction to pest species or a local safety hazard fig 7 3 2 revegetation vegetation in rehabilitated areas will have equivalent environmental values as surrounding natural ecosystems soil properties will be appropriate to support target ecosystem 3 fauna rehabilitated areas will provide appropriate habitat for fauna abundance and diversity of fauna must be present in appropriate proportions given the specified post mining land use 4 water surface and groundwater hydrological patterns flows will not be adversely affected any water runoff or leaching from tailings dams overburden dumps and residual infrastructure shall have quality compatible with maintenance of local land and water values 5 infrastructure and waste during decommissioning and through closure wastes will be managed consistent with the waste minimization principles no infrastructure left on site unless agreed to by regulators and post mining land managers owners disturbed surfaces must be rehabilitated to facilitate future specified land use the location and details of any buried hazards will be clearly defined and robust markers will be installed and maintained in general there are three basic stages to developing an effective closure plan the first stage is the development of a target closure outcome and goals which are manifested in a conceptual closure plan this plan is developed and used during exploration pre feasibility feasibility design and construction to guide the direction of activities its active life can be 3 5 years if well defined and based on effective community and stakeholder engagement it cannot change much during this time the second stage involves the ongoing development and implementation of a detailed closure plan which increases the understanding of specific goals and milestones as well as the actions and outcomes of activities to meet these this plan is used continuously during operations and has an active life that could range from 5 to 30 years or more obviously during this time it must be updated the fin

al stage is the effective transition to closure which can be manifest as a decommissioning and post closure plan its active life can be as little as a year or two although it can extend many years past that time depending on post closure responsibilities icmm 2008 7 1 2 2 reclamation mine reclamation is the procedure of taking land after utilized by mining operations and changing it into land with alternative uses reclamation includes aspects related to surface and groundwater and air purity erosion issues generated from storm water and sometimes wind revegetation of appropriate plant species and wildlife habitats the best time to start the reclamation procedure of mine works and associated installations is just before the first excavations are undertaken in planning for the reclamation of a given mine there are many issues that must be considered the first of these is the safety of the mine site especially if the area is open to the general public the second major issue is rehabilitation of the land surface fig 7 4 the water quality and the waste disposal zones so that long term water contamination soil erosion dust production or vegetation issues do not occur the final concern is the subsequent use of the land after mining is completed the last stage in reclamation is monitoring in this process all reclaimed areas are monitored and assessed for vegetation survival and growth rates plants in areas that are to be used for grazing will be tested to ensure that they contain acceptable levels of metals and other possible contaminants reclamation has been used in a general way simply to mean returning a mine site to some other land use whether it be the same as before mining began or different it includes the physical stabilization of the land e g waste rock piles landscaping rehabilitating topsoil and return of the land to a helpful finality the art of mine reclamation has progressed from straightforward revegetation operations to a more complex discipline that includes utilization of native plants to mimic natural ecosystem in most cases entire reclamation is almost impossible but sound remediation and rehabilitation can result in the opportune setting of a functional ecosystem by planning the mine for a subsequent development it is possible to improve the value of the disturbed land and help to change it to a utilization that the public will consider clearly positive thus old mine sites can be converted to wildlife habitat and refuge recreational areas shopping mall golf course airport lake underground storage facility solid waste disposal area mining and power plant waste storage museum site of special scientific interest and regionally important geological site industrial land pisciculture pond and many other economically or ecologically productive land utilizations that can benefit society the conversion of an abandoned mine for practical commercial purposes depends upon the geolog

ical and hydrogeological conditions as well as the nature and geometry of the mining that took place there is a great variety of terms used in mining reclamation the terms remediation restoration rehabilitation and reclamation itself are all applied to express mine closure activities that attempt to alter the biological and physical state of a site however they have slightly different meanings they are many times utilized interchangeably but refer to different stages in the preparation of the site for another utilization thus remediation is the cleanup of the polluted area to safe levels by extracting or isolating contaminants at mine sites remediation commonly consists of isolating contaminated material in pre existing tailings storage facilities capping tailings and waste rock piles with clean topsoil and gathering and processing polluted mine water as far as restoration is concerned it commonly refers to returning a mined area to its previous condition and land use such as where a surface mine is filled and the restored land returned to agriculture the meaning of rehabilitation and reclamation in the context of mining is not as widely accepted as the meaning of restoration nevertheless rehabilitation also referred to as regeneration can be regarded as the establishment of a stable and self sustaining ecosystem but not indispensably the one that existed previous mining works started therefore rehabilitation is the procedure utilized to remedy the impacts caused for the mining activities on the environment the long term aims of rehabilitation procedure can change from merely converting an area to a safe and stable condition to restoring the pre mining conditions as closely as possible to support the future sustainability of the site an environmental management system ems is an essential part of a larger management system or an organization the ems is utilized to define an environmental policy and to control the environmental aspects of the organization activities products and services this control includes interrelated components such as responsibilities authorities relationships functions processes procedures practices and resources a management system utilizes these components to define policies and goals and to develop ways of using these policies and achieving these objectives thus ems is a group set of procedures and practices that allow an organization to decrease its environmental impacts and increment its operating effectiveness being a powerful tool for managing the unfavorable impacts of activities of an organization on the environment aspects the profits of an environmental management system are the following a diminishes the environmental responsibilities applying well defined mitigation techniques b increases the effective utilization of resources c decreases waste production by appropriate planning d proves a well accepted corporate image e motivates awareness of environme

ntal concern f increments better knowledge of environmental impacts of business activities and g increments the skill and effectiveness generating higher productivity at lesser costs and higher benefits applying an ems the company can prove to all people that they take environmental impacts actively moreover an efficient ems can also enhance company operations and generating economic profits the bigger organizations decide certification is more meaningful when taking into account the potential trade and market benefits of an internationally identified and certified ems for this reason iso 14000 families of certifications assure diminishing the negative effect of operations on environmental aspects and comply with applicable laws regulations and other environmentally oriented mitigations all these standards are periodically reviewed by iso to assure that they still meet market needs it is important to note that environmental management systems do not by themselves define environmental objectives rather they only lead the management procedure of a company to assure that environmental programs can be efficiently developed setting of policies and goals is one of the important functions defined within such a management system iso 14001 issued in 2004 offers standards by which an organization may put in place and implement a series of practices and procedures that when taken together result in an environmental management systemother relevant families of certification used in an ems are iso 9000 and iso 18000 for example the former ensures quality system management and it is established to help organizations that they satisfy the requirements of customers the iso 14001 standard is the most important within the iso 14000 series and it sets out the criteria for an environmental management system ems iso 14001 is the internationally accepted environmental management standard that certifies that an organization is committed to reducing the environmental impact of its products and operations and is constantly monitoring and seeking to identify ways of reducing that impact further it prescribes controls for those activities that have an effect on the environment these include the use of natural resources handling and treatment of waste and energy consumption thus the standard requires the company has a procedure for monitoring that regulatory requirements are being met international standard iso 14001 2004 from the international organization for standardization iso defines an environmental management system ems as organization structure responsibilities practices procedures processes and resources for implementing and maintaining environmental management it is a flexible risk based plan do check act continual improvement approach that requires formal documented processes for many of its elements most mining companies are committed to managing its environmental aspects impacts and risks through adhe

rence to the internationally recognized iso 14001 2015 ems standard it is known as a generic management system standard meaning that it is relevant to any organization seeking to improve and manage resources more effectively today many large scale mines operating worldwide have already attained iso 14001 certification the iso 14001 ems standard requires every mining company the highest most acceptable level of efficiency in terms of extracting minerals while at the same time ensuring that the environment is not compromise the five main stages of an ems as defined by the iso 14001 standard are fig 7 7 1 commitment and policy top management commits to environmental improvement and establishes the organization s environmental policy 2 planning an organization first identifies environmental aspects of its operations and then determines which aspects are significant by choosing criteria considered most important by the organization 3 implementation an organization follows through with the action plan using the necessary resources human financial etc an important component is employee training and awareness for all employees 4 evaluation a company monitors its operations to evaluate whether targets are being met 5 review top management reviews the results of the evaluation to see if the ems is working management determines whether the original environmental policy is consistent with the organization s values the plan is then revised to optimize the effectiveness of the ems in the last three decades the terms sustainable development and sustainability have been in use by the governments and policy makers worldwide it is commonly agreed that sustainable development was early defined in 1987 by the brundtland commission our common future world commission on environment and development united nations as a system of development that meets the basic needs of all people without compromising the ability of future generations to meet their own life sustaining needs since then a rich discussion has ensued about what this means in practical terms though many other sets of words have been suggested for defining sustainable development the brundtland commission definition has stood the test of time in mining world these words were possible first utilized in the early 1990s in the rio summit 1992 in recent years the word sustainability has also found its way into common use the ideas of sustainable development and sustainability are different but synchronous sustainability is a more general term that captures the idea that we need to maintain certain important aspects of the world over the long term these features vary from primary requirements of human society such as air water food clothing shelter and basic human rights to a group of perceptions that would collectively be termed quality of life and not only for people but also for other forms of life sustainable development is th

e human or action part of this set of ideas together these ideas are very appealing but their translation to practical action remains much debate this is not surprising since there are about 200 countries across the world and the global ecosystem is complex and not fully understood hodge 2011 at the base of the interlinked ideas of sustainability and sustainable development is the easy perception that the human activities obviously including mining should be carried out in such a way that the activity itself and the products originated together afford a net contribution to human and ecosystem well being over the long term an optimum balance clearly requires to be maintained between sustainable development and eco friendly environment haldar 2013 since the release of our common future including the aforementioned brundtland report many of the major industries in the world including mining companies many of its governments and the united nations have adopted a policy of sustainable development in this sense the mining industry has been a particularly active locus of sustainability related policy and practice innovations because a the potential implications of mining activities and the minerals and metals that result are significant b many interests are touched by mining c the role of many of these interests in decision making is growing e g communities and indigenous people d the nature of contemporary communications systems has brought the often dramatic nature of mining operations into the public eye and e industry governments civil society organizations and the public in general are all anxious to ensure mining makes a positive contribution that is fairly shared hodge 2011 however the focus is not on how mining can be sustainable identifying that mining operations has a finite useful life but on how mining industries can help to sustainable development this is a conceptual change from a singular analysis and mitigation of impacts to a more complete study that looks at the broader contribution of the industry and its products icmm 2012a in this sense financial aspects are essential to meet the sustainable development objectives box 7 3 the equator principles today mining companies employ the principles of sustainable development in their environmental policies this has resulted in positive development for the industry and has allowed mining companies to view the impacts of their operations in a more comprehensive manner the process has not been easy conflict is still present and consensus is not always possible stevens 2010 in summary a sustainable mining operation must be safe proves significant practices in ems and community engagement is financially robust and which very importantly effectively utilizes the mineral resource thus mine managers establish a sustainable mining operation if they focus on the five areas safety environment economy efficiency and co

mmunity laurence 2011 at present almost all mining companies include in their web pages a heading or subheading entitled sustainability or sustainable development thus headings such as socioeconomic development environment community or indigenous relations are common and annual sustainability reports updated regularly are available in almost all mining web pages but application of sustainability concepts to the mining minerals and metals industry needs attention paid to the full project and mineral life cycles that is including exploration design and construction operation closure and reclamation in the late 1990s and faced with growing concern about access to capital land and human resources the chief executive officers of nine of the world s largest mining companies took an unprecedented step working through the world business council for sustainable development they started the global mining initiative gmi they commissioned the international institute for environment and development london to carry out a global review that would lead to identification of how mining can contribute in the best form to the transition to sustainable development the resulting project mining minerals and sustainable development sparked a large and rich literature including the final report of the project entitled breaking new ground mining minerals and sustainable development as a direct result of mmsd the international council of mining and metals icmm was founded at 2001 it is an international organization devoted to enhance the social and environmental performance of the mining industry formed by 23 mining and metal companies and 34 regional and commodity associations icmm represents the views of most of them in addressing the core sustainable development issues facing the industry in may 2003 icmm s ceo led council committed member companies to implement and measure their performance against ten sustainable development principles they are based on the issues identified in the mining minerals and sustainable development project and all icmm member companies have committed to following this set of ten principles the ten principles published by icmm are the following 1 implement and maintain ethical business practices and sound systems of corporate governance 2 integrate sustainable development considerations within the corporate decision making process 3 uphold fundamental human rights and respect cultures customs and values in dealings with employees and others who are affected by our activities 4 implement risk management strategies based on valid data and sound science 5 seek continual improvement of our health and safety performance 6 seek continual improvement of our environmental performance 7 contribute to conservation of biodiversity and integrated approaches to land use planning 8 facilitate and encourage responsible product design use reuse recycling and dispos