Improving Low-Grade Ore Recovery With the Use of Efficient

8/12/2019 Improving Low-Grade Ore Recovery With the Use of Efficient

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Improving Low Grade Ore Recovery with the Use of EfficientBlasting Techniques Floyd

ABSTRACTDrilling and blasting operations have historically been viewed as anecessary evil part of mining, whose costs should be minimised bywhatever means possible. In t he past, when operations depe ndedprimarily on crushing and milling for ore recovery, it has been difficult toaccurately quantify the downstream effects of blast performance. As aresult, blast performance has been typically evaluated in terms of cost pertonne or kilograms of explosive per tonne. This assessment has led toblast designs that were inefficient and actually increased the overall costof an operation due to oversized fragmentation. This culture has tochange to take full advantage of the application of heap leachtechnologies for low-grade deposits.

Recent advances in heap leach/solvent extraction processes havelowered the economic cut-off grades to relatively low levels 0 1 percent). In run of mine heap leaching the fragmentation produced byblasting is one of the major factors that controls the percentage of orerecovered. Small reductions in the average fragment size will providesubstantial increases in recovery, even with relatively low-grade deposits.To produce smaller blast fragmentation the cost of drilling and blastingwill generally increase. In many cases the existing drilling and blastingcosts can be doubled to achieve an optimum fragmentation size thatprovides the best recovery and in turn the highest overall profitability.The challenge is to de fine the o pti mum blast design based on therelationship between drilling and blasting costs and overall recovery. Thischallenge can only be met by accurately quantifying blast performance interms of cost and fragmentation. Once this relationship has beenestablished, an economic model can be developed that takes into accounttotal reserves, average grade and potential recovery based on fragmentsize. This mo del c an then b e used to guide the refinement of the blastdesigns.Before changing a design to improve fragmentation it is important todefine where the oversize is originating from. There are specific designmodifications that should be evaluated to reduce oversize in each zone.Without the proper quantification of blast performance and blastdesign refinement it is unlikely that a mining operation can approach atruly optimised level of overall cost efficiency.

INTRODUCTIONTh e metal mmmg industry is undergoing major operationalchanges. T his is due in part to the application of newtechnologies, such as r un of mine ROM) heap leaching, thatprovide increased recovery as well as tools to track the efficiencyof various phases of the mining process. Drilling and blastingpractices are also evolving to keep pace with the new methods.In the past it has been difficult to quantify the downstreambenefits of blasting. As a result, blast performance has beentypically evaluated in terms of cost per tonne or kilograms ofexplosive per tonne. This assessment can lead to blas t designsthat are inefficient and increase the overall cost of an operationdue to oversized fragmentation. The recent implementation ofimage analysis techniques has provided a way to quantify blastperformance in terms of the fragmentation size distribution. Thisdistribution has a direct influenc e on the recovery of ROM)leach processes as well as excavation, crushing and milling costs.

The copper mining industry has historically depended on highproduction rates to maximise their return on investment. This hasled to an emphasis on the quantity of tonnes produced instead of

I. President, Blast Dynamics Inc, Box 2384, Steamboat Springs, CO8 477 USA.

achieving high recovery rates. However, rece nt advances insolvent extraction heap leach technology has lowered ROM cuto ff grades to relatively low levels 0.10 per cent). Instead ofdepending primarily on crushing and milling for ore recovery,some operations have shifted their emphasis to ROM leachrecovery.In this scenario, low-grade, supergene sulphide and oxide oresthat cannot be economically crushed and milled are hauleddirectly from the blast site to the leach pad. The fragment size ofthe ROM material directly influences the percentage of orerecovered for most types of disseminated orebodies.

INFLUENCE OF FRAGMENTATION ONHEAPLEACH RECOVERYIn leaching operations the rock fragment size controls theeffective ore recovery in a variety of ways. Typically the leachsolution will penetrate a solid fragment from 20 to 40 mm. Thiszone of penetration is known as the recovery ring and isillustrated in Figure I.

re overy r n

FIG I Cross-section of rock fragment showing recovery ring .

Obviously, as the fragment increases in size the percentageof leachable ore decreases. This relationship is shown here inTable I

T LE 1 elationship between fragment size and potential recovery

Frae:ment size cm) 15 20 25 30Frae:ment volume cc) 1767 4189 8 181 14137Reaction rine: thickness cm) 3.5 3.5 3.5 3.5Recovery rine: volume cc) 1499 3038 5127 7766Maximum recovery possible ) 85 73 63 55

Another way that oversized material reduces recovery is by thes hadowing effect that occurs as the leaching solution flowsthrough the pad. This effect is illustrated in Figure 2.Conversely, if the fragment size is too small the permeability

of the leach pad can be reduced, resulting in lower ore recovery.Owing to the direct influence of fragment size on recovery, ROMoperations should focus on the quantification and optimisation ofblast induced fragmentation.

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FIG 2 The effect of oversize material on solution dispersion.

FRAGMENTATION ECONOMICSThe potential benefits of increased ore recovery resulting fromefficient blasting are economically attractive. A summary of atypical cost/recovery analysis is shown in Table 2

For most rock structures the cost of drilling and blasting mustbe increased in order to achieve smaller fragmentation. Theinitial design in Table 2 used a 270 mm blasthole drilled on a 1by 11 m pattern and had an energy factor of 614 k per tonne.According to the Kuz-Ram algorithm for a rock with average'blastability' this design would produce an average post blastfragment size of 32.4 cm. In the other three options the explosiveenergy level was increased by reducing the pattern dimensions.As expected, the Kuz-Rarn algorithm predicts reductions in the

average fragment size, which will increase the ultimate orerecovery. The value of this additional recovery in this model wastwo to three times the increased drilling and blasting costs. Evenin Option 3, where the drilling and blasting costs were nearlydouble those of the initial design, the recovery value/cost ratiowas 1.95 to I. Obviously, the validity of this analysis dependson the precise quantification of a blas t's fragmentationdistribution, the depth of the recovery ring and the recoverypercentage within the recovery ring.As a blast's energy level is raised the amount of fine materialproduced typically increases. Since excessive fine material canreduce the permeability of the leach pad the adverse effect of thisfine material should also be taken into account. With anunderstanding of these site specific parameters a cost/recoverymodel can be developed to help define the optimum blast design.

DEFINING BLAST PERFORMANCEThe relationship between fragmentation and the resultant orerecovery must be established to optimise the blast design. Todetermine this relationship it is necessary to first quantify theperformance of the current blast designs.

This quantification can be difficult if the designs are notimplemented correctly in the field. One way to achieve goodimplementation consistency is to have documented proceduresfor the drilling, loading and performance evaluation of the blast.When these field procedures are carefully applied it is possible todetermine the influence that various design parameters have onthe fragmentation produced. Otherwise it will be difficult todetermine if the blast performance was the result of the design orcaused by plan deviations during implementation.

TABLE 2Recovery cost model

Initial design Ootion 1 Option 2 Ootion3Estimated production 0 50000 000 50000000 50000000 50000000Chaf te diameter mm) 270.00 270.00 270.00 270.00Burden (m) 10.00 9.00 8.00 7.00Spacin2 (m) 11.00 10.00 9.00 8.00Energv factor (ki t) 614 750 938 1206Powder factor (kg t) 0.19 0.23 0.29 0.38Avera2e blast fragment size (cm) 32.4 27.6 23 1 18 9Fragment volume (cc) 17868 11044 6462 3535Drilling and blasting costs ( ) 8171524 9987418 12484272 16051207Difference ( ) 1815894 4312749 7879684Drilling and blasting costs ( t) 0.163 0.200 0.250 321Average grade ) 0.20 0.20 0.20 0.20Ore available t 100000 100000 100000 100000Ore value ( O 1653 1653 1653 1653Est reaction ring thickness (cm) 3.5 3.5 3.5 3.5Maximum recoverY nossible ) 52 58 66 75Estimated leach recoverY (.%) 4 4 40 40Estimated recoverY (t) 20710 23350 26450 30016Estimated overall recoverY ) 21 23 26 30Value of ore recovered ( ) 34233973 38597500 43721464 49616034Difference from initial design ( ) 4363527 9487491 15382061Increased orofit ( ) 2547633 5174742 7502377Recoverv value/Cost ratio ( ) 2.40 2.20 1 95

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Even with careful design implementation the actual siteconditions and loading data must be comprehensivelydocumented using a daily blast report. Included in the blastreport should be the: blast number, type of blast - finals or production, date and time of blast, centre of blast - Northing, centre of blast - Easting, rock b last ab il it y b ased o n a comb in at ion of rock hardness,density, friability, structure, consistency, etc), tonnes blasted, total drill ti me required, man h ou rs required for loading, total number of holes, number of lost unloadable) holes, location of lost holes, location of wet holes, b la sth ol e diameter, bench height, burden, spacing, subdrill, stem length, stem type, average hole depth, average charge per hole, total charge weight, average exp lo si ve density, energy factor, timing configuration diagram showing pattern, point ofinitiation, delay configuration, and direction ofdisplacement), and general blast performance fragmentation, flyrock,overbreak, movement, etc).

Thi s d at a needs to b e r ecor ded in a timely fashion, preferablythe day of t he blast. Du ring the blast refinement process theability to sort and evaluate the data recorded will be veryimportant. h daily blast data should be entered into a databaset hat can sto re the i nfo rm at io n for future an aly sis and cal cul atethe following information: av er ag e energ y factor b y l ocati on, drill cost, average drill cos t by location, labor cost, average l ab or c ost by loca tion, average h ol es l oaded p er man-ho ur, explosives cost, average b last in g cost by l ocati on , drilling and bla sti ng cost, and dr il lin g an d b last in g cost to-date.

T he sort and e xtrac t functions of the database will help todefine cost and performance trends on a shot-by-shot and pit-bypit basis. In addition to cost information, the database should alsotrack the following information: pattern lay out - as surveyed, surveyed drill pattern, wet hole locations, blast overbreak, and relative rock hardnes s - from the drill log.

IMPROVING LOW-GRADE ORE RECOVERY

With this i nf or matio n the sit e con di ti on s and dril l and b lastperformance can be quantified on a shot-by-shot basis in termsof: drill accuracy, n o b las thol e zones - to help dete rmine th e ca us e of oversize, hardness zones, wet hole zones, average tons per truck - to help quantify blast fragmentation,and po ten tial dilut ion.

Al ong with the d ri ll ing and b last in g d at ab ase it is suggestedthat video recordings be made of every blast to provide a visualrecord t hat can b e used to q uali fy b last perfo rm an ce. The videorecordings can provide insight into the origin of oversize,stemm ing perf or mance, face confi nement , in iti at ion systemfunction, burden displacement and the degree of overbreak.Since the recovery efficiency of ROM leaching is directlyrelated to fragment size the fragmentation produced by the blastdesign must be quantified.Recent advances in i mage an al ysis have m ad e i t p ossi bl e toaccurately define the fragmentation distribution of a blast. Thisprocess uses digital edge tracing techniques to define eachfragment size and then cal cul at es the overall d istrib utio n. Theaccuracy of this analysis typically depends on the resolution ofthe images and the number of images analysed per blast. Ideally,a drive-through imaging station is s et up to record the image ofeach truck load of every blast. Thi s will p ro vi de eno ug h d at aneeded to accurately determine the fragmentation distribution ofthe overall blast. is often useful to record images of theworking face to help define the location of the oversize withinthe muckpile.O nce pr oced ur es are in place to ensure the proper fieldimplementation and performance analysis of the blasts thedesigns can be modified to achieve the desired level offragmentation.

DEVELOPING RECOVERY OPTIMISEDBL ST DESIGNS

The optimisation of blast designs should be considered acontinuing process of refinement.To optimise blast performance in terms of o re recov ery it isnecessary to define the objective of each blast. For example, thefragmentation goal of a 1 per cen t l each abl e or eb ody may be

35 cm while the recovery of a 0 .2 p er cen t g rade j usti fi es a 20 cmsize. Once a blast fragmentation goal has been established withthe cost/recovery model, a logical, step-by-step approach can bedeveloped to achieve the goal.There are four key design factors that control a blast s

fragmentation of the rockmass.They are:

explosive energy distribution - the explosives must be evenlydistributed in the rockmass to produce uniformfragmentation; explosive energy confinement - the explosive energy must beconfined long enough to allow the gases to extend fracturesand displace the rockmass; ex pl osiv e en ergy level - the sho ck energ y level must b e highenough to overcome the compressive and tensile strength ofthe rock and the gas energy must be high enough to provideproper expansion of the rockmass; and geolog y - the r ock s density, streng th and stru ct ur e all play

important roles in the fragmentation produced by a blast.Before chang in g a desig n to i mp ro ve f ragmentatio n it isimportant to define where the oversize is originating from. Thiscan be done through visual ins pection of the muck pile and

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communication with the excavator operators. A post-blastmuckpile can be divided into five zones as shown in Figure 3There are specific and different design modifications that shouldbe evaluated to reduce oversize in each zone.l st muckpile n lysis

I 3 - Muckpile cross sectionOne of the main sources of oversize is from the top area of thebench. When large blastholes are used for relatively short benchheights a significant amount of the oversize comes from thestemming zone. Often copper operations use 311 mm or largerblasthole diameters for 15 m benches to reduce drillrequirements. These large holes can require stem lengths of over

8 m to adequately confine the explosive energy and reducedilution. This results in poor vertical energy distribution in theupper portion of the bench as shown in Figure 4 In this design53 per cent of the bench has poor explosive energy distribution.To compensate for this poor energy distribution the patterns andthe stemming length are often reduced. This leads to excessivefines production in the loaded portion of the bench. In addition,flyrock and premature loss of explosive energy occur due to thepoor confinement of the short stemming column. Basically, toimprove the breakage in the top region of the blasthole theexplosive energy distribution must be improved whilemaintaining energy confinement.

bench topv I \ poor J ___ ragmentation ) L..v stem length IS m/ -- -.---f- : : benchheightgrade

FIG 4 - Typical energy distribution of large blastholes

The simplest way to improve the vertical energy distribution isto use less stemming. However, if the stemming length is tooshort it may not be able to confine the explosive energy andpremature venting and or flyrock can occur. Table 3 providessome basic stemming length guidelines for explosive densitiesgreater than 1.2 glcc.It should be noted that the proper use of crushed rock forstemming will considerably improve the breakage of the upperportion of the bench. oversize from the top portion of the bench is still producedwith use of these guidelines then the following modificationsshould be evaluated:

reduce the stem length by 0.5 m - expect loss of confinementand flyrock; place small diameter charge in the bottom of the stemmingcolumn; replace 1m of the top of the explosive column and onemetre

of stemming with a two metre air deck; reduce the stem length and use a stemming plug; evaluate the use of a higher velocity/energy explosive;

TABLE 3Suggested stemming engths

Stemmin uidelines( for ex losive densities>1.2 ccHole Minimum of IS m Minimum of IS mdiameter drill bench crushed benchcuttings unloaded rock stem unloaded

stem len th len th171 4 1 27 3.4 23200 4.8 32 4.0 27230 5.5 37 4.6 31270 6.5 43 5.4 36311 7.5 50 6.3 42381 9 1 61 7.6 51

place a high velocity explosive deck in the stemmingcolumn; drill 'stab' holes between the standard pattern; and reduce the blasthole diameter and pattern.These modifications are listed beginning with the leastexpensive to the most expensive to implement. However, themore expensive modifications also perform better due toincreased energy distribution.Another common source of oversize is the zone between theproduction blasts. Often blasts break back beyond acceptablelimits. This back break causes pre-conditioning of the rockmass,which results in the production of oversized material. To reducethe amount of backbreak a path of energy relief away from theback of the blast must be established. The first modification thatshould be considered to improve relief is to simply increase thetiming between the last two rows of blastholes. this is notpractical or does not provide the desired results then the burden

of the last row of holes should be reduced. This will providemore energy to displace the material away from the wall.If the overbreak is still excessive then the charge in the lastrow of holes should be reduced by 20 to 40 per cent whileretaining the reduced burden. This buffer row may need to beairdecked to ensure adequate fragmentation of the upper part ofthe bench. The optimum load and burden will need to be definedby field evaluations.Another option for controlling the overbreak is to reduce thespacing on the last row of holes. This will make the blast tie inmore complex but in some geologic condi tions it is the bestsolution to the problem.Oversize coming from the face is usually caused by overbreakfrom the previous blast or poor energy distribution in the first

row of blastholes. The first step to improve the fragmentation ofan existing face is to determine its profile. Once the face profileis known the pattern can be adjusted to meet existing conditions.For example, if a large toe burden exists then the followingmodifications should be considered: use a higher energy product in the toe region; angle drill the blastholes to match the angle of the face; and reduce the spacing on the first row of holes.

the face has a uniform burden and excessive oversize isgenerated then the burden may need to be reduced. However, theburden dimension should not be less than 20 charge diameters orexcessive energy loss will occur. the burden needs to bereduced below 20 charge diameters then the charge diametershould be reduced. In addition, the spacing should not be morethan 1.5 times the actual face burden.When the floor region produces oversize fragmentation thefollowing field checks and modifications are suggested:

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compare the designed subdrill depth to the actual subdrilldepth; increase the subdrill (up to one half the burden dimension); check the priming procedure; place the primers at grade level; increase the primer size; use high energy toe load reduce the pattern; and reduce the charge diameter and blasthole pattern.Oversize that originates from the body of the blast generallyindicates insufficient explosive energy levels or improper timingconfigurations. This may be because of poor explosiveperformance, incorrect explosive selection, bad design or simplytoo low of an energy factor (kJ per tonne). The recommendationsfor reducing oversize from the body of the blast are:

check explosive quality control; check priming, loading and stemming procedures; modify the initiation configuration; match the explosive to the rock type; reduce the pattern; and reduce the chargediameter and the pattern.When evaluating a blast site for recovery optimisation it isimportant to consider the influence that geology has onfragmentation. In highly bedded and fractured rockmasses theultimate fragment size will be dictated by the rock structure asopposed to the explosive selected. In addition, if an energy levelhas been reached that separates and breaks the joints and beddingplanes little benefit will be gained by increasing the explosiveenergy. Among the geological characteristics that influencefragmentation and should be defined are:

IMPROVING LOW-GRADE ORE RECOVERY

jointing in terms of frequency, persistence, orientation,dilation and fill; bedding in terms of thickness, strength, relative hardness,orientation; in situ water conditions - can dictate explosive selection; rock strength under compressive, tension and shear loading;and rock density - to understand the displacement characteristics.In most cases the influence of adverse geology such as blockyjointing can best be overcome by reducing the charge diameterand blasthole pattern.

BLASTHOLE PATTERNAND CHARGEDIAMETER CONSIDERATIONSOne of the primary ways to reduce fragmentation for most rocktypes is to improve explosive energy distribution. Typically thiscan be accomplished by reducing the charge diameter andreducing the blasthole pattern. In the past blasthole patterns havebeen expanded to reduce drill costs without a completeunderstanding of the adverse effects downstream. Since therecovery of ROM leaching depends of fragment size it isappropriate to reevaluate the charge diameter and patternselection process. Table 4 illustrates the influence of chargediameter on both pattern size, vertical energy distribution andfragmentation produced. For example a 311 mm charge willtypically require 7.5 m of stemming which results in only 50 percent of the bench being loaded with explosives. A 171 mmcharge requires only 4.1 m of stemming and 73 per cent of thebench is vertically loaded with explosives. should be noted thatthe Kuz-Ram fragmentation model does not consider stemminglength when calculating the average fragment size. As a result,the estimated fragmentation advantages of the smaller charge

TABLE 4 he relationship between charge diameter and recovery311 mm 270 mm 230 mm 200 mm 171mm

Estimated nroduction t) 50000000 50000000 50000000 50000000 50000000Charge diameter mm) 311 270 230 200 171Burden m) 10.20 9.30 8.30 7.50 6.50Snacin m) 11.20 10.10 8.90 7.90 7.00Stemming m) 7.5 6.5 5.5 4.8 4.1Vertical ener v ( ) 50 57 63 68 73Ener v factor kilt 716.08 718.94 721.06 717.82 719.56Blast fragment size cm) 29.6 28.6 27.4 26.5 25.3Drill production reo. m) 202000 245682 312399 389484 507185Drill fleet size 4 5 6 8 10Drillin and blastin cost ) 9234980 9569548 10056007 10 555950 11392326Difference ) 334568 821027 1320970 2157346Drilling and blastin cost /t) 0.1847 0.1914 0.2011 0.2111 0.2278Difference /t) 0.0067 0.0164 0.0264 0.0431Tonnes available 100000 100000 100000 100000 100000Ore value perpound 0.75 0.75 0.75 0.75 0.75Ore value /t) 1653 1653 1653 1653 1653Reaction rin thickness cm) 3.5 3.5 3.5 3.5 3.5Max recoverY nossible ( ) 55 57 59 60 62Est leach recoverY ) 40 40 40 40 40Est overall recoverY ( ) 22.2 22.8 23.5 24.1 24.9Increased profit ) 634492 1319106 1778645 2244767

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diameters should be considered to be very conservative for thisexample. Even with the conservative fragmentation estimationthere is an economic advantage provided by the smaller chargediameters.As the patterns are reduced the drill fleet requirementsincrease. a transition is made from a 311 to a 171 mmblasthole the fleet size would have to increase by 2.5 times.However the 311 mm drills are approximately twice as expensive

as 171 mm drills so the actual increase in capital expense is onlyaround 25 per cent. Another advantage to a larger fleet is itsadded flexibility for day-to-day mining operations. Obviously thesize and grade of the orebody and the anticipated marketconditions will dictate whether the rate of return on investmentjustifies the additional drills.PRODUCTIVITY IMPROVEMENT

Another economic factor that should be considered whenevaluating the advantages of smaller fragmentation for ROMleach operations is excavator productivity. Typically, excavatorsare more productive when digging finer material. For example, inTable 5, Option 3 s blast design has nearly twice the energy asthe initial design, so it is reasonable to expect that the resultantmuckpile would be easier to dig. one assumes a conservative productivity increase of five percent the estimated production would increase by 2 500 000tonnes. This increase in production would increase the profit overthe existing design to 9 180000.Once again the validity of this model will depend on theaccurate determination of site specific parameters includingexcavator productivity and actual ore recovery. However, the

model shown in Table 5 is based on industry standard costs fordrilling and blasting and typical grade and recovery values. Itaccurately demonstrates the value of increased fragmentation forROM leaching operations.DEVELOPINGA PLAN OF ACTION

To increase the overall cost-efficiency of blast designs for ROMleaching operations a specific plan of action must be defined andagreed to by representatives from upper management,production, engineering, geology, surveying and ore recoverygroups. The initial step will be to establish a baseline of currentblast performance. With this baseline an accurate recovery/costmodel can be developed to analyse the effect of fragmentation onthe overall profitability of the operation. The keys factors in thisanalysis that need to be accurately defined are: drilling and blasting costs, drill utilisation, average fragmentation size, fragmentation distribution, average dilution, total reserves, ore value, average grade, average recovery ring depth, and anticipated recovery percentage within the recovery ring.Once these factors have been defined and the modelconstructed it will be fairly easy to evaluate the benefit of variousdesign modifications. This evaluation process can serve as a riskanalysis guide for future blast design refinement.

T LESnfluence production on overallprofit

Initial s i ~ n Ootionl tion2 tion3Production (t) 5 5 5 5Estimated productivitv increase ) 0 3 4 5Estimated production (t) 5 5 5 52 525Charge diameter (mm) 270.00 270.00 270.00 270.00Burden (m) 10.00 9.00 8.00 7.00Spacing (m) 11.00 10.00 9.00 8.00Energv factor (kjlt) 614 750 938 1206Powder factor k ~ / t 0.19 0.23 0.29 0.38Average blast fragment size (cm) 32.4 27.6 23.1 18.9Fragment volume (cc) 17 868 11 044 6462 3535Drilling and blasting costs ( ) 8171 524 287 4 2983643 6853768Difference ( ) 2 55 7 48 2 2 8682244Drilling and blasting costs ( /t) 0.163 0.200 0.250 0.321Average grade ) 0.20 0.20 0.20 0.20Ore available (t) 100000 103000 104000 105000Ore value ( /t) 1653 1653 1653 1653Est reaction ring thickness (cm) 3.5 3.5 3.5 3.5Maximum recovery possible ) 52 58 66 75Estimated leach recoyery ) 40 40 40 40Estimated recovery (t) 2 7 24 5 27508 3 5 7Estimated overall recovery ) 21 23 26 30Value of ore recovered ( ) 34233973 39755425 4547 323 52 96836Difference from initial design ( ) - 552 452 23635 7862863Increased profit ( ) - 34 5935 642423 9 8 6 9Recovery value/Cost ratio ( ) - 2 61 2.34 2.06

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ON LUS ONThe optimisation blasting for ROM leaching operationsrequires a shift in focus from the traditional maximiseproduction mindset to an emphasis placed on the percentage ore recovered. This is a cultural change for most operations thathave historically achieved reasonable profit margins bymaintaining high production levels. However the substantialeconomic benefits provided by increased blast fragmentationjustify the change in focus.

The goal any drilling and blasting program for ROMleaching operations besides safety should be to maximisefragmentation while controlling dilution and fines production.This can substantially increase the drilling and blasting costs so

IMPROVING LOW GR DE ORE RECOVERY

the downstream benefits must be accurately quantified.Unfortunately most operations have downsized their engineeringstaffs to the point where there is no time available to accuratelyquantify blast performance. To optimise blast performanceoperations must be prepared to allocate more resources to definethe fragmentation produced by blasting and its influence onoverall profitability. The quantification of blast performance interms of fragmentation cost and ore recovery allows the blastdesigns to be optimised to match the existing site conditions. sa result the overall profit of the operation will increase. Withoutthe proper quantification of blast performance it is highlyunlikely that a mining operation can approach a truly optimisedlevel overall cost efficiency.

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Improving Low-Grade Ore Recovery With the Use of Efficient