Massmin 2004 491

1 INTRODUCTION

Cullinan Diamond Mine (previously called Premier Mine)started mining diamonds in 1903. The kimberlite pipe, thelargest in South Africa is cut by a flat dipping 75 m thickgabbro sill at approximately 400 m below surface, shown infigure 1, together with the position of current mining blocks.Mining above the sill was initially open cast mining, laterlong hole benching (early 60’s) and block caving (late 60’s).Below the sill, resources in the BA5 and BB1E mining blocksare currently exploited by retreat panel caving. BA5 andBB1E presently have a combined production ofapproximately 13,000 tons per day. In BA5, mining startedin 1988; 130 m below the gabbro sill and this mining blockhas a current life of mine until 2005. It is anticipated that theBB1E, where production started in 1996 approximately 230m below the sill, will cease operations in 2009. In 2005, themine plans to start producing kimberlite ore from the BB1EAdvanced Undercut Cave providing interim tons until theCentenary Cut (previously referred to as C-Cut) commencesmining at approximately 900 m below surface and startsproduction in 2009.

Draw Control in the current block caves BA5 and BB1Ehas always been regarded as strategic (Rood & Bartlett,1994, Bartlett & Nesbitt, 2000, Nesbitt & Vorster, 2000). Agreat deal of effort and capital have been spent over theyears on infrastructure, computer programs and other toolsto monitor the drawn volumes from the cave blocks. Thereare several reasons to understand why Draw Control isconsidered important, not only at Cullinan Diamond Minebut also at most caving operations worldwide.

2 VITAL REASONS FOR DRAW CONTROL

Cullinan Diamond Mine hasn’t experienced serious mudrushes or seismicity and therefore these two supplementary

risks dictating Draw Control at many other sites are notdiscussed.

2.1. Avoid premature gabbro dilutionDraw Control is very crucial in avoiding early ingress of

the overlying gabbro waste as this premature dilution wouldreduce the overall ore recovery and shorten the life of cave.Right from the Feasibility Study stage for BA5 and BB1Eonwards, fragmentation of the kimberlite was predicted tobe coarse and that of the overlying gabbro sill to be fine(Rood and Bartlett, 1994).

At Cullinan Diamond Mine, it is anticipated that a recovery of85 percent of the in situ ore can be achieved if proper DrawControl is exercised. Poor draw practice results in a much lowerore recovery rate as drawpoints will be forced to close earlierthan anticipated for two possible reasons. Firstly, cut-offs duethe influx of gabbro into the drawpoints adjacent to ‘overdrawn’drawpoints occurs much earlier than planned. Secondly,inconsistent draw practice stimulates migration of material overconsiderable vertical and horizontal distances, inducing thepremature mixing of waste with ore, especially as gabbrofragments are fine and would thus move through the columnquickly, (Bartlett, 1998). To compound matters, it was found thatthe kimberlite fines percentage (a function of kimberliteaccelerated weathering) was underestimated at the time ofinitial block cave feasibilities in the mid 80’s (BA5) and early90’s (BB1E).

2.2. Minimise gabbro into plant headfeedThe gabbro not only sterilises the drawn ore but also

causes problems at the Dense Media Separator in thediamond recovery plant due to its high specific density.

2.3. Reduce risk of ore recompactionLack of good Draw Control results in static columns of

cave rock, resulting in ore re-compaction, generating point

Santiago Chile, 22-25 August 2004

AbstractCullinan Diamond Mine (previously known as Premier Mine) currently employs two mechanized block caves and plansanother extraction level at approximately 900 m below surface. As with all major block cave operations, challengingsituations and difficult events occurred during the implementation phase, unforeseen throughout the project feasibilitystudy. The panel caves in the kimberlite pipe have experienced problems of various types that caused deviations from theoriginal planned mining sequences. In combination with (the traditional) production pressures, numerous problemsresulted in not achieving good Draw Control practice. A drastic change to the weekly Draw Control planning wasintroduced with the buy-in from production personnel and mine management. In conjunction with the improved DrawControl practice, an innovative but simple waste determination process has been developed and implemented. Both theDraw Control and the Waste Management at Cullinan Diamond Mine are currently based on ‘back to basics’ principles,straightforward and not controlled (yet) by impressive computer programs.This paper describes some of the geotechnicaland practical related difficulties that were encountered during the implementation phase and how those were tackled withvarying degrees of success. The importance and impact of Draw Control and Waste Management on the overall mineperformance is illustrated.

Status of draw control practice and waste Management

at Cullinan diamond mineGert van Hout, De Beers Consolidated Mines, Technical Support Services, Operations GeotechnicalStephen Allen, Mark Breed, John Singleton, De Beers Consolidated Mines, Cullinan Diamond Mine

492 Massmin 2004

loads on the extraction level that damage the productioninfrastructure. In kimberlite, if the draw of ore occurs morethan three months after the undercut has taken place, thematerial in the drawbell and above the major apex maycompact. This ore re-compaction creates uneven loadingconditions on the extraction level or excessive localisedstresses that adversely affect tunnels. This becomesapparent as support integrity worsens or when tunnelscollapse. Experience in the BA5 and BB1E caves showslocalised re-compaction of kimberlite becoming a majorissue when the drawpoint was closed for rehabilitation formore than six weeks. Re-opening of compacted drawpointsrequires a high level of secondary blasting, furtherdamaging the brow area and in some cases it has taken aslong as eight weeks to re-open a drawpoint.

2.4. Maximum Draw Zone InteractionIn both the BA5 and BB1E, the offset herringbone

drawpoint layout (figure 2) was used with the drawpointspacing across the major apex ranging between 24.2m to24.7m, possibly creating interaction problems across themajor apex in some areas as the Isolated Draw Zone (IDZ)varies from 9m to 11m, depending on the kimberlite rocktype.

Figure 2 shows the zones of draw at the three differentdraw interaction modes according to Laubscher (2000). Ifdrawpoints draw in isolation, (the horizontal section of) thezone of material affected by this draw can be approximatedby a circle with a diameter equal to the IDZ. If there is evendraw between the two drawpoints within the same drawbell,the affected area has an elliptical footprint, one and a halftimes larger than the IDZ. When there is interaction betweenadjacent drawbells, the zone of influence enlarges anotherone and half times.

2.5. Optimal ore fragmentationUneven draw or drawing at too rapid a rate may lead to

very coarse fragmentation, poor grade control and severewaste dilution. As mentioned before, coarse orefragmentation and fine waste fragments induce rapidgabbro waste movement from the top, through the column,to the drawpoints, thereby sterilising the drawpointprematurely and creating problems at the recovery plant.

It has often been observed that drawpoints with coarsefragmentation were subjected to draw, far above the callallowed by the maturity rules. If material is drawn tooquickly, there is not enough ‘residence time’ for thekimberlite material: there is a lack of mechanical interactionbetween the ore fragments and insufficient communition ofprimary fragments as material gravitates down the cavecolumn.

Figure 2: Interaction modes (a: isolated, b: interaction withindrawbell and c: interaction across minor apex)

Large blocks cause high hang-up frequencies in thedrawpoints, create problems in the ore handling systemand have a negative effect on the productivity as well ason the operating costs. Removal of drawpoint hang-upsmay result in long down-time and are costly because ofthe secondary breaking requirements. Oversized oreblocks in the drawpoints must be reduced to reasonablesizes that can be handled by the load-haul-dump (LHD)machines.

Back analysis of hang-up data during the period betweenJuly 1998 and May 2000 (Rahal and Smith, 2000) revealedthat in any given shift, 34 percent of the available

Santiago Chile, 22-25 August 2004

Figure 1: Diagrammatic plan and section of the kimberlitepipe showing geology and mining blocks.

Massmin 2004 493

drawpoints are hung up and that the vast majority of thesehang-ups were cleared within one day.

3 THE HISTORY OF DRAW CONTROL SYSTEMS EMPLOYED AT CULLINAN DIAMOND MINE

To impose Draw Control on the current mining blocks,various systems and software packages were implemented.Some systems had more success than others.

A comprehensive Draw Control system should at leastconsist of an integrated system of three major components:an accurate and dynamically updated ore resourcedatabase, a reliable vehicle monitoring system and aplanning system.

3.1. Ore Resource databaseThe very first version of PC-BC, developed for Cullinan

Diamond Mine in 1988, was cumbersome to use: it took along time (2 to 3 hours) to deplete all drawpoint loads on adaily basis and it did not have the fine graphics displayed bythe present version. After some time, mine personnel movedtowards spreadsheet type applications to store dailyproduction data from the drawpoints. Later, a MicrosoftAccess database was employed to store the drawn volumesin combination with the status of each drawpoint. A userinterface was then developed to present this data in agraphical format and to allow management to extractcomprehensive summary reports. This application calledBLOCINFO, also permitted the user also to reconcile thedrawpoint production figures with the tons recorded by thetreatment plant.

In 1999, MinRAS an SQL based product that alsocontained the mixing algorithms, enabling the MineralResource Manager to derive a more accurate and auditableore reserve statement (Guest et al, 2000).

3.2. Vehicle Monitoring SystemReconciling tons, calculated from the loads that are

recorded by the vehicle monitoring system (VMS) with thetons from the weightometers at the plant is essential in anygood planning or effective Draw Control program to obtain acorrect and representative mineral resource database.

Various VMS options have been trialled at Premierincluding a beacon system using micro-wave technology(Nesbitt & Vorster, 2000) followed by a gyroscopic basedmonitoring system. None of the systems were a hundredpercent satisfactory due to technical problems, as well asresistance from production personnel who saw it as amanagement policing tool.

A combination of the radio-based voice communication(utilising the leaky feeder to establish contact betweencontrol room at surface and underground) and a manualrecording based information system, currently in use, yieldsthe best results. However, it requires production crews tobuy into Draw Control.

As Cullinan Diamond Mine has different size LHD units,there is an issue with the average bucket factor applied toderive ‘tons mined’ from ‘buckets loaded’ at each drawpointand until recently, the total tons hoisted were consistentlylarger than the value based on the recorded buckets.

3.3. Planning SystemUp until 1998, Production planning at Cullinan Diamond

Mine was founded on empirical geotechnical guidelines(Bartlett and Nesbitt, 2000) and did not take into account thefull effect of resource and equipment availabilities. Theempirical guidelines were derived from extensive block caveexperience at Cullinan Diamond Mine and have beendescribed by Bartlett, 1998.

A more pro-active approach was initiated in 1998 whenthe weekly planning also incorporated mining constraints

such as LHD availability, ore pass capacity, haulage andhoisting capability. The next draw control related conceptestablished was that of the ‘ideal depletion surface’. Apredetermined ideal depletion sequence up until the life ofdraw determines the short-term (week) draw schedule inthat the plan attempts to come as near to the ideal depletionstate as possible. At any stage, mining is in function of theideal depletion profile and the call per drawpoint isinfluenced by its draw history (corrective call when therewas poor draw in the past).

Planning on a monthly and weekly basis was also carriedout using spreadsheets. These files produced satisfactoryoutput as it catered for the input of all parties involved inDraw Control. It was rather cumbersome to use but hasserved its purpose to stimulate interaction betweengeotechnical, mining and mineral resource managementdepartments. Regular meetings were held between thesedepartments to agree upon the monthly production planproduced by these excel files but adherence to this plancould be improved.

4 DISCUSSION OF CURRENT DRAW CONTROL PRACTICE

4.1. The Integrated Draw Control SystemIn 1999, the ‘Integrated Draw Control System’ (IDCS) with

a Mixed Integer Linear Programming (MILP) componentdescribed by Guest et al , 2000 was introduced on mine.

The long and medium term schedule program based onthe MILP was originally developed at Koffiefontein Mine forits Front Cave (Hannweg and van Hout, 2001), and iscurrently being used in the BB1E Advanced Undercut atCullinan Diamond Mine. This scheduling module is the firstplanning optimisation tool in block cave operations that isable to optimise over the life of mine as well as over multi-time periods. It incorporates all geotechnical, mining andfinancial constraints, in a unique way.

Long term production planning for the older BA5 andBB1E blocks is still done by the use of spreadsheets anddoes not incorporate all ore flow constraints or geotechnicalrules, except for the draw rate limits. The reason for theimplementation of the excel files instead of MILP isthreefold. Firstly, those panel caves are considered toodepleted to optimise according to the principles within theMILP. Secondly, the main focus of those caves currently isavoiding tunnel collapses occurring from vertical loadingand keeping porosity in the areas that hasn’t experienceddestructive stress levels. And lastly, the MILP versionallowing remote access only became available late 2003.

The current Draw Control system at Cullinan does notcater for planning based on maximising NPV as the gradesin the ore columns are set to an average column value andthe mixing algorithms do not cater for vertical mixing withinan ore column. The choice of an average column grade isjustified, as there is generally very little resolution in theassumed grade profile vertically across the massiveorebody.

An optimal (and in South Africa legally prescribed) plan forall mining operations should be based on maximum orerecovery, thus maximising tons instead of maximising NPV,the last being a method relying rather on grade and revenueper carat. Block cave mining is a massive mining operationwhere principles of selective mine planning, based onfinancial parameters, cannot determine the production plan.These principles may constrain the schedule but an optimalplan is primarily based on geotechnical considerations.

The mixing algorithms mentioned in section 3.1 weredeveloped on site to simulate the ore movements within thecave and the parameters were calibrated successfully: thepredicted time of drawpoint closure in the BA5 cave waswithin one month from the actual date of closure. These

Santiago Chile, 22-25 August 2004

494 Massmin 2004

mixing algorithms are still being used but it is expected thatREBOP,(Pierce et al, 2004), will be used as the standardtool to update the ore resource database. This tool shouldthen also provide an accurate production waste ingress andgrade profile (or carat production graph).

4.2. The back to basics approachTowards the end of 2002, a major drive from

management, the ‘back to basics’ principle occurred, notonly in terms of ‘keeping it simple’ but of increasedadherence to the basic Draw Control rules outlined in theCullinan Diamond Mine Code of Practice, (Bartlett, 2003)and ameliorating interaction between Draw Control andProduction Departments. Some of the simple but criticalprocedures for a successful Draw Control Practice arediscussed in this section. With issues of interaction beinginherited from design (see section 2), the main aim of thecurrent BA5 and BB1E Draw Control system is to drawequally throughout the caves with all drawpoints inproduction at one time and to minimise dilution from thegabbro sill. Future optimising codes such as the MILP areseen to be not applicable simply due to the maturity statusof the BA5 and the BB1E and past Draw Control practices.

The key to the whole short-term Draw Control process(figure 3) is the accumulation, storage, processing andpresentation of data. The key relationship is between DrawControl and Production. The culmination of the wholeprocess is presented at the weekly meetings that are heldwhere all parties "strategise" key loading and tunnel ordrawpoint rehabilitation patterns around Draw Control.Production and short-term planning understand that DrawControl needs alignment to the official annual productionplan, therefore by applying correct Draw Control principleslong-term cave management and production targets can beachieved.

Figure 3: Process flow chart on Draw Control at CullinanDiamond Mine.

Draw Control Observers gather the occurrence and typeof drawpoint hang-ups and record it into the Draw Control

system daily (Bartlett & Nesbitt, 2000). This information, incombination with daily production data, enables the DrawControl engineer to analyse the effect of the draw rates anddraw history on the frequency and type of hang-up as wellas waste entry parameters.

Extraction rate limits at Cullinan Diamond Mine havehence been determined in terms of tonnage per day using amaturity classification, based on the accumulativeproduction or life of draw from a drawpoint. Four classeswere established and the associated draw rates increasedfrom a maximum of 50 tons per day for a new drawpoint toa maximum of 200 tons per day for a mature drawpoint.

As can be seen in figure 4, since the end of 2002, adherenceto Draw Control has improved significantly (the averagedeviation in 2000 was approximately 73%). The graph displaysthe deviation (actual production - planned), averaged over allBB1E drawpoints with the weighting factor being the plannedtons. A value around 10% is considered to be very good. AProduction Factor (van Hout & Guest, 2000), based on thisdata has not been implemented at the mine as it is felt thataverage weighted deviation is adequate enough tocommunicate how well Draw Control is adhered to.

Figure 4: Weighted Average Deviation (datapoints andtrendline) from the weekly Draw Control plan for BB1E cave.

Cullinan Diamond Mine personnel are confident that thepresent recording, storage and presentation of actual minedtonnages in the MinRAS is satisfactory. Initially, the actualproduction per drawpoint was entered into the system on aweekly basis. This data is now imported on a shift to shiftbasis, in combination with other information associated withthe drawpoint status (produced volume, hang-up type,waste content, remedial support status, etc.).

Presentation of the draw data is usually in graphicalformat, accessible for all people involved in Draw Control toget a clear idea of the mined tonnage profile over a userdefined period as well as of the actual drawpoint status.Figure 5 shows an example of the weekly Draw Control planthat has been derived on a Friday afternoon, afterconsultation between Draw Control and Production. Copiesof this sheet are given to the Draw Control Officers (whoenter it into MinRAS) and Production Mine Overseers (whodistribute it to the Shift Bosses). The Mine Overseers alsowrite this information onto ‘Draw Control loading’whiteboards and compare the planned tons with the actualproduction data on a shift to shift basis.

Listed below are some of the more important DrawControl production principles developed with the "back tobasics approach" that are vigorously implemented with theaim of achieve correct block cave management:

Santiago Chile, 22-25 August 2004

Massmin 2004 495

• Drawpoints closest to the orebody perimeter (highlydepleted or not), are continually loaded, at a reduced rateif necessary. This allows for porosity in the caves andprevents the movement of groundwater from the contactareas to the centre of the ore body.

• A strict minimum (120 tons) and maximum (1,200 tons)weekly call per drawpoint is implemented with a maximumdaily call of 300 tons. This prevents the loading of allplanned production from a drawpoint in a single shift, withno loading during the remainder of the week.

• A target for the weighted average deviation (figure 4) hascurrently been fixed at ten percent with acceptance fromboth production crews and senior management.

• It is strived to achieve equal draw across the major apexand continuous production per drawpoint throughout theweek. This ensures achieving a maximum zone ofinfluence (as in figure 2c).

• Frequent interactions between Draw Control andproduction to communicate clearly the availability, wastecontent and status of drawpoints to anticipate correctloading calls.

• Reducing the closure/maintenance time from six to threeweeks where possible, to avoid re-compaction.

Figure 5: Weekly Draw Plan for the BB1E block cave.

The implementation of above principles shoulddramatically improve fragmentation across the caves,creating further reductions in secondary blasting and thepossible achievement of monthly "production" targets atacceptable waste percentage.

A secondary function of Draw Control was developed inFeb 2002 and consists of a qualitative assessment of thephysical state of drawpoints. The system involved a monthlyrating of each drawpoint on the basis of condition, stressdamage, water and LHD damage. The ratings aretransferred onto mine plans for future analysis.Fragmentation data in line with Laubscher’s, (2000), RockMass Rating classification were added to the datacollection. The data is currently used in back analysis for thefragmentation analysis programs in order to model futureblock caves within the same ore body.

Another Draw Control function is to maintain waste levelsat twelve percent or below. Past sampling practices did notrecord levels of gabbro in each drawpoint. A wastemanagement system developed by the Mineral ResourceManagement department assists in the prediction of wastetons and is discussed below.

5 WASTE CALCULATION ON SURFACE

5.1. Current practiceFor the last five years the official measurement of global

waste percentage has been determined by taking a sampleof approximately 50 kilograms with a plough sampler pershift on the Sortex tailings stream. The size fraction on thisbelt is -65mm, +32mm. The sample is washed and hand-sorted into three different piles: internal waste, externalwaste and kimberlite. The piles are then weighed and theirrelative percentages calculated. Different tests have beencarried out to ascertain that this process of wastedetermination is appropriate as the following underlyingassumptions could be questioned:• The waste percentage in the -65mm to +32mm range is

representative for the total size distribution of theheadfeed.

• One sample of 50kg material per shift is an adequaterepresentation of the entire volume fed into the plantduring that shift.

• The waste percentage does not depend on the personwho performs the test.

The first test involved the waste analysis in the +4mm sizedistribution classes. It is impossible to quickly andaccurately recognise rock types in fragments smaller than4mm by manual visual methods. Results for this analysiswere very similar to those of the -65mm to +32mm range. Itcan therefore be concluded that waste is evenly distributedacross the different size fractions and the current fragmentsize range is adequate.

During the second test, samples were taken every 15minutes from the -65mm +32mm stream. The results fromthis test did not indicate that the current practice of onesample per shift needed to be adjusted.

The last test consisted of an identical series of samplesgiven to four different laboratory assistants. As can be seenin figure 6, results may vary depending on the lab assistantbut would not justify the extra cost of additional personnel.

Figure 6: Analytical bias due to different lab assistants

5.2. Research and future technologiesResearch was undertaken to identify technology that

could recognise waste accurately in - and possibly removeit from - the ore flow within a short time span. Providers oftechnology based on Microwave Attenuation, Infra red,Laser Induced Fluorescence, Natural Gamma Emissionwere approached and three different optical sortersunderwent testing and extensive assessments.

Santiago Chile, 22-25 August 2004

496 Massmin 2004

All applications were successful in differentiating betweenwaste and kimberlite to some degree on surface (conveyorbelts) but none were suitable for underground application.Optical sorter technology, widely used in the food and glassindustries, proved to be the most effective method inrecognising and ejecting waste from an ore stream. Theability to eject waste from an ore stream offers obvious,additional advantages in ore processing, allowing improvedflexibility, an increased ore extraction ratio by recoveringmore diamonds from previously considered non payabledrawpoints, lower crushing costs and ultimately improvedrevenues.

6 WASTE CALCULATION UNDERGROUND

To manage waste effectively, an accurate means ofmeasuring the waste percentage in each drawpoint must beestablished but the following factors complicate thisprocess:• Dust, generated by LHD’s, makes visual observations

extremely difficult.• Washing the ore in the drawpoint with water to get rid of

the dust settled on the muckpile can result in rapiddisintegration of the ore, thereby biasing the sample takento determine the waste content.

• There are different types of waste and differentpercentages of waste within different size fractions of ore,making the derivation of an average waste value ratherdifficult.

• The finer the fragment size the more difficult it is todifferentiate between the different waste and kimberlitetypes. The ore fragment sizes depend largely on the rocktype and the maturity of the cave.

At Cullinan Diamond Mine waste is classified as eitherinternal or external waste. Internal waste is that whichslumped back into the pipe during volcanic emplacement ofthe kimberlite pipe and consists mainly of felsite, Waterbergquartzite, norite and metasediments. The internal wastealso includes barren late stage carbonatite dykes. In themetallurgical process these "floats" are separated from theore stream via a process of dense media separation, asthese rock types have a lower specific gravity.

External waste consists of the country rock norite and thegabbro sill. These two rock types are mineralogically similarand can differ only slightly in texture. The norite enters thecave through the boundary drawpoints when country rockblocks detach, slump down, and cuts off or sterilizes parts ofthe resource It also enters the ore flow through the tippingof waste development into ore passes. External wastefragments are known in the metallurgical process as "sinks".Their specific gravity is similar to that of diamond bearingkimberlite, and it therefore reports to the concentrate of thedense media separation.

Before 2002, the waste content was measured by visuallyestimating the waste in each drawpoint on a daily basis. Lossof historical waste data combined with the inaccuracy of visualestimates made it impossible to compare waste estimates fromunderground with the surface measurement of waste.

The test work described in section 5 showed that thesampling methodology used on surface yields adequatewaste percentage values. It was therefore decided tochange the underground waste determination process fromthe visual estimation to one similar as applied on surface.This involves samples taken from a drawpoint, transportedto a lab analysed and results are entered into a database.

7 WASTE MANAGEMENT UNDERGROUND AND BENIFTS THEREOFAs mentioned above, the waste percentage of the

headfeed needs to be kept below a critical level, above

which the plant recovery would be less optimal. Waste atCullinan Diamond Mine has become increasing challengingover the last few years, as the current block caves becomeolder and the reserves in the block are depleting fast.Keeping the average waste content below a threshold hashistorically been addressed by stopping undergrounddrawpoints with waste content higher than 15% but this hassterilised large portions of the kimberlite resource. Wasteproblems can be controlled to some degree by blending, orefrom various sources underground and on surface canassist to draw higher waste drawpoints longer, therebymaximising extraction.

Prediction and control of waste tons is a task performedby Draw Control. Multiplying drawn tons per drawpoint witha waste percentage and adding this for all drawpointsacross the two caves represents a value that indicates theexpected waste tons. Initially (2002) there was an extremelyclose match between the predicted waste tons and theactual recorded waste tons. But of late, differences of 4% -5% have been observed, with the predicted values basedon the underground results always exceeding the onsurface determined results.

Benefits of the current waste management system arelisted below:• The greatest benefit from a mineral resource perspective

is that more accurate forecasts and estimates can bemade. Financial contribution of drawpoints can beestablished and assist in the decision making process,together with geotechnical factors, whether or notdrawpoints or tunnels need to be closed.

• When production planning is done, the expected wastetons can be calculated for each draw scenario. On thebasis thereof, optimal draw and waste percentage can bederived. The estimated waste percentage is of great valueto the metallurgical department as unexpected andexcessive high density waste negatively affects recoveryefficiencies.

• A third benefit lies in the improved understanding of themigration of gabbro sill material as the cave depletes. Thedrawpoint waste data recorded since 2002 is still tooscarce but correlation between the column depletionstatus and waste percentage will be analysed todetermine waste ingress curves that can be used in futureore depletion planning.

8 SUMMARY AND CONCLUSIONS

Cullinan Diamond Mine has experienced Draw Controlchallenges, resulting in early waste ingress and seriousloading onto production tunnels. After a drive from seniormanagement for ‘back to basics’, Draw Control adherenceand ground conditions have improved drastically. SeveralDraw Control procedures are outlined in this paper.

Waste is and always will be a mining and treatmentconstraint requiring constant management to ensureoptimum extraction of ore.

The introduction of a system that recognises and caneject waste from the ore flow will reduce the constraint ofwaste on Draw Control and treatment efficiencies. CullinanDiamond Mine and the greater De Beers Group arevigorously pursuing the implementation of optical sortingtechnology, having completed extensive testing. A fullfeasibility study of the project is being undertaken.

ACKNOWLEDGEMENTS

The authors are grateful to all their colleagues who helpedand supported them during the development andimplementation of this work, in particular AR Guest, MPreece, C Baltus, HP Grobler and PJ Bartlett. The authorsacknowledge the permission of the Director Operations and

Santiago Chile, 22-25 August 2004

Massmin 2004 497

the Cullinan Diamond Mine, General Manager to publishthis technical paper.

REFERENCES

• Bartlett, P.J. 1998. Planning a mechanised cave withcoarse fragmentation in kimberlite. PhD. Thesis.University of Pretoria, South Africa.

• Bartlett, P.J. & Nesbitt, K. 2000. Draw Control at PremierMine. Proc. MassMin200, Brisbane. Vol 1: pp, 485-493.

• Bartlett, P.J. 2003. Block Cave Code of Practice forCullinan Diamond Mine.

• Guest, A.R., van Hout, G.J., von Johannedis, A &Scheepers, L.F. 2000. An application of linearprogramming for block cave Draw Control. Proc.MassMin2000, Brisbane. Vol 1: pp, 461-468.

• Hannweg, L.A. & van Hout, G.J 2001. Draw Control atKoffiefontein Mine. Proc. VIth International Symposium onMine Mechanisation and Automation, SAIMM, 2000, Vol1:pp, 93-96.

• Laubscher, D.H.L 2000. Block Cave Manual.

• Nesbitt, K & Vorster, J.A. 2000. Premier mine DrawControl and underground vehicle monitoring and controlsystem. Proc. VIth International Symposium on MineMechanisation and Automation, SAIMM, 2000, Vol 1:pp,93-96.

• Pierce, M., van Hout, G.J. & Singleton J 2004. DrawControl of the BA5 cave Cullinan Diamond Mine: BackAnalysis with REBOP. Proc. MassMin2004, Santiago.

• Rahal, D.C. & Smith, M.L. 2000. De Beers Site Visit,unpublished internal report. Corporate Head Quarters, DeBeers Consolidated Mines.

• Rood, H.R. & Bartlett, P.J. 1994. Mechanized Caving atPremier Mine. Proc. XVth CMMI Congress,Johannesburg, SAIMM, 1994, Vol 1: pp, 219-225.

• van Hout, G.J. & Guest A.R. 2000. Production Factor andDraw Control Factor, presentation to the InternationalCaving Study.

• Malope, P. 2001, Waste distribution in different sizefractions of the kimberlite ore at Premier Mine,unpublished internal report, Premier Mine, De BeersConsolidated Mines.

Santiago Chile, 22-25 August 2004