inthekimberley division of debeersconsolidated mines limited · extremely complex. at any level...

Mining practice in the Kimberley Division ofDe Beers Consolidated Mines Limited

by J. V. CLEASBY*. B.Se.. A.R.S.M. (Fellow).H. J. WRIGHT*. B.Se.. M.Se.. (Fellow). andM. T. G. DAVIES*. B.Se. (Visitor)

SYNOPSIS

T his paper highlights the changes that are taking place at De Beers Consolidated Mines Limited in mining methods,mechanization, and employment practices. De Beers has four underground mines in Kimberley itself (Dutoitspan,Bultfontein, De Beers, and Wesselton), and two open-cast mines outside Kimberley (Finsch and Koffiefontein).Emphasis is placed on the new method envisaged for Koffiefontein when it becomes an underground mine. Thepaper also includes notes on chemical drilling and on winding practices.

SAMEVATTING

Hierdie referaat laat die klem val op die veranderinge wat by De Beers Consolidated Mines Beperk aan die gangis wat betref mynboumetodes, meganisering en indiensnemingspraktyke. De Beers het vier ondergrondse myne inKimberley self (Dutoitspan, Bultfontein, De Beers en Wesselton) en twee oopgroefmyne buite Kimberley (Finschen Koffiefontein). Die nuwe metode wat vir Koffiefontein beoog word wanneer dit 'n ondergrondse myn word,word veral benadruk. Die referaat sluit ook aantekeninge oor chemiese boorwerk en oor wenasgebruike in.

INTRODUCTION

The Kimberley Division of DeBeers Consolidated Mines Limitedis composed of four undergroundmines in Kimberley itself (Dutoits-pan, Bultfontein, De Beers, andWesselton) and two open-cast minesoutside Kimberley (Finsch andKoffiefontein). Fig. 1 is a map ofthe Kimberley district showing thelocation of these min'3s. Finsch is150 km west of Kimberley andKoffiefontein is 80 km south ofKimberley. Kimberley also con-

*De Beers Consolidated Mines Limited.

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tains the head office of the DeBeers Company, and the diamond-sorting and trading companies forgoods produced in Southern Africa,which are newly housed in a buildingspecially designed for the purpose.

Diamonds were first discoveredin the Kimberley area at Hopetownin 1866 on the banks of the OrangeRiver. This and later finds triggeredthe start of the great 'diamondrush'. In 1870 the Jagersfontein(now closed) and Dutoitspan pipeswere discovered, followed by thoseat Bultfontein, De Beers, and Kim-berley (now closed) in 1871, Koffie-fontein in 1880, and Wesselton in

1891. Finsch Mine was a morerecent discovery by A. T. Finchamin 1961.

The 'Big Hole' remains as amonument to the Kimberley Mine,which was closed in 1913, and todayis a great South Mrican touristattraction, second only to the KrugerNational Park. De Beers have builta museum at the edge of the 'BigHole', which preserves buildings,mining equipment, shops, and goodsfrom the early Kimberley days.

Finsch and Koffiefontein Minesare both open-pit bench mines andare fully self-contained, with theirown treatment plants, housing, ser-

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Limited in the Kimberley area

JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY DECEMBER 1975 247

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vices, etc. The four mines in Kim-berley feed ore by conveyor to acentral treatment plant and enjoyjoint services. These mines utilizethe block-caving method of mining,which has almost entirely replacedthe previous method of chambering.The combined tonnage of ore pro-duced by the Kimberley Mines is15000 t per day, Koffiefontein12 000 t per day, and Finsch 13 000 tper day.

GEOLOGY

The Kimberley pipes are approxi-mately circular or oval in shape,and are deeply eroded volcanicnecks, which, at the present landsurface, have average diametersranging from approximately 230 to500 m. The upper parts of all thepipes decrease in area with increas-ing depth, the average dip of thecontacts being approximately 80°.At depths of more than 500 m, thisregular decrease in area is notalways maintained, and the pipesassume highly irregular forms. Thecontact between the pipe and thewall-rock varies in inclination rapidlyover short vertical intervals, and amarked effect of the kimberliteintrusion by structures in the wall-rock is evident. This irregularityat depth is most pronounced at the

248 DECEMBER 1975

Wesselton, De Beers, and Dutoits-pan pipes (Fig. 2).

From surface to approximately100 m, the wallrocks around theKimberley group of pipes consist ofblack and grey shalcs of the KarooSystem, containing numerous andgenerally concordant dolcrite sills.The shales overlie a variable thick-ness (300 to 1000 m) of Ventersdorplavas with intervening quartzitehorizons. The Ventersdorp rock restsuncomfortably on Basementgranite-gneiss. The VentersdorpSystem is not present at Koffie-fontein, where Karoo shales, withintervening dolerite sills, rest directlyon granite-gneiss at a depth ofapproximately 250 m. The wall-rocks at Finsch consist of 130 mof banded ironstone separated fromthe underlying dolomite, limestone,dolomitic shale, and chert of theDolomite Stage by a sequence ofpassage beds approximately 25 mthick. The passage beds consist ofcolourful, rhythmic alternations ofthin dolomitic, siliceous, and iron-rich layers.

Several stages of intrusion haveresulted in the presence of separatecolumns of kimberlite and kimber-lite breccias within the four Kim-berley pipes. Internal contacts be-tween these separate phases are

generally sharp, indicating thatearlier intrusions were completelyconsolidated prior to the intrusionof later material. At Finsch andKoffiefontein Mines only one majorphase of intrusion is apparent at thepresent levels of exposure, but, asin the Kimberley pipes, includedfragments of earlier kimberlite indi-cate a more complex intrusivehistory.

Most varieties of kimberlite arecharacteristically hygroscopic,swelling and crumbling when wetowing to the absorption of water byclay minerals in the rocks. Thischaracteristic makes wet drilling ofkimberlite extremely difficult, andadditional complications arise fromthe generally incompetent, low-strength characteristics of kimber-lite, compounded by the abundanceof structural discontinuities (shearplanes and fractures). These featuresmake kimberlite difficult to supportbut are an advantage during block-cave mining operations since theyfacilitate collapse and break-up ofground within the caves.

The occurrence of diamonds inthese pipes and separate intrusionswithin individual pipes ranges fromapproximately I part in 8 millionto less than I part in 100 million.The distribution of diamonds is

JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY

extremely complex. At any levelin the pipes, the grade of separateintrusions may be similar or mayvary by a factor of five or more.Similarly, pronounced changes inhorizontal grade may occur withina single intrusive phase. Verticalvariations of grades within indi-vidual intrusions may be relativelylimited, may change in more orless linear fashion, or may vary

irregularly over successive depthzones. In general, however, boththe grade and the average size ofdiamonds decrease with depth.

CHEMICAL DRILLING

axial hole of the drill steel effectivelyallays dust, water alone cannot beused during the drilling of kimber-lite because it coagulates the dustparticles into a thick clay thatcauses the drill steel to stick in thehole. In addition, the roof, side-walls, and footwall are weakened bywater and therefore become difficultto keep safe. Fortunately, however,there is no free silica in kimberlite,

The problem of dust during drill-ing operations has long been oneof the biggest single mining hazards.Unlike other mining operations,where water flushing through the

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and thus the dust hazard is muchsmaller than in some mines. Mostof the drilling in kimberlite hashitherto been dry, but mining regu-lations introduced in 1965 calledfor a dust count of less than 500particles per millilitre. Attemptswere made as far back as 1949 tosuppress the dust, and various typesof dust-extraction filters, mobiledust cars, and chamber dust carswere used with a fair measure ofsuccess. However, it was eventuallyfound that greater efficiency couldbe obtained from the use of achemical dispersant introduced intoa small amount of flushing water.

During the development phase,experiments on various chemicalswere conducted, but it was eventu-ally found that a dispersant calledDispex N40 was the most effectiveand economical. It was also possibleto drill both soft and hard kimberlitewith Dispex, and the overall pene-tration rates were faster as a result.The number of dust particles permillilitre at the drilling face withthe chemical method is 85, comparedwith 244 for dry drilling with dust-extraction units, and 500 as thepermissible standard. The cost isapproximately RO,Ol per metre.

A valve having the followingcharacteristics is necessary to con-trol the mix of water and Dispexto the machine:(a) an adjustable flowrate but with

a set drilling position,(b) a set drilling position that

cannot be easily or inad-vertently altered by the machinecrew,

(c) a closed position to preventwaste of solution during de-lays, and

(d) a flushing action that altersthe set flowrate only whileflushing is required.

It was found that Newman Hen-der control valves modified to injectsufficient chemical solution to givethe desired consistency of sludge ataverage penetration rates (Fig. 3)were the most suitable.

The drilling fluid is mixed in andreticulated from a mixing tank thatis calibrated and set to give a0,5 per cent concentration of Dispex.The 'chemical' rock drill has alonger hard-chromed water tube,which requires a recess and a seal

250 DECEMBER 1975

in the shank of the drill steel toallow the water tube to penetrateinto the steel for approximately58 mm (Fig. 3). The head of thedrill steel has two holes drilledadjacent to the T.O. insert thatintersect the axial hole to ensureproper wetting and reduce blockages.

Encouraging results have beenachieved with standard non-ventedrock drills. Special permission wasobtained from the Mines Depart-ment for an experiment, the ad-vantages being(1) less leakage due to increased

pressure on the seal,(2) no air blowing onto the face

from the front-head releaseports, thus reducing dust forma-tion, and

(3) no 'fogging' in the event of afaulty seal or water tube.

Because Dispex N40 is adispersant, any dirt in the pipesand mixing tanks is loosened,causing blocked water tubes andthus rock-drill breakdowns. How-ever, this is avoided by ensuringthat the inline filters on the pipecolumn are kept in good conditionand are cleaned regularly. DispexN40 also affects the machine lubri-cant, which has necessitated theaddition of an additive to reduceits detergent action.

WINDING PRACTICE

The shafts, for the sake of con-venience, can be divided into thecategories of main shaft for thehoisting of rock, men, and materials,and service shafts for the hoistingof men and materials. Each mainshaft is equipped with a rockwinder and a man and materialswinder, and each service shaft witha man and materials winder.

The rock winders are conventionaldrum winders with Ward Leonardcontrols designed for depths upto 1200 m and a speed of 17 m/soThey are on automatic operation,i.e., the skips are automaticallyloaded from weight-batched flasks.Winding-engine drivers are usedonly for start-up, shut-down, andre-set operations, apart from rope,winder, and shaft inspections. Forthese purposes they are drawnfrom a drivers' pool at the Bult-fontein Mine or from the WesseltonMine man and materials winder.

Jeto bottom-dump skips are usedat De Beers and Bultfontein Mines,and Sala bottom-dump skips atWesselton Mine.

The man and material winderson the Bultfontein and De Beersmain shafts (and, from 1976, theWesselton main shaft) are automaticelevators with a payload of 5000kg and a speed of 7,5 m/s, and aredesigned for a maximum windingdepth of 975 m. In operation, theyare identical to an automatic eleva-tor in a building, no driver or opera-tor being required. The stationgates and conveyance doors areoperated manually, but are electric-ally interlocked to ensure that theyare closed before the conveyancemoves, and mechanically interlockedto prevent them from being openedexcept when the conveyance hasdecked at its destination.

The conveyance is called to astation by the pressing of a callbutton as in a building. During shifttimes and material-handling times,the call buttons are made inoperativeby the turn of a key switch,and control is then limited to theconveyance control panel only, whichmeans that the person in chargeretains complete control.

Owing to the depth and speed ofwind, the use of trailing signalcable is unpractical, and a radio-type 23-channel signalling systemis installed, with the signal generatormounted in the conveyance andpowered by a battery. A signal-receiving set is installed in theheadgear. This set receives, filters,and amplifies the signals receivedand feeds them to the controlsystem. For safety, a minimumnumber of two signals is requiredto be correctly received before thecontrol panel is activated. In thecase of an emergency, the emer-gency stop button in the conveyanceis pressed, which cuts the carriersignal and thus prevents any othersignals from being transmitted.

A feature of these elevators is theaccurate decking achieved, the maxi-mum variance being about 25 mm.This is maintained by the mountingof magnetic switches at each station.They are activated by a vane onthe conveyance that can be ad-justed to very close tolerances.For shaft inspection, the machine

JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MIN ING AND METALLURGY

is controlled from the inspectionplatform mounted above the con-veyance, the speed being limited toa pre-adjusted inspection speed. Thesame applies to rope inspection,which is controlled from the bailie

Because of the difficulty of slinginglong materials above or below anelevator cage, the conveyance forthese machines has been built toaccommodate materials up to 7 mlong inside the conveyance. Anair-driven chain hoist is permanently

mounted on the bridle to facilitateloading and unloading.

The man and material winderson the service shafts are all auto-matic elevators with a payload ofabout 2700 kg and a speed of2,5 m/s at a maximum length ofwind of 360 m. In operation, theyare identical to the machines onthe main shafts, except that theyare controlled by a trailing cable.For the development phase on theseshafts, a skip and cage combination

was installed with the skip having apayload of 3 t.

Further progress in automation isbeing planned for Koffiefontein Mine,where a new shaft is nearing com-pletion. This will be equipped withthree fully automatic winders, whichwill not be equipped with the norm-al driver's control console, andno winding engine drivers will berequired or be on call.

The rock winder will be a thy-ristor drive, three-rope Koepe with

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JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY DECEMBER 1975 25t

a sheave of 5 m diameter. In opera-tion, it will be completely automatic,i.e., when switched on, it will hoistore continuously provided that itis available in the undergroundstorage bins and the headgear binsare able to receive it. For shaftinspection, it will be controlled atinspection speed only, from theplatform above the skip. For ropeexamination, it will be controlledat examination speed from a positionin the headgear, the bank, or theshaft bottom (for tail ropes). Con-trols are also provided for skipinspections and starting up afteran unscheduled stop. This machinewill be licensed as an elevatordespite the fact that it is poweredby 3850 kW and has a payload of23 t.

The man and materials winderwill be an automatic elevator withthe same general specification asthe existing main-shaft elevators. Itis designed for a maximum lengthof wind of 1000 m.

The third winder is a heavy-materials winder, which is capableof raising or lowering a load of 30 tat a speed of 1,25 m/so Its duty isvery much the same as that of acrane. It will be operated from apendant control, with control but-tons for 'Up', 'Down', 'Creep Up',

'Creep Down', and 'Stop', that canbe plugged in at any station. Inaddition, it will be possible todespatch the load to a specificstation.

The gradual automation of windersover the past thirteen years hasresulted in a significant reductionin the complements of windingengine drivers, bankmen, onsetters,and cage assistants. Automatedmachines are safer as the controlsoperate only within predeterminedlimits that cannot readily be by-passed. Although the maintenanceof automated winders is more com-plex than that of manually operatedmachines, very little difficulty hasbeen experienced in training artisansfor this duty.

BLOCK-CAVING PRACTICE

The introduction of block cavingis described in a paper publishedin 1960, by W. S. Gallagher andW. K. B. Loftus. Fig. 4 shows ageneral layout of a block cave. Thepresent paper deals with the subse-quent weight problems encounteredin the Bultfontein 580 m blockcave, changes in layout and designto overcome the weight problem,and brief descriptions of the subse-quent layouts at all four of theKimberley Mines.

Weight Problems

The general layout of the 580 mblock-cave section, Bultfontein Mine,is shown in Fig. 5. Early practicewas to carry out undercutting bypillar wrecking with long holes,which required prior installation ofthe concrcted drifts to permitremoval of the broken ground fromthe undercut horizon. This resultedin serious abutment damage tothe drifts as the undercut areaincreased in size. It was plannedto bring the southern half of theblock into production initially in1960, followed by the northern halfsome three years later. However,installation of the completed driftsin the northern half continuedahead of the undercutting in thesouthern half, and by the timeundercutting was completed in thesouthern section up to Drift No. 8,serious abutment damage wasoccurring as far as Drift No. 13in the northern section.

Initially, the undercut floor wascarried 6 m above the drift floor,but subsequently this distance wasincreased to 7,4 m to lessen abut-ment damage. However, initial pro-duction difficulties led to the topsof the cones being sliped off bylong holes to reduce the distance

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252 DECEMBER '1975 JOURNAL OF THE SOUT H AFRICAN INSTITUTE OF MINING AND METALLURGY

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from floor of drift to top of cone backto approximately 6 m. A section ofthe cone layout is shown in Fig.6(A).

Soon after the southern sectionattained its full production of4320 tjd, the central area, showndotted in Fig. 5, collapsed. Con-certed and continued drift-repairefforts over several years failed toregain this area, as pressures andweight were excessive. As shortlengths of drifts were regained,excessive pressure crushed the con-crete lining of the drifts almostovernight, and finally all regainingwork in this area was abandoned.

In 1964 work was started tobring the northern half of the 580 mlevel into production as the orereserves in the southern half werenearing depletion. All the drifts inthe northern half had to be recon-structed as they had deterioratedseverely since initial installation.Then, when undercutting of thissection was started, it was decidedto leave a pillar, not undercut, inthe centre, approximating to thearea that had collapsed in thesouthern section. This proved to bea costly decision.

BUlTFONTEIN MINE

595 & 61Om SUB CAVES

BUlTFONTEIN MINE580.595.610m CAVES


DECEMBER 1975 253

As full production of the northernsection was being reached, thecentral pillar became a focus ofintense pressure. The ends of thedrifts adjoining the pillar werepushed back laterally, sometimesat the rate of a few millimetres perday, and intense top and side pres.sure on the drifts occurred approxi.mately halfway between the pillarand the rock contact. Determinedefforts to advance to the pillar inorder to undercut it failed. At thesame time, a large number of drift.repair crews made little progressin repairing the damaged drifts. Orereserves on the southern sectionwere running out, and call product.ion could not be achieved on thenorthern section. The call productionwas then reduced from 4320 to2540 tjd, and plans were made fora rescue operation.

Installation of Sub-level Caves

It was decided to construct smallblock. cave sections below the centralcollapsed area of the southern sectionon the 595 m level, and below thepillar area of the northern sectionon the 610 m level, to recover thelost ore reserves in. these areas. Onthe south side it was decided tomake use of existing ventilationlevel development for the undercuthorizon on the 585 m level, with thedrifts on the 595 m level, and toelevate the ore by incline to the580 m level haulage.

Because of the intense pressureexerted by the pillar on the northside, it was decided to site the sub.cave lower down, with the undercuton the 600 m level and the driftson the 610 m level, 30 m below the580 m level drifts. There the orewould be conveyed horizontally toan existing ore pass, No. 10, inthe country rock. The plan andsection view of the sub. caves isshown in Fig. 7.

At the same time, some radicalre. thinking took place in the designand procedures for block caving.

Summary of Changes in Designand Procedures

The approach to the weight prob-lem was two-pronged: firstly, todesign a system where the weighton the drifts would be minimized,and, secondly, to make the drift

254 DECEMBER 1975

lining as strong as possible towithstand the peripheral stress onthe drifts.

In the first category, it was ob-viously desirable to site the undercuthorizon as high as possible abovethe drift horizon commensurate withpractical production requirements.Also, if the undercut could be stopedprior to the installation of thedrifts, undercut abutment damageto the drifts could be avoided. It wasdecided to increase the undercutfloor height from 6 to 10 m, as itwas felt that 10 m was the limit ofheight at which 'action' work couldbe effectively carried out. 'Action'work is the name given to the opera-tion of breaking or bringing down

large lumps that block the top of thecones on the undercut floor horizonand require the 'action' crews toenter the drawpoints either to drilland blast the lumps, or to placelarge pack blasts to displace thelumps. Cone geometry could alsobe varied. They could be sited soas to converge over the drifts,leaving a pillar between the drifts(Fig. 6C) or be located betweendrifts so as to leave a pillar overthe drifts (Fig. 6B). The latterproblem was submitted to the De-partment of Mining of the Universityof the Witwatersrand, who carriedout photo-elastic stress studies withplastic two-dimensional models ofthe two layouts. These studies

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clearly indicated that stresses onthe margins of the drifts would bemuch lower where the cones con-verged over the drifts (Fig. 6C), andthis layout was adopted.

Stoping of the undercut operationcould be carried out by breast-stoping panels of suitable widthand scraping the broken groundback to ore passes situated in thecountry rock. As the kimberlite inthe Kimberley mines is compara-tively weak and incompetent-crushing strengths vary from 15to 85 MPa with 55MPa being con-sidered a reasona ble average--itwas considered advisable to limitface lengths to about 30 m, and toinduce early caving behind the faceby drilling and blasting 5 m hanging-wall wrecking holes at 50° into thehangingwall. Stope width was 1,7 m.Fig. 8 shows a typical stopinglayout. Special attention had tobe paid to dense mat pack and propsupport close to the face to preventhanging collapse at the face, andto complete removal of supportbehind the face where hangingwallwrecking was carried out. Under-cutting by stoping was completelysuccessful and eliminated all abut-ment damage to drifts. In addition,pressure on drifts prior to con-creting was considerably reduced asthe undercutting tended to de-stressthe drift horizon.

In the second approach to theproblem, pneumatic placing of theconcrete was replaced by pumping,to avoid segregation of the concreteand to enable a concrete of lowerwater-cement ratio, and hencegreater strength, to be transported.Samples of the aggregates weresubmitted to the Portland CementInstitute, who designed the requisitemix for pumping, to achieve aminimum 28 day strength of 44MPa. Strict quality control wasmaintained on the supplies ofaggregates by sieving analyses, andon the quality of concrete by slumpand cube tG3ts. A double-actingconcrete pump is shown in Fig. 9,and diagrammatic sections of abatching plant and the supply ofaggregates and cement are given inFig. 10. Aggregate supplies werestored above the pump and fedto paddle mixers by modern auto-mated weight-batching equipment.

Because of the weak nature of thekimberlite, drifts were initially de-veloped as pilot tunnels 1,4 by2,1 m across the pipe and then slipedfor concreting to 3,5 by 3,3 m.Sliping was carried some 10 to 12 mahead of the finished concrete,which permitted a 5 m long concreteshell, I m thick, to be poured on anexisting concrete floor together witha further 5 m concrete floor aheadof it for the next shell. The insidedimensions of the finished drift were1,72 by 1,83 m. Special attentionwas paid to obtain smooth-blastedperiphery in the sliped portion,and roof-bolt support was in-stalled to prevent fall out.

Drifts were sliped to a normalarch shape, and the concrete fillingwas also arch-shaped. Special effortswere made to obtain a completeconcrete fill to the roof of theexcavation. The shuttering waschanged from the early monolithictype to a simple shuttering of smallplates supported on standard rigidarches. The monolithic type becamevery difficult to install because ofearly distortion due to normal wearand tear. Although arch-shapeddrifts were considered desirable inearlier practice, they could not beattained because it was not alwayspossible to control the profile ofthe sliped excavation in the weakkimberlite, nor was it possible tofill to the roof with concrete thatwas pneumatically placed into theshuttering. Fig. 11 is a view ofshuttering in place ahead of com-pleted concrete, but with the frontmasking removed. Fig. 12 shows acompleted drift.

One further problem had to beovercome in the design of the twosub-level caves: the transport of theore from the 595 m drift to the580 m haulage for the one cave, andfrom the 610 m drifts to No. 10pass in the country rock for thesecond cave section. As the transporttunnels in both cases were situatedin the weak kimberlite, and thefinished tunnel would require aI m thick concrete lining, there wasobviously a limit to the size of theraw excavation that could be sup-ported and adequately controlledprior to concreting, and hence tothe finished size of the concretetunnel. Obviously, a finished tunnel


to carry Granby cars was completelyimpracticable. In addition, in theconventional block-cave system, alllumps of ore that could pass throughthe drawpoints (1,2 by 1,2 m)could be handled by the scrapingand tramming equipment, and wereeventually reduced in size by thelarge underground crusher, soavoiding the necessity of costlygrizzly blasting. If this feature wasto be retained, and this was mostdesirable, conventional conveyorbelts could not be used for thetransport process.

It was decided to equip thetransport tunnels with heavy-dutyPanzer or armoured conveyors, asused in longwall coal mining inEurope. Although expensive in initialcost, these proved to be extremelysuccessful for the purpose required.They were robust and could handleall the large lumps delivered bythe scraper scoops, as well as beingeconomical to operate. The Panzerconveyor on 610 m level is shownin Fig. 13.

Production from the Sub-levelCaves

Production commenced from thesetwo sub-level caves (595 m and610 m) some 18 months after thestart of the whole operation.Initially, six drawpoints in eachdrift in line were opened for pro-duction. Drawpoints were 5 mapart, and thus the width of theproducing strip was 30 m. Noproblems were encountered. Afterpulling from the strip for abouttwo months, during which a cushionof broken ground built up above theproducing drawpoints, the strip wasslowly moved across the pipe, byfirst closing the rear drawpoint andthen opening the next drawpointin front of the strip. Mter a furthertwo months of production in thisposition, the process was repeated,so that gradually the producingstrip was moved across the wholecave area. This rescue operationproved to be completely successful.No damage occurred, and the pro-duction from these small layoutsreached 1600 tjd, when the totalproduction from the mine wassuspended for a few years becauseof a recession in diamond sales.It was evident that all the ore re-

DECEMBER1975 255

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.ere <c')pvP7';'~c;-;;,~

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Fig. ID-A batching plant for pumping concrete

256 DECEMBER 1975 JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY

Fig. I I-Concrete shuttering with front masking partially removed

Fig. 12-View of a completed block-cave drift


Fig. 13-View of a Panzer conveyor on 610_m:level.:Bultfontein Mine

s~rves lost in the centre of the 580 mlevel would be successfully recovered.It should be noted that effectivedraw control, which is essentialfor optimum recovery of ore reserves,can be achieved only where weightcan be controlled and severe driftdamage avoided.

Change in Basic Design of the700 m Block Cave

Whilst the construction phase ofthe sub-level caves was in progress,development of a conventional block-cave layout on the 700 m level,Bultfontein was proceeding. Thehaulage from the main shaft to thepipe had been completed, and thehaulage tunnel together with the ac-cess tunnel round the pipe was beingdeveloped in the country rock.However, the country rock fromthe shaft to the pipe, a competent

258 DECEMBER 1975

granite gneiss, soon changed to avery incompetent chlorite-talcschist as the haul ages and accom-panying access tunnels on each sidecommenced to encircle the pipe.Both haulages and access tunnelswere supported with yieldable steelarches, the haulages with 29 kg/msections and the access tunnelswith 16 kg/m sections, each spaced0,6 m apart. As this developmentproceeded, despite keeping the steelarch support right up to the face,it became increasingly evident thatthese excavations would not remainsufficiently stable to serve as extracttunnels for the 700 m production.It was at this stage that the designof the 595 m and 620 m sub-cavesand the operation of the Panzerconveyors were seen to be entirelysuccessful. Accordingly, the designof the 700 m layout was changed

to embody the successful features ofthe sub-caves. As the schist countryrock on the 700 m level was lesscompetent than the kimberlite, itwas decided to use Panzer conveyorsin concrete-lined tunnels in thekimberlite as ore conveyors, insteadof trolley locomotive traim in thecountry rock. Accordingly, the arch-lined haulages in the country rockwere concrete lin0d to form circularaccess tunn'31s, the existing con-ventional access tunn01s were wastefilled, and Panzer conveyors wereinstalled in concrete-lined drifts inthe kimberlite 10 m below the pro-duction drifts, with short passesequipped with chain-link doors feed-ing down from the production drifts.Production drifts 15 m apart wereinstalled across the pipe from thenow-circular concrete-lined accesstunnol, after the undercut had beenstoped. The drift layout is shown inplan in Fig. 14, and Fig. 15 showsthe plan view of the Panzer transferlevel. Fig. 16 shows a section throughthe tramfor pass. Initia] productionfrom this cave had just commencedwhen the production of the minewas suspended, as mentioned above.However, no serious problems areenvisaged when production is againcommencod from this section.

760 m Layout, Dutoitspan Mine

The main development of the760 m block cave layout at Dutoits-pan was being carried out slightlyahead of that of the 700 m atBu]tfontein. This was also a con-ventiona] layout. The country rockon the south side was a competentgranite-gneiss, whereas that on thenorth side was a weak schist,although stronger than the Bu]t-fontein schist. The north-side haul-age, access tunnels, and winchchambers had been supported withyieldable arches. Although theseexcavations appeared to be reason-ably stable, it was decided to rein-force them with concrete after theexperience with the Bultfontein 700m layout. The haulage was linedwith a 0,75 m thickness of concreteinside the arches, permitting justsufficient clearance for the operationof 6 t Granby cars, but not the6 t trolley locomotives. These trainswould be hauled by battery loco-motives. The winch chambers were


,\";,I,'\ '..',"

,\\ 3~l

~/lCc,::-.ss ~

Fig. I4-Plan of 701l~m block cave,:Bultfontein Mine

SCN/S7

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Fig. IS-Plan of 710 m Panzer transfer level, Bultfontein Mine

also concrete-lined inside arches,but not the access tunnels. Thelatter were heavily injected withColgrout. The layout is shown inFig. 17.

785 m Layout, Wesselton Mine

The drift and haulage layout isshown in Fig. 18. As can be seen,the pipe was split into three lobes,but it is of interest that primarysampling development on the 930 m

level shows the lobes to have coal-esced into one pipe body again.

Initially, the layout was designedwith a single haulage tunnel be-tween the pipe and the main shaft,but the necessity for hauling largetonnages ultimately (about 8300 t/d)required the addition of the lineconnecting the shaft with the north-ern part of the pipe, thus completingthe haulage loop and making ituni-directional. This would also

JOURNAL OF THE SOUTH ,AFRICAN INSTITUTE OF MINING AND METALLURGY

facilitate any future automationof the trains.

The general layout in the cavesystem itself was not changed.However, the following innovationswere introduced.(a) Pozzolith was used as an addi-

tive to the concrete. This re-sulted in an increase of thefinal minimum 28-day strengthfrom 44 to 54 MPa.

(b) On completion of the con-

DECEMBER 1975 259

"""",,'V'?,,' .In"'.I",,')'u,,,;' .1/"'" """/<1

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'"Fig. 17-Layout of 760 m block cave, Dutoitspan Mine

260 DECEMBER 1975 JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY

,..."."., 7><!~""'fl Onc6 "-17.,..,

~

Fig. IS-Layout of 785 m block cave, Wesselton Mine

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Fig. If-Layout of proposed 745 m block cave, De Beers Mine

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creting of a drift, grout wasinjected into the roof of eachshell to ensure a complete fillbetween the concrete and thekimberlite.

(c) All block-cave haulages in theKimberley mines had beenequipped with 6 t Granby carsand 6 t trolley d.c. locomotives.It was decided to equip theWesselton haulage with 10 tGranby cars and 10 t a.c.trolley locomotives.

(d) In the stoping operation, the5 m wrecking holes drilled intothe hanging and blasted 8 to 1Ombehind the face were discon-tinued. Instead, the stope wascarried 1,9 to 2,0 m wide, and1,5 m holes were drilled at 50°into the hanging behind theface. These were designed, notto 'wreck' the hanging, but tobreak an additional 1,0 m fromthe hanging and so increase thestope width. This led to moresta ble face conditions and wouldinduce earlier caving.

(e) Klockner-Ferromatik HydraulicProps were introduced as facesupport, instead of mat packs.Three rows were installed 1,5 mapart, and props were 1,5 mapart. These were successfuland saved timber and labour.However, in friable ground,especially near the rock con-tacts, mat packs had to beused as well.

(f) A light two-boom drill rig hasrecently been introduced andis being used to complete thehaulage loop.

(g) A complete investigation wasmade into full automation ofthe haulage (driverless trainsand remote control of fillingand tipping). However, the costof automation is not economicat present wage levels.

745 m Layout, De Beers Mine

This is the most recent of theblock-cave systems, and the pro-posed layout is shown in Fig. 19.

A feature of this layout is that

horizontal ore storage has beenprovided on the same level as theunderground crusher, and the orewill be reclaimed from below thehorizontal storage bins by a Panzerconveyor that feeds onto an in-clined Panzer conveyor, deliveringthe ore into the crusher. This crushertreats the ore from the existingproduction levels on the 500 and620 m levels. If conventional storagein passes above the crusher hadbeen adopted for the new layout,an additional crusher and accesscross-cut from the shaft would havebeen required. The 745 ID level hasbeen estimated to be the economiccut-off level of this section of thepipe.

The 745 ID haulage from the shaftwas commenced with a two-boommedium drill rig (Fig. 20). Afterinitial training of crews and teethingtroubles, the development has settleddown into a smooth operation. Therig is operated by three .:Bla.cks,.who also carry out the completecleaning operation with a front-end

262 DECEMBER 1975

Fig. 20- Twin-boom pneumatic drill rig used at De Beers Mine


PREM'ER ZARR'!SA

8 rP0JA,ERS<ONIE'N GUTOITSPAN

FINSCH lETSENG KOFFIEFONTEI

~~~WEOCELTON 8UlTFONTEIN DE BEERS

MWAD'J,

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,'RAPA TAlAlA CONGO

0 D \"\V(/'eJ

Fig. 21-Relative sizes of some kimberlite pipes

loader and Granby cars. On athree-shift operation, the 3,5 by3,4 m haulage is advanced 5 m perday. It is also intended to carry outthe development around the pipe,haulage, access tunnels, and driftsin kim berlite with the smaller drillrig at present in use at Wesselton.

Research Investigations

The Mining Department of theUniversity has taken a keen interestin a number of aspects for improvingthe block-caving system, during thecourse of which they developed asophisticated and effective stress-strain measuring instrument. Asmentioned for the Bultfontein sub-level caves, stress distributionsaround drifts for different cone con-figurations were measured using thephoto-elastic stress technique. Theresults led to the adoption of aconfiguration that has proved highlysuccessful.

At present the Rock MechanicsDepartment of the University iscarrying out a similar investigationof a cone configuration comprisinga continuous slot between drifts,


Fig. 22-Aerial view of Finsch Mine

DECEMBER 1975 263

which would be cut by a mechanizedrig. The technique of finite elementanalysis is being used to comparethis proposed configuration with theexisting successful one.

General Statistics

Output per Whiteunderground shift

Output per Blackunderground shift

Output per man (Blackand White)

Output per case ofexplosives

Output per winch pershift

Cost per centare stopedCost per cone developedCost per metre of

concrete drift R250,00Cost per tonne, including

treatment and generalexpenses

318 t

20 t

250 t

100 tR17,00

R300,00

R2,60

OPEN-CAST MINING ATFINS CH AND KOFFIEFONTEIN

Finsch Mine has now .been inproduction for almost eleven years,during which 43 000 000 t of wasterock have been removed and24 000 000 t of diamondiferous orehave been treated. The pipe is roughlycircular and is approximately 500 min diameter with a surface area of17,9 hectares. The size of the Finschpipe relative to other major pipescan be seen in Fig. 21.

The mining layout is a seriesof 12 m benches, which were origin-ally cut at an extremely shallowangle but which have gradually beensteepened to an angle of 45 o. Theshape of the pit is polygonal,roughly approximating the shapeof the pipe (Fig. 22). To eliminatethe number of corners inherent ina zig-zag roadway, an 18 m widthspiral roadway has been laid outat a gradient of 8 per cent (I in12). To date, the pit has reacheda depth of 148 m below the surface.

Koffiefontein Mine was re-openedin January 1970 after having laindormant for 40 years. Since then,37000000 t of waste have beenmined, and II 000 000 t of ore havebeen treated (Fig. 23). Initially,Koffiefontein was regarded as amarginal proposition, but more re-cently viable reserves have beenproven for a life in excess of twenty

264 DECEMBER 1975

19 t

years. It became obvious that Koffie-fontein would not be mined through-out its life as an open pit, andmajor planning exercises were initi-ated to cater for the eventual dropdown to an underground miningoperation. Nevertheless, in the opera-tion of the open pit, the equipment,final slope angles, and the ultimateopen-pit bottom require constantre-assessment. This extremelyinteresting phase in Koffiefontein'slife will extend until about 1981,when the transition from open-castto underground mining will becomplete.

Equipment

The equipment currently used atFinsch and Koffiefontein is asshown in Table 1.

plant have been reduced, thenumber of men employed on second-ary breaking being reduced fromfour to one.

Selection of Equipment

During the past decade there hasbeen a tendency to move towardslarger-capacity equipment. The pri-mary advantages in this escalationin size have been a reduction in thenumber of units required duringany specific phase of the life of thepit, and an increase in the ratedduty of units such as drill rigs. Thusthe number of operators has tendedto decrease, the maintenance re-quirements have tended to becomeeasier, and the traffic density inthe pit has fallen.

However, larger units have some

TABLE 1EQUIPMENT USED AT FINSCR AND KOFFIEFONTEIN MINES

Finsch Koffiefontein

4 rotary drill rigsDrilling

1 6 yd3 electric shovel3 4,5 yd 3 electric shovels1 10 yd 3 front-end loader

10 70 t haul units

Loading

Hauling11

75

Service and Sundry1 crawler mounted dozer 12 rubber-tyred dozers 33 graders 22 water carts 21 padding truck 11 explosive truck 11 Anfex truck 1

1

Where possible, standardization ofequipment has been attempted,although in certain instances thishas not been possible owing topoor delivery dates.

An interesting development hasbeen the recent introduction, atKoffiefontein, of a hydraulic impactbreaker mounted on a hydraulicexcavator (Fig. 24). One of themajor problems at Koffiefontein hasbeen the poor fragmentation of thedolerite and the soft kimberlite,resulting in a disproportionateamount of secondary blasting. Untilrecently, this duty was carried outby rotary percussive drill rigs andhas been expensive in terms of menand materials, and disrupting tothe pit cycle because of blasting andthe consequent dozing of fly rock.The introduction of the hydraulicimpact breaker has boon very im-pressive. Delays in the pit and

6 rotary drill rigs2 rotary percussive drill rigs

4 6! yd 3 electric shovels4 10 yd 3 front-end loaders

70 t haul units50 t haul units35 t haul units

crawler mounted dozerrubber-tyred dozersgraderswater cartspadding truckexplosive truckAnfex truckhydraulic breaker mounted on ahydraulic excavator.

disadvantages such as a reduction inthe flexibility of the operation, andthe mismatching of the larger unitswith permanent or semi-permanentequipment such as the treatmentplant and the shovel fleet. It isextremely important, therefore, toconsider the entire system in whicha unit will operate, and not the unitin isolation.

The present selection techniquesare based on three broad factors:(I) operational effectiveness or 'Will

it work in the situation?'(2) operational efficiency or 'How

much will it cost?'(3) distributor service or 'Will spare

parts and technical advice beavailable from the distributor/manufactured' .

To effect this type of technique, theunits under consideration are studiedby three departments: the Mining,Engineering, and Operations Re-


Fig. 23-Aerlal view of Kofflefonteln Mine

Fig. 24-Hydraulic rock breaker used instead of secondary blasting


search Departments.The Mining Departm~".,is re-

quired to comment on the operationof each unit. Where possible, per-sonnel are sent to look at each unitunder operational conditions to pickup information on performance andgeneral characteristics. TheEngineering Department is requiredto comment on the probable main-tenance costs based on previousexperience, interpolation of resultsachieved by others, and a knowledgeof stores holding and workshopfacilities. The Operations ResearchDepartment is required to analysethe information and simulationsreceived from manufacturers andidentify any significant differencesin unit performance or cost.

The most important selection inthe future will be that of haul units.The shovel fleet is relatively young sothat, unless the decision is taken topurchase shovels with larger bucketcapacity, it will probably not re-quire replacement. Similarly, thedrill fleet is young, with an a1/:erageage of 2000 hours. The ha1l1 fleet,however, requires continual replace-ment, and an exercise is currentlybeing carried out to determine thetruck best suited to the operation.The boundaries of the system inwhich these haul units will operateare the 4t yd3 (approximately 9 t)electric shovels and the 450 t/htreatment plants, limiting the choiceto the 50 to 70 t range.

DevelopmentPhilosophy

When Finsch Mine was originallyplanned, considerable thought wasgiven to the rate at which wastestripping should be effected. Thechoice lay between the two extremesof mining each waste bench to itsfinal limit before commencing themining of the underlying bench, orstripping at the instantaneous strip-ping rate, which means mining onlyenough waste to liberate the orerequired. The problem was mademore difficult by the fact that thefinal slope angles, and thus theultimate pit configuration, couldonly be guessed. To gain experiencein the necessary mining techniquesand to allow time to establish thefinal slope angle, the decision was

of Strippinga

266 DECEMBER 1975

made to sub-divide the miningsequence into four main stages.

The first stage involved miningwithin the ore body, and thus nostripping was involved. The secondstage required waste stripping tobe carried to final pit limits, theslope angle being kept fairly shal-low (approximately 22°). During thisstage it was envisaged that workwould be carried out to determinethe final slope angle. The strippingratio was fixcd at 1,37 to 1, whichwas comiderably highcr than theminimum stripping ratio andallowed a margin for error. Thethird stage necessitated the miningback of the waste benches to thefinal limits set by the slope angle,and stage four was the miningback of the flat ore benches to themaximum safe ore slope angle.

The mining pattern has followedthe original plan fairly closely, butduring the past two years the majordisadvantage of mining to an averagestripping ratio, that of a detrimentalcash flow, has become accentuatedby spiralling rates of inflation. Thisdisadvantage is compounded byindications that the final safe slopeangle may be as steep as 60 o inthe ironstone. Thus, the strippingratio has been gradually reducedto the present ratio of 1 to 1 andcould be reduced further when cur-rent investigatiom determine thefinal slope angle.

As this ratio is reduced and thecash flow enhanced, there will, ofcourse, be a price to pay in loss offlexibility in the mining sequenceand the possibility that ore pro-duction could be lost if wastestripping were held up. Anotherdisadvantage will be the requirementof an increasingly large haul fleetas the pit deepens.

The final decision will probablybe a compromise that will follow thelead given by the original planningteam. However, it should be possibleto reduce insurance margins becauseof improved knowledge of the pro-perties of the country rock, andexperience in the mining operation.

EconomicFinsch

Open-pit Depth at

Initial exercises to determine theultimate depth of the open pit

used the 'ratio of areas' rule, whichpropounds that

(i) the instantaneous stripping ratiois equal to the l'~ip of therespective plan areas of wastestripping and ore mining, and

(ii) thus, if the surface waste strip-ping limits are fixed, the instant.aneous stripping ratio is thesame whatever pit slope istaken.

As the area of the orebody wasknown and the economic strippingratio (the value of the imtantaneousstripping ratio when the cost ofopen-cast mining is equal to thecost of underground mining) couldbe calculated, then the total sur-face area of waste stripping couldbe determined. The final slope angleswere assumed to be 45 o in waste and35 o in ore, and the ultimate open-pitdepth was estimated to be 275 m.

The significant factors in thedetermination of final open- pit depthare the final slope artglegoitnd therelative costs of open-pit and under-ground mining. Costs are a con-stantly changing variable andnecessitate continuous updating ofthe pit- bottom calculatiom.

Currently, work is under way ona detailed examination of the pro-perties of the country rock in anattempt to obtain more accurateestimates of the final slope anglesthat can be achieved in the wastecuts. The major areas of investiga-tion are the detailed mapping of thejoint planes and core drilling toestablish the nature of passage bedsthat are known to exist between theironstones and underlying dolo-mites.

Economic Open-pit Depth atKoffiefontein

The mining sequence at Koffie-fontein was complicated by analready-existing excavation, and theslope angle of the excavation was,in effect, the failure angle of thecountry rock. Thus, the open-castmining of Koffiefontein was plannedin three distinct phases or cuts(Fig. 25).

The dimensions of the first cutwere a minimum, commensuratewith haul road requirements andthe configuration of the originalopen pit to enable ore productionto commence at the earliest possible


5..1.

,., .

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date.The first waste cut was com-menced in January 1970 and wascompleted in February 1972. Theremoval of 17000000 t of wasteexposed 12 500 000 t of ore. Thesecond waste cut, which dovetailedinto the first cut, commenced inOctober 1971 and was due to becompleted in May 1975. This cutwas to remove 18 000 000 t of wasteto expose a further 11 000000 t ofore. The third waste cut, which wasstarted in September 1974, will becompleted in December 1977 andwill remove 24 000 000 t of wasteto expose 9 000 000 t of ore.

Work is currently being carried outto determine the critical slope anglefor the Koffiefontein pit. The prob-lem is not the normal slope-stabilityproblem in that, in most stabilitycalculations, the slope is allowedto fail when open-pit operationshave ceased. At Koffiefontein, theslope must remain stable while thepipe is being mined underground.Thus, it could be required to standfor up to 30 years after the closureof the opencast operation.

The problem is further compli-cated by the fact that an unstableshale layer was detected during thesinking of the main rock shaft.According to present planning, thisshale layer will be intersected inthe near vertical side of the pipe,and slaking tests indicate that theshale will weather and fail. Thisfailure could cause failure of theoverlying and underlying granites,which would cause erosion of therim of the pipe until the naturalangle of repose of the country rock

12.

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'(,~4B ..

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Fig. 2S-Section showing pit in Koffiefontein Mine

is reached. This would cause mass-ive dilution of the ore in the under-ground mine and the possible failureof underground drives due to theimpact of rimrock falling onto theworkings below.

A possible method of dealingwith the shale band would be toseal it, but this would pose theproblem of access to the band inthe near vertical pipe. If currentinvestigations indicate that the wastebenches could be carried at a steeperangle than the present 450, it wouldbe possible to adjust the miningpattern below the 76 m level toallow the shale band to be carriedin the deeper waste' benches. Thiswould also allow access to theadjacent granites, which might re-quire anchoring. The determinantin this problem will be the economicsof deepening the pit versus the costof rim failure.

Future Developments in Open-pit Desi~n

To date, all the calculations forpit design and pit bottom have beendone manually. The results achievedfor any set of parameters areadequate, but, owing to the com-plexity of the calculations, only twoor three of the many variables aretaken into account, and the exer-cise tends to be updated at in-frequent intervals.

To overcome some of these prob-lems, a computerized open-pit de-sign system is to be introduced.The system will be used to re-valuate the work already done atFinsch and Koffiefontein, and to


update the exercises when signifi-cant changes in parameters areencountered.

Other areas of inve3tigation atpresent being pursued are the de-velopment of an automated product-ion reporting system that will in-clude the maintenance of the earth-moving fleets, and the developmentof a computerized ore-reservesystem.

UNDERGROUND MINING ATKOFFIEFONTEIN

Initial exercises indicated thatthe economic open-pit bottom atKoffiefontein will be the 240 mlevel, which will be reached in1981. In mid-1973, initial planningfor the change-over from open-pitto underground mining began, oneof the first steps being the considera-tion of various mining methods forthe Koffiefontein pipe.

Block caving and sub.levelstoping, which are the main methodsused in the Group, were consideredfirst. Block caving is a relativelysimple mining method and allows amoderate degree of mechanization,and its use at Koffiefontein wouldmean that any future refinementscould be used in the KimberleyDivision. Unfortunately, the rela-tively large area of the Koffiefonteinpipe and the high daily tonnage callmean that the amount of pre-production construction would beimmense. A total of 74 scraper driftswould be required, and, to utilize thisnumber of winches, the pipe wouldhave to be bisected with a centralaccess tunnel. To improve loco-

DECEMBER 1975 267

motive utilization, the simple china-man boxes would have to be replacedwith ore passes in the kimberlite. Afurther problem would be that theventilation requirement of 190 m3fswould need large-section tunnelsthat would be difficult to keep openunder the pressures developed by acave. Finally, rain falling in theopen-pit catchment area, withoutany overburden to soak up thismoisture as in the Kimberley under-ground mines, would percolatethrough the broken kimberlite andcause serious ground-handling pror-lems.

The second method consideredwas the sub-level stoping methodused with success at the PremierMine, which lends itself to a largepipe and also to large productiontonnages. However, the method isfairly labour-intensive and wouldtend to preclude a high degree ofmechanization. In addition, theKoffiefontein kimberlite is muchsofter than at Premier, which wouldresult in excessive wear at thebrows of the grizzley levels andnecessitate extensive support andmaintenance of these brows.

A third mining method known aslong-hole chambering has been prac-tised at Wesselton Mine for aboutfive years. The method is a refine-ment of the extremely labour-intensive chambering method, andhas been brought to a greater degreeof efficiency by the use of moderntrackless-mining equipment.

The Long-holeMethod

Chambering of approximately 3000 t capacity.]'rom these passes, short belts willfeed the ore to the measuring flasks(Fig. 28).

Feasibility Test

Before the adoption of the long-hole chambering method to minethe Koffiefontein pipe, a feasibilitytest was set up in the Koffiefonteinopen pit to determine(a) the viability of developing com-

petent 3,4 m by 3,4 m drives inkimberlite,

(b) the viability of developing abreaking slot,

(c) the type and make of unitsbest suited to the operation, and

(d) the timing of the various sec-tions of the production cycle.

During the test a variety ofequipment was used to drive a3,4 by 3,4 m tunnel for a distanceof 50 m under a 17 m lip. Thereafter,a slot was established at the end ofthe tunnel, and a series of fans wasdrilled and blasted into the slot fromthe tunnel, the broken ground beingloaded and trammed away via thetunnel.

The long-hole chambering methodwas found to be acceptable becauseof the following.(a) The construction period re-

quired for initial productionfalls well within the economiclife of the open pit.

(b) A very rapid build-up to fullproduction can be achieved.

(c) The method is highly mechan-

r,j1'1J*IlSMt. /'AS

Production levels will be developedat 30 m vertical intervals, beginningjust below the open-pit bottom.Each level will consist of an accesstunnel driven around the rim of thepipe in the country rock (Fig. 26).From this access tunnel, 18 paralleldrilling drives will be developedat 18 m centres across the pipe. Atright angles to these drives, a slotwill be developed across the otheraxis of the pipe. This slot will breakthrough to the level above and willprovide a free breaking face for theblasting of a fan pattern of longholes (Fig. 27). The fan is designedto form a continuous cone alongthe line of the drive that will tendto funnel the broken ground to the'low point' to facilitate loading. Ithas been estimated that each fanblast will liberate approximately3600 t of ore (25 per cent of oneday's production).

The broken ground will be trans-ported by rubber-tyred load-haul-dump units via the drive to the rimaccess tunnel and will be tippedinto one of eight ore passes, whichwill be vertical raise-bored passesdeveloped from the 52 level viaall the production levels to the28 level. Ore transport on the mainhaulage level will be by 20 t carspulled by electric locomotives. Theore will be tipped into primarycrushers sited near the main shaftand will gravitate into storage passes

~= Jo.!!'~ =c~:r.-*=J.t.'ir;::: = = = = =-

268 DECEMBER 1975

Fig. 26-Plan of a production level-Koffiefontein proposed underground-mining method


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Fig. 27-Diagrammatic view of production drilling and blasting-Koffiefonteinproposed underground-mining method


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ized and is not labour-intensive,(d) The method is flexible. If pro-

duction experience indicatesthat the vertical interval be-tween loading levels is toosmall, the level spacing can beincreased without any disrupt-ion to the production effort.

(e) No return ventilation shaft isrequired, all the return airbeing exhausted into the openpit.

(f) The effect of rain can beminimized by leaving the wetbroken ground, and drilling andblasting fresh dry ground. (Thisis a major consideration, andpossibly the overriding one.)

(g) Pressure problems on drivesand tunnels should be minimizedas the deeper tunnels lie in thecountry granites and thereshould never be more than 90 mof ground overlying the drivesin kimberlite.

Operation

All production and developmentloading, hauling, and drilling, exceptthe hauling duty on the mainhaulage level, will be effected byself-propelled rubber-tyred units. Forthe initial development phase, fourelectrically powered rigs equippedwith twin hydraulic booms and

270 DECEMBER 1975

hydraulic drifters have been ordered.Hydraulic drifters were chosen inpreference to pneumatic machinesbecause of their superior efficiencyand to improve environmental condi-tions at the drilling face. They willalso avoid expensive and inefficientcompressed-air reticulation systems.The rigs will be able to drill anelliptically shaped tunnel 28,5 m2in area from a single set up. Thebooms are equipped with a parallelholding device, and the rig has theability to drill fans and roof-boltholes. Six diesel-powered load-haul-dump units fitted with 5 yd3buckets have been ordered to handlethe loading and hauling duties duringthe development phase.

Production fan drilling will becarried out by means of electricdrill rigs carrying hydraulic drifters.On the top level it will be necessaryto blast up to nine fans per dayowing to a low initial recovery of theblasted ground. This requirementwill drop to four or five fans perday on underlying levels. To facili-tate inter-level movement, all levelsincluding the main haulage levelwill be connected by a figyre-8ramp, which will also serve as amajor intake airway.

Ventilation calculations have beenbased on the provision of 0,05 m3/s

of air per rated horsepower of theproduction units. With the provisionof a 30 per cent safety margin, thetotal volume of air required willbe 425 m3Is. The intake air will besplit into two main streams: ap-proximately 140 m3/s will be broughtinto the 28 level, which will be thetop production level connected tothe shaft, and the remaining 285 m3/swill enter the mine via a specialairway on the 52 haulage level andwill then be carried up two 3,7mdiameter raise-bored airways tothe 28 production level and sub-sequently to the underlying levelsas they come into production. Eachdrilling drive on the productionlevels will be equipped with a plug-in fan so that a quantity of 8,5 m3/scan be exhausted from each opera-ting end. The return air will beexhausted to the open mine viaraise- bored ventilation passes andworked out areas.

All the water that falls into theopen pit will run into the drivesdeveloped on the upper productionlevels. It is intended to concretethe footwall of these drives, andthe water will be led from the drivesto the rim tunnel and via a waterpass that connects with all levelsto the main sumps on the 58 level.The sumps have been designed with

JOURNAL Of THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY

a total capacity of 25 million litres,and the main pumps will be capableof delivering 1 500 000 litres perhour. The system will be able tocope with a 100 mm cloudburstover the open-pit catchment area.

Thus, the method will be highlymechanized, electric power and dieselpower being dominant. Compressedair, for a change, will play a veryminor role, being used only for main-shaft chute operation and otherminor work, for which it will besupplied by small individual com-pressors.

MANAGEMENT AND LABOUR

Improved methods of mining andhigher productivity in general callfor higher standards of labour,supervision, and management, andit is considered to be of value torecord the steps being taken in thisdirection.

A management training pro-gramme was instituted in 1973,starting with top management, andthis has now progressed as far assecond-line supervisors (i.e., minersand artisans). Upon completion atthis level, the first-line supervisors(i.e., team leaders) will be trained.The value of using the same coursematerial for all levels of manage-ment is already apparent in thatall levels have clear objectives andunderstanding of the companypolicy. Managers now feel free toinnovate within the policy para-meters, making productivity schemesmore readily accepted and applied.For senior staff, a more intensiveand advanced management trainingscheme is now being introduced thatspecifically deals with objectives,organization, and motivation. Thistraining will also be given to morejunior managers. It is also plannedto parallel this programme withtraining in social skills and inter-personal relationships so that morevalue will be obtained from thegroup management sessions.

Great benefit is being obtained inKimberley from the use of localBlack labour rather than migratorylabour. At present 1150 out of the2550 Black workers are local menwho live in the Kimberley town-ships, and these men are conveyedby the Company to and from workeach day. They take normal leave

each year (approximately threeweeks depending on rank) and aretherefore a permanent and stableforce, allowing the Company tospend far more time and money ontheir training and development.Supervisors can become acquaintedwith their workers as people, know.ing their names, their familyba.ck-ground, and their problems. Thisis assisted by their knowledge ofEnglish or Mrikaans, which inmost instances is fluent.

It is intended to extend the con-cept of local labour at Kimberley,and a start has been made at Koffie-fontein, where a township exists. AtFinsch, where there is no township,the problem is greater, but con-sideration is being given to con-veying local labour from a township20 km away, or building a newtownship on the mine once approvalfrom the Bantu Administration canbe obtained.

Localization, of course, createsnew problems. Housing in the town-ships very often is not up to areasonable standard, and it hasbeen found necessary to start abuilding programme. De Beers isshortly to build 250 houses, whichhave 3 bedrooms, a full bathroom,and all facilities. Since they haveto be built in the township, privateownership is not at present allowed;they have to be given to the BantuAdministration, but it is possibleto reserve occupation for Companyemployees only. It is envisagedthat this building programme willhave to be extended and thathouses at Koffiefontein will also berequired.

Localization emphasizes communi-cation problems in that the acceptedhostel machinery falls away. Twomain steps have been taken toovercome this problem. Blacks whohave graduated in the personnelfield have been trained to takesenior positions in which they dealwith their own people, includingtraining, selection and manning,welfare, and assistant personnel offi-cer positions. The division nowemploys eight graduates and,although they are essentially a partof management, they provide anextremely effective and useful lineof communication with the Blackemployees.


In addition, works committees arebeing formed to be followed by aco-ordinating works committee. Thefirst committee has been elected, andthe representatives have been trainedto undertake their duties. Workscommittees, as opposed to liaisoncommittees, were chosen becausemore relaxed discussion will takeplace when the representatives dis-cuss matters within an all-Blackbody, and the resolutions that arepresented to management are morelikely to be their true feelings. It istoo early to expect these men todiscuss their problems openly whilesitting in awe of senior ;management.

To improve communication 'downthe line' to all employees, a systemof briefing groups is to be established.Starting at the senior manager, eachman briefs the next level below himon matters of importance andinterest at meetings held once amonth. The intention is that, ifemployees are given correct andmotivating information, 'grape vine'sources will be avoided togetherwith the disputes and problemsthat arise from misunderstanding.

It is now accepted in industrializedcountries that communications upand down the line cannot be achievedsatisfactorily by the same system,and that representatives of theunion or works committee, eitherdirectly or via a consultative com-mittee, provide the essential 'upthe line' communication while aseparate system such as the briefinggroup concept should provide the'down the line' communication.

Other problems encountered dur-ing localization were absenteeismand job expectation.

The former was a short-livedalthough serious problem. Intensivecounselling was required to instilla sense of responsibility into thosewho felt that taking a day off forone of many reasons (drinking beinga particular problem) was notserious. It was here that the Blackgraduates were particularly goodat improving the attitudes of theabsentees. After 18 months oflocalization, the avoidable absenteerate is less than 1,0 per cent, aremarkably low figure.

The local men are in general,relatively well educated, and they ex-pect more job satisfaction, not being

DECEMBER 1975 271

happy in menial or purely manualwork. Consequently, re-organizationof work and mechanization becomeessential. They are also more awareof differences in rates of pay andthe evaluated level of work, andit was necessary to question the payrate for certain jobs. An addedcomplication is that the Companyis in a competitive market and hasto compete with the South AfricanRailways and other industry andbusiness in Kimberley. Of course,this is not an unhealthy situationprovided the men are allowed to beproductive.

The training of workers to domore than one job has significantlyimproved productivity. In the blockcaves, for example, a machine opera-tor who drilled hang-ups and largerocks in the drawpoints was alsotrained to drive the scraper winch.This put him into a higher category

of pay and allowed a 30 per centreduction in the complement. Theintroduction of rigs and largerloaders into development with acrew trained to do all the jobs alsoincreased productivity. This multi-training of the workers is proving agreat success in all areas of the minesand plants. So far, 440 men out ofa trained total of 1000 have receivedtraining in more than one job.

To date 70 artisan aides have beentrained and introduced into thework situation. Acceptance of theaide is improving, and some aidesare doing really productive work,allowing the artisan to concentrateon the more highly skilled jobs.There is no doubt that the engineer-ing field offers great scope for in-creased productivity, and, with thepresent shortage of artisans and thelarge number of new mining andindustrial projects in the pipeline,

it seems to be essential that morenon-Whites must be trained.

CONCLUSIONThe mining industry will un-

doubtedly present very great chal-lenges in the future. Working costsare increasing at an astronomicalpace, and commodity prices, ingeneral, are not rising as fast andin some cases are falling. Bettermethods, and increased efficiencyand productivity are the onlyanswers to this problem, and thisin most cases means more mechaniza-tion and better utilization of thelabour resources available.

In conclusion, thanks are extendedto De Beers Consolidated MinesLimited for permission to publishthis paper. Thanks are also due toMessrs Vertue, Clements, and Michieof De Beers Consolidated MinesLimited who assisted in its compila-tion.

Company AffiliatesThe following members have beenadmitted to the Institute as Com-pany Affiliates.

AE & Cl Limited.AfroxjDowson and Dobson Limited.Amalgamated Collieries ofS.A. Limit-

ed.Apex Mines Limited.Associated Manganese Mines of S.A.

Limited.Blackwood Hodge (S.A.) Limited.Blyvooruitzicht G.M. Co. Ltd.Boart & Hard Metal Products S:"A.

Limited.Bracken Mines Limited.Buffelsfontein G.M. Co. limited.Cape Asbestos South Africa (Pty) Ltd.Compair S.A. (Pty) Limited.Consolidated Murchison (Tv') Gold-

fields & Development Co. limited.Deelkraal Gold Mining Co. Ltd.Doornfontein G.M. Co. limited.Durban Roodepoort Deep limited.East Driefontein G.M. Co. Limited.East Rand Prop. Mines limited.Envlrotech (Pty) Ltd.Free State SaaiplaasG.M. Co. limited.Fraser & Chalmers S.A. (Pty) limited.

Gardner-Denver Co. Africa (Pty) Ltd.Goldfields of S.A. limited.The Grootvlei (Pty) Mines Limited.Harmony Gold Mining Co. limited.Hartebeesfontein G.M. Co. Limited.Highveld Steel and Vanadium Corpo-

ration limited.Hudemmco (Pty) limited.Impala Platinum Limited.Ingersoll Rand Co. SA (Pty) Ltd.Kinross Mines Limited.Kloof Gold Mining Co. limited.LefHI'ings Ho1dings limited.Leslie G.M. Limited.libanon G.M. Co. limited.Lonrho S.A. limited.Loraine Gold Mines Limited.Marievale Consolidated Mines Limit-

ed.Matte Smelters (Pty) limited.Northern Lime Co. Limited.O'okiep Copper Company Limited.Palabora Mining Co. Limited.Placer Development S.A. (Pty) Ltd.President Stern G.M. Co. Limited.Pretoria Portland Cement Co. limIt-

ed.Prieska Copper Mines (Pty) Limited.Rand Mines limited.

Rooiberg Minerals Development Colimited.

Rustenburg Platinum Mines limited(Union Section).

Rustenburg Platinum Mines limited(Rustenburg Section).

St. Helena Gold Mines Limited.Shaft Sinkers (Pty) limited.S.A. Land Exploration Co. limited.Stilfontein G.M. Co. limited.The Griqualand Exploration and Fi-

nance Co. Limited.The Messina (Transvaal) Develop-

ment Co. limited.The Steel Engineering Co. Ltd.Trans-Natal Coal Corporation Limic-

ed.Tvl Cons. Land & Exploration Co.Tsumeb Corporation limited.Union Corporation Limited.Vaal Reefs Exploration & Mining Co.

Limited.Venterspost G.M. Co. limited.Vergenoeg MiningCo. (Pty) limited.Vlakfontein G.M. Co. Limited.Welkom Gold Mining Co. limited.West Driefontein G.M. Co. limited.Western Deep Levels limited.Western Holdings limited.Wlnkelhaak Mines limited.

272 DECEMBER 1975

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inthekimberley division of debeersconsolidated mines limited · extremely complex. at any level...

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