trackiessmining - saimm · trackiessmining inadditiontothefourpapersalready...

Trackiess MiningIn addition to the four papers already given in this issue, the following four contributions

to the colloquium on the above topic were received for publication.

1. TRACKLESS MININGAT OAMITES

by K. E. MANTELL *Oamites Mine, brought into pro-

duction in late 1971, is located 50 kmsouth of Windhoek, South WestAfrica, on the northern boundary ofand just outside the Rehoboth Ge-bied. Oamites was known as apossible mining proposition at theturn of the century when Hansea-tische Minen Gesellschaft was aditmining on the adjacent farm Kam-zwas.

Rand Mines Limited carried out a .

small amount of prospecting in theearly 1960s, Falconbridge Explora-tions Limited later taking over theprospect. Approximately 4600 m ofdiamond drilling was carried outbetween 1965 and 1967.

Feasibility studies indicated aviable proposition and, with a rela.tively low capitalization ot R5million and the participation of TheIndustrial Development Corporationof South Africa, Limited, the minewas brought into production with atarget of 45 000 tonnes of ore permonth at a head grade of 1,33 percent copper and 23 gjt silver.

Sub-level stoping was chosen asthe mining method because theore body was ideally suited to thismethod and production cost was ofprime importance. After carefulstudy, a trackless mining method wasdeveloped for the following reasons:(1) to break away from the tra.

ditional labour-intensive opera-tions of Southern Africa in con-sideration of the inevitable risein wages arid .possible labourshortage;

(2) the ramp system of opening upthe mine was considered to becheaper than conventional shaftsinking;

(3) the mine could be brought intoproduction early since sub-leveldevelopment could be carriedout simultaneously with thesinking of the decline; and

"'Manager, Oamites Mining Company(Pty) Limited

(4) development lashing could begreatly speeded up.

The orebody outcrops on thesurface and is located in a highlyvariable sequence of metamorphosedsedimentary rocks. The dip is con-sistent at 83 to 90 degrees, and, al-though the width varies between3,5 and 23 m, it is fairly consistent at14 to 16 m over the proven strikelength of approximately 500 m. Theorebody has been proven to a depthof 360 m. Exploration is continuingeastwards and westwards, and alsodown dip.

This tabular, steeply dipping ore-body lends itself ideally to longi-tudinal sub-level stoping methods.The ore itself consists of conglom-erates and quartzites, the principalminerals being borniteand chal-copyrite, with lesser quantities ofpyrite and galena.

LabourThe total labour force at Oamites

is 480, consisting of 50 Europeans,80 Basters, and 350 Ovambos. Actualmining employs about half thelabour force, the remainder beingemployed in the Concentrator, En-gineering, Technical, and Adminis-tration departments. Local policyis to train as many of the localBaster population as possible up tosupervisory positions; to date, six

Basters have been awarded specialBlasting Certificates.

Development and Mine LayoutThe main hoisting decline was

driven at an inclination of 14degrees below horizontal on thehangingwall side of the ore body for ahorizontal distance of 850 m at5,5 m by 2,7 m, using ST5B Scoop-trams for lashing. The decline wasdriven at this dimension in order toaccommodate a 36 in conveyor-beltsystem and afford traffic facilities forScooptrams, Landrovers, and othervehicles. (See Photo A.)

Between 8 level and 18 level (80and 180 m below surface), crosscutswere driven from the shaft at

. vertical intervals of 25 m to inter:-sect the orebody.Fromthe..cross-cuts, sub-drives wj:Jre driven east-wards and westwards in ore to thelimits of the present proven strikelength. At thj:Jse limits, the sub-drives were connected by means of aram ping system to afford accesswhen retreating from stoping faces.

Along the proven strike length,the ore body is divided into stopingpanels of 50 m in length with 15 mrib pillars between every two panels.The rib pillars will be recovered at alater stage (Fig. 1).

The present extraction level is18 level (Photo B), and a haulage

JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY

Photo A-Oamltes Mine showln, conveying system at the top of the Main Decline

AUGUST 197339

a:«..J..J

ii

u::«..J..J

ii:mit 17 STOPE

a;«..J..J

a-mit

a;«..J..Ja-m ---it; 20 STOPE

SLOT RIIISE"'.

:PREPARATION FOR

;: MINING OF 20 STOP

FIG.'

TRANSVERSE SECTION SHOWING METHOD OF MINING

was driven in the hangingwall parall-el to the 18 sub-drives and con-nected by drawpoint crosscuts exca-vated to accommodate Wagner ST5BScooptrams (Fig. 2).

The primary jaw crusher is situ-ated on 20 level and is connected tothe tramming level by means of afinger raise orepass system.

The crusher discharges via araise onto a 36 in conveyor runningfrom 22 level to the surface.

StopingA typical stope is mined as follows.From the sub-drives, and ad-

jacent to the rib pillars, slot cross-cuts are driven northwards andsouthwards to the hangingwall andfootwall limits of the ore body. Aslot raise is driven from 18 level to10 m above 8 level to connect thecrosscuts on the hangingwall side.

Longhole drilling then commences,utilizing 21 in diameter up anddown holes. The length of up anddown holes has been varied but itappears that the optimum is 15 mup and 10 m down. The slot is cutcompletely from 18 level to above8 level by means of vertical paralleldrilling breaking into the slot raise.

When the slot is complete, 18 levelis completely undercut by means ofconventional ring drilling. On thislevel, a half-cone is formed, leavingas far as practicable the lower-grade ore on the footwall side (Fig. 3).

When blasting of 18 level is com-

40 AUGUST 1973

. suB DRIVE

15 5U. DRIVE

,. SUB DRIVE

plete, the stope is mined out byring blasting (Fig. 1). Rings aredrilled with a strike burden of1,7 m and a maximum toe spacingof 2,4 m. Gardner Denver CH123and CH99 drifters are in use with1 m by 1 in hex. extension equip-ment and 21 in tungsten carbidecross-bits. Blasting has been carriedout conventionally to date with45 by 560 mm gelignite, initiated byCordtex and Milli Second Electricdetonators. However, Anfex is slow-ly being introduced into stoping andwill be extended to developmentshortly.

Tramming with Trackless EquipmentScooptrams are used for all tram-

ming and development lashing. On18 level extraction haulage, theaverage tramming distance is 200 m.There is a fleet of six Scooptramsand, of these, three are used on athree-shift basis to tram 45 000tonnes of ore per month. However,with the recent changeover to con-crete roadways, it is possible that atwo-shift system may be introduced.Another Scoop tram is fully em-ployed on development lashing, oneis continuously on major overhaul,and one is on standby.

Routine maintenance and repairsare carried out in an undergroundworkshop on the tramming level,Scooptrams coming to the surface

Photo I-Oamites Mine, concreted haulale at 18 level


DRAW POINTS

STOPE

only for major overhauls.The Scooptrams used at Oamites

are the Wagner Model ST-5B typeof 5 yd3 capacity. A Scooptram is adual-purpose machine designed toload in the manner of a front-endloader and to then transport ortram the load over a distance. Themachine thus performs the twofunctions of a conventional loaderand truck. The Wagner Scooptram ispowered by a Deutz air-cooled en-gine noted for its relatively cleanexhaust characteristics. The chassisis of the articulated type mounted onfour pneumatic-tyred wheels. Driveis applied front and rear to all fourwheels through Clark torque con-verter and full power-shift trans-

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Fig. 3

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Fig. 2

mission. The design and geometryof the bucket actuation and controlprovides for a powerful crowdingaction into the load pile in con-junction with the drive from thewheels, together with full tilt intothe horizontal position to facilitatetrucking or tramming over a distancewith a full bucket. The machines arepurpose-designed for undergroundmining operations, and are ex-ceptionally low and narrow in pro-file so that they can operate inconditions of restricted headroomand space.

These machines are of very ruggedconstruction and have performedsatisfactorily. The two initial ma-chines are still working and haveboth completed 25 000 hours. Twoother Scooptrams have completed15 000 hours. Some of the modifi-cations carried out to the machinesto enhance safety and improveoperatioQs are listed below.(1) Initially the machines were

equipped with water scrubbers.These were found to be trouble-some, and all machines now.employ either oxy-catalyst scrub-

bers or fume diluters.(2) Transfer of batteries to old

water-box area. (Batteries other-wise are directly under the oil-filler cap, and oil is spilt ontothem.)

(3) All filters were removed fromunder the machine for easieraccess.

(4) Dry air cleaners were fitted inplace of the oil type (far sup-erior under operating conditions).


STOPE.0:

(5) The front cutting edges of thebucket were replaced with thetype that will take bolt-oncutting edges (4 edges cost R280as against R800, and can be re-placed in two hours as againstfive days for the welding of theold type of cutting edge).

(6) The machines are fitted withdual-service brakes, an emer-gency brake system, and aparking brake.(a) The service brake comprises

an air over hydraulic system(Bendix-Westinghouse) ap-plied front and rear (dual) toall four wheels.

(b) The emergency brake systemprovides for the automaticapplication of the servicebrakes and the parking brakeshould a failure in the airsystem occur. Such a failureresults in a pressure drop inthe auxiliary air receiver con-trolling the brakes, whichare then immediately ap-plied. Tests are being carriedout on additional emergencysystems to provide for theautomatic application of theservice brakes in the event ofengine failure or overspeed.

(c) The parking brake is a disctype that is applied to themain driveline connectingthe front and rear axles.

(7) The later-model machines arefitted with a non-spin different-ial on the front axle. This

AUGUST 1973 41

system imsutes that front andrear drive iR maintained in awheel spin as long as one wheelin the front is turning, in contrastwith the conventional differentialwhere, if two wheels front orrear spin, the drive to the othertwo is lost.

One of the primary considerationsin trackless mining is the conditionof the road surfaces. If the surface isuneven, tramming is slow and themaintenance cost is high. This shouldbe borne in mind when developing,where lifters should be drilled togive an even grade. At Oamites,long development ends are surfacedwith 1 in and 2 in gravel or crushedstone, this being maintained towithin 15 m of the face and gradedregularly. Gravel is not satisfactoryfor ore tramming from drawpoints,because of the continuous gradingrequired, and in this case concrete isused. Tests are being carried out onthe optimum mix of concrete andthe method of placing. The con-crete roads have improved Scoop-tyre life from an average of 900hours to an average of 1600 hours,with a best-ever of 1835 hours. Thislife has been achieved with standarddeeptread XT8 Goodyear tyres. Themine is in the process of changingthe bucket end tyres to DunlopSuper Deep Smooth, the so-calJed'semi-slick' or 5:1 ratio ,tyre. Thedesign of this type of tyre iR acompromise effort to achieve theobvious advantages of extra lifefrom the greater proportion ofrubber that is evident with thetreadless or 'slick' type of tyre, andat the same time to retain sometread or lugs for the purposes ofefficient traction and braking. Alife of 2500 hours is expected. Tyresare filled with 80 per cent water and20 per cent air by volume. This in-creases tyre life through improvedtraction due to the weight of thewater. Another less important ad-vantage of using water is thatpunctures soon become visibly ap-parent.

To accommodate Scooptrams,haulages are driven at 4 m by 3 mwith arched backs, and sub-drivesat 4 by 2,5 m with a rectangularsection.

All ramps are driven downgradesince driving upgrade presents diffi-culties in lashing with Scooptrams.

42 AUGUST 1973

'I"he weight of the vehicle has to beovercome, and bucket penetrationinto the muck pile is poor. Tractionis also poor, causing excessive wheel-spin and tyre wear. Ramps aredriven at 1 in 4, and are used onlyfor access and materials transport.Lately, the inclination has been re-duced to 1 in 5.

All Scooptram drivers areOvambos who undergo a two-monthtraining course before qualifying.Standby drivers are being con-tinually trained and travel on the

Scooptrams during production. Turn-over of Scoop drivers is very Iowbecause of high incentive pay andhigh job status, which gives thempride in their jobs.

The maintenance staff consist of awell-qualified Scooptram Foreman,with two European and three BasteI'mechanics. Preventive mainten-ance schedules are shown in Sched-ules I to Ill. Staff are encouraged totake part in practical courses tokeep abreast of new Scooptram de-velopments.

SCHEDULE I

DAILY MAINTENANCE OF WAGNER SCOOPTRAM 2-520

Frequency:Target Time:Oil:

Daily

1 hour Carrie,d out by: Scoop Fitter

Check engine oil level. 4dd if necessary

Check engine oil pressure

Check converter and governor oil levels. Add if necessary

Check transmission oil pressure

Check hydraulic oil level. Add if necessary

Check for hydraulic leaks. Repair if any

Check footbrake, handbrake, and emergency brake

Check brake fluid in master cylinder

Check tyres for wear and damage

Check tyre pressure

Clean aircleaner oil bath or blowout aircleaner element

Check battery water

Check lights

Check ammeter for charging

Drain oil from air receivers

Check for air leaks. Repair if any

Check alternator and compressor V-belt tension

Check exhaust system for leaks. Repair if any

Check bucket boom for possible cracksFlange bearing

Steering cylinder pins

Dump cylinder pins

Boom to bogie pins

Boom to bucket pins

Hoist cylinder pins

Stabilizer-arm bucket pins

Hinge pins

Seat suspension

Oscillating axle

Hydraulic:

Brakes:

Tyres:

Aircleaner:

Batteries:

A ir Receivers:

Grease:

Signed : """"""""""""""

Scoop FitterDate:

" :.;.............................................

Signed : """"

Foreman


SCHEDULE IIWEEKLY MAINTENANCE OF WAGNER SCOOP'l'RAM 2.-52£>,

Frequency: WeeklyTarget Time: 10 hours

Clean scoopCheck all items on Daily Maintenance ChartChange engine oilChange engine filter (1)Check oil level in injection pump and governorClean oil fine filterbody and change cartridgeClean pre-cleaner on fuel filterChange fuel filters (2)Change airfilter in highpressure lineCheck air pipes for leaks. Repair if anyClean out transmission oil coolers (2)Change transmission oil filters (2)Check transmission pipes for scuffing. Replace if necessaryChange hydraulic oil filterCheck hydraulic hoses for scuffing. Replace if necessaryCheck differential and planetary gears oil levelCheck engine mounting bolts for tightnessClean cooling finsRemove engine covers, clean out cylinder finsGrease universal jointsTighten universal joint boltsCheck brake adjustmentCheck bucket lip for wear

Carried out by: Scoop, Fitter

Signed :..." , , , ".."....................................

Scoop FitterDate: ,..................................

Signed : , ,..,.., ,.., , ,.......

Foreman

SCHEDULE IIISIX-WEEKLY MAINTENANCE OF WAGNER SCOOPTRAM 2-520

Frequency: 6 WeeklyTarget Time: 18 hours Carried out by: Scoop Fitter

Check all items on Weekly Maintenance ChartCheck valve clearanceAfter valve setting take compression testClean wire gauze in breather pipeClean radial-fin oil filterCheck injectorsRemove and clean starterRemove and clean alternatorClean brass filtersClean magnetic filter in hydraulic tankChange bucket wear caps

Signed : ,.., ,..,..,.., , ,.., ,...

Scoop FitterDate:..., ".." ,..................

Signed : , ,..,..,..., ,..,..,..".....,Foreman


At Oamites, great emphasis isplaced on operation and mainten-ance of Scooptrams in an effort toreach optimum Scooptram perform-ance. In addition to a preventivemaintenance system, there is a goodbackup service from the agents inWindhoek, Messrs Hubert Davies,who, apart from normal after~salesservice, carry out 15 000 hour over-hauls in their Windhoek workshops.

The average tramming distanceon 18-level haulage is 200 m. Thecost of tramming is 35 cents pertonne of ore, broken down asfollows:

Cents pe,rtonne

Fuel and oil. . . . .Tyres. . . . . . . .Labour (including

maintenance)Spares

76

1111

Total cost . . . . . . 35

Crushing and Hoisting

The primary crusher is located on20 level, approximately 20 m belowthe tramming level. Ore is crushedto minus 6 in and discharges via avIbratory feeder onto the conveyorsystem on 22-level horizon. The 36 inconveyor belt transports the ore tosurface in three stages, having twointermediate transfer stations. Aweightometer at the shaft bottomrecords tonnage and is used tocontrol the feed rate onto the con-veyor belt.

Conclusions

Once there is a territorial nucleusof trained operational and mainten-ane~ personnel for heavy L.H.D.equipment, it is suggested that atrackless decline system of op~ningup the majority of shallow' andmedium-depth prospects would be anoptimum solutIOn, giving good capi-tal return and reducing infrastruct-ure costs.

Trackless mining provides. a veryefficient mining method for certaintypes of orebody, and reduces labourcosts and labour dependability.

AUGUST 1973 43

2. TRACKLESS DRA W-POINT LOADING AT

NCHANGA CONSOLI-DATED COPPER MINES

LIMITED, ROKANADIVISION

by J. P. RAISIN*

IntroductionRokana Division is the largest

underground producer of the threeCopperbelt mining operations withinthe N.C.C.M. Group. The minetownship of Rokana is part ofKitwe, which is the second largestcity in Zambia. Ore productionfrom underground sources at Ro-kana averages about 440000 tonnesper month at a mill head grade ofabout 1,70 per cent copper.

The three underground mines atRokana are situated on the easternlimb of the Nkana Syncline. SouthOrebody Shaft and Central Shaftextract ore from the southern sect-ion of the orebody, which extendsnorthwards from the outcrop of thesyncline over a strike length ofapproximately 19 000 ft. The ore-body continues north but is poorlymineralized for about 4000 ft. Min-dola Mine (northern section of theorebody) extends northwards fromthis 'Barren Gap' for a strike lengthof about 14 000 ft (Fig. 1).

In general, the orebody rangesfrom 10 to 40 ft in thickness, anddips westwards at about 50 degrees.Large folding systems in the south-ern section of the orebody oftenproduce extremely thick synclinesand anticlines. The northern sectionis relatively tabular and rangesfrom about 20 ft true width at adip of 40 degrees in the far north, toa thickness of 30 to 35 ft at 70 to 80degrees in the south.

Stoping M ethndThe principal method of mining

used at Rokana is sub-level stoping.Main haulages are mined at verticalintervals of 260 ft, and sub-leveldrilling drives are mined close tothe hangingwall at vertical intervalsof approximately 50 ft. Cut-outcrosscuts, which delineate each stopeblock, are driven to the orebodyfootwall, and a. cut-out raise (slotraise) intersects each of these cross-cuts over the full dip length of the

"Underground Manager, Rokana Division

44 AUGUST 1973

stope. Each stope has a strike lengthof 30 ft, and its rib pillar has thesame dimension. Extraction andsizing of ore takes place in twogrizzly crosscuts, which are minedfrom a drive situated approximately30 ft true width from geologicalfootwall and 70 ft above the footwallextraction haulage. Where poorground conditions preclude the min-ing of orebody drill drives, sub-leveldevelopment is carried approxi-mately 30 ft true width above assayhangingwall.

Application of Trackless Draw-pointLoading

Trackless draw-point loading as ameans of production at Rokana hastaken three basic forms.(1) Draw-point loading from an

intermediate level, in conjunct-ion with conventional grizzlieson the lower extraction level.This split back method aims atcomplementing grizzly product-ion in order to improve re-covery and is in operation atMindola Shaft.

(2) Draw-point loading in fold areas.Severe folding in certain areasat Central Shaft and South Ore-body Shaft leaves a relativelythick but flat dipping synolinebetween two conventional 'grav-ity' limbs. Immediate footwallground conditions in the synclinearea are extremely poor, andare unsuitable for grizzly, box-raise, and collection-haulage de-velopment. For this reason, dieselload-haul-dump machines areused to transport ore to the con-ventional limb raises and haul-ages that have been developed inthe more competent, uncontortedfootwall.

(3) Extraction of wlde orebodles.Orebody thICknesses in excess of100 ft are being encountered inthe steeply dipping 10wer sect-ions at South Orebody Shaft,and, in view of poor ground con-ditions in the orebody andhangingwall, it lS apparent thata conventional sub-level stopingsystem as practised at Rokanahas severe limItations.

Although this new system hasnot yet been implemented, it isintended to extrart the orebodyby means of a footwall stope andhangingwall stope, leaving an

intermediate strike pillar thatwill eventually be wrecked intoboth these stopes. Extractionfrom the footwall stope will bethrough the conventional grizz-lies, and loaders will be used toextract the hangingwall stope,carrying ore back to footwallhaulage boxes. As opposed tothe split-back system, which alsoutilizes both loader crosscuts andgrizzlies, both extraction pointsin this method are on the sameelevation.

Since the method is only nowemerging from the design stage,it is not intended to describe itin this discussion, and the follow-ing description will thus be re-stricted to the draw-point load-ing system that is currently inoperation at Mindola Shaft.

The Introduction of Split-back Stopingat Mindola Shaft

Mindola is the largest of theunderground mines at Rokana, aver-age production over recent yearsbeing about 270 000 tonnes permonth at 1,9 per cent copper and0,14 per cent cobalt. Production atpresent is from twelve stope faces,but approximately 60 per cent of thetotal output comes from the sixfaces in the sub-vertical shaft sys-tem, each of these producing be-tween 25 000 and 30 000 tonnes permonth.

Ground conditions vary consider-ably on strike, but, basically, faceson the southern retreat are stopedfrom orebody development, while onthe northern retreat most sub-development is in the waste hanging-wall. It was in these waste drivesbetween the 3140 and 3920 ft levelsthat trackless-loader lashing of sub-level development was introduced in1968/69.

Access to the sub-levels is madefrom a spiral connecting the upperand lower haulages. The first spiralwas mined in the hangingwall waste,which was considered to be the mostcompeteut ground, but all subse-quent spirals have been mined in thefootwall since this has the addedadvantage of maintaining a perman-ent access between levels. Muchexperience has been gained at Min-dola in the mining of inclinedaccesses. The first spiral was minedwith long inclined straights and


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flat curves in order to offset anysurvey and mining difficulties and tofacilitate the easier breaking awayof intermediate levels. Subsequentspirals of a similar design but withinclined curves were mined withoutdifficulty, and this led to the presentcorkscrew spiral layout (Fig. 2). An

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interesting feature here is that theoverall mining footage is a spiral, andits associated development hasbeen reduced from about 3400 ft inthe initial spiral to about 2500 ft inthe present layouts.

The average ore tonnage con-tained in each stope and its as-

sociated pillars is about 50000tonnes.

Recovery* from the high-pro-duction sub-vertical area has beenabout 65 to 70 per cent, the main

"'Extracted tonnes of copper- X 100%

Block tonnes of copper

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Fig. 2-lnclined accesses at Mindola Mine

JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY AUGUST 1973 45

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reasons for dilution being as follows:(a) failure ofrib pillars,(b) failure of hangingwall,(0) loss of rib-pillar remnants, and(d) over-riding of waste to the

grizzly level soon after theblasting of the crown pillar(this over-riding of waste in-creases as dips decrease from thevertical).

In an effort to improve recoveries,it was decided in 1969 to introduce aform of split- back stoping usingtrackless equipment loading fromfootwall draw-points that were minedfrom an intermediate level. Thiswould allow recovery of ore from thefootwall of the stope, which hadpreviously been 'lost' as soon ascrown-pillar waste over-rode to thegrizzly level (Fig. 3). In addition tothis, it was hoped that the effects ofhangingwall and rib-pillar deterio-ration would be minimized by thespeeding~up ()fextraction of eachblock.

Because the development faces inthe sub~vertical sections at Mindolaare usually carried between eighteenmonths and two years ahead of theproduction face, all attempts so farat the introduction of draw-pointloading production have had theadvantage of being compatible with,but not affecting, conventional sub-level stoping methods.

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46 AUGUST 1973

Fig. 4-A loader drive connecting the access crosscuts, Mindola Mine


tnitiai attempts at split-back pro-duction had only limited success.The reasons for this were as follows:

(1) Poor ground conditions. Thefootwall loader drive was lo-cated too close to the orebody,and, although conditions weregood at first, rapid deteriorationof the hangingwall side of thedrive occurred about 200 ftahead of the stope face, whichnecessitated heavy support ofthe drive and loader crosscuts.

(2) Poor ventilation. Many of thedraw-point crosscuts holed theexisting cut-out crosscut~, anduse was made of this to connectthe draw-point ventilation sys-tem with the conventionalsection ventilation. This hadadverse effects on both systems,and the experiment was even-tually discontinued. However,experience gained here was usedin the development of the presentmethod.

The Present Application of Split-backStoping at Mindola

Access crosscuts are driven fromthe intermediate draw-point levelinto the footwall at 250 ft intervalson strike. At a position approxi-mately 80 ft from footwaH (thisposition being determined by select-ion of the most suitable miningground from visual inspection ofthe crosscuts), a loader drive con-necting the access crosscuts is minedin the foot wall argiUite (Fig. 4).Raises with a diameter of 6 ft arebored from the loader drive to boxpositions in the lower haulage at250 ft intervals on strike. The raisesare also connected into the lowerwater drive (ventilation returndrive). Three raises are in use at anyone time as intake, tip, and return.Draw-point crosscuts are mined at30 ft strike interval from the loaderdrive to the orebody footwall, and aventilation drive is mined about20 ft from foot wall connecting eachdraw-point crosscut.

During the initial experiment, achamber drive was mined in theorebody above the draw-point ele-vation to define an intermediatecrown piUar and to facilitate possibleindependent extraction of the upper

and iower sectIons of the spIlt-backstope. This was unsuccessful, andwas discontinued for the followingreasons.

(1) The draw-point connecting theloader crosscuts to the inter-mediate chamber drive sloughedbadly along strike, causing thecollapse of the chamber driveinto draw-points.

(2) Extraction of the lower 'mini'stope through two conventionalgrizzlies was much quicker thanthe draw-point extraction of theupper stope. This initially createda remnant area in the uppersoction, and the excessive press-ures that were evident in theintermediate crown pillar re-sulted in closure of holes anddifficult driUing conditions.

In view of this, no development iscarried into the ore body from thepresent loader crosscuts, and thusthey are non-productive until suchtime as conventional stope blastingpasses above their elevation. Thishas not been a problem from theproduction point of view, since atMindola two adjacent stopes arealways on draw and a state is alwaysreached where production is con-tinuous from successive draw-points.

To date, extraction from the draw-points has been of the order of12 000 to 15 000 tonnes per month,and the recoveries from stopes haveincreased by between 10 and 15 percent.

Production from the draw-pointsis by means of 2 yd3 loaders (WagnerST2B), the norm being two operatingloaders and one back-up loader perproduction area. Wagner ST5A load-ers (5 yd3 capacity) were tried atone stage, but the size of excavationrequired for these loaders, particu-larly at junctions of crosscuts,caused many support problems. Inthe initial experiment, what ap-peared to be reasonably strongargiIlite deteriorated rapidly alongcross-joint planes, and eventually,intensive steel support was re-quired in the loader drive and at thecrosscut junctions.

Moving the drive further into thefootwall and reducing its size largelyeliminated these problems.


Within the limits of its design,the present method of split-backstoping appears to be workingreasonably well, but the full econ-omic appraisal, which offsets thebenefits of increased recovery againstthe cost of the entire intermediate-level operation, can be undertakenonly when several stopes have beenextracted by this method. Only thencan a firm decision be made on theviability of the method.

Distribution, Maintenance, and Oper-ation of Loaders

Wagner ST5A loaders were ini-tially introduced at Mindola aslarge-capacity machines to be usedin a cut-and-fill experiment. A com-parison with other makes of loadersindicated that the Wagner wassimpler to operate and maintain,and was more suited to workingconditions at Mindola.

The subsequent failure of thecut-and-fiH experiment left theST5A's available for draw-pointproduction, but, after tests, it wasdecided that the size of excavationrequired for successful operation ofthese loaders was too large. Alimited use has been found for thesemachines in some of the footwaHdrawpoints at South Ore body Shaft,but it is probable that they will bereplaced with 2B loaders as theybecome uneconomic to operate. Ma-chines of 2 yd3 capacity were laterintroduced at Mindola for sub-development lashing, and, as withthe 5 yd3 loaders, it was felt thatthe Wagners were mechanicallysimpler and more robust than theother types of loaders tested, andhad a profile that was better suitedto Mindola conditions.

In an attempt to reduce develop-ment sizes, a 1 yd3 loader (WagnerH.S.T.l) was purchased, but manyproblems were experienced with thetransmission and hydraulic systems,and the tramming speed of theloader was limited by its high centreof gravity. The need for a 1 yd3loader still exists, but it is felt atRokana that a suitable low-profilemachine of this capacity has notyet been developed for use under-ground.

The present diesel loader fleet atRokana is distributed as follows:

AUGUST 1973 47

Mindola ShaftCentral ShaftSouth Orebody Shaft

Wagner 2B

19148

The term 'service vehicle' in thistable is a misnomer, since the vehiclesreferred to are Benford transporters.These are used mainly for trans-porting explosives and small miningequipment, and do not specificallyenter into any function concernedwith maintenance of the diesel-loader fleet.

The trackless transport of rock orpersonnel over long distances is notpractised at Rokana, since all mech-anized sections have been minedfrom long-established haulages thatare furnished with standard rail-track equipment. Thus, once aloader is delivered to a section, itoperates within the geographicallimits of that section until it isrequired to be brought to surface formajor overhaul or replacement.

Every area where loaders operateat Rokana has its own workshop,and all maintenance on loaders iscarried out underground as follows:

Daily service (duration about 2hours)

lOO-hour service (duration about3 to 4 hours)

200-hour service (duration about4 to 6 hours)

600-hour service (duration about8 to 10 hours)

1200-hour service (usually under-taken over a week-end)

2400-hour service (usually under-taken over a week-end).

After 6000 hours, all units are sentto surface for overhaul, and it isanticipated that units will be writtenoff after 15000 hours.

No overhauls of components arecarried out underground. All de-fective or suspect components arechanged and sent to the CentralMechanization Workshop, wherethere are comprehensive facilities forthe overhaul of all loader partsexcept electrical components, whichare repaired under contract.

The total labour force employedto maintain the loader fleet averages2,9 men per machine (excludingservice vehicles). This includes allcategories from Cleaner to the ShaftMechanization Engineer. Skilled ex-patriate Heavy-vehicle Artisans are

48 AUGUST 1973

2A

300

Service vehicles5A

102

8

2

2

generally recruited from Britain andaccount for approximately 20 percent of the labour force.

Suitably qualified Zambians areselected after induction for trainingas Mechanics. After a three-monthperiod in the Mechanic TrainingSchool (which includes both theo-retical and bench work), the traineesreturn to operating sections forpractical experience. Further train-ing depends entirely on an 'on thejob' assessment from their ArtisanForeman. It is possible under thisscheme, by a series of alternatepractical and theoretical trainingperiods, for a Zambian to rise toLeading Mechanic level; the mini-mum period is 186 weeks. If theyhave attained suitable academicqualifications, Leading Mechanicscan proceed to Artisan level andthence to Foreman level through thenormal channels of progression.

For higher-educated Zambians, amore-advanced training scheme ex-ists through the Government-spon-sored Trades Training Institutes.This is an accelerated apprentice-ship course, and its objective is toproduce a qualified artisan in theminimum period of 3t years. Thisincludes a diagnostic period of 6months (to determine the candi-date's suitable trade), followed by2 years of concentrated practicaland theoretical trade training, and aminimum of 1 year's 'on the job'experience. These men can alsoprogress to Foreman level.

Loader drivers are trained in theTraining School at South OrebodyShaft. The course covers all types ofloaders in use at Rokana and lastsfor two months. It is now a pre-requisite that employees starting thecourse have a blasting licence.

At Central and South OrebodyShafts, loaders are widely distrib-uted, with the result that someloaders in isolated areas cannot beused to their full capacity and pro-vision of adequate back-up loadersis not always possible. This situ-ation will obviously improve as de-velopment in these sections expandsand production is started. The

loader sections at Mindola are local-

ized and have the added advantageof being interconnected by footwallspirals. Because of this, close super-

vision is possible, and effectivedistribution can provide each loaderwith a regular, even work load. Theback-up requirement is also con-siderably reduced in this case.

Ventilation Aspects

Zambian Mining Regulation 913states:

The Manager of any mine in which anyself propelled diesel unit runs, shall bysystematic sampling ensure that no suchunit runs underground(a) if the exhaust gases of the engine are

found to contain more than 0.2 %by volume of carbon monoxide or0.1 % by volume of oxides of nitrogen.

(b) if the engine has any defect which maycause danger to persons.

For general purposes, MiningRegulation 902 (2) describes themaximum allowable concentrationsof noxious gases in the general bodyof the air as follows:

Parts perGas MillionCarbon Dioxide 7500Carbon Monoxide 100Nitrous Fumes 10Sulphur Dioxide 20Hydrogen Sulphide 20

At Rokana, samples are takenmonthly in all places where loadersoperate, and these concentrationshave not been exceeded in more than1 per cent of all the samples taken.For this reason, more attention ispaid to combating the problemsassociated with heat in undergrounddiesel-loader operation at Rokana.

Rokana has an unusually highgeothermic gradient (about 1°F per103 ft of depth), and virgin-rocktemperatures (VRT) on the 3920 ftlevel at Mindola have been meas-ured at 114°F (about 45°C). Mostof the loaders at the mine operate inareas where the VRT is about110°F (43,3°C).

In addition to this, rock-skintemperatures can rise by a further6 or 7 of (up to 4 °C), even in well-

ventilated ends or draw-points whereloaders operate. In order to definethe upper limit of working con-ditions, it is now stated at Rokanathat work must stop in any areawhere the wet-bulb temperatureexceeds 87,5 of. Because tempera-tures below this are difficult andexpensive to maintain by con-ventional ventilation and refriger-


RtIon methods, efforts at Rokanahave been directed towards personal,or micro-climate, cooling, which willenable loader drivers to operateeffectively in higher wet-bulb temp-eratures.

Over recent years, the followingthree aspects of micro-climate cool-ing have been considered.

(1) Refrigerated Cabs. This methodwas rejected because of thepractical difficulties involved inproviding a durable sealed cabthat would give the driver 3600vision.

(2) Vortex-tube cooled jackets. Theair supply for this type ofcooling was taken from thecompressor of the loader. How-ever, it was found'that the com-pressor was tOJ s~all to serve adual purpose, and that a largeroil-free unit would be required.The expense involved in this con-version proved prohibitive.

(3) Frozen jackets. Research under-take:1. by the South AfricanChamber of Mines HumanSciences Laboratory indicatesthat this method of micro-climate cooling might prove tobe the most effective and cheap-est, and a refrigerated room hasbeen installed on the 3660 ftlevel at Mindola. The jackets aremade with small pockets that aredesigned to spread about 10 lbof ice evenly about the body andare worn underneath an in-sulating jacket. It is anticipatedthat the jackets will be effectivefor about 4 hours. Since testingof this method of cooling istaking place only now, resultswill not be available for sometime, but the success of the ex-periment could have far-reachingimplications, since loader driversat Mindola will be required tooperate in increasingly adversetemperature conditions.

The Future Draw-point Loading atllokana

The benefits of the application ofdraw-point loading at Mindola Shafthave yet to be fully assessed. Theremust, however, be some doubts aboutthe potential success of draw-point

loadIng in any relatIvely narrow,steeply dipping area from which ahigh level of production is expected.This point of view is further empha-sized by the fact that the system asintroduced at Mindola must operatewithin the constraints of an alreadydeveloped and operating method ofproduction.

The transition from hand lashingof sub-level development to loaderlashing in the lower sections atMindola has already been made, andthe increase in size of developmentrequired to bring about this changehas permitted the introduction oflarger, independent rotation driftersfor stope drilling. To date, mech-anized sub-level development rigs atRokana have been tested but havenot yet been established success-fully. This will undoubtedly be thenext step in the mechanization pro-cess. It is therefore possible that thefuture utilization of trackless loadersat Mindola will be restricted to de-velopment lashing in fully mech-anized sections.

The application of draw-pointloading in the lower fold at CentralShaft can certainly be regarded asreasonably successful, and, whilstnot necessarily being cheaper thanconventional methods, developmentof the system could lead to pro-duction from several of the foldblocks that have previously beenleft because application of con-ventional layouts has been con-sidered to be impracticable or un-economic.

Similarly, at South Ore body Shaftit is thought that good recoveriesfrom the thick lower orebody sect-ions will be difficult to achievewithout some form of draw-pointloading.

Acknowledgements

The author wishes to thank R. G.Crisp (Divisional Engineer, RokanaDivision, N.C.C.M. Ltd) and A. R.Bell (Ventilation Engineer, RokanaDivision, N.C.C.M. Ltd) for as-sistance in the preparation of thispaper, and the Managing Director,N.C.C.M. Ltd, for permitting thepresentation of the paper.

JOURNAL OFTHE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY

~. TRIALS TO ASSESSTHE POTENTIAL OFTRACKLESS MININGIN THE GOLD MINESOF THE UNION COR-

PORATION GROUP OFCO MP ANIES

by G. MAUDE*

Introduction

It has long been realized that thelabour intensiveness of present gold-mining methods causes the industryto be vulnerable both to rapidlyincreasing unit costs as wages in-crease, and to fluctuation in pro-duction if foreign labour becomesunwilling to continue to work in thiscountry. It is essential that mech-anized methods be sought that willdecrease the demand for unskilledlabour, particularly in the morearduous occupations, and thus en-able cost inflation to be contained.

Gold mining pow> particularlydifficult mechanization problems,which stem from the hard rock, thinseams, and variable payability of thedeposits. Considering only rock-handling, small tonnages of rock perunit area are broken daily over verylarge areas and the mechanization ofloading and transporting the brokenore is a very different problem fromthat encountered in the working ofmassive open-cast deposits.

The appearance on the market ofcompact 1 yd3 rubber-tyred load-haul-dump machines aroused in-terest in that these appeared moreclosely suited to the needs of goldmines than the larger machinespreviously available. In October1970, one was purchased and put ontrial at Winkelhaak Mines, Limited,and, in April 1972, the results of thetrial were closely assessed, leadingto the conclusions expressed here.

Objectives of the Trial

It was essential to specify closelythe objectives of the trial, since theabsence of experience with thesemachines in gold mining meant thatthe trial conditions would probablybe very different from the conditionsunder which the machine wouldwork if introduced on a large scale.The objectives can be summarizedas follows:

*Union Corporation, Limited

AUGUST 1973 49

(a) to determine whether small load-haul-dump machines offer anyadvantages over conventionalgold-mining methods,

(b) to determine the probable costper ton of using L.H.D. ma-chines on a large scale,

(c) to determine at what level ofBantu wages the replacement ofBantu by L.H.D. machineswould be profitable,

(d) to determine the most suitablestope layout for these machines,and

(e) to gain experience in the mainten-ance and running problemsassociated with L.H.D. machinesunder gold-mining condition/;.

Results of the TrialThe trial provided a good basis

on which to assess the potential ofL.H.D. machines in gold mines. Thefollowing are the more importantconclusions drawn.(1) When compared with the Union

Corporation strike-track systemof mining, the introduction ofL.H.D. machines could reducethe underground Bantu comple-ment by about 7 per cent, or by350 Bantu at a mine having anunderground strength of 5000.

(2) The most probable running costper ton for loading, hauling, anddumping would be 30 cents ex-cluding the cost of the driver.

(3) The replacement of Bantu byL.H.D. machines would be profit-able at a Bantu wago and com-pound cost in excess of R4 pershift.

(4) The design of stope layouts andramps is important, and theL.H.D. machine would performmost economically in a mine orpart of a mine specifically de-signed for it, rather than in anestablished area modified to suitit.

(5) From the maintenance and run-ning point of view, it was learntthat one spare machine is re-quired for every three machinesworking. Convenient and cleanworkshops must be providedunderground, and particular at-tention must be paid to tyres ifeconomic results are to be ob-tained.

GeneralNo more than a very brief account

of the trial and its results can be

50 AUGUST 1973

given here. Much detail has beenamassed and, if any aspect of thiscontribution arouses particular in-terest, it could be dealt with morefully by corrcspondence. Here, onlybrief items of interest arising fromthe trial can be mentioned.

Stope layout

The L.H.D. test was run in atypical strike-track stope. The onlymodifications made were the con-struction of a dip L.H.D.-travellingway running parallel to the centregully, bridges laid across the centregully for tipping, and strike cuttings(carried without tracks) 2 m wide and1,9 m high at the normal 10 mspacing.

After blasting, about one-third ofthe ore blasted is scattered in theface and two-thirds lie in the cutting.The third of the blast lying in theface had to be lashed to the cutting,and this adversely affected theefficiency of the method. A smallwinch, for face scraping this scatter-ing, was tried, but no really adequatesolution was found.

Tyres

At the start of the trial, the sharpbroKen quartzite, on which the frontwheels skid during loading, causedpneumatic-tyre life to be well under100 hours. Much attention was givento this problem, and a life of 500hours, from a solid wire-reinforcedsmooth tyre (including one rebuild),can now be expected as a matter ofcourse.

Tyre chains were tried and foundto be completely unsuitable.

Drivers

Bantu drivers were used through-out, and after training performedwell. Part of the reduction of tyrecosts was due to the better treat-ment of the tyres as the drivers be-came more proficient.

Evaluation

The results of the trial wereevaluated by a Monte Carlo tech-nique, as this was considered to bethe only way of using all the ex-perience gained to influence theassessment. Probability curves ofeach independent cost factor weredrawn and discussed with the ope-rators, manufacturers, and tyre sup-pliers. The figures used in this con-tribution were derived from the 50

per cent probability estimates ofthe Monte Carlo curves.

AcknowledgementsThe trial was carried out in a

normal producing stope at Winkel.haak Mines, Limited, and it wasonly because of the interest andenthusiasm of the General Managerand his staff that the trial was ableto produce a valid assessment of theuse of an L.H.D. machine undergold-mining conditions.

Thanks are also due to the SeniorConsulting Engineer of Union Cor-poration, Limited, for permission tomake this contribution.

4. TRACKLESS MININGAT O'OKIEP COPPERCO MP ANY LIMITEDby J. B. NANGLE*, B.Sc.,

F.I.M.M. (Member)

Some 4,5 million tons have beenmined by trackless-mining methodsby the O'okiep Copper CompanyLimited since the introduction ofload-haul-dump (L.H.D.) equipmentin January 1970.

In total, O'okiep is currentlymilling 255 000 tons per month, ofwhich about 65 per cent is obtainedfrom trackless-mining sections. Thereare eight producing mines andanother five deposits in variousstages of preparation. All are under-ground operations, and the sub-levelopen stoping method is standard.

The ore reserves of individualmines vary considerably from 0,25to 8,0 million tons. Orebodies arecontained within steeply dipping,mainly dyke-like, bodies of maficrock emplaced within granitic gneiss.There is considerable variation indepth, from deposits mineablethrough adits to ore depths of up to1200 metres below surface.

In this short contribution, com-ments are confined to some particularapplications of trackless-miningmethods at O'okiep and to a sum-mary of operational features, costs,and statistics for L.H.D. equipment.

Three methods are discussedbelow.

The Direct Trucking MethodThree adit mines have been de-

*General Superintendent (Mining Opera-tions), O'okiep Copper Company Limited


Ilse borer SLo! &is".

.5GCO'p-fr..,.., .Ioa.d./nS' /J~b:J$no.i\,d P B Cfj~~

KOPERBERC! CENTRAL.. Mu~£

PLAI-I OF' 700 LEVEL AclT

SCALE 1:2.000fiG. 1.

veloped for direct trucking from thestope drawpoints to central crushingplants. The largest of these, Koper-berg Mine, had an original ore re-serve of 1,2 million tons and issituated 3,4 km from the Carolus-berg Mine complex. In this range ofreserve tonnages it has provedmore economical to truck uncrushedore to existing crushing plants, thanto install additional crushers at theoutside mines.

Exploitation

Koperberg Mine was developedusing one Wagner ST-5B and oneST-2B Scooptram. The first MainAdit development round was blast-ed on 1st March, 1970, and pro-duction commenced in December1970.

Surf""", fro/de

~~-..:"":'

~~LJ~Y.n~

:'~--

S/op£Cl ~

T3~L~ sc.ool--/'~IL./

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Figs. 1 and 2 show the sequenceof mine exploitation in plan andvertical projection. Development wascompleted in the following generalsequence.

(1) The Main Adit crosscut was de-veloped to the footwall of theore zone.

(2) The central undercut drive wasdeveloped eastwards in ore, cross-cutting to the hangingwall andfootwall of the orebody to checkthe orebody outline.

(3) The footwall extraction haulageand Scooptram drawpoints weredeveloped.

(4) The central slot raise and easternrock raise were raise bored fromthe upper to the Main Adit levels,concurrent with Alimak develop-

Old 400 AdiJ kvI!:1.

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if

V//j tlndi<nki T~~ LI!:vd c~"'pfl!:il!:If1-. e.;u;.I 0/"sfof- Mm" s.l~.I 1;, 580 .i",ve/. drill",:! otown.ov>d uf

.I""",6.35 .I",ve!

/~". Mml!: $/~f" .l"'-C£ 7"/7"'0"£';':1 ~w ds "d.. kn~TC<dI/;'J' ~ 580 c./evd/op.\;\\\ mine uflu / / 01 c..u;.le//, /'/ockIIII A'e/rc..,u We.s/e.rn .6{,Ck; in "";':1.1. I'a.ce ofaMMl.

K..oFER.6ER~ CENTRAL ~-'1iE

VE~:!:!~~~.£.~q,[gCTI2!:i.

SCALE I: 2000 fIG.2.


~

"

ment of the eastern manwayraise.

(5) An ST-2B incline ramp was de-veloped to 635 level to hole thecentral slot raise.

(6) The western end of the orebodywas developed by means of aditsub-levels on 525 and 635 ele-vations.

Stoping of the eastern and thenthe western ends of the orebodyfollowed.(a) The 700 level was undercut com-

pletely, east of the central slot.(b) The slot was mined to 580 level,

drilling down and up from 635level.

(c) The stope face was retreatedeastwards, undercutting the east-ern block at 580 elevation.

(d) The upper part of the easternblock was mined.

(e) The western block was retreatedin a single-face operation.

Complete exploitation of the minerequired 4482 m of development.The tonnage stoped per metre de-veloped was 268.

Production SystemFig. 1 is a plan of the 700 Main

Adit level showing the east andwest split of the production haulagein the footwall of the ore body.

The ore is hauled from the draw-points by a Wagner ST-5B Scoop-tram and tipped into Bedford IO-tontractor- trailer units. The main con-siderations in the choice of theIO-ton Bedford units, rather thanlarger trucks, were as follows.(1) Under the terms of labour agree-

ments, any truck with a pay-load of more than 10 tons mustbe driven by a White person.The Bedford units have Coloureddrivers.

(2) The local dealer service is excel-lent.

(3) The unit is widely used through-out the Transport Department.

The truck turning loops developedon the south side of the haulagegive short Scooptram hauls fromthe drawpoints to the truck-loadingpoints, the average haul lengthbeing about 30 m. The truck routesunderground are indicated on Fig. 1.

The movement of the trucks intoand within the mine is controlled bya series of robot lights operatedmanually by the truck drivers. Aseries of daylight to darkness lights

AUGUST 1973 51

is installed inside the adit portal toaccustom the drivers to the changein light intensity.

Various types of roadbed materialfor the Main Adit and productionhaulages have been tried. The bestresults have been obtained withminus 5 cm crushed aggregate. Theroadbeds are maintained with aroad grader adapted for under-ground use.

The length of the return haulfrom the underground loading pointsto the central tip at CarolusbergMine (Photo A) is 6,8 km.

A hydraulic pump unit is mountedat the ore tip, obviating the need fortruck-mounted hydraulics.

The average monthly productionrate is 30 000 tons, working twoeight-hour shifts. Five trucks pershift are used, one truck beingavailable as a standby. The pro-duction crew per shift consists of:

1 MinerWh '""\ Ite1 Scooptram operator l c I d.

J 0 oure5 Truck dI'lvers2 Tip attendants L

BJ antu1 LabourerThere is one spare Scooptram

operator/truck drivel' on the day-shift. In an average month of 26working days, at a production rateof 30 000 tons, an efficiency of 55tons per manshift is obtained.

The tractor/trailer combinationused is shown in Photo B. Thetractor is a Bedford KHA 70 of100 kW and tows a lO-ton articu-lated trailer manufactured to O'okiepdesign. The tractor has a wheelbaseof 2,45 m (8 ft), and the trailer is4,34 m (14 ft 3 in) long, The widthof the unit is 2,18 m (7 ft 2 in), andthe height 2,51 m (8 ft 3 in). Theheight of the trailer is 1,9 m (6 ft3 in).

The Iow profile of the trailerobviates the necessity for largeexcavations in the hangingwall forloading and also minimizes thepossibility of fouling of the trailerbody by the Scooptram bucket, Thedump cylinder assembly of L.H.D.equipment has been found to bevulnerable to such jarring.

A modification has been made tothe original layout at Jan CoetzeeSouth West Mine, where a truckingloop completely separate from theScooptram haulage has been de-veloped. Difference in elevations and

52 AUGUST 1973

Photo A-Central ore tip at Carolusberg Mine

right-angle loading make for amore efficient operation (Photo C).It also allows the use of standardBedford 10-ton rear-dump trucks,which have higher-profile bodiesthan thc O'okiep trailers.

production from the upper levelscontinued was discarded in favourof developing a Conveyor and AccessDecline Shaft from the existingcrusher level, coupled with theinstallation of an underground crush-er under the orebody. Crushed rockis conveyed to the existing shaft-loading system.

ExploitationA decline 4,9 m wide and 2,7 m

high was developed using a WagnerST-5B Scooptram, at a dip of 1 in 4from the existing crusher level of

The Conveyor Decline Method

Two alternatives existed for themining of a 273 OOO-ton orebodysituated below the bottom mainlevel of East O'okiep Sub-VerticalShaft.

Deepening of the shaft while


Photo B-Bedford KHA 70 truck

the mine for a total dip length of300 m. The arrangement of the de-velopment is shown in Fig. 3.

The extraction haulage, all draw-points, the Crusher Chamber, andPump Station were developed fromthe Decline by means of an ST-5B.The sub-levels were developed con-ventionally from a twin Alimakrock and manway raise system. Atotal of 2374 m of development wasrequired for the project.

During the development stage,while the crusher and the conveyorwere being installed, the develop-ment rock was hauled up the declineby the Scooptram. When the crusherand conveyor installation was com-pleted, all rock was handled throughthe crusher.

Production System

The ST-5B Scooptram on pro-duction, on an average haul of 40 m,hauls the ore from the stope draw-points into a small surge bin abovethe 91 cm-by-61 cm Hadfield crusher,which has a capacity of 150 tons perhour. The crushed ore is fed directonto the decline conveyor by meansof a vibratory feeder. The 0,76 m-wide conveyor has a length of 270 mand a capacity of 250 tons per hour.A short transfer conveyor at thehead of the decline conveyor de-livers the ore into the sub-verticalshaft crushed-ore bin.

The production target rate is1000 tons per day on a three-shiftbasis. The production crew per shiftconsists of:

1 MinerWhite

1 Scooptram operator l c I df 0 oure1 Crusher operator3 Labourers l B t

fan u

2 Conveyor attendants

In a month of 26 working days,at the target production rate, 42 tonsare produced per manshift.

The planned installation of closed-circuit television on the crusher/conveyor system will enable theColoured crusher operator to lookafter the whole system, therebyeliminating the need for conveyorattendants.

Ore Spiral Method

The Rietberg Mine of O'okiep hasan ore reserve of 4,0 million tons at agrade of 1,44 per cent copper. The

general position and shape of theore body make the mine eminentlysuited to exploitation by tracklessmethods.

The orebody is contained in theRietberg, which rises to a height ofabout 300 m above the general levelof the surface. This configurationpermits exploitation by means ofhorizontal and declined adits, andcomplete trackless mechanization ofdevelopment and production.

Ground conditions in both oreand country rock are good, andstope width is about 35 m. Strikelength of mineable blocks within theseparate ore lenses is approximately130 m.

Access to a considerable part ofthe lower section of the ore body wasgained by means of a main rampdeveloped in footwall waste, fromwhich mechanized development ofsub-levels was possible, and fromwhich access could be gained duringthe whole of the stoping operation.However, such conditions were notapplicable to the upper part of theorebody. Ramps developed in thefootwall would have required largefootages of waste development forrelatively small tonnages of ore.Further, Rietberg Mine is situatedin the Steinkopf Coloured Reserve,and Coloured persons make up thecomplete hourly-paid work force ofthe Mining Department. Such labouris, in total, considerably more ex-pensive than the traditional White/Bantu combination, and harbours astrong resistance to the physical


Photo C-Loading at Jan Coetzee South West Mine

AUGUST 1973 53

effort involved in traditional sub-level development methods.

The Ore Spiral Method resultedfrom these considerations, and is anattempt to mechanize developmentwhile at the same time avoiding theprohibitive cost of waste ramp de-velopment in areas of small orereserve tonnages. It is illustrated inFig. 4.

Development was by means of anHST-l and an ST-2B Scooptram,with sub-levels at 15 m intervals. Thesub-level development end spiralsdownwards on the ore contactsholing alternately on each sub-levelelevation, to a 1,22m-diameterraise-bored slot raise, or a 1,52 m-diameter raise-bored manway.

Drifting in the direction of theslot is done at an upgrade of 1,5 percent. Drifting away from the slot,towards the man way raise, is at adowngrade of 25 per cent (14 O),while slot crosscutting is on levelgrade. Sub-levels declined away fromthe slot obviate the possibility ofwater entering the stope during drill-ing operations and of persons in-advertent.1y slipping towards theopen stope.

The method has application insub-level stopes wider than about15 m, where sub-level drives on eachwall are required for efficient long-hole drilling. In narrower stopes,where one drift on either contactsuffices, use of the method results in

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Fig. 4

unnecessary duplication of develop- crews soon adapted themselves toment. working on ramps.

The 25 per cent inclination of the The following disadvantages must

ramp drives would, it is thought, be weighed against the benefit of

make the use of mechanized long- reduced waste development resulting

hole rigs difficult. Therefore, all from this method.

long-hole drilling in the two blocks(1) As soon as slotting commences,

that have used the ore spiral method access down the spiral is cut off.

has been done with Gardner DenverStope service must then be

CF-99 drifters on bar H-rigs. Rig-through the manway raise.

ging problems were expected, but(2) Use of the method in narrow

orebodies involves duplication ofdevelopment.

(3) Ramps of 25 per cent grade aremore difficult to clean after astope blast than level stopcdrives.

(4) There is no possibility of multi-end development, sub-level de-velopment being confined to asingle face throughout develop-ment of the stope block.

Cost Analysis

The costs given below are thetotal direct costs for trucks andScooptrams and are made up asfollows:

Operating Costs1. Truck-driver labour2. Fuel, lubricating oils, greases, and

tyres

Maintenance Costs1. Labour for maintenance and

major overhau1s

/490 Exha.dion hauJa.JE

flOf. "xh..dicn h.=/"';9".;.fem.d Cr't_~her

\ 5=a.l' S=f~

- bev";of ck.d/n"

- Aa',,;of ,;,.1"""",,'/ CTJ<-$her =r"?/2x

- !ie.Y...,0f """,v, /raod./"

e-,,/r~c,n h<UJ'«-:1e ""'et

- bu"/of ftU4/Id "w;"""K- ""'OM"",,!!dJld

"""'"r<use.:;

I« !ic¥dcf "',..,/ YC,d'£WM ":Isle".,.

dr~fo'n.ls on f10S ieve!

EAST O'OKIEP MINE

VER.Tt C-AL PROJECTION

ScALE 1: 2000.

54 AUGUST 1973

Fig. 3


2. SuppliesThe percentage monthly utili-

zation in a 25-day month is definedas:

Actual engine-running hours100

600X

ST-5B Scooptrams Costs, KoperbergMineCost per hour:

1973 to date. . . . . R71972 R9From inception. . . . R9

Cost per ton:1973 to date . . . . . 16cents1972 . . . . . 16 centsFrom inception 15 centsThe Koperberg ST-5B cost per

hour and cost per ton are very closeto the Company average costs forST-5B operation on production anddevelopment.

Bedford KHA 70 Trucking Costs,Koperberg Mine

Cost per Cost perton ton km

1973 to date 23 101972 . . . .

"24 11

From inception. 22 9ST-5B Costs, East O'okiep MineCost per hour-1973 to date: R8Cost per ton-1973 to date: 12cUtilization of ST-2B and ST-5B

1972 39,6 %1973 to date 43,8 %

Tyre Life

Tyre life has increased graduallysince the start of the mechanizationowing to greater care in road-bedconstruction and maintenance, andbetter operator training.

Some statistics are as follows:Scrapped-tyre life, including retreads(hours) : ST-2B ST-5B

1972 1973 1972 1973Average 423 1192 933Best 1167 2501

The best life of tyres still inservice, including retread !ife, is2866 and 3658 hours for the ST-2Band ST-5B models respectively. Con-siderable improvements in total tyrelife have been reaJized through im-proved retreading, the total avoid-ance of water in road beds, and theuse of the virgin-rock footwall asdrawpoint road beds.

List of Equipment

Wagner ST-5B . . . . . .13Wagner ST-2B . . . . . . 5Wagner HST-1 . 1

Landrover material carriers. 4Roadgrader. . . . . . . 2Further equipment is in the pro-

cess of delivery.

Safety Devices

The following safety devices, de-veloped at O'okiep, are fitted toScooptrams engaged in inclinedworking:

(1) a device that automatically ap-plies the brakes in the event ofengine failure,

(2) an overspeed device designed tocause automatic brake appli-cation at speeds in excess of10 km/h, and

(3) a first-gear transmission lock.The devices are illustrated sche-

matically in Fig. 5.A T-piece is fitted on the air-

cooler oil pipe, A, which is mountedon the right-hand side of the engine.The T-piece is connected to anadjustable pressure switch, B, setto dose its contacts at 280 kPa(normal engine oil pressure is 400kPa).

The overspeed switch, C, is mount-

Iq" SV{. MainSw.

F

c

ed on the propeller shaft and drivenby means of pulleys and a V-belt.It is set to close at a propeller-shaftspeed equivalent to a speed of10 km/h. The solenoid, D, is fittedunderneath the emergency brakevalve, E. When the solenoid isenergized, it moves the emergencybrake valve to the 'ON' position,which in turn actuates the brakes.

The overspeed device can beswitched out when speeds higherthan 10 km/h are safe. This is doneby means of the switch F. To use theoverspeed device, a machine must belocked in first gear. A light, G, isinstalled on the instrument panel toindicate whether the overspeed de-vice is switched in or out.

Acknowledgements

The author wishes to thank thestaff of the O'okiep Copper Com-pany Limited for their assistance inthe preparation of this contribution,and the General Manager for hispermission to present these com-ments.

""' ""....8a.flery

-

On-DIE$HtlCh..

G'

I ~~ J-ss.ue s.-i/ch.-"""'Y

cI.sui.

rr-I 11 9"" Mf~ I_~;'£

Y £'-"9---'7' "N'~ v4I .

£n.

coolu.

-


So/&",,;"'.

SA"&TY ~EVIc.&S Fo~WA<oNER. ST- 5B . ST- 2B SCOOPTfi:lto.Io\S.

Fig.5

AUGUST1973 55

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