Geology and Mining operations atPalabora Mining Company limited,Phalaborwa, N-E Transvaal

O. H. Kusehke, M.Se.* (Visitor) and M.J. H. Tonking, A.C.S.M., BA Se., (Min. Eng.) (Toronto) (Member)

SYNOPSIS

A description is given of the general geology, structure and minerals of economic significance of the Loole-kop copper orebody at Phalaborwa. The open pit mining method is described with details of drilling, blasting,loading, hauling and primary crushing operations. A brief description is given of mine planning and its relation-ship to the control of the mining operation.

INTRODUCTION

The Loolekop coppel orebody is being mined by thePalabora. Mining Company Limited by open pit methods.The orebody is situated four km. south of the townPhalaborwa in the north-eastern Transvaal, Republicof South Africa; at latitude 23 °57 'S and longitude31°WE. The distance by road from Johannesburg toPhalaborwa is 550 km. The nearest harbour is LourencoMarques, some 340 km. by rail, situated on the eastcoast of Southern Africa.

Recent archeological work seems to indicate thatancients recovered copper from the Loolekop orebodyover one thousand years ago. Before modern miningstarted many shallow workings were discovered in theorebody, indicating the areas where the ancients minedoxide ore which they smelted in small primitive claysmelters in the vicinity of the orebody.

A prospector, Carl Mauch, was the first European torecord the copper occurrence at Loolekop, while recon-naissance mapping of a portion of the Transvaal andRhodesia during the period 1868-71. However, thefirst mining calTied out by Europeans in the vicinity ofLoolekop was for phosphates in 19303, and vermiculitein 19361. The latter mineral was discovered by Mr. C. H.Cleveland, one of the pioneer prospectors of this area,who noted that large books of "rotten mica" had ex-foliated during a grass fire. The late Dr. Hans Merenskyplayed an active part in the prospecting for phosphatesand vermiculite during and following the second worldwar.

Events leading to prospecting for copper in recentyears date back to 1952 when members of the Geo-

*R.T.Z. Management Services.

**Asst. Mine Superintendent-operations

Company, Limited.Palabora Mining

logical Unit of the Atomic Energy Board discovered thepresence of uranothorianite in the carbonatite fromLoolekop. During the period 1953 to 1956 the MineralDevelopment Section of the Department of Mines, andthe Geological Unit of the Atomic Energy Board,conducted a prospecting programme which includedsome underground development and surface diamonddrilling. This prospecting established that the con-centration of radio-active minerals, as such, was of noeconomic significance, but that the presence of copperminerals could render the deposit of value.

Palabora Mining Company Limited was incorporatedon the 22nd August, 1956, for the purpose of acquiringcertain options and prospecting rights in the Loolekoparea.

During the period 1957 to 1962 this company carriedout an extensive drilling programme. One hundred andeleven BX size surface inclined boreholes were drilled,totalling nearly 41 400 m. The drilling probed the depositto a depth of 1 000 m. and demonstrated the pipelikeform and remarkable vertical continuity of rock type,sulphide mineralization, grade, and distribution of thecopper, magnetite and apatite. The drilling programmeconfirmed the existence of over 300 million t. of oreamenable to opencast extraction, from a pit with di-mensions of 1 500 m. by 900 m. on surface, and a finaldepth of 370 m. at a finished pit slope of 45 ° (Fig. 2).

In October 1960 shaft sinking started, and during theperiod June, 1961 to March, 1962 a total of 1 610 m.of development was done on the 122 m. level. The rockfrom this development was bulk sampled and used torun a 100 t. per day pilot plant.

The results obtained from these investigations formeda reliable basis for the planning of full-scale mining,milling, concentrating and smelting operations on acsale hitherto unknown in South Africa.

12 AUGUST 1971 JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY

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SECTION: 1 GEOLOGY

General

The Phalaborwa area is underlain by Archaeangranite which contains remnants of highly alteredsedimentary, basic, and schistose rock of the BasementComplex. Some twenty km. west of the copper depositis a younger porphyritic granite intrusion known as thePalabora Granite massif. It occupies an elliptical areaof roughly 30 km. in an east-west direction and 15 km.north-south.

Also intrusive into the Archaean granite is the Pala-bora Alkali Complex, the basic phase of which is anelongate pipelike intrusion with a north-south axis of8 km. and measuring 3 km. in a,n east-west direction.The alkali phase consists of numerous pluglike in-trusions of syenite into the Archaean granite.

The major pipe filling of the basic phase is a pyro-xenite consisting of a pale green diopside with varyingamounts of phlogopite and/or biotite and apatite. Sur-rounding the pyroxenite is a rim of felspathic pyro-xenite which is separated from the enveloping Archaeangranite by an irregular fenite zone.

Fig. 1

Within this major pipe two subsidiary pipes arerecognizable; a serpentine-phlogopite-pegmatoid to thenorth, and the copper-bearing deposit known as theLoolekop orebody which is situated near the centre ofthe major pipe.

Geology of the Loolekop orebody

Lombaard et 3012were able to distinguish between thefollowing rock types comprising the Loolekop orebody:

(i) Phoscorite, which is a local name for a coarsegrained to pegmatoid rock, consisting essentially ofpartially serpentinized olivine, magnetite andapatite. The relative proportions of these mainconstituents vary greatly. Bands of almost pureolivine with widths of up to 15 m. are common.Frequently a rude vertical banding effect is ap-parent, caused by the alignment of magnet,itecrystals. The accessory minerals are mica andbaddeleYlte (natural zirconia). Varying amounts ofcalcite are present.

(ii) Banded carbonatite, which is a medium-grained tocoal se-grained rock, consisting of calcite, magnetiteand dolomite, with subordinate amounts of olivine,

JOURNAL OF.THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY AUGUST 1971 13

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14 AUGUST 1971 JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY

apatite and chondrodite.The coloUl is a light-greyto dark-grey. The sub-parallel arrangement oflenses and bands of magnetite exhibits a roughbanding effect. It is possible to recognize twodistinct generations of banded carbonatite.

(iii) Transgressive carbonatite, which has the samemineral composition as the banded carbonatite. Thetexture varies from coarse to fine sugary. Thebanded orientation of magnetite, characteristic ofthe banded carbonatite, is poorly developed orabsent.

(iv) A number of Karroo dolerite dykes, trending north-east, cut the rocks of the Palabora Complex. Themaximum width is 75 m. Even where these dykescut across the carbonatites, no alteration of thewall rocks is visible.

Structure of the orebody

The structure of the Loolekop ore body is that of anannular vertical pipe. In plan (Fig. 3) the pipe is el-liptical in shape with the long axis lying in an east-westdirection. The dimensions of the pipe are 1 200 m. alongthe long axis, and 670 m. north-south. Carbonatite is thepredominant rock of the central part of the pipe, gradingoutwards into a concentric zone in which phoscoritepredominates, the latter in turn giving place to mica-ceous pyroxenite which forms the wall rock. The contactbetween the phoscorite and surrounding pyroxenite isnot sharp, but is a zone made up of discontinuous bandsof varying thickness of these two rock types.

Lombaard et 0.12expressed the opiniop that the rocksof the Loolekop orebody were formed in a pipeIikeconduit, and that the concentric pattern of the phos-corite and the banded carbonatite was the result of theemplacement of these rocks parallel to the walls of sucha pipe.

Subsequeptly, this pipe was intruded by a latergeneration of carbonatite, having a transgressive re-lationship to the ea1lier structures. Pre-existing fracturesystems controlled to a very large extent the emplace-ment of the transgrEssive carbonatite. It is thoughtthat these fractures were not due to regional tectonicfeatures, but were probably the result of diffmentialstructural conditions within the pipJ locm.

The transgressive cat bonatite forms a well-definedgeological unit, some 100 m. wide near the centre of thepipe, but fingers out at both ends into a dykelike pro-trusions. It also occurs in the eastern part of the pipeas a numb et" of fairly large crescentic bodies whichconform to the ring-like structure of the pipe. In ad-dition to the major occurrences of transgressive car-bonatite, it constitutes a multitude of discontinuoussteeply dipping veinlets, ranging in width from afraction of a centimetre to a metre, cutting the bandedcarbonatite, phoscorite, and occasionally extending intothe pyroxenite.

Minerals of economic significance

Economically, the most impmtant mineralization thatoccurred was the introduction of copper sulphides alongminute fractures within the phoscorite and the car-bonatites. The highest concentration of copper sul-

phides is found in the transgressive carbonatite. Lom.baard et 8012advanced the theory that the latter car-bonatite, which was aligned along a structurally un-stable locus, was repeatedly fractured, thus affordingabundant access for invading copper-bearing solutions.However, copper sulphides within the phoscorite fre-quently occur independently of fractures in the form ofsmall patches of massive ore. These seem to have formedby replacement of constituent minerals of phoscorite.

The primary copper sulphides, in descending order ofimportance, are chalcopyrite, bornite, cubanite, val-leriite and chalcocite.

Chalcopyrite occurs in irregular, thin, discontinuousveinlets and in coarse grains. Intergrowths of bornite-chalcopyrite are common. The carbonatites are the mostimpm tant host rocks for the chalcopyrite.

Bornite is most frequently found occurring in coarbeblebs, and is more commonly associated with phos-corite.

Cubanite generally occurs in coarse intergcowth withchalcopyrite.

Valleriite is a dull, bronze-coloured, platy, mineralwith a copper content of about twenty-three per cent.It is.soft and easily soils the fingers. It is the last of thecopper sulphide minerals to have formed, and partiallyreplaced the other sulphides as well as magnetite,carbonatite and silicate gangue.

Chalcocite, apart from occurring in bleb-like form, isfrequently found associated with bornite in graphicintergrowth.

Next in economic importance is magnetite which formabout twenty-five per cent by weight of the wholeorebody. The magnetite occurs in grains and blebs, inirregular lenses and bands of widely variable widtp,from a few centimetres to a metre. The magnetite waspresumably introduced at the same time as the otherrock-forming minerals of the carbonat,ites and phos-corite.

Titanium is present in solid solution in the magnetiteand also in the form of titanium minerals, e.g. ilmenite,ulvospinel hogbomite. The magnetite which is 0.1:'-sociated with the transgressive carbonatite, has anaverage titania-content of less than 0,5 per cent, whereasthe titania-content of magnetite in phoscorite frequentlyexceeds six per cent.

The economic phosphate mineral apatite, which con-tains a low percentage of fluorine, is present in thecarbonatites in small quantities, resulting in an averageof less than three per cent phosphorus pentoxide. In thephoscorite the overall average phosphorus pentoxideexceeds seven per cent. The apatite occurs as coarseanhedral grains and irregular veins, lenses and blebs inthe phoscorite and carbonatite.

The important ancillary heavy minerals which arepresent in minute quantities are baddeleyite and urano-thorianite. The baddeleyite, which occurs in small blackslender prismatic crystals, is mostly confined to thephoscorite. Uranothorianite is more often associatedwith the carbonatites.

JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY AUGUST 1971 15

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JOURNALOFTHESOUTHAFRICAN INSTITUTEOF MINING AND METALLURGY

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Fig. 4-Shows a general plan of the open pit workings.

General description

On the basis of present planning, the Palabora open pitoperation will result in a pit measuring I 500 m. by1 100 m. on surface, and 430 m. in depth. Finished slopewill be 450. Approximately 460 million t. of copper willhave been dug from this enormous excavation, givingan overall waste-to-ore ratio of 0,93:1.

The need to blend material from several loadingfaces (to avoid large grade fluctuations) and to segregateore types (according to the titanium concentration inmagnetite) precludes the use of very large loading units.Nearly all ore and internal waste is loaded by 3,4 and4,6 m3 shovels, whilst the one 9,2 m3 machine is devotedprimarily to overburden removal.

The pit benches run on east west axes with the mainentrance ramp on the south east side of the pit. Fromthis ramp haul roads lead to the primary crushers andthe main discard dumps.

Haul roads are designed with a maximum adversegrade of 8 per cent, and at the start of each new bencha ramp is mined down in the form of a box cut on thisgrade.

At present, ore is delivered to the crushers at theapproximate rate of 62 000 t. per day, six days a week,to feed the mill at a rate of approximately 53 000 t.per day, milling seven days a week. Five ore benchesare in operation to maintain this production.

Ore is segregated into two principal types: copper ore,associated with low titanium magnetite, and copper oreassociated with high titanium magnetite. The loading isscheduled so that each of the two primary crushersreceives only one ore type. Low titanium-bearingmagnetite ore is then kept separate throughout thecrushing and milling operation, and finally upgraded forsale.

Fig. S-An aerial photograph of the Palabora OpenPit.

MANNING STRUCTURE AND ORGANISATIONALCONTROL

Reference to Fig. 6 shows the overall manningstructure. In June 1970 a total of 497 persons wereemployed in the open pit, broken down as follows:

SalariedDay RateBantu

Operations .J\!laintenance Crushers18 1650 67 3

247 87 9

Total34

120343

Productivity for June 1970 was 259,6 t. per manshift;this included shifts worked by the Mine EngineeringDepartment, chargeable to the open pit.

On each shift there is one foreman, each with oneshovel and one truck shift boss; in addition, there is oneconstruction shift boss on day shift only. A drilling and

JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY AUGUST 1971 17

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blasting foreman works on day shift, with one blastingand one drilling shift boss. On afternoon and night shifta lead hand driller is in charge of drilling operations.

Afternoon and night shifts are of 8 hours duration,whilst the day shift is 7 hours 40 minutes to allow20 minutes for blasting. Change of shift takes place"on the job" except at the end of day shift. Shift fore-men receive loading and other instructions in a ShiftLog Book; continuity between shifts is maintained inthis way.

InstJ;uction and training of drivers and machineoperators takes place on day shift under an instructionshift.boss assisted by one Bantu instructor.

There is an open pit safety officer, assisted by oneBantu safety instructor. The five-point Quebeo SafetySystem is practised in addition to a Safety AwardScheme.

Communication is by two-way radio between all pitvehicles, and there is a centrally situated observationtower that is manned on each shift by one of the operat-ing officials. The observation tower is also in contactwith the shovels on a separate radio frequency. Thisallows the operating official to control haul truck move-ments, verify and report breakdowns and to order anynecessary shovel moves.

An open pit fire engine, mounted on a II t. L.D.V.,is kept at all times at the Observation Tower. In theevent of a fire, it is immediately taken to the spot bythe official on duty. All pit personnel are trained inits use.

Mine Engineering Services, Le.sampling and long-range planning,required.

geology, survey,are provided as

Drilling

Blast holes are laid out by surveyors, subject tomodification by the Drilling and Blasting Foremen.Various patterns are used depending upon the rockformation to be drilled. In general, three row shots arelaid out along the east-west axis of the pit, Le. parallel

18 AUGUST 1971

to the bench axis. Holes are sub-drilled to a depth of2,13 m. below the 12,2 m. benches. The soft weatheredrock and fresh dolerite dykes are usually drilled ver-tically, whilst in the hard ore body they are drilled at 150rock and fresh dolerite dykes are usually drilled ver-tically, whilst in the hard orebody they are drilled at 150

JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY

Fig. 7-Bucyrus-Erie 6O-R Rotary Drill.

m/shiftBit LifeAverage

Hole Rock Type m/shift mDrill Diameter

cm Jan.-June Jan.-June>Dolerite Carbonatite Weathered 1970 1970

Ground Average Average

I-RQuarrymaster 22,9 20 37 91 51,8 1729

B-E60-R/45-R 25,0 49 85 210.300 85,0 425

off vertical. At present there are three standard drillingpatterns.

7,3 m. spacing by 6,7 m. burden used for carbonatiteore

8,2 m. spacing by 6,6 m. burden used for doleritedyke

9,1 m. spacing by 7,9 m. burden used for weatheredground.

Blast hole drilling equipment consists of 6 diesel-powered self-propelled, down-the-hole Ingersoll-RandQuarrymaster machines, one Bucyrus-Erie 60-R electricrotary drill. The former machines drill holes of 22,9 cmdiameter, using tungsten carbide button insert bits;the latter machines drill holes of 25 cm diameter usingeither steel tooth or tungsten carbide button insert tri-cone bits, depending on rock type.

The table above shows average performance of drillsand bit performance, although these vary greatly withrock type:

During the first half of 1970, 66547 m. were drilledwith the two rotary drills and 89349 m. with the Quarry-masters.

Secondary drilling amounts to approximately 9 000m. per month with two Ingersoll-Rand crawler drillsdrilling 50 mm. diameter holes, and eight jackhammersdrilling 36 mm. diameter holes.

Blasting

Primary blasting in the pit is carried out with alu-minised ammonium nitrate slurry and pumptruckemplacement. Solution consisting of ammonium nitrate,sodium nitrate, and water is mixed and stored at73,3 °C in insulated, heated tanks at the mine. The hotAqueous ammonium nitrate solution is delivered in20 t. insulated road tankers from Sasolburg.

Two grades of dry premix are used, named DBA(Dense Blasting Agent) 37 and DBA 31; the former ismore powerful than the DBA 31 and is used to obtain astronger bottom loading of the hole. This premix,previously imported from IRECO Chemicals in theUnited States, is now prepared on site principally fromlocal ingredients.

The slurry pump truck carries an insulated solutiontank and two premix bins. Solution and premix are fed

at a predetermined calibrated rate into a mixer, and arethen pumped through a 50 mm hose into the blast holeat a rate of from 180 to 225 kg per minute. Approximately544 kg of slurry is required for a blast hole in sulphideore.

The blast is initiated by electric detonator connectedto cordtex trunk lines going to each hole. Each line ofholes is fired utilising millisecond relays. From thetrunk lines two cordtex leads are fed down each holeand two 397 g. Pentolite boosters are used to detonatethe charge which is tamped with drill hole cuttings.

Blast size averages approximately 100 000 t. althoughthey can range from 50 000 t. to 500 000 t. Shots arenormally fired once per working day at 3.50 p.m. duringshift change.

For secondary blasting ammon dynamite is used, andsecondary shots are usually tied into primary shots withcordtex.

Reference to the table below will show the primaryblasting efficiency for the first half of 1970.

A typical primary blast layout is shown in Fig. 8.

Loading

Loading equipment consists of two 3,4 m3 dieselelectric, five 4,6 electric, and one 9,2 m3 electric shovels,all manufactured by the Harnischfeger Corporation.The 3,4 m3 shovels being fairly manouverable, are usedto gain flexibility on the removal of ore or discardmaterial. Ore production and pit internal discard ma-terial removal is carried out by the 4,6 m3 shovels,whilst the 9,2 m3. shovel is employed almost exclusivelyon stripping of overburden.

Loading on both sides of the shovel is normal practiceand a bulldozer, rubber-tyred or tracked, is maintainedat each shovel to keep the loading area free from spilledrock.

Shovel power is supplied at 3300 v. from a ringfeed around the pit. Feeder cables are tapped into thisfeeder at suitable points, and then fed to the shovel viaa link kiosk with overload protection. Shovels areequipped with automatic lubrication systems and onlyrequire pre-shift checks between the two-weekly majorservices.

t brokenkg

Explosives In Blastedt broken per m

of Hole

18812210 4934820

t broken per kg ofExplosive

127,33,81 147 767

JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY AUGUST 1971 19

km per t per t-kmper Shift Shift per(loaded) Truck Shift

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Shovel performance for the first half of 1970 is shownbelow:

Shovelt. per

Operating Hour

3,4 m34,6 m39,2 m3

520749

2026

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Fig. 9-4,6 m3. Shovel loading into a 59-t. Haul Truck.

20 AUGUST 1971

Hauling

The haulage fleet consists of thirty 59 t. KW -Darttrucks and 90 t. Ml00 Lectrahaul trucks. The averageore haul distance to the primary crushers of 3 048 m.and 5 182 m. on the waste haul. At presentapproxi-mately 28 trucks per shift are required to satisfy pro-duction requirements with the balance either in main.tenance or on standby.

Each truck is fuelled and has its oils, water and tyreschecked once each shift; this is carried out on a con.tinuous basis throughout the shift, making use ofstandby trucks where possible.

The truck factor is variable, depending on the materialbeing handled; at present it is approximately 57 t. forthe. KW-Dart and 92 t. for the MlOO Lectrahauls.

General Motors or Cummins 644 hp diesel enginesdriving through torque converters are used in theKW. Dart trucks, whilst the Lectrahaul trucks areequipped with 973 hp Caterpillar diesels driving aGeneral Electric generator supplying current to motorsin the rear wheels.

Truck performance for the first half of 1970 is shownbelow.

Haul road profile51are designed to give the lowestadverse grade, and in no case does this exceed 8 per cent.Road maintenance assumes great importance, and fourgraders and four water sprinkler trucks are used toensure that road surfaces are kept smooth and rock-free.Roads on waste rock or outside the ore limits are top.dressed with weathered dolerite or weathered magnetite.

Truck Type

KW-DartM100 Lectrahaul

JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY

Within the ore limits, reclaimed crushed ore, from thesecondary crushers, is used, especially in areas aroundworking shovels. A fifteen-tonne Grid-Iron roller is atpresent being used on an experimental basis. Results sofar have been encouraging. Any protruding rocks thatcannot be removed by dozing or grading are drilled andblasted.

Since tyre cost is a major element in the operation,continuous tests are carried out in an attempt to findthe most suitable type for the operation. At Palabora,tyre duty is extremely arduous due to the high averagehaul speeds that cause dangerous heat build-up in thetyres, especially on the longer waste haul. Depending ontyre size, pressures vary from 5,2 to 7,1 bars and arenitrogen-filled to exclude humidity and to promotecooler running temperatures.

Tyre life is variable, according to the haulage duty,and is especially affected by ambient temperature andweather conditions generally. Consumption is in theorder of 40 tyres a month.

To ensure equal tyre duty on all trucks, once every24 hours long-haul waste trucks are changed with theshorter-haul trucks, all tyres are checked for pressureand wear daily, and during stoppages any small rocksembedded in the tyres are removed by the drivers.

Fig. 10-9,2 m3 Shovel loading 90-1.truck.

Primary crushing

Ore from the open pit is delivered to twin Allis-Chalmers 137 cm gyratory crushers set to 17,8 cm.Optimum crusher capacity is 2 400 t. per hour per unit.Crushing takes place on three-shifts, and in June 19701,58 million t. of ore were crushed at an average rateof 1 400 L/hr. per crusher. Both crushers are used inorder to obtain the required ore split into low titaniumand high titanium magnetite-bearing ore. The plantis fully automated and is controlled by the operatorfrom a central observation control room. In order toprevent damage to the apron feeders below each crusher,a low level radio-active isotope is used to control theore level; this ensures that a cushion of ore is left onthe apron feeder at all times and that, if the level fallsbelow the isotope probe, the feeder stops.

Crusher chokes are prevented by means of a highlevel radioactive isotope; should the ore level rise to thispoint, a danger light and audible signal is activated inthe control room.

Crusher ore is fed to the coarse ore belts dischargingon to two 33 000 t. live capacity stockpiles from whereit is drawn as required.

Fig. 11-59-1. Haul Truck tipping at the PrimaryCrusher.

Planned maintenance

A Planned Maintenance scheme is operated for allequipment used in the open pit. This is based either on acalendar system or on engine hours run, e.g. shovelshave a major service once every 14 days, whilst haul-trucks and other equipment are serviced according toaccumulated tacograph hours. Unit mechanical avail-ability for the first half of 1970 was as follows:

Unit % Availability-----

Quarrymaster DrillsB.E. 60-R DrillB.E. 45.R Drill3,4 cu m Shovels4,6 cu m Shovels .. . . .9,2 cu m Shovels. . . . . .Haultrucks (not including L-H)Rubber-tyred Dozers.Tracked Dozers

""'"Graders""" "'"

92,7%93,7%89,0%83,6%93,7%90,0%87,8%85,1 %81,3%81,0%

The preventive maintenance system is in the processof being computerized, to give a yet closer control overequipment performance and repair costs.

Control - mine planning

Over a period of two years the mine short term plan-ning has been developed by the open pit operating staff.In this way many major difficulties and problems havebeen recognized and. solved on paper, before beingtackled in the field. The importance of short termplanning, i.e. from one week up to six months, cannotbe overstressed. The geological formation of the Loole-kop orebody is such that it is essential that sound,workable plans are developed prior to mining operations.Planning has to be adapted to suit the following maingeological features:

(a) wide grade fluctuations(b) two separate ore types(c) an orebody crossed by several barrcn dolerite

dykes.

JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY AUGUST 1971 21

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22 AUGUST 1971

Fig. 12-Blast Sheet.

JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY