The Platinum and Palladium Resources of the Bushveld Complex

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In September 1924, Dr Hans Merensky and Andries Lombaardmade a remarkable discovery, on the farm Maandagshoek nearSteelpoort in the Northern Province of South Africa, in theeastern Bushveld Complex (Fig. 1), of a platiniferous ore body,which now bears the name MerenskyReef.1 Theenormity of thediscovery rapidly becameapparent to Merensky, and he and his

andcolleagues tracedits outcropwithin months forsome 80 km.

In 1925 he identified an even more promising occurrence in thenorthern limb (Fig. 1), and the first major deposit to be pro-moted, near Potgietersrus and called the Platreef. Its operationswere relatively short lived, but the area is now being mined asPotgietersrust PlatinumsLtd,a partof AngloAmericanPlatinumCorporation, and has potential to be the largest platinum- and

palladium-producing mine (see below). In the same year,Merensky also located the reef under thick black soil cover in anarc from Brits, through Rustenburg to Thabazimbi (Fig. 1).

The last 75 years have seen the overall consumption and usesof platinum expand dramatically. But what of its potential sup-ply, use and demand in the next millennium? Demand (andhence also its price) and uses are impossible to predict far intothe future, but the resources and potential supply of platinumand palladium can be computed with some degree of confi-dence.

Platinum hadbeenreported fromthe Bushveld Complex priorto Merensky’s discovery. In fact, the Geological Survey of SouthAfrica had initiated a study of its occurrence in the chromititelayers, but only uneconomic amounts were found.2 Subse-

quently, higher grades in chromititeswereidentified, but exploi-tation had to await the development of suitable metallurgicaltechniques to separate the platinum from its very refractoryhost.3 However, now the Upper Group 2 Chromitite layer hassurpassed the Merensky Reef as a platinum reserve (see below).Until the 1970s, the Merensky Reef was the sole source of plati-num in South Africa. First, Lonmin began mining the UG2, andother companiesare nowactivelyminingit as well. For example,Anglo American Platinum Ltd4 reports that, currently, 40 % of platinum produced from underground is from the UG2,compared to 15 % five years ago. Furthermore, in the last decadeopen-cast mining has been re-established on the Platreef.

At the time of Merensky’s discovery annual platinum con-

sumption was in the region of 100 000 ounces (subsequently allfigures will be quoted in million ounces), with most being supplied fromalluvialdeposits in Russiaand Columbia,and as a

by-product from nickel mining at Sudbury in Canada. Thedemand was sufficiently low that Merensky5 noted in his calcu-lations of what grade could be considered economic for mining on the new-found ore body, that the extra production coming from the Bushveld Complex might drive down prices by40 % from $100 an ounce. Remarkably, he calculated a figure of 2.3gt–1 at $100 per ounce, or3 g t–1 at a lower price due to marketoversupply, as the cut-off grade for open-pit mining, almost thesame value (actually 2.5 g t–1) as reported by Anglo AmericanPlatinum Ltd4 for their current open-pit operation nearPotgietersrus. What Merensky could not predict was that plati-

num demand and price would slump over the next decade as aresult of the Depression in the United States, and would not be-gin a sustained recovery until after the Second World War. 6

Merensky died in 1952, by which time mining of the MerenskyReef wasonly just beginningto increase,and so Merenskyneverwitnessed the dominant role his discovery was to play in theworld platinum markets. In 1950s annual consumption hadincreased to 0.3 million ounces, with South African productioncontributing about one third. By 1998, consumption had in-creased to 5 million ounces, with South Africa producing about75 %.7 These figures correspond to an average increase of about6 % per year for almost half a century. Can the resources sustainsuch further increases?

Platinum is but one (albeit the most important) of six closelyrelated elements, includingpalladium,rhodium, iridium, ruthe-nium and osmium (the platinum-group metals or PGM). Allhave slightly different uses.7 Platinum and palladium are by far

Platinum in South Africa South African Journal of Science 95, November/December 1999 481

*Department of Geology, University of the Witwatersrand, Private Bag 3, WITS, 2050South Africa. E-mail: [email protected]

The Bushveld Complex is well-known for its large proportion of the

world’s platinum and palladium resources.There are three very dif-

ferent ore bodies, the Merensky Reef, the Upper Group 2 (UG2)

chromitite, which together can be traced on surface for 300 km in

two separate arcs, and the Platreef, which extends for over 30 km.

Their global importance has justified several resource calculations

in the past. Such historical data are compared with the informationin recent mining company annual reports. Resource calculations

tend to be bigger by a considerable factor, because mining com-

pany reports include only proven and probable reserves, where

sufficient information is available rigorouslyto justifysucha classi-

fication. However, the remarkable continuity of layers within the

Bushveld Complex certainly justifies qualitative extrapolation to

adjacent areas, although current mines are probably exploiting the

most favourable sections of reefs. The major platinum mining

companies hold most of the mineral rights to these areas.

Historical estimates of platinum and palladium in these reefs,

which indicate about 770 and 480 million ounces, respectively

(down to a depth of 1200 metres), do not distinguish between the

different categories of proven and probable reserves and inferred

resource. The present calculations indicate about 204 and 116

million ounces of proven and probable reserves of platinum and

palladium,respectively, and 939 and 711 million ounces of inferred

resources, down to a depth of 2 km. Already mining is taking place

at 2 km in the Bushveld Complex, and so inferred resources, and

ultimately minable ore, could almost certainly be considered far

greater than even these calculations suggest. These figures repre-

sent about 75 and 50 % of the world’s platinum and palladium

resources, respectively. These figures for proven and probable re-

serves in the Bushveld Complex alone are sufficient for the next 40

years at current rate of production. However, estimated world

resourcesare suchas to permitextractionat an annually increasing

rateof 6 % per annum for over50 years. Expected sufficiency isless

for palladium. Thereafter, down-dip extensions of existingBushveld mines, lower grade areas of the Platreef and the Middle

Group Chromitite layers may become payable Demand, and hence

price, will be the determining factor in such mining activities rather

than availability of ore.

The platinum and

palladium resources of

the Bushveld Complex R.G. Cawthorn



the most abundant in all deposits, and the other four are alwaysminor by-products from exploitation of platinum-palladiumdeposits, except in alluvial occurrences (which are now rela-tively minor producers), where osmium and iridium may beabundant. Hence, in this account only data for the principal twoelements — platinum and palladium — will be reported.

Typically, in the Merensky Reef, Platreef and UG2 the propor-tions of platinum and palladium are about 55 % and 32 %, 44 %and 46%, and 46 % and 30%, respectively, with the other metalscomprising about 15 %.

All world resource estimates recognize the importance of theBushveld Complex in such globalfigures,and so informationonthis body will be the focus of this report.

Formation of the Bushveld Complex and its layering

The Bushveld Complex formed by the repeated injection of lava (or magma) into a sub-volcanic, shallow-level chamber.Having an areal extent of over 65 000 km2 — that much is pre-served today — and a thickness reaching 7 km, it is the largestlayered intrusion in theworld. Because of theenormous volume

of magma involved, cooling and crystallization were extremelyslow processes. Different minerals precipitated as the tempera-ture fell, in a sequence determined by phase relations, anddepending on the instantaneous composition of the magma.Theseminerals accumulatedinto sub-horizontal layers building up fromthe base of the chamber. Intermittent replenishment byhotter magma (analogous to repeated volcanic eruptions) led toa repetition of this crystallization sequence, which produced arepetition of the mineral layering. The rocks produced, and therepetition of the chromite-and magnetite-rich layers, areshownin Fig. 2. Most of the minerals forming from magma are of mini-mal economic significance, but this process of accumulation of layers, often composed of single minerals, leads to the concen-

tration of certain minor minerals which are of economic impor-tance. In the case of the Bushveld Complex, layers of chromiteand vanadium-bearing magnetite illustrate this principle. Theaverage concentration of the element chromium (Cr) in a

magma is about 1000 ppm (parts per million), equivalent to1000 g t–1 or 0.1 %. In most rocks this Cr is locked in minerals atlow concentration and not amenable to extraction. The mineralchromite contains up to 30 % Cr, and so layers of pure chromite,found in the bottom part of the intrusion, are enriched by a fac-torof 300 relative to the magma. Theenrichment of vanadium is

482 South African Journal of Science 95, November/December 1999 Platinum in South Africa

Fig.1. Generalmapof theBushveldComplex(centre), withsectorsshowingthedifferent mining operations (explodedviews).The gradeof PGMandthickness of the Merensky and UG2 reefs are shown for each mine.

Fig.2. StratigraphicsectionthroughtheBushveldComplex,showingthelocations of the platiniferous layers, the UG2 Chromitite and Merenskyreefs.



less spectacular, only about 30-fold, but the vanadium-bearing magnetitelayers near thetop of theBushveld Complex areprof-itably mined for their vanadium. The enrichment factors forplatinum andpalladium aregreater than for chromium or vana-dium.Themagmamay have contained only a fewppb (partsper

billion), whereas the ore-bearing reefs may contain up to a fewppm, or a 1000-fold enrichment. Such concentration processesareveryrare innature; because they dependuponaccumulationfrom large volumes of slowly cooling magma, and so almost allof theworld’s PGM(and chromium) resources areto be found in

layered intrusions.

Previous resource estimates

BecauseofthegreatimpactonworldplatinumresourcesintheBushveld Complex, there have been several previous esti-mates.8–10 It is of interest to examine the consistency of earlierfigures compared to data now available as an indication of thereliability of long-term predictions and extrapolations.

The confidence attached to any mineral resource estimate inany deposit is a function of the amount of information availablefor that deposit, its continuity and complexity. Categories of proven and probable reserves,and inferred resources maybe applied,depending upon the information base.11 A proven reserve is de-fined as ore available for mining without further development;

probable reserve is ore available beyond existing development, but which has been fully evaluated by drilling. An inferredmineral resource is defined as one where there are reasonableand realistic prospects for eventual economic extraction, butwhere the data base on quantity, grade and continuity have not

been sufficiently rigorously evaluated to consider it a reserve. Inthecase of theBushveld Complex information cansometimesbedivided into these three categories. Annual reports by mining companies now define their proven and probable reserves inline with the requirements of SAMREC,11 but resources are notalways presented. Furthermore, these data do not cover theentire length and down-dip occurrence of known ore-bearing horizons, because there are insufficient data in some sections.

Earlier estimates were based on broad extrapolations, using minimal data, because such information was not available orwasconfidential. Such calculationsmust be consideredto definean inferred resource. However, given that the Merensky Reef

and UG2 Chromitite layers can be traced for many tens of kilo-metres without any physical breaks, and for distances of 300 kmwherevertheBushveldComplex crops out(Fig.1), confidence inthe economic potential of such inferred resources must be con-sidered very favourably.

ThesePGM deposits are subdividedinto well-established geo-graphic regions of the Bushveld Complex, as shown in Fig. 1. Intheeastern andwesternlimbsthe stratigraphic sectionsarequitesimilar (Fig. 2), and the outcrops of the Merensky and UG2chromitite reefs lie approximately parallel to each other in

semi-circular arcs,with theMerenskyReef 40—400 metres abovethe UG2. In the northern limb, a very similar sequence isobserved intherocksoverlyingthe platiniferousreef, butthe ore

body itself is very much thicker than in the east or west. Histori-cal data for these regions are compiled in Table 1. These data aregenerally obtained by considering a series of uniform rectangu-lar blocks of a constant thickness, grade, dip and measured out-crop length.

In these calculations von Gruenewaldt8 and Vermaak 9 deter-mined the resource to a depth of 1200 metres. This was consid-ered a maximum miningdepthin theplatinumminingindustry,

because rock temperatures reach over 40 °C at such depths, andrefrigeration becomes necessary at greater depths, which in-creases miningcosts. Vermaak 9 quotedboth an in situ grade, and

a grade likely to be reported for the recovered ore entering theprocessing plants, for which he incorporated a dilution factor of about 25 % due to waste and the influence of undergroundlosses due to mining requirements, structural and other influ-ences,and referred to a millhead grade.The lower figure is tabu-lated here, because it is more comparable to mining companydata. For consistency, in Table 1 the calculations of vonGruenewaldt8 have also been reduced by 25 %, because it is of more importance to knowthe realistically extractableamount of metal rather than the total content in the rocks underground.

Differences between the two estimates in Table 1 arise forseveral reasons. Whenvon Gruenewaldt8 madehis compilation,the exact thickness and grade of Merensky and UG2, especially

in the eastern Bushveld, were not known, and he used averagefigures for the entire Bushveld Complex. Furthermore, the con-tinuation of the Bushveld Complex below younger sedimentarycover in the northern end of the eastern limb (Fig. 1) could have


Table 1. Platinum and palladium resources in the Bushveld Complex.8,9

Region Pt grade (g t–1) Pd grade (g t–1) Pt (106 oz) Pd (106 oz) Pt grade (g t–1) Pd grade (g t–1) Pt (106 oz) Pd (106 oz)

Von Gruenewaldt8 Vermaak9

Platreef 1.3 1.4 123 135 1.8 2.0 59 66

Eastern Bushveld Merensky Reef 3.2 1.4 134 57 2.4 1.4 146 83

UG2 Chromitite 2.4 2.0 153 127 1.8 1.6 153 137

Western Bushveld (north of Pilanesberg)

Merensky Reef 3.2 1.4 44 19 3.2 1.5 35 15

UG2 Chromitite 2.4 2.0 51 42 2.1 1.0 33 16

Western Bushveld (southeast of Pilanesberg)

Merensky Reef 3.2 1.4 77 33 2.5 1.2 164 82

UG2 Chromitite 2.4 2.0 115 95 2.1 1.0 183 84

Totals 698 508 773 484

Thedata of Vermaak9 were based on hisestimated millhead grade.The in situ data of von Gruenewaldt8 have been reduced by 25 % to allow formining losses, dilution,and processing losses, to make it consistent with recommendations of SAMREC.11

(Notethat Vermaakdeducted an amount fororealreadymined out,which yielded a finalresource of 728.8 million ounces.Unfortunately, there is a misprint in hisTable2.7and the number appears as 128.8.)



been expected, but no exploration had been undertaken to con-firmtheexistenceofeitherreefatminabledepthinthatarea,andso was not included in his calculation. Subsequent explorationand mining (at the now-dormant Messina mine) has defined aplatinum reserve under cover of younger sedimentary rocks.Von Gruenewaldt8 estimated that there was a strike length of only 30 km of reef southof theSteelpoort River (Fig. 1). The areaunderlyingthe SteelpoortRiver valley is complicatedby faulting and lack of exposure. However, in 1980s drilling in the valley byBarplats Mines Ltd12 indicated the existence of Merensky Reef and UG2 at depth at the proposed Rhodium Reef mine (Fig. 1).Because of theseadditionaldata, Vermaak 9 usedstrikelengthsof

107 and 47 km north and south of the Steelpoort River, some-whatgreaterthanthe90and30kmusedbyvonGruenewaldt. 8

More information is available for the western than the easternlimb, because of theintensity of mining. Data from there may besubdivided into a northern andsouthern sector, as a resultof theemplacement of the Pilanesberg intrusion (Fig. 1), which termi-nates outcrop for some 25 km. Geological differences in theMerenskyReef existon eitherside of this break,with thicknessesgreater to the north. The geographic extent of the northernsector is quite well defined by the Crocodile River Fault in thenortheast (Fig. 1) and the Pilanesberg in the southwest. Rocksfrom the Bushveld Complex have been identified east of theCrocodile River Fault, but thus far only the uppermost layers,and no platinum mineralization, have been reported. There is a

further complication to these calculations, resulting fromthe elimination of reef in two so-called ‘gap’ areas. The exactposition of terminationof ore is reliably known near surface, butwhat may happen at great depth is not known.

Theeastern terminations of theplatiniferous reefs southeastof the Pilanesberg are more uncertain. The Bushveld Complexdegenerates into a series of thinner sheets which interdigitatewith thehostsedimentary rocks and the layering becomes morediffuse near Pretoria. TheMerenskyReef canbe identified to theeast of theEastern Platinum Mine,but it thickens,and gradeandPt/Pd ratio decrease. However, it is well-known in the platinumindustry that the total platinum content in a single verticalsection (cm g –1) may remain comparable regardless of thickness

of reef.13

Hence, if it ever becomes economic to mine a greaterwidth at lower grade, the same resource of platinum per unitstrike length may be obtained from this thick reef as elsewhere.As a result of recognition of this continuity, Vermaak 9 calculated

resources based on a greater strike length along this southernsector of 108 km compared to 70 km used by von Gruenewaldt.8

East of Brits and the Crocodile River, the UG2 degenerates andexploitation will not be possible much further east.

The UG2 underlies the Merensky Reef in the western limb by40 — 140 metres from north to south, and so in all cases bothlayers can be extracted concurrently with current mining tech-niques. Vermaak 9 showed that, like the Merensky Reef, the UG2grade decreases from north to south, but is less marked in thecase of theUG2, andthe decrease is partiallycompensatedby anincrease in thickness. Such subtleties were unknown when vonGruenewaldt8 made his estimates. As a result, the UG2 has

greater potential than the Merensky Reef in the sector east of Eastern Platinum Mine. The dormant Crocodile River mine wasexploiting the UG2, and one of the reasons for its suspension of mining was the frequency of faulting near Brits, leading to anescalation of mining costs, rather than poor grade. The shorterstrike length for the UG2 south of the Pilanesberg used by vonGruenewaldt8 than Vermaak 9 resulted in considerably increasedinferred resource for the UG2 in the latter’s estimate.

In thenorthern limb estimation of theresource is much harder.Unlike the Merensky and UG2 reefs, the Platreef does not havesharply defined boundaries in terms of PGM content (Fig. 3),and is much more irregular laterally. The layer can be tracedalong the lower contact of the Bushveld Complex north of Potgietersrus, and a comparable layer exists to the south of the

town. Von Gruenewaldt8 estimated the strike length at 60 km,whereas Vermaak 9 usedfigures of 35and 15 km forthe northernand southern sectors. Very little information was publicly avail-able when vonGruenewaldt8 made hiscompilation and he usedathicknessof25mandatotalPGMgradeof3gt–1. Vermaak 9 hadaccess to considerably more drilling information and usedfigures of 10 m width and a Pt (and total PGM) grade of 1.7 (and4.1) g t–1. Current mining exploits a thickness of 20 m at a totalPGM grade of 4.9 g t–1, but this is obviously in the best area interms of thickness and grade, and these figures should not beextrapolated to the entire Platreef.

There areno chromititelayers in thenorthern limb with signif-icant PGM contents.

In summary, the differences between the two estimates inTable 1 are probably small compared to the uncertainties whichare embedded in these calculations. Collectively, they suggest aresource in the order of 800 and 500 million ounces of platinum


Fig. 3. Vertical sections through thedifferentplatinumore bodiesshowing thedistributionof PGM(+Au) within thereefs. Data aretaken from Viljoenand Schurmann10 and White.17 Note the very sharp cut-off of mineralization in the Merensky and UG2 reefs, but the irregular distribution in thePlatreef,making estimation of reservesand resources difficult. A., Cr, F.P., H., N., P.P. and X. refer to anorthosite, chromitite, feldspathic pyroxenite,hornfels (floor sedimentary rocks), norite, pegmatitic pyroxenite, and xenoliths (of hornfels).



andpalladium,respectively, to a depth of 1200 m.Theincreaseinthe data base over the 25-year period which elapsed betweenthese two calculations has made a relatively insignificant differ-ence to resource estimates.

Proven and probable reserves

It is difficult to make a precise comparison between these

estimates in Table 1 with the information quoted by the majormining companies in their annual reports, from which the datain Tables 2 and 3 havebeencompiled. The main limitation isthatvon Gruenewaldt8 and Vermaak 9 did not subdivide their data

into the categories of proven and probable reserves andresources. (Insufficient information was available in the publicdomain for von Gruenewaldt8 to do so.) The mining companydata are sometimes so defined. In other cases, the distinction isnot made. In the latter situation reserves have been conserva-tivelyindicated as thelowest levelof confidenceusing theabovecriteria. In some cases, as a result of this conservative reporting,

there may be only probable ore reserves on active mines; somemust obviouslybe considered proven. Thedepth to which thesecalculations have been made is not always indicated. In somecases,it isas deepas 2000metres, inothersit isless, or only to the


Table 2. Reserves and resources of platinum and palladium in Merensky Reef and Platreef as reported by mining and exploration companies.

Mining Area Ore (106 tons) Pt (106 oz) Pd (106 oz) Ore (106 tons) Pt (106 oz) Pd (106 oz) Ore (106 tons) Pt (106 oz) Pd (106 oz)

Proven reserves Probable reserves Inferred resources

Platreef 33.5 2.3 2.6 157.1 7.6 8.7 2084 136 136

Eastern Bushveld Lebowa/Atok 7.1 0.8 0.4 60.3 6.9 2.9

Platexco 31.7 3.2 1.5

Other 2951 286 165


Union/Amandelbult 28.0 3.7 1.7 76.8 9.6 4.8

Northam 3.2 0.5 0.3

Other 7.8 0.8 0.4


RPM 30.4 3.7 1.8 116.4 14.9 7.5

Impala 11.2 1.9 0.9 58.7 8.1 3.6

Lonmin 273 23.8 10.0

Other 1332 113 56

Total 113.4 12.9 7.7 774 74.1 39.0 6375 536 357

In some cases, only total PGM reserves have been reported by mining companies, and the split into Pt and Pd has been estimated based on published ratios of thedifferent PGMs from the nearest available area. (RPM, Rustenburg Platinum Mines, including Bafokeng-Rasimone, excluding Union and Amandelbult; Lonmin, Karee,Eastern and Western Platinum Mines).Resources have been calculated by subtracting the mining lease areas of the different mines from the total potential area where the reefs continue to a depth of 2000metres, and calculating the remaining tonnage based on information for grade and thickness using grade and thickness of adjacent mines.

Table 3. Reserves and resources of platinum and palladium in UG2 Chromitite as reported by mining and exploration companies.

Mining Area Ore (106 tons) Pt (106 oz) Pd (106 oz) Ore (106 tons) Pt (106 oz) Pd (106 oz) Ore (106 tons) Pt (106 oz) Pd (106 oz)

Proven reserves Probable reserves Inferred resources

Eastern Bushveld

Lebowa 217 17.8 15.2

Platexco 29.8 2.3 2.2Rhodium Reefs 136.5 17.9 15.3

Other 3488 306 301


Union/Amandelbult 27.1 2.2 1.0 238.5 19.5 9.7

Northam* 0.2

Other 7.5 0.5 0.2


RPM/Bafokeng 10.0 1.0 0.4 56.1 5.5 2.3

Impala 11.6 1.9 1.0 70.3 9.5 4.8

Lonmin 415 37.4 17.0

Crocodile River 13.5 1.3 0.5

Other (total) 1529 96 53Total 48.9 5.1 2.4 1176.7 111.2 67.0 5025 402 354

See footnote to Table 2 for details.*At Northam considerable UG2 ore exists, but has not been proven by drilling, and modification to mill design would be required before it could be beneficiated.



limit of the property owned by thecompany. In instances wheredepth is known to be less than 200 metres, information has been

calculated to a depth of 2000 m, but included as inferred re-sources.

The total (proven and probable) reserves reported for thesemining companies amount to 204 and 116 million ounces of platinum and palladium, respectively (Tables 2, 3). Data aretaken from annual reports and press releases by mining compa-nies.4,14,15 The areas for which specific reserve data are availableare shown in Fig .1, from which it can be seen that there are long stretches of reef that are not included in such calculations

because they have not been sufficiently evaluated. An attempthas been made to estimate ore in these sections, using the sameprinciple as used by von Gruenewaldt8 and Vermaak.9 All suchdata, regardless of which mining company holds the mineral

rights, have been combined into a single inferred resourceestimate for each limb of the Bushveld. Inferred resources areapproximately five times that of proven and probable reserves.

A comparison is made in Table4 between thedata of Vermaak 9

and those determined in Tables 2 and 3. The figures quoted byVermaak 9 arequiteconservativein total compared to thecurrentfigures, andespecially forthePlatreef andeastern Bushveld,butthe reverse is true for the western Bushveld. However, thecurrent figures are determined to a depth of 2000 metres, com-pared to 1200 metres used by Vermaak.9 If the data of Vermaak were to be extrapolated to 2000 metres, they would exceed thefigures given here. The reason for the preferred greater depthused here is discussed below.

In Table 5 these figures are compared with those reported by

Viljoen and Schurmann,10 also apparently taken from companyannual reports. Their data were presented in a different formatfrom those here, and it is only possible to compare total PGMcontent, not individual metals, for most of the mines. Platinumandpalladium typicallycomprise about 85 % of thetotal PGMinthe ore. Their figures, especially for the UG2, appear to beinflated compared to those quoted here. The reason for theirhigherfigures is not known. This comparison indicates the diffi-culty of obtaining a precise figure for the metals, which resultsfrom different classifications of reserves and resources, and theenormity of the projections of the ore bodies.

Limits to mining

Table1includesresourcestoadepthof1200metres.Atthetimeof those compilations, it wasconsidered unlikely that miningac-tivitywould extend beyond thatdepth,at least while there werestill abundant reserves of shallow-level ore available more

cheaply, because rock temperatures would reach over 40 °C, re-quiring the introduction of expensive cooling by refrigerationprocesses. The developments on Northam platinum mine16

demonstrate that mining can be undertaken at greater depthusing hydropower at <5 °C for both refrigeration and running equipment. Backfilling of mined-out areas with waste andcrushed rock is also used there to limit the volume of under-ground workings which need to be ventilated and cooled. The

deepest levelof currentmining(in 1999) is at 1987 metres, whererock temperatures are 63 °C and plans to mine to 2365 m are

being implemented. These developments indicate the financialand technical viability of mining well below 1200 m. In thisnorthern part of the western limb an added incentive to deepermining is that the grade increasesslightly down-dip, possibly asa result of the merging of the Merensky Reef with underlying very low-grade layers.16 However, this change is associated witherosion of the footwall by the Merensky Reef, producing aless-regularbasal contact to,and thicknessof, theore body. Suchmining demonstrates that ultimately mining may well continueto greater depths, especially once shallow ore has been largelyextracted. In the gold mining industry of South Africa, there is a

major research programme being pursued by the Chamber of Mines Research Organization to develop mining techniqueswhich will permit mining at depths greater than 4 km, and sothere is no reason to assume that the experience gained in the


Table 4. Comparison of calculated estimates and mining company statements.

Region Pt (106 oz) Pd (106 oz) Pt (106 oz) Pd (106 oz) Pt (106 oz) Pd (106 oz)

Vermaak9 Mining companies’ Inferred resource

proven and probable reserves

Platreef 59 66 9.9 11.3 136 136

Eastern Bushveld

Merensky Reef 146 83 10.9 4.8 286 165

Eastern Bushveld

UG2 Chromitite 153 137 38.0 32.7 306 301

Western Bushveld

Merensky Reef 199 97 66.2 30.6 114 56

Western Bushveld

UG2 Chromitite 216 100 78.3 36.7 97 53

Totals 773 484 203.3 116.1 939 711

Data from Tables 1–3.

Table 5. Comparison between Pt + Pd (106 oz) reserves for certainmining and exploration areas reported by Viljoen and Schurmann,9 and

this report.

Viljoen and Schurmann10 ** This report

Mine/Company Merensky UG2 Merensky UG2

Lebowa 19.6 39.9 11.0 33.0

Amplats* 57.9 120.2 48.5 41.6

Platexco 4.7 4.5

Rhodium Reef 33.2

Northam 0.8

Impala 55.9 48.0 14.5 17.2

Lonmin 16.9 37.9 33.8 54.4

Crocodile R 0 84.4 0 1.8

Platreef 42.8 0 21.2 0

Total 193.0 330.4 134.5 185.7

*Amplats refers to Rustenburg, Bafokeng, Union and Amandelbult mines.**The data published by Viljoen and Schurmann10 were quoted as total PGMs.These figureshave beendecreasedto 85 %, becausethat is thetypicalpercentageof Pt and Pd in total PGMs.



gold mining industry will not ultimately be applied to the plati-num mines. Extrapolation of the above data to greater depththan 2 km is therefore not unrealistic, and would obviouslygreatly increase the inferred resource in the tables.

Down-dip continuity

Thecontinuityof layersdown-dip cannot be proven except bydrilling. The deepest boreholes on the Platreef extend to 1500metres,17 and for other mines depths of 3300 metres have beendrilled.10 With the exception of the variation noted above in theNorthamsection, there is no evidence that theMerensky or UG2change in grade or thickness down-dip. Indeed, given that thelayers can be traced on surface with minimal variation for manytens of kilometres, it is unlikely that sudden changes will occurwhen traced down-dip for less than 10 km from the surface out-crop.

Indirect support for the continuity at depth comes fromgeophysical data, but such interpretations do not yield uniquesolutions,nor canthey prove theexistence of specific layerssuchas the Merensky Reef, nor the grade. Gravity data identify

sequences of rocks with anomalous densities, and so theBushveld Complex, which has higher density than most of thesurrounding rocks, can be qualitatively traced through positivegravity (Bouguer) anomalies. Numerous studies have shownthat the Bushveld Complex is continuous at depth. In fact, thegravity data have been shown to be consistent with continuity

between the eastern and western limbs.18

Vibroseis techniques offer a more quantitative technique fortracing layers, or moreprobably packages of layersof distinctiverock types, to depth. One example of theuse of this technique inthe Bushveld Complex was described by Campbell,19 whoshowedthatthedepth to the top of the Bushveld Complex inthewestern limb, hidden under cover of granitic rocks, may be less

than predicted from extrapolation of a uniform dip as observedat surface. He showedthat the layered rocks form a gentle domemid-way between Rustenburg and Thabazimbi. The vibroseissection also was interpreted to show the existence of theMerensky Reef package. It is inferred to be present at a depth of about 6 km, which rules out its viability as a plausible futuresource of platinum, but illustrates that the Merensky Reef may

be considered to have extreme lateral and down-dip continuity,far beyond the limits of current drilling.

Response to platinum demand

Seventy-five years ago, Merensky5 foresaw that overproduc-tion of the abundant platinum resources at shallow level in theBushveld Complex could lead to a decrease in price.Conversely,

increases in price or demand would encourage expansion of production. Mines in the Bushveld Complex have a doubleadvantage over mines elsewhere in the world (as discussed be-low). Allexcept themines at Stillwater Complex in UnitedStatesandGreatDykeinZimbabweproducethePGMsasaby-productof nickel and copper mining, and the income from the PGMs isrelatively small, although important. Hence, adjusting suchmining operations to increased platinum demand is much moredifficult than on Bushveld mines. Furthermore, these copper–nickel mines produce more palladium than platinum, as doesthe Stillwater mine. The Great Dyke and Bushveld ores areunique in having more platinum than palladium. In the case of the Merensky Reef the ratio is greater than 2, whereas for Great

Dyke,UG2, Platreef andStillwater theratio decreasesfrom 1.7to1.5 to 1.0 to 0.3. Consequently, mines on the Merensky Reef focus on platinum production and can respond specifically toincreased demand in the market.

Future potential

Future expansion, or the ability to maintain production, willdepend entirely upon demand and the price of platinum andpalladium. The inferred resources of the Bushveld Complex aresubstantial even to a depth of only 1200 metres. However,several scenarios can be envisaged well into the future if

demand necessitates.The most immediately obvious potential for the future lies inadapting the knowledge from deep gold mining on thegold-bearing Witwatersrand mines to the Merensky and UG2ores.Being regular, gently dipping, tabular bodies, withminimalfaulting, they offer the minimum of complications, except hightemperatures, for future mining.

The eastern Bushveld hosts only one relatively small mine,Atok/Lebowa Platinum. Current interest is focused on thePlatexco venture on the farm Winnaarshoek, which may haveone of the highest grades in the eastern limb (Fig. 1). The ratio of Pt/Pd inthe oreisslightlylowerin theeast thanthe west,9 but the

biggest obstacle to the potential for development of MerenskyReef along a comparable strike length in the eastern limb is

currently the poorer infrastructure in terms of rail, a localsupport industry, and especially water, compared to the west.One hopes that mining and local infrastructure can develop intandem in this area for the financial upliftment of the localcommunity.

Mining the Platreef at Potgietersrus offers various opportuni-ties. Unlike the Merensky and UG2, the Platreef mineralizationdoes nothave sharply defined boundaries(Fig. 3).The miningof 1 metre of ore on the former bodies leaves minimal lower gradeorebehind.Bycontrast,the morediffuseboundaries to theore atPotgietersrus make the mine planning and ore evaluation morecomplicated. At present, the mine operates a cut-off grade of 1.1(or2.5)gt–1 of Pt(ortotal PGMs).Anincrease inproduction would

lower operating costs perunit mined,and so permit lower gradeoreand increasedwidth to bemined. Currently, lowergradeore,extracted from the open pit, is stockpiled. Increases in the priceof PGMs may permit lower grade ore to be mined, therebyincreasing the in situ resource and/or allowing the processing of stockpiled material. These comments apply to the entire strikelength of thePlatreef, where thedefinition of ore-gradematerialdepends on financial considerations, not geologicalboundaries.Current mining is from an open pit. The dip of the ore body isabout 40°, and the ratio of overlying waste rock, which has to

be removed, to ore becomes greater with increasing depth.Ultimately, onceshallowore hasbeenexhausted, itwill beneces-sary to develop underground mining methods. However, giventhe steep dip, mining of such a thick reef to depthshouldbe per-

fectly feasible.Even longer-term considerations for the supply of platinum

and palladium enter the realms of speculation. The grades of PGMs withinthe many other layersof chromititebelowthe UG2have not been widelyreported. However, the few data availablesuggest that some layers may ultimately be considered of economic potential. Reported grades are given in Fig. 4. TheMiddle Group Chromitites have total PGM grades up to 3 g t–1.The few analyses published indicate considerable variation,more so than in the Merensky and UG2, but far more data haveto be assembled before that suggestion can be substantiated.Furthermore, their thicknesses are not as constant as the UG2.For example, in the eastern limb, northwest of the Steelpoort

River valley, they are too thin to be considered economic what-ever their grades. However, in the west, and southeast of theSteelpoort valley they attain thicknesses of approximately onemetre. They are currently not considered economic in terms of




their chromium potential because their Cr/Fe ratio is too low foreconomic smelting. However, if higher grade chromite atshallow depth becomes depleted, or if metallurgical technolo-

gies evolve, the MG chromitites may become a future source of chromium. In this event, the possibility of concurrent extractionof the PGM could be considered.

The extraction of PGMs from the UG2 chromitite has resultedin the production of large stockpiles of relatively low-gradechromite ‘waste’ and research is currently aimed at its benefici-ation. It is possible that the converse trend mayultimately applyto the MG chromitite layers, with attempts to beneficiate thePGMs as a bonus in therefining of chromeore. However, like theplatinum resource, that of chrome ore in the Bushveld Complexis equally enormous, and the timing of mining of alternative

chromitite layers lies well into the future. In this event, grademay notbe the only consideration in PGM mining. Theability torecover the PGMs will be influenced by the extremelysmall-scaletextural relationship between the platinum-bearing mineralsand the host chromite grains. The envelopment of tiny PGMgrains within refractory chromite grains could cause severe lib-

eration problems.20

In terms of the SAMREC11

definitions, itwould be justifiable to refer to these layers as containing aninferred resource of PGMs, since grades and thicknesses andareal extent are known. However, it would be misleading tocombine these data with those for the Merensky, UG2 andPlatreef, as their exploitation possibly awaits the depletion of allshallow-level ore on those other horizons. Exploitation of thelower chromitite layers probably lies at least 50 years from now,and so falls outside the definition of an inferred resource.

Deposits elsewhere in the world

Although the Bushveld Complex dominates world platinumproduction and resources, there are other deposits which pro-duce platinum and palladium, or may do so in the future,

depending upon economic forces. The information about theseresources in Table 6 is taken largely from the compilation of Vermaak.9

In some deposits andoccurrences platinum andpalladium areassociated with nickel and copper sulphides, and represent a

by-product. As such, their production depends upon thedemand for the base metal, although their contribution to totalrevenue may be significant. However, PGM production cannot

be geared to the PGM market alone.The Great Dyke in Zimbabwe is another layered intrusion like

the BushveldComplex, although witha differentoverall geome-try. Ithasa strikelength of 550km,with mineralization occurring in four elliptical bodies with a total strike length of 350 km. PGM

grades, at about 3 g t–1

, are lower than in the Bushveld Complex, but the ratio of Pt/Pd at 1.5 is relatively high compared to mostores.

Data from Russia are difficult to obtain, but the Noril’sk-Talnakh deposit has proved to be a major palladium source inthe past, and one assumes considerable resources remain to bemined. The compilation of Vermaak 9 indicates that much of theremaining ore may be of the disseminated, lower grade type. Inview of the large proportion of the world’s palladium sourcedfromthe Noril’sk region, oregrades andeconomic factorswillbecritical for continued supply of this metal.


Table 6. Platinum and palladium resources in other countries, compared to South Africa.

Geological formation Country Ore (106

tons) Pt (106

oz) Pd (106

oz)

Great Dyke Zimbabwe 2574 143 87

Penikat Finland 0 ?93 ?248

Noril’sk/Talnakh Russia 1645 89 314

Stillwater USA 320 36 130

Sudbury Canada 427 9 11

Duluth U.S.A. 0 ?9 ?32

Jinchuan China 500 6 3

Voisey’s Bay Canada 125 ?2 ?2

Total 387 825

Bushveld Complex

Reserves — proven and probable 203 116

Resources 937 710

World total 1527 1651

Percentage of world’s Pt and Pd in Bushveld Complex 75 50

Note that theresources forFinland, Duluthand Voisey’sBay arepreceded by a question mark, because no mininghas yetbeenundertaken on these deposits.The otheroccurrences are currently being mined, and so represent a more plausible immediate resource.

Fig. 4. Stratigraphic section, not drawn to scale, of the chromitite layersof the Bushveld Complex, and their PGM contents, based on data fromLee and Parry,21 Scoon and Teigler,22 von Gruenewaldt and Merkle,23

and von Gruenewaldt et al.24



TheStillwater Complex is theclosest analogue to theBushveldComplex. It is more geologically disturbed, however, and only asmall remnant (42 km long) of what was probably a very muchlarger layered intrusion now survives. Its PGM resource iscorrespondingly much less than the Bushveld. Although totalPGM grades are higher than in thelatter, they are dominated by

palladium, with a Pt/Pd ratio of 0.3.There are also chromitite layers in both Stillwater and GreatDyke, but none has grades of PGMs which indicate that theycould ever be mined.

In Finland there are a number of layered intrusions thatcontain base metal and PGM mineralization. Some containhigh-grade areas,but suffer fromtwo problems.Themineraliza-tion occurs in verythin layers, and gradeshave sometimes beenquotedfortheorezone,whichmaybelessthanaminimummin-ing width. Also, these bodies have been deformed, folded anddisrupted, and so tracing the mineralization is difficult.Vermaak 9 has assumed continuity to a depth of 1200 m for hiscalculations, but structural complexity make that assumptionuncertain.

The Duluth Intrusion in the United States is being extensivelyexplored, and widespread disseminated mineralization of nickel–copper sulphideshasbeen reported. These rocks containonly 0.1–0.2 g t–1 of PGMs and no economic base metal deposithas yet been located.

There has recently been considerable interest in the nickeldiscovery at Voisey’s Bay in Labrador. Relatively recent esti-mates put the resource at 125 million tonnes with over 1.5 % Ni.Estimates of platinum content are in the order of 2 millionounces. Further discoveries in the area are possible, but thesefigures put the size of discovery into a perspective relative toother deposits.

In Table 6 it is suggested that world resources, excluding the

Bushveld, could be 387 million ounces of platinum. However, itshouldbe pointed outthat miningof thedeposit with the largestpotential, the Great Dyke, has only recently been initiated, (andone mine is currently not operational), and further mining andexplorationare needed to substantiatethose data.For thesecondlargest resource, in Finland, no mining has yet begun, so theseresources have yet to be brought to any account.

Summary

Mining company annual reports from mines operating on thePlatreef, Merensky Reef and UG2 Chromitite in the BushveldComplex declare proven and probable ore reserves totalling about 204 and 116 million ounces of platinum and palladium todepths of 2 km. These calculations exclude enormous sections

where these ore bodies are known to occur, but where drilling density is insufficient to justify defining the resource with anygreater certainty. These ore bodiesare notably continuous along strike and so potential ore can be considered to exist in theseintervals. They could provide an additional 939 and 711 millionounces of platinum and palladium, respectively.

Recent developments at Northam Platinum have shown thatmining to 2 km depth at rock temperatures of 65 °C is alreadyeconomically viable. There is no evidence that the platinumgradewill not continue to even greater depths,and so extrapola-tion of the data in this report to greater depths is justifiable.

The tabulations indicate that the total proven and probablereserves of platinum in the Bushveld Complex is in the order of

204 million ounces. Given an annual consumption at present of

5 million ounces, that is sufficient for 40 years, excluding orefromanywhereelse in theworld.Total reserves andresourcesof platinum amount to 1140 million ounces in the Bushveld and afurther 387million ounces worldwide. Given a demand increas-ing at 6 % per year, those existing resources would supply allneeds for over 50 years. Somewhat shorter time-scales of suffi-

ciency exist for palladium. In the longer term, the inferredresources of the Eastern Bushveld would almost certainly

become exploitable; deeper mining could be considered in theWestern Bushveld using technology being developed on thegold mines; lower grade ore could be mined in the Potgietersrusarea; and ultimately the Middle Group Chromitites could beexploitedfor theirplatinum and chromium. Such developmentswould enormously extend these resource calculations, but theirexploitation will be controlled by price and demand of theprecious metals.

I thank the geologists at Anglo American Platinum, Impala, Lonplats and

Northam for correcting and confirming various aspects of the data in this article.

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The Platinum and Palladium Resources of the Bushveld Complex

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