Layered mafic-ultramafic massifs remain themain focus of mineral exploration for the platinumgroup elements (PGEs). The large PGE reserves inthe Bushveld, Stillwater, Sudbury and Great Dykecomplexes provide the major share of platinummetals production, particularly the Bushveld, inSouth Africa. However, looking back to the begin-ning of the 20th century, it is surprising howimportant PGE lode mining was from unique geo-logical structures like Onverwacht and Mooihoek(South Africa), and Nizhny Tagil (Urals, Russia).The iron-rich platinum pipe bodies found through-out the eastern lobe of the Bushveld Complexwere probably discovered during early explorationof this igneous complex. In fact, the first discover-ies of economic levels of PGEs were in theOnverwacht and Mooihoek platinum pipes. Theterm IRUP, iron-rich ultramafic pegmatite (1, 2),describes the crosscutting pipes, veins and sub-concordant sheets of very coarse-grainedultramafic pegmatite that disrupt the BushveldCritical Zone in South Africa (3).

Ural-Alaskan Type Complexes (U-ATCs) are agroup of zoned mafic-ultramafic intrusive bodies,generally of sub-circular/stock-like shape, rarely

exceeding 10 km in diameter. They are well knownas a source of platinum placers in the Urals, in thefar east of Russia, in south-east Alaska, Colombia,Australia and other regions (4–6). Some of thebiggest platinum placers in the world were discov-ered in the Urals over 150 years ago, and duringthe first hundred years of operation yielded about400 tons of platinum. Despite this placer produc-tion, there has been very limited lode mining fromthe source rocks. The disparity in productionbetween placer and lode deposits is due partly tothe disseminated nature of the PGE mineralisationand partly to the difficulty of identifying andexploring narrow diameter pipes. Typical PGEmineralisation, found in Nizhny Tagil and theIRUPs of South Africa, is concentrated in discretecore zones (of 10 to 24 m diameter); it comprisesfine to very fine disseminated platinum alloys witha large range of compositions. Platinum is the mainelement. There are also bonanzas with rich con-centrations of PGEs up to 2000 g tonne–1 (7–9).

The occurrence of these platiniferous pipes isclosely linked to geodynamic environments thathave a long history of multistage magmatic-meta-somatic-hydrothermal evolution.

Platinum Metals Rev., 2006, 50, (3), 134–142 134

DOI:10.1595/147106706X128791

Phoscorite-Carbonatite Pipe ComplexesA PROMISING NEW PLATINUM GROUP ELEMENT TARGET IN BRAZIL

By Juarez FontanaPolytechnic School of University of São Paulo, Mining and Petroleum Engineering Department, LCT – Technological

Characterization Laboratory, São Paulo, Brazil; E-mail: juarez@argusplat.com.br

The background to a project in Brazil is described that has found promising concentrationsof platinum group elements (PGEs) in phoscorite-carbonatite complexes. Further geochemicaland mineralogical research is underway to determine their potential as ore deposits. The well-established industrial demand and current level of prices for the platinum group metalshave encouraged the exploration of geological environments other than the layered mafic-ultramafic intrusions that provide the bulk of platinum metals. Environments, such as the Ural-Alaskan Type Complexes (U-ATCs) and the associated placer deposits were for many yearsthe only known sources of the PGEs. This paper attempts to show a connection betweenplatiniferous dunite-pyroxenite pipes in the Ural Platinum Belt and those on the eastern marginof the Bushveld Complex, both being significant PGE producers in the past, and phoscorite-carbonatite pipe (PCP) complexes. PCP complexes may be a promising source of PGEs. FourBrazilian PCP complexes are sampled (Salitre, Tapira, Ipanema and Catalão) as well as thePhalaborwa PCP complex in South Africa.

Platinum Metals Rev., 2006, 50, (3) 135

Phoscorite-Carbonatite Pipe (PCP)Complexes

Multistage, phoscorite-carbonatite zoned com-plexes are found worldwide, but the mostinteresting are in the Kola Peninsula, atMaymeicha-Kotui in northern Siberia, at the AldanShield in the far east of Russia, in Alaska, in theeast coast countries of Africa, and in the central-southern region of Brazil.

Phoscorite-carbonatite complexes are small,pipe-like bodies. They may take the form of dikes,sills, small plugs or irregular masses. A typical pipe-like body is of subcircular or elliptical cross-sectionand 3 to 4 km in diameter. Pipes extend to depthsof 3 to 13 km or more (10).

The magmatic mineralisation in pipe-like car-bonatite is commonly found in crescent-shaped,steeply dipping zones. Metasomatic mineralisationoccurs as irregular forms or veins (11). PCP com-

plexes possess a deep-step structure, and haveexperienced a prolonged, multistage metasomatic-hydrothermal evolution. Their complexcomposition and internal structure is clearlyindicative of multiple intrusions/injections ofmolten partially crystallised magmatic masses.Tectonic discontinuities, layering, banding andsteep inward concentric dips all indicate episodicdiapiric emplacement mechanisms. Phoscoritesand carbonatites are present as paired rocks; theyoccur near the nuclear area of the PCP complexes.Phoscorites are practically always associated withcarbonatites, but many carbonatite complexes,especially those of linear structure, do not containphoscorites.

Phoscorites, by definition, are medium andcoarse-grained igneous rocks of magnetite-forsterite-apatite composition (12). Besides typicalphoscorites, there are a variety of rock types of

Fig. 1 Map of southern Brazilshowing alkaline and alkaline-carbonatite occurrences (afterUlbrich and Gomes (26)).Catalão, Salitre, Tapira andIpanema PCP complexes areindicated. Some occurrences arein the sea; the dots near theshore and in the sea representintrusive alkaline volcanicrocks, including some volcanicsea islands. Those alkalineintrusions and volcanic islandsare related to the post-creta-ceous mechanism that resultedin the formation of the SouthAtlantic Ocean

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similar mineral composition in the same geologicalenvironment. Some of these contain diopsideinstead of forsterite, while others contain actino-lite, with or without relicts of diopside orphlogopite and tetraferriphlogopite (13). In thePCP complexes calcite-carbonatite is the dominantrock type, followed by dolomite-carbonatite.

Carbonatites occur in close spatial and tempo-ral association with phoscorites and often formmultiphase phoscorite-carbonatite series. Thephoscorite-carbonatite series are mantle-derivedrocks, and much discussion centres on whethercarbonatite and phoscorites separate by fractionalcrystallisation and accumulation, by liquid immisci-bility, or by both mechanisms. The existence ofmultistage phoscorite-carbonatite complexes, thesimilar mineral association and their geochemicalpeculiarities indicate, without doubt, that bothrocks were formed from a parental magma bysome method of differentiation. The mantle originof phoscorite has been confirmed by both radi-ogenic and stable isotope studies (13, 14).Recently, a growing body of evidence has suggest-ed that such magmas could be derived directlyfrom depths in excess of 70 km by partial meltingof the carbonated mantle peridotite (15, 16).

Multiple intrusions are revealed by the litholog-ical and structural arrangement of successive stagesof paired phoscorite-carbonatite; there are six atKovdor (Russia) (14), two at Solki (Finland) (17),at least two in Phalaborwa (South Africa) (18, 19)and five in Tapira (Brazil) (20, 21).

The economic relevance of the PCP complexesis demonstrated by the presence of large hosted

mining operations, such as phosphate mining atPhalaborwa, Jacupiranga, Tapira and Catalão(Brazil); Kovdor (Russia); baddeleyite mining atPhalaborwa and Kovdor; copper mining atPhalaborwa; iron mining at Kovdor; niobium min-ing at Araxá and Catalão (Brazil), see Figures 1 and2, and uranium mining at Phalaborwa and Araxá.

The evolution of carbonatite and alkaline com-plexes could be related to crustal evolutiondynamics and to continental rifting; carbonatiteand alkaline complexes were formed shortly beforethe continental break-up and the opening of theocean basins. Continental-type U-ATCs are close-ly related to PCP complexes; for instance, the largecylindrical platiniferous dunite-pyroxenite/alkalineintrusive complexes at Inagly, Kondyor and Guliplatinum province in the Aldan Shield, easternSiberia. These alkali-ultrabasic complexes are wide-spread in tectonically stable areas of eastern Russia.These complexes usually exhibit well-formed, con-centric zoned structures, and are mainly composedof platinum-bearing chrome-spinel dunites andpyroxenites, which are very similar to those occur-ring in the Ural Platinum Belt (UPB) (22).However, in contrast to the Uralian ultramaficmassifs, the Aldanian massifs occur as isolated,pipe-like bodies intruding the Archean crystallinebasement.

The strong similarities between the Uralian andAldanian platinum-bearing ultramafic rocks isthought to reflect similar melt-rock interactionmechanisms during their individualisation in theshallow mantle, before their emplacement in dif-ferent geodynamic contexts. The geodynamic

Fig. 2 A panoramic view of the Catalão PCP minetaken in October 2004. The sides show the benchesof typical mines. This mine is still in operation andbesides phosphate, a significant amount of niobi-um ore is being mined here

Platinum Metals Rev., 2006, 50, (3) 137

setting was probably subduction-related for theUralian-Alaskan zoned complexes and it is clearlyintra-continental, possibly related to a rift zone forthe Aldanian massifs (23).

Could PCP Complexes GeneratePGE Ore Deposits?

PCP complexes are assumed to be associatedwith the continental-type U-ATCs series, similarto the Aldanian massifs, and have been examinedas a potential source for research on minerals ofthe PGEs. The question is, could some highlysiderophile mantelic magma, by recurrent andmultiphase magmatic-metasomatic-hydrothermalevolution, result in PGE ore deposits? Indicationsof such a process are isolated, for instance:• Platinum group metals have been recoveredfrom electrolytic refinery sludge at Phalaborwa formany years (24).• PGE mineral phases have been reported insome ore concentrates from Phalaborwa andKovdor (25).

Despite the suggestion that the PGE and gold-silver mineralisation of the Kovdor andPhalaborwa complexes has a close spatial andprobably genetic relationship with the multistagemagmatic and post-magmatic processes, there isno consistent empirical evidence to support this.

The strategy of the current research was to usegeological knowledge accumulated at PCP com-plexes that have been mined over a number ofyears. A field and laboratory research programmewas drawn up to survey four typical PCP intru-sions located in central southern Brazil: Ipanema,Tapira, Salitre I and Catalão II, and also atPhalaborwa in South Africa.

It was assumed that a selective survey of rockgeochemistry could define any potential PGEenrichment in the PCP complexes and could pro-vide sufficient data to establish a connectionbetween the evolution of the PCP phases and thePGE concentration. The survey used a mineralexploration approach to look for PGE concentra-tions at ore standard. Current geological conceptsand exploration methodology, known to be effec-tive in this area, were used. However, explorationis not driven by highly specialised models or by

using a range of techniques, so a follow-up explo-ration is necessary in order to establish appropriatetechniques that can be adapted for effective explo-ration.

The Brazilian PCP Complexes Voluminous flood basalt magmatism occurred

in central and southern Brazil from the EarlyCretaceous period to the Eocene time. Theseregions include the extensive Early CretaceousParaná continental flood basalt province and anumber of Early Cretaceous to Eocene alkalineigneous provinces that surround the Paraná Basin,see Figure 1.

Some quite large (up to 65 km2) intrusive, car-bonatite-bearing ultramafic complexes are locatedin these provinces (21). The main PCP complexesare: Catalão I, Catalão II, in southern Goias State;Serra Negra, Tapira, Salitre I, Salitre II and Araxáin south-west Minas Gerais State; Ipanema,Jacupiranga and Juquiá in east São Paulo State, andLajes and Anitapolis, the southern intrusionsfound in Sta Catarina State.

With kamafugites, lamproites and kimberlites,these complexes are multistage intrusionsemplaced into Late-Proterozoic metamorphic ter-rains (20). The PCP complexes are formed by theamalgamation of multiphase intrusions comprisingmainly ultramafic rocks (dunite, wehrlite andclinopyroxenite), see Figure 3, with subordinatecalcite-carbonatite, phoscorite and syenite.

The phoscorite-carbonatite rock pair in theBrazilian PCP complexes is represented mainly byapatite, magnetite, diopside (minor phlogopite)

Fig. 3 A specimen of magnetite-biotite-perovskite-pyroxenite from the Tapira phosphate mine in Brazil

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phoscorite rock associated with calcite-carbonatite,see Figure 4.

The surface shape expression of all PCP com-plexes is almost rounded or oval, internallyconcentrically zoned, with diameters varying from1 to 7 km, depending on the level of erosion.However, the size of the actual phoscorite-carbon-atite bodies is even smaller (27). Rockidentification at the surface is quite difficult, aschemical weathering results in deep soil formationand a poor fresh rock exposure, see Figure 5.

The Phalaborwa PCP Complex The Phalaborwa complex intruded the Archean

basement at the edge of the Kapvaal Craton inEarly Proterozoic times (2.06 million years ago)

and consists of concentrically zoned, multipleintrusions, which decrease in age from the marginto the core. The core is an elliptically-shaped verti-cal intrusion known as the Loolekop pipe (18, 19).The host Phalaborwa complex is mainly composedof ultramafic rocks (dunite and pyroxenite) with acore of carbonatite and phoscorite. Minor rocktypes include glimmerite, syenite and fenite. Thecore of the composite intrusion shows a concentricarrangement of phoscorite around the margin anda core of banded carbonatite. Both these rocktypes were intruded by the central transgressivecarbonatite, see Figure 6.

The phoscorite is composed of olivine, mag-netite, apatite and phlogopite. The mineralcomposition and grain size present a wide rangevariation. The banded carbonatite consists largelyof magnetite-rich calcite-carbonatite, with minoramounts of apatite, olivine, phlogopite and biotite.The transgressive carbonatite is mineralogicallysimilar to the banded carbonatite, but lacks thebanding and represents a younger crosscuttingintrusive rock (24).

Field and Laboratory Surveys The present research was oriented to identify

possible PGE concentrations (at ore standard) andto establish if there was a relationship between thePGE concentration and individual rock types fromthe selected PCP complexes. To avoid the weath-ered upper zone, sampling was done on fresh rock

Fig. 4 A rock specimen from a Brazilian PCP complexof a phoscorite-carbonatite rock pair showing whitestreaks of calcite-carbonatite in phoscorite rock

Fig. 5 A Fosfertil mine geologist standing among deeplyweathered magnetite rich phoscorite in a phosphate minein Catalão, Brazil

Fig. 6 A specimen of banded carbonatite (white rock)and phlogopite magnetite phoscorite (dark rock) from theFoskor phosphate mine in Phalaborwa, South Africa

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exposures from the lower benches of the open pitphosphate mines.

In order to avoid the “nugget effect”, large vol-ume chip rock samples (15 kg on average) werecollected from every kind of rock type at theIpanema, Tapira, Salitre I, Catalão II andPhalaborwa PCP intrusions. In all 70 samples werecollected, amounting to 1500 kg (Table I).

Rock sampling was planned after considerationof all geological data available from the selectedPCP complexes. Representative samples were col-lected from the main rock types, represented by:

Tapira: pyroxenite (Figure 3) and phoscorite;Salitre: pyroxenite, phoscorite and carbonatite; Catalão: phoscorite and carbonatite (Figure 4);Ipanema: phoscorite and magnetitite; andPhalaborwa: pyroxenite, phoscorite, bandedcarbonatite (Figure 6) and transgressive car-bonatite.Each rock sample was crushed, homogenised,

cross-split and finally pulverised in an oscillatingmill to less than 0.044 mm particle size, beforebeing taken for chemical assay. The first round ofchemical analyses (54 samples), was performed bythe Analytical Science Division of Mintek (SouthAfrica), using the fire assay technique with NiScollection and ICP-OES for the final PGE nota-tion. The laboratory procedures were certified;SARM7 (Standard South Africa) was the referencesample and every sample was assayed twice.

The results from Mintek at the beginning of2005 were conclusive in indicating that PCP com-

plexes are, in fact, very suitable for the enrichmentof PGEs at ore level standards. Three PCP intru-sions (Ipanema, Catalão and Phalaborwa) gavevery consistent data indicating a high concentra-tion of PGE:Ipanema: up to 5.15 ppm in total of Pt, Pd,

Rh, Ru, Os;Catalão: 4.47 ppm in total of Pt, Pd, Rh, Os;Phalaborwa: 16.67 ppm in total of Ir, Os.The other two (Salitre and Tapira) show no PGEenrichment at all.

It should be noted that the rock samples fromSalitre and Tapira were taken from available drillcores, so were not as representative as the samplesfrom Catalão, Ipanema and Phalaborwa collectedfrom the mining pit benches. The negative resultobtained for these areas must take the samplingconstraints into account, and consequently shouldnot be taken as a definitive statement.

On comparing the data, it can be seen that therelative abundance of PGE in Brazilian PCP com-plexes shows a distinct enrichment in rhodium (upto 0.60 ppm), with no indication of iridium con-centration, whereas the rocks from Phalaborwa donot register rhodium enrichment, but show a verysignificant iridium concentration (up to 13.5 ppm).

A general statement of PGE concentration is:Catalão: Pt > Pd > Ru > Rh > OsIpanema: Pt > Pd > Os > Rh > RuPhalaborwa: Pt > Pd > Ru > Ir > Os

All the rock samples were graded for particlesize distribution by wet screening, followed by

Table I

Main Characteristics of Samples from the Brazilian and Phalaborwa PCP Complexes

Main Tapira* Salitre I* Catalão II* Ipanema* Phalaborwa†characteristics

Age 70 Ma. 80 Ma. 83 Ma. 123 Ma. 2060 Ma.

Surface, km2 33.0 15.0 14.5 9.0 20.0

Shape Oval Oval Circular Circular Kidney-shaped

Main rocks Peridotite Peridotite Peridotite — —Clinopyroxenite Clinopyroxenite Clinopyroxenite Clinopyroxenite ClinopyroxeniteCalcite-carbonatite Calcite-carbonatite Calcite-carbonatite Calcite-carbonatite Calcite-carbonatitePhoscorite Phoscorite Phoscorite Phoscorite PhoscoriteSyenite Alkalic-syenite — Syenite —

* Ref. (27) CBMM †Ref. (18) Vielreicher et al.

Platinum Metals Rev., 2006, 50, (3) 140

chemical and mineralogical analyses as well as mag-netic separation studies.

The research, which is still in progress, will befollowed by systematic chemical and mineralogicalstudies. At present, total rock geochemical analysis,including major and minor trace elements, includ-ing the rare earths, is being determined by AASand/or ICP spectroscopy. The rock samples willbe surveyed for process mineralogy studies, andthin-polished samples will be prepared for opticaland scanning electron microscopy analyses.Mineralogical analyses will be performed by X-raydiffraction, optical mineralogy and scanning elec-tron microscopy with energy dispersive X-rayspectrometer (SEM-EDS). Gravitational concen-tration and heavy minerals extraction for asensitive mineralogical (microprobe) study will alsobe undertaken.

The author is aware that the following miner-alogical study will be much more difficult and time

consuming, and is of higher risk. The Brazilian lab-oratory expertise and technical apparatus may notbe sufficient. So it is further intended to ask for thecollaboration of Russian mineralogists, especiallythose linked with St. Petersburg University or withNATI Research JSC, St. Petersburg.

The main aim will be to identify the PGE min-eralogical phases and to establish their relationshipwith associated silicate and oxide minerals, lookingfor a probable genetic connection between thePGE concentration process and the evolution ofthe phoscorite-carbonatite complexes. The labora-tory procedures will be performed at theUniversity of São Paulo, and other internationalacademic and commercial research facilities.

Discussion and ConclusionsThe PGEs, rhenium and gold comprise the so-

called highly siderophile elements (HSE), theabundances of which in the upper mantle are often

Table II

PGE Crust and Mantle Abundance Compared with PGE Concentration in Combined Rock Types fromPCP Complexes

Material Platinum, Paladium, Rhodium, Osmium, Iridium, Ruthenium,ppt* ppt ppt ppt ppt ppt

Crustal average† 400 400 60 50 50 100PGE abundance

Upper mantle (peridotite)‡Average abundance 6500 5700 n.a. 3500 3500 5800

Catalão PCP 300,000 300,000 140,000 120,000 n.a. 120,000up to up to up to up to up to

2,860,000 810,000 600,000 200,000 200,000

Ipanema PCP 300,000 200,000 400,000 400,000 n.a. 150,000up to up to up to up to

3,200,000 1,330,000 540,000 490,000

Phalaborwa PCP 150,000 260,000 n.a. 300,000 1,100,000 120,000up to up to up to up to

580,000 3,280,000 13,500,000 160,000

Ore concentration, 0.15 0.26 0.14 0.12 1.10 0.12g t–1 up to up to up to up to up to up to

3.20 1.33 0.60 3.28 13.50 0.49

Concentration rate: 89 45 n.a. 57 315 27PCP composition/ up to up to up to up to up tomantle abundance 492 times 233 times 937 times 3857 times 85 times

* ppt = parts per trillion †Crustal average, Ref. (29) Wedepohl (1995) ‡Upper Mantle, Ref. (28) Morgan et al.

Platinum Metals Rev., 2006, 50, (3) 141

in the parts per trillion (ppt) range, and, which inthe undepleted primitive upper mantle, are inapproximately chondritic proportions (28, 29).

Phoscorite-carbonatite pipes (PCP) are gener-ated in a geodynamic environment which providesappropriate structural control to enable the verti-cal migration of dense iron-rich melts, overthousands of metres, and, equally important, theirconcentration into relatively small core zones.There is a limited understanding of the role of themagma mixing, assimilation, crustal metasomatismand other subsolidus processes in the origin andevolution of PCP complexes. However, the role ofmetasomatism, including late-stage alteration isalso important in the ultimate understanding ofthe PGE enrichment processes.

PGE mineralisation has a close spatial andprobably genetic relationship with the multistagemagmatic and post-magmatic evolution of PCPcomplexes. The PGE enriched zones, in the corezones of PCP complexes, represent the final prod-uct of a series of superimposed events like theprogressive PGE fractionation during the evolu-tion of mantle magma and the recurrence ofmagmatic pulse events.

The parental sulfur-poor/oxygen-rich melt sys-tem tends to result in a PGE ore mineralogyassemblage similar to those from classical ultra-mafic platiniferous pipes. These pipes arecommercially very attractive because of the lowcapital cost of establishing ore dressing facilities,that is, the bulk of the PGEs could be recoveredby conventional gravity and magnetic separationtechnologies.

The PGE concentrations in Catalão, Ipanemaand Phalaborwa provide solid evidence of thePGE potential of PCP complexes, particularly inregare to their ore concentration level. The PGEoccurrence in Ipanema shows the need to payattention to the detection of Fe-Cr and PGE-richvein-type varieties of spinels. The wide develop-ment of such Fe-spinel veins is indicative of a lowerosion level at the PCP complex cupola, and con-sequently, a better PGE potential (22).

The theoretical and factual data encourage theassumption that PCP intrusions are a very promis-ing target for PGE mineralisation. It is proposed

that the platiniferous pipe conceptual modelshould be extended to take into account PCPcomplexes as a promising new member. For sys-tematic mineral exploration, the PGE explorationstrategy for PCP complexes must be directedmainly to a selective structural and geochemistrysurvey, instead of to conventional saturation rocksampling geochemistry.

AcknowledgementsFoskor Limited, Jan H. van der Merwe and the

mining staff from Fosfertil SA, Tapira and Catalãoare gratefully thanked for permission, technicalassistance, hospitality and discussions during fieldwork and sampling at the Phalaborwa, Tapira andCatalão mines, respectively. This study has beenpartly supported by the São Paulo Research andDevelopment Agency (FAPESP – Grant03/09481-0) and hosted by the LCT –Technological Characterization Laboratory,Polytechnic School of the University of São Paulo(USP, Mining and Petroleum EngineeringDepartment).

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The AuthorDr Juarez Fontana is professor and a mineralexploration expert at the University of São Paulo,Brazil. He is interested in both academic (geologicalmodels) and commercial projects, connected withPGE mineralisation and metallogenic processes,especially those related to the alkalic phoscorite-carbonatite intrusive complexes.