Abstract
In the present study, we document the nature of contact-style platinum-group element (PGE) mineralization along >100 km of strike in the northern lobe of the Bushveld Complex. New data from the farm Rooipoort are compared to existing data from the farms Townlands, Drenthe, and Nonnenwerth. The data indicate that the nature of the contact-style mineralization shows considerable variation along strike. In the southernmost portion of the northern Bushveld, on Rooipoort and adjoining farms, the mineralized sequence reaches a thickness of 700 m. Varied-textured gabbronorites are the most common rock type. Anorthosites and pyroxenites are less common. Chromitite stringers and xenoliths of calcsilicate and shale are largely confined to the lower part of the sequence. Layering is locally prominent and shows considerable lateral continuity. Disseminated sulfides may reach ca. 3 modal % and tend to be concentrated in chromitites and melanorites. Geochemistry indicates that the rocks can be correlated with the Upper Critical Zone. This model is supported by the fact that, in a down-dip direction, the mineralized rocks transform into the UG2-Merensky Reef interval. Between Townlands and Drenthe, the contact-mineralized sequence is thinner (up to ca. 400 m) than in the South. Chromitite stringers occur only sporadically, but ultramafic rocks (pyroxenites, serpentinites, and peridotites) are common. Xenoliths of calcsilicate, shale, and iron formation are abundant indicating significant assimilation of the floor rocks. Sulfides may locally form decimeter- to meter-sized massive lenses. PGE grades tend to be higher than elsewhere in the northern Bushveld. The compositions of the rocks show both Upper Critical Zone and Main Zone characteristics. At Nonnenwerth, the mineralized interval is up to ca. 400 m thick. It consists largely of varied-textured gabbronorites, with minor amounts of igneous ultramafic rocks and locally abundant and large xenoliths of calcsilicate. Layering is mostly weakly defined and discontinuous. Disseminated sulfides (<ca. 3 modal %) occur throughout much of the sequence. Geochemistry indicates that the rocks crystallized mainly from tholeiitic magma and thus have a Main Zone signature. The implication of our findings is that contact-style PGE mineralization in the northern lobe of the Bushveld Complex cannot be correlated with specific stratigraphic units or magma types, but that it formed in response to several different processes. At all localities, the magmas were contaminated with the floor rocks. Contamination with shale led to the addition of external sulfur to the magma, whereas contamination with dolomite may have oxidized the magma and lowered its sulfur solubility. In addition to contamination, some of the magmas, notably those of Upper Critical Zone lineage present at the south-central localities, contained entrained sulfides, which precipitated during cooling and crystallization.
Similar content being viewed by others
References
Armitage PEB, McDonald I, Edwards JS, Manby GM (2002) Platinum-group element mineralisation in the Platreef and calc-silicate footwall at Sandsloot, Potgietersrus District, South Africa. Trans Inst Min Metall 111:B36–B45
Ashwal LD, Webb SJ, Knoper MW (2005) Magmatic stratigraphy in the Bushveld northern lobe: continuous geophysical and mineralogical data from the 2950 m Bellevue drillcore. S Afr J Geol 108:199–232
Barnes S-J, Maier WD (1999) The fractionation of Ni, Cu and the noble metals in silicate and sulphide liquids. In: Keays RR, Lesher CM, Lightfoot PC, Farrow CEG (eds) Dynamic processes in magmatic ore deposits and their application to mineral exploration. Geological Association of Canada, Short Course Notes 13:69–106
Barnes S-J, Maier WD (2002a) Platinum-group elements and microstructures of normal Merensky Reef from Impala platinum mines, Bushveld Complex. J Petrol 43:103–128
Barnes S-J, Maier WD (2002b) Platinum-group element distributions in the Rustenburg Layered Suite of the Bushveld Complex, South Africa. In: Cabri, L (ed) The geology, geochemistry, mineralogy and mineral benefication of the platinum-group elements. CIM Spec Vol 54:431–458
Barton JM, Cawthorn RG, White J (1986) The role of contamination in the evolution of the Platreef of the Bushveld Complex. Econ Geol 81:1096–1104
Botha MJ (1985) Geology of the Rustenburg Layered Suite and associated mineralization on the farms Moordrift 289 KR, Jaagbaan 291 KR, and Grasvally 293 KR, south of Potgietersrus. Internal Report, Gold Fields of South Africa
Boudreau AE, Meurer WP (1999) Concentration of platinum-group elements by magmatic fluids in layered intrusions. Econ Geol 94:1830–1848
Buchanan DL, Rouse JE (1984) Role of contamination in the precipitation of sulfides in the Platreef of the Bushveld Complex. In: Buchanan DL, Jones MJ (eds) Sulfide deposits in mafic and ultramafic rocks. IMM, London, pp 141–146
Buchanan DL, Nolan J, Suddaby, Rouse MJ, Davenport JWJ (1981) The genesis of sulphide mineralisation in a portion of the Potgietersrus limb of the Bushveld Complex. Econ Geol 76:568–579
Cawthorn RG, Barton JM Jr, Viljoen MJ (1985) Interaction of floor rocks with the Platreef on Overysel, Potgietersrus, northern Transvaal. Econ Geol 80:988–1006
Cawthorn RG, Merkle RKW, Viljoen MJ (2002) Platinum-group element deposits in the Bushveld Complex, South Africa. In: Cabri LJ (ed) The geology, geochemistry, mineralogy and mineral beneficiation of platinum-group elements. CIM Spec Vol 54:389–429
Chaumba JB, Harris C, Tredoux M (1998) Oxygen, strontium and osmium isotope geochemistry of the Platreef of the northern lobe of the Bushveld Complex, South Africa. Absr., 8th Int Platinum Symposium, 71–72
Curl EA (2001) Parental magmas of the Bushveld Complex, South Africa. PhD thesis, Department of Earth Sciences, Monash University, Australia, 140 pp
De Klerk WJ (1992) Petrogenesis of the Upper Critical Zone in the western Bushveld Complex. Unpubl. PhD thesis, Rhodes University, Grahamstown, RSA, 294 pp
De Klerk L (2005) Bushveld stratigraphy on Rooipoort, Potgietersrus limb. Workshop on Platinum exploration and exploitation in Africa, October 2005, Johannesburg
De Waal SA (1975) Carbon dioxide and water from metamorphic reactions as agents for sulfide and spinel precipitation in mafic magmas. Trans Geol Soc S Afr 80:193–196
Eales HV, Cawthorn RG (1996) The Bushveld Complex. In: Cawthron RG (ed) Layered intrusions. Elsevier, Amsterdam, The Netherlands, pp 181–229
Eales HV, De Klerk WJ, Teigler B (1990) Evidence for magma mixing processes within the Critical and Lower Zones of the northwestern Bushveld Complex, South Africa. Chem Geol 88:261–278
Eales HV, Botha WJ, Hattingh PJ, De Klerk WJ, Maier WD, Odgers ATR (1993) The mafic rocks of the Bushveld Complex: a review of emplacement and crystallization history, and mineralization, in the light of recent data. J Afr Earth Sci 16:121–142
Gain SB, Mostert AB (1982) The geological setting of the platinoid and base metal sulphide mineralisation in the Platreef of the Bushveld Complex on Drenthe, north of Potgietersrus. Econ Geol 77:1395–1404
Harris C, Chaumba JB (2001) Crustal contamination and fluid–rock interaction during the formation of the Platreef, northern limb of the Bushveld Complex, South Africa. J Petrol 42:1321–1347
Holwell DA, McDonald I (2006) Petrology, geochemistry and the mechanisms determining the distribution of platinum-group elements and base metal sulfide mineralization in the Platreef at Overysel, northern Bushveld Complex, South Africa
Holwell DA, Armitage PEB, McDonald I (2005) Observations on the relationship between the Platreef and its hangingwall. Trans Inst Min Metall B 114:199–207
Holwell DA, McDonald I, Armitage PEB (2006) Platinum-group mineral assemblages in the Platreef at the Sandsloot Mine, northern Bushveld Complex, South Africa. Mineral Mag 70:83–101
Hsu LC, Lechler PJ, Nelson JH (1991) Hydrothermal solubility of palladium in chloride solutions from 300°C to 700°C: Preliminary experimental results. Econ Geol 86:422–427
Hulbert LJ (1983) A petrographical investigation of the Rustenburg Layered Suite and associated mineralization south of Potgietersrus. DSc dissertation, University of Pretoria, 511 pp
Hutchinson D, Kinnaird JA (2005) Complex multistage genesis for the Ni–Cu–PGE mineralisation in the southern region of the Platreef, Bushveld Complex, South Africa. Trans Inst Min Metall B 114:208–224
Kinnaird JA (2005) Geochemical evidence for multiphase emplacement in the southern Platreef. Trans Inst Min Metall 114:225–242
Kinnaird JA, Hutchinson D, Schurmann L, Nex PAM, de Lange R (2005) Petrology and mineralization of the southern Platreef: northern limb of the Bushveld Complex, South Africa. Miner Depos 40:576–597
Klein C, Beukes NJ (1989) Geochemistry and sedimentology of a facies transition from limestone to iron-formation deposition in the early Proterozoic Transvaal Supergroup, South Africa. Econ Geol 84:1733–1774
Kruger FJ (2005) Filling the Bushveld Complex magma chamber: lateral expansion, roof and floor interaction, magmatic unconformities, and the formation of giant chromitite, PGE and Ti-V magnetite deposits. Miner Depos 40:451–472
Lee C, Sharpe MR (1980) Further examples of silicate liquid immiscibility and spherical aggregation in the Bushveld Complex. Earth Planet Sci Lett 48:131–147
Li C, Ripley EM, Merino E, Maier WD (2004) Replacement of base metal sulfides by actinolite, epidote, calcite, and magnetite in the UG2 and Merensky Reef of the Bushveld Complex, South Africa. Econ Geol 99:173–184
Liebenberg L (1970) The sulfides in the layered sequence of the Bushveld igneous Complex. Geol Soc S Afr Spec Pub 1:108–208
Maier WD, Eales HV (1997) Correlation within the UG2-Merensky Reef interval of the Western Bushveld Complex, based on geochemical, mineralogical and petrological data. Council for Geosciences, Bull Geol Surv S Afr 120, 56 pp
Maier WD, Barnes S-J (1998) Concentrations of rare earth elements in silicate rocks of the Lower, Critical and Main Zones of the Bushveld Complex. Chem Geol 150:85–103
Maier WD, Barnes S-J (1999) Platinum-group elements in silicate rocks of the Lower, Critical, and Main Zones at Union Section, western Bushveld Complex. J Petrol 40:1647–1671
Maier WD, Barnes S-J (2003) Platinum-group elements in the Boulder Bed, western Bushveld Complex, South Africa. Miner Depos 38:370–380
Maier WD, Arndt NT, Curl EA (2000) Progressive crustal contamination of the Bushveld Complex: evidence from Nd isotopic analyses of the cumulate rocks. Contrib Mineral Petrol 140:316–327
Maier WD, Gomwe T, Barnes S-J, Li C, Theart H (2004) Platinum-group elements in the Uitkomst Complex, South Africa. Econ Geol 99:499–516
Manyeruke TD (2003) The petrology and geochemistry of the Platreef on the farm Townlands, near Potgietersrus, northern Bushveld Complex. MSc thesis, University of Pretoria, 99 pp
Manyeruke TD (2007) Geochemical variation of the Platreef in the northern limb of the Bushveld Complex: Implications for the origin of the PGE mineralization. PhD thesis, University of Pretoria (submitted)
Manyeruke TD, Maier WD, Barnes S-J (2005) Major and Trace Element Geochemistry of the Platreef on the farm Townlands, northern Bushveld Complex. S Afr J Geol 108:381–396
McDonald I, Holwell DA, Armitage PEB (2005) Geochemistry and Mineralogy of the Platreef and “Critical Zone” of the Northern Lobe of the Bushveld Complex, South Africa: Implications for Bushveld Stratigraphy and the Development of PGE Mineralization. Miner Depos 40:526–549
McDonough WF, Sun S-S (1995) The composition of the Earth. Chem Geol 120:223–253
Mitchell AA (1986) The petrology, mineralogy and geochemistry of the Main Zone of the Bushveld Complex at Rustenburg Platinum Mines, Union Section. PhD thesis, Rhodes University, Grahamstown, SA
Naldrett AJ (2004) Magmatic sulfide deposits. Springer, Berlin Heidelberg New York, p 727
Peregoedova A, Barnes S-J, Baker DR (2004) The formation of Pt–Ir alloys and Cu–Pd rich sulfide melts by partial desulfurization of Fe–Ni–Cu sulfides: results of experiments and implications for natural systems. Chem Geol 208:247–264
Potts PJ, Tindle AG, Webb PC (1992) Geochemical reference material compositions. CRC Press, Boca Raton, FL
Ruiz J, Barra F, Ashwal LD, Le Grange M (2004) Re–Os systematics on sulfides from the Platreef, Bushveld Complex, South Africa. Abstr., Geoscience Africa, Wits University, Johannesburg, p 564
Scoon RJ, Teigler B (1994) Platinum-group element mineralization in the Critical Zone of the Western Bushveld Complex: I sulfide-poor chromitites below the UG2. Econ Geol 89:1094–1121
Sharman-Harris ER, Kinnaird JA, Harris C, Horstmann UE (2005) A new look at sulphide mineralisation of the northern limb, Bushveld Complex: a stable isotope study. Trans Inst Min Metall B 114:252–263
Sharpe MR, Crous SP, Gain SB, Chunnett, GK, Lee CA (2002) Sheba’s Ridge—an unconventional setting for Platreef, UG2 and Merensky-style PGE BMS deposits in the Bushveld Complex. Abstr. 9th Int Platinum Symposium, Billings, Montana, p. 407–408
Stevens M (2004) Constraining Platreef petrogenesis, northern limb of the BushveldComplex, South Africa. BSc Hns thesis, Australian National University, 154 pp
Streckeisen A (1976) To each plutonic rock its proper name. Earth Sci Rev 12:1–33
Teigler B, Eales HV (1996) The Lower and Critical Zones of the western limb of the Bushveld Complex, as indicated by the Nooitgedacht boreholes. Bull Geol Surv S Afr, 111, 126 pp
van der Merwe MJ (1976) The layered sequence of the Potgietersrus limb of the Bushveld Complex. Econ Geol 71:1337–1351
Vermaak CF (1995) The platinum-group metals—a global perspective. Council for Mineral Technology, Randburg, 247 pp
Viljoen MJ, Schürmann LW (1998) Platinum group metals. In: Wilson MGC, Anhaeusser CR (eds) The Mineral Resources of South Africa. Council for Geoscience, Pretoria, pp 532–568
Wagner A (1929) The platinum deposits and mines of South Africa. Oliver & Boyd, Edinburgh, UK, pp 366
White JA (1994) The Potgietersrus project geology and exploration history: Proceedings, 15th CMMI Congress, South African Institute of Mining and Metallurgy, pp 173–182
Acknowledgements
Caledonia Mining is thanked for allowing access to their property and giving permission to publish the data.
Author information
Authors and Affiliations
Corresponding author
Additional information
Editorial handling: P. Lightfoot
Rights and permissions
About this article
Cite this article
Maier, W.D., de Klerk, L., Blaine, J. et al. Petrogenesis of contact-style PGE mineralization in the northern lobe of the Bushveld Complex: comparison of data from the farms Rooipoort, Townlands, Drenthe and Nonnenwerth. Miner Deposita 43, 255–280 (2008). https://doi.org/10.1007/s00126-007-0145-3
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00126-007-0145-3