Abstract
The Platreef unit of the northern Bushveld Complex comprises a diverse package of pyroxenites, peridotites and mafic lithologies with associated Ni–Cu–platinum-group element (PGE) mineralisation. Base metal sulphides (BMS) are generally more abundant in the Platreef than in other Bushveld PGE deposits, such as the Merensky Reef and the UG2 chromitite, but the Platreef, though thicker, has lower overall PGE grades. Despite a commonly held belief that PGEs are closely associated with sulphide mineralisation, a detailed study by laser ablation ICP-MS (LA-ICP-MS) on a core through the Platreef at Turfspruit suggests that this is not strictly the case. While a significant proportion of the Pd, Os and Ir were found to be hosted by BMS, Pt, irrespective of its whole-rock concentration, was not. Only at the top of the Platreef is Pt directly associated with sulphide minerals where Pt–Pd–(±Sb)–Te–Bi-bearing inclusions were detected in the chalcopyrite portions of large composite sulphides. In contrast, Pd, Os, and Ir occur in solid solution and as discrete inclusions within the BMS throughout the core. For Os and Ir, this is usually in the form of Os–Ir alloys, whereas Pd forms a range of Pd–Te–Bi–(Sb) phases. Scanning electron microscope observations on samples from the top of the core revealed the presence of ≤0.2-mm-long (PtPd)2(Sb,Te,Bi)2 michenerite–maslovite laths within the chalcopyrite portions of large composite sulphides. Additional Pt-bearing minerals, including sperrylite and geversite, and a number of Pd(–Te–Bi–Sb) minerals were observed in, or close to, the alteration rims of these sulphides. This textural association was observed throughout the core. Similar platinum-group minerals (PGMs) were observed within the felsic assemblages composed of quartz, plagioclase, alkali feldspar and clinopyroxene produced by late-stage felsic melts that permeated the Platreef. Many of these PGMs occur a significant distance away from any sulphide minerals. We believe these features can all be linked to the introduction of As, Sb, Te and Bi into the magmatic system through assimilation of sedimentary footwall rocks and xenoliths. Where the degree of contamination was high, all of the Pt and some of the Pd formed As- and Sb-bearing PGM that were expelled to the edges of the sulphide droplets. Many of these were redistributed where they came into contact with late-stage felsic melts. Where no felsic melt interactions occurred, the expelled Pt- and Pd-arsenides and antimonides remained along the margins of the sulphides. At the top of the Platreef, where the effects of contamination were relatively low, some of the Pt remained within the sulphide liquids. On cooling, this formed the micro-inclusions and blade-like laths of Pt–Pd–(Sb)–Bi–Te in the chalcopyrite.
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References
Armitage PEB, McDonald I, Edwards SJ, Manby GM (2002) Platinum-group element mineralization in the Platreef and calc-silicate footwall at Sandsloot, Potgietersrus District, South Africa. Appl Earth Sci (Trans. Inst. Min. Metall. B) 111:B36–B45
Ashwal LD, Webb SJ, Knoper MW (2005) Magmatic stratigraphy in the Bushveld Northern Lobe: continuous geophysical and mineralogical data from the 2,950m Bellevue drillcore. S Afr J Geol 108:109–232
Barnes S-J, Cox RA, Zientek ML (2006) Platinum-group element, gold, silver and base metal distribution in compositionally zoned sulphide droplets from Medvezky Creek Mine, Noril’sk, Russia. Contrib Mineral Petrol 152:187–200
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
Buchanan DL, Rouse JE (1984) Role of contamination in the precipitation of sulphides in the Platreef of the Bushveld Complex. In: Buchanan DL, Jones MJ (eds) Sulphide deposits in mafic and ultramafic rocks. Institute of Mining Metallurgy, London, pp 141–146
Buchanan DL, Nolan J, Suddaby P, Rouse JE, Viljoen MJ, Davenport JWJ (1981) The genesis of sulfide mineralization in a portion of the Potgietersrus lobe of the Bushveld Complex. Econ Geol 76:568–579
Cabri LJ, Laflamme JHG (1976) The mineralogy of the platinum-group elements from some copper–nickel deposits of the Sudbury area. Econ Geol 71:1159–1195
Cawthorn RG, Lee CA, Schouwstra RP, Mellowship P (2002) Relationship between PGE and PGM in the Bushveld Complex. Can Mineral 40:311–328
Glotov AI, Polyakov GV, Akimtzev V, Hoa TT, Balykin PA, Akimtsev VA, Krivenko AP, Tolstykh ND, Phuong NT, Thanh HH, Hung TQ, Petroa TE (2001) The Ban Phuc Ni–Cu–PGE deposit related to the phanerozoic komatiite–basaltic association in the Song Da rift, northwestern Vietnam. Can Mineral 39:573–589
Godel B, Barnes S-J, Maier WD (2007) Platinum-group elements in sulphide minerals, platinum-group minerals, and whole-rocks of the Merensky Reef (Bushveld Complex, South Africa): implications for the formation of the reef. J Petrol 48:1569–1604
Harris C, Chaumba JB (2001) Crustal contamination and fluid–rock interaction during the formation of the Platreef, Northern Limb of the Bushveld Complex. S Afr J Petrol 42:1321–1347
Holwell DA, Jordaan A (2006) Three-dimensional mapping of the Platreef at the Zwartfontein South mine: implications for the timing of magmatic events in the Northern Limb of the Bushveld Complex, South Africa. Appl Earth Sci (Trans Inst Min Metall) 115:B41–48
Holwell DA, McDonald I (2006) Petrology, geochemistry and the mechanisms determining the distribution of platinum-group element and base metal sulphide mineralization in the Platreef at Overysel, northern Bushveld Complex, South Africa. Miner Depos 41:575–598
Holwell DA, McDonald I (2007) Distribution of platinum-group elements in the Platreef at Overysel, northern Bushveld Complex: a combined PGM and LA-ICP-MS study. Contrib Mineral Petrol 154:171–190
Holwell DA, Armitage PEB, McDonald I (2005) Observations on the relationship between the Platreef and its hangingwall. Appl Earth Sci (Trans. Inst. Min. Metall. B) 114:199–207
Holwell DA, McDonald I, Armitage PEB (2006a) Platinum-group mineral assemblages in the Platreef at the South Central Pit, Sandsloot mine, northern Bushveld Complex, South Africa. Mineral Mag 70:83–101
Holwell DA, Boyce AJ, McDonald I (2006b) A sulphur isotope study of the Platreef, northern Bushveld Complex: genetic implications for the formation of an enigmatic deposit. 29th Mineral Deposits Studies Group meeting, London, 6–7th January 2006, abstract.
Holwell DA, Boyce AJ, McDonald I (2007) Sulfur isotope variations within the Platreef: genetic implications for the origin of sulphide mineralization. Econ Geol 102:1091–1110
Huminicki MAE, Cabri L, Sylvester PJ, Tubreet MN (2004) Determinations of Platinum-Group Element (PGE) Distributions Using Whole-rock, SEM, EMPA, Image Analysis, and LA-ICP-MS Techniques in the Kelly Lake Ni–Cu–PGE Deposit, Sudbury. Eos. Trans. AGU, 85(17), Joint Assembly Supplied Abstract.
Hutchinson D, Kinnaird JA (2005) Complex multi-stage genesis for the Ni–Cu–PGE mineralization in the southern region of the Platreef, Bushveld Complex, RSA. Appl Earth Sci (Trans. Inst. Min. Metall. B) 114:208–224
Hutchinson D, McDonald I (2005). Breaking the rules. Divergent behavior of platinum and palladium in the Northern Limb of Bushveld Complex, R.S.A. In: Törmänen TO, Alapieti TT (eds) 10th International Platinum Symposium, Extended Abstracts, pp. 118–121
Hutchinson D, Kinnaird JA, Schürmann LW (2004) Complex multi-stage mineralization history in the southern sector of the Platreef, Bushveld Complex, South Africa. In: Geoscience Africa 2004, Abstract Volume, University of the Witwatersrand, Johannesburg, South Africa, Ashwal (ed.) 293–294
Kinloch ED (1982) Regional trends in the platinum-group mineralogy of the critical zone of the Bushveld Complex, South Africa. Econ Geol 77:1328–1347
Kinloch ED, Peyerl W (1990) Platinum-group minerals in various rock types of the Merensky Reef, genetic implications. Econ Geol 85:537–555
Kinnaird JA (2005) Geochemical evidence of multiphase emplacement in the southern Platreef. Appl Earth Sci (Trans Inst Min Metall) 114:B225–242
Kinnaird JA, McDonald I (2005) An introduction to mineralization in the Northern Limb of the Bushveld Complex. Appl Earth Sci (Trans Inst Min Metall) 114:B194–198
Kinnaird JA, Hutchinson D, Schürmann L, Nex PAM, Lange R-de (2005) Petrology and mineralization of the southern Platreef: Northern Limb of the Bushveld Complex, South Africa. Mineralium Deposita 40:576–597
Kruger FJ (2005a) The Main Zone of the Bushveld Complex: source of the Merensky Reef and the Platreef. In: Törmänen TO, Alapieti TT (eds) 10th International Platinum Symposium, Extended Abstracts, pp. 468–471
Kruger FJ (2005b) 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
Li C, Ripley EM, Merino E, Maier WD (2004) Replacement of base metal sulfides by actinolite, epidote, calcite and magnetite in the UG2 chromitite and Merensky Reef of the Bushveld Complex, South Africa. Econ Geol 99:173–184
Maier WD (2002) Pt, Pd, Cu and sulphur contents of the Platreef on the farm Townlands, northern Bushveld Complex: in Boudreau A (ed.) 9th Int. Platinum Symp., Ext. Abstract, 21–25th July 2002, Billings, Montana, USA.
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 (2005) Development of sulphide standards for the in-situ analysis of platinum-group elements by laser ablation inductively coupled plasma-mass spectroscopy (LA-ICP-MS)’. In: Törmänen TO, Alapieti TT (eds) 10th International Platinum Symposium, Extended Abstracts, pp. 468–471
McDonald I (2008) Platinum-group element and sulphide mineralogy from ultramafic complexes at Andriamena, Madagascar. Applied Earth Science (Trans Inst Min Metall) 117:1–10
McDonald I, Holwell DA (2007) Did Lower Zone magma conduits store PGE-rich sulphides that were later supplied to the Platreef? S Afr J Geol 110:611–616
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
McLaren CH, de Villers JPR (1982) The platinum-group chemistry and mineralogy of the UG-2 chromitite layer of the Bushveld Complex. Econ Geol 77:1348–1366
Nex PAM (2005) The structural setting of mineralization on Tweefontein Hill, Northern Limb of the Bushveld Complex, South Africa. Appl Earth Sci (Trans Inst Min Metall) 114:B243–291
Prichard HM, Hutchinson D, Fisher PC (2004) Petrology and crystallization history of multiphase sulphide droplets in a mafic dike from Uruguay: Implications for the origin of Ni–Cu–PGE sulphide deposits. Econ Geol 99:365–376
Ripley EM (1990) Platinum-group element geochemistry of Cu–Ni mineralization in the basal zone of the Babbitt Deposit, Duluth Complex, Minnesota. Econ Geol 85:830–841
Sharman-Harris ER, Kinnaird JA, Harris C, Horstmann UE (2005) A new look at sulphide mineralization of the Northern Limb, Bushveld Complex: a stable isotope study. Appl Earth Sci (Trans. Inst. Min. Metall. B) 114:252–263
Sproule RA, Sutcliffe R, Tracanelli H, Lesher CM (2007) Palaeoproterozoic Ni–Cu–PGE mineralization in the Shakespeare intrusion, Ontario, Canada: a new style of Nipissing gabbro-hosted mineralization. Applied Earth Science (Trans. Inst. Min. Metall. B) 116:188–200
Tredoux M, Lindsay NM, Davies G, McDonald I (1995) The fractionation of the platinum-group elements in magmatic systems with the suggestion of a novel causal mechanism. S Afr J Geol 98:157–167
van der Merwe MJ (1976) The layered sequence of the Potgietersrus limb of the Bushveld Complex. Econ Geol 71:1337–1351
van der Merwe MJ (1978) Unpublished PhD thesis. University of the Witwatersrand, Johannesburg
Vermaak CF, Hendriks LP (1976) A review of the mineralogy of the Merensky Reef, with specific reference to new data on the precious metal mineralogy. Econ Geol 71:1244–1268
Viljoen MJ, Schürmann LW (1998) Platinum-group metals. In: Wilson MGC, Anhaeusser CR (eds.) The mineral resources of South Africa. Council for Geoscience Handbook 16:532–568
White JA (1994) The Potgietersrus prospect—geology and exploration history. XVth CMMI Congress, Johannesburg. SAIMM 3:173–181
Acknowledgements
This project was sponsored by Ivanhoe Nickel and Platinum Ltd. and undertaken at the University of the Witwatersrand. Special thanks go to Professor Judith Kinnaird at the University of the Witwatersrand for financial support, to Dr Louis Schürmann and Ivanhoe Nickel and Platinum Ltd. for their continued funding and support for this project, and to THRIP for their financial aid. We would also like to thank the staff at Moruo Minerals and Spectrau (University of Johannesburg) for their assistance with the SEM and microprobe data. Reviews and comments by Thomas Oberthur, Sarah Barnes, Bernd Lehmann and Madelein Gerber significantly improved the paper.
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Hutchinson, D., McDonald, I. Laser ablation ICP-MS study of platinum-group elements in sulphides from the Platreef at Turfspruit, northern limb of the Bushveld Complex, South Africa. Miner Deposita 43, 695–711 (2008). https://doi.org/10.1007/s00126-008-0190-6
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DOI: https://doi.org/10.1007/s00126-008-0190-6