Mineralium Deposita

, Volume 48, Issue 2, pp 193–210 | Cite as

Sulfide-associated mineral assemblages in the Bushveld Complex, South Africa: platinum-group element enrichment by vapor refining by chloride–carbonate fluids

Article
First Online:
Received:
Accepted:

Abstract

The petrology of base metal sulfides and associated accessory minerals in rocks away from economically significant ore zones such as the Merensky Reef of the Bushveld Complex has previously received only scant attention, yet this information is critical in the evaluation of models for the formation of Bushveld-type platinum-group element (PGE) deposits. Trace sulfide minerals, primarily pyrite, pyrrhotite, pentlandite, and chalcopyrite are generally less than 100 microns in size, and occur as disseminated interstitial individual grains, as polyphase assemblages, and less commonly as inclusions in pyroxene, plagioclase, and olivine. Pyrite after pyrrhotite is commonly associated with low temperature greenschist alteration haloes around sulfide grains. Pyrrhotite hosted by Cr- and Ti-poor magnetite (Fe3O4) occurs in several samples from the Marginal to Lower Critical Zones below the platiniferous Merensky Reef. These grains occur with calcite that is in textural equilibrium with the igneous silicate minerals, occur with Cl-rich apatite, and are interpreted as resulting from high temperature sulfur loss during degassing of interstitial liquid. A quantitative model demonstrates how many of the first-order features of the Bushveld ore metal distribution could have developed by vapor refining of the crystal pile by chloride–carbonate-rich fluids during which sulfur and sulfide are continuously recycled, with sulfur moving from the interior of the crystal pile to the top during vapor degassing.

Keywords

Bushveld Complex Igneous sulfide Platinum-group element deposits Chlorite–carbonate fluids 
This is a preview of subscription content, log in to check access.

Notes

Acknowledgments

This work was completed as part of a Senior Thesis by the senior author at Duke University. We wish to thank Grant Cawthorn of the University of the Witwatersrand, Gordon Chunnett of Anglo Platinum Ltd., and the geologists at the Rustenburg and Marula platinum mines for some of the samples used in this study. This work was improved by the comments of Ed Ripley, Chusi Li, Sarah Penniston-Dorland, Peter Lightfoot, Jacob Hanley, Mike Lesher, and an anonymous reviewer. This work was supported by NSF grant EAR 04-7928.

Supplementary material

126_2012_427_MOESM1_ESM.doc (102 kb)
Table 1 A summary of rock samples and major sulfide mineral assemblages (DOC 102 kb)
126_2012_427_MOESM2_ESM.docx (66 kb)
Table 2 Electron microprobe analysis of sulfide minerals (DOCX 66 kb)
126_2012_427_MOESM3_ESM.docx (12 kb)
Table 3 Microprobe analysis of mixed magnetite-pyrrhotite phase from sample LCZ-105 (DOCX 12.1 kb)
126_2012_427_MOESM4_ESM.docx (14 kb)
Table 4 Average Bushveld noble metal values of various units from the Western Limb of the Bushveld Complex (from Barnes and Maier 2002) and calculated theoretical original footwall source concentrations (DOCX 14 kb)
126_2012_427_MOESM5_ESM.docx (12 kb)
Table 5 Parameters for PALLADIUM model run. All concentrations are in weight fraction, except as noted (DOCX 11.6 kb)

References

  1. Aird H, Boudreau AE (2012) High-temperature carbonates in the Stillwater Complex, Montana, USA. 35th Mineral Deposits Studies Group, Cardiff University, UK, 3-6 January. AbstractGoogle Scholar
  2. Andersen JCØ (2006) Postmagmatic sulphur loss in the Skaergaard Intrusion: implications for the formation of the Platinova Reef. Lithos 92:198–221CrossRefGoogle Scholar
  3. Ballhaus CG, Stumpfl EF (1985) Occurrence and petrological significance of graphite in the Upper Critical zone, western Bushveld complex, South Africa. Earth Planet Sci Lett 74:58–68CrossRefGoogle Scholar
  4. Ballhaus CG, Stumpfl EF (1986) Sulfide and platinum mineralization in the Merensky reef: evidence from hydrous silicates and fluid inclusions. Contrib Mineral Petrol 94:193–204CrossRefGoogle Scholar
  5. Barnes S-J, Maier WD (2002) PGE distributions in the Rustenburg Layered Suite of the Bushveld Complex, South Africa. In: Cabri L (ed) The geology, geochemistry, mineralogy and mineral beneficiation of PGE. Can Inst Metallurgy Spec 54:553–580Google Scholar
  6. Barnes S-J, Savard D, Bédard LP, Mairer WD (2009) Selenium and sulfur concentrations in the Bushveld Complex of South Africa and implications for formation of the platinum-group element deposits. Miner Depos 44:647–664CrossRefGoogle Scholar
  7. Blaine, FA (2010) The Effect of Volatiles (H2O, Cl and CO2) on the Solubility and Partitioning of Platinum and Iridium in Fluid-Melt Systems. PhD Dissertation University of Waterloo 170 ppGoogle Scholar
  8. Blaine FA, Rl L, Holtz F, Bruegmann GE (2011) The effect of Cl on Pt solubility in haplobaslatic melt: implications for micronugget formation and evidence for fluid transport of the PGEs. Geochim Cosmochim Acta 75:7792–7805CrossRefGoogle Scholar
  9. Boudreau AE (2004) PALLADIUM—a program to model the chromatographic separation of the platinum-group elements, base metals and sulfur in a solidifying igneous crystal pile. Can Mineral 42:393–403CrossRefGoogle Scholar
  10. Boudreau AE, McCallum IS (1992) Concentration of Platinum-group elements by magmatic fluids in layered intrusions. Econ Geol 87:1830–1848CrossRefGoogle Scholar
  11. Boudreau AE, Meurer WP (1999) Chromatographic separation of the platinum-group elements, gold, base metals and sulfur during degassing of a compacting and solidifying crystal pile. Contrib Mineral Petrol 134:174–185CrossRefGoogle Scholar
  12. Boudreau AE, Simon A (2007) Halogen variations and degassing in the Basement Ferrar sill, Antartica. J Petrol 48:1369–1386CrossRefGoogle Scholar
  13. Boudreau AE, Mathez EA, McCallum IS (1986) Halogen geochemistry of the Stillwater and Bushveld Complexes: evidence for transport of the platinum-group elements by Cl-rich fluids. J Petrol 27:967–986CrossRefGoogle Scholar
  14. Campbell IH, Naldrett AJ, Barnes SJ (1982) A model for the origin of the platinum-rich sulfide horizons in the Bushveld and Stillwater Complexes. J Petrol 24:133–165CrossRefGoogle Scholar
  15. Cawthorn RG (1998) Emplacement and crystallization time for the Bushveld Complex. J Pet 39:1669–1687CrossRefGoogle Scholar
  16. Cawthorn RG (1999) Platinum-group element mineralization in the Bushveld Complex; a critical reassessment of geochemical models. S Afr J Geol 102:268–281Google Scholar
  17. 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 beneficiation of platinum-group elements. Canadian Institute of Mining, Metallurgy and Petroleum, Special Volume 54:389–430Google Scholar
  18. Davies G, Tredoux M (1985) The platinum-group element and gold contents of the marginal rocks and sills of the Bushveld Complex. Econ Geol 80:838–848CrossRefGoogle Scholar
  19. Dreibus G, Palme H, Spettel B, Zipfel J, Wänke H (1995) Sulfur and selenium in chondritic meteorites. Meteoritics 30:439–445CrossRefGoogle Scholar
  20. Eales HV, Cawthorn RG (1996) The Bushveld Complex. In: Cawthorn RG (ed) Layered intrusions. Elsevier, Amsterdam, pp 181–229CrossRefGoogle Scholar
  21. Hanley JJ, Gladney ER (2011) The presence of carbonic-dominant volatiles during the crystallization of sulfide-bearing mafic pegmatites in the North Roby Zone, Lac des Iles Complex, Ontario. Econ Geol 106:33–54CrossRefGoogle Scholar
  22. Hanley JJ, Mungall JE, Pettke T, Spooner ETC, Bray CJ (2008) Fluid and halide melt inclusions of magmatic origin in the Ultramafic and Lower Banded Series, Stillwater Complex, Montana, USA. J Petrol 49:1133–1160CrossRefGoogle Scholar
  23. Haughton DR, Roeder PL, Skinner BJ (1974) Solubility of sulfur in mafic magmas. Econ Geol 69:451–467CrossRefGoogle Scholar
  24. Kinloch ED (1982) Regional trends in platinum-group mineralogy of the Critical Zone of the Bushveld Complex, South Africa. Econ Geol 77:1328–1347CrossRefGoogle Scholar
  25. Kruger FJ, Cawthorn RG, Walsh KL (1987) Strontium isotopic evidence against magma addition in the Upper Zone of the Bushveld Complex. Earth Planet Sci Lett 84:51–58CrossRefGoogle Scholar
  26. Larocque ACL, Stimac JA, Keith JD, Huminicki MAE (2000) Evidence for open-system behavior in immiscible Fe-S-O liquids in silicate magmas: implications for contributions of metals as sulfur to ore-forming fluids. Can Mineral 38:1233–1249CrossRefGoogle Scholar
  27. Lee CA (1996) A review of mineralization in the Bushveld Complex and some other layered mafic intrusions. In: Cawthorn RG (ed) Layered intrusions. Elsevier, Amsterdam, pp 103–146CrossRefGoogle Scholar
  28. Li C, Ripley EM (2009) Sulfur contents at sulfide-liquid or anhydrite saturation in silicate melts: empirical equations and example applications. Econ Geol 104:405–412CrossRefGoogle Scholar
  29. Li C, Ripley EM, Merino E, Maier W (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 99:173–184Google Scholar
  30. Liebenberg L (1970) The sulfides in the layered sequence of the Bushveld Igneous Complex. Geol Soc S Afr Spec Publ 1:108–208Google Scholar
  31. Maier WD, Barnes SJ (1999) Platinum-group Elements in Silicate Rocks of the Lower, Critical, and Main Zones at Union Section, Western Bushveld Complex. J Petrol 40:1647–1671CrossRefGoogle Scholar
  32. Mathez EA (1976) Sulfur solubility and magmatic sulfides in submarine basalt glass. J Geophys Res 81:4269–4275CrossRefGoogle Scholar
  33. Mathez EA, Webster JD (2005) Partitioning behavior of chlorine and fluorine in the system apatite-silicate melt-fluid. Geochim Cosmochim Acta 69:1275–1286CrossRefGoogle Scholar
  34. Mathez EA, Dietrich VJ, Holloway JR, Boudreau AE (1989) Carbon distribution in the Stillwater Complex and evolution of vapor during crystallization of Stillwater and Bushveld Magmas. J Petrol 30:153–173CrossRefGoogle Scholar
  35. McDonough WF, S-s S (1995) The composition of the Earth. Cehm Geol 120:223–253CrossRefGoogle Scholar
  36. McLaren CH, De Villiers JPR (1982) The platinum-group chemistry and mineralogy of the UG-2 chromitite layer of the Bushveld Complex. Econ Geol 77:1348–1366CrossRefGoogle Scholar
  37. Meurer WP, Willmore CC, Boudreau AE (1998) Metal redistribution during fluid exsolution and migration in the Middle Banded series of the Stillwater Complex, Montana. Lithos 47:143–156CrossRefGoogle Scholar
  38. Miller JD Jr, Andersen JCØ (2002) Attributes of Skaergaard-type PGE reefs. In: Boudreau AE (ed) 9th Int Platinum Symp Abstr. Duke University, Durham, pp 305–308Google Scholar
  39. Miller DJ, Cervantes P (2002) Sulfide mineral chemistry and petrography and platinum group element composition in gabbroic rocks from the Southwest Indian Ridge. In: Natland JH, Dick HJB, Miller DJ, Von Herzen RP (eds.) Proceedings of the Ocean Drilling Program, Scientific Results v. 176 doi: 10.2973/odp.proc.sr.176.009.2002
  40. Naldrett AJ (2004) Magmatic sulfide deposits: geology, geochemistry and exploration. Springer-Verlag, Berlin 727 ppGoogle Scholar
  41. Naldrett AJ (2009) Secular variation of magmatic sulfide deposits and their source magmas. Econ Geol 105:669–688CrossRefGoogle Scholar
  42. Naldrett AJ, Wilson A, Kinnaird J, Chunnett G (2009) PGE tenor and metal ratios within and below the Merensky Reef, Bushveld Complex: implications for its genesis. J Petrol 50:625–659CrossRefGoogle Scholar
  43. Newton RC, Manning CE (2002) Experimental determination of calcite solubility in H2O-NaCl solutions at deep crust/upper mantle pressures and temperatures: implications for metasomatic processes in shear zones. Am Mineral 87:1401–1409Google Scholar
  44. Peyerl W (1982) The influence of the Driekop dunite pipe on the platinum-group mineralogy of the UG-2 chromitite in its vicinity. Econ Geol 77:1432–1438CrossRefGoogle Scholar
  45. Prichard HM, Hutchinson D, Fisher PC (2004) Petrology and crystallization history of multiphase sulfide droplets in a Mafic Dike from Uruguay: implications for the Origin of Cu-Ni-PGE Sulfide Deposits. Econ Geol 99:365–376CrossRefGoogle Scholar
  46. Safonov OG, Perchuk LL, Litvin YA (2007) Melting relations in the chloride–carbonate–silicate systems at high pressure and the model for formation of alkali diamond-forming liquids in the upper mantle. Earth Planet Sci Lett 253:112–128CrossRefGoogle Scholar
  47. Sharpe MR (1985) Strontium isotope evidence for preserved density stratification in the Main Zone of the Bushveld Complex, South Africa. Nature 316:119–126CrossRefGoogle Scholar
  48. Sharpe MR, Hulbert LJ (1985) Ultramafic sills beneath the Eastern Bushveld Complex: mobilized suspensions of early Lower Zone Cumulates in a parental magma with boninitic affinities. Econ Geol 80:849–871CrossRefGoogle Scholar
  49. Shirley DN (1986) Compaction of igneous cumulates. J Geol 94:795–809CrossRefGoogle Scholar
  50. Simon AC, Pettke T (2009) Platinum solubility and partitioning in a felsic melt-vapor-brine assemblage. Geochim Cosmochim Acta 73:438–454Google Scholar
  51. Stumpfl EF, Tarkian M (1976) Platinum genesis: new mineralogical evidence. Econ Geol 71:1451–1460CrossRefGoogle Scholar
  52. Su S, Lesher M (2012) Genesis of PGE mineralization in the Wengeqi mafic-ultramafic complex, Guyang Country, Inner Mongolia, China. Miner Deposita 47:197–207Google Scholar
  53. Vermaak CF (1976) The Merensky Reef—thoughts on its environment and genesis. Econ Geol 71:1270–1298CrossRefGoogle Scholar
  54. Von Gruenewaldt G (1973) The main and upper zones of the Bushveld Complex in the Roossenekal area, eastern Transvaal. Geol Soc S Afr Trans 76:53–61Google Scholar
  55. Von Gruenewaldt G (1976) Sulfides in the upper zone of the eastern Bushveld Complex. Econ Geol 71:1324–1336Google Scholar
  56. Von Gruenewaldt G, Sharpe MR, Hatton CJ (1985) The Bushveld Complex: introduction and review. Econ Geol 80:803–812CrossRefGoogle Scholar
  57. Wager LR, Vincent EA, Smales AA (1957) Sulphides in the Skaergaard Intrusion, East Greenland. Econ Geol 52:855–903CrossRefGoogle Scholar
  58. Wager LR, Vincent EA, Smales AA (1958) The behaviour of sulphur during fractionation of basic magma. Geochim Cosmochim Acta 14:165–166Google Scholar
  59. Wagner PA (1929) The platinum deposits and mines of South Africa. Oliver & Boyd, Edinburgh, 326 ppGoogle Scholar
  60. Walther JV (1997) Determining the activity coefficients of neutral species in supercritical H2O solutions. Geochim Cosmochim Acta 61:3311–3318CrossRefGoogle Scholar
  61. Willmore CC, Boudreau AE, Kruger FJ (2000) The halogen geochemistry of the Bushveld Complex, Republic of South Africa: implications for chalcophile element distribution in the lower and critical zones. J Petrol 41:1517–1539CrossRefGoogle Scholar
  62. Wulf AV, Palme H, Jochum KP (1995) Fractionation of volatile elements in the early solar system: evidence from heating experiments on primitive meteorites. Planet Space Sci 43:451–468CrossRefGoogle Scholar

Copyright information

© Springer-Verlag 2012

Authors and Affiliations

  1. 1.Department of Earth and Ocean SciencesDuke UniversityDurhamUSA
  2. 2.Department of Earth and Planetary ScienceUniversity of CaliforniaBerkeleyUSA

Personalised recommendations