Chromite composition and PGE content of Bushveld chromitites: Part 1

Abstract

This paper is based on 465 new analyses of Ni, Cu, S and PGE from the 19 chromitite horizons between the LG-1 and UMG-2 from 6 sectors around the Bushveld Complex, along with microprobe analyses of representative samples of 41 chromites. Two trends in chromite composition, A and B, are distinguished on a plot of cation% Mg/(Mg + Fe²⁺) versus Cr/(Cr+Al). Trend A, that has a negative slope, is close to that predicted as the result of the reciprocal exchange substitution of Cr and Fe²⁺ for Mg and Al between spinel and liquid affecting the Mg-Fe²⁺ spinel-liquid K_d². Trend B, that has a positive slope and is defined primarily by the LG-5 to MG-2 chromitites, is the result of the progressive increase in the activity of Al₂O₃ as a result of the fractional crystallization of orthopyroxene. Overall, the average PGE concentrations in massive chromitite increase upward. The LG-1 to LG-4 chromities have low (Pt+Pd)/(Rh+Ru+Ir+Os) ratios (0·1 to 0·3), above which there is an abrupt jump to higher ratios in the LG-5 (0·9 to 10) and all overlying chromitites (also documented by Scoon and Teigler). The Pt/Ru and Pd/Ru ratios are very variable, but the Ru/Ir, Ru/Rh and Ru/Os ratios of all chromitites are relatively constant, indicating that Pt and Pd respond to different concentration mechanisms to the other PGE. Rh, Ru, Ir and Os were likely concentrated by chromite itself, probably as grains of laurite and alloys incorporated in growing chromite crystals, but the bulk of the Pt, Pd along with lesser proportions of the other PGE were concentrated by sulphide liquid. Most chromitites now have very low contents of S, but mineragraphic and chemical data support the suggestion of Naldrett and Lehmann that vacancies in chromite forming above 900°C were filled by Fe²⁺ derived from the destruction of interstitial sulphide liquid. Data on En composition through the Bushveld CriticalZone, indicate that the LG-1 to LG-4 chromitites formed at a stage when influxes of magma into the chamber were rapid and primitive, and overrode the effect of fractional crystallization, whereas above this, fractionation mostly overrode influxes of new magma. Irvine's model of mixing of resident magma with influxes of more primitive magma is invoked as the origin of the chromitite horizons. It is shown, using the equation for sulphur solubility and the programme MELTS, that influxes and mixing of fresh primitive magma from depth with that in the chamber (i.e. as envisaged for the LG-1 to LG-4) would not have caused sulphide immiscibility along with chromitite crystallisation, but that influxes and mixing of slower-ascending magma, that fractionated en route, could give rise to sulphide liquid segregating along with the chromitite (i.e. the scenario for the LG-5 and overlying chromitites). The modelling also shows that the more fractionated the magma in the chamber becomes, the more sulphide will form, accounting for the overall upward increase in Pt and Pd above the LG-5.

Get full access to this article

View all access options for this article.

References

Ahmed

A. H

. and Arai

A. S.

: 2002, Unexpectedly high-PGE chromitite from the deeper mantle section of the northern Oman ophiolite and its tectonic implications, Contributions to Mineralogy and Petrology, 2002), 143, 263–278.

Allan

J. F.

, Sack

R. O

. and Batiza

: 1988, Cr-rich spinels as petrogenetic indicators: MORB-type lavas from the Lamont seamount chain, eastern Pacific American Mineralogist, 73, 741–753.

Barnes

S. J.

and Roeder

P. L.

: 2001, The range of spinel compositions in terrestrial mafic and ultramafic ricks, Journal of Petrology, 42, 2279–2302.

Beattie

: 1993, Olivine-melt and orthopyroxene-melt equilibria, Contributions to Mineralogy and Petrology, 115, 103–111.

Bockrath

, Balhaus

and Holzheid

: 2004, Stabilities of laurite Ru52 and monosulphide solid solution at magmatic temperature, Chemical Geology, 208, 265–271.

Boudreau

A. E.

and McCallum

I. S.

: 1992, Concentration of platinum-group elements by magmatic fluids in layered intrusions, Economic Geology, 87, 1830–1848.

Brenan

J. M

. and Andrews

: 2001, High-temperature stability of laurite and ru—Os—Jr alloy and their role in PGE fractionation in mafic magmas, The Canadian Mineralogist, 39, 341–360.

Buchla

, Brugmann

and Batanova

V. G.

: 2004, Formation of podiform chromitite deposits: implications from PGE abun-dances and Os isotopic compositions of chromites from the Troodos complex, Cyprus, Chemical Geology, 208, 217—232

Cameron

E. N.

: 1975, Postcumulus and subsolidus equilibration of chromite and coexisting silicates in the Eastern Bushveld complex. Geochimica and Cosmochimica Acta, 39, 1021–1033.

10.

Cameron

E. N.

: 1977, Chromite in the central sector of the Eastern Bushveld Complex, South Africa, American Mineralogist, 62, 1082–1096.

11.

Cameron

E. N.

: 1978. The lower zone of the eastern Bushveld com-plex in the Olifants river trough. Journal of Petrology, 19, 437–462.

12.

Cameron

E. N.

: 1980. Evolution of the Lower Critical Zone Central Sector eastern Bushveld Complex and its chromite deposits. Economic Geology, 75, 845–871.

13.

Cameron

E. N.

: 1982. The Upper Critical Zone of the eastern Bushveld Complex - precursor to the Merensky Reef. Economic Geology, 77, 1307–1327.

14.

Campbell

I. H.

, Naldrett

A. J.

and Barnes

S. J.

: 1983, A model for the origin of the platinum-rich sulphide horizons in the Bushveld and Stillwater Complexes. Journal of Petrology, 24, 133–165.

15.

Cawthorn

R. G.

: (2005). Pressure fluctuations and the formation of the PGE rich Merensky and chromitite reefs, Bushveld Complex. Mineralium Deposita, 40, 231–235.

16.

Cawthorn

R. G

. and Walraven

: (1998), Emplacement and crystallization time for the Bushveld complex. Journal of Petrology, 39, 1669–1687.

17.

Cawthorn

R. G.

and Webb

S. J.

: 2001, Connectivity between the Eastern and Western limbs of the Bushveld Complex, Tectonophysics„ 330, 195–209

18.

Cawthorn

R. G.

, Merkle

R. K.

and Viljoen

M. J.

: 2002, Platinum-Group Element Deposits in the Bushveld Complex South Africa. In The Geology Geochemistry Mineralogy and Mineral Beneficiation of Platinum-Group Elements (ed. Cabri

L. J.

) Ottawa Ontario. Canadian Institute of Mining and Metallurgy, Special Volume 54, pp. 389–429.

19.

Cocherie

, Auge

and Meyer

: 1989, Geochemistry of the platinum-group elements in various types of spinels from the Vourinos ophiolitic complex, Greece, Chemical Geology, 77 (1989) 27–39

20.

Cousins

C. A

. and Feringa

: 1964, The chromite deposits of the western belt of the Bushveld Complex, in Haughton

S. H.

, ed., The geology of some ore deposits in Southern Africa, volume II, Geological Society of South Africa, Johannesburg, pp. 183–202

21.

Craig

J. R.

: 1973, Pyrite-pentlandite assemblages and other low temperature relations in the Fe-Ni-S System, American Journal of Science 273A, 496–510.

22.

Craig

J. R

., and Kullerud

: 1969. Phase relations in the Cu-Fe-Ni-S system and their application to magmatic ore deposits. Economic Geology Monograph, 4, 344–358.

23.

Davies

, Cawthorn

R. G.

, Barton

J. M.

Jr. , Morton

: 1980. Parental magma to the Bushveld Complex. Nature, 287, 33–35.

24.

de Waal

S. A.

, Maier

W. D.

, Armstrong

R. A.

, and Gauert

C. D. K.

: 2001, Parental magma and emplacement of the stratiform Uitkomst Complex: Canadian Mineralogist, 39, 557–571.

25.

Eales

H. V.

: 2000, Implications of the chromium budget of the Western Limb of the Bushveld Complex, South African Journal of Geology, 103, 141–150.

26.

Eales

H. V.

and Cawthorn

R. G.

: 1996, The Bushveld Complex. In: Cawthorn

R. G.

(ed.) Layered Intrusions. Amsterdam: Elsevier, pp. 181–230.

27.

Eales

H. V.

, de Klerk

W. J

. and Teigler

: 1990, Evidence for magma mixing processes within the Critical and Lower Zones of the Northwestern Bushveld Complex, South Africa, Chemical Geology, vol. 88, 261–278

28.

Fedorova

Zh.

N. and Sinyakova

E. F.

: 1993, Experimental investigation of physicochemical conditions of pentlandite forma-tion, Russian Journal of Geology and Geophysics, 34, (2), 79–87.

29.

Finnigan

C. S.

, Brenan

J. M.

, Mungall

J. E

. and McDonough : 2008, Experiments and models bearing on the role of chromite as a collector of platinum group minerals by local reduction, Journal of Petrology, 49, 1647–1665

30.

Fourie

G. P.

: 1959, The chromite deposits in the Rustenburg area, South Africa Geological Survey Bulletin, 27, pp. 45.

31.

Gain

S. B.

: 1985, The geological setting of the platiniferous UG-2 chromitite layer at the farm Mandagshoek, Eastern Bushveld Complex, Economic Geology, 80, 925–943.

32.

Gauert

C. D. K.

: 1998, The petrogenesis of the Uitkomst Complex, Mpumalanga Province, South Africa: Unpublished Ph. D. thesis, University of Pretoria, Pretoria, South Africa, 315 pp.

33.

Gauert

C. D. K.

, de Waal

S. A.

, and Wallmach

: 1995, Geology of the ultrabasic to basic Uitkomst Complex, eastern Transvaal, South Africa: An overview: Journal of African Earth Sciences, 21, 553–570.

34.

Ghiorso

M. S.

, and Sack

R. O.

: 1995, Chemical mass transfer in magmatic processes IV. A revised and internally consistent thermodynamic model for the interpolation and extrapolation of liquid—solid equilibria in magmatic systems at elevated tempera-tures and pressures. Contributions to Mineralogy and Petrology, 119, 197–212.

35.

Hall

A. L.

and Humphrey

W. A.

: 1908. On the occurrence of chromite along the southern and eastern margins of the Bushveld plutonic complex. Transactions of the Geological Society of South Africa, 11, 69–77

36.

Harmer

R. E.

and Sharpe

M. R.

: 1985. Field relations and Sr isotope systematics of the marginal rocks of the eastern Bushveld Complex. Economic Geology 80, 813–837.

37.

Hatton

C. J

. and von Gruenewaldt

: 1987, The geological setting and petrogenesis of the Bushveld chromitite layers, in Stowe

C. W.

ed. Evolution of chromium ore fields, Van Nostrand Reinhold Company, New York, NY, pp. 109–143.

38.

Hatton

C. J

., and von Gruenewaldt

: 1985, Chromite from the Swartkop Chrome Mine — an estimate of the effects of sub-solidus equilibration, Economikc Geology, 80, 911–924.

39.

Hiemstra

S. A.

: 1979. The role of collectors in the formation of platinum deposits in the Bushveld. Canadian Mineralogist, 17, 469–482.

40.

Hiemstra

S. A.

: 1985. ‘The distribution of some platinum group elements in the UG-2 chromitite layer of the Bushveld Complex.‘ Economic Geology, 80, 944–957.

41.

Irvine

T. N.

: 1967, Chromian spinel as a petrogenetic indicator. Part 2. Petrological applications. Canadian Journal of Earth Sciences, 4, 71–103.

42.

Irvine

T. N.

: 1977. Origin of chromite layers in the Muskox intrusion and other stratiform intrusions: a new interpretation. Geology, 5, 273–277.

43.

Jackson

E. D.

: 1969, Chemical variation in coexisting chromite and olivine in chromitite zones of the Stillwater complex, Economic Geology, Monograph 4, pp. 41–71.

44.

Kinnaird

J. A.

, Kruger

F. J.

, Nex

P. A. M.

and Cawthorn

R. G.

: 2002, Chromite formation - a key to understanding processes of platinum enrichment. Transactions of the Institution of Mining and Metallurgy, 111, B23—B35.

45.

Kruger

F. J.

: 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-magnetitite deposits, Mineralium Deposita 40, 451–472

46.

Kruger

F. J.

: 1994, The Sr-isotope stratigraphy of the Western Bushveld Complex, South African Journal of Earth Sciences, 97, 393–398

47.

Kruger

F. J.

and Marsh

J. S.

: 1982. Significance of 5r87/5r86 ratios in the Merensky cyclic unit of the Bushveld Complex. Nature, 298, 53–55.

48.

Lee

C. A.

and Parry

S. J.

: 1988. Platinum group element geochemistry of the lower and middle group chromitites of the eastern Bushveld Complex. Economic Geology, 85, 877–883

49.

and Ripley

E. M.

: 2009. Sulphur Contents at Sulphide-Liquid or Anhydrite Saturation in Silicate Melts: Empirical Equations and Example Applications, Economic Geology, 104, 405–412.

50.

, and Ripley

E. M.

: 2005, Empirical Equations to Predict the Sulphur Content of Mafic Magmas At Sulphide Saturation and Applications to Magmatic Sulphide Deposits, Mineralium Deposita, 40, 218–230.

51.

Maier

W. D

. and Barnes

S-J

: 2008, Platinum-group elements in the UG1 and UG2 chromitites, and the Bastard reef, at Impala platinum mine, western Bushveld Complex, South Africa: Evidence for late magmatic cumulate instability and reef constitution, South African Journal of Geology, 111, 159–176.

52.

Mavrogenes

J. A

. and O'Neill

H. S. C.

: 1999, The relative effects of pressure temperature and oxygen fugacity on the solubility of sulphide in mafic magmas. Geochimica Cosmochimica Acta, 63, 1173–1180.

53.

McCandless

T. E

, Ruiz

, Adair

B. I

. and Freydier

: 1999, Re-Os isotope and Pd/Ru variations in chromitites from the Critical Zone, Bushveld Complex, South Africa. Geochimica et Cosmochimica Acta, 63, 911–923.

54.

McLaren

C. H.

and de Villiers

J. P. R.

: 1982, The Platinum-group chemistry and mineralogy of the UG-2 chromitite Layer of the Bushveld complex, Economic Geology, 77, 1348–1366.

55.

Melcher

, Grum

, Thalhammer

T. V.

and Thalhammer

O. A. R.

: 1999, The giant chromite deposits at Kempirsai, Urals: constraints from trace element (PGE, REE) and isotope data, Mineralium Deposita 34, 250–272

56.

Merkle

R. K. W.

: 1992, Platinum-group element minerals in the middle group of chromitite layers, western Bushveld complex: Indications for collection mechanisms and postmagmatic mod-ification, Canadian Journal of Earth Sciences, 29, 209–221.

57.

Misra

K. S.

and Fleet

M. E.

: 1973, The chemical compositions of synthetic and natural pentlandite assemblages, Economic Geology, 68, 518–539.

58.

Mitchell

A. A.

and Scoon

R. N.

: 2007, The Merensky Reef at Winnaarshoek, Eastern Bushveld Complex: A primary magmatic hypothesis based on a wide reef facies, Economic Geology, 102, 971–1009.

59.

Molyneaux

T. G.

: 1974. A geological investigation of the Bushveld Complex in Sekhukhunelan and apart of the Steelpoort Valley. Geological Society of South Africa Transactions, 77, 329–338.

60.

Mondal

S. K.

and Mathez

E. A.

: 2007, Origin of the UG2 Chromitite Layer, Bushveld Complex, Journal of Petrology, 48, 495-510.7

61.

Mondal

S. K.

, Frei

, Ripley

E. M.

: (2007) Os isotope systematics of Mesoarchean chromitite PGE deposits in the Singhbhum Craton (India): implications for the evolution of lithospheric mantle. Chem. Geol., 244, 391–408

62.

Mondal

S. K.

and Zhou

M. F.

: (2009) Enrichment of PGE through interaction of evolved boninitic magmas with early formed cumulates in a gabbro—breccia zone of the Mesoarchean Nuasahi massif (eastern India). Mineral. Deposita, DOT 10.1007/ s00126-009-0264–0.

63.

Mondal

S. K

, Ripley

E. M.

, Li

, Frei

: 2006, The genesis of Archaean chromitites from the Nuasahi and Sukinda massifs in the Singhbhum Craton, India, Precambrian Research, 148, 45–66.

64.

Mungall

: 2002. A model for co-precipitation of platinum group minerals with chromite from silicate melts. In: Abstracts, 9th International Platinum Symposium, July, Stillwater, USA. (Available at http://www.nicholas.duke.edu/people/faculty/bou-dreau/IPS_Abstracts.htm.)

65.

Naldrett

A. J.

: 2004, Magmatic Sulphide Deposits: Geology, geochemistry and exploration, Springer Verlag, Heidelberg, 728 pp.

66.

Naldrett

A. J.

, and Duke

J. M.

: 1980, Platinum Metals in Magmatic Sulphide Ores. Science, 208, 1417–1424.

67.

Naldrett

and Lehmann

: 1988. Spinel non-stoichiometry as the explanation for Ni- Cu- and PGE-enriched sulphides in chromitites. In Geoplatinum ‘87 (eds. Prichard

Potts

Bowles

and Cribb

) Elsevier London p. 93–110.

68.

Naldrett

A. J

. and von Gruenewaldt

: 1989. The association of PGE with chromitite in layered intrusions and ophiolite com-plexes. Economic Geology 84, 180–187.

69.

Naldrett

A. J.

, Hoffman

E. L.

, Green

A. H.

, Chou

C. L.

, Naldrett

S. R.

and Alcock

R. A.

: 1979, The composition of Ni-sulphide ores with particular reference to their content of PGE and Au. Can. Mineralogist, 17, Pt. 2,403–415.

70.

Naldrett

Tony

, Kinnaird

Judith

, Wilson

Allan

and Chunnett

Gordon

: 2008, The concentration of PGE in the earth's crust with special reference to the Bushveld Complex. Earth Science Frontiers 15, (5), 264–297.

71.

Naldrett

A. J.

, Wilson

Allan

, Kinnaird

Judith

and Chunnett

Gordon

: 2009, PGE Tenor and Metal Ratios within and below the Merensky Reef, Bushveld Complex: Implications for its Genesis, Journal of Petrology, Doi:10.1093/Petrology/Egp015

72.

Naldrett

A. J.

, Craig

J. R

. and Kullerud

: 1967. The central portion of the Fe-Ni-S system and its bearing on pentlandite solution in iron-nickel sulphide ores. Economic Geology, 62, 826–847.

73.

Nex

P. A. M.

: 2004, Formation of bifurcating chromitite layers of the UG1 in the Bushveld Igneous Complex, an analogy with sand volcanoes. Journal of the Geological Society, London, 161, 903–909.

74.

Ohnenstetter

, Watkinson

D. H.

, Jones

P. C.

and Talkington

: 1986, Cryptic compositional variations in laurite and enclosing chromite from the Bird River sill, Manitoba: Economic Geology, 81, 1159–1168.

75.

Page

N. J.

and Talkington

R. W.

: 1984, Palladium, platinum, rhodium, ruthenium and iridium in peridotites and chromitites from ophiolite complexes in Newfoundland, Canadian Mineralogist, 22, 137–149

76.

Page

N. J.

, Cassard

and Haffty

: 1982. Palladium, platinum, rhodium, ruthenium and iridium in chromitites from the Massif du Sud and Teibaghi Massif, New Caledonia. Economic Geology, 77, 1571–1577.

77.

Page

N. J.

, Engin

, Singer

D. A.

and Haffty

: 1984. Distribution of platinum-group elements in the Bati Kef chromite deposit, Guleman-Elazig area, Eastern Turkey, Economic Geology, 70, 177–184.

78.

Penberthy

C. J.

and Merkle

R. K. W.

: 1999, Lateral variations in the platinum-group element content and mineralogy of the UG-2 chromitite layer, Bushveld complex, South African Journal of Geology, 102, 240–250.

79.

Prichard

H. M.

Lord

R. A.

and Neary

C. R.

: 1996, A model to explain the occurrence of Platinum- and Palladium-rich Ophiolite Complexes, Journal of the Geological Society, London, 153, 323–328.

80.

Prichard

H. M.

, Neary

C. R.

, Fisher

P. C

. and O'Hara

M. J.

: 2008, PGE-rich podiform chromitites in the Al ‘Ays ophiolite complex, Saudi Arabia: An example of critical mantle melting to extract and concentrate PGE, Economic Geology, 103, 1507–1529.

81.

Raghaven

: 2004a, Fe-Ni-S (iron-nickel-sulphur), Journal of Phase Equilibria and Diffusion, 25, 373–381.

82.

Raghaven

: 2004b, Cu-Fe-S (Copper-iron-sulphur), Journal of Phase Equilibria and Diffusion, 25, 450–454.

83.

Raghaven

: 2004c, Cu-Fe-Ni-S (copper-iron-nickel-sulphur), Journal of Phase Equilibria and Diffusion, 25. 458–461

84.

Schurmann

L. W

., Grabe

P-J.

and Steenkamp

C. J.

: 1998, Chromium, In The Mineral Resources of South Africa. Handbook, (eds. Wilson

M. G. C.

and Anhaeusser

C. R.

) Handbook 16, Council for Geosciences, CTP Book Printers, Cape Town, pp. 90–105

85.

Scoates

J. S.

and Friedman

R. M.

: 2008, Precise age of the platiniferous Merensky Reef, Bushveld Complex, South Africa, by the U-Pb zircon chemical abrasion ID-TIMS technique. Economic Geology 103, 465–471

86.

Scoon

R. N

. and Teigler

: 1994, Platinum-group element mineralization in the Critical Zone of the Western Bushveld Complex: I. Sulphide-poor chromitites below the UG-2, Economic Geology, 89, 1094–1121.

87.

Seabrook

C. L.

, Cawthorn

R. G.

and Kruger

F. J.

: 2005, The Merensky Reef, Bushveld Complex: Mixing of minerals not mixing of magmas. Economic Geology, 100, 1191–1206.

88.

Shewman

R. W.

and Clark

L. A.

: 1970, Pentlandite phase relations in the Fe-Ni-S System and notes on the monosulphide solid solution, Canadian Journal of Earth Science, 7, 67–85.

89.

Shima

and Naldrett

: 1975. Solubility of sulphur in an ultramafic melt and the relevance of the system Fe-S-O. Economic Geology, 70, 960–967.

90.

Spier

C. A.

and Ferreira Filho

C. F.

: 2001, The Chromite Deposits of the Bacuri Mafic-Ultramafic Layered Complex, Guyana Shield, Amapa State, Brazil Economic Geology, 96, 817–835

91.

Sugawara

: 2000, Empirical relationship between temperature, pressure and MgO content in olivine and pyroxene saturated liquid, Journal of Geophysical Research, 105, 8457–8472.

92.

Teigler

and Eales

H. V.

: 1993, Correlation between chromite composition and PGE mineralization in the Critical Zone of the Western Bushveld Complex, Mineralium Deposita, 28, 291–302.

93.

Van der Menve

M. J.

: 2008, The geology and structure of the Rustenburg Layered Suite in the Potgietersrus/Mokapane area of the Bushveld Complex, South Africa. Mineralium Deposita 43, 405–420.

94.

Van der Walt

C. F. G.

: (1941) Chromite ore of the Western Bushveld Complex, Transactions of the Geological Society of South Africa, 44, 79–112

95.

Van Niekerk

C. B.

: 1962, The age of the Gemspost Dyke from the Venterspost gold mine, Transactions of the Geological Society of South Africa, 65, 105–111.

96.

Von Gruenewaldt

: 1973. The main and upper zones of the Bushveld complex in the Roossenekal area Eastern Transvaal. Geological Society of South Africa Transactions, 76, 207–227.

97.

Von Gruenewaldt

: 1979. A review of some recent concepts of the Bushveld Complex with particular reference to sulphide mineralization. Canadian Mineralogist, 17, 233–256.

98.

Von Gruenewald

, Hatton

C. J.

, Merkle

R. K. W.

and Gain

S. B.

: 1986, Platinum group element-chromitite associations in the Bushveld Complex. Economic Geology, 81, 1067–1079.

99.

Voordouw

, Gutzmer

and Beukes

N. J.

: 2009, Intrusive origin for Upper Group (UG1, UG2) stratiform chromitite seams in the Dwars River area, Bushveld Complex, South Africa, Mineralogy and Petrology, DOI 10.1007/s00710-009-0072–3

100.

Wagner

P. A.

: 1929, The platinum deposits and mines of South Africa. Oliver and Boyd, Edinburgh, 326pp

101.

Walraven

: 1997, Geochronology of the Rooiberg Group, Transvaal Supergroup, South Africa. Economic Geology Research Institute Information Circular 316, University of the Witwatersrand, Johannesburg, 21pp.

102.

Webb

S. J.

, Cawthorn

R. G.

, Nguuri

and James

: 2004, Gravity modelling of Bushveld Complex connectivity supported by South African seismic results, South African Journal of Geology, 107, 207–218.

103.

Wendlandt

: 1982. Sulphur saturation of basalt and andesite melts at high pressures and temperatures. American Mineralogist, 67, 877–885.

104.

Wilson

A. H.

: 1982. The geology of the great ‘Dyke’, Zimbabwe: The ultramafic rocks. Jour. Petrol. 42, 109–124.

105.

Wilson

A. H

. and Chunnett

G. C

: 2006, Trace Element and Platinum Group Element Distributions and the Genesis of the Merensky Reef, Western Bushveld Complex, South Africa. Journal of Petrology, 47, 2369–2403.

106.

Zhou

Mei-Fu

, Sun

Min

, Keays

Reid R.

, and Kerrich

Robert W.

: 1998, Controls on platinum-group elemental distributions of podiform chromitites: A case study of high-Cr and high-Al chromitites from Chinese orogenic belts, Geochimica et Cosmochimica Acta, 62, 677–688.

Chromite composition and PGE content of Bushveld chromitites: Part 1 – the Lower and Middle Groups

Abstract

Get full access to this article

References