Advertisement

Mineralium Deposita

, Volume 23, Issue 2, pp 150–157 | Cite as

Complex unmixed spinels in layered intrusions within an obducted ophiolite in the Natal-Namaqua mobile belt

  • H. V. Eales
  • A. H. Wilson
  • I. M. Reynolds
Article

Abstract

Spinellids showing unmixed intergrowths of chromite or chromian spinel (sensu stricto) and magnetite or chromian magnetite are not known in mafic or ultramafic igneous rocks. They do occur within metamorphosed rocks that attained temperatures sufficiently high (upper amphibolite facies) for the formation of homogeneous Al-Cr-Fe3+-Ti spinel phases with compositions not matched in slowly cooled igneous rocks. In the Tugela Rand intrusion complex intergrowths of chromian spinel, chromian magnetite, ulvöspinel, ilmenite and a transparent aluminous spinel are observed and interpreted in terms of the thermal history of the rocks. Compositional differences between the separate areas of chromian spinel and chromian magnetite in complex intergrowths exhibited by the metamorphosed Tugela Rand and Mambulu Complexes confirm the extension of the magnetite-hercynite solvus (Turnock and Eugster 1962) towards magnesium- and chromium-rich compositions. The Tugela Rand spinellids are compared with those from the Carr Boyd Complex (Purvis et al. 1972) and the ultramafic rocks of the Giant Nickel Mine (Muir and Naldrett 1973) and the Red Lodge district (Loferski and Lipin 1983). Significant differences between the spinels from the Red Lodge district compared to the other three occurrences may reflect the different metamorphic histories of these areas.

Keywords

Nickel Igneous Rock Thermal History Ultramafic Rock Sensu Stricto 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Basta, E.Z.: Natural and synthetic titanomagnetites. (The system Fe3O-Fe2TiO-FeTiO3.) Neues Jahrb. Min. Abh. 94:1017–1048 (1960)Google Scholar
  2. Beeson, M.H., Jackson, E.D.: Chemical composition of altered chromites from Stillwater Complex, Montana. Amer. Mineral., 54:1084–1100 (1969)Google Scholar
  3. Bliss, N.W., Maclean, W.H.: The paragenesis of zoned chromite from central Manitoba. Geochim. Cosmochim. Acta 39:973–990 (1975)Google Scholar
  4. Buddington, A.F., Lindsley, D.H.: Iron-Titanium oxide minerals and synthetic equivalents. J. Petrology 5:310–357 (1964)Google Scholar
  5. Cain, A.C.: A preliminary review of the stratigraphic relationships and distribution of metamorphism in the northern part of the Natal-Namaquarides, South Africa. Geol. Rundschau 64:192–216 (1975)Google Scholar
  6. Champness, P.E., Lorimer, G.W.: Exsolution in silicates. In: Electron Microscopy in Mineralogy (H.R. Wend, Ed.) pp. 174–204. Berlin-Heidelberg-New York: Springer 1976Google Scholar
  7. Cremer, V.: Die Mischkristallbildung im System Chromit-Magnetit-Hercynit zwischen 1,000°C und 500°C. Neues Jahrb. Min. Abh. 111:184–205 (1969)Google Scholar
  8. De Waal, S.A.: On the origin of hydrogrossularite and other calcium silicates in serpentinites. Trans. Geol. Soc. South Africa 72:23–27 (1969)Google Scholar
  9. Dix, O.R.: High-grade metamorphism and possible overturning of the Tugela Rand layered intrusion in southeast Africa. Geology 9:155–160 (1979)Google Scholar
  10. Du Toit, A.L.: The Geology of the Country Surrounding Nkandhla, Natal. South African Geol. Surv. Expln. Sheet No. 109:111 p. (1931)Google Scholar
  11. Eales, H.V., Reynolds, I.M.: Factors influencing the composition of chromite and magnetite in some southern African Rocks. In: Proc. 1st Int. Conf. Applied Mineralogy (ICAM) Randburg, 1981 (1983)Google Scholar
  12. Eales, H.V., Reynolds, I.M., Gouws, D.A.: Spinel-group minerals of the Central Karoo tholeiitic province. Trans. Geol. Soc. South Africa 83:243–253 (1980)Google Scholar
  13. Eales, H.V., Snowden, D.V.: Chromiferous spinels of the Elephant's Head dike. Mineral. Deposita 14:227–242 (1979)Google Scholar
  14. Evans, B.W., Frost, B.R.: Chrome spinel in progressive metamorphism. Geochim. Cosmochim. Acta 39:959–972 (1975)Google Scholar
  15. Gierth, E., Krause, H.: Die ilmenite-lagerstatte Tellnes (Sud Norwegen). Norsk Geol. Tidsskr. 53:359–402 (1973)Google Scholar
  16. Henderson, P.: Reactive trends shown by chrome spinels of the Rhum layered intrusion. Geochim. Cosmochim. Acta 39:1035–1044 (1975)Google Scholar
  17. Henderson, P., Suddaby, P.: The nature and origin of the chrome-spinel of the Rhum layered intrusion. Contr. Mineral. Petrology 33:21–31 (1971)Google Scholar
  18. Hill, R., Roeder, P.: The crystallization of spinel from basaltic liquid as a function of oxygen fugacity. J. Geol. 82:709–729 (1974)Google Scholar
  19. Irvine, T.N.: Chromian spinel as a petrogenetic indicator Part 1. Theory. Can. J. Earth Sci. 2:648–672 (1965)Google Scholar
  20. Loferski, P.J., Lipin, B.R.: Exsolution in metamorphosed chromite from the Red Lodge district, Montana. Amer. Mineral. 68:777–789 (1983)Google Scholar
  21. Matthews, P.E.: Possible Precambrian obduction and plate tectonics in southeastern Africa. Nature Phys Sci. 240:37–39 (1972)Google Scholar
  22. Matthews, P.E.: Eastern or Natal sector of the Namaqua-Natal mobile belt in southern Africa. In: Precambrian of the Southern Hemisphere (D.R. Hunter, ed.) pp. 705–715. Elsevier, Amsterdam 1981Google Scholar
  23. Medaris, L.G.: Coexisting spinel and silicates in alpine peridotites of the granulite facies. Geochim. Cosmochim. Acta 39:947–958 (1975)Google Scholar
  24. Muan, A.: Phase relations in chromium oxide-containing systems at elevated temperatures. Geochim. Cosmochim Acta 39:791–802 (1975)Google Scholar
  25. Muir, J.E., Naldrett, A.J.: A natural occurrence of two-phase chromium-bearing spinels. Can. Mineral. 11:930–939 (1973)Google Scholar
  26. Navrotsky, A.: Thermochemistry of chromium compounds. Geochim. Cosmochim. Acta 39:819–832 (1975)Google Scholar
  27. Price, G.D.: Microstructures in titanomagnetites as guides to cooling rates of a Swedish intrusion. Geol. Mag. 116:313–318 (1979)Google Scholar
  28. Purvis, A.C., Nesbitt, R.W., Hallberg, J.A.: The geology of part of the Carr Boyd Rocks complex. Econ. Geol. 67:1093–1113 (1972)Google Scholar
  29. Reynolds, I.M.: The mineralogy and petrography of some vanadium-bearing titaniferous iron ores of the Mambula Complex, Zululand. In: Mineral Deposits of Southern Africa. 11. (C.R. Anhaeusser and S. Maske, Eds.) Geol. Soc. S. Afr. 1695–1708 (1986)Google Scholar
  30. Reynolds, I.M.: An occurrence of iron-rich högbomite in metamorphosed titaniferous iron ores of the Mambula Complex, Zululand. S. Afr. J. Geol. 90:64–71 (1987)Google Scholar
  31. Roeder, P.L., Campbell, I.H., Jamieson, H.: A re-evaluation of the olivine-spinel geothermometer. Contr. Mineral. Petrology 68:325–334 (1979)Google Scholar
  32. Stevens, R.E.: Composition of some chromites of the Western Hemisphere. Amer. Mineral. 29:1–4 (1944)Google Scholar
  33. Turnock, A.C., Eugster, H.P.: Fe-Al oxides: phase relationships below 1,000°C. J. Petrology 3:533–565 (1962)Google Scholar
  34. Ulmer, G.C.: Experimental investigations of chromite spinels. In: Magmatic Ore Deposits, Monograph 4 (H.D.B. Wilson, ed.) pp. 114–131. Econ. Geol. Publ. Co. (1969)Google Scholar
  35. Vincent, E.A., Wright, J.B., Chevallier, R., Mathiew, S.: Heating experiments on some natural titaniferous magnetites. Mineral. Mag. 31:624–655 (1957)Google Scholar
  36. Wilson, A.H.: The geology of the Great “Dyke”, Zimbabwe. J. Petrology 23:240–292 (1982)Google Scholar
  37. Winkler, H.J.F.: Petrogenesis of Metamorphic Rocks. 4th ed. Berlin-Heidelberg-New York: Springer 1976Google Scholar

Copyright information

© Springer-Verlag 1988

Authors and Affiliations

  • H. V. Eales
    • 1
  • A. H. Wilson
    • 2
  • I. M. Reynolds
    • 1
  1. 1.Department of GeologyRhodes UniversityGrahamstownSouth Africa
  2. 2.Department of GeologyUniversity of NatalPietermaritzburgSouth Africa

Personalised recommendations