Abstract
The copper deposits of the O'okiep District rank amongst the top three S. African producers, with an annual output of 3 million metric tons grading 1.65% Cu on average. They occur in what is now considered the S. extension of the 1200 m. y. Kibaran orogenic belt. Copper mineralization is linked to cross-cutting bodies of "noritoid" RO=0.7126−0.7250) which have been emplaced into the granulite facies metamorphic country rocks 1100 m. y. ago. The results of 150 electron probe analyses show that orthopyroxene in the non-ore-bearing noritoids is En51–52, in the ore-bearing noritoids En60–65. There is a concomitant variation in the composition of phlogopitic mica which carries higher Fe in non-ore-bearing noritoids. The Ticontents of magnetite are below 0.1%; there are significant chromium values. Spinel exsolution lamellae contain up to 14% ZnO. The copper sulphides occur as granular aggregates with silicates, on grain boundaries and on cleavage planes of hypersthene and mica; they also replace altered Fe-Ti-oxides. Pyrite (up to 1.4% Co) and pentlandite (up to 5% Co) are not widespread. The possible derivation of the noritoids from a reservoir of basic magma at depth is considered. A source-bed model, involving generation of noritoid "magma" from Cu-bearing members of the stratigraphic sequence, during the peak of metamorphism (800–1000 °C, 6–8 kb) is tentatively proposed. Stratabound base metal concentrations (Aggeneys, Gamsberg) in lower grade (amphibolite facies) metamorphic terrains to the East have not been mobilized.
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formerly, Mineralogisch-Petrographisches Institut, Universität Hamburg
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Stumpfl, E.F., Clifford, T.N., Burger, A.J. et al. The copper deposits of the O'okiep District, South Africa: New data and concepts. Mineral. Deposita 11, 46–70 (1976). https://doi.org/10.1007/BF00203094
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DOI: https://doi.org/10.1007/BF00203094