Occurrence of Magnetite and its Relationship to Pegmatitic Carbonatite, Pyroxene Carbonatites at the Alkaline Igneous-Carbonatite Complex, Okorusu, Namibia. (Geology/Geophysics Section).

* Shivdasan, P. and R.D. Hagni. Department of Geology and Geophysics, University of Missouri-Rolla. OCCURRENCE OF MAGNETITE AND ITS RELATIONSHIP TO PEGMATITIC GARB ONATITE, PYROXENE GARB ONATITES AT THE ALKALINE IGNEOUS-CARBONATITE COMPLEX, OKORUSU, NAMIBIA. Previously unrecognized carbonatites at Okorusu in North-Central Namibia, pyroxene carbonatite and pegmatitc carbonatite, have been found to be comparable in mineralogical composition during the field mapping, and the modal percentages of magnetites are unusually high. The magnetites in the pyroxene carbonatites are medium grained embayed crystals whereas in pegmatitic carbonatite they are very coarse and euhedral crystals that tend to form at the margins of their contacts especially with the Na-fenite host rocks. Magnetite rims of thickness up to 2 feet and magnetite disseminations occur within the pegmatitic carbonatite. Magnetite contains inclusions of calcite, apatite, phlogopite, and pyroxenes. Electron microprobe analysis of magnetites indicate that they are not zoned with regard to their Ti contents, in contrast to magnetite associated with carbonatites at Jacupiranga, Brazil. Okorusu magnetites exhibit abundant exsolutions of ulvospinel in a characteristic cloth texture, and oxidation exsolution occurred subsequently. Supported by two National Science Foundation International Travel grants and two Society of Economic Geologists research grants.