1.02 GA GRANITE MAGMATISM IN THE TATI GRANITE-GREENSTONE TERRANE OF BOTSWANA - IMPLICATIONS FOR MINERALIZATION AND TERRANE EVOLUTION

The results of ion microprobe analyses of cores and rims of grains of zircon from a peraluminous leucogranite intruding and intruded by the Ni-Cu mineralization of the Phoenix deposit in the Tati Granite-Greens tone Terrane of Botswana are interpreted to indicate that: 1) rims for med 1022 +/- 16 Ma ago during emplacement of the granite and 2) the co res are xenocrysts, derived from the sources of the granitic magma, wh ich contain zircon of ages between about 1036 Ma and 1786 Ma. These re sults were unexpected because the Tati Granite-Greenstone Terrane is g enerally assumed to be part of the Zimbabwe Craton and hence composed of rocks of Archaean age. Emplacement of leucogranite in this area at about 1022 Ma clearly challenges this assumption. Because the leucogra nite contains lenses and veins of massive Fe-Ni-Cu sulphides, this min eralization must have occurred more recently than about 1022 Ma. It is possible that the emplacement of mafic to ultramafic magma with its p robable immiscible Fe-Ni-Cu-S magma provided the heat to melt rocks of the Penhalonga or Selkirk Formations to produce the leucogranitic mag ma. If so, all of the Ni-Cu mineralization in the Phoenix deposit took place about 1022 Ma ago.