Regional setting and nature of gold mineralization in Tanzania and southwest Kenya
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The most productive gold deposits in Tanzania and southwest Kenya are in the Nyanzian greenstone belts (2700 Ma) and the Ubendian System (2000 Ma). The deposits occur in the form of massive or disseminated Fe-sulphide-rich bodies in banded iron formation (BIF) or tuffs, mineralized shear zones in mafic rocks and shear-zone-controlled quartz reefs. Mineralization is mostly interpreted as epigenetic, although for some deposits a syngenetic origin is possible. There are also base-metal-rich massive sulphide deposits of probable syngenetic origin in the Nyanzian greenstone belts. Iron-rich mafic rocks are the most favourable hosts in the lower Nyanzian belts as well as in the Ubendian System, whereas BIF is the dominant host rock in the upper Nyanzian System. To date about two-thirds of the gold production has come from shear-zone-controlled mineralization, and about one-third from stratiform-stratabound deposits.