The Migori Segment of the Archean Nyanza Greenstone Belt, Kenya: Geology, Geochemistry and Economic Mineral Potential

Abstract

The 80 x 20 km Migori segment of the Nyanza greenstone belt, Kenya, lies within the Archean Tanzanian Craton (2.8-2.5 Ga). Volcanic facies mapping has delineated eleven formations comprising the Macalder and Lolgorien Subgroups of the Migori Group. The subgroups represent adjacent volcanic centres with well-developed central and proximal facies, and interfingering distal facies. Rocks at the base of the group are submarine tholeiitic basalt and dolerite, and calc-alkaline dacite and rhyolite; overlying subaerial dacites and late granite intrusions define a high-K calc-alkaline suite. The tholeiitic volcanic rocks have 3.8 $<$ Zr/Y $<$ 6.5 and 1.0 $<$ La$ sb{ rm N}$/Yb$ sb{ rm N}$ $<$ 2.4, the calc-alkaline volcanic rocks 10 $<$ Zr/Y $<$ 21 and 19 $<$ La$ sb{ rm N}$/Yb$ sb{ rm N}$ $<$ 42, and the high-K calc-alkaline dacites 9 $<$ Zr/Y $<$ 16 and 21 $<$ La$ sb{ rm N}$/Yb$ sb{ rm N}$ $<$ 22. The calc-alkaline - high-K association in the segment points to a continental arc tectonic setting for the Migori segment. The central and proximal facies provide the greatest potential for volcanogenic sulphide deposits, whereas vein and stratabound gold mineralisation are present in all the facies.