The large-scale occurrence of ruby and sapphire in Kenya is represented by contemporary river-bed and valley alluvial placers. The first ones are characterized by a high content of ruby (up to 10,4 ct/m 3 ), the second type is interesting due to the amount of forecasted resources: up to 2,3 million ct of ruby and 1,2 million ct of sapphire. It turned out to trace the mechanism of corundum concentrations forming, the mineral crystallized in Archean high-alumina gneisses affected by Precambrian basites (ultrabasites), and then survived a complicated way: – ancient eluvium – ancient alluvium – transportation by basaltic Pleistocenic magma – Holocenic weathering crust of volcanites – talus – contemporary alluvium.
