The mineralogy and geochemistry of the sediments of northwestern Lake Victoria

In the nearshore area of northwestern Lake Victoria a thin strip of quartzarenite sand occurs which grades lakeward into silty clay consisting of quartz with subordinate amounts of K-feldspar, plagioclase, kaolinite, illite, vermiculite and organic matter. Varimax matrix determinations of the element concentrations in the lake-bottom sediments extractable by aqua regia indicate that: (1) there is a strong association of Cr, Cu, Zn and Ni; (2) there is a strong association of Fe, Mn and Co; (3) Cu and Ni show moderate to slight associations with organic matter; (4) Ca is relatively independent of the other elements. The general decrease in the pH values of the surface and bottom waters outward from the lake shore, with consistently higher values for the surface water relative to the bottom waters, results from decreasing levels of photosynthetic activity.