The Occurrence of Heavy Mineral Sands along the Tanzanian Coast

Heavy mineral sands containing garnet, ilmenite, kyanite, zircon, rutile, magnetite and monazite occur along the eastern coastal belt of Tanzania. Concentrations of these heavy minerals vary along the coast from south to north, but the mineralogical assemblage is fairly constant, the average for the entire coast being garnet 39.2%, ilmenite 33.8%, kyanite+zircon 21.7%, rutile 3.8%, others 1.4%, total heavy minerals 23%.

The heavy mineral concentrations are restricted to the Mtoni Terrace, consisting of lagoons, swamps, raised coral reefs and beach ridges of Pleistocene to Recent age, the richer concentrations being found north of the mouths of the bigger rivers, e.g., the Msimbati Peninsula, north of the Ruvuma River. The source rocks are the Precambrian Basement rocks to the immediate west of the coastal belt and, to a lesser extent, the younger sedimentary rocks from Karroo to Recent in age.

A study of beach profiles and of heavy mineral concentrations at five selected localities along the coast has shown that higher concentrations occur during November to January and May to July, coinciding with the beginnings of the monsoonal periods, when the erosive action of the sea is greatest.