Abstract
The tin mineralization at Rondonia, W. Brazil, is characterized by the association cassiterite and topaz. Both minerals occur as replacements in Precambrian to Early Paleozoic granites. The tin mineralization of the Eastern Cordilleras of Bolivia, on the other hand, has cassiterite and tourmaline as characteristic mineral association, and is related to the occurence of large granitic batholiths. The origin of the two tin mineralizations is discussed.