ABSTRACT
Bed samples of the Amazon River were collected from Iquitos (Peru) to Belém (Brazil). 28 selected samples were analysed and 12 types of heavy minerals were found: tourmaline, zircon, garnet, staurolite, hypersthene, pyroxene (augite), amphibole (hornblende), tremolite, magnetite or ilmenite and leucoxene. Most of the samples presented large amount of idiomorphic unstable minerals such as hypersthene, augite and amphibole pointing towards basic and ultra-basic rocks source. These unstable minerals diminish toward the lower portion of the river. Stable minerals such as zircon and tourmaline have showed both angular and round shapes, which indicate more than one source but in any case originating from acid rocks. A cluster analysis method was applied to the data and two main clusters were determined. The first group, located at the upper Amazon River, is rich in unstable minerals, probably from an Andean source. The second group, which includes samples located below the confluence of the Juruá River, presents a high zircon and tourmaline percentage which indicates a contribution from the Precambrian Shields in adition to the Andean source.