A roughly circular structure 2.5 km in diameter occurs in dense rain forest. It is situated on a very large fault trending northwest-southeast, extending south into Brazil and lying on the eastern edge of the Roraima structure.
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Located during the RADAM Project, Seis Lagos consists of three circular structures aligned north-south with approximate diameters of 5.5, 0.75 and 0.5 km. They form laterite covered hills surrounded by gneisses and migmatites of the peneplained Guianense complex.
This is an elongated area within the Guianese gneiss complex consisting of aegirine-riebeckite and aegirine granites with orientated, cataclastic fabrics. Biotite and occasionally fluorite are present. Boundaries to the peralkaline granite have not been mapped.
Sucunduri is a 700 km2 dome in the Precambrian Teles Pires and Beneficente Groups, which is pierced by a number of plugs, necks and dykes of alkali syenite, lusitanite and nepheline syenite, with some phonolite and trachyte flows.
This irregularly shaped intrusion, approximately 5x2.5 km, consists principally of syenites but with granites and trachytes/phonolites also occurring.