The Kaituma intrusion of peralkaline quartz syenite covers about 70 km2 and appears to grade westwards into biotite granite. It comprises microcline perthite, albite-oligoclase, quartz, aegirine, arfvedsonite, biotite and accessory sphene, orthite, magnetite and apatite.
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Makarapan forms a mountain some 8 to 9 km in diameter and rising to 800 m. Two smaller hills, Urume and Wurumu, lie to the east, but all three areas probably belong to the same intrusion of riebeckite granite.
The Muri alkaline complex is centred on the Muri Mountains, which run along the Guyana-Brazil border, and is emplaced in Precambrian granodiorite and gneiss which are locally fenitized.