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 granite comprises microcline perthite, quartz, riebeckite (<5%), which is sometimes intergrown with aegirine, together with accessory biotite, zircon, opaques, sphene, apatite and fluorite. The rocks are strongly foliated and occasionally intensely granulated.
BERRANGE, J.P. 1970. The riebeckite granite of Makarapan Mountain - a reinterpretation. Proceedings of the Eighth Guiana Geological Conference, Georgetown, II: 1-14.
SNELLING, N.J. and MCCONNELL, R.B. 1969. The geochronology of Guyana. Records, Geological Survey of Guyana, 6: XI, 1-26