Cerro Manomo lies 20 km northeast of the Velasco Alkaline Province (No. 7) and forms a treeless mesa of 4x6 km flanked by cliffs and talus slopes and rising 400 m above a jungle-covered peneplain of lateritized Precambrian gneiss.
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Covering 440 km2 and extending over 80 km, the Velasco Province consists of an early suite of volcanics, 14 overlapping ring and elliptical plutons and the Cerro Manomo carbonatite, which is some 20 km northeast of the plutons and is described above (No. 6).
Two intrusions of teschenite with syenitic differentiates occur to the south of Lago Buenos Aires, one 11 km southeast of Los Antiguos, the other in the Rio Jeinemeni on the border with Chile, 30 km south-southwest of Los Antiguos (Busteros & Lapido, 1983, Fig. 1_1).
Essexites and essexitic gabbros are described from the Rio Carbon area, northeast of Lago San Martin. They contain orthoclase and a little analcime, and are only marginally alkaline.