Cerro Sapo

The size of this intrusion has not been determined accurately because of the high relief and dense vegetation, but it is smaller than Cerro San Cristobal (022-00-001), although there is a much more strongly developed contact aureole. Samples collected by Ahlfeld (1966), mostly from boulders, varied considerably in the proportions of the minerals present. One specimen consisted of 30% orthoclase, 5% albite-oligoclase, 15% sodalite, 10% nepheline, 20% brown amphibole, 15% aegirine, secondary cancrinite and accessory apatite. Other samples contained green biotite and small amounts of carbonate; one sample was veined with sodalite and ankerite. Another rock type included olivine, partly altered to amphibole and biotite, and a sodic amphibole with diopsidic inclusions, in a groundmass with abundant nepheline. The intrusion is cut across by a dyke at least one km in length and up to 5 m thick, which alters the adjacent sedimentary country rocks. The dyke consists of ankerite with lenticles, up to 50 cm across, of sodalite. In one outcrop abundant baryte is present, removal of which in part has revealed sodalite dodecahedra as much as 3 cm in diameter. J. Gittins (Tuttle & Gittins, 1966, p. 536) suggested to F. Ahlfeld that this rock might be carbonatite, with which he concurred.