This irregularly shaped intrusion, approximately 5x2.5 km, consists principally of syenites but with granites and trachytes/phonolites also occurring. The syenites comprise essentially perthite, a little oligoclase, rare quartz, biotite, plentiful hastingsite and rarer riebeckite or arfvedsonite. The granites are apparently not peralkaline, but the trachytes, which form dykes and included blocks, contain phenocrysts of K-feldspar, abundant aegirine and cancrinite, which is considered to be primary, while fine micaceous patches are thought to be after nepheline. Rare violet fluorite occurs and carbonate is also present.
LEAL, J.W.L., SILVA, G.H., SANTOS, D.B. dos, TEIXEIRA, W. LIMA, M.I.C. de, FERNANDES, C.A.C. and PINTO, A.do C. 1978. DNPM. Projeto Radambrasil. Folha SC.20 Porto Velho. Levantamento de Recursos Naturais, Geologia, 16: 19-184