Alkaline Rocks and Carbonatites of the World

Setup during HiTech AlkCarb: an online database of alkaline rock and carbonatite occurrences



Occurrence number: 
Longitude: -51.05, Latitude: -16.68

Amorinopolis is a volcanic vent of the Ipora Group standing 250 m above the surrounding Devonian sandstones. It consists of a central plug surrounded by a series of ring dykes, which outcrop as annular ridges, and a system of radiating dykes. An intrusion of nephelinite breccia cuts the complex in the northeast and also forms two small intrusions east of the main complex. The central plug of the main complex consists of tephrite, basanite and augitite, while the ring dykes and radial dykes comprise essentially olivine melaleucitite (ugandite) and olivine-leucite melanephelinite, which contain about 30% olivine and titanaugite microphenocrysts in a matrix of Ti-magnetite, perovskite, leucite and a little K-feldspar. A small plug some 300 m in diameter lies 2. 5 km south-southwest of the main complex and consists of olivine-leucite melilitite (katungite) which contains 30% magnesian olivine phenocrysts in a matrix of melilite, leucite, perovskite, Ti-magnetite, phlogopite and (?)kalsilite with secondary zeolite and calcite. Danni (1985) gives chemical analyses of a range of rock types and of olivine and melilite.

DANNI, J.C.M. 1985. Rochas da serie kamafugitica na regiao de Amorinoplis, Goais. Contribuicoes a Geologia e a Petrologia Nucleo de Minas Gerais-SBGM: 5-13. GLASER, I., BEZ, L., MARQUES, V.J. and RIPPEL, C. 1970. Excursao No. 3: Regiao de Ipora. Anais Congresso Brasileira de Geologia, 2: 39-58
Fig. 1_196 The Ipora Group of occurrences of alkaline intrusions of central Goias. and Fig. 1_199 Amorinopolis (after map provided by J. C. M. Danni).
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