Alkaline Rocks and Carbonatites of the World

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Amorinopolis

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Occurrence number: 
025-00-052
Country: 
Brazil
Region: 
Goias
Location: 
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.

References: 
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.196 The Ipora Group of occurrences of alkaline intrusions of central Goias. Fig. 199 Amorinopolis (after map provided by J. C. M. Danni).
Location: 
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith