Alkaline Rocks and Carbonatites of the World

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Canaa

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Occurrence number: 
025-00-082
Country: 
Brazil
Region: 
Rio de Janeiro
Location: 
Longitude: -43.28, Latitude: -22.6

Canaa is a 20 km2, approximately circular intrusion emplaced into Precambrian quartzofeldspathic gneisses and migmatites, in which foliated and banded litchfieldites surround a core of alkali syenite. The litchfieldite comprises alkali feldspar, nepheline, cancrinite, sodalite, 'lepidomelane' and accessories, while corundum is abundant in the vicinity of the contacts with the country rocks. Pegmatitic varieties are common with nephelines up to 15x5 cm, sodalites 5 cm in diameter and zircons of 3 cm. Trachyte dykes occur.

Economic: 
Alluvial concentrations of corundum are found in parts of the area with crystals up to 30 cm in length.
References: 
LIMA, P.R.A. dos S. 1976. Geologia dos macicos alcalinos do estado do Rio de Janeiro. Semana de Estudos Geologicos, Itaguai: 205-59
Fig.204 Distribution of alkaline rocks around Rio de Janeiro. Fig. 208 Canaa (after Lima, 1976, p. 237).
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith