Alkaline Rocks and Carbonatites of the World

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



Occurrence number: 
Longitude: -39.88, Latitude: -15.5

One large and a number of smaller bodies extend north-south over some 40 km and cover about 26 km2. They comprise principally a variable suite of nepheline syenites including variants rich in sodalite and arfvedsonite. Some varieties have a strongly developed gneissose fabric. Biotite is the usual mafic mineral and cancrinite is abundant. Sodalite comprises more than 30% of some rocks and appears to have replaced nepheline. The feldspar is essentially perthite. Small plugs and dykes of porphyritic biotite tinguaite occur up to 12 km from the principal intrusions. Syenites, some with a little quartz, also occur and may be (?)fenites.

K-Ar on amphibole from syenite gave 765±40 Ma and on biotite 469±14 and 424±35 Ma (Cordani et al. 1974).
CORDANI, U., HALPERN, M. and BERENHOLE, M. 1974. Comentarois sobre as determinacoes geocronologicas do Folha Porto Alegre SH.22. In. Carta Geologica do Brasil ao miliuonesimo: texto explicativo. 70-88. Ministerio das Minas e Energia, Departamento Nacional da Producao Mineral, Brasilia. FUJIMORI, S. 1967. Rochas alcalinas do sul do Estado da Bahia. Ministerio das Minas e Energia. Notas Preliminares e Estudos, 141. SOUTO, P.G. 1972. Geologia e petrologia da area de Potiragua, Bahia, Brasil. M.Sc. Thesis, 1-65 (unpublished), Instituto Geociencias, University of Sao Paulo. 65 pp
Fig. 1_195 The Bahia province of alkaline rocks (based principally on the Carta Geologica do Brasil ao milionesimo: Folha Salvador SD. 24 accompanying Pedreira et al. 1976).
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith