Alkaline Rocks and Carbonatites of the World

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Fazenda Hiassu


Occurrence number: 
Longitude: -39.63, Latitude: -15.07

These two intrusions, which are emplaced in Precambrian gneisses, granulites and metamorphosed ultrabasic rocks, are composed mainly of litchfieldite and pyroxene, amphibole and sodalite litchfieldite, but also sodalite syenites, tawite and alkaline pegmatites. The tawites consist mainly of blue sodalite, including hackmanite. Nepheline-sodalite-bearing pegmatites are widespread. The contacts are poorly exposed but sometimes appear to be gradational. Chemical analyses and detailed petrography will be found in Fujimori (1978).

Sodalite-rich rock is quarried for ornamental stone.
K-Ar on trachyte gave 370±9 and 356±7 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. 1978. Rochas alcalinas da Fazenda Hiassu, Itaju do Colonia Bahia. Puplicacao Especial, Sociedade Brasileira de Geologia, 2: 1-117
Fig. 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).
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