stripes
Essentially a volcanic province of flows, pyroclastic deposits and numerous vents and plugs covering in all some 300 km2. Lavas and breccias of analcimite and olivine analcimite are predominant and contain phenocrysts of titanaugite, olivine, which is invariably altered, and analcime in a matrix of titanaugite, analcime, magnetite, perovskite, zeolite, nepheline, phlogopite, apatite and kaersutite. Leucite has been reported but J. C. M. Danni (personal communication, 1981) suggests that analcime was probably mis-identified. Abundant amygdales are filled with zeolite and calcite. Plugs and dykes are principally fourchites and melamonchiquites with rare analcime phenocrysts, and are hypabyssal equivalents of the lavas. Gaspar and Danni (1979) describe analcime phenocrysts ascribing to them a primary igneous origin. Phonolites are rare. Moraes (1984) has described melilite melanephelinite and basaltoid flows and pyroclastics. Dunite and wehrlite nodules occur. Carbonatitic lavas and pyroclastics locally cap the analcimites. Various types are described, usually comprising carbonatitic and silicate fractions, the former ranging between 30 and 65% (Gaspar and Danni, 1981).
BEZ, L., GUIMARAES, J. and GUIMARAES, D. 1971. Distrito vulcanico de Rio Verde. Anais Congresso Brasileira de Geologia, 25(1): 121-8.
GASPAR, J.C. and DANNI, J.C.M. 1979. Analcima nas rochas vulcanicas de Santo Antonio da Barra, Goias, e suas possivels implicacoes petrogeneticas. Boletim Mineralogico, Recife, 6: 41-9.
GASPAR, J.C. and DANNI, J.C.M. 1981. Aspectos petrograficos e vulcanologicos da provincia alcalino-carbonatitica de Santo Antonio da Barra, sudoeste de Goias. Revista Brasileira de Geociencias, Sao Paulo, 11: 74-83.
HASUI, Y., CARTNER-DYER, R. and IWANUCH, W. 1971. Geochronologia das rochas alcalinas de Santo Antonio da Barra, Go. Anais, Congresso Brasileiro de Geologia, 25(1): 253-8.
MORAES, L.C. 1984. Petrologia, estratigrafia e potencial diamantifero da suite vulcanica alcalina de regiao de Santo Antonio da Barra, Goias. B.Sc. Thesis (unpublished), Departamento Geociencias, Universidade de Brasilia. 130 pp
