Alkaline Rocks and Carbonatites of the World

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

Montes Claros De Goias (Salobinha)


Occurrence number: 
Longitude: -51.38, Latitude: -16.05

This is an elliptically-shaped intrusion of the Ipora Group covering some 50 km2 and intruded into Devonian sandstones of the Furnas Formation, which are metamorphosed to pyroxene hornfelses. The northeastern and southwestern parts are occupied by ultramafic rocks which are separated by a nepheline syenite intrusion. Dunites are the most abundant rocks comprising a magnesian olivine, which is variably serpentinized, and a little pyroxene and opaques. Pyroxenites are concentrated in the southwest and contain both clino- and orthopyroxene; they are cut by fine veins of plagioclase, quartz and alkali feldspar. The syenites are extremely variable and consist of orthoclase, anorthoclase, albite/oligoclase, nepheline, ferrohastingsite, augite/aegirine-augite, melanite, sphene, biotite and opaques. Theralitic essexites and nordmarkites also occur and dykes, including monchiquites, are very abundant both within the intrusion and cutting the country rocks.

Alluvial concentrations of chromite and magnetite occur.
89 Ma (Danni quoted by Asmus, 1978, p. 54, No. 45).
ASMUS, H.E. 1978. Hipoteses sobre a origem dos sistemas de zonas de fratura oceanicas alinhamentos continentais que ocorrem nas regioes sudeste e sul do Brasil. In. Petrobras. Aspectos estruturais da margem continental leste e sudeste do Brasil. CENPES/DINTEP, Rio de Janeiro (Serie Projeto Remac, no. 4): 39-73. BEZ, L. 1970. Petrografia do macico alcalino de Montes Claros de Goias, GO. Boletim Congresso Brasileira de Geologia, 24(1): 361-4. PENA, G.S. and FIGUEIREDO, A.J.A. 1975. Projeto Goiama II, relatorio final. Departamento Nacional da Producao Mineral. Companhia de Pesquisa de Recursos Minerais, 1: 121-61
Fig. 1_196 The Ipora Group of occurrences of alkaline intrusions of central Goias.
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