Die Ultrabasitmassive im Präkambrium des Staates Goiäs/Brasilien |
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| Authors: | Höhst Quade Gerd -Andreas Stache |
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| Institution: | 1. Geologie au?ereurop?ischer L? nder, Geologisches Institut der TU Clausthal, Leibnizstr. 10, D-3392, Clausthal-Zellerfeld
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| Abstract: | The Brazilian state of Goiás and parts of Mato Grosso represent the centre of the Brazilian shield, between the Guaporé craton in the west and the São Francisco craton in the east. In contrast to opinions before, early Precambrian gneisses and migmatites form only small parts of the shield complex whereas middle and late Precambrian sequences dominate. From tectonic position, an eugeosynclinal central zone can be distinguished accompanied by younger miogeosynclinal series to the east and west. The ultrabasic massifs of Goiás can be differentiated into following types: - alpinotype serpentinised dunites and peridotites,
- gabbro-pyroxenite-peridotite associations,
- pyroxenite-metagabbro associations,
- dunite-pyroxenite-alkalisyenite associations,
- lamprophyre dykes.
Nos. 1, 2 and 3 are of Precambrian age whereas 4 and 5 are surely of post-Devonian, probably of Cretaceous age and can be attributed to the phase of Paraná volcanism. The most economic types at the moment (Nos. 1 and 2) yield Ni, Cu and Co in lateritic enrichment, Cr, Pt and related elements as primary constituents. Latest, the types 4 and 5 cause special interest. From their association with carbonatites they are related to the Araxá complex of Minas Gerais and anticipate mineralizations of Nb, Ta, Ti and P. |
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