Orbicular magnetitite from the Catalão I phoscorite-carbonatite complex

PALMIERI, M.; PEREIRA, G. S. B.; BROD, J. A.; JUNQUEIRA-BROD, T. C.; PETRINOVIC, I.A.

Frankfurt

Congreso; 9th International Kimberlite Conference; 2008

The Catalão I phoscorite-carbonatite complex is part of the Late-Cretaceous Alto Paranaíba Igneous Province (APIP), which also includes other major plutonic, carbonatite-bearing complexes, such as Tapira, Araxá, Salitre I and II, Serra Negra, and Catalão II (Fig. 1).It is a roughly circular, 5.5 x 6 km dome structure composed of ultramafic, carbonatitic and phoscoritic rocks. The complex contains unexploited deposits of REE, Ti, and vermiculite, and is currently mined for Nb and phosphate. Fresh rock outcrops occurring in the Copebrás phosphate mine (Anglo American Group), in the NW portion of the dome, allowed the distinction of three main petrogenetic series. The phoscorite series comprises phoscorites, nelsonites, apatitites, and magnetitites; the carbonatite series consists of dolomite carbonatite and calcite carbonatite; the bebedourite series is represented by ultramafic silicate rocks almost entirely converted to metasomatic phlogopitites. Except for the phlogopitites, all the other rocks occur as stockworks of dykes of variable thickness which crosscut each other and the phlogopitite. Liquid immiscibility textures recognized in the fresh rock comprise apatite aggregates within carbonatites, carbonate globules in silicate rocks, and orbicular structures. The aim of this work is to characterize the orbicular structures using petrography, mineral chemistry, and C and O stable isotopes.