COMPOSITION OF PRIDERITE IN PHLOGOPITITES FROM THE CATALAO-I CARBONATITE COMPLEX, BRAZIL

Magnetite grains with exsolved ilmenite lamellae may be replaced by py rite or carbonate in phlogopitites of the Catalao I carbonatite comple x, Goias State, Brazil. The ilmenite is transformed in part to prideri te and sometimes to rutile. Priderite occurs as small anhedral grains (<0.2mm) or composite crystals associated with ilmenite and rutile. Ch alcopyrite, magnetite, monazite, and pyrochlore also occur inside the area of original magnetite grains. The priderite belongs to the K2FeTi 7O16-BaFeTi7O16 series with K/(K + Ba) ranging from 1.0 to 0.53. The h ighest contents for other elements are: V2O3 2.65, Cr2O3 4.1, and Nb2O 5 1.98 wt.%. Priderites associated with magnetite have the highest V, Cr, and Nb contents whereas others have the highest Ba content. Zoning characterized by K-Ba substitution is patchy but always present. V- a nd Cr-poor priderites are similar in composition to priderites from la mproites, and the V- and Cr-rich ones are compositionally similar to h ollandite-group minerals found in kimberlites.