A circular complex 4.5 km in diameter, Araxa cuts and domes quartzites and schists of the Proteroxoic Araxa Group. Fenitization extends up to 2.5 km from the contact and involves mainly quartzites, to which are added alkali feldspar, eckermannite, arfvedsonite, aegirine-augite, apatite and dolomite. The main complex is concealed by a deeply weathered mantle up to 230 m thick which consists of an upper lateritic soil (2-30 m) and an intermediate residium of goethite, magnetite, baryte, pyrochlore, monazite, gorceixite, etc. in which at deeper levels monazite and gorceixite decrease and apatite appears. The bottom few metres consist of weathered carbonatite. Drilling has proved the central area of the complex to be principally of carbonatite with an outer collar of glimmerites. The carbonatites are coarse to medium grained sovites and dolomitic carbonatites passing with increasing proportions of phlogopite into glimmerites. They comprise calcite, dolomite and ankerite, phlogopite, magnetite, baryte, apatite, pyrite and pyrochlore. Silexites of chalcedony form dykes and veins and are considered to be hydrothermal. Apart from a little pyroxenite the other silicate rocks referred to by earlier workers have not been encountered during the intensive drilling. Both concentric and radial dykes are abundant in the country rocks and include sovites and lamprophyric types,containing olivine, phlogopite, magnetite, perovskite, carbonate, aegirine and melanite. Analyses of carbonatites will be found in Silva et al. (1979, Tables 1 and 2).