Catalão I Alkaline Complex: Gravimetric and Magnetic Inversions

The Catalão I Alkaline Carbonatitic Complex is a phosphate mineral deposit located at the central portion of Brazil, in Goiás state (18°08’S, 47°48’N). This intrusive body is the object of this study. The geophysical potential methods, gravimetry and<br>magnetometry are widely used in mining geophysics and are used here for the Goiás Alkaline Complex study. The complex is made basically of ultramafic rocks (piroxenites and dunites) with a secondary carbonatitic intrusive phase. The ultramafic phase is denser and more magnetic than the surrounding geology (basically schists); this generates a positive density/magnetic contrast, which allowed a good determination of physical parameters of the complex, such as average density/susceptibility, volume and shape. The alkaline complex generates a Bouguer anomaly of 24mGal and a magnetic anomaly characterized by a normal dipole with an amplitude of 9000 nT. Both anomalies were inverted using the UBC Geophysical Inversion Facility, which generated two 3D models. The inversion results for both methods were very similar in shape, what was expected, since the denser rock is also the magnetic rock. A less denser/magnetic area was detected inside the complex model. This area probably contains the highest<br>carbonatite concentrations, since the carbonatite is less dense/magnetic then the surrounding rocks of the complex. This shows that these methods are adequate, not only to delimitate and locate the intrusive body, but also to find and delimitate the carbonatite inside the complex, which is the main commercial mineral exploited in this complex.