Integrated Geophysical characterization of the Passa Quatro Alkaline Complex (SE Brazil): Insights into lateritic bauxite formation and REE potential

The Passa Quatro Alkaline Complex (PQAC), located in the central segment of the Cabo Frio Magmatic Lineament (southeastern Brazil), is related to Late Cretaceous–Eocene rifting associated with the final stages of Gondwana breakup. This complex hosts lateritic bauxite deposits developed over alkaline lithologies under tropical weathering conditions. To investigate the internal structure of this lateritic system, a high-resolution audio-magnetotelluric (AMT) survey was conducted using eight closely spaced stations (50 m spacing), integrated with magnetic, gravity, and radiometric data. The AMT results define three main geoelectrical domains: a shallow conductive layer associated with bauxite and colluvial materials; an intermediate resistive unit corresponding to the gneissic basement; and a deeper moderately conductive zone interpreted as fractured quartz–biotite schist affected by fluid circulation. The alkaline complex itself is primarily constrained by magnetic, gravity, and radiometric signatures. The integrated interpretation indicates that the alkaline massif acted as the primary source of aluminum-rich material, later weathered, mobilized, and redeposited along the slope. In addition, the magmatic setting may have contributed to rare earth element (REE) enrichment within the bauxitic profile. These results provide new insights into the architecture and formation of lateritic bauxite deposits over alkaline terrains, highlighting the combined roles of magmatism, weathering, and geomorphological processes, as well as their implications for REE mineralization.