Influence of weathering and hydrothermal alteration on the REE and δ56Fe composition of iron formation, Cauê Formation, Iron Quadrangle, Brazil

Continental margin (Superior-type) iron formation of the Cauê Formation, Iron Quadrangle, Brazil, is composed of a laminated, magnetite-rich chemical meta-mudstone that was altered during hydrothermal circulation of basinal fluids, greenschist to amphibolite facies metamorphism, and subsequent supergene enrichment of Fe. The absence of traction current deposits and storm-generated structures suggests that deposition occurred on the distal shelf, possibly as deep as the continental slope. Paragenesis-based lithogeochemical analyses of two drill cores with contrasting alteration styles highlight the importance of hydrothermal, metamorphic, and supergene processes on the rare-earth element plus yttrium (REE + Y) and δ56Fe compositions of iron formation. The first drill core penetrates to a depth of 540 m in the Ouro Fino Syncline (OFS) where lithofacies have experienced intense hydrothermal and supergene alteration. The second core is from the Gandarela Syncline (GS) and contains 450 m of metamorphosed iron formation that has undergone later supergene enrichment of Fe.