The Rio Itapicuru greenstone belt, Bahia, Brazil: geologic evolution and review of gold mineralization

Abstract.

Shear-hosted gold deposits in the Rio Itapicuru greenstone belt occur within supracrustal rocks metamorphosed under greenschist to amphibolite facies conditions. Integration of host-rock geochemistry, fluid-inclusion studies, geochronology, and structural geology supports a model of metallogenic evolution intimately associated with a Paleoproterozoic history of tectonic convergence, involving early arc/back-arc magmatism, and subsequent collision and granitoid emplacement. In this context, gold mineralization occurred mainly during late collisional tectonism at ~2,050 Ma, and resulted from a crustal-scale hydrothermal system characterized by carbonic and low salinity aqueous-carbonic fluids of distinct sources. The fluids migrated and interacted with host rocks of different compositions. In the southern part of the belt, structurally controlled fluid circulation within iron-rich mafic rocks gave rise to the Weber gold belt, which contains the largest gold deposits of northeastern Brazil. In contrast, fluid–rock interaction with volcaniclastic–carbonaceous sedimentary rocks, both in the southern and northern parts of the belt, resulted in the development of relatively smaller deposits, suggesting that local-scale structural and lithological attributes were critical controls in the size of the deposits.