Geology of the Riacho do Pontal iron oxide copper-gold (IOCG) prospect, Bahia, Brazil: hydrothermal alteration approached via hierarchical cluster analysis

摘要

The Riacho do Pontal prospect is situated on the border between the Borborema Province and the S?o Francisco Craton, in Bahia state. It comprises rocks polydeformed during the Neoproterozoic. The prospect area includes migmatites and gneissic rocks intruded by several sin- to post-tectonic granites. Structural analysis indicates a strong relationship between the development of ductile to brittle-ductile shear zones and associated hydrothermalism. The main tracts of high-strain rate are represented by the Riacho do Pontal (north) and Macururé (south) shear zones. Several copper occurrences have been mapped within the Riacho do Pontal prospect along secondary shear zones. In these areas, the gneissic rocks were affected by intense hydrothermal alteration. Hierarchical cluster analysis permitted the identification of the main hydrothermal mineral associations present in these rocks, which resulted from potassic (biotite) and sodic-calcic (amphibole-albite) alteration, in addition to silicification and iron alteration (hematite). These hydrothermal alteration types are similar to those typically found in iron oxide copper-gold deposits developed at intermediate crustal levels. Hematite-quartz-albite-chalcopyrite-pyrite hydrothermal breccias host the highest-grade copper ore (chalcopyrite-pyrite-chalcocite) zones. The spatial relationship between copper deposits and shear zones improves the metallogenic potential for copper of the Borborema Province and has important implications for mineral exploration in the region.