Abstract
The Riacho do Pontal prospect is situated on the border between the Borborema Province and the São 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.
Highlights
REGIONAL GEOLOGICAL SETTINGThe Riacho do Pontal prospect is located in the southern portion of the Borborema Province (Brito-Neves 1975, 1983; Almeida et al 1976), near the contact with the northern section of the São Francisco Craton (Almeida 1977; Fig. 1), in Bahia state
The possibility of copper deposits associated with iron oxides in the Borborema Province, similar to those of the iron oxide copper-gold deposits (IOCG deposits; Hitzman et al 1992; Hitzman 2000), was emphasized only in more recent studies, such as those conducted by Maas et al (2003) and Machado (2006), in the Orós-Jaguaribe Belt, and by Huhn et al (2011), in the Cariri region
These studies related the occurrence of copper deposits, associated with quartz-hematite breccias in the region bounded by the towns of Mandacaru, São Julião, Fronteiras, and Pio IX (Piauí state) and Campos Sales (Ceará state), to the economically important IOCG deposits; these have previously been identified in Brazil in notably large deposits from the Carajás region (Huhn & Nascimento 1997; Xavier et al 2008; Monteiro et al 2008; Grainger et al 2008; Groves et al, 2010)
Summary
The Riacho do Pontal prospect is located in the southern portion of the Borborema Province (Brito-Neves 1975, 1983; Almeida et al 1976), near the contact with the northern section of the São Francisco Craton (Almeida 1977; Fig. 1), in Bahia state. The contact of the Borborema Province with the northern portion of the São Francisco Craton (Fig. 1) is represented by the fronts of the Brasiliano nappes, where the studied region is positioned This area is characterized as a Brasiliano collisional zone (0.75 – 0.57 Ga) developed during the convergence of Neo- to Mesoproterozoic terrains due to a tangential tectonic event with a transpressive component and mass transport towards the São Francisco Craton (Alkmin et al 1993).
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