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

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 (amphibolealbite) 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-chalcopyritepyrite 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.

Favorability potential for IOCG type deposits in the Riacho do Pontal Belt: new insights for identifying prospects of IOCG-type deposits in NE Brazil

“…According to Bueno et al (2009) and Hühn et al (2014), the central portion of the Riacho do Pontal prospect is mainly composed by gneisses and tonalites of the Sobradinho Remanso Complex (Fig. 2).…”

“…The metasedimentary cover is composed of quartzite and schists. Petrographic studies using Energy Dispersive X-ray Spectrometry coupled with Scanning Electron Microscope allowed the characterization of hydrothermal mineral signature (Hühn et al 2014). Hydrothermal alteration led to a pervasive calcic-potassic and calcic-ferric overprint of the host gneisses and migmatites.…”

“…Gamma ray spectrometric data have been very useful for mapping geological units and hydrothermal zones of Riacho do Pontal prospect (Hühn et al 2014). The ternary image of Figure 6 (RGB colors) represents a compositional map of U, Th and K. Different subdomains can be recognized.…”

“…The significance of the Neoproterozoic copper deposits of the Borborema Province as potential IOCG deposits was first emphasized by Maas et al (2003), Machado (2006) and Hühn et al (2011). These authors interpreted the geological and geochemical signature of copper occurrences associated with quartz-hematite breccias in the region of Mandacaru, São Julião, Fronteiras and Pio IX, Campos Sales and Aurora as a succession of IOCG mineralizations, formed as a response of intensive hydrothermal alteration in km-scale shear zones (Hühn et al 2014). The most important deposit is the Riacho Seco Copper Project (5 Mt @ 0.8% Cu), which is part of the Riacho do Pontal Fold Belt (RPFB) and was discovered by Companhia Baiana de Pesquisa Mineral (CBPM) in 1974.…”

Mapping New IOCG Mineral Systems in Brazil: The Vale do Curaçá and Riacho do Pontal Copper Districts

“…High concentrations of sulfides, however, can also occur in norite-and biotite-rich shear rocks and in calcsilicate rocks. Recently, new geologic [24,[26][27][28][29], tectonic [26,30], isotopic, and geochemical [27] studies have shown evidence that copper mineralization is related to the diverse family of IOCG deposits. In the last 10 years, high-resolution airborne geophysical surveys have been completed.…”