Petrography of Mesoproterozoic Kuroko-type hydrothermal alteration zones from the Serra do Itaberaba Group and its use in mineral exploration

Abstract

In the volcano-sedimentary Serra do Itaberaba Group, located within the central part of the Ribeira Fold Belt, Mesoproterozic paleo-hydrothermal systems developed surrounding small bodies of andesites and rhyodacites. These systems were responsible for the hydrothermal alteration of basic and intermediate igneous and volcaniclastic rocks. Despite the overprinting of two medium-grade and one low-grade metamorphic-deformational events, well-defined zones generated by different types and intensities of hydrothermal alteration are still recognizable. An initial large chloritic alteration zone (ZC1) was overprinted by restricted chloritic (ZC2) alteration zones, similar to those associated with Kuroko-type base metal deposits. The metamorphic products from ZC1 have magnesium amphibole(s) in different proportions (cummingtonite-anthophyllite rocks) and those from ZC2, Mg-chlorite (meta-chloritites). These rocks are composed of exotic mineralogic associations and can be used as exploration guides for Kuroko-type base metal deposits present in metamorphosed volcano-sedimentary sequences.