Geology and hydrothermal alteration of the Santa Bárbara polymetallic deposit (Cu, Zn, Pb, Ag, Au): Insights into the Ediacaran-Cambrian rift system evolution, Camaquã basin, southern Brazil
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Abstract
The Santa Bárbara deposit is a small polymetallic target (Cu, Zn, Pb, Au, Ag) located northwest of the ediacaran Caçapava do Sul granite, near the namesake city, in the Riograndense shield. It is genetically linked to other two historical cooper occurrences of the Cerro dos Andradas area, the Primavera and Andrada deposits. This study explores the Cerro dos Andradas occurrences in the context of the tectonic evolution of the ediacaran Camaquã rift system, focusing on the geological and hydrothermal characterization of the Santa Bárbara deposit. Mainly hosted in metamorphic rocks (Passo Feio Complex) these occurrences have not been considered products of Camaquã basin evolution, unlike the other major mineralizations of the region. The data were obtained by field work, petrographic analysis of thin sections, mineral reflectance spectroscopy of core samples, alongside geochemical and geological data acquired from a mineral exploration company. The mineralizations are mainly hosted in the damage zone of a master fault of the Camaquã Basin (Andradas fault). The fault’s NNE-SSW orientation is parallel to the mylonitic foliation of the footwall rocks, which comprise a sin magmatic shear belt (Passo Feio Complex or Cerro dos Andradas shear zone) developed in the western wall of the granitic pluton. The host rocks include subvolcanic and volcanic lithotypes (basalt and andesite) of the hanging wall block of the Andradas Fault, related to the Bom Jardim Group. The results indicate that the mineralized veins consist of chalcopyrite, bornite, sphalerite, galena, quartz, calcite, ankerite, gypsum, and barite, with concentrations up to 0.8% copper, 0.6% zinc, and 0.3% lead, as well as notable gold and silver concentrations. Together with the definition of hydrothermal processes near the ore (carbonatization and argilization), these findings support the interpretation of an epithermal mineral system for the Cerro dos Andradas deposits, similar to those proposed for other deposits in the Camaquã Basin.
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