Isotopic study of the Pb-Zn (Cu-Ag) Santa Maria Deposit, Cacapava do Sul Region, Rio Grande do Sul, Brazil

The Camaqua Mines, in the central-southern region of Rio Grande do Sul State, Brazil, contain the largest deposits of base metals (Camaqua, Cu; Santa Maria, Pb-Zn) in the Camaqua Basin. The host rocks are consisted of sandstones and conglomerates of the Santa Barbara Group and interbedded volcanic rocks of undefined stratigraphic position. Peperitic features were identified in a mineralized trachytic sill. An age of 565 +/- 5 Ma (U-Pb LA-MC-ICP-MS) was obtained for another trachytic rock, which allowed for the identification, for the first time, of the Acampamento Velho Formation in the Camaqua Mines region. Stratigraphic relations demonstrate that both rocks represent this magmatism. Data from Pb isotopes and spatial relationship observed in the field indicate a possible genetic link between Acampamento Velho Formation and Camaqua mineralization. Pb isotopic data also suggest a predominantly older crustal source (1.07 Ga model age) for Pb and possibly for the other metals, with intermediate or mixed origin, suggesting that magmatic-hydrothermal fluids leached the metals from the percolated rocks of the basement.