Ba and Pb-Zn occurrences in the Chanarcillo Group, Northern Chile: Sr and S isotope constraints

Various Ba and Pb-Zn stratiform and vein-type occurrences are hosted by the Lower Cretaceous carbonate rocks of the Chanarcillo Group, Northern Chile, deposited in a back-are basin setting. The occurrences are at different stratigraphic positions between the underlying volcanic rocks of the Bandurrias Formation and an evaporite-bearing carbonate unit that is also mineralized. The strontium isotopic compositions of the barites are comprised between the Sr-87/Sr-86 ratio of Lower Cretaceous seawater and the initial Sr-87/Sr-86 ratio of the volcanic rocks of the Bandurrias Formation. Their sulfur isotope values are mainly grouped around the Lower Cretaceous seawater value. The covariation in strontium and sulfur isotopic composition, and strontium content of the barites indicates various degrees of mixing between a hydrothermal fluid that has leached volcanic rocks of the Bandurrias Formation and a locally derived sulfate-bearing fluid, probably with some interaction of the hydrothermal fluid with the carbonate and evaporite host rocks of the Chanarcillo Group.