LAUSR

Abstract Fluorite-mica-feldspar hydrothermal veins and stockworks host Pb-Zn-Cu sulphides in the Sao Gabriel Terrane, Southern Brazil. The veins fill second- and third-order structures in Neoproterozoic calcitic marbles on the Cambaizinho Complex. Veins are mostly symmetrically zoned showing, from borders to the centre, fluorite and sericite, muscovite, adularia and albite (minor quartz, calcite and iron oxides). Galena, sphalerite, chalcopyrite, pyrite and minor cassiterite are disseminated in the veins and concentrated in ore pockets. Vein petrography, mineral chemistry and microthermometric measurements in fluorite fluid inclusions indicate that the hydrothermal veins were formed in a shallow crust environment from epithermal fluids near 140 °C. Their origin is attributed to a fossil geothermal system related to the post-collisional alkaline volcanism and caldera system of the Acampamento Velho Formation (574-549 Ma). This hydrothermal system is interpreted as genetically associated to fluorite and Pb-Zn-Cu occurrences on rhyolites and miarolitic cavities of related alkaline granitoids, Pb-Zn-Cu anomalies on stream sediment and soil analyses and Au quartz veins hosted by alkaline granitoids accompanied by pyrite, sericite and fluorite alteration halos in the same region. Although there is no mineral deposit discovered so far, the studied veins linked to the other base metal occurrences would indicate that the northwestern Sao Gabriel Terrane may host a poorly preserved mineralized epithermal system.