Isotopic fluid changes in a Neoproterozoic porphyry–epithermal system: The Uruguay mine, southern Brazil

•The Camaquã mine is a pulsed, low-sulfidation porphyry-type deposit.•Sulfide and sulfate precipitations are related to magmatic and meteoric water.•Sequence of sulfide crystallization with an exhausting S magmatic reservoir is described.•Silicates and carbonate are associated with an increasing proportion of meteoric water.

Identifying the source, origin and time of emplacement of copper and gold deposits in the Neoproterozoic volcano-sedimentary and plutonic series of southern Brazil is a longstanding research goal. In this geological context, the Camaquã and Lavras do Sul areas are reported to be a post-collisional domain related to the Braziliano–Pan-African Orogenic Cycle. This study focused on the Uruguay open-pit mine through a detailed assessment of the mineralogy, geochemistry and (S, O, H and C) stable isotopes of pyrite, chalcopyrite, clay minerals and carbonates as veins or disseminated sulfides in sedimentary rocks. The results indicate that the Camaquã mine is a low-sulfidation epithermal-type deposit with sulfide precipitations related to a mixture of magmatic (δ34S = 1 to 4‰; δ18O: 3 to 9‰) and meteoric waters (δ18O = − 4 to − 12‰) and a temperature varying from 350 to 80 °C. Ore precipitation is associated with sequential sulfide crystallization exhausting the S magmatic source.