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.