CONICET | Buscador de Institutos y Recursos Humanos

The Los Chihuidos and El Porvenir deposits of the Neuquén Basin are examples of sediment-hosted stratiform Cu deposits generated by interaction of hydrocarbons and formation water with host red beds and metal-charged basinal brines. During early diagenesis of red beds precipitated hematite, kaolinite at 60 °C from meteoric water followed by calcite 1 (δ 13 C − 8 to − 3.3?) and barite (δ 34 S + 4.1?) with increasing temperature (75?85 °C) from an evolved surface fluid (δ 18 O fluids + 0.9 to + 2.7?). During the Tertiary Andean orogeny, hydrocarbons and formation water migrated and reacted with the red beds resulting in bleaching of the sandstone. Smectite (fluid δ 18 O − 2.2? and δD − 73.7?), chlorite-smectite mixed-layer minerals (fluid δ 18 O − 6.9? and δD − 84?), pyrite (δ 34 S + 10.2?), and calcite 2 (δ 13 C − 12.9 to − 6.8?) formed as by-product of the redox reactions. Calcite 2 formed from low-salinity fluids (0.4 to 5.9 wt% NaCl equiv.) at slightly higher temperatures (125?145 °C) at El Porvenir and at Los Chihuidos deposit (80?105 °C). During subsequent uplift, metal-charged basinal brines flowed into the bleached sandstone and precipitated chalcopyrite-bornite (δ 34 S + 12.3?) followed by chalcocite-spionkopite (δ 34 S − 64 to + 4.1?). Calcites 3a (δ 13 C − 19 to − 10.1?) and 3b (δ 13 C − 31.4 to − 9.5?) that accompanied Fe-Cu and Cu sulfides, respectively, formed from saline fluids (up to 21.3 wt% NaCl equiv.) at temperatures of 159?70 °C. The δ 18 O values (+ 5.6 to + 11.4?) of fluids in equilibrium with calcite 3a are similar to oilfield and basinal brines. Fluids in equilibrium with calcite 3 in Los Chihuidos and calcite 3b in El Porvenir show much lighter δ 18 O values (− 7.3 to − 4.6? and − 0.6 to + 2.3?, respectively), which suggests the involvement of methane as the main reductant and possibly meteoric water interaction.