Stable isotope and fluid inclusion study of stratiform copper deposits from the Neuquén Basin, Argentina

RAINOLDI, ANA LAURA; FRANCHINI, MARTA; BOYCE, ADRIAN; GIUSIANO, ADOLFO; CESARETTI, NORA NOEMÍ; PONS, JOSEFINA; RÍOS, FRANCISCO

MINERALIUM DEPOSITA

SPRINGER

Lugar: Berlin; Año: 2019 vol. 54 p. 415 - 436

0026-4598

The Los Chihuidos and El Porvenir deposits of the Neuquén Basin are examples of sediment-hosted stratiform Cu depositsgenerated by interaction of hydrocarbons and formation water with host red beds and metal-charged basinal brines. During earlydiagenesis of red beds precipitated hematite, kaolinite at 60 °C from meteoric water followed by calcite 1 (δ13C − 8 to − 3.3?)and barite (δ34S + 4.1?) with increasing temperature (75?85 °C) from an evolved surface fluid (δ18Ofluids + 0.9 to + 2.7?).During the TertiaryAndean orogeny, hydrocarbons and formation watermigrated and reacted with the red beds resulting in bleachingof the sandstone. Smectite (fluid δ18O − 2.2?and δD − 73.7?), chlorite-smectite mixed-layer minerals (fluid δ18O − 6.9?and δD− 84?), pyrite (δ34S + 10.2?), and calcite 2 (δ13C − 12.9 to − 6.8?) formed as by-product of the redox reactions. Calcite 2 formedfrom low-salinity fluids (0.4 to 5.9 wt% NaCl equiv.) at slightly higher temperatures (125?145 °C) at El Porvenir and at LosChihuidos deposit (80?105 °C). During subsequent uplift, metal-charged basinal brines flowed into the bleached sandstone andprecipitated chalcopyrite-bornite (δ34S + 12.3?) followed by chalcocite-spionkopite (δ34S − 64 to + 4.1?). Calcites 3a (δ13C − 19to − 10.1?) and 3b (δ13C − 31.4 to − 9.5?) that accompanied Fe-Cu and Cu sulfides, respectively, formed from saline fluids (up to21.3 wt% NaCl equiv.) at temperatures of 159?70 °C. The δ18Ovalues (+ 5.6 to + 11.4?) of fluids in equilibrium with calcite 3a aresimilar to oilfield and basinal brines. Fluids in equilibrium with calcite 3 in Los Chihuidos and calcite 3b in El Porvenir show muchlighter δ18O values (− 7.3 to − 4.6? and −0.6 to +2.3?, respectively), which suggests the involvement of methane as the mainreductant and possibly meteoric water interaction.