Petrogenesis of the Rio Blanco epithermal Au-Ag mineralization in the Cordillera Occidental of southwestern Ecuador: Assessment from host rocks petrochemistry and ore constituents isotopic (O, S, H, and Pb) compositions

Magmatic rocks spatially associated with the Rio Blanco Au-Ag mineralization also show a significant radiogenic signature, which was acquired through assimilation of various basement rocks within the upper crust, thus leading to heterogeneous and wide Pb isotopic composition ranges (206Pb/204Pbi = 18.605-19.174; 207Pb/204Pbi = 15.621-15701; 208Pb/204Pbi = 38.442-39.043). Sulfides and electrum are radiogenic as well (206Pb/204Pb ratios are between 19.002 and 19.143, whereas 207Pb/204Pb and 208Pb/204Pb ratios span from 15.644 to 15.697 and from 38.827 to 38.998, respectively) and overlap the compositions of the highly radiogenic magmatic rocks, indicating Pb and by inference, the other metals such as Au and Ag are of magmatic origin like S, which δ34S (V-CDT) values range between −3 and 4.9‰. Unlike S and metals of magmatic origin, the degased (as indicted by δD (V-SMOW) values range between −92.54 and −78.89‰) mineralizing H2O is a mixture between magmatic and meteoric fluids as supported by their δ18O (V-SMOW) values ranging from −0.959-4.21‰.