Jurassic magmatism and Au-Ag mineralization in the Deseado Massif (Patagonia Argentina): Lead and sulfur isotopic studies

Abstract

Lead isotope analyses of volcanic rocks and hydrothermal minerals and sulfide isotope analyses of sulfurs from Au-Ag La Josefina prospect (Deseado Massif geological province, Argentina) are reported. Lead isotope ratios for sphalerite and pyrite have mean values of 18.48, 15.69 and 38.61 for Pb-206/Pb-204, Pb-207/Pb-204 and Pb-208/Pb-204, respectively, and are similar to Pb isotope ratios for the Jurassic volcanic rocks of Bajo Pobre and Chon Aike Formations. delta S-34 parts per thousand values of sphalerite, pyrite and galena cluster between 1.3 and 3.8 parts per thousand, suggesting that the sulfur at La Josefina was primarily of magmatic origin. These results are interpreted to indicate that the Jurassic volcanic rocks are closely related with low sulfidation Au-Ag occurrences.