The sulfur isotope evolution of the Duobuza Cu-Au porphyry deposit in the Duolong district, Central Tibet, China

Understanding the sulfur isotope cycle is essential in developing genetic models of porphyry copper deposits. In this paper, we characterize the sulfur isotope evolution of the Duobuza deposit, a typical porphyry Cu-Au deposit, using the sulfur isotope composition of sulfides in successive hydrothermal stages. We show (1) an increase of δ³⁴S values from the inner potassic core (−4.8 to −0.4‰, n = 37) to the peripheral propylitic halo (1.2 to 4.8‰, n = 5) during the early stage; (2) an increase from the early stage potassic alteration to the transitional stage sericite-chlorite alteration (−2.6 to 0.6‰, n = 25); (3) a progressive enrichment, from the quartz-dominated veins (−3.1 to 0.5‰, n = 10), through the anhydrite-dominated veins (−2 to 0.6‰, n = 7), and to the pyrite-dominated veins (−0.7 to 2.3‰, n = 7) during the late stage. The integration of sulfur and oxygen isotope and fluid inclusion data, modeling and mineralogical evidence suggests that the ³⁴S depletion within the potassic core compared to the propylitic halo can be best explained by boiling-induced oxidation of hydrothermal fluids. The increase in δ³⁴S from potassic alteration, through sericite-chlorite alteration, to the late stage hydrothermal veins is interpreted to be related to the partial reduction of an oxidized fluid by water-rock interaction. Our findings highlight the potential of sulfur isotope data to assist exploration for Cu-Au porphyry deposits where a predictable zonation pattern is present.