Characteristics of sulfur and lead isotopes and tracing of mineral sources in the Tongchanggou porphyry Mo(Cu) deposit at the southern edge of Geza arc belt, Yunnan

Located on the southern margin of the Geza island arc, the Tongchanggou porphyry deposit is a large-sized Mo(Cu) polymetallic deposit discovered in recent years in southwest Sanjiang region. In this paper, the authors investigated the sources of minerals through sulfur and lead isotope tracer study. Testing results show that the δ³⁴S values of ore sulfides vary in the range of -0.7‰-+3.8‰, 0.79‰ on average. The variation range is very small, which indicates a single source of the sulfur isotope and displays the characteristics of magmatic source sulfur isotopic composition. The lead isotopic composition of ore minerals is characterized by ²⁰⁶Pb/²⁰⁴Pb ranging from 18.3325 to 18.694, ²⁰⁷Pb/²⁰⁴Pb ranging from 15.588 to 15.663, and ²⁰⁸Pb/²⁰⁴Pb ranging from 38.454 to 39.008, exhibiting relatively stable Pb isotopic composition and showing the normal lead characteristics. There is a significant positive correlation between lead isotopic composition and characteristic parameters (△β and △γ, V₁ and V₂). Lead structural model identification and genetic classification comprehensive analysis suggest that the lead isotopes of the Tongchanggou porphyry Mo(Cu) deposit were mainly derived from the depth and show the crust-mantle mixed source characteristics. The mineralization had a close relationship with Yanshanian magmatic intrusion, with the minerals of the strata also making some contribution.