Petrogenesis and tectonic setting of the Shiduolong skarn Pb–Zn deposit in the East Kunlun Orogenic Belt: Constraints from whole‐rock geochemical, zircon U–Pb and Hf isotope analyses

摘要

> The Shiduolong Pb–Zn deposit, located in the East Kunlun Orogenic Belt, is a medium‐scale skarn deposit (0.4?Mt metal reserves with a grade of 1.46% Pb and 4.38% Zn). The mineralization occurs along the contact zone between Carboniferous marbles and Triassic quartz diorite and granodiorite. Zircon LA‐ICP‐MS dating indicates that the Shiduolong quartz diorite is coeval with the granodiorite (245?Ma). Whole‐rock geochemical analysis shows that both phases are high‐K calc‐alkaline metaluminous (A/CNK??1) I‐type granites with similar rare earth (REE) element contents and (La/Yb) _N values, indicating that they formed via crystal fractionation from a common parental magma. However, the granodiorite has higher SiO ₂ contents, lower total Fe ₂ O ₃ , TiO ₂ , MgO, Sr, and Ba contents, and more negative Eu anomalies than the quartz diorites, suggesting that the granodiorite experienced stronger fractional crystallization during magmatic evolution. The zircon ε _Hf (t) values of the quartz diorite range from ?3.3 to 1.6. The two‐stage model ages (T _DM2 ) vary from 1,175 to 1,487?Ma. Hf isotope data indicate that the magma of the quartz diorite was mainly derived from partial melting of Mesoproterozoic lower crustal materials with contributions from mantle‐derived magmas. Combined with the regional tectonic and magmatic activities, we propose that the Shiduolong Pb–Zn deposit might have formed during the hydrothermal event associated with the release of magmatic water from the granodiorite‐quartz diorite intrusions, which were generated by the subduction of the Paleo‐Tethys oceanic slab in the Early Triassic.