Age, alteration, and mineralization of fault-controlled distal skarn Pb-Zn deposit: Example from Dongzhongla deposit of eastern Gangdese-Nyainqêntanglha belt, Xizang

The eastern Gangdese-Nyainqêntanglha belt is a major Pb-Zn province in China, yet persistent debates over ore genesis—specifically the links between mineralization, metal sources, and multiple magmatic events—have hindered robust metallogenic model and exploration targeting. To resolve these uncertainties, we present an integrated study of the Dongzhongla deposit (∼0.5 Mt Pb + Zn @ 13 wt%; 15,000 t Cu @ 0.5 wt%) within this belt, combining detailed geological fieldwork, ore geology, geochronology (zircon, garnet, apatite, titanite U-Pb), and S-Pb-Sr-Nd isotope geochemistry of sulfides and apatite. Orebodies occur as veins and lenses (sphalerite, galena, chalcopyrite) localized at granite porphyry–limestone/marble contacts, slate interfaces, and fracture zones, with main mineralization progressing through prograde/retrograde skarn, quartz-sulfide stages. Zircon U-Pb dating reveals an Early Cretaceous magmatic event from 128 ± 1 Ma to 124 ± 2 Ma for the spatially associated granite porphyry. Crucially, hydrothermal garnet (60.7 ± 2.6 Ma), apatite (60.6 ± 3.7 Ma), and titanite (60.8 ± 3.5 Ma) yield consistent Paleocene U-Pb ages. This significant age discrepancy demonstrates the granite porphyry is genetically unrelated to mineralization, directly linking ore formation instead to the Indian-Asian main collisional stage and regional Paleocene skarn Pb-Zn deposits. Sulfide δ 34 S values (−3.5‰ to 4.8‰) indicate a dominantly magmatic sulfur source. In situ sulfide Pb isotopes ( 206 Pb/ 204 Pb: 18.642–18.671, 207 Pb/ 204 Pb:15.701–15.731, 208 Pb/ 204 Pb:39.109–39.251) show limited variation, plotting within the Nyainqêntanglha Group crystalline basement field and above the upper crustal evolution curve, supporting a lead source from this ancient basement. Hydrothermal apatite Sr-Nd isotopes resemble Paleocene-Eocene Gangdese-Nyainqêntanglha skarn-related granitoids, confirming Pb-Zn deposit related to Paleocene granitoids derived from ancient Lhasa terrane continental crust. These results demonstrate that the Dongzhongla deposit is a fault-controlled, distal skarn system genetically linked to a concealed Paleocene intrusion, which sourced from the ancient crust of the Lhasa terrane. Consequently, fault extensions proximal to the concealed intrusion represent key targets for future regional exploration.