Identification of an Early–Middle Jurassic oxidized magmatic belt,south Gangdese,Tibet,and geological implications

The south Gangdese region is the site of subduction of the Neo-Tethys and subsequent continental col- lision. Compared with widespread Cretaceous and Cenozoic magmatism, Early-Middle Jurassic magmatic rocks and related deposits are rarely reported, Our work identified a 〉200 km long felsic rock belt asso- ciated with Cu mineralization in the south Gangdese region. We report here zircon U-Pb ages, zircon Ce4＋/Ce3＋ values, and mineral assemblages of two Cu mineralized intrusions within the belt. A horn- blende granite and a diorite porphyry were emplaced at 177.3Ma and 166.3Ma, respectively. Geological occurrence and magmatic hematite-magnetite-chalcopyrite intergrowths suggest that Cu mineralization formed coeval with Jurassic intrusions. Mineralized intrusions have high zircon Ce4＋/ Ce3＋ and EuN/EuN ratios, and hematite-magnetite intergrowths, suggesting their parent magmas were highly oxidized, Hornblende is common and primary fluid inclusions are found in titanite and apatite, indicating their parent magmas were water-saturated and exsotved volatile phases at early stage of rnag- matic evolution. Those magma characters contribute to the formation of porphyry Cu deposits. Given that majority subduction-related porphyry Cu systems have been eroded following uplift and denudation, the well-preserved Early-Middle Jurassic cu mineralized igneous rocks in south Gangdese are favorable prospecting targets for subduction-related porphyry Cu deposits.

The south Gangdese region is the site of subduction of the Neo-Tethys and subsequent continental collision. Compared with widespread Cretaceous and Cenozoic magmatism, Early–Middle Jurassic magmatic rocks and related deposits are rarely reported. Our work identified a >200 km long felsic rock belt associated with Cu mineralization in the south Gangdese region. We report here zircon U–Pb ages, zircon Ce^(4+)/Ce^(3+)values, and mineral assemblages of two Cu mineralized intrusions within the belt. A hornblende granite and a diorite porphyry were emplaced at 177.3 Ma and 166.3 Ma, respectively.Geological occurrence and magmatic hematite–magnetite–chalcopyrite intergrowths suggest that Cu mineralization formed coeval with Jurassic intrusions. Mineralized intrusions have high zircon Ce^(4+)/Ce^(3+)and EuN/Eu?N ratios, and hematite–magnetite intergrowths, suggesting their parent magmas were highly oxidized. Hornblende is common and primary fluid inclusions are found in titanite and apatite,indicating their parent magmas were water-saturated and exsolved volatile phases at early stage of magmatic evolution. Those magma characters contribute to the formation of porphyry Cu deposits. Given that majority subduction-related porphyry Cu systems have been eroded following uplift and denudation, the well-preserved Early–Middle Jurassic Cu mineralized igneous rocks in south Gangdese are favorable prospecting targets for subduction-related porphyry Cu deposits.