Petrologic genesis of ore-bearing porphyries in Tiegelongnan giant Cu (Au, Ag) deposit, Tibet and its implications for the dynamic of Cretaceous mineralization, Duolong

Tiegelongnan is a newly discovered giant porphyry-epithermal copper (gold and silver) deposit in the Duolong ore concentrated area, Tibet. As a typical representative products of the important Early Cretaceous ore-forming event in western part of the Bangong Co-Nujiang metallogenic belt, the petrology and dynamic of the mineralization of the ore-bearing porphyries in this deposit are still in hot debate. Based on detailed geological and petrological characteristics of the Tiegelongnan deposit, the SHRIMP U-Pb chronology data of the zircons showed the emplacement time of the granodiorite porphyry from Tiegelongnan was 121.2 +/- 2.4 Ma, which was consistent with the magmatic emplacement time of the Early Cretaceous ore-bearing porphyries in Duolong district. At the same time, the detailed petrogeochemical analysis showed that the ore-bearing porphyries in the Tiegelongnan deposit and the Duolong ore concentrated area were mainly granodiorite porphyry, together with minor diorite porphyry and granite porphyry, which belonged to the series of high-K-calc-alkaline or shoshonite. They were enriched in light rare earth elements (LREE) and big ionic lithophilic elements (LILE, e.g. Rb, Ba, U), depleted in heavy rare earth elements (HREE) and high field strength elements (HESE, e.g. Nb, Ta, Ti), with typical arc magmatic characteristics. Besides, the geochemistry and Sr-Nd-Pb-Hf isotopic compositions revealed that the magmatic source of the ore-bearing porphyries was from Duolong, and it might be related to partial melting of the enriched metasomatized mantle modified by the slab-derived fluids. Finally, the detailed petrological probes studies and regional magmatic activity characteristics suggested that the key dynamics of the giant Cretaceous mineralization in the Duolong ore concentrated area might be related to the roll-back of the north-subduction plate from Bangong Co-Nujiang Ocean (130 similar to 110Ma).