Abstract:
The Middle-Lower Yangtze River Valley Metallogenic Belt is an external response to the crust-mantle interaction in the background of NW subduction of the paleo-pacific plate during the Yanshannian, which is a direct result of long-term diagenetic and metallogenic activity.However, the diagenetic and metallogenic events in the Fengshan district have not been analyzed in detail.In this study, a comprehensive study for the ore-related granodiorite porphyry from the Jilongshan skarn Cu-Au deposit, Fengtian orefield, is conducted.The results reveal that the ore-related granodiorite porphyry from the Jilongshan deposit is high-K calc-alkaline and metaluminous granitoids (A/CNK generally below 1), which are also characterized by adakitic features(high Sr/Y).Zircon LA-ICP-MS dating yields an age of 147.5±1.4 Ma, indicating that the mineralized intrusion was formed in the Late Jurassic.Combined with previous studies, it is revealed that the ore-related granodiorite porphyry from the Jilongshan deposit is adakitic granitoids characterized by volcanic arc magmatic features.The ore-forming rock mass was derived from partial melting of enriched lithosphere mantle which had experienced contaminations from crustal materials during ascending.Based on the statistical analysis of the diagenetic and metallogenic events in the Fengshan field, this paper concludes that there were two diagenetic and metallogenic stages in the Fengshan field from 152 to 145 Ma and 142 to 138 Ma.The first stage of diagenetic and metallogenic events corresponds to the formation of porphyry-skarn Cu-Au-Mo deposits, while the second stage of diagenetic and metallogenic events corresponds to the formation of porphyry mineralization system.Due to the differential uplift-ablation on the southwest and northeast sides of the study area, it shows that the porphyry Cu-Au-Mo deposits and the shallow-formed low-temperature hydrothermal Au deposits on the northeast side of the study area were well preserved.On the other hand, there are no shallow-formed low-temperature hydrothermal Au deposits on the periphery of the Jilongshan(porphyry-) skarn-type Cu-Au-Mo deposits on the southwest side.The southwest Baiguoshu rock body was completely missed without any mineralization.This study is important for understanding the diagenetic and metallogenic process of the Fengshan deposit, as well as for mineral prospecting.