Thermal doming-extension metallogenic system of Jiaodong type gold deposits

Jiaodong type gold deposits have unique metallogenic characteristics and genetic mechanism, which is different from the known gold deposit types in the world. In order to deepen the understanding of the geological factors and metallogenic processes that control the formation, change and preservation of ore deposits, the characteristics and tectonic setting of Late Mesozoic magmatism, tectonic activity and mineralization in Jiaodong Peninsula are comprehensively analyzed. We proposed that deep magmatic activity, rapid crustal uplift, and shallow extensional structures controlled the ore-forming series and ore-forming evolution process of Au-dominated deposits in this area, which is called thermal doming-extension metallogenic system. In Late Mesozoic, strong magmatic activity took place in Jiaodong Peninsula, and the geochemical characteristics of magmatic rocks changed obviously from Jurassic to Cretaceous, and as a result, the geochemical characteristics of granitoids change from high potassium calc-alkaline series and peraluminous to peridotite series and meta-aluminous, from Ba- and Sr-rich and Y-poor to Ba-, Sr-poor and Y-rich, as well as from positive Eu anomaly to negative Eu anomaly. The geochemical characteristics of basic dike rocks changed from island arc type to ocean island type, while the volcanic rocks changed from shoshonite series to high titanium alkaline basalt series. The geochemical characteristics of magmatic rocks indicate that the magmatic source area is transformed from enriched lithospheric mantle to asthenosphere mantle. In Early Cretaceous, Jiaodong Peninsula experienced a rapid crustal and magmatic uplift and cooling, and the rate of magmatic cooling was more than twice that of the Late Jurassic. During this period, extensive extensional structures such as Linglong metamorphic core complex, Tanlu fault, Zhaoping detachment fault and Jiaolai pull-apart basin were produced. At the same time, large-scale metal deposits mineralization occurred, forming Au (Ag), Cu, Pb, Zn and Mo metallogenic series dominated in gold. The ore-forming time is consistent with the transformation time of magmatic geochemical characteristics and mantle geochemical properties. The ore-forming material and fluid have the characteristics of crust-mantle mixed source. The gold deposits have not suffered significant destruction and denudation after ore-forming. The contents of K2O, Na2O, Ba and Sr in mineralized altered rocks are in good agreement with those of Weideshan and Laoshan granites, indicating that the fluids related to these two magmatic activities are involved in the mineralization process. The abundance of gold in Weideshan-type granites from the same time to the later time of gold mineralization is obviously lower than that of geological units before gold mineralization, indicating that transformation of Au coincided with the change of geochemical characteristics of magmatic rocks. The comprehensive analysis shows that Jiaodong type gold mineralization system was formed in the post-subduction extensional environment of the subduction and retreat of the paleo-Pacific plate. Due to upwelling of asthenosphere and lithospheric mantle properties changed from enrichment to depletion, which resulted in the change of geochemical characteristics of magmatic rocks and the adjustment of geochemical elements. So, mantle-derived gold-bearing fluid mixed with crust-derived gold-bearing fluid precipitated from remelting lower crust to form gold-rich fluid reservoir and produce gold-poor granite. Large-scale magmatic activity provided the thermal dynamic conditions for the activation and migration of ore-forming elements, and the fault structure generated by the extension of the upper crust provided a good space for the accumulation of ore-forming elements. Thermal doming-extension metallogenic system is an important metallogenic system of eastern China in the Late Mesozoic.