3 years ago

Decratonic gold mineralization: Evidence from the Shangzhuang gold deposit, eastern North China Craton

Decratonic gold mineralization: Evidence from the Shangzhuang gold deposit, eastern North China Craton
The Jiaodong Peninsula in the eastern North China Craton (NCC) hosts some of the world-class gold deposits. Among these, the Shangzhuang gold deposit represents a typical fault-zone hosted disseminated- and stockwork-style gold mineralization. The mineralization is characterized by intense hydrothermal alteration halos in the wallrocks with the mineralized veins intruding into altered wallrocks. Zircon U-Pb isotope dating constrains the timing of emplacement of the Guojialing granodiorite as 130±1Ma. Five molybdenite samples from the main mineralization stage veins yielded a well-fitted isochron age of 126±2Ma (MSWD=1.3), marking the timing of gold mineralization. Four types of fluid inclusions are identified at Shangzhuang, and their petrographic and microthermometric features suggest fluid immiscibility followed by fluid mixing. This inference is also supported by oxygen and hydrogen isotopic data of quartz veins from stage III. The measured δ18O values of quartz are +12.3 to +13.7‰ for stage II and +11.7 to +12.0‰ for stage III, with calculated δ18Ofluid values for stage II ranging from +5.9 to +7.3‰ and for stage III from +3.4 to +3.7‰. δD values for stage II and III quartz range from −65.3 to −75.2‰ and −70.6 to −74.7‰, respectively. The data suggest that the ore-forming fluids were initially derived from magmatic sources, followed by mixing with meteoric water. SIMS in-situ sulfur isotope analyses of two types of pyrite (Py I and Py II) from different mineralization stages show different sulfur isotope features. The δ34S values for Py I (+10.2 to +11.3‰, mean=+10.8‰, n =25) are higher than those of the later mostly gold-related Py II (+4.1 to +6.8‰, mean=+5.4‰, n =27). The higher δ34S values of Py I are correlated to degassing of mantle wedge metasomatized by the slab fluids. The relatively lower δ34S values of Py II might suggest increasing of f O2 through fluid mixing between ore-forming fluids and meteoric water. The temporal, spatial and tectonic relations between the giant gold mineralization and destruction of the NCC suggest a genetic linkage. The gold mineralization between 126 and 117Ma at Jiaodong was probably initiated at the peak of decratonization (ca. 125Ma) of the eastern NCC. Phanerozoic craton margin orogeny also played a critical role in the generation of the early Cretaceous giant gold deposits in the eastern NCC. Integrated geological characteristics, mineralization features, metallogenic age, sources of ore-forming fluids and sulfur, and tectonic settings favor a decratonic gold mineralization model for the Shangzhuang gold deposit. The geodynamic scenario proposed for the early Cretaceous giant gold mineralization event in the eastern NCC includes the paleo-West Pacific plate subduction, asthenospheric upwelling, multiple subduction-collision processes along the margins.

Publisher URL: www.sciencedirect.com/science

DOI: S1342937X17303180

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