Research on zircon U-Pb, S-Pb isotopes and trace elements of pyrite from the Dongji Au(Ag) deposit in Zhenghe County, Fujian Province

The Dongji Au(Ag) deposit is a cryptoexplosive breccia deposit in the southeastern coastal area, with reserves of 12.5 tons Au and 135.9 tons Ag, and hosted in late Yanshanian Nanyuan Formation. To discuss metallogenic and metal material source of the Dongji deposit, the authors carried out multiple isotope (S-Pb) and electron microprobe analysis (EPMA). Pyrite Co/Ni ratio is 3-94 (averaging 23), Co is 500×10^-6-1070×10^-6 (averaging 799×10^-6), Fe/(S+As) is 0.827-0.871 (averaging 0.860), Au/Ag is 0.9-5.5 (averaging 2.6), which suggests that the Dongji Au(Ag) deposit is an epithermal deposit resulting from volcanism. δ³⁴S of pyrite ranges from -0.7‰ to -6.6‰, ²⁰⁶Pb/²⁰⁴Pb is 17.9801-18.4303, ²⁰⁷Pb/²⁰⁴Pb is 15.2689-15.9397, and ²⁰⁸Pb/²⁰⁴Pb is 37.9052-38.7871, which suggests that metal materials were mainly derived from crust-mantle granite magma and partly from metamorphic basement and volcanic wall rocks. Based on zircon U-Pb ages of crystal tuff and granite porphyry combined with regional mineralizaton in the Zhenghe-Jianou area, the authors hold that the metallogenic epoch of the Dongji deposit should be late early Cretaceous.