Abstract:

Xincheng gold deposit of Shandong Province is a typical altered rock type gold deposit in the Jiaojia-Xincheng gold ore belt. The ore body is mainly located in the footwall of the Jiaojia-Xincheng fault zone within the pyrite phylic and the cataclasite of pyrite phylic near the fracture surface and it is significantly controlled by the fractured zone. The main ore minerals are pyrite, chalcopyrite, galena, sphalerite, native gold, electrum and argentit, etc. The main types of wall-rock alteration zone contain pyrite phyllic, phyllic, sericite, silicification, potassium and carbonate, etc., and the gold mineralization has a close relationship with pyrite phyllic and silicification alteration. The petrographic, microthermometric, laser Raman microspectroscopic in the single fluid inclusion were studied here, results showed that the hydrogen and oxygen isotope analysis on fluid inclusions were developed in auriferous ore of Xincheng gold deposit in the deep position. Also, it indicated that the numbers of the pure CO₂ fluid inclusions are conspicuously increased in the deep position of the deposit, with the existence of the CO₂-bearing fluid inclusions and the aqueous two-phrase fluid inclusions at the same time. The ore-forming fluids show the characteristics of low salinity (2.06%-10.24%), low density (0.54-0.97 g/cm³). Mineralization temperature is concentrated in 260-300 ℃, and the pressure ranges from 65 to 113 MPa, which equals to a depth of 6.51-8.82 km. And fluid immiscibility occurred in CO₂-NaCl-H₂O system in the ore-forming process. The hydrogen and oxygen isotope analysis indicated that the δD_SMOW of the ore-forming fluids is -75.1 ‰--61.4‰ and the δ¹⁸O_H2O is 4.80‰-6.40‰. Compare the characteristics and source of fluid to the typical “Jiaojia style” gold deposit, it showed that the ore-forming fluids of the Xincheng deposit are mainly from deep mantle fluids. Comprehensive study shows that the genesis of the deposit is the type of mantle-derived fluid mineralization in mesothermal type gold deposits.

Key words: fluid inclusion, ore-forming fluid, genesis of deposit, Xincheng gold deposit, Shandong