Geological Characteristics And Metallogenesis In The Miaoling Golddeposit, Western Henan Province

The Miaoling gold deposit is located in the Xiong`ershan destrict, a large Au polymetallic ore district along the south margin of the North China Craton. It is a typical structurealtered rock type Au deposit, and the gold orebodies appear in fracture structures running south-north. The mineralization types include finely disseminated pyrite structurealtered rock type and quartz pyrite vein type. Potassic, silicification, Sericitization, beresitization, chloritization, epidotization, flouritization and carbonatization comprise the wall rock alteration. LA-ICPMS zircon U-Pb dating, geochemistry, fluid inclusions and isotope reserch are used to study the characteristics and genesis of the granite porphyry dykes, the nature and evolution of the ore-forming fluid, the source of the ore-forming materials and genesis of the Miaolig gold deposit.The ore-forming process can be divided into four stages such as: quartz- potassium feldspar vein stage(Ⅰ), quartz-pyrite vein stage(Ⅱ), quartz-polymetallic sulfides stage(Ⅲ) and quartz-carbonate vein stage(Ⅳ).LA-ICPMS zircon U-Pb dating of the granite porphyry yield an age of 157 Ma, which is earlier than the mineralization age(117Ma) approximately 40 Ma, so we infer that the granite porphyry dykes did not cause the gold mineralization. Geochemistry and isotopic compositions suggest that the granite porphyry dykes are highly fractionated I-type granites and the product of the partial melting of the lower crust.The characteristics of REE composition of the Au-bearing pyrites are similar to the reginoal Yanshanian granitoid batholith and the wall rocks, which suggest that the ore-forming fluid has multiple sources. The nagetive anomalies in Eu and no anomalies in Ce suggest that the ore-forming fluid is weak reductive. The trace element characteristics of Au-bearing pyrite reflect the pyrites are hydrothermal genesis pyrites and the ore-forming fluid is related to the post-magmatic hydrothermal closely.Comprehensive study of fluid inclusions show that the ore-forming fluid of Miaoling gold deposit is magmatic fluid, and the ore-forming fluid, which is alkaline environment, was evolved from medium temperature and medium-low salinity H2O-Na Cl-CO2 system to low temperature and low salinity H2O-Na Cl system, and the atmospheric water mixed into in the late. C-H-O isotopic compositions indicate that ore-forming fluid most likely evolved from the Yanshanian post-magmatic fluid producted by the emplacement and crystallization in Xiong`ershan region. Pb isotopic compositions display that the metallogenic materials come from the magmatic minerals. Au come from the late Mesozoic granitic magma formed by partial melting of Taihua Group caused by lithospheric rapid thinning. The migration of Au in the post-magmatic fluid is in the form of Au(HS) and HAu(HS)2. Physical and chemical environments have been changed through the boiling and fixing of the ore-forming and fluid-rock interaction, which are the major actors of Au precipitation.