Ore-forming fluid characteristics and metallogenic mechanism of Fenghuang Pb-Zn deposit, Hunan Province

The southeastern margin of the Yangtze block is an important Pb-Zn metallogenic belt in China, however, the systematical research of Fenghuang ore field is still in progress. Taking the deposit as the research object, the characteristics, source and composition of ore-forming fluid were studied by means of fluid inclusion geology, isotope geochemistry and micro-laser Raman spectroscopy. The results show that LV type fluid inclusions are well developed in the deposit. The homogenization temperature, salinity and density are between 111.2-177℃, 4.1%-25.2%, and 0.98-1.09 g/cm³ respectively. Generally, it is a low-temperature, medium-high salinity and medium-density fluid. The gas phase composition of the inclusions in quartz and sphalerite is mainly CH₄, and the liquid phase is mainly H₂O. The results of H-O isotope analysis show that the ore-forming fluid is mainly formation-water. It is considered that the formation-water from the basin extracts the ore-forming materials in the deep strata, forming reducing ore-forming fluid together with CH₄ and other reducing agents produced by organic matter retorting in the sediments, and moves upward along the contemporaneous fault structure and other channels. Finally, lead and zinc precipitate in the dolomite of the shallow Aoxi formation.