Abstract:

The Jijiawa gold deposit is located in the western part of Xiong’er mountain gold polymetallic ore district, Henan Province. It represents a mixing gold deposit, consisting of structure-controlled alteration type, as well as the quartz vein type.The ore-forming process can be divided into four stages: pyrite-quartz vein stage(Ⅰ), quartz-pyrite vein stage(Ⅱ), quartz-polymetallic sulfides stage(Ⅲ), quartz-carbonate vein stage(Ⅳ). Through the studies of fluid inclusion microscopic temperature measurement, Laser-Raman spectra and H and O isotopes, we obtained the ore-forming fluid temperature, salinity, density and the type and source of ore-forming fluid, and discussed the mechanism of mineralization. The results show as follows: Two types of fluid inclusions in stage Ⅰ and Ⅱ are indentified as CO₂ type and gas-liquid type; but stage Ⅲ and Ⅳ quartz contain exclusively gas-liquid type fluid inclusions. The homogenization temperatures of ore-forming fluids from stage Ⅰ to stage Ⅳ are 232-333 ℃, 143-266 ℃, 135-227 ℃ and 106-166 ℃ respectively, with the corresponding salinities being 3.76%-16.05%,1.74%-17.34%, 0.7%-17.26% and 0.35%-11.34%. In general, the ore-forming fluid was evolved from CO₂-H₂O-NaCl system, which is characterized by medium-low temperature and medium-low salinity, to H₂O-NaCl system. The H-O isotopes composition reveals that in the Jijiawa gold deposit, the hydrothermal system gradually transited from a magmatic-dominated fluid to a meteoric-dominated fluid. Fluid mixing action and fluid immiscibility are the most important factors that caused the gold precipitation and enrichment, and fluid-rock interaction also contributes to the gold precipitation and enrichment.

Key words: fluid inclusion, H-O isotopes, ore-forming fluid, fluid immiscibility, the Jijiawa gold deposit, Xiong’er mountain