Abstract:

The Qiyugou gold deposit in Henan Province, located in the northeastern Xionger metallogenetic district, southern margin of the North China craton, is a typical breccia pipe-type deposit. Discovering of critical-supercritical fluid inclusions is important to study ore-forming fluid evolution and metallogenic mechanism. Petrography, microthermometry and laser Raman microprobe (LRM) of fluid inclusions in the samples from the J4 breccia of Qiyugou deposit were analyzed. The research shows that the critical-supercritical fluid inclusions exist in stage Ⅱ(mainly) and stage Ⅰ. Laser Raman spectroscopy analysis suggests this kind of fluid inclusions contain CO₂. Critical-supercritical fluid inclusions are mostly included in the samples collected from the elevation of 400-460 m in the J4 breccia pipe, where occurs a certain prospect with a higher gold grade, thicker ore bodies and considerable reserves. Combined with existing fluid inclusion data, a conclusion can be drawn that the supercritical fluid come from magmatic-hydrothermal transitional processes and the magma system was rich in volatile constituent and high oxygen fugacity. The evolution process of ore-forming fluid can be listed as magmatic-hydrothermal system→critical-supercritical fluid(CO₂-H₂O-NaCl system)→vapor phase with low salinity (CO₂-H₂O system) and liquid phase with high salinity (H₂O-NaCl system)→low salinity (H₂O-NaCl system)→H₂O System. The homogenization temperatures of the boiling fluid inclusion changes from  383.7 ℃ to 387.2 ℃. The fluid boiling played an important role in forming of the Qiyugou gold deposit.

Key words: Qiyugou gold deposit, ore-forming fluid, fluid inclusion, critical-supercritical fluid, Xionger metallogenietic district