Abstract:

Zijinshan Au-Cu deposit of Fujian Province which located in the middle part of Zijinshan ore field is controlled by volcanic mechanism. Its characteristics of mineralization are well-developed the crypto-explosion breccia vein, and obvious alteration zoning with controls the corresponding mineralization strictly. With the crypto-explosion breccia dike as the center, from center to outside, top to bottom, there are the silicified zone, the alunite alteration zone, the dickite alteration zone and the phyllic alteration zone. The silicified zone controls gold ore body in the upper, the alunite alteration zone controls high sulfidation type copper ore body in the lower. Four occurrence status types of the alunite are classified, which are the alterated-rock type, the intergrowthwith-Cu-sulphide type, the alunite-vein type and the powder type. The results of microthermometry of fluid inclusion in alunite show that (1) Most of inclusions have two phases (liquid and vapor), which belong to NaCl-H₂O system; (2) The ore-forming fluid is of the density ranges from 0.5 to 1.0 g/cm³, the homogenization temperature concentrated in 200-360 ℃, and the salinity less than 20%，which belongs to a fluid system with medium-low temperature and medium-low salinity; (3)The values of homogenization temperature and salinity of the fluid inclusions of alunite have a decreasing trend from the alteratedrock type, the intergrowth-with-Cu-sulphide type, the alunite-vein type to the powder type;(4) The range of ore-forming pressure is concentrated in 40×10⁵-160×10⁵Pa, corresponding to the depth range from 500 to 1,600 m; (5)The mineralizing fluid is mainly from magmatic water and later mixed with atmospheric precipitation. Boiling and immiscibility occurred during the ore-forming processes.

Key words: fluid inclusion, alunite, Zijinshan gold-copper deposit;, Fujian