Characteristics of fluid inclusions of the Malian gold deposit in Heilongjiang Province and their geological significance

Abstract: Detailed fluid inclusion and H-O isotope characteristics of metallogenic period quartz veins were studied to reveal the ore-forming fluid features. Petrography and microthermometric studies of fluid inclusions suggest that the main types of fluid inclusions of the Malian gold deposit are gaseous inclusions, liquid inclusions and pure liquid inclusions. Temperature test shows that the homogenization temperature and salinity of fluid inclusions vary from 148 to 255℃, mostly in the range of of 180?210℃, and 1.7%?7.5%NaCleqv (the peak values vary in the range of 2%?4%NaCleqv), respectively. Based on these results, the authors have reached the conclusion that the ore-forming fluids of the Malian deposit should be of low temperature and salinity. Laser Raman and group fluid inclusions content studies indicate that gas composition of the ore-forming fluids are mainly H2O, with some CO2 and CH4, whereas liquid compositions of the ore-forming fluids are mainly Ca2+, Na+, SO42? and F?, with some K+, Mg2+, NO3? and Cl?. The ore-forming fluids are then defined to be of the NaCl?H2O±CO2±CH4 system. The hydrogen and oxygen isotopic compositions of the ore-forming fluids show thatδDV-SMOW values of the ore-forming fluid are between ?92.3‰ and ?113.6‰, and δ18OH2O are between 2.5‰ and 3.5‰, which indicates that the ore-forming fluids were derived from the mixing of magmatic water and meteoric water. Based on the characteristics of ore-forming fluids, it is concluded that gold deposition in the Malian gold deposit was related to the phase separation.