Study on fluid inclusions of the Akexike Fe-Au deposit in northern Junggar, Xinjiang

Abstract: The Akexike Fe-Au deposit on the northern margin of the Junggar Basin occurs in the contact zone between volcanic rocks and tuffs of the Nanmingshui Formation. The orebodies are podiform, veined, and lenticular in form. The deposit has expereinced silicification, sericitization, chloritization, pyritization and carbonatization. Field evidence and petrographic analysis indicate two periods of metallogenesis: the volcanic-sedimentary period associated with the development of Fe mineralization and the hydrothermal period associated with Au mineralization. Liquid- and a few CO2- rich inclusions characterize the volcanic-sedimentary period, whereas CO2- and carbon (CH4 and C4H6)-rich inclusions characterize the hydrothermal period. Volcanic-sedimentary period had NaCl-H2O-CO2 fluids with moderate temperature (major Th of 180-320 ℃), low salinity (mainly 6-10 wt% NaCleq), and modereate to low density (0.59-0.98 g/cm3). Hydrothermal period has NaCl-H2O-CO2-CH4 fluids with moderate temperature (major Th of 220-320℃), low salinity ( mainly 2-10 wt% NaCleq), and moderate to low density (0.55-1.03 g/cm3). Stable isotope analysis of quartz yielded values of -129.9‰ to -97.9‰ for δD, 7.9‰ to 12.3‰ for δ18OSMOW, and -2.6‰ to 4.4‰ for δ18Ofluid, indicating that the ore-forming fluids were magmatic fluids mixed with seawater. δD, δ18OSMOW, and δ18Ofluid values of the hydrothermal period are -129.8‰--102.6‰, 11.2‰-16.1‰, and 3.1‰-7.4‰, respectively, indicating that the ore-forming fluids were metamorphic water mixed with deeply circulated meteoric water. Combined with geological characteristics and fluids composition, the authors hold that Au mineralization of hydrothermal period was closely associated with CO2-CH4 fluids.