Fluid inclusion characteristics and ore-forming fluid evolution of the Tuokuzibayi gold deposit in the southern margin of Altay

The Tuokuzibayi (Bayi) gold deposit in the northwestern part of Xinjiang is located at the southern margin of the Siberian ancient plate the boundary between the Kelan arc basin and the Haba inter-arc basin in the Altai continental margin. Since its discovery, it has been the subject of many attentions. Based on the previous studies, the detailed field investigations, fluid inclusion temperature measurement, laser Raman composition test, and hydrogen-oxygen isotope analysis have been carried out in our study in order to better understand the ore-forming hydrothermal stage, the source of ore-forming hydrothermal fluids and the genetic type of the deposit. According to the characteristics of field vein interpenetration-mineral combination-spatial distribution and structure, the mineralization of the Bayi gold deposit can be divided into four metallogenetic stages which are quartz-magnetite stage (I), quartz-pyrite stage (II), quartz-pyrite-chalcopyrite stage (III) and quartz-calcite stage (IV) • The primary fluid inclusions of the deposit are mainly of four types: liquid-rich, gas-rich, crystals-included and CO2-contained three-phase aqueous solution inclusion. The uniform temperatures (352. 9 ~413. 4t) and salinities (7.3% ~ 14. 7% NaCleqv) were obtained from the inclusions of the quartz pyrite stage. The inclusions from the quartz-pyrite stage have a uniform temperature range of 186. 0 ~339. 8°C, and the salinity varies from 2. 7% to 44. 3% NaCleqv. The uniformity temperature of the ore-forming fluid in the quartz-pyrite-chalcopyrite stage is 141. 0 ~ 186. 4°C, and the salinity is 0 ~ 8. 8% NaCleqv. The inclusions in the quartz-calcite stage show a uniform temperature range of 102. 0 ~ 140.0°C coupled with salinity range of 0. 2% to 4. 3% NaCleqv. Our study shows that the temperature and salinity of the deposit from the early stage of mineralization to the late stage of mineralization display a downward trend, and that the boiling is present in the major metallogenetic stages (II and III). The δ18O and <5D ranges in different mineralization stages are 5. 31% and-85. 10% in the early stage of mineralization (I), 1. 53% ~ 1. 50% and -97. 4% ~-81.1% in the main stage of mineralization (II and III), -3. 52% ~-3. 42% and-93. 9% ~-87. 1 % in the late stage of mineralization (IV), respectively. This indicates that indicating the ore-forming fluid is mainly the metamorphic water source and later with minor participation of atmospheric water. Combined with the geological and regional information, our study shows that the Bayi deposit is related to a low salinity NaCl-H2O-CO2 fluid system and the gold mineralization should be triggered by the fluid boiling, pressure dropping and mixing, which is similar to the characteristics of ore-forming fluids in orogenic gold deposits. Thus, it is speculated that the Bayi deposit is mainly formed under the collisional orogeny between the Kalatongke Island Arc and the Siberian Plate during the Late Carboniferous-Permian. © 2020 Science Press. All rights reserved.