A study of the fluid inclusions and chronology of the Shanwanzi gold deposit in Chifeng, Inner Mongolia

The Shanwanzi gold deposit in Chifeng of Inner Mongolia which is located in the east of Chifeng-Chaoyang gold metallogenic belt occurs in the andesite of the early Cretaceous Yixian Formation. In order to discuss the metallogenic age and genetic characteristics of the deposit, the authors, through the study of petrography, microthermometry, hydrogen, oxygen isotope and chronology of the the fluid inclusions, have reached the following conclusions:The fluid inclusions are mainly composed of pure liquid inclusions and a small amount of gas-liquid two-phase inclusions, and the gas composition of the inclusions is mainly H₂O and CO₂, which reflects the NaCl-H₂O-CO₂ system; uniform temperature range is 219-249℃, and salinity is 0.35%-3.23% NaCl eqv., suggesting that the temperature and salinity of the principal metallogenic period is low; the metallogenic pressure is 2.7-33.8MPa, and the metallogenic pressure depth is 2.78 km, indicating that the mineralization exhibits a shallow characteristic; the formation age of andesite determined by ICP-MS U-Pb zircon is 123.6 Ma and 124.5 Ma, which is consistent with the age of early Cretaceous period of the Chaoyang-Chifeng gold metallogenic belt. Combining ore deposit characteristics with the study of the metallogenic fluid, the authors hold that the Shanwanzi gold deposit is a low sulfur, low temperature hypabyssal hydrothermal deposit.