Abstract:

  Aritekshan Cu-Mo deposit is a newly discovered concealed porphyry deposit, located in the central-north part of the northern Qaidam basin. The orebodies occurred in the contact area between the Late Hercynian-Indosinian granodiorite (porphyry) and Paleoproterozoic Dakendaban Group. In order to explore the characteristics of ore-forming fluids, the ore-forming mechanism and genesis of the deposit, this paper systematically studied the field geological characteristics, fluid inclusions and stable isotope composition of the deposit. According to the relationship between different types of ore veins, the hydrothermal metallogenic stages can be divided into the early mineralization quartz stage, molybdenum-polymetallic sulfide-quartz stage and late mineralization quartz-calcite stage. The fluid inclusions are mainly Type Ⅰ (liquid-rich L+V two-phase aqueous inclusions), Type Ⅱ (gas-rich L+V two-phase aqueous inclusions) and Type Ⅲ (three-phase aqueous solution inclusions containing daughter minerals). The results of microthermometry and inclusion Raman spectrum analysis show that the ore-forming fluid system is NaCl-H₂O system with medium-high temperature, medium-low salinity, and medium-high density. In the late stage of mineralization, the properties of the fluids changed to low temperature, low salinity and high density fluid, with the deposit formation depth of 0.40-4.00 km. The values of D_V-SMOW and δ¹⁸ O_H2O range from -92.9‰ to -78.4‰ and -7.4‰ to 2.0‰ respectively, indicating that the ore-forming fluids are mainly mixed fluids. With the evolution of ore-forming fluids, the continuous mixing of meteoric water affects mineralization. Theδ³⁴S of metal sulfide in the ore ranges from 9.4‰ to 11.7‰, with an average value of 10.2‰, showing obvious characteristics of strata sulfur, which is caused by the interaction between magmatic hydrothermal fluid and surrounding rock strata. It is believed that  Aritekshan Cu-Mo deposit is a skarn-porphyry type deposit, which was formed in the subduction and collision during Late Hercynian-Indosinian, which is consistent with the diagenetic age of granodiorite. The strong immiscibility of mixed ore-forming fluids is the main mechanism of the formation of porphyry Cu-Mo deposit.

Key words: fluid inclusion, stable isotope, porphyry Cu-Mo deposit, Aritekeshan, northern Qaidam basin