Fluid Inclusion Characteristics And Ore Genesis Of The Daqingshan Gold Deposit In Beishan Area, Xinjiang Province

The Daqingshan gold deposit is located in Hongshijing-Baishan gold-copper metallogenic belt, in the southern subzone of Beishan rift, between Southern Keziletage fault and Kuluke fault. So far, previous studies basically focused on geological characteristics of the deposit, the feature and source of ore-forming fluid, and ore genesis have not been well discussed. This study mainly worked on geology, fluid inclusion and isotope geochemistry of the Daqingshan gold deposit. According to field investigation and laboratory analysis, the genetic type of the deposit has been determined and a metallogenic model has been preliminary established.The Daqingshan gold deposit is hosted by greenschist facies metamorphic rocks of early Carboniferous age, under the control of a series of nearly E-W trending imbricated listric thrust faults on the north of Kuluke brittle-ductile shear zone. Carbonaceous phyllite and siliceous siltstone are the main ore-bearing lithologies. According to the metamorphism and crosscutting relationships, three periods of quartz veins were identified, corresponding with three metamorphisms and deformations in this area. Among these, quartz veins of the second period are the main gold-bearing quartz veins, whose strike is NEE and dip is N or NW. Wall rock alterations such as silicification, pyritization and sericitization are closely related to gold mineralization.There are two types of ore in the Daqingshan gold deposit, quartz vein type and altered rock type, and the former is the main ore type. Ore textures basically contain euhedral granular texture, xenomorphic granular texture, reaction rim texture, crumpled texture and solid solution separation texture, etc. Meanwhile, Ore structures mainly contain massive structure, vein structure, brecciated structure, disseminated structure and banded structures, etc. Native gold, pyrite, arsenopyrite, chalcopyrite, galena, sphalerite and pyrrhotine are primary metallic minerals in the ore, while quartz, sericite, ankerite and calcite are main non-metallic minerals.Petrography, microthermometry and Laser Raman analysis of fluid inclusions indicated that quartz veins of three periods in the Daqingshan gold deposit mainly contain liquid-vapor two-phase aqueous inclusions and CO2-H2 O three-phase inclusions. Generally, fluids in the three periods all belong to H2O-CO2±CH4 ±N2 system, with moderate-high temperature, low salinity and moderate density. Moreover, fluid immiscibility occurred in mineralizing period, which was considered to be the primary mechanism leading to precipitation of ore-forming elements. Study of hydrogen and oxygen isotope geochemistry showed that ore-forming fluid in the Daqingshan gold deposit mainly derived from metamorphism, and isotope exchange occurred between fluid and wall rock.In conclusion, characteristics of the Daqingshan gold deposit exhibited in metallogenic background, geology, ore-controlling structure, mineral assemblage, wall rock alteration, the feature and source of ore-forming fluid are all consistent with those of OGD origins, indicated that the Daqingshan gold deposit is a typical orogenic gold deposit.