Geological-geochemical Characteristics And Genesis Of Duhuangling Gold(Copper) Deposit In Yanbian, Jilin

Duhuangling gold deposit, located in the east segment of Xingmeng orogenic belt in Jilin province in China, is strictly limited by the Palaeo- Asian Ocean and Pacific tectonic domain. Complicated structure and intensive magmatism were exposed in mining area indicating a good minerogenic potentiality and prospect.The early Cretaceous quartz diorite contains numerous orebodies including two ore types composed of cryptoexplosion breccias type and altered rock. The ore minerals predominantly consist of pyrite, chalcopyrite and sphalerite with minor bismutinite, bornite, chalcocite and covellite followed by limonite formed by supergenesis. The ores are mainly characterized by euhedral-subhedral, residual and exsolution texture and distinguished by veinlet, stockwork and geode structure. Three main paragenetic stages of Duhuangling gold deposit have been recognized based on petrographic observation, which are the quartz pyrite stage(I), the quartz polymetallic sulfide stage(II) chiefly contributing to gold mineralization, and the carbonate quartz stage(III).The results of major elements show that the ore-bearing quartz diorite which has high SiO2, K2 O and Na2 O are metaluminous and peraluminous generally considered as I type granite. They are enriched in LREE and large-ion lithophile elements(Rb, Ba, K, Sr) and depleted in HREE and high field strength elements(Nb, Ta, P, Zr, Ti) indicating subduction-related arc magmatism. Combining regional tectonic setting and previous views, we suggest the quartz diorite were produced by subsequent fluid-bearing melt-mantle interaction and assimilation of basement rocks due to the northwestward subducted Yizenaiqi oceanic crust beneath the Asian block.Petrographic observations in room temperature revealed that various types of fluid inclusions present in different ore-forming stage.comprising mainly vapor-liquid two-phase inclusions, vapor inclusions, liquid inclusions and daughter minera-bearing multiphase inclusions. All types are abundant in the former two stages, but only vapor-liquid two-phase inclusions are recognized in the third stage. Laser Raman spectroscopic analyses indicate a different composition of fluid inclusions between the former two stages and the third stage. The liquid and vapor phase of these inclusions related to the former two ore-forming stage are almost H2 O with minor CO2, But the liquid and vapor phase of the inclusions discovered in the third stage are solely H2 O. The results of microthermometry show the ore-forming fluids are characterized by medium to high temperature, salinity and low density. Owing to the gradually decrease in temperature, density and pressure of mineralization-related fluid, two fluid evolution episodes can be identified as mixing and boiling respectively which were responsible for main metal precipitation.After comprehensive analysis of regional geological setting, geological features of deposit and the new findings about fluid inclusions, we proposal that Duhuangling gold deposit is a meso-hydrothermal deposit characterized by medium to high salinity and low density.