Genesis of the Haigou gold deposit, Jilin Province, NE China: evidence from fluid inclusions, 40Ar/39Ar geochronology and isotopes

Abstract

The Haigou gold deposit is one of the largest known lode gold deposits in the Jiapigou‐Haigou gold belt of the Yanbian area of NE China. Although this area contains a significant amount of gold mineralization, identifying new resources has been problematic. Here, we present the results of a systematic study of the ore geology and fluid inclusion characteristics of deep‐seated mineralization in this area, as compiled from previous research. We use these data to determine the genetic processes that formed these deposits and outline the key criteria that should be used for future exploration. The Haigou deposit is hosted by a monzonitic granite (monzonite) with mineralization present within quartz veins. The gold mineralization is associated with silicification, and four stages of mineralization have been identified: milky quartz, pyrite‐quartz, quartz‐polymetallic sulphides and quartz‐carbonate. The second and third stages host the majority of the mineralization. Three main types of fluid inclusion are present within the deposit: CO2–H2O, aqueous and pure CO2. The early milky quartz vein stage of mineralization hosts CO2–H2O and aqueous inclusions, whereas the main stages of mineralization are associated with all three types of fluid inclusions, which are randomly distributed but are especially well developed within pyrite‐quartz veins. These stages of mineralization are also associated with clusters of CO2–H2O inclusions that coexist with large but variable amounts of aqueous phase fluid inclusions. The only fluid inclusions associated with the later stages of mineralization are aqueous inclusions within calcite‐quartz veins. Microthermometric data indicate that the inclusions associated with metallogenesis homogenize at 145–410 °C and contain medium‐ to low‐salinity fluids (<11.93 wt.% NaCl equivalent). The mineralization in this area formed during the Middle Jurassic (163–161 Ma), as evidenced by 40Ar/39Ar dating of hydrothermal sericite from the main stage of mineralization. Integrated C‐H‐O‐S‐Pb isotope analysis indicates that the initial ore‐forming fluid was derived from CO2‐rich magmas produced by the anatexis of lower crustal material. This fluid is then mixed and underwent fluid immiscibility during ore formation. The Haigou gold deposit is a typical medium‐ to low‐temperature quartz lode gold deposit that formed after the collision of continental terranes during the transition from compressive to extensional tectonics. The data presented here indicate that this area has significant potential for deep‐seated mineralization; an area that should be the focus of future exploration. Copyright © 2016 John Wiley & Sons, Ltd.