Metamorphic deformation characters and forming process of ore bodies in the Hongtoushan massive sulfide deposit, Northeast China

The Hongtoushan volcanic-hosted massive sulfide(VMS)deposit, located in the northern margin of North China craton, is the largest Archean VMS in China.The main orebodies and host rocks in the deposit have undergone metamorphism and deformation of high amphibolite facies and hydrothermal overprinting.Based on field and mineralogical observation, its main ore types are divided into following four types: a.massive sulfide ores, mainly stratiform and massive in shape, medium-sized, isogranular and crystalloblastic in textures; b.coarse-grained ores, generally lenticular and massive in shape, giant metacryst and interstitial in texture; c.mylonitized sulfide ores, also called ore mylonites, lenticular and crumpled in shape, fine-grained and recrystallized in textures; and d.copper-rich sulfide ores, also called as "copper bar", veined and laminated in shape, metasomatic residual and emulsion textures.Combined with mineral fabric and assemblage, field relationships, and deformation characteristics, the genesis and formation process of the above four types of ores are summarized.The massive sulfide ores are produced by regional metamorphism and recrystallization from primary VMS ores, while ductile deformation and hydrothermal overprinting are unobvious.The coarse-grained ores are dominated by nearly undeformed giant metacrysts with extremely low content of chalcopyrite and sphalerite, representing the residual phase during intensive metamorphic recrystallization and remobilization.Mylonite ores show strongest ductile deformation, with obviously higher contents of chalcopyrite, sphalerite and galena than massive ores, representing extensive ductile deformation and remobilization of massive sulfide ore.Deformation and overprinting structure are developed in copper bars in which sulfide in copper bars is dominated by chalcopyrite, followed by some sphalerite, minor carrollite, and depleted in pyrite or pyrrhotite, indicating mechanical reactivation and metamorphic hydrothermal precipitation under lower temperature.