Geological Characteristics And Genesis Of Qinggouzi Stibnite Deposit,Linjiang City,Jilin Province,NE China

Orogenic gold deposits constitute a major part of the world's total gold production.They are the most critical unique genetic class of epigenetic mineralization associated with silicification.They are formed from Archean to Cenozoic in compressional or transpressional regimes.This gold deposit class is characteristically associated with deformed and metamorphosed mid-crustal blocks,particularly in spatial association with major crustal structures.These types of deposits are hosted in the brittle-ductile shear zone associated with intense structural control.Qinggouzi stibnite deposit is located in the NE margin of Jilin province and the eastern margin of Archean North China Craton(NCC).The study area lies within Liao-Ji active belt,bounded by Longgang Block in the north and Langlin Block in the south.It has gone through multiple episodes of deformation,resulting in forming a series of thrust and normal faults in the region.In the study area,igneous,volcano-sedimentary and metamorphic rocks from Archean to Cenozoic are well exposed.This deposit is hosted in the axis of Qinggouzi inverted anticline in quartz containing sulfide veins.These veins are hosted in metamorphic rocks of the Paleoproterozoic Dalizi Formation and Linjiang Formation.K-Ar dating results of whole rock from Lamprophyre samples indicate that the upper age limit of mineralization in Qinggouzi stibnite deposit is127.49±8.38ma.The shear zone is correlated with two stages of deformation.In the first stage,bedding(S₀)is used as a deformation surface to form axially closed isoclinic folds in the north-south direction.Due to intense deformation and metamorphism,those primary planar features were placed by secondary planar structures(S₁).In the second phase,the northwest trending inclined fold was formed with(S₁).As a result,fan-shaped cleavages and fractures developed at the edge of inverted anticline.The veins are controlled by fault structures,and the occurrence of the ore body in vein belts has noticeable changes,reflecting multi-stage structural complex processing.The ore body has poor continuity in the vein zone,showing pinch out reappearance and lateral distribution.The host rocks include quartzite,phyllite,and sericite schist.Combining field observation and indoor microscopic analysis,the main types of wall rock alterations observed are carbonatization,silicification,and sericitization.The mineralization includes pyrite and arsenopyrite mineralization.The sulfide mineral assemblages are dominated by stibnite,pyrite,and arsenopyrite.The gangue minerals include quartz,calcite,biotite,sericite,and so on.Textures of minerals vary from large euhedral crystals to fine-grain euhedral to subhedral crystals,either massive,breccia,or disseminated.Mineralization is confined to veins,veinlets,and mostly fine mesh veins.Ore textures include granular,radial,and metasomatic textures.Based on detailed petrographic evidence,it is concluded that mineralization in the Qinggouzi stibnite deposit is divided into one hydrothermal period and four paragenetic stages,i.e.(i)quartz-pyrite-arsenopyrite,(ii)quartz-granular stibnite,(iii)quartz-fine-grained hair-like stibnite,and(iv)quartz-carbonatization stage.The whole-rock geochemical analysis was conducted on phyllite samples,chosen from Dalizi Formation.Analytical results for major,trace elements,and rare earth elements are discussed in the thesis.It is concluded that these rocks are enriched in Si O₂ and Al₂O₃.They have moderate to high concentrations of Fe₂O₃+Fe O,K₂O,and Na₂O.However,concentrations of Ca O,Mg O,Mn O,P₂O_5,and Ti O₂ are low.The trace elements composition shows that these rocks are enriched in As,Sb,and Mn content.The trace element compositions are moderate to high in Zr,Rb,Ba,Zn,and Ni.The Pb,W,Sn indicate low concentrations.The concentration of Au is low,range between 0.18to 0.27 ppm.The results from fluid inclusions distribution indicate that fluids associated with Sb mineralization in quartz veins and veinlets have low salinity,averaging 6.24 wt%Na Cl_eqv,and low density up to 1.02 g/cm³.These ores may have formed at a temperature range between 114.8°C to 422°C.The pressure is calculated as 11.65 to42.33 MPa,and depth is assumed to be between 1.16km and 4.23km.The H-O isotopes results indicate that the ore-forming fluids originated from a deep source and later on contaminated by meteoric water.The S isotopes further confirm that the sulfides most likely have a deep magma source.After thorough consideration of all the elements discussed in the thesis,i.e.,tectonic settings,petrographical,mineralogical,structural,geochemistry,and fluid inclusions analysis,the findings of this thesis suggest that Qinggouzi stibnite deposit is formed at shallow depth,and is characterized as epizonal Au-Sb orogenic deposit in terms of orogenic deposit series.