| Sinongduo Ag polymetallic deposit is located in the middle part of the northern margin of the Gangdise metallogenic belt,is the first low sulfurized epithermal deposit recognized in the volcanic rocks of Linzizong group,which has important research significance.Previous studies on the diagenetic and metallogenic age,metallogenic tectonic background,fluid source and alteration mineral characteristics of the deposit have been carried out,but there is no study on the trace element characteristics of pyrite and sphalerite,which are important metal minerals of the deposit.It is of great significance to find out the trace element geochemical characteristics of pyrite and Sphalerite in the mining area for exploring the genesis of minerals and tracing the evolution process of ore-forming fluids.Based on the full collection of previous data,through field geological survey,borehole logging,microscopic identification and analysis of LA-ICP-MS,this paper has carried out detailed mineralogical and mineralogical studies on pyrite and Sphalerite in the Sinongduo mining area,and systematically discussed the genesis of pyrite and sphalerite and their significance to the evolution process of ore-forming fluid.The following major progress has been made:?1?It is found out that pyrite and zinc blende are mainly massive and veined in crystalline tuff and breccia,while early pyrite is mainly in the stage of sphalerite chalcopyrite pyrite quartz and the stage of galena sphalerite silver mineral?Py1?,mostly in light yellow,in the form of self semi self-formed grains,with skeletal crystal structure,metasomatic residual structure and cataclastic structure;late pyrite is in the form of pyrite stone In the stage of quartz calcite?Py2?,most of them are copper yellow,which are granular in shape,with the common metasomatic residual structure and dissolution structure.Sphalerite occurs in the form of disseminated and aggregate vein in the crystalline tuff and breccia,and chalcopyrite in the form of solid solution is developed in the interior.In the early stage,sphalerite occurs in the stage of sphalerite chalcopyrite pyrite quartz?Sp1?,mostly in dark gray,which is in the form of crystallographic grain and common harbor structure.In the late stage,sphalerite occurs in the stage of galena sphalerite silver mineral?Sp2?,mostly in brown gray,which is in the form of granular structure It is common to have metasomatic residual structure and crystallographic structure.?2?The characteristics of trace elements in pyrite and sphalerite of the slong silver polymetallic deposit are found out:pyrite is rich in trace elements such as Cu,As,Ag,Sb,Pb,Zn,Mo,Ti,Ge,Se,Tl.depleted REE;Sphalerite is rich in trace elements such as Mn,Fe,Cu,Pb,Ag,Cd,In,Sn,Sb,depleted REE.From the early stage of mineralization to the late stage of mineralization,the contents of Cu,Zn,Pb,Ag,Co,As and Sb in pyrite increased,the contents of Mn and Fe in sphalerite decreased,and the contents of Cd,Cu,In,Pb,As,Ag,Se,Sn,Sb and other elements increased,indicating that the temperature of ore-forming fluid gradually decreased from the early stage of mineralization to the late stage of mineralization.?3?The occurrence states of trace elements in pyrite and sphalerite are found out:Mo,Cr,Pb,Bi,Zn,Cd,Ag,Cu and Se in pyrite are mainly in the form of micro inclusions,Co,Ni,As,Sb and Ge are mainly in the form of isomorphism,Tl is mainly in the form of isomorphism,and a few are in the form of micro inclusions.In sphalerite,Pb,As,Sb,Tl,Co,Se,Ag,Sn and Bi are mainly in the form of micro inclusions,Mn,Cd,In,Ga and Ge are mainly in the form of isomorphism,while Cu and Fe are partly in the form of isomorphism,and part of chalcopyrite is in the form of micro inclusions?4?This paper discusses the genesis of pyrite and sphalerite:pyrite has the characteristics of low V and high Se,the average Co/Ni value of Py1 is 1.8,the maximum is 3.4,the average Co/Ni value of Py2 is 4.06,the maximum is 5.33,indicating that pyrite is hydrothermal;the Cd content of sphalerite is generally greater than 2000×10-6,the ratio of Cd/Fe is 0.16?2.56,the average value is 0.97,Sn is higher(1.38×10-6?2546.72×10-6),Co is lower(0.97×10?639.55×10-6),Ga/In ratio is 0.01?0.5,Co/Ni ratio is 4.03?351.22,the average value is 73.82,indicating that sphalerite is of magmatic hydrothermal origin.?5?The trace significance of the trace element characteristics of pyrite and sphalerite to the evolution process of ore-forming hydrothermal solution is found out:through the comparison of the trace element composition characteristics of pyrite and typical metal sulfide deposits in the strondou deposit,it is found that the content of some elements of pyrite?such as Cu,Co,Ni?in the strondou deposit is significantly lower than that in the VMS and skarn deposits of medium high temperature,and the trace elements of sb,Tl,Se,etc From the early stage to the late stage of mineralization,Se element content gradually decreased,indicating that the temperature of ore-forming hydrothermal solution gradually decreased.Sphalerite is poor in Fe,Mn,Sn and rich in Cd and In,which also shows the characteristics of obvious low-temperature deposits.The corresponding mineralization temperature of lg Ga/Ge is 150?230?,and the temperature of ore-forming hydrothermal solution gradually decreases from the early stage to the late stage of mineralization.The ore-forming hydrothermal solution of the slong silver polymetallic deposit is a mixture of atmospheric precipitation and post magmatic hydrothermal solution.The atmospheric precipitation is driven by magmatic heat and circulates continuously in the stratum.The useful components in the stratum are extracted.The ore-forming material mainly comes from the useful components in the post magmatic hydrothermal solution and volcanic rock stratum. |
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