Ore-forming Geological Body-Structure-Mineralization Regularity And Prospecting Directions Of The Lehong-Xiaohe Pb-Zn Deposits,the Deposit Concentration In The Northeast Of Yunnan,China

Lehong and Xiaohe Pb-Zn deposit is one of the typical lead-zinc deposits in the Sichuan-Yunnan-Guizhou(SYG)polymetallic metallogenic area,which is located in the southwestern margin of the Yangtze block.The deposit are characterized as high Pb+Zn grade,high content of germanium,cadmium,indium,and argentine and high ore-forming temperature.On the basis of the seniors’ research,the article based on "the theory and method of prospecting and prospecting in prospecting area(Geological Body-Structure Mineralization theory)",Four elements of the mineralization of the "time-spacematerial-evolution" for the technical route,We researched the mineralization process,the tectono-metallogenic system and markers of ore-forming fluid.The metallogenic geological body and mineralized structural facies of the deposits are identified by us,and mineralization characteristic indications can be revealed.The article summarized the metallogenic regularity of "Ore-forming Geological Body-Structure Mineralization theory"of the deposits.The prospecting models have been built,then block out the prediction region on the basis of the model.The research and results are listed as following:(1)Based on the ore-forming time,space and material source of Lehong-Xiaohe lead-zinc deposit,it is concluded that the combination of NW-trending fault and the altered dolomite of Sinian Dengying Formation(Z2dn)is the ore-forming geological body of the deposits.(2)According to the structure and mineralized structural facies of the deposits,the mineralized structural facies have been established,which is mainly composed by the lithology facies,structure facies,physical and chemical facies.Among them,the lithologic structure is mainly composed of light gray,medium-thick layer of fine-grained dolomite(permeable layer),the upper part is gray-dark gray and thick layer with white silty siltstone,carbonaceous mudstone(non-permeable layer),Which constitutes a good geochemical barrier of the ore-forming fluid traps.(3)Using large scale alteration petrography mapping method.Select the middle piece of deposit 1290 as a instance,we analysis the composition,type and structure of alteration by the comparative study about different features in mineralization and alteration and find out what alteration feature of the Le-hong lead and deposit.Studies suggest that alteration types of the deposit are:hydrothermal dolomitization,calcilization,silicification,pyritization and the main mineralization is sphalerite and galena.Finally,we establish the alteration petrofacies zoning patterns of Lehong deposit:the marginal zone of mineralization(Ⅰ)→the transitional zone of mineralization(Ⅱ)→the central zone of mineralisation(Ⅲ),and the corresponding minerational associations are Dol+Cal+Py、Dol+Cal+Py+Qt+Sp and Dol+Cal+Py+Qt+Sp+Gn.(4)The rare earth elements and C-H-O-S-Pb-Sr isotopic studies show that the source of metallogenic material of the deposit is characterized by "multi-source fluids mixing".Sulfur is mainly derived from the TSR product of the sulfate in the Devonian formation,but it can not be excluded BSR has a certain influence on the source of sulfur in the mine.The carbon in the ore-forming fluid is derived from the dissolution of the marine carbonate.:The carbonate isotopic characteristics indicate that the ore-forming fluid is derived from the mixture of atmospheric precipitation and deep-sourced fluid.The process of C evolution is:marine carbonate→ altered dolomite→calcite;H-O isotopic characteristics indicate that the ore-forming fluids are derived from the mixture of meteoric water and deep-sourced fluids.The Sr isotopic composition indicates that the ore-forming material is derived from the sedimentary cover and the basement rocks;The REE characteristic indicates that the ore-forming fluid may be derived from the mixing of rock formation water and the deep-sourced fluid.(5)According to the fluid-inclusion studies,which are discovered in sphalerite,quartz,barite and calcite from the different mineralization stages,the origin,property and evolution of ore-forming fluid and the metallogenic processes have been expounded.The homogenization temperature in the barite stage is vary 240.3℃ to 319.3℃,the salinity is vary 2.24wt%NaCl eqv.to 10.73 wt%NaCl eqv.,and it is show that the fluid occurs in medium-high temperature and low-middle salinity.By three-phase inclusions with CO2 in S3,it is estimated that the pressure and depth of mineralization vary from 45 MPa to 74.9 MPa with an average of 58.2MPa,and 1.7 Km to 2.8Km,respectively.The homogenization temperatures of different stages can roughly indicate the evolutionary process of the ore-forming fluid from early stage to late stage.The temperature appears in evolutionary trend of medium-high temperature and medium-low salinity→medium temperature and medium salinity→ medium-low temperature and medium and low salinity.(6)Based on the analysis of the previous studies,it is concluded that the mineralization process of Lehong-Xiaohe lead-zinc deposit is that the deep-sourced fluid is driven by tectonic dynamic and thermodynamic,and the deep-sourced fluid of high temperature and low salinity of the early stage migrated on a large scale.The fluid in the early stage decompressed and boiled by structural stress,and mixed with meteoric water at the same time.Hydrothermal fluid migrated upward along the Lehong fault from the depth,and injected into the faults in the wall rocks.When the physical-chemical conditions of ore-forming fluid changed,the ore-forming materials in the fluid precipitated in secondary faults or cracks near the Lehong-Shanwangmiao fault,and formed the Lehong-Xiaohe lead-zinc deposit.Meanwhile,strong dolomitization,pyritization and silicification,etc.alterations occur near the edges of fault zones.This discussion about metallogenic process is not only provides important evidences to further the metallogenic model of "structural fluid penetration mineralization",but also has important significances in predicting the location of the ore-bodies.Combined with "Geological Body-Structure-Mineralization"mineralization regularity,the genesis type of the deposit is Huize Type(HZT).(7)On the base of synthetic research of ore-forming rule is generalized,combined with domestic and foreign research results of this lead-zinc deposits,the "Ore-forming Geological Body-Structure-Mineralization" prospecting prediction model of LehongXiaohe Pb-Zn deposits have been established.The study points out the promising prospecting areas for buried deposits,which laid the foundation for guiding the exploration of the area.