| Huamuqing Pb-Zn deposit belongs to Dongchuan,Yunnan province and is tectonically located in western margin of Yangtze platform,the ore bodies mainly occur in carbonate rocks in Sinian Dengying formation that is controlled by both north-south Xiaojiang fault,north-east Jinniuchang-Kuangshanchang fault and the Sinian-Cambrian transition horizon,most of them have characteristic of lamellar distribution,the ore fabrics always behave as subhedral xenomorphic granular structure,metasomatic relict structure,massive structure,disseminated structure and vesicular structure,and the wall-rock alterations consist of silicification,baritization,pyritization and carbon acid salinization.The research in this area began in middle 19th,but the deposit research,especially the study of the genesis of the deposit is very weak,therefore,relying on the National Natural Science Fund Project "Study on the mechanism of fluid mixing and mineralization of carbonate type lead-zinc deposits in Central Yunnan",on the basis of collecting relevant information,carried out the field geological survey and analysis and testing indoor,systematic analyzed the geological background,fluid inclusions geochemistry and elements geochemistry,and then putted forward its genesis understanding,all results are as follows:1.According to the characteristics of mineral assemblage,the mineralization can be divided into hydrothermal mineralization stage and supergene oxidation stage,the first period mainly formed coarse grained pyrite,sphalerite,galena,chalcopyrite,tennantite and fine grained pyrite,and was companied by gangue minerals calcite and quartz;the main manifestation of the second period is that primary minerals long-term exposured to the surface,then oxidized limonite,malachite,covellite formed.2.Hydrothermal pyrite mainly behaviors Eu positive anomaly,Ce negative anomaly while calcite possesses Eu positive anomaly,Ce weak anomaly,indicating the slight change of redox condition in the mineralization process;3.Trace elements in pyrite indicate that the ore-forming fluid is rich in Cl,the results of fluid inclusions show that homogenization temperature mainly changes in the range of 240?-280?,salinity concentration is in the range of 1-6wt%NaCl,while the density changes mainly in the range of 0.75-0.95g/cm3,whose average value is 0.86g/cm3,the main pressure is 180*105Pa-230*105Pa,average of it is 200.3*105Pa,at last,the depth of mineralization are mostly concentrated in 600-800m and its average is 679m,besides,we can know from the fluid inclusions that there existed mixing effect between ore-forming fluids and foreign fluids in the mineralization process;4.The ?13CPDB and ?18OSMOW values of hydrothermal caLcite vary in a narrow range of-0.64‰--0.18‰ and 17.549‰-18.44‰,respectively,all the samples are plotted into the field between the marine carbonate and mantle in the diagram of ?13CPDB vs.?18OSMOW,considering CO2 are mainly produced by dissolution of marine carbonate and affected by mantle degassing and sedimentary organic matter dehydroxylating effect;5.The average ?34S values of sulfide deposits in the ore deposits is about 15‰ indicating that the sulfur in the ore-forming fluids may be derived from marine sulfate;6.As for Pb isotope,its composition shows characteristic of stable,values of 206Pb/204Pb,207Pb/204Pb and 208Pb/204Pb ratios are 18.184-18.393,15.575-15.691 and 38.325-38.436,respectively,which locate in the region between orogenic belt and upper crust Pb area and plot into the filed of basement rocks and Mount Emei basalt,explaining the ore-forming metal mainly comes from basement rocks;7.The variation range of ?66ZnJMC is from 0.19‰ to 0.52‰,with an average value about 0.34‰,which is similar to that of Pb isotope,indicating that the ore-forming metals may be mainly derived from basement rocks;8.The sulfide initial value of 87Sr/86Sr is 0.71106±0.00011,which is higher than that of ore hosting rock(0.708464)while lower than the value of basement rock(87Sr/86Sr=0.7283,0.7288),displaying that the ore-forming fluid maybe flows through the basement rock.The Rb-Sr isochron age of sphalerite is 204.1±1.7 Ma,reflecting the deposit may be formed in the early Yanshan.9.In summary,Huamuqing Pb-Zn deposit is a epithermal hydrothermal deposit,may be formed under the background of the dynamic transformation from Indosinian to Yanshan and be the product of mixed fluid mineralization. |
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