Metallogenic Metal Source Of Jinding Giant Lead-zinc Deposit,Yunnan Province

The Jinding Zn-Pb deposit is a giant which more completely records the chemical or bio-chemical processes of moderate-low temperature fluid mineralizations during Cenozoic in NW-Yunnan,China.But the Zn-derivation in the mineralization is debated much more and we do not clearly know whether a chemistry or a bio-chemistry was the key for the mineralization.The Zn-isotopic compositions vary evidently in the earth and extraterrestrial rocks and ores.The trace Zn,a life nutritional element,widely takes part in the bio-geochemical process which result in Zn-isotopic fractionation.The Zn-isotope is an effective tool to trace the Zn-derivation and mineralization style.In this paper,by analyzing and testing the zinc and lead isotopic compositions of rocks and minerals from different strata and areas of Jinding lead-zinc deposit,we try to reveal the possible sources of metallogenic metals in Jinding directly from the isotopic characteristics of metallogenic elements;In addition,the in-situ Sr isotopic analysis of calcite（with flat or smooth arc boundary）which coexists with sphalerite and has no obvious metasomatic relationship was carried out under microscope to reveal the evolution characteristics and possible sources of Strontium in ore-forming fluid;The temperature change of ore-forming fluid is revealed by in-situ trace element analysis of sphalerite with different location and structural characteristics in hydrothermal ore-forming period.The evolution characteristics of ore-forming fluid in the process of sphalerite precipitation are revealed from the micro scale（100-200μm）through the analysis of transverse dense in-situ point and formation profile of colloidal sphalerite.The above test and analysis methods are proved by each other from different angles in order to restrict the source of metallization in Jinding.The main achievements of this paper are as follows:（1）The range of zinc isotopic composition of Jinding sphalerite is large,δ⁶⁶Zn is between-0.69⁰.51‰,the mean value is-0.06‰,and its fractionation is greatly affected by microorganism and organic matter,but there are many ways of influence.However,the zinc isotope of the sedimentary strata in the mining area may be controlled by the sedimentary environment,which is shown as follows:the marine carbonate（0.91‰）of the upper Triassic Sanhedong formation,the sea land alternating siltstone variegated layer（0.21‰）of the Middle Jurassic huakaizuo formation,and then the quartz sandstone（-0.04‰）of the Jingxing formation,which belongs to the fluvial facies deposition,with a decreasing trend ofδ66zn.According to the comparative analysis of zinc isotopes of rocks and ores,it is considered that zinc may be the mixture of low value sandstone zinc and high value limestone zinc,that is,it mainly comes from the sedimentary strata of Lanping Basin,but this study cannot exclude the possibility of the source of upper mantle.（2）The lead isotopic characteristics show that ²⁰⁶Pb/²⁰⁴Pb values range from 18.363 to18.636,with an average of 18.445.After 2006,the 50 ore lead isotopic ratios all fall between the evolution curves of orogenic belt and upper crust,showing the characteristics of pure crust source,but theirμvalues range from 9.50 to 9.63,with an average of 9.576,falling between the sedimentary rocks（9.705）in the mining area and the upper mantle rocks（9.27）in western Yunnan,Moreover,it is closer to theμvalue of sedimentary rocks in numerical value.Based on comprehensive comparative analysis,it is believed that the lead mainly comes from the upper crust,i.e.the sedimentary strata of Lanping Basin,and part of it comes from the upper mantle.（3）The ⁸⁷Sr/⁸⁶Sr value of hydrothermal calcite in Jinding ore is between 0.7097 and0.7103,which is higher than the average value of mantle source Strontium of 0.7035,and lower than the average value of shell source Strontium of 0.7119.However,the Sr isotopic ratios of Paomaping（0.7093）,Jiayashan（0.70924）and beichangxi stope（0.70994）increased,suggesting that the ⁸⁷Sr/⁸⁶Sr ratios of ore-forming fluids gradually increased from the east to the West.In Jinding conglomerate hosted lead-zinc ore,the ratio of⁸⁷Sr/⁸⁶Sr of calcite increases gradually in the early middle late stages,suggesting that the evolution of ⁸⁷Sr/⁸⁶Sr value of early ore-forming fluid from early to late is from low to high,indicating that the migration of early mantle derived strontium from the east to the west is continuously affected by the crust,and the strontium isotopes of calcite and crust derived strontium tend to be the same in the late stage.It is suggested that the strontium of ore-forming fluid may mainly come from the upper crust,but mantle fluid was added in the early stage.（4）In situ trace elements of Jinding sphalerite（Zn/Cd value is between 9.52 and441.2,n=10,with an average of 166）.The mineralization process of the sphalerite in Jinding mining area mainly experienced the change of medium low temperature,showing a trend of high in the East and low in the West.The characteristics of some samples（Zn/Cd=902,1186.9）and trace elements of Sphalerite in micro region indicate that the formation of colloidal Sphalerite in Jinding local area may have experienced three stages of temperature change,i.e.high,medium and low,suggesting that there may be the addition of deep thermal fluid.