扬子地块西缘灯影组层控铅锌矿床成因的地球化学论证

The Geochemical Constraints on Genesis of Stratabound Pb Zn Deposits in Dengying Formation at Western Margin of Yangtze Platform

扬子地块西缘灯影组层控铅锌矿床成因的地球化学论证邵世才（有色总公司北京矿产地质研究所，北京１０００１２）李朝阳（中国科学院地球化学研究所，贵阳５５０００２）关键词层控铅锌矿床地球化学矿床成因扬子地块西缘１矿床地质特征扬子地块西缘灯影组铅锌矿床呈南北向...

The Pb Zn deposits in Dengying formation at western margin of Yangtze platform located in the southern Sichuan and northeastern Yunnan.They occur in the upper part of easy breaking or porous carbonate rocks below the aquifuge of Lower Cambrian black sandstones and shale formations and are controlled by fault and lithology.The most abundant metallic minerals in the deposits are sphalerite,galena and pyrite.The gangue minerals are calcite,quartz and dolomite.Wallrock alterations are mainly silicification,dolomitization,baritization and fluoritization. Lead isotope compositions of ores from most deposits are within a narrow changing ranges and belong to normal lead,while the lead isotopes of large sized Tianbaoshan,Daliangzi and Maozu deposits vary considerably and belong to mixed lead,which are different from the rock lead from post Sinian system and similar to that of pre Sinian system.So metals are chiefly derived from pre Sinian basement.However,ore lead of Jinsha deposit is all radiogenic anomalous lead,and similar to that of Lower Cambrian rocks in which U Th deposits occur. All δ 34 S values of hydrothermal sulfides in deposits are more than 6 per mil and characteristic of heavy sulfur which is generally produced through the reduction of seawater sulfates by organic matter.Dengying formation contains evaporates like gypsum,mirabilite,etc.So the ultimate source of sulfur is from seawater sulfates. A study of the hydrogen and oxygen isotopes of inclusions in ores and gangue minerals indicates that the ore forming fluids belong to Na + K + Ca 2+ Cl - SO 2- 4 type,the ores are formed at temperature of about 80￣120℃ and the fluids are meteoric source. According to the sources of metal,sulfur and fluid,the mixing metallogenic model could be proposed.Metal bearing deep fluid mixed with sulfur bearing shallow fluid in appropriate tectonic space results in precipitation of sulfide minerals because of reaction of metal ions with reduced sulfur.