Research On Geology, Geochemistry And Genesis Of Carbonate-type Lead-zinc Deposits In Central Yunnan

Central Yunnan,an important part of Sichuan-Yunnan-Guizhou metallogenic domain,is located in the southwestern margin of the Yangtze block,more than 100 lead-zinc deposits(points)have been found there.Most of lead-zinc deposits occur in dolomite,limestone and in other carbonate rocks,while a small amount of deposits are weathering leaching type.Compared with the study of lead-zinc deposits in the northeastern Yunnan and the southwestern Sichuan,the study in centural Yunnan is very weak,especially in geochemistry and geochronology.Based on the detailed field investigation about 26 lead-zinc deposits in the study area(point),preferably choose Da xiao,Hua mu jing,Lu lu,Re shui tang,Su zu-Mu yang,Huang tian lead-zinc deposits as the typical,which occur in six different layers.Combining the study of the metallogenic geological background,geological features,fluid inclusions characteristics,element geochemistry,isotope geochemistry,isotope chronology and other aspects of the lead-zinc deposits with the analysis of its spatial distribution,ore bearing strata position,ore lithology,facies of ancient geography,structure and other factors,this paper achieved the following main results and understandings:1.Lead-zinc deposits in Central Yunnan are mainly produced in the ancient continental margin,the edge of the secondary branch basin in epicontinental domestic which controlled by synsedimentary fault,or produced in fourteen stratigraphic unit in the transition zone of underwater uplift and depression,where semi restricted Bay,lagoon and reef beach sediment.The host rocks are mainly dolomite,limestone and other carbonate rocks containing biologies or bioclasts.Besides,from north to south,west to east,the age of ore-host strata changes from old to new.Lead-zinc deposits is controlled not only by stratigraphic facies and lithologic,but also by fractures in N-S direction,N-E direction,N-W direction,E-W direction.Lead-zinc ore-bodies mostly appear in stratiform and stratoid bedded,a small amount output in veins;2.The sulfur in Lead zinc deposits in Da xiao,Hua mu jing,Lu lu,Re shui tang,Su zu-Mu yang,Huang tian mainly derived from ore bearing strata.The composition of Sulfide sulfur isotope occurring in typical deposits shows the same composition features with marine sulphate sulfur isotope forming in ore-forming period;carbon and oxygen are mainly from marine carbonate dissolution;some of sulfur,carbon,oxygen of Huang tian deposit are from the formation,and some may come from deep magmatism;3.The mineral sources of Lead-zinc deposit in centural Yunnan is complex,ore-forming materials of Huang tian deposit may be from ore-host carbonate rocks and Yanshanian magmatism,while five other deposits'mineral sources come from ore-host carbonate rocks and sedimentary basement;4.The Lead-zinc deposit in central Yunnan has two mineralization epochs,the first formed during the late Indosinian epoch-the early Yanshan period(188?227Ma),second metallogenic period is the late Yanshan period(83Ma);5.Fluid inclusions indicate the lead-zinc deposits in central Yunnan are shallow epithermal deposits with low-middle salinity and low density;6.Integrating the geological characteristics of the deposit,geochemical characteristics and characteristics of the isotope,preliminary consideration about lead-zinc deposits in central Yunnanis is there are two different genetic types:Deposition-Mixed hydrothermal lead-zinc deposits and magmatic hydrothermal alteration lead-zinc deposits.And compared with the MVT lead-zinc deposits and typical lead-zinc deposits in eastern Yunnan and southwestern Sichuang,a deposit-construction-mixed hydrothermal mineralization model of lead-zinc deposits is established.