Lead-zinc Deposits In Yunnan Maozu Geochemical Characteristics And Genesis Research

Northeastern Yunnan lead-zinc ore belt lies in Sichuan-Yunnan-Guizhou Province lead-zinc metallogenic zone which is located in southwestern margin of Yang Zi metallogenic domain.The ore belt is delimited to west by the north-south Xiaojiang Fault,links to east with western metallogenic zone of Guizhou province,the southeastern boundry is Shizong-Mile fault,ended in the border of Sichuan and Yunnan province.The Northeastern Yunnan metallogenic zone is an imported Lead Zinc and Silver polymetallic metallogenic region.Maozu Pb-Zn ore deposit is a large-size deposit developed in this belt, the ore body is mainly confine by stratum fold nearly north-south Maozu reverse faults and northeastern Choushuigou fracture.The ore body mainly occurred within siliceous dolomites in Dengying formation of presinian with bedded and quasi bedded and nervation forms. Althoug has a long history of exploiting and earlier geological prospecting work implementing,the study on deposit is scrce,specially on the genesis of the deposit.This paper took the three years prospecting plan "Project of Maozu-Baimachang in Qiaojia area prospecting comprehensive study "conducted byYunnan Province Nonferrous Geological Bureau as the basis,based on a lot of collecting the data, through field geological working and summarizing and researching indoor, analyzed the ore-forming geological background, geological characteristics, ore deposit Geochemistry etc characteristics of the Maozu Pb-Zn deposit in systemic way, finally, discussed the causes of Maozu Pb-Zn deposits on all the above bases. The paper has achieved the following results and understanding:1, the deposit is hosted within the dolomites in Dengying Formation of Upper Sinian with bedded and quasi bedded and nervation forms.the ore boby was crumpled with the same pace of wall rocks and has the same attitude to hosted rocks,which indicates that ore body and hosted rocks sedimented in the same period.2, ore-bearing strata were developed with many sedimentary exhalative original firestons and siliceous dolomites,lead-zinc orebody enrichment are closely related to the development, according to the macroscopic and microscopic characteristics,the writer considered that Maozu Pb-Zn ore forming should be relevanted to the hydrothermal exhalative sedimentation.3, Baritized fluoritized siliconized and other alteration rocks often developed nearby wall rocks, the macroscopic and microscopic characteristics manifest that the formation of Maozu Pb-Zn deposit is closely connected with the hydrothermal superimposition4, according to Maozu Pb-Zn deposit geological feature and micoroscopic texture and structure, the Mao mineralization process is divided to the three stages of sedimentary exhalation period and hydrothermal superimposition period and supergene period.(1) sedimentary exhalative period:the mineralization process of seabed sedimentary exhalation was drived by rised hydrothermal fluids created by activity of basal stractures and contemporaraneous faulting between late Sinian and Early Cambrian.with the process metallogenic elements dispersed in basal metallogenic constructer was transported up to seabed and formed sedimentarily lean ore body or ore source layer.(2) hydrothermal superimposition period:massive area of basalt was erupted upwards due to the intense motion of the crust and sequential motion of basal structure during late hercynian.the heat results from the uphill basalt lava leaded to activation of ore-forming fluid in formation and forming the pb-zn ore when it was thansported and enriched to the favorable structure position. (3)hydrothermal superimposition periods can be subdivided into four metallogenic stages:(I)pyrite-dolomites stage (Ⅱ) pyrite-quartz-galenite-sphalerite stage,(Ⅲ) dolomite-galenite-sphalerite-,chalcopyrite stage,(Ⅳ) calcite stage.5, conclusions based on the studing and analyzing of ore deposit geochemistry feature:(1) the rare elements characteristics and contribution pattern of ore approximate to that of wall rocks,which manifests that the rare elements resource is similar to wall rocks and the both are homological.(2) lead isotopes indicates that pb-zn elements came from the upper crust and various sedimentary rock in orogenic belt,including fractural base and sedimentary cover lithology.(3) the δ34S datas of Maozu pb-zn deposit approximates to that of marine sulfate in ore-bearing strata.for the matter,the metallogenic sulphur element maybe derive from the marine sulfate of the ore-bearing strata.(4) the study of metallogenic fluid inclusion shows that the fluid has a lower salinity and the homogenized temperature from129centigrade to210centigrade.which illustrates that the mainly metallogenic temperature is low temperature, deoxided H2and CH4and so on gas are additional ingredients in the gas inclusion,which designates the ore forming took place in the deeply intensive deoxided and sedimentary environment.6, Maozu Pb-Zn deposits should belong to sedimentary exhalation-hydrothermal superimposed Pb-Zn deposit.