Research On Metallization Of Devonian Mississippi Valley-type Lead-zinc Deposits Of Nanling Region,China

Nanling region is one of the world's famous mining sites of tungsten,tin and lead-zinc.It developed a group of Pb-Zn deposits in Devonian platform carbonate rock,which have no obvious connection with magmatic mineralization.But the genesis and mineralization regularity of the Pb-Zn deposits has been in controversy.This article took Fankou,Siding,Beishan Pb-Zn deposits as the typical deposits,to discuss the geological geochemical characteristics and metallogenic mechanism of this kind of Pb-Zn deposits in Nanling region.Combined with the geological and geochemical characteristics research of Fankou,Siding and Beishan,these three Pb-Zn deposits is obvious different from SEDEX deposits and magmatic hydrothermal type Pb-Zn deposit.It can be compared with the typical MVT Pb-Zn deposit.Through the analogy between the typical MVT Pb-Zn deposit and Fankou,Siding,Beishan Pb-Zn deposits,we found that the three deposits have an associated genetic relationship.The composition of sulfur and lead isotope in Fankou,Siding and Beishan Pb-Zn deposits is quite different.Sulfur isotopic compositions is influenced by strata and related to the ore-forming mechanism.Lead isotope research shows that the metallogenic material mainly comes from the upper crust.The lead isotope of Fankou,Siding and Beishan has a good linear relationship,suggested that these deposits have a similar origin of lead.Carbon and oxygen isotope research shows that carbon might be mainly provided by the dissolution of the marine sedimentary carbonate.Strontium isotope research shows that the metallogenic fluid is caused by selective leaching the rock or from the underlying older basement.Basing on the intercalated relationship between diabase and orebody,and using the method of SHRIMP U-Pb,the indirect determination of Fankou Pb-Zn metallogenic epoch is the late Cretaceous.The chronological study shows that the metallogenic epoch of Fankou Pb-Zn deposit is 100 Ma±.It is relative to the Late Cretaceous red beds in South China and the metallogenic epoch of uranium deposit.By the studying of strontium isotopic compositions of sedimentary gypsum,which is from Cretaceous salt mine in red beds baisn,the strontium isotopic of gypsum is 0.7135?0.713981.It is overlapped with the regional dolomite,the calcites and dolomite of the Pb-Zn mine and the strontium ratios of uranium mine.The strontium ratios outclass the ratios,which is in the marine carbonate in synchronization.It is basically identical with the concentrated brine in modern saline.It shows the genetic connection between regional basin brine with the red beds baisn development.It is the first time to put forward the genetic connection between MVT Pb-Zn deposit in Nanling region with the red beds baisn of Cretaceous,which is enrichment of gypsum-salt construction.Based on the 1:200000 regional geological survey data as the foundation,and the research of several typical geological geochemical profile,this article found that there exits the extensive traces of the regional basin brine between Tiaomajian formation and Qiziqiao formation,which are in the middle Devonian.Large-scale regional dolomitization developed at the bottom of carbonate rock.It is west to Xingan in Guangxi province,north to Hengyang in Hunan province,east to south part of Jiangxi province,south to Yingde in Guangdong province.In the purple sandstone of middle Devonian,the fading alteration developed widely.In Nanling region,MVT Pb-Zn deposits is mainly distributed in the southern and western area of the regional dolomitization belt,namely the fronts of regional dolomitization.Based on the study of the geological and geochemical characteristics and regional dolomitization,combined with the geochemical characteristics of ore-forming elements,this paper holds that MVT Pb-Zn deposit formed in the mixing of two fluid.The ore body is controlled by silicon-calcium interface.The contemporaneous fault provides the requisite conditions for mineralization.Finally,this paper discussed the metallogenic mechanism of MVT Pb-Zn deposit and established the trinity geological prospecting prediction model for MVT Pb-Zn deposit in Nanling region for the first time.