Study On Geological Features And Genesis Of Zhaibu Pb-Zn Deposit In The Baotan Area,North Guangxi

Baotan area in northern Guangxi is located in the western part of the Jiangnan orogenic belt.It is an important Au-As-Sb-Hg-Pb-Zn low-temperature hydrothermal metallogenic belt.There are three types of Pb-Zn deposits in this area:one is magmatic hydrothermal vein type Pb-Zn deposit in the periphery of Sn deposit,the other is sedimentary transformation type deposit in Devonian carbonate rock,and the third is Pb-Zn deposit directly developed in Sibao fault zone,Zhaibu Pb-Zn deposit is a typical representative of this type of deposit.At present,the formation age and genesis of the third type of Pb-Zn deposits are not clear.This paper focuses on the Zhaibu Pb-Zn deposit,through detailed field geological survey,combined with lithofacies analysis,isotope geochemical analysis,fluid inclusion test analysis,sphalerite Rb-Sr dating and other methods,to analyze the characteristics of the deposit,the physical and chemical environment and the source of hydrothermal material,and then determine the mineralization age,analyze the genesis of the deposit,and further discuss the metallogenic model.The Zhaibu Pb-Zn deposit is controlled by the multi-stage tectonic activity along the NNE-trending Sibao fault and the accompanying multi-stage fluid activity.It occurs in the fault fracture zone of biotite granite and shallow metamorphic clastic rocks.There are two ore bodies in the mining area,the average grade of Pb is 3.3%,Zn is 4.1%,Cu is 0.6%,and associated Ag.Metallogenesis can be divided into hydrothermal and epigenetic stages,in which hydrothermal stage can be divided into three stages:fluorite-quartz stage,quartz-sulfides stage and quartz stage.Quartz-sulfides stage is the main metallogenic stage.In this study,a 115+14Ma of Rb-Sr isochron age of Sphalerite in Zhaibu Pb-Zn deposit has been determined.In-situ sulfur isotope test and single mineral melting test results show that the?³⁴S of galena in Pb-Zn ore is 5.7‰⁹.0‰,sphalerite is6.6‰¹1.5‰,chalcopyrite is 6.0‰⁹.7‰,and pyrite is 7.7‰¹1.1‰,average value of sulfides is 8.3‰,The ²⁰⁸Pb/²⁰⁴Pb,²⁰⁷Pb/²⁰⁴Pb and ²⁰⁶Pb/²⁰⁴Pb values of galena,chalcopyrite and chalcopyrite were 38.965³9.226,15.744¹5.8,and 19.054¹9.112.The S and Pb isotopic compositions of sulfides are quite different from those of Pb-Zn deposits in the periphery of tin deposits in the area.The Pb isotopic compositions show that the ore-forming materials mainly come from the upper crust;the(⁸⁷Sr/⁸⁶Sr)_i of sphalerite is 0.7043,indicating that the fluid is derived from magmatic hydrothermal fluid;the ¹⁴⁷Sm/¹⁴⁴Nd ratio of fluorite in hydrothermal period is 0.1667⁰.1775,the¹⁴³Nd/¹⁴⁴Nd ratio is 0.512072-0.512089,and the?_Nd?115Ma?value is-12.1^-9.9,with an average of-10.6,indicates that Nd in fluorite mainly comes from the crust.The temperature measurement results of fluorite fluid inclusions in hydrothermal period show that the metallogenic temperature of main metallogenic stage is190²10?,which is consistent with the temperature calculated by content of Zn and Fe in sphalerite at 150-200?.Raman analysis of inclusions shows that the ore-forming fluid is H₂O-NaCl-CH₄?organic matter?system,fluorite trace elements indicate that the fluid is in a reducing environment,indicating the addition of hot brine.Zhaibu Pb-Zn deposit is consistent with Dachang Sn deposit in the west of the region in metallogenic age and Sr and Nd isotope characteristics.There are obvious geochemical anomalies of Pb-Zn-As-Sb-Hg in the study area,which indicates that the ore-forming fluid of Zhaibu lead-zinc deposit may originate from the Yanshanian granitic magmatic hydrothermal fluid in the periphery or deep part of the study area and belongs to a low temperature hydrothermal deposit of tectonic-controlled magmatic hydrothermal fluid mixed hot brine.Suggest a metallogenic model of"distal migration of magmatic hydrothermal fluid"in the Cretaceous lithospheric extension environment.