LA-ICP-MS analysis of trace element characteristics and geological implications in sphalerites from Fozichong lead-zinc ore field,Guangxi Autonomous Region,China
The western part of Qinhang metallogenic belt where the Fozichong Pb-Zn ore field is located is an important polymetallic ore concentration area in Guangxi Zhuang Autonomous Region.The Pb-Zn ore deposits found in the orefield have banded,disseminated and hydrothermal veined ores.Among these three types of ores,sphalerite is characterized with the most enriched Fe element,enriched Cd element,relatively enriched Co element,depleted in element,and little changed low contents of Ge,As,Mo.However,there are some differences in Fe contents of sphalerites among the three types of ores,with w(Fe)of the banded sphalerite<that of the disseminated sphalerite<that of the hydrothermal vein sphalerite.The elements of Mn,Fe,Co,Cd,and In occurred in the lattice of three types of sphalerites in the form of isomorphism,while the elements of Cu,Pb,and Bi occurred in the form of independent minerals(chalcopyrite,galena,bismuthite)or micron inclusions in sphalerites.However,Ag occurred in different forms in three types of sphalerites.Especially,Ag occurred mainly in forms of independent mineral(natural silver)or micron inclusion in sphalerites of banded and hydrothermal veined ores,while it could occur in form of isomorphism in the lattice of sphalerite of the disseminated ore.There are some differences in the roles of Fe for substituting Cd(or Mn,Co,In)and Zn in the three types of sphalerites.Fe in the sphalerite of banded ore may play a certain role for promoting the substitution of Zn by Cd(or Mn),but its role in the substitution mechanism of Zn by Co(or In)is unknown.Fe In disseminated sphalerite promotes the substitution of Cd(or Mn,Co,In)and Zn.In the sphalerite of hydrothermal veined ore,Fe promoted the substitution of Zn by Cd(or Mn,Co,In)and Zn.However,in the sphalerite of hydrothermal veined ore,Fe promoted the substitution of Zn by Mn,the substitution of Zn by Cd(or In)to some extent,but inhibited the substitution of Zn by Co.The formation of three types of sphalerites is closely related to the magmatic activity.However,the sedimentary transformation also played an important role in the formation of sphalerite in the banded ore.The sphalerite of banded ore could be formed in medium-low temperature environment,while sphalerites of disseminated and hydrothermal veined ores could be formed in medium-high temperature environment.Especially,the sphalerite of hydrothermal veined ore could be formed at a higher temperature than that of the disseminated ore.Combined with plots of Ga/Ge-Zn/Cd and Zn/Cd-Mn and comprehensive analysis of previous research results,it is suggested that there are three genetic types of deposits including the Sedex,skarn,and magmatic hydrothermal types in the Fozichong Pb-Zn orefield.