Mineralogical Characteristics And Genetic Significanceof Zhaxikanglead Zinc Antimony Silver Deposit,Southern Tibet

The Zhaxikang deposit,located in the north of Himalaya gold antimony metallogenic belt,is still lack of systematic studies on metallogenic environment and evolution characteristics.The study of the mineralogical characteristics of typical minerals in lead-zinc deposits has important implications for indicating the metallogenic environment and mineralization process.We divided the Zhaxikang deposit into two metallogenic epoch and six metallogenic stages.Themineralogical study of the sulfide sulphosalts,silver minerals,pyrite,ferromanganese carbonate category of the zhaxikang deposit is carried out in this paper.There are three generations of sphalerite in theZhaxikang deposit: the first generation of sphalerite was mainly existed in the form of granular fine lamellar ferromanganese carbonate,reddish brown;second generations of sphalerite was mainly existed in xenomorphic granular lumps,globose,circular structure ore,dark brown color;third generation is mainly existed in the sphalerite brecciated quartz vein,reddish brown-yellow brown.In the early stage of sphalerite formation,rich Fe and Mn,poor Zn;late poorFe,Mn,rich Zn.Boulangerite is mainly acicular aggregate sphalerite package,or a large anhedral granular quartz crystal filling in the gap,or it is shaped by chalcopyrite,ferromanganese carbonate inclusions,as well as part of the growth in mineral surface euhedral acicular.Jamesonite is fine anhedral granular filling in the gap in the quartz crystal,the symbiotic mineral is quartz,pyrite and arsenopyrite.Bournonite is fine anhedral granular distribution in galena and forming a ring in galena surrounding edge,coexisting with galena,chalcopyrite and freibergite.Freibergite is fine anhedral granular distribution,coexisting minerals are galena,bournonite,jamesonite.S isotopicgeothermometer showed the temperatureof second stages and third stagesof Zhaxikangdeposit are 242 ? ³25 ? and 317 ?.The Mn/Fe ratio in ferromanganese carbonate is 1.55⁰.87,indicating that the ore-forming fluid in the first mineralization stage was in a strong reducing environment and riched in CO2.The relationship between FeS molecular content and sulfur fugacity of sphalerite,the relationship sulphosalts combined with temperature and S fugacity,show that thesulfur fugacity of Zhaxikang deposit from one to five mineralization stages are-13.9^-13.2,-14.5^-13.6,-13.3^-9.8,-14.6^-15.6,-16.9^-14.9.The sulfur fugacity of early ore-froming stage is low,and the mixingof external fluidresulted inthe sudden increase in sulfur fugacity of third mineralization stage and gradual decrease during themineralization processes.With the decrease in temperature,the Zn²⁺ and Pb²⁺crystal out from fluid of first metallogenic epoch ofZhaxikang deposit.In the second metallogenic epoch,with the increase of temperature,the one or two generations of sphalerite and galena are active and reacting.The ore-forming fluid mixing with external fluid makes the sulfur fugacity rise,a large amount of sphalerite and rich Ag galena crystals come out,the temperature decreases,Pb²⁺,Sb²⁺,Ag⁺,Fe²⁺,Zn²⁺ and so on form independent silver minerals.With Pb²⁺ and Sb²⁺ mineralization,mainly formed by Pb-Sb sulfur salt minerals,Fe²⁺ formed mainly of pyrite and arsenopyrite,with Fe²⁺,Pb²⁺ Sb²⁺ completely consumed in the form of stibnite ore-forming fluid precipitation of ore-forming fluid in the mineral consumption is completed,the end of the mineralization activity in quartz ± calcite form.