Geochemical Characteristics And Genesis Research Of Zigangping Pb-Zn Deposit,Jiulong County,Sichuan Province

Zigangping Pb-Zn deposit is located between Xianshuihe fault zone and Ganzi Litang suture zone on the southeast margin of Songpan Ganzi orogenic belt.In this paper,the provenance of ore-forming materials and the fluid,the metallogenetic process and mineralization are discussed and analyzed through the research of geological characteristics,the mineragraphic and geochemical characteristics of the Zigangping Pb-Zn deposit,as well as the sulfur isotopes.Finally,deposit genesis and metallogenic model are preliminarily discussed.The ore bodies are layered and lenticular in the interlayer fault zone between the garnet bearing cline biotite quartz schist and garnet bearing Na mica schist with quartz schist.Ore minerals include magnetite,sphalerite,galena,and a small number of chalcopyrite,lead and vanadium.In addition,there are trace minerals such as hematite,limonite,argentite,copper blue,etc.;gangue minerals are mainly mica,quartz,garnet and a small number of amphibole,garnet,chlorite,barite,etc.The alteration types are mainly silicification and magnetization.According to the electron probe analysis,pyrrhotite should have formed in a high-temperature environment.The ore-forming fluid is a high-temperature hydrothermal fluid,which may be accompanied by the addition of sea water or atmospheric precipitation and other formation water,resulting rapid cooling in the ore-forming process.In addition,there are only hexagonal magnetite typomorphism in the ore,which is related to the homogeneity of monoclinic variant caused by later metamorphism.The metallogenic process can be roughly divided into four stages: sedimentary metallogenic stage,regional metamorphism stage,hydrothermal reformation metallogenic stage,regional metamorphism stage and supergene stage.The recovery of the primary rock of the surrounding rocks of the Zigangping Pb-Zn deposit indicates that it is argillaceous rock and sandstone with basic volcanic rocks.The primary rocks of para-metamorphic rocks are mainly argillaceous rocks,and the provenance is felsic igneous provenance area;a few are sandstones,and the provenance is quartzite sedimentary source area.These meta-sedimentary rocks are mainly in the rift tension environment.According to the analysis of trace and rare earth elements in the surrounding rock,the surrounding rock was formed in the oxidation sedimentary environment.In addition,the ore-forming elements Pb,Cu and Zn in the surrounding rock of the mining area have been obviously enriched,which may provide the ore-forming source for the formation of Zigangping lead-zinc deposit.Ba element in the ore is obviously enriched.Most ore samples show strong Eu positive anomaly and weak Ce negative anomaly,indicating that the ore-forming fluid should be high-temperature hydrothermal fluid.A few samples show weak Eu negative anomaly and weak Ce negative anomaly at the same time,which is related to the rapid temperature drop caused by the mixing of infiltration seawater or ground water.In addition,according to the content of Zr and HF in the ore and the ratio of U/Th to Zn/(Zn+Pb),it is believed that the ore-forming fluid is mainly related to hot water deposition,there is no inevitable relationship between the ore-forming fluid and the deep source mantle material,and there may be a small amount of jet hot brine.The log(δCe)value shows that the ore formed in the reducing environment,indicating that the ore-forming fluid should be high temperature reducing thermal fluid.Therefore,ore-forming minerals should mainly come from the surrounding rock of the mining area.The study of sulfur isotopes indicates that the sulfur in the ore shows the characteristics of mixed sulfur.The sulfur mainly comes from the reduction of sulfate minerals in the surrounding rock,and a few mantle sulfur.The major function of ore-forming fluid in reducing sulfur is thermochemical sulfate reduction,and the fluid is mainly formation water with the characteristics of deep thermal fluid.Most of the sulfur isotopes in the ore samples have not reached the fractionation equilibrium state,and there may be multiple stages of mineralization and fractionation.The U-Pb chronology study of zircon in the surrounding rocks found that the original ore-forming materials are likely to be derived from clastic rock materials related to the Liwu rock group.In addition,the basic volcanic eruption of the Variscan age also provided ore-forming materials for the later formation of deposits.Zigangping Pb-Zn deposit may be another type of supplement of Liwu Cu-Zn deposit.