Geochemical Characterisitics And Genesis Of The Aqishan Pb-Zn Deposit,Eastern Tianshan,Xinjiang

The Aqishan Pb-Zn deposit is located in the Aqishan-Yamansu island arc on the Jueluotage East Tianshan Xingjiang Provinece.The study is focus on the field geological survey for the Aqishan Pb-Zn deposit.We researched the geological characteristics of deposit,tectonic setting of ore-forming tectonics,source of ore-forming materials and metallogenic epochs through the rock geochemistry,Electron probe,fluid inclusions temperature and stable isotopes,Sm-Nd isochronal dating,and obtain an in-depth understanding for the genesis of the Aqishan Pb-Zn deposit as follows:The Aqishan Pb-Zn deposit occurs in the lower carboniferous andesitic tuff.The ores occur as massive,disseminated and striped.The early stage of hydrothermal mineralization dominated by garnet-diopsid with the mean temperature of fluid inclusions being 288 ?;The late stage of hydrothermal mineralization,mainly composed of lacrosse-tremolite-magnetite,fluid inclusions homogenization temperature reaches the maximum,which is 340 ?;Sulfide stage,concluding quartz,epidote and chlorite with the mean temperature reducing to 224 ?,Carbonation stage has the lowest temperature with 130 ??Yamansu group volcanic rocks of the Aqishan Pb-Zn deposit belong to medium-basic series,and its chemical composition belongs to calc-alkaline series.The primitive mantle-normalized rocks enrich LILE?K?Rb?Th?,and depleted in high field strength elements?HFSE??Nb?Ta?P?Ti?,showing geochemical characteristics of continental island arc volcanic rocks overall.The trace element curves standardized by chondrite were inclining overall to the right.Their REE model is characterized by enrichment of light REE.The Aqishan Pb-Zn deposit garnets belong to andradite-grossular series.The content of the main elements shows a regular pattern,Si O₂ and Ca O remain stable,while Fe O contents are increased with Al₂O₃ decreasing from the core to the edge.This phenomenon maybe because that it is an acidic reducing environment in the early stage of the formation of garnet,ore-forming fluid evolved from acidity to weakly alkaline during the formation process.The early stage provides the condition for the enrichment of metal sulfides such as Pb,Zn and Fe.The value ?³⁴S of Sulfides is about-5‰.It reflects a typical volcanic hydrothermal sulfur isotopic characteristics.The Sm-Nd isotope age of altered mineral?for garnet,epidote?symbioticing with Pb-Zn ore and Cu ore is 292 Ma,reflecting that the Aqishan Pb-Zn deposit formed in late stage of Late Carboniferous volcanic-magmatism.relating to the shallow formation of a porphyry invasion of Late Carboniferous.Combining with the above study,we can initially identified it as a volcanic hydrothermal type Pb-Zn deposit.