Relationship Between Intrusive Rocks And The Mineralization In Caixiashan Pb-Zn Deposit,Middle Tianshan,Xinjiang

The Central Tianshan Terrane,occupied the southern margin of the Central Asian Orogenic Belt,is considered to be the one of the most important polymetallic metallogenic belts in Xinjiang,Northwest China.Numerous lead-zinc deposits are reported in this polymetallic metallogenic belt,such as Caixiashan,Jiyuan,Yuxi,Shaquanzi and Baoyuan.The Caixiashan deposit is the only large-scale deposit,which has attracted many attentions.Previous studies are mainly focused on No.?mineralization zone.The relationship between magmatic activities and mineralization is still unclear,and the formation mechanisms is highly dabateable.In this study,systematic mineralogy,petrology,isotope geochemistry and geochronology were conducted to clearify the mechanism for the formation of the Caixiashan deposit.This study will shed new light on the further Pb-Zn exploration in the Central Tianshan.The Caixiashan lead-zinc deposits located in the western segement of the Central Tianshan Terrane and hosted in the first lithologic section of the Neoproterozoic Kawabulake Group which consist of dolomitic marble and quartz sandstone.Four mineralized alteration zones are recognized in the Caixiashan deposit and the ore bodies are mainly occurred as veined,stratiform-like and lenticular.Based on field investigation and mineral assemblages,the mineralization can be divided into four episodes,including sedimentary exhalative,hydrothermal,deformed metamorphic and supergene episodes.The hydrothermal episode contributes to the most of the Pb-Zn reserves in the Caixiashan deposit and can further subdivided into three mineralization stages,namely,tremolite,sphalerite-pyrrhotite and galena-polymetallic sulfide stages.The hydrothermal alterations of the Caixiashan deposit are represented by tremolization,dolomitization and silicification.The ore minerals are mainly galena and sphalerite characterized by anhedral grains and aggregation with residual textures by replacement,whereas the sulfides comprised of pyrite,pyrrhotite and chalcopyrite which replaced by galena and sphalerite.Intrusive rocks widely developed in the Caixiashan area and the diorite porphyrite and granodiorite emplaced in the northeast part of the Caixiashan deposit,wchih yielded zircon U-Pb ages of 317.0±1.1Ma and 343.1±1.5Ma,respectively.The whole-rock geochemical data suggested the diorite porphyrite and granodiorite are characterized by arc-like magmatic rocks(i.e.enrichment of large ion lithophile elements and depleted in high field strength elements)and formed in island arc dynamic setting associated with subduction of the South Tianshan Ocean.The?³⁴S values of sulfides in the Caixiashan deposit are variable and ranged from-21.11 to+19.10‰,indicating the sulphur mainly originated from the Precambrian marine sulfates by thermochemical sulfate reduction with minor sulphur derived from magmaic source.Additionally,the ²⁰⁶Pb/²⁰⁴Pb,²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios of sulfides ranged from 17.161 to 17.336,15.501 to 15.61 and36.160 to 37.321,respectively.implying the ore-forming materials may originated from the a mixture of upper crust and mantle components.The C-O isotopic compositions of calcite suggested that the ore-forming fluids of the Caixiashan deposit are dominated by low-temperature dissolution of marine carbonates with little magmatic contamination.In conclusion,we proposed that the Caixiashan lead-zinc deposits are pyrometasomatic deposit associated with concealed Carboniferous granitoid rocks.